The role played by power converting circuits is extremely important to almost any electronic system built today. Circuits that use converters of any type depend on power that is consistent in form and reliable in order to properly function. In addition, today's demands require more efficient use of energy, from large stationary systems such as power plants all the way down to small mobile devices such as laptops and cell phones. This places a need to reduce any losses to a minimum. The power conversion circuitry in a system is a very good place to reduce a large amount of unnecessary loss. This can be done using circuit topologies that are low loss in nature. For low loss and high performance, soft switching topologies have offered solutions in some cases. Also, limited study has been performed on device aging effects on switching mode power converting circuits. The impact of this effect on a converter's overall efficiency is theoretically known but with little experimental evidence in support. In this thesis, non-isolated buck type switching converters will be the main focus. This type of power conversion is widely used in many systems for DC to DC voltage step down. Newer methods and topologies to raise converter power efficiency are discussed, including a new synchronous ZVT topology . Also, a study has been performed on device aging effects on converter efficiency. Various scenarios of voltage conversion, switching frequency, and circuit components as well as other conditions have been considered. Experimental testing has been performed in both cases, ZVT's benefits and device aging effects, the results of which are discussed as well.

This dissertation presents control, analysis, and design of silicon carbide (SiC)-based critical conduction mode (CRM) high-frequency soft-switching three-phase ac-dc converters (inverter and rectifier). The soft-switching technique with SiC devices grounded in CRM makes the operation of the ac-dc converter at hundreds of kHz possible while maintaining high efficiency with high power density. This is beneficial for rapidly growing fields such as electric vehicle charging, photovoltaic (PV) systems, and uninterruptable power supplies, etc. However, for the soft-switching technique to be practically adopted to real products in the markets, there are a lot of challenges to overcome. In this dissertation, four types of the challenges are carefully studied and discussed to address them. First, the grid-tied inverters used for distributed energy resources, such as PV systems, must continue operating to deliver power to the grid, when it faces flawed grid conditions such as voltage drop and voltage rise. During abnormal grid conditions, delivering constant active power from the inverter to the grid is essential to avoid large voltage ripples on the dc side because it could trigger over-voltage protection or harm the circuitries, eventually shutting down the inverter. Hence, in such cases, unbalanced ac currents need to be injected into the grid. When the grid voltages and the ac currents are not balanced, there is a chance for the CRM soft-switching inverter to lose its soft-switching capability. Continuous conduction mode operation emerges, causing hard-switching where discontinuous conduction mode (DCM) operation is expected. This leads to huge turn-on loss and high dv/dt noise at the active switch's turn-on moment. To eradicate the hard-switching problem, two improved modulation schemes are developed; one with off-time extension in the CRM phase, the other by skipping switching pulses in the DCM phase. The DCM pulse skipping is applied for a variety of grid imbalance cases, and it is proven that it can be a generalized solution for any kinds of unbalanced grid conditions. Second, the CRM soft-switching scheme with 2-channel interleaving achieves high efficiency at heavy load. Nevertheless, the efficiency plunges as the output load is reduced. This is not suitable for PV inverters, which take account of light load efficiency in terms of "weighted efficiency". Small inductor currents at light load cause the switching frequency to soar because of its CRM-based operation characteristic, causing large switching loss. To increase the inductor current dealt with by the first channel, a phase shedding control is proposed. Gate signals for the second channel are not excited, increasing the first channel's inductor current, thus cutting down the first channel's switching frequency. To prevent the unwanted circulating current formed by shared zero-sequence voltage in the paralleled structure, only two phases in the second channel working in high frequency are shed. The proposed phase shedding control achieves a 0.5 to 3.9 % efficiency improvement with light loads. Third, due to the usage of SiC devices, high dv/dt generated at switching nodes over the system parasitic capacitance causes substantial common