The technological developments required to reduce the electrical power system component weights from the state-of-the-art 2.0 kg/kW to the range of 0.1 to 0.2 kg/kW are discussed. Power level requirements and their trends in aerospace applications are identified and presented. The projected weight and launch costs for a 1MW power converter built using state-of-the-art technology are established to illustrate the need for reliable, ultralightweight advanced power components. The key factors affecting converter weight are given and some of the tradeoffs between component ratings and circuit topology are identified. The weight and launch costs for a 1MW converter using 0.1 kg/kW technology are presented. Finally, the objectives and goals of the Multi-Megawatt Program at the NASA Lewis Research Center, which is funded by the SDIO through the Air Force, are given

Baumann, E. D.

English

NASA Technical Reports Server

NASA Technical Memorandum 102577
_:_........ Power Conditioning Techniques
E.D. Baumann
Lewis Research Center
Cleveland, Ohio
Prepared for the
- _ " Neutral Particle Beam Technology Symposmm i _ ' _ _:
sponsored by Strategic Defense Initiative Organization
'_ _ Monterey, California, July 18-21, 1989 .......
("JAS A-TM-1 0 9D 7 7 ) pf3w_R CQNnITInNING
TECHNI_IJt_S (NASA) 7 p CSCL O-)C
N90-20301 _-=
unclas
https://ntrs.nasa.gov/search.jsp?R=19900010985 2020-03-19T22:45:37+00:00Z
---- :_ ZJ
-4p
UNCLASSIFIED
POWER CONDITIONING TECHNIQUES (U)
E. D. Baumann
NASA Lewis Research Center
Cleveland, Ohio 44135
oo
o
t.o
I
(U) Power level requirements for aerospace missions continue to increase (figure 1).
Historically, aircraft have dominated their spacecraft counterparts in the need for electric
power by an order of magnitude. For example, the power systems on board the Boeing 747
and DC-10 are rated for a few hundred kilowatts. The Space Shuttle power system, on the
other hand, provides just a few tens of kilowatts. Currently, the Space Station Freedom
baseline design calls for a modest 75 kW power system; a factor of two smaller than the
jumbo airliners designed 20 years ago. Growth Station, projected for operation in 2010, will
provide 150 kW to its users. When completed, spacecraft power levels will finally approach
the size of today's aircraft power systems. Future missions, such as the National Aero-Space
Plane (NASP), a Manned Lunar Base, and a Manned Mission to Mars are each expected
to require about one megawatt. To date, the largest space type power system deployed is
aboard the Space Shuttle and is rated for only 25 kW. Figure 1 also shows that the electric
power requirements for SDIO missions, which include the Neutral Particle Beam, will
exceed one megawatt with projections to 10 MW already envisioned.
(U) State-of-the-art power electronics technology is best demonstrated by considering the
Space Station Freedom's 75 kW power system. Solar arrays provide DC power to a bank
of inverters operating at 20 kHz which, in turn, supply regulated 440 VAC to the
distribution bus. Each inverter module has a specific weight of 3.7 kg/kW and provides
12.5 kW. Since each module contains 8 active switches, each switch handles about 1600 W.
A 1984 NASA contract with Hughes resulted in a resonant converter near 2 kg/kW
supplying 25 kW at 1000 VDC from a 250-350 VDC input. It required only four D7ST
switching transistors for the active switches, each handling just over 6 kW. Scaled to one
megawatt, the Space Station design would require 640 switches and 80 modules, whereas
the Hughes design would require 160 switches and 40 modules. The major differences
between the two designs are topology and reliability. A conservative design approach is used
for the Space Station due to the nature of the mission; while the goal of the Hughes design
was to demonstrate the maximum power handling capability of state-of-the-art switches.
(U) If a 1 MW DC-to-DC converter were built using the Hughes 2 kg/kW technology, it
would weigh two metric tons, roughly the equivalent of 26, 170-1b people. Assuming launch
costs of $10,000/kg, the price of launching the converters alone into low earth orbit would
exceed $20 million.
(U) A key to reducing power system weight is to understand the Weight distribution among
the various components. In most converters, the weight is shared among the capacitors,
inductors, switching devices, control circuitry, and supporting structure. Capacitors, for
example, are used as components in filters, resonant tanks, switch snubbers, and many other
applications. Inductors are used as filters, current limiters, components in resonant tanks,
and, when mutually coupled, as transformers. Transformers provide step-up, step-down, and
UNCLASSIFIED
UNCLASSIFIED
isolation for AC voltages. Switching devices can be fully controllable (eg. BJT, FET, GTO,
and SIT), partially controllable (eg. SCR and LASS), or uncontrollable (eg. rectifiers and
flyback diodes). The switching device structure may be P-N junction, field-effect, or Schottky
Barrier which give certain operating characteristics to the device. Finally, the supporting
structure holds everything together, provides cooling, and possibly acts to furnish paths for
electrical conduction. Since circuit topology limits the choice of components and vice versa,
understanding the complex relationships between circuit operation and component selection
will result in megawatt level power converters with very light weight.
