ABSTRACT
The development of technologies affects the demands of industries at the present time. Thus, automatic control has played a vital role in the advance of engineering and science. In today’s industries, control of DC motors is a common practice. Therefore, implementation of DC motor controller is required. There are many types of controller that can be used to implement the elegant and effective output. One of them is by using a PID controller. PID stands for Proportional and Integral and Differential Controllers which are designed to eliminate the need for continuous operator attention thus provide automatic control to the system. This project is focused on implementing PI and PID controllers to control speed of a dc motor. The DC motor was modelled mathematically and simulated using MATLAB/SIMULINK. The overall project is divided into two parts. The first part is concern with the simulation of the DC Motor using MATLAB SIMULINK where the second part dealt with the simulation of the DC motor and PI,PID controllers. From the results obtained, it was shown that the due to inrush current at start-up, the armature current of the DC motor has high transient. From the controlled motor, it was observed that the PID showed a reduced overshoot and increased settling time.
TABLE OF CONTENTS
Title Page i
Declaration ii
Certification iii
Dedication iv
Acknowledgements v
Table of Contents vi
List of Tables viii
List of Figures ix
Abstract x
CHAPTER 1: INTRODUCTION 1
1.1 Background
of the Study 1
1.2 Problem
Statement 5
1.3 Aim and Objectives of the Study 6
CHAPTER 2: LITERATURE REVIEW 7
2.1 Speed
Control of Convectional Induction Motor 9
2.2 Theory
of Inverse Parallel Controller 19
2.3 MOSFET
as Switching Device 22
CHAPTER 3: MATERIALS AND
METHODS 24
3.1 Dynamic Modelling of the Three Phase Inverse
Parallel Controller 24
3.2 V rms Expression for
Three Phase Inverse Parallel Thyristor 26
3.3 Dynamic Modeling of
Thyristor Control 29
3.4 Dynamic Modeling of
Thyristor Parameter 30
3.5 Switching Sequence of the Inverse Parallel
Thyristor 32
3.6
Matlab/Simulink Implementation of Three Phase Inverse Parallel
Controller 36
3.7
Total Harmonic Distortion Analysis of the AC Control 38
CHAPTER 4: RESULTS AND
DISCUSSION 41
4.1
Simulation of Thyristor and Mosfet Base Three Phase Inverse Parallel
Controller 41
4.1.1 Simulation of thyristor base three phase
inverse parallel controller 42
4.1.2
Simulation of mosfet base three phase inverse parallel controller 49
CHAPTER 5: CONCLUSION AND
RECOMMENDATIONS 55
5.1 Conclusion 55
References 56
LIST OF
TABLES
PAGE
3.1: Pole voltage for the
three phase inverse parallel controller 34
3.2: Phase-to-neutral
voltage for the three-phase inverse parallel controller 35
3.3: Line-to-line
voltage for three phase inverse parallel controller 35
3.4: Instantaneous controller voltage 39
4.1: Variation
of delay angle with load voltage 54
LIST OF
FIGURES
PAGE
3.1 Three phase AC full wave voltage controller 25
3.2 Gate drive signal for step mode of operation 34
3.3 Matlab/Simulink implementation of firing delay circuit 36
3.4 Matlab/Simulink
implementation of a thyristor base three phase
inverse
parallel controller with R-L load 37
3.5 Matlab/Simulink implementation of a
MOSTFET base three phase inverse
parallel
controller with R-L load
38
4.1 Three phase gate pulse for implementation
thyristor T1, T2, T3 42
4.2 Three phase gate pulse for implementation
thyristor T1, T4 43
4.3 Thyristor voltages for T1, T2, T3 at
conduction period 0.02 second 44
4.4 Thyristor gate voltage (Vt) for T1, T4 for
three phase controller 45
4.5 Thyristor gate currents
for T1, T4 for the thyristor based three phase
controllers 46
4.6 Load voltage (VL) for the
thyristor base three phase controller
under
R-L load 47
4.7 Load current for three phase controller
under R-L load 48
4.7 Five phase gate for implementation thyristor T1, T4 49
4.8 MOSFET gate voltage for T1, T2, T3 50
4.9 MOSTFET gate current for T1, T4 to the
inverse parallel controller 51
4.10 Load voltage (Lv) for MOSTFET base inverse
parallel controller 52
4.11 Current (IL) for the MOSTFET
base inverse parallel controller 53
4.12 Graph of percentage difference in load
voltage firing angle 54
CHAPTER
1
INTRODUCTION
1.1 BACKGROUND OF THE STUDY
Over
the past decades DC machines were used extensively for variable speed
applications due to the decoupled control of torque and flux that can be
achieved by armature and field current control respectively. DC drives are
advantageous in many aspects as in delivering high starting torque, ease of
control and nonlinear performance. But due to the major drawbacks of DC machine
such as presence of mechanical commutator and brush assembly, DC machine drives
have become obsolete today in industrial applications Bose (1997). The
robustness, low cost, the better performance and the ease of maintenance make
the asynchronous motor advantageous in many industrial applications or general
applications.
