With the development of solar energy, power conversion systems responsible for energy delivering from photovoltaic (PV) modules to ac or dc grid attract wide attentions and have significantly increased installations worldwide. Modular power conversion system has the highest efficiency of maximum power point tacking (MPPT), which can transfer more solar power to electricity. However, this system suffers the drawbacks of low power conversion efficiency and high cost due to a large number of power electronics converters. High-power density can provide potentials to reduce cost through the reduction of components and potting materials. Nowadays, the power electronics converters with the conventional silicon (Si) based power semiconductor devices are developed maturely and have limited improvements regarding in power conversion efficiency and power density. With the availability of wide bandgap devices, the power electronics converters have extended opportunities to achieve higher efficiency and higher power density due to the desirable features of wide bandgap devices, such as low on-state resistance, small junction capacitance and high switching speed. This dissertation focuses on the application of wide bandgap devices to the dc-dc power conversion for the modular PV applications in an effort to improve the power conversion efficiency and power density. Firstly, the structure of gallium-nitride (GaN) device is studied theoretically and characteristics of GaN device are evaluated under testing with both hard-switching and soft-switching conditions. The device performance during steady-state and transitions are explored under different power level conditions and compared with Si based devices. Secondly, an isolated high-efficiency GaN-based dc-dc converter with capability of wide range regulation is proposed for modular PV applications. The circuit configuration of secondary side is a proposed active-boost-rectifier, which merges a Boost circuit and a voltage-doubler rectifier. With implementation of the proposed double-pulse duty cycle modulation method, the active-boost-rectifier can not only serve for synchronous rectification but also achieve the voltage boost function. The proposed converter can achieve zero-voltage-switching (ZVS) of primary side switches and zero-current-switching (ZCS) of secondary side switches regardless of the input voltages or output power levels. Therefore, the proposed converter not only keeps the benefits of highly-efficient series resonant converter (SRC) but also achieves a higher voltage gain than SRC and a wide range regulation ability without adding additional switches while operating under the fixed-frequency condition. GaN devices are utilized in both primary and secondary sides. A 300-W hardware prototype is built to achieve a peak efficiency of 98.9% and a California Energy Commission (CEC) weighted efficiency of 98.7% under nominal input voltage condition. Finally, the proposed converter is designed and optimized at 1-MHz switching frequency to pursue the feature of high-power density. Considering the ac effects under high frequency, the magnetic components and PCB structure are optimized with finite element method (FEM) simulations. Compared with 140-kHz design, the volume of 1-MHz design can reduce more than 70%, while the CEC efficiency only drops 0.8% at nominal input voltage condition. There are also key findings on circuit design techniques to reduce parasitic effects. The parasitic inductances induced from PCB layout of primary side circuit can cause the unbalanced resonant current between positive and negative half cycles if the power loops of two half cycles have asymmetrical parasitic inductances. Moreover, these parasitic inductances reflecting to secondary side should be considered into the design of resonant inductance. The parasitic capacitances of secondary side could affect ZVS transitions and increase the required magnetizing current. Because of large parasitic capacitances, the dead-time period occupies a large percentage of entire switching period in MHz operations, which should be taken into consideration when designing the resonant frequency of resonant network. / Doctor of Philosophy / Solar energy is one of the most promising renewable energies to replace the conventional fossils. Power electronics converters are necessary to transfer power from solar panels to dc or ac grid. Since the output of solar panel is low voltage with a wide range and the grid side is high voltage, this power converter should meet the basic requirements of high step up and wide range regulation. Additionally, high power conversion efficiency is an important design purpose in order to save energy. The existing solutions have limitations of narrow regulating range, low efficiency or complicated circuit structure. Recently, the third-generation power semiconductors attract more and more attentions who can help to reduce the power loss. They are named as wide band gap devices. This dissertation proposed a wide band gap devices based power converter with ability of wide regulating range, high power conversion efficiency and simple circuit structure. Moreover, this proposed converter is further designed for high power density, which reduces more than 70% of volume. In this way, small power converter can merge into the junction box of solar panel, which can reduce cost and be convenient for installations.

