WIRELESS POWER TRANSFER BY USING ELECTROMAGNETIC INDUCTION AND MAGNETICALLY COUPLED RESONANCE

 

AHMAD FAHMI BIN ALIAS

 

A report submitted is a partial fulfilment of the requirements for the award of the Bachelor Degree of Engineering (Electrical)

Faculty of Electrical Engineering Universiti Teknologi Malaysia

JUNE 2015  

iii  

To my family

iv  

ACKNOWLEDGEMENT        

First and foremost, I would like to express my gratitude to my supervisor, Dr. Ahmad Safawi Bin Mokhtar, regarding his comments and guidance during the completion of my final year project. May Allah bless you.

Finally, I would like to express my appreciation to my family who has been so tolerant and supporting me all these years. I would like to express my appreciation to my father Alias Bin Jusoh and my mother Fauziah Binti Busu who have given me moral support and courage to me towards the completion of this final year project.    

v  

 

ABSTRACT        

Wireless power transfer by using electromagnetic induction is the method of transferring power from a source of electrical to the load without using any type of physical interconnection. It can make an extraordinary change in the field of the electrical engineering which eliminates the use of conventional copper wires and current carrying wires. Unlike the far field wireless power transmission systems based on traveling electromagnetic waves, wireless power employs near field inductive coupling through magnetic fields similar to those found in transformers except that the primary coil and secondary winding are physically separated, and tuned to resonate to increase their magnetic coupling. This project is concerned about the characteristics of wireless power transfer based on the number of turns, the input voltage, and the frequency of coils. The project consists of modelling and construction of the hardware to prove the feasibility of wireless power transfer. The simulation of the project has been done by using Multisim 11.0 software and the purpose is to design the desired circuit in order to transfer power wirelessly. However, this simulation can only prove the theoretical aspect of wireless power transfer. Thus, to demonstrate, the hardware circuit is required. The hardware contains primary and secondary coils and it is separated by using 3 obstacles which are aluminium, plastic, and paper in order to test the feasibility of wireless power transfer in different medium. The primary and secondary coils are also separated in various distance to measure the percentage of power transferred from primary to secondary coils. In the receiver system, more than 50% of the power that is supplied by the actual source is delivered to the load; LED. When the distance of separation increases, the efficiency will drop. In the future, this technology will become more effective and can eliminate the usage of wires.  

vi   

ABSTRAK        

Pemindahan

tenaga

tanpa

wayar

dengan

menggunakan

induksi

elektromagnetik adalah kaedah memindahkan kuasa daripada sumber elektrik kepada beban tanpa menggunakan apa-apa jenis sambungan fizikal. Ia boleh membuat perubahan yang luar biasa dalam bidang kejuruteraan elektrik yang menghapuskan penggunaan wayar tembaga konvensional dan wayar yang membawa arus. Tidak seperti bidang jauh sistem penghantaran kuasa tanpa wayar berdasarkan perjalanan gelombang elektromagnetik, tenaga tanpa wayar menggunakan padang berhampiran gandingan induktif melalui medan magnet sama seperti yang terdapat dalam transformer kecuali gegelung rendah dan menengah penggulungan secara fizikal dipisahkan, dan ditala bergema untuk meningkatkan magnetik mereka gandingan. Projek ini mengambil berat tentang ciri-ciri pemindahan tenaga tanpa wayar berdasarkan bilangan lilitan, voltan input, dan kekerapan gegelung. Projek ini terdiri daripada model dan pembinaan perkakasan untuk membuktikan kemungkinan pemindahan tenaga tanpa wayar. Simulasi projek itu telah dilakukan dengan menggunakan perisian Multisim 11.0 dan tujuannya adalah untuk mereka bentuk litar yang dikehendaki bagi memindahkan kuasa secara wayarles. Walaubagaimanapun, simulasi ini hanya boleh membuktikan aspek teori pemindahan tenaga tanpa wayar. Oleh itu, untuk menunjukkan, litar perkakasan diperlukan. Perkakasan yang mengandungi gegelung rendah dan menengah dan ia dipisahkan dengan menggunakan 3 halangan iaitu aluminium, plastik, dan kertas untuk menguji kemungkinan pemindahan tenaga tanpa wayar dalam medium yang berbeza. Gegelung penghantar dan penerima juga dipisahkan dalam pelbagai jarak untuk mengukur peratusan kuasa dipindahkan dari rendah kepada gegelung penerima. Dalam sistem penerima, lebih daripada 50% daripada kuasa yang dibekalkan oleh sumber asal dihantar kepada beban; LED. Apabila jarak pemisahan meningkat, kecekapan akan turun. Pada masa akan datang, teknologi ini akan menjadi lebih berkesan dan boleh menghapuskan penggunaan wayar.

