Enhanced Common-Mode Voltage Suppression in a Modified Three-Phase Four-Leg Quasi-Z-Source Inverter

In order to solve the leakage current issue in transformerless grid-connected photovoltaic (PV) systems due to common-mode voltage (CMV) fluctuations, this paper analyzes the CMV in a quasi-Z-source inverter (q-ZSI), and more importantly, a modified three-phase four-leg q-ZSI is proposed. Compared with the conventional q-ZSI, it not only suppresses the CMV by splitting the input inductance into two pieces so that the CMV is shared between the source and the grid ground, but also adds a fourth leg, which improves the voltage utilization and has a wide voltage gain range, which is very suitable for distributed power generation, especially for PV systems. In addition, this modified four-leg inverter further suppresses CMV by using an innovative modulation method. Simulation results validate the effectiveness of the proposed strategy.