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International audience; In this work, seven commercially available high temperature(HT) membrane electrode assemblies (MEAs), using a phos-phoric acid doped polybenzimidazole (PBI) membrane, weretested at six constant current densities during mostly around540 h: 1, 0.6, 0.4, 0.2, 0.1, and 0 A cm–2. The MEA aged at0.6 A cm–2appears to be the less degraded one and the MEAsworking at 0 and 1 A cm–2seem to be the most degradingones. Degradations are supposed to be mainly due to the car-bon corrosion of electrodes and the loss of electrolyte withthe MEA aged at 1 A cm–2. The characterization periods havea significant impact on cell ageing. The corrosion of carbonsupport is considered here to be the major degradation forthe tests carried out between 0 and 0.6 A cm–2. A degradationrate was calculated using the voltage from the polarizationcurves and it appears to be more relevant compare to thedegradation rate calculated using the voltage during endur-ance period. The modeling approach shows promisingresults and it seems that the electrochemical surface area,measured by cyclic voltammetry, can be included into themodeling in order to obtain higher parameter consistency.

High-Temperature Proton Exchange Membrane Fuel Cell constant current ageing tests highlighted that the characterizations used to monitor the state of health of single cells could be potentially degrading. An experimental campaign to analyze potential degradation due to polarization curves was carried out. More exactly, four methodologies to generate a polarization curve including Electrochemical Impedance Spectroscopies (EIS) were cycled 30 times. The tested single cells were based on a commercial PBI Membrane Electrodes Assembly (MEA) with an active surface of 45 cm2 (BASF Celtec®-P 1100 type). Before the first cycling test and after the last cycling one, complete characterizations, composed by a voltammetry and a polarization curve including EIS, were performed. The results show that one of the MEA has a voltage which increased for one of the four methods to obtain the polarization curve. This growth is linked to a decrease of ohmic losses: in an unexpected way, it could be considered as a way to improve the break-in period. Similarly, the monitoring of CO2 emission (as corrosion has been suspected to be involved at high voltage, i.e. low current density) confirms the potential degradation of the electrodes during the measurement of the polarization curve.

In this work, a commercially available Membrane Electrode Assembly (MEA) from Advent Technology Inc., developed for a use in High Temperature Proton Exchange Membrane Fuel Cell (HT-PEMFC), was tested under various operating conditions (OCs) according to a design of experiments (DOE) with three factors varying on three levels: hydrogen gas over-stoichiometry (1.05, 1.2, 1.35), air gas over-stoichiometry (1.5, 2, 2.5) and temperature (140°C, 160°C, 180°C). A polarization curve (V-I curve) was performed for each set of operating conditions (27 curves in total) by characterizing 22 current levels. A semi-empirical and macroscopic (1D) model of the cell voltage was developed in steady state in order to model these experimental data. The proposed parameterization approach for this model (called here “multi-VI” approach) is based on the sensitivity to the OCs specific to each physicochemical phenomenon involved. With this method, only one set of parameters is used in order to model all the experimental curves (simultaneous optimization with 27 curves). The obtained results are very good: an average error less than 0.8 % and a maximum error around 2.6% between modelled and measured voltages. The obtained parameters appear consistent regardless the OCs. The proposed “multi-VI” approach with only one set of parameters seems to be an interesting way in order to converge towards a uniqueness of consistent parameters.

Nowadays, fuel cells are regarded as a promising solution in the context of development of a “More Electrical Aircraft”. Indeed, the integration of fuel cell systems in aircraft allows generating electrical energy with high efficiency and low environmental impact. However, there are still many questions about the functioning and the performance of these systems in typical aeronautical conditions. The present work is focused on aeronautical conditions linked to cabin applications. Therefore, a particular attention is paid to low pressure operation, with experimental investigations carried out at subatmospheric pressures. Given the complexity of the possible interactions, an experimental database was created using the Design of Experiments method. The experimental results are first presented and discussed, then exploited via a modelling approach. The objective is to define a model for the polarization curve able to describe its evolution when the operating conditions change. The methodology used to construct the model is introduced step-by-step as well as the modelling results for the various involved phenomena. At the end, the predictive behaviour of the model is investigated with polarization curves carried out at operating conditions taken outside the definition range of the DoE.

