Method for operating a fuel cell system

Abstract

The invention relates to a method for operating a fuel cell system (100). The method has the steps of determining a need to check a dynamic transmission behavior of the fuel cell system (100); setting a first trigger if a need to check the dynamic transmission behavior has been determined; planning and preparing a check of the dynamic transmission behavior of the fuel cell system (100); setting a second trigger if the planning and preparation of the checking of the dynamic transmission behavior of the fuel cell system (100) is completed; checking the dynamic transmission behavior of the fuel cell system (100) if the second trigger has been set, the step of checking the dynamic transmission behavior of the fuel cell system (100) involving the process of exciting the fuel cell system (100) using different frequencies and determining a response of the fuel cell system (100); evaluating the process of checking the dynamic transmission behavior of the fuel cell system (100); and carrying out at least one specified measure on the basis of the result of the evaluation of the process of checking the dynamic transmission behavior of the fuel cell system (100).

Description

[0001] R.416589

[0002] - 1 -

[0003] Description

[0004] title

[0005] Method for operating a fuel cell system

[0006] State of the art

[0007] Hydrogen-based fuel cell systems are considered a mobility concept of the future, as they emit only water as exhaust gas and enable rapid refueling. Fuel cell systems require oxygen, typically from the ambient air in vehicles, and hydrogen for the chemical reaction. The only reaction product is water, which is released in varying proportions as a gas and a liquid. The water is produced at the catalyst layer on one side of the cathode and transported by a gas diffusion layer (GDL) towards the respective gas flow channels.

[0008] The operation of a fuel cell system is a complex interplay between the fuel cell stacks and the involved subsystems or balance of plant (BoP) systems: air system for supplying the cathode paths, anode system for supplying the anode and coupling to the H2 tank system, coolant system for temperature control of the stacks and other components, electrical system for connecting the stacks and actuators to the vehicle's electrical system, and control system for regulation / control, including sensors. Heavy-duty applications, in particular, require very long service lives (>10,000 operating hours). During this extended operating period, significant aging occurs in various components. The aging of a fuel cell stack is multidimensional, meaning that a multitude of different processes lead to a deterioration of the state of health (SOH).This includes, among other things, the loss of electrochemically active area (ECSA loss), erosion of membrane material (membrane thinning) and the deterioration of water- R.416589.

[0009] - 2 - Transport properties (loss of hydrophobicity, especially in GDL). A particular challenge is the change in system behavior due to component degradation.

[0010] Despite the advantages of state-of-the-art measures, such as diagnostics and adaptations, these still offer potential for improvement. Many state-of-the-art measures, such as diagnostics and adaptations, consider the system only based on steady-state operating conditions and do not address dynamic operation under changing conditions.

[0011] Disclosure of the invention

[0012] Within the scope of the present invention, a method for operating a fuel cell system, a fuel cell system, a motor vehicle, and a computer program product are therefore proposed, which largely avoid the disadvantages of known methods for operating a fuel cell system, a fuel cell system, a motor vehicle, and a computer program product, and which in particular improve or optimize the dynamic operation of a fuel cell system with the complex interaction of the subsystems, in particular the air system, anode system, coolant system, control system, electrical system, and stacks.In particular, the method according to the invention is intended to increase the robustness of the system, including the robustness of the control loops, to perform adaptations over the lifetime with regard to system switching / system adjustments / boundary conditions, thereby also ensuring functionality and minimizing degradation, to perform improved diagnostics of the controlled systems and the control loops, to enable a comparison of the stacks with regard to dynamic performance (ranking), to measure amplitude spectra and frequency response behavior for both the controlled system and the controlled system during operation of a fuel cell system (single- or multi-stack system) (in the case of multi-stack systems, preferably with opposing excitation of the individual fuel cell systems to mutually neutralize power amplitudes / battery to compensate for power deviations in multi-stack systems or to equalize power amplitudes in single-stack systems), and to take appropriate measures based on this data. R.416589.

[0013] - 3 -

[0014] A method according to the invention for operating a fuel cell system, comprising the steps, wherein individual or all steps can be repeated:

[0015] Determining the need to verify the dynamic transfer behavior of the fuel cell system,

[0016] Setting an initial trigger if a need to check the dynamic transfer behavior has been identified,

[0017] Planning and preparing a review of the dynamic transfer behavior of the fuel cell system,

[0018] Setting a second trigger if the planning and preparation of the verification of the dynamic transfer behavior of the fuel cell system is completed,

[0019] Performing the verification of the dynamic transfer behavior of the fuel cell system if the second trigger has been set, wherein the verification of the dynamic transfer behavior of the fuel cell system includes exciting the fuel cell system with different frequencies and determining a response of the fuel cell system,

[0020] Evaluating the verification of the dynamic transfer behavior of the fuel cell system, and

[0021] Taking at least one predetermined action depending on a result of the evaluation of the review of the dynamic transfer behavior of the fuel cell system.

[0022] By determining the need to verify the dynamic transfer behavior of the fuel cell system, the first trigger is only set if such a need exists, so that the method is only initiated when required. The method according to the invention can be triggered from and carried out during operation. If a need to verify the dynamic transfer behavior is identified, the subsequent steps of the method are triggered by the first trigger. The first trigger requests the execution of the tests. However, it is very advantageous to prepare and predictively schedule the execution of the tests beforehand in order to avoid forced impairments of R.416589.

