NASA / TM--2002-211836 IE CE C-2002-20043

Performance of High-Frequency High-Flux

Magnetic Cores at Cryogenic Temperatures

Scott S. Gerber

ZIN Teclmologies, Inc., Brook Park, Ohio

Ahmad Hammoud

QSS Group, Inc., Cleveland, Ohio

Malik E. Elbuluk

University of Akron, Akron, Ohio

Richard L. Patterson

Glepa_ Research Center, Cleveland, Ohio

September 2002
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NASA/TM--2002-211836 IECEC-2002-20043

Performance of High-Frequency High-Flux

Magnetic Cores at Cryogenic Temperatures

Scott S. Gerber

ZIN "Iectmologies, Inc., Brook Park, Ohio

Ahmad f--tammoud

QSS Gro up, Inc., Cleveland, Ohio

Malik E. Elbuluk

University of Akron, Akron, Ohio

Richard L. Patterson

Glelm Research Center, Cleveland, Ohio

Prepared for the

37th Intersociety En.ergy Conversion Engineering Conference

sponsored by the Institute of Electrical and Electronics Engineers,

Electron Devices Society

Washington., DC, July 28-August 2, 2002

National Aeronautics and

Spa ce Ad.minis tration

Gleam Research Center

September 2002
Acknowledgments

This work is supported by the NASA Glenn Research Center GESS Contract NAS3---00145.

The authors acknowledge Magnetics, Inc. for providing samples of the cores.

Trade names or manufacturers' names are used in this report for

identificatiot_ only. This usage does not constitute at_ official

endorsement, either expressed or implied, by the Natiotml

Aeronautics and Space Administration.

NASA Center for Aerospace Information

7] 21 Standard Drive

Hanover, MD 2] 076

Available frorn

National Technical Information Service

5285 Port Royal Road

Springfield, VA 22100

Available electronically at http://gltrs.grc.nasa.gov
PERFORMANCE OF HIGH-FREQUENCY HIGH-FLUX

MAGNETIC CORES AT CRYOGENIC TEMPERATURES

Scott S. Gerber

ZIN Technologies, Inc.

Brook Park, Ohio 44142

E-mail: _-asa. qov

Ahmad Hammoud

QSS Group, Inc.

Cleveland, Ohio 44135

E-mail: al__ ov

Malik E. Elbuluk

University of Akron

Akron, Ohio 44325

E-mail: melbuluk@ uakror',edu

Richard L. Patterson

National Aeronautics and Space Administration

Glenn Research Center

Cleveland, Ohio 44135

E-mail: .[j.g!!&Ld:].:.p.a_t £[&9.C,_._]£gi&s a:..qg!L

ABSTRACT

Three magnetic powder cores and one ferrite core,

which are commonly used in inductor and transformer

design for switch mode power supplies, were selected

for investigation at cryogenic temperatures. The

powder cores are Molypermalloy Core (MPC), High

Flux Core (HFC), and Kool Mu Core (KMC). The

performance of four inductors utilizing these cores has

been evaluated as a function of temperature from 20 °C

to -180 °C. All cores were wound with the same wire

type and gauge to obtain equal values of inductance at

room temperature. Each inductor was evaluated in

terms of its inductance, quality (Q) factor, resistance,

and dynamic hysteresis characteristics (B-H loop) as a

function of temperature and frequency. Both sinusoidal

and square wave excitations were used in these

investigations. Measured data obtained on the

inductance showed that both the MPC and the HFC

cores maintain a constant inductance value, whereas

with the KMC and ferrite core hold a steady value in

inductance with frequency but decrease as temperature

is decreased. All cores exhibited dependency, with

varying degrees, in their quality factor and resistance on

test frequency and temperature. Except for the ferrite,

all cores exhibited good stability in the investigated

properties with temperature as well as frequency.

Details of the experimental procedures and test results

are presented and discussed in the paper.

INTRODUCTION

Many deep space missions require power electronic

components and systems that can operate reliably and

efficiently in cryogenic temperature environments.

Presently, spacecraft operating in the cold environment

of deep space carry on-board a large number of

radioisotope heating units (RHUs) to maintain an

operating temperature for the electronics of

approximately 20 °C [1]. This is not an ideal solution

because the RHUs are always producing heat, even

when the spacecraft is already too hot, thus requiring

an active thermal control system for the spacecraft. In

addition, they are very expensive and require elaborate

containment structures. Therefore, electronics capable

of operation at cryogenic temperatures will not only

tolerate the hostile environment of deep space but also

reduce system size and weight by eliminating

radioisotope heating units and associated structures;

thereby reducing system development and launch

costs, improving reliability and lifetime, and increasing

energy densities.

