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Sökning: WFRF:(Sou Kin Cheong)

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1.
  • Andréasson, Niclas, 1976, et al. (författare)
  • An Introduction to Continuous Optimization, 3rd edition
  • 2016
  • Bok (övrigt vetenskapligt/konstnärligt)abstract
    • This is the third edition of a book that was originally published in 2005. The book is used primarily in the teaching of the Chalmers course TMA947 Nonlinear Optimization.
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2.
  • Hendrickx, Julien M., et al. (författare)
  • Efficient Computations of a Security Index for False Data Attacks in Power Networks
  • 2014
  • Ingår i: IEEE Transactions on Automatic Control. - 0018-9286 .- 1558-2523. ; 59:12, s. 3194-3208
  • Tidskriftsartikel (refereegranskat)abstract
    • The resilience of Supervisory Control and Data Acquisition (SCADA) systems for electric power networks for certain cyber-attacks is considered. We analyze the vulnerability of the measurement system to false data attack on communicated measurements. The vulnerability analysis problem is shown to be NP-hard, meaning that unless P = NP there is no polynomial time algorithm to analyze the vulnerability of the system. Nevertheless, we identify situations, such as the full measurement case, where the analysis problem can be solved efficiently. In such cases, we show indeed that the problem can be cast as a generalization of the minimum cut problem involving nodes with possibly nonzero costs. We further show that it can be reformulated as a standard minimum cut problem (without node costs) on a modified graph of proportional size. An important consequence of this result is that our approach provides the first exact efficient algorithm for the vulnerability analysis problem under the full measurement assumption. Furthermore, our approach also provides an efficient heuristic algorithm for the general NP-hard problem. Our results are illustrated by numerical studies on benchmark systems including the IEEE 118-bus system.
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3.
  • Shi, Guodong, et al. (författare)
  • A graph-theoretic approach on optimizing informed-node selection in multi-agent tracking control
  • 2014
  • Ingår i: Physica D-Nonlinear Phenomena. - : Elsevier BV. - 0167-2789 .- 1872-8022. ; 267, s. 104-111
  • Tidskriftsartikel (refereegranskat)abstract
    • A graph optimization problem for a multi-agent leader follower problem is considered. In a multi-agent system with n followers and one leader, each agent's goal is to track the leader using the information obtained from its neighbors. The neighborhood relationship is defined by a directed communication graph where k agents, designated as informed agents, can become neighbors of the leader. This paper establishes that, for any given strongly connected communication graph with k informed agents, all agents will converge to the leader. In addition, an upper bound and a lower bound of the convergence rate are obtained. These bounds are shown to explicitly depend on the maximal distance from the leader to the followers. The dependence between this distance and the exact convergence rate is verified by empirical studies. Then we show that minimizing the maximal distance problem is a metric k-center problem in classical combinatorial optimization studies, which can be approximately solved. Numerical examples are given to illustrate the properties of the approximate solutions. (C) 2013 Elsevier B.V. All rights reserved.
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4.
  • Sootla, Aivar, et al. (författare)
  • Frequency Domain Model Reduction Method for Parameter-Dependent Systems
  • 2010
  • Ingår i: ; , s. 3082-3087, s. 3082-3087
  • Konferensbidrag (refereegranskat)abstract
    • In this paper a modification of a recently proposed model simplification method for linear time invariant parameterized models is presented. It is able to obtain models with explicit parameter dependence. The method is based on convex optimization with semidefinite constraints. Computation of the reduced model requires only the frequency samples of the full one, hence it is possible to apply the methods to large-scale models. Numerical examples showing the drawbacks and the advantages of the method are also presented.
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5.
  • Sootla, Aivar, et al. (författare)
  • Parametrized model reduction based on semidefinite programming
  • 2013
  • Ingår i: Automatica. - : Elsevier BV. - 0005-1098. ; 49:9, s. 2840-2844
  • Tidskriftsartikel (refereegranskat)abstract
    • A parametrized model in addition to the control and state-space variables depends on time-independent design parameters, which essentially define a family of models. The goal of parametrized model reduction is to approximate this family of models. In this paper, a reduction method for linear time-invariant (LTI) parametrized models is presented, which constitutes the development of a recently proposed reduction approach. Reduced order models are computed based on the finite number of frequency response samples of the full order model. This method uses a semidefinite relaxation, while enforcing stability on the reduced order model for all values of parameters of interest. As a main theoretical statement, the relaxation gap (the ratio between upper and lower bounds) is derived, which validates the relaxation. The proposed method is flexible in adding extra constraints (e.g., passivity can be enforced on reduced order models) and modifying the objective function (e.g., frequency weights can be added to the minimization criterion). The performance of the method is validated on a numerical example. (C) 2013 Elsevier Ltd. All rights reserved.
