Importance

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Abstract

An induction motor has a multi-phase primary winding (stator winding) and a multi-phase secondary winding (rotor winding) which are connected to each other in opposite phase relation. The both windings are fed with variable frequency A.C. current from a common frequency converter. A position sensor for sensing a rotor position is mounted on the induction motor. The position signal of the position sensor is in phase with an air gap flux between the primary winding and the secondary winding. Magnitude of a motor current is controlled in accordance with a torque command signal indicative of an error between a speed command signal and a speed feedback signal and with a voltage command signal for determining a terminal voltage, and a phase difference of the motor current relative to the position signal is controlled in accordance with the torque command signal and the voltage command signal. In this manner, the torque generated can be varied while maintaining amount of air gap flux and hence the terminal voltage constant.

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First Claim