Thèses sur le sujet « Multi-fuel cell stacks system »

This thesis presents an experimental investigation into the feasibility of using a functionally thermal fluid to enhance the performance of a Proton Exchange Membrane (PEM) Fuel Cell. Specifically, a fluid was developed that utilised a liquid-solid phase change to enhance heat transport within the fuel cell. Increasing the convective heat transfer coefficient could permit the use of smaller volumetric flow rates and reduce pumping power. The objective of the thermal fluid was to create isothermal conditions across a fuel cell and to reduce parasitic loadings from pumps and other components to enhance the overall system performance. Additionally, the fluid could reduce the system size and component cost, and stabilise temperature fluctuations within the system. The thermal fluid that was developed constituted a mix of fine, Microencapsulated Phase Change Material (MicroPCM) particles suspended in a single-phase working fluid. For successful integration with the fuel cell, the microPCMs thermal and fluid properties, and their effectiveness in transferring heat, had to be fully characterised and understood. Research consisted of experimental investigations of the fuel cell, followed by microPCM development. Experimentation on the fuel cell stack revealed a requirement for thermal stability and reduction in parasitic load from the pumps. Quantitative characterisation and development of the microPCM properties involved state of the art equipment to measure the latent heat of fusion, melting and freezing points, surface morphology and viscosity of the microPCM slurry. The effects of repeated use of solid to liquid phase change particles upon melting and solidification were studied. This lead to the further development of microPCM particles and experimentally examined in a fuel cell system. The use of MicroPCM developed in this study balanced the improvement in thermal capacity of the fluid with the increase in pumping load, when compared to the use of water alone. The study suggested that with further development of the microPCM slurry, it has the potential to significantly increase the thermal capacity of the fluid and stabilise temperatures across the fuel cell, which in turn would results in improved stack performance and electrical conversion efficiency.

The growth of distributed energy resources together with the incorporation of new technologies in the generation and storage of energy are imposing new control and operational strategies. Due to its storage capability and that it is considered to be clean energy; fuel cell (FC) is one of the most promissory technologies as a stationary energy source in micro grids and also in transportation applications. Therefore, two main issues are addressed in this work; the conception, design, and setup of a fully instrumented test bench for proton exchange membrane (PEM) FC stacks and the design and experimental test of a new dynamic energy-exchange control strategy for multi source and multi load systems. To define the test bench instrument requirements, in the first part a complete dynamic model review is given. In the next section, relevant information regarding the setup of the FC test bench design and implementation is included, i.e., specification criteria of the instruments and acquisition and data display system. Some experimental results are performed in order to demonstrate the potentialities of the setup. In the following chapter, a new dynamic energy exchange control strategy (DSER) is introduced and tested in a two port system via simulation and experimentation. In order to establish a comparison and integrate the DSER in a FC application, in the fifth chapter a three port system - including a static model of FC - and two different control approaches, are tested via simulation. The thesis is closed with some concluding remarks and some potential research topics generated from this work.

Research and prototyping of a fuel cell stack system for micro aerial vehicles (MAVs) was conducted by Virginia Tech in collaboration with Luna Innovations, Inc, in an effort to replace the lithium battery technology currently powering these devices. Investigation of planar proton exchange membrane (PEM) and direct methanol (DM) fuel cells has shown that these sources of power are viable alternatives to batteries for electronics, computers, and automobiles. However, recent investigation about the use of microtubular fuel cells (MTFCs) suggests that, due to their geometry and active surface areas, they may be more effective as a power source where size is an issue. This research focuses on hydrogen MTFCs and how their size and construction within a stack affects the power output supplied to a MAV, a small unmanned aircraft used by the military for reconnaissance and other purposes. In order to conduct this research effectively, a prototype of a fuel cell stack was constructed given the best cell characteristics investigated, and the overall power generation system to be implemented within the MAV was modeled using a computer simulation program. The results from computer modeling indicate that the MTFC stack system and its balance of system components can eliminate the need for any batteries in the MAV while effectively supplying the power necessary for its operation. The results from the model indicate that a hydrogen storage tank, given that it uses sodium borohydride (NaBH4), can fit inside the fuselage volume of the baseline MAV considered. Results from the computer model also indicate that between 30 and 60 MTFCs are needed to power a MAV for a mission time of one hour to ninety minutes, depending on the operating conditions. In addition, the testing conducted on the MTFCs for the stack prototype has shown power densities of 1.0, an improvement of three orders of magnitude compared to the initial MTFCs fabricated for this project. Thanks to the results of MTFC testing paired with computer modeling and prototype fabrication, a MTFC stack system may be possible for implementation within an MAV in the foreseeable future.
Master of Science

