Method for operating a fuel cell system, control unit and fuel cell system

Abstract

The invention relates to a method for operating a fuel cell system (100) with at least one fuel cell stack (101) and at least one air system (10), wherein a stack bypass path (13) with a bypass valve (ByCath), in particular a tightly closing one, is provided in the air system (10) between an air supply path (11) and an exhaust air path (12) to the at least one fuel cell stack (101), and wherein a sensor (S) for measuring a humidity and / or an oxygen content is arranged in the exhaust air path (12) in the air system (10), preferably downstream of a supply line of the stack bypass path (13) to the exhaust air path (12) and preferably upstream of an EGR / EGT branch from the exhaust air path (12), comprising: - carrying out a first measurement (F1) of a humidity and / or oxygen content of outside air, - Carrying out a second measurement (F2) of a humidity and / or oxygen content of a stack exhaust gas, - carrying out a third measurement (F3) of a humidity and / or an oxygen content of a transferred air of an exhaust gas recirculation (EGR) and / or an exhaust gas transfer (EGT), - taking into account at least one measurement (F1, F2, F3) when operating the fuel cell system (100), in particular during exhaust gas recirculation (EGR) and / or exhaust gas transfer (EGT).

Description

[0001] The invention relates to a method for operating a fuel cell system. Furthermore, the invention relates to a computer program product, a control unit, and a fuel cell system. State of the art

[0002] In vehicles (FCV, English for "Fuel Cell Vehicle") in which the drive energy is supplied (among other things) by one (or more) fuel cell systems (FCS, English for "Fuel Cell System"), the oxidizing agent oxygen from the ambient air is usually used to react with hydrogen in the fuel cell to form water (or water vapor) and thus to supply electrical power through electrochemical conversion.

[0003] The cathode exhaust gas is oxygen-depleted.

[0004] Lambda sensors (originally developed for combustion engines) are often used in the exhaust gas path of fuel cell systems to control and / or monitor the reaction.

[0005] In some systems, exhaust gas recirculation (EGR) is used in the cathode path to recirculate part of the exhaust gas back into the intake air path, e.g. to deoxygenate the intake air of the stack cathode paths.

[0006] In some systems, an exhaust gas transfer (EGT) path is used to transfer part of the exhaust gas from one stack to the intake air path of another stack.

[0007] In some systems, operating strategies are used that inertize the cathode region of the stack and, if necessary, also the anode path.

[0008] A lambda probe can be used before the aforementioned processes to determine the oxygen content of the exhaust gas and to enable targeted implementation of an operating strategy / control and / or diagnostics / plausibility checks.

[0009] Oxygen sensors are usually installed upstream of the stack bypass path's entry into the exhaust gas path in order to be able to directly measure the stack's exhaust gas. Disclosure of the invention

[0010] The present invention provides a method for operating a fuel cell system having the features of the independent method claim. Furthermore, the invention provides a corresponding computer program product, a corresponding control unit, and a corresponding fuel cell system having the features of the independent claims. Features and details described in connection with the various embodiments and / or aspects of the invention naturally also apply in connection with the other embodiments and / or aspects, and vice versa, so that reciprocal reference is or can always be made to the individual embodiments and / or aspects with regard to the disclosure.

[0011] The present invention provides, according to the first aspect: a method for operating a fuel cell system having at least one fuel cell stack and at least one air system.

[0012] In the air system, a stack bypass path with a, in particular tightly closing, bypass valve is provided between a supply air path and an exhaust air path to the at least one fuel cell stack.

[0013] In the air system, a sensor for measuring a humidity and / or an oxygen content is arranged in the exhaust air path, preferably downstream of a feed line of the stack bypass path to the exhaust air path and preferably upstream of an EGR / EGT branch from the exhaust air path (or also in an exhaust gas recirculation and / or an exhaust gas transfer path).

[0014] The procedure comprises the following steps: - Carrying out a first measurement of the humidity and / or oxygen content of the outside air, especially with the open or partially open bypass valve, preferably with closed stack shut-off valves, - Carrying out a second measurement of the humidity and / or oxygen content of a stack exhaust gas, especially with the closed, preferably tightly closed, bypass valve, preferably with the open or partially open stack shut-off valves, - Carrying out a third measurement of a humidity and / or oxygen content of a transferred air of an exhaust gas recirculation and / or an exhaust gas transfer, - Consider at least one measurement when operating the fuel cell system, especially with exhaust gas recirculation (EGR) and / or exhaust gas transfer (EGT).

