Transient Inrush Current Analysis and Suppression for Grid-Forming Converters Under Grid Faults

Grid-forming (GFM) converters have emerged as essential technologies for ensuring the stability of power systems dominated by renewable energy sources. Nevertheless, their restricted overcurrent capacity may trigger protection during grid faults. While existing studies emphasize the design and optimization of overcurrent mitigation strategies, precise characterization of fault current and dynamic analysis of transient inrush current are still lacking, leading to occurrences of protection malfunction. To bridge this research gap, this article considers the impact of filter parameters and current loop parameters on the equivalent impedance of the converter, and on this basis, establishes a precise fault current characterization model for GFM converters. Based on the model, the key factors influencing inrush current can be analyzed, including voltage amplitude, impedance magnitude, and power angle. Finally, a precise virtual impedance-based inrush current suppression method is proposed, which effectively limits the inrush current to the desired level while ensuring system stability. Both theoretical analysis and experimental results are carried out to validate the robustness and adaptability of the proposed strategy under various grid strengths and grid voltage sags.