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Power System Dynamic Simulations using a Parallel Two-level Schur-complement Decomposition ; ; Van Cutsem, Thierry in IEEE Transactions on Power Systems (in press) As the need for faster power system dynamic simulations increases, it is essential to develop new algorithms that exploit parallel computing to accelerate those simulations. This paper proposes a parallel ... [more ▼] As the need for faster power system dynamic simulations increases, it is essential to develop new algorithms that exploit parallel computing to accelerate those simulations. This paper proposes a parallel algorithm based on a two-level, Schur complement-based, domain decomposition method. The two-level partitioning provides high parallelization potential (coarse and fine-grained). In addition, due to the Schur-complement approach used to update the sub-domain interface variables, the algorithm exhibits high global convergence rate. Finally, it provides significant numerical and computational acceleration. The algorithm is implemented using the shared-memory parallel programming model, targeting inexpensive multi-core machines. Its performance is reported on a real system as well as on a large test system combining transmission and distribution networks. [less ▲] Detailed reference viewed: 126 (7 ULg)Trajectory-Based Supplementary Damping Control for Power System Electromechanical Oscillations Wang, Da ; Glavic, Mevludin ; Wehenkel, Louis in IEEE Transactions on Power Systems (2014), 29(6), 2835-2845 This paper considers a trajectory-based approach to determine control signals superimposed to those of existing controllers so as to enhance the damping of electromechanical oscillations. This approach is ... [more ▼] This paper considers a trajectory-based approach to determine control signals superimposed to those of existing controllers so as to enhance the damping of electromechanical oscillations. This approach is framed as a discrete-time, multi-step optimization problem which can be solved by model-based and/or by learning-based methods. This paper proposes to apply a model-free tree-based batch mode Reinforcement Learning (RL) algorithm to perform such a supplementary damping control based only on information collected from observed trajectories of the power system. This RL-based supplementary damping control scheme is first implemented on a single generator and then several possibilities are investigated for extending it to multiple generators. Simulations are carried out on a 16-generators medium size power system model, where also possible benefits of combining this RL-based control with Model Predictive Control (MPC) are assessed. [less ▲] Detailed reference viewed: 112 (11 ULg)A generic approach for solving nonlinear-discrete security-constrained power flow problems in large-scale systems ; ; et al in IEEE Transactions on Power Systems (2014), 29(3), 1194-1203 This paper proves the practicality of an iterative algorithm for solving realistic large-scale SCOPF problems. This algorithm is based on the combination of a contingency filtering scheme, used to ... [more ▼] This paper proves the practicality of an iterative algorithm for solving realistic large-scale SCOPF problems. This algorithm is based on the combination of a contingency filtering scheme, used to identify the binding contingencies at the optimum, and a network compression method, used to reduce the complexity of the post-contingency models included in the SCOPF formulation. We show that by combining these two complementary ideas, it is possible to solve in a reasonable time SCOPF problems on large power system models with a large number of contingencies. Unlike most results reported for large-scale SCOPF problems, our algorithm uses a non-linear AC network model in both pre-contingency and post-contingency states, optimizes both active/reactive powers flows jointly, and treats the discrete variables. The proposed algorithm is implemented with state-of-the-art solvers and applied to two systems: a national grid with 2563 buses and 1297 contingencies, and a model of the European transmission network with 9241 buses and 12000 contingencies. [less ▲] Detailed reference viewed: 82 (7 ULg)Accelerated and Localized Newton Schemes for Faster Dynamic Simulation of Large Power Systems ; ; et al in IEEE Transactions on Power Systems (2013), 28(4), 4936-4947 This paper proposes two methods to speed up the demanding time-domain simulations of large power system models. First, the sparse linear system to solve at each Newton iteration is decomposed according to ... [more ▼] This paper proposes two methods to speed up the demanding time-domain simulations of large power system models. First, the sparse linear system to solve at each Newton iteration is decomposed according to its bordered block diagonal structure, in order to solve only those parts that need to be solved, and update only sub-matrices of the Jacobian that need to be updated. This brings computational savings without degradation of accuracy. Next, the Jacobian structure is further exploited to localize the system response, i.e. involve only the components identified as active, with an acceptable and controllable decrease in accuracy. The accuracy and computational