Modified DTC of a Six-Phase Induction Motor With a Second-Order Sliding-Mode MRAS-Based Speed Estimator

This paper deals with a model reference adaptive system (MRAS) estimator based on the second-order sliding-mode (SOSM) strategy for speed-sensorless direct torque control (DTC) of a six-phase induction motor. A compensated flux observer is proposed using the well-known supertwisting algorithm, which is inherently an SOSM technique. This observer is adopted as the reference model in the MRAS-based speed estimator to overcome the chattering problem of the classical sliding-mode techniques. The estimator is robust against parameter uncertainties and dc offsets. In addition, a supertwisting-algorithm-based second-order sliding-mode (ST-SOSM) controller is designed for the speed loop in the DTC strategy to increase its robustness under applying external load disturbances. The speed control loop needs the load torque signal. For this purpose, an ST-SOSM load torque observer is proposed, where it provides a robust performance without the penalty of high chattering. Simulation and experimental results confirm the validity and the effectiveness of the proposed approaches.