Diagnostic method for identifying damage to at least one fuel cell membrane of a fuel cell stack

Abstract

The present invention relates to a diagnostic method for identifying damage to at least one fuel cell membrane (116) of a fuel cell stack (110) of a fuel cell system (100), characterised by the following steps: determining a reference by way of measurements and / or by way of theoretical calculations; operating the fuel cell stack (110) with a working current, wherein the working current is applied at the fuel cell stack (110) and / or is tapped at the fuel cell stack (110), overlaying the working current at the fuel cell stack (110) with a measurement current; determining a fuel cell system response at the fuel cell stack (110) as a result of the overlaid measurement current; and comparing the fuel cell system response with the reference in order to identify damage to the at least one fuel cell membrane (116) of the fuel cell stack (110), characterised in that the diagnostic method has a prior step in which a parameter of the fuel cell system (100) is monitored and the step of overlaying with measurement current, and the steps subsequent thereto, are only carried out if a predetermined condition is met, wherein the diagnostic method is carried out with a determined frequency of the measurement current when a determined damage type appears likely, wherein the determined damage type appears likely when a prediagnosis indicates the determined damage type.

Description

[0001] Diagnostic method for detecting damage to at least one fuel cell membrane of a fuel cell stack

[0002] The present invention relates to a diagnostic method for detecting damage to at least one fuel cell membrane of a fuel cell stack of a fuel cell system, a computer program product for carrying out such a diagnostic method and a diagnostic device.

[0003] Fuel cell stacks with PEM fuel cells (proton exchange membrane fuel cells) are known in the state of the art. Such fuel cells have a fuel cell membrane. The fuel cell membrane of such a fuel cell separates the anode of the fuel cell from the cathode of the fuel cell. The fuel cell membrane must not become too dry, as otherwise it could be damaged. In particular, holes could form in the fuel cell membrane. In order to adjust the humidity of the fuel cell membrane, the humidity of the fuel cell membrane must first be measured. The humidity can be measured using a humidity sensor, for example. However, this is technically complex, as a humidity sensor is required, which must be installed close to the fuel cell membrane. Theoretical simulations of the humidity of the fuel cell membrane are also possible.However, such simulations are quite inaccurate.

[0004] Against this background, one object of the present invention is to at least partially remedy the disadvantages described above. In particular, the object of the present invention is to provide a diagnostic method with which damage to at least one fuel cell membrane of a fuel cell stack, and in particular drying out of at least one fuel cell membrane of a fuel cell stack, can be detected.

[0005] The above objects are achieved by a diagnostic method having the features of claim 1, a computer program product having the features of claim 14, and a diagnostic device having the features of claim 15. Further features and details of the invention emerge from the subclaims, the description, and the drawings. Features and details described in connection with the diagnostic method according to the invention naturally also apply in connection with the computer program product according to the invention and the diagnostic device according to the invention, and vice versa, so that with regard to the disclosure of the individual aspects of the invention, reference is always made to each other.

[0006] Accordingly, a diagnostic method for detecting damage to at least one fuel cell membrane of a fuel cell stack of a fuel cell system is described. The diagnostic method comprises the following steps:

[0007] - Determining a reference by measurements and / or theoretical calculations,

[0008] - Operating the fuel cell stack with a working current, wherein the working current is applied to the fuel cell stack and / or tapped at the fuel cell stack,

[0009] - Superimposing the working current on the fuel cell stack with a measuring current,

[0010] - determining a fuel cell system response at the fuel cell stack based on the superimposed measuring current, and

[0011] - Comparing the fuel cell system response with a reference to detect damage to at least one fuel cell membrane of the fuel cell stack.

[0012] The diagnostic method according to the invention has a preceding step in which a parameter of the fuel cell system is monitored, and only if a predetermined condition is met are the step of superimposing the measuring current and the subsequent steps carried out. Accordingly, a preliminary diagnosis is carried out, i.e. the preceding step represents a preliminary diagnosis. The remaining steps of the diagnostic method are only carried out if the condition of the preliminary diagnosis is met. In the diagnostic method according to the invention, the reference is determined by measurements and / or theoretical calculations. The measurements can be carried out, for example, on a test bench. For example, the measurements for determining the reference can be carried out on a fuel cell stack which has at least one fuel cell membrane with known damage.The result obtained here can then be used to determine the reference. Alternatively or additionally, theoretical considerations can be applied, and the reference can be calculated based on these theoretical considerations.