Induction heating has become a popular alternative to other heat sources for stovetop cooking applications due to performance, efficiency, control response, and safety. The main drawback is that extreme difficulty is encountered when trying to head low-resistivity, non-ferromagnetic metals such as aluminum and copper, which are commonly used for cookware in several societies. The lack of ferromagnetic properties, resulting in no hysteresis dissipation, and low resistivity of such metals results in an impractically low resistance reflected through the work coil. The resultant impedance complicates inverter design, as it is too low to be efficiently driven with conventional inverter topologies. The magnitudes of current involved in exciting this impedance also severely impact the efficiency of the coil and resonant components, requiring extreme care in coil design. This work explores various techniques that have been proposed and/or applied to efficiently heat low-resistivity cookware and the associated limitations. A transformer-coupled series-load-resonant topology driven by a full-bridge inverter is proposed as a means of efficiently heating aluminum cookware within practical design constraints. The experimental circuit is built and successfully tested at an output power of 1.66kW. The procedure of optimizing the work coil for improved efficiency is also presented along with the procedure of measuring coil efficiency. An improved circuit incorporating switch voltage detection to guarantee zero-voltage switching is then built in order to overcome limitations of this design. / Master of Science

Ce travail concerne l’étude et la réalisation d’une architecture multicellulaire de conversion d’énergie électrique haute tension avec étage intermédiaire alternatif moyenne fréquence destinée à la traction électrique ferroviaire. L’objectif de ce travail est de diminuer la masse et le volume de l’étage de conversion alternatif-continu que l’on retrouve dans les engins de traction conçus pour circuler sur les réseaux alternatifs 25kV-50Hz ou 15kV-16Hz2/3. La recherche de gains sur l’étage de conversion alternatif-continu s’applique aussi bien sur les automotrices où l’on cherche à gagner de la place disponible pour y placer des passagers que sur les locomotives ou encore sur les motrices de TGV où l’on recherche un gain de masse étant donné que ces engins sont en limite de charge à l’essieu. Le contexte de la haute tension implique l’utilisation d’interrupteurs de forts calibres en tension pour limiter au maximum le nombre de cellules de conversions utilisées. D’un autre côté, la recherche de gains sur le transformateur nécessite une fréquence de découpage élevée, génératrice de pertes en commutation dans les interrupteurs. L’architecture de conversion retenue permet par l’association de structures duales d’obtenir des conditions de commutation douce, ce qui est favorable à une montée en fréquence avec des interrupteurs de forts calibres en tension. Le convertisseur élémentaire associe un onduleur de tension commandé au blocage et un commutateur de courant commandé à l’amorçage. Afin d’évaluer le rendement de l’architecture considérée, un prototype d’un bloc de conversion élémentaire, d’une puissance de 280 kVA, a été réalisé au laboratoire PEARL. Les interrupteurs sont réalisés sur la base de modules IGBT 6,5kV/200A. Les essais en commutation douce ont permis d’évaluer, dans des conditions de fonctionnement réelles, les pertes dans les modules IGBT. Compte tenu de ces résultats, il est possible de déterminer les limites de fonctionnement de la structure de conversion et d’effectuer un dimensionnement en considérant le compromis rendement-poids-volume pour un engin de traction donné. / This thesis concerns the study and the rating of a high voltage multicellular converter with an intermediate medium frequency stage dedicated to railway traction. The objective is to reduce the weight and the volume of the AC-DC conversion stage which is implemented in railway engines running on 25kV-50Hz or 15kV-16Hz2/3 railways. Reduction on weight and size of the AC-DC converter may be applied on multiple unit trains where the transformer causes room loss for passengers and on locomotives and high speed trains where the axle load is limited. On one hand high voltage switches are required in order to minimize the number of cells used to build the converter. On the other hand, reducing the size and the weight of the transformer requires a high switching frequency, causing high commutation losses. To achieve soft switching conditions with high voltage semiconductors, the proposed topology is based on an association of dual structures. Each elementary converter combines a controlled turn-off voltage source inverter and a controlled turn-on current source inverter. In order to estimate the efficiency of the new topology, a prototype of one elementary cell working at 280 kVA, was built at the Power Electronics Associated Research Laboratory (PEARL). The switches are standard 6.5 kV/200A IGBTs modules. Soft-switching tests, in real operating conditions, allow evaluating IGBTs and diodes switching losses. Thanks to these results, it is possible to find the structure operating limits and to size the transformer considering the trade-off between the system efficiency and the transformer weight.

