Method and controller for operating a hydrogen subsystem of a fuel cell system, and fuel cell system

Abstract

The invention relates to a method for operating a hydrogen subsystem (110) of a fuel cell system (100), which is designed as a proton exchange membrane fuel cell system. The method comprises reading in sensor signals (105) via an interface (121) of sensor devices (101, 102, 103) of the fuel cell system (100). The sensor signals (105) represent present measured values of physicochemical operating conditions of the fuel cell system (100). The method comprises applying an operating specification (123) to the measured values in order to determine target operating variables (125) of the hydrogen subsystem (110). The operating specification (123) comprises constraints ascertained for the hydrogen subsystem (110), the constraints comprising a minimum hydrogen partial pressure at an anode outlet, a minimum gas velocity in the region of a flow field of an anode, a minimum anode pressure and a maximum anode pressure. The method comprises generating a control signal (127) using the determined target operating variables (125). The control signal (127) comprises predefined values for manipulated variables which can be set by means of actuating devices (112, 114) of the hydrogen subsystem (110) depending on the target operating variables (125). The method comprises providing the control signal (127) for output via an interface (121) to the actuating devices (112, 114) in order to operate the hydrogen subsystem (110).

Description

[0001] R. 414367

[0002] - 1 -

[0003] Description

[0004] title

[0005] Method and control unit for operating a hydrogen subsystem of a fuel cell system and fuel cell system

[0006] State of the art

[0007] The invention relates to a device or a method according to the preamble of the independent claims. The present invention also relates to a computer program.

[0008] Hydrogen-based PEM fuel cells are considered a mobility concept of the future, as they emit only water as exhaust gas and allow for fast refueling times. In fuel cell systems, oxygen (from the air) and hydrogen react to form water, waste heat, and electricity (to power, for example, an electric motor) in a so-called "cold combustion" process.

[0009] Disclosure of the invention

[0010] Against this background, the approach presented here comprises a method, a control unit that uses this method, and finally a corresponding computer program according to the main claims. Advantageous further developments and improvements of the device specified in the independent claim are possible through the measures listed in the dependent claims.

[0011] According to embodiments, in particular, a determination of a pressure and mass flow requirement of an anode of a fuel cell system and a corresponding operating strategy can be provided. For example, an operating range of an anode side of a fuel cell can be defined. R. 414367

[0012] - 2 -

[0013] Stacks can be functionally described in such a way that they can be operated with a variety of hydrogen system architectures. This also avoids the unnecessarily high power consumption of an anode recirculation blower, if present. Instead of a stoichiometry or mass flow rate setting that depends solely on the electric current, a functionally motivated operating mode can be implemented. Various operating limits can be defined, which can be applied to the essential operating conditions of pressure and stoichiometry or hydrogen ratio. In contrast to conventional operating modes, the proposed operating mode in the hydrogen system eliminates the need for a purely current-dependent setting of stoichiometry or hydrogen ratio, whereby the set stoichiometry or...The set hydrogen ratio may depend, based on the physicochemical relationships presented herein, particularly on the anode pressure, the current strength and the gas composition.

[0014] Advantageously, according to embodiments, reduced stoichiometry requirements, hydrogen ratio requirements, mass flow requirements, and hydrogen mass flow requirements can be achieved, particularly at low partial loads. This results in reduced energy consumption for recirculation, a greater number of possible architectures, and thus potential cost savings. Functional stack requirements can also be met, improving the efficiency and lifespan of the fuel cell system. The operating concept presented here relies on measured system parameters and can therefore be implemented, for example, in a vehicle's fuel cell control unit (FCCU), perhaps as a complement to water activity-based control of the fuel cell system's air system.The approach presented here can be used to implement an anode operating mode that is as general as possible, for example with regard to temperature range, load range, etc., and largely independent of specific stack characteristics; that is, different stacks can be accommodated simply by changing the parameter settings. The approach presented here can also be used in R. 414367.

[0015] - 3 - will be used to derive the operating field of the anode, e.g., to derive requirements for the hydrogen subsystem and its components.

