U.S. patent application number 13/903432 was filed with the patent office on 2014-04-24 for fuel cell system for generating energy and water.
This patent application is currently assigned to AIRBUS OPERATIONS GMBH. The applicant listed for this patent is Airbus Operations GmbH. Invention is credited to Thorsten Otto.
Application Number | 20140113207 13/903432 |
Document ID | / |
Family ID | 46049701 |
Filed Date | 2014-04-24 |
United States Patent
Application |
20140113207 |
Kind Code |
A9 |
Otto; Thorsten |
April 24, 2014 |
FUEL CELL SYSTEM FOR GENERATING ENERGY AND WATER
Abstract
Fuel cell systems aboard means of transport can be used for
generating energy and for producing water. In order to reduce the
overall weight of the system, the fuel cell is controlled or
regulated in dependence on a current fill level or a limit level of
the water tank, as well as a predicted future water consumption. In
this way, it may be possible to minimize the water quantity to be
stored in the water tank.
Inventors: |
Otto; Thorsten; (Hamburg,
DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Airbus Operations GmbH |
Hamburg |
|
DE |
|
|
Assignee: |
AIRBUS OPERATIONS GMBH
Hamburg
DE
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20130252118 A1 |
September 26, 2013 |
|
|
Family ID: |
46049701 |
Appl. No.: |
13/903432 |
Filed: |
May 28, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/EP2011/070714 |
Nov 22, 2011 |
|
|
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13903432 |
|
|
|
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61417527 |
Nov 29, 2010 |
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Current U.S.
Class: |
429/414 ;
429/450 |
Current CPC
Class: |
B64D 2041/005 20130101;
C25B 5/00 20130101; H01M 8/04291 20130101; B64D 11/02 20130101;
Y02T 50/44 20130101; H01M 8/04828 20130101; B64D 41/00 20130101;
H01M 2250/20 20130101; Y02E 60/50 20130101; Y02E 60/566 20130101;
Y02T 50/40 20130101; Y02T 90/32 20130101; H01M 8/04992 20130101;
H01M 8/04313 20130101; Y02T 90/36 20130101; Y02T 90/40 20130101;
H01M 8/04694 20130101; Y02T 50/46 20130101; H01M 8/04492 20130101;
H01M 8/04164 20130101 |
Class at
Publication: |
429/414 ;
429/450 |
International
Class: |
C25B 5/00 20060101
C25B005/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 29, 2010 |
DE |
10 2010 052 839.0 |
Claims
1. A fuel cell system for generating electric energy and water for
use aboard a means of transport, with the fuel cell system
comprising: a fuel cell; a water tank for storing water delivered
by the fuel cell; a control or regulating device for controlling or
regulating the fuel cell in dependence on a current fill level or
limit level of the water tank and on a predicted future water
consumption.
2. The fuel cell system of claim 1, wherein the control or
regulating device is furthermore configured for controlling or
regulating the fuel cell in dependence on a previous water
consumption.
3. The fuel cell system of claim 1, wherein the control or
regulating device comprises a fill level control or regulating
device with a fill level sensor or a limit level sensor for
determining a fill level or a limit level in the water tank.
4. The fuel cell system of claim 1, wherein the control or
regulating device is configured for controlling or regulating the
fuel cell with consideration of a current flight phase.
5. The fuel cell system of claim 1, furthermore comprising: a
condensation device for condensing the water delivered by the fuel
cell before the water is fed to the tank; wherein the control or
regulating device is configured for controlling or regulating the
fuel cell with consideration of a current efficiency of the
condensation device.
6. The fuel cell system of claim 5, wherein the control or
regulating device comprises a performance demand signal control
configured for determining a nominal value for the water production
rate of the fuel cell with consideration of the current efficiency
of the condensation device.
7. The fuel cell system of claim 6, wherein a continuous decrease
of the efficiency of the condensation device leads to a continuous
increase of the nominal value.
