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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

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“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

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“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

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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.

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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.

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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.

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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

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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

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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

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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

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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.

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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.

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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.

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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.

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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].

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(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.