Method for operating a fuel cell system, computer program product, 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), wherein the fuel cell system (100) comprises an air system (10) for supplying the at least one fuel cell stack (101) with an oxygen-containing reactant, wherein the air system (10) has at least one turbine (T) acting on a compression path, the procedure serves to to increase a compression ratio and / or a cathode pressure, in particular without a significant increase in the electrical power requirement of the air system (10), demonstrating the procedure: (S1) Operating the fuel cell system (100), (S2) Check whether the compression ratio and / or the cathode pressure should be increased, (S3) Increasing a stack temperature (TStack).

Description

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

[0002] In vehicles (Fuel Cell Vehicle or FCV for short) where propulsion energy is supplied (among other things) by one (or more) fuel cell system(s) (Fuel Cell System or FCS for short), oxygen from the ambient air is usually used as the oxidizing agent and hydrogen as the reducing agent or fuel to react in a fuel cell stack to form water (or water vapor) and thus deliver electrical power through electrochemical conversion.

[0003] Ambient air is supplied to a fuel cell stack via an air system comprising an air supply system and / or an air compression system. The air supply system provides a corresponding (variable) air mass flow and pressure level.

[0004] The air conveying system typically includes at least one thermal turbomachine (or in other words, an air compressor) which is driven by an electric motor (English: "Electric Driven Air Compressor" or EAC for short).

[0005] Optionally, in addition to air compression (single-stage or multi-stage), energy recovery from outgoing moist air (which can also be referred to as exhaust gas) can be achieved using a turbine.

[0006] A turbine can be implemented, for example, by an electrically driven turbocharger, or EACT for short.

[0007] A turbine can be implemented, for example, by a turbocharger without an electric drive, or TAC for short, which is driven solely by the exhaust gas. The TAC can also be called an exhaust gas turbocharger, or ATL for short. In this case, the exhaust gas enthalpy is used to drive a compressor wheel via the turbine.

[0008] Higher system pressures, e.g. to obtain high-performance FCS systems, require two-stage compression and energy recuperation using one or two turbines.

[0009] The use of turbines can be advantageous for cost reasons or due to system design and consumption optimization. Disclosure of the invention

[0010] The present invention provides a method for operating a fuel cell system with the features of the independent method claim. Furthermore, the invention provides a corresponding computer program, a corresponding control unit, and a corresponding fuel cell system with the features of the dependent claims. Features and details described in connection with the different embodiments and / or aspects of the invention naturally also apply in connection with the other embodiments and / or aspects, and vice versa, so that the disclosure relating to the individual embodiments and / or aspects always includes, or can include, reciprocal references.

[0011] According to the first aspect, the present invention provides: a method for operating a fuel cell system (hereinafter referred to simply as the system) with at least one (or more) fuel cell stack(s) (hereinafter referred to simply as the stack).

[0012] The fuel cell system includes an air system for supplying at least one fuel cell stack with an oxygen-containing reactant.

[0013] The air system can include at least one turbine.

[0014] The turbine can act directly (e.g. via a compressor shaft, this is called mechanical coupling) or indirectly (this is called electrical coupling) on ​​a compression path.

[0015] The method advantageously serves to increase a (particularly requested) compression ratio and / or a (particularly requested) cathode pressure, especially without a significant increase in the electrical power requirement of the air system.

[0016] The process involves the following steps: (S1) Operating the fuel cell system, (S2) Check whether the compression ratio and / or the cathode pressure should be increased, (S3) Increasing a stack temperature.

[0017] The fuel cell system (or system for short) can have several fuel cell stacks (or stacks for short), each with several 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.

[0018] Preferably, the fuel cell system can comprise several modules in the form of individual stacks and the associated functional systems.

[0019] The air system may include an air compressor with turbine assistance.

[0020] The air system can have two air compressors, at least one of which can be turbine-driven.

[0021] Multiple stacks can be supplied by a common air system.

[0022] The common air system can include an air compressor with turbine assistance.

[0023] The common air system can have two air compressors, at least one or both of which can be turbine-driven.

[0024] The air system can generally have the following designs: - EACT - TAC-EAC or EAC-TAC - EACT-TAC or TAC-EACT - EACT-EACT - EAC-EACT or EACT-EAC.

[0025] The fuel cell system can be used for mobile applications, e.g. in vehicles (FCV, short for "Fuel Cell Vehicle"), where the drive energy is supplied, among other things, by a (PEM) fuel cell system (FCS, short for "Fuel Cell System") with one or more fuel cell stacks.

[0026] The fuel cell system can also be used for stationary applications, e.g. in generators.

[0027] The invention recognizes, firstly, that compensating for a decreasing ambient pressure, such as during high-altitude operation / mountain travel, and / or an increase in cathode pressure is accompanied by a significant increase in the electrical power requirement of the air system or air compression system.

