U.S. patent application number 11/289837 was filed with the patent office on 2006-04-13 for method and system for controlling and recovering short duration bridge power to maximize backup power.
Invention is credited to Michael Cardin, Mark Lillis, Lawrence Moulthrop, A. John Speranza, John Zagaja.
Application Number | 20060078773 11/289837 |
Document ID | / |
Family ID | 26986606 |
Filed Date | 2006-04-13 |
United States Patent
Application |
20060078773 |
Kind Code |
A1 |
Speranza; A. John ; et
al. |
April 13, 2006 |
Method and system for controlling and recovering short duration
bridge power to maximize backup power
Abstract
A system for providing back-up power to a load powered by a
primary power source comprises: a fuel cell arrangement for
generating back-up power for the load, a bridging power source for
generating bridge power for the load, and a controller in operable
communication with the fuel cell arrangement and the bridging power
source. The controller is adapted to initiate application of the
bridge power to the load upon detecting a deterioration of power
from the primary power source, and is further adapted to initiate
application of the back-up power to the load upon detecting a power
capability of the back-up power to power the load.
Inventors: |
Speranza; A. John; (West
Hartford, CT) ; Cardin; Michael; (Berlin, CT)
; Moulthrop; Lawrence; (Windsor, CT) ; Lillis;
Mark; (South Windsor, CT) ; Zagaja; John;
(East Granby, CT) |
Correspondence
Address: |
CANTOR COLBURN, LLP - PROTON
55 GRIFFIN ROAD SOUTH
BLOOMFIELD
CT
06002
US
|
Family ID: |
26986606 |
Appl. No.: |
11/289837 |
Filed: |
November 30, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10065387 |
Oct 11, 2002 |
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11289837 |
Nov 30, 2005 |
|
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60328996 |
Oct 12, 2001 |
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60410412 |
Sep 13, 2002 |
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Current U.S.
Class: |
429/9 ; 320/101;
429/417; 429/418; 429/430; 429/515; 429/900 |
Current CPC
Class: |
Y02B 90/10 20130101;
Y10S 429/90 20130101; H01M 10/465 20130101; Y02E 60/10 20130101;
Y02E 60/50 20130101; H01M 8/0488 20130101; H01M 16/003 20130101;
H01M 8/04208 20130101; H01M 8/0656 20130101; H01M 8/04567 20130101;
H01M 8/04626 20130101; H02J 2300/30 20200101; H02J 9/06 20130101;
H01M 8/04656 20130101; H02J 7/345 20130101; H01M 8/04888 20130101;
H01M 8/04955 20130101 |
Class at
Publication: |
429/023 ;
429/021; 429/009; 320/101; 429/013 |
International
Class: |
H01M 8/04 20060101
H01M008/04; H01M 8/18 20060101 H01M008/18; H01M 16/00 20060101
H01M016/00 |
Claims
1. A system for providing back-up power to a load powered by a
primary power source, the system comprising: a fuel cell
arrangement for generating back-up power for the load; a bridging
power source for generating bridge power for the load; and a
controller in operable communication with the fuel cell arrangement
and the bridging power source, the controller adapted to initiate
application of the bridge power to the load upon detecting a
deterioration of power from the primary power source, the
controller further adapted to initiate application of the back-up
power to the load upon detecting a power capability of the back-up
power to power the load.
2. The system of claim 1, further comprising: a converter coupled
between the primary power source and the load, the converter for
converting power from the primary power source to power anticipated
by the load.
3. The system of claim 2, wherein the converter comprises a
rectifier to convert AC power from the primary power source to DC
power for the load.
4. The system of claim 1, wherein the fuel cell arrangement
comprises a regenerative fuel cell arrangement.
5. The system of claim 4, wherein the regenerative fuel cell
arrangement comprises: a fuel cell for generating the back-up
power; a hydrogen storage device in communication with the fuel
cell for providing hydrogen thereto; and an electrolysis cell in
communication with the hydrogen storage device, the electrolysis
cell for generating hydrogen to be stored at the hydrogen storage
device.
6. The system of claim 5, wherein the electrolysis cell is in
communication with the primary power source to power the
electrolysis cell.
7. The system of claim 1, wherein the bridging power source
comprises a battery.
8. A method for providing back-up power to a load powered by a
primary power source, the method comprising: generating back-up
power for the load from a fuel cell arrangement; generating bridge
power for the load from a bridging power source; initiating
application of the bridge power to the load upon detecting a
deterioration of power from the primary power source; and
initiating application of the back-up power to the load upon
detecting a power capability of the back-up power to power the
load.
9. The method of claim 8, further comprising: converting power from
the primary power source to power anticipated by the load.
10. The method of claim 9, wherein the converting power comprises
converting AC power from the primary power source to DC power for
the load.
11. A system for providing back-up power to a load powered by a
primary power source, the system comprising: a fuel cell
arrangement for generating back-up power for the load, wherein the
fuel cell arrangement comprises a fuel cell for generating the
back-up power; a hydrogen storage device in communication with the
fuel cell for providing hydrogen thereto; and an electrolysis cell
in communication with the hydrogen storage device, the electrolysis
cell for generating hydrogen to be stored at the hydrogen storage
device; a bridging power source for generating bridge power for the
load; a controller in operable communication with the fuel cell
arrangement and the bridging power source, the controller adapted
to initiate application of the bridge power to the load upon
detecting a deterioration of power from the primary power source,
the controller further adapted to initiate application of the
back-up power to the load upon detecting a power capability of the
back-up power to power the load; and a converter coupled between
the primary power source and the load, the converter for converting
power from the primary power source to power anticipated by the
load.
12. The system of claim 11, wherein the converter comprises a
rectifier to convert AC power from the primary power source to DC
power for the load.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation application of U.S.
patent application Ser. No. 10/065,387 filed Oct. 11, 2002, which
claims the benefit of U.S. Provisional Application No. 60/328,996,
filed Oct. 12, 2001 and U.S. Provisional Application No.
