Scaled Current Tracking Control for Doubly Fed Induction Generator to Ride-Through Serious Grid Faults

For doubly fed induction generator (DFIG)-based wind turbine, the main constraint to ride-through serious grid faults is the limited converter rating. In order to realize controllable low voltage ride through (LVRT) under the typical converter rating, transient control reference usually need to be modified to adapt to the constraint of converter's maximum output voltage. Generally, the generation of such reference relies on observation of stator flux and even sequence separation. This is susceptible to observation errors during the fault transient; moreover, it increases the complexity of control system. For this issue, this paper proposes a scaled current tracking control for rotor-side converter (RSC) to enhance its LVRT capacity without flux observation. In this method, rotor current is controlled to track stator current in a certain scale. Under proper tracking coefficient, both the required rotor current and rotor voltage can be constrained within the permissible ranges of RSC, thus it can maintain DFIG under control to suppress overcurrent and overvoltage. Moreover, during fault transient, electromagnetic torque oscillations can be greatly suppressed. Based on it, certain additional positive-sequence item is injected into rotor current reference to supply dynamic reactive support. Simulation and experimental results demonstrate the feasibility of the proposed method.