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A01-16923
AIAA2001-1147Past, Present & Future ofAircraft Electrical Power SystemsJ. WeimerAir Force Research LaboratoryWright Patterson AFB, OH
39th Aerospace Sciences Meeting & Exhibit8-11 January 2001
Reno, Nevada
For permission to copy or to republish, contact the American Institute of Aeronautics and Astronautics,1801 Alexander Bell Drive, Suite 500, Rcston, VA, 20191-4344.
(c)2001 American Institute of Aeronautics & Astronautics or Published with Permission of Author(s) and/or Author(s)' Sponsoring Organization.
PAST, PRESENT & FUTUREOF
AIRCRAFT ELECTRICAL POWER SYSTEMS
Joseph A. WeimerPower Division
Propulsion DirectorateAir Force Research Laboratory
Wright Patterson AFB, Ohio 45433-7251
ABSTRACT
The first aircraft electrical power systemgenerated and distributed hundreds of watts ofelectricity to a very small number of loads.Today's aircraft electrical system has grown by 3orders of magnitude in the amount of powergenerated and distributed (1.2 megawatts on theUSAF E-4B Command Post). During the 1960s,1970s and 1980s aircraft electrical powerrequirements and complexity grew. The Air Forceand Navy instituted research and developmentprograms to make electrical power systems morereliable, fault tolerant and autonomous. The AirForce focused on 400-hertz systems, developingvariable speed constant frequency (VSCF)generator technology and autonomous/faulttolerant power distribution. The Navy developed270 VDC power generation and distributionsystem technologies. These technologies,though different in approach, made their way on toseveral military aircraft. In the 1990s the AirForce and Navy led the nation in a new initiative inaircraft electrical power, taking advantage of thetechnologies developed in the prior threedecades. The Air Force/Navy and its universityand industrial partners have pursued an extensiveresearch and development on electrical powersystem and component technologies to enable a"more electric" aircraft power system. Thisinitiative has been commonly called the MoreElectric Aircraft (MEA). The MEA initiative hasrecently completed the first generation milestonesthrough a Joint Strike Fighter technologymaturation effort. The Air Force continues topursue MEA technologies, which will enableelectrical starter/generators to be integrated intothe turbine engine. The MEA initiative endorsesthe notion of driving aircraft subsystemselectrically, which have been powered byhydraulic, mechanical and pneumatic means. Thepurpose of this paper is to briefly review the
history of conventional aircraft power systemsprior to the MEA initiative, review the MEAinitiative by discussing recently completedprograms and on-going technology programs, anda brief look at what's beyond.
INTRODUCTION
The past, present and future of aircraft electricalpower systems cannot be captured in a singletechnical paper. Therefore, it is the intent of thispaper to review significant historical events thathave shaped today's aircraft electrical powersystems. The paper will also briefly project thefuture of military aircraft electrical power systems.This paper places emphasis on military aircraftelectrical power systems, since it has paced thedevelopment for all aircraft power systems.
PAST
Electrical power has played a significant role fromthe first powered flight to the present day. TheWright brother's first flight was dependent uponelectrical power to supply energy to the engine'signition system. In 1936, the first DC-3 aircrafthad two 50 ampere 14.25 VDC generators whocombined power was 1425 watts, comparable totoday's automotive electrical system. As powerdemands increased, the industry developedhigher voltage 28 VDC electrical systems in orderto minimize the weight impact. The first militaryaircraft to use AC power was the B-36 in 1946.The engineers selected the 115/200 VAC, 3-phase, 400-hertz electrical system because itoffered the lightest weight solution for increasedpower demand. This system would become thestandard for the industry and is still used today inmodern military aircraft. The clear advantage ofthis 400-hertz AC system over the 28 VDC systemwas lower weight, which was a critical issue, asaircraft became larger and hungrier for electrical
This paper is declared a work of the U.S. Government andis not subject to coovrisht nrotection in the United States. 1
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power. However, in the 1980s, high voltage directcurrent (HVDC) power or 270 VDC power wouldprove to be the power of choice for reducingaircraft mass. 270 VDC power was selected over400-hertz for the F-22 because of reduced weight.Also during the 1980s and 1990s, other forms ofpower were investigated for aircraft utilization.This included high frequency AC power or 20-kilohertz power, variable frequency variablevoltage (VFVV) and variable frequency constantvoltage (VFCV) systems. NASA Lewis ResearchCenter led the research and development of 20-kilohertz power. The 20 kilohertz power systemnever transitioned to any production aircraft. TheVFVV and the VFCV systems are the simplestforms of producing electrical power and require nopower electronics in the output stage. The VFVVsystem can be implemented with a permanentmagnet generator and was initially proposed forthe all-electric aircraft in the late 1970s. TheVFCV system was implemented with asynchronous generator and the output isregulated to a constant voltage over the entirespeed range. This type of system is used todayon a select few aircraft.
