CA2422209A1 - Method for operating a fuel cell and a fuel cell arrangement - Google Patents
Method for operating a fuel cell and a fuel cell arrangement Download PDFInfo
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- CA2422209A1 CA2422209A1 CA002422209A CA2422209A CA2422209A1 CA 2422209 A1 CA2422209 A1 CA 2422209A1 CA 002422209 A CA002422209 A CA 002422209A CA 2422209 A CA2422209 A CA 2422209A CA 2422209 A1 CA2422209 A1 CA 2422209A1
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M8/00—Fuel cells; Manufacture thereof
- H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
- H01M8/04298—Processes for controlling fuel cells or fuel cell systems
- H01M8/04313—Processes for controlling fuel cells or fuel cell systems characterised by the detection or assessment of variables; characterised by the detection or assessment of failure or abnormal function
- H01M8/04664—Failure or abnormal function
- H01M8/04671—Failure or abnormal function of the individual fuel cell
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M8/00—Fuel cells; Manufacture thereof
- H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
- H01M8/04298—Processes for controlling fuel cells or fuel cell systems
- H01M8/04313—Processes for controlling fuel cells or fuel cell systems characterised by the detection or assessment of variables; characterised by the detection or assessment of failure or abnormal function
- H01M8/04537—Electric variables
- H01M8/04544—Voltage
- H01M8/04552—Voltage of the individual fuel cell
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
- G01R19/165—Indicating that current or voltage is either above or below a predetermined value or within or outside a predetermined range of values
- G01R19/16504—Indicating that current or voltage is either above or below a predetermined value or within or outside a predetermined range of values characterised by the components employed
- G01R19/16523—Indicating that current or voltage is either above or below a predetermined value or within or outside a predetermined range of values characterised by the components employed using diodes, e.g. Zener diodes
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
- G01R31/3644—Constructional arrangements
- G01R31/3646—Constructional arrangements for indicating electrical conditions or variables, e.g. visual or audible indicators
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
- G01R31/382—Arrangements for monitoring battery or accumulator variables, e.g. SoC
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
- G01R31/396—Acquisition or processing of data for testing or for monitoring individual cells or groups of cells within a battery
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M8/00—Fuel cells; Manufacture thereof
- H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
- H01M8/04298—Processes for controlling fuel cells or fuel cell systems
- H01M8/04313—Processes for controlling fuel cells or fuel cell systems characterised by the detection or assessment of variables; characterised by the detection or assessment of failure or abnormal function
- H01M8/04537—Electric variables
- H01M8/04604—Power, energy, capacity or load
- H01M8/04611—Power, energy, capacity or load of the individual fuel cell
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M8/00—Fuel cells; Manufacture thereof
- H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
- H01M8/04298—Processes for controlling fuel cells or fuel cell systems
- H01M8/04313—Processes for controlling fuel cells or fuel cell systems characterised by the detection or assessment of variables; characterised by the detection or assessment of failure or abnormal function
- H01M8/04537—Electric variables
- H01M8/04634—Other electric variables, e.g. resistance or impedance
- H01M8/04641—Other electric variables, e.g. resistance or impedance of the individual fuel cell
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/50—Fuel cells
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- Life Sciences & Earth Sciences (AREA)
- Engineering & Computer Science (AREA)
- Manufacturing & Machinery (AREA)
- Sustainable Development (AREA)
- Sustainable Energy (AREA)
- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Fuel Cell (AREA)
Abstract
The invention relates to a fuel cell(2) or a fuel cell arrangement (1) comprising a plurality of fuel cells (2), and enables reliable monitoring of the operatability of each/said fuel cell (2) using particularly simple means . According to the invention, a proportion (12) of the output current (1) provided by each/said fuel cell (2) is guided via an optically active elemen t (12). The degree of operatability of the fuel cell (2) can be deduced from a n output signal (A) produced by the optically active element (12).
Description
W WO 02/23658 "" PCT/DE01/03367 .-Description Method for operating a fuel cell, and a fuel cell arrangement The invention relates to a method for operating a fuel cell, and to a fuel cell arrangement having a number of series-connected fuel cells. It also relates to such a fuel cell arrangement.
Fuel cells may be used to generate electricity in an environmentally friendly manner. This is because a process which essentially represents reversal of electrolysis is carried out in a fuel cell. A fuel which includes hydrogen is supplied to an anode, and an auxiliary substance which includes oxygen is supplied to a cathode in a fuel cell. The anode and cathode are in this case electrically isolated from one another via an electrolyte layer, in which case, although the electrolyte layer allows ions to be exchanged between the fuel and the oxygen, it otherwise ensures gastight separation of the fuel and auxiliary substance, however. Owing to the exchange of ions, hydrogen which is contained in the fuel can react with the oxygen to form water, with electrons being enriched at the fuel-side electrode or anode, and electrons being absorbed at the electrode on the auxiliary substance side, or cathode. A potential difference or voltage is thus formed between the anode and cathode during operation of the fuel cell. The electrolyte layer, which may be in the form of a ceramic solid electrolyte in the case of a high-temperature fuel cell or may be in the form of a polymer membrane in the case of a low-temperature fuel cell, thus has the function of separating the reactants from one another, of transferring the charge in the form of ions, and of preventing an electron short circuit.
_ 2 _ On the basis of the electrochemical potentials of the substances which are normally used, an electrode voltage of about 0.6 to 1.0 V can be formed in normal operating conditions in a fuel cell such as this, and can be maintained during operation. For technical applications in which a significantly higher total voltage may be required depending on the purpose or the planned load, a number of fuel cells are thus normally connected electrically in series in the form of a fuel cell stack, in such a way that the sum of the electrode voltages supplied from each of the fuel cells corresponds to the required total voltage, or is greater than it. Depending on the required total voltage, the number of fuel cells in a fuel cell stack such as this may, for example, be 50 or more.
When using such a fuel cell stack in a fuel cell arrangement, it may be important to monitor the functionality of each individual fuel cell continuously or cyclically. This is because, by way of example, a defect in the form of a hole can occur in the electrolyte layer in a fuel cell as a result of aging or other influences, so that the hydrogen contained in the fuel cell could come into direct contact with the oxygen. In the process, it would be possible for catalytic combustion of hydrogen to occur, associated with the release of energy, which could become wider if the gas supply to the fuel cell were to be maintained, further enlarging the affected area of damage. For safe and reliable operation of such a fuel cell stack, means can thus be provided which interrupt the gas supply to the relevant fuel cell within a very short reaction time when malfunctions occur and, in particular, when gas breaks through the electrolyte layer, in order in this way to safely avoid propagation of the damage.
i~10 02/23658 PCT/DE01/03367 _ 3 _ The electrode voltage produced by the respective fuel cell can be used as a suitable monitoring parameter for detecting such a defect or gas breakthrough. This is because a gas breakthrough in a fuel cell is evident, inter alia, from a characteristic reduction in the electrode voltage. A characteristic limit voltage value can therefore be specified for a fuel cell, for example as a function of its design, with the other operating parameters being known. If the electrode voltage falls below this limit voltage value, it is assumed that a defect of the type mentioned above has occurred, and the gas supply to the relevant fuel cell is interrupted.
