Research on cascade multilevel inverter with single DC source by using three-phase transformers

Abstract

One of the most significant recent advances in power electronics is the multilevel inverter. Using this concept the power conversion is performed with enhanced power quality. In this scenario cascade H-bridge multilevel inverter (CHBMLI) is an exceptional one and it has many inherent benefits like: (1) its modular structure, (2) it can be easily implemented through the series connection of identical H-bridges, (3) generate near sinusoidal voltages with only fundamental frequency switching and finally and (4) no electromagnetic interference or common-mode voltages. This flexibility has resulted CHBMLI topology in various applications like medium-voltage industrial drives, electric vehicles and the grid connection of photovoltaic-cell generation systems. But one of the major limitations of the cascade multilevel converters is requirement of isolated dc voltage sources for each H-bridge, this increases the converter cost and reduces the reliability of the system. This drawback is the key motivation for the present work. The present paper investigates different cascade multilevel inverter (CMI) based topologies with reduced dc sources and finally the proposed CMI with single dc source by employing low frequency transformers is presented. Proposed topology significantly reduces size when compared with conventional topologies and increases the reliability. To verify the performance of proposed architecture, prototype experiments are carried out and adequate results are presented.