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

Abstract

The invention relates to a method for operating a fuel cell system (100) having at least one fuel cell stack (11) and a cathode system (300), in which a cathode supply line (31), a cathode discharge line (32) and a humidifier (37) are arranged, wherein the humidifier (37) can be fluidically connected to the cathode supply line (31) and the cathode discharge line (32), wherein at least one means for regulating the mass flow (33, 34) is configured to divert a mass flow of cathode gas at least proportionally to the humidifier (37) when a characteristic value of the humidifier (37) is exceeded.

Description

[0001] R. 417084

[0002] - 1 -

[0003] Description

[0004] title

[0005] Methods for operating a fuel cell system and fuel cell system

[0006] The invention relates to a method for operating a fuel cell system with the features of the preamble of independent claim 1 and a fuel cell system with the features of the preamble of independent claim 11.

[0007] State of the art

[0008] It is known from the prior art that fuel cell systems include a fuel cell stack, an anode system, a cathode system and a cooling circuit.

[0009] During operation of the fuel cell system, the reactants fuel and air flow into the fuel cell stack to obtain electrical energy in a cold combustion reaction.

[0010] Disclosure of the invention

[0011] The inventive method for operating a fuel cell system and the inventive fuel cell system have the advantage that a diversion of the cathode gas is enabled when a characteristic value of the humidifier is exceeded. This reduces the load on the humidifier and increases its service life by minimizing the risk of internal leakage due to high mass flow rates. In addition, the inventive fuel cell system protects the humidifier from overload by implementing a bypass line in the cathode outlet, which effectively limits the mass flow rate and increases the service life of the humidifier. R. 417084

[0012] - 2 -

[0013] It is advantageous if the humidifier's characteristic value corresponds to a maximum permissible mass flow rate of cathode gas. By specifying the humidifier's characteristic value as the maximum permissible mass flow rate, direct control and precise limitation of the cathode gas mass flowing through the humidifier is possible, thus reducing the stress on the membrane.

[0014] Advantageously, the humidifier's characteristic value corresponds to a maximum permissible pressure difference. This allows the humidifier's characteristic value to be defined alternatively as a pressure difference, since the pressure difference indirectly limits the mass flow and enables simple implementation and monitoring via, for example, pressure sensors.

[0015] Advantageously, a first means of regulating the mass flow is configured to divert at least a portion of the cathode gas mass flow in the cathode outlet to the humidifier when the humidifier's characteristic value is exceeded. This enables targeted control of the cathode gas mass flow, thus allowing for optimized operation and reduced stress on the humidifier.

[0016] It is advantageous if a second mass flow control device is configured to divert at least a portion of the cathode gas mass flow in the cathode supply line to the humidifier when the humidifier's characteristic value is exceeded. This complements the mass flow control capability in the cathode supply line, enabling additional control of the supplied cathode gas mass flow and thus maintaining the cathode gas mass flows in the cathode supply and cathode outlet lines at essentially the same level.

[0017] Advantageously, the mass flow rate of the cathode gas in the cathode outlet is determined via a pressure difference between a first pressure, corresponding to the pressure of the cathode gas in the cathode outlet before entering the humidifier, and a second pressure, corresponding to the pressure of the cathode gas in the cathode outlet after exiting the humidifier. The indirect determination of the mass flow rate of the cathode gas via a first and a second pressure in the cathode outlet also allows for a precise indirect determination of R. 417084.

[0018] - 3 -

[0019] mass flow and allows for precise limitation of the mass flow through the humidifier.

[0020] It is advantageous to determine the mass flow rate of cathode gas in the cathode supply line via a pressure difference between a third pressure, corresponding to the pressure of the cathode gas in the cathode supply line before entering the humidifier, and a fourth pressure, corresponding to the pressure of the cathode gas in the cathode supply line after exiting the humidifier. Indirect determination of the cathode gas mass flow rate via a first pressure and a second pressure in the cathode outlet also enables precise control and allows for accurate limitation of the mass flow rate through the humidifier.

