Low Voltage Ride Through Strategy for Grid-Forming Converters Based on Adaptive Line Impedance and Current Constraint

To address the challenge of balancing voltage support and current limitation in grid-forming converters (GFCs)—a challenge induced by the uncontrollability of active power during transient faults in microgrids and weak grids—a low voltage ride through (LVRT) strategy utilizing adaptive virtual impedance with a variable resistance-to-inductance ratio is proposed. This strategy is designed to maximize the satisfaction of reactive power support and current limiting characteristics. By adaptively generating virtual impedance based on changing line parameters, the method enables adaptation to large disturbance conditions involving variations in line impedance and Short Circuit Ratio (SCR). First, a transient model of the virtual impedance for GFCs is established to clarify the transient instability mechanism. During the transient period, the power loop is controlled to prevent power angle divergence. Second, the influence mechanism of virtual impedance on reactive current and output current during transients is analyzed. By integrating inrush current limitation and LVRT requirements, an adaptive virtual impedance control strategy is formulated to achieve collaborative optimization of transient LVRT and current limiting. Finally, the effectiveness of the proposed control strategy is verified through MATLAB/Simulink simulation experiments.