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A Caltech Library Repository Feedhttp://www.rssboard.org/rss-specificationpython-feedgenenTue, 16 Apr 2024 15:35:25 +0000SMDS measurements and modeling to predict performance
https://resolver.caltech.edu/CaltechAUTHORS:20170810-135509827
Authors: {'items': [{'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'S. H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Nichols-K-M', 'name': {'family': 'Nichols', 'given': 'K. M.'}}]}
Year: 1992
DOI: 10.1109/INFCOM.1992.263435
The authors describe a performance study of a trial switched multimegabit data service (SMDS) link (intended for inter-LAN connection) from the perspective of customers evaluating the feasibility of the link for some target applications. The goals were to take all measurements on the customer premises and to develop a methodology general enough to be used by customers to evaluate the link. The authors measured a lightly loaded system and developed a model of the SMDS connection suitable for evaluating applications via analysis or simulation. They document their methodology and present the SMDS connection delay values as well as a likely breakdown of the constituents of that delay. They used these data to create a simulation model and to simulate a simple application. In the trial configuration, where geographical distances were small, SMDS network delay was one of the notable components of end-to-end delay in the SMDS connection. However, for most packets, throughput is limited by the T1 capacity for transmitting SMDS cells, not by the SMDS network capacity.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/85ser-x0728Stability of a class of dynamic routing protocols (IGRP)
https://resolver.caltech.edu/CaltechAUTHORS:20170810-135815455
Authors: {'items': [{'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Varaiya-P-P', 'name': {'family': 'Varaiya', 'given': 'Pravin'}}]}
Year: 1993
DOI: 10.1109/INFCOM.1993.253311
An exact analysis of the dynamic behavior of IGRP, an adaptive shortest-path routing algorithm, is performed. The distance metric is a weighted sum of traffic-sensitive and traffic-insensitive delay components. The optimality and stability of the protocol is related to the ratio of the weights. In particular, it is shown that if the traffic-sensitive component is not given enough weight, then starting from any initial routing, the subsequent routings after finitely many update periods will oscillate between two worst cases. Otherwise, the successive routings will converge to the unique equilibrium routing. It is also shown that load sharing among routes whose distances are within a threshold of the minimum distance helps stabilize the dynamic behavior.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/dwzdz-93g12Probabilistic conformance testing of protocols with unobservable transitions
https://resolver.caltech.edu/CaltechAUTHORS:20170810-135651335
Authors: {'items': [{'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 1993
DOI: 10.1109/ICNP.1993.340890
A probabilistic approach to conformance testing of protocols containing unobservable transitions is proposed. It is said that an implementation conforms to its specification if their observable behavior is probabilistically the same, when both are subject to the same random environment simulated by the tester. Under the randomized inputs, faults in unobservable transitions may manifest themselves in certain statistics measurable from the implementation, and hence can be detected by comparing these measurements against the desirable statistics computed from the specification. The sensitivity of the nonconformance criterion to the uncertainty in our knowledge of desirable statistics is also studied. The conventional testing of protocols without unobservable transitions uses mismatch in outputs to detect faults. Here, one relies, in addition, on mismatch in the dynamics of the protocol under input randomization.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/a0tmz-wca60A new approach to service provisioning in ATM networks
https://resolver.caltech.edu/CaltechAUTHORS:LOWieeeacmtn93
Authors: {'items': [{'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven L.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Varaiya-P-P', 'name': {'family': 'Varaiya', 'given': 'Pravin P.'}}]}
Year: 1993
DOI: 10.1109/90.251913
The authors formulate and solve a problem of allocating resources among competing services differentiated by user traffic characteristics and maximum end-to-end delay. The solution leads to an alternative approach to service provisioning in an ATM network, in which the network offers directly for rent its bandwidth and buffers and users purchase freely resources to meet their desired quality. Users make their decisions based on their own traffic parameters and delay requirements and the network sets prices for those resources. The procedure is iterative in that the network periodically adjusts prices based on monitored user demand, and is decentralized in that only local information is needed for individual users to determine resource requests. The authors derive the network's adjustment scheme and the users' decision rule and establish their optimality. Since the approach does not require the network to know user traffic and delay parameters, it does not require traffic policing on the part of the network.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/5zskg-9ef63Electronic marking and identification techniques to discourage document copying
https://resolver.caltech.edu/CaltechAUTHORS:BRAinfocom94
Authors: {'items': [{'id': 'Brassil-J', 'name': {'family': 'Brassil', 'given': 'J.'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'S.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Maxemchuk-N', 'name': {'family': 'Maxemchuk', 'given': 'N.'}}, {'id': "O'Gorman-L", 'name': {'family': "O'Gorman", 'given': 'L.'}}]}
Year: 1994
DOI: 10.1109/INFCOM.1994.337544
Modern computer networks make it possible to distribute documents quickly and economically by electronic means rather than by conventional paper means. However, the widespread adoption of electronic distribution of copyrighted material is currently impeded by the ease of illicit copying and dissemination. In this paper we propose techniques that discourage illicit distribution by embedding each document with a unique codeword. Our encoding techniques are indiscernible by readers, yet enable us to identify the sanctioned recipient of a document by examination of a recovered document. We propose three coding methods, describe one in detail, and present experimental results showing that our identification techniques are highly reliable, even after documents have been photocopied.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/900jx-96a58The Use of Communications Networks to Increase Personal Privacy
https://resolver.caltech.edu/CaltechAUTHORS:20120215-152259404
Authors: {'items': [{'id': 'Maxemchuk-N-F', 'name': {'family': 'Maxemchuk', 'given': 'N. F.'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'S.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 1995
DOI: 10.1109/INFCOM.1995.515915
Communications networks can separate as well as join information. This ability can be used to increase personal privacy in an environment where advances in technology makes it possible to collect and correlate increasing amounts of information about individuals. The tools and principles necessary to increase personal privacy are demonstrated by creating an anonymous credit card, in which a person's identity and purchases are separated, and a national health insurance plan, in which treatment, payment and an individual's identity are separated. An analysis technique is developed to determine how well the information is separated.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/ks0dt-c0774Document Identification To Discourage Illicit Copying
https://resolver.caltech.edu/CaltechAUTHORS:20120223-090026500
Authors: {'items': [{'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Lapone-A-M', 'name': {'family': 'Lapone', 'given': 'Aleta M.'}}, {'id': 'Maxemchuk-N', 'name': {'family': 'Maxemchuk', 'given': 'Nicholas F.'}}]}
Year: 1995
DOI: 10.1109/GLOCOM.1995.502594
An important application of future communications networks will be electronic publishing and digital library, provided copyright can be protected. A way to discourage illicit copying and distribution of documents is to uniquely mark each document copy by shifting certain lines or words slightly so that the original registered recipient can be identified from an illicit copy by detecting its mark. In this paper we present two techniques for reliable document identification, the centroid and the correlation detection. By analyzing the noise characteristics, we obtain the maximum likelihood detectors for both methods and their probabilities of error. We have applied these results to implement a marking and identification strategy proposed earlier, which marks a line both vertically by line shift and horizontally by word shift to make the marking robust against distortions in either direction. Preliminary experimental results are presented.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/w21bw-gw259Collusion analysis of cryptographic protocols
https://resolver.caltech.edu/CaltechAUTHORS:20120131-134121360
Authors: {'items': [{'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Maxemchuk-N-F', 'name': {'family': 'Maxemchuk', 'given': 'Nicholas F.'}}]}
Year: 1996
DOI: 10.1109/GLOCOM.1996.594324
As network applications such as electronic commerce proliferate, complex communications protocols that employ cryptographic building blocks, such as encryption and authentication, will become more common. We view a cryptographic protocol as a process by which information is transferred among some users and hidden from others. The collusion problem determines whether a subset of users can discover, through collusion, the information that is designed to be hidden from them after a protocol is executed. Earlier we introduced a model for cryptographic protocols and its collusion analysis, and solved a special case of the collusion problem. In this paper we present an algorithm that solves the general case.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/pwp2c-qf614Anonymous credit cards and their collusion analysis
https://resolver.caltech.edu/CaltechAUTHORS:LOWieeeacmtn96
Authors: {'items': [{'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Maxemchuk-N-F', 'name': {'family': 'Maxemcheuk', 'given': 'Nicholas F.'}}, {'id': 'Paul-S', 'name': {'family': 'Paul', 'given': 'Sanjoy'}}]}
Year: 1996
DOI: 10.1109/90.556339
Communications networks are traditionally used to bring information together. They can also be used to keep information apart in order to protect personal privacy. A cryptographic protocol specifies a process by which some information is transferred among some users and hidden from others. We show how to implement anonymous credit cards using simple cryptographic protocols. We pose, and solve, a collusion problem which determines whether it is possible for a subset of users to discover information that is designed to be hidden from them during or after execution of the anonymous credit card protocol.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/9y97e-2he88An optimization approach to ABR control
https://resolver.caltech.edu/CaltechAUTHORS:20111215-103604063
Authors: {'items': [{'id': 'Lapsley-D-E', 'name': {'family': 'Lapsley', 'given': 'David'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 1998
DOI: 10.1109/ICC.1998.683074
Available bit rate (ABR) sources react to network feedback by adjusting their transmission rates. Most schemes fall into one of two types depending on what is fed back and where the control decision is made. Explicit congestion notification schemes allow sources to make control decisions but only with incomplete information on congestion. Explicit rate schemes use more accurate congestion information but make the control decision inside the network without regard to the different desires of various sources. We propose an optimization approach that attempts to combine the advantage of both types of scheme. The objective is to maximize the total utility of all sources over their transmission rates. The dual problem suggests treating network links and ABR sources as processors in a distributed computation system to solve the dual problem using the gradient projection algorithm. In this system ABR sources select transmission rates that maximize their own benefits and network links adjust bandwidth prices to coordinate the sources' decisions. We show how to implement such a system using features defined in the ABR standard. We provide an asynchronous distributed algorithm for links and sources and illustrate their behavior with preliminary simulation results.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/99y7e-n8t43An IP implementation of optimization flow control
https://resolver.caltech.edu/CaltechAUTHORS:20111221-081205365
Authors: {'items': [{'id': 'Lapsley-D', 'name': {'family': 'Lapsley', 'given': 'David'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 1998
DOI: 10.1109/GLOCOM.1998.776627
Flow control allows sources to adjust their bandwidth usage to the level of availability in a network, and hence reduces packet loss, increases network utilization, and prevents/reacts to network congestion. The Internet uses TCP flow control; asynchronous transfer mode networks will use rate based flow control. In this paper we present an optimization approach to rate based flow control. We describe an implementation of this flow control on an IP network, and we present some performance results of this implementation.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/fcfcw-2sv23Optimization flow control with Newton-like algorithm
https://resolver.caltech.edu/CaltechAUTHORS:ATHglobecom99
Authors: {'items': [{'id': 'Athuraliya-S', 'name': {'family': 'Athuraliya', 'given': 'Sanjeewa'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 1999
DOI: 10.1109/GLOCOM.1999.829974
We proposed earlier an optimization approach to reactive flow control where the objective of the control is to maximize the aggregate utility of all sources over their transmission rates. The control mechanism is derived as a gradient projection algorithm to solve the dual problem. In this paper we extend the algorithm to a scaled gradient projection. The diagonal scaling matrix approximates the diagonal terms of the Hessian and can be computed at individual links using the same information required by the unscaled algorithm. We prove the convergence of the scaled algorithm and present simulation results that illustrate its superiority to the unscaled algorithm.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/w49js-9wz86Resource allocation in a multicast tree
https://resolver.caltech.edu/CaltechAUTHORS:20170810-132912401
Authors: {'items': [{'id': 'Kodialam-M', 'name': {'family': 'Kodialam', 'given': 'Murali'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 1999
DOI: 10.1109/INFCOM.1999.749291
We consider how to allocate bandwidth in a multicast tree so as to optimize some global measure of performance. In our model each receiver has a budget to be used for bandwidth reservation on links along its path from the source, and each link has a cost function depending on the amount of total bandwidth reserved at the link by all receivers using that link. We formulate and solve a problem of allocating bandwidth in the multicast tree such that the sum of link costs is minimized.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/yhqzx-vt180Copyright protection for the electronic distribution of text documents
https://resolver.caltech.edu/CaltechAUTHORS:BRAprocieee99
Authors: {'items': [{'id': 'Brassil-J-T', 'name': {'family': 'Brassil', 'given': 'Jack T.'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Maxemchuk-N', 'name': {'family': 'Maxemchuk', 'given': 'Nicholas F.'}}]}
Year: 1999
DOI: 10.1109/5.771071
Each copy of a text document can be made different in a nearly invisible way by repositioning or modifying the appearance of different elements of text, i.e., lines, words, or characters. A unique copy can be registered with its recipient, so that subsequent unauthorized copies that are retrieved can be traced back to the original owner.
In this paper we describe and compare several mechanisms for marking documents and several other mechanisms for decoding the marks after documents have been subjected to common types of distortion. The marks are intended to protect documents of limited value that are owned by individuals who would rather possess a legal than an illegal copy if they can be distinguished. We will describe attacks that remove the marks and countermeasures to those attacks.
An architecture is described for distributing a large number of copies without burdening the publisher with creating and transmitting the unique documents. The architecture also allows the publisher to determine the identity of a recipient who has illegally redistributed the document, without compromising the privacy of individuals who are not operating illegally.
Two experimental systems are described. One was used to distribute an issue of the IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, and the second was used to mark copies of company private memoranda.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/k4nww-k6n74Optimization flow control -- I: Basic algorithm and convergence
https://resolver.caltech.edu/CaltechAUTHORS:LOWieeeacmtn99
Authors: {'items': [{'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven L.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Lapsley-D-E', 'name': {'family': 'Lapsley', 'given': 'David E.'}}]}
Year: 1999
DOI: 10.1109/90.811451
We propose an optimization approach to flow control where the objective is to maximize the aggregate source utility over their transmission rates. We view network links and sources as processors of a distributed computation system to solve the dual problem using a gradient projection algorithm. In this system, sources select transmission rates that maximize their own benefits, utility minus bandwidth cost, and network links adjust bandwidth prices to coordinate the sources' decisions. We allow feedback delays to be different, substantial, and time varying, and links and sources to update at different times and with different frequencies. We provide asynchronous distributed algorithms and prove their convergence in a static environment. We present measurements obtained from a preliminary prototype to illustrate the convergence of the algorithm in a slowly time-varying environment. We discuss its fairness property.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/wm1h1-1nq41An enhanced random early marking algorithm for Internet flow control
https://resolver.caltech.edu/CaltechAUTHORS:ATHinfocomm00
Authors: {'items': [{'id': 'Athuraliya-S', 'name': {'family': 'Athuraliya', 'given': 'Sanjeewa'}}, {'id': 'Lapsley-D-E', 'name': {'family': 'Lapsley', 'given': 'David'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2000
DOI: 10.1109/INFCOM.2000.832540
We propose earlier an optimization based flow control for the Internet called Random Early Marking (REM). In this paper we propose and evaluate an enhancement that attempts to speed up the convergence of REM in the face of large feedback delays. REM can be regarded as an implementation of an optimization algorithm in a distributed network. The basic idea is to treat the optimization algorithm as a discrete time system and apply linear control techniques to stabilize its transient. We show that the modified algorithm is stable globally and converges exponentially locally. This algorithm translates into an enhanced REM scheme and we illustrate the performance improvement through simulation.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/egmab-2hb43Anonymous credit card transactions
https://resolver.caltech.edu/CaltechAUTHORS:20170810-135046300
Authors: {'items': [{'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven Hwye'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Maxemchuk-N-F', 'name': {'family': 'Maxemchuk', 'given': 'Nicholas Frank'}}, {'id': 'Paul-S', 'name': {'family': 'Paul', 'given': 'Sanjoy'}}]}
Year: 2000
Techniques for performing credit-card transactions without disclosing the subject matter of the transaction to the institution providing the credit card. The techniques include the use of a communications exchange so that information and funds may be transferred without the destination for the transfer knowing the source of the information or funds and the use of public key encryption so that each party to the transaction and the communications exchange can read only the information the party or the exchange needs for its role in the transaction. Also disclosed are techniques for authenticating a card holder by receiving personal information from the card holder, using the information to ask the card holder one or more questions, and using the answers to authenticate the card holder.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/ymnrx-jrd56Price computation in random early marking (REM)
https://resolver.caltech.edu/CaltechAUTHORS:ATHicon00
Authors: {'items': [{'id': 'Athuraliya-S', 'name': {'family': 'Athuraliya', 'given': 'Sanjeewa'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2000
DOI: 10.1109/ICC.2000.853366
We proposed earlier a flow control algorithm derived from solving the dual of a welfare maximization problem. The algorithm however requires communication between network links and sources that is not achievable on the current Internet. We then extended the basic algorithm to a Random Early Marking (REM) scheme which can be implemented using only binary feedback. In this paper we proposed a new price computation algorithm for REM and present simulation results to illustrate its superior performance over the previous versions.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/v7san-q8p41Equilibrium bandwidth and buffer allocations for elastic traffics
https://resolver.caltech.edu/CaltechAUTHORS:LOWieeeacmtn00
Authors: {'items': [{'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven L.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2000
DOI: 10.1109/90.851983
Consider a set of users sharing a network node under an allocation scheme that provides each user with a fixed minimum and a random extra amount of bandwidth and buffer. Allocations and prices are adjusted to adapt to resource availability and user demands. Equilibrium is achieved when all users optimize their utility and demand equals supply for nonfree resources. We analyze two models of user behavior. We show that at equilibrium expected return on purchasing variable resources can be higher than that on fixed resources. Thus users must balance the marginal increase in utility due to higher return on variable resources and the marginal decrease in utility due to their variability. For the first user model we further show that at equilibrium where such tradeoff is optimized all users hold strictly positive amounts of variable bandwidth and buffer. For the second model we show that if both variable bandwidth and buffer are scarce then at equilibrium every user either holds both variable resources or none.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/wk0ap-hrn72Document copying deterrent method
https://resolver.caltech.edu/CaltechAUTHORS:20170810-102749497
Authors: {'items': [{'id': 'Brassil-John-T', 'name': {'family': 'Brassil', 'given': 'John T'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Maxemchuk-N-F', 'name': {'family': 'Maxemchuk', 'given': 'Nicholas F.'}}, {'id': "O'Gorman-Lawrence-P", 'name': {'family': "O'Gorman", 'given': 'Lawrence P.'}}]}
Year: 2000
The present invention is directed to a method of deterring the illicit copying of electronically published documents. It includes utilizing a computer system to electronically publish a plurality of copies of a document having electronically created material thereon for distribution to a plurality of subscribers and operating programming within the computer system so as to perform the identification code functions. The steps are to encode the plurality of copies each with a separate, unique identification code, the identification code being based on a unique arrangement of the electronically created material on each such copy; and, creating a codebook to correlate each such identification code to a particular subscriber. In some embodiments, decoding methods are included with the encoding capabilities. The unique arrangement of the electronically created material may be based on line-shift coding, word-shift coding, or feature enhancement coding (or combinations of these) and may be effected through bitmap alteration of document format file alteration.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/6rhp6-gn132Simulation comparison of RED and REM
https://resolver.caltech.edu/CaltechAUTHORS:ATHicon01a
Authors: {'items': [{'id': 'Athuraliya-S', 'name': {'family': 'Athuraliya', 'given': 'Sanjeewa'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2000
DOI: 10.1109/ICON.2000.875770
We propose earlier an optimization based low control for the Internet called Random Exponential Marking (REM). REM consists of a link algorithm, that probabilistically marks packets inside the network, and a source algorithm, that adapts source rate to observed marking. The marking probability is exponential in a link congestion measure, so that the end-to-end marking probability is exponential in a path congestion measure. Because of the finer measure of congestion provided by REM, sources do not constantly probe the network for spare capacity, but settle around a globally optimal equilibrium, thus avoiding the perpetual cycle of sinking into and recovering from congestion. In this paper we compare the performance of REM with Reno over RED through simulation.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/3shtq-j5q80Capacity of text marking channel
https://resolver.caltech.edu/CaltechAUTHORS:20170810-135348454
Authors: {'items': [{'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Maxemchuk-N-F', 'name': {'family': 'Maxemchuk', 'given': 'Nicholas F.'}}]}
Year: 2000
DOI: 10.1109/97.883364
We have proposed earlier watermarking text documents by slightly shifting certain text lines. Such a text line represents a noisy channel, and marking represents the transmission of a signal through this channel. The power of the signal represents the size of the shift and must be small for the marks to be imperceptible. We formulate the channel capacity under a constraint or individual signal power. We show that to achieve the capacity, the shifts should be normally distributed, have maximum power, and adjacent shifts should be negatively correlated.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/9tk6r-xy760Convergence of REM flow control at a single link
https://resolver.caltech.edu/CaltechAUTHORS:YINieeecl01
Authors: {'items': [{'id': 'Yin-Q', 'name': {'family': 'Yin', 'given': 'Qinghe'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2001
DOI: 10.1109/4234.913159
Various TCP congestion control schemes can be interpreted as approximately carrying out a certain basic algorithm to maximize aggregate source utility, different schemes corresponding to different choices of utility functions. The basic algorithm consists of a link algorithm that updates a congestion measure based on its traffic load, and a source algorithm that adapts the source rate to congestion in its path. Though convergent, this algorithm can lead to large equilibrium backlogs. This problem can be eliminated by modifying the basic algorithm to include backlog in the update of the congestion measure. This article proves that the modified algorithm converges when the network can be modeled as a single bottleneck link. Moreover, in equilibrium, the source rates are matched to the link capacity while the buffer is cleared.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/9f94n-e7g45MATE: MPLS adaptive traffic engineering
https://resolver.caltech.edu/CaltechAUTHORS:20170810-111700737
Authors: {'items': [{'id': 'Elwalid-A', 'name': {'family': 'Elwalid', 'given': 'Anwar'}}, {'id': 'Jin-Cheng', 'name': {'family': 'Jin', 'given': 'Cheng'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Widjaja-I', 'name': {'family': 'Widjaja', 'given': 'Indra'}}]}
Year: 2001
DOI: 10.1109/INFCOM.2001.916625
Destination-based forwarding in traditional IP routers has not been able to take full advantage of multiple paths that frequently exist in Internet service provider networks. As a result, the networks may not operate efficiently, especially when the traffic patterns are dynamic. This paper describes a multipath adaptive traffic engineering mechanism, called MATE, which is targeted for switched networks such as multiprotocol label switching (MPLS) networks. The main goal of MATE is to avoid network congestion by adaptively balancing the load among multiple paths based on measurement and analysis of path congestion. MATE adopts a minimalist approach in that intermediate nodes are not required to perform traffic engineering or measurements besides normal packet forwarding. Moreover MATE does not impose any particular scheduling, buffer management, or a priori traffic characterization on the nodes. This paper presents an analytical model, derives a class of MATE algorithms, and proves their convergence. Several practical design techniques to implement MATE are described. Simulation results are provided to illustrate the efficacy of MATE under various network scenarios.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/v7t5s-72a65REM: active queue management
https://resolver.caltech.edu/CaltechAUTHORS:ATHieeen01
Authors: {'items': [{'id': 'Athuraliya-S', 'name': {'family': 'Athuraliya', 'given': 'Sanjeewa'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Li-Victor-H', 'name': {'family': 'Li', 'given': 'Victor H.'}}, {'id': 'Yin-Qinghe', 'name': {'family': 'Yin', 'given': 'Qinghe'}}]}
Year: 2001
DOI: 10.1109/65.923940
We describe a new active queue management scheme, random exponential marking (REM), that aims to achieve both high utilization and negligible loss and delay in a simple and scalable manner. The key idea is to decouple the congestion measure from the performance measure such as loss, queue length, or delay. While the congestion measure indicates excess demand for bandwidth and must track the number of users, the performance measure should be stabilized around their targets independent of the number of users. We explain the design rationale behind REM and present simulation results of its performance in wireline and wireless networks.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/qefkj-hpb45Understanding TCP Vegas: a duality model
https://resolver.caltech.edu/CaltechAUTHORS:20161129-163917093
Authors: {'items': [{'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Peterson-L-L', 'name': {'family': 'Peterson', 'given': 'Larry'}}, {'id': 'Wang-Limin', 'name': {'family': 'Wang', 'given': 'Limin'}}]}
Year: 2001
DOI: 10.1145/378420.378787
This paper presents a model of the TCP Vegas congestion control mechanism as a distributed optimization algorithm. Doing so has three important benefits. First, it helps us gain a fundamental understanding of why TCP Vegas works, and an appreciation of its limitations. Second, it allows us to prove that Vegas stabilizes at a weighted proportionally fair allocation of network capacity when there is sufficient buffering in the network. Third, it suggests how we might use explicit feedback to allow each Vegas source to determine the optimal sending rate when there is insufficient buffering in the network. We present simulation results that validate our conclusions.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/b3agn-2w871Understanding TCP Vegas: a duality model
https://resolver.caltech.edu/CaltechAUTHORS:20161129-164526605
Authors: {'items': [{'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Peterson-L-L', 'name': {'family': 'Peterson', 'given': 'Larry'}}, {'id': 'Wang-Limin', 'name': {'family': 'Wang', 'given': 'Limin'}}]}
Year: 2001
DOI: 10.1145/384268.378787
This paper presents a model of the TCP Vegas congestion control mechanism as a distributed optimization algorithm. Doing so has three important benefits. First, it helps us gain a fundamental understanding of why TCP Vegas works, and an appreciation of its limitations. Second, it allows us to prove that Vegas stabilizes at a weighted proportionally fair allocation of network capacity when there is sufficient buffering in the network. Third, it suggests how we might use explicit feedback to allow each Vegas source to determine the optimal sending rate when there is insufficient buffering in the network. We present simulation results that validate our conclusions.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/99139-9yv82Flow control in networks with multiple paths
https://resolver.caltech.edu/CaltechAUTHORS:20170810-112123164
Authors: {'items': [{'id': 'Wang-Wei-Hua', 'name': {'family': 'Wang', 'given': 'Wei-Hua'}}, {'id': 'Palaniswami-M', 'name': {'family': 'Palaniswami', 'given': 'Marimuthu'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2001
DOI: 10.1117/12.434306
We propose two flow control algorithms for networks with multiple paths between each source-destination pair. Both are distributed algorithms over the network to maximize aggregate source utility. Algorithm 1 is a first order Lagrangian method applied to a modified objective function that has the same optimal solution as the original objective function but has a better convergence property. Algorithm 2 is based on the idea that, at optimality, only paths with the minimum price carry positive flows, and naturally decomposes the overall decision into flow control (determines total transmission rate based on minimum path price) and routing (determines how to split the flow among available paths). Both algorithms can be implemented as simply a source-based mechanism in which no link algorithm nor feedback is needed. We present numerical examples to illustrate their behavior.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/fhgq6-j4v94Scalable laws for stable network congestion control
https://resolver.caltech.edu/CaltechAUTHORS:PAGdcc01
Authors: {'items': [{'id': 'Paganini-F', 'name': {'family': 'Paganini', 'given': 'Fernando'}}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John'}, 'orcid': '0000-0002-1828-2486'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2001
Discusses flow control in networks, in which sources control their rates based on feedback signals received from the network links, a feature present in current TCP protocols. We develop a congestion control system which is arbitrarily scalable, in the sense that its stability is maintained for arbitrary network topologies and arbitrary amounts of delay. Such a system can be implemented in a decentralized way with information currently available in networks plus a small amount of additional signaling.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/c16cq-var28An empirical validation of a duality model of TCP and queue management algorithms
https://resolver.caltech.edu/CaltechAUTHORS:ATHwsc01
Authors: {'items': [{'id': 'Athuraliya-S', 'name': {'family': 'Athuraliya', 'given': 'Sanjeewa'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2001
DOI: 10.1109/WSC.2001.977445
In this paper we validate through simulations a duality model of TCP and active queue management (AQM) proposed earlier. In this model, TCP and AQM are modeled as carrying out a distributed primal-dual algorithm over the Internet to maximize aggregate source utility. TCP congestion avoidance algorithms, such as Reno and Vegas, iterate on source rates, the primal variable. AQM algorithms, such as RED and REM, iterate on marking probability, the dual variable.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/b69hc-9pc52Internet congestion control
https://resolver.caltech.edu/CaltechAUTHORS:LOWieeecsm02
Authors: {'items': [{'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Paganini-F', 'name': {'family': 'Paganini', 'given': 'Fernando'}}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John C.'}, 'orcid': '0000-0002-1828-2486'}]}
Year: 2002
DOI: 10.1109/37.980245
This article reviews the current transmission control protocol (TCP) congestion control protocols and overviews recent advances that have brought analytical tools to this problem. We describe an optimization-based framework that provides an interpretation of various flow control mechanisms, in particular, the utility being optimized by the protocol's equilibrium structure. We also look at the dynamics of TCP and employ linear models to exhibit stability limitations in the predominant TCP versions, despite certain built-in compensations for delay. Finally, we present a new protocol that overcomes these limitations and provides stability in a way that is scalable to arbitrary networks, link capacities, and delays.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/yx9qg-arn69High-density model of content distribution network
https://resolver.caltech.edu/CaltechAUTHORS:20170810-102351659
Authors: {'items': [{'id': 'Cameron-C-W', 'name': {'family': 'Cameron', 'given': 'Craig'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Wei-Xiaoliang-David', 'name': {'family': 'Wei', 'given': 'David X.'}}]}
Year: 2002
DOI: 10.1109/IDC.2002.995378
It is well known that optimal server placement is NP-hard. We present an approximate model of a content distribution network for the case when both clients and servers are dense, and propose a simple server allocation and placement algorithm based on high-rate quantization theory. The key idea is to regard the location of a request as a random variable with probability density that is proportional to the demand at that location, and the problem of server placement as source coding, i.e., to optimally map a source value (request location) to a codeword (server location) to minimize distortion (network cost). This view leads to a joint server allocation and placement algorithm that has a time-complexity that is linear in the number of users.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/hsfqx-tnq16Understanding TCP Vegas: A Duality Model
https://resolver.caltech.edu/CaltechAUTHORS:20111101-161123893
Authors: {'items': [{'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Peterson-L-L', 'name': {'family': 'Peterson', 'given': 'Larry L.'}}, {'id': 'Wang-Limin', 'name': {'family': 'Wang', 'given': 'Limin'}}]}
Year: 2002
DOI: 10.1145/506147.506152
We view congestion control as a distributed primal--dual algorithm carried out by sources and links over a network to solve a global optimization problem. We describe a multilink multisource model of the TCP Vegas congestion control mechanism. The model provides a fundamental understanding of delay, fairness and loss properties of TCP Vegas. It implies that Vegas stabilizes around a weighted proportionally fair allocation of network capacity when there is sufficient buffering in the network. It clarifies the mechanism through which persistent congestion may arise and its consequences, and suggests how we might use REM active queue management to prevent it. We present simulation results that validate our conclusions.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/nb5vf-9r853High-density model for server allocation and placement
https://resolver.caltech.edu/CaltechAUTHORS:20160812-143246677
Authors: {'items': [{'id': 'Cameron-C-W', 'name': {'family': 'Cameron', 'given': 'Craig W.'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Wei-Xiaoliang-David', 'name': {'family': 'Wei', 'given': 'David X.'}}]}
Year: 2002
DOI: 10.1145/511334.511354
It is well known that optimal server placement is NP-hard. We present an approximate model for the case when both clients and servers are dense, and propose a simple server allocation and placement algorithm based on high-rate vector quantization theory. The key idea is to regard the location of a request as a random variable with probability density that is proportional to the demand at that
location, and the problem of server placement as source coding, i.e., to optimally map a source value (request location) to a codeword (server location) to minimize distortion (network cost). This view has led to a joint server allocation and placement algorithm that has a time-complexity that is linear in the number of clients.
Simulations are presented to illustrate its performance.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/7sxhk-sh147High-density model for server allocation and placement
https://resolver.caltech.edu/CaltechAUTHORS:20160812-143232076
Authors: {'items': [{'id': 'Cameron-C-W', 'name': {'family': 'Cameron', 'given': 'Craig W.'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Wei-Xiaoliang-David', 'name': {'family': 'Wei', 'given': 'David X.'}}]}
Year: 2002
DOI: 10.1145/511399.511354
It is well known that optimal server placement is NP-hard. We present an approximate model for the case when both clients and servers are dense, and propose a simple server allocation and placement algorithm based on high-rate vector quantization theory. The key idea is to regard the location of a request as a random variable with probability density that is proportional to the demand at that
location, and the problem of server placement as source coding, i.e., to optimally map a source value (request location) to a codeword (server location) to minimize distortion (network cost). This view has led to a joint server allocation and placement algorithm that has a time-complexity that is linear in the number of clients.
Simulations are presented to illustrate its performance.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/ataa9-0re45Enhancing TCP Performance over Wireless Networks
https://resolver.caltech.edu/CaltechAUTHORS:20170810-133629598
Authors: {'items': [{'id': 'Li-Victor-H', 'name': {'family': 'Li', 'given': 'Victor H.'}}, {'id': 'Liu-Zhi-Qiang', 'name': {'family': 'Liu', 'given': 'Zhi-Qiang'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2002
TCP flow control algorithms have been designed for wireline networks where congestion is measured by packet loss due to buffer overflow. However, wireless networks also suffer from significant packet losses due to bit errors and handoffs. TCP responds to all the packet losses by invoking congestion control and avoidance algorithms and this results in degraded end-to-end performance in wireless networks. In this paper, we describe a Wireless Random Exponential Marking (WREM) scheme which effectively improves TCP performance over wireless networks by decoupling loss recovery from congestion control. Moreover, WREM is capable of handling the coexistence of both ECN-Capable and Non-ECN-Capable routers. We present simulation results to show its effectiveness and compatibility.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/8kjy3-0gt89Dynamics of TCP/RED and a scalable control
https://resolver.caltech.edu/CaltechAUTHORS:20170810-135606639
Authors: {'items': [{'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Paganini-F', 'name': {'family': 'Paganini', 'given': 'Fernando'}}, {'id': 'Wang-Jintao', 'name': {'family': 'Wang', 'given': 'Jiantao'}}, {'id': 'Adlakha-S', 'name': {'family': 'Adlakha', 'given': 'Sachin'}}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John C.'}, 'orcid': '0000-0002-1828-2486'}]}
Year: 2002
DOI: 10.1109/INFCOM.2002.1019265
We demonstrate that the dynamic behavior of queue and average window is determined predominantly by the stability of TCP/RED, not by AIMD probing nor noise traffic. We develop a general multi-link multi-source model for TCP/RED and derive a local stability condition in the case of a single link with heterogeneous sources. We validate our model with simulations and illustrate the stability region of TCP/RED. These results suggest that TCP/RED becomes unstable when delay increases, or more strikingly, when link capacity increases. The analysis illustrates the difficulty of setting RED parameters to stabilize TCP: they can be tuned to improve stability, but only at the cost of large queues even when they are dynamically adjusted. Finally, we present a simple distributed congestion control algorithm that maintains stability for arbitrary network delay, capacity, load and topology.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/fgmq0-ewv80Using AQM to improve TCP performance over wireless networks
https://resolver.caltech.edu/CaltechAUTHORS:20170810-133902128
Authors: {'items': [{'id': 'Li-Victor-H', 'name': {'family': 'Li', 'given': 'Victor H.'}}, {'id': 'Liu-Zhi-Qiang', 'name': {'family': 'Liu', 'given': 'Zhi-Qiang'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2002
DOI: 10.1117/12.473023
TCP flow control algorithms have been designed for wireline networks where congestion is measured by packet loss due to buffer overflow. However, wireless networks also suffer from significant packet losses due to bit errors and handoffs. TCP responds to all the packet losses by invoking congestion control and avoidance algorithms and this results in degraded end-to-end performance in wireless networks. In this paper, we describe an Wireless Random Exponential Marking(WREM) scheme which effectively improves TCP performance over wireless networks by decoupling loss recovery from congestion control. Moreover, WREM is capable of handling the coexistence of both ECN-Capable and Non-ECN-Capable routers. We present simulation results to show its effectiveness and compatibility.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/gf8sj-w0m62Cost of AQM in stabilizing TCP
https://resolver.caltech.edu/CaltechCSTR:2002.008
Authors: {'items': [{'id': 'Kim-Ki-Baek', 'name': {'family': 'Kim', 'given': 'Ki Baek'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2002
DOI: 10.7907/84yds-ahh93
In this paper, we propose a unified mathematical framework based on receding horizon control for analyzing and designing AQM (Active Queue Management) algorithms in stabilizing TCP (Transfer Control Protocol). The proposed framework is based on a dynamical system of the given TCP and a linear quadratic cost on transients in queue length and flow rates. We derive the optimal receding horizon AQMs (RHAs) that stabilizes the linearized dynamical system with the minimum cost. Conversely, we show that any AQM with an appropriate structure solves the same optimal control problem with appropriate weighting matrix. We interpret existing AQM's such as RED, REM, PI and AVQ as different approximations of the optimal AQM, and discuss the impact of these approximations on performance.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/84yds-ahh93Analysis and Design of AQM for stabilizing TCP
https://resolver.caltech.edu/CaltechCSTR:2002.009
Authors: {'items': [{'id': 'Kim-Ki-Baek', 'name': {'family': 'Kim', 'given': 'Ki Baek'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2002
DOI: 10.7907/Z9T43R25
In this paper, we propose a unified AQM (Active Queue Management) framework and stabilizing optimal AQMs in stabilizing a given TCP (Transmission Control Protocol) and a real-queue dynamics. Since we formulate the AQM design problem for the given TCP as state-space models, we get three important features. First, we propose a PD-type (Proportional-Derivative) control structure and by applying integral control action technique, a PID-type (Proportional-Integral-Derivative) control structure. Second, we propose memory control structures to compensate explicitly delays
in congestion measure by using memory control structures. Third, we propose stabilizing optimal AQMs by minimizing linear quadratic costs on the transients in queue length, aggregate rate, jitter in the aggregate rate, and congestion measure, which are called RHA (Receding Horizon AQM) in this paper. Conversely, we show that any AQM with an appropriate structure solves the same stabilizing optimal control problem with appropriate weighting matrices.
Finally, we interpret existing AQMs such as RED (Random Early Detection), REM (Random Exponential Marking), PI
(Proportional-Integral) and AVQ as different approximations of the unified AQM structures, and discuss the impact of each structures on performance from the results of the stabilizing optimal AQMs. We illustrate our results through simulation examples for the linearized system of a given nonlinear TCP and queue dynamical system.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/ymq8a-1g369A server allocation and placement algorithm for content distribution
https://resolver.caltech.edu/CaltechAUTHORS:20170522-162939354
Authors: {'items': [{'id': 'Cameron-C-W', 'name': {'family': 'Cameron', 'given': 'Craig'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Wei-Xiaoliang-David', 'name': {'family': 'Wei', 'given': 'David X.'}}]}
Year: 2002
DOI: 10.1109/ITW.2002.1115407
It is well known that optimal server placement is NP-hard. We present an approximate model for the case when both clients and servers are dense, and propose a simple server allocation and placement algorithm based on high-rate vector quantization theory. The key idea is to regard the location of a request as a random variable with probability density that is proportional to the demand at that location, and the problem of server placement as source coding, i.e., to optimally map a source value (request location) to a codeword (server location) to minimize distortion (network cost). This view has led to a joint server allocation and placement algorithm that has a time-complexity that is linear in the number of clients. Simulations are presented to illustrate its performance.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/2w43f-hgg42Design of AQM in Supporting TCP Based on the Well-Known AIMD Model
https://resolver.caltech.edu/CaltechCSTR:2003.001
Authors: {'items': [{'id': 'Kim-Ki-Baek', 'name': {'family': 'Kim', 'given': 'Ki Baek'}}, {'id': 'Tang-Ao', 'name': {'family': 'Tang', 'given': 'Ao'}, 'orcid': '0000-0001-6296-644X'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2003
DOI: 10.7907/Z9DB7ZTC
In this paper, we investigate how to design AQM with a low-pass
filter (average queuing) in supporting TCP based on the well-known
AIMD dynamic model. Since we formulate the AQM design problem for
the given TCP as state-space models, we get three important
features. First, we derive PD-type (Proportional-Derivative) AQM
structure with a low-pass filter which includes P-type
(Proportional) RED in terms of queue length. Second, we compensate
for delays in congestion measure explicitly by adding a memory
control structure that uses the previous dynamic information.
Third, we obtain a stabilizing optimal gains of the proposed AQM
structure by minimizing a linear quadratic cost of the transients
on queue length, aggregate rate, and congestion measure. Finally,
we illustrate the above theoretical results through \emph{ns}
simulations for TCP Reno.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/d9dvj-f2e58Stabilized Vegas
https://resolver.caltech.edu/CaltechAUTHORS:20111026-082612870
Authors: {'items': [{'id': 'Choe-H', 'name': {'family': 'Choe', 'given': 'Hyojeong'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2003
DOI: 10.1109/INFCOM.2003.1209249
We show that the current TCP Vegas algorithm can become unstable in the presence of network delay and propose a modification that stabilizes it. The stabilized Vegas remains completely source-based and can be implemented without any network support. We suggest an incremental deployment strategy for stabilized Vegas when the network contains a mix of links, some with active queue management and some without.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/48hq5-r4168An Empirical Study on the Connectivity of Ad Hoc Networks
https://resolver.caltech.edu/CaltechAUTHORS:20111028-093653374
Authors: {'items': [{'id': 'Tang-Ao', 'name': {'family': 'Tang', 'given': 'Ao'}, 'orcid': '0000-0001-6296-644X'}, {'id': 'Florens-C', 'name': {'family': 'Florens', 'given': 'Cédric'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2003
DOI: 10.1109/AERO.2003.1235249
This paper discusses the probability of connectivity of ad hoc networks. An empirical formula is proposed to fit the simulation results. The parameters of the formula are determined for different cases and the asymptotic behavior is discussed. Finally, a new metric is proposed to quantify the connectivity of an ad hoc network.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/hj1xx-qdp28Optimal flow control and routing in multi-path networks
https://resolver.caltech.edu/CaltechAUTHORS:20170810-112123357
Authors: {'items': [{'id': 'Wang-Wei-Hua', 'name': {'family': 'Wang', 'given': 'Wei-Hua'}}, {'id': 'Palaniswami-M', 'name': {'family': 'Palaniswami', 'given': 'Marimuthu'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2003
DOI: 10.1016/S0166-5316(02)00176-1
We propose two flow control algorithms for networks with multiple paths between each source–destination pair. Both are distributed algorithms over the network to maximize aggregate source utility. Algorithm 1 is a first order Lagrangian method applied to a modified objective function that has the same optimal solution as the original objective function but has a better convergence property. Algorithm 2 is based on the idea that, at optimality, only paths with the minimum price carry positive flows, and naturally decomposes the overall decision into flow control (determines total transmission rate based on minimum path price) and routing (determines how to split the flow among available paths). Both algorithms can be implemented as simply a source-based mechanism in which no link algorithm nor feedback is needed. We present numerical examples to illustrate their behavior.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/svz98-q0y31Can shortest-path routing and TCP maximize utility
https://resolver.caltech.edu/CaltechAUTHORS:20190306-132657017
Authors: {'items': [{'id': 'Wang-Jintao', 'name': {'family': 'Wang', 'given': 'Jiantao'}}, {'id': 'Li-Lun', 'name': {'family': 'Li', 'given': 'Lun'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John C.'}, 'orcid': '0000-0002-1828-2486'}]}
Year: 2003
DOI: 10.1109/INFCOM.2003.1209226
TCP-AQM protocol can be interpreted as distributed primal-dual algorithms over the Internet to maximize aggregate utility. In this paper, we study whether TCP-AQM together with shortest-path routing can maximize utility with appropriate choice of link cost, on a slower timescale, over both source rates and routes. We show that this is generally impossible because the addition of route maximization makes the problem NP-hard. We exhibit an inevitable tradeoff between routing instability and utility maximization. For the special case of ring network, we prove rigorously that shortest-path routing based purely on congestion prices is unstable. Adding a sufficiently large static component to link cost, stabilizes it, but the maximum utility achievable by shortest-path routing decreases with the weight on the static component. We present simulation results to illustrate that these conclusions generalize to general network topology, and that routing instability can reduce utility to less than that achievable by the necessarily stable static routing.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/pbv64-4wx74A new TCP/AQM for stable operation in fast networks
https://resolver.caltech.edu/CaltechAUTHORS:20170810-131233358
Authors: {'items': [{'id': 'Paganini-F', 'name': {'family': 'Paganini', 'given': 'Fernando'}}, {'id': 'Wang-Zhikui', 'name': {'family': 'Wang', 'given': 'Zhikui'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John C.'}, 'orcid': '0000-0002-1828-2486'}]}
Year: 2003
DOI: 10.1109/INFCOM.2003.1208662
This paper is aimed at designing a congestion control system that scales gracefully with network capacity, providing high utilization, low queueing delay, dynamic stability, and fairness among users. In earlier work we had developed fluid-level control laws that achieve the first three objectives for arbitrary networks and delays, but were forced to constrain the resource allocation policy. In this paper we extend the theory to include dynamics at TCP sources, preserving the earlier features at fast time-scales, but permitting sources to match their steady-state preferences, provided a bound on round-trip-times is known. We develop two packet-level implementations of this protocol, using (i) ECN marking, and (ii) queueing delay, as means of communicating the congestion measure from links to sources. We discuss parameter choices and demonstrate using ns-2 simulations the stability of the protocol and its equilibrium features in terms of utilization, queueing and fairness. We also demonstrate the scalability of these features to increases in capacity, delay, and load, in comparison with other deployed and proposed protocols.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/jz4r0-bvs41Maximum and asymptotic UDP throughput under CHOKe
https://resolver.caltech.edu/CaltechAUTHORS:20170104-155944142
Authors: {'items': [{'id': 'Wang-Jintao', 'name': {'family': 'Wang', 'given': 'Jiantao'}}, {'id': 'Tang-Ao', 'name': {'family': 'Tang', 'given': 'Ao'}, 'orcid': '0000-0001-6296-644X'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2003
DOI: 10.1145/781027.781038
A recently proposed active queue management, CHOKe, aims to protect TCP from UDP flows. Simulations have shown that as UDP rate increases, its bandwidth share initially rises but eventually drops. We derive an approximate model of CHOKe and show that, provided the number of TCP flows is large, the UDP bandwidth share peaks at (e+1)^-1 = 0.269 when the UDP input rate is slightly larger than the link capacity, and drops to zero as UDP input rate tends to infinity, regardless of the TCP algorithm.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/qee23-c8k16Maximum and asymptotic UDP throughput under CHOKe
https://resolver.caltech.edu/CaltechAUTHORS:20170104-160731603
Authors: {'items': [{'id': 'Wang-Jintao', 'name': {'family': 'Wang', 'given': 'Jiantao'}}, {'id': 'Tang-Ao', 'name': {'family': 'Tang', 'given': 'Ao'}, 'orcid': '0000-0001-6296-644X'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2003
DOI: 10.1145/885651.781038
A recently proposed active queue management, CHOKe, aims to protect TCP from UDP flows. Simulations have shown that as UDP rate increases, its bandwidth share initially rises but eventually drops. We derive an approximate model of CHOKe and show that, provided the number of TCP flows is large, the UDP bandwidth share peaks at (e+1)^-1 = 0.269 when the UDP input rate is slightly larger than the link capacity, and drops to zero as UDP input rate tends to infinity, regardless of the TCP algorithm.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/7shkx-rh353Analysis and design of AQM based on state-space models for stabilizing TCP
https://resolver.caltech.edu/CaltechAUTHORS:20170810-131823045
Authors: {'items': [{'id': 'Kim-Ki-Baek', 'name': {'family': 'Kim', 'given': 'Ki Baek'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2003
DOI: 10.1109/ACC.2003.1238948
In this paper, we formulate the AQM (active queue management) design problem for stabilizing a given TCP (Transmission Control Protocol) as state-space models. Thereby, we show that PD-type (proportional-derivative) AQM is a natural state-feedback control structure to stabilize the given TCP for the first time, to our knowledge, in the networking literature and by applying integral control action, a PID-control structure that is a unified framework for analysis and design of AQM. Next, we compensate for delays in congestion measure explicitly by using a memory control. Third, we obtain stabilizing optimal gains of the proposed feedback control structures for linearized systems of the given TCP. We interpret existing AQMs, including a simplified random early detection, random exponential marking, PI and a simplified adaptive virtual queue, as different approximations of the unified AQM structure. We discuss the impact of each structure on the performance from the results of the stabilizing optimal AQMs. Finally, we illustrate our results through simulations for TCP Reno.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/rr5ed-zw596A control theoretical look at internet congestion control
https://resolver.caltech.edu/CaltechAUTHORS:20170810-131419777
Authors: {'items': [{'id': 'Paganini-F', 'name': {'family': 'Paganini', 'given': 'Fernando'}}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John'}, 'orcid': '0000-0002-1828-2486'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2003
DOI: 10.1007/3-540-36589-3_2
Congestion control mechanisms in today's Internet represent perhaps the largest artificial feedback system ever deployed, and yet one that has evolved mostly outside the scope of control theory. This can be explained by the tight constraints of decentralization and simplicity of implementation in this problem, which would appear to rule out most mathematically-based designs. Nevertheless, a recently developed framework based on fluid flow models has allowed for a belated injection of control theory into the area, with some pleasant surprises. As described in this chapter, there is enough special structure to allow us to "guess" designs with mathematically provable properties that hold in arbitrary networks, and which involve a modest complexity in implementation.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/vqwq3-03x96A duality model of TCP and queue management algorithms
https://resolver.caltech.edu/CaltechAUTHORS:LOWieeeacmtn03
Authors: {'items': [{'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2003
DOI: 10.1109/TNET.2003.815297
We propose a duality model of end-to-end congestion control and apply it to understanding the equilibrium properties of TCP and active queue management schemes. The basic idea is to regard source rates as primal variables and congestion measures as dual variables, and congestion control as a distributed primal-dual algorithm over the Internet to maximize aggregate utility subject to capacity constraints. The primal iteration is carried out by TCP algorithms such as Reno or Vegas, and the dual iteration is carried out by queue management algorithms such as DropTail, RED or REM. We present these algorithms and their generalizations, derive their utility functions, and study their interaction.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/f7wwm-d3n30The case for delay-based congestion control
https://resolver.caltech.edu/CaltechAUTHORS:20170810-131854762
Authors: {'items': [{'id': 'Jin-Cheng', 'name': {'family': 'Jin', 'given': 'Cheng'}}, {'id': 'Wei-Xiaoliang-David', 'name': {'family': 'Wei', 'given': 'David X.'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2003
DOI: 10.1109/CCW.2003.1240796
We argue that, in the absence of explicit feedback, delay-based algorithms become the preferred approach for end-to-end congestion control as networks scale up in capacity. Their advantage is small at low speed but decisive at high speed. The distinction between packet-level and flow-level problems of the current TCP exposes the difficulty of loss-based algorithms at large congestion windows.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/hckkk-5zj18Necessary and sufficient conditions for optimal flow control in multirate multicast networks
https://resolver.caltech.edu/CaltechAUTHORS:20170810-112123268
Authors: {'items': [{'id': 'Wang-W-H', 'name': {'family': 'Wang', 'given': 'W.-H.'}}, {'id': 'Palaniswami-M', 'name': {'family': 'Palaniswami', 'given': 'M.'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'S. H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2003
DOI: 10.1049/ip-com:20030591
The authors consider the optimal flow control problem in multirate multicast networks where all receivers of the same multicast group can receive service at different rates with different QoS. The objective is to achieve the fairness transmission rates that maximise the total receiver utility under the capacity constraint of links. They first propose necessary and sufficient conditions for the optimal solution to the problem, and then derive a new optimal flow control strategy using the Lagrangian multiplier method. Like the unicast case, the basic algorithm consists of a link algorithm to update the link price, and a receiver algorithm to adapt the transmission rate according to the link prices along its path. In particular if some groups contain only one receiver and become unicast, the algorithm will degrade to their previously proposed unicast algorithm.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/dx89v-s8s24Optimizing 10-Gigabit Ethernet for Networks of Workstations, Clusters, and Grids: A Case Study
https://resolver.caltech.edu/CaltechAUTHORS:20161019-142754228
Authors: {'items': [{'id': 'Feng-Wu-chun', 'name': {'family': 'Feng', 'given': 'Wu-chun'}}, {'id': 'Hurwitz-J', 'name': {'family': 'Hurwitz', 'given': 'Justin (Gus)'}}, {'id': 'Newman-H-B', 'name': {'family': 'Newman', 'given': 'Harvey'}, 'orcid': '0000-0003-0964-1480'}, {'id': 'Ravot-S', 'name': {'family': 'Ravot', 'given': 'Sylvain'}}, {'id': 'Cottrell-R-L', 'name': {'family': 'Cottrell', 'given': 'R. Les'}}, {'id': 'Martin-Olivier', 'name': {'family': 'Martin', 'given': 'Olivier'}}, {'id': 'Coccetti-F', 'name': {'family': 'Coccetti', 'given': 'Fabrizio'}}, {'id': 'Jin-Cheng', 'name': {'family': 'Jin', 'given': 'Cheng'}}, {'id': 'Wei-Xiaoliang-David', 'name': {'family': 'Wei', 'given': 'Xiaoliang (David)'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2003
DOI: 10.1145/1048935.1050200
This paper presents a case study of the 10-Gigabit Ethernet (10GbE) adapter from Intel ®. Specifically, with appropriate optimizations to the configurations of the 10GbE adapter and TCP, we demonstrate that the 10GbE adapter can perform well in local-area, storage-area, system-area, and wide-area networks.
