The development of technology for a fail-operatonal power system controller (PSC) utilizing microprocessor technology for managing the distribution and power processor subsystems of a large multi-kW space electrical power system is discussed. The specific functions which must be performed by the PSC, the best microprocessor available to do the job, and the feasibility, cost savings, and applications of a PSC were determined. A limited function breadboard version of a PSC was developed to demonstrate the concept and potential cost savings

Graves, J. R.

Lanier, J. R., Jr.

Lollar, L. F.

English

NASA Technical Reports Server

NASA NASA-TP-193919820003236
Technical
Paper
1939
November 1981
Concept for a Power System
Controller for Large Space
Electrical Power Systems
Louis F. Lollar,
Jolm R. Lanier, Jr., " :
and James R. Graves
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https://ntrs.nasa.gov/search.jsp?R=19820003236 2020-03-21T11:32:00+00:00Z

NASA
Technical
Paper
1939
1981
Concept for a Power System
Controller for Large Space
Electrical Power Systems
Louis F. Lollar,
John R. Lanier, Jr.,
and James R. Graves
George C. Marshall Space Flight Center
Marshall Space Flight Center, Alabarna
NIA
National Aeronautics
and Space Administration
Scientific and Technical
Information Branch

TABLE OF CONTENTS
Page
INTRODUCTION ............................ ........................... I
PSC TASKS ........................................................... 1
MICROPROCESSOR COMPARISONS ...................................... 3
PSC FOR THE 25 kW POWER MODULE EPS BREADBOARD .................. 4
PSC EXTRAPOLATION TO A 25 kW POWER MODULE EPS .................... 4
CONCLUSIONS ....................................................... 10
REFERENCES ........................................................ 11
°°°
Ul
LIST OF ILLUSTRATIONS
Figure Title Page
1. Typical electrical power and distribution system ...................... 2
2. 25 kW Power Module breadboard ............ .................... 5
3. SDK-86 system design kit ...................................... 6
4. I]O board .................................................. 7
5. PSC breadboard .............................................. 8
6. General flowchart ............................................ 9
iv
TECHNICAL PAPER
CONCEPT FOR A POWER SYSTEM CONTROLLER FOR
LARGE SPACE ELECTRICAL POWER SYSTEMS
INTRODUCTION
As a result of the Skylab and 25 kW Power Module programs, a need for autono-
mous control of large space electrical power systems has emerged. Autonomous control
implies the need for a device or devices which will make system level decisions and take
the necessary action(s) required to implement the decision(s) correctly and quickly without
a man-machine interface. Therefore, a Marshall Space Flight Center Director's Discretionary
Fund task was undertaken to develop technology for a fail-operational Power System Con-
troller (PSC) utilizing microprocessor technology for managing the distribution and power
processor subsystems of a large multi-kW space Electrical Power System (EPS). The task
involved determining the specific functions which must be performed by the PSC to enable
autonomous EPS operation, determining the best microprocessor available to do the job,
and determining the feasibility, cost savings and applications of a PSC. Finally, a limited
function breadboard version of a PSC was developed to demonstrate the concept and the
potential cost savings of a power system containing a PSC. The results of this task are
discussed in this paper.
PSC TASKS
The primary functions of a PSC are to monitor the status of the Electrical Power
and Distribution System (EPDS) (Fig. 1), make system level computations and decisions,
and to initiate required system actions by appropriate commands to the various distribution
and processing components, such as relays, remote power controllers, remote control circuit
breakers, and programmable power processors (p3). A total of eight specific functions are
required of the PSC to enable autonomous EPS operation. They are as follows:
1) Provide a single point interface between the spacecraft and the power system.
In the case of the 25 kW Power Module, used as a basis for this study, this involves providing
an interface between the p3,s and distribution components and the remote interface unit
(RIU) of the spacecraft command and data handling (C&DH) system.
2) Update subsystem parameters as required for proper management and control
of the EPS. This includes updating voltage and current parameters of individual solar arrays,
