wpt project doc

8/18/2019 WPT Project Doc

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ABSTRACT:

Wireless power transfer is a novel technology and the theory is based on magnetic resonant

circuit. The energy can be transferred via magnetic resonant circuit using non-radiative near

field. The self resonance coils were designed according to parallel resonant circuitconfiguration and operated in a strongly coupled regime. The energy transfer technique

involved the concept of near field where the distance of transmission is a few times the

diameter of the antenna and a quarter of the wavelength of the transmitted signal. The near

field energy itself is non-radiative. The advantage of using non-radiative field is the fact that

the power not taken by the receiving coil is returned to the sending unit, instead of being

radiated into the surrounding and getting wasted. Though with such a design the power

transfer has a limited range, and the range will be smaller for smaller receiving coils. A

theoretical and analytical model is proposed and implemented in this project. We have

implemented wireless power transmission via magnetic resonant circuit. ased on this system

the induced electromagnetic force !"#$% in the receiving coil has been e&perimentally tested.

The primary design is involved of a source with bridge rectifier. The second set-up isdesigned with a transmitter circuit. And the third set-up is involved with the receiving coil.

We also have used an intermediate coil in between the transmitter coil and receiver coil. We

have achieved significant improvements in terms of power transfer efficiency by using this

intermediate coil. "&perimental results show that the proposed system can transfer energy

through different non-metallic objects. Through precise designing of the prototypes the

performance of the system can be significantly improved. This proposed system could be

made commercially viable through further research work.


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INTRODUCTION:

'ower is very important to modern systems. $rom the smallest sensors, bionic implants,

deliver power means other than classical wires or transmission lines. Wireless transmission isuseful in cases where instantaneous or continuous energy transfer is needed but

interconnecting wires are inconvenient, ha(ardous, or impossible. )n the case of biological

implants, there must be a battery or energy storage element present that can receive and hold

energy. This element takes up valuable space inside a person body. )n the case of satellites,

*A+s and oil platforms, solar panels, fuel cells, or combustion engines are currently used to

supply power. olar panels take up a great deal of weight and bulk in terms of energy density

and must have a tracking system to ma&imi(e e&posure to the sun. $uel cells and combustion

cells needs fuel and maintenance to be delivered on site.

Wireless 'ower Transmission !W'T% is the efficient transmission of electric power from one

point to another through vacuum or an atmosphere without the use of wire or any other

substance. This can be used for applications where either an instantaneous amount or a

continuous delivery of energy is needed, but where conventional wires are unaffordable,

inconvenient, e&pensive, ha(ardous, unwanted. The power can be transmitted using )nductive

coupling for short range, esonant )nduction for mid range and "lectromagnetic wave power

transfer. W'T is a technology that can transport power to locations, which are otherwise not

possible or impractical to reach.


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HISTORICAL BACKGROUND:

ate scientist /ikola Tesla was the one who first conceived the idea Wireless 'ower

Transmission and demonstrated 0the transmission of electrical energy without wires1.

That depends upon electrical conductivity as early as 2342. )n 2345, Tesla demonstrated the

illumination of vacuum bulbs without using wires for power transmission at the World

6olumbian "&position in 6hicago. The Wardenclyffe tower was designed and constructed by

Tesla mainly for wireless transmission of electrical power rather than telegraphy.

chemes for wireless power transmission attempted by /ikola Tesla, required large scale

construction of 788 ft tall masts. )t also produced undesirably and sometimes dangerously

high voltages that approached 28, 88, 88,888+. ater attempts at wireless power led to the

development of microwave power transmission, but its line-of-sight requirements meant that

any practical power source needed to be high in the sky. 'revious proposed projects included

large power platforms as well as microwave-beaming satellites. oth Tesla9s devices and the

later microwave power were forms of radiative power transfer. adiative power transfer,

which is used in wireless communication, is not particularly suitable for power transmission

due to its low efficiency and radiative loss due to its :mni-directional nature.

After the ace of wireless power transmission started with ;r. /ikola Tesla, now there is

tremendous interest in wireless devices and gadgets in 72 st 6entury, with the compactness of

such devices created a need for cord-less charging systems and power supply.


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OBJECTIVES OF THIS WORK:

ow power devices commonly have an energy storage element like a battery or a capacitor to

provide energy for their different electronic circuits. )n order to be recharged, the energystorage element must be cable connected to a voltage regulator and the main power supply.

egulator, wiring and conductors as well as the energy storage itself, especially in case of a

battery, are often sources of error. The need of wiring, connectors or even batteries in

electronic equipment can be eliminated by wireless energy transmission. )t is the ideal

solution when little board space is available and low costs are of paramount importance

because the costs of the charger can be eliminated from the total cost. The objectives of this

project is given below-

• To design and construct a method to transmit wireless electrical power through space.

• The system will work by using resonant coils to transmit power from A6 line to a

resistive load.

• To investigate various geometrical and physical form factors that was evaluated in

order to increase coupling between transmitter and receiver.

• To ma&imi(e power transfer by using resonant coupling.

Introduction to th th!i!

We have implemented a system that can transmit power wirelessly. The whole system andrelated theories have been described in seven main chapters.

)n 6hapter 7, we discussed about the #agnetic esonant 6oupling theory and its principles.

)n 6hapter 5, we discussed about the , we presented the block diagram of the wireless power transfer system.

