wireless power transfer...• magnetic resonance coupling for wireless power transfer is termed wpt....

Wireless Power

Transfer

John M. Miller

Matthew B. Scudiere

John W. McKeever

Cliff White

for:

Oak Ridge National Laboratory's Power Electronics Symposium Friday, July 22, 7:30 AM – 3:30 PM (EDT) Oak Ridge National Laboratory (ORNL) Conference Center, Oak Ridge, Tennessee

Patents Pending

2 Managed by UT-Battelle for the U.S. Department of Energy

Introduction: What is the Need?

• There is need for an efficient method for transferring large power levels over moderate distances to hybrid electric vehicles (HEVs) in the near future:

First to parked vehicles,

Then expand to opportunity charging, and

Eventually to highway charging while driving.

• Loosely coupled resonant mode transformers have the potential to accomplish this.

• Magnetic resonance coupling for wireless power transfer is termed WPT.


Introduction: Near Term Vision for WPT

• Electric vehicle charging must be:

• Safe, compact and efficient in order to be convenient for customers

• Power levels commensurate with application:

• 3 kW to 7 kW residential and garage; 60 kW to >100 kW on-road dynamic

WPT alignment tolerance should be under closed loop DSRC control between

the transmit coil and vehicle mounted capture coil.

Graphics Left: J.M. Miller, “Wireless Power Transfer for Electric Vehicles,” PREA meeting, Utah State Univ, Energy Dynamics

Laboratory, Ogden, UT, 7 Feb. 2011

Right: J.M.Miller, ORNL internal presentation.

Background: Barriers to Success

• Efficiency

– across cascade of components >90%

– coil-to-coil ~98%

• Meet international field emission standards (ICNIRP and ARPANSA)*

• Efficient high frequency power inverter (20 – 140 kHz)

• Implement vehicle to infrastructure (V2I) communications compliant with DOT recommendations for DSRC

* International Commission on Non-Ionizing Radiation Protection ICNIRP, Secretariat, c/o Gunde Ziegelberger, c/o

Bundesamt fu¨r Strahlenschutz, Ingolstaedter Landstrasse 1, 85764 Oberschleissheim, Germany.

* The Radiation Protection Series is published by the Australian Radiation Protection and Nuclear Safety Agency

(ARPANSA)

Background: Measures of Success

• Interoperability

– Any OEM vehicle with any WPT charger

– Means coil size fixed, operating frequency fixed, alignment tolerance & emissions fixed and communications fixed.

• Safety and emissions

– Transparent to vehicle occupants

• Communications

– DSRC following U.S. DOT recommendations for V2I

– Private and secure


Objective: PEV Stationary WPT Charging

• Solution demands a system design that focuses on utility to vehicle battery terminal overall efficiency

• SAE J2954 targets plug-battery efficiency >90%

Zone 1: Active field, ~1m2, <500uT

Zone 2: 300mm boundary

Zone 3: Field focusing & shielding

<62.5mG

ORNL developed

power inverter to

drive resonant

antenna pad

WPT resonant antenna system

Emissions levels and coupling

zone definitions per SAE

Graphic: Lindsey Marlar ORNL graphics services


Objective: Integrating WPT into a PEV

Solution: Design and develop coupling coil system suitable for vehicle integration for stationary and on-road stationary at high power levels (SAE Level 2: 3 kW to 7 kW) & high eff.

Technically: a non-radiating, near field reactive zone power transfer method

Practically: a convenient, safe and flexible means to charge electric vehicles.

Vehicle to WPT communications

RFID localizer for positioning

Use existing on-board charger,

or dedicated fast-charge and

energy management strategy

Active zone field meets

international standards (ICNIRP)

Smart grid compliant utility feed

and modern power electronics

Graphic: Lindsey Marlar ORNL graphics services


Approach: ORNL WPT System

• Synthesize the driving point high power waveform, magnetically couple, rectify

and deliver charging power to the vehicle on-board energy storage system.

Isupply

Vdc_link

Itransmitter

Vcapacitor

Vload

Iload

HALF-BRIDGE INVERTER

Vtransmitter_in

CONSTANT

VOLTAGE

LOAD

RECEIVERTRANSMITTER

I re

ce

ive

r_lo

op

Rectifier

-23.33

23.26

-10.00

0

10.00

1.48m 1.73m1.55m 1.60m 1.65m

Load Current

AM3.I [A]

AM4.I [A]

• Series-parallel L-C magnetic resonant coupling


Approach: Analytical Perspective

Wireless power transfer to unloaded vs. loaded coupling

Maximum impedance

frequency – unloaded:

fo1 = 24.8 kHz

fo2= 25.6 kHz

fzmx~ fo1



For S-P resonant coil system the operating frequencies shift due to:

• Degree of receiver coil loading (charging power demanded)

• Coefficient of coupling between coils (vehicle receiver coil to transmit pad gap)

• Tuning of various receiver coils relative to transmit coil tuning.

