Synchronization Stability of PLL-Based Power Converters Connected to Weak AC Grid

In this paper, the synchronization stability of converter system based on the phase-locked loop (PLL) is studied, especially when it is connected to a weak AC grid. First, the small signal model considered PLL, power control, current control and voltage feedforward (VFF) control is built. The open-loop transfer function can analyze the stability of the system but hides the dynamic of PLL. So the conjugated circuit is proposed, which describes the dynamics of PLL and the other part separately. Based on the Bode diagrams, we explore how the grid impedance and converter controller parameters influence the stability of the system. In order to verify the analysis results, simulations are conducted in MATLAB/Simulink.