Classifications

• • 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
  • H01M8/04082—Arrangements for control of reactant parameters, e.g. pressure or concentration
  • H01M8/04089—Arrangements for control of reactant parameters, e.g. pressure or concentration of gaseous reactants
  • H01M8/04119—Arrangements for control of reactant parameters, e.g. pressure or concentration of gaseous reactants with simultaneous supply or evacuation of electrolyte; Humidifying or dehumidifying
  • H01M8/04156—Arrangements for control of reactant parameters, e.g. pressure or concentration of gaseous reactants with simultaneous supply or evacuation of electrolyte; Humidifying or dehumidifying with product water removal
  • H01M8/04164—Arrangements for control of reactant parameters, e.g. pressure or concentration of gaseous reactants with simultaneous supply or evacuation of electrolyte; Humidifying or dehumidifying with product water removal by condensers, gas-liquid separators or filters
• • 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
  • H01M8/0432—Temperature; Ambient temperature
  • H01M8/04343—Temperature; Ambient temperature of anode exhausts
• • 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
  • H01M8/04679—Failure or abnormal function of fuel cell stacks
• • 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

Definitions

• the invention relates to a method and an apparatus for diagnosis of a separator module in a fuel cell system.
• a fuel cell system comprises a fuel cell or a plurality of fuel cells which are connected in series and/or in parallel to form a fuel cell stack.
• PEM-FC proton exchange membrane fuel cells
• methane, methanol or glucose solution it is also known for methane, methanol or glucose solution to be used as the fuel.
• the fuel, in particular hydrogen is fed into the fuel cell stack at an inlet on an anode side of the fuel cell or of the fuel cell stack.
• the anode offgases from the fuel cell or the fuel cell stack emerge at an outlet and, when using hydrogen, are composed inter alia of unused hydrogen and water.
• the unused fuel can be made available again at the inlet, via a recirculation circuit.
• a separator module to be arranged in the anode circuit.
• the separator module comprises a sensor for detection of a filling level, a so- called level sensor.
• the separator module is in this case operated such that, when an upper switching point is exceeded, that is to say when a maximum filling level is exceeded, emptying of the separator module is initiated. Emptying is ended as soon as a lower switching point is undershot, that is to say a minimum filling level has been detected.
• the level sensor has at least two sensors or the like.
• a float switch it is known for a float switch to be used as a level sensor, with two or more switching points.
• a float switch such as this is, however, very unreliable and/or can be operated only with a large amount of complexity, with adequate reliability.
• Errors in the determination of the upper and/or the lower switching point can cause irreparable damage to the fuel cell system. For example, if the lower switching point is detected too late, then this can lead to a fuel gas, for example hydrogen, escaping into the environment. If the separator module is emptied too late, on the other hand, then this can lead to the liquid which has been created in the separator module running back into the anode circuit, and this can result in overheating of the system.
• a fuel gas for example hydrogen
• the object of the invention is to provide a method and an apparatus by means of which faults in detection of a filling level in a separator module and associated fault causes can be reliably identified.
• This object is achieved by a method and an apparatus for diagnosis of a separator module in a fuel cell system, in which an anode gas concentration in an anode circuit and/or a cathode off-gas line is detected, and fault diagnosis is carried out on the basis of the detected anode gas concentration.
• anode gas concentration in an anode circuit and/or a cathode off-gas line is detected, and fault diagnosis is carried out on the basis of the detected anode gas concentration.
• hydrogen is used as the anode gas.
• An apparatus for this purpose comprises at least one control and/or computation unit and at least one sensor by means of which the anode gas concentration in an anode circuit and/or a cathode off-gas line can be determined, in which a detected anode gas concentration can be supplied to the control and/or computation unit, and the control and/or computation unit has means by which fault diagnosis can be carried out based on the determined anode gas concentration.
• the filling level is predicted as a function of at least one current physical state variable of the fuel cell system, and the predicted value of the filling level is compared with a value, detected by a sensor, of the filling level for a plausibility check.
• the control and/or computation unit refinement comprises means for this purpose, by which at least one current physical state variable of the fuel cell system can be detected, the filling level can be predicted as a function of the at least one physical state variable, and the predicted value of the filling level can be compared with the value, detected by a sensor, of the filling level, for a plausibility check.