Coupling mode theory facilitates

understanding the fundamentals of WPT

and what parameters are key to optimized

performance.

During vehicle ESS charging the presence

of a dc potential at the secondary forces the

current and voltage responses to be very

nonlinear: fzmx to fzmn transitions



Resonance shifting is not an issue for stationary wireless charging, but

• For on-road dynamic charging is an issue

• Will require dynamic load tracking and inverter control using DSRC Illustration of ideal cases: k= 0.3, 0.22, 0.15, 0.1 and RL=2.5

Then, k=0.22 and RL= 5, 2.5, 1.8, 0.8

For a given value of coupling coefficient, k, the maximum power transfer occurs

when the reflected load matches the surge impedance of the system.


Timeline and Milestones

Duration

(mo)

Task Milestone

2 Resolve instrumentation issues on laboratory sensors

and monitoring equipment. Validate accuracy at

WPT operating frequency

Manufacturer contacted, sensor/equipment

calibration validated and documented.

10 Design, develop and fabricate a SAE level 2 WPT

charger rated 7 kW at PF and frequency level

dictated by vehicle systems team.

Demonstration and validation against program

targets using laboratory WPT apparatus. Verify

that 20 kHz < f < 140 kHz is attainable.

6 Analysis, model and simulation of level 2 WPT

charging system

Validate simulation against laboratory apparatus to

extent possible.

4 Extend WPT design to next generation coil and

evaluate performance against targets.

Next generation coil design meets specifications

8 Develop vehicle integrate coils and install on mule

vehicle.

Demonstrate WPT to vehicle mounted receiver coil

and passive load. Validate targets met.

8 Procure DSRC and integrate into mule vehicle and

interface to vehicle CAN (w/ OEM help)

Demonstrate WPT to mule vehicle battery pack

with grid converter regulation via DSRC.

3 Validation of stationary charging at 3 – 7 kW using

DSRC for regulation and messaging.

Must demonstrate that power, plug to battery

efficiency, magnetic field emissions and packaging

constraints are met.


Summary of Accomplishments

• Prior LDRD developed Evanescent Power Transfer apparatus is used for testing

• Alternative coupling coil designs directed research activities into ac resistive effects contributing to coil losses: skin and proximity effects

• Analytical work continues on both parasitic effects and on application of magnetic vector potential to the coupling field itself.

• Coil designs aimed at vehicle integration are not covered in this presentation.



Validation of laboratory instrumentation accuracy

Current sensor calibration at high frequency

Instrumentation errors due to low power factor (Agilent LCR)

Error in losses due to current redistribution in conductors

Reconfigured the WPT apparatus for:

Initial 120 Vdc lamp loads (series connected), to

240 Vdc (parallel connected), to

270 Vdc using new, higher power bulbs.

Refinement of DSP load voltage regulator.



• Developing deeper understanding of transmit and receiver coil

electromagnetic behavior

• Experimental finding that multiple “ribbon” coils operating in parallel offer no benefit in terms of loss reduction.

Two such coils in close proximity (~15mm) exhibit virtually unchanged Rac and Ls

Top: End on view of flux lines for 3 turn ribbon coil antenna. Bottom: end on view of ribbon coil conductor current density plots

shown extensive skin effect and proximity effects in two outside bars. Isovalues ResultsQuantity : Equi flux Weber Time (s.) : 20E-6Line / Value 1 / 1.5868E-6 2 / 9.36209E-6 3 / 17.13739E-6 4 / 24.91269E-6 5 / 32.68798E-6 6 / 40.46328E-6 7 / 48.23858E-6 8 / 56.01387E-6 9 / 63.78917E-6 10 / 71.56446E-6 11 / 79.33976E-6 12 / 87.11506E-6 13 / 94.89035E-6 14 / 102.66565E-6 15 / 110.44095E-6 16 / 118.21625E-6 17 / 125.99154E-6 18 / 133.76684E-6 19 / 141.54214E-6 20 / 149.31743E-6 21 / 157.09273E-6

