Method for diagnosing a fuel cell system

Abstract

The presented invention relates to a method (100) for diagnosing a fuel cell system (200). The method (100) has the steps of: - closing (101) an anode subsystem and a cathode subsystem of a fuel cell stack (201) of the fuel cell system (200); - determining (103) a duration of a stagnation phase; - assigning (105) the determined duration to a state of the fuel cell system (200); - outputting (107) the state assigned to the determined duration, wherein the stagnation phase begins at a first point in time (t1) at which an anode pressure (111) in the anode subsystem corresponds to a cathode pressure (113) in the cathode subsystem, and wherein the stagnation phase ends at a second point in time (t2) at which a rate of change in the profile of the anode pressure (111) and / or the cathode pressure (113) is above a predefined threshold value.

Description

[0001] R. 414555

[0002] - 1 -

[0003] Description

[0004] title

[0005] Methods for diagnosing a fuel cell system

[0006] The presented invention relates to a method for diagnosing a fuel cell system, a fuel cell system and a program product according to the attached claims.

[0007] State of the art

[0008] In a polymer electrolyte membrane (PEM) fuel cell system, oxygen and hydrogen are converted into electrical energy, heat energy and water.

[0009] A fuel cell system includes an anode subsystem that provides hydrogen and a cathode subsystem that provides oxygen in the form of air.

[0010] As a rule, a medium flowing out at the anode outlet is returned to the anode inlet or recirculated in a closed circuit.

[0011] The supply of fresh hydrogen is metered so that a predetermined anode pressure is established in the anode subsystem. Due to operational requirements, the anode pressure is usually higher than the cathode pressure in the cathode subsystem.

[0012] Disclosure of the invention

[0013] Within the scope of the presented invention, a method for diagnosing a fuel cell system, a fuel cell system and an R. 414555

[0014] - 2 -

[0015] The program product is presented. Further features and details of the invention will become apparent from the respective dependent claims, the description, and the drawings. Features and details described in connection with the method according to the invention naturally also apply in connection with the fuel cell system or the program product according to the invention, and vice versa, so that the disclosure regarding the individual aspects of the invention always refers to each other.

[0016] The presented invention serves in particular to provide a means of diagnosing the condition of a fuel cell system.

[0017] Thus, according to a first aspect of the presented invention, a method for diagnosing a fuel cell system is presented.

[0018] The presented method comprises closing an anode subsystem and a cathode subsystem of a fuel cell stack of the fuel cell system, determining the duration of a stagnation phase, assigning the determined duration to a state of the fuel cell system, and outputting the state assigned to the determined duration, wherein the stagnation phase begins at a first time point at which an anode pressure in the anode subsystem corresponds to a cathode pressure in the cathode subsystem, and wherein the stagnation phase ends at a second time point at which a rate of change of a profile of the anode pressure and / or the cathode pressure is above a predetermined threshold.

[0019] In the context of the presented invention, "outputting a state" means displaying the state on an output unit, such as a display, and / or storing a state in a memory, such as an error memory.

[0020] The presented invention is based on the principle that as soon as a fuel cell system is shut down, its cathode subsystem and anode subsystem are switched off at their previously set or currently applied pressure. This means that all valves or flaps of the R. 414555

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[0022] The anode subsystem and cathode subsystem are closed. Accordingly, when the fuel cell system is switched off, the anode subsystem mainly contains hydrogen and the cathode subsystem mainly contains air.

[0023] After the fuel cell system is switched off, diffusion of the individual molecules takes place via the respective membranes of the fuel cells of the fuel cell system between the anode subsystem and the cathode subsystem.

[0024] The diffusion of molecules is primarily driven by the respective partial pressures of the respective molecules or substances.

[0025] Due to the higher diffusion rate of hydrogen compared to nitrogen or oxygen, a pressure increase initially occurs in the cathode subsystem and a pressure drop in the anode subsystem.

[0026] Experiments surprisingly demonstrated that diffusion processes slow down at the point of total pressure equilibrium between the anode and cathode subsystems. However, this behavior is temporary, as the pressure curves return to their pre-slow state shortly afterward.

[0027] The period during which the diffusion processes slow down is referred to below as the duration of a stagnation phase. The stagnation phase therefore lies between a first point in time, at which the anode pressure in the anode subsystem equals the cathode pressure in the cathode subsystem, and a second point in time, at which the rate of change of the anode pressure and / or the cathode pressure exceeds a predefined threshold. Accordingly, the rate of change of the anode pressure and the cathode pressure also exceeds the predefined threshold before the first point in time.

[0028] Furthermore, experiments have surprisingly shown that the duration of the stagnation phase differs between various fuel cell systems R. 414555

[0029] - 4 - differentiates. Accordingly, the duration of the stagnation phase can be used to infer the state of a given fuel cell system.

