References of "Ernst, Damien"
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See detailApoptosis characterizes immunological failure of HIV infected patients
Mhawej, Marie-José; Brunet-Francois, Cécile; Fonteneau, Raphaël ULg et al

in Control Engineering Practice (2009), 17(7), 798-804

This paper studies the influence of apoptosis in the dynamics of the HIV infection. A new modeling of the healthy CD4+ T-cells activation-induced apoptosis is used. The parameters of this model are ... [more ▼]

This paper studies the influence of apoptosis in the dynamics of the HIV infection. A new modeling of the healthy CD4+ T-cells activation-induced apoptosis is used. The parameters of this model are identified by using clinical data generated by monitoring patients starting Highly Active Anti-Retroviral Therapy (HAART). The sampling of blood tests is performed to satisfy the constraints of dynamical system parameter identification. The apoptosis parameter, which is inferred from clinical data, is then shown to play a key role in the early diagnosis of immunological failure. [less ▲]

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See detailInferring bounds on the performance of a control policy from a sample of one-step system transitions
Fonteneau, Raphaël ULg; Murphy, Susan A.; Wehenkel, Louis ULg et al

in 28th Benelux Meeting on Systems and Control (2009)

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See detailEvaluation of network equivalents for voltage optimization in multi-area power systems
Phulpin, Yannick; Miroslav, Begovic; Petit, Marc et al

in IEEE Transactions on Power Systems (2009), 24(2), 729-743

The paper addresses the problem of decentralized optimization for a power system partitioned into several areas controlled by different transmission system operators (TSOs). The optimization variables are ... [more ▼]

The paper addresses the problem of decentralized optimization for a power system partitioned into several areas controlled by different transmission system operators (TSOs). The optimization variables are the settings for taps, generators’ voltages and compensators’, and the objective function is either based on the minimization of reactive power support, the minimization of active power losses, or a combination of both criteria. We suppose that each TSO assumes an external network equivalent for its neighboring areas and optimizes without concern for the neighboring systems’ objectives its own optimization function. We study, in the context where every TSO adopts the same type of objective function, the performance of an iterative scheme, where every TSO refreshes at each iteration the parameters of its external network equivalents depending on its past internal observations, solves its local optimization problem, and then, applies its “optimal actions” to the power system. In the context of voltage optimization, we find out that this decentralized control scheme can converge to nearly optimal global performance for relatively simple equivalents and simple procedures for fitting their parameters. [less ▲]

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See detailWhat is the likely future of real-time transient stability ?
Ernst, Damien ULg; Wehenkel, Louis ULg; Pavella, Mania ULg

in Proceedings of the 2009 IEEE/PES Power Systems Conference & Exposition (PSCE 2009) (2009)

Despite very intensive research efforts in the field of transient stability during the last five decades, the large majority of the derived techniques have hardly moved from the research laboratories to ... [more ▼]

Despite very intensive research efforts in the field of transient stability during the last five decades, the large majority of the derived techniques have hardly moved from the research laboratories to the industrial world and, as a matter of fact, the very large majority of today's control centers do not make use of any real-time transient stability software. On the other hand, along all these years the techniques developed for real-time transient stability have mainly focused on the definition of stability margins and speeding-up techniques rather than on preventive or emergency control strategies. In the light of the above observations, this paper attempts to explain the reasons for lack of industrial interest in real-time transient stability, and also to examine an even more fundamental question, namely: is transient stability, as has been stated many decades ago, still the relevant issue in the context of the new power systems morphology towards more dispersed generation, higher penetration of power electronics, larger and more complex structures, and, in addition, of economic and environmental constraints? Or, maybe, there is a need for techniques different from those developed so far? [less ▲]

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See detailInferring bounds on the performance of a control policy from a sample of trajectories
Fonteneau, Raphaël ULg; Murphy, Susan; Wehenkel, Louis ULg et al

in Proceedings of the IEEE International Symposium on Adaptive Dynamic Programming and Reinforcement Learning (ADPRL-09) (2009)

We propose an approach for inferring bounds on the finite-horizon return of a control policy from an off-policy sample of trajectories collecting state transitions, rewards, and control actions. In this ... [more ▼]

We propose an approach for inferring bounds on the finite-horizon return of a control policy from an off-policy sample of trajectories collecting state transitions, rewards, and control actions. In this paper, the dynamics, control policy, and reward function are supposed to be deterministic and Lipschitz continuous. Under these assumptions, a polynomial algorithm, in terms of the sample size and length of the optimization horizon, is derived to compute these bounds, and their tightness is characterized in terms of the sample density. [less ▲]