However, the monitoring of the individual electrode voltages in a fuel cell arrangement having a large number of fuel cells is actually comparatively complex.
On the one hand, in this case, it would be possible to monitor only the total voltage of the fuel cell arrangement or of a fuel cell stack although it would not be possible to use a drop in the overall voltage to identify the individually affected fuel cell, and thus the cause of the fault. On the other hand, an individual voltage measurement on each individual fuel cell or on suitably combined fuel cell groups within a fuel cell stack is made more difficult by the comparatively high electrical potential of the fuel cells overall. This can assume values up to the kilovolt range, for example, depending on the total number of series-connected fuel cells.
Measurement systems which are intended for individual voltage measurement on each individual fuel cell and which satisfy the requirements for isolation and rate of response may, for example, include upstream isolating amplifiers for potential isolation in each measurement channel. In this case, the cell voltage signals which are tapped off can be processed further - 3a in order to form a switching-off signal by means of voltage comparators which are in each case provided, with the respective switching-off signal being produced when a fixed predetermined voltage limit value is undershot. Measurement devices such as these which allow the individual detection of electrode voltages of individual fuel cells within an extensive fuel cell arrangement are, however, particularly complex especially owing to the requirements for isolation and for a fast response speed, with the comparatively large number of measurement channels required also being a significant factor here.
A method and a device for monitoring the electric voltage of a fuel cell is known from EP-A-0 982 788, in which the fuel cell is connected with an optocoupler and a protective resistor connected in series and the functionality of the fuel cell is deduced from an output signal produced by the optocoupler. In this case, the optocoupler is selected such that, when an output voltage of the fuel cell is at the same level as a specified voltage limit value, this output voltage corresponds to a threshold voltage characteristic for the photoemitter of the optocoupler.
The invention is thus based on the object of specifying a method for operating a fuel cell or a fuel cell arrangement having a large number of fuel cells, which allows reliable monitoring of the fuel cell or of each fuel cell, or of a group of fuel cells, for functionality using simple means. A further aim is to specify a fuel cell arrangement which is particularly suitable for carrying out the method.
With regard to the method, this obj ect is achieved according to the invention in that, for the fuel cell or for each fuel cell, a component of the output current supplied from this fuel cell is A1lENDED PAGE
- 4a -passed via an optically active element, with the degree of functionality of the fuel cell being deduced from an output signal which is produced by the optically active element.
The invention is in this case based on the idea that a reliable method for monitoring the functionality of individual fuel cells should be based on the monitoring of the respectively supplied electrode voltage. For further processing with comparatively little effort, the voltage value should be converted at an early stage to a signal form which on the one hand makes it possible to keep the number of required components low and which on the other hand allows safe potential isolation or isolation of evaluation units from the actual fuel cell block AMENDED PAGE
- S
in a particularly simple and suitable manner. To this end, the invention provides for the electrode voltage, which is suitable for use as a parameter for monitoring the operation of the fuel cell, to be converted to an optical signal at a particularly early stage.
An optocoupler or a photodiode is expediently used as the active optical element. Components for both of these alternatives are particularly easily available, and the components can also be integrated in appropriate measurement circuits in a particularly simple manner. Furthermore, a digitized output signal which is characteristic of the functionality of the respective fuel cell can be produced in each case in these arrangements, thus allowing central evaluation, in an evaluation unit which is shared by all the fuel cells, in a particularly simple manner.
For reliable functional monitoring of fuel cells, which can be carried out using comparatively simple means even when a large number of fuel cells need to be monitored, it may be sufficient just to compare the respective electrode voltage with a limit value. One monitoring concept which can be implemented with particularly little complexity is thus in a particularly advantageous refinement based on monitoring for each individual fuel cell to determine whether the electrode voltage of this fuel cell is actually greater than or less than a voltage limit value which can be predetermined, without any evaluation of the absolute value of the respective electrode voltage.
In order to use a limit value such as this, a bias element that is associated with the optically active element is advantageously adjusted such that, when the fuel cell emits an output voltage or electrode voltage which is at the same level as the voltage limit value - 5a -which can be predetermined, the component of the output current which is supplied to the optically active element corresponds to a threshold current which is characteristic of it. In this case, .. CA 02422209 2003-03-12 the voltage and current values are set such that, when the electrode voltage is at least at the same level as the voltage limit value which can be predetermined, the current which is supplied to the active optical element is greater than its activation threshold, so that it produces an optical output signal in this case. If, on the other hand, the output voltage or electrode voltage which is supplied from the fuel cell is less than the voltage limit value which can be predetermined, the current which is supplied to the optically active element is thus also less than its activation limit so that, in this situation, no optical output signal is emitted. The functionality of the respective fuel cell is then identified by checking whether the associated optically active element is or is not producing an optical output signal.
When monitoring a number of fuel cells which are electrically connected in series, a defect is advantageously identified in the form of a logic "OR"
link, with a fault signal for the entire fuel cell arrangement or for an entire fuel cell stack being emitted on identifying a defect in one of the monitored fuel cells. This can be achieved in that each fuel cell in a fuel cell arrangement which comprises a number of series-connected fuel cells is advantageously respectively monitored for functionality by an optically active element which is associated with it.
Individual association with the actual fault source is in this case made possible by the photodiodes each additionally emitting an optically visible signal which can be observed by the operator.
With regard to a fuel cell arrangement having a number of fuel cells, the stated object is achieved in that the output electrodes of the or each fuel cell are each connected to one another via a side loop which is connected in parallel with a load circuit, and into each of which an optically active element is connected.
The side loop, which is connected in parallel with the load circuit and hence also in parallel with the other fuel cells that are connected in series with the respectively monitored fuel cell, in this case makes it possible to tap off a component of the output current that is supplied from the fuel cell, and this can be used to feed the optically active element which is connected in the side loop.
Depending on the characteristic parameters of the components that are used in this case, there is in this case a unique functional relationship between the current which is supplied to the optically active element and the output or electrode voltage which is supplied from the respectively monitored fuel cell.
Monitoring of the current which is supplied to the optically active element thus makes it possible to draw conclusions about the output or electrode voltage that is supplied by the fuel cell.
The current which is supplied to the optically active element can also be converted in the optically active element to an optical output signal in a unique manner.
This output signal is thus likewise correlated in a unique manner with the output or electrode voltage which is supplied by the fuel cell, so that, by monitoring the optical output signal, it is also possible to monitor the output or electrode voltage of the fuel cell, and hence to monitor the functionality of the fuel cell.
