In electrical power distribution and power electronic applications, a transformer is an indispensable component which performs many functions. At its operating frequency (60/50 Hz), it is one of the most bulky and expensive components. The concept of the electronic transformer introduced previously has shown considerable reduction in size, weight, and volume by operating at a higher frequency. In this dissertation, the concept of the electronic transformer is further extended to the auto-connected phase-shifting type to reduce harmonics generated by nonlinear loads. It is shown that with the addition of primary side and secondary side AC/AC converters achieves phase-shifting. With the addition of converters, magnetic components are operated at a higher frequency to yield a smaller size and weight. Two types of auto-connected electronic transformer configurations are explored. In the first configuration, the secondary converter is eliminated and the output is suitable for rectifier type loads such as adjustable speed drives. In the second configuration, the secondary converter is added to obtain a sinusoidal phase-shifted AC output voltage. This approach is applicable in general applications. With the proposed approaches, the th and 7th harmonic in utility line currents, generated by two sets of nonlinear loads, are subtracted within the electronic transformer, thereby reducing the total harmonic distortion (THD) of the line current. The analysis and simulation results are presented. In the second part of the dissertation, the electronic transformer concept is applied to a telecommunication power supply (-48 VDC) system. The proposed approach consists of a matrix converter to convert the low frequency three-phase input AC utility to a high frequency AC output without a DC-link. The output of the matrix converter is then processed via a high frequency isolation transformer to produce -48 VDC. Digital control of the system ensures that the output voltage is regulated and the input currents are of high quality, devoid of low frequency harmonics and at near unity input power factor under varying load conditions. Due to the absence of DC-link electrolytic capacitors, the power density of the proposed rectifier is shown to be higher. Analysis, design example and experimental results are presented from a three-phase 208 V, 1.5 kW laboratory prototype converter.

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.