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See detailPlanning under uncertainty, ensembles of disturbance trees and kernelized discrete action spaces
Defourny, Boris ULg; Ernst, Damien ULg; Wehenkel, Louis ULg

in Proceedings of the IEEE International Symposium on Adaptive Dynamic Programming and Reinforcement Learning (ADPRL-09) (2009)

Optimizing decisions on an ensemble of incomplete disturbance trees and aggregating their first stage decisions has been shown as a promising approach to (model-based) planning under uncertainty in large ... [more ▼]

Optimizing decisions on an ensemble of incomplete disturbance trees and aggregating their first stage decisions has been shown as a promising approach to (model-based) planning under uncertainty in large continuous action spaces and in small discrete ones. The present paper extends this approach and deals with large but highly structured action spaces, through a kernel-based aggregation scheme. The technique is applied to a test problem with a discrete action space of 6561 elements adapted from the NIPS 2005 SensorNetwork benchmark. [less ▲]

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See detailPolicy search with cross-entropy optimization of basis functions
Busoniu, Lucian; Ernst, Damien ULg; De Schutter, Bart et al

in Proceedings of the IEEE International Symposium on Adaptive Dynamic Programming and Reinforcement Learning (ADPRL-09) (2009)

This paper introduces a novel algorithm for approximate policy search in continuous-state, discrete-action Markov decision processes (MDPs). Previous policy search approaches have typically used ad-hoc ... [more ▼]

This paper introduces a novel algorithm for approximate policy search in continuous-state, discrete-action Markov decision processes (MDPs). Previous policy search approaches have typically used ad-hoc parameterizations developed for specific MDPs. In contrast, the novel algorithm employs a flexible policy parameterization, suitable for solving general discrete-action MDPs. The algorithm looks for the best closed-loop policy that can be represented using a given number of basis functions, where a discrete action is assigned to each basis function. The locations and shapes of the basis functions are optimized, together with the action assignments. This allows a large class of policies to be represented. The optimization is carried out with the cross-entropy method and evaluates the policies by their empirical return from a representative set of initial states. We report simulation experiments in which the algorithm reliably obtains good policies with only a small number of basis functions, albeit at sizable computational costs. [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 detailA fair method for centralized optimization of multi-TSO power systems
Phulpin, Yannick; Begovic, Miroslav; Petit, Marc et al

in International Journal of Electrical Power & Energy Systems (2009), 31

This paper addresses the problem of centralized optimization of an interconnected power system partitioned into several regions controlled by different transmission system operators (TSOs). It is assumed ... [more ▼]

This paper addresses the problem of centralized optimization of an interconnected power system partitioned into several regions controlled by different transmission system operators (TSOs). It is assumed that those utilities have agreed to transferring some of their competencies to a centralized control center, which is in charge of setting the control variables in the entire system to satisfy every utility’s individual objective. This paper proposes an objective method for centralized optimization of such multi-TSO power systems, which relies on the assumption that each TSO has a real-valued optimization function focusing on its control area only. This method is illustrated on the IEEE 118 bus system partitioned into three TSOs. It is applied to the optimal reactive power dispatch problem, where the control variables are the voltage settings for generators and compensators. After showing that the method has some properties of fairness, namely freedom from envy, efficiency, accountability, and altruism, we emphasize its robustness with respect to certain biased behavior of the different TSOs. [less ▲]

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See detailApprentissage par renforcement appliqué à la commande des systèmes électriques
Dai, Jing; Phulpin, Yannick; Vannier, Jean-Claude et al

in Proceedings of "Les Journées Electrotechnique du Futur 2009" (2009)

Cet article propose une revue de littérature concernant les applications de l’apprentissage par renforcement à la commande des systèmes électriques. L'apprentissage par renforcement a pour caractéristique ... [more ▼]

Cet article propose une revue de littérature concernant les applications de l’apprentissage par renforcement à la commande des systèmes électriques. L'apprentissage par renforcement a pour caractéristique principale de résoudre des problèmes de commande optimale à partir de la seule observation des trajectoires du système. Il présente l’intérêt de ne pas requérir de connaissance à priori sur la dynamique du système à commander et convient ainsi aux problèmes de commande des systèmes complexes. Dans un premier temps, l’article détaille les caractéristiques des problèmes auxquels l’apprentissage par renforcement s’applique, puis cette technique est décrite. Ensuite, deux exemples classiques d’application aux systèmes électriques sont présentés. [less ▲]

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See detailBounds for Multistage Stochastic Programs using Supervised Learning Strategies
Defourny, Boris ULg; Ernst, Damien ULg; Wehenkel, Louis ULg

in Watanabe, Osamu; Zeugmann, Thomas (Eds.) Stochastic Algorithms: Foundations and Applications (2009)

