Les dispositifs DBD se répandent dans un grand nombre d’applications industrielles. Utilisés depuis plus de 150 ans pour la production d’ozone afin de décontaminer l’eau à grande échelle, ils ont depuis la fin du XXème siècle investi les domaines du traitement de surface polymère, du dépôt de couche mince sur substrat et de l’émission lumineuse pour la décontamination ainsi que la médecine. Ces dispositifs sont mis en oeuvre avec un générateur électrique dont les caractéristiques impactent fortement la qualité de la décharge. Ce travail s’inscrit en partie dans le cadre du développement d’une application de traitement de surface à pression atmosphérique. Il aborde la problématique de l’augmentation de la vitesse de dépôt de couche mince au travers des paramètres de l’alimentation électrique. Plus précisément, ce travail s’intéresse aux apports d’une alimentation en courant rectangulaire et aborde également les problématiques liées à la conception et à la fabrication de ce convertisseur. En particulier, une grande attention est portée sur l’étude du transformateur élévateur, car au travers de ses éléments parasites capacitifs, ce dernier peut limiter le transfert de puissance entre la source électrique et le dispositif DBD. Un deuxième aspect de cette étude consiste à entrevoir l’intérêt que revêtent deux convertisseurs statiques dédiés à l’alimentation de dispositifs DBD. Le premier consiste en une alimentation résonante en régime de conduction discontinue dont la particularité est de posséder trois degrés de liberté (fréquence, tension d’entrée et largeur d’impulsion), ce qui lui confère un intérêt exploratoire. Le second convertisseur consiste en une alimentation résonante haute tension et haute fréquence permettant l’éviction du transformateur élévateur, et mettant en oeuvre des interrupteurs au nitrure de gallium (GaN) afin d’atteindre une fréquence de fonctionnement supérieure au mega-Hertz avec un faible niveau de pertes. / DBD devices are widely used in industrial applications. 150 years ago, they were only employed in ozoners for water decontamination. In recent decades, the progress of knowledge and technology allowed to use them in many other applications like surface treatment, medical applications and light emission. Actually, these devices are supplied with an electrical source which parameters can strongly impact the discharge behaviour. An important part of this work comes within the framework of the development of an atmospheric pressure surface treatment involving DBDs. The issue of the influence of the generator's electrical parameters on the treatment speed is discussed. In particular, this work focuses on the merits of a rectangular shaped current source concerning the behavior of an atmospheric pressure discharge in nitrogen ; the problems related to the design and the fabrication of such a converter are highlighted. The design of the high voltage transformer is then described in detail since its lumped elements play an important role as they can strongly limit the power transfer between the electrical source and the DBD device. A second aspect of this work is to establish the interests of two particular power converters. The first one is a resonant converter operating in a discontinuous conduction mode ; its merits is to exhibit three degrees of freedom (input voltage, frequency, current pulse width) instead of two, which is a tremendous asset for exploring purposes. The second one is a high-frequency resonant converter where a resonant inductance and the DBD device structural capacitances are used instead of a high voltage transformer to perform the voltage amplification, which circumvents the issue related to the transformer parasitic elements. This converter is based on GaN HEMT switches in order to reach a low semiconductor losses level and a fairly high operating frequency (above the mega-Hertz).

Dissertation (DTech(Electrical Engineering))--Cape Peninsula University of Technology, 2012 / The confluence of the limited resources of fossil fuels (e.g. coal, oil and natural gas), environmental degradations leading to climate change, security of supplies and fossil fuels high costs have demanded a tremendous efforts on humanity to seek for a sustainable and unlimited natural energy sources. Amongst these renewable energy sources stands out solar energy because of its ubiquitousness. Solar energy is converted to DC electricity by the photovoltaic effect. Photovoltaic (PV) power systems installed in commercial and industrial buildings are a good example of distributed power generation. Here the energy consumption and production match and thus electricity taken from the grid during daytime peak hours can be reduced. This is beneficial as the transmission losses in the grid are avoided and also transmission need is reduced. The cost effectiveness of a solar energy system has hindered its wide adoption and deployment in terms of the initial capital cost even though it has a zero energy cost and very minimal operating and maintenance costs. Different governments have instituted many financial incentives for fast adoption of PV systems for both residential and commercial applications. However, all these incentives are not sustainable in the longer term forecast. For PV system to attain grid parity requires more than unsustainable approach of many governments providing time limited subsidies. The technical solution to the problem is to reduce the overall system cost through technical innovations. One such method is the adoption of transformerless inverter technology as the grid interface system. Transformerless inverter topology provides galvanic isolation through innovative inverter topology and switching strategies that eliminates problems created by not employing the service of transformer.

