State Key Laboratory of Power Transmission Equipment & System Security and New Technology(Chongqing University), Chongqing 400044, China

In the large-scale grid-connected photovoltaic(PV)system, the multi-inverter paralleled structure is used to improve the capacity of the system. According to this structure, as PV capacity is increased, the value of grid impedance can be equivalently enlarged with respect to a single PV power generation unit, which will directly result in failure of the control strategy for inverters, and finally a failure of connecting the PV system to grid. Based on the switch averaged model of the grid-connected PV system, this paper analyzes the influence of grid impedance on inverter output current and voltage. Then, by the output current feedback method, the automatic coordination between reference current and actual output current is realized to equivalently eliminate the influence of grid impedance on the stability of grid-connected voltage and the power quality, so as to guarantee the normal operation of system. Finally, the correctness of the theory is verified by the simulation analysis and experiment.