The stability of a voltage source converters(VSC)system based on phase-locked loop(PLL)is very important issue during asymmetric grid faults.This paper establishes a transient synchronous stability model of a dual-seq...The stability of a voltage source converters(VSC)system based on phase-locked loop(PLL)is very important issue during asymmetric grid faults.This paper establishes a transient synchronous stability model of a dual-sequence PLL-based VSC system during low voltage ride-through by referring to the equivalent rotor swing equation of syn-chronous generators.Based on the model,the synchronization characteristics of the VSC system under asymmetric grid faults are described,and the interaction mechanisms,as well as the transient instability phenomena of positive and negative sequence PLL during asymmetric faults are explained.Using the equal area criterion,the influences of sequence control switching action,detection delay,and interaction between the positive and negative sequence PLL on the transient synchronous stability of the VSC system are analyzed,respectively.In addition,a transient stabil-ity assessment criterion based on the critical fault clearance angle and time and an enhancement control strategy based on the improved positive and negative sequence PLL are proposed.Finally,the analytical results are validated through simulation and experiments.展开更多
基金supported in part by the National Natural Science Foundation of China under Grant 51977019in part by the Joint Research Fund in Smart Grid(U1966208)under cooperative agreement between the National Natural Science Foundation of China and State Grid Corporation of China.
文摘The stability of a voltage source converters(VSC)system based on phase-locked loop(PLL)is very important issue during asymmetric grid faults.This paper establishes a transient synchronous stability model of a dual-sequence PLL-based VSC system during low voltage ride-through by referring to the equivalent rotor swing equation of syn-chronous generators.Based on the model,the synchronization characteristics of the VSC system under asymmetric grid faults are described,and the interaction mechanisms,as well as the transient instability phenomena of positive and negative sequence PLL during asymmetric faults are explained.Using the equal area criterion,the influences of sequence control switching action,detection delay,and interaction between the positive and negative sequence PLL on the transient synchronous stability of the VSC system are analyzed,respectively.In addition,a transient stabil-ity assessment criterion based on the critical fault clearance angle and time and an enhancement control strategy based on the improved positive and negative sequence PLL are proposed.Finally,the analytical results are validated through simulation and experiments.