The objective of the proposed research is to investigate feasible approaches to dynamic control of the power grid. Growth in the demand for electric power, and an increase in the penetration of renewable energy resources are causing congestion on an already aging power grid. Conventional grid control involves the use of static assets that operate on long time scales. These assets provide no dynamic control on the grid, and are typically used for scheduled support. Existing solutions (FACTS devices) to dynamic grid control have seen minimal market penetration because of high cost and low reliability. The proposed research provides a solution for dynamic control of the power grid that augments existing grid assets with a thin AC converter (TACC) to realize enhanced dynamic control. The TACC is a direct AC converter with filter elements and no bulk energy storage that dynamically reflects the asset value on the grid. The converter has a fail-normal mode of operation that returns the asset to its initial operating state, thereby not degrading system reliability. Some applications of TACCs include Inverter-Less STATCOMs and Controllable Network Transformers, which are realized by augmenting shunt VAR capacitors and load tap changers respectively. The principle of virtual quadrature sources is proposed to enable conditioning of AC voltages and currents. The concept is a novel method to realize control of phase angle and, or harmonics in single-phase AC converters, with no bulk energy storage. This concept is used to control the TACC and provides the asset with significantly enhanced control capabilities. Scaling of the TACC to utility voltage and power levels has been addressed by proposing a novel multilevel direct AC converter. The concept proposes the use of commercially available low cost semiconductor devices to realize high power converters. The specific application chosen to validate the concept of TACCs, through a medium voltage design, is the Inverter-less STATCOM.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This thesis proposes a design of a power supply for high-pressure discharge lamps based on a high efficiency and high power factor electronic ballast, without exciting the intrinsic acoustic resonance. The ballast consists on a bipolar buck chopper operating in continuous conduction mode (CCM), with an input filter, and an igniter circuit. It works with a switching frequency of 33 kHz and supplies the lamp in the mains frequency. The igniter circuit provides the necessary high voltage for the lamp's startup initial procedure. It is controlled by an 8 bits microcontroller, thus contributing to reduction in the number of parts and the ballast final cost, without compromising its reliability. Two possible solutions for an igniter circuit are proposed, the first based on a igniter device, and the second on a LC resonant circuit. A study on the ignition process and the required circuits to guarantee it, and a brief review on the electrical characteristics of electromagnetic ballasts are also included as secondary contributions. Experimental results with a 70W HPS lamp supplied by a 220V±20% and 60 Hz mains, are presented to validate the proposed ballast. The behavior of the experimental ballast shows that it is a good choice in avoiding unstable effects provoked by acoustic resonance phenomenon. / Esta dissertação apresenta o projeto de uma fonte de alimentação para lâmpadas de descarga em alta pressão baseada em um reator eletrônico com alto rendimento e ótimo fator de potência que não excita de forma destrutiva a ressonância acústica (AR). O reator consiste de um conversor buck bipolar operando em modo continuo (CCM), com filtro de entrada acoplado e com um circuito de ignição. O conversor opera em 33 kHz e alimenta a lâmpada em freqüência de rede. O circuito de ignição fornece a alta tensão para a formação inicial do arco elétrico. O controle do reator é implementado em um microcontrolador de 8 bits, o que contribui com a redução do número de componentes e do custo final do sistema, sem prejudicar a confiabilidade do mesmo. Duas propostas de circuito de ignição são apresentadas, uma baseada em um dispositivo ignitor, e a segunda em um circuito LC ressonante. Uma breve revisão e avaliação das características elétricas do reator eletromagnético é também apresentada a título de comparação. Um estudo do processo de ignição e os circuitos necessários a formação do arco é também incluído. Resultados experimentais para uma lâmpada HPS de 70W alimentada a partir de uma rede de 220V±20% e 60Hz são apresentados para validar o reator proposto e demonstram que este é uma boa escolha para evitar os efeitos danosos do fenômeno da ressonância acústica.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This thesis proposes to improve the efficiency of public illumination systems by means of AC chopper based power converters. A comparative study of high performance AC/AC converters feeding high pressure sodium lamps on mains frequency is presented. These converters are obtained using standard DC/DC topologies with bi-directional switches (four quadrants). A high pressure lamp ballast design methodology is also presented, based on the suppositions of high input power factor and without exciting acoustic resonances at destructive levels. The topologies used are the Buck-Boost, Ćuk, SEPIC and ZETA operating on continuous current mode, with or without input filter, and an ignition circuit. The converters' switching frequencies are 33 kHz feeding the lamp at low frequency (mains frequency). The ignition circuit providing the high voltage required to guarantee the initial arc to start-up the lamp, is presented, analyzed and optimized in the thesis. To control the ballast a 32 bits microcontroller is used, contributing to reduce the component count and the overall system cost. The base to propose a new control design methodology and power circuit parts specification is the Brazilian standards and a comparison with the electromagnetic ballasts output waveforms. Experimental results supplying a 70 W HPS lamp, connected to the mains (220 V ±20% e 60 Hz) through the proposed ballasts, are presented in order to validate the thesis. / Este trabalho visa aprimorar os sistemas de iluminação pública aplicando reatores eletrônicos baseados em conversores CA/CA. Apresenta-se um comparativo entre conversores tradicionais CC/CC, aplicando a eles interruptores bidirecionais em tensão e corrente, de modo a alimentar a lâmpada de alta pressão de sódio na frequência da rede de alimentação, formando um conversor estático CA/CA com alto rendimento. Apresenta uma metodologia de projeto para fonte de alimentação de lâmpadas de descarga em alta pressão baseada em reatores eletrônicos com alto rendimento e elevado fator de potência, que não excitam de forma destrutiva a ressonância acústica (AR). O reator consiste dos conversores Buck-Boost, Ćuk, SEPIC e ZETA bipolares operando por modulação de largura de pulso (PWM) em modo de condução de corrente contínua (CCM), com ou sem filtro de entrada acoplado e com um circuito de ignição. O conversor opera em 33 kHz e alimenta a lâmpada na frequência da rede. O circuito de ignição fornece a alta tensão para a formação inicial do arco elétrico e neste trabalho de doutoramento foi equacionado e otimizado quando comparado ao modelo tradicional. O controle do reator é implementado em um microcontrolador de 32 bits, o que contribui com a redução do número de componentes e do custo final do sistema, sem prejudicar a confiabilidade do mesmo. As formas de onda de saída de reatores eletromagnéticos e as normas vigentes servem de base para o dimensionamento dos componentes e a obtenção de uma nova metodologia de controle. Resultados experimentais para uma lâmpada HPS de 70 W alimentada a partir de uma rede de 220 V ±20% e 60 Hz são apresentados para validar os reatores propostos.

This paper proposes two new topological arrangements consisting in connecting the AC power supply in series with two DC converters, one operating during the positive half-cycle and the other during the negative half cycle. It is noteworthy that these DC converters in series in a case are Buck EIE converters and on the other a buck. The results obtained with both arrangements are analyzed and compared. The control strategy is developed with the goal of imposing an AC voltage output within the limits imposed by the rules in order to mitigate the problems associated with Sags and Swells from the AC power supply . The principles of operation as well as the experimental and simulation results obtained in both steady and transient state are presented and validated for a 1kVA experimental prototype. Finally, some works still on progress related to this dissertation are presented, like the multilevel compensation and the three phase compensation. / Este trabalho propõe dois novos arranjos topológicos que consistem em se conectar a alimentação CA em série com dois conversores CC, um para operar durante o semiciclo positivo e o outro durante o semiciclo negativo. Vale ressaltar que estes conversores CC em série, em um caso são conversores Buck EIE e no outro um conversor Buck. Os resultados obtidos com ambos os arranjos são analisados e comparados. A estratégia de controle é desenvolvida com o intuito de impor uma tensão de saída CA dentro dos limites impostos pelas normas de forma a mitigar os problemas associados com Sags e Swells da rede de alimentação CA. Os princípios de operação, os resultados experimentais e de simulação obtidos, tanto em regime permanente quanto em condições transitórias de operação, são apresentados e validados para um protótipo experimental de 1kVA. Por fim apresentam-se os trabalhos relacionados a esta dissertação que ainda estão em desenvolvimento, que são a compensação em multinível e a compensação trifásica. / Mestre em Ciências