savings are assessed on a large-scale test system. [less ▲] Detailed reference viewed: 333 (61 ULg)Reconstructing and Tracking Network State from a Limited Number of Synchrophasor Measurements ; Van Cutsem, Thierry in IEEE Transactions on Power Systems (2013), 28 A method is proposed to reconstruct and track network state from a limited number of Phasor Measurement Unit (PMU) data. To deal with the resulting unobservability, the state with bus powers and generator ... [more ▼] A method is proposed to reconstruct and track network state from a limited number of Phasor Measurement Unit (PMU) data. To deal with the resulting unobservability, the state with bus powers and generator voltages closest to previously estimated values is computed. Those values, treated as pseudomeasurements, are obtained from the last reconstructed state, in a recursive manner. The method involves solving an optimization problem with linear constraints. It is scalable insofar as it accommodates from a few PMUs up to configurations ensuring full network observability. Reconstruction of only a region is possible. These and other features are demonstrated on the Nordic32 test system, with synchronized phasors obtained from detailed time simulation of a situation evolving towards instability. Suitable choices of PMU location and pseudo-measurements are also discussed. [less ▲] Detailed reference viewed: 247 (32 ULg)Computation of worst operation scenarios under uncertainty for static security management ; Wehenkel, Louis in IEEE Transactions on Power Systems (2013), 28(2), 1697-1705 This paper deals with day-ahead static security assessment with respect to a postulated set of contingencies while taking into account uncertainties about the next day system conditions. We propose a ... [more ▼] This paper deals with day-ahead static security assessment with respect to a postulated set of contingencies while taking into account uncertainties about the next day system conditions. We propose a heuristic approach to compute the worst-case under operation uncertainty for a contingency with respect to overloads. We formulate this problem as a non-convex nonlinear bilevel program that we solve approximately by a heuristic approach which relies on the solution of successive optimal power flow (OPF) and security-constrained optimal power flow (SCOPF) problems of a special type. The method aims at revealing those combinations of uncertainties and contingencies for which the best combination of preventive and corrective actions would not suffice to ensure security. Extensive numerical results on a small, a medium, and a very large system prove the interest of the approach. [less ▲] Detailed reference viewed: 80 (10 ULg)Contingency ranking with respect to overloads in very large power systems taking into account uncertainty, preventive, and corrective actions ; ; et al in IEEE Transactions on Power Systems (2013) This paper deals with day-ahead security management with respect to a postulated set of contingencies, while taking into account uncertainties about the next day generation/load scenario. In order to help ... [more ▼] This paper deals with day-ahead security management with respect to a postulated set of contingencies, while taking into account uncertainties about the next day generation/load scenario. In order to help the system operator in decision making under uncertainty, we aim at ranking these contingencies into four clusters according to the type of control actions needed to cover the worst uncertainty pattern of each contingency with respect to branch overload. To this end we use a fixed point algorithm that loops over two main modules: a discrete bi-level program (BLV) that computes the worst-case scenario, and a special kind of security constrained optimal power flow (SCOPF) which computes optimal preventive/corrective actions to cover the worst-case. We rely on a DC grid model, as the large number of binary variables, the large size of the problem, and the stringent computational requirements preclude the use of existing mixed integer nonlinear programming (MINLP) solvers. Consequently we solve the SCOPF using a mixed integer linear programming (MILP) solver while the BLV is decomposed into a series of MILPs. We provide numerical results with our approach on a very large European system model with 9241 buses and 5126 contingencies. [less ▲] Detailed reference viewed: 70 (8 ULg)Cautious operation planning under uncertainties Capitanescu, Florin ; ; et al in IEEE Transactions on Power Systems (2012), 27(4), 1859-1869 This paper deals with day-ahead power systems security planning under uncertainties, by posing an optimization problem over a set of power injection scenarios that could show up the next day and modeling ... [more ▼] This paper deals with day-ahead power systems security planning under uncertainties, by posing an optimization problem over a set of power injection scenarios that could show up the next day and modeling the next day's real-time control strategies aiming at ensuring security with respect to contingencies by a combination of preventive and corrective controls. We seek to determine whether and which day-ahead decisions must be taken so that for scenarios over the next day there still exists an acceptable