A modified direct torque control for induction motor sensorless drive

Direct torque control (DTC) is known to produce quick and robust response in AC drives. However, during steady state, notable torque, flux and current pulsations occur. They are reflected in speed estimation, speed response, and also in increased acoustical noise. This paper introduces a new direct torque and flux control based on space-vector modulation (DTC-SVM) for induction motor sensorless drives. It is able to reduce the acoustical noise, the torque, flux, current, and speed pulsations during steady state. The DTC transient merits are preserved, while better quality steady-state performance is produced in sensorless implementation for a wide speed range. The flux and torque estimator is presented and an improved voltage-current model speed observer is introduced. The proposed control topologies, simulations, implementation data, and test results with DTC and DTC-SVM are given and discussed. It is concluded that the proposed control topology produces better results for steady-state operation than the classical DTC.