A steady-state analysis of a quasi-resonant zero current boost converter is performed in its application to a single-phase power factor correction circuit. The known closed-form expressions are used to design the boost converter and the multiloop control circuit. The operating characteristics are simulated by using PSPICE and are experimentally verified. Considerations for a practical design are based upon hardware operating at a maximum of 1 megahertz, with a 115 VRMS input, 200 VDC and 100 watt output. / Master of Science

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Three novel power factor correction (PFC) techniques are developed for both single-phase and three-phase applications. These techniques have advantages over the conventional approaches with regard to the converter efficiency, power density, cost, and reliability for many applications. The single-phase parallel PFC (PPFC) technique was established. Different from the conventional two-cascade-stage scheme, the PPFC technique allows 68% of input power to go to the output through only one time high frequency power conversion, but still achieves both unity power factor and tight output regulation. A family of PPFC converters were proposed for different power levels, which are simpler and more efficient than the conventional two-cascade-stage systems. Since isolated boost converters are adopted as the main power stage in some of the PPFC converters, a device based soft-switching technique was proposed for using IGBTs as the main power switches, which ensures the lower cost and higher efficiency benefits of the PPFC technique. The single-ended boost converter is the most frequently used converter in the single-phase PFC applications. For high power and/or high voltage applications, the major concerns of the conventional boost converter are the inductor volume and weight, and Iosses on the power devices, which will affect converter efficiency, power density, and cost. In this dissertation, a novel three-level boost converter was developed, which can use a much smaller inductor and lower voltage devices than the conventional one, yielding higher power density, higher efficiency, and lower cost. In three-phase applications, the three-phase boost rectifier is the most popular topology for the PFC purpose. A novel high performance boost PFC rectifier was developed, which provides several superior features than the conventional one with nearly no cost increase. lt inherently provides six-step PWM operation, which is the optimal PWM scheme with no circulating energy, minimum input ripple current, and minimum . switching events. It also greatly reduces the bridge diode reverse recovery loss, which is one of the major switching Iosses in the conventional three-phase boost rectifier. Furthermore, it can adopt very simple soft-switching techniques even with three independent analog controllers to further improve the performance. Several simple soft switched three-phase boost rectifiers have been developed. Besides, the bridge shoot-through problem is virtually eliminated. As a result, these new three-phase boost rectifiers have higher efficiency, higher power density, lower cost, and higher reliability compared with the conventional one. / Ph. D.

Three recently-proposed power conversion technologies, the zero-current-switching (ZCS) and zero-voltage-switching (ZVS) quasi-resonant techniques, and the zero-voltage-switching multi-resonant technique, are evaluated for high-frequency, off-line applications. The study is performed with emphasis on the conversion-frequency range, efficiency, load range, input-voltage range, output power, dynamic response, and power density. A comprehensive dc analysis of the half-wave and full-wave, half-bridge zero-current-switched quasi-resonant converters (QRCs) is presented. Design procedures for closed-loop design of the converters are also derived. The procedures are used to design and fabricate half-wave and full-wave converters operating in the low-megahertz range and experimentally assess their suitability for high-frequency, off-line power conversion. The zero-voltage-switching technique is employed to further increase the conversion frequency. First, the half-bridge zero-voltage-switched quasi-resonant converter is analyzed and the trade-offs between its frequency range, load range, and efficiency are examined in detail. The multi-resonant-switch concept is applied to this converter to improve its characteristics, primarily its load range. A complete dc analysis of the zero-voltage-switched multi-resonant converter (MRC) is given and the dc voltage-conversion-ratio characteristics are derived. A graphic design procedure for the converter is established and is used to build an experimental 100 W, off-line converter operating in the frequency range of 2 MHz to 8 MHz. Finally, a comprehensive comparison of the QRCs and MRCs is performed and conditions where their applications appears most desirable are defined. / Ph. D.

