Abstract：In the background of a high proportion of new energy source connected to grid，the phenomenon of

new energy interface inverters being connected to the grid through long-distance AC lines is becoming increasingly

significant. The traditional vector controlled weak grid connected voltage source converter（VSC）based on phase

locked loop（PLL）synchronization is prone to PLL synchronization instability. To improve the PLL synchronization

stability of weakly connected VSC，an analytical model to reveal the PLL synchronization instability mechanism of

weakly connected VSC was established. Through theoretical analysis，the influence of the dynamic coupling

characteristics of PLL and different time scale control links on the PLL synchronization instability mechanism was

revealed. Based on the theoretical analysis results，a PLL dynamic compensation control strategy suitable for

multiple time scales was designed to improve the PLL synchronization stability of weakly connected VSC. The

simulation results based on Matlab/Simulink verify the correctness of the theoretical analysis and the effectiveness

of the compensation control strategy.

      Key words：voltage source converter（VSC）；PLL synchronous stability；mechanism analysis model；control

loops interaction；compensation control strategy