An Open-Loop Sensorless Slip Position Estimator of a DFIM Based on Air-gap Active Power Calculations—Sensitivity Study

This paper presents a sensitivity study for a new sensorless method for the direct estimation of the slip position of the wound-rotor induction machine. The method estimates directly the slip position as the difference between two angles: the rotor current position measured in the rotor reference frame and the same variable computed in the reference frame synchronous with the stator electromotive force. This is obtained using the active power that crosses the airgap as an auxiliary variable. Since the slip position is directly obtained, it is not necessary to knowthe stator flux in order to implement the field orientation. The method is not dependent on the stator selfinductance, being robust to parameter variations. Accuracy mainly depends on the mismatch of the ratio between the stator and mutual inductances. The estimation error is low in a large region of the dq rotor current plane except near the d-axis. Simulation and experimental results show that the method is appropriate for vector control of the doubly fed induction machine (DFIM) in a wide variety of applications.