[0016] A method for operating a hydrogen subsystem of a fuel cell system, designed as a proton exchange membrane fuel cell system, is presented, wherein the method comprises the following steps:

[0017] Reading sensor signals via an interface from sensor devices of the fuel cell system, wherein the sensor signals represent current measured values ​​of physicochemical operating conditions of the fuel cell system;

[0018] Applying an operating procedure to the measured values ​​to determine target operating parameters of the hydrogen subsystem, wherein the operating procedure for the hydrogen subsystem includes determined boundary conditions comprising a minimum hydrogen partial pressure at an anode outlet, a minimum gas velocity in the region of a flow field of an anode, a minimum anode pressure and a maximum anode pressure;

[0019] Generating a control signal using the specified target operating parameters, wherein the control signal includes setpoint values ​​for manipulated variables adjustable by means of actuators of the hydrogen subsystem depending on the target operating parameters; and

[0020] Providing the control signal for output via an interface to the actuators in order to operate the hydrogen subsystem.

[0021] The procedure may also include a step of outputting the control signal via the interface to the actuators. The operating rule applied in the application step may also include estimated values ​​or predefined values ​​of other operating variables or operating conditions. The measured values ​​or operating conditions may also be referred to as R. 414367.

[0022] - 4 -

[0023] These can be referred to as measured variables, system variables, or state variables. The flow field can also be called a flow field.

[0024] The fuel cell system can be used as a propulsion system for a motor vehicle. The fuel cell system can be a PEM fuel cell system (PEM = Proton Exchange Membrane;

[0025] The fuel cell system can be designed as a proton exchange membrane (PEM) fuel cell system or polymer electrolyte (PEM) fuel cell system. Thus, the fuel cell system can be described as a mobile PEM fuel cell system. The fuel cell system can comprise multiple fuel cell modules designed as PEM fuel cells. These can also be referred to as a fuel cell stack or, more precisely, a PEM fuel cell stack. Such fuel cell stacks can include many individual fuel cell modules or cells, which can be stacked and, for example, held together by a clamping system. Each individual cell can include a membrane that separates the media on the anode side and the cathode side.

[0026] Hydrogen can be supplied to the stack at the anode side. To prevent localized reactant depletion, which would lead to rapid stack aging, the anode can be operated superstoichiometrically. This means that the hydrogen mass flow rate supplied at the anode inlet can be greater than the mass flow rate consumed in the stack. The excess hydrogen can typically be recirculated in an anode circuit and passed through the stack again. An anode recirculation blower (ARB), a jet pump, or a combination of both can be used to pump the recirculated hydrogen.

[0027] The stack requirements can be important for component sizing and the feasibility of different architectures.

[0028] Traditionally, a target stoichiometry can be specified as a function of the current. However, particularly at low partial loads, very high stoichiometries, for example greater than 10, are sometimes required, which lead to R. 414367.

[0029] - 5 -

[0030] For example, these requirements can be very difficult or even impossible to fulfill with a pure jet pump. If an ARB (Automatic Reactor Booster) is present, a high stoichiometry or a high mass flow rate can be achieved, but this can lead to an unnecessarily high electrical power consumption of the ARB. By no longer relying solely on stoichiometry as a requirement, as described in certain embodiments, a safe and efficient stack operation or operation of the fuel cell system can be achieved.

[0031] For water management of the stack, a water activity-based control strategy can be implemented, for example. Based on current target and actual state variables of the system (e.g., temperature), target values ​​for stoichiometry (air mass flow) and pressure of the stack can be derived to ensure a specific target humidity or target activity of the cathode.

[0032] According to one embodiment, the boundary conditions of the operating procedure applied in the application step can be linked to the measured values ​​and, additionally or alternatively, to the target operating parameters via predefined physicochemical relationships. Additionally or alternatively, the boundary conditions of the operating procedure applied in the application step can be experimentally determined for a precise configuration of the hydrogen subsystem. Such an embodiment offers the advantage that a safe, reliable, and economical operating strategy can be implemented, based on key constraints of operating requirements.

[0033] The minimum hydrogen partial pressure at the anode outlet can be related to a mole fraction of hydrogen at the anode inlet, a hydrogen ratio related to the anode reaction, and a total pressure at the anode outlet. Additionally or alternatively, the minimum gas velocity can be related to a mass flow rate, a gas density, and a cross-sectional area through which the gas flows. Additionally or alternatively, the maximum and minimum anode pressures can be related to a cathode pressure and a maximum pressure difference between the anode and cathode. Such an embodiment offers the advantage of R. 414367

[0034] - 6 - that only a few, but relevant for the operation, physicochemical relationships can be taken into account.

