No description available.

The work detailed in the thesis compares the performance of single-phase thyristor bridge converters under different control strategies; considering in particular the efficiency, ac side power factor and harmonic content of the current and voltage waveforms. Extensive practical investigations were performed, in which, analogue and digital control circuits were developed to provide the drive signals necessary for a converter to operate in the different control modes for: a) A series -connected fully-controlled double thyristor bridge (used mainly in traction applications) operating under sequence control and; b) A fully controlled single-bridge operating under sequence and conventional control. A novel pulse-width modulation control strategy was developed for the single-bridge converter, using gate turn-off thyristors as the switching elements, whereby output voltage control is obtained by variation of the modulation index. Turn-on and turn-off signals for the power devices were obtained using an analogue control circuit. The advantages and disadvantages of this switching strategy compared with conventional and sequence control were studied, and results clearly showed that an improved input power factor and lower supply current and load voltage harmonics were all obtained. Mathematical models for single and double bridge converters operating under sequence and conventional control were developed using tensor techniques. Using these models, computer programmes were written in Fortran 77 on the University mainframe computer, to assemble automatically and solve the network equations as the converter topology changes. In addition, analytical models were also developed on the assumption that the load current is completely smooth. However, such an assumption is not justifiable with ac-to-dc converters and consequently a novel technique was developed to include the load current ripple in calculating the supply current harmonics. The results obtained are compared with both the computed and experimental ones.

No description available.

This thesis is concerned primarily with the optimization of the current regulation in bi-directional ac-dc power converters through the use of appropriate current control methods. Following a review into prior current control technology, current control methods which attempt to achieve Zero Average Current Error (ZACE) in each switching period are presented. A ZACE controlled converter offers independent real and reactive power flow control with negligible low order current harmonics, a relatively narrow switching frequency band, and relative immunity to power circuit parameter variations, including DC link or AC line voltage harmonics. ZACE and other desirable characteristics in a current control method are discussed. The single phase ac and dc ripple current is characterized.Two new types of ZACE current control techniques for directly controlling the inductor current in switched power converters are introduced in this thesis together with variations for certain applications. Slope-generated hysteresis (SGH), the first to be developed, is a hysteresis method which uses the slopes of the current error signal alone to generate a hysteresis band which will result in a fixed switching frequency. Slope-generated hysteresis-clock (SGHC) is presented as an alternative with a dual clock to force a narrow switching frequency band.Ramptime current control is the second type of ZACE current control presented. Developed as an improvement over SGH, ramptime produces ZACE in each switching period by using the timing of a previous switching instant relative to the coincident previous current error signal excursion time to determine each switching instant. The digital current error polarity signal is the only variable input required to produce a pwm output.Variations of ramptime current control are also presented. Polarized ramptime is a subset of ramptime which maintains a narrow ++ / switching frequency band despite switching delays. Dual ramptime is the final enhancement of ramptime where two polarized ramptime regulators are used together to provide the appropriate choice between full-bridge and half-bridge switching in a single phase current controlled full-bridge voltage source inverter with the ac ripple current minimized without compromising the transient response. Using this technique, excellent fidelity and a narrow switching frequency band are demonstrated.The ZACE current control techniques are applied to a three phase voltage source inverter. A "standing phase" system of control for a three wire, three phase inverter is chosen over individual phase control since only two current regulators are required to control two decoupled current error signals, and the effective switching frequency is reduced by one third.The new ZACE methods are found to compare favourably in simulation to existing linear and hysteresis type current control techniques. SGH current control has equivalent fidelity to any other hysteresis control in delivering the reference current waveform, but is prone to noise in the hysteresis band determination requiring filtering. This, combined with the effect of switching delays compromises the narrowness of the switching frequency band. SGHC current control is also prone to noise in the generation of the hysteresis band, and results in a decrease in the fidelity of reproduction of the reference waveform. Ramptime current control is a robust technique, largely immune to power circuit parameter and voltage variances, with good fidelity and a relatively narrow switching frequency band. Polarized ramptime current control is shown to produce excellent fidelity with a narrow switching frequency band.The operation of the ZACE methods in single and three phase prototype converters is demonstrated. A field installation of a ++ / grid-connected ramptime current controlled converter is shown to source 20 kW of real power onto the grid from a photovoltaic array with a maximum power point tracking control, while independently providing grid voltage support through reactive power control.The effect of the synchronization of the current regulators on the ac and dc current ripple are presented. Synchronized polarized ramptime regulators are shown to produce the minimum ripple current in simulation and in the prototype operation.ZACE current control techniques, and ramptime and polarized ramptime in particular, are presented as a significant contribution to the control of current in power electronic converters.