8. The fuel cell system of claim 1, wherein the control or
regulating device comprises a performance demand signal limiter
configured for limiting a nominal value for the performance of the
fuel cell with consideration of a current power consumption of the
electric consumers aboard the means of transport or with
consideration of a fuel supply for the fuel cell.
9. A means of transport with a fuel cell system, the fuel cell
system comprising: a fuel cell; a water tank for storing water
delivered by the fuel cell; a control or regulating device for
controlling or regulating the fuel cell in dependence on a current
fill level or limit level of the water tank and on a predicted
future water consumption.
10. The means of transport of claim 9 realized in the form of an
aircraft.
11. A method for generating electric energy and water aboard a
means of transport by a fuel cell system, with said method
comprising: supplying fuel to a fuel cell; generating electric
energy by the fuel cell; obtaining water from waste gas of the fuel
cell; filling a water tank with the obtained water; controlling or
regulating the fuel cell in dependence on a current fill level or
limit level of the water tank and on a predicted future water
consumption.
12. The method of claim 11, further comprising: controlling or
regulating the fuel cell with consideration of a previous water
consumption.
13. The method of claim 11, further comprising: controlling or
regulating the fuel cell with consideration of a current flight
phase or a current efficiency of a condensation device.
14. The method of claim 11, further comprising: limiting a nominal
value for the performance of the fuel cell with consideration of a
current power consumption of the electric consumers aboard the
means of transport or with consideration of a fuel supply for the
fuel cell.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a continuation of International
Patent Application No. PCT/EP2011/070714, filed Nov. 22, 2011,
which claims priority from German Patent Application No. 10 2010
052 839.0 filed Nov. 29, 2010, and which claims the benefit of the
filing date of U.S. Provisional Patent Application No. 61/417,527
filed Nov. 29, 2010, all of which are hereby incorporated herein by
reference.
FIELD OF THE INVENTION
[0002] The invention pertains to fuel cell systems. The invention
particularly pertains to a fuel cell system for generating electric
energy and water for use aboard a means of transport, to a method
for generating electric energy and water aboard a means of
transport by means of a fuel cell system, to a means of transport
with a fuel cell system, as well as to the use of a fuel cell
system for supplying energy to electric consumers and for producing
fresh water aboard a means of transport.
TECHNICAL BACKGROUND
[0003] Fuel cell systems aboard aircraft are not only able to
generate electric energy, but also water by cooling the hot and
humid fuel cell waste gas in a condenser and subsequently
separating the condensed water from the waste gas in a water
separator.
[0004] DE 10 2006 034 814 B1 and US 2008179050 A1 describe
conventional fuel cell systems aboard aircraft.
[0005] The control of the fuel cell system may be based on the
respective electric power demand.
[0006] The water produced by the fuel cell may furthermore be
intermediately stored in a tank and fed to the water consumers
aboard the aircraft in case of need.
[0007] The water tank needs to have corresponding dimensions in
order to ensure that a sufficient quantity of water is always
available.
BRIEF SUMMARY OF THE INVENTION
[0008] An aspect of the invention may be seen in proposing a fuel
cell system that is characterized by a reduced overall weight.
[0009] According to a first aspect of the invention, a fuel cell
system for generating electric energy and water for use aboard a
means of transport is proposed, wherein said fuel cell system
features a fuel cell, a water tank and a control or regulating
device. The water tank serves for storing water delivered by the
fuel cell. For example, the fuel cell emits hot and humid fuel cell
waste gas that is subsequently cooled. The thusly condensed water
can then be collected in the water tank.
[0010] The control or regulating device serves for controlling or
regulating the fuel cell in dependence on a current fill level of
the water tank or in dependence on a current limit level of the
water tank and/or a predicted future water consumption.
[0011] Consequently, the quantity of water being produced may not
or at least not only be dependent on the power demand of the
electric loads aboard the means of transport. It may be possible,
in particular, to control or regulate the water production rate
independently of the power demand of the electric loads, i.e. the
electric consumers.
