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Thesis (M.Eng.)--Memorial University of Newfoundland, 2003. / Bibliography: leaves 254-261.

O presente trabalho visa o desenvolvimento de metodologias para a conexão de sistemas de Geração Distribuída (GD) em redes de distribuição utilizando conversores CC-CA como também, a produção de energia elétrica dentro dos padrões estabelecidos por normas nacionais e internacionais. Para a produção de energia com índices de qualidade satisfatórios, duas situações vão ser consideradas: uma quando o sistema está conectado à rede e outra quando a rede está indisponível. Após a ocorrência do ilhamento, é necessária a mudança da variável a ser sintetizada pelo conversor CC-CA, ou seja, antes da contingência ocorrer a GD está sendo gerenciada no modo potência e/ou corrente e após passa a ser controlada no modo tensão. Além disso, espera-se que os resultados obtidos forneçam subsídios às concessionárias de energia elétrica e aos produtores e autoprodutores de energia para a conexão sistemas de geração distribuída em redes de distribuição como também, os procedimentos necessários a serem adotados por eles quando o sistema de distribuição estiver sob contingência (ilhamento). / This work proposes a set of analysis to connecting a distributed generation system to a distribution network using a three-phase power converter (DC-AC) as well as, the power generation produced by the DG (Distributed Generation) system must follow the national and international power quality standards. For producing energy with satisfactory power quality indexes, two situations will be considered: when the power converter operates connected to the grid, the power/current is used as control variable. However, if the power converter is operating in stand-alone mode (contingency or islanding mode) the control variable must be changed to voltage and the terminal voltage of the power converter must be controlled. Finally, the main concerning of the present study is to obtain results to the electrical energy companies and self-producers for connecting DG system to the grid as well as, the essential procedures that must be adopted by them when the distribution system is operating in contingency or islanding mode.

O presente trabalho visa o desenvolvimento de metodologias para a conexão de sistemas de Geração Distribuída (GD) em redes de distribuição utilizando conversores CC-CA como também, a produção de energia elétrica dentro dos padrões estabelecidos por normas nacionais e internacionais. Para a produção de energia com índices de qualidade satisfatórios, duas situações vão ser consideradas: uma quando o sistema está conectado à rede e outra quando a rede está indisponível. Após a ocorrência do ilhamento, é necessária a mudança da variável a ser sintetizada pelo conversor CC-CA, ou seja, antes da contingência ocorrer a GD está sendo gerenciada no modo potência e/ou corrente e após passa a ser controlada no modo tensão. Além disso, espera-se que os resultados obtidos forneçam subsídios às concessionárias de energia elétrica e aos produtores e autoprodutores de energia para a conexão sistemas de geração distribuída em redes de distribuição como também, os procedimentos necessários a serem adotados por eles quando o sistema de distribuição estiver sob contingência (ilhamento). / This work proposes a set of analysis to connecting a distributed generation system to a distribution network using a three-phase power converter (DC-AC) as well as, the power generation produced by the DG (Distributed Generation) system must follow the national and international power quality standards. For producing energy with satisfactory power quality indexes, two situations will be considered: when the power converter operates connected to the grid, the power/current is used as control variable. However, if the power converter is operating in stand-alone mode (contingency or islanding mode) the control variable must be changed to voltage and the terminal voltage of the power converter must be controlled. Finally, the main concerning of the present study is to obtain results to the electrical energy companies and self-producers for connecting DG system to the grid as well as, the essential procedures that must be adopted by them when the distribution system is operating in contingency or islanding mode.

Este trabalho apresenta o estudo comparativo do desempenho de três topologias de conversores do sistema monofásico para o sistema trifásico com número reduzido de componentes, para o acionamento de um motor de indução do tipo rotor gaiola de esquilo. O funcionamento de cada topologia é descrito e simulado digitalmente. O desempenho desses conversores é avaliado em diferentes modos de operação, com sequência de fase positiva ou negativa, com ênfase na qualidade de energia em termos de redução da distorção harmônica total e da melhoria do fator de potência na fonte. Com vistas à redução de custos, foi desenvolvido um protótipo experimental baseado no uso de módulo integrado de chaves semicondutoras de potência e de um microcontrolador de baixo custo. Os resultados experimentais se equiparam aos resultados obtidos por simulação. / This work presents the comparative performance of three topologies of single-phase to three-phase converters with reduced number of components while driving an induction motor of type squirrel-cage. The operation of each topology is described by means of simulation results. The performance of these converters is evaluated in different modes of operation, according to the positive or negative sequence, with an emphasis on power quality in terms of reduced total harmonic distortion and improved power factor at the input source. With a viewpoint for achieving reduced costs, an experimental prototype has been developed, based on the use of integrated module of power semiconductor switches and a cheap microcontroller. Experimental results comparable to those obtained by simulations are obtained.

