Improved Direct Torque Control of Induction Motor With Space Vector Modulation

Abstract

The Direct Torque Control (DTC) is a type of vector control technique which is used to regulate the torque and hence speed of an induction motor drive. This method is very efficient, cheap and is very easy to execute. The absence of mechanical speed estimators along with the ease of processing and computations make it the most preferred option among all vector control techniques. In this method, only the voltage and current are sensed and they are used to estimate the torque, flux and the angle between the rotor and stator flux. Depending on the torque and flux errors, a suitable voltage vector is selected to keep the errors within the desired tolerance region. At present times, three phase induction motors have become the backbone of industries. Lifts, agricultural pumps, conveyor belts, lathes, cranes, drilling machine, etc. are some of the prominent areas where induction motors have been very effective. These motors can be controlled using the scalar V/F control techniques. However, for applications requiring quick response vector control techniques like DTC are preferred. But the problem lies in the presence of torque ripples in case of DTC of three phase induction motor drive. The study is done by simulation using the MATLAB/Simulink Power System Block set that allows a complete representation of the power section (inverter and induction motor) and the control system. The performance of the two control schemes i.e a conventional DTC method and space vector modulation DTC is evaluated in terms of torque and current ripple, and transient response to step variations of the torque command, and emphasizing advantages and disadvantages. A comparative study between both the method has been carried out.