Louis Wehenkel | University of Liege (original) (raw)

Papers by Louis Wehenkel

Research paper thumbnail of Projecting Generation Decisions Induced by a Stochastic Program on a Family of Supply Curve Functions

Research paper thumbnail of PreDetector : Prokaryotic Regulatory Element Detector

Research paper thumbnail of On multi-area security assessment of large interconnected power systems

Research paper thumbnail of Ensembles of extremely randomized trees and some generic applications

Research paper thumbnail of Iteratively Extending Time Horizon Reinforcement Learning

Research paper thumbnail of On the Encoding of Proteins for Disordered Regions Prediction

Research paper thumbnail of A Cautious Approach to Generalization in Reinforcement Learning

Research paper thumbnail of Contingency Filtering Techniques for Preventive Security-Constrained Optimal Power Flow

IEEE Transactions on Power Systems, Nov 1, 2007

Research paper thumbnail of ROC curves on PDB30 dataset

Research paper thumbnail of Accuracy evaluation on the CASP10 dataset

Research paper thumbnail of Association des Ingénieurs de Montefiore (A.I.M.)

Raphaël Marée2Benelearn is the annual machine learning conference of Belgium and The Netherlands.... more Raphaël Marée2Benelearn is the annual machine learning conference of Belgium and The Netherlands. It serves as a forum for researchers to exchange ideas, present recent work, and foster collaboration in the broad field of Machine Learning and its applications. Benelearn 2008 is organised by the Systems and Modeling and Bioinformatics and Modeling research units of the Department of Electrical Engineering and Computer Science and GIGA-Research of the University of Liège. The conference takes place in the Solcress seminar center, at walking distance from the center of the city of Spa located in the Belgian Ardennes. Conference Chair

Research paper thumbnail of Chance-Constrained Outage Scheduling Using a Machine Learning Proxy

IEEE Transactions on Power Systems, 2019

Shie Mannor received the B.Sc. degree in electrical engineering, the B.A. degree in mathematics, ... more Shie Mannor received the B.Sc. degree in electrical engineering, the B.A. degree in mathematics, and the Ph.D. degree in electrical engineering from the Technion

Research paper thumbnail of Hybrid Adaptive Nearest Neighbor Approaches to Dynamic Security Assessment

IFAC Proceedings Volumes, 1997

We develop a general hybrid k Nearest Neighbors (kNN) approach, where kNNs take advantage of prob... more We develop a general hybrid k Nearest Neighbors (kNN) approach, where kNNs take advantage of problem-specific information provided by decision trees and of generalpurpose optimization provided by genetic algorithms. This general methodology is then adapted to two concerns of power system dynamic security that kNNs are conceptually well appropriate to handle. One such question of paramount importance is how to detect outliers; these are cases "too far away" from the preanalyzed cases of the data base used to train kNNs. The other question is how to avoid dangerous diagnostics which could arise from an erroneous identification of the relevant majority class of neighbors. In this paper, these two questions are tackled in the context of transient stability and illustrated on the Hydro-Quebec power system.

Research paper thumbnail of SIME: A Comprehensive Approach to Fast Transient Stability Assessment

IEEJ Transactions on Power and Energy, 1998

The Single Machine Equivalent (SIME) is a hybrid method resulting from the coupling of a time-dom... more The Single Machine Equivalent (SIME) is a hybrid method resulting from the coupling of a time-domain transient stability program with the equal-area criterion. Its aim is to set up a software as general as the time-domain program with which it is coupled but much more powerful and faster than it. The paper shows how the method reaches the threefold objective : to properly and readily assess transient stability limits (such as critical clearing times and power limits) under any power system modelling and stability scenario, to identify the relevant system machines and to appraise stability margins. In turn, these latter pieces of information open possibilities towards handy sensitivity analysis and transient stability monitoring. In short, they pave the way for real-time transient stability preventive monitoring and control. A variety of sample simulations highlight the method and its specifics.

