In the last twenty years, industrial and academic research has produced over one hundred new converter topologies for drives applications. Regrettably, most of the published work has been directed towards a single topology, giving an overall impression of a large number of unconnected, competing techniques. To provide insight into this wide ranging subject area, an overview of converter topologies is presented. Each topology is classified according to its mode of operation and a family tree is derived encompassing all converter types. Selected converters in each class are analysed, simulated and key operational characteristics identified. Issues associated with the practical implementation of analysed topologies are discussed in detail. Of all AC-AC conversion techniques, it is concluded that softswitching converter topologies offer the most attractive alternative to the standard hard switched converter in the power range up to 100kW because of their high performance to cost ratio. Of the softswitching converters, resonant dc-link topologies are shown to produce the poorest output performance although they offer the cheapest solution. Auxiliary pole commutated inverters, on the other hand, can achieve levels of performance approaching those of the hard switched topology while retaining the benefits of softswitching. It is concluded that the auxiliary commutated resonant pole inverter (ACPI) topology offers the greatest potential for exploitation in spite of its relatively high capital cost. Experimental results are presented for a 20kW hard switched inverter and an equivalent 20kW ACPI. In each case the converter controller is implanted using a digital signal processor. For the ACPI, a new control scheme, which eliminates the need for switch current and voltage sensors, is implemented. Results show that the ACPI produces lower overall losses when compared to its hardswitching counterpart. In addition, device voltage stress, output dv/dt and levels of high frequency output harmonics are all reduced. Finally, it is concluded that modularisation of the active devices, optimisation of semiconductor design and a reduction in the number of additional sensors through the use of novel control methods, such as those presented, will all play a part in the realisation of an economically viable system.

Variable frequency drives typically have employed dc voltage or current links for power distribution between the input and output converters and as a means to temporarily store energy. The dc link based power conversion systems have several inherent limitations. One of the important limitations is the high switching loss and high device stress which occur during switching intervals. This severely reduces the practical switching frequencies. Additionally, while the cost, size, and weight of the basic voltage sourced PWM drive is attractive, difficulties with input harmonics, output dV/dt and over-voltage, EMI/RFI, tripping with voltage sags, and other problems significantly diminish the economic competiveness of these drives. Add-ons are available to mitigate these problems, but may result in doubling or tripling the total costs and losses, with accompanying large increases in volume and weight. This research investigates the design, control, operation and efficiency calculation of a new power converter topology for medium and high power ac-ac, ac-dc and dc-ac applications. An ac-link formed by an inductor-capacitor pair replaces the conventional dc-link. Each leg of the converter is formed by two bidirectional switches. Power transfer from input to output is accomplished via a link inductor which is first charged from the input phases, then discharged to the output phases with a precisely controllable current PWM technique. Capacitance in parallel with the link inductor produces low turn-off losses. Turn-on is always at zero voltage as each switch swings from reverse to forward bias. Reverse recovery is with low dI/dt and also is buffered due to the link capacitance.

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

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

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第18989号 / 工博第4031号 / 新制||工||1621 / 31940 / 京都大学大学院工学研究科電気工学専攻 / (主査)教授 引原 隆士, 教授 木本 恒暢, 教授 松尾 哲司 / 学位規則第4条第1項該当

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第22069号 / 工博第4650号 / 新制||工||1725(附属図書館) / 京都大学大学院工学研究科電気工学専攻 / (主査)教授 引原 隆士, 教授 松尾 哲司, 准教授 三谷 友彦 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第18989号 / 工博第4031号 / 新制||工||1621(附属図書館) / 31940 / 京都大学大学院工学研究科電気工学専攻 / (主査)教授 引原 隆士, 教授 木本 恒暢, 教授 松尾 哲司 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