mode (CM) noise compared to that with Si devices. In this case, a balance technique with PCB winding inductors can effectively reduce the CM noise. First, winding interleaving structure is selected to minimize the eddy current loss in the windings. But the interwinding capacitance caused by the winding interleaving structure aggravates the CM noise. Impact of the interwinding capacitance on the CM noise is analyzed with a new inductor model containing the interwinding capacitance. Then, finally, a novel inductor structure is proposed to remove the interwinding capacitance and to improve the CM noise reduction performance. The soft-switching ac-dc converter built with the final PCB magnetics features almost similar efficiency compared to that with litz-wire inductor and 14 to 18 dB CM noise reduction up to 15 MHz. Lastly, the soft-switching technique is extended to inverters in standalone mode. To meet tight ac voltage total harmonic distortion requirements, a current control in dq-frame is introduced. As for the ac voltage regulation at no-load, on top of the improved phase shedding control, a frequency limiting with fixed frequency DCM method is applied to prevent excessive increase in the switching frequency. Then, how to deal with short-circuit at the output load is investigated. Since the soft-switching modulation violates inductor voltage-second balance during the short-circuit, the modulation method is switched to a conventional sinusoidal PWM at fixed frequency. It is concluded that all the additional requirements for the standalone inverters can be satisfied by the introduced control strategies. / Doctor of Philosophy / The world is facing an unprecedented weather crisis. Global warming is getting more severe because of excessive amount of carbon emission. In an effort to overcome this crisis, paradigm of energy and lifestyle of people have changed. Penetration of distributed energy resources (DERs) such as wind turbines, and photovoltaic systems has been dramatically increased. Instead of internal combustion engine vehicles (EVs), electric vehicles hit the mainstream. In these changes, power electronics plays a critical role as the key element of the systems. Especially, three-phase inverter/rectifiers are essential parts in such applications. Most important aspects of the three-phase inverter/rectifier are efficiency and power density. In the past decades, Silicon (Si) power devices were mostly used for the systems and the technology based on Si has almost reached to its physical limits. The switching frequency of Si-based inverter/rectifier is limited below 20 – 30 kHz to reduce switching loss. This impedes high power density due to bulky passive components such as inductors and capacitors. Nowadays, the advent of wideband gap such as Silicon Carbide (SiC) and Gallium Nitride (GaN) power devices gives us a great opportunity to improve the efficiency and the power density with its high switching speed capability, low switching energy and low on-resistance. The SiC power devices are more suitable for DERs and EVs due to higher voltage rating. Using SiC power devices allows to increase inverter/rectifier' switching frequency about five times to have similar efficiency with those based on Si power devices, making the power density high. However, there is still room to push the switching frequency even higher to hundreds of kHz with soft-switching. In this sense, studies on soft-switching techniques for three-phase inverter/rectifier have been intensively conducted. Particularly, soft-switching techniques based on critical conduction mode (CRM) are regarded as the most promising solutions because it does not have any additional circuits to achieve the soft-switching, keeping the system as straightforward as possible. However, most of the studies for the CRM-based soft-switching three-phase inverter/rectifier mainly focus on limited occasions such as ideal operation conditions. For this technique to be widely used and adopted in industry, more practical cases for the systems need to be studied. In this dissertation, the soft-switching three-phase inverter/rectifier under diverse situations are investigated in depth. First, behavior of the soft-switching inverter/rectifier under unbalanced grid conditions are analyzed and control methods are developed to maintain its soft-switching capability. Second, how to improve light load efficiency is explored. Circulating current issue for the light load efficiency improvement is analyzed and a control method is proposed to eliminate the circulating current. Third, a design methodology and considerations of inductors based on PCB magnetics are discussed to reduce electromagnetic noise and improve system efficiency. Lastly, the soft-switching technique is extended to standalone mode applications dealing with strict voltage regulation, no-load operation, and output short-circuit.

