Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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SYSTEM AND METHOD OF RADIO FREQUENCY CONTROL
FOR AIRCRAFT ELECTRIC POWER DISTRIBUTION CONTACTORS
Field of the Invention
The instant invention relates generally to aircraft electric power
distribution systems
and components, and more particularly to the radio frequency control of the
distribution
contactors of an aircraft electric power generation and distribution system.
Background Art
A typical aircraft electric power generation and distribution system for use
on large
commercial aircraft has from two to four main generators, depending on the
number of engines
and system eiectrical load requirements. Each of these generators are coupled
to various load
distribution busses through main line contactors typically known as generator
control breakers
(GCBs). To provide redundancy of power sources and enhanced fault clearing
capability, the
individual generators may also be coupled together through bus tie breakers
(BTBs) on a tie
bus to allow parallel operation. Additionally, at least one auxiliary source
of power is typically
provided on the aircraft to supply power in case of main generator failure, or
on the ground
with main engines shut down. This auxiliary source of power is coupled either
directly to each
of the individual generator busses through individual auxiliary power breakers
(APBs), or to
the tie bus through a single auxiliary power breaker (APB). On four channel
systems, often the
tie bus is separated into two halves by a cross tie breaker (XTB). In this
case the auxiliary
source may be coupled separately to each half of the tie bus by two APBs.
While on the
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ground at the terminal, ground power may be provided to the aircraft through
an external
power breaker (EPB) coupled to the tie bus.
Control for this distribution system is effected through several control
units. Each
individual generating channel is controlled by its own generator control unit
(GCU). In
addition to providing voltage and frequency output regulation of its
generator, the GCU also
coordinates the configuration of its channel by sensing and controlling the
GCB and BTB for
its channel. Coordination of the configuration of the APBs, the EPB, and the
XTB is
accomplished by a bus power control unit (BPCU) which senses and controls
these breakers.
Additionally, since the BPCU is responsible for the coordination of
multichannel operation, it
must also sense the status of the individual channel's breakers.
The status of each of the individual breakers on the aircraft is typically
provided by
auxiliary contacts within the breaker housing. These auxiliary contacts are
actuated by a
transition of the main power contactors of the breaker. The control units use
an open/ground
sense type circuit to detect whether the auxiliary contact is open, indicating
the breaker is
open, or whether the auxiliary contact is closed, indicating the breaker is
closed. Due to the
high intensity radiated fields (HIRE) and lightning strikes to which the
aircraft may be
subjected during flight, two wires (a positive and a return) are used to sense
each auxiliary
contact to prevent coupling of the electromagnetic energy into the control
units. In addition to
the sensing lines, control Lines are also coupled to the breakers. To conserve
energy on the
aircraft, the breakers are typically latching type cut-throat relays requiring
both a trip and a
close command line, as well as a common return line to prevent coupling of the
electromagnetic energy into the control units as described above.
A totaling of these discrete wires for sensing and control of the various
breakers on the
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aircraft results in over one hundred individual wires. In a modern aircraft
utilizing a distributed
distribution system, these wires may be required to be run hundreds of feet
from the control
unit to the distributed distribution center. One problem associated with these
long wire runs is
that the chance of a failure, either an open circuit due to a broken wire or a
short circuit, is
greatly increased. Additionally, the weight of these hundreds of wires run
throughout the
aircraft is a detriment because each pound of additional weight relates
directly to increased fuel
burn, increased cost of operation, and decreased range of the aircraft. These
issues have, to
the present day, been an accepted aspect of aircraft system design.
One method used in other industries to substantially eliminate the need for
sense and
control wires is radio remote control. An early system of radio remote control
for aircraft is
illustrated in U.S. Patent No. 2,580,453, entitled "Remote-Control System for
Aircraft",
granted on January l, 1952 to Murray et al. This early system transmits
control information
from a ground station to control a target plane in flight via manually
selectable channels which
change the transmit frequency to avoid interference with other remotely
controlled aircraft.
However, because of the number of commercial aircraft in service today, the
number of
channels which would be required to ensure no interference between aircraft
becomes
prohibitive.
The problem of requiring multiple frequency channels to control multiple
vehicles is
overcome by U.S. Patent No. 3,403,381, entitled "System ofRadio Communication
by
Asynchronous Transmission of Pulses Containing Address Information and Command
Information", granted on September 24, 1968 to Haner. This system uses a
single Garner
frequency to control multiple vehicles. This control is accomplished by
transmitting pulses
random in time, each pulse containing a single address to identify each
individual vehicle. The
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control information for the vehicle is delayed for a period of time after the
address is
transmitted to avoid inadvertent control of a non-addressed vehicle. Aircraft
control, unlike
the locomotive control of the Haner '381 system, requires the ability for
continuous control.