)n 6hapter ?, we described the working principles and constructions of various components.

)n 6hapter @, we presented the theoretical model and circuit implementation of wireless

power transfer system.

)n 6hapter 3, we described the performance and analysis of the implemented wireless power

transfer system.


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)n 6hapter 4, we presented the cost of the project and the overall discussion of wireless

power transfer system.

CHA"TER#$

%AGNETIC RESONANT COU"LING

The most common wireless power transfer technologies are the electromagnetic induction

and the microwave power transfer. $or efficient mid range power transfer, the wireless power

transfer system must satisfy three conditions !a% high efficiency, !b% large air gaps and !c%

high power.

The microwave power transfer has a lower efficiency. $or near field power transfer this

method may be inefficient, since it involves radiation of electromagnetic waves.

'ower can be transferred wirelessly via electric field coupling, but electric field coupling

provides an inductively loaded electrical dipole that is an open capacitor or dielectric disk.

"&traneous objects may provide a relatively strong influence on electric field coupling.

#agnetic field coupling may be preferred, since e&traneous objects in a magnetic field have

the same magnetic properties as empty space.

"lectromagnetic induction method has a short range. ince magnetic field coupling is a non-radiative power transfer method, it has higher efficiency. Bowever, the power transfer range

can be increased by applying magnetic coupling with resonance phenomenon applied on.

%AGNETIC FIELD

A magnetic field is generated when electric charge carriers such as electrons move through

space or within an electrical conductor. The geometric shapes of the magnetic flu& lines

produced by moving charge carriers !electric current% are similar to the shapes of the flu&

lines in an electrostatic field. ut there are differences in the ways electrostatic and magnetic

fields interact with the environment.

"lectrostatic flu& is impeded or blocked by metallic objects. #agnetic flu& passes through

most metals with little or no effect, with certain e&ceptions, notably iron and nickel. These

two metals, and alloys and mi&tures containing them, are known as ferromagnetic materials

because they concentrate magnetic lines of flu&.

Where, ) denotes the current and is the magnetic field due to the current.

%AGNETIC COU"LING

)nductive or magnetic coupling works on the principle of electromagnetism. When a wire is

pro&imity to a magnetic field, it generates a magnetic field in that wire. Transferring energy

between wires through magnetic fields is inductive coupling.


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)f a portion of the magnetic flu& established by one circuit interlinks with the second circuit,

then two circuits are coupled magnetically and the energy may be transferred from one circuit

to the other circuit. This energy transfer is performed by the transfer of the magnetic field

which is common to the both circuits.

#agnetic coupling between two individual circuits are shown in $igure 7.7. $or the purpose

of analysis we assume the total flu& which is established by !circuit-2 current%, namely is

divided into two components. :ne component of is that part which links with circuit-2 but

not with circuit-7, namely. The second component of is which links with both circuit-7 and

circuit-2. )n this similar way the flu& established by !circuit-7 current%, namely has also two

components. :ne component of is which links only circuit-7 but not with circuit-2. Again

another component of is which links both circuit-7 and circuit-2.

Bere is a fractional part of, which links with the turns of circuit-7. o is called the mutual flu& produced by circuit-2.

)n the same way the fractional part of is which links with the turns of circuit-7.

o is called the mutual flu& produced by circuit-7.

This is the phenomenon how the magnetic coupling takes place between two individual

circuits. This effect can be magnified or amplified through coiling the wire.

'ower transfer efficiency of magnetic coupling can be increased by increasing the number of

turns in the coil, the strength of the current, the area of cross-section of the coil and thestrength of the radial magnetic field. #agnetic fields decay quickly, making magnetic

coupling effective at a very short range.

RESONANT FRE&UENC'

esonance is a phenomenon that causes an object to vibrate when energy of a certain

frequency is applied. )n physics, resonance is the tendency of a system !usually a linear

system% to oscillate with larger amplitude at some frequencies than at others. These are

known as the system9s resonant frequencies. At these frequencies, even small periodic driving

forces can produce large amplitude oscillations.

%AGNETIC RESONANT COU"LING


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#agnetic esonant coupling uses the same principles as inductive coupling, but it uses

resonance to increase the range at which the energy transfer can efficiently take place.

esonance can be two types !a% series resonance and !b% parallel resonance. The principle of

these both types of resonance is to get ma&imum energy transfer same but the methods are

quite different.

$igure 7.= shows how the resonance occurs. Bere the circuit-2 is called primary circuit and

the circuit-7 is called secondary circuit. The energy transfer will occur between these two

circuits. The resonant conditions in such circuit either in the primary circuit, when the

primary current is in phase with the input voltage, or in the secondary circuit, when the

secondary circuit current is in phase with the secondary induced voltage. The former

resonance is called primary particular resonance and the latter is a secondary particular resonance. The full resonance occurs when both the primary and the secondary circuits are in

the resonant condition.

esonant energy transfer or resonant inductive coupling is the short distance wireless

transmission of energy between two coils that are highly resonant at the same frequency. The

equipment to do this is sometimes called a resonant transformer. While many transformers

employ resonance, this type has a high


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The resonant frequency can be calculated from the equivalent circuit. To satisfy the resonance

condition, the reactance of $igure 7.= must be (ero, as in equation !7.5%. The condition in

equation !7.5% can be satisfied by two resonant frequencies as calculated in equation !7.=% and

!7.>%. The coupling coefficient k can be calculated from equation !7.=% and !7.>%. The

coupling coefficient is represented in equation !7.?%. )t represents the strength of the magnetic

coupling between the antennas, which is closely related to factors such as the air gap betweenthe antennas and the obstacles between them.

