U.S. patent application number 16/178938 was filed with the patent office on 2019-03-07 for droop compensation using current feedback.
The applicant listed for this patent is NANTENERGY, INC.. Invention is credited to Ramkumar KRISHNAN, Mark NADEN.
Application Number | 20190074689 16/178938 |
Document ID | / |
Family ID | 50384490 |
Filed Date | 2019-03-07 |
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United States Patent
Application |
20190074689 |
Kind Code |
A1 |
NADEN; Mark ; et
al. |
March 7, 2019 |
DROOP COMPENSATION USING CURRENT FEEDBACK
Abstract
A system includes a boost converter configured to amplify input
voltage received from one or more power sources into output
voltage. The system also includes a current sensor configured to
sense a current of the input voltage for example, by induction. The
system further includes a controller configured to adjust an
amplification of the boost converter in response to the current
sensed by the current sensor. When utilized in each of a plurality
of power source modules coupled to a common load, the power source
modules adjust the amplifications of their boost converters towards
equalization of their output voltages and their currents in
response to sensed currents of the input voltages changing through
demand of the common load. Associated systems and methods are also
disclosed.
Inventors: |
NADEN; Mark; (Oro Valley,
AZ) ; KRISHNAN; Ramkumar; (Scottsdale, AZ) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NANTENERGY, INC. |
Scottsdale |
AZ |
US |
|
|
Family ID: |
50384490 |
Appl. No.: |
16/178938 |
Filed: |
November 2, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14039285 |
Sep 27, 2013 |
|
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16178938 |
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61707478 |
Sep 28, 2012 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02M 2001/0025 20130101;
Y10T 307/707 20150401; H02M 3/1584 20130101; H02J 1/102
20130101 |
International
Class: |
H02J 1/10 20060101
H02J001/10; H02M 3/158 20060101 H02M003/158 |
Claims
1. A system comprising: a plurality of boost converters each
coupled to a respective one or more electrochemical cells for
receiving an input signal therefrom, each of the boost converters
being configured to amplify voltage of the input signal received
from its respective one or more electrochemical cells into an
output signal, the output signals being supplied simultaneously to
a common load; a current sensor associated with each of the
plurality of boost converters, each current sensor being configured
to sense a current of the input signal for its associated boost
converter prior to amplification of the input signal by the boost
converter; and a controller associated with each of the plurality
of boost converters, each controller being configured to adjust the
voltage amplification of the associated boost converter in response
to the current sensed by the associated current sensor, wherein the
adjustment decreases the amplification as the current sensed
increases based on demand from the load; wherein the boost
converters and their controllers are independent of one another
such that the boost converters operate independently of one another
to cause the respective currents of the input signals to trend
towards mutual equilibrium with each other.
2. The system of claim 1, wherein each current sensor is configured
to sense the current of the associated input signal by
induction.
3. The system of claim 1, wherein each current sensor is configured
to sense the current of the associated input signal by a resistive
method.
4. The system of claim 1, wherein each controller is further
configured to adjust the amplification of the boost converter in
response to the voltage of the output signal.
5. The system of claim 1, wherein each controller is further
configured to: receive a fixed reference voltage; adjust the fixed
reference voltage in response to the current sensed by the current
sensor into a voltage reference; adjust the voltage reference in
response to the output voltage into a current reference; and adjust
the current reference in response to the current sensed by the
current sensor into an error output associated with the current
reference.
6. The system of claim 5, wherein the fixed reference voltage is
received from the one or more electrochemical cells.
7. The system of claim 5, wherein each controller is configured to
adjust the fixed reference voltage by: converting the current
sensed by the current sensor into a voltage associated with the
current; scaling the voltage associated with the current into a
reduced voltage associated with the current and the fixed reference
voltage; and subtracting the reduced voltage from the fixed
reference voltage.
8. The system of claim 7, wherein scaling the voltage comprises
reducing the voltage associated with the current relative to the
fixed reference voltage and the output voltage.
9. The system of claim 7, wherein each controller is further
configured to adjust the fixed reference voltage by subtracting a
software-generated voltage adjustment.
10. The system of claim 9, wherein the software-generated voltage
adjustment is received as a user input.
11. The system of claim 9, further comprising time delaying the
reduced voltage associated with the current.
12. The system of claim 5, wherein each controller is further
configured to adjust the voltage reference in response to the
output voltage by: scaling the output voltage relative to fixed
reference voltage as a scaled output voltage; and subtracting the
scaled output voltage from the fixed reference voltage.
