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i
DEVELOPMENT OF CONTROL SHCEME FOR DC MOTOR SPEED CONTROL
APPLICATIONS
SITI NURNADIRAH BINTI AHMAD LATFI
This thesis is submitted as partial fulfillment of the requirements for the award of the
Bachelor of Electrical Engineering (Hons.) (Power System)
Faculty of Electrical & Electronics Engineering
Universiti Malaysia Pahang
NOVEMBER, 2010
ii
“I hereby acknowledge that the scope and quality of this thesis is qualified for the
award of the Bachelor Degree of Electrical Engineering (Power System)”
Signature : ______________________________
Name : RAJA MOHD TAUFIKA BIN RAJA ISMAIL
Date : 11 NOVEMBER 2010
iii
“All the trademark and copyrights use herein are property of their respective owner.
References of information from other sources are quoted accordingly; otherwise the
information presented in this report is solely work of the author.”
Signature : ____________________________
Author : SITI NURNADIRAH BINTI AHMAD LATFI
Date : 11 NOVEMBER 2010
v
ACKNOWLEDGEMENT
First and foremost, I would like to express my heartily gratitude to my
supervisor, Mr. Raja Mohd Taufika bin Raja Ismail for the guidance and enthusiasm
given throughout the progress of this project. In preparing this thesis, I was in contact
with many people, researchers, academicians, and practitioners. They have
contributed towards my understanding and thoughts. In particular, I wish to express
my sincere appreciation to my main project supervisor, Mr. Raja Mohd Taufika bin
Raja Ismail, for encouragement, guidance, critics and friendship and for giving me
guidance, advices and motivation. Without his continued support and interest, this
thesis would not have been the same as presented here.
I am also indebted to Universiti Malaysia Pahang (UMP) for funding my
Bachelor study. Librarians at UMP, and University Technology Malaysia and also
deserve special thanks for their assistance in supplying the relevant literatures. My
fellow final year students should also be recognized for their support. My sincere
appreciation also extends to all my colleagues and others who have provided
assistance at various occasions. Their views and tips are useful indeed. I am grateful
to all my family members.
My appreciation also goes to my family who has been so tolerant and
supports me all these years. Thanks for their encouragement, love and emotional
supports that they had given to me.
vi
ABSTRACT
Nowadays, DC motors plays a vital role in most of the industrial areas, it can
be seen in most of the electronic devices. The purpose of a motor speed controller is
to take a signal representing the demanded speed, and to drive a motor at that speed.
In this project, the power converter for DC motor application is developed. One of
the most common methods is by using PWM wave to control the speed of the motor.
Therefore, to provide the required power to the motor, SPMS is used to supply the
DC motor from AC power supply. Rectifier which converted AC/DC and buck
converter are combined which output can be supplied to the DC motor. The SMPS
which supplies the DC motor is developed and the output is controlled by using
PWM. TL494 is used to generate the PWM wave which can be varied in duty ratio.
In the end of this project, the motor speed will satisfied the desired speed control as
expected.
vii
ABSTRAK
Pada masa kini, DC motor memainkan peranan penting didalam kawasan
perindustrian yang dapat dilihat penggunanaannya untuk peralatan elektronik. Tujuan
mengawal kelajuan motor adalah bagi mengambil isyarat yang mewakili kelajuan
yang diminta dan untuk mengawal motor pada kelajuan yang telah ditetapkan.
Melalui projek ini, penukar kuasa untuk aplikasi motor DC telah dihasilkan. Salah
satu cara yang sering digunakan adalah melalui gelombang PWM untuk mengawal
kelajuan motor. Walau bagaimanapun, untuk menghasilkan kuasa yang diperlukan
oleh motor, SPMS digunakan untuk memberi kuasa kepada motor AC dari motor
DC. Perata arus (Rectifier) yang mengubah AC/DC dan ‘buck converter’
digabungkan dimana keluaran dapat dibekalkan kepada motor DC. SMPS yang
membekalkan motor DC telah dikembangkan dan keluaran dikawal oleh PWM. PIC
microcontroller digunakan untuk menghasilkan gelombang PWM yang dapat
dikawal melalui perbandingan bebas (duty ratio). Di akhir projek ini, kelajuan motor
akan memenuhi kelajuan yang ditetapkan.