De nos jours, les énergies renouvelables remplacent les énergies fossiles. Pour assurer une l’interconnexion entre toutes ces installations électriques, l’électronique de puissance est nécessaire. Les principales spécifications de la prochaine génération de convertisseur de puissances sont un rendement et une densité de puissance élevés, fiabilité et faibles coûts. L’intégration PCB des composants actifs et/ou passifs est perçue comme une approche prometteuse, peu onéreuse et efficace. Les délais ainsi que les coûts de fabrication des convertisseurs de puissance peuvent considérablement réduits. L’intégration permet également d’améliorer les performances des convertisseurs. Dans ce but, un concept original d’inductance 3D pliable utilisant la technologie PCB est présenté. Il permet un coût faible pour une production en série, ainsi qu’une excellente reproductibilité. Un usinage partiel de la carte PCB est utilisé, permettant le pliage et la conception des enroulements de l’inductance. Différents prototypes sont développés par le biais d’une procédure d’optimisation. Des tests électriques et thermiques sont réalisés pour valider l’applicabilité du concept au sein de convertisseurs de puissance.Le développement d’une procédure d’optimisation appliqué aux convertisseurs hautement intégrés utilisant l’enterrement PCB est présenté. Tous les choix importants, facilitant l’intégration PCB, e.g. réduction des composants passifs, sont présentés. Cela inclut la sélection de la topologie adéquate avec la modulation associée. La procédure de design et les modèles analytiques sont introduits. Il en résulte un convertisseur comprenant quatre pont-complet entrelacés avec des bras fonctionnant à basse (50 Hz) et haute (180 kHz) fréquences. Cette configuration autorise une variation de courant importante dans les inductances, assurant ainsi la commutation des semi-conducteurs à zéro de tension (ZVS), et ceux sur une période complète du réseau. L’impact de la forte variation de courant sur le filtre CEM est compensé par l’entrelacement. Deux prototypes d’un convertisseur AC/DC bidirectionnel de 3.3 kW sont présentés, les résultats théorique et pratique sont analysés.Pour augmenter la densité de puissance du system, un filtre actif de type “Buck” est étudié. La procédure d’optimisation est adaptée à partir de la procédure implémentée pour le convertisseur AC/DC. L’approche utilisée, mène à un convertisseur opérant également en ZVS durant une période compète du réseau, et ce, à fréquence de commutation fixe. Les technologies sélectionnées, condensateur céramique et inductance compatible avec la technologie PCB sont favorable à l’intégration et sont implémenté sur le prototype. / Nowadays, the green energy sources are replacing fossil energies. To assure proper interconnections between all these different electrical facilities, power electronics is mandatory. The main requirements of next generation converters are high efficiency, high power density, high reliability and low-cost. The Printed Circuit Board (PCB) integration of dies and/or passives is foreseen as a promising, low-cost and efficient approach. The manufacturing time and cost of power converters can be drastically reduced. Moreover, integration allows the converter performances to be improved. For this purpose, an original 3D folded power inductor concept using PCB technology is introduced. It is low cost for mass production and presents good reproducibility. A partial milling of the PCB is used to allow bending and building the inductor winding. Prototypes are designed through an optimisation procedure. Electrical and thermal tests are performed to validate the applicability in power converters. The development of an optimisation procedure for highly integrated converters, using PCB embedding, is presented. All important choices, facilitating the PCB integration, e.g. reduction of passive components, are presented. It includes the selection of the suitable converter topology with the associated modulation. The design procedure and implemented analytical models are introduced. It results in four interleaved full-bridges operating with low (50 Hz) and high (180 kHz) frequency legs. The configuration allows high current ripple in the input inductors inducing zero voltage switching (ZVS) for all the semiconductors, and for a complete grid period. The impact of high current ripple on the EMI filter is compensated by the interleaving. Two prototypes of a 3.3 kW bidirectional AC/DC converters are presented, theoretical and practical results are discussed. To further increase the power density of the overall system, a Buck power pulsating buffer is investigated. The optimisation procedure is derived from the procedure implemented for the AC/DC converter. The result favours an original approach, where the converter also operates with ZVS along the entire main period at a fixed switching frequency. The selected technologies for prototyping are integration friendly as ceramic capacitors and PCB based inductors are implemented in the final prototype.

