wireless battery charger (rf/microwave to dc … · wireless battery charger (rf/microwave to dc...

International Journal of Advance Electrical and Electronics Engineering (IJAEEE)

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ISSN (Print): 2278-8948, Volume-3 Issue-4, 2014

17

Wireless Battery Charger (RF/Microwave to DC Conversion)

1Vyjayanthi A S,

2Channabasappa Baligar

1M Tech, 6

th Semester VLSI Design and Embedded Systems, VTU Extension Centre, UTL Technologies Bangalore –

22, Karnataka, India. 2Professor, VTU Extension Centre, UTL Technologies Bangalore - 22, Karnataka, India.

Email: [email protected],

[email protected]

Abstract: -Because of technological advancements in

electronics it is now possible to charge the portable devices

batteries using wireless power transfer technology. This

paper deals with wireless battery charging, its current

limitations, and exploration on communication possibilities

to conserve power. Also, efficiency improvement of wireless

power transfer was accomplished with modified receiver

architecture.

Wireless power transfer contains transmitter & receiver,

the hand held will have the power receiver circuit which

charges the battery and communicate the status back to

vary the power intensity or charge status. There is a need

to use the best matching power frequency to get max power

transfer by suitably fine tuning the antenna parameters

and getting the maximum efficiency. This paper describes

the design of wireless battery charger receiver side module

and also modelling of spiral coil and array of coils to

achieve maximum & efficient power transfer.

Keywords: Array of coils, Intelligent Battery charging,

Power transmitter, power receiver, Spiral coils, Safety

mode of charging Wireless power transfer, WPC.

I. INTRODUCTION

The world is moving towards complete wireless,

including battery charging for user convenience; even

we do not need the power cable too. Wireless power is

beginning to show great potential in the consumer

market. The ability to power an electronic device

without the use of wires provides a convenient solution

for the users of portable devices. This technology’s

benefits can be seen in the many portable devices, from

cell phones to electric cars that normally operate on

battery power. Inductive coupling is the method by

which efficient and versatile wireless power can be

achieved. Power efficiency is a crucial aspect of wireless

power transmission. With diminishing resources and the

threatening climate change in mind we cannot no longer

afford to waste energy, especially for general purpose

applications.

However, at low power the efficiency of the system will

be low. But compared to a power supply, the result may

look different. An additional aspect of saving resources

and standby power arises, if one wireless power system

replaces several individual supplies.

For ease of use and the benefit of both designers and

consumers, the Wireless Power Consortium (WPC) has

developed a standard that creates interoperability

between the device providing power (power transmitter,

charging station) and the device receiving power (power

receiver, portable device). A typical application diagram

is as shown in figure 1. The WPC standard defines the

type of inductive coupling (coil configuration) and the

communications protocol to be used for low-power

wireless devices [1]. Any device operating under this

standard will be able to pair with any other WPC-

compliant device. One key benefit to this approach is

that it makes use of the coils for communications

between the power transmitter and the power receiver.

Figure 1. A typical application block diagram

Under the WPC standard, ―low power‖ for wireless

transfer means a draw of 0 to 5 W. Systems that fall

within the scope of this standard are those that use

inductive coupling between two planar coils to transfer

power from the power transmitter to the power receiver.

The distance between the two coils is typically 5 mm.

Regulation of the output voltage is provided by a global

digital control loop where the power receiver

communicates with the power transmitter and requests

more or less power. Communication is unidirectional

from the power receiver to the power transmitter via

backscatter modulation [1]. In backscatter modulation,

the power-receiver coil is loaded, changing the current

draw at the power transmitter. These current changes are

monitored and demodulated into the information

required for the two devices to work together. The WPC

standard defines the three key areas of the system—the


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power transmitter that will supply power, the power

receiver that will use the power and the communications

protocol between the two devices. These three areas are

explored in next sections.