For local-area, storage-area, and system-area networks in support of networks of workstations, network-attached storage, and clusters, respectively, we can achieve over 7-Gb/s end-to-end throughput and 12-µs end-to-end latency between applications running on Linux-based PCs. For the wide-area network in support of grids, we broke the recently-set Internet2 Land Speed Record by 2.5 times by sustaining an end-to-end TCP/IP throughput of 2.38 Gb/s between Sunnyvale, California and Geneva, Switzerland (i.e., 10,037 kilometers) to move over a terabyte of data in less than an hour. Thus, the above results indicate that 10GbE may be a cost-effective solution across a multitude of computing environments.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/bjpmj-p9j82A stabilizing AQM based on virtual queue dynamics in supporting TCP with arbitrary delays
https://resolver.caltech.edu/CaltechAUTHORS:20170810-132013399
Authors: {'items': [{'id': 'Kim-Ki-Baek', 'name': {'family': 'Kim', 'given': 'Ki Baek'}}, {'id': 'Tang-Ao', 'name': {'family': 'Tang', 'given': 'Ao'}, 'orcid': '0000-0001-6296-644X'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2003
DOI: 10.1109/CDC.2003.1271718
This paper studies how to design a stabilizing AQM in supporting TCP (Transmission Control Protocol) with arbitrary delays. For the well-known AIMD (Additive Increase Multiplicative Decrease) dynamic model of TCP, our study shows that we can compensate for arbitrary delays explicitly by applying a modified virtual queue dynamics that makes the equilibrium queuing delay zero. This study also verifies that a simplified AQM AVQ (Adaptive Virtual Queue) is the state-feedback control for the AIMD model based on the virtual queue dynamics.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/ssc23-hg079Linear stability of TCP/RED and a scalable control
https://resolver.caltech.edu/CaltechAUTHORS:20170810-140056148
Authors: {'items': [{'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Paganini-F', 'name': {'family': 'Paganini', 'given': 'Fernando'}}, {'id': 'Wang-Jintao', 'name': {'family': 'Wang', 'given': 'Jiantao'}}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John C.'}, 'orcid': '0000-0002-1828-2486'}]}
Year: 2003
DOI: 10.1016/S1389-1286(03)00304-9
We demonstrate that the dynamic behavior of queue and average window is determined predominantly by the stability of TCP/RED, not by AIMD probing nor noise traffic. We develop a general multi-link multi-source model for TCP/RED and derive a local stability condition in the case of a single link with heterogeneous sources. We validate our model with simulations and illustrate the stability region of TCP/RED. These results suggest that TCP/RED becomes unstable when delay increases, or more strikingly, when link capacity increases. The analysis illustrates the difficulty of setting RED parameters to stabilize TCP: they can be tuned to improve stability, but only at the cost of large queues even when they are dynamically adjusted. Finally, we present a simple distributed congestion control algorithm that maintains stability for arbitrary network delay, capacity, load and topology.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/x4tq8-fws05Optimization flow control with estimation error
https://resolver.caltech.edu/CaltechAUTHORS:20170810-134030592
Authors: {'items': [{'id': 'Mehyar-M', 'name': {'family': 'Mehyar', 'given': 'Mortada'}}, {'id': 'Spanos-D-P', 'name': {'family': 'Spanos', 'given': 'Demetri'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2004
DOI: 10.1109/INFCOM.2004.1356985
We analyze the effects of price estimation error in a dual-gradient optimization flow control scheme, and characterize the performance of the algorithm in this case. By treating estimation error as inexactness of the gradient, we utilize sufficient conditions for convergence subject to bounded error to characterize the long-term dynamics of the link utilization in terms of a region, which the trajectory enters in finite time. We explicitly find bounds for this region under a particular quantization error model, and provide simulation results to verify the predicted behavior of the system. Finally, we analyze the effects of the stepsize on the convergence of the algorithm, and provide analytical and numerical results, which suggest a particular choice for this parameter.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/0gqar-8xr78A mathematical framework for designing a low-loss, low-delay internet
https://resolver.caltech.edu/CaltechAUTHORS:20170810-135831815
Authors: {'items': [{'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Srikant-R', 'name': {'family': 'Srikant', 'given': 'R.'}}]}
Year: 2004
DOI: 10.1023/B:NETS.0000015657.07692.be
We survey some recent results on modeling, analysis and design of congestion control schemes for the Internet. Using tools from convex optimization and control theory, we show that congestion controllers can be viewed as distributed algorithms for achieving fair resource allocation among competing sources. We illustrate the use of simple mathematical models to analyze the behavior of currently deployed Internet congestion control protocols as well as to design new protocols for networks with large capacities, delays and general topology. These new protocols are designed to nearly eliminate loss and queueing delay in the Internet, yet achieving high utilization and any desired fairness.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/qs06e-te943Global stability of Vegas-like TCP flow
https://resolver.caltech.edu/CaltechAUTHORS:20170810-104523250
Authors: {'items': [{'id': 'Choe-Hyojeong', 'name': {'family': 'Choe', 'given': 'Hyojeong'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Lee-Jin-S', 'name': {'family': 'Lee', 'given': 'Jin S.'}}]}
Year: 2004
A TCP Vegas flow adapts its sending rate to maintain a constant backlog in its path. The stability of nonlinear adaptation has been analyzed based on linearization and only accounted for a small signal. We extend the error model of TCP-like flow to a state-dependent coefficient form with nonlinear state feedback. The nonlinear feedback is here approximated by a saturation function. Using a quadratic Lyapunov function approach, we find a domain of attraction to show that the unique equilibrium point of the system is asymptotically stable in the domain.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/vn5bd-mkb70Allocating commodity resources in aggregate traffic networks
https://resolver.caltech.edu/CaltechAUTHORS:20170810-111128809
Authors: {'items': [{'id': 'Duffield-N-G', 'name': {'family': 'Duffield', 'given': 'N. G.'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'S. H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2004
DOI: 10.1016/j.peva.2003.10.009
We examine the relation between cost and quality in networks which carry aggregate traffic. A powerful tool in this is the burstiness or indifference curve associated with a stochastic traffic flow. We relate burstiness to quality and use this relation to explore the quality experienced by aggregated flows under various rules for allocating resources to them. An example is motivated by the controlled load service specification. We show how the imposition of costs associated with buffer space and service capacity leads to the notion of a cost-optimal allocation of resources. This defines the cheapest operating point in a network where resources are commodities to be purchased as necessary to satisfy quality requirements. We define a notion of cost-based admission control: a linear admission rule which can be based on declared or measured traffic parameters.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/21kc5-1ea55Understanding CHOKe: throughput and spatial characteristics
https://resolver.caltech.edu/CaltechAUTHORS:TANieeeacmtn04
Authors: {'items': [{'id': 'Tang-Ao', 'name': {'family': 'Tang', 'given': 'Ao'}, 'orcid': '0000-0001-6296-644X'}, {'id': 'Wang-Jintao', 'name': {'family': 'Wang', 'given': 'Jiantao'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2004
DOI: 10.1109/TNET.2004.833162
A recently proposed active queue management, CHOKe, is stateless, simple to implement, yet surprisingly effective in protecting TCP from UDP flows. We present an equilibrium model of TCP/CHOKe. We prove that, provided the number of TCP flows is large, the UDP bandwidth share peaks at (e+1)/sup -1/=0.269 when UDP input rate is slightly larger than link capacity, and drops to zero as UDP input rate tends to infinity. We clarify the spatial characteristics of the leaky buffer under CHOKe that produce this throughput behavior. Specifically, we prove that, as UDP input rate increases, even though the total number of UDP packets in the queue increases, their spatial distribution becomes more and more concentrated near the tail of the queue, and drops rapidly to zero toward the head of the queue. In stark contrast to a nonleaky FIFO buffer where UDP bandwidth shares would approach 1 as its input rate increases without bound, under CHOKe, UDP simultaneously maintains a large number of packets in the queue and receives a vanishingly small bandwidth share, the mechanism through which CHOKe protects TCP flows.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/ykxe2-5ev09Stabilized Vegas
https://resolver.caltech.edu/CaltechAUTHORS:20170810-105114024
Authors: {'items': [{'id': 'Choe-Hyojeong', 'name': {'family': 'Choe', 'given': 'Hyojeong'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2004
DOI: 10.1007/978-3-540-31597-1_2
TCP Vegas was introduced in 1994 [5] as an alternative to TCP Reno. Unlike Reno (or its variants such as NewReno and SACK), that uses packet loss as a measure of congestion, Vegas uses queueing delay as a measure of congestion [15, 18]. Vegas introduces a new congestion avoidance mechanism that corrects the oscillatory behavior of AIMD (Additive Increase Multiplicative Decrease). While the AIMD algorithm induces loss to learn the available network capacity, a Vegas source adjusts its sending rate to keep a small number of packets buffered in the routers along the path. Provided there is enough buffering, a network of Vegas sources will stabilize around a proportionally fair equilibrium and packet loss will be eliminated; see [15] for details. In this paper, we study the stability of this equilibrium in the presence of network delay, motivated by two lines of recent research.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/s9d3t-4jk94FAST TCP: From Theory to Experiments
https://resolver.caltech.edu/CaltechCACR:2004.207
Authors: {'items': [{'id': 'Jin-Cheng', 'name': {'family': 'Jin', 'given': 'C.'}}, {'id': 'Wei-Xiaoliang-David', 'name': {'family': 'Wei', 'given': 'D.'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'S. H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Buhrmaster-Gary', 'name': {'family': 'Buhrmaster', 'given': 'G.'}}, {'id': 'Bunn-J', 'name': {'family': 'Bunn', 'given': 'J.'}, 'orcid': '0000-0002-3798-298X'}, {'id': 'Choe-Hyojeong-D', 'name': {'family': 'Choe', 'given': 'H. D.'}}, {'id': 'Cottrell-R-L-A', 'name': {'family': 'Cottrell', 'given': 'R. L. A.'}}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'J. C.'}, 'orcid': '0000-0002-1828-2486'}, {'id': 'Feng-Wu-chun', 'name': {'family': 'Feng', 'given': 'W.'}}, {'id': 'Martin-Oliver', 'name': {'family': 'Martin', 'given': 'O.'}}, {'id': 'Newman-H-B', 'name': {'family': 'Newman', 'given': 'H.'}, 'orcid': '0000-0003-0964-1480'}, {'id': 'Paganini-Fernando', 'name': {'family': 'Paganini', 'given': 'F.'}}, {'id': 'Ravot-Sylvain', 'name': {'family': 'Ravot', 'given': 'S.'}}, {'id': 'Singh-Suresh', 'name': {'family': 'Singh', 'given': 'S.'}}]}
Year: 2004
We describe a variant of TCP, called FAST, that can sustain high throughput and utilization at multi-Gbps over large distance. We present the motivation, review the background theory, summarize key features of FAST TCP, and report our first experimental results.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/ygj33-23272Analysis of nonlinear delay differential equation models of TCP/AQM protocols using sums of squares
https://resolver.caltech.edu/CaltechAUTHORS:20110831-081433118
Authors: {'items': [{'id': 'Papachristodoulou-A', 'name': {'family': 'Papachristodoulou', 'given': 'Antonis'}}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John C.'}, 'orcid': '0000-0002-1828-2486'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2004
DOI: 10.1109/CDC.2004.1429529
The simplest adequate models for congestion
control for the Internet are in the form of deterministic
nonlinear delay differential equations. However the absence
of efficient, algorithmic methodologies to analyze
them at this modelling level usually results in the investigation of their linearizations including delays; or in the analysis of nonlinear yet undelayed models. In this
paper we present an algorithmic methodology for efficient
stability analysis of network congestion control schemes at
the nonlinear delay-differential equation model level, using
the Sum of Squares decomposition and SOSTOOLS.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/fd6d7-z1f46The UltraLight Project: The Network as an Integrated and Managed Resource in Grid Systems for High Energy Physics and Data Intensive Science
https://resolver.caltech.edu/CaltechCACR:2005.109
Authors: {'items': [{'id': 'Newman-H-B', 'name': {'family': 'Newman', 'given': 'Harvey'}, 'orcid': '0000-0003-0964-1480'}, {'id': 'Bunn-Julian-J', 'name': {'family': 'Bunn', 'given': 'Julian'}, 'orcid': '0000-0002-3798-298X'}, {'id': 'Cavanaugh-R', 'name': {'family': 'Cavanaugh', 'given': 'Richard'}}, {'id': 'Legrand-I', 'name': {'family': 'Legrand', 'given': 'Iosif'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'McKee-S', 'name': {'family': 'McKee', 'given': 'Shawn'}}, {'id': 'Nae-D', 'name': {'family': 'Nae', 'given': 'Dan'}}, {'id': 'Ravot-S', 'name': {'family': 'Ravot', 'given': 'Sylvan'}}, {'id': 'Steenberg-C-D', 'name': {'family': 'Steenberg', 'given': 'Conrad'}}, {'id': 'Su-X', 'name': {'family': 'Su', 'given': 'Xun'}}, {'id': 'Thomas-Michael', 'name': {'family': 'Thomas', 'given': 'Michael'}}, {'id': 'van-Lingen-Frank', 'name': {'family': 'van Lingen', 'given': 'Frank'}}, {'id': 'Xia-Y', 'name': {'family': 'Xia', 'given': 'Yang'}}]}
Year: 2005
We describe the NSF-funded UltraLight project. The project's goal is to meet the data-intensive computing challenges of the next generation of particle physics experiments with a comprehensive, network-focused agenda. In particular we argue that instead of treating the network traditionally, as a static, unchanging and unmanaged set of inter-computer links, we instead will use it as a dynamic, configurable, and closely monitored resource, managed end-to-end, to construct a next-generation global system able to meet the data processing, distribution, access and analysis needs of the high energy physics (HEP) community. While the initial UltraLight implementation and services architecture is being developed to serve HEP, we expect many of UltraLight's developments in the areas of networking, monitoring, management, and collaborative research, to be applicable to many fields of data intensive e-science. In this paper we give an overview of, and motivation for the UltraLight project, and provide early results within different working areas of the project.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/eysap-48c12FAST TCP: from theory to experiments
https://resolver.caltech.edu/CaltechAUTHORS:JINieeen05
Authors: {'items': [{'id': 'Jin-Cheng', 'name': {'family': 'Jin', 'given': 'Cheng'}}, {'id': 'Wei-Xiaoliang-David', 'name': {'family': 'Wei', 'given': 'David X.'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Bunn-J', 'name': {'family': 'Bunn', 'given': 'Julian'}, 'orcid': '0000-0002-3798-298X'}, {'id': 'Choe-Hyojeong-D', 'name': {'family': 'Choe', 'given': 'Hyojeong D.'}}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John C.'}, 'orcid': '0000-0002-1828-2486'}, {'id': 'Newman-H-B', 'name': {'family': 'Newman', 'given': 'Harvey'}, 'orcid': '0000-0003-0964-1480'}, {'id': 'Ravot-Sylvain', 'name': {'family': 'Ravot', 'given': 'Sylvain'}}, {'id': 'Singh-Suresh', 'name': {'family': 'Singh', 'given': 'Suresh'}}, {'id': 'Paganini-Fernando', 'name': {'family': 'Paganini', 'given': 'Fernando'}}, {'id': 'Buhrmaster-Gary', 'name': {'family': 'Buhrmaster', 'given': 'Gary'}}, {'id': 'Cottrell-R-L-A', 'name': {'family': 'Cottrell', 'given': 'Les'}}, {'id': 'Martin-Oliver', 'name': {'family': 'Martin', 'given': 'Oliver'}}, {'id': 'Feng-Wu-chun', 'name': {'family': 'Feng', 'given': 'Wu-chun'}}]}
Year: 2005
DOI: 10.1109/MNET.2005.1383434
We describe a variant of TCP, called FAST, that can sustain high throughput and utilization at multigigabits per second over large distances. We present the motivation, review the background theory, summarize key features of FAST TCP, and report our first experimental results.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/w8fm4-xwm05Congestion control for high performance, stability, and fairness in general networks
https://resolver.caltech.edu/CaltechAUTHORS:PAGieeeacmtn05
Authors: {'items': [{'id': 'Paganini-F', 'name': {'family': 'Paganini', 'given': 'Fernando'}}, {'id': 'Wang-Zhikui', 'name': {'family': 'Wang', 'given': 'Zhikui'}}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John C.'}, 'orcid': '0000-0002-1828-2486'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2005
DOI: 10.1109/TNET.2004.842216
This paper is aimed at designing a congestion control system that scales gracefully with network capacity, providing high utilization, low queueing delay, dynamic stability, and fairness among users. The focus is on developing decentralized control laws at end-systems and routers at the level of fluid-flow models, that can provably satisfy such properties in arbitrary networks, and subsequently approximate these features through practical packet-level implementations. Two families of control laws are developed. The first "dual" control law is able to achieve the first three objectives for arbitrary networks and delays, but is forced to constrain the resource allocation policy. We subsequently develop a "primal-dual" law that overcomes this limitation and allows sources to match their steady-state preferences at a slower time-scale, provided a bound on round-trip-times is known. We develop two packet-level implementations of this protocol, using 1) ECN marking, and 2) queueing delay, as means of communicating the congestion measure from links to sources. We demonstrate using ns-2 simulations the stability of the protocol and its equilibrium features in terms of utilization, queueing and fairness, under a variety of scaling parameters.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/gdkjg-76417Joint congestion control and media access control design for ad hoc wireless networks
https://resolver.caltech.edu/CaltechAUTHORS:20170810-103408504
Authors: {'items': [{'id': 'Chen-Lijun', 'name': {'family': 'Chen', 'given': 'Lijun'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John C.'}, 'orcid': '0000-0002-1828-2486'}]}
Year: 2005
DOI: 10.1109/INFCOM.2005.1498496
We present a model for the joint design of congestion control and media access control (MAC) for ad hoc wireless networks. Using contention graph and contention matrix, we formulate resource allocation in the network as a utility maximization problem with constraints that arise from contention for channel access. We present two algorithms that are not only distributed spatially, but more interestingly, they decompose vertically into two protocol layers where TCP and MAC jointly solve the system problem. The first is a primal algorithm where the MAC layer at the links generates congestion (contention) prices based on local aggregate source rates, and TCP sources adjust their rates based on the aggregate prices in their paths. The second is a dual subgradient algorithm where the MAC sub-algorithm is implemented through scheduling link-layer flows according to the congestion prices of the links. Global convergence properties of these algorithms are proved. This is a preliminary step towards a systematic approach to jointly design TCP congestion control algorithms and MAC algorithms, not only to improve performance, but more importantly, to make their interaction more transparent.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/xcehv-y5c92Equilibrium of Heterogeneous Congestion Control Protocols
https://resolver.caltech.edu/CaltechCSTR:2005.005
Authors: {'items': [{'id': 'Tang-Ao', 'name': {'family': 'Tang', 'given': 'Ao'}, 'orcid': '0000-0001-6296-644X'}, {'id': 'Wang-Jintao', 'name': {'family': 'Wang', 'given': 'Jiantao'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Chiang-Mung', 'name': {'family': 'Chiang', 'given': 'Mung'}}]}
Year: 2005
DOI: 10.7907/Z9FB50XP
When heterogeneous congestion control protocols that react to different pricing signals share the same network, the resulting equilibrium may no longer be interpreted as a solution to the standard utility maximization problem. We prove the existence of equilibrium in general multi-protocol networks under mild assumptions. For almost all networks, the equilibria are locally unique, and finite and odd in number. They cannot all be locally stable unless it is globally unique. Finally, we show that if the price mapping functions that map link prices to effective prices observed by the sources are similar, then global uniqueness is guaranteed. Numerical examples are used throughout the paper to illustrate these results.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/qpy2w-n0y44Optimization model of internet protocols
https://resolver.caltech.edu/CaltechAUTHORS:20161129-162643807
Authors: {'items': [{'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John'}, 'orcid': '0000-0002-1828-2486'}, {'id': 'Li-L', 'name': {'family': 'Li', 'given': 'L.'}}, {'id': 'Tang-Ao', 'name': {'family': 'Tang', 'given': 'A.'}, 'orcid': '0000-0001-6296-644X'}, {'id': 'Wang-Jiantao', 'name': {'family': 'Wang', 'given': 'J.'}}]}
Year: 2005
DOI: 10.1145/1064212.1064245
Layered architecture is one of the most fundamental and influential structures of network design. Can we integrate the various protocol layers into a single coherent theory by regarding them as carrying out an asynchronous distributed primal-dual computation over the network to implicitly solve a global optimization problem? Different layers iterate on different subsets of the decision variables using local information to achieve individual optimalities, but taken together, these local algorithms attempt to achieve a global objective. Such a theory will expose the interconnection between protocol layers and can be used to study rigorously the performance tradeoff in protocol layering as different ways to distribute a centralized computation. In this talk, we describe some preliminary work towards this goal and discuss some of the difficulties of this approach.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/axcpq-9g913Optimization and Control of Communication Networks
https://resolver.caltech.edu/CaltechAUTHORS:20160831-160652019
Authors: {'items': [{'id': 'Chiang-Mung', 'name': {'family': 'Chiang', 'given': 'Mung'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2005
DOI: 10.1145/1071690.1064244
Recently, there has been a surge in research activities that utilize the power of recent developments in nonlinear
optimization to tackle a wide scope of work in the analysis and design of communication systems, touching every
layer of the layered network architecture, and resulting in both intellectual and practical impacts significantly
beyond the earlier frameworks. These research activities are driven by both new demands in the areas of
communications and networking, and new tools emerging from optimization theory. Such tools include new
developments of powerful theories and highly efficient computational algorithms for nonlinear convex
optimization, as well as global solution methods and relaxation techniques for nonconvex optimization.
Optimization theory can be used to analyze, interpret, or design a communication system, for both forward-engineering and reverse-engineering. Over the last few years, it has been successfully applied to a wide range of
communication systems, from the high speed Internet core to wireless networks, from coding and equalization to
broadband access, and from information theory to network topology models. Some of the theoretical advances
have also been put into practice and started making visible impacts, including new versions of TCP congestion
control, power control and scheduling algorithms in wireless networks, and spectrum management in DSL
broadband access networks.
Under the theme of optimization and control of communication networks, this Hot Topic Session consists of five
invited talks covering a wide range of issues, including protocols, pricing, resource allocation, cross layer design,
traffic engineering in the Internet, optical transport networks, and wireless networks.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/ds913-h2v73Optimization and Control of Communication Networks
https://resolver.caltech.edu/CaltechAUTHORS:20160831-160656108
Authors: {'items': [{'id': 'Chiang-Mung', 'name': {'family': 'Chiang', 'given': 'Mung'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2005
DOI: 10.1145/1064212.1064244
Recently, there has been a surge in research activities that utilize the power of recent developments in nonlinear
optimization to tackle a wide scope of work in the analysis and design of communication systems, touching every
layer of the layered network architecture, and resulting in both intellectual and practical impacts significantly
beyond the earlier frameworks. These research activities are driven by both new demands in the areas of
communications and networking, and new tools emerging from optimization theory. Such tools include new
developments of powerful theories and highly efficient computational algorithms for nonlinear convex
optimization, as well as global solution methods and relaxation techniques for nonconvex optimization.
Optimization theory can be used to analyze, interpret, or design a communication system, for both forward-
engineering and reverse-engineering. Over the last few years, it has been successfully applied to a wide range of
communication systems, from the high speed Internet core to wireless networks, from coding and equalization to
broadband access, and from information theory to network topology models. Some of the theoretical advances
have also been put into practice and started making visible impacts, including new versions of TCP congestion
control, power control and scheduling algorithms in wireless networks, and spectrum management in DSL
broadband access networks.
Under the theme of optimization and control of communication networks, this Hot Topic Session consists of five
invited talks covering a wide range of issues, including protocols, pricing, resource allocation, cross layer design,
traffic engineering in the Internet, optical transport networks, and wireless networks.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/tx4gh-d6907Cross-layer optimization in TCP/IP networks
https://resolver.caltech.edu/CaltechAUTHORS:WANiatnet05
Authors: {'items': [{'id': 'Wang-Jiantao', 'name': {'family': 'Wang', 'given': 'Jiantao'}}, {'id': 'Li-Lun', 'name': {'family': 'Li', 'given': 'Lun'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John C.'}, 'orcid': '0000-0002-1828-2486'}]}
Year: 2005
DOI: 10.1109/TNET.2005.850219
TCP-AQM can be interpreted as distributed primal-dual algorithms to maximize aggregate utility over source rates. We show that an equilibrium of TCP/IP, if exists, maximizes aggregate utility over both source rates and routes, provided congestion prices are used as link costs. An equilibrium exists if and only if this utility maximization problem and its Lagrangian dual have no duality gap. In this case, TCP/IP incurs no penalty in not splitting traffic across multiple paths. Such an equilibrium, however, can be unstable. It can be stabilized by adding a static component to link cost, but at the expense of a reduced utility in equilibrium. If link capacities are optimally provisioned, however, pure static routing, which is necessarily stable, is sufficient to maximize utility. Moreover single-path routing again achieves the same utility as multipath routing at optimality.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/n04qt-0cs93Network equilibrium of heterogeneous congestion control protocols
https://resolver.caltech.edu/CaltechAUTHORS:TANinfocom05
Authors: {'items': [{'id': 'Tang-Ao', 'name': {'family': 'Tang', 'given': 'Ao'}, 'orcid': '0000-0001-6296-644X'}, {'id': 'Wang-Jintao', 'name': {'family': 'Wang', 'given': 'Jiantao'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Chiang-Mung', 'name': {'family': 'Chiang', 'given': 'Mung'}}]}
Year: 2005
DOI: 10.1109/INFCOM.2005.1498359
When heterogeneous congestion control protocols that react to different pricing signals share the same network, the resulting equilibrium may no longer be interpreted as a solution to the standard utility maximization problem. We prove the existence of equilibrium under mild assumptions. Then we show that multi-protocol networks whose equilibria are locally non-unique or infinite in number can only form a set of measure zero. Multiple locally unique equilibria can arise in two ways. First, unlike in the single-protocol case, the set of bottleneck links can be non-unique with heterogeneous protocols even when the routing matrix has full row rank. The equilibria associated with different sets of bottleneck links are necessarily distinct. Second, even when there is a unique set of bottleneck links, network equilibrium can still be non-unique, but is always finite and odd in number. They cannot all be locally stable unless it is globally unique. Finally, we provide various sufficient conditions for global uniqueness. Numerical examples are used throughout the paper to illustrate these results.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/e6mfd-9jh94The "robust yet fragile" nature of the Internet
https://resolver.caltech.edu/CaltechAUTHORS:DOYpnas05
Authors: {'items': [{'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John C.'}, 'orcid': '0000-0002-1828-2486'}, {'id': 'Anderson-Dav-L', 'name': {'family': 'Anderson', 'given': 'David L.'}}, {'id': 'Li-Lun', 'name': {'family': 'Li', 'given': 'Lun'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Roughan-M', 'name': {'family': 'Roughan', 'given': 'Matthew'}}, {'id': 'Shalunov-S', 'name': {'family': 'Shalunov', 'given': 'Stanislav'}}, {'id': 'Tanaka-Reiko', 'name': {'family': 'Tanaka', 'given': 'Reiko'}}, {'id': 'Willinger-W', 'name': {'family': 'Willinger', 'given': 'Walter'}}]}
Year: 2005
DOI: 10.1073/pnas.0501426102
PMCID: PMC1240072
The search for unifying properties of complex networks is popular, challenging, and important. For modeling approaches that focus on robustness and fragility as unifying concepts, the Internet is an especially attractive case study, mainly because its applications are ubiquitous and pervasive, and widely available expositions exist at every level of detail. Nevertheless, alternative approaches to modeling the Internet often make extremely different assumptions and derive opposite conclusions about fundamental properties of one and the same system. Fortunately, a detailed understanding of Internet technology combined with a unique ability to measure the network means that these differences can be understood thoroughly and resolved unambiguously. This article aims to make recent results of this process accessible beyond Internet specialists to the broader scientific community and to clarify several sources of basic methodological differences that are relevant beyond either the Internet or the two specific approaches focused on here (i.e., scale-free networks and highly optimized tolerance networks).https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/3gtmf-gww63The Ultralight project: the network as an integrated and managed resource for data-intensive science
https://resolver.caltech.edu/CaltechAUTHORS:NEWcse05
Authors: {'items': [{'id': 'Newman-H-B', 'name': {'family': 'Newman', 'given': 'Harvey'}, 'orcid': '0000-0003-0964-1480'}, {'id': 'Bunn-Julian-J', 'name': {'family': 'Bunn', 'given': 'Julian'}, 'orcid': '0000-0002-3798-298X'}, {'id': 'Legrand-I', 'name': {'family': 'Legrand', 'given': 'Iosif'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Nae-D', 'name': {'family': 'Nae', 'given': 'Dan'}}, {'id': 'Ravot-S', 'name': {'family': 'Ravot', 'given': 'Sylvain'}}, {'id': 'Steenberg-C-D', 'name': {'family': 'Steenberg', 'given': 'Conrad'}}, {'id': 'Su-X', 'name': {'family': 'Su', 'given': 'Xun'}}, {'id': 'Thomas-Michael', 'name': {'family': 'Thomas', 'given': 'Michael'}}, {'id': 'van-Lingen-Frank', 'name': {'family': 'van Lingen', 'given': 'Frank'}}, {'id': 'Xia-Y', 'name': {'family': 'Xia', 'given': 'Yang'}}, {'id': 'Cavanaugh-R', 'name': {'family': 'Cavanaugh', 'given': 'Richard'}}, {'id': 'McKee-S', 'name': {'family': 'McKee', 'given': 'Shawn'}}]}
Year: 2005
DOI: 10.1109/MCSE.2005.127
Looks at the UltraLight project which treats the network interconnecting globally distributed data sets as a dynamic, configurable, and closely monitored resource to construct a next-generation system that can meet the high-energy physics community's data-processing, distribution, access, and analysis needs.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/8r74a-2md93Global Stability of FAST TCP in Single-Link Single-Source Network
https://resolver.caltech.edu/CaltechAUTHORS:20170810-105402423
Authors: {'items': [{'id': 'Choi-Joon-Young', 'name': {'family': 'Choi', 'given': 'Joon-Young'}}, {'id': 'Koo-Kyungmo', 'name': {'family': 'Koo', 'given': 'Kyungmo'}}, {'id': 'Lee-Jin-S', 'name': {'family': 'Lee', 'given': 'Jin S.'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2005
DOI: 10.1109/CDC.2005.1582427
We consider a single-link single-source network with FAST TCP source, and propose a static approximation of queuing delay dynamics at the link. The static approximation turns out to be a form with network feedback delay, which enables to analyze FAST TCP reflecting the effect of network feedback delay. Based on a continuous-time dynamic model of FAST TCP, we achieve the boundedness of window size and a sufficient condition for global asymptotic stability. The simulation results illustrate the validity of the sufficient condition for global asymptotic stability.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/nqwzw-h3b53Equilibrium and Fairness of Networks Shared by TCP Reno and Vegas/FAST
https://resolver.caltech.edu/CaltechAUTHORS:20191009-132246224
Authors: {'items': [{'id': 'Tang-Ao', 'name': {'family': 'Tang', 'given': 'Ao'}, 'orcid': '0000-0001-6296-644X'}, {'id': 'Wang-Jintao', 'name': {'family': 'Wang', 'given': 'Jiantao'}}, {'id': 'Hegde-S', 'name': {'family': 'Hegde', 'given': 'Sanjay'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2005
DOI: 10.1007/s11235-005-5499-1
It has been proved theoretically that a network with heterogeneous congestion control algorithms that react to different congestion signals can have multiple equilibrium points. In this paper, we demonstrate this experimentally using TCP Reno and Vegas/FAST. We also show that any desired inter-protocol fairness is in principle achievable by an appropriate choice of Vegas/FAST parameter, and that intra-protocol fairness among flows within each protocol is unaffected by the presence of the other protocol except for a reduction in effective link capacities. Dummynet experiments and ns-2 simulations are presented to verify these results.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/wyde3-qrt80Distributed Averaging on Asynchronous Communication Networks
https://resolver.caltech.edu/CaltechAUTHORS:20170517-164222886
Authors: {'items': [{'id': 'Mehyar-M', 'name': {'family': 'Mehyar', 'given': 'Mortada'}}, {'id': 'Spanos-D-P', 'name': {'family': 'Spanos', 'given': 'Demetri'}}, {'id': 'Pongsajapan-J', 'name': {'family': 'Pongsajapan', 'given': 'John'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Murray-R-M', 'name': {'family': 'Murray', 'given': 'Richard M.'}, 'orcid': '0000-0002-5785-7481'}]}
Year: 2005
DOI: 10.1109/CDC.2005.1583363
Distributed algorithms for averaging have attracted interest in the control and sensing literature. However, previous works have not addressed some practical concerns that will arise in actual implementations on packet-switched communication networks such as the Internet. In this paper, we present several implementable algorithms that are robust to asynchronism and dynamic topology changes. The algorithms do not require global coordination and can be proven to converge under very general asynchronous timing assumptions. Our results are verified by both simulation and experiments on a real-world TCP/IP network.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/4yh97-6b303The Design and Demonstration of the Ultralight Testbed
https://resolver.caltech.edu/CaltechAUTHORS:20110426-151150267
Authors: {'items': [{'id': 'Newman-H-B', 'name': {'family': 'Newman', 'given': 'Harvey'}, 'orcid': '0000-0003-0964-1480'}, {'id': 'Bourilkov-D', 'name': {'family': 'Bourilkov', 'given': 'Dimitri'}}, {'id': 'Bunn-Julian-J', 'name': {'family': 'Bunn', 'given': 'Julian'}, 'orcid': '0000-0002-3798-298X'}, {'id': 'Cavanaugh-R', 'name': {'family': 'Cavanaugh', 'given': 'Richard'}}, {'id': 'Legrand-I', 'name': {'family': 'Legrand', 'given': 'Iosif'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'McKee-S', 'name': {'family': 'McKee', 'given': 'Shawn'}}, {'id': 'Nae-D', 'name': {'family': 'Nae', 'given': 'Dan'}}, {'id': 'Ravot-S', 'name': {'family': 'Ravot', 'given': 'Sylvain'}}, {'id': 'Steenberg-C-D', 'name': {'family': 'Steenberg', 'given': 'Conrad'}}, {'id': 'Su-Xun', 'name': {'family': 'Su', 'given': 'Xun'}}, {'id': 'Thomas-Michael', 'name': {'family': 'Thomas', 'given': 'Michael'}}, {'id': 'van-Lingen-Frank', 'name': {'family': 'van Lingen', 'given': 'Frank'}}, {'id': 'Xia-Yang', 'name': {'family': 'Xia', 'given': 'Yang'}}]}
Year: 2006
DOI: 10.1109/BROADNETS.2006.4374312
In this paper we present the motivation, the design, and a recent demonstration of the UltraLight testbed at SC|05. The goal of the Ultralight testbed is to help meet the data-intensive computing challenges of the next generation of particle physics experiments with a comprehensive, network- focused approach. UltraLight adopts a new approach to networking: instead of treating it traditionally, as a static, unchanging and unmanaged set of inter-computer links, we are developing and using it as a dynamic, configurable, and closely monitored resource that is managed from end-to-end. To achieve its goal we are constructing a next-generation global system that is able to meet the data processing, distribution, access and analysis needs of the particle physics community. In this paper we will first present early results in the various working areas of the project. We then describe our experiences of the network architecture, kernel setup, application tuning and configuration used during the bandwidth challenge event at SC|05. During this Challenge, we achieved a record-breaking aggregate data rate in excess of 150 Gbps while moving physics datasets between many Grid computing sites.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/dxvkm-7sf21Equilibrium of heterogeneous congestion control protocols
https://resolver.caltech.edu/CaltechAUTHORS:20110811-093852596
Authors: {'items': [{'id': 'Tang-Ao', 'name': {'family': 'Tang', 'given': 'Ao'}, 'orcid': '0000-0001-6296-644X'}, {'id': 'Wang-Jintao', 'name': {'family': 'Wang', 'given': 'Jiantao'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Chiang-Mung', 'name': {'family': 'Chiang', 'given': 'Mung'}}]}
Year: 2006
DOI: 10.1109/CISS.2006.286548
When heterogeneous congestion control protocols that react to different pricing signals share the same network, the resulting equilibrium may no longer be interpreted as a solution to the standard utility maximization problem. We prove the existence of equilibrium in general multi-protocol networks under mild assumptions. For almost all networks, the equilibria are locally unique, and finite and odd in number. They cannot all be locally stable unless it is globally unique. Finally, we show that if the price mapping functions that map link prices to effective prices observed by the sources are similar, then global uniqueness is guaranteed.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/ygwfp-sgp79Cross-layer Congestion Control, Routing and Scheduling Design in Ad Hoc Wireless Networks
https://resolver.caltech.edu/CaltechAUTHORS:20110120-103630156
Authors: {'items': [{'id': 'Chen-Lijun', 'name': {'family': 'Chen', 'given': 'Lijun'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Chiang-Mung', 'name': {'family': 'Chiang', 'given': 'Mung'}}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John C.'}, 'orcid': '0000-0002-1828-2486'}]}
Year: 2006
DOI: 10.1109/INFOCOM.2006.142
This paper considers jointly optimal design of crosslayer congestion control, routing and scheduling for ad hoc
wireless networks. We first formulate the rate constraint and scheduling constraint using multicommodity flow variables, and formulate resource allocation in networks with fixed wireless channels (or single-rate wireless devices that can mask channel variations) as a utility maximization problem with these constraints.
By dual decomposition, the resource allocation problem
naturally decomposes into three subproblems: congestion control,
routing and scheduling that interact through congestion price.
The global convergence property of this algorithm is proved. We
next extend the dual algorithm to handle networks with timevarying
channels and adaptive multi-rate devices. The stability
of the resulting system is established, and its performance is
characterized with respect to an ideal reference system which
has the best feasible rate region at link layer.
We then generalize the aforementioned results to a general
model of queueing network served by a set of interdependent
parallel servers with time-varying service capabilities, which
models many design problems in communication networks. We
show that for a general convex optimization problem where a
subset of variables lie in a polytope and the rest in a convex set,
the dual-based algorithm remains stable and optimal when the
constraint set is modulated by an irreducible finite-state Markov
chain. This paper thus presents a step toward a systematic way
to carry out cross-layer design in the framework of "layering as
optimization decomposition" for time-varying channel models.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/dznbh-6gn98The Motivation, Architecture and Demonstration of Ultralight
Network Testbed
https://resolver.caltech.edu/CaltechAUTHORS:20110728-121139631
Authors: {'items': [{'id': 'Newman-H-B', 'name': {'family': 'Newman', 'given': 'Harvey'}, 'orcid': '0000-0003-0964-1480'}, {'id': 'Bunn-Julian-J', 'name': {'family': 'Bunn', 'given': 'Julian'}, 'orcid': '0000-0002-3798-298X'}, {'id': 'Bourilkov-D', 'name': {'family': 'Bourilkov', 'given': 'Dimitri'}}, {'id': 'Cavanaugh-R', 'name': {'family': 'Cavanaugh', 'given': 'Richard'}}, {'id': 'Legrand-I', 'name': {'family': 'Legrand', 'given': 'Iosif'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'McKee-S', 'name': {'family': 'McKee', 'given': 'Shawn'}}, {'id': 'Nae-D', 'name': {'family': 'Nae', 'given': 'Dan'}}, {'id': 'Ravot-S', 'name': {'family': 'Ravot', 'given': 'Sylvain'}}, {'id': 'Steenberg-C-D', 'name': {'family': 'Steenberg', 'given': 'Conrad'}}, {'id': 'Su-X', 'name': {'family': 'Su', 'given': 'Xun'}}, {'id': 'Thomas-Michael', 'name': {'family': 'Thomas', 'given': 'Michael'}}, {'id': 'van-Lingen-Frank', 'name': {'family': 'van Lingen', 'given': 'Frank'}}, {'id': 'Xia-Y', 'name': {'family': 'Xia', 'given': 'Yang'}}]}
Year: 2006
In this paper we describe progress in the NSF-funded Ultralight project and a recent demonstration of Ultralight technologies at SuperComputing 2005 (SC|05). The goal of the
Ultralight project is to help meet the data-intensive computing challenges of the next generation of particle physics experiments with a comprehensive, network-focused approach. Ultralight adopts a new approach to networking: instead of treating it traditionally, as a static, unchanging and unmanaged set of inter-computer links, we are developing and using it as a dynamic, configurable, and closely monitored resource that is managed from end-to-end. Thus we are constructing a next-generation global system that is able to meet the data processing, distribution, access and analysis needs of the particle physics community. In this paper we present the motivation for, and an overview of, the Ultralight project. We then cover early
results in the various working areas of the project. The remainder of the paper describes our experiences of the Ultralight network architecture, kernel setup, application tuning and configuration used during the bandwidth challenge event at SC|05. During this Challenge, we
achieved a record-breaking aggregate data rate in excess of 150 Gbps while moving physics datasets between many sites interconnected by the Ultralight backbone network. The exercise highlighted the benefits of Ultralight's research and development efforts that are enabling new and advanced methods of distributed scientific data analysis.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/eg3sr-1c078Layering As Optimization Decomposition: Framework and Examples
https://resolver.caltech.edu/CaltechAUTHORS:20190306-130031273
Authors: {'items': [{'id': 'Chiang-Mung', 'name': {'family': 'Chiang', 'given': 'Mung'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Calderbank-A-R', 'name': {'family': 'Calderbank', 'given': 'A. Robert'}}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John C.'}, 'orcid': '0000-0002-1828-2486'}]}
Year: 2006
DOI: 10.1109/ITW.2006.1633780
Network protocols in layered architectures have historically been obtained primarily on an ad-hoc basis. Recent research has shown that network protocols may instead be holistically analyzed and systematically designed as distributed solutions to some global optimization problems in the form of Network Utility Maximization (NUM), providing insight into what they optimize and structures of the network protocol stack. This paper presents a short survey of the recent efforts towards a systematic understanding of 'layering' as 'optimization decomposition', where the overall communication network is modeled by a generalized NUM problem, each layer corresponds to a decomposed subproblem, and the interfaces among layers are quantified as functions of the optimization variables coordinating the sub-problems. Different decompositions lead to alternative layering architectures. We summarize several examples of horizontal decomposition into distributed computation and vertical decomposition into functional modules such as congestion control, routing, scheduling, random access, power control, and coding.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/y6b7y-8rk46Layering As Optimization Decomposition: Current Status and Open Issues
https://resolver.caltech.edu/CaltechAUTHORS:20170508-173109246
Authors: {'items': [{'id': 'Chiang-Mung', 'name': {'family': 'Chiang', 'given': 'Mung'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Calderbank-A-R', 'name': {'family': 'Calderbank', 'given': 'A. Robert'}}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John C.'}, 'orcid': '0000-0002-1828-2486'}]}
Year: 2006
DOI: 10.1109/CISS.2006.286492
Network protocols in layered architectures have historically been obtained on an ad-hoc basis, and much of the recent cross-layer designs are conducted through piecemeal approaches. Network protocols may instead be holistically analyzed and systematically designed as distributed solutions to some global optimization problems in the form of generalized network utility maximization (NUM), providing insight on what they optimize and structures of the network protocol stack. This paper presents a short survey of the recent efforts towards a systematic understanding of "layering" as "optimization decomposition", where the overall communication network is modeled by a generalized NUM problem, each layer corresponds to a decomposed subproblem, and the interfaces among layers are quantified as functions of the optimization variables coordinating the subproblems. Furthermore, there are many alternative decompositions, each leading to a different layering architecture. Industry adoption of this unifying framework has also started. Here we summarize the current status of horizontal decomposition into distributed computation and vertical decomposition into functional modules such as congestion control, routing, scheduling, random access, power control, and coding. Key messages and methodologies arising out of many recent work are listed. Then we present a list of challenging open issues in this area and the initial progress made on some of them.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/e5hgh-e8n26On Asymptotic Optimality of Dual Scheduling Algorithm In A Generalized Switch
https://resolver.caltech.edu/CaltechAUTHORS:20110203-100201578
Authors: {'items': [{'id': 'Chen-Lijun', 'name': {'family': 'Chen', 'given': 'Lijun'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John C.'}, 'orcid': '0000-0002-1828-2486'}]}
Year: 2006
DOI: 10.1109/WIOPT.2006.1666500
Generalized switch is a model of a queueing system where parallel servers are interdependent and have time-varying service capabilities. This paper considers the dual scheduling algorithm that uses rate control and queue-length based scheduling to allocate resources for a generalized switch. We consider a saturated system in which each user has infinite amount of data to be served. We prove the asymptotic optimality of the dual scheduling algorithm for such a system, which says that the vector of average service rates of the scheduling algorithm maximizes some aggregate concave utility functions. As the fairness objectives can be achieved by appropriately choosing utility functions, the asymptotic optimality establishes the fairness properties of the dual scheduling algorithm.
The dual scheduling algorithm motivates a new architecture for scheduling, in which an additional queue is introduced to interface the user data queue and the time-varying server and to modulate the scheduling process, so as to achieve different performance objectives. Further research would include scheduling with Quality of Service guarantees with the dual scheduler, and its application and implementation in various versions of the generalized switch model.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/da85c-6j644Counter-intuitive throughput behaviors in networks under end-to-end control
https://resolver.caltech.edu/CaltechAUTHORS:TANiatnet06
Authors: {'items': [{'id': 'Tang-Ao', 'name': {'family': 'Tang', 'given': 'Ao'}, 'orcid': '0000-0001-6296-644X'}, {'id': 'Wang-Jintao', 'name': {'family': 'Wang', 'given': 'Jiantao'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2006
DOI: 10.1109/TNET.2006.872552
It has been shown that as long as traffic sources adapt their rates to aggregate congestion measure in their paths, they implicitly maximize certain utility. In this paper we study some counter-intuitive throughput behaviors in such networks, pertaining to whether a fair allocation is always inefficient and whether increasing capacity always raises aggregate throughput. A bandwidth allocation policy can be defined in terms of a class of utility functions parameterized by a scalar a that can be interpreted as a quantitative measure of fairness. An allocation is fair if alpha is large and efficient if aggregate throughput is large. All examples in the literature suggest that a fair allocation is necessarily inefficient. We characterize exactly the tradeoff between fairness and throughput in general networks. The characterization allows us both to produce the first counter-example and trivially explain all the previous supporting examples. Surprisingly, our counter-example has the property that a fairer allocation is always more efficient. In particular it implies that maxmin fairness can achieve a higher throughput than proportional fairness. Intuitively, we might expect that increasing link capacities always raises aggregate throughput. We show that not only can throughput be reduced when some link increases its capacity, more strikingly, it can also be reduced when all links increase their capacities by the same amount. If all links increase their capacities proportionally, however, throughput will indeed increase. These examples demonstrate the intricate interactions among sources in a network setting that are missing in a single-link topology.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/gqjp0-a5m72Guest Editorial: Nonlinear Optimization of Communication Systems
https://resolver.caltech.edu/CaltechAUTHORS:CHIieeejsac06
Authors: {'items': [{'id': 'Chiang-Mung', 'name': {'family': 'Chiang', 'given': 'Mung'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Luo-Zhi-Quan', 'name': {'family': 'Luo', 'given': 'Zhi-Quan'}}, {'id': 'Shroff-N-B', 'name': {'family': 'Shroff', 'given': 'Ness B.'}}, {'id': 'Yu-Wei', 'name': {'family': 'Yu', 'given': 'Wei'}}]}
Year: 2006
DOI: 10.1109/JSAC.2006.879335
Linear programming and other classical optimization techniques have found important applications in communication systems for many decades. Recently, there has been a surge in research activities that utilize the latest developments in nonlinear optimization to tackle a much wider scope of work in the analysis and design of communication systems. These activities involve every "layer" of the protocol stack and the principles of layered network architecture itself, and have made intellectual and practical impacts significantly beyond the established frameworks of optimization of communication systems in the early 1990s. These recent results are driven by new demands in the areas of communications and networking, as well as new tools emerging from optimization theory. Such tools include the powerful theories and highly efficient computational algorithms for nonlinear convex optimization, together with global solution methods and relaxation techniques for nonconvex optimization.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/seeza-4qa15Grid Networks and TCP Services, Protocols, and Technologies
https://resolver.caltech.edu/CaltechAUTHORS:20170810-104241948
Authors: {'items': [{'id': 'Wydrowski-B-P', 'name': {'family': 'Wydrowski', 'given': 'Bartek'}}, {'id': 'Hegde-S', 'name': {'family': 'Hegde', 'given': 'Sanjay'}}, {'id': 'Suchara-M', 'name': {'family': 'Suchara', 'given': 'Martin'}}, {'id': 'Witt-R', 'name': {'family': 'Witt', 'given': 'Ryan'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2006
DOI: 10.1002/0470028696.ch8
[No abstract]https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/5zrtn-ns835Rate Control for Multicast with Network Coding
https://resolver.caltech.edu/CaltechCDSTR:2006.004
Authors: {'items': [{'id': 'Chen-Lijun', 'name': {'family': 'Chen', 'given': 'Lijun'}}, {'id': 'Ho-Tracey', 'name': {'family': 'Ho', 'given': 'Tracey'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Chiang-Mung', 'name': {'family': 'Chiang', 'given': 'Mung'}}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John'}, 'orcid': '0000-0002-1828-2486'}]}
Year: 2006
Recent advances in network coding have shown great potential for efficient information multicasting in communication networks, in terms of both network throughput and network management. In this paper, we address the problem of rate control at end-systems for network coding based multicast flows. We develop two adaptive rate control algorithms for the networks with given coding subgraphs and without given coding subgraphs, respectively. With random network coding, both algorithms can be implemented in a distributed manner, and work at transport layer to adjust source rates and at network layer to carry out network coding. We prove that the proposed algorithms converge to the globally optimal solutions. Some related issues are discussed, and numerical examples are provided to complement our theoretical analysis.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/9rz0z-ect67Layering as Optimization Decomposition: Questions and Answers
https://resolver.caltech.edu/CaltechAUTHORS:20170508-172152981
Authors: {'items': [{'id': 'Chiang-Mung', 'name': {'family': 'Chiang', 'given': 'Mung'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Calderbank-A-R', 'name': {'family': 'Calderbank', 'given': 'A. Robert'}}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John C.'}, 'orcid': '0000-0002-1828-2486'}]}
Year: 2006
DOI: 10.1109/MILCOM.2006.302293
Network protocols in layered architectures have historically been obtained on an ad-hoc basis, and much of the recent cross-layer designs are conducted through piecemeal approaches. Network protocols may instead be holistically analyzed and systematically designed as distributed solutions to some global optimization problems in the form of generalized Network Utility Maximization (NUM), providing insight on what they optimize and on the structures of network protocol stacks. In the form of 10 Questions and Answers, this paper presents a short survey of the recent efforts towards a systematic understanding of "layering" as "optimization decomposition". The overall communication network is modeled by a generalized NUM problem, each layer corresponds to a decomposed subproblem, and the interfaces among layers are quantified as functions of the optimization variables coordinating the subproblems. Furthermore, there are many alternative decompositions, each leading to a different layering architecture. Industry adoption of this unifying framework has also started. Here we summarize the current status of horizontal decomposition into distributed computation and vertical decomposition into functional modules such as congestion control, routing, scheduling, random access, power control, and coding. We also discuss under-explored future research directions in this area. More importantly than proposing any particular crosslayer design, this framework is working towards a mathematical foundation of network architectures and the design process of modularization.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/j9v2d-wea54The Design and Implementation of the Transatlantic Mission-Oriented Production and Experimental Networks
https://resolver.caltech.edu/CaltechAUTHORS:20170502-174109168
Authors: {'items': [{'id': 'Newman-H-B', 'name': {'family': 'Newman', 'given': 'Harvey'}, 'orcid': '0000-0003-0964-1480'}, {'id': 'Bourilkov-D', 'name': {'family': 'Bourilkov', 'given': 'Dimitri'}}, {'id': 'Bunn-Julian-J', 'name': {'family': 'Bunn', 'given': 'Julian'}, 'orcid': '0000-0002-3798-298X'}, {'id': 'Cavanaugh-R', 'name': {'family': 'Cavanaugh', 'given': 'Richard'}}, {'id': 'Legrand-I', 'name': {'family': 'Legrand', 'given': 'Iosif'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'McKee-S', 'name': {'family': 'McKee', 'given': 'Shawn'}}, {'id': 'Nae-D', 'name': {'family': 'Nae', 'given': 'Dan'}}, {'id': 'Ravot-S', 'name': {'family': 'Ravot', 'given': 'Sylvain'}}, {'id': 'Steenberg-C-D', 'name': {'family': 'Steenberg', 'given': 'Conrad'}}, {'id': 'Su-Xun', 'name': {'family': 'Su', 'given': 'Xun'}}, {'id': 'Thomas-Michael', 'name': {'family': 'Thomas', 'given': 'Michael'}}, {'id': 'van-Lingen-Frank', 'name': {'family': 'van Lingen', 'given': 'Frank'}}, {'id': 'Xia-Yang', 'name': {'family': 'Xia', 'given': 'Yang'}}]}
Year: 2006
DOI: 10.1109/E-SCIENCE.2006.261126
In this paper we present the design and implementation of the mission-oriented USLHCNet for HEP research community and the UltraLight network testbed. The design philosophy for these networks is to help meet the data-intensive computing challenges of the next generation of particle physics experiments with a comprehensive, network-focused approach. Instead of treating the network as a static, unchanging and unmanaged set of intercomputer links, we are developing and using it as a dynamic, configurable, and closely monitored resource that is managed from end-to-end. In this paper we will present our work in the various areas of the project including infrastructure construction, protocol research and application development. Our goal is to construct a next-generation global system that is able to meet the data processing, distribution, access and analysis needs of the particle physics community.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/kaa44-4z777Global Exponential Stability of FAST TCP
https://resolver.caltech.edu/CaltechAUTHORS:20170508-165210453
Authors: {'items': [{'id': 'Choi-Joon-Young', 'name': {'family': 'Choi', 'given': 'Joon-Young'}}, {'id': 'Koo-Kyungmo', 'name': {'family': 'Koo', 'given': 'Kyungmo'}}, {'id': 'Wei-Xiaoliang-David', 'name': {'family': 'Wei', 'given': 'David X.'}}, {'id': 'Lee-Jin-S', 'name': {'family': 'Lee', 'given': 'Jin S.'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2006
DOI: 10.1109/CDC.2006.377711
We consider a single-link multi-source network with the FAST TCP sources. We propose a continuous-time dynamic model for the FAST TCP sources and a static model to describe the queuing delay behavior at the link. The proposed model turns out to be in a form revealing the network feedback delay, which allows us to analyze FAST TCP in due consideration of the network feedback delay. Based on the proposed model, we show the boundedness of both each source's congestion window and the queuing delay at the link; and the global exponential stability under a trivial condition that each source's congestion control parameter a is positive. The simulation results illustrate the validity of the proposed model and the global exponential stability of FAST TCP.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/deaz4-3qm82FAST TCP: Motivation, Architecture, Algorithms, Performance
https://resolver.caltech.edu/CaltechAUTHORS:WEIieeeacmtn06
Authors: {'items': [{'id': 'Wei-Xiaoliang-David', 'name': {'family': 'Wei', 'given': 'David X.'}}, {'id': 'Jin-Cheng', 'name': {'family': 'Jin', 'given': 'Cheng'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Hegde-S', 'name': {'family': 'Hegde', 'given': 'Sanjay'}}]}
Year: 2006
DOI: 10.1109/TNET.2006.886335
We describe FAST TCP, a new TCP congestion control algorithm for high-speed long-latency networks, from design to implementation. We highlight the approach taken by FAST TCP to address the four difficulties which the current TCP implementation has at large windows. We describe the architecture and summarize some of the algorithms implemented in our prototype. We characterize its equilibrium and stability properties. We evaluate it experimentally in terms of throughput, fairness, stability, and responsiveness.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/c3vmh-t3e61Application-Oriented Flow Control: Fundamentals, Algorithms and Fairness
https://resolver.caltech.edu/CaltechAUTHORS:WANiatnet06
Authors: {'items': [{'id': 'Wang-W-H', 'name': {'family': 'Wang', 'given': 'Wei-Hua'}}, {'id': 'Palaniswami-M', 'name': {'family': 'Palaniswami', 'given': 'Marimuthu'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2006
DOI: 10.1109/TNET.2006.886318
This paper is concerned with flow control and resource allocation problems in computer networks in which real-time applications may have hard quality of service (QoS) requirements. Recent optimal flow control approaches are unable to deal with these problems since QoS utility functions generally do not satisfy the strict concavity condition in real-time applications. For elastic traffic, we show that bandwidth allocations using the existing optimal flow control strategy can be quite unfair. If we consider different QoS requirements among network users, it may be undesirable to allocate bandwidth simply according to the traditional max-min fairness or proportional fairness. Instead, a network should have the ability to allocate bandwidth resources to various users, addressing their real utility requirements. For these reasons, this paper proposes a new distributed flow control algorithm for multiservice networks, where the application's utility is only assumed to be continuously increasing over the available bandwidth. In this, we show that the algorithm converges, and that at convergence, the utility achieved by each application is well balanced in a proportionally (or max-min) fair manner.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/p1t1x-6n314Reverse Engineering TCP/IP-like Networks using
Delay-Sensitive Utility Functions
https://resolver.caltech.edu/CaltechAUTHORS:20101005-121412518
Authors: {'items': [{'id': 'Pongsajapan-J', 'name': {'family': 'Pongsajapan', 'given': 'John'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2007
DOI: 10.1109/INFCOM.2007.56
TCP/IP can be interpreted as a distributed primal-dual algorithm to maximize aggregate utility over source rates. It has recently been shown that an equilibrium of TCP/IP, if it exists, maximizes the same delay-insensitive utility over both source rates and routes, provided pure congestion prices are used as link costs in the shortest-path calculation of IP. In practice, however, pure dynamic routing is never used and link costs are weighted sums of both static as well as dynamic components. In this paper, we introduce delay-sensitive utility functions and identify a class of utility functions that such a TCP/IP equilibrium optimizes. We exhibit some counter-intuitive properties that any class of delay-sensitive utility functions optimized by TCP/IP necessarily possess. We prove a sufficient condition for global stability of routing updates for general networks. We construct example networks that defy conventional wisdom on the effect of link cost parameters on network stability and utility.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/8w14h-arr72Optimization Based Rate Control for Multicast with Network Coding
https://resolver.caltech.edu/CaltechAUTHORS:20100826-092317616
Authors: {'items': [{'id': 'Chen-Lijun', 'name': {'family': 'Chen', 'given': 'Lijun'}}, {'id': 'Ho-Tracey', 'name': {'family': 'Ho', 'given': 'Tracey'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Chiang-Mung', 'name': {'family': 'Chiang', 'given': 'Mung'}}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John C.'}, 'orcid': '0000-0002-1828-2486'}]}
Year: 2007
DOI: 10.1109/INFCOM.2007.139
Recent advances in network coding have shown
great potential for efficient information multicasting in communication
networks, in terms of both network throughput and
network management. In this paper, we address the problem of
rate control at end-systems for network coding based multicast
flows. We develop two adaptive rate control algorithms for
the networks with given coding subgraphs and without given
coding subgraphs, respectively. With random network coding,
both algorithms can be implemented in a distributed manner, and
work at transport layer to adjust source rates and at network
layer to carry out network coding. We prove that the proposed
algorithms converge to the globally optimal solutions for intrasession
network coding. Some related issues are discussed, and
numerical examples are provided to complement our theoretical
analysis.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/w4e9r-dpk91Opportunistic Source Coding for Data Gathering in Wireless Sensor Networks
https://resolver.caltech.edu/CaltechAUTHORS:20100827-112133009
Authors: {'items': [{'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Chen-Lijun', 'name': {'family': 'Chen', 'given': 'Lijun'}}, {'id': 'Ho-Tracey', 'name': {'family': 'Ho', 'given': 'Tracey'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Andrew-L-L-H', 'name': {'family': 'Andrew', 'given': 'Lachlan L. H.'}}]}
Year: 2007
DOI: 10.1109/MOBHOC.2007.4428675
We propose a jointly opportunistic source coding and opportunistic routing (OSCOR) protocol for correlated data gathering in wireless sensor networks. OSCOR improves data gathering efficiency by exploiting opportunistic data compression and cooperative diversity associated with wireless broadcast advantage. The design of OSCOR involves several challenging issues across different network protocol layers. At the MAC layer, sensor nodes need to coordinate wireless transmission and packet forwarding to exploit multiuser diversity in packet reception. At the network layer, in order to achieve high diversity and compression gains, routing must be based on a metric that is dependent on not only link-quality but also compression opportunities. At the application layer, sensor nodes need a distributed source coding algorithm that has low coordination overhead and does not require the source distributions to be known. OSCOR provides practical solutions to these challenges incorporating a slightly modified 802.11 MAC, a distributed source coding scheme based on network coding and Lempel-Ziv coding, and a node compression ratio dependent metric combined with a modified Dijkstra's algorithm for path selection. We evaluate the performance of OSCOR through simulations, and show that OSCOR can potentially reduce power consumption by over 30% compared with an existing greedy scheme, routing driven compression, in a 4 x 4 grid network.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/v67bc-w4e96Modelling and stability of FAST TCP
https://resolver.caltech.edu/CaltechAUTHORS:20101029-153050412
Authors: {'items': [{'id': 'Wang-Jintao', 'name': {'family': 'Wang', 'given': 'Jiantao'}}, {'id': 'Wei-Xiaoliang-David', 'name': {'family': 'Wei', 'given': 'David X.'}}, {'id': 'Choi-Joon-Young', 'name': {'family': 'Choi', 'given': 'Joon-Young'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2007
DOI: 10.1007/978-0-387-48945-2_14
We discuss the modelling of FAST TCP and prove four stability results. Using the traditional continuous-time flow model, we prove, for general networks, that FAST TCP is globally asymptotically stable when there is no feedback delay and that it is locally asymptotically stable in the presence of feedback delay provided a local stability condition is satisfied. We present an experiment on an emulated network in which the local stability condition is violated. While the theory predicts instability, the experiment shows otherwise. We believe this is because the continuous-time model ignores the stabilizing effect of self-clocking. Using a discrete-time model that captures this effect, we show that FAST TCP is locally asymptotically stable for general networks if all flows have the same feedback delay, no matter how large the delay is. We also prove global asymptotic stability for a single bottleneck link in the absence of feedback delay. The techniques developed here are new and applicable to other protocols.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/9gq55-tdf26Modelling and stability of FAST TCP
https://resolver.caltech.edu/CaltechAUTHORS:20101202-160829940
Authors: {'items': [{'id': 'Wang-Jintao', 'name': {'family': 'Wang', 'given': 'Jiantao'}}, {'id': 'Wei-Xiaoliang-David', 'name': {'family': 'Wei', 'given': 'David X.'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2007
DOI: 10.1109/INFCOM.2005.1498323
We introduce a discrete-time model of FAST TCP that fully captures the effect of self-clocking and compare it with the traditional continuous-time model. While the continuous-time model predicts instability for homogeneous sources sharing a single link when feedback delay is large, experiments suggest otherwise. Using the discrete-time model, we prove that FAST TCP is locally asymptotically stable in general networks when all sources have a common round-trip feedback delay, no matter how large the delay is. We also prove global stability for a single bottleneck link in the absence of feedback delay. The techniques developed here are new and applicable to other protocols.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/msnwd-y4x66Dual scheduling algorithm in a generalized switch: asymptotic optimality and throughput optimality
https://resolver.caltech.edu/CaltechAUTHORS:20170810-103710158
Authors: {'items': [{'id': 'Chen-Lijun', 'name': {'family': 'Chen', 'given': 'Lijun'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John C.'}, 'orcid': '0000-0002-1828-2486'}]}
Year: 2007
DOI: 10.1007/1-84628-274-8_7
In this article, we consider the dual scheduling algorithm for a generalized switch. For a saturated system, we prove the asymptotic optimality of the dual scheduling algorithm and thus establish its fairness properties. For a system with exogenous arrivals, we propose a modified dual scheduling algorithm, which is throughput-optimal while providing some weighted fairness among the users at the level of flows.
