Improvement of DTC of induction motors by using a three-level inverter and fuzzy speed controller

The direct torque control of induction motor has good dynamic performance of torque and flux. However, the switching frequency (in the case of conventional DTC) is variable and difficult to control due to the use of hysteresis controllers. This lack of control over frequency is the origin of torque and flux ripples. Similarly, the use of a voltage inverter with two levels limits the power of the drive system. To overcome these problems, we propose to study in this paper a modified DTC approach which use a three-level inverter (NPC structure) instead of the two-level inverter and a PI fuzzy controller instead the classic PI controller. This allows not only minimizing the undulations of flux and torque but also to getting higher the power range of the drive system and giving an intelligence control.