Transient Voltage Stability Analysis and Enhancement of Grid-Following Converters Considering Current Limitation

High penetration of renewable energy resources is widely connected to the grid via grid-following converters, which may threaten the transient voltage stability of the system. However, most researchers only pay attention to the transient voltage stability of inductive motors in the electromechanical transient time scale, and the electromagnetic dynamics of voltage source converters (VSCs) are ignored for simplicity. Therefore, the potential transient voltage instability risk of the system in the electromagnetic transient time scale is concealed. To fill this gap, the transient voltage instability mechanisms for grid-following VSCs with various control strategies are revealed, which can be concluded that the positive-feedback process after the state variable exceeds the unstable equilibrium point is the main cause. Then, the effect of the current limitation of VSCs on the transient voltage stability and transient performance of the system is theoretically illustrated. On this basis, the indexes for transient voltage stability margin considering the active power recovery process are presented, and a robust current limitation based stability enhancement scheme is proposed to stabilize the system. Simulation results verify the correctness of the theoretical analysis and the effectiveness of the proposed control strategies.