[0015] The steps of the method can be performed in the specified order or in a modified order. The steps of the method can be performed simultaneously, at least partially simultaneously, and / or sequentially.

[0016] The fuel cell system (or "system" for short) can preferably be used for mobile applications, for example, in vehicles, particularly fuel-powered vehicles, preferably in the commercial vehicle sector with high service life requirements. The fuel cell system can serve as the main energy supplier for a vehicle. Furthermore, the fuel cell system according to the invention can serve as an energy supply for a power take-off drive and / or an auxiliary drive of a vehicle, for example, a hybrid vehicle. However, the fuel cell system can also be used for stationary applications, for example, in generators.

[0017] The fuel cell system can comprise multiple fuel cell stacks (or stacks for short), each with multiple stacked fuel cells and the associated functional systems, including media systems (air or cathode system, fuel or anode system, cooling system) and an electrical system. Preferably, the fuel cell system can comprise multiple modules in the form of individual stacks with multiple stacked fuel cells.

[0018] The method addresses the use of oxygen sensors, particularly in a multi-stack system with exhaust gas recirculation (EGR) and / or exhaust gas transfer (EGT).

[0019] The invention recognizes that oxygen sensors measure humidity in addition to oxygen content.

[0020] It is proposed: I. to arrange an oxygen sensor (e.g. lambda probe or lambda sensor) in the exhaust air path (or exhaust gas path), preferably downstream of the supply line of the stack bypass path to the stack exhaust air path and upstream of an EGR / EGT branch from the exhaust air path (or also in an exhaust gas recirculation and / or an exhaust gas transfer path). II. to design a bypass valve, preferably a tightly closing valve.

[0021] It is proposed: F1: first measurement of humidity and / or oxygen content of the outside air, F2: second measurement of humidity and / or oxygen content in the stack exhaust gas, preferably with the cathode bypass valve ByCath tightly closed, F3: third measurement of humidity and / or oxygen content of the recirculated and / or transferred exhaust air.

[0022] In F1, the oxygen sensor is used to determine the humidity and / or oxygen content (e.g., when driving through a tunnel, parking garage, etc.) of the outside air or the input humidity in the cathode path (without an external humidifier) ​​or the input humidity in the humidifier. This can be done at startup, temporarily during operation (especially in standby, during start-stop, etc.), or before / when shutting down a stack. In systems with EGT, this can be enabled simultaneously with the operation of another stack. This can be done when the ambient conditions are unknown or changing.

[0023] At F2, the stack exhaust gas can be accurately detected and, if necessary, adjusted if the cathode bypass is tightly shut off, ie, the bypass valve is switched to sealing mode.

[0024] At F3, the recirculated and / or transferred exhaust air can be measured and adjusted if necessary.

[0025] The procedure can achieve several key benefits: - Extended use of oxygen sensor to improve operating strategies, control, diagnostics, plausibility checks, etc., - Detection of outside air (humidity and oxygen content) possible temporarily or in parallel with normal operation.

[0026] As already mentioned above, it can be planned that the first measurement is carried out under unknown or changing ambient conditions, e.g. when driving through an environment with potentially reduced oxygen content, such as a tunnel, parking garage, or similar. In principle, it is conceivable that the first measurement is carried out before the second measurement and / or before the third measurement. Furthermore, it is conceivable that the first measurement is carried out between the second measurement and / or before the third measurement, e.g. in start-stop phases, e.g. when at least one stack is transferred to standby and / or is switched off or is switched off. In this way, the outside air (humidity and oxygen content) can be measured temporarily or in parallel with normal operation. Different functions, operating strategies, control, diagnostics, and plausibility checks can benefit from this.