Research paper thumbnail of to Electrical Power System Control

Copyright c○2005 by the authors. All rights reserved. No part of this publication may be reproduc... more Copyright c○2005 by the authors. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of the publisher, bepress, which has been given certain exclusive rights by the

Research paper thumbnail of Extended equal area criterion revisited

This paper reports on a case study conducted on the EHV French power system in order to revisit t... more This paper reports on a case study conducted on the EHV French power system in order to revisit the extended equal area criterion and test its suitability as a fast transient stability indicator. The assumptions underlying the method are reexamined, causes liable to invalidate them are identified, and indices are devised to automatically circumvent them. The selection of candidate critical machines is also reconsidered and an augmented criterion is proposed. The various improvements are developed and tested on about 1000 stability scenarios, covering the entire 400-kV system; the severity of the scenarios, resulting from the combination of weakened both pre- and post-fault configurations, subjects the method to particularly stringent conditions. The obtained results show that the devised tools contribute to significantly reinforce its robustness and reliability.

Research paper thumbnail of Multi-period power loss optimization with limited number of switching actions for enhanced continuous power supply

2014 16th International Conference on Harmonics and Quality of Power (ICHQP), 2014

ABSTRACT This paper deals with multi-period active power loss minimization. We formulate this pro... more ABSTRACT This paper deals with multi-period active power loss minimization. We formulate this problem as a mixed-integer nonlinear programming (MINLP) problem, including constraints that specifically limit the number of switching actions between two successive anticipated system states. We solve this problem using the Mixed Integer Hybrid Differential Evolution (MIHDE), a modified Differential Evolution algorithm, which we adapt for our application. The effectiveness of the proposed approach is proven using a 60-bus system.

Research paper thumbnail of Power system security assessment: A position paper

Research paper thumbnail of Optimal power flow computations with constraints limiting the number of control actions

2009 IEEE Bucharest PowerTech, 2009

This paper focuses on optimal power flow (OPF) computations in which no more than a pre-specified... more This paper focuses on optimal power flow (OPF) computations in which no more than a pre-specified number of controls are allowed to move. The benchmark formulation of this OPF problem constitutes a mixed integer nonlinear programming (MINLP) problem. To avoid the prohibitive computational time required by classical MINLP approaches to provide a (potentially sub-optimal) solution, we propose instead two alternative approaches. The first one consists in reformulating the MINLP problem as a mathematical program with equilibrium constraints (MPEC). The second approach includes in the classical OPF problem a nonlinear constraint which approximates the integral constraint limiting the number of control variables movement. Both approaches are solved by an interior point algorithm (IPA), slightly adapted to the particular characteristics of each approach. We provide numerical results with the proposed approaches on two test systems and for two practical problems: minimum cost to remove thermal congestion, and minimum cost of load curtailment to restore a feasible equilibrium point.

Research paper thumbnail of Optimized Look-ahead Tree Search Policies

Lecture Notes in Computer Science, 2012

We consider in this paper look-ahead tree techniques for the discrete-time control of a determini... more We consider in this paper look-ahead tree techniques for the discrete-time control of a deterministic dynamical system so as to maximize a sum of discounted rewards over an infinite time horizon. Given the current system state xt at time t, these techniques explore the lookahead tree representing possible evolutions of the system states and rewards conditioned on subsequent actions ut, ut+1,. . .. When the computing budget is exhausted, they output the action ut that led to the best found sequence of discounted rewards. In this context, we are interested in computing good strategies for exploring the look-ahead tree. We propose a generic approach that looks for such strategies by solving an optimization problem whose objective is to compute a (budget compliant) tree-exploration strategy yielding a control policy maximizing the average return over a postulated set of initial states. This generic approach is fully specified to the case where the space of candidate tree-exploration strategies are "best-first" strategies parameterized by a linear combination of look-ahead path features-some of them having been advocated in the literature before-and where the optimization problem is solved by using an EDA-algorithm based on Gaussian distributions. Numerical experiments carried out on a model of the treatment of the HIV infection show that the optimized tree-exploration strategy is orders of magnitudes better than the previously advocated ones.