The dual scheduling algorithm motivates a new architecture for scheduling, in which an additional queue is introduced to interface the user data queue and the time-varying server and to modulate the scheduling process, so as to achieve different performance objectives. Further research stemming out of this article includes scheduling with Quality of Service guarantees with the dual scheduler, and its application and implementation in various versions of the generalized switch model.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/fnwed-6cv31An Accurate Link Model and Its Application to Stability Analysis of FAST TCP
https://resolver.caltech.edu/CaltechAUTHORS:20101008-113059058
Authors: {'items': [{'id': 'Tang-Ao', 'name': {'family': 'Tang', 'given': 'Ao'}, 'orcid': '0000-0001-6296-644X'}, {'id': 'Jacobsson-K', 'name': {'family': 'Jacobsson', 'given': 'Krister'}}, {'id': 'Andrew-L-L-H', 'name': {'family': 'Andrew', 'given': 'Lachlan L. H.'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2007
DOI: 10.1109/INFCOM.2007.27
This paper presents a link model which captures the queue dynamics when congestion windows of TCP sources change. By considering both the self-clocking and the link integrator effects, the model is a generalization of existing models and is shown to be more accurate by both open loop and closed loop packet level simulations. It reduces to the known static link model when flows' round trip delays are similar, and approximates the standard integrator link model when the heterogeneity of round trip delays is significant. We then apply this model to the stability analysis of FAST TCP. It is shown that FAST TCP flows over a single link are always linearly stable regardless of delay distribution. This result resolves the notable discrepancy between empirical observations and previous theoretical predictions. The analysis highlights the critical role of self-clocking in TCP stability and the scalability of FAST TCP with respect to delay. The proof technique is new and less conservative than the existing ones.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/5h49v-2ws14Layering as Optimization Decomposition: A Mathematical Theory of Network Architectures
https://resolver.caltech.edu/CaltechAUTHORS:20170810-104152899
Authors: {'items': [{'id': 'Chiang-Mung', 'name': {'family': 'Chiang', 'given': 'Mung'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Calderbank-A-R', 'name': {'family': 'Calderbank', 'given': 'A. Robert'}}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John C.'}, 'orcid': '0000-0002-1828-2486'}]}
Year: 2007
DOI: 10.1109/JPROC.2006.887322
Network protocols in layered architectures have historically been obtained on an ad hoc basis, and many of the recent cross-layer designs are also conducted through piecemeal approaches. Network protocol stacks may instead be holistically analyzed and systematically designed as distributed solutions to some global optimization problems. This paper presents a survey of the recent efforts towards a systematic understanding of layering as optimization decomposition, where the overall communication network is modeled by a generalized network utility maximization problem, each layer corresponds to a decomposed subproblem, and the interfaces among layers are quantified as functions of the optimization variables coordinating the subproblems. There can be many alternative decompositions, leading to a choice of different layering architectures. This paper surveys the current status of horizontal decomposition into distributed computation, and vertical decomposition into functional modules such as congestion control, routing, scheduling, random access, power control, and channel coding. Key messages and methods arising from many recent works are summarized, and open issues discussed. Through case studies, it is illustrated how layering as Optimization Decomposition provides a common language to think about modularization in the face of complex, networked interactions, a unifying, top-down approach to design protocol stacks, and a mathematical theory of network architectures.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/x0zpr-rff66WAN-in-Lab: Motivation, deployment and experiments
https://resolver.caltech.edu/CaltechAUTHORS:20170810-135412130
Authors: {'items': [{'id': 'Lee-George-S', 'name': {'family': 'Lee', 'given': 'George S.'}}, {'id': 'Andrew-L-L-H', 'name': {'family': 'Andrew', 'given': 'Lachlan L. H.'}}, {'id': 'Tang-Ao', 'name': {'family': 'Tang', 'given': 'Ao'}, 'orcid': '0000-0001-6296-644X'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2007
WAN-in-Lab is a hardware testbed for the design, development, testing and evaluation of high speed network protocols. It uses real carrier-class networking hardware to avoid the artifacts introduced by network simulation and emulation, while being localized to allow detailed measurement of network performance. WAN-in-Lab is an open resource, available for use by the networking community. This paper describes the structure of WAN-in-Lab and the rationale behind it, issues encountered, and experimental results that illustrate its applications.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/1d5mx-wca85Global finite-time convergence of TCP Vegas without feedback information delay
https://resolver.caltech.edu/CaltechAUTHORS:20170810-105633790
Authors: {'items': [{'id': 'Choi-Joon-Young', 'name': {'family': 'Choi', 'given': 'Joon-Young'}}, {'id': 'Koo-Kyungmo', 'name': {'family': 'Koo', 'given': 'Kyungmo'}}, {'id': 'Lee-Jin-S', 'name': {'family': 'Lee', 'given': 'Jin S.'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2007
We prove that TCP Vegas globally converges to its equilibrium point in finite time assuming no feedback information delay. We analyze a continuous-time TCP Vegas model with discontinuity and high nonlinearity. Using the upper right-hand derivative and applying the comparison lemma, we cope with the discontinuous signum function in the TCP Vegas model; using a change of state variables, we deal with the high nonlinearity. Although we ignore feedback information delay in analyzing the model of TCP Vegas, the simulation results illustrate that TCP Vegas in the presence of feedback information delay shows very similar dynamic trends to TCP Vegas without feedback information delay. Consequently, dynamic properties of TCP Vegas without feedback information delay can be used to estimate those of TCP Vegas in the presence of feedback information delay.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/qtxv6-j4718Heterogeneous Congestion Control: Efficiency, Fairness and Design
https://resolver.caltech.edu/CaltechAUTHORS:TANicnp06
Authors: {'items': [{'id': 'Tang-Ao', 'name': {'family': 'Tang', 'given': 'Ao'}, 'orcid': '0000-0001-6296-644X'}, {'id': 'Wei-Xiaoliang-D', 'name': {'family': 'Wei', 'given': 'David'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Chiang-Mung', 'name': {'family': 'Chiang', 'given': 'Mung'}}]}
Year: 2007
DOI: 10.1109/ICNP.2006.320206
When heterogeneous congestion control protocols that react to different pricing signals (e.g. packet loss, queueing delay, ECN marking etc.) share the same network, the current theory based on utility maximization fails to predict the network behavior. Unlike in a homogeneous network, the bandwidth allocation now depends on router parameters and flow arrival patterns. It can be non-unique, inefficient and unfair. This paper has two objectives. First, we demonstrate the intricate behaviors of a heterogeneous network through simulations and present a rigorous framework to help understand its equilibrium efficiency and fairness properties. By identifying an optimization problem associated with every equilibrium, we show that every equilibrium is Pareto efficient and provide an upper bound on efficiency loss due to pricing heterogeneity. On fairness, we show that intra-protocol fairness is still decided by a utility maximization problem while inter-protocol fairness is the part over which we don¿t have control. However it is shown that we can achieve any desirable inter-protocol fairness by properly choosing protocol parameters. Second, we propose a simple slow timescale source-based algorithm to decouple bandwidth allocation from router parameters and flow arrival patterns and prove its feasibility. The scheme needs only local information.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/78ve5-mts17Packet Loss Burstiness: Measurements and Implications for Distributed Applications
https://resolver.caltech.edu/CaltechAUTHORS:20170419-174638253
Authors: {'items': [{'id': 'Wei-Xiaoliang-David', 'name': {'family': 'Wei', 'given': 'David X.'}}, {'id': 'Cao-Pei', 'name': {'family': 'Cao', 'given': 'Pei'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2007
DOI: 10.1109/IPDPS.2007.370412
Many modern massively distributed systems deploy thousands of nodes to cooperate on a computation task. Network congestions occur in these systems. Most applications rely on congestion control protocols such as TCP to protect the systems from congestion collapse. Most TCP congestion control algorithms use packet loss as signal to detect congestion. In this paper, we study the packet loss process in sub-round-trip-time (sub-RTT) timescale and its impact on the loss-based congestion control algorithms. Our study suggests that the packet loss in sub-RTT timescale is very bursty. This burstiness leads to two effects. First, the sub-RTT burstiness in packet loss process leads to complicated interactions between different loss-based algorithms. Second, the sub-RTT burstiness in packet loss process makes the latency of data transfers under TCP hard to predict. Our results suggest that the design of a distributed system has to seriously consider the nature of packet loss process and carefully select the congestion control algorithms best suited for the distributed computation environments.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/mvqrw-jmx06Asynchronous Distributed Averaging on Communication Networks
https://resolver.caltech.edu/CaltechAUTHORS:MEHieeeacmtn07
Authors: {'items': [{'id': 'Mehyar-M', 'name': {'family': 'Mehyar', 'given': 'Mortada'}}, {'id': 'Spanos-D-P', 'name': {'family': 'Spanos', 'given': 'Demetri'}}, {'id': 'Pongsajapan-J', 'name': {'family': 'Pongsajapan', 'given': 'John'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Murray-R-M', 'name': {'family': 'Murray', 'given': 'Richard M.'}, 'orcid': '0000-0002-5785-7481'}]}
Year: 2007
DOI: 10.1109/TNET.2007.893226
Distributed algorithms for averaging have attracted interest in the control and sensing literature. However, previous works have not addressed some practical concerns that will arise in actual implementations on packet-switched communication networks such as the Internet. In this paper, we present several implementable algorithms that are robust to asynchronism and dynamic topology changes. The algorithms are completely distributed and do not require any global coordination. In addition, they can be proven to converge under very general asynchronous timing assumptions. Our results are verified by both simulation and experiments on Planetlab, a real-world TCP/IP network. We also present some extensions that are likely to be useful in applications.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/90y8e-k4732Opportunistic Source Coding for Data Gathering in Wireless Sensor Networks
https://resolver.caltech.edu/CaltechCSTR:2007.003
Authors: {'items': [{'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Chen-Lijun', 'name': {'family': 'Chen', 'given': 'Lijun'}}, {'id': 'Ho-Tracey', 'name': {'family': 'Ho', 'given': 'Tracey'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2007
DOI: 10.7907/Z9G73BP6
We propose a jointly opportunistic source
coding and opportunistic routing (OSCOR) protocol for
correlated data gathering in wireless sensor networks.
OSCOR improves data gathering efficiency by exploiting
opportunistic data compression and cooperative diversity
associated with wireless broadcast advantage. The design
of OSCOR involves several challenging issues across different
network protocol layers. At MAC layer, sensor nodes
need to coordinate wireless transmission and packet forwarding
to exploit multiuser diversity in packet reception.
At network layer, in order to achieve high diversity and
compression gains, routing must be based on a metric that
is dependent on not only link-quality but also compression
opportunities. At application layer, sensor nodes need a distributed
source coding algorithm that has low coordination
overhead and does not require the source distributions to
be known. OSCOR provides practical solutions to these
challenges incorporating a slightly modified 802.11 MAC,
a distributed source coding scheme based on Lempel-Ziv
code and network coding, and a node compression ratio
dependent metric combined with a modified Dijkstra"s
algorithm for path selection. We evaluate the performance
of OSCOR through simulations, and show that OSCOR
reduces the number of transmissions by nearly 25%
compared with existing greedy scheme in small networks.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/dd849-24158Optimal Strategies for Efficient Peer-to-Peer File Sharing
https://resolver.caltech.edu/CaltechAUTHORS:MEHicassp07
Authors: {'items': [{'id': 'Mehyar-M', 'name': {'family': 'Mehyar', 'given': 'Mortada'}}, {'id': 'Gu-WeiHsin', 'name': {'family': 'Gu', 'given': 'WeiHsin'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Effros-M', 'name': {'family': 'Effros', 'given': 'Michelle'}}, {'id': 'Ho-Tracey', 'name': {'family': 'Ho', 'given': 'Tracey'}}]}
Year: 2007
DOI: 10.1109/ICASSP.2007.367325
We study a model for peer-to-peer file sharing. The goal is to distribute a file from a server to multiple peers. We assume the upload capacity of each peer is the only bottleneck. We examine the finish times of peers under different transmission strategies. Pareto optimality, min-max finish time, and optimal average finish time of the model are studied. We believe the results provide fundamental insights into practical peer-to-peer systems such as BitTorrent.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/manj6-p7b87Equilibrium of Heterogeneous Congestion Control: Existence and Uniqueness
https://resolver.caltech.edu/CaltechAUTHORS:TANieeeacmtn07
Authors: {'items': [{'id': 'Tang-Ao', 'name': {'family': 'Tang', 'given': 'Ao'}, 'orcid': '0000-0001-6296-644X'}, {'id': 'Wang-Jintao', 'name': {'family': 'Wang', 'given': 'Jiantao'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Chiang-Mung', 'name': {'family': 'Chiang', 'given': 'Mung'}}]}
Year: 2007
DOI: 10.1109/TNET.2007.893885
When heterogeneous congestion control protocols that react to different pricing signals share the same network, the resulting equilibrium may no longer be interpreted as a solution to the standard utility maximization problem. We prove the existence of equilibrium in general multiprotocol networks under mild assumptions. For almost all networks, the equilibria are locally unique, finite, and odd in number. They cannot all be locally stable unless there is a globally unique equilibrium. Finally, we show that if the price mapping functions, which map link prices to effective prices observed by the sources, are sufficiently similar, then global uniqueness is guaranteed.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/t9md6-zs710Contention control: A game-theoretic approach
https://resolver.caltech.edu/CaltechAUTHORS:CHEcdc07
Authors: {'items': [{'id': 'Chen-Lijun', 'name': {'family': 'Chen', 'given': 'Lijun'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John C.'}, 'orcid': '0000-0002-1828-2486'}]}
Year: 2007
DOI: 10.1109/CDC.2007.4435015
We present a game-theoretic approach to contention control. We define a game-theoretic model, called random access game, to capture the contention/interaction among wireless nodes in wireless networks with contention-based medium access. We characterize Nash equilibria of random access games, study their dynamics and propose distributed algorithms (strategy evolutions) to achieve the Nash equilibria. This provides a general analytical framework that is capable of modelling a large class of systemwide quality of service models via the specification of per-node utility functions, in which systemwide fairness or service differentiation can be achieved in a distributed manner as long as each node executes a contention resolution algorithm that is designed to achieve the Nash equilibrium. We thus design medium access method according to distributed strategy update mechanism achieving the Nash equilibrium of random access game. In addition to guiding medium access control design, the random access game model also provides an analytical framework to understand equilibrium and dynamic properties of different medium access protocols and their interactions.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/y1aw1-ctj82ACK-Clocking Dynamics: Modelling the Interaction between Windows and the Network
https://resolver.caltech.edu/CaltechAUTHORS:20170810-130929589
Authors: {'items': [{'id': 'Jacobsson-K', 'name': {'family': 'Jacobsson', 'given': 'Krister'}}, {'id': 'Andrew-L-L-H', 'name': {'family': 'Andrew', 'given': 'Lachlan L. H.'}}, {'id': 'Tang-Ao', 'name': {'family': 'Tang', 'given': 'Ao'}, 'orcid': '0000-0001-6296-644X'}, {'id': 'Johansson-K-H', 'name': {'family': 'Johansson', 'given': 'Karl H.'}}, {'id': 'Hjalmarsson-H', 'name': {'family': 'Hjalmarsson', 'given': 'Håkan'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2008
DOI: 10.1109/INFOCOM.2008.281
A novel continuous time fluid flow model of the dynamics of the interaction between ACK-clocking and the link buffer is presented. A fundamental integral equation relating the instantaneous flow rate and the window dynamics is derived. Properties of the model, such as well-posedness and stability, are investigated. Packet level experiments verify that this new model is more accurate than existing models, correctly predicting qualitatively different behaviors, for example when round trip delays are heterogeneous.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/y34pw-fjt23Progress on pricing with peering
https://resolver.caltech.edu/CaltechAUTHORS:20100721-152913560
Authors: {'items': [{'id': 'Lee-Eui-woong', 'name': {'family': 'Lee', 'given': 'Eui-woong'}}, {'id': 'Buchfuhrer-D', 'name': {'family': 'Buchfuhrer', 'given': 'David'}}, {'id': 'Andrew-L-L-H', 'name': {'family': 'Andrew', 'given': 'Lachlan L. H.'}}, {'id': 'Tang-Ao', 'name': {'family': 'Tang', 'given': 'Ao'}, 'orcid': '0000-0001-6296-644X'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2008
DOI: 10.1109/CISS.2008.4558537
This paper examines a simple model of how a
provider ISP charges customer ISPs by assuming the provider
ISP wants to maximize its revenue when customer ISPs have
the possibility of setting up peering connections. It is shown that
finding the optimal pricing is NP-complete, and APX-complete.
Customers can respond to price in many ways, including throttling
traffic as well as peering. An algorithm is studied which
obtains a 1/4 approximation for a wide range of customer
responses.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/z56fc-7de71A Game-Theoretic Framework for Medium Access Control
https://resolver.caltech.edu/CaltechAUTHORS:CUIieeejsac08
Authors: {'items': [{'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Chen-Lijun', 'name': {'family': 'Chen', 'given': 'Lijun'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2008
DOI: 10.1109/JSAC.2008.080909
In this paper, we generalize the random access game model, and show that it provides a general game-theoretic framework for designing contention based medium access control. We extend the random access game model to the network with multiple contention measure signals, study the design of random access games, and analyze different distributed algorithms achieving their equilibria. As examples, a series of utility functions is proposed for games achieving the maximum throughput in a network of homogeneous nodes. In a network with n traffic classes, an N-signal game model is proposed which achieves the maximum throughput under the fairness constraint among different traffic classes. In addition, the convergence of different dynamic algorithms such as best response, gradient play and Jacobi play under propagation delay and estimation error is established. Simulation results show that game model based protocols can achieve superior performance over the standard IEEE 802.11 DCF, and comparable performance as existing protocols with the best performance in literature.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/gv77s-5zg41Implementation of Provably Stable MaxNet
https://resolver.caltech.edu/CaltechAUTHORS:20100802-104528960
Authors: {'items': [{'id': 'Suchara-M', 'name': {'family': 'Suchara', 'given': 'Martin'}}, {'id': 'Andrew-L-L-H', 'name': {'family': 'Andrew', 'given': 'Lachlan L. H.'}}, {'id': 'Witt-R', 'name': {'family': 'Witt', 'given': 'Ryan'}}, {'id': 'Jacobsson-K', 'name': {'family': 'Jacobsson', 'given': 'Krister'}}, {'id': 'Wydrowski-B-P', 'name': {'family': 'Wydrowski', 'given': 'Bartek P.'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2009
DOI: 10.1109/BROADNETS.2008.4769143
MaxNet TCP is a congestion control protocol that uses explicit multi-bit signalling from routers to achieve desirable properties such as high throughput and low latency. In this paper we present an implementation of an extended version of MaxNet. Our contributions are threefold. First, we extend the original algorithm to give both provable stability and rate fairness. Second, we introduce the MaxStart algorithm which allows new MaxNet connections to reach their fair rates quickly. Third, we provide a Linux kernel implementation of the protocol. With no overhead but 24-bit price signals, our implementation scales from 32 bit/s to 1 peta-bit/s with a 0.001% rate accuracy. We confirm the theoretically predicted properties by performing a range of experiments at speeds up to 1 Gbit/sec and delays up to 180 ms on the WAN-in-Lab facility.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/zka2f-32463An Improved Link Model for Window Flow Control and Its Application to FAST TCP
https://resolver.caltech.edu/CaltechAUTHORS:20090415-081549907
Authors: {'items': [{'id': 'Jacobsson-K', 'name': {'family': 'Jacobsson', 'given': 'Krister'}}, {'id': 'Andrew-L-L-H', 'name': {'family': 'Andrew', 'given': 'Lachlan L. H.'}}, {'id': 'Tang-Ao', 'name': {'family': 'Tang', 'given': 'Ao (Kevin)'}, 'orcid': '0000-0001-6296-644X'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Hjalmarsson-H', 'name': {'family': 'Hjalmarsson', 'given': 'Håkan'}}]}
Year: 2009
DOI: 10.1109/TAC.2009.2012986
This paper presents a link model which captures the queue dynamics in response to a change in a transmission control protocol (TCP) source's congestion window. By considering both self-clocking and the link integrator effect, the model generalizes existing models and is shown to be more accurate by both open loop and closed loop packet level simulations. It reduces to the known static link model when flows' round trip delays are identical, and approximates the standard integrator link model when there is significant cross traffic. We apply this model to the stability analysis of fast active queue management scalable TCP (FAST TCP) including its filter dynamics. Under this model, the FAST control law is linearly stable for a single bottleneck link with an arbitrary distribution of round trip delays. This result resolves the notable discrepancy between empirical observations and previous theoretical predictions. The analysis highlights the critical role of self-clocking in TCP stability, and the proof technique is new and less conservative than existing ones.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/3mrrd-var15End-to-end fair rate optimization in wired-cum-wireless networks
https://resolver.caltech.edu/CaltechAUTHORS:20090922-143224543
Authors: {'items': [{'id': 'Wang-Xingang', 'name': {'family': 'Wang', 'given': 'Xingang'}}, {'id': 'Kar-K', 'name': {'family': 'Kar', 'given': 'Koushik'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2009
DOI: 10.1016/j.adhoc.2008.05.003
In this paper, we address the end-to-end rate optimization problem in a wired-cum-wireless network, where CSMA/CA based wireless LANs extend a wired backbone and provide access to mobile users. The objective is to achieve proportional fairness amongst the end-to-end sessions in the network. Since the network contains wireless links whose attainable throughput is a (non-convex and non-separable) function of MAC protocol parameters, the problem requires joint optimization at both the transport and the link layers. A dual-based algorithm is proposed in this paper to solve this cross-layer rate optimization problem. It is implemented in the distributed manner, and works at the link layer to adjust scheduling rates for the wireless links in the basic service sets, and at the transport layer to adjust end-to-end session rates. We prove rigorously that the proposed algorithm converges to the globally optimal rates. Simulation results are provided to support our conclusions.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/1a086-zh233Optimal job fragmentation
https://resolver.caltech.edu/CaltechAUTHORS:20161206-155547391
Authors: {'items': [{'id': 'Nair-J', 'name': {'family': 'Nair', 'given': 'Jayakrishnan'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2009
DOI: 10.1145/1639562.1639570
It has been recently discovered that on an unreliable server, the job completion time distribution function (df) can be heavy-tailed (HT) even when job size df is light-tailed (LT) [1, 5]. A key to this phenomenon is the RESTART feature where if a job is interrupted in the middle of its processing, the entire job needs to restart from the beginning, i.e., the work that is partially completed is lost.
A standard mechanism for reducing the job completion
time in an unreliable service environment is checkpointing
[3, 4, 6]. We view checkpointing as a job fragmentation operation, where the server processes one fragment of the job at a time. If the server becomes unavailable, say due to failure, then only the work corresponding to the fragment being processed at the time of failure is lost. In this paper, we are motivated by the question: Can fragmentation 'lighten' the tail df of the completion time? In Section 3, we provide sufficient conditions on the fragmentation policy that gives rise to LT completion time so long as the job size df is LT. We then characterize the optimal fragmentation policy seeking to minimize the expected job completion time. This policy
requires a priori knowledge of the job size. We then describe a sub-optimal fragmentation policy that is blind to the job size and is provably very close to optimal. We also describe the asymptotic tail behavior of the job completion time df under both policies. Assuming the server unavailability periods are LT, both policies produce LT completion times when the job size df is LT. For the case of regularly varying job size df, the job completion time under both policies is regularly varying with the same degree - this is the lightest possible asymptotic tail behavior (in the degree sense).https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/6tbes-vrn02How Bad is Single-Path Routing
https://resolver.caltech.edu/CaltechAUTHORS:20170327-172614113
Authors: {'items': [{'id': 'Wang-Meng', 'name': {'family': 'Wang', 'given': 'Meng'}}, {'id': 'Tan-Chee-Wei', 'name': {'family': 'Tan', 'given': 'Chee Wei'}}, {'id': 'Tang-Ao', 'name': {'family': 'Tang', 'given': 'Ao'}, 'orcid': '0000-0001-6296-644X'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2009
DOI: 10.1109/GLOCOM.2009.5425408
This paper investigates the network performance loss of using only single-path routing when multiple paths are available. The performance metric is the aggregate utility achieved by the joint optimization of congestion control and routing. As computing the exact loss for a general network topology is NP-hard, we develop analytical bounds on this "cost of not splitting". Our bound is independent of the number of source-destination pairs when the latter one is larger than the number of links in a network. We also propose a vertex projection method and combine it with branch-and-bound to provide progressively tighter bounds on the performance loss. Numerical examples are used to show the effectiveness of our approximation technique.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/vypy0-0bf02Understanding XCP: Equilibrium and Fairness
https://resolver.caltech.edu/CaltechAUTHORS:20100122-142759802
Authors: {'items': [{'id': 'Andrew-L-L-H', 'name': {'family': 'Andrew', 'given': 'Lachlan L. H.'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Wydrowski-B-P', 'name': {'family': 'Wydrowski', 'given': 'Bartek P.'}}]}
Year: 2009
DOI: 10.1109/TNET.2009.2013242
We prove that the XCP equilibrium solves a constrained max-min fairness problem by identifying it with the unique solution of a hierarchy of optimization problems, namely those solved by max-min fair allocation, but solved by XCP under an additional constraint. This constraint is due to the "bandwidth shuffling" necessary to obtain fairness. We describe an algorithm to compute this equilibrium and derive a lower and upper bound on link utilization. While XCP reduces to max-min allocation at a single link, its behavior in a network can be very different. We illustrate that the additional constraint can cause flows to receive an arbitrarily small fraction of their max-min fair allocations. We confirm these results using ns2 simulations.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/wcf1j-5ja56Congestion control algorithms from optimal control perspective
https://resolver.caltech.edu/CaltechAUTHORS:20170810-133936531
Authors: {'items': [{'id': 'Lavaei-J', 'name': {'family': 'Lavaei', 'given': 'Javad'}}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John C.'}, 'orcid': '0000-0002-1828-2486'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2009
DOI: 10.1109/CDC.2009.5399554
This paper is concerned with understanding the connection between the existing Internet congestion control algorithms and the optimal control theory. The available resource allocation controllers are mainly devised to derive the state of the system to a desired equilibrium point and, therefore, they are oblivious to the transient behavior of the closed-loop system. This work aims to investigate what dynamical functions the existing algorithms maximize (minimize). In particular, it is shown that there exist meaningful cost functionals whose minimization leads to the celebrated primal and dual congestion algorithms. An implication of this result is that a real network problem may be solved by regarding it as an optimal control problem on which some practical constraints, such as a real-time link capacity constraint, are imposed.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/kt7kw-y0808File Fragmentation over an Unreliable Channel
https://resolver.caltech.edu/CaltechAUTHORS:20110401-160938362
Authors: {'items': [{'id': 'Nair-J', 'name': {'family': 'Nair', 'given': 'Jayakrishnan'}}, {'id': 'Andreasson-M', 'name': {'family': 'Andreasson', 'given': 'Martin'}}, {'id': 'Andrew-L-L-H', 'name': {'family': 'Andrew', 'given': 'Lachlan L. H.'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John C.'}, 'orcid': '0000-0002-1828-2486'}]}
Year: 2010
DOI: 10.1109/INFCOM.2010.5461953
It has been recently discovered that heavy-tailed
file completion time can result from protocol interaction even
when file sizes are light-tailed. A key to this phenomenon is
the RESTART feature where if a file transfer is interrupted
before it is completed, the transfer needs to restart from the
beginning. In this paper, we show that independent or bounded
fragmentation guarantees light-tailed file completion time as long
as the file size is light-tailed, i.e., in this case, heavy-tailed file
completion time can only originate from heavy-tailed file sizes.
If the file size is heavy-tailed, then the file completion time is
necessarily heavy-tailed. For this case, we show that when the
file size distribution is regularly varying, then under independent
or bounded fragmentation, the completion time tail distribution
function is asymptotically upper bounded by that of the original
file size stretched by a constant factor. We then prove that if the
failure distribution has non-decreasing failure rate, the expected
completion time is minimized by dividing the file into equal sized
fragments; this optimal fragment size is unique but depends on
the file size. We also present a simple blind fragmentation policy
where the fragment sizes are constant and independent of the
file size and prove that it is asymptotically optimal. Finally, we
bound the error in expected completion time due to error in
modeling of the failure process.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/hw8ym-bf685Utility Functionals Associated With Available Congestion Control Algorithms
https://resolver.caltech.edu/CaltechAUTHORS:20110406-104430537
Authors: {'items': [{'id': 'Lavaei-J', 'name': {'family': 'Lavaei', 'given': 'Javad'}}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John C.'}, 'orcid': '0000-0002-1828-2486'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2010
DOI: 10.1109/INFCOM.2010.5462103
This paper is concerned with understanding the connection between the existing Internet congestion control algorithms and the optimal control theory. The available resource allocation controllers are mainly devised to derive the state of the system to a desired equilibrium point and, therefore, they are oblivious to the transient behavior of the closed-loop system. To take into account the real-time performance of the system, rather than merely its steady-state performance, the congestion control problem should be solved by maximizing a proper utility functional as opposed to a utility function. For this reason, this work aims to investigate what utility functionals the existing congestion control algorithms maximize. In particular, it is shown that there exist meaningful utility
functionals whose maximization leads to the celebrated primal, dual and primal/dual algorithms. An implication of this result is that a real network problem may be solved by regarding it as an optimal control problem on which some practical constraints, such as a real-time link capacity constraint, are imposed.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/nhkrb-ceq04Method and apparatus for network congestion control using queue control and one-way delay measurements
https://resolver.caltech.edu/CaltechAUTHORS:20170810-125710516
Authors: {'items': [{'id': 'Jin-Cheng', 'name': {'family': 'Jin', 'given': 'Cheng'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Wei-Xiaoliang-David', 'name': {'family': 'Wei', 'given': 'David X.'}}, {'id': 'Wydrowski-B-P', 'name': {'family': 'Wydrowski', 'given': 'Bartek'}}, {'id': 'Tang-Ao', 'name': {'family': 'Tang', 'given': 'Ao'}, 'orcid': '0000-0001-6296-644X'}, {'id': 'Choe-Hyojeong', 'name': {'family': 'Choe', 'given': 'Hyojeong'}}]}
Year: 2010
The invention provides a congestion control scheme that is a delay based scheme that includes a scalable queue size and one-way queueing delay measurement to reduce network congestion. Queue size is managed by queue control, a scalable utility function, dynamic alpha tuning, and/or randomized alpha tuning. One-way queueing delay is accomplished by measuring backward queueing delay management using various methods of estimating the receiver clock period. Embodiments include estimating the receiver clock period using single sample and multiple sample periods. The system includes a method for detecting route change.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/2vty0-91x25Equilibrium of Heterogeneous Congestion Control: Optimality and Stability
https://resolver.caltech.edu/CaltechAUTHORS:20100709-142523769
Authors: {'items': [{'id': 'Tang-Ao', 'name': {'family': 'Tang', 'given': 'Ao'}, 'orcid': '0000-0001-6296-644X'}, {'id': 'Wei-Xiaoliang-David', 'name': {'family': 'Wei', 'given': 'Xiaoliang (David)'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Chiang-Mung', 'name': {'family': 'Chiang', 'given': 'Mung'}}]}
Year: 2010
DOI: 10.1109/TNET.2009.2034963
When heterogeneous congestion control protocols
that react to different pricing signals share the same network,
the current theory based on utility maximization fails to predict
the network behavior. The pricing signals can be different types
of signals such as packet loss, queueing delay, etc, or different
values of the same type of signal such as different ECN marking
values based on the same actual link congestion level. Unlike in a
homogeneous network, the bandwidth allocation now depends on
router parameters and flow arrival patterns. It can be non-unique,
suboptimal and unstable. In Tang et al. ("Equilibrium of heterogeneous
congestion control: Existence and uniqueness," IEEE/ACM
Trans. Netw., vol. 15, no. 4, pp. 824–837, Aug. 2007), existence and
uniqueness of equilibrium of heterogeneous protocols are investigated.
This paper extends the study with two objectives: analyzing
the optimality and stability of such networks and designing control
schemes to improve those properties. First, we demonstrate the
intricate behavior of a heterogeneous network through simulations
and present a framework to help understand its equilibrium
properties. Second, we propose a simple source-based algorithm
to decouple bandwidth allocation from router parameters and
flow arrival patterns by only updating a linear parameter in the
sources' algorithms on a slow timescale. It steers a network to
the unique optimal equilibrium. The scheme can be deployed
incrementally as the existing protocol needs no change and only
new protocols need to adopt the slow timescale adaptation.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/08rep-x3j02Zero Duality Gap in Optimal Power Flow Problem
https://resolver.caltech.edu/CaltechCDSTR:2010.004
Authors: {'items': [{'id': 'Lavaei-J', 'name': {'family': 'Lavaei', 'given': 'Javad'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2010
The optimal power flow (OPF) problem is nonconvex
and generally hard to solve. We provide a sufficient
condition under which the OPF problem is equivalent to
a convex problem and therefore is efficiently solvable.
Specifically, we prove that the dual of OPF is a semidefinite program and our sufficient condition guarantees that the duality gap is zero and a globally optimal solution of OPF is recoverable from a dual optimal solution. This sufficient condition is satisfied by standard
IEEE benchmark systems with 14, 30, 57, 118 and 300 buses
after small resistance (10^(-5) per unit) is added to every transformer that originally assumes zero resistance.
We justify why the condition might hold widely in practice from algebraic and geometric perspectives. The main underlying reason is that physical quantities such as resistance, capacitance and inductance, are all positive.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/934zs-f4t59Random Access Game and Medium Access Control Design
https://resolver.caltech.edu/CaltechAUTHORS:20100907-110446104
Authors: {'items': [{'id': 'Chen-Lijun', 'name': {'family': 'Chen', 'given': 'Lijun'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John C.'}, 'orcid': '0000-0002-1828-2486'}]}
Year: 2010
DOI: 10.1109/TNET.2010.2041066
Motivated partially by a control-theoretic viewpoint, we propose a game-theoretic model, called random access game, for contention control. We characterize Nash equilibria of random access games, study their dynamics, and propose distributed algorithms (strategy evolutions) to achieve Nash equilibria. This provides a general analytical framework that is capable of modeling a large class of system-wide quality-of-service (QoS) models via the specification of per-node utility functions, in which system-wide fairness or service differentiation can be achieved in a distributed manner as long as each node executes a contention resolution algorithm that is designed to achieve the Nash equilibrium. We thus propose a novel medium access method derived from carrier sense multiple access/collision avoidance (CSMA/CA) according to distributed strategy update mechanism achieving the Nash equilibrium of random access game. We present a concrete medium access method that adapts to a continuous contention measure called conditional collision probability, stabilizes the network into a steady state that achieves optimal throughput with targeted fairness (or service differentiation), and can decouple contention control from handling failed transmissions. In addition to guiding medium access control design, the random access game model also provides an analytical framework to understand equilibrium and dynamic properties of different medium access protocols.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/369d2-rk609Load-shedding probabilities with hybrid renewable power generation and energy storage
https://resolver.caltech.edu/CaltechAUTHORS:20170314-151537459
Authors: {'items': [{'id': 'Xu-Huan', 'name': {'family': 'Xu', 'given': 'Huan'}}, {'id': 'Topcu-U', 'name': {'family': 'Topcu', 'given': 'Ufuk'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Clarke-C-R', 'name': {'family': 'Clarke', 'given': 'Christopher R.'}}, {'id': 'Chandy-K-M', 'name': {'family': 'Chandy', 'given': 'K. Mani'}}]}
Year: 2010
DOI: 10.1109/ALLERTON.2010.5706912
The integration of renewable energy resources, such as solar and wind power, into the electric grid presents challengs partly due to the intermittency in the power output. These difficulties can be alleviated by effectively utilizing energy storage. We consider, as a case study, the integration of renewable resources into the electric power generation portfolio of an island off the coast of Southern California, Santa Catalina Island, and investigate the feasibility of replacing diesel generation entirely with solar photovoltaics (PV) and wind turbines, supplemented with energy storage. We use a simple storage model alongside a combination of renewables and varying load-shedding characterizations to determine the appropriate area of PV cells, number of wind turbines, and energy storage capacity needed to stay below a certain threshold probability for load-shedding over a pre-specified period of time and long-term expected fraction of time at load-shedding.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/hr890-8f768Two Market Models for Demand Response in Power Networks
https://resolver.caltech.edu/CaltechAUTHORS:20170810-104228265
Authors: {'items': [{'id': 'Chen-Lijun', 'name': {'family': 'Chen', 'given': 'Lijun'}}, {'id': 'Li-Na', 'name': {'family': 'Li', 'given': 'Na'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John C.'}, 'orcid': '0000-0002-1828-2486'}]}
Year: 2010
DOI: 10.1109/SMARTGRID.2010.5622076
In this paper, we consider two abstract market models for designing demand response to match power supply and shape power demand, respectively. We characterize the resulting equilibria in competitive as well as oligopolistic markets, and propose distributed demand response algorithms to achieve the equilibria. The models serve as a starting point to include the appliance-level details and constraints for designing practical demand response schemes for smart power grids.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/wscs9-cx135Queue Dynamics With Window Flow Control
https://resolver.caltech.edu/CaltechAUTHORS:20101124-110950283
Authors: {'items': [{'id': 'Tang-Ao', 'name': {'family': 'Tang', 'given': 'Ao'}, 'orcid': '0000-0001-6296-644X'}, {'id': 'Andrew-L-L-H', 'name': {'family': 'Andrew', 'given': 'Lachlan L. H.'}}, {'id': 'Jacobsson-K', 'name': {'family': 'Jacobsson', 'given': 'Krister'}}, {'id': 'Johansson-K-H', 'name': {'family': 'Johansson', 'given': 'Karl H.'}}, {'id': 'Hjalmarsson-H', 'name': {'family': 'Hjalmarsson', 'given': 'Håkan'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2010
DOI: 10.1109/TNET.2010.2047951
This paper develops a new model that describes the queueing process of a communication network when data sources use window flow control. The model takes into account the burstiness in sub-round-trip time (RTT) timescales and the instantaneous rate differences of a flow at different links. It is generic and independent of actual source flow control algorithms. Basic properties of the model and its relation to existing work are discussed. In particular, for a general network with multiple links, it is demonstrated that spatial interaction of oscillations allows queue instability to occur even when all flows have the same RTTs and maintain constant windows. The model is used to study the dynamics of delay-based congestion control algorithms. It is found that the ratios of RTTs are critical to the stability of such systems, and previously unknown modes of instability are identified. Packet-level simulations and testbed measurements are provided to verify the model and its predictions.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/ghc8g-zy466Relationship between power loss and network topology in power systems
https://resolver.caltech.edu/CaltechAUTHORS:20170810-134325354
Authors: {'items': [{'id': 'Lavaei-J', 'name': {'family': 'Lavaei', 'given': 'Javad'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2010
DOI: 10.1109/CDC.2010.5717352
This paper is concerned with studying how the minimum power loss in a power system is related to its network topology. The existing algorithms in the literature all exploit nonlinear, heuristic, or local search algorithms to find the minimum power loss, which make them blind to the network topology. Given certain constraints on power level, bus voltages, etc., a linear-matrix-inequality (LMI) optimization problem is derived, which provides a lower bound on the minimum active loss in the network. The proposed LMI problem has the property that its objective function depends on the loads and its matrix inequality constraint is related to the topology of the power system. This property makes it possible to address many important power problems, such as the optimal network reconfiguration and the optimal placement/sizing of distributed generation units in power systems. Moreover, a condition is provided under which the solution of the given LMI problem is guaranteed to be exactly equal to the minimum power loss. As justified mathematically and verified on IEEE test systems, this condition is expected to hold widely in practice, implying that a practical power loss minimization problem is likely to be solvable using a convex algorithm.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/62mbz-5w718A simple optimal power flow model with energy storage
https://resolver.caltech.edu/CaltechAUTHORS:20170810-102952651
Authors: {'items': [{'id': 'Chandy-K-M', 'name': {'family': 'Chandy', 'given': 'K. Mani'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Topcu-U', 'name': {'family': 'Topcu', 'given': 'Ufuk'}}, {'id': 'Xu-Huan', 'name': {'family': 'Xu', 'given': 'Huan'}}]}
Year: 2010
DOI: 10.1109/CDC.2010.5718193
The integration of renewable energy generation, such as wind power, into the electric grid is difficult because of the source intermittency and the large distance between generation sites and users. This difficulty can be overcome through a transmission network with large-scale storage that not only transports power, but also mitigates against fluctuations in generation and supply. We formulate an optimal power flow problem with storage as a finite-horizon optimal control problem. We prove, for the special case with a single generator and a single load, that the optimal generation schedule will cross the time-varying demand profile at most once, from above. This means that the optimal policy will generate more than demand initially in order to charge up the battery, and then generate less than the demand and use the battery to supplement generation in final stages. This is a consequence of the fact that the marginal storage cost-to-go decreases in time.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/cd7d5-pat18Nonnegative Matrix Inequalities and their Application to Nonconvex Power Control Optimization
https://resolver.caltech.edu/CaltechAUTHORS:20111025-095823883
Authors: {'items': [{'id': 'Tan-C-W', 'name': {'family': 'Tan', 'given': 'Chee Wei'}}, {'id': 'Friedland-S', 'name': {'family': 'Friedland', 'given': 'Shmuel'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2011
DOI: 10.1137/090757137
Maximizing the sum rates in a multiuser Gaussian channel by power control is a nonconvex NP-hard problem that finds engineering application in code division multiple access (CDMA) wireless communication network. In this paper, we extend and apply several fundamental nonnegative matrix inequalities initiated by Friedland and Karlin in a 1975 paper to solve this nonconvex power control optimization problem. Leveraging tools such as the Perron–Frobenius theorem in nonnegative matrix theory, we (1) show that this problem in the power domain can be reformulated as an equivalent convex maximization problem over a closed unbounded convex set in the logarithmic signal-to-interference-noise ratio domain, (2) propose two relaxation techniques that utilize the reformulation problem structure and convexification by Lagrange dual relaxation to compute progressively tight bounds, and (3) propose a global optimization algorithm with ϵ-suboptimality to compute the optimal power control allocation. A byproduct of our analysis is the application of Friedland–Karlin inequalities to inverse problems in nonnegative matrix theory.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/4ttxb-nq422Power flow optimization using positive quadratic programming
https://resolver.caltech.edu/CaltechAUTHORS:20170810-134634427
Authors: {'items': [{'id': 'Lavei-J', 'name': {'family': 'Lavei', 'given': 'Javad'}}, {'id': 'Rantzer-A', 'name': {'family': 'Rantzer', 'given': 'Anders'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Stephen'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2011
DOI: 10.3182/20110828-6-IT-1002.02588
The problem to minimize power losses in an electrical network subject to voltage and power constraints is in general hard to solve. However, it has recently been discovered that semidefinite programming relaxations in many cases enable exact computation of the global optimum. Here we point out a fundamental reason for the successful relaxations, namely that the passive network components give rise to matrices with nonnegative offdiagonal entries. Recent progress on quadratic programming with Metzler matrix structure can therefore be applied.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/xsaq2-06862Spectrum Management in Multiuser Cognitive Wireless Networks: Optimality and Algorithm
https://resolver.caltech.edu/CaltechAUTHORS:20110302-113943034
Authors: {'items': [{'id': 'Tan-C-W', 'name': {'family': 'Tan', 'given': 'Chee Wei'}}, {'id': 'Friedland-S', 'name': {'family': 'Friedland', 'given': 'Shmuel'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2011
DOI: 10.1109/JSAC.2011.110214
Spectrum management is used to improve performance in multiuser communication system, e.g., cognitive radio or femtocell networks, where multiuser interference can lead to data rate degradation. We study the nonconvex NP-hard problem of maximizing a weighted sum rate in a multiuser Gaussian interference channel by power control subject to affine power constraints. By exploiting the fact that this problem can be restated as an optimization problem with constraints that are spectral radii of specially crafted nonnegative matrices, we derive necessary and sufficient optimality conditions and propose a global optimization algorithm based on the outer approximation method. Central to our techniques is the use of nonnegative matrix theory, e.g., nonnegative matrix inequalities and the Perron-Frobenius theorem. We also study an inner approximation method and a relaxation method that give insights to special cases. Our techniques and algorithm can be extended to a multiple carrier system model, e.g., OFDM system or receivers with interference suppression capability.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/nh5he-b8w58Cross-layer design in multihop wireless networks
https://resolver.caltech.edu/CaltechAUTHORS:20110315-091124013
Authors: {'items': [{'id': 'Chen-Lijun', 'name': {'family': 'Chen', 'given': 'Lijun'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John C.'}, 'orcid': '0000-0002-1828-2486'}]}
Year: 2011
DOI: 10.1016/j.comnet.2010.09.005
In this paper, we take a holistic approach to the protocol architecture design in multihop wireless networks. Our goal is to integrate various protocol layers into a rigorous framework, by regarding them as distributed computations over the network to solve some optimization problem. Different layers carry out distributed computation on different subsets of the decision variables using local information to achieve individual optimality. Taken
together, these local algorithms (with respect to different layers) achieve a global optimality. Our current theory integrates three functions—congestion control, routing and scheduling—in transport, network and link layers into a coherent framework. These three functions interact through and are regulated by congestion price so as to achieve a global optimality, even in a time-varying environment. Within this context, this model allows us to systematically derive the layering structure of the various mechanisms of different protocol layers, their interfaces, and the control information that must cross these interfaces to
achieve a certain performance and robustness.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/xekag-ac411Effect of buffers on stability of Internet congestion controllers
https://resolver.caltech.edu/CaltechAUTHORS:20120403-131857340
Authors: {'items': [{'id': 'Sojoudi-S', 'name': {'family': 'Sojoudi', 'given': 'Somayeh'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John C.'}, 'orcid': '0000-0002-1828-2486'}]}
Year: 2011
Almost all existing fluid models of congestion control assume that the fluid flow at the output of a link is the same as the fluid flow at the input of the link. This means that all links in the path of a flow see the original source rate. In reality, a fluid flow is modified by the queueing processes on its path, so that an intermediate link will generally not see the original source rate. In this paper, we propose a simple model that explicitly takes into account of the effect of buffering on output flows. We study the dual and primal-dual algorithms that use implicit feedback and show that, while they are always asymptotically stable if feedback delay is ignored, they can be unstable in the new model.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/7pfse-91y07Max-min weighted SINR in coordinated multicell MIMO downlink
https://resolver.caltech.edu/CaltechAUTHORS:20170810-095519100
Authors: {'items': [{'id': 'Cai-Desmond-W-H', 'name': {'family': 'Cai', 'given': 'Desmond W. H.'}, 'orcid': '0000-0001-9207-1890'}, {'id': 'Quek-Tony-Q-S', 'name': {'family': 'Quek', 'given': 'Tony Q. S.'}}, {'id': 'Tan-Chee-Wei', 'name': {'family': 'Tan', 'given': 'Chee Wei'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2011
DOI: 10.1109/WIOPT.2011.5930029
This paper studies the optimization of a multicell multiple-input-single-output (MISO) downlink system in which each base station serves multiple users, and each user is served by only one base station. First, we consider the problem of maximizing the minimum weighted signal-to-interference-plus-noise ratio (SINR) of all users subject to a single weighted-sum power constraint, where the weights can represent relative power costs of serving different users in each cell. We apply concave Perron-Frobenius theory to propose a joint power control and linear beamforming algorithm which converges geometrically fast to the optimal solution. As a by-product, we resolve an open problem of convergence of a previously proposed algorithm by Wiesel, Eldar, and Shamai in 2006. Next, we study the max-min weighted SINR problem subject to multiple weighted-sum power constraints and we show that it can be decoupled into its associated single-constrained subproblems.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/j9w21-fez97Greening geographical load balancing
https://resolver.caltech.edu/CaltechAUTHORS:20161128-151734850
Authors: {'items': [{'id': 'Liu-Zhenhua', 'name': {'family': 'Liu', 'given': 'Zhenhua'}}, {'id': 'Lin-Minghong', 'name': {'family': 'Lin', 'given': 'Minghong'}}, {'id': 'Wierman-A', 'name': {'family': 'Wierman', 'given': 'Adam'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Andrew-L-L-H', 'name': {'family': 'Andrew', 'given': 'Lachlan L. H.'}}]}
Year: 2011
Energy expenditure has become a significant fraction of data center operating costs. Recently, "geographical load balancing" has been suggested to reduce energy cost by exploiting the electricity price differences across regions. However, this reduction of cost can paradoxically increase total energy use.
This paper explores whether the geographical diversity of Internet-scale systems can additionally be used to provide environmental gains. Specifically, we explore whether geographical load balancing can encourage use of "green" renewable energy and reduce use of "brown" fossil fuel energy. We make two contributions. First, we derive two distributed algorithms for achieving optimal geographical load balancing. Second, we show that if electricity is dynamically priced in proportion to the instantaneous fraction of the total energy that is brown, then geographical load balancing provides significant reductions in brown energy use. However, the benefits depend strongly on the degree to which systems accept dynamic energy pricing and the form of pricing used.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/hww5w-9w763Greening geographical load balancing
https://resolver.caltech.edu/CaltechAUTHORS:20120522-080032032
Authors: {'items': [{'id': 'Liu-Zhenhua', 'name': {'family': 'Liu', 'given': 'Zhenhua'}}, {'id': 'Lin-Minghong', 'name': {'family': 'Lin', 'given': 'Minghong'}}, {'id': 'Wierman-A', 'name': {'family': 'Wierman', 'given': 'Adam'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Andrew-L-L-H', 'name': {'family': 'Andrew', 'given': 'Lachlan L. H.'}}]}
Year: 2011
DOI: 10.1145/1993744.1993767
Energy expenditure has become a significant fraction of data center operating costs. Recently, "geographical load balancing" has been suggested to reduce energy cost by exploiting the electricity price differences across regions. However, this reduction of cost can paradoxically increase total energy use.
This paper explores whether the geographical diversity of Internet-scale systems can additionally be used to provide environmental gains. Specifically, we explore whether geographical load balancing can encourage use of "green" renewable energy and reduce use of "brown" fossil fuel energy. We make two contributions. First, we derive two distributed algorithms for achieving optimal geographical load balancing. Second, we show that if electricity is dynamically priced in proportion to the instantaneous fraction of the total energy that is brown, then geographical load balancing provides significant reductions in brown energy use. However, the benefits depend strongly on the degree to which systems accept dynamic energy pricing and the form of pricing used.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/14c3j-8my38Geographical Load Balancing with Renewables
https://resolver.caltech.edu/CaltechAUTHORS:20110614-094637693
Authors: {'items': [{'id': 'Liu-Zhenhua', 'name': {'family': 'Liu', 'given': 'Zhenhua'}}, {'id': 'Lin-Minghong', 'name': {'family': 'Lin', 'given': 'Minghong'}}, {'id': 'Wierman-A', 'name': {'family': 'Wierman', 'given': 'Adam'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Andrew-L-L-H', 'name': {'family': 'Andrew', 'given': 'Lachlan L. H.'}}]}
Year: 2011
Given the significant energy consumption of data centers, improving
their energy efficiency is an important social problem.