60/410,412, filed Sep. 13, 2002; the contents of all of which are
incorporated by reference herein in their entirety.
BACKGROUND OF INVENTION
[0002] This disclosure relates generally to power systems, and
especially relates to the storage and recovery of energy from a
renewable power source and electrochemical cells.
[0003] Geographically remote areas such as islands or mountainous
regions are often not connected to main utility electrical grids
due to the cost of installing and maintaining the necessary
transmission lines to carry the electricity. Even in remote
communities where the transmission lines are in place, it is not
uncommon for frequent and extended power outages due to weather
related faults. In either case, to prevent economic loss in times
of an electrical outage, it is often necessary for these
communities or industries in these regions to create local "micro"
electrical grids to ensure a reliable and uninterruptible power
system. This uninterruptible power system may be either a primary
system where there is no connection to the main utility grid, or a
backup system that activates when an outage occurs.
[0004] Electrical power for the local grids comes from a variety of
sources including hydrocarbon based and renewable power sources.
Within a particular grid it is not uncommon to have multiple
generation sources, such as diesel generators, natural gas
generators, photovoltaic arrays, and wind turbines working in
combination to meet the needs of the grid.
[0005] Electrical demands placed on the local grid will vary during
the course of a day, week, or season. Since it is not often
practical or possible to turn generation sources on and off,
inevitably excess power will be generated. This excess energy is
typically converted into another form of energy such as heat for
storage in another medium such as water. In cold climates, the
heated water can then be used for other purposes such as heating
buildings, cooking or maintaining temperature in equipment. As the
load requirements of the grid increase, it is difficult or
impossible to recapture the converted energy back into electrical
energy for use in the electrical grid. Further complicating matters
is that renewable power sources do not typically run continuously
at full power and will experience extended periods of low to no
energy output (e.g. night time or seasonal low wind periods).
[0006] Electrochemical cells are energy conversion devices, usually
classified as either electrolysis cells or fuel cells commonly
employed to address back-up power requirement when a grid fails or
when a renewable energy source is unavailable. An electrolysis cell
typically generates hydrogen by the electrolytic decomposition of
water to produce hydrogen and oxygen gases, whereas in a fuel cell
hydrogen typically reacts with oxygen to generate electricity. In a
typical fuel cell, hydrogen gas and reactant water are introduced
to a hydrogen electrode (anode), while oxygen gas is introduced to
an oxygen electrode (cathode). The hydrogen gas for fuel cell
operation can originate from a pure hydrogen source, methanol or
other hydrogen source. Hydrogen gas electrochemically reacts at the
anode to produce hydrogen ions (protons) and electrons, wherein the
electrons flow from the anode through an electrically connected
external load, and the protons migrate through a membrane to the
cathode. At the cathode, the protons and electrons react with the
oxygen gas to form resultant water, which additionally includes any
reactant water dragged through the membrane to cathode. The
electrical potential across the anode and the cathode can be
exploited to power an external load.
[0007] This same configuration is conventionally employed for
electrolysis cells. In a typical anode feed water electrolysis
cell, process water is fed into a cell on the side of the oxygen
electrode (in an electrolytic cell, the anode) to form oxygen gas,
electrons, and protons. The electrolytic reaction is facilitated by
the positive terminal of a power source electrically connected to
the anode and the negative terminal of the power source connected
to a hydrogen electrode (in an electrolytic cell, the cathode). The
oxygen gas and a portion of the process water exit the cell, while
protons and water migrate across the proton exchange membrane to
the cathode where hydrogen gas is formed. The hydrogen gas
generated may then be stored for later use by an electrochemical
cell.
[0008] In certain arrangements, the electrochemical cells can be
employed to both convert electricity into hydrogen, and hydrogen
back into electricity as needed. Such systems are commonly referred
to as regenerative fuel cell systems. Regenerative fuel cells may
be used in power generation systems as either primary or secondary
power sources. However, because regenerative fuel cell systems
generally take a certain amount of time from the point of initial
activation to delivering full power, there may be a brief delay of
power attendant thereto when switching over from a primary power
supply to backup power generated by a fuel cell supply. What is
needed in the art is a cost effective apparatus and method for
bridging short duration power interruptions.
SUMMARY OF INVENTION
[0009] Disclosed herein is a power system, comprising: a primary
power source in electrical communication with a bus and a bridging
power source, wherein the bridging power source comprises at least
one of a capacitor, a battery, and an electrolysis cell, and the
bridging power source is in electrical communication with said the;
and a secondary power source in electrical communication with the
bus, wherein the secondary power source comprises a fuel cell.
[0010] Also disclosed herein is a method for operating a power
system, comprising: monitoring a primary power source; if the
primary power source exhibits selected characteristics, directing
power from a bridging power source to a bus and initiating a
secondary power source wherein the secondary power source comprises
a fuel cell, and the bridging power source comprises at least one
of a capacitor, a battery, and an electrolysis cell; and unless the
secondary power source exhibits the selected characteristics,
powering the bus with the secondary power source and ceasing the
directing power from the bridging power source.
[0011] Further, disclosed herein is a storage medium encoded with a
machine-readable computer program code, said code including
instructions for causing a computer to implement the abovementioned
method for operating a power system.
[0012] Further, disclosed herein is a computer data signal, said
computer data signal comprising: instructions for causing a
computer to implement the abovementioned method for operating a
power system.
[0013] Also disclosed herein in an exemplary embodiment is a method
for operating a power system, comprising: if a primary power source
exhibits first selected characteristics and a secondary power
source comprising a fuel cell exhibits second selected
characteristics, powering selected loads with an electrolysis cell.
The first selected characteristics and the second selected
characteristics, individually include at least one of, unavailable
inoperable, inadequate to provide power at expected parameters, and
unfueled.
[0014] The above discussed and other features will be appreciated
and understood by those skilled in the art from the following
detailed description and drawings.
