Thesis (M.S.)--Michigan State University. Electrical Engineering, 2008. / Title from PDF t.p. (viewed on Aug. 5, 2009) Includes bibliographical references (p. 230-231). Also issued in print.

Thesis (MScEng)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: The three-level neutral-point-clamped(NPC) converter, being a widely used multilevel inverter, received a lot of attention recently due to problems associated with de-link capacitor voltage balancing. There are mainly two problems associated with the neutralpoint voltage of the NPC inverter: 1. At high modulation indices a low frequency ripple occurs on the neutral-point voltage. 2. Steady-state unbalance in the neutral-point voltage may arise due to a variety of factors including component imperfections, transients and other non-idealities and imbalances. In this thesis we study the balancing problem with focus on the steady-state imbalance. This is achieved by a systematic and mathematically rigorous study of the natural balancing mechanisms of the three-level three-phase NPC inverter. Orthogonality of two sets of switching spectra in the frequency domain would imply that the DC-bus voltages balance in the steady state. This is done through mathematical analysis using Carrara's PWM strategy of alternative phase opposition disposition(APOD), phase opposition disposition( POD) and phase disposition(PD); and Bennet's geometric model for double Fourier series adapted for use with power converter systems by Bowes. The theory is verified through simulation. / AFRIKAANSE OPSOMMING: Aangesien die drie-vlak, geklemde, neutrale-punt omsetter(NPC) 'n algemene omsetter konfigurasie is, is daar onlangs baie aandag gegee aan die probleme wat geassosieer word met die balansering van die omsetter se gelykstroombuskapasitorspanning. Die twee hoof probleme wat gepaart gaan met die neutraalpuntspanning van die NPC omsetter is: 1. Met 'n ho modulasie-indeks ontstaan daar 'n lae frekwensie rippel op die neutralepuntspanning. 2. 'n Bestendige toestand wanbalans van die neutrale-puntspanning kan ontstaan as gevolg van 'n verskeidenheid faktore, onder andere komponent nie-idealiteite, oorgangs- en ander wanbalanse. In hierdie tesis word op die bestendige-toestandwanbalans gefokus. Dit word gedoen deur middel van die neutraalbalanseeringsmeganisme van die drie-vlak, drie-fase NPC omsetter, sistematies en gedetaileerd wiskundig te bestudeer. In die bestendige toestand sal orgonaliteit van twee stelle skakel spektras in die frekwensie gebied, GS-bus spanning balans impliseer. Dit word wiskundig geanaliseer deur gebruik te maak van Carrara se alternatiewe fase opposiesie disposisie (APOD), fase oposisie disposisie (POD) en fase disposisie(PD), puls-wydte modulasie strategie, asook Bennet se geometriese modelle vir die dubbel Fourier reeks wat aangepas is vir drywingsomsetters deur Bowes. Ten slotte is die teorie geverifieer deur simulasies.

