DETERMINATION DEVICE AND METHOD FOR CALCULATING A MOISTURE VALUE IN A FUEL CELL SYSTEM

Abstract

The present invention relates to a determination device (1; 1′) for a fuel cell system (2; 2′) having a fuel cell stack (4), comprising a virtual moisture sensor (7) for recording predefined determination values and a computing unit (10) for calculating a moisture value in a cathode inlet region (5) upstream of a cathode section of the fuel cell stack (4) based on the recorded determination values. The invention further relates to a fuel cell system (2; 2′) having such a determination device (1; 1′), methods for determining the moisture value, a computer program product (11) and a storage means having a computer program product (11) stored thereon.

Claims

1. Determination device (1; 1′) for a fuel cell system (2; 2′) with a fuel cell stack (4), having a virtual moisture sensor (7) comprising a first moisture sensor determination value input (7a) for recording a cathode outlet moisture determination value, a second moisture sensor determination value input (7b) for recording a stack outlet water mass flow determination value, a third moisture sensor determination value input (7c) for recording a stack outlet air mass flow determination value, a fourth moisture sensor determination value input (7d) for recording a system inlet water mass flow determination value, a fifth moisture sensor determination value input (7e) for recording a system inlet air mass flow determination value, a sixth moisture sensor determination value input (7f) for recording a cathode inlet temperature determination value, a seventh moisture sensor determination value input (7g) for recording a cathode outlet temperature determination value, an eighth moisture sensor determination value input (7h) for recording a cathode inlet pressure determination value, and a ninth moisture sensor determination value input (7i) for recording a cathode outlet pressure determination value, and a computing unit (10) for calculating a moisture value in a cathode inlet region (5) upstream of a cathode section of the fuel cell stack (4) based on the recorded determination values.

2. Determination device (1; 1′) according to claim 1, characterised by a virtual system inlet sensor (8) having a first system inlet sensor determination value input (8a) for recording an ambient temperature determination value, a second system inlet sensor determination value input (8b) for recording an ambient pressure determination value, a third system inlet sensor determination value input (8c) for recording an ambient humidity determination value, and a fourth system inlet sensor determination value input (8d) for recording a system inlet air mass flow determination value wherein the computing unit (10) is configured to calculate the system inlet water mass flow determination value based on the determination values.

3. Determination device (1; 1′) according to claim 1, characterised by a virtual stack sensor (9) having a first stack sensor determination value input (9a) for recording a cathode inlet water mass flow determination value, a second stack sensor determination value input (9b) for recording a cathode inlet temperature determination value, a third stack sensor determination value input (9c) for recording a cathode outlet temperature determination value, a fourth stack sensor determination value input (9d) for recording a cathode inlet pressure determination value, a fifth stack sensor determination value input (9e) for recording a cathode outlet pressure determination value, and a sixth stack sensor determination value input (9f) for recording a system inlet air mass flow determination value, wherein the computing unit (10) is configured to calculate the cathode outlet moisture determination value based on the determination values.

4. Determination device (1; 1′) according to claim 3, wherein the computing unit (10) is configured to calculate the cathode inlet water mass flow determination value based on the determination values.

5. Fuel cell system (2; 2′) with a determination device (1; 1′) according to claim 1 for determining a moisture value in the cathode inlet region (5) upstream of the cathode section of the fuel cell stack (4).

6. Fuel cell system (2, 2′) according to claim 5, wherein the fuel cell system (2, 2′) has a system inlet (6), wherein an air humidifier (3) is arranged downstream of the system inlet (6).

7. Fuel cell system (2, 2′) according to claim 6, wherein the fuel cell stack (4) is downstream of the air humidifier (3).

8. Fuel cell system (2, 2′) according to claim 6, wherein the fuel cell system (2, 2′) has a return line (12), through which cathode exhaust gas and thus water components can be circulated back from the cathode section of the fuel cell stack (4) into the air humidifier (3).

9. Fuel cell system (2, 2′) according to claim 6, wherein a bypass is provided, wherein the air humidifier (3) can be bypassed via the bypass.