Isovalues ResultsQuantity : Current density A/(square mm) Time (s.) : 222E-6Line / Value 1 / 7.96021E-3 2 / 90.54364E-3 3 / 173.12708E-3 4 / 255.71051E-3 5 / 338.29397E-3 6 / 420.8774E-3 7 / 503.46082E-3 8 / 586.04425E-3 9 / 668.62774E-3 10 / 751.21117E-3 11 / 833.79459E-3 12 / 916.37802E-3 13 / 998.96145E-3 14 / 1.08154 15 / 1.16413 16 / 1.24671 17 / 1.3293 18 / 1.41188 19 / 1.49446 20 / 1.57705 21 / 1.65963

Source: Field flux plot simulation: Dr. Pan-Seok Shin



• Developing deeper understanding of transmit and receiver coil

electromagnetic behavior

Plot of coil field at 20kHz excitation in air

L and R of Ribbon Antennae

12

13

14

15

16

17

18

1 10 100

Frequency, kHz

Ind

uc

tan

ce

(L

), m

H

0

5

10

15

20

25

30

35

40

45

50

Re

sis

tan

ce

(R

), m

W

L_1_3-turn ribboncoil

L_3_3-turn ribboncoils

L_4_3-turn ribboncoils

L_4_3-turn Cu tubecoils

R_1_3-turn ribboncoil

R_3_3-turn ribboncoilscoils

R_4_3-turn ribboncoils

R_4_3-turn Cu tubecoils

Isovalu

es R

esu

ltsQ

ua

ntity

: Eq

ui flu

x W

eb

er

Tim

e (s.) : 2

E-6

Lin

e / V

alu

e 1

/ -2.2

44

12

E-6

2 / -2

.01

97

E-6

3 / -1

.79

52

9E

-6 4

/ -1.5

70

88

E-6

5 / -1

.34

64

7E

-6 6

/ -1.1

22

06

E-6

7 / -8

97

.64

64

3E

-9 8

/ -67

3.2

34

81

E-9

9 / -4

48

.82

32

2E

-9 1

0 / -2

24

.41

16

1E

-9 1

1 / 0

12

/ 22

4.4

11

61

E-9

13

/ 44

8.8

23

22

E-9

14

/ 67

3.2

34

81

E-9

15

/ 89

7.6

46

43

E-9

16

/ 1.1

22

06

E-6

17

/ 1.3

46

47

E-6

18

/ 1.5

70

88

E-6

19

/ 1.7

95

29

E-6

20

/ 2.0

19

7E

-6 2

1 / 2

.24

41

2E

-6

Anamolous Rac behavior at 12 kHz has been

resolved and found to be due to LCR meter

Source: coil CAD drawings courtesy: Dr. Matthew Scudiere, Laboratory test data: Dr. John McKeever

Field flux plot simulation: Dr. Pan-Seok Shin



Validated coefficient of coupling, coil spacing, and alignment sensitivity of WPT

Future Work

• Develop design for grid converter and communications (base side)

Future Work: WPT Communications

Source: Walton Fehr, Mgr. Systems Engineering, U.S. Dept. Transportation, “Layered

Communications Enabling V-I Applications: Connected Vehicle Core Systems,” 12 June 2011


Future Work: Design Considerations

• Power inverter must match the WPT network

Analysis of efficiency considered inverter kVA/kW requirement

Off resonance kVA/kW rating can be excessive

Therefore, inverter must maintain close tracking of coupled power factor

• Further study of secondary rectification and filtering stage must be performed.

• ORNL internal power inverter development supports the WPT systems project

• Industrial partner would greatly accelerate progress in WPT for Level 2 stationary charging case.

• Transition from laboratory to in-vehicle


Topics to be Addressed for WPT

Vehicle Integration

• Interoperability with existing Electric Vehicle Supply Equipment

• Recommend stationary charging demonstration as 1st in-vehicle appl.

• Field shaping and shielding for vehicle mounted receiver

• Minimize loading due to proximity with vehicle chassis, and

• Insure WPT will not corrupt CAN network(s)

• Comply with International Regulations (ICNIRP)

• ORNL WPT has <1G (100uT) at >15” from antenna at 4kW

ICNIRP requires <62.5mG in zone outside vehicle footprint

• Power factor compensation – Investigate LCL topology

• Smart control and transfer of information:

• IEEE 802.15.4/IEEE 802.11p protocols for low rate wireless CAN


Conclusions

• Only need a simple design to efficiently transfer large power levels over moderate distances.

• Demonstrated >4 kW at 10” separation with 92% transfer efficiency.

• Can be constructed with commercial-off-the-shelf components (20 kHz IGBT’s).

• Challenges being addressed by the ORNL team:

• Minimization of coupling coil ac resistance effects,

• load tracking and compliance with interoperability,

• power inverter kVA/kW limits and

• appropriate vehicle to grid side communications.

wireless power transfer...• magnetic resonance coupling for wireless power transfer is termed wpt....

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