BRIEF DESCRIPTION OF DRAWINGS
[0015] Referring now to the drawings, which are meant to be
exemplary and not limiting, and wherein like elements are numbered
alike:
[0016] FIG. 1 is a block diagram of a power system featuring a
power bridging power source;
[0017] FIG. 2 is a block diagram of a power system featuring a
power bridging power source including an electrolysis cell;
[0018] FIG. 3 is a simplified block diagram of a power system
featuring a power bridging power source and an electrolysis cell
operably connected with a single power converter;
[0019] FIG. 4 is a block diagram of a portion of a power system
depicting an exemplary embodiment employing an electrolysis cell to
maintain system loads;
[0020] FIG. 5 is a block diagram of a portion of a power system
depicting an exemplary embodiment employing an electrolysis cell to
maintain system loads, eliminating a power supply;
[0021] FIG. 6 is a block diagram of a portion of a power system
depicting an exemplary embodiment employing an electrolysis cell to
maintain system loads, eliminating an input power converter;
[0022] FIG. 7 is a block diagram of a portion of a power system
depicting an exemplary embodiment employing an electrolysis cell to
maintain system loads, eliminating all power converters;
[0023] FIG. 8 is a flowchart depicting an exemplary methodology of
control of a portion of an exemplary power system;
[0024] FIG. 9 is a flowchart depicting another exemplary
methodology of control of a portion of an exemplary power
system;
[0025] FIG. 10 is a flowchart depicting yet another exemplary
methodology of control of a portion of an exemplary power
system;
[0026] FIGS. 11A and 11B are a pair of tables that illustrate the
energy storage capacity for a 7,700 .mu.F, and a 1,000 .mu.F
capacitor for a variety of different voltage ratings; and
[0027] FIG. 12 is a graphical representation of the 7,700 .mu.F
capacitor energy storage versus charge voltage.
DETAILED DESCRIPTION
[0028] The following description will provide specific examples
with respect to the load and power source voltages for example
only. It will also be understood that the method and apparatus for
bridging short duration power interruptions may be used with
different types of primary/secondary sources and/or other operating
voltages, and is not limited to the implementations described
herein. Various power sources can range from grid power to solar
power, hydroelectric power, tidal power, wind power, fuel cell
power, and the like, as well as combinations comprising at least
one of the foregoing power sources (e.g., via solar panel(s), wind
mill(s), dams with turbines, electrochemical cell systems, and the
like).
[0029] FIG. 1 depicts a block diagram of a portion of power system
10 having a primary power source 32 such as generated grid power or
that from a renewable source, a secondary power source 100 and a
load 36, which load 36 is fed from a feeder bus 38. In the example
shown, the primary power source 32 provides power along a primary
bus 40; e.g., 120/240 volts alternating current (VAC). It will be
appreciated that the actual primary supply voltage is based upon
the type of power source including, but not limited to other
alternating current (AC) voltage sources, direct current (DC)
sources renewable sources such as wind, solar and the like.
[0030] Optionally, a conversion device 42 can be employed to
rectify the power type (e.g., AC to DC, or DC to AC), or to
transform the voltage level (e.g., 48 volts direct current (VDC) to
24 VDC). For example, rectifier 43 can convert 120/240 VAC supply
voltage fed from the primary power source 32 to a 24 VDC supply,
fed through feeder bus 38 to load 36.
[0031] A secondary power source 100 may comprise an electrochemical
cell system. The electrochemical cell system may include a fuel
cell 34, or a regenerative fuel cell system comprising a fuel cell
34, electrolysis cell 62, an optional power converter 61, optional
associated hardware, optional storage devices 64, controls, and the
like. The size, i.e., the number of cells, of the fuel cell 34 and
optional electrolysis cell 62, and the desired hydrogen production
of the electrolysis cell 62 is dependent upon the desired power
output of the secondary power source 100 and specifically fuel cell
34. For example, a secondary power source 100 can include a fuel
cell 34 that provides about 50 to about 100 VDC output voltage for
use by the load 36.
[0032] In order to provide backup power for the load 36, a
controller/DC-DC power supply 44 may be used to convert the power
from the secondary power source 100 to a power receivable by the
feeder bus 38. For example, the input from the fuel cell 34 is
converted to an output that is connected to feeder bus 38, wherein
a smooth output is an uninterrupted power that has an average
voltage fluctuation of less than or equal to about 10% over several
seconds. An uninterrupted power is a less than or equal to about
0.005 second delay between cease of power supply from primary power
source 32 and introduction of power from controller/DC-DC power
supply 44.
[0033] During operation with a regenerative fuel cell system, the
primary power source 32 provides power via optional power converter
61 to an electrolysis cell 62 e.g., an electrolyzer, which
generates hydrogen gas. When the optional power converter 61 is not
employed, the electrolysis cell 62 may be directly connected to the
primary bus 40 via line 65. The hydrogen generated by the
electrolysis cell 62 is stored in an appropriate storage device 64
for later use. At such a point in time as required for operation
such as outages of the primary power source 32 and the like, or for
a renewable power source, during the day or season where the power
generation capability of the renewable power source declines (e.g.,
night time), the primary power source 32 or secondary power source
100 will need to offset the loss in capacity. The hydrogen
previously stored in storage device 64 is supplied to a hydrogen
electrochemical device, e.g., fuel cell 34, which converts the
hydrogen into electricity to supply to the load 36. Power
generation will continue until the hydrogen in the storage device
64 is exhausted or the power is no longer required. Reasons for
ending power generation may include, for example, the restoration
of the grid power, restoration of renewable energy sources (such as
solar, wind, wave power, or the like), and/or the determination
that peak-shaving is no longer cost effective or no longer
required.
[0034] Once the amount of hydrogen in the hydrogen storage device
64 decreases below a pre-determined level, the electrolysis cell 62
engages to replenish the hydrogen supply. Preferably, hydrogen will
be replenished whenever the hydrogen storage level in the hydrogen
storage device 64 is less than full, and there is power available
from the primary power source 32 for the electrolysis operation to
ensure the longest possible operational duration capability for the
secondary power source 100, e.g., the fuel cell 34. Alternatively,
hydrogen may be replenished with the addition of hydrogen from
another source. For example, another hydrogen generating means, or
replacement, replenishment, or supplementation of the existing
hydrogen storage device 64.