(U) In a paper study performed at the NASA Lewis Research Center on a state-of-the-
art 2 kg/kW, 500 kW, 20 kHz resonant converter, the weight contribution from each
component type was determined. The results show that the weight distribution in the power
circuit components is 63% capacitors, 30% inductors, and 7% switches. This seems to
indicate a need for technology development in capacitors and, to a lesser extent, inductors
to realize significant weight reductions. However, the circuit studied is a resonant circuit.
This type of topology tends to have higher capacitor weight due to the resonant capacitor.
From this example it can be determined that advances in both component technology and
circuit topology are the key to reducing the specific weight of space type power systems.
(U) Since circuit topology is one factor affecting component weight distribution in a
converter, the NASA Lewis Research Center has established programs with the University
of Wisconsin and the University of Toledo to study converter circuit topologies. The goal
of these studies is to survey the operational characteristics of a wide range of converter
topologies. Among the characteristics under consideration are: efficiency, switch utilization,
fault energy handling, component types required, and specific weight. From the survey
results, promising circuit topologies are chosen for design, build-up and characterization.
The circuits typically operate at a few kilowatts and consideration is given to potential
difficulties in scaling the units to higher power levels. The work indicates that no single
topology will meet every requirement for all space-based power systems; rather, the "right"
converter topology is application specific.
(U) Power circuit topologies under consideration range form hard-switched to resonant with
quasi-resonant types falling in between. A hard-switched converter chops DC directly into
a transformer. It may not require capacitors provided that the switches can handle the
voltage transients caused by the transformer leakage inductance. Fully controllable switches
are mandatory in a hard-switch converter if one wishes to avoid the extra weight associated
with forced commutation circuitry. Resonant converters require capacitors in their tank
circuits but provide natural commutation to the switches. Circulating current is the major
drawback in resonant topologies because the circuit Q forces the switches to handle more
power than is being supplied to the load.
(U) Switch utilization, which is defined as the converter output power divided by the total
volt-ampere product of the switches, represents how well a circuit topology uses the
capability of its switches to achieve the output power. Resonant circuits have low switch
utilization due to high circulating currents. Hard-switched converters can have high switch
utilization provided that the switching voltage transients, due to transformer leakage, can
be snubbed; but snubbering leads to the inclusion of capacitors in the circuit.
(U) Operating a converter at a fixed frequency allows filters to be tuned; thus eliminating
the need to design wide band filters and further reducing weight. Yet, tuned resonant filters
UNCLASSIFIED
UNCLASSIFIED
require inductors and capacitors which are the heaviest of all the components to choose
from. Some topologies require less output filtering but at the expense of additional input
filtering. One consideration would be to match the filtering requirements to the load and
the source.
(U) Source and load limitations impose the boundary conditions within which the power
management and distribution (PMAD) system must function. An electric power source
provides some output voltage range, output impedance, and other restrictions that must be
matched by the PMAD system to a load having a certain voltage range, ripple voltage,
and other power requirements. If power is supplied by a 100 VDC source, it is likely that
switches having very low forward voltage drop will be used in the converter. Every 1-volt
drop in a 100 VDC system results in decreasing efficiency by 1%. In full bridge
configurations for DC-to-DC conversion, two 1-volt switch drops in the chopper and two
more in the output rectifier translates to a 96% efficiency and this is before losses
contributed by other components and cables are taken into account. Another consideration
is radiation effects on the switches. Nuclear reactor powered systems, which use
thermoelectric or thermionic devices, provide high power at low voltage. Efficient
transmission of this power to the user requires converters, located near the reactor, to step
up the voltage for transmission. We have a program at the Lewis Research Center where
radiation effects on BJT's, FETs, and other switches are being studied.
(U) Finally, fault tolerance ensures that the power management and distribution system will
be able to withstand load shorts or arcs. Ideally, stored energy within the power system
should be low to protect the load from catastrophic failure by preventing burnouts. In a
neutral particle beam system this amount to only a few tens of joules.
(U) If we can develop the technology to build a 0.1 kg/kW converter operating at a
megawatt, it would weigh 0.1 metric tons, about the weight of a 220-1b man. Launch costs
would decrease dramatically from $20 million, for the 2 kg/kW converter, to $100K. The
cost savings represent an order of magnitude decrease in converter specific weight and an
order of magnitude increase in power level over state-of-the-art systems.