The still increasing demand of electrical energy and the rising popularity of renewable energy sources in today's world are two important developments that necessitate the need for innovative solutions in the field of power electronics. Parallel operation of converters is one possible method in trying to bridge an increased current demand. The classical two-level converters, which are the standard in low voltage applications, are rarely adopted in medium and high voltage applications due to the voltage limits on power semiconductor devices. That is one reason for the growing popularity of multilevel converter topologies in medium and high-voltage applications. Although an increase in the number of voltage levels of a multilevel converter has its advantages, there are also challenges posed due to the increased number of switching devices. This has resulted in three-level converters being the most popular compared to converters of higher voltage levels. In this dissertation, the unified operation of parallel connected three-level converter units as a multilevel converter of higher voltage levels is proposed. The mathematical basis for operating parallel connected converter units as a single multilevel converter and the governing equations for such systems are derived. The analysis and the understanding of these equations are important for assessing practicality of the system and devising appropriate control structures. Parallel operation of converter units operating as multilevel converter have their own set of challenges, the two foremost being that of load-sharing and the possibility of circulating and cross currents. Developing solutions to address these challenges require a thorough understanding of how these manifest in the proposed system. Algorithms are then developed for tackling these issues. The control structures are designed and the developed algorithms are implemented. The operation of the system is verified experimentally. / Die weiterhin steigende Nachfrage nach elektrischer Energie und die zunehmende Verwendung erneuerbarer Energiequellen in der heutigen Welt sind zwei wichtige Entwicklungen, die die Notwendigkeit innovativer Lösungen im Bereich der Leistungselektronik erfordern. Der Parallelbetrieb von Stromrichtern ist eine mögliche Methode, um einen erhöhten Strombedarf zu decken. Der klassische Zweipunkt-Spanungszwischenkreisstromrichter, der bei Niederspannungsanwendungen weit verbreitet ist, wird aufgrund der Spannungsgrenzen für Leistungshalbleiterbauelemente zunehmend weniger in Mittel- und Hochspannungsanwendungen eingesetzt. Die begrenzte Spannungsbelastbarkeit der Leistungshalbleiterbauelemente ist ein Grund für die wachsende Beliebtheit von Mehrpunkt-Stromrichtertopologien in Mittelund Hochspannungsanwendungen. Obwohl eine Erhöhung der Anzahl der Spannungsstufen eines Mehrpunkt-Stromrichters Vorteile hat, gibt es auch Herausforderungen und Nachteile aufgrund der erhöhten Anzahl von Leistungshalbleitern. Dies hat dazu geführt, dass der Dreipunkt-Stromrichter die verbreiteste Topologie im Vergleich zu anderen Stromrichtern mit einer höheren Anzahl von Spannungsstufen ist. In dieser Dissertation wird der Betrieb von parallel geschalteten Dreipunkt-Stromrichtereinheiten als ein Mehrpunkt-Stromrichter mit erhöhter Anzahl an Spannungsstufen vorgeschlagen. Die mathematische Basis für den Betrieb von parallel geschalteten Stromrichtereinheiten als ein Mehrpunkt-Stromrichter und die beschreibenden Gleichungen eines solchen Systems werden abgeleitet. Die Analyse und das Verständnis dieser Gleichungen sind wichtig für die Beurteilung der Praktikabilität des Systems und die Erarbeitung geeigneter Regelstrukturen. Der parallele Betrieb von Stromrichtereinheiten hat seine eigenen Herausforderungen, wobei die beiden wichtigsten die Lastverteilung und die Möglichkeit von Kreis- und Querströmen sind. Die Entwicklung von Lösungen zur Bewältigung dieser Herausforderungen erfordert ein gründliches Verständnis dafür, wie sich diese Phänomene in dem vorgeschlagenen System manifestieren. Algorithmen zur Lösung dieser Probleme werden anschlieend entwickelt. Die Regelstrukturen werden entworfen und die entworfenen Algorithmen implementiert. Die Funktionsweise des Systems wird experimentell überprüft.

Este trabalho apresenta o estudo comparativo do desempenho de três topologias de conversores do sistema monofásico para o sistema trifásico com número reduzido de componentes, para o acionamento de um motor de indução do tipo rotor gaiola de esquilo. O funcionamento de cada topologia é descrito e simulado digitalmente. O desempenho desses conversores é avaliado em diferentes modos de operação, com sequência de fase positiva ou negativa, com ênfase na qualidade de energia em termos de redução da distorção harmônica total e da melhoria do fator de potência na fonte. Com vistas à redução de custos, foi desenvolvido um protótipo experimental baseado no uso de módulo integrado de chaves semicondutoras de potência e de um microcontrolador de baixo custo. Os resultados experimentais se equiparam aos resultados obtidos por simulação. / This work presents the comparative performance of three topologies of single-phase to three-phase converters with reduced number of components while driving an induction motor of type squirrel-cage. The operation of each topology is described by means of simulation results. The performance of these converters is evaluated in different modes of operation, according to the positive or negative sequence, with an emphasis on power quality in terms of reduced total harmonic distortion and improved power factor at the input source. With a viewpoint for achieving reduced costs, an experimental prototype has been developed, based on the use of integrated module of power semiconductor switches and a cheap microcontroller. Experimental results comparable to those obtained by simulations are obtained.

