Envisagée à partir des 15 à 30 années à venir dans l'industrie aéronautique, la propulsion hybrideélectrique permet d'intégrer de nouvelles briques technologiques offrant des degrés de libertésupplémentaires pour améliorer les performances des aéronefs, limiter l'utilisation de ressourcesfossiles et réduire l’impact environnemental des avions. Aujourd'hui, la technologie hybrideélectrique est principalement appliquée aux transports terrestres, aux voitures, aux bus et auxtrains, mais aussi aux navires. La faisabilité pour le transport aérien doit encore être établie etl'amélioration des performances des aéronefs reste à démontrer. Cette thèse vise à évaluer lesgains énergétiques apportés par l'hybridation électrique d'un avion régional de 70 places. Toutd'abord, les opportunités d'économie d'énergie sont identifiées à partir de l'analyse desrendements propulsifs et aérodynamiques d'un avion bi-turbopropulsé conventionnel. Les gainspotentiels provenant de la variation de la taille des moteurs principaux et de nouvelles gestions depuissance par l'utilisation de batteries sont étudiés. De plus, les possibles améliorationsaérodynamiques émanant de nouveaux positionnements des hélices sont considérées. Pourchaque sujet, des analyses simplifiées fournissent une estimation d'économie d'énergie. Cesrésultats sont ensuite utilisés pour sélectionner quatre systèmes propulsifs électrifiés qui sontétudiés plus en détail dans la thèse: un hybride parallèle, un turboélectrique avec propulsiondistribuée, un turboélectrique partiel à hélices hypersustentatrices, et un tout-électrique.L'évaluation des avions hybrides électriques sélectionnés est d'autant plus difficile que ledimensionnement des différentes composants, les stratégies de gestion d'énergie et les profils demission que l'on peut imaginer sont nombreux et variés. En outre, le processus global deconception de l'avion et les outils d'évaluation doivent être adaptés en conséquence. L'outilinterne de conception par optimisation multidisciplinaire d'Airbus nommé XMDO, qui inclut laplupart des modifications requises, est finalement sélectionné et développé au cours de la thèse.Par exemple, de nouveaux modèles paramétriques de composants (voilure soufflée, moteurélectrique, turbine à gaz, hélice, etc...) sont créés, une formulation générique pour résoudrel'équilibre du système de propulsion est mise en place, et les modèles de simulation de décollageet d'atterrissage sont améliorés. Afin d'évaluer l'efficacité énergétique des avions hybridesélectriques, un avion de référence équipé d'un système propulsif conventionnel est d'abordoptimisé avec XMDO. Différents algorithmes d'optimisation sont testés, et la consistance de lanouvelle méthode de conception est vérifiée. Par la suite, les configurations hybrides électriquessont toutes optimisées selon les mêmes exigences de conception que l'avion de référence. Pourles composants électriques, deux niveaux de technologie sont définis selon la date d'entrée enservice de l'aéronef. Les résultats d'optimisation pour le turbo-électrique et le turbo-électriquepartiel sont utilisés pour mieux appréhender les gains aérodynamiques potentiels identifiés enpremière partie de thèse. Les optimisations pour l'hybride parallèle, comprenant différentsscénarios de recharge batterie, mettent en évidence les meilleures stratégies de gestion d'énergielorsque des batteries sont utilisées comme sources d'énergie secondaire. Tous les résultats sontfinalement comparés à la référence en termes de consommations de carburant et d'énergie, pourles deux niveaux de technologie électrique. La dernière partie de la thèse se concentre sur l'aviontout électrique. Elle vise à identifier l'énergie spécifique minimale requise pour les batteries enfonction de la distance maximale à parcourir. Une étude de sensibilité est également réalisée enfonction de la date d'entrée en service pour les autres composants électriques / Envisioned in the next 15 to 30 years in the aviation industry, hybrid-electric propulsion offers theopportunity to integrate new technology bricks providing additional degrees of freedom to improveoverall aircraft performance, limit the use of non-renewable fossil resources and reduce the aircraftenvironmental footprint. Today, hybrid-electric technology has mainly been applied to groundbased transports, cars, buses and trains, but also ships. The feasibility in the air industry has to beestablished and the improvement in aircraft performance has still to be demonstrated. This thesisaims to evaluate the energy savings enabled by electric power in the case of a 70-seat regionalaircraft. First, energy saving opportunities are identified from the analysis of the propulsion andaerodynamic efficiencies of a conventional twin turboprop aircraft. The potential benefits comingfrom the variation of the size of prime movers and the new power managements with the use ofbatteries are studied. Also, possible aerodynamic improvements enabled by new propellerintegrations are considered. For each topic, simplified analyses provide estimated potential ofenergy saving. These results are then used to select four electrified propulsion systems that arestudied in more detail in the thesis: a parallel-hybrid, a turboelectric with distributed propulsion, apartial-turboelectric with high-lift propellers and an all-electric. Evaluating the selected hybrid-electric aircraft is even more challenging that the sizing of the different components, the energymanagement strategies and the mission profiles one can imagine are many and varied. Inaddition, the overall aircraft design process and the evaluation tools need to be adaptedaccordingly. The Airbus in-house Multidisciplinary Design Optimisation platform named XMDO,which includes most of the required modifications, is eventually selected and further developedduring the thesis. For examples, new parametric component models (blown wing, electrical motor,gas turbine, propeller, etc…) are created, a generic formulation for solving the propulsion systemequilibrium is implemented, and simulation models for take-off and landing are improved. In orderto evaluate the energy efficiency of the hybrid-electric aircraft, a reference aircraft equipped with