Most aerospace power management systems are

DC-based. To supply loads at different voltage and

power levels, switching regulators represent a viable

class of power electronics circuits that convert

unregulated DC input voltages into regulated DC

outputs. The design of these converters to operate at

cryogenic temperatures is expected to result in more

efficient systems than room temperature systems. This

improvement requires from better electronic switches

and filter components that can operate at low

temperatures [2].

A typical switching power converter consists of

components such as switches (transistors and diodes),

transformers, inductors and capacitors for filtering.

These components are designed to operate at

frequency that ranges from a few kHz to several MHz

and at power levels that range from a few mWs to

MWs. Inductors represent a key element in the design

and operation of such regulators as they play an

important role in the filter design to achieve the required

level of power quality at both input and output terminals.

NASA/TM--2002-211836 1
The core losses of amorphous and ferrite cores as a

function of temperature were investigated in the

temperature range of -150 °C to 150 °C [3-4]. The

performance of MPC and high temperature

superconducting (HTS) inductor in a boost converter

was evaluated at cryogenic temperatures [5].

Magnetic powder cores are known to be an ideal

choice for use in the design of inductors and

transformers in switch-mode power supplies due to their

low loss and high Q-factor. These powder cores, such

as MPC, High Flux, and Kool Mu, offer soft saturation,

high magnetic flux density (Brnax) and excellent

temperature stability [3-5]. Molypermalloy (MPC)

powder cores can be manufactured with different

permeability and varying core sizes. Inductors designed

with this family of cores can operate in a temperature

range between -65 °C and 125 °C with variation in their

inductance value limited to less than 10% [6].

High Flux powder cores have higher energy storage

capacity than MPC and Kool Mu cores. They are very

close to MPC in terms of permeability and core size,

and are commonly used in inductors, in-line noise

filters, pulse transformers, and flyback transformers [7].

Kool Mu powder cores are distributed air gap cores

formulated for low loss, high frequency applications or

for extremely low magnetostriction power applications,

such as in energy storage filter inductor in switch-mode

power supplies. These cores also come in different

permeability and sizes and are economically priced

between MPC cores and ferrite cores [8].

Ferrite cores exhibit low loss characteristics and are

designed to operate in the temperature range of -30 °C

to 70 °C. They possess high permeability from 750 to

2000 and are ideal for high-frequency (20 kHz to

3 MHz) power supplies applications. Ferrite cores can

be un-gapped or gapped for saturating or nonsaturating modes for both inductor and transformer

designs [9].

In this work, a ferrite core and three powder cores

consisting of Molypermalloy (MPC), High Flux Core

(HFC), and Kool Mu Core (KMC) were selected for

characterization for potential use in extreme

temperature environments. Some of the properties of

these cores are listed in Table I [6-9]. Four inductors

were designed using these four toroidal-shaped cores

for evaluation under cryogenic conditions. All cores

were wound with the same wire type and gauge to give

equal values of inductance at room temperature.

Measurements of each core inductance, Q-factor,

resistance, and dynamic hysteresis-loop as a function

of temperature were obtained in the frequency range

from 1 kHz to 200 kHz. The test temperature ranged

from 20 °C to -180 °C. The desired test temperature

was obtained using a Sun Systems environmental

chamber utilizing liquid nitrogen as the coolant. A

temperature rate of change of 10 °C/min was used

throughout this work. At every test temperature, the

device under test was allowed to soak at that

temperature for a period of 30 minutes before any

measurements were made. After the last measurement

was taken at -180 °C, the cores were allowed to

stabilize to room temperature and then the

measurements were repeated to determine if the

thermal cycling had produced any effect on their

operational characteristics.

RESULTS AND DISCUSSIONS

The inductance of the four cores as a function of

frequency and temperature is shown in Figure 1. It can

be clearly seen that all cores, at any given temperature,

exhibit steady inductance value with increase in

frequency up to 100 kHz. At the highest test frequency

of 200 kHz, however, the ferrite core declines slightly

while the other three cores undergo slight increase. In

terms of temperature, the MPC and the High Flux cores

do not exhibit much variation in their inductance

between 25 °C and -190 °C. The ferrite and the Kool

Mu cores, on the other hand, suffer a reduction in their

inductance as temperature is decreased. These

temperature-induced changes are evident at every test

frequency.

TABLE I. PROPERTIES OF MAGNETIC CORES [3-6].

