Shorted-Stator Mode Control of Doubly-Fed Induction Generator Connected to a Weak Grid

A doubly-fed induction generator connected to a weak grid is presented. The grid is characterized by unbalanced voltage conditions, which introduces a negative sequence voltage to the stator windings. The negative sequence voltage conditions generate pulsations in the torque and power quantities of the generator, which affects its stability. Proportional plus resonant controllers are introduced into direct control of torque and power schemes to mitigate the pulsations. In order to extend the speed range of operation of the DFIG, the shorted-stator mode operation is considered so that at low wind speed some corresponding power are still generated into the PCC. The control of the shorted-stator mode shows more robustness against the unbalanced voltage conditions at the PCC with no pulsations in the electromagnetic torque. Some results are presented for a 5hp machine.