abstract: This thesis investigates different unidirectional topologies for the on-board charger in an electric vehicle and proposes soft-switching solutions in both the AC/DC and DC/DC stage of the converter with a power rating of 3.3 kW. With an overview on different charger topologies and their applicability with respect to the target specification a soft-switching technique to reduce the switching losses of a single phase boost-type PFC is proposed. This work is followed by a modification to the popular soft-switching topology, the dual active bridge (DAB) converter for application requiring unidirectional power flow. The topology named as the semi-dual active bridge (S-DAB) is obtained by replacing the fully active (four switches) bridge on the load side of a DAB by a semi-active (two switches and two diodes) bridge. The operating principles, waveforms in different intervals and expression for power transfer, which differ significantly from the basic DAB topology, are presented in detail. The zero-voltage switching (ZVS) characteristics and requirements are analyzed in detail and compared to those of DAB. A small-signal model of the new configuration is also derived. The analysis and performance of S-DAB are validated through extensive simulation and experimental results from a hardware prototype. Secondly, a low-loss auxiliary circuit for a power factor correction (PFC) circuit to achieve zero voltage transition is also proposed to improve the efficiency and operating frequency of the converter. The high dynamic energy generated in the switching node during turn-on is diverted by providing a parallel path through an auxiliary inductor and a transistor placed across the main inductor. The paper discusses the operating principles, design, and merits of the proposed scheme with hardware validation on a 3.3 kW/ 500 kHz PFC prototype. Modifications to the proposed zero voltage transition (ZVT) circuit is also investigated by implementing two topological variations. Firstly, an integrated magnetic structure is built combining the main inductor and auxiliary inductor in a single core reducing the total footprint of the circuit board. This improvement also reduces the size of the auxiliary capacitor required in the ZVT operation. The second modification redirects the ZVT energy from the input end to the DC link through additional half-bridge circuit and inductor. The half-bridge operating at constant 50% duty cycle simulates a switching leg of the following DC/DC stage of the converter. A hardware prototype of the above-mentioned PFC and DC/DC stage was developed and the operating principles were verified using the same. / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2017

Este trabalho aborda a detecção da condição de ilhamento e de seus impactos em redes de distribuição e em gerações distribuídas que empregam conversores CC-CA. Na literatura são encontradas dois grupos de técnicas para este tipo de aplicação. As técnicas passivas, que identificam a condição de ilhamento através do ajuste dos limites de variação dos relés de proteção, e as técnicas ativas, que inserem um sinal de realimentação positiva de forma a tornar o sistema instável no momento da desconexão. As técnicas ativas, por apresentarem um menor tempo de detecção e simples implementação em hardware, são preferencialmente utilizadas, apesar da injeção de distúrbios no sistema de controle da geração distribuída. O estado-da-arte em termos de detecção de ilhamento consiste em desenvolver uma técnica que possua alta capacidade de detecção, porém sem injeção de distúrbios no sistema de geração distribuída quando conectado à rede de distribuição. Neste trabalho, são abordadas duas formas para a redução da injeção de distúrbios e do tempo de detecção. Em uma primeira abordagem é proposto um projeto ótimo para o algoritmo de sincronização PLL (phase-locked loop), o qual permite a redução do ganho de realimentação positiva para técnicas em frequência e, consequentemente, a redução da injeção de distúrbios. Em uma segunda abordagem é utilizada a metodologia fuzzy de forma a garantir a detecção da condição de ilhamento sem nenhuma injeção de distúrbios no sistema de controle. Resultados de simulação e experimentais, obtidos por meio de uma bancada experimental controlada por DSP, são apresentados para validar as propostas presentes nesta dissertação / This thesis deals with the islanding detection and its impact on distribution networks when distributed generation systems are driven by DC-AC converters. Two groups of techniques are found in the literature. The passive techniques in which adjusting the variation limits of protective relays identify the islanding condition, and the active techniques that insert a positive feedback signal in order to make the system unstable when the contingency is on progress. The active techniques present a reduced detection time and simple hardware implementation. They are preferably used in despite of the injection of disturbances in the control system. In this thesis two ways to reduce injection of disturbances and detection time are proposed. In a first approach is shown an optimal design for the synchronization algorithm PLL (Phase-Locked Loop) which allows to reduce the positive feedback gain in frequency techniques in order to decrease the injection of disturbances. In a second approach a fuzzy methodology is used to ensure the islanding detection with the aforementioned requirements. Simulation analysis and experimental results are presented to validate the proposed approach