[0023] - 4 -

[0024] The first trigger is to avoid problems with the vehicle's drive system or its entire energy system, including testing one or more fuel cell systems. The second trigger initiates the actual test of the fuel cell system's dynamic transfer behavior. This second trigger initiates the test of the dynamic transfer behavior as soon as the preparation is complete and the scheduled time has arrived. During the test, the fuel cell system is excited at various frequencies, and the system response is determined or measured. The dynamic system behavior of the fuel cell system or the respective (sub)systems is determined from the test(s). At low frequencies, both signals—the applied signal and the measured response signal—follow the respective target value without any phase shift.At higher frequencies, the air system in particular exhibits low-pass filtering behavior with corresponding attenuation and phase shift. Based on the data, potential aging, for example of the compressor, can be diagnosed, which would lead to increased attenuation and a phase shift that begins even at lower frequencies. Appropriate measures are then derived and evaluated from the results.

[0025] The method according to the invention is cost-neutral, as it is only carried out by means of appropriate software or software adaptation. The method is applicable to all hardware configurations / topologies. The method can be executed during operation. The method is imperceptible to the driver or driving requirements, i.e., performance-neutral. It allows for standardization (standard test) and thus general and very good comparability across different vehicles, across multiple systems within a vehicle, for different use cases and boundary conditions / operating conditions, as well as for different aging states. This also makes fleet-wide evaluations possible, as it has a broad application range. The method does not require a workshop visit for diagnostics and is therefore customer-friendly. Predictive maintenance is possible with the method. The method allows for an increase in availability.Reliability of fuel cell systems and the prevention of fuel cell vehicle breakdowns. The procedure allows for R.416589.

[0026] - 5 - Vehicle-specific solution without additional development effort. Furthermore, the method allows for a stack-specific or system-specific solution (in the case of multi-stack systems). Additionally, the method allows for automatic adaptation when parts are replaced.

[0027] Determining the need to review the dynamic transfer behavior of the fuel cell system can involve evaluating information about the fuel cell system. This involves assessing various data points (current, historical, predictive). This allows for a reliable determination of whether a review is actually necessary.

[0028] Information concerning the fuel cell system from at least one source can be provided both within and / or outside the fuel cell system. This allows for the evaluation of various data points (current, historical, predictive) originating from diverse sources, such as measurement data within the vehicle or from external sources, model calculations in control units and / or cloud / server data, diagnostic data, maintenance / workshop data, and many others. This enables a particularly reliable determination of whether an inspection is even necessary.

[0029] The need to verify the dynamic transfer behavior of the fuel cell system can be determined if the information concerning the fuel cell system indicates at least one parameter selected from the group consisting of: aging of at least one component of the fuel cell system, adaptation of an operating strategy of the fuel cell system and / or a control loop of the fuel cell system, exceeding a predetermined threshold of an asymmetry of stacks of the fuel cell system, replacement or repair of at least one component of the fuel cell system, a fault in the operation of the fuel cell system, a change in an application case of the fuel cell system and / or a dynamic requirement for system operation of the fuel cell system, a change in a boundary condition and / or environmental condition and / or an operating range of the fuel cell system.These parameters clearly indicate the need for verification. R.416589.

[0030] - 6 -

[0031] The process can revert to or continue normal system operation if the first trigger is not set. If the first trigger is not set, system operation continues initially without a check, during which further investigations are conducted to determine whether a check is necessary. These investigations can be continuous or periodic, and can be time-triggered or event-triggered. Preferably, a complete check is performed when individual triggers are set according to the parameters mentioned above.

[0032] Planning and preparing a review of the dynamic transfer behavior of the fuel cell system can include considering data regarding the driving trajectory and / or driving task of a vehicle equipped with the fuel cell system, the energy management of the fuel cell system, environmental data of the fuel cell system, system data of the fuel cell system, the states of energy storage devices and the energy converters of the fuel cell system, and managing the energy storage devices of the fuel cell system to a predetermined or adaptively optimized state of charge (SOC) range. Thus, the review of the dynamic transfer behavior of the fuel cell system is planned in such a way that the system requirements for the review do not, or only minimally, affect the operation of the vehicle or the vehicle's energy system.

[0033] The process can return to or continue with the step of planning and preparing a review of the dynamic transfer behavior of the fuel cell system if the second trigger is not set. The second trigger is activated as soon as the preparation is complete and the planned / desired time has arrived. Otherwise, the preparation continues, or a new suitable time is planned if a previously desired time has expired or proven unsuitable.

[0034] Exciting the fuel cell system at different frequencies can involve imposing a vibration, the frequency of which is changed during testing (i.e., increased or decreased), on setpoint values ​​for operating parameters of the fuel cell system, particularly in the form of a sine wave whose frequency is changed during testing. Thus, R.416589

[0035] - 7 -

[0036] The fuel cell system is excited in the form of a sweeping sine wave. Depending on the excited operating parameter, various operating parameters such as currents, voltages, pressures, mass flows, temperatures, humidity, activities, and other possible system variables are specified as setpoints for controlling the fuel cell system and its subsystems. The setpoints also oscillate periodically. The actual values ​​of the operating parameters, such as currents, voltages, pressures, mass flows, temperatures, humidity, activities, and other possible system variables at the stack inlet, at the stack outlet, or at other points in the respective fuel cell system, are acquired using the available sensors. A Fast Fourier Transform allows the frequency-dependent transfer characteristics of individual variables, in the form of damping and phase shift, to be determined.

