Note: Descriptions are shown in the official language in which they were submitted.
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A MULTI-VOLTAGE POWER SUPPLY FOR A UNIVERSAL
AIRPLANE GROUND SUPPORT EQUIPMENT CART
This application is a continuation-in-part of U.S. patent application No.
12/250,265
filed October 13, 2008, US publication No. 2009/0121552 Al which is a non-
provisional of
provisional application Serial No. 60/984,164 filed October 31, 2007 and
provisional
application Serial No. 61/036,722 filed March 14, 2008, all of which may be
referred to for
further details.
CROSS-REFERENCE TO RELATED APPLICATIONS
The present patent application is one of a set of commonly owned applications
filed on the same day as the present application, sharing some inventors in
common,
and relating to airplane ground support equipment and carts. The other
applications
in this set, listed here, are noted, namely:
"An Adjustable Cooling System for Airplane Electronics," Jeffrey E. Montminy
and
Steven E. Bivens (US 2009/0107657 Al, Atty. Doc. No. 50-003 ITW 21585U); "A
Frame and Panel System for Constructing Modules to be Installed on an Airplane
Ground Support Equipment Cart," Jeffrey E. Montminy, Brian A. Teeters, and
Kyta
Insixiengmay (US 2009/0108549 Al, Atty. Doc. No. 50-004 ITW 21588U); "A
System of Fasteners for Attaching Panels onto Modules that are to be Installed
on an
Airplane Ground Support Equipment Cart," Jeffrey E. Montminy, Brian A.
Teeters,
and Kyta Insixiengmay (US 2009/0110471 Al, Atty. Doc. No. 50-005 ITW 21587U);
"Airplane Ground Support Equipment Cart Having Extractable Modules and a
Generator Module that is Separable from Power and Air Conditioning Modules,"
James W. Mann, III and Jeffrey E. Montminy (US 2009/0108552 Al, Atty. Doc. No.
50-006 ITW 21586U); "An Adjustable Air Conditioning Control System for a
Universal Airplane Ground Support Equipment Cart," James W. Mann, HI, Jeffrey
E.
Montminy, Benjamin E. Newell, and Ty A. Newell (US 2009/0107159 Al, Atty. Doc.
No. 50-007 ITW 21606U); "A Compact, Modularized Air Conditioning System that
can be Mounted Upon an Airplane Ground Support Equipment Cart," Jeffrey E.
Montminy, Kyta Insixiengmay, James W. Mann, III, Benjamin E. Newell, and Ty A.
Newell (US 2009/0107160 Al, Atty. Doc. No. 50-008 ITW 21583U); and
"Maintenance and Control System for Ground Support Equipment," James W. Mann,
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III, Jeffrey E. Montminy, Steven E. Bivens, and David Wayne Leadingham (US
2009/0112368 Al, Atty. Doc. No. 50-009 ITW 21605U).
BACKGROUND OF THE INVENTION
1. FIELD OF THE INVENTION
The present invention relates generally to the field of power supplies and
more
specifically to multi-voltage power supplies suitable for use in a universal
airplane
ground support equipment cart.
2. DESCRIPTION OF THE RELATED ART
When an airplane is on the ground with its engines shut down, the airplane is
typically unable to provide power for its electrical systems and chilled air
for its air
conditioning systems; and some airplanes are also unable to provide liquid
coolant for
some critical electronic (or "avionic") components. It is customary to connect
such a
grounded airplane to an airplane ground support equipment system. Such a
system
may have its components mounted upon a mobile equipment cart that is called an
airplane ground support equipment cart and that may be parked, placed, or
mounted
conveniently close to an airplane requiring ground support. Such a cart
typically
contains an air conditioner that can provide conditioned and cooled air to an
airplane
plus an electrical power converter that can transform power drawn from the
local
power grid into power of the proper voltage (AC or DC) and frequency required
by
the airplane. Such an airplane ground support equipment cart may also contain
a
diesel engine connected to an electrical generator that enables the cart to
provide both
air conditioning and also electrical power for an airplane without any
connection to
the local power grid. And if an airplane requires a source of cooled liquid
for its
electronics, some carts may also include a source of liquid coolant, typically
a
polyalphaolefin, or PAO, heat transport fluid or liquid coolant.
As discussed when an airplane is on the ground with its engines shut down,
the airplane is typically unable to provide power for its electrical systems;
it is
customary to connect such a grounded airplane to an electrical power supply.
Such a
power supply may have its components permanently mounted in a fixed location
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inside a facility, outside a facility on a tarmac, flight line or similar
area, or the power
supply may be mounted on a mobile platform such as a trailer to allow the
power
supply to be transported between locations. The output cables of this
converter may
connect directly to the aircraft if the location permits, or connected to a
distribution
system in order to supply power to several locations. The electrical power
converter
transforms power drawn from the local power grid into power of the proper
voltage
(AC or DC) and frequency required by the airplane. It is possible that a
facility or
location may need one type of power at the time the converter is initially
installed,
and then require a second type of power as new aircraft arrive on location.
Some airplanes require their electrical power to be adjusted to 115 volts of
alternating current (A.C.) which alternates, or flows back and forth, 400
times each
second (115 volts, 400 Hz A.C.). Other airplanes require 270 volts direct
current (270
volts, D.C.) that does not flow back and forth.
In the past, particularly with regard to military airplanes, such converters
supplied either 400 Hz AC or 270 VDC power depending on the particular type of
aircraft, but not both. A second converter would need to be acquired if the
need arose
for the other type of power.
SUMMARY OF THE INVENTION
An embodiment of the invention relates to a multi-voltage A.C. and D.C.
power supply. A power supply module has an A.C. power input, at least one A.C.
and
one D.C. power output, and an incoming power output selection signal. This
module
contains a sine wave synthesizer which has a D.C. power input and a
synthesized A.C.
power output which connects to the module's A.C. power output, and which
synthesizer also has as an input receiving one or more sine wave synthesizing
control
signals.
In a further embodiment of the invention relates to a multi-voltage A.C. and
D.C. power supply that may be initially delivered as a dual output power
supply, or
may be delivered as one type of power supply upgradable in the field to add
the
second type of power output. For example, a power supply may be delivered with
an
output of 115 VAC, 400 Hz to supply power to aircraft that require this type
of power.
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When new aircraft arrive on location that require 270 VDC power, this power
supply
could then be upgraded on location to add the 270 VDC capability in addition
to the
115 VAC 400 Hz capability. Therefore, the design of these converters not only
includes 115 VAC, 400 Hz and 270 VDC output capability, but also includes the
inherent capability to be upgraded to add the second type of power when only
one
type of power was originally purchased.
A power supply has an A.C. power input, at least one A.C. and/or one D.C.
power output. The power selection may be an incoming power output selection
signal
or input from the operator on the user interface. This power supply, when both
400
Hz and 270 VDC are included, contains a sine wave synthesizer which has a D.C.
power input and a synthesized A.C. power output which connects to the module's
A.C. power output, and which synthesizer also has as an input receiving one or
more
sine wave synthesizing control signals. A first rectifier connects the
module's A.C.
power input to the synthesizer's D.C. power input, and a second rectifier
connects the
synthesizer's A.C. power output to the module's D.C. power output. A control
system receives measurements of voltages at the module's A.C. and D.C. power
outputs and also receives the module's A.C. or D.C. power output selection
signal.
This control system generates the sine wave synthesizing control signals and
adjusts
them to regulate whichever output signal, A.C. or D.C., is selected by the
selection
signals so that selected output signal is maintained at a predetermined A.C.
or D.C.
preset voltage level.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an isometric view of an airplane ground support equipment cart
containing a power conversion module designed in accordance with the present
invention.
