New direct torque control scheme for induction motors

Abstract

In this paper a novel controller based on direct torque control is presented. This controller has been designed to be applied in the control of induction motors fed with a three-level voltage source inverter (VSI). This type of inverter has several advantages over the standard two-level VSI, such as a greater number of levels in the output voltage waveforms, less harmonic distortion and lower switching frequencies. In the new controller the hysteresis regulators and look-up table are not used, and instead, the torque and stator flux errors are used together with the motor speed to generate a reference voltage vector that can be synthesized using different techniques afterwards. Experimental results of the novel system are presented and compared with those obtained for classical DTC system when employing two-level VSI. The new controller is shown to reduce the ripple in the torque and flux responses. Lower current distortion and switching frequency of the semiconductor devices are also obtained in the new presented system