[0012] The control or regulation of the fuel cell system for
supplying the water system may make it possible to adapt the
operation of the fuel cell system in dependence on the water demand
such that the quantity of water to be stored in the tank can be
minimized. This may result in a reduction of the overall weight of
the fuel cell system and therefore the means of transport. The
thusly achieved reduction of the size of the water tank may also
make it possible to reduce the required installation space for the
fuel cell system.
[0013] The instantaneous water tank fill level, the previous water
consumption and the anticipated, predicted water demand can be
taken into account in the control or regulation of the fuel cell
system such that the fuel cell may, if applicable, even be operated
at its optimal operating point of, for example, about 30 to 50% of
the maximum load during the entire flight or at least a significant
portion of the flight. In this way, electric energy is generated
with the highest electrical efficiency possible and a long service
life of the fuel cell is simultaneously achieved.
[0014] According to another embodiment of the invention, the
control or regulating device features a fill level control or
regulating device with a fill level sensor or a limit level sensor
for determining a fill level or a limit level in the water
tank.
[0015] Due to the measurement of the current fill level or the
limit level, it may be possible to determine if and at which rate
the water tank needs to be filled.
[0016] According to another embodiment of the invention, the
control or regulating device is designed for controlling or
regulating the fuel cell with consideration of the current flight
phase. In other words, the fuel cell may be controlled or regulated
depending on the current flight phase.
[0017] Since the current flight phase is taken into consideration,
it may be possible to determine if the water consumption will
increase or decrease in the near future. It is also possible to
determine if it is even necessary to additionally fill the water
tank, for example, because the water reserves in the water tank
suffice for the remainder of the flight.
[0018] According to another embodiment of the invention, the fuel
cell system furthermore features a condensation device, if
applicable, with a downstream water separator for condensing (and
separating) the water delivered by the fuel cell before it is fed
to the tank. In this case, the control or regulating device is
designed for controlling or regulating the fuel cell with
consideration of the current efficiency of the condensation device
(or of the combination of the condensation device and the water
separator).
[0019] For example, it may be necessary to increase the water
production rate of the fuel cell because the efficiency of the
condensation device decreases (and vice versa).
[0020] According to another embodiment of the invention, the
control or regulating device features a performance demand signal
control that is designed for determining a nominal value for the
water production capacity of the fuel cell with consideration of
the current efficiency of the condensation device.
[0021] In addition to the current efficiency of the condensation
devices, other measured variables may also be incorporated into the
determination of the nominal value. These consist, for example, of
different physical parameters such as, e.g., the cooling
temperature of the condenser, the ambient pressure of the condenser
and the air inflow velocity of the condenser. Corresponding sensors
are provided in order to determine these different physical
parameters.
[0022] According to another embodiment of the invention, the
control or regulating device is designed in such a way that a
continuous decrease of the efficiency of the condensation device
leads to a continuous increase of the nominal value for the water
production capacity of the fuel cell (and vice versa).
[0023] Alternatively, it may be provided that a continuous decrease
of the efficiency leads to an erratic, i.e. step-like increase of
the nominal value after the efficiency falls short of a certain
threshold value, and that a continuous increase of the efficiency
of the condensation device leads to an erratic, i.e. step-like,
decrease of the nominal value after the efficiency exceeds a
certain threshold value.
[0024] According to another embodiment of the invention, the
control or regulating device features a performance demand signal
limiter that is designed for limiting the nominal value for the
performance of the fuel cell with consideration of the current
power consumption of the electric loads aboard the means of
transport and/or with consideration of a fuel supply for the fuel
cell.
[0025] In this way, it may be possible to limit the performance of
the fuel cell even if the upstream performance demand signal
control has defined a higher nominal value.
[0026] This limitation may also be defined in dependence on the
flight phase.
