Aerospace electromechanical actuators utilizing induction motors are under development in sizes up to 40 kW. While these actuators have immediate application to the Advanced Launch System (ALS) program, several potential applications are currently under study including the Advanced Aircraft Program. Several recent advances developed for the Space Station Freedom have allowed induction motors to be selected as a first choice for such applications. Among these technologies are bi-directional electronics and high frequency power distribution techniques. Each of these technologies are discussed with emphasis on their impact upon induction motor operation

Hansen, Irving G.

English

NASA Technical Reports Server

NASA Technical Memorandum 102482
Aerospace Induction Motor
Actuators Driven From
a 20-kHz Power Link
Irving G. Hansen
Lewis Research Center
Cleveland, Ohio
Prepared for the
Fourth International Conference on Power Electronics
and Variable Speed Drives
sponsored by the Institution of Electrical Engineers (lEE)
London, England, July 17-19, 1990
https://ntrs.nasa.gov/search.jsp?R=19900010769 2020-03-19T22:47:11+00:00Z

AEROSPACE INDUCTION MOTOR ACTUATORS DRIVEN FROM A 20-kHz POWER LINK
Irving G. Hansen
National Aeronautics and Space Administration
Lewis Research Center
Cleveland, Ohio 44135
Aerospace electromechanical actuators utiliz-
ing induction motors are under development in
sizes up to 40 kW. While these actuators have
immediate application to the Advanced Launch
System (ALS) program, several potential appli-
cations are currently under study including
the Advanced Civil Aircraft program.
Several recent technology advances developed
for the Space Station Freedom have allowed
induction motors to be selected as a first
choice for such applications. Among these
technologies are bi-directional electronics
and high frequency power distribution tech-
niques. Each of these technologies will be
discussed with emphasis on their impact upon
induction motor operation.
BACKGROUND
For over a decade NASA Lewis Research Center
has been evaluating, and defining power compo-
nents and system characteristics as part of
our OAST charter. This work provided a foun-
dation for the Advanced Aircraft Secondary
Power System Study in 1985 which concluded
that a 20 kHz ac system had great advantages
particularly when multikilowatt, multiply re-
dundant, distribution was involved (i). This
study also recognized the advantage of high
frequency power for motor operation. In the
intervening years, the technology has been
reduced to practice and evaluated with several
full power testbeds. The initially baselined
20 kHz power distribution for Space Station
is shown in the diagram (Fig. I). The system
comprised two independently powered feeders
(left and right) similar to conventional air-
craft practice. All loads had current limit-
ing remote power controllers (RPC's) and
could draw power from either feeder subject
to power management.
Differential protection was provided between
nodes to monitor soft and hard faults. In
this system the RPC's were programmable for:
off, on, trip level, monitors indicated switch
status, the current flowing, and produced a
flag when over current trips occurred. Simi-
lar instrumentation, but no current limiting
or tripping, was provided by the node switches
or remote bus isolators (RBI's) located on the
feeder lines. This system was assembled at
NASA Lewis and operated with complete success
for over a year (2,3).
It is the confidence gained from the Space
Station Testbeds, advanced components, and
operating experience that forms the founda-
tion for advanced electrical power, distri-
bution, and control. These advances in power
control and newly demonstrated capabilities
for control of a larger class of inherently
rugged, induction motors using pulse-
population-modulation with field-oriented
control powered from a high frequency source
makes this approach even more attractive.
For example, selective steering of high fre-
quency, low energy pulses and switching at
zero crossing significantly reduces the size
and weight of the electronics while greatly
reducing EMI/EMC effects.
WHY HIGH FREQUENCY POWER DISTRIBUTION
Electrical system reliability is, in reality,
the probability of suitable electrical power
being available to user loads. Long term
availability is most efficiently achieved by
parallel redundant elements in a single dis-
tribution block consisting of a source, stor-
age (if required), and a distribution system
all under active control and management.
Uninterruptible, or secure power, for criti-
cal loads may be implemented by an additional
block, or blocks, depending upon the require-
ments. Within a single block, fault limiting,
fault isolation, and fault recovery through
reconfiguration are implemented to maintain as
much post fault capability as possible. This
