DEVELOPMENTS OF PC BASED CONTROLLER FOR BUCK …

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DEVELOPMENTS OF PC BASED CONTROLLER FOR BUCK CONVERTER DRIVEN DC MOTOR

NURSYAHIDA ASHIKIN BINTI NOR IZLANIN

This thesis is submitted as partial fulfillment of the requirements for the award of the

degree of Bachelor of Electrical Engineering (Power Systems)

Faculty of Electrical & Electronics Engineering

University Malaysia Pahang

NOVEMBER, 2010

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SUPERVISOR’S DECLARATION

I hereby declare that I have read this project report and in my opinion this project report is

sufficient in terms of scope and quality for the award of Bachelor in Electrical Engineering

(Power System)

Signature :

Name of Supervisor : MR RAJA MOHD AUFIKA RAJA ISMAIL

Date :

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STUDENT’S DECLARATION

I hereby declare that the work in this report is my own except for quotations and summaries

which have been duly acknowledged. The report has not been accepted for any degree and is not

concurrently submitted for award of other degree.

Signature :

Name : NURSYAHIDA ASHIKIN BINTI NOR IZLANIN

ID Number : EC07016

Date : 09 NOVEMBER 2010

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ACKNOWLEDGEMENT

I would like to express my gratitude and appreciation to all those who gave me the

possibility to complete this report. Special thanks is due to my supervisor Mr. Raja Mohd

Taufika Raja Ismail who’s help, stimulating suggestions and encouragement helped me in all

time to successful this project and in writing this report.

Many thanks go to the all lecturer and supervisors who have given their full effort in

guiding the team in achieving the goal as well as their encouragement to maintain our progress in

track. My profound thanks go to all classmates, especially to my friends for spending their time

in helping and giving support. Not forgetting for my parent and family who are fully support me

in every condition. Thanks All.

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ABSTRACT

Switched Mode Power Supplies (SMPS) is the technique proposed in this investigation

to control the speed of DC motor. In the design of these power supplies, the semiconductor

devices are either switched on or off. It is highly efficient because of the low voltage drop across

the semiconductor device when it is on and cause the power consumption is low. The power

supply is consists of rectifier and Buck converter. The implementation the PWM Chopper with a

MOSFET also needed because nowadays, the chopper switch is obviously a fast power

MOSFET with very short switching times and low resistance that reduce the conductive losses

but produce extremely high voltage- and current-rates. As the result, PWM signal is used to

control the speed of the motor and the output voltage of the buck converter with the adding of PC

interface in order to make it easy and friendly user system.

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ABSTRAK

Switched Mode Power Supply (SMPS) adalah teknik yang dicadangkan dalam

penyiasatan untuk menyiapkan projek ini iaitu untuk mengawal kelajuan motor arus terus (DC).

Dalam mereka pembekal kuasa ini, semikonduktor samada suisnya buka atau tutup, ia

mempunyai kecekapan yang tinggi kerana kadar kejatuhan voltage adalah rendah apabila melalui

semikonduktor dan mengakibatkan penggunaan kuasa juga adalah rendah. Pembekal kuasa ini

adalah terdiri daripada rectifier dan buck converter. Penghasilan PWM Chopper dengan

MOSFET juga sangat diperlukan sekarang kerana suis chopper adalah terbukti sebagai MOSFET

yang mempunyai masa suis yg sangat rendah dan rintangan yang rendah yang dapat

mengurangkan kehilangan konduktor tetapi menghasilkan kadar voltan dan elektrik yang tinggi.

Kesimpulannya, Pulse Width Modulation (PWM) digunakan untuk mengawal kelajuan motor

dan kadar keluran voltan daripada buck converter dengan penambahan sistem interface komputer

dalam menghasilkan sistem yang mudah dan selesa bagi pengguna.