• the state variables can be detected by means of sensors which are already provided in the system, and can be made available to the control and/or computation unit via control inputs.
• an increase in the filling level and therefore the reaching of an upper switching point can be determined as a function of at least one state variable of the system comprising a group: the temperature of a coolant at a coolant inlet, the temperature of the coolant at a coolant outlet, the temperature of the fuel at an anode inlet, the temperature of the fuel in a fuel reservoir, a current drawn from a fuel cell stack and the environmental temperature of the system.
• the following relationships can be taken into account for the filling level of a separator in an anode circuit: the dependency on the temperature difference between the temperature of a coolant at an outlet from a fuel cell stack and the temperature of the fuel in a fuel reservoir; the dependency on the current drawn from the fuel cell stack; the dependency on the system temperature change at a coolant inlet when the system is started; the dependency on temperature differences between an environmental temperature and system temperatures, the dependency on the temperature difference between a temperature at the coolant outlet and at an anode inlet.
• the dependency of the filling level on further variables and/or on further relationships may be of interest.
• a decrease in the filling level and thus the reaching of a lower switching point a re determined on the basis of a determination and/or a prediction of the amount of liquid which ha s flowed away.
• the lower switching point is, for example, determined as a function of a flow coefficient (Kv value) and/or as a function of the pressure ratio across a separator outlet flow.
• Kv value a flow coefficient
• at least one filling level is predicted which is located between an upper and a lower switching point, in which case the sensor is arranged such that this filling level can be detected.
• the tolerance band may in this case be defined in a suitable form.
• the tolerance band may be designed to be variable, in which case, for example, greater accuracy may be required depending on specific state variables.
• the apparatus is coupled to signal and/or indication means and/or is designed with them, by means of which a fault or an irregularity can be indicated.
• various warning signals can be used so that, for example, only a visual signal is emitted when minor discrepancies occur while, in contrast, an audible continuous signal is additionally emitted when relatively major discrepancies occur, so that the need for immediate action is signalled to a user.
• a fault cause can also be indicated on an indication unit.
• indicator lights are provided in order to visually mark fault locations.
• Faults which occur in a separator module can in principle be subdivided into two groups: the detected filling level is higher than the predicted filling level, or the detected filling level is lower than the predicted filling level. However, this grouping does not yet in its own right make it possible to clearly determine the cause of the fault.
• the anode gas concentration is therefore additionally used for evaluation, according to the invention.
• FIG. 1 shows a block diagram of a fuel cell system according to the invention
• Figure 2 shows a schematic illustration of a separator module
• Figure 3 shows a block diagram of a part of a control unit according to the invention.
• FIG. 1 shows, schematically, a block diagram of a fuel cell system 1.
• the fuel cell system 1 comprises a fuel cell stack 10 which is formed from a plurality of fuel cells, which are electrically connected in series and/or in parallel. Anode sides of individual fuel cells in the fuel cell stack 10 provide the anode side 103 of the fuel cell stack 10. In the same way, the cathode sides of the fuel cells provide the cathode side 102 of the fuel cell stack 10.
• Cathode and anode circuits 2, 3, which are illustrated in a simplified form, are arranged respectively on the cathode side 102 and on the anode side 103.
• a cooling circuit 4 is provided, with an inlet 41 and an outlet 42.
• the anode circuit 3 which is illustrated in a simplified form, comprises a fuel reservoir 30, with the fuel, for example hydrogen, being supplied via an inlet 31 to the fuel cell stack 10.
• An anode offgas is dissipated via an outlet 32 from the fuel cell stack 10.
• a recirculation unit 33 is provided, by means of which at least some of the anode offgas can be fed back to the inlet 31 again.
• an anode circuit 3 can be closed at a different point, for example by feeding back at least some of the anode offgas to the fuel reservoir 30.
• a separator module 34 is provided in the anode circuit 3, by means of which water or some other condensate which is produced in the anode circuit 3 is removed from time to time.
• FIG. 2 shows, schematically, a corresponding separator module 34.
