U.S. patent application number 13/248543 was filed with the patent office on 2012-01-26 for fuel cell stack flow diversion.
This patent application is currently assigned to FORD GLOBAL TECHNOLOGIES, LLC. Invention is credited to Fred G. Brighton, II, Victor D. Dobrin, Hans Buus Gangwar.
Application Number | 20120021322 13/248543 |
Document ID | / |
Family ID | 40362076 |
Filed Date | 2012-01-26 |
United States Patent
Application |
20120021322 |
Kind Code |
A1 |
Brighton, II; Fred G. ; et
al. |
January 26, 2012 |
FUEL CELL STACK FLOW DIVERSION
Abstract
A fuel cell system has a compressor delivering compressed gas to
a fuel cell stack and a control valve affecting the flow of
compressed gas. A load dump condition is determined for the fuel
cell stack. The flow through the compressor is increased and the
additional flow diverted away from the fuel cell stack by the
control valve to provide additional load for the fuel cell stack.
The fuel cell stack may then be operated at a higher output power
for the purpose of generating more waste heat to more rapidly warm
itself.
Inventors: |
Brighton, II; Fred G.; (Ann
Arbor, MI) ; Gangwar; Hans Buus; (Livonia, MI)
; Dobrin; Victor D.; (Ypsilanti, MI) |
Assignee: |
FORD GLOBAL TECHNOLOGIES,
LLC
Dearborn
MI
|
Family ID: |
40362076 |
Appl. No.: |
13/248543 |
Filed: |
September 29, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11839838 |
Aug 16, 2007 |
8057949 |
|
|
13248543 |
|
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Current U.S.
Class: |
429/444 |
Current CPC
Class: |
H01M 8/04089 20130101;
H01M 8/04955 20130101; Y02T 10/70 20130101; Y02E 60/50 20130101;
B60L 50/40 20190201; H01M 8/04268 20130101; Y02T 90/40 20130101;
H01M 8/04776 20130101; H01M 8/04395 20130101; H01M 8/0494 20130101;
H01M 8/04753 20130101; H01M 8/04365 20130101; H01M 2250/20
20130101; H01M 8/0687 20130101; H01M 8/04947 20130101 |
Class at
Publication: |
429/444 |
International
Class: |
H01M 8/04 20060101
H01M008/04 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] The invention was made with Government support under
Contract No. DE-FC36-04G014287. The Government has certain rights
to the invention.
Claims
1. A method of operating a fuel cell stack used for generating
electrical energy, at least a portion of the generated electrical
energy powering a compressor for providing compressed gas to the
fuel cell stack at a first flow rate, the method comprising:
providing compressed gas flow from the compressor at a second flow
rate greater than the first flow rate; generating additional
electrical energy by the fuel cell stack to power the compressor to
provide the compressed gas flow at the second flow rate; and
diverting gas corresponding to a difference between the second flow
rate and the first flow rate through a control valve before the
compressed gas reaches the fuel cell stack; thereby using the
compressor as an additional load on the fuel cell stack above what
is required to provide the fuel cell stack with compressed gas.
2. The method of claim 1 further comprising warming the fuel cell
stack with heat produced by generating the additional electrical
energy.
3. The method of claim 1 further comprising determining when a
surge condition exists in the compressor, increasing flow through
the compressor to avoid compressor surge, and selectively operating
the control valve to divert the increased flow away from the fuel
cell stack.
4. The method of claim 1 further comprising changing an
environmental condition of a passenger compartment with the
diverted compressed gas.
5. The method of claim 1 further comprising changing the
temperature of a radiator with the diverted compressed gas.
6. The method of claim 1, wherein the compressed gas reaching the
fuel cell stack has a substantially constant absolute pressure.
7. The method of claim 1 further comprising monitoring at least one
property of the compressed gas and regulating the control valve
based on the monitored property.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a divisional of application Ser. No.
11/839,838, filed Aug. 16, 2007, the entire contents of which are
hereby incorporated by reference.
BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention
[0004] The invention relates to the use of compressors and
compressed gas in fuel cell systems.
