Control of circulating current for direct parallel grid-connected inverters in photovoltaic power generation

The generating mechanism of circulating currents for direct parallel photovoltaic grid-connected inverters is analyzed in detail at first. Then state average model of the parallel photovoltaic grid-connected inverters is constructed in dq rotating coordinates. Based on this model, interaction between the parallel photovoltaic grid-connected inverters is analyzed and the influence on circulating current when it is used zero vectors with space vector pulse width modulation (SVPWM) is also analyzed. The paper adopts a novel method based on which the circulating current can be effectively inhibited by controlling the operation time for different zero vectors in each PWM cycle. The simulated and experimental results show that the control strategy can effectively inhibit circulating current, so the feasibility and correctness.