viii
TABLE OF CONTENTS
CHAPTER TITLE PAGE
TITLE PAGE i
DECLARATION iii
DEDICATION iv
ACKNOWLEDGEMENT v
ABSTRACT vi
ABSTRAK vii
TABLE OF CONTENTS viii
LIST OF TABLES xi
LIST OF FIGURES xiii
LIST OF APPENDICES xiv
1 INTRODUCTION 1
1.1 Introduction 1
1.2 Background 1
1.3 Objective of the project 2
1.4 Scope of the project 2
1.5 Problem statement 2
1.6 Project background 3
1.6.1 Overview of Pulse Width Modulator 3
1.6.2 Methodology of the project 3
ix
1.7 Thesis outline 4
2 LITERATURE REVIEW 5
2.1 Introduction 5
2.2 DC Motor 5
2.3 Pulse Width Modulator (PWM) 7
2.4 Full wave rectifier 10
2.5 DC-DC converter 12
2.5.1 Step down (buck) converter 12
2.5.2 Continuous conduction mode 15
2.5.3 Buck converter operation 18
(a) Mode 1 18
(b) Mode 2 19
2.6 Power MOSFET 20
2.6.1 MOSFET circuit model 21
3 METHODOLOGY 24
3.1 Introduction 24
3.2 Pulse Width Modulation (PWM) Generation 25
3.2.1 TL494 25
3.3 Atmel AVR 28
3.3.1 ATmega48 28
3.4 The Proportional Integral Derivative (PID) Algorithm 30
3.5 Speed measurement by using optical encoder 31
3.6 RS232 serial port 33
x
4 BUCK CONVERTER DRIVEN DC MOTOR BY
USING PI CONTROLLER
35
4.1 Introduction 35
4.2 Model of Buck Converter Driven DC Motor System 35
4.2.1 Modelling of the Buck Converter Driven DC
Motor
36
4.2.2 Proportional Integral (PI) Control Scheme 37
4.3 MatLab 39
5 RESULT AND DISCUSSION 40
5.1 Introduction 40
5.2 Software Implementation 40
5.3 Optimization Process 42
6 CONCLUSION AND RECOMMENDATION 44
6.1 Introduction 44
6.2 Conclusion 44
6.3 Recommendations 45
REFERENCES 47
xi
LIST OF FIGURES
FIGURE
NO.
TITLE PAGE
1.1 Block diagram of the project 4
2.1 Switch mode dc-dc conversion 8
2.2 Pulse Width Modulator:
(a) block diagram; (b) comparator signals
9
2.3 (a) Full wave rectifier bridge
(b) Current direction of the cycle
11
2.4 Step down dc-dc converter 14
2.5 Step down converter states (assume flows
continuously):
(a) switch ON; (b) switch OFF
16
2.6 Equivalent Circuit for First Mode Operation 19
2.7 Equivalent Circuit for Second Mode Operation 19
2.8 Power MOSFET 20
2.9 (a) Cross sectional view of n-channel MOSFET
(b) MOSFET equivalent circuit for transient analysis in cut
off and active regions
(c) MOSFET equivalent circuit in the ohmic region
(d) Variation n gate drain capacitance with drain source
voltage
22
3.1 Block Diagram of the System 24
3.2 TL494 Pin Diagram 26
xii
3.3 TL494 Modulation Technique 27
3.4 Pin Diagram of Atmel48 29
3.5 A Block Diagram of PID Controller 31
3.6 Sample Disc of Encoder 31
3.7 Basic schematic circuit of optical encoder 32
3.8 Handshake looping a PC serial connector 34
4.1 Description of the buck converter driven dc motor system 36
4.2 PI Control structure of buck converter driven dc motor 38
4.3 Buck driven motor by PI controller system 39
4.4 Parameter for Positive IS setting 40
4.5 Parameter of Buck Driven Motor 40
5.1 Input to buck driven DC motor/Signal constrain 42
5.2 Optimization Progress 42
5.3 Angular velocity of the input and output 43
xiii
LIST OF TABLES
TABLE
NO.
TITLE PAGE
2.1 Advantages and disadvantages of various types of DC
motor
6
3.1 RS232 pin assignments (DB9 PC signal set) 33
xiv
LIST OF SYMBOLS
= Sawtooth voltage
= Dc input voltage
= Average output voltage
= Settling time
= Inductor/positive voltage
= Input power
= Output power
= Resistor
= Inductor
= Capacitor
= Inductor current
= Duty ratio
= Centimetre
= Silicon
= Silicon dioxide
= Oscillator frequency
= Hertz
= Timing capacitor
= milivolt
= rotation per minute
= Pulse width modulation
xv
LIST OF APPENDICES
APPENDIX TITLE PAGE
A Parameter of buck driven motor 49
B Hardware Implementation 50
C Schematic Diagram 51
1
CHAPTER 1
INTRODUCTION
1.1 Introduction
This chapter will explain the objective of the project, scope of the project,
problem statement and the project background. In this introduction section the
review of full wave rectifier, buck converter and pulse width modulation (PWM)
control will be explained. At the end of chapter 1 the thesis outline is briefly
describe.
1.2 Background
Nowadays, the direct current (DC) motor is a device that is used through
many industries in order to convert electrical energy into mechanical energy.