[0005] 2. Background Art
[0006] Fuel cell systems produce electrical energy by combining
fuel and an oxidant in a fuel cell stack. In one form of fuel cell
system, the fuel is hydrogen and the oxidant is oxygen, which may
be mixed with other gases as in air. The oxidant is typically
gaseous and is often delivered to the fuel cell stack as a
compressed flow.
[0007] Typically, fuel cell stacks operate more efficiently under
certain operating conditions, including fuel cell stack
temperature. In particular, it is desirable for the fuel cell stack
to operate at or above a particular temperature, which may be above
ambient temperature. Therefore, there is a need to heat the fuel
cell stack at various times such as, for example, during
startup.
[0008] Different types of compressors may be used to provide
oxidant to the fuel cell stack. For example, non-positive
displacement compressors are sometimes used for a variety of
reasons such as size, weight, efficiency, noise, vibration, and
harshness characteristics. However, non-positive displacement
compressors may operate in an undesirable condition known as surge.
Surge occurs when the compressor is operated at low flow rates in
combination with a high ratio of output pressure to input pressure.
Under these conditions, surge may result in vibrations which can
lead to poor operation, malfunction system damage, and the like. In
fuel cell systems that use ambient air to provide the oxidant,
variations in air density and pressure can affect compressor
performance. This is particularly true at higher elevations, where
the onset of surge is more likely.
[0009] Fuel cell stacks are typically placed in a housing. Unwanted
gasses may accumulate in the housing, requiring some mechanisms to
vent or purge the unwanted gasses.
[0010] Fuel cell systems are often part of a larger system such as,
for example, an automotive vehicle. These larger systems often
require various environmental modification systems that could
benefit from synergistic operation with the fuel cell system.
[0011] Accordingly, a need exists for improved fuel cell system
operation which addresses some or all of the above issues without
unduly affecting cost, complexity, performance, and the like.
SUMMARY OF THE INVENTION
[0012] The present invention provides a control valve to affect the
flow of compressed gas in a fuel cell system.
[0013] In one embodiment, a compressor supplies compressed gas to
the fuel cell stack. The compressor may be used as a load dump for
energy produced by the fuel cell stack. In this case, the
compressor generates an excess flow of compressed gas which is
diverted by a control valve away from the fuel cell stack. In one
application, excess work done by the fuel cell stack to power the
compressor generates heat which warms the fuel cell stack.
[0014] Control logic may be used to manage the compressor and the
control valve so as to maintain efficient fuel cell stack operating
conditions. This control logic may receive as input one or more
conditions of the compressed gas, ambient air, compressor, fuel
cell stack, control valve, and the like.
[0015] The control valve may be used to avoid a surge condition in
the compressor. The compressor may generate an increased flow to
avoid surge. The control valve may then divert the increased flow
away from the fuel cell stack.
[0016] According to an embodiment of the present invention,
componentry incorporated for expending electrical energy from the
fuel cell stack may be reduced or eliminated by running the
compressor at a level above that needed to supply compressed gas to
the fuel cell stack and diverting excess flow away from the fuel
cell stack.
[0017] Another embodiment involves utilizing compressed gas
diverted away from the fuel cell stack. This diverted gas may be
used to modify the environmental conditions of a wide variety of
systems such as, for example, a passenger compartment, a radiator,
and the like. The diverted gas may also be used to evacuate gases
from the fuel cell stack housing or enclosure.
[0018] In another embodiment, the fuel cell system may be utilized
in an automotive vehicle.
[0019] Other aspects, features, and uses of the disclosed
inventions will become apparent to one skilled in the art from a
study of the following description and associated drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a schematic diagram illustrating a fuel cell
system according to an embodiment of the present invention;
[0021] FIG. 2 is a flow diagram illustrating operation of a fuel
cell system according to an embodiment of the present
invention;
[0022] FIG. 3 is a graph illustrating surge avoidance according to
an embodiment of the present invention; and
[0023] FIG. 4 is a schematic diagram illustrating an automotive
vehicle according to an embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
[0024] As required, detailed embodiments of the present invention
are disclosed herein; however, it is to be understood that the
disclosed embodiments are merely exemplary of the invention that
may be embodied in various and alternative forms. The figures are
not necessarily to scale; some features may be exaggerated or
minimized to show details of particular components. Therefore,
specific structural and functional details disclosed herein are not
to be interpreted as limiting, but merely as a representative basis
for the claims and/or as a representative basis for teaching one
skilled in the art to utilize the present invention.
