NASA Technical Memorandum 87314

Space Station 20-kHz Power Managementand Distribution System

( N A S A - T M - 8 7 3 1 4 ) SFACi S T A T I O N 2G-kHz POHEE N86-24747M A N A G E M E N T A N D C I S 1 R I E O T I C N S Y S T E M ( N A S A )11 p HC A G 2 / M * 101 CSCL 22B

UnclasG3/20 43029

Irving G. Hansen and Gale R. SundbergLewis Research CenterCleveland, Ohio

Prepared for the1986 Power Electronics Specialists Conferencesponsored by the Institute of Electrical and Electronics EngineersVancouver, Canada, June 23-27, 1986

NASA

https://ntrs.nasa.gov/search.jsp?R=19860015276 2018-03-18T05:20:23+00:00Z

SPACE STATION 20-kHz POWER MANAGEMENT AND DISTRIBUTION SYSTEM

Irving G. Hansen and Gale R. Sundberg

National Aeronautics and Space AdministrationLewis Research CenterCleveland, Ohio 44135

ABSTRACT

During the conceptual design phase a 20-kHzpower distribution system was selected as thereference for the space station. The system issingle-phase 400 VRMS, with a sinusoidal waveform. The initial user power level w i l l be 75 kWwith growth to 300 kW. The high-frequency systemselection was based upon considerations of effi-ciency, weight, safety, ease of control, interfacewith computers, and ease of paralleling forgrowth. Each of these aspects will be discussedas well as the associated trade-offs involved.An advanced development program has been instit-uted to accelerate the maturation of the high-frequency system. Some technical aspects of theadvanced development program w i l l be discussed.

BACKGROUND

The National Aeronautics and Space Adminis-tration is developing a manned space station tobe operable in the mid-nineties. The power systemfor the space station must initially supply apower level of 75 kW, and allow for eventualgrowth to 300 kW. Figure 1 is an outline of thespace station as currently conceived. The powermanagement and distribution (PMAD) system mustaccept energy from the photovoltaic solar arraysand the solar dynamic generators and deliver con-trolled power to numerous dispersed loads. Duringeclipse periods power is supplied by the energystorage systems.

One significant system driver appeared earlyin the study - cost. The cost of electrical powergenerated by the space station will be enormous:>500 dollars/kWh. This cost permeates all aspectsof the power system, and precludes many conven-tional approaches. Therefore, great care must beexercised when adapting existing relativelyinefficient PMAD technology.

During the conceptual design phase of thisprogram a unique power system was used as thereference for comparison. As presently developed,the system delivers 440 VRMS, 20 kHz, single-phase

ower, using a sinusoidal waveform. To data thishigh-frequency power system has demonstratedmarked technical advantages in efficiency, lowparts count, low system mass, safety, ease of

control, simple interfaces with load managementcomputers, and ease of paralleling the many mod-ules for growth.

AC SYSTEM CONCEPTS

As presently configured the system deliversregulated 440 V, 20 kHz, single-phase sinusoidalac power. The justification for the selection ofan electrical PMAD system with these characteris-tics is given below. A distribution voltage of440 VRMS represents the near term capabilities ofdirectly coupled high-frequency solid-state powerdevices. Even though developments of high voltageswitching components are ongoing, present effortsseem to be centered near the 500 V range. Thesesolid-state switching devices are to be operateddirectly off line in remote power controllers, andin voltage/frequency controlled synthesizers toallow variable speed ac motor operation. In thecase of motor operation, 440 RMS single-phasepower w i l l allow direct off line synthesis of 3phase, 115/208 V ac power with a voltage overrange of 10 percent. The 20 kHz operating fre-quency allows a good balance between power ratingper module, audio noise considerations, and com-ponent sizing. A line regulation of 2.5 percentat the user interface will, for a large class ofuser loads, not require any further regulation.Making additional voltage regulation unnecessarywill in turn avoid additional energy loss, andreduce the end to end system part count.

COMPONENT SIZING

In the case of magnetic components, however,size reduction is not a linear function ofincreasing frequency. As an example the relativemass of a 25 kW 20 kHz transformer relative to anequivalent 400 Hz transformer is only about 8/1notwithstanding the 50/1 reduction in operatingfrequency. The difference in scale results fromnecessary substitutions of magnetic materials, andreduction of flux levels at high frequency.Furthermore a 20 kHz transformer would have alllinear dimensions reduced by about a factor oftwo, and all heat conducting surfaces reduced bya factor of about four. In the case of multi-kilowatt transformers this reduction of surfacewil l necessitate improved heat transfertechniques (1,2,3).

