Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02905116 2015-09-21
SYSTEMS AND METHODS FOR REDUCING CIRCULATING CURRENT AND
PHASE-TO-PHASE IMBALANCE IN A PARALLEL MODULAR CONVERTER
SYSTEM
BACKGROUND
Embodiments of the present disclosure relate generally to power management
and specifically to a system and method for controlling phase-to-phase
imbalances
and reducing the circulating current in a parallel modular converter system.
Modern vehicles use a large number of electronics, motors, heaters, and other
electrically driven equipment. Electric motors, in particular, are ubiquitous
in modern
vehicles, including aircraft, and power everything from hydraulic pumps to
cabin fans.
Conventionally, each of these electric motors has been driven by an
independent
motor controller. Each motor controller is sized to be able to carry the
maximum
amount of current required to power its respective motor at full power for an
extended
period of time (and generally, includes some additional capacity for safety)
without
overheating or malfunctioning.
As a result, each aircraft carries an excessive number of motor controllers,
each of which is oversized and underutilized a majority of the time. In other
words,
the motor controller includes enough capacity to run the motor at full power
for an
extended period of time plus a safety margin, but motors are rarely, if ever,
run at full
capacity. This is because the motors themselves have some safety margin built
in
and because, a majority of the time, the motors are operating in a lower
demand
regime (e.g., the cabin fan is not always on "High"). In addition, some motors
are
only used occasionally, or during specific flight segments, and are unused the
remainder of the time. As a result, many of an aircraft's complement of heavy,
expensive motor controllers spend a majority of their service life either
inactive or
significantly below their rated power outputs.
What is needed, therefore, is a system architecture that enables the use of
multiple, modular, assignable, dynamically reconfigurable parallel motor
controllers
1
that can work alone or in parallel with other parallel motor controllers to
meet power
control needs. The system should enable one or more parallel controllers to be
assigned to each active electrical load in the aircraft, as necessary, to meet
existing
power demands. The system should enable the use of such parallel controllers,
while
minimizing phase-to-phase imbalances and reducing circulating current. It is
to such
a system that embodiments of the present disclosure are primarily directed.
SUMMARY
It should be appreciated that this Summary is provided to introduce a
selection
of concepts in a simplified form that are further described below in the
Detailed
Description. This Summary is not intended to be used to limit the scope of the
claimed subject matter.
Embodiments of the present disclosure relate to systems and methods related
to a modular power distribution and power conversion system for electrical
loads.
The system can include a plurality of parallel modular converter modules
("modules")
linked to form a parallel modular converter ("converter"). The system and
method can
operate multiple modules simultaneously and in parallel, while maintaining
substantially equal output from each module.
In one embodiment, there is provided a system for powering a plurality of
electrical loads. The system includes a first parallel modular converter
module having
a first input and a first output configured to provide a first alternating
current (AC)
output to a first load of the plurality of electrical loads. The system
further includes a
second parallel modular converter module having a second input and a second
output configured to provide a second AC output to the first load. The system
further
includes a load balancer connected to the first input, the second input, the
first output,
and the second output. The load balancer is configured to compare the first
output
from the first parallel modular converter module with the second output from
the
second parallel modular converter module. The load balancer is further
configured to
modify, upon determining an imbalance exists between the first output and the
second output, an associated control algorithm for one or both of the first
parallel
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modular converter module and the second parallel modular converter module to
thereby equalize the first output and the second output. The system further
includes
a controller configured to generate one or more control signals corresponding
to one
or more selected control algorithms of a plurality of control algorithms,
wherein the
plurality of control algorithms includes the associated control algorithm. The
system
further includes a control switching network comprising a plurality of
switching
elements and configured to transmit a first control signal of the one or more
control
signals to apply the associated control algorithm to the first parallel
modular converter
module and to the second parallel modular converter module when coupled with
the
first load.
In another embodiment, there is provided a parallel modular converter. The
parallel modular converter includes a first parallel modular converter module
configured to provide a first alternating current (AC) output and connected to
a
module communications bus, and a second parallel modular converter module
configured to provide a second AC output and connected to the module
communications bus. The parallel modular converter includes a master logic
controller configured to assign the first parallel modular converter module
and the
second parallel modular converter module to power a first load. The parallel
modular
converter further includes a master communications controller connected to the
module communications bus and configured to route messages between the master
logic controller and the first parallel modular converter module and the
second
parallel modular converter module, whereby a calculated ideal load sharing
value is
applied to control the first AC output and to control the second AC output.
The
parallel modular converter further includes a load balancer connected to a
respective
input and a respective output of each of the first parallel modular converter
module
and the second parallel modular converter module. The load balancer is
configured
to determine, responsive to application of the calculated ideal load sharing
value, that
an imbalance exists between the first AC output and the second AC output, and
modify, responsive to determining that the imbalance exists, an associated
control
algorithm for one or both of the first parallel modular converter module and
the
second parallel converter module to thereby equalize the first AC output and
the
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second AC output. The parallel modular converter further includes a motor
control
system configured to generate one or more control signals according to one or
more
selected control algorithms of a plurality of control algorithms, wherein the
plurality of
control algorithms includes the associated control algorithm. The parallel
modular
converter further includes a control switching network comprising a plurality
of
switching elements and is configured to transmit a first control signal of the
one or
more control signals to apply the associated control algorithm to the first
parallel
modular converter module and to the second parallel modular converter module
when
coupled with the first load.
In another embodiment, there is provided a method for balancing outputs
between a plurality of parallel modular converter modules. The method involves
receiving, at a system controller, a request from a vehicle controller to
power a first
load, and calculating, using a load balancer coupled with the system
controller, a first
number of parallel modular converter modules sufficient to power the first
load. The
method further involves placing in parallel, using a master logic controller
coupled
with the load balancer, the first number of modules selected from a plurality
of parallel
modular converter modules. The method further involves configuring, responsive
to a
first control signal from the system controller, a control switching network
to transmit,
from a plurality of received control signals corresponding to a plurality of
control
algorithms, a second control signal to the selected modules to apply a first
control
algorithm thereto, the first control algorithm selected from the plurality of
control
algorithms, the control switching network comprising a plurality of switching
elements
and arranged between the system controller and the load balancer. The method
further involves sensing, using the load balancer, a respective output from
each of the
selected modules, and modifying, using the load balancer and upon determining
an
imbalance exists between the respective outputs of the selected modules, the
first
control algorithm for one or more individual modules of the selected modules
to
equalize the outputs of the selected modules.
