Transient and Quasi-Steady State Fault Current Limiting Control for Grid-Forming Inverters

For grid-forming (GFM) inverters, it is challenging to limit the fault current without affecting the inverter voltage-source behaviors and simultaneously address the transient over-current problem with existing fault current limiting methods. To address this issue, a transient and steady-state fault current limiting control method with proper feedback inverter output current and feedforward PCC voltage is proposed for VSG-based GFM inverters upon grid voltage faults. The proposed method can effectively limit both transient and steady-state overcurrent as well as dampen the current dynamic oscillations. The GFM system with the proposed method can maintain its voltage-source behaviors during the fault and automatically restore normal GFM operation after the fault, improving the robustness and adaptivity of the fault current limitation. The proposed method's effectiveness and superiority are verified by theoretical analysis and comparative simulations.