Research on Power Equalization and Leakage Current Suppression of Non-Isolated Cascaded H-Bridge PV Inverter Based on Hybrid Modulation

The non-isolated (NI) cascade H-bridge (CHB) grid-connected inverter (GCI) are widely used in photovoltaic (PV) systems. However, the leakage current loop is inevitably formed because of lack of galvanic isolation. This undesirable current results in additional electromagnetic interference (EMI) and safety issues. Power equalization is one of the key metrics of CHB inverter. Unfortunately, there is few research that takes into account both. To fill this research gap, firstly, the mathematical model of the five-level CHB is established and the constraints for eliminating the leakage current are derived. Secondly, the combination of the power output of each module under CHB with two-module is analyzed and preferred. Finally, a hybrid modulation strategy is proposed to achieve power equalization while effectively suppressing the leakage current. The proposed method combines traditional PD-PWM and PS-PWM, with the characteristics of low harmonics and natural power equalization. At the same time, it completely eliminates the high-frequency component of the sum of parasitic capacitor voltages, keeping the leakage current at a negligible level. Simulation and experiments have demonstrated the correctness of the above methods.