When the PV inverter is connected to the weak grid,it will couple with the time-varying grid impedance to affect the stability of the system and even lead to harmonic resonance problem. Firstly,the equivalent circuit model of LCL-type PV inverter parallel system is established. The stability condition of the grid-connected PV inverter system under weak grid condition is analyzed by impedance analysis method. It is concluded that the output impedance of the inverter and the grid impedance have a certain phas...