SU%%AR'

#agnetic coupling is an old and well understood method in the field of wireless power

transfer. ut as the magnetic field decay very quickly, magnetic field is effective only at a

very short distance. y applying resonance with in magnetic coupling, the power transfer at a

greater distance can be obtained.


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CHA"TER#(

&UALIT'#FACTOR

)n physics and engineering the


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Generally < is defined in terms of the ratio of the energy stored in the resonator to the energy

being lost in one cycle

FACTOR AND DA%"ING

The < factor determines the qualitative behaviour of simple damped oscillators. A system

with low quality factor !< H F% is said to be over damped. uch a system doesn9t oscillate at

all, but when displaced from its equilibrium steady-state output it returns to it by e&ponential

decay, approaching the steady state value asymptotically. )t has an impulse response that is

the sum of two decaying e&ponential functions with different rates of decay. As the quality

factor decrease the slower decay mode becomes stronger relative to the faster mode and

dominates the system9s response resulting in a slower system. A second-order low-pass filter

with a very low quality factor has a nearly first-order step responseD the system9s output

responds to a step input by slowly rising toward an asymptote.

A system with high quality factor !< I F% is said to be under-damped. *nder-damped system

combined oscillation at a specific frequency with decay of the amplitude of the signal. *nder

damped system with a low quality factor !a little above < E F% may oscillate only once or a

few times before dying out. As the quality factor increases, the relative amount of damping

decreases. A high quality bell rings with a single pure tone for a long time after being struck.

A purely oscillatory system, such as a bell that rings forever, has an infinite quality factor.#ore generally, the output of a second Jorder low pass filter with a very high quality factor

responds to a step input by quickly rising above, oscillating around, and eventually

converging to a steady- state value.

A system with an intermediate quality factor !


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)n negative feedback systems, the dominant closed-loop response is often well-modelled by a

second- order system. The phase margin of the open Jloop system sets the quality factor < of

the closed-loop systemD as the phase margin decreases, the appro&imate second-order closed-

loop system is made more oscillatory !i.e., has a higher quality factor%.

"h)!ic*+ intr,rt*tion o- &

'hysically, < is 7K times the ratio of the total energy stored divided by the energy lost in a

single cycle or equivalently the ratio of the stored energy dissipated per one radian of the

oscillation.

)t is a dimensionless parameter that compares the time constant for decay of an oscillating

physical system9s amplitude to its oscillation period. "quivalently, it compares the frequency

at which a system oscillates to the rate at which it dissipates its energy.

Where is the resonant frequency, and, the bandwidth, is the width of the range of frequencies

for which the energy is at least half its peak value.

The factors !i.e.. when the system is under damped%, it has two comple&

conjugate poles that each have a real part of M .That is, the attenuation parameter M represents

the rate of e&ponential decay of the oscillations !e.g. , after an impulse% of the system. Ahigher quality factor implies a lower attenuation, and so high < system oscillate for long

times. $or e&ample, high quality bells have an appro&imately pure sinusoidal tone for a long

time after being struck by a hammer.

& -*ctor in E+ctric*+ !)!t.!

$or an electrically resonant system, the < factor represents the effect of electrical resistance

and, for electromechanical resonators such as quart( crystals, mechanical friction.

The frequency a&is of this symbolic diagram can be linear or logarithmically scaled.


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$igure 5.7 shows the definition of bandwidth !% for a band pass filter. Where, is the centre

frequency, is the higher cut-off frequency, and is the lower cut-off frequency. The 8 d level

is the level of the peak of the band pass response, which is not necessarily located at the

centre frequency. Also the centre frequency is located at either the arithmetic or geometric

mean of the upper and lower cut-offs depending on conte&t and conventions.

& -*ctor in RLC circuit!

)n an ideal series 6 circuit and in a turned radio frequency receiver !T$% the < factor is

Where, , and 6 are respectively the resistance, inductance and capacitance of the turned

circuit.

$or a parallel 6 circuit, the < factor is the inverse of the series case.

!5.28%

)n a parallel 6 circuit where the is in series with the , < is the same. This is the most

common circumstance because, for resonators, limiting the resistance of the inductor to

improve < and narrowing the bandwidth is the desired result.

$or a circuit where , and 6 are all in parallel, the lower the parallel resistance, the more

effect it will have in damping the circuit and thus the lower the


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CHA"TER#/

O"TI%I0ATION OF WIRELESS "OWER TRANSFER S'STE%

The power transfer efficiency versus normali(ed distance i.e. the ratio of the separation

between the coils is a commonly used performance metric for comparing different designs.

ecause of the low


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The voltage across the receiver capacitor is defined to be the output of the coupled system.

When this output voltage is at ma&imum, the energy in the capacitor is at ma&imum. When

the energy stored in the capacitor is at ma&imum, the energy in the receiver can be assumed

as ma&imum.

At ma&imum voltage level on receiver circuit, current becomes (ero and no current flows

from the circuit. At this point energy stored in receiver inductor is (ero because current is

(ero. Thus ma&imi(ed receiver energy is

To e&plicitly determine this ma&imum receiver energy, it is necessary to first determine the

output voltage and its ma&imum value. The load is connected across the receiver capacitance.

