Constant switching frequency torque controller for DTC of induction motor drives with three-level NPC inverter

This paper presents Direct Torque Control (DTC) of induction motor drives using three-level Neutral Point Clamped (NPC) inverter. The usage of hysteresis controller that utilized in conventional DTC lead to varying switching operation, therefore a Constant Switching Frequency (CSF) torque controller is proposed to replace the torque hysteresis controller. The proposed CSF controller consists of Proportional-Integrator (PI) controller and triangular carrier waveforms are compared with the output of PI controller to produce a torque error status to implement DTC control. The proposed controller is able to improve the DTC drives performance in terms of torque ripple reduction and constant switching frequency operation. The improvement of proposed method is verified using experimental works.