Filter-Less Sub-Multilevel DC/AC Power Converters for MV Connection

DC Smart Grids based on renewable energies are emerging as a tangible reality. Nevertheless, some transitional technologies are required toward the advent of DC distribution networks. In this phase, interlink power converters between DC and AC grids play a fundament role in the connection with the MV existent power system. The authors want to investigate filter-less DC/AC power converter topologies providing direct connection of available PV sources to the MV AC grid. The focus is on medium power class converters avoiding the double power conversion stage (DC/DC converters). The aim of this study is to present and compare some sub-multilevel converters adopted as PV string inverters with multiple inputs and to discuss design, performance, feasibility. A hybrid cascade configuration based on sub-multilevel cells is also discussed. The performances are analyzed on the basis of number of power devices, power quality, efficiency, total withstanding voltage. Advantages and disadvantages of the presented converters are highlighted.