Detection of shaft-edge field of induction motor for stable torque control

Detection of the rotor information of squirrel-cage induction motors for stable torque control is carried out by using a highly sensitive Magneto-Impedance micro magnetic sensor. The magnetic field detected near an edge of the rotor shaft is estimated to be proportional to the rotor current with a slip frequency (psf/2) and a torque when the motor is driven with a constant V/f inverter. Stable stationary torque control is realized independently of the motor temperature variation.