A single phase, 440 VRMS, 20 kHz power distribution system with a regulated sinusoidal wave form is discussed. A single phase power system minimizes the wiring, sensing, and control complexities required in a multi-sourced redundantly distributed power system. The single phase addresses only the distribution link; mulitphase lower frequency inputs and outputs accommodation techniques are described. While the 440 V operating potential was initially selected for aircraft operating below 50,000 ft, this potential also appears suitable for space power systems. This voltage choice recognizes a reasonable upper limit for semiconductor ratings, yet will direct synthesis of 220 V, 3 power. A 20 kHz operating frequency was selected to be above the range of audibility, minimize the weight of reactive components, yet allow the construction of single power stages of 25 to 30 kW. The regulated sinusoidal distribution system has several advantages. With a regulated voltage, most ac/dc conversions involve rather simple transformer rectifier applications. A sinusoidal distribution system, when used in conjunction with zero crossing switching, represents a minimal source of EMI. The present state of 20 kHz power technology includes computer controls of voltage and/or frequency, low inductance cable, current limiting circuit protection, bi-directional power flow, and motor/generator operating using standard induction machines. A status update and description of each of these items and their significance is presented

Hansen, I. G.

English

NASA Technical Reports Server

NASA Technical Memorandum 87346
Description of a 20 Kilohertz
Power Distribution System
(NASA-M-87346) DESCBIPIION OF & 20- N86-31584
I KI10HEBTZ POHEB DISTBIBOTIOH SYSTEM (NASA)
7 p CSCL 21E
Dnclas
G3/07 43505
Irving G. Hansen
Lewis Research Center
Cleveland, Ohio
Prepared for the
21st Intersociety Energy Conversion Engineering Conference (IECEC)
cosponsored by the ACS, SAE, ANS, ASME, IEEE, AIAA, and AIChE
San Diego, California, August 25-29, 1986
NASA
https://ntrs.nasa.gov/search.jsp?R=19860022112 2020-03-20T13:11:37+00:00Z
DESCRIPTION OF A 20 KILOHERTZ °OWER .DISTRIBUTION SYSTEM
Irving G. Hansen
National Aeronautics and Space Administration
Lewis Research Center
Cleveland, Ohio 44135
ABSTRACT
The power distribution system to be discussed is
a single phase, 440 VRMS, 20 kHz system, with a regu-
lated sinusoidal wave form. The rationale for select-
ing each of these characteristics follows. A single
phase power system minimizes the wiring, sensing, and
control complexities required in a multi-sourced
redundantly distributed power system. The single
phase addresses only the distribution link, multi
phase lower frequency inputs and outputs accommodation
techniques are described. While the 440 V operating
potential was initially selected for aircraft operat-
ing below 50 000 ft, this potential also appears suit-
able for space power systems. This voltage choice
recognizes a reasonable upper limit for semiconductor
ratings, yet will allow direct synthesis of 220 V, 3
power. A 20 kHz operating frequency was selected to
be above the range of audibility, minimize the weight
of reactive components, yet allow the construction of
single power stages of 25 to 30 kW.
The regulated sinusoidal distribution system has
several advantages. With a regulated voltage, most
ac/dc conversions involve rather simple transformer
rectifier applications. A sinusoidal distribution
system, when used in conjunction with zero crossing
switching, represents a minimal source of EMI. The
present state of 20 kHz power technology includes
computer controls of voltage and/or frequency, low
inductance cable, current limiting circuit protection,
bi-directional power flow, and motor/generator operat-
ing using standard induction machines. A status
update and description of each of these items and
their significance will be presented.