Fuel cells are electricity generators which convert chemical energy of hydrogen directly to electricity by means of electrochemical oxidation and reduction reactions. A single proton exchange membrane (PEM) fuel cell can only generate electricity with a potential between 0.5V and 1V. The useful potential can be achieved by stacking cells in series to form a PEM fuel cell stack. There is a potential to utilize 100W class fuel cells. Fuelling is the major problem of the portable fuel cells. The aim of this thesis is to design and manufacture a PEM fuel cell stack which can be used for portable applications. The PEM fuel cell stack is planned to be incorporated to a NaBH4 hydrolysis reactor for H2 supply. Within the scope of this thesis a new coating technique called &ldquo
ultrasonic spray coating technique&rdquo
is developed for membrane electrode assembly (MEA) manufacturing. New metal and graphite bipolar plates are designed and manufactured by CNC technique. A fuel cell controller hardware is developed for fuel supply and system control. The power densities reached with the new method are 0.53, 0.74, 0.77, and 0.88 W/cm2 for 20%, 40%, 50%, 70% Pt/C catalyst by keeping 0.4mg Pt/cm2 platinum loading constant, respectively. The power density increase is 267% compared to &ldquo
spraying of catalyst ink with air pressure atomizing spray gun&rdquo
. All parts of the PEM fuel cell stack designed were produced, assembled, and tested. The current density reached is 12.9A at 12 V stack potential and the corresponding electrical power of the stack is 155W.

Le système de pile à combustible à membrane échangeuse de protons (PEMFC) a été considéré comme la nouvelle technologie de production d'énergie, car il présente l'avantage d'une densité de puissance élevée, d'une absence d'émissions, d'un rendement élevé et d'un démarrage rapide. C'est pourquoi cette thèse est consacrée à la recherche sur l'intégration du système, le contrôle des paramètres du système et l'optimisation des performances du système pour les systèmes PEMFC à cathode ouverte et à cathode fermée. Pour les systèmes PEMFC à cathode ouverte, la température de la pile est le facteur clé affectant la performance de sortie du système. Afin d'améliorer les performances de suivi dynamique de la température dans des conditions de changement de charge, un contrôle adaptatif inverse et une prédiction grise basés sur un contrôle adaptatif sans modèle sont proposés pour un contrôle optimal de la température du système. En outre, afin d'améliorer l'efficacité du système, une stratégie de contrôle de l'efficacité maximale basée sur l'optimisation de l'efficacité maximale et la commande prédictive généralisée par contrainte est proposée dans cette thèse. Pour le système PEMFC à cathode fermée, compte tenu de la non-linéarité existante et du fort couplage entre les paramètres de fonctionnement tels que la température de la pile et le taux d'excès d'oxygène (OER), une stratégie de contrôle multivariable à double boucle basée sur un contrôle adaptatif en mode glissant sans modèle MIMO est proposée pour la régulation de la température de la pile et du débit d'air du système PEMFC à cathode fermée. En outre, un banc d'essai de système PEMFC à cathode ouverte de 300 W et un banc d'essai de système PEMFC à cathode fermée de 5 kW sont établis. Toutes les stratégies de contrôle et d'optimisation des performances sont vérifiées sur le banc d'essai des systèmes PEMFC à cathode ouverte et à cathode fermée
Proton exchange membrane fuel cell (PEMFC) system has been considered as the new power generation technology as it has the advantage of high power density, zero emission, high efficiency, and fast start-up characteristics. Therefore, this thesis is devoted to researching system integration, system parameter trcking control, and system performance optimization for open-cathode and closed-cathode PEMFC systems. For open-cathode PEMFC system, the stack temperature is the key factor sffecting the output performance of the system. In order to improve the dynamic temperature tracking performance under load changing conditions, adaptive inverse control and grey prediction based model free adaptive control is proposed for optimal temperature control of system. Further, in order to enhance the system efficiency of system, a maximum efficiency control strategy based on maximum efficiency optimization and constraint generalized predictive control is proposed in this thesis. For closed-cathode PEMFC system, considering the existed nonlinearity and strong coupling between operating parameters such as stack temperature and oxygen excess ratio (OER), a dual loop multivariable control strategy based on MIMO model free adaptive sliding mode control is proposed for stack temperature and air flow rate regulation of closed-cathode PEMFC system. Moreover, a 300 W open-cathode PEMFC system test bench and a 5-kW closed-cathode PEMFC system tests bench are established. All the control strategies and the performance optimization strategies are verified on the established test bench of open-cathode and closed-cathode PEMFC systems