To arrive at the specification for the transmitter and

receiver and for greater understanding of this new

emerging technology the WPC standard has been

referred and important specifications are summarised in

the following sections

A. Power Transmitter

The direction of power transfer is always from the

power transmitter to the power receiver. The key circuits

of the power transmitter are the primary coil, used to

transfer power to the power-receiver coil; the control

unit for driving the primary coil; and the

communications circuit for demodulating the voltage or

current from the primary coil. Flexibility of the power-

transmitter design is limited to provide consistent power

and voltage levels to the power receiver. The power

receiver identifies itself to the power transmitter as a

compliant device and also provides configuration

information. Once the transmitter initiates power

transfer, the power receiver sends error packets to the

power transmitter requesting more or less power. The

power transmitter stops supplying power upon receiving

an ―End Power‖ message or if no packets is received for

more than 1.25 seconds. While no power is being

transmitted, the power transmitter enters a low-power

standby mode. The power transmitter, typically a flat

surface upon which the user places the power receiver,

is connected to the power source. The coils of a WPC-

compliant device operate as a resonant half bridge on a

50% duty cycle, with a 19-V DC input (±1 V). If more

or less power is needed at the power receiver, the

frequency in the coil changes but stays between 110 and

205 kHz, depending on power demands.

B. Power Receiver

The power receiver is typically a portable device. The

key circuits of the power receiver are the secondary coil,

used to receive power from the power-transmitter coil;

the rectification circuit, used to convert AC to DC; the

power conditioning circuit, which buffers the

unregulated DC into regulated DC; and the

communications circuit, which modulates the signal to

the secondary coil. The power receiver is responsible for

all communications of its authentication and power

requirements, as the power transmitter is only a

―listener.‖ While design of the power transmitter is

restricted to keep it WPC-compliant, much more

freedom is permitted for designing the power receiver.

The coil voltage at the power receiver is full-wave

rectified, with a typical efficiency of 70% for a 5-V,

500-mA output. Because communication between the

two devices is unidirectional, the WPC selected the

power receiver to be the ―talker.‖ Inductive power

transfer works by coupling a magnetic field from

primary to secondary coils. Uncoupled field lines rotate

around the primary coil and do not represent loss as long

as the field lines don’t couple a parasitic load (for

example, eddy-current loss in metal).

C. Communications protocol

The communications protocol includes analog and

digital pinging; identification and configuration; and

power transfer. A typical start-up sequence that occurs

when a power receiver is placed on a power transmitter

proceeds as follows:

a. An analog ping from the power transmitter

detects the presence of an object.

b. A digital ping from the power transmitter is a

longer version of the analog ping and gives the power

receiver time to reply with a signal-strength packet. If

the signal strength packet is valid, the power transmitter

keeps power on the coil and proceeds to the next phase.

c. During the identification and configuration

phase, the power receiver sends packets that identify it

and that provide configuration and setup information to

the power transmitter.

d. In the power-transfer phase, the power receiver

sends control error packets to the power transmitter to

increase or decrease the power supply. These packets are

sent approximately every 250 ms during normal

operation or every 32 ms during large signal changes.

Also during normal operation, the power transmitter

sends power packets every 5 seconds.

e. To end the power transfer, the power receiver

sends an ―End Power‖ message or sends no

communications for 1.25 seconds. Either of these events

places the power transmitter in a low-power state [1].

II. MODELING OF SWITCH MODE

POWER SUPPLY FOR EFFICINECY

IMPROVEMENT

Modern day smart phones, tablets and other consumer

devices are being designed with USB ports for charging

and other communication. Switch-mode topology is

ideally suited for fast charging from USB ports. The

idea is to modify the receiver side circuitry to have the

switch mode charging for mobile devices for faster

charging. For switch mode charging we make use of

Switch Mode Regulator (Switcher), which uses pulse

width modulation to control the voltage, Low power

dissipation over wide variations in input and battery

voltage. It is more efficient than linear regulators but

more complex. It needs a large passive LC (inductor and

capacitor) output filter to smooth the pulsed waveform

[2]. Component size depends on current handling

capacity but can be reduced by using a higher switching

frequency, typically 50 kHz to 500 kHz, Since the size

of the required inductors and capacitors is inversely

proportional to the operating frequency [3] and also it is

the same frequency range at which the wireless charging

evaluation kits are being designed to operate as per the

wireless power consortium standards. However,


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switching heavy currents gives rise to EMI and electrical

noise. This has to be carefully taken care of by better

design parameters. All of these factors have contributed

to the need for the development of an efficient wireless

battery charging receiver side module system.