O presente trabalho apresenta os estudos, especificaÃÃes, instalaÃÃo e operaÃÃo de um sistema fotovoltaico com a finalidade de fornecer energia elÃtrica a uma escola pÃblica, localizada em uma Ãrea isolada do sul do Estado do PiauÃ. O sistema foi proposto e seu protÃtipo constituÃdo por painel fotovoltaico, banco de baterias, carregador do banco de bateria e conversor CC/CC elevador, que alimenta as cargas em corrente contÃnua, projetado para uma autonomia de trÃs dias, mesmo em condiÃÃes mÃnimas de radiaÃÃo solar. A energia solar capturada pelo painel solar à armazenada em um banco de baterias estacionÃrias do tipo chumbo-Ãcido. O carregador de baterias trabalhando no ponto de mÃxima potÃncia (MPP) do painel à responsÃvel pelo carregamento deste banco. A carga à suprida pelo conversor CC/CC elevador de alto ganho (24 Vdc para 311 Vdc). O projeto completo do sistema à apresentado ao longo deste trabalho, bem como sÃo apresentados os principais resultados experimentais do protÃtipo mostrado e instalado em campo. / This work presents the studies, specifications, installation and operation of a photovoltaic system in order to provide electricity to a public school located in an isolated area of the southern state of PiauÃ. The system was proposed and its prototype constituted by photovoltaic panel, battery bank, charger from the battery bank and converter DC / DC elevator, that feed the chargers in direct current designed for a range of three days, even in minimum solar radiation. The solar energy captured by solar panel is stored in a stationary batteries, lead acid type. The battery charger working at maximum power point (MPP) of the panel is responsible for load bank. The load is supplied by the DC / DC converter lift high gain (24 Vdc to 311 Vdc). The complete design system and its control are presented throughout this work, as well as presented the main results of the experimental prototype shown and installed in the field.

Este trabalho aborda a detecção da condição de ilhamento e de seus impactos em redes de distribuição e em gerações distribuídas que empregam conversores CC-CA. Na literatura são encontradas dois grupos de técnicas para este tipo de aplicação. As técnicas passivas, que identificam a condição de ilhamento através do ajuste dos limites de variação dos relés de proteção, e as técnicas ativas, que inserem um sinal de realimentação positiva de forma a tornar o sistema instável no momento da desconexão. As técnicas ativas, por apresentarem um menor tempo de detecção e simples implementação em hardware, são preferencialmente utilizadas, apesar da injeção de distúrbios no sistema de controle da geração distribuída. O estado-da-arte em termos de detecção de ilhamento consiste em desenvolver uma técnica que possua alta capacidade de detecção, porém sem injeção de distúrbios no sistema de geração distribuída quando conectado à rede de distribuição. Neste trabalho, são abordadas duas formas para a redução da injeção de distúrbios e do tempo de detecção. Em uma primeira abordagem é proposto um projeto ótimo para o algoritmo de sincronização PLL (phase-locked loop), o qual permite a redução do ganho de realimentação positiva para técnicas em frequência e, consequentemente, a redução da injeção de distúrbios. Em uma segunda abordagem é utilizada a metodologia fuzzy de forma a garantir a detecção da condição de ilhamento sem nenhuma injeção de distúrbios no sistema de controle. Resultados de simulação e experimentais, obtidos por meio de uma bancada experimental controlada por DSP, são apresentados para validar as propostas presentes nesta dissertação / This thesis deals with the islanding detection and its impact on distribution networks when distributed generation systems are driven by DC-AC converters. Two groups of techniques are found in the literature. The passive techniques in which adjusting the variation limits of protective relays identify the islanding condition, and the active techniques that insert a positive feedback signal in order to make the system unstable when the contingency is on progress. The active techniques present a reduced detection time and simple hardware implementation. They are preferably used in despite of the injection of disturbances in the control system. In this thesis two ways to reduce injection of disturbances and detection time are proposed. In a first approach is shown an optimal design for the synchronization algorithm PLL (Phase-Locked Loop) which allows to reduce the positive feedback gain in frequency techniques in order to decrease the injection of disturbances. In a second approach a fuzzy methodology is used to ensure the islanding detection with the aforementioned requirements. Simulation analysis and experimental results are presented to validate the proposed approach

