Study of Induction motor drive with Direct Torque Control scheme and Indirect Field Oriented control scheme with Space Vector Modulation

Abstract

Induction motors are the starting point to design an electrical drive system which is widely used in
many industrial applications. In modern control theory, different mathematical models describe
induction motor according to the employed control methods. Vector control strategy can be
applied to this electrical motor type in symmetrical three phase version or in unsymmetrical two
phase version. The operation of the induction motor can be analyzed similar to a DC motor
through this control method. With the Joint progress of the power electronics and numerical
electronics it is possible today to deal with the axis control with variable speed in low power
applications. With these technological projections, various command approaches have been
developed by the scientific community to master in real time, the flux and the torque of the
electrical machines, the direct torque control (DTC) scheme being one of the most recent steps in
this direction. This scheme provides excellent properties of regulation without rotational speed
feedback. In this control scheme the electromagnetic torque and stator flux magnitude are
estimated with only stator voltages and currents and this estimation does not depend on motor
parameters except for the stator resistance.
In this dissertation report conventional DTC scheme has been described. Induction motor
has been simulated in stationary d-q reference frame and its free acceleration characteristics are
drawn. Conventional DTC scheme has been simulated with a 50 HP, 460V, 60Hz induction motor.
Literature review has been done to study the recent improvements in DTC scheme which
somehow is able to overcome the drawbacks of conventional one.
The space vector modulation technique (SVPWM) is applied to 2 level inverter control in
the vector control based induction motor drive system, thereby dramatically reducing the torque
ripple. Later in this project space vector PWM technique will be applied to DTC drive system to
reduce the torque ripple.



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