[0035] Returning to FIG. 1 once again, and to discussion of the
secondary power source 100, because fuel cell systems generally
take a certain amount of time from the point of initial activation
to delivering full power, there may be a brief delay of power
attendant thereto when switching over a primary power source 32 to
secondary power source 100 and power generated by a fuel cell 34.
To address this time lapse, a power system may employ a bridging
power source 46. The bridging power source 46 stores electrical
energy and temporarily provides power to load 36 in the event of
any gap or delay between the transfer of power delivery from the
primary power source 32 to the power delivery from the secondary
power source 100, namely, fuel cell 34. For example, power system
10 may include a monitor of the primary power source 32 (e.g., a
grid, solar power, another electrochemical system, and the like);
and upon a cease in power from the primary power source 32,
start-up an secondary power system 100 and introduce power from the
bridging power source 46 during the time lapse. The bridging power
source 46 may comprise a capacitor 48 and/or battery 49 and
optionally a power converter 50.
[0036] Charging of the capacitor 48 and/or battery 49 may be
accomplished in various fashions, depending upon the type of
primary power source 32 and the voltage of feeder bus 38 or primary
bus 40, accordingly. The capacitor 48 or battery 49 can be charged
with power from primary bus 40 via optional power converter 50.
Power converter 50 converts the voltage from the bus voltage on
feeder bus 38 (or primary 40 depending upon the implementation) to
the capacitor/battery voltage. Meanwhile, a conversion device 42
can be employed, if desired, to adjust the voltage of primary bus
40 to the desired voltage for the feeder bus 38. Alternatively, the
power can pass from primary bus 40 through conversion device 42, to
feeder bus 38. Power converter 50 may alternatively convert
voltages from feeder bus 38 to charge to the capacitor 48 and/or
battery 49. Finally, it will be appreciated, that capacitor 48
and/or battery 49 may be operably connected to either primary bus
40 or feeder bus 38 directly. In this embodiment, power from
primary bus 40 can be converted from AC to DC, and/or the DC
voltage of the feeder bus 38 may be converted to the desired
capacitor voltage via power converter 50. For example, the energy
used to charge capacitor 48 or battery 49 can come from the output
of rectifier 43 that converts 120 (or 240) VAC on primary bus 40 to
24 VDC on feeder bus 38. The power converter 50 then converts the
low voltage (e.g., 24 VDC) input into an appropriate voltage
output, which is then used to charge capacitor 48 and/or battery
49.
[0037] The output of capacitor 48 and/or battery 49 is connected to
controller/DC-DC power supply 44. When capacitor 48 and/or battery
49 is used to bridge the gap in power between a switch-over from
primary power source 32 to the secondary power source 100, the
controller/DC-DC power supply 44 may be employed to convert the
power from the power level of the capacitor 48 to the power level
of the feeder bus 38. Preferably, power is supplied by capacitor 48
and/or battery 49 for the period of time from a cease in the power
supply from primary power source 32 until commencement of power
supply from fuel cell 34 (i.e., when the fuel cell 34 attains
operating conditions and begins to supply a predetermined amount of
power).
[0038] In order to determine when, and for what period, to draw
power from capacitor 48, sensing lines 52 and 54 are connected from
the primary bus 40 and the output of the secondary power source 100
to the controller/DC-DC power supply 44. In this manner,
controller/DC-DC power supply 44 can monitor the status of the
primary power source 32 and the secondary power source 100 so that
the switching to an appropriate power source may be determined and
controlled. It will easily be appreciated that in controller/DC-DC
power supply 44, the DC-DC power supply may optionally be separated
from the controller.
[0039] During a normal mode of operation, the power supplied from
primary power source 32 (e.g., 120/240 VAC or optionally a DC
source) on primary bus 40 is converted (in the depicted
configuration) to a DC voltage by rectifier 43 of conversion device
42. The load 36 draws current from feeder bus 38, regardless of the
source of the power thereto. During the normal mode, bridging power
source 46 maintains stored electrical energy in the event of a
temporary power interruption.
[0040] In the event of a loss of power from the primary power
source 32, controller/DC-DC power supply 44 senses the loss on the
primary bus 40 through sensing line 52. A signal is then sent by
controller/DC-DC power supply 44 to the secondary power source 100
(through line 56) to begin generating backup power for feeder bus
38. Because of the inherent time delay of a fuel cell 34 in
producing full power, controller/DC-DC power supply 44 converts the
output voltage of capacitor 48 and/or battery 49 to voltage that is
directed to feeder bus 38 until the secondary power source 100, and
more specifically the fuel cell 34 is ready to take over so that
load 36 sees an uninterrupted supply of power.
[0041] Once controller/DC-DC power supply 44 senses that the fuel
cell 34 is generating a desired amount of power, the capacitor 48
and/or battery 49 may be disconnected (circuit broken) from feeder
bus 38 and backup power is now directed from the secondary power
source 100 and more specifically the fuel cell 34, through
controller/DC-DC power supply 44, and onto feeder bus 38.
Optionally, at the same time, capacitor 48 and/or battery 49 may be
recharged through line 58 from feeder bus 38 and power converter
50. The connecting and disconnecting of the capacitor 48 and/or
battery 49 to the DC-DC converter within controller/DC-DC power
supply 44 may be accomplished with one or more device(s) such as a
power field effect transistor(s) (FET; not shown), transistor(s),
thyrister(s), relay(s), switching device(s), and the like, as well
as combinations including at least one of the foregoing.
Optionally, controller/DC-DC power supply 44 may leave capacitor 48
and/or battery 49 in the circuit but draw essentially no power
therefrom. If power from the primary power source 32 is
subsequently restored, this will be sensed by controller/DC-DC
power supply 44. This time, however, there is no need to discharge
capacitor 48 and/or battery 49, since controller/DC-DC power supply
44 may seamlessly switch from the secondary power source 100 and
fuel cell 34 back to primary power source 32 by deactivating the
fuel cell 34.
