A novel optimization of Torque performance using DTC strategy implemented in a 3L-NPC for induction machines

This article presents an optimization in implementing a DTC control scheme using a 3L-NPC inverter to control the speed of a three-phase induction machine. Regarding the DTC strategy, 3 and 5-level hysteresis controllers were used to control the stator flux and electromagnetic torque, respectively. The traditional implementation of the scheme [2], shows good results regarding the motor speed response; however, the electromagnetic torque developed by the motor presents various issues: significant ripples in torque produced by a poor choice of the hysteresis controller amplitude, poor tracking of the torque reference signal in steady state, and high torque peaks in large speed steps, which translate into current peaks that exceed the motor’s thermal limit. This work proposes new strategies for adjusting the flux and electric torque hysteresis controllers, which will correct the problems presented in the traditional implementation. Finally, a comparison will be made between the modified DTC strategy and the traditional DTC strategy of [2].