Robust Direct Torque and Flux Control of Adjustable Speed Sensorless PMSM

Abstract

Direct torque control (DTC) is known to produce fast response and robust control in ac adjustablespeed drives. However, in the steady-state operation, notable torque, flux, and current pulsations occur. a new sensorless direct torque control method for voltage inverter – fed PMSM is presented. The control method is used a modified direct torque control scheme with constant inverter switching frequency using space vector modulation (DTC-SVM). The variation of stator resistance due to changes in temperature or frequency deteriorates the performance of DTC controller by introducing errors in the estimated flux linkage and the electromagnetic torque. As a result, this approach will not be suitable for high power drives such as those used in tractions, as they require good torque control performance at considerably lower frequency. A novel stator resistance estimator during the operation of the motor is proposed. The estimation method is implemented using the Extended Kalman Filter (EKF) schemes. . Finally extensive simulation results are presented to validate the proposed technique and a very satisfactory performance has been achieved.