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Este trabalho apresenta um estudo sobre a corrente de fuga de modo comum em inversores monofásicos sem transformador utilizados para a conexão de sistemas fotovoltaicos (FV) à rede de distribuição de energia elétrica. O estudo se concentra em inversores do tipo fonte de tensão que empregam a topologia em ponte completa. A partir da adequada modelagem do sistema (rede, conversor e módulo fotovoltaico) identifica-se e quantifica-se a contribuição das tensões de modo comum e modo diferencial para a corrente de fuga. Conclui-se que a tensão de modo comum de alta frequência produzida pelo inversor, que depende da estratégia de modulação por largura de pulso (PWM Pulse Width Modulation) empregada, fornece a maior contribuição para produção da corrente de fuga. Esse estudo mostra que os inversores sem transformador, com topologia em ponte completa e modulação que produz tensão de saída com três níveis, necessitam de medidas adicionais para a minimização da corrente fuga quando aplicados em sistemas fotovoltaicos conectados à rede. Algumas soluções propostas na literatura para a minimização da corrente de fuga baseadas em topologias modificadas e filtros de modo comum são listadas e discutidas. Neste trabalho é proposto um filtro integrado de modo comum e modo diferencial com amortecimento passivo de baixas perdas, para minimizar a corrente de fuga produzida por um inversor monofásico sem transformador. Um exemplo de aplicação do filtro proposto é apresentado juntamente com seu procedimento de projeto, resultados de simulação e experimentais que validam a proposta. Além disso, a influência da variação da indutância da rede elétrica e da capacitância parasita do sistema fotovoltaico no comportamento do filtro proposto é analisada. A influência da variação da indutância da rede no comportamento do sistema de controle e o impacto da corrente de modo comum no projeto dos indutores do lado do conversor também são analisados. / This paper presents a study on the common mode leakage current in single-phase transformerless inverters for grid-connected photovoltaic (PV) systems. The study focuses on voltage source inverters (VSI) employing the full-bridge topology. The common mode and differential mode voltages that contribute to the leakage current are identified and quantified from the analysis of the system model (utility grid, converter and PV module). The system model analysis shows that the high frequency common mode voltage produced by the inverter, which depends on the Pulse Width Modulation (PWM) strategy, is the main source contributing to the leakage current. This work shows that transformerless inverters employing the full-bridge topology and a modulation strategy that produces a three-level output voltage require some leakage current minimization strategy when they are employed in grid-connected PV systems. Some solutions proposed in the literature for leakage current minimization based on modified topologies and common mode filters are listed and discussed. In this dissertation an integrated common and differential filter with low loss passive damping is proposed to minimize the leakage current produced by a single-phase transformerless PV inverter. An application example of the proposed filter is presented with design procedure, simulation and experimental results validating the proposal. Additionally, the influence of grid inductance and PV module parasitic capacitance variations on the behavior of the proposed filter is analyzed. The behavior of the control system considering the grid inductance variation and the impact of the common mode current on the converter side inductors design are also analyzed.