aconventional propulsion system is first optimised with XMDO. Different optimisation algorithms aretested, and the consistency of the new design method is checked. Then, all the hybrid-electricconfigurations are optimised under the same aircraft design requirements as the reference. Forthe electrical components, two levels of technology are defined regarding the service entry date ofthe aircraft. The optimisation results for the turboelectric and the partial-turboelectric are used tobetter understand the potential aerodynamic improvements identified in the first part of the thesis.Optimisations for the parallel-hybrid, including different battery recharge scenarios, highlight thebest energy management strategies when batteries are used as secondary energy sources. All theresults are finally compared to the reference in terms of fuel and energy efficiencies, for the twoelectrical technology levels. The last part of the thesis focuses on the all-electric aircraft, and aimsat identifying the minimum specific energy required for batteries as a function of the aircraft designrange. A trade study is also carried-out in accordance with the service entry date for the otherelectrical components

Aircraft design is an example of complex engineering where dimensioning tools can be valuable for the designers and decision makers in the early stage of the development process. These tools can be in form of a database over key numbers for different components or technologies. One of the critical parts of an aircraft is the actuator system. Conventional hydraulic actuators are demanding regarding maintenance which implies high operation costs. Therefore in recent years the focus has been set on electro-hydrostatic and electro-mechanical actuators. The aim of this work is to build a platform which can make it easier for designers and decision makers to analyze, compare and optimize different technologies regarding the actuator system. For this reason a simplified quasi-static actuator model, including reactive power consumption has been developed. This model makes it possible to reduce the complexity of the actuator models to such extent that the resulting computional tool can be used for studies of the system performance during entire flight missions and/or for optimization. Power density, cost and weight of the actuator systems are some of the important key numbers for comparing purpose and as a platform for the dimensioning of the aircraft. The ambition is then to build up a database of different actuator solutions with the key technical parameters mentioned above, that can be used in modeling and dimensioning of an aircraft. In order to avoid time consuming finite element calculations when analyzing an electrical machine a reluctance network model can be used. The basic idea of the proposed network model is to divide the rotor and the stator into a grid of small reluctance elements and provide those that correspond to the permanent magnet and the air gap between the magnets with time varying reluctances. The suggested computationally approach constitute a fast way to evaluate permanent magnet electrical machines with the respect to their performance. A preferred electrical machine provided with balance teeth and concentrated windings showed good electromechanical and thermal behavior. A balance tooth is a tooth without winding between each adjacent phases that has a cooling effect on the nearest windings, resulting in less copper losses. The balance teeth increases the voltage-time area, leading to higher induced voltage and higher torque production. Another advantage of the chosen design is its redundancy and fault tolerance capabilities. The machine comprises two independent half machines that also offers a high level of redundancy with two separate power channels. / QC 20100914

More electric aircraft systems, high power avionics, and a reduction in heat sink capacity have placed a larger emphasis on correctly satisfying aircraft thermal management requirements during conceptual design. Thermal management systems must be capable of dealing with these rising heat loads, while simultaneously meeting mission performance. Since all subsystem power and cooling requirements are ultimately traced back to the engine, the growing interactions between the propulsion and thermal management systems are becoming more significant. As a result, it is necessary to consider their integrated performance during the conceptual design of the aircraft gas turbine engine cycle to ensure that thermal requirements are met. This can be accomplished by using thermodynamic modeling and simulation to investigate the subsystem interactions while conducting the necessary design trades to establish the engine cycle. As the foundation for this research, a parsimonious, transparent thermodynamic model of propulsion and thermal management systems performance was created with a focus on capturing the physics that have the largest impact on propulsion design choices. A key aspect of this approach is the incorporation of physics-based formulations involving the concurrent usage of the first and second laws of thermodynamics to achieve a clearer view of the component-level losses. This is facilitated by the direct prediction of the exergy destruction distribution throughout the integrated system and the resulting quantification of available work losses over the time history of the mission. The characterization of the thermodynamic irreversibility distribution helps give the designer an absolute and consistent view of the tradeoffs associated with the design of the system. Consequently, this leads directly to the question of the optimal allocation of irreversibility across each of the components. An irreversibility allocation approach based on the economic concept of resource allocation is demonstrated for a canonical propulsion and thermal management systems architecture. By posing the problem in economic terms, exergy destruction is treated as a true common currency to barter for improved efficiency, cost, and performance. This then enables the propulsion systems designer to better fulfill system-level requirements and to create a system more robust to future requirements.