[0042] Either during operation of the secondary power source 100
(via feeder bus 38) and/or after reconnection to primary power
source 32 (via primary bus 40), the bridging power source 46,
namely the capacitor 48 and/or battery 49 may be charged (or
recharged, as is appropriate). During charging, current supplied
from feeder bus 38 is sent through line 60 to power converter 50,
which converts the voltage of feeder bus 38 to that appropriate to
charge capacitor 48 and/or battery 49. It should be noted, that
once capacitor 48 and/or battery 49 is/are charged, no significant
current would be drawn by power converter 50 (if used) from feeder
bus 38. Alternatively, it will be further appreciated that in an
implementation where primary power source 32 and primary bus 40
comprise a VDC power source, power may be optionally be drawn
directly from the primary bus 40 (or optionally through the power
converter 50) to charge the capacitor 48 and/or battery 49.
[0043] Moreover, the power converter 50 may, be configured as an
AC/DC converter (rectifier) coupled directly to the primary power
source 32 and primary bus 40. In addition, for yet another
alternative embodiment, the output voltage of controller/DC-DC
power supply 44 may be generated at a slightly lower value than
that resultant from the conversion device 42 (e.g., by about 1 to
about 3 volts). In so doing, any current flow from controller/DC-DC
power supply 44 onto feeder bus 38 would be limited until such time
as the primary power source 32 is unavailable.
[0044] Referring now to FIGS. 11A and 11B, there is shown a pair of
tables, which illustrate the energy storage capacity for a 7,700
.mu.F (microfarad), and a 1,000 .mu.F capacitor for a variety of
different voltage ratings. (Also see the graphical representation
of FIG. 12) Such a capacitor as depicted in the figure may be
employed as capacitor 48 in an exemplary embodiment as described
herein. In an exemplary embodiment, the capacitor exhibits a
capacitance range of about 1,000 .mu.F (microfarad) to about 7,700
.mu.F at of voltage range of about 450 VDC. Naturally, the higher
the capacitance and the voltage ratings, the more energy is stored
and the more power delivery capability. Likewise, it will be
appreciated that various capacitances and voltage ranges may be
employed to suit a selected implementation. While a capacitance of
about 1,000-7,700 .mu.F at a voltage of about 450 VDC has been
disclosed, these values are purely illustrative. Many other values
are conceivable both larger and smaller and at higher or lower
voltages. The voltages for charging the capacitor 48 may be
selected as desired for ease of implementation, in an exemplary
embodiment, the voltage for capacitor 48 is selected to be about 5
to 10 times the voltage of the feeder bus 38.
[0045] The tables of FIGS. 11A and 11B further illustrate the "hold
up" or discharge time of the capacitor 48 at a power output of 10
kW. Again, the more energy that is stored, the longer it takes for
the capacitor 48 to discharge and hence the longer the bridging
power source 46 will be able to bridge power between the primary
power source 32 and the secondary power source 100. It should be
noted that the actual hold up time of capacitor 48 would be reduced
as a function of normal inefficiencies associated with the
controller/DC-DC power supply 44 and other system components and
interconnections.
[0046] Employing a system comprising an electrochemical system in
conjunction with a high voltage, medium-sized capacitor as part of
a power bridging power source, a cost-effective uninterrupted power
supply system is realized. This is especially the case when one or
more of the sources have an inherent power-up time associated
therewith, such as secondary power source 100 including a fuel cell
34. It should also be noted that the number of components employed
may be reduced as disclosed by employing commonality in selected
components, e.g., using a common the DC-DC power supply 44
connected to both the capacitor 48 and/or battery 49 and the fuel
cell 34 instead of multiple power supplies.
[0047] Referring now to FIG. 2 there is depicted an alternative
embodiment of the power system described above and as depicted in
FIG. 1. FIG. 2 depicts a block diagram of a portion of a power
system 10a, very similar to power system 10 of FIG. 1, again,
having a primary power source 32 such as generated grid power or
that from a renewable source, a secondary power source 100 and a
load 36, which load 36 is fed from a feeder bus 38.
[0048] As described earlier, to provide backup power for the load
36, the controller/DC-DC power supply 44 is used to convert the
power from the secondary power source 100 to a power receivable by
the feeder bus 38. Likewise, during operation with a regenerative
fuel cell system, the primary power source 32 provides power via
optional power converter 61 to an electrolysis cell 62, e.g., an
electrolyzer, which generates hydrogen gas. The hydrogen generated
by the electrolysis cell 62 is stored in an appropriate storage
device 64 for later use.
[0049] The hydrogen previously stored in storage device 64 is
supplied to a hydrogen electrical generator e.g. fuel cell 34,
which converts the hydrogen into electricity to supply the load 36.
Power generation will continue until the hydrogen in the storage
device 64 is exhausted or the power is no longer required.
[0050] As previously discussed, due to the inherent delay in
start-up of the secondary power source 100 and the fuel cell 34, in
addition to the fuel cell 34, a bridging power source 46a may be
employed to enable the uninterrupted supply of power to load 36. In
this exemplary embodiment, the bridging power source 46a may
comprise the electrolysis cell 62 (operating as an electrical
source to replace or supplement capacitor 48 and/or battery 49) and
optionally a power converter 50 and/or power converter 61.
[0051] Continuing with FIG. 2, the electrical input to the
electrolysis cell 62 may be disconnected from the primary bus 40 of
primary power source 32 and/or the optional power converter 61 and
instead connected as an output to supply electrical power as
depicted via line 63. During bridging, the electrolysis cell 62 may
be employed to generate electricity by utilizing the hydrogen
remaining within the electrolysis cell 62 to generate and supply
bridging power to feeder bus 38 (via controller/power supply 44).
