Stator Flux Active Damping Methods for Field-Oriented Doubly Fed Induction Generator

The doubly fed induction generator is characterized by natural stator flux oscillations with small damping. It has an unstable region when it is controlled with stator flux orientation with impressed rotor currents. Several techniques can be used for the stabilization and damping of this system. This paper describes, analyses, and compares three methods. The first method consists in lowering the bandwidth of the rotor current controllers. It has the disadvantage of allowing high rotor-disturbance currents during stator flux disturbances. The second method, the back-ims method, uses higher bandwidth control loops and corrects the direct rotor current reference proportionally to the derivative of the flux. It has good performances in steady state but uses considerable additional rotor currents to damp the system when transients occur. The third method, the two-axes damping system, is based on the correction of the dq rotor current references proportionally to the variations of the system variables, i.e., the stator flux and the so-called angle. When compared with the back-ims method, the two-axes damping method uses smaller additional damping currents. Experimental verification based on a small laboratory prototype is presented.