In this dissertation, new high frequency link power conversion systems for the fuel cell power conditioning are proposed to improve the performance and optimize the cost, size, and weight of the power conversion systems. The first study proposes a new soft switching technique for the phase-shift controlled bi-directional dc-dc converter. The described dc-dc converter employs a low profile high frequency transformer and two active full-bridge converters for bidirectional power flow capability. The proposed new soft switching technique guarantees soft switching over wide range from no load to full load without any additional circuit components. The load range for proposed soft switching technique is analyzed by mathematical approach with equivalent circuits and verified by experiments. The second study describes a boost converter cascaded high frequency link direct dc-ac converter suitable for fuel cell power sources. A new multi-loop control for a boost converter to reduce the low frequency input current harmonics drawn from the fuel cell is proposed, and a new PWM technique for the cycloconverter at the secondary to reject the low order harmonics in the output voltages is presented. The performance of the proposed scheme is verified by the various simulations and experiments, and their trade-offs are described in detail using mathematical evaluation approach. The third study proposes a current-fed high frequency link direct dc-ac converter suitable for residential fuel cell power systems. The high frequency full-bridge inverter at the primary generates sinusoidally PWM modulated current pulses with zero current switching (ZCS), and the cycloconverter at the secondary which consists of only two bidirectional switches and output filter capacitors produces sinusoidally modulated 60Hz split single phase output voltage waveforms with near zero current switching. The active harmonic filter connected to the input terminal compensates the low order input current harmonics drawn from the fuel cell without long-term energy storage devices such as batteries and super capacitors.

In this dissertation, new high frequency link power conversion systems for the fuel cell power conditioning are proposed to improve the performance and optimize the cost, size, and weight of the power conversion systems. The first study proposes a new soft switching technique for the phase-shift controlled bi-directional dc-dc converter. The described dc-dc converter employs a low profile high frequency transformer and two active full-bridge converters for bidirectional power flow capability. The proposed new soft switching technique guarantees soft switching over wide range from no load to full load without any additional circuit components. The load range for proposed soft switching technique is analyzed by mathematical approach with equivalent circuits and verified by experiments. The second study describes a boost converter cascaded high frequency link direct dc-ac converter suitable for fuel cell power sources. A new multi-loop control for a boost converter to reduce the low frequency input current harmonics drawn from the fuel cell is proposed, and a new PWM technique for the cycloconverter at the secondary to reject the low order harmonics in the output voltages is presented. The performance of the proposed scheme is verified by the various simulations and experiments, and their trade-offs are described in detail using mathematical evaluation approach. The third study proposes a current-fed high frequency link direct dc-ac converter suitable for residential fuel cell power systems. The high frequency full-bridge inverter at the primary generates sinusoidally PWM modulated current pulses with zero current switching (ZCS), and the cycloconverter at the secondary which consists of only two bidirectional switches and output filter capacitors produces sinusoidally modulated 60Hz split single phase output voltage waveforms with near zero current switching. The active harmonic filter connected to the input terminal compensates the low order input current harmonics drawn from the fuel cell without long-term energy storage devices such as batteries and super capacitors.

This thesis introduces the design and analysis of a single-stage inverter. A circuit was designed and simulated as a proof of concept to investigate the possibility of using boost and buck-boost converters to provide an AC output. The proposed circuit utilizes non-synchronous boost and buck-boost converters due to their simplicity in control signals as opposed to synchronous converters. The application of the proposed inverter is for use with individual solar cells. The aim of the inverter for a single cell is to improve the efficiency of a solar panel, whose performance is limited to the performance of the least efficient cell. With each cell independent of any other cell in the solar panel, the overall efficiency of the panel can be improved. This circuit uses a 3.6VDC input from the solar cell to produce a 10VPP 60Hz square wave output. The inverter consists of a solar cell, two DC-DC converters, two linear dropout (LDO) regulators, a square wave generator, and a switching circuit . The design and analysis of all parts were investigated individually in detail. The different parts of the circuit were then simulated using LTspice before testing the overall circuit. Simulation results demonstrate the feasibility of the proposed inverter with all design requirements but efficiency meeting or exceeding the goals.

