MODULATION STRATEGY TO REDUCE LEAKAGE CURRENT IN TRANSFORMERLESS CASCADED MULTILEVEL INVERTER FOR GRID-CONNECTED SOLAR SYSTEM

Abstract

The transformerless cascade multilevel H – bridge inverters have been popularized in the application of solar system due to the advantages of low cost and high efficiency. However, the topology makes a path for leakage current to flow through parasitic capacitance formed between the PV module and the ground. Hence, this paper first establishes the common-mode equivalent model of the inverter with the parasitic capacitance, and analyzes the characteristics of leakage current in the symmetrical and asymmetrical inductance circuit respectively. The analysis shows that the leakage current can be eliminated through optimizing the modulation methods for symmetric circuits, while with asymmetric circuits it is impossible. In this parper, we propose a modified phase disposition pulse width modulation strategy (MPDPWM) for the symmetrical circuit which can eliminate the leakage current effectively with simple implementation. Finally, simulation results are reported along with evaluation and comparison results against a Phase Disposition Pulse Width Modulation (PDPWM) and Hybrid Multicarrier Pulse Width Modulation (H-MCPWM)