FIG. 2 is an isometric view of the cart shown in FIG. 1 with the power
generation module separated from the other elements of the cart.
FIG. 3 is an isometric view of the power conversion module shown in FIG. 1
and FIG. 2 to illustrate how it is mounted to slide away from the cart for
maintenance
purposes.
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FIG. 4 is a block diagram of a multi-voltage power supply for ground support
equipment as constructed in accordance with the present invention.
FIG. 5 is a circuit diagram of one embodiment of a transformer used in FIG. 4.
FIG. 6 is a circuit diagram of one embodiment of a rectifier used in FIG. 4.
FIG. 7 is a circuit diagram of one embodiment of a switching 400-Hz sine
wave synthesizer used in FIG. 4.
FIG. 8 is a circuit diagram of one embodiment of a switch used in FIG. 7.
FIG. 9 is a circuit diagram of one embodiment of an output transformer and
filter used in FIG. 4.
FIG. 10 is a circuit diagram of one embodiment of a 270 V DC rectifier used
in FIG. 4.
FIG. 11 is a circuit diagram of one embodiment of an output clamp switch
used in FIG. 4.
FIG. 12 is a block diagram of the networking together of the various modules
within the cart and the cart control module.
FIG. 13 is an illustration of a main menu that is shown on the display screen
and that permits selection of the type or class of airplane that is to be
serviced.
FIG. 14 is an illustration of the maintenance menu that can be displayed on
the
display screen.
FIG. 15 illustrates an upgrade Rectifier Assembly provided as a factory pre-
build for placement as shown in the power converter module field assembly
400Hz
converter module of FIG. 16 for 270 Volt D.C. electrical power.
FIG. 16 shows the power converter module 400Hz converter assembly
upgraded by having installed the upgrade Rectifier Assembly of FIG. 15 as
illustrated
for D.C. electrical power in accordance with a present described embodiment.
FIG. 17 shows the power converter module upgraded with a field installed
Transformer Rectifier Unit PCB for controlling DC Voltage electrical power.
FIG. 18 shows the power converter module upgraded by having installed the
DC Smoothing Capacitor (3034, 3036, 3038, 3040), DC Output Contactor (3103),
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Transient Dump Resistors (3108), and Output Filter Inductor (3010) for
controlling
DC Voltage levels with placement as illustrated for 270 Volt D.C. electrical
power as
other components that are field installable for upgrade.
FIG. 19 is a block diagram of a multi-voltage power supply for ground support
equipment as constructed in accordance with the present invention.
FIG. 20 is a circuit diagram of one embodiment of a transformer used in FIG.
19.
FIG. 21 is a circuit diagram of one embodiment of a rectifier used in FIG. 19.
FIG. 22 is a circuit diagram of one embodiment of a switching 400-Hz sine
wave synthesizer used in FIG. 19.
FIG. 23 is a circuit diagram of one embodiment of a switch used in FIG. 22.
FIG. 24 is a circuit diagram of one embodiment of an output transformer and
filter used in FIG. 19.
FIG. 25 is a circuit diagram of one embodiment of a 270 V DC rectifier used
in FIG. 19.
FIG. 26 is a circuit diagram of one embodiment of an output clamp switch
used in FIG. 22.
DETAILED DESCRIPTION OF THE INVENTION
The following detailed description includes a first part A, which describes
the
environment of the present invention; and a second part B, which focuses in
particular
on the details of an embodiment the present invention ¨ a multi-voltage
electric power
conversion module.
A. MODULAR AND UNIVERSAL AIRPLANE GROUND SUPPORT
EQUIPMENT CART
Airplane ground support equipment carts are wheeled, towable carts or fixed
mounted (permanently or temporarily) devices that provide air conditioning,
avionics
equipment liquid cooling, and electrical power conversion and generation
services to
airplanes whose engines are shut down. These carts preferably should be
conveyed
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by military and other airplanes to airports and military bases all over the
world, so it
would be convenient and an advantage to have this equipment be no larger than
a
standard military equipment conveyance palette. However, many such carts today
do
not fit one standard palette, and this reduces the numbers of ground support
equipment that is available in the field. Traditionally, such ground support
equipment
carts are custom-designed ¨ they provide such services to only one type or
class of
airplane. Hence, different carts must be provided for each different type of
airplane.
Also traditionally, the air conditioning components mounted on such carts are
so
bulky that they occupy the entire area of the cart, making it necessary to
sandwich
electrical power conversion and other components wherever there is room and
thereby
making it extremely awkward to service or replace such cart-mounted
components.
The present invention is embodied in a universal airplane ground support
equipment cart ¨ universal in the sense that it is designed to service the
varied needs
of a variety of types and classes of airplanes, rather than just one type or
class. This
ground support equipment cart is also modular ¨ its components are rectangular
modules that may be easily separated or removed from the cart for service or
exchange. The modules may also be used independently of the cart, and modules
not
needed for a particular type of airplane may be readily removed and used
elsewhere,
standing by themselves, in a highly flexible manner. Such a cart 10 and
several of its
modules ¨ an electrical power generation module 14, an electrical power
conversion
module 20, and a dual air conditioning module 400 (which also provides PAO
liquid
cooling) ¨ are illustrated in simplified form in FIGS. 1-3. (Much more
detailed
drawings of these components are included in this application and also in the
related
applications cited above).
In use, the cart 10 is mounted near or drawn up to an airplane (not shown) by
a
suitable tractor or truck (not shown). An operator connects an air
conditioning
plenum or air duct 26 from the dual air conditioning module 400 to a cooled
air input
port (not shown) on the airplane. And if the airplane has avionics or other
electronic
components that require a supply of liquid coolant, then the operator also
connects a
pair of PAO liquid coolant conduits 28 from the air conditioning module 400 to
a pair
of PAO ports on the airplane. The operator then uses a suitable electrical
power cable
(not shown) to connect an electrical power output port or receptacle (not
shown in
FIGS. 1-3) on the electrical power conversion module 20 to a matching port or
cable
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on the airplane. To supply the varying needs of different types of airplanes,
there may
be as many as two electrical power conversion modules 20 the cart 10, a first
module
20 having both a 115 volt, 400 Hz AC power output port and also a separate 270
volt
DC power output port, and a second module 1208 (FIG. 12) having a 28 volt DC
power output port (one or the other of these modules 20 or 1208 may be removed
from the cart 10).
Next, with reference to FIGS. 12, the operator depresses a "Start" pushbutton
1216 on the front panel of a control module 22 having a display screen 24 that
then
displays a main menu such as that shown in FIG. 13. If the airplane is a T-50
Golden
Eagle, the operator depresses one of four pushbuttons 1204 that is adjacent
the label
"T-50 Golden Eagle" on this menu (FIG. 13), and then the operator depresses
one of
four pushbuttons 1202 that is adjacent the label "Start" on a "T-50" menu that
then
appears (FIG. 14). In response, all of the modules automatically reconfigure
themselves as needed to service this specific type of airplane with air
conditioning of
the proper pressure and volume of air, with electrical power of the proper
type,
voltage, and frequency, and with liquid coolant (if needed). If the operator
selects the
wrong type of airplane, pressure and air flow measurements can detect this and
shut
down the system, illuminating a colored status light 1214 to signal an error
and
displaying an appropriate error message on the control panel 24 to the
operator. The
system is halted when the operator depresses a "Stop" pushbutton 1218 on the
front of
the control 22 or a pushbutton 1202 or 1204 that is adjacent the label "Stop"
on one
of the display screen 24 menus (FIG. 13 and 14).