[0035] The target operating parameters determined in the application step can also include an anode inlet pressure and, additionally or alternatively, an anode outlet pressure, a mass flow rate through the anode, optionally a mass flow rate in a recirculation path, and additionally or alternatively, optionally a purge rate. Such an embodiment offers the advantage that pressure and mass flow requirements, which are particularly important for operation, can be determined reliably and accurately.

[0036] Furthermore, during the provisioning step, the control signal can be provided for output via the interface to at least one hydrogen metering valve, one pressure regulating valve, optionally one anode recirculation blower, and additionally or alternatively one purge valve as actuators. Such an embodiment offers the advantage that the setpoint values ​​can be easily and precisely adjusted using the control variables available from such actuators.

[0037] Furthermore, the measured values ​​represented by the sensor signals read in the acquisition step can include an electric current, a cathode input pressure, a cathode outlet temperature, an anode input pressure, an anode outlet pressure, and additionally or alternatively, a hydrogen content. Such an embodiment offers the advantage that the operational control can be implemented using measurement values ​​that are already available.

[0038] This process can be implemented, for example, in software or hardware, or in a hybrid form of software and hardware, for example in a control unit.

[0039] The approach presented here further creates a control unit that is configured to carry out, control, or implement the steps of a variant of the method presented here in corresponding devices. This embodiment of the invention, in the form of a control unit R. 414367, also achieves this.

[0040] - 7 - the problem underlying the invention can be solved quickly and efficiently.

[0041] For this purpose, the control unit can have at least one processing unit for processing signals or data, at least one storage unit for storing signals or data, at least one interface to a sensor or actuator for reading sensor signals from the sensor or for outputting control signals to the actuator, and / or at least one communication interface for reading or outputting data embedded in a communication protocol. The processing unit can be, for example, a signal processor, a microcontroller, or the like, while the storage unit can be flash memory or a magnetic storage device.The communication interface can be configured to read or output data wirelessly and / or via wired connections, whereby a communication interface that can read or output wired data can, for example, read this data electrically or optically from or output it into a corresponding data transmission line.

[0042] In this context, a control unit can be understood as an electrical device that processes sensor signals and outputs control and / or data signals accordingly. The control unit can have an interface, which can be implemented in hardware and / or software. In the case of a hardware-based interface, the interfaces can, for example, be part of a so-called system ASIC, which incorporates various functions of the control unit. However, it is also possible that the interfaces are separate integrated circuits or at least partially comprised of discrete components. In the case of a software-based interface, the interfaces can be software modules, which, for example, are located on a microcontroller alongside other software modules.

[0043] A fuel cell system is also presented, designed as a proton exchange membrane fuel cell system, the fuel cell system having the following features: R. 414367

[0044] - 8 -

[0045] Sensor devices for recording current measured values ​​of physicochemical operating conditions of the fuel cell system; a hydrogen subsystem with actuators; and an embodiment of a control unit mentioned herein, wherein the control unit is connected to the sensor devices and to the actuators in a signal-transmitting manner.

[0046] Thus, in conjunction with the fuel cell system, an embodiment of a control unit mentioned herein can be advantageously employed or used to operate the hydrogen subsystem or to control its operation. The control unit can also be spatially separated from the other components of the fuel cell system, for example, as part of a vehicle's fuel cell control unit.

[0047] Also advantageous is a computer program product or computer program with program code that can be stored on a machine-readable carrier or storage medium such as a semiconductor memory, a hard disk memory or an optical memory and is used to carry out, implement and / or control the steps of the method according to one of the embodiments described above, in particular if the program product or program is executed on a computer or device.

[0048] Examples of the approach presented here are shown in the drawings and explained in more detail in the following description. It shows:

[0049] Fig. 1 shows a schematic representation of an embodiment of a fuel cell system;

[0050] Fig. 2 shows a flowchart of an embodiment of a method for operating a hydrogen subsystem of a fuel cell system; R. 414367

[0051] - 9 -

[0052] Fig. 3 shows a schematic stoichiometry-pressure diagram related to the fuel cell system from Fig. 1 and / or the method from Fig. 2; and

[0053] Fig. 4 shows a schematic representation of an operating instruction in connection with the fuel cell system from Fig. 1 and / or the method from Fig. 2.

[0054] In the following description of favorable embodiments of the present invention, the same or similar reference numerals are used for the elements shown in the various figures and acting similarly, without repeating these elements.

