Abstract: With the implementation of the "emission peak, carbon neutrality" strategy, the proportion of renewable energy is increasing, and the grid strength of the power system is getting weaker. This leads to high transient over-voltage problems caused by AC short circuits. The paper analyzes the impact of phase-locked loop (PLL) dynamics on the transient over-voltage in a voltage source converter (VSC) due to switching delays after low voltage ride-through (LVRT). The results show that the point of common coupling (PCC) voltage phase generally jumps backward at the moment of fault clearing, and the reactive current during the switching delay no longer equals the reference value due to PLL. When VSC only injects reactive current during LVRT, the phenomenon will improve the transient over-voltage. However, if the active current is injected simultaneously, the transient over-voltage level may deteriorate under some parameters of PLL. In addition, this paper also analyzes the principle of PLL parameter adjustment to ensure that the PLL dynamics improve the transient over-voltage. Electromagnetic transient simulation by MATLAB verifies the results.