A synchronous generator coupled to constantspeed drive (CSD) transmission has been thepreferred method to produce 400-hertz power onmilitary and commercial aircraft. The CSD istypically located on an aircraft mounted accessorydrive (AMAD) or gearbox. This gearbox has avariable speed, due to changes in the enginespeed (typically a 2 to 1 speed ratio). The CSDchanges the variable speed to a constant"synchronous" speed (i.e. 6000 RPM) to drive thegenerator. Most electrical systems, in use today,employ a CSD/synchronous generator. Figure 1shows schematically the key elements of thesystem.
In the 1970s, Variable Speed Constant Frequency(VSCF) generator systems were developed tooffer an alternative approach to generate 400-hertz power. The main advantage of the VSCFsystem over the CSD system was the potentialimprovements in reliability. This technology wasenabled by advancements in power electronicdevices. Two VSCF converter topologies weredeveloped and produced primarily for militaryfighter aircraft.
GEARDIFFERENTIAL
VARIABLESPEED —INPUT
VARIABLE FIXEDDISPLACEMENT DISPLACEMENT
HZHD-%. .jHYDRAULIC UNITS
Figure 1. Schematic Diagram of a ConstantSpeed Drive
The first VSCF converter topology was thecycloconverter, which used silicon controlledrectifier (SCR) thyristors for switching. Thecycloconverter changed higher frequency ACpower (typically 1200 to 2400-hertz) to lowerfrequency 400-hertz power. The cycloconverter isa matrix converter, which required multiple ACswitches that interconnected each input phasefrom the generator to each of the 3 output phasesto produce 115/200 volt, 400-hertz power. Figure2 illustrates the schematic of the VSCFcycloconverter system. Figure 3 shows theresulting output 400-hertz waveform. The numberof SCRs to implement the cycloconverter washigh (36 to 54 devices depending on the numberof input phases) thus impacting the overallreliability of the system. However, thecycloconverter produced near sinusoidal powerwhich reduced output filter size and weight andwas capable of bi-directional power flow, whichwould be advantages for starter/generatorapplications.
Figure 2. VSCF Cycloconverter Schematic
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The other competing VSCF topology was the DClink VSCF system. The DC link VSCF systemused a 2-stage power conversion approach toproduce 400-hertz power. A synchronousgenerator would produce variable frequencypower and the output would be rectified to DC.The DC power would be filtered to establish a lowimpedance voltage source or DC link, whichwould be inverted by a 3-phase bridge to produce400-hertz power. Figure 4 shows the blockdiagram of the DC-link VSCF generator system.The advantage of this system is that a widevariety of modulation techniques could be used toproduce 400-hertz sinusoidal power. Thedisadvantage of the system was the powerhandling limitation of the inverter's powersemiconductors and the inability of the system tobe used as a starter/generator.
Figure 4. Block Diagram of the DC-link VSCFGenerator System
In 1972, VSCF power generation equipment wasneeded to solve an A-4 electrical system problem.The excellent results obtained in the A-4 program,coupled with the ever-increasing high life-cyclecosts of constant speed drives, drove the AirForce to invest in VSCF technology. The Air Forceinvested in the development of higher temperature
and more powerful power electronic devices andsponsored key demonstrations of the technology.During this same VSCF development period, theAir Force Material Laboratory was leading anational effort in the development of rare earthpermanent magnets. In 1974, the Air ForceMaterial Laboratory and the Air Force AeroPropulsion Laboratory jointly awarded a contractto demonstrate a 150 KVA samarium cobalt VSCFstarter/generator system. The program wascompleted in 1978. Later that year, the Air Forceinitiated an advanced development program toflight test a 60 KVA starter/generator for the A-10aircraft. This program demonstrated that VSCFcould electrically start a turbine engine (GeneralElectric TF34 engine) and produce primaryelectrical power for the aircraft. The combinedfunction of starting the turbine engine andproviding primary electrical power into one systemgreatly reduced the weight and improved theoverall aircraft reliability.
