To address the issue of reduced system stability caused by the dynamic interaction between the phase-locked loop, grid impedance and current control loop, this paper first utilizes the Hurwitz criterion for analysis. This analytical method can reveal the inherent impact mechanism of grid impedance fluctuations on the stability margin of the phase-locked loop synchronization process, and the analysis results indicate that grid impedance is an important unstable factor in the phase-locked loop-based synchronization system. Then, a grid impedance adaptive collaborative phase-locked loop control structure is proposed. Based on the proposed improved phase-locked loop control structure, a phase correction link is added in series to the current control loop to reshape the output impedance of the grid-connected inverter, thereby significantly enhancing the robustness of the grid-connected system under weak grid conditions. Finally, simulation and experimental results confirm the accuracy of theoretical analysis, indicating the feasibility of the improved strategy.