batteries, power processors, and buses, either from information located in a storage device,
such as a p3, or sensing these values directly and storing them in the PSC's memory.
] BUS1
1 OF N SA CHG REG •i I
I BAT
I II
I .... _=
I i
I
I
BAT
Figure 1. Typical electrical power and distribution system.
3) Detect EPS faults and take corrective action by load reassignment and/or load
shedding. For example, in a power system with multiple channels, this would involve
detecting a faulted channel, removing it from the load bus, and then, based on system
capability, either shedding loads or re-configuring loads such that they are shared equally
by the remaining channels.
4) Predict load requirements and system capabilities to determine priorities and
sequences of experiment operations to maximize use of available power and experiment
hardware. This involves real-time load management or pre-determined load sequences which
are programmed in the PSC memory prior to launch.
5) Detect system degradation and implement corrective action. This involves moni-
toring the key components of the power system, determining the degree of degradation,
and at some point, reducing the degraded elements load, switching to a redundant element,
or removing the element from service.
6) Implement periodic maintenance procedures to lengthen the life of the system.
An example of this is battery reconditioning which results in extended battery lifetime with
dependable, useable capacity.
7) Adjust subsystem parameters automatically or from ground commands. This
requires sensing subsystem parameters and implementing required parameter changes based
on internal calculations or ground commands.
8) Perform a redundant configuration to assure fail-operational capability.
2
Implementation of these eight functions is feasible with the present EPDS and PSC
state-of-the-art technology. However, as technology advances are made and space power
systems become even more complicated, this list could grow. Therefore, a PSC should be
versatile enough to accommodate additional capabilities in the future.
MICROPROCESSOR COMPARISONS
PSC requirements dictate the use of a fast, powerful central processing unit (CPU).
The CPU must be able to perform numerous string operations, to handle multiple input/
output functions with interrupts and to perform multiplication and division functions
quickly. As a result, two new state-of-the-art 16-bit microprocessors, the ZILOG Z8000 and
the INTEL 8086, were considered and compared in their abilities to perform the necessary
functions required of the PSC.
The Z8000 microprocessor is a register-oriented CPU from Zilog with well-organized
minicomputer-like architecture. Sixteen general-purpose registers, each two-bytes (one 16-
bit word) wide, are available to the user. Over 100 instructions, and 400 combinations of
instructions can be used to manipulate data between the CPU registers, memory and I/O
[11.
The 8086 is a third generation CPU from Intel which is seven to ten times more
powerful than the second generation 8080A. The standard operating speed of the 8086
CPU is 5 MHz (200 nanosecond cycle time) with a selected 8 MHz version also available.
Up to 1 megabyte of memory can be addressed, along with a separate 65K I/O spare. The
CPU has a complement of eight 16-bit general registers. These registers are subdivided into
two sets of four registers each: the data registers, and the pointer and index registers. In
addition, there are four segment registers used to manipulate large (64K) segments of
memory. The 8086 has a repertory of about 100 assembled language instructions which
can be combined to produce about 300 machine-level instructions [2].
Because of the new technology involved with both of these CPU's, complete support
for the devices is difficult to obtain. Using a single board evaluation kit for each of the
CPU's, a comparison was completed with the 8086 CPU used as a baseline for the PSC
software. This was necessary as a result of the lack of Z8000 support at the present time.
The baselined program contained three major operations. These were: (1) I/O
operations to five different devices; (2) string messages and string manipulating; and (3)
moving data into and out of memory. In the 8086 CPU all I/O operations have to use two
fixed registers. One register contains the address of the I/O port and the other contains the
data to be input or output. This limits the programmer since there are a limited number of
registers. The Z8000 CPU can input or output data through any of its 16 registers with the