10. Fuel cell system (2, 2′) according to claim 8, wherein the bypass establishes a connection to the return line (12) arranged downstream of the air humidifier (3) and upstream of the fuel cell stack (4).

11. Method for calculating a moisture value in a cathode inlet region (5) upstream of a cathode section of a fuel cell stack (4) in a fuel cell system (2; 2′), comprising the steps: recording a cathode outlet moisture determination value, a stack outlet water mass flow determination value, a stack outlet air mass flow determination value, a system inlet water mass flow determination value, a system inlet air mass flow determination value, a cathode inlet temperature determination value, a cathode outlet temperature determination value, a cathode inlet pressure determination value, and a cathode outlet pressure determination value by means of a virtual moisture sensor (7), and calculating the moisture value based on the recorded determination values by means of a computing unit (10).

12. Method according to claim 11, wherein in order to calculate the moisture value in the cathode inlet region (5) based on the recorded determination values, the computing unit (10) carries out the following steps: determining difference values between the system inlet water mass flow determination value and the stack outlet water mass flow determination value, the system inlet air mass flow determination value and the stack outlet air mass flow determination value, the cathode inlet temperature determination value and the cathode outlet temperature determination value and/or the cathode inlet pressure determination value and the cathode outlet pressure determination value; and determining the moisture value in the cathode inlet region (5) based on the cathode outlet moisture determination value and at least one of the difference values.

13. Method according to claim 11, wherein an ambient temperature determination value, an ambient pressure determination value, an ambient humidity determination value and a system inlet air mass flow determination value are recorded by a virtual system inlet sensor (8), and the system inlet water mass flow determination value is calculated by a computing unit (10) based on the recorded determination values.

14. Method according to claim 11, wherein a cathode inlet water mass flow determination value, a cathode inlet temperature determination value, a cathode outlet temperature determination value, a cathode inlet pressure determination value, a cathode outlet pressure determination value and a system inlet air mass flow determination value are recorded by a virtual stack sensor (9), and the cathode outlet moisture determination value is calculated by a computing unit (10) based on the recorded determination values.

15. Method according to claim 11, wherein the cathode inlet water mass flow determination value is calculated by the computing unit (10) based on the determination values.

16. Method predicting a moisture state of an electrolyte membrane of the fuel cell stack (4) based on a moisture value in a cathode inlet region (5) upstream of a cathode section of a fuel cell stack (4) in a fuel cell system (2; 2′), wherein the moisture value is calculated according to a method according to claim 11.

17. Method for monitoring the moisture in a fuel cell system (2; 2′) based on a predicted moisture state of an electrolyte membrane of the fuel cell stack (4), wherein the moisture state is predicted using a method according to claim 16.

18. Computer program product (11) comprising commands that cause the computer program product (11) to carry out the method according to claim 11.

19. Storage means with a computer program product (11) according to claim 18 stored thereon.

Description

[0037] In each case schematically:

[0038] FIG. 1 shows a fuel cell system with a determination device according to a first embodiment of the present invention installed therein,

[0039] FIG. 2 shows a fuel cell system with a determination device according to a second embodiment of the present invention installed therein,

[0040] FIG. 3 shows a virtual moisture sensor according to a preferred embodiment of the present invention,

[0041] FIG. 4 shows a virtual system inlet sensor according to a preferred embodiment of the present invention,

[0042] FIG. 5 shows a virtual stack sensor according to a preferred embodiment of the present invention, and

[0043] FIG. 6 shows a flowchart serving to explain a method according to a first embodiment of the present invention.

[0044] Elements with the same function and mode of action are each provided with the same reference signs in FIGS. 1 to 6.

[0045] FIG. 1 shows, schematically, a fuel cell system 2 with a determination device 1 according to a first embodiment installed therein. The fuel cell system 2 has a system inlet 6, an air humidifier 3 arranged downstream of the system inlet 6 and a fuel cell stack 4 arranged downstream of the air humidifier 3. The fuel cell stack 4 has an anode section and a cathode section, wherein an electrolyte membrane (not shown) is arranged between the anode section and the cathode section. According to the exemplary embodiment shown in FIG. 1, a virtual system inlet sensor 8 is assigned to the system inlet 6. A virtual moisture sensor 7 is assigned to the air humidifier 3. A virtual stack sensor 9 is assigned to the fuel cell stack 4. The system inlet sensor 8, the moisture sensor 7 and the stack sensor 9 are in each case in signal connection with a computing unit 10 of the fuel cell system 2. A computer program product 11 is installed in the computing unit 10.