13. The system of claim 5, wherein each controller is further
configured to adjust the current reference by: converting the
current sensed by the current sensor into a voltage associated with
the current; and subtracting the voltage associated with the
current from the current reference.
14. The system of claim 13, wherein each controller is further
configured to adjust the current reference by subtracting a
software-generated current adjustment from the voltage associated
with the current.
15. The system of claim 14, wherein the software-generated current
adjustment is received as a user input.
16. The system of claim 5, wherein each boost converter comprises a
pulse width modulator, and wherein each controller is configured to
adjust the amplification of the boost converter by receiving the
error output associated with the current reference into the pulse
width modulator.
17. The system of claim 1, wherein the respective one or more
electrochemical cells coupled to each boost converter is a
plurality of electrochemical cells, and wherein each of the
plurality of boost converters receives the input signal from its
respective plurality of electrochemical cells.
18. The system of claim 17, wherein the electrochemical cells
comprise metal air cells.
19. The system of claim 1 wherein the one or more power
electrochemical cells are coupled in parallel to a voltage bus.
20. The system according to claim 1, wherein the boost converters
are also configured to operate independently of one another to also
cause the voltages of the output signals to trend towards
equilibrium.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This Application is a Continuation Application of U.S. Ser.
No. 14/039,285 filed, Sep. 27, 2013 which in turn claims priority
to U.S. Provisional Application Ser. No. 61/707,478, filed Sep. 28,
2012. The contents of each of these application is incorporated
herein by reference in entirety., the entirety of which is hereby
incorporated herein by reference.
FIELD
[0002] The present invention is generally related to power sources,
and more particularly to controllers associated therewith.
BACKGROUND
[0003] It is often advantageous to couple different power sources
together to supply a greater quantity of power than achievable by
any individual source. For example, electrochemical cells are often
coupled together to form electrochemical cell systems (i.e.,
batteries). In some electrochemical cell systems, it may be
advantageous to control each electrochemical cell therein, or
subsets of the electrochemical cells therein, so as to increase
overall system efficiency in supplying power to a load. For
example, where one or more electrochemical cells (e.g., grouped
into modules) in the electrochemical cell system fail or experience
a performance drop relative to the other electrochemical cells or
modules, it may be desirable to attempt to equalize currents
between different cells, while sharing power between the modules.
In particular, generally equal module lifespan across the system
may be based more on the current draw associated with each module
than on the total energy or power supplied by the module. Such a
configuration may facilitate a uniform replacement schedule for
modules in the system by generally equalizing the lifespans of each
of the modules of the system.
[0004] Conventionally, to share currents across electrochemical
cells, slave cells or modules are tied to a master cell or module,
so that the master cell or module establishes the current draw for
the system. Where the master cell or module fails or experiences
other performance degradation, however, the entire system's
performance may correspondingly degrade. Among other disadvantages,
this conventional method fails to maintain the independence of
modules.
[0005] Accordingly, the disclosure of the present application
endeavors to accomplish these and other results.
SUMMARY
[0006] According to an embodiment, a system includes a boost
converter configured to amplify input voltage received from one or
more power sources into output voltage. The system also includes a
current sensor configured to sense a current of the input voltage.
Current can be measured by a magnetic method (i.e. induction) or
purely resistive method (i.e. precise resistor) or a combination of
these methods. The system further includes a controller configured
to adjust an amplification of the boost converter in response to
the current sensed by the current sensor.
[0007] According to another embodiment, a system includes a
plurality of power source modules. Each power source module
includes a boost converter configured to amplify input voltage
received from one or more power sources into output voltage. Each
power source module also includes a current sensor configured to
sense a current of the input voltage for example, by induction.
Each power source module further includes a controller configured
to adjust an amplification of the boost converter in response to
the current sensed by the current sensor. The plurality of power
source modules are coupled to a common load through the output
voltage. The plurality of power source modules adjust the
amplifications of their boost converters towards equalization of
their output voltages and their currents in response to sensed
currents of the input voltages changing through demand of the
common load.
[0008] According to another embodiment, a method of equalizing
current across a plurality of power sources coupled to a common
load includes, for each of the power sources, amplifying, using a
boost converter, input voltage received from one or more power
sources into output voltage. For each of the power sources, the
method also includes sensing, using a current sensor, a current of
the input voltage by induction. For each of the power sources, the
method further includes adjusting an amount of said amplifying in
response to the current sensed by the current sensor. By adjusting
the amount of said amplifying, the plurality of power sources
approach a stable equilibrium of output voltages and currents.