[0037] In this method, a control variable of the fuel cell system, in particular current, can be excited at different frequencies. Thus, the fuel cell system, such as its current, can be excited in the form of a swept sine wave. Depending on the excited operating parameter, such as current, various operating parameters, such as pressures, mass flows, temperatures, humidity, activities, and other possible system variables, are specified as setpoints for controlling the fuel cell system and its subsystems. The setpoints also oscillate periodically. The actual values ​​of the operating parameters, such as pressures, mass flows, temperatures, humidity, activities, and other possible system variables at the stack inlet, at the stack outlet, or at other points in the respective fuel cell system, are acquired using the available sensors.A Fast Fourier Transform allows the frequency-dependent transfer behavior of individual quantities to be determined in the form of damping and phase shift.

[0038] Determining the response of the fuel cell system can include acquiring actual values ​​of operating parameters of the fuel cell system, performing a Fast Fourier Transform on the acquired actual values, and determining a frequency-dependent transfer characteristic of at least one setpoint to the actual values ​​in the form of attenuation and phase shift. At low frequencies, the applied signal and the measured signal(s) follow without R.416589.

[0039] - 8 -

[0040] Phase shift compared to the applied setpoint. At higher frequencies, the air system in particular exhibits low-pass behavior with corresponding damping and phase shift. Based on the data, potential aging, e.g., of the compressor, can be diagnosed, which would lead to increased damping and a phase shift that begins even at lower frequencies. A similar evaluation using the vibration test is also possible for other parameters, such as pressures, temperatures, rotational speeds, stack tension, etc.

[0041] Evaluating the dynamic transfer behavior of the fuel cell system can include determining the frequency response and amplitude response for a control loop of the fuel cell system and / or for the transfer behavior of a control loop and a control unit of the fuel cell system. This is particularly useful for determining whether the fuel cell system is operating correctly or is experiencing substandard operation.

[0042] The predetermined action cannot be an action if the evaluation of the dynamic transfer behavior of the fuel cell system shows that the fuel cell system is operating correctly. If the evaluation of the dynamic transfer behavior of the fuel cell system shows that the fuel cell system is not operating correctly or is operating substandard, the predetermined action can be at least one action selected from the group consisting of: adjusting the dynamic limitations of the fuel cell system, creating a dynamic ranking, adjusting at least one parameter of a control unit of the fuel cell system, adjusting an operating strategy of the fuel cell system, restricting an operating range of the fuel cell system, replacing or repairing at least one component of the fuel cell system, or a higher-level action for multiple vehicles.

[0043] Furthermore, a fuel cell system with at least one fuel cell stack and at least one control unit is proposed. The control unit is R.416589.

[0044] - 9 - designed to carry out a procedure according to one of the embodiments described above or below.

[0045] Furthermore, a motor vehicle is proposed that incorporates such a fuel cell system.

[0046] Finally, a computer program product is proposed with program code means which, when the computer program product is executed on a computer, configure the computer to perform a method according to one of the embodiments described above or below.

[0047] The proposed computer program product could be, for example, a file to be downloaded from a server or a data carrier, such as a CD-ROM or a USB stick.

[0048] The advantages which have been described in detail with regard to the operating method for operating a fuel cell system according to the invention apply equally to the vehicle according to the invention and to the computer program product according to the invention.

[0049] Within the scope of the present invention, a fuel cell system can be understood as a system comprising at least one fuel cell stack, an anode path comprising an anode, an anode gas supply line and an anode gas return line, a cathode path comprising a cathode, a cathode gas supply line and a cathode gas return line, a sensor unit for acquiring data to determine a state and / or a load change of the fuel cell system, a processing unit for determining a state and / or a load change of the fuel cell system, and a control unit. The control unit is configured to regulate the operation of the fuel cell system or the fuel cell stack. A fuel cell stack comprises at least two fuel cells, preferably at least 10 fuel cells, and even more preferably at least 100 fuel cells.Within the scope of the present invention, the term fuel cell stack is used synonymously with the term fuel cell stack. A fuel cell consists of electrodes, between R.416589.

[0050] - 10 - containing an electrolyte (ion conductor). The electrodes are the previously mentioned anode and cathode. A liquid, such as alkalis or acids, or molten alkali carbonate can be used as the electrolyte. In high-temperature fuel cells, a solid is used as the electrolyte, such as ion-conducting ceramic, which then forms a solid electrolyte. Membranes are also used. These are semipermeable membranes that are only permeable to one type of ion, e.g., protons. A membrane can also separate two different liquid electrolytes from each other. The energy is supplied by a reaction of oxygen with the fuel. This is often hydrogen, but organic compounds such as methane or methanol are also used. Both reactants are continuously supplied via the electrodes.The fuel cell system may further comprise a housing in which the at least one fuel cell stack is accommodated. The fuel cell system may further comprise a control unit for activating a device for the targeted adjustment of the water loading of a membrane of the fuel cell system, as well as a device for the targeted adjustment of the water loading of a membrane of the fuel cell system.

