Transient Overcurrent Suppression and Fault Ride-through Strategy for Grid-forming DFIGs Based on Flux Linkage Tracking Control

Virtual synchronous generator (VSG) technology is widely investigated and applied for doubly-fed induction generators (DFIGs) to provide virtual inertia. However, under grid faults, the conventional VSG-based DFIG faces challenges of transient overcurrent and instability. The critical limitation for grid-forming DFIGs to withstand serious grid faults is the rotor-side converter (RSC)'s inability to quickly generate proper rotor voltage to counteract transient electromotive force (EMF), which results in transient overcurrent and damage to the RSC. To fill this gap, this study introduces a novel low-voltage ride-through (LVRT) control strategy for the grid-forming DFIG under symmetrical grid fault conditions. To mitigate transient overcurrent, the core mechanism is to regulate the rotor flux linkage to align with the stator flux linkage in an optimal proportion. Under the proposed control strategy, both post-fault rotor current and required rotor voltage are constrained within operational limits. Moreover, fluctuations in electromagnetic torque are efficiently suppressed during grid disturbances. Consequently, the dynamic stability and power support capacity of the DFIG system remain intact throughout the transient process. Finally, simulation studies and experimental results are provided to verify the feasibility of the proposed approach.