In this thesis, a new HVDC-based converter system for wind farms is investigated. It is based on a mutually commutated soft-switching converter system and provides a unique integrated solution for the wind turbine generator drive systems, the wind turbine interconnection, and the power conversion for HVDC transmission. In a wind farm, the mutually commutated converter system is a distributed system. A medium-frequency collection grid connects the converter station, equipped with a single-phase voltage source converter and a medium-frequency transmission transformer, with the wind turbines, each containing a cycloconverter and a medium-frequency distribution transformer. In this thesis, various system aspects regarding the application of a distributed mutually commutated converter system in a wind farm are investigated. Special attention is paid to the design of a medium-frequency collection grid that has an acceptable level of transient overvoltages, the design of medium-frequency transformers with suitable magnetic, electric and thermal properties, and the development of a strategy to commutate the voltage source converter during low power generation. In order to adapt the mutually commutated converter system for an application in a wind farm, it had to be further developped. Different carrier-based and space-vector oriented modulation methods have been investigated. It turns out that for any load angle there is a quasi-discontinuous pulse width modulation strategy that can produce the same pulse patterns as space vector modulation. In addition, a modulation strategy has been developed that allows to replace the IGBTs in the cycloconverter with cheap, robust, and reliable fast thyristors, despite their absence of turn-off capability. The feasibility of different modulation strategies for mutually commutated converter systems has been verified on a down-scaled prototype converter system with both IGBT- and thyristor-based cycloconverters. Finally, a feasible wind farm layout is proposed, which considerably reduces the energy generation costs for large winds farms distant to a strong grid connection point. As a consequence, the proposed solution may facilitate the establishment of remotely located wind farms. / QC 20100802

Switched mode power supplies (SMPS) have found wide spread acceptance in all power processing applications. The design demand is moving towards higher power densities. For reduction in size and weight, it is imperative to process the power at a higher switching frequency. High switching frequency requires soft switching techniques to reduce the switching losses. Several families of soft switching converters have emerged in the past two decades. Analysis and modelling methods have been proposed in relation with these topologies. Active clamp converters are the recently introduced soft switching topologies. Steady state analysis and model of these converters have been reported in literature. This thesis presents a unified equivalent circuit oriented model for the family of active clamp converters. Analytical expressions for DC conversion ratio in terms of pole current and throw voltage are derived for all the DC-DC converters with active clamp. The special feature is that, the conversion ratio exhibits a load dependent drop (IRd), where I is the pole current and Rd is the damping resistance. The damping resistance Rd is a mathematical artifact to represent the voltage loss on account of delay in the turn-on of the active switch. There is no energy loss associated with this load dependent drop. This is conveniently expressed as an appropriate lossless resistance in the equivalent circuit model. The proposed equivalent circuit models are valid for both steady-state and dynamic performance. A spread sheet based design is presented for the basic DC-DC converters with active clamp. A prototype design following the spreadsheet is made. The performance of the same is validated and verified by simulation and measurements. Steady state and dynamic results are presented. The stability criterion for the active clamp converters under current programming is investigated. The same is verified through simulation and validated on a current programmed active clamp converter prototype. The active clamp converters suffer from a few disadvantages: Higher VA ratings of switches, load dependent ZVS performance and increased component count. Several soft switching topologies have been reported in literature. Efficiency improvement and increase in switching frequency are obtained to different degrees. This thesis proposes a new family of soft switching converters. This family of converters switch at constant frequency and maintains the advantages of traditional PWM converters. The proposed topology employs an auxiliary circuit to achieve soft switching. The auxiliary circuit consists of a dependent voltage source, an auxiliary switch, a series diode and a set of resonant elements (Inductor and capacitor). The switching transitions of both the active switch and the auxiliary switch are lossless. The novelty in the proposed circuit is the method of generating the dependent source required to enable zero current switching of the auxiliary switch. The dependent source is realized by a coupled winding in the energy storage inductor or tapped from the energy transfer transformer of non-isolated and isolated converters respectively. The proposed topology is applicable to most of the isolated and non-isolated DC-DC converters. The circuit equations governing the sub-intervals of the converter are expressed in terms of pole current and throw voltage. With such a definition, performance results and the design equations are identical for all types of DC-DC converters. Equivalent circuit models are obtained for the whole family of DC-DC converters. The proposed model is valid for steady state and dynamic performance. Analytical expressions of DC conversion ratio for all topologies, in terms of pole current and throw voltage are derived. The special feature is that, the conversion ratio exhibits a load dependent drop (IRd), where I is the pole current and Rd is the damping resistance. The damping resistance Rd is a mathematical artifact to represent the voltage loss on account of delay in the turn-on of the active switch. There is no energy loss associated with this load dependent drop. This is conveniently expressed as an appropriate lossless resistance in the equivalent circuit model. Design guidelines are established for the whole family of proposed converters; the same are validated through prototype converters.

