Effect of connection cable impedance on multi-inverter parallel system and an optimized controller with zero steady circulating current

The effect of the connection cable impedance on the performances of individual inverter and multi-inverter parallel system is analyzed based on the small signal model. The theoretical analysis and the simulated results show that the cable impedance has little impact on the individual inverter performance, but it has great effect on the multi-inverter parallel system, even it may result in instability. Furthermore, the relationship of the gain of the current-sharing loop and the steady circulating current is observed. A novel optimized PR controller with infinite gain at the fundamental output frequency is proposed to minimize the circulating current. Two experimental 220 Vac /1 kW inverters are built and paralleled to verify the theoretical analysis.