However, energy efficiency is necessary but not sufficient
for sustainability, which demands reduced usage of
energy from fossil fuels. This paper investigates the feasibility
of powering internet-scale systems using (nearly) entirely
renewable energy. We perform a trace-based study
to evaluate three issues related to achieving this goal: the
impact of geographical load balancing, the role of storage,
and the optimal mix of renewables. Our results highlight
that geographical load balancing can significantly reduce the
required capacity of renewable energy by using the energy
more efficiently with "follow the renewables" routing. Further,
our results show that small-scale storage can be useful,
especially in combination with geographical load balancing,
and that an optimal mix of renewables includes significantly
more wind than photovoltaic solar.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/y1yzt-cvx11Optimal demand response based on utility maximization in power networks
https://resolver.caltech.edu/CaltechAUTHORS:20120330-135152938
Authors: {'items': [{'id': 'Li-Na', 'name': {'family': 'Li', 'given': 'Na'}}, {'id': 'Chen-Lijun', 'name': {'family': 'Chen', 'given': 'Lijun'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2011
DOI: 10.1109/PES.2011.6039082
Demand side management will be a key component of future smart grid that can help reduce peak load and adapt elastic demand to fluctuating generations. In this paper, we consider households that operate different appliances including PHEVs and batteries and propose a demand response approach based on utility maximization. Each appliance provides a certain benefit depending on the pattern or volume of power it consumes. Each household wishes to optimally schedule its power consumption so as to maximize its individual net benefit subject to various consumption and power flow constraints. We show that there exist time-varying prices that can align individual optimality with social optimality, i.e., under such prices, when the households selfishly optimize their own benefits, they automatically also maximize the social welfare. The utility company can thus use dynamic pricing to coordinate demand responses to the benefit of the overall system. We propose a distributed algorithm for the utility company and the customers to jointly compute this optimal prices and demand schedules. Finally, we present simulation results that illustrate several interesting properties of the proposed scheme.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/nkymn-pk975Optimal Charging of Plug-in Hybrid Electric Vehicles in Smart Grids
https://resolver.caltech.edu/CaltechAUTHORS:20120406-131234298
Authors: {'items': [{'id': 'Sojoudi-S', 'name': {'family': 'Sojoudi', 'given': 'Somayeh'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2011
DOI: 10.1109/PES.2011.6039236
Plug-in hybrid electric vehicles (PHEVs) play an important role in making a greener future. Given a group of PHEVs distributed across a power network equipped with the smart grid technology (e.g. wireless communication devices), the objective of this paper is to study how to schedule the charging of the PHEV batteries. To this end, we assume that each battery must be fully charged by a pre-specified time, and that the charging rate can be time-varying at discrete-time instants. The scheduling problem for the PHEV charging can be augmented into the optimal power flow (OPF) problem to obtain a joint OPF-charging (dynamic) optimization. A solution to this highly nonconvex problem optimizes the network performance by minimizing the generation and charging costs while satisfying the network, physical and inelastic-load constraints. A global optimum to the joint OPF-charging optimization can be found efficiently in polynomial time by solving its convex dual problem whenever the duality gap is zero for the joint OPF-charging problem. It is shown in a recent work that the duality gap is expected to be zero for the classical OPF problem. We build on this result and prove that the duality gap is zero for the joint OPF-charging optimization if it is zero for the classical OPF problem. The results of this work are applied to the IEEE 14 bus system.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/31kqm-vmp47Method and apparatus for network congestion control
https://resolver.caltech.edu/CaltechAUTHORS:20170810-125711000
Authors: {'items': [{'id': 'Jin-Cheng', 'name': {'family': 'Jin', 'given': 'Cheng'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Wei-Xiaoliang-David', 'name': {'family': 'Wei', 'given': 'Xiaoliang (David)'}}]}
Year: 2011
The present invention is a delay based model and in fact uses queuing delay as a congestion measure, providing advantages over prior art loss based systems. One advantage is that queuing delay can be more accurately estimated than loss probability. This is because packet losses in networks with large bandwidth-delay product are rare events under TCP Reno and its variants (probability on the order 10.sup.-7 or smaller), and because loss samples provide coarser information than queuing delay samples. Indeed, measurements of delay are noisy, just as those of loss probability. Thus, another advantage of the present invention is that each measurement of queuing delay provides multi-bit information while each measurement of packet loss (whether a packet is lost) provides only one bit of information for the filtering of noise. This makes it easier for an equation-based implementation to stabilize a network into a steady state with a target fairness and high utilization. In addition, the dynamics of queuing delay provides scaling with respect to network capacity. This helps maintain stability as a network scales up in capacity.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/rakp7-a3j71Real-time demand response with uncertain renewable energy in smart grid
https://resolver.caltech.edu/CaltechAUTHORS:20170810-131626157
Authors: {'items': [{'id': 'Jiang-Libin', 'name': {'family': 'Jiang', 'given': 'Libin'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2011
DOI: 10.1109/Allerton.2011.6120322
We consider a set of users served by a single load serving entity (LSE) in the electricity grid. The LSE procures capacity a day ahead. When random renewable energy is realized at delivery time, it actively manages user load through real-time demand response and purchases balancing power on the spot market to meet the aggregate demand. Hence, to maximize the social welfare, decisions must be coordinated over two timescales (a day ahead and in real time), in the presence of supply uncertainty, and computed jointly by the LSE and the users since the necessary information is distributed among them. We formulate the problem as a dynamic program. We propose a distributed heuristic algorithm and prove its optimality when the welfare function is quadratic and the LSE's decisions are strictly positive. Otherwise, we bound the gap between the welfare achieved by the heuristic algorithm and the maximum in certain cases. Simulation results suggest that the performance gap is small. As we scale up the size of a renewable generation plant, both its mean production and its variance will likely increase. We characterize the impact of the mean and variance of renewable energy on the maximum welfare. This paper is a continuation of [2], focusing on time-correlated demand.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/agqe2-xdb37Optimal power flow over tree networks
https://resolver.caltech.edu/CaltechAUTHORS:20170810-095656194
Authors: {'items': [{'id': 'Bose-Subhonmesh', 'name': {'family': 'Bose', 'given': 'Subhonmesh'}, 'orcid': '0000-0002-3445-4479'}, {'id': 'Gayme-D-F', 'name': {'family': 'Gayme', 'given': 'Dennice F.'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Chandy-K-M', 'name': {'family': 'Chandy', 'given': 'K. Mani'}}]}
Year: 2011
DOI: 10.1109/Allerton.2011.6120323
The optimal power flow (OPF) problem is critical to power system operation but it is generally non-convex and therefore hard to solve. Recently, a sufficient condition has been found under which OPF has zero duality gap, which means that its solution can be computed efficiently by solving the convex dual problem. In this paper we simplify this sufficient condition through a reformulation of the problem and prove that the condition is always satisfied for a tree network provided we allow over-satisfaction of load. The proof, cast as a complex semi-definite program, makes use of the fact that if the underlying graph of an n × n Hermitian positive semi-definite matrix is a tree, then the matrix has rank at least n-1.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/6xz0p-emq71Frequency-based load control in power systems
https://resolver.caltech.edu/CaltechCDSTR:2011.007
Authors: {'items': [{'id': 'Zhao-Changhong', 'name': {'family': 'Zhao', 'given': 'Changhong'}, 'orcid': '0000-0003-0539-8591'}, {'id': 'Topcu-U', 'name': {'family': 'Topcu', 'given': 'Ufuk'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2011
Maintaining demand-supply balance and regulating frequency are key issues in power system control. Conventional approaches focus on adjusting the generation so that it follows the load. However, relying on solely regulating generation is inefficient, especially for power systems where contingencies like sudden loss in generation or sudden change in load frequently occur and the proportion of intermittent renewable power is increasing. We present a frequency-based load control scheme for demand-supply balancing and frequency regulation. We formulate a load control optimization problem which aims to balance the change in load with the change in supply while minimizing the overall end-use disutility. By studying the power system model that characterizes the frequency response to
real power imbalance between demand and supply, we design
decentralized synchronous and asynchronous algorithms which
take advantage of local frequency measurements to solve the load control problem. Case studies show that the proposed load control scheme is capable of relatively quickly balancing the power and restoring the frequency under generation-loss like contingencies or renewable power penetration. Case studies also show that the proposed scheme still works well when users have the knowledge
of a simplified system model instead of an accurate one.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/888vf-8bb79Optimal design of hybrid energy system with PV/wind turbine/storage: A case study
https://resolver.caltech.edu/CaltechAUTHORS:20170810-125833627
Authors: {'items': [{'id': 'Huang-Rui', 'name': {'family': 'Huang', 'given': 'Rui'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Topcu-U', 'name': {'family': 'Topcu', 'given': 'Ufuk'}}, {'id': 'Chandy-K-M', 'name': {'family': 'Chandy', 'given': 'K. Mani'}}, {'id': 'Clarke-C-R', 'name': {'family': 'Clarke', 'given': 'Christopher R.'}}]}
Year: 2011
DOI: 10.1109/SmartGridComm.2011.6102376
Hybrid energy systems with renewable generation are built in many remote areas where the renewable resources are abundant and the environment is clean. We present a case study of the Catalina Island in California for which a system with photovoltaic (PV) arrays, wind turbines, and battery storage is designed based on empirical weather and load data. To determine the system size, we formulate an optimization problem that minimizes the total construction and operation cost subject to maximum tolerable risk. Simulations using the Hybrid Optimization Model for Electric Renewable (HOMER) is used to determine the feasible set of the optimization problem.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/y43yg-pnk53Inverter VAR control for distribution systems with renewables
https://resolver.caltech.edu/CaltechAUTHORS:20170810-112707612
Authors: {'items': [{'id': 'Farivar-M', 'name': {'family': 'Farivar', 'given': 'Masoud'}}, {'id': 'Clarke-C-R', 'name': {'family': 'Clarke', 'given': 'Christopher R.'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Chandy-K-M', 'name': {'family': 'Chandy', 'given': 'K. Mani'}}]}
Year: 2011
DOI: 10.1109/SmartGridComm.2011.6102366
Motivated by the need to cope with rapid and random fluctuations of renewable generation, we presents a model that augments the traditional Volt/VAR control through switched controllers on a slow timescale with inverter control on a fast timescale. The optimization problem is generally nonconvex and therefore hard to solve. We propose a simple convex relaxation and prove that it is exact provided over-satisfaction of load is allowed. Hence Volt/VAR control over radial networks is efficiently solvable. Simulations of a real-world distribution circuit illustrates that the proposed inverter control achieves significant improvement over the IEEE 1547 standard in terms of power quality and power savings.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/56qs2-jnm02GRIP - Grids with intelligent periphery: Control architectures for Grid2050^π
https://resolver.caltech.edu/CaltechAUTHORS:20170215-173725326
Authors: {'items': [{'id': 'Bakken-D', 'name': {'family': 'Bakken', 'given': 'D.'}}, {'id': 'Bose-A', 'name': {'family': 'Bose', 'given': 'A.'}}, {'id': 'Chandy-K-M', 'name': {'family': 'Chandy', 'given': 'K. M.'}}, {'id': 'Khargonekar-P-P', 'name': {'family': 'Khargonekar', 'given': 'P. P.'}}, {'id': 'Kuh-A', 'name': {'family': 'Kuh', 'given': 'A.'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'S.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'von-Meier-A', 'name': {'family': 'von Meier', 'given': 'A.'}, 'orcid': '0000-0003-4675-752X'}, {'id': 'Poolla-K', 'name': {'family': 'Poolla', 'given': 'K.'}}, {'id': 'Varaiya-P-P', 'name': {'family': 'Varaiya', 'given': 'P. P.'}}, {'id': 'Wu-F', 'name': {'family': 'Wu', 'given': 'F.'}}]}
Year: 2011
DOI: 10.1109/SmartGridComm.2011.6102397
A distributed control and coordination architecture for integrating inherently variable and uncertain generation is presented. The key idea is to distribute the intelligence into the periphery of the grid. This will allow coordination of generation, storage, and adjustable demand on the distribution side of the system and thus reduce the need to build new transmission facilities to accommodate large amounts of renewable generation.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/0kg75-e8b44Optimal Decentralized Protocols for Electric Vehicle Charging
https://resolver.caltech.edu/CaltechCDSTR:2011.009
Authors: {'items': [{'id': 'Gan-Lingwen', 'name': {'family': 'Gan', 'given': 'Lingwen'}}, {'id': 'Topcu-U', 'name': {'family': 'Topcu', 'given': 'Ufuk'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2011
We propose decentralized algorithms for optimally scheduling electric vehicle charging. The algorithms exploit the elasticity and controllability of electric vehicle related loads in order to fill the valleys in electric demand profile. We formulate a global optimization problem whose objective is to impose a generalized notion of valley-filling, study properties of the optimal charging profiles, and give decentralized offline and online algorithms to solve the problem. In each iteration of the proposed algorithms, electric vehicles choose their own charging profiles for the rest horizon according to the price profile broadcast by the utility, and the utility updates the price profile to guide their behavior. The offline algorithms are guaranteed to converge to optimal charging profiles irrespective of the specifications (e.g., maximum charging rate and deadline) of electric vehicles at the expense of a restrictive assumption that all electric vehicles are available for negotiation at the beginning of the planning horizon. The online algorithms relax this assumption by using a scalar prediction of future total charging demand at each time instance and yield near optimal charging profiles. The proposed algorithms need no coordination among the electric vehicles, hence their implementation requires low communication and computation capability. Simulation results are provided to support these results.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/fgea1-qdv23Optimal demand response: Problem formulation and deterministic case
https://resolver.caltech.edu/CaltechAUTHORS:20170810-104829103
Authors: {'items': [{'id': 'Chen-Lijun', 'name': {'family': 'Chen', 'given': 'Lijun'}}, {'id': 'Li-Na', 'name': {'family': 'Li', 'given': 'Na'}}, {'id': 'Jiang-Libin', 'name': {'family': 'Jiang', 'given': 'Libin'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2011
DOI: 10.1007/978-1-4614-1605-0_3
We consider a set of users served by a single load-serving entity (LSE). The LSE procures capacity a day ahead. When random renewable energy is realized at delivery time, it manages user load through real-time demand response and purchases balancing power on the spot market to meet the aggregate demand. Hence, optimal supply procurement by the LSE and the consumption decisions by the users must be coordinated over two timescales, a day ahead and in real time, in the presence of supply uncertainty. Moreover, they must be computed jointly by the LSE and the users since the necessary information is distributed among them. In this chapter, we present a simple yet versatile user model and formulate the problem as a dynamic program that maximizes expected social welfare. When random renewable generation is absent, optimal demand response reduces to joint scheduling of the procurement and consumption decisions. In this case, we show that optimal prices exist that coordinate individual user decisions to maximize social welfare, and present a decentralized algorithm to optimally schedule a day in advance the LSE's procurement and the users' consumptions. The case with uncertain supply is reported in a companion paper.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/vhfv5-bc902Optimal decentralized protocol for electric vehicle charging
https://resolver.caltech.edu/CaltechAUTHORS:20131003-100205684
Authors: {'items': [{'id': 'Gan-Lingwen', 'name': {'family': 'Gan', 'given': 'Lingwen'}}, {'id': 'Topcu-U', 'name': {'family': 'Topcu', 'given': 'Ufuk'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2011
DOI: 10.1109/CDC.2011.6161220
Motivated by the power-grid-side challenges in the integration of electric vehicles, we propose a decentralized protocol for negotiating day-ahead charging schedules for electric vehicles. The overall goal is to shift the load due to electric vehicles to fill the overnight electricity demand valley. In each iteration of the proposed protocol, electric vehicles choose their own charging profiles for the following day according to the price profile broadcast by the utility, and the utility updates the price profile to guide their behavior. This protocol is guaranteed to converge, irrespective of the specifications (e.g., maximum charging rate and deadline) of electric vehicles. At convergence, the l2 norm of the aggregated demand is minimized, and the aggregated demand profile is as "flat" as it can possibly be. The proposed protocol needs no coordination among the electric vehicles, hence requires low communication and computation capability. Simulation results demonstrate convergence to optimal collections of charging profiles within few iterations.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/cjrzr-pn804Multi-period optimal energy procurement and demand response in smart grid with uncertain supply
https://resolver.caltech.edu/CaltechAUTHORS:20170306-162127856
Authors: {'items': [{'id': 'Jiang-Libin', 'name': {'family': 'Jiang', 'given': 'Libin'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2011
DOI: 10.1109/CDC.2011.6161320
We propose a simple model that integrates two-period electricity markets, uncertainty in renewable generation, and real-time dynamic demand response. A load-serving entity decides its day-ahead procurement to optimize expected social welfare a day before energy delivery. At delivery time when renewable generation is realized, it sets prices to manage demand and purchase additional power on the real-time market, if necessary, to balance supply and demand. We derive the optimal day-ahead decision, propose real-time demand response algorithm, and study the effect of volume and variability of renewable generation on the social welfare.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/s78cv-h5711Geographical load balancing with renewables
https://resolver.caltech.edu/CaltechAUTHORS:20161128-151114708
Authors: {'items': [{'id': 'Liu-Zhenhua', 'name': {'family': 'Liu', 'given': 'Zhenhua'}}, {'id': 'Lin-Minghong', 'name': {'family': 'Lin', 'given': 'Minghong'}}, {'id': 'Wierman-A', 'name': {'family': 'Wierman', 'given': 'Adam'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Andrew-L-L-H', 'name': {'family': 'Andrew', 'given': 'Lachlan L. H.'}}]}
Year: 2011
DOI: 10.1145/2160803.2160862
Given the significant energy consumption of data centers, improving their energy efficiency is an important social problem. However, energy efficiency is necessary but not sufficient for sustainability, which demands reduced usage of energy from fossil fuels. This paper investigates the feasibility of powering internet-scale systems using (nearly) entirely renewable energy. We perform a trace-based study to evaluate three issues related to achieving this goal: the impact of geographical load balancing, the role of storage, and the optimal mix of renewables. Our results highlight that geographical load balancing can significantly reduce the required capacity of renewable energy by using the energy more efficiently with "follow the renewables" routing. Further, our results show that small-scale storage can be useful, especially in combination with geographical load balancing, and that an optimal mix of renewables includes significantly more wind than photovoltaic solar.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/jz61t-zg441Fast Load Control with Stochastic Frequency Measurement
https://resolver.caltech.edu/CaltechCDSTR:2011.010
Authors: {'items': [{'id': 'Zhao-Changhong', 'name': {'family': 'Zhao', 'given': 'Changhong'}, 'orcid': '0000-0003-0539-8591'}, {'id': 'Topcu-U', 'name': {'family': 'Topcu', 'given': 'Ufuk'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2011
Matching demand with supply and regulating frequency
are key issues in power system operations. Flexibility
and local frequency measurement capability of loads offer new regulation mechanisms through load control. We present a
frequency-based fast load control scheme which aims to match
total demand with supply while minimizing the global end-use
disutility. Local frequency measurement enables loads to make decentralized decisions on their power from the estimates of total demand-supply mismatch. To resolve the errors in such estimates caused by stochastic frequency measurement errors, loads communicate via a neighborhood area network. Case studies show that the proposed load control can balance demand with supply and restore the frequency at the timescale faster than AGC, even when the loads use a highly simplified system model in their algorithms. Moreover, we discuss the tradeoff between communication and performance, and show with experiments that a moderate amount of communication significantly improves the performance.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/95tzm-njn41Stochastic Distributed Protocol for Electric Vehicle Charging with Discrete Charging Rate
https://resolver.caltech.edu/CaltechCDSTR:2011.011
Authors: {'items': [{'id': 'Gan-Lingwen', 'name': {'family': 'Gan', 'given': 'Lingwen'}}, {'id': 'Topcu-U', 'name': {'family': 'Topcu', 'given': 'Ufuk'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2011
To address the grid-side challenges associated with the anticipated high electric vehicle (EV) penetration level, various charging protocols have been proposed in the literature. Most if not all of these protocols assume continuous charging rates and allow intermittent charging. However, due to charging technology limitations, EVs can only be charged at a fixed rate, and the intermittency in charging shortens the battery lifespan. We consider these charging requirements, and formulate EV charging scheduling as a discrete optimization problem.
We propose a stochastic distributed algorithm to approximately
solve the optimal EV charging scheduling problem in an
iterative procedure. In each iteration, the transformer receives
charging profiles computed by the EVs in the previous iteration,
and broadcasts the corresponding normalized total demand to
the EVs; each EV generates a probability distribution over
its potential charging profiles accordingly, and samples from
the distribution to obtain a new charging profile. We prove
that this stochastic algorithm almost surely converges to one of
its equilibrium charging profiles, and each of its equilibrium
charging profiles has a negligible sub-optimality ratio. Case
studies corroborate our theoretical results.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/d5316-qwp84Zero Duality Gap in Optimal Power Flow Problem
https://resolver.caltech.edu/CaltechAUTHORS:20120227-144014854
Authors: {'items': [{'id': 'Lavaei-J', 'name': {'family': 'Lavaei', 'given': 'Javad'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2012
DOI: 10.1109/TPWRS.2011.2160974
The optimal power flow (OPF) problem is nonconvex and generally hard to solve. In this paper, we propose a semidefinite programming (SDP) optimization, which is the dual of an equivalent form of the OPF problem. A global optimum solution to the OPF problem can be retrieved from a solution of this convex dual problem whenever the duality gap is zero. A necessary and sufficient condition is provided in this paper to guarantee the existence of no duality gap for the OPF problem. This condition is satisfied by the standard IEEE benchmark systems with 14, 30, 57, 118, and 300 buses as well as several randomly generated systems. Since this condition is hard to study, a sufficient zero-duality-gap condition is also derived. This sufficient condition holds for IEEE systems after small resistance (10^(-5) per unit) is added to every transformer that originally assumes zero resistance. We investigate this sufficient condition and justify that it holds widely in practice. The main underlying reason for the successful convexification of the OPF problem can be traced back to the modeling of transformers and transmission lines as well as the non-negativity of physical quantities such as resistance and inductance.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/89psq-3c794Optimal Max-min Fairness Rate Control in Wireless Networks: Perron-Frobenius Characterization and Algorithms
https://resolver.caltech.edu/CaltechAUTHORS:20121127-111501274
Authors: {'items': [{'id': 'Cai-Desmond-W-H', 'name': {'family': 'Cai', 'given': 'Desmond W. H.'}, 'orcid': '0000-0001-9207-1890'}, {'id': 'Tan-Chee-Wei', 'name': {'family': 'Tan', 'given': 'Chee Wei'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2012
DOI: 10.1109/INFCOM.2012.6195808
Rate adaptation and power control are two key resource allocation mechanisms in multiuser wireless networks. In the presence of interference, how do we jointly optimize end-to-end source rates and link powers to achieve weighted max-min rate fairness for all sources in the network? This optimization problem is hard to solve as physical layer link rate functions are nonlinear, nonconvex, and coupled in the transmit powers. We show that the weighted max-min rate fairness problem can, in fact, be decoupled into separate fairness problems for flow rate and power control. For a large class of physical layer link rate functions, we characterize the optimal solution analytically by a nonlinear Perron-Frobenius theory (through solving a conditional eigenvalue problem) that captures the interaction of multiuser interference. We give an iterative algorithm to compute the optimal flow rate that converges geometrically fast without any parameter configuration. Numerical results show that our iterative algorithm is computationally fast for both the Shannon capacity, CDMA, and piecewise linear link rate functions.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/c4x65-fnb29Frequency-Based Load Control in Power Systems
https://resolver.caltech.edu/CaltechAUTHORS:20121003-154738717
Authors: {'items': [{'id': 'Zhao-Changhong', 'name': {'family': 'Zhao', 'given': 'Changhong'}, 'orcid': '0000-0003-0539-8591'}, {'id': 'Topcu-U', 'name': {'family': 'Topcu', 'given': 'Ufuk'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2012
DOI: 10.1109/ACC.2012.6315283
Maintaining demand-supply balance and regulating frequency are key issues in power system control. Conventional approaches focus on adjusting the generation so that it follows the load. However, relying on solely regulating generation is inefficient, especially for power systems where contingencies like a sudden loss in generation or a sudden change in load frequently occur. We present a frequency-based load control scheme for demand-supply balancing and frequency regulation. We formulate a load control optimization problem which aims to balance the change in load with the change in supply while minimizing the overall end-use disutility. By studying the power system model that characterizes the frequency response to real power imbalance between demand and supply, we design decentralized synchronous and asynchronous algorithms which take advantage of local frequency measurements to solve the load control problem. Case studies show that the proposed load control scheme is capable of relatively quickly balancing the power and restoring the frequency under generation-loss like contingencies, even when users only have the knowledge of a simplified system model instead of an accurate one.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/f5xnd-c8z22Energy-efficient congestion control
https://resolver.caltech.edu/CaltechAUTHORS:20161025-154452155
Authors: {'items': [{'id': 'Gan-Lingwen', 'name': {'family': 'Gan', 'given': 'Lingwen'}}, {'id': 'Walid-A', 'name': {'family': 'Walid', 'given': 'Anwar'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2012
DOI: 10.1145/2254756.2254770
Various link bandwidth adjustment mechanisms are being developed to save network energy. However, their interaction with congestion control can significantly reduce network throughput, and is not well understood. We firstly put forward a framework to study this interaction, and then propose an easily implementable dynamic bandwidth adjustment (DBA) mechanism for the links. In DBA, each link updates its bandwidth according to an integral control law to match its average buffer size with a target buffer size. We prove that DBA reduces link bandwidth without sacrificing throughput---DBA only turns off excess bandwidth---in the presence of congestion control. Preliminary ns2 simulations confirm this result.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/dnr2g-fc688Energy-efficient congestion control
https://resolver.caltech.edu/CaltechAUTHORS:20130109-105014583
Authors: {'items': [{'id': 'Gan-Lingwen', 'name': {'family': 'Gan', 'given': 'Lingwen'}}, {'id': 'Walid-Anwar', 'name': {'family': 'Walid', 'given': 'Anwar'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2012
DOI: 10.1145/2318857.2254770
Various link bandwidth adjustment mechanisms are being
developed to save network energy. However, their interaction
with congestion control can significantly reduce throughput,
and is not well understood. We firstly put forward an easily
implementable link dynamic bandwidth adjustment (DBA)
mechanism, and then study its iteration with congestion control.
In DBA, each link updates its bandwidth according
to an integral control law to match its average buffer size
with a target buffer size. We prove that DBA reduces link
bandwidth without sacrificing throughput-DBA only turns
off excess bandwidth-in the presence of congestion control.
Preliminary ns2 simulations confirm this result.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/dajde-cy387Stochastic distributed protocol for electric vehicle charging with discrete charging rate
https://resolver.caltech.edu/CaltechAUTHORS:20170810-112506562
Authors: {'items': [{'id': 'Gan-Lingwen', 'name': {'family': 'Gan', 'given': 'Lingwen'}}, {'id': 'Topcu-U', 'name': {'family': 'Topcu', 'given': 'Ufuk'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2012
DOI: 10.1109/PESGM.2012.6344847
To address the grid-side challenges associated with the anticipated high electric vehicle (EV) penetration level, various charging protocols have been proposed in the literature. Most if not all of these protocols assume continuous charging rates and allow intermittent charging. However, due to charging technology limitations, EVs can only be charged at a fixed rate, and the intermittency in charging shortens the battery lifespan. We consider these charging requirements, and formulate EV charging scheduling as a discrete optimization problem. We propose a stochastic distributed algorithm to approximately solve the optimal EV charging scheduling problem in an iterative procedure. In each iteration, the transformer receives charging profiles computed by the EVs in the previous iteration, and broadcasts the corresponding normalized total demand to the EVs; each EV generates a probability distribution over its potential charging profiles accordingly, and samples from the distribution to obtain a new charging profile. We prove that this stochastic algorithm almost surely converges to one of its equilibrium charging profiles, and each of its equilibrium charging profiles has a negligible sub-optimality ratio. Case studies corroborate our theoretical results.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/1n3dg-b2s46Optimal inverter VAR control in distribution systems with high PV penetration
https://resolver.caltech.edu/CaltechAUTHORS:20170206-172908857
Authors: {'items': [{'id': 'Farivar-M', 'name': {'family': 'Farivar', 'given': 'Masoud'}}, {'id': 'Neal-R', 'name': {'family': 'Neal', 'given': 'Russell'}}, {'id': 'Clarke-C', 'name': {'family': 'Clarke', 'given': 'Christopher'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2012
DOI: 10.1109/PESGM.2012.6345736
The intent of the study detailed in this paper is to demonstrate the benefits of inverter var control on a fast timescale to mitigate rapid and large voltage fluctuations due to the high penetration of photovoltaic generation and the resulting reverse power flow. Our approach is to formulate the volt/var control as a radial optimal power flow (OPF) problem to minimize line losses and energy consumption, subject to constraints on voltage magnitudes. An efficient solution to the radial OPF problem is presented and used to study the structure of optimal inverter var injection and the net benefits, taking into account the additional cost of inverter losses when operating at non-unity power factor. This paper will illustrate how, depending on the circuit topology and its loading condition, the inverter's optimal reactive power injection is not necessarily monotone with respect to their real power output. The results are demonstrated on a distribution feeder on the Southern California Edison system that has a very light load and a 5 MW photovoltaic (PV) system installed away from the substation.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/q23mz-x9q46A Stochastic Power Network Calculus for Integrating Renewable Energy Sources into the Power Grid
https://resolver.caltech.edu/CaltechAUTHORS:20120807-081558429
Authors: {'items': [{'id': 'Wang-Kai', 'name': {'family': 'Wang', 'given': 'Kai'}}, {'id': 'Ciucu-F', 'name': {'family': 'Ciucu', 'given': 'Florin'}}, {'id': 'Lin-Chuang', 'name': {'family': 'Lin', 'given': 'Chuang'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2012
DOI: 10.1109/JSAC.2012.120703
Renewable energy such as solar and wind generation will constitute an important part of the future grid. As the availability of renewable sources may not match the load, energy storage is essential for grid stability. In this paper we investigate the feasibility of integrating solar photovoltaic (PV) panels and wind turbines into the grid by also accounting for energy storage. To deal with the fluctuation in both the power supply and demand, we extend and apply stochastic network calculus to analyze the power supply reliability with various renewable energy configurations. To illustrate the validity of the model, we conduct a case study for the integration of renewable energy sources into the power system of an island off the coast of Southern California. In particular, we asses the power supply reliability in terms of the average Fraction of Time that energy is Not-Served (FTNS).https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/mhcbm-tjn40Adaptive VAR Control for Distribution Circuits With Photovoltaic Generators
https://resolver.caltech.edu/CaltechAUTHORS:20121127-113956570
Authors: {'items': [{'id': 'Yeh-H-G', 'name': {'family': 'Yeh', 'given': 'Hen-Geul'}}, {'id': 'Gayme-D-F', 'name': {'family': 'Gayme', 'given': 'Dennice F.'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2012
DOI: 10.1109/TPWRS.2012.2183151
We show how an adaptive control algorithm can improve the performance of distributed reactive power control in a radial distribution circuit with a high penetration of photovoltaic (PV) cells. The adaptive algorithm is designed to balance the need for power quality (voltage regulation) with the desire to minimize power loss. The adaptation law determines whether the objective function minimizes power losses or voltage regulation based on whether the voltage at each node remains close enough to the voltage at the substation. The reactive power is controlled through the inverter on the PV cells. The control signals are determined based on local instantaneous measurements of the real and reactive power at each node. We use the example of a single branch radial distribution circuit to demonstrate the ability of the adaptive scheme to effectively reduce voltage variations while simultaneously minimizing the power loss in the studied cases. Simulations verify that the adaptive schemes compares favorably with local and global schemes previously reported in the literature.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/xjb5s-se637Swing Dynamics as Primal-Dual Algorithm for Optimal Load Control
https://resolver.caltech.edu/CaltechCDSTR:2012.001
Authors: {'items': [{'id': 'Zhao-Changhong', 'name': {'family': 'Zhao', 'given': 'Changhong'}, 'orcid': '0000-0003-0539-8591'}, {'id': 'Topcu-U', 'name': {'family': 'Topcu', 'given': 'Ufuk'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2012
Frequency regulation and generation-load balancing are key issues in power transmission networks. Complementary to generation control, loads provide flexible and fast responsive sources for frequency regulation, and local frequency measurement capability of loads offers the opportunity of decentralized control. In this paper, we propose an optimal load control problem, which balances the load reduction (or increase) with the generation shortfall (or surplus), resynchronizes the bus frequencies, and minimizes a measure of aggregate disutility of participation in such a load control. We find that, a frequency-based load control coupled with the dynamics of swing equations and branch power flows serve as a distributed primal-dual algorithm to solve the optimal load control problem and its dual. Simulation shows that the proposed mechanism can restore frequency, balance load with generation and achieve the optimum of the load control problem within several seconds after a disturbance in generation. Through simulation, we also compare the performance of optimal load control with automatic generation control (AGC), and discuss the effect of their incorporation.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/n4c7f-cfb62Congestion Control for Multicast Flows With Network Coding
https://resolver.caltech.edu/CaltechAUTHORS:20121008-112913029
Authors: {'items': [{'id': 'Chen-Lijun', 'name': {'family': 'Chen', 'given': 'Lijun'}}, {'id': 'Ho-Tracey', 'name': {'family': 'Ho', 'given': 'Tracey'}}, {'id': 'Chiang-Mung', 'name': {'family': 'Chiang', 'given': 'Mung'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John C.'}, 'orcid': '0000-0002-1828-2486'}]}
Year: 2012
DOI: 10.1109/TIT.2012.2204170
Recent advances in network coding have shown great potential for efficient information multicasting in communication networks, in terms of both network throughput and network management. In this paper, the problem of flow control at end-systems for network-coding-based multicast flows is addressed. Optimization-based models are formulated for network resource allocation, based on which two sets of decentralized controllers at sources and links/nodes for congestion control are developed for wired networks with given coding subgraphs and without given coding subgraphs, respectively. With random network coding, both sets of controllers can be implemented in a distributed manner, and work at the transport layer to adjust source rates and at network layer to carry out network coding. The convergence of the proposed controllers to the desired equilibrium operating points is proved, and numerical examples are provided to complement the theoretical analysis. The extension to wireless networks is also briefly discussed.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/s7xxe-f8n93Max-Min SINR Coordinated Multipoint Downlink Transmission—Duality and Algorithms
https://resolver.caltech.edu/CaltechAUTHORS:20121029-090718734
Authors: {'items': [{'id': 'Cai-Desmond-W-H', 'name': {'family': 'Cai', 'given': 'Desmond W. H.'}, 'orcid': '0000-0001-9207-1890'}, {'id': 'Quek-Tony-Q-S', 'name': {'family': 'Quek', 'given': 'Tony Q. S.'}}, {'id': 'Tan-Chee-Wei', 'name': {'family': 'Tan', 'given': 'Chee Wei'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2012
DOI: 10.1109/TSP.2012.2208631
This paper considers the max-min weighted signal-to-interference-plus-noise ratio (SINR) problem subject to multiple weighted-sum power constraints, where the weights can represent relative power costs of serving different users. First, we study the power control problem. We apply nonlinear Perron-Frobenius theory to derive closed-form expressions for the optimal value and solution and an iterative algorithm which converges geometrically fast to the optimal solution. Then, we use the structure of the closed-form solution to show that the problem can be decoupled into subproblems each involving only one power constraint. Next, we study the multiple-input-single-output (MISO) transmit beamforming and power control problem. We use uplink-downlink duality to show that this problem can be decoupled into subproblems each involving only one power constraint. We apply this decoupling result to derive an iterative subgradient projection algorithm for the problem.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/14e1k-thz31Equivalence of Branch Flow and Bus Injection Models
https://resolver.caltech.edu/CaltechAUTHORS:20130731-091844876
Authors: {'items': [{'id': 'Subhonmesh-B', 'name': {'family': 'Subhonmesh', 'given': 'Bose'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Chandy-K-M', 'name': {'family': 'Chandy', 'given': 'K. Mani'}}]}
Year: 2012
DOI: 10.1109/Allerton.2012.6483453
A branch flow model has recently been proposed for the analysis and optimization of power flows. In this paper we show that the model is equivalent to the more popular bus injection model. Moreover, we prove the equivalence of various relaxations of these two models.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/rk6zp-gad61Swing dynamics as primal-dual algorithm for optimal load control
https://resolver.caltech.edu/CaltechAUTHORS:20130828-101518387
Authors: {'items': [{'id': 'Zhao-Changhong', 'name': {'family': 'Zhao', 'given': 'Changhong'}, 'orcid': '0000-0003-0539-8591'}, {'id': 'Topcu-U', 'name': {'family': 'Topcu', 'given': 'Ufuk'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2012
DOI: 10.1109/SmartGridComm.2012.6486046
In electricity transmission networks, loads can provide flexible, fast responsive, and decentralized sources for frequency regulation and generation-demand balancing, complementary to generation control. We consider an optimal load control (OLC) problem in a transmission network, when a disturbance in generation occurs on an arbitrary subset of the buses. In OLC, the frequency-insensitive loads are reduced (or increased) in real-time in a way that balances the generation shortfall (or surplus), resynchronizes the bus frequencies, and minimizes the aggregate disutility of load control. We propose a frequency-based load control mechanism and show that the swing dynamics of the network, together with the proposed mechanism, act as a decentralized primal-dual algorithm to solve OLC. Simulation shows that the proposed mechanism can resynchronize the bus frequencies, balance demand with generation and achieve the optimum of OLC within several seconds after a disturbance in generation. Through simulation, we also compare the performance of the proposed mechanism with automatic generation control (AGC), and discuss the effect of their incorporation.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/w6w9y-cfd86Exact Convex Relaxation of OPF for Radial Networks using Branch Flow Model
https://resolver.caltech.edu/CaltechAUTHORS:20130826-134301716
Authors: {'items': [{'id': 'Li-Na', 'name': {'family': 'Li', 'given': 'Na'}}, {'id': 'Chen-Lijun', 'name': {'family': 'Chen', 'given': 'Lijun'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2012
DOI: 10.1109/SmartGridComm.2012.6485951
The optimal power flow (OPF) problem is generally nonconvex. Recently a second-order cone relaxation for OPF has been proposed using the branch flow model. In this paper, we provide sufficient conditions under which the relaxation is exact, and demonstrate that these conditions hold for a wide class of practical power distribution systems.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/e6qj1-29t23Demand response in radial distribution networks: Distributed algorithm
https://resolver.caltech.edu/CaltechAUTHORS:20130802-082120272
Authors: {'items': [{'id': 'Li-Na', 'name': {'family': 'Li', 'given': 'Na'}}, {'id': 'Chen-Lijun', 'name': {'family': 'Chen', 'given': 'Lijun'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2012
DOI: 10.1109/ACSSC.2012.6489288
Demand response has recently become a topic of active research. Most of work however considers only the balance between aggregate load and supply, and abstracts away the underlying power network. In this paper, we study demand response in a radial distribution network, by formulating it as an optimal power flow problem that maximizes the aggregate user utilities and minimizes the supply cost and the power line losses, subject to the power flow constraints and operating constraints. We propose a fully distributed algorithm for the users to coordinate their demand response decisions through local communication with their neighbors so as to achieve the optimum. Numerical examples with the real-world distribution circuits are provided to complement our theoretical analysis.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/8v9tq-x2v45Some Problems in Demand Side Management
https://resolver.caltech.edu/CaltechAUTHORS:20130815-100621563
Authors: {'items': [{'id': 'Gan-Lingwen', 'name': {'family': 'Gan', 'given': 'Lingwen'}}, {'id': 'Jiang-Libin', 'name': {'family': 'Jiang', 'given': 'Libin'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Topcu-U', 'name': {'family': 'Topcu', 'given': 'Ufuk'}}, {'id': 'Zhao-Changhong', 'name': {'family': 'Zhao', 'given': 'Changhong'}, 'orcid': '0000-0003-0539-8591'}]}
Year: 2012
We present a sample of problems in demand side
management in future power systems and illustrate how they
can be solved in a distributed manner using local information.
First, we consider a set of users served by a single load-serving
entity (LSE). The LSE procures capacity a day ahead. When
random renewable energy is realized at delivery time, it manages
user load through real-time demand response and purchases
balancing power on the spot market to meet the aggregate
demand. Hence optimal supply procurement by the LSE and the
consumption decisions by the users must be coordinated over two
timescales, a day ahead and in real time, in the presence of supply
uncertainty. Moreover, they must be computed jointly by the
LSE and the users since the necessary information is distributed
among them. We present distributed algorithms to maximize
expected social welfare. Instead of social welfare, the second
problem is to coordinate electric vehicle charging to fill the valleys
in aggregate electric demand profile, or track a given desired
profile. We present synchronous and asynchronous algorithms
and prove their convergence. Finally, we show how loads can
use locally measured frequency deviations to adapt in real time
their demand in response to a shortfall in supply. We design
decentralized demand response mechanism that, together with
the swing equation of the generators, jointly maximize disutility
of demand rationing, in a decentralized manner.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/a5yj9-kj319On the exactness of convex relaxation for optimal power flow in tree networks
https://resolver.caltech.edu/CaltechAUTHORS:20131220-094526108
Authors: {'items': [{'id': 'Gan-Lingwen', 'name': {'family': 'Gan', 'given': 'Lingwen'}}, {'id': 'Li-Na', 'name': {'family': 'Li', 'given': 'Na'}}, {'id': 'Topcu-U', 'name': {'family': 'Topcu', 'given': 'Ufuk'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2012
DOI: 10.1109/CDC.2012.6426045
The optimal power flow problem is nonconvex, and a convex relaxation has been proposed to solve it. We prove that the relaxation is exact, if there are no upper bounds on the voltage, and any one of some conditions holds. One of these conditions requires that there is no reverse real power flow, and that the resistance to reactance ratio is non-decreasing as transmission lines spread out from the substation to the branch buses. This condition is likely to hold if there are no distributed generators. Besides, avoiding reverse real power flow can be used as rule of thumb for placing distributed generators.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/xqngg-p9h45Deadline differentiated pricing of deferrable electric power service
https://resolver.caltech.edu/CaltechAUTHORS:20170201-153706452
Authors: {'items': [{'id': 'Bitar-E', 'name': {'family': 'Bitar', 'given': 'Eilyan'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2012
DOI: 10.1109/CDC.2012.6425944
As the penetration of wind and solar energy into the electric grid continues to grow, there will be an increasing need to evolve demand-side solutions capable of compensating the inherent variability in power supply from such renewable resources. Today, demand is largely treated as inelastic. However, the power requirements of many commercial and residential loads are such that a fraction of power demand at any given moment is inherently deferrable in time subject to a deadline constraint on the total energy supplied. Examples include thermal systems such as refrigerators, water heaters, HVAC systems, data centers, and, assuming mass adoption of plug-in electric vehicles, batteries. In this paper, we discuss some limitations of dynamic pricing mechanisms (e.g., real-time pricing) as a means of inducing demand response and suggest a novel forward contracting mechanism for deadline-differentiated deferrable energy contracts to alleviate some of these difficulties. Essentially, consumers who consent to deferral of their consumption in time - subject to a pre-specified deadline - will receive a discounted per-unit price for said energy. In this way, the supplier is capable of extracting flexibility in the delivery of energy to participating deferrable loads, while consumers receive a discount on energy with an associated deadline guarantee on delivery. The supply side is modeled as random to capture variability in renewable power supply. Using a general model for consumer preferences to capture the effect of consumption deferral on utility, we prove the existence of a competitive equilibrium and provide a characterization of deadline-differentiated prices yielding such an equilibrium. We also discuss provably optimal online scheduling policies to dynamically allocate the variable supply to a bundle of deadline-differentiated energy tasks.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/d112d-rtb18Branch flow model: Relaxations and convexification
https://resolver.caltech.edu/CaltechAUTHORS:20131220-084709018
Authors: {'items': [{'id': 'Farivar-M', 'name': {'family': 'Farivar', 'given': 'Masoud'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2012
DOI: 10.1109/CDC.2012.6425870
We propose a branch flow model for the analysis and optimization of mesh as well as radial networks. The model leads to a new approach to solving optimal power flow (OPF) problems that consists of two relaxation steps. The first step eliminates the voltage and current angles and the second step approximates the resulting problem by a conic program that can be solved efficiently. For radial networks, we prove that both relaxation steps are always exact, provided there are no upper bounds on loads. For mesh networks, the conic relaxation is always exact and we characterize when the angle relaxation may fail. We propose a simple method to convexify a mesh network using phase shifters so that both relaxation steps are always exact and OPF for the convexified network can always be solved efficiently for a globally optimal solution. We prove that convexification requires phase shifters only outside a spanning tree of the network graph and their placement depends only on network topology, not on power flows, generation, loads, or operating constraints. Since power networks are sparse, the number of required phase shifters may be relatively small.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/f03t1-zt633Branch flow model for radial networks: convex relaxation
https://resolver.caltech.edu/CaltechAUTHORS:20170810-114313789
Authors: {'items': [{'id': 'Gan-Lingwen', 'name': {'family': 'Gan', 'given': 'Lingwen'}}, {'id': 'Li-Na', 'name': {'family': 'Li', 'given': 'Na'}}, {'id': 'Topcu-U', 'name': {'family': 'Topcu', 'given': 'Ufuk'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2012
Power flow optimization is generally nonlinear and non-convex, and a second-order cone relaxation has been proposed recently for convexification. We prove several sufficient conditions under which the relaxation is exact. One of these conditions seems particularly realistic and suggests guidelines on integrating distributed generations.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/0vwxf-41144An optimization-based demand response in radial distribution networks
https://resolver.caltech.edu/CaltechAUTHORS:20130730-133244823
Authors: {'items': [{'id': 'Li-Na', 'name': {'family': 'Li', 'given': 'Na'}}, {'id': 'Gan-Lingwen', 'name': {'family': 'Gan', 'given': 'Lingwen'}}, {'id': 'Chen-Lijun', 'name': {'family': 'Chen', 'given': 'Lijun'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2012
DOI: 10.1109/GLOCOMW.2012.6477803
Demand response has recently become a topic of active research. Most of work however considers only the balance between aggregate load and supply, and abstracts away the underlying power network and the associated power flow constraints and operating constraints. In this paper, we study demand response in a radial distribution network, by formulating it as an optimal power flow problem that maximizes the aggregate user utilities and minimizes the power line losses, subject to the power flow constraints and operating constraints. As the resulting problem is non-convex and difficult to solve, we propose a convex relaxation that is usually exact for the real-world distribution circuits. We then propose a distributed algorithm for the load-serving entity to set the price signal to coordinate the users' demand response so as to achieve the optimum. Numerical examples show that the proposed algorithm converges fast for real-world distribution systems.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/qtmgt-jpt39Real-time deferrable load control: handling the uncertainties of renewable generation
https://resolver.caltech.edu/CaltechAUTHORS:20161025-161438752
Authors: {'items': [{'id': 'Gan-Lingwen', 'name': {'family': 'Gan', 'given': 'Lingwen'}}, {'id': 'Wierman-A', 'name': {'family': 'Wierman', 'given': 'Adam'}}, {'id': 'Topcu-U', 'name': {'family': 'Topcu', 'given': 'Ufuk'}}, {'id': 'Chen-Niangjun', 'name': {'family': 'Chen', 'given': 'Niangjun'}, 'orcid': '0000-0002-2289-9737'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2013
DOI: 10.1145/2487166.2487179
Real-time demand response is essential for handling the uncertainties of renewable generation. Traditionally, demand response has been focused on large industrial and commercial loads, however it is expected that a large number of small residential loads such as air conditioners, dish washers, and electric vehicles will also participate in the coming years. The electricity consumption of these smaller loads, which we call deferrable loads, can be shifted over time, and thus be used (in aggregate) to compensate for the random fluctuations in renewable generation. In this paper, we propose a real-time distributed deferrable load control algorithm to reduce the variance of aggregate load (load minus renewable generation) by shifting the power consumption of deferrable loads to periods with high renewable generation. At every time step, the algorithm minimizes the expected variance to go with updated predictions. We prove that suboptimality of the algorithm vanishes as time horizon expands. Further, we evaluate the algorithm via trace-based simulations.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/m4gqe-7j072Optimal Decentralized Protocol for Electric Vehicle Charging
https://resolver.caltech.edu/CaltechAUTHORS:20131003-094643635
Authors: {'items': [{'id': 'Gan-Lingwen', 'name': {'family': 'Gan', 'given': 'Lingwen'}}, {'id': 'Topcu-U', 'name': {'family': 'Topcu', 'given': 'Ufuk'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2013
DOI: 10.1109/TPWRS.2012.2210288
We propose a decentralized algorithm to optimally schedule electric vehicle (EV) charging. The algorithm exploits the elasticity of electric vehicle loads to fill the valleys in electric load profiles. We first formulate the EV charging scheduling problem as an optimal control problem, whose objective is to impose a generalized notion of valley-filling, and study properties of optimal charging profiles. We then give a decentralized algorithm to iteratively solve the optimal control problem. In each iteration, EVs update their charging profiles according to the control signal broadcast by the utility company, and the utility company alters the control signal to guide their updates. The algorithm converges to optimal charging profiles (that are as "flat" as they can possibly be) irrespective of the specifications (e.g., maximum charging rate and deadline) of EVs, even if EVs do not necessarily update their charging profiles in every iteration, and use potentially outdated control signal when they update. Moreover, the algorithm only requires each EV solving its local problem, hence its implementation requires low computation capability. We also extend the algorithm to track a given load profile and to real-time implementation.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/6bhnt-fy360Towards smart, flexible and efficient power systems: Vision and research challenges
https://resolver.caltech.edu/CaltechAUTHORS:20170810-114148121
Authors: {'items': [{'id': 'Topcu-U', 'name': {'family': 'Topcu', 'given': 'Ufuk'}}, {'id': 'Gayme-D-F', 'name': {'family': 'Gayme', 'given': 'Dennice'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Khargonekar-P-P', 'name': {'family': 'Khargonekar', 'given': 'Pramod'}}]}
Year: 2013
DOI: 10.1109/ACC.2013.6580653
The electric power infrastructure is transforming into a smarter, increasingly flexible, and more efficient system with the potential to play an integral role in the changing energy landscape. This paper and the accompanying tutorial session at the 2013 American Control Conference provide an overview of this transformation. It then highlights three emerging optimization and controls techniques that can help facilitate the necessary changes to power grid design, operation and management.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/5xpw8-e5b06Multipath TCP algorithms: theory and design
https://resolver.caltech.edu/CaltechAUTHORS:20161207-173639173
Authors: {'items': [{'id': 'Peng-Qiuyu', 'name': {'family': 'Peng', 'given': 'Qiuyu'}}, {'id': 'Walid-A', 'name': {'family': 'Walid', 'given': 'Anwar'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2013
DOI: 10.1145/2494232.2466585
Multi-path TCP (MP-TCP) has the potential to greatly improve application performance by using multiple paths transparently. We propose a fluid model for a large class of MP-TCP algorithms and identify design criteria that guarantee the existence, uniqueness, and stability of system equilibrium. We characterize algorithm parameters for TCP-friendliness and prove an inevitable tradeoff between responsiveness and friendliness. We discuss the implications of these properties on the behavior of existing algorithms and motivate a new design that generalizes existing algorithms. We use ns2 simulations to evaluate the proposed algorithm and illustrate its superior overall performance.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/awnxr-ytb91Multipath TCP Algorithms: Theory and Design
https://resolver.caltech.edu/CaltechAUTHORS:20130828-103050742
Authors: {'items': [{'id': 'Peng-Qiuyu', 'name': {'family': 'Peng', 'given': 'Qiuyu'}}, {'id': 'Walid-A', 'name': {'family': 'Walid', 'given': 'Anwar'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2013
DOI: 10.1145/2494232.2466585
Multi-path TCP (MP-TCP) has the potential to greatly improve
application performance by using multiple paths transparently.
We propose a fluid model for a large class of MP-TCP
algorithms and identify design criteria that guarantee
the existence, uniqueness, and stability of system equilibrium.
We characterize algorithm parameters for TCP-friendliness
and prove an inevitable tradeoff between responsiveness
and friendliness. We discuss the implications of
these properties on the behavior of existing algorithms and
motivate a new design that generalizes existing algorithms.
We use ns2 simulations to evaluate the proposed algorithm
and illustrate its superior overall performance.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/e5xj7-b8y78Exact convex relaxation for optimal power flow in distribution networks
https://resolver.caltech.edu/CaltechAUTHORS:20161025-153928779
Authors: {'items': [{'id': 'Gan-Lingwen', 'name': {'family': 'Gan', 'given': 'Lingwen'}}, {'id': 'Li-Na', 'name': {'family': 'Li', 'given': 'Na'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Topcu-U', 'name': {'family': 'Topcu', 'given': 'Ufuk'}}]}
Year: 2013
DOI: 10.1145/2494232.2465535
The optimal power flow (OPF) problem seeks to control the power generation/consumption to minimize the generation cost, and is becoming important for distribution networks. OPF is nonconvex and a second-order cone programming (SOCP) relaxation has been proposed to solve it. We prove that after a "small" modification to OPF, the SOCP relaxation is exact under a "mild" condition. Empirical studies demonstrate that the modification to OPF is "small" and that the "mild" condition holds for all test networks, including the IEEE 13-bus test network and practical networks with high penetration of distributed generation.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/agta3-mdn57Exact Convex Relaxation for Optimal Power Flow in Distribution Networks
https://resolver.caltech.edu/CaltechAUTHORS:20131008-160444682
Authors: {'items': [{'id': 'Gan-Lingwen', 'name': {'family': 'Gan', 'given': 'Lingwen'}}, {'id': 'Li-Na', 'name': {'family': 'Li', 'given': 'Na'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Topcu-U', 'name': {'family': 'Topcu', 'given': 'Ufuk'}}]}
Year: 2013
DOI: 10.1145/2494232.2465535
The optimal power flow (OPF) problem seeks to control the
power generation/consumption to minimize the generation
cost, and is becoming important for distribution networks.
