Diagnostic method for diagnosing state of fuel cell system and fuel cell system

Abstract

The invention relates to a diagnostic method (100) for diagnosing a state of a fuel cell system (300), comprising: ascertaining (101) a pressure in a fuel cell stack (301) of the fuel cell system (300) after the fuel cell stack is switched off in a predetermined time range, comparing (103) the ascertained pressure with a predetermined reference value (207), and outputting (105) a fault report indicating a leakage of the fuel cell stack (301) if a diagnostic value of the ascertained pressure deviating from the reference value (207) is less than a predefined diagnostic threshold value.

Description

Technical Field

[0001] The present invention relates to a diagnostic method for diagnosing the state of a fuel cell system, a fuel cell system and a program product Background Art

[0002] A PEM fuel cell stack consists of many individual cells that are stacked and held together by a clamping system. The core element of an individual cell (ie fuel cell) is the membrane that separates the media on the anode and cathode sides.

[0003] Between the individual cells are so-called bipolar plates, in which cooling water flows in order to dissipate the heat losses of the chemical reaction. Therefore, the anode side, which conducts the hydrogen, must be sealed to the outside, ie to the environment.

[0004] The external seal can be provided, for example, by an elastomeric seal arranged in the bipolar plate. Such a seal may become leaky, for example due to aging, so that hydrogen leakage may occur.

[0005] Methods are known for diagnosing the leak tightness of a fuel cell stack, in which a diagnosis is performed during shutdown or during maintenance, for example by means of a pressure drop test or a sniff test.

[0006] During operation, leaks are detected by a hydrogen sensor which is placed in the housing of the fuel cell stack and measures the hydrogen concentration. Summary of the invention

[0007] Within the framework of the present invention, a diagnostic method for diagnosing the state of a fuel cell system, a fuel cell system and a program product are proposed. Further features and details of the present invention are derived from the claimed technical solution, the description and the drawings. Here, the features and details described in connection with the diagnostic method according to the invention are of course also applicable to the fuel cell system according to the invention and the program product according to the invention, and vice versa, so that the disclosures about the various inventive aspects are always referred to each other or can be referred to each other.

[0008] The proposed invention is used, inter alia, for automatically identifying and reporting leakage of hydrogen from a fuel cell system into the environment.

[0009] Therefore, according to a first aspect of the present invention, a diagnostic method for diagnosing a state of a fuel cell system is provided.

[0010] The proposed diagnostic method includes: obtaining the pressure in the fuel cell stack of the fuel cell system within a predetermined time period after shutting down the fuel cell stack, comparing the obtained pressure with a predetermined reference value, and outputting a fault report when a diagnostic value in which the obtained pressure deviates from the reference value is less than a predetermined diagnostic threshold, wherein the fault report indicates a fuel cell stack leak.

[0011] In the context of the present invention, outputting a fault message is understood to mean providing the fault message to an external source, for example as image information on a display, as audio information from a loudspeaker and / or as a message in a memory, in particular a fault memory.

[0012] The invention is based on the principle that the fuel cell stack cools down after being switched off, so that the gas enclosed in the fuel cell stack contracts and the pressure of the fuel cell stack decreases.

[0013] Furthermore, after shutting down the fuel cell stack, oxygen diffuses through the membrane from the cathode side to the anode side and reacts with the hydrogen there to form water, so that the amount of gas in the fuel cell stack becomes smaller and the pressure drops further.

[0014] In the case of an intact fuel cell stack without leaks, the pressure rapidly drops to below the ambient pressure (0 barg) when the anode shut-off valve is shut off and remains virtually constant over a longer period of time.

[0015] In the case of a fuel cell stack with a high leakage, the pressure rises rapidly again after a brief drop phase.

[0016] Accordingly, a defective fuel cell stack, ie a fuel cell stack with a high hydrogen leakage into the environment, can be identified by a diagnostic value of the pressure ascertained within a predefined time range after switching off the fuel cell stack deviating from a reference value by less than a predefined diagnostic threshold value.

[0017] Since the pressure remains almost constant when the fuel cell stack is intact, the pressure differs from the reference value provided according to the present invention by a diagnostic value that is greater than the diagnostic threshold value provided according to the present invention.

[0018] The time range of the invention depends on the topology of the corresponding fuel cell system and begins in particular when the pressure in a good fuel cell stack transitions into a plateau phase after shutdown. In a defective fuel cell stack, the plateau phase does not appear or only appears slightly, because the pressure in the defective fuel cell stack increases rapidly again after shutdown and accordingly exhibits a parabolic curve.

