Abstract: Under high permeability, LCL filtered grid-connected inverters may cause system instability due to the interaction of phase locked loop (PLL) and grid impedance. Based on the above background, the equivalent control block diagram of PLL considering the influence of grid impedance is established. By using the function relation between the output phase angle of PLL and the disturbance quantity, the main reason of the system robustness decline is revealed, and the main disadvantages of the traditional pre-filter PLL are analyzed. In view of this, from the perspective of optimizing the control structure of PLL, a new design scheme of PLL is proposed, and the equivalent transfer function of the proposed PLL is deduced. At the same time, the specific parameter design method is given through the design example. Theoretical analysis shows that the proposed new PLL has the same harmonic attenuation characteristics as the traditional pre-second-order low-pass filter PLL, the robustness of the system is guaranteed, and the unit power factor of grid connected common point can be realized without additional phase compensation link. Finally, the effectiveness of the proposed new PLL design scheme is verified by simulation and experimental results.