Ride-Through Control of a Doubly Fed Induction Generator Under Unbalanced Voltage Sags

This paper deals with the control of doubly fed induction generators to ride through unbalanced voltage sags. A control strategy is proposed by choosing certain current reference values in the positive and negative sequences so that the torque and the dc voltage are kept stable during such unbalanced sags. Both rotor- and grid-side converters are considered, detailing the control scheme of each converter while considering the effect of the crowbar protection. The control strategy is validated by means of simulations.