analysis and optimization of wireless power transfer link

International Conference on Technology and Innovation Management

and IOE Graduate Conference

Oct 10-11, 2014

Analysis and Optimization of Wireless Power Transfer Link

Ajay Kumar Sah

Dr. Dibakar Raj Pant

Outline

• Introduction

• Problem Statement

• Objective

• Methodology

• Radiation and safety level

• Conclusion

• Future Work

• Scope/Application

• References

2International Conference on Technology and Innovation Management and IOE Graduate Conference, Oct 10-11, 2014

Introduction: What is Wireless Power Transfer

(WPT)?

• Types are:

3

Figure 1: Types of WPT System

The transmission of power from

one place to another without

using wires, cables or chords.

International Conference on Technology and Innovation Management and IOE Graduate Conference, Oct 10-11, 2014

Problem Statement

• When the distance between Tx & Rx changes,

there is the frequency splitting issue which

substantially deteriorates the power transfer

efficiency of the WPT System.

4

• Users have to plug in

their electronic devices

when the battery runs

out so are not truly

portable.


Objective

• Analysis and optimization of wireless powertransfer link for maximum power transferefficiency

5

Block diagram of the system

Figure 2: Basic Block diagram of 4 coil WPT Link


Methodology

6

Figure 3: (a) Simplified schematic (b) Equivalent circuit of 4 coil antenna system


Methodology: Design of Class-E Power Amplifier

7

Class-E power

amplifier has

high efficiency,

fewer components

and yielding high

reliability[1].Figure 4: Class E power amplifier

It consists of a RF choke Lc, a switch T1, a shunt

capacitor (which includes the transistor capacitance)

Cs, a load networks L-C and a load RL.


Methodology: GaN HEMT

• GaN HEMT is a High Electron Mobility Transistor.

• The compound Gallium Nitride is a very hard material.

• Its wide band gap of 3.4 eV affords it special properties

for applications in optoelectronic, high-power and high-

frequency devices.

• Due to high mobility of carrier electron, HEMT has very

low stray capacitance such as Cgs and Cds .

• Low Cgs enables high frequency gate drive with low

input power.

• Low Cds enables low switching loss for switched power

supplies.


Design of GaN HEMT Class-E Power Amplifier

• Setting Vcc to 5V, RL to 1 Ohm, Lc to 100uH and QL

to 10 and using Equations in [16] gives the

component values displayed in Table 1.

• The switch is replaced by GaN HEMT enhancement

type MOSFET transistor, EPC1010

• VPULSE input is used to drive the transistor

9

Table 1: Design Limits of GaN HEMT Class E Amplifier


Design of GaN HEMT Class E Power Amplifier

10

Figure 5: GaN class e amplifier PSpice Schematic

Figure 6: Transient analysis of GaN class e amplifier

It can be seen

from the figure

6, the input to

the class E

amplifier is 5v

square wave

and the output is

160v sine wave

which is better

than h-bridge

amplifier used

in [20].


Simulation of 4 Coil WPT Link

• 4 Coil WPT Link is simulated on Advanced

Design System (ADS) as shown in figure 7.

11

Figure 7: Equivalent circuit of WPT system on ADS


Analysis of frequency splitting phenomena

12

• At remote distances, the efficiency peaks only at the resonant

frequency.

• Closer distance leads to frequency splitting.

• The shorter the transfer distance, more obvious the phenomena is.

•When the distance

between transmitter and

receiver changes, the

coupling coefficient (k)

also varies and the

resonant frequency

(13.56MHz) splits as

shown in figure 8.

Figure 8: Frequency splitting phenomena


Frequency splitting & Cause Analysis

• At close distances, the input impedance at the original resonant

frequency point is characteristic of extremely large impedance

angle and relatively low amplitude.

• Large impedance angle causes very low transferred power, and

much is exchanged between the Power and the transmitter Coil.

• Small amplitude results in a large source current, thus increasing

the source internal resistance loss.

• Both these two factors reduce efficiency.

• While at below and above the original resonant frequency, the

input impedance is characteristic of extremely small impedance

angle and relatively high amplitude.

• Due to the opposite characteristics, efficiency peaks at these two

frequency points.


Related Factors of Frequency splitting

• The related factors, i.e. the source internal

resistance (Rs), the mutual inductance between

the Power coil and the Transmitter coil (M12),

and the mutual inductance between the load coil

and the receiving coil (M34)[23].

• When the source internal resistance increases, the

input impedance is changed into small amplitude

and large impedance angle.

• This leads to Frequency splitting.



Mutual Inductance of Source & Transmitter Coil

15

It can be seen from the figure 8

that decreasing the coupling

coefficient k23 between

transmitter & receiver coil i.e.

bringing the transmitter and

receiver closer keeping the k12

& k34 fixed,

efficiency of the system decreases and frequency splitting takes

place. When the coupling between power coil and transmitter coil

k12 increase from 0.1 to 0.2 i.e. bringing the power coil and

transmitter coil closer eliminates the frequency splitting

phenomena and the efficiency of the system increases.