La variation de vitesse des machines électriques est une application très porteuse de l’électronique de puissance. La solution de conversion la plus répandue consiste à connecter en cascade deux convertisseurs statiques et d’effectuer une double conversion (AC/DC/AC). Une autre solution, faiblement répandue dans l’industrie, effectue une conversion directe AC/AC. Ce mémoire effectue une synthèse sur les solutions de conversion directe ainsi que sur les stratégies de modulation des convertisseurs matriciels et matriciels « double étage » dans le but de piloter des machines électriques triphasées à partir d’un réseau alternatif triphasé. Cette synthèse a permis de développer une modulation scalaire généralisée, associée à un modulateur par porteuse, équivalente à la modulation vectorielle et applicable aux différents convertisseurs matriciels. Les modulations, à nombre de commutation réduit par période de découpage, ont été approfondies. Cette généralisation a permis de mettre en évidence une solution réduisant les pertes et améliorant le comportement électromagnétique du dispositif comparativement aux modulations traditionnellement utilisées. La présentation des contraintes réelles (commande rapprochée des interrupteurs, Les protections ainsi que le filtrage) est abordée et a été utilisée pour développer une maquette laboratoire. Les stratégies de modulation ont été implantées expérimentalement et valident l’étude théorique. Enfin, un fonctionnement direct à la fréquence réseau, sans modulation donc à faibles pertes, est proposé. Un fonctionnement particulier est introduit, permettant d’effectuer le transitoire du mode modulé classique au fonctionnement direct non modulé / In the power electronics field, the adjustable speed drives is a growing application for electric motors control. The most common conversion solution is to connect in series two static converters and perform a double conversion (AC/DC/AC). Another solution, hardly proposed by industry, uses a direct AC/AC conversion. This thesis aims to make a direct conversion solutions and matrix converters and ‘‘two stage’’ matrix converters modulation strategies synthesis for the purpose to control three-phase electric motor with a three phase input network. This synthesis has developed a generalized scalar modulation, combined with a carrier wave modulator, equivalent to the space vector modulation and applied to matrix converters and the ‘‘two stage’’ matrix converters. Some attention has been done to reduced the switching number during the modulation period. The generalization allows to propose a modified modulation which reduces the losses and improves the electromagnetic performance compared to the traditional modulations used for these kind of converters. The practical constraint (switches control, protection system and filtering) are discussed and has been used to develop a laboratory prototype. The modulations strategies have been implemented experimentally and validate the theoretical study. Finally, a direct function mode with an equal frequency between the input and output network is proposed, without modulation and therefore low losses. In the last part, a particular operation mode is then introduced, permitting the transient operation between the modulated conventional mode to the direct mode without modulation

L’objectif principal de cette thèse consiste à développer des stratégies de modélisation et de contrôle pour la conversion de fréquence en utilisant un convertisseur multi-modulaire sans utilisation de lien en continu. Ce convertisseur est nécessaire pour l’intégration des énergies renouvelables offshore dans un réseau de transport à basse fréquence. La basse fréquence électrique profite à la fois des avantages des réseaux alternatif et continu. L’utilisation de convertisseurs modulaires dans ces réseaux permet, entre autres, de supprimer le transformateur du côté de la basse fréquence électrique. Dans cette optique, l’énergie est convertie depuis la fréquence nominale à 50 Hz ou 60 Hz (considérée comme la haute fréquence) vers un tiers de 50 Hz. Le convertisseur est aussi capable de transformer d’autres valeurs de fréquence. Dans un premier temps, la méthode de modélisation du convertisseur est reliée à la théorie du transformateur de voltage triphasé avec un couplage en YDY. En deuxième lieu, l’application du théorème de superposition nous permet d’évaluer séparément la contribution de chaque fréquence. Dans un dernier temps, le contrôle principal du convertisseur utilise des correcteurs résonants, capables donc de travailler directement avec les courants internes du convertisseur qui sont à deux fréquences nominales. Grâce au découplage entre l’entrée du convertisseur et sa sortie, les défauts et les situations de déséquilibre ne se propagent pas vers la sortie du convertisseur, fonctionnement requis pour l’application en offshore. / The purpose of this thesis is to develop strategies to model and control a modular multilevel converter in order to transform frequency without passing through a direct current link. This converter is needed for application in offshore systems where the energy, produced by the offshore renewables, is transmitted using low frequency links. Low frequency presents benefits from alternative and direct current technologies. Moreover, a voltage transformer is not required at the low frequency side when the proposed converter is used as a frequency transformer. In this scenario, frequencies are converted from the highest nominal frequency (50 Hz or 60 Hz) to one third of 50 Hz. Conversion to other frequency values has been tested as well using the same converter. A methodology based on the electrical transformer theory when connected in YΔY coupling and, the superposition theorem to separate the contribution from both frequencies, are proposed to link these currents with the two three-phase systems at different nominal frequencies. Resonant controllers are introduced to efficiently correct internal current signals of the converter that nominally are constituted of two frequencies: input and output frequencies. The converter is able to decouple the input side from the output. Therefore, faults and unbalanced conditions on the input side are not propagated to the output-side of the converter, which is required for offshore applications.

Single stage cycloconverters generally incorporate hard switching at turn on and soft switching at turn off. This hard switching at turn on combined with the slow switching speeds of thyristors (the switch of choice for standard cycloconverters) limits their use to lower frequency applications. This thesis explores the analysis and design of a pulse density modulated (PDM), soft switching cycloconverter. Unlike standard cycloconverters, the controller in this converter does not adjust thyristor firing angles. It lets only complete half cycles of the input waveform through to the output. This allows and requires a much greater frequency step down from the input to the output. The advantages, shortcomings and tradeoffs of this topology are explored as this converter is designed, built and tested. The resulting cycloconverter has many deficiencies, but proves the concept of the PDM soft switching technique. Cases for further improvement and study are outlined. In the end, this converter shows much promise for applications requiring a high step down in frequency, as well as where the lower electromagnetic interference (EMI) of soft switching may be beneficial.