Performance comparison of direct torque control of two level and three level neutral point clamped inverter fed three phase induction motor

Abstract

This paper proposes performance comparison of Direct Torque Control of induction motor drive system based on conventional hysteresis controller scheme and modified DTC schemes with sinusoidal PWM. Direct Torque Control (DTC) is a control technique used in AC drive systems to obtain high performance torque control. The main principle of DTC is based on simultaneously decoupling the stator flux and electromagnetic torque. DTC drives utilizing conventional hysteresis comparators suffer from high torque ripple and variable switching frequency. The proposed schemes reduces torque and flux ripples and preserve DTC transient merits such as fast torque response. In the work, modeling of two level and three level Neutral Point Clamped (NPC) inverter, modeling of 3 phase induction motor, DTC schemes with conventional hysteresis controller, modified DTC employing sinusoidal pulse width modulation has been done, analyzed and compared using Matlab/Simulink software. Then modified DTC scheme using sinusoidal PWM is employed for three level NPC inverter. The performance of 2 level and 3 level inverter fed induction motor is then compared. Simulation results show that torque, flux, stator current waveforms improve when three level inverter and modified DTC is employed.