It is now well recognized that highly dynamic power demands accelerate the ageing of a fuel cell. A solution is to hybridize it with an electrochemical storage device (ultracapacitors, Li-ion battery...). Whatever the technique implemented to manage energy, the hybridization principle forces the storage device to take in charge the rapid power changes to protect the fuel cell. Several electrical architectures are possible to interconnect the fuel cell and the storage device: indirect hybridization via power converters, or direct hybridization without power converters. The work here focuses on direct hybridization between a fuel cell and ultracapacitors. Classically, this kind of connection concerns the hybridization of a fuel cell stack with an ultracapacitors' pack. The authors here investigate another rather original option by implementing this hybridization at the scale of each cell of a fuel cell stack. In this approach, each elementary ultracapacitor can be connected either to one cell or to two cells. Before applying the concept to a real fuel cell stack (the final objective), the authors studied the concepts with single cells. This paper is going to present the intensive experimental works achieved to apprehend the principles. Static and dynamics properties of such hybridization are analyzed and modeled.

International audience; In this paper, the authors investigate four original methodologies for sizing a battery bank inside a passive wind turbine system. This device interacts with wind and load cycles, especially for a stand-alone application. Generally, actual wind speed measurements are of long duration which leads to extensive processing time in a global optimization context requiring a wide number of system simulations. The first part of this article outlines two sizing methodologies based on a statistical approach for the sizing of the electrochemical storage device of a stand-alone passive wind turbine system. Two other efficient methodologies based on the synthesis of compact wind speed profiles by means of evolutionary algorithms are described in the second part of this paper. The results are finally discussed with regard to the relevance of the battery bank sizing and in terms of computation cost, this later issue being crucial to an Integrated Optimal Design (IOD) process.

PurposeA wide number of applications requires classifying or grouping data into a set of categories or clusters. The most popular clustering techniques to achieve this objective are K‐means clustering and hierarchical clustering. However, both of these methods necessitate the a priori setting of the cluster number. The purpose of this paper is to present a clustering method based on the use of a niching genetic algorithm to overcome this problem.Design/methodology/approachThe proposed approach aims at finding the best compromise between the inter‐cluster distance maximization and the intra‐cluster distance minimization through the silhouette index optimization. It is capable of investigating in parallel multiple cluster configurations without requiring any assumption about the cluster number.FindingsThe effectiveness of the proposed approach is demonstrated on 2D benchmarks with non‐overlapping and overlapping clusters.Originality/valueThe proposed approach is also applied to the clustering analysis of railway driving profiles in the context of hybrid supply design. Such a method can help designers to identify different system configurations in compliance with the corresponding clusters: it may guide suppliers towards “market segmentation”, not only fulfilling economic constraints but also technical design objectives.

International audience; In this article, we investigate a procedure for generating signals with genetic algorithms. Signals are obtained from elementary patterns characterized by different degrees of freedom. These patterns are repeated and combined in order to reach specific signal shapes. The whole signal parametrization has to be determined by solving a difficult inverse problem of high dimensionality and strong multimodality. This can be carried out using evolutionary algorithms with the aim of finding all pattern configurations in the signal. The different signal synthesis schemes are evaluated, tested and applied to the generation of particular railway driving profiles.

International audience; In this paper, the authors face the problem of wind speed processing as environmental variable of a wind turbine system. Generally, the information on wind speed measurements is processed over long periods of time to be relevant with respect to the site characteristics (average and maximum speeds, statistics). Subsequent large scale profiles of wind speed lead to long processing time for simulation analysis and especially for optimization design that penalizes the search of optimal solutions. An original synthesis approach of a compact and representative wind speed profile using an Evolutionary Algorithm (EA) is proposed. This approach is compared to a purely statistical approach based on random number generators. It allows reducing the actual wind profile duration with compression ratios greater (two months of wind speed measurements are compressed in only 1 hour). Then, the synthesis approach by EA is applied to the sizing of an autonomous hybrid system based on wind turbine with battery storage for stand-alone energy systems. It has proven its effectiveness in reducing 200 days of wind speed measurements in only 10 days, allowing sizing the storage system with a significant gain in terms of computing time in the framework of the optimization process.

Energy systems design, particularly electrical, is nowadays increasingly influenced by social issues linked to energy economy policies and the reducing the impact on the environment. To this, numerous technical demands are added, such as volume and mass, lifetime, reliability, quality (susceptibility, harmonic pollution), stability and recyclability. Being strongly linked to cost criteria, these demands require design to be tackled according to a “technico-economic” approach. Thus, the end of the 20th century was marked by a notable evolution towards a more complete evaluation of costs over the whole of the life cycle of the system (production, maintenance and usage costs, even dismantling/recycling costs). Faced with these new considerations, designers are called upon to consider in more detail the environment in which their systems will evolve. It is therefore primordial, even imperative, to evolve toward a “systems design” approach, enabling, on one hand, an understanding of the coupling between system constituents, and facilitating, on the other, the integration of the "finality" (mission) and “environmental variables” of the device being designed, from the first stages of design.

