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See detailIdentification of dangerous contingencies for large scale power system security assessment
Fonteneau-Belmudes, Florence ULg

Doctoral thesis (2012)

This thesis presents an approach for identifying a maximal number of dangerous contingencies in large scale power system security assessment problems with bounded computational resources. The method ... [more ▼]

This thesis presents an approach for identifying a maximal number of dangerous contingencies in large scale power system security assessment problems with bounded computational resources. The method developed in this work relies on the definition of an objective function associating to each contingency a real value that quantifies its severity for the security of the system, this value being greater than or equal to a given threshold only for dangerous contingencies. The value of this function for a given contingency is computed from the result of a security analysis executed on the post-contingency configuration. The framework we propose for identifying dangerous contingencies is derived from an algorithm from the optimization literature so as to find, with a given number of evaluations of the objective function, a maximal number of contingencies whose value of this function exceeds the adopted threshold. This approach performs successive samplings of the space gathering all the contingencies, and exploits the information contained in each of these samples in order to direct the subsequent sampling process towards contingencies with high values of the objective function. Our algorithm is first introduced in the case where the search space is a Euclidean space. Then we propose an extension of this approach to the more common case where the search space is discrete, thanks to a procedure allowing to embed a discrete contingency space in a Euclidean space, over which a metric is defined. The efficiency of the developed method is evaluated on several case studies: an N − 3 analysis of a benchmark test system, the IEEE 118 bus test system, and N − 1 and N − 2 studies of a real system, the Belgian transmission network. Afterwards, we consider the case where several of these iterative sampling algorithms are available. Assuming that these algorithms are executed sequentially, we propose two different strategies for selecting on-line which of them to execute at the next step in order to identify as many dangerous contingencies as possible, while still respecting the given computational budget. We finally provide an adapted version of the developed iterative sampling algorithm allowing to estimate the probability of occurrence of a dangerous contingency and the number of dangerous contingencies in a discrete search space. [less ▲]

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See detailConsequence driven decomposition of large-scale power system security analysis
Fonteneau, Florence ULg; Ernst, Damien ULg; Druet, Christophe et al

in Proceedings of the 2010 IREP Symposium - Bulk Power Systems Dynamics and Control - VIII (2010, August)

This paper presents an approach for assessing, in operation planning studies, the security of a large-scale power system by decomposing it into elementary subproblems, each one corresponding to a ... [more ▼]

This paper presents an approach for assessing, in operation planning studies, the security of a large-scale power system by decomposing it into elementary subproblems, each one corresponding to a structural weak-point of the system. We suppose that the structural weak-points are known a priori by the system operators, and are each one described by a set of constraints that are localized in some relatively small area of the system. The security analysis with respect to a given weak-point thus reduces to the identification of the combinations of power system configurations and disturbances that could lead to the violation of some of its constraints. We propose an iterative rare-event simulation approach for identifying such combinations among the very large set of possible ones. The procedure is illustrated on a simplified version of this problem applied to the Belgian transmission system. [less ▲]

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See detailPseudo-geographical representations of power system buses by multidimensional scaling
Belmudes, Florence ULg; Ernst, Damien ULg; Wehenkel, Louis ULg

in Proceedings of the 15th International Conference on Intelligent System Applications to Power Systems (ISAP 2009) (2009)

Graphical representations of power systems are systematically used for planning and operation. The coordinate systems commonly used by Transmission System Operators are static and reflect the geographical ... [more ▼]

Graphical representations of power systems are systematically used for planning and operation. The coordinate systems commonly used by Transmission System Operators are static and reflect the geographical positions of each equipment of the system. We propose in this work to position on a twodimensional map the different buses of a power system in a way such that their coordinates also highlight some other physical information related to them. These pseudo-geographical representations are computed by formulating multidimensional scaling problems which aim at mapping a distance matrix combining both geographical and physical information into a vector of two-dimensional bus coordinates. We illustrate through examples that these pseudo-geographical representations can help to gain insights into the power system physical properties. [less ▲]

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See detailA rare-event approach to build security analysis tools when N-k (k > 1) analyses are needed (as they are in large-scale power systems)
Belmudes, Florence ULg; Ernst, Damien ULg; Wehenkel, Louis ULg

in Proceedings of the 2009 IEEE Bucharest PowerTech (2009)

We consider the problem of performing N − k security analyses in large scale power systems. In such a context, the number of potentially dangerous N − k contingencies may become rapidly very large when k ... [more ▼]

We consider the problem of performing N − k security analyses in large scale power systems. In such a context, the number of potentially dangerous N − k contingencies may become rapidly very large when k grows, and so running a security analysis for each one of them is often intractable. We assume in this paper that the number of dangerous N − k contingencies is very small with respect to the number of non-dangerous ones. Under this assumption, we suggest to use importance sampling techniques for identifying rare events in combinatorial search spaces. With such techniques, it is possible to identify dangerous contingencies by running security analyses for only a small number of events. A procedure relying on these techniques is proposed in this work for steady-state security analyses. This procedure has been evaluated on the IEEE 118 bus test system. The results show that it is indeed able to efficiently identify among a large set of contingencies some of the rare ones which are dangerous. [less ▲]

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See detailModelling the influence of activation-induced apoptosis of CD4+ and CD8+ T-cells on the immune system response of a HIV-infected patient
Stan, Guy-Bart; Belmudes, Florence ULg; Fonteneau, Raphaël ULg et al

in IET Systems Biology (2008), 2(2), 94-102

On the basis of the human immunodeficiency virus (HIV) infection dynamics model proposed by Adams, the authors propose an extended model that aims at incorporating the influence of activation-induced ... [more ▼]

On the basis of the human immunodeficiency virus (HIV) infection dynamics model proposed by Adams, the authors propose an extended model that aims at incorporating the influence of activation-induced apoptosis of CD4+ and CD8+ T-cells on the immune system response of HIV-infected patients. Through this model, the authors study the influence of this phenomenon on the time evolution of specific cell populations such as plasma concentrations of HIV copies, or blood concentrations of CD4+ and CD8+ T-cells. In particular, this study shows that depending on its intensity, the apoptosis phenomenon can either favour or mitigate the long-term evolution of the HIV infection. [less ▲]

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See detailCross-entropy based rare-event simulation for the identification of dangerous events in power systems
Belmudes, Florence ULg; Ernst, Damien ULg; Wehenkel, Louis ULg

in Proceedings of the 10th International Conference on Probabilistic Methods Applied to Power Systems (PMAPS-08) (2008)

We propose in this paper a novel approach for identifying rare events that may endanger power system integrity. This approach is inspired by the rare-event simulation literature and, in particular, by the ... [more ▼]

We propose in this paper a novel approach for identifying rare events that may endanger power system integrity. This approach is inspired by the rare-event simulation literature and, in particular, by the cross-entropy (CE) method for rare event simulation. We propose a general framework for exploiting the CE method in the context of power system reliability evaluation, when a severity function defined on the set of possible events is available. The approach is illustrated on the IEEE 30 bus test system when instability mechanisms related to static voltage security are considered. [less ▲]

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