SYSTEM CONCEPTS
The 20 kHz power distribution system is somewhat
like any ac utility power system. Distribution of ac
power allows an easy adjustment of operating voltages
to specific local user needs. Also voltage adjustment
transformers provide the isolation of common mode
potentials necessary to control electrical noise and
cross talk. However, low frequency utility systems
are rotating machine derivatives and are at best
inflexible in accommodating varying voltage or fre-
quency requirements. The 20 kHz system is based upon
rapid semiconductor switching, low stored reactive
energy, and cycle by cycle control of energy flow
allowing the tailoring of voltage levels and wave
shape by synthesis. The fundamental system concept,
is the "split" converter (Fig. 1) in which a conven-
tional dc/ac/dc converter is split into a dc/ac sec-
tion, an ac transmission line, and a ac/dc conversion
section. The converter operating at 20 kHz is of
parallel resonant Mapham configuration (1*) with the
output load across the capacitor. Resonant conversion
in general avoids the high frequency turn off loss
*Numbers in parenthesis designate References at end.
of paper.
term, and the capacitor output provides a suitable
source for voltage distribution. A complete descrip-
tion of the converter circuitry together with full
test data is contained in the final contract report
(2). The systematic advantage of the parallel con-
verter is shown in Fig. 2. Topologically the resonant
inductors act as current sources which are "sunk" by
a single (parallel combination) capacitor. If the
converters are triggered in synchronism no further
control is required for load sharing.
For load conversion the second "half" conversion
may be tailored to user specific requirements
(Fig. 3). Several generic load converter circuits
have been designed and tested (3). These system con-
cepts have been verified using a 25 kW, single phase,
ac test bed system. The system accepts dc or three
phase ac power at any frequency up to 2.5 kHz, con-
verts the power to 20 kHz ac, transmits it over a
100 m line, and load converts it into variable or
fixed voltage ac or dc, or variable frequency ac. All
energy flow, and all set points are under computer
control. Of particular note is the relative simplic-
ity and ease with which variable voltage, variable
frequency power, such as that required for motor oper-
ation may be synthesized. Control circuits designed
for their eventual incorporation into integrated cir-
cuits have been developed to perform the functions
described as well as controlling bi-directional power
flow, and maintaining converter status (4).
A unique regulation scheme also has been devel-
oped (Fig. 4). Regulation is achieved by controlling
a variable phase relationship between phasor summed
synchronized converters. This concept is particularly
valuable when receiving energy from a multi-phase low
frequency source. When a dedicated resonant converter
is employed in each phase, the source "sees" a contin-
uous linear loading which in turn, maintains the sinu-
soidal waveshape of both the voltage and the current.
Maintenance of waveshape fidelity in turn maximizes
conversion efficiency and reduces electro-magnetic
interference.
ELECTROMAGNETIC INTERFERENCE (EMI) - In a high
frequency power system the electromagnetic spectrum
is limited to frequencies evenly clustered about the
fundamental (carrier) frequency. The result is the
capability of accepting and transmitting low frequency
energy without radiating electromagnetic energy at the
low frequencies. Consider a voltage regulated high
frequency power system as shown in Fig. 5. In a low
impedance or regulated power system the voltage must
remain constant. If the system is to deliver only
400 Hz energy for example, the amplitude of 20 kHz
current must then vary at a 400 Hz rate. This ampli-
tude variation results in a class of modulation
defined-as double sideband suppressed carrier. Such
modulation contains only an upper sideband located at
20 kHz + 400 Hz (20 400 Hz), and a lower sideband
located at 20 kHz - 400 Hz (19 600 Hz). Translation
of the low frequency energy to higher frequencies not
only removes the source of low frequency EMI, but
allows shielding to be accomplished much more
efficiently at the higher frequencies.
COMPONENT TECHNOLOGY STATUS
POWER CABLE - As part of the advanced development
effort a low inductance cable was designed (5) to be
compatible with the Lewis Research Center ac test bed.
This particular design (6) is a flat construction to
allow flexure in at least one axis. Each conductor
consists of flat braided individually insulated "Litz"
wires which control the ac resistance at 20 kHz. The
flat conductors comprise a double sided stripline
having very low inductance and as a direct consequence
the radiated magnetic field about the cable is also
very low. Alternate cable configurations, having
similar electrical characteristics are being evaluated
for possible advantages in terms of ease of termina-
tion, additional flexibility, or better adaptation to
inline splicing.
REMOTE POWER CONTROLLER (Leach Corp.) - Contract
No. NASA3-24660 - A current limiting remotely setable
power controller is under development. In addition
to its current limiting protection and power system
programming capabilities this device also provides
current sensing and status required for power system
management. All functions, other than current limit-
ing, are controlled by a computer interface with the
power system controller, the current limiting char-
acteristics of the controller provides not only fault
protection but also protects the power system from
inrush upon load turn on.