[0030] It may be provided that the threshold corresponds to a rate of change of the anode pressure and / or cathode pressure before the first time point.

[0031] Since the anode pressure and cathode pressure profiles change at a comparable rate before and after the stagnation phase, the threshold can be determined based on the rate of change of the anode pressure and / or cathode pressure profile before the first time point.

[0032] It may also be provided that at the second time point, an amount of the slope of the anode pressure and / or the cathode pressure is above the threshold value.

[0033] By considering the absolute value of the respective slopes of the anode pressure and cathode pressure curves, a single threshold value can be chosen to determine the duration of the stagnation phase, which results in a particularly computationally efficient process for the presented method.

[0034] It may also be provided that at the second time point the slope of the anode pressure curve is below an anode threshold value and / or the slope of the cathode pressure curve is above a cathode threshold value.

[0035] By using a specific threshold for the anode pressure profile, namely an anode threshold and / or a specific threshold for the cathode pressure profile, namely a cathode threshold, the duration of the stagnation phase can be determined particularly accurately.

[0036] It may also be provided that the assignment of the determined duration to the state of the fuel cell system is based on a predefined R. 414555

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[0038] Assignment schemes are carried out, whereby the assignment scheme is determined using a test fuel cell system.

[0039] Using a test fuel cell system, i.e., a fuel cell system examined, for example, in a laboratory, its state can be systematically determined, for example, by disassembling individual components of the fuel cell system. The determined state can then be assigned to a corresponding duration of a stagnation phase previously determined for the test fuel cell system. Accordingly, if a given fuel cell system exhibits a stagnation phase duration that corresponds to, or essentially corresponds to, the duration of the stagnation phase of the test fuel cell system, it can be assumed that the state of the respective fuel cell system corresponds to the state of the

[0040] This corresponds to a test fuel cell system. A multitude of states, determined via, for example, a multitude of test fuel cell systems, can be assigned to the respective durations of the stagnation phases in an assignment scheme.

[0041] It may also be provided that the assigned state includes at least one parameter from the following list of parameters of the fuel cell system: age of fuel cells of the fuel cell system, relative humidity in the fuel cell stack, temperature in the fuel cell stack.

[0042] Surprisingly, experiments with test fuel cell systems have shown that the duration of the stagnation phase changes when the age of the fuel cells in the fuel cell system, the relative humidity in the fuel cell stack, and the temperature in the fuel cell stack change.

[0043] It may also be provided that at least one sensor of the fuel cell system is calibrated based on measured values ​​obtained by that at least one sensor at the first time. R. 414555

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[0045] Using a characteristic state of a fuel cell system, the respective sensors of the fuel cell system can be checked or calibrated by, for example, calculating and outputting a change in the respective measured values ​​determined by a sensor during several initial time points.

[0046] It may also be provided that at least one sensor of the fuel cell system is adjusted based on measured values ​​determined by the at least one sensor at the first time.

[0047] For example, if measured values ​​obtained by a sensor at several initial time points differ from each other, a sensor drift can be output and measured values ​​obtained by the sensor can be corrected according to the deviation.

[0048] According to a second aspect, the presented invention relates to a fuel cell system for converting energy.

[0049] The presented fuel cell system comprises a fuel cell stack and a computing unit, the computing unit being configured to carry out one possible embodiment of the presented method.

[0050] In the context of the presented procedure, a computing unit is understood to be a computer, a processor, a control unit or any other programmable circuit.

[0051] According to a third aspect, the presented invention relates to a program product, wherein the program product comprises program code means which, when the program product is executed on a computing unit, configure the computing unit to carry out a possible embodiment of the presented method.

[0052] The advantages described in detail in the method for diagnosing a fuel cell system according to the first aspect of the invention apply equally to the fuel cell system for conversion R. 414555

[0053] - 7 - of energy according to the second aspect of the invention as well as in the program product according to the third aspect of the invention and vice versa.

[0054] Further advantages, features, and details of the invention will become apparent from the following description, in which exemplary embodiments of the invention are described in detail with reference to the drawings. The features mentioned in the claims and in the description can each be essential to the invention individually or in any combination.

[0055] They each show schematically:

[0056] Figure 1 shows a possible embodiment of the presented method,

[0057] Figure 2 shows a detailed representation of pressure profiles according to the method shown in Fig. 1 and

[0058] Figure 3 shows a possible embodiment of the presented fuel cell system.

[0059] Figure 1 shows a method 100 for diagnosing a fuel cell system 200.

