nÃo hà / The electric vehicle is increasingly present in our cities every day, and in the technological context it has shown great progress. Two essential elements to the success of these vehicles are the electric energy storage devices and electronic converters for processing and management of this energy. In this context, this dissertation presents a study on the current situation of the electric vehicle on the world scenario and its embedded technologies. Another object of research are supercapacitors for application in electric vehicles as an energy storage source and fast energy transfer. Thus, these studies provide the basis for achieving the main objective of this work: developing a bidirectional dc-dc converter for managing the energy flow provided by a supercapacitor module applied in an electric vehicle. A 2 kW laboratory a prototype with two phase interleaved dc-dc bidirectional topology has been implemented. Also, all used methodology is exposed, such as qualitative analysis, dimensioning of components, modeling and design of PI type controllers for the proposed converter. The digital implementation of the control circuit was designed using the dsPIC30f4011 by Microchip. Through simulation and experimental tests, it was evaluated the behavior of the converter and a performance comparison was held, with the converter showing efficiency above 90%. Thus, through theoretical and practical results it was possible to evaluate the performance of the converter and future studies involving the complete structure of a model of a small electric vehicle. / O veÃculo elÃtrico està cada vez mais presente em nossas cidades, e no Ãmbito tecnolÃgico ele vem apresentando grandes avanÃos. Dois elementos essenciais para o sucesso desses veÃculos sÃo os dispositivos de armazenamento de energia elÃtrica e os conversores eletrÃnicos para processamento e gerenciamento dessa energia. Nesse contexto, esta dissertaÃÃo apresenta um estudo sobre a atual situaÃÃo do veÃculo elÃtrico no cenÃrio mundial e suas tecnologias embarcadas. Outro objeto de pesquisa sÃo os supercapacitores para aplicaÃÃo em veÃculos elÃtricos como fonte de armazenamento e transferÃncia rÃpida de energia. Neste contexto o presente trabalho aborda o desenvolvimento de um conversor cc-cc bidirecional para gerenciamento do fluxo de energia em um mÃdulo de supercapacitores para utilizaÃÃo em um veÃculo elÃtrico. à projetado e desenvolvido em laboratÃrio um protÃtipo com potÃncia de 2 kW, cuja topologia adotada à um conversor cc-cc bidirecional intercalado de duas fases. Deste modo, à exposta toda metodologia empregada onde à abordada a anÃlise qualitativa, o dimensionamento dos componentes, a modelagem e o projeto dos controladores tipo PI para o conversor proposto. Para a implementaÃÃo digital do circuito de controle foi utilizado o dsPIC30f4011 da Microchip. Por meio de simulaÃÃo e dos ensaios experimentais avaliou-se o comportamento do conversor e realizou-se uma comparaÃÃo de desempenho, tendo o conversor apresentado rendimento acima de 90%. Assim, pelos resultados teÃricos e prÃticos foi possÃvel avaliar o desempenho do conversor e creditar a continuidade de sua aplicaÃÃo a trabalhos futuros envolvendo a estruturaÃÃo completa de um modelo de veÃculo elÃtrico de pequeno porte.

The solution for the generating energy derived from non-polluting sources configures a worldwide problem, which is undetermined, complex, and gradual; and certainly, passes through the diversification of the energetic matrix. Diversification means not only having different sources converted into useful energy, like the electricity, but also decentralizing the energy generation in order to fit with higher adequacy the demand, which is decentralized too. Distributed Generation proposes this sort of development but in order to increase its penetration several technical barriers must be overpassed. One of them is related to the conversion systems, which must be more flexible, modular, efficient and compatible with the different energy sources, since they are very specific for a certain area. The present study drives its efforts towards this direction, i.e. having a system with several inputs for combining different renewable energy sources into a single and efficient power converter for the grid connection. It focuses on the design and control of an 11.7 kW hybrid renewable generation system, which contains two parallel circuits of photovoltaic panels and a wind turbine. A multicell converter divided in two stages accomplishes the convertion: Generation Side Converter (GSC) and Mains Side Converter (MSC). Two boost converters responsible for the photovoltaic generation and a rectifier and a third boost, for the wind constitue the GSC. It allows the conversion to the fixed output DC voltage, controlling individually and performing the maximum power point tracking in each input. On the other side, the single-phase 4- cell MSC accomplishes the connection to the grid through an LCL filter. This filter uses an Intercell Transformer (ICT) in the first inductor for reducing the individual ripple generated by the swicthing. The MSC controls the DC-link voltage and, by doing that, it allows the power flow from the generation elements to the network.

