A DFIG sensorless method for direct estimation of slip position

A sensorless method for the direct detection of the slip position of the wound-rotor induction machine is described in this paper. The slip position is necessary for the implementation of control by flux orientation. The method proposed is based on the phase comparison of estimated and measured rotor currents. The estimation of rotor currents is implemented in the field reference frame with the aid of the active and reactive powers transferred in the air gap. The proposed method can be implemented in the rotor or in the field reference frames with a hysteresis or with a PI controller. The method is sensitive to the stator self inductance parameter, but this dependence is not very important allowing 20% error. Simulation and experimental results show that the method is appropriate for the vector control of the doubly fed induction machine. Conversely to other methods, this method gives acceptable results when the load is small. In addition it does not need a flux estimator for the implementation of flux orientation.