SINGLE-PHASE DISTRIBUTION

From a user point of view the single-phasehigh-frequency system provides essentially con-stant power. However, and perhaps more impor-tantly, system status sensing, reconfiguration',and subsequent status verification is simplified.For a single-phase system the total numbers ofconductors, contactors, controls, and sensors arereduced by a factor of three as compared to athree-phase system.

MODULE SIZING

Generally in any electronic power converterthe maximum permissible operating voltage islimited by the semiconductor ratings. Once thesemiconductor voltage limit is reached, furtherincreases in power must then be met by increasingthe current. In the case of a resonant converteran increase in energy transfer at fixed maximumvoltage requires a reduction in the tank charac-teristic impedance. For example; typically a10 kW converter operating at 20 kHz would requirea capacitor of about 1 pF, and a resonantinductance of only about 10 yH.

As the inherent circuit parasitic inductanceof a 10 kW converter wi l l become noticeable whendealing with resonant inductances of a few micro-heneries, the result is a form of eventualfrequency-power product limit for any given cir-cuit layout. Based upon several hardware builds,experience would indicate that single-stage powerlevels of 20 to 30 kW, and high efficiencies (96to 97 percent) are very realistic goals at 20 kHz(4-6). It should be noted that a resonant con-verter with its sinusoidal current (minimumdi/dt) wi l l operate at a higher frequency-powerproduct than an equivalent nonsinusoidalconverter.

EMI/RFI AUDIO SUSCEPTIBILITY

The use of a low inductance transmission line(which is required due to other system con-straints) insures that little magnetic fieldextends "outside" the cable, since the impliedclose proximity of the conductors cancels theelectric field (similar to the case of a co-axcable). The EMI isolation taken together with thefact that the wave form is a single high-frequencysinusoid results in an inherently clean system.As an alternate example consider the oftenencountered square wave power waveform thatgenerates an extremely wide noise spectrum.

SYSTEM SAFETY

While no data seems to be available whichdeals directly with 20 kHz power, observations maybe drawn from tests performed at dc, 60 Hz, 10kHz, and under one cycle pulse conditions (10).These tests indicate that the "let-go-potential"at 20 kHz is significantly higher than at either60 Hz or 400 Hz. In addition systems whichoperate at lower frequency, or at dc would requireextensive modification in order to match theenergy limited characteristics inherent in the

resonant converter. As an example the maximumenergy in a 75 kW resonant power system is lessthan 2 J.

SOURCE CONVERSION

One central concept of the high-frequencydistribution system is the application of theparallel resonant (Mapham) converter as shown inFig. 2 (7). This particular resonant configura-tion provides the necessary low output impedance,and due to the sinusoidal nature of the resonantcurrent, experiences very little turn off lossesin the semiconductor switches. The resonant turnoff concept is shown in Fig. 3. In this illustra-tion the resonant frequency is higher than thetriggered system frequency. This condition allowsresonant turn off, and provides a dead timebetween half cycles for housekeeping and statusupdates. The resonant capacitor integrates thecurrent into a relatively low distortion (>5 per-cent THD) voltage source. Also to be noted onFig. 3 is the inherent symmetry of the bridgetopology. This symmetry is also shown in Fig. 4,which has been redrawn to illustrate the high-frequency port's parallel capacitance, and thelow-frequency port with series inductance. It isthis symmetry of the full bridge resonant con-verter that allows controlled bi-directional fourquadrant power flow. Functionally the converterperforms a modulation/demodulation function(Fig. 5). When modulating power from a low-frequency source, the low frequency (input)establishes the modulation envelope. In the fre-quency domain the resulting modulation would beclassified as double sideband suppressed carrier(DSSC).

Not shown for simplicity, is the presence ofa low pass input filter which decouples thesource. As in any switching converter, the inputfilter capacitor supplies the high-frequency cur-rent to the converter. A significant advantageis this switching converter, however, is therelatively low operating frequency in the filtercapacitor due to the sinusoidal current. Alsonotable is the fact that during modulation theinput current remains a continuous undistortedanalog of the voltage. This is very importantwhen dealing with a source unable to supplyreactive power.

