A sensorless speed control using stator ripple currents for an induction motor drive with space phasor PWM

In the present paper a simple sensorless speed estimation scheme is presented, where the speed information is obtained from the motor phase current ripple. The scheme measures the stator current phasor deviation direction to determine the back EMF vector position during inverter zero vector switching states. This measurement of rotor flux position is done indirectly by computing the motor back EMF position which is orthogonal to the rotor flux position. The space vector PWM voltage output in motor phase generates a current ripple pattern, which depends upon the ripple voltage and equivalent stator leakage inductance. For high speed operation when the time duration for the zero vector switching states are small an indirect method for flux position estimation is proposed, where the effect of active voltage vectors on the stator ripple current is eliminated by creating a virtual short circuit at the motor terminals. (6 pages)