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See detailDecomposition, Localization and Time-Averaging Approaches in Large-Scale Power System Dynamic Simulation
Fabozzi, Davide ULg

Doctoral thesis (2012)

Present-day interconnected electric power systems are the largest machines in the world. Guaranteeing a stable supply of electric power is vital for modern societies: power systems must be able to ... [more ▼]

Present-day interconnected electric power systems are the largest machines in the world. Guaranteeing a stable supply of electric power is vital for modern societies: power systems must be able to withstand plausible disturbances. A certain number of simulations of the post-disturbance behavior are routinely executed by some transmission system operators to assess that the system is operated in a secure way. Usually this assessment has to be performed within a predefined time frame, using the available computing resources. Improving the simulation speed allows the operators to perform a wider assessment, thus making better use of the available computational power. A large part of this research took place in the context of the PEGASE project, supported by European Commission (Seventh Framework Programme) and has resulted in some novel algorithms for faster dynamic simulations, one of the PEGASE project main goals. First, this thesis revisits the Newton method used to solve the differential-algebraic model. Then, three original algorithmic improvements are presented, namely (i) decomposition, (ii) localization and (iii) time-averaging of the system response. Finally, the combination of these approaches is shown to provide a fast and reliable tool for dynamic security assessment. All the presented techniques have been thoroughly tested on an academic system, a large real-life system and a realistic system of unprecedented size, representative of the whole continental European synchronous grid. [less ▲]

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See detailA Schur Complement Method for DAE Systems in Power System Simulations
Aristidou, Petros ULg; Fabozzi, Davide ULg; Van Cutsem, Thierry ULg

Scientific conference (2012, June 28)

The power system networks in North America and Europe are the largest man-made interconnected systems in the world. Many power system applications rely on time consuming dynamic simulations of large-scale ... [more ▼]

The power system networks in North America and Europe are the largest man-made interconnected systems in the world. Many power system applications rely on time consuming dynamic simulations of large-scale power systems in order to optimize the operation and ensure the reliability of the electricity network. Dynamic simulations of power systems involve the solution of a series of initial value, stiff, hybrid DAE systems over a time window. To achieve this, the time window is discretized and a new DAE system is formed and solved at each time step, with initial values taken from the previous time step solution. At each new time step, the DAE system to be solved can be different because of the discrete variables involved in the formulation (e.g. a differential equation can become algebraic and vice versa). A non-overlapping domain decomposition is proposed to speed up the solution of the DAE system using the Schur Complement Method. The special structure of the physical system helps define the domain partitioning scheme and eliminates the need for a partitioning algorithm. It allows the formulation and solution of the reduced system using sparse, direct solvers to obtain the interface variables. Afterward, the parallel evaluation of the internal subdomain variables is possible and efficient load balancing is achieved. Numerically, the method shows no convergence degradation when compared to the integrated method, which is traditionally used for solving power system DAEs. The aspects of decomposition, solution and optimization of the algorithm for the specific problem are discussed and results from the application of the DDM on realistic power system models are presented. [less ▲]

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See detailCombining Full Transients and Phasor Approximation Models in Power System Time Simulation
Plumier, Frédéric ULg; Fabozzi, Davide ULg; Geuzaine, Christophe ULg et al

in Proceedings of the 21th International Conference on Domain Decomposition Methods (DD21) (2012, June)

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See detailSimplified dynamic simulation
Van Cutsem, Thierry ULg; Fabozzi, Davide ULg

Conference (2011, December 06)

These are the slides of an invited presentation at the panel session "Pan European Grid Advanced Simulation and State Estimation (PEGASE)", aimed at disseminating the results of the PEGASE project funded ... [more ▼]

These are the slides of an invited presentation at the panel session "Pan European Grid Advanced Simulation and State Estimation (PEGASE)", aimed at disseminating the results of the PEGASE project funded by European Community’s 7th Framework Programme (grant agreement No. 211407) [less ▲]

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See detailAssessing the Proximity of Time Evolutions through Dynamic Time Warping
Fabozzi, Davide ULg; Van Cutsem, Thierry ULg

in IET Generation, Transmission & Distribution (2011), 5(12), 1268-1276

Comparing time-series is a frequent task in many scientific fields. In power systems, in particular, it may be of interest to compare the outputs of a simplified and a detailed model, or to validate the ... [more ▼]

Comparing time-series is a frequent task in many scientific fields. In power systems, in particular, it may be of interest to compare the outputs of a simplified and a detailed model, or to validate the output of a model with respect to a measured time response. The classical Euclidean distance, involving pairs of points of the two data series aligned in time, is not suited to the practical time evolutions met in power systems, which often involve variable time delays and jumps at discrete times. In this paper, an alternative measure of proximity, stemming from other scientific fields, is proposed for power system applications. It consists in warping the time axis to guarantee the best match between the two time-series, i.e. it maps points on two curves that are not aligned in time so as to minimize the sum of squared differences of their ordinates. Modifications and adaptations of the classical algorithm to better fit power system problems are discussed. The method is illustrated through three representative curve comparison problems. A multi-dimensional extension allowing system-wide measures of similarity is also proposed. [less ▲]

