Ibrahim Mohd Alsofyani, Keon Young Kim, Sze Sing Lee, and Kyo-Beum Lee, "A Modified Flux Regulation Method to Minimize Switching Frequency and Improve DTC-Hysteresis-Based Induction Machines In Low-Speed Regions," IEEE Journal of Emerging and Selected Top > Paper

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

studies were able to attain flux regulation by imposing the continuous switching of forward and reverse active voltage vectors

by causing torque overshoots in the torque hysteresis bands (THBs). This led to an excessive increase in the switching frequency

and larger torque and current ripples, thus reducing the drive efficiency. In this paper, a modified flux regulation method is proposed

for the classical DTC using a single THB when flux droop occurs in a low-rotor-speed range. The proposed method can protect the

DTC from flux droops at low speeds by reducing the duration of zero-voltage vectors and minimizing the number of reverse-

voltage vectors. In addition, the proposed strategy is efficient in reducing torque and current ripples while operating at low

motor speeds. Furthermore, a significant reduction in the switching frequency is obtained. The effectiveness of the proposed strategy

is confirmed by simulation and experimental results.