Figure 9: Power transfer efficiency at

different coupling coefficient



• Mutual Inductance of Load & Receiver Coil

16

It can be seen from the figure 10 that

decreasing the coupling coefficient k23

between transmitter & receiver coil i.e.

bringing the transmitter and receiver

closer keeping the k12 & k34 fixed,

efficiency of the system decreases and

frequency splitting takes place.

When the coupling between receiver coil and load coil k34 increase from 0.1 to

0.25 i.e. bringing the receiver coil and load coil closer eliminates the frequency

splitting phenomena and the efficiency of the system increases.

Figure 10: Power transfer efficiency at

different coupling coefficient


Comparative Study on Antenna Topology

• Here using the same parameters as used in series-series topology, a

mixed topology called LCC topology is shown in figure 11.

17

The resonant frequency of this

circuit, neglecting internal resistance

of the coil is calculated as:

𝑓 =1

2𝜋 𝐿 𝐶1 + 𝐶22

Where,

L= Parallel Inductance, C1= Series Capacitance, C2= Parallel

Capacitance

Figure 11: LCC Topology


Comparative Study on Antenna Topology

18

Figure 12: Power transfer efficiency at different k for LCC & Series-series topology

In series-series topology, aslight variation of 0.006 incoupling coefficient causes thesystem efficiency to drop to 15% and also frequency splittingtakes place.

On the other hand, thechange of 0.025 in couplingcoefficient of LCC topologyonly causes a change of 20%i.e. a decrease from 80% to60% in the link efficiency.


Comparative Study on Different Wire Gauge of Antenna

• The skin depth is defined as:

𝛿 =2

𝜔𝜎𝜇3

• With 𝜎=5.96 x 107 for copper. For f=13.56 MHz, the skin depth is≈ 18𝜇𝑚.

• For the study purpose American Gauge Wire AWG14, 18 and 22are selected.

• Using same inductance and capacitance of all the antennas, theother parameters like coil antenna length, diameter, and resistanceare calculated using equations in [8-9].

• The study can be summarized as: Helical antenna 1 (0.5≤ FormFactor ≤ 0.6), Helical antenna 2 (1≤ Form Factor ≤ 1.65) andSpiral Antenna


Helical antenna 1 (0.5≤ Form Factor ≤ 0.6)

• The parameters of helical antenna 1 withvarying wire gauge are given below in table 2

20

An

ten

na

Ind

uct

anc

e (

uH

)

Co

re

Dia

me

ter

(mm

)

Pit

ch

(mm

)

Nu

mb

er

of

Tu

rns

Form

Fact

or

An

ten

na

Len

gth

(cm

)

Wir

e

Len

gth

(cm

)

Re

sist

anc

e (

m-

oh

m)

AW

G

Wir

e

Po

we

r

0.5 60

10 3 0.55 3.5 58.1 4.8 14

10 3 0.55 3.3 57.5 11.95 18

10 3 0.5 3.2 57.15 30.2 22

Tran

smit

t

er

1.3 80

10 4 0.6 4.65 1.5 8.45 14

10 4 0.6 4.4 100 21.2 18

10 4 0.55 4.25 100 53.55 22

Re

ceiv

er

0.4 80

18 2 0.55 3.9 51.3 4.25 14

18 2 0.55 3.8 50.9 10.6 18

18 2 0.55 3.75 50.65 26.75 22

Load 0.1 60

21 1 0.5 2.25 19.35 1.6 14

22 1.5 0.5 4.6 28.75 6 18

22 1.5 0.5 4.55 28.6 15.1 22Table 2: parameters of helical antenna1 with varying wire gauge


Helical antenna 1 (0.5≤ Form Factor ≤ 0.6)

• The simulation result of maximum efficiency of wireless

power transfer link using AWG 14, 18 and 22 wire for

helical antenna 1 is shown in figure 13 and both

calculated & simulated are shown in table 3.

21

Helical antenna (0.5≤ Form Factor ≥0.6)

Wire Gauge

Efficiency (%)

CalculatedSimulation

AWG 22 64.64 64.59

AWG 18 82.81 82.67

AWG 14 92.35 92.34

Table 4: Efficiency comparison of

helical antenna1 at varying wire gauge

Figure 13: Power transfer efficiency of

different wire gauge


Helical antenna 2 (1≤ Form Factor ≤ 1.65)

• The parameters of helical antenna 2 with

varying wire gauge are given below in table 4.