In recent years, the interest for parallel multicell converters has grown, which is partially due to the possibility of coupling the inductors used to connect the different commutation cells together. Coupling the inductors to form an InterCell Transformer (ICT) does not usually modify the output current, but it reduces the current ripple in the windings and the flux swing in some regions of the core. It can be shown that this brings a reduction of copper and core losses in the magnetic component. The reduction of the phase current ripple also reduces the difference between turn on and turn off current in the switches, which brings a reduction of switching losses for devices generating more losses at turn off than at turn on. The design of an ICT is not that different from any other magnetic component but it is very specific and inherent features must be taken into account. Taking full benefit of the potential advantages of ICTs requires the development of special tools and methods which are the focus of the study. We show how to design ICTs considering several topologies and different methods, from the most precise and time-consuming to the less accurate but more quickly calculated. The explanation of the ICT design is divided in four main parts: Copper Losses, Core Losses, Flux Density Saturation and Thermal Aspects. Further attention is given to high frequency copper losses since complex phenomena such as skin and proximity effects highly influence the ICT design. Based on Finite Element Method simulations, smart practices are suggested to reduce high and low frequency copper losses, not only in ICTs but also in inductors and transformers. Simple tables are developed to help transformer designers to identify the best configuration of conductors inside a given core window, depending on the current waveform and frequency, number of turns and geometrical parameters. Optimization routines to reduce the ICT total mass, volume, losses or cost are developed and multidimensional interpolation of pre-simulated values of AC resistance and leakage inductance is used to speed up the optimization routine. Comparison of ICT designs with regard to core and conductor material, number of cells and switching frequency is performed. Comparison with regular inductors is also made in order to verify the benefits of this kind of magnetic component. Multilevel converter control aspects applied to three- hase systems is also investigated in terms of the ICT flux. Zero sequence signals, specific for a PWM strategy and converter/load topology, are created in order to minimize the flux in ICTs and consequently reduce even further the mass and size of these components. Comparison between several PWM methods are performed and experimentally verified.

Time Interleaved Analog-to-Digital Converters (TI-ADCs) utilize an architecture which enables conversion rates well beyond the capabilities of a single converter while preserving most or all of the other performance characteristics of the converters on which said architecture is based. Most of the approaches discussed here are independent of architecture; some solutions take advantage of specific architectures. Chapter 1 provides the problem formulation and reviews the errors found in ADCs as well as a brief literature review of available TI-ADC error correction solutions. Chapter 2 presents the methods and materials used in implementation as well as extend the state of the art for post conversion correction. Chapter 3 presents the simulation results of this work and Chapter 4 concludes the work. The contribution of this research is three fold: A new behavioral model was developed in SimulinkTM and MATLABTM to model and test linear and nonlinear mismatch errors emulating the performance data of actual converters. The details of this model are presented as well as the results of cumulant statistical calculations of the mismatch errors which is followed by the detailed explanation and performance evaluation of the extension developed in this research effort. Leading post conversion correction methods are presented and an extension with derivations is presented. It is shown that the data converter subsystem architecture developed is capable of realizing better performance of those currently reported in the literature while having a more efficient implementation.

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Fuel cells are a clean, high-efficiency source for power generation. This innovative technology is going to penetrate all aspects in our life, from utility distributed power, transportation applications, down to power sources for portable devices such as laptop computer and cell phones. To enable the usage of fuel cell, developing power converters dedicated for fuel cells becomes imminent. Currently, the full-bridge converter is the dominating topology in high power dc/dc applications. Although multiphase converters have been proposed, most of them are dealing with high input-voltage systems, and their device characteristic is not suitable for a low voltage source such as a fuel cell. For a high power fuel cell system, high voltage conversion ratios and high input currents are the major obstacles to achieving high-efficiency power conversions. This dissertation proposes a novel 3-phase 6-leg dc/dc power converter with transformer isolation to overcome these obstacles. Major features of the proposed converter include: (1) Increase converter power rating by paralleling phases, not by paralleling multiple devices; (2) Double the output voltage by transformer delta-wye connection, thus lowering the turns-ratio; (3) Reduce the size of output filter and input dc bus capacitor with interleaved control; (4) Achieve Zero-Voltage Zero-Current Switching (ZVZCS) over a wide load range without auxiliary circuitry. High conversion efficiency above 96% is verified with different measurement approaches in experiments. This dissertation also presents the power stage and control design for the proposed converter. Control design guideline is provided and the design result is confirmed with both simulation and hardware experiments. When using the fuel cell for stationary utility power applications, a low-frequency ripple interaction was identified among fuel cell, dc/dc converter and dc/ac inverter. This low frequency ripple tends to not only damage the fuel cell, but also reduce the source capability. This dissertation also investigates the mechanism of ripple current propagation and exploits the solutions. A linearized ac model is derived and used to explain the ripple propagation. An active ripple reduction technique by the use of the current loop control is proposed. This active current loop control does not add extra converters or expensive energy storage components. Rather, it allows a reduction in capacitance because the ripple current flowing into the capacitor is substantially reduced, and less capacitance can be used while maintaining a clean dc bus voltage. The design process and guideline for the proposed control is suggested, and the effectiveness of this active control is validated by both simulation and experimental results. / Ph. D.