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See detailOn simplified handling of state events in time-domain simulation
Fabozzi, Davide ULg; Chieh, Angela S.; Panciatici, Patrick et al

in Proceedings of the 17th PSCC (2011, August)

The power system models typically used in dynamic simulations involve discrete events in addition to the standard differential-algebraic equations. Those events cause the system to jump from one ... [more ▼]

The power system models typically used in dynamic simulations involve discrete events in addition to the standard differential-algebraic equations. Those events cause the system to jump from one continuous behavior to another. Solvers have to handle those jumps. This paper focuses on simplified time simulation where large steps are used in conjunction with stiff-decay integration methods to obtain approximate solutions in short computing times. In the proposed simulation scheme, the simulation time steps are not synchronized with the system jumps, which are treated a posteriori in a corrective step. In this context, the paper analyzes several simple nonlinear models involving limiters, switches, minimum gates, etc. from which some precautions to be taken at the modelling and solving stages are stressed. The paper also reports on results obtained with a representative power system model. [less ▲]

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See detailOn angle references in long-term time-domain simulations
Fabozzi, Davide ULg; Van Cutsem, Thierry ULg

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 ▲]

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See detailLocalization and latency concepts applied to time simulation of large power systems
Fabozzi, Davide ULg; Van Cutsem, Thierry ULg

in Proceedings of the 2010 IREP Symposium (2010, August)

This paper reports on investigations to speed up time domain simulations of large electric power systems. First, a decomposed scheme is considered which exploits the bordered block diagonal structure of ... [more ▼]

This paper reports on investigations to speed up time domain simulations of large electric power systems. First, a decomposed scheme is considered which exploits the bordered block diagonal structure of the original Jacobian involved in the Newton iterations, and keeps the resulting “local” Jacobians constant over multiple iterations. Next, a localization technique is considered, allowing to perform less iterations on the system components with lower activity. Finally, a third scheme consists of visiting only a subset of components, identified as active, and skipping the other ones, identified as latent. The first two techniques solve the whole set of equations with the required accuracy, while the third one involves an adjustable degree of approximation. The methods are illustrated on a small system, while preliminary checks of computational savings from a large test system are reported. Additional results deal with the application of the localization and latency techniques to simplified simulation of the detailed model. [less ▲]

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See detailSecurity Assessment by Multiple Transmission System Operators Exchanging Sensitivity and Tie-Line Power Flow Information
Fabozzi, Davide ULg; Glavic, Mevludin; Wehenkel, Louis ULg et al

in Proceedings of the 2009 IEEE PES Power Tech conference (2009, July)

This paper considers a procedure for multi-area static security assessment of large interconnected power systems operated by a team of Transmission System Operators (TSOs). In this procedure, each TSO ... [more ▼]

This paper considers a procedure for multi-area static security assessment of large interconnected power systems operated by a team of Transmission System Operators (TSOs). In this procedure, each TSO provides the other TSOs with his own equivalent model as well as the detailed effects of contingencies in his control area on all tie-line flows. The paper deals with the implementation of sensitivity-based equivalents suitable for static security assessment. Accuracy with respect to the unreduced model and computational efficiency are considered in evaluating the proposed approach. The relevance of the procedure in the context of recent UCTE operational security policy recommendations is also stressed. The procedure has been implemented in an AC power flow program and tested on a three-area variant of the IEEE 118-bus test system. [less ▲]

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See detailSimplified time-domain simulation of detailed long-term dynamic models
Fabozzi, Davide ULg; Van Cutsem, Thierry ULg

in Proceedings of the 2009 IEEE PES General Meeting (2009, July)

Time-domain simulation of power system long-term dynamics involves the solution of large sparse systems of nonlinear stiff differential-algebraic equations. Simulation tools have traditionally focused on ... [more ▼]

Time-domain simulation of power system long-term dynamics involves the solution of large sparse systems of nonlinear stiff differential-algebraic equations. Simulation tools have traditionally focused on the accuracy of the solution and, in spite of many algorithmic improvements, time simulations still require a significant computational effort. In some applications, however, it is sufficient to have an approximate system response of the detailed model. The paper revisits the merits of the Backward Euler method and proposes a strategy to control its step size, with the objective of filtering out fast stable oscillations and focusing on the aperiodic behaviour of the system. The proposed method is compared to detailed simulation as well as to the quasi-steadystate approximation. Illustrative examples are given on a small but representative system, subject to long-term voltage instability. [less ▲]

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