Thesis (M.S.)--Brigham Young University. Dept. of Computer Science, 2006. / Includes bibliographical references (p. 127-129).

Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 140-147).

Thesis (MScEng)--University of Stellenbosch, 2002. / ENGLISH ABSTRACT: This thesis presents the design and implementation of a voltage controller for an Uninterruptible Power Supply (UPS) Inverter. The inverter is capable of producing a nearly sinusoidal output voltage waveform, thereby keeping the Total Harmonic Distortion (THD) to a minimum. Digital controllers introduce a time delay in the control law that causes system instability. Various control techniques, which includes Pade approximations and system augmentation, are investigated to eliminate the effect of the time delay. These controllers employ classical control as well as modem control techniques. The selection of the various control parameters is verified by mathematical equations. A load-disturbance compensation scheme, implementing feed-forward and gain scheduling, is also developed to improve voltage distortion when varying loads, such as non-linear loads, are connected to the system. It is shown that the constructed pulse-width modulated (PWM) control scheme can achieve fast dynamic response as well as a low THD. / AFRIKAANSE OPSOMMING: Hierdie verhandeling ondersoek die ontwerp en implementering van 'n spanningsbeheerder vir 'n ononderbroke kragtoevoer omsetter. Die stelsel produseer 'n uittree spannigsgolfvorm met 'n lae Totale Harmoniese Distorisie (THD). Digital beheerders veroorsaak 'n tydvertraging in die beheerwet wat stelsel onstabiliteit kan veroorsaak. Verskeie beheertegnieke wat gebaseer is op die Pade benaderings van die tydvertraging en stelsel aanpassings, is ondersoek. Hierdie beheerders maak gebruik van klassieke en moderne beheertegnieke. Die seleksie van die verskeie beheerderveranderlikes word gestaaf deur wiskundige vergelykings. Spannigsvervorming word tot 'n minimum beperk deur gebruik te maak van 'n lasveranderings-kompensasietegniek wat onderskeidelik vorentoe-voer en aanwins skedulering implementeer. Verder word daar bewys dat die pulswydte modulasie (PWM) beheerskema vinnige dinamiese gedrag asook 'n lae THD bewerkstellig.

Thesis (MScEng)--University of Stellenbosch, 2002. / ENGLISH ABSTRACT: This thesis presents results of a study on the small-signal stability of a single-machine infinite-bus power system. Conditions of generator loading and network impedance are identified that require additional stability support. Two methods of stability enhancement are investigated, namely the power system stabilizer and the controlled series capacitor. Both stabilizers employ the conventional (classic) control structure, and parameters are evaluated for optimum performance using an integral-of-the-squared-error-based method. Results for damping capability versus generator loading and system impedance were generated. The ability of the power system stabilizer and controlled series capacitor to provide stability support is compared. This comparison is based on (a) the ability to provide more damping torque when needed, and (b) the amount of damping torque contributed by the stabilizer. / AFRIKAANSE OPSOMMING: Hierin word die resultate van 'n studie op die klein-sein stabiliteit van 'n enkel-masjien oneindige-bus kragstelsel weergegee. Kondisies van generator belasting en netwerk impedansie waar dempings-ondersteuning benodig word, word geïdentifiseer. Twee metodes van stabiliteits-verbetering word ondersoek, naamlik die kragstelstel stabiliseerder en die beheerde serie kapasitor. Beide stabiliseerders maak gebruik van die konvensionele (klassieke) beheerstruktuur, waarvan parameters geëvalueer word deur gebruik te maak van 'n integraal-van-die-vierkant-fout-gebaseerde metode. Resultate vir dempingsvermoë teenoor generator belasting en stelsel impedansie word verkry. Die vermoë van die kragstelsel stabiliseerder en beheerde serie kapasitor om stabiliteits-ondersteuning te verskaf, word vergelyk. Hierdie vergelyking is gebasseer op (a) die vermoë om meer dempingswrinkrag te voorsien wanneer benodig, en (b) die hoeveelheid dempingswrinkrag deur die stabiliseerder bygedra.

