Diagnostic method, diagnostic system and computer program product for diagnosing state of fuel cell system
Through the diagnostic method of current guidance, constant current is loaded and fuel cell stack voltage is measured, which solves the problems of low efficiency and high data complexity of existing voltage guidance methods, and achieves fast and accurate fuel cell system status diagnosis and characteristic value output.
Patent Information
- Application Number
- CN202380069743.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2022-07-29
- Filing Date
- 2023-06-23
- Publication Date
- 2025-05-13
AI Technical Summary
When diagnosing the state of the fuel cell system, the existing voltage-guided diagnostic methods have problems of low efficiency and high data complexity, making it difficult to quickly and accurately obtain the status characteristic values of the fuel cell system.
The current-guided diagnostic method is used to load a constant current on the fuel cell stack, measure the voltage of each fuel cell, and obtain the quantized characteristic values according to the voltage change process, including the electrochemical active area, short-circuit resistance, etc.
It realizes rapid and accurate diagnosis of the fuel cell system status, improves diagnostic efficiency, simplifies data processing, and can effectively output key characteristic values of the fuel cell system.
Smart Images
Figure CN119998968A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to a diagnostic method, a calculation unit and a computer program product for diagnosing the state of a fuel cell system according to the appended claims. Background Art
[0002] Voltage-based diagnostic methods, such as cyclic voltammetry, are often used to diagnose the state of a fuel cell system. Here, each individual fuel cell of the fuel cell stack is repeatedly exposed to a voltage triangle in order to determine characteristic values, in particular the active platinum area, i.e. the electrochemically active area of the individual fuel cells. Summary of the invention
[0003] Within the scope of the proposed invention, a diagnostic method, a diagnostic system and a computer program product are proposed. Further features and details of the invention are derived from the subsequent dependent claims, the description and the drawings. Features and details described in conjunction with the diagnostic method according to the invention are of course also applicable in conjunction with the diagnostic system according to the invention or the computer program product according to the invention, and vice versa, respectively, so that the disclosure of the individual inventive aspects always refers to one another or can refer to one another.
[0004] The proposed invention serves in particular to provide a possibility for ascertaining the state of a fuel cell system.
[0005] Therefore, according to the first aspect of the proposed invention, a diagnostic method for diagnosing the state of a fuel cell system is proposed. The diagnostic method comprises: applying a constant current from a current source to a fuel cell stack of the fuel cell system; measuring the voltage applied to each fuel cell of the fuel cell stack; obtaining a characteristic value for quantifying the state of the fuel cell system based on the measured voltage; and outputting the characteristic value on an output unit, wherein the voltage on each fuel cell of the fuel cell stack is measured simultaneously.
[0006] In the context of the proposed invention, a characteristic value is understood to be a value on a scale or a numerical value.
[0007] The proposed diagnostic method is based on a current-guided method. This means that a predetermined current is applied as an independent variable to the fuel cell stack or to the individual fuel cells of the fuel cell stack in order to determine and evaluate the change in the voltage applied to the individual fuel cells in response to the current loading as a dependent variable, i.e., to determine a characteristic value. Accordingly, a characteristic value that quantifies the fuel cell state or the fuel cell system state is determined based on the voltage change process during current loading and during subsequent self-discharge.
[0008] The determined characteristic values are output on an output unit, for example on a display and / or a memory, ie, are provided or stored.
[0009] To measure the voltage across the individual fuel cells of the fuel cell system, a so-called “cell voltage monitoring system” of the fuel cell system or an external voltage measuring device can be used.
[0010] From the respective voltages determined, the respective characteristic values can be derived with the aid of equation (1) by, for example, taking into account the voltage at 400 mV (=U lb ) and 500mV(=U ub ) is fitted to the measured data by equation (1). Only within this range will no electrochemical reaction occur on the catalyst.
[0011]
[0012] Here, U(t) represents the measured voltage at time t, I Q Represents the loaded current, R SC Indicates short-circuit resistance, t lb Indicates that U is reached during charging lb Time, C dl represents the double layer capacitance and I H2 Indicates the discharge current that is independent of voltage.
[0013] During self-discharge, no current flows through the short-circuit resistor, causing the double-layer capacitor to be ub To U lb Only I H2 Discharge:
[0014]
[0015] With the help of double layer capacitance, U ub and U lb This discharge rate between (2) can eliminate the double layer capacitance from equation (1):
[0016]
[0017] Therefore, only during charging must the variable I H2 and R sc Fit this equation to the voltage U lb and U ub At the measuring points between.
[0018] When applying current, provision can be made to use a current which corresponds to between 2 and 4 times the hydrogen permeation current of the corresponding fuel cell system or which results in a charging of the fuel cell stack within a period of between 20 and 50 seconds.
[0019] It may be provided that the cathode of the fuel cell system is used as working electrode and is operated in a nitrogen atmosphere, and that the anode of the fuel cell system is used as counter electrode and is operated in a hydrogen atmosphere.
