Samer Saleh Hakami, Ibrahim Mohd Alsofyani, and Kyo-Beum Lee, "Improved Constant Switching Frequency Torque Controller-based DTC of Induction Motor fed by TL-NPC Inverter," 대한전기학회 전기기기 및 에너지변환시스템부문회 하계학술대회 논문집, pp. 901–902, 2019. > Paper

This paper proposes a simple control method for improving direct torque control with a constant switching frequency torque 

controller (CSFTC-DTC) in induction machine fed by three-level neutral-point clamped (TL-NPC) inverter. The conventional CSFTC-

DTC was initially introduced to minimize torque ripple and fix the switching frequency in TL-NPC inverter. However, the conventional 

CSFTC-DTC algorithm suffers from flux droop when the motor operates at low speed, which leads to undesirable current distortions. 

This paper improves the CSFTC to minimize the flux droop by adding carrier for low speed operation and maintaining the simple 

single-carrier for high speed operation. Simulation results are provided to validate the effectiveness of proposed methods.