vii  

TABLE OF CONTENTS

CHAPTER

1

     

TITLE

PAGE

TITLE PAGE

i

DECLARATION

ii

DEDICATION

iii

ACKNOWLEDGEMENT

iv

ABSTRACT

v

ABSTRAK

vi

TABLE OF CONTENTS

vii

LIST OF TABLES

x

LIST OF FIGURES

xi

LIST OF ABBREVIATIONS

xiii

LIST OF SYMBOLS

xiv

INTRODUCTION

1

1.1

Background of Study

1

1.2

Problem Statement

2

1.3

Objectives

3

1.4

Scopes of the Project

4

viii  

2

3

LITERATURE REVIEW

5

2.1 Wireless Power Transfer in 19th Century

5

2.2 Resonance

8

2.3 Electromagnetic Induction

8

2.4 Electromagnetic Induction with Resonance coils

9

2.5 Power coupling

10

2.6 Resonant Magnetic Coupling

10

2.7 Wireless Power in the 21st Century

12

2.8 Human Safety Consideration

12

METHODOLOGY

14

3.1 Inductive Coupling

14

3.2 Resonant Coupling Model Calculation`

16

3.3 Construction of Transmitter

17

3.4 Construction of Receiver

19

RESULT AND DISCUSSION

21

4.1 Predictable Outcomes

21

4.2 Results

22

 

4

ix  

4.2.1 Software Simulation

23

4.2.2 Hardware Model

24

5

CONCLUSION AND RECOMMENDATION

32

6

PROJECT MANAGEMENT

34

REFERENCES

38

 

x        

    LIST OF TABLES

TABLE NO.

TITLE

PAGE

   

4.1

Voltage induced versus distance between coils

24

4.2

Current versus distance between coils

26

4.3

Power versus distance between coils

27

4.4

Efficiency versus distance between coils

27

4.5

Medium between coils and conductivity

30

6.1

Project Gantt chart for Final Year Project One

35

(FYP1) 6.2

Project Gantt chart for Final Year Project Two

36

(FYP2) 6.3

 

Cost estimation for the system

37

xi  

LIST OF FIGURES

FIGURE NO.

TITLE

PAGE

2.1

Tesla Tower

7

2.2

Tesla Coil Diagram

7

2.3

Magnetic Coupling

11

3.1

Magnetic Field

15

3.2

Electromagnetic Flux

15

3.3

Block Diagram Of Wireless Power Transfer

16

3.4

Construction Of Transmitter

18

3.5

Primary Circuit Configuration

18

3.6

Secondary Circuit Configuration

19

3.7

Receiver Circuitry

19

3.8

Simulation Wireless Power Transfer Using Multisim

20

4.1

Circuit Diagram

22

4.2

Transmitter Configuration

22

4.3

Signal Of Oscilloscope

23

4.4

Two Coil Separate With Different Distance

24

4.5

Graph Of Voltage Versus Distance For 12 Turns Coil

25

4.6

Graph Of Voltage Versus Distance For 6 Turns Coil

25

4.7

Graph Of Efficiency Versus Distance For 12 And 6

27

Turn Coils 4.8

Type Of Obstacles

28

4.9

Plastic Between Two Coils

29

4.10

Paper Between Two Coils

29

4.11

Aluminium Between Two Coils

30

xii  

LIST OF ABBREVIATIONS          

Hz

-

Hertz

DC

-

Direct Current

AC

-

Alternating Current

MOSFET

-

Metal-oxide Semiconductor Field-effect

MULTISIM

-

Multiple Simulator Networking Program

EMF

-

Electromagnetic Field

LED

-

Light Emitting Diode

NI

-

National Instrument

RF

-

Radio Frequency

       

                           

xiii  

LIST OF SYMBOLS

 

W

-

Watt Power

L

-

Inductor

C

-

Capacitor

R

-

Resistor

f

-

Frequency

Q

-

Quality Factor

H

-

Henry

F

-

Farad

µ

-

Relative Permeability

ߠ

-

Angle

Ω

-

Resistor

cm

-

Centimeter

m

-

Meter

B

-

Magnetic Flux Density

ܺ

-

Reactance

CHAPTER 1

INTRODUCTION

1.1

Background of Study

   

It is hard to imagine passing a day without electricity, as it is a necessity of modern life. The conventional way to deliver electricity is through cables. The main issue in power system is loss occurred during the transmittance of electrical energy with interconnecting wires. As demand rapidly increasing time to time, the power generation inclines, hence the power loss. The main reason for power loss is the resistance of wired used for transmission and distribution [1].    

