Stability Analysis of Adaptive Virtual Impedance-Based Current Limitation of Grid-Forming Inverters

The adaptive virtual impedance (AVI)-based solution is an effective method to restrict the output overcurrent of grid-forming inverters during voltage-dip faults. Differing from the state-of-art conclusion that a large adjustment coefficient is beneficial for the current limitation, it is found in this paper that the system may lose stability as the increase of adjustment coefficient. A simplified model is established based on the discrete dynamics. It is revealed that a large adjustment coefficient will make the absolute value of the derivative at the fixed point greater than one leading to instability. The critical value of the adjustment coefficient is derived and the best effect that the AVI-based scheme can realize is also given. Finally, the analysis is confirmed by the verification results.