SOURCE REGULATION

A phasor regulation scheme is shown inFigs. 8 and 9. In this configuration synchro-nized, but phase delayed, multiple converters havetheir outputs added as phasors. The amplitude ofthe single-phase resultant is controlled by timedelaying the common clock pulse. For three phaseac input power a similar configuration isolateseach low-frequency input phase with a dedicatedconverter. The resulting amplitude modulation(Fig. 5) will be cancelled when series summationis performed. In this configuration each phaseof the low frequency input undergoes continuousand linear loading. Finally a combination ofphasor regulation (bi-phase) and, modulationenvelope cancellation is shown in Fig. 9. Each

SPACE STATION 20-kHz POWER MANAGEMENT AND DISTRIBUTION SYSTEM

Irvin ndberg

ASSTRAt-?—

National Aeronautics and Space Administration

During the conceptual design phase a 20-kHzpower distribution system was selected as thereference for the space station. The system issingle-phase 400 VRMS, with a sinusoidal waveform. The initial user power level will be 75 kWwith growth to 300 kW. The high-frequency systemselection was based upon considerations of effi-ciency, weight, safety, ease of control, interfacewith computers, and ease of paralleling forgrowth. Each of these aspects w i l l be discussedas well as the associated trade-offs involved.An advanced development program has been instit-uted to accelerate the maturation of the high-frequency system. Some technical aspects of theadvanced development program wi l l be discussed.

BACKGROUND-X \

Thfe National Aeronautics and Space Adminis-tration is developing a manned space station tobe operable in the mid-nineties. The power systemfor the space station must initially supply apower level of 75 kW, and allow for eventualgrowth to 300 kW. Figure 1 is an outline of thespace station as currently conceived. The powermanagement and distribution (PMAD) system mustaccent energy from the photovoltaic solar arraysand rhe solar dynamic generators and deliver con-trol lei. power to numerous dispersed loads. Duringeel ipse pwiads power is supplied by the energystorage systems.

One significant system driver appeared eaj fyin the study - cost. The cost of electrical powergenerated by the space station will be enormous:>500 dollars/kWh. This cost permeates all aspectsof the power system, and precludes many conven-tional approaches. Therefore, great care must beexercised when adapting existing relativelyinefficient PMAD technolc

During the conceptual design phase of thisprogram a unique power system was used as thereference for comparison. As presently developed,the system delivers 440 VRMS, 20 kHz, single-phase

ower, using a sinusoidal waveform. To data thishigh-frequency power system has demonstratedmarked technical advantages in efficiency, lowparts count, low system mass, safety, ease of

rol, simple interfic&s--w4*h--load management•i:! ease ;>t oar a I lei i M'Icomputers,

ules for

AC SYSTEM CONCEPTS

the many mod-

resently configured the system deliversregulated 440 V, 20 kHz, single-phase sinusoidalac power'.-^tbe justification for the selection ofan electrical-PMAD system with these characteris-tics i-s given beTttw^^A distribution voltage of440 VRMS represents tn>-~uear term capabilities ofdirectly coupled high-frequency solid-state powerdevices. Even though developments of high voltageswitching components are ongoing.^ present effortsseem to be centered ne-ar the 500 V range. Thesesolid-state switctfuig devices are to be operateddirectly off line in rejnote power controllers, andin voltage/frequency controlled synthesizers toallow variable speed ac motor operation. In thecase of motor operation, 440 RMS single-phasepower wi l l allow direct off line synthesis of 3phase, 115/208 V ac power with a voltage overrange of 10 percent. The 20 kHz operating fre-quency allows a goodUaTance between power ratingper module, aacFio noi sevens i derations, and com-ponent sf7lng. A line regulation of 2.5 percentat the user interface will, for a large class ofuser loadsv not require any further regulation.Making additional voltage regjjjjt*orr~unnecessarywill in turrv avoid add_i£4-onaT~energy loss, andreduce the eRd t&-eff3system part count.

COMPONENT SIZING

In the case of magnetic componentSjhowever,size reduction is not a linear function ofincreasing frequency. As an example the relativemass of a'25 kW 20 kHz transformer relative to anequivalent 400 Hz transformer is only about 8/1notwithstanding the 50/1 reductton in operatingfrequency. The difference in scale results fromnecessary substitutipirsof magnetic materials, andreduction of f^y -•fnvf1s _nt h' h frftq'ipnr^Furthermore a .20 kHz transformer would have alllinear dimensions reduced by about a factor oftwo, and all heat conducting surfaces reduced bya factor of about four. In the case of multi-kilowatt transformers this reduction of surfacewill necessitate improved heat transfertechniques (1,2,3).

of the described configurations has been verifiedby actual full power system tests. The testresults together with schematics, waveforms,efficiency measurements, and system stabilitymeasurements are contained in Refs. 4, 6, and 8.