In another embodiment, there is provided a parallel modular converter. The
parallel modular converter includes a first parallel modular converter module
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configured to provide a first alternating current "AC" output and connected to
a
module communications bus, and a second parallel modular converter module
configured to provide a second AC output and connected to the module
communications bus. The parallel modular converter further includes a master
communications controller connected to the module communications bus and a
master logic controller to route messages therebetween, and a load balancer
connected to an input and an output of both the first parallel modular
converter
module and the second parallel modular converter module. The load balancer is
configured to calculate the number of parallel converter modules required to
power a
first load. The master logic controller is configured to place the first
parallel modular
converter module and the second parallel modular converter module in parallel
using
a power switching network and to assign the first load to the first parallel
modular
converter module and the second parallel modular converter module, the module
communications bus connecting the first parallel modular converter module and
the
second parallel modular converter module. The load balancer is configured to
modify
the input to the first parallel modular converter module to equalize the
output of the
first parallel modular converter module with the output of the second parallel
modular
converter module.
In another embodiment, there is provided a method for balancing outputs
between a plurality of parallel modular converter modules. The method involves
receiving a request to power a first load from a vehicle controller at a
system
controller, and calculating a number of parallel modular converter modules
required to
power the first load with a load balancer. The method further involves placing
the
calculated parallel modular converter modules required to power the first load
in
parallel with a master logic controller, and sensing an output from each of
the
calculated parallel modular converter modules with the load balancer. The
method
further involves modifying an input signal to one or more of the calculated
parallel
modular converter modules with the load balancer such that the output of each
of the
calculated parallel modular converter modules is equal.
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The features, functions, and advantages that have been discussed can be
achieved independently in various embodiments of the present disclosure or may
be
combined in yet other embodiments, further details of which can be seen with
reference to the following description and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is an electrical schematic depicting a parallel modular converter
module
("module") for use in a parallel modular converter in a high voltage DC input
application, in accordance with some embodiments of the present disclosure.
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Fig. 2 is an electrical schematic depicting a module for use in a parallel
modular converter in an AC input application, in accordance with some
embodiments
of the present disclosure.
Figs. 3A-3C are electrical schematics depicting a parallel module converter
("converter") using multiple modules in a high voltage DC current regime, in
accordance with some embodiments of the present disclosure.
Fig. 4 is an electrical schematic depicting an output configuration, in
accordance with some embodiments of the present disclosure.
Fig. 5 is an electrical schematic depicting an alternative module with shared
controllers in a high voltage DC input application, in accordance with some
embodiments of the present disclosure.
Figs. 6A-6C are electrical schematics depicting an alternative converter in a
high voltage DC input application, in accordance with some embodiments of the
present disclosure.
Fig. 7 is an electrical schematic depicting a power switching network, in
accordance with some embodiments of the present disclosure.
Fig. 8 is an electrical schematic depicting a parallel modular converter, in
accordance with some embodiments of the present disclosure.
Figs. 9A-9C are electrical schematics depicting an alternative converter, in
accordance with some embodiments of the present disclosure.
Fig. 10 is an electrical schematic depicting an overall system architecture
for
the converter, in accordance with some embodiments of the present disclosure.
Fig. 11 is a detailed electrical schematic depicting a control switching
network
and a power switching network of Fig. 10, in accordance with some embodiments
of
the present disclosure.
Fig. 12 is a flowchart depicting a method of distributing power, in accordance
with some embodiments of the present disclosure.
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Fig. 13 is a flowchart depicting a method for reapportioning loads to a
plurality
of modules, in accordance with some embodiments of the present disclosure.
Fig. 14 is a flowchart depicting a method for equalizing current between
parallel modules, in accordance with some embodiments of the present
disclosure.
Fig. 15 is an electrical schematic depicting an overall system architecture
for a
converter with a load balancer, in accordance with some embodiments of the
present
disclosure.
Each figure shown in this disclosure shows a variation of an aspect of the
embodiment presented, and only differences will be discussed in detail.
DETAILED DESCRIPTION
Embodiments of the present disclosure relate generally to power distribution
and power conversion systems and more particularly to a parallel modular
converter
for distributing electrical loads without the need for individual controllers
at each
electrical load. The converter can utilize a load balancer to monitor the
inputs and
outputs to each parallel modular converter module in the parallel module
converter to
match the output currents. This can result in reduction of circulating current
and
phase-to-phase imbalances, among other things.
To simplify and clarify explanation, the disclosure is described herein as a
system for allocating power on an aircraft. One skilled in the art will
recognize,
however, that the disclosure is not so limited. The system can also be used,
for
example and not limitation, with automobiles, other types of vehicles, and in
power
distribution networks. The disclosure can be used to improve control and
reduce the
cost and expense of distributing power in numerous situations by reducing the
number of controllers required and eliminating excess controller capacity and
reducing, or eliminating circulating current and phase-to-phase imbalances.
The materials and components described hereinafter as making up the various
elements of the present disclosure are intended to be illustrative and not
restrictive.
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Many suitable materials and components that would perform the same or a
similar
function as the materials and components described herein are intended to be
embraced within the scope of the disclosure. Such other materials and
components
not described herein can include, but are not limited to, materials and
components
that are developed after the time of the development of the disclosure.
As mentioned above, a problem with conventional power distribution systems
is that, generally, each electrical load is provided with an individual
controller for
power distribution purposes. Unfortunately, this leads to an excess of
controller
capacity because each individual controller must be rated for the maximum load
that
the requisite electrical appliance can draw. In addition, in most cases, the
controllers
are actually designed to provide some margin of safety even though (1) the
electrical
load itself (e.g., an electric motor) may have some inherent safety margin and
(2)
many electrical loads are generally used at less than full power and/or are
only used
intermittently.