[0051] The fuel cell system has several subsystems, such as the anode subsystem or hydrogen subsystem, which includes the anode path and one or more hydrogen tanks, the cathode subsystem, which includes the cathode path, an air compressor and optionally a humidifier, the electrical subsystem, which includes electrical components such as electrical connections, battery, energy storage, and the cooling system, which includes coolant, coolant pump and fan.

[0052] In the context of the present invention, the term "transfer behavior" can be understood as the behavior of the fuel cell system and its subsystems when a control variable of the fuel cell system is changed. In systems theory, every process can be represented as a so-called "black box," characterized only by the relationship between its input and output variables. This "black box" is then referred to as a system. R.416589

[0053] - 11 -

[0054] A system is always characterized by its demarcation from its environment and the associated exchange of information. A distinction is made between concrete and mathematical systems. A concrete system is a spatially defined part of reality. It also includes certain selected relationships to its internal material structure and its environment. Mathematical systems contain, for example, variables, equations, or operators. Various methods have developed for describing systems. In the context of technical systems, the most widespread approach is that of a transmission system. Every system is characterized by a set of input variables and a set of output variables. The relationship between input and output variables is described by the transfer function (the transfer behavior).If the input and output variables are physical quantities, then the system is a physical system; if they are informational quantities, then it is a cybernetic system. If such quantities change over time, then the system is called a dynamic system; otherwise, it is a static system.

[0055] In the context of the present invention, a trigger can be understood as an impulse that is generated by a triggering event. The triggering event can be, for example, an input voltage exceeding a threshold, the elapsed time, or the occurrence of a specific event, such as the occurrence of a predetermined air pressure, load drop, aging, and the like.

[0056] Brief description of the drawings

[0057] Further optional details and features of the invention will become apparent from the following description of preferred embodiments, which are shown schematically in the figures.

[0058] They show:

[0059] Figure 1 shows a schematic representation of a fuel cell system according to an embodiment of the present invention in a vehicle, R.416589

[0060] - 12 -

[0061] Figure 2 shows a schematic representation of a possible embodiment of a method for operating a fuel cell system according to an embodiment of the present invention.

[0062] Figure 3 shows a schematic representation of one step for performing the verification of the dynamic transfer behavior of the fuel cell system, and

[0063] Figure 4 shows a schematic representation of a step for evaluating the verification of the dynamic transfer behavior of the fuel cell system.

[0064] Embodiments of the invention

[0065] Figure 1 shows a schematic representation of a fuel cell system 100 according to an embodiment of the present invention. The fuel cell system 100 is shown by way of example arranged in a vehicle 200. The vehicle 200 can be a passenger car or a truck, although other types of vehicles are conceivable in principle.

[0066] The fuel cell system 100 comprises at least one fuel cell stack 102. The fuel cell stack 102 includes several fuel cells, of which only one is shown for illustrative purposes. The fuel cell system 100 further comprises an anode path 104, which includes an anode 106, an anode gas supply line 108, and an anode gas return line 110. The fuel cell system 100 further comprises a cathode path 112, which includes a cathode 114, a cathode gas supply line 116, and a cathode gas return line 118. The fuel cell system 100 further comprises at least one sensor unit 120 for recording operating parameters of the fuel cell stack 102. The sensor unit 120 can also be configured to record data for determining the state and / or load change of the fuel cell system 100.The fuel cell system may include a processing unit (not shown) for determining the state and / or load change of the fuel cell system 100. The fuel cell system 100 also includes a control unit 122. R.416589.

[0067] - 13 -

[0068] Control unit 122 is designed to control the operation of the fuel cell system 100 or the fuel cell stack 102. The fuel cell stack 102 is housed in a casing 124. The fuel cell system 100 may further comprise a control unit (not shown) for activating a device for the targeted adjustment of the water loading of a membrane of the fuel cell system 100, as well as a device for the targeted adjustment of the water loading of a membrane of the fuel cell system 100.

[0069] Figure 2 shows a schematic representation of a possible embodiment of a method for operating a fuel cell system 100 according to an embodiment of the present invention.

[0070] In step S10, the fuel cell system 100 is in system operation. The procedure can be triggered from within the ongoing operation and carried out during operation.

[0071] Step S20 involves determining the necessity of verifying the dynamic transfer behavior of the fuel cell system 100. This determination includes evaluating information concerning the fuel cell system. The information regarding the fuel cell system 100 is provided by at least one unspecified information source, located within and / or outside the fuel cell system 100.The need to check the dynamic transfer behavior of the fuel cell system 100 is determined if the information concerning the fuel cell system 100 indicates at least one parameter S21 to S27 selected from the group consisting of: aging of at least one component of the fuel cell system 100 (S21), adaptation of an operating strategy of the fuel cell system 100 and / or a control loop of the fuel cell system 100 (S22), exceeding a predetermined threshold of an asymmetry of fuel cell stacks of the fuel cell system 100 (S23), a replacement or repair of at least one component of the fuel cell system 100 (S24), an error R.416589.

[0072] - 14 - in the operation of the fuel cell system 100 (S25), a change in an application of the fuel cell system 100 and / or a dynamic requirement for a system operation of the fuel cell system 100 (S26), a change in a boundary condition and / or environmental condition and / or an operating range of the fuel cell system 100 (S27).