The present work aims to increase the diagnosis systems capabilities by choosing the location of sensors in the process. Therefore, appropriate sensor location will lead to better diagnosis performance and implementation easiness. The work is based on structural models ands some simplifications are considered in order to only focus on the sensor placement analysis. Several approaches are studied to solve the sensor placement problem. All of them find the optimal sensor configuration. The sensor placement techniques are applied to a fuel cell stack system. The model used to describe the behaviour of this system consists of non-linear equations. Furthermore, there are 30 candidate sensors to improve the diagnosis specifications. The results obtained from this case study are used to strength the applicability of the proposed approaches.
El present treball té per objectiu incrementar les prestacions dels diagnosticadors mitjançant la localització de sensors en el procés. D'aquesta manera, instal·lant els sensors apropiats s'obtenen millors diagnosticador i més facilitats d'implementació. El treball està basat en models estructurals i contempla una sèrie de simplificacions per tal de entrar-se només en la problemàtica de la localització de sensors. S'utilitzen diversos enfocs per tal de resoldre la localització de sensors, tot ells tenen com objectiu trobar la configuració òptima de sensors. Les tècniques de localització de sensors són aplicades a un sistema basat en una pila de combustible. El model d'aquest sistema està format per equacions no lineals. A més, hi ha la possibilitat d'instal·lar fins a 30 sensors per tal de millorar la diagnosis del sistema. Degut a aquestes característiques del sistema i del model, els resultats obtinguts mitjançant aquest cas d'estudi reafirmen l'aplicabilitat dels mètodes proposats.

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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Ce mémoire propose une stratégie de contrôle sans commutation d’algorithme pour un système hybride constituée d’une pile à combustible comme source principale et d’un pack de supercondensateurs comme source auxiliaire. Trois structures de système hybride ont été étudiées. Après avoir évoqué les différentes structures des systèmes hybrides électriques et des techniques utilisées pour les contrôler, deux approches sont traitées. La première est basée sur la notion de platitude permettant d’assurer la gestion des flots d’énergie dans une source hybride et plus généralement dans un système multi sources/multi charges. La stratégie proposée repose sur la génération d’un modèle d’ordre réduit du système et la gestion des flots d’énergie via des trajectoires de référence de certaines grandeurs énergétiques du système. L’impact de ce mode de contrôle sur le dimensionnement des éléments passifs (inductances, condensateurs) de la source hybride a été expliqué. Dans la deuxième stratégie, l’énergie totale stockée dans les hacheurs est prise en compte dans l’élaboration de la commande du système multi sources/multi charges en utilisant une linéarisation entrée/sortie sur les convertisseurs des charges. Un observateur non linéaire a été proposé pour estimer la variation de la caractéristique statique de pile à combustible et permet de garantir un fonctionnement optimal du système hybride. Les architectures de puissance et les modes de commande proposés ont été validés par des résultats simulés et/ou expérimentaux
This work deals with a nonlinear control strategy of an electrical hybrid system which is composed of a fuel cell as the main source and a supercapacitor bank as the auxiliary source. Any algorithm commutation is not used in the proposed control strategy whereas the system works in different operating modes. After a review of various structures of the electrical hybrid systems and different control methods of these systems, two new approaches are developed. The first one is flatness-based method to ensure the energy management in the proposed hybrid systems and generally in a multi source / multi loads system. The proposed strategy is based on generation of a reduced-order model of the system. The energy management is carried out through the reference trajectories of the stored electrostatic energy of the system. The effect of the proposed control method on design of the system components (inductors and capacitors) is explained. In the second approach, the total energy stored in the choppers is taken into account to control the load converters of a multi-source/multi load system by use of the input/output linearization method. A nonlinear observer is proposed to estimate the variation of voltage-power output characteristic of the fuel cell which leads to an optimal performance of the hybrid system. The simulation and experimental results prove validity of the proposed control strategy

