Low voltage ride-through control of doubly-fed induction generator at synchronism

The doubly-fed induction generators operating at synchronous speed offers some advantages. At this working mode, the power flowing in the rotor is not significant and thus the converter rating is reduced considerably. The drive can be implemented with the support of a hydro-dynamically controlled gearbox (Voith) which allows the generator works at a determined speed regardless of the rotor speed. This work introduces control methods to ride-through the temporary low voltage for both symmetrical and asymmetrical voltage dip cases at synchronism. For symmetrical dip, a rotor voltage control method is proposed with a determination of transient stator flux. On the other hand, under asymmetrical dip, the electromagnetic vibrations are deal with by controlling the positive and negative sequence separately. Optimal methods to determine the reference values of the negative sequence controller are proposed to eliminate the oscillations simultaneously. The control method is validated by means of simulations.