[0073] In other words, to determine the need for a review of the dynamic transmission behavior of the fuel cell system 100 or its subsystems, various pieces of information—i.e., current, historical, and predictive data—are evaluated. These can originate from various sources, such as measurement data in the vehicle 200 or from external sources, model calculations in control units and / or cloud / server data, diagnostic data, maintenance / workshop data, and the like. A trigger for reviewing the dynamic transmission behavior can arise, in particular, from the following data, information, and / or evaluations.

[0074] Significant aging or degradation of components of the fuel cell system 100 usually also leads to changes in the dynamic behavior of the system. In the fuel cell stack 102, various sub-components and materials are subject to aging, some of which have a significant impact on the dynamic system behavior of the fuel cell system 100. For example, there are over 25 known aging mechanisms in the fuel cell stack 102. As described in more detail below, the method according to the invention can be used to determine the effects of these aging processes on the dynamic system behavior and to initiate measures for improving system operation.

[0075] Conventionally, adaptations to the operating strategy and control loops can be made to compensate for changed system behavior. However, this often carries the risk that the adaptations will lead to oscillations in the control loops or a deterioration in accuracy, especially if the dynamic behavior is not sufficiently known. The method according to the invention allows the system behavior to be tested after such adaptations and the robustness of the measure to be assessed. R.416589

[0076] - 15 -

[0077] So-called multi-stack systems, i.e., fuel cell systems with several fuel cell stacks 102, are generally operated symmetrically, especially when system couplings are present. If stack-specific aging / degradation processes and / or component replacement lead to significant asymmetry of the individual stacks or individual systems, this has a significant impact on dynamic operation. If it is determined that the asymmetry exceeds a certain threshold, the method according to the invention is triggered.

[0078] When individual components are replaced or repaired, particularly in a workshop, this can also lead to changes in the dynamic behavior of the system and / or a subsystem. In these cases, the method according to the invention is triggered, which standardizes the dynamic transmission behavior during operation after the replacement. This is advantageous because the workshop then does not have to make complex adjustments to the software configuration / application and / or perform complex tests.

[0079] If individual components, subsystems, or fuel cell systems fail in a so-called multi-stack system, system operation must be adjusted accordingly, for example, through system switching, restricted operation, and the like. This also affects the dynamic system behavior. These events can also trigger further steps in the process.

[0080] For various reasons, the use case of vehicle 200 and the dynamic requirements for system operation can change, such as the introduction of a sport function via software, the repurposing of the commercial vehicle, or systems operating dynamically instead of in a stationary state. In these cases, it is also proposed to trigger the verification of the dynamic transmission behavior.

[0081] If boundary conditions, environmental conditions or operating areas change significantly, such as vehicle 200 being transported from a temperate climate zone to the tropics, or vehicle 200 being located in a mountainous region instead of at R.416589

[0082] - 16 - the coast, then it is also proposed to trigger a review of the dynamic transmission behavior to ensure the robustness of the system operation.

[0083] In a subsequent step S30, an initial trigger is set if a need to check the dynamic transmission behavior was identified in step S20. Conversely, the procedure returns to or continues regular system operation if the initial trigger in step S30 is not set. If the initial trigger is not set, system operation continues in step S10 without checking the dynamic transmission behavior, with further investigations taking place in step S20. These investigations can be continuous or periodic, time-triggered or event-triggered. Preferably, a complete check is performed in step S20 if individual triggers from parameters S21 to S27 are set.

[0084] Following step S30, step S40 involves planning and preparing a check of the dynamic transfer behavior of the fuel cell system 100. The first trigger in step S30 requests the execution of the transfer behavior check. However, it is highly advantageous to both prepare and predictively schedule the execution of the transfer behavior check beforehand.Planning and preparing a review of the dynamic transfer behavior of the fuel cell system 100 can take into account data regarding the driving trajectory and / or driving order of a vehicle 200 equipped with the fuel cell system 100, the energy management of the fuel cell system 100, environmental data of the fuel cell system 100, system data of the fuel cell system 100, states of energy storage devices and energy converters of the fuel cell system 100, and the control of energy storage devices of the fuel cell system 100 to a predetermined or adaptively optimized SOC range. In other words, available information from the driving trajectory / driving order of the vehicle 200, energy management, environmental data, system data, states of the energy storage devices and energy converters (fuel cell systems / stacks) is considered. Furthermore, the energy storage devices, such as those described in R.416589, are also taken into account.

[0085] - 17 - the high-voltage battery is guided in advance to a specific or adaptively optimized SOC range between SOCMinTest and SOCMaxTest, as the battery can advantageously support the procedure.

[0086] In a subsequent step S50, a second trigger is set if the planning and preparation for the review of the dynamic transfer behavior of fuel cell system 100 is complete. This second trigger in step S50 initiates a subsequent step S60 as soon as the preparation is complete and the scheduled / desired time has arrived. Conversely, if the second trigger in step S50 is not set, the process returns to step S40 of planning and preparing the review of the dynamic transfer behavior of fuel cell system 100, or resumes regular system operation. In other words, the preparation in step S40 continues, or a new, more suitable time is scheduled if, for example, a previously desired time has expired or proven unsuitable.