Depending upon the amount of hydrogen available within the
electrolysis cell 62, electricity may be supplied for the duration
of the above mentioned power interruption between loss of the
primary power source 32 and the generation of power from the
secondary power source 100, more specifically fuel cell 34. In an
exemplary embodiment, an electrolysis cell 62 may supply about 30
watts decaying to about 1 watt of power over about 10 minutes.
[0052] In an exemplary embodiment, the electrolysis cell 62 is
operably connected to controller/DC-DC power supply 44 in a manner
to facilitate the electrolysis cell 62 supplying current to
controller/DC-DC power supply 44. When the electrolysis cell 62 is
used to bridge the gap in power between a switch-over from primary
power source 32 to the secondary source 100, the controller/DC-DC
power supply 44 may optionally be employed to convert the voltage
from the voltage level output by the electrolysis cell 62 to the
voltage level of the feeder bus 38. Preferably, power is supplied
by electrolysis cell 62 for the period of time from a cease in the
power supply from primary power source 32 until commencement of
power supply from the secondary power source 100 (i.e., when the
fuel cell 34 attains operating conditions and begins to supply a
predetermined amount of power). Otherwise the electrolysis cell 62
may, as described earlier be supplemented with a capacitor 48
and/or battery 49. It will be appreciated, that employing the
electrolysis cell 62 in this manner will facilitate elimination of
the capacitor 48 and/or battery 49 from the power system 10.
Alternatively, the size of the capacitor 48 and/or battery 49 may
be reduced because of the net increase in bridge power available
with the electrolysis cell 62. Finally, the addition of the
electrolysis cell 62 to the bridging power source 46a may result in
reduced maintenance and replacement for storage components such as
the capacitor 48 and/or battery 49.
[0053] During a normal mode of operation, in this embodiment, the
power supplied from primary power source 32 (e.g., 120/240 VAC if
an AC source) on primary bus 40 is converted (in the depicted
configuration) to a DC voltage by rectifier 43 of conversion device
42. The load 36 draws current from feeder bus 38, regardless of the
source of the power thereto. During the normal mode, bridging power
source 46a maintains stored electrical energy in the event of a
temporary power interruption, while the electrolysis cell 62 is
operatively configured to receive electrical power and generate
hydrogen for storage if needed. Moreover, preferably, the
electrolysis cell 62 has fully filled the hydrogen storage device
64 and therefore the electrolysis cell 62 is idle but configured to
provide an electrical output to controller/DC-DC power supply 44
and thereby the feeder bus 38. It will be further appreciated that
the electrical connection and configuration could be arranged such
that the electrolysis cell 62 supplies only a subset of the full
load on the feeder bus 38. For example, the load of the feeder bus
38 may be logically partitioned as needed to support various
priority loading schemes. Moreover, the load may be further
partitioned in consideration of the available backup or bridging
power available. For example, the load partition could be modified
as backup power storage capability is diminished, providing
additional protection for the critical system components and
interfaces, such as system controllers, monitors, or watchdog
circuits.
[0054] As stated above, in the event of a loss of power from the
primary power source 32, here again, controller/DC-DC power supply
44 senses the loss on the primary bus 40 through sensing line 52. A
signal is then sent by controller/DC-DC power supply 44 to the
secondary power source 100 and fuel cell 34 (through line 56) to
begin generating backup power for feeder bus 38. Because of the
inherent time delay of a fuel cell 34 in producing full power,
controller/DC-DC power supply 44 converts the output voltage of
electrolysis cell 62 (and/or capacitor 48 and/or battery 49) to
voltage that is directed to feeder bus 38 and appropriate
partitions thereof, until the secondary power source 100, and more
specifically the fuel cell 34 is ready to take over so that load 36
sees an uninterrupted supply of power.
[0055] Once controller/DC-DC power supply 44 senses that the fuel
cell 34 is generating a desired amount of power, electrolysis cell,
62, and/or the capacitor 48 and/or battery 49 are disconnected and
backup power is now directed from the secondary power source 100
and more specifically the fuel cell 34, through controller/DC-DC
power supply 44, and onto feeder bus 38. Optionally, at the same
time, capacitor 48 and/or battery 49 may be recharged through
feeder bus 38 and power converter 50. The connecting and
disconnecting of the electrolysis cell 62, and/or capacitor 48,
and/or battery 49 to the DC-DC converter within controller/DC-DC
power supply 44 may be accomplished with a device such as a power
field effect transistor (FET; not shown), or the like. Optionally,
controller/DC-DC power supply 44 may leave capacitor 48 and/or
battery 49 in the circuit but draw essentially no power therefrom.
If power from the primary power source 32 is subsequently restored,
this will be sensed by controller/DC-DC power supply 44
facilitating a seamless switch from the secondary power source 100
and fuel cell 34 back to primary power source 32 by deactivating
the fuel cell 34.
[0056] Employing a power system including an electrolysis cell 62
as part of a bridging power source 46a, a cost-effective
uninterrupted power supply system is realized. This is especially
the case when one or more of the sources have an inherent power-up
time associated therewith, such as secondary power source 100
including a fuel cell 34.
[0057] Turning now to FIG. 3, a power system 10b similar once again
to the power system 10 and 10a from FIGS. 1 and 2 respectively is
depicted to illustrate yet another exemplary embodiment where the
electrolysis cell 62 is operably connected to provide power for
system control and/or load applications. In this embodiment, as
depicted in the figure, it will be appreciated that a bridging
power source 46b no longer includes optional power converter 61 and
thereby power system 10b is simplified. The electrolysis cell 62 in
this instance (as it could also be for the embodiments disclosed
above) is configured to be operably connected to optional power
converter 50. Once again, it will also be appreciated that while in
an exemplary embodiment a DC/DC power converter is disclosed the
power converter 50 may be selected to address the configuration of
the primary power source 32 whether AC grid power or DC such as
from a renewable source, such as wind power generators,
photovoltaic and the like as well as a battery bus and so on.
