Improvement of Torque Capability of Direct Torque Control of Induction Machines

Abstract

A control strategy for overmodulation operation of direct torque control hysteresis based in induction machine is proposed. The strategy is to extend the constant torque region as well as to improve the torque capability. The proposed overmodulation strategy is different to SVM based system where the reference stator voltage is available. In order for DTC hysteresis based system to be able to achieve that, several modifications have been applied so that the proposed overmodulation can be achieved by gradually transforming the PWM voltage waveform to six-step mode. Simulated results were provided to demonstrate the effectiveness of the strategy. Keyword: Constant torque region Direct torque control Hysteresis based Induction machine Overmodulation Copyright © 2017 Institute of Advanced Engineering and Science.All rights reserved. Corresponding Author:Auzani Jidin, Faculty of Electrical Engineering, Universiti Teknikal Malaysia Melaka (UTeM), Malacca, Malaysia. Email: auzani@utem.edu.my INTRODUCTIONThe availability of constant power is very important in applications such as in vehicle drive. In induction machine, various combinations of stator voltage, current and speed is used to estimate the flux and torque. The control of Direct Torque Control (DTC) of induction machines is based on selecting proper voltage vectors to maintain torque and stator flux within the hysteresis band [1]. In [2], voltage vector selection strategy that uses switching table is widely used because of the easy to understand concept a simple implementation. The drawback of a conventional DTC is that the switching frequency is unpredictable according to the machine parameters and speed condition. The system performance will degrade in a certain operating region such as at the low speed region.In [3], a common approach, space vector modulation (SVM) is used to exploit the overmodulation region in DTC. This strategy manages to obtain maximum torque output in field weakening region. This strategy requires voltage reference to define the mode of overmodulation in SVM. However, DTC hysteresis based is not capable to operate in overmodulation to complete six-step mode.This paper presents a strategy to extend the constant torque region and improve the torque capability of DTC hysteresis based without ruining the simplicity of basic DTC-hysteresis based structure. This proposed strategy introduces overmodulation strategy by gradually transforming the PWM voltage waveform to six-step mode. The method is different from SVM based system where the reference stator voltage is available and the overmodulation is achieved by modifying the reference voltage.

Hybrid DTC strategy based on predictive control with optimization of the PI controller parameters for TPIM drives

“…In spite of these advantages, this method suffers from high torque and flux ripples, as well as variable switching frequency. In recent years, different schemes have been proposed to enhance the performance of the conventional DTC method (Ismail et al, 2017;Jidin et al, 2017;Jannati et al, 2013).…”