We propose a generic method for obtaining quickly good upper bounds on the minimal value of a multistage stochastic program. The method is based on the simulation of a feasible decision policy ... [more ▼]

We propose a generic method for obtaining quickly good upper bounds on the minimal value of a multistage stochastic program. The method is based on the simulation of a feasible decision policy, synthesized by a strategy relying on any scenario tree approximation from stochastic programming and on supervised learning techniques from machine learning. [less ▲]

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See detailReinforcement learning versus model predictive control: a comparison on a power system problem
Ernst, Damien ULg; Glavic, Mevludin; Capitanescu, Florin ULg et al

in IEEE Transactions on Systems, Man & Cybernetics : Part B (2009), 33(2), 517-519

This paper compares reinforcement learning (RL) with model predictive control (MPC) in a unified framework and reports experimental results of their application to the synthesis of a controller for a ... [more ▼]

This paper compares reinforcement learning (RL) with model predictive control (MPC) in a unified framework and reports experimental results of their application to the synthesis of a controller for a nonlinear and deterministic electrical power oscillations damping problem. Both families of methods are based on the formulation of the control problem as a discrete-time optimal control problem. The considered MPC approach exploits an analytical model of the system dynamics and cost function and computes open-loop policies by applying an interior-point solver to a minimization problem in which the system dynamics are represented by equality constraints. The considered RL approach infers in a model-free way closed-loop policies from a set of system trajectories and instantaneous cost values by solving a sequence of batch-mode supervised learning problems. The results obtained provide insight into the pros and cons of the two approaches and show that RL may certainly be competitive with MPC even in contexts where a good deterministic system model is available. [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 detailHVDC control strategies to improve transient stability in interconnected power systems
Hazra, Jagabondhu; Phulpin, Yannick; Ernst, Damien ULg

in Proceedings of the 2009 IEEE Bucharest PowerTech (2009)

This paper presents three HVDC modulation strategies to improve transient stability in an interconnected power system. AC variables such as rotor speeds, voltage phasors, and tieline power flows are used ... [more ▼]

This paper presents three HVDC modulation strategies to improve transient stability in an interconnected power system. AC variables such as rotor speeds, voltage phasors, and tieline power flows are used as input to the controller that modifies the power flow settings through the HVDC-links. The proposed techniques are tested on the IEEE 24-Bus reliability test system and critical clearing times obtained for several contingencies are analyzed. The paper shows that HVDC modulation can lead to substantial improvement in transient stability. [less ▲]

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See detailDecentralized reactive power dispatch for a time-varying multi-TSO system
Phulpin, Yannick; Begovic, Miroslav; Petit, Marc et al

in Proceedings of the 42nd Hawaii International Conference on System Sciences (HICSS-42) (2009)

This paper addresses the problem of reactive power dispatch in a power system partitioned into several areas controlled by different transmission system operators. Previous research has shown that nearly ... [more ▼]

This paper addresses the problem of reactive power dispatch in a power system partitioned into several areas controlled by different transmission system operators. Previous research has shown that nearly optimal performance could be achieved in a time-invariant system by using a specific iterative decentralized control scheme with no information exchange. At each iteration of this scheme, every transmission system operator concurrently schedules its own control settings for the next iteration while representing the neighboring areas with external network equivalents. This paper focuses on some parameter tracking techniques to extend the range of application of the decentralized control scheme to time-varying systems, where the time-varying nature of the system is modeled as a succession of steady-state operating conditions with variation of the load demand. Those new techniques are evaluated in the context of IEEE 118 bus system partitioned into three control areas. [less ▲]

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See detailResearch and Education Activities in Electric Power Systems at the University of Liège
Wehenkel, Louis ULg; Ernst, Damien ULg; Rousseaux, Patricia ULg et al

in Revue E Tijdschrift (2008), (4), 54-59

This paper presents research and education activities of the power systems group of the Department of Electrical Engineering and Computer Science of the University of Liège. These activities cover power ... [more ▼]

This paper presents research and education activities of the power systems group of the Department of Electrical Engineering and Computer Science of the University of Liège. These activities cover power systems stability, security, reliability, and markets, within the contexts of expansion planning, operation planning and real-time operation and automatic control. The paper also reviews the international collaborations of the team. [less ▲]

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See detailVariable selection for dynamic treatment regimes: a reinforcement learning approach
Fonteneau, Raphaël ULg; Wehenkel, Louis ULg; Ernst, Damien ULg

in The annual machine learning conference of Belgium and the Netherlands (BeNeLearn 2008) (2008, May)

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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 detailVariable selection for dynamic treatment regimes
Fonteneau, Raphaël ULg; Wehenkel, Louis ULg; Ernst, Damien ULg

in 27th Benelux Meeting on Systems and Control (2008)

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