capability (fault tolerance) involves status
sensing, intelligence, current limiting, and
active switching. When all available technol-
ogies are fully reviewed, it becomes obvious
that these requirements may be much more
easily met by utilizing a distributed, alter-
nating current (ac) system. The system phys-
ics, the system fault recoverability, and the
overwhelming terrestrial experience support
this conclusion. Given an ac system several
engineering decisions remain as regards the
distribution voltage, waveform, and frequen-
cies. While each specific application must
be eva]uated, point designs and operating
experience to date support the selection of
ultrasonic, sinusoidal power systems operated
at the highest voltage appropriate to the sit-
uation. Both the proposed advanced secondary
power system (i), and the Space Station Free-
dom power system involved multi-redundant sys-
tems delivering multikil_watts of power over
distances of many yards. For these applica-
tions, a single phase, 20 kHz, 440 V distribu-
tion system was selected. In the case of the
Space Station, the distribution voltage within
pressurized elements was reduced to 220 V out
of consideration of reduced pressure break-
down. Similar arc over conditions would also
exist on a transatmospheric vehicle. This
20 kHz, single phase, high voltage, high fre-
quency distribution system is the source used
to supply the four quadrant induction motor
drive circuitry.
WHY INDUCTION MOTORS
Induction motors possess very desirable cha-
racteristics for aerospace applications.
They are very rugged, will operate at high
temperature, and due to their lack of perma-
nent field excitation they tend to fail gra-
ciously. Until recently, however, they have
also displayed low efficiency and required
complex controls. The induction motor in its
simplest form (Fig. 2) is that of a trans-
former with its secondary free to move. Two
currents are involved in the motor action, the
primary (stator) current (proportional to the
applied voltage divided by the applied fre-
quency)whichestablishes the magneticflux
density, anda secondary(rotor) current pro-
portional to both the magneticflux density
andthe rate at which the magnetlines are
cut (slip frequency).
As the slip frequencyresults form the spacialdifferences betweenthe stator field andthe
rotor conductors, at least one of themmustbe
"moving." Reviewedin its simplest form then
an induction motorhas a magneticfield which
is; capable of rotation, and proportional to
the ratio of applied voltage to frequency and
a rotor current proportional to the difference
in rotation between the magnetic field and the
rotor itself.
The point to be made is that when an induction
motor is operated from a multi-phase control-
ler whose voltage and frequency are indepen-
dently variable, both the rotor and the stator
currents are independently controllable, and
furthermore, the rotor current is "instantly"
variable. As is usually the case these sim-
plistic concepts have their limitations, but
nonetheless, they provide an excellent first
order explanation.
PULSE POPULATION MODULATION
Independently variable voltage and frequency
waveforms are easily synthesized from a high
frequency power source (Fig. 3). With zero
voltage switching, the output consists of a
series of half sinusoids. The frequency is
contrulled by the waveform, and the voltage
is controlled by the number of pulses (popula-
tion) wi[hin the envelope. What has occurred,
not unlike radio transmission, is that all
switching and energy control is done at the
carrier frequency and not at the machine fre-
quency. A three phase set of synthesized
400 Hz waveforms is shown in Figure 4. This
frequency translation results in greatly re-
duced component sizes particularly as regards
electromagnetic filtering. Also loss generat-
ing waveform distortions are much reduced as
compared with conventional (PDM) control.
FIELD ORIENTED (VECTOR) CONTROL
Although pulse population synthesis has advan-
tages for driving any ac machine, it has
marked advantage as regards field oriented
control of induction machines. In vector con-
trol each stator current is controlled rela-
tive to the rotor field and consists of a flux
producing current, and a orthogonal tor_ae
producing current.
These required flux and torque producing cur-
rents bear obvious relation to the voltage
and frequency synthesis described earlier.
Figure 5 shows an induction motor under vec-
tor control with output torque as the control
parameter. Two points are of interest; the
torque is "instantly" variable, and is held
constant over a speed range including reversa:
through zero speed.
CONCLUSION
Electrical actuators driven from a high fre-
quency link, and using induction motors have
many advantages. They provide high efficienc>
over a wide operating range, high peak torque