combination of preventive and corrective controls ensuring system security for any postulated contingency. We formulate this task as a three-stage feasibility checking problem, where the first stage corresponds to day-ahead decisions, the second stage to preventive control actions, and the third stage to corrective post-contingency controls. We propose a solution approach based on the problem decomposition into successive optimal power flow (OPF) and security-constrained optimal power flow (SCOPF) problems of a special type. Our approach is illustrated on the Nordic32 system and on a 1203-bus model of a real-life system. [less ▲] Detailed reference viewed: 117 (7 ULg)Exploiting the use of DC SCOPF approximation to improve iterative AC SCOPF algorithms ; Capitanescu, Florin ; et al in IEEE Transactions on Power Systems (2012), 27(3), 1459-1466 This paper focuses on improving the solution techniques for the AC SCOPF problem of active power dispatch by using the DC SCOPF approximation within the SCOPF algorithm. Our approach brings two benefits ... [more ▼] This paper focuses on improving the solution techniques for the AC SCOPF problem of active power dispatch by using the DC SCOPF approximation within the SCOPF algorithm. Our approach brings two benefits compared to benchmark SCOPF algorithms: it speeds-up the solution of an iterative AC SCOPF algorithm thanks to a more efficient identification of binding contingencies, and allows improving the objective by an appropriate choice of a limited number of corrective actions for each contingency. The proposed approach is illustrated on 5 test systems of 60, 118, 300, 1203, and 2746 buses. [less ▲] Detailed reference viewed: 110 (9 ULg)Assessing reactive power reserves with respect to operating constraints and voltage stability Capitanescu, Florin in IEEE Transactions on Power Systems (2011), 26(4), 2224-2234 This paper proposes a two-step approach to evaluate reactive power reserves with respect to operating constraints and voltage stability for a set of postulated operating scenarios. The first step ... [more ▼] This paper proposes a two-step approach to evaluate reactive power reserves with respect to operating constraints and voltage stability for a set of postulated operating scenarios. The first step determines the minimum overall needed reactive power reserves of generators such that the system withstands, from a static viewpoint, any postulated scenario. This problem is formulated as a security constrained optimal power flow (SCOPF) which includes operating constraints relative to all postulated scenarios. Particular attention is paid to the techniques aimed to reduce the large size of the SCOPF problem. The second step determines additional reserves to ensure voltage stability of scenarios for which, when modeling dynamic system behaviour, the reserves obtained by SCOPF are insufficient. These reserves are computed using a heuristic technique which relies on dynamic simulation. Numerical results on four test systems of 60, 118, 618, and 1203 buses support the interest of the approach. [less ▲] Detailed reference viewed: 75 (5 ULg)Receding-horizon multi-step optimization to correct nonviable or unstable transmission voltages ; ; et al in IEEE Transactions on Power Systems (2011), 26(3), 1641-1650 In this paper, a receding-horizon multi-step optimization is proposed to correct non viable transmission voltages and prevent long-term voltage instability. The proposed control scheme is based on real ... [more ▼] In this paper, a receding-horizon multi-step optimization is proposed to correct non viable transmission voltages and prevent long-term voltage instability. The proposed control scheme is based on real-time control, inspired by model predictive control, and steady state power-flow-based equations. In order to anticipate load behavior and avoid using dynamic equations in the control scheme, explicit formulations are used to model evolution of load with time. The simulation results of the proposed technique are presented on the Nordic32 test system. [less ▲] Detailed reference viewed: 131 (25 ULg)Redispatching active and reactive powers using a limited number of control actions Capitanescu, Florin ; Wehenkel, Louis in IEEE Transactions on Power Systems (2011), 26(3), 1221-1230 This paper deals with some essential open questions in the field of optimal power flow (OPF) computations, namely: the limitation of the number of controls allowed to move, the trade-off between the ... [more ▼] This paper deals with some essential open questions in the field of optimal power flow (OPF) computations, namely: the limitation of the number of controls allowed to move, the trade-off between the objective function and the number of controls allowed to move, the computation of the minimum number of control actions needed to satisfy constraints, and the determination of the sequence of control actions to be taken by the system operator in order to achieve its operation goal. To address these questions, we propose approaches which rely on the computation of sensitivities of the objective function and inequality constraints with respect to control actions. We thus determine a subset of controls allowed to move in the OPF, by solving a sensitivity-based mixed integer linear