Power electronics building blocks (PEBBs) are standardized building blocks used to integrate power electronics systems. The PEBB approach can achieve low cost, high redundancy, high reliability, high flexibility and easy maintenance for large-scale power electronics systems. This thesis presents the implementation of a 100kW PEBB-based soft-switched bus regulator for an 800V DC distributed power system. The zero current transition (ZCT) soft-switching technique is used to improve the performance of the bus regulator by minimizing switching loss and improving overall efficiency. PEBB modules and a digital control building block are the subsystems of the DC bus regulator. This thesis addresses the design issues at subsystem and system levels. These include: operational principles and design of ZCT PEBB modules; design and implementation of the digital control block, based on DSP and EPLD; and modeling and control design of the DC bus regulator. There are several considerations when using the ZCT soft-switching technique in three-phase applications: the timing of the auxiliary switch gate signals must be arranged differently; there are low-frequency harmonics caused by the pulse width limits; and there is high thermal stress on the resonant capacitors. These issues are resolved by utilizing the sensed phase current information and the design freedom in the PWM modulator. A PWM modulation technique is proposed that can considerably reduce the switching events and further remove the associated loss while keeping THD low. Reduced switching events alleviate the thermal issue of the resonant capacitors. The same modulation technique can avoid the low-frequency harmonics caused by the pulse width limits and double the sampling frequency. The phase current information is used to deal with the control timing issue of the auxiliary switches and to control the three-phase soft-switching operation in order to achieve better efficiency. Additionally, the phase current information is used to implement dead time compensation to reduce THD. The soft-switched DC bus regulator has been tested up to a 100kW power level with 20kHz switching frequency. Experimental results demonstrate that high performance of the DC bus regulator is accomplished in terms of wide control bandwidth, low THD, unity power factor, high efficiency and high power density. / Master of Science

Depuis les dix dernières années, dans les domaines liés aux transports (automobile, avionique, ferroviaire, naval), les technologies thermiques et hydrauliques tendent à laisser de plus en plus de place aux systèmes électriques. L’intérêt et le dynamisme de la Recherche en électronique de puissance se justifient par le rôle déterminant que la discipline joue au sein du développement des systèmes embarqués "plus électriques". Ce mémoire de thèse s’intéresse à l’étude de convertisseurs d’électronique de puissance, les onduleurs à source impédante, en tant que topologies alternatives aux architectures existantes au sein des systèmes de traction électrique. Plusieurs études sont établies suivant différents critères, qui, au delà d’une simple comparaison avec les architectures conventionnelles, proposent des solutions et des améliorations intervenant aussi bien dans le contrôle du système que dans sa topologie initiale. Ces études sont toutes appliquées à un système de traction électrique muni d’une machine synchrone à aimants et d’un onduleur à source impédante alimentée par une source de tension continue. Les résultats qui en découlent ont montré de larges intérêts de ces topologies concernant la maîtrise de la qualité du courant de batterie (annulation de ses ondulations hautes fréquences) mais aussi la maîtrise de certaines contraintes liées aux vieillissement des machines (possibilité de maîtriser les dv/dt). Certains inconvénients sont néanmoins établis comme le fait que la topologie n’offre guère d’amélioration du rendement (en comparaison avec les structures classiques) ou comme le fait que l’architecture rende dépendantes les commandes de l’onduleur à source impédante (côté DC) et de la machine (côté AC) / Over the past ten years, hydraulic and thermal technologies tend to make room for electrical system. Fields related to transportation (automotive, avionics, railway or naval) are directly impacted. The interest and dynamism in power electronics Research are justified by the impact of such a field in the development of embedded systems. This thesis focuses on the study of impedance-source inverters as possible topologies to replace conventional ones. Several studies are conducted according to different criteria and do not aim at only comparing the topologies. It proposes solutions and improvements in the control system as well as in its basis architecture. These studies are all applied to an electric traction system composed of an synchronous machine fed by an impedance-source inverter. It is showed that large interests come out of the obtained results. For instance, the cancellation of the high-frequency current ripples allows mastering the quality of the battery current. Moreover, some constraints as regards machine ageing can be reduced by mastering the slew rates dv/dt. Some drawbacks are nevertheless pointed out. There is no need in using such a topology to improve efficiency that is above the same as conventional structures. Moreover, controls of DC-side AC-side of the system are dependent due to the fact that inverter’s control is used to step up the DC-bus voltage

