Sensorless direct voltage control for stand-alone DFIG with improved negative-sequence voltage compensation

The control system for doubly-fed induction generator (DFIG) operating in stand-alone mode is commonly based on the direct voltage control method, and employs negative-sequence compensation through rotor side converter (RSC) to improve the output voltage quality and support unbalanced loads. This paper demonstrates the limitations of the conventional sensorless direct voltage control method to support full range of unbalanced loads, because it cannot obtain the slip angle, and proposes a method to solve this problem by modifying the stand-alone control system. Simulation and experiments for a 1.1 kW prototype DFIG are carried out to compare the conventional and the proposed methods, and validate the proposed method.