Method and apparatus for controlling a fuel cell system, fuel cell system, vehicle, computer program product and storage medium

Abstract

The technology disclosed herein relates to a method for controlling a fuel cell system (10) comprising the steps of: determining a stoichiometric fuel flow rate of a quantity of fuel stoichiometrically converted in a fuel cell (11), determining a recirculation flow rate, determining an inert gas concentration at an anode (12), determining an average inert gas concentration in the fuel cell (11), determining an inert gas crossover flow rate in the fuel cell (11) based on the stoichiometric fuel flow rate, the recirculation flow rate, the inert gas concentration at the anode (12), the average inert gas concentration in the fuel cell (11), and controlling the fuel cell system (10) based on the determined inert gas crossover flow rate.The technology further relates to a device (80), a fuel cell system (10), a vehicle (100) and a computer program product (40) for carrying out the method, as well as a computer-readable storage medium (50) on which the computer program product (40) is stored.

Description

[0001] The technology disclosed herein relates to a method and a device for controlling a fuel cell system. The technology further relates to a fuel cell system, a vehicle, and a computer program product for executing the method. The method also relates to a computer-readable storage medium on which such a computer program product is stored.

[0002] Fuel cell systems for mobile applications are known in the prior art. In a vehicle, fuel cell systems are typically configured to generate electrical energy for the vehicle's drive motor. Typical fuel cell systems comprise a fuel cell stack. The fuel cell stack includes several fuel cells, each with two electrodes and a membrane arrangement between the two electrodes. Within the fuel cell stack, fuel reacts with oxygen via reverse electrolysis, thereby generating electricity. The fuel can be supplied to the fuel cell stack from at least one pressure vessel in the vehicle. The oxygen can be drawn from the ambient air.

[0003] Furthermore, it is known to control the operating mode of the fuel cell system depending on current operating states and / or operating parameters within the fuel cell system. One such operating state can be the crossover behavior of inert gas between the anode and the cathode of the fuel cell. However, with known systems, the inert gas crossover behavior can either not be estimated at all, only in a highly simplified manner, and / or with corresponding inaccuracies. Moreover, in conventional systems, the inert gas crossover behavior, if defined at all, is only determined for new fuel cell systems and subsequently not changed. The inert gas crossover behavior can, however, change due to the aging of the fuel cell system. Due to the uneven distribution of the inert gas quantity within the fuel cell, the inert gas crossover behavior is difficult to determine.

[0004] To determine the inert gas concentration in and / or on the fuel cell, it is known to use special fuel sensors to obtain fuel measurements, based on which inert gas values ​​and corresponding inert gas behavior can then be deduced. When using gas concentration sensors outside the fuel cell stack, it is not possible to unambiguously infer the inert gas crossover behavior with known systems.

[0005] The purpose of the present technology is to create improved methods and devices for controlling a fuel cell system.

[0006] The aforementioned problem is solved by the claims. In particular, the aforementioned problem is solved by the method according to claim 1 and by the device, the fuel cell system, the vehicle, the computer program product, and the computer-readable storage medium according to the dependent claims. Further advantages of the disclosed technology will become apparent from the subclaims, the description, and the figures. Features described in connection with the method also apply in connection with the device, the fuel cell system, the vehicle, the computer program product, and the storage medium, and vice versa, so that the disclosure always makes and / or can make reciprocal references to the individual aspects.

[0007] According to a first aspect of the present technology, a method for controlling a fuel cell system is proposed. The fuel cell system comprises a fuel cell with an anode and a cathode, an anode inlet, an anode outlet, a fuel path, an anode inlet path, an anode exhaust path, a recirculation path, and a mixing section. In the mixing section, fuel from the fuel path is mixed with anode exhaust from the recirculation path, and the resulting mixture is fed into the anode inlet path. The method comprises the following steps: - Determining a stoichiometric fuel flow rate of a quantity of fuel stoichiometrically converted in the fuel cell, - Determining a recirculation flow rate in the recirculation path, - Determining an inert gas crossover flow rate in the fuel cell based on the stoichiometric fuel flow rate and the recirculation flow rate and - Controlling the fuel cell system based on the determined inert gas crossover flow rate.