• the separator module 34 is arranged between the anode circuit 3 and a cathode off-gas line 2a, with the separator module 34 being emptied into the cathode off-gas line 2a.
• the separator module 34 comprises a separator container 340, a filter 342 and a valve 343.
• the separator module 34, in particular the valve 343, is operated or regulated by means of a control unit 6.
• the control unit 6 comprises an input 60 for a measurement signal from a filling level sensor 5, as well as a plurality of inputs 61, by means of which further state variables or system variables can be supplied to the control unit 6.
• the control unit 6 also comprises an outlet 62 for operating the separator valve 343.
• separator water is collected in the separated container 340.
• the separator module 34 is in this case operated such that the filling level is regulated between a lower value F_min and an upper value F_max.
• the separator valve 343 is opened when the filling level reaches the upper switching point F_max.
• the filling level of the water which has been collected or deposited is on the one hand detected by means of the filling level sensor 5.
• the illustrated filling level sensor 5 is in this case arranged such that the lower switching point can be detected. On the other hand, the filling level is observed.
• the control unit 6 determines the upper switching point, from which emptying of the separator container 340 is intended to start, as a function of various state variables which are supplied to the control unit 6 at the control inputs 61.
• the state variables are, for example, the temperature T_KM_in of a coolant at the inlet 41 as shown in Figure 1, the temperature T_KM_out of the coolant at the outlet 42, the temperature of the fuel, in particular of the hydrogen, T_H2 _in at the inlet 31, the temperature T_Tank of the fuel at the fuel reservoir 30, the instantaneous current I_BZ drawn from the fuel cell stack 10, and/or the environmental temperature T_UM of the system.
• these variables can be used to increase the amount of water or the filling level in the separator module 34 as a function of the temperature difference T_KM_out - T_Tank between the temperature of the coolant at the outlet 42 and the temperature T_Tank in the fuel reservoir 30, thus making it possible to take account of mixing of very cold or relatively cold hydrogen from the reservoir 30 with very moist anode offgas in the anode circuit 3. Furthermore, a relationship is possible between the filling level and a current I_BZ drawn from the fuel cell.
• the determined variables make it possible to take account of the filling level as a function of the rate of change of the system temperature d(T_KM_in/dt on starting the system, taking account of the fact that water is stored in membranes in the fuel cell stack 10 when the temperature of the fuel cell stack 10 is relatively cold, and is emitted as a result of a temperature increase.
• the temperature difference T_KM_out - T_H2_in between the temperature of the coolant at the outlet 41 and the temperature of the fuel at the inlet 31 can be taken into account as a further influence on the filling level.
• the separator valve 343 can be opened, and the separator container 340 can be appropriately emptied.
• a lower switching point is detected by the filling level sensor 5.
• the lower switching point is predicted by the control unit 6.
• an outlet flow rate can be taken into account as a function of a flow factor (Kv value) , including characteristics of the valve 343 and of the lines and of the filter 342, and/or as a function of the pressure ratio, for example of the system pressure in the anode circuit 3 and/or in the separator container 340 in comparison to the environmental pressure.
• Kv value flow factor
• the value, detected by the sensor 5, of the filling level is compared with the value, predicted by the control unit 6, of the filling level, for a plausibility check. If the two values differ from one another, then this indicates faulty operation of the separator module 34. This fault can be signalled by suitable means which are not illustrated. This makes it possible to avoid consequential damage to the fuel cell system by timely maintenance and/or replacement of individual components or of the separator module 34. Possible faults in the separator module 34 may in this case result from various causes.
• the illustrated sensor 5 for detection of the lower switching point F_min indicates that the switching point is being reached earlier than the observed reaching of the switching point, then this may on the one hand be caused by a fault in the sensor 5 itself, for example by mechanical sticking of a float body at the switching point.
• the separator valve 343 it is also possible for the separator valve 343 to be leaky, for example, because of mechanical jamming on the separator valve 343 or because of dirt deposits.
• the separator module 34 may have developed a leak elsewhere.
• the illustrated sensor 5 for detection of the lower switching point F_min indicates that this switching point is being reached later than the observed reaching of the switching point, then this can likewise be caused by a fault in the sensor 5 itself. Furthermore, however, it is also possible for the separator valve 343 to have become blocked, for example because of dirt deposits.