A universal airplane ground support equipment cart is designed to provide
flexible support for the needs of many different types and classes of
airplanes having
widely varying air conditioning and liquid cooling and electrical power
support needs.
The present invention can provide different pressures and volumes of cooled
air and
cooled liquid to different airplanes, and it can provide different types and
quantities of
electrical power to different airplanes. It also provides a simplified,
integrated control
panel where airplane service personnel can simply select the type of airplane
that is to
be serviced and have the various appliances on the cart automatically
configured to
optimize the support for that particular type of airplane.
A modular airplane ground support equipment cart is one where the different
support systems provided by the cart are each confined to rugged, compact,
optionally
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EMI shielded, rectangular modules that may be easily removed, serviced,
replaced,
and used stand-alone separate from the cart and its other modular components.
In the cart 10, for example, a two-stage air conditioning module 400 contains
all of the air conditioning components of the cart 10, including a liquid PAO
cooling
system. An electrical power converter module 20 contains the power conversion
components of the cart 10, including a 270 volt D.C. supply and a 115 volt 400
Hz
A.C. supply; and the module 20 may be replaced or supplemented with another
similar module 1208 (FIG. 12) that includes a 28 volt D.C. supply, providing
up to
three different types of electrical power conversion in accordance with the
specialized
needs of different types and classes of airplanes.
A power supply module 14 contains a diesel engine and a generator for
producing 60 cycle, three-phase, 460 volt electrical power when the cart
cannot be
conveniently hooked up to a 360 to 500 volt, 50 or 60 cycle A.C., three phase
supply
provided by the local power grid. The power supply module 14 is confined to
one
end of the cart 10 and may be detached from the cart 10, as is illustrated in
FIG. 2.
Any or all of these modules 14, 20, 400, and 1208 may optionally be equipped
with an internal transformer (not shown) that transforms the incoming high
voltage
electrical power down to 120 volts or 240 volts at 50- or 60-Hz and feeds this
low
voltage to standard, weather protected outlets (not shown) which can be used
to
provide power to hand tools and to portable lighting equipment and the like,
with
ground fault protection also provided to these appliances.
As is illustrated in FIG. 12, a control module 22 is mounted on the cart 10
above the power converter module 20. The control module 22 has on its front
panel a
pair of start and stop pushbuttons 1216 and 1218, colored status lights 1214,
and a
display screen 24 having sets of four pushbuttons 1202 and 1204 positioned
adjacent
the display screen 24's left and right sides. When turned on, the display
screen 24
presents a main menu display, shown in FIG. 13, which permits airplane
maintenance
personnel to select the type of plane that is to be serviced by depressing one
of the
adjacent pushbuttons 1202 and 1204. A special pushbutton depression pattern,
known
only to airplane service personnel, can bring up a maintenance menu display
(not
shown) which permits those service personnel to view and (in some cases) to
alter the
state of the air conditioning and PAO module 400, the electrical power
converter
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modules 20 and 1208, and the power supply module 14. As is illustrated
schematically in FIG. 12, all of the modules 14, 20, 22, 400, and 1208 are
automatically networked together by a network 1212 when they are installed
upon the
cart 10. In addition, each of the modules 14, 20, 22, 400, and 1208 is
equipped with
a network jack (not shown) that can be connected to an external portable
computer
(not shown) which can then serve as the control module and display for all of
the
modules, with mouse clicks on the menus shown in FIGS. 13 and 14 replacing
depressions of the pushbuttons 1202 and 1204.
The cart 10 is optionally mounted upon two wheel and axle truck assemblies
18 and 19. In the space on the cart 10 between the power generation module 14
and
the two-stage air conditioning module 400, one or both of the electrical power
converter modules 20 and 1208 may be slid into place and attached to the cart
10, as
is illustrated in Figures 2 and 3. (If both are installed, they may be on
opposite sides
of the cart, as shown, or they may be installed one above the other.)
If the power generation module 14 is not required for a particular airplane
support task, the module 14 and the wheel and axle truck assembly 19 beneath
the
module 14 may be completely detached from the rest of the cart 10, as is
illustrated in
Figure 2, and removed to be used entirely separately elsewhere, wherever a
portable
source of 60 Hz, 460 volt, three-phase power is required. As illustrated in
FIGS. 2
and 3, the electrical power converter modules 20 and 1208 may be slid out on
tracks
and locked in position to give service personnel convenient access for the
servicing of
these modules 20 and 1208 and their internal electrical and electronic
components.
They may also be removed for repair or for use elsewhere as stand-alone power
converters, or they may be replaced with different power converter modules
that
generate different voltages and frequencies as needed for the servicing of
different
airplanes.
B. DESCRIPTION OF MULTI-VOLTAGE POWER CONVERTER MODULE
While the present invention will be illustrated with reference to a particular
power conversion module 20, having particular components, and used in a
particular
environment, it should be understood at the outset that the invention may also
be
implemented with other power supplies, components, and used in other
environments.
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Referring now to FIG. 4, a multi-voltage power conversion module 20 for
ground support equipment is shown. The module 20 receives multi-phase, 50-Hz
to
60-Hz electrical power in the range of 380 to 500 volts (RMS) from a power
input
402 and transforms it into either 115 volts, 400 Hz, A.C. electrical power or
270 volt
D.C. electrical power in accordance with the electrical power requirements of
the
airplane being serviced. With reference to FIG. 13, the airplane service
personnel
select an airplane by touching the airplane's name on a displayed menu, and
the
electric power converter module 20 responds by programming itself
automatically to
generate whichever of these two voltages that the airplane requires. A
processor 1206
(FIG. 12) within a control module 22 contains a display screen 24. To select
an
airplane, a support technician depresses one of the pushbuttons 1204 to select
an
airplane type, and in response to this, the processor 1206 generates a power
output
selection signal that is conveyed over a bus 1212 to a control system 410
(FIG. 4)
within the power conversion module 20. In response to this signal, the control
system 410 sends out power conversion control signals 606, 708, (etc.)
(described
below) which program the remaining components 400, 500, 600, 700, 900, and
1000
shown in FIG. 4, which may be collectively referred to as a power conversion
system,
to generate a particular type (A.C. or D.C.) and voltage of electrical power
for the
type or class of airplane selected. The control system 410 also monitors (at
442 and at
446) the output A.C. or D.C. voltage and adjusts the power conversion control
signals,
and in particular the sine wave synthesizing control signals 708, to regulate
the output
voltage and to thereby maintain it at a predetermined voltage level, as
mandated by
the power output selection signal.
The incoming power passes from the power input 402 through a common core
filter and inductor circuit 404 to a multi-phase transformer 500. The
transformer 500
creates two out-of-phase sets of multi-phase power signals and feeds them to a
rectifier 600. The rectifier 600 converts the multi-phase 50-Hz to 60-Hz power
signals
into an approximately 600 volt DC signal and presents this DC signal to a
switching
400-Hz sine wave synthesizer 700.
The switching 400-Hz sine wave synthesizer 700 converts the 600 volt DC
power signal into a 400-Hz 115 volt multi-phase (RMS) power signal (as is
explained
below, this voltage will vary from 115 volts when 270 volts of D.C. power is
being
generated). The 400-Hz multi-phase power signal is fed into a transformer and
filter
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circuit 900, which filters and smoothes the 400-Hz power signal into a
relatively pure
sine wave signal. The smoothed 400-Hz 115 volt (RMS) multi-phase power signal
is
then fed to first and second output switches 406 and 408.
