Wireless Power Transfer - CST · PDF fileIntegral Equation Solver good ... in Magnetostatic solver in CST EM STUDIO ... Wireless power transfer is a field of active research

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Wireless Power Transfer


Some History

1899 - Tesla 1964 - Brown1963 - Schuder

from Garnica et al. (2013) from Schuder et al. (1963) from Brown (1964)


1990s onward: mobile device charging

Now: commercialization & standardization

Commercialization

greencarreports.com - October 25th

techradar.com - October 18th

consumerreports.org - October 7thtechradar.com - October 16th

http://www.wirelesspowerconsortium.com/

http://www.wirelesspowerconsortium.com/

http://www.powermatters.org/

http://www.powermatters.org/


Nearfield Coupling:

Inductive and Resonant Coils

Goals

• maximum power transfer

• high energy efficiency

• range & freedom of movement


Wireless Charging Example

15 mm

d (= 10 mm)

transmitter

receiver50 Ω

port

chip with

complex

dispersive

impedance

12mm

0.2 mm

frequency:

13.56 MHz(λ = 22.5m)

Simulation issue:electrically small with

small details

frequency domain

technique


Equivalent Circuit Extraction

Why an equivalent circuit model? Fundamental description of geometry

Can intuitively understand energy transfer

mechanism (inductive vs. capacitive)

Quick what-if analyses by circuit simulation

Final detailed analysis & design in full-wave 3D simulation tool!


1. Construct equivalent circuit model topology


each coil:

self inductance L

self capacitance Cself

resistance R

between coils:

mutual inductance M

mutual capacitance C21


2. 3D sim. results estimate main component values


Z-parameter phase

L1 = L2 ≈ 400 nHM ≈ 26 nH k ≈ 0.065

phases ~ 90º inductive


3. optimise equivalent circuit (goal: match 3D results)


original optimised

original optimised

L 400 nH 400.5 nH

M 26 nH 26.1 nH

Cs 0 0.27 pF

C12 0 0.13 pF

R 0 0.55 Ω


No matching = no coupling Matching = coupling

Matching


No matching = no coupling Matching = coupling

Matching


CST DESIGN STUDIO full circuit simulation tool (including harmonic balance)

tight link with 3D EM field results

very flexible optimisation and project construction

general multiport matching

broadband and multiband matching

optimisation using real components

bidirectional link to CST STUDIO SUITE

Matching Options


Matching in Optenni

various matching circuit optionsCST DS


Matching in CST DESIGN STUDIO

real components (e.g. from Optenni)

3D CST MWS modelTOUCHSTONE import

or circuit elements

(also non-linear)


Impedances!

Port 1: 50 Ω

Port 2: complex and

frequency dependent


real components (e.g. from Optenni)

TOUCHSTONE import

or circuit elements

(also non-linear)



“efficiency” = |S21|2

input output

Zport1 = 50 Ω

Zport2 variable

S-parameters



power = V∙I’1 V input output

Zport1 = 0 Ω

Zport2 variable

Pout/Pin ≈ 0.87

Pout = 17 mW

AC Task



power = V∙I’1 V input output

AC Task

Zport1 = 50 Ω

Zport2 variable

Pout/Pin ≈ 0.85

Pout = 4 mW



1V input


Coil Separation: 2 to 20 mm

matching circuit designed

for 10 mm separation


Coil Separation

matching circuit designed

for 2 mm separation


Coil Separation

System Assembly Modelling:

optimise matching circuit for

each separation distance

sweep distance

optimise matching

goal: maximise S21

matching circuit adjusted for each separation

(e.g. Ricketts et al. (2013) or Beh et al. (2013))


Lateral offset causes large

drop off in coupling

Horizontal Offset & Rotation

x = 0 axially aligned

x = 0

x = ±5 mm

x = ±10 mm

d = 10 mm


Rotation between coils has

very small effect


0º < θ < 180º

coils

axially

aligned

θ

d = 10 mm


Lateral offset causes large

drop off in coupling



x = 0

x = ±12 mm

x = ±6 mm

d = 2 mm


Spiral Coil Design

based on Casanova et al. (2009)

43 mmH-field

magnitude at

2 mm above

coil plane


Spiral Coil Coupling


x = 0

x = ±12 mm


Resonant Coupling


Resonant Coil Transfer Example

systems of coupled resonators

Integral Equation Solver good

for metal structures

Source: Sample et al. (2011)

drive

loop

load

loop

TX coil RX coil

dcoils

dsource


1. Add capacitor to resonate drive loop

2. Modify coil geometry for self-resonance

Tuning the Coil

drive

loop

coil

60 cm


strong coupling

Coupling to Second Coil

strong coupling – but at different frequencies!

d = 30 cm


even and odd mode coupling “frequency splitting”

Coupling to Second Coil

even mode: 7.1 MHz odd mode: 7.9 MHz


good coupling possible but tuning required

Frequency Splitting

Source: Sample et al. (2011)


strong coupling (S21 = -2.5 dB) even at 110 cm

Critical Coupling Distance


|S21| coupling insensitive to

±40º rotation of receiving coil

Rotation of Coils

rotation angle

coils 110 cm apart

axially aligned


Multiple Coils

4.4 m

|S21| of -5.8 dB at 4.4 m coil separation!


Multiple Coils Around a Corner

|S21| of -5.9 dB for

curved path


Shielding – High Power

Two coils 10 cm apart

30 turns

1000 A

Coils modelled in

simplified fashion

in Magnetostatic solver

in CST EM STUDIO

Aluminium housing

and ferrite shielding (μr = 1000)


Shielding – High Power

No shielding Ferrite shield

lower coupling (184 μH)higher field leakage

higher coupling (385 μH)

much lower field leakage


Wireless power transfer is a field of active research

and an increasing number of commercial applications

Simulation is an important tool in designing wireless

power transfer systems, both nearfield and farfield

CST STUDIO SUITE provides tools for addressing all

aspects of design, from circuit to 3D EM to system

level

Conclusion

Wireless Power Transfer - CST · PDF fileIntegral Equation Solver good ... in Magnetostatic solver in CST EM STUDIO ... Wireless power transfer is a field of active research

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