BI-DIRECTIONAL CONTROL ELECTRONICS - A high fre-
quency power distribution system involves source con-
version, transmission and user load conversions. In
the assemblage of such a system there occurs many
replications of identical circuit functions. This
contract (4) divided the necessary control functions
into basic blocks which could then be fabricated as
dedicated integrated circuit chips. The following
applications were examined; variable voltage dc input,
and multiphase variable voltage/variable frequency
inputs. Identical outputs were also accommodated and
bi-directional power flow between any combination of
the various inputs and outputs was examined. This
effort resulted in the definition and design of only
seven chips which when properly combined will perform
all the control functions of a multi-kilowatt power
system and provide computer control interfaces. All
voltage set points, current limits, input and output
frequencies, and energy flow are under computer con-
trol. In this capability the computer supplies only
set points, the cycle by cycle control is handled by
the dedicated chips. In case of computer failure the
power system reverts to a "dumb" system status and
controls to the last or other prearranged setpoint.
SEMICONDUCTOR PACKAGING (contract No. NASA3-
24622 - Allen Bradley) - This contract will result in
the development of an improved semiconductor packaging
for high power space environments. The package will
provide long term hermetic sealing of semiconductor
packages. The package also supplies the necessary
electrical/thermal interface separation. Performing
this separation internal to the package provides major
benefits; it allows all electrical connections to be
made at a single surface allowing low inductance con-
nections. Also the electrically "hot" surfaces which
radiate an electric field are held to minimum dimen-
sions and contained within the metallic package. It
is expected that control of the connection inductance
and the common mode capacitance will allow relief of
some parasitic elements and their interference effects
which are common in all power converters.-
DEVELOPMENT OF FAST SWITCHING HIGH POWER SEMI-
CONDUCTORS (RFP 3-170905) -r At this writing proposals
have been received to develop high power semiconduc-
tors which are tailored specifically to 20 kHz
resonant converter applications. The goal of this
work is a device which allows direct offline conver-
sion from a 440 V, 20 kHz power bus. The semiconduc-
tor will be a bilateral conducting device which is
controlled directly from logic power. Functionally
the device will resemble an extremely fast (nanosec-
ond) triac being controlled (off and on) by a logic
gate. This particular device has application in power
converters, load converters and remote power control-
lers. This device.will have a dramatic impact on
reducing the system parts count even further with the
usual attendant improvement in cost and reliability.
20 kHz SYSTEM APPLICATIONS - Two power system
design studies involving 20 kHz technology have been
completed thus far. The first concerned the applica-
tion of high frequency power to an "all electric"
secondary power system for a Boeing 767 (6). In this
study all existing secondary power system functions
were performed by electrically powered systems operat-
ing from a dual redundant 20 kHz power distribution
system. In this application the high frequency power
system resulted in both a significant weight reduction
and an increased efficiency. Overall the aircraft dry
weight was reduced by 10 percent and the fuel consump-
tion was reduced by 9 percent. The second system
design was evaluated as the power distribution system
for the NASA Space Station currently in the study
phase (7). As presently planned, the Space Station
power system will have an initial power capability of
75 kW and allow eventual growth to 300 kW. Both
photovoltaic and solar dynamic power sources are
accommodated with high voltage (440 V) high frequency
power being transmitted station wide. Again evalua-
tions of this particular design showed that the
intrinsic low weight and high efficiency of the 20 kHz
system would result in an initial cost savings of
about 100 million dollars. Several other applications
for high frequency power are under consideration at
this time. Among these are the Naval Air ship pro-
gram, electrically operated flight controllers for
Shuttle II, the SP 100 power system (both the thermo-
electric and Stirling cycle cases), spacecraft 2000
and the newly proposed transatmospheric vehicle.
CONCLUSIONS
The 20 kHz power technology is rapidly approach-
ing technical maturity. It represents a."clean sheet"
end to end system concept and is based upon proven
technology and was designed specifically for aerospace
applications. When the high frequency system is
viewed from a total end to end perspective it requires
a minimum number of power conversion steps. High
efficiency together with low parts count and weight
result in the highest reliability and lowest cost.