The popularity of the internal combustion engine (ICE) vehicles has contributed to global warming problem and degradation of air quality around the world. Furthermore, the vehicles??? massive demand on gas has played a role in the depletion of fossil fuel reserves and the considerable rise in the gas price over the past twenty years. Those existing challenges force the auto-industry to move towards the technology development of vehicle electrification. An electrified vehicle is driven by one or more electric motors. And the electricity comes from the onboard energy storage system (ESS). Currently, no single type of green energy source could meet all the requirements to drive a vehicle. A hybrid energy storage system (HESS), as a combination of battery and ultra-capacitor units, is expected to improve the overall performance of vehicles??? ESS. This thesis focuses on the design of HESS and the development of a HESS prototype for electric vehicles (EVs) and hybrid electric vehicles (HEVs). Battery unit (BU), ultra-capacitor unit (UC) and a DC/DC converter interfacing BU and UC are the three main components of HESS. The research work first reviews literatures regarding characteristics of BU, UC and power electronic converters. HESS design is then conducted based on the considerations of power capability, energy efficiency, size and cost optimization. Besides theoretical analysis, a HESS prototype is developed to prove the principles of operation as well. The results from experiment are compared with those from simulation.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This study proposes an auxiliary commutation circuit, applied to a double-conversion uninterruptible power supply, operating with a three-level PWM full-bridge inverter. In order to construct this circuit, we use the concept of integration of auxiliary commutation circuit: the case study of ZVT. The concept of iCAC is not directly applied to three-level PWM inverters. Then, it is necessary the use of classic auxiliary commutation techniques combined with the concept of integration. In this study, it is presented a hybrid auxiliary commutation circuit. Due to the restrictions imposed by the iCAC, just one of the inverter legs can be integrated. To the other inverter leg it is used a conventional auxiliary commutation circuit. The proposed system aims at achieving a better performance if compared to the same uninterruptible power supply operating with a classic ZVT auxiliary commutation circuit. There is also the advantage that all the auxiliary switches operate with ZVS and/or ZCZ soft switching. Through the use of iCAC it is obtained a minimization of circulating reactive energy in the auxiliary commutation circuits and it contributes to increase the global performance of the uninterruptible power supply. The number of additional components is reduced in relation to the classic CAC and, consequently, the system becomes more attractive to the industry. During this study, the analysis of the system and the simulation results are presented. Finally, experimental results are presented, comparing the efficiency of the CAC iZVT proposed system versus the classic CAC ZVT, in order to validate the proposed system. / Este trabalho propõe um circuito de auxílio à comutação, aplicado a uma fonte ininterrupta de energia de dupla conversão, operando com inversor PWM ponte completa modulado em três níveis de tensão. Para obtenção desse circuito, este trabalho utiliza o conceito de integração de circuitos de auxílio à comutação: O estudo do caso ZVT. O conceito de iCAC não é aplicável diretamente a inversores PWM modulados em três níveis de tensão. Dessa forma faz-se necessário a utilização de técnicas clássicas de auxílio à comutação em conjunto com o conceito de integração. A partir deste estudo é proposto um circuito de auxílio à comutação híbrido. Devido às restrições impostas pelo iCAC apenas uma das pernas do inversor pode ser integrada. Para a outra perna do inversor é então utilizado um circuito de auxílio à comutação convencional. O sistema proposto visa obter melhor rendimento em relação à mesma fonte ininterrupta de energia operando com circuito de auxílio à comutação clássicos do tipo ZVT. Há também a vantagem de que todas as chaves auxiliares operam com comutação suave ZVS e/ou ZCS. Com uso do conceito de iCAC é obtida a minimização da energia reativa circulante nos circuitos de auxílio à comutação, o que contribui para elevar o rendimento global da fonte ininterrupta de energia. O número de componentes adicionais é reduzido em relação ao CAC clássico, tornando assim o sistema atrativo à indústria. Ao longo desse estudo, são apresentadas as análises do funcionamento do sistema e resultados de simulação são apresentados. Por fim, resultados experimentais são apresentados, comparando a eficiência do sistema proposto CAC iZVT versus CAC ZVT clássico, para dessa forma validar o sistema proposto.