Cette thèse traite de la conception d’un convertisseur DC / DC destiné aux véhicules électriques et hybrides (2,5 kW, 400V/14V, 250kHz). Dérivé de la topologie LLC à résonance, ce convertisseur bénéficie des nombreux avantages propres à cette structure particulière. C’est ainsi que le prototype réalisé présente un rendement très élevé, une densité de puissance très forte avec des perturbations EMI très réduites. La première partie de cette thèse est consacrée à l’analyse théorique du circuit LLC afin de dégager un modèle de conversion et une stratégie de contrôle adaptée à l’application visée. Afin de conserver un rendement important sur une large plage de charge, une structure basée sur la mise en parallèle de deux modules LLC est proposée. Une nouvelle stratégie de contrôle à deux boucles est également proposée pour équilibrer le courant entre les deux modules. La seconde partie de la thèse fait appel à la simulation et à l’expérimentation. Il s’agit de minimiser la masse et l’encombrement tout en maximisant le rendement. Un composant magnétique spécial est conçu puis dimensionné pour intégrer le transformateur et diverses inductances de résonance. Ce convertisseur met également en œuvre un système de redressement synchrone robuste avec une compensation de phase, un module de puissance avec une résistance thermique très faible et un système de refroidissement efficace par air. Le rendement maximal mesuré est 95%. Le rendement demeure supérieur à 94% sur une plage de puissance s’étalant de 500 W à 2 kW. La densité de puissance est 1W/cm3. La CEM du convertisseur est développée dans cette thèse. / In this dissertation, a 2.5kW 400V/14V, 250kHz DC/DC converter prototype is developed targeted for electric vehicle/hybrid vehicle applications. Benefiting from numerous advantages brought by LLC resonant topology, this converter is able to perform high efficiency, high power density and low EMI. A first part of this dissertation is the theoretical analysis of LLC: topology analysis, electrical parameter calculation and control strategy. To arrange high output current, this thesis proposes parallel connected LLC structure with developed novel double loop control to realize an equal current distribution. The second part concerns on the system amelioration and efficiency improvement of developed LLC. A special transformer is dimensioned to integrate all magnetic components, and various types of power losses are quantified based on different realization modes and winding geometries to improve its efficiency. This converter also implements a robust synchronous rectification system with phase compensation, a power semiconductor module, and an air-cooling system. The power conversion performance of this prototype is presented and the developed prototype has a peak efficiency of 95% and efficiency is higher than 94% from 500W to 2kW, with a power density of 1W/cm3. The CEM analysis of this converter is also developed in this thesis.

Les convertisseurs électriques sont présents dans tous les équipements électroniques. Les besoins en alimentations stabilisées des appareils et la variabilité des sources d'énergie imposent l'omniprésence des convertisseurs. Dans un environnement embarqué, la conversion, majoritairement DC/DC, subit de multiples contraintes environnementales dues au milieu dans lequel elle évolue, que ce soit dans un aéronef ou un véhicule terrestre. Les équipements ferroviaires doivent ainsi subir des contraintes vibratoires et volumiques fortes imposant à la fois l'absence de pièces mobiles telles que des ventilateurs, ainsi qu'un volume minimal afin de ne pas empiéter sur l'espace utile des cabines de trains.Une contrainte plus spécifique à l'environnement ferroviaire est la très large plage de tension d'alimentation devant être supportée par le convertisseur. Cette plage de tension, s'étendant de 12 V à 154 V, due à la multiplicité des standards électriques de par le monde représente le principal défi à la conception de convertisseurs DC/DC compacts.Dans ce mémoire, les topologies de convertisseurs existantes sont dans un premier temps analysées en fonction des contraintes du cahier des charges. Les deux structures les plus pertinentes sont ensuite étudiées plus profondément, par des simulations comportementales et des modélisations de pertes, afin de confirmer leur pertinence et d'étudier leurs carences.Dans les deux derniers chapitres de ce mémoire, les stratégies de dimensionnement propres à notre application sont décrites. Finalement, les technique de contrôle élaborées spécifiquement pour notre application sont décrites puis testées sur les prototypes des convertisseurs. Les mesures réalisées sur les prototypes ont permis de confirmer l'apport des techniques de contrôle et de dimensionnement décrites précédemment, améliorant significativement les performances des convertisseurs ainsi que l'encombrement de leurs éléments passifs / Electric converters can be found on almost every electronic device. The need for a stabilized power supply and the variability of the power sources make the power converters unavoidable. In embedded applications, the power conversion, mostly DC/DC conversion, must sustain various constraints due to their environment, airborne or in ground vehicles. Devices for railway applications endure severe