The first output switch 406 connects the 115 volt 400-Hz A.C. multi-phase
power signals A, B, and C to the module 20's 115 volt 400 Hz A.C. power output
407. The 115 volt A.C. power signals then flow from the 115 volt 400-Hz A.C.
power output 407 over suitable cables to an airplane requiring 115 volt 400 Hz
A.C.
power. The second output switch 408 connects that same multi-phase set of
power
signals to a rectifier 1000. The rectifier 1000 converts the 400-Hz 115 volts
(RMS)
multi-phase power signal into 270 volt DC power signals V2+ and V2- that pass
through an airplane disconnect switch 1103 and a clamp circuit 1100 and flow
to the
module 20's 270 volt D.C. power output 409. The clamp circuit 1100 protects
the
circuitry within the power converter module 20 from transients. The 270 volt
DC
power signals then flow from the 270 volt D.C. power output 409 over suitable
cables
to an airplane requiring 270 volt DC power.
Referring now to FIG. 5, the power transformer 500 receives an input multi-
phase electrical power signal 502 from the common core filter and inductor
circuit
404 which was described in FIG. 4. Within the power transformer 500, the input
multi-phase power signal 502 is sent through an input set of Y windings 504.
The
power transformer produces two multi-phase power signal outputs. A Y-connected
set of secondary windings 506 produces a set of output power signals 510, and
a
second delta connected set of windings 508 produces a set of output power
signals
512, out of phase with the signals 510. Both sets of output signals 510 and
512 are
fed to a rectifier 600 as described in FIG. 6. (The transformer 500 is an ITW
Military
part, number TT5105.)
Referring now to FIG. 6, a rectifier circuit 600 receives the two multi-phase
power signal outputs 510 and 512 from the power transformer 500. Each of the
multi-
phase power signals 510 and 512 is fed to a rectifying circuit comprising a
diode 604
and a thyristor 602.
The rectifier circuit 600 is comprised of 6 sets each including a thyristor
and a
diode used in combination. Using the first thyristor and diode set as an
example, this
set includes the diode 604 and the thyristor 602 which together receive a
power signal
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from the power transformer 500 described in FIG. 5. The received power signal
is the
signal Ui, one of the six signals which from the pair of multi-phase power
signals 510
and 512 that flow out of the power transformer 500. The first set of multi-
phase power
signals 510 are represented as a multi-phase set of three AC power signals U1,
V1, and
W1. The second set of multi-phase power signals 512 are represented as a multi-
phase set of three AC power signals U2, V2, and W2. As shown, the AC power
signal
U1 is connected to the cathode of the diode 604 and to the anode of the
thyristor 602
of the first thyristor and diode set. The gate of the thyristor 602 receives
triggering
timing signals 606 from the control system 410 which can vary the performance
of the
rectifier circuit 600. The cathode of the thyristor 602 is connected to the
positive
output terminal V1+ of the rectifier circuit 600. The anode of the diodes 604
is
connected to the negative output terminal V1-. Each of the remaining five
thyristor
and diode sets is connected in the same manner to differently-phased incoming
signals
and to the same output signals. Timing signals 606 are used to gate the
thyristors at
startup. The gating of the thyristors at startup allows the input current from
the power
input 402 to never increase above the maximum rated current as capacitor 432
is
charged from a zero potential. This provides a soft-start function which
precludes an
overload trip of the power source connected to the power input 402.
A filter capacitor 432, shown in FIG. 4, is connected across the rectifier
circuit
600's D.C. output terminals V1+ and V1-. The six sets of thyristors and diodes
act as
A.C. voltage positive and negative peak detectors and rectifiers which fully
charge
this D.C. output filter capacitor 432 (shown in FIG. 1) six times during each
cycle of
the incoming A.C. power signal to a voltage level that approximately equals
the
difference between the most positive and the most negative voltage levels
reached by
these power signals. The six signals U1, Vi, W1, U2, V2, and W2 each peak
positively
and negatively at six different times within each 50th or 60th of a second
(depending
upon the frequency of the incoming power signal). Whenever one of these six
signals
reaches its peak positive voltage, another one of these same six signals
simultaneously
reaches its peak negative voltage; and these two peaking signals work together
to
fully charge the filter capacitor 432. The signal peaking in the positive
direction
supplies cun-ent through its corresponding diode into the V+ terminal of the
capacitor
432, and simultaneously the signal peaking in the negative direction draws
current
through its corresponding thyristor from the V- terminal of the capacitor 432,
thereby
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fully charging the capacitor 432 to approximately the voltage level difference
between
the positive and negative peak signals.
The capacitor 432, a 37 microfarad, high voltage capacitor, acts as a
smoothing capacitor to smooth out the resulting D.C. power signal produced by
the
rectifier 600. The V1+ and V1- output terminals feed this D.C. power directly
into the
switching 400-Hz sine wave synthesizer and filter circuit 700 which is
described in
FIG. 7.
Referring now to FIG. 7, the switching 400-Hz sine wave synthesizer 700 is
shown. This circuit includes six pairs of switches 702 and 704 connected in
series
across Vi+ and Vi- (FIGS. 1 and 6) as shown. A typical pair of switches
comprises a
first switch 704 and a second switch 702 which are shown in FIG. 7 connected
in
series. The first switch 704 connects to V1+ and the second switch connects to
V1-.
The junction 706 of the first and second switches 704 and 702 presents a power
signal
li that is a pulse-width-modulated square wave that fluctuates between three
states
V1+, V1-, or 0 V. Switches 704 and 702 construct the pulse-width-modulated
representation of the 400Hz power signal at phase A of transformer 900. When
the
voltage at phase A of transformer 900 is positive, the power signal 1 I will
switch
between 0 V and V1+, and when negative power signal 1 I will switch between OV
and
V1-. Every 83.33 [Es (12 kHz) the possibility of the switch changing state
exists and is
based on load. Connected to both the first and second switches 702 and 704 are
pulse-width-modulated switching control signals 708 that originate in the
control
system 410. The control system 410 generates these switching signals to cause
the
first and second switches 702 704 to alternate in conducting the respective
V1+ and
V1- power signals into the power signal 1 1. This alternation is timed in such
a manner
that, after all higher harmonics above the 400 Hz fundamental have been
filtered out
(by the output transformer and filter 900 and the capacitors 34, 36, and 38),
the signal
li becomes a sinusoid having a controlled amplitude which may be adjusted by
the
control system 410 to regulate the output voltage level supplied to an
airplane.
A companion signal 12 is generated in a similar manner, but is out of phase
with the signal 1 1. Additional pairs of signals 21 and 22 and also 31 and 32
are
generated in the same manner as just described for the signals li, and 12, but
the
signals 21 and 22 are 120 degrees phase shifted with respect to the signals li
and 12;
and the signals 31 and 32 are 240 degrees phase shifted with respect to the
signals li
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and 12. Accordingly, after filtering, the signals shown at 710 become a 3-
phase, 400
Hz set of power signals.
In FIG. 4, current amplitude "I" is measured in the output signals 12, 22, and
32. These current measurements 448 are relayed to the control system 410
(measurements 440) as a measure of the current and power being drawn from the
power converter module 20. Hall effect current sensors are used to measure
current.
These can be obtained from the LEM SA (Geneva, Switzerland) as current
transducer
part number LF 505-S.
Referring now to FIG. 8, a circuit diagram of the switches used in FIG. 7 is
shown. The switch 702 in an IGBT transistor which, as shown, may be visualized
as
a power field effect transistor having a gate 810 and having incorporated into
its
design a diode 804 interconnecting its source 806 and drain 808. The switch
702 thus
operates somewhat as a switch bypassed by a diode. The switch 702 is an
integrated
circuit manufactured by Eupec, Inc. (Lebanon, New Jersey) with part number
BSM300GB120DLC.