[0025] Referring now to FIG. 1, a schematic diagram illustrating a
fuel cell system according to an embodiment of the present
invention is shown. A simplified oxidant path of a fuel cell
system, shown generally by 20, includes fuel cell stack 22. Fuel
cell stack 22 generates electrical energy, shown as 24, by
combining ionized fuel and oxidant. The oxidant is provided by fuel
cell stack inlet 26. Unused oxidant, and other gases in some
systems, exits the fuel cell stack at outlet 28. A wide variety of
fuel cell types are available based on different fuels and
oxidants, cell stack configuration, desired power output, fuel cell
application, and the like. As will be recognized by one of ordinary
skill in the art, the present invention does not depend upon the
type or construction of the fuel cell stack used.
[0026] Fuel cell system 20 also includes compressor 30 and control
valve 32. Compressor 30 receives gas at compressor inlet 34 and
produces compressed gas at compressor outlet 36. Compressor 30 runs
on electrical energy, shown by 38, which is at least a portion of
fuel cell stack generated electrical energy 24. The operation of
compressor 30 is controlled by compressor control signal 40
provided by control logic 42. Compressor control signal 40 may be
one or more of analog voltage signals, analog current signals,
pulse width modulated signals, digital signals, and the like.
Compressor electrical supply may be AC or DC and may be controlled
by control logic 40 so as to provide compressor control signal 40.
A wide variety of compressors are available for use in the present
invention depending upon the type of oxidant used; flow parameters
including pressure, temperature, and velocity; amount of
compression needed; fuel cell system application; and the like. In
one embodiment, compressor 30 is a centrifugal compressor. As will
be recognized by one of ordinary skill in the art, a wide variety
of compressor types and configurations may be used in the present
invention.
[0027] Control valve 32 is disposed in the flow path between
compressor outlet 36 and fuel cell stack inlet 26. Control valve 32
diverts flow from compressor 30 away from fuel cell stack 22.
Control valve 32 is controlled by valve control signal 44 from
control logic 42. Control signal 44 may be any type of analog or
digital signal depending upon the type of control valve 32 chosen,
including electrical, magnetic, pneumatic, hydraulic, optical, and
the like. In addition, any suitable type of control valve 32 may be
used. While a single control valve is illustrated, the term control
valve includes one or more control valves controlled by one or more
valve control signals. As will be recognized by one of ordinary
skill in the art, a wide variety of control valve types and
configurations may be used to implement the present invention.
Moreover, various other components may be disposed in the flow
path, including intercooler, filters, water injectors, humidifiers,
and the like.
[0028] Control logic 42 generates compressor control signal 38 and
valve control signal 44 based on one or more control inputs 46, the
specific connections of which are not shown for clarity. Control
inputs may include flow parameters including mass flow rate, volume
flow rate, velocity, temperature, and the like, at various
locations in fuel cell system 20 such as compressor inlet 34,
compressor outlet 36, fuel cell stack inlet 26, fuel cell stack
outlet 26, ambient, and the like. Control logic 42 may also monitor
various components in fuel cell system 20 including fuel cell stack
22, compressor 30, control valve 32, and the like. Control inputs
46 may include inputs from a user or another controller. In one
embodiment, control logic 46 measures a temperature related to the
operation of fuel cell stack 22 and uses compressor 30 as an
electrical load for warming fuel cell stack 22. Control logic 42
may be implemented as a computer executing software, as
programmable logic, as discrete logic components, as
electromechanical, hydraulic, or pneumatic systems, any combination
of these, and the like. Control logic 42 may be a single unit or
may be distributed between or amongst various units. As will be
recognized by one of ordinary skill in the art, the present
invention may be implemented in a wide variety of control logic
types and configurations.
