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

Abstract

The invention relates to a method (100) for deactivating a fuel cell system (300) comprising a plurality of fuel cell stacks (301, 303) and a temperature control system connecting the fuel cell stacks (301, 303), wherein the method (100) comprises: - selecting (101) a fuel cell stack (301) to be activated first for a subsequent start-up of the fuel cell system from the plurality of fuel cell stacks (301, 303); - initiating (103) a first drying phase in response to a command to deactivate the fuel cell system (300); - initiating (105) a second drying phase after the first drying phase, wherein during the first drying phase a coolant flow through the selected fuel cell stack (301) is adjusted by directing at least part of the coolant flow to a further fuel cell stack (303) of the plurality of fuel cell stacks (301, 303) such that a temperature in the selected fuel cell stack (301) remains within a predetermined temperature range, wherein during the second drying phase, the coolant flow is cooled by a cooler (307) and is directed through the selected fuel cell stack (301) at a volume flow rate that is increased relative to the first drying phase.

Description

[0001] Description

[0002] title

[0003] Methods for deactivating a fuel cell system and fuel cell system

[0004] The presented invention relates to a method for deactivating a fuel cell system and a fuel cell system according to the attached claims.

[0005] State of the art

[0006] Hydrogen-based fuel cell systems are considered a mobility concept of the future, as they only emit water as exhaust gas and allow for fast refueling times.

[0007] In commercial vehicles, multiple fuel cell stacks are combined in a single fuel cell system to increase power output. During a frost start, i.e., a start in ambient conditions where water freezes, this system layout presents the challenge of warming both fuel cell stacks above freezing as quickly as possible and without the use of external heat sources, thus bringing them into an operational state. An important prerequisite for this is that the fuel cell stacks are preconditioned, i.e., dried, to enable self-starting.

[0008] Drying methods for drying fuel cell stacks are known, but these are potentially damaging to the fuel cell stack.

[0009] Disclosure of the Invention: The invention presents a fuel cell system and a method for deactivating the fuel cell system. Further features and details of the invention will become apparent from the respective dependent claims, the description, and the drawings. Features and details described in connection with the method according to the invention naturally also apply in connection with the fuel cell system according to the invention, and vice versa, so that the disclosure of the individual aspects of the invention always refers to, or can refer to, each other.

[0010] The presented invention serves in particular to provide a possibility for a compact and robust fuel cell system.

[0011] Thus, according to a first aspect of the presented invention, a method for deactivating a fuel cell system comprising at least one fuel cell stack and a temperature control system is presented.

[0012] The presented method comprises initiating a first drying phase in response to a command to deactivate the fuel cell system and initiating a second drying phase after the first drying phase, wherein during the first drying phase a coolant flow is set through the at least one fuel cell stack, e.g. by stopping or adjusting the speed of the coolant pump responsible for supplying the coolant flow, so that a temperature in the at least one fuel cell stack remains within a predetermined temperature range, and wherein during the second drying phase the coolant flow is cooled by a cooler and passed through the at least one fuel cell stack with an increased volume flow rate compared to the first drying phase.

[0013] It can further be provided that the presented method includes selecting a fuel cell stack to be activated first for a subsequent start of the fuel cell system from a plurality of fuel cell stacks of the fuel cell system, wherein during the first drying phase a coolant flow is set through the selected fuel cell stack by directing at least part of the coolant flow to another fuel cell stack of the plurality of fuel cell stacks, so that a temperature in the selected fuel cell stack remains within a predetermined temperature range, and wherein during the second drying phase the coolant flow is cooled by a cooler and directed through the selected fuel cell stack with an increased volume flow compared to the first drying phase.

[0014] By selecting one fuel cell stack from a multitude of fuel cell stacks for a freeze start, i.e., a self-start under freezing conditions without assistance, it can be selectively prepared for the freeze start, while other fuel cell stacks from the multitude of fuel cell stacks are gently deactivated or deactivated in a way that optimizes their lifespan.

[0015] Accordingly, only one fuel cell stack is selected from the multitude of fuel cell stacks. This can be done, for example, by alternating between different fuel cell stacks within the multitude of fuel cell stacks, or depending on a condition of the fuel cell stacks, such as their operating hours, so that the most homogeneous wear of the different fuel cell stacks is achieved.

[0016] To prepare or condition the selected fuel cell stack for the freeze-start process, it is held within a predefined temperature range, e.g., 60°C to 65°C, during an initial drying phase to maximize water removal. This is achieved by reducing, or even completely shutting off, the cooling of the selected fuel cell stack by decreasing the coolant flow through it.

[0017] According to the invention, the reduction of the coolant flow through the selected fuel cell stack is achieved by directing at least a portion of the coolant flow that normally flows to the selected fuel cell stack to another fuel cell stack of the plurality of fuel cell stacks. Alternatively, the coolant flow can be reduced or adjusted by reducing or adjusting the coolant pump speed.