Squirrel
cage induction motors (SCIM) are more widely used than all the rest of the
electric motors as they have all the advantages of AC motors and are cheaper in
cost as compared to Slip Ring Induction motors; require less maintenance and
rugged construction. Because of the absence of slip rings, brushes maintenance
duration and cost associated with the wear and tear of brushes are minimized.
Due to these advantages, the induction motors have been the execution element
of most of the electrical drive system for all related aspects: starting,
braking, speed change and speed reversal etc Vasudevan et al (2005).
To
reach the best efficiency of induction motor drive (IMD), many new techniques
of control has been developed in the last few years. Now-a-days, using modern
high switching frequency power converters controlled by microcontrollers, the
frequency, phase and magnitude of the input to an AC motor can be changed,
hence the motor speed and torque can be controlled. Today, it is possible to
deal with the axis control of machine drives with variable speed in low power
applications mostly due to joint progress of the power electronics and
numerical electronics. The dynamic operation of the induction machine drive
system has an important role on the overall performance of the system of which
it is a part Takahashi and Noguchi (1986).
The
advent of power electronics and therefore the means of controlling the speed of
induction machines, has led to ac variable speed induction motor drives, which
are by far the most popular and most used in meeting many applications
nowadays. Venter et al (2012).
In
recent years, the field oriented control of induction motor drive is widely
used in high performance drive system because of its advantages. Now a day’s
there is a great demand in industry for adjustable speed drives. Even though
investigations have been carried out for decades for the efficient control of
the speed of induction motor. Sachin and Satya (2012).
Efficiency improvements of
constant-speed, variable torque drives are different from those of constant
speed and constant torque applications. During the past 20 years, beginning
with the Nola Controller, attempts have been made to design simple, inexpensive
thyristor/triac controllers. Such controllers are able to sense the torque of a
drive and subsequently adjust the input voltage and current of single- and
three-phase induction motors as they are used in appliances and commercial
applications, where the torque required changes with load Ewald et al (2002). In order to accurately
measure additional losses in controllers and induction motors, as well as power
factors including the total harmonic distortions of currents and voltages at
the input and output of the controller, computer-aided testing (CAT) circuits
are used. Most single-phase controllers generate dc current components of the
input and output currents through imperfect gating signals. Such dc components
cause additional losses, vibration, and audible noise.
Three-phase
induction motors are inherently more efficient than single-phase motors.
Therefore, the percentage power savings due to a controller can be expected to
be less for three-phase machines than for single-phase motors Ewald et al (2002). Power electronic converters are
used as interface between three-phase grid supply and the driving motor Wheeler
et al (2002).
In this thesis, an induction motor drive is analyzed.
The focus here will be to model a power electronic control scheme for speed
control of the induction motor.
The power electronic converter is the backbone of a
variable speed drive Rodriguez et al (2012). It is used to process the
electrical power of utility grid and supply to the electric motor. The rapid
growth in the semiconductor material and switching devices has led to
tremendous improvements in the power converters and in the development of
numerous species. Without proper control of the induction motor speed, it is
practically impossible to achieve the desired task for a specified application
Iqbal (2006).
