Voltage inverter for electrical actuators : processes of reliability by disjunction of commutaion's cells and reorganization

Ce mémoire de thèse s'inscrit dans le cadre du programme « avion plus électrique », il comprend deux parties.La première est consacrée à la présentation détaillée du contexte, c'est-à-dire du processus qui conduit à électrifier la plupart des systèmes présents dans l'avion, un exemple d'actionneur électromécanique spécifique, conçu dans ce cadre sera aussi détaillé notamment pour ce qui concerne son mode d'alimentation. La seconde partie, plus longue, est consacrée à différents processus de fiabilisation de structures d'électroniques de puissance. Du fait de l'électrification croissante de l'avion, ces structures vont se multiplier à bord, mais la fiabilité connue de ces dispositifs n'est pas apte à satisfaire aux exigences de l'aéronautique. Les processus de fiabilisation, dans leur majorité, sont orientés, en cas de panne, vers un isolement de la source du défaut, pour permettre un fonctionnement en mode dégradé, supporté par le système. Par ailleurs, un dispositif de sécurisation de bras d'onduleur est décrit : un sectionneur commandé à thyristors et fusible (SCTF2). Ce système permet d'isoler électriquement le bras d'onduleur victime d'un défaut au sein d'un onduleur triphasé. L'emplacement de prédilection du SCTF2 est la connexion bras d'onduleur et bus continu d'alimentation. Les simulations de ce système de fiabilisation sont menées sur PSIM. Ce mémoire propose des modélisations approchées, pour l'outil de CAO adopté, des composants IGBT et fusibles, lorsque ces derniers sont soumis à un régime de courant extrême (court-circuit).This manuscript of thesis was written in two parts for the "More Electric Aircraft" program. The first part presents in great detail the context of the thesis that is (i.e) the processes which allow electrifying the most of classic aircraft-systems. In this part, an example of special electromechanical actuator build in the More Electric aircraft program will be presented with meticulous care, in particular its command and supply systems. The second part, more extensive, is devoted to various solutions which improve the reliability of the power-electric systems. With the growth of the electrification of the aircrafts, several solutions of this kind will be multiplicated on board, but today most of these solutions haven't the reliability intended to the aeronautical applications. For the most part, the reliability processes consist in isolating the origins of a breakdown, in order that the system can continue to work in a debased mode. In addition, a system which protects inverter's legs is described; it's a controlled circuit breaker which uses thyristors and fuses (SCTF2). This system of reliability allows electrical isolating of faulty inverter's leg in a three phase inverter. The preferential position of a SCTF2 is the connexion between inverter's leg and the DC bus. Simulations of the SCTF2 are done on PSIM software. For PSIM, this manuscript poposes some approximative modelisations of the components like IGBT and fuse when they are subjected to a dangerous high-current (short-circuit)

Conservation‐relevant reproductive parameters from long‐term tagging of two globally important sea turtle nesting aggregations in Central Africa

Assessing abundance and monitoring ecology and population trends are of critical importance for animal species of conservation concern. For sea turtles, annual nest counts represent the most common method of estimating population size. However, to develop a better understanding of population trends, these data need to be complemented by other reproductive parameters, which are lacking for many nesting populations across central Africa.To this end, an intensive capture-mark-recapture programme was conducted spanning 21 years (1997-2018) in the most important nesting sites on the Atlantic coast of central Africa (Gabon and Congo) for leatherback (Dermochelys coriacea) and olive ridley (Lepidochelys olivacea) sea turtles.A total of 18,105 encounters of 14,109 D. coriacea individuals and 2678 encounters of 2427 L. olivacea individuals were recorded. Biological and technical parameters such as clutch frequency, inter-nesting interval, remigration interval, annual survival rate, somatic growth, size trends, tag loss and number of annual nesting females were estimated through a variety of methods and models.The study detected a decline in body size and low survival probability (not due to tag loss) in both species but no clear decline in estimated annual number of nesting females. High fidelity to nesting sites (<30 km for both species) implies that the current conservation strategy, protecting the main nesting areas, could be effective.We recommend that local conservation managers promote: (i) continued monitoring of the nesting activity of the two species through capture-mark-recapture programmes; (ii) continued nest counts at long-term monitoring sites, which may also detect possible spatial shifts; and (iii) strengthening of cross-border cooperation between Gabon and Republic of the Congo given the observed connectivity between nesting sites of the two countries