In the 1960s and early 1970s, power supplies were linear

designs with efficiencies in the range of 30% to 50%.

With the introduction of switching techniques in the

1980s, this rose to 60% to 80%. In the mid-1980s, power

densities were about 50 W/in3. With the introduction of

resonant converter techniques in the 1990s, this was

increased to 100 W/in3 [4]. When high speed and power

hungry processors were introduced during the mid-

1990s, much attention was focused on transient

response, and industry trends were to mix linear and

switching systems to obtain the best of both worlds.

Low dropout (LDO) regulators were introduced to

power noise-sensitive and fast transient loads in many portable products. In the late 1990s, power management

and digital control concepts and many advanced

approaches were introduced into the power supply and

overall power management.

A basic topology of the switch mode power supply

(SMPS) for wireless power receiver system has been

modelled using Liner Technology Corporation’s LT

SPICE IV, circuit simulation software and the simulated

circuit is shown in figure 2. A highly efficient DC-DC

buck boost converter, LTC 3789 is utilised for design of

SMPS in this work.

Figure 2. SMPS circuit schematic

The dual resonant circuit shall have the following

resonant frequencies:

………… (1)

… (2)

Each capacitor can then be calculated using Equations

3& 4:

……………..(3)

……… (4)

Where fS is 100 kHz +5/-10% and fD is 1 MHz ±10%.

C1 must be chosen first prior to calculating C2.

The quality factor must be greater than 77 and can be

determined by Equation 5:

……………. .. (5)

Where R is the DC resistance of the receiver coil. All

other constants are defined above.

Where:

1. VIN is a square-wave power source that should

have a peak-to-peak operation of 15-19V.

2. CP is the primary series resonant capacitor (i.e. 100

nF ).

3. LP is the primary coil of interest.

4. LS is the secondary coil of interest.

5. CS is the series resonant capacitor chosen for the

receiver coil.

6. CD is the parallel resonant capacitor chosen for the

receiver coil.

7. CB is the bulk capacitor of the diode bridge

(voltage rating should be at least 25 V and

capacitance value of at least 10μ F)

The diode bridge is constructed of Schottky diodes.

The simulated output voltage, current and power

waveforms are plotted as shown in figures 3 & 4.

Figure 3. Output Voltage & current waveform

Figure 4. Output power waveform


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20

III. MODELING OF SPIRAL COIL

The range of wireless power is mainly function of coil

dimensions and the core shape. The reliable power

transfer is usually facilitated when distance between

coils doesn't exceed 1/4...1/2 of the coil diameter for flat

coils [5].

Planar spirals over a highly scalable geometry are

appropriate for wireless power transfer via strongly

coupled inductive resonators [6]. We analyse a simple

model to identify design considerations for a specific

material & dimensions. Two aligned spiral model

simulated using the HFSS design environment is as

depicted in figure 5 and top-down view is as shown in

figure 6.

Two coils were modelled to test the coupling efficiency

and design optimization. Device dimensions were do =

55 mm; n = 3; w = 4.5 mm: and di=do = 0.35 (considered

optimal). Coil#1 (transmitter) & coil#2 (receiver) were

modelled on a 5 mm: thick Rogers 4350B substrate (tan

_ = 0:0037). The devices were provided with excitation

ports at the entry point and excited.

The primary coil acts as the transmitter and is excited by

the source. The transmitter coil is resonated at the

operating frequency of 110-210 KHz. The loosely

coupled secondary coil acts as the receiver. The receiver

output is fed into the integrated circuitry which

optimizes the power to the battery of charging device.

