Due to advances in power electronic switchesadmin / February 10, 2019
Due to advances in power electronic switches, and microprocessors, variable speed drive system using various control system have been generally used in many applications, some of them include field oriented control, or vector control, sensor less vector control and direct torque control.
DIRECT TORQUE CONTROL:
Due to its efficiency and low sensitive to parameter variation it have been generally accepted in the control of motor speed widely in all industrial applications because of its technique.
Despite its importance, it has a major setback associated with it. That is the large torque and flux ripple at steady state operation of the motor. These ripples can affect the accuracy of speed consideration of motor.
In the past, effort have been made using the space vector modulation and the multi-level inverter methods to reduce these ripples. These methods when used though, achieved some degree of success in reducing the ripples but they are difficult and costly to implement.
In this chapter, a lot of control techniques were treated, the work done in increasing the torque and flux ripples using direct torque control is highlighted. The proposed fuzzy logic with duty ratio control is equally treated in detail.
In DTC drives, the uncoupling of the torque and flux components are achieved by using hysteresis comparators which compares the actual and considered values of the electromagnetic torque and stator flux. The DTC drive consists of DTC controller, torque and flux calculator, and a Voltage Source Inverter (VSI).
2.1METHOD OF OPERATION
DTC is one way of using variable frequency drives to control the torque and finally the speed of three phase motors. This involves calculating an estimate of the motors magnetic flux and torque based on the evaluated voltage and current of the motor.
Stator flux linkage is considered by integrating the stator voltages. Torque is considered as a cross product of considered stator flux linkage vector and evaluated motor current vector. The considered flux or torque deviates from the reference motor than permitted tolerance, the transistors of the