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6.
  • Sou, Kin Cheong, et al. (författare)
  • A Quasi-Convex Optimization Approach to Parameterized Model Order Reduction
  • 2005
  • Ingår i: 42nd Design Automation Conference, Proceedings 2005. ; , s. 933-938
  • Konferensbidrag (refereegranskat)abstract
    • In this paper an optimization based model order reduction (MOR) framework is proposed. The method involves setting up a quasiconvexprogram that explicitly minimizes a relaxation of the optimal H∞ norn MOR problem. The method generates guaranteedstable and passive reduced models and it is very flexible in imposingadditional constraints. The proposed optimization approach isalso extended to parameterized model reduction problem (PMOR).The proposed method is compared to existing moment matchingand optimization based MOR methods in several examples. APMOR model for a large RF inductor is also constructed.
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7.
  • Sou, Kin Cheong, et al. (författare)
  • A Quasi-Convex Optimization Approach to Parameterized Model Order Reduction
  • 2008
  • Ingår i: IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems. - 0278-0070 .- 1937-4151. ; 27:3, s. 456-469
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper, an optimization-based model orderreduction (MOR) framework is proposed. The method involvessetting up a quasi-convex program that solves a relaxation of theoptimal H∞ norm MOR problem. The method can generate guaranteedstable and passive reduced models and is very flexible inimposing additional constraints such as exact matching of specificfrequency response samples. The proposed optimization-basedapproach is also extended to solve the parameterized modelreductionproblem (PMOR). The proposed method is compared to existing moment matching and optimization-basedMOR methodsin several examples. PMOR models for large RF inductors oversubstrate and power-distribution grid are also constructed.
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8.
  • Sou, Kin Cheong, et al. (författare)
  • A Singular Value Decomposition Based Closed Loop Stability Preserving Controller Reduction Method
  • 2010
  • Ingår i: 2010 AMERICAN CONTROL CONFERENCE. - 0743-1619. - 9781424474264 ; , s. 1079-1084
  • Konferensbidrag (refereegranskat)abstract
    • In this paper a controller reduction method whichpreserves closed loop stability is described. A Lyapunov inequalitybased sufficient condition is proposed in the search ofthe reduced controller. The reduced controller leads to a stableclosed loop system with guaranteed approximation quality. Furthermore,the proposed problem can be formulated as a matrixapproximation problem which can be solved efficiently usingsingular value decomposition. Numerical application examplesare shown in the end to evaluate the generality of the proposedreduction method.
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9.
  • Sou, Kin Cheong, et al. (författare)
  • A SVD Based Controller Reduction Method
  • 2010
  • Ingår i: SICE Annual Conference 2010, SICE 2010. - 9784907764364 ; , s. 2564-2569
  • Konferensbidrag (refereegranskat)abstract
    • In this paper an efficient controller reduction method which guarantees closed loop stability is described. The reduced controller is obtained by solving a generalized controllability Grammian type Lyapunov inequality. This Lyapunov inequality based reduced controller search can be formulated as a generalized minimum rank matrix approximation problem to which an efficient singular value decomposition based solution procedure is available. This paper contains theoretical and numerical results on the merit of the proposed reduction method.
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10.
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11.
  • Sou, Kin Cheong, et al. (författare)
  • Bounding L2 Gain System Error Due to Approximations of the Nonlinear Vector Field
  • 2007
  • Ingår i: Proceedings of the IEEE Conference on Computer-Aided Design. ; , s. 879-886
  • Konferensbidrag (refereegranskat)abstract
    • Typical nonlinear model order reduction approachesneed to address two issues: reducing the order ofthe model, and approximating the vector field. In this paperwe focus exclusively on the second issue, and present resultscharacterizing the repercussions at the system level of vector fieldapproximations. The error assessment problem is formulatedas the L2 gain upper bounding problem of a scaled feedbackinterconnection. Applying the small gain theorem in the proposedsetup, we prove that the L2 gain of the error system is upperbounded by the L2 gain of the vector field approximationerror, provided it is small. In addition, the paper also presentsa numerical procedure, based on the IQC/LMI approach, toperform the error estimation task with less conservatism. Anumerical example is given in this paper to demonstrate thepractical implications of the presented results.
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12.