Este trabalho apresenta um estudo sobre a corrente de fuga de modo comum em inversores monofásicos sem transformador utilizados para a conexão de sistemas fotovoltaicos (FV) à rede de distribuição de energia elétrica. O estudo se concentra em inversores do tipo fonte de tensão que empregam a topologia em ponte completa. A partir da adequada modelagem do sistema (rede, conversor e módulo fotovoltaico) identifica-se e quantifica-se a contribuição das tensões de modo comum e modo diferencial para a corrente de fuga. Conclui-se que a tensão de modo comum de alta frequência produzida pelo inversor, que depende da estratégia de modulação por largura de pulso (PWM Pulse Width Modulation) empregada, fornece a maior contribuição para produção da corrente de fuga. Esse estudo mostra que os inversores sem transformador, com topologia em ponte completa e modulação que produz tensão de saída com três níveis, necessitam de medidas adicionais para a minimização da corrente fuga quando aplicados em sistemas fotovoltaicos conectados à rede. Algumas soluções propostas na literatura para a minimização da corrente de fuga baseadas em topologias modificadas e filtros de modo comum são listadas e discutidas. Neste trabalho é proposto um filtro integrado de modo comum e modo diferencial com amortecimento passivo de baixas perdas, para minimizar a corrente de fuga produzida por um inversor monofásico sem transformador. Um exemplo de aplicação do filtro proposto é apresentado juntamente com seu procedimento de projeto, resultados de simulação e experimentais que validam a proposta. Além disso, a influência da variação da indutância da rede elétrica e da capacitância parasita do sistema fotovoltaico no comportamento do filtro proposto é analisada. A influência da variação da indutância da rede no comportamento do sistema de controle e o impacto da corrente de modo comum no projeto dos indutores do lado do conversor também são analisados. / This paper presents a study on the common mode leakage current in single-phase transformerless inverters for grid-connected photovoltaic (PV) systems. The study focuses on voltage source inverters (VSI) employing the full-bridge topology. The common mode and differential mode voltages that contribute to the leakage current are identified and quantified from the analysis of the system model (utility grid, converter and PV module). The system model analysis shows that the high frequency common mode voltage produced by the inverter, which depends on the Pulse Width Modulation (PWM) strategy, is the main source contributing to the leakage current. This work shows that transformerless inverters employing the full-bridge topology and a modulation strategy that produces a three-level output voltage require some leakage current minimization strategy when they are employed in grid-connected PV systems. Some solutions proposed in the literature for leakage current minimization based on modified topologies and common mode filters are listed and discussed. In this dissertation an integrated common and differential filter with low loss passive damping is proposed to minimize the leakage current produced by a single-phase transformerless PV inverter. An application example of the proposed filter is presented with design procedure, simulation and experimental results validating the proposal. Additionally, the influence of grid inductance and PV module parasitic capacitance variations on the behavior of the proposed filter is analyzed. The behavior of the control system considering the grid inductance variation and the impact of the common mode current on the converter side inductors design are also analyzed.

Moving parts cause vibrations and tend to wear out. In applications where maintenance is complicated, solutions without moving parts are therefore advantageous. Electrohydrodynamic pumps are such a solution. Instead of mechanical propulsion, they use strong electric fields to induce movement in a dielectric cooling liquid. These pumps require very little power, but to generate sufficiently strong electric fields, they need to be fed with very high voltage.  This project explored various methods for designing DC/DC-converters which fulfil the demands of an electrohydrodynamic pump. This was done by altering and combining existing topologies that were deemed to be relevant. The main method for testing and evaluation was by simulating in LTspice. The project also briefly investigated methods of overcurrent protection. This was relevant because gas bubbles in the cooling fluid can cause electric arcs which damage the pumps. Three converter topologies were chosen for further evaluation. First, a conventional resonant Royer-based converter that has previously been used by APR Technologies which was altered by the inclusion of a feedback loop. Second, a high-frequency resonant Royer-based converter with a planar air-core transformer. Third, a transformerless converter with a switched boost converter IC. All circuits included a Cockroft-Walton voltage multiplier bridge. The two resonant Royer-based converters fulfilled all requirements except the one on efficiency, while the transformerless converter fulfilled all requirements except the one on cost, set by APR. The more expensive transformerless converter had a significantly higher efficiency and a wider range of acceptable input voltages. Furthermore three general conclusions were drawn. The first was that planar air-core transformers are not beneficial compared to conventional transformers in these type of applications. The second was that a discrete voltage regulator controlled by feedback from the output is more effective than using a voltage regulator without feedback, as it also eliminates temperature and load variations. The third conclusion was that to protect the circuits from overcurrent, a large series resistor is needed, which causes significantly lowered efficiency.