This work demonstrates the design and implementation of a digitally encoded Sinusoidal Pulse Width Modulation strategy for the switching of bi-directional secondary side power switches of an AC-link. Through this method, high frequency (200 kHz) half sinusoid or haversine voltage pulses produced by the Parallel Loaded Resonant converter working in discontinuous mode at primary side are converted to low frequency (400/60/50 Hz) waveforms at the output. This control strategy allows the converter to operate at high power density, as soft switching (ZCS/ZVS) is possible at both the turn-on and turn-off of switches. Also through this strategy the output waveform at load will have low Total Harmonic Distortion (THD).

M.Ing. (Electrical And Electronic Engineering) / DC to AC converters are used daily in industry, shipping and aviation as power .. supplies, standby power supplies or uninterrupted power supplies. Power levels vary from a few watts to several megawatts. This thesis investigates a composite converter with a high frequency link as such a DC to AC converter. There are two basic building blocks, the primary inverter as a push-pull inverter and the secondary converter as a cyclo-converter. A existing 2.5kVA system with bipolar transistors in the primary inverter and asymmetrical thyristors in the secondary converter is investigated. In the primary inverter, regenerative snubbers are used to minimise switching losses. A second 2.5kVA system with mosfets in the primary inverter and IGBT's in the secondary is developed. Switching losses in the primary inverter are minimised by including a resonant circuit concisting of a non-linear inductor and linear capacitor. This resonant circuit in the primary inverter, was originally simmulated by a PSPICE simmulation program, after which it was build up experimentally. The simmulated results and experimental results coincided, and development of the secondary converter started. The switches in the secondary had to comply to two conditions viz, low conducting lossses and the ability to switch at switching frequencies higher than 20kHz. IGBT's were consequently chosen and were implemented with the necessary gate drive circuits. With the higher switching frequency of 25kHz to the 5kHz of the first system, the ripple on the load current was significantly reduced. Furthermore, the construction of the composite converter with the gate drive switches was easy and compact, and the total cost of developing such a converter were reduced.

Doctor of Philosophy / Department of Electrical and Computer Engineering / Behrooz Mirafzal / Corrective schemes for facilitating continued operation of dc-ac converters during internal and external abnormalities are presented in this dissertation. While some of the developed techniques are suited for any dc-ac converter topology, most of the presented methodologies are designed specifically for cascaded H-bridge (CHB) multilevel converters. While CHB provide increased scalability and efficiency compared to traditional topologies, these converters are more likely to experience internal faults due to the additional components required. Realizing the full potential of CHB converters requires fault tolerant techniques, such as those demonstrated in this dissertation. Adaptive sinusoidal pulse width modulation (ASPWM) is introduced in this dissertation as a method which enables CHB to directly utilize time-variant dc sources, increasing CHB flexibility when compared to traditional pulse width modulation (PWM) methods which require dc sources with equal magnitudes or with magnitudes existing in specific ratios. Two alternative algorithms are presented to enable ASPWM implementation, providing a trade off between system performance and required sensor circuitry. This dissertation also introduces a load independent analytical approach for identifying discordant operating points, i.e. operating points where some cells in an asymmetric CHB leg regenerate power while the overall leg delivers power, or vice-versa. Identification of these points is essential due to the deleterious effects which can result from extended discordant operation, for instance overcharging of batteries leading to lifespan degradation or even catastrophic failures such as fires or explosions. Additionally, a method for rapidly identifying, isolating, and verifying internal IGBT open-circuit and gate-driver faults is presented in this dissertation to address the increased probability of switch failures occurring within CHB. The proposed approach enables converter operation to continue in the event of gate-driver or open-circuit faults, but avoids unnecessary converter reconfiguration due to gate-misfiring faults. For a CHB leg with M cells, the proposed technique identifies and isolates open-circuit switch faults in less than 2M measurement (sampling) cycles, and verification is completed in less than one full fundamental cycle. Furthermore, this dissertation introduces a real-time implementable atypical PWM technique which enables increased dc bus utilization under a wide range of non-ideal operating conditions. While this approach is suitable for a wide range of converters operating under external abnormalities, for instance maximizing dc bus utilization for converters providing auxiliary services such as negative-sequence compensation, this approach also facilitates operation of CHB with faulty cells. The proposed method can be used with any control technique and any carrier-based PWM method, enabling its implementation in both symmetric and asymmetric CHB. In addition to these fault tolerant techniques, a novel approach for analyzing the active- and reactive-power deliverable by grid-interactive converters is proposed. This method facilitates performance comparisons for various converter configurations, simplifying the process for selecting filter components, dc bus voltages, and other system parameters. This analytical approach also enables converter performance to be analyzed during internal and external fault events, allowing assessment of converter robustness. The efficacy of the developed techniques are supported by MATLAB/Simulink simulations as well as experimental data obtained using a laboratory-scale cascaded H-bridge multilevel converter.