(U) The approach will require new circuit topologies, the development of very light weight
capacitors and inductors, and new switching devices capable of handling large currents with
low forward voltage drop. Potential circuit topologies under consideration are resonant, soft-
switched, square wave, voltage multiplication or some combination. The NASA Lewis
Research Center has in-house and university grant work already underway in these areas.
Light weight capacitors are being studied in-house and at the State University of New York
at Buffalo. The MOS Controlled Thyristor (MCT), a new controllable switch with low
forward voltage drop, is under development at GE.
(U) Ultra-lightweight converter technology can meet the needs of many users. The Strategic
Defense Initiative Office is planning on orbiting platforms for systems such as the Neutral
Particle Beam and Free Electron Laser systems. The Air Force and commercial aircraft
industry could replace heavy and leak prone hydraulic systems with electric control surface
actuator systems to reduce weight and minimize down time. Two weeks time is spent on the
Space Shuttle in preparation for its next launch due to checking and qualifying its hydraulic
actuator systems. NASA needs lightweight converter technology for a Manned Lunar Base,
Space Based Manufacturing, interplanetary travel, and a Manned Mission to Mars. The
Army could have large mobile power systems capable of powering electromagnetic
UNCLASSIFIED
UNCLASSIFIED
launchers. Finally, the Navy could increase the payload on board its ships by decreasing the
weight of its electric power systems.
(U) The goal of a joint development program between NASA, the Air Force, and the
Strategic Defense Initiative Office, is to build a 1 MW DC-to-DC converter with a specific
weight of 0.1 kg/kW for a total converter weight of 100 kg. The output voltage will be
100 kV DC developed from an input voltage of 500-5000 VDC. The system will be fault
tolerant and store only a few tens of joules to prevent burnouts during fault conditions. We
project that the system will be completed in a 3-5 year time span with a demonstrable
1 MW hardware as an output. NASA is currently in the procurement stage through a
NASA Research Announcement (NRA).
(U) In conclusion, a 1 MW, 0.1 kg/kW 100 kV DC-DC converter seems to be attainable
in 3 to 5 years. Circuit topology and light weight component technology are key factors in
achieving ultra-lightweight, high power converters. The goal of this work is to demonstrate
a 0.1 kg/kW converter operating at the one megawatt power level.
ACKNOWLEDGEMENTS (U)
This work is being supported by the Strategic Defense Initiative Office through the U.S. Air
Force under funding document MIPR FY1455-89-N0655, June 1989.
REFERENCES (U)
1. M. H. Kheraluwala, "High Power Density DC/DC Converter - Selection of Converter
Topology," Interim Report, NASA Grant No. NAG3-804, June 1988.
2. R. R. Robson, "25 kW Resonant dc/dc Power Converter," Final Report, NASA Contract
No. NAS3-23159, September 1983.
qlF
UNCLASSIFIED
4
UNCLASSIFIED
10,ooo, POWER LEVEL TRENDS
FOR
AEROSPACE MISSIONS
Q0
I-
I-
,I[
3:
o
!
n.
uJj:
o
G.
10OO
100
10
1870
ELECTRIC
1880 1980 2000 2010
INITIAL OPERATING CONDITIONS
2020
MANNED
2030
FIGURE 1.
UNCLASSIFIED
5
Report Documentation PageNaliona[ Aeronautics and
Space Administralion
1. Report No.
NASA TM-102577
4. Title and Subtitle
Power Conditioning Techniques
7, Author(s)
E.D. Baumann
2. Government Accession No,
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
3. Recipient's Catalog No.
5. Report Date
6. Performing Organization Code
8. Performing Organization Report No.
E-5408
10. Work Unit No.
506-41-3F
11. Contract or Grant No.
13. Type of Report and Period Covered
Technical Memorandum
14, Sponsoring Agency Code
15. Supplementary Notes
Prepared for the Neutral Particle Beam Technology Symposium sponsored by Strategic Defense Initiative
Organization, Monterey, California, July 18-21, 1989. This research is supported by the Strategic Defense
Initiative Office through the U.S. Air Force under funding document MIPR FY1455-89-NO655, June 1989.
16. Abstract
This paper discusses the technological developments required to reduce the electrical power system component
weights from the state-of-the-art 2.0 kg/kW to the range of 0.1-0.2 kg/kW.-Power level requirements and their
trends in aerospace applications are identified and presented. The projected weight and launch costs for a IMW
power converter built using state-of-the-art technology are established to illustrate the need for reliable, ultralight-
weight advanced power components. The key factors affecting converter weight are given and some of the
tradeoffs between component ratings and circuit topology are identified. The weight and launch costs for a IMW
converter using 0.1 kg/kW technology are presented. Finally, the objectives and goals of the Multi-Megawatt
Program at the NASA Lewis Research Center, which is funded by the SDIO through the Air Force, are given.
17. Key Words (Suggested by Author(s))
Megawatt
Power systems
Lightweight
18, Distribution Statement
Unclassified- Unlimited
Subject Category 33
19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No, of pages 22, Price*
Unclassified Unclassified 7 A02
NASAFORM1626OCT86 *For sale by the National Technical Information Service, Springfield, Virginia 22161


Power conditioning techniques

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server