The filed plot of energy transfer between transmitter and

receiver is as shown in figure 7.

Figure 5. Spiral model

Figure 6. Top-down view (substrate layer hidden)

Figure7. Field plot of energy transfer between Spiral

coils using HFSS

When we have analysed the simulated data while

simulating the simple planar spiral coils for different

dimensions, and found that, the substrate material,

thickness, coil geometry, coil material, spacing between

coils and quality factor does plays a crucial role in

optimizing the efficiency of wireless power transfer

between the spiral models.

The strong coupling is concentrated at the centre of the

coils as depicted in the field plot diagram shown in

figure 8. The lumped elements for coils are extracted by

using s-parameter values as shown in figures 8, 9 and 10

in order to evaluate simulated inductive power between

the coils. However, the tool is not supporting resonant

frequency range of 110 kHz-210 kHz. To obtain

simulation results, the operating frequency range is

considered in terms of GHz.

For this simulation, strong coupling is achieved for

distances of the order ~2 do [6].

The radiation pattern, s-parameter polar plot and the

field energy plot are given below in the following

figures for the simulated planar coils. In the radiation

pattern we can observe that there is strong radiation on

lateral side of the model.

Figure 8. Radiation pattern between Spiral coils (aligned)

Figure 9.S-parameter magnitude

Figure 10. S-parameter polar plot


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Figure 10. S-parameter magnitude in dB

Variation of electric field intensity around the

transmitter and receiver was also simulated in this work.

In most of the cases, the transmitter and receiver

orientation plays a vital role in the wireless power

transmission. The maximum power coupling between

the transmitter and receiver is achieved under no case of

misalignment [7]. Significant coupling under resonance

is efficient considering proper orientation of transmitter

and receiver coils. The orientation of the receiver coil

with respect to the transmitter coil is simulated as given

in figure 11.

Figure 11. Coil modelling (misaligned coils)

Figure 12. Field-intensity Vs time

The graph as in figure 12 gives the comparison of

electric field intensity between the transmitter and

receiver coils with and without the misalignment. We

can clearly observe that the intensity is high for coil

coupled without any misalignment. The orientations of

the coils are vital for the maximum energy to be coupled

by the receiver [7]. The misalignment of modelled coils

gives us the idea about electric field intensity

distribution around the receiver coil. It can be inferred

from the graph that the field intensity is maximum only

under the case of proper orientation.

IV. MODELING OF ARRAY OF SPIRAL

COILS

While high power transfer efficiency is critical for low

power systems, area-constrained systems can require

larger power transfer through smaller area coils at an

acceptable loss in efficiency. With a fixed distance

between two coils, larger coils result in larger k and

higher efficiency. However, using larger coils requires

more silicon area, and it ultimately decreases the power

transfer density. Therefore, a parallel power transfer

scheme can be taken into consideration in order to

increase power density and maximize the amount of

power delivery through the same area, as illustrated in

figure 13. The radiation pattern of 3 X 3 array coil with

single and two coils excited are as shown in figures 14

and 15.

Figure 13.Simulation setup for parallel inductive spiral

coils: 3x3 array of 50mmX50mm coils

Figure 14. Radiation pattern for 3X3 array of coils with

single coil excited.

Figure 15. Radiation pattern of two coils excited.

The modelling and simulation of power transmitter and

receiver coils has been carried out using trial/student

version of the simulation tool. The tool works better at

higher frequency range. At resonant frequency range of

140 khz, the tool was taking more than 72 hours to

complete the simulation for 3x3 array. As a result, more

accurate representation and evaluation of the wireless

power transfer coils /structure is not fruitful.

V. HARDWARE CONFIGURATION OF

THE PROPOSED WIRLESS BATTERY

CHARGING RECEIVER SIDE MODULE.

The objective is to provide a small, general wireless

battery charging receiver system utilizing switch mode

technology. Ideally, the wireless charging receiver

system will be able to charge mobile devices under

voltage variation conditions, and also ensures faster

charging with safety features.


