PLL-Based Sliding Mode Observer Estimators for Sensorless Control of Rotor-Tied DFIG Systems

In this paper, a slip speed/position estimator for sensorless control of rotor-tied doubly-fed induction generator (DFIG) systems is presented. The proposed slip speed/position estimator is based on the association of the phase locked loop and the sliding mode observer. The proposed sliding mode observer uses the three-phase stator currents and the back electromotive force as state variables. This allows for the estimation of the slip speed/position before the rotor-tied DFIG is connected to the grid or to a load. The proposed phase locked loop helps in tracking the slip speed/position. The performance of the proposed slip speed/position estimation for sensorless operations are validated through experiments using a 5.5-kW custom-designed rotor-tied DFIG in grid-connected mode.