A Low-Voltage-Ride-Through Strategy for Grid-Forming Converters Based on Reactive Power Synchronization

The low-voltage-ride-through (LVRT) of grid-forming converters (GFMCs) requires that GFMCs can limit current and remain synchronized with grids under and post severe voltage sags. To avoid the instability caused by phase-locked loops during current limiting processes, GFMCs usually retain the active-power angle synchronization (P-Syn) algorithm under low voltage faults when the current saturation is triggered. When voltage sags happen, the virtual power angle stability highly depends on durations and levels of faults with the P-syn method. This paper analyzes the P-syn LVRT mechanism and proposes an LVRT strategy for GFMCs based on reactive power synchronization (Q-Syn) under voltage sags. The Q-Syn LVRT method ensures the transient stability of GFMCS regardless of fault durations or fault levels. Furthermore, stable maximum active power support within the current limit and faster recovery to normal operation can be achieved with the Q-Syn LVRT method. The advantages of the proposed Q-syn method over the P-syn method are verified in experiments.