[0028] The invention also recognizes that the gradient of the increase can be reduced with a turbine.

[0029] The idea addresses compensation. - a decreasing ambient pressure, such as during operation at high altitude / a mountain journey, and / or - an increase in the required compression ratio and / or cathode pressure without a significant increase in the power requirement of the air system.

[0030] A procedure is proposed for compensation. • an increase in the compression ratio of the air system, e.g. due to the decreasing ambient air pressure during high-altitude operation / mountain travel (stack pressure remains constant but the compression ratio increases), and / or • a requested increase in the cathode pressure of the stacks without a significant increase in the power requirement of the air system by • Increase in stack temperature or coolant temperature.

[0031] The measure can preferably be implemented depending on the operating point and can also be used only temporarily, e.g. in particular to compensate for a decreasing air pressure, and / or at higher pressure levels.

[0032] Significant advantages can be achieved using this method: - Higher compression ratio and / or higher cathode pressure are almost performance-neutral

[0033] The chain of effects can be explained as follows: • Stack temperature / coolant temperature is increased • Cathode outlet temperature is increased • Turbine inlet temperature or inlet enthalpy is increased • Turbine power increases • resulting in a higher pressure ratio across the air compressor (e.g., through TAC) at similar electrical power consumption • thereby compensating for a drop in ambient pressure, e.g. during high-altitude operation / mountain travel, and / or an increase in cathode pressure (even at a constant ambient pressure) • In addition, the efficiency of the air compressor increases (since it is operated at a higher load)

[0034] One possibility is that increasing the stack temperature could be achieved by increasing the coolant temperature.

[0035] On the other hand, it is conceivable that increasing the stack temperature could be achieved by reducing heat dissipation from the stack via a coolant system. For example, the coolant could be circulated more slowly. A cooler coolant could flow more directly around the stack, while a warmer coolant could flow more directly around a cooler.

[0036] Furthermore, it may be provided that the procedure, in particular step (S2) and / or step (S3), is carried out during operation. In this way, the procedure can react to a decrease in ambient pressure and / or an increase in the requested cathode pressure.

[0037] Furthermore, it may be provided that the procedure, in particular step (S2) and / or step (S3), is carried out predictively. This can be advantageous, in particular to take into account the thermal inertia of a coolant system.

[0038] Advantageously, the procedure, in particular step (S3), can be designed to be executed when the ambient pressure falls below a threshold. This can be referred to as a trigger for initiating step (S3). In this way, the procedure can react to situations that arise, for example, during operation at high altitude and / or during uphill travel.

[0039] Furthermore, it can be advantageous to carry out the procedure, in particular step (S3), when an increased compression ratio and / or an increased cathode pressure is required, especially if the requirements cannot be met by increasing the operation of a compressor stage that is not coupled to the turbine. In this case, the other compression stage with the turbine can perform the compensation.

[0040] Advantageously, the process, in particular step (S3), can be scheduled to be executed when a requested compression ratio and / or a requested cathode pressure exceeds a threshold. This can be considered a trigger for initiating step (S3). In this way, the process can be carried out particularly efficiently without a significant increase in the electrical power consumption of the air system.

[0041] In principle, the process, especially step (S3), can only be carried out if component limitations in a compression stage coupled to the turbine permit it, and / or if component protection, particularly in the at least one fuel cell stack (e.g., if the stack has aged and higher temperatures are no longer permissible), allows it. In this way, the process can be used in a particularly gentle manner for the system components.

[0042] Furthermore, the procedure can exhibit: (S4) Check whether an increased stack temperature should be maintained, (S5) Stop increasing the stack temperature when: - the ambient pressure has risen above a threshold, and / or - a requested compression ratio and / or a requested cathode pressure falls below a threshold value.

[0043] In this way, the method can only be used temporarily, as long as there is a need to compensate for low ambient pressure and / or higher requested cathode pressure, especially without electrical losses.

[0044] According to a further aspect, the invention provides a computer program product comprising instructions which, when executed by a computer, such as the processing unit of a control unit, cause the computer to carry out the method, which can proceed as described above. The same advantages described above in connection with the method according to the invention can be achieved with the computer program product. These advantages are fully referenced herein.

[0045] 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 processing unit of the control unit, this program performs a procedure that can proceed as described above. The same advantages described above in connection with the method according to the invention can be achieved with the help of the control unit. These advantages are fully referenced herein.

[0046] A corresponding fuel cell system also constitutes an aspect of the invention, wherein the fuel cell stack includes a corresponding control unit. The same advantages described above in connection with the method according to the invention can be achieved using the fuel cell system. These advantages are fully referenced herein. Preferred embodiments:

[0047] The invention, its further developments, and its advantages are explained in more detail below with reference to the drawings. Each drawing schematically shows: Fig. 1 exemplary system topology and Fig. 2. A sketch to explain the effect of increasing the stack temperature.

