Hardware-Based Modulation Strategy to Suppress the Leakage Current for Transformerless Odd-Module Cascaded H-Bridge Inverter in PV System

Transformerless cascaded H-bridge (CHB) grid-connected inverters are widely used in engineering due to its advantages in volume, cost, and efficiency. However, the lack of electrical isolation results in a leakage current loop between the system and earth, creating additional electromagnetic interference and safety issues First, the CHB model with parasitic capacitance is established, and proved that the leakage current of odd-module CHB (OM-CHB) cannot be suppressed solely by modulation. Then, a new hardware-based pulsewidth modulation (HB-PWM) strategy is proposed to suppress the leakage current of OM-CHB. In the proposed strategy, two new redundant states are created by adding two power switches in the intermediate module. These extra switching states are applied to the HB-PWM strategy, which can eliminate the high-frequency component of the sum of parasitic capacitive voltage (SPCV), thus, suppress the leakage current, and available generalizes to CHB with arbitrary odd-module. Finally, the effectiveness of the proposed method is verified by a MATLAB/Simulink simulation model and an experimental prototype with a rated power of 550 W. The experimental results show that the SPCV of the proposed method does not contain high-frequency components, and the value of the leakage current meets the standard of VDE 0126-1-1.