Adaptive Virtual Impedance Control Strategy Based on Grid-Forming Equivalent Model

Grid-forming converters, which behave as voltage sources, are crucial for enhancing grid stability. However, they face the risk of damage from fault currents during grid faults, which may also lead to the disconnection of new energy units. This paper proposes an adaptive virtual impedance control strategy based on the equivalent model of grid-forming converters to effectively suppress fault currents. The analysis begins with the closed-loop reactive power-voltage droop control of the converter, deriving its equivalent models for both normal operation and fault conditions with virtual impedance. Subsequently, a dynamic adjustment mechanism is incorporated into the proposed control strategy to modify virtual impedance parameters in real-time based on variations in system control parameters and grid connection voltage. This allows for efficient suppression of fault currents. Finally, fault simulations are conducted to verify the effectiveness of the proposed strategy. The results demonstrate that during severe grid faults with voltage drops to 0.2 pu, the grid-forming converter can effectively limit fault currents and achieve fault ride-through, thereby ensuring stable grid operation.