To replace this conventional way, wireless power transfer by using electromagnetic induction and magnetically coupled resonance is introduced. For over the century, researcher and engineers keep making research for this technology. New wireless power transfer system makes use of electromagnetic induction and magnetically coupled resonance principle to achieve safe and effective transmission of electrical energy and it also overcomes many problems existed in conventional way. Electromagnetic induction and magnetically coupled resonance wireless power transfer technology will be broad application prospects [2].

2  

It has features of being safe and convenient and thus, our lives will be affected largely because of this technology. The system contains of transmitter and receiver that have magnetic loop antennas tuned to the same frequency [3].        

1.2

Problem Statement

   

The problem of wireless power transfer differs from the wireless telecommunications, such as radio [4]. Recently, the extent of energy received gets to be critical just in the event that it is too low for the signal to be recognized from the background noise. RF broadcast techniques, which transfer power in an omnidirectional form, allow for power sent out anywhere in the coverage zone. In this case, mobility is maintained, but end-to-end efficiency decreases since power density decreases [5]. The microwave energy is sent to the long distances and can be received through antenna which can convert it back to electrical energy. But the problem is the diameter of antenna should be in order of kilometer [1]. Such as lasers, but this is not very practical and can even be unsafe. Laser is beamed to the photo voltaic cells which extract the electrical energy. This i s very difficult to implement and manage [1].    

With wireless electricity, efficiency is the more significant factor. A large part of the power transfer by the generating plant must arrive at the receiver to make the system efficient [6]. The most common form of wireless power is carried out using direct induction followed by resonant magnetic induction [1]. The distance and rate of the recommended wireless energy transfer system are the first subjects of examination, without seeing yet energy waste from the system for use into work [7]. Resonant inductive coupling has key implications in solving the two main problems associated with non-resonant inductive coupling and electromagnetic radiation which is distance and efficiency [8].

3  

1.3

Objectives

                    

The idea of transferring electricity through the air has been around for over a few decades. Most methods to wireless power transfer use an electromagnetic field of some frequency as the means by which the energy is transferred. The objectives are:    



To design wireless power transfer system by magnetic resonant coupling by using software Multisim 11.0 and implementing the hardware of the circuit. With wireless power in near field, the system must fulfil two conditions; high proficiency and high power. Efficiency is the more important factor. The electricity is transferred by the generating plant, as it must arrive at the receiver to make the system efficient.

   



To make sure the magnetic resonance between transmitter and receiver coils operating at a similar resonance frequency. The frequency at which the amplitude of the waves produced in the system is maximum called resonance frequency. The resonance frequency is attained by varying different parameters affecting the gain of voltage created within the coils.

   



To ensure that the efficiency of power received at receiver from transmitter within a reasonable range and to test feasibility of wireless power transfer in different obstacles between two coils, such as paper, plastic and metal.

4  

1.4

Scope of the Project

   

Every project has its own scope to make sure that the project is on track and will not go astray. This project involves in brief research about existing methods. The main part in this project is analysis, simulation and hardware implementation. Analysis is done by joining electromagnetic induction theory with the magnetically coupled resonance coils. In this project, MULTISIM software is used to model and to observe some parameters of the system.

CHAPTER 2

LITERATURE REVIEW

2.1

Wireless Power Transfer in 19th Century

In 1864, James C. Maxwell anticipated the presence of radio waves via mathematical expression. They alleged Maxwell equations are the most famous and best equations. In 1884, John H. Poynting understood that the Poynting vector would assume an essential part in measuring electromagnetic field. In 1888, supported by Maxwell’s concept, Heinrich Hertz first succeeded in showing investigational proof of radio waves using his spark-gap radio transmitter [9]. The forecast and confirmation of radio waves to the end of the 19th Century was the start of wireless power transfer.  

At the same time, when Marchese G. Marconi and Reginald Fessenden established communication using radio waves, Nicola Tesla suggested the idea of wireless electricity and done the first wireless power transfer trials in 1899. He said “this power will be collected all over the circle preferably in small amounts, ranging from a friction of one to a few horse-power”.

.

6  

Tesla actually constructed a coil that was linked to a 200 feet high mast with a 3 feet diameter ball at its top. The instrument was called the “Tesla Tower”, as shown in Figure 2.1. Tesla supply 300 kW of power to the coil that resonated at a frequency of 150 kHz. The radio frequency potential at the top sphere touched 100MV. But, the research was unsuccessful because the transferred power was spread in all directions using 150 kHz radio waves. Figure 2.2 shows the coil diagram [9].    

In 1905, Nikola Tesla with a group of laborers in the little township of Shoreham, New York toiled to erect a truly amazing structure. More than a time of quite a long while the men had figured out how to collect the structure and wiring for the 187-foot-tall Wardenclyffe Tower, regardless of serious spending plan setbacks and a couple designing obstacles. The project was supervised by its designer, the eccentric-yet-ingenious inventor Nikola Tesla. A top his tower was perched a fiftyfive ton dome of conductive metals, and beneath it stretched an iron root system that penetrated more than 300 feet into the Earth’s crust [7].

