Future microprocessor poses many challenges to its dedicated power supplies, the voltage regulators (VRs), such as the low voltage, high current, fast load transient, etc. For the VR designs using multiphase buck converters, one of the results from these stringent challenges is a large amount of output capacitors, which is undesired from both a cost and a motherboard real estate perspective. In order to save the output capacitors, the control-loop bandwidth must be increased. However, the bandwidth is limited in the practical design. The influence from the switching frequency on the control-loop bandwidth has not been identified, and the influence from multiphase is not clear, either. Since the widely-used average model eliminates the inherent switching functions, it is not able to predict the converter's high-frequency performance. In this dissertation, the primary objectives are to develop the methodology of high-frequency modeling for the buck and multiphase buck converters, and to analyze their high-frequency characteristics. First, the nonlinearity of the pulse-width modulator (PWM) scheme is identified. Because of the sampling characteristic, the sideband components are generated at the output of the PWM comparator. Using the assumption that the sideband components are well attenuated by the low-pass filters in the converter, the conventional average model only includes the perturbation-frequency components. When studying the high-frequency performance, the sideband frequency is not sufficiently high as compared with the perturbation one; therefore, the assumption for the average model is not good any more. Under this condition, the converter response cannot be reflected by the average model. Furthermore, with a closed loop, the generated sideband components at the output voltage appear at the input of the PWM comparator, and then generate the perturbation-frequency components at the output. This causes the sideband effect to happen. The perturbation-frequency components and the sideband components are then coupled through the comparator. To be able to predict the converter's high-frequency performance, it is necessary to have a model that reflects the sampling characteristic of the PWM comparator. As the basis of further research, the existing high-frequency modeling approaches are reviewed. Among them, the harmonic balance approach predicts the high-frequency performance but it is too complicated to utilize. However, it is promising when simplified in the applications with buck and multiphase buck converters. Once the nonlinearity of the PWM comparator is identified, a simple model can be obtained because the rest of the converter system is a linear function. With the Fourier analysis, the relationship between the perturbation-frequency components and the sideband components are derived for the trailing-edge PWM comparator. The concept of multi-frequency modeling is developed based on a single-phase voltage-mode-controlled buck converter. The system stability and transient performance depend on the loop gain that is affected by the sideband component. Based on the multi-frequency model, it is mathematically indicated that the result from the sideband effect is the reduction of magnitude and phase characteristics of the loop gain. With a higher bandwidth, there are more magnitude and phase reductions, which, therefore, cause the sideband effect to pose limitations when pushing the bandwidth. The proposed model is then applied to the multiphase buck converter. For voltage-mode control, the multiphase technique has the potential to cancel the sideband effect around the switching frequency. Therefore, theoretically the control-loop bandwidth can be pushed higher than the single-phase design. However, in practical designs, there is still magnitude and phase reductions around the switching frequency in the measured loop gain. Using the multi-frequency model, it is clearly pointed out that the sideband effect cannot be fully cancelled with unsymmetrical phases, which results in additional reduction of the phase margin, especially for the high-bandwidth design. Therefore, one should be extremely careful to push the bandwidth when depending on the interleaving to cancel the sideband effect. The multiphase buck converter with peak-current control is also investigated. Because of the current loop in each individual phase, there is the sideband effect that cannot be canceled with the interleaving technique. For higher bandwidths and better transient performances, two schemes are presented to reduce the influence from the current loop: the external ramps are inserted in the modulators, and the inductor currents are coupled, either through feedback control or by the coupled-inductor structure. A bandwidth around one-third of the switching frequency is achieved with the coupled-inductor buck converter, which makes it a promising circuit for the VR applications. As a conclusion, the feedback loop results in the sideband effect, which limits the bandwidth and is not included in the average model. With the proposed multi-frequency model, the high-frequency performance for the buck and multiphase buck converters can be accurately predicted. / Ph. D.

Ce mémoire présente le travail de thèse réalisé auprès des laboratoires LAPLACE et SATIE ainsi que les services EDYNE3 et EDYYLIC d'AIRBUS OPERATIONS. Le sujet porte sur les problèmes CEM apparaissant dans les convertisseurs de puissance embarqués à bord des futurs avions plus électriques. Le manuscrit est composé de cinq parties. La première partie, d'introduction, traite de la problématique CEM avion, la deuxième de la modélisation des éléments de la chaine de conversion DC/AC étudiée. Le troisième est composé d'une étude comparative par simulation des différentes solutions. La quatrième partie traite de la réalisation de la solution choisie et enfin le cinquième et dernier chapitre de l'étude expérimentale de celle-ci. / The studies conducted during this thesis deals with conducted EMC problems of an inverter associated to its actuator. Accurate high frequency models of every element of the DC/AC converter and actuator have been realised from measures. Then a comparative study of different topologies of converters have been led from simulations in order to determine the best solution minimising EMC current. The selected inverter was realised and the experimental results were compared to simulations validating them. Finally, a comparison of EMC filters architecture led to choose a better solution in order to avoid the increasing of mass.

