Current-Limiting Control for Low-Voltage Ride-Through of GFM Converters Based on Capacity Constraints and Adaptive Virtual Impedance

Abstract

Grid-forming (GFM) converters are prone to overcurrent during low-voltage ride-through (LVRT) because of their voltage-source characteristics and the limited overcurrent capability of power semiconductor devices. To address this issue, this paper proposes an LVRT current-limiting strategy based on capacity constraints and adaptive virtual impedance. A dynamic power capacity boundary is constructed based on the voltage at the point of common coupling (PCC) and the maximum allowable converter current. The active and reactive power references are reconstructed online according to the reactive-power-priority principle, ensuring that the power commands remain within the achievable operating range of the converter. The virtual impedance is adjusted dynamically according to the voltage sag depth and the output current deviation. This adjustment increases the equivalent output impedance during the low-voltage period, suppresses transient overcurrent, and enables a smooth transition during voltage recovery. Simulation studies are conducted in PSCAD/EMTDC by applying balanced three-phase voltage sags of different depths to the equivalent grid voltage source. The results show that the proposed strategy reduces the peak output current while satisfying the reactive power support requirement. It also prevents sustained overcurrent during the low-voltage period and improves the LVRT capability of the GFM converter.