The power output signals 710 of the 400-Hz sine wave synthesizer 700 are fed
through a power output transformer and filter 900 shown in FIG. 9. The pair of
power
output signals 11 and 12 are applied to a first winding of the power output
transformer
900's primary windings 904. The pair of power output signals 21 and 22 are fed
to a
second winding of the power output transformer 900's primary windings 904. The
pair of power output signals 31 and 32 is fed to a third winding of the power
output
transformer 900's primary windings 904.
Secondary windings 906 on the other side of the transformer and filter 900
present multi-phase, sinusoidal, Y-connected power output signals 908 which
are
labeled A, B, C, and N for neutral. These power output signals present multi-
phase,
400-Hz power whenever the module 20 is in operation. The voltage presented
varies
depending upon the output voltage which the electric power converter module 20
is
called upon to produce. The control system 410 measures the voltages presented
by
the signals A. B, and C, and these voltage measurements 442 are fed into the
control
system 410 as part of the voltage and current measurements 440. When the
module
20 is called upon to generate 115 volts 400 Hz A.C. power, the control system
410
commands the sine wave synthesizer 700 to produce waveforms on the signal
lines li,
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12, 21, 22, 31, and 32 adjusted in pulse width to maintain the sinusoidal
voltages
presented by the signals A, B, and C (measured at 442) at 115 volts (RMS)
independent of the load. However, the system shuts down if the current and
power
drain is excessive (power is voltage multiplied by current). Different current
and
power limits may be established for different airplanes. The control system
410
closes the switch 406 and presents the power signals A, B, and C at the 115
volt 400
Hz A.C. power output 407 which are connected to the airplane by suitable
cables.
The voltage measurement 442 is a measurement of the voltage at the power
output
407 when the switch 406 is closed.
When the power converter module 20 is called upon to generate 270 volts
D.C. for an airplane requiring power converted in this manner, the control
system 410
opens the switch 406 and closes the switch 408 so that the signals A, B, and C
are fed
through and rectified by the 270 volt D.C. rectifier 1000 and are presented at
the 270
volt D.C. power output 409 which are connected to the airplane by suitable
cables.
The control system 410 ignores the voltage of the signals A, B, and C and
measures
instead the D.C. output current I (current measurement 448) and voltage V2+
(voltage
measurement 446) both of which are measured at the positive terminal of the
D.C.
power output 409 (in FIG. 4) and adjusts the pulse widths generated by the
sine wave
synthesizer 700 to produce waveforms on the signal lines 11, 12, 21, 22, 31,
and 32
adjusted in pulse width to hold the D.C. output voltage stable at 270 volts,
provided
the current and power drain is not excessive. Different current and power
limits may
be established for different airplanes.
As was just explained, the signals 908 (A, B, and C) are routed (in FIG. 4) to
a
first A.C. output switch 406 and to a second D.C. output switch 408. The
signals 908
(A, B, and C) are also connected to a set of smoothing capacitors 434, 436,
and 438
(shown in FIG. 4) which further suppress any remaining harmonics of 400
cycles.
Referring now to FIG. 10, the second rectifier 1000 is shown. The rectifier
1000 rectifies the 400 Hz power signals A, B, and C 908 whenever the D.C.
power
switch 408 is closed. When 270 volts D.C. is being generated, the voltages
presented
by the power signals A, B, and C are adjusted up or down to maintain the 270
volt
D.C. power output 409 (FIG. 4) at 270 volts D.C. FIG. 10 shows that each of
the
three power signals A, B, and C (shown at 908) is connected to a respective
set of
four rectifier diodes 1002, 1004, and 1006. Each set 1002, 1004, and 1006 of
four
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diodes, for example the illustrative set of four diodes 1016, 1018, 1020, and
1022,
includes two pairs of diodes 1016-1018 and 1020-1022 connected in parallel.
The
anodes of the two parallel-connected diodes 1016-1018 connect to the power
signal
A, and the cathodes of these two diodes connect to a D.C. positive output line
1030.
The cathodes of the two parallel-connected diodes 1020-1022 connect to the
power
signal A, and the anodes of these two diodes connect to a D.C. negative output
line
1032. The remaining two four-diode sets 1004 and 1006, likewise, respectively
connect the incoming power lines B and C to the positive and negative output
lines
1030 and 1032. The output lines 1030 and 1032 are coupled to a first filter
capacitor
1008. The circuit arrangement just described causes the diode sets 1002, 1004,
and
1006 to develop across the filter capacitor 1008 a D.C. voltage that
approximately
equals the instantaneous voltage difference between the most positive and the
most
negative voltage swings of the three power signals A, B, and C, in signal peak
detector rectifier fashion.
D.C. current flows from capacitor 1008 through a filter inductor 1010 and into
a bank of four 4700uf, 400 volt filter capacitors 1034, 1026, 1038, and 1040.
The
DC voltage developed across this bank of filter capacitors is presented as the
270 volt
filtered D.C. output voltage V2+ and V2- at 1028.
Referring now to FIG. 11, the clamp circuit 1100 is shown. This clamp circuit
1100 includes a voltage-spike-capturing capacitor 1118 and an electronic clamp
circuit 1104-1106 which is connected directly across the 270 volt D.C. power
output
409 of the electrical power conditioning module 20 (shown in FIG. 4). This
clamp
circuit is connected in series with the airplane disconnect switch 1103 (a
relay
controlled by the control system 410) across the 270 volt D.C. power signals
V2+ and
V2- 1028 which flow from the rectifier 1000 (shown in FIG. 10). The capacitor
1110
protects the electronic clamp circuits from sudden transient voltage rises
that might
exceed the breakdown voltages of the switches 1104, 1106, 1112, and 1114. The
two
clamp circuits 1104-1106 and 1112-1114 short out surge currents caused by
arcing or
inductive arc back or other sources of electrical transients that might feed
back from
an airplane. When the switch 1103 disconnects the D.C. power supply entirely
from
the airplane, the clamp circuit 1100 prevents arcing of the relay contact
points of the
switch 1103 and dissipates any charge that may be stored on the DC buss
attached to
the converter. In some circumstances it is possible for the airplane to feed
power back
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towards the converter. During such events, the clamping circuit 1100
dissipates such
power and prevents arcing across the switch 1103 and damage to the power
supply
while the feedback event is ongoing.
The clamp circuit 1100 contains a serially-connected pair of electronic
switches 1104-1106. These switches are of the type shown in FIG. 8.
The pair of switches 1104-1106 includes a first switch 1106 and a second
switch 1104 connected with the source and gate of the second switch 1104
connected
to the drain of the first switch 1106 as shown (FIGS. 8 and 11). The source
and drain
of the first switch 1106 are connected in parallel with a capacitor 1110. The
source
and gate of the first switch 1106 are connected to the control system 410 by
clamping
emergency signals 1116. The source and drain of the second switch 1104 are
connected in parallel with a resister 1108. This arrangement makes it possible
for the
two switches to withstand the high voltages that can arise at this point in
the circuit.
With reference to FIG. 4, to enable the control system 410 to provide all the
control signals described above, the control system must receive measurements
of
voltage "V" and of current "I" at both the 115 volt 400 Hz A.C. power signal
output
407 and at the 270 volt D.C. power output 409. As can be seen in FIG. 4, both
voltage and current are measured at the D.C. power output 409. The 400 Hz.
