Enhanced DTC induction motor drives- THD reduction multilevel inverter fed drives control

Abstract

Direct Torque Control (DTC) is a control method that controls speed and torque of Induction Motor (IM) directly, accurately and independently without pulse encoder feedback from the motor shaft. However, in Fast Fourier Transform (FFT) analysis of Total Harmonic Distortion (THD) for motor drive, DTC control with a conventional inverter leads to higher THD. Therefore, the main challenge of this study is to reduce the THD in three-phase line current DTC IM drive while maintaining the drive's speed and torque performance. A Multilevel Inverter (MLI) based DTC IM drive system is proposed in this study with the aim to reduce THD in three-phase line current while remaining the good speed and torque response of DTC IM drive system. The proposed MLI are realized by three-level neutral point clamped (NPC) MLI fed DTC of IM. In proposed MLI, pulse width modulation (PWM) is a control strategy used to control the switching at appropriate conducting angles. Proposed MLI based THD reduction DTC IM drive has several advantages over conventional inverter, which enable the operation with multiple switches instead of one switch that generates higher output voltage with low distortion, has ability to operate under low switching frequency, and it allowed the system to work with renewable energy to convert DC voltage into AC voltage. In order to verify the effectiveness of proposed MLI in THD reduction in DTC IM drive, simulation is conducted with MATLAB Simulink to investigate the performance and THD of IM drive system under different operating speed. The results show the THD of the three-phase line current has been decreased with the implementation of proposed MLI based THD reduction DTC IM drive as compared with the conventional DTC IM drive.