Abstract

The advantage of AC drive over DC drive is rugged construction and low cost. Due to this reason most of the industrial applications uses induction motor drive. For the speed control of induction motor drive we need inverter. Conventionally three level sinusoidal pulse width modulated (SPWM) inverters are popular for this application. But the drawback of three level SPWM inverters is high switching losses due to high switching frequency. So conventional inverters are limited for low power applications only. For medium and high power application multilevel inverters (MLI) are proposed in literature. Out of various configurations of MLI Dioide clamped MLI is popular. It has the advantages of simple configuration and requires less number of individual DC sources. In this paper we have considered 3 Level, 5 Level and 7 Level MLI fed induction motor drive. We have done the analyses of effect of voltage levels and modulation index on total harmonic distortion (THD). A Simulink based model is developed and simulation results are presented for various test cases. It is clearly shown that as we increase the voltage levels and modulation index THD is reducing. The maximum levels of the inverter limited to seven based on cost factor of the drive.