[0046] FIG. 2 shows a fuel cell system 2′ with a determination device 1′ according to a second embodiment. The second embodiment substantially corresponds to the first embodiment. The distinguishing feature is a return line 12 through which cathode exhaust gas and thus water components can be circulated back from the cathode section of the fuel cell stack 4 into the air humidifier 3.

[0047] FIG. 1 and FIG. 2 in each case show a system overview, the subsystems of which are then explained in detail with reference to FIGS. 3 to 5.

[0048] The virtual moisture sensor 7 shown in FIG. 3 has a first moisture sensor determination value input 7a for recording a cathode outlet moisture determination value, a second moisture sensor determination value input 7b for recording a stack outlet water mass flow determination value, a third moisture sensor determination value input 7c for recording a stack outlet air mass flow determination value, a fourth moisture sensor determination value input 7d for recording a system inlet water mass flow determination value, a fifth moisture sensor determination value input 7e for recording a system inlet air mass flow determination value, a sixth moisture sensor determination value input 7f for recording a cathode inlet temperature determination value, a seventh moisture sensor determination value input 7g for recording a cathode outlet temperature determination value, an eighth moisture sensor determination value input 7h for recording a cathode inlet pressure determination value and a ninth moisture sensor determination value input 7i for recording a cathode outlet pressure determination value.

[0049] The virtual moisture sensor 7 also has a signal output 7k for transmitting the recorded determination values to the computing unit 10. Based on the determination values recorded by the moisture sensor 7, the computing unit 10 can calculate a moisture value in a cathode inlet region 5 upstream of the cathode section of the fuel cell stack 4.

[0050] Difference values can be determined mathematically, for example by forming a difference between absolute amounts of a value pair of recorded determination values which are measured, in relation to the same parameter, at the cathode inlet and at the cathode outlet respectively. The moisture value in the cathode inlet region can also be determined mathematically in that the computing unit 10 places the cathode outlet moisture determination value in relation to a factor. The factor is based on a function whose function variables comprise at least one of the recorded determination values, in particular a difference value, which is determined from the determination values recorded in relation to the same parameter, and may optionally include an absolute temperature value.

[0051] The virtual system inlet sensor 8 shown in FIG. 4 has a first system inlet sensor determination value input 8a for recording an ambient temperature determination value, a second system inlet sensor determination value input 8b for recording an ambient pressure determination value, a third system inlet sensor determination value input 8c for recording an ambient humidity determination value and a fourth system inlet sensor determination value input 8d for recording a system inlet air mass flow determination value. The virtual system inlet sensor 8 also has a signal output 8e for transmitting the recorded determination values to the computing unit 10. Based on the determination values recorded by the system inlet sensor 8, the computing unit 10 can calculate the system inlet water mass flow determination value.

[0052] The virtual stack sensor 9 shown in FIG. 5 shows a first stack sensor determination value input 9a for recording a cathode inlet water mass flow determination value, a second stack sensor determination value input 9b for recording a cathode inlet temperature determination value, a third stack sensor determination value input 9c for recording a cathode outlet temperature determination value, a fourth stack sensor determination value input 9d for recording a cathode inlet pressure determination value, a fifth stack sensor determination value input 9e for recording a cathode outlet pressure determination value and a sixth stack sensor determination value input 9f for recording a system inlet air mass flow determination value. The virtual stack sensor 9 also has a signal output 9g for transmitting the recorded determination values to the computing unit 10. Based on the determination values recorded by the stack sensor 9, the computing unit 10 can calculate the cathode outlet moisture determination value and the cathode inlet water mass flow determination value.