A abordagem principal desse trabalho é o estudo de técnicas anti-ilhamento ativas com realimentação positiva em um sistema de Geração Distribuída (GD) composto por um Inversor Fonte de Tensão (VSI,do inglês Voltage Source Inverter) e com cargas locais conectadas em paralelo. Na literatura são encontrados dois grupos de técnicas empregadas como proteção anti-ilhamento: as ativas e as passivas. Os métodos de detecção de ilhamento ativos são utilizados, pois possuem menores zonas de não detecção em comparação às técnicas passivas, porém injetam distúrbios contínuos no sistema de GD. Esses distúrbios degradam a qualidade de energia elétrica fornecida pelo conversor eletrônico. Nesse contexto, como escopo dessa dissertação, é realizado o estudo da estrutura de controle empregada no sistema de GD conectado com a rede de distribuição, com o intuito de avaliar o funcionamento do gerenciamento de tensão e de potência ativa e reativa. E em seguida, são discutidas técnicas de detecção de ilhamento ativas em frequência e tensão, ambas, com realimentação positiva e ganho fixo com o objetivo de investigar o desempenho das mesmas em relação ao tempo de detecção e a injeção de distúrbios no sistema de controle da GD. A partir dessa análise, são desenvolvidas técnicas anti-ilhamento com intuito de reduzir a injeção de distúrbios em diferentes pontos de operação da GD e garantir uma eficiência semelhante aos métodos tradicionais em casos de difícil detecção. Essas técnicas são baseadas na implementação do cálculo de um ganho com realimentação positiva variável inversamente proporcional a variação de potência ativa ou reativa entregue a rede. Para validação das propostas presentes nesta dissertação, são obtidos resultados em simulações computacionais e, posteriormente são adquiridos resultados práticos através de uma bancada experimental compatível com o sistema de GD simulado. / The main approach of this thesis is the study of active anti-islanding techniques with positive feedback in a Distributed Generation (DG) system composed by a Voltage Source Inverter (VSI) and local loads. In literature two groups of techniques are used as anti-island protection: the active and the passive techniques. The active islanding detection methods are preferably used because of the smaller non-detection zones compared to passive techniques, however they inject continuous disturbances in the DG system, reducing the power quality provided by the VSI. In this context, as the scope of this dissertation, it is firstly carried out the study of control structures employed in grid-tied distribution system, to evaluate the operation of the voltage control loops, and the active-and reactive power managements. Additionally, we discuss active islanding detection techniques in frequency and voltage with positive feedback and constant gain, based on the classical, with the objective of investigating their performance in relation to the detection time and the injection of disturbances in the DG system. From this analysis, antiislanding techniques are developed to guarantee efficiency similar to the traditional methods in cases of small-power flow through the grid and minimize disturbances. These techniques are based on the calculation of the positive feedback variable gain inversely proportional to the deviation of active or reactive power delivered or absorbed from the grid. To validate this proposal, the results are obtained through computational simulations and experimental analysis, as well.

