Adaptive droop-controlled grid-forming inverters with fast transient and current limiting under grid voltage sag faults

Grid-forming (GFM) inverters are considered a promising solution for integrating renewable energy into the grid. However, during grid voltage sag faults, GFMs face critical challenges, including synchronization instability, prolonged recovery time, and overcurrent issues. To address these challenges, an adaptive droop-controlled GFM strategy is presented. The proposed method employs virtual impedance combined with a virtual power angle limiting scheme to ensure effective current limiting and transient stability under large disturbances. The impact of this strategy on post-fault recovery time is analyzed, and an adaptive droop control strategy is proposed to enable the inverter to resume normal operation rapidly after fault clearance. Furthermore, combined with a frequency-feedforward approach, the proposed method guarantees improved dynamic current response and effectively eliminates transient current overshoot. The effectiveness is verified by simulations and hardware-in-loop experiments.