In this paper, the authors investigate two methodologies for synthesizing compact wind speed profiles by means of evolutionary algorithms. Such profile can be considered as input parameter in a prospective design process by optimization of a passive wind system with storage. Compact profiles are obtained by aggregating elementary patterns in order to fulfil some target indicators. The main difference between both methods presented in the paper is related to the choice of these indicators. In the first method, they are related to the storage system features while they only depend on wind features in the second.

This work presents a methodological approach aiming at analyzing and processing mission profiles and more generally environmental variables (e.g. solar or wind energy potential, temperature, boundary conditions) in the context of system design. This process constitutes a key issue in order to ensure system effectiveness with regards to design constraints and objectives. In this thesis, we pay a particular attention on the use of compact profiles for environmental variables in the frame of system level integrated optimal design, which requires a wide number of system simulations. In a first part, we propose a clustering approach based on partition criteria with the aim of analyzing mission profiles. This phase can help designers to identify different system configurations in compliance with the corresponding clusters: it may guide suppliers towards "market segmentation" not only fulfilling economic constraints but also technical design objectives. The second stage of the study proposes a synthesis process of a compact profile which represents the corresponding data of the studied environmental variable. This compact profile is generated by combining parameters and number of elementary patterns (segment, sine or cardinal sine) with regards to design indicators. These latter are established with respect to the main objectives and constraints associated to the designed system. All pattern parameters are obtained by solving the corresponding inverse problem with evolutionary algorithms. Finally, this synthesis process is applied to two different case studies. The first consists in the simplification of wind data issued from measurements in two geographic sites of Guadeloupe and Tunisia. The second case deals with the reduction of a set of railway mission profiles relative to a hybrid locomotive devoted to shunting and switching missions. It is shown from those examples that our approach leads to a wide reduction of the profiles associated with environmental variables which allows a significant decrease of the computational time in the context of an integrated optimal design process.; Ce travail présente une démarche méthodologique visant le " traitement de profils " de " mission " et plus généralement de " variables environnementales " (mission, gisement, conditions aux limites), démarche constituant la phase amont essentielle d‟un processus de conception systémique. La " classification " et la " synthèse " des profils relatifs aux variables d‟environnement du système constituent en effet une première étape inévitable permettant de garantir, dans une large mesure, la qualité du dispositif conçu et ce à condition de se baser sur des " indicateurs " pertinents au sens des critères et contraintes de conception. Cette approche s‟inscrit donc comme un outil d‟aide à la décision dans un contexte de conception systémique. Nous mettons en particulier l‟accent dans cette thèse sur l‟apport de notre approche dans le contexte de la conception par optimisation qui, nécessitant un grand nombre d‟itérations (évaluation de solutions de conception), exige l‟utilisation de " profils compacts " au niveau informationnel (temps, fréquence,...). Nous proposons dans une première phase d‟étude, une démarche de " classification " et de " segmentation " des profils basée sur des critères de partitionnement. Cette étape permet de guider le concepteur vers le choix du nombre de dispositifs à concevoir pour sectionner les produits créés dans une gamme. Dans une deuxième phase d‟étude, nous proposons un processus de " synthèse de profil compact ", représentatif des données relatives aux variables environnementales étudiées et dont les indicateurs de caractérisation correspondent aux caractéristiques de référence des données réelles. Ce signal de durée réduite est obtenu par la résolution d‟un problème inverse à l‟aide d‟un algorithme évolutionnaire en agrégeant des motifs élémentaires paramétrés (sinusoïde, segments, sinus cardinaux). Ce processus de " synthèse compacte " est appliqué ensuite sur des exemples de profils de missions ferroviaires puis sur des gisements éoliens (vitesse du vent) associés à la conception de chaînes éoliennes. Nous prouvons enfin que la démarche de synthèse de profil représentatif et compact accroît notablement l'efficacité de l‟optimisation en minimisant le coût de calcul facilitant dès lors une approche de conception par optimisation.

In this paper, hybridization of a BB460000 locomotive is proposed integrating a reduced power diesel generator, batteries and ultracapacitors as storage elements. The power mission of the BB460000 locomotive is studied in order to analyze its ability to be hybridized and to identify the most critical mission. An energy management strategy based on a frequency sharing is proposed. It allows strongly decreasing the nominal power of the diesel generator. Then, through a power flow sizing model, the hybrid locomotive is sized with Ni-Cd batteries and ultracapacitors. The uselessness of ultracapacitors on energetic, geometrical, financial and lifetime plans is shown.