 

In Tesla’s power transfer scheme, he hypothesized the Earth to be a giant charged sphere that could be driven at its resonant frequency and that he could close the circuit using giant electric fields in the Earth’s ionosphere. Much of his exploration on wireless power involved radiative electromagnetic waves that are practical for transferring information but pose immense difficulties for wireless power transfer for two reasons. First of all, omnidirectional radiation is very uneconomical and if we were to use unidirectional radiation instead, we would need a direct line of sight and complicated tracking mechanisms [9].

7  

Figure 2.1: Tesla Tower    

To concentrate on the transferred electricity and to build the exchange effectiveness, a greater frequency than that utilized by Tesla is needed. In the 1930s, an arrangement of improvement in producing great-power micro waves in the 1-10 GHz range was completed.    

Figure 2.2: Tesla coil diagram

8  

2.2

Resonance

   

The accomplishment of the suggested resonance based wireless energy transfer plan depends firmly on the robustness of the objects' resonances. Along these lines, their affectability to the close vicinity of random non-resonant extraneous objects is another criteria of the proposed scheme that obliges investigation [7].  

Resonant inductive coupling has key ramifications in tackling the primary issues connected with non-resonant inductive coupling and electromagnetic radiation which is separation and proficiency. Thus, proficiency is inversely proportional to distance [8].  

Over more prominent separations the non-resonant induction method is wasteful and inefficient much of the transmitted energy just to increase distance. This is where the resonance comes in and helps the efficiency dramatically by "tunneling" the electromagnetic field to a secondary coil that resonates at the similar frequency [10].

2.3

Electromagnetic Induction

   

Maxwell combined Faraday’s and Ampere’s Law into the equations. Previous Maxwell’s equations, it was known from Faraday’s and Ampere’s Law that a current generates an electromagnetic field and a changing magnetic field re-forms a current. The conductors are mentioned as mutual-inductively coupled a magnetically coupled when they are designed such that a change in the current flow though one conductor induces a voltage thru the ends of the other by electromagnetic induction.

9  

In the existing system the electric power has been transmitted wirelessly over the distance of 1 feet by using electromagnetic inductive coupling. That is using induction principle the electricity can be transmitted from primary coil to the secondary coil. The transmitted coil will be oscillating in certain frequency, when the primary coil is kept near the secondary coil then the electromagnetic field will get induced [8].

Electromagnetic induction chips away at the standard of an essential coil producing a prevalently electromagnetic field and an optional coil being inside of that field so a current is induced inside of its coils. This effects the moderately small distance because of the measure of force needed to create a magnetic field [10].

2.4

Electromagnetic Induction with Resonance Coils

Principle of inductive resonance wireless power transmission and principle of electromagnetic induction are basically the same, and both of them use the law of electromagnetic induction [11]. The dissimilarity is that two coils of resonant inductive wireless power transmission system occurs self-resonant in the high frequency, resulting in a time varying magnetic field which the center is coil and the medium is air. Between the two resonant coils, power exchanges continuously to realize wireless energy transmission [2].  

Wireless electricity is founded on strong coupling between electromagnetic resonant objects to transmit power wirelessly between source and load. The primary coil generate the tuned magnetic fields, it can be set to interact strongly with complemented receiving windings but far more weakly with any surrounding materials or things for example biological tissues [8].

10  

2.5

Power coupling

Power coupling happens when a power source has a means of transmitting power to another things [3]. When we a closed loop use as a coil, the coil generates an electromagnetic field. The magnetic field transfer wireless energy. This is inductive coupling wireless power transfer. Inductive coupling wireless power transfer is based on Faraday’s and Ampere’s circuital law of induction. The efficiency of wireless power transfer be determined by on the coupling coefficient, which in turn depends on the distance between the transmitter and receiver coils [9]. Thus, wireless power cannot be transferred over a distance more than a small number of millimeters with proficiency using inductive coupling. The frequency used in inductive coupling is below couple of megahertz. Wireless energy through coupled electric fields is practical and easily verified at high energy levels [12].

Inductive coupling methods do not depend on transmitting magnetic waves. In its place, they operate at ranges less than a wavelength of the signal being transferred. Inductive coupling is a long-standing and surely knew technique for wireless electricity. The source drives a transmitting coil, making a sinusoidal varying electromagnetic field, which prompts a voltage over the terminals of an optional coil, and accordingly transmit energy to a load [13].        

