Ibrahim Mohd Alsofyani, Byung-Moon Han, and Kyo-Beum Lee, "Flux Regulation with Minimized Torque Ripple of DTC of Induction Machines at Low Speed by Controlling Single Hysteresis-Torque Band," in Proc. ICEE Conf., Jun. 2018. > Paper

Direct torque control (DTC) suffers from flux droop owing to the long zero-voltage vectors at low motor speed. The previous

studies can obtain the flux regulation by continuous switching of forward and revers active voltage vectors by causing torque

overshoots at the hysteresis torque bands. As a result, the torque ripple will increase, and the drive efficiency will reduce. This

paper proposes new and simple flux regulation strategy for the classical DTC using a single hysteresis torque band when flux

droop occurs at low motor speed operation. The proposed method can prevent the flux droop at low speed by reducing the

duration of zero-voltage vectors instead of activating reverse voltage vectors. In addition, the torque ripple reduces considerably

by the proposed strategy. The effectiveness of the proposed scheme is confirmed by simulation. Results show a significant

enhancement in the flux regulation and the torque ripple reduction.