The power electronics controller for induction
motor is a group of devices that serves to govern in some predetermined manner
the performance of an electric motor. A motor controller might include a manual
or automatic means for starting and stopping the motor, selecting forward or
reverse rotation, selecting and regulating the speed, regulating or limiting
the torque, and protecting against overloads and faults. On the other hand, the
main advantages of modern controllers are; high efficiency, low weight and
small dimensions makes it compact and portable, fast operation as a result of
no moving part compared to mechanical switches and high power densities are
gained using it in the switch mode operation. With the corresponding control,
power electronics controllers are good and simple methods for changing the
motor voltage. These electronics not only control the motor’s speed, but can
improve the motor’s dynamic and steady state characteristics. In addition,
power electronics can reduce the system’s average power consumption and noise
generation of the motor Okoro(2013).
A
three phase induction motor is basically a constant speed motor so it’s
somewhat difficult to control its speed. The speed control of induction motor
is done at the cost of decrease in efficiency and low electrical power factor. Electric drives play an important
role in the field of power electronics since they are used in a wide range of
applications. In this context it is important to match the correct drive to the
application in accordance with its requirements. In the recent decades, a huge
step had been taken in power semiconductors and microprocessors development. As
a result, modern drive system technology had changed dramatically, and
accordingly more studies were done on electric drive systems to fulfill the
various needs of different application. The continuous improvements in power
electronics field made it easier to develop modern switch mode inverters based
on high speed power transistors, like MOSFET and IGBT Badran et al (2013).
Motion control is the backbone of
automation system widely used in every section of industrial and commercial
activities, the heart of this motion control is variable speed drives (VSDs).
An induction motors (AC drives) are widely used VSDs as a result of its low
maintenance cost while offering equal and often superior dynamic performance
over their DC drives counterparts in all possible scales (Large, Medium and
small) of motion control tasks such as production machine, industrial robots,
proportional tasks in electric transit vehicles, electric elevators, pumps and similar
Okakwu and Oluwasogo (2014)
Dynamic
simulations play an important role in the pre-testing of motor drive systems.
Pre-testing is conducted by engineers in industry as well as by researchers in
academia. Pre-testing using dynamic simulations can help researchers to
determine the experimental setup that will be used for a given set of
experimental tests. The transient behaviour of an electric machine is of
particular importance when the drive system is to be controlled. Many different
methods and control algorithms are available in the literature for controlling
the three-phase induction motor Vasudevan and Arumuyam (2004). A dynamic model
of a machine leads to insight into the electrical transients Vasudevan et al (2005).
There is an increasing trend of
using fast switching devices for several industrial applications. Thyristors
are known to have low switching frequency of the order of hundreds of Hz. Hence
the alternative is to use fast switching devices such as MOSFETs and IGBTs. Thus
a simulation model was developed by them incorporating a soft start system using
IGBTs . The motor speed response to various conduction angles were also
depicted. It was once again observed that the response settling time is
inversely proportional to the conduction angle. Moreover, the speed response is
smoother compared to the thyristor soft starts case.
The
advantage of using IGBTs is that due to same extinction angle as that of firing
angle, the fundamental current in this case is in phase with the voltage, hence
displacement factor becomes unity. A plot of the power factor vs firing angle
was also illustrated in their work. They revealed that the power factor varies
significantly with change in the firing angle especially- for IGBT based soft
starter. Nevertheless, it was higher for thyristor based system Riyaz et al (2009).
1.2 PROBLEM STATEMENT
The
three phase induction motor drives have found application in the industries,
but not without problems associated with efficient control, without reduction
in system’s dynamic performance. Previous works on the dynamic models of
inverse parallel controllers for speed control of induction machines have been
developed using thyristor based controllers. There is need for the use of
MOSFET based inverse parallel controllers to be adopted for the speed control
of induction machines. This power transistor such as MOSFET makes the drive
lighter, reduces cost, it is also has a high switching speed and good
efficiency at low voltages.
1.3 AIM AND OBJECTIVES OF THE STUDY
This
research project aims at investigating the dynamic performances of a
three-phase MOSFET and thyristor based inverse parallel controllers for
improved performance.
The
specific objectives for this research are;
·
To critically review the
current developments in controllers by adequate review of some relevant
literatures.
·
To critically review the
current developments in inverse parallel controllers by adequate review of some
relevant literatures.
·
To model and simulate an
inverse parallel MOSFET controller and compare it with an inverse parallel
thyristor controller.
·
To model and simulate the
both controllers connected to R-L load.
·
To use computer
simulations to validate theoretical findings.
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