2.6

Resonant Magnetic Coupling

 

Magnetic coupling take place when two items exchange vitality through their shifting or oscillating magnetic fields. Coupling happens when the regular frequencies of the two things give or take the similar as shown in Figure 2.3 [14]. Magnetic resonant coupling can be used to transfer electicity from a power source coil to one or many small load coils, with lumped capacitors at the coil terminals

11  

providing a simple means to match resonant frequencies for the coils. This scheme is a potentially robust means for conveying wireless energy to different receivers from a source coil [13].    

Resonant evanescent coupling is where the coupling is mediated through the overlap of the non-radiative close fields of the two things. This famous physic leads insignificantly to the result that power can be efficiently coupled between things in the near field [7]. Electromagnetic induction method has small range.

Figure 2.3: Magnetic coupling  

Magnetic resonant coupling uses the comparative standards as inductive coupling. It can be two types; parallel and series. In these both sorts of resonance, the rule of getting maximum power is same but the techniques are not the same [15]. Naturally, two resonant things of the similar resonant frequency tend to interchange power efficiently. In the methods of coupled resonances, there is frequently a general “strongly coupled” system of operation. In the event that one can work in a given framework, the energy transfer is required to be exceptionally proficient [16]. Midrange energy move actualized along these lines can be almost of existing in every direction and effective, independent of the geometry of the encompassing medium, with little obstruction and misfortunes into eco-friendly things [14].

12  

2.7

Wireless Power in the 21st Century

   

Alliance for Wireless Power is the first standard based on electromagnetic resonance [17]. The Alliance for Wireless Power offers only one choice: “single coil, loosely coupled, resonant”. That configuration is not ideal for all applications [18]. In December 2008, the Wireless Power Consortium was recognized to develop wireless charging of smart phones.

In December 2010, Wireless Power Consortium introduced the “Qi” standard for inductive coupling wireless power transfer. Even though there were some inductive coupling wireless power transfer, the work did not shoulder any economically effective items. The “Qi” standard spread fast and wireless chargers using this type of standard have been able to be bought. Furthermore, the wireless power transfer, different collusions, consortiums and gatherings for setting up a wireless power transfer standard and for advancing business applications have emerged [9].    

2.8

Human Protection Consideration

   

A typical question about wireless power transfer systems is about safety. These systems can effectively trade power over middle ranges, individuals may expect that they are being presented to huge and conceivably perilous electromagnetic fields when utilizing with these systems [19]. With appropriate design the stray electric and electromagnetic fields can be kept below the safety limits that standardise all electromagnetic consumer devices including smart phones and radio transmitters [20].    

13  

In latest analyses of the collected scientific works, the ICNIRP and IEEE teams have decided that there is no proven evidence showing that exposure to radio frequency electromagnetic fields causes’ cancer [21]. However there is a well-known proof showing that radio frequency may increase a person’s body temperature or may warmth body tissues and stimulate nerve and muscle tissue [18].

CHAPTER 3

RESEARCH METHODOLOGY

3.1

Inductive Coupling

When use a coil as a closed loop, the coil produces a magnetic field transfer wireless electricty. This is an inductive coupling wireless power transfer transfer based on Faraday’s and Ampere’s circuital law of induction. Faraday’s and Ampere’s circuital law of induction are approximations of Maxwell’s equations. Ampere’s circuital law describes the relationship between the integrated magnetic field around a closed loop (coil) and the electric current passing through the loop. Faraday’s law of induction describes the relationship between a time varying magnetic field and an induced electric field. The electrical power is carried through the magnetic field between two coils.

.

15   

Figure 3.1: Magnetic field

The blue lines in Figure 3.1 symbolise the magnetic field produced when current flows through a coil. When the current reverses direction, the magnetic field also reverses its direction. In Figure 3.2, the lines of magnetic flux are close together where the magnetic field is strong and farther apart where the field is weaker.

Figure 3.2: Electromagnetic flux

Wireless power transfer can be divided into three parts as shown in Figure 3.3. First, transmitter electromagnetically transfer power by inductive coils which supply a wireless electricity

to receiver unit. Second, inductive coupling, the

inductive coupling in this case are the two coils and forward to the receiver unit (capacitor and diode). Third part is load, in this case, load is a LED. Load gets the power from receiver unit to light up the LED.

   

16   

Figure 3.3: Block diagram of wireless electricity

3.2

Resonant Coupling Model Calculation

Resonant coupling is a phenomenon whereby two similar frequency resonant objects tend to couple, while interacting weakly with other off-resonant environmental objects. Therefore, the resonant frequencies of the transmitting element and the receiving element are the most important parameters in our wireless power transmission.

The resonant frequencies of both the transmitting and receiving coils can be obtained through the calculation of inductance of a circular coil, resistance of the winding , resonant frequency, capacitive reactance and inductive reactance.