LOAD CONVERSION

When functioning as a demodulator the low-frequency output is synthesized by high frequencyhalf sine pulses. The resulting modulation (pulsepopulation) has its voltage controlled by thepulse density, and its frequency controlled by thepulse polarity pattern. This in turn allows theoutput frequency to be controlled independentlyof the output voltage. This particular capabilityhas very important implications for variable speedmotor operation as it allows independent controlof both the speed, and the torque. It alsosimplifies bi-directional control of ac power (8).

Finally on Fig. 4, the resonant circuit hasbeen redrawn as an equivalent low pass L.C. filterwith the output taken across the capacitor.Parallel operation of such converters whencommonly clocked is inherently stable. Operationunder such conditions becomes the equivalent ofsumming synchronized, in phase, current sources(inductors) into a common current sink (paralleledcapacitors). Under these conditions each con-verter w i l l supply current to the common capacitorload independently of the other converters.Normally no further current balance is needed.If the energy flow, however, from a particularsource is to be altered, as for example to balancea battery, the current supplied by any particularconverter may be controlled by adjusting its com-puter controlled voltage reference. Additionalconverters, additional distribution networks, oradditional loads may be accommodated withoutdisturbing this inherent load sharing.

The ease with which synchronized convertersmay be paralleled is illustrated in Fig. 5. In alaboratory demonstration in which two 10-kW con-verters were synchronized from a common clock.Step paralleling was accomplished by a mechanicalswitch. The oscillographs illustrate the char-acteristically stable load sharing.

END-TO-END CONSIDERATIONS

An important concept of the high-frequencypower system concerns the minimization of theconversion steps between the energy source and theusing load. Each conversion of energy adds com-plexity, weight, waveform distortion, andincreased losses. Any end-to-end power systemdesign must early address the problem of contain-ing all of the effects of a large number of powerconversions. Examination of a so-called dc/dcconverter (Fig. 7) wi l l quickly show that in factseveral conversions are employed; a dc/acconversion, a dc isolation transformer, and aac/dc conversion. Another equivalent converteris also shown in Fig. 7. In this configurationthe dc/ac converter is split in two. The dc/acportion now serves as an ac source driving thetransmission line. The ac/dc portion of the

process is now free to become specificallydedicated to the requirements of a particularload. In such a system the number of conversionsteps is required to provide isolated regulatedpower minimal, and the accommodations of a users'particular needs may be optimized. The variousinterface details and demands are easilycontrolled with a few standardized circuits (8).

POWER FEEDER DESIGN

At high audio frequencies a power cablebecomes sensitive to skin effects and theattendant increase in effective resistance. Theuse of standard wiring techniques (Litz) and lowinductance cable geometries limit distributionlosses to less than 2 percent and the total feederdrop both inductive and resistive to less than 3percent. These low values of feeder voltage dropslimit crosstalk effects, and enable a regulated"utility system" concept. The present developed25 kW cable has the following measured parameters:R = 0.83 po/m; L = 0.035 pH/m; C = 0.0014 pf/m.

STATION POWER SYSTEM

The space station power system is configuredas a split system. The low-frequency ports in thesource converters will accept energy as either dcin the case of a photovoltaic source, or low-frequency ac as in the case of a solar dynamicsource. All source converters have theirregulated outputs paralleled onto a common single-phase distribution bus. Those converters whichare configured to be bi-directional w i l l also passenergy from their high-frequency port to theirlow-frequency port. This latter capability maybe required for start up sequences, and duringfailure correction, or shuttle docking exercises.Each load converter accepts energy at its high-frequency port and delivers either ac, dc, or somerequired combination at its low-frequency port.With this configuration, a true utility conceptis formed in that all sources and all loads arein parallel sharing a common feeder line. As ina utility this distribution concept allows the acvoltage to be adjusted to local requirements bymeans of transformers. On the space station forexample, areas subject to depressurization couldhave local supply voltages reduced to preventelectrical breakdown. With a 20 kHz distributionfrequency the single-phase isolation transformersrequired will have a relatively small mass impact,typically in the range of 0.2 kg/kW. These trans-formers also provide another significant advantageto the system, since their inclusion in the systemwill restore the common mode isolation requiredfor single-point grounding, and allow the use ofground fault interrupters.