[0048] 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.

[0049] The Fig. 1 and Fig. 2 serve to explain the invention idea, which proposes: a method for operating a fuel cell system 100 (hereinafter referred to as system 100) with at least one (or more) fuel cell stack(s) 101 (hereinafter referred to as stack(s) 101).

[0050] As it is Fig. As indicated in Figure 1, the fuel cell system 100 has an air system 10 for supplying the at least one fuel cell stack 101 with an oxygen-containing reactant.

[0051] As it is Fig. As indicated in 1, the air system 10 can have at least one turbine T.

[0052] The turbine T can act directly, e.g. via a compressor shaft, (mechanical coupling) or indirectly (electrical coupling) on ​​a compression path of an air compressor Comp.

[0053] The method was developed to increase a (particularly requested) compression ratio and / or a (particularly requested) cathode pressure, especially without a significant increase in the electrical power requirements of the air system 10.

[0054] The procedure comprises the following steps: S1 Operating the fuel cell system 100, S2 Check whether the compression ratio and / or the cathode pressure should be increased. S3 Increasing a stack temperature TStack.

[0055] The fuel cell system can, in principle, have several fuel cell stacks 101.

[0056] However, the air system 10 can also have an air compressor Comp with turbine assistance (not shown for the sake of simplicity).

[0057] As it is Fig. As indicated in 1, the air system 10 can have two air compressors Comp1, Comp2, of which at least one air compressor Comp1 and / or Comp2 can be turbine-driven.

[0058] Several stacks of 100 can be supplied by a common air system 10, as is the case with the Fig. 1 suggests.

[0059] The common air system 10 can include an air compressor Comp with turbine assistance (not shown for simplicity).

[0060] The common air system 10 can have two air compressors Comp1, Comp2, of which at least one or both air compressors Comp1 and / or Comp2 can be turbine-driven (a turbine T is shown by way of example in the Fig. 1 shown).

[0061] The air system 10 can basically have the following configurations: - EACT - TAC-EAC or EAC-TAC - EACT-TAC or TAC-EACT - EACT-EACT - EAC-EACT or EACT-EAC.

[0062] The invention recognizes that in order to compensate for a decreasing ambient pressure, such as during high-altitude operation / mountain travel, and / or an increase in the required cathode pressure, a significant increase in the electrical power requirement of the air system 10 or air compression system is necessary.

[0063] The invention also recognizes that the gradient of the increase in the electrical power requirement of the air system 10 can be reduced with the help of a turbine T.

[0064] The idea proposes compensation. - a decreasing ambient pressure, such as during operation at high altitude / a mountain journey, and / or - an increase in a requested compression ratio and / or the requested cathode pressure without a significant increase in the power requirement of the air system through an increase in the stack temperature TStack, as the Fig. 2 explained schematically.

[0065] Fig. Figure 2 shows a function of the electrical power PEI of the air system 10 (in the example of an EAC-TAC topology of the Fig. Figure 1 shows the power of the EAC as a function of the cathode inlet pressure pStkin for different stack temperatures TStack 60 °C, 75 °C and 95 °C (at constant or comparable mass flow rate) for A) Topology according to Fig. 1 with GGHX1 and GGHX2 (example on the right in the Fig. 2) B) Topology according to Fig. 1 with GGHX1 without GGHX2 (example on the left in the Fig. 2)

[0066] The results were obtained using system simulation. An increase in the stack temperature TStack, particularly at higher pressure levels, shows a virtually "performance-neutral" increase in the compression ratio or cathode pressure.

[0067] This applies, for example, to the operating points circled by the solid line.

[0068] At slightly lower pressures, the pressure increase is associated with a small increase in power (operating points circled with a dashed line).

[0069] At even lower pressures, however, a significant increase in performance (operating points not circled) is necessary.

[0070] The operational strategy measure in step S3 can be implemented (or triggered) depending on the operating point, e.g.: - if the pressure level rises above a threshold and / or - when the ambient pressure drops below a threshold.

[0071] The measure can preferably be implemented depending on the operating point and can also be used only temporarily, e.g. in particular to compensate for a decreasing air pressure, and / or at higher required pressure levels in the cathode path.

[0072] Using this method, a higher compression ratio and / or higher cathode pressure can be achieved with virtually no increase in power consumption.

[0073] The chain of effects can proceed as follows: • Stack temperature / coolant temperature is increased • Cathode outlet temperature is increased • Turbine inlet temperature or inlet enthalpy is increased • Turbine power increases • resulting in a higher pressure ratio across the air compressor (e.g., through TAC) at similar electrical power consumption • thereby compensating for a drop in ambient pressure, e.g. during high-altitude operation / mountain travel, and / or an increase in cathode pressure (even at a constant ambient pressure) • In addition, the efficiency of the air compressor increases (since it is operated at a higher load)

[0074] One way to increase the stack temperature S3 TStack is by increasing the coolant temperature.