The optically active element which is associated with each of the fuel cells is in this case expediently in the form of an optocoupler or photodiode. In a further advantageous refinement, the output side of the photodiode is connected via an optical system to an associated optical sensor, in particular to a photo transistor. In these arrangements, a digital signal or a signal which can be digitized is thus emitted as a - 7a -function of the output signal which is supplied from the optically active element, with reliable isolation and potential decoupling _ g _ from the fuel cell or fuel cell arrangement to be monitored at the same time being ensured in a particularly simple manner.
The current/voltage character of the photodiode is advantageously designed such that, when the fuel cell emits an output voltage or electrode voltage which is at the same level as the voltage limit value which can be predetermined, the component of the output current which is supplied to the photodiode corresponds to a threshold current which is characteristic for it. In an alternative advantageous refinement, a bias element is connected in series with the or each optically active element in the respective side loop. This bias element is in this case advantageously dimensioned or designed such that, when the fuel cell is emitting an output or electrode voltage which is at the same level as a voltage limit value which can be predetermined, the component of the output current which flows through the side loop is set such that it just reaches a threshold current which is characteristic for that optical element.
These two alternatives thus ensure that the optically active element emits an output signal only when the output or electrode voltage of the respective fuel cell reaches or exceeds the voltage limit value. When the output or electrode voltage of the fuel cell is less than the voltage limit value, on the other hand, the optically active element does not emit any output signal. A downstream evaluation unit can thus use the presence of an output signal being emitted from the respective optically active element to directly deduce the functionality of the associated fuel cell.
The bias element may in this case in particular be in the form of a bias resistor. At relatively high output voltages, for example when monitoring a group _ CA 02422209 2003-03-12 . ~ _ g _ of interconnected fuel cells altogether, a zener diode can also be provided as the bias element.
In a further advantageous refinement, each optically active element has an associated transformation unit for converting an output signal to an electrical diagnosis signal, in which case the diagnosis signals can be supplied to a common evaluation unit. Thus, if necessary, individual monitoring which is directed at individual fuel cells or global monitoring which is directed at the fuel cell arrangement overall or at groups of fuel cells can be carried out in the common evaluation unit.
The advantages which can be achieved by the invention are, in particular, that supplying a component of the output current that is supplied from the respective fuel cell to an optically active element makes it possible to produce a particularly advantageous signal form, which is characteristic of the functionality of the respectively monitored fuel cell. The capability to produce an optical signal, which is characteristic of the output or electrode voltage of the fuel cell, in the immediate physical vicinity of the fuel cell makes it possible firstly to keep the number of components which are arranged in the immediate vicinity of the fuel cell and are thus subject to the particular thermal loads caused by it low while, on the other hand, this allows potential isolation of the fuel cell arrangement, per se, in a particularly simple manner.
Those components, in particular the optocoupler or photodiode, which are provided in the immediate physical vicinity of the respective fuel cell are also comparatively small, thus making it possible to mount them in a particularly simple manner directly adjacent to the location of the fuel cell. The potential isolation of a downstream evaluation unit from the fuel cell arrangement to be monitored also allows isolation voltages up to any desired level to be achieved, in _ 9a _ particular by the use of optical waveguides in conjunction with a photodiode.
An exemplary embodiment of the invention will be explained in more detail with reference to a drawing, in which:
Figure 1 shows, schematically, a fuel cell arrangement having a number of fuel cells and having a monitoring system, and Figure 2 shows an alternative embodiment of a fuel cell arrangement.
Identical parts are provided with the same reference symbols in the two figures.
The fuel cell arrangement 1 shown in Figure 1 is in the form of a direct-current source for producing electrical power. The fuel cell arrangement 1 has a number of fuel cells 2 which are electrically connected in series, of which only three are shown, illustrated in a schematic form, in the exemplary embodiment.
However, the fuel cell arrangement 1 may also have any desired number of fuel cells other than 2 although, in this specific case, the total number of fuel cells provided is two on the basis of the overall required voltage, which is governed by the purpose or the load, and the output or electrode voltage which can be supplied by an individual fuel cell 2. The overall output voltage which can be supplied from the fuel cell arrangement 1 by connecting the fuel cells 2 in series is given by the sum of the output voltages of the individual fuel cells 2, so that it is possible to ensure by suitable choice of the number of fuel cells 2 that the fuel cell arrangement 1 can supply any required nominal voltage as the output voltage. The fuel cell arrangement 1 and hence also the series-connected fuel cells 2 are connected via a load circuit 4, which is indicated in Figure l, to a load that is not illustrated in any more detail, for example to a direct-current load.
In addition to the fuel cells 2, the fuel cell arrangement 1 has a monitoring system 10, which makes it possible to check the functionality of each of the fuel cells 2 continuously or cyclically. For each fuel cell 2, the monitoring system 10 has an optically active element 12 which is associated with this fuel cell 2 and is in the form of an optocoupler in the exemplary embodiment 1 shown in Figure 1. On the input side, each optically active element 12 is connected via lines 14, 16 to the electrodes 18, 20 of the respectively associated fuel cell 2. The lines 14, 16 thus form a side loop 22, in which the respective optically active element 12 is connected. The side loop 22 is connected electrically in parallel with the load circuit 4 and with the respective other further fuel cells 2, which are connected in series with that particular fuel cell 2. Furthermore, a bias element 24, specifically a bias resistor in the exemplary embodiment, is electrically connected in series with the optically active element 12 within each side loop 22.
On the output side, the optically active elements 12, which are in the form of optocouplers in the exemplary embodiment shown in Figure 1, are connected to an evaluation unit 26. In this case, the evaluation unit 26 is designed in particular for processing and digitization of the signals which are supplied from the optically active elements 12. Further processing of these signals is thus in the exemplary embodiment carried out in digitized form, so that a unique association between a signal to be evaluated and the originally monitored fuel cell 2 can be produced even when using a comparatively small number of lines or a bus system. In order to produce a fault signal S, the evaluation unit 26 is also designed in the form of a logic "OR" link such that a fault signal S for the entire fuel cell arrangement 1 is produced for any - lla fault that is identified for an individual fuel cell 2.
A fault signal S which is produced by the evaluation unit 26 leads, in the manner of a protective disconnection and in a manner which is not i~TO 02/23658 PCT/DE01/03367 illustrated in any more detail, to the fuel supply to the respectively affected fuel cell 2 or, if necessary, to the entire fuel cell arrangement 1 being turned off.
