Improved Direct Resonant Control for Suppressing Torque Ripple and Reducing Harmonic Current Losses of DFIG-DC System

The most prominent problem of the doubly fed induction generator-dc (DFIG-dc) system is the highly distorted stator voltage due to the diode bridge on stator side. The highly distorted stator voltage not only influences the stator voltage orientation control but also causes harmonic currents and torque ripples. In this paper, an enhanced stator fundamental voltage orientation method is proposed to deal with the highly distorted stator voltage. Furthermore, the relationship between torque ripples and harmonic currents is investigated. And then an improved direct resonant control strategy is proposed for suppressing the torque ripple and reducing the harmonic currents simultaneously. In this way, the loss of harmonic currents can be reduced while suppressing the torque ripple. Finally, the experimental results are presented to validate the effectiveness of the proposed control strategy.