The total output energy is defined to be the power dissipated by the load integrated over the

life time of the output waveform. The output voltage across the load resistor is found by

using the equivalent output impedance in a Thevenin9s equivalent circuit.


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Where, is the series resistance, is the effective resistance , is the inductance of coil,

"ffective )nductance of coil, 6 p is the resonating capacitor, 6 is the capacitance of thereceiver and " is the effective series resistance.

To improve the


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HIGH &UALIT' FACTOR COIL DESIGNING

)n case of wireless power transmission, the purpose of the coil is not only to possess

inductance but to create a region of space having a definite magnetic flu& density.

$or the greater efficiency, the coils must possess high quality factor also. To achieve high

quality factors coils with low effective series resistance !"% are required. The power

handling capacity of a coil can be increased by building it from thicker wire. At short-wave

frequencies, a phenomenon named skin effect forces all current to flow into the outside layer

of metal. As a result, a wire tube will be as effective as the same diameter of solid wire.

CO""ER LOSS

6opper loss is the heat produced by electrical currents in the coil. 6opper losses are an

undesirable transfer of energy, as are core losses, which result from induced currents inadjacent components. The term is applied regardless of whether the coils are made of copper

or another conductor, such as aluminium.

6opper oss E )7 !=.7=%

Where, ) is the current flowing in the conductor and the resistance of the conductor.

With high-frequency currents, loss in a coil is affected by pro&imity effect and skin effect,

and cannot be calculated as simply. $or low-frequency applications, the power lost can be

minimi(ed by employing conductors with a large cross-sectional area, made from low

resistivity metals.

AC RESISTANCE

At high frequencies, skin and pro&imity effect increases the ", When direct current is

applied to a straight conductor it distributes itself evenly throughout the wire9s cross-sectional

area. When an alternating current is applied to a straight conductor, eddy current develop and

the current will tend to flow on the surface. As the A6 frequency is increased it becomes

increasingly difficult for the current to penetrate into the centre of the conductor, which flows

along the conductor surface !skin%. This increases the effective resistance of the wire and is

called skin effect and is the major source of resistivity in a high frequency solenoid.

A6E F A6 ;6


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Where, A6 is the A6 resistance, F AC is A6 flu& and ;6 is the ;6 resistance.

kin effect is essentially the inability of current to penetrate from the periphery toward the

center of a conductor as the frequency is increased. This is a direct result of eddy currents

established in the conductor from the changing A6 flu& !$igure =.>%. The eddy current

reinforces current $low on the conductor9s 0kin1, decreasing e&ponentially as they movetoward the center.

At low frequencies, < increases with frequency and for I due to the dominance of pro&imity

effect on A6 resistance, the


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Annealed 6opper tandard%. )ts strength, formability, eases of joining, resistance to creep,

high thermal conductivity, and resistance to corrosion are also of equal importance.

$or all practical purposes, copper is better than more e&pensive materials such as silver and

gold, and is somewhat better than aluminium. 6opper, however, can be more easily o&idi(ed

than aluminium. ince the impact of skin effect is that the current will flow on the outside of the conductor, copper should be protected from o&idation by a spray coating such as clear

Prylon acrylic spray paint.

& FACTOR OF A SINGLE LA'ER AIR CORE COIL

The < factor of an inductor is the ratio of its inductive reactance to its series resonance . The

larger the ratio, the better the inductor is.

Where,

fE frequency !B(%

E inductances in henries

, is determined by multiplying the length of the wire, used to wind the coil, by the ;6

resistance per unit length for the wire gage used.

< changes dramatically as a function of frequency. At lower frequencies, < is very good

because only the ;6 resistance of the windings !which is very low% has an effect. As

frequency goes up, < will increase up to about the point where the skin effect and the

combined distributed capacitance begin to dominate. At the self resonance frequency of thecoil < falls rapidly and becomes 8.

SU%%AR'

esonant based power delivery is an alternative wireless power transfer technique which is

used for high power transfer efficiently.

)n this chapter a more comprehensive circuit-based model for the system is presented and the

effect of each design parameter is analy(ed. tep-by-step design procedure was followed to

optimi(e the wireless power transfer systems.

$rom the analysis it has been demonstrated that, parallel connection of load, ma&imi(ing

mutual inductance and coupling coefficient, and impedance matching increases the power

transfer efficiency.


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CHA"TER#1

BLOCK DIAGRA% RE"RESENTATION OF WIRELESS "OWER TRANSFER

S'STE%

The choice of an effective principle for power transfer is necessary for its success. The

drawbacks associated with radiative transfer method are more pronounced than its

advantages. Therefore an alternate method includes designing the source coil and receiving

coil at same resonant frequency for mid range energy transfer so that the distance of energy

transmission is of a few times the si(e of the antennas. 6onsidering the dangers of electric

fields on living organisms, the magnetic field is relatively safer and therefore more suitable

for transmitting power wirelessly. o the two systems were operated in a strongly coupled

magnetic resonance. )n this chapter, we have described the block diagram representation of

wireless power transfer system. The components used in this block diagram are alsodescribed.

BLOCK DIAGRA% OF WIRELESS "OWER TRANSFER S'STE%

At first an ac source is taken and it is connected with the rectifier. Then the rectifier is

connected to the oscillator. :scillator transfers current to the transmitter coil. A magneticfield is then created between the transmitter coil and receiver coil. The magnetic field energy

is transferred to the load without using any wire. An intermediate coil is also used. )t is placed

in between of the transmitter coil and receiver coil.

