Enhanced Direct Torque Control of Induction Motors Using Constant Switching Frequency Torque Controller and Fuzzy Logic Control

Abstract

The Direct Torque Control (DTC) methods for AC machines are commonly utilized in many variable-speed drives, especially in cases where torque control is more desired than speed control. Two major problems that are usually related to DTC drives are: 1) switching frequency that varies with operating conditions; and 2) high torque ripple. To solve these problems and, at the same time, improve the simple control structure of DTC, a constant switching frequency torque controller is proposed to replace the conventional hysteresis-based controller. The best features of the voltage source inverter (VSI) and the direct current (DTC) method are combined to create the right voltage vectors when the input power factor is 0.9. The results show that the system's dynamic response is of high quality and reliability, and they also show that both steady-state and transient motor ripple torque are kept to a minimum. We suggest a way to use VSI-based DTC in IM drives to choose the right switching vectors for controlling torque with small changes in the stator flux within the hysteresis band. This paper presents a novel control scheme based on a fuzzy logic controller (FLC). This paper reviews the research and development in direct torque control of VSI-fed IM. Such a review helps the highly effective control strategies for AC machines to provide very fast torque and flux control. In this technical context, an overview of VSI-fed induction motors has been carried out based on reports from the literature presented in the past two decades.