Modified controls for grid-connected wind-turbine Doubly Fed Induction Generator under Unbalanced Voltage Dip for Torque Stability and Reduction of Current Harmonic

This paper presents modified Stator Voltage Oriented Control (SVOC) for Doubly Fed Induction Generator (DFIG) in wind turbines to reduce torque pulsation during unbalanced voltage dips, and current waveforms are also improved with the decreasing of harmonics. The proposed schemes utilize multiple PI controllers with anti-windup to obtain commanded rotor currents and also introduce extra commanded values for rotor current; as well, Notch filters are used to eliminate the second-order harmonic components. The designed system consists of a wound-rotor induction generator and back-to-back power-electronic converters connected to both rotor and grid sides. Wherein, the modifications are applied to the control of rotor side converter (RSC). Simulations in Matlab/Simulink illustrate the enhanced stability of torque response and the improvement of current waveform. Comparisons of the simulation results with a traditional Stator Flux Oriented Control (SFOC) and a previously suggested modification of SFOC for operation under unbalanced voltage dip are provided to evaluate the newly proposed methods in the paper.