To this end, embodiments of the present disclosure relate to a networked
system of modular power controllers that can be used individually or in
parallel to
meet existing power demands. Because every electrical load in an aircraft will
rarely,
if ever, be on at the same time, the system can be designed with a capacity
more
closely related to nominal or average power consumption (plus some safety
margin)
rather than "worst case scenario." As a result, the number of components
required,
component weight, size, and cost can be reduced, system efficiency can be
improved, and improved system redundancy can be provided. In the event of a
motor
controller failure, for example, the system can be reconfigured to assign the
load to a
functioning motor controller, improving reliability. In addition, if the loads
are such
that the system is operating at full capacity, all loads can still be powered,
albeit at a
reduced capacity in some cases.
As shown in Fig. 1, a building block of the system can comprise a plurality of
parallel modular converter modules ("modules") 100 that can be networked
together
to form a parallel modular converter ("converter"), discussed below. In some
embodiments, as shown in Fig. 1, each module 100 can comprise onboard
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processing. In this configuration, the module 100 can comprise at least three
processors: the Motor Control Digital Signal Processor ("DSP") 105, the
protection
processor 110, and the logic processor 115. Alternatively, protection
processor 110
may be denoted a protection controller, and logic processor 115 may be denoted
a
logic controller.
In some embodiments, therefore, the DSP 105 can generate, for example, a
high-frequency gate drive pulse width modulation signal (PWM) 120 to activate
the
gate driver 125. The gate driver 125 acts essentially as the switching side of
the
power module 100, much like an electrical relay. In other words, the output
180 of
the module 100 is regulated by the PWM signal 120. To determine the proper PWM
signal 120, the DSP 105 can utilize signals from various sensors via a signal
processor 135 and/or signals via a module communications bus 140, discussed
below.
In some embodiments, the DSP 105 can utilize sensors including, for example
and not limitation, temperature sensors 150 and shoot-through sensors 155 to
detect
potentially damaging conditions. In other embodiments, the DSP 105 can utilize
sensors including current sensors (to detect overcurrent conditions), voltage
sensors
(to detect overvoltage conditions), motor speed and position sensors (to
detect over-
speed conditions). In addition, many of these sensors (e.g., current, voltage,
rotor
speed and position sensors can also be used to perform motor control). In some
embodiments, the signal processor 135 can condition signals from the sensors
and
can include an Analog to Digital Converter (ADC) 136a. In other embodiments,
the
ADC 135 can be a discrete unit that connects via a communications interface to
the
processors 105, 110, 115. In still other embodiments, the ADC 135 can be
integrated
into one or more of the processors 105, 110, 115.
Sensor data can comprise, for example and not limitation, module input and
output current and voltage, motor position, DC link DM (differential mode) and
CM
(common mode), voltage and current, motor speed, and power module temperature.
In some embodiments, the DSP 105 pulse width modulation method and output
power level can be configured by the logic processor 115. To enable
communication
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between module processors 105, 110, 115 and controllers external to the module
100, a module communications bus 140 can be utilized. In some embodiments, to
enhance module 100 debugging and verification, for example, load sensor
signals
and DSP configurations can comprise datasets to be transmitted to a master
data
logger 310, as discussed below.
It is preferable, and sometimes required, to synchronize the reference clocks
between the modules 100 and the motor control DSP 105 to generate synchronous
output waveforms 180. Failure to synchronize reference clocks can result in
the
motor control DSP 105 generating waveforms that are out-of-phase from the
waveforms of other modules 100. This, in turn, can potentially create short
circuits,
which can damage or destroy the modules 100. Variances in the high-frequency
system clock of the DSP 105 are relatively insignificant; however, as a few
nanoseconds will have little, or no, effect on the output waveforms. The
reference
clocks are preferably at least synchronized between parallel modules 100
(e.g.,
.. modules 100 that are currently feeding power to the same load). In some
embodiments, for very accurate synchronization, methods known in the art such
as,
for example, synchronization via fiber optic cables can be used. Fiber optic
can be
advantageous because it is immune to the EMI noise generated by the power
module
switching. As discussed below, in some embodiments, all motor control PWM
signals 120 can be executed on a central processor, which distributes PWM gate
signals 120 directly to the gate drive circuitry 125 of the IGBT switch
modules. This
can reduce synchronization issues because paralleled modules receive identical
gate
signals 120.
In some embodiments, the protection processor 110 can enable safe operation
of the module 100. The protection processor 110 can monitor various sensors
for
unsafe operating conditions including, but not limited to, output AC current
and
voltage sensors 145, gate driver and inverter temperatures 150, and shoot-
through
current 155. In some embodiments, the protection processor 110 can also
monitor,
for example, motor over-speed, over-voltage (DC link), overcurrent at input or
output,
over-voltage at input and output, CM (common mode) current, excessive voltage
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ripple, unbalanced input/output current, open phase, and computer failure
protection
(e.g., if the DSP fails, the protection processor 110 can disable the gate
driver 125
independently). In still other embodiments, the protection processor 110 can
also
compare actual PWM configuration to the commanded PWM configuration. If these
signals do not match, the gate driver 125 can also be disabled. In some
embodiments, the protection processor 110 can be directly connected to the
gate
driver 125 enabling nearly instantaneous shutdowns of the inverter 160 should
a fault
be detected.
Module 100 input fault protection can also be provided by the protection
processor 110 in communication with a master protection controller 305 over
the
module communications bus 140. Should the protection processor 110 detect a
fault,
for example, the protection processor 110 can instruct the master protection
controller
305 to externally disable the module 100. In some embodiments, module 100
faults
can also be recorded by the protection processor 110. In some embodiments, the
fault can be stored in the memory 110a (e.g., non-volatile memory) of the
protection
processor 110 and the module 100 can be disabled until it can be repaired or
replaced. To aid in debugging, in some embodiments, the protection processor
110
can also log some or all events with the master data logger 310. In this
manner,
information regarding module faults, communications, master logic commands and
other pertinent information can comprise datasets for logging by the master
data
logger 310.
In some embodiments, the logic processor 115 can regulate the DSP 105 by
configuring the modulation method and output power. Coordination between logic
processors 115 in parallel modules 100 can enable equal load sharing and clock
synchronization. As a result, each logic processor 115 can communicate with
the
master logic controller 320 for instructions on which load it is assigned to
power at
present.