The French National Railways Company (SNCF) is interested in the design of a hybrid locomotive based on various storage devices (accumulator, flywheel, and ultracapacitor) and fed by a diesel generator. This paper particularly deals with the integration of a flywheel device as a storage element with a reduced-power diesel generator and accumulators on the hybrid locomotive. First, a power flow model of energy-storage elements (flywheel and accumulator) is developed to achieve the design of the whole traction system. Then, two energy-management strategies based on a frequency approach are proposed. The first strategy led us to a bad exploitation of the flywheel, whereas the second strategy provides an optimal sizing of the storage device. Finally, a comparative study of the proposed structure with a flywheel and the existing structure of the locomotive (diesel generator, accumulators, and ultracapacitors) is presented.

International audience; RESUME-Afin de dimensionner un système énergétique par hybridation directe d'une pile à combustible avec une batterie pour une application aéronautique, un modèle électrique équivalent de cette hybridation a été développé. Le dimensionnement optimal de ce système est réalisé par un algorithme combinatoire pour, d'une part, répondre aux besoins de la mission et, d'autre part, minimiser sa masse. La mise en oeuvre d'un modèle électrique équivalent de l'hybridation à partir de modèles statiques des composants permet de réduire son temps de résolution. Pour s'assurer de la validité du modèle statique de l'hybridation, il est comparé avec un modèle dynamique. Plusieurs technologies de batteries, Nickel Cadmium (NiCd) ou Lithium-ion (Li-ion), sont proposées afin d'étudier les avantages et les inconvénients de chaque batterie utilisée lors de cette hybridation. Les caractéristiques de la batterie apparaissent déterminantes dans le dimensionnement des éléments du système. La préchauffe de la pile, assurée par la batterie, contraint également sa taille.

International audience; In this paper, the authors report the development of a Systemic Optimization Process (SOP) devoted to a passive wind turbine system with electrochemical storage bank. Aim of the SOP is to find the optimal combination and sizing among sets of system components, that meets the desired system requirements with the lowest system owning cost. The passive wind system associated to the storage bank interacts with wind and load cycles (deterministic data). Sets of passive wind turbines are obtained through an Integrated Optimal Design (IOD) process. The system cost model is inspired from constructor data for the wind turbines and related to the battery cycles for the storage bank. An optimization problem is developed and performed using an exhaustive search. The optimization results are finally exposed and discussed

International audience

In order to size the elements of a storage system for an aeronautical application, a simplified model of a High Temperature Proton Exchange Membrane Fuel cell (HT-PEMFC)-Battery passive hybridization has been developed. It is compared to a dynamic model for validation. Sizing, done by a combinatorial algorithm, must meet a dual objective: on the one hand, satisfy the mission profile, and on the other hand, minimize the mass of the system. Several battery technologies, NiCd or lithium-ion, are studied in order to analyze the advantages and disadvantages of each in such hybridization. The characteristics of the battery appear to be decisive in the sizing of the system. The fuel cell preheating, provided by the battery, also constrains its size.

International audience; In this paper, the authors investigate a robust Integrated Optimal Design (IOD) devoted to a passive wind turbine system with electrochemical storage bank: this stand alone system is dedicated to rural electrification. The aim of the IOD is to find the optimal combination and sizing among a set of system components that fulfils system requirements with the lowest system Total Cost of Ownership (TCO). The passive wind system associated with the storage bank interacts with wind speed and load cycles. A set of passive wind turbines spread on a convenient power range (2 - 16 kW) are obtained through an IOD process at the device level detailed in previous papers. The system cost model is based on data sheets for the wind turbines and related to battery cycles for the storage bank. From the range of wind turbines, a "system level" optimization problem is stated and solved using an exhaustive search. The optimization results are finally exposed and discussed through a sensitivity analysis in order to extract the most robust solution versus environmental data variations among a set of good solutions.

International audience

International audience; Afin de dimensionner un système énergétique par hybridation directe d'une pile à combustible avec une batterie pour une application aéronautique, un modèle électrique équivalent de cette hybridation a été développé. Le dimensionnement optimal de ce système est réalisé par un algorithme combinatoire pour, d'une part, répondre aux besoins de la mission et, d'autre part, minimiser sa masse. La mise en oeuvre d'un modèle électrique équivalent de l'hybridation à partir de modèles statiques des composants permet de réduire son temps de résolution. Pour s'assurer de la validité du modèle statique de l'hybridation, il est comparé avec un modèle dynamique. Plusieurs technologies de batteries, Nickel Cadmium (NiCd) ou Lithium-ion (Li-ion), sont proposées afin d'étudier les avantages et les inconvénients de chaque batterie utilisée lors de cette hybridation. Les caractéristiques de la batterie apparaissent déterminantes dans le dimensionnement des éléments du système. La préchauffe de la pile, assurée par la batterie, contraint également sa taille.

International audience