[0075] On the other hand, increasing the stack temperature (TStack) can be achieved by reducing heat dissipation from the stack via a coolant system. For example, the coolant can be circulated more slowly. A cooler coolant can flow more freely around the stack, while a warmer coolant can flow more freely around a cooler.

[0076] As mentioned above, the procedure, in particular step S2 and / or step S3, can be carried out during operation.

[0077] Furthermore, the process, in particular step S2 and / or step S3, can be carried out predictively, preferably to compensate for a thermal inertia of a coolant system.

[0078] As mentioned above, the procedure, in particular step S3, can be carried out when an ambient pressure falls below a threshold (trigger to initiate step S3).

[0079] Furthermore, the procedure, in particular step S3, can be carried out if an increased compression ratio and / or an increased cathode pressure is required. This measure can also be used if the requirements cannot be met by increasing the operation of a compressor stage that is not coupled to turbine T (see, for example, EAC in...). Fig. 1) In this case, the other compaction stage (see TAC in Fig. 1) Perform the compensation using turbine T.

[0080] As mentioned above, the procedure, in particular step S3, can be carried out when a requested compression ratio and / or a requested cathode pressure exceeds a threshold (trigger to initiate step S3).

[0081] In principle, it can be stipulated that the procedure, in particular step S3, will only be carried out if: - if component limitations in a compression stage coupled with turbine T allow it, and / or - if component protection allows it, especially in the at least one fuel cell stack 101, for example if the stack has aged and higher temperatures are no longer permitted.

[0082] Furthermore, the procedure can exhibit: S4 Check whether an elevated stack temperature TStack should be maintained, S5 Stop increasing stack temperature TStack when: - the ambient pressure has risen above a threshold, and / or - a requested compression ratio and / or a requested cathode pressure falls below a threshold value.

[0083] 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.

[0084] The preceding explanation of the embodiments describes the present invention solely by way of examples. Naturally, individual features of the embodiments can be freely combined with one another, provided this is technically feasible, without departing from the scope of the present invention.

Claims

[1] Method for operating a fuel cell system (100) comprising at least one fuel cell stack (101), wherein the fuel cell system (100) comprises an air system (10) for supplying the at least one fuel cell stack (101) with an oxygen-containing reactant, wherein the air system (10) has at least one turbine (T) acting on a compression path, the procedure serves to to increase a compression ratio and / or a cathode pressure, in particular without significantly increasing the electrical power requirement of the air system (10), demonstrating the procedure: (S1) Operating the fuel cell system (100), (S2) Check whether the compression ratio and / or the cathode pressure should be increased, (S3) Increasing a stack temperature (TStack). [2] Method according to claim 1, where increasing (S3) the stack temperature (TStack) is carried out by increasing a coolant temperature, and / or wherein the increase (S3) of the stack temperature (TStack) is carried out by a reduced heat removal from the at least one fuel cell stack (101) by a coolant system. [3] Method according to any one of the preceding claims, where the procedure, in particular step (S2) and / or step (S3), is carried out during operation and / or in anticipatory measures, to take into account, in particular, the thermal inertia of a coolant system. [4] Method according to one of the preceding claims, wherein the method, in particular step (S3), is carried out when an ambient pressure falls below a threshold value. [5] Method according to any one of the preceding claims, wherein the procedure, in particular step (S3), is carried out when an increased compression ratio and / or an increased cathode pressure is requested, especially in the event that if the requirements cannot be met by increasing the operation of a compressor stage that is not coupled to the turbine (T). [6] Method according to any of the preceding claims, wherein the method, in particular step (S3), is carried out when a requested compression ratio and / or a requested cathode pressure rises above a threshold. [7] Method according to any one of the preceding claims, the procedure, in particular step (S3), is only carried out if if component limitations in a compression stage coupled with the turbine (T) allow it, and / or if component protection, in particular in the at least one fuel cell stack (101), allows it. [8] Method according to any of the preceding claims, further comprising: (S4) Check whether to maintain an elevated stack temperature (TStack), (S5) Stop increasing stack temperature (TStack) when: - the ambient pressure has risen above a threshold, and / or - a requested compression ratio and / or a requested cathode pressure falls below a threshold value. [9] Computer program product comprising instructions which, when the computer program product is executed by a computer, cause it to perform a method according to any of the preceding method claims. [10] Electronic control unit (ECU) comprising a computing unit and a storage unit in which a code is stored which, when at least partially executed by the computing unit, performs a method according to any one of the preceding method claims 1 to 9. [11] Fuel cell system (100) comprising a control unit (ECU) according to the preceding claim.

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