[0008] Within the framework of the technology described here, it was found that the inert gas crossover flow rate in the fuel cell can be determined relatively easily and reliably based on the aforementioned parameters and / or operating conditions of the fuel cell system. Consequently, the fuel cell system can be monitored accordingly, simply and reliably, based on the determined inert gas crossover flow rate. Furthermore, the proposed method enables a high level of operational reliability when monitoring the fuel cell system. The proposed method can be implemented with relatively simple sensors. Various functional components of the fuel cell system can be evaluated using the inert gas crossover flow rate. The fuel cell system can then be monitored based on the evaluation of these functional components.The inert gas crossover flow rate can be understood as a characteristic value and / or characteristic behavior of the fuel cell. Accordingly, the operating mode of the fuel cell system can be adjusted or controlled based on the inert gas crossover flow rate, such that the flow rate is adjusted to a desired value or maintained at its current value. Based on the inert gas crossover flow rate, the distribution of inert gas within the fuel cell along its length and / or the temporal behavior of this distribution can be determined. Based on this distribution and / or behavior, the operating mode of the fuel cell system can be controlled.

[0009] Controlling can be understood as adjusting, steering, and / or regulating. Controlling the fuel cell system based on the inert gas crossover flow rate means that the operating mode of the fuel cell system can be adjusted and / or changed depending on the currently determined inert gas crossover flow rate. Determining can be understood as measuring, estimating, modeling, and / or calculating. For example, measured values ​​can be obtained using sensors and / or a virtual model, which are then processed by a computing unit to infer the desired values ​​and / or flow rates. The inert gas crossover flow rate can be understood as the quantity of inert gas that diffuses from the cathode to the anode in a specific time. Fuel can be understood as hydrogen and / or a hydrogen-containing gas.Inert gas can be nitrogen or a nitrogen-containing gas. Determining the recirculation flow rate can mean determining the flow rate of the total gas flowing through the recirculation path. Concentration can be any type of proportion of a whole, for example, a volume fraction, a mass fraction, and / or a substance fraction ( ).

[0010] Furthermore, it is possible that the procedure includes the following steps: - Determining the inert gas concentration at the anode and - Determining an average inert gas concentration in the fuel cell, and - Determining the inert gas crossover flow rate based on the inert gas concentration at the anode and the average inert gas concentration in the fuel cell.

[0011] It was recognized that the inert gas concentration and the average inert gas concentration in the fuel cell can be determined relatively easily, and that the inert gas crossover flow rate can be determined simply, more accurately, and more reliably by considering these parameters. The inert gas concentration can be determined at a predefined fuel cell humidity in and / or at the fuel cell and / or at a predefined fuel temperature in and / or at the fuel cell. The inert gas concentration can be understood as a fraction of the inert gas. A concentration can be understood as a fraction of a total quantity. The respective fraction can be used as a dimensionless quantity.Determining the stoichiometric fuel flow rate in the fuel cell can be understood as determining the stoichiometric fuel flow rate into the fuel cell and / or the stoichiometric fuel flow rate within the fuel cell. Determining the inert gas concentration at the anode can be understood as determining the inert gas concentration in the region of the anode outlet, in the region of the anode inlet, outside the fuel cell near the anode, and / or inside the fuel cell near the anode. For example, the inert gas concentration can be determined at the anode inlet and / or at the anode outlet.

[0012] According to one implementation variant of the technology described here, it is possible that the fuel cell system includes a purge path and the process comprises the following steps: - Determining a purge mixture flow through the purge path and - Determining the inert gas crossover flow rate based on the determined purge flow rate.

[0013] It was recognized that the purge flow rate can be determined relatively easily and that the inert gas crossover flow rate can be determined even more accurately and / or reliably by taking the purge flow rate into account. The purge flow rate can be understood as a portion of the anode exhaust gas that is routed through the purge path into the environment of the fuel cell system and is therefore not directed into the recirculation path.

[0014] Furthermore, the procedure described here can include the following steps: - Providing a fuel cell length variable, - Providing a fuel cell length and - Determining the inert gas crossover flow rate based on the fuel cell length variable and the fuel cell length.