[0055] Fig. 1 shows a schematic representation of an embodiment of a fuel cell system 100. The fuel cell system 100 is designed as a proton exchange membrane fuel cell system. The fuel cell system 100 is intended, for example, for use in the powertrain of a motor vehicle.

[0056] The fuel cell system 100 comprises a plurality of sensor devices 101, 102, 103. The sensor devices 101, 102, 103 are configured to acquire current measured values ​​of the physicochemical operating conditions of the fuel cell system 100. Furthermore, the sensor devices 101, 102, 103 are configured to output or make available for output the acquired measured values ​​in the form of sensor signals 105. The measured values ​​include, for example, an electric current, a cathode input pressure, a cathode outlet temperature, an anode input pressure, an anode outlet pressure, and / or a hydrogen content.

[0057] The fuel cell system 100 also includes a hydrogen subsystem 110, which has a plurality of actuators 112, 114. The actuators 112, 114 of the hydrogen subsystem 110 are configured to supply the anode of the fuel cell system 100 with at least R. 414367

[0058] - 10 - to adjust mass flow and pressure. The adjusting devices 112, 114 include, for example, at least one hydrogen metering valve, one pressure regulating valve, optionally an anode recirculation blower and / or a purge valve.

[0059] The fuel cell system 100 further comprises a control unit 120, which is configured to operate the hydrogen subsystem 110 or to control the operation of the hydrogen subsystem 110. The control unit 120 is connected to the sensor devices 101, 102, 103 and to the actuators 112, 114 via signal transmission. According to one embodiment, the control unit 120 is designed as a single assembly together with the other components of the fuel cell system 100. According to another embodiment, the control unit 120 is provided separately from the other components of the fuel cell system 100, for example in a vehicle control unit or the like.

[0060] Figure 1 shows, by way of example, only three sensor devices 101, 102, 103, whereby, according to exemplary embodiments, any number of sensor devices 101, 102, 103 can be provided. Furthermore, Figure 1 shows, by way of example, two of the sensor devices 101, 102, 103 outside the hydrogen subsystem 110 and one of the sensor devices 101, 102, 103 inside the hydrogen subsystem 110, whereby, according to exemplary embodiments, any distribution of the sensor devices 101, 102, 103 can be provided.

[0061] The control unit 120 comprises a reading device 122, an application device 124, a generation device 126, and a provision device 128. Furthermore, the control unit 120 comprises an interface 121. The control unit 120 is connected via the interface 121 to the sensor devices 101, 102, 103 and to the actuators 112, 114 for signal transmission.

[0062] The reading device 122 is configured to read the sensor signals 105 from the sensor devices 101, 102, 103 via the interface 121. The reading device 122 is further configured to transmit the sensor signals 105 to the R. 414367

[0063] - 11 -

[0064] Application device 124 is configured to transmit the determined target operating parameters 125 of the hydrogen subsystem 110 to the sensor signal 105. The application device 124 is configured to apply an operating rule 123 to the measured values ​​represented by the sensor signal 105 in order to determine these target operating parameters 125. The operating rule 123 comprises boundary conditions determined for the hydrogen subsystem 110. These boundary conditions include a minimum hydrogen partial pressure at an anode outlet, a minimum gas velocity in the region of a flow field of an anode, a minimum anode pressure, and a maximum anode pressure. The application device 124 is configured to transmit the determined target operating parameters 125 to the generation device 126.

[0065] According to one embodiment, the boundary conditions of the operating procedure 123 applied by means of the application device 124 are linked to the measured values ​​or sensor signals 105 and / or to the target operating parameters 125 via predefined physicochemical relationships. Additionally or alternatively, the boundary conditions of the operating procedure 123 applied by means of the application device 124 are determined experimentally for a precise configuration of the hydrogen subsystem 110. The minimum hydrogen partial pressure at the anode outlet is related to a mole fraction of hydrogen at an anode inlet, a hydrogen ratio related to the anode reaction, and a total pressure at the anode outlet. Additionally or alternatively, the minimum gas velocity is related to a mass flow rate, a gas density, and a cross-sectional area through which the gas flows.Additionally or alternatively, the maximum anode pressure and the minimum anode pressure are related to a cathode pressure and a maximum pressure difference between anode and cathode. The target operating parameters 125 include, for example, an anode inlet pressure and / or an anode outlet pressure, a mass flow rate through the anode, optionally a mass flow rate in a recirculation path, and / or optionally a purge rate.

