Scalar Control of Induction Motor Drives Based on Rotor Flux Adaptation

Abstract

This paper proposes a speed-sensorless closed-loop scalar control strategy for three-phase induction motor drives based on a rotor-flux model reference adaptive system (RF-MRAS). The proposed approach enhances the conventional constant V/f control by introducing a closed-loop slip compensation mechanism, eliminating both the mechanical speed sensor and the proportional-integral based speed controller. Rotor speed is estimated via the adaptive mechanism of the RF-MRAS using the deviation between the rotor flux vectors obtained from the voltage and current models. The rotor flux angle obtained from the voltage model is then used to estimate the synchronous speed so that slip estimation and compensation can be performed. To reduce the high frequency noise due to the differentiation of the flux angle, a first-order low-pass filter is included in the compensation loop. Extensive simulation studies under load torque disturbances and dynamic speed reference profiles show that the proposed method can achieve accurate speed tracking, robust performance, and stable operation compared with the typical open-loop scalar control. The results show that the proposed scheme is an effective low-complexity alternative for speed sensorless induction motor drive applications.