The inductance of a circular coil is obtained directly by the following formula: Where

ln

1.75

is radius, a represent cross section of the coil,

(3.1) represents the number of

turns.

The resistance of the winding is obtained by following formula: (3.2) ,

and

represent area between two coils, length of the coil and resistivity of

copper respectively.

   

17   

The length of the coil and circular area between two coils is given by following formula: 2

(3.3)

The resonant frequency is calculated by applying the following formula: (3.4)

√

Inductance reactance and capacitance reactance are obtained straight by the following formula: 2

(3.5) (3.6)

Finally, the resonant frequencies of both the transmitting and receiving coils can by using following formula: (3.7)

3.3

Construction of Transmitter

Current flows in a primary coil is coupled with a resonant LC secondary coil. Current is induced in secondary coil at the transmission frequency, which frequency want to set as our resonance frequency. The resonant frequency of the secondary coil can be calculated from the inductance and capacitance of the LC circuit. Because of the high magnetic flux density as a result from our resonant coil, the receivers can design to sit on a surface that separates the transmitter and receivers by a certain distance. By using Multisim, the drive primary circuit is designed as shown in Figure 3.5.



√

(3.8)  

 

18   

DC Source

RC Circuit

Transistor

Transmitter Coil

Figure 3.4: Construction of Transmitter Developing from left to the right of the flow diagram in Figure 3.4, the input power to the system is DC power. The magnetic field produced by the transmitter couples to the receiver, exciting the resonator and causing energy to build up in it. This energy is coupled out of the receiver to do valuable work. For example, directly powering a load. Energy oscillates at the resonant frequency between the inductor (energy stored in the magnetic field) and the capacitor (energy stored in the electric field) and is degenerates in the resistor. The quality factor for this resonator are:



(3.9)

The expression for Q shows the quality factor in the circuit. So, by reducing R, the quality factor of the system will increase.

Figure 3.5: Primary circuit configuration

   

19   

3.4

Construction of Receiver

In designing the receivers as shown in Figure 3.6, know that the current flowing in the resonant coil is greater than to the current in the primary coil. Capacitor is used as a filter circuit and to smoothen the peak voltages.

Figure 3.6: Secondary circuit configuration

Receiver coil

Circuit

LED

Figure 3.7: receiver circuitry

The main function of a diode is to block the current in one direction, and allow current to flow in the other direction. Current flowing through the diode is called forward current. Simulation wireless power transfer has been done us Multisim 11.0 software, as shown in Figure 3.7.

   

20   

Figure 3.8: Simulation wireless power transfer using Multisim software

Figure 3.8 shows the overall circuit in Multisim 11.0 software. Multisim is an industry standard, best in class spice simulation environment. It is the NI circuits teaching solution to build expertise through practical application in designing, prototyping, and testing electrical circuits. The simulation purpose is to design circuit in order to transfer power wirelessly and to the resonance frequency. The simulation only proves the theoretical part, while by developing the hardware model, it can prove this theory. By simulation and developing hardware, the wireless electricity can be analysed .

   

CHAPTER 4

RESULTS AND DISCUSSION

4.1 Predictable Outcomes

The main expected result here is obviously to see this wireless power device working although in a small-scale application. Consequently, great assessment will be succeeded with a few centimeter measurements to have a confirmation that this wireless electric transfer has advantage in future to replace copper wire.

Subsequently it must have better ability of high proficiency and small losses. In this manner, there are a few graphical investigations to help seeing more about this topic.

22   4.2 Results 4.2.1 Software simulation

Figure 4.1: Circuit Diagram

From the simulation result in Figure 4.1, the frequency at transmitter side is 24.6 kHz and the frequency at receiver side is 24.8 kHz. The frequencies at both sides are almost similar. When the frequencies are same at both sides, the circuit will be at resonance. It also can be known as the resonant frequency of the circuit. The efficiency of power induced from transmitter to receiver will increase. From this simulation, although the frequency is not exactly same, it is a good achievement with that value.

23  

Figure 4.2: Transmitter configuration

Figure 4.3: Signal of oscilloscope

This transmitter circuit in Figure 4.2 was designed by using Mutisim 11.0 software. This circuit consists of resistor, capacitor and transistor. Figure 4.3 portrays the output signal in oscilloscope DC at the transmitter circuit. Form the output, the voltage at transmitter coil is 4.95V. The voltage was reducing from 6V voltage supply due to resistance and others component in the circuit.