I/O port being addressed directly. As a result one Z8000 instruction is equivalent to three
8086 instructions in addition to the programmer being able to designate his own register
for I/O operations in the Z8000 CPU. In performing string manipulations, the 8086 CPU
requires approximately 15 instructions to output a known fixed length message. To accom-
plish the same operation in the Z8000 CPU requires approximately 10 instructions. Finally,
because of the limited number of general purpose registers in the 8086 CPU, memory has
to be addressed for temporary storage of data, thus requiring more processing time and
more memory space. In each of these three areas, the 8086 CPU requires more instructions
to do the given job. This results in slower execution time and higher cost due to the longer
programs.
PSC FOR THE 25 kW POWER MODULE EPS BREADBOARD
To demonstrate the PSC concept, a limited function PSC was designed for installa-
tion in the 25 kW Power Module EPS Breadboard (Fig. 2). As previously noted, the 8086
microprocessor was used as the baseline CPU for this PSC. The test PSC consists of an Intel
MCS-86 system design kit, the SDK-86, a printed circuit (PC) board with the I/O devices
and their associated logic, and the PSC software. This breadboard PSC samples data from
the four p3 's in the 25 kW Power Module Breadboard, stores the data in its memory, and
then outputs the data to a teletype on request.
The hardware for the PSC consists of two items, Intel's SDK-86 and the I/O PC
board. The SDK-86 (Fig. 3) consists of the 8086 CPU with a clock frequency of 5 MHz,
8 K bytes of PROM memory, 2 K bytes of RAM memory, and the data bus, address bus and
control bus buffering needed to fan out from the board. The I/O PC board (Fig. 4) consists
of five programmable communication interface integrated circuits (8251A) and the logic
and buffering required to "talk" to the correct device. As a system (Fig. 5), data from any
of the four p3,s may be requested from the teletype, thus simplifying p3 monitoring.
The software for the PSC consists of initialization, repeated sampling, and an
interrupt driven output to the teletype. The general flowchart for the software is shown in
Figure 6. The initialization routine consists of programming the five 8251A's and then
sending a prompt to each p3 to verify correct operation (the program assumes that the four
p3 's are turned on). If there is a problem_ a "Q" is sent back to the teletype informing the
user that a problem has occurred. Next, the program samples each p3 and retrieves the
required data needed to maintain operation of the system. To obtain this data, the user
types a C1, R1, C2, or R2 which stands for Charger 1, Regulator 1, Charger 2, or Regulator
2, respectively. After display the program returns to the sample loop.
PSC EXTRAPOLATION TO A 25 kW POWER MODULE EPS
Using the 25 kW Power Module Phase A EPS concept, a preliminary cost study was
conducted to determine the potential cost savings which could be realized by using a PSC.
The Phase A concept with twenty-four p3,s (12 chargers and 12 regulators) required five
RIU's to interface with the C&DH system. At a cost of $250K for each RIU, the potential
cost savings to be achieved by reducing the number of RIU's required is considerable and
very real.
SOLAR ARRAY SIMULATOR R ARRAY SIMULATOR
I
Figure 2. 25 kW Power Module breadboard.
Figure 3. SDK-86 system design kit.
SDK-86
z
[-.-c/6 I
1--c/6' TO =
,t--c/5 8ZSlA's -- =_ __
AO _ _C/D ; ,
A1 Cl 8251A
A2 R1 8251A
A3 C2 8251A
-
A15 OF R2 8251A ¢o
A14 Im
,DORESSi ,,3 _ IBUS A12OF All ]> _>"= I
soK-88 AlO _ _/
A9 ¢_
A8 ooC TO
'11
A7 -n p3,s
A5
A4
BUFFER _
OFFBOARD ON ]>
-
RD_ _-_
w--_ -__ _'_
ONTO.TO LINE TOSDK--86 BUFFER 8251A'sPCLK_ CLK m_
RESET
OUT _ RESET
Figure 4. I/O board.
--3
oo
_j 8251A
& _ TO p3 C1
ADDRESS BUFFER
16-BIT DECODE
ADDRESS BUS LOGIC AND
BUFFERS
_- _, 8251A
& _ TO p3 R1
BUFFER
I
TO _ +5
POWER
SUPPLIES -12
GND
" (_
SDK-86 ' _- 8251A
& _ TO p3 C2
BUFFER
TELETYPE
& -_ TO p3R2
BUFFER[
8-BIT D._TA BUS II
Figure 5. PSC breadboard.
I NITIALIZE IMEMORY
l-
J INITIALIZE/0 DEVICES I
1
CHECK I
STATUSOF
EACHp3
OUTPUT"o'
AND WAIT
NO _ FORA 'Q'
COMMAND
TO CONTINUE
E5 WHICH_P°
SAMPLE I INTERRiPTED
C1PARAMETERS
_y OUTPUT // PARAMETERSFROM /ES / MEMORYOFTI_AT /
/ PARTICULARP_ /
[ sRA1MPALEAMETERs I
I SAMPLE [C2PARAMETERS
J-_AM,LEIR_,ARA"ETER_!
Figure 6. General flowchart.
9
Using the breadboard PSC data as a baseline, a study of the feasibility of using one
PSC to talk to 24 p3 's and to interface with one RIU was made. Starting with the software,