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TABLE OF CONTENTS

CHAPTER TITLE PAGE

SUPERVISOR’S DECLARATION i STUDENT’S DECLARATION ii DEDICATION iii ACKNOWLEDGEMENT iv ABSTRACT v ABSTRAK vi TABLE OF CONTENT vii LIST OF TABLE x LIST OF FIGURE xi

1 INTRODUCTION

1.1 Introduction 1

1.2 Background 1

1.3 Objective 2

1.4 Scope of the Project 2

1.5 Problem Statement 2

1.6 Project Background 3

1.6.1 Overview of chopper drive and buck-converter 3

1.6.2 Methodology of the Project 3

1.7 Thesis Outline 4

2 LITERATURE REVIEW

2.1 Introduction 5

2.2 DC Motor 6

2.3 Chopper Drive 7

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2.4 Switched Mode Power Supply (SMPS) 9

2.4.1 DC-DC Converter 11

2.4.2 Buck Converter 11

2.5 Pulse Width Modulation (PWM) 16

3 METHODOLOGY

3.1 Introduction 18

3.2 PWM Chopper Drive 18

3.3 PWM Signal Generation 20

3.4 Speed Feedback 20

3.5 Control Signal Generation and Implementation of PIC

Controller In Software. 21

3.6 Main Component 21

3.6.1 DC Motor 21

3.6.2 Buck Converter 22

3.6.3 RS232 DB9 Connector 23

4 HARDWARE DESIGN

4.1 Introduction 25

4.2 Designing Input Voltage of The Buck Converter 25

4.3 Designing The Buck Converter 26

4.4 Pulse Width Modulation (PWM) Generation 27

4.5 Development of the Project 28

4.7.1 Simulation Stage 28

4.7.1.1 Rectification Design 28

4.7.1 2 Buck Converter Simulation 28

4.7.2 Hardware Stage 29

4.7.2.1 Rectification Hardware 29

4.7.2.2 Buck Converter Hardware 30

4.7.3 PWM Generator Hardware 30

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4.7.4 PC Interface 31

5 RESULT AND CONCLUSION

5.1 Introduction 33

5.2 Simulation Result 33

5.2.1 Voltage Output From Buck Converter 33

5.2.2 PWM Output From PIC 16F877A 34

5.3 Hardware Result 34

5.3.1 Buck Converter Construction 35

5.3.2 Buck Converter Output Result 35

5.4 Rectification Result 38

5.5 PWM Output 38

5.5.1 PWM Output From Motor 39

5.5.2 PWM Output From Serial Port 42

5.6 Analysis 45

5.7 Discussion 45

5.8 Summary 45

6 CONCLUSION AND RECOMMENDATION

6.1 Introduction 46

6.2 Conclusion 46

6.3 Future Recommendation 47

6.4 Costing And Commercialization 47

REFERENCES

APPENDICES

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LIST OF TABLES

Table No. Title Page

2.1 DC Motor Characteristics and Applications 6

5.1 Result for DC Motor Speed 36

6.1 Costing for the Project 48

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LIST OF FIGURES

Figure No. Title Page

1.1 The block diagram of the project 4

2.1 Step-Down Chopper Circuit 8

2.2 Step-down chopper switching waveform 8

2.3 Basic SMPS block diagram 10

2.4 General Block Diagram for DC to DC converter 11

2.5 Buck Regulator Step Down 12

2.6 Circuit When Switch is On 14

2.7 Circuit When Switch is Off 15

2.8 The Resultant of Wave When Switch is On and Off 15

2.9 A simple PWM circuit 16

2.10 Duty Cycle of 50% Pulse Width from 5V supply 17

2.11 Duty Cycle of 70% Pulse Width from 5V supply 17

3.1 Chooper Drive Block Diagram 18

3.2 The Resultant Voltage Wave 19

3.3 The Basic Chopper Circuit 19

3.4 Process to generate PWM Wave 20

3.5 The Sensor For Giving Feedback 20

3.6 Process for PIC controller 21

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3.7 The Resultant for the Chopper Switch 22

