WO1998034318A1

WO1998034318A1 - System and method of radio frequency control for aircraft electric power distribution contactors

Info

Publication number: WO1998034318A1
Application number: PCT/US1998/001839
Authority: WO
Inventors: Roy S. Baker
Original assignee: Sundstrand Corporation
Priority date: 1997-01-31
Filing date: 1998-01-30
Publication date: 1998-08-06
Also published as: CA2281711A1

Abstract

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. The switching devices include a digital signal processor and a logic processor for receiving, decoding, conditioning, and controlling the main contactor portion of the device. Additionally, the switching devices 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.

Description

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 electrical 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 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 (HIRF) 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 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 1, 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 of Radio Communication by Asynchronous Transmission of Pulses Containing Address Information and Command Information", granted on September 24, 1968 to Haner. This system uses a single carrier 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 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 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 HIRF 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 further 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 (HIRF) 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 a wireless control system allowing simultaneous control of multiple distribution components

from multiple control units.

Summary of the Invention

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. 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. 5a illustrates an exemplary control word bit pattern in accordance with an aspect

of the instant invention;

FIG. 5b illustrates an exemplary status word bit pattern in accordance with an aspect of

the instant invention; and

FIG. 5c 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 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 (HIRF) 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 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 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 HIRF 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 carrier waveform which may be modulated using a variety of techniques known in the art, such as amplitude modulation, frequency modulation, 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 1 10 providing 4,096

different addressable aircraft should be sufficient as illustrated in FIGs. 5a-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. 5c, or all controllers may

receive and process all information as identified by its source as illustrated in FIGs. 5a, 5b

(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 116 is needed. If more word types are 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. 5 a), 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. 5b or FIG. 5c). 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. 1 is constructed utilizing the power center techniques of U.S.

Patent Number 5,466,974, Aircraft Electric Power Distribution Center, or of U.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 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.

Claims

CLAIMSI claim:

1. An aircraft electric power distribution system, comprising: a first and a second generator driven by external sources of motive power, said first and said second generator producing output electric power; first and second distribution means coupled to said first and said second generators

respectively for distributing said electric power to aircraft electrical loads;

first and second electric power switching means interposed within said first and said second distribution means respectively for interrupting and enabling said distribution of said electric power; and

first and second electric power distribution controllers in wireless communication with each of said first and said second switching means respectively.

2. The system of claim 1, wherein each of said controllers transmits control information to its associated switching means, each associated electric power switching means

interrupting and enabling said distribution of said electric power in response thereto.

3. The system of claim 2, wherein each of said electric power switching means transmits status

information to its associated controller.

4. The system of claim 3, wherein said status information contains controller addressing information.

5. The system of claim 2, wherein each of said electric power switching means transmits status

information to its associated controller upon interrupting and enabling said distribution of said electric power.

6. The system of claim 2, wherein each of said controllers transmits polling information to its

associated electric power switching means, said associated electric power switching means transmitting status information to said controller in response thereto.

7. The system of claim 2, wherein said control information contains electric power switching

means addressing information.

8. The system of claim 7, wherein said first and said second electric switching means are remotely distributed from said first and said second controllers, and wherein said control information contains vehicle addressing information.

9. The system of claim 7, wherein said first and said second electric power switching means

are located in close proximity to said first and said second controllers respectively,

within a first and a second common housing respectively, and wherein said control

information is transmitted at low power so that control of devices external to said first

and said second common housings are not affected.

10. The system of claim 3, wherein each of said first and said second electric power switching means comprises a digital signal processor for conditioning said control information, and logic circuitry, said logic circuitry processing said conditioned control information to control said interruption and enabling of said distribution.

11. The system of claim 10, wherein said logic circuitry monitors a status of said electric

power switching means and commands transmission of said status to said controller.

12. The system of claim 11, wherein each of said first and said second electric power

switching means further comprises means for monitoring electric power current flow through said electric power switching means producing a monitored current signal, and wherein said logic circuitry conditions said monitored current signal producing current flow information, and wherein said status information contains said current flow information.

13. An electric power distribution system for an aircraft having at least two sources of electric

power coupled through a distribution network having individual channels to a plurality

of utilization equipment, each of the individual channels comprising:

electric power switching means for interrupting and enabling a flow of electric power to the utilization equipment coupled to each channel; and a controller in wireless communication with said electric power switching means, said controller transmitting control information to said electric power switching

means; and wherein said electric power switching means transmits status information to said

controller.

14. The system of claim 13, wherein said electric power switching means comprise a plurality

of smart contactors.

15. The system of claim 14, wherein said control information contains contactor addressing information to allow control of individual smart contactors.

16. The system of claim 14, wherein said smart contactors comprise a digital signal processor

for conditioning said control information, and logic circuitry, said logic circuitry processing said conditioned control information to control said interruption and

enabling of said distribution.

17. The system of claim 13, wherein said status information contains controller addressing

information.

18. The system of claim 13, wherein said electric power switching means transmits said status information upon interrupting and enabling said distribution of said electric power.

19. The system of claim 13, wherein said control information comprises polling information,

and wherein said electric power switching means transmits said status information in

response to said polling information.

20. The system of claim 13, wherein said control information comprises vehicle addressing

information.