Grid-connected performance optimization control strategy of DFIG with coaxial high-inertia flywheel system

The high penetration of grid-connected renewable energy has significantly reduced power system inertia, bringing critical challenges to frequency stability and voltage support. To improve the operation resilience of low-inertia systems, this paper presents a grid-connected performance optimization control strategy for the combined topology of a doubly-fed induction generator (DFIG) and a coaxial high-inertia flywheel. The DFIG stator is directly connected to the grid, and the flywheel provides fast kinetic energy support through mechanical coupling. The grid-side converter maintains stable DC voltage and unity power factor, while the rotor-side converter realizes decoupled control of stator active and reactive power. To enhance frequency stability, a system frequency response model is established, and real-time active power compensation is generated via droop and inertia control. A variable-parameter optimization strategy is further proposed to adjust droop and inertia coefficients dynamically. For grid voltage sag conditions, an optimized feed-forward transient current control scheme is adopted to enhance low-voltage ride-through capability. Both theoretical analysis and results verify that the proposed topology and control strategy can effectively improve the frequency and voltage stability of low-inertia power systems, providing technical support for the reliable operation of high-renewable power systems.