Study of Control for Grid Connected Transformerless Photovoltaic System with Improved Modulation Method

This paper discusses the modulation method to suppress the ground current for the single-phase grid-connected photovoltaic inverters. Hybrid modulation (HPWM) is a commonly modulation method for the single-phase inverters. But its application in the non-isolated photovoltaic grid-connected inverters will lead to large ground current. This paper establishes the common-mode model for the parallel single-phase gridconnected inverters with a front-end DC-DC boost converter. The expression of the ground current is given. An improved hybrid modulation method is proposed. The influence of the modulation mode and the circuit parameters on the inter-phase circulating current is also analyzed. The MPPT control algorithm is selected and the control loop for the system is designed based on PI control and repetitive control. The simulation results are given to verify the design based on Matlab\Simulink.