Made available in DSpace on 2014-06-11T19:30:51Z (GMT). No. of bitstreams: 0 Previous issue date: 2013-06-25Bitstream added on 2014-06-13T20:40:37Z : No. of bitstreams: 1 brito_mag_dr_ilha.pdf: 5064752 bytes, checksum: 82cb4f68cac0b9124f16164ae4f2e99d (MD5) / Esta proposta de tese se baseia na necessidade atual e tendência mundial na busca por sistemas cada vez mais eficientes e que se baseiem em fontes de energia alternativas menos poluentes, renováveis e que produzam pouco impacto ambiental. Desta forma, são desenvolvidos sistemas de geração de energia elétrica de pequeno porte baseado em painéis solares fotovoltaicos. Com o intuito de aumentar o rendimento e a densidade de potência dos sistemas, são apresentadas novas estruturas de inversores monofásicos e trifásicos integrados para aplicação como sistemas isolados e/ou conectados à rede de distribuição em corrente alternada (CA), operando como sistemas de geração distribuídos. Os inversores integrados são apresentados com o intuito de substituir os usuais sistemas de conversão de energia a duplo estágio. Incorporado aos inversores integrados são implementados métodos e dispositivos para extração da máxima potência possível dos painéis fotovoltaicos (algoritmo de MPPT), aumentando assim o aproveitamento de energia advinda destes painéis. Além disso, em virtude da necessidade de conexão segura destes sistemas à rede de distribuição de energia elétrica em corrente alternada, são realizadas análises e a implementação de métodos de sincronismo com a rede de CA em baixa tensão; além da análise e síntese de métodos híbridos para detecção e gestão do efeito de ilhamento, a fim de garantir a segurança do sistema. O controle dos conversores e as técnicas de MPPT, gestão e detecção de ilhamento, bem como de sincronismo com a rede em CA são implementadas de forma digital, com o objetivo de propiciar maior flexibilidade na concepção das lógicas de controle adequadas às aplicações propostas. Finalmente, destaca-se que o trabalho trouxe contribuições significativas para a melhoria na implementação... / This work is based on the actual necessity and world tendency for high-efficiency systems based on renewable energy sources which are less pollutant and produces little environmental impact, and, for this purpose, it is developed some photovoltaic electrical generation systems to operate as a small distribution generation system (DG). With the purpose to increase efficiency and power density, new single-phase and three-phase integrated inverter topologies are presented for operating as stand-alone and/or grid-connected systems. The main idea of these inverters is the replacement of the conventional two-stage cascaded solutions. Main maximum power point tracking techniques are implemented and tested in order to increase energy utilization. Furthermore, because of safe-operation grid connection necessities this work presents analysis and implementation of active and hybrid anti-island detection techniques and synchronization methods with the AC low voltage grid. The converters control system and MPPT techniques, anti-island detection and management system together with the synchronization are implemented digitally, with the purpose of increasing flexibility for the overall control circuitry. Finally, this work has presented significant contributions regarding the P&O and IC based on PI MPPT techniques and has presented the integration procedures in order to obtain new families of single and three-phase inverters. Moreover, this is the first thesis that has presented the tri-state three-phase inverters injecting power into the grid. These inverters have inovations at its control and modulation that permit the input to... (Complete abstract click electronic access below)

CAPES / Este trabalho apresenta o estudo, projeto e implementação digital usando DSP de um Filtro Ativo de Potência Paralelo (FAPP) trifásico com potência de 4,5kVA, sendo este implementado utilizando três topologias de inversores monofásicos em ponte completa compartilhando o mesmo barramento de tensão CC. O FAPP é utilizado em sistemas trifásicos a quatro-fios para supressão de harmônicos de corrente, compensação de reativos e compensação de desbalanços das correntes de carga. Dentre as características mais relevantes desta topolgia de FAPP, pode-se citar: possibilidade de controle de corrente independente entre as fases; tensão reduzida no barramento CC; isolação galvânica entre o FAPP e a rede elétrica; e modularidade. Os algoritmos adotados para obtenção das correntes de referência de compensação são fundamentados no método de controle baseado no sistema de eixos de referência síncrona (SRF). Estes podem ser empregados em sistemas monofásicos bastando, para isso, a criação de um sistema trifásico fictício. Desse modo, em um sistema trifásico a quatro-fios, cada uma das correntes de fase pode ser controlada de forma independente. Duas estratégias distintas de operação do FAPP são implementadas. Na primeira delas, chamada de Controle de Corrente Independente por Fase (CCIF), o FAPP atua na supressão de correntes harmônicas da carga e compensação de potência reativa. Neste caso, as correntes da rede serão senoidais, no entanto desequilibradas. Na segunda estratégia, além de atuar na supressão de harmônicas da carga e compensação de potência reativa, o FAPP também atua na Compensação dos Desequilíbrios das Correntes de Carga (CDCC). Assim, as correntes da rede, além de senoidais, serão equilibradas. Análises matemáticas são realizadas de forma a obter o modelo matemático que representa o sistema físico do FAPP. Além disso, é apresentada uma metodologia de projeto para a obtenção dos ganhos dos controladores das malhas de corrente e de tensão do barramento CC. Resultados de simulação e experimentais são apresentados de forma a validar o desenvolvimento teórico realizado e avaliar o desempenho do FAPP. / This work deals with the study, design and digital implementation by means of digital signal processor (DSP) of a 4.5kVA three-phase shunt active power filter (SAPF), which is implemented by using three single-phase full-bridge converters sharing the same dc-bus voltage. The SAPF is applied to three-phase four-wire systems performing harmonic current suppression, reactive power compensation and load unbalance compensation. The main characteristics of the SAPF topology can be related: possibility of independent current control; low DC-link voltage; galvanic isolation between the SAPF and the grid utility; and possibility of modular implementation. The algorithms adopted for obtaining the current references are based on the synchronous reference frame (SRF) control method. They can be employed in single-phase systems by creating a fictitious three-phase system. Thereby, in a three-phase four-wire system, it is possible the controlling of each phase current independently. Two different operation strategies of the SAPF are implemented. In the first one, which is called Independent Phase-Current Control (IPCC), the SAPF performs harmonic current suppression and reactive power compensation. In this case, the source current will become sinusoidal although unbalanced. In the second strategy, besides acting in the harmonic current suppression and reactive power compensation, the SAPF performs Load Unbalance Compensation (LUnC). In this case, the source currents will become sinusoidal and balanced. Mathematical analyses are carried out in order to obtain the mathematical model which represents the physical system of the SAPF. Additionally, a design methodology is presented, which is used to obtain the controller gains of both current and dc-bus voltage loops. Simulation and experimental results will be presented in order to validate the presented theoretical development and evaluate the performance of the SAPF.