  • Sou, Kin Cheong, et al. (författare)
  • Computing critical k-tuples in power networks
  • 2012
  • Ingår i: IEEE Transactions on Power Systems. - 0885-8950 .- 1558-0679. ; 27:3, s. 1511-1520
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper the problem of finding the sparsest (i.e., minimum cardinality) critical k-tuple including one arbitrarily specified measurement is considered. The solution to this problem can be used to identify weak points in the measurement set, or aid the placement of new meters. The critical k-tuple problem is a combinatorial generalization of the critical measurement calculation problem. Using topological network observability results, this paper proposes an efficient and accurate approximate solution procedure for the considered problem based on solving a minimum-cut (Min-Cut) problem and enumerating all its optimal solutions. It is also shown that the sparsest critical k -tuple problem can be formulated as a mixed integer linear programming (MILP) problem. This MILP problem can be solved exactly using available solvers such as CPLEX and Gurobi. A detailed numerical study is presented to evaluate the efficiency and the accuracy of the proposed Min-Cut and MILP calculations.
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13.
  • Sou, Kin Cheong, et al. (författare)
  • Controller reduction via minimum rank matrix approximation
  • 2012
  • Ingår i: Automatica. - : Elsevier BV. - 0005-1098 .- 1873-2836. ; 48:6, s. 1069-1076
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper a controller reduction method for discrete-time linear time-invariant systems is described. Using the bounded-real lemma, the proposed method generates reduced controllers with closed loop stability and H∞ norm performance guarantee. Information of the full controller is used as a basis for reduction using singular value decomposition. This is different from traditional model reduction schemes such as weighted balanced truncation. Numerical assessment of the proposed method is given in the end of the paper.
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14.
  • Sou, Kin Cheong, et al. (författare)
  • Controller Reduction with Closed Loop Performance Guarantee
  • 2010
  • Ingår i: IEEE Conference on Decision and Control. ; , s. 6207-6212
  • Konferensbidrag (refereegranskat)abstract
    • This paper describes a modification of a singular value decomposition (SVD) based controller reduction method recently proposed in \cite{SR10}. Instead of formulating a $\mathcal{H}_2$ norm characterizing generalized controllability Gramian inequality as in the previous case, the current method applies the bounded-real lemma to certify the closed loop performances in $\mathcal{H}_\infty$ norm. In addition, unlike the previous method, the current one does not suffer from the lack of symmetry that all the data from the plant is not utilized. Yet, the current method inherits the same merit as the previous one that the formulated problem can be solved as a generalized minimum rank matrix approximation problem which can be solved efficiently using SVD. Extensions and numerical examples are shown in the end.
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15.
  • Sou, Kin Cheong, et al. (författare)
  • Convex Relaxation Approach to the Identification of the Wiener-Hammerstein Model
  • 2008
  • Ingår i: Proceedings of the 47th IEEE Conference on Decision and Control. ; , s. 1375-1382
  • Konferensbidrag (refereegranskat)abstract
    • In this paper, an input/output system identificationtechnique for the Wiener-Hammerstein model and its feedbackextension is proposed. In the proposed framework, the identificationof the nonlinearity is non-parametric. The identificationproblem can be formulated as a non-convex quadratic program(QP). A convex semidefinite programming (SDP) relaxation isthen formulated and solved to obtain a sub-optimal solution tothe original non-convex QP. The convex relaxation turns out tobe tight in most cases. Combined with the use of local search,high quality solutions to the Wiener-Hammerstein identificationcan frequently be found. As an application example, randomlygenerated Wiener-Hammerstein models are identified.
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16.
  • Sou, Kin Cheong, et al. (författare)
  • Data Attack Isolation in Power Networks Using Secure Voltage Magnitude Measurements
  • 2014
  • Ingår i: IEEE Transactions on Smart Grid. - 1949-3053 .- 1949-3061. ; 5:1, s. 14-28
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper a procedure to detect and isolate data attacks on power network power flow measurements is proposed. This method can be used in conjunction with available bad data detection (BDD) methods to isolate multiple bad data which are otherwise difficult to handle. The proposed procedure relies on secure measurements of bus voltage magnitudes to define a measurement residual using potentially compromised active and reactive power flow measurements on transmission lines. The proposed residual can be calculated in real-time. In addition, the component of the proposed residual on any particular line depends only locally on the component of the data attack on the same line. This makes the proposed residual well-suited for distributed data attack isolation in large-scale power networks. Furthermore, it can be shown that the proposed procedure becomes more effective when measurements from multiple time instances can be utilized. A detailed numerical case study on the IEEE 14-bus benchmark system demonstrates the effectiveness of the proposed procedure.
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17.