constraint on their volume and immunity to vibration. Thus, they have to be built without any mobile part including fans, and to be as small as possible to minimize their impact on the payload capacity of the trains.The most specific constraint in railway application is the wide input voltage range sustained by the power converter. This voltage range, from 12 V to 154 V, is due to the large amount of electric standards worldwide. This characteristic is the main challenge for the design of compact DC/DC converters.In this thesis, in a first time the current converters topologies are analysed under the scope of our specifications. Then, the two most relevant structures are more deeply studied. Behavioural simulations and loss models are described, leading to the confirmation of their relevancy and the study of their lacks.In the last two chapters of this thesis, the sizing strategies used to fit our specifications are described. Then, the control techniques elaborated to meet the specificities of our application are described then tested on prototypes. The measurements made on the prototypes have confirmed the gain due to these control techniques and the sizing strategies previously described. These improvements have led to significant improvements in the performance of the converters and in the volume reduction of their passive elements

This thesis examines converter topologies suitable for Module Integrated Converters (MICs) in grid interactive photovoltaic (PV) systems, and makes a contribution to the development of the MIC topologies based on the two-inductor boost converter, which has received less research interest than other well known converters. The thesis provides a detailed analysis of the resonant two-inductor boost converter in the MIC implementations with intermediate constant DC links. Under variable frequency control, this converter is able to operate with a variable DC gain while maintaining the resonant condition. A similar study is also provided for the resonant two-inductor boost converter with the voltage clamp, which aims to increase the output voltage range while reducing the switch voltage stress. An operating point with minimized power loss can be also established under the fixed load condition. Both the hard-switched and the soft-switched current fed two-inductor boost converters are developed for the MIC implementations with unfolding stages. Nondissipative snubbers and a resonant transition gate drive circuit are respectively employed in the two converters to minimize the power loss. The simulation study of a frequency-changer-based two-inductor boost converter is also provided. This converter features a small non-polarised capacitor in a second phase output to provide the power balance in single phase inverter applications. Four magnetic integration solutions for the two-inductor boost converter have also been presented and they are promising in reducing the converter size and power loss.

Le véhicule aérien a connu de nombreuses révolutions durant les dernières décennies afin d’être plus économe en énergie et plus respectueux de l’environnement. Dans cet objectif, l’électricité est apparue comme le vecteur énergétique le plus adapté associé aux sources conventionnelles d’énergie. C’est dans ce contexte que nos recherches se sont portées sur ce mode de transport qui va voir des bouleversements structurels importants et de plus en plus d’équipements électriques installés à bord. Ce travail de recherche s’intéresse à une brique de conversion DC/DC nécessaire au transfert d’énergie entre les bus HVDC et LVDC présents sur les avions actuels, pour cela nous avons étudié la structure et le contrôle de la topologie Dual Active Bridge qui apparaît comme le meilleur candidat pour atteindre les objectifs techniques, de rendement et compacité. Un dimensionnement ainsi que des résultats expérimentaux sont présentés pour valider nos choix avec un démonstrateur de 3,75kW. Des pistes de réflexions sont enfin proposées pour poursuivre et étendre certaine assertions vers une structure tri-ports pour l’interfaçage de multiples réseaux et moyen de stockage. L’originalité de ses travaux réside dans la volonté de concevoir un produit industrialisable dans le domaine de l’aéronautique en favorisant plusieurs ruptures technologiques jusqu’alors rédhibitoire chez les avionneurs. / Avionics is intended to become more and more efficient in terms of energy saving thanks to increased efficiency of embedded system. Today, electricity is presented as the best energy vector compared to hydraulic or pneumatic. This is why current researches aim to focus on power electronic converters in order to meet the future electrical power demand in aircraft networks. This research project presents a DC/DC dual active bridge converter which is expected as the best candidate to meet the complex requirements of an aircraft environment, especially the high voltage dynamics. This persuaded us to study the structure and modulations which are explained and brought face to face with a 3,75kW demonstrator in order to validate the theoretical assumptions. Some food for thought is proposed to extend this work toward a three-port converter to interface multiple network as well as storage systems. The originality of this work is to build a new kind of active conversion system promoting break through technologies to prove it suits to aircraft specifications.