The fuel cell arrangement 1 and, in particular, the monitoring system 10 are designed for particularly simple monitoring of the functionality of the fuel cells 2. This is because each fuel cell 2 produces an output or electrode voltage U during operation of the fuel cell arrangement 1. This electrode voltage U
results in the respective fuel cell 2 supplying an output current I, which is subdivided into a first component I1 that is fed to the load circuit 4 and a second component I2 that is fed to the associated side loop 22. The subdivision ratio of the components I1 and I2 is in this case governed by the distribution of the resistance in the load circuit 4 and in the side loop 22. If the resistance ratio between the load circuit 4 and the side loop 22 is known, it is thus also possible to use the component I2 which is fed to the side loop 22 to draw conclusions about the electrode voltage U of the respective fuel cell 2.
The aim is to compare the electrode voltage U which is supplied from a fuel cell 2 with a voltage limit value UG as a criterion for determining whether that fuel cell is functional: if the electrode voltage U of a fuel cell 2 is greater than the voltage limit value UG, the deduction is made that the fuel cell 2 is functional. If, on the other hand, the electrode voltage U of the fuel cell 2 is less than the voltage limit value UG, the deduction is made that the fuel cell 2 is faulty, and the fuel supply to this fuel cell 2 is turned off immediately.
In order to determine whether a fuel cell 2 is producing an electrode voltage U of more than the voltage limit value UG and can thus be regarded as - 12a being functional, the fuel cell arrangement 1 is designed such that the optical element 12 which is associated with a fuel cell 2 produces _ 13 _ an output signal A which can be passed to the evaluation unit 26 when the electrode voltage U of the corresponding fuel cell 2 exceeds the voltage limit value UG. However, the optically active element 12 does not produce any output signal A when the electrode voltage U of the fuel cell 2 is less than the voltage limit value UG.
For this purpose, the active optical element 12, which is in the form of an optocoupler, and the bias element 24, which is connected in series with it in the respective side loop 22, are dimensioned such that -also with respect to the resistance ratios in the load circuit 4 - in the situation in which the associated fuel cell 2 is producing an output or electrode voltage U at the same level as the voltage limit value UG, the component I2 of the output current I from the fuel cell 2 in the side loop 22 is at precisely the same level as the characteristic threshold current of the optically active element 12. The characteristic threshold current is in this case defined by the optically active element 12 producing an optical output signal A in response to current levels that are greater than this threshold current, but not producing any such optical output signal A when the currents are less than this threshold current.
In the fuel cell arrangement 1, this therefore ensures that, in the situation where all the optically active elements 12 are producing an output signal A, it can be assumed that all the fuel cells 2 are operating without any faults. However, if the output signal A for at least one of the optically active elements 12 is missing, then it can be assumed that there is a defect in the associated fuel cell 2. In this case, the fuel supply to the affected fuel cell 2 is turned off, and a fault signal S is produced for the entire fuel cell arrangement 1.
' WO 02/23658 PCT/DE01/03367 - 13a -' The fuel cell arrangement 1' as shown in Figure 2 has a photodiode as the optically active element 12, which is connected in the respectively associated side loop 22 for a fuel cell 2. On the output side, each of the photodiodes is ' H10 02/23658 PCT/DE01/03367 connected via an optical waveguide 30, in particular via a glass fiber cable, to an associated light-sensitive component, namely to a photo transistor 32.
The photo transistors 32 are in this case connected such that an appropriate output signal A is produced, and is passed to the evaluation unit 26, when an optical signal O arrives via the optical waveguide 30.
The photodiodes that are provided as the optically active element 12 in the exemplary embodiment shown in Figure 2 and the bias element 24 that is associated with them are also designed, particularly with respect to the load circuit 4, such that, when the electrode voltage U of the fuel cells 2 reaches or exceeds the voltage limit value UG, a component I2 of the output current from the fuel cell 2 is produced in the side loop 22 that is above a characteristic threshold current for the respective photodiode. This therefore ensures in this embodiment as well that the photodiodes which are provided as the optically active element 12 each produce an optical output signal A, and emit it via the respective optical waveguide 30, only when the electrode voltage U of the respective fuel cell 2 is sufficiently high, and the fuel cell 2 is thus functional.
The fuel cell arrangement 1' shown in Figure 2 can furthermore be used in a particularly flexible manner especially as a result of the use of the optical waveguides 30, in particular also allowing comparatively high isolation voltages, that is to say a comparatively high level of electrical decoupling between the evaluation unit 26 and the actual fuel cells 20.
In one alternative embodiment, the fuel cell arrangement 1' as shown in Figure 2 can also be designed without the bias elements 24 in the side loops 22. In this situation, which may be - 14a significant depending in particular on the characteristic operating parameters for the fuel cells 2 and/or for the load that is connected in the load circuit 4, the photodiodes are chosen, per se, such that their current/voltage characteristic is matched in the intended manner to the voltage limit value UG which can be predetermined: the photodiodes are in this case chosen or designed such that the component I2 of the output current I from the respective fuel cell 2 which is fed into the side loop 22 when the electrode voltage U is at the same level as the voltage limit value UG
corresponds to a characteristic threshold current for the respective photodiode.
In all the situations mentioned, the invention ensures that, in a situation where an optically active element 12 is producing an output signal A, it can be deduced from this that the associated fuel cell 2 is producing an electrode voltage U of more than the intended voltage limit value UG, and is thus functional.
Continuous or cyclic functional monitoring, depending on the requirement, of each individual fuel cell 2 is thus possible in a particularly simple manner, in which case the lack of an output signal A can be used to deduce that a fault has occurred in the associated fuel cell 2. This monitoring concept also promotes a particularly high degree of fail-safety since the functionality of the fuel cells 2 is provided by active components, namely the optically active elements 12:
functionality of the associated fuel cell 2 can thus be assumed with a particularly high degree of confidence when an output signal A is present, irrespective of the operating state or the availability of the auxiliary components.
Fuel cells may be used to generate electricity in an environmentally friendly manner. This is because a process which essentially represents reversal of electrolysis is carried out in a fuel cell. A fuel which includes hydrogen is supplied to an anode, and an auxiliary substance which includes oxygen is supplied to a cathode in a fuel cell. The anode and cathode are in this case electrically isolated from one another via an electrolyte layer, in which case, although the electrolyte layer allows ions to be exchanged between the fuel and the oxygen, it otherwise ensures gastight separation of the fuel and auxiliary substance, however. Owing to the exchange of ions, hydrogen which is contained in the fuel can react with the oxygen to form water, with electrons being enriched at the fuel-side electrode or anode, and electrons being absorbed at the electrode on the auxiliary substance side, or cathode. A potential difference or voltage is thus formed between the anode and cathode during operation of the fuel cell. The electrolyte layer, which may be in the form of a ceramic solid electrolyte in the case of a high-temperature fuel cell or may be in the form of a polymer membrane in the case of a low-temperature fuel cell, thus has the function of separating the reactants from one another, of transferring the charge in the form of ions, and of preventing an electron short circuit.