[0019] It can be set that the reference value has a negative value.

[0020] Since the pressure in the fuel cell stack becomes lower than the ambient pressure after shutdown, the reference value provided according to the invention can be lower than the ambient pressure, ie in particular have a negative value.

[0021] It can also be provided that the diagnostic value comprises a quantity, so that a fault message is output if the ascertained pressure value deviates from the reference value by an amount less than a predefined diagnostic threshold value.

[0022] The quantity, i.e. the sign-independent value, makes it possible to detect deviations not only in the upward direction but also in the downward direction, so that both in the case of strong pressure drops, which lead to a positive difference between the reference value and the measured pressure, and in the case of slight pressure drops, which lead to a negative difference between the reference value and the measured pressure, can be identified as a leak.

[0023] It can also be provided that the diagnostic value includes a time component, so that a fault message is output if the ascertained pressure drops continuously within a predefined time range.

[0024] The time component, for example the integral or derivative function of the profile of the measured pressure in the fuel cell stack within a predefined time range, enables a more precise diagnosis, thereby reducing the risk of false positive reports.

[0025] It can also be provided that an error message is output if the ascertained pressure is greater than a reference value.

[0026] The error message when the ascertained pressure is greater than the reference value leads to a very sensitive diagnosis which has a low risk of a false-negative message.

[0027] It can also be provided that an error message is output if the ascertained pressure is less than a reference value.

[0028] The error message when the ascertained pressure is less than the reference value leads to a robust diagnosis which has a low risk of false positive messages, since the error message is only output in the case of a significant pressure loss.

[0029] It can also be provided that the time period begins when the temperature of the fuel cell stack falls below a predefined temperature threshold value.

[0030] Since the fuel cell stack cools down after being switched off and this cooling causes a characteristic pressure curve, the temperature of the fuel cell stack can be used to infer the time point from which the measured pressure value is suitable for carrying out the proposed diagnostic method. Accordingly, the reliability of the diagnostic method can be maximized by combining the temperature threshold value and the predefined time range.

[0031] It may also be provided that the diagnostic value and / or the reference value is selected as a function of the temperature of the fuel cell stack.

[0032] Since the pressure in the fuel cell stack changes as a function of the temperature, the reliability of the diagnostic method can be maximized by adapting or selecting the diagnostic value or reference value as a function of the temperature.

[0033] According to a second aspect, the invention relates to a fuel cell system for energy conversion.

[0034] The proposed fuel cell system comprises a fuel cell stack, a pressure sensor arranged in the fuel cell stack, and a computing unit, wherein the computing unit is configured to carry out a possible embodiment of the proposed diagnostic method as a function of a value ascertained by the pressure sensor.

[0035] The proposed diagnostic method is used in particular for diagnosing a hydrogen leak at the proposed fuel cell system.

[0036] In the context of the present invention, a computing unit is understood to be a computer, a processor, a control device or any other programmable circuit.

[0037] It can also be provided that the computing unit is configured to operate for a predefined time period after switching off the fuel cell stack or to be activated at a predefined time after switching off the fuel cell stack in order to carry out the diagnostic method.

[0038] Since the time period described according to the present invention occurs after shutting down the fuel cell stack and, if necessary, after shutting down the entire fuel cell system, the computing unit used to execute the diagnostic method can be activated shortly before the time period set according to the present invention, or continue to operate until the diagnostic method is executed.

[0039] According to a third aspect, the invention relates to a program product comprising a program code which, when the program product is executed on a computing unit, configures the computing unit to carry out a possible configuration of the proposed diagnostic method.

[0040] The advantages described in detail for the diagnostic method for diagnosing the state of a fuel cell system according to the first aspect of the invention also apply to the fuel cell system for energy conversion according to the second aspect of the invention and the program product according to the third aspect of the invention.

[0041] Further advantages, features and details of the invention are apparent from the following description, in which embodiments of the invention are described in detail with reference to the accompanying drawings. The features mentioned in the technical solution and the description may be essential to the invention individually or in any combination. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The accompanying drawings show:

[0043] Figure 1Possible configurations of the proposed diagnostic method,

[0044] Figure 2 Detailed view of the evaluation according to the proposed diagnostic method,

[0045] Figure 3 Possible configurations of the proposed fuel cell system. DETAILED DESCRIPTION

[0046] Figure 1 A diagnostic method 100 for diagnosing a state of a fuel cell system is shown.

