This dissertation focuses on quantifying the effects of multi-user co-channel interference for an avionic communication system operating in a heavy-traffic aeronautical mobile environment and proposes advanced interference cancellation techniques to mitigate the interference. The dissertation consists of two parts. The first part of the work investigates the use of a visualization method to quantify and characterize the multi-user co-channel interference (multiple access interference) effects impinging on an avionic communication system. The interference is caused by complex interactions of thousands of RF signals transmitted from thousands of aircraft; each attempts to access a common communication channel, which is governed by a specific channel contention access protocol. The visualization method transforms the co-channel interference, which is specified in terms of signal-overlaps (signal collisions), from a visual representation to a matrix representation for further statistical analysis. It is found that the statistical Poisson and its cumulative distribution provide the best estimates of multi-user co-channel interference. It is shown, using Monte Carlo simulation, that the co-channel interference of a victim aircraft operating in the heavy-traffic environment could result in as high as eight signal-overlaps. This constitutes to approximately 83.4% of success rate in signal detection for the entire three thousand aircraft environment using conventional FSK receiver. One key finding shows that high-quality communications, up to 98.5% success rate, is achievable if only three overlapping signals can be decoded successfully. The interference results found in the first part set the stage for interference cancellation research in the second part. The second part of the work proposes the use of advanced interference cancellation techniques, namely sequential interference cancellation (SIC) and parallel interference cancellation (PIC), as potential solutions to mitigating the interference effects. These techniques can be implemented in radio receivers to perform multi-signal decoding functionality to remove the required interferers (three overlapping signals) so that high-quality communication, as described in the first part, can be achieved. Various performance graphs are shown for B-FSK and B-PSK for both SIC and PIC techniques. One key finding is that the system performance can be improved substantially to an additional 15% in signal reception success rate by using SIC or PIC. This means that critical information transmitted from 450 aircraft (out of approximately three thousand aircraft in the environment) is preserved and successfully decoded. Multi-signal decoding using these interference cancellation receivers comes at a small penalty of 2 - 4.5 dBs in Eb/No when sufficient signal-to-interference (SIR) ratio (7-12 dB) is provided. / Ph. D.

Le domaine aéronautique connait de nos jours un engouement sans précédent autour de l’avion plus électrique. L’importance du nombre d’équipements électriques est à un tel point que l’amélioration de leur fiabilité devient incontournable. Actuellement, les composants passifs occupent 75 % des éléments électroniques utilisés en avionique dont la moitié correspond à des condensateurs. Ces derniers doivent donc répondre aux exigences environnementales avioniques assez contraignantes. C’est dans ce contexte que nous nous sommes intéressés particulièrement à l’étude des condensateurs à technologie film utilisant le polypropylène ou le polyester comme diélectrique. Afin de mieux comprendre le comportement fréquentiel de cette technologie, deux modèles fins de condensateurs films ont été développés, permettant ainsi de suivre les évolutions de leurs grandeurs électriques dans des conditions cohérentes avec l’application. Dans un deuxième temps, l’effet des contraintes en tension et en température constantes a été étudié sous la forme de facteurs d’accélération du vieillissement. Cela a été établi par l’intermédiaire de plusieurs essais, permettant d’établir les lois d’évolutions temporelles des paramètres électriques des condensateurs. Comme ces contraintes constantes ne sont pas toujours représentatives des conditions réelles d’utilisation, les cinétiques de dégradation ont été comparées à celles où les condensateurs sont sollicités par de fortes ondulations de courant, seules ou associées à une tension continue. Enfin, la dernière partie de notre travail expose l’utilisation des données expérimentales issues des essais de vieillissement dans un objectif de diagnostic en ligne. Les techniques utilisées assurent l'analyse de la dégradation de ces composants, étape essentielle dans la prédiction de l’état de santé des condensateurs en ligne / Nowadays, aeronautic research field is moving towards a more electric aircraft. Although this evolutionary path offers many advantages from a financial and ecological point of view, the increased power source usage sets additional constraints on the different electrical systems used onboard. Currently, passive components occupy 75% of the overall electronic equipments used in avionics, whose 50% corresponds to capacitors. Consequently, these latter must be able to withstand the harsh avionic operating conditions. In this thesis we were particularly interested