This thesis makes significant contributions to improving the use of Airport Safety Areas (ASAs) as aviation accident risk mitigation measures by developing improved accident frequency models and risk assessment methodologies. In recent years, the adequacy of ASAs such as the Runway End Safety Area and Runway Safety Area has come under increasing scrutiny. The current research found flaws in the existing ASA regulations and airport risk assessment techniques that lead to the provision of inconsistent safety margins at airports and runways. The research was based on a comprehensive database of ASA-related accidents, which was matched by a representative sample of normal operations data, such that the exposure to a range of operational and meteorological risk factors between accident and normal flights could be compared. On this basis, the criticality of individual risk factors was quantified and accident frequency models were developed using logistic regression. These models have considerably better predictive power compared to models used by previous airport risk assessments. An improved risk assessment technique was developed coupling the accident frequency models with accident location data, yielding distributions that describe the frequency of accidents that reach specific distances beyond the runway end or centreline given the risk exposure profile of the particular runway. The application of the proposed methodology was demonstrated in two case studies. Specific recommendations on ASA dimensions were made for achieving consistent levels of safety on each side of the runway. Advances made in this study have implications on the overall assessment and management of risks at airports.

Cette thèse propose une nouvelle méthode pour modéliser les fonctions non linéaires de modulations d’amplitude et de fréquence de signaux multicomposantes non stationnaires de durée longue. La méthode repose sur une décomposition du signal en segments courts pour une modélisation locale sur les segments. Pour initialiser la modélisation, nous avons conçu une première étape qui peut être considérée comme un estimateur indépendant et non paramétrique des fonctions de modulations. L’originalité de l’approche réside dans la définition d’une matrice de convergence totale intégrant simultanément les valeurs d’amplitude et de fréquence et utilisé pour l’association d’un pic à une composante selon un critère d’acceptation stochastique. Suite à cette initialisation, la méthode estime les fonctions de modulations par l'enchaînement des étapes de segmentation, modélisation et fusion. Les fonctions de modulations estimées localement par maximum de vraisemblance sont connectées dans l'étape de fusion, qui supprime les discontinuités, et produit l’estimation globale sur la durée totale du signal. Les étapes sont conçues afin de pouvoir modéliser des signaux multicomposantes avec des morts et naissances, ce qui en fait une de ses originalités par rapport aux techniques existantes. Les résultats sur des signaux réels et simulés ont illustré les bonnes performances et l’adaptabilité de la méthode proposée. / In this thesis, a novel method is proposed for modeling the non-linear amplitude and frequency modulations of non-stationary multi-component signals of long duration. The method relies on the decomposition of the signal into short time segments to carry out local modelings on these segments. In order to initialize the modeling, a first step is designed which can be considered as an independent estimator of the modulations over the entire duration of the signal. The originality of this approach lies in the definition of the total divergence matrix integrating simultaneously the amplitude and frequency values, which are employed for the association of a peak to a component according to a stochastic acceptation criteria. Following the initialization, the proposed method estimates the modulations by the step sequence of segmentation, modeling and fusion. The locally obtained modulation functions estimated by maximum likelihood are finally connected in the fusion step which suppresses their discontinuity and yields the global estimation over the entire signal duration. All these steps are defined in order to be able to model multicomponent signals with births and deaths, making one of its original features compared to existing techniques. The results on real and simulated signals have shown the good performance and adaptability of the proposed method.

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Le résonateur matriochka est conçu à partir de résonateurs coaxiaux ré-entrants créant ainsi des sauts d’impédances (SIR). La thèse développe alors des innovations théoriques sur la technologie matriochka en proposant des modèles analytiques précis sur le comportement fréquentiel et du facteur de qualité du résonateur. Les modélisations mettent en relief l’existence de degrés de liberté au sein du résonateur matriochka induisant une flexibilité du rapport de forme du résonateur. Les degrés de liberté créent ainsi une multitude de configurations du résonateur matriochka pour une fréquence fondamentale et un facteur de qualité donnés. Par conséquent, une optimisation en volume est réalisée pour concevoir deux filtres en bande L et C afin de minimiser leur encombrement. Une étude de la tenue en puissance dans le vide est également effectuée pour le filtre en bande L. Une méthode conjointe d’optimisation de la tenue en puissance et de minimisation en volume est alors proposée pour ce filtre. Ainsi, les modélisations et les optimisations sont employées afin de concevoir et de fabriquer deux filtres hyperfréquences. Le premier est un filtre de transmission en bande L conçu pour l’application de navigation Galileo qui propose une alternative d’encombrement et une tenue en puissance dans le vide élevée. Enfin, le second est un filtre de réception en bande C conçu, fabriqué et mesuré pour l’application de télémesure qui propose de meilleures performances en réjection et un volume réduit par rapport à l’existant. Finalement, la technologie matriochka est une alternative de résonateur par rapport à l’état de l’art en proposant, selon les configurations, un rejet élevé des harmoniques et un volume réduit pour une fréquence fondamentale et un facteur de qualité donnés. / The matriochka resonator is based on reentrant coaxial Stepped Impedance Resonator (SIR). So, the thesis develops theoretical innovations on the matriochka technology offering accurate analytical models on the frequency and the quality factor behaviors of the resonator. The models prove the existence of degrees of freedom within the matriochka resonator which allows to get different form factors of the resonator. The degrees of freedom create many configurations of the matriochka resonator for a fundamental frequency and a quality factor. Consequently, a volume optimization is realized to design a L-band filter and a C-band filter. A multipactor study is also carried out for the L-band filter. So, a joint optimization method of the multipactor and the volume minimization is proposed for this filter. Thus, the models and optimisations are used in the order to to design and fabricate the microwave filters. The first one is a transmission L-band filter for the navigation application Galileo which offers a volume alternative and a high power in the vaccum. Then, the second one is a reception C-band filter for the telemetry application which offers wide spurious free-performance and a low volume compared to the state of the art. Finally, for a frequency and a quality factor and depending on the configurations, the matriochka technology offers an alternative of the resonator volume, and it offers a wide spurious free- performance and a low volume compared to the state of the art.