it was necessary to determine whether the 8086 CPU could sample the needed parameters
of the 24 p3,s fast enough to meet the EPS data requirement of 10 samples/second. Using
the 5 MHz clock cycle time of 8086 CPU, an estimation was made of the calculation times
required for certain functions. For sampling four p3 's and then storing this data in memory,
it takes approximately 42 microseconds to initialize the PSC, 4.25 milliseconds to sample a
charger, and about 2.66 milliseconds to sample a regulator. Expanding this to a system
composed of 12 p3 chargers and 12 p3 regulators, it would take approximately 0.21 milli-
seconds for initialization, 51 milliseconds to sample the chargers, and 32 milliseconds to
sample the regulators. This totals to an approximate time of 83.21 milliseconds which is
below the 100 millisecond minimum requirement.
Again, using the breadboard PSC software as a baseline, the following estimates of
manpower and cost for an in-house design were made:
Packaging Design 0.5 Man Year
Quality Control 0.25 Man Year
Testing 0.25 Man Year
Software (3000 lines 0.75 Man Year
of assembly line
code)
Hardware (piece parts $1 OK
& packaging)
Thus, a total non-recurring development cost of less than 2.0 man years and a recurring
cost of approximately $10K would be required for a PSC. This would result in savings of
approximately $750K on the 25 kW Power Module, even with a redundant PSC and RIU
used.
CONCLUSIONS
This effort, performed using the Center Director's Discretionary Funds, has demon-
strated the viability and the potential for sizeable cost savings by using the PSC concept in
large space electrical power systems. This was the goal of the task. Plans for the future
include expanding the hardware and software to demonstrate additional capabilities in the
25 kW Power Module Breadboard, continued evaluation of the Z8000 CPU, and incorpora-
tion of the concepts developed in a technology program for autonomously managed multi-
hundred kilowatt space power systems. Anticipations are that as technology increases in
the area of smaller, more powerful microcomputers and power control devices, future
large space power systems will require less, rather than more, ground surveillance and
support. This will result in ever increasing cost savings and increased productivity of opera-
tion in space.
10
REFERENCES
1. AM96/4016 AMZ8000 Evaluation Board User's Manual; Advanced Micro
Computers, Publications Department, 3340 Scott Blvd., Santa Clara, CA 95051;
November 1979.
2. The 8086 Family User's Manual; Intel Corporation, Literature Department, 3065
Bowers Avenue, Santa Clara, CA 95051 ; October 1979.
11
I. REPORT NO. 2. GOVERNMENT ACCESSION NO. 3. RECIPIENT_S CATALOG NO.
NASA TP-1939
4. TITLE AND SUBTITLE 5. REPORT DATE
November 1981
Concept for a Power System Controller for Large Space Electrical
Power Systems 6. PERFORMING ORGANIZATION CO,DE
7. AUTHOR(S) B. PERFORMING ORGANIZATION REPORT #
Louis F. Lollar, John R. Lanier, Jr., and James R. Graves
9. PERFORMING ORGANIZATION NAME AND ADDRESS I0. WORK UNIT NO.
M-363
George C. Marshall Space Flight Center 11. CONTRACTORGRANTNO.
Marshall Space Flight Center, AL 35812
13. TYPE OF REPORT & PERIOD COVERED
12. SPONSORING AGENCY NAME AND ADDRESS
National Aeronautics and Space Administration Technical Paper
Washington, D.C. 20546
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
Prepared by Electronics and Control Laboratory, Science and Engineering
16. ABSTRACT
A need for autonomous control of large electrical power systems has emerged. A Marshall
Space Flight Center Director's Discretionary Fund task is undertaken to develop technology for a
fail-operational Power System Controller (PSC)utilizing microprocessor technology for managing
the distribution and power processor subsystems of a large multi-kW space Electrical Power System.
The task involved determining the specific functions which must be performed by the PSC, deter-
mining the best microprocessor available to do the job, and determining the feasibility, cost savings,
and applications of a PSC. A limited function breadboard version of a PSC was developed to demon-
strate the concept and potential cost savings.
17. KE _f WORDS 18. DISTRIBUTION STATEMENT
Power System Controller Unclassified - Unlimited
Large Space Electrical Power Systems
Microprocessors
Subject Category 20
19. SECURITY CLASSIF. (of this report_ 20. SECURITY CLASSI F. (of this page) 21. NO. OF PAGES 22. PRICE
Unclassified Unclassified 14 A02
For sale by National Technical Information Service, Springfield, Virginia 2 21 _ 1

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