and rapid response. From a systems stand-
point, their rugged construction, and soft
failure characteristics are particularly
attractive.
REFERENCES
1. Hoffman, A.C.; Hansen, I.G., Beach, R.F.,
Plencner, R.M., Dengler, R.P.,
Jefferies, K.S., and Frye, R.J.: "Ad-
vanced Secondary Power System for Trans-
port Aircraft," NASA TP-2463, 1985.
Hansen, I.G.: "Status of 20 kHz Space
Station Power Distribution Technology,
Presented at the IEEE Applied Power Elec-
tronics Conference and Exposition, (APEC
88), New Orleans, LA., 1988.
Hansen, I.G., and Sundberg, G.R.: "Space
Station 20 kHz Power Management and Dis-
tribution," NASA TM-87314, 1986.
Sood, P.A., Lipo, T.A., and Hansen, I.G.:
"A Versatile Power Converter for High Fre-
quency Link Systems," IEEE Trans. Power
Electro., Oct. 1988, _, (4), pp. 383-390
XFR_• 440 VAC XFMR r 1t40 VAC
NSA_ \ /-RESOURCE NODES NSA-_ ', r q(lo VAC
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; LOADS ( IYP)
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J
t/ I'-qqO VAC XFMR J i ,.-q_O VAC
, L qqO VAC
'-NSA
XFMR
FIGURE I. - MODULE PRIMARY DISTRIBUTION ARCHITECIURE.
JEM I
2
T1 Zl T½/S Z_
FIGURE 2, - EQUIVALENT CIRCUIT OF THE POLYPHASEMOTOR,
IRON LOSSES DUE TO THE MAIN FLUX NEGLECTED.
PHASE +250
VOLTAGE,
Vc(V) -250
LINE
VOLTAGE,
Vab(V)
-50O
REFERENCE +250
VOLTAGE,
Va(V ) -250
(A) COMPUTER SIMULATION OF LOW FREQUENCY SYNTHESIS (UNIVERSITY OF WISCONSIN).
20O
(B) OUTPUT OF BREADBOARD SYN-
THESIZER (UNIVERSITY OF
WISCONSIN).
0 50 0O0
START STOP
FREQUENCY, Hz
(C) SPECTRUM OF BREADBOARD SYNTHESIZER (UNIVERSITY
OF WISCONSIN) (IST SIDE&_ND SET).
FIGURE 3. - WAVEFORM SYNTHESIS. CD-88-91081
REFERENCE
VOLTAGE
v_(v)
+2soE_
-250
PHASE
VOLTAGE
Va(V)
+250
-25oE t,'_""_
PHASE
VOLTAGE
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VOLTAGE
Vab (v)
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{-1 ms-1
-500
FIGURE 4. - SYNTHESIS OF A BALANCED SET OF VOLTAGES HAVING
SINUSOIDAL. FUND/V4ENTALFREQUENCY IS 400 Hz WITH A MOD-
ULATION INDEX Of=0.9.
MAIN
MENU ..._.....
l
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: _SPEED
....... !_ ....... Z40 rpmxliv
.. /--TORQUE COMMAND
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_1.88 s f531.9mHz CH I .2V =
T/di .5 x CH 2 .2V =
Trig .00 -CHAN I<
(a) SPEED REVERSAL OF 2-Mp I_VKHINE.
+500 .......
-500[-
LINK
VOLTAGE
V HF (V)
LINE
VOLTAGE
Vab (V)
+500 .... • - iml• .............
-500 l mw,nu,.w.w.w _ __ sl ...............
LINE
CURRENT
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+30 _A_AA _ AA#_ _ ^,,,,...... ^^_ '_
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ELECTROMAG.
TORQUE
Te <Nt.-m>
LOW FREQ.
CURRENT
iLF(A)
+5 _._
-5
+30
-30
(b) P_ CONVERTER SYSTEM OPERATION.
FIGURE 5. - INDUCTION _CH[NE UNDER BOTH MOTORING AND GENERATION.
National Aeronautics and
Space Administration
1. Report No.
NASA TM- 102482
4. Title and Subtitle
Report Documentation Page
2. Government Accession No.
Aerospace Induction Motor Actuators Driven From a 20-kHz Power Link
3. Recipient's Catalog No.
5. Report Date
7. Author(s)
Irving O. Hansen
9. Performing Organization Name and Address
National Aeronautics and Space Administration
Lewis Research Center
Cleveland, Ohio 44135-3191
12. Sponsoring Agency Name and Address
National Aeronautics and Space Administration
Washington, D.C. 20546-0001
January 1990
6. Performing Organization Code
8. Performing Organization Report No.
E-5272
10. Work Unit No.
506-41-41
11. Contract or Grant No.
13. Type of Report and Period Covered
Technical Memorandum
14. Sponsoring Agency Code
15. Supplementary Notes
Prepared for the Fourth International Conference on Power Electronics and Variable Speed Drives sponsored by
The Institution of Electrical Engineers, London, England, July 17-19, 1990.
16. Abstract
Aerospace electromechanical actuators utilizing induction motors are under development in sizes up to 40 kW.
While these actuators have immediate application to the Advanced Launch System (ALS) program, several
potential applications are currently under study including the Advanced Civil Aircraft program. Several recent
technology advances developed for the Space Station Freedom have allowed induction motors to be selected as a
first choice for such applications. Among these technologies are bi-directional electronics and high frequency
power distribution techniques. Each of these technologies will be discussed with emphasis on their impact upon
induction motor operation.
17. Key Words (Suggested by Author(s))
Electric actuators
Power distribution
18. Distribution Statement
Unclassified - Unlimited
Subject Category 07
19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of pages
Unclassified Unclassified 6
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Aerospace induction motor actuators driven from a 20-kHz power link

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