1

Siqi Li, Tommy Nugyen, Weihan Li

Chris Mi, Ph.D, Fellow IEEE

Professor, Department of Electrical and Computer Engineering

Director, DOE GATE Center for Electric Drive Transportation

Unplugging the Electric Car - Wireless charging of electric vehicles with

extremely high efficiency and misalignment

tolerance

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

Methods of WPT

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

Wireless market $17 Billion in 2019

Latest Development in Wireless EV Charging

MIT 2007

Tokyo 2009

Intel 2008

Korea KAIST

Leaf 2012

Witricity/Delphi

Japan

India

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

design Low efficiency

five patent

disclosures

Limited distance

Sensitive to vehicle alignment

The Topology

• Analytical

– Equivalent circuit analysis; S-parameter analysis; Analytical solutions of inductance and capacitances

• Numerical

– Finite element analysis – electromagnetic; High frequency structure simulation - HFSS

– Coupled field and lumped parameter analysis

• Experimental

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 2.00

Distance [meter]

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

Ma

g_

B [u

Te

sla

]

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.

9

Experimental Verification

Max power: 8kW Max Eff.: 97%

Input voltage

Output current Input current Output voltage

Vehicle Demonstration

• Working closely, we are making a vehicle level demonstration by end of 2013 or early 2014

• We are also working with DENSO to bench mark the design with existing wireless charging systems

• UM is also signing an agreement with Mia Motors, Inc. to commercialize the wireless charging for electric buses.