A abordagem principal desse trabalho é o estudo de técnicas anti-ilhamento ativas com realimentação positiva em um sistema de Geração Distribuída (GD) composto por um Inversor Fonte de Tensão (VSI,do inglês Voltage Source Inverter) e com cargas locais conectadas em paralelo. Na literatura são encontrados dois grupos de técnicas empregadas como proteção anti-ilhamento: as ativas e as passivas. Os métodos de detecção de ilhamento ativos são utilizados, pois possuem menores zonas de não detecção em comparação às técnicas passivas, porém injetam distúrbios contínuos no sistema de GD. Esses distúrbios degradam a qualidade de energia elétrica fornecida pelo conversor eletrônico. Nesse contexto, como escopo dessa dissertação, é realizado o estudo da estrutura de controle empregada no sistema de GD conectado com a rede de distribuição, com o intuito de avaliar o funcionamento do gerenciamento de tensão e de potência ativa e reativa. E em seguida, são discutidas técnicas de detecção de ilhamento ativas em frequência e tensão, ambas, com realimentação positiva e ganho fixo com o objetivo de investigar o desempenho das mesmas em relação ao tempo de detecção e a injeção de distúrbios no sistema de controle da GD. A partir dessa análise, são desenvolvidas técnicas anti-ilhamento com intuito de reduzir a injeção de distúrbios em diferentes pontos de operação da GD e garantir uma eficiência semelhante aos métodos tradicionais em casos de difícil detecção. Essas técnicas são baseadas na implementação do cálculo de um ganho com realimentação positiva variável inversamente proporcional a variação de potência ativa ou reativa entregue a rede. Para validação das propostas presentes nesta dissertação, são obtidos resultados em simulações computacionais e, posteriormente são adquiridos resultados práticos através de uma bancada experimental compatível com o sistema de GD simulado. / The main approach of this thesis is the study of active anti-islanding techniques with positive feedback in a Distributed Generation (DG) system composed by a Voltage Source Inverter (VSI) and local loads. In literature two groups of techniques are used as anti-island protection: the active and the passive techniques. The active islanding detection methods are preferably used because of the smaller non-detection zones compared to passive techniques, however they inject continuous disturbances in the DG system, reducing the power quality provided by the VSI. In this context, as the scope of this dissertation, it is firstly carried out the study of control structures employed in grid-tied distribution system, to evaluate the operation of the voltage control loops, and the active-and reactive power managements. Additionally, we discuss active islanding detection techniques in frequency and voltage with positive feedback and constant gain, based on the classical, with the objective of investigating their performance in relation to the detection time and the injection of disturbances in the DG system. From this analysis, antiislanding techniques are developed to guarantee efficiency similar to the traditional methods in cases of small-power flow through the grid and minimize disturbances. These techniques are based on the calculation of the positive feedback variable gain inversely proportional to the deviation of active or reactive power delivered or absorbed from the grid. To validate this proposal, the results are obtained through computational simulations and experimental analysis, as well.

This diploma thesis is dealing with the design of a DC / AC converter for the control of PMSM motors. In the first step, the type of motor and the possibilities of sensing the position of the rotor are described. Subsequently, the power section is designed and the losses, heating, and approximate efficiency of the inverter are calculated. In the following step, the processor is selected and individual communication and protection circuits are designed. At the same time, control algorithms are analyzed. The last part is describing the implementation of the PCB and the inverter as a whole.

Este trabalho, constitui-se em uma contribuição para o estudo das estratégias de mo-dulação direta baseadas em histerese e que funcionam em frequência fixa de comutação. Tem como objetivo principal propor a estratégia delta modificada, que diferencia-se na forma de ajuste da largura de banda de histerese, alterando-se seus limites e em como executa o comando de bloqueio das chaves de potência, para que a corrente de saída se mantenha em frequência fixa de operação e apresente rápida resposta dinâmica no sistema controlado. Para tanto, não necessita da utilização de derivadas, nem de uma corrente média de referência, tão pouco, se utiliza dos tempos de comutação. A estratégia proposta, comprova que é possível produzir os adequados pulsos de comando para o processamento da energia proveniente de célula combustível, através do conversor estático de potência, utilizando-se, principalmente, dos valores de ultrapassagem nos limites estabelecidos de histerese. Como objetivo secundário desta pesquisa, desenvolve-se um conversor CC/CC auxiliar para adaptar e estabilizar a energia proveniente da CAC, compondo-se um sistema útil que serve de base para fornecer energia, aos mais diversos tipos de cargas em CC. Além disso, apresenta-se uma revisão das estratégias de modulação em modo direto para o controle da corrente de saída no conversor estático, tendo como base a tensão nos terminais de um indutor. Contudo, outras estratégias são naturalmente citadas, no transcorrer deste trabalho, devido haver combinações entre as diferentes estratégias moduladoras e controladoras comentadas. / This work, is a contribution to the study of direct modulation strategies based on hysteresis and that operate at fixed switching frequency. Its main objective is to propose the modified delta strategy, which differentiates from the others strategies in the form of adjustment of hysteresis bandwidth, changing its limits and in executing the locking command of the power keys, so that the output current is maintain at fixed frequency of operation and a rapid dynamic response in the controlled system. In order to do so, it does not require the use of derivatives or a reference average current and also the switching times are not used. This strategy shows that it is possible to produce the appropriate command pulses for the processing of fuel cell energy by the static power converter using mainly the exceedance limit values. As a secondary objective of this research, an auxiliary DC/DC converter is developed to adapt and stabilize the energy coming from the fuel cell, forming a useful system that serves as a base to supply power to the most diverse types of DC loads. In addition, we present a review of the direct-mode modulation strategies for the control of the output current in the static converter, updating data, and based on the voltage at the terminals of an inductor; how-ever, others strategies are naturally cited because there are combinations between the different modulating strategies and controllers commented on in the course of this work.

