New Hybrid SVPWM Techniques for Direct Torque Controlled Induction Motor Drive to Reduce Current and Torque Ripples without Angle and Sector Estimation

The main objective of this paper is to present different hybrid space vector pulsewidth modulation (HSVPWM) strategies for direct torque controlled induction motor drives using the concept of imaginary switching times to reduce steady state ripple in current, torque and flux. The proposed PWM techniques are designed based on the notion of stator flux ripple, which is a measure of ripple in line current. Expressions for RMS ripple, over a subcycle are derived for each switching sequence in terms of reference voltage vector, imaginary switching times and subcycle duration. This analysis together with the total harmonic distortion (THD) performance of the different sequences is used to design new HSVPWM techniques for induction motor drives, which result in reduction of THD. In this control strategy by using the error between reference and estimated flux vectors three reference voltages are generated from which, the imaginary switching times are derived. These imaginary times are used to generate the switching pulses for the PWM inverter. To validate the proposed method, the simulation has been carried out and the results are presented and compared.