Core Outer Inner Height Temp P,r

Dia. Dia. (in.) (°C)

(in.) (in.)

MPC 1.06 0.58 0.44 -65 to 125 125

KMC 1.06 0.58 0.44 -65 to 125 125

HFC 1.06 0.58 0.44 -65 to 125 125

Ferrite 0.88 0.58 0.22 -30 to 70 900

With the exception of the ferrite core, all cores

display typical characteristics in their quality factor with

frequency as shown in Figure 2. The MPC, High Flux,

and the Kool Mu cores attain a peak value in their Qfactor between 80 and 180 in the vicinity of a frequency

of 10 kHz. This peak, however, shifts toward lower

frequency as test temperature is decreased. The ferrite

core, on the other hand, exhibits inconsistent behavior

in its Q-factor with frequency as shown in Figure 2.

While it initially increases with frequency up to 10 kHz,

the quality factor begins to decline, remains steady, or

increases afterwards. These trends in the variation of

the quality factor at frequencies above 10 kHz seem to

be dependent on the test temperature. At 25 and

-50 °C, for example, the Q-factor increases with

increase in frequency, while the opposite holds true at -

100 and -150 °C. At temperature of -190 °C, the ferrite

core maintains a relatively steady value in its quality

factor throughout the entire frequency range.

Figure 3 depicts the resistance of the cores as a

function of frequency at various temperatures. All cores

exhibit similar trend in this property with both test

parameters. It can be clearly seen that while the

resistance of any of these cores remain unaffected with

frequency up to 100 kHz, it dramatically increases as

the frequency is increased further. This is due to the

fact that the ac core and wiring losses portion of the

inductor resistance become more dominant at high

frequencies. The effect of temperature is more

noticeable in the flat region where the resistance, as

NASA/TM--2002-211836 2
expected, drops down in value with a decrease in

temperature.

The inductor response to a 100 kHz square wave

input excitation is shown in Figure 4 for all four cores at

25 °C and at -180 °C. While not much variation is

observed in the response behavior of the MPC, HFC,

and KMC cores at the two different test temperatures,

the ferrite core exhibits a significant increase in the

intensity level associated with a mild saturation-like

distortion in its inductor current at the extreme

temperature of -180 °C. The loss of the inductance of

this core, as was shown in Figure 1, is largely

responsible for the increase in this inductor current.

The dynamic hysteresis characteristics of the tested

cores are displayed in Figure 5 at room temperature as

well as -180 °C. These characteristics, which are

represented by the B-H loops, are indicative of the core

loss of the magnetic materials. These loops are

obtained by integrating the coil voltage and plotting it

against its excitation current. It can be seen that the

ferrite core, unlike the other three cores, exhibits a great

dependency in its loss characteristics on temperature.

A drastic increase in core loss, i.e., widening of the B-H

loop, occurs at the extreme temperature of -180 °C for

this type of magnetic material.

CONCLUSION

Four different types of magnetic cores were

investigated for potential use in cryogenic applications.

These cores consisted of a ferrite and three powderbased cores. The powder cores were Molypermalloy

(MPC), High Flux (HFC), and Kool Mu (KMC). The

performance of four inductors utilizing these cores has

been evaluated as a function of temperature from 20 °C

to-180 °C. Each inductor was evaluated in terms of its

inductance, quality (Q) factor, resistance, and dynamic

hysteresis characteristics (B-H loop) as a function of

temperature and frequency. The results obtained on the

inductance showed that both the MPC and the HFC

cores maintain a constant inductance value, whereas

the KMC and Ferrite hold steady values in inductance

with frequency but decrease as temperature is

decreased. All cores exhibit dependency, with varying

degrees, in their quality factor and resistance on test

frequency and temperature. Except for the ferrite, all

cores exhibited good stability in the investigated

properties with temperature as well as frequency.

Further and more comprehensive testing is, however,

required to access performance of these cores under

long-term exposure to low temperature.

REFERENCES

1. R.L. Patterson, A. Hammoud, J.E. Dickman, S.S. Gerber

and E. Overton, "Development of Electronics for Low

Temperature Space Missions," 4 th European Workshop

on Low Temperature Electronics, Noordwijk, The

Netherlands, June 21-23, 2000.

2. J.M. Niedra, "Comparative Wide Temperature Core Loss

Characteristics of Two Candidate Ferrites for the

NASA/TRW 1500 W PEBB Converter," NASA/CR_1999-

209302, August 1999.

