An improved direct torque control strategy for induction motor drive

Abstract

The object of this study is to study a new control structure for sensorless induction machine dedicated to electrical drives using a three-level Voltage Source Inverter (VSI). The major problem with DTC drives is the high torque ripple, to solve this problem two approaches are proposed to replace the conventional hysteresis-based controller. The output voltages of the three-level VSI can be represented by four groups: the zero voltage vectors, the small voltage vectors, the middle voltage vectors and the large voltage vectors in (d, q) plane. Then, the amplitude and the rotating velocity of the flux vector can be controlled freely. Both fast torque and optimal switching logic can be obtained. The selection is based on the value of the stator flux and the torque. Both approaches are simulated for a induction motor. The results obtained show superior performances over the conventional DTC one without need to any mechanical sensor