[0015] It has been found that the inert gas crossover flow rate can be determined with particular accuracy and yet still relatively easily by taking into account the fuel cell length variables and the fuel cell length itself. Furthermore, this method allows for the calculation of the inert gas concentration with resolution across the fuel cell length. This is especially advantageous when the fuel cell is a split fuel cell stack, the inert gas concentration is measured as accurately as possible between the two stack sections, and subsequently, an average inert gas concentration at the fuel cell inlet and / or outlet needs to be determined. The fuel cell length variable can be understood as a variable gas flow length of anode gas between the anode inlet and the anode outlet. At the anode outlet, the anode gas can be understood as an anode exhaust gas.The fuel cell length variable can be understood as the length over which anode gas is passed within the fuel cell. The fuel cell length can also be understood as a standardized length of the fuel cell. If the fuel cell refers to a fuel cell stack with multiple fuel cell units, the fuel cell length can be understood as a standardized fuel cell stack length, particularly in one direction of gas flow through the fuel cell stack.

[0016] In the method described here, the inert gas crossover flow rate can be determined based on the following relationship: yN2(x)=yN2Out⋅n˙Rezi+x / L⋅n˙N2Crossn˙Pg+(n˙H2Stoic+n˙H2Cross)⋅(1−x / L)+n˙Rezi+x / L⋅n˙N2Cross , where: ṅ Pg = Purge flow rate [mol / s], ṅ H2Stoich = Flow rate of stoichiometrically converted fuel [mol / s], ṅ dp= Flow rate responsible for pressure change in fuel cell [mol / s], ṅ H2Cross = fuel crossover flow rate [mol / s], ṅ N2Cross = inert gas crossover flow rate [mol / s], ṅ Rezi = Recirculation flow rate [mol / s], y N2 = Inert gas concentration [-], and y N2Out = Inert gas concentration at the anode outlet [-].

[0017] It was found that the inert gas crossover flow rate can be determined relatively accurately and yet simply using this equation. To carry out the procedure, it can be assumed that the pressure in a fuel supply system is kept constant. Furthermore, ṅ dp= 0. According to the proposed equation, a steady-state operating point can be determined and / or considered, based on which the fuel cell system can be easily controlled. The stoichiometrically converted fuel can be understood as the fuel converted stoichiometrically and / or electrochemically in the fuel cell. The corresponding fuel flow rate can be determined based on a calculated fuel cell flow rate and / or fuel cell stack flow rate, as well as Faraday's law. The purge flow rate can be determined based on a calculated anode pressure and a specific valve equation. The recirculation flow rate can be determined based on the ratio ṅ Rezi / ṅ H2StoicThis ratio can be determined based on known and / or determined measured values ​​of a recirculation module, such as an injector / ejector, a blower, and / or a pump. The equation mentioned can be used analogously for the alternative implementation variants of the process described herein. If, for example, the purge flow rate is not to be considered, it can be omitted from the equation. Similarly, if the fuel cell length variable and / or the fuel cell length are not to be considered, these can also be omitted from the equation. The abbreviations N2 and H2 are placeholders for inert gas, in particular nitrogen, and fuel, in particular hydrogen.

[0018] According to another variant of the procedure described here, it is possible to perform the following steps: - Determining a change in the average inert gas concentration and - Determining the inert gas crossover flow rate based on the change in the average inert gas concentration.

[0019] Within the framework of the technology described here, it was found that the inert gas crossover flow rate can be determined particularly easily and accurately based on the change in the average inert gas concentration. Furthermore, it was found that the average inert gas concentration can be determined particularly easily and accurately based on the following relationships: yN2Aver=1L∫0LyN2Out⋅n˙Rezin˙Pg+n˙H2Stoic⋅(1−xL)+n˙Rezi and yN2Aver=yN2Out⋅n˙Rezin˙H2Stoic⋅ln(n˙Pg+n˙H2Stoic+n˙Rezin˙Pg+n˙Rezi) , where: y N2Aver = Average inert gas concentration in fuel cell [-].

