Method for operating a fuel cell system, and control device

Abstract

The invention relates to a method for operating a fuel cell system (1), comprising a fuel cell stack (2) and a cooling circuit (3) which conducts a coolant and into which the fuel cell stack (2) is integrated, wherein, during normal operation, the coolant is circulated with the aid of a coolant pump (4) which is integrated into the cooling circuit (3). According to the invention, in the event of a shutdown, the coolant pump (4) is activated intermittently and / or at specific time intervals and the coolant is conducted through an ion exchanger (5) integrated into the cooling circuit (3) such that any acids or bases produced in the coolant are bonded with the aid of the ion exchanger (5). The invention also relates to a control device for a fuel cell system (1).

Description

[0001] Description

[0002] Procedures for operating a

[0003] The present invention relates to a method for operating a fuel cell system with the features of the preamble of claim 1. Furthermore, the invention relates to a control unit for carrying out the method or for carrying out steps of the method.

[0004] The preferred application area is mobile fuel cell systems or fuel cell vehicles.

[0005] State of the art

[0006] Fuel cells, such as polymer electrolyte membrane (PEM) fuel cells, convert hydrogen into electrical energy using oxygen, generating waste heat and water in the process. Converting hydrogen in this context means that hydrogen molecules are consumed or removed at the anode.

[0007] The PEM fuel cell has an anode supplied with hydrogen and a cathode supplied with air. A membrane, the polymer electrolyte membrane, is positioned between them. In practical applications, several of these individual cells are stacked to increase the generated electrical voltage. Within this stack are supply channels that provide the individual cells with hydrogen and air, and also remove the depleted humid air and the depleted anode exhaust. In mobile fuel cell systems or fuel cell vehicles, the waste heat generated in the fuel cells during operation is typically dissipated via a liquid-cooled cooling circuit. During startup, especially a cold start, the cooling system can be used to supply heat to the stack to bring it up to operating temperature.

[0008] The fluid typically used as a coolant in a cooling circuit has certain properties and / or additives that give it these characteristics. These can include additives that provide freeze protection and / or corrosion protection. Furthermore, additives may be included to maintain insulation properties and / or electrical conductivity. The main components of a coolant are generally water and glycol. These must be present in the fluid at a specific concentration to ensure the required properties.

[0009] An important factor in this context is the pH value of the coolant. If it falls below a certain threshold, components through which the coolant flows, such as a heat exchanger integrated into the cooling circuit, can be damaged by corrosion. The drop in pH is due to chemical processes that lead to the formation of acids in the coolant. If ion exchangers are used in the cooling circuits of fuel cell systems, a minimum pH value can be maintained through ion binding. This is necessary to ensure a minimum insulation value for the coolant to prevent voltage buildup on accessible parts of the vehicle. The ion exchanger removes acids / bases from the coolant and thus regulates its pH value.Corrosive processes, which would dissolve further ions and thus contribute to exacerbating the problem, are therefore prevented.

[0010] The present invention is concerned with the objective of preventing the pH value of the coolant from dropping below a minimum value even when the fuel cell system is switched off, in order to avoid damage, in particular corrosion damage, to components through which the coolant flows.

[0011] To solve the problem, the method with the features of claim 1 is proposed. Advantageous embodiments of the invention are described in the dependent claims. Furthermore, a control unit for executing steps of the method is specified.

[0012] Disclosure of the invention

[0013] A method for operating a fuel cell system is proposed, comprising a fuel cell stack and a cooling circuit carrying a coolant, into which the fuel cell stack is integrated. During normal operation, the coolant is circulated by means of a coolant pump integrated into the cooling circuit. According to the invention, when the system is shut down, the coolant pump is activated intermittently and / or at specific intervals, and the coolant is passed through an ion exchanger integrated into the cooling circuit, so that any acids or bases formed in the coolant are bound by the ion exchanger.

