NASA Technical Reports Server (NTRS) 20000105198: SSP Power Management and Distribution

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Sp'ace Solar Power PMAD 2000 Power System Conference Thomas Lynch
Boeing
SSP Power Management and Distribution
Thomas H. Lynch
Associate Technical Fellow
The Boeing Company
ABSTRACT 'The power level for this study is 3GW. It is
generated by 340 solar arrays, approximately
Space Solar Power is a NASA program 10MW each.
sponsored by Marshall Space Flight
Center. The Paper presented here System Description
represents the architectural study of a
large power management and The PMAD system is comprised of power
distribution (PMAD) system. The processing electronics starting at the solar
PMAD supplies power to a microwave array farm and ending with the microwave
array for power beaming to an earth
rectenna (Rectifier Antenna). The power
Stage A
is in the GW level. conversion _ Stage B
conversion _r*w.,=
at end of
3 Phase tower atantenna _80YVdc
INTRODUCTION
100KV 10KVAC 3.18 GW
10KHz 3 phase
The Space Solar Power PMAD (Power
Management & Distribution) is designed Figure 2
Space Solar Power
to process power from a solar array to
PMAD Block Diagram
the microwave planar antenna. This
paper will describe an architecture for
the PMAD. The power beaming and antenna as shown in the following Figure 2.
rectenna are beyond the scope of this The solar array produces DC at a level of
approximately 5000V. A resonant bridge
paper.
converter' generated a 10KHz sinusoid, three
The following Figure I shows one of the phase at 100KV for the 15 km down link}
system concepts as a tower of solar cable. At the bottom of the cable, the three
arrays feeding a microwave planar array. phase AC is transformer reduced in two steps
to feed 80 VDC to the microwave antenna.
Other array structures have been
proposed but not analyzed to this extent.
Trade Studies
'-I'he PMAD was designed to achieve
minimum mass from the Solar array to the
MMIC antenna array. Cable weight depends
upon current and to lower the weight we are
Figure 1. Sun Tower Concept
driven to high voltages.
07/31/00 Page 1 of 3
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Space Solar Power PMAD 2000 Power System Conference Thomas Lynch
Boeing
The cable weight drove the selection of 10KHz. There is a trade of transformer core
cable voltage. Weight is inverse with weight and loss versus frequency. Through
voltage. The design utilizes 100KV, an iterative design process, we chose 10KHz
three phase AC. This approach as the bus power frequency. Higher
simplifies the upper and lower PMAD frequencies will have serious phase loss.
interface. A transformer can be used to Lower frequencies will increase the
transform the voltage without using solid transformer coupling sizes.
state power conversion. An approach
was show using conventional DC to DC With 1KVDC distribution, the cables were
infrastructure equipment. This has a very too massive, almost equal to the Antenna
heavy weight penalty. Other approaches Converter weight total. This drove a choice
using Super Conductor cable is under of 10KVAC for the distribution cables. The
study. lower transformer had included a 12 pulse
rectifier. This was now placed in the Antenna
At the lower end of the tower, the Converter. The Antenna Converter grows
transformer we encountered a second slightly (16%) versus a Distribution cable
cable distribution weight problem. The gain of 90%.
Lower Transformer was elevated by 100
meters above the Antenna Array to avoid The Antenna Converter sizing is based on the
obstructing the antenna thermal radiation power required by the smallest replaceable
field of view by the size/temperatur e of segment. We used some design rules to
the transformer module [See Figure 3]. establish the sizes and weights. This is shown
With 3GW of power transmission, the in table 1.
transformer was estimated to be 300
Efficiency 95%
degree C because of 51VIW of internal
Density 500 w 3er Ib
dissipation.
Volume 50 w 3er in3
Table 1 Power Supply
Design Factors
The assumption of 95% efficiency is possible
with steady state operation with SSP. It is
also necessary to reduce the thermal rise
Distribution .
within theelectronics. The density and
> Cables
Blind _ /"------ Oneper " volume f_actors preclude use of active cooling
Mating" / , , Antenna
hardware. The module must be designed to
radiate upward away from the antenna array.