Only being able to transmit control signals randomly in time, and being
required to delay the
control information for a fixed period is wholly unacceptable for application
on a commercial
aircraft electric power distribution system having multiple controlled
components.
Ground based electric power generation and distribution systems have utilized
radio
remote control for several years. One such ground based system is described in
U.S. Patent
No. 4,199,761, entitled "Multichannel Radio Communication System for Automated
Power
Line Distribution Networks", granted April 22, 1980 to Whyte et al. This
system is based on a
central control transmitter utilizing different frequency channels to control
distribution
equipment within an approximate sixty mile radius. As with the Murray et al.
'453 patent,
however, the number of different channels required to avoid interference
between many aircraft
in and around even a relatively small airport becomes prohibitive.
Another electric power distribution system utilizing radio remote control is
described in
U.S. Patent No. 4,352,992, entitled "Apparatus for Addressably Controlling
Remote Units"
granted October 5, 1982 to Buennagel et al. This remote control system also
uses a central
transmitter to signal individual load controllers which connect and disconnect
various loads to
and from the power generating source. it uses three tone pairs and two
different code sets to
identify and control individual load controllers. While the addressing of
individual load
controllers by zone and address lessens the possibility of a command signal
being wrongly
acted upon by a non-addressed load controller, this system does not
discriminate between, nor
allow for, multiple transmitters. Additionally, the control allows for no
feedback of the actual
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status of the individual load controllers.
While radio remote control has been known and used in these various other
industries
for over fifty years, it has not been used in commercial air transport for
various reasons. One
such reason is the fear that interference from HIRE and lightning strikes as
described above
will interrupt control, resulting in unsafe operation. While at least some of
the above described
systems provide for fail safe operation during lost communications, an
aircraft system cannot
simply scram its generators in mid flight as may be an option for ground based
systems.
Additionally, with an ever increasing number of aircraft in service, there is
a concern that radio
control signals from one aircraft may affect the control of a nearby aircraft.
Unlike a central
transmission based ground system, the internal control of several individual
distribution
systems requires a system unknown in the prior art.
It is, therefore, an objective of the instant invention to provide a new and
improved
system of control for an airborne electric power distribution system. It is a
fixrther objective of
the instant invention to provide a radio frequency control system for an
airborne electric power
distribution system, thus eliminating the requirement of control and sense
wiring to and from
system breakers. Additionally, it is an object of the instant invention to
ensure that control and
status signals from one aircraft do not interfere with the control and status
signals of another
aircraft in close proximity thereto. Further, it is an object of the instant
invention to provide a
wireless control system which can safely control electric power distribution
equipment in the
presence of high intensity radiated electromagnetic fields (HIRE) and during
lightning strikes.
It is also an object of the instant invention to provide wireless feedback
from the controlled
components to all control units. Additionally, it is an object of the instant
invention to provide
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a wireless control system allowing simultaneous control of multiple
distribution components
from multiple control units.
In a preferred embodiment of the instant invention, an aircraft electric power
distribution system comprises two electric power generators each producing
output electric
power which is coupled to aircraft electrical loads by distribution feeders
having electric power
switching devices interposed therein. These switching devices are operative to
interrupt and
enable distribution of the electric power to the aircraft loads. The system of
the instant
invention further comprises electric power distribution controllers which are
in wireless
communication with each of the switching devices. Preferably, control
information is
transmitted to the switching devices individually through the use of contactor
addressing
information to command interruption or enablement of the electric power
distribution.
Additionally, status information is transmitted from the switching devices to
the controllers,
either individually through controller addressing or collectively.
Interference between aircraft
is avoided through the use of vehicle addressing information and/or low power
control and
status signal transmissions.
In a preferred embodiment of the instant invention, the switching devices are
smart
contactors which include a digital signal processor and a logic processor for
receiving,
decoding, conditioning, and controlling the main contactor portion of the
device. Additionally,
the smart contactors include current sensing capability for sensing, scaling,
and transmitting the
current flow information to the controllers for use thereby. The position of
the main contactor
portion of the smart contactor is also monitored and transmitted for use by
the controllers.
