VECTOR CONTROL OF INDUCTION-MOTOR WITHOUT SHAFT ENCODER

A new method of induction motor drive, which requires no shaft encoder, is presented. This system has both torque and speed controls that are performed by vector control. The proposed vector-control scheme is based on a rotor-flux speed control, which is performed by torque-producing current and rotor flux, derived from the stator voltages and currents. If it is possible to obtain both precise torque-producing current and rotor flux, this system will have a good torque and speed performance because of the direct control of the torque and rotor flux. The characteristics of the vector control employing stator voltages and currents usually deteriorate as the speed gets lower because the calculated rotor flux depends on the stator resistance, and it is difficult to calculate rotor flux at standstill. In this new system, the rotor-flux estimator is improved to reduce the stator-resistance influence and to make it possible to calculate rotor flux at standstill.