Algoritmos de busca do ponto de máxima potência (MPPT) são largamente utilizados para se obter a potência máxima fornecida em sistemas fotovoltaicos. Apesar de existirem diversas técnicas de MPPT, os métodos heurísticos de busca como o método da perturbação e observação (P&O) e o método da Condutância Incremental (InC) são os mais usuais por serem simples e confiáveis. Assim, é proposto uma lei de controle com realimentação da tensão de saída de um painel fotovoltaico (PV) de forma a manter o mesmo operando próximo ao ponto de máxima potência, possibilitando com isso uma melhora do desempenho do algoritmo de P&O e InC inclusive quando o painel PV é submetido a rápidas mudanças na irradiação solar. Além disso, devido às características não lineares dos painéis fotovoltaicos, a utilização de técnicas inteligentes que empregam controladores fuzzy para o controle da tensão terminal do PV, parece ser uma solução viável quando comparada aos controladores clássicos com PI e PID, principalmente, porque tais estruturas de controle proporcionam uma lenta resposta dinâmica e problemas de estabilidade relacionados às oscilações em torno do ponto de máxima potência, decorrente do funcionamento dos algoritmos P&O e InC. / Maximum power point tracking (MPPT) techniques are widely used to achieve the maximum output power of a photovoltaic (PV) system. Although there are many MPPT techniques, the heuristic search methods such as perturb and observe (P&O) and incremental conductance (InC) method are the most commonly used because they are simple and reliable in the pursuit of maximum power point. A control law with feedback of the output voltage of a photovoltaic (PV) panel is proposed, in order to maintain it working nearby the maximum power point, enabling an improvement in the performance of the algorithm for P&O and InC even when the PV array is subjected to rapid changes in solar irradiance. Moreover, due to the nonlinear characteristics of the photovoltaic panels, the technique that employ fuzzy logic control seems to be a viable option when compared with conventional proportional and integral or proportional, integral and derivative controllers, mainly because such control structures provide a slow dynamic response and stability issues related to oscillations around the maximum power point due to operation of P&O and InC algorithms.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This Master Thesis presents a study considering multilevel inverters formed from two and three level cascaded inverters. The literature presents several papers on asymmetric multilevel inverters and most studies are related to control and/or modulation techniques considering a binary or trinary topology. Also, there are studies that consider a small variation of the inverters input voltage and analyses the system behavior. However, any of these studies performs analysis to obtain the best relation between input voltage of the multilevel system, while this together with switching angles are capable of generating an output voltage with minimum THD. This Master Thesis was developed aiming to get this voltage relation for multilevel systems formed by two and three level inverters. Furthermore, it seeks to find a pattern for the voltage ratio for several cascaded inverters. To obtain the desired results, techniques of selective harmonic elimination was applied to reduce low order harmonics, reducing the need for output filter. To reduce the computational efforts for obtaining the switching angles, the author used considerations of genetic algorithms. This is necessary due to the significant increase of the variables to be determined as the number of cascaded inverters increase. / Esta dissertação de mestrado apresenta um estudo considerando inversores multiníveis formados a partir de inversores dois e três níveis conectados em cascata. Na literatura são apresentados vários trabalhos envolvendo inversores multiníveis assimétricos. As pesquisas, na sua maioria, tratam sobre técnicas de modulação considerando uma topologia binária ou trinaria. Ainda, são apresentadas pesquisas que consideram uma pequena variação nas tensões de entrada dos inversores e analisam o comportamento do sistema. Contudo, ainda não existe um estudo que realize uma análise para obtenção da melhor relação entre as tensões de entrada do sistema multinível. Sendo que estas relações de tensão, juntamente com os ângulos de comutação, são capazes de gerar uma tensão de saída com uma THD mínima. Esta dissertação foi realizada buscando obter esta relação de tensões para sistemas multiníveis formados a partir de inversores dois e três níveis. Além disso, é realizada a busca de um padrão para esta relação de tensão para n inversores conectados em cascata. Para a obtenção dos resultados desejados foram aplicadas técnicas de eliminação seletiva de harmônicos. Com esta técnica, as harmônicas de baixa ordem são eliminadas, reduzindo a necessidade do filtro de saída. Além disso, considerações sobre algoritmos genéticos são realizadas. Este algoritmo é utilizado para reduzir o esforço computacional para a obtenção dos ângulos de comutação. Isto é necessário devido ao aumento significativo das variáveis a serem determinadas à medida que se eleva o número de inversores conectados em cascata.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / This Ph. D. dissertation presents contributions to the investigation of soft-switching cells with integrated components, presenting three main approaches: (i) Soft-switching cells with filter coupled inductor; (ii) Integrated soft-switching cells of the ZVT type for multipole systems; and (iii) Integrated soft-switching cells for several soft-switching techniques for multipole systems. Firstly it is presented a generic diagram for softswitching inverters with coupled filter inductor. From the generic diagram the turn-on snubber, ZVT and ZCZVT inverters topologies are derived. It is based on an auxiliary loop, which presents an inductor coupled to the filter inductor. The magnetic coupling allows annulling the current through the main switches during the switching transitions and, as a result, reducing the commutation losses. The basic differences among the techniques obtained by this method are the way of implementing the auxiliary switches and the time instants when these switches are triggered. The topological variations are a result of the choice of the voltage applied through the auxiliary loop by its connection to the inverter topology. Analytical expressions for the derived topologies are obtained aiming to evaluate the operation conditions, as well the main features of each topology. It is proposed a design procedure for each derived topology and the operation principles of each topology are verified by means of experimental and simulation results. Then the integrated softswitching cells of the ZVT type for multipole systems are studied. The synthesis methodology presented is based on generating every topological possibility of symmetrical auxiliary cells. The redundant cells are removed from the set of generated topologies resulting in only four diagrams, which are used to derive the integrated ZVT converters already known in the literature, as well several yet unpublished. The synthesis methodology is applied on an interruptible power supply system, which is experimentally evaluated. Finally it is proposed a generalized methodology to obtain integrated auxiliary commutation cells from several soft-switching techniques concerning multipole systems. The integration possibilities among the models obtained for the chosen soft-switching techniques are investigated, resulting in integrated models. The practical implementation of the resulting models is studied originating integrated topologies for multipole systems. The poles of the system can present the same soft-switching technique or different ones. Experimental results are presented in order to validate the concepts proposed herein. / Esta tese de doutorado apresenta contribuições ao estudo de células de comutação suave com componentes integrados, apresentando três abordagens principais: (i) Células de comutação suave com indutor de filtro acoplado; (ii) Células de comutação suave integradas do tipo ZVT para sistemas multi-pólos; e (iii) Células de comutação suave integradas considerando-se diversas técnicas de comutação para sistemas multi-pólos. Inicialmente é apresentado um diagrama genérico para os conversores com comutação suave e indutor de filtro acoplado. A partir do diagrama genérico são derivadas topologias de inversores snubber de turn-on, ZVT e ZCZVT. Este diagrama genérico é baseado em uma malha auxiliar que apresenta um indutor acoplado ao indutor de filtro. O acoplamento magnético permite fazer com que a corrente através das chaves principais se anule durante as transições de comutação e, como resultado, ocorre a redução das perdas de comutação. A diferença básica entre as técnicas obtidas através deste método é o modo escolhido para implementar as chaves auxiliares e os instantes de acionamento das mesmas. As variações entre as topologias ocorrem em função da escolha da tensão aplicada à malha auxiliar. São obtidas expressões para as topologias derivadas no intuito de avaliar as condições de operação, bem como algumas de suas características. É proposto um procedimento de projeto e verificado o princípio de funcionamento destes inversores através de resultados experimentais e de simulação. A seguir são estudadas as células de comutação suave do tipo ZVT compartilhadas por sistemas que possuem múltiplos pólos. Esta metodologia de síntese é baseada na geração de todas as possibilidades de configurações para as células auxiliares simétricas. A partir disto, as configurações redundantes são eliminadas chegando-se a quatro diagramas capazes de gerar os conversores ZVT integrados presentes na literatura, bem como alguns ainda inéditos. A metodologia de síntese é aplicada para um sistema de fornecimento ininterrupto de energia, sendo que alguns resultados experimentais são apresentados. Finalmente é proposta uma metodologia generalizada para integrar as células auxiliares de diversas técnicas de comutação suave para conversores com múltiplos pólos. Partindo-se da obtenção de modelos para algumas das técnicas de comutação suave, procura-se verificar todas as possibilidades de combinação entre os modelos inicialmente obtidos, gerando-se modelos integrados e a partir disto, obtendo-se topologias integradas tanto para pólos que comutam auxiliados pela mesma técnica de comutação, como para pólos auxiliados por técnicas distintas. São apresentados resultados experimentais comprovando a viabilidade dos conceitos propostos.

