Elimination of saturation effects in sensorless position controlled induction motors

Owing to the variable magnetic coupling between the stator windings and the discrete rotor bars of an induction motor, a quasi-continuous rotor position signal can be acquired by instantaneous measurement of the total leakage inductance of the three stator phases. The signals are sampled in synchronism with the regular commutations of the PWM process, thus making the injection of additional high-frequency carriers obsolete. The acquired position signal exhibits high spatial resolution and high dynamic bandwidth. Magnetic saturation also influences upon the total leakage inductances and hence constitutes a disturbance for position identification. The paper presents a detailed analysis of the saturation effects and proposes methods to eliminate their undesired impact on the position signal. Experimental results of closed loop sensorless position control at full load and high dynamic performance are presented.