As shown, the module 100 can accept a high-voltage DC power (HVDC) that
has been rectified by an external rectifier unit. In some embodiments, the
input
current and voltage can be monitored by current and voltage sensors 165. The
DC
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waveforms can be filtered by a DC electromagnetic inference (EMI) filter 170,
which
can reduce noise on the DC bus and stabilize input current and voltage. The
inverter
module 160 can then generate AC waveforms, which can be filtered by an output
AC
EMI filter 175, for use by the system loads. In some embodiments, additional
filters
and processors can be used to remove switching transients and smooth the
output
waveform. In some embodiments, each module 100 can comprise one small input
EMI filter 170, for example, and a larger output EMI filter 175 for each load
(connecting EMI filters in series improves filter attenuation).
Current and voltage waveforms can also be monitored by additional sensors
after the output AC EMI Filter 175. In some embodiments, one or more voltage
and/or current sensors at the module 100 and one or more voltage and/or
current
sensors on the load side. This can enable fault detection in the power
switching
network 325, discussed below.
As shown in Fig. 2, in some embodiments, rather than using an external
rectifier, a rectifier 205 can be integrated into the module 200. In this
configuration,
the module 200 can utilize an AC power input, such as a 3-Phase AC power
input.
The rectifier 205 can comprise, for example and not limitation, an active
front end
(comprising solid state switches) or traditional passive rectifiers (e.g.,
multi-pulse
autotransformer rectifier units, transformer rectifier units, or diode
rectifiers). This
configuration can provide increased reliability because, for example, a
rectifier 205
failure affects only one module 200. In addition, reliability and safety are
improved
because there is also a decreased circulating current between modules 200
(e.g., as
each module 200 can be isolated from other modules 200). Of course, this
approach
incurs a slight increase in cost, weight, volume, and complexity of the
modules 200 as
the result of the additional components 205, 210. In some embodiments,
additional
current and voltage sensors 210 can be used after the rectifier 205 to sense
fault
conditions.
Figs. 3A-3C depict an overall system 300 architecture for a converter. The
master controller 302 can comprise, for example and not limitation, a master
communications controller 315, a master logic controller 320, a master
protection
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controller 305, a master data logger 310 or master data logging controller,
and a
power switching network (PSN) 325. The master communications controller 315
can
connect each module, via each module's 100 module communications bus 140,
enabling message exchanges between modules 100. In addition, messages from the
master logic controller 320 can also be routed by the master communications
controller 315 to their respective destinations (e.g., to modules 100,
external aircraft
systems 350, etc.).
In some embodiments, to aid debugging, messages processed by the master
communications controller 315 can be duplicated and transmitted to the master
data
logger 310 where they are recorded for concurrent or future analysis. In some
embodiments, the master communications controller 315 can facilitate
communications between the modules 100 and external aircraft systems 350
(e.g.,
aircraft systems 350 external to the system 300 requesting power). In some
embodiments, the master logic controller 320 can receive requests for loads at
a
specified power level (e.g., current and/or voltage) from external airplane
systems.
The master logic controller 320 can then allocate modules 100 to fulfill power
requests by selecting and configuring the modules 100 and power switching
network
325 accordingly.
To ensure that any fault conditions occurring in the system 300 are detected
and interrupted, the master protection controller 305 can monitor the inputs
and
outputs to each module 100 including, for example and not limitation, the
input
current and voltage waveforms of the high-voltage DC Bus and the low-voltage
DC
Bus. In some embodiments, should a fault occur, the master protection
controller 305
can signal the corresponding power switch 330 to disconnect the module 100,
record
the failure in the master protection controller memory 305a, and send a
message of
the failure to the master data logger 310. The master protection controller
305 can
disable the module 100 until it has been, for example, repaired or replaced.
Logging of control messages and sensor readings, on the other hand, can be
handled by the master data logger 310. The master data logger 310 can record
the
data it receives to a data storage medium 335 via a data logging bus 345,
which can
CA 02905116 2015-09-21
be in communication via the data storage interface (DSO 310a. In
some
embodiments, such as when high-frequency sensor readings are to be written to
the
data storage, high-speed high-capacity storage devices can be used. In some
embodiments, the reliability of the system 300 can be enhanced using redundant
low-
voltage DC connections to the master controllers (e.g., the master protection
controller 305, master data logger 310, master communications controller 315,
and
master logic controller 320) and the module's 100 processors (e.g., the motor
control
DSP 105, protection processor 110, and logic processor 115).
In this configuration, the modules 100 can be powered through rectifier units
(rectifiers) 340 external to the modules 100. Each rectifier 340 can power N
(any
number of) modules 100. Of course, decreasing the number, N, powered by each
rectifier 340 can increase reliability, at the expense of increased weight and
complexity. As a result, if there are M rectifiers 340, for example, this
would result in
a total of N*M modules 100. As above, the rectifier 340 can be, for example
and not
limitation, an AFE, passive diode, or multi-pulse autotransformer unit
rectifiers.
In some embodiments, as shown in Fig. 4, the output system 400 can include
the power switching network 325. The power switching network 325 can switch
the
array of module 100 outputs (415-1 to 415-N) to their assigned loads through
the
array of load connectors (420-1 to 420-K). Load fault identification and
interruption
can be provided by the monitoring of current and voltage waveforms by the
power
switching network protection controller 405. Should the power switching
network
protection controller 405 detect fault conditions, it can open some or all
power
switching network 325 switches 410 connected to the load. In some embodiments,
the power switching network protection controller 405 can also record the
fault in
NVM to aid with either reclosing the switch 410 (e.g., when the fault has been
corrected) or permanently disconnecting a switch 410 (e.g., until it is
replaced). The
power switching network protection controller 405 can also inform the power
switching network 325 of the fault. The power switching network 325 can then
open
all switches connected to the load, thereby providing redundant system
protection. In
some embodiments, the output of the system 300 can include a final stage of
EMI
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attenuation, if required. Each load can have one or more dedicated AC Output
EMI
filters that can filter the combined waveforms from all parallel modules 100.
In some
embodiments, the switches 410 can be, for example and not limitation, solid
state
switches or electromechanical contactors.
