Low Voltage Ride-through Control of Grid-Forming/Grid-Following Hybrid System Based on Current Limiting Feasible Region

Abstract

: The deployment of grid-forming converters (GFMC) in weak-grid renewable energy stations can provide voltage support for grid-following converters (GFLC). However, the coupling between the two types of converters may cause the voltage-support capability of the GFMC to be constrained by its overcurrent capacity during short-circuit faults, thereby increasing the risk of transient synchronism instability. To address this issue, a voltage–current phasor coupling model of the hybrid system is first established, and the interaction between the GFMC and GFLC under fault current constraints is quantitatively analyzed. Subsequently, a transient-stability assessment method based on the critical phasor trajectory is proposed. Electrical-variable functions are constructed to determine the existence of a stable equilibrium point, and the effects of network and control parameters on the stability of the hybrid system are systematically investigated. Furthermore, a collaborative transient-control strategy based on the current-limiting feasible region is developed. By adjusting the active-power reference of the GFMC to maintain power-angle stability during the fault, the internal potential of the GFMC and the active power current range of the GFLC are coordinated to limit the fault current. Finally, simulation results verify the accuracy of the proposed assessment method and demonstrate the effectiveness and advantages of the proposed control strategy.