28-10-2016, 04:25 PM
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ABSTRACT
At present, induction motors are the dominant drives in various industries around the world, owing to their rugged construction and easy maintenance. However, it is quite cumbersome to control an induction motor because of its poor dynamic response in comparison to the DC motor drives. Consequent to the painstaking research put in by Power Electronic engineers around the globe, the dynamic response of an induction motor is brought on par to that of a separately excited DC motor drive.
With the DTC scheme employing a Voltage Source Inverter (VSI), it is possible to control directly the stator flux linkage and the electromagnetic torque by the optimum selection of inverter switching vectors. The selection of inverter switching vector is made to restrict the flux and torque errors within the respective flux and torque hysteresis bands. This achieves a fast torque response, low inverter switching frequency and low harmonic losses. The modeling and simulation of an induction motor drive employing DTC is performed and the results are reported.
INTRODUCTION
Facts are due to the induction motors advantages over the rest of the motors. The main advantage is that induction motors do not require an electrical connection between stationary and rotating parts of the motor. Therefore, they do not need any mechanical Commutator (brushes), leading to the fact that they are maintenance free motors. Induction motors also have low weight and inertia, high efficiency and a high overload capability. Therefore, they are cheaper and more robust, and less proves to any failure at high speeds. Furthermore, the motor can work in explosive environments because no sparks are produced.
Taking into account all the advantages outlined above, induction motors must be considered the perfect electrical to mechanical energy converter. However, mechanical energy is more than often required at variable speeds, where the speed control system is not a trivial matter.
DTC is said to be one of the future ways of controlling the induction machine in four quadrants. In DTC it is possible to control directly the stator flux and the torque by selecting the appropriate inverter state.
DTC main features are as follows:
Direct control of flux and torque.
Indirect control of stator currents and voltages.
Approximately sinusoidal stator fluxes and stator currents.
High dynamic performance even at stand still.
The main advantages of DTC are:
Absence of co-ordinate transforms.
Absence of voltage modular block, as well as other controllers such as PID for motor flux and torque.
Minimal torque response time, even better than the vector controllers.
However, some disadvantages are also present such as:
Possible problems during starting.
Requirement of torque and flux estimators, implying the consequent parameters identification. .
Inherent torque and stator flux ripple.
Introduction To Matlab
What is MATLAB?
MATLAB (Matrix Laboratory)
MATLAB is developed by The Math Works, Inc.
MATLAB is a high-level technical computing language and interactive environment for algorithm development, data visualization, data analysis, and numeric computation.
MATLAB can be install on Unix, Windows
Cont…
MATLAB is a high-level language and interactive environment that enables you to perform computationally intensive tasks faster than with traditional programming languages such as C, C++, and Fortran.
History Of Matlab
Fortran subroutines for solving linear (LINPACK) and eigen value (EISPACK) problems
Developed primarily by Cleve Moler in the 1970’s
Later, when teaching courses in mathematics, Molar wanted his students to be able to use LINPACK and EISPACK without requiring knowledge of Fortran
MATLAB developed as an interactive system to access LINPACK and EISPACK
Cont…
The Mathworks, Inc. was created in 1984
The Mathworks is now responsible for development, sale, and support for MATLAB
The Mathworks is located in Natick,
Products Of Math Works
APPLICATIONS
1.Technical computing
2.Engineering and sciences applications
Electrical Engineering
DSP and DIP
Automation
Communication purpose
Aeronautical
Pharmaceutical
Financial services.
Strengths of MATLAB
MATLAB is relatively easy to learn.
MATLAB code is optimized to be relatively quick when performing matrix operations.
MATLAB may behave like a calculator or as a programming language.
MATLAB is interpreted, errors are easier to fix.
Weaknesses of MATLAB
MATLAB is NOT a general purpose programming language.
MATLAB is an interpreted language (making it for the most part slower than a compiled language such as C++).
Other Features
2-D and 3-D graphics functions for visualizing data
Tools for building custom graphical user interfaces
Functions for integrating MATLAB based algorithms with external applications and languages, such as C, C++, Fortran, Java, COM, and Microsoft Excel
Components of MATLAB Interface
Workspace
Current Directory
Command History
Command Window
Current Directory Window
To quickly access files on the MATLAB path.
Command Window
To execute commands in the MATLAB environment.
Work Space Window
To view variable definitions and variable memory allocations.
Command History Window
Displays all commands issued in MATLAB since the last session (good for learning and verification).
Simulink
It is a commercial tool for modeling, simulating and analyzing multidomain dynamic systems.
Its primary interface is a graphical block diagramming tool and a customizable set of block libraries.
Simulink is widely used in control theory and digital signal processing for multidomain simulation and Model-based design.