Analysis and reduction of common-mode ground leakage current in transformerless PV inverters with rectified sine wave DC-link voltage

Abstract An essential requirement for transformerless photovoltaic (PV) inverters is the suppression of common-mode (CM) ground leakage currents. Transformerless PV inverters normally provide a voltage step-up capability to extend energy harvesting from PV arrays. In dual-mode time-sharing transformerless PV inverter topologies, a step-up (boost) stage operates alternatively with a step-down (buck) stage to create a rectified sine wave DC-link voltage, which is then unfolded to the grid by an H bridge. This study systematically analyzes and quantifies CM leakage current generation in topologies with rectified sine wave DC-link voltage. It highlights the role of the DC-link capacitor in CM current generation, explains why its capacitance needs to be low, and relates its value to the inverter output current amplitude and power factor. Then, it presents the mechanism of CM current generation by deriving analytical expressions for CM current root-mean-square values under different modes of inverter operation. This study also focuses on the design of the output filter and considers a split-inductor configuration that can reduce CM currents by up to 70%. The theoretical results are verified by simulations in MATLAB/Simulink and experiments involving a comprehensive laboratory setup.