_ 2 _ On the basis of the electrochemical potentials of the substances which are normally used, an electrode voltage of about 0.6 to 1.0 V can be formed in normal operating conditions in a fuel cell such as this, and can be maintained during operation. For technical applications in which a significantly higher total voltage may be required depending on the purpose or the planned load, a number of fuel cells are thus normally connected electrically in series in the form of a fuel cell stack, in such a way that the sum of the electrode voltages supplied from each of the fuel cells corresponds to the required total voltage, or is greater than it. Depending on the required total voltage, the number of fuel cells in a fuel cell stack such as this may, for example, be 50 or more.
When using such a fuel cell stack in a fuel cell arrangement, it may be important to monitor the functionality of each individual fuel cell continuously or cyclically. This is because, by way of example, a defect in the form of a hole can occur in the electrolyte layer in a fuel cell as a result of aging or other influences, so that the hydrogen contained in the fuel cell could come into direct contact with the oxygen. In the process, it would be possible for catalytic combustion of hydrogen to occur, associated with the release of energy, which could become wider if the gas supply to the fuel cell were to be maintained, further enlarging the affected area of damage. For safe and reliable operation of such a fuel cell stack, means can thus be provided which interrupt the gas supply to the relevant fuel cell within a very short reaction time when malfunctions occur and, in particular, when gas breaks through the electrolyte layer, in order in this way to safely avoid propagation of the damage.
i~10 02/23658 PCT/DE01/03367 _ 3 _ The electrode voltage produced by the respective fuel cell can be used as a suitable monitoring parameter for detecting such a defect or gas breakthrough. This is because a gas breakthrough in a fuel cell is evident, inter alia, from a characteristic reduction in the electrode voltage. A characteristic limit voltage value can therefore be specified for a fuel cell, for example as a function of its design, with the other operating parameters being known. If the electrode voltage falls below this limit voltage value, it is assumed that a defect of the type mentioned above has occurred, and the gas supply to the relevant fuel cell is interrupted.
However, the monitoring of the individual electrode voltages in a fuel cell arrangement having a large number of fuel cells is actually comparatively complex.
On the one hand, in this case, it would be possible to monitor only the total voltage of the fuel cell arrangement or of a fuel cell stack although it would not be possible to use a drop in the overall voltage to identify the individually affected fuel cell, and thus the cause of the fault. On the other hand, an individual voltage measurement on each individual fuel cell or on suitably combined fuel cell groups within a fuel cell stack is made more difficult by the comparatively high electrical potential of the fuel cells overall. This can assume values up to the kilovolt range, for example, depending on the total number of series-connected fuel cells.
Measurement systems which are intended for individual voltage measurement on each individual fuel cell and which satisfy the requirements for isolation and rate of response may, for example, include upstream isolating amplifiers for potential isolation in each measurement channel. In this case, the cell voltage signals which are tapped off can be processed further - 3a in order to form a switching-off signal by means of voltage comparators which are in each case provided, with the respective switching-off signal being produced when a fixed predetermined voltage limit value is undershot. Measurement devices such as these which allow the individual detection of electrode voltages of individual fuel cells within an extensive fuel cell arrangement are, however, particularly complex especially owing to the requirements for isolation and for a fast response speed, with the comparatively large number of measurement channels required also being a significant factor here.
A method and a device for monitoring the electric voltage of a fuel cell is known from EP-A-0 982 788, in which the fuel cell is connected with an optocoupler and a protective resistor connected in series and the functionality of the fuel cell is deduced from an output signal produced by the optocoupler. In this case, the optocoupler is selected such that, when an output voltage of the fuel cell is at the same level as a specified voltage limit value, this output voltage corresponds to a threshold voltage characteristic for the photoemitter of the optocoupler.
The invention is thus based on the object of specifying a method for operating a fuel cell or a fuel cell arrangement having a large number of fuel cells, which allows reliable monitoring of the fuel cell or of each fuel cell, or of a group of fuel cells, for functionality using simple means. A further aim is to specify a fuel cell arrangement which is particularly suitable for carrying out the method.
With regard to the method, this obj ect is achieved according to the invention in that, for the fuel cell or for each fuel cell, a component of the output current supplied from this fuel cell is A1lENDED PAGE
- 4a -passed via an optically active element, with the degree of functionality of the fuel cell being deduced from an output signal which is produced by the optically active element.
The invention is in this case based on the idea that a reliable method for monitoring the functionality of individual fuel cells should be based on the monitoring of the respectively supplied electrode voltage. For further processing with comparatively little effort, the voltage value should be converted at an early stage to a signal form which on the one hand makes it possible to keep the number of required components low and which on the other hand allows safe potential isolation or isolation of evaluation units from the actual fuel cell block AMENDED PAGE
- S
in a particularly simple and suitable manner. To this end, the invention provides for the electrode voltage, which is suitable for use as a parameter for monitoring the operation of the fuel cell, to be converted to an optical signal at a particularly early stage.
An optocoupler or a photodiode is expediently used as the active optical element. Components for both of these alternatives are particularly easily available, and the components can also be integrated in appropriate measurement circuits in a particularly simple manner. Furthermore, a digitized output signal which is characteristic of the functionality of the respective fuel cell can be produced in each case in these arrangements, thus allowing central evaluation, in an evaluation unit which is shared by all the fuel cells, in a particularly simple manner.
For reliable functional monitoring of fuel cells, which can be carried out using comparatively simple means even when a large number of fuel cells need to be monitored, it may be sufficient just to compare the respective electrode voltage with a limit value. One monitoring concept which can be implemented with particularly little complexity is thus in a particularly advantageous refinement based on monitoring for each individual fuel cell to determine whether the electrode voltage of this fuel cell is actually greater than or less than a voltage limit value which can be predetermined, without any evaluation of the absolute value of the respective electrode voltage.
In order to use a limit value such as this, a bias element that is associated with the optically active element is advantageously adjusted such that, when the fuel cell emits an output voltage or electrode voltage which is at the same level as the voltage limit value - 5a -which can be predetermined, the component of the output current which is supplied to the optically active element corresponds to a threshold current which is characteristic of it. In this case, .. CA 02422209 2003-03-12 the voltage and current values are set such that, when the electrode voltage is at least at the same level as the voltage limit value which can be predetermined, the current which is supplied to the active optical element is greater than its activation threshold, so that it produces an optical output signal in this case. If, on the other hand, the output voltage or electrode voltage which is supplied from the fuel cell is less than the voltage limit value which can be predetermined, the current which is supplied to the optically active element is thus also less than its activation limit so that, in this situation, no optical output signal is emitted. The functionality of the respective fuel cell is then identified by checking whether the associated optically active element is or is not producing an optical output signal.