[0058] Continuing now with FIG. 3, the electrical input to the
electrolysis cell 62 may be disconnected from the primary bus 40 of
primary power source 32 (FIG. 2) and/or the optional power
converter 50 and instead connected as an output to supply
electrical power as depicted via line 63. The electrolysis cell 62
utilizes the remaining internal hydrogen to generate and supply
bridging power to feeder bus 38 (via controller/DC-DC power supply
44) for the duration of the above mentioned power interruption
between loss of the primary power source 32 and the generation of
power from the secondary power source 100, more specifically fuel
cell 34. Operation of the power system 10b is similar to that
described for power systems 10 and 10a for FIGS. 1 and 2
respectively. Only specific differences are address here. It will
be appreciated that the FIG. 3 provides a depiction intended to
illustrate the operation of power system 10b in the absence of
power converter 61.
[0059] Turning now to FIG. 4 a portion of the power system 10 from
FIGS. 2 and 3 is depicted to illustrate an exemplary embodiment
where the electrolysis cell 62 is operably connected to provide
power for system control and/or load application. It is note worthy
to appreciate that in an embodiment as depicted the electrolysis
cell 62 may under certain configurations be utilized entirely to
provide bus power in the absence of the primary power source
32.
[0060] Turning now to FIG. 5, in yet another exemplary embodiment a
portion of the power system 10b from FIG. 3 is depicted to
illustrate an exemplary embodiment where the electrolysis cell 62
is operably connected to provide power for system control and load
applications. It is note worthy to appreciate that in an embodiment
as depicted, the electrolysis cell 62 may be configured and
utilized to provide bus power to a load without employing a DC/DC
power supply 44 on the output of the electrolysis cell 62 in the
absence of the primary power source 32. In such a configuration,
the electrolysis cell 62 and/or selected loads may be configured to
facilitate operable interconnection between the electrolysis cell
62 and selected loads. For example, the system may be configured to
limit the loads applied to the electrolysis cell 62 to the most
essential loads (such as system control, monitoring, and
diagnostics) and those loads may be configured to operate directly
from the voltage output by the electrolysis cell 62. It will be
appreciated, that depending upon the power available, loads may be
added and deleted as desired.
[0061] Turning now to FIG. 6, in yet another exemplary embodiment a
portion of the power system 10 from FIGS. 2 and 3 is depicted to
illustrate an exemplary embodiment where the electrolysis cell 62
is operably connected to provide power for system control and load
application. In this embodiment as depicted, the electrolysis cell
62 is configured to be interfaced with and may be operably
connected to the primary power source 32 without the intervening
power converter 50 as described earlier. In such a configuration,
once again the electrolysis cell 62 is utilized to provide bus
power to the feeder bus 38, and thereby to a load 36 in the absence
of the primary power source 32. Once again, in such a
configuration, the elimination of the power converter 50 provides
for additional system simplification and reduced cost.
[0062] Optionally, it will be appreciated that the embodiment
described above may be further simplified to include the
elimination of the controller/DC-DC power supply 44 for conversion
of the voltage from the electrolysis cell 62 to the feeder bus 38
and loads 36. Once again, in such a configuration as depicted in
FIG. 7, the electrolysis cell 62 may be operably connected to
receive power directly from the primary power source 32 e.g. a
renewable source with a DC output. Furthermore, the electrolysis
cell 62 and/or selected loads may be configured to facilitate
operable interconnection between the electrolysis cell 62 and
selected loads directly.
[0063] Continuing now with FIGS. 1, 2, and 3 and turning as well to
FIG. 8, a flow chart depicting an exemplary method of a control
process 200 for a power system is depicted. The process 200
initiates with monitoring and evaluation of the power source at
block 210. Such monitoring may include evaluation of the voltage on
the primary bus 40 (FIGS. 1, 2, and 3), or as depicted in this
instance, wind speed or light level for a renewable power source as
the primary power source 32. As disclosed earlier, such a renewable
power source (FIGS. 1, 2, and 3) includes solar wind, tidal,
geothermal resources, and the like as well as combinations
including at least one of the foregoing. Decision block 212
includes a determination that the primary power source 32 is
adequate for electrolysis. For example, is the input power
available from the primary power source greater than or equal to
about 500 watts. If so, a determination is made at a second
decision block 214 as to whether the electrolysis cell 62 is
already operating. If so, a determination is made to continue
generation of hydrogen with the electrolysis cell 62 as depicted at
block 216 and thereafter the processing returns to block 210. If
the electrolysis cell 62 is not operating, yet there is adequate
power from the primary power source 32, the selected
ancillary/parasitic loads may be started and added as the load. For
example as loads added to feeder bus 38. Additionally, the
electrolysis cell 62 is powered to generated hydrogen and recharge
any depleted hydrogen. The addition of loads is depicted at blocks
218 and 220 respectively. Processing then returns to the initial
functions at block 210.
[0064] Returning to decision block 212, if there is inadequate
power at the primary power source 32, e.g., low light, no wind,
grid interruption, and the like, a determination is made at
decision block 222 as to whether there is any portion of the system
operable, e.g., any power available from any source to operate as
opposed to all sources depleted. For example, insufficient power
available for electrolysis and yet still electrolyzing. If so, an
orderly elimination of loads is initiated at block 224 with the
termination of electrolysis, and thereafter shedding of ancillary
loads as shown at 226. Finally, block 228 depicts operating the
electrolysis cell 62 (denoted E/C) as an electrical power source to
power control circuitry and monitoring. Processing thereafter
returns to block 210 to repeat the cycle.
[0065] Continuing now with FIGS. 1, 2, and 3 and turning as well
now to FIG. 9, an alternative embodiment is depicted showing
exemplary process 201 and control for the power system 10 when
experiencing a brief power loss. Such a brief power loss may
include but not be limited to, cloud cover for solar systems, wind
droop for wind systems, momentary and short grid interruptions, and
the like. Processing in this embodiment is similar to that
described for process 200 in association with FIG. 8 except that
following the block 224 to halt hydrogen generation from the
electrolysis cell 62 a decision block, 230 is added to determine if
the power interruption is expected or anticipated. For example, in
a solar power system, to ascertain if an interruption is due to
cloud cover as opposed to sunset. If the interruption satisfies
selected criteria for an unexpected interruption, then the process
transfers to block 232. Selected criteria may include, but not be
limited to a time duration based upon time of day, date, current
conditions, weather conditions, geographic position, and the like,
as well as combinations including one or more of the foregoing.
