Switching-Cell Arrays - An Alternative Design Approach in Power Conversion

© 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting /republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other worksThe conventional design of voltage-source power converters is based on a two-level half-bridge configuration and the selection of power devices designed to meet the full application specifications (voltage, current, etc.). This leads to the need to design and optimize a large number of different devices and their ancillary circuitry and prevents taking advantage from scale economies. This paper proposes a paradigm shift in the design of power converters through the use of a novel configurable device consisting on a matrix arrangement of highly-optimized switching cells at a single voltage class. Each switching cell consists of a controlled switch with antiparallel diode together with a self-powered gate driver. By properly interconnecting the switching cells, the switching cell array (SCA) can be configured as a multilevel active-clamped leg with different number of levels. Thus, the SCA presents adjustable voltage and current ratings, according to the selected configuration. For maximum compactness, the SCA can be conceived to be only configurable by the device manufacturer upon the customer needs. For minimum cost, it can also be conceived to be configurable by the customer, leading to field-configurable SCAs. Experimental results of a 6x3 field-configurable SCA are provided to illustrate and validate this design approach.Peer ReviewedPostprint (author's final draft

Fault Tolerant DC–DC Converters at Homes and Offices

The emergence of direct current (DC) microgrids within the context of residential buildings and offices brings in a whole new paradigm in energy distribution. As a result, a set of technical challenges arise, concerning the adoption of efficient, cost-effective, and reliable DC-compatible power conditioning solutions, suitable to interface DC microgrids and energy consuming elements. This thesis encompasses the development of DC–DC power conversion solutions, featuring improved availability and efficiency, suitable to meet the requirements of a comprehensive set of end-uses commonly found in homes and offices. Based on the energy consumption profiles and requirements of the typical elements found at homes and offices, three distinctive groups are established: light-emitting diode (LED) lighting, electric vehicle (EV) charging, and general appliances. For each group, a careful evaluation of the criteria to fulfil is performed, based on which at least one DC–DC power converter is selected and investigated. Totally, a set of five DC–DC converter topologies are addressed in this work, being specific aspects related to fault diagnosis and/or fault tolerance analysed with particular detail in two of them. Firstly, mathematical models are described for LED devices and EV batteries, for the development of a theoretical analysis of the systems’ operation through computational simulations. Based on a compilation of requirements to account for in each end-use (LED lighting, EV charging, and general appliances), brief design considerations are drawn for each converter topology, regarding their architecture and control strategy. Aiming a detailed understanding of the two DC–DC power conversion systems subjected to thorough evaluation in this work – interleaved boost converter and fault-tolerant single-inductor multiple-output (SIMO) converter – under both normal and abnormal conditions, the operation of the systems is evaluated in the presence of open-circuit (OC) faults. Parameters of interest are monitored and evaluated to understand how the failures impact the operation of the entire system. At this stage, valuable information is obtained for the development of fault diagnosis strategies. Taking profit of the data collected in the analysis, a novel fault diagnostic strategy is presented, targeting interleaved DC–DC boost converters for general appliances. Ease of implementation, fast diagnostic and robustness against false alarms distinguish the proposed approach over the state-of-the-art. Its effectiveness is confirmed through