• the sensor 5 can be arranged such that an upper switching point F_max can be detected by the sensor.
• the filling level sensor is arranged in a range between the upper and the lower switching point. In this case, it is possible to predict not only a time at which the associated filling level will be exceeded but also a time at which the associated filling level will be undershot. An arrangement such as this is possible, for example, to detect not only leakage by means of the filling level being undershot too early, but also blocking of an outlet flow, as a result of the filling level being exceeded too early.
• the fault signal is diagnosed by means of the control unit 6.
• Figure 3 shows, schematically, a block diagram for fault diagnosis. As described, two fault situations are identified by means of the prediction of the filling level and of the filling level sensor 5:
• fault situation A the detected filling level is unexpectedly high, that is to say the filling level detected by the filling level sensor 6 is higher than the predicted filling level.
• fault situation B the detected filling level is unexpectedly low, that is to say the value detected by the filling level sensor 5 is lower than the predicted value.
• these two fault situations A, B are diagnosed on the basis of the anode gas concentrations detected by the sensors 7, 8.
• the control unit 6 has means by which the values determined by the sensors 7, 8 are compared with maximum values MAX at junction points 70, 80 as shown in Figure 3. The result is either positive + or negative -.
• appropriate further processing is carried out, with a distinction being drawn between five diagnosis results Diag 1, ... , Diag 5.
• diagnosis result Diag 5 a situation referred to as diagnosis result Diag 5 has occurred, in which the detected filling level is correct and the prediction is erroneous.
• diagnosis result Diag 5 may, for example, be that an outlet flow from the separator module 34 as illustrated in Figure 2 has become blocked.
• This fault can be rectified by initiating measures which prevent the separated liquid from accumulating in the anode circuit 3 and thus being able to enter the fuel cell stack 10 illustrated in Figure 1. In some circumstances, such ingress could lead to very high temperatures and to irreversible damage to the fuel cell stack 10.
• a countermeasure it would be feasible to change the operating mode of the fuel cell system 1 illustrated in Figure 1, by choosing an operating mode with little moistur e, thus minimizing water enhancement in the anode circuit 3.
• diagnosis result Diag 3 can be used to initiate measures which prevent the anode gas concentration in the cathode offgas from exceeding a critical value.
• One feasible measure for example, is to increase the cathode flow in order to dilute the anode gas concentration in the offgas to a greater extent.
• this fault may have two possible causes.
• the cause is analysed further by evaluation of a second sensor 8, which is provided in the anode circuit 3.
• the value detected by the sensor 8 is compared with a maximum value at a junction point 80. If this comparison is also negative, that is to say if the value of the anode gas concentration does not exceed the maximum value either in the cathode offgas or in the anode circuit, then this leads to the conclusion that the situation referred to as diagnosis result Diag 1 has occurred, in which the predicted value is qualitatively better than the value measured by the sensor 5, so that the sensor 5 is incorrectly indicating an excessively low filling state.
• diagnosis result Diag 4 a situation which is referred to as diagnosis result Diag 4 has occurred, indicating an external leakage from the separator module 34.
• measures should be initiated which ensure that the fuel cell system 1 as shown in Figure 1 is shut down in a manner which is safe for people and the environment. In the event of a fault such as this, dangerous anode gas concentrations can build up in an uncontrolled manner outside the anode circuit 3, or even outside the fuel cell system 1.
• one possible measure for a fuel cell hybrid vehicle system would be to immediately shut down the fuel cell system and to continue driving the vehicle, if possible for a limited time, exclusively by the alternative drive.
• an appropriate warning message can be emitted to the driver so that he can drive appropriately to a suitable driving position or the like.
• Warning signals can likewise also be emitted in other situations so that, as appropriate, defective components can be replaced and/or a dirt deposit can be removed.

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Citations (6)

• 2007
  • 2007-08-22 DE DE102007039564A patent/DE102007039564A1/de not_active Withdrawn
• 2008
  • 2008-06-26 WO PCT/EP2008/005203 patent/WO2009024206A1/en active Application Filing

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