[0027] According to another aspect of the invention, a means of
transport with a fuel cell system of the type described above and
below is proposed.
[0028] The term means of transport used in this description may
refer to an aircraft such as, for example, an airplane, a
helicopter, an airship or a spacecraft, as well as to a land craft
or a watercraft.
[0029] According to another aspect of the invention, the use of a
fuel cell system of the type described above and below for
supplying energy to electric loads and for producing fresh water
aboard a means of transport is proposed.
[0030] According to another aspect of the invention, a method for
generating electric energy and water aboard a means of transport by
means of a fuel cell system of the type described above and below
is proposed, wherein fuel is supplied to a fuel cell, electric
energy is generated by the fuel cell and water is obtained from a
waste gas of the fuel cell. The thusly obtained water is used for
filling a water tank. Furthermore, the fuel cells are controlled or
regulated in dependence on a current fill level or limit level of
the water tank and a predicted future water consumption of
consumers aboard the means of transport.
[0031] According to another embodiment of the invention, the fuel
cell is controlled or regulated with consideration of a previous
water consumption aboard the means of transport, a current flight
phase or traveling phase of the means of transport and/or a current
efficiency of a condensation device.
[0032] According to another embodiment of the invention, the
nominal value for the performance of the fuel cell is limited with
consideration of a current power consumption of the electric loads
aboard the means of transport or a fuel supply for the fuel
cell.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] Exemplary embodiments of the invention are described below
with reference to the figures.
[0034] FIG. 1 shows a fuel cell system with a water supply
according to an exemplary embodiment of the invention.
[0035] FIG. 2 shows a fuel cell system with a power supply
according to an exemplary embodiment of the invention.
[0036] FIG. 3 shows a flow chart of a control or regulating process
according to an exemplary embodiment of the invention.
[0037] FIG. 4 shows the dependence of the maximum permissible water
tank fill level, the upper limiting value of the water tank fill
level and the lower limiting value of the water tank fill level on
the time.
[0038] FIG. 5 shows the dependence of the condensation efficiency
on the temperature of the condenser.
[0039] FIG. 6 shows a flowchart of a process for regulating the
water tank fill level.
[0040] FIG. 7 shows two tables for elucidating the characteristics
of the fill level control or regulating process.
[0041] FIG. 8A shows four tables for elucidating the
characteristics of the performance demand signal control according
to an exemplary embodiment of the invention.
[0042] FIG. 8B shows a diagram for elucidating the characteristics
of the performance demand signal control according to another
exemplary embodiment of the invention.
[0043] FIG. 8C shows a diagram for elucidating the characteristics
of the performance demand signal control according to the exemplary
embodiment of FIG. 8B.
[0044] FIG. 9 shows a flow chart of a performance demand signal
limiting process according to an exemplary embodiment of the
invention.
[0045] FIG. 10 shows an aircraft according to an exemplary
embodiment of the invention.
DETAILED DESCRIPTION
[0046] The figures show schematic illustrations that are not
true-to-scale.
[0047] In the following description of the figures, identical or
similar elements are identified by the same reference symbols.
[0048] FIG. 1 shows a fuel cell system 100 according to an
exemplary embodiment of the invention. The power supply system for
distributing the electric energy generated by the fuel cell 101 to
the on-board loads, i.e. consumers, is not illustrated (in this
respect, see FIG. 2).
[0049] A water generation system 102 featuring, for example, one or
more condensers and a water separator is arranged downstream of the
fuel cell 101. The water obtained from the waste gas of the fuel
cell 101 in this fashion is then fed to a water tank 103 and stored
therein.
[0050] The water consumers 104 are connected to the water tank 103
by means of a corresponding pipe system. A drain valve 105 is also
provided on the water tank 103 in order to prevent the water tank
103 from being overfilled. The excess water may be discharged, for
example, into the surroundings of the means of transport.
