An Improved Direct Torque Control of Three-Level Dual Inverter Fed Open-Ended Winding Induction Motor Drive Based on Modified Look-Up Table

The induction motor (IM) drive with direct torque control scheme (DTC) turns prominent for industrial applications. However, it retains disadvantage of high torque ripples. The conventional look-up table for DTC scheme is structured with selection of reverse voltage vectors (VVs) when flux and torque errors crosses lower hysteresis boundary condition. This results in higher torque ripples and increase in switching frequency. In this article, modified look-up table for DTC of three-level dual voltage source inverter fed open-ended winding IM drive is proposed, where the VVs selection for lower hysteresis boundary conditions of torque and flux are restructured with null voltage states. The selection of suitable null voltage switching states from the various possible combinations of dual inverter switchings is based on minimization of switching state transitions. To nullify flux instability at zero speed, proper active VVs are placed at hysteresis flux 1 and torque 0 condition in the modified look-up table. These overall effective modifications in the proposed DTC scheme enjoys the benefits of reduction in torque ripple, switching frequency, and stable flux maintenance. The MATLAB simulations and practical investigations are conducted for existing and proposed DTC schemes. From these results, the benefits of the proposed DTC over existing DTC schemes are verified.