Suppressing leakage current for cascaded H-bridge inverters in renewable energy and storage systems

Leakage current in a transformerless cascaded H-bridge inverter is a problem that deteriorates the system performance and causes safety concerns. In this paper, a common-mode equivalent circuit is established for analyzing the occurrence of leakage current in an m-level cascaded H-bridge inverter with either asymmetrical or symmetrical inductance output filter configurations. The analysis provides a comparison between traditional phase shifted pulse width modulation, phase disposition pulse width modulation and the proposed leakage current reduction pulse width modulation. It is reported that grid leakage current cannot be suppressed in an asymmetrical inductance filter configuration solely based on modulation methods. The proposed LCRPWM pulse width modulation can effectively reduce the grid leakage current in a symmetrical filter configuration nine-level cascaded H-bridge inverter. Simulation and experimental studies for aforementioned methods are provided and their performances are evaluated.