[0009] Other aspects of the present invention will become apparent
from the following detailed description, the accompanying drawings,
and the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] Embodiments of the invention will now be described, by way
of example only, with reference to the accompanying schematic
drawings in which corresponding reference symbols indicate
corresponding parts, and in which:
[0011] FIG. 1 depicts a schematic view of an electrochemical cell
system having a plurality of modules, each containing a plurality
of electrochemical cells therein; and
[0012] FIG. 2 depicts a schematic control diagram of a control
circuit associated with each module, configured to perform droop
compensation for an associated module relative to other modules in
the electrochemical cell system of FIG. 1.
DETAILED DESCRIPTION
[0013] FIG. 1 illustrates a schematic view of an electrochemical
cell system 100. In the illustrated embodiment, the electrochemical
cell system 100 includes a plurality of cell modules 110
(individually cell modules 110a, 110b, and 110N-N being an integer
of 3 or more), each including a plurality of electrochemical cells
therein. It may be appreciated that the electrochemical cell system
100 may include any appropriate number of cell modules 110 therein
(e.g., two or more). In various embodiments, the cell modules 110
may include a different number of electrochemical cells 120
therein. In the illustrated embodiment, each module 110 includes
eight electrochemical cells 120 (specifically, electrochemical
cells 120a(i-viii) in cell module 110a, electrochemical cells
120b(i-viii) in cell module 110b, and electrochemical cells
120N(i-viii) in cell module 110N).
[0014] In an embodiment the electrochemical cells 120 of each cell
module 110 may be subdivided into two interface groups, each having
an associated cell interface unit 130. As shown, cell interface
unit 130a(a) may group cells 120a(i)-(iv), while cell interface
unit 130a(b) may group cells 120a(v)-(viii). Similarly, cell
interface unit 130b(a) may group cells 120b(i)-(iv), while cell
interface unit 130b(b) may group cells 120b(v)-(viii). Furthermore,
cell interface unit 130N(a) may group cells 120N(i)-(iv), while
cell interface unit 130N(b) may group cells 120N(v)-(viii). In an
embodiment, the cell interface units 130 may link the cells 120
associated therewith in series. Additionally, the cell interface
units 130 may themselves be linked in series. As such, the voltage
of each of the cells 120 in a given cell module 110 may add up. In
the illustrated embodiment, with eight electrochemical cells 120 in
each cell module 110, if each electrochemical cell 110 supplies 1
VDC volt, then the eight cells 120 in series may supply 8 VDC. It
may be appreciated that different cell modules 110 may supply
different voltages (e.g., one cell module supplies 8 VDC, while
another supplies 6 VDC).
[0015] While the electrochemical cells 120 may vary across
embodiments, in some embodiments one or more of the cells 120,
and/or other features of the electrochemical cell system 100, may
include elements or arrangements from one or more of U.S. patent
application Ser. No. 12/385,217 (issued as U.S. Pat. No.
8,168,337), Ser. No. 12/385,489 (issued as U.S. Pat. No.
8,309,259), Ser. No. 12/549,617 (issued as U.S. Pat. No.
8,491,763), Ser. Nos. 12/631,484, 12/776,962, 12/885,268,
13/028,496, 13/083,929, 13/167,930, 13/185,658, 13/230,549,
13/299,167, 13/362,775, 13/531,962, 13/532,374 13/566,948, and
13/668,180, each of which are incorporated herein in their
entireties by reference. That is, the cells (and the system made up
of those cells) may be a rechargeable power source (also referred
to as secondary cells), which may be charged by an external power
source (e.g., solar cells, wind turbines, geothermally generated
electricity, hydrodynamically generated electricity, engine/brake
generated electricity, the main power grid, etc.) and discharged as
needed/desired (e.g., as back-up power, to discharge stored power,
in lieu of a fossil fuel engine, etc.).
[0016] In some embodiments the cell interface units 130 may be
configured to monitor the status of each cell 120 associated
therewith, and may provide switching or other functionality
configured to isolate or otherwise bypass faulty cells 120, such as
is described in U.S. patent application Ser. No. 13/299,167,
incorporated by reference above. As another example, in embodiments
where one or more of the electrochemical cells 120 are metal-air
cells, the cells 120 may be utilized at least in part to power a
cathode blowers 140 (individually cathode blowers 140a, 140b, and
140N as illustrated) associated with the cell modules 110, which
may be configured to direct a flow of air or other oxidant to
oxidant electrodes associated with each of the cells 120, as
described in U.S. patent application Ser. No. 13/531,962, entitled
"Immersible Gaseous Oxidant Cathode for Electrochemical Cell
System," incorporated by reference in its entirety above.