The Air Force continued to look at other options tomake VSCF power generating systems. Thisincluded the development of the cascaded doublyfed VSCF generating system which showedpromise to greatly improve power density and theresonant link VSCF generating systems whichenable significant improvement in efficiency andpower density. Both systems were developed anddemonstrated in the laboratory, but never broughtto flight qualified hardware. Today, VSCFelectrical generating systems flies on severalmilitary aircraft including the F-18, F-16, AV8-B,TR-1, and F-117 to name a few.
In the 1960s, 1970s, and 1980s, the Air Forceinvested in research and development ofautonomous power management and distributionsystems. Electrical power systems were nowflight critical due to the implementation of "fly-by-wire". Now electrical systems were "flight critical"and the approach at the time was to use a "bruteforce" method to provide back up, fault reliabletolerant electrical power. Unfortunately, thismethod was heavy and unreliable due to theincrease number of electrical system components.Key to the development of an autonomous powermanagement and distribution system was thesolid state power controller (SSPCs) whichreplaced electromechanical circuit breakers andelectro-mechanical relays. A dedicated serial databus was developed to interface the SSPCs with a
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system controller. A considerable amount ofweight could be saved with the serial data bus byreplacing hardwire analog controls with a dualredundant serial data bus. The system controllercould provide a load management function byautonomously powering loads during differentphases of flight. It could also autonomously shedloads in the event the demand exceeded the totalpower generation capacity. The B1-B bomberwas the first aircraft to use data bus control on theelectrical system. However, the B1-B bomber didnot use SSPCs, instead it used electro-mechanical relays for control and thermal circuitbreakers for over current protection. The B1-Bbomber was the first aircraft to use a "doublevoltage system which increased the voltage of theexisting 400-hertz, 3-phase system from a115/200 volts to a 230/400 volt system. Thedouble voltage system, in addition to the~serialdata bus control, would significantly reduce wireweight. In 1984, the Air Force went on contractwith Boeing to develop a 400-hertz fault tolerantelectrical power system (FTEPS) for an advancedfighter aircraft. The objective of this program wasto develop and laboratory demonstrate a reliablefault tolerant electrical power system through theintegration of VSCF generators and bus contactorcontrols with SSPCs. This highly integratedsystem would minimize weight and volume andreduce the likelihood of cascading faults in theelectrical system. In fact, the system was to beconsidered to be "bullet proof and would providehighly reliable power to flight critical loads thatpreviously required dedicated permanent magnetgenerator backup.
While the Air Force was developing VSCFtechnologies in the 1960s, 1970s and 1980s, theNaval Air Development Center was developing270 VDC technologies for aircraft utilization duringthis same time period. This was a major shift fromconventional 400-hertz power. Generating 270VDC power was less complicated and inherentlymore reliable than CSD or VSCF powergeneration technology. The 270 VDC generatingsystem was like the DC-link system without theinverter. A block diagram of a 270 VDC generatorsystem is shown in Figure 5. Though thegenerator was simple and straightforward, therewere other concerns with the use 270VDC thatneeded to be addressed. The Navy implementedseveral research and development programs thatmitigated the risk of using 270 VDC.
AC 270 VDC.
Figure 5. Block Diagram of a 270 VDC GeneratorSystem
Also, during the 1970s the Air Force pursued highpower electrical generators based on a perceivedneed for high power electronic warfare (EW)systems and directed energy weapon (DEW)systems in the future. The Aero PropulsionLaboratory entered into a research contract withthe AiResearch Manufacturing Company todevelop a 10-megawatt power generationsystem(s) for EW and DEW applications. Thecontractor selected a 5-megawatt permanentmagnet design (2 generators in parallel to meetthe 10-megawatt requirement) that would operateat 18,000 RPM, with a line to line voltage of 1000volts. The generator was designed for a lifetimeof 100 hours with a 5 minute run time and a 5-minute cool down period. The projected weight ofthe system was an impressive 530 pounds! Thehardware was developed, but problems wereencountered in the testing of the rotor structure.Figure 6 shows a conceptual design of the 5-megawatt generator. Because of the technicalproblems, the generator was never fully tested.This class of generator never went into productionand is considered today to be ahead of its time.