Applications of distributed-power systems are on the rise. They are already used in telecommunication power supplies, aircraft and shipboard power-distribution systems, motor drives, plasma applications, and they are being considered for numerous other applications. The successful operation of these multi-converter systems relies heavily on a stable design. Conventional analyses of power converters are based on averaged models, which ignore the fast-scale instability and analyze the stability on a reduced-order manifold. As such, validity of the averaged models varies with the switching frequency even for the same topological structure. The prevalent procedure for analyzing the stability of switching converters is based on linearized smooth averaged (small-signal) models. Yet there are systems (in active use) that yield a non-smooth averaged model. Even for systems for which smooth averaged models are realizable, small-signal analyses of the nominal solution/orbit do not provide anything about three important characteristics: region of attraction of the nominal solution, dependence of the converter dynamics on the initial conditions of the states, and the post-instability dynamics. As such, converters designed based on small-signal analyses may be conservative. In addition, linear controllers based on such analysis may not be robust and optimal. Clearly, there is a need to analyze the stability of power converters from a different perspective and design nonlinear controllers for such hybrid systems. In this Dissertation, using bifurcation analysis and Lyapunov's method, we analyze the stability and dynamics of some of the building blocks of distributed-power systems, namely standalone, integrated, and parallel converters. Using analytical and experimental results, we show some of the differences between the conventional and new approaches for stability analyses of switching converters and demonstrate the shortcomings of some of the existing results. Furthermore, using nonlinear analyses we attempt to answer three fundamental questions: when does an instability occur, what is the mechanism of the instability, and what happens after the instability? Subsequently, we develop nonlinear controllers to stabilize parallel dc-dc and parallel multi-phase converters. The proposed controllers for parallel dc-dc converters combine the concepts of multiple-sliding-surface and integral-variable-structure control. They are easy to design, robust, and have good transient and steady-state performances. Furthermore, they achieve a constant switching frequency within the boundary layer and hence can be operated in interleaving or synchronicity modes. The controllers developed for parallel multi-phase converters retain many of the above features. In addition, they do not require any communication between the modules; as such, they have high redundancy. One of these control schemes combines space-vector modulation and variable-structure control. It achieves constant switching frequency within the boundary layer and a good compromise between the transient and steady-state performances. / Ph. D.

The DC-side floating capacitors in the floating power modules of power converters are subject to high voltage fluctuation, due to the presence of reactive harmonic components. Utilizing passive capacitors, as done in traditional methods, helps reduce the DC-bus voltage ripple but makes the system bulky. An active capacitor can be integrated with the floating H-bridge power modules to remove the effect of the ripple powers on the DC bus. The auxiliary circuit, which is much smaller in size compared to an equivalent passive capacitor, helps increase the power density of the system. This work focuses on the analysis of power components, and the extension of the active capacitor to the Perturbation Injection Unit (PIU), in which the DC side is highly distorted by multiple harmonic components. A control scheme is proposed to compensate for these multiple harmonics and balance the DC-link voltage in the active capacitor. Also, an equivalent DC-bus impedance model is introduced, which is more accurate than that in existing works. Simulation studies and evaluation of the design have verified the effectiveness of the active capacitor solution. / Single-phase power converters have been widely used in many applications such as electric vehicles, photovoltaic (PV) systems, and grid integration. Due to their popular application, there is a need to reduce the sizes and volumes while still maintaining good performances of the systems. One of the most effective methods, which is a subject in many research works, is to replace the bulky passive capacitor bank in a system by an active capacitor. The active capacitor is designed to absorb the ripple components in the DC side of the converters, which results in a constant DC-link voltage. In comparison to the passive capacitor solution, the active capacitor is much smaller in size but can give a better DC-bus ripple performance. Therefore, the active capacitor has become an attractive solution for the single-phase converters. The active capacitor for the traditional rectifier, where the DC side is directly connected to a load, has been intensively investigated in the past decade. However, there is limited research regarding the active capacitor for rectifiers with floating H-bridge power modules. This work extends the application of the active capacitor to the Perturbation Injection Unit (PIU), which is a grid-connected single-phase rectifier with floating H-bridge power modules. The selection of a suitable active capacitor for the PIU is based on the evaluation of various active capacitor banks. Limits in existing control schemes, which prevent the extension of the active capacitor to the PIU, are thoroughly studied. An effective voltage-mode control scheme is then proposed for the selected active capacitor, which makes it an attractive solution for the PIU. Moreover, limits of the DC-bus impedance analysis using traditional assumptions in existing works are investigated, and an improved DC-bus impedance model is proposed. Based on the operation conditions of the PIU and the proposed impedance model, the active capacitor's components can be properly designed, and improved configurations in terms of the equivalent impedance can be analyzed. Simulation results, as well as the design and evaluation of the active capacitor, demonstrate great improvements in terms of volume and weight over the traditional passive capacitor bank.