L'objectif du projet CONCIGI-HT (CONvertisseur alternatif-continu Compact à Isolement Galvanique Intégré Haute Tension) est d'augmenter le rendement des chaînes de traction tout en réduisant la masse et le volume de la fonction de conversion Alternatif/Continu. Pour cela, l'ensemble transformateur basse fréquence - redresseur est remplacé par une structure multi-convertisseurs, directement connectée à la caténaire haute tension et intégrant des transformateurs fonctionnant en moyenne fréquence (plusieurs kHz). Cette thèse concerne plus particulièrement la caractérisation et la mise en œuvre de composants semi-conducteurs haute tension dans des structures de conversion statiques à étage intermédiaire moyenne fréquence. L'étude est effectuée sur la base d'une chaîne de traction de 2 MW fonctionnant sur un réseau 25 kV/50 Hz. Le premier chapitre présente l'état de l'art de l'Automotrice à Grande Vitesse (AGV) récemment produite par ALSTOM. C'est la chaîne de traction de cet engin qui sert de référence pour l'étude des nouvelles topologies à transformateur moyenne fréquence. Le deuxième chapitre décrit tout d'abord la structure d'une chaîne de traction classique et présente ensuite deux topologies multicellulaires à transformateur moyenne fréquence applicables en traction électrique ferroviaire (la structure indirecte à redresseur de courant MLI et convertisseur DC/DC à résonance ainsi que la topologie directe associant des convertisseurs duaux). Les avantages et inconvénients de ces topologies sont mis en évidence. Le troisième chapitre concerne la mise en œuvre et la caractérisation en commutation douce de composants Silicium 6,5 kV dans les deux topologies présentées précédemment. Deux bancs de test, représentant un étage élémentaire de conversion, ainsi que des allumeurs spécifiques dédiés à la commutation douce, ont été réalisés. Ils permettent l'étude des semi-conducteurs en régime permanent dans des conditions nominales de fonctionnement (3,6 kV / 100 A). Le quatrième chapitre présente la mise en œuvre et la caractérisation de composants en carbure de silicium (SiC). Pour cela des modules de puissance à base de puces 10 kV (MOSFET et Diodes) ont été réalisés. Les résultats expérimentaux, obtenus sur les bancs de test réalisés au chapitre précédent, mettent en évidence une réduction significative des pertes et démontrent la viabilité de la topologie à convertisseurs duaux pour une application en 25 kV/50 Hz. La conclusion présente un premier design d'un bloc élémentaire et les gains en masse et volume ainsi que les économies d'énergies qui pourront être obtenus par rapport à une structure classique. / The objective of the CONCIGI-HT project (Compact AC/DC converter with Integrated High Voltage Galvanic Insulation) is to increase the efficiency of traction drives while reducing the mass and volume of the AC/DC conversion. To do that, the part low-frequency transformer - rectifier is replaced by a multi-converter topology, directly connected to the high voltage power supply and incorporating medium frequency transformers (several kHz). This thesis relates more particularly to the characterization and implementation of high voltage semiconductors in conversion topologies with intermediate medium frequency link. The study is performed on the basis of a traction drive of 2 MW operating on a 25 kV/50 Hz power supply. The first chapter presents the state of the art of the Automotrice à Grande Vitesse (AGV) recently produced by ALSTOM. The traction drive of this vehicle is used as a reference for the study of new topologies with medium frequency transformer. The second chapter first describes the structure of a conventional traction drive and then presents two multicellular topologies with medium frequency transformer applicable to railway traction (the indirect structure with PWM rectifier and DC/DC resonant converter and the direct topology combining dual converters). The advantages and disadvantages of these topologies are highlighted. The third chapter deals with the implementation and soft switching characterization of 6.5 kV Silicon components in both topologies presented above. Two test benches, representing a basic conversion stage, as well as specific drivers dedicated to the soft