[0029] Referring now to FIG. 2, a flow diagram illustrating
operation of a fuel cell system according to an embodiment of the
present invention is shown. As will be appreciated by one of
ordinary skill in the art, the operations illustrated are not
necessarily sequential operations. The order of steps may be
modified within the spirit and scope of the present invention and
the order shown here is for logical presentation. Also, methods
illustrated may be implemented by any combination of hardware,
software, firmware, and the like, at one location or distributed.
The present invention transcends any particular implementation and
the embodiments are shown in sequential flow chart form for ease of
illustration.
[0030] The fuel cell stack generates electricity to drive the
compressor, as in block 60. The compressor provides a flow of
compressed gas to the fuel cell stack at a first flow rate, as in
block 62. This flow rate may be determined by one or more of a
variety of techniques, including directly or indirectly measuring
the mass flow rate, the volumetric flow rate, and the like.
[0031] A check is made to determine whether or not to increase the
flow rate above the flow needed by the fuel cell stack, as in block
64. This increase may be triggered, for example, by the need to
increase the load on the fuel cell stack. One purpose for
increasing the load may be to generate heat for warming the fuel
cell stack. Another purpose for increasing the load may be to test
the fuel cell stack and/or some other component of the fuel cell
system. In addition, or rather than, responding to a need to
increase fuel cell stack load, the flow rate may be increased so as
to generate excess flow for purposes other than to provide oxidant
to the fuel cell stack. This excess flow may be used to modify an
environmental condition of an element within or outside of the fuel
cell system.
[0032] If flow is to be increased, the fuel stack electrical output
is increased to drive the compressor, as in block 66. Additional
flow is provided from the compressor, as in block 68. The
additional flow is diverted away from the fuel cell stack, as in
block 70. The diverted flow may be directly or indirectly returned
to the compressor or vented to the atmosphere. The diverted flow
may also be used for a variety of purposes, as disclosed elsewhere
herein.
[0033] Returning again to FIG. 1, various embodiments for use of
diverted flow according to the present invention are shown. Fuel
cell stack 22 is contained in housing 80. Operation of fuel cell
stack may cause the formation of gases within housing 80, shown
generally by 82. Diverted flow 84 from control valve 32 may be
routed into housing 80 to purge housing gases 82 from housing
80.
[0034] Diverted flow 84 may also be routed to radiator 86, heat
exchanger 88, direct application 90, and the like for modifying one
or more environmental parameters. Radiator 86 may use diverted flow
84 to heat or cool a liquid such as, for example, coolant used to
regulate the temperature of an internal combustion engine or an
electronic circuit. Radiator 86 may also function as a heat sink
for electrical componentry cooled by diverted flow 84. Heat
exchanger 88 may provide heat from diverted flow 84 to a
surrounding environment such as, for example, a passenger
compartment (not shown for clarity). Direct application 90 provides
diverted flow 84 directly into an environment to be modified. The
path of diverted flow 84 may include various other components such
as diffusers, expanders, intercoolers, humidifiers, and the like
for regulating properties of diverted flow 84 prior to use by
radiator 86, heat exchanger 88, or direct application 90.
[0035] Output flow, shown generally by 92, can include one or more
of the flow from fuel stack outlet 28 and the diverted flow 84 uses
such as purging housing 80, radiator 86, heat exchanger 88, direct
application 90, and the like. Some or all of output flow 92 may be
returned to compressor inlet 34, may be vented to ambient, may be
routed for other uses, and the like.
[0036] Referring now to FIG. 3, a graph illustrating surge
avoidance according to an embodiment of the present invention is
shown. A compressor operating map, shown generally by 100, plots
mass flow rate through an exemplary compressor as a function of
compressor pressure ratio. The compressor pressure ratio refers to
the ratio of air pressure exiting the exemplary compressor outlet
to air pressure entering the exemplary compressor inlet.