Figure 6. Conceptual 5-megawatt Generator
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Present (The MEA
In the early 1990s, the Air Force formulated theMore Electric Aircraft (MEA) initiative, whichembraced the concept of using electrical powerfor driving aircraft subsystems that are typicallydriven by hydraulic, pneumatic and mechanicalpower. Mechanical power is extracted from thecore of the propulsion engine through a towershaft to drive engine gearboxes and the AMAD.The engine gearbox drives accessories dedicatedto make the engine function. For example, theengine gearbox drives a fuel pump to deliver fuelto the engine, a hydraulic pump for nozzle andvain control and typically a small generator toprovide power to the engine controller andsensors. The AMAD is linked to the enginegearbox via a power take off (PTO) shaft. TheAMAD drives the aircraft electrical generator andhydraulic pumps, which are used for utility andflight control actuation. Pneumatic power isdirectly extracted from the main propulsion engineto drive the environmental control system's (ECS)compressor. Figure 7 illustrates a typical aircraftpower system and its complexity with pneumatic,hydraulic, mechanical and electrical power. TheMEA initiative emphasized the use of electricalpower in lieu of hydraulic, mechanical andpneumatic power for optimizing the aircraft(s)warfighting capability and life cycle cost. Forexample, the MEA would replace hydraulicactuators and hydraulic plumbing with an electricmotor driven actuator and electrical wiring.Studies for the Air Force have shown that theMEA concept provides significant improvement inreliability, maintainability and supportability. Thedecision to convert to electrically drivensubsystems depends on the overall cost andwarfighting benefit. Each subsystem would bestudied to determine the benefit. Therefore, aMEA could be as simple as adding an electric fuelpump (more electric) or a full implementationwhere all subsystems are driven electrically (allelectric). In the 1990s the focus has been on the"more electric" where as the near future is focusedto the "all electric". The "all electric" aircraft willtotally eliminate mechanical and pneumatic powerextraction from the main propulsion engine andwill integrate an electric starter/generator into thepropulsion engine's turbine core. Integrating thestarter generator into the engine will eliminate thetower shaft, gearboxes and AMAD, which willreduce cross sectional area and drag torque
during engine starting. Figure 8 illustrates the all-electric aircraft power system and its relativesimplicity when compared to the conventionalsecondary power system.
Figure 7. A Typical Aircraft Power System
Figure 8. The All-Electric Aircraft Power System
The MEA initiative has been characterized as arevolutionary concept, however from a technologyviewpoint it is evolutionary. In 1943, theengineers at the Douglas Company made thetrade between using electrical power andhydraulic power for flight control and utilityactuation. The state-of-the-art for electrical powerin 1943 was 24 VDC brush generators and motorsand electro-mechanical relays and potentiometersfor controls. They concluded that a vastimprovement in electrical generators, motors anddrives must be made before the low weight andefficiency of hydraulic pumps and motors can beequaled. The roots of MEA initiative goes back tothe work accomplished by the Air Force/Navy indeveloping and maturing VSCF electrical powergenerator systems, fault tolerant electrical powersystems, high energy density permanent magnet
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materials for motors and generators, and 270VDC system and component technologies.
In 1991, Mr. Richard E. Quigley Jr., Chief of theAerospace Power Division, Aero Propulsion andPower Division, Wright Laboratory, United StatesAir Force laid out the vision for the More ElectricAircraft initiative. He knew the concept was notnew, but the timing was right, since several keytechnologies were in place to make it happen. In1992, the Air Force Scientific Advisory Boardrecommended that the MEA initiative invest in 4key technology demonstrations in order to besuccessful. The four key technologies were 1) theintegral starter/generator, 2) the integrated powerunit, 3) the fault tolerant 270 VDC electrical powersystem, and 4) the high horse power electricactuator. Once these technologies weredemonstrated and in place, it was conceivable totransition the MEA concept to a fighter aircraft.Figure 9 pictorially shows the 4 key technologiesto be demonstrated. The Air Force and Navyjointly funded the four key demonstrationprograms and these technologies are describedbelow.
• • • :
Figure 9. The Four Key MEA Technologies
External Integral Starter/Generator (EIS/G)
The external integral starter generator combinesthe engine start function and the generation ofprimary electrical power into a single "integral"device. The machine developed for the externalstarter/generator would also have to work for theinternal starter/generator application. It wasdecided early in the MEA initiative, that switched
reluctance technology needed to be demonstratedexternal to the engine, before it would beintegrated into the engine. This decision wasbased on cost and risk. The machine of choicefor the internal starter/generator was switchedreluctance. Switched reluctance machines werean old technology that was enabled byadvancements in power electronics and digitalsignal processors. Switched reluctance machineshave several advantages over conventional typeof electrical machines. First, the machine has avery simple electro-magnetic structure, thusinherently reliable. This consists of a salient polerotor made of only soft magnetic material andsalient pole stator made with soft magneticmaterials with independent coil windings.Second, the machine could operate in a hightemperature environment (i.e. at internal enginetemperatures) but was limited by the magneticmaterial and winding insulation temperatures.Third, the machine is capable of being faulttolerant since the phase windings are electricallyisolated, and a failure in a winding could beisolated by the power electronics. Fourth, themachine could seamlessly transition frommotoring to generating mode, which was criticalfor aircraft applications. A 270 VDC, 250-kilowattstarter/ generator was developed and laboratorydemonstrated. This machine laid the groundworkfor a follow-on flight test demonstration for theJoint Strike Fighter Office. Figure 10 shows theswitched reluctance starter/generator under test.
