In modern power systems with a high penetration of renewable energy, the issues of synchronization instability and fault current limit violations in grid-forming (GFM) converters, triggered by deep grid voltage sags, are becoming increasingly prominent. To address the low voltage ride-through (LVRT) requirements for GFM converters, this paper investigates the fault capability of droop control that incorporates a low-pass filter. In the absence of current limiting measures, the paper analyzes the GFM converter fault ride-through characteristics by plotting phase-plane diagrams for post-fault conditions, considering different depths of voltage sags, for cases where an equilibrium point on the power-angle curve either exists or does not. When current limiting measures are activated, the theoretical conditions for the GFM converter's transition between normal operation and current-limiting modes are established based on thed-axis current priority method. By plotting power-angle curves, the fault recovery trajectories of the converter are systematically analyzed under various depths of grid voltage sags. Finally, the correctness of the theoretical analysis is verified through simulations.
Zhong et al. (2026) studied this question.