Adaptive Virtual Inductor‐Based Current‐Limiting Control Strategy and Transient Stability Design for Grid‐Forming Converters Under Symmetrical Grid Faults

ABSTRACT Under severe symmetrical grid faults, grid‐forming (GFM) converters may suffer from excessive fault currents and transient stability issues. To restrict fault current, current limiters provide a simple and effective solution. However, they convert GFM control into grid‐following control, leading to the loss of voltage‐source characteristics. Virtual impedance–based methods can preserve the voltage‐source behaviour of GFM converters during faults. However, the commonly used resistive–inductive virtual impedance introduces power coupling, surplus capacity requirements, and small‐signal stability issues. Therefore, an adaptive virtual inductor (AVI)‐based current‐limiting control strategy is proposed. This strategy introduces an output current amplitude control loop to dynamically adjust the virtual inductance, thereby limiting the fault current while enhancing reactive current injection capability. In addition, the small‐signal stability and virtual inductance gains are investigated by establishing a small‐signal model of the output current amplitude control loop. The AVI control strategy proposed in this paper not only achieves power decoupling but also ensures that the fault current accurately tracks the current limit reference under any symmetrical fault conditions. Consequently, precise reactive current injection is guaranteed, thereby satisfying national grid code requirements. A large‐signal model is further developed to analyse transient stability using P–δ curves and phase portraits. Based on this analysis, an enhanced transient stability design method is proposed, in which a power‐reference regulation term is incorporated into the active power reference to ensure transient stability while expanding the critical power angle. Finally, simulation and experimental results are presented to validate the feasibility and effectiveness of the proposed method.