Today's benchmark system for the Boeing 757/767/A310 airplanes and future trends in hydromechanical aircraft power generating systems are discussed. The 757/767/A310 system represents the commercial state of the art and the direction in which Sundstrand Corp. is headed, particularly in regard to weight reduction. Sundstrand introduced microprocessor control in an in service system in the Boeing 767 and was the first to use databus communications between the controls. Plans to develop this technology are briefly discussed. Alternative ways to produce and use power in aircraft are discussed. The integrated starter drive is discussed

Glennon, T.

English

NASA Technical Reports Server

wN84 10056 /
400-Hz AIRCRAFT POWER-GENERATINGSYSTEMS - ADVANCING THE BASELINE
Timothy Glennon
Sundstrand Corp.
Rockford, Illinois 61128
The weight evolution of the 400-Hz hydromechanica]aircraft power-
generating system (f'Ig.i) began in 1945 when the specific weight was of the
order of 8 Ib/kVA. This weight has steadily decreased with various advance-
ments in particular technologies. Current hydromechanica]systems typically
weigh 1.3 to 1.4 ]blkVA. A 60-kVA system, including the generator and hydro-
mechanical drive as an integratedpackage, at present weighs about 71 lb. The
controls weigh about 9 lb and are getting to be a substantialpart of the power
system weight. Also over the years the reliability of hydromechanical systems
has improved, the logical result of many millions of hours of experience•
This paper covers two areas: today's benchmark system for the
75717671A310airplanes and future trends• The 757/7671A310 system represents
the commercial state of Lhe art and the direction in which Sundstrand is
headed, particularly in regard to weight reduction• Sundstrand introduced
microprocessorcontrol in an in-service system in the Boeing 767 and was the
first to use databus communicationsbetween the controls. This paper briefly
discusses Sundstrand'splans to deve]op this technology. Much of the rest of
this conference is devoted to discussions of alternativ ways to produce and
use power in aircraft. Sundstrand has a few ideas to share with you about
that and about the integrated starter drive.
' 7571767/A310Systems - Today's Benchmark
The 757 and 767 are two-engine airplanes. Fhey have an integrateddriveI
generator (IDG) at each engine and an auxiliary power unit (APU) generator
. (fig. Z). All three generators are rated at 90 kVA.
: Figure 3, a one-line diagram of the 757/767 bus arrangement,shows the
number of components. There are three identical generator control units (GCU)
i and one bus protection control unit (BPCU). All of these control units use
: { the microprocessortechnology and communicate over the databus. A cnmplete
control system that is used in current aircraft is shown in figure 4, includingi
a number of current transformers (CT's). Boeing chose to have a completely
I protected bus system, including the tie bus, and so there are some additional
CT's.i
i Because of the microprocess system a new differentialprotection scheme ,
1 was implementedwherein the bus connections could be adjusted in real time if
there was enough CT information and enough communicationbetween units. It
was made possible by the microprocessor and the databus control.
Sundstrand introduced the microprocessorto aircraft power-generating
system control. Figure 5 is a block diagram of the generator control unit.
In this partlcular unit the voltage Is regulated with analog circuits, but
breaker contro3, protection, and built-in testing is controlled by an eight-bit
microprocessor. Sundstrand uses the 8085 Intel system in a standard configur-
ation with read-only memory, random access memory, independentwatch-dog con-
trol for the microprocessor,and some nonvolatilememory, which Is essential
to the built-ln test system. The built-in test system (BITE) for this par-
tJcular airplane Is a revolutionary system and the first of its kind.