AC SOURCE

A power supply is a device that supplies electric power to an electrical load. The term is most

commonly applied to devices that convert one form of electrical energy to another, though it

may also refer to devices that convert another form of energy !mechanical, chemical, solar% to

electrical energy. A regulated power supply is one that controls the output voltage or current


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to a specific valueD the controlled value is held nearly constant despite variations in either

load current or the voltage supplied by the power supply9s energy source.

Bere a !778+->8B(% ac source is used.

RECTIFIER

A rectifier is an electrical device that converts alternating current !A6%, which periodically

reverses direction, to direct current !;6%, which flows in only one direction. The process is

known as rectification. 'hysically, rectifiers take a number of forms, including vacuum

tube diodes, mercury arc valves, solid state diodes, silicon controlled rectifiers and other

silicon-based semiconductor switches.

ectifiers have many uses, but are often found serving as components of ;6 power

supplies and high-voltage direct current power transmission systems. ectification may serve

in roles other than to generate direct current for use as a source of power. As

noted, detectors of radio signals serve as rectifiers. )n gas heating systems flamerectification is used to detect presence of flame.

The simple process of rectification produces a type of ;6 characteri(ed by pulsating voltages

and currents !although still unidirectional%. ;epending upon the type of end-use, this type of

;6 current may then be further modified into the type of relatively constant voltage ;6

characteristically produced by such sources as batteries and solar cells.

Bere, bridge rectifier circuit is used.

OSCILLATOR

An electronic oscillator is an electronic circuit that produces a repetitive electronic signal,

often a sine wave or a square wave. They are widely used in many electronic devices.

6ommon e&amples of signals generated by oscillators include signals broadcast

by radio and television transmitters, clock signals that regulate computers and quart( clocks,

and the sounds produced by electronic beepers and video games.

:scillators designed to produce a high-power A6 output from a ;6 supply are usually

called inverters.

TRANS%ITTER COIL

The transmitter coil constitutes of an inductor and capacitor and connected with the

transmitter circuit. Bere a copper tube is used as an inductor. The parameters of the inductor

and capacitor are chosen to produce resonance at a particular frequency.

INTER%EDIATE COIL

The intermediate coil constitutes of an inductor and capacitor which is supposes to produce

resonance with the magnetic field generated from source resonant circuit in order to receive

energy. )t also consists of an ";.

RECEIVER COIL


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The receiver coil constitutes of an inductor, a capacitor and a ";. Bere "; is used as the

load.

SU%%AR'

)n this chapter the block diagram representation of wireless power transmission is described.This block diagram represents the step by step process to design the wireless power transfer

system. We can get a brief e&planation of ac source, oscillator and rectifier from here.


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CHA"TER#2

CO%"ONENTS

;ifferent components are used during the implementation of the wireless energy transfer

model. These are resistor, capacitor, #:$"Ts, radio frequency chokes etc. The power that is

transmitted has to be applied across the 6 combination. o, all these components should be

added to the transmitter and receiver circuit.

D!cri,tion

A 'ower #:$"T is a specific type of #etal :&ide emiconductor $ield-"ffect Transistor

!#:$"T% designed to handle large amounts of power. 6ompared to the other power

semiconductor devices !)GT, Thyristor%, its main advantages are high commutation speedand good efficiency at low voltages. )t shares with the )GT an isolated gate that makes it

easy to drive. )t was made possible by the evolution of 6#: technology, developed for

manufacturing )ntegrated circuits in the late 24@8s. The power #:$"T shares its operating

principle with its low-power counterpart, the lateral #:$"T.

The power #:$"T is the most widely used low-voltage !i.e. less than 788 +% switch. )t can

be found in most power supplies, ;6 to ;6 converters, and low voltage motor controllers.

We used an /-channel B"N$"T power #:$"T in our project. )t is used as a low voltage

switch.

Th Brid3 Rcti-ir

The ridge rectifier rectifies that source voltage !778+, >8B(% to 23+ ;6. )t uses =

individual rectifying diodes connected in a 0bridged1 configuration to produce the desired

output but does not require a special centre tapped transformer, thereby reducing its si(e and

cost. The single secondary winding is connected to one side of the diode bridge network and

the load to the other side as shown in figure ?.7.

The = diodes labelled to are arranged in 0series pairs1 with only two diodes conducting

current during each half cycle !$igure ?.7%.

Th ,o!iti4 H*+-#c)c+

;uring the positive half cycle of the supply, diodes ;2 to ;7 conduct in series while diodes

;5 and ;= are reversed biased and the current flows through the load as shown in figure ?.5.


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Th S.oothin3 C*,*citor

The single phase half-wave rectifier produces an output wave every half cycle and that it was

not practical to use this type of circuit to produce a steady ;6 supply. The full-wave bridge

rectifier however, gives a greater mean ;6 value !8.?@5+ma&% with less superimposed ripple

while the output waveform is twice that of the frequency. Therefore, its average ;6 output

level can be increased even higher by connecting a suitable smoothing capacitor across the

output of the bridge circuit as shown in figure ?.>.

The smoothing capacitor converts the full-wave rippled output of the rectifier into a smooth

;6 output voltage. Two important parameters are considered while choosing a suitable

capacitor.

