Title: Direct Torque Control of an Induction Motor using Fuzzy Logic Based Controller


    D.C. motors have been used widely during the last century in applications where variable-speed operation was needed, because its flux and torque can be controlled easily by means of changing the field and the armature currents respectively. With the advancement in inverter techniques and Electric drives AC machines have taken over the major part of industry. The most economical IM speed control methods are realized by using frequency converters. Many different topologies of frequency converters are available however, a converter consisting of a diode rectifier, a dc- link and a Pulse Width Modulated (PWM) voltage inverter is the most applied used in industry. The main goal of the chosen control method is to provide the best possible parameters of drive. Additionally, a very important requirement regarding control method is simplicity (simple algorithm, simple tuning and operation with small controller dimension leads to low price of final product). There are
   two kind of control for AC machines: Scalar control and Vector control.
   Our project involves Direct Torque Control of Induction Motors using SVPWM. Direct torque control has advantages over simpler field control methods in sense of quick response and accurate torque achievement. DTC does not need any expensive sensor like tachometer or speed sensor for its operation. The only sensing device is current sensor and hence precision is improved in DTC. The basic idea of the DTC technique is to choose the best vector of the reference voltage, which makes the flux rotate and produce the desired torque. In the DTC motor drive, the stator flux linkage and the electromagnetic torque can be directly controlled by the selection of optimum inverter switching states. The flux and the torque errors are kept within acceptable limits by hysteresis controllers. Torque is controlled by switching between the six non-zero states of inverter or otherwise called as space vectors. The limitation of six space vectors in general DTC introduces inherent ripple in its control over cur
   rent and torque. This drawback is countered using improved technique of DTC using space vector pulse width modulation.
   Space vector is an efficient modulation technique that enables smooth running of AC motors and offers better performance in terms of DC utilization and harmonic quality. It produces 15-16 percent more output as compared with SPWM under same supply conditions In this technique reference vector is approximated by using two closest non-zero vectors and two zero vectors by calculation of dwell times. In this way many combinations of space vectors are possible. Its application in DTC has more significance because the increase in number of possible vectors solvesthe problem of inherent ripple.
   DTC technique has diverse applications in industry like hybrid cars, traction trains and heavy duty cranes. Electric Vehicles (EV) were developed for greener environment and cost efficiency. The mechanical engine is replaced by AC motor and a control technique is provided to carry out the commands of acceleration and brake. It has been proved that DTC in such application provides smooth control and quick response to these commands. High torque applications i.e. traction train, jet catapults and cranes require accurate control of torque as in DTC.

Advisor:  Dr. Syed Abdul Rahman Kashif  

Group Members:

Name: Fahad Shahbaz
Phone: 0336-6546950

Name: Mansoor Ahmed
Phone: 0333-6541872

Name: M. Hasnain Asif
Phone: 0323-6611369

Name: Nouman Alam Siddiqui
Phone: 03217214565