OPF is nonconvex and a second-order cone programming
(SOCP) relaxation has been proposed to solve it. We prove
that after a "small" modification to OPF, the SOCP relaxation is exact under a "mild" condition. Empirical studies
demonstrate that the modification to OPF is "small" and
that the "mild" condition holds for all test networks, including the IEEE 13-bus test network and practical networks
with high penetration of distributed generation.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/2d15y-8ry21Convexifying Optimal Power Flow: Recent Advances in OPF Solution Methods
https://resolver.caltech.edu/CaltechAUTHORS:20131219-091842168
Authors: {'items': [{'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Gayme-D-F', 'name': {'family': 'Gayme', 'given': 'Dennice'}}, {'id': 'Topcu-U', 'name': {'family': 'Topcu', 'given': 'Ufuk'}}]}
Year: 2013
The optimal power flow (OPF) problem is nonconvex and generally hard to solve, see e.g. [1], [2]. In this tutorial, we will provide an overview of two different solution approaches. The first uses the bus injection model, which is the standard model for power flow analysis and optimization. It focuses on nodal variables such as voltages, current and power injections and does not directly deal with power flows on individual branches. A key advantage is the simple linear relationship I = Y V between the nodal current injections I and the bus voltages V through the admittance matrix Y. Recently, it has been observed that this form of OPF can be reformulated as a nonconvex QCQP (quadratic constrained quadratic program), which leads to a standard convex relaxation through semidefinite programming [3]-[5]. For radial networks, different sufficient conditions have been derived under which the semidefinite relaxation turns out to be exact [6]-[8]. The second solution technique employs the branch flow model, which focuses on currents and powers on the branches rather than the nodal variables. The branch flow model has been historically used primarily for modeling distribution circuits, which tend to be radial. It has therefore received far less attention. A branch flow model has recently been proposed for the analysis and optimization of mesh as well as radial networks. The model leads to a new approach to solving OPF that consists of two relaxation steps. The first step eliminates the voltage and current angles and the second step approximates the resulting problem by a conic program that can be solved efficiently. For radial networks, both relaxation steps are always exact, provided there are no upper bounds on loads [9]. For mesh networks, the conic relaxation is always exact and we provide a simple way to determine if a relaxed solution is globally optimal. We describe a simple method to convexify a mesh network using phase shifters so that both relaxation steps are alw- ys exact and OPF for the convexified network can always be solved efficiently for a globally optimal solution. We prove that convexification requires phase shifters only outside a spanning tree of the network graph and their placement depends only on network topology, not on power flows, generation, loads, or operating constraints [10]. The tutorial will describe precisely the bus injection model and the semidefinite relaxation of OPF as well as the branch flow model and its associated relaxations. We prove sufficient conditions for exact relaxations and verify our results on simulations of various IEEE test systems. Finally we explain the equivalence between the bus injection model and branch flow model.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/q9rrm-sds41Convex relaxation of optimal power flow: A tutorial
https://resolver.caltech.edu/CaltechAUTHORS:20170130-172039929
Authors: {'items': [{'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2013
DOI: 10.1109/IREP.2013.6629391
This is a short survey of recent advances in the convex relaxation of the optimal power flow problem. Our focus is on understanding structural properties, especially the underlying convexity structure, of optimal power flow problems rather than different computational algorithms.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/96ne9-50515Branch Flow Model: Relaxations and Convexification—Part II
https://resolver.caltech.edu/CaltechAUTHORS:20130916-151203881
Authors: {'items': [{'id': 'Farivar-M', 'name': {'family': 'Farivar', 'given': 'Masoud'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2013
DOI: 10.1109/TPWRS.2013.2255318
We propose a branch flow model for the analysis and optimization of mesh as well as radial networks. The model leads to a new approach to solving optimal power flow (OPF) that consists of two relaxation steps. The first step eliminates the voltage and current angles and the second step approximates the resulting problem by a conic program that can be solved efficiently. For radial networks, we prove that both relaxation steps are always exact, provided there are no upper bounds on loads. For mesh networks, the conic relaxation is always exact but the angle relaxation may not be exact, and we provide a simple way to determine if a relaxed solution is globally optimal. We propose convexification of mesh networks using phase shifters so that OPF for the convexified network can always be solved efficiently for an optimal solution. We prove that convexification requires phase shifters only outside a spanning tree of the network and their placement depends only on network topology, not on power flows, generation, loads, or operating constraints. Part I introduces our branch flow model, explains the two relaxation steps, and proves the conditions for exact relaxation. Part II describes convexification of mesh networks, and presents simulation results.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/ndxj1-n1k24Branch Flow Model: Relaxations and Convexification—Part I
https://resolver.caltech.edu/CaltechAUTHORS:20131003-153831161
Authors: {'items': [{'id': 'Farivar-M', 'name': {'family': 'Farivar', 'given': 'Masoud'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2013
DOI: 10.1109/TPWRS.2013.2255317
We propose a branch flow model for the analysis and optimization of mesh as well as radial networks. The model leads to a new approach to solving optimal power flow (OPF) that consists of two relaxation steps. The first step eliminates the voltage and current angles and the second step approximates the resulting problem by a conic program that can be solved efficiently. For radial networks, we prove that both relaxation steps are always exact, provided there are no upper bounds on loads. For mesh networks, the conic relaxation is always exact but the angle relaxation may not be exact, and we provide a simple way to determine if a relaxed solution is globally optimal. We propose convexification of mesh networks using phase shifters so that OPF for the convexified network can always be solved efficiently for an optimal solution. We prove that convexification requires phase shifters only outside a spanning tree of the network and their placement depends only on network topology, not on power flows, generation, loads, or operating constraints. Part I introduces our branch flow model, explains the two relaxation steps, and proves the conditions for exact relaxation. Part II describes convexification of mesh networks, and presents simulation results.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/vsdpk-r8b62Congestion window control based on queuing delay and packet loss
https://resolver.caltech.edu/CaltechAUTHORS:20170810-125112061
Authors: {'items': [{'id': 'Jin-Cheng', 'name': {'family': 'Jin', 'given': 'Cheng'}}, {'id': 'Liu-Victor', 'name': {'family': 'Liu', 'given': 'Victor'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Gururajan-Santosh-Rao', 'name': {'family': 'Gururajan', 'given': 'Santosh Rao'}}, {'id': 'Yang-Lingfeng', 'name': {'family': 'Yang', 'given': 'Lingfeng'}}]}
Year: 2013
A method of controlling size of a congestion window, includes, at a transmitting device, transmitting a plurality of data packets over a communication channel from the transmitting device to a receiver, determining a queuing delay and a loss rate of the transmission, comparing the queuing delay to a threshold queuing delay, comparing the loss rate to a threshold loss rate, and in response to a determination that the queuing delay is greater than the threshold queuing delay and the loss rate is greater than the threshold loss rate, resetting the size of the congestion window in accordance with a function of the current size of the congestion window, the queuing delay, and the loss rate, wherein at equilibrium the function generates a value inversely proportional to a weighted sum of an excess queuing delay and an excess loss rate.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/vjzce-kpv94The redistribution of power flow in cascading failures
https://resolver.caltech.edu/CaltechAUTHORS:20170810-133558423
Authors: {'items': [{'id': 'Lai-Chengdi', 'name': {'family': 'Lai', 'given': 'Chengdi'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2013
DOI: 10.1109/Allerton.2013.6736639
Understanding the redistribution of power flow is crucial to understanding the dynamics of cascading failures. Such redistribution is complicated, with monotonicity being the exception rather than the norm. We study the monotonicity of a quadratic function of branch power flow with respect to link failure and load shedding, respectively. The quadratic function can be considered as a measure of the aggregate network loading. We show that the value of this measure increases when (more) link failure occurs. On the other hand, while arbitrary load shedding can increase the measure value, we establish the existence of load shedding that can guarantee its reduction. Utilizing these monotonicity properties, we show that the failure of a link will cause the power flow over its adjacent link to have a change in the same direction (away or towards their commonly incident bus) as the original flow over the failed link.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/we34e-nw941Demand Response Optimization for Smart Home Scheduling Using Genetic Algorithm
https://resolver.caltech.edu/CaltechAUTHORS:20170810-105100899
Authors: {'items': [{'id': 'Chen-Chao-Rong', 'name': {'family': 'Chen', 'given': 'Chao-Rong'}}, {'id': 'Lan-Ming-Jen', 'name': {'family': 'Lan', 'given': 'Ming-Jen'}}, {'id': 'Huang-Chi-Chen', 'name': {'family': 'Huang', 'given': 'Chi-Chen'}}, {'id': 'Hong-Ying-Yi', 'name': {'family': 'Hong', 'given': 'Ying-Yi'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2013
DOI: 10.1109/SMC.2013.252
For mitigating the urgency of constructing power plant, alleviating supply pressure of power company, electricity scheduling of customers is a very important issue, wherein to promote demand response is a key factor. The demand response is mainly through electricity price publicized by utility company to guide customers in electricity scheduling, and by use of price negotiating mechanism, to reach mutual benefits for both sides of demand and supply. The paper proposes a method of minimizing tariff for customers through changing elastic load use time intervals where customers' electricity use time is divided into inelastic and elastic intervals by electricity use characteristics. In the paper, customer's one day electricity used is assumed to conduct simulation, by genetic algorithm, comparing variations among scheduling and tariff under different electricity use limitation situations. As shown in the results, it is found that through elastic load use time interval changes, minimum tariff objective can be reached, and feasibility of the proposed method is verified.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/2pj21-3mz75Optimal Load Control via Frequency Measurement and Neighborhood Area Communication
https://resolver.caltech.edu/CaltechAUTHORS:20131203-091918486
Authors: {'items': [{'id': 'Zhao-Changhong', 'name': {'family': 'Zhao', 'given': 'Changhong'}, 'orcid': '0000-0003-0539-8591'}, {'id': 'Topcu-U', 'name': {'family': 'Topcu', 'given': 'Ufuk'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2013
DOI: 10.1109/TPWRS.2013.2261096
We propose a decentralized optimal load control scheme that provides contingency reserve in the presence of sudden generation drop. The scheme takes advantage of flexibility of frequency responsive loads and neighborhood area communication to solve an optimal load control problem that balances load and generation while minimizing end-use disutility of participating in load control. Local frequency measurements enable individual loads to estimate the total mismatch between load and generation. Neighborhood area communication helps mitigate effects of inconsistencies in the local estimates due to frequency measurement noise. Case studies show that the proposed scheme can balance load with generation and restore the frequency within seconds of time after a generation drop, even when the loads use a highly simplified power system model in their algorithms. We also investigate tradeoffs between the amount of communication and the performance of the proposed scheme through simulation-based experiments.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/wdh99-fkz82Impact of residential PV adoption on Retail Electricity Rates
https://resolver.caltech.edu/CaltechAUTHORS:20131213-111904382
Authors: {'items': [{'id': 'Cai-Desmond-W-H', 'name': {'family': 'Cai', 'given': 'Desmond W. H.'}, 'orcid': '0000-0001-9207-1890'}, {'id': 'Adlakha-S', 'name': {'family': 'Adlakha', 'given': 'Sachin'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'De-Martini-P', 'name': {'family': 'De Martini', 'given': 'Paul'}}, {'id': 'Chandy-K-M', 'name': {'family': 'Chandy', 'given': 'K. Mani'}}]}
Year: 2013
DOI: 10.1016/j.enpol.2013.07.009
The price of electricity supplied from home rooftop photo voltaic (PV) solar cells has fallen below the retail price of grid electricity in some areas. A number of residential households have an economic incentive to install rooftop PV systems and reduce their purchases of electricity from the grid. A significant portion of the costs incurred by utility companies are fixed costs which must be recovered even as consumption falls. Electricity rates must increase in order for utility companies to recover fixed costs from shrinking sales bases. Increasing rates will, in turn, result in even more economic incentives for customers to adopt rooftop PV. In this paper, we model this feedback between PV adoption and electricity rates and study its impact on future PV penetration and net-metering costs. We find that the most important parameter that determines whether this feedback has an effect is the fraction of customers who adopt PV in any year based solely on the money saved by doing so in that year, independent of the uncertainties of future years. These uncertainties include possible changes in rate structures such as the introduction of connection charges, the possibility of PV prices dropping significantly in the future, possible changes in tax incentives, and confidence in the reliability and maintainability of PV.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/r68eb-k0712Optimal power flow in tree networks
https://resolver.caltech.edu/CaltechAUTHORS:20170810-113418095
Authors: {'items': [{'id': 'Gan-Lingwen', 'name': {'family': 'Gan', 'given': 'Lingwen'}}, {'id': 'Li-Na', 'name': {'family': 'Li', 'given': 'Na'}}, {'id': 'Topcu-U', 'name': {'family': 'Topcu', 'given': 'Ufuk'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2013
DOI: 10.1109/CDC.2013.6760226
The optimal power flow (OPF) problem seeks to control power generation/demand to optimize certain objectives such as minimizing the generation cost or power loss. It is becoming increasingly important for tree distribution networks due to the emerging distributed generation and controllable loads. The OPF problem is nonconvex. We prove that after modifying the OPF problem, its global optimum can be recovered via a second-order cone programming (SOCP) relaxation for tree networks, under a condition that can be checked in advance. Empirical studies justify that the modification is "small", and that the condition holds, for the IEEE 13-bus network and two real-world networks.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/16qrb-p1t76Optimal branch exchange for feeder reconfiguration in distribution networks
https://resolver.caltech.edu/CaltechAUTHORS:20170810-131659189
Authors: {'items': [{'id': 'Peng-Qiuyu', 'name': {'family': 'Peng', 'given': 'Qiuyu'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2013
DOI: 10.1109/CDC.2013.6760333
The feeder reconfiguration problem chooses the on/off status of the switches in a distribution network in order to minimize a certain cost such as power loss. It is a mixed integer nonlinear program and hence hard to solve. A popular heuristic search consists of repeated application of branch exchange, where some loads are transferred from one feeder to another feeder while maintaining the radial structure of the network, until no load transfer can further reduce the cost. Optimizing each branch exchange step is itself a mixed integer nonlinear program. In this paper we propose an efficient algorithm for optimizing a branch exchange step. It uses an AC power flow model and is based on the recently developed convex relaxation of optimal power flow. We provide a bound on the gap between the optimal cost and that of our solution. We prove that our algorithm is optimal when the voltage magnitudes are the same at all buses. We illustrate the effectiveness of our algorithm through the simulation of real-world distribution feeders.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/cqytx-nhs12Optimal Power Flow in Direct Current Networks
https://resolver.caltech.edu/CaltechAUTHORS:20170810-113122736
Authors: {'items': [{'id': 'Gan-Lingwen', 'name': {'family': 'Gan', 'given': 'Lingwen'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2013
DOI: 10.1109/CDC.2013.6760774
The optimal power flow (OPF) problem seeks to control power generation/demand to optimize certain objectives such as minimizing the generation cost or power loss. Direct current (DC) networks (e.g., DC-microgrids) are promising to incorporate distributed generation. This paper focuses on the OPF problem in DC networks. The OPF problem is nonconvex, and we study solving it via a second-order cone programming (SOCP) relaxation. In particular, we prove that the SOCP relaxation is exact if there are no voltage upper bounds, and that the SOCP relaxation has at most one solution if it is exact.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/1dyvw-6kd28Equilibrium and dynamics of local voltage control in distribution systems
https://resolver.caltech.edu/CaltechAUTHORS:20170810-113209963
Authors: {'items': [{'id': 'Farivar-M', 'name': {'family': 'Farivar', 'given': 'Masoud'}}, {'id': 'Chen-Lijun', 'name': {'family': 'Chen', 'given': 'Lijun'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2013
DOI: 10.1109/CDC.2013.6760555
We consider a class of local volt/var control schemes where the control decision on the reactive power at a bus depends only on the local bus voltage. These local algorithms form a feedback dynamical system and collectively determine the bus voltages of a power network. We show that the dynamical system has a unique equilibrium by interpreting the dynamics as a distributed algorithm for solving a certain convex optimization problem whose unique optimal point is the system equilibrium. Moreover, the objective function serves as a Lyapunov function implying global asymptotic stability of the equilibrium. The optimization based model does not only provide a way to characterize the equilibrium, but also suggests a principled way to engineer the control. We apply the results to study the parameter setting for the inverter-based volt/var control in the proposed IEEE 1547.8 standard.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/dps39-gck77Pricing Link by Time
https://resolver.caltech.edu/CaltechAUTHORS:20140804-112817922
Authors: {'items': [{'id': 'Lai-Chengdi', 'name': {'family': 'Lai', 'given': 'Chengdi'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Stephen H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Leung-Ka-Cheong', 'name': {'family': 'Leung', 'given': 'Ka-Cheong'}, 'orcid': '0000-0001-7999-2572'}, {'id': 'Li-Victor-O-K', 'name': {'family': 'Li', 'given': 'Victor O. K.'}}]}
Year: 2014
DOI: 10.1145/2591971.2591974
The combination of loss-based TCP and drop-tail routers
often results in full buffers, creating large queueing delays. The challenge with parameter tuning and the drastic consequence of improper tuning have discouraged network administrators from enabling AQM even when routers support
it. To address this problem, we propose a novel design principle for AQM, called the pricing-link-by-time (PLT) principle. PLT increases the link price as the backlog stays above a threshold β, and resets the price once the backlog goes below β. We prove that such a system exhibits cyclic behavior that is robust against changes in network environment and protocol parameters. While β approximately controls the level of backlog, the backlog dynamics are invariant for β across a wide range of values. Therefore, β can be chosen to reduce delay without undermining system performance. We validate these analytical results using packet-level simulation.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/33gaz-zr760Energy Efficient Multipath TCP for Mobile Devices
https://resolver.caltech.edu/CaltechAUTHORS:20140820-114017534
Authors: {'items': [{'id': 'Peng-Qiuyu', 'name': {'family': 'Peng', 'given': 'Qiuyu'}}, {'id': 'Chen-Minghua', 'name': {'family': 'Chen', 'given': 'Minghua'}}, {'id': 'Walid-Anwar', 'name': {'family': 'Walid', 'given': 'Anwar'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2014
DOI: 10.1145/2632951.2632971
Most mobile devices today come with multiple access interfaces, e.g., 4G and WiFi. Multipath TCP (MP-TCP) can greatly improve network performance by exploiting the connection diversity of multiple access interfaces, at the expense of higher energy consumption. In this paper, we design MP-TCP algorithms for mobile devices by jointly considering the performance and energy consumption. We consider two main types of mobile applications: realtime applications that have a fixed duration and file transfer applications that have a fixed data size. For each type of applications, we propose a two-timescale algorithm with theoretical guarantee on the performance. We present simulation results that show that our algorithms can reduce energy consumption by up to 22% without sacrificing throughput compared to a baseline MP-TCP algorithm.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/gk9g2-93559Solving quadratically constrained quadratic programs on acyclic graphs with application to optimal power flow
https://resolver.caltech.edu/CaltechAUTHORS:20150501-091249022
Authors: {'items': [{'id': 'Bose-Subhonmesh', 'name': {'family': 'Bose', 'given': 'Subhonmesh'}, 'orcid': '0000-0002-3445-4479'}, {'id': 'Gayme-D-F', 'name': {'family': 'Gayme', 'given': 'Dennice F.'}}, {'id': 'Chandy-K-M', 'name': {'family': 'Chandy', 'given': 'K. Mani'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2014
DOI: 10.1109/CISS.2014.6814135
This paper presents a class of non-convex quadratically constrained quadratic programs that can be solved in polynomial time when their underlying graph is acyclic, provided the constraints satisfy a technical condition. We demonstrate its use on optimal power flow problems over radial networks.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/zxwv3-g7g20Convex Relaxation of Optimal Power Flow — Part I: Formulations and Equivalence
https://resolver.caltech.edu/CaltechAUTHORS:20140521-104006650
Authors: {'items': [{'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2014
DOI: 10.1109/TCNS.2014.2309732
This tutorial summarizes recent advances in the convex
relaxation of the optimal power flow (OPF) problem, focusing on structural properties rather than algorithms. Part I presents two power flow models, formulates OPF and their relaxations in each model, and proves equivalence relationships among them. Part II presents sufficient conditions under which the convex relaxations are exact.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/436tr-60p50Greening Geographical Load Balancing
https://resolver.caltech.edu/CaltechAUTHORS:20150112-084413455
Authors: {'items': [{'id': 'Liu-Zhenhua', 'name': {'family': 'Liu', 'given': 'Zhenhua'}}, {'id': 'Lin-Minghong', 'name': {'family': 'Lin', 'given': 'Minghong'}}, {'id': 'Wierman-A', 'name': {'family': 'Wierman', 'given': 'Adam'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Andrew-L-L-H', 'name': {'family': 'Andrew', 'given': 'Lachlan L. H.'}}]}
Year: 2014
DOI: 10.1109/TNET.2014.2308295
Energy expenditure has become a significant fraction of data center operating costs. Recently, "geographical load balancing" has been proposed to reduce energy cost by exploiting the electricity price differences across regions. However, this reduction of cost can paradoxically increase total energy use. We explore whether the geographical diversity of Internet-scale systems can also provide environmental gains. Specifically, we explore whether geographical load balancing can encourage use of "green" renewable energy and reduce use of "brown" fossil fuel energy. We make two contributions. First, we derive three distributed algorithms for achieving optimal geographical load balancing. Second, we show that if the price of electricity is proportional to the instantaneous fraction of the total energy that is brown, then geographical load balancing significantly reduces brown energy use. However, the benefits depend strongly on dynamic energy pricing and the form of pricing used.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/nqgqj-djm27Branch flow model: Relaxations and convexification
https://resolver.caltech.edu/CaltechAUTHORS:20170124-173857414
Authors: {'items': [{'id': 'Farivar-M', 'name': {'family': 'Farivar', 'given': 'Masoud'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2014
DOI: 10.1109/TDC.2014.6863260
We propose a branch flow model for the analysis and optimization of mesh as well as radial networks. The model leads to a new approach to solving optimal power flow (OPF) that consists of two relaxation steps. The first step eliminates the voltage and current angles and the second step approximates the resulting problem by a conic program that can be solved efficiently. For radial networks, we prove that both relaxation steps are always exact, provided there are no upper bounds on loads. For mesh networks, the conic relaxation is always exact but the angle relaxation may not be exact, and we provide a simple way to determine if a relaxed solution is globally optimal. We propose convexification of mesh networks using phase shifters so that OPF for the convexified network can always be solved efficiently for an optimal solution. We prove that convexification requires phase shifters only outside a spanning tree of the network and their placement depends only on network topology, not on power flows, generation, loads, or operating constraints. Part I introduces our branch flow model, explains the two relaxation steps, and proves the conditions for exact relaxation. Part II describes convexification of mesh networks, and presents simulation results.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/ge52c-d6z17Design and Stability of Load-Side Primary Frequency Control in Power Systems
https://resolver.caltech.edu/CaltechAUTHORS:20140529-094709292
Authors: {'items': [{'id': 'Zhao-Changhong', 'name': {'family': 'Zhao', 'given': 'Changhong'}, 'orcid': '0000-0003-0539-8591'}, {'id': 'Topcu-U', 'name': {'family': 'Topcu', 'given': 'Ufuk'}}, {'id': 'Li-Na', 'name': {'family': 'Li', 'given': 'Na'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2014
DOI: 10.1109/TAC.2014.2298140
We present a systematic method to design ubiquitous continuous fast-acting distributed load control for primary frequency regulation in power networks, by formulating an optimal load control (OLC) problem where the objective is to minimize the aggregate cost of tracking an operating point subject to power balance over the network. We prove that the swing dynamics and the branch power flows, coupled with frequency-based load control, serve as a distributed primal-dual algorithm to solve OLC. We establish the global asymptotic stability of a multimachine network under such type of load-side primary frequency control. These results imply that the local frequency deviations on each bus convey exactly the right information about the global power imbalance for the loads to make individual decisions that turn out to be globally optimal. Simulations confirm that the proposed algorithm can rebalance power and resynchronize bus frequencies after a disturbance with significantly improved transient performance.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/srhae-p5128Pricing link by time
https://resolver.caltech.edu/CaltechAUTHORS:20161121-153645812
Authors: {'items': [{'id': 'Lai-Chengdi', 'name': {'family': 'Lai', 'given': 'Chengdi'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Leung-Ka-Cheong', 'name': {'family': 'Leung', 'given': 'Ka-Cheong'}}, {'id': 'Li-Victor-O-K', 'name': {'family': 'Li', 'given': 'Victor O. K.'}}]}
Year: 2014
DOI: 10.1145/2637364.2591974
The combination of loss-based TCP and drop-tail routers often results in full buffers, creating large queueing delays. The challenge with parameter tuning and the drastic consequence of improper tuning have discouraged network administrators from enabling AQM even when routers support it. To address this problem, we propose a novel design principle for AQM, called the pricing-link-by-time (PLT) principle. PLT increases the link price as the backlog stays above a threshold β, and resets the price once the backlog goes below β. We prove that such a system exhibits cyclic behavior that is robust against changes in network environment and protocol parameters. While β approximately controls the level of backlog, the backlog dynamics are invariant for β across a wide range of values. Therefore, β can be chosen to reduce delay without undermining system performance. We validate these analytical results using packet-level simulation.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/h1e5n-rdr69Pricing data center demand response
https://resolver.caltech.edu/CaltechAUTHORS:20161128-163510694
Authors: {'items': [{'id': 'Liu-Zhenhua', 'name': {'family': 'Liu', 'given': 'Zhenhua'}}, {'id': 'Liu-Iris', 'name': {'family': 'Liu', 'given': 'Iris'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Wierman-A', 'name': {'family': 'Wierman', 'given': 'Adam'}}]}
Year: 2014
DOI: 10.1145/2591971.2592004
Demand response is crucial for the incorporation of renewable energy into the grid. In this paper, we focus on a particularly promising industry for demand response: data centers. We use simulations to show that, not only are data centers large loads, but they can provide as much (or possibly more) flexibility as large-scale storage if given the proper incentives. However, due to the market power most data centers maintain, it is difficult to design programs that are efficient for data center demand response. To that end, we propose that prediction-based pricing is an appealing market design, and show that it outperforms more traditional supply function bidding mechanisms in situations where market power is an issue. However, prediction-based pricing may be inefficient when predictions are inaccurate, and so we provide analytic, worst-case bounds on the impact of prediction error on the efficiency of prediction-based pricing. These bounds hold even when network constraints are considered, and highlight that prediction-based pricing is surprisingly robust to prediction error.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/8s4tj-11n34Pricing Data Center Demand Response
https://resolver.caltech.edu/CaltechAUTHORS:20140804-133949957
Authors: {'items': [{'id': 'Liu-Zhenhua', 'name': {'family': 'Liu', 'given': 'Zhenhua'}}, {'id': 'Liu-Iris', 'name': {'family': 'Liu', 'given': 'Iris'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Wierman-A', 'name': {'family': 'Wierman', 'given': 'Adam'}}]}
Year: 2014
DOI: 10.1145/2591971.2592004
Demand response is crucial for the incorporation of renewable energy into the grid. In this paper, we focus on a particularly promising industry for demand response: data centers. We use simulations to show that, not only are data centers large loads, but they can provide as much (or possibly more) flexibility as large-scale storage if given the proper incentives. However, due to the market power most data centers maintain, it is difficult to design programs that are efficient for data center demand response. To that end, we propose that prediction-based pricing is an appealing market design, and show that it outperforms more traditional supply function bidding mechanisms in situations where market power is an issue. However, prediction-based pricing may be inefficient when predictions are inaccurate, and so we provide analytic, worst-case bounds on the impact of prediction error on the efficiency of prediction-based pricing. These bounds hold even when network constraints are considered, and highlight that prediction-based pricing is surprisingly robust to prediction error.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/8vqy3-0p575Convex Relaxation of Optimal Power Flow - Part II: Exactness
https://resolver.caltech.edu/CaltechAUTHORS:20150922-153930585
Authors: {'items': [{'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2014
DOI: 10.1109/TCNS.2014.2323634
This tutorial summarizes recent advances in the convex relaxation of the optimal power flow (OPF) problem, focusing on structural properties rather than algorithms. Part I presents two power flow models, formulates OPF and their relaxations in each model, and proves equivalence relations among them. Part II presents sufficient conditions under which the convex relaxations are exact.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/jdcgw-gqx82Chordal relaxation of OPF for multiphase radial networks
https://resolver.caltech.edu/CaltechAUTHORS:20150203-145330203
Authors: {'items': [{'id': 'Gan-Lingwen', 'name': {'family': 'Gan', 'given': 'Lingwen'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2014
DOI: 10.1109/ISCAS.2014.6865509
We formulate optimal power flow problem for unbalanced multiphase radial networks. We show that there is an equivalent single-phase mesh network that has a radial structure at the macro-level and a clique structure corresponding to each line in the radial network. Existing sufficient conditions for exact semidefinite relaxation are therefore applicable to unbalanced multiphase networks. In particular, they imply that if a semidefinite relaxation is exact over each of the cliques in the mesh equivalent network, then it is exact for the entire network.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/szyhw-g8827Convexification of AC optimal power flow
https://resolver.caltech.edu/CaltechAUTHORS:20170123-174612725
Authors: {'items': [{'id': 'Gan-Lingwen', 'name': {'family': 'Gan', 'given': 'Lingwen'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2014
DOI: 10.1109/PSCC.2014.7038373
This overview paper summarizes the key elements of semidefinite relaxations of the optimal power flow problem, and discusses several open challenges.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/qy345-88r41Convex relaxations and linear approximation for optimal power flow in multiphase radial networks
https://resolver.caltech.edu/CaltechAUTHORS:20170810-114020714
Authors: {'items': [{'id': 'Gan-Lingwen', 'name': {'family': 'Gan', 'given': 'Lingwen'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2014
DOI: 10.1109/PSCC.2014.7038399
Distribution networks are usually multiphase and radial. To facilitate power flow computation and optimization, two semidefinite programming (SDP) relaxations of the optimal power flow problem and a linear approximation of the power flow are proposed. We prove that the first SDP relaxation is exact if and only if the second one is exact. Case studies show that the second SDP relaxation is numerically exact and that the linear approximation obtains voltages within 0.0016 per unit of their true values for the IEEE 13, 34, 37, 123-bus networks and a real-world 2065-bus network.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/1fcqw-beg37Advanced optimization methods for power systems
https://resolver.caltech.edu/CaltechAUTHORS:20170810-130952392
Authors: {'items': [{'id': 'Panciatici-P', 'name': {'family': 'Panciatici', 'given': 'P.'}}, {'id': 'Campi-M-C', 'name': {'family': 'Campi', 'given': 'M. C.'}}, {'id': 'Garatti-S', 'name': {'family': 'Garatti', 'given': 'S.'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'S. H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Molzahn-D-K', 'name': {'family': 'Molzahn', 'given': 'D. K.'}}, {'id': 'Sun-A-X', 'name': {'family': 'Sun', 'given': 'A. X.'}}, {'id': 'Wehenkel-L', 'name': {'family': 'Wehenkel', 'given': 'L.'}}]}
Year: 2014
DOI: 10.1109/PSCC.2014.7038504
Power system planning and operation offers multitudinous opportunities for optimization methods. In practice, these problems are generally large-scale, non-linear, subject to uncertainties, and combine both continuous and discrete variables. In the recent years, a number of complementary theoretical advances in addressing such problems have been obtained in the field of applied mathematics. The paper introduces a selection of these advances in the fields of non-convex optimization, in mixed-integer programming, and in optimization under uncertainty. The practical relevance of these developments for power systems planning and operation are discussed, and the opportunities for combining them, together with high-performance computing and big data infrastructures, as well as novel machine learning and randomized algorithms, are highlighted.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/t0qvx-ca337Dynamical bandwidth adjustment of a link in a data network
https://resolver.caltech.edu/CaltechAUTHORS:20170810-113125473
Authors: {'items': [{'id': 'Walid-Angwar-I', 'name': {'family': 'Walid', 'given': 'Anwar I.'}}, {'id': 'Gan-Lingwen', 'name': {'family': 'Gan', 'given': 'Lingwen'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2014
An apparatus includes a first node configured to receive the data packets from a plurality of source nodes of the data network and to selectively route some of the received data packets to a link via a port of the first node. The apparatus also includes a link-input buffer that is located in the first node and is configured to store the some of the received data packets for transmission to the link via the port. The first node is configured to power off hardware for transmitting received data packets to the link in response to a fill level of the link-input buffer being below a threshold.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/swyj7-wzp22Optimal load-side control for frequency regulation in smart grids
https://resolver.caltech.edu/CaltechAUTHORS:20150203-091127023
Authors: {'items': [{'id': 'Mallada-E', 'name': {'family': 'Mallada', 'given': 'Enrique'}, 'orcid': '0000-0003-1568-1833'}, {'id': 'Zhao-Changhong', 'name': {'family': 'Zhao', 'given': 'Changhong'}, 'orcid': '0000-0003-0539-8591'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2014
DOI: 10.1109/ALLERTON.2014.7028527
Frequency control rebalances supply and demand while maintaining the network state within operational margins. It is implemented using fast ramping reserves that are expensive and wasteful, and which are expected to grow with the increasing penetration of renewables. The most promising solution to this problem is the use of demand response, i.e. load participation in frequency control. Yet it is still unclear how to efficiently integrate load participation without introducing instabilities and violating operational constraints. In this paper we present a comprehensive load-side frequency control mechanism that can maintain the grid within operational constraints. Our controllers can rebalance supply and demand after disturbances, restore the frequency to its nominal value and preserve inter-area power flows. Furthermore, our controllers are distributed (unlike generation-side), can allocate load updates optimally, and can maintain line flows within thermal limits. We prove that such a distributed load-side control is globally asymptotically stable and illustrate its convergence with simulation.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/k2vxs-4nb81Optimal Power Flow in Direct Current Networks
https://resolver.caltech.edu/CaltechAUTHORS:20141205-135843283
Authors: {'items': [{'id': 'Gan-Lingwen', 'name': {'family': 'Gan', 'given': 'Lingwen'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2014
DOI: 10.1109/TPWRS.2014.2313514
The optimal power flow (OPF) problem determines power generations/demands that minimize a certain objective such as generation cost or power loss. It is non-convex and NP-hard in general. In this paper, we study the OPF problem in direct current (DC) networks. A second-order cone programming (SOCP) relaxation is considered for solving the OPF problem. We prove that the SOCP relaxation is exact if either 1) voltage upper bounds do not bind; or 2) voltage upper bounds are uniform and power injection lower bounds are negative. Based on 1), a modified OPF problem is proposed, whose corresponding SOCP is guaranteed to be exact. We also prove that SOCP has at most one optimal solution if it is exact. Finally, we discuss how to improve numerical stability and how to include line constraints.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/zf7qf-8jb24The role of a market maker in networked Cournot competition
https://resolver.caltech.edu/CaltechAUTHORS:20170810-101313051
Authors: {'items': [{'id': 'Bose-Subhonmesh', 'name': {'family': 'Bose', 'given': 'Subhonmesh'}, 'orcid': '0000-0002-3445-4479'}, {'id': 'Cai-Desmond-W-H', 'name': {'family': 'Cai', 'given': 'Desmond W. H.'}, 'orcid': '0000-0001-9207-1890'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Wierman-A', 'name': {'family': 'Wierman', 'given': 'Adam'}}]}
Year: 2014
DOI: 10.1109/CDC.2014.7040088
We study the role of a market maker (or market operator) in a transmission constrained electricity market. We model the market as a one-shot networked Cournot competition where generators supply quantity bids and load serving entities provide downward sloping inverse demand functions. This mimics the operation of a spot market in a deregulated market structure. In this paper, we focus on possible mechanisms employed by the market maker to balance demand and supply. In particular, we consider three candidate objective functions that the market maker optimizes - social welfare, residual social welfare, and consumer surplus. We characterize the existence of Generalized Nash Equilibrium (GNE) in this setting and demonstrate that market outcomes at equilibrium can be very different under the candidate objective functions.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/7ak7c-qp636Optimal decentralized primary frequency control in power networks
https://resolver.caltech.edu/CaltechAUTHORS:20170123-165356940
Authors: {'items': [{'id': 'Zhao-Changhong', 'name': {'family': 'Zhao', 'given': 'Changhong'}, 'orcid': '0000-0003-0539-8591'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2014
DOI: 10.1109/CDC.2014.7039765
We augment existing generator-side primary frequency control with load-side control that are local, ubiquitous, and continuous. The mechanisms on both the generator and the load sides are decentralized in that their control decisions are functions of locally measurable frequency deviations. These local algorithms interact over the network through nonlinear power flows. We design the local frequency feedback control so that any equilibrium point of the closed-loop system is the solution to an optimization problem that minimizes the total generation cost and user disutility subject to power balance across entire network. With Lyapunov method we derive a sufficient condition for any equilibrium point of the closed-loop system to be asymptotically stable. A simulation demonstrates improvement in both the transient and steady-state performance over the traditional control only on generators, even when the total control capacity remains the same.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/5szw4-8t878Distributional analysis for model predictive deferrable load control
https://resolver.caltech.edu/CaltechAUTHORS:20170810-105540217
Authors: {'items': [{'id': 'Chen-Niangjun', 'name': {'family': 'Chen', 'given': 'Niangjun'}, 'orcid': '0000-0002-2289-9737'}, {'id': 'Gan-Lingwen', 'name': {'family': 'Gan', 'given': 'Lingwen'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Wierman-A', 'name': {'family': 'Wierman', 'given': 'Adam'}}]}
Year: 2014
DOI: 10.1109/CDC.2014.7040398
Deferrable load control is essential for handling the uncertainties associated with the increasing penetration of renewable generation. Model predictive control has emerged as an effective approach for deferrable load control, and has received considerable attention. Though the average-case performance of model predictive deferrable load control has been analyzed in prior works, the distribution of the performance has been elusive. In this paper, we prove strong concentration results on the load variation obtained by model predictive deferrable load control. These results highlight that the typical performance of model predictive deferrable load control is tightly concentrated around the average-case performance.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/10c4g-rc417Buffering Dynamics and Stability of Internet Congestion Controllers
https://resolver.caltech.edu/CaltechAUTHORS:20150109-091116665
Authors: {'items': [{'id': 'Sojoudi-S', 'name': {'family': 'Sojoudi', 'given': 'Somayeh'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John C.'}, 'orcid': '0000-0002-1828-2486'}]}
Year: 2014
DOI: 10.1109/TNET.2013.2287198
Many existing fluid-flow models of the Internet congestion
control algorithms make simplifying assumptions on the
effects of buffers on the data flows. In particular, they assume that the flow rate of a TCP flow at every link in its path is equal to the original source rate. However, a fluid flow in practice is modified by the queueing processes on its path, so that an intermediate link will generally not see the original source rate. In this paper, a more accurate model is derived for the behavior of the
network under a congestion controller, which takes into account the effect of buffering on output flows. It is shown how this model can be deployed for some well-known service disciplines such as first-in–first-out and generalized weighted fair queueing. Based on the derived model, the dual and primal-dual algorithms are studied
under the common pricing mechanisms, and it is shown that these algorithms can become unstable. Sufficient conditions are provided to guarantee the stability of the dual and primal-dual algorithms. Finally, a new pricing mechanism is proposed under which these congestion control algorithms are both stable.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/2qaks-zjf17Exact Convex Relaxation of Optimal Power Flow in Radial Networks
https://resolver.caltech.edu/CaltechAUTHORS:20150203-084513340
Authors: {'items': [{'id': 'Gan-Lingwen', 'name': {'family': 'Gan', 'given': 'Lingwen'}}, {'id': 'Li-Na', 'name': {'family': 'Li', 'given': 'Na'}}, {'id': 'Topcu-U', 'name': {'family': 'Topcu', 'given': 'Ufuk'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2015
DOI: 10.1109/TAC.2014.2332712
The optimal power flow (OPF) problem determines a network operating point that minimizes a certain objective such as generation cost or power loss. It is nonconvex. We prove that a global optimum of OPF can be obtained by solving a second-order cone program, under a mild condition after shrinking the OPF feasible set slightly, for radial power networks. The condition can be checked a priori, and holds for the IEEE 13, 34, 37, 123-bus networks and two real-world networks.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/7byye-f8609Equivalent relaxations of optimal power flow
https://resolver.caltech.edu/CaltechAUTHORS:20150112-101936328
Authors: {'items': [{'id': 'Bose-Subhonmesh', 'name': {'family': 'Bose', 'given': 'Subhonmesh'}, 'orcid': '0000-0002-3445-4479'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Teeraratkul-T', 'name': {'family': 'Teeraratkul', 'given': 'Thanchanok'}}, {'id': 'Hassibi-B', 'name': {'family': 'Hassibi', 'given': 'Babak'}}]}
Year: 2015
DOI: 10.1109/TAC.2014.2357112
Several convex relaxations of the optimal power flow (OPF) problem have recently been developed using both bus injection models and branch flow models. In this paper, we prove relations among three convex relaxations: a semidefinite relaxation that computes a full matrix, a chordal relaxation based on a chordal extension of the network graph, and a second-order cone relaxation that computes the smallest partial matrix. We prove a bijection between the feasible sets of the OPF in the bus injection model and the branch flow model, establishing the equivalence of these two models and their second-order cone relaxations. Our results imply that, for radial networks, all these relaxations are equivalent and one should always solve the second-order cone relaxation. For mesh networks, the semidefinite relaxation and the chordal relaxation are equally tight and both are strictly tighter than the second-order cone relaxation. Therefore, for mesh networks, one should either solve the chordal relaxation or the SOCP relaxation, trading off tightness and the required computational effort. Simulations are used to illustrate these results.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/cm86v-dwe23Distributed Generator and Load-Side Secondary Frequency Control in Power Networks
https://resolver.caltech.edu/CaltechAUTHORS:20150429-072859434
Authors: {'items': [{'id': 'Zhao-Changhong', 'name': {'family': 'Zhao', 'given': 'Changhong'}, 'orcid': '0000-0003-0539-8591'}, {'id': 'Mallada-E', 'name': {'family': 'Mallada', 'given': 'Enrique'}, 'orcid': '0000-0003-1568-1833'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2015
DOI: 10.1109/CISS.2015.7086825
We design a distributed secondary frequency control scheme for both generators and controllable loads. The proposed scheme operates via local sensing and computation, and neighborhood communication. Equilibrium and stability
analysis of the closed-loop system is performed with a power
network model including turbines and governors of generators
and nonlinear AC power flows. After a change in power supply
or demand, the proposed scheme is able to stabilize the system, restore bus frequencies and net inter-area power exchanges, and minimize total generation cost minus user utility at equilibrium.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/kpymp-a2s93Feeder Reconfiguration in Distribution Networks Based on Convex Relaxation of OPF
https://resolver.caltech.edu/CaltechAUTHORS:20150112-094953179
Authors: {'items': [{'id': 'Peng-Qiuyu', 'name': {'family': 'Peng', 'given': 'Qiuyu'}}, {'id': 'Tang-Yujie', 'name': {'family': 'Tang', 'given': 'Yujie'}, 'orcid': '0000-0002-4921-8372'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2015
DOI: 10.1109/TPWRS.2014.2356513
The feeder reconfiguration problem chooses the on/off status of the switches in a distribution network in order to minimize a certain cost such as power loss. It is a mixed-integer nonlinear program and, hence, hard to solve. In this paper, we propose a heuristic algorithm that is based on the recently developed convex relaxation of the ac optimal power flow problem. The algorithm is computationally efficient and scales linearly with the number of redundant lines. It requires neither parameter tuning nor initialization for different networks. It successfully computes an optimal configuration on all four networks we have tested. Moreover, we have proved that the algorithm solves the feeder reconfiguration problem optimally under certain conditions for the case where only a single redundant line needs to be opened. We also propose a more computationally efficient algorithm and show that it incurs a loss in optimality of less than 3% on the four test networks.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/59t7c-rdd16Quadratically Constrained Quadratic Programs on Acyclic Graphs With Application to Power Flow
https://resolver.caltech.edu/CaltechAUTHORS:20170810-100823060
Authors: {'items': [{'id': 'Bose-Subhonmesh', 'name': {'family': 'Bose', 'given': 'Subhonmesh'}, 'orcid': '0000-0002-3445-4479'}, {'id': 'Gayme-D-F', 'name': {'family': 'Gayme', 'given': 'Dennice F.'}}, {'id': 'Chandy-K-M', 'name': {'family': 'Chandy', 'given': 'K. Mani'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2015
DOI: 10.1109/TCNS.2015.2401172
This paper proves that nonconvex quadratically constrained quadratic programs can be solved in polynomial time when their underlying graph is acyclic, provided the constraints satisfy a certain technical condition. We demonstrate this theory on optimal power-flow problems over tree networks.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/5h1p1-dnz43Systems and Methods for Optimal Power Flow on a Radial Network
https://resolver.caltech.edu/CaltechAUTHORS:20170810-134608572
Authors: {'items': [{'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Peng-Qiuyu', 'name': {'family': 'Peng', 'given': 'Qiuyu'}}]}
Year: 2015
Node controllers and power distribution networks in accordance with embodiments of the invention enable distributed power control. One embodiment includes a node controller including a distributed power control application; a plurality of node operating parameters describing the operating parameter of a node and a set of at least one node selected from the group consisting of an ancestor node and at least one child node; wherein send node operating parameters to nodes in the set of at least one node; receive operating parameters from the nodes in the set of at least one node; calculate a plurality of updated node operating parameters using an iterative process to determine the updated node operating parameters using the node operating parameters that describe the operating parameters of the node and the set of at least one node, where the iterative process involves evaluation of a closed form solution; and adjust node operating parameters.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/ez5rt-h6983Distributed Algorithm for Optimal Power Flow on an Unbalanced Radial Network
https://resolver.caltech.edu/CaltechAUTHORS:20160217-095123759
Authors: {'items': [{'id': 'Peng-Qiuyu', 'name': {'family': 'Peng', 'given': 'Qiuyu'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2015
DOI: 10.1109/CDC.2015.7403309
The optimal power flow (OPF) problem is fundamental in power systems operation and planning. Large-scale renewable penetration calls for real-time feedback control, and hence the need for distributed solutions for the OPF problem. In this paper we propose a solution for an unbalanced radial distribution network. Our distributed algorithm is based on alternating direction method of multiplier (ADMM). The main idea is to exploit the tree topology of distribution networks and decompose the OPF problem in such a way that the subproblems in each ADMM macro-iteration either have closed-form solutions or reduce to eigenvalue problems whose size remains constant as the network size scales up. We present simulations on IEEE 13, 34, 37 and 123 bus unbalanced distribution network to illustrate the scalability and optimality of the proposed algorithm.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/bjnkn-68v07A differential analysis of the power flow equations
https://resolver.caltech.edu/CaltechAUTHORS:20160217-080729960
Authors: {'items': [{'id': 'Dvijotham-K', 'name': {'family': 'Dvijotham', 'given': 'Krishnamurthy'}, 'orcid': '0000-0002-1328-4677'}, {'id': 'Chertkov-M', 'name': {'family': 'Chertkov', 'given': 'Michael'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2015
DOI: 10.1109/CDC.2015.7402082
The AC power flow equations are fundamental in all aspects of power systems planning and operations. They are routinely solved using Newton-Raphson like methods. However, there is little theoretical understanding of when these algorithms are guaranteed to find a solution of the power flow equations or how long they may take to converge. Further, it is known that in general these equations have multiple solutions and can exhibit chaotic behavior. In this paper, we show that the power flow equations can be solved efficiently provided that the solution lies in a certain set. We introduce a family of convex domains, characterized by Linear Matrix Inequalities, in the space of voltages such that there is at most one power flow solution in each of these domains. Further, if a solution exists in one of these domains, it can be found efficiently, and if one does not exist, a certificate of non-existence can also be obtained efficiently. The approach is based on the theory of monotone operators and related algorithms for solving variational inequalities involving monotone operators. We validate our approach on IEEE test networks and show that practical power flow solutions lie within an appropriately chosen convex domain.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/f16pb-7ff49Systems and Methods for Convex Relaxations and Linear Approximations for Optimal Power Flow in Multiphase Radial Networks
https://resolver.caltech.edu/CaltechAUTHORS:20170810-114535705
Authors: {'items': [{'id': 'Gan-Lingwen', 'name': {'family': 'Gan', 'given': 'Lingwen'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2015
Centralized node controllers in accordance with embodiments of the invention enable linear approximation of optimal power flow. One embodiment includes a centralized node controller including: a network interface, a processor, and a memory containing: a centralized power control application a network topology, where the network is multiphase unbalanced and comprises a plurality of connected nodes; wherein the processor is configured by the centralized controller application to: request node operating parameters from the plurality of connected nodes; calculate network operating parameters using a linear approximation of optimal power flow and the node operating parameters from the plurality of connected nodes; send network operating parameters to the plurality of connected nodes.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/s2r8t-0h109On Channel Failures, File Fragmentation Policies, and Heavy-Tailed Completion Times
https://resolver.caltech.edu/CaltechAUTHORS:20160317-122351101
Authors: {'items': [{'id': 'Nair-J', 'name': {'family': 'Nair', 'given': 'Jayakrishnan'}}, {'id': 'Andreasson-M', 'name': {'family': 'Andreasson', 'given': 'Martin'}}, {'id': 'Andrew-L-L-H', 'name': {'family': 'Andrew', 'given': 'Lachlan L. H.'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John C.'}, 'orcid': '0000-0002-1828-2486'}]}
Year: 2016
DOI: 10.1109/TNET.2014.2375920
It has been recently discovered that heavy-tailed completion times can result from protocol interaction even when file sizes are light-tailed. A key to this phenomenon is the use of a restart policy where if the file is interrupted before it is completed, it needs to restart from the beginning. In this paper, we show that fragmenting a file into pieces whose sizes are either bounded or independently chosen after each interruption guarantees light-tailed completion time as long as the file size is light-tailed; i.e., in this case, heavy-tailed completion time can only originate from heavy-tailed file sizes. If the file size is heavy-tailed, then the completion time is necessarily heavy-tailed. For this case, we show that when the file size distribution is regularly varying, then under independent or bounded fragmentation, the completion time tail distribution function is asymptotically bounded above by that of the original file size stretched by a constant factor. We then prove that if the distribution of times between interruptions has nondecreasing failure rate, the expected completion time is minimized by dividing the file into equal-sized fragments; this optimal fragment size is unique but depends on the file size. We also present a simple blind fragmentation policy where the fragment sizes are constant and independent of the file size and prove that it is asymptotically optimal. Both these policies are also shown to have desirable completion time tail behavior. Finally, we bound the error in expected completion time due to error in modeling of the failure process.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/jzwt1-qyv02Multipath TCP: Analysis, Design, and Implementation
https://resolver.caltech.edu/CaltechAUTHORS:20150109-090127092
Authors: {'items': [{'id': 'Peng-Qiuyu', 'name': {'family': 'Peng', 'given': 'Qiuyu'}}, {'id': 'Walid-A', 'name': {'family': 'Walid', 'given': 'Anwar'}}, {'id': 'Hwang-Jaehyun', 'name': {'family': 'Hwang', 'given': 'Jaehyun'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2016
DOI: 10.1109/TNET.2014.2379698
Multipath TCP (MP-TCP) has the potential to greatly improve application performance by using multiple paths transparently. We propose a fluid model for a large class of MP-TCP algorithms and identify design criteria that guarantee the existence, uniqueness, and stability of system equilibrium. We clarify how algorithm parameters impact TCP-friendliness, responsiveness, and window oscillation and demonstrate an inevitable tradeoff among these properties. We discuss the implications of these properties on the behavior of existing algorithms and motivate our algorithm Balia (balanced linked adaptation), which generalizes existing algorithms and strikes a good balance among TCP-friendliness, responsiveness, and window oscillation. We have implemented Balia in the Linux kernel. We use our prototype to compare the new algorithm to existing MP-TCP algorithms.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/2c1mb-gkg87Dynamic adjustment of receive window utilized by a transmitting device
https://resolver.caltech.edu/CaltechAUTHORS:20170810-125112138
Authors: {'items': [{'id': 'Jin-Cheng', 'name': {'family': 'Jin', 'given': 'Cheng'}}, {'id': 'Lee-George-S', 'name': {'family': 'Lee', 'given': 'George S.'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Ng-Darren', 'name': {'family': 'Ng', 'given': 'Darren'}}, {'id': 'Witt-R', 'name': {'family': 'Witt', 'given': 'Ryan'}}]}
Year: 2016
A method of controlling size of a receive window includes transmitting packets over a communication channel from a transmitting device to a receiver, and receiving acknowledgment packets from the receiver, the received acknowledgement packets from the receiver including an advertised receive window size. The method further includes determining a backlog parameter for the receiver in accordance with the advertised receive window size, determining a queuing delay in accordance the received acknowledgment packets, resetting a size of a congestion window in accordance with a function of a current size of the congestion window and a factor proportional to the queuing delay, and resetting a size of a receive window in accordance with a function of a current size of the receive window and the backlog parameter. A network window is reset in accordance with the smaller of the size of the congestion window and the size of the receive window.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/rg31r-nas45Dynamic Frequency Control in Power Networks
https://resolver.caltech.edu/CaltechAUTHORS:20170712-205943130
Authors: {'items': [{'id': 'Zhao-Changhong', 'name': {'family': 'Zhao', 'given': 'Changhong'}, 'orcid': '0000-0003-0539-8591'}, {'id': 'Mallada-E', 'name': {'family': 'Mallada Garcia', 'given': 'Enrique'}, 'orcid': '0000-0003-1568-1833'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2016
Node controllers in power distribution networks in accordance with embodiments of the invention enable dynamic frequency control. One embodiment includes a node controller comprising a network interface a processor; and a memory containing a frequency control application; and a plurality of node operating parameters describing the operating parameters of a node, where the node is selected from a group consisting of at least one generator node in a power distribution network wherein the processor is configured by the frequency control application to calculate a plurality of updated node operating parameters using a distributed process to determine the updated node operating parameter using the node operating parameters, where the distributed process controls network frequency in the power distribution network; and adjust the node operating parameters.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/dc5wm-58t35Distributed Gradient Descent for Solving Optimal Power Flow in Radial Networks
https://resolver.caltech.edu/CaltechAUTHORS:20170810-114246561
Authors: {'items': [{'id': 'Gan-Lingwen', 'name': {'family': 'Gan', 'given': 'Lingwen'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2016
Node controllers and power distribution networks in accordance with embodiments of the invention enable distributed power control, One embodiment includes a node controller comprising a memory containing: a plurality of node operating parameters; and a plurality of node operating parameters describing operating parameters for a set of at least one node selected from the group consisting of at least one downstream node and at least one upstream node; wherein the processor is configured by the node controller application to: receive and store in memory a plurality of coordinator parameters describing operating parameters of a node coordinator by the network interface; and calculate updated node operating parameters using an iterative gradient projection process to determine updated node parameters using node operating parameters that describe operating parameters of node and operating parameters of the set of at least one node, where each iteration is determined by the coordinator parameters.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/kapyv-n6202Demand Response With Capacity Constrained Supply Function Bidding
https://resolver.caltech.edu/CaltechAUTHORS:20160408-101533727
Authors: {'items': [{'id': 'Xu-Yunjian', 'name': {'family': 'Xu', 'given': 'Yunjian'}}, {'id': 'Li-Na', 'name': {'family': 'Li', 'given': 'Na'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2016
DOI: 10.1109/TPWRS.2015.2421932
We study the problem faced by an operator who aims to allocate a certain amount of load adjustment (either load reduction or increment) to multiple consumers so as to minimize the aggregate consumer disutility. We propose and analyze a simple uniform-price market mechanism where every consumer submits a single bid to choose a supply function from a group of parameterized ones. These parameterized supply functions are designed to ensure that every consumer's load adjustment is within an exogenous capacity limit that is determined by the current power system operating condition. We show that the proposed mechanism yields bounded efficiency loss at a Nash equilibrium. In particular, the proposed mechanism is shown to achieve approximate social optimality at a Nash equilibrium, if the total capacity limit excluding the consumer with the largest one is much larger than the total amount of load to be adjusted. We complement our analysis through numerical case studies.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/38eaz-zmz59An Online Gradient Algorithm for Optimal Power Flow on Radial Networks
https://resolver.caltech.edu/CaltechAUTHORS:20160426-075434882
Authors: {'items': [{'id': 'Gan-Lingwen', 'name': {'family': 'Gan', 'given': 'Lingwen'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2016
DOI: 10.1109/JSAC.2016.2525598
We propose an online algorithm for solving optimal power flow (OPF) problems on radial networks where the controllable devices continuously interact with the network that implicitly computes a power flow solution given a control action. Collectively the controllable devices and the network implement a gradient projection algorithm for the OPF problem in real time. The key design feature that enables this approach is that the intermediate iterates of our algorithm always satisfy power flow equations and operational constraints. This is achieved by explicitly exploiting the network to implicitly solve power flow equations for us in real time at scale. We prove that the proposed algorithm converges to the set of local optima and provide sufficient conditions under which it converges to a global optimum. We derive an upper bound on the suboptimality gap of any local optimum. This bound suggests that any local minimum is almost as good as any strictly feasible point. We explain how to greatly reduce the gradient computation in each iteration by using approximate gradient derived from linearized power flow equations. Numerical results on test networks, ranging from 42-bus to 1990-bus, show a great speedup over a second-order cone relaxation method with negligible difference in objective values.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/hb1hg-80v18A unified framework for frequency control and congestion management
https://resolver.caltech.edu/CaltechAUTHORS:20160823-102449874
Authors: {'items': [{'id': 'Zhao-Changhong', 'name': {'family': 'Zhao', 'given': 'Changhong'}, 'orcid': '0000-0003-0539-8591'}, {'id': 'Mallada-E', 'name': {'family': 'Mallada', 'given': 'Enrique'}, 'orcid': '0000-0003-1568-1833'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Bialek-J', 'name': {'family': 'Bialek', 'given': 'Janusz'}}]}
Year: 2016
DOI: 10.1109/PSCC.2016.7541028