switching, has been made. They allow the study of semiconductors in nominal operating conditions (3.6 kV / 100 A). The fourth chapter presents the implementation and characterization of silicon carbide components (SiC). For this, power modules based on 10 kV chips (MOSFET and Diodes) have been achieved. The experimental results obtained on test benches made in the previous chapter, show a significant reduction in losses and demonstrate the viability of the dual converter topology for a 25 kV/50 Hz application. The conclusion presents the first design of an elementary block and gains in mass and volume as well as the energy savings that can be achieved compared to a conventional structure.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This Ph. D. Thesis presents a in deep study of the mechanism of resonant transition soft-switching techniques. By means of the principles that rules the PWM resonant transition converters, a novel tool for analysis and synthesis have been developed. This novel tool also permit to be verified some of the main factors that made possible to he ZVT technique to achieve its technology level. By means of this tool and with the definition of the basic requirements of the resonant transition converters a new concept concerning the ZCZVT technique have been generated, the ZCZVT converters with discontinuous auxiliary voltage source . The development of this new concept gives rise to a new family of ZCZVT converters with magnetically coupled auxiliary circuit. It also allowed a better perspective of the ZCZVT converters characteristics, advantages, drawbacks and limitations, which contributed significantly with the grown of the technology. Two of the six topologies with bi-directional auxiliary circuits proposed in the thesis have been mathematically analised. A design methodology based on constrains and dynamic characteristics of the IGBT and diode semiconductors under ZCS and ZVS conditions have been presented. Finally, experimental results proved the efficiency gain of the novel ZCZVT inverters with magnetically coupled auxiliary circuit. The ZCZVT inverter with magnetically coupled auxiliary circuit prototype have been compared with its Undeland snubber counterpart, presenting an efficiency of about 4% superior. It corroborates to the thesis proposal of developing novel topologies with better performance and simplicity. / O presente trabalho apresenta um estudo aprofundado do mecanismo de comutação presente nas técnicas de comutação suave com transição ressonante. Por meio da definição dos princípios que governam as comutações dos conversores PWM com transição ressonante, desenvolveu-se uma nova ferramenta para análise e síntese de novos circuitos com características aperfeiçoadas. Também através desta ferramenta de análise pode-se verificar alguns dos principais fatores que possibilitaram o amadurecimento da técnica de comutação ZVT. Com esta ferramenta e com a definição dos requisitos básicos para a operação dos conversores com transição ressonante foi gerado o conceito de conversores ZCZVT com fonte auxiliar descontínua. O desenvolvimento deste conceito deu origem a uma nova família de conversores ZCZVT com acoplamento magnético. O desenvolvimento de uma nova família de conversores ZCZVT permitiu uma melhor percepção das características destes circuitos e o amadurecimento da técnica de comutação suave ZCZVT. Duas das seis topologias de circuitos auxiliares bidirecionais propostas na tese para os novos inversores ZCZVT monofásicos com acoplamento foram analisadas matematicamente. Uma metodologia de projeto para estes inversores foi apresentada. Esta metodologia é baseada em restrições obtidas das características dinâmicas dos IGBTs e dos diodos que operam sob comutação em zero de corrente (ZCS) e zero de tensão (ZVS). Por fim, foram apresentados resultados experimentais que comprovam o ganho de eficiência do inversores ZCZVT com acoplamento magnético e circuitos auxiliares em derivação proposto. O protótipo do inversor ZCZVT foi comparado experimentalmente com um inversor utilizando snubber de Undeland, apresentando uma eficiência em média 4% superior. O que corroborou com a proposta inicial de desenvolver topologias ZCZVT com desempenho melhorado e maior simplicidade.