[0021] Advantageously, at least one means of regulating the mass flow is designed as an electrically controlled valve. This allows for flexible and dynamic adjustment of the mass flow to the operating conditions.

[0022] It is advantageous if at least one mass flow control device is designed as a passive valve. This results in a mass flow control device that allows for a simple and robust design with minimal control effort.

[0023] Advantageously, at least one means of regulating the mass flow is designed as a passive throttle. This allows for the integration of a cost-effective component into the fuel cell system that ensures reliable mass flow limitation, particularly when no variation in the limiting of the cathode gas mass flow is required.

[0024] It is advantageous if a second bypass line, containing a second mass flow control device, is connected to the cathode outlet upstream of the humidifier in the cathode supply line and terminates downstream of the humidifier in the cathode outlet. This bypass line supplements the fuel cell system design by providing an additional diversion of the cathode gas mass flow around the humidifier, thus improving the humidifier's performance and service life. R. 417084

[0025] - 4 -

[0026] The inventive method and the inventive fuel cell system are explained in more detail below with reference to drawings with preferred embodiments.

[0027] They show:

[0028] Fig. 1 shows an embodiment of the fuel cell system according to the invention and

[0029] Fig. 2 shows a first embodiment of the method according to the invention and

[0030] Fig. 3 shows a second embodiment of the method according to the invention.

[0031] Figure 1 shows a schematic topology of a first embodiment of a fuel cell system 100 according to the invention, comprising at least one fuel cell stack 11, a cathode system, a cooling circuit (not shown) and an anode system (not shown).

[0032] The cathode system supplies a cathode compartment in at least one fuel cell stack 11 with oxygen (O2) as a reactant. Oxygen is a component of air.

[0033] In the cathode system, a cathode inlet 31, a cathode outlet 32, a first bypass line 36 and a second bypass line 35 are arranged.

[0034] The cathode supply line 31 leads into the at least one fuel cell stack 11. Oxygen is supplied to the at least one fuel cell stack 11 via the cathode supply line 31.

[0035] The cathode outlet 32 ​​is connected to the at least one fuel cell stack 11. Gases, such as cathode exhaust gas and / or fluids, such as product water, are discharged from the cathode system via the cathode outlet 32. R. 417084

[0036] - 5 -

[0037] A humidifier 37 is connected to the cathode inlet 31 and the cathode outlet 32 ​​via a fluid flow.

[0038] In the cathode system at least one means for regulating the mass flow 33, 34 is arranged.

[0039] The first bypass line 36 is connected to the cathode outlet 32 ​​in the direction of flow upstream of the humidifier 37. The first bypass line

[0040] 36 leads into the cathode outlet 32 ​​in the direction of flow behind the humidifier

[0041] 37 into the cathode outlet 32. In the first bypass line 36 a first means for regulating the mass flow 34 is arranged.

[0042] The second bypass line 35 is connected to the cathode supply line 31 upstream of the humidifier 37 in the direction of flow and opens into the cathode supply line 31 downstream of the humidifier 37 in the direction of flow. A second means for regulating the mass flow 33 is arranged in the second bypass line 35.

[0043] In a first embodiment, the at least one means for regulating the mass flow 33, 34 is designed as an electrically controllable valve.

[0044] In a second embodiment, at least one means for regulating the mass flow 33, 34 is designed as a passive valve.

[0045] In a third embodiment, at least one means for regulating the mass flow 33, 34 is designed as a passive throttle.

[0046] In the cooling circuit (not shown), a first cooling circuit line is arranged, forming a closed fluid circuit. A coolant is circulated in the cooling circuit line by means of a pumping unit. The coolant flows through a coolant path of the fuel cell stack 11 and regulates the temperature of the fuel cell stack 11. A coolant bypass line allows the coolant to be routed at least partially or completely away from a vehicle radiator.

[0047] The anode system (not shown) supplies an anode compartment of the at least one fuel cell stack 11 with a fuel, in particular hydrogen (H2), as a reactant. Fuel is supplied to the R. 417084

[0048] - 6 -

[0049] The fuel is made available as a reactant in the anode compartment of the fuel cell system 100.