In addition, the sinusoidal cycle by cycle energy
control with zero crossing switching provides applica-
tion flexibility and minimizes electromagnetic
interference.
REFERENCES
1. Mapham, N. IEEE Trans. Ind. Gen. Appl., 1967
IGA-3, 176-187.
2. Mildice, J. and Waapes, L., NASA CR-175069, 1986.
3. Mildice, J., NASA CR-175068, 1986.
4. Mildice, J., NASA CR-175070, 1986.
5. Patel, M.R., NASA CR-175071, 1986.
6. Hoffman, A.C., et al., NASA TP-2463, 1985.
7. Hansen, I.G. and Sundberg, G.R., NASA TM-87314,
1986.
DC IN
TO CHANGE DC VOLTAGE LEVELS (DC/DC CONVERTER)
DC/AC/DC CONVERTERS
DC OUT WITH HIGH SWITCHING
(DIFFERENT VOLTAGE) FREQUENCY IN-SERVICE
IN SPACE, ON GROUND,
IN SHIPSSQUARE WAVE AC
DC/AC(l/2 CONVERTER)
^
• LOAD CONVERTER MAY BE TAILORED TO
USER NEEDS
• MINIMUM NUMBER OF POWER
CONVERSION STEPS INVOLVED
• SAME PIECE PARTS AS IN DC/AC/DC
CONVERTER, SEMI-CONDUCTORS,
CAPACITORS, MAGNETICS ETC.
Figure 1.
CONVERTER)
DC OUT
AC OUT
SPLIT SYSTEM
•
i-i RESONANT
J L
 CONVERTER
1
RESONANT
CONVERTER^
. #2
TRANSMISSION
LINE
• OUTPUT CAPACITORS
ARE IN PARALLEL
• IF CONVERTERS ARE IN
SYNCHRONISM THEY SHARE
THE LOAD EQUALLY
• BY CONVERTING TO HIGH FREQUENCY. ANY SOURCE MAY ADD
ENERGY TO THE TRANSMISSION LINE BY ONLY A 1/2 CONVERSION STEP
• MAXIMUM ENERGY AVAILABLE TO A SYSTEM FAULT IS THE CHARGE
STORED IN THE CAPACITORS
Figure 2.
TRANSFORMER
RECTIFIER UNIT (TR)
UNREGULATED D.C.
20KHz
SINE WAVE
VARIABLE VOLTAGE
REGULATED D.C.
20KHz
SINE WAVE
VARIABLE VOLTAGE
VARIABLE FREQUENCY A.C.
20KHz
SINE WAVE
OR
V/F CONTROL FOR
VARIABLE SPEED MOTOR
OPERATION AT HIGH POWER
FACTOR
AVERAGE
LOAD CONVERTERS
Figure 3.
#1 TRIGGER
#2 TRIGGER
VARIABLE DELAY
OF #2 CONVERTER
TRIGGER VARIES <D
E O U T = E 1 + E2
(A). NORMAL
OPERATION
0) NEARLY ZERO ACCOMMODATES
OPEN CIRCUIT SYSTEM VOLTAGE
DROP, COLD TO HOT LOADED ARRAY,
NEW TO OLD ARRAY VOLTAGE
(B) OPERATION WITH
UNLOADED COLD
EOUT FOLD OVER
CURRENT LIMIT
ARRAY (ENERGY STORAGE
FAILURE) ^EARRAY
(C) OPERATION IN A
FOLD OVER MODE
TO LIMIT CURRENT
IN A FAULT
El
\Z LOAD x I LOAD
El
PHASOR REGULATION
Figure 4.
DC OR
400 Hz
SOURCE
SOURCE
CONVERTER
CONSTANT VOLTAGE
20 KHz DISTRIBUTION
SYSTEM
LOAD
CONVERTER
400 Hz
LOAD (MOTOR)
• THE VOLTAGE REMAINS CONSTANT
• THE DISTRIBUTION CURRENT WILL BE 20 KHz WITH A
400 KHz AMPLITUDE VARIATION
sinA sinB = 1/2 cos(A-B)-l/2 cos
(A + B)
(19.6KHz) (20.4KHz)
• THE ENERGY SPECTRUM OF THE DISTRIBUTION SYSTEM CONTAINS
ONLY 19.6 KHz, 20 KHz AND 20.4 KHz
• THERE IS NO LOW FREQUENCY EMI SOURCE PRESENT IN THE
DISTRIBUTION SYSTEM
Figure 5. - System EMI spectrum.
