Low voltage ride-through capability improvement of DFIG-based wind turbines under unbalanced voltage dips

• The paper improves the LVRT capability of DFIG under unbalanced voltage dips.
• LVRT method is realized through joint use of RSC control and an asymmetrical SDR.
• Asymmetrical SDR resistors are activated only in phase(s) experiencing low voltage.
• DFIG is controlled such that no unbalance voltage appears on the stator voltage.
• The method removes fluctuation of transient response appeared during the fault.

This paper proposes a competent and effective scheme to enhance the ride-through capability of DFIG-based wind turbines under unbalanced voltage dip conditions. The proposed method is realized through joint use of the rotor-side converter control and a three-phase stator damping resistor (SDR) placed in series with the stator windings. By means of an asymmetrical SDR idea, during the unbalanced voltage dip the SDR resistors are activated only in phase(s) experiencing low voltage. Then, the rotor current is controlled such that no unbalance voltage appears on the stator voltage. The proposed ride-through approach limits the peak values of the rotor inrush current, electromagnetic torque and DFIG transient response at the times of occurrence and clearing the fault. It also suppresses fluctuation of the electromagnetic torque and DFIG transient response appeared during unbalanced voltage dips due to negative sequence component.