._:_.OK'VAC .._ OneAntennaConverter
L_:_Antenna _ _ per64 ElementArray The Antenna Converter contains a
_&,,?_-'4NCoenrvter _ __S_egment
transformer to reduce the 10KV 3 phase AC
PartofAntennaArray to 500VDC with a 12 pulse rectifier. The
Fiaure 3 Antenna Arrav Second stage is a current fed DC-DC
converter down to the 80VDC antenna grid.
The converter was sized with state-of-the-art
This transformer dissipation is primarily
core loss at the chosen fiequency of
07/31/00 Page 2 of 3
Space Solar Power PMAD 2000 Power System Conference Thomas Lynch
Boeing
factors listed in Table 1and the results
ITransformer 3ph 4488W
10KVAC
Weight 2 k9
Volume 8,503 cm3
PMAD
Length 20.4 em
Dissipation 105 Watts
IModule Power 4488 W
.._...i..i_i.i.iii_i.-"..i!_
l Weight 4.1 kg
Volume 1,471 in3
iiiiiiiiiiiiiiiiiiiiiiiiiiiii iiii::-
Length 28.9 cm
Dissipation 224 Watts
_ Element
ITotal 36 cm
Weight 6 kg MMIC Module
Volume 9,974 cm3
Length 21.5 cm Figure 4
Dissipation 329 Watts Placement of Antenna Converter
Table 2
Antenna Converter Sizing
Results and Conclusions
appear in Table 2 below.
The antenna Converter must be closely
Three primary challenges exist for SSP
attached to the 64 element module to
PMAD:
minimize the loss and voltage drops in
* Mass Less than lkg/kw
the 80 volt MMIC input power bus.
, Voltage Greater than IKV
With the estimated power needs of the
• Temperature 300 degree C
64 element l_anel, we calculate a volume
of 9,974 cm" or a cube 21.5 cm on a
These challenges interact. We are driven to
side. We also calculate a thermal loss of
small boxes to keep within the mass
329 watts. This thermal loss must be
allocation. This causes the temperature to rise
radiated outward, preferably away from
because no active cooling - the mass
the antenna. This is a difficult packaging
allocation includes everything the PMAD
problem. The first approach was to
requireg. _
position the power converter on the 64
element array panel..
An estimation of the overall PMAD mass is
tabulated below in Table 3.
We see in Figure 4, the converter covers
kg Ikw
most of the array sub panel. This blocks
ArrayConverters 3_362,061 1.06
the thermal radiation from the MMICs.
UpperTransformer 88,712 0.03
3phasecable 1,463_049 0.46
LowerTransformer 88,712 0.03
An idea is to reduce the aspect ratio of
DistributionCables 390,296 0.12
the converter. For example, the
AntennaConverters 2r890,909 0.91
converter could be squeezed into half of Total 8,283,740 2.61
the thickness with twice the length or
Table 3 PMAD Mass
10.5 by 42 cm. This covers 29% of the
radiating surface of the antenna segment.
The overall factor of 2.61 in the table 3,
This is clearly a difficult design
challenge for the high interface voltage• above, exceeds the allocation of lkg/kw.
07/31/00 Page 3 of3
Space Solar Power PMAD 2000 Power System Conference Thomas Lynch
Boeing
Clearly we have a challenge to reduce
mass. A beginning challenge is to build
a 300 degree C power converter with
less than lkg/kw density. The Array
Converters and the Antenna Converters
are the largest components of the mass
distribution.
PMAD for SSP is a difficult challenge
but no less than the other issues for SSP.
We have 20 years to full deployment to
work through the myriad of issues and
design challenges.
Acknowledgements
This worked was done under funding of
Space Solar SERT contract from MSFC
through Boeing, Huntington Beach. I
wish to thank Mark Henley, Seth Potter
and James McSpadden (Boeing Seattle)
for the many hours of technical
discussions.
List of Acronyms
PMAD Power Management And
Distribution
SSP Space Solar Power
MMIC Monolythic Microwave
Integrated Circuit
GW Gigawatt, 109 watts
/
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