  • Sou, Kin Cheong, et al. (författare)
  • Detection and identification of data attacks in power system
  • 2012
  • Ingår i: American Control Conference (ACC), 2012. - : IEEE Computer Society. - 9781457710957 ; , s. 3651-3656
  • Konferensbidrag (refereegranskat)abstract
    • In this paper a power system state estimator cyber-attack detection and identification scheme is presented. The proposed scheme considers the information from both the active power measurements and the reactive power measurements. Under the scenario that the network operator can take multiple different samples of measurements and the attackers can attack only once, the proposed scheme can detect the presence of what has been described as stealth (or unobservable) attacks. The detection is provably correct. Furthermore, if an attack is present, the proposed scheme can identify exactly the attacked transmission lines.
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18.
  • Sou, Kin Cheong, et al. (författare)
  • Electric Power Network Security Analysis via Minimum Cut Relaxation
  • 2011
  • Ingår i: 50th IEEE Conference on Decision and Control and European Control Conference.
  • Konferensbidrag (refereegranskat)abstract
    • In this paper an efficient computation schemefor analyzing the security of power transmission networks ispresented. In order to strategically allocate protection devicesin the network, the problem of finding the sparsest stealthy falsedata attack to the state estimator is studied. While the attacksearch problem is traditionally solved as a generic constrainedcardinality minimization problem, this paper exploits the problemstructure intrinsic to the power network application toobtain a polynomial time approximate algorithm based on aminimum cut relaxation. Experiment results from realistic testcases are presented to demonstrate the efficiency and accuracyof the proposed algorithm.
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19.
  • Sou, Kin Cheong, 1979, et al. (författare)
  • Energy and CO2 efficient scheduling of smart home appliances
  • 2013
  • Ingår i: 2013 European Control Conference, ECC 2013. - 9783033039629 ; , s. 4051-4058
  • Konferensbidrag (refereegranskat)abstract
    • A major goal of smart grid technology (e.g., smart meters) is to provide consumers with demand response signals such as electricity tariff and CO 2 footprint so that the consumers can consciously control their electricity consumption patterns. These demand response signals provide incentives for the consumers to help reduce peak energy demand by load balancing, as this is particularly relevant in a situation with high level of renewable energy penetration. However, the volume of information can be overwhelming for the consumers. Further, in some situation minimization of electricity bill and CO2 emission can be conflicting goals and a trade-off analysis is required. To enable the consumers to participate in smart grid effort this paper proposes a decision aiding framework for optimal household appliances scheduling and trade-off analysis through Pareto frontier exploration. To compute the optimal schedules associated with Pareto optimal points, linear optimization problems with SOS2 (special ordered set of type 2) constraints are solved using CPLEX, in the case where the demand response signals are assumed to be piecewise constant. For arbitrary demand response signals, a corresponding dynamic programming solution is proposed. A numerical study demonstrates that in a realistic test case the Pareto frontier analysis can provide valuable information leading to schedules with drastically different electricity and CO2 emission patterns. In addition, the case study verifies that the Pareto frontier can be computed in real-time in a realistic residential computing environment.
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20.
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21.
  • Sou, Kin Cheong, et al. (författare)
  • Exact LASSO solutions for a class of constrained cardinality minimization problems
  • Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
    • This paper shows that the least absolute shrinkage and selection operator (LASSO) can provide an exact optimal solution to a special type of constrained cardinality minimization problem, which is motivated from a sensor network measurement robustness analysis problem. The constraint matrix of the considered problem is totally unimodular. This is shown to imply that LASSO leads to a tight linear programming relaxation of the considered cardinality minimization problem. The presented result is based on a deterministic argument, which differs from other well-known deterministic results for LASSO such as mutual incoherence and restricted isometry property. There exist cases given in this paper where the proposed result is applicable, while mutual incoherence and restricted isometry property are not.
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22.
  • Sou, Kin Cheong, et al. (författare)
  • Fast time-domain simulation for large-order linear time-invariant state space systems
  • 2005
  • Ingår i: International Journal for Numerical Methods in Engineering. - : Wiley. - 0029-5981 .- 1097-0207. ; 63:5, s. 681-708
  • Tidskriftsartikel (refereegranskat)abstract
    • Time-domain simulation is essential for both analysis and design of complex systems. Unfortunately, high model fidelity leads to large system size and bandwidths, often causing excessive computation and memory saturation. In response we develop an efficient scheme for large-order linear time-invariant systems. First, the A matrix is block diagonalized. Then, subsystems of manageable dimensions and bandwidth are formed, allowing multiple sampling rates. Each subsystem is then discretized using a O(n(s)) scheme, where n(s) is the number of states. Subsequently, a sparse matrix O(n(s)) discrete-time system solver is employed to compute the history of the state and output. Finally, the response of the original system is obtained by superposition. In practical engineering applications, closing feedback loops and cascading filters can hinder the efficient use of the simulation scheme. Solutions to these problems are addressed in the paper. The simulation scheme, implemented as a MATLAB function fast1sim, is benchmarked against the standard LTI system simulator 1sim and is shown to be superior for medium to large systems. The algorithm scales close to O(n(s)(2)) for a set of benchmarked systems. Simulation of a high-fidelity model (n ≈ 2200) of the Space Interferometry Mission spacecraft illustrates real world application of the method.
