Samer Saleh Hakami, Ibrahim Mohd Alsofyani, and Kyo-Beum Lee, "Low-Speed Performance Improvement of Direct Torque Control for Induction Motor Drives Fed by Three-Level NPC Inverter," Electronics, vol. 9, no. 77, pp. 1–14, Jan. 2020. -SCIE > Paper

Classical direct torque control (DTC) is considered one of the simplest and fastest control algorithm in motor drives. However, it

produces high torque and flux ripples due to the implementation of three-level hysteresis torque regulator (HTR). Although,

increasing the level of HTR and utilizing multilevel inverters has a great contribution in torque and flux ripples reduction, stator flux

magnitude of induction motor (IM) droops at every switching sector transition, particularly at low-speed operation. This problem

occurs due to the utilization of zero voltage vector where the domination of stator resistance is very high. A simple flux regulation

strategy (SFRS) is applied for low-speed operation for DTC of IM. The proposed DTC-SFRS modifies the output status of the five-

level HTR depending on flux error, torque error and stator flux position. This method regulates the stator flux for both forward and

reverse rotational directions of IM with retaining the basic structure of classical DTC. By using the proposed algorithm, the stator flux

is regulated hence pure sinusoidal current waveform is achieved which results in lower total harmonics distortion (THD). The

effectiveness of the proposed DTC-SFRS is verified through simulation and experimental results.