[0013] According to the invention, the diagnostic method is carried out with a specific frequency of the measuring current if a specific type of damage appears likely, wherein the specific type of damage is considered likely if a preliminary diagnosis indicates this specific type of damage. Advantageously, the precise frequency for the measuring current can be selected at which a fuel cell system response is expected, with which the type of damage can be reliably detected. If a preliminary diagnosis detects that, for example, the efficiency of the fuel cell is too low, then it is likely that, for example, the fuel cell membrane has dried out. In this case, the diagnostic method applies a specific frequency for the measuring current at which a corresponding fuel cell system response is obtained, at which it can be clearly seen that, for example, the fuel cell membrane has dried out.

[0014] By determining the fuel cell system response as described and comparing it with a reference, the diagnostic procedure can be performed very quickly and accurately. Furthermore, this diagnostic procedure requires only minimal computational effort. Furthermore, a separate humidity sensor, which would have to be located near a fuel cell membrane, is eliminated.

[0015] The measurement current can, in particular, be an alternating current. The fuel cell system response is, in particular, an impedance, i.e., an alternating current resistance, of the fuel cell stack. In particular, the so-called HFR (High Frequency Resistance) is determined. In particular, the frequency of the measurement current can be varied. Accordingly, impedance spectroscopy can be performed on the fuel cell stack.

[0016] The real part of the impedance of the fuel cell stack, i.e., the ohmic resistance of the fuel cell stack, is proportional to the moisture content of the fuel cell membranes. Accordingly, the real part of the impedance can provide information about the moisture content of the fuel cell membranes. Thus, the diagnostic method can be used to detect, in particular, drying out of the fuel cell membranes.

[0017] Alternatively, the fuel cell system response can also be a voltage or a current.

[0018] The working current is in particular the current which is present and / or applied to the electrical terminals of the fuel cell stack during operation of the fuel cell stack.

[0019] Alternatively, instead of the working current and the measuring current, a working voltage and a measuring voltage can be used.

[0020] The reference contains, in particular, predetermined values ​​that are compared with the fuel cell system response. Depending on the outcome of the comparison of the fuel cell system response with the reference, damage to the at least one fuel cell membrane is detected, or it is detected that no damage to the at least one fuel cell membrane is present.

[0021] The fuel cell membrane of a fuel cell separates the anode from the cathode. Specifically, the fuel cell membrane is a REM (proton exchange membrane).

[0022] Damage to the fuel cell membrane occurs when the fuel cell membrane does not function as intended. Various types of damage can lead to damage to the fuel cell membrane. In particular, the types of damage that can occur include drying out of the fuel cell membrane, holes in the fuel cell membrane, and / or poisoning of the fuel cell membrane. The fuel cell system can have multiple fuel cell stacks. In this case, the diagnostic procedure can be performed on one fuel cell stack. Alternatively, the diagnostic procedure can also be performed on multiple fuel cell stacks of the fuel cell system.

[0023] The measuring current can be applied to the existing connections of the fuel cell stack for the working current.

[0024] According to one embodiment of the diagnostic method, the measurement current is only temporarily superimposed. "Temporarily superimposed" means that the superimposition does not occur permanently. For example, a specific event is required and / or a parameter condition must be met for the superimposition of the measurement current to be triggered. A specific event can be, for example, the expiration of a period of time. The parameter can be a parameter of the fuel cell system, such as the efficiency of the fuel cell system, the output voltage of the fuel cell system, and the pressure situation within the fuel cell system.

[0025] The parameters include, for example, the efficiency of the fuel cell system, the output voltage of the fuel cell system, and the pressure situation within the fuel cell system. If such a parameter reaches a value (i.e., fulfills a predetermined condition) that indicates that a more detailed inspection of the fuel cell system is necessary, then the step of superimposing the measurement current and the subsequent steps are performed.

[0026] The parameter can also be time. Only when a certain time has elapsed is the step of superimposing the measuring current performed. The predetermined condition can then be a certain period of time that must elapse.

[0027] According to a further embodiment of the diagnostic method, the reference is determined for different frequencies of the measuring current. The reference is therefore determined such that it has different values ​​for different frequencies of the measuring current. For example, a frequency range of possible measuring currents is traversed. In this case, the fuel cell system response of a fuel cell stack with a fuel cell membrane with known damage is measured, e.g. on a test bench, at several frequencies from the frequency range. From this result, a reference can be determined which is dependent on the frequency. The reference is thus determined for different frequencies which the measuring current can have. Alternatively, theoretical calculations can be carried out to calculate the reference for different possible frequencies of the measuring current.