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23.
  • Sou, Kin Cheong, 1979 (författare)
  • Minimum equivalent precedence relation systems
  • 2015
  • Ingår i: 54th IEEE Conference on Decision and Control, CDC 2015, Osaka, Japan, 15-18 December 2015. - 0743-1546 .- 2576-2370. - 9781479978861 ; , s. 3299-3304
  • Konferensbidrag (refereegranskat)abstract
    • In this paper two related simplification problems for systems of linear inequalities describing precedence relation systems are considered. Given a precedence relation system, the first problem seeks a minimum equivalent subset of the precedence relations (i.e., inequalities) which has the same solution set as that of the original system. The second problem is similar to the first one, but the minimum equivalent system need not be a subset of the original system. This paper shows that the first problem is NP-hard. However, a sufficient condition is derived under which the first problem is solvable in polynomial-time. In addition, a decomposition of the first problem into independent tractable and intractable subproblems is derived. The second problem is shown to be solvable in polynomial-time, with a full parameterization of all solutions described. The results in this paper generalize those in [Moyles and Thompson 1969, Aho, Garey, and Ullman 1972] for the minimum equivalent graph problem and transitive reduction problem, which are applicable to unweighted directed graphs.
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24.
  • Sou, Kin Cheong, 1979, et al. (författare)
  • Nonserial Dynamic Programming with Applications in Smart Home Appliances Scheduling - Part I : Precedence Graph Simplification
  • 2014
  • Ingår i: 2014 European Control Conference (ECC). - : IEEE. - 9783952426913 ; , s. 1643-1648
  • Konferensbidrag (refereegranskat)abstract
    • In this and a companion paper a dynamic programming (DP) approach to solve a smart home appliances scheduling problem is considered. The challenge with solving the scheduling problem is the coupling of decision variables due to some time precedence constraints. In general, the system of precedence constraints may contain redundant constraints that offer opportunities for simplification. This simplification is desirable for reducing the computation effort of the nonserial DP procedure presented in the companion paper (i.e., Part II). The current paper establishes the uniqueness of the maximum set of redundant constraints and its polynomial-time solvability with optimality guarantee, under the sufficient and necessary condition that the precedence graph (a graph representation of the precedence constraints system) does not contain any cycle with nonnegative weight. A numerical case study indicates the efficiency of the proposed simplification algorithm versus the brute-force enumerative search. Besides helping to reduce the computation effort in the DP procedure described in the companion paper, the algorithm in the current paper solves a generalization of a precedence graph simplification problem arising from application areas such as parallel computing.
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25.
  • Sou, Kin Cheong, 1979, et al. (författare)
  • Nonserial Dynamic Programming with Applications in Smart Home Appliances Scheduling - Part II : Nonserial Dynamic Programming
  • 2014
  • Ingår i: 2014 European Control Conference (ECC). - : IEEE. - 9783952426913 ; , s. 1663-1668
  • Konferensbidrag (refereegranskat)abstract
    • In this paper a dynamic programming (DP) solution approach to a nonconvex resource allocation problem (RAP) is presented. The problem in this paper generalizes the smart home appliances scheduling problem introduced in the companion paper (i.e., Part I). The computation difficulty with solving the RAP depends on the decision variable coupling, which can be described by an interaction graph. This paper proposes a DP algorithm to solve the RAP in the special setting where the interaction graph is a tree. This extends the applicability result of DP to RAP beyond the standard serial case where the interaction graph is a line. The extension of the result is achieved by establishing that even in the tree case DP computation effort is polynomial in the number of decision variables. For RAP in its general form, this paper proposes a modification to the nonserial DP procedure originally introduced by Bertele and Brioschi. Contrary to that of the previous method, the computation effort of the proposed method can be characterized by a well-known minimum feedback vertex set problem. Case studies on known examples indicate that both nonserial DP methods are similarly efficient.
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26.