[0027] When performing the first measurement, at least one of the following actions can be performed: - Opening, partially opening and / or regulating the bypass valve, - Closing, in particular tightly closing, and / or keeping stack shut-off valves closed, - optionally closing, in particular tightly closing, and / or keeping closed an exhaust gas recirculation valve and / or an exhaust gas transfer, - Operating at least one air compressor, preferably in a cathode bypass mode.

[0028] In this way, the stack bypass path can be used for the first measurement of humidity and / or oxygen content of outside air.

[0029] When performing the second measurement, at least one of the following actions can be performed: - Closing, in particular tightly closing, and / or keeping the bypass valve closed, - Opening, partially opening and / or regulating stack shut-off valves, - optionally closing, in particular tightly closing, and / or keeping closed an exhaust gas recirculation valve and / or an exhaust gas transfer valve.

[0030] In this way, the second measurement of a humidity and / or oxygen content of a stack exhaust gas can be carried out.

[0031] When performing the third measurement, at least one of the following actions can be performed: - Closing, in particular tightly closing, and / or keeping the bypass valve closed, - Opening, partially opening and / or regulating stack shut-off valves, - Opening, partially opening and / or regulating an exhaust gas recirculation valve and / or an exhaust gas transfer valve, in particular to set a desired oxygen concentration and / or humidity in the supply air path.

[0032] In this way, the third measurement of humidity and / or oxygen content of the recirculated and / or transferred exhaust air can be carried out.

[0033] During the second and / or third measurement, it is generally conceivable to consider stack, bypass, EGR, and / or EGT mass flows when determining an oxygen concentration and / or humidity at the stack outlet if an operating strategy requires that the stack bypass path, exhaust gas recirculation, and / or exhaust gas transfer path be flowed through during ongoing stack operation. By considering the mass flows and, if necessary, stack operating conditions, such as current, various oxygen concentrations and / or humidity states of the individual fluid flows can be determined.

[0034] In systems with multiple stacks and / or multiple air systems, it may be advantageous to perform at least one of the following actions when performing the first measurement: - Opening, partially opening and / or regulating a first bypass valve, - closing, in particular tightly closing, and / or keeping closed stack shut-off valves of a first stack, - optionally closing, in particular tightly closing, and / or keeping closed an exhaust gas recirculation valve and / or an exhaust gas transfer, - Operating at least one first air compressor, preferably in a cathode bypass operating mode.

[0035] In this way, at least one stack bypass path can be used for the initial measurement of humidity and / or oxygen content of outside air. The other stack and / or the other air system can remain idle during this time.

[0036] In systems with multiple stacks and / or multiple air systems, it may be advantageous to perform at least one of the following actions when performing the first measurement and / or the second measurement: - Opening, partially opening and / or regulating a first bypass valve, - closing, in particular tightly closing, and / or keeping closed a second bypass valve, - closing, in particular tightly closing, and / or keeping closed stack shut-off valves of a first stack, - Opening, partially opening and / or regulating stack shut-off valves of another stack, - Operating at least one first air compressor, preferably in a cathode bypass operating mode, - Operating at least a second air compressor, preferably in a normal operating mode.

[0037] In this way, a combined measurement of a humidity and / or an oxygen content at the stack outlet can be carried out, preferably comprising the first measurement of a humidity and / or an oxygen content of an outside air and / or the second measurement of a humidity and / or an oxygen content of a stack exhaust gas.

[0038] In systems with multiple stacks and / or multiple air systems, it may be advantageous to perform at least one of the following actions when performing the second measurement and / or the third measurement: - closing, in particular tightly closing, and / or keeping closed a first bypass valve, - closing, in particular tightly closing, and / or keeping closed a second bypass valve, - Opening, partially opening and / or regulating stack shut-off valves of a first stack, - Opening, partially opening and / or regulating stack shut-off valves of another stack, - Opening, partially opening and / or regulating an exhaust gas transfer valve, in particular to set a desired oxygen concentration and / or humidity in the supply air of a second stack, - Operating at least one first air compressor, preferably in a normal operating mode, - Operating at least a second air compressor, preferably in a normal operating mode.

[0039] In this way, a combined measurement of a humidity and / or an oxygen content at the stack outlet can be carried out, preferably comprising the second measurement of a humidity and / or an oxygen content of a stack exhaust gas and / or the third measurement of a humidity and / or an oxygen content of the recirculated and / or transferred exhaust air.