3.8 RS232 DB9 Pin out 24

4.1 Simulation Buck Converter Circuit 26

4.2 Duty Cycle from PIC using PROTUSE software 27

4.3 Hardware of Rectification 29

4.4 Buck Converter Hardware 30

4.5 Hardware for PWM generator 31

4.6 Connection of DB09 and hardware 32

5.1 Result of MOSFET From Simulation 34

5.2 Buck Converter connected to the DC motor 35

5.3 Graph of Speed in RPM versus Duty Ratio 37

5.4 Graph of Output voltage versus Duty Cycle 37

5.5 Rectification Result from Hardware 38

5.6 PWM for 0% duty cycle 39

5.7 PWM for 12.5% duty cycle 39









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CHAPTER 1

INTRODUCTION

1.1 Introduction

This chapter will explain the objectives of the project, scope of the project,

problem statement and the project background. The review of the DC motor, chopper

drive, buck converter and pulse width modulation (PWM) control also will be

explained in this chapter. At the end of chapter 1 the thesis outline is briefly

described.

1.2 Background

The DC motor is an attractive piece of equipment in many industrial

applications requiring variable speed and load characteristics due to its ease of

controllability. The “Chopper drive” based speed controlling method is superior in

comparison to “Thyristor Controlled Bridge Rectifier” method as far as DC motor

speed controlling is concerned. PC based software controlling is adopted to retain

simplicity & ease of implementation.

By using PC and a circuit driver in controlling speed of a DC motor, the speed

of a DC motor can easily handle and measure by the user. From this project also will

shows the required signal generation to drive the chopper.

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A Closed-loop designing a complete automatic speed control system for a DC

motor and will brings the motor to the speed set by the user irrespective of the load.

1.3 Objective Of The Project

The project has these following objectives:

To evolve of a PWM Signal Generator for chopper drive

To design and apply chopper circuit in controlling DC motor

To develop software implementation for interface

1.4 Scope Of The Project

This project is developed by using input from PWM signal generation to get

PWM output. The implementation the PWM Chopper with a MOSFET also needed

because nowadays, the chopper switch is obviously a fast power MOSFET with very

short switching times and low resistance that reduce the conductive losses but

produce extremely high voltage- and current-rates [2]. Program code also will be

created to drive the hardware circuitry by using MATLAB and the implementation of

PIC controller will be used for this project.

1.5 Problem Statement

Due to its ease of controllability, the DC motor is an attractive piece in

requiring variable speed and load characteristics. Hence, the ‘Chopper drive” based

speed controlling method detected as superior in comparison to “Thyristor

Controlled Bridge Rectifier” method. It is also adopted to retain simplicity and ease

of implementation. PC interfacing also will be giving the easier way to the user on

how to control the motor speed.

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1.6 Project Background

The overview of chopper drive and buck-converter will take part for this

section besides the methodology in developing this project. In addition, the

methodology will be best described in the block diagram as in Figure 1.

1.6.1 Overview Of Chopper Drive And Buck-Converter

The chopper is used to control the armature voltage of a DC motor [1].

Chopper drive circuits are also referred to as constant current drives because they

generate a somewhat constant current in each winding rather than applying a

constant voltage. A Buck converter consists of the power stage and feedback control

circuit. The power stage includes power switch and output filter. It converts a higher

input voltage to a lower output voltage. The feedback control circuit regulates the

output voltage by modulating the power switch duty cycle. The three basic this dc-

dc converters use a pair of switches, usually one controlled (MOSFET) and one

uncontrolled (diode) in order to achieve unidirectional power flow from input to

output.

1.6.2 Methodology of the Project

In the research of this project, motor will receives the input from the DC

source. Signal also will be send to the motor through the chopper after PWM

generator gives the output to the chopper that is result from the feedback speed.

Feedback speed that comes from the sensor attached to motor will be the input to the

PWM generator and PIC controller. This project will be applying the closed-loop

system. A closed-loop designing a complete automatic speed control system for a DC

motor and will brings the motor to the speed set by the user irrespective of the load.