a set of operation scenarios, implemented in both simulation environment and experimental context. Finally, an extensive set of reconfiguration strategies is presented and evaluated, aiming to grant fault tolerance capability to the multiple DC–DC converter topologies under analysis. A hybrid reconfiguration approach is developed for the interleaved boost converter. It is demonstrated that the combination of reconfiguration strategies promotes remarkable improvements on the post-fault operation of the converter. In addition, an alternative SIMO converter architecture, featuring inherent tolerance against OC faults, is presented and described. To exploit the OC fault tolerance capability of the fault-tolerant SIMO converter, a converter topology targeted at residential LED lighting systems, two alternative reconfiguration strategies are presented and evaluated in detail. Results obtained from computational simulations and experimental tests confirm the effectiveness of the approaches. To further improve the fault-tolerant SIMO converter with regards to its robustness against sensor faults, while simplifying its hardware architecture, a sensorless current control strategy is presented. The proposed control strategy is evaluated resorting to computational simulations.O surgimento de micro-redes em corrente contínua (CC) em edifícios residenciais e de escritórios estabelece um novo paradigma no domínio da distribuição de energia. Como consequência disso, surge uma panóplia de desafios técnicos ligados à adopção de soluções de conversão de energia, compatíveis com CC, que demonstrem ser eficientes, rentáveis e fiáveis, capazes de estabelecer a interface entre micro-redes em CC e as cargas alimentadas por esse sistema de energia. Até aos dias de hoje, os conversores CC–CC têm vindo a ser maioritariamente utilizados em aplicações de nicho, que geralmente envolvem níveis de potência reduzidos. Porém, as perspectivas futuras apontam para a adopção, em larga escala, destas tecnologias de conversão de energia, também em equipamentos eléctricos residenciais e de escritórios. Tal como qualquer outra tecnologia de conversão electrónica de potência, os conversores CC–CC podem ver o seu funcionamento afectado por falhas que degradam o seu bom funcionamento, sendo que essas falhas acabam por afectar não apenas os conversores em si, mas também as cargas que alimentam, limitando assim o tempo de vida útil do conjunto conversor + carga. Desta forma, é fulcral localizar a origem da falha, para que possam ser adoptadas acções correctivas, capazes de limitar as consequências nefastas associadas à falha. Para responder a este desafio, esta tese contempla o desenvolvimento de soluções de conversão de energia CC–CC altamente eficientes e fiáveis, capazes de responder a requisitos impostos por um conjunto alargado de equipamentos frequentemente encontrados em habitações e escritórios. Com base nos perfis de consumo de energia eléctrica e nos requisitos impostos pelas cargas tipicamente utilizadas em habitações e escritórios, são estabelecidos três grupos distintos: iluminação através de díodos emissores de luz, carregamento de veículo eléctrico (VE) e aparelhos eléctricos em geral. Para cada grupo, é efectuada uma avaliação cuidadosa dos critérios a respeitar, sendo com base nesses critérios que será escolhida e investigada pelo menos uma topologia de conversor CC–CC. No total, são abordadas cinco topologias de conversores CC–CC distintas, sendo que os aspectos ligados ao diagnóstico de avarias e/ou tolerância a falhas são analisados com particular detalhe em duas dessas topologias. Inicialmente, são estabelecidos modelos matemáticos descritivos do comportamento das principais cargas consideradas no estudo – díodos emissores de luz e baterias de VEs – visando a análise teórica do funcionamento dos sistemas em estudo, suportada por simulações computacionais. Com base numa compilação de requisitos a ter em conta em cada aplicação – iluminação através de díodos emissores de luz, carregamento de veículo eléctrico (VE) e aparelhos eléctricos em geral – são estabelecidas considerações ligadas à escolha de cada topologia de conversor não isolado, no que respeita à sua