[0066] The generating unit 126 is designed to generate a control signal 127 using the specified target operating parameters 125. The control signal 127 comprises setpoint values ​​for the actuators 112, R. 414367.

[0067] - 12 -

[0068] The control units 114 and 125 are adjustable depending on the target operating parameters. The generating unit 126 is also configured to transmit the generated control signal 127 to the supply unit 128. The supply unit 128 is configured to provide the control signal 127 for output via interface 121 to the actuators 112 and 114 to operate the hydrogen subsystem 110. The control unit 120 is configured to output the control signal 127 via interface 121 to the actuators 112 and 114 to operate the hydrogen subsystem 110.

[0069] Fig. 2 shows a flowchart of an embodiment of method 220 for operating a hydrogen subsystem of a fuel cell system. Method 220 for operation can be implemented to operate the hydrogen subsystem from Fig. 1 or a similar hydrogen subsystem. The steps of method 220 for operation can be carried out using the control unit from Fig. 1 or a similar control unit. In other words, the components of the control unit from Fig. 1 are configured to perform the steps of method 220 for operation. Method 220 for operation comprises a reading step 222, an application step 224, a generation step 226, and a provision step 228.

[0070] In step 222 of the reading process, sensor signals are read via an interface from sensor devices of the fuel cell system. The sensor signals represent current measured values ​​of the physicochemical operating conditions of the fuel cell system. Subsequently, in step 224 of the application process, an operating procedure is applied to the measured values ​​to determine target operating parameters of the hydrogen subsystem. The operating procedure specifies boundary conditions determined for the hydrogen subsystem, including a minimum hydrogen partial pressure at an anode outlet, a minimum gas velocity in the flow field of an anode, a minimum anode pressure, and a maximum anode pressure. Following this, in step 226 of the generation process, a control signal is generated using the determined target operating parameters. This signal sets predefined values ​​for actuators of the R. 414367.

[0071] - 13 -

[0072] The hydrogen subsystem has adjustable control variables depending on the target operating parameters. In step 228 of the provisioning process, the control signal is then provided for output via an interface to the actuators in order to operate the hydrogen subsystem.

[0073] Fig. 3 shows a schematic stoichiometry-pressure diagram 300 in connection with the fuel cell system from Fig. 1 and / or the method from Fig. 2. In Fig. 3, functionally derived operating limits or the boundary conditions of the operating procedure are schematically represented. The pressure p is plotted on an abscissa axis, while the hydrogen ratio A, also referred to as stoichiometry, is plotted on an ordinate axis.

[0074] Diagram 300 shows the minimum anode pressure p_min and the maximum anode pressure p_max, between which a maximum pressure difference Ap_max is also shown. Furthermore, Diagram 300 shows the minimum hydrogen partial pressure p_H2_min at the anode outlet, a corresponding first boundary line 331, the minimum gas velocity u_min in the flow field of the anode, and a corresponding second boundary line 333.

[0075] The respective impermissible sides or ranges of the various operating limits or boundary conditions p_min, p_max, p_H2_min, and u_min are indicated by the hatching. The permissible operating range is defined as the area in which none of the limits or boundary conditions are violated. A change in the anode gas composition affects the position of the minimum hydrogen partial pressure p_H2_min and the minimum gas velocity u_min. If the hydrogen fraction x_H2 decreases, these two limits shift qualitatively towards their respective boundary lines 331 and 333, as illustrated by the arrows. The position of the pressure limits or anode pressures p_min and p_max depends only on the cathode pressure and the permissible membrane pressure difference Ap_max.

[0076] Fig. 4 shows a schematic representation of an operating instruction 123 in connection with the fuel cell system from Fig. 1 and / or the method from Fig. 2. In other words, Fig. 4 shows a structure of the anode operating strategy with a variant at the hydrogen concentration x_H2, which R. 414367

[0077] - 14 - is assumed, measured, or estimated using a model. The operating instruction 123 or operating strategy incorporates the sensor signals 105, boundary conditions 430, and assumptions 440. The target operating parameters 125 are determined using the operating instruction 123.

