Fault Ride-Through Strategy for Grid-Forming Photovoltaic Systems under Unbalanced Voltage

This paper investigates the grid-forming control strategy for two-stage photovoltaic (PV) systems, focusing on addressing current imbalance and low-voltage ride-through (LVRT) challenges under grid asymmetric faults. An enhanced dual closed-loop positive/negative sequence decoupling control method is proposed: the positive- and negative-sequence components of grid voltage are separated using a real-time sequence decomposition algorithm, and reverse compensation currents are actively injected into the current control loop to suppress negative-sequence current components. Combined with virtual impedance technology, this method achieves rapid fault current limiting for inverter output. Simulation results demonstrate that under single-phase or two-phase short-circuit faults, the proposed strategy confines the PV inverter's fault current within safe limits while ensuring balanced three-phase operation and maintaining voltage-source characteristics to provide active voltage support. This method offers a reliable solution for renewable energy power stations to address extreme voltage imbalance scenarios, holding significant engineering value for the stable operation of integrated wind-PV-storage grids.