[0017] For each module 110, a cluster control unit 150
(individually cluster control units 150a, 150b, and 150N in the
illustrated embodiment) links the cell interface units 130, and
provides programmatic control thereof via a serial communications
interface (SCI) associated with each. The cluster control units 150
may be linked to each other through a Controller Area Network (CAN)
Bus 160. Programmatic or other control of the cell modules 110 may
be provided from a main control unit 170, which may also be linked
to the CAN Bus 160. Embodiments of such programmatic control are
described in greater detail below. In some embodiments, such as
that illustrated, an AC Fail circuit 180 may also be implemented in
the electrochemical cell system 100, and may be coupled to the main
control unit 170 and each of the cluster control units 150. The AC
Fail circuit 180 may be configured to direct the cluster control
units 150 of the cell modules 110 to supply power to an AC Bus 190
on an as-needed basis. For example, if AC power on the grid fails,
the AC Fail circuit 180 may be configured to draw power from the
electrochemical cells 120. It may be appreciated that in some
embodiments the AC Bus 190 may generally receive DC power from the
cell modules 110, however may be associated with an inverter
configured to convert the DC power to AC power. In other
embodiments, each cell module 110 may include one or more
inverters, configured to supply AC voltage across the AC Bus 190.
In some embodiments, the AC Bus 190 may be coupled to the main
control unit 170 (e.g., through any appropriate sensor or sensing
system), as illustrated by the dashed line therebetween in FIG. 1.
In an embodiment, the main control unit 170 may control an inverter
associated with the AC bus 190. In some embodiments, the functions
of the AC Fail circuit 180 may be combined with the CAN Bus 160, or
any other appropriate another control link.
[0018] It may be desirable to perform droop compensation in the
electrochemical cell system 100, so as to facilitate equalization
of currents, which may correspondingly equalize a lifecycle of the
cell modules 110 and the electrochemical cells 120 therein. By
equalization of currents, it may be understood that the droop
compensation may facilitate generally or essentially equalizing the
currents (e.g., driving the currents towards equalization, into a
state generally regarded in the art as being equalized). In an
embodiment, droop compensation may be performed utilizing a control
circuit associated with a controller in each cluster control unit
150. As such, in some embodiments droop compensation may be
performed on a cell module by cell module basis. In other
embodiments, droop compensation may be performed among subsets of
the cell modules 110, such as by being implemented at the level of
the cell interface units 130. In still other embodiments, droop
compensation may be performed on a cell by cell basis, being
implemented associated with each individual electrochemical cells
120. Other implementations are also possible.
[0019] FIG. 2 illustrates a control block diagram for a control
circuit 200 illustrating an example of how droop compensation may
be implemented (e.g., on the electrochemical cell system 100)
according to an embodiment. In the illustrated embodiment, the
control circuit 200 shows that the control scheme operates on a
conversion from a boost input voltage 210 to a boost output voltage
220, via a boost circuit 225 (i.e., a converter), described in
greater detail below. In the example illustrated, the boost input
voltage 210 is shown as being 8 VDC nominal. It may be appreciated
that such an input voltage may result from the summation in series
of each of the eight electrochemical cells 120 associated with each
electrochemical cell module 110, outputting 1 VDC each.
Additionally, as shown, in an embodiment the boost output voltage
220 may be stepped up (i.e., amplified) to 52 VDC nominal by the
boost circuit 225. In the example illustrated, the 52 VDC.fwdarw.42
VDC range may be based on telecom requirements, wherein all loads
are active at 52 VDC, noncritical loads (NCL) drop out at 48 VDC,
and only critical loads (CL) are kept active around 42-45 VDC.
While having a CL voltage range instead of a fixed value is
uncommon, the range may be based on any customer desired range. It
may be appreciated that one could adjust scaling factors to
accommodate the ranges. As described in greater detail below, the
amplification of the boost circuit 225 may be variable, so as to
provide the desired droop compensation. In an embodiment, the boost
output voltage 220 may be output to the AC Bus 190 of the
electrochemical cell system 100.
