Analysis and Design of Wireless Power Transfer

Syiska Yana, Emil Sinaga and Fahmi

Department Electrical Engineering, Faculty of Engineering, University of Sumatera Utara,Medan, Indonesia

Keywords: Wireless power transfer; energy technology.

Abstract: One of the most important basic needs of human life today is electrical energy, where the process of

shipping from a power source to the electrical load, in general, is still using the power cord. This paper

discusses Wireless Power Transfer, which is a way of transmitting electrical energy through the air media so

that electrical energy can be transmitted from a power source to an electrical load without using a conductor

or cable. The method used for wireless energy delivery systems is by using the principle of electromagnetic

resonance induction, which consists of a transmitter circuit and a receiver circuit. The effect of distance

between the transmitter and receiver is very influential. The maximum distance that the transmitter can send

to the receiver is 5 cm with a voltage of 1.3 volts.The farther the distance between the transmitter and the

receiver, the smaller the voltage will be, and the transmitted power will be smaller as well. Similarly, if the

distance between the receiver and transmitter is closer, the voltage, and power that can be emitted will be

even greater.The maximum power that can be generated from the transmitter circuit at the maximum

voltage of the adapter 15 volts at a distance of 2cm is 1.38 watts with a voltage of 2.76 volts.

1 INTRODUCTION

Along with the development of technology, we now

have developed electrical energy transfer system

without using cable.

Wireless Power Transfer is one way to transmit

electrical energy through the air media so that

electrical energy can be transmitted from a power

source to the load without going through a cable.

This development has an impact on the reduction of

cable usage because it can be replaced by Wireless

Power Transfer.

Wireless energy delivery technology was first

discovered and introduced by a physicist named

Nikola Tesla by building a tower named

Wardenclyffe Tower (Ahsan, 2015) shown in Figure

1. However, this study was discontinued for cost

reasons. Subsequent research on the delivery of

wireless energy was halted for decades until it was

re-developed by MIT researchers Marin Soljajic in

2007 who managed to transfer electrical power

without cables with a distance of more than 2 meters

and power of 60 watts, where the efficiency reaches

40 % (Kurs, 2007).Even in subsequent research, it

has been developed for the implementation of

Wireless Power Transfer system for transportation

system especially railway (Hwang, 2012).

The delivery of wireless electrical energy is a

method of sending electrical energy from a power

source to an electrical load without the use of a cable

intermediary. Generally, the Wireless Power

Transfer system consists of a series of Transmitters

and Receivercircuits.

Figure 1: Wardenclyffe Tower (Ahsan,2012).

Yana, S., Sinaga, E. and Fahmi, .

Analysis and Design of Wireless Power Transfer.

DOI: 10.5220/0008882000360040

In Proceedings of the 7th International Conference on Multidisciplinary Research (ICMR 2018) - , pages 36-40

ISBN: 978-989-758-437-4

2 MATERIALS AND METHOD

There are two underlying concepts about the

transmission of electrical energy without cables,

namely the concept of near field and the concept of

far field (Stanimir, 2012). With a near-field method,

it is capable of transmitting electrical energy just

less than 1 meter while the concept of far-field

allows further distance delivery.

The delivery of electrical energy, as well as the

transmission of wireless information based on the

concept of far field, i.e., a laser beam (narrow beam)

and radio waves,is often used in the field of

telecommunications. Radio transmission is very

ineffective in the delivery of wireless electrical

energy because most of the radiated power delivered

is wasted into free air. To increase the amount of

energy that can be captured by the receiving side,

the power delivered from the sender side must be

large as well.

With the concept of direct radiation as shown in

Figure 2, the antenna is directly directed from the

source to the receiver, the energy acceptable to the

receiver is increased, but it will have a direct impact

with the organism and can be dangerous. So the

concept of direct radiation cannot be used eitherin

the delivery of electrical energy without wires.

Figure 2: Direct Radiation Concepts (Stanimir,2012).

The technology of wireless power transmission

referred to in this paper is non-irradiated and refers

to the near-field method. The concept of the near

field is different from that of radio waves and direct

radiation because the process of power delivery does

not require a barrier between the transmitter circuit

and the receiver circuit.

