NASA / TMm2001-2109 73 IECEC2001-AT-16

i Low Temperature Performance of High Power

Density DC/DC Converter Modules

Malik E. Elbuluk

University of Akron, Akron, Ohio

Ahmad Hammoud

QSS Group, Inc., Brookpark, Ohio

Scott Gerber

ZIN Technologies, Inc., Brookpark, Ohio

Richard L. Patterson and Eric Overton

Glenn Research Center, Cleveland, Ohio

July 2001
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t
NASA / TM--2001-210973 IECEC2001-AT-16

Low Temperature Performance of High Power

Density DC/DC Converter Modules

Malik E. Elbuluk

University of Akron, Akron, Ohio

Ahmad Hammoud

QSS Group, Inc., Brookpark, Ohio

Scott Gerber

ZIN Technologies, Inc., Brookpark, Ohio

Richard L. Patterson and Eric Overton

Glenn Research Center, Cleveland, Ohio

Prepared for the

36th Intersociety Energy Conversion Engineering Conference

sponsored by the American Society of Mechanical Engineers

Savannah, Georgia, July 29-August 2, 2001

National Aeronautics and

Space Administration

Glenn Research Center

July 2001
Acknowledgments

This work is supported by Glenn Research Center, Contract NAS3-00145, GESS Task 0020.

This report contains preliminary

findings, subject to revision as

analysis proceeds.

NASA Center for Aerospace Information

7121 Standard Drive

Hanover, MD 21076

Available from 2 ;2

National Technical Information Service

5285 Port Royal Road

Springfield, VA 22100

z

Available electronically at ht_://gltrs.g-rc.nasa.gov/GLTRS
Low Temperature Performance of High Power Density DC/DC Converter Modules

Malik E. Elbuluk

University of Akron

Akron, Ohio 44325

Scott Gerber

ZIN Technologies

Brook Park, Ohio 44142

Ahmad Hammoud

QSS Group, Inc.

Brook Park, Ohio 44142

Richard L. Patterson and Eric Overton

National Aeronautics and Space Administration

Glenn Research Center

Cleveland, Ohio 44135

ABSTRACT

In this paper, two second-generation high power

density DC/DC converter modules have been evaluated

at low operating temperatures. The power rating of one

converter (Module l) was specified at 150 W with an

input voltage range of 36-75 V and output voltage of

12 V. The other converter (Module 2) was specified at

100 W with the same input voltage range and an output

voltage of 3.3 V. The converter modules were evaluated

in temls of their performance as a function of operating

temperature in the range of 25 °C to -140 °C. The

experimental procedures along with the experimental

data obtained are presented and discussed in this paper.

INTRODUCTION

Presently, spacecraft operating in the cold

environment of deep space carry on-board a large

number of radioisotope heating units to maintain

an operating temperature for the electronics of

approximately 25 °C. To reduce system

development and launch costs, improve reliability

and lifetime, and increase energy densities,

electronic components and systems capable of

low-temperature operation will be required for

many future space missions. These improvements

will require proper system and circuit design,

component selection and the development of

components better suited for operation at

extremely low temperatures. At the NASA Glenn

Research Center, the Low Temperature

Electronics Program focuses on research and

development of "low temperature" electrical

components and systems suitable for deep space

mission.

Past and present activities of the Low

Temperature Electronics Program have included

characterization and evaluation of components

such as semiconductor switching devices,

integrated circuits, resistors, magnetic

In addition to deep space applications, low

temperature electronics have potential uses in

terrestrial applications that include magnetic

levitation transportation systems, medical

diagnostics, cryogenic instrumentation, and superconducting magnetic energy storage systems.

ADVANCES IN DC/DC CONVERTERS

Recently, there has been a great progress in the

design of DC/DC converters with high power

density. Converters that operate at power densities

of 50% or more greater than the available standard

conventional converter designs have been

developed. This increase in power density is

achieved using new designs, advanced devices and

components, and packaging techniques. Today's

leading edge DC/DC converter modules use

synchronous rectifiers with multi-layer thick film

hybrid packaging. This provides more usable

output power without the use of a heat sink than

do the conventional DC/DC converters that use

Schottky diode with a heat sink and thick-film

single-layer packaging. The first generation of

DC/DC converter modules has a typical power

rating of 10-15 W. The second-generation of

DC/DC converters has a power rating of about

100-150 W with packaging and thermal

management that provide high power density with

small temperature gradients. Extensive use of

silicon integration resulted in about one third the

part count of a first generation converter.