[0087] In step S60, the dynamic transfer behavior of the fuel cell system 100 is then checked if the second trigger was set in step S50. Checking the dynamic transfer behavior of the fuel cell system 100 involves exciting the fuel cell system 100 at different frequencies and determining its response, and is described in more detail below. Exciting the fuel cell system 100 at different frequencies involves applying an oscillation, the frequency of which is changed (i.e., increased or decreased) during the check, to setpoint values ​​for operating parameters of the fuel cell system 100, in particular in the form of a sine wave whose frequency is changed during the check. Preferably, a reference variable of the fuel cell system 100, in particular a current, is excited at different frequencies.Preferably, for example, a sine wave is applied to the target values, the frequency of which is progressively changed during the verification. It is explicitly emphasized that the verification can be performed separately for individual parts of the fuel cell system, as for example in sub-step S61 for a first fuel cell stack, in R.416589.

[0088] - 18 -

[0089] Substep S62 for a second fuel cell stack, etc., and in substep S63 for a battery.

[0090] During the check(s), appropriate data recording is preferably carried out to enable evaluation in a subsequent step S70. Data processing can also be performed in parallel with the check. Preferably, the check is carried out during the operation of the vehicle 200 in such a way that the driver's request or vehicle demand is implemented without any impairment, i.e., the checks are imperceptible, meaning the requirements are met (power-neutral). For this purpose, in a single-stack system, electrical energy storage devices, such as a high-voltage battery, are used to compensate for the power fluctuations of the fuel cell system 100. In a multi-stack system, the individual fuel cell systems or stacks are subjected to opposing sine waves of the same frequency, so that the power fluctuations are approximately balanced.In addition, electrical energy storage devices, such as high-voltage batteries, are used to compensate for the residual ripple of the power or the unbalanced portion of the fuel cell systems.

[0091] Determining a response of the fuel cell system 100 includes recording actual values ​​of operating parameters of the fuel cell system 100, performing a fast Fourier transform of the recorded actual values, and determining a frequency-dependent transfer behavior of at least one setpoint to the actual values ​​in the form of damping and phase shift.

[0092] In a subsequent step S70, the verification of the dynamic transfer behavior of the fuel cell system 100 is evaluated. From the verification(s) in step S60, the dynamic system behavior of the respective (sub)systems is determined. Frequency response and amplitude response for the transfer behavior of the controlled system or the transfer behavior of the controlled system and the control unit 122 can be determined. A detailed description of the evaluation follows below. R.416589

[0093] - 19 -

[0094] In a subsequent step S80, at least one predetermined action is taken depending on the result of the evaluation of the verification of the dynamic transfer behavior of the fuel cell system 100. The predetermined action is not an action (S81) if the evaluation of the verification of the dynamic transfer behavior of the fuel cell system 100 shows that the fuel cell system 100 is operating correctly. If the evaluation in step S70 shows that the fuel cell system 100 or the systems are operating correctly and robustly, no further action is necessary.

[0095] If the evaluation of the verification of the dynamic transfer behavior of the fuel cell system 100 in step S70 reveals that the fuel cell system 100 is not operating properly or is operating poorly, the predetermined action shall be at least one action selected from the group consisting of: Adjusting the dynamic limitations of the fuel cell system 100 (S82), Creating a dynamic ranking (S83), Adjusting at least one parameter of the control unit 122 of the fuel cell system 100 (S84), Adjusting an operating strategy of the fuel cell system 100 (S85), Restricting an operating range of the fuel cell system 100 (S86), Replacing or repairing at least one component of the fuel cell system 100 (S87), or a higher-level action for multiple vehicles 200 (S88).

[0096] If, for example, the system is at risk of becoming unstable under higher dynamic conditions, such as increased susceptibility to vibration, then the dynamic limit of the system or the individual system can be reduced. If necessary, and if the dynamic requirements for the electrical energy storage are increased, the state-of-charge (SOC) limits of the electrical energy storage can also be adjusted.

[0097] In a multi-stack system, a dynamic ranking can be created. If greater dynamic performance is requested, this can be passed on to the system exhibiting the best dynamic system behavior. The slower-responding system may receive less dynamic performance than required. R.416589

[0098] - 20 -

[0099] The control unit(s) 122 and their parameters can be adjusted (adapted) to restore the robustness of the control loop. After adaptation, a further check can be performed if necessary.

[0100] Operating strategies can also be adapted. For example, the prediction horizon can be extended, system switching can be slowed down, and operating parameters can be changed, such as the water management in the fuel cell stack 102 with pressure, mass flow, temperature, and humidity requirements.

[0101] The operating range can be restricted. This helps avoid operating ranges where the system could become unstable.

[0102] You may be required to take your vehicle to a workshop for an inspection or parts replacement. Predictive maintenance is preferred, meaning intervention occurs before the vehicle breaks down or can no longer significantly meet the requirements of the driver / vehicle.

[0103] Since the proposed method, which uses amplitude and frequency response behavior, provides standardized results for the dynamic system behavior, the systems can be readily compared both within a single vehicle (200 vehicles) and across vehicles within a fleet. Therefore, evaluating entire fleets allows for insights into changes in system behavior over time, across different use cases, and under various boundary conditions. These results can then be incorporated into measures such as software updates, application updates, and the like.

[0104] The procedure then returns to step S10. There, the procedure can be repeated.

