Compensating Stator Transient Flux during Symmetric and Asymmetric Faults using Virtual Flux based on Demagnetizing Current in DFIG Wind Turbines

Abstract

Under normal working conditions, the stator flux of doubly-fed induction generators only includes the forced component; thus, controllers are mainly designed in accordance to this component. During fault conditions, in addition to this component, the zero sequence component appears. Under this new condition, the conventional control strategies cannot control the DFIG properly. So, the induced voltage in the rotor windings increases, which leads to the rotor current overshoot, overvoltage of DC link and mechanical stress caused by electromagnetic torque oscillations. In this article, a new control strategy is presented that fulfills low voltage ride through requirements by using virtual flux based on demagnetizing current. This method can improve the transient response of the stator flux during symmetric and asymmetric faults by creating a demagnetizing current to meet the grid code requirements. Finally, the validity of the proposed method is verified by the simulation results for a 1.5 MW wind turbine in MATLAB/SIMULINK environment and the results have been discussed and analyzed in the last section of the article to show the proficiency of the proposed method.