Transient Stability Analysis Between SG and Grid-forming VSCs with Current Saturation Control Considering Backward-swing DynamicsOA

This paper analyzes the transient angle stability between synchronous generators(SGs)and grid-forming voltage source converters(GFM-VSCs),considering backward-swing dynamics.The impact mechanism of current saturation control(CSC)on the backward-swing and forward-swing stability is addressed.Based on the second-order rotor motion equation,the conventional energy-based method for transient stability evaluation becomes rough driven by the interactions between SG and GFM-VSC.To overcome the barrier,a forward-time integral(FTI)method is proposed for calculating the critical clearing time(CCT).We discover that the CSC can affect the stable and unstable equilibrium points of the post-fault system,leading to both the backward-swing and forward-swing synchronism instability.Based on the mechanism,an enhanced synchronization control(ESC)is proposed.It combines a modified frequency control with a current-limit strategy to avoid backward-swing instability while enhancing forward-swing stability.Time-domain simulation verifies the theoretical analysis as well as the effectiveness and robustness of the proposed ESC.