1984001988-004
https://ntrs.nasa.gov/search.jsp?R=19840001989 2020-03-22T07:25:05+00:00Z
Historicallyspeaking, built-in testing has been an afterthought, it has
not worked very well because it simply has not been very accurate. With the
advent of the microprocessorSundstrand has been able to incorporate active
testing on a continuous and specific Oasis in order to address faults in the
system apd to isolate them on the basis of tests, not probabilities. The
microprocessor processes almost all of the system informationon a continuous
basis anyway. Sundstrand took advantage of that and used it for the built-in
test features. Any particular system malfunction is detected immediately,and
an isolation routine is included in the fault-clearingoperation. The non-
volatile memory is used to store the information. (For example, for the first
time we can seriously address problems such as intermittence.) This particular
system contains a bus protection control unit and an alphanumeric display,
which tells the flight-linemechanic in plain language exactly what is wrong,
what the fault is, and what the line-replaceableunit (LRU) is. Boeing has
found this to be very helpful in introducing the 767. Figure 6 shows, in a
bar-chart form, that historicallymany parts have been removed that turned out
not to be the problem. The common assumption is that systems consist only of
an IDG and a GCU. This fails to take into account the 15 or 20 other signif-
icant parts that can also fail (e.g., wiring connectors and coolers). A BITE
system that does not address those parts is inadequate. Therefore Sundstrand
tried to address many of those parts in this new system. As a result the
system should achieve a 95-percent confidence level in LRU identification-
based on testing and not probability.
Future Trends
4 A typical assumption is that hydromechanicalpower-generatingsystems
constitute a mature technology with little improvementpossible. Nothing could
._ be further from the truth. The technology is changing and being applied in
the same way as the technologies for other approaches. By 1987 the weight of
., a typical system should be down to 0.8 IblkVA. That is almost a 50-percent
reduction from 1977 levels (fig. 7).
" Weight reduction should come from the following technologicaladvance-
ments:
(1) Improved materials. Sundstrand is examining improvedmaterials
usage, particularly in the constant-speeddrive area. We are testi,g a
24 O00-rpm generator. Present generators run at 12 000 rpm, aridtherefore the
increasedspeed should result in some generator weight reduction.
Figure 8 is a sketch of a 24 O00-rpm two-pole generator that Sundstrand
is building. It gives some idea of the rotor construction. There is nothing
revolutionaryabout a two-pole machine: the idea certainly has been around
for a long time. Several other people are building them. We are trying to
build an extremely reliable one and we are spending some time to do that.
(2) Improvedelectromagneticpower density. Again, Sundstrand has been
a pioneer in improving the power density of the electromagneticsin aircraft
through spray-oil cooling and other means by integration into the system.
This activity is contiPuing. Recall from figure 1 that the generator control
unit is a significantpart (more than 10 percent) of the power system weight. , _
We think there is substantial room for improvementby using large-scale inte-
gratlon and increasingthe role of the microprocessor in the power-generating i
system.
(3) Large-scale integrationand expanded microprocessorrole. In the i
enerator control unit and the bus protection control unit, one of the obvious
mprovements is to include all of the system controls in the microprocessor.
Sundstrand has an active program to do that. The kinds of controls that are
2 i °"
1984001988-005
intended to be included are, for example, voltage regulation of the generator,
frequency control, all of the parallel-systemcontrols that might be used for
those aircraft that require a parallel system, _oad management, and configura-
tion management. In the 757/767 system Sundstrand began with load management,
through the bus protection and control unit. We actually do remove loads based '
on the system configuration. Some studies show that management of more of the
load system is desirable, and this can also be accomplished. In configuration
managementyou can observe what is happening and configure the system for your
particularmission arrangement. Any standard databus that is used on an air-
craft can be used to interface and communicate betwep'-Lne units. Also remote
display is probably an inevitabledevelopment si_e a central display is pre-
ferred over individualdisplays for each pic_ of equipment.
Figure 9 shows the architectureof a breadboard GCU that Sundstrand is
presently working with. It uses two 16-bit 8086 Intel microprocessors and is
an extremely powerful combination of equipment. However, it has fewer parts
than, for example, the KC-135 re-engine GCU's. This decrease in parts with an
increase in complexity is an expected resJlt of a digital approach. The input-
output conditioning is probably conventional. The two units are completely
independentbut can communicate back and forth and have their own local memor-
" ies, watch-dog timers, and so forth. If one unit fails, the GCU can still
operate to some extent with the other unit or use the other unit for other
purposes.
(4) Alternative power. Presently most systems have 400-Hz power with
some 28-V dc power. In 1918, Sundstrand suggested that 2000-Hz constant-
-. frequency power be used as a possible _pproach for weight reduction. A number
of aircraft have already been configured with double-voltage systems to reduce
distribution system weight. More and different kinds of direct-currentpower,
perhaps 270 V, 100 V, or just more 28 V, or maybe a mixture, could be used.