[0037] Compressor pressure ratio, being a function of mass flow, is
also dependent upon the velocity with which the compressor rotates
its impellers. Six exemplary compressor operating lines with
corresponding angular velocities, indicated on compressor operating
map 100, are marked by respective 30, 45, 60, 75, 90, and 97
thousands of revolutions per minute (krpm). Compressor operating
maps, such as 100, are typically created by setting a compressor at
a constant angular velocity and subsequently varying mass flow
through the compressor.
[0038] Compressor surge typically occurs when a compressor operates
at low flow rates in combination with relatively high compressor
pressure ratios. For the example provided, operating the compressor
to the left of surge line 102 will more than likely result in
compressor 30 experiencing surge. This surge condition may cause
unsteady aerodynamic loading, observed in flow and pressure
oscillation, which may result in damage to equipment or otherwise
affect operation.
[0039] The present invention may be used to avoid a surge condition
in the compressor. For example, various components in the fuel cell
system may be monitored, such as the compressor inlet and
compressor outlet. Preexisting compressor performance data may be
stored such as, for example, that shown on compressor operating map
100. Surge line 102 represents the pressure at which surge can be
expected to occur for a given mass flow rate. When the compressor
operates in an intervention region, shown generally by shaded
region 104, the compressor may be controlled to increase output
flow, thereby avoiding or removing surge. As previously described,
this increased flow may be diverted from the fuel cell stack. For
example, if the compressor is operating at surge condition 106,
mass flow can be increased through the compressor. As flow is
increased, operation moves along operating line 108 until stable
flow and pressure condition 110 is reached beyond surge line
102.
[0040] Control of flow rate may also prevent the compressor from
initially reaching surge. For this reason, intervention region 104
may encompass surge line 102 and overlap a portion of conditions in
which compressor 30 may be operating satisfactorily. For example,
if the compressor is operating at 75 krpm and its mass flow rate
drops to 120 kg/h, the compressor flow may be increased before the
compressor ever reaches a surge condition.
[0041] Referring now to FIG. 4, a schematic diagram illustrating an
automotive vehicle utilizing a fuel cell system according to an
embodiment of the present invention is shown. An automotive
vehicle, shown generally by 120, is driven by electric motor 122
receiving fuel cell stack generated electrical energy 24. Electric
motor 122 may drive axle 124 extending between wheels 126. While
electric motor 122 is shown to propel vehicle body 120, one skilled
in the art will realize that there are countless alternative
applications onboard a motor vehicle which involve an electric
motor driving a component. These applications may include
operating, for example, power windows, an automatic vehicle
closure, power steering, or a plow attached to a vehicle body.
[0042] Air filter 128 may be included to purify ambient air 130
prior to its use in fuel cell system 20. Compressor 30, also driven
by fuel cell stack generated electrical energy 24, compresses
ambient air 130. Air exiting compressor 30 may have an excessive
temperature unsuitable for further usage. Air intercooler 132 may
be included to modify the temperature of air flow exiting
compressor 30 back within a usable range.
[0043] In the embodiment shown in FIG. 4, fuel cell system 20
includes control valves 32a and 32b. Control logic 42 operates
control valves 32a and 32b for a variety of purposes, such as to
provide fuel cell stack 22 with substantially constant absolute
pressure compressed air flow for particular operating
conditions.
[0044] In one application, fuel cell stack 22 is operated at a
higher output power solely for the purpose of generating more waste
heat to warm itself and any system coolant volume faster. A portion
of the output power of fuel cell stack is dumped into compressor 30
for operation at a higher speed. For example, a 50% efficient fuel
cell stack generates 1 kW of heat for every 1 kW of output
power.
[0045] Vehicle 120 includes passenger compartment 134. Passenger
compartment 134 may utilize diverted flow 84 passing through heat
exchanger 88 to change an environmental condition of passenger
compartment 134. Alternatively, heat exchanger 88 may use air flow
prior to, or instead of, passing through air intercooler 132.
[0046] While embodiments of the invention have been illustrated and
described, it is not intended that these embodiments illustrate and
describe all possible forms of the invention. Rather, the words
used in the specification are words of description rather than
limitation, and it is understood that various changes may be made
without departing from the spirit and scope of the invention.
* * * * *