24   4.2.2 Hardware Model 4.2.2.1 Distance between Coils

ON 

Figure 4.4: Two coils are separated in different distance

Table 4.1: Voltage induced versus distance between coils Distance 0 1 2 3 4 5 6 7

Voltage (V) 6 Turns 3.5 3.11 2.82 2.56 2.23 1.95 1.73 1.51

Voltage (V) 12 Turns 4.5 4.35 4.11 3.95 3.73 3.25 2.91 2.75

25   Voltage Against Distance (12 turns) VOLTAGE (V)

5 4 3 2 1 0 0

1

2

3

4

5

6

7

DISTANCE (cm) Figure 4.5: Graph of voltage versus distance for 12 turns coil

VOLTAGE (V)

Voltage Against Distance (6 turns) 4 3.5 3 2.5 2 1.5 1 0.5 0 0

1

2

3

4

5

6

7

DISTANCE (cm) Figure 4.6: Graph of voltage versus distance for 6 turns coil

For both number of turns (6 and 12), the graph in Figure 4.5 and 4.6 was constructed by using the data from Table 4.1. It shows that the voltage induced slightly decrease when the distance between two coils are higher. First the coils are closely together and the coils separately by 1cm until the LED turn off as shown in Figure 4.4.

26   If two coils, transmitter and receiver are placed relatively to each other, some of the flux produced by the current in transmitter circuit becomes linked to receiver coil. Since a change of current in one coil is accompanied by a change of flux linked with the other coil and therefore by an electromagnetic field induced in the latter, the two coils are said to have mutual inductance.

When the distance of two coils increases, the electromagnetic field induced will decrease until at certain range, the induce electromagnetic field is too small. When electromagnetic field induced is too small, the LED cannot ON.

The numbers of turn of the transmitter and receiver coil also affect the value of electromagnetic field induced. When the numbers of turn increase, the electromagnetic field will induce more. From the graph above, the distance of 0cm is the most efficient wireless power transfer, voltage induced for 6 turn coils is 3.5V, while for 12 turn coils, and the voltage induced is 4.5V. The different is about 1V between 6 and 12 turn. From the above mentioned graph, the wireless power transfer is higher when the distance of coil is closer.

Table 4.2: current versus distance between coils Distance 0

Current (A) 6 Turns 0.035

Current (A) 12 Turns 0.062

1

0.030

0.055

2

0.024

0.049

3

0.019

0.043

4

0.013

0.038

5

0.009

0.032

6

0.005

0.026

7

0.001

0.022

27   Table 4.3: power versus distance between coils Distance

Power (W) 6 Turns 0.1125 0.0933 0.0677 0.0486 0.0290 0.0176 0.0087 0.0015

0 1 2 3 4 5 6 7

Power (W) 12 Turns 0.279 0.239 0.201 0.170 0.142 0.104 0.076 0.061

Table 4.4: Efficiency versus distance between coils Distance

Efficiency (%) 6 Turns 22.69 17.28 12.53 9.01 5.37 3.25 1.60 0.28

0 1 2 3 4 5 6 7

Efficiency (%) 12 Turns 51.67 44.31 37.30 31.46 26.24 19.26 14.01 11.20

Efficiency vs Distance EFFICIENCY (%)

60 50 40 30 20

6 Turns

10

12 Turns

0 0

1

2

3

4

5

6

7

DISTANCE (cm) Figure 4.7: graph of efficiency versus distance for 12 and 6 turn coils

28   The power transfer efficiency is a crucial factor for wireless power transfer system. In Table 4.2, 4.3, and 4.4 shows the values of current, power and efficiency versus distance for 12 and 6 turn coils. Output power at the receiving coil divides with power input at the transmitting coil to the value of power efficiency. The graph in Figure 4.7 shows that the power efficiency reduces as the distance between coils increase. This is happen when the distance between transmitter and receiver coil increases, the resistance of the leakage path will increase. As the result, a loss throughout the power transfer increases. At the distance of 0cm, the efficiency for 6 turn coils is 22.69%, while for 12 turn coils, the efficiency is 51.67%. The distance increases until LED turns OFF which is at 7cm. At 7cm range between coils, the efficiency for 6 turn coils is 0.2796%, while for 12 turn coils, the efficiency is 11.2037%. So, for the best efficiency for wireless power transfer, is 51.67% by using 12 turn coils at 0cm. The power efficiency is more than 50%, which is a massive achievement for a small wireless power transfer system using a DC voltage. Therefore, power transfer method via wireless power transfer using resonant coupling is a high efficiency.

4.2.2.2 Obstacles between Coils

Figure 4.8: Type of obstacles

29  

The wireless power transfer circuit is also tested using barrier or obstacles (Figure 4.8) between the transmitter and receiver coil. Aluminium, paper and plastic acted as the obstacles between two coils. The experiment purpose is to make sure the wireless power transfer will not be a solution for power transfer over different medium.