When monitoring a number of fuel cells which are electrically connected in series, a defect is advantageously identified in the form of a logic "OR"
link, with a fault signal for the entire fuel cell arrangement or for an entire fuel cell stack being emitted on identifying a defect in one of the monitored fuel cells. This can be achieved in that each fuel cell in a fuel cell arrangement which comprises a number of series-connected fuel cells is advantageously respectively monitored for functionality by an optically active element which is associated with it.
Individual association with the actual fault source is in this case made possible by the photodiodes each additionally emitting an optically visible signal which can be observed by the operator.
With regard to a fuel cell arrangement having a number of fuel cells, the stated object is achieved in that the output electrodes of the or each fuel cell are each connected to one another via a side loop which is connected in parallel with a load circuit, and into each of which an optically active element is connected.
The side loop, which is connected in parallel with the load circuit and hence also in parallel with the other fuel cells that are connected in series with the respectively monitored fuel cell, in this case makes it possible to tap off a component of the output current that is supplied from the fuel cell, and this can be used to feed the optically active element which is connected in the side loop.
Depending on the characteristic parameters of the components that are used in this case, there is in this case a unique functional relationship between the current which is supplied to the optically active element and the output or electrode voltage which is supplied from the respectively monitored fuel cell.
Monitoring of the current which is supplied to the optically active element thus makes it possible to draw conclusions about the output or electrode voltage that is supplied by the fuel cell.
The current which is supplied to the optically active element can also be converted in the optically active element to an optical output signal in a unique manner.
This output signal is thus likewise correlated in a unique manner with the output or electrode voltage which is supplied by the fuel cell, so that, by monitoring the optical output signal, it is also possible to monitor the output or electrode voltage of the fuel cell, and hence to monitor the functionality of the fuel cell.
The optically active element which is associated with each of the fuel cells is in this case expediently in the form of an optocoupler or photodiode. In a further advantageous refinement, the output side of the photodiode is connected via an optical system to an associated optical sensor, in particular to a photo transistor. In these arrangements, a digital signal or a signal which can be digitized is thus emitted as a - 7a -function of the output signal which is supplied from the optically active element, with reliable isolation and potential decoupling _ g _ from the fuel cell or fuel cell arrangement to be monitored at the same time being ensured in a particularly simple manner.
The current/voltage character of the photodiode is advantageously designed such that, when the fuel cell emits an output voltage or electrode voltage which is at the same level as the voltage limit value which can be predetermined, the component of the output current which is supplied to the photodiode corresponds to a threshold current which is characteristic for it. In an alternative advantageous refinement, a bias element is connected in series with the or each optically active element in the respective side loop. This bias element is in this case advantageously dimensioned or designed such that, when the fuel cell is emitting an output or electrode voltage which is at the same level as a voltage limit value which can be predetermined, the component of the output current which flows through the side loop is set such that it just reaches a threshold current which is characteristic for that optical element.
These two alternatives thus ensure that the optically active element emits an output signal only when the output or electrode voltage of the respective fuel cell reaches or exceeds the voltage limit value. When the output or electrode voltage of the fuel cell is less than the voltage limit value, on the other hand, the optically active element does not emit any output signal. A downstream evaluation unit can thus use the presence of an output signal being emitted from the respective optically active element to directly deduce the functionality of the associated fuel cell.
The bias element may in this case in particular be in the form of a bias resistor. At relatively high output voltages, for example when monitoring a group _ CA 02422209 2003-03-12 . ~ _ g _ of interconnected fuel cells altogether, a zener diode can also be provided as the bias element.
In a further advantageous refinement, each optically active element has an associated transformation unit for converting an output signal to an electrical diagnosis signal, in which case the diagnosis signals can be supplied to a common evaluation unit. Thus, if necessary, individual monitoring which is directed at individual fuel cells or global monitoring which is directed at the fuel cell arrangement overall or at groups of fuel cells can be carried out in the common evaluation unit.
The advantages which can be achieved by the invention are, in particular, that supplying a component of the output current that is supplied from the respective fuel cell to an optically active element makes it possible to produce a particularly advantageous signal form, which is characteristic of the functionality of the respectively monitored fuel cell. The capability to produce an optical signal, which is characteristic of the output or electrode voltage of the fuel cell, in the immediate physical vicinity of the fuel cell makes it possible firstly to keep the number of components which are arranged in the immediate vicinity of the fuel cell and are thus subject to the particular thermal loads caused by it low while, on the other hand, this allows potential isolation of the fuel cell arrangement, per se, in a particularly simple manner.
Those components, in particular the optocoupler or photodiode, which are provided in the immediate physical vicinity of the respective fuel cell are also comparatively small, thus making it possible to mount them in a particularly simple manner directly adjacent to the location of the fuel cell. The potential isolation of a downstream evaluation unit from the fuel cell arrangement to be monitored also allows isolation voltages up to any desired level to be achieved, in _ 9a _ particular by the use of optical waveguides in conjunction with a photodiode.
An exemplary embodiment of the invention will be explained in more detail with reference to a drawing, in which:
Figure 1 shows, schematically, a fuel cell arrangement having a number of fuel cells and having a monitoring system, and Figure 2 shows an alternative embodiment of a fuel cell arrangement.
Identical parts are provided with the same reference symbols in the two figures.
The fuel cell arrangement 1 shown in Figure 1 is in the form of a direct-current source for producing electrical power. The fuel cell arrangement 1 has a number of fuel cells 2 which are electrically connected in series, of which only three are shown, illustrated in a schematic form, in the exemplary embodiment.
However, the fuel cell arrangement 1 may also have any desired number of fuel cells other than 2 although, in this specific case, the total number of fuel cells provided is two on the basis of the overall required voltage, which is governed by the purpose or the load, and the output or electrode voltage which can be supplied by an individual fuel cell 2. The overall output voltage which can be supplied from the fuel cell arrangement 1 by connecting the fuel cells 2 in series is given by the sum of the output voltages of the individual fuel cells 2, so that it is possible to ensure by suitable choice of the number of fuel cells 2 that the fuel cell arrangement 1 can supply any required nominal voltage as the output voltage. The fuel cell arrangement 1 and hence also the series-connected fuel cells 2 are connected via a load circuit 4, which is indicated in Figure l, to a load that is not illustrated in any more detail, for example to a direct-current load.
In addition to the fuel cells 2, the fuel cell arrangement 1 has a monitoring system 10, which makes it possible to check the functionality of each of the fuel cells 2 continuously or cyclically. For each fuel cell 2, the monitoring system 10 has an optically active element 12 which is associated with this fuel cell 2 and is in the form of an optocoupler in the exemplary embodiment 1 shown in Figure 1. On the input side, each optically active element 12 is connected via lines 14, 16 to the electrodes 18, 20 of the respectively associated fuel cell 2. The lines 14, 16 thus form a side loop 22, in which the respective optically active element 12 is connected. The side loop 22 is connected electrically in parallel with the load circuit 4 and with the respective other further fuel cells 2, which are connected in series with that particular fuel cell 2. Furthermore, a bias element 24, specifically a bias resistor in the exemplary embodiment, is electrically connected in series with the optically active element 12 within each side loop 22.