Ce mémoire propose une stratégie de contrôle sans commutation d’algorithme pour un système hybride constituée d’une pile à combustible comme source principale et d’un pack de supercondensateurs comme source auxiliaire. Trois structures de système hybride ont été étudiées. Après avoir évoqué les différentes structures des systèmes hybrides électriques et des techniques utilisées pour les contrôler, deux approches sont traitées. La première est basée sur la notion de platitude permettant d’assurer la gestion des flots d’énergie dans une source hybride et plus généralement dans un système multi sources/multi charges. La stratégie proposée repose sur la génération d’un modèle d’ordre réduit du système et la gestion des flots d’énergie via des trajectoires de référence de certaines grandeurs énergétiques du système. L’impact de ce mode de contrôle sur le dimensionnement des éléments passifs (inductances, condensateurs) de la source hybride a été expliqué. Dans la deuxième stratégie, l’énergie totale stockée dans les hacheurs est prise en compte dans l’élaboration de la commande du système multi sources/multi charges en utilisant une linéarisation entrée/sortie sur les convertisseurs des charges. Un observateur non linéaire a été proposé pour estimer la variation de la caractéristique statique de pile à combustible et permet de garantir un fonctionnement optimal du système hybride. Les architectures de puissance et les modes de commande proposés ont été validés par des résultats simulés et/ou expérimentaux
This work deals with a nonlinear control strategy of an electrical hybrid system which is composed of a fuel cell as the main source and a supercapacitor bank as the auxiliary source. Any algorithm commutation is not used in the proposed control strategy whereas the system works in different operating modes. After a review of various structures of the electrical hybrid systems and different control methods of these systems, two new approaches are developed. The first one is flatness-based method to ensure the energy management in the proposed hybrid systems and generally in a multi source / multi loads system. The proposed strategy is based on generation of a reduced-order model of the system. The energy management is carried out through the reference trajectories of the stored electrostatic energy of the system. The effect of the proposed control method on design of the system components (inductors and capacitors) is explained. In the second approach, the total energy stored in the choppers is taken into account to control the load converters of a multi-source/multi load system by use of the input/output linearization method. A nonlinear observer is proposed to estimate the variation of voltage-power output characteristic of the fuel cell which leads to an optimal performance of the hybrid system. The simulation and experimental results prove validity of the proposed control strategy

