Multilevel converters for renewable energy systems

In an attempt to decrease the cost of energy, increase the energy conversion efficiency, reliability, power density, and comply with the stringent grid codes, the power electronic converters have emerged in a rigorous manner. In contrary to the standard practice of using multilevel converters for high-power and medium-voltage power conversion systems such as wind energy, the current industry also uses multilevel converters for low-voltage, low-power, high-performance, high-efficiency, high-power-quality applications such as photovoltaic energy. This chapter provides an overview of multilevel converters used in wind and photovoltaic energy systems. From the market-based survey, the most successful multilevel converter configurations are addressed along with few promising topologies available in the literature. For wind energy systems, the multilevel converters are classified into four categories: back-to-back connected converters, passive generator-side converters, multiphase generator-side converters, and direct ac-ac converters. The central, string, and multistring inverter configurations for photovoltaic energy systems are also discussed with respect to the configuration and operation.