College of Electrical Engineering, Zhejiang University, Hangzhou 310027, China

The increasing penetration of power electronic devices in power grids has led to a decrease in grid strength and inertia, and the transient synchronization stability problem under grid faults is becoming more and more prominent. To address the transient loss problem of grid-connected inverters during weak grid faults, a transient synchronization model for grid-connected inverters is developed considering the phase-locked loop damping and the initial angular velocity at the moment of fault occurrence. The influence law of variations in phase-locked loop damping and initial angular velocity on transient synchronization stability is analyzed. Furthermore, an additional damping control method of phase-locked loop based on the feedback correction of frequency deviation is proposed to enhance the transient synchronization stability of grid-connected inverters. To address the transient loss problem posed by serious grid faults without stable equilibrium points, a dynamic compensation method for output angular velocity of phase-locked loop is proposed to achieve the stable operation of the system after fault recovery. Finally, a hardware-in-the-loop experimental platform is constructed to verify the theoretical analysis and control methods.