• )t9s working voltage, which must be higher than the no-load output of the rectifier.

• )t9s capacitance value, which determines the amount of ripple that will appear

superimposed on top of the ;6 voltage. )f the value of the capacitance is too low, then

the capacitor will have little effect.

The main advantages of a full-wave bridge rectifier is that it has a smaller A6 ripple value for

a given load and a smaller reservoir or smoothing capacitor that an equivalent half-wave

rectifier. Therefore, the fundamental frequency of the ripple voltage is twice that of the A6


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supply frequency !288B(% where for the half-wave rectifier it is e&actly equal to the supply

frequency !>8B(%.

The amount of ripple voltage that is superimposed on top of the ;6 supply voltage by the

diodes can be virtually eliminated by adding a much improved Q-filter !pi-filter% to the output

terminals of the bridge rectifier. This type of low-pass filter consists of two smoothingcapacitors, usually of the same value and a choke or inductance across them to introduce a

high impedance path to the alternating ripple component.

Another more practical and cheaper alternative is to use a 5-terminal voltage regulator )6,

such as a #@38> which can reduce the ripple by more than @8d while delivering over

lamp of output current.

Th O!ci++*tor Circuit

A oyer :scillator is an electronic oscillator which has the advantages of simplicity, low

component count, sinusoidal waveforms and easy transformer isolation. )t was first described by George B. oyer in ;ecember 24>= in "lectrical #anufacturing. The asic oyer

:scillator is shown in $igure ?.?.

The circuit consists of a saturable core transformer with a center tapped primary winding, a

feedback winding and a secondary winding. A capacitor is connected across the primary to

make a resonant circuit. "ach half of the primary is driven by a transistor in a push-pull

configuration. The feedback winding couples a small amount of the transformer flu& back into the transistor bases to provide positive feedback, generating oscillation. The oscillation

frequency is determined by the ma&imum magnetic flu& density, power supply voltage, and

inductance of the primary winding.

The prototype oscillator circuit designed for the wireless power transfer system is a modified

oyer oscillator. This oscillator circuit is incredibly simple yet a powerful design. +ery high

oscillating current can be achieved with this circuit depending on the semiconductor used.

Bere high current is necessary to increase the strength of the magnetic field. Although,

)nsulated Gate ipolar Transistors !)GT% are recommended for this type of oscillator, but

)GTs has limitations in high frequencies.


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O!ci++*tor Circuit O,r*tion

The circuit consists of with two chokes labelled and, two semiconductors !Bere /-channel

enhancement power-#:$"Ts% labelled and, a resonating capacitor labelled 6 and inductor

!here the transmitter coil% labelled . 6ross-coupled feedback is provided via the diodes and.,

and, are the biasing network for #:$"Ts *nd !$igure ?.@%.

When power is applied, ;6 current flows through the two sides of the coil and to the

transistor9s drain. At the same time the voltage appears on both gates and starts to turn the

transistors :/. :ne transistor is invariably a little faster than the other and will turn :/

more. The added current flowing in that side of the coil does two things. :ne, it takes away

drive from the other transistor. Two, the auto-transformer action impresses a positive voltage

on the conducting transistor, turning it hard :/. The current would continue to increase untilthe coil !transformer% saturates. The resonating capacitor 6 causes the voltage across the

primary to first rise and then fall in a standard sine wave pattern.

Assuming that turned on first, the voltage at the drain of 9s will be clamped to near ground

while the voltage at 9s drain rises to a peak and then fall as the tank formed by the capacitor

and the coil primary oscillator through one half cycle.

The oscillator runs at the frequency determined by the inductance of the coil, the capacitor

value and to a lesser e&tent, the load applied to the secondary !ource 6oil%.

The operating frequency is the familiar formula for resonance,


26/36

O!ci++*tor circuit u!d in thi! ,ro5ct:

O!ci++*tor Co.,onnt!

6omponents used are given in the table ?.2

T*6+ 278 O!ci++*tor Co.,onnt!

Component’s Name Co.,onnt9! V*+u or cod

+oltage ource, 28-=8v

6apacitors ?.3n$

esistor, 2 28k ohm

esistor, 7 28kohm

esistor, 5 =@8 ohm

esistor, = =@8 ohm

;iode, ;2 2/>5=4

;iode, ;7 2/>5=4

;iode,;5 #*2>?8


27/36

;iode,;= #*2>?8

#:$"T, 8/

adio $requency 6hoke, 2 288RB,?A

adio $requency 6hoke, 7 288RB,?ATr*n!.ittr coi+ L 23@.> nB

Sourc Coi+ Scond*r) coi+ *nd Lo*d coi+

$or the e&periment, the source coil, intermediate coil and the load coil was constructed using

8.?mm copper tube with radius ?.> inches.

R*dio Fr;unc) Cho


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CHA"TER#=

D!i3n *nd I.,+.nt*tion o- Wir+!! "o>r Tr*n!-r S)!t.

The problem with many of today9s electronic devices, such as cell phones, laptop computers

and personal digital organi(ers, is that despite their probability and ability to communicate

wirelessly, these devices still require regular charging J usually by plugging into a wall

outlet. The ability to provide power for these and other electric devices wirelessly would

greatly increase their portability and accessibility for the public.