[0014] According to the proposed method, the coolant pump is activated periodically even when the system is shut down, in order to bind any potentially locally occurring acids or bases in the coolant via an ion exchanger. This ensures that the pH value does not fall below a minimum level, even when the system is shut down. As a result, corrosion-prone components are protected from corrosive attack even when the system is not in use.

[0015] The duration and / or frequency of the coolant pump activation when the engine is shut down may depend on various factors.

[0016] Preferably, the duration and / or frequency of the coolant pump activation during shutdown is selected based on the coolant temperature. It is known that higher temperatures decompose the coolant more quickly, thus promoting the formation of unwanted acids. Therefore, preferably, the duration and / or frequency of the coolant pump activation increases with the coolant temperature. This means that the higher the coolant temperature, the longer and / or more frequently the coolant pump is activated to bind the acids in the ion exchanger.

[0017] Since the coolant temperature generally rises with the ambient temperature, it is further proposed that the duration and / or frequency of the coolant pump activation during shutdown be selected depending on the ambient temperature, preferably increasing with the ambient temperature. This means that at higher ambient temperatures, the coolant pump is activated for a longer period and / or more frequently.

[0018] Furthermore, the duration and / or frequency of the coolant pump activation during shutdown is preferably selected based on the age of the coolant. Newer coolants contain more inhibitors, i.e., components that can neutralize acids or bases formed as anions or cations. Consequently, the activation duration and / or frequency of the coolant pump can be lower. In other words, the duration and / or frequency of the coolant pump activation preferably increases with the age of the coolant.

[0019] The same principle applies to the age or service life of the ion exchanger. Its capacity to bind ions decreases with service life. A heavily loaded ion exchanger or ion filter must therefore be subjected to a longer flow rate than an unloaded or only lightly loaded ion filter to absorb the same amount of ions. This is because the capacity of the ion exchange material to bind with the ions diminishes over time.

[0020] In a further development of the invention, it is therefore proposed that the duration and / or frequency of the coolant pump activation during shutdown is / are selected depending on the operating time of the ion exchanger, preferably increasing with the operating time of the ion exchanger. Preferably, the coolant pump is activated during shutdown by means of a monitoring and / or wake-up function. The monitoring function can, for example, be a type of "sleeping" monitoring function. The monitoring and / or wake-up function guarantees the activation of the coolant pump during shutdown. Furthermore, preferably, the monitoring and / or wake-up function is / are implemented in a control unit of the fuel cell system. The activation of the coolant pump during shutdown is thus ensured by the control unit.

[0021] Furthermore, a control unit for a fuel cell system is proposed, wherein the control unit is configured to execute steps of a method according to the invention. In particular, a monitoring and / or wake-up function can be implemented in the control unit to activate the coolant pump in the event of a shutdown. Preferably, at least one piece of information, such as the age of the coolant and / or the operating time of the ion exchanger, is stored in the control unit, so that the duration and / or frequency of the activation of the coolant pump can be determined depending on this at least one piece of information. Alternatively or additionally, at least one measured parameter, such as the coolant temperature and / or the ambient temperature, can be available to the control unit, so that the duration and / or frequency of the activation of the coolant pump can be determined depending on this at least one piece of information.

[0022] When the control unit is used in a fuel cell system, it enables the implementation of the previously described method according to the invention, so that the fuel cell system can be operated according to this method, whereby the shutdown state is considered a specific phase in the operation of the fuel cell system. This means that the operation of the fuel cell system also includes the shutdown state. This is particularly true since at least parts of the fuel cell system remain activated or reactivatable during the shutdown state.

[0023] The invention and its advantages are described in more detail below with reference to the accompanying drawing. This shows a schematic representation of a fuel cell system that is suitable for carrying out the method or can be operated according to the method.