[0020] The following conditions may apply: n˙N2Cross,n˙H2Cross< <n˙Rezi,n˙H2Stoich,n˙Pg

[0021] That is, in the two equations mentioned, for y N2Aver Can the aforementioned condition and / or assumption be used to solve the previously mentioned equation for y? N2 (x) to simplify. A significant difference in the respective quantity flows can be understood to mean that the quantity flows ṅ N2Cross and ṅ H2Cross less than 10%, less than 1%, less than 0.1% or less than 0.01% of the quantity flows ṅ Rezi , ṅ H2Stoich , ṅ Pg can or should be.

[0022] Furthermore, it is possible that the average inert gas concentration in the procedure described here is determined based on the following relationships: yN2Aver=1L∫0LyN2Out⋅n˙Rezin˙H2Stoic⋅(1−xL)+n˙Rezidx and yN2Aver=yN2Out⋅n˙Rezin˙H2Stoic⋅ln(n˙H2Stoic+n˙Rezin˙Rezi)=yN2Out⋅β⋅ln(1+1 / β) , where yN2Aver = Average inert gas concentration in fuel cell [-], and β=Recirculation ratio˙Rezin˙H2Stoic[−].

[0023] This approach is particularly useful when purging is not performed. In this case, the relationship can be simplified accordingly. The recirculation ratio β can be determined especially easily. There is no need to directly determine the mass flows. That is, only the ratio according to β is required.

[0024] Furthermore, it is possible that the procedure includes the following steps: - Determining an inert gas partial pressure at the anode, - Determining an inert gas partial pressure at the cathode, - Determining the inert gas concentration at the cathode, - Determining a crossover factor and - Determining the inert gas crossover flow rate based on the inert gas partial pressure, the inert gas concentration, and the crossover factor.

[0025] It has been found that the inert gas crossover flow rate can be determined particularly accurately and relatively easily by taking these parameters and / or operating conditions into account. The crossover factor is generally known to those skilled in the art. In this case, the crossover factor can be determined and / or provided depending on a temperature in and / or at the fuel cell and / or depending on a specific activation energy. That is, the crossover factor can be determined dynamically and / or read out as a predefined value from a storage medium. The inert gas crossover flow rate can be determined based on the following relationship: n˙N2Cross=D⋅(pKath⋅yN2Kath−pAnod⋅yN2Aver) , where p Kath = Total pressure at the cathode, p Anod = Total pressure at the anode, y N2Kath = inert gas concentration at the cathode, y N2Aver = Average inert gas concentration in fuel cell, and D = Crossover Factor.

[0026] The pressures can be determined using sensors and / or models. If the fuel cell is operated with air or pure oxygen, the inert gas concentration at the cathode is particularly easy to determine. The inert gas partial pressure at the anode corresponds to the product p Anod · y N2Aver . The inert gas partial pressure at the cathode corresponds to the product p Kath · y N2Kath .

[0027] According to another aspect of the technology described here, a device with a control unit is proposed, wherein the control unit is configured to execute a procedure as described above. For this purpose, the control unit may include a control unit, an ECU, a computer, sensors, and / or actuators, which may be configured to perform the procedure.

[0028] According to another aspect of the technology described herein, a fuel cell system with the device described above is proposed. The fuel cell system also includes a fuel cell with an anode and a cathode, a fuel path, an anode inlet path, an anode exhaust path, a recirculation path, and a mixing section in which fuel from the fuel path is mixed with anode exhaust from the recirculation path and fed as a mixed gas into the anode inlet path. The fuel cell system can be configured to perform a process as described above. The fuel cell system can be configured as a PEM fuel cell system.

[0029] The fuel cell system is preferably configured for mobile applications such as vehicles. The fuel cell system can be configured to provide electrical energy to at least one of the vehicle's drive units. The drive unit can be a machine, for example, an electric motor, used to propel the vehicle. The term "fuel cell" can refer to a single fuel cell or, in particular, a fuel cell stack with multiple fuel cells. In its simplest form, the fuel cell is an electrochemical energy converter that converts fuel and oxidant into reaction products, generating electricity and heat in the process. The anode and cathode of a single fuel cell can be separated by an ion-selective or ion-permeable separator.If the fuel cell is configured in the form of a fuel cell stack, the anode can be understood as an anode area of ​​the fuel cell stack and the cathode as a cathode area of ​​the fuel cell stack.