[0053] A method for calculating the moisture value in the cathode inlet region 5 will be explained with reference to FIG. 6. For this purpose, in a first step S1, the cathode outlet moisture determination value, the stack outlet water mass flow determination value, the stack outlet air mass flow determination value, the system inlet water mass flow determination value, the system inlet air mass flow determination value, the cathode inlet temperature determination value, the cathode outlet temperature determination value, the cathode inlet pressure determination value and the cathode outlet pressure determination value are recorded or detected by means of the virtual moisture sensor 7. In a second step S2, the moisture value and the cathode inlet water mass flow determination value are then calculated by the computing unit 10 based on these recorded or considered determination values.

[0054] In addition to the embodiments depicted, the invention allows for further design principles. That is to say, the invention should not be considered to be limited to the exemplary embodiments explained with reference to the figures.

[0055] For example, within the framework of the method, the ambient temperature determination value, the ambient pressure determination value, the ambient humidity determination value and the system inlet air mass flow determination value can be recorded by the virtual system inlet sensor 8. The system inlet water mass flow determination value can then be calculated by the computing unit 10 based on these determination values.

[0056] In addition, the cathode inlet water mass flow determination value, the cathode inlet temperature determination value, the cathode outlet temperature determination value, the cathode inlet pressure determination value, the cathode outlet pressure determination value and the system inlet air mass flow determination value can be recorded by the virtual stack sensor 9. The cathode outlet moisture determination value can then be calculated by the computing unit 10 based on these determination values.

[0057] In other words, the water mass fraction of the airflow in the cathode path can be calculated based on signals indicating the air mass flow at the system inlet 6, as well as the pressures, the temperatures and the relative moisture values at the fuel cell stack 4. The relative humidity at the cathode outlet and the water mass flow at the system inlet 6 are used as supplementary input signals for the virtual moisture sensor. The moisture transfer can then be determined dynamically using parameters of the air humidifier 3 such as a membrane thickness, a membrane surface area and/or a membrane density of the air humidifier 3 and the relative moisture on the dry and the moist sides of the air humidifier 3. The value of the relative moisture at the cathode input can be calculated relatively accurately with the aid of the explicitly selected temperature values, pressure values and mass flow values.

[0058] The total mass flow of water from the fuel cell system 2, 2′ is calculated in the fuel cell system 2, 2′ from the inflowing water, the generated water and the part of the water which diffuses to the anode. In addition to the generated water mass, a power requirement for the system can also be used as an additional signal input.

[0059] In a humidifier model, the method can also easily be adapted to a system with external humidification by means of water injection. In particular, the humidifier model is structured in such a way that it is not limited to a passive humidification, but is also applicable to systems with active humidification.

[0060] In addition, the method can also be further developed in order to predict a moisture state of an electrolyte membrane of the fuel cell stack 4 based on the moisture value in the cathode inlet region 5 upstream of the cathode section of the fuel cell stack 4 in the fuel cell system 2, wherein the moisture value is calculated as described above. In addition, it is possible that a method for monitoring the moisture in a fuel cell system 2 based on a predicted moisture state in an electrolyte membrane of the fuel cell stack 4 is carried out, wherein the moisture state is predicted using a method as described above.

[0061] The calculation of the moisture value according to the invention can also be carried out depending on the current power requirement of the fuel cell system, i.e. if a lot of power is required, a correspondingly increased air intake can be assumed.

[0062] The amount of water produced in the fuel cell stack 4 also increases depending on this power demand or electricity demand, which is reflected in the amount of water which leaves the cathode and flows into the humidifier. This results in better humidification in the humidifier and thus, again, in a higher humidity at the cathode input.

LIST OF REFERENCE SIGNS

[0063] 1.1′ determination device [0064] 2.2′ fuel cell system [0065] 3 air humidifier [0066] 4 fuel cell stack [0067] 5 cathode inlet region [0068] 6 system inlet [0069] 7 virtual moisture sensor [0070] 7a-7i moisture sensor determination value inputs [0071] 8 virtual system inlet sensor [0072] 8a-8d system inlet sensor determination value inputs [0073] 9 virtual stack sensor [0074] 9a-9g stack sensor determination value input [0075] 10 computing unit [0076] 11 computer program product [0077] 12 return line