[0051] Several sensors 106 to 111 are provided and measure, for
example, the fill level or limit level of the water tank 103
(sensor 110), the efficiency of the water generation system 102
(sensor 108) and/or certain parameters of the fuel cell 101 (sensor
106). The waste gas rate of the fuel cell 101 can also be measured,
for example, with the sensor 107. The sensor 109 measures the
actual water production rate, for example, by measuring the flow
through the water pipe between the water generation system 102 and
the tank 103.
[0052] Other sensors 111 may be provided in order to measure the
water demand and/or the energy demand of the on-board loads
104.
[0053] The control or regulating device 115 is supplied with the
sensor data from the sensors 106 to 111 via a data bus 112 and
controls the fuel cell 101 based on the sensor data of one or more
of these sensors. For this purpose, a control line 113 is provided
and connects the control or regulating device 115 to the fuel cell
101. The control or regulating device 115 can also control the
drain valve 105 via the control line 114.
[0054] It should be noted that it would also be possible to provide
more or fewer sensors. In a simple scenario, only a limit level
sensor is provided in order to detect a limit level of the water
tank 103.
[0055] The control or regulating device 115 can adjust the
operating point of the fuel cell 101. The fuel cell system delivers
electric energy to the on-board electrical system together with
other energy generators (see FIG. 2) while the water production
system delivers water into the tank 103, from which the water
consumers 104 aboard the means of transport are supplied.
[0056] At this point, it should be noted that a plurality of fuel
cells 101 may also be provided.
[0057] According to FIG. 2, additional energy generators 202 for
generating electric energy may be provided and connected to the
electrical network 203 of the means of transport analogous to the
fuel cell 101. The electric loads 204 are supplied with electric
energy via this electrical network 203.
[0058] FIG. 3 shows a flow chart of a regulating process according
to an exemplary embodiment of the invention. The control or
regulating device 115 features a tank fill level control or
regulating device 301, a downstream performance demand signal
control 302, a performance demand signal limiter 303 arranged
downstream thereof and a fuel cell performance regulator 304
arranged downstream of the performance demand signal limiter.
[0059] The tank fill level control or regulating device 301
comprises, for example, a two-position controller that detects
limit fill levels. If the lower limiting value of the water tank
fill level V.sub.Tu is not reached, the device 301 sends a demand
signal for the production of water to the performance demand signal
control 302. The demand signal is once again reset once the water
level in the tank rises and the upper limiting value V.sub.To is
exceeded (see FIG. 4). If the maximum permissible fill level
V.sub.Tmax is exceeded, a drain valve 105 opens and discharges the
excess water outward into the surroundings of the means of
transport (for example, of the aircraft).
[0060] The control or regulating device may be expanded in order to
achieve a more precise control or regulation of the fill level in
the tank V.sub.T and to operate the fuel cell at the optimal
operating point, i.e., in the partial-load range, for as long as
possible. In this case, the water quantity V.sub.V consumed in the
last time interval and/or the current flight phase are taken into
consideration. It is checked if the consumed water quantity V.sub.V
exceeds a critical limiting value V.sub.Vkrit and if the catering
for the passengers and the higher water consumption associated
therewith (e.g., for the preparation of coffee or tea) will take
place in the near future. A demand signal for the water quantity
V.sub.Gsoll to be produced in the next time interval is output with
the aid of a suitable calculation method in dependence on the three
influencing variables tank fill level V.sub.T, water consumption
V.sub.V and flight phase. In this case, the signal V.sub.Gsoll can
assume the three states "no water production," "water production at
optimal operating point" or "maximum water production." One
possible method is illustrated in an exemplary fashion in FIGS. 6
and 7.
[0061] The consumed water quantity can be measured, e.g., with a
flow sensor in the supply pipe on the water tank outlet. Another
option consists of calculating the water consumption from the
opening times of the individual consumers (e.g., water faucets and
flushing valves in the toilets) and the water pressure in the
system.