IXXXXXXXXXXXXXXT-
i
, MEASURED DATA ON CABLE
R = 0.83MILLIOHMS/METER
L = 0.035 \i HENRY/METER
C =0.00137 M FARAD/METER
CORONA INCEPTION: 1400 VOLTS
/- PVC SCUFF JACKET
/ LAB TEST ONLY)
,,— "L17Z" RETURN STRAP
'„-— POLYPROPYLENE DIELECTRIC
"— -— "L17Z" HOT CONDUCTOR
—--— "L17Z" RETURN STRAP
OUTER (RETURN) STRAPS
SERVE TO BALANCE AND
CANCEL ELECTRIC AND
MAGNETIC FIELDS
'440VRMS
(60 AMPERE RATING)
Figured.
1. Report No
NASA TM-87346
2. Government Accession No. 3. Recipient's Catalog No.
4. Title and Subtitle 5. Report Date
Description of a 20 Kllohertz Power Distribution
System 6. Performing Organization Code
506-41-4A
7 Authors)
Irving G. Hansen
8 Performing Organization Report No.
E-3094
10. Work Unit No.
9 Performing Organization Name and Address
National Aeronautics and Space Administration
Lewis Research Center
Cleveland, Ohio 44135
11. Contract or Grant No.
12 Sponsoring Agency Name and Address
National Aeronautics and Space Administration
Washington, D.C. 20546
13. Type ol Report and Period Covered
Technical Memorandum
14 Sponsoring Agency Code
15. Supplementary Notes
Prepared for the 21st Intersodety Energy Conversion Engineering Conference
(IECEC), cosponsored by the ACS, SAE, ANS, ASME, IEEE, AIAA, and AIChE, San
Diego, California, August 25-29, 1986.
16. Abstract
The power distribution system to be discussed 1s a single phase, 440 VRMS, 20 kHz
system, with a regulated sinusoidal wave form. The rationale for selecting each
of these characteristics follows. A single phase power system minimizes the
wiring, sensing, and control complexities required 1n a multl-sourced redundantly
distributed power system. The single phase addresses only the distribution link,
multl phase lower frequency Inputs and outputs accommodation techniques are des-
cribed. While the 440 V operating potential was Initially selected for aircraft
operating below 50 000 ft, this potential also appears suitable for space power
systems. This voltage choice recognizes a reasonable upper limit for semiconduc-
tor ratings, yet will allow direct synthesis of 220 V, 3 power. A 20 kHz operat-
ing frequency was selected to be above the range of audibility, minimize the
weight of reactive components, yet allow the construction of single power stages
of 25 to 30 kW. The regulated sinusoidal distribution system has several advan-
tages. With a regulated voltage, most ac/dc conversions Involve rather simple
transformer rectifier applications. A sinusoidal distribution system, when used
1n conjunction with zero crossing switching, represents a minimal source of EMI.
The present state of 20 kHz power technology Includes computer controls of volt-
age and/or frequency, low Inductance cable, current limiting circuit protection,
bi-directional power flow, and motor/generator operating using standard Induction
machines. A status update and description of each of these Items and their sig-
nificance will be presented.
17. Key Words (Suggested by Author(s))
Power system
18 Distribution Statement
Unclassif ied
STAR Category
19 Security Classil (ot this report) 20. Security Classil. (of this page)
Unclassif ied Unclassif ied
- unlimited
07
21. No. of pages 22. Price'
'For sale by the National Technical Intormalio". Service. Sprmglield. Virginia 22)61
National Aeronautics and
Space Administration
Lewis Research Center
Cleveland. Ohio 44135
Official Business
Penalty tor Private Use $300
SECOND CLASS MAIL
ADDRESS CORRECTION REQUESTED
S.MAJL
Postage and Fees Paid
National Aeronautics and
Space Administration
NASA-451
NASA


Description of a 20 Kilohertz power distribution system

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server