Dans un contexte global de réduction des émissions de gaz à effet de serre, des solutions doivent être trouvées pour limiter les pollutions liées aux transports. Dans le domaine aéronautique, l’efficacité énergétique des avions peut être améliorée entre autres par l’utilisation de sources alternatives, comme les piles à combustible. Cette technologie est un dispositif électrochimique permettant de convertir le dihydrogène et le dioxygène en électricité, eau et chaleur. Néanmoins, le coût et la durée de vie de la pile sont des points faibles de cette technologie et doivent être améliorés.Dans le cadre d’une utilisation à bord d’un avion de ligne, l'analyse de la durabilité d'un système pile à combustible PEMFC est menée, en lien avec l'industriel Zodiac Aerospace. La prise en compte du vieillissement de la pile à combustible dans la gestion du système pile est essentielle pour limiter l’impact de conditions locales inappropriées du cœur de pile qui diminuent sa durée de vie. Dans ce travail, une étude complète est proposée pour corréler les mécanismes de vieillissement du cœur de pile (dégradation de la membrane, dissolution du catalyseur) aux conditions locales de la pile définies en partie par les performances des auxiliaires du système pile, le profil de puissance et les conditions environnementales du système. L'objectif est de prédire les performances de la pile et sa durée de vie afin de suggérer des stratégies d’optimisation pour l'application visée. L’approche proposée est basée sur la simulation numérique et validée par des essais de durabilité.Un modèle multi-physique existant au CEA est développé dans cette thèse pour corréler les usages aux mécanismes de dégradation. Une description physique de la pile à combustible est réalisée dans ce modèle, avec la prise en compte des réactions électrochimiques, des mécanismes de diffusion de l’eau et des gaz à l’échelle microscopique dans la pile, ainsi que de la thermique. Des améliorations y sont apportées, afin de mieux représenter la géométrie des plaques distributrices de gaz utilisées pour les essais. Un travail sur le circuit de refroidissement permet en outre d’affiner la distribution de température à la surface de la cellule. Enfin, l’ajout de mécanismes de dégradation est effectué pour modéliser le vieillissement de la pile. Pour cela, deux approches différentes sont couplées, l’une basée sur des équations physiques de l’électrochimie («Bottom-Up») et l’autre sur des lois semi-empiriques («Top-Down»).Les résultats de la modélisation sont confrontés à des essais expérimentaux dédiés. En particulier, deux tests de 2000 heures en conditions aéronautiques ont été effectués, avec deux régimes de fonctionnement différents (stabilisé et dynamique). Les méthodes usuelles de caractérisations électrochimiques (spectroscopie d’impédance, voltampérométries), des analyses post-mortem ainsi que des mesures locales de densité de courant et de température réalisées durant les essais aident à la validation des modèles.En particulier, les différentes mesures montrent que le modèle développé est capable de simuler la répartition hétérogène des conditions locales dans le cœur de pile en fonction des conditions opératoires (conditions asséchantes, humides, etc.). Il permet alors de calculer le comportement de paramètres internes de la pile non accessibles par l’expérience (humidités relatives, fractions molaires, etc.). De plus, le modèle permet de retrouver l’impact de différents modes opératoires sur le vieillissement, apportant également des informations sur les mécanismes de dégradation qui agissent sur les matériaux. Enfin, des stratégies d’optimisation sont proposées pour améliorer la durée de vie de la pile, basées sur le cycle réel envisagé par Zodiac Aerospace pour l’application de la pile à combustible à bord d’un avion de ligne (hors propulsion)
In a global context of greenhouse gases emissions reduction, solutions need to be found to limit the pollution from transportation. In the aeronautics, the energy efficiency of planes can be improved by using alternative energy sources, such as fuel cells. This technology is an electrochemical device that converts hydrogen into electricity, water and heat. Nevertheless, cost and lifetime of fuel cells are weaknesses of this technology and need to be improved.As part of the use onboard commercial airplanes, analysis of a PEM fuel cell system durability is conducted, in collaboration with Zodiac Aerospace. Taking the fuel cell aging into account in the fuel cell system management is essential to limit the impact of inappropriate fuel cell core local conditions, which decrease the fuel cell lifetime. In this work, a complete study is proposed to correlate the fuel cell internal aging mechanisms (membrane degradation, catalyst dissolution) to the fuel cell local conditions which are defined partly by the system ancillaries’ performances, the power profile and the system environmental conditions. The objective is to be able to predict the fuel cell operation and its durability in order to suggest optimization strategies for the targeted application. The proposed approach is based on modeling and validated by experimental durability tests.A multi-physical model existing at the CEA is developed in this PhD to correlate the uses to the degradation mechanisms. The physical description of the fuel cell is done in this model, where electrochemical reactions, fuel cell water and gas diffusion mechanisms at micro scale and heat transfers are taken into account. Improvements are added, in order to better model the geometry of the gases distributing plates used in the tests. Besides, a work on the cooling circuit enables to refine the temperature distribution at the cell surface. Finally, degradation mechanisms are added to model the fuel cell aging. Two different approaches are used, one based on physical electrochemical equations (“Bottom-Up”) and the other one based on semi-empirical laws (“Top-Down”).Results from the modeling part are compared with dedicated tests. In particular, two tests of 2,000 hours each in aeronautical conditions are performed, with two different operating modes (stabilized and dynamic). Usual methods of electrochemical characterization (impedance spectroscopy, voltammetries), post-mortem analyses along with in-situ measurements of the current density and temperature performed during the tests help validating the model.In particular, the measures show that the developed model is able to simulate the heterogeneous distribution of the local conditions inside the fuel cell in function of the operating conditions (dry, wet, etc.). It gives the possibility to monitor the behavior of fuel cell internal parameters which are not reachable by the tests (relative humidity, molar fractions, etc.). Moreover, the model enables to find back the impact of several operating regimes on the aging, giving as well information about the degradation mechanisms acting on the materials. Last but not least, strategies are proposed to improve the fuel cell durability, based on the real cycle considered by Zodiac Aerospace for the use of the fuel cell system onboard a commercial airplane (apart from the propulsion)