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Figure 1: The block diagram of the project

1.7 Thesis Outline

This thesis is divided into 6 chapters which the content of each chapter is summarized as below.

Chapter 1 will be discussed about the overview of the concept of the project,

objective of the project and scope of the project.

Chapter 2 will be described briefly the hardware components used in this

project, including their description of operation and article review of the project.

Chapter 3 will be focused on the methodology of this research project which

includes the generation of power supply, generation of PWM waveform for the

motor and full circuit diagram of the project.

Chapter 4 will elaborated in detailed about the designing step of buck

converter and chopper drive, PMW generation and the PIC controller design.

Chapter 5 will focused on the result obtained from the simulation design

using MATLAB and PROTUSE, the result obtained from hardware design and PC

interface.

Chapter 6 will described the conclusion from the result and observation, the

future recommendation and costing besides the commercialization of the project.

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CHAPTER 2

LITERATURE REVIEW

2.1 Introduction

In this chapter will explain in detail the operation of buck converter and

chopper drive. Besides that, DC motor and pulse width modulation also will be part

of the explanation in this chapter. In addition, all the circuit diagram and element that

are related in order to develop this project also will be reviewed in detail.

2.2 Dc Motor

DC motor is a mechanical workhorse. Many large pieces equipment depend

on a DC motor for power to move. A DC motor rotates as a result of two magnetic

fields interacting with one another. There are three categories for the DC motor like

series DC motor, shunt DC motor and compound DC motor.

The speed control is concerned not only with starting the motor but also with

maintaining or controlling the motor speed while it is running. There are a number of

conditions to be considered for speed control for example constant speed, varying

speed, adjustable speed and multispeed[3].

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Table 2.1 : DC Motor Characteristics and Applications [7]

Speed Regulation

Speed Control Starting Torque Pull-out Torque Application

Series DC MotorVaries inversely as the load. Races on light loads and full voltages in

Zero to maximum, depending on control and load.

High. Varies as square of voltage. Limited by the communication, heating, and line capacity.

High. Limited by communication, heating, and line capacity.

Where high torque is required and speed can be regulated.

Shunt DC MotorDrops 3% to 5% from no load to full load.

Any desired range, depending on motor design and type of system

Good with constant field, varies directly as voltage applied to the armature

High. Limited by communication, heating, and line capacity

Where constant speed is needed and starting conditions are not severe

Compound DC MotorDrops 3% to 2% from no load to full load depending on the amount of compounding

Any desired range, depending on motor design and type of control

Higher than for shunt, depending on the amount of compounding

High. Limitedby communication, heating, and line capacity

Where high starting torque combine with fairly constant speed is required.

For this project, stepper motor is chosen that its speed will be controlled by

the computer. The stepper motor is designed to move in finite increments (steps) in

either direction and to keep track of how many steps have been taken at any point in

time. The stepper motor can be used with mechanical linkages to provide precise

positioning. [2]

2.3 Chopper Drive

DC motor drives are used for many speed and position control systems where

their excellent performance, ease of control and high efficiency are desirable

characteristics. DC motor speed control can be achieved using switch mode DC to

DC chopper circuits.

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Chopper Driver is chosen for this project due to the advantages against the

Thyristor. These are the following advantages over Thyristor Bridge Rectifiers

method:

High energy efficiency

Flexibility in control

Quick Response

Light weight & compact control unit

Less ripple in the armature current

Small discontinuous conduction region in the Speed-Torque plane

Small discontinuous conduction region improves the speed regulation and

transient response of the drive

Less amount of machine losses due to less ripple in the armature current

Ability to control down to very low speeds [4]

For step-down converter operation the chopper circuit in figure can be used.

The average voltage applied to the motor, and hence its speed, is controlled by

varying the duty cycle of the switch, S.