Front-end converters with power factor correction (PFC) capability are widely used in distributed power systems (DPSs). Most of the front-end converters are implemented using a two-stage approach, which consists of a PFC stage followed by a DC/DC converter. The purpose of the front-end converter is to regulate the DC output voltage, supply all the load converters connected to the distributed bus, guarantee current sharing, and charge a bank of batteries to provide backup energy when the power grid breaks down. One of the main concerns of the power supply industry is to obtain a front-end converter with a low-cost PFC stage, while still complying with required harmonic standards, especially for high-power three-phase applications. Having this statement in mind, the main objective of this dissertation is to study front-end converters for DPS applications with PFC to meet harmonic standards, while still maintaining low cost and performance indices. To realize the many aforementioned objectives, this dissertation is divided into two main parts: (1) two-stage front-end converters suitable for telecom applications, and (2) single-stage low-cost AC/DC converters suitable for mainframe computers and server applications. The use of discontinuous conduction mode (DCM) boost rectifiers is extensively explored to achieve simplicity, while reducing the cost for DPS applications. Interleaving of DCM boost rectifiers is also explored as an alternative approach to further reduce the system cost by reducing the filtering requirements. All the solutions discussed are implemented for 3kW applications, while 6kW is obtained by interleaving two converters. / Ph. D.

The More-electric aircraft (MEA) concept has been raised since 1990s in order to increase fuel economy and reduce environmental impact of aircrafts. The fundamental of the concept is to replace pneumatic, hydraulic and mechanical systems in conventional aircrafts with its electrical equivalent that is lighter and more reliable. In this movement, power electronics technology plays a key role in interfacing the new types of electrical loads to the new aircraft electrical power system. One of the major tasks for power electronics circuits in MEA is to transfer aircraft variable frequency AC voltage into DC voltage, which could be conveniently utilized by different types of loads or power buses. The converters carrying out the task is commonly known as "rectifiers". This work aims at designing and constructing rectifiers that can work efficiently and reliably in more-electric aircrafts. One of the major challenge for these rectifiers comes from the complex aircraft environment. The ambient temperature could be as high as 70 ºC. Moreover, active cooling for converters may not be desirable. To deal with this, rectifiers should achieve extreme efficiency (especially at full load) so that all the components are not overheated without active cooling. This work aims at achieving extreme converter efficiency through advanced converter topologies and design. Both single-phase and three-phase rectifiers are discussed in this work. For single-phase rectifiers, this work focused on boost-type power factor correction (PFC) converters due to the promising efficiency and good PFC characteristics. The well-known two-level semi-bridgeless PFC boost rectifier, together with its interleaved and three-level counterparts, are studied and compared in this work. The operation principles of the converters are analyzed. Models and methods for converter efficiency evaluation are discussed. The efficiency evaluation of the topologies shows the advantage of three-level topologies and interleaved topologies in achieving higher efficiency and better thermal management. For three-phase rectifiers, two-level boost rectifier, three-level neutral point clamped (NPC) rectifier and Vienna rectifier are investigated. The evaluation shows the advantage of Vienna rectifier in achieving high efficiency due to reduced switching loss. Based on the evaluation of single-phase and three-phase active rectifiers, the author selected interleaved Vienna rectifier to achieve extreme efficiency and avoid overheating problem. The operation principle of the interleaved Vienna rectifier is introduced, with particular attention paid to the circulating current generated by interleaving operation. The design procedure for achieving maximum efficiency is described. Finally, a prototype of the proposed converter is constructed, which achieves 99.26% efficiency at nominal load. / Master of Science