22

An

ten

na

Ind

uct

ance

(uH

)

Co

re

Dia

me

ter

(mm

)

Pit

ch (

mm

)

Nu

mb

er o

f

Turn

s

Form

Fac

tor

An

ten

na

Len

gth

(cm

)

Wir

e L

en

gth

(cm

)

Re

sist

ance

(m-o

hm

)

AW

G W

ire

Po

we

r

0.5 60

20 4 1.45 8.65 77.45 6.4 14

20 4 1.4 8.4 76.7 15.95 18

20 4 1.4 8.25 76.2 40.25 22

Tran

smit

te

r 1.3 80

15 5 1.05 8.3 130 10.55 14

15 5 1 8 125 26.5 18

15 5 1 7.8 125 66.95 22

Re

ceiv

er

0.4 80

32 3 1.2 10.1 76.95 6.35 14

32 3 1.2 9.9 76.35 15.9 18

32 3 1.2 9.8 76 40.15 22

Load 0.1 60

52 2 1.65 10.7 38.7 3.2 14

52 2 1.65 10.6 38.35 8 18

52 2 1.65 10.55 38.1 20.15 22

Table 4: parameters of helical antenna 2 with varying wire gaugeInternational Conference on Technology and Innovation Management and IOE Graduate Conference, Oct 10-11, 2014

Helical antenna 1 (1≤ Form Factor ≤ 1.65)

• The simulation result of maximum efficiency of wireless

power transfer link using AWG 14, 18 and 22 wire for

helical antenna 2 is shown in figure 14 and both

calculated & simulated are shown in table 5.

23



Helical antenna (1≤ Form Factor ≥1.65)

Wire GaugeEfficiency (%)

Calculated Simulation

AWG 22 55.20 55.13

AWG 18 76.39 76.30

AWG 14 89.3089.13


helical antenna2 at varying wire gauge


Methodology: Spiral Antenna

• The parameters of spiral antenna with varying wire gauge are given below in table 6.

24

An

ten

na

Ind

uct

ance

(u

H)

Co

re D

iam

ete

r

(mm

)

Th

ickn

ess

(m

m)

Nu

mb

er o

f La

yers

Co

il D

ep

th (

mm

)

Wir

e L

en

gth

(cm

)

Re

sist

ance

(m

-

oh

m)

AW

G W

ire

Po

we

r

0.5 60

2 2 3 39.6 3.25 14

2 2 1.9 38.9 8.1 18

1 1.5 1.2 28.85 15.25 22

Tran

smit

t

er

1.3 80

2 2.5 4.45 66.3 5.45 14

2 2.5 2.8 65 13.55 18

1 2.5 1.75 64.2 33.95 22

Re

ceiv

er

0.4 80

2 1.5 3 39.1 3.25 14

2 1.5 1.9 38.6 8.05 18

1 1.5 1.2 38.25 20.2 22

Load 0.1 60

2 1 1.6 19.35 1.6 14

2 1 1 19.15 4 18

1 1 0.65 19.05 10.05 22

Table 6: parameters of spiral antenna with varying wire gauge


Methodology: Spiral Antenna

• The simulation result of maximum efficiency of

wireless power transfer link using AWG 14, 18 and

22 wire for spiral antennas is shown in figure 15 and

both calculated & simulated are shown in table 7.

25

Spiral antenna

Wire Gauge

Efficiency (%)

Calculated Simulation

AWG 22 71.74 71.58

AWG 18 86.86 86.56

AWG 14 94.30 94.15




spiral antenna at varying wire gauge


Radiation and Safety Level

• Power transfer takes place due to magnetic induction,

so non-radiative.

• Moreover, Certain frequencies like 6.78MHz and

13.56MHz are designated by the ITU for industrial,

scientific and medical (ISM) RF applications

• At these frequencies, Special International Committee

on Radio Interference (CISPR) 11 places no limits on

RF emissions [7].


Conclusion

• From the observations and analyses done so

far in this thesis, it can be concluded that the

use of AWG 14 wire, spiral antenna and LCC

topology gives the best efficiency in the

Wireless Power Transfer Link.

• In addition to this, it has been observed that

GaN HEMT class E amplifier has better

performance than h bridge amplifier in the

Wireless Power Transfer Link


Future Work

• The prototype of wireless power transfer link with

class E amplifier, spiral antenna using AWG 14

wire in LCC topology can be developed to verify

the theory and to discuss the realizable

performance of implemented WPT link using

vector network analyzer (VNA).


Scope/Application

• Some probable field where it can be used for

wireless powering & charging are:

Implantable medical devices (ventricular assist

devices, pacemaker, defibrillator, etc.)

High tech military systems (Wireless sensors,

unmanned mobile robots, etc.)

Consumer electronics (phones, laptops, game

controllers and etc.)


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Thank You !


analysis and optimization of wireless power transfer link

Technology

ioe graduate conference

innovation management

transmission of power

wireless power transfer

low input power

class e power amplifierit

switched power supplies

high efficiency