The still increasing demand of electrical energy and the rising popularity of renewable energy sources in today's world are two important developments that necessitate the need for innovative solutions in the field of power electronics. Parallel operation of converters is one possible method in trying to bridge an increased current demand. The classical two-level converters, which are the standard in low voltage applications, are rarely adopted in medium and high voltage applications due to the voltage limits on power semiconductor devices. That is one reason for the growing popularity of multilevel converter topologies in medium and high-voltage applications. Although an increase in the number of voltage levels of a multilevel converter has its advantages, there are also challenges posed due to the increased number of switching devices. This has resulted in three-level converters being the most popular compared to converters of higher voltage levels. In this dissertation, the unified operation of parallel connected three-level converter units as a multilevel converter of higher voltage levels is proposed. The mathematical basis for operating parallel connected converter units as a single multilevel converter and the governing equations for such systems are derived. The analysis and the understanding of these equations are important for assessing practicality of the system and devising appropriate control structures. Parallel operation of converter units operating as multilevel converter have their own set of challenges, the two foremost being that of load-sharing and the possibility of circulating and cross currents. Developing solutions to address these challenges require a thorough understanding of how these manifest in the proposed system. Algorithms are then developed for tackling these issues. The control structures are designed and the developed algorithms are implemented. The operation of the system is verified experimentally. / Die weiterhin steigende Nachfrage nach elektrischer Energie und die zunehmende Verwendung erneuerbarer Energiequellen in der heutigen Welt sind zwei wichtige Entwicklungen, die die Notwendigkeit innovativer Lösungen im Bereich der Leistungselektronik erfordern. Der Parallelbetrieb von Stromrichtern ist eine mögliche Methode, um einen erhöhten Strombedarf zu decken. Der klassische Zweipunkt-Spanungszwischenkreisstromrichter, der bei Niederspannungsanwendungen weit verbreitet ist, wird aufgrund der Spannungsgrenzen für Leistungshalbleiterbauelemente zunehmend weniger in Mittel- und Hochspannungsanwendungen eingesetzt. Die begrenzte Spannungsbelastbarkeit der Leistungshalbleiterbauelemente ist ein Grund für die wachsende Beliebtheit von Mehrpunkt-Stromrichtertopologien in Mittelund Hochspannungsanwendungen. Obwohl eine Erhöhung der Anzahl der Spannungsstufen eines Mehrpunkt-Stromrichters Vorteile hat, gibt es auch Herausforderungen und Nachteile aufgrund der erhöhten Anzahl von Leistungshalbleitern. Dies hat dazu geführt, dass der Dreipunkt-Stromrichter die verbreiteste Topologie im Vergleich zu anderen Stromrichtern mit einer höheren Anzahl von Spannungsstufen ist. In dieser Dissertation wird der Betrieb von parallel geschalteten Dreipunkt-Stromrichtereinheiten als ein Mehrpunkt-Stromrichter mit erhöhter Anzahl an Spannungsstufen vorgeschlagen. Die mathematische Basis für den Betrieb von parallel geschalteten Stromrichtereinheiten als ein Mehrpunkt-Stromrichter und die beschreibenden Gleichungen eines solchen Systems werden abgeleitet. Die Analyse und das Verständnis dieser Gleichungen sind wichtig für die Beurteilung der Praktikabilität des Systems und die Erarbeitung geeigneter Regelstrukturen. Der parallele Betrieb von Stromrichtereinheiten hat seine eigenen Herausforderungen, wobei die beiden wichtigsten die Lastverteilung und die Möglichkeit von Kreis- und Querströmen sind. Die Entwicklung von Lösungen zur Bewältigung dieser Herausforderungen erfordert ein gründliches Verständnis dafür, wie sich diese Phänomene in dem vorgeschlagenen System manifestieren. Algorithmen zur Lösung dieser Probleme werden anschlieend entwickelt. Die Regelstrukturen werden entworfen und die entworfenen Algorithmen implementiert. Die Funktionsweise des Systems wird experimentell überprüft.