[0020] In an embodiment, to perform the droop compensation using
the control circuit 200, a fixed reference voltage 230 is received
at a first summation junction 240. In the illustrated embodiment,
the fixed reference voltage 230 is 5 VDC. It may be appreciated
that the 5 VDC may be an exemplary scaling point, and could be
anywhere from 1 VDC to 10 VDC in some embodiments, depending on
nominal board operating voltage. The fixed reference voltage 230
may be provided by any appropriate source, including, for example,
ultimately from one or more of the electrochemical cells 120, or
from a separate power source. At the first summation junction 240,
the fixed reference voltage 230 may have a first voltage modifier
250 subtracted therefrom. As described in greater detail below, the
first voltage modifier 250 may be computed from a sensed current
(I) associated with the boost input voltage 210. A software voltage
adjustment 260 may also be applied at the first summation junction
240, also being subtracted from the fixed voltage reference 230. In
some embodiments, the software voltage adjustment 260 may be
computed or otherwise derived from properties of the cell, or may
be received as a user input. In an embodiment, the software voltage
adjustment 260 may range from 0V to 0.962V, as described in greater
detail below. It may be appreciated that the value 0.962 may be
calculated as a scaling factor based on the 5 VDC reference. When
the scaling factor is at zero, boost output voltage is 52 VDC. When
the scaling factor is at 0.962, however, the boost output voltage
is 42 VDC. The adjustment alteration may be based on user control
of what loads are active (i.e. critical loads, non-critical loads).
The value may be any number and is only dependent the boost output
voltage range desired. The summation of the fixed reference voltage
230, minus the software voltage adjustment 260 and the first
voltage modifier 250, may be output as a voltage reference 270.
[0021] The voltage reference 270 may be input into a second
summation junction 280. At the second summation junction 280, a
second voltage modifier 290 may be subtracted from the voltage
reference 270. As shown in the illustrated embodiment, the second
voltage modifier 290 may be computed based on the boost output
voltage 220, which may form a PI loop (i.e., a
proportional-integral loop, wherein the control circuit 200
comprises a PI controller). In particular, in an embodiment, the
boost output voltage 220 may be fed into a step down op-amp 300,
which in the exemplary embodiment of FIG. 2, has a gain of 0.096.
This is so in the illustrated embodiment because the boost output
voltage 220 is nominally 52 VDC, while the fixed reference voltage
230 is 5 VDC (52 VDC*0.096.apprxeq.5 VDC).
[0022] If there were no load associated with the boost output
voltage 220, then there would be no current associated with the
boost input voltage 210. As such, the first voltage modifier 250
associated with the lack of a sensed current would be zero, and
(absent any software voltage adjustment 260) the voltage reference
270 would be the same as the fixed reference voltage 230. With the
gain of the step down op-amp 300 being associated with the fixed
reference voltage 230, in such a situation the voltage reference
270 would be equal to the second voltage modifier 290, resulting in
an error output 310, i.e., e(t), of zero. It may be appreciated
that where the boost output voltage 220 drops, the second voltage
modifier 290 also drops, creating a non-zero error output 310. As
described in greater detail below, the error output 310 may be
utilized to modify the amplification of the boost circuit 225 from
the boost input voltage 210 to the boost output voltage 220, to
compensate for the change.
[0023] When a load is applied to the boost output voltage 220, the
first voltage modifier 250, associated with a current associated
with the boost input voltage 210, may adjust the voltage reference
270. Specifically, with the addition of a load, the current
associated with the boost input voltage 210 may increase from zero
to a positive value. As shown in FIG. 2, to detect the current of
the boost input voltage 210, the boost circuit 225 may include
therein a current sensor 320. In an embodiment, a wire carrying the
boost input voltage 210 may be run through the current sensor 320,
which may pick up an associated magnetic field associated
therewith, and output an inductor current measurement 325 that is
proportional to the magnetic field. The current may be measured by
the current sensor 320 as amperes (A). Such an ampere inductor
current measurement 325 may be converted into a voltage reading by
a current to voltage converter 330 (as the controls implemented in
the control circuit 200 may generally operate in voltages). The
inductor current measurement 325, as converted to a voltage, may
then be fed back through the control circuit 200 to establish the
first voltage modifier 250, described above. It may therefore be
appreciated that because the first voltage modifier 250 is utilized
in establishing the voltage reference 270, the inductor current
measurement 325 is also utilized to establish the error output 310.
In some embodiments, the current sensor 320 may sense current by
other means besides induction. For example, a current sense
resistor may be employed with known precision resistance.