LOW TEMPERATURE POWER CONVERTERS

Most aerospace power management systems

are DC-based, and they require DC/DC power

converters that operate with different inputs and

outputs at various power levels. However, most of

components, and capacitors [1-3]. In addition, low the existing DC/DC converter systems are

temperature device development activities have specified to operate at low temperatures between

been conducted primarily in the area of -40 °C and -55 °C.

semiconductor switching devices through Phase I

Small Business Innovation Research Grants. The

program has also been extensively involved in

investigating DC/DC converters for low

temperature space missions.

The Low Temperature Electronics Program has

gone through a number of stages in building,

testing and evaluating DC/DC converters for

potential low temperature missions. During the

first stage, a number of DC/DC converters were

NASA/TM--2001-210973 1
designed or modified to operate from room

temperature to -196 °C using commercially

available discrete components such as CMOS-type

devices and MOSFET switches. These converters

had output power in the range of 5 W to 1 kW and

switching frequencies of 50kHz to 200kHz.

Pulse-width modulation technique was

implemented in most of these systems with open

as well as closed-loop control. The topologies

included buck, boost, multi-resonant, push-pull

and full-bridge configuration [5-9].

The second stage followed the recent

advancement in design and manufacturing of low

power DC/DC convener modules. Several

commercial-off-the-shelf (COTS) DC/DC

conveners have been characterized in terms of

their performance as a function of temperature in

the range of 20 °C to - 180 °C. These converters

ranged in electrical power from 8 W to 13 W,

input voltage from 9 V to 75 V and an output

voltage of 3.3 V. Test results showed that they

operated as expected within the manufacturer's

specified temperature range, but at low

temperature results varied. For some conveners

performance degraded rapidly, with others,

reasonably good performance was seen down to

temperatures between -80°C and -100°C. For

temperatures below -100°C, performance was

either out of range, erratic, or non-existent for

most of the conveners [ 10-12].

The third evaluation stage is presented in this

paper. Two of the second-generation high power

density DC,rDC converter modules have been

evaluated at low temperature. The converters had

power rating of 100 W and 150 W, input voltage

range of 36V to 75 V and output voltages of 3.3 V

to 12 V, respectively. The converters were

evaluated in terms of their performance as a

function of temperature in the range of 25 °C to

-140 °C. The experimental procedure along with

the experimental data obtained are presented and

discussed. -

EXPERIMENTAL PROCEDURE

The steady-state performances of the DC/DC

converters were characterized as a function of

temperature from 25 °C to -i40 °C in terms of

output voltage and efficiency. In addition, output

voltage ripple, input current ripple and output

current ripple waveforms were obtained. At a

given temperature, these properties were obtained

at various input voltages and at different load

levels: from light-load to full-load conditions. The

tests were performed as a function of temperature

using a environmental chamber cooled by liquid

nitrogen. A temperature rate of change of

10 °C/min was used throughout this work. At

ever), test temperature, the module 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 the lowest

temperature, the conveners were allowed to

stabilize to room temperature and then the

measurements were repeated at room temperature

to determine the effect of low temperature

exposure on the conveners.

RESULTS AND DISCUSSIONS

Figure 1 shows the output voltage and

efficiency of Module 1, normalized to their

respective room temperature values, at different

load currents and as a function of temperature.

The output voltage and efficiency were

normalized to compensate for the voltage drop and

power loss resulting from long wires connecting

the module, inside the chamber, to the equipment

and measuring instruments outside the chamber.

At a given load current, the normalized output

voltage (Figure la) maintains a steady value from

room temperature down to -120 °C. The effect of

temperature on the efficiency of Module 1 (Figure

l b) under different load conditions showed that, in

general, the normalized efficiency drops as the

temperature is lowered with temperature having

the least effect on the heavy load condition. Figure

1 represents data taken at a nominal input voltage

of 49V. Additional, sets of data were taken with

input voltages of 36V, 62 V and 75 V. The data

obtained at these input voltages is very similar to

that Shown in Figure 1_ A7 ..... ......... ....

Figure 2 shows the output Voltage and

efficiency of Module 2, measured at different

loads, input voltage and as a function of

temperature. Similar to Module 1, the output

voltage and efficiency were normalized to their

values at room temperature. In Figure 2a, the

normalized output voltage maintains a steady

value from room temperature down to -20 °C. For

temperatures below -20 °C the normalized output

voltage increased with heavy loads values being

higher than light load values. This effect was

observed only at the lower input voltage of 36 V,

In Figure 2c, for an input voltage of 48 V, the

normalized output voltage remained constant,

similar to that of Module 1.

The effect of temperature on the efficiency of

Module 2 under different input voltage and load

conditions is shown in Figures 2b and 2d.

Opposite to that of Module 1, the normalized

efficiency increases as the temperature is lowered.