arquitectura e estratégia de controlo. Visando o conhecimento aprofundado das duas topologias de conversor CC–CC alvo de particular enfoque neste trabalho – conversor entrelaçado elevador e conversor de entrada única e múltiplas saídas, tolerante a falhas – quer em funcionamento normal, quer em funcionamento em modo de falha, é avaliado o funcionamento de ambas as topologias na presença de falhas de circuito aberto nos semicondutores activos. Para o efeito, são monitorizados e analisados parâmetros úteis à percepção da forma como os modos de falha avaliados neste trabalho impactam o funcionamento de todo o sistema. Nesta fase, é obtida informação fundamental ao desenvolvimento de estratégias de diagnóstico de avarias, particularmente indicadas para avarias de circuito aberto nos semicondutores activos dos conversores em estudo. Com base na informação recolhida anteriormente, é apresentada uma nova estratégia de diagnóstico de avarias direccionada a conversores CC–CC elevadores entrelaçados utilizados em aparelhos eléctricos, em geral. Facilidade de implementação, rapidez e robustez contra falsos positivos são algumas das características que distinguem a estratégia proposta em relação ao estado da arte. A sua efectividade é confirmada com recurso a uma multiplicidade de cenários de funcionamento, implementados quer em ambiente de simulação, quer em contexto experimental. Por fim, é apresentada e avaliada uma gama alargada de estratégias de reconfiguração, que visam assegurar a tolerância a falhas das diversas topologias de conversores CC–CC em estudo. É desenvolvida uma estratégia de reconfiguração híbrida, direccionada ao conversor entrelaçado elevador, que combina múltiplas medidas de reconfiguração mais simples num único procedimento. Demonstra-se que a combinação de múltiplas estratégias de reconfiguração introduz melhorias substanciais no funcionamento do conversor ao longo do período pós-falha, ao mesmo tempo que assegura a manutenção da qualidade da energia à entrada e saída do conversor reconfigurado. Noutra frente, é apresentada e descrita uma arquitectura alternativa do conversor de entrada única e múltiplas saídas, com tolerância a falhas de circuito aberto. Através da configuração proposta, é possível manter o fornecimento de energia eléctrica a todas as saídas do conversor. Para tirar máximo proveito da tolerância a falhas do conversor de entrada única e múltiplas saídas, uma topologia de conversor indicada para sistemas residenciais de iluminação baseados em díodos emissores de luz, são apresentadas e avaliadas duas estratégias de reconfiguração do conversor, exclusivamente baseadas na adaptação do controlo aplicado ao conversor. Os resultados de simulação computacional e os resultados experimentais obtidos confirmam a efectividade das abordagens adoptadas, através da melhoria da qualidade da energia eléctrica fornecida às diversas saídas do conversor. São assim asseguradas condições essenciais ao funcionamento ininterrupto e estável dos sistemas de iluminação, já que a qualidade da energia eléctrica fornecida aos sistemas de iluminação tem impacto directo na qualidade da luz produzida. Por fim, e para aprimorar o conversor de entrada única e múltiplas saídas tolerante a falhas, no que respeita à sua robustez contra falhas em sensores, é apresentada uma estratégia de controlo de corrente que evita o recurso excessivo a sensores e, ao mesmo tempo, simplifica a estrutura de controlo do conversor. A estratégia apresentada é avaliada através de simulações computacionais. A abordagem apresentada assume vantagens em múltiplos domínios, sendo de destacar vantagens como a melhoria da fiabilidade de todo o sistema de iluminação (conversor + carga), os ganhos atingidos ao nível do rendimento, a redução do custo de implementação da solução, ou a simplificação da estrutura de controlo.This work was supported by the Portuguese Foundation for Science and Technology (FCT) under grant number SFRH/BD/131002/2017, co-funded by the Ministry of Science, Technology and Higher Education (MCTES), by the European Social Fund (FSE) through the ‘Programa Operacional Regional Centro’ (POR-Centro), and by the Human Capital Operational Programme (POCH)