STATION DISTRIBUTION LENGTHS

Long distribution lengths are often cited asa potential problem, it should be assessed howeverin the actual application. A voltage fed powerdistribution system must have low source andtransmission impedances relative to the loadimpedance to achieve efficient energy transfer.In any system, the resultant impedance mismatch

will cause reflections of energy from the loadback to the source. For 20 kHz transmission lines300 ft long the reflection is only about 4°delayed from the incident wave and causes noproblems. The relative long wave length at 20 kHz(15 km) compared to the physical length of thespace station power feeder (100 m) precludes anysignificant effect due to reflected energy.

PRESENT STATUS

A 25 kW system has been assembled and tested.This system wi l l accept either ac or dc energy,transmit 25 kW of 20 kHz energy over a 100 m lineat 440 VRMS, and convert the energy into variableac or dc power. All output waveforms, voltagelevels, and energy flows are under the cycle-by-cycle control of a central computer (6).

For the space station power system applica-tion a 75 kW photovoltaic power system was evalu-ated on an end-to-end basis. The RCA price codes,and actual existing hardware characteristics wereutilized. The resulting cost estimates werecompared to these obtained using existing charac-teristics of conventional 400 Hz equipment. Thiscosting exercise indicated an acquisition costsavings of 100 million dollars, and a life cyclecost savings of 500 million dollars for the spacestation.

AIRCRAFT IMPLICATIONS

To illustrate the advantages of high-frequency distribution, the secondary power systemof a Boeing 767 was redesigned with the coopera-tion of the Boeing Aircraft Company. The aircraftsecondary power system was configured as an "allelectric" airplane using the 20 kHz system asdescribed. Computer "flights" were made on air-craft using both the original and the modifiedsecondary power system. The results of the studyshowed both a weight savings, and a fuel savingsof about 10 percent each (9).

FUTURE APPLICATIONS

The power technology division of NASA Lewisconsiders the high-frequency power system to be aprime candidate for a large number of potentialand ongoing power system studies. Among thesepotential applications are; Shuttle II, Trans-atmospheric Vehicles, SP 100 (both thermalelectric and Stirling engine), and Spacecraft2000. For each of these applications, theversatility of the high-frequency power systemrepresents an enabling technology allowing a large

number of mass-limited missions for new genera-tions of aero-spacecraft, many versitile powersystem configurations, and accommodation of allconceivable user load interface requirements.

CONCLUSIONS

The 20-kHz power system has been brought toa mature state of development, component, andcircuit design concepts are supported by a decadeof development aimed directly at aerospaceapplications. The high demonstrated efficiency,low mass, and versitility of this power managementconcept allows the assemblage of large complexsystems, retains full end-to-end control, and iseasily adaptable to a wide range of users needs.

REFERENCES

!• I. Hansen, Description of a 2.3 kW powertransformer for space applications," NASATM-79138, 1979.

2. I.G. Hansen and M. Chester, "Heat pipe coolingof power processing magnetics," AIAA Paper79-2082, Oct. 1979.

3. J.P. Welsh, "Design and development of multikilowatt power electronic transformer," NASACR-168082, 1983.

4. J. Mildice and L. Waapes, "Resonant ac Powersystem proof-of-concept," NASA CR-175069,1986.

5. R. Robson and D. Hancock, "10 kW seriesresonant converter design, transistorcharacterization, and base-drive optimiza-tion," NASA CR-165546, 1981.

6. J. Mildice, "Ac power system test bed," NASACR-175068, 1986.

7. N. Mapham, "An SCR inverter with good regula-tion and sine-wave output," IEEE Trans. Ind.Gen. Appl.. vol. IGA-3, pp. 176-187, 1967.

8. J. Mildice, "Bi-directional power convertercontrol electronics," NASA CR-175070, 1986.

9. A.C. Hoffman, I.G. Hansen, R.F. Beach, R.M.Plencner, R.P. Dengler, K.S. Jefferies, andR.J. Frye, "Advanced secondary power systemfor transport aircraft," NASA TP-2463, 1985.

10. Accident Prevention Manual for IndustrialOperations, 6th Edition, Chicago:Safety Council, 1969.

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Figure 1. - Basic space station layout. All dimensions are approximate.

1 L h SWITCHED FULL BRIDGERESONANT LOAD(LOW IMPEDANCE) OUTPUT

RESONANT CONVERTER

SWITCHCURRENT

LOADCURRENT

CURRENTS ARE HALF SINUSOIDSALL SWITCHING AT ZERO CURRENT

• NO FREQUENCY DEPENDENTSWITCH LOSS

• NO SECOND BREAKDOWN

Figure 2. - Parallel resonant conversion (MAPHAM).

