New Hybrid SVPWM Methods for Direct Torque Controlled Induction Motor Drive for Reduced Current Ripple

This paper presents novel hybrid SVPWM (HSVPWM) methods for direct torque controlled induction motor drives without angle estimation to reduce steady state ripple in current, torque and flux. The proposed PWM technique is designed based on the notion of stator flux ripple, which is a measure of line current ripple. Expressions for RMS ripple, over a sub-cycle are derived for each switching sequence in terms of reference voltage vector, imaginary switching times and sub-cycle duration. This analysis together with the THD performance is used to design new HSVPWM techniques, which result in reduction in THD. The proposed PWM methods simplify the control algorithm and also reduce the execution time. Also to improve the speed performance under uncertainties caused by load torque, a robust speed controller with an integral sliding switching surface is used. To validate the proposed method, the results are presented.