magnetic core materials in hf applications dr. jonas ......core materials overview of different core...

APEC 2014

Magnetic Core Materials in HF Applications

Dr. Jonas Mühlethaler

APEC 2014

IntroductionWhat We Expect from Higher Switching Frequencies

Two Main Issues

Selection of materialModeling of material

Switching Frequency

Component Size

APEC 2014

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Core MaterialsOverview of Different Core Materials (1)

Gecko-Simulations AG Jonas Mühlethaler

APEC 2014

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Core MaterialsOverview of Different Core Materials (2)

[1] M. S. Rylko, K. J. Hartnett, J. G. Hayes, M.G. Egan, “Magnetic Material Selection for High Power High Frequency Inductors in DC-DC Converters”, in Proc. of the APEC 2009.

[1]


APEC 2014

Core MaterialsExample

SiFe vs. Ferrite2 kHz vs. 20 kHz

Modeling with GeckoMAGNETICS

www.gecko-simulations.com

APEC 2014

Core MaterialsGeckoMAGNETICS Example

Ferrite (N87)

SiFe (M165-35S)

2 kHz / Tmax = 65 °C / L = 2.5 mH / Solid Round Wires

Sat. Limit

APEC 2014

Core MaterialsGeckoMAGNETICS Example

Ferrite (N87)

SiFe (M165-35S)

20 kHz / Tmax = 65°C / L = 1 mH / Litz Wires

Therm. Limit

APEC 2014

B sat

Core Loss

Increasing f

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Core MaterialsMaterial Selection Criteria (2)


APEC 2014

IntroductionMaterial Selection Criteria (1)

Laminated Steel Cores Ferrites / Amorphous / Iron Powder

Ferrites / Nanocrystalline Materials

Sat. Flux Density LossesSelection Criteria

MaterialsFrequency

Often superposition of HF and LF components...

Saturation Flux Density

vs. Core Losses

Major Loop

Minor Loop

Sat. Limit Therm. Limit

Ferrites

< 2 Mhz (approx.)Manganese-zinc ferrite

> 2 Mhz (approx.)Nickel-zinc ferrite

Lower permeability, Lower Bsat

APEC 2014

B sat

Core Loss

Increasing f

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Core MaterialsMaterial Selection Criteria (2)


Best for components with LF and HF components?

(e.g. boost inductor?)

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Losses in gapped tape wound cores higher than expected!

www.vacuumschmelze.de

Core MaterialsEffect in Tape Wound Cores

Thin ribbons (approx. 20 µm)

Wound as toroid or as double C core.

Amorphous or nanocrystalline materials.


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Figure from [10]

In [10] a core loss increase with increasing air gap length has been observed.

Core MaterialsEffect in Tape Wound Cores - Orthogonal Flux Lines

[10] H. Fukunaga, T. Eguchi, K. Koga, Y. Ohta, and H. Kakehashi, “High Performance Cut Cores Prepared From Crystallized Fe-Based Amorphous Ribbon”, in IEEE Transactions on Magnetics, vol. 26, no. 5, 1990.


Fringing

flux

Main flux

Eddy current

Eddy current

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Horizontal Displacement Vertical Displacement

An experiment that illustrates well the loss increase due to an orthogonal flux is given here.

Core MaterialsEffect in Tape Wound Cores - Orthogonal Flux Lines

Core Loss Results

Displacements


APEC 2014

B sat

Core Loss

Increasing f

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Core MaterialsCore Material Pareto Front


Transformers /

CM Chokes

inductors

APEC 2014

19.02.14 15

Core MaterialsConclusion

It is crucial to understand the core materials in detail.


Orthogonal FluxRelaxation Effect

+ other effects, e.g. dimensional resonance

Effects that become more important at HF:

Often material selection is not trivial (HF + LF).

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Waveform

iGSE

Understanding Core Lossesi2GSE – Motivation

Results

Conclusion

Losses in the phase of constant flux!


( )v

0

1 dd

d

T

i

BP k B t

T t

αβ α−= ∆∫

α βv

ˆP k f B=

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Relaxation Losses

Rate-dependent BH Loop.

Reestablishment of a thermal equilibrium is governed by relaxation processes.

Restricted domain wall motion.

Understanding Core LossesDerivation of the i2GSE – B-H-Loop

Current Waveform


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Model Part 1

Understanding Core LossesDerivation of the i2GSE – Model Part 1


( ) ∑∫=

− +∆=n

ll

T

i PtBt

Bk

TP

1r

0

v dd

d1 αβα

( )

−∆=

−τβ

α1

r

r

e1)(d

d1rr

t

l BtBt

kT

P

ΔE

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Explanation

1) For values of D close to 0 or close to 1 a loss underestimation is expected when calculating losses with iGSE (no relaxation losses included).

2) For values of D close to 0.5 the iGSE is expected to be accurate.3) Adding the relaxation term leads to the upper loss limit, while the iGSE represents the lower loss limit. 4) Losses are expected to be in between the two limits, as has been confirmed with measurements.

Waveform Power Loss

Understanding Core LossesDerivation of the i2GSE – Model Part 2 (1)


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Waveform Power Loss

Understanding Core LossesDerivation of the i2GSE – Model Results


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The improved-improved Generalized Steinmetz Equation (i2GSE) [9]

with

and

Understanding Core LossesDerivation of the i2GSE – Summary

[9] J. Mühlethaler, J. Biela, J.W. Kolar, and A. Ecklebe, “Improved Core Loss Calculation for Magnetic Components Employed in Power Electronic Systems”, in Proc. of the APEC, Ft. Worth, TX, USA, 2011.


( ) ∑∫=

− +∆=n

lll

T

i PQtBt

Bk

TP

1rr

0

v dd

d1 αβα

ttB

ttBq

lQd/)(d

d/)(d

r

r

e −+−

=

( )

−∆=

−τβ

α1

r

r

e1)(d

d1rr

t

l BtBt

kT

P

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i2GSE

Understanding Core LossesDerivation of the i2GSE – Example

Evaluated for each piecewise-linear flux segment

Evaluated for each voltage step, i.e. for each corner point in a piecewise-linear flux waveform.

Example

Qr1 = Qr2 = 0with


for 0 and 22

0 for 2 and 2d

dfor 2 and

2

0 for and

Bt t T t

T t

t T t t TB

Btt T t T t

T t

t T t t T

γγ

γ

γγ

γ

∆ ≥ < − − ≥ − <= ∆− ≥ < − −

≥ − <

( ) ∑∫=

− +∆=n

lll

T

i PQtBt

Bk

TP

1rr

0

v dd

d1 αβα

( )2

v r r1

2

2i l ll

T t BP k B Q P

T T t

αβ αγ

γ

−

=

− ∆= ∆ +− ∑

( )r

r

r1 r2 r

11 e

2

tB

P P k BT T t

γα

β τ

γ

− ∆= = ∆ − ÷ ÷−

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magnetic core materials in hf applications dr. jonas ......core materials overview of different core...

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