Este trabalho, constitui-se em uma contribuição para o estudo das estratégias de mo-dulação direta baseadas em histerese e que funcionam em frequência fixa de comutação. Tem como objetivo principal propor a estratégia delta modificada, que diferencia-se na forma de ajuste da largura de banda de histerese, alterando-se seus limites e em como executa o comando de bloqueio das chaves de potência, para que a corrente de saída se mantenha em frequência fixa de operação e apresente rápida resposta dinâmica no sistema controlado. Para tanto, não necessita da utilização de derivadas, nem de uma corrente média de referência, tão pouco, se utiliza dos tempos de comutação. A estratégia proposta, comprova que é possível produzir os adequados pulsos de comando para o processamento da energia proveniente de célula combustível, através do conversor estático de potência, utilizando-se, principalmente, dos valores de ultrapassagem nos limites estabelecidos de histerese. Como objetivo secundário desta pesquisa, desenvolve-se um conversor CC/CC auxiliar para adaptar e estabilizar a energia proveniente da CAC, compondo-se um sistema útil que serve de base para fornecer energia, aos mais diversos tipos de cargas em CC. Além disso, apresenta-se uma revisão das estratégias de modulação em modo direto para o controle da corrente de saída no conversor estático, tendo como base a tensão nos terminais de um indutor. Contudo, outras estratégias são naturalmente citadas, no transcorrer deste trabalho, devido haver combinações entre as diferentes estratégias moduladoras e controladoras comentadas. / This work, is a contribution to the study of direct modulation strategies based on hysteresis and that operate at fixed switching frequency. Its main objective is to propose the modified delta strategy, which differentiates from the others strategies in the form of adjustment of hysteresis bandwidth, changing its limits and in executing the locking command of the power keys, so that the output current is maintain at fixed frequency of operation and a rapid dynamic response in the controlled system. In order to do so, it does not require the use of derivatives or a reference average current and also the switching times are not used. This strategy shows that it is possible to produce the appropriate command pulses for the processing of fuel cell energy by the static power converter using mainly the exceedance limit values. As a secondary objective of this research, an auxiliary DC/DC converter is developed to adapt and stabilize the energy coming from the fuel cell, forming a useful system that serves as a base to supply power to the most diverse types of DC loads. In addition, we present a review of the direct-mode modulation strategies for the control of the output current in the static converter, updating data, and based on the voltage at the terminals of an inductor; how-ever, others strategies are naturally cited because there are combinations between the different modulating strategies and controllers commented on in the course of this work.

The Diploma thesis deals with control of three-phase active rectifier and a three-phase DC/AC converter. It also explains phase-locked loop principle. The theoretical part including first three chapters lists several control approaches to three phase active rectifier and three phase DC/AC converter. Described control approaches to the active rectifier are control in dq frame and control in dq UVW frame. Listed control approaches to the DC/AC converter include cascaded control structure and a full state feedback control. The practical part is divided into last three chapters and includes mathematical description of phase-locked loop principle, model of active rectifier controlled in dq frame and a model of DC/AC converter controlled both by a cascaded control and a full¬ state feedback. The models are created in Matlab Simulink.

The topic of this diploma thesis is a traction drive of electrocar with fuel cell. The drive is supplied with hydrogen fuel cell with power of 2 kW. The traction drive consists of the three-phase DC/AC converter and the asynchronous machine. The main part of this work is a creation of the mathematical model of the traction drive in program Matlab–Simulink.