[0020] Alternatively, it may be provided that the anode of the fuel cell system is used as working electrode and is operated in a nitrogen atmosphere, and that the cathode of the fuel cell system is used as counter electrode and is operated in a hydrogen atmosphere.
[0021] Since nitrogen is an inert gas for fuel cells, the corresponding electrode operated under a nitrogen atmosphere can be used as a working electrode.
[0022] Furthermore, it may be provided that at least one characteristic number from the following list of characteristic numbers is determined as the characteristic value: electrochemically active area, hydrogen membrane leakage, double layer capacitance, catalyst capacitance, roughness factor and membrane short-circuit resistance.
[0023] The characteristic value can be output as a value obtained in a digital manner, or can be assigned to a scale value, such as a color model and / or a value on an ordinal scale (Ordinal Scale) by means of an assignment pattern and then output. Of course, the characteristic value can include a plurality of sub-characteristic values, which respectively include characteristic numbers or are based on respective characteristic numbers.
[0024] Furthermore, it may be provided that the fuel cell system is discharged by self-discharge after being charged with current.
[0025] In order to be able to detect the electrochemical properties of individual fuel cells, self-discharge has proven to be particularly suitable, since in this type of discharge the voltage drops slowly, ie over a period of several seconds, which is attributable solely to the physical properties of the fuel cell, as given in equation (2).
[0026] The voltage measurement provided according to the invention can be carried out in particular during a discharge process of the fuel cell stack, ie on the falling branch of the voltage curve.
[0027] Furthermore, it can be provided that the fuel cell stack is charged with current in a single charging cycle.
[0028] In contrast to the voltage-based method, the proposed diagnostic method can be performed with a single charging cycle. This means that the fuel cell is charged once with a predefined current value to a predefined maximum voltage value and then self-discharged. Each fuel cell should have reached a voltage of at least 500 mV (U ub ) so that analytical evaluation can be performed.
[0029] Furthermore, it can be provided that when determining the characteristic value the short-circuit resistance of the individual fuel cells of the fuel cell stack is determined from the rising region of the voltage curve when the fuel cell stack is loaded with current, as given in equation (3).
[0030] The short-circuit resistance of the individual fuel cells can be determined quickly and easily using so-called “fitting functions”.
[0031] Furthermore, it can be provided that when determining the characteristic value, the voltage-independent discharge current (I H2 ), which corresponds to the CV / LSV method describing the transfer of molecular H2 through the fuel cell membrane.
[0032] The voltage-independent discharge current of the individual fuel cells can also be determined quickly and easily using the "fitting function". In the self-discharge range, the voltage-independent discharge current at U ub and U lb The discharge rate between the two can also be used to determine the double layer capacitance C dl .
[0033] Due to the simple relationship in equation (2), the double layer capacitance C in equation (1) can be replaced by the known variable dl , which leads to equation (3). Therefore, the fitting algorithm only has to determine two unknown quantities I simultaneously H2 and R sc .
[0034] At this time, in order to calculate the roughness factor of desorption, the variables determined above are used to examine the lb The following charging range.
[0035] Hydrogen desorption can be viewed as a capacitor in parallel with the double layer, the charge of which does not increase linearly or remain constant with voltage.
[0036] The following relationships apply:
[0037] Two capacitors C dl and C Pt By the maximum 400mV (U lb ) is charged with a net charging current of:
[0038]
[0039] Solution
[0040]
[0041] From the capacitor formula we get:
[0042]
[0043] Using the above equation results in:
[0044]
[0045] From "Charging Start" to U lb (400mV) time period To perform "integration":
[0046]
[0047] The time t0 describes the point in time at which the voltage level U0 is exceeded and the evaluation begins (approximately or slightly above OCV).
[0048] Calculation of roughness factor for H2 desorption
[0049]
[0050]
[0051] Calculation of roughness factor for H2 desorption
[0052]
[0053]
[0054] According to a second aspect, the proposed invention relates to a diagnostic system. The proposed diagnostic system comprises a computing unit which is configured to implement a possible configuration of the proposed diagnostic method.
[0055] In the context of the proposed invention, a computing unit is understood to be a computer, a processor, a control device or any other programmable circuit. The computing unit can be, in particular, a control device of the respective fuel cell system.
[0056] According to a third aspect, the proposed invention relates to a computer program product having program code means which, when the computer program product is executed on a computer, configure the computer into possible configurations for carrying out the proposed diagnostic method.
[0057] The proposed computer program product may be, for example, material available for downloading on a server or a data carrier, such as a CD-ROM or a USB flash drive.
[0058] Further advantages, features and details of the invention can be derived 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 claims and in the description may be essential to the invention individually or in any combination. BRIEF DESCRIPTION OF THE DRAWINGS
[0059] The accompanying drawings show:
[0060] Figure 1 Schematic diagram of one possible configuration of the proposed diagnostic method,
[0061] Figure 2 according to Figure 1 Detailed diagram of the diagnostic method,
[0062] Figure 3 One possible configuration of the proposed diagnostic system. DETAILED DESCRIPTION
[0063] exist Figure 1 A diagnostic method 100 for diagnosing a fuel cell system status is shown in FIG.