[0028] According to a further embodiment of the diagnostic method, the reference is determined for various types of damage to the at least one fuel cell membrane. The measurements to determine the reference are performed on fuel cell stacks with different fuel cell membranes, each exhibiting a different type of damage, for example, drying out of the fuel cell membrane, holes in the fuel cell membrane, or poisoning of the fuel cell membrane. The result determined here can then be used to determine the reference. In particular, the frequency can be scanned for each fuel cell stack with a different fuel cell membrane, so that an information matrix can be created that combines information about the type of damage and the respective frequency.Using this information matrix, a reference can be determined, which then forms a reference matrix of damage type and frequency.

[0029] According to a further embodiment of the diagnostic method, the reference contains information at different frequencies and for different types of damage. By comparing the fuel cell system response with the reference, a specific type of damage to the at least one fuel cell membrane can be identified. The reference represents a matrix. The matrix contains values ​​at different frequencies and for different types of damage. If the diagnosis is carried out with a specific frequency or with multiple frequencies of a measuring current, the type of damage can be identified by comparing the fuel cell system response or the fuel cell system responses with the reference, i.e. with the reference in the form of a matrix. According to a further embodiment of the diagnostic method, aging of the at least one fuel cell membrane is taken into account in the reference.This allows for the fact that abnormalities in the fuel cell system response for a specific damage at a specific frequency shift in frequency with the aging of the fuel cell membrane. This means that the frequencies where the abnormalities in the fuel cell system response occur shift over time due to the aging of the fuel cell membrane. This then also results in frequency shifts in the reference thresholds.

[0030] According to a further embodiment of the diagnostic method, a plausibility check is performed to determine whether damage to the at least one fuel cell membrane is plausible after an elapsed operating time. Advantageously, the plausibility check can be used to perform a further analysis. The elapsed operating time is the total time the fuel cell stack has been in operation. Alternatively, it is not only possible to determine whether it is plausible that damage has occurred, but also to perform a plausibility check for a specific type of damage.

[0031] The reference can take into account the entire operating life of the fuel cell stack. The fuel cell system response to the measurement current can change with the aging of the fuel cell stack. Damage can plausibly occur at any time.

[0032] According to a further embodiment of the diagnostic method, the measuring current is an alternating current, wherein a frequency of the measuring current is in the range from 1000 Hz to 10000 Hz, and in particular in the range from 1000 Hz to 5000 Hz. In particular, the frequency of the measuring current can be in the high-frequency range.

[0033] According to a further embodiment of the diagnostic method, an output is provided indicating that damage to the at least one fuel cell membrane is present if a comparison of the fuel cell system response with the reference leads to this result, or an output is provided indicating that no damage to the at least one fuel cell membrane is present if a comparison of the fuel cell system response with the reference leads to this result. In particular, the output can be provided acoustically, visually, or as a data stream.

[0034] Furthermore, the present invention relates to a computer program product comprising instructions which, when executed by a computer, cause the computer to perform the steps of a diagnostic method according to the invention. Thus, a computer program product according to the invention also provides the same advantages as those explained in detail with reference to a diagnostic method according to the invention.

[0035] Furthermore, a diagnostic device for detecting damage to at least one fuel cell membrane of a fuel cell stack of a fuel cell system is provided. The diagnostic device comprises a working current operating module for operating the fuel cell stack with a working current, wherein the working current is applied to the fuel cell stack and / or tapped at the fuel cell stack, a measurement current superposition module for superimposing a measurement current on the working current at the fuel cell stack, a determination module for determining a fuel cell system response at the fuel cell stack based on the superimposed measurement current, and a comparison module for comparing the fuel cell system response with a reference in order to detect damage to the at least one fuel cell membrane of the fuel cell stack.

[0036] The working current operating module, the measuring current superposition module, the determination module and / or the comparison module are designed to carry out the diagnostic method according to the invention.

[0037] The bias current operating module, the measurement current superposition module, the determination module, and the comparison module can be configured as separate components. Alternatively, two or more of the aforementioned modules can be configured as a single component. In particular, the bias current operating module and the measurement current superposition module can be configured as a single component. Further possible implementations of the invention also include combinations of features not explicitly mentioned above or described below with respect to the exemplary embodiments. Those skilled in the art will also add individual aspects as improvements or additions to the respective basic form of the invention.

[0038] Further advantages, features, and details of the invention will become apparent from the following description, in which exemplary embodiments are described in detail with reference to the drawings. They show:

[0039] Fig. 1 is a schematic view of a fuel cell system with a fuel cell stack and a diagnostic device; and

[0040] Fig. 2 is a diagram showing the steps of a diagnostic procedure.

