Identification of rotor position and speed of standard induction motors at low speed including zero stator frequency

The total leakage inductance as seen from the stator windings of standard induction motors varies with the rotor position angle. The effect is exploited to extract the rotor position, and speed, from measured stator voltages. The extraction algorithm is incorporated based on a modification of the pulsewidth modulator. Experimental results demonstrate accurate position measurement at high resolution and high bandwidth at any speed including standstill. Preliminary results of a sensorless vector controled ac drive system are presented.