[0047] The diagnostic method 100 includes: an ascertainment step 101, in which the pressure in the fuel cell stack of the fuel cell system within a predetermined time range is ascertained after the fuel cell stack is shut down; a comparison step 103, in which the ascertained pressure is compared with a predetermined reference value; and an output step 105, in which a fault report is output for the situation that a diagnostic value by which the ascertained pressure deviates from the reference value is less than a predetermined diagnostic threshold value, wherein the fault report indicates a fuel cell stack leak.

[0048] Figure 2 A first graph 201 and a second graph 203 are shown, which each extend on their ordinate over a pressure measured at the fuel cell stack and on their abscissa over time.

[0049] In both the first diagram 201 and the second diagram 203 , a profile of an ambient pressure 205 and a reference value 207 are shown.

[0050] In a first diagram 201 , a first profile 209 of the pressure in a fault-free fuel cell stack (with permissible leakage) is shown.

[0051] After the fuel cell stack is shut down at time t0, the fuel cell stack cools down, the gas enclosed therein contracts and the pressure drops, at which time the variation curve 209 drops continuously and remains essentially constant at time t1, so that the difference between the reference value 207 and the variation curve 209 is large at time t1.

[0052] In the second diagram 203 , a second profile 211 of the pressure in a defective fuel cell stack (with inadmissibly severe leakage) is shown.

[0053] After the fuel cell stack is turned off at time t0, the fuel cell stack cools down, the gas enclosed therein contracts and the pressure drops, at which time the variation curve 211 only drops briefly and then rises rapidly again, so that the difference between the reference value 207 and the variation curve 211 is small at time t1. Accordingly, a fuel cell stack with an allowable leak and a fuel cell stack with an inadmissible leak can be distinguished based on the difference between the corresponding variation curves 209, 211 and the reference value at time t1.

[0054] Figure 3 A fuel cell system 300 for energy conversion is shown. The fuel cell system 300 includes a fuel cell stack 301 , a pressure sensor 303 arranged in the fuel cell stack 301 , and a computing unit 305 .

[0055] The calculation unit 305 is configured to perform a calculation based on the value obtained by the pressure sensor 303. Figure 1 Diagnostic methods 100.

Claims

1. A diagnostic method (100) for diagnosing a state of a fuel cell system (300), wherein: The diagnostic method (100) comprises: determining (101) a pressure in a fuel cell stack (301) of the fuel cell system (300) within a predetermined time range after the fuel cell stack (301) has been switched off, Comparing the pressure determined (103) with a predetermined reference value (207), If the diagnostic value of the deviation between the ascertained pressure and the reference value (207) is less than a predefined diagnostic threshold value, a fault message is output (105), wherein the fault message indicates a leak in the fuel cell stack (301).

2. The diagnostic method (100) according to claim 1, characterized in that: The reference value (207) has a negative value.

3. The diagnostic method (100) according to claim 1 or 2, characterized in that: The diagnostic value comprises a quantity, so that the fault message is output if the ascertained pressure deviates from a reference value (207) by an amount that is less than a predefined diagnostic threshold value.

4. The diagnostic method (100) according to any one of the preceding claims, characterized in that The diagnostic value comprises a time component, so that the fault message is output if the ascertained pressure drops continuously within a predefined time range.

5. The diagnostic method (100) according to any one of the preceding claims, characterized in that The fault message is output if the ascertained pressure is greater than a reference value.

6. The diagnostic method (100) according to any one of the preceding claims, characterized in that The fault message is output if the ascertained pressure is less than a reference value.

7. The diagnostic method (100) according to any one of the preceding claims, characterized in that The time range begins when the temperature of the fuel cell stack (301) drops below a predefined temperature threshold value.

8. The diagnostic method (100) according to any one of the preceding claims, characterized in that The diagnostic value and / or the reference value (207) is selected according to the temperature of the fuel cell stack (301).

9. A fuel cell system (300) for energy conversion, wherein: The fuel cell system (300) comprises: A fuel cell stack (301), a pressure sensor (303) arranged in the fuel cell stack (301), A computing unit (305), The computing unit (305) is configured to carry out the diagnostic method (100) according to any one of claims 1 to 8 based on the value ascertained by the pressure sensor (303).

10. The fuel cell system (300) according to claim 9, characterized in that: The computing unit (305) is configured to operate for a predetermined time period after the fuel cell stack (301) is switched off or to be activated at a predetermined time after the fuel cell stack (301) is switched off in order to execute the diagnostic method (100).

11. A program product comprising a program code which configures a computing unit to carry out the diagnostic method (100) according to any one of claims 1 to 8 when the program product is executed on the computing unit.

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