[0040] If, in systems with multiple stacks and / or multiple air systems, an operating strategy requires that at least one stack bypass path, one exhaust gas recirculation path and / or one exhaust gas transfer path should be flowed through during ongoing stack operation, at least one of the following actions may be performed when performing the second measurement and / or the third measurement: - Opening, partially opening and / or regulating a first and / or a second bypass valve, - Opening, partially opening and / or regulating stack shut-off valves of a first stack, - Opening, partially opening and / or regulating stack shut-off valves of another stack, - optionally opening, partially opening and / or regulating the exhaust gas transfer valve, in particular to set a desired oxygen concentration and / or humidity in the supply air of a second stack, - Operating a first air compressor, preferably in a normal operating mode, - Operating a second air compressor, preferably in a normal operating mode.

[0041] Furthermore, when determining an oxygen concentration and / or humidity at the stack outlet during the second measurement and / or the third measurement, stack, bypass, EGR, and / or EGT mass flows can be taken into account if an operating strategy requires that at least one stack bypass path, exhaust gas recirculation, and / or exhaust gas transfer path be flowed through during ongoing stack operation. By taking the mass flows into account and, if necessary, taking stack operating conditions, such as current, into account, various oxygen concentrations and / or humidity states of the individual fluid flows can be determined.

[0042] Advantageously, the first bypass valve can be used to oxygen-enrich an exhaust air from the first stack and transfer it to an intake air from the other stack. Consequently, the sensor can be used in a first air system for mixing gas streams via a first stack bypass path and a first exhaust air path.

[0043] According to a further aspect, the invention provides a computer program product comprising instructions that, when the computer program product is executed by a computer, such as the processing unit of the control unit, cause the computer to perform the method, which can proceed as described above. The computer program product can achieve the same advantages as described above in connection with the method according to the invention. These advantages are incorporated herein by reference.

[0044] A corresponding control unit provides a further aspect of the invention. A computer program in the form of code can be stored in a memory unit of the control unit. When the code is executed by a computing unit of the control unit, the program performs a method that can proceed as described above. The control unit can achieve the same advantages as those described above in connection with the method according to the invention. These advantages are incorporated herein by reference in their entirety.

[0045] A corresponding fuel cell system with a corresponding control unit provides a further aspect of the invention. Using the fuel cell system, the same advantages described above in connection with the method according to the invention can be achieved. These advantages are incorporated herein by reference. Preferred embodiments:

[0046] The invention and its further developments, as well as their advantages, are explained in more detail below with reference to the accompanying drawings. They show schematically: Fig. 1 an example system topology, Fig. 2 another example system topology, Fig. 3 another example system topology, Fig. 4 another example system topology, Fig. 5a a first measurement, Fig. 5b a second measurement, Fig. 5c a third measurement, Fig. 5d a measurement with bypass, Fig. 6a a first measurement, Fig. 6b a combined (first and second) measurement, Fig. 6c a combined (second and third) measurement, and Fig. 6d a measurement with bypass.

[0047] In the different figures, identical parts of the invention are always provided with the same reference numerals, which is why they are usually only described once.

[0048] The Fig. 5a to 5d and 6a to 6d serve to explain a method which was developed for operating a fuel cell system 100 with at least one fuel cell stack 101 and at least one air system 10, - wherein in the air system 10, between an air supply path 11 and an exhaust air path 12 to the at least one fuel cell stack 101, a stack bypass path 13 with a, in particular tightly closing, bypass valve ByCath is provided, - and wherein in the air system 10 in the exhaust air path 12 a sensor S for measuring a humidity and / or an oxygen content is arranged, preferably downstream of a feed line of the stack bypass path 13 to the exhaust air path 12 and preferably upstream of an EGR / EGT branch from the exhaust air path 12.

[0049] Fig. 1 to 4 show different embodiments of a fuel cell system 100 with at least one fuel cell stack 101 and at least one air system 10.

[0050] Fig. 1 to 3 show different embodiments of a fuel cell system 100 with an exhaust gas recirculation EGR.