ON 

Figure 4.9: Plastic between two coils

ON 

Figure 4.10: Paper between two coils

30  

OFF  OFF 

Figure 4.11: Aluminium between two coils    

Figure 4.9 and 4.10 shows the test using plastic and paper. The power transfer gives positive result where light emitting diode (LED) is ON. The signal did not loss and those materials did not affect wireless power transfer. The electromagnetic field can go through paper and plastic without any difficulties and the power transfer is not affected. The result of the experiment as shown in Table 4.5.

Table 4.5: Medium between coils and conductivity Medium

Conductivity

Paper

Yes

Aluminium

No

Plastic

Yes

31   However, the power transfer gives negative result when the aluminium is put between transmitter and receiver coil as shown in Figure 4.11. The aluminium represents metal, and wireless power transfer is not feasible across metal object as the thicker objects absorb a bigger percentage of the wireless signal and the signal will be lost. This is known as the skin effect in which high frequency radio waves or electromagnetic waves travel thru the surface of an object without penetrating its depth. Electrically conductive or dense objects such as aluminium increase wireless signal degradation.

CHAPTER 5

 

CONCLUSION AND RECOMMENDATION        

The goal of this project was to design and implement a wireless power transfer system via magnetic resonant coupling. It was proven that power can be transmitted via resonantly coupled coils. Using this constructed circuit, the efficiency of wireless power transfer is more than 50% when 12 turns coil was used. In meantime, the wireless power transfer using near field resonant coupling is feasible across paper and plastic but not by metal obstacles.    

Compared to the traditional wired power transfer technology, inductively wireless power transmission technology is more flexible, safe and reliable and can achieve power transfer within near distance between powered device and power device.    

However, some problems still need to be studied. Such as: (l) the circuit structure can be improved on this basis to get a high efficiency of power transfer, not only at a short distance but also at a medium distance. (2) The influence of material and number of turns of primary and secondary coils to the efficiency of power transfer can make a further research.

33  

Future research must be invented to enhance and to improve this system. There is marketable value possible which this device can be sold or proposed to government who wants to provide free wireless electricity to public or private sector to commercialise.  

CHAPTER 6

PROJECT MANAGEMENT

6.1

Introduction

 

Project management is frequently related to designing activities, having a good planning, organizing, and controlling of resources in specified time period. Hence, to achieve the project goals the application of processes, methods, knowledge, skills and experience are needed. In order to provide a clear guideline, Gantt chart has been used as a project plan to make sure the task to be completed within the time. To ensure the project accomplish the required requirement and to make sure minimal project cost, the cost approximation on the all components must be performed precisely.

35   

6.2

Project Planning

 

The process for final year project one is to study or research the background of project, electronic components to be used in develop the system. In study the project background, several steps were taken in order to get full understanding about the project by reading research paper on related product and scientific journal. The current technology about the project was search via web. Hence, from there many ideas can come out to fulfill the needs, objectives and scope of the project. Table 6.1 shows the project gantt chart for final year project one.

Table 6.1: Project Gantt chart for Final Year Project One (FYP1) Activity / Week Determining topic Literature review Progress Evaluation 1 Project proposal Progress evaluation 2 Study of software Progress evaluation 3 Prepare for seminar FYP 1 seminar FYP 1 report

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

36   

Gantt chart for final year project two was shown in Table 6.2. For this semester, fabrication on the project was developed for both hardware and software. For first three weeks the design for wireless power transfer was proposed to the supervisor, and then the design was model on breadboard. In the second semester, the time more spend on constructing, testing and improving the system.

Table 6.2: Project Gantt chart for Final Year Project Two (FYP2) Activity / Week Proposed Design Testing Using Software Buy The Components Progress Evaluation 1 Develop The Hardware Model Progress Evaluation 2 Improve The Hardware Progress Evaluation 3 Prepare The Seminar FYP 2 Exhibition & Demonstration Submit Report Draft And Journal Paper Submit Hard Bound Thesis

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

37   

6.3

Cost Estimation

 

In this part, Table 6.3 will explain the details about cost estimation for hardware and electronic components used in developing the project system. Table 6.3 shows the details about the cost estimation for overall system.

Table 6.3: Cost estimation for the system Components

Cost (per unit)

Unit

Subtotal

Battery

RM 1.40

4

RM 5.6

Cable

RM 1

1

RM 1

Capacitor

RM 0.40

6

RM 2.40

Traansistor

RM 0.40

1

RM 0.40

Resistor

RM 0.05

5

RM 0.25

LED

RM 0.10

1

RM 0.10

Diode

RM 0.20

1

RM 0.20

Total

6.4

RM 9.95

Conclusion

To reach the objective and to satisfy the user needs, all the aspects such as cost estimation and project plan must be considered beforehand because user will check on and consider the price and the advantage of product.

38  

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