A Novel Leakage Current Attenuation Method for Nonisolated Odd-Module Cascade H-Bridge in Single-Phase PV System

Nonisolated (NI) cascaded H-bridge (CHB) grid-connected inverter (GCI) is widely used in photovoltaic (PV) systems. However, the lack of electrical isolation results in leakage currents, which raises safety concerns. First, the CHB model with parasitic capacitance is established, proving that leakage current is positively correlated with the differential value of the sum of parasitic capacitive voltage (SPCV), and the inability to suppress odd-module CHB (OM-CHB) leakage current by modulation alone. Second, a universal method for leakage current suppression in OM-CHB is proposed, which is done by dividing modules into symmetric group and intermediate module to eliminate high-frequency components (HFCs) of the SPCV separately. For a symmetrical group, a mechanism of differential-mode voltage (DMV) cancellation and common-mode voltage (CMV) constant is designed. For the intermediate module, the new constraint without HFC is derived. Then, hardware modification is employed in the intermediate module according to the new constraint, oH5 topology is selected for its fewer extra devices, and an optimized phase disposition pulsewidth modulation (OPD-PWM) strategy is proposed. The proposed method applies to any OM-CHB and is unaffected by dc voltage and switching frequency. Finally, the validity of the proposed method is verified by MATLAB/Simulink simulations and testing on a 550-W prototype.