ACTUAL CIRCUIT CONSIDERATIONS

pnnnn

• CURRENT TRIGGERFREQUENCY, 20 kHz

• CIRCUIT RESONANTFREQUENCY, 28 kHz

HOUSEKEEPINGDECISION TIME

CAPACITORINTEGRATES28 kHz CURRENTS

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OUTPUT (CAPACITOR)VOLTAGE, 20kHz

Figure 3. - Waveforms at resonant capacitor.

BASIC CONCEPTS

LOW FREQUENCYPORT

D HIGH FREQUENCYPORT

LOW PORT C <—™°DnT—> D HIGH PORT A

<. . r UK I t^iw?RESONANT BRIDGE WILL PASS ENERGY BETWEEN LOW FREQUENCYPORT AND HIGH FREQUENCY PORT BI-DIRECTIONALLY

Figure 4. -Circuit symmetry.

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Figure 5. - Resonant circuit transfer waveforms.

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Ip4, TRANSIENT RESPONSE Ip6, TRANSIENT RESPONSE

Figure 6. - Step paralleled converters. (General Dynamics)

TO CHANGE DC VOLTAGE LEVELS (DC/DC CONVERTER)

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DC OUT

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AC/ACNO CONVERTER

Figure 7. - "Split" system concept.

A,B ,C

PHASOR SUMMATION

A,B,-C

PHASORREGULATION

A + B + (-C) = SINGLE PHASE

VARIATION IN 0(TIME) CAUSESVARIATION IN /AMPLITUDE / 0

Figure 8. - Basic concepts.

LOWFRE-QUENCY

MULTI-PHASE

ANY TWO OR MORE SYNCHRONOUSPHASORS MAY BE TIME DELAYEDTO PROVIDE REGULATION

• SIX UNITS MAY BE CONNECTEDTO PROVIDE PHASE BY PHASE

HIGHFREQUENCY

SINGLEPHASE

REGULATION

INPUT CONVERTERS (A. B. C) REMAIN BALANCED (120° PHASE RELATION)

OUTPUT CONVERTERS ARE PHASED FOR REGULATION

Figure 9. - Phase by phase regulation.

MATERIALS

POWER GENERATION

• SOLAR• NUCLEAR• FUEL CELLS• DYNAMIC MACHINES

HIGH TEMPERATUREHIGH THERMALCONDUCTIVITYINTERCALATED GRAPHITEGRAPHITE/cu; SiC

POWER MANAGEMENTAND DISTRIBUTION

• HIGH FREQUENCY• ALL SOURCE COMPATIBLE• SMART SYSTEMS• HIGH TEMPERATURE• RADIATION HARD

USER LOADS

• FLIGHT CONTROL• ENVRONMENTAL• AVIONICS• PULSE NETWORKS

Figure 10. - LeRC program for mass limited missions.

1. Report No.

NASA TM-87314

2. Government Accession No. 3. Recipient's Catalog No.

4. Title and Subtitle 5. Report Date

Space Station 20-kHz Power Management andDistribution System 6. Performing Organization Code

506-41-4A

7. Author(s)

Irving G. Hansen and Gale R. Sundberg

8. Performing Organization Report No.

E-3045

10. Work Unit No.

9. Performing Organization Name and Address

National Aeronautics and Space AdministrationLewis Research CenterCleveland, Ohio 44135

11. Contract or Grant No.

12. Sponsoring Agency Name and Address

National Aeronautics and Space AdministrationWashington, D.C. 20546

13. Type of Report and Period Covered

Technical Memorandum

14. Sponsoring Agency Code

15. Supplementary Notes

Prepared for the 1986 Power Electronics Specialists Conference, sponsored by theInstitute of Electrical and Electronics Engineers, Vancouver, Canada, June 23-27,1986.

16. Abstract

During the conceptual design phase a 20-kHz power distribution system wasselected as the reference for the space station. The system 1s single-phase 400VRMS, with a sinusoidal wave form. The Initial user power level will be 75 kWwith growth to 300 kW. The high-frequency system selection was based uponconsiderations of efficiency, weight, safety, ease of control, Interface withcomputers, and ease of paralleling for growth. Each of these aspects will bediscussed as well as the associated trade-offs Involved. An advanceddevelopment program has been Instituted to accelerate the maturation of thehigh-frequency system. Some technical aspects of the advanced developmentprogram will be discussed.

17. Key Words (Suggested by Author(s))

Power systemResonant conversion

18. Distribution Statement

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Unclassified20. Security Classif. (of this page)

Unclassified21. No. of pages 22. Price'

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