[0062] The flight phase or the elapsed and the remaining flying
time are known from the on-board computer that is also connected to
the control or regulating device 115. The termination of the
catering phases may either be preadjusted or input by the cabin
crew during the flight.
[0063] According to FIG. 3, sensor measurement data with respect to
the water tank fill level V.sub.T and the current water consumption
rate V.sub.V, as well as information on the flight phase, is fed to
the tank fill level control or regulating device 301.
[0064] The device 301 calculates the water generation rate
V.sub.Gsoll thereof in the form of a nominal value.
[0065] For example, information on the cooling temperature of the
condenser T.sub.K, the ambient pressure P.sub.U and the air inflow
velocity v.sub.L may be fed to the performance demand signal
control 302.
[0066] The performance demand signal control 302 translates the
output signal V.sub.Gsoll of the tank fill level regulating device
301 into a performance demand signal P.sub.Wsoll for the fuel cell
that is required for the water production, for example, with
consideration of the efficiency of the condensation K of the
condenser. The signal V.sub.Gsoll may assume, for example, three
values that represent no water production, average water production
and maximum water production.
[0067] The condensation efficiency K describes the proportion of
the water actually produced in the water production system in
relation to the absolute water quantity in the fuel cell waste gas.
Due to the characteristics of the system, it is not possible to use
the entire water quantity contained in the waste gas for the water
system. The exhaust air exiting the water separator contains a
residual quantity of water. The cooling temperature of the
condenser T.sub.K can have the most significant operational
influence on the condensation efficiency (see FIG. 5). A very high
condensation efficiency is achieved at cruising altitudes and the
correspondingly low outside temperatures, wherein the condensation
efficiency is much lower on the ground and the correspondingly high
outside temperatures. A mathematical model of the condensation
efficiency K as a function of different physical parameters such
as, e.g., the cooling temperature T.sub.K, the ambient pressure
P.sub.U and the air inflow velocity v.sub.L is stored in the
performance demand signal control 302 and serves for calculating
the instantaneous condensation efficiency.
[0068] Two options for calculating the performance demand for the
water generation (nominal value) P.sub.Wsoll are described
below:
[0069] 1. It is determined if the instantaneous condensation
coefficient K has fallen short of a limiting value K.sub.krit. The
performance demand signal P.sub.Wsoll required for the water
production is generated in the increments "no performance demand,"
"performance demand at optimal operating point P.sub.Bzopt" and
"maximum performance demand P.sub.BZmax" in dependence on the
result of the aforementioned determination and in connection with
the output signal V.sub.Gsoll of the tank fill level regulating
device (see FIG. 8A).
[0070] 2. In case the tank fill level regulating device 301 outputs
the value "water production at optimal operating point" for the
signal V.sub.Gsoll, the output signal of the performance demand
signal control P.sub.Wsoll may alternatively be variably adjusted
between the fuel cell performance at optimal operating point
P.sub.Bzopt and the value "maximum performance demand P.sub.BZmax"
in accordance with the following equation (see also FIG. 8B):
P Wsoll = 1 K P BZopt ##EQU00001##
[0071] An advantage may be that the performance demand signal is
not increased erratically, but rather continuously as the
condensation efficiency decreases and the maximum value may not be
reached as often.
[0072] The performance demand signal limiter 303 limits the
performance demand signal P.sub.Wsoll required for the water
production to an actual performance demand for the fuel cell
P.sub.BZsoll.
[0073] The output signal of the performance demand signal control
P.sub.Wsoll is based exclusively on the water demand and only
limited with respect to its peak value by the design-related
maximum performance of the fuel cell system P.sub.BZmax. The
performance demand signal limiter 303 may receive measured values
that concern the fill level of the supply tank for the fuel cell.
This fill level consists, for example, of the fill level of the
hydrogen tank m.sub.H2. It may also receive data with respect to
the current power demand of the loads P.sub.V and data with respect
to the current flight phase and the remaining flying time.