[0018] In particular, during the first drying phase, a coolant flow supplied to the selected fuel cell stack cannot be passed through a cooler to cool the coolant flow or bypassed the cooler, so that thermal energy stored in the selected fuel cell stack is used to evaporate water stored in the selected fuel cell stack and finally drive it out of the selected fuel cell stack.

[0019] After the first drying phase, the selected fuel cell stack can be cooled quickly in a second drying phase, i.e., with a larger coolant flow relative to the first phase, possibly by means of a cooler, so that it cools down quickly.

[0020] It may also be provided that during the first drying phase, the coolant flows and / or air masses directed into different fuel cell stacks of the fuel cell system differ from each other or are different.

[0021] For example, an air mass can be maximized in a fuel cell stack selected for a freeze start, while an air mass is reduced in the other fuel cell stacks.

[0022] Increasing the air mass maximizes water discharge from the selected fuel cell stack.

[0023] It may also be provided that in the first drying phase the coolant flow is directed entirely to the next fuel cell stack.

[0024] By completely diverting the coolant flow to the other fuel cell stack, cooling of the selected fuel cell stack by the temperature control system is prevented, so that the selected fuel cell stack maintains its temperature constant for as long as possible or cools down slowly, and water discharge from the selected fuel cell stack is maximized accordingly.

[0025] It may also be stipulated that the first drying phase is carried out for a predetermined duration.

[0026] The first drying phase can, for example, last between 1 minute and 5 minutes.

[0027] It may also be provided that the coolant flow is pre-cooled by the additional fuel cell stack before the second drying phase is initiated.

[0028] To pre-cool the coolant flow, the additional fuel cell stack can, for example, guide the coolant flow through a cooler that includes a fan to transfer thermal energy from the coolant flow into an environment.

[0029] It may also be provided that during the first drying phase the selected fuel cell stack is kept within a predetermined temperature range and the other fuel cell stack is continuously cooled.

[0030] Continuous cooling of the remaining fuel cell stack and drying with a reduced air mass ensures particularly gentle deactivation, thus extending its lifespan.

[0031] It can also be provided that, in order to increase the coolant flow through the selected fuel cell stack in the second drying phase, the coolant flow is increased according to a predefined transition function. A transition function, such as a ramp function or a gradual transition over a predefined time, prevents thermal shock to the selected fuel cell stack.

[0032] It may also be stipulated that the procedure is only executed if the ambient temperature is below a predetermined threshold.

[0033] To prevent unnecessary stress on the fuel cell stacks, the presented procedure can only be carried out if a freeze start is expected, i.e., if the ambient temperature is below a predetermined threshold.

[0034] According to a second aspect, the presented invention relates to a fuel cell system for providing electrical energy.

[0035] The presented fuel cell system comprises a multitude of fuel cell stacks, a temperature control system connecting the multitude of fuel cell stacks, and a computing unit, the computing unit being configured to carry out one possible embodiment of the presented method.

[0036] In the context of the presented invention, a computing unit is to be understood as a computer, a control unit, a processor or any other programmable circuit.

[0037] The fuel cell system may include a valve configured to provide, in a first position, a coolant flow to a selected fuel cell stack that is reduced relative to the coolant flow to another fuel cell stack, and in a second position, a coolant flow to the selected fuel cell stack that is increased relative to the coolant flow to the other fuel cell stack. A valve, such as a 3-way valve, integrated into a cooling circuit supplying multiple fuel cell stacks, allows for easy and rapid adjustment, and in particular, complete redirection, of the coolant flow to each fuel cell stack.

[0038] It may still be provided that the temperature control system only includes a coolant pump.

[0039] The topology of the presented fuel cell system and the presented method allow for different thermal treatment of multiple fuel cell stacks, even though they are connected by a common cooling circuit. Accordingly, the cooling circuit can be driven by a central coolant pump, resulting in a particularly compact and robust fuel cell system.

[0040] Advantages described in detail for the method of deactivating a fuel cell system according to the first aspect of the invention apply equally to the fuel cell system for providing electrical energy according to the second aspect of the invention and vice versa.

[0041] Further advantages, features, and details of the invention will become apparent from the following description, in which exemplary embodiments of the invention are described in detail with reference to the drawings. The features mentioned in the claims and in the description can each be essential to the invention individually or in any combination.

[0042] They each show schematically:

[0043] Figure 1 shows a possible embodiment of the presented method,

[0044] Figure 2 shows a detailed representation of the process according to Fig. 1.

[0045] Figure 3 shows a representation of a possible design of the presented

[0046] fuel cell system, and Figure 4 shows a representation of the flow of coolant during the process according to Fig. 1.

[0047] Fig. 1 shows a method 100 for deactivating a fuel cell system comprising a plurality of fuel cell stacks and a temperature control system connecting the fuel cell stacks.

[0048] Method 100 comprises an optional selection step 101, in which a fuel cell stack to be activated first for a subsequent start of the fuel cell system is selected from the plurality of fuel cell stacks, a first initiation step 103, in which a first drying phase is initiated in response to a command to deactivate the fuel cell system, and a second initiation step 105, in which a second drying phase is initiated after the first drying phase, wherein during the first drying phase a coolant