[0030] Another aspect of the proposed technology concerns a vehicle with a fuel cell system as described above, wherein the fuel cell system is configured to generate electricity in the vehicle. The vehicle may have at least one electric motor for propelling the vehicle, and the fuel cell system may be configured to supply power to this at least one electric motor. Thus, the vehicle offers the same advantages as described in detail with regard to the fuel cell system. The term "vehicle" can refer to a motor vehicle such as a motorized two-wheeler, a passenger car, or a truck. It can also refer to a road vehicle, an aircraft, a watercraft, a rail vehicle, or a robot.The term "vehicle" can also include a purely electric vehicle and a hybrid electric vehicle, which, in addition to at least one electric motor, has an internal combustion engine for propulsion. The term "vehicle" can also include a fuel cell vehicle and / or a so-called FCEV (Fuel Cell Electric Vehicle).

[0031] Furthermore, the technology disclosed herein comprises a computer program product and a computer-readable, in particular non-volatile, storage medium on which the computer program product is stored. Thus, the computer program product and the computer-readable storage medium also offer the advantages described above. The computer program product can include instructions which, when executed by a computer, for example, a computer of a vehicle control unit, cause the computer to execute the proposed method in a vehicle as described above.

[0032] The computer program product can be implemented as machine-readable instruction code in any suitable programming language and / or machine language, such as Java, C++, C#, and / or Python. The computer program product can be stored on a machine-readable storage medium such as a data disk, removable drive, volatile or non-volatile memory, or onboard memory / processor. The instruction code can program a computer and other programmable devices, such as a control unit, to perform the desired functions. Furthermore, the computer program product can be made available on a network, such as the internet, from which it can be downloaded by a user as needed.The computer program product can be implemented using software, one or more special electronic circuits (i.e., in hardware), or in any hybrid form (i.e., using software components and hardware components).

[0033] Further features and combinations of features of the proposed technology will become apparent from the following description of various embodiments, which are schematically illustrated in the figures. All features and / or advantages arising from the claims, the description, and the figures, including design details and spatial arrangements, can be significant both individually and in combination with one another.

[0034] They each show schematically: Fig. 1 a fuel cell system according to an embodiment of the present technology, Fig. 2 a vehicle with a fuel cell system according to an embodiment of the present technology, Fig. 3 a computer-readable storage medium with a computer program product stored thereon according to an embodiment of the present technology, Fig. 4 a flowchart to explain a process according to an embodiment of the present technology, Fig. 5 a model for determining an inert gas crossover mass flow rate and Fig. 6 a diagram for determining an inert gas crossover flow rate.

[0035] Elements with the same function and mode of operation are each provided with the same reference symbols in the figures.

[0036] Fig. Figure 1 shows a fuel cell system 10 according to a possible embodiment in the form of a PEM fuel cell system. The fuel cell system 10 shown comprises a fuel cell 11 with an anode 12 and a cathode 13. The fuel cell 11 has an anode inlet 21, an anode outlet 22, a cathode inlet 23, and a cathode outlet 24. The fuel cell system 10 further comprises a fuel path 14, an anode inlet path 15, an anode exhaust path 16, a recirculation path 17, a cathode inlet path 26, a cathode exhaust path 27, an injector / ejector 18, a purge path 19, and a purge valve 25. Fuel can be supplied via the fuel path 14 as primary fluid from a Fig. The pressure vessel 70 of a vehicle 100, as depicted in Figure 2, is directed to the injector / ejector 18. Anode gas can be directed as a mixed gas from the injector / ejector 18 into the fuel cell 11 via the anode inlet path 15. Anode exhaust gas can be directed out of the fuel cell 11 via the anode exhaust path 16. Anode exhaust gas from the fuel cell 11 can be directed or drawn into the injector / ejector 18 as secondary fluid via the recirculation path 17 and then directed back into the fuel cell 11 via the anode inlet path 15. Anode exhaust gas from the fuel cell 11 can be directed into the cathode exhaust path 27 via the purge path 19. In the injector / ejector 18 there is a mixing area 29 in which anode exhaust gas from the recirculation path 17 is mixed with fuel from the fuel path 14.