[0105] Figure 3 shows a schematic representation of step S60 for performing the verification of the dynamic transfer behavior of the fuel cell system 100. Thus, in a current-controlled system, substep R.416589

[0106] - 21 -

[0107] In step S610, the current I is excited in the form of a sliding sine wave. Therefore, the test can also be described as an oscillation test. The current I thus excited is fed to the control system or the control loop as a reference input in step S620. Depending on the current I, different setpoints for pressures, mass flows, and temperatures are specified by the control system or the control loop in step S630. In particular, different setpoints for the coolant temperature T and the cathode mass flow m are specified for the subsystems in step S640. ca thode, of the pressure of the cathode p ca method, the anode mass flow m ano de, of the pressure of the anode p anThe setpoints are specified. In sub-step S650, these setpoints influence the electrical subsystem 126, the thermal subsystem 128, the cathode subsystem or air subsystem 130, and the anode subsystem or hydrogen subsystem 132. The setpoints also oscillate periodically. In sub-step S660, these setpoints provide the input conditions for the fuel cell stack 102. In sub-step S670, the response of the fuel cell stack 102 is recorded. The actual values ​​of the pressures, mass flows, and temperatures at the stack inlet 134 are recorded in sub-step S680 using the existing sensor unit 120 as an output variable, for example, in the form of an electrical voltage U. stac k of the fuel cell stack 102. A Fast Fourier Transform in substep S690 allows the frequency-dependent transfer behavior of individual quantities in the form of damping and phase shift to be determined.

[0108] Significant aging or degradation of components of the fuel cell system 100 usually also leads to changes in the dynamic behavior of the system. In the fuel cell stack 102, various sub-components and materials are subject to aging, some of which significantly affect the dynamic system behavior of the fuel cell system 100. For example, there are over 25 known aging mechanisms in the fuel cell stack 102. The gas diffusion layer is hydrophobic when new and becomes more hydrophilic over its lifetime. Thus, with increasing aging, there tends to be more water in the gas diffusion layers. An increase in current during vibration testing tends to result in a deep voltage drop, as the reactant transport limit is reached sooner. Due to aging, less electrochemically active surface area (ECSA) is available in the fuel cell stack 102. R.416589

[0109] - 22 -

[0110] Increasing the current in the oscillation test tends to result in a deep voltage drop, as the reactant transport limit is reached earlier.

[0111] The membrane humidifier is subject to significant degradation, comparable to the fuel cell stack 102, and thus also influences the change in dynamic transfer behavior. As the membrane humidifier ages, water transfer deteriorates. In the vibration test, this is visible as an increased damping of the stack inlet moisture compared to the stack outlet moisture.

[0112] Air compressor units can become stiffer or start up less reliably due to altered friction in the bearings. This affects the dynamic system behavior. The anode recirculation blower can also cause changes in system behavior due to aging. Therefore, in an aged state, a dampened or delayed response to excitation can generally be expected compared to a new unit.

[0113] The throttle valves and other valves in the air system have seals whose sealing effect diminishes, leading to increased leakage. Additionally, friction in the actuators can also alter system behavior. Similarly, valves in the anode circuit, such as a hydrogen metering valve, can influence system behavior due to aging or friction. This can result in slower opening or greater damping of the actual value compared to the target value in an aged state.

[0114] Heat exchangers can drift, become damaged, or leak over their lifespan, for example due to frost damage. As a result, their efficiency decreases, and temperature fluctuations on the hot side are now more dampened on the cold side.

[0115] The filters in the system, i.e., the air system and, if applicable, the anode path 104, can become clogged over their service life and affect system behavior. This leads to a greater reduction in the fresh air flow. As a result, the increased pressure loss, especially at full load, must be compensated for by the air compressor EAC. R.416589

[0116] - 23 - serated. Furthermore, the compressor operating points (partial load / full load) diverge. The full load point is reached later than when the filter is new, resulting in increased damping of the pressure and mass flow dynamics in the vibration test.

[0117] Various mechanisms can also occur within the cooling system that lead to altered system behavior, such as deposit formation on the vehicle radiators, damage to the radiator fans, coolant aging, and stiffness or friction in the actuators (e.g., radiator fans). Increased friction generally leads to a delayed response of the component, resulting in increased damping during vibration testing.

[0118] The dynamic behavior of sensors can change. This affects the subsystems of all three media systems: air system, anode system, and coolant system. It also affects sensors in the electrical system (sensors for stack voltage and cell voltages). Depending on the aging mechanism, the transmission behavior of a sensor (physical value to sensor value) can change differently. This results in altered damping in vibration tests.

[0119] Figure 4 shows a schematic representation of step S70 for evaluating the verification of the dynamic transfer behavior of the fuel cell system 100. In Figure 4, the frequency of the applied current fi in Hz is shown logarithmically on the x-axis in both the upper and lower parts of the figure. The normalized amplitude log(A) is shown on the y-axis in the upper part. nor m) shown logarithmically. The phase shift A is shown in the lower part. <t>i n The temperature at the inlet of the fuel cell stack 102 is shown in degrees. Curve 136 represents the signal of the setpoint for the cathode mass flow at the stack inlet. Curve 138 represents the signal of the actual value for the cathode mass flow at the stack inlet. Figure 4 shows only an exemplary evaluation of a vibration test. The mass flow at the cathode inlet is compared with the setpoint specified by the control unit 122. At low frequencies, both signals follow the current-dependent setpoint without phase shift or with a negligible phase shift 140. At higher frequencies, the air system in particular exhibits low-pass behavior with corresponding damping 142 and increasing phase shift 144. Based on the data, an R.416589