This thesis presents novel battery pack designs and control methods to be used with battery packs enhanced with power electronics. There are two areas of focus: 1) intelligent battery packs that are constructed out of many hot swappable modules and 2) smart cells that form the foundation of a completely decentralised battery management system (BMS). In both areas, the concept of active loading/charging is introduced. Active loading/charging balances the cells in a battery pack by loading each cell in proportion to its capacity. In this way, the state of charge of all cells in a series string remain synchronized at all times and all of the energy storage potential from every cell is utilized, despite any differences in capacity there may be. Experimental results from the intelligent battery show how the capacity of a pack of variably degraded cells can be increased by 46% from 97 Wh to 142 Wh using active loading/charging. Engineering design challenges of building a practical intelligent battery pack are addressed. Start up and shut down procedures, and their respective circuits, were carefully designed to ensure zero current draw from the battery cells in the off state, yet also provide a simple mechanism for turning on. Intra-pack communication was designed to provide adequate information flow and precise control. Thus, two intra-pack networks were designed: a real time communication network, and a data communication network. The decentralised control algorithms of the smart cell use a small filtering inductor as a multi-purpose sensor. By analysing the voltage across this filtering inductor, the switching actions of a string of smart cells can be optimised. Experimental results show that the optimised switching actions reduce the output voltage ripple by 83% and they synchronize the terminal voltages of the smart cells, and by extension, their states of charge. This forms the basis of a decentralised BMS that does not require any communication between cells or with a centralised controller, but can still achieve cell balancing through active loading/charging.