[0074] The electric power of the fuel cell associated with the
required water production is fed into the on-board network of the
aircraft. In order to prevent more power than that currently
consumed from being generated, the performance demand signal
P.sub.Wsoll can be compared with the current power consumption
P.sub.V. If the current power consumption is exceeded, the
performance demand signal for the fuel cell P.sub.BZsoll is limited
to the actual power demand of the loads P.sub.V (see also FIG.
9).
[0075] In addition, the demand signal can be set to zero or at
least reduced if the supply of fuel for the fuel cell falls short
of a minimum supply, e.g., with consideration of the still
remaining flying time. In this way, the availability of the fuel
cell system as an energy supplier (e.g., an emergency power system)
is ensured up to the end of the flight (see, for example, FIG.
9).
[0076] Since other energy generators also feed power into the
on-board network, the performance demand signal for the fuel cell
P.sub.BZsoll can be used for limiting the power to be delivered by
the other energy generators to the differential amount between the
instantaneous power consumption P.sub.V and the performance demand
P.sub.BZsoll.
[0077] The thusly calculated and, if applicable, limited fuel cell
performance is forwarded to the fuel cell performance regulating
device 304 in the form of a nominal value P.sub.BZsoll.
[0078] FIG. 4 shows an example of the maximum permissible tank fill
level 403, the upper limiting value for the tank fill level 404
(that lies below the maximum permissible tank fill level) and the
lower limiting value for the tank fill level 405 (that lies below
the upper limiting value) as a function of the time. According to
the exemplary embodiment shown in FIG. 4, these three fill level
limiting values are not time-variant. However, it would be
possible, for example, that the lower limiting value decreases over
time because the remaining traveling time become shorter and
shorter.
[0079] FIG. 5 shows the dependence of the condensation efficiency K
502 on the cooling temperature of the condenser T.sub.K 501.
According to the curve 504, the condensation efficiency drops in a
non-linear fashion as the temperature increases and has a value
that is lower than the limiting value of the condensation
efficiency K.sub.krit 503 above a limiting temperature.
[0080] FIG. 6 shows a flow chart of a process for controlling or
regulating the tank fill level. The tank fill level is measured in
step 601 and it is determined if the measured tank fill level is
higher than the upper limiting value for this fill level in step
602. If this is the case, no water generation takes place (step
603). If this is not the case, it is determined if the measured
tank fill level is lower than the lower limiting value for the tank
fill level in step 604.
[0081] If this is the case, it is determined if the water
consumption (or the water consumption rate) in the interval in
question is higher than a limiting value for the water consumption
in step 605. If this is the case, the command for maximizing the
water generation is output (step 606).
[0082] If this is not the case, it is determined if catering of the
passengers is imminent in step 607.
[0083] If this is the case, the command for increasing the water
generation to a maximum value is output (step 608).
[0084] If this is not the case, the water generation is adjusted to
an average value (step 609).
[0085] If it is determined that the tank fill level does not lie
below the lower limiting value in step 604, the next step to be
carried out is step 610, in which it is determined if the water
consumption in the interval in question is higher than a limiting
value for the water consumption.
[0086] If this is the case, it is determined if catering is
imminent in step 611. If this is the case, the water generation is
increased to a maximum value in step 612. If this is not the case,
the water generation is set to an average value in step 613.
[0087] However, if it is determined that the water consumption in
the interval in question does not lie above the limiting value for
the water consumption in step 610, the next step to be carried out
is step 614, in which it is determined if a catering phase is
imminent. If this is the case, the value for the water generation
is set to an average value (see step 613). If this is not the case,
it is determined that no water generation should take place in step
615.
[0088] FIG. 7 shows two tables for elucidating the characteristics
of the tank fill level control process. If the current tank fill
level lies above the upper limiting value for the tank fill level
(value 0), the command that no water should be produced is
output.