Research paper thumbnail of Projecting Generation Decisions Induced by a Stochastic Program on a Family of Supply Curve Functions

Research paper thumbnail of PreDetector : Prokaryotic Regulatory Element Detector

Research paper thumbnail of On multi-area security assessment of large interconnected power systems

Research paper thumbnail of Ensembles of extremely randomized trees and some generic applications

Research paper thumbnail of Iteratively Extending Time Horizon Reinforcement Learning

Research paper thumbnail of On the Encoding of Proteins for Disordered Regions Prediction

Research paper thumbnail of A Cautious Approach to Generalization in Reinforcement Learning

Research paper thumbnail of Contingency Filtering Techniques for Preventive Security-Constrained Optimal Power Flow

IEEE Transactions on Power Systems, Nov 1, 2007

Research paper thumbnail of ROC curves on PDB30 dataset

Research paper thumbnail of Accuracy evaluation on the CASP10 dataset

Research paper thumbnail of Association des Ingénieurs de Montefiore (A.I.M.)

Raphaël Marée2Benelearn is the annual machine learning conference of Belgium and The Netherlands.... more Raphaël Marée2Benelearn is the annual machine learning conference of Belgium and The Netherlands. It serves as a forum for researchers to exchange ideas, present recent work, and foster collaboration in the broad field of Machine Learning and its applications. Benelearn 2008 is organised by the Systems and Modeling and Bioinformatics and Modeling research units of the Department of Electrical Engineering and Computer Science and GIGA-Research of the University of Liège. The conference takes place in the Solcress seminar center, at walking distance from the center of the city of Spa located in the Belgian Ardennes. Conference Chair

Research paper thumbnail of Chance-Constrained Outage Scheduling Using a Machine Learning Proxy

IEEE Transactions on Power Systems, 2019

Shie Mannor received the B.Sc. degree in electrical engineering, the B.A. degree in mathematics, ... more Shie Mannor received the B.Sc. degree in electrical engineering, the B.A. degree in mathematics, and the Ph.D. degree in electrical engineering from the Technion

Research paper thumbnail of Hybrid Adaptive Nearest Neighbor Approaches to Dynamic Security Assessment

IFAC Proceedings Volumes, 1997

We develop a general hybrid k Nearest Neighbors (kNN) approach, where kNNs take advantage of prob... more We develop a general hybrid k Nearest Neighbors (kNN) approach, where kNNs take advantage of problem-specific information provided by decision trees and of generalpurpose optimization provided by genetic algorithms. This general methodology is then adapted to two concerns of power system dynamic security that kNNs are conceptually well appropriate to handle. One such question of paramount importance is how to detect outliers; these are cases "too far away" from the preanalyzed cases of the data base used to train kNNs. The other question is how to avoid dangerous diagnostics which could arise from an erroneous identification of the relevant majority class of neighbors. In this paper, these two questions are tackled in the context of transient stability and illustrated on the Hydro-Quebec power system.

Research paper thumbnail of SIME: A Comprehensive Approach to Fast Transient Stability Assessment

IEEJ Transactions on Power and Energy, 1998

The Single Machine Equivalent (SIME) is a hybrid method resulting from the coupling of a time-dom... more The Single Machine Equivalent (SIME) is a hybrid method resulting from the coupling of a time-domain transient stability program with the equal-area criterion. Its aim is to set up a software as general as the time-domain program with which it is coupled but much more powerful and faster than it. The paper shows how the method reaches the threefold objective : to properly and readily assess transient stability limits (such as critical clearing times and power limits) under any power system modelling and stability scenario, to identify the relevant system machines and to appraise stability margins. In turn, these latter pieces of information open possibilities towards handy sensitivity analysis and transient stability monitoring. In short, they pave the way for real-time transient stability preventive monitoring and control. A variety of sample simulations highlight the method and its specifics.