No description available.

Le CEA-Leti propose des transistors bidirectionnels courant-tension sur base de la technologie récente HEMT GaN récemment appliquée à l’interrupteur de puissance. La caractéristique bidirectionnelle 4 segments ouvre de nouvelles perspectives en termes de structures d’électronique de puissance et amène à explorer les topologies qui requièrent ce type d'interrupteurs afin de permettre la conversion AC/DC ou AC/AC mono-étage. Ces structures, qui requièrent alors moins d’interrupteurs, permettent potentiellement de gagner en termes de compacité et de rendement. Les interrupteurs 4 segments CEA Leti ont la particularité d’être mono-grille, ce qui permet le pilotage d’un de ces interrupteurs avec un seul signal de commande. En revanche, cette spécificité amène à laisser de côté des stratégies de commande classique et à explorer de nouveaux modes de contrôle : dans ce cadre, ce travail de thèse s’est intéressé à des stratégies de commutation automatiques appliquées à l’interrupteur bidirectionnel mono-grille. Un « cadre de commutation » spécifique a été définit comme prérequis à la définition de toute topologie implémentant ce type d’interrupteur afin de mettre en œuvre des stratégies d’auto-commutation de type ZCS ou bien ZVS. Sur cette base, deux topologies, l’une ZCS, l’autre ZVS, ont été étudiées dans le cadre d’une conversion AC/DC avec fonction PFC et réversibilité en puissance. La topologie à commutations ZVS a été privilégiée pour une mise en œuvre expérimentale. Dans cette perspective, un circuit de driver capable de générer des auto-commutations ZVS a été conçu. Le fonctionnement du convertisseur en auto-commutations ZVS est validé par des essais sur un prototype en fonctionnement AC/DC. / CEA-Leti offers bidirectional current-voltage transistors based on the HEMT GaN technology recently applied to the power switch design. The 4-segment bidirectional feature opens new perspectives in terms of power electronics structures and leads to explore the topologies that require this type of switches, allowing to design single-stage AC-DC or AC-AC conversion systems. These structures, which then require fewer switches, offer potential benefits in terms of compactness and efficiency. The 4-segment CEA Leti switch has the particularity of being single-gate type, which allows to control one bidirectional switch with just one control signal. On the other hand, this specificity leads to avoid classical control strategies and to explore new modes of control: in this context, this thesis work was interested in automatic switching strategies applied to the single gate bidirectional switch. A specific "switch frame" has been defined as a preliminary condition for the definition of any topology implementing this type of switch in order to implement ZCS or ZVS self-switching strategies. On this basis, two topologies, one ZCS, the other ZVS, were studied in the context of an AC/DC conversion with PFC function and power reversibility. The ZVS switching topology has been selected for experimental implementation. In this perspective, a specific ZVS auto-switching driver circuit has been designed. The converter operation, in ZVS auto-switching, is validated by tests on a prototype in AC/DC conversion mode.