DTC of induction motor drive fed by NPC three level inverter based on fuzzy logic

The direct torque control of induction motor has good dynamic performance of torque and flux. However, the switching frequency is variable and difficult to control due to the use of hysteresis controllers. That is the origin of torque and flux ripples. And the use of a two levels voltage inverter limits the drive system power. To overcome these problems, we propose to study in this paper a modified DTC approach by using a three-level inverter (NPC structure) instead of the two-level inverter, the two hysteresis controllers of flux and torque are replaced by one fuzzy controller and finally a PI fuzzy speed controller is used instead the classical PI controller. All these changes are designed to not only minimize the ripples of flux and torque but also to increase the power range of the drive system and provide an intelligence control.