Figure 10. Switched ReluctanceStarter/Generator
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Integrated Power Unit (IPU)
The Integrated power unit is an electricalstarter/generator directly coupled to a high-speedturbo-machinery prime mover. The purpose of theIPU is to combine three separate functions (andhardware) into a single unit. The IPU providesmain engine starting whether on the ground orduring flight (when linked to the integral startergenerator), auxiliary power for ground checkout,and emergency power for in-flight backup ofprimary electrical power. This is a critical elementin the MEA concept and is primarily responsiblefor the elimination of most of the ground supportequipment necessary to support a conventionalfighter aircraft power system. For example, theIPU can power an electric motor drivenenvironmental control system compressor, inaddition to providing aircraft power for groundmaintenance and checkout of avionics and othersubsystems. Thus eliminating the need forground power carts and other ground supportequipment. The Air Force entered into anexploratory development contract withAlliedSignal Aerospace Inc. to demonstrate anIPU. Several new technologies were exploredand integrated into the design. This included ahigh speed switched reluctance machine (SRM) toelectrical start the turbo-machinery and provide270 VDC electrical power, magnetic bearings forlong life and high efficiency, and high speedpower and control electronics to process thepower. The system was designed to integrate theelectric machine between the compressor and theturbine of the turbo-machinery and would use thecompressor air for cooling. This integrationeliminated the need for additional bearings for theSRM. The program successfully demonstrated ahigh speed SRM producing over 30 kW of 270VDC power at 30,000 RPM on magnetic bearings.The Air Force awarded a follow-on advanceddevelopment program to Sundstrand Aerospaceto develop a flight packaged IPU with anintegrated power head. The starter/generator is aSRM, but is mounted external to the turbo-machinery. The program objective was todevelop an IPU that meets the major goalsidentified in Table 1. The program is nearing thecompletion of the fabrication phase. A test phasewill follow to verify the performance of the unit.
The MEA will need a highly reliable, fault tolerant,autonomously controlled electrical power systemto deliver high quality power from the sources tothe load. This type of system has similarrequirements to the FTEPS, but with severalunique challenges. First, the MEA concept adds asubstantial amount of high power and dynamicmotor loads to the power system, which impactpower quality. Second, most of these loads willhave a low input impedance EMI filter thatpresents an in-rush current problem during power-up. Third, most of these loads have a constantpower characteristic, which tends to destabilizethe power system during transient events. Fourth,MEA loads such as flight control actuatorsproduce regenerative electrical energy that musteither be consumed in the actuator as heat ortransferred back to the power distribution systemfor utilization. Fifth, a high percentage of the loadsare flight critical and loss of power to these loadscould result in the loss of the aircraft. Thus, theperformance and integrity of the power distributionsystem becomes critical. In order to addressthese electrical power system challenges, the AirForce awarded a contract to Northrop Corporationin the fall of 1991 to develop and demonstrate apower management and distribution system for aMEA. The contract, commonly called MADMEL,brought together several state-of-the-art andemerging technologies to laboratory demonstratea highly reliable, fault tolerant power system. Themajority of the more electric and avionic loadsrequired 270 VDC power. The generation ancdistribution of 270 VDC power has its own set otechnical issues that were addressed under th<program. The MADMEL program was successful!1completed in the spring of 1999.
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High Horsepower Electric Actuators
The Air Force recognized the need todemonstrate a high horsepower electrical actuatorto meet the demands of the horizontal tail for anadvanced fighter aircraft. This demonstration wasconsidered to be essential for electrical actuationto transition to the next generation fighter. Electricactuation had been demonstrated on smallhorsepower surfaces, but this was not sufficient totransition the MEA concept. Several aerospacecompanies under internal funding initiated thedevelopment of high horsepower electricalactuators. This included the electro-mechanicalactuator (EMA) and the electro-hydrostaticactuator (EHA). The EMA used an electric motorto drive a ball screw actuator and the EHA usedan electric motor driven hydraulic pump, whichdrove a hydraulic cylinder. These units"werelaboratory demonstrators and did not meet thepower density goals necessary to transition to anaircraft. The Air Force entered into an agreementwith Sundstrand Aerospace to develop a highhorsepower, electro-mechanical actuator. Thefocus of this agreement was to reduce the sizeand weight of an electric actuator motor drive by afactor of 2! The Join Strike Fighter Office wasalso interested in the high horsepower, electricalactuators and funded an additional effort tomature the technology.
