Common Mode Current Reduction of Three-phase Cascaded Multilevel Transformerless Inverter for PV System

The reduction of common mode leakage current in centralized inverter for grid-connected PV (photovoltaic) system has been well studied. However, the research in cascaded multilevel inverter PV system is not far enough. This paper focuses on analyzing the generation mechanism of common mode leakage current and building equivalent circuit model of cascaded PV system. By clarifying the reason why the conventional cascaded H4 (full-bridge inverter) PV system fails to reduce the common mode leakage current, a new cascaded iH6 inverter PV system is proposed. The related theoretical analysis and simulation results are given, and it is verified that the common mode leakage current in three phase grid-connected system with proposed converters can be greatly reduced compared with the conventional cascaded H4 system.