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Figure 16 illustrates the concept of modified receiver

circuitry with an efficient switching regulator and other

functional units.

Figure 16. Configuration of proposed wireless battery

charging receiver side module block diagram.

In the modified receiver architecture, the power

inductively coupled to receiver coil is fed to tuning

circuit followed by rectification full wave bridge and

detection circuit. Voltage regulation, smoothing is

performed by the highly efficient DC-DC regulator. In

order to charge the battery, a charge controller IC is

utilized. USB host connector is provided as a means to

connect mobile/smart phones for charging purpose. MSP

430 launch pad integrated with 16 X 2 LCD display is

interfaced externally & manually for monitoring and

display of battery charging status.

There are several basic steps involved in producing

hardware (PCB). Most designs begin with a hand drawn

schematic and design plan. With these, the circuit is

prototyped and tested to verify that the design works

correctly. Then, using software, an electronic version of

the schematic is created. A net list file is created from

the electronic schematic and used in other software to

create the physical layout of the PCB. Next, the

components are placed and routed in the physical layout

software and Gerber files are created. These Gerber files

are used in a prototyping system to mill, drill, and cut

the PCB substrate. The components are then placed and

soldered to the substrate. Finally, the board is tested to

verify that it works as expected.

Then, with the PCB still undowered, we have used a

multi meter to verify the correct pin connections through

the traces. When all verification seems well, then DC

supply is applied with testing and troubleshooting to

follow as necessary. All repairs such as soldering or de-

soldering of components, etc to the board were

conducted by Lab technician only, as it is very easy to

damage the PCB when soldering or conducting other

repairs. Finally a fully functional wireless battery

charging receiver side prototype as shown in figure 17 is

ready for conducting tests for efficiency improvements

as aimed in this paper.

Figure 17. Wireless Battery charging PCB prototype

VI. SOFTWARE DESIGN

In this work software activity is limited to monitor the

battery charging process and communication of status on

charging or completed charging to output device. In this

work we have chosen 16 character X 2 lines LCD

display for displaying the charging status instead of

hyper terminal.

For smart work like controlling of battery charging and

status updates MSP430 low power microcontroller of

G2553 series has been chosen. Texas Instrument’s

single-chip digital base band microcontroller MSP430

family was designed specifically for low-power

embedded systems. The customizable platforms help to

achieve a lower component count, save board space, and

reduce power consumption. MSP430 microcontroller is

a good fit for Li-Ion battery charging solution because of

integrated peripherals.

LaunchPad has an integrated DIP target socket that

supports up to 20 pins, allowing MSP430 Value Line

devices to be dropped into the LaunchPad board. Also,


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23

an on-board flash emulation tool allows direct interface

to a PC for easy programming, debugging, and

evaluation.

IAR embedded work bench, which is an integrated

development environment (IDE) has been utilized for

coding and compiling. IAR kick start, a code-limited

version, which is available for download is utilized. This

IDE will run full-featured on the available MSP430

Value Line devices, as this device will not encounter the

4kB size limit of IAR, or the 16kB size limit of CCS.

Figure 18. LCD 16X2 Character display flow diagram

Software activity is usually started with a flow chart

which depicts the flow of the program and also eases the

coding of the software. Flow chart for monitoring of

Charging status and display of charging status for the

wireless battery charger is as shown in figure 18.

Once the code is written, it is flashed in the MSP430

launch pad and programme is complied and run in the

IAR embedded work bench. The LCD screen has started

displaying the message of ―Charging ―of the load/mobile

connected to the prototype module using USB connector

and the LCD display is depicted as shown in figure 19.

Figure 19. 16X2 LCD display unit indicating charging

status

VII. TESTS & RESULTS

The wireless battery charging receiver side

module/prototype functionality testing is done as

described in the procedure below [8-9]. The list of

required hardware and software for testing the wireless

battery charging prototype is as given below.

1. Tools required for testing

The setup tools used to test the wireless battery charging

prototype designed and fabricated in this work are as

listed below.