Electromagnetic induction is an event of electric

current caused by the change of magnetic flux.

Magnetic flux is the number of lines of magnetic

force penetrating a plane.

In a transformer, an electric current flows into

the primary coil and induces the secondary coil, the

two coils are not touching but are at a very close

distance. The transformer's efficiency level will be

greatly reduced if both coils are kept away.

EMF (Electromotive force) induction can occur

at both ends of the coil if inside the coil changes the

number of magnetic force lines (magnetic flux).

EMF arising from the change in the number of

magnetic force lines in the coils is called EMF

induction. Electric current induced is called induced

current. The incidence of induced EMF and induced

current due to changes in the number of magnetic

force lines is called electromagnetic induction.

2.1 Factor magnitude EMF

There are three factors that affect EMF induction,

namely:

a. The speed of magnetic movement

b. Number of windings (N)

c. Magnetic field (B)

The electric flux generated by the B field on the

surface of the area of dA is represented by Eq. 1.

B = ∅ / A

(1)

Where :

B = Power field strength (Wb / m2 or Tesla)

Ø = electric flux (Weber)

A = Surface area (m2)

2.2 Inductance

The inductance is a property of the circuit that

connects the voltage induced by the flux change

with the rate of change of current (William, 1984).

The initial equation which can explain the

inductance is to connect the induced voltage to the

rate of flux change which includes a circuit. The

induced voltage is represented by Equation 2.







(2)

Where :

e = induced voltage (Volt)

φ = number of series axle fluxes (Weber-turns)

If the current in the circuit varies, the magnetic field

it generates will also vary. If it is assumed that the

Analysis and Design of Wireless Power Transfer

medium in which the magnetic field is generated has

constant permeability, the amount of the coupling

flux is directly proportional to the current, and

therefore the induced voltage is proportional to the

rate of change in current. So the induced voltage

obtained can be shown by Equation 3.

  





(3)

Where:

L = Inductance (H)

at / dt = Current rate change (A / s)

2.3 Principle of Energy Delivery

Magnetic

The wireless energy delivery system uses the

principle of electromagnetic resonance induction

consisting of a transmitter circuit and a receiver

circuit. In the transmitter circuit, an alternating

current source is rectified in advance with a DC

module, then into the LC circuit, in this case, the

Inductor (L) and capacitor (C), to create a non-

radiative, On the receiver side circuit, there is also

an LC circuit, where L and C function to generate

resonance from the magnetic field generated by the

transmitter circuit to receive electrical power

This type of winding will be designed in a Wireless

Power Transfer system using a copper cable. As for

many windings required for the sender,the side

circuit can be found using Equation 4.

L =











(4)

Where:

L = Inductance (H)

N = Number of turns

r = The coil radius (m)

l = Length of coil (m)

The design of the winding at the receiving end shall

be equal to or close to the existing coil on the sender

side.

2.4 Electromagnetic Resonance

Electromagnetic resonance is closely related to the

phenomena of the electromagnetic field which is

also closely related to the process of electric current.

Electromagnetic fields can be classified in electric

fields and magnetic fields. And because the

magnetic field is much safer when compared to the

electric field, the magnetic field becomes an

appropriate choice to be used as an energy delivery

medium when compared to the electric field in its

utilization for electromagnetic resonance energy

transfer (Kautsar, 2010).

Two systems with the same resonant frequency

will produce strong magnetic resonance and form a

magnetic resonance system. If there are more than

two resonance generators in the range that are still

effective, they can also join this magnetic resonance

system. The magnitude of the resonant frequency

can be calculated using Equation 5.







√



(5)

where :

= Resonance Frequency (Hertz)

L = Inductance (Henry)

C = Capacitance (Farad)

2.5 Experimental Set up

The method used in the delivery of cordless

electrical energy is by using the principle of

electromagnetic resonance induction. The steps

taken in the manufacture of this cordless energy

transfer system are as follows:

In the initial calculation phase, a calculation of

the area of the loop cross-section, the number of

loops and the length of the wire required to form the

transmitter and receiver windings.

The design of Wireless Power Transfer system is

done by using software for electronic circuit design.