[0064] The diagnostic method 100 includes: a loading step 101, in which a constant current from a current source is loaded to a fuel cell stack of a fuel cell system; a measuring step 103, in which a voltage applied to each fuel cell of the fuel cell stack is measured; an obtaining step 105, in which a characteristic value quantifying a state of the fuel cell system is obtained based on the measured voltage; and an output step 107, in which the characteristic value is output on an output unit, wherein in the measuring step 103, the voltage on each fuel cell of the fuel cell stack, for example, on each fuel cell coupled to a CVM system or on all fuel cells, is measured simultaneously.
[0065] exist Figure 2 2 shows a graph 200 which extends over time on its abscissa and over a voltage measured at the fuel cell on its ordinate.
[0066] Since it has been experimentally determined that the short-circuit resistance Rsc in the falling branch of the voltage curve 201 or when the fuel cell stack is discharged is more than 2000 times greater than when the fuel cell stack is charged, the voltage-independent discharge current I H2 The double layer capacitance C is calculated from the measured voltage in the falling branch, in particular between 500 mV and 400 mV. dl .
[0067] With the help of the “fitting function”, the discharge current I independent of the voltage can be found based on the measured voltage curve 201. H2 and short-circuit resistor R sc Here, according to the fitting function, I H2 Over the extended 600mV to 300mV voltage range (U ub To U lb ) to determine the double layer capacitance C dl , as indicated by arrow 203, while the measured voltage curve 201 in the range between 300 mV and 0 mV is affected by both the double layer capacitance C dl Also affected by the catalyst layer capacitance C H2Pt , as indicated by arrow 205 .
[0068] Since the catalyst layer or its catalyst layer capacitance C H2Pt Only by I H2 discharge, so the charge Q of the catalyst layer can be directly determined from this Pt From this charge, the roughness factor rf for hydrogen desorption can be inferred des The roughness factor can be used to infer the electrochemically active area for hydrogen desorption.
[0069] exist Figure 3 The diagnostic system 300 is shown in FIG. The diagnostic system 300 comprises a computing unit 301 in the form of a control device and an optional constant current source 303, the control device being configured to execute a Figure 1 Diagnostic methods 100.
[0070] The computing unit 301 includes an interface 305 for communication coupling and / or electrical coupling with a battery voltage monitoring system.
Claims
1. A diagnostic method (100) for diagnosing a fuel cell system state, in, The diagnostic method (100) comprises: - loading (101) the fuel cell stack of the fuel cell system with a constant current from a current source (303), - measuring (103) the voltage applied to each fuel cell of the fuel cell stack, - determining (105) a characteristic value quantifying the state of the fuel cell system based on the measured voltage, - outputting (107) the characteristic value at an output unit, The voltage on each fuel cell of the fuel cell stack is measured simultaneously (103).
2. The diagnostic method (100) according to claim 1, It is characterized in that The cathode of the fuel cell system is used as a working electrode and operated in a nitrogen atmosphere, and The fuel cell system uses the anode as a counter electrode and operates in a hydrogen atmosphere or a hydrogen / nitrogen atmosphere.
3. The diagnostic method (100) according to claim 1, It is characterized in that The anode of the fuel cell system is used as a working electrode and operated in a nitrogen atmosphere, and The cathode of the fuel cell system is used as a counter electrode and is operated in a hydrogen atmosphere.
4. The diagnostic method (100) according to any one of the preceding claims, It is characterized in that At least one characteristic number from the following characteristic number list is obtained as a characteristic value: electrochemical active area, hydrogen membrane leakage, double layer capacitance, catalyst capacitance, roughness factor and membrane short circuit resistance.
5. The diagnostic method (100) according to any one of the preceding claims, It is characterized in that After being charged with current, the fuel cell system is discharged by self-discharge.
6. The diagnostic method (100) according to any one of the preceding claims, It is characterized in that The current loading of the fuel cell stack takes place in a single charging cycle.
7. The diagnostic method (100) according to any one of the preceding claims, It is characterized in that When determining the characteristic value, the short-circuit resistance of the individual fuel cells of the fuel cell stack is determined from the rising region of the current curve when the fuel cell stack is loaded with current.
8. The diagnostic method (100) according to any one of the preceding claims, It is characterized in that When determining the characteristic value, the voltage-independent discharge current of the individual fuel cells of the fuel cell stack is determined from the rising region of the current curve when the fuel cell stack is loaded with current.
9. A diagnostic system (300) for diagnosing a fuel cell system status, wherein: The diagnostic system (300) comprises a computing unit (301) configured to execute the diagnostic method (100) according to any one of claims 1 to 8.
10. A computer program product having program code means which, when executed on a computer, configure the computer to carry out the diagnostic method (100) according to any one of claims 1 to 8.