On the output side, the optically active elements 12, which are in the form of optocouplers in the exemplary embodiment shown in Figure 1, are connected to an evaluation unit 26. In this case, the evaluation unit 26 is designed in particular for processing and digitization of the signals which are supplied from the optically active elements 12. Further processing of these signals is thus in the exemplary embodiment carried out in digitized form, so that a unique association between a signal to be evaluated and the originally monitored fuel cell 2 can be produced even when using a comparatively small number of lines or a bus system. In order to produce a fault signal S, the evaluation unit 26 is also designed in the form of a logic "OR" link such that a fault signal S for the entire fuel cell arrangement 1 is produced for any - lla fault that is identified for an individual fuel cell 2.
A fault signal S which is produced by the evaluation unit 26 leads, in the manner of a protective disconnection and in a manner which is not i~TO 02/23658 PCT/DE01/03367 illustrated in any more detail, to the fuel supply to the respectively affected fuel cell 2 or, if necessary, to the entire fuel cell arrangement 1 being turned off.
The fuel cell arrangement 1 and, in particular, the monitoring system 10 are designed for particularly simple monitoring of the functionality of the fuel cells 2. This is because each fuel cell 2 produces an output or electrode voltage U during operation of the fuel cell arrangement 1. This electrode voltage U
results in the respective fuel cell 2 supplying an output current I, which is subdivided into a first component I1 that is fed to the load circuit 4 and a second component I2 that is fed to the associated side loop 22. The subdivision ratio of the components I1 and I2 is in this case governed by the distribution of the resistance in the load circuit 4 and in the side loop 22. If the resistance ratio between the load circuit 4 and the side loop 22 is known, it is thus also possible to use the component I2 which is fed to the side loop 22 to draw conclusions about the electrode voltage U of the respective fuel cell 2.
The aim is to compare the electrode voltage U which is supplied from a fuel cell 2 with a voltage limit value UG as a criterion for determining whether that fuel cell is functional: if the electrode voltage U of a fuel cell 2 is greater than the voltage limit value UG, the deduction is made that the fuel cell 2 is functional. If, on the other hand, the electrode voltage U of the fuel cell 2 is less than the voltage limit value UG, the deduction is made that the fuel cell 2 is faulty, and the fuel supply to this fuel cell 2 is turned off immediately.
In order to determine whether a fuel cell 2 is producing an electrode voltage U of more than the voltage limit value UG and can thus be regarded as - 12a being functional, the fuel cell arrangement 1 is designed such that the optical element 12 which is associated with a fuel cell 2 produces _ 13 _ an output signal A which can be passed to the evaluation unit 26 when the electrode voltage U of the corresponding fuel cell 2 exceeds the voltage limit value UG. However, the optically active element 12 does not produce any output signal A when the electrode voltage U of the fuel cell 2 is less than the voltage limit value UG.
For this purpose, the active optical element 12, which is in the form of an optocoupler, and the bias element 24, which is connected in series with it in the respective side loop 22, are dimensioned such that -also with respect to the resistance ratios in the load circuit 4 - in the situation in which the associated fuel cell 2 is producing an output or electrode voltage U at the same level as the voltage limit value UG, the component I2 of the output current I from the fuel cell 2 in the side loop 22 is at precisely the same level as the characteristic threshold current of the optically active element 12. The characteristic threshold current is in this case defined by the optically active element 12 producing an optical output signal A in response to current levels that are greater than this threshold current, but not producing any such optical output signal A when the currents are less than this threshold current.
In the fuel cell arrangement 1, this therefore ensures that, in the situation where all the optically active elements 12 are producing an output signal A, it can be assumed that all the fuel cells 2 are operating without any faults. However, if the output signal A for at least one of the optically active elements 12 is missing, then it can be assumed that there is a defect in the associated fuel cell 2. In this case, the fuel supply to the affected fuel cell 2 is turned off, and a fault signal S is produced for the entire fuel cell arrangement 1.
' WO 02/23658 PCT/DE01/03367 - 13a -' The fuel cell arrangement 1' as shown in Figure 2 has a photodiode as the optically active element 12, which is connected in the respectively associated side loop 22 for a fuel cell 2. On the output side, each of the photodiodes is ' H10 02/23658 PCT/DE01/03367 connected via an optical waveguide 30, in particular via a glass fiber cable, to an associated light-sensitive component, namely to a photo transistor 32.
The photo transistors 32 are in this case connected such that an appropriate output signal A is produced, and is passed to the evaluation unit 26, when an optical signal O arrives via the optical waveguide 30.
The photodiodes that are provided as the optically active element 12 in the exemplary embodiment shown in Figure 2 and the bias element 24 that is associated with them are also designed, particularly with respect to the load circuit 4, such that, when the electrode voltage U of the fuel cells 2 reaches or exceeds the voltage limit value UG, a component I2 of the output current from the fuel cell 2 is produced in the side loop 22 that is above a characteristic threshold current for the respective photodiode. This therefore ensures in this embodiment as well that the photodiodes which are provided as the optically active element 12 each produce an optical output signal A, and emit it via the respective optical waveguide 30, only when the electrode voltage U of the respective fuel cell 2 is sufficiently high, and the fuel cell 2 is thus functional.
The fuel cell arrangement 1' shown in Figure 2 can furthermore be used in a particularly flexible manner especially as a result of the use of the optical waveguides 30, in particular also allowing comparatively high isolation voltages, that is to say a comparatively high level of electrical decoupling between the evaluation unit 26 and the actual fuel cells 20.
In one alternative embodiment, the fuel cell arrangement 1' as shown in Figure 2 can also be designed without the bias elements 24 in the side loops 22. In this situation, which may be - 14a significant depending in particular on the characteristic operating parameters for the fuel cells 2 and/or for the load that is connected in the load circuit 4, the photodiodes are chosen, per se, such that their current/voltage characteristic is matched in the intended manner to the voltage limit value UG which can be predetermined: the photodiodes are in this case chosen or designed such that the component I2 of the output current I from the respective fuel cell 2 which is fed into the side loop 22 when the electrode voltage U is at the same level as the voltage limit value UG
corresponds to a characteristic threshold current for the respective photodiode.
In all the situations mentioned, the invention ensures that, in a situation where an optically active element 12 is producing an output signal A, it can be deduced from this that the associated fuel cell 2 is producing an electrode voltage U of more than the intended voltage limit value UG, and is thus functional.