[0041] Fig. 1 shows a schematic view of a fuel cell system 100 with a fuel cell stack 110 and a diagnostic device 10. The fuel cell stack 110 has a plurality of fuel cells, each with an anode 112, a cathode 114, and a fuel cell membrane 116. The respective fuel cell membrane 116 separates the respective anode 112 and the respective cathode 114. Electrical connections 118 are located at the ends of the fuel cell stack 110. The working current and / or the measuring current are supplied via the electrical connections 118. The electrical connections 118 are each in electrical contact with a bipolar plate 120. The bipolar plates 120 serve to conduct the electrical current. Furthermore, the sections for supplying anode supply gas, for discharging anode exhaust gas, for supplying cathode supply gas and for discharging cathode exhaust gas are not shown in Fig. 1.

[0042] The diagnostic device 10 has a working current operating module 20, a measuring current superposition module 30, a determination module 40, and a comparison module 50. The diagnostic device 10 serves to detect damage to at least one fuel cell membrane 116 of the fuel cell stack 110. The working current operating module 20 is electrically connected to the electrical connections 118 of the fuel cell stack 110. The working current operating module 20 serves to operate the fuel cell stack 110 with a working current, wherein the working current is applied to the fuel cell stack 110 via the electrical connections 118 and / or tapped off from the fuel cell stack 110 via the electrical connections 118. The measuring current superposition module 30 is also electrically connected to the electrical connections 118 of the fuel cell stack 110.By means of the measurement current superposition module 30, the operating current at the fuel cell stack 110 can be superimposed with a measurement current. Furthermore, the determination module 40 is also electrically connected to the electrical connections 118 of the fuel cell stack 110 in order to tap a fuel cell system response at the electrical connections 118 of the fuel cell stack 110. By means of the determination module 40, the fuel cell system response at the fuel cell stack 110 can be determined based on the superimposed measurement current. The comparison module 50 is connected to the determination module 40 in order to receive the fuel cell system response from the determination module 40. The comparison module 50 serves to compare the fuel cell system response with a reference in order to detect damage to the at least one fuel cell membrane 116 of the fuel cell stack 110.

[0043] Fig. 2 shows a diagram with the steps of a diagnostic method. The diagnostic method serves to detect damage to at least one fuel cell membrane 116 of a fuel cell stack 110 of a fuel cell system 100. The diagnostic method comprises the following steps:

[0044] In a first step S1, the fuel cell stack 110 is operated with a working current. For this purpose, the working current is applied to the fuel cell stack 110 and / or tapped from the fuel cell stack 110.

[0045] In a second step S2, the working current at the fuel cell stack 110 is superimposed with a measuring current.

[0046] In a third step S3, a fuel cell system response at the fuel cell stack 110 is determined based on the superimposed measurement current.

[0047] In a fourth step S4, the fuel cell system response is compared with a reference in order to detect damage to the at least one fuel cell membrane 116 of the fuel cell stack 110. The reference represents, in particular, a condition. Such a condition can be that the fuel cell system response lies within a range specified by the reference. Alternatively, the condition can also be that the fuel cell system response is greater or smaller than the reference. If such a condition is met, then an output is provided, for example, that damage to at least one fuel cell membrane 116 of the fuel cell stack 110 is present. Otherwise, an output is provided, for example, that no damage to a fuel cell membrane 116 of the fuel cell stack 110 is present. The reference can be determined by measurements in a test bench and / or calculated using theoretical considerations.

[0048] In particular, the measuring current is not constantly superimposed, but only when a certain condition or event has occurred, or, for example, a period of time has elapsed.

[0049] The measurement current can be an alternating current. The frequency of the measurement current is preferably in the high-frequency range. The fuel cell system response is preferably an impedance, i.e., an alternating current resistance, of the fuel cell stack 110. The real part of the impedance of the fuel cell stack 110, i.e., the ohmic resistance of the fuel cell stack 110, is proportional to the humidity of the fuel cell membranes 116. This makes the diagnostic method particularly suitable for detecting drying out of the fuel cell membranes 116.

[0050] The reference can be created in the form of a matrix. For this purpose, the reference is created for various possible measurement currents. Secondly, the reference is created using fuel cell stacks 110, each with different fuel cell membranes 116, on a test bench, whereby the fuel cell membranes 116 all exhibit a known type of damage. Overall, a reference is obtained for various types of damage and, for each type of damage, for different frequencies. A type of damage is, for example, drying out of the fuel cell membrane 116, holes in the fuel cell membrane 116, or poisoning of the fuel cell membrane 116. Once such a reference has been created in the form of a matrix, a specific type of damage can be deduced during the diagnostic process by comparing the fuel cell system response with the reference.It is also possible to run the diagnostic procedure with a specific measurement current frequency if a particular type of damage appears likely. The diagnostic procedure can then be used to verify whether this type of damage is actually present, because a specific fuel cell system response is expected for this type of damage and this measurement current frequency. In particular, a particular type of damage appears likely if a preliminary diagnosis indicates this specific type of damage.