The existing frequency control framework in power systems is challenged by lower inertia and more volatile power injections. We propose a new framework for frequency control and congestion management. We formulate an optimization problem that rebalances power, restores the nominal frequency, restores inter-area flows and maintains line flows below their limits in a way that minimizes the control cost. The cost can be squared deviations from the reference generations, minimizing the disruption from the last optimal dispatch. Our control thus maintains system security without interfering with the market operation. By deriving a primal-dual algorithm to solve this optimization, we design a completely decentralized primary frequency control without the need for explicit communication among the participating agents, and a distributed unified control which integrates primary and secondary frequency control and congestion management. Simulations show that the unified control not only achieves all the desired control goals in system equilibrium, but also improves the transient compared to traditional control schemes.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/9qbcj-wfm82Real-Time Recommendation Algorithm of Battery Swapping Stations for Electric Taxis
https://resolver.caltech.edu/CaltechAUTHORS:20161117-095916202
Authors: {'items': [{'id': 'You-Pengcheng', 'name': {'family': 'You', 'given': 'Pengcheng'}, 'orcid': '0000-0003-1532-8773'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Yang-Zaiyue', 'name': {'family': 'Yang', 'given': 'Zaiyue'}, 'orcid': '0000-0002-8288-3833'}, {'id': 'Zhang-Yongmin', 'name': {'family': 'Zhang', 'given': 'Yongmin'}}, {'id': 'Fu-Lingkun', 'name': {'family': 'Fu', 'given': 'Lingkun'}}]}
Year: 2016
DOI: 10.1109/PESGM.2016.7741620
This paper proposes a real-time algorithm that recommends battery swapping stations (BSSs) to electric taxis (ETs) that need their batteries swapped. The algorithm takes into consideration available batteries at BSSs, driving ranges of ETs and the current traffic conditions, etc, in order to avoid long queues at BSSs. We consider a basic model that assumes past decisions are perfectly executed, and formulate an optimal ET-to-BSS assignment problem. This problem is an integer program and therefore hard to scale. For real-time implementation, we approximate the optimal assignment problem by a repeated potential game and propose an iterative best response algorithm to compute ET-to-BSS assignments. Preliminary numerical results suggest that our heuristic algorithm solves the optimal assignment problem approximately.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/a12q9-51s14Optimal charging schedule for a battery switching station serving electric buses
https://resolver.caltech.edu/CaltechAUTHORS:20170616-102356802
Authors: {'items': [{'id': 'You-Pengcheng', 'name': {'family': 'You', 'given': 'Pengcheng'}, 'orcid': '0000-0003-1532-8773'}, {'id': 'Yang-Zaiyue', 'name': {'family': 'Yang', 'given': 'Zaiyue'}, 'orcid': '0000-0002-8288-3833'}, {'id': 'Zhang-Yongmin', 'name': {'family': 'Zhang', 'given': 'Yongmin'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Sun-Youxian', 'name': {'family': 'Sun', 'given': 'Youxian'}}]}
Year: 2016
DOI: 10.1109/PESGM.2016.7741397
We propose a model of a battery switching station (BSS) for electric buses (EBs) that captures the predictability of bus operation. We schedule battery charging in the BSS so that every EB arrives to find a battery ready for switching. We develop an efficient algorithm to compute an optimal schedule. It uses dual decomposition to decouple the charging decisions at different charging boxes so that independent subproblems can be solved in parallel at individual charging boxes, making the algorithm inherently scalable as the size of the BSS grows. We propose a direct projection method that solves these subproblems rapidly. Numerical results illustrate that the proposed approach is far more efficient and scalable than generic algorithms and existing solvers.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/qck3j-rv138Monotone operator approach to power flow solutions
https://resolver.caltech.edu/CaltechAUTHORS:20170810-111302484
Authors: {'items': [{'id': 'Dvijotham-K', 'name': {'family': 'Dvijotham', 'given': 'Krishnamurthy'}, 'orcid': '0000-0002-1328-4677'}, {'id': 'Chertkov-M', 'name': {'family': 'Chertkov', 'given': 'Michael'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2016
DOI: 10.1109/ACC.2016.7525174
The AC power flow equations underlie all operational aspects of power systems. In this paper, Here we solve this problem using the theory of monotone operators. We show that it is possible to characterize a "contractivity domain" in the power flow variables (voltage magnitudes and phases). The construction of these domains depends on the specific representation chosen for the power flow equations, so that different representations lead to different domains. Given this domain, there is a simple efficient algorithm that will either find a solution in the domain, or certify that no solutions exist in it. We validate the approach on several IEEE test cases.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/vk8eg-25q59Demand response with capacity constrained supply function bidding
https://resolver.caltech.edu/CaltechAUTHORS:20170615-105827991
Authors: {'items': [{'id': 'Xu-Yunjian', 'name': {'family': 'Xu', 'given': 'Yunjian'}}, {'id': 'Li-Na', 'name': {'family': 'Li', 'given': 'Na'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2016
DOI: 10.1109/PESGM.2016.7741247
We study the problem faced by an operator who aims to allocate a certain amount of load adjustment (either load reduction or increment) to multiple consumers so as to minimize the aggregate consumer disutility. We propose and analyze a simple uniform-price market mechanism where every consumer submits a single bid to choose a supply function from a group of parameterized ones. These parameterized supply functions are designed to ensure that every consumer's load adjustment is within an exogenous capacity limit that is determined by the current power system operating condition. We show that the proposed mechanism yields bounded efficiency loss at a Nash equilibrium. In particular, the proposed mechanism is shown to achieve approximate social optimality at a Nash equilibrium, if the total capacity of all consumers (excluding the consumer with the largest capacity) is much larger than the total amount of load to be adjusted. We complement our analysis through numerical case studies.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/a1pm0-4gv67The role of strong convexity-concavity in the convergence and robustness of the saddle-point dynamics
https://resolver.caltech.edu/CaltechAUTHORS:20170217-154230896
Authors: {'items': [{'id': 'Cherukuri-A', 'name': {'family': 'Cherukuri', 'given': 'Ashish'}, 'orcid': '0000-0002-7609-5080'}, {'id': 'Mallada-E', 'name': {'family': 'Mallada', 'given': 'Enrique'}, 'orcid': '0000-0003-1568-1833'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Cortés-J', 'name': {'family': 'Cortés', 'given': 'Jorge'}}]}
Year: 2016
DOI: 10.1109/ALLERTON.2016.7852273
This paper studies the projected saddle-point dynamics for a twice differentiable convex-concave function, which we term saddle function. The dynamics consists of gradient descent of the saddle function in variables corresponding to convexity and (projected) gradient ascent in variables corresponding to concavity. We provide a novel characterization of the omega-limit set of the trajectories of these dynamics in terms of the diagonal Hessian blocks of the saddle function. Using this characterization, we establish global asymptotic convergence of the dynamics under local strong convexity-concavity of the saddle function. If this property is global, and for the case when the saddle function takes the form of the Lagrangian of an equality constrained optimization problem, we establish the input-to-state stability of the saddle-point dynamics by providing an ISS Lyapunov function. Various examples illustrate our results.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/mebm6-zf506Optimal Charging Schedule for a Battery Switching Station Serving Electric Buses
https://resolver.caltech.edu/CaltechAUTHORS:20160829-152749308
Authors: {'items': [{'id': 'You-Pengcheng', 'name': {'family': 'You', 'given': 'Pengcheng'}, 'orcid': '0000-0003-1532-8773'}, {'id': 'Yang-Zaiyue', 'name': {'family': 'Yang', 'given': 'Zaiyue'}, 'orcid': '0000-0002-8288-3833'}, {'id': 'Zhang-Yongmin', 'name': {'family': 'Zhang', 'given': 'Yongmin'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Sun-Youxian', 'name': {'family': 'Sun', 'given': 'Youxian'}}]}
Year: 2016
DOI: 10.1109/TPWRS.2015.2487273
We propose a model of a battery switching station (BSS) for electric buses (EBs) that captures the predictability of bus operation. We schedule battery charging in the BSS so that every EB arrives to find a battery ready for switching. We develop an efficient algorithm to compute an optimal schedule. It uses dual decomposition to decouple the charging decisions at different charging boxes so that independent subproblems can be solved in parallel at individual charging boxes, making the algorithm inherently scalable as the size of the BSS grows. We propose a direct projection method that solves these subproblems rapidly. Numerical results illustrate that the proposed approach is far more efficient and scalable than generic algorithms and existing solvers.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/5ch6g-0n827Optimal placement of energy storage in distribution networks
https://resolver.caltech.edu/CaltechAUTHORS:20170111-145514472
Authors: {'items': [{'id': 'Tang-Yujie', 'name': {'family': 'Tang', 'given': 'Yujie'}, 'orcid': '0000-0002-4921-8372'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2016
DOI: 10.1109/CDC.2016.7798759
We study the problem of optimally placing energy storage devices in distribution networks to minimize total energy loss, focusing on structural results. We use a continuous linearized branch-flow model to model the distribution network. For the special case of a linear network, modeling a main feeder, we explicitly derive the optimal solution when all loads have the same shape and prove several useful monotonicity properties of the optimal solution. We illustrate through simulations that these structural properties hold approximately also on radial networks modeled by standard discrete nonlinear power flow models and even when loads have different shapes. We discuss how these structural results provide insight for the planning of energy storage devices.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/1etyk-65845Decentralized Optimal Frequency Control of Interconnected Power Systems with Transient Constraints
https://resolver.caltech.edu/CaltechAUTHORS:20170111-135813725
Authors: {'items': [{'id': 'Wang-Zhaojian', 'name': {'family': 'Wang', 'given': 'Zhaojian'}, 'orcid': '0000-0002-4998-6339'}, {'id': 'Liu-Feng', 'name': {'family': 'Liu', 'given': 'Feng'}, 'orcid': '0000-0003-2279-2558'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Zhao-Changhong', 'name': {'family': 'Zhao', 'given': 'Changhong'}, 'orcid': '0000-0003-0539-8591'}, {'id': 'Mei-Shengwei', 'name': {'family': 'Mei', 'given': 'Shengwei'}, 'orcid': '0000-0002-2757-5977'}]}
Year: 2016
DOI: 10.1109/CDC.2016.7798345
We design decentralized frequency control of multi-area power systems that will re-balance power and drive frequencies to their nominal values after a disturbance. Both generators and controllable loads are utilized to achieve frequency stability while minimizing regulation cost. In contrast to recent results, the design is completely decentralized and does not require communication between areas. Our control enforces operational constraints not only in equilibrium but also during transient. Moreover, our control is capable of adapting to unknown load disturbance. We show that the closed-loop system is asymptotically stable and converges to an equilibrium that minimizes the regulation cost. We present simulation results to demonstrate the effectiveness of our design.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/0h1k9-nza14Adaptive charging network for electric vehicles
https://resolver.caltech.edu/CaltechAUTHORS:20170811-093351619
Authors: {'items': [{'id': 'Lee-George', 'name': {'family': 'Lee', 'given': 'George'}}, {'id': 'Lee-Ted', 'name': {'family': 'Lee', 'given': 'Ted'}}, {'id': 'Low-Zhi-H', 'name': {'family': 'Low', 'given': 'Zhi'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Ortega-C', 'name': {'family': 'Ortega', 'given': 'Christine'}}]}
Year: 2016
DOI: 10.1109/GlobalSIP.2016.7905971
We describe a snapshot of an adaptive charging network (ACN) for electric vehicles at Caltech. We overview the system design, from the power distribution system to advanced charger design to control and communication system and the software system that integrates the overall network. We present a simple mathematical formulation of the charging problem. We have collected three months' of baseline charging data from the Caltech ACN. We demonstrate, by simulating a charging algorithm on the baseline data, the large potential benefit of ACN in saving infrastructure costs.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/6qqbz-5vk54An Efficient and Incentive Compatible Mechanism for Wholesale Electricity Markets
https://resolver.caltech.edu/CaltechAUTHORS:20170111-125209937
Authors: {'items': [{'id': 'Xu-Yunjian', 'name': {'family': 'Xu', 'given': 'Yunjian'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2017
DOI: 10.1109/TSG.2015.2483523
Being widely used in many deregulated wholesale electricity markets, the locational marginal pricing (LMP) mechanism is known to achieve social optimality in a competitive market. When profit-maximizing generators act strategically to manipulate prices; however, LMP may lead to high loss of economic efficiency. In this paper, we apply the Vickrey-Clarke–Groves (VCG) mechanism to wholesale electricity markets. We show that the VCG mechanism minimizes the total cost at a truth-telling dominant strategy equilibrium. We establish an important comparative result that the VCG mechanism always results in higher per-unit electricity prices than the LMP mechanism under any given set of reported supply curves. Numerical results show that the difference between the per-unit prices resulting from the two mechanisms is negligibly small (about 4%) in the IEEE 14-bus and 30-bus test systems. Finally, we apply the VCG mechanism to a day-ahead setting with start-up cost (of conventional generators) and intermittent renewable generation. We show that the VCG mechanism induces the truth-telling behavior of conventional generators in dominant strategies and yields each conventional generator a non-negative expected profit.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/hc1fy-1t885Real-time OPF based on quasi-Newton methods
https://resolver.caltech.edu/CaltechAUTHORS:20170517-151532951
Authors: {'items': [{'id': 'Tang-Yujie', 'name': {'family': 'Tang', 'given': 'Yujie'}, 'orcid': '0000-0002-4921-8372'}, {'id': 'Dvijotham-K', 'name': {'family': 'Dvijotham', 'given': 'Krishnamurthy'}, 'orcid': '0000-0002-1328-4677'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2017
DOI: 10.1109/CISS.2017.7926163
Optimal power flow is a central problem in the operation of power systems. So far the majority of the literature deals with offline algorithms for traditional applications, but the proliferation of distributed energy resources and smart appliances in power networks motivates real-time and scalable algorithms. We introduce a real-time OPF algorithm based on quasi-Newton methods that can track the optimal operation when the state of the network is changing. Theory and simulations show that the proposed algorithm has guaranteed tracking performance and is computationally efficient.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/yq9ka-f2127Adaptive Charging Algorithms for a Network of Electric Vehicles
https://resolver.caltech.edu/CaltechAUTHORS:20170810-134608665
Authors: {'items': [{'id': 'Low-Zhi-H', 'name': {'family': 'Low', 'given': 'Zhi H.'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2017
Electric vehicle node controllers in accordance with embodiments of the invention enable adaptive charging. One embodiment includes one or more centralized computing systems; a communications network; a plurality of electric vehicle node controllers, where each electric vehicle node controller in the plurality of node controllers contains: a network interface; a processor; a memory containing: an adaptive charging application; a plurality of electric vehicle node parameters describing charging parameters of an electric vehicle node in the electric vehicle charging network; where the processor is configured by the adaptive charging application to: send electric vehicle node parameters to the one or more centralized computing systems; and charge the electric vehicle node using a charging rate received from the one or more centralized computing systems; where the one or more centralized computing systems is configured to: receive the electric vehicle node parameters from the plurality of electric vehicle node controllers; calculate a plurality of charging rates for the plurality of electric vehicle node controllers using the electric vehicle node parameters, a plurality of adaptive charging parameters, and a cost function; and send the charging rates to the plurality of electric vehicle node controllers.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/fngar-bpr28Smoothed Least-laxity-first Algorithm for EV Charging
https://resolver.caltech.edu/CaltechAUTHORS:20170515-140123828
Authors: {'items': [{'id': 'Nakahira-Yorie', 'name': {'family': 'Nakahira', 'given': 'Yorie'}, 'orcid': '0000-0003-3324-4602'}, {'id': 'Chen-Niangjun', 'name': {'family': 'Chen', 'given': 'Niangjun'}, 'orcid': '0000-0002-2289-9737'}, {'id': 'Chen-Lijun', 'name': {'family': 'Chen', 'given': 'Lijun'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2017
DOI: 10.1145/3077839.3077864
We formulate EV charging as a feasibility problem that meets all EVs' energy demands before departure under charging rate constraints and total power constraint. We propose an online algorithm, the smoothed least-laxity-first (sLLF) algorithm, that decides on the current charging rates based on only the information up to the current time. We characterize the performance of the sLLF algorithm analytically and numerically. Numerical experiments with real-world data show that it has significantly higher rate of generating feasible EV charging than several other common EV charging algorithms.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/1gjze-jr229Event detection and localization in distribution grids with phasor measurement units
https://resolver.caltech.edu/CaltechAUTHORS:20180208-150455146
Authors: {'items': [{'id': 'Ardakanian-O', 'name': {'family': 'Ardakanian', 'given': 'Omid'}, 'orcid': '0000-0002-6711-5502'}, {'id': 'Yuan-Ye', 'name': {'family': 'Yuan', 'given': 'Ye'}, 'orcid': '0000-0001-7858-0437'}, {'id': 'Dobbe-R', 'name': {'family': 'Dobbe', 'given': 'Roel'}, 'orcid': '0000-0003-4633-7023'}, {'id': 'von-Meier-A', 'name': {'family': 'von Meier', 'given': 'Alexandra'}, 'orcid': '0000-0003-4675-752X'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Tomlin-C', 'name': {'family': 'Tomlin', 'given': 'Claire'}}]}
Year: 2017
DOI: 10.1109/PESGM.2017.8273895
The recent introduction of synchrophasor technology into power distribution systems has given impetus to various monitoring, diagnostic, and control applications, such as system identification and event detection, which are crucial for restoring service, preventing outages, and managing equipment health. Drawing on the existing framework for inferring topology and admittances of a power network from voltage and current phasor measurements, this paper proposes an online algorithm for event detection and localization in unbalanced three-phase distribution systems. Using a convex relaxation and a matrix partitioning technique, the proposed algorithm is capable of identifying topology changes and attributing them to specific categories of events. The performance of this algorithm is evaluated on a standard test distribution feeder with synthesized loads, and it is shown that a tripped line can be detected and localized in an accurate and timely fashion, highlighting its potential for real-world applications.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/py6df-w6k87Analytical Methods for Network Congestion Control
https://resolver.caltech.edu/CaltechAUTHORS:20170816-110227980
Authors: {'items': [{'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2017
DOI: 10.2200/S00778ED1V01Y201705CNT018
The congestion control mechanism has been responsible for maintaining stability as the Internet scaled up by many orders of magnitude in size, speed, traffic volume, coverage, and complexity over the last three decades. In this book, we develop a coherent theory of congestion control from the ground up to help understand and design these algorithms. We model network traffic as fluids that flow from sources to destinations and model congestion control algorithms as feedback dynamical systems. We show that the model is well defined. We characterize its equilibrium points and prove their stability. We will use several real protocols for illustration but the emphasis will be on various mathematical techniques for algorithm analysis.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/29dm1-0an59Optimal Online Adaptive Electric Vehicle Charging
https://resolver.caltech.edu/CaltechAUTHORS:20180209-075953281
Authors: {'items': [{'id': 'Guo-Linqi', 'name': {'family': 'Guo', 'given': 'Linqi'}}, {'id': 'Erliksson-K-F', 'name': {'family': 'Erliksson', 'given': 'Karl F.'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2017
DOI: 10.1109/PESGM.2017.8274166
We propose an online linear program (OLP) based algorithm for scheduling electric vehicle (EV) charging. To determine the charging rates in each control period, OLP solves a linear program based only on EVs currently in the charging facility, assuming no future EV arrivals. We prove that OLP achieves the offline optimal where all future EV arrivals are assumed to be known in advance, provided the cost coefficients are uniformly monotone. For general cost functions, we prove that the competitive ratio is upper bounded by the variability in the cost coefficients. We demonstrate the performance of OLP using real charging data from Google and Caltech's Adaptive Charging Network.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/15bpb-0ct28Monotonicity Properties and Spectral Characterization of Power Redistribution in Cascading Failures
https://resolver.caltech.edu/CaltechAUTHORS:20180409-162520984
Authors: {'items': [{'id': 'Guo-Linqi', 'name': {'family': 'Guo', 'given': 'Linqi'}}, {'id': 'Liang-Chen', 'name': {'family': 'Liang', 'given': 'Chen'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2017
DOI: 10.1145/3152042.3152074
In this work, we apply spectral graph theory methods to study the monotonicity and structural properties of power redistribution in a cascading failure process. We demonstrate that in contrast to the lack of monotonicity in physical domain, there is a rich collection of monotonicity one can explore in the spectral domain, leading to a systematic way to define topological metrics that are monotonic. It is further shown that many useful quantities in cascading failure analysis can be unified into a spectral inner product, which itself is related to graphical properties of the transmission network. Such graphical interpretations precisely capture the Kirchhoff's law expressed in terms of graph structural properties and gauge the impact of a line when it is tripped.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/8fan2-dq173Load-side Frequency Regulation with Limited Control Coverage
https://resolver.caltech.edu/CaltechAUTHORS:20180409-162519432
Authors: {'items': [{'id': 'Pang-John-Z-F', 'name': {'family': 'Pang', 'given': 'John Z. F.'}, 'orcid': '0000-0002-6485-7922'}, {'id': 'Guo-Linqi', 'name': {'family': 'Guo', 'given': 'Linqi'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2017
DOI: 10.1145/3152042.3152071
Increasing renewable energy increases uncertainty in energy systems. As a consequence, generator-side control for frequency regulation, impacted by the slow reaction of generators to meet urgent needs, may no longer suffice. With increasing integration of smart appliances which are able to sense, communicate and control, load-side control can help alleviate the aforementioned problem as it reacts fast and helps to localize disturbances. However, almost all existing methods for optimal load-side control require full information control coverage in the system. Framing the problem as an optimization problem and applying saddle-point dynamics, we obtain a control law that rebalances power and asymptotically stabilizes frequency after a disturbance. We generalize previous work to design a controller which only requires partial control coverage over all nodes, yet still achieves secondary frequency control. We verify these results via simulation.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/4wtxc-vg851Battery Swapping Assignment for Electric Vehicles
https://resolver.caltech.edu/CaltechAUTHORS:20180409-142619118
Authors: {'items': [{'id': 'You-Pengcheng', 'name': {'family': 'You', 'given': 'Pengcheng'}, 'orcid': '0000-0003-1532-8773'}, {'id': 'Sun-Youxian', 'name': {'family': 'Sun', 'given': 'Youxian'}}, {'id': 'Pang-John-Z-F', 'name': {'family': 'Pang', 'given': 'John'}, 'orcid': '0000-0002-6485-7922'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Chen-Minghua', 'name': {'family': 'Chen', 'given': 'Minghua'}}]}
Year: 2017
DOI: 10.1145/3152042.3152068
This paper formulates a multi-period optimal station assignment problem for electric vehicle (EV) battery swapping that takes into account both temporal and spatial couplings. The goal is to reduce the total EV cost and station congestion due to temporary shortage in supply of available batteries. We show that the problem is reducible to the minimum weight perfect bipartite matching problem. This leads to an efficient solution based on the Hungarian algorithm. Numerical results suggest that the proposed solution provides a significant improvement over a greedy heuristic that assigns EVs to nearest stations.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/5kh3w-dkz90Monotonicity Properties and Spectral Characterization of Power Redistribution in Cascading Failures
https://resolver.caltech.edu/CaltechAUTHORS:20180125-135003175
Authors: {'items': [{'id': 'Guo-Linqi', 'name': {'family': 'Guo', 'given': 'Linqi'}}, {'id': 'Liang-Chen', 'name': {'family': 'Liang', 'given': 'Chen'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2017
DOI: 10.1109/ALLERTON.2017.8262836
In this work, we apply spectral graph theory methods to study the monotonicity and structural properties of power redistribution in a cascading failure process. We demonstrate that in contrast to the lack of monotonicity in physical domain, there is a rich collection of monotonicity one can explore in the spectral domain, leading to a systematic way to define topological metrics that are monotonic. It is further shown that many useful quantities in cascading failure analysis can be unified into a spectral inner product, which itself is related to graphical properties of the transmission network. Such graphical interpretations precisely capture the Kirchhoff's law expressed in terms of graph structural properties and gauge the impact of a line when it is tripped. We illustrate that our characterization leads to a tree-partition of the network so that failure cascading can be localized.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/hwwv8-eb206Real-time Optimal Power Flow
https://resolver.caltech.edu/CaltechAUTHORS:20170517-150114536
Authors: {'items': [{'id': 'Tang-Yujie', 'name': {'family': 'Tang', 'given': 'Yujie'}, 'orcid': '0000-0002-4921-8372'}, {'id': 'Dvijotham-K', 'name': {'family': 'Dvijotham', 'given': 'Krishnamurthy'}, 'orcid': '0000-0002-1328-4677'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2017
DOI: 10.1109/TSG.2017.2704922
Future power networks are expected to incorporate a large number of distributed energy resources, which introduce randomness and fluctuations as well as fast control capabilities. But traditional optimal power flow methods are only appropriate for applications that operate on a slow timescale. In this paper, we build on recent work to develop a real-time algorithm for AC optimal power flow, based on quasi-Newton methods. The algorithm uses second order information to provide suboptimal solutions on a fast timescale, and can be shown to track the optimal power flow solution when the estimated second order information is sufficiently accurate. We also give a specific implementation based on L-BFGS-B method, and show by simulation that the proposed algorithm has good performance and is computationally efficient.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/m23ne-7bw40Optimal Placement of Energy Storage in Distribution Networks
https://resolver.caltech.edu/CaltechAUTHORS:20170613-162646711
Authors: {'items': [{'id': 'Tang-Yujie', 'name': {'family': 'Tang', 'given': 'Yujie'}, 'orcid': '0000-0002-4921-8372'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2017
DOI: 10.1109/TSG.2017.2711921
We study the problem of optimal placement and capacity of energy storage devices in a distribution network to minimize total energy loss. A continuous tree with linearized DistFlow model is developed to model the distribution network. We analyze structural properties of the optimal solution when all loads have the same shape. We prove that it is optimal to place storage devices near the leaves of the network away from the substation, and that the scaled storage capacity monotonically increases towards the leaves. Moreover, under optimal storage placement, the locational marginal value of storage is equalized wherever nonzero storage is deployed and increases from the substation towards any leaf node over places where there is zero storage deployment. We illustrate through simulations that these structural properties are robust in that they hold approximately when some of our modeling assumptions are relaxed.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/7j9nx-td052Guest Editorial: Distributed Control and Efficient Optimization Methods for Smart Grid
https://resolver.caltech.edu/CaltechAUTHORS:20180119-140349830
Authors: {'items': [{'id': 'Lavaei-J', 'name': {'family': 'Lavaei', 'given': 'Javad'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Baldick-R', 'name': {'family': 'Baldick', 'given': 'Ross'}}, {'id': 'Zhang-Baosen', 'name': {'family': 'Zhang', 'given': 'Baosen'}}, {'id': 'Molzahn-D-K', 'name': {'family': 'Molzahn', 'given': 'Daniel'}}, {'id': 'Dörfler-F', 'name': {'family': 'Dörfler', 'given': 'Florian'}}, {'id': 'Sandberg-H', 'name': {'family': 'Sandberg', 'given': 'Henrik'}}]}
Year: 2017
DOI: 10.1109/TSG.2017.2758907
Smart grid proactively uses the state-of-the-art technologies in communications, computing, and control to improve efficiency, reliability, sustainability, and stability of the electrical grid. In particular, distribution networks are expected to undergo dramatic changes by incorporating a large number of sensors and thousands of controllable devices such as distributed generators, batteries and flexible loads. To be able to efficiently operate such complex large-scale systems, new sets of control and optimization tools should be developed. On a slow time scale, optimization theory plays a major role in solving various large-scale decision-making problems for future power transmission and distribution systems. One major challenge is the design of computational methods for handling fairly detailed power system models that often include continuous and discrete nonlinearities. It is also important to develop distributed computation techniques to shift the computation from a centralized platform to many computing devices.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/0c4at-y0z55Distributed Control and Efficient Optimization Methods for Smart Grid
https://resolver.caltech.edu/CaltechAUTHORS:20171109-112814794
Authors: {'items': [{'id': 'Lavaei-J', 'name': {'family': 'Lavaei', 'given': 'Javad'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Baldick-R', 'name': {'family': 'Baldick', 'given': 'Ross'}}, {'id': 'Zhang-Baosen', 'name': {'family': 'Zhang', 'given': 'Baosen'}}, {'id': 'Molzahn-D-K', 'name': {'family': 'Molzahn', 'given': 'Daniel'}}, {'id': 'Dörfler-F', 'name': {'family': 'Dörfler', 'given': 'Florian'}}, {'id': 'Sandberg-H', 'name': {'family': 'Sandberg', 'given': 'Henrik'}}]}
Year: 2017
DOI: 10.1109/TSG.2017.2758907
Smart grid proactively uses the state-of-the-art technologies in communications, computing, and control to improve efficiency, reliability, sustainability, and stability of the electrical grid. In particular, distribution networks are expected to undergo dramatic changes by incorporating a large number of sensors and thousands of controllable devices such as distributed generators, batteries and flexible loads. To be able to efficiently operate such complex large-scale systems, new sets of control and optimization tools should be developed. On a slow time scale, optimization theory plays a major role in solving various large-scale decision-making problems for future power transmission and distribution systems. One major challenge is the design of computational methods for handling fairly detailed power system models that often include continuous and discrete nonlinearities. It is also important to develop distributed computation techniques to shift the computation from a centralized platform to many computing devices.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/s2bk8-gcd08A Survey of Distributed Optimization and Control Algorithms for Electric Power Systems
https://resolver.caltech.edu/CaltechAUTHORS:20170726-151527403
Authors: {'items': [{'id': 'Molzahn-D-K', 'name': {'family': 'Molzahn', 'given': 'Daniel K.'}}, {'id': 'Dörfler-F', 'name': {'family': 'Dörfler', 'given': 'Florian'}}, {'id': 'Sandberg-H', 'name': {'family': 'Sandberg', 'given': 'Henrik'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Chakrabarti-S', 'name': {'family': 'Chakrabarti', 'given': 'Sambuddha'}}, {'id': 'Baldick-R', 'name': {'family': 'Baldick', 'given': 'Ross'}}, {'id': 'Lavaei-J', 'name': {'family': 'Lavaei', 'given': 'Javad'}}]}
Year: 2017
DOI: 10.1109/TSG.2017.2720471
Historically, centrally computed algorithms have been the primary means of power system optimization and control. With increasing penetrations of distributed energy resources requiring optimization and control of power systems with many controllable devices, distributed algorithms have been the subject of significant research interest. This paper surveys the literature of distributed algorithms with applications to optimization and control of power systems. In particular, this paper reviews distributed algorithms for offline solution of optimal power flow (OPF) problems as well as online algorithms for real-time solution of OPF, optimal frequency control, optimal voltage control, and optimal wide-area control problems.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/e7pd5-zer96System Level Synthesis: A Tutorial
https://resolver.caltech.edu/CaltechAUTHORS:20180126-080200870
Authors: {'items': [{'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John C.'}, 'orcid': '0000-0002-1828-2486'}, {'id': 'Matni-N', 'name': {'family': 'Matni', 'given': 'Nikolai'}, 'orcid': '0000-0003-4936-3921'}, {'id': 'Wang-Yuh-Shyang', 'name': {'family': 'Wang', 'given': 'Yuh-Shyang'}, 'orcid': '0000-0001-7357-7247'}, {'id': 'Anderson-James-D', 'name': {'family': 'Anderson', 'given': 'James'}, 'orcid': '0000-0002-2832-8396'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2017
DOI: 10.1109/CDC.2017.8264074
This tutorial paper provides an overview of the System Level Approach to control synthesis; a scalable framework for large-scale distributed control. The system level approach is composed of three central components: System Level Parameterizations (SLPs), System Level Constraints (SLCs) and System Level Synthesis (SLP) problems. We describe how the combination of these elements parameterize the largest known class of constrained controllers that admit a convex formulation.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/c5bs6-ncw54Spectral Characterization of Controllability and Observability for Frequency Regulation Dynamics
https://resolver.caltech.edu/CaltechAUTHORS:20180126-083110449
Authors: {'items': [{'id': 'Guo-Linqi', 'name': {'family': 'Guo', 'given': 'Linqi'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2017
DOI: 10.1109/CDC.2017.8264611
We give a full characterization using spectral graph theory of the controllability and observability of the swing and power flow dynamics in frequency regulation. In particular, we show that the controllability/observability of the system depends on two orthogonal conditions: 1) intrinsic structure of the system graph 2) algebraic coverage of buses with controllable loads/sensors. Condition 1) encodes information on graph symmetry and is shown to hold for almost all practical systems. Condition 2) captures how buses interact with each other through the network and can be verified using the eigenvectors of the graph Laplacian matrix. Based on this framework, the optimal placement of controllable loads and sensors in the network can be formulated as a set cover problem. We demonstrate how our results identify the critical buses in real systems by performing simulation in the IEEE 39-bus New England interconnection test system. We show that for this testbed, a single well chosen bus is capable of providing full controllability/observability.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/3kkv8-ayb51Optimal Load-side Control for Frequency Regulation in Smart Grids
https://resolver.caltech.edu/CaltechAUTHORS:20171101-115726975
Authors: {'items': [{'id': 'Mallada-E', 'name': {'family': 'Mallada', 'given': 'Enrique'}, 'orcid': '0000-0003-1568-1833'}, {'id': 'Zhao-Changhong', 'name': {'family': 'Zhao', 'given': 'Changhong'}, 'orcid': '0000-0003-0539-8591'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2017
DOI: 10.1109/TAC.2017.2713529
Frequency control rebalances supply and demand while maintaining the network state within operational margins. It is implemented using fast ramping reserves that are expensive and wasteful, and which are expected to become increasingly necessary with the current acceleration of renewable penetration. The most promising solution to this problem is the use of demand response, i.e., load participation in frequency control. Yet it is still unclear how to efficiently integrate load participation without introducing instabilities and violating operational constraints. In this paper, we present a comprehensive load-side frequency control mechanism that can maintain the grid within operational constraints. In particular, our controllers can rebalance supply and demand after disturbances, restore the frequency to its nominal value, and preserve interarea power flows. Furthermore, our controllers are distributed (unlike the currently implemented frequency control), can allocate load updates optimally, and can maintain line flows within thermal limits. We prove that such a distributed load-side control is globally asymptotically stable and robust to unknown load parameters. We illustrate its effectiveness through simulations.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/p6tpf-bzs41Distributed Algorithm for Time-varying Optimal Power Flow
https://resolver.caltech.edu/CaltechAUTHORS:20180126-083431585
Authors: {'items': [{'id': 'Tang-Yujie', 'name': {'family': 'Tang', 'given': 'Yujie'}, 'orcid': '0000-0002-4921-8372'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2017
DOI: 10.1109/CDC.2017.8264138
Future power system applications may require real-time optimization of a large network of distributed energy resources. This has motivated recent development of online algorithms for solving time-varying optimal power flow problems. We have proposed a centralized quasi-Newton algorithm and have derived theoretical guarantees for its tracking performance. In this paper we show how this algorithm can be implemented in a distributed manner by a network of controllable energy resources coordinated by an operator. The proposed distributed implementation now can handle general convex quadratic constraints on power injections, and only requires minimal communication between the operator and local controllers. Simulation shows that the proposed distributed implementation has good performance.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/cv55z-8d480Battery Swapping Assignment for Electric Vehicles: A Bipartite Matching Approach
https://resolver.caltech.edu/CaltechAUTHORS:20180126-075222317
Authors: {'items': [{'id': 'You-Pengcheng', 'name': {'family': 'You', 'given': 'Pengcheng'}, 'orcid': '0000-0003-1532-8773'}, {'id': 'Pang-John-Z-F', 'name': {'family': 'Pang', 'given': 'John Z. F.'}, 'orcid': '0000-0002-6485-7922'}, {'id': 'Chen-Minghua', 'name': {'family': 'Chen', 'given': 'Minghua'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Sun-Youxian', 'name': {'family': 'Sun', 'given': 'Youxian'}}]}
Year: 2017
DOI: 10.1109/CDC.2017.8263853
This paper formulates an optimal station assignment problem for electric vehicle (EV) battery swapping that takes into account both temporal and spatial couplings. The goal is to reduce the total EV cost and station congestion due to temporary shortage in supply of available batteries. We show that the problem is reducible to the minimum weight perfect bipartite matching problem. This leads to an efficient solution based on the Hungarian algorithm. Numerical results suggest that the proposed solution provides a significant improvement over a greedy heuristic that assigns nearest stations to EVs.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/h2fy8-vbr82Distributed Optimal Power Flow Algorithm for Radial Networks, I: Balanced Single Phase Case
https://resolver.caltech.edu/CaltechAUTHORS:20160711-103700266
Authors: {'items': [{'id': 'Peng-Qiuyu', 'name': {'family': 'Peng', 'given': 'Qiuyu'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2018
DOI: 10.1109/TSG.2016.2546305
The optimal power flow (OPF) problem determines a network operating point that minimizes a certain objective such as generation cost or power loss. Traditionally, OPF is solved in a centralized manner. With increasing penetration of renewable energy in distribution system, we need faster and distributed solutions for real-time feedback control. This is difficult due to the nonlinearity of the power flow equations. In this paper, we propose a solution for balanced radial networks. It exploits recent results that suggest solving for a globally optimal solution of OPF over a radial network through the second-order cone program relaxation. Our distributed algorithm is based on alternating direction method of multiplier (ADMM), but unlike standard ADMM-based distributed OPF algorithms that require solving optimization subproblems using iterative method, our decomposition allows us to derive closed form solutions for these subproblems, greatly speeding up each ADMM iteration. We illustrate the scalability of the proposed algorithm by simulating it on a real-world 2065-bus distribution network.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/pvjsj-k7t94Profit Maximizing Planning and Control of Battery Energy Storage Systems for Primary Frequency Control
https://resolver.caltech.edu/CaltechAUTHORS:20170810-105250761
Authors: {'items': [{'id': 'Zhang-Ying-Jun', 'name': {'family': 'Zhang', 'given': 'Ying Jun'}}, {'id': 'Zhao-Changhong', 'name': {'family': 'Zhao', 'given': 'Changhong'}, 'orcid': '0000-0003-0539-8591'}, {'id': 'Tang-Wanrong', 'name': {'family': 'Tang', 'given': 'Wanrong'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2018
DOI: 10.1109/TSG.2016.2562672
We consider a two-level profit-maximizing strategy, including planning and control, for battery energy storage system (BESS) owners that participate in the primary frequency control (PFC) market. Specifically, the optimal BESS control minimizes the operating cost by keeping the state of charge (SoC) in an optimal range. Through rigorous analysis, we prove that the optimal BESS control is a "state-invariant" strategy in the sense that the optimal SoC range does not vary with the state of the system. As such, the optimal control strategy can be computed offline once and for all with very low complexity. Regarding the BESS planning, we prove that the the minimum operating cost is a decreasing convex function of the BESS energy capacity. This leads to the optimal BESS sizing that strikes a balance between the capital investment and operating cost. Our work here provides a useful theoretical framework for understanding the planning and control strategies that maximize the economic benefits of BESSs in ancillary service markets.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/xjzab-d1m36Combating Bufferbloat in Multi-Bottleneck Networks: Equilibrium, Stability, and Algorithms
https://resolver.caltech.edu/CaltechAUTHORS:20181023-103508493
Authors: {'items': [{'id': 'Ye-Jiancheng', 'name': {'family': 'Ye', 'given': 'Jiancheng'}, 'orcid': '0000-0002-1296-171X'}, {'id': 'Leung-Ka-Cheong', 'name': {'family': 'Leung', 'given': 'Ka-Cheong'}, 'orcid': '0000-0001-7999-2572'}, {'id': 'Li-Victor-O-K', 'name': {'family': 'Li', 'given': 'Victor O. K.'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2018
DOI: 10.1109/INFOCOM.2018.8486251
Bufferbloat is a phenomenon where router buffers are constantly being filled, resulting in high queueing delay and delay variation. Larger buffer size and more delay-sensitive applications on the Internet have made this phenomenon a pressing issue. Active queue management (AQM) algorithms, which play an important role in combating bufferbloat, have not been widely deployed due to complicated manual parameter tuning. Moreover, AQM algorithms are often designed and analyzed based on models with a single bottleneck link, rendering their performance and stability unclear in multi-bottleneck networks. In this paper, we propose a general framework to combat bufferbloat in multi-bottleneck networks. We first conduct an equilibrium analysis for a general multi-bottleneck TCP/ AQM system and develop an algorithm to compute the equilibrium point. We then decompose the system into single-bottleneck subsystems and derive sufficient conditions for the local asymptotic stability of the subsystems. Using the proposed framework, we present a case study to analyze the stability of the recently proposed Controlled Delay (CoDel) in multi-bottleneck networks and devise Self-tuning CoDel to improve the system stability and performance. Extensive simulation results show that Self-tuning CoDel effectively stabilizes queueing delay in multi-bottleneck scenarios, and thus contributes to combating bufferbloat.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/zad0y-v8j28Efficient Online Station Assignment for EV Battery Swapping
https://resolver.caltech.edu/CaltechAUTHORS:20180529-104115111
Authors: {'items': [{'id': 'You-Pengcheng', 'name': {'family': 'You', 'given': 'Pengcheng'}, 'orcid': '0000-0003-1532-8773'}, {'id': 'Cheng-Peng', 'name': {'family': 'Cheng', 'given': 'Peng'}}, {'id': 'Pang-John-Z-F', 'name': {'family': 'Pang', 'given': 'John Z. F.'}, 'orcid': '0000-0002-6485-7922'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2018
DOI: 10.1145/3208903.3212032
This paper investigates the online station assignment for (commercial) electric vehicles (EVs) that make battery swapping requests to a central operator, with the aim of minimizing cost to EVs and congestion at service stations. Inspired by a polynomial-time solvable offline solution via a bipartite matching approach, we develop an efficient online station assignment algorithm that provably achieves a tight (optimal) competitive ratio under mild conditions.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/8w8sn-pxw38Disaggregation for Networked Power Systems
https://resolver.caltech.edu/CaltechAUTHORS:20181102-085439162
Authors: {'items': [{'id': 'Anderson-James-D', 'name': {'family': 'Anderson', 'given': 'James'}, 'orcid': '0000-0002-2832-8396'}, {'id': 'Zhou-Fengyu', 'name': {'family': 'Zhou', 'given': 'Fengyu'}, 'orcid': '0000-0002-2639-6491'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2018
DOI: 10.23919/PSCC.2018.8442521
Electricity data such as supply, demand, prices, and line flows, are sensitive. Utility companies, understandably do not want to, in fact often cannot, make this data publicly available. However, such data is critical in many fundamental areas in power systems research. As a compromise, aggregated data sets are sometimes made available. In such a setting it may be the case that data is aggregated over a geographical region and time. This forces researchers to try and "invert" the data to obtain dis aggregated data sets. In this paper we rigorously formulate the disaggregation problem for networked power systems and present two algorithms that provide solutions to the DC version of the problem. We show that it is possible to invert the data, but that does not imply that ground truth solutions are obtained, thus the utility companies maintain a notion of privacy. The aim of this paper is to highlight the potential benefits to both the research community and utility companies of releasing aggregated data.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/r7dvm-95871Cyber Network Design for Secondary Frequency Regulation: A Spectral Approach
https://resolver.caltech.edu/CaltechAUTHORS:20180906-143422101
Authors: {'items': [{'id': 'Guo-Linqi', 'name': {'family': 'Guo', 'given': 'Linqi'}}, {'id': 'Zhao-Changhong', 'name': {'family': 'Zhao', 'given': 'Changhong'}, 'orcid': '0000-0003-0539-8591'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2018
DOI: 10.23919/PSCC.2018.8442814
We present a preliminary theoretical framework based on spectral graph theory that captures how the cyber topology of a distributed secondary frequency control scheme impacts the stability, optimality, and transient performance of our power system as a cyber-physical network. We show that a collection of polynomials defined in terms of the cyber and physical Laplacian eigenvalues encode information on the interplay between cyber and physical networks. It is demonstrated that to understand the impact of adding cyber connectivity, one should separate the low-damping and high-damping regimes. Although adding cyber connectivity always improves the performance for high-damping systems, it is not the case for low-damping scenarios. Based on the theoretical study, we discuss how a good cyber network should be designed. Our empirical study shows that for practical systems, the number of communication channels that is needed to achieve near-optimal performance is usually less than twice the number of buses.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/7cwt2-6p715The Role of Convexity on Saddle-Point Dynamics: Lyapunov Function and Robustness
https://resolver.caltech.edu/CaltechAUTHORS:20171204-104144520
Authors: {'items': [{'id': 'Cherukuri-A', 'name': {'family': 'Cherukuri', 'given': 'Ashish'}, 'orcid': '0000-0002-7609-5080'}, {'id': 'Mallada-E', 'name': {'family': 'Mallada', 'given': 'Enrique'}, 'orcid': '0000-0003-1568-1833'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Cortés-J', 'name': {'family': 'Cortés', 'given': 'Jorge'}}]}
Year: 2018
DOI: 10.1109/TAC.2017.2778689
This paper studies the projected saddle-point dynamics associated to a convex–concave function, which we term saddle function. The dynamics consists of gradient descent of the saddle function in variables corresponding to convexity and (projected) gradient ascent in variables corresponding to concavity. We examine the role that the local and/or global nature of the convexity–concavity properties of the saddle function plays in guaranteeing convergence and robustness of the dynamics. Under the assumption that the saddle function is twice continuously differentiable, we provide a novel characterization of the omega-limit set of the trajectories of this dynamics in terms of the diagonal blocks of the Hessian. Using this characterization, we establish global asymptotic convergence of the dynamics under local strong convexity–concavity of the saddle function. When strong convexity–concavity holds globally, we establish three results. First, we identify a Lyapunov function (that decreases strictly along the trajectory) for the projected saddle-point dynamics when the saddle function corresponds to the Lagrangian of a general constrained convex optimization problem. Second, for the particular case when the saddle function is the Lagrangian of an equality-constrained optimization problem, we show input-to-state stability (ISS) of the saddle-point dynamics by providing an ISS Lyapunov function. Third, we use the latter result to design an opportunistic state-triggered implementation of the dynamics. Various examples illustrate our results.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/jkd5v-pne67Profit-Maximizing Planning and Control of Battery Energy Storage Systems for Primary Frequency Control
https://resolver.caltech.edu/CaltechAUTHORS:20190104-140522282
Authors: {'items': [{'id': 'Zhang-Angela-Yingjun', 'name': {'family': 'Zhang', 'given': 'Angela Yingjun'}}, {'id': 'Zhao-Changhong', 'name': {'family': 'Zhao', 'given': 'Changhong'}, 'orcid': '0000-0003-0539-8591'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Tang-Wanrong', 'name': {'family': 'Tang', 'given': 'Wanrong'}}]}
Year: 2018
DOI: 10.1109/pesgm.2018.8586290
We consider a two-level profit-maximizing strategy, including planning and control, for battery energy storage system (BESS) owners that participate in the primary frequency control (PFC) market. Specifically, the optimal BESS control minimizes the operating cost by keeping the state of charge (SoC) in an optimal range. Through rigorous analysis, we prove that the optimal BESS control is a "state-invariant" strategy in the sense that the optimal SoC range does not vary with the state of the system. As such, the optimal control strategy can be computed offline once and for all with very low complexity. Regarding the BESS planning, we prove that the the minimum operating cost is a decreasing convex function of the BESS energy capacity. This leads to the optimal BESS sizing that strikes a balance between the capital investment and operating cost. Our work here provides a useful theoretical framework for understanding the planning and control strategies that maximize the economic benefits of BESSs in ancillary service markets.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/8fsct-8gh48Distributed Frequency Control with Operational Constraints, Part II: Network Power Balance
https://resolver.caltech.edu/CaltechAUTHORS:20190104-142158857
Authors: {'items': [{'id': 'Wang-Zhaojian', 'name': {'family': 'Wang', 'given': 'Zhaojian'}, 'orcid': '0000-0002-4998-6339'}, {'id': 'Liu-Feng', 'name': {'family': 'Liu', 'given': 'Feng'}, 'orcid': '0000-0003-2279-2558'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Zhao-Changhong', 'name': {'family': 'Zhao', 'given': 'Changhong'}, 'orcid': '0000-0003-0539-8591'}, {'id': 'Mei-Shengwei', 'name': {'family': 'Mei', 'given': 'Shengwei'}, 'orcid': '0000-0002-2757-5977'}]}
Year: 2018
DOI: 10.1109/pesgm.2018.8586037
In Part I of this paper we propose a decentralized optimal frequency control of multi-area power system with operational constraints, where the tie-line powers remain unchanged in the steady state and the power mismatch is balanced within individual control areas. In Part II of the paper, we propose a distributed controller for optimal frequency control in the network power balance case, where the power mismatch is balanced over the whole system. With the proposed controller, the tie-line powers remain within the acceptable range at equilibrium, while the regulation capacity constraints are satisfied both at equilibrium and during transient. It is revealed that the closed-loop system with the proposed controller carries out primal-dual updates with saturation for solving an associated optimization problem. To cope with discontinuous dynamics of the closed-loop system, we deploy the invariance principle for nonpathological Lyapunov function to prove its asymptotic stability. Simulation results are provided to show the effectiveness of our controller.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/2r1bj-9d227Optimal Power Flow in Stand-alone DC Microgrids
https://resolver.caltech.edu/CaltechAUTHORS:20180208-073227198
Authors: {'items': [{'id': 'Li-Jia', 'name': {'family': 'Li', 'given': 'Jia'}}, {'id': 'Liu-Feng', 'name': {'family': 'Liu', 'given': 'Feng'}, 'orcid': '0000-0003-2279-2558'}, {'id': 'Wang-Zhaojian', 'name': {'family': 'Wang', 'given': 'Zhaojian'}, 'orcid': '0000-0002-4998-6339'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Mei-Shengwei', 'name': {'family': 'Mei', 'given': 'Shengwei'}, 'orcid': '0000-0002-2757-5977'}]}
Year: 2018
DOI: 10.1109/TPWRS.2018.2801280
Direct-current microgrids (DC-MGs) can operate in either grid-connected or stand-alone mode. In particular, stand-alone DC-MG has many distinct applications. However, the optimal power flow problem (OPF) of a stand-alone DC-MG is inherently non-convex. In this paper, the OPF of DC-MG is investigated considering convex relaxation based on second-order cone programming. Mild assumptions are proposed to guarantee the exactness of relaxation, which only require uniform nodal voltage upper bounds and positive network loss. It is revealed that the exactness of second-order conic (SOC) relaxation of DC networks does not rely on topology or operating mode of DC networks, and an optimal solution must be unique if it exists. If line constraints are considered, the exactness of SOC relaxation may not hold. In this regard, two heuristic methods are proposed to give approximate solutions. Numerical experiments confirm the theoretic results.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/br9qh-8x868Failure Localization in Power Systems via Tree Partitions
https://resolver.caltech.edu/CaltechAUTHORS:20190128-124902110
Authors: {'items': [{'id': 'Guo-Linqi', 'name': {'family': 'Guo', 'given': 'Linqi'}}, {'id': 'Liang-Chen', 'name': {'family': 'Liang', 'given': 'Chen'}}, {'id': 'Zocca-A', 'name': {'family': 'Zocca', 'given': 'Alessandro'}, 'orcid': '0000-0001-6585-4785'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Wierman-A', 'name': {'family': 'Wierman', 'given': 'Adam'}}]}
Year: 2018
DOI: 10.1145/3305218.3305247
Cascading failures in power systems propagate non-locally, making the control and mitigation of outages extremely hard. In this work, we use the emerging concept of the tree partition of transmission networks to provide an analytical characterization of line failure localizability in transmission systems. Our results rigorously formalize the well-known intuition that failures cannot cross bridges, and reveal a finer-grained concept that encodes more precise information on failure propagation within tree-partition regions. Specifically, when a non-bridge line is tripped, the impact of this failure only propagates within components of the tree partition defined by the bridges. In contrast, when a bridge line is tripped, the impact of this failure propagates globally across the network, affecting the power flow on all remaining lines. This characterization suggests that it is possible to improve the system robustness by temporarily switching off certain transmission lines, so as to create more, smaller components in the tree partition; thus spatially localizing line failures and making the grid less vulnerable to large outages.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/pk4s9-k5586Failure Localization in Power Systems via Tree Partitions
https://resolver.caltech.edu/CaltechAUTHORS:20190128-094206311
Authors: {'items': [{'id': 'Guo-Linqi', 'name': {'family': 'Guo', 'given': 'Linqi'}}, {'id': 'Liang-Chen', 'name': {'family': 'Liang', 'given': 'Chen'}}, {'id': 'Zocca-A', 'name': {'family': 'Zocca', 'given': 'Alessandro'}, 'orcid': '0000-0001-6585-4785'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Wierman-A', 'name': {'family': 'Wierman', 'given': 'Adam'}}]}
Year: 2018
DOI: 10.1145/3305218.3305240
Cascading failures in power systems propagate non-locally, making the control and mitigation of outages extremely hard. In this work, we use the emerging concept of the tree partition of transmission networks to provide an analytical characterization of line failure localizability in transmission systems. Our results rigorously establish the well perceived intuition in power community that failures cannot cross bridges, and reveal a finer-grained concept that encodes more precise information on failure propagations within tree-partition regions. Specifically, when a non-bridge line is tripped, the impact of this failure only propagates within well-defined components, which we refer to as cells, of the tree partition defined by the bridges. In contrast, when a bridge line is tripped, the impact of this failure propagates globally across the network, affecting the power flow on all remaining transmission lines. This characterization suggests that it is possible to improve the system robustness by temporarily switching off certain transmission lines, so as to create more, smaller components in the tree partition; thus spatially localizing line failures and making the grid less vulnerable to large-scale outages. We illustrate this approach using the IEEE 118-bus test system and demonstrate that switching off a negligible portion of transmission lines allows the impact of line failures to be significantly more localized without substantial changes in line congestion.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/hfpa5-89z53Some Emerging Challenges in Electricity Markets
https://resolver.caltech.edu/CaltechAUTHORS:20180925-152901176
Authors: {'items': [{'id': 'Bose-Subhonmesh', 'name': {'family': 'Bose', 'given': 'Subhonmesh'}, 'orcid': '0000-0002-3445-4479'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2018
DOI: 10.1007/978-3-319-98310-3_2
Energy deregulation in the 90s led to the development of power markets in the United States. The Public Utilities Regulatory Policies Act (PURPA) in 1978 laid down the early foundations of deregulation. Subsequent legislations included the Energy Policy Act of 1992 (EPAct92) and FERC Order No. 888 in 1996. They established the rules to "remove impediments to competition in the wholesale bulk power marketplace" by promoting "non-discriminatory transmission services" [1]. These legislations led to the development of two different market architectures in different parts of the US. In one, utility companies established a bilateral market to transact with independent power producers and/or other utilities. In others, a third-party nonprofit facilitator—an Independent System Operator (ISO) or a Regional Transmission Organization (RTO)—was established to mediate between the buyers and the sellers of power at the wholesale level. Our discussion in this article will primarily revolve around the latter.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/x1rhb-bz413Large-Scale Adaptive Electric Vehicle Charging
https://resolver.caltech.edu/CaltechAUTHORS:20190104-154430902
Authors: {'items': [{'id': 'Lee-Zachary-J', 'name': {'family': 'Lee', 'given': 'Zachary J.'}}, {'id': 'Chang-Daniel', 'name': {'family': 'Chang', 'given': 'Daniel'}}, {'id': 'Jin-Cheng', 'name': {'family': 'Jin', 'given': 'Cheng'}}, {'id': 'Lee-George-S', 'name': {'family': 'Lee', 'given': 'George S.'}}, {'id': 'Lee-Rand', 'name': {'family': 'Lee', 'given': 'Rand'}}, {'id': 'Lee-Ted', 'name': {'family': 'Lee', 'given': 'Ted'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2018
DOI: 10.1109/smartgridcomm.2018.8587550
Large-scale charging infrastructure will play an important role in supporting the adoption of electric vehicles. In this paper, we address the prohibitively high capital cost of installing large numbers of charging stations within a parking facility by oversubscribing key pieces of electrical infrastructure. We describe a unique physical testbed for large-scale, high- density EV charging research which we call the Adaptive Charging Network (ACN). We describe the architecture of the ACN including its hardware and software components. We also present a practical framework for online scheduling, which is based on model predictive control and convex optimization. Based on our experience with practical EV charging systems, we introduce constraints to the EV charging problem which have not been considered in the literature, such as those imposed by unbalanced three-phase infrastructure. We use simulations based on real data collected from the ACN to illustrate the trade-offs involved in selecting models for infrastructure constraints and accounting for non-ideal charging behavior.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/yvb0d-sqe61Distributed plug-and-play optimal generator and load control for power system frequency regulation
https://resolver.caltech.edu/CaltechAUTHORS:20180327-084750901
Authors: {'items': [{'id': 'Zhao-Changhong', 'name': {'family': 'Zhao', 'given': 'Changhong'}, 'orcid': '0000-0003-0539-8591'}, {'id': 'Mallada-E', 'name': {'family': 'Mallada', 'given': 'Enrique'}, 'orcid': '0000-0003-1568-1833'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Bialek-J', 'name': {'family': 'Bialek', 'given': 'Janusz'}}]}
Year: 2018
DOI: 10.1016/j.ijepes.2018.03.014
A distributed control scheme, which can be implemented on generators and controllable loads in a plug-and-play manner, is proposed for power system frequency regulation. The proposed scheme is based on local measurements, local computation, and neighborhood information exchanges over a communication network with an arbitrary (but connected) topology. In the event of a sudden change in generation or load, the proposed scheme can restore the nominal frequency and the reference inter-area power flows, while minimizing the total cost of control for participating generators and loads. Power network stability under the proposed control is proved with a relatively realistic model which includes nonlinear power flow and a generic (potentially nonlinear or high-order) turbine-governor model, and further with first- and second-order turbine-governor models as special cases. In simulations, the proposed control scheme shows a comparable performance to the existing automatic generation control (AGC) when implemented only on the generator side, and demonstrates better dynamic characteristics than AGC when each scheme is implemented on both generators and controllable loads. Simulation results also show robustness of the proposed scheme to communication link failure.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/37nnq-6dv36Large-Scale Adaptive Electric Vehicle Charging
https://resolver.caltech.edu/CaltechAUTHORS:20190228-160214269
Authors: {'items': [{'id': 'Lee-Zachary-J', 'name': {'family': 'Lee', 'given': 'Zachary J.'}}, {'id': 'Chang-Daniel', 'name': {'family': 'Chang', 'given': 'Daniel'}}, {'id': 'Jin-Cheng', 'name': {'family': 'Jin', 'given': 'Cheng'}}, {'id': 'Lee-George-S', 'name': {'family': 'Lee', 'given': 'George S.'}}, {'id': 'Lee-Rand', 'name': {'family': 'Lee', 'given': 'Rand'}}, {'id': 'Lee-Ted', 'name': {'family': 'Lee', 'given': 'Ted'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2018
DOI: 10.1109/GlobalSIP.2018.8646472
Large-scale charging infrastructure will play an important role in supporting the adoption of electric vehicles. In this extended abstract, we describe a unique physical testbed for large-scale, high-density EV charging research which we call the Adaptive Charging Network (ACN). We describe the architecture of the ACN including its hardware and software components. We also present a practical framework for online scheduling, which is based on model predictive control and convex optimization. We use simulations based on real data collected from the ACN to illustrate the trade-offs involved in accounting for non-ideal charging behavior.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/4y0cd-7e894Scheduling of EV Battery Swapping, II: Distributed Solutions
https://resolver.caltech.edu/CaltechAUTHORS:20171221-153230416
Authors: {'items': [{'id': 'You-Pengcheng', 'name': {'family': 'You', 'given': 'Pengcheng'}, 'orcid': '0000-0003-1532-8773'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Zhang-Liang', 'name': {'family': 'Zhang', 'given': 'Liang'}, 'orcid': '0000-0003-3115-1752'}, {'id': 'Deng-Ruilong', 'name': {'family': 'Deng', 'given': 'Ruilong'}, 'orcid': '0000-0002-8158-150X'}, {'id': 'Giannakis-G-B', 'name': {'family': 'Giannakis', 'given': 'Georgios B.'}, 'orcid': '0000-0002-0196-0260'}, {'id': 'Sun-Youxian', 'name': {'family': 'Sun', 'given': 'Youxian'}}, {'id': 'Yang-Zaiyue', 'name': {'family': 'Yang', 'given': 'Zaiyue'}, 'orcid': '0000-0002-8288-3833'}]}
Year: 2018
DOI: 10.1109/TCNS.2017.2774012
In Part I of this paper, we formulate an optimal scheduling problem for battery swapping that assigns to each electric vehicle (EV) a best station to swap its depleted battery based on its current location and state of charge. The schedule aims to minimize a weighted sum of EVs' travel distance and electricity generation cost over both station assignments and power flow variables, subject to EV range constraints, grid operational constraints, and ac power flow equations. We propose there a centralized solution based on second-order cone programming relaxation of optimal power flow and generalized Benders decomposition that is applicable when global information is available. In this paper, we propose two distributed solutions based on the alternating direction method of multipliers and dual decomposition, respectively, that are suitable for systems where the distribution grid, stations, and EVs are managed by separate entities. Our algorithms allow these entities to make individual decisions, but coordinate through privacy-preserving information exchanges to solve a convex relaxation of the global problem. We present simulation results to show that both algorithms converge quickly to a solution that is close to optimum after discretization.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/2azc2-xcq26Scheduling of EV Battery Swapping, I: Centralized Solution
https://resolver.caltech.edu/CaltechAUTHORS:20171221-154244882
Authors: {'items': [{'id': 'You-Pengcheng', 'name': {'family': 'You', 'given': 'Pengcheng'}, 'orcid': '0000-0003-1532-8773'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Tushar-W', 'name': {'family': 'Tushar', 'given': 'Wayes'}, 'orcid': '0000-0003-1055-7200'}, {'id': 'Geng-Guangchao', 'name': {'family': 'Geng', 'given': 'Guangchao'}, 'orcid': '0000-0002-3626-0766'}, {'id': 'Yuen-Chau', 'name': {'family': 'Yuen', 'given': 'Chau'}, 'orcid': '0000-0002-9307-2120'}, {'id': 'Yang-Zaiyue', 'name': {'family': 'Yang', 'given': 'Zaiyue'}, 'orcid': '0000-0002-8288-3833'}, {'id': 'Sun-Youxian', 'name': {'family': 'Sun', 'given': 'Youxian'}}]}