[0024] As shown, the error output 310 is utilized to establish a
current reference 335 (i.e., "I-ref") for the control circuit 200.
It may be appreciated that in some embodiments the system
implementing the control circuit 200 (e.g., the system 100) may
have a current limit of 40 ADC. Such a current limit may correspond
to a 2.5 VDC limit in the control circuit 200. It may be
appreciated that the 40 ADC limit may be by user requirement, and
may be a protection limit so, for example, if customer load sources
more than 40 A out of module, this will limit input current from
modules. If bus is shorted, 40 A limit will clamp, thus only
allowing 40 A for protection purposes. The example selection of a
2.5V limit in the illustrated embodiment is user selected, and in
some embodiments could range from approximately 1V to 10V. If bus
is overloaded (e.g., a shorted out bus), the output voltage is
forced to zero, and the error output will saturate. The saturated
error output may command I-ref to go high (however capped by the
limit). As an example, with a current swing or a customer demand of
40 A, the boost output voltage will go below 52 VDC, but it is
desirable to stay above 48 VDC so as not to drop out critical loads
CL. Accordingly, when input current is 40 A, the 480 mV value may
be scaled from the 5 VDC exemplary selection, similar to the
software adjustments. In the illustrated embodiment, the error
output 310 associated with the voltage reference 270 passes through
a voltage limiter 340, which limits the error output 310 to 2.5V,
corresponding to 40 ADC. The error output 310, as limited by the
voltage limiter 340, may be considered the current reference 335.
Similarly, because a 40 A limit may exist for the measurement of
the current sensor 320, the current to voltage converter 330 may
also correspond to a limit of 2.5V, which amounts to 62.5 mV/A. A
step down op-amp 350 having a gain or 0.192 may reduce the
influence of the inductor current on the control circuit 200 to 12
mV/A (480 mV=40 ADC). In some embodiments, the reduced voltage
associated with the inductor current may then be fed into a timing
delay 360. In the illustrated embodiment, the timing delay 360 may
be for 100 ms. Other time delays are also possible in other
embodiments. It may be appreciated that the timing delay 360 may be
configured to slow down the operation of the control loop, which
may dampen out the loop of the control circuit 200, to prevent high
oscillation before achieving stability, as described in greater
detail below. It may be appreciated that some embodiments might not
include a timing delay 360, but might include other mechanisms to
prevent undesirable oscillation of the loop of the control circuit
200.
[0025] The reduced voltage associated with the inductor current,
which in the illustrated embodiment results from the step down
op-amp 350, and may be time delayed by the timing delay 360, may
thus be fed back into the first summation junction 240 as the first
voltage modifier 250, which determines the voltage reference 270.
Having utilized the inductor current to establish the error output
310 associated with the voltage reference 250, the inductor current
may then be utilized to establish an error output 370 associated
with the current reference 335. Specifically, the current reference
335, established based on the voltage reference 270 and the reduced
boost output voltage 220 (as the second voltage modifier 290) may
be adjusted at a third summation junction 380. In an embodiment the
inductor current measurement 325, converted to a voltage by the
current to voltage converter 330, may be subtracted directly from
the current reference 325. In other embodiments, such as that
illustrated, a fourth summation junction 390 may allow the inductor
current measurement 325, as converted to a voltage, to be modified
by a software current adjustment 400. In some embodiments, the
software current adjustment 400 may be computed or otherwise
derived from properties of the cell, or may be received as a user
input. In an embodiment, the software current adjustment 400 may be
measured as a voltage, and may be between 0 and 2.5V, corresponding
to being between 0 and 40 ADC, as described above. Regardless, by
subtracting the inductor current measurement 325 (e.g., as
converted to voltage by the current to voltage converter 330, and
potentially as modified by the software current adjustment 400)
from the current reference 335, the error output 370 associated
with the current reference 335 may be computed. The error output
370 may then be received by the boost circuit 225, and may
determine an error input for a pulse width modulator 410 thereof.
The pulse width modulator 410 may be configured to dictate how much
current is drawn by the boost circuit 225, and may be tied into the
boost circuit 225 in such a manner so as to modify the boost
amplification from the boost input voltage 210 to the boost output
voltage 220, as described below.