[0051] Fig. 4 shows an embodiment of a fuel cell system 100 with an exhaust gas transfer EGT.

[0052] As the Fig. As Figures 5a to 5c illustrate, the procedure has: - Carrying out a first measurement F1 of the humidity and / or oxygen content of the outside air (cf. Fig. 5a), especially with the open or partially open bypass valve ByCath, preferably with closed stack shut-off valves Vi, Va, - Carrying out a second measurement F2 of the humidity and / or oxygen content of a stack exhaust gas or exhaust air L2 (cf. Fig. 5b), especially with the closed, preferably tightly sealed, bypass valve ByCath, preferably with the open or partially open stack shut-off valves Vi, Va, - Carrying out a third measurement F3 of a humidity and / or an oxygen content of a transferred air of an exhaust gas recirculation EGR and / or an exhaust gas transfer EGT (cf. Fig. 5c), - Considering at least one measurement F1, F2, F3 when operating the fuel cell system 100, especially with exhaust gas recirculation EGR and / or exhaust gas transfer EGT.

[0053] On the one hand, it is proposed: I. to arrange an oxygen sensor S (e.g. lambda probe or lambda sensor) in the exhaust air path or exhaust gas path, preferably downstream of the feed line of the stack bypass path 13 to the exhaust air path 12 and upstream of an EGR / EGT branch from the exhaust air path 12 (or also in an exhaust gas recirculation EGR and / or an exhaust gas transfer path EGT, cf. indicated sensor S in the Fig. 1 to 4). II. to design a bypass valve ByCath, preferably a tightly closing valve.

[0054] On the other hand, it is proposed: F1: first measurement of humidity and / or oxygen content of the outside air, F2: second measurement of humidity and / or oxygen content in the stack exhaust gas or exhaust air L2, preferably with the cathode bypass valve ByCath tightly closed, F3: third measurement of humidity and / or oxygen content of the recirculated and / or transferred exhaust air.

[0055] In F1, the oxygen sensor S is used to determine the humidity and / or oxygen content (e.g., when driving through a tunnel, parking garage, etc.) of the outside air or the input humidity in the cathode path (without an external humidifier) ​​or the input humidity in the humidifier. This can be done at start-up, temporarily during operation (especially in standby, during start-stop, etc.), or before / when shutting down a stack 101, n. In systems with EGT, this can be enabled simultaneously with the operation of another stack 101, n + 1 (see [Fig. 11]. Fig. 6b).

[0056] At F2, the stack exhaust gas or the exhaust air L2 can be precisely detected and, if necessary, regulated if the stack bypass path 13 can be tightly shut off or if the bypass valve ByCath can be switched to sealing mode.

[0057] At F3, the recirculated and / or transferred exhaust air can be measured and adjusted if necessary.

[0058] The procedure can achieve several key benefits: - Extended use of oxygen sensors S to improve operating strategies, control, diagnostics, plausibility checks, etc., - Detection of outside air (humidity and oxygen content) possible temporarily or in parallel with normal operation.

[0059] As the Fig. As illustrated in Figure 5a, when performing the first measurement F1, at least one of the following actions can be performed: - Opening, partially opening and / or regulating the ByCath bypass valve, - Closing, in particular tightly closing, and / or keeping closed stack shut-off valves Vi, Va, - optionally closing, in particular tightly closing, and / or keeping closed an exhaust gas recirculation valve VEGR and / or an exhaust gas transfer valve VEGT, - Operating at least one air compressor Comp, preferably in a cathode bypass operating mode.

[0060] In this way, the stack bypass path 13 can be used for the first measurement F1 of a humidity and / or an oxygen content of an outside air.

[0061] As the Fig. As illustrated in Figure 5b, when performing the second measurement F2, at least one of the following actions can be performed: - Closing, in particular tightly closing, and / or keeping the ByCath bypass valve closed, - Opening, partially opening and / or regulating stack shut-off valves Vi, Va, - optionally closing, in particular tightly closing, and / or keeping closed an exhaust gas recirculation valve VEGR and / or an exhaust gas transfer valve VEGT.

[0062] In this way, the second measurement F2 of a humidity and / or oxygen content of a stack exhaust gas or the exhaust air L2 can be carried out.

