Optimal placement of additional switch in the photovoltaic single-phase grid-connected transformerless full bridge inverter for reducing common mode leakage current

Single phase converters are popular for grid connected applications at low power. In photovoltaic (PV) application, it is possible to remove the transformer from the PV system in order to improve the efficiency and reduce losses, size, and cost. The direct conductive connection of the grid and the DC source through transformerless PV inverter introduce a leakage current. Stray capacitance between the earth and the PV panels cause to the leakage current. This current increases current harmonics injected into the utility grid, the radiated and conducted electromagnetic emissions, and losses. Spectrum and amplitude of the leakage current depends on the converter topology, switching strategy and the resonant circuit formed by the parasitic capacitance, the AC filter, the converter and the grid. In this paper, an additional switch is added to the full-bridge inverter to reduce the common mode leakage current. Then the fifth switch is located in four places and the MATLAB/SIMULINK simulation results of these four configurations are presented and compared. Finally, the optimized placement for this switch is investigated based on simulation results.