Industrial machinery is often driven by electric motors that have provisions for speed
adjustment. Such motors are simply larger, more powerful versions of those driving
familiar appliances such as food blenders or electric drills. These motors normally
operate at a fixed speed. If speed control is required, then the controller is called an
adjustable speed drive or a variable speed controller.
The speed of a DC motor needs to be controlled by a circuit driver, in order to
cater to the users’ needs. Basically, it should be able to vary the speed from
minimum speed to maximum speed. The voltage must also be limited to 24 Vdc,
which is the maximum voltage of the motor itself.
2
1.3 Objective of the Project
The objectives of the project are as follows:
(i) To develop rectifier to rectify 230 Vac to 24 Vdc
(ii) To develop buck converter that produces dc output voltage that can be varied
from 0 Vdc to 24 Vdc
(iii) To control dc motor speed by varying PWM
1.4 Scope of the Project
This project is developed by using input of 240 Vac from TNB. To control
and vary the output voltage of power supply, the PWM control technique is used. At
the end of the buck converter output DC voltage can be produce in the range of 0 –
24 V. Then a DC motor is connected to the buck converter output to vary the speed.
1.5 Problem Statement
DC Motor is widely used in speed control system which needs high control
requirements. So, it is crucial to control the motor speed in order to achieve good
production. One of the most common methods to drive a dc motor is by using PWM
signals with respect to the motor input voltage.
3
1.6 Project Background
This section will describe the overview of Pulse Width Modulator (PWM)
and the methodology to develop this project. The methodology will be described by
using the block diagram.
1.6.1 Overview of Pulse Width Modulator
Pulse Width Modulator (PWM) is used to control the frequency and the
magnitude of the ac voltage across the load and to reduce the harmonic contents in
the output voltage or current. There are a number of PWM techniques, but the most
common type is the sinusoidal PWM [7].
1.6.2 Methodology of the Project
In the research of this project, the 230 Vac power supply is step down by the
transformer. Then, the ac voltage is rectified to produce pure dc voltage. Dc voltage
is then feed as input of buck converter. MOSFET is used as the power switch of
this project. The output voltage of the converter is then varied by using pulse width
modulation control which varies the duty cycle of the switch.
1.7 Thesis Outline
This thesis wa
summarized as below.
Chapter 1 discussed the ove
the project and scope of the project.
Chapter 2 described briefly the hardware components used in this project,
including their description of operation and article review of the project.
Chapter 3 foc
included the generation of power supply, generation of PWM waveform and full
circuit diagram of the project.
Chapter 4 elaborated
and the PI controller design.
Chapter 5 focuse
using MatLab and the result obtained from hardware design.
Chapter 6 describe
and commercialization of the project.
Figure 1.1: Block diagram of the project
Thesis Outline
This thesis was divided into 6 chapters which the content of each chapter was
summarized as below.
Chapter 1 discussed the overview of the concept of the project, objective of
the project and scope of the project.
Chapter 2 described briefly the hardware components used in this project,
including their description of operation and article review of the project.
Chapter 3 focused on the methodology of this research project which
the generation of power supply, generation of PWM waveform and full
circuit diagram of the project.
Chapter 4 elaborated in detailed about the designing step of buck converter
ler design.
Chapter 5 focused on the result obtained from the simulation design
and the result obtained from hardware design.
Chapter 6 described the conclusion, the future recommendation and costing
and commercialization of the project.
4
h the content of each chapter was
rview of the concept of the project, objective of
Chapter 2 described briefly the hardware components used in this project,
including their description of operation and article review of the project.
research project which
the generation of power supply, generation of PWM waveform and full
in detailed about the designing step of buck converter
on the result obtained from the simulation designed by
the conclusion, the future recommendation and costing
5
CHAPTER 2
LITERATURE REVIEW
2.1 Introduction
This chapter includes the study of different types of DC motors. In this
chapter will explain in detail the operation of pulse width modulation control, full
wave rectifier and buck converter. Besides, all the circuit diagram and element that
had been used to develop this project will be review in detail.
2.2 DC Motor
There are several types of DC motors that are available. Their advantages,
disadvantages, and other basic information are listed below in the Table 2.1. In this
project, I had chose DC permanent magnet servo motor which is small, compact and
easy to find. This type of motor is inexpensive to get. However, this type of DC
motor is generally small and cannot vary the magnetic field strength.
6
Table 2.1 Advantages and disadvantages of various types of DC motor.
Type Advantages Disadvantages
Stepper Motor Very precise speed and
position control. High
Torque at low speed.
Expensive and hard to
find. Require a switching
control circuit
DC Motor w/field coil Wide range of speeds and
torques. More powerful
than permanent magnet
motors
Require more current
than permanent magnet
motors, since field coil
must be energized.