  • Sou, Kin Cheong, et al. (författare)
  • On a generalized matrix approximation problem in the spectral norm
  • 2012
  • Ingår i: Linear Algebra and Its Applications. - : Elsevier BV. - 1873-1856 .- 0024-3795. ; 436:7, s. 2331-2341
  • Tidskriftsartikel (refereegranskat)abstract
    • Abstract in UndeterminedIn this paper theoretical results regarding a generalized minimum rank matrix approximation problem in the spectral norm are presented. An alternative solution expression for the generalized matrix approximation problem is obtained. This alternative expression provides a simple characterization of the achievableminimum rank, which is shown to be the same as the optimal objective value of the classical problem considered by Eckart–Young–Schmidt–Mirsky, as long as the generalized problem is feasible. In addition, this paper provides a result on a constrained version of the matrix approximation problem, establishing that the later problem is solvable via singular value decomposition.
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27.
  • Sou, Kin Cheong, et al. (författare)
  • On the Exact Solution to a Smart Grid Cyber-Security Analysis Problem
  • 2013
  • Ingår i: IEEE Transactions on Smart Grid. - : IEEE Press. - 1949-3053 .- 1949-3061. ; 4:2, s. 856-865
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper considers a smart grid cyber-security problem analyzing the vulnerabilities of electric power networks to false data attacks. The analysis problem is related to a constrained cardinality minimization problem. The main result shows that an l1 relaxation technique provides an exact optimal solution to this cardinality minimization problem. The proposed result is based on a polyhedral combinatorics argument. It is different from well-known results based on mutual coherence and restricted isometry property. The results are illustrated on benchmarks including the IEEE 118-bus, IEEE 300-bus and the Polish 2383-bus and 2736-bus systems.
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28.
  • Sou, Kin Cheong, et al. (författare)
  • On the Minimum Rank of a Generalized Matrix Approximation Problem in the Maximum Singular Value Norm
  • 2010
  • Ingår i: Proceedings of the 19th International Symposium on Mathematical Theory of Networks and Systems, MTNS 2010. ; , s. 227-234
  • Konferensbidrag (refereegranskat)abstract
    • In this paper theoretical results regarding a generalizedminimum rank matrix approximation problem in themaximum singular value norm are presented. Using the idea ofprojection, the considered problem can be shown to be equivalentto a classical minimum rank matrix approximation whichcan be solved efficiently using singular value decomposition. Inaddition, as long as the generalized problem is feasible, it isshown to have exactly the same optimal objective value as thatof the classical problem. Certain comments and extensions ofthe presented theorem are included in the end of the paper.
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29.
  • Sou, Kin Cheong, et al. (författare)
  • Resilient Scheduling of Control Software Updates in Power Distribution Systems
  • 2022
  • Ingår i: 2022 IEEE 61ST CONFERENCE ON DECISION AND CONTROL (CDC). - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 6146-6153
  • Konferensbidrag (refereegranskat)abstract
    • In response to newly found security vulnerabilities, or as part of a moving target defense, a fast and safe control software update scheme for networked control systems is highly desirable. We here develop such a scheme for intelligent electronic devices (IEDs) in power distribution systems, which is a solution to the so-called software update rollout problem. This problem seeks to minimize the makespan of the software rollout, while at the same time guaranteeing acceptable voltage and current levels at all buses despite possible worst-case update failure where malfunctioning IEDs may inject harmful amount of power into the system. Utilizing the nonlinear DistFlow equations, we can rewrite the voltage and current conditions as a set of load and network dependent linear inequalities with respect to the rollout schedule with quantifiable degree of conservatism. Assuming update failure detectors such as out-of-range voltage relays, the optimal software rollout schedule can be time-slotted so that the rollout problem can be reformulated as a variant of the classical combinatorial bin packing problem. Demonstration with a realistic distribution system benchmark is provided to verify the practical significance of our work.
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30.
  • Sou, Kin Cheong, et al. (författare)
  • Resilient Scheduling of Control Software Updates in Radial Power Distribution Systems
  • 2023
  • Ingår i: IEEE Transactions on Control of Network Systems. - : Institute of Electrical and Electronics Engineers (IEEE). - 2325-5870. ; , s. 1-12
  • Tidskriftsartikel (refereegranskat)abstract
    • In response to newly found security vulnerabilities, or as part of a moving target defense, a fast and safe control software update scheme for networked control systems is highly desirable. We here develop such a scheme for intelligent electronic devices (IEDs) in power distribution systems, which is a solution to the so-called software update rollout problem. This problem seeks to minimize the makespan of the software rollout, while guaranteeing safety in voltage and current at all buses and lines despite possible worst-case update failure where malfunctioning IEDs may inject harmful amounts of power into the system. Based on the nonlinear DistFlow equations, we derive linear relations relating software update decisions to the worst-case voltages and currents, leading to a decision model both tractable and more accurate than previous models based on the popular linearized DistFlow equations. Under reasonable protection assumptions, the rollout problem can be formulated as a vector bin packing problem and instances can be built and solved using scalable computations. Using realistic benchmarks including one with 10,476 buses, we demonstrate that the proposed method can generate safe and effective rollout schedules in real-time.