A l’aide de la Représentation Energétique Macroscopique (REM) comme outil de modélisation graphique, la modélisation et la gestion d’énergie d’une application stationnaire isolée à base d’un système PEMFC couplé à l’énergie solaire photovoltaïque comme source principale d’énergie sont développées. Afin d’assurer une autonomie du système en combustible, un électrolyseur PEM est intégré au dispositif. En outre, des packs de batteries et de supercondensateurs permettent un stockage d’énergie et de puissance.Grâce à la modularité de la REM, les modèles respectifs des différentes entités énergétiques du système ont été développés avant de les assembler pour reconstituer un modèle global. Une caractéristique propre de la REM étant la commande, une Structure Maximale de Commande (SMC) est déduite du modèle REM du système par application de règles d’inversion.Le phénomène d’effet échelle a permis de dimensionner le système grâce à un profil de consommation domestique d’énergie électrique. Une stratégie de gestion énergétique basée sur la méthode du bilan des flux de puissance et prenant en compte les dynamiques de chaque source a été développée. Différents modes de fonctionnement ont été étudiés. Grâce è un profil d’ensoleillement d’une journée, la pertinence du modèle a été évaluée. Il a été en outre introduit un couplage entre la méthode du bilan des flux de puissance et la logique floue afin que la stratégie de gestion redéfinisse les références des grandeurs électriques en tenant compte de l’état de charge des batteries et de celui des supercondensateurs
A stand alone multi-source system based on the coupling of photovoltaic energy and both a PEM electrolyser and a PEMFC for stationary application is studied. The system gathers photovoltaic array as main energy source, ultracapacitors and batteries packs in order to smooth respectively fast and medium dynamic by supplying the load or by absorbing photovoltaic source overproduction. Because of the necessity of fuel availability, especially for islanding application like this one, a PEM electrolyser is integrated to the system for in situ hydrogen production.The main purpose being modeling and management of the power flows in order to meet the energy requirement without power cut, a graphical modeling tool namely Energetic Macroscopic Representation (EMR) is used because of its analysis and control strengths. Thanks to the modular feature of the EMR, the different models of each energetic entity of the system are performed before their assembling.By using scale effect, the energetic system sizing is performed according to a household power profile. Then, by the help of the multi-level representation, the maximal control structure (MCS) is deduced from the system EMR model. The electrical reference values of the MCS are generated by applying the power balancing method involving the own dynamic of each source into the energy management strategy. Different behavior modes are taken into account. By considering an irradiance profile for one day, the system is simulated highlighting its suitable behaviour. Moreover, the relevance of the introduced coupling between fuzzy logic controller and the power balancing method is pointed out