An efficient method for wireless power transfer would also enable advances in such diverse

areas as embossed computing, mobile computing, sensor networks and micro robotics. The

need to minimi(e the energy consumption is often the main design driver in applications

where devices need to operate without adhered. "nergy consumption often restricts or

severely limits functionally in such applications. The work described in this paper ismotivated by potential application of magnetic resonant coupling as a means for wireless

power transfer from a source coil to a single load. Through simple e&perimental setups and

corresponding circuit models, we address issues that are involved in applying the basic

mechanism to a single receiver.

Thortic*+ %od+

:ur e&perimental reali(ation of the scheme consists of three coils that are tuned at the same

frequency. An oscillating circuit is connected with a source coil . 6oil is coupled resonant

inductively to an intermediate 6oil


29/36

The load coil , tuned at the same resonant frequency, receives the power through the

magnetic field generated by the intermediate coil r Tr*n!-r S)!t.

The equivalent circuit diagram of power transfer model is given in figure @.7. The power transfer occurs from coil to coil . The power loss in coil < is neglected here, since the coil

< has a very small resistance.

E?,ri.nt*+ !t#u, *nd d!i3n

)n the practical e&periment, = different set-ups are made.

• An 23+ transformer is used as the power supply. This transformer is connected with

the rectifier circuit.

• An oscillator circuit is used as the transmitter.

• Two copper coil with capacitor connected is used as the receiver.

• A "; is used as the load which is connected with the receiver.

Fi3ur I.,+.nt*tion o- >ir+!! ,o>r tr*n!-r !)!t.

The total implementation of the project is given belowJ

• The 23+ transformer with rectifier circuit is connected to the transmitter or oscillator

circuit.

• The $ chokes present in the transmitter circuit creates a magnetic field.

• The receiver coil which constitutes of an inductor and capacitor is placed at a distance

from the transmitter circuit.


30/36

• The 6 circuit of the receiver coil produces resonance with the magnetic field

generated from the source and transmitter circuit.

• When the switching is performed, the "; we have used as a load lit up to a

ma&imum distance of ?8 centimeter with voltage measured 7.7 volts.

Su..*r)

The theoretical model and circuit implementation of the wireless power transfer system was

designed based on the concept of magnetic resonant coupling. +arious optimi(ation factors

were also considered while designing the whole system. ;ue to generali(ed approach,

presented wireless power transfer system can be optimi(ed for new design constraints or for

different applications.

CHA"TER#@

"r-or.*nc *nd An*+)!i!

Wireless power transfer is a very efficient project. ut the primary concern with e&posure to

this new technology is its potential risk of using high frequency radio signal. The approach

suggested by Tesla, included strong electric field radiation which was one of the primereasons why his theory is not incorporated in modern technology. A different measurement

was taken while the wireless energy transfers. A voltage source and resonant frequency is

used while taking the measurements. The power transfer efficiency is to be determined in this

process and we can know how much the power dissipated.

E--icinc) *nd E4*+u*tion o- "o>r Lo!!!:

#easurements have been taken providing 58+ with resonant frequency 2.> #B( across the

transmitter and without the intermediate coil.

2% A 5 watt bulb lit up at its full strength at a distance of 2@ centimeter with voltage measured

2> volts.

7% A 5 watt bulb lit up to a ma&imum distance of =2 centimeter with voltage measured 28

volts.

5% A "; lit up to a ma&imum distance of @8 centimeter with voltage measured 7.7 volts.

=% +oltage measured at a distance >.7> meter was 5 milli-volts.

5 watt bulb !without intermediate coil%


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Table Theoretical and practical comparison for 5 watt bulb

!Without intermediate coil%

;istance :utput +oltage

!Theoretical%

:utput +oltage

!'ractical%

2@cm 2@ volts 2> volts

7>cm 2> volts 25.2 volts

5=cm 27 volts 22 volts

=2cm 22 volts 28 volts

"; !without intermediate coil%

Table Theoretical and practical comparison for ";

!Without intermediate coil%


!Theoretical%

:utput +oltage

!'ractical%

52cm >.@ volts =.2 volts

=5cm =.3 volts 5.5 volts >3cm =.2 volts 7.4 volts

@8cm 5.> volts 7.7 volts

#easurements have been taken with intermediate coil placed in between transmitter and

receiver at a distance 27 cm apart from the transmitter.

2% A 5 watt bulb lit up at its full strength at a distance of 5= centimeter with voltage measured

2> volts.

7% A 5 watt bulb lit up to a ma&imum distance of ?2 centimetres with voltage measured 28

volts.

5% A "; lit up to a ma&imum distance of 42 centimetres with voltage measured 7.7 volts.

=% +oltage measured at a distance >.48 meters and the voltage measured ? milli-volts.

5 watt bulb !with intermediate coil%

Table Theoretical and practical comparison for 5 watt bulb

!With intermediate coil%


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!Theoretical%

:utput +oltage

!'ractical%

5=cm 23 volts 2> volts

=>cm 2?.> volts 2= volts

>=cm 25 volts 27.= volts

?2cm 22 volts 28 volts

"; !with intermediate coil%

Table Theoretical and practical comparison for ";

!With intermediate coil%


!Theoretical%

:utput +oltage

!'ractical%

>2cm =.> volts 5.@ volts

?=cm =.2 volts 5.= volts

@3cm 5.? volts 7.4 volts

42cm 7.@ volts 7.7 volts

$or the e&perimental setup with a single receiver, the root mean square !rms% voltage acrossthe transmitter is 72.7+. The output rms voltage across a 247-S resistive load 5=cm away

from the coil is 28.?+.