[0037] The fuel cell system 10 shown comprises a first pressure sensor 31, a second pressure sensor 32, a first gas sensor 33, and a second gas sensor 34. The first pressure sensor 31 is configured to determine a gas pressure at the anode 12 and / or to measure pressure values ​​in the anode inlet path to determine an inert gas partial pressure at the anode 12. The second pressure sensor 32 is configured to determine a gas pressure at the cathode 13 and / or to measure pressure values ​​in the cathode inlet path 26 to determine an inert gas partial pressure at the cathode 13. The first gas sensor 33 is configured to determine gas concentrations or gas fractions in the anode inlet path 15. The second gas sensor 34 is configured to determine gas concentrations or gas fractions in the recirculation path 17.Furthermore, the fuel cell system 10 includes a current and / or voltage sensor 35, by means of which the current, voltage, and / or power of the fuel cell 11 can be determined. In addition, the fuel cell system 10 includes a control unit 20. The control unit 20 and the various sensors 31, 32, 33, 34, 35 form the main components of a device 80, which is configured to carry out a subsequently described method for controlling the fuel cell system 10.

[0038] In Fig. Figure 2 shows a vehicle 100 in the form of a passenger car. The vehicle 100 has a fuel cell system 10 as described above, comprising a fuel cell 11 and a pressure vessel 70 for fuel. The vehicle 100 also has two electric motors 60 for propelling the vehicle 100. The fuel cell system 10 is configured to generate electrical current in the vehicle 100, which can be used to power the electric motors 60. In addition, the vehicle 100 has a control unit 20 configured to execute the procedure described above.

[0039] Fig. Figure 3 shows a computer-readable and non-volatile storage medium 50 on which a computer program product 40 is stored. The storage medium 50 is in the form of a flash drive. The computer program product 40 comprises instructions which, when executed by a computer, cause the computer program product 40 to execute the described method in the fuel cell system 10 shown. The term "computer" can refer to a part of the control unit 20 and / or the device 80 described above.

[0040] With reference to Fig. Section 4 describes a method for controlling the fuel cell system 10. In a first step S1, various operating parameters of the fuel cell system 10 are determined. In a step S1a, a stoichiometric fuel flow rate of a stoichiometrically converted quantity of fuel in the fuel cell 11 is determined. In a step S1b, a recirculation flow rate in the recirculation path 17 is determined. In a step S1c, an inert gas concentration at the anode 12 is determined. In a step S1d, an average inert gas concentration in the fuel cell 11 is determined. In a step S1e, a purge flow rate through the purge path 19 is determined. In a step S2, a fuel cell length variable x and a fuel cell length L are provided.In a third step S3, an inert gas crossover flow rate in the fuel cell 11 is determined based on the stoichiometric fuel flow rate, the recirculation flow rate, the inert gas concentration at the anode 12, the average inert gas concentration in the fuel cell 11, the purge flow rate, the fuel cell length variable x, and the fuel cell length L. In a fourth step S4, the fuel cell system 10 is controlled based on the determined inert gas crossover flow rate.

[0041] Fig. Figure 5 shows a model for determining an inert gas crossover flow rate according to the method described above in further detail or according to a possible implementation variant. In particular, in Fig. Figure 5 shows the flow rates of the respective gases at the various areas of the fuel cell 11 and, in particular, at the anode 12. In the example shown, the inert gas crossover flow rate is determined based on the following relationship: yN2(x)=yN2Out⋅n˙Rezi+x / L⋅n˙N2Crossn˙Pg+n˙H2Stoic+n˙H2Cross⋅(1−x / L)+n˙Rezi+x / L⋅n˙N2Cross , where: ṅ Pg = Purge flow rate [mol / s], ṅ H2Stoich = Flow rate of stoichiometrically converted fuel [mol / s], ṅ dp = Flow rate responsible for pressure change in fuel cell [mol / s], ṅ H2Cross = fuel crossover flow rate [mol / s], ṅ N2Cross = inert gas crossover flow rate [mol / s], ṅ Rezi = Recirculation flow rate [mol / s], y N2 = Inert gas concentration [-], and y N2Out = Inert gas concentration at the anode outlet [-].

