A Ground Current Suppression Method for Single-Phase Photovoltaic (PV) Inverters

For single-phase PV inverter systems, when relays connected to the grid live line are switched on and the DC/AC has not yet entered Pulse Width Modulation (PWM) mode, the ground current is distorted. Because the ground current is not sinusoidal, high-frequency harmonics can easily trip the ground current protection breaker, causing the system to be disconnected from the grid. The cause of ground current distortion is investigated in this paper, and solutions to suppress ground current distortion are proposed. First, the topology and control logic for the single-phase PV inverter are explained, followed by illustration of ground current distortion. The analysis for the operation during the ground current distortion is then presented, which includes four stages. Furthermore, the voltage of the DC-bus to ground and the ground current are expressed mathematically. Based on the analysis, solutions to suppress ground current distortion are proposed, as well as the detailed concept and implementation. The ground current suppression concept is to regulate the DC-bus voltage, and four detailed implementations are presented. Finally, an experimental platform is built, and the experimental results are presented to validate the proposed method.