The difference between supplied and received power for the system with a single receiver is

accounted for power dissipation in resistances.

>8O of the power that leaves the terminals of the actual source !ideal source in series with

internal resistance% is delivered to the load resistance.

An*+)!i!:

The dominant loss occurs in the internal source resistance. This loss occurs whenever a

source delivers power to a load, whatever through wires or through a wireless power transfer

method. The high internal resistance of the oscillator, used here only for concept

demonstration, can be significantly reduced by using a more practical power source.

Appro&imately half remaining power is delivered to the load resistance, with dissipation in

the source coil resistance, the largest loss beyond the actual source terminals. y using an

intermediate coil close to the source coil increases the


33/36

Su..r)

Apart from losses due to non-ideal characteristics of the inductor and capacitor, radiation loss

and ohmic lossD the total power transmitted might not be received because of the loading

effect of the receiver which causes the system to 0de-tune1 from resonance and weakening

the coupling factor. Also wave attenuation occurs when it passes through a lossy dielectricmedium !free space, air%. )f the effect of the losses can be minimi(ed then the efficiency of

the overall system can be improved to desired levels.

CHA"TER#

Di!cu!!ion!

)n our project the main goal was to design and implement a system that transmits power

without wire. )n this purpose, a transmitter circuit was implemented. At the end of the

transmitter circuit an antenna was connected, which transmits the power. Another antenna

was used to receive the power wirelessly from the transmitter circuit. )n this project hollow

copper pipes were used as antenna, because it has high


34/36

)t was at first thought that in the circuit +acuum Tube transistors would be used which

provides much higher power than the typical power #:$"Ts. ater this idea was

eliminated as vacuum could not be found in the shops available.

$or the oscillator circuit, low " polypropylene capacitors are highly recommended to

handle the high current flowing through the 6 tank. #oreover, other type of capacitor creates high spikes in the sinusoidal wave at the 6 tank circuit and effects the #:$"Ts.

Bowever, #ylar capacitors at first were used which has polyester as the dielectric. The circuit

was found unstable with this type of capacitor. ater #P' capacitors were used which

performed much better.

+arious high speed n-channel #:$"Ts was e&perimented. #:$"Ts with low drain to

source on resistance and higher power dissipation was found to perform better in the circuit.

At first, the transmitter circuit did not oscillateD instead it shorted the power supply and one

#:$"T and inductor heated up rapidly. ater it was found short circuit that was caused by

power supply voltage which was rising too slowly on power-up. This was solved by using aswitch on the low voltage side that was placed between the oscillator circuit and the rectifier.

Another problem faced when the oscillator circuit started to oscillate so that very little power

was available on the load coil. ecause the receiver coil was slightly out of resonance, it

could not pick up the power properly. This was solved by building both 6-tank circuits with

identical loops and capacitances, so that 5rd of the circuits have the same resonant frequency.

Co!t o- th ,ro5ct

T*6+ Co!t o- th "ro5ct

N*. &u*ntiti! Co!t Tor


35/36

• To transmit the power to a greater distance a high power radio frequency amplifier

connected with an oscillator is needed. ut the construction of the bulky $ power

amplifier requires much time and patience.

• Bigh power vacuum tube transistor amplifier with high current will make the system

more efficient.

• The receiver coil can also be fabricated on a '6 board in order to attach with

electronic gadgets.

• A layer of silver coat can also be applied over the conductor material in order to

decrease the surface resistance and increase the conductivity.

$urther effort on this same project can yield some real solutions that can solve the problem

we faced. The knowledge of this project will help those who want to design a wireless power

transmission.

Conc+u!ion:

The goal of this project was to design and implement a wireless power transfer system via

magnetic resonant coupling. After analy(ing the whole system step by step for optimi(ation, a

system was designed and implemented. "&perimental results showed that significant

improvements in terms of power-transfer efficiency have been achieved. #easured results are

in good agreement with the theoretical models.

We have described and demonstrated that magnetic resonant coupling can be used to deliver

power wirelessly from a source coil to a load coil with an intermediate coil placed betweenthe source and load coil and with capacitors at the coil terminals providing a simple means to

match resonant frequencies for the coils. This mechanism is a potentially robust means for

delivering wireless power to a receiver from a source coil.

We have used an intermediate coil in our project. )t is placed in between the transmitter coil

and receiver coil. The intermediate coil receives power from the transmitter coil. The distance

is increased by using this coil. )t consists of capacitor, inductor and a receiver load !"; or

ulb%. We have got output voltage 7.7 volts and ma&imum distance covered is 42cm by using

a "; as the load of the intermediate coil. We also have got output voltage 28 volts and

ma&imum distance covered is =2cm by using a 5 watt bulb as the load of the intermediate

coil. )ntermediate coil makes the power transfer more efficient.

We have achieved that the prototype of the system was successful at transferring a significant

amount of power wirelessly up to a certain range. This method can be made commercially

feasible if the non-ideal conditions are taken care by substitution with e&ternal components.

This work lays the foundation for wireless power technology to be implemented in

commercial product, for instance charging the battery of the laptops, cell phone, ';A and all

kinds of portable devices or supplying power to personal computers, lamps, sensors and other

product wirelessly.


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wpt project doc

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