The effect of temperature is greater with the heavy

load condition than that of the light load. This

effect is greater at the lower input voltage (Figure

2b) than at the higher input voltage (Figure 2d).

Additional, sets of data were taken with input

voltages of 60V and 72V. The data obtained at

NASA/TM--2001-210973 2
these input voltages is very similar to that

obtained at 48V input (Figures 2c and 2d).

Figures 3 and 4 show the waveforms of the

output voltage ripple, the output current ripple and

the input current ripple at room temperature

(25 °C) and at a low temperature (-I00 °C) for

Module 1, respectively. The corresponding ripple

in output voltage, input and output current

increases with decreasing temperature. Also,

instabilities in the input current are observed with

the heavy load conditions being more prominent.

Figures 5 and 6 show the waveforms of the

output voltage ripple and the input current ripple

at room temperature (25 °C) and at the low

temperature (-80 °C) for Module 2, for light load

and heavy load conditions. The output voltage

ripple changes slightly between room temperature

and the low temperature, with very high spikes

occurring during heavy loading conditions.

Opposite to Module 1, the input current ripple at

room temperature is higher than that of the low

temperature (i.e. the tipple decreases with

decreasing temperature). The output current was

not recorded because the data under heavy loading

could not be taken due to the need of high current

probe. Similar to Module 1, instabilities in the

input current are observed with the heavy load

conditions being more prominent.

CONCLUSIONS

Two commercially available DC/DC

converters were characterized in terms of their

performance as a function of temperature in the

range of 25 °C to -140 °C. The converters were

evaluated with respect to their output voltage

regulation, efficiency, output voltage ripple, input

current tipple and output current ripple in

response to environmental temperature. The two

converters generally displayed somehow similar

behavior with change in temperature. The

intensity of any occurring changes, however,

varied with the converter type and the test

temperature. This work represents only a

preliminary investigation into the steady-state

effects of low temperature on these two secondgeneration high power density DC/DC converter

modules. To fully characterize their performance

at low temperature, further testing and analysis is

required.

REFERENCES

1. Ray, B., Gerber, S.S., Patterson, R.L. and Myers, I.T.,

"Power Control Electronics for Cryogenic

Instrumentation," Advances in b_st. and Control, Vol.

50, Part I, Int. Soc. for Measurement and Control,

1995, pp.131-139.

2. Patterson, R.L., Dickman, J.E., Hammoud, A. and

Gerber S.S., "Low Temperature Power Electronics

Program," NASA EEE Links, Electronic Packaging

and Space Parts News, Vol. 4, No. 1,January 1998.

3. Patterson, R.L., Hammoud, A. and Gerber, S.S.,

"Evaluation of Capacitors at Cryogenic Temperatures

for Space Applications," IEEE International

Conference on Electrical Insulation, Washington DC,

June 7-10, 1998.

4. Ray, B., Gerber, S.S., Patterson, R.L. and Myers, I.T.,

"77K Operation of a Multi-Resonant Power

Converter," IEEE PESC Record, Vol. 1, 1995, pp.55-

60.

5. Ray, B., Gerber, S.S., Patterson, R.L. and Myers, I.T.,

"Liquid Nitrogen Temperature Operation of a

Switching Power Converter," Symp. o11Low Temp.

Electronics & High Temperature Supercond, wtivity,

The Electrochemical Society, Vol. 9, 1995, pp.345-

352.

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

"Low Temperature Performance of a Boost Converter

with MPP and HTS Inductor," IEEE APEC 96

Conference, Vol. 2, 1996, pp.883-888.

7. Gerber, S.S., Patterson, R.L., Ray, B. and Stell, C.,

"Performance of a Spacecraft DC-DC Converter

Breadboard Modified for Low Temperature Operation,"

IECEC 96, Vol.1, 1996, pp. 592-598.

8. Ray, B., Gerber, S.S. and Patterson, R.L., "Low

Temperature Performance of a Full-Bridge DC-DC

Converter," IECEC '96, Vol. l, 1996, pp. 553-559.

9. Gerber, S.S. Miller, T., Patterson, R.L. and Hammoud,

A., "Performance of a Closed-Loop Controlled High

Voltage DC/DC Converter at Cryogenic Temperature,"

IECEC '98, Vol. 1, 1998.

10. M. Elbuluk, S. Gerber, A. Hammoud and R. Patterson,

"Evaluation of Low Power DC/DC Converter Modules at

Low Temperatures," Proceedings of IEEE PESC'00,

Galway, Ireland.

11. Elbuluk, S. Gerber, A. Hammoud and R. Patterson,

"Efficiency and Regulation of Low Power DC/DC

Converter Modules at Cryogenic Temperatures,"

Proceedings of IEEE IECEC'00, Las Vegas.