Pcm telemtry- a new approach using all- magnetic techniques

Digital all-magnetic circuit technique used in pulse code modulation telemetry system

High Efficiency LED Drivers: A Review

Recently various soft switching techniques have been developed for various DC-DC based LED drivers. Typical driver circuits in the market have efficiency between 80% - 95% with majority having efficiency between 80% - 90%. Various topologies and strategies are available to obtain the best performance. A comparison and discussion of different buck and floating buck topologies used as driver in LED lighting application are presented in this paper

Optocoupler Integration of LTCC-based Gate Driver in a SiC Power Module

The growing demand for electrical energy in today’s industrialized economy has driven the need for innovative approaches to meet diverse application requirements. Notably, advancements have been made in the field of power electronic systems, as reliable power electronic converters are essential for managing multiple power sources and loads. However, the development of these systems poses challenges related to power device switching speed, system weight and size, and power losses. The integration of a gate driver into a SiC power module offers a solution to many of these challenges, thereby driving the advancement of electrical power density expansion. An LTCC-based gate driver with an LTCC-based optical isolator was developed and integrated into a fabricated 1.2kV SiC power module. This development was done specifically for high temperature applications as part of a wider research on the reliability of the integrated power module at higher temperatures. Therefore, this high temperature gate driver integrated SiC power module was tested from 25oC to 200oC. Double pulse testing of the fabricated integrated SiC power module was done to characterize the switching performance of the power module. The test results indicate a minimal voltage overshoot of approximately 3.5V during both the turn-on and turn-off periods. Additionally, the current overshoot ranges from ~5A to ~8A as the temperature increases from 25oC to 200oC. The results show good switching performance resulting in minimal losses over higher temperatures. Therefore, with these results, the integrated SiC power module can enhance better power density, and lower losses even in high temperature applications

Optocoupler Integration of LTCC-based Gate Driver in a SiC Power Module

The growing demand for electrical energy in today’s industrialized economy has driven the need for innovative approaches to meet diverse application requirements. Notably, advancements have been made in the field of power electronic systems, as reliable power electronic converters are essential for managing multiple power sources and loads. However, the development of these systems poses challenges related to power device switching speed, system weight and size, and power losses. The integration of a gate driver into a SiC power module offers a solution to many of these challenges, thereby driving the advancement of electrical power density expansion. An LTCC-based gate driver with an LTCC-based optical isolator was developed and integrated into a fabricated 1.2kV SiC power module. This development was done specifically for high temperature applications as part of a wider research on the reliability of the integrated power module at higher temperatures. Therefore, this high temperature gate driver integrated SiC power module was tested from 25oC to 200oC. Double pulse testing of the fabricated integrated SiC power module was done to characterize the switching performance of the power module. The test results indicate a minimal voltage overshoot of approximately 3.5V during both the turn-on and turn-off periods. Additionally, the current overshoot ranges from ~5A to ~8A as the temperature increases from 25oC to 200oC. The results show good switching performance resulting in minimal losses over higher temperatures. Therefore, with these results, the integrated SiC power module can enhance better power density, and lower losses even in high temperature applications

Isolated and Bidirectional DC-DC Converter for Electric Vehicles

O estado da arte iniciou com a análise na literatura de topologias de conversores DC-DC. Técnicas de modulação são estudadas com vista a melhorar a eficiência de conversão, realçando as vantagens e limitações inerentes das mesmas. Após a análise da literatura, o foco projeto passou a ser a topologias de dupla ponte com dispositivos ativos e com isolamento galvânico intermédio entre as duas pontes (conhecido em inglês por dual active bridge). Algumas técnicas de modulação que permitem o funcionamento do conversor são analisadas no documento e suportadas com resultados obtidos em ambiente de simulação. O dimensionamento do transformador de potência é realizado assim como a descrição dos passos. É relizado uma análise de mercado de dispositivos de comutação com a tecnologia "Silicon Carbide" e são apresentados estimativas de perdas e eficiência de operação na utilização de transistores com a techonoloa SiC no conversor analisado. Os resultados são obtidos com recurso a simulações computacionais que através de modelos de aproximação permitem aproximar o conversor a uma situação mais proxima da real. Em termos de implementação, é esperado a implementação um circuito de comando para dois MOSFETS com tecnologia SiC com a configuração em meia ponte ligada a uma carga