[0060] The procedure 100 comprises a closing step 101, in which an anode subsystem and a cathode subsystem of a fuel cell stack 201 of the fuel cell system 200 are closed, a determination step 103, in which a duration of a stagnation phase is determined, an assignment step 105, in which the determined duration is assigned to a state of the fuel cell system 200, and an output step 107, in which the state assigned to the determined duration is output, i.e., displayed on a screen.

[0061] The stagnation phase begins at a first time t1, at which the anode pressure in the anode subsystem corresponds to a cathode pressure in the cathode subsystem, and ends at a second time t2, at which R. 414555

[0062] - 8 - a rate of change of an anode pressure and / or cathode pressure curve exceeds a predetermined threshold.

[0063] The rate of change of the anode pressure and / or cathode pressure curve can be determined, for example, by calculating the slope or derivative of the respective curve.

[0064] Figure 2 shows a diagram 110 which spans time on its abscissa and pressure on its ordinate.

[0065] A first course 111 corresponds to an anode pressure after a corresponding fuel cell system 200 has been shut down.

[0066] A second curve 113 corresponds to a cathode pressure after the fuel cell system 200 was shut down.

[0067] The first curve 111 decreases with a constant rate of change until a first time t1 and at the first time t1 enters a stagnation phase in which the curve decreases with a significantly reduced rate of change.

[0068] At a second time point t2, the trend 111 declines again more rapidly, i.e., with a higher rate of change compared to the stagnation phase. Therefore, the duration of the stagnation phase can be determined by the time interval between the first time point t1 and the second time point t2.

[0069] The second curve 113 increases with a constant rate of change until a first time t1 and at the first time t1 enters a stagnation phase in which the curve increases with a significantly reduced rate of change.

[0070] At a second time point t2, the trend 113 rises again more rapidly, i.e., with a higher rate of change compared to the stagnation phase. Therefore, the duration of the stagnation phase can be determined by the time interval between the first time point t1 and the second time point t2. R. 414555

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[0072] Figure 3 shows a fuel cell system 200 for converting energy. The fuel cell system 200 comprises a fuel cell stack 201 and a computing unit 203 configured to perform the method 100 according to Figure 1.

Claims

R. 414555 - 10 - Claims 1. Method (100) for diagnosing a fuel cell system (200), wherein the method (100) comprises: Closing (101) of an anode subsystem and a cathode subsystem of a fuel cell stack (201) of the fuel cell system (200), Determining (103) the duration of a stagnation phase, Assigning (105) the determined duration to a state of the fuel cell system (200), Output (107) of the state associated with the determined duration, wherein the stagnation phase begins at a first time (t1) at which an anode pressure (111) in the anode subsystem corresponds to a cathode pressure (113) in the cathode subsystem, and wherein the stagnation phase ends at a second time (t2) at which a rate of change of a course of the anode pressure (111) and / or the cathode pressure (113) is above a predetermined threshold.

2. Method (100) according to claim 1 , characterized in that the threshold corresponds to a rate of change of the anode pressure (111) and / or the cathode pressure (113) before the first time (t1).

3. Method (100) according to claim 1 or 2, characterized in that at the second time point (t2) an amount of a slope of the anode pressure (111) and / or the cathode pressure (113) is above the threshold value.

4. Method (100) according to claim 1 or 2, characterized in that at the second time point (t2) the slope of the anode pressure (111) below an anode threshold value and / or the R. 414555 - 11 - The slope of the cathode pressure curve (113) is above a cathode threshold value.

5. Method (100) according to one of the preceding claims, characterized in that the assignment (105) of the determined duration to the state of the fuel cell system (200) is carried out using a predetermined assignment scheme, wherein the assignment scheme is determined using a test fuel cell system.

6. Method (100) according to one of the preceding claims, characterized in that the associated state comprises at least one parameter from the following list of parameters of the fuel cell system (200): age of fuel cells of the fuel cell system (200), relative humidity in the fuel cell stack (201), temperature in the fuel cell stack (201).

7. Method (100) according to one of the preceding claims, characterized in that at least one sensor of the fuel cell system (200) is calibrated on the basis of measured values ​​determined by the at least one sensor at the first time (t1).

8. Method (100) according to one of the preceding claims, characterized in that at least one sensor of the fuel cell system (200) is adjusted on the basis of measured values ​​determined by the at least one sensor at the first time (t1).

9. Fuel cell system (200) for converting energy, wherein the fuel cell system (200) comprises: a fuel cell stack (201), a computing unit (203), R. 414555 - 12 - wherein the computing unit (203) is configured to perform a method (100) according to any one of claims 1 to 8.

10. Program product, wherein the program product comprises program code resources which, if the The program product is executed on a computing unit, and the computing unit is configured to perform a method (100) according to any one of claims 1 to 8.

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