CAPES / Este trabalho apresenta o estudo, projeto e implementação digital usando DSP de um Filtro Ativo de Potência Paralelo (FAPP) trifásico com potência de 4,5kVA, sendo este implementado utilizando três topologias de inversores monofásicos em ponte completa compartilhando o mesmo barramento de tensão CC. O FAPP é utilizado em sistemas trifásicos a quatro-fios para supressão de harmônicos de corrente, compensação de reativos e compensação de desbalanços das correntes de carga. Dentre as características mais relevantes desta topolgia de FAPP, pode-se citar: possibilidade de controle de corrente independente entre as fases; tensão reduzida no barramento CC; isolação galvânica entre o FAPP e a rede elétrica; e modularidade. Os algoritmos adotados para obtenção das correntes de referência de compensação são fundamentados no método de controle baseado no sistema de eixos de referência síncrona (SRF). Estes podem ser empregados em sistemas monofásicos bastando, para isso, a criação de um sistema trifásico fictício. Desse modo, em um sistema trifásico a quatro-fios, cada uma das correntes de fase pode ser controlada de forma independente. Duas estratégias distintas de operação do FAPP são implementadas. Na primeira delas, chamada de Controle de Corrente Independente por Fase (CCIF), o FAPP atua na supressão de correntes harmônicas da carga e compensação de potência reativa. Neste caso, as correntes da rede serão senoidais, no entanto desequilibradas. Na segunda estratégia, além de atuar na supressão de harmônicas da carga e compensação de potência reativa, o FAPP também atua na Compensação dos Desequilíbrios das Correntes de Carga (CDCC). Assim, as correntes da rede, além de senoidais, serão equilibradas. Análises matemáticas são realizadas de forma a obter o modelo matemático que representa o sistema físico do FAPP. Além disso, é apresentada uma metodologia de projeto para a obtenção dos ganhos dos controladores das malhas de corrente e de tensão do barramento CC. Resultados de simulação e experimentais são apresentados de forma a validar o desenvolvimento teórico realizado e avaliar o desempenho do FAPP. / This work deals with the study, design and digital implementation by means of digital signal processor (DSP) of a 4.5kVA three-phase shunt active power filter (SAPF), which is implemented by using three single-phase full-bridge converters sharing the same dc-bus voltage. The SAPF is applied to three-phase four-wire systems performing harmonic current suppression, reactive power compensation and load unbalance compensation. The main characteristics of the SAPF topology can be related: possibility of independent current control; low DC-link voltage; galvanic isolation between the SAPF and the grid utility; and possibility of modular implementation. The algorithms adopted for obtaining the current references are based on the synchronous reference frame (SRF) control method. They can be employed in single-phase systems by creating a fictitious three-phase system. Thereby, in a three-phase four-wire system, it is possible the controlling of each phase current independently. Two different operation strategies of the SAPF are implemented. In the first one, which is called Independent Phase-Current Control (IPCC), the SAPF performs harmonic current suppression and reactive power compensation. In this case, the source current will become sinusoidal although unbalanced. In the second strategy, besides acting in the harmonic current suppression and reactive power compensation, the SAPF performs Load Unbalance Compensation (LUnC). In this case, the source currents will become sinusoidal and balanced. Mathematical analyses are carried out in order to obtain the mathematical model which represents the physical system of the SAPF. Additionally, a design methodology is presented, which is used to obtain the controller gains of both current and dc-bus voltage loops. Simulation and experimental results will be presented in order to validate the presented theoretical development and evaluate the performance of the SAPF.

