A Robust Control Scheme for Induction Motor Drives for Applications in the Field-Weakening Speed Range

A torque control scheme that utilizes the stator flux components as control variables, applied to a speed-sensorless induction motor drive, is presented. The proposed scheme allows the motor to ex-ploit the maximum torque capability in the whole speed range, and shows a reduced dependence from the motor parameters. It is based on a control algorithm that decreases the d-component of the stator flux as soon as the voltage corresponding to the maximum torque exceeds the available voltage. The control scheme produces a smooth transition into and out of the field weakening region and preserves the torque dynamic. The feasibility of the field weakening technique is confirmed by experimental tests.