Dynamic torque response improvement of direct torque controlled induction motor

Abstract

Induction motor is extensively being used with variable frequency drive (VFD) in variable speed service. Direct Torque control (DTC) of induction machines is simple compared to the Field oriented control (FOC). Although DTC has advantages there are some disadvantages like torque ripple is high, switching frequency is variable. This paper proposes a dynamic over modulation strategy which can be implemented in DTC to improve the dynamic response and to reduce the torque ripple. The objectives are achieved by switching voltage vector that produces the most tangential component to the circular flux locus. The principle advantage of the proposed technique is its effortlessness, since it requires a minor change to the conventional DTC-hysteresis-based structure. 80% reduction in torque ripple and 40% improvement in dynamic response are achieved in the proposed method compared to conventional method.