[0050] A control unit 500 is provided to regulate and control all control processes in the fuel cell system 100. This also includes the processing of a measured value for the execution of the method according to the invention.

[0051] In an alternative embodiment, more than one fuel cell stack 11 can also be arranged in the fuel cell system 100 without restricting the implementation of the method according to the invention.

[0052] Figure 2 shows a first embodiment of the method according to the invention.

[0053] The method according to the invention enables the cathode gas to be diverted when a characteristic value of the humidifier 37 is exceeded. This reduces the load on the humidifier 37 and increases its service life by minimizing the risk of internal leakage due to high mass flows.

[0054] In particular, the first embodiment of the method according to the invention is suitable if the first means for controlling the mass flow 33 and the second means for controlling the mass flow 34 are designed as a passive valve or as a passive throttle.

[0055] The process is initiated in step S100. The process according to the invention takes place during the operation of the fuel cell system 100.

[0056] Subsequently, in a step S200, at least one means for controlling the mass flow 33, 34 diverts the mass flow of cathode gas to the humidifier 37 at least partially when the characteristic value of the humidifier 37 is exceeded.

[0057] In a first embodiment, the characteristic value of the humidifier 37 corresponds to a maximum permissible mass flow rate of cathode gas.

[0058] In a second embodiment, the characteristic value of the humidifier 37 corresponds to a maximum permissible pressure difference. R. 417084

[0059] - 7 -

[0060] In step S300, the inventive method is terminated. The inventive method can be terminated when the fuel cell system 100 is shut down or is in an operational standstill.

[0061] The method according to the invention can also be carried out, at least in part, by the control unit 500 of the fuel cell system 100. A computer program in the form of code can be stored in a memory unit of the control unit 500. When executed by a processing unit of the control unit 500, this code performs a process that can proceed as described above. The same advantages described above in connection with the method according to the invention can be achieved using the control unit 500. These advantages are fully referenced herein.

[0062] Furthermore, the control unit 500 can be in a communication link with an external computing unit in order to outsource some process steps and / or calculations completely or partially to the external computing unit.

[0063] According to another aspect, the invention provides a computer program product comprising instructions which, when executed by a computer, such as the processing unit of the control unit 500, cause the computer to carry out the method, which can proceed as described above. The computer program product offers the same advantages described above in connection with the method and / or the control unit 500 according to the invention. These advantages are fully referenced herein.

[0064] Figure 3 shows a second embodiment of the method according to the invention. The second embodiment of the method according to the invention corresponds to the first embodiment of the method according to the invention except for the differences mentioned below.

[0065] In the second embodiment, step S101 is performed after step S100. In step S101, the mass flow rate of cathode gas in the cathode outlet 32 ​​is controlled by a pressure difference between a first pressure, which corresponds to the pressure of the cathode gas in the cathode outlet 32 ​​before entering the humidifier 37, and a second pressure, which corresponds to the pressure of the R. 417084

[0066] - 8 -

[0067] The amount of cathode gas in the cathode outlet 32 ​​after exiting the humidifier 37 is determined.

[0068] Subsequently, in step S102, the mass flow rate of cathode gas in the cathode outlet 32, determined in step S101, is compared with the characteristic value of the humidifier 37. If the mass flow rate of cathode gas in the cathode outlet 32, determined in step S101, exceeds the characteristic value of the humidifier 37, step S200 is then executed.

[0069] In step S200, the first means for controlling the mass flow 34 diverts the mass flow of cathode gas in the cathode outlet 32 ​​at least partially to the humidifier 37 when the characteristic value of the humidifier 37 is exceeded, so that the characteristic value of the humidifier 37 is again undershot.

