Modified PWM Technique for a Multi-Pulse Converter Fed Multilevel Inverter Based IM Drive

Abstract

This article presents a 36-pulse converter and five-level cascaded H-bridge multilevel inverter (CHB-MLI) fed medium voltage induction motor drive (MVIMD) system. The multiwinding transformer (MWT) for a 36-pulse ac–dc converter is designed in such a way that it requires the least number of windings and enhances power quality at the grid end. This is helpful to reduce the size, weight, and cost of the presented MVIMD. The modified carrier level shifted pulsewidth modulation (MC-LSPWM) is used to control five-level CHB-MLI fed induction motor, which adheres the power quality standard IEEE519 at drive end. The main characteristic of used PWM is that it has inherent rotating switching pattern nature, which is helpful to enhance the power quality performance and to decrease the continuous conduction time of the H-bridge. Whereas, this continuous conduction among H-bridges, is not balanced in the level-shifted pulsewidth modulation (LSPWM). Therefore, conduction losses among the H-bridges of CHB-MLI are balanced and reduced by this MC-LSPWM for continuous operation, which is not possible with the conventional LSPWM. The practicality of this MVIMD with an indirect field-oriented control and MC-LSPWM technique, is substantiated via a comparison with the configuration reported in the literature, simulation, and experimentation, respectively. Performance of the drive system is evaluated during different operating conditions, such as starting, steady-state, speed and load perturbations. Further, a detailed comparative analysis of results is presented, which demonstrates that presented MWT configuration has fewer number of windings (only thirty-three windings), less conductor material and minimum losses. Thus, the presented configuration of MVIMD shows excellent performance characteristics with reduced size and weight such as currents total harmonic distortion is 2.5% (grid end), 3.66% (drive end) and efficiency of the drive is 88.101%, when the drive runs at rated conditions.