Two-Stage Frequency Response Strategy for DFIGs Based on Adaptive Speed–Frequency Coordinated Optimization

Doubly fed induction generators (DFIGs) may suffer from excessive rotor deceleration during frequency support and secondary frequency drop (SFD) during rotor speed recovery. To address these issues, this paper proposes a two-stage frequency response strategy for DFIGs based on adaptive speed–frequency coordinated optimization. In the frequency support stage, the strategy simultaneously considers the initial rotor speed and real-time speed, thereby dynamically characterizing the remaining kinetic energy of the wind turbine and its release process. This allows the turbine to improve the system frequency secondary frequency drop and extend the effective support time under high-wind-speed conditions, while actively limiting support intensity under low-wind-speed conditions. In the rotor speed recovery stage, a DFIG rotor speed recovery method based on dynamic adaptive adjustment of recovery time is proposed. This method converts the conventional Rate of Change of Frequency (RoCoF) security constraint into a ramp rate constraint on the withdrawal of wind power and, combined with the turbine’s kinetic energy recovery capability, iteratively determines the recovery time online. This coordination ensures that the power withdrawal process aligns with the primary frequency regulation response of synchronous generators, thereby reducing the risk of SFD. Simulation results validate the effectiveness of the proposed strategy.