In some embodiments, as shown in Fig. 5, rather than multiple module
controllers (e.g., the motor control DSP 105, protection processor 110, and
logic
processor 115), the modules 100 can be primarily controlled by the motor
control
DSP 105. In this configuration, transferring the logic processor 115 functions
to the
master logic controller 320 can reduce the number of processors required by
the
module 100. In some embodiments, this can also eliminate, for example, the
power
distribution negotiation process between each module's logic processor 115. In
this
configuration, the motor control DSP 105 can be configured by the master logic
controller 320. Load sensor signals can be transmitted by the master logic
controller
320 to the motor control DSP 105, as required. In addition, system 300
reference
.. clock synchronization to generate synchronous waveforms can still be
provided by
the motor control DSP 105.
In this configuration, the protection processor 110 functions can be
integrated
into the reference clock synchronization to generate synchronous waveforms. In
most cases, processing the relatively small number of additional signals does
not add
significant burden to the motor control DSP 105. Should the motor control DSP
105
identify fault conditions, the motor control DSP 105 can disable the module
100
simply by stopping the PWM signal 120.
In some embodiments, to reduce the bandwidth requirements of the module
communications bus 140, the modules 100 can also comprise a separate data-
logging communications bus 505. In this manner, the relatively high-bandwidth
data-
logging communications can be handled by the data-logging communications bus
505, while the controls communications 510, which are relatively low-
bandwidth, high
reliability communications, can remain on the module communications bus 140.
In
this manner, the motor control DSP 105 can be connected to both communications
.. buses 505, 510 enabling both types of communications.
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In still other embodiments, as shown in Figs. 6A-6C, the system 600 can
comprise a more prominent master logic controllers 320 and master data loggers
310, enabling the elimination of the master communications controller 315. In
this
configuration, the master logic controller 320 can connect to every module's
logic
.. communications bus to enable configurations to be transmitted to the
modules 100.
Power distribution between parallel modules 100 and communication with
external
aircraft systems 605 (e.g., aircraft systems external the system 600, not the
aircraft)
can be controlled by the master logic controller 320. The master data logger
310 can
connect to each module's data-logging communications bus 505 enabling higher
frequency data logging. In some embodiments, additional connections can be
made
to the master protection controller 305 and/or the master logic controller 320
for data
storage, while the master protection controller 305 can operate substantially,
as
discussed above.
In some embodiments, as shown in Fig. 7, the system 700 can comprise load
sensor signal processing that has been relocated from the individual modules
100 to
the system 300 output. In this configuration, the power switching network
protection
controller 405 can monitor load signals ensuring no faults occur (e.g., over-
temperature or over-speed conditions). The power switching network protection
controller 405 can relay sensor data including, but not limited to, load
temperature
705 and load position 710, to the master logic controller 320 for distribution
to the
modules 100.
Fig. 8 depicts an alternative module 800 architecture that eliminates
reference
synchronization issues (e.g., the synchronization of reference clocks between
the
modules 100, discussed above). In some embodiments, this can be achieved by
relocating the motor controller DSP 105 to the Master Control 302. As
mentioned
above, the motor controller DSP 105 computes PWM states and then transmits
them
(e.g., via switch state messages over fiber optics) to the module 800. Fiber
optics
can be used for intermodule communication, for example, to prevent data
corruption
on unshielded electrical wires. In this configuration, a fiber optic
transceiver 805 can
receive the switch state messages.
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CA 02905116 2015-09-21
A decoder 805a within the fiber optic transceiver 805 can then generate a gate
drive signal 810 for the gate driver 815. The fiber optic transceiver 805 can
transmit,
receive, encode, and decode signals from electrical domain to optical and vice
versa.
Fiber optics signals can be advantageous because optical signals are immune to
the
EMI noise generated by the power switching network. Optical media can be
useful,
therefore, to transmit information over relatively long distances (e.g.,
between
modules 100).
The decoder 805a can be a logic circuit such as, for example and not
limitation, a field programmable gate array (FPGA), complex programmable logic
device (CPLD), application specific integrated circuit (ASIC), or processor.
The
protection processor 110 can provide basic protection by monitoring the
current and
voltage sensors 812,817 for the DC input and the AC output, respectively, the
temperature of module devices 820, and inverter shoot-through 825, among other
things. Should a fault occur, the protection processor 110 can disable the
inverter
830 and inform the master protection controller 305 of the fault. In some
embodiments, the protection processor 110 can communicate with the master
protection controller 305 via the fiber optic transceiver 805. In other
embodiments,
the protection processor 110 can communicate with the master protection
controller
305 via the module communications bus 140. In some embodiments, switch state
messages and protection messages can be transmitted at different frequencies
to
enable concurrent communication.
In yet other embodiments, as shown in Figs. 9A-9C, the motor controller DSPs
105 can be relocated from the module 100 to the master controller 302. By
consolidating motor controller DSPs 105, clock synchronization is less
difficult due to
the close proximity of the devices (e.g., most of the time delay element is
removed
from the synchronization). In some embodiments, the motor controller DSPs 105
can
be placed on a modular accessory board to facilitate repairs of the system
900. The
number of motor controller DSPs 105 can be equal to the maximum number of
simultaneous loads, K, to be controlled by the system 900. In this
configuration, each
motor controller DSP 105 can calculate the PWM state then transmit a switch
state
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CA 02905116 2015-09-21
message to the modules 100, with parallel modules 100 receiving switch state
messages from the same motor controller DSPs 105. In some embodiments, a PWM
router 905 can be used to route the switch state messages to parallel modules
100.
Sensor signals such as, for example, load currents and voltages, can be routed
to the
respective motor controller DSPs 105 by a load sensors router 910.
In some embodiments, the master logic controller 320 can communicate
directly with each motor controller DSPs 105 to configure the necessary
control
variables (e.g., pulse width and magnitude). In some embodiments, as above,
fiber
optic transceivers 805 can be used to communicate with the modules 100.
Multiple
wavelengths/frequencies can also be used to enable the concurrent transmission
and/or reception of switch state messages and module fault messages.