[0063] As the Fig. As illustrated in Figure 5c, when performing the third measurement F3, at least one of the following actions can be performed: - Closing, in particular tightly closing, and / or keeping the ByCath bypass valve closed, - Opening, partially opening and / or regulating stack shut-off valves Vi, Va, - Opening, partially opening and / or regulating an exhaust gas recirculation valve VEGR and / or an exhaust gas transfer valve VEGT, in particular to set a desired oxygen concentration and / or humidity in the supply air path 11.

[0064] In this way, the third measurement F3 of a humidity and / or oxygen content of the recirculated and / or transferred exhaust air can be carried out.

[0065] As the Fig. 5d, it is generally conceivable that in the second measurement F2 and / or the third measurement F3, when determining an oxygen concentration and / or humidity at the stack outlet: - Stack, bypass, EGR, and / or EGT mass flows are taken into account, especially if an operating strategy requires that the stack bypass path 13, an EGR exhaust gas recirculation system, and / or an EGT exhaust gas transfer path be flowed through during ongoing stack operation. By considering the mass flows and, if necessary, stack operating conditions, such as current, various oxygen concentrations and / or humidity states of the individual fluid flows can be determined.

[0066] As the Fig. As illustrated in Figure 6a, when performing the first measurement F1, at least one of the following actions can be performed: - Opening, partially opening and / or regulating a first bypass valve ByCath, - Closing, in particular tightly closing, and / or keeping closed stack shut-off valves Vi, Va of a first stack 101, n, - optionally closing, in particular tightly closing, and / or keeping closed an exhaust gas recirculation valve VEGR and / or an exhaust gas transfer VEGT - Operating at least one first air compressor Comp, preferably in a cathode bypass operating mode.

[0067] In this way, at least one stack bypass path 13 can be used for the first measurement F1 of a humidity and / or an oxygen content of an outside air.

[0068] In the example of Fig. 6a, the other stack 101, n + 1 and / or the other air system 10 may be at rest during the first measurement F1.

[0069] In the example of Fig. 6b the other stack 101, n + 1 can be operated during the first measurement F1.

[0070] As the Fig. As illustrated in Figure 6b, when performing the first measurement F1 and / or the second measurement F2, at least one of the following actions can be performed: - Opening, partially opening and / or regulating a first bypass valve ByCath, - Closing, in particular tightly closing, and / or keeping closed a second bypass valve ByCath, - Closing, in particular tightly closing, and / or keeping closed stack shut-off valves Vi, Va of a first stack 101, n, - Opening, partially opening and / or regulating stack shut-off valves Vi, Va of another stack 101, n+1, - Operating at least one first air compressor Comp, preferably in a cathode bypass operating mode, - Operating at least a second air compressor Comp, preferably in a normal operating mode.

[0071] In this way, a combined measurement F1 + F2 of a humidity and / or an oxygen content at the stack outlet can be carried out, preferably comprising the first measurement F1 of a humidity and / or an oxygen content of an outside air and / or the second measurement F2 of a humidity and / or an oxygen content of a stack exhaust gas or the exhaust air L2.

[0072] As the Fig. As illustrated in Figure 6c, when performing the second measurement F2 and / or the third measurement F3, at least one of the following actions can be performed: - Closing, in particular tightly closing, and / or keeping closed a first bypass valve ByCath, - Closing, in particular tightly closing, and / or keeping closed a second bypass valve ByCath, - Opening, partially opening and / or regulating stack shut-off valves Vi, Va of a first stack 101, n, - Opening, partially opening and / or regulating stack shut-off valves Vi, Va of another stack 101, n+1, - Opening, partially opening and / or regulating an exhaust gas transfer valve VEGT, in particular to set a desired oxygen concentration and / or humidity in a supply air L1 of a second stack, - Operating at least one first air compressor Comp, preferably in a normal operating mode, - Operating at least a second air compressor Comp, preferably in a normal operating mode.

[0073] In this way, a combined measurement F2 + F3 of a humidity and / or an oxygen content at the stack outlet can be carried out, preferably comprising the second measurement F2 of a humidity and / or an oxygen content of a stack exhaust gas or the exhaust air L2 and / or the third measurement of a humidity and / or an oxygen content of the exhaust air recirculated by EGR and / or transferred by EGT.