A.C.
voltages are measured at the signals A, B, and C, and the 400 Hz. A. C.
current is
measured using Hall effect current sensors at the signals 12, 22, and 32.
These voltage
and current measurements are fed into the control system 410, and the control
system
410 analyzes the appropriate ones of these voltages and currents and then
makes the
necessary corrections in the width of the pulses that comprise the switching
control
signals 708 to either stabilize the 400 Hz. A.C. voltage at 115 volts or to
stabilize the
D.C. voltage at 270 volts, whichever type of power is currently being fed to
an
airplane.
Referring now to Fig. 12, a block diagram of the signal interaction between
the various modules of the ground support equipment cart 10 is illustrated.
The
display 24 and a universal control and diagnostic processor 1206 are part of
the
control module 22. The display 24 normally displays to the user the main menu
that
is shown in FIG. 13. This main menu permits the user to configure all the
modules on
the cart 10 for a particular type or class of airplane by simply depressing
one of the
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push buttons 1202 or 1204 that designates the type or class of airplane that
is to be
serviced. Once an airplane type or class is designated, the universal control
and
diagnostic processor 1206 sends control signals to a network bus driver 1210
and over
a CAN bus 1212 to the various modules14, 20, 400, and 1208 that are mounted
upon
the ground support equipment cart 10. The various modules 14, 20, 400, and
1208 are
configured by these signals so that all the modules can be used safely with
the user-
selected type or class of airplane. In the case of the power converter module
20, the
control signals cause the control system 410 to: close the switch 406 if the
airplane
requires 115 volt, 400 Hz power; close the switch 408 if the airplane requires
270 volt
D.C. power; or open both the switches 406 and 408 if the airplane requires 28
volts
D.C. power ¨ in which case the control signals turn on the 240 volt D.C. power
converter module 1208 if it is present on the cart 10.
Referring now to Fig. 13, the main menu of the display 24 is shown. The
display 24 allows a user to designate a specific type or class of airplane, in
which case
all of the modules are automatically configured properly for that particular
type or
class of airplane. The user may also select some other option, such as
"Maintenance."
If the user selects the "Maintenance" option, then the maintenance menu shown
in
FIG. 14 is displayed. One of the options on this maintenance menu is "270 Volt
Maintenance," which leads to one or more screens that report the status of the
power
conversion module 20 ¨ such things as voltage, cuiTent, and power generated,
state
(115 volt 400 Hz A.C., 270 volt D.C., or standby), and history log. Service
personnel
with the proper passwords may be permitted to alter various characteristics,
such as
the voltage level and the alarming and shut-down current and power levels.
FIG. 15 illustrates an upgrade Rectifier Assembly 2100, provided as a factory
pre-build for placement as shown in FIG. 16 and described below, pre-built in
factory
for placement in the power converter module 21 which receives multi-phase, 50-
Hz to
60-Hz electrical power in the range of 380 to 500 volts (RMS) from a power
input
2402, allowing the upgrade Rectifier Assembly 2100 to transforms into A.C.
electrical
power to 270 Volt D.C. electrical power. FIG. 16 shows the power converter
module
21, a field assembly 400Hz converter module which generates 115 volts, 400 Hz,
A.C. electrical power as upgraded by having installed the upgrade Rectifier
Assembly
2100 with placement as illustrated for 270 Volt D.C. electrical power as
described
herein. FIG. 17 shows the power converter module 21 upgraded by having a field
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installed Transformer Rectifier Unit (PCB 3000) for controlling DC Voltage
levels
with placement as illustrated for 270 Volt D.C. electrical power. FIG. 18
shows the
power converter module 21 upgraded by having installed the DC Smoothing
Capacitor (3034, 3036, 3038, 3040), DC Output Contactor (3103), Transient Dump
Resistors (3108), and Output Filter Inductor (3010) for controlling DC Voltage
levels
with placement as illustrated for 270 Volt D.C. electrical power as other
components
that are field installable for upgrade.
Referring now to FIG. 19, an alternate embodiment multi-voltage power
supply for ground support equipment is shown. While the present invention will
be
illustrated with reference to a particular power supply, having particular
components,
and used in a particular environment, it should be understood at the outset
that the
invention may also be implemented with other power supplies, components, and
used
in other environments. The module 21 receives multi-phase, 50-Hz to 60-Hz
electrical power in the range of 380 to 500 volts (RMS) from a power input
2402 and
transforms it into either 115 volts, 400 Hz, A.C. electrical power or 270 volt
D.C.
electrical power in accordance with the electrical power requirements of the
airplane
being serviced. The power output type desired may be by a remote control
panel,
external signal, or input from the control panel on the power supply itself.
In
response to one of these signals, the control system 2410 sends out power
conversion
control signals 2606, 2708, (etc.) (described below) which program the
remaining
components 2400, 2500, 2600, 2700, 2900, and 3000 shown in FIG. 19, which may
be collectively referred to as a power conversion system, to generate a
particular type
(A.C. or D.C.) and voltage of electrical power for the type or class of
airplane being
serviced. The control system 2410 also monitors (at 2442 and at 2446) the
output
A.C. or D.C. voltage and adjusts the power conversion control signals, and in
particular the sine wave synthesizing control signals 2708, to regulate the
output
voltage and to thereby maintain it at a predetermined voltage level, as
mandated by
the power output selection signal. The control system generates the power
conversion
control signal and adjusts it to regulate the power module's output to a
predetermined
preset voltage level as mandated by the power output selection signal. In the
present
described embodiment a multi-voltage or upgradable power supply has A.C. and
D.C.
capability, A.C. only capability with an upgrade kit available to add D.C.
capability in
addition to the A.C. capability, D.C. only capability with an upgrade kit
available to
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add A.C. capability in addition to the D.C. capability. The power supply
module,
which has an A.C. power input, at least one power output, and which, receives,
when
A.C. and D.C. output capability are installed, the power output selection
signal as an
incoming signal or by selection from the operator.
The incoming power passes from the power input 2402 through a common
core filter and inductor circuit 2404 to a multi-phase transformer 2500. The
transformer 2500 creates two out-of-phase sets of multi-phase power signals
and
feeds them to a rectifier 2600. The rectifier 2600 converts the multi-phase 50-
Hz to
60-Hz power signals into an approximately 600 volt DC signal and presents this
DC
signal to a switching 400-Hz sine wave synthesizer 2700.
The switching 400-Hz sine wave synthesizer 2700 converts the 600 volt DC
power signal into a 400-Hz 115 volt A.C. multi-phase (RMS) power signal (as is
explained below, this voltage will vary from 115 volts when 270 volts of D.C.
power
is being generated). The 400-Hz multi-phase power signal is fed into a
transformer
and filter circuit 2900, which filters and smoothes the 400-Hz power signal
into a
relatively pure sine wave signal. The smoothed 400-Hz 115 volt (RMS) multi-
phase
power signal is then fed to first and second output switches 2406 and 2408.
The first output switch 2406 connects the 115 volt 400-Hz A.C. multi-phase
power signals A, B, and C to the module 21's 115 volt 400 Hz A.C. power output
2407. The 115 volt A.C. power signals then flow from the 115 volt 400-Hz A.C.
power output 2407 over suitable cables to an airplane requiring 115 volt 400
Hz A.C.
power. The second output switch 2408 connects that same multi-phase set of
power
signals to a rectifier 3000. The rectifier 3000 converts the 400-Hz 115 volts
(RMS)
multi-phase power signal into 270 volt DC power signals, V2+ and V2-, that
pass
through an airplane disconnect switch 1103 and a clamp circuit 3100 and flow
to the
module 21's 270 volt D.C. power output 2409. The clamp circuit 3100 protects
the
circuitry within the power converter module 21 from transients. The 270 volt
DC
power signals then flow from the 270 volt D.C. power output 2409 over suitable
cables to an airplane requiring 270 volt DC power.
