Direct torque control using space vector modulation and dynamic performance of the drive, via a fuzzy logic controller for speed regulation

This paper presents a method of controlling the Torque of an asynchronous motor that is fed by a PWM-Inverter. The control method that is used is a modified direct torque control (DTC) scheme with constant switching frequency, using space vector modulation (SVM). In this scheme a closed loop of torque control is applied. Small and rapid changes on motor´s torque are achieved by applying an appropriate voltage vector, which is responsible for the jerky movement of the stator´s flux vector. The voltage vector can be of any magnitude and angle and is produced using Space Vector Pulse Width Modulation. The modified method of DTC using SVM improves the electrical magnitudes of asynchronous machine, such as reduction of current and flux ripple and also fading out the edges of torque ripple which are occurred during the sector changes of stator flux vector. Another point of this paper is the presentation of speed control in dynamic situations. The production of the reference torque value is achieved by using a fuzzy logic speed controller. The response of the fuzzy PI is compared to the response of a classic PI speed controller. Results, shows that the fuzzy PI speed controller has a better response in a wide range area of motor speed. Combining the characteristics of DTC-SVM scheme and the fuzzy logic speed controller we can have a high performance vector controlled asynchronous motor drive.