Este trabalho apresentou a análise e a implementação prática do conversor CC-CC trifásico série ressonante operando no modo ZCS. A estrutura deste conversor foi modificada a fim de gerar um barramento CC isolado em alta frequência com tensões simetricamente divididas. Com base na teoria de retificadores multipulsos, a ponte de Graetz do estágio de saída do conversor CC-CC foi substituída por dois retificadores trifásicos, em ponte completa, conectados em série. O transformador isolador também necessitou de alterações, no sentido de alimentar isoladamente esses retificadores, conferindo independência ao funcionamento dos mesmos. Com isso, conseguiu-se grampear cada uma das saídas dos retificadores em uma tensão proporcional a tensão de alimentação do conversor, sem o uso de controladores. Nesse aspecto, o objetivo de gerar um barramento simétrico, propício à alimentação de inversores multiníveis do tipo NPC foi plenamente satisfeito. Demonstrou-se que a estratégia de geração de um barramento com tensões simetricamente divididas pode ser estendida a inversores com mais do que três níveis, caso do NPC. Todos os resultados teóricos foram confirmados através da implementação de um protótipo de 2 kW que atingiu um rendimento superior a 95%. / This work presents the analysis and practical implementation of the three-phase resonant series CC-CC converter operating in ZCS mode. The structure of this converter has been modified in order to generate a DC bus insulated at high frequency with symmetrically divided voltages. Based on the theory of multipulse rectifiers, the Graetz bridge of the output stage of the DC-DC converter has been replaced by two full-bridge three-phase rectifiers connected in series. The isolating transformer also needed changes, in the sense of feeding these rectifiers in isolation, giving independence to the operation of the same. As a result, each of the rectifier outputs was stapled to a voltage proportional to the drive voltage, without the use of controllers. In this respect, the objective of generating a symmetrical bus, suitable for feeding NPC multilevel inverters, was fully satisfied. It has been shown that the strategy of generating a bus with symmetrically divided voltages can be extended to inverters with more than three levels, in the case of the NPC. All theoretical results were confirmed by the implementation of a 2 kW prototype that achieved an efficiency of over 95%.

A presente dissertação tem como objetivo principal propor um conversor bridgeless SEPIC trifásico com elevado fator de potência, baseado em um conversor monofásico apresentado em Costa (2015). Como objetivo secundário e a fim de assimilar o funcionamento do conversor, é estudado o conversor monofásico e então é proposta uma modulação alternativa para comando dos transistores. Outro objetivo secundário é a aplicação do retificador proposto em um sistema de aerogerador de pequeno porte (AGPP), a fim de que este conversor possa processar a energia elétrica gerada sendo proposta também uma metodologia de controle de maximização da potência gerada (MPPT). No desenvolvimento do retificador monofásico é apresentada a análise teórica com cada modulação e posterior equacionamento. Posteriormente, são mostrados os resultados de simulação e experimentais para as duas modulações, podendo-se comparar rendimento, THD e fator de potência. As condições nominais para o conversor monofásico são: tensão eficaz de entrada de 220 V, tensão de saída de 200 V, frequência de comutação de 50 kHz e potência de saída de 500 W. Contextualizando a aplicação do retificador trifásico, é apresentado o funcionamento de um sistema de geração eólica, onde primeiramente tem-se uma introdução dos principais conceitos de energia eólica, seguido de um panorama do aproveitamento da energia eólica no mundo e no Brasil. Em seguida pode-se ver o funcionamento dos sistemas eólicos, apresentando as turbinas e geradores utilizados. Então, propõe-se um modelo, baseado em um retificador trifásico bridgeless SEPIC PFC em MCD processando a energia proveniente do aerogerador. O conversor proposto é então simulado e implementado, utilizando o método MPPT para controlá-lo, a fim de comprovar o modelo e a teoria proposta. As especificações para o conversor trifásico são: tensão eficaz de entrada de 90 V, tensão de saída de 250 V, frequência de comutação de 25 kHz e potência de saída de 1500 W. / The main objective of this dissertation is to propose a three-phase bridgeless SEPIC PFC rectifier, based on a single-phase converter presented in Costa (2015). As a secondary objective and in order to assimilate the operation of the converter, the single-phase converter is studied, and an alternative modulation is proposed for controlling the transistors compared with a traditional PWM modulation, in order to obtain results that justify or not its use in the converter proposed. Another secondary objective is the application of the proposed rectifier in a small-scale wind turbine system, in order that this converter can process the electric energy generated; also is proposed a methodology of control of maximization (MPPT) of generated power. To develop this study, is presented the theoretical analysis with each modulation, followed by design equations. Subsequently are shown the results of numerical simulation and experimental for the two modulations, being able to compare efficiency, THD and power factor. The nominal conditions for the single-phase converter are: rms input voltage of 220 V, output voltage of 200 V, switching frequency of 50 kHz and output power of 500 W. Contextualizing the application of the three-phase rectifier: has an introduction of the main wind power concepts, followed by an overview of wind energy in the world and in Brazil. Then one can see the operation of wind turbines and electrical generators. Next, is propose a system based on a three-phase bridgeless PFC SEPIC rectifier in DCM processing the energy from the wind turbine. This proposed model is then simulated and implemented using the MPPT method to control it, to prove the model and the proposed theory. The specifications for the three-phase converter are: rms input voltage of 90 V, output voltage of 250 V, switching frequency of 25 kHz and output power of 1500 W.