[0066] Continuing with FIG. 9 at block 232 a timer is initiated to
track the duration of the brief loss of the primary power source
32, once again, in this instance a renewable power source. During
this time interval, the ancillary system may be powered using the
electrolysis cell 62 (denoted E/C) as a source of electricity as
depicted at block 234. The status of the primary power source 32 is
monitored to determine the availability of the primary power source
32, namely the return to desirable power generation as depicted at
block 236. Should the primary power return to acceptable parameters
within a selected time-frame, as depicted at decision block 238 the
process 201 transfers to block 220 for initiation hydrogen
generation with the electrolysis cell 62. If the primary power
source in not available within the selected window, the process 201
transfers to block 226 to shut down ancillary loads as described
earlier. Similarly, returning to decision block 230, if the
interruption of the power source does not satisfy selected criteria
for an expected interruption, then the process 201 also transfers
to block 226 to shut down as described earlier.
[0067] Continuing once again with FIGS. 1, 2, and 3 and turning to
FIG. 10, yet another alternative embodiment is depicted showing
exemplary control process 202 for the power system 10 employing
various configurations of selected power converters e.g.,
conversion device 42, power converters 50 and 61, and
controller/DC-DC power supply 44, to facilitate control of the
electrolysis cell 62 as well as the loads applied thereto. More
specifically, this embodiment address an optional configuration of
the power systems described earlier where the electrolysis cell 62
and loads are connected to a single conversion device 42 (or power
converter 50) and the operation of the conversion device 42 as a
power converter in light of such a connection. Additionally, in
this embodiment, evaluation of the availability of power or a
resource is monitored to facilitate determination of the
appropriate control action. For example, the process 202 may
evaluate the presence of a primary power source 32 such as from a
grid, availability of a secondary power source 100, or the status
of renewable sources such as wind, light, tidal, geothermal, and
the like, as well as combinations including at least one of the
foregoing.
[0068] Turning to the figure, the process 202 is initiated at block
210 as described earlier, and continues with a decision block 240.
Decision block 240 includes a determination that the primary power
source 32 (once again, in this instance, a renewable power source,
e.g., solar, wind) is adequate for powering selected systems and
loads. If not, the process 202 transfers to decision block 214 and
thereafter block 224, 226 and 228 as described earlier. Returning
to decision block 240, if there is adequate power for other loads
the process 202 transfers to decision block 212 where a
determination is made as to whether adequate power is available to
generate hydrogen with the electrolysis cell 62. If so, similar to
previous embodiments, the process 202 transfers to decision block
214, where a determination is made as to whether the electrolysis
cell 62 (denoted E/C) is operating. If so, a determination is made
to continue generation of hydrogen for the electrolysis cell 62 as
depicted at block 216 and thereafter the processing returns to
block 210. If the electrolysis cell 62 is not operating, as
determined at decision block 214, yet there is adequate power from
the primary power source, e.g., 32, the selected
ancillary/parasitic loads may be started and added as a load as
depicted at decision block 242 and block 218. Moreover, as depicted
at block 244, the conversion device 42 may be operated in a current
regulation mode to facilitate powering the electrolysis cell 62 and
thereby generation of hydrogen to storage in the storage device 64.
Process 202 thereafter returns to block 210 to continue.
[0069] Returning to decision block 212, if it is determined that
there is inadequate power available for electrolysis and hydrogen
generation, the process 202 transfers to block 244 where the
regulation of the conversion device 42 is set to voltage control
mode for controlling selected loads. The process 202 then continues
to block 246 were the conversion device 42 regulates and limits the
voltage from the primary power source 32 to less than a selected
value. Such a configuration facilitates operating various loads
without providing sufficient excitation to the electrolysis cell 62
to promote hydrogen generation. In an exemplary embodiment, this
voltage would be less than or equal to about 1.4 VDC per cell of
the cell stack of the electrolysis cell 62. Preferably, less than 1
VDC per cell. In an exemplary embodiment employing a 20 cell stack
in the electrolysis cell 62, the potential across the cell stack of
the electrolysis cell 62 would be less than or equal to 10 VDC. The
process 202 thereafter continues to block 218 where ancillary load
are started and powered. Finally, process 202 returns to block 210
to continue the control cycle.
[0070] The disclosed invention can be embodied in the form of
computer or controller implemented processes and apparatuses for
practicing those processes. The present invention can also be
embodied in the form of computer program code containing
instructions embodied in tangible media 70, such as floppy
diskettes, CD-ROMs, hard drives, or any other computer-readable
storage medium, wherein, when the computer program code is loaded
into and executed by a computer or controller, the computer becomes
an apparatus for practicing the invention. The present invention
may also be embodied in the form of computer program code or signal
72, for example, whether stored in a storage medium, loaded into
and/or executed by a computer or controller, or transmitted over
some transmission medium, such as over electrical wiring or
cabling, through fiber optics, or via electromagnetic radiation,
wherein, when the computer program code is loaded into and executed
by a computer, the computer becomes an apparatus for practicing the
invention. When implemented on a general-purpose microprocessor,
the computer program code segments configure the microprocessor to
create specific logic circuits.
[0071] While the invention has been described with reference to a
preferred embodiment, it will be understood by those skilled in the
art that various changes may be made and equivalents may be
substituted for elements thereof without departing from the scope
of the invention. In addition, many modifications may be made to
adapt a particular situation or material to the teachings of the
invention without departing from the essential scope thereof.
Therefore, it is intended that the invention not be limited to the
particular embodiment disclosed as the best mode contemplated for
carrying out this invention.
* * * * *