Current Limiting Strategy for Grid-Forming STATCOM Based on Individual Phase Control

The increasing penetration of renewable energy sources has significantly weakened the power grid's stability. Grid-forming STATCOM, characterized by its voltage source behavior, provides a reliable approach to improving system voltage stability and damping. However, it is prone to overcurrent due to sudden voltage dips. In this paper, an adaptive current-limiting control method based on individual phase control is proposed. It eliminates the need for sequence component separation and transformations among multiple reference frames. For a star-connected cascaded STATCOM, a grid-forming individual phase control based on instantaneous current tracking through a proportional-resonant (PR) controller is first presented. Based on this, an adaptive virtual impedance current-limiting strategy for each phase is developed. It integrates virtual impedance control for sustained current limiting throughout the fault duration and instantaneous overcurrent peak suppression. The key parameters are then designed by considering the most severe fault scenarios. Finally, the effectiveness of the proposed strategy and parameter design is validated through detailed simulation results.