[0078] The sensor signals 105 are the model input parameters, typically the current operating conditions relevant for anode operation, namely electrical current, cathode inlet pressure, cathode outlet temperature (determined from the coolant outlet temperature in a fuel cell with unidirectional flow through the cathode and cooling channels), anode inlet pressure, anode outlet pressure, and / or optionally hydrogen content. During operation of the stack or fuel cell system, these parameters must be optimally aligned with the available control variables of the hydrogen subsystem or hydrogen subsystem: control of the hydrogen metering valve; control of the purge valve; if present, control of a second hydrogen metering valve or hydrogen metering valve in the bypass; and, if present, control of the anode recirculation fan.The target operating parameters 125 of the anode include, for example, an anode inlet pressure and / or an anode outlet pressure, a mass flow rate through the anode, optionally a mass flow rate in a recirculation path, and / or optionally a purge rate. The boundary conditions 430 include, for example, the boundary conditions shown in Fig. 3. The assumptions 440 or estimated values ​​can be fixed scalar values, results of detailed models, or measured variables. The assumptions 440 optionally include, for example, the hydrogen content, humidity at the anode outlet, and an amount of fresh hydrogen during Faraday consumption (only during steady-state operation), no hydrogen crossover, no purge losses, etc.

[0079] In particular, the hydrogen content in the anode recirculation may not be directly available via a sensor, depending on the vehicle. Several options exist to address this: 1. Assuming a typical value based on prototype tests. 2. Implementing a simple physical model with nitrogen diffusion and water transport from the cathode side as the primary contributions. 3. Using a virtual sensor. R. 414367

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[0081] The emptying of the water separator and the triggering of drain events are not included in operating procedure 123 due to the weak interaction with the rest of the anode operation.

[0082] With reference to the figures described herein, exemplary embodiments are summarized below and briefly presented in other words.

[0083] In particular, the operating requirements of the fuel cell system 100, or stack operating requirements, can be reduced to at least three different boundary conditions: a. Hydrogen partial pressure at the anode outlet p_H2_out_min: A sufficient reactant partial pressure must be provided throughout the anode catalyst layer. Otherwise, local depletion could occur, which could cause undesirable electrochemical side reactions (current reversal carbon corrosion on the cathode side). This could damage the fuel cells and reduce their remaining service life. Since the hydrogen partial pressure decreases along the flow path, this risk particularly affects the anode outlet area. Therefore, a lower limit for the hydrogen partial pressure in the flow field at the outlet pH2 is defined. anThe minimum hydrogen partial pressure p_H2_min at the anode outlet is specified as ,out. The resulting outlet partial pressure can be directly derived from the mole fraction %H2,in, stoichiometry A an and total pressure at the anode outlet p an , ou t can be calculated: p H 2, an ,out =%H2,in (A an - 1) / ((1 + ) A an + %H2) p an ,out, with = p H 20,in / (pin - pH20,in). takes into account the water vapor partial pressure at the anode inlet. Thus, a minimum setpoint of pH2 can be achieved. an A suitable combination of outlet pressure and stoichiometry must be found, see also Fig. 3. The required partial pressure in the flow field depends on the flow rate: the higher the reactant consumption, the higher the partial pressure should be chosen to ensure a sufficient diffusion current through the gas diffusion layer. b. Minimum gas velocity u_min: R. 414367

[0084] - 16 -

[0085] Liquid water can occur in the gas diffusion layers. This should be drained via the channel, as otherwise larger quantities of water can accumulate in the gas diffusion layer. This water would impair the diffusion of hydrogen to the catalyst layer and could thus also lead to a local deficiency of reactants (flooding). It has been shown that the water discharge depends essentially on the gas velocity u. The higher the velocity, the more liquid water can be transported out of the cell via two-phase transport in the flow field. If too low a gas velocity were chosen, the water could also accumulate in the flow field to form large droplets, which would severely restrict the gas flow through the flow field (slug flow) and consequently lead to another local deficiency of reactants.The minimum velocity is stack-dependent and can be determined through targeted experiments, simplified as a function of the electric current and thus the water production. In the vehicle, the velocity u can be determined with a known mass flow rate m and gas density p using the cross-sectional area A through which the fluid flows: u = m / p (A). The density p can be determined from pressure and temperature, assuming an ideal gas mixture. c. Maximum and minimum pressure p_min and p_max, or maximum and minimum anode pressure:

[0086] Since the membrane is relatively thin at approximately 20 micrometers or less, significant mechanical stress caused by pressure differences between the cathode and anode should be avoided. Because the air system, due to the necessary compressors, reacts considerably more slowly to a required pressure change than the hydrogen system, the anode pressure is adjusted to match the cathode pressure so that no large pressure differences A plowed (e.g., > 500 mbar) or Ap_max occur. The cathode pressure p ca This, in turn, depends primarily on the selected operating temperature. This directly results in operating limits for the hydrogen system: p_min = p ca - A p a iiowed and p_max = p ca + Ap a ii O Wed.

