Transient stability analysis and enhancement of wind farm integrated VSC-HVDC system

Following severe faults in wind farm integrated voltage source converter (VSC) based high-voltage direct current (HVDC) system, wind turbines (WTs) may lose synchronization with wind farm side VSC (WFVSC), which jeopardizes the reliable delivery and consumption of wind power. This paper investigates the transient stability mechanism and enhancement strategy of wind farm integrated VSC-HVDC system considering the interactions between AC voltage control (AVC) of VSC and phase locked loop (PLL) of WT. First, a 4th-order transient stability model considering the dynamics of AVC and PLL is established. Second, the transient stability mechanism of wind farm integrated VSC-HVDC system is analyzed by the equivalent swing equation and equal-area criterion. Based on the findings of the analysis, a novel strategy utilizing both the capabilities of WT and WFVSC is proposed to improve the transient stability. Third, the interactions between AVC and PLL and other paramters's effects are revealed by using the 4th-order model and numerical integration method. Besides, the effects AVC on the transient stability are further analyzed by region of attraction analysis. Finally, intensive simulations verify the theoretical analyses and the efficacy of the transient stability enhancement strategy.