The architecture discussed above can provide high reliability because each
module's 100 controllers operate nearly independently. In most cases,
interaction
with other controllers is limited to the allocation of power distribution
between the
logic processors 115 of various modules 100 and the distribution of load and
power
by the master logic controller 320. In this configuration, for example, a
module 100
failure will not affect the operation of other modules 100. In addition,
communication
is simplified as the module communications bus 140 provides and interface
between
the various module processors (e.g. the DSP 105, the protection processor 110,
and
the logic processor 115) and the master controllers. However this architecture
can be
somewhat less cost effective and more difficult to implement. Utilization of a
dedicated logic controller for minimal tasks, for example, can result in
unused
processing power increasing module costs. Integration of logic controller
functions
into other controllers such as the master logic controller 320, on the other
hand,
would decrease costs and module complexity. Implementation of synchronized
reference clocks can add complexity and cost to the module.
The overall system architecture, including the subsystems discussed in Figs.
1-9C, is shown in Figs. 10 and 11, the system 1000 can control a system of
parallel
modular inverters 1015 to drive multiple and/or different types of AC or DC
machines
1010. The system 1000 can comprise a plurality of parallel modular inverters
1015
CA 02905116 2015-09-21
connected in parallel, each of which is able to be configured to receive any
of a
plurality control algorithms 1022a, 1022b, 1022c embedded in a motor control
system
1020 via a reconfigurable control switching network 1025. Each of the parallel
modular inverters 1015 can be configured to drive one or more of the plurality
of AC
machines 1010 on the load side via a reconfigurable power switching network
1030.
This configuration enables, for example, the ability to dynamically
reconfigure
both the control switching network 1025 and power switching network 1030. In
addition, any of the inverters from the plurality inverters 1015 in parallel
is accessible
to drive any motor of the plurality motors 1010 (or other electrical loads) on
the load
side and any control algorithm of a plurality of control algorithms 1022
embedded in
the system 1000 is accessible to control any of the plurality inverters 1015.
As a
result, one or more inverters 1015 can drive one motor 1010, as necessary to
meet
load requirements, and/or a plurality of motors 1010 on the load side can be
driven at
the same time, each of which can be driven with one or more inverters 1015. In
addition, a plurality of motors 1010 on the load side can be driven at the
same time
with the same control algorithm (e.g., 1020a) or a different control algorithm
(e.g.,
1020b).
As shown in Fig. 10, the system can comprise a system controller 1035
configured to communicate with a vehicle controller 1040 to, for example,
obtain
operation commands from the vehicle controller 1040 and provide system 1000
status signals to the vehicle controller 1040, among other things. In
some
embodiments, the system controller 1035 can also reconfigure the power
switching
network 1030 to provide an appropriate number of inverter modules 1015 in
parallel
to drive a motor 1010 in real time. In other words, when the load from a motor
1010
is increased, the system controller 1035 can signal the power switching
network 1030
to place more inverter modules 1015 in parallel. Conversely, of course, when
motor
load is decreased, the system controller 1035 can signal the power switching
network
1030 to disengage one or more inverter modules 1015. If necessary, the system
controller 1035 can then place them in parallel with other inverter modules
1015 to
drive other loads 1010.
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CA 02905116 2015-09-21
In some embodiments, the system controller 1035 can also reconfigure the
control switching network 1025 to provide appropriate motor control algorithms
1022
to one or more of inverter modules 1015 driving one or more motor types. The
system controller 1035 can provide algorithms related to, for example and not
limitation, field oriented control (FOC), direct torque control (DTC), voltage
over
frequency control (V/F). This can be useful, for example, to efficiently drive
specific
motor types (e.g., induction motors, synchronous motors, permanent magnet
synchronous motors, brushless DC motors, etc.).
In some embodiments, the system controller 1035 can also send, for example
and not limitation, motor speed, torque, or power reference values to
corresponding
motors 1010 (or motor controllers). In some embodiments, the system controller
1035 can be stored and run on an embedded controller. The system controller
1035
can comprise, for example and not limitation a microcontroller processor,
FPGA, or
ASIC. In some embodiments, the system controller 1035 can use a real time
.. simulator/emulator or can be run in real-time.
In some embodiments, the number of motor controller algorithms 1022 can be
determined by the number of different motor loads. If the system 1000 has
three
different types of motors 1010 to drive, for example, then three motor
controller
algorithms 1022 can be developed, with each motor control algorithm 1022
specific to
the motor load. Of course, if all three motors 1010 perform the same function
with the
same motor, it is possible that all three loads can be powered using the same
algorithm 1022.
The control switching network 1025 can dynamically configure one or more
inverters 1015 each of which can be driven by a specific control algorithm
1022, or a
common control algorithm 1022, which is routed through control switching
network
1025 per commands from the system controller 1035. In some embodiments, time
delay between signals into and out of control switching network 1025 can be
minimized to improve motor drive performance.
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CA 02905116 2015-09-21
The control switching network 1025 can be, for example, in a software or
hardware implementation. In some embodiments, a software coded control
switching
network 1025 can be run on, for example and not limitation, an embedded
controller,
real-time simulator, or computer. In other embodiments, the control switching
network 1025 can be implemented using a hardware device such as, for example
and
not limitation, CPLDs, ASICs, or FPGAs.
In some embodiments, the power switching network 1030 can dynamically
configure one or more inverters to drive one or more motors per one or more
specific
control algorithms from the system controller 1035. In some embodiments, the
power
switching network 1030 can act as a short circuit and/or over current
protection
device. In this case, the power switches 1030a associated with the short-
circuit or
over-current load open when a fault is detected.
The power switching network 1030 can be implemented using, for example
and not limitation, solid state relays, mechanical relays, transistors, and
other
controllable power switches. Of course, the inverters 1015 convert DC power to
the
requested AC power (e.g., at different voltage levels, frequencies, waveforms,
etc.) to
drive various AC machines (e.g., AC motors 1010) per the motor algorithm 1022
and
system controller 1035. The inverters can comprise, for example and not
limitation,
insulated-gate bipolar transistors (IGBTs), metal¨oxide¨semiconductor field-
effect
transistors (MOSFETs), and bipolar junction transistors (BJTs).
In still other embodiments, the system 1000 can assign loads based on a load
priority factor. In other words, if, for example, the number of loads
requested by
external aircraft systems 1040 (e.g., external to the system 1000) is larger
than can
be provided by the module 100, the system 1000 can assign loads by a load
priority
factor, with higher priority loads being powered before lower priority loads.