Generally heavier than
permanent magnet
motors. More difficult to
obtain.
DC permanent magnet
motor
Small, compact, and easy
to find. Very inexpensive
Generally small. Cannot
vary magnetic field
strength.
Gasoline (small two
stroke)
Very high power/weight
ratio. Provide Extremely
high torque. No batteries
required.
Expensive, loud, difficult
to mount, very high
vibration.
7
2.3 Pulse Width Modulator (PWM)
In principle, all modulation schemes aim to create trains of switched pulses
which have the same fundamental volt-second average (i.e., the integral of the
voltage waveform over time) as a target reference waveform at any instant. The
major difficulty from these trains of switched pulses is that they also contain
unwanted harmonic components which should be minimized. Hence for any PWM
scheme, a primary objective can be identified which is to calculate the converter
switch ON times which create the desired (low frequency) target output voltage or
current [2]. Having satisfied this primary objective, the secondary objective for a
PWM strategy is to determine the most effective way of arranging the switching
processes to minimize unwanted harmonic distortion, switching losses or any other
specified performance criterion.
In dc-dc converter, the average dc output voltage must be controlled to equal
a desired level, though the input voltage and the output load may fluctuate [3].
Switch mode dc-dc converters utilize one or more switches to transform dc form one
level to another. In a dc-dc converter with a given input voltage, the average output
voltage is controlled by controlling the switch ON and OFF durations ( and )
[2, 3]. To illustrate the switched mode conversion concept, consider a basic dc-dc
converter shown in figure 2.1a. The average value of the output voltage in
figure 2.1b depends on and . One of the methods for controlling the output
voltage employs switching at a constant frequency hence, a constant switching time
period, = + and adjusting the ON duration of the switch to control the
average output voltage [3]. In this method, called pulse width modulation (PWM)
switching, the switch duty ratio, D, which is defined as the ration of the ON duration
to the switching time period, is varied [3, 4, 5].
8
(a)
(b)
Figure 2.1: Switch mode dc-dc conversion: (a) Basic dc-dc converter; (b) The
average value of the output voltage
In the PWM switching at a constant switching frequency, the switch control
signal which controls the state (ON or OFF) of the switch is generated by comparing
a signal level control voltage, with a repetitive waveform as shown in figure
2.2b. The control voltage signal generally is obtained by amplifying the error or the
difference between the actual output voltage and its desired value. The frequency of
repetitive waveform with a constant peak which is shown to be a saw tooth, establish
the switching frequency. This frequency is keep constant in a PWM control and is
chosen to be on a few kilohertz to a few hundred kilohertz range [3]. When the
amplified error signal, which varies very slowly with time relative to the switching
frequency, is greater than the saw tooth waveform, the switch control signal becomes
high causing the witch to turn ON. Otherwise, the switch is OFF.
-
VoR
+
+
-
Vd
0
9
(a)
(b)
Figure 2.2: Pulse Width Modulator: (a) block diagram; (b) comparator signals
In terms of and the peak of the saw tooth waveform in figure
2.2b, the switch duty ration can be expresses as;
= = (2.1)
( )Switch
control signal( ) Comparator
Amplifier
Repetitive waveform
(Amplified error)
= ℎ
t0
>
OnOnSwitch control signal
Off Off <
10
The dc-dc converters can have two distinct modes of operation:
(i) Continuous current conduction
(ii) Discontinuous current conduction
In practice, a converter may operate in both modes, which have significantly
different characteristics [3, 5]. Therefore, a converter and its control should be
designed based on both modes of operation.
2.4 Full Wave Rectifier
DC voltage and current are required for electronic devices, hence, is
necessary to covert AC into DC by a process called rectification. There are several
ways of connecting diodes to make a rectifier to convert AC to DC.
The bridge rectifier is the most important and it produces full-wave varying DC [6].
The objective of a full wave rectifier is to produce a voltage or current that is purely
DC or has some specified DC component [4]. Rectification of AC voltages and
currents is accomplished by means of diodes [3].
During the positive half-cycle, shown in red, the top end of the transformer
winding is positive with respect to the bottom half. Therefore, the transformer pushes
electrons from its bottom end, through D3 which is forward biased, and through the
load resistor in the direction shown by the red arrows. Electrons then continue
through the forward-biased D2, and from there to the top of the transformer winding.
This forms a complete circuit, so current can indeed flow. At the same time, D1 and
D4 are reverse biased, so they do not conduct any current.
During the negative half-cycle, the top end of the transformer winding is
negative. Now, D1 and D4 are forward biased, and D2 and D3 are reverse biased.
Therefore, electrons move through D1, the resistor, and D4 in the direction shown by
the blue arrows. As with the positive half-cycle, electrons move through the resistor
from left to right.