Equipment

1) bqTESLA Transmitter

Power for the wireless battery charging prototype

receiver is supplied through a Texas instruments

bqTESLA transmitter bq500110 EVM-688/9 EVM or

WPC-certified transmitter. The input ac voltage is

applied to the receiver through the coil located in the

receiver bottom.

2) Voltage source

Input power supply to the bqTESLA transmitter is

typically 19 Vdc ±200 mV at 500 mA maximum is

applied using programmable power supply of Gwinstek

PST-3202 make. It is a three channel highly accurate

DC power supply. To simulate an external adapter, an

additional channel programmed for 5 V at the 1-A is

used.

3) Meters

Output voltage can be monitored at TP7 with a

voltmeter. Input current into the load must be monitored

with an appropriate ammeter. Transmitter input current

and voltage can be monitored also but the meter must

use averaging function for reducing error due to

communications packets.

4) Loads

A single load is required for 5 V with a maximum

current of 1 A. The load can be resistive or electronic.

A 100 ohm rheostat is used.


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24

5) Oscilloscope

A multichannel Tektronix make TPS 2014 model, 100

MHz Digital storage oscilloscope with appropriate

probes is used to observe the RECT voltage and other

signals.

2. Equipment Setup

1. With the power supply off, connect supply to the

bqTESLA™ transmitter.

2. Place the Wireless Battery charging prototype

receiver on the transmitter.

3. Connect load to J201, monitor current through load

with ammeter,

4. Typical output voltage is 5 V, and the output

current range is 0 mA to 1 A.

3. Equipment test Setup

The diagram of Figure 20 shows the equipment test. At

no load the system is drawing an input current of 82 ma

as shown in figure 21.

Figure 20.Equipment test setup

The following test is conducted to validate the wireless

battery charging technology using the above mentioned

test setup.

4. Load Step

The procedure for load step is as follows:

1. The test bench is setup as described in Step 2 and is

as shown in figure 23.

2. The TX is powered with 19 V DC supply.

3. The Rx is placed and properly aligned on the

transmitter.

4. Provided a load step from no load (high

impedance) to 5 Ω or 1000 mA , 10 Ω or 500 mA,

20 Ω or 250 mA and 50 Ω or 100 mA (if using a

current source load), etc.

5. Monitored the load current, rectifier voltage, and

output voltage.

Figure 21. Test setup with no load, input current is 82

ma

5. System Efficiency

The efficiency is measured from input of TX EVM,

HPA688 to output of wireless battery charger prototype

receiver EVM, with Vin = 19-V input. Due to the

communication packet that occurs at an approximate

250-ms rate, averaging of input current and voltage is

required for good accuracy [9]. The efficiency

calculation for wireless battery charging receiver side

module is given in table 1 below.

Table1: Wireless battery charging receiver side

efficiency calculation

The graph in the figure 22 shows the plot of efficiency

v/s output power

Figure 22. Wireless battery charger receiver module

efficiency v/s output power


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25

Note: For measuring receiver efficiency alone, we have

considered 100% power available at the Tx coil.

6. Tests Results

The design improvement is done for efficiency of 1 amp.

But we could test only upto 100mA of load current.

Efficiency is comparable to reference design of Ti’s

evaluation module. This module has been designed to

get better efficiency at or >1 amp load current and an

output voltage of 5 V. We could show the efficiency

improvements with 100 mA of load current since the

receiver side power management wireless IC is pre-

programmed for 100 mA of output current. And the

programming of wireless IC is not allowed to User, we

could achieve only up to 100 mA. With this result we

could charge the mobile battery as it can be connected to

the USB connector provided in the design module

without any hindrance. Once the mobile is connected the

charging indication is displayed on the LCD display unit

integrated with module and also in the connected mobile

device. The entire test setup and results output are

indicated in the following figures 23 and 24.