[0074] As the Fig. 6d indicates that if, in systems with multiple stacks 101 and / or multiple air systems 10, an operating strategy requires that at least one stack bypass path 13, one exhaust gas recirculation EGR and / or one exhaust gas transfer path EGT should be flowed through during ongoing stack operation, at least one of the following actions can be performed when performing the second measurement F2 and / or the third measurement F3: - Opening, partially opening and / or regulating a first and / or a second bypass valve ByCath, - Opening, partially opening and / or regulating stack shut-off valves Vi, Va of a first stack 101, n, - Opening, partially opening and / or regulating stack shut-off valves Vi, Va of another stack 101, n+1, - optional opening, partial opening and / or regulation of the exhaust gas transfer valve VEGT, in particular to set a desired oxygen concentration and / or humidity in a supply air L1 of a second or other stack 101, n+1, - Operating a first air compressor Comp, preferably in a normal operating mode, - Operating a second air compressor Comp, preferably in a normal operating mode.

[0075] Advantageously, when determining an oxygen concentration and / or humidity at the stack outlet during the second measurement F2 and / or the third measurement F3, stack, bypass, EGR, and / or EGT mass flows can be taken into account if an operating strategy requires that at least one stack bypass path 13, one exhaust gas recirculation (EGR), and / or one exhaust gas transfer path (EGT) be flowed through during ongoing stack operation. By taking the mass flows into account and, if necessary, stack operating conditions, such as current, various oxygen concentrations and / or humidity states of the individual fluid flows can be determined.

[0076] Furthermore, it is conceivable that, with the aid of the first bypass valve ByCath, an exhaust air from the first stack 101, n can be oxygen-enriched and transferred to an inlet air of the other stack 101, n+1. Consequently, the sensor S can be used in a first air system 10 to mix gas streams via a first stack bypass path 13 and a first exhaust air path 12.

[0077] A corresponding computer program product, a corresponding control unit ecu and a corresponding fuel cell system 100 with a corresponding control unit ecu represent further aspects of the invention.

[0078] The above explanation of the embodiments describes the present invention exclusively within the scope of examples. Of course, individual features of the embodiments can be freely combined with one another, provided they are technically feasible, without departing from the scope of the present invention.