This paper presents the study and development of a topology of nonisolated converter operating at high frequency, which is suitable for the integration of battery banks, photovoltaic panels, and a high voltage dc link in a single conversion stage. The topology is based on the bidirectional version of the three-state switching cell and is recommended for battery charging, while a 200V dc link can be obtained in a single conversion stage using photovoltaic (PV) panels. The presented converter is able to supply a 200V dc link using a battery bank and a PV array and, depending on the solar irradiance level, it is also possible to charge the batteries by using a single conversion stage. Moreover, all the switches of the converter are able to operate under zero voltage switching (ZVS) condition over a wide operation range. The experimental results are obtained from a 500W laboratory prototype, which has been developed and tested in three situations: energy flow from the battery bank to the load, energy flow from the PV panel to the load; and energy flow from the panel to the battery bank, achieving the efficiency of 94,18%, 96,09% e 94,67% respectively. The high gain afforded by this topology and the excellent performance obtained in all operations mode, shows as a solution where the requirement of increasing the voltage to 200V or 400V from low input voltage energy sources, typically 12V, 24V or 48V, provided by batteries, solar panels or others sources of energy, for Uninterruptable Power Supply (UPS), or a DC link, for example. / Este trabalho tem por escopo apresentar o estudo e desenvolvimento de um conversor CC-CC nÃo isolado de trÃs portas, adequado à integraÃÃo em um Ãnico estÃgio de conversÃo: um banco de baterias, um conjunto de painÃis fotovoltaicos e o link CC. A topologia proposta apresenta um conversor boost de alto ganho baseado na versÃo bidirecional da cÃlula de comutaÃÃo de trÃs estados na qual se tem integrado um banco de baterias e um conjunto de painÃis fotovoltaicos com capacidade para gerar um barramento CC de 200V em um Ãnico estÃgio de processamento. A caracterÃstica bidirecional da topologia permite aos painÃis fotovoltaicos carregar as bateiras e alimentar a carga dependendo da incidÃncia solar. No caso de ausÃncia de sol, o banco de baterias supre a carga. Outra importante caracterÃstica deste conversor à a comutaÃÃo suave em modo ZVS para todas as chaves. Foi desenvolvido um protÃtipo experimental com potÃncia nominal de 500W de forma a validar todo o embasamento teÃrico e de simulaÃÃo apresentados. O conversor desenvolvido foi submetido a trÃs condiÃÃes: o fluxo de energia da bateria para a carga, do painel fotovoltaico para a carga e do painel para o banco de baterias, sendo obtido o rendimento de 94,18%, 96,09% e 94,67% respectivamente para cada condiÃÃo. AlÃm disso, as formas de ondas experimentais e de simulaÃÃo para cada condiÃÃo e o comparativo de rendimento de topologias, tambÃm sÃo apresentados. O alto ganho e o rendimento alcanÃado nesta topologia, a torna uma forte soluÃÃo quando hà necessidade de elevar a tensÃo a partir de baterias ou painÃis fotovoltaicos, quando os valores fornecidos por estes geralmente sÃo de 12V, 24V ou 48V. Ressalte-se que este trabalho contribui cientificamente na Ãrea da eletrÃnica de potÃncia, mais especificamente, no que concerne ao estudo e desenvolvimento de novas topologias de conversores CC-CC nÃo isolados de trÃs portas para aplicaÃÃes em energias renovÃveis.

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