programming (MILP) problem. We study the performances of these approaches on three test systems (of 60, 118, and 618 buses) and by considering three different OPF problems important for a system operator in emergency and/or in normal states, namely the removal of thermal congestions, the removal of bus voltage limits violation, and the reduction of the active power losses. [less ▲] Detailed reference viewed: 138 (13 ULg)On angle references in long-term time-domain simulations Fabozzi, Davide ; Van Cutsem, Thierry in IEEE Transactions on Power Systems (2011), 26(1), 483-484 Abstract—In power system dynamic models the complex network equations and the various phasors are projected onto reference axes. After a short critical review of commonly chosen reference axes, this ... [more ▼] Abstract—In power system dynamic models the complex network equations and the various phasors are projected onto reference axes. After a short critical review of commonly chosen reference axes, this letter proposes to use the center-of-inertia at the previous integration time step. This approach is shown to combine the advantages of the center-of-inertia with a sparser Jacobian structure and an easier handling of network splits. [less ▲] Detailed reference viewed: 259 (50 ULg)Sensitivity-based approaches for handling discrete variables in optimal power flow computations Capitanescu, Florin ; Wehenkel, Louis in IEEE Transactions on Power Systems (2010), 25(4), 1780-1789 This paper proposes and compares three iterative approaches for handling discrete variables in optimal power flow (OPF) computations. The first two approaches rely on the sensitivities of the objective ... [more ▼] This paper proposes and compares three iterative approaches for handling discrete variables in optimal power flow (OPF) computations. The first two approaches rely on the sensitivities of the objective and inequality constraints with respect to discrete variables. They set the discrete variables values either by solving a mixed-integer linear programming (MILP) problem or by using a simple procedure based on a merit function. The third approach relies on the use of Lagrange multipliers corresponding to the discrete variables bound constraints at the OPF solution. The classical round-off technique and a progressive round-off approach have been also used as a basis of comparison. We provide extensive numerical results with these approaches on four test systems with up to 1203 buses, and for two OPF problems: loss minimization and generation cost minimization, respectively. These results show that the sensitivity-based approach combined with the merit function clearly outperforms the other approaches in terms of: objective function quality, reliability, and computational times. Furthermore, the objective value obtained with this approach has been very close to that provided by the continuous relaxation OPF. This approach constitutes therefore a viable alternative to other methods dealing with discrete variables in an OPF. [less ▲] Detailed reference viewed: 65 (5 ULg)Energy and Transmission Allocation in the presence of Overlapping Electricity Markets Marinakis, Adamantios ; ; Van Cutsem, Thierry in IEEE Transactions on Power Systems (2010), 25(3), 1402-1414 The possibility for market participants to simultaneously place their bids in different markets across an interconnection is investigated in this paper. Transaction schedulers settle multilateral ... [more ▼] The possibility for market participants to simultaneously place their bids in different markets across an interconnection is investigated in this paper. Transaction schedulers settle multilateral transactions among participants, while a central entity coordinates the overall operation through interactions with the transaction schedulers. Two issues are dealt with in this context. First, the market participants are allowed to place their bids simultaneously in more than one transactions scheduler’s market, and, second, the available transmission capacity is fairly shared among the transaction schedulers. Economically interesting transactions are favored, while confidentiality of market data and independence of transaction schedulers’ clearing mechanisms are preserved. The corresponding iterative algorithm is illustrated in detail on a 15-bus as well as the IEEE-RTS system. [less ▲] Detailed reference viewed: 127 (18 ULg)Optimal power flow computations with a limited number of controls allowed to move Capitanescu, Florin ; Wehenkel, Louis in IEEE Transactions on Power Systems (2010), 25(1), 586-587 This letter focuses on optimal power flow (OPF) computations in which no more than a pre-specified number of controls are allowed to move. To determine an efficient subset of controls satisfying this ... [more ▼] This letter focuses on optimal power flow (OPF) computations in which no more than a pre-specified number of controls are allowed to move. To determine an efficient subset of controls satisfying this constraint we rely on the solution of a mixed integer linear programming (MILP) problem fed with sensitivity information of controls' impact on the objective and constraints. We illustrate this approach on a 60-bus system and for the OPF problem of minimum load curtailment cost to remove thermal