Abstract: Compared with analog control,the LCL grid-connected inverter with digital control will introduce control delay,which significantly reduces system stability in weak grids with substantial grid impedance variations. Then a proportional-phase lag compensation strategy is proposed to enhance the robustness of the digital controlled LCL-type grid-connected inverter against variations in grid impedance. Firstly,the stability of the system within a broad range of grid impedance variation is analyzed,taking into account the control delay. Then the stable region is identified based on Nyquist stability criterion,and the parameters of the proportional and phase lag compensator is reasonably designed so that the improved system can still operate stably even when the grid impedance varies widely. Finally,simulation and semi-physical experimental results can verify the feasibility and effectiveness of the proposed method.