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31.
  • Sou, Kin Cheong, et al. (författare)
  • Scheduling Smart Home Appliances Using Mixed Integer Linear Programming
  • 2011
  • Ingår i: 50th IEEE Conference on Decsion and Control and European Control Conference. - : IEEE.
  • Konferensbidrag (refereegranskat)abstract
    • This paper considers the minimum electricity costscheduling problem of smart home appliances. Operation characteristics,such as expected duration and peak power consumptionof the smart appliances, can be adjusted through a powerprofile signal. The optimal power profile signal minimizes cost,while satisfying technical operation constraints and consumerpreferences. Constraints such as enforcing uninterruptible andsequential operations are modeled in the proposed frameworkusing mixed integer linear programming (MILP). Several realisticscenarios based on actual spot price are considered,and the numerical results provide insight into tariff design.Computational issues and extensions of the proposed schedulingframework are also discussed.
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32.
  • Teixeira, André, et al. (författare)
  • Quantifying Cyber-Security for Networked Control Systems
  • 2013
  • Ingår i: Control of Cyber-Physical Systems. - Switzerland : Springer International Publishing. - 0170-8643. - 9783319011585 ; , s. 123-142
  • Bokkapitel (refereegranskat)abstract
    • In this paper we consider a typical architecture for a networked control system under false-data injection attacks. Under a previously proposed adversary modeling framework, various formulations for quantifying cyber-security of control systems are proposed and formulated as constrained optimization problems. These formulations capture trade-offs in terms of attack impact on the control performance, attack detectability, and adversarial resources. The formulations are then discussed and related to system theoretic concepts, followed by numerical examples illustrating the various trade-offs for a quadruple-tank process.
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33.
  • Teixeira, André, et al. (författare)
  • Secure control systems : A quantitative risk management approach
  • 2015
  • Ingår i: IEEE Control Systems. - 1066-033X. ; 35:1, s. 24-45
  • Tidskriftsartikel (refereegranskat)abstract
    • Critical infrastructures must continuously operate safely and reliably, despite a variety of potential system disturbances. Given their strict operating requirements, such systems are automated and controlled in real time by several digital controllers receiving measurements from sensors and transmitting control signals to actuators. Since these physical systems are often spatially distributed, there is a need for information technology (IT) infrastructures enabling the timely data flow between the system components. These networked control systems are ubiquitous in modern societies [1]. Examples include the electric power network, intelligent transport systems, and industrial processes.
  •  
34.
  • Teixeira, A., et al. (författare)
  • Secure Control Systems A Quantitative Risk Management Approach
  • 2015
  • Ingår i: Ieee Control Systems Magazine. - : Institute of Electrical and Electronics Engineers (IEEE). - 1066-033X .- 1941-000X. ; 35:1, s. 24-45
  • Tidskriftsartikel (refereegranskat)abstract
    • Critical infrastructures must continuously operate safely and reliably, despite a variety of potential system disturbances. Given their strict operating requirements, such systems are automated and controlled in real time by several digital controllers receiving measurements from sensors and transmitting control signals to actuators. Since these physical systems are often spatially distributed, there is a need for information technology (IT) infrastructures enabling the timely data flow between the system components. These networked control systems are ubiquitous in modern societies [1]. Examples include the electric power network, intelligent transport systems, and industrial processes.
  •  
35.
  • Vuković, Ognjen, et al. (författare)
  • Network-Aware Mitigation of Data Integrity Attacks on Power System State Estimation
  • 2012
  • Ingår i: IEEE Journal on Selected Areas in Communications. - 0733-8716 .- 1558-0008. ; 30:6, s. 1108-1118
  • Tidskriftsartikel (refereegranskat)abstract
    • Critical power system applications like contingency analysis and optimal power flow calculation rely on the power system state estimator. Hence the security of the state estimator is essential for the proper operation of the power system. In the future more applications are expected to rely on it, so that its importance will increase. Based on realistic models of the communication infrastructure used to deliver measurement data from the substations to the state estimator, in this paper we investigate the vulnerability of the power system state estimator to attacks performed against the communication infrastructure. We define security metrics that quantify the importance of individual substations and the cost of attacking individual measurements. We propose approximations of these metrics, that are based on the communication network topology only, and we compare them to the exact metrics. We provide efficient algorithms to calculate the security metrics. We use the metrics to show how various network layer and application layer mitigation strategies, like single and multi-path routing and data authentication, can be used to decrease the vulnerability of the state estimator. We illustrate the efficiency of the algorithms on the IEEE 118 and 300 bus benchmark power systems.