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

In this dissertation the ac-link universal power converters, which are a new class of power converters, are introduced and studied in detail. The inputs and outputs of these converters may be dc, ac, single phase, or multi-phase. Therefore, they can be used in a variety of applications, including photovoltaic power generation, wind power generation, and electric vehicles. In these converters the link current and voltage are both alternating and their frequency can be high, which leads to the elimination of the dc electrolytic capacitors and the bulky low-frequency transformers. Therefore, the ac-link universal power converters are expected to have higher reliability and smaller size. Moreover, these converters are soft switching, which results in negligible switching losses and minimized current and voltage stress over devices. In the first part of the dissertation, the parallel ac-link universal power converter is studied in detail. This converter is an extension of the buck-boost converter. The series ac-link universal power converter, which is dual of the parallel ac-link universal power converter, is proposed in the second part of this dissertation. This converter is an extension of the Cuk converter. A modified configuration with fewer switches, named sparse ac-link universal power converter is proposed in the third part of this dissertation. The sparse ac-link universal power converters can appear as parallel or series. The performance of all these configurations is evaluated through simulations and experiments.

Made available in DSpace on 2016-08-17T14:53:28Z (GMT). No. of bitstreams: 1 Dissertacao Felipe Simoes Freitas e Silva.pdf: 5795737 bytes, checksum: dc589a2115d1b568db1a3c2b9de3f80c (MD5) Previous issue date: 2014-04-25 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / This work presents the study, modelling and assembling of a three-phase bidirectional DCAC converter suitable for operating as an interface between an energy storage system based on a battery bank and an isolated microgrid. The converter consists of two stages: a DC-DC stage implemented with a bidirectional half-bridge converter that operates on buck or boost mode (during charge or discharge of the ESS, respectively), and a DC-AC full-bridge three-phase bidirectional inverter. The two stages are connected through a DC link, which also works as a power-decoupling element. Isolation from the microgrid is obtained with a :-Y low frequency transformer. A control strategy is proposed where the DC-DC stage regulates the DC link voltage level while the DC-AC controls the three-phase output voltage and frequency, therefore acting as a grid-forming converter (GFC). A 15kW prototype was successfully built and tested in different situations. Simulation and experimental results are shown. / Esta dissertação apresenta o estudo, modelagem e montagem de um conversor bidirecional CC-CA trifásico de múltiplos estágios, projetado para operar como interface entre um sistema de armazenamento e uma minirrede isolada. O conversor consiste de dois estágios de conversão: um estágio de conversão CC-CC, implementado com um conversor buck-boost de meia ponte, que opera em modo buck ou boost (durante o carga ou descarga do sistema de armazenamento, respectivamente), e um estágio de conversão CC-CA composto por um conversor CC-CA trifásico. Os dois estágios são conectados por um elo CC, que funciona como um elemento de desacoplamento de potência. Isolação galvânica é obtida através de um transformador de baixa frequência. Uma estratégia de controle é utilizada na qual o estágio CC-CC controla a tensão do elo CC enquanto o estágio CC-CA controla a tensão e a frequência da minirrede, atuando, portanto, como um conversor formador de rede (CFR). Um protótipo foi montado e testado em diferentes situações. Resultados de simulação e de testes de bancada são mostrados.