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Brief Description of the Drawings
While the specification concludes with claims particularly pointing out and
distinctly
claiming that which is regarded as the present invention, the organization,
the advantages, and
further objects of the invention may be readily ascertained by one skilled in
the art from the
following detailed description when read in conjunction with the accompanying
drawings in
which:
FIG. 1 is a single line interconnect diagram of an electric power generation
and
distribution system to which the instant invention may be applied;
FIG. 2 is a block diagram of a smart contactor comprising an aspect of the
instant
invention;
FIG. 3 is a communication and control block diagram of the contactors of the
instant
invention;
FIG. 4 is a flow diagram of the digital signal processor (DSP) logic of the
instant
invention; and
FIG. Sa illustrates an exemplary control word bit pattern in accordance with
an aspect
of the instant invention;
FIG. Sb illustrates an exemplary status word bit pattern in accordance with an
aspect of
the instant invention; and
FIG. Sc illustrates an alternative exemplary status word bit pattern in
accordance with
an aspect of the instant invention.
Description of the Preferred Embodiments
With reference to FIG. 1, an exemplary embodiment of an aircraft electric
power
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generation and distribution system 10 in accordance with the instant invention
typically
comprises at least two generating channels 12, 14. Each channel is comprised
of a generator
16 (18) which is coupled to a load distribution bus 20 (22), to which is
connected the aircraft's
utilization equipment, through a distribution means 24 (26). Typically, this
distribution means
24 (26) comprises power feeders, bus bars, bus work, cables, wires, etc. A
typical system 10
also includes an auxiliary power unit generator 28 and provision for
connection of a source of
external power 30, although these need not be provided if not required by the
particular system
application. Interposed within the distribution means 24 (26) are electric
power switching
means, illustrated in FIG. 1 as contactors 32-44. The actual switching
mechanism may be
mechanical latching, electrically held, cutthroat, hybrid, solid state, etc.
as the needs of the
system demand. Each of the generating channels 12, 14 are controlled by a
controller, such as
generator control unit (GCU) 46, 48. This control typically combines voltage
regulation,
control, protection, and switching functions. A bus power control unit (BPCU)
50 is also
included to control the bus transfer functions including application of
external and auxiliary
power to the system.
As contemplated by the instant invention, the control of the switching means
(hereinafter contactors) is effected through the use of radio frequency
command and status
signals. In a typical aircraft electric power generation and distribution
system, hard wires are
needed to effectuate the control and status information for these contactors.
Due to the
electromagnetic interference (EMI) and high intensity radiated fields (HIRE)
requirements
imposed on aircraft systems, the number of wires required for each contactor
to provide status
information and to receive trip and close commands becomes excessive. These
wires add
additional weight and cost to the aircraft, as well as reducing the
reliability and increasing the
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complexity of the system. While it may seem obvious to the untrained eye to
use wireless
communications for the contactor control, the electromagnetic environment (up
to 200 volts
per meter radiated fields) and the criticality of the electronic switching
control on an aircraft
has heretofore precluded such application. The instant invention overcomes
these concerns
and provides a reliable means of wireless control of the electric power
switching means for an
aircraft.
As part of the solution to the wireless control problem, the instant invention
contemplates a smart contactor 52 to be included in the electric power
distribution system as
the electric power switching means 32-44 of FIG. 1. These smart contactors 52
comprise a
typical switching mechanism 54 which may be of any typical technology as
discussed above.
The control for the switching mechanism, however, is provided by a contactor
control module
56 which drives a control coil 58 to close a control contactor 60 which
energizes the main
contactor coil 62 to trip or close the main contacts 64a-c. The contactor
control module 56
receives and transmits control and status information via an antenna 66 which
may be
incorporated within the smart contactor housing to minimize the possibility of
damage thereto.
Preferably, the smart contactor 52 also includes current sensing means, such
as current
transformers 68a-c, for providing current flow information to the contactor
control module 56.
The contactor control module 56 may use this information for internal
protection, e.g.,
overcurrent protection of the smart contactor, as well as transmitting this
information to its
associated control unit (46, 48, or 50).
The contactor control module 56, as illustrated in more detail in FIG. 3,
comprises a
receiver 70 coupled through a digitizer 72 to a digital signal processor (DSP)
74. This DSP 74
outputs control information to a coil driver 76, as well as control and status
information to the
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logic processor 78. The coil driver 76 preferably utilizes the aircraft 28
volt supply 80 to drive
the control coil 58 (see FIG. 2). In addition to the inputs received from the
DSP 74, the logic
processor 78 also receives status information from the coil driver 76, from
the current sensors
68a-c, and from auxiliary contacts 82 which transition with the main contacts
64a-c (see FIG.
2). The logic processor also outputs control information to the coil driver
76, as well as status
information to a transmitter 84.
