Adaptive Coordination of Rotor Inertia and Super-Capacitor Storage for Fault Ride Through of DFIG Wind Turbines

The direct stator connection of a doubly fed induction generator (DFIG) makes it highly sensitive to grid-voltage disturbances. Although a supercapacitor-supported dynamic voltage restorer (SC-DVR) can restore the machine-terminal voltage, assigning the entire fault-induced power imbalance to the supercapacitor increases the required storage capacity. To address this problem, an adaptive coordinated fault ride-through control strategy is proposed for a DFIG–SC-DVR wind–storage system. A unified dynamic model is first established to describe the electromagnetic response, dc-link energy imbalance, rotor kinetic-energy exchange, and series voltage compensation under symmetrical and asymmetrical voltage sags. The remaining adjustable kinetic-energy margin of the rotor and the remaining adjustable energy margin of the supercapacitor are then used to construct an online coordination coefficient. Accordingly, the active-power references of the DFIG and SC-DVR are dynamically adjusted to match their instantaneous regulation capabilities. Time-domain simulations show that the proposed strategy maintains the machine-terminal voltage and keeps the rotor current, dc-link voltage, and rotor speed within prescribed limits. Compared with non-coordinated control, it reduces the SC-DVR absorbed energy by 51.43% and 57.72% under symmetrical and asymmetrical faults, respectively; compared with fixed-ratio coordination, the corresponding reductions are 34.69% and 29.81%. Supplementary sweeps over wind speeds of 10–12 m/s and short-circuit ratios of 2–10 further verify the bounded applicability of the method without retuning the controller.