[0120] - 24 - Possible aging of the compressor, for example, can be diagnosed, which would lead to increased damping and a phase shift that begins even at lower frequencies. A similar evaluation using the vibration test is also possible for other parameters, such as pressures, temperatures, rotational speeds, stack stress, etc. This evaluation then allows the implementation of the measures described above.< / t>

Claims

R.416589 - 25 - Claims 1. Method for operating a fuel cell system (100), comprising the steps: Determining the need to verify the dynamic transfer behavior of the fuel cell system (100), Setting an initial trigger if a need to check the dynamic transfer behavior has been identified, Planning and preparing a review of the dynamic transfer behavior of the fuel cell system (100), Setting a second trigger if the planning and preparation of the verification of the dynamic transfer behavior of the fuel cell system (100) is completed, Performing the verification of the dynamic transfer behavior of the fuel cell system (100) if the second trigger has been set, wherein the verification of the dynamic transfer behavior of the fuel cell system (100) includes exciting the fuel cell system (100) with different frequencies and determining a response of the fuel cell system (100), Evaluating the verification of the dynamic transfer behavior of the fuel cell system (100), and Taking at least one predetermined action depending on a result of the evaluation of the verification of the dynamic transfer behavior of the fuel cell system (100).

2. Method according to the preceding claim, wherein determining the need to verify the dynamic transfer behavior of the fuel cell system (100) comprises evaluating information relating to the fuel cell system (100). R.416589 - 26 - 3. Method according to the preceding claim, wherein the information relating to the fuel cell system (100) is provided by at least one information source inside and / or outside the fuel cell system (100).

4. A method according to one of the two preceding claims, wherein the need to verify the dynamic transfer behavior of the fuel cell system (100) is determined if the information concerning the fuel cell system (100) indicates at least one parameter selected from the group consisting of: aging of at least one component of the fuel cell system (100), adaptation of an operating strategy of the fuel cell system (100) and / or a control loop of the fuel cell system (100), exceeding a predetermined threshold of an asymmetry of stacks of the fuel cell system (100), replacement or repair of at least one component of the fuel cell system (100), a fault in the operation of the fuel cell system (100), a change in an application case of the fuel cell system (100) and / or a dynamic requirement for system operation of the fuel cell system (100).a change in a boundary condition and / or environmental condition and / or an operating range of the fuel cell system (100).

5. Method according to any of the preceding claims, wherein the method reverts to regular system operation or continues regular system operation if the first trigger is not set.

6. A method according to any of the preceding claims, wherein the planning and preparation of a verification of the dynamic transfer behavior of the fuel cell system (100) includes taking into account data relating to a driving trajectory and / or driving order of a vehicle (200) having the fuel cell system (100), an energy management system of the fuel cell system (100), environmental data of the fuel cell system (100), system data of the fuel cell system (100), states of energy storage devices and the energy converters of the fuel cell system (100). R.416589 - 27 - and guiding energy storage of the fuel cell system (100) to a predetermined or adaptively optimized SOC range includes 7. Method according to one of the preceding claims, wherein the method returns to the step of planning and preparing a check of the dynamic transfer behavior of the fuel cell system (100) or continues regular system operation if the second trigger is not set.

8. Method according to one of the preceding claims, wherein the excitation of the fuel cell system (100) with different frequencies comprises imposing a vibration, the frequency of which is changed during the verification, on setpoint values ​​for operating parameters of the fuel cell system (100), in particular in the form of a sine wave, the frequency of which is changed during the verification.

9. Method according to the preceding claim, wherein a control variable of the fuel cell system (100), in particular a current intensity, is excited at different frequencies.

10. Method according to one of the two preceding claims, wherein determining a response of the fuel cell system (100) comprises acquiring actual values ​​of operating parameters of the fuel cell system (100), performing a fast Fourier transform of the acquired actual values ​​and determining a frequency-dependent transfer behavior of at least one setpoint to the actual values ​​in the form of damping and phase shift.

11. Method according to one of the preceding claims, wherein the evaluation of the verification of the dynamic transfer behavior of the fuel cell system (100) comprises determining a frequency response and amplitude behavior for a transfer behavior of a control loop of the fuel cell system (100) and / or for a transfer behavior of a control loop and a control unit (122) of the fuel cell system (100). R.416589 - 28 - 12. A method according to any one of the preceding claims, wherein the predetermined measure is not a measure if the evaluation of the verification of the dynamic transfer behavior of the fuel cell system (100) reveals proper operation of the fuel cell system (100), or if the evaluation of the verification of the dynamic transfer behavior of the fuel cell system (100) reveals improper or substandard operation of the fuel cell system (100), at least one measure is selected from the group consisting of: adjusting the dynamic limitations of the fuel cell system (100), creating a dynamic ranking, adjusting at least one parameter of a control unit (122) of the fuel cell system (100), adjusting an operating strategy of the fuel cell system (100), restricting an operating range of the fuel cell system (100), replacing or repairing at least one component of the fuel cell system (100).overarching measure for several vehicles (200).

13. Fuel cell system (100) comprising at least one fuel cell stack (102) and at least one control unit (122), wherein the control unit (122) is configured to carry out a method according to one of the preceding claims.

14. Vehicle (200) comprising a fuel cell system (100) according to the preceding claim.

15. Computer program product comprising program code means which, when the computer program product is executed on a computer, configure the computer to perform a method according to any one of claims 1 to 12.

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