[0026] Because the boost output voltage 220 is fed back through the
control circuit 200 in a manner that in part determines the error
output 310 associated with the reference voltage 270, and because
that boost output voltage 220, in conjunction with the load
demands, varies the current supplied in the boost input voltage 210
(sensed by the current sensor 320 as inductor current 325), which
is fed back to determine at least in part the voltage reference 270
and the current reference 335, it may be understood that the boost
circuit 225 as a whole will modulate the boost in response to
current demands associated with the load coupled to the boost
output voltage 220. With multiple boost circuits 225 coupled to a
common load, where each is controlled by control schemes such as
that found in the control circuit 200, the boost circuits 225 are
independent from one another in their operation, however may
respond to one another through the demands of the load on the
associated boost output voltages 220. The operation of this
responsiveness is discussed below.
[0027] It may be appreciated that the cell or cells associated with
whichever one of the boost circuits 225 is outputting a greatest
boost output voltage 220 would initially attempt to supply all of
the power to the load. The effect of that boost circuit 225
attempting to supply all of the power to the load would be an
associated increase in the inductor current, as discussed above.
The increase in inductor current then causes the control circuit
200 to droop the boost output voltage 220 for that boost circuit
225. Once the boost output voltage 220 from the boost circuit 225
falls below that of a second boost circuit 225 (having what was
previously the second highest boost output voltage 220) the second
boost circuit 225 would then itself attempt to supply all of the
power to the load. This would cause the second boost circuit 225 to
droop its boost output voltage 220. The process would then repeat,
creating a cycle where the boost circuits 225 and associated cells
attempt to supply all of the power to the load, and the output
voltages "droop" in response, which causes other boost circuits 225
and associated cells to continue the cycle. It may be appreciated
that the amount by which the boost circuit 225 droops the boost
output voltage 220 depends on the error output 370 established
based on the current reference 335. For example, where the current
reference 335 saturates at the 40 A limit, the boost circuit 225
may droop the boost output voltage 220 close to zero to
compensate.
[0028] Through the cycle, the different boost circuits 225 and
associated cells may oscillate as to which is attempting to fully
power the load. Eventually, all boost circuits 225 would trend
towards a stable equilibrium, where each of the boost circuits 225
have the same boost output voltage 220 and similarly, have the same
current reference 335. Even though the current reference 335 will
be driven towards equalization across all controllers, the output
current from the boost circuits 225 (e.g., associated with the
boost output voltages 220, and coupled in parallel to the load) may
be different for each converter. Accordingly, the current
associated with the boost input voltage 210 (e.g., as measured by
the current sensor 320 as the input inductor current 325) would
also be driven towards equalization by the boost circuit 225. It
may be appreciated that the equalization of currents, and the
common boost output voltage 220 across different cells or cell
modules, is independent of the boost input voltage 210 obtained
from the cell or cell modules.
[0029] Such independent ability of each cell or module to attempt
to equalize current may be beneficial to enhance performance and
lifespan of the cells of the system. To apply this understanding in
the context of the system 100 in FIG. 1, if the control schemes of
the control circuit 200 are implemented in each of the cluster
control units 150, a load associated with the AC Bus 190 may cause
the cluster control units 150 to react to one another, varying the
amplification of the boost circuits 225 associated with each to
attempt to equalize current demands across the cell modules 110.
Thus, if the cell module 110a initially has the highest boost
output voltage 220 being output to the AC Bus 190, the
electrochemical cells 120a(i-viii) would attempt to supply all of
the power to the load, and the current sensor 320 would identify
the increased current associated therewith. The sensed current
would be fed back through the control circuit 200 of the cell
module 110a, causing the boost circuit 225 of the cluster control
unit 150a to droop the amplification to supply a smaller boost
output voltage 220. If cell module 110b subsequently has the
greatest boost output voltage 220, then the electrochemical cells
120b(i-viii) would attempt to supply all of the power to the load
via the AC Bus 190, causing a corresponding increase in the current
sensed in the cluster control unit 150b. The current would be fed
back through the control circuit 200 of the cluster control unit
150b, causing the boost circuit 225 to similarly droop the
amplification. This may occur through the boost circuits 225
associated with each of the cluster control units 130 of the cell
modules 110, until each of the boost circuits 225 achieve a
stabilization point, with generally equal current being drawn by
the cell modules 110.
[0030] It may be appreciated that the boost circuit 225 may vary
across embodiments, and may be of any appropriate configuration.