Claims

[1] Method for operating a fuel cell system (100) with at least one fuel cell stack (101) and at least one air system (10), wherein in the air system (10) between a supply air path (11) and an exhaust air path (12) to the at least one fuel cell stack (101) a stack bypass path (13) with a, in particular tightly closing, bypass valve (ByCath) is provided, and wherein in the air system (10) in the exhaust air path (12) a sensor (S) for measuring a humidity and / or an oxygen content is arranged, preferably downstream of a supply line of the stack bypass path (13) to the exhaust air path (12) and preferably upstream of an EGR / EGT branch line from the exhaust air path (12), comprising: - carrying out a first measurement (F1) of a humidity and / or oxygen content of outside air, especially with the open or partially open bypass valve (ByCath), preferably with closed stack shut-off valves (Vi, Va), - Carrying out a second measurement (F2) of a humidity and / or oxygen content of a stack exhaust gas, especially with the closed, preferably tightly closed, bypass valve (ByCath), preferably with the open or partially open stack shut-off valves (Vi, Va), - carrying out a third measurement (F3) of a humidity and / or an oxygen content of a transferred air of an exhaust gas recirculation (EGR) and / or an exhaust gas transfer (EGT), - taking into account at least one measurement (F1, F2, F3) when operating the fuel cell system (100), in particular during exhaust gas recirculation (EGR) and / or exhaust gas transfer (EGT). [2] Method according to claim 1, wherein the first measurement (F1) is carried out under unknown and / or changing environmental conditions, e.g. when driving through an environment with potentially reduced oxygen content, such as a tunnel drive, a parking garage drive, etc., and / or wherein the first measurement (F1) is carried out before the second measurement (F2) and / or before the third measurement (F3), and / or wherein the first measurement (F1) is carried out between the second measurement (F2) and / or before the third measurement (F3), in particular in start-stop phases, preferably when the at least one stack (101) is transferred to standby and / or is switched off and / or is switched off. [3] Method according to one of the preceding claims, wherein when performing the first measurement (F1) at least one of the following actions is performed: - Opening, partially opening and / or regulating the bypass valve (ByCath), - Closing, in particular tightly closing, and / or keeping stack shut-off valves (Vi, Va) closed, - optionally closing, in particular tightly closing, and / or keeping closed an exhaust gas recirculation valve (VEGR) and / or an exhaust gas transfer valve (VEGT), - Operating at least one air compressor (Comp), preferably in a cathode bypass operating mode. [4] Method according to one of the preceding claims, wherein when performing the second measurement (F2) at least one of the following actions is performed: - Closing, in particular tightly closing, and / or keeping the bypass valve (ByCath) closed, - Opening, partially opening and / or regulating stack shut-off valves (Vi, Va), - optionally closing, in particular tightly closing, and / or keeping closed an exhaust gas recirculation valve (VEGR) and / or an exhaust gas transfer valve (VEGT). [5] Method according to one of the preceding claims, wherein when performing the third measurement (F3) at least one of the following actions is performed: - Closing, in particular tightly closing, and / or keeping the bypass valve (ByCath) closed, - Opening, partially opening and / or regulating stack shut-off valves (Vi, Va), - Opening, partially opening and / or regulating an exhaust gas recirculation valve (VEGR) and / or an exhaust gas transfer valve (VEGT), in particular to set a desired oxygen concentration and / or humidity in the supply air path (11). [6] Method according to one of the preceding claims, wherein when determining an oxygen concentration and / or humidity at the stack outlet in the second measurement (F2) and / or in the third measurement (F3), Stack, bypass, EGR and / or EGT mass flows are taken into account, if an operational strategy requires that the stack bypass path (13), an exhaust gas recirculation (EGR) and / or an exhaust gas transfer path (EGT) are / will be flowed through during ongoing stack operation, and / or wherein, for carrying out the method, the sensor (S) for measuring a humidity and / or an oxygen content is arranged downstream of a feed line of the stack bypass path (13) to the exhaust air path (12) and preferably upstream of an EGR / EGT branch line from the exhaust air path (12). [7] Method according to one of the preceding claims, wherein when performing the first measurement (F1) and / or the second measurement (F2) at least one of the following actions is performed: - Opening, partially opening and / or regulating a first bypass valve (ByCath), - Closing, in particular tightly closing, and / or keeping closed a second bypass valve (ByCath), - closing, in particular tightly closing, and / or keeping closed stack shut-off valves (Vi, Va) of a first stack (101, n), - Opening, partially opening and / or regulating stack shut-off valves (Vi, Va) of another stack (101, n+1), - Operating at least one first air compressor (Comp), preferably in a cathode bypass operating mode, - Operating at least a second air compressor (Comp), preferably in a normal operation mode. [8] Method according to one of the preceding claims, wherein when performing the second measurement (F2) and / or the third measurement (F3) at least one of the following actions is performed: - Closing, in particular tightly closing, and / or keeping closed a first bypass valve (ByCath), - Closing, in particular tightly closing, and / or keeping closed a second bypass valve (ByCath), - opening, partially opening and / or regulating stack shut-off valves (Vi, Va) of a first stack (101, n), - Opening, partially opening and / or regulating stack shut-off valves (Vi, Va) of another stack (101, n+1), - Opening, partially opening and / or regulating an exhaust gas transfer valve (VEGT), in particular to set a desired oxygen concentration and / or humidity in a supply air (L1) of a second stack, - Operating at least one first air compressor (Comp), preferably in a normal operating mode, - Operating at least a second air compressor (Comp), preferably in a normal operation mode. [9] Computer program product comprising instructions which, when the computer program product is executed by a computer, cause the computer to carry out a method according to one of the preceding claims. [10] Control unit (ecu), comprising a computing unit and a memory unit in which a code is stored which, when at least partially executed by the computing unit, carries out a method according to one of the preceding claims 1 to 8. [11] Fuel cell system (100) comprising a control unit (200) according to the preceding claim.

Images