A presente dissertação apresenta uma análise comparativa entre os resultados experimentais de dois retificadores monofásicos. Também apresenta o estudo e projeto de um retificador trifásico, o qual é destinado ao processamento de energia elétrica proveniente de aerogeradores de pequeno porte. Ambos retificadores possuem elevado fator de potência, são modulados por largura de pulso e são baseados no conversor CC-CC SEPIC operando no modo de condução descontínuo. Com a finalidade de validar os estudos teóricos, são apresentados os resultados obtidos via simulação numérica e os resultados experimentais obtidos de cada um dos três retificadores. As especificações dos retificadores monofásicos são: potência processada de 500W; tensão de entrada de 220V; tensão de saída de 200V; frequência de comutação de 50kHz. As especificações do retificador trifásico são as mesmas que a dos monofásicos, exceto, pela potência processada que é de 1,5kW. / The present master thesis presents a comparative analysis between the experimental results of two single-phase rectifiers. Also presents the study and design of a three-phase rectifier, which is intended for processing power from small wind turbines. Both rectifiers have high power factor, is modulated by pulse width and are based on DC-DC SEPIC converter operating in discontinuous conduction mode. In order to validate the theoretical studies, presents the results obtained by numerical simulation and experimental results for each of the three rectifiers. The specifications of the single-phase rectifiers are: processed power of 500W; input voltage of 220V; output voltage of 200V; 50kHz switching frequency. The specifications of the three-phase rectifier is the same as that of single phase, except that it is processed by the power of 1.5kW.

A presente dissertação apresenta uma análise comparativa entre os resultados experimentais de dois retificadores monofásicos. Também apresenta o estudo e projeto de um retificador trifásico, o qual é destinado ao processamento de energia elétrica proveniente de aerogeradores de pequeno porte. Ambos retificadores possuem elevado fator de potência, são modulados por largura de pulso e são baseados no conversor CC-CC SEPIC operando no modo de condução descontínuo. Com a finalidade de validar os estudos teóricos, são apresentados os resultados obtidos via simulação numérica e os resultados experimentais obtidos de cada um dos três retificadores. As especificações dos retificadores monofásicos são: potência processada de 500W; tensão de entrada de 220V; tensão de saída de 200V; frequência de comutação de 50kHz. As especificações do retificador trifásico são as mesmas que a dos monofásicos, exceto, pela potência processada que é de 1,5kW. / The present master thesis presents a comparative analysis between the experimental results of two single-phase rectifiers. Also presents the study and design of a three-phase rectifier, which is intended for processing power from small wind turbines. Both rectifiers have high power factor, is modulated by pulse width and are based on DC-DC SEPIC converter operating in discontinuous conduction mode. In order to validate the theoretical studies, presents the results obtained by numerical simulation and experimental results for each of the three rectifiers. The specifications of the single-phase rectifiers are: processed power of 500W; input voltage of 220V; output voltage of 200V; 50kHz switching frequency. The specifications of the three-phase rectifier is the same as that of single phase, except that it is processed by the power of 1.5kW.

Thesis (MScIng (Electrical and Electronic Engineering))--University of Stellenbosch, 2009. / A bi-directional, direct conversion switch-mode converter is proposed for use in distributed household renewable energy systems. The converter is intended as the central interface between the household energy system’s low voltage Direct Current bus and the high voltage Alternating Current bus. The low voltage DC bus is connected to renewable generation and storage devices, while the high voltage AC bus is connected to the user’s equipment and the mains grid. The converter overcomes the inherent reverse-duty cycle problem associated with bi-directional converters by using a combination step-up / step-down half-bridge converter on the high voltage side of a high frequency transformer. The low voltage side of the transformer is driven by a full bridge inverter that acts as a rectifier during reverse mode. In order to control the flow of power in both directions the converter implements Average Current Mode Control. A method is developed to determine the transfer functions of common switch-mode converters by inspection alone. This method is applied to the proposed converter, and both current and voltage mode control loops are designed with the frequency response method. The control system is implemented using a Digital Signal Processor. A method of simultaneously simulating both the converter hardware and software is developed using VHDL. This method greatly reduced the development effort of the converter. The operation of the proposed converter is verified through this method of simulation. A prototype converter is constructed and successfully tested, thereby proving the viability of the proposed converter topology and control methodology.