Même si l’hydrogène est en plein essor, les véhicules électriques à pile à combustible sont encore rares sur le marché. Leur volume et leur complexité encore trop importants comptent parmi les freins au développement des systèmes PEM (Proton Exchange Membrane) dans le secteur des transports. Ces travaux de thèse visent à étudier deux nouveaux circuits fluidiques permettant à la fois de simplifier et de réduire le volume du système. Il s’agit de la recirculation de l’air, et du Ping-Pong, une architecture fluidique permettant d’alterner la localisation de l’alimentation en combustible dans le stack. Les performances des deux architectures ont été étudiées expérimentalement en conditions automobile sur un système de 5 kW. Une analyse multi-échelles a été conduite pour comparer, à d’autres architectures connues, les performances du système, du stack et l’homogénéité des tensions de cellules du stack. L’étude a été complétée par un test de durabilité en Ping-Pong afin d’évaluer l’impact de ce nouveau mode de fonctionnement sur le stack. A nouveau, les données expérimentales sont analysées à différentes échelles jusqu’à l’expertise post-mortem des assemblages-membrane-électrode
Although hydrogen is booming, fuel cell electric vehicles are still rare on the market. Their high volume and complexity are still major hurdles to the development of PEM (Proton Exchange Membrane) systems for transport applications. This PhD. work aimed at studying two new fluidic circuits that can both simplify and reduce the system volume. Namely, the cathodic recirculation, and the Ping-Pong, which is a new fluidic architecture that alternate the fuel feed locations during operation. The performances of both architectures have been studied experimentally in automotive conditions on a 5 kW system. A multiscale analysis was conducted to compare, with other known architectures, the performances of the system, the stack and the homogeneity of the cell voltages inside the stack. The study was completed with a Ping-Pong durability test to evaluate the impact of this new operation on the fuel cell stack. The experimental data have been analyzed at different scales up to the post-mortem expertise of membrane-electrode assemblies

博士
國立清華大學
動力機械工程學系
97
本論文以多尺度模擬設計中低溫平板型微固態氧化物燃料電池堆系統，結合分子動態模擬(Molecular dynamics)與計算流體力學(Computational fluid dynamics)。分子動態模擬用來求出固態氧化物燃料電池電解質的最佳摻雜濃度，而且此固態電解質能夠在中低溫操作下仍具有良好離子傳導性能。本論文針對中低溫型固態電解質氧化釤-鈰固態電解質(samarium-doped ceria)與氧化釓-鈰固態電解質(gadolinium-doped ceria)比較傳統型釔安定化氧化鋯(yittria-stablized zirconia)固態電解質在中低溫下的性能表現。透過分子動態模擬探討摻雜濃度與操作溫度對於固態電解質中離子傳導率的影響，以及利用計算流體力學合併電化學反應方程式研究中低溫平板型微固態氧化物燃料電池堆性能。 利用分子動態模擬，可以觀察氧離子在電解質內的傳遞現象，係藉由氧空洞的位置進行不連續性的動態傳遞，從分子動態模擬結果中得知，釤-鈰固態電解質與氧化釓-鈰固態電解質存在一最佳摻雜濃度。受到溫度影響，固態電解質內離子遷移性在較高溫時其傳導率越佳。最後，比對實驗結果證明分子動態模擬結果與實驗數據具有良好的匹配性。 利用多尺度模擬，進行中低溫平板型微固態氧化物燃料電池堆性能研究，由計算流體力學合併電化學反應方程式針對不同固態電解質與進氣岐管設計進行電池性能差異研究。在873K中低溫平板型微固態氧化物燃料電池堆系統使用氧化釤-鈰固態電解質能獲得較高的性能，相較於傳統型釔安定化氧化鋯固態電解質在中低溫操作環境下電池性能表現較差。為了改善中低溫平板型微固態氧化物燃料電池堆系統性能，利用新設計的進氣岐管來改善氣體利用率，由電池性能模擬結果顯示，此新型進氣岐管設計確實能夠獲得較高的電池性能。