[0087] All limitations and boundary conditions 430 can be plotted in a pressure stoichiometry diagram or the pressure stoichiometry diagram 300 in Fig. 3. From this, the operating procedure and the operating instructions 123 can be directly derived. R. 414367

[0088] - 17 -

[0089] If an embodiment includes an “and / or” connection between a first feature and a second feature, this is to be read as meaning that the embodiment according to one embodiment has both the first feature and the second feature, and according to another embodiment either only the first feature or only the second feature.

Claims

R. 414367 - 18 - Claims 1. Method (220) for operating a hydrogen subsystem (110) of a fuel cell system (100) designed as a proton exchange membrane fuel cell system, wherein the method (220) comprises the following steps: Reading (222) sensor signals (105) via an interface (121) from sensor devices (101 , 102, 103) of the fuel cell system (100), wherein the sensor signals (105) represent current measured values ​​of physicochemical operating conditions of the fuel cell system (100); Applying (224) an operating procedure (123) to the measured values ​​to determine target operating parameters (125) of the hydrogen subsystem (110), wherein the operating procedure (123) for the hydrogen subsystem (110) includes boundary conditions (430) determined, which include a minimum hydrogen partial pressure (p_H2_min) at an anode outlet, a minimum gas velocity (u_min) in the region of a flow field of an anode, a minimum anode pressure (p_min) and a maximum anode pressure (p_max); Generating (226) a control signal (127) using the specified target operating parameters (125), wherein the control signal (127) has setpoint values ​​for manipulated variables adjustable by means of actuators (112, 114) of the hydrogen subsystem (110) depending on the target operating parameters (125); and Providing (228) the control signal (127) for output via an interface (121) to the actuators (112, 114) to operate the hydrogen subsystem (110). R. 414367 - 19 - 2. Method (220) according to claim 1, wherein the boundary conditions (430) of the operating procedure (123) applied in step (224) are linked to the measured values ​​and / or to the target operating parameters (125) via predefined physicochemical relationships and / or are determined experimentally for an accurate configuration of the hydrogen subsystem (110).

3. Method (220) according to claim 2, wherein the minimum hydrogen partial pressure (p_H2_min) at the anode outlet is related to a mole fraction of hydrogen at an anode inlet, a hydrogen ratio related to the anode reaction and a total pressure at the anode outlet, and / or wherein the minimum gas velocity (u_min) is related to a mass flow rate, a gas density and a cross-sectional area through which the gas flows, and / or wherein the maximum anode pressure (p_max) and the minimum anode pressure (p_min) are related to a cathode pressure and a maximum pressure difference between anode and cathode.

4. Method (220) according to one of the preceding claims, wherein the target operating parameters determined in step (224) of application (125) include an anode inlet pressure and / or an anode outlet pressure, a mass flow through the anode, optionally a mass flow in a recirculation path and / or optionally a purge rate.

5. Method (220) according to one of the preceding claims, wherein in the step (228) of providing the control signal (127) is provided for output via the interface (121) to at least one hydrogen metering valve, one pressure regulating valve, optionally one anode recirculation blower and / or one purge valve.

6. Method (220) according to one of the preceding claims, wherein the measured values ​​represented by the sensor signals read in step (222) of the reading process are an electric current, a R. 414367 - 20 - Cathode input pressure, cathode outlet temperature, anode input pressure, anode outlet pressure and / or hydrogen content.

7. Control unit (120) configured to execute and / or control the steps of the method (220) according to any of the preceding claims in corresponding units (122, 124, 126, 128).

8. Fuel cell system (100) designed as a proton exchange membrane fuel cell system, wherein the fuel cell system (100) has the following features: Sensor devices (101, 102, 103) for recording current measured values ​​of physicochemical operating conditions of the fuel cell system (100); a hydrogen subsystem (110) with actuators (112, 114); and a control unit (120) according to claim 7, wherein the control unit (120) is connected to the sensor devices (101, 102, 103) and to the actuators (112, 114) in a signal-transmitting manner.

9. Computer program configured to execute and / or control the steps of the method (220) according to any one of claims 1 to 6.

10. Machine-readable storage medium on which the computer program according to claim 9 is stored.

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