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This work presents the research and development of a connection method for static converters, called Optimized Cascade, which aims to reduce the redundant power processing in multiple stage topologies for LED driving. An initial analysis of possible solutions available on the literature is conducted, where different kinds of solutions are demonstrated, their characteristics and how they can be classified. Afterward, an analysis of the general characteristics of the optimized cascade is presented, as well as the method employed to reduce the bus capacitance value. This reduction aims to replace the electrolytic capacitor for alternative technologies, in order to increase the lifespan of the LED driver. One of the inovations of this work is the proposal of a project methodology, focusing the conversion efficiency and the capacitance reduction. Besides that, a mathematical model of the optimized cascade was derived, so as to establish the impact of the bus voltage ripple on the LED current. From this model, it has been possible to determine parameters for choosing the best operating mode for the second stage and the estimation of capacitance reduction-. Also, some controllers were analyzed to control the PC stage, on which the resonant controller has been proposed for demanding projects, regarding the capacitance value and LED current ripple. Finally, two prototypes were mounted and tested, where an efficiency of thereabout 90% was get with a power factor of 0; 99, along with total compliance with the power quality parameters and flicker. In both prototypes film capacitors were employed, contributing to enhance the lifespan of the converter, making it compatible with LED lifespan. / Este trabalho apresenta o estudo e desenvolvimento de um método de conexão de conversores, chamado Cascata Otimizada, o qual visa reduzir o processamento redundante de energia em topologias de múltiplos estágios para acionamento de LEDs. Uma análise preliminar das soluções disponíveis atualmente na literatura acadêmica é realizada, na qual são demonstrados diferentes tipos de soluções, suas características e como podem ser classificadas. Em seguida, uma análise das características gerais da cascata otimizada é apresentada, bem como o método empregado para redução da capacitância de barramento. Tal redução visa a substituição de capacitores eletrolíticos por tecnologias alternativas, com o intuito do aumento da vida útil do driver. Uma das inovações deste trabalho é a proposição uma metodologia de projeto, com foco na eficiência e na redução da capacitância. Além disso, também foi elaborado um modelo matemático, de forma a determinar o impacto da ondulação da tensão no barramento sobre a corrente nos LEDs. A partir desse modelo, foi possível estabelecer parâmetros para a escolha do melhor modo de operação para o segundo estágio e estimação da redução do capacitor de barramento. Também foram analisados diversos controladores para o segundo estágio, sendo proposto o uso do controle ressonante para projetos mais exigentes com respeito ao valor do capacitor de barramento e da ondulação na corrente de saída. Por fim, dois protótipos foram montados e testados, obtendo uma eficiência de aproximadamente 90%, fator de potência de 0;99 e total observância aos parâmetros de qualidade de energia e flicker. Em ambos os protótipos foram empregados capacitores de filme, o que contribui para elevar a vida útil do conversor, compatibilizando-a com a vida útil da carga LED.

nÃo hà / Esta tese de doutorado apresenta duas novas topologias de conversores CA-CC com uso de neutro comum: conversor de cinco nÃveis intercalado e conversor de cinco nÃveis tipo T. AlÃm disso, uma nova forma de implementaÃÃo da tÃcnica de controle indireto da corrente (Indirect Current Control - ICC) à apresentada. Assim, para comprovaÃÃo da praticidade dos conversores apresentados, toma-se como base o conversor CA-CC de trÃs nÃveis convencional e entÃo à realizada uma anÃlise comparativa de desempenho entre esses trÃs conversores CA-CC monofÃsicos para aplicaÃÃo em no-breaks. Os conversores analisados possuem como caracterÃstica comum a correÃÃo do fator de potÃncia, o controle digital realizado por FPGA e a conexÃo da fonte de alimentaÃÃo com o estÃgio de saÃda, facilitando o uso de inversor e by-pass para no-breaks. O primeiro conversor analisado à o conversor de trÃs nÃveis convencional que apresenta como principal caracterÃstica o reduzido nÃmero de componentes. O segundo conversor analisado à o conversor de cinco nÃveis intercalado que apresenta como principal caracterÃstica as reduzidas perdas de comutaÃÃo e conduÃÃo. Finalmente, o terceiro conversor analisado à o conversor de cinco nÃveis tipo T que apresenta como principais caracterÃsticas: reduzidas perdas de comutaÃÃo e conduÃÃo; os elementos magnÃticos operam com o dobro da frequÃncia de comutaÃÃo reduzindo desta maneira o peso e o volume. A anÃlise teÃrica dos conversores monofÃsicos, os conceitos bÃsicos sobre o controle digital e a tÃcnica de modulaÃÃo, a metodologia de projeto, simulaÃÃo e resultados experimentais dos protÃtipos construÃdos sÃo apresentados para validar o princÃpio de funcionamento dos conversores propostos. / This thesis presents two novel topologies of AC-DC converters with common neutral: five-level interleaved converter and five-level T type converter. Besides, a novel type of implementation of Indirect Current Control (ICC) is also presented. Thus, a comparative analysis of performance between three single phase AC-DC converters for UPS applications is realized. The analyzed converters have as common characteristics: power factor correction, digital control using FPGA and connection between input power supply and converter output enabling the use of UPS inverter and by-pass. The first one analyzed converter is the conventional three level converter which presents as main feature reduced numbers of power semiconductors and components. The second one analyzed converter is the five level interleaving converter which presents as main feature reduced conduction and commutation losses. Finally, the last one analyzed converter is the T type five level converter which presents as main features: reduced conduction and commutation losses and magnetic components operating with the double of switching frequency reducing weight and volume. Theoretical analysis of the single phase converters, basics concepts of digital control and modulation technique, design procedure, simulation and experimental results of lab models are presented in order to validate the principle of operation of the proposed converters.