With the current increased emphasis on the development of energy optimized vehicle systems architectures during the early phases in aircraft conceptual design, accurate predictions of these off-nominal requirements are needed to justify architecture concept selection. A process was developed for capturing architecture specific performance degradation strategies and optimally imposing their associated requirements. This process is enabled by analog extensions to traditional safety design and assessment tools and consists of six phases: Continuous Functional Hazard Assessment, Architecture Definition, Load Shedding Optimization, Analog System Safety Assessment, Architecture Optimization, and Architecture Augmentation. Systematic off-nominal analysis of requirements was performed for dissimilar architecture concepts. It was shown that traditional discrete application of safety and reliability requirements have adverse effects on the prediction of requirements. This design bias was illustrated by cumulative unit importance metrics. Low fidelity representations of the loss/hazard relationship place undue importance on some units and yield under or over-predictions of system performance.

Dans le contexte de l’avion plus électrique, les réseaux électriques aéronautiques sont en pleine évolution. Cette évolution est poussée par le besoin d’une intégration à forte densité énergétique ce qui pose des défis aux concepteurs en termes d’architectures, de systèmes et de méthodes de dimensionnement.Un réseau de bord est composé d’un ensemble de systèmes électriques multidisciplinaire qui proviennent de différents fournisseurs dont le design est actuellement effectué en répondant à des standards de qualité spécifiés par l’agrégateur. L’objectif de la thèse est de proposer de nouvelles approches intégrées qui permettent de gérer la complexité des réseaux électriques tout en convergeant vers un résultat optimal, offrant des gains de masses en référence à un design par des « approches mécanistes » reposant sur un agrégat de boucles d’optimisation locales. Une approche multiniveau a été développée en s’inspirant des travaux sur la MDO « Multidisciplinary Design Optimization ». L’élaboration de cette approche a été le résultat d’une expertise accumulée en appliquant différentes méthodes disponibles dans la bibliographie. L’optimisation porte plus spécifiquement sur les filtres d’entrée des charges du réseau ainsi que sur le filtre de sortie du canal de génération du réseau électrique embarqué. L’optimisation multiniveau vise, dans un contexte collaboratif, à itérer entre le niveau agrégateur (niveau réseau) et le niveau équipementier (charges et source du réseau). L’utilisation d’une formulation agrégée au niveau réseau et le respect des causalités au niveau des sous-problèmes sont les principaux atouts de cette approche qui conduit à des solutions proches de l’optimum global de masse de filtres. / Within more electric aircraft context, electric systems and networks have to evolve. High energy density integration pushes designers to reconsider their systems, architectures and tools.An aircraft network contains a large number of multidisciplinary systems which come from different manufacturers. Each manufacturer designs its system separately following quality standards specified by the aggregator. The goal of this thesis is to provide system approaches which could deal with the high-level of complexity of the network while reaching the optimal design of all the system and so reduce the total weight in comparison with mechanistic approaches based on independent optimization loops for the different subsystems.Consulting MDO “Multidisciplinary Design Optimization” researches, we have developed a multilevel approach based on our previous studies and conclusions on classical approaches used in the design of electrical systems. The optimization concerns the input filters of the loads connected to the HVDC bus and the output filter of the generating channel which supply the electric power. The multilevel collaborative optimization allows an automated exchange of data between the aggregator (system level) and manufacturers (sub-system level) and thanks to that, the optimal design of all the system is joined. The strong points of this approach are the aggregated formulation and causality connections between sub-systems.