[0070] In an alternative embodiment of the second embodiment, in step S101 the mass flow rate of cathode gas in the cathode supply line 31 is additionally determined via a pressure difference between a third pressure, which corresponds to the pressure of the cathode gas in the cathode supply line 31 before entering the humidifier 37, and a fourth pressure, which corresponds to the pressure of the cathode gas in the cathode supply line 31 after exiting the humidifier 37.

[0071] In the alternative embodiment of the second embodiment of the method according to the invention, in step S200 the second means for controlling the mass flow 33 additionally diverts the mass flow of cathode gas in the cathode supply line 31 at least partially to the humidifier 37 when the characteristic value of the humidifier 37 is exceeded, so that the characteristic value of the humidifier 37 is undershot.

Claims

R. 417084 - 9 - Claims 1. Method for operating a fuel cell system (100) with at least one fuel cell stack (11) and a cathode system (300) in which a cathode supply line (31), a cathode outlet (32) and a humidifier (37) are arranged, wherein the humidifier (37) is connected to the cathode supply line (31) and the cathode outlet (32) in a fluid-permeable manner, characterized in that at least one means for controlling the mass flow (33, 34) is configured to divert at least a proportionate amount of a mass flow of cathode gas to the humidifier (37) when a characteristic value of the humidifier (37) is exceeded.

2. Method according to claim 1, characterized in that the characteristic value of the humidifier (37) corresponds to a maximum permissible mass flow rate of cathode gas.

3. Method according to claim 1, characterized in that the characteristic value of the humidifier (37) corresponds to a maximum permissible pressure difference.

4. Method according to claim 1, characterized in that a first means for controlling the mass flow (34) is configured to divert at least a proportionate amount of the mass flow of cathode gas in the cathode outlet (32) to the humidifier (37) when the characteristic value of the humidifier (37) is exceeded.

5. Method according to claim 1, characterized in that a second means for controlling the mass flow (33) is configured to divert a mass flow of cathode gas in the cathode supply line (31) at least partially to the humidifier (37) when the characteristic value of the humidifier (37) is exceeded.

6. Method according to claims 1 and 4, characterized in that the mass flow of cathode gas in the cathode outlet (32) is controlled by a pressure difference between a first pressure, which corresponds to the pressure of the cathode gas in the cathode outlet (32) before entering the humidifier (37), and a R. 417084 - 10 - second pressure, which corresponds to the pressure of the cathode gas in the cathode outlet (32) after exiting the humidifier (37).

7. Method according to claims 1 and 5, characterized in that the mass flow rate of cathode gas in the cathode supply line (31) is determined via a pressure difference between a third pressure, which corresponds to the pressure of the cathode gas in the cathode supply line (31) before entering the humidifier (37), and a fourth pressure, which corresponds to the pressure of the cathode gas in the cathode supply line (31) after exiting the humidifier (37).

8. Method according to claim 1, characterized in that the at least one means for controlling the mass flow (33, 34) is designed as an electrically controllable valve.

9. Method according to claim 1, characterized in that the at least one means for controlling the mass flow (33, 34) is designed as a passive valve.

10. Method according to claim 1, characterized in that the at least one means for controlling the mass flow (33, 34) is designed as a passive throttle.

11. Fuel cell system (100) with at least one fuel cell stack (11) and a cathode system (300) in which a cathode inlet (31), a cathode outlet (32) and a humidifier (37) are arranged, wherein the humidifier (37) is connected to the cathode inlet (31) and the cathode outlet (32) in a fluid-permeable manner, characterized in that a first bypass line (36) in which a first means for controlling the mass flow (34) is arranged is connected to the cathode outlet (32) in the direction of flow upstream of the humidifier (37) and opens into the cathode outlet (32) downstream of the humidifier (37) in the direction of flow.

12. Fuel cell system (100) upwards, characterized in that a second bypass line (35), in which a second means for controlling the mass flow is arranged (33), is connected in the cathode supply line (31) in the flow direction upstream of the humidifier (37) to the cathode outlet (31) and in the R. 417084 - 11 - Cathode outlet (31) in the direction of flow behind the humidifier (37) into the Cathode outlet (31) leads to the end.

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