Wireless Power Transfer - Oak Ridge National Laboratory

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

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

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

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%
WPT resonant antenna system
Emissions levels and coupling
zone definitions per SAE
Graphic: Lindsey Marlar ORNL graphics services
6 Managed by UT-Battelle
for the U.S. Department of Energy
ORNL developed
power inverter to
drive resonant
antenna pad
Zone 1: Active field, ~1m 2 ,

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.
Graphic: Lindsey Marlar ORNL graphics services
7 Managed by UT-Battelle
for the U.S. Department of Energy
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

Approach: ORNL WPT System
• Series-parallel L-C magnetic resonant coupling
Isupply
Vdc_link
-23.33
• Synthesize the driving point high power waveform, magnetically 1.55m couple, 1.60m rectify
1.65m
and deliver charging power to the vehicle on-board energy storage system.
8 Managed by UT-Battelle
for the U.S. Department of Energy
HALF-BRIDGE INVERTER
Itransmitter
Vcapacitor
Vtransmitter_in
TRANSMITTER
RECEIVER
Ireceiver_loop
23.26
10.00
-10.00
Rectifier
0
Iload
Vload
Load Current
CONSTANT
VOLTAGE
LOAD
1.48m 1.73m
AM
AM

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

Approach: Analytical Perspective
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.
10 Managed by UT-Battelle
for the U.S. Department of Energy
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: f zmx to f zmn transitions

Approach: Analytical Perspective
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 R L=2.5
Then, k=0.22 and R L= 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.
11 Managed by UT-Battelle
for the U.S. Department of Energy

Timeline and Milestones
Duration
(mo)
2
10
6
4
8
8
3
12 Managed by UT-Battelle
for the U.S. Department of Energy
Task Milestone
Resolve instrumentation issues on laboratory sensors
and monitoring equipment. Validate accuracy at
WPT operating frequency
Design, develop and fabricate a SAE level 2 WPT
charger rated 7 kW at PF and frequency level
dictated by vehicle systems team.
Analysis, model and simulation of level 2 WPT
charging system
Extend WPT design to next generation coil and
evaluate performance against targets.
Develop vehicle integrate coils and install on mule
vehicle.
Procure DSRC and integrate into mule vehicle and
interface to vehicle CAN (w/ OEM help)
Validation of stationary charging at 3 – 7 kW using
DSRC for regulation and messaging.
Manufacturer contacted, sensor/equipment
calibration validated and documented.
Demonstration and validation against program
targets using laboratory WPT apparatus. Verify
that 20 kHz < f < 140 kHz is attainable.
Validate simulation against laboratory apparatus to
extent possible.
Next generation coil design meets specifications
Demonstrate WPT to vehicle mounted receiver coil
and passive load. Validate targets met.
Demonstrate WPT to mule vehicle battery pack
with grid converter regulation via DSRC.
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.
13 Managed by UT-Battelle
for the U.S. Department of Energy

Summary of Accomplishments
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.
14 Managed by UT-Battelle
for the U.S. Department of Energy

Summary of Accomplishments
• 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 R ac and L s
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 Results
Quantity : Equi flux Weber
Source: Field flux plot simulation: Dr. Pan-Seok Shin
15 Managed by UT-Battelle
for the U.S. Department of Energy
Time (s.) : 20E-6
Line / 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

Isovalues Results
Quantity : Equi flux Weber
Time (s.) : 2E-6
Line / Value
1 / -2.24412E-6
2 / -2.0197E-6
3 / -1.79529E-6
4 / -1.57088E-6
Summary of Accomplishments
• Developing deeper understanding of transmit and receiver coil
electromagnetic behavior
Plot of coil field at 20kHz excitation in air
16 Managed by UT-Battelle
for the U.S. Department of Energy
Inductance (L), mH
18
17
16
15
14
13
12
L and R of Ribbon Antennae
1 10 100
Frequency, kHz
50
45
40
35
30
25
20
15
10
5
0
Resistance (R), mW
L_1_3-turn ribbon
coil
L_3_3-turn ribbon
coils
L_4_3-turn ribbon
coils
L_4_3-turn Cu tube
coils
R_1_3-turn ribbon
coil
R_3_3-turn ribbon
coilscoils
R_4_3-turn ribbon
coils
R_4_3-turn Cu tube
coils
Anamolous R ac 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

Summary of Accomplishments
Validated coefficient of coupling, coil spacing, and alignment sensitivity of WPT
17 Managed by UT-Battelle
for the U.S. Department of Energy

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

Topics to be Addressed for WPT
Vehicle Integration
• Interoperability with existing Electric Vehicle Supply Equipment
• Recommend stationary charging demonstration as 1 st 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 15” from antenna at 4kW
� ICNIRP requires

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