Improved Performance of direct torque control of Induction Motor Using multi -level inverter

The direct torque control scheme is a simple configuration structure compared to the Field oriented control. This method is widely used in many applications of motor drive. But the current and torque distortion changes the switching frequency at low speed. The torque ripple causes noise and vibrations and current ripples are in turn responsible for the EMI. The reason of the high current and torque ripple in DTC [4]is the presence of hysteresis comparators together with limited number of available voltage vectors.
In this paper In order to improve the output performances, modified Direct Torque Control scheme is employed with three level inverter. Increasing the number of voltage levels in the inverter without the need for higher nominal rates in individual components, can raise nominal power. voltage source inverters structure, allows them reaches to high voltage with low harmonic without transformer or series and simultaneously switching components. The the harmonic of output voltage waveform significantly reduced if The number of voltage levels go up. The results show that torque and flux ripples are more reduced when three level inverter is employed.