(5) Integrated starter drive. Sundstrand has been a pioneer in the fie1_
i of integratedstarter drives In the early Ig60's we introduced electric
starting for aircraft on the 727. At that time the engine was in the design
t stage. As the required thrust increased, the engine outgrew the capability of :'
•
the starter. Since that time we have been constantly studying this system and
• we feel that, with a simple change in the arrangement of the constant-speed
drive components, an integrated starter drive can start the toughest engines.
Figure 10 is a block diagram of one arrangementof a 150-kVA integrated
starter drive. In the start mode, alternating-currentpower is applied to the "
k motor-generator,which would accelerate as an induction motor by using a
patented static switch arrangementfor the rotor. At that point the hydraulic
i drive is feathered (i.e., no torque is being transmitted through the transmis-
sion). So the motor is completely unloaded. Once it is at speed, it is con-
vetted to a synchronousmotor, which has very high efficiency and certainly
i does not disturb the quality of power on the bus. The unit is then broughtinto stroke and the system can be started easily wit working pressures no
exceeding 5000 psid, less than, for example, the two-per-unitpressures in the
hydraulic units and hence very conservative.Figure 11 shows how th 150-kVA in egratedstarter drive system would _
i work with a _TgD engl_e, a tough-to-startengine. The drag-torque curves are
shown for 59 and -69 F. As you can see, the engine can be started hot or
cold, under any condition, in 25 seconds with a very reliable torque margin.
F gure 12 is a diagr m f the in egratedstarter drive system. Although
the number of CT loops could be reduced, the basic point of this diagram is
}
1984001988-006
that, with the exception of pressure, which is fed back from the hydraulic
units, and the real power limit, all of the control variables are normally
found in a parallel generating system. The system includes electronic control
of freq_ency (servovalve into the constant-speed drive area). This will be
more prevalent and allow for presynchronizedparalleling even in split-bus
systems.
In summary, then, I have attempted to share with you the state of the art
of the 757/767/A310hydromechanicalaircraft power-generatingsystems: that
Sundstrand has 1.3- to 1.4-lb/kVA systems in service, has introduceddatabus
communications,and has introducedthe microprocessor. Further substantial
weight reductions are possible, to 0.8 Ib/kVA in the foreseeable future. The
microprocessorcontrol is a powerful, flexible, dual 16-bit system that can
handle any parallel-generating-systemor starting arrangements that are envis-
ioned. And, of course, the BITE is a landmark system and will continue to be
so. Alternative forms of power are not excluded by considering this approach.
Higher frequency,higher voltage, and mixed direct-current power can be usqd
if needed. Finally, this system provides an extremely high torque margin for
reliable engine starting.
t
.i
m.._J
4
1984001988-007
ORIGINAL PAGE NI
OF POOR QUALITY.
"_ LOsJkVA
_ $-_H ydraulic Today's 60 kVA System
! 4
Geared
1 _.-.aC.,.._j Total Sundstrand
System
I _r
' I li55 l ;_Ts I
1945 1965 1985
Year
Figure I. - Integrated-drivegenerator weight evolution.
IDG_
/ I : I APU
GCUe
BPCUAND
CTAI
moo _
t
SP_ BUS _kVA
Figure 2. - 7571757 genermtlngsyst_.
5
1984001988-008
f(_c(IGiNAL PAGE IS
OF POOR QUALITY
,--t , ...... *=1 Ir GCU J GCO 1 -r.......1 GCU l
I I I .4
I i !