Continuous or cyclic functional monitoring, depending on the requirement, of each individual fuel cell 2 is thus possible in a particularly simple manner, in which case the lack of an output signal A can be used to deduce that a fault has occurred in the associated fuel cell 2. This monitoring concept also promotes a particularly high degree of fail-safety since the functionality of the fuel cells 2 is provided by active components, namely the optically active elements 12:
functionality of the associated fuel cell 2 can thus be assumed with a particularly high degree of confidence when an output signal A is present, irrespective of the operating state or the availability of the auxiliary components.
Claims (11)
1. A method for operating a fuel cell (2), in which a component (12) of the output current (I) which is supplied from the fuel cell (2) is passed via an optically active element (12), with the degree of functionality of the fuel cell (2) being deduced from an output signal (A) which is produced by the optically active element (12), in which a bias element (24), which is associated with the optically active element (12), is adjusted such that, when an output voltage (U) of the fuel cell (2) is emitted which is at the same level as a voltage limit value (UG) which can be predetermined, the component (12) of the output current (I) which is supplied to the optically active element (12) corresponds to a threshold current which is characteristic of it.
2. The method as claimed in claim 1, in which an optocoupler is used as the optically active element (12).
3. The method as claimed in claim 1, in which a photodiode whose output signal (A) is supplied to an optical sensor, in particular to a photo transister (32), is used as the optically active element (12).
4. The method as claimed in one of claims 1 to 3, in which each fuel cell (2) in a fuel cell arrangement (1) which comprises a number of series-connected fuel cells (2) is respectively monitored for functionality by an optically active element (12) which is associated with it.
5. A fuel cell arrangement (1) having a number of fuel cells (2), whose output electrodes are each connected to one another via a side loop (22) which is connected in parallel with a load circuit (4), and into each of which an optically active element (12) and a bias element (24) is connected, in which the bias element (24) is designed in such a way that, when the fuel cell (2) emits an output voltage (U) which is at the same level as a voltage limit value (UG) which can be predetermined, the component (12) of the output current (I) which is supplied to the optically active element (12) corresponds to a threshold current which is characteristic of it.
6. The fuel cell arrangement (1) as claimed in claim 5, in which the optically active element (12) which is associated with each of the fuel cells (2) is in the form of an optocoupler.
7. The fuel cell arrangement (1) as claimed in claim 5 or 6, in which each active optical element (12) has an associated transformation unit for converting its output signal to an electrical diagnosis signal, in which case the diagnosis signals can be supplied to a common evluation unit (26).
8. A fuel cell arrangement (1) having a number of fuel cells (2), whose output electrodes are each connected to one another via a side loop (22) which is connected in parallel with a load circuit (4), and into each of which a photodiode (12) is connected, in which the current/voltage characteristic of the photodiode is designed such that, when the fuel cell (2) emits an output voltage (U) which is at the same level as a voltage limit value (UG) which can be predetermined, the component (12) of the output current (1) which is supplied to the photodiode (12) corresponds to a threshold current which is characteristic for it.
9. The fuel cell arrangement (1) as claimed in claim 8, in which each photodiode is connected on the output side via an optical system, in particular via an optical waveguide, to an associated optical sensor, in particular to a phototransistor (32).
10. The fuel cell arrangement (1) as claimed in claim 8 or 9, in which a bias element (24) is connected in series with each photodiode (12) in the respective side loop (22).
11. The fuel cell arrangement (1) as claimed in one of the claims 8 to 10, in which a transformation unit is allocated to each photodiode (12) for converting its output signal to an electrical diagnosis signal, in which case the diagnosis signals can be supplied to a common evaluation unit (26).
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE10045435.6 | 2000-09-14 | ||
| DE10045435 | 2000-09-14 | ||
| PCT/DE2001/003367 WO2002023658A1 (en) | 2000-09-14 | 2001-09-03 | Method for operating a fuel cell and a fuel cell arrangement |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2422209A1 true CA2422209A1 (en) | 2003-03-12 |
Family
ID=7656161
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002422209A Abandoned CA2422209A1 (en) | 2000-09-14 | 2001-09-03 | Method for operating a fuel cell and a fuel cell arrangement |
Country Status (5)
| Country | Link |
|---|---|
| EP (1) | EP1323204B1 (en) |
| JP (1) | JP2004512633A (en) |
| CA (1) | CA2422209A1 (en) |
| DE (1) | DE50102290D1 (en) |
| WO (1) | WO2002023658A1 (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6953630B2 (en) * | 2001-07-25 | 2005-10-11 | Ballard Power Systems Inc. | Fuel cell anomaly detection method and apparatus |
| DE102006008254A1 (en) * | 2006-02-22 | 2007-08-30 | Siemens Ag | Gas leakage detection method in fuel cell arrangement, involves supplying air to fuel cell arrangement and oxygen fraction in discharge gas is determined and gas leakage is closed on basis of oxygen fraction |
| US7687174B2 (en) * | 2006-04-04 | 2010-03-30 | Gm Global Technology Operations, Inc. | Optical fuel cell stack cell voltage monitor |
| FR2988226B1 (en) * | 2012-03-14 | 2014-04-18 | Helion | BATTERY COMPRISING A PLURALITY OF ELECTROCHEMICAL CELLS AND, FOR EACH CELL, A DEVICE FOR CONTROLLING THE VOLTAGE AT THE TERMINALS OF THE SAME CELL |
| DE102022112494A1 (en) | 2022-05-18 | 2023-11-23 | H-Tec Systems Gmbh | Electrochemical cell monitoring device, electrochemical cell monitoring system and method |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH01211860A (en) * | 1988-02-18 | 1989-08-25 | Fuji Electric Co Ltd | Control device for fuel cell power generating system |
| EP0982788A3 (en) * | 1998-08-21 | 2001-10-31 | General Motors Corporation | Method and apparatus for safeguarding fuel cells against reverse polarization damage |
| DE19907369C2 (en) * | 1999-02-20 | 2002-12-12 | Forschungszentrum Juelich Gmbh | Power source with cells connected in series |
-
2001
- 2001-09-03 WO PCT/DE2001/003367 patent/WO2002023658A1/en active IP Right Grant
- 2001-09-03 JP JP2002527598A patent/JP2004512633A/en not_active Withdrawn
- 2001-09-03 EP EP01978085A patent/EP1323204B1/en not_active Expired - Lifetime
- 2001-09-03 CA CA002422209A patent/CA2422209A1/en not_active Abandoned
- 2001-09-03 DE DE50102290T patent/DE50102290D1/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| WO2002023658A1 (en) | 2002-03-21 |
| EP1323204B1 (en) | 2004-05-12 |
| EP1323204A1 (en) | 2003-07-02 |
| DE50102290D1 (en) | 2004-06-17 |
| JP2004512633A (en) | 2004-04-22 |
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