This work presents and discusses the application of power electronics for the integration of several distributed generation sources, as well as those related to it, the microgrids and the smart grids, to the power sector. Trends and challenges are addressed for the area of study and an embracing overview of the main technologies and techniques is presented for future investigation. As there are many power electronics devices available for employment, in each one of these crucial, modern, sustainable electrical systems, it is important for students, researchers and professionals to understand and compare the state of the art of them all, for the right choice in their respective uses. These apparatuses not only allow grid matching, but also provide new functions that enhance these artifacts’ operations, and of the entire power system. Thus, in this paper, the relationship between power electronics and distributed generation is detailed, with the role and classification of each static converter for the improved operation of wind power, photovoltaic systems, fuel cells, small hydro and microturbines exposed. While the first two are more widely covered in the literature, the last three are rarely discussed and differentiated, in terms of their power electronics interfaces. Then, the same is made for microgrids and smart grids, also scarcely approached in other works, with regard to the characteristics of the power converters applied, confirming their superior performances with the use of power electronics. Finally, conclusions are given.

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Microgrids are relatively smaller but complete power systems. They incorporate the most innovative technologies in the energy sector, including distributed generation sources and power converters with modern control strategies. In the future smart grids, they will be an essential element in their architecture. Their potential to offer many economic, social and environmental services through advanced electrical techniques has led to a growing interest in the theme. Although the islanding condition is a very important feature of microgrids, only with the implementation of grid connection and seamless transition they will demonstrate their full capacity. However, there are still many questions surrounding these operation modes and this paper tries to answer part of them. To do that, several aspects in the field are approached. The history and late development of microgrids are revisited. The main concepts are presented. The islanded mode is revised, since it is intrinsically linked to the other working states of the microgrid. The requirements for the interconnection of microgrids to an external grid are discussed. The operation elements are also analyzed. A crucial part of the grid-connected microgrids and their seamless transfer conditions, the control methods found in the literature are extensively reviewed. The paper is concentrated in the analysis of control methods for AC microgrids and AC power systems, therefore, it does not enter in detail or investigates profoundly the topologies applied in the power electronics structures nor DC microgrids and DC power systems.INDEX TERMS Microgrid, grid-connected mode, seamless transition, islanded mode, droop control, distributed generation, smart grid, power electronics.

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RESUMOO aumento no consumo de energia elétrica, o surgimento e a expansão de tecnologias inovadoras como a geração distribuída, a eletrônica de potência e os dispositivos de armazenamento de energia, a falta de acesso à eletricidade para milhões de pessoas e as preocupações com o meio ambiente e as mudanças climáticas estão mudando radicalmente o sistema elétrico. Estas condições fizeram nascer um forte interesse sobre as microrredes elétricas modernas. Unindo produção, distribuição e uso de energia elétrica em uma estrutura única, avançada, pequena e local, elas podem resolver grande parte dos problemas contemporâneos do setor energético, melhorar a vida das pessoas e tornar suas atividades econômicas mais sustentáveis. Todavia, há ainda pouca compreensão profunda sobre o tema. Neste contexto, o objetivo deste artigo é elucidar os conceitos fundamentais envolvendo microrredes, fornecendo uma visão geral sobre o assunto. Inicialmente, elas são definidas e suas características são apresentadas. Em seguida, sua história e sua situação atual de desenvolvimento são analisadas. Seus componentes principais, ou seja, os recursos energéticos distribuídos, os conversores estáticos, a proteção, a cogeração e as cargas, são investigadas. Por último, as técnicas de controle para microrredes são categorizadas e discutidas.