D.Ing. (Electrical and Electronic Engineering) / This thesis presents a series of analyses developed for several voltage source inverter topologies, which are indispensable in aiding the understanding and the design of these circuits. It describes the groundwork that is required for the development of custom design software for voltage source inverters. The different circuits that can be designed by using this program, are analyzed using conventional circuit analysis techniques. The equations are used to simulate the switching behaviour and to specify the required or recommended ratings of the main devices. The custom design program can be used to design three different topologies of voltage source inverters: a) hard switching (snubberless) six pulse bridge; b) hard switching (snubberless) six pulse bridge, equipped with a simple voltage clamp; and c) soft switching (snubbed) six pulse bridge, equipped with a conventional dissipative snubber circuit. The snubberless behaviour of a voltage source inverter leg is both experimentally and analytically investigated. Approximate equations are formulated which can be used to. determine the peak ratings of the main devices in the inverter, taking the reverse recovery of the freewheel diodes into account. The snubberless behaviour of an inverter leg, equipped with a simple voltage clamp across the dc link, is experimentally and theoretically investigated. Equations for design and determining the required peak ratings of the main devices are developed. It is shown that the simple voltage clamp can operate in two different modes, either as a fast discharging or as a slow discharging voltage clamp and that the ranges of applicability of thetwo modes of operation are different. Design rules for both modes of operation are presented. In order to develop the design equations for a snubbed inverter leg a suitable topology had to be identified first. A method for objectively comparing different inverter toplogies is proposed in this thesis, according to which the minimum on- and off-states of the main devices in the different topologies are compared for identical applications. This method is used to compare four different snubbed voltage source inverter topologies both theoretically and experimentally. As both methods indicate that the conventional snubber circuit allows the highest PWM switching frequency of the uncontrolled snubber circuits, this circuit is further investigated in its dissipative topology to develop the equations required for simulation and for inclusion in the program. The influence of snubber circuits on inductive inverter loads is also investigated. It is shown that for normal snubber sizes the effect of dead time forms the larger part of the output voltage distortion and that the effects of the snubber elements are normally of secondary importance. The effect of asymmetry of a specific snubber circuit on inverter loads is investigated and it is found that it introduces a de component in the output voltage. Finally the application of linear snubbers to switches that exhibit tail-forming characteristics is analyzed and optimized. The results allow the designer to minimize the total losses of the converter by identifying the optimal snubber size. The theoretical results are experimentally verified

No description available.

Approved for public release; distribution is unlimited / The naval vessels of the future will require lighter, more compact, and more versatile power electronics systems. With the advent of the DC Zonal Electrical Distribution System, more innovative approaches to the conversion of the dc bus power to ac power for motor drives will enhance the efficiency and warfighting capability of tomorrow's ships. This thesis explores the concept of a hybrid dc-ac power converter that combines a hysteresis controlled inverter with a six-step bulk inverter. A six-step bulk inverter is built from discrete components and tested in simulation and hardware. The two inverters are connected in parallel to provide a high-fidelity current source for a three-phase load. The addition of the hysteresis inverter to the bulk inverter adds a closed current loop for more robust control and improves the quality of the output load current. / Major, United States Marine Corps

Thesis Submitted in Partial Fulfilment of the Requirements for the Degree of Master of Technology: Electrical Engineering (Energy) in the Department of Electrical, Electronic and Computer Engineering at the Cape Peninsula University of Technology, South Africa. / In photovoltaic power systems, the DC/AC conversion efficiency depends on weather conditions causing PV inverters to operate under fluctuating input power from PV modules. The peak efficiency stated by the inverter manufacturers are often used by project designers to estimate how much power PV plants can produce. However, the varying nature of the DC input power to the inverters, occasioned by varying irradiation and temperature, leads to deviations of the actual efficiency from the peak efficiency. Literature surveys prove that inverter efficiencies must be evaluated against local irradiation profiles to get more precise annual energy yield estimations, since meteorological conditions and solar irradiation profiles vary from one site to another around the planet.

