Coordinated Power Allocation in Wind Farms with Supercapacitor Energy Storage Systems for Fast Frequency Response

The increasing penetration of inverter-based resources has significantly reduced system inertia, motivating the emergence of Fast Frequency Response (FFR) as a dedicated ancillary service. Existing methods for enabling wind power systems to deliver FFR universally treat the wind farm as a single equivalent turbine under uniform wind conditions, an assumption that is invalid in real large-scale wind farms where heterogeneous turbine types, rated capacities, inertia constants, and spatially non-uniform wind speed distributions render uniform allocation strategies suboptimal or operationally unsafe. This paper proposes a centralized wind farm-level FFR control framework that coordinates heterogeneous wind turbine generators (WTGs) and supercapacitor energy storage systems (SCESSs) through a prioritized two-tier dispatch hierarchy, in which SCESSs are assigned the highest dispatch priority and WTGs are engaged only when aggregate storage capacity is insufficient. A constrained optimization problem is formulated to allocate the individual FFR contribution of each WTG by minimizing the total kinetic energy extracted from the wind farm, while enforcing torque, electrical power, and rotor speed constraints for every unit with respect to turbine type, inertia constant, and prevailing wind condition. A coordinated rotor speed recovery strategy further eliminates secondary frequency disturbances during the post-FFR transition. The proposed framework is validated on a 138 MW heterogeneous wind farm simulation model comprising both Doubly-Fed Induction Generator and Permanent Magnet Synchronous Generator units interconnected to a modified IEEE 14-bus test system. The proposed method achieves a 38.85% improvement in frequency nadir relative to a baseline with no FFR provision, outperforming all investigated state-of-the-art approaches, while reducing total kinetic energy extraction from the wind turbine generators and eliminating secondary frequency disturbances during the post-FFR recovery phase.