Wireless Power Transfer System consists of a series

of Power Supply, Transmitter, and Receiver. The

Power Supply circuit intended in this research is a

series of adapters. This Adapter circuit serves to

convert electric current from AC current into DC

current. A DC Power Supply or Adapter basically

has 4 main parts in order to produce a stable DC

current. The four main parts are shown in Figure 3,

i.e., Transformer, Rectifier, Filter and Voltage

Regulator.

ICMR 2018 - International Conference on Multidisciplinary Research

Figure 3: DC Power Supply Block Diagram (Adapter)

The transmitter circuit is a very important circuit

in the Wireless Power Transfer system because

without a transmitter circuit the electromagnetic

resonance process will not happen and the

transmission of electrical energy without cables is

not possible. The transmitter circuit works on the

principle of electromagnetic resonance generated by

an oscillator. The oscillator functions as a resonator

that generates electromagnetic waves of a certain

frequency and is induced inductively to the receiver

circuit. The oscillator used in this paper is Osley

Oscar.

The Receiver circuit consists only of the inductor

in the form of a wire winding which is not much

different from the wire winding on the transmitter

which is then connected to the load. The Receiver

circuit acts as a magnetic resonance induction

capture from the transmitter circuit to receive

electrical power to be supplied to the load. The

diagram block of the Wireless Power Transfer

system comprising thetransmitter and receiver

circuit is shown in Figure 4.

Figure 4: Block Diagram of the System.

The wireless energy delivery system that has

been designed is shown in Figure 5.

Figure 5: Wireless Power Transfer Setup.

Testing of Wireless Power Transfer system is

done on two types of copper loops with different

diameter cross-section. The diameter of the first

copper wire is 0.3 mm and the diameter of the

second copper wire is 0.6 mm. For each type of

copper wire diameter tested, 3 kinds of testing are

done by varying the input voltage ranging from 8

volts, 12 volts, and 15 volts. As for each tested

voltage, the value also varied the distance between

the transmitter and receiver side until the LED

indicator lights up.

3 RESULTS AND DISCUSSION

The results data of all the tests that have been

performed are shown in Table 1. Of the three tests

performed, the magnitude of the voltage sent from

the sender side greatly affects the acceptable

voltage. The distance between the transmitter and

receiver side also greatly affects the acceptable

voltage level. The farther the distance between the

transmitter loop and the receiver loop shown in

Figure 4, the more acceptable power the receiver

side will be. The effects of electromagnetic fields

that can be captured by the side of the smaller

receivers make the acceptable power smaller.

Similarly, if the distance between the transmitter and

the receiver's side is closer, the electromagnetic field

generated by the transmitter side will be greater

captured by the receiver side.

Analysis and Design of Wireless Power Transfer

Table 1: Data Testing the cross-sectional area of the loop

of 0.6 mm.

From the test data in Table 1, when the 8-volt

source voltage with the distance between the sender

and receiver side 2 cm and 2.5 cms, the accepted

voltage by the receiver side is 2.6 volts,and 2.5 volts

and the LED indicator lit with currents of 0.019

amperes and 0.018 amperes. But when the distance

between the transmitter and the receiver side is 3 cm

the LED indicator turns off, with the voltage on the

receiver is 2 volts.

The maximum power that can be generated from

the transmitter circuit at the maximum voltage of the

adapter 15 volts at a distance of 2cm with a voltage

of 2.76 volts and maximum current 0.034 A. The

Power output, therefore, can reach up to 1.38 watt.

The affecting factor is the increasing distance of

transmission between the two coils so that the

electromagnetic induction will also be smaller.

Conversely, when the closer the voltage gets

bigger the better the radiated power so that the LED

indicator lights very bright.

4 CONCLUSION

Based on the results of the discussion the

conclusions are:

1. Transfer of electrical energy can be done

without using cable.

2. The farther the distance between the receiver

circuit and the transmitter circuit the smaller

the power that can be received by the receiver

circuit.

3. The change in energy value sent is proportional

to the input energy given, the greater the input

energy,the greater the energy delivered.

4. The maximum power that can be generated

from the transmitter circuit at the maximum

voltage of the adapter 15 volts at a distance of

2cm is 1.38 watts with a voltage of 2.76 volts.

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ICMR 2018 - International Conference on Multidisciplinary Research