3. J.M. Niedra, G.E. Schwarze, "Wide Temperature Core

Loss Characteristics of Magnetically Annealed

Amorphous Tapes for High Frequency Aerospace

Magnetics," NASA/TIvl_1999-209297, August 1999.

4. Kirschman, R.K., "Cold Electronics: An Overview,"

Cryogenics, Vol. 25, No. 3, 1985, pp. 115-122.

5. Ray, B., Gerber, S.S., Patterson, R.L. and Dickman, J.,

"Low Temperature Performance of a Boost Converter with

MPP and HTS Inductor," IEEEAPEC 96 Conference, Vol.

2, 1996, pp. 883-888.

6. "Molypermalloy Powder Cores," Magnetics, Inc., Brochure

MPC-I.0 5H.

7. "High Flux Powder Cores," Magnetics, Inc., Brochure

HFC-I.1 11H.

8. "Kool Mu Powder Cores," Magnetics, Inc., Brochure

KMC-2.3 3J.

9. "Ferrite Cores," Magnetics, Inc., Brochure FC-601-11H.

NASA/TM--2002-211836 3
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NASA/TM--2002-211836 5
lnductor Voltage

E (500mA/div) Inductor Current

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Figure 4. Response of inductors to a 100 kHz square wave excitation.

NASA/TM--2002-211836 6
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Figure 5. Effect of temperature on dynamic hysteresis characteristics.

NASA/TM--2002-211836 7
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September 2.002. Technical Memorandum

4. TITLE AND SUBTITLE 5. FUNDING NUMBERS

Performance of High-Frequency High-Flux Magnetic Cores

at Cryogenic Temperatures

6. AUTHOR(S)

Scott S. Gerber, Abroad tlammoud, Malik E. Elbuluk, and Richard L. Patterson

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration

John H. Glenn Research Center at Lewis Field

Cleveland, Ohio 44135 - 3191

WU--297-60-10-00

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REPORT NUMBER

E---13536

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSORING/MONITORING

AGENCY REPORT NUMBER

National Aeronautics and Space Administration NASA TM--2002-211836

Washington, DC 20546- 0001 IECEC-2002-20043

11. SUPPLEMENTARY NOTES

Prepared for the 37th Intersociety Energy Conversion Engineering Conference sponsored by the Institute of Electrical and Electronics En#neers, Electron Devices Society, Washington, DC, July 28---.August 2, 2002. Scott S. Gerber, ZIN Technologies, Inc., 3000

Aerospace Parkway, Brook Park, Ohio 44142; Ahmad Hammoud, QSS Group, Inc., Cleveland, Ohio 44135; Malik E. Elbuluk,

University of Akron, Electrical Engineering DepartmenL Akron, Ohio 44325---3904; Richard L. Patterson, NASA Glenn Research

Center. Responsible person, Richard L. Patterson, organization code 5480, 216---433---8166.

12a, DISTRIBUTION/AVAILABILITY STATEMENT

Unclassified - Unlimited

Subject Category: 33 Distribution: Nonstandard

Available electronicaJly at bttp://glt:.-s._rc.nasa.aov

"l-hispublication is ava_ilable from the NASA Center for AeroSpace In_brmadon, 301-621-0390.

12b. DISTRNBUTIONCODE

13. ABSTRACT (Maximum 200 words)

Three magnetic powder cores and one ferrite core, which are commonly used in inductor and trans_brmer design for

switch mode power supplies, were selected fbr investigation at cryogenic temperatures. The powder cores are

Molypermalloy Core (MPC), High Flux Core (HFC), and Kool Mu (7ore (KMC). The performance of four inductors

utilizing these cores has been evaluated as a function of temperature tYom 20 °C to -180 °C. All cores were wound with

the same wire type and gauge to obtain equal values of inductance at room temperature. Each inductor was evaluated in

terms of its inductance, quality (Q) factor, resistance, and dynamic hysmresis characteristics (B-H loop) as a function of

temperature and frequency. Both sinusoidal and square wave excitations were used in these investigations. Measured data

obtained on the inductance showed that both the MPC and the HFC cores maintain a constant inductance value, whereas

with the KMC and ferrite core hold a steady value in inductance with frequency but decrease as temperature is decreased.

All cores exhibited dependency, with varying degrees, in their quality factor and resistance on test frequency and temperalure. Except for the l)rrite, all cores exhibited good stability in the investigated properties with mmperature as well as

l>equency. Details of the experimental procedures and test results are presented and discussed in the paper.

14. SUBJECT TERMS

Inductors; Magnetics; Cryogenics; Power supplies

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