Figure below shows the switching waveforms for the circuit. During the on

time, ton, the supply voltage, Vdc is applied to the motor and the armature current

starts to increase. Neglecting the on-state resistance of the switch and the armature

winding resistance the voltage across the armature inductance is Vdc-Ea and so the

rate of rise of armature current is given by:

La

EaVdc

dt

dIa

When the switch turns off the energy stored in the armature inductance must

be dissipated. The polarity of the voltage across La reverses, the diode D becomes

forward biased and the armature current continues to flow.

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Assuming that the motor speed remains constant and neglecting the forward

voltage drop of the freewheeling diode the inductor voltage is equal to -Ea. The rate

of fall of armature current is given by:

La

Ea

dt

dIa

Figure 2.1: Step-Down Chopper Circuit

Figure 2.2: Step-down chopper switching waveform

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If this switching sequence is repeated at some frequency, then the motor

voltage can be controlled by altering the relative duration of the on period and off

period. Variation of the duty cycle of the switch (ton/T) to control the motor voltage

is referred to as Pulse Width Modulation (PWM) control. As the average voltage

across the inductor over a period must be zero then:

T

t L

t

L

T

Lon

on

dtVdtVdtV 0...00

The integral of inductor voltage for the interval ton corresponds to the

shaded area1 in figure, whilst the integral of inductor voltage for the toff interval

corresponds to the shaded area 2 in the Figure 2.2.

These two areas must be equal and so from equations and figure the transfer

function of the controller is given by:

dcon

a VT

tV .

2.4 Switched Mode Power Supply (SMPS)

For many years the world of power supply design has seen a gradual

movement away from the use of linear power supplies to the more practical Switched

Mode Power Supply (SMPS). The linear power supply contains a mains transformer

and a dissipative series regulator. This means the supply has extremely large and

heavy 50/60 Hz transformers, and also very poor power conversion efficiencies, both

serious drawbacks. Typical efficiencies of 30% are standard for a linear. This

compares with efficiencies of between 70 and 80%, currently available using SMPS

designs.

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Furthermore, by employing high switching frequencies, the sizes of the

power transformer and associated filtering components in the SMPS are dramatically

reduced in comparison to the linear. This means an SMPS design can produce very

compact and lightweight supplies. This is now an essential requirement for the

majority of electronic systems. The supply must slot into an ever shrinking space left

for it by electronic system designers.

Figure 2.3: Basic SMPS block diagram

An SMPS can be a fairly complicated circuit, as can be seen from the block

diagram shown in figure above. (This configuration assumes a 50/60Hz mains input

supply is used.) The ac supply is first rectified, and then filtered by the input

reservoir capacitor to produce a rough DC input supply. This level can fluctuate

widely due to variations in the mains. In addition the capacitance on the input has to

be fairly large to hold up the supply in case of a severe droop in the mains. The

SMPS can also be configured to operate from many suitable dc input, in this case the

supply is called a DC to DC converter. In a switching converter circuit, the transistor

operates as an electronic switch by being completely on or completely off and this

circuit is also known as a DC chopper [6].

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2.4.1 DC – DC Converter

DC to DC converter is an electronic circuit which converts a source of direct

current (DC) from one voltage level to another.

There are few converters that are listed in this DC to DC converter such as:

Buck Converter

Boost Converter

Buck Boost Converter

Cuk converter

Full bridge converter

Figure 2.4: General Block Diagram for DC to DC converter

Switching power supplies offer higher efficiency than traditional linear

power supplies. They can step-up, step-down, and invert. Some designs can isolate

output voltage from the input. The switching regulator used in DC-DC converter and

this may be a simple way of converting a DC supply voltage to a lower Dc voltage

and regulating the output[6].

2.4.2 Buck Converter

A buck converter is a step-down DC to DC converter. Its design is similar to

the step-up boost converter. It is a switched-mode power supply that uses two

switches (a transistor and a diode), an inductor and a capacitor similarly like the

Boost Converter. The diode provides a path for the inductor current when the switch

is opened and is reverse biased when the switch is closed.

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