in the study of metallized film capacitors technology using polyester or polypropylene as dielectric. A first approach consisted on the modeling of these components as function of frequency in order to study the evolution of their electrical parameters under consistent avionic stresses. These models were also developed on the purpose of tracking the degradation of the capacitors parameters over time. This operation was done by the means of accelerated floating ageing tests, where capacitors were subjected to different constant voltages and temperatures. Original capacitance ageing laws were thus proposed based on the identification of voltage and temperature degradation kinetics. However, since traditional floating ageing tests, do not reflects the normal ageing of the component, degradation kinetics of metallized films capacitors under high ripple currents, alone or combined with a DC voltage across the devices terminals where also studied, and the associated failure mechanisms were identified. A final step consisted on the health monitoring of metallized film capacitors online based on the experimental ageing data

La révolution technologique majeure des nouveaux aéronefs repose sur une électrification intensive de nombreux constituants de l'appareil et le fait que la vitesse des génératrices électriques n'est plus fixe mais variable. Cette nouvelle manière de générer la puissance électrique engendre des variations de tension sur les réseaux DC. De plus, pour accroître la compacité des Machines Synchrones à Aimants Permanents (MSAP) à puissance donnée, on augmente autant que possible leur vitesse d'entrainement, en les associant pour certaines applications à des réducteurs mécaniques. La variation du niveau de tension du bus DC alimentant une MSAP haute vitesse implique son dimensionnement afin d'assurer sa contrôlabilité sur toute la plage de vitesse reportant d'importantes contraintes sur l'onduleur de tension. Pour pallier ce problème, une solution consiste à intercaler un convertisseur DC/DC entre le filtre d'entrée et l'onduleur de tension pour maintenir la tension DC d'entrée de l'onduleur à une valeur adaptée au fonctionnement de la MSAP et optimiser son dimensionnement. Cependant, cette solution augmente l'ordre du système, ce qui accroît la complexité de son contrôle, accentuée par les contraintes liées à la nature haute-fréquence des MSAP considérées.Les travaux menés dans cette thèse concernent l'étude, l'optimisation et le contrôle des structures d'alimentation des actionneurs haute vitesse connectés aux réseaux DC avioniques à tension variable. Il en résulte que pour les applications avioniques considérées, ces architectures d'alimentation intégrant un convertisseur DC/DC supplémentaire permettent de réduire sa masse et son volume sans dégrader le rendement global de la chaîne de conversion notamment avec les convertisseurs à source impédante qui permettent de supprimer structurellement les ondulations de courant en entrée du convertisseur. De plus, des stratégies de commande Pulse Amplitude Modulation employées avec des architectures de contrôle non-linéaires (platitude, passivité) permettent d'assurer le contrôle de ces MSAP haute-vitesse tout en assurant leur stabilité sur toute la plage de fonctionnement / The main technological revolution of the new aircrafts is based on intensive electrification of many components of the aircraft. Moreover, the speed of electrical generators is no longer fixed but variable. This new way of generating electrical power generates voltage variations on DC networks. Besides, to increase the compactness of the Permanent Magnet Synchronous Machines (PMSM) at a given power, their mechanical speed is increased as much as possible by combining them with mechanical reducers for certain applications. The variation of the voltage level of the DC bus supplying a high-speed PMSM implies its sizing in order to ensure its controllability over the entire speed range which carries significant stresses on the Voltage Source Inverter (VSI). To solve this problem, one solution consists in adding an extra DC / DC converter between the input filter and the VSI to maintain the inverter input voltage at a value adapted to the operating point of the PMSM and to optimize its dimensioning. However, this solution increases the order of the system, which increases the complexity of its control, accentuated by the constraints related to the high-frequency nature of the PMSMs considered. The work carried out in this thesis concerns the study, the optimization and the control of the power supply architecture of the high-speed actuators connected to variable-voltage avionic DC networks. As a result, for the avionics applications considered, these power supply architectures integrating an additional DC / DC converter make it possible to reduce the mass and the volume of the power supply structure without degrading the overall efficiency of the conversion chain, in particular by using the impedance-source converters which allow to cancel the DC input current ripples. In addition, Pulse Amplitude Modulation (PAM) control strategies used with non-linear control architectures (flatness, passivity) make it possible to control these high-speed PMSMs while ensuring their stability over the entire operating range