  •  
36.
  • Vuković, Ognjen, et al. (författare)
  • Network-layer protection schemes against stealth attacks on state estimators in power systems
  • 2011
  • Ingår i: IEEE SmartGridComm 2011. - : IEEE. - 9781457717024
  • Konferensbidrag (refereegranskat)abstract
    • The power system state estimator is an important application used to calculate optimal power flows, to maintain the system in a secure state, and to detect faulty equipment. Its importance in the operation of the smart grid is expected to increase, and therefore its security is an important concern. Based on a realistic model of the communication infrastructure used to deliver measurement data from the substations to the state estimator, in this paper we investigate the vulnerability of the power system state estimator to attacks performed against the communication infrastructure. We define security metrics that quantify the importance of individual substations and the cost of attacking individual measurements. We provide efficient algorithms to calculate these metrics, and use the metrics to show how various network layer and application layer mitigation strategies can be used to decrease the vulnerability of the state estimator. We illustrate the efficiency of the algorithms on the IEEE 118 and 300 bus benchmark power systems.
  •  
37.
  • Wanlu, Sun, 1986, et al. (författare)
  • D2D-based V2V Communications with Latency and Reliability Constraints
  • 2014
  • Ingår i: 2014 IEEE Globecom Workshops, GC Wkshps 2014; Austin; United States; 8 December 2014 through 12 December. - 9781479974702 ; , s. 1414-1419
  • Konferensbidrag (refereegranskat)abstract
    • Direct device-to-device (D2D) communication has been proposed as a possible enabler for vehicle-to-vehicle (V2V) applications, where the incurred intra-cell interference and the stringent latency and reliability requirements are challenging issues. In this paper, we investigate the radio resource management problem for D2D-based V2V communications. Firstly, we analyze and mathematically model the actual requirements for vehicular communications and traditional cellular links. Secondly, we propose a problem formulation to fulfill these requirements, and then a Separate Resource Block allocation and Power control (SRBP) algorithm to solve this problem. Finally, simulations are presented to illustrate the improved performance of the proposed SRBP scheme compared to some other existing methods.
  •  
38.
  • Wanlu, Sun, 1986, et al. (författare)
  • Radio Resource Management for D2D-based V2V Communication
  • 2016
  • Ingår i: IEEE Transactions on Vehicular Technology. - 0018-9545 .- 1939-9359. ; 65:8, s. 6636-6650
  • Tidskriftsartikel (refereegranskat)abstract
    • Direct device-to-device (D2D) communication has been proposed as a possible enabler for vehicle-to-vehicle (V2V) applications, where the incurred intra-cell interference and the stringent latency and reliability requirements are challenging issues. In this paper, we investigate the radio resource management problem for D2D-based V2V communications. Firstly, we analyze and mathematically model the actual requirements for vehicular communications and traditional cellular links. Secondly, we propose a problem formulation to fulfill these requirements, and then a Separate Resource Block allocation and Power control (SRBP) algorithm to solve this problem. Finally, simulations are presented to illustrate the improved performance of the proposed SRBP scheme compared to some other existing methods.
  •  
39.
  • Wu, Xuyang, et al. (författare)
  • A Fenchel dual gradient method enabling regularization for nonsmooth distributed optimization over time-varying networks
  • 2023
  • Ingår i: Optimization Methods and Software. - : Informa UK Limited. - 1055-6788 .- 1029-4937. ; 38:4, s. 813-836
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper, we develop a regularized Fenchel dual gradient method (RFDGM), which allows nodes in a time-varying undirected network to find a common decision, in a fully distributed fashion, for minimizing the sum of their local objective functions subject to their local constraints. Different from most existing distributed optimization algorithms that also cope with time-varying networks, RFDGM is able to handle problems with general convex objective functions and distinct local constraints, and still has non-asymptotic convergence results. Specifically, under a standard network connectivity condition, we show that RFDGM is guaranteed to reach ϵ-accuracy in both optimality and feasibility within (Formula presented.) iterations. Such iteration complexity can be improved to (Formula presented.) if the local objective functions are strongly convex but not necessarily differentiable. Finally, simulation results demonstrate the competence of RFDGM in practice.
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