Analysis on low-voltage fault ride-through capability of droop control-based converter

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.