[0051] List of reference symbols

[0052] 10 Diagnostic device

[0053] 20 Working current operating module

[0054] 30 measuring current superposition module

[0055] 40 Determination module

[0056] 50 Comparison module

[0057] 100 fuel cell system

[0058] 1 10 fuel cell stacks

[0059] 1 12 Anode

[0060] 114 Cathode

[0061] 1 16 Fuel cell membrane

[0062] 1 18 electrical connection

[0063] 120 bipolar plate

[0064] S1 first step

[0065] S2 second step

[0066] S3 third step

[0067] S4 fourth step

Claims

Patent claims 1 . Diagnostic method for detecting damage to at least one fuel cell membrane (116) of a fuel cell stack (110) of a fuel cell system (100), characterized by the steps: - Determining a reference by measurements and / or theoretical calculations, - operating the fuel cell stack (110) with a working current, wherein the working current is applied to the fuel cell stack (110) and / or tapped off from the fuel cell stack (110), - superimposing the working current on the fuel cell stack (110) with a measuring current, - determining a fuel cell system response at the fuel cell stack (110) based on the superimposed measuring current, and - comparing the fuel cell system response with the reference in order to detect damage to the at least one fuel cell membrane (116) of the fuel cell stack (110), characterized in that the diagnostic method has a preceding step in which a parameter of the fuel cell system (100) is monitored, and only if a predetermined condition is met, the step of superimposing the measuring current and the subsequent steps are carried out, wherein the diagnostic method is carried out with a specific frequency of the measuring current if a specific type of damage appears likely, wherein the specific type of damage appears likely if a preliminary diagnosis indicates this specific type of damage.

2. Diagnostic method according to claim 1, characterized in that the measuring current is only temporarily superimposed.

3. Diagnostic method according to one of the preceding claims, characterized in that the reference is determined for different frequencies of the measuring current.

4. Diagnostic method according to one of the preceding claims, characterized in that the reference is determined for different types of damage to the at least one fuel cell membrane.

5. Diagnostic method according to one of the preceding claims, characterized in that the reference contains information at different frequencies and at different types of damage, and by comparing the fuel cell system response with the reference, a specific type of damage to the at least one fuel cell membrane (116) can be recognized.

6. Diagnostic method according to one of the preceding claims, characterized in that an aging of the at least one fuel cell membrane (1 16) is taken into account in the reference.

7. Diagnostic method according to one of the preceding claims, characterized in that a plausibility check is carried out as to whether the damage to the at least one fuel cell membrane (116) is plausible after an elapsed operating time.

8. Diagnostic method according to one of the preceding claims, characterized in that the measuring current is an alternating current, wherein a frequency of the measuring current is in the range from 1000 Hz to 10000 Hz and in particular in the range from 1000 Hz to 5000 Hz.

9. Diagnostic method according to one of the preceding claims, characterized in that an output is provided which indicates that the damage to the at least one fuel cell membrane (1 16) is present if a comparison of the fuel cell system response with the reference leads to this result, or that an output is provided which indicates that no damage to the at least one fuel cell membrane (1 16) is present if a comparison of the fuel cell system response with the reference leads to this result.

10. A computer program product comprising instructions which, when executed by a computer, cause the computer to carry out the steps of a diagnostic method having features of any of claims 1 to 9. 1 1. Diagnostic device (10) for detecting damage to at least one fuel cell membrane (116) of a fuel cell stack (110) of a fuel cell system (100), characterized by a working current operating module (20) for operating the fuel cell stack (110) with a working current, wherein the working current is applied to the fuel cell stack (110) and / or tapped off at the fuel cell stack (110), a measuring current superposition module (30) for superimposing a measuring current on the working current at the fuel cell stack (110), a determination module (40) for determining a fuel cell system response at the fuel cell stack (110) based on the superimposed measuring current, and a comparison module (50) for comparing the fuel cell system response with a reference in order to detect damage to the at least one fuel cell membrane (116) of the fuel cell stack (110), wherein the Working current operating module (20),the measuring current superposition module (30), the determination module (40) and / or the comparison module (50) are designed to carry out the diagnostic method according to one of claims 1 to 9.,

Images