[0024] Detailed description of the drawing

[0025] The figure shows a fuel cell system 1 that can be operated according to a method according to the invention. The illustration of the fuel cell system 1 is limited to a fuel cell stack 2 and a cooling circuit 3 into which the fuel cell stack 2 is integrated. The waste heat generated in the fuel cell stack 2 during operation can be dissipated via the cooling circuit 3. In the event of a start-up, particularly a cold start, the fuel cell stack 2 can be brought up to operating temperature with the aid of the cooling circuit 3.

[0026] The cooling circuit 3 shown incorporates a coolant pump 4 and a radiator 7. The heat absorbed by the coolant in the fuel cell stack 2 from the fuel cell is dissipated to the environment via the radiator 7. In mobile applications, the radiator 7 is preferably the vehicle's radiator. The radiator 7 can be bypassed via a bypass path 8, which is connected to the cooling circuit 3 via a directional control valve 9. Bypassing the radiator 7 is particularly advantageous during startup.

[0027] The cooling circuit 3 shown also incorporates an ion exchanger 5, which can be switched on and off via a valve 6. The ion exchanger 5 binds acids or bases that may have formed in the coolant over time, thus preventing the pH value of the coolant from falling below a minimum value. This, in turn, reduces the risk of corrosion damage to components through which the coolant flows.

[0028] In the event of a shutdown, the coolant pump 4 is usually deactivated. To prevent the pH value of the coolant from dropping below the minimum value during a prolonged shutdown period, the method according to the invention can be carried out. In this method, the coolant pump 4 is activated temporarily and / or at specific intervals during the shutdown, whereby the coolant is passed through the ion exchanger 5. Any acids or bases contained in the coolant are then bound in the ion exchanger 5. The duration and / or frequency of the activation of the coolant pump 4 during the shutdown can be selected, in particular, depending on the temperature of the coolant and / or the ambient temperature. Furthermore, the age of the coolant and / or the ion exchanger 5 can be taken into account. The activation of the coolant pump 4 can, for example, be effected by means of a control unit (not shown) of the fuel cell system 1, which, among other things,It serves to control the coolant pump 4.

Claims

Claims 1. Method for operating a fuel cell system (1), comprising a fuel cell stack (2) and a cooling circuit (3) carrying a coolant, in which the fuel cell stack (2) is integrated, wherein in normal operation the coolant is circulated by means of a coolant pump (4) integrated into the cooling circuit (3), characterized in that in the case of shutdown the coolant pump (4) is activated temporarily and / or at certain time intervals and the coolant is passed through an ion exchanger (5) integrated into the cooling circuit (3), so that any acids or bases formed in the coolant are bound by means of the ion exchanger (5).

2. Method according to claim 1, characterized in that the duration and / or frequency of activation of the coolant pump (4) in the event of shutdown is / are selected depending on the coolant temperature, wherein preferably the duration and / or frequency of activation increases with the level of the coolant temperature.

3. Method according to claim 1 or 2, characterized in that the duration and / or frequency of activation of the coolant pump (4) in the event of shutdown is / are selected depending on the ambient temperature, wherein preferably the duration and / or frequency of activation increases with the level of the ambient temperature.

4. Method according to one of the preceding claims, characterized in that the duration and / or frequency of activation of the coolant pump (4) in the event of shutdown is / are selected depending on the age of the coolant, wherein preferably the duration and / or frequency of activation increases with the age of the coolant.

5. Method according to one of the preceding claims, characterized in that the duration and / or frequency of the activation of the coolant pump (4) in the event of shutdown is / are selected depending on the operating time of the ion exchanger (5), wherein preferably the duration and / or frequency of the activation increases with the operating time of the ion exchanger (5).

6. Method according to one of the preceding claims, characterized in that the coolant pump (4) is activated in the event of shutdown by means of a monitoring and / or wake-up function, which is / are preferably implemented in a control unit of the fuel cell system (1).

7. Control unit for a fuel cell system (1), wherein the control unit is configured to perform steps of a method according to any of the preceding claims.

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