Les convertisseurs statiques triphasés AC/DC/AC à structure tension sont largement utilisés dans de nombreuses applications de puissance. La continuité de service de ces systèmes ainsi que leur sécurité, leur fiabilité et leurs performances sont aujourd'hui des préoccupations majeures de ce domaine lié à l'énergie. En effet, la défaillance du convertisseur peut conduire à la perte totale ou partielle du contrôle des courants de phase et peut donc provoquer de graves dysfonctionnements du système, voire son arrêt complet. Afin d'empêcher la propagation du défaut aux autres composants du système et assurer la continuité de service en toute circonstance lors d'une défaillance du convertisseur, des topologies de convertisseur "fault tolerant" associées à des méthodes efficaces et rapides de détection et de compensation de défaut doivent être mises en oeuvre. Dans ce mémoire, nous étudions la continuité de service de trois topologies de convertisseurs AC/DC/AC avec ou sans redondance, lors de la défaillance d'un de leurs interrupteurs. Deux applications sont ciblées : l'alimentation d'une charge RL triphasée et un système éolien de conversion de l'énergie basé sur une MADA. Un composant FPGA est utilisé pour la détection du défaut, afin de réduire autant que possible son temps de détection. Des variantes permettant d'optimiser la méthode de détection de défaut sont également proposées et évaluées. Les trois topologies de convertisseurs proposées, associées à leurs contrôleurs, ont été validées de la modélisation/ simulation à la validation sur banc de test expérimental, en passant par le prototypage "FPGA in the Loop" du FPGA, destiné plus spécifiquement à la détection du défaut / AC/DC/AC converters are widely being used in a variety of power applications. Continuity of service of these systems as well as their reliability and performances are now of the major concerns. Indeed, the failure of the converter can lead to the total or partial loss of the control of the phase currents and can cause serious system malfunction or shutdown. Thus, uncompensated faults can quickly endanger the system. Therefore, to prevent the spread of the fault to the other system components and to ensure continuity of service, fault tolerant converter topologies associated to quick and effective fault detection and compensation methods must be implemented. In this thesis, we present the continuity of service of three AC/DC/AC fault tolerant converters with or without redundancy, in the presence of a fault in one of their switches. Two types of applications are studied: the supply off a three-phase charge and a wind energy conversion system based on a DFIG. An FPGA based implementation is used for fault detection, in order to reduce the detection time as much as possible. Three optimizations in the fault detection method are also presented. During these researches, the three proposed converter topologies and their controllers are validated in simulations and also experimentally, while being validated in a "FPGA in the Loop" prototyping

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

High frequency link power converters for DC – 3Φ AC applications are investigated. Low cost, reduced size, galvanic isolation and efficient large boosting of voltage level are the key motivations behind the selection of such topologies. This thesis proposes high frequency link 3Φ inverters for three wire and four wire systems. The proposed topologies have the simplest power circuit configuration and commutation requirements among all high frequency link topologies reported in the literature. A full load efficiency greater than 90% is achieved with a passive snubber. The effect of various circuit non-idealities are common and important for desirable performances of these topologies. A few such issues are highlighted. Firstly, the special commutation requirement of the power circuit causes a non-linear distortion in the output voltages and thus makes the gain of the power converter time varying. A simple compensation technique is adopted to mitigate the problem. Secondly, the high frequency transformer should operate with only switching frequency component. However, in the practical situations a significant amount of low frequency component gets injected into the transformer and results in peaky transformer magnetizing current unless it is over designed. A suitable measure is incorporated in the proposed topologies to achieve a magnetic protection. The power circuit topology is used as stand-by AC power supply. These are of interest for Uninterruptible Power Supply (UPS) and Micro-grid applications. One of the main objectives of such supplies is to provide a high quality and highly reliable power to the connected loads. A voltage regulation loop based on proportional + multiresonant controller is proposed to achieve excellent quality of the output voltage with unbalanced and nonlinear loadings. The factors influencing regulation and stability of the voltage waveform are identified and necessary modifications are carried out to improve the performance. The potential of this voltage regulation loop along with P/Q droop technique and a simple resistive virtual output impedance loop is exploited to achieve decentralized paralleling of inverters. A trade off between the output voltage power quality and the sharing accuracy is examined. The total harmonic distortion and degree of unbalance in the output voltage waveform are experimentally measured well below the specified limit for stand alone AC supplies with an excellent sharing accuracy. Some of the grid interactive modes are addressed for the completeness of the work. A shunt compensator system and a double conversion system based on the same high frequency link converter are experimentally evaluated. These systems can find their application in UPS systems. A few important observations on the power circuit performances are indicated.