Year: 2018
DOI: 10.1109/TCNS.2017.2773025
We formulate an optimal scheduling problem for battery swapping that assigns to each electric vehicle (EV) a best battery station to swap its depleted battery based on its current location and state of charge. The schedule aims to minimize a weighted sum of EVs' travel distance and electricity generation cost over both station assignments and power flow variables, subject to EV range constraints, grid operational constraints, and ac power flow equations. To deal with the nonconvexity of power flow equations and the binary nature of station assignments, we propose a solution based on second-order cone programming (SOCP) relaxation of optimal power flow and generalized Benders decomposition. When the SOCP relaxation is exact, this approach computes a global optimum. We evaluate the performance of the proposed algorithm through simulations. The algorithm requires global information and is suitable for cases where the distribution grid, battery stations, and EVs are managed centrally by the same operator. In Part II of this paper, we develop distributed solutions for cases where they are operated by different organizations that do not share private information.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/9302n-ajh28Graph Laplacian Spectrum and Primary Frequency Regulation
https://resolver.caltech.edu/CaltechAUTHORS:20190204-110323666
Authors: {'items': [{'id': 'Guo-Linqi', 'name': {'family': 'Guo', 'given': 'Linqi'}}, {'id': 'Zhao-Changhong', 'name': {'family': 'Zhao', 'given': 'Changhong'}, 'orcid': '0000-0003-0539-8591'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2018
DOI: 10.1109/CDC.2018.8619252
We present a framework based on spectral graph theory that captures the interplay among network topology, system inertia, and generator and load damping in determining the overall grid behavior and performance. Specifically, we show that the impact of network topology on a power system can be quantified through the network Laplacian eigenvalues, and such eigenvalues determine the grid robustness against low frequency disturbances. Moreover, we can explicitly decompose the frequency signal along scaled Laplacian eigenvectors when damping-inertia ratios are uniform across buses. The insight revealed by this framework partially explains why load-side participation in frequency regulation not only makes the system respond faster, but also helps lower the system nadir after a disturbance. Finally, by presenting a new controller specifically tailored to suppress high frequency disturbances, we demonstrate that our results can provide useful guidelines in the controller design for load-side primary frequency regulation. This improved controller is simulated on the IEEE 39-bus New England interconnection system to illustrate its robustness against high frequency oscillations compared to both the conventional droop control and a recent controller design.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/ezh7h-8fd72Failure Localization in Power Systems via Tree Partitions
https://resolver.caltech.edu/CaltechAUTHORS:20190201-135634765
Authors: {'items': [{'id': 'Guo-Linqi', 'name': {'family': 'Guo', 'given': 'Linqi'}}, {'id': 'Liang-Chen', 'name': {'family': 'Liang', 'given': 'Chen'}}, {'id': 'Zocca-A', 'name': {'family': 'Zocca', 'given': 'Alessandro'}, 'orcid': '0000-0001-6585-4785'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Wierman-A', 'name': {'family': 'Wierman', 'given': 'Adam'}}]}
Year: 2018
DOI: 10.1109/cdc.2018.8619562
Cascading failures in power systems propagate non-locally, making the control and mitigation of outages extremely hard. In this work, we use the emerging concept of the tree partition of transmission networks to provide an analytical characterization of line failure localizability in transmission systems. Our results rigorously establish the well perceived intuition in power community that failures cannot cross bridges, and reveal a finer-grained concept that encodes more precise information on failure propagations within tree-partition regions. Specifically, when a non-bridge line is tripped, the impact of this failure only propagates within well-defined components, which we refer to as cells, of the tree partition defined by the bridges. In contrast, when a bridge line is tripped, the impact of this failure propagates globally across the network, affecting the power flow on all remaining transmission lines. This characterization suggests that it is possible to improve the system robustness by temporarily switching off certain transmission lines, so as to create more, smaller components in the tree partition; thus spatially localizing line failures and making the grid less vulnerable to large-scale outages. We illustrate this approach using the IEEE 118-bus test system and demonstrate that switching off a negligible portion of transmission lines allows the impact of line failures to be significantly more localized without substantial changes in line congestion.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/76deq-fe812A Primal-Dual Gradient Method for Time-Varying Optimization with Application to Power Systems
https://resolver.caltech.edu/CaltechAUTHORS:20190128-132503883
Authors: {'items': [{'id': 'Tang-Yujie', 'name': {'family': 'Tang', 'given': 'Yujie'}, 'orcid': '0000-0002-4921-8372'}, {'id': "Dall'Anese-E", 'name': {'family': "Dall'Anese", 'given': 'Emiliano'}}, {'id': 'Bernstein-A', 'name': {'family': 'Bernstein', 'given': 'Andrey'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'S. H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2018
DOI: 10.1145/3308897.3308939
We consider time-varying nonconvex optimization problems where the objective function and the feasible set vary over discrete time. This sequence of optimization problems induces a trajectory of Karush-Kuhn-Tucker (KKT) points. We present a class of regularized primal-dual gradient algorithms that track the KKT trajectory. These algorithms are feedback-based algorithms, where analytical models for system state or constraints are replaced with actual measurements. We present conditions for the proposed algorithms to achieve bounded tracking error when the cost and constraint functions are twice continuously differentiable. We discuss their practical implications and illustrate their applications in power systems through numerical simulations.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/r2smp-y7309A Feedback-Based Regularized Primal-Dual Gradient Method for Time-Varying Nonconvex Optimization
https://resolver.caltech.edu/CaltechAUTHORS:20190204-111158128
Authors: {'items': [{'id': 'Tang-Yujie', 'name': {'family': 'Tang', 'given': 'Yujie'}, 'orcid': '0000-0002-4921-8372'}, {'id': "Dall'Anese-E", 'name': {'family': "Dall'Anese", 'given': 'Emiliano'}}, {'id': 'Bernstein-A', 'name': {'family': 'Bernstein', 'given': 'Andrey'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2018
DOI: 10.1109/CDC.2018.8619225
This paper considers time-varying nonconvex optimization problems, utilized to model optimal operational trajectories of systems governed by possibly nonlinear physical or logical models. Algorithms for tracking a Karush-Kuhn-Tucker point are synthesized, based on a regularized primal-dual gradient method. In particular, the paper proposes a feedback-based primal-dual gradient algorithm, where analytical models for system state or constraints are replaced with actual measurements. When cost and constraint functions are twice continuously differentiable, conditions for the proposed algorithms to have bounded tracking error are derived, and a discussion of their practical implications is provided. Illustrative numerical simulations are presented for an application in power systems.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/za34x-x0j92Unified Distributed Control of Stand-alone DC Microgrids
https://resolver.caltech.edu/CaltechAUTHORS:20171006-110526562
Authors: {'items': [{'id': 'Wang-Zhaojian', 'name': {'family': 'Wang', 'given': 'Zhaojian'}, 'orcid': '0000-0002-4998-6339'}, {'id': 'Liu-Feng', 'name': {'family': 'Liu', 'given': 'Feng'}, 'orcid': '0000-0003-2279-2558'}, {'id': 'Chen-Ying', 'name': {'family': 'Chen', 'given': 'Ying'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Mei-Shengwei', 'name': {'family': 'Mei', 'given': 'Shengwei'}, 'orcid': '0000-0002-2757-5977'}]}
Year: 2019
DOI: 10.1109/TSG.2017.2757498
Stand-alone direct current (dc) microgrids may belong to different owners and adopt various control strategies. This brings great challenge to its optimal operation due to the difficulty of implementing a unified control. This paper addresses the distributed optimal control of dc microgrids, which intends to break the restriction of diversity to some extent. First, we formulate the optimal power flow problem of stand-alone dc microgrids as an exact second-order cone program and prove the uniqueness of the optimal solution. Then a dynamic solving algorithm based on primal–dual decomposition method is proposed, the convergence of which is proved theoretically as well as the optimality of its equilibrium point. It should be stressed that the algorithm can provide control commands for the three types of microgrids: 1) power control; 2) voltage control; and 3) droop control. This implies that each microgrid does not need to change its original control strategy in practice, which is less influenced by the diversity of microgrids. Moreover, the control commands for power controlled and voltage controlled microgrids satisfy generation limits and voltage limits in both transient process and steady state. Finally, a six-microgrid dc system based on the microgrid benchmark is adopted to validate the effectiveness and plug-n-play property of our designs.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/fzxec-gxq21Distributed Optimal Frequency Control Considering a Nonlinear Network-Preserving Model
https://resolver.caltech.edu/CaltechAUTHORS:20180809-152132536
Authors: {'items': [{'id': 'Wang-Zhaojian', 'name': {'family': 'Wang', 'given': 'Zhaojian'}, 'orcid': '0000-0002-4998-6339'}, {'id': 'Liu-Feng', 'name': {'family': 'Liu', 'given': 'Feng'}, 'orcid': '0000-0003-2279-2558'}, {'id': 'Pang-John-Z-F', 'name': {'family': 'Pang', 'given': 'John Z. F.'}, 'orcid': '0000-0002-6485-7922'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Mei-Shengwei', 'name': {'family': 'Mei', 'given': 'Shengwei'}, 'orcid': '0000-0002-2757-5977'}]}
Year: 2019
DOI: 10.1109/TPWRS.2018.2861941
This paper addresses the distributed optimal frequency control of power systems considering a network-preserving model with nonlinear power flows and excitation voltage dynamics. Salient features of the proposed distributed control strategy are fourfold, first, nonlinearity is considered to cope with large disturbances, second, only a part of generators are controllable, third, no load measurement is required, fourth, communication connectivity is required only for the controllable generators. To this end, benefiting from the concept of "virtual load demand," we first design the distributed controller for the controllable generators by leveraging the primal-dual decomposition technique. We then propose a method to estimate the virtual load demand of each controllable generator based on local frequencies. We derive incremental passivity conditions for the uncontrollable generators. Finally, we prove that the closed-loop system is asymptotically stable and its equilibrium attains the optimal solution to the associated economic dispatch problem. Simulations, including small and large-disturbance scenarios, are carried on the New England system, demonstrating the effectiveness of our design.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/kf8w3-9fn59Distributed Frequency Control with Operational Constraints, Part II: Network Power Balance
https://resolver.caltech.edu/CaltechAUTHORS:20170726-155035857
Authors: {'items': [{'id': 'Wang-Zhaojian', 'name': {'family': 'Wang', 'given': 'Zhaojian'}, 'orcid': '0000-0002-4998-6339'}, {'id': 'Liu-Feng', 'name': {'family': 'Liu', 'given': 'Feng'}, 'orcid': '0000-0003-2279-2558'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Zhao-Changhong', 'name': {'family': 'Zhao', 'given': 'Changhong'}, 'orcid': '0000-0003-0539-8591'}, {'id': 'Mei-Shengwei', 'name': {'family': 'Mei', 'given': 'Shengwei'}, 'orcid': '0000-0002-2757-5977'}]}
Year: 2019
DOI: 10.1109/TSG.2017.2731811
In Part I of this paper, we propose a decentralized optimal frequency control of multi-area power system with operational constraints, where the tie-line powers remain unchanged in the steady state and the power mismatch is balanced within individual control areas. In Part II of this paper, we propose a distributed controller for optimal frequency control in the network power balance case, where the power mismatch is balanced over the whole system. With the proposed controller, the tie-line powers remain within the acceptable range at equilibrium, while the regulation capacity constraints are satisfied both at equilibrium and during transient. It is revealed that the closed-loop system with the proposed controller carries out primal–dual updates with saturation for solving an associated optimization problem. To cope with discontinuous dynamics of the closed-loop system, we deploy the invariance principle for nonpathological Lyapunov function to prove its asymptotic stability. Simulation results are provided to show the effectiveness of our controller.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/7dpz2-fda60Distributed Frequency Control with Operational Constraints, Part I: Per-Node Power Balance
https://resolver.caltech.edu/CaltechAUTHORS:20170726-160828931
Authors: {'items': [{'id': 'Wang-Zhaojian', 'name': {'family': 'Wang', 'given': 'Zhaojian'}, 'orcid': '0000-0002-4998-6339'}, {'id': 'Liu-Feng', 'name': {'family': 'Liu', 'given': 'Feng'}, 'orcid': '0000-0003-2279-2558'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Zhao-Changhong', 'name': {'family': 'Zhao', 'given': 'Changhong'}, 'orcid': '0000-0003-0539-8591'}, {'id': 'Mei-Shengwei', 'name': {'family': 'Mei', 'given': 'Shengwei'}, 'orcid': '0000-0002-2757-5977'}]}
Year: 2019
DOI: 10.1109/TSG.2017.2731810
This paper addresses the distributed optimal frequency control of multi-area power system with operational constraints, including the regulation capacity of individual control area and the power limits on tie-lines. Both generators and controllable loads are utilized to recover nominal frequencies while minimizing regulation cost. We study two control modes: 1) the per-node balance mode and 2) the network balance mode. In Part I of this paper, we only consider the per-node balance case, where we derive a completely decentralized strategy without the need for communication between control areas. It can adapt to unknown load disturbance. The tie-line powers are restored after load disturbance, while the regulation capacity constraints are satisfied both at equilibrium and during transient. We show that the closed-loop systems with the proposed control strategies carry out primal-dual updates for solving the associated centralized frequency optimization problems. We further prove the closed-loop systems are asymptotically stable and converge to the unique optimal solution of the centralized frequency optimization problems and their duals. Finally, we present simulation results to demonstrate the effectiveness of our design. In Part II of this paper, we address the network power balance case, where transmission congestions are managed continuously.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/4d9wj-z6b42System level synthesis
https://resolver.caltech.edu/CaltechAUTHORS:20190513-131853183
Authors: {'items': [{'id': 'Anderson-James-D', 'name': {'family': 'Anderson', 'given': 'James'}, 'orcid': '0000-0002-2832-8396'}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John C.'}, 'orcid': '0000-0002-1828-2486'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Matni-N', 'name': {'family': 'Matni', 'given': 'Nikolai'}, 'orcid': '0000-0003-4936-3921'}]}
Year: 2019
DOI: 10.1016/j.arcontrol.2019.03.006
This article surveys the System Level Synthesis framework, which presents a novel perspective on constrained robust and optimal controller synthesis for linear systems. We show how SLS shifts the controller synthesis task from the design of a controller to the design of the entire closed loop system, and highlight the benefits of this approach in terms of scalability and transparency. We emphasize two particular applications of SLS, namely large-scale distributed optimal control and robust control. In the case of distributed control, we show how SLS allows for localized controllers to be computed, extending robust and optimal control methods to large-scale systems under practical and realistic assumptions. In the case of robust control, we show how SLS allows for novel design methodologies that, for the first time, quantify the degradation in performance of a robust controller due to model uncertainty – such transparency is key in allowing robust control methods to interact, in a principled way, with modern techniques from machine learning and statistical inference. Throughout, we emphasize practical and efficient computational solutions, and demonstrate our methods on easy to understand case studies.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/w427c-j6093ACN-Sim: An Open-Source Simulator for Data-Driven Electric Vehicle Charging Research
https://resolver.caltech.edu/CaltechAUTHORS:20190614-091204247
Authors: {'items': [{'id': 'Lee-Zachary-J', 'name': {'family': 'Lee', 'given': 'Zachary'}}, {'id': 'Johansson-D', 'name': {'family': 'Johansson', 'given': 'Daniel'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2019
DOI: 10.1145/3307772.3330170
Electric vehicles have recently garnered significant attention in the research community due to their potential has a large, highly controllable load which can be used in demand response, load shaping, and renewable energy integration. However, research into practical charging algorithms has been hampered by the lack of a widely available, realistic simulation environment. To meet this need in the community, we are releasing ACN-Sim, a data-driven, open-source simulator based on our experience building and operating real-world charging systems. This simulator provides researchers who may lack access to real EV charging systems with a realistic environment to evaluate their algorithms and test their assumptions. It also provides a common platform on which algorithms can be evaluated head-to-head, allowing researchers to better understand and articulate how their work fits into the existing literature.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/ycfa4-mw888ACN-Data: Analysis and Applications of an Open EV Charging Dataset
https://resolver.caltech.edu/CaltechAUTHORS:20190614-091205559
Authors: {'items': [{'id': 'Lee-Zachary-J', 'name': {'family': 'Lee', 'given': 'Zachary J.'}}, {'id': 'Li-Tongxin', 'name': {'family': 'Li', 'given': 'Tongxin'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2019
DOI: 10.1145/3307772.3328313
We are releasing ACN-Data, a dynamic dataset of workplace EV charging which currently includes over 30,000 sessions with more added daily. In this paper we describe the dataset, as well as some interesting user behavior it exhibits. To demonstrate the usefulness of the dataset, we present three examples, learning and predicting user behavior using Gaussian mixture models, optimally sizing on-site solar generation for adaptive electric vehicle charging, and using workplace charging to smooth the net demand Duck Curve.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/yvh76-f6d35Corrective control: stability analysis of Unified Controller combining frequency control and congestion management
https://resolver.caltech.edu/CaltechAUTHORS:20190627-103322354
Authors: {'items': [{'id': 'Khamisov-O-O', 'name': {'family': 'Khamisov', 'given': 'O. O.'}}, {'id': 'Chernova-T-S', 'name': {'family': 'Chernova', 'given': 'T. S.'}}, {'id': 'Bialek-J-W', 'name': {'family': 'Bialek', 'given': 'J. W.'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'S. H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2019
DOI: 10.48550/arXiv.1806.10303
This paper analyses stability of the Unified Controller (UC) that combines frequency control and congestion management and therefore makes it possible to move from preventive to corrective power system control. Earlier work by the authors of UC proved asymptotic stability of the methodology but the proof was based on a simplified first-order model of the turbine and turbine governor. We show that a higher order model of the turbine governor leads to eigenvalues with small but positive real parts. Consequently, we develop a modification of the methodology that decouples the physical and control systems and therefore results in all the eigenvalues having negative real parts. We illustrate the effectiveness of the modification on a realistic model of 39-bus model of New England power system implemented in Power System Toolbox (PST).https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/grqda-tv814Buy or Sell? Energy Sharing of Prosumers on Constrained Networks
https://resolver.caltech.edu/CaltechAUTHORS:20190626-144159570
Authors: {'items': [{'id': 'Chen-Yue', 'name': {'family': 'Chen', 'given': 'Yue'}}, {'id': 'Mei-Shengwei', 'name': {'family': 'Mei', 'given': 'Shengwei'}, 'orcid': '0000-0002-2757-5977'}, {'id': 'Wei-Wei', 'name': {'family': 'Wei', 'given': 'Wei'}, 'orcid': '0000-0002-1018-7708'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Wierman-A', 'name': {'family': 'Wierman', 'given': 'Adam'}}, {'id': 'Liu-Feng', 'name': {'family': 'Liu', 'given': 'Feng'}, 'orcid': '0000-0003-2279-2558'}]}
Year: 2019
DOI: 10.48550/arXiv.1906.09891
The advent of intelligent agents who produce and consume energy by themselves has led the smart grid into the era of "prosumer", offering the energy system and customers a unique opportunity to revaluate/trade their spot energy via a sharing initiative. To this end, designing an appropriate sharing mechanism is an issue with crucial importance and has captured great attention. This paper addresses the prosumers' demand response problem via energy sharing. Under a general supply-demand function bidding scheme, a sharing market clearing procedure considering network constraints is proposed, which gives rise to a generalized Nash game. The existence and uniqueness of market equilibrium are proved in non-congested cases. When congestion occurs, infinitely much equilibrium may exist because the strategy spaces of prosumers are correlated. A price-regulation procedure is introduced in the sharing mechanism, which outcomes a unique equilibrium that is fair to all participants. Properties of the improved sharing mechanism, including the individual rational behaviors of prosumers and the components of sharing price, are revealed. When the number of prosumers increases, the proposed sharing mechanism approaches social optimum. Even with fixed number of resources, introducing competition can result in a decreasing social cost. Illustrative examples validate the theoretical results and provide more insights for the energy sharing research.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/9swdj-98q23Exact Convex Relaxation of Optimal Power Flow in Tree Networks
https://resolver.caltech.edu/CaltechAUTHORS:20190628-105122130
Authors: {'items': [{'id': 'Gan-Lingwen', 'name': {'family': 'Gan', 'given': 'Lingwen'}}, {'id': 'Li-Na', 'name': {'family': 'Li', 'given': 'Na'}}, {'id': 'Topcu-U', 'name': {'family': 'Topcu', 'given': 'Ufuk'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2019
DOI: 10.48550/arXiv.1208.4076
The optimal power flow (OPF) problem seeks to control power generation/demand to optimize certain objectives such as minimizing the generation cost or power loss in the network. It is becoming increasingly important for distribution networks, which are tree networks, due to the emergence of distributed generation and controllable loads. In this paper, we study the OPF problem in tree networks. The OPF problem is nonconvex. We prove that after a "small" modification to the OPF problem, its global optimum can be recovered via a second-order cone programming (SOCP) relaxation, under a "mild" condition that can be checked apriori. Empirical studies justify that the modification to OPF is "small" and that the "mild" condition holds for the IEEE 13-bus distribution network and two real-world networks with high penetration of distributed generation.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/ncdc2-0yt10Distributed Load Balancing with Nonconvex Constraints: A Randomized Algorithm with Application to Electric Vehicle Charging Scheduling
https://resolver.caltech.edu/CaltechAUTHORS:20190628-094804246
Authors: {'items': [{'id': 'Gan-Lingwen', 'name': {'family': 'Gan', 'given': 'Lingwen'}}, {'id': 'Topcu-U', 'name': {'family': 'Topcu', 'given': 'Ufuk'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2019
DOI: 10.48550/arXiv.1401.7604
With substantial potential to reduce green house gas emission and reliance on fossil fuel, electric vehicles (EVs) have lead to a booming industry, whose growth is expected to continue for the next few decades. However, EVs present themselves as large loads to the power grid. If not coordinated wisely, the charging of EVs will overload power distribution circuits and dramatically increase power supply cost. To address this challenge, significant amount of effort has been devoted in the literature to schedule the charging of EVs in a power grid friendly way. Nonetheless, the majority of the literature assumes that EVs can be charged intermittently at any power level below certain rating, while in practice, it is preferable to charge an EV consecutively at a pre-determined power to prolong the battery lifespan. This practical EV charging constraint is nonconvex and complicates scheduling. To schedule a large number of EVs with the presence of practical nonconvex charging constraints, a distributed
and randomized algorithm is proposed in this paper. The algorithm assumes the availability of a coordinator which can communicate with all EVs. In each iteration of the algorithm, the coordinator receives tentative charging profiles from the EVs and computes a broadcast control signal. After receiving this broadcast control signal, each EV generates a probability distribution over its admissible charging profiles, and samples from the distribution to update its tentative charging profile. We prove that the algorithm converges almost surely to a charging profile in finite iterations. The final charging profile (that the algorithm converges to) is random, i.e., it depends on the realization. We characterize the final charging profile—a charging profile can be a realization of the final charging profile if and only if it is a Nash equilibrium of the game in which each EV seeks to minimize the inner product of its own charging profile and the aggregate electricity demand. Furthermore, we provide a uniform suboptimality upper bound, that scales O(1=n) in the number n of EVs, for all realizations of the final charging profile.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/1caq0-gv292Branch Flow Model: Relaxations and Convexification (Parts I, II)
https://resolver.caltech.edu/CaltechAUTHORS:20190628-073720381
Authors: {'items': [{'id': 'Farivar-M', 'name': {'family': 'Farivar', 'given': 'Masoud'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2019
DOI: 10.48550/arXiv.1204.4865
We propose a branch flow model for the analysis and optimization of mesh as well as radial networks. The model leads to a new approach to solving optimal power flow (OPF) problems that consists of two relaxation steps. The first step eliminates the voltage and current angles and the second step approximates the resulting problem by a conic program that can be solved efficiently. For radial networks, we prove that both relaxation steps are always exact, provided there are no upper bounds on loads. For mesh networks, the conic relaxation is always exact and we characterize when the angle relaxation may fail. We propose a simple method to convexify a mesh network using phase shifters so that both relaxation steps are always exact and OPF for the convexified network can always be solved efficiently for a globally optimal solution. We prove that convexification requires phase shifters only outside a spanning tree of the network graph and their placement depends only on network topology, not on power flows, generation, loads, or operating constraints. Since power networks are sparse, the number of required phase shifters may be relatively small.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/5g3ad-4bt56Differential Privacy of Aggregated DC Optimal Power Flow Data
https://resolver.caltech.edu/CaltechAUTHORS:20190626-153106599
Authors: {'items': [{'id': 'Zhou-Fengyu', 'name': {'family': 'Zhou', 'given': 'Fengyu'}, 'orcid': '0000-0002-2639-6491'}, {'id': 'Anderson-James-D', 'name': {'family': 'Anderson', 'given': 'James'}, 'orcid': '0000-0002-2832-8396'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2019
DOI: 10.48550/arXiv.1903.11237
We consider the problem of privately releasing aggregated network statistics obtained from solving a DC optimal power flow (OPF) problem. It is shown that the mechanism that determines the noise distribution parameters are linked to the topology of the power system and the monotonicity of the network. We derive a measure of "almost" monotonicity and show how it can be used in conjunction with a linear program in order to release aggregated OPF data using the differential privacy framework.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/cwcrk-zzr18Compositional Set Invariance in Network Systems with Assume-Guarantee Contracts
https://resolver.caltech.edu/CaltechAUTHORS:20190201-135605069
Authors: {'items': [{'id': 'Chen-Yuxiao', 'name': {'family': 'Chen', 'given': 'Yuxiao'}, 'orcid': '0000-0001-5276-7156'}, {'id': 'Anderson-James-D', 'name': {'family': 'Anderson', 'given': 'James'}, 'orcid': '0000-0002-2832-8396'}, {'id': 'Kalsi-Karan', 'name': {'family': 'Kalsi', 'given': 'Karan'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Ames-A-D', 'name': {'family': 'Ames', 'given': 'Aaron D.'}, 'orcid': '0000-0003-0848-3177'}]}
Year: 2019
DOI: 10.23919/ACC.2019.8814437
This paper presents an assume-guarantee reasoning approach to the computation of robust invariant sets for network systems. Parameterized signal temporal logic (pSTL) is used to formally describe the behaviors of the subsystems, which we use as the template for the contract. We show that set invariance can be proved with a valid assume-guarantee contract by reasoning about individual subsystems. If a valid assume-guarantee contract with monotonic pSTL template is known, it can be further refined by value iteration. When such a contract is not known, an epigraph method is proposed to solve for a contract that is valid, -an approach that has linear complexity for a sparse network. A microgrid example is used to demonstrate the proposed method. The simulation result shows that together with control barrier functions, the states of all the subsystems can be bounded inside the individual robust invariant sets.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/875b0-fjn33Distributed Optimal Frequency Control Considering a Nonlinear Network-Preserving Model
https://resolver.caltech.edu/CaltechAUTHORS:20200210-125626205
Authors: {'items': [{'id': 'Wang-Zhaojian', 'name': {'family': 'Wang', 'given': 'Zhaojian'}, 'orcid': '0000-0002-4998-6339'}, {'id': 'Liu-Feng', 'name': {'family': 'Liu', 'given': 'Feng'}, 'orcid': '0000-0003-2279-2558'}, {'id': 'Pang-John-Z-F', 'name': {'family': 'Pang', 'given': 'John'}, 'orcid': '0000-0002-6485-7922'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Mei-Shengwei', 'name': {'family': 'Mei', 'given': 'Shengwei'}, 'orcid': '0000-0002-2757-5977'}]}
Year: 2019
DOI: 10.1109/pesgm40551.2019.8974065
This paper addresses the distributed optimal frequency control of power systems considering a network-preserving model with nonlinear power flows and excitation voltage dynamics. Salient features of the proposed distributed control strategy are fourfold: i) nonlinearity is considered to cope with large disturbances; ii) only a part of generators are controllable; iii) no load measurement is required; iv) communication connectivity is required only for the controllable generators. To this end, benefiting from the concept of "virtual load demand", we first design the distributed controller for the controllable generators by leveraging the primal-dual decomposition technique. We then propose a method to estimate the virtual load demand of each controllable generator based on local frequencies. We derive incremental passivity conditions for the uncontrollable generators. Finally, we prove that the closed-loop system is asymptotically stable and its equilibrium attains the optimal solution to the associated economic dispatch problem. Simulations, including small and large-disturbance scenarios, are carried on the New England system, demonstrating the effectiveness of our design.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/45z9q-1wc55On Identification of Distribution Grids
https://resolver.caltech.edu/CaltechAUTHORS:20190201-153603443
Authors: {'items': [{'id': 'Ardakanian-O', 'name': {'family': 'Ardakanian', 'given': 'Omid'}, 'orcid': '0000-0002-6711-5502'}, {'id': 'Wong-Vincent-W-S', 'name': {'family': 'Wong', 'given': 'Vincent W. S.'}, 'orcid': '0000-0003-3821-4365'}, {'id': 'Dobbe-R', 'name': {'family': 'Dobbe', 'given': 'Roel'}, 'orcid': '0000-0003-4633-7023'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'von-Meier-A', 'name': {'family': 'von Meier', 'given': 'Alexandra'}, 'orcid': '0000-0003-4675-752X'}, {'id': 'Tomlin-C-J', 'name': {'family': 'Tomlin', 'given': 'Claire J.'}, 'orcid': '0000-0003-3192-3185'}, {'id': 'Yuan-Ye', 'name': {'family': 'Yuan', 'given': 'Ye'}, 'orcid': '0000-0001-7858-0437'}]}
Year: 2019
DOI: 10.1109/tcns.2019.2891002
Large-scale integration of distributed energy resources into distribution feeders necessitates careful control of their operation through power flow analysis. While the knowledge of the distribution system model is crucial for this analysis, it is often unavailable or outdated. The recent introduction of synchrophasor technology in low-voltage distribution grids has created ample opportunity to learn this model from high-precision, time-synchronized measurements of voltage and current phasors at various locations. This paper focuses on joint estimation of admittance parameters and topology of a polyphase distribution network from the available telemetry data via the lasso, a method for regression shrinkage and selection. We propose tractable convex programs capable of tackling the low-rank structure of the distribution system and develop an online algorithm for early detection and localization of critical events that induce a change in the admittance matrix. The efficacy of these techniques is corroborated through power flow studies on four three-phase radial distribution systems serving real and synthetic household demands.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/zrs5v-8dg96Guest Editorial: Special Issue on Analysis, Control and Optimization of Energy Networks
https://resolver.caltech.edu/CaltechAUTHORS:20190822-152029926
Authors: {'items': [{'id': 'Chertkov-M', 'name': {'family': 'Chertkov', 'given': 'Michael'}}, {'id': 'Jovanovic-M', 'name': {'family': 'Jovanovic', 'given': 'Mihailo'}}, {'id': 'Lesieutre-B', 'name': {'family': 'Lesieutre', 'given': 'Bernie'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Van-Hentenryck-P', 'name': {'family': 'Van Hentenryck', 'given': 'Pascal'}}, {'id': 'Wehenkel-L', 'name': {'family': 'Wehenkel', 'given': 'Louis'}}]}
Year: 2019
DOI: 10.1109/TCNS.2019.2936194
The deployment of new technologies, e.g., renewable generation and electric vehicles, is rapidly transforming power networks by blurring the previously distinct spatio-temporal scales that many traditional approaches rely on for designing, analyzing and operating power grids. Other energy systems, such as natural gas systems, are undergoing similar revolutionary transformations. This trend can be characterized as a disruptive surge in complexity that challenges design and operation, but also offers opportunities to deliver unprecedented efficiency and reliability.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/t47ck-mp716ACN-Sim: An Open-Source Simulator for Data-Driven Electric Vehicle Charging Research
https://resolver.caltech.edu/CaltechAUTHORS:20191204-131602950
Authors: {'items': [{'id': 'Lee-Zachary-J', 'name': {'family': 'Lee', 'given': 'Zachary J.'}}, {'id': 'Johansson-D', 'name': {'family': 'Johansson', 'given': 'Daniel'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2019
DOI: 10.1109/smartgridcomm.2019.8909765
Smart electric vehicle charging has recently garnered significant attention in the research community due to need to charge vast numbers of electric vehicles (EVs) economically, as well as the potential of providing grid services using EVs. However, research into practical online charging algorithms has been hampered by the lack of a widely available, realistic simulation environment in which to evaluate algorithms and test assumptions. To meet this need, we have developed ACN-Sim, a data-driven, open-source simulator based on our experience building and operating real-world charging systems. ACN-Sim provides a modular, extensible architecture which models the complexity of real charging systems, including battery charging behavior and unbalanced three-phase infrastructure. In addition, ACN-Sim integrates with a broader ecosystem of research tools for EV charging, including ACN-Data, an open dataset of EV charging sessions to provide realistic simulation scenarios, and ACN-Live, a framework for field-testing charging algorithms.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/p40d5-h5819Distributed Load-Side Control: Coping with Variation of Renewable Generations
https://resolver.caltech.edu/CaltechAUTHORS:20190627-102755990
Authors: {'items': [{'id': 'Wang-Zhaojian', 'name': {'family': 'Wang', 'given': 'Zhaojian'}, 'orcid': '0000-0002-4998-6339'}, {'id': 'Mei-Shengwei', 'name': {'family': 'Mei', 'given': 'Shengwei'}, 'orcid': '0000-0002-2757-5977'}, {'id': 'Liu-Feng', 'name': {'family': 'Liu', 'given': 'Feng'}, 'orcid': '0000-0003-2279-2558'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Yang-Peng', 'name': {'family': 'Yang', 'given': 'Peng'}}]}
Year: 2019
DOI: 10.1016/j.automatica.2019.108556
This paper addresses the distributed frequency control problem in a multi-area power system taking into account of unknown time-varying power imbalance. Particularly, fast controllable loads are utilized to restore system frequency under changing power imbalance in an optimal manner. The imbalanced power causing frequency deviation is decomposed into three parts: a known constant part, an unknown low-frequency variation and a high-frequency residual. The known steady part is usually the prediction of power imbalance. The variation may result from the fluctuation of renewable resources, electric vehicle charging, etc., which is usually unknown to operators. The high-frequency residual is also unknown and treated as an external disturbance. Correspondingly, in this paper, we resolve the following three problems in different timescales: (1) allocate the steady part of power imbalance economically; (2) mitigate the effect of unknown low-frequency power variation locally; (3) attenuate unknown high-frequency disturbances. To this end, a distributed controller combining consensus method with adaptive internal model control is proposed. We first prove that the closed-loop system is asymptotically stable and converges to the optimal solution of an optimization problem if the external disturbance is not included. We then prove that the power variation can be mitigated accurately. Furthermore, we show that the closed-loop system is robust against both parameter uncertainty and external disturbances. The New England system is used to verify the efficacy of our design.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/p982t-ha254Sufficient Conditions for Exact Semi-definite Relaxation of Optimal Power Flow in Unbalanced Multiphase Radial Networks
https://resolver.caltech.edu/CaltechAUTHORS:20200911-103127164
Authors: {'items': [{'id': 'Zhou-Fengyu', 'name': {'family': 'Zhou', 'given': 'Fengyu'}, 'orcid': '0000-0002-2639-6491'}, {'id': 'Chen-Yue', 'name': {'family': 'Chen', 'given': 'Yue'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2019
DOI: 10.1109/cdc40024.2019.9029827
This paper proves that in an unbalanced multi-phase network with a tree topology, the semi-definite programming relaxation of optimal power flow problems is exact when critical buses are not adjacent to each other. Here a critical bus either contributes directly to the cost function or is where an injection constraint is tight at optimality. Our result generalizes a sufficient condition for exact relaxation in single-phase tree networks to tree networks with arbitrary number of phases.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/6ny6f-f9r98Less is More: Real-time Failure Localization in Power Systems
https://resolver.caltech.edu/CaltechAUTHORS:20190626-143544929
Authors: {'items': [{'id': 'Guo-Linqi', 'name': {'family': 'Guo', 'given': 'Linqi'}}, {'id': 'Liang-Chen', 'name': {'family': 'Liang', 'given': 'Chen'}}, {'id': 'Zocca-A', 'name': {'family': 'Zocca', 'given': 'Alessandro'}, 'orcid': '0000-0001-6585-4785'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Wierman-A', 'name': {'family': 'Wierman', 'given': 'Adam'}}]}
Year: 2019
DOI: 10.1109/CDC40024.2019.9029393
Cascading failures in power systems exhibit nonlocal propagation patterns, which make the analysis and mitigation of failures difficult. In this work, we propose a distributed control framework inspired by the recently proposed concepts of unified controller and network tree-partition that offers strong guarantees in both the mitigation and localization of cascading failures in power systems. In this framework, the transmission network is partitioned into several control areas which are connected in a tree structure, and the unified controller is adopted by generators or controllable loads for fast timescale disturbance response. After an initial failure, the proposed strategy always prevents successive failures from happening, and regulates the system to the desired steady state where the impact of initial failures are localized as much as possible. For extreme failures that cannot be localized, the proposed framework has a configurable design, that progressively involves and coordinates more control areas for failure mitigation and, as a last resort, imposes minimal load shedding. We compare the proposed control framework with Automatic Generation Control (AGC) on the IEEE 118-bus test system. Simulation results show that our novel framework greatly improves the system robustness in terms of the N - 1 security standard, and localizes the impact of initial failures in majority of the load profiles that are examined. Moreover, the proposed framework incurs significantly less load loss, if any, compared to AGC.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/pqhxh-6sk78Learning Graph Parameters from Linear Measurements: Fundamental Trade-offs and Application to Electric Grids
https://resolver.caltech.edu/CaltechAUTHORS:20200915-153320598
Authors: {'items': [{'id': 'Li-Tongxin', 'name': {'family': 'Li', 'given': 'Tongxin'}, 'orcid': '0000-0002-9806-8964'}, {'id': 'Werner-Lucien', 'name': {'family': 'Werner', 'given': 'Lucien'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2019
DOI: 10.1109/cdc40024.2019.9029949
We consider a specific graph learning task: reconstructing a symmetric matrix that represents an underlying graph using linear measurements. We study fundamental trade-offs between the number of measurements (sample complexity), the complexity of the graph class, and the probability of error by first deriving a necessary condition (fundamental limit) on the number of measurements. Then, by considering a two-stage recovery scheme, we give a sufficient condition for recovery. In the special cases of the uniform distribution on trees with n nodes and the Erdös-Rényi (n, p) class, the sample complexity derived from the fundamental trade-offs is tight up to multiplicative factors. In addition, we design and implement a polynomial-time (in n) algorithm based on the two-stage recovery scheme. Simulations for several canonical graph classes and IEEE power system test cases demonstrate the effectiveness of the proposed algorithm for accurate topology and parameter recovery.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/fmwp0-rn435A Second-Order Saddle Point Method for Time-Varying Optimization
https://resolver.caltech.edu/CaltechAUTHORS:20200911-133139018
Authors: {'items': [{'id': 'Tang-Yujie', 'name': {'family': 'Tang', 'given': 'Yujie'}, 'orcid': '0000-0002-4921-8372'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2019
DOI: 10.1109/cdc40024.2019.9028955
Time-varying optimization studies algorithms that can track solutions of optimization problems that evolve with time. A typical time-varying optimization algorithm is implemented in a running fashion in the sense that the underlying optimization problem is updated during the iterations of the algorithm, and is especially suitable for optimizing large-scale fast varying systems. In this paper, we propose and analyze a second-order method for time-varying optimization. Each iteration of the proposed method can be formulated as solving a quadratic-like saddle point problem that incorporates curvature information. Theoretical results on the tracking performance of the proposed method are presented, and discussions on their implications and comparison with existing second-order and first-order methods are also provided.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/kq858-70711Learning Graphs from Linear Measurements: Fundamental Trade-offs and Applications
https://resolver.caltech.edu/CaltechAUTHORS:20200228-131223093
Authors: {'items': [{'id': 'Li-Tongxin', 'name': {'family': 'Li', 'given': 'Tongxin'}, 'orcid': '0000-0002-9806-8964'}, {'id': 'Werner-Lucien', 'name': {'family': 'Werner', 'given': 'Lucien'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2020
DOI: 10.1109/tsipn.2020.2975368
We consider a specific graph learning task: reconstructing a symmetric matrix that represents an underlying graph using linear measurements. We present a sparsity characterization for distributions of random graphs (that are allowed to contain high-degree nodes), based on which we study fundamental trade-offs between the number of measurements, the complexity of the graph class, and the probability of error. We first derive a necessary condition on the number of measurements. Then, by considering a three-stage recovery scheme, we give a sufficient condition for recovery. Furthermore, assuming the measurements are Gaussian IID, we prove upper and lower bounds on the (worst-case) sample complexity for both noisy and noiseless recovery. In the special cases of the uniform distribution on trees with n nodes and the Erdős-Rényi (n,p) class, the fundamental trade-offs are tight up to multiplicative factors with noiseless measurements. In addition, for practical applications, we design and implement a polynomial-time (in n ) algorithm based on the three-stage recovery scheme. Experiments show that the heuristic algorithm outperforms basis pursuit on star graphs. We apply the heuristic algorithm to learn admittance matrices in electric grids. Simulations for several canonical graph classes and IEEE power system test cases demonstrate the effectiveness and robustness of the proposed algorithm for parameter reconstruction.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/kxenq-ds892Privacy-preserving Energy Scheduling for Smart Grid with Renewables
https://resolver.caltech.edu/CaltechAUTHORS:20200327-122618326
Authors: {'items': [{'id': 'Yang-Kai', 'name': {'family': 'Yang', 'given': 'Kai'}, 'orcid': '0000-0002-5983-198X'}, {'id': 'Jiang-Libin', 'name': {'family': 'Jiang', 'given': 'Libin'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Liu-Sijia', 'name': {'family': 'Liu', 'given': 'Sijia'}}]}
Year: 2020
DOI: 10.1109/access.2020.2983110
We consider joint demand response and power procurement to optimize the average social welfare of a smart power grid system with renewable sources. The renewable sources such as wind and solar energy are intermittent and fluctuate rapidly. As a consequence, the demand response algorithm needs to be executed in real time to ensure the stability of a smart grid system with renewable sources. We develop a demand response algorithm that converges to the optimal solution with superlinear rates of convergence. In the simulation studies, the proposed algorithm converges roughly thirty time faster than the traditional subgradient algorithm. In addition, it is fully distributed and can be realized either synchronously or in asynchronous manner, which eases practical deployment.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/p04xn-v4194An Energy Sharing Game With Generalized Demand Bidding: Model and Properties
https://resolver.caltech.edu/CaltechAUTHORS:20190626-132932886
Authors: {'items': [{'id': 'Chen-Yue', 'name': {'family': 'Chen', 'given': 'Yue'}, 'orcid': '0000-0002-7594-7587'}, {'id': 'Mei-Shengwei', 'name': {'family': 'Mei', 'given': 'Shengwei'}, 'orcid': '0000-0002-2757-5977'}, {'id': 'Zhou-Fengyu', 'name': {'family': 'Zhou', 'given': 'Fengyu'}, 'orcid': '0000-0002-2639-6491'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Wei-Wei', 'name': {'family': 'Wei', 'given': 'Wei'}, 'orcid': '0000-0002-1018-7708'}, {'id': 'Liu-Feng', 'name': {'family': 'Liu', 'given': 'Feng'}, 'orcid': '0000-0003-2279-2558'}]}
Year: 2020
DOI: 10.1109/tsg.2019.2946602
This paper proposes a novel energy sharing mechanism for prosumers who can produce and consume. Different from most existing works, the role of individual prosumer as a seller or buyer in our model is endogenously determined. Several desirable properties of the proposed mechanism are proved based on a generalized game-theoretic model. We show that the Nash equilibrium exists and is the unique solution of an equivalent convex optimization problem. The sharing price at the Nash equilibrium equals to the average marginal disutility of all prosumers. We also prove that every prosumer has the incentive to participate in the sharing market, and prosumers' total cost decreases with increasing absolute value of price sensitivity. Furthermore, the Nash equilibrium approaches the social optimal as the number of prosumers grows, and competition can improve social welfare.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/g9dmq-51371Worst-Case Sensitivity of DC Optimal Power Flow Problems
https://resolver.caltech.edu/CaltechAUTHORS:20200707-112527402
Authors: {'items': [{'id': 'Anderson-James-D', 'name': {'family': 'Anderson', 'given': 'James'}, 'orcid': '0000-0002-2832-8396'}, {'id': 'Zhou-Fengyu', 'name': {'family': 'Zhou', 'given': 'Fengyu'}, 'orcid': '0000-0002-2639-6491'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2020
DOI: 10.23919/ACC45564.2020.9147770
In this paper we consider the problem of analyzing the effect a change in the load vector can have on the optimal power generation in a DC power flow model. The methodology is based upon the recently introduced concept of the OPF operator. It is shown that for general network topologies computing the worst-case sensitivities is computationally intractable. However, we show that certain problems involving the OPF operator can be equivalently converted to a graphical discrete optimization problem. Using the discrete formulation, we provide a decomposition algorithm that reduces the computational cost of computing the worst-case sensitivity. A 27-bus numerical example is used to illustrate our results.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/pz4tz-smj42Real-time Flexibility Feedback for Closed-loop Aggregator and System Operator Coordination
https://resolver.caltech.edu/CaltechAUTHORS:20200707-095020631
Authors: {'items': [{'id': 'Li-Tongxin', 'name': {'family': 'Li', 'given': 'Tongxin'}, 'orcid': '0000-0002-9806-8964'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Wierman-A', 'name': {'family': 'Wierman', 'given': 'Adam'}}]}
Year: 2020
DOI: 10.48550/arXiv.2006.13814
Aggregators have emerged as crucial tools for the coordination of distributed, controllable loads. However, to be used effectively, aggregators must be able to communicate the available flexibility of the loads they control to the system operator in a manner that is both (i) concise enough to be scalable to aggregators governing hundreds or even thousands of loads and (ii) informative enough to allow the system operator to send control signals to the aggregator that lead to optimization of system-level objectives, such as cost minimization, and do not violate private constraints of the loads, such as satisfying specific load demands. In this paper, we present the design of a real-time flexibility feedback signal based on maximization of entropy. The design provides a concise and informative signal that can be used by the system operator to perform online cost minimization and real-time capacity estimation, while provably satisfying the private constraints of the loads. In addition to deriving analytic properties of the design, we illustrate the effectiveness of the design using a dataset from an adaptive electric vehicle charging network.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/rsjeg-8d180Localization & Mitigation of Cascading Failures in Power Systems, Part III: Real-time Mitigation
https://resolver.caltech.edu/CaltechAUTHORS:20200707-100438853
Authors: {'items': [{'id': 'Guo-Linqi', 'name': {'family': 'Guo', 'given': 'Linqi'}}, {'id': 'Liang-Chen', 'name': {'family': 'Liang', 'given': 'Chen'}}, {'id': 'Zocca-A', 'name': {'family': 'Zocca', 'given': 'Alessandro'}, 'orcid': '0000-0001-6585-4785'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Wierman-A', 'name': {'family': 'Wierman', 'given': 'Adam'}}]}
Year: 2020
DOI: 10.48550/arXiv.2005.11319
Cascading failures in power systems propagate non-locally, making the control of outages extremely difficult. In Part III of this work, we leverage the properties of tree partitioning developed in Parts I and II to propose a distributed control strategy that offers strong guarantees in both the mitigation and localization of cascading failures. Specifically we adopt a recently developed distributed frequency regulation approach, called the Unified Control, that integrates primary and secondary control as well as congestion management at frequency control timescale. When the balancing areas over which the Unified Control operates form a tree partition, our proposed strategy will regulate the system to a steady state where the impact of initial line outages is localized within the areas where they occur whenever possible and stop the cascading process. When initial line outages cannot be localized, the proposed strategy provides a configurable design that involves and coordinates progressively more balancing areas for failure mitigation in a way that can be optimized for different priorities. We compare the proposed control strategy with the classical automatic generation control (AGC) on the IEEE 118-bus and 2736-bus test networks. Simulation results show that our strategy greatly improves overall reliability in terms of the N-k security standard, and localizes the impact of initial failures in majority of the load profiles that are examined. Moreover, the proposed framework incurs significantly less load loss, if any, compared to AGC, in all of our case studies.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/58pdy-njb94DeepOPF: A Feasibility-Optimized Deep Neural Network Approach for AC Optimal Power Flow Problems
https://resolver.caltech.edu/CaltechAUTHORS:20200707-112147912
Authors: {'items': [{'id': 'Pan-Xiang', 'name': {'family': 'Pan', 'given': 'Xiang'}}, {'id': 'Chen-Minghua', 'name': {'family': 'Chen', 'given': 'Minghua'}}, {'id': 'Zhao-Tianyu', 'name': {'family': 'Zhao', 'given': 'Tianyu'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2020
DOI: 10.48550/arXiv.2007.01002
The AC-OPF problem is the key and challenging problem in the power system operation. When solving the AC-OPF problem, the feasibility issue is critical. In this paper, we develop an efficient Deep Neural Network (DNN) approach, DeepOPF, to ensure the feasibility of the generated solution. The idea is to train a DNN model to predict a set of independent operating variables, and then to directly compute the remaining dependable variables by solving the AC power flow equations. While this guarantees the power-flow balances, the principal difficulty lies in ensuring that the obtained solutions satisfy the operation limits of generations, voltages, and branch flow. We tackle this hurdle by employing a penalty approach in training the DNN. As the penalty gradients make the common first-order gradient-based algorithms prohibited due to the hardness of obtaining an explicit-form expression of the penalty gradients, we further apply a zero-order optimization technique to design the training algorithm to address the critical issue. The simulation results of the IEEE test case demonstrate the effectiveness of the penalty approach. Also, they show that DeepOPF can speed up the computing time by one order of magnitude compared to a state-of-the-art solver, at the expense of minor optimality loss.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/20wfz-z0p43Combining Model-Based and Model-Free Methods for Nonlinear Control: A Provably Convergent Policy Gradient Approach
https://resolver.caltech.edu/CaltechAUTHORS:20200707-095652399
Authors: {'items': [{'id': 'Qu-Guannan', 'name': {'family': 'Qu', 'given': 'Guannan'}}, {'id': 'Yu-Chenkai', 'name': {'family': 'Yu', 'given': 'Chenkai'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Wierman-A', 'name': {'family': 'Wierman', 'given': 'Adam'}}]}
Year: 2020
DOI: 10.48550/arXiv.2006.07476
Model-free learning-based control methods have seen great success recently. However, such methods typically suffer from poor sample complexity and limited convergence guarantees. This is in sharp contrast to classical model-based control, which has a rich theory but typically requires strong modeling assumptions. In this paper, we combine the two approaches to achieve the best of both worlds. We consider a dynamical system with both linear and non-linear components and develop a novel approach to use the linear model to define a warm start for a model-free, policy gradient method. We show this hybrid approach outperforms the model-based controller while avoiding the convergence issues associated with model-free approaches via both numerical experiments and theoretical analyses, in which we derive sufficient conditions on the non-linear component such that our approach is guaranteed to converge to the (nearly) global optimal controller.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/eh5cv-5em69Mitigating Cascading Failures via Local Responses
https://resolver.caltech.edu/CaltechAUTHORS:20210113-163505900
Authors: {'items': [{'id': 'Liang-Chen', 'name': {'family': 'Liang', 'given': 'Chen'}}, {'id': 'Zhou-Fengyu', 'name': {'family': 'Zhou', 'given': 'Fengyu'}, 'orcid': '0000-0002-2639-6491'}, {'id': 'Zocca-Alessandro', 'name': {'family': 'Zocca', 'given': 'Alessandro'}, 'orcid': '0000-0001-6585-4785'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Wierman-A', 'name': {'family': 'Wierman', 'given': 'Adam'}}]}
Year: 2020
DOI: 10.1109/smartgridcomm47815.2020.9302934
This work proposes an approach for failure mitigation in power systems via corrective control named Optimal Injection Adjustment (OIA). In contrast to classical approaches, which focus on minimizing load loss, OIA aims to minimize the post-contingency flow deviations by adjusting node power injections in response to failures. We prove that the optimal control actions obtained from OIA are localized around the original failure and use numerical simulations to highlight that OIA achieves near-optimal control costs despite using localized control actions.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/gjbhs-0b062Learning Optimal Power Flow: Worst-Case Guarantees for Neural Networks
https://resolver.caltech.edu/CaltechAUTHORS:20210113-163505813
Authors: {'items': [{'id': 'Venzke-Andreas', 'name': {'family': 'Venzke', 'given': 'Andreas'}, 'orcid': '0000-0002-6101-6001'}, {'id': 'Qu-Guannan', 'name': {'family': 'Qu', 'given': 'Guannan'}, 'orcid': '0000-0002-5466-3550'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Chatzivasileiadis-Spyros', 'name': {'family': 'Chatzivasileiadis', 'given': 'Spyros'}}]}
Year: 2020
DOI: 10.1109/smartgridcomm47815.2020.9302963
This paper introduces for the first time a framework to obtain provable worst-case guarantees for neural network performance, using learning for optimal power flow (OPF) problems as a guiding example. Neural networks have the potential to substantially reduce the computing time of OPF solutions. However, the lack of guarantees for their worst-case performance remains a major barrier for their adoption in practice. This work aims to remove this barrier. We formulate mixed-integer linear programs to obtain worst-case guarantees for neural network predictions related to (i) maximum constraint violations, (ii) maximum distances between predicted and optimal decision variables, and (iii) maximum sub-optimality. We demonstrate our methods on a range of PGLib-OPF networks up to 300 buses. We show that the worst-case guarantees can be up to one order of magnitude larger than the empirical lower bounds calculated with conventional methods. More importantly, we show that the worst-case predictions appear at the boundaries of the training input domain, and we demonstrate how we can systematically reduce the worst-case guarantees by training on a larger input domain than the domain they are evaluated on.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/xw1d2-9sz32DeepOPF+: A Deep Neural Network Approach for DC Optimal Power Flow for Ensuring Feasibility
https://resolver.caltech.edu/CaltechAUTHORS:20210113-163505726
Authors: {'items': [{'id': 'Zhao-Tianyu', 'name': {'family': 'Zhao', 'given': 'Tianyu'}}, {'id': 'Pan-Xiang', 'name': {'family': 'Pan', 'given': 'Xiang'}, 'orcid': '0000-0002-6565-2339'}, {'id': 'Chen-Minghua', 'name': {'family': 'Chen', 'given': 'Minghua'}}, {'id': 'Venke-Andreas', 'name': {'family': 'Venzke', 'given': 'Andreas'}, 'orcid': '0000-0002-6101-6001'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2020
DOI: 10.1109/smartgridcomm47815.2020.9303017
Deep Neural Networks approaches for the Optimal Power Flow (OPF) problem received considerable attention recently. A key challenge of these approaches lies in ensuring the feasibility of the predicted solutions to physical system constraints. Due to the inherent approximation errors, the solutions predicted by Deep Neural Networks (DNNs) may violate the operating constraints, e.g., the transmission line capacities, limiting their applicability in practice. To address this challenge, we develop DeepOPF+ as a DNN approach based on the so-called "preventive" framework. Specifically, we calibrate the generation and transmission line limits used in the DNN training, thereby anticipating approximation errors and ensuring that the resulting predicted solutions remain feasible. We theoretically characterize the calibration magnitude necessary for ensuring universal feasibility. Our DeepOPF+ approach improves over existing DNN-based schemes in that it ensures feasibility and achieves a consistent speed up performance in both light-load and heavy-load regimes. Detailed simulation results on a range of test instances show that the proposed DeepOPF+ generates 100% feasible solutions with minor optimality loss. Meanwhile, it achieves a computational speedup of two orders of magnitude compared to state-of-the-art solvers.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/rgw7s-71x60Separation event-constrained optimal power flow to enhance resilience in low-inertia power systems
https://resolver.caltech.edu/CaltechAUTHORS:20210112-144610987
Authors: {'items': [{'id': 'Püschel-Løvengreen-Sebastián', 'name': {'family': 'Püschel-Løvengreen', 'given': 'Sebastián'}, 'orcid': '0000-0002-0248-9618'}, {'id': 'Ghazavi-Dozein-Mehdi', 'name': {'family': 'Ghazavi Dozein', 'given': 'Mehdi'}, 'orcid': '0000-0003-2574-7082'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Mancarella-Pierluigi', 'name': {'family': 'Mancarella', 'given': 'Pierluigi'}, 'orcid': '0000-0002-9247-1402'}]}
Year: 2020
DOI: 10.1016/j.epsr.2020.106678
Weakly interconnected power systems face separation risk during extreme weather events or due to cascading failures. These contingencies may become particularly severe in low-inertia grids, where the sub-regions resulting after system split need to procure enough resources to respond to low (importing areas) and high (exporting areas) frequency conditions. This paper introduces a separation event-constrained optimal power flow (SECOPF) with considerations of inertia and frequency response resources allocation in each balancing area to be capable to withstand, besides the largest generation and load contingencies, also the loss of selected interconnectors. The model, cast as mixed integer linear program, is tested on a reduced version of the Australian power system and validated via dynamic simulation. The results show how the system's frequency resilience to extreme events can be effectively enhanced for both high- and low-frequency conditions that arise in different areas after an interconnector's trip . This is achieved by co-optimising the interconnector flow magnitudes along with the distribution of frequency response resources and inertia levels in each area.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/b7nyk-ajc03Pricing EV charging service with demand charge
https://resolver.caltech.edu/CaltechAUTHORS:20210107-153400550
Authors: {'items': [{'id': 'Lee-Zachary-J', 'name': {'family': 'Lee', 'given': 'Zachary J.'}, 'orcid': '0000-0002-5358-2388'}, {'id': 'Pang-John-Z-F', 'name': {'family': 'Pang', 'given': 'John Z. F.'}, 'orcid': '0000-0002-6485-7922'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2020
DOI: 10.1016/j.epsr.2020.106694
Pricing electric vehicle (EV) charging services is difficult when the electricity tariff includes both time-of-use energy cost and demand charge based on peak power draw. In this paper, we propose a pricing scheme that assigns a session-specific energy price to each charging session at the end of the billing period. The session price precisely captures the costs of energy, demand charge, and infrastructure congestion for which that session is responsible in that month while optimizing the trade-off between inexpensive time-of-use pricing and peak power draw. While our pricing scheme is calculated offline at the end of the billing period, we propose an online scheduling algorithm based on model predictive control to determine charging rates for each EV in real-time. We provide theoretical justification for our proposal and support it with simulations using real data collected from charging facilities at Caltech and JPL. Our simulation results suggest that the online algorithm can approximate the offline optimal reasonably well, e.g., the cost paid by the operator in the online setting is higher than the offline optimal cost by 9.2% and 6.5% at Caltech and JPL respectively. In the case of JPL, congestion rents are enough to cover this increase in costs, while at Caltech, this results in a negligible average loss of $18 per month.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/8hkmq-h5806Classification of electric vehicle charging time series with selective clustering
https://resolver.caltech.edu/CaltechAUTHORS:20210112-144610886
Authors: {'items': [{'id': 'Sun-Chengxi', 'name': {'family': 'Sun', 'given': 'Chenxi'}}, {'id': 'Li-Tongxin', 'name': {'family': 'Li', 'given': 'Tongxin'}, 'orcid': '0000-0002-9806-8964'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Li-Victor-O-K', 'name': {'family': 'Li', 'given': 'Victor O. K.'}}]}
Year: 2020
DOI: 10.1016/j.epsr.2020.106695
We develop a novel iterative clustering method for classifying time series of EV charging rates based on their "tail features". Our method first extracts tails from a diversity of charging time series that have different lengths, contain missing data, and are distorted by scheduling algorithms and measurement noise. The charging tails are then clustered into a small number of types whose representatives are then used to improve tail extraction. This process iterates until it converges. We apply our method to ACN-Data, a fine-grained EV charging dataset recently made publicly available, to illustrate its effectiveness and potential applications.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/hgwjy-e8s47A Sufficient Condition for Local Optima to be Globally Optimal
https://resolver.caltech.edu/CaltechAUTHORS:20210121-152558409
Authors: {'items': [{'id': 'Zhou-Fengyu', 'name': {'family': 'Zhou', 'given': 'Fengyu'}, 'orcid': '0000-0002-2639-6491'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2020
DOI: 10.1109/cdc42340.2020.9303868
Consider an optimization problem with a convex cost function but a non-convex compact feasible set X, and its relaxation with a compact and convex feasible set X̂ ⊃ X. We prove that if from any point x ∈ X̂∖X there is a path connecting x to X along which both the cost function and a Lyapunov-like function are improvable, then any local optimum in X for the original non-convex problem is a global optimum. We use this result to show that, for AC optimal power flow problems, a wellknown sufficient condition for exact relaxation also guarantees that all its local optima are globally optimal. This helps explain the widespread empirical experience that local algorithms for optimal power flow problems often work extremely well.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/c481g-2ep34An integrated approach for failure mitigation & localization in power systems