J/IST Program
In 1995, the Joint Strike Fighter Office initiated amulti year $118 million Joint/Integrated StrikeFighter (J/IST) program to mature critical MEAsubsystem technologies and reduce associatedrisk. The Joint Strike Fighter Office recognizedMEA technologies offered advantages throughsubsystem integration. Benefit studies conductedby the J/IST contractors showed a 2-3% reductionin life cycle cost and 500-700 pound reduction ingross take off weight by using MEA technologiesin a JSF type vehicle. Given this motivation, theJ/IST program established 4 major technologymaturation demonstrations. This included 1)thermal energy management module (T/EMM)system demonstration, 2) the T/EMM engineintegration demonstration, 3) the electric powerintegration demonstration and 4) the electricalpower & actuation flight demonstration. The J/ISTdemonstration programs were a logical extensionof the Air Force/Navy MEA program. The critical
technologies such as the high speed SRM andmagnetic bearings used in the T/EMM wereinitially demonstrated under the MEA IPUprograms. The electric actuation and flightdemonstration program used the AFTI/F-16 as thetest vehicle. Many of the technologies used in theAFTI/F-16 flight test program were developedunder the MEA initiative. This includes the EIS/Gand MADMEL 270 VDC distribution technologies.Figure 11 illustrates the key MEA technologiesdemonstrated in the AFTI/F-16. All of the J/ISTprograms were recently and successfullycompleted.
Figure 11. The AFTI/F-16 Key MEA Technologies
FUTURE
It is anticipated that military aircraft electricalpower systems will evolve again to have a majorimpact on weapon systems. This time it willenable directed energy weapon (DEW) systemson aircraft. The amount of power needed for theseDEW systems ranges from hundreds of kilowattsto tens of megawatts of average power. Lowaverage power/high pulse power (gigawatt andhigher) systems will also be needed. MEAtechnologies will enable the lower end of thepower spectrum, but new power technologies willbe needed for these high power (>megawatt) andpulse power systems. Compact and lightweightgenerators, capacitors, power conditioning andthermal management technologies are the keytechnologies to enable aircraft DEW electricalpower systems. The Air Force is formulatingelectrical power technology programs to meet thefuture aircraft DEW needs.
SUMMARY
Aircraft electrical power have evolved from a"hundreds of watts" system to today's "hundredsof kilowatts" system. Through out this evolution
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several major milestones were accomplished.This includes: 1) The development of theCSD/synchronous generator, which enabled 400-hertz systems and is still the workhorse today. 2)The development of the VSCF and 270 VDCtechnologies in the 1960s and throughout the1980s, were the precursors to the MEA. 3) Theforesight to start the MEA initiative by recognizingthat timing was right for an old idea. 4) The J/ISTdemonstration programs, that mitigated the risk totransition MEA technologies. Thesedevelopments are the product of the ingenuity,perseverance and dedication of the industry.
References:1. R. E. Quigley Jr., "More Electric Aircraft,"
Conference Record, IEEE Applied PowerElectronics Conference, March 7-11, 1993,pp. 906-911
2. J. A. Weimer, et a!., "Power Technology forthe More Electric Aircraft," ConferenceRecord, AIAA/AHS/ASEE Aerospace DesignConference, February 16-19 1993
3. C. A. Ferreira and E. Richter, "DetailedDesign of a 250kW Switched reluctanceStarter/Generator for an Aircraft Engine," SAE1993 Transaction, Vol102, Journal ofAerospace, Section 1, pp. 289-300
4. G. P. Koerner and E.U.A. Siddiqui,"Permanent Magnet Variable Speed ConstantFrequency Power Generation System," AirForce Technical Report - AFWAL-TR-85-2112, March 1986
5. "Aircraft Electrical Engineering," Copyright,1943, by The McGraw-Hill Book Company,The Maple Press Company, York PA.
6. P. G. Colegrove, "Integrated Power Unit for aMore Electric Airplane," Conference Record,AIAA/AHS/ASEE Aerospace DesignConference, February 16-19 1993
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