[0042] Fig. Figure 6 shows a diagram according to another embodiment in which the inert gas crossover flow rate is determined based on a change in the average inert gas concentration. The following equations are used to supplement the equation above: yN2Aver=1L∫0LyN2Out⋅n˙Rezin˙Pg+n˙H2Stoic⋅(1−x / L)+n˙Rezidx and yN2Aver=yN2Out⋅n˙Rezin˙H2Stoic⋅lnn˙Pg+n˙H2Stoic+n˙Rezin˙Pg+n˙Rezi , where: y N2Aver = Average inert gas concentration in fuel cell [-] assuming: n˙H2Cross,n˙H2Cross< <n˙Rezi,n˙H2Stoich,n˙Pg

[0043] Furthermore, the following applies: n˙N2Cross=D⋅(pKath⋅yN2Kath−pAnod⋅yN2Aver) , where p Anod = Total pressure at the anode 12, p Kath = Total pressure at the cathode 13, and Y N2Kath = inert gas concentration at cathode 13.

[0044] In Fig. Figure 6 shows the inert gas concentration or the nitrogen concentration plotted against a standardized fuel cell or fuel stack length. In the case of the Fig. In example 6, the inert gas concentration at the anode outlet 22 (y) is shown. N2Out ) determined. Alternatively or additionally, the inert gas concentration at the anode inlet 21 could be determined. Based on the determined inert gas concentrations or corresponding concentration and / or proportion values, an average inert gas concentration in the fuel cell (y) is calculated. N2AverThe average inert gas concentration is determined. Subsequently, a change in the average inert gas concentration is calculated. Based on this change, the inert gas crossover flow rate can be determined. In the example shown, an inert gas crossover of 0.3 volume percentage points from cathode 13 to anode 12 can be inferred. Based on this, a corresponding inert gas crossover flow rate is derived.

[0045] The technology disclosed here allows for further design principles in addition to those illustrated. That is to say, the technology should not be considered limited to the embodiments explained with reference to the figures. Reference symbol list 10 Fuel cell systems 11 Fuel cell 12 Anode 13 Cathode 14 Fuel Path 15 Anode inlet path 16 Anode exhaust path 17 Recirculation pathway 18 Injector / Ejector 19 Purge Trail 20 Control unit 21 Anode input 22 Anode output 23 Cathode input 24 Cathode output 25 Purge valve 26 Cathode inlet path 27 Cathode exhaust path 29 Mixing area 31 First pressure sensor 32 Second pressure sensor 33 First gas sensor 34 Second gas sensor 35 Current and / or voltage sensor 40 Computer program product 50 storage medium 60 electric motor 70 pressure vessels 100 vehicles L Fuel cell length x Fuel cell length variable