Submitted by Cátia Araújo (catia.araujo@unipampa.edu.br) on 2017-01-24T14:12:57Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Controle Adaptativo Aplicado a Conversores com Filtro LCL co.pdf: 2879378 bytes, checksum: a4bb30418fb9767ce153f5d1d4203eff (MD5) / Approved for entry into archive by Cátia Araújo (catia.araujo@unipampa.edu.br) on 2017-01-24T14:16:10Z (GMT) No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Controle Adaptativo Aplicado a Conversores com Filtro LCL co.pdf: 2879378 bytes, checksum: a4bb30418fb9767ce153f5d1d4203eff (MD5) / Made available in DSpace on 2017-01-24T14:16:10Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Controle Adaptativo Aplicado a Conversores com Filtro LCL co.pdf: 2879378 bytes, checksum: a4bb30418fb9767ce153f5d1d4203eff (MD5) Previous issue date: 2016-07-01 / A disseminação de conversores estáticos para os mais diversos fins de aplicação teve grande crescimento a partir da década de 80. Pode-se destacar sua utilização em aplicações tais como em filtragem ativa e geração distribuída. Esta ultima associada a implementação de microrredes de energia e associadas intrinsecamente as chamadas redes elétricas inteligentes. Tradicionalmente quando estes conversores são utilizados para fins de conexão com a rede utiliza-se um filtro em série com o conversor a fim de suprimir harmônicos oriundos do processo de comutação das suas chaves semicondutoras. Estes filtros são, em geral, do tipo L ou LCL, sendo que, devido a sua maior capacidade de atenuação de componentes harmônicas associada a comutação do conversor o filtro LCL é preferencialmente empregado para esta finalidade. Porem, a utilização do filtro LCL, por se tratar de um filtro de terceira ordem, requer uma estratégia de controle mais complexa não só para a rejeição de distúrbios provindos da rede como também para manter a estabilidade do sistema. Para tratar tais problemas diversos trabalhos na literatura ponderam entre diferentes escolhas da variável de controle, como a corrente de saída do conversor ou a de saída do filtro e diversas técnicas de controle como deadbeat, controle por histerese, entre outras. Este trabalho aborda a utilização da corrente média ponderada do filtro LCL de saída como variável de controle a fim de simplificar o problema de controle resultante da utilização deste tipo de filtro. Utilizou-se uma técnica de Controle por Modelo de Referência em conjunto com um Controlador Adaptativo com ação Feedforward como estratégia para garantir a estabilidade e rejeição de distúrbios no sistema. Também foi realizada uma abordagem com objetivo de garantir a estabilidade do sistema frente a situações de saturação da ação de controle a ser sintetizada pelo conversor, utilizando uma t_ecnica de Controle por Modelo de Referência Adaptativo e novamente um Controlador Adaptativo com ação Feedforward. São realizadas análises e provas matemáticas da estabilidade dos controladores em conjunto com resultados de simulação e experimentais demonstrando a aplicabilidade da proposta. / The widespred use of static converters for different application purposes experienced a grown mainly since 80's, with a great increase of interest in recent years. It is possible to highlight their use in grid connected systems such as in power filters and distributed generation sources. The last contributed for the dissemination of microgrids and the advent of smartgrids. For grid connected applications, a filter is used to interface the converter with the grid in order to suppress the harmonic content due to the switching process of the converter. These filters may be purely inductive or of L type, or inductive-capacitive inductive or of LCL type. Due to its higher harmonic attenuation capacity, the LCL filter is preferably employed. However the LCL filter has some disadvantages quite evident. For example, it is a third-order filter, wich requires more complex control strategy not only to reject disturbances arisen from the grid, but also for stability and control purposes. To address such problems, several works in the literature consider different choices regarding the controlled quantity namely, the converter current or the grid current, and several control techniques such as deadbeat, hysteresis control, PI in synchronous reference frame, among others. This work discusses the use of the weighted average current of the LCL-filter as a control variable in order to alleviate the problem of control resulting from the use of this type of filter. It was used Model Reference Control in conjunction with an Adaptive Feedforward Cancellation scheme as a strategy to ensure stability and disturbance rejection for the system. It was also applied an approach to ensure the stability of the system facing situations of saturation of the control action using a Model Reference Adaptive Controller with an Adaptive Feedforward Cancellation scheme, designed to cope with the effect of saturation. Mathematical analysis and proofs of stability are presented with simulation and experimental results, that demonstrate the applicability of the proposal.