Abstract
The use of a direct torque control (DTC) drive is a well-known control strategy that is applied frequently to induction motors. Although torque and stator flux ripples are major disadvantages of this approach, using a higher-level inverter helps to overcome these issues. In this paper, we propose a novel switching table with a modified control strategy for a three-level inverter to achieve ripple minimization, as well as smooth switching and neutral point balance; the latter features are generally ignored in many works. The proposed model is compared with a conventional DTC and an improved three-level inverter-fed voltage vector synthesis model in the Matlab/Simulink® environment with low, normal, and high-speed operation under load torque disturbances. The performance indexes and the comparative results confirm the effectiveness of the proposed model in reducing the torque and stator flux ripples by up to 70% and 78%, respectively, generating a lower total harmonic distortion (THD%) in all scenarios, in addition to maintaining the neutral point balance and preventing voltage jumps across the switches of the inverter.
Highlights
The conventional direct torque control (DTC) drive has been investigated and developed as a replacement for field-oriented control (FOC) in high-performance AC motor drives [1]
A series of comprehensive simulations were carried out in the MATLAB® platform to show the effectiveness of the proposed strategy on a 10 horsepower (HP) induction motor
Due to the fact that the synthesis vector method required fast vector injection, the sampling time for this method was set to 10 microseconds, while the conventional DTC and our proposed model were simulated for microseconds
Summary
The conventional direct torque control (DTC) drive has been investigated and developed as a replacement for field-oriented control (FOC) in high-performance AC motor drives [1]. DTC is well-known for its fast torque response, which requires no coordinate transformation, current control or modulation techniques [2]. Considering the fact that rotor speed encoders are expensive, can have high maintenance costs and are not suitable for harsh environments, numerous sensorless DTC strategies have been proposed [8,9,10]. Torque hysteresis controller-based DTC (THC-DTC) is considered to be a fast dynamic response controller, its main drawbacks are high torque ripple and flux droop in the low-speed region [11,12]. Torque ripple has a direct relationship with mechanical loss and tensions on the motor shaft, while flux ripple indicates harmonics and a distorted current waveform
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