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Attack detection and identification in cyberphysical systems
 IEEE Trans. Automat. Contr
"... Cyberphysical systems are ubiquitous in power systems, transportation networks, industrial process control and critical infrastructures. These systems need to operate reliably in the face of unforeseen failures and external malicious attacks. In this paper (i) we propose a mathematical framework fo ..."
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Cited by 30 (4 self)
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Cyberphysical systems are ubiquitous in power systems, transportation networks, industrial process control and critical infrastructures. These systems need to operate reliably in the face of unforeseen failures and external malicious attacks. In this paper (i) we propose a mathematical framework for cyberphysical systems, attacks, and monitors; (ii) we characterize fundamental monitoring limitations from systemtheoretic and graphtheoretic perspectives; and (iii) we design centralized and distributed attack detection and identification monitors. Finally, we validate our findings through compelling examples. I.
Distributed robust power system state estimation
 IEEE TRANS. POWER SYST
, 2013
"... Deregulation of energy markets, penetration of renewables, advanced metering capabilities, and the urge for situational awareness, all call for systemwide power system state estimation (PSSE). Implementing a centralized estimator though is practically infeasible due to the complexity scale of an i ..."
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Cited by 23 (3 self)
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Deregulation of energy markets, penetration of renewables, advanced metering capabilities, and the urge for situational awareness, all call for systemwide power system state estimation (PSSE). Implementing a centralized estimator though is practically infeasible due to the complexity scale of an interconnection, the communication bottleneck in realtime monitoring, regional disclosure policies, and reliability issues. In this context, distributed PSSE methods are treated here under a unified and systematic framework. A novel algorithm is developed based on the alternating direction method of multipliers. It leverages existing PSSE solvers, respects privacy policies, exhibits low communication load, and its convergence to the centralized estimates is guaranteed even in the absence of local observability. Beyond the conventional leastsquares based PSSE, the decentralized framework accommodates a robust state estimator. By exploiting interesting links to the compressive sampling advances, the latter jointly estimates the state and identifies corrupted measurements. The novel algorithms are numerically evaluated using the IEEE 14, 118bus, and a 4200bus benchmarks. Simulations demonstrate that the attainable accuracy can be reached within a few interarea exchanges, while largest residual tests are outperformed.
Probabilistic guarantees for the N1 security of systems with wind power generation
 International Conference on Probabilistic Methods Applied to Power Systems
, 2012
"... Abstract — This paper proposes a novel framework for designing a N1 secure generation dayahead dispatch for power systems with a high penetration of fluctuating power sources, e.g. wind or PV power. To achieve this, we integrate the security constraints in a DC optimal power flow optimization and ..."
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Cited by 20 (9 self)
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Abstract — This paper proposes a novel framework for designing a N1 secure generation dayahead dispatch for power systems with a high penetration of fluctuating power sources, e.g. wind or PV power. To achieve this, we integrate the security constraints in a DC optimal power flow optimization and formulate a stochastic program with chance constraints, which encode the probability of satisfying the transmission capacity constraints of the lines. To solve the resulting problem numerically, we transform the initial problem to a tractable one by using the so called scenario approach, which is based on sampling the uncertain parameter (in this paper the wind power) while keeping the desired probabilistic guarantees. To generate wind power scenarios a Markov chain based model is employed. To illustrate the effectiveness of the proposed technique we apply it to the IEEE 30bus network, and compare it with the solution of a deterministic variant of the problem, where the operator determines a secure generation dispatch based only on the available wind power forecast. A MonteCarlo simulation study is conducted to collect statistical results regarding the performance of our method.
Cyberphysical attacks in power networks: Models, fundamental limitations and monitor design
, 2011
"... Future power networks will be characterized by safe and reliable functionality against physical and cyber attacks. This paper proposes a unified framework and advanced monitoring procedures to detect and identify network components malfunction or measurements corruption caused by an omniscient adve ..."
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Cited by 17 (4 self)
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Future power networks will be characterized by safe and reliable functionality against physical and cyber attacks. This paper proposes a unified framework and advanced monitoring procedures to detect and identify network components malfunction or measurements corruption caused by an omniscient adversary. We model a power system under cyberphysical attack as a linear timeinvariant descriptor system with unknown inputs. Our attack model generalizes the prototypical stealth, (dynamic) falsedata injection and replay attacks. We characterize the fundamental limitations of both static and dynamic procedures for attack detection and identification. Additionally, we design provablycorrect (dynamic) detection and identification procedures based on tools from geometric control theory. Finally, we illustrate the effectiveness of our method through a comparison with existing (static) detection algorithms, and through a numerical study.
A LinearProgramming Approximation of AC Power Flows
, 2013
"... Linear activepoweronly DC power flow approximations are pervasive in the planning and control of power systems. However, these approximations fail to capture reactive power and voltage magnitudes, both of which are necessary in many applications to ensure voltage stability and AC power flow feasib ..."
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Cited by 17 (4 self)
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Linear activepoweronly DC power flow approximations are pervasive in the planning and control of power systems. However, these approximations fail to capture reactive power and voltage magnitudes, both of which are necessary in many applications to ensure voltage stability and AC power flow feasibility. This paper proposes linearprogramming models (the LPAC models) that incorporate reactive power and voltage magnitudes in a linear power flow approximation. The LPAC models are built on a convex approximation of the cosine terms in the AC equations, as well as Taylor approximations of the remaining nonlinear terms. Experimental comparisons with AC solutions on a variety of standard IEEE and MATPOWER benchmarks show that the LPAC models produce accurate values for active and reactive power, phase angles, and voltage magnitudes. The potential benefits of the LPAC models are illustrated on two “proofofconcept” studies in power restoration and capacitor placement.
