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Wireless Power Transfer System for

Electrical Vehicle Charging

Dr. Christian Kremers


Motivation

Wireless Power Transfer is one of the

key technologies for widespread

acceptance electrical vehicles.


Outline

Accurate broadband simulation of a magnetic

coupler system

How to deal with Litz Wires ?

Maximum achievable efficiencies as

Design Parameter

Extraction of equivalent circuit

Construct compensation network

System Simulation

Efficiency …

Stray Field and Safety Concerns

Discussion …


Magnetic Coupler: 3D Model

Aluminum

shield

PEC wire with

12 number of turns

TDK/EPCOS N87 core

described by complex

𝜇 = 𝜇′ + 𝑗 𝜇′′

Winding and core

embedded in PVC with

휀 = 4 and 𝑡𝑎𝑛𝛿 = 0.06

Transmitter = Receiver

Ferrite Core

lossy PVC

𝑑𝑥

𝑑𝑧

M. Budhia et al, IEEE Trans. Power Electronics., vol. 26, no. 11, 2011

discrete

Port

PEC wire


Litz Wire Homogenized bundle

M. Etemadrezaei et al, IEEE ECCE, 3833-3840, 2012

1. Analytic formulas for skin effect and

proximity losses on strand level

2. Assumption: Each strand contributes in the

same manner to the overall losses

3. Skin effect losses (𝜔) 𝜎 𝜔 휀′′(𝜔)

Proximity losses (𝜔) 𝜇′′ 𝜔

𝑑𝑠𝑡𝑟𝑎𝑛𝑑 = 0.1 𝑚𝑚 𝑑𝑏𝑢𝑛𝑑𝑙𝑒 = 3.6 𝑚𝑚 𝑛𝑠 = 810


Litz Wire: Resistance

homogenized material

8.9 meter

wire length

Touchstone for

lumped resistance With TOUCHSTONE describing broadband

resistance of the litz wire, winding losses can be

taken into account in the Schematic


Magnetic Coupler incl. Litz Wire

𝑑𝑧 = 150 𝑚𝑚 𝑑𝑥 = 0 𝑚𝑚

Inducta

nce /

Henry

Range of validity for MQS (0 − 200 𝑘𝐻𝑧)

coupling coefficient:

quality factor:

Equivalent Circuit extraction @ 100 kHz is possible with MQS

𝐿11 = 6.7 ⋅ 10−5 𝐹

𝑀 = 4 ⋅ 10−6 𝐹

𝑄 = 277


Extract Equivalent Circuit

𝑑𝑧 = 150 𝑚𝑚 𝑑𝑥 = 0 𝑚𝑚

@ 100 kHz

𝑅𝑤𝑖𝑛𝑑𝑖𝑛𝑔 ≈ 0.09 Ω

Optimization:

• 𝐶1 = 𝐶𝑤𝑖𝑛𝑑𝑖𝑛𝑔 = 127.41 𝑝𝐹

• 𝐶12 = 𝐶𝑐𝑜𝑢𝑝𝑙𝑖𝑛𝑔 = 0.86 𝑝𝐹

𝐿12 = 𝑀


Matching and Efficiency (AC Analysis) One particular choice: SP configuration

• 𝐶2𝑝 in resonance with 𝐿11

• 𝐶1𝑠 so that ∠ 𝑈𝑖𝑛 , 𝐼𝑖𝑛 = 0

@ 100 𝑘𝐻𝑧, 𝑅𝐿 = 600 Ω

Pow

er

Eff

icie

ncy 𝜂

@ 100 kHz

Load Resistance RL / Ω

Real

Imag

𝜂𝑚𝑎𝑥 @ 𝑅𝐿 ≈ 624 Ω

𝐶1𝑠 𝐶2𝑝


System Simulation (I)

230V, 50 Hz

Rectifier Inverter

Matched Coupler

t_dead


System Simulation (II) In

put

Pow

er

𝑃𝑖𝑛

/ W

att

Eff

icie

ncy 𝜂

∠

𝑃𝑖𝑛

,𝑄𝑖𝑛

/ d

eg

Dead Time / ms

𝑅𝐿 = 600 Ω

Check to judge

whether non-linear

effects have to be

considered

Dead Time / ms

Curr

ent

/ A

Safe: “Outside” 𝐁𝑅𝑀𝑆 < 70 𝜇𝑇

Curr

ent

/ A

𝐼1 𝐼2

𝐼1

𝐼2


Influence of the Car Steel Plate (Lossy Metal)

≡ car chassis

Tabulated Surface Impedance representing Concrete

≡ Floor


Equivalent Circuit Again

Up to now:

• Magnetic Coupler in WPT System is driven with

small spectral width around fundamental

frequency 𝑓

• At 𝑓 = 100 𝑘𝐻𝑧 we are in the MQS domain

Stranded Coil with

𝑛 turns and resistance 𝑅

MQS at 𝑓 can be used to determine the impedance matrix equivalent circuit


Sweep Relative Positions 𝑑𝑥

𝑑𝑧

Q-Factor max efficiency k

𝑑𝑥 = 0

𝑑𝑧 = 160

𝑑𝑧 = 220

𝑑𝑧 = 70

𝑑𝑥 = 0

𝑑𝑥 = 280

coupling coeff. k determines the efficiency !


Solver Technologies: Pro and Cons

Broadband

Full wave

Easy connection to circuit world

Winding of the coil has to be

modelled

Stranded Coil can be used

Winding resistance is a

coil property

Magneto Quasi Static (MQS)

Connection to circuit via

equivalent circuit

Pro

Con


S. Li et al, “Wireless Power Transfer for Electric Vehicle

Applications”, IEEE Journal of Emerging and Selected Topics in

Power Electronics, vol. 3, no. 1, 2015

M. Budhia et al, “Design and Optimization of Circular Magnetic

Structures for Lumped Inductive Power Transfer Systems”, IEEE

Transactions on Power Electronics, vol. 26, no. 11, 2011

M. Etemadrezaei et al, “Equivalent Complex Permeability and

Conductivity of Litz Wire in Wireless Power Transfer Systems”,

IEEE Energy Conversion Congress and Exposition, 3833-3840, 2012

Citations

wireless power transfer system for electrical vehicle · pdf fileinfluence of the car steel...

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