The role of diodes in the leakage current suppression mechanism of decoupling transformerless PV inverter topologies

Conventional DC/AC inverters used for the integration of photovoltaic (PV) energy sources to the utility grid are known to give rise to ground leakage currents, which can damage the PV cells and cause safety hazards. A modern solution to the leakage current problem is offered by transformerless PV inverter topologies. This paper focuses on the class of decoupling transformerless topologies and provides a complete explanation of their leakage current suppression mechanism, by considering the commonly neglected role of the inverter diodes. It is demonstrated that, apart from additional semiconductor switches, the diodes are essential for achieving leakage current suppression, while the leakage current that flows through them radically affects the waveform of the inverter common-mode voltage. The presented analysis is supported by simulation results in MATLAB-Simulink.