Monitoring and Optimization for Power Grids: A Signal Processing Perspective
 IEEE SIGNAL PROCESSING MAGAZINE
, 2012
"... ..."
Chance Constrained Optimal Power Flow: RiskAware Network Control under Uncertainty
, 2012
"... Abstract. When uncontrollable resources fluctuate, Optimum Power Flow (OPF), routinely used by the electric power industry to redispatch hourly controllable generation (coal, gas and hydro plants) over control areas of transmission networks, can result in grid instability, and, potentially, cascadi ..."
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Cited by 16 (4 self)
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Abstract. When uncontrollable resources fluctuate, Optimum Power Flow (OPF), routinely used by the electric power industry to redispatch hourly controllable generation (coal, gas and hydro plants) over control areas of transmission networks, can result in grid instability, and, potentially, cascading outages. This risk arises because OPF dispatch is computed without awareness of major uncertainty, in particular fluctuations in renewable output. As a result, grid operation under OPF with renewable variability can lead to frequent conditions where power line flow ratings are significantly exceeded. Such a condition, which is borne by simulations of real grids, would likely resulting in automatic line tripping to protect lines from thermal stress, a risky and undesirable outcome which compromises stability. Smart grid goals include a commitment to large penetration of highly fluctuating renewables, thus calling to reconsider current practices, in particular the use of standard OPF. Our Chance Constrained (CC) OPF corrects the problem and mitigates dangerous renewable fluctuations with minimal changes in the current operational procedure. Assuming availability of a reliable wind forecast parameterizing the distribution function of the uncertain generation, our CCOPF satisfies all the constraints with high probability while simultaneously minimizing the cost of economic redispatch. CCOPF allows efficient implementation, e.g. solving a typical instance over the 2746bus Polish network in 20s on a standard laptop.
Spontaneous synchrony in powergrid networks
 IEEE 57 〈z(0)z(t)〉, ε≈0.02 p.u. 〈xT(0)x(t)〉, ε≈0.02 p.u. 〈z(0)z(t)〉, ε≈0.17 p.u. 〈xT(0)x(t)〉, ε≈ 0.17
, 2013
"... An imperative condition for the functioning of a powergrid network is that its power generators remain synchronized. Disturbances can prompt desynchronization, which is a process that has been involved in large power outages. Here we derive a condition under which the desired synchronous state of ..."
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Cited by 15 (1 self)
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An imperative condition for the functioning of a powergrid network is that its power generators remain synchronized. Disturbances can prompt desynchronization, which is a process that has been involved in large power outages. Here we derive a condition under which the desired synchronous state of a power grid is stable, and use this condition to identify tunable parameters of the generators that are determinants of spontaneous synchronization. Our analysis gives rise to an approach to specify parameter assignments that can enhance synchronization of any given network, which we demonstrate for a selection of both test systems and real power grids. Because our results concern spontaneous synchronization, they are relevant both for reducing dependence on conventional control devices, thus offering an additional layer of protection given that most power outages involve equipment or operational errors, and for contributing to the development of “smart grids ” that can recover from failures in real time. 1 ar
Controllability Metrics, Limitations and Algorithms for Complex Networks
"... Abstract — This paper studies the problem of controlling stable and symmetric complex networks, that is, the joint problem of selecting a set of control nodes and of designing a control input to drive a network to a target state. We adopt the smallest eigenvalue of the controllability Gramian as met ..."
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Cited by 14 (2 self)
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Abstract — This paper studies the problem of controlling stable and symmetric complex networks, that is, the joint problem of selecting a set of control nodes and of designing a control input to drive a network to a target state. We adopt the smallest eigenvalue of the controllability Gramian as metric for the controllability degree of a network, as it identifies the energy needed to accomplish the control task. In the first part of the paper we characterize tradeoffs between the control energy and the number of control nodes, based on the network topology and weights. Our bounds show for instance that, if the number of control nodes is constant, then the control energy increases exponentially with the number of network nodes. Consequently, despite the classic controllability notion, few nodes cannot in practice arbitrarily symmetric control complex networks. In the second part of the paper we propose a distributed openloop strategy with performance guarantees for the control of complex networks. In our strategy we select control nodes based on network partitioning, and we design the control input based on optimal and distributed control techniques. For our control strategy we show that the control energy depends on the controllability properties of the clusters and on their coupling strength, and it is independent of the network dimension. I.
Optimal placement of phasor measurement units via convex relaxation
 IEEE Trans. Power Syst
, 2012
"... Abstract—Instrumenting power networks with phasor measurement units (PMUs) facilitates several tasks including optimum power flow, system control, contingency analysis, visualization, and integration of renewable resources, thus enabling situational awareness—one of the key steps toward realizing th ..."
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Cited by 12 (2 self)
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Abstract—Instrumenting power networks with phasor measurement units (PMUs) facilitates several tasks including optimum power flow, system control, contingency analysis, visualization, and integration of renewable resources, thus enabling situational awareness—one of the key steps toward realizing the smart grid vision. The installation cost of PMUs currently prohibits their deployment on every bus, which in turn motivates their strategic placement across the power grid. As state estimation is at the core of grid monitoring, PMU deployment is optimized here based on estimationtheoretic criteria. Considering both voltage and incident current readings per PMUinstrumented bus and incorporating conventionally derived state estimates under the Bayesian framework, PMU placementisformulatedasanoptimal experimental design task. To bypass the combinatorial search involved, a convex relaxation is developed to obtain solutions with numerical optimality guarantees. In the tests performed on standard IEEE 14, 30, and 118bus benchmarks, the proposed relaxation approaches and oftentimes attains the optimum PMU placement. Index Terms—Gradient projection method, maximum aposteriori estimation, optimal experimental design, phasor measurement units, SCADA measurements, semidefinite programming. I.