Les avantages que présentent les systèmes électriques par rapport aux autres systèmes (mécaniques, hydrauliques et pneumatiques) ont permis d’intensifier l’électrification des systèmes embarqués à bord des aéronefs : c’est le concept d’avion plus électrique. Dans ce contexte, l’approche de conception intégrée par optimisation (CIO) de ces systèmes s’avère aujourd’hui une nécessité pour pouvoir répondre aux exigences en termes d’efficacité énergique, de fiabilité et de masse... Dans cette thèse, nous avons appliqué la CIO à une chaine de conversion électromécanique utilisée dans le système de conditionnement d’air d’un avion. Deux objectifs sont ciblés : la minimisation de la masse du système et l’augmentation de son efficacité énergétique. Ces objectifs sont intégrés à diverses contraintes hétérogènes, allant de la qualité réseau au respect de la mission de vol dans le plan couple – vitesse, en passant par la thermique,… Compte tenu de la complexité du système étudié et de son caractère multidisciplinaire, des approches de conception par optimisation dites « MDO » (pour Multidisciplinary Design Optimization) sont étudiées. En effet, au delà des compétences physiques et techniques, la conception intégrée par optimisation des systèmes complexes nécessite des efforts supplémentaires en termes de méthodologies de conception. Nous avons présenté dans cette thèse trois approches : Approches mono-niveau : séquentielle et globale ; Approche multi-niveaux, couplant niveaux système et niveau constituants (filtre, onduleur, machine) ; des formulations adaptées à notre problème de conception sont présentées afin de résoudre les problèmes liés aux optimisations mono-niveau. Les performances des différentes approches de conception sont présentées analysées et comparées. Les résultats obtenus montrent clairement les avantages que présente la formulation multi-niveaux par rapport aux approches classiques de conception. / The benefits of electrical systems compared to other systems (mechanical, hydraulic and pneumatic) are a serious motivation for the electrification of embedded systems in “more electric aircraft”. In this framework, the integrated optimal design of these systems appears necessary to meet requirements in terms of efficiency, reliability and weight reduction. In this thesis, we have applied the integrated optimal design to an electromechanical system used in the air conditioning system of a more electric aircraft. Two objectives are targeted: the minimization of the system weight and the increase of its efficiency. Both objectives are integrated with several heterogeneous constraints, from network quality till flight mission fulfilment in the torque vs speed plan. Because of the complexity of the studied system and its multidisciplinary nature, "MDO" approaches (for multidisciplinary Design Optimization) are studied. In fact, beyond physical and technical skills, integrated optimal design of complex systems requires additional efforts in terms of design methodologies. Three approaches are presented in this thesis: One-level Approaches: sequential and global; Multilevel approach, coupling “system” level with “device” level (filter, inverter, electric machine); a set of formulations adapted to our design problem are presented to solve the issues associated to the one-level approaches. The performance of these design approaches are presented, analyzed and compared. The results clearly show the advantages that involves multilevel formulation compared to conventional design approaches.

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The research reported in this dissertation focuses on the development of optimization tools for the design of subsystems in a modern aircraft power distribution system. The baseline power distribution system is built around a 270V DC bus. One of the distinguishing features of this power distribution system is the presence of regenerative power from the electrically driven flight control actuators and structurally integrated smart actuators back to the DC bus. The key electrical components of the power distribution system are bidirectional switching power converters, which convert, control and condition electrical power between the sources and the loads. The dissertation is divided into three parts. Part I deals with the formulation of an optimization problem for a sample system consisting of a regulated DC-DC buck converter preceded by an input filter. The individual subsystems are optimized first followed by the integrated optimization of the sample system. It is shown that the integrated optimization provides better results than that obtained by integrating the individually optimized systems. Part II presents a detailed study of piezoelectric actuators. This study includes modeling, optimization of the drive amplifier and the development of a current control law for piezoelectric actuators coupled to a simple mechanical structure. Linear and nonlinear methods to study subsystem interaction and stability are studied in Part III. A multivariable impedance ratio criterion applicable to three phase systems is proposed. Bifurcation methods are used to obtain global stability characteristics of interconnected systems. The application of a nonlinear design methodology, widely used in power systems, to incrementally improve the robustness of a system to Hopf bifurcation instability is discussed. / Ph. D.