Research paper thumbnail of to Electrical Power System Control

Copyright c○2005 by the authors. All rights reserved. No part of this publication may be reproduc... more Copyright c○2005 by the authors. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of the publisher, bepress, which has been given certain exclusive rights by the

Research paper thumbnail of Extended equal area criterion revisited

This paper reports on a case study conducted on the EHV French power system in order to revisit t... more This paper reports on a case study conducted on the EHV French power system in order to revisit the extended equal area criterion and test its suitability as a fast transient stability indicator. The assumptions underlying the method are reexamined, causes liable to invalidate them are identified, and indices are devised to automatically circumvent them. The selection of candidate critical machines is also reconsidered and an augmented criterion is proposed. The various improvements are developed and tested on about 1000 stability scenarios, covering the entire 400-kV system; the severity of the scenarios, resulting from the combination of weakened both pre- and post-fault configurations, subjects the method to particularly stringent conditions. The obtained results show that the devised tools contribute to significantly reinforce its robustness and reliability.

Research paper thumbnail of Multi-period power loss optimization with limited number of switching actions for enhanced continuous power supply

2014 16th International Conference on Harmonics and Quality of Power (ICHQP), 2014

ABSTRACT This paper deals with multi-period active power loss minimization. We formulate this pro... more ABSTRACT This paper deals with multi-period active power loss minimization. We formulate this problem as a mixed-integer nonlinear programming (MINLP) problem, including constraints that specifically limit the number of switching actions between two successive anticipated system states. We solve this problem using the Mixed Integer Hybrid Differential Evolution (MIHDE), a modified Differential Evolution algorithm, which we adapt for our application. The effectiveness of the proposed approach is proven using a 60-bus system.

Research paper thumbnail of Power system security assessment: A position paper

Research paper thumbnail of Optimal power flow computations with constraints limiting the number of control actions

2009 IEEE Bucharest PowerTech, 2009

This paper focuses on optimal power flow (OPF) computations in which no more than a pre-specified... more This paper focuses on optimal power flow (OPF) computations in which no more than a pre-specified number of controls are allowed to move. The benchmark formulation of this OPF problem constitutes a mixed integer nonlinear programming (MINLP) problem. To avoid the prohibitive computational time required by classical MINLP approaches to provide a (potentially sub-optimal) solution, we propose instead two alternative approaches. The first one consists in reformulating the MINLP problem as a mathematical program with equilibrium constraints (MPEC). The second approach includes in the classical OPF problem a nonlinear constraint which approximates the integral constraint limiting the number of control variables movement. Both approaches are solved by an interior point algorithm (IPA), slightly adapted to the particular characteristics of each approach. We provide numerical results with the proposed approaches on two test systems and for two practical problems: minimum cost to remove thermal congestion, and minimum cost of load curtailment to restore a feasible equilibrium point.

Research paper thumbnail of Optimized Look-ahead Tree Search Policies

Lecture Notes in Computer Science, 2012

We consider in this paper look-ahead tree techniques for the discrete-time control of a determini... more We consider in this paper look-ahead tree techniques for the discrete-time control of a deterministic dynamical system so as to maximize a sum of discounted rewards over an infinite time horizon. Given the current system state xt at time t, these techniques explore the lookahead tree representing possible evolutions of the system states and rewards conditioned on subsequent actions ut, ut+1,. . .. When the computing budget is exhausted, they output the action ut that led to the best found sequence of discounted rewards. In this context, we are interested in computing good strategies for exploring the look-ahead tree. We propose a generic approach that looks for such strategies by solving an optimization problem whose objective is to compute a (budget compliant) tree-exploration strategy yielding a control policy maximizing the average return over a postulated set of initial states. This generic approach is fully specified to the case where the space of candidate tree-exploration strategies are "best-first" strategies parameterized by a linear combination of look-ahead path features-some of them having been advocated in the literature before-and where the optimization problem is solved by using an EDA-algorithm based on Gaussian distributions. Numerical experiments carried out on a model of the treatment of the HIV infection show that the optimized tree-exploration strategy is orders of magnitudes better than the previously advocated ones.