Claims

[1] Method for controlling a fuel cell system (10), wherein the fuel cell system (10) comprises a fuel cell (11) with an anode (12) and a cathode (13), an anode inlet (21), an anode outlet (22), a fuel path (14), an anode inlet path (15), an anode exhaust path (16), a recirculation path (17) and a mixing area (29), wherein in the mixing area (29) fuel from the fuel path (14) is mixed with anode exhaust from the recirculation path (17) and is directed as a mixed gas into the anode inlet path (15), comprising: - Determining a stoichiometric fuel flow rate of a quantity of fuel stoichiometrically converted in the fuel cell (11), - Determining a recirculation flow rate in the recirculation path (17), - Determining an inert gas crossover flow rate in the fuel cell (11) based on the stoichiometric fuel flow rate and the recirculation flow rate, and - Checking the fuel cell system (10) based on the determined inert gas crossover flow rate. [2] Method according to claim 1, comprising: - Determining an inert gas concentration at the anode (12), - Determining an average inert gas concentration in the fuel cell (11), and - Determining the inert gas crossover flow rate based on the inert gas concentration at the anode (12) and the average inert gas concentration in the fuel cell (11). [3] Method according to any one of the preceding claims, wherein the fuel cell system (10) comprises a purge path (19), comprising: - Determining a purge mixture flow through the purge path (19) and - Determining the inert gas crossover flow rate based on the determined purge flow rate. [4] Method according to any one of the preceding claims, comprising: - Providing a fuel cell length variable (x), - Providing a fuel cell length (L) and - Determining the inert gas crossover flow rate based on the fuel cell length variable (x) and the fuel cell length (L). [5] Method according to any of the preceding claims, wherein the inert gas crossover flow rate is determined based on the following relationship: yN2(x)=yN2Out⋅n˙Rezi+x / L⋅n˙N2Crossn˙Pg+n˙H2Stoic+n˙H2Cross⋅(1−x / L)+n˙Rezi+x / L⋅n˙N2Cross , where: ṅ Pg = Purge flow rate [mol / s], ṅ H2Stoich = Flow rate of stoichiometrically converted fuel [mol / s], ṅ dp = Flow rate responsible for pressure change in fuel cell [mol / s], ṅ H2Cross = fuel crossover flow rate [mol / s], n N2Cross = inert gas crossover flow rate [mol / s], ṅ Rezi= Recirculation flow rate [mol / s], y N2 = Inert gas concentration [-], and Y N2Out = Inert gas concentration at the anode outlet [-]. [6] Method according to any one of the preceding claims, comprising: - Determining a change in the average inert gas concentration and - Determining the inert gas crossover flow rate based on the change in the average inert gas concentration. [7] Method according to any of the preceding claims, wherein the average inert gas concentration is determined based on the following relationships: yN2Aver=1L∫0LyN2Out⋅n˙Rezin˙Pg+n˙H2Stoic⋅(1−x / L)+n˙Rezidx and yN2Aver=yN2Out⋅n˙Rezin˙H2Stoic⋅ln(n˙Pg+n˙H2Stoic+n˙Rezin˙Pg+n˙Rezi) , where y N2Aver = Average inert gas concentration in fuel cell [-]. [8] Method according to any of the preceding claims, wherein the average inert gas concentration is determined based on the following relationships: yN2Aver=1L∫0LyN2Out⋅n˙Rezin˙H2Stoic⋅(1−x / L)+n˙Rezidx and yN2Aver=yN2Out⋅n˙Rezin˙H2Stoic⋅ln(n˙H2Stoic+n˙Rezin˙Rezi)=yN2Out⋅β⋅ln(1+1 / β) , where y N2Aver = Average inert gas concentration in fuel cell [-], and β=Recitulation ratio˙Rezin˙H2Stoic[−]. [9] Method according to any one of the preceding claims, comprising: - Determining an inert gas partial pressure at the anode (12), - Determining an inert gas partial pressure at the cathode (13), - Determining an inert gas concentration at the cathode (13), - Determining a crossover factor and - Determining the inert gas crossover flow rate based on the inert gas partial pressure, the inert gas concentration, and the crossover factor. [10] Device (80) comprising a control unit (20) configured to perform a method according to any of the preceding claims. [11] Fuel cell system (10) comprising a fuel cell (11) with an anode (12) and a cathode (13), an anode inlet (21), an anode outlet (22), a fuel path (14), an anode inlet path (15), an anode exhaust path (16), a recirculation path (17) and a mixing area (29), wherein in the mixing area (29) fuel from the fuel path (14) is mixed with anode exhaust from the recirculation path (17) and is directed as mixed gas into the anode inlet path (15), and a control unit (20) according to claim 10. [12] Vehicle (100) with a fuel cell system (10) according to claim 11, wherein the fuel cell system (10) is configured to generate electrical current in the vehicle (100). [13] Computer program product (40), comprising instructions which, when the computer program product (40) is executed by a computer, cause it to execute the method according to one of claims 1 to 9 in a fuel cell system (10) according to claim 11 and / or in a vehicle (100) according to claim 12. [14] Computer-readable storage medium (50) with a computer program product (40) stored thereon according to claim 13.

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