12. M. Etbuluk, S. Gerber, A. Hammoud and R. Patterson,

"Characterization of Low Power DC/DC Converter

Modules at Low Temperatures," Proceedings of IEEE

IAS'00, Rome, Italy.

NASA/TM--2001-210973 3
2.0 --

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X 10.0 A

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-120 -100 -80 -00 -40 -20 0 20 40

Temperature (°C)

(a) Vin = 49V

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(b) Vin = 49V

Figure I. Normalized output voltage and efficiency versus temperature at various load currents

for Module#l.

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(a) Vin = 36V

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Temperature (°C)

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(d) Vin = 48V

Figure 2. Normalized output voltage and efficiency versus temperature at various load currents

for Module #2.

NASA/TM--2001-210973 4
i (200 mV/div) Output Voltage Ripple

I I I I I I I 1 I I

(20 mA/div) Output Current Ripple

- 200 mV/div) Output Voltage Ripple

m

! I I I I I I I I 1

(20A,_ mA/div) Output Current Ripple ; _,AA_ A,____,_f,

"(200 mA/div) Input Current Ripple

/%_ f_A,A/_ A,A q,A,,;'\P_n,f_A,

Time (10 us/div)

(a) Temperature = 25°C

I (200 mA/div) Input Current Ripple

_v_1'_ __"___'_1'_"

Time (10 us/div)

(b) Temperature = -100°C

Figure 3. Module #1 operation with 49V input and under light load condition (I.0A).

(50 mV/div) Output Voltage Ripple

I t I I I I I I I I

(20 mA/div) Output Current Ripple

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(50 mV/div) Output Voltage Ripple

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- (20 rnAldiv) Output Current Ripple

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(b) Temperature = -100°C

Figure 4. Module #1 operation with 49V input and under heavy load condition (12.5A).

NASA/T/vl--2001-210973 5
(200 mV/div)

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I I i .... I I t t a | I

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(a) Temperature = -80°C

Figure 5. Module #2 operation with 48V input and under light load (5.0A).

(200 mV div) Output Voltage Ripple

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Figure 6. Module #2 operation with 48V input and under heavy load (30A).

NASA/TM--2001-210973 6

REPORT DOCUMENTATION PAGE I FormApproved

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1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE

July 2001

4. TITLE AND SUBTITLE

Low Temperature Performance of High Power Density

DC/DC Converter Modules

6. AUTHOR(S)

Malik E. Elbuluk, Ahmad Hammoud, Scott Gerber,

Richard L. Patterson, and Eric Overton

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

9. SPONSORINGIMONITORING AGENCY NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration

Washington, DC 20546-0001

3. REPORT TYPE AND Technical DATES Memorandum COVERED

5. FUNDING NUMBERS

WU-755-A4-12_30

8. PERFORMING ORGANIZATION

REPORT NUMBER

E-12827

10. SPONSORING/MONITORING

AGENCY REPORT NUMBER

NASA TM--2001-210973

IECEC200 I-AT- 16

11. SUPPLEMENTARY NOTES

Prepared for the 36th Intersociety Energy Conversion Engineering Conference sponsored by the American Society of Mechanical Engineers, Savannah,

Georgia, July 29-August 2, 2001. Malik E. Etbuluk, University of Akron, Electrical Engineering Department, Akron, Ohio 44325-3904 (work funded by

NASA Contract NAS3_0145); Ahmad Hanunoud. QSS Group, Inc., 2000 Aerospace Parkway, Brookpark, Ohio 44142; Scott Gerber, ZIN Technologies, Inc., 3000 Aerospace Parkway. Brookpark, Ohio 44142; and Richard L. Patterson and Eric Overton NASA Glenn Research Center. Responsible

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

12a. DISTRIBUTION/AVAILABILITY STATEMENT

Unclassified - Unlinfited

Subject Category: 33 Distribution: Nonstandard

Available electronically at htlp://gltrs._c.nasa,_ov/GLTRS

This publication is available from the NASA Center for AeroSpace Information, 301-621-0390.

12b. DISTRIBUTION CODE

13. ABSTRACT (Maximum 200 words)

In this paper, two second-generation high power density DC/DC converter modules have been evaluated at low operating

temperatures. The power rating of one converter (Module 1) was specified at 150 W with an input voltage range of 36 to

75 V and output voltage of 12 V. The other converter (Module 2) was specified at 100 W with the same input voltage

range and an output voltage of 3.3 V. The converter modules were evaluated in terms of their performance as a function

of operating temperature in the range of 25 to -140 °C. The experimental procedures along with the experimental data

obtained are presented and discussed in this paper.

14. SUBJECT TERMS

Cryogenics; DC/DC converters; Electronics; Low temperature

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