The use of the digitizer 72, the DSP 74, and the logic processor 78 in
combination
enables the use of this wireless technology for an airborne system by ensuring
the reliability
necessary for operation under HIRE conditions. As illustrated in FIG. 4, upon
start up 88, the
digitizer 72 and the DSP 74 extract the control word (control signal) from the
noise 90. The
encrypted control word is then decoded 92 and analyzed. If the control word is
not intended
for this particular contactor 94 {as will be described more fully below), the
algorithm returns to
wait for another signal. If it is determined to be a control signal for this
contactor, the control
word is analyzed to determine if it is a control command 96. If it is a
control command, the
contactor is driven to the commanded state 98. The status of the contactor is
then checked to
verify its status 100, and this information is then transmitted 102. If,
however, the control
word does not contain a control command, the word is analyzed to determine if
it contains a
status request 106. If it does, then the status of the contactor is checked
100, and the
information is transmitted 102. If the analysis of the control word cannot
definitively
determine if it is either a control command or a status request, then a re-
transmit request is
transmitted 108 before the algorithm ends 104.
The control signal is carried by a Garner waveform which may be modulated
using a
variety of techniques known in the art, such as amplitude modulation,
frequency modulation,
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quadrature amplitude modulation, or quadrature digital phase shift keying to
name a few. If
amplitude or frequency modulation is used, the carrier frequency may be
advantageously
between 5 and 10 MHz. The actual amplitude or frequency modulation
transmission frequency
would be in the range of 20 to 30 kHz. This frequency is determined by the
control signal or
control word bit structure as described more fully below.
For the above described system (see FIG. 1) utilizing distributed contactors
32-44, a
system of vehicle or aircraft identification must be included in the control
words to prevent
spurious operation of the contactors on other aircraft due to control
transmissions on the
subject aircraft. Based upon safety margins which take into effect the number
of aircraft in any
regional proximity at any one time, a vehicle address of twelve (12) bits 110
providing 4,096
different addressable aircraft should be sufficient as illustrated in FIGs. Sa-
c. However, if more
addresses are required for perceived safety benefits, more bits may be added
to the vehicle
addressing portion of the control words. These additional bits will only
affect the transmission
rates of the control words, but should not degrade the performance of the
system. In addition
to the vehicle addressing bits, each contactor on the aircraft needs to be
addressed in the
control word. For a system such as is illustrated in FIG. 1, a three (3) bit
contactor address
112 is sufficient, although more may be required for more complex systems.
Additionally,
each controller 46, 48, 50 may be addressed 114 as illustrated in FIG. Sc, or
all controllers may
receive and process all information as identified by its source as illustrated
in FIGs. Sa, Sb
(through the contactor addressing information).
Once the correct vehicle 110 and contactor 112 have been addressed, the type
of word
to follow must be identified. Since the exemplary embodiment of the invention
includes only
control words and status words, a single word type bit I 16 is needed. If more
word types are
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included, more word type bits must be included to identify each type so that
proper decoding
may occur. If the word type bit 116 indicates that a control word is being
transmitted (see
FIG. Sa), the actual control portion of the control word may follow. For the
exemplary
embodiment of the invention described above having trip, close, and request
status commands,
the use of two control bits 118 are sufficient. If the word type bit 116
indicates that a status
word is being transmitted, the status information will follow (see FIG. Sb or
FIG. Sc). Since a
contactor may either be open or closed, a single status bit 120 is sufficient
to indicate its status.
For the monitored current information, the number of current status bits 122
are dependant on
the desired resolution needed for the system. As an example, if the system
current were to
vary from 0 amps to 1000 amps and 8 bits were used, the resolution of the
current transition is
approximately 4 amps. Depending on the needs of the system, more or fewer bits
may be
used.
If the system of FIG. I is constructed utilizing the power center techniques
of U. S.
Patent Number 5,466,974, Aircraft Electric Power Distribution Center, or
ofU.S. Patent
Number 5,594,285, Power Distribution Center, both assigned to the assignee of
the instant
invention, which disclosures are herein incorporated by reference, then the
transmission power
required may be greatly reduced. This has a double benefit in that it
conserves power and that
it dramatically reduces the possibility that another aircraft will pick up the
control
transmissions for the subject aircraft. Utilization of the low power
transmission may eliminate
the need for the vehicle identification bits, allowing the transmission rates
to increase.
Numerous modifications and alternative embodiments of the invention will be
apparent
to those skilled in the art in view of the foregoing description. Accordingly,
this description is
to be construed as illustrative only and is for the purpose of teaching those
skilled in the art the
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best mode of carrying out the invention. The details of the structure may be
varied
substantially without departing from the spirit of the invention, and the
exclusive use of all
modifications which come within the scope of the appended claims is reserved.
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