LEFT m _ RIGHT I
I ! GCB . . _ l
Gc.__ t. ;. ' ' ._,ELCU 1,-,,llJ_V_ I I_ ELCU2 4P IGHT MAIN,
| L_ 4 ' TO LEFT MAIN, ELCU 3 _FII _ _A,L_EY AND .,GHTuse I "I_ I GALLEY AND j, II ! ; UTIL'•TY, AND GROUND
I LEFT UTILITY UBR 2., _ '_I sER-vICE BUS LOADI BUS LOADS
I I|
I II
OVERLAP._CT ..- z,.-----D" _ _,_,1 OVERLAP._ECT .,--;_" -- _ -- -'Jl' _ DPCT--._ I•- -- --_ :DPCT r-----'_>_.DPCT TC GROUNDI .'_ "_'l HANDLING&
I LEFT'" RIGHT'' : APB"
I
"" IDPCT DPCT_- ..... ' i DPCT_4 OLCT_" I, /_'_ -"_ EXTERNAL
I , I y ' POWER
• I
L -- - - _ - _ P" -" I INPUT
i I
,
Figure 3. - Schematic of 757/767 EPGS.
Ftgure4. - Coa_letecontrol systm usedtn current aircraft.
6
1
j_
1984001988-009
ORIGINALPAGE II
OF POOR QUALITY
.,P
I-I I iANALOG TO EXCITERPOR VOLTAGE _-REGULATOR I FIELD
"°" I 'tl _ i,.o.,.olGIN. CT'tl
BURDEN REBnITORI I ROTATING I
I nsczmtn I
IDETECTORJ
POR 28 VDC i I
|NORTllD 1
_" PMG
• PEAK DIITICTOR
CIRCUITS | I
LINE .... l OIL IN BULII
CT'I OUT IULb
AOC LOAD IITIR
ANALOG
ORCUml
i
, ,. ATnOUTGIN.
CT'BtI ilion
, I , IERIAL IIRIAL
MPU DATA " --
LINK DATA
TO IPCU :;
.iOVERLAP CT , ,,
MICROPROCEIIBORsYBTEM___
11
OUTPUT _ DfllC:RITI
INPUT l BUFFERS11 CONDITIONING ICISCRITI
INPUTS !"1• VOLATILE"_ IIIMORY
,!
y
"_'! Figure 5. - Block dtagria of 757/767 generet|ng systeL%
-i
_ 7
1984001988-010
O,, J_,,,-.,L l:L'lt , _ J¢'-
OF F"F.K)RQUALITY
Traditional BITE "
IDG CONTROLS
'=_-I -- I '=u-'-'I
Microprocessor BITE
REMOVALRATEApt)ROACHES
FAILURER "E
,=u.,,] ',_Lu.:,1L FAILUR2.
Figure 6. - Tranditional ".ndmicroprocessor BITE'S.
2
ENHANCEMENTS
'!
-I
t 1
- ----//-., , • I _ ;
YEAR
J
Ftgure l. - Future I06 weight t,'_,_ls, t
i
t
1984001988-011
°,
Figure 8. - Two-pole,24 000-rpm generator rotor,
SFIELD
+ 2$DISCRETE'-'--'+ CONDITIONING CONDITION_G
_-+ INPUTS
GCRDRIVE
_ _ PROTECTION
I _ MICROPROCESSOR _ GLC DRIVE
'! ! LOC."I
! "t"°"'I
Figure g. - Block diagram of advanced-architecture generator control un%t.
_._
ii+l ,
1984001988-012
_ ORI_NAL PAGE IS
OF POOR QUALITY
Description of Operation
• V Unit Feathered, In,: ;tion Motor Start Up
• V UnitStroked, Hydromechanical EngineStart
Up Controlled at 5,000 PSID
• Working Pressure Decreases With Increasing
Input Speed When in CSD Mode
_, Figure lO. - 150-kVa i_,tegratedstarter drive.
600
JT9D ENGINE
2:1 SPEED RATIO
";0,000 MAX. SPEED AT PAD
S00 5 000 IDLE SPEED AT PAD
_,. 4,500 STARTER CUT-OUTSPEED AT PAD
" 21 SLUG FT." INERTIA AT PAD
m START TIME 23-25 SEC.
"400
w _z
. _
1000 2000 4000
ENGINE PAl) SPEED -- RPM
ii] Figure II. - Torque as a function of speed for 150-kVa integratedstarter drive
on JTgO engine.
} IO _ t
] 98400 ] 988-0 ] 3



The 400-Hz aircraft power-generation systems: Advancing the baseline

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