Figure 23. Wireless Battery charger receiver side

module with test setup & results output

Figure 24. Wireless battery charger receiver side module

charging a mobile

The MSP 430 launch pad interfaced with LCD display

unit is connected to PC through USB cable. Using IAR

embedded work bench with spy bi-wire setting we have

loaded code for monitoring the charge status and display

of charging status on LCD in the MSP430 launch pad.

Once the charging is started it will be indicated on LCD

and when charging is complete same will be indicated

on LCD screen and the LEDs provided near the battery

charger IC will be off. Thus, power transfer from

transmitter to receiver coil is suspended and undue

power dissipation is avoided and energy is conserved.

The active wireless power communication scheme, end

of power transfer and modulation of received data

(power) and controlling of power transfer are performed

by the wireless power transfer monitoring IC bq5101x .

This wireless battery charging technology could be used

to power a battery possibly on or embedded in the rotor

shaft or in any hermetically sealed enclosure with

improved efficiency and very lesser power loss and thus

ensuing a hassle free battery charging. And also it can be

utilized for charging of cars and other battery operated

vehicles, Global positioning Devices, Smart phones,

Digital cameras, MP3 players etc.

VIII. CONCLUSION

With the reference design module, wireless power

transfer efficiency is measured and then carried out the

design and development of wireless battery charger

receiver side module. This module transfers power

wirelessly using near field resonant inductive coupling.

In order to increase the absolute power transfer amount,

power density is critical & it depends on the distance &

coil technology.

Wireless power transfer and hence charging of Li-ion

battery /mobile device has been accomplished in this

work. It is an efficient and power conserving topology

and thus energy saving is ensured through intelligent

and safe mode charging, which is most sought after the

ever increasing power hungry portable device

development technology. The wireless battery charging

receiver module has been tested successfully for its

functionality using Texas Instrument’s transmitter

evaluation kit. These features show that though it has

been developed primarily for application in the portable

device segment, it can be used for any application that

requires fast, safe, hassle free and efficient charging.

The system is reliable and works without wireless power

transfer failure and maximum power transfer efficiency

of 27% is achieved in this work. Overall efficiency of

wireless power transfer system is realized for an output

current of 100 mA, because of the battery charger and

receiver side power monitoring ICs pre-programmed for

an output of 100 mA and that is what could be tested.

Under this limitation performance test is conducted and

results are as tabulated in table 1, and also at low power

the efficiency of the system will be low. If we can

establish data communication with the transmitter and

request for more power & get the power from

transmitter then probably we can get the designed power

and calculate the designed efficiency to get the feel.


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26

REFERENCES

[1] Wireless power specification, Part 1; version

1.0.3, September 2011.

[2] Eric Lo, Hau Troung, Louis, Elnatan, Alvin & Ha

Nfuyen, ― Wireless Battery Charger‖, Dec

02,2005 , EE 198B- White paper.

[3] Abraham I. Pressman, Keith Billings & Taylor

Morey, ―Switching power supply design‖ third

edition, Mc Graw Hill 2009.

[4] Nihal Kularatna, ―Electronic Circuit Design, from

concept to Implementation‖, CRC Press, 2008.

[5] An introduction to the wireless power consortium

standard and TI’s compliant solutions, 1Q 2011

Analog Applications Journal.

[6] Avraham Kleina, Nadav Katz, ― Strong coupling

Optimization with planar spiral resonators ,

Racah Institute, Hebrew University of Jerusalem,

Givat Ram, Israel, arXiv:1111.5271v1 [physics.

Optics] 22 Nov 2011.

[7] R.Selvakumaran, W. Liu, B.H Soong, Luo Ming

and S.Y Loon, School of Electrical & Electronics

Engineering, Nanyang Technological University,

Singapore 639798, ―Design of Inductive Coil for

Wireless Power Transfer‖, 978-1-4244-2853-3,

PP.584-589, IEEE, September 2009.

[8] Data sheets of Qi compliant Wireless power kit-

Texas Instruments SLUSAEOA-November 2010-

Revised April-2011.

[9] Data sheets of integrated wireless power receiver,

Qi compliant -Texas Instruments SLUSAY6-

March 2012.

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