Referring now to FIG. 20, the power transformer 2500 receives an input multi-
phase electrical power signal 2502 from the common core filter and inductor
circuit
2404, which was described in FIG. 22. Within the power transformer 2500, the
input
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multi-phase power signal 2502 is sent through an input set of Y windings 2504.
The
power transformer produces two multi-phase power signal outputs. A Y-connected
set of secondary windings 2506 produces a set of output power signals 2510,
and a
second delta connected set of windings 2508 produces a set of output power
signals
2512, out of phase with the signals 2510. Both sets of output signals 2510 and
2512
are fed to a rectifier 2600 as described. (The transformer 500 is an ITW
Military part,
number TT5105.)
Referring now to FIG. 21, a rectifier circuit 2600 receives the two multi-
phase
power signal outputs 2510 and 2512 from the power transformer 2500. Each of
the
multi-phase power signals 2510 and 2512 is fed to a rectifying circuit
comprising a
diode 2604 and a thyristor 2602.
The rectifier circuit 2600 is comprised of 6 sets each including a thyristor
and
a diode used in combination. Using the first thyristor and diode set as an
example, this
set includes the diode 2604 and the thyristor 2602 which together receive a
power
signal from the power transformer 2500 described. The received power signal is
the
signal Ul, one of the six signals, which from the pair of multi-phase power
signals
2510 and 2512 that flow out of the power transformer 2500. The first set of
multi-
phase power signals 2510 are represented as a multi-phase set of three AC
power
signals Ul, V1, and Wl. The second set of multi-phase power signals 2512 are
represented as a multi-phase set of three AC power signals U2, V2, and W2. As
shown, the AC power signal Ul is connected to the cathode of the diode 2604
and to
the anode of the thyristor 2602 of the first thyristor and diode set. The gate
of the
thyristor 2602 receives triggering timing signals 2606 from the control system
2410,
which can vary the performance of the rectifier circuit 2600. The cathode of
the
thyristor 2602 is connected to the positive output terminal V1+ of the
rectifier circuit
2600. The anode of the diodes 2604 is connected to the negative output
terminal V1-.
Each of the remaining five thyristor and diode sets is connected in the same
manner to
differently-phased incoming signals and to the same output signals. Timing
signals
2606 are used to gate the thyristors at startup. The gating of the thyristors
at startup
allows the input current from the power input 2402 to never increase above the
maximum rated current as capacitor 2432 is charged from a zero potential. This
provides a soft-start function, which precludes an overload trip of the power
source
connected to the power input 2402.
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A filter capacitor 2432, shown in FIG. 19, is connected across the rectifier
circuit 2600's D.C. output terminals V1+ and V1-. The six sets of thyristors
and
diodes act as A.C. voltage positive and negative peak detectors and rectifiers
which
fully charge this D.C. output filter capacitor 2432 (shown in FIG. 19) six
times during
each cycle of the incoming A.C. power signal to a voltage level that
approximately
equals the difference between the most positive and the most negative voltage
levels
reached by these power signals. The six signals Ul, V1, Wl, U2, V2, and W2
each
peak positively and negatively at six different times within each 50th or 60th
of a
second (depending upon the frequency of the incoming power signal). Whenever
one
of these six signals reaches its peak positive voltage, another one of these
same six
signals simultaneously reaches its peak negative voltage; and these two
peaking
signals work together to fully charge the filter capacitor 2432. The signal
peaking in
the positive direction supplies cun-ent through its corresponding diode into
the V+
terminal of the capacitor 2432, and simultaneously the signal peaking in the
negative
direction draws cun-ent through its corresponding thyristor from the V-
terminal of the
capacitor 2432, thereby fully charging the capacitor 2432 to approximately the
voltage level difference between the positive and negative peak signals.
The capacitor 2432, a 37 microfarad, high voltage capacitor, acts as a
smoothing capacitor to smooth out the resulting D.C. power signal produced by
the
rectifier 2600. The V1+ and V1- output terminals feed this D.C. power directly
into
the switching 400-Hz sine wave synthesizer and filter circuit 2700, which is
described
in FIG. 22.
Referring now to FIG. 22, the switching 400-Hz sine wave synthesizer 2700 is
shown. This circuit includes six pairs of switches 2702 and 2704 connected in
series
across V1+ and V1- as shown. A typical pair of switches comprises a first
switch
2704 and a second switch 2702 which are shown in FIG. 22 connected in series.
The
first switch 2704 connects to V1+ and the second switch connects to V1-. The
junction 2706 of the first and second switches 2704 and 2702 presents a power
signal
11 that is a pulse-width-modulated square wave that fluctuates between three
states
V1+, V1-, or 0 V. Switches 2704 and 2702 construct the pulse-width-modulated
representation of the 400Hz power signal at phase A of transformer 2900. When
the
voltage at phase A of transformer 2900 is positive, the power signal li will
switch
between 0 V and V1+, and when negative power signal li will switch between OV
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and V1-. Every 83.33 us (12 kHz) the possibility of the switch changing state
exists
and is based on load. Connected to both the first and second switches 2702 and
2704
are pulse-width-modulated switching control signals 2708 that originate in the
control
system 2410. The control system 2410 generates these switching signals to
cause the
first and second switches 2702 2704 to alternate in conducting the respective
V1+ and
V1- power signals into the power signal 1 1. This alternation is timed in such
a manner
that, after all higher harmonics above the 400 Hz fundamental have been
filtered out
(by the output transformer and filter 2900 and the capacitors 2434, 2436, and
2438),
the signal ii becomes a sinusoid having a controlled amplitude which may be
adjusted by the control system 2410 to regulate the output voltage level
supplied to an
airplane.
A companion signal 12 is generated in a similar manner, but is out of phase
with the signal 1 1. Additional pairs of signals 21 and 22 and also 31 and 32
are
generated in the same manner as just described for the signals li, and 12, but
the
signals 21 and 22 are 120 degrees phase shifted with respect to the signals li
and 12;
and the signals 31 and 32 are 240 degrees phase shifted with respect to the
signals 11
and 12. Accordingly, after filtering, the signals shown at 710 become a 3-
phase, 400
Hz set of power signals.
In FIG. 19, current amplitude "I" is measured in the output signals 12, 22,
and
32. These current measurements 2448 are relayed to the control system 2410
(measurements 2440) as a measure of the current and power being drawn from the
power converter module 21. Hall Effect current sensors are used to measure
current.
These can be obtained from the LEM SA (Geneva, Switzerland) as current
transducer
part number LF 505-S.
Referring now to FIG. 23, a circuit diagram of the switches used in FIG. 22 is
shown. The switch 2702 in an IGBT transistor which, as shown, may be
visualized as
a power field effect transistor having a gate 2810 and having incorporated
into its
design a diode 2804 interconnecting its source 2806 and drain 2808. The switch
2702
thus operates somewhat as a switch bypassed by a diode. The switch 2702 is an
integrated circuit manufactured by Eupec, Inc. (Lebanon, New Jersey) with part
number BSM300GB120DLC.
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The power output signals 2710 of the 400-Hz sine wave synthesizer 2700 are
fed through a power output transformer and filter 2900 shown in FIG. 24. The
pair of
power output signals li and 12 are applied to a first winding of the power
output
transformer 2900's primary windings 2904. The pair of power output signals 21
and
22 are fed to a second winding of the power output transformer 2900's primary
windings 2904. The pair of power output signals 31 and 32 is fed to a third
winding of
the power output transformer 2900's primary windings 2904.
