Direct Torque Control of induction motor with reduction of torque ripple

Abstract

It is widely known that Direct Torque Control (DTC) has fast dynamic torque response. It originates in the fact that torque and flux is directly controlled by instantaneous space voltage vector unlike Field Oriented Control (FOC). For the reason, Direct Torque Control gradually has been used in the field requiring fast response since its introduction in the mid-1980's. In spite of these merits, Direct Torque Control has several problems. These problems are : (1) the variation of the switching frequency by hysteresis band and speed; (2) the increase of the torque ripple in the low speed region; (3) the short control period (25 /spl mu/s) for the good performances etc. To solve the problems of Direct Torque Control, several studies were carried out. This paper improves one of the drawbacks of Direct Torque Control, torque ripple, with the constant switching frequency. In some papers it was tried to improve the drawback, but some papers are very complicated and didn't show large improvement. Their methods even resulted in losing the merits of Direct Torque Control. In this paper Direct Torque Control method is performed with constant switching frequency. So this scheme is easy to be realized with digital signal processor and also minimizes torque ripple.