[0089] If the current tank fill level lies between the lower
limiting value and the upper limiting value (value 1), the water
consumption in the interval in question lies below the
corresponding limiting value (value 0) and no catering is planned
in the near future (value 0), the command that no water should be
produced is output (see second line of the first table).
Accordingly, it is also determined if the command for producing
water should be output with an average production rate or a maximum
production rate as already described above with reference to FIG.
6.
[0090] FIG. 8A shows several tables that elucidate how the
performance demand signal control according to the exemplary
embodiment described above under option 1 can be operated. In this
case, the determination of the performance demand signal
P.sub.Wsoll required for the water production takes place
erratically. In column 1 of the upper table, the value 0 means that
the nominal value for the water production is 0. The value 1 means
that the nominal value for the water production assumes an average
value, and the value 2 means that the nominal value for the water
production assumes a maximum value. In the second column, the value
0 means that the condensation efficiency lies below a limiting
value and the value 1 means that the condensation efficiency lies
above this limiting value.
[0091] In the third column, the value 0 means that the performance
demand signal P.sub.Wsoll required for the water production is 0,
the value 1 means that the performance demand signal has an average
value (at which the fuel cell operates at the optimal operating
point) and the value 2 means that the performance demand signal has
a maximum value, at which the fuel cell delivers maximum power.
[0092] For example, if the nominal value for the water production
is set to an average value (V.sub.Gsoll=1) and the condensation
efficiency lies below the critical value (K=0), the performance
demand signal is set to its maximum (P.sub.Wsoll=2).
[0093] FIG. 8B shows the dependence of the performance demand
signal 802 on the cooling temperature of the condenser 801. In this
case, the erratic curve 804 corresponds to the first exemplary
embodiment and the curve 805 corresponds to the second exemplary
embodiment, in which P.sub.Wsoll is continuously adjusted.
[0094] The curve 803 shows the dependence of the condensation
efficiency on the cooling temperature of the condenser.
[0095] FIG. 8C shows the dependence of the performance demand
signal 811 on the condensation efficiency 810. The curve 812 shows
the erratic dependence according to exemplary embodiment 1 and the
curve 813 shows the continuous dependence according to exemplary
embodiment 2 (see above).
[0096] FIG. 9 shows a flow chart of a performance demand signal
limiting process. The performance demand signal P.sub.Wsoll
required for the water production is output in step 901 and this
signal is compared with the instantaneous power consumption of the
electric loads in step 902. If P.sub.Wsoll is higher than the
instantaneous power consumption P.sub.V, the actual performance
demand for the fuel cell is set to the instantaneous power
consumption in step 903. If this is not the case, the actual
performance demand for the fuel cell is set to P.sub.Wsoll in step
904.
[0097] It can furthermore be determined if a critical hydrogen
supply has been reached in step 905. If this is the case,
P.sub.BZsoll (i.e., the actual performance demand for the fuel
cell) is set to 0 in step 906. If this is not the case, P.sub.Wsoll
is compared with the instantaneous power consumption P.sub.V in
step 907. If P.sub.Wsoll is higher than P.sub.V, the actual
performance demand for the fuel cell is set to the instantaneous
power consumption P.sub.V in step 908. If this is not the case, the
actual performance demand for the fuel cell is set to P.sub.Wsoll
in step 909.
[0098] FIG. 10 shows an aircraft 1000 according to an exemplary
embodiment of the invention. The aircraft 1000 features a fuselage
1001, into which a fuel cell system 100 is installed.
[0099] As a supplement, it should be noted that "comprising" and
"featuring" do not exclude any other elements or steps, and that
"a" or "an" does not exclude a plurality. It should furthermore be
noted that characteristics or steps that were described with
reference to one of the above exemplary embodiments can also be
used in combination with other characteristics or steps of other
above-described exemplary embodiments. Reference symbols in the
claims should not be interpreted in a restrictive sense.
* * * * *