Secondary windings 2906 on the other side of the transformer and filter 2900
present multi-phase, sinusoidal, Y-connected power output signals 2908 which
are
labeled A, B, C, and N for neutral. These power output signals present multi-
phase,
400-Hz power whenever the module 21 is in operation. The voltage presented
varies
depending upon the output voltage, which the electric power converter module
21 is
called upon to produce. The control system 2410 measures the voltages
presented by
the signals A. B, and C, and these voltage measurements 2442 are fed into the
control
system 2410 as part of the voltage and current measurements 2440. When the
module
21 is called upon to generate 115 volts 400 Hz A.C. power, the control system
2410
commands the sine wave synthesizer 2700 to produce waveforms on the signal
lines
11, 12, 21, 22, 31, and 32 adjusted in pulse width to maintain the sinusoidal
voltages
presented by the signals A, B, and C (measured at 2442) at 115 volts (RMS)
independent of the load. However, the system shuts down if the current and
power
drain is excessive (power is voltage multiplied by current). Different current
and
power limits may be established for different airplanes. The control system
2410
closes the switch 2406 and presents the power signals A, B, and C at the 115
volt 400
Hz A.C. power output 2407, which are connected to the airplane by suitable
cables.
The voltage measurement 2442 is a measurement of the voltage at the power
output
2407 when the switch 2406 is closed.
When the power converter module 21 is called upon to generate 270 volts
D.C. for an airplane requiring power converted in this manner, the control
system
2410 opens the switch 2406 and closes the switch 2408 so that the signals A,
B, and C
are fed through and rectified by the 270 volt D.C. rectifier 3000 and are
presented at
the 270 volt D.C. power output 2409 which are connected to the airplane by
suitable
cables. The control system 2410 ignores the voltage of the signals A, B, and C
and
measures instead the D.C. output current I (current measurement 2448) and
voltage
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V2+ (voltage measurement 2446) both of which are measured at the positive
terminal
of the D.C. power output 2409 (in FIG. 19) and adjusts the pulse widths
generated by
the sine wave synthesizer 2700 to produce waveforms on the signal lines 11,
12, 21,
22, 31, and 32 adjusted in pulse width to hold the D.C. output voltage stable
at 270
volts, provided the current and power drain is not excessive. Different
current and
power limits may be established for different airplanes.
As was just explained, the signals 2908 (A, B, and C) are routed (in FIG. 19)
to a first A.C. output switch 2406 and to a second D.C. output switch 2408.
The
signals 2908 (A, B, and C) are also connected to a set of smoothing capacitors
2434,
2436, and 2438 (shown in FIG. 19) which further suppress any remaining
harmonics
of 400 cycles.
Referring now to FIG. 25, the second rectifier 3000 is shown. The rectifier
3000 rectifies the 400 Hz power signals A, B, and C 2908 whenever the D.C.
power
switch 2408 is closed. When 270 volts D.C. is being generated, the voltages
presented
by the power signals A, B, and C are adjusted up or down to maintain the 270
volt
D.C. power output 2409 (FIG. 19) at 270 volts D.C. FIG. 25 shows that each of
the
three power signals A, B, and C (shown at 2908) is connected to a respective
set of
four rectifier diodes 3002, 3004, and 3006. Each set 3002, 3004, and 3006 of
four
diodes, for example the illustrative set of four diodes 3016, 3018, 3020, and
3022,
includes two pairs of diodes 3016-3018 and 3020-3022 connected in parallel.
The
anodes of the two parallel-connected diodes 3016-3018 connect to the power
signal
A, and the cathodes of these two diodes connect to a D.C. positive output line
3030.
The cathodes of the two parallel-connected diodes 3020-3022 connect to the
power
signal A, and the anodes of these two diodes connect to a D.C. negative output
line
3032. The remaining two four-diode sets 3004 and 3006, likewise, respectively
connect the incoming power lines B and C to the positive and negative output
lines
3030 and 3032. The output lines 3030 and 3032 are coupled to a first filter
capacitor
3008. The circuit arrangement just described causes the diode sets 3002, 3004,
and
3006 to develop across the filter capacitor 3008 a D.C. voltage that
approximately
equals the instantaneous voltage difference between the most positive and the
most
negative voltage swings of the three power signals A, B, and C, in signal peak
detector rectifier fashion.
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D.C. cuiTent flows from capacitor 3008 through a filter inductor 3010 and into
a bank of four 4700uf, 400 volt filter capacitors 3034, 3026, 3038, and 3040.
The
DC voltage developed across this bank of filter capacitors is presented as the
270 volt
filtered D.C. output voltage V2+ and V2- at 3028.
Referring now to FIG. 26, the clamp circuit 3100 is shown. This clamp circuit
3100 includes an electronic clamp circuit 3104-3106, which is connected
directly
across the 270 volt D.C. power output 2409 of the electrical power
conditioning
module 21 (shown in FIGS. 16 and 19). This clamp circuit is connected in
series with
the airplane disconnect switch 3103 (a relay controlled by the control system
2410)
across the 270 volt D.C. power signals V2+ and V2- 3028 which flow from the
rectifier 3000 (shown in FIG. 25). The two clamp circuits 3104-3106 and 3112-
3114
short out surge currents caused by arcing or inductive arc back or other
sources of
electrical transients that might feed back from an airplane. When the switch
3103
disconnects the D.C. power supply entirely from the airplane, the clamp
circuit 3100
prevents arcing of the relay contact points of the switch 3103 and dissipates
any
charge that may be stored on the DC buss attached to the converter. In some
circumstances, it is possible for the airplane to feed power back towards the
converter.
During such events, the clamping circuit 3100 dissipates such power and
prevents
arcing across the switch 3103 and damage to the power supply while the
feedback
event is ongoing.
The clamp circuit 3100 contains a serially-connected pair of electronic
switches 3104-3106. These switches are of the type shown in FIG. 23.
The pair of switches 3104-3106 includes a first switch 3106 and a second
switch 3104 connected with the source and gate of the second switch 3104
connected
to the drain of the first switch 3106 as shown (FIGS. 23 and 26). The source
and gate
of the first switch 3106 are connected to the control system 2410 by clamping
emergency signals 3116. The source and drain of the second switch 3104 are
connected in parallel with an 11 Ohm resister 3108. This arrangement makes it
possible for the two switches to withstand the high voltages that can arise at
this point
in the circuit.
With reference to FIG. 19, to enable the control system 2410 to provide all
the
control signals described above, the control system must receive measurements
of
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voltage "V" and of current "r at both the 115 volt 400 Hz A.C. power signal
output
2407 and at the 270 volt D.C. power output 2409. As can be seen in FIG. 19,
both
voltage and current are measured at the D.C. power output 2409. The 400 Hz.
A.C.
voltages are measured at the signals A, B, and C, and the 400 Hz. A. C.
current is
measured using Hall Effect current sensors at the signals 12, 22, and 32.
These voltage
and current measurements are fed into the control system 2410, and the control
system 2410 analyzes the appropriate ones of these voltages and currents and
then
makes the necessary corrections in the width of the pulses that comprise the
switching
control signals 2708 to either stabilize the 400 Hz. A.C. voltage at 115 volts
or to
stabilize the D.C. voltage at 270 volts, whichever type of power is currently
being fed
to an airplane.
While embodiments of the invention have been disclosed, those skilled in the
art will recognize that numerous modifications and changes may be made without
departing from the scope of the claims as defined by the claims annexed to and
forming a
part of this specification.
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