Stacking of IGBT devices for fast high-voltage high-current applications

The development of solid-state switches for pulsed power applications has been of considerable interest since high-power semiconductor devices became available. However, the use of solid-state devices in the pulsed power environment has usually been restricted by device limitations in either their voltage/current ratings or their switching speed. The stacking of fast medium-voltage devices, such as IGBTs, to improve the voltage rating, makes solid-state switches a potential substitute for conventional switches such as hard glass tubes, thyratrons and spark gaps. Previous studies into stacking IGBTs have been concerned with specific devices, designed or modified particularly for a specific application. The present study is concerned with stacking fast and commercially available IGBTs and their application to the generation of pulsed electric field and the switching of a high intensity Xenon flashlamp. The aim of the first section of the present study was to investigate different solid-state switching devices with a stacking capability and this led to the choice of the Insulated Gate Bipolar Transistor (IGBT). It was found that the collector-emitter voltage decreases in two stages in most of the available IGBTs. Experiments and simulation showed that a reason for this behaviour could be fast variations in device parasitic parameters particularly gate-collector capacitance. Choosing the proper IGBT, as well as dealing with problems such as unbalanced voltage and current sharing, are important aspects of stacking and these were reported in this study. Dynamic and steady state voltage imbalances caused by gate driver delay was controlled using an array of synchronised pulses, isolated with magnetic and optical coupling. The design procedure for pulse transformers, optical modules, the drive circuits required to minimise possible jitter and time delays, and over-voltage protection of IGBT modules are also important aspects of stacking, and were reported in this study. The second purpose of this study was to investigate the switching performance of both magnetically coupled and optically coupled stacks, in pulse power applications such as Pulse Electric Field (PEF) inactivation of microorganisms and UV light inactivation of food-related pathogenic bacteria. The stack, consisting of 50 1.2 kV IGBTs with the voltage and current capabilities of 10 kV, 400 A, was incorporated into a coaxial cable Blumlein type pulse - generator and its performance was successfully tested with both magnetic and optical coupling. As a second application of the switch, a fully integrated solid-state Marx generator was designed and assembled to drive a UV flashlamp for the purpose of microbiological inactivation. The generator has an output voltage rating of 3 kV and a peak current rating of 2 kA, although the modular approach taken allows for a number of voltage and current ratings to be achieved. The performance of the switch was successfully tested over a period of more than 10⁶ pulses when it was applied to pulse a xenon flashlamp.The development of solid-state switches for pulsed power applications has been of considerable interest since high-power semiconductor devices became available. However, the use of solid-state devices in the pulsed power environment has usually been restricted by device limitations in either their voltage/current ratings or their switching speed. The stacking of fast medium-voltage devices, such as IGBTs, to improve the voltage rating, makes solid-state switches a potential substitute for conventional switches such as hard glass tubes, thyratrons and spark gaps. Previous studies into stacking IGBTs have been concerned with specific devices, designed or modified particularly for a specific application. The present study is concerned with stacking fast and commercially available IGBTs and their application to the generation of pulsed electric field and the switching of a high intensity Xenon flashlamp. The aim of the first section of the present study was to investigate different solid-state switching devices with a stacking capability and this led to the choice of the Insulated Gate Bipolar Transistor (IGBT). It was found that the collector-emitter voltage decreases in two stages in most of the available IGBTs. Experiments and simulation showed that a reason for this behaviour could be fast variations in device parasitic parameters particularly gate-collector capacitance. Choosing the proper IGBT, as well as dealing with problems such as unbalanced voltage and current sharing, are important aspects of stacking and these were reported in this study. Dynamic and steady state voltage imbalances caused by gate driver delay was controlled using an array of synchronised pulses, isolated with magnetic and optical coupling. The design procedure for pulse transformers, optical modules, the drive circuits required to minimise possible jitter and time delays, and over-voltage protection of IGBT modules are also important aspects of stacking, and were reported in this study. The second purpose of this study was to investigate the switching performance of both magnetically coupled and optically coupled stacks, in pulse power applications such as Pulse Electric Field (PEF) inactivation of microorganisms and UV light inactivation of food-related pathogenic bacteria. The stack, consisting of 50 1.2 kV IGBTs with the voltage and current capabilities of 10 kV, 400 A, was incorporated into a coaxial cable Blumlein type pulse - generator and its performance was successfully tested with both magnetic and optical coupling. As a second application of the switch, a fully integrated solid-state Marx generator was designed and assembled to drive a UV flashlamp for the purpose of microbiological inactivation. The generator has an output voltage rating of 3 kV and a peak current rating of 2 kA, although the modular approach taken allows for a number of voltage and current ratings to be achieved. The performance of the switch was successfully tested over a period of more than 10⁶ pulses when it was applied to pulse a xenon flashlamp