Impact of the PLL’s Phase Delay Effect on the Stability of the Weak-Grid-Tied Grid-following VSCs

This paper develops a simplified model to analyze the impact of the PLL’s phase delay effect on the active power control stability. The novel simplified single-input single-output (SISO) model is developed and used to analyse the impact of the PLL and the non-minimum phase zeros on the stability margin of the active power control. We find that the PLL produces a phase delay effect due to the right half plane non-minimum phase zeros in weak grids, which decrease the stability and the damping. Time domain simulation results validate the analysis in this paper.