congestion. [less ▲] Detailed reference viewed: 69 (7 ULg)Minimal Reduction of Unscheduled Flows for Security Restoration: Application to Phase Shifter Control Marinakis, Adamantios ; ; Van Cutsem, Thierry in IEEE Transactions on Power Systems (2010), 25(1), 506-515 More and more transmission system operators, noticeably in Europe, equip their systems with phase shifting transformers to counteract transit flows that take place in a large meshed interconnection. This ... [more ▼] More and more transmission system operators, noticeably in Europe, equip their systems with phase shifting transformers to counteract transit flows that take place in a large meshed interconnection. This paper proposes algorithms for the coordinated control of several phase shifters by one operator with the objective of reducing the unscheduled flow through its system. Minimum reduction of unscheduled flow and minimum deviation with respect to present operating point are sought in order to minimize the trouble caused, while ensuring secure operation. Attention is paid to combining pre and post-contingency controls. The resulting algorithms, simple and compatible with real-time applications, are illustrated on a realistic test system. [less ▲] Detailed reference viewed: 120 (24 ULg)Securing Transient Stability using Time-Domain Simulations within an Optimal Power Flow ; Van Cutsem, Thierry ; et al in IEEE Transactions on Power Systems (2010), 25(1), 243-253 This paper provides a methodology to restore transient stability. It relies on a well-behaved optimal power flow model with embedded transient stability constraints. The proposed methodology can be used ... [more ▼] This paper provides a methodology to restore transient stability. It relies on a well-behaved optimal power flow model with embedded transient stability constraints. The proposed methodology can be used for both dispatching and redispatching. In addition to power flow constraints and limits, the resulting optimal power flow model includes discrete time equations describing the time evolution of all machines in the system. Transient stability constraints are formulated by reducing the initial multi-machine model to a one-machine infinite-bus equivalent. This equivalent allows imposing angle bounds that ensure transient stability. The proposed optimal power flow model is tested and analyzed using an illustrative 9-bus system, the well-known New England 39-bus, 10-machine system and a real-world 1228-bus system with 292 synchronous machines. [less ▲] Detailed reference viewed: 151 (17 ULg)Wide-area Detection of Voltage Instability from Synchronized Phasor Measurements. Part I: Principle ; Van Cutsem, Thierry in IEEE Transactions on Power Systems (2009), 24(3), 1408-1416 This two-part paper deals with the early detection of an impending voltage instability from the system states provided by synchronized phasor measurements. Recognizing that voltage instability detection ... [more ▼] This two-part paper deals with the early detection of an impending voltage instability from the system states provided by synchronized phasor measurements. Recognizing that voltage instability detection requires assessing a multi-dimensional system, the method fits a set of algebraic equations to the sampled states, and performs an efficient sensitivity computation in order to identify when a combination of load powers has passed through a maximum. The important effects of overexcitation limiters are accounted for. The approach does not require any load model. This first part of the paper is devoted to theoretical foundations of sensitivity calculation along the system trajectory, derivation of the algebraic model, and illustration on a simple 5-bus system involving the long-term dynamics of a load tap changer and a field current limiter. [less ▲] Detailed reference viewed: 246 (26 ULg)Wide-area Detection of Voltage Instability from Synchronized Phasor Measurements. Part II: Simulation results ; Van Cutsem, Thierry in IEEE Transactions on Power Systems (2009), 24(3), 1417-1425 This two-part paper deals with the early detection of an impending voltage instability from the system states provided by synchronized phasor measurements. Recognizing that voltage instability detection ... [more ▼] This two-part paper deals with the early detection of an impending voltage instability from the system states provided by synchronized phasor measurements. Recognizing that voltage instability detection requires assessing a multidimensional system, the method fits a set of algebraic equations to the sampled states, and performs an efficient sensitivity in order to identify when a combination of load powers has passed through a maximum. This second part of the paper presents simulation results obtained from detailed time-domain simulation of the Nordic32 test system, without and with measurement noise, respectively. Several practical improvements are described such as anticipation of overexcitation limiter activation, and use of a moving average filter. Robustness to load behaviour, non updated topology and unobservability is also shown. Finally a comparison with Thevenin impedance matching criterion is provided. [less ▲] Detailed reference viewed: 229 (31 ULg) |
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