Boost circuits 225 typically include two or more semiconductor
switches. For example, in the illustrated embodiment the boost
circuit 225 includes a Field Effect Transistor (FET) 420, and a
diode 430. The FET 420 opens and closes according to a duty cycle
440 (i.e., "D") provided by the pulse width modulator 410. Boost
circuits 225 may further include one or more energy storage
elements. In the illustrated embodiment, the boost circuit 225
includes an input inductor 450, and a pair of capacitors 460. In
operation, the switching of the FET 420, in conjunction with the
stored energy in the input inductor 450 and the capacitors 460,
results in the boost output voltage 220 being greater than the
boost input voltage 210, with the amount of amplification, in the
present embodiment, being variable depending on the duty cycle 440
from the pulse width modulator 410.
[0031] It may be appreciated that the control circuit 200 may be
implemented in a variety of systems, including but not limited to
system 100 of FIG. 1. Further, the source of the boost input
voltage 210 may vary across embodiments. While in the illustrated
embodiment eight cells (e.g., 120N(i-viii)) are electrically
coupled together in series to provide an 8 VDC source for the boost
input voltage 210, in other embodiments, the control circuits 200
may be implemented on individual electrochemical cells 120 (e.g.,
such that the boost input voltage 210 is 1 VDC). It may further be
appreciated that the cell modules 110 and/or the electrochemical
cells 120 therein may vary across embodiments.
[0032] As noted above, in some embodiments, the electrochemical
cells 120 may include features from those listed applications
incorporated by reference herein. For example, in some embodiments
the electrochemical cells 120 may include a plurality of permeable
electrode bodies. In some embodiments the plurality of permeable
electrode bodies may be configured to be electrically connected to
one another through charging of the electrochemical cell 120. In
some embodiments the permeable electrode bodies may be selectively
coupled to either an anode or a cathode in the electrochemical cell
120 during charging of the electrochemical cell 120, so as to form
a plurality of electrochemical cells within each electrochemical
cell 120 (e.g., by alternatively associating different permeable
electrode bodies with the anode and the cathode, so that fuel grows
on some of the permeable electrode bodies towards others of the
permeable electrode bodies).
[0033] Likewise, during discharge of the cells 120, in some
embodiments, the external load associated with the AC Bus 190 may
only be coupled to the terminal permeable electrode body, distal
from an oxidant reduction electrode of each electrochemical cell
120, so that fuel consumption may occur in series from between each
of the permeable electrode bodies. In other embodiments, the
external load may be coupled to some of the electrode bodies in
parallel, as described in detail in U.S. patent application Ser.
No. 12/385,489, incorporated above by reference. In some
embodiments, a switching system such as that described in U.S.
patent application Ser. No. 13/299,167, incorporated above by
reference, may facilitate selective electrical connections between
the permeable electrode bodies. In some embodiments, the cells may
be configured for charge/discharge mode switching, as is described
in U.S. patent application Ser. No. 12/885,268, incorporated by
reference above.
[0034] In some embodiments including a switching system, switches
associated therewith may be controlled by a controller, which may
be of any suitable construction and configuration. In the system
100 of FIG. 1, such controllers may be associated with each cell
120, each cell interface unit 130, each cluster control unit 150,
or with the main control unit 170. In some embodiments, the
controllers may have a hierarchal association with one another,
such that a more superior controller (e.g., in the main control
unit 170) may transmit commands to lower controllers (e.g., in the
cluster control units 150). In some embodiments, one or more of the
controllers may include features conforming generally to those
disclosed in U.S. application Ser. Nos. 13/083,929, 13/230,549 and
13/299,167, incorporated by reference above. In various
embodiments, the control of the switches of a switching system may
be determined based on a user selection, a sensor reading, or by
any other input. In some embodiments, the controller(s) may also
function to manage connectivity between the load and the AC Bus
190, or may selectively supply power (e.g., over the AC Bus 190) to
the electrochemical cells 120 for recharging thereof. As noted
above, in some embodiments, the controller may include appropriate
logic or circuitry for actuating bypass switches associated with
each electrochemical cell 120 coupled in the cell interface units
130 or otherwise in the cell modules 110, in response to detecting
a voltage reaching a predetermined threshold (such as drop below a
predetermined threshold).
[0035] The foregoing illustrated embodiments have been provided
solely for illustrating the structural and functional principles of
the present invention and are not intended to be limiting. For
example, the present invention may be practiced using a variety of
fuels, oxidizers, electrolytes, and/or overall structural
configurations or materials. Thus, the present invention is
intended to encompass all modifications, substitutions,
alterations, and equivalents within the spirit and scope of the
following appended claims.
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