Chris Mi, Ph.D, Fellow IEEEProfessor, Department of Electrical and Computer Engineering

Director, DOE GATE Center for Electric Drive Transportation

University of Michigan-Dearborn, (313)583-6434; mi@ieee.org

High Efficiency Wireless Charging

of Electric Vehicles for Safe and

Economic Future Transportation

Conventional EV Charging

1 2

Fast charging

Mostly DC charging in

15 to 30 minutes.

For an EV with a

24kWh battery pack,

charging in 15 minutes

means 96kW. This is

way over the power

available in private

homes.

3

Battery swapping

Investment of battery

packs; standardization

is difficult; swapping

stations need a lot

investment, space and

manpower; safety and

reliability is of concern

Normal charging

AC charging using

level 1 or level

2， voltage at 110V,

220V， 6-10 hours per

charge

Charge at home or

public space, need

large installation of

charge stations

Wireless Charging

Issues of Con. Charging and Battery Swapping

Electric safety is of concern: electric shock due to rain, etc.

Charge station, plug and cable can be easily damaged, stolen

Charge/swap station takes a lot of space and affect the views

Definition of WPT

Wireless power transfer (WPT) Inductive power transfer (IPT) Contactless power system (CPS), Wireless energy transfer Strongly coupled magnetic resonance High-efficiency inductive-power distribution The essential principles are the same given the

distances over which the power is coupled is almost always within one quarter of a wavelength and therefore, the fundamental operation of all of these systems can be described by simple coupled models

Grant Covic and John Boys, “Modern Trends in Inductive Power Transfer for Transportation

Applications,” IEEE journal of emerging and selected topics in power electronics, vol. 1, no. 1, march

2013

Methods of Wireless Power Transfer

Wireless Power Transfer

电能的无线传输

Electromagnetic Induction

电磁感应式

Electromagnetic Resonance

电磁谐振式

Radiation

辐射式

Microwave

微波

Laser

激光

Ultrasound

超声波

Radio wave

无线电波

In 1830’s, Faraday's law of induction In 1890’s, Tesla had a dream to send energy wirelessly GM EV1 used an Inductive charger in the 1990’s 2007, MIT demonstrated a system that can transfer 60W of

power over 2 m distance at very low efficiency Wireless/inductive chargers are available on the market Qualcomm, Delphi (Witricity), Plugless Power, KAIST, etc.

have developed EV wireless charger prototypes

Predicted Wireless

Charging Market

$17 Billion in 2019

High cost

Problems and Difficulties Magnetic field is diminishing proportional to1/r3 Often the mutual inductance is less than 20% or 10% of the self

inductance Analytical calculation of coil mutual inductance is next to impossible Further analytical method is needed Numerical simulation and coupled field - lumped parameter

simulation is also of paramount importance High frequency HFSS instead of static FEM for high frequency

Large size

Need novel designs

and methods to

study these systems

Low efficiency

Limited distance

Sensitive to vehicle alignment

A Wireless Power Transfer System

Secondary controlled WPT

Covic, G.A.; Boys, J.T., "Inductive Power Transfer," Proceedings of the IEEE , vol.101,

no.6, pp.1276,1289, June 2013.

Equivalent Circuit Series-Series

1 111 1

22 2

2

1( )

0 1( )

m

m L

R j L j LCV I

Ij L R R j L

C

Series-Series Resonance Structure

L1, L2 – Self inductance

Lm – Mutual inductance

L1= L1σ +Lm; L2= L2σ +Lm

Power Transferred

Power of output side

Power of the input side

Efficiency

2 22 1

2 2 2 21 2

( )| |

| [ ( ) ] |m L

Lm

V L RP I R

Z Z L

22

21 2 1 2

( )| [ ( ) ] | cos

m L

m

P L RP Z Z Z L

Calculated

efficiency

21 2

1 1 1 21 2

| || | | | cos cos

| ( ) |m

V ZP V I

Z Z L

0 1 2 3 4 5 6 7 8 9 100

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

System Topology at UMD Key inventions:

- Optimized multi-coil design for maximum coupling, with bipolar architecture- LCC topology for soft switching to further increase efficiency and frequency- Distributed circuit parameters to minimize the capacitor size and voltage rating- Bidirectional LCL Power factor correction circuit to maximize the front end efficiency

and reduce system cost- Foreign object detection and electromagnetic field emissions for human and animal

safety for the developed system.

11

Double-sided LCC Compensated Wireless Power Transfer

S1

C1 CO

D1

Battery Pack

+-

LoS3

S2 S4

L1

D2

D3

D4

Vin VoutA

B

L2

Sending Side Receiving Side

C2

i1 i2

M+

+ ++

Lf1Cf1

+Cf2

Lf2+

iLf1 iLf2

Topology

• Important Characteristic:

• The output current at resonant frequency:

• The output power can be expressed as:

2 2 _1 120 0

mLf Lf

f f

U LI I k U

L L

2 2 _1 1 220

Lff

LP U I k U U

L

Comparison of Coil Design

(a) Circular pads, (b) flux-pipe pads (c) DD-DDQ bipolar pads

Trong-Duy Nguyen, Siqi Li, Weihan Li, Chunting Chris Mi, Feasibility Study on Bipolar Pads for Efficient Wireless Power