https://resolver.caltech.edu/CaltechAUTHORS:20200707-103725840
Authors: {'items': [{'id': 'Liang-Chen', 'name': {'family': 'Liang', 'given': 'Chen'}}, {'id': 'Guo-Linqi', 'name': {'family': 'Guo', 'given': 'Linqi'}}, {'id': 'Zocca-Alessandro', 'name': {'family': 'Zocca', 'given': 'Alessandro'}, 'orcid': '0000-0001-6585-4785'}, {'id': 'Yu-Shuyue', 'name': {'family': 'Yu', 'given': 'Shuyue'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Wierman-A', 'name': {'family': 'Wierman', 'given': 'Adam'}}]}
Year: 2021
DOI: 10.48550/arXiv.2004.10401
The transmission grid is often comprised of several control areas that are connected by multiple tie lines in a mesh structure for reliability. It is also well-known that line failures can propagate non-locally and redundancy can exacerbate cascading. In this paper, we propose an integrated approach to grid reliability that (i) judiciously switches off a small number of tie lines so that the control areas are connected in a tree structure; and (ii) leverages a unified frequency control paradigm to provide congestion management in real time. Even though the proposed topology reduces redundancy, the integration of tree structure at regional level and real-time congestion management can provide stronger guarantees on failure localization and mitigation. We illustrate our approach on the IEEE 39-bus network and evaluate its performance on the IEEE 118-bus, 179-bus, 200-bus and 240-bus networks with various network congestion conditions. Simulations show that, compared with the traditional approach, our approach not only prevents load shedding in more failure scenarios, but also incurs smaller amounts of load loss in scenarios where load shedding is inevitable. Moreover, generators under our approach adjust their operations more actively and efficiently in a local manner.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/0hpmn-9pp50A Note on Branch Flow Models with Line Shunts
https://resolver.caltech.edu/CaltechAUTHORS:20201015-152732679
Authors: {'items': [{'id': 'Zhou-Fengyu', 'name': {'family': 'Zhou', 'given': 'Fengyu'}, 'orcid': '0000-0002-2639-6491'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2021
DOI: 10.1109/tpwrs.2020.3029732
When the shunt elements in the Π circuit line model are assumed zero, it has been proved that branch flow models are equivalent to bus injection models and that the second-order cone relaxation of optimal power flow problems on a radial network is exact under certain conditions. In this note we propose a branch flow model that includes nonzero line shunts and prove that the equivalence and the exactness of relaxation continue to hold under essentially the same conditions as for zero shunt elements.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/rptvr-h5712Reinforcement Learning for Decision-Making and Control in Power Systems: Tutorial, Review, and Vision
https://resolver.caltech.edu/CaltechAUTHORS:20210831-203850710
Authors: {'items': [{'id': 'Chen-Xin', 'name': {'family': 'Chen', 'given': 'Xin'}, 'orcid': '0000-0002-0952-0008'}, {'id': 'Qu-Guannan', 'name': {'family': 'Qu', 'given': 'Guannan'}, 'orcid': '0000-0002-5466-3550'}, {'id': 'Tang-Yujie', 'name': {'family': 'Tang', 'given': 'Yujie'}, 'orcid': '0000-0002-4921-8372'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Li-Na', 'name': {'family': 'Li', 'given': 'Na'}}]}
Year: 2021
DOI: 10.48550/arXiv.2102.01168
With large-scale integration of renewable generation and distributed energy resources (DERs), modern power systems are confronted with new operational challenges, such as growing complexity, increasing uncertainty, and aggravating volatility. Meanwhile, more and more data are becoming available owing to the widespread deployment of smart meters, smart sensors, and upgraded communication networks. As a result, data-driven control techniques, especially reinforcement learning (RL), have attracted surging attention in recent years. In this paper, we provide a tutorial on various RL techniques and how they can be applied to decision-making in power systems. We illustrate RL-based models and solutions in three key applications, frequency regulation, voltage control, and energy management. We conclude with three critical issues in the application of RL, i.e., safety, scalability, and data. Several potential future directions are discussed as well.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/sjc89-s6m10Safety-Critical Control Synthesis for Network Systems With Control Barrier Functions and Assume-Guarantee Contracts
https://resolver.caltech.edu/CaltechAUTHORS:20200707-113800670
Authors: {'items': [{'id': 'Chen-Yuxiao', 'name': {'family': 'Chen', 'given': 'Yuxiao'}, 'orcid': '0000-0001-5276-7156'}, {'id': 'Anderson-James-D', 'name': {'family': 'Anderson', 'given': 'James'}, 'orcid': '0000-0002-2832-8396'}, {'id': 'Kalsi-Karan', 'name': {'family': 'Kalsi', 'given': 'Karan'}}, {'id': 'Ames-A-D', 'name': {'family': 'Ames', 'given': 'Aaron D.'}, 'orcid': '0000-0003-0848-3177'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2021
DOI: 10.1109/TCNS.2020.3029183
This article aims at the safety-critical control synthesis of network systems such that the satisfaction of the safety constraints can be guaranteed. To handle the large state dimension of such systems, an assume-guarantee contract is used to break the large synthesis problem into smaller subproblems. Parameterized signal temporal logic (pSTL) is used to formally describe the behaviors of the subsystems which we use as the template for the contract. We show that robust control invariant sets (RCIs) for the subsystems can be composed to form a robust control invariant set (RCI) for the whole network system under a valid assume-guarantee contract. An epigraph algorithm is proposed to solve for a contract that is valid, an approach that has linear complexity for sparse networks, which leads to a RCI for the whole network system. Implemented with control barrier function (CBF), the state of each subsystem is guaranteed to stay within the safe set. Furthermore, we propose a contingency tube model predictive control approach based on the RCI, which is capable of handling severe contingencies, including topology changes of the network. A power grid example is used to demonstrate the proposed method. The simulation result includes both set point control and contingency recovery, and the safety constraint is always satisfied.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/wdtra-wzn87Reverse and Forward Engineering of Local Voltage Control in Distribution Networks
https://resolver.caltech.edu/CaltechAUTHORS:20200514-142330504
Authors: {'items': [{'id': 'Zhou-Xinyang', 'name': {'family': 'Zhou', 'given': 'Xinyang'}, 'orcid': '0000-0001-8526-2357'}, {'id': 'Farivar-Masoud', 'name': {'family': 'Farivar', 'given': 'Masoud'}, 'orcid': '0000-0001-7298-3526'}, {'id': 'Liu-Zhiyuan', 'name': {'family': 'Liu', 'given': 'Zhiyuan'}, 'orcid': '0000-0003-4356-4183'}, {'id': 'Chen-Lijun', 'name': {'family': 'Chen', 'given': 'Lijun'}, 'orcid': '0000-0001-6694-4299'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2021
DOI: 10.1109/tac.2020.2994184
The increasing penetration of renewable and distributed energy resources in distribution networks calls for real-time and distributed voltage control. In this article, we investigate local Volt/VAR control with a general class of control functions, and show that the power system dynamics with nonincremental local voltage control can be seen as a distributed algorithm for solving a well-defined optimization problem (reverse engineering). The reverse engineering further reveals a fundamental limitation of the nonincremental voltage control: the convergence condition is restrictive and prevents better voltage regulation at equilibrium. This motivates us to design two incremental local voltage control schemes based on the subgradient and pseudo-gradient algorithms, respectively, for solving the same optimization problem (forward engineering). The new control schemes decouple the dynamical property from the equilibrium property, and have much less restrictive convergence conditions. This article presents another step toward developing a new foundation—network dynamics as optimization algorithms—for distributed real-time control and optimization of future power networks.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/njr0v-2bd65Approaching Prosumer Social Optimum via Energy Sharing with Proof of Convergence
https://resolver.caltech.edu/CaltechAUTHORS:20210503-115704998
Authors: {'items': [{'id': 'Chen-Yue', 'name': {'family': 'Chen', 'given': 'Yue'}, 'orcid': '0000-0002-7594-7587'}, {'id': 'Zhao-Changhong', 'name': {'family': 'Zhao', 'given': 'Changhong'}, 'orcid': '0000-0003-0539-8591'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Mei-Shengwei', 'name': {'family': 'Mei', 'given': 'Shengwei'}, 'orcid': '0000-0002-2757-5977'}]}
Year: 2021
DOI: 10.1109/ciss50987.2021.9400276
The conventional power system operation approach has been proven to be effective and reliable for decades. Specially, at the demand side, customers are managed centrally by aggregators and usually not price-responsive. With the prevalence of distributed energy resources (DERs), traditional consumers are now endowed with the ability to produce energy, turning into so-called prosumers. Prosumers can tradeoff between supply and demand and participate in energy management proactively. At the same time, the intermittent and uncertain nature of DERs call for a stronger capability of dealing with real-time energy fluctuation. In this context, exploiting demand-side flexibility to support real-time energy balancing, which can reduce required generation reserves and save costs, is a promising direction for energy system modernization. However, the traditional centralized scheme fails to allow a prosumer to act upon its profit-maximizing philosophy, which reduces prosumer incentives and restricts demand-side flexibility. Therefore, a new prosumer-oriented approach is desired.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/wb0wr-p3f29Approaching Prosumer Social Optimum via Energy Sharing With Proof of Convergence
https://resolver.caltech.edu/CaltechAUTHORS:20210113-163505633
Authors: {'items': [{'id': 'Chen-Yue', 'name': {'family': 'Chen', 'given': 'Yue'}, 'orcid': '0000-0002-7594-7587'}, {'id': 'Zhao-Changhong', 'name': {'family': 'Zhao', 'given': 'Changhong'}, 'orcid': '0000-0003-0539-8591'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Mei-Shengwei', 'name': {'family': 'Mei', 'given': 'Shengwei'}, 'orcid': '0000-0002-2757-5977'}]}
Year: 2021
DOI: 10.1109/tsg.2020.3048402
With the advent of prosumers, the traditional centralized operation may become impracticable due to computational burden, privacy concerns, and conflicting interests. In this article, an energy sharing mechanism is proposed to accommodate prosumers' strategic decision-making on their self-production and demand in the presence of capacity constraints. Under this setting, prosumers play a generalized Nash game. We prove main properties of the game: an equilibrium exists and is partially unique; no prosumer is worse off by energy sharing and the price-of-anarchy is 1−O(1/I) where I is the number of prosumers. In particular, the PoA tends to 1 with a growing number of prosumers, meaning that the resulting total cost under the proposed energy sharing approaches social optimum. We prove that the corresponding prosumers' strategies converge to the social optimal solution as well. Finally we propose a bidding process and prove that it converges to the energy sharing equilibrium under mild conditions. Illustrative examples are provided to validate the results.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/8gdt7-0wv71Smoothed Least-Laxity-First Algorithm for EV Charging
https://resolver.caltech.edu/CaltechAUTHORS:20210510-080403337
Authors: {'items': [{'id': 'Chen-Niangjun', 'name': {'family': 'Chen', 'given': 'Niangjun'}, 'orcid': '0000-0002-2289-9737'}, {'id': 'Kurniawan-Christian', 'name': {'family': 'Kurniawan', 'given': 'Christian'}}, {'id': 'Nakahira-Yorie', 'name': {'family': 'Nakahira', 'given': 'Yorie'}, 'orcid': '0000-0003-3324-4602'}, {'id': 'Chen-Lijun', 'name': {'family': 'Chen', 'given': 'Lijun'}, 'orcid': '0000-0001-6694-4299'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2021
DOI: 10.48550/arXiv.2102.08610
Adaptive charging can charge electric vehicles (EVs) at scale cost effectively, despite the uncertainty in EV arrivals. We formulate adaptive EV charging as a feasibility problem that meets all EVs' energy demands before their deadlines while satisfying constraints in charging rate and total charging power. We propose an online algorithm, smoothed least-laxity-first (sLLF), that decides the current charging rates without the knowledge of future arrivals and demands. We characterize the performance of the sLLF algorithm analytically and numerically. Numerical experiments with real-world data show that it has a significantly higher rate of feasible EV charging than several other existing EV charging algorithms. Resource augmentation framework is employed to assess the feasibility condition of the algorithm. The assessment shows that the sLLF algorithm achieves perfect feasibility with only a 0.07 increase in resources.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/7tm6y-8ht67A Spectral Representation of Power Systems with Applications to Adaptive Grid Partitioning and Cascading Failure Localization
https://resolver.caltech.edu/CaltechAUTHORS:20210716-225840003
Authors: {'items': [{'id': 'Zocca-Alessandro', 'name': {'family': 'Zocca', 'given': 'Alessandro'}, 'orcid': '0000-0001-6585-4785'}, {'id': 'Liang-Chen', 'name': {'family': 'Liang', 'given': 'Chen'}}, {'id': 'Guo-Linqi', 'name': {'family': 'Guo', 'given': 'Linqi'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Wierman-A', 'name': {'family': 'Wierman', 'given': 'Adam'}}]}
Year: 2021
DOI: 10.48550/arXiv.2105.05234
Transmission line failures in power systems propagate and cascade non-locally. This well-known yet counter-intuitive feature makes it even more challenging to optimally and reliably operate these complex networks. In this work we present a comprehensive framework based on spectral graph theory that fully and rigorously captures how multiple simultaneous line failures propagate, distinguishing between non-cut and cut set outages. Using this spectral representation of power systems, we identify the crucial graph sub-structure that ensures line failure localization -- the network bridge-block decomposition. Leveraging this theory, we propose an adaptive network topology reconfiguration paradigm that uses a two-stage algorithm where the first stage aims to identify optimal clusters using the notion of network modularity and the second stage refines the clusters by means of optimal line switching actions. Our proposed methodology is illustrated using extensive numerical examples on standard IEEE networks and we discussed several extensions and variants of the proposed algorithm.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/1d53p-zja18The Optimal Power Flow Operator: Theory and Computation
https://resolver.caltech.edu/CaltechAUTHORS:20200707-114446351
Authors: {'items': [{'id': 'Zhou-Fengyu', 'name': {'family': 'Zhou', 'given': 'Fengyu'}, 'orcid': '0000-0002-2639-6491'}, {'id': 'Anderson-James-D', 'name': {'family': 'Anderson', 'given': 'James'}, 'orcid': '0000-0002-2832-8396'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2021
DOI: 10.1109/TCNS.2020.3044258
Optimal power flow (OPF) problems are mathematical programs to determine how to distribute power over networks subject to power flow and operational constraints. In this article, we treat an OPF problem as an operator that maps user demand to generated power, and allow the problem parameters to take values in some admissible set. We formalize this operator theoretic approach, define and characterize restricted parameter sets under which the mapping has a singleton output, independent binding constraints, and is differentiable. We show that for any power network, these analytical properties hold under almost all operating conditions and can thus be relied upon in applications. We further provide a closed-form expression for the Jacobian matrix of the OPF operator and describe how various derivatives can be computed using a recently proposed scheme based on homogenous self-dual embedding. In contrast to related work in the optimization literature, our results have a clear physical interpretation.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/qhb3h-1ry70Information Aggregation for Constrained Online Control
https://resolver.caltech.edu/CaltechAUTHORS:20210607-115053999
Authors: {'items': [{'id': 'Li-Tongxin', 'name': {'family': 'Li', 'given': 'Tongxin'}, 'orcid': '0000-0002-9806-8964'}, {'id': 'Chen-Yue', 'name': {'family': 'Chen', 'given': 'Yue'}, 'orcid': '0000-0002-7594-7587'}, {'id': 'Sun-Bo', 'name': {'family': 'Sun', 'given': 'Bo'}, 'orcid': '0000-0003-3172-7811'}, {'id': 'Wierman-A', 'name': {'family': 'Wierman', 'given': 'Adam'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2021
DOI: 10.1145/3410220.3461737
We consider a two-controller online control problem where a central controller chooses an action from a feasible set that is determined by time-varying and coupling constraints, which depend on all past actions and states. The central controller's goal is to minimize the cumulative cost; however, the controller has access to neither the feasible set nor the dynamics directly, which are determined by a remote local controller. Instead, the central controller receives only an aggregate summary of the feasibility information from the local controller, which does not know the system costs. We show that it is possible for an online algorithm using feasibility information to nearly match the dynamic regret of an online algorithm using perfect information whenever the feasible sets satisfy a causal invariance criterion and there is a sufficiently large prediction window size. To do so, we use a form of feasibility aggregation based on entropic maximization in combination with a novel online algorithm, named Penalized Predictive Control (PPC).https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/ah7r7-edq95Information Aggregation for Constrained Online Control
https://resolver.caltech.edu/CaltechAUTHORS:20210604-111535691
Authors: {'items': [{'id': 'Li-Tongxin', 'name': {'family': 'Li', 'given': 'Tongxin'}, 'orcid': '0000-0002-9806-8964'}, {'id': 'Chen-Yue', 'name': {'family': 'Chen', 'given': 'Yue'}, 'orcid': '0000-0002-7594-7587'}, {'id': 'Sun-Bo', 'name': {'family': 'Sun', 'given': 'Bo'}, 'orcid': '0000-0003-3172-7811'}, {'id': 'Wierman-A', 'name': {'family': 'Wierman', 'given': 'Adam'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2021
DOI: 10.1145/3460085
This paper considers an online control problem involving two controllers. A central controller chooses an action from a feasible set that is determined by time-varying and coupling constraints, which depend on all past actions and states. The central controller's goal is to minimize the cumulative cost; however, the controller has access to neither the feasible set nor the dynamics directly, which are determined by a remote local controller. Instead, the central controller receives only an aggregate summary of the feasibility information from the local controller, which does not know the system costs. We show that it is possible for an online algorithm using feasibility information to nearly match the dynamic regret of an online algorithm using perfect information whenever the feasible sets satisfy a causal invariance criterion and there is a sufficiently large prediction window size. To do so, we use a form of feasibility aggregation based on entropic maximization in combination with a novel online algorithm, named Penalized Predictive Control (PPC) and demonstrate that aggregated information can be efficiently learned using reinforcement learning algorithms. The effectiveness of our approach for closed-loop coordination between central and local controllers is validated via an electric vehicle charging application in power systems.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/nha5m-d8388Pricing flexibility of shiftable demand in electricity markets
https://resolver.caltech.edu/CaltechAUTHORS:20210629-211519470
Authors: {'items': [{'id': 'Werner-Lucien', 'name': {'family': 'Werner', 'given': 'Lucien'}}, {'id': 'Wierman-A', 'name': {'family': 'Wierman', 'given': 'Adam'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2021
DOI: 10.1145/3447555.3464847
Enabling participation of demand-side flexibility in electricity markets is key to improving power system resilience and increasing the penetration of renewable generation. In this work we are motivated by the curtailment of near-zero-marginal-cost renewable resources during periods of oversupply, a particularly important cause of inefficient generation dispatch. Focusing on shiftable load in a multi-interval economic dispatch setting, we show that incompatible incentives arise for loads in the standard market formulation. While the system's overall efficiency increases from dispatching flexible demand, the overall welfare of loads can decrease as a result of higher spot prices. We propose a market design to address this incentive issue. Specifically, by imposing a small number of additional constraints on the economic dispatch problem, we obtain a mechanism that guarantees individual rationality for all market participants while simultaneously obtaining a more efficient dispatch. Our formulation leads to a natural definition of a uniform, time-varying flexibility price that is paid to loads to incentivize flexible bidding. We provide theoretical guarantees and empirically validate our model with simulations on real-world generation data from California Independent System Operator (CAISO).https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/1fzny-bps82On the Implementation of OPF-Based Setpoints for Active Distribution Networks
https://resolver.caltech.edu/CaltechAUTHORS:20210129-120019482
Authors: {'items': [{'id': 'Liu-Michael-Ziguang', 'name': {'family': 'Liu', 'given': 'Michael Z.'}, 'orcid': '0000-0002-9609-4544'}, {'id': 'Ochoa-Luis-F', 'name': {'family': 'Ochoa', 'given': 'Luis F.'}, 'orcid': '0000-0002-7853-4286'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2021
DOI: 10.1109/tsg.2021.3054387
In the context of active distribution networks, AC Optimal Power Flow (OPF) has shown great potential to calculate setpoints for controllable devices. Although considerable literature exists, temporal aspects that may affect the actual execution of these setpoints are rarely investigated. Due to the diverse operating characteristics of controllable devices (i.e., delays, ramp rates and deadbands), when these setpoints are executed by multiple devices without adequate considerations, the resulting outcome can differ drastically from what is expected; leading to violations of network constraints and excessive control actions. Therefore, this work proposes a series of necessary adaptations within the controllers of existing devices as well as in the OPF formulation to cater for the diversity in operating characteristics, ensuring that calculated setpoints are adequately implemented by controllable devices. This involves the direct control of conventional devices and enforcing a new ramping behavior for inverter-interfaced devices. Furthermore, a linear, mixed-integer formulation is proposed to handle discrete devices and improve scalability in large networks. Co-simulation results (using a U.K. test network with the objective of maximizing renewable energy production and considering 1s time-step) demonstrate that, by catering for the operating characteristics of controllable devices, the expected outcome from OPF-based setpoints can be achieved.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/xmfyf-whv73Exactness of OPF Relaxation on Three-Phase Radial Networks With Delta Connections
https://resolver.caltech.edu/CaltechAUTHORS:20210412-095431267
Authors: {'items': [{'id': 'Zhou-Fengyu', 'name': {'family': 'Zhou', 'given': 'Fengyu'}, 'orcid': '0000-0002-2639-6491'}, {'id': 'Zamzam-Ahmed-S', 'name': {'family': 'Zamzam', 'given': 'Ahmed S.'}, 'orcid': '0000-0002-1175-2801'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Sidiropoulos-Nicholas-D', 'name': {'family': 'Sidiropoulos', 'given': 'Nicholas D.'}, 'orcid': '0000-0002-3385-7911'}]}
Year: 2021
DOI: 10.1109/TSG.2021.3066530
Simulations have shown that while semi-definite relaxations of AC optimal power flow (AC-OPF) on three-phase radial networks with only wye connections tend to be exact, the presence of delta connections seem to render them inexact. This article shows that such inexactness originates from the non-uniqueness of relaxation solutions and numerical errors amplified by the non-uniqueness. This finding motivates two algorithms to recover the exact solution of AC-OPF in unbalanced distribution networks featuring both wye and delta connections. In simulations using IEEE 13, 37 and 123-bus systems, the proposed algorithms provide exact optimal solutions up to numerical precision.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/0trtw-nqr14Combating Bufferbloat in Multi-Bottleneck Networks: Theory and Algorithms
https://resolver.caltech.edu/CaltechAUTHORS:20210412-072637490
Authors: {'items': [{'id': 'Ye-Jiancheng', 'name': {'family': 'Ye', 'given': 'Jiancheng'}, 'orcid': '0000-0002-1296-171X'}, {'id': 'Leung-Ka-Cheong', 'name': {'family': 'Leung', 'given': 'Ka-Cheong'}, 'orcid': '0000-0001-7999-2572'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2021
DOI: 10.1109/TNET.2021.3066505
Bufferbloat is a phenomenon in computer networks where large router buffers are frequently filled up, resulting in high queueing delay and delay variation. More and more delay-sensitive applications on the Internet have made this phenomenon a pressing issue. Interacting with the Transmission Control Protocol (TCP), active queue management (AQM) algorithms run on routers play an important role in combating bufferbloat. However, AQM algorithms have not been widely deployed due to complicated manual parameter tuning. Moreover, they are often designed and analyzed based on network models with a single bottleneck link, rendering their performance and stability unclear in multi-bottleneck networks. In this paper, we propose a general framework to combat bufferbloat in multi-bottleneck networks. We first present an equilibrium analysis for a general multi-bottleneck TCP/AQM system and provide sufficient conditions for the uniqueness of an equilibrium point in the system. We then decompose the system into single-bottleneck subsystems and derive sufficient conditions for the local asymptotic stability of the subsystems. Using our framework, we develop an algorithm to compute the equilibrium point of the system. We further present a case study to analyze the stability of the recently proposed Controlled Delay (CoDel) in multi-bottleneck networks and devise Self-Tuning CoDel to improve the system stability. Extensive numerical and packet-level simulation results not only verify our theoretical studies but also show that our proposed Self-Tuning CoDel significantly stabilizes queueing delay in multi-bottleneck networks, thereby mitigating bufferbloat.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/pk98z-sbx87Line Failure Localization of Power Networks Part II: Cut Set Outages
https://resolver.caltech.edu/CaltechAUTHORS:20200707-095927831
Authors: {'items': [{'id': 'Guo-Linqi', 'name': {'family': 'Guo', 'given': 'Linqi'}, 'orcid': '0000-0001-5771-2752'}, {'id': 'Liang-Chen', 'name': {'family': 'Liang', 'given': 'Chen'}, 'orcid': '0000-0002-0015-7206'}, {'id': 'Zocca-Alessandro', 'name': {'family': 'Zocca', 'given': 'Alessandro'}, 'orcid': '0000-0001-6585-4785'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Wierman-A', 'name': {'family': 'Wierman', 'given': 'Adam'}}]}
Year: 2021
DOI: 10.1109/TPWRS.2021.3068048
Transmission line failure in power systems prop-agate non-locally, making the control of the resulting outages extremely difficult. In Part II of this paper, we continue the study of line failure localizability in transmission networks and characterize the impact of cut set outages. We establish a Simple Path Criterion, showing that the propagation pattern due to bridge outages, a special case of cut set failures, are fully determined by the positions in the network of the buses that participate in load balancing. We then extend our results to general cut set outages. In contrast to non-cut outages discussed in Part I whose subsequent line failures are contained within the original blocks, cut set outages typically impact the whole network, affecting the power flows on all remaining lines. We corroborate our analytical results in both parts using the IEEE 118-bus test system, in which the failure propagation patterns exhibit a clear block-diagonal structure predicted by our theory, even when using full AC power flow equations.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/5epx3-x6t87Line Failure Localization of Power Networks Part I: Non-Cut Outages
https://resolver.caltech.edu/CaltechAUTHORS:20200707-101019648
Authors: {'items': [{'id': 'Guo-Linqi', 'name': {'family': 'Guo', 'given': 'Linqi'}, 'orcid': '0000-0001-5771-2752'}, {'id': 'Liang-Chen', 'name': {'family': 'Liang', 'given': 'Chen'}, 'orcid': '0000-0002-0015-7206'}, {'id': 'Zocca-Alessandro', 'name': {'family': 'Zocca', 'given': 'Alessandro'}, 'orcid': '0000-0001-6585-4785'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Wierman-A', 'name': {'family': 'Wierman', 'given': 'Adam'}}]}
Year: 2021
DOI: 10.1109/tpwrs.2021.3066336
Transmission line failures in power systems propagate non-locally, making the control of the resulting outages extremely difficult. In this work, we establish a mathematical theory that characterizes the patterns of line failure propagation and localization in terms of network graph structure. It provides a novel perspective on distribution factors that precisely captures Kirchhoff's Law in terms of topological structures. Our results show that the distribution of specific collections of subtrees of the transmission network plays a critical role on the patterns of power redistribution, and motivates the block decomposition of the transmission network as a structure to understand long-distance propagation of disturbances. In Part I of this paper, we present the case when the post-contingency network remains connected after an initial set of lines are disconnected simultaneously. In Part II, we present the case when an outage separates the network into multiple islands.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/xtnd5-5ye52Conditions for Exact Convex Relaxation and No Spurious Local Optima
https://resolver.caltech.edu/CaltechAUTHORS:20210510-075841014
Authors: {'items': [{'id': 'Zhou-Fengyu', 'name': {'family': 'Zhou', 'given': 'Fengyu'}, 'orcid': '0000-0002-2639-6491'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2021
DOI: 10.1109/TCNS.2021.3112758
Non-convex optimization problems can be approximately solved via relaxation or local algorithms. For many practical problems such as optimal power flow (OPF) problems, both approaches tend to succeed in the sense that relaxation is usually exact and local algorithms usually converge to a global optimum. In this paper, we study conditions which are sufficient or necessary for such non-convex problems to simultaneously have exact relaxation and no spurious local optima. Those conditions help us explain the widespread empirical experience that local algorithms for OPF problems often work extremely well.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/4kk8d-6v016Adaptive Charging Networks: A Framework for Smart Electric Vehicle Charging
https://resolver.caltech.edu/CaltechAUTHORS:20210503-115705210
Authors: {'items': [{'id': 'Lee-Zachary-J', 'name': {'family': 'Lee', 'given': 'Zachary J.'}, 'orcid': '0000-0002-5358-2388'}, {'id': 'Lee-George-S', 'name': {'family': 'Lee', 'given': 'George'}}, {'id': 'Lee-Ted', 'name': {'family': 'Lee', 'given': 'Ted'}, 'orcid': '0000-0002-5793-7457'}, {'id': 'Jin-Cheng-S', 'name': {'family': 'Jin', 'given': 'Cheng'}}, {'id': 'Lee-Rand', 'name': {'family': 'Lee', 'given': 'Rand'}}, {'id': 'Low-Zhi-H', 'name': {'family': 'Low', 'given': 'Zhi'}, 'orcid': '0000-0003-4962-7771'}, {'id': 'Chang-Daniel', 'name': {'family': 'Chang', 'given': 'Daniel'}}, {'id': 'Ortega-Christine', 'name': {'family': 'Ortega', 'given': 'Christine'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2021
DOI: 10.1109/TSG.2021.3074437
We describe the architecture and algorithms of the Adaptive Charging Network (ACN), which was first deployed on the Caltech campus in early 2016 and is currently operating at over 100 other sites in the United States. The architecture enables real-time monitoring and control and supports electric vehicle (EV) charging at scale. The ACN adopts a flexible Adaptive Scheduling Algorithm based on convex optimization and model predictive control and allows for significant over-subscription of electrical infrastructure. We describe some of the practical challenges in real-world charging systems, including unbalanced three-phase infrastructure, non-ideal battery charging behavior, and quantized control signals. We demonstrate how the Adaptive Scheduling Algorithm handles these challenges, and compare its performance against baseline algorithms from the deadline scheduling literature using real workloads recorded from the Caltech ACN and accurate system models. We find that in these realistic settings, our scheduling algorithm can improve operator profit by 3.4 times over uncontrolled charging and consistently outperforms baseline algorithms when delivering energy in highly congested systems.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/f00wy-s1473Learning-based Predictive Control via Real-time Aggregate Flexibility
https://resolver.caltech.edu/CaltechAUTHORS:20210510-084600512
Authors: {'items': [{'id': 'Li-Tongxin', 'name': {'family': 'Li', 'given': 'Tongxin'}, 'orcid': '0000-0002-9806-8964'}, {'id': 'Sun-Bo', 'name': {'family': 'Sun', 'given': 'Bo'}, 'orcid': '0000-0003-3172-7811'}, {'id': 'Chen-Yue', 'name': {'family': 'Chen', 'given': 'Yue'}, 'orcid': '0000-0002-7594-7587'}, {'id': 'Ye-Zixin', 'name': {'family': 'Ye', 'given': 'Zixin'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Wierman-A', 'name': {'family': 'Wierman', 'given': 'Adam'}}]}
Year: 2021
DOI: 10.1109/TSG.2021.3094719
Aggregators have emerged as crucial tools for the coordination of distributed, controllable loads. To be used effectively, an aggregator must be able to communicate the available flexibility of the loads they control, as known as the aggregate flexibility to a system operator. However, most of existing aggregate flexibility measures often are slow-timescale estimations and much less attention has been paid to real-time coordination between an aggregator and an operator. In this paper, we consider solving an online optimization in a closed-loop system and present a design of real-time aggregate flexibility feedback, termed the maximum entropy feedback (MEF). In addition to deriving analytic properties of the MEF, combining learning and control, we show that it can be approximated using reinforcement learning and used as a penalty term in a novel control algorithm – the penalized predictive control (PPC), which modifies vanilla model predictive control (MPC). The benefits of our scheme are (1). Efficient Communication . An operator running PPC does not need to know the exact states and constraints of the loads, but only the MEF. (2). Fast Computation . The PPC often has much less number of variables than an MPC formulation. (3). Lower Costs We show that under certain regularity assumptions, the PPC is optimal. We illustrate the efficacy of the PPC using a dataset from an adaptive electric vehicle charging network and show that PPC outperforms classical MPC.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/j0s8j-1aa33ACN-Sim: An Open-Source Simulator for Data-Driven Electric Vehicle Charging Research
https://resolver.caltech.edu/CaltechAUTHORS:20210510-085201964
Authors: {'items': [{'id': 'Lee-Zachary-J', 'name': {'family': 'Lee', 'given': 'Zachary J.'}, 'orcid': '0000-0002-5358-2388'}, {'id': 'Sharma-Sunash', 'name': {'family': 'Sharma', 'given': 'Sunash'}, 'orcid': '0000-0002-8763-5927'}, {'id': 'Johansson-Daniel', 'name': {'family': 'Johansson', 'given': 'Daniel'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2021
DOI: 10.1109/TSG.2021.3103156
ACN-Sim is a data-driven, open-source simulation environment designed to accelerate research in the field of smart electric vehicle (EV) charging. It fills the need in this community for a widely available, realistic simulation environment in which researchers can evaluate algorithms and test assumptions. ACN-Sim provides a modular, extensible architecture, which models the complexity of real charging systems, including battery charging behavior and unbalanced three-phase infrastructure. It also integrates with a broader ecosystem of research tools. These include ACN-Data, an open dataset of EV charging sessions, which provides realistic simulation scenarios and ACN-Live, a framework for field-testing charging algorithms. It also integrates with grid simulators like MATPOWER, PandaPower and OpenDSS, and OpenAI Gym for training reinforcement learning agents.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/s94ac-pr864Exploiting Linear Models for Model-Free Nonlinear Control: A Provably Convergent Policy Gradient Approach
https://resolver.caltech.edu/CaltechAUTHORS:20220628-677879700
Authors: {'items': [{'id': 'Qu-Guannan', 'name': {'family': 'Qu', 'given': 'Guannan'}, 'orcid': '0000-0002-5466-3550'}, {'id': 'Yu-Chenkai', 'name': {'family': 'Yu', 'given': 'Chenkai'}, 'orcid': '0000-0001-8683-7773'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Wierman-A', 'name': {'family': 'Wierman', 'given': 'Adam'}, 'orcid': '0000-0002-5923-0199'}]}
Year: 2021
DOI: 10.1109/cdc45484.2021.9683735
Model-free learning-based control methods have seen great success recently. However, such methods typically suffer from poor sample complexity and limited convergence guarantees. This is in sharp contrast to classical model-based control, which has a rich theory but typically requires strong modeling assumptions. In this paper, we combine the two approaches. We consider a dynamical system with both linear and non-linear components and use the linear model to define a warm start for a model-free, policy gradient method. We show this hybrid approach outperforms the model-based controller while avoiding the convergence issues associated with model-free approaches via both numerical experiments and theoretical analyses, in which we derive sufficient conditions on the non-linear component such that our approach is guaranteed to converge to the (nearly) global optimal controller.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/p99an-mjp78DeepOPF-V: Solving AC-OPF Problems Efficiently
https://resolver.caltech.edu/CaltechAUTHORS:20210510-075001060
Authors: {'items': [{'id': 'Huang-Wanjun', 'name': {'family': 'Huang', 'given': 'Wanjun'}, 'orcid': '0000-0002-6851-3705'}, {'id': 'Pan-Xiang', 'name': {'family': 'Pan', 'given': 'Xiang'}, 'orcid': '0000-0002-6565-2339'}, {'id': 'Chen-Minghua', 'name': {'family': 'Chen', 'given': 'Minghua'}, 'orcid': '0000-0003-4763-0037'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2022
DOI: 10.1109/TPWRS.2021.3114092
AC optimal power flow (AC-OPF) problems need to be solved more frequently in the future to maintain stable and economic power system operation. To tackle this challenge, a deep neural network-based voltage-constrained approach (DeepOPF-V) is proposed to solve AC-OPF problems with high computational efficiency. Its unique design predicts voltages of all buses and then uses them to reconstruct the remaining variables without solving non-linear AC power flow equations. A fast post-processing process is also developed to enforce the box constraints. The effectiveness of DeepOPF-V is validated by simulations on IEEE 118/300-bus systems and a 2000-bus test system. Compared with existing studies, DeepOPF-V achieves decent computation speedup up to four orders of magnitude and comparable performance in optimality gap, while preserving feasibility of the solution.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/5tnxk-4aj52Robustness and Consistency in Linear Quadratic Control with Untrusted Predictions
https://resolver.caltech.edu/CaltechAUTHORS:20210716-225846876
Authors: {'items': [{'id': 'Li-Tongxin', 'name': {'family': 'Li', 'given': 'Tongxin'}, 'orcid': '0000-0002-9806-8964'}, {'id': 'Yang-Ruixiao', 'name': {'family': 'Yang', 'given': 'Ruixiao'}}, {'id': 'Qu-Guannan', 'name': {'family': 'Qu', 'given': 'Guannan'}, 'orcid': '0000-0002-5466-3550'}, {'id': 'Shi-Guanya', 'name': {'family': 'Shi', 'given': 'Guanya'}, 'orcid': '0000-0002-9075-3705'}, {'id': 'Yu-Chenkai', 'name': {'family': 'Yu', 'given': 'Chenkai'}, 'orcid': '0000-0001-8683-7773'}, {'id': 'Wierman-A', 'name': {'family': 'Wierman', 'given': 'Adam'}, 'orcid': '0000-0002-5923-0199'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2022
DOI: 10.1145/3508038
We study the problem of learning-augmented predictive linear quadratic control. Our goal is to design a controller that balances consistency, which measures the competitive ratio when predictions are accurate, and robustness, which bounds the competitive ratio when predictions are inaccurate.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/p10m3-kqj37Stability Constrained Reinforcement Learning for Real-Time Voltage Control
https://resolver.caltech.edu/CaltechAUTHORS:20220304-172338061
Authors: {'items': [{'id': 'Shi-Yuanyuan', 'name': {'family': 'Shi', 'given': 'Yuanyuan'}, 'orcid': '0000-0002-6182-7664'}, {'id': 'Qu-Guannan', 'name': {'family': 'Qu', 'given': 'Guannan'}, 'orcid': '0000-0002-5466-3550'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Anandkumar-A', 'name': {'family': 'Anandkumar', 'given': 'Anima'}, 'orcid': '0000-0002-6974-6797'}, {'id': 'Wierman-A', 'name': {'family': 'Wierman', 'given': 'Adam'}, 'orcid': '0000-0002-5923-0199'}]}
Year: 2022
DOI: 10.48550/arXiv.2109.14854
Deep reinforcement learning (RL) has been recognized as a promising tool to address the challenges in real-time control of power systems. However, its deployment in real-world power systems has been hindered by a lack of formal stability and safety guarantees. In this paper, we propose a stability constrained reinforcement learning method for real-time voltage control in distribution grids and we prove that the proposed approach provides a formal voltage stability guarantee. The key idea underlying our approach is an explicitly constructed Lyapunov function that certifies stability. We demonstrate the effectiveness of the approach in case studies, where the proposed method can reduce the transient control cost by more than 30\% and shorten the response time by a third compared to a widely used linear policy, while always achieving voltage stability. In contrast, standard RL methods often fail to achieve voltage stability.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/39nvc-h9r75Online Station Assignment for Electric Vehicle Battery Swapping
https://resolver.caltech.edu/CaltechAUTHORS:20201209-153308228
Authors: {'items': [{'id': 'You-Pengcheng', 'name': {'family': 'You', 'given': 'Pengcheng'}, 'orcid': '0000-0003-1532-8773'}, {'id': 'Pang-John-Z-F', 'name': {'family': 'Pang', 'given': 'John Z. F.'}, 'orcid': '0000-0002-6485-7922'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2022
DOI: 10.1109/tits.2020.3033731
This paper investigates the online station assignment for (commercial) electric vehicles (EVs) that request battery swapping from a central operator, i.e., in the absence of future information a battery swapping service station has to be assigned instantly to each EV upon its request. Based on EVs' locations, the availability of fully-charged batteries at service stations in the system, as well as traffic conditions, the assignment aims to minimize cost to EVs and congestion at service stations. Inspired by a polynomial-time offline solution via a bipartite matching approach, we develop an efficient and implementable online station assignment algorithm that provably achieves the tight (optimal) competitive ratio under mild conditions. Monte Carlo experiments on a real transportation network by Baidu Maps show that our algorithm performs reasonably well on realistic inputs, even with a certain amount of estimation error in parameters.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/wnzah-8xz59Smoothed Least-Laxity-First Algorithm for Electric Vehicle Charging: Online Decision and Performance Analysis with Resource Augmentation
https://resolver.caltech.edu/CaltechAUTHORS:20220127-230706500
Authors: {'items': [{'id': 'Chen-Niangjun', 'name': {'family': 'Chen', 'given': 'Niangjun'}, 'orcid': '0000-0002-2289-9737'}, {'id': 'Kurniawan-Christian', 'name': {'family': 'Kurniawan', 'given': 'Christian'}, 'orcid': '0000-0002-3178-4042'}, {'id': 'Nakahira-Yorie', 'name': {'family': 'Nakahira', 'given': 'Yorie'}, 'orcid': '0000-0003-3324-4602'}, {'id': 'Chen-Lijun', 'name': {'family': 'Chen', 'given': 'Lijun'}, 'orcid': '0000-0001-6694-4299'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2022
DOI: 10.1109/tsg.2021.3138615
Adaptive charging can charge electric vehicles (EVs) at scale cost effectively, despite of the uncertainty in EV arrivals. We formulate adaptive EV charging as a feasibility problem that meets all EVs' energy demands before their deadlines while satisfying constraints in charging rate and total charging power. We propose an online algorithm, smoothed least-laxity-first (sLLF), that decides the current charging rates without the knowledge of future arrivals and demands. We characterize the performance of the sLLF algorithm analytically and numerically. Numerical experiments with real-world data show that it has a significantly higher rate of feasible EV charging than several other existing EV charging algorithms. Resource augmentation framework is employed to assess the feasibility condition of the algorithm. The assessment shows that the sLLF algorithm achieves perfect feasibility with only a 7% increase in the maximal power supply of the charging station.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/61zpj-ex175Stability Constrained Reinforcement Learning for Real-Time Voltage Control
https://resolver.caltech.edu/CaltechAUTHORS:20230315-336401000.3
Authors: {'items': [{'id': 'Shi-Yuanyuan', 'name': {'family': 'Shi', 'given': 'Yuanyuan'}, 'orcid': '0000-0002-6182-7664'}, {'id': 'Qu-Guannan', 'name': {'family': 'Qu', 'given': 'Guannan'}, 'orcid': '0000-0002-5466-3550'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Anandkumar-A', 'name': {'family': 'Anandkumar', 'given': 'Anima'}, 'orcid': '0000-0002-6974-6797'}, {'id': 'Wierman-A', 'name': {'family': 'Wierman', 'given': 'Adam'}, 'orcid': '0000-0002-5923-0199'}]}
Year: 2022
DOI: 10.23919/acc53348.2022.9867476
Deep reinforcement learning (RL) has been recognized as a promising tool to address the challenges in real-time control of power systems. However, its deployment in real-world power systems has been hindered by a lack of formal stability and safety guarantees. In this paper, we propose a stability constrained reinforcement learning method for real-time voltage control in distribution grids and we prove that the proposed approach provides a formal voltage stability guarantee. The key idea underlying our approach is an explicitly constructed Lyapunov function that certifies stability. We demonstrate the effectiveness of the approach in case studies, where the proposed method can reduce the transient control cost by more than 30% and shorten the response time by a third compared to a widely used linear policy, while always achieving voltage stability. In contrast, standard RL methods often fail to achieve voltage stability.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/rqwbe-dd932Robustness and Consistency in Linear Quadratic Control with Untrusted Predictions
https://resolver.caltech.edu/CaltechAUTHORS:20220802-839213000
Authors: {'items': [{'id': 'Li-Tongxin', 'name': {'family': 'Li', 'given': 'Tongxin'}, 'orcid': '0000-0002-9806-8964'}, {'id': 'Yang-Ruixiao', 'name': {'family': 'Yang', 'given': 'Ruixiao'}}, {'id': 'Qu-Guannan', 'name': {'family': 'Qu', 'given': 'Guannan'}, 'orcid': '0000-0002-5466-3550'}, {'id': 'Shi-Guanya', 'name': {'family': 'Shi', 'given': 'Guanya'}, 'orcid': '0000-0002-9075-3705'}, {'id': 'Yu-Chenkai', 'name': {'family': 'Yu', 'given': 'Chenkai'}, 'orcid': '0000-0001-8683-7773'}, {'id': 'Wierman-A', 'name': {'family': 'Wierman', 'given': 'Adam'}, 'orcid': '0000-0002-5923-0199'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2022
DOI: 10.1145/3489048.3522658
We study the problem of learning-augmented predictive linear quadratic control. Our goal is to design a controller that balances "consistency", which measures the competitive ratio when predictions are accurate, and "robustness", which bounds the competitive ratio when predictions are inaccurate. We propose a novel λ-confident controller and prove that it maintains a competitive ratio upper bound of 1 + min {O(λ²ε)+ O(1-λ)²,O(1)+O(λ²)} where λ∈ [0,1] is a trust parameter set based on the confidence in the predictions, and ε is the prediction error. Further, motivated by online learning methods, we design a self-tuning policy that adaptively learns the trust parameter λ with a competitive ratio that depends on ε and the variation of system perturbations and predictions. We show that its competitive ratio is bounded from above by 1+O(ε) /(Θ)(1)+Θ(ε))+O(μVar) where μVar measures the variation of perturbations and predictions. It implies that by automatically adjusting the trust parameter online, the self-tuning scheme ensures a competitive ratio that does not scale up with the prediction error ε.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/qb28c-gj814Reinforcement Learning for Selective Key Applications in Power Systems: Recent Advances and Future Challenges
https://resolver.caltech.edu/CaltechAUTHORS:20220307-188369000
Authors: {'items': [{'id': 'Chen-Xin', 'name': {'family': 'Chen', 'given': 'Xin'}, 'orcid': '0000-0002-0952-0008'}, {'id': 'Qu-Guannan', 'name': {'family': 'Qu', 'given': 'Guannan'}, 'orcid': '0000-0002-5466-3550'}, {'id': 'Tang-Yujie', 'name': {'family': 'Tang', 'given': 'Yujie'}, 'orcid': '0000-0002-4921-8372'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Li-Na', 'name': {'family': 'Li', 'given': 'Na'}, 'orcid': '0000-0001-9545-3050'}]}
Year: 2022
DOI: 10.1109/tsg.2022.3154718
With large-scale integration of renewable generation and distributed energy resources, modern power systems are confronted with new operational challenges, such as growing complexity, increasing uncertainty, and aggravating volatility. Meanwhile, more and more data are becoming available owing to the widespread deployment of smart meters, smart sensors, and upgraded communication networks. As a result, data-driven control techniques, especially reinforcement learning (RL), have attracted surging attention in recent years. This paper provides a comprehensive review of various RL techniques and how they can be applied to decision-making and control in power systems. In particular, we select three key applications, i.e., frequency regulation, voltage control, and energy management, as examples to illustrate RL-based models and solutions. We then present the critical issues in the application of RL, i.e., safety, robustness, scalability, and data. Several potential future directions are discussed as well.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/1mttm-4w433Running Primal-Dual Gradient Method for Time-Varying Nonconvex Problems
https://resolver.caltech.edu/CaltechAUTHORS:20220811-235221000
Authors: {'items': [{'id': 'Tang-Yujie', 'name': {'family': 'Tang', 'given': 'Yujie'}, 'orcid': '0000-0002-4921-8372'}, {'id': "Dall'Anese-Emiliano", 'name': {'family': "Dall'Anese", 'given': 'Emiliano'}}, {'id': 'Bernstein-Andrey', 'name': {'family': 'Bernstein', 'given': 'Andrey'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2022
DOI: 10.1137/20m1371063
This paper focuses on a time-varying constrained nonconvex optimization problem, and considers the synthesis and analysis of online regularized primal-dual gradient methods to track a Karush--Kuhn--Tucker (KKT) trajectory. The proposed regularized primal-dual gradient method is implemented in a running fashion, in the sense that the underlying optimization problem changes during the execution of the algorithms. In order to study its performance, we first derive its continuous-time limit as a system of differential inclusions. We then study sufficient conditions for tracking a KKT trajectory, and also derive asymptotic bounds for the tracking error (as a function of the time-variability of a KKT trajectory). Further, we provide a set of sufficient conditions for the KKT trajectories not to bifurcate or merge, and also investigate the optimal choice of the parameters of the algorithm. Illustrative numerical results for a time-varying nonconvex problem are provided.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/02jhx-97p42DeepOPF: A Feasibility-Optimized Deep Neural Network Approach for AC Optimal Power Flow Problems
https://resolver.caltech.edu/CaltechAUTHORS:20221010-454096500.22
Authors: {'items': [{'id': 'Pan-Xiang', 'name': {'family': 'Pan', 'given': 'Xiang'}, 'orcid': '0000-0002-6565-2339'}, {'id': 'Chen-Minghua', 'name': {'family': 'Chen', 'given': 'Minghua'}, 'orcid': '0000-0003-4763-0037'}, {'id': 'Zhao-Tianyu', 'name': {'family': 'Zhao', 'given': 'Tianyu'}, 'orcid': '0000-0002-9541-0197'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2022
DOI: 10.1109/jsyst.2022.3201041
To cope with increasing uncertainty from renewable generation and flexible load, grid operators need to solve alternative current optimal power flow (AC-OPF) problems more frequently for efficient and reliable operation. In this article, we develop a deep neural network (DNN) approach, called DeepOPF, for solving AC-OPF problems in a fraction of the time used by conventional iterative solvers. A key difficulty for applying machine learning techniques for solving AC-OPF problems lies in ensuring that the obtained solutions respect the equality and inequality physical and operational constraints. Generalized a prediction-and-reconstruction procedure in our previous studies, DeepOPF first trains a DNN model to predict a set of independent operating variables and then directly compute the remaining ones by solving the power flow equations. Such an approach not only preserves the power-flow balance equality constraints but also reduces the number of variables to be predicted by the DNN, cutting down the number of neurons and training data needed. DeepOPF then employs a penalty approach with a zero-order gradient estimation technique in the training process toward guaranteeing the inequality constraints. We also drive a condition for tuning the DNN size according to the desired approximation accuracy, which measures its generalization capability. It provides theoretical justification for using DNN to solve AC-OPF problems. Simulation results for IEEE 30/118/300-bus and a synthetic 2000-bus test cases demonstrate the effectiveness of the penalty approach. They also show that DeepOPF speeds up the computing time by up to two orders of magnitude as compared to a state-of-the-art iterative solver, at the expense of < 0.2% cost difference.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/pvbnj-1nm65Towards balanced three-phase charging: Phase optimization in adaptive charging networks
https://resolver.caltech.edu/CaltechAUTHORS:20221010-449776900.1
Authors: {'items': [{'id': 'Ye-Zixin', 'name': {'family': 'Ye', 'given': 'Zixin'}, 'orcid': '0000-0002-4107-3842'}, {'id': 'Li-Tongxin', 'name': {'family': 'Li', 'given': 'Tongxin'}, 'orcid': '0000-0002-9806-8964'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2022
DOI: 10.1016/j.epsr.2022.108322
We study the problem of phase optimization for electric-vehicle (EV) charging. We formulate our problem as a non-convex mixed-integer programming problem whose objective is to minimize the charging loss. Despite the hardness of directly solving this non-convex problem, we solve a relaxation of the original problem by proposing the PXA algorithm where "P", "X", and "A" stand for three variable matrices in the formed phase optimization problems. We show that under certain conditions, the solution is given by the PXA precisely converges to the global optimum. In addition, using the idea of model predictive control (MPC), we design the PXA-MPC, which is an online implementation of the PXA. Compared to other empirical phase balancing strategies, the PXA algorithm significantly improves the charging performance by maximizing energy delivery, minimizing charging price, and assisting future energy planning. The efficacy of our algorithm is demonstrated using data collected from a real-world adaptive EV charging network (ACN).https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/8k3x6-7ec55Dispatch-aware planning for feasible power system operation
https://resolver.caltech.edu/CaltechAUTHORS:20221011-128968500.6
Authors: {'items': [{'id': 'Christianson-Nicolas-H', 'name': {'family': 'Christianson', 'given': 'Nicolas'}, 'orcid': '0000-0001-8330-8964'}, {'id': 'Werner-Lucien-D', 'name': {'family': 'Werner', 'given': 'Lucien'}}, {'id': 'Wierman-A', 'name': {'family': 'Wierman', 'given': 'Adam'}, 'orcid': '0000-0002-5923-0199'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2022
DOI: 10.1016/j.epsr.2022.108597
Maintaining stable energy production with increasing penetration of variable renewable energy requires sufficient flexible generation resources and dispatch algorithms that accommodate renewables' uncertainty. In this work, we study the feasibility properties of real-time economic dispatch (RTED) algorithms and establish fundamental limits on their performance. We propose a joint methodology for resource procurement and online economic dispatch with guaranteed feasibility. Our algorithm, Feasible Fixed Horizon Control (FFHC) is a regularized form of Receding Horizon Control (RHC) that balances exploitation of good near-term demand predictions with feasibility requirements. Empirical evaluation of FFHC in comparison to the standard RHC on realistic load profiles highlights that FFHC achieves near-optimal performance while ensuring feasibility in high-ramp scenarios where RHC becomes infeasible.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/tmnrt-9y586Inverse Power Flow Problem
https://resolver.caltech.edu/CaltechAUTHORS:20230502-984953000.1
Authors: {'items': [{'id': 'Yuan-Ye', 'name': {'family': 'Yuan', 'given': 'Ye'}, 'orcid': '0000-0001-7858-0437'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Ardakanian-Omid', 'name': {'family': 'Ardakanian', 'given': 'Omid'}, 'orcid': '0000-0002-6711-5502'}, {'id': 'Tomlin-Claire-J', 'name': {'family': 'Tomlin', 'given': 'Claire J.'}, 'orcid': '0000-0003-3192-3185'}]}
Year: 2023
DOI: 10.1109/tcns.2022.3199084
We formulate an inverse power flow problem that infers a nodal admittance matrix from voltage and current phasors measured at a number of buses. We show that the admittance matrix can be uniquely identified from a sequence of measurements corresponding to different steady states when every node in the system is equipped with a measurement device, and a Kron-reduced admittance matrix can be determined even if some nodes in the system are not monitored (hidden nodes). We propose an effective algorithm to uncover the actual admittance matrix of a radial system with hidden nodes from its Kron-reduced admittance matrix.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/99twq-8jn27An Energy Sharing Mechanism Considering Network Constraints and Market Power Limitation
https://resolver.caltech.edu/CaltechAUTHORS:20230502-727238500.2
Authors: {'items': [{'id': 'Chen-Yue', 'name': {'family': 'Chen', 'given': 'Yue'}, 'orcid': '0000-0002-7594-7587'}, {'id': 'Zhao-Changhong', 'name': {'family': 'Zhao', 'given': 'Changhong'}, 'orcid': '0000-0003-0539-8591'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Wierman-A', 'name': {'family': 'Wierman', 'given': 'Adam'}, 'orcid': '0000-0002-5923-0199'}]}
Year: 2023
DOI: 10.1109/tsg.2022.3198721
As the number of prosumers with distributed energy resources (DERs) grows, the conventional centralized operation scheme may suffer from conflicting interests, privacy concerns, and incentive inadequacy. In this paper, we propose an energy sharing mechanism to address the above challenges. It takes into account network constraints and fairness among prosumers. In the proposed energy sharing market, all prosumers play a generalized Nash game. The market equilibrium is proved to have nice features in a large market or when it is a variational equilibrium. To deal with the possible market failure, inefficiency, or instability in general cases, we introduce a price regulation policy to avoid market power exploitation. The improved energy sharing mechanism with price regulation can guarantee the existence and uniqueness of a socially near-optimal market equilibrium. Some advantageous properties are proved, such as the prosumer's individual rationality, a sharing price structure similar to the locational marginal price, and the tendency towards social optimum with an increasing number of prosumers. For implementation, a practical bidding algorithm is developed with a convergence condition. Experimental results validate the theoretical outcomes and show the practicability of our model and method.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/npwrx-d8m85DeepOPF-AL: Augmented Learning for Solving AC-OPF Problems with a Multi-Valued Load-Solution Mapping
https://authors.library.caltech.edu/records/4h351-qdc18
Authors: {'items': [{'id': 'Pan-Xiang', 'name': {'family': 'Pan', 'given': 'Xiang'}, 'orcid': '0000-0001-9108-944X'}, {'id': 'Huang-Wanjun', 'name': {'family': 'Huang', 'given': 'Wanjun'}, 'orcid': '0000-0002-6851-3705'}, {'id': 'Chen-Minghua', 'name': {'family': 'Chen', 'given': 'Minghua'}, 'orcid': '0000-0003-4763-0037'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2023
DOI: 10.1145/3575813.3576874
<p>The existence of multi-valued load-solution mapping in general non-convex problems poses a fundamental challenge to deep neural network (DNN) schemes. A well-trained DNN in the existing supervised learning framework fails to learn the multi-valued mapping accurately and generates inferior solutions. We propose augmented learning as a methodological framework to tackle this challenge. We focus on AC-OPF as an important example and develop DeepOPF-AL to solve it. The main idea is to train a DNN to learn a single-valued mapping from an augmented input, i.e., (load, initial point), to the solution generated by an iterative OPF solver with the load and initial point as intake. We then apply the learned augmented mapping to solve AC-OPF problems much faster than conventional solvers. Simulation results over IEEE test cases show that DeepOPF-AL achieves noticeably better optimality and similar feasibility and speedup performance as compared to a recent DNN scheme, with the same DNN size yet larger training-data size. We believe the augmented-learning approach will find applications in various problems with a multi-valued input-solution mapping.</p>https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/4h351-qdc18Pricing Uncertainty in Stochastic Multi-Stage Electricity Markets
https://authors.library.caltech.edu/records/bns0y-j6t74
Authors: {'items': [{'id': 'Werner-Lucien', 'name': {'family': 'Werner', 'given': 'Lucien'}}, {'id': 'Christianson-Nicolas', 'name': {'family': 'Christianson', 'given': 'Nicolas'}, 'orcid': '0000-0001-8330-8964'}, {'id': 'Zocca-Alessandro', 'name': {'family': 'Zocca', 'given': 'Alessandro'}, 'orcid': '0000-0001-6585-4785'}, {'id': 'Wierman-A', 'name': {'family': 'Wierman', 'given': 'Adam'}, 'orcid': '0000-0002-5923-0199'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2023
DOI: 10.1109/cdc49753.2023.10384022
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<div>This work proposes a pricing mechanism for multi-stage electricity markets that does not explicitly depend on the choice of dispatch procedure or optimization method. Our approach is applicable to a wide range of methodologies for the economic dispatch of power systems under uncertainty, including multi-interval dispatch, multi-settlement markets, scenario-based dispatch, and chance-constrained dispatch policies. We prove that our pricing scheme provides both ex-ante and expost dispatch-following incentives by simultaneously supporting per-stage and ex-post competitive equilibria. In numerical experiments on a ramp-constrained test system, we demonstrate the benefits of scheduling under uncertainty and show how our price decomposes into components corresponding to energy, intertemporal coupling, and uncertainty.</div>
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</div>https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/bns0y-j6t74Modeling Unbalanced Power Flow with Δ-connected Devices
https://authors.library.caltech.edu/records/2sgyc-4rz86
Authors: {'items': [{'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2023
DOI: 10.1109/cdc49753.2023.10383695
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<div>In this tutorial we present a simple approach to modeling unbalanced three-phase power flows. We allow general non-ideal models of voltage sources, ZIP loads as well as distribution lines and transformers. The basic idea is to explicitly separate a device/transformer model into an internal model, that depends on the characteristics of the single-phase devices or transformers, and a conversion rule, that depends on their configuration. This approach provides two benefits. First it facilitates the modeling of secondary distribution circuits where only the end devices are directly controllable, not the currents or powers at the secondary transformers. Second it allows us to exploit common structures across different device/transformer variants and derive their external models that are general and unified. We illustrate these benefits by extending a three-phase backward forward sweep method in the literature to allow secondary circuits and formulating a three-phase optimal power flow problem as a quadratically constrained quadratic program.</div>
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</div>https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/2sgyc-4rz86Convergence of Backward/Forward Sweep for Power Flow Solution in Radial Networks
https://authors.library.caltech.edu/records/jedfs-0zx20
Authors: {'items': [{'id': 'Fang-Bohang', 'name': {'family': 'Fang', 'given': 'Bohang'}, 'orcid': '0009-0004-1055-4872'}, {'id': 'Zhao-Changhong', 'name': {'family': 'Zhao', 'given': 'Changhong'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2023
DOI: 10.1109/cdc49753.2023.10383981
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<div>Solving power flow is perhaps the most fundamental calculation related to the steady state behavior of alternating-current (AC) power systems. The normally radial (tree) topology of a distribution network induces a spatially recursive structure in power flow equations, which enables a class of efficient solution methods called backward/forward sweep (BFS). In this paper, we revisit BFS from a new perspective, focusing on its convergence. Specifically, we describe a general formulation of BFS, interpret it as a special Gauss-Seidel algorithm, and then illustrate it in a single-phase power flow model. We prove a sufficient condition under which the BFS is a contraction mapping on a closed set of safe voltages and thus converges geometrically to a unique power flow solution. We verify the convergence condition, as well as the accuracy and computational efficiency of BFS, through numerical experiments in IEEE test systems.</div>
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</div>https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/jedfs-0zx20Stability Constrained Reinforcement Learning for Decentralized Real-Time Voltage Control
https://authors.library.caltech.edu/records/v26v8-j6q25
Authors: {'items': [{'id': 'Feng-Jie', 'name': {'family': 'Feng', 'given': 'Jie'}, 'orcid': '0000-0002-5049-9423'}, {'id': 'Shi-Yuanyuan', 'name': {'family': 'Shi', 'given': 'Yuanyuan'}, 'orcid': '0000-0002-6182-7664'}, {'id': 'Qu-Guannan', 'name': {'family': 'Qu', 'given': 'Guannan'}, 'orcid': '0000-0002-5466-3550'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Anandkumar-A', 'name': {'family': 'Anandkumar', 'given': 'Anima'}, 'orcid': '0000-0002-6974-6797'}, {'id': 'Wierman-A', 'name': {'family': 'Wierman', 'given': 'Adam'}, 'orcid': '0000-0002-5923-0199'}]}
Year: 2023
DOI: 10.1109/tcns.2023.3338240
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<div>Deep reinforcement learning has been recognized as a promising tool to address the challenges in real-time control of power systems. However, its deployment in real-world power systems has been hindered by a lack of explicit stability and safety guarantees. In this paper, we propose a stability-constrained reinforcement learning (RL) method for real-time implementation of voltage control, that guarantees system stability both during policy learning and deployment of the learned policy. The key idea underlying our approach is an explicitly constructed Lyapunov function that leads to a sufficient structural condition for stabilizing policies, i.e., monotonically decreasing policies guarantee stability. We incorporate this structural constraint with RL, by parameterizing each local voltage controller using a monotone neural network, thus ensuring the stability constraint is satisfied by design. We demonstrate the effectiveness of our approach in both single-phase and three-phase IEEE test feeders, where the proposed method can reduce the transient control cost by more than 26.7% and shorten the voltage recovery time by 23.6% on average compared to the widely used linear policy, while always achieving voltage stability. In contrast, standard RL methods often fail to achieve voltage stability.</div>
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</div>https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/v26v8-j6q25