碩士
國立臺灣科技大學
電子工程系
98
Recently, clean energy resources, such as wind turbines, photovoltaic systems or fuel cells, have been exploited for developing renewable electric power generation systems. Among them, the rapid advances in fuel cell technology have enabled the significant developments in fuel cell power system. The fuel cells feature numerous advantages, such as high energy density, high current output ability, and high-efficiency operation. However, the fuel cell stacks present a low voltage output and a wide range of voltage variations under different load, temperature, humidity and electrochemical reaction conditions. A step-up power converter is therefore applied to obtain a high output voltage from the fuel cell system. A high-performance isolated multi-phase power converter for fuel cell power systems is studied and implemented. A digital controller is also designed to perform the interleaved operation of the paralleled multi-phase power modules. Finally, a 10-kW converter prototype is implemented and tested to verify the feasibility of the studied topology and control strategy.

M. Tech. (Engineering Department Applied Electronics and Electronic Communication, Faculty of Engineering) Vaal University of Technology
This study presents the design of a proton exchange membrane fuel cell stack that can be used to replace conventional sources of electrical energy in an uninterruptible power supply system, specifically for use in the telecommunications industry. One of the major concerns regarding the widespread commercialization of fuel cells is the high cost associated with fuel cell components and their manufacturing. A fuel cell design is presented in which existing, low-cost, technologies are used in the manufacture of cell components. For example, printed circuit boards are used in the manufacturing of bipolar flow plates to significantly reduce the cost of fuel cells. The first objective was to design, construct and test a single fuel cell and small fuel cell stack in order to evaluate the use of printed circuit boards in bipolar plate manufacturing. Since the use of copper in a fuel cell environment was found to reduce the lifetime of the cells, the bipolar plates were coated with a protective layer of nickel and chrome. These coatings proved to increase the lifetime of the cells significantly. Power outputs of more than 4 W per cell were achieved. The second objective was to analyze a small fuel cell stack in order to obtain a model for predicting the performance of larger stacks. A mathematical model was developed which was then used to design an electronic circuit equivalent of a fuel cell stack. Both models were adapted to predict the performance of a fuel cell stack containing any number of cells. The models were proven to be able to accurately predict the performance of a fuel cell stack by comparing simulated results with practical performance data. Finally, the circuit equivalent of a fuel cell stack was used to evaluate the capability of a switch mode boost converter to maintain a constant voltage when driven by a fuel cell stack, even under varying load conditions. Simulation results showed the ability of the boost converter to maintain a constant output voltage. The use of supercapacitors as a replacement for batteries as a secondary energy source was also evaluated.

碩士
國立臺灣科技大學
電機工程系
94
This thesis focuses on the design and implementation of a digital signal processor based multi-leg dc-dc power converter for fuel-cell power supply systems. A multi-leg boost converter is designed in this system to reduce the output current ripple and increase the life time of fuel-cell. According to input and output voltage feedback and current feedback controls, the multi-leg power converter can not only balance the current of each leg, but also provide a steady output voltage to load. Besides, a bi-directional dc-dc power converter is used in this system to charge or discharge the batteries and balance the system power. The redundant power of fuel-cell can be stored in batteries by the power control between fuel-cell and batteries. Battery discharge will occur momentarily to meet the instant need of high system current and thereby raise the response speed when load changes. Fuel-cell can thus be operated in the average power point which fit in with the load. In this thesis, the mathematical models and controller of multi-leg dc-dc power converter are built and used for digital control. Then, a high-performance, low-cost digital signal processor (DSP, TMS320F2812) is used as the control core. The control of power converter and the method of power balance control are accomplished by software so as to reduce the cost. A prototype of 1kW multi-leg dc-dc power converter for fuel-cell is developed. The input voltage range is between 26V and 40V. The output voltage is 40V. Moreover, the experimental data show that the efficiency of the system reaches 93%, and the input current ripple of fuel-cell is less than 5%. Simulation and experimental results are given to justify the analysis.