Chargers, IEEE Applied Power Electronics Conference, Fort Worth, TX, USA, March16-20, 2014

Typical Misalignment

Door-to-door (right-left)is more difficult Front-rear is easier to align

Z (height)

Rectangular bipolar pads

Rectangular Unipolar pads

Five Studied Cases

 Case 1:

480x1000Case 2: 600x800

Case 3: 693x693

Case 4: 800x600

Case 5: 1000x480

Ferrite bar dimension

( L x W x H *)

Sender771.4 x 16 x

16600 x 16 x 16

589.1 x 16 x 16

415.4 x 16 x 16

360 x 16 x 16

Receiver925.7 x 16 x

16720 x 16 x 16

589.1 x 16 x 16

498.5 x 16 x 16

432 x 16 x 16

Number of ferrite bars 7 9 11 13 15

Coil

Sender 480 x 1000 x 6 600 x 800 x 6 693 x 693 x 6 600 x 800 x 6 1000 x 480 x 6

Receiver 480 x 1000 x 8 600 x 800 x 8 693 x 693 x 8 600 x 800 x 8 1000 x 480 x 8

Coils: Similar area

Ferrites: Similar volumeY (w

idth)

X (depth / length)

Z (height)

X & Y Misalignment

0.00 100.00 200.00 300.00 400.00y_misalligned [mm]

-0.10

-0.05

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

Coup

ling

1_2_S2R2_X600xY800_noShield_dyKy (front-to-rear misallignment)Curve Info

Ky_600x800Ky_693x693Ky_800x600Ky_480x1000Ky_1000x480

The topology with bigger Y-size has

a better Y-misalignment tolerance

0.00 100.00 200.00 300.00 400.00 500.00 600.00 700.00 800.00x_misalligned [mm]

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

Coup

ling

1_1_S2R2_X600xY800_noShield_dxKx (door-to-door misallignment)

Curve Info

Kx_480x1000Kx_600x800Kx_693x693Kx_800x600Kx_1000x480

1. The maximum coupling coefficient

decreases with the increase of coil’s

X-length

2. X-misalignment tolerance

increases with the coil’s X-length

Y (width)

X (length)

Z (h

eight)

Angular Misalignment

Typically, when a driver parks an EV, the worst angular misalignment can be limited at about 30°

Coupling coefficient vs x, y, theta

X

Z

YFinite element analysis using Maxwell 3D

Coupling Coefficient Profile versus Door-to-door and Front-to-rear Misalignments

Safety issues

With chassis - maximum misaligned position

Range of flux density

is within 1-1.2 meters,

=> It is safe to install

this WPC in an

electric vehicle

chassis, typically

about 1.8meter door-

to-door size

with chassis - perfectly aligned position

Exposed field to a human of 1.8-meter high

0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00Distance [meter]

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

Mag

_B [u

Tesla

]

Field exposed to a man of 1.8met height

Curve Info

Time='13250ns'Time='13500ns'Time='13750ns'Time='14000ns'Time='14250ns'Time='14500ns'Time='14750ns'Time='15000ns'Time='15250ns'Time='15500ns'Time='15750ns'Time='16000ns'Time='16250ns'

Human’s height [in meter]

Human body is exposed to maximum about 1.6uTesla in foot area

while about 0.06uT in head area.

21

Experimental Verification

Max power: 8kW

Max Eff.: 97%

Input voltage

Output currentInput currentOutput voltage

Experiment Results

Xmis=0mm, Gap =200mm Xmis=300mm, Gap =200mm Xmis=125mm, Gap =400mm

(Rectifier + PFC) + Buck + Wireless

PFC – power factor correction >0.98 Buck for charge control WPT: fixed frequency, auto-tuned system.

WPT

System Efficiency for Different Vbat

Dynamic In-Motion Charging

Buried tracks

Results of Foreign Object Test #1

Experiment Result: the gum wrapper was burned and there left an

imprint, which means the temperature is high.

Conclusions

Misalignment tolerance was analyzed and discussed Two kinds of coupling coefficient detection methods were

proposed 8 kW wireless charger prototype with 200mm gap and

300mm door-to-door misalignment tolerance had been built and tested

Coupling coefficient maintains at 18.8%~31.1% With a 200mm gap, 95.66% efficiency (at about 8kW)

from DC to DC was obtained at desired position 95.39% efficiency (at about 4kW) at 300mm X-

misalignment and 200mm Gap

Department of Energy- GATE Program

DENSO International US China Clean Energy Center GATE Industrial Partners

- Chrysler, Ford, DENSO International, Mathworks, dSPACE, ANSYS, Hp Pelzer, EDTA, PSIM, GaN Systems

Acknowledgement

IEEE Workshop and TPEL Special Issue on Wireless Power

2015 WoW Sponsored by six Societies of IEEE PELS, IAS, IES, VTS, MAG, PES June 5-6 (Fri.-Sat.), 2015, Daejeon, Korea Held just after the 2015 ECCE-Asia (June 1-4) in Seoul General Chairs: Dr. Chun Rim, Dr. Chris Mi TPC: Dr. John Miller http://www.2015wow.org

IEEE Transactions on Power Electronics (Guest-EIC) IEEE Journal on Emerging and Selected Topics on Power

Electronics (Guest-EIC)