If the
aircraft 1040 makes a request for a large load, such as to lower the landing
gear, for
example, the system 1000 can temporarily reassign some or all of the modules
1015
to power the landing gear motors. When the landing gear is down and locked, in
turn,
the system 1000 can reassign the modules 1015 to their previous loads (or to
now
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CA 02905116 2015-09-21
existing loads). So, for example, the cabin fan can be temporarily deactivated
in
favor of the landing gear and then restarted when the gear is down.
In some embodiments, such as when there are an excess of low priority loads
that collectively exceed the power rating of the system 1000, the system 1000
may
power some or all of the loads at a reduced setting. In this manner, all loads
are
powered, but may operate at a lower speed or capacity. So, for example, the
aircraft
cabin fans, lighting, and entertainment system may request power at the same
time in
excess of the system 1000 rating. As a result, the system 1000 can, for
example,
provide full power to the entertainment system, but slightly reduce cabin fan
speeds
and lighting intensity to reduce overall power demand.
As shown in Fig. 12, embodiments of the present disclosure can also comprise
a method 1200 for distributing power. In some embodiments, the method 1200 can
comprise receiving 1205 a load request from the vehicle (e.g., load requests
from the
vehicle controller 1040). The controller can then determine 1210 if the load
.. requested is above or below the power rating for a single module. If the
load request
is below the rating for a single module, the controller can assign 1220a the
load to a
single module. If, on the other hand, the load is greater than a single module
can
power, the controller can parallel 1215 the number of modules ("X") together
that are
required to power the load and then assign 1220b the load to the X modules.
The
controller can then activate 1225 the modules providing the necessary load.
When the vehicle no longer needs the power supply (e.g., the landing gear is
down), the vehicle can request 1230 that the load be disconnected and the
controller
can disconnect 1235 the module, or modules. In some embodiments, the system
can
also continuously or periodically check 1240 for current system requirements
and
reassign modules as required.
Example 1
In one example, each module 100 can have a 10A rating. With ten modules
100 in a converter 300, therefore, the converter can provide 100A. If the
aircraft
requests a 25A load to power the hydraulic motors for the landing gear, for
example,
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CA 02905116 2015-09-21
the system 300 can determine that the load requires at least three modules
100,
place three modules 100 in parallel, and then assign and activate three
modules 100
to the load. If, during the operation of the landing gear, for example, the
power
requirements change ¨ e.g., the power required to start the motors is greater
than the
continuous power to run the motors ¨ the system 300 can remove (or add)
modules
100 as the load changes.
Similarly, as shown in Fig. 13, embodiments of the present disclosure can also
comprise a method 1300 for distributing power for multiple loads. In some
embodiments, the method 1300 can comprise receiving 1305 at least two load
requests from the vehicle. The controller can then determine 1310 if the load
requests are above or below the power rating for a single module. If the load
requests are below the rating for a single module, the controller can assign
1320b
each load to a single module. If, on the other hand, either (or both) load is
greater
than a single module can power, the controller can parallel 1315a, 1315c two
or more
modules together and then assign 1320a, 1320c the loads to the parallel
modules, as
required. The system can then activate 1325 the modules. In some embodiments,
the system can also continuously or periodically check 1340 for current system
requirements and reassign 1320 modules as required. When the vehicle no longer
needs the power supply for one or both loads, the vehicle can request 1330
that the
load be disconnected and the controller can disconnect 1335 the module, or
modules
for that load.
Example 2
In another example, as above, each module 100 can again have a 10A rating
and ten modules 100 in a converter 300 for a total of 100A capacity. If the
aircraft
requests a first, 15A, load to power the hydraulic motors for the landing
gear, for
example, and a second, 7.5A, load to turn the cabin fan on low, the system 300
can
determine that the load requires at least three modules 100. The system 300
can
place a first module 100 and a second module 100 in parallel. The system 300
can
then assign the first load to the first module 100 and the second module 100
and the
second load to a third module 100.
CA 02905116 2015-09-21
The system 300 can again continuously or intermittently check to see if the
vehicle power requirements have changed 1340. If, during the operation of the
landing gear, for example, the power requirements change ¨ e.g., the power
required
to start the motors is greater than the continuous power to run the motors ¨
and/or
.. the vehicle requests that the cabin fan be placed on high, the system 300
can
decouple 1315c the first and second modules, pair the second and third modules
and
assign 1320c the first load (the landing gear) to the first module 100 and the
second
load (the cabin fan) to the second and third modules 100 as the load changes.
Having a plurality of modules 100 in parallel enables the modules 100 to power
loads that exceed their individual power ratings. Any number of modules 100
could
theoretically be ganged together to power any load. In practice, however, the
same
input signal does not necessarily produce the same output signal in all
modules 100.
This can be due to, for example and not limitation, manufacturing tolerances
in the
modules 100, varying resistances (impedances) in the wiring and connections of
the
.. system 300, and variances in the input signals. These variances, in turn,
cause
variances in the outputs of the modules 100, which results in load imbalances
between parallel modules 100.
If the load imbalance is large enough, system components can be damaged or
destroyed. Because current divides between parallel modules 100 in inverse
proportion to their impedance, a larger current flows through the module 100
with
smaller impedance. As a result, a module 100 with lower impedance (and
relatedly, a
lower load capacity) can be overloaded, while a higher impedance module 100
would
be loaded below its capacity. Similarly, the effect of phase imbalances from
the AC
source (e.g., one phase has a large amplitude than the other) is that each
module
.. 100 shares the total load unequally.
Whether from a phase imbalance, poorly matched impedance, or other
causes, for a 30A load, for example, each of three modules might not see a
consistent 10A, but instead see 15A, 8A, and 7A. The load sees the correct 30A
and
thus operates normally (e.g., the load does not "care" how the power is
distributed.)
The IGBTs in the inverters 1015, on the other hand, may carry more than their
rated
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CA 02905116 2015-09-21
current and this might cause overheating, destruction of the IGBT devices, or
erratic
tripping of over-current protection, among other things. This can result in
failure of
the lower impedance module 100, poor system utilization, maintenance issues,
and
poor system reliability.
To this end, embodiments of the present disclosure can also comprise
systems and methods 1400 for balancing loads, controlling phase-to-phase
imbalance, and reducing circulating current between parallel modules 100.
Embodiments of the present disclosure can comprise a method 1400 for balancing
the output current between paralleled modules, as shown in Fig. 14.
In some embodiments, the method 1400 can comprise receiving a load
request from an external aircraft system 1405. As before, the method 1400 can
then
comprise calculating the number of parallel modules required to power the
request,
as shown at 1410. So, for example, if a 45A load is requested, and the system
uses
10A modules, the system can determine that a minimum of 5 parallel modules is
required. The method 1400 can continue by calculating the theoretical ideal
load
sharing between the modules, as shown at 1415. In other words, the load that
each
module would power if the impedance of each module was perfectly matched. In
the
example above, if each module were perfectly matched, for example, each would
provide 9A to power the load. As mentioned above, the modules can be activated
by
the system controller 1035 and an appropriate motor control algorithm 1022.
The method 1400 can then measure the output current of each of the activated
modules, as shown at 1425, and then determine if the actual output of each
module
is approximately equal to the ideal load (from 1415), as shown at 1430. In
some
embodiments, this can be done by direct measurement of the output current or
voltage for each module. In other embodiments, the system can monitor other
types
of feedback in the system, such as, for example and not limitation, inverter
temperature, circulating current, or phase imbalance at the load. Modules with
higher
outputs, for example, will have higher operating temperatures than modules
with
lower outputs.
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CA 02905116 2015-09-21
As discussed above, because the system uses a single algorithm to calculate
the control signals (e.g., PWM gate signals) the outputs of paralleled modules
are
phase synchronized by design. As a result, any significant imbalance at the
load can
be an indication of a problem somewhere in the system, such as failing motor
windings or insulation causing a short-circuit or an IGBT is beginning to
fail. Thus,
imbalance at the load can be used as an indication of a fault condition.
In some cases, the terminal voltage of the power switches is small and can be
difficult to measure, especially in the presence of large amounts of EMI
(generated by
the fast switching times) and large currents. As a result, current
measurements are
generally considered a practical means of determining current sharing
imbalances
between paralleled modules. If an imbalance exists between the modules, the
method can continue by modifying the motor control algorithm to balance the
outputs
of the modules, as shown at 1435.
If one phase of one module is providing more current than the others it is
paralleled with, for example, the pulse width can be slightly reduced to that
module
and increased on the other modules to balance their outputs. It is also
possible to
modify the motor control algorithm to compensate for imbalances. In FOC, for
example, the method 1400 can take motor measurements and input commands to
generate an "average" output command in rotating coordinate system, and a
correction can be applied per module. The method 1400 can then generate a
different set of PWM signals for each module based on those corrections. In
most
cases, inputs are all digital including, for example and not limitation, a
variable
computed in the control algorithm or direct digital logic PWM signals.
This method 1400 can continue while the load is being powered. In some
embodiments, the output current can be monitored constantly, for example, or
at a
predetermined interval (e.g., once per second). In some embodiments, the
method
1400 can end when the vehicle controller indicates the load no longer needs to
be
powered, for example, or when main power to the aircraft is cut (e.g., for
overnight
storage of the aircraft).
23
CA 02905116 2015-09-21
In other embodiments, as shown in Fig. 15, the system 1500 can comprise a
load balancer 1505 for balancing the output current for a plurality of
modules, or
inverters 1015. The load balancer 1505 can receive inputs from the system 1500
including, for example and not limitation, the requested load from the system
controller 1035, the input motor control signal 1510 from the motor control
system
1020 (via the control switching network 1025) for each inverter 1015, and the
output
current 1515 for each inverter 1015. So, for example, if each inverter 1015 is
receiving the same input 1510, but a first inverter 1015 is providing a lower
output
current 1515, the load balancer 1505 can modify the input motor control signal
1510
to the first inverter 1015 to obtain a matched output current 1515 to the
remaining
inverters 1015.
In some embodiments, the load balancer 1505 can comprise many types of
feedback controllers. In some embodiments, the load balancer 1505 can
comprise,
for example and not limitation, a proportional-integral (PI), proportional-
integral-
derivative (PID) controller, fuzzy logic, or neural net. In other embodiments,
the load
balancer 1505 can calculate the theoretical "ideal" load for each inverter
1015 (as
previously shown at 1415). In some embodiments, the ideal load can assign an
equal portion of the load to each inverter 1015. In this manner, the load
balancer
1505 can monitor the output current 1515 for each inverter 1015 and adjust the
input
motor control signal 1510 accordingly. In this configuration, the error for
the load
balancer 1505 is the difference between the output current 1515 for each
inverter
1015 and the ideal output current (e.g., such that each inverter 1015 is
providing the
same proportion of the total load requested from the vehicle controller 1040).
The
load balancer 1505 can then minimize the error (e.g., current imbalance) by
adjusting
the input motor control signal 1510 to each inverter 1015.
While several possible embodiments are disclosed above, embodiments of the
present disclosure are not so limited.
For instance, while several possible
configurations have been disclosed for the parallel module converter
components,
other suitable configurations and components could be selected without
departing
from the spirit of the disclosure. The load balancer 1505 is depicted as a
separate
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CA 02905116 2015-09-21
controller, for example; however, the load balancer 1505 could also be
incorporated
into an existing controller (e.g., the system controller 1035) to decrease the
number of
separate components in the system. In addition, the location and configuration
used
for various features of embodiments of the present disclosure such as, for
example,
the number of modules, the types of electronics used, etc. can be varied
according to
a particular aircraft or application that requires a slight variation due to,
for example,
the size or construction of the aircraft, or weight or power constraints. Such
changes
are intended to be embraced within the scope of this disclosure.
The specific configurations, choice of materials, and the size and shape of
various elements can be varied according to particular design specifications
or
constraints requiring a device, system, or method constructed according to the
principles of this disclosure. Such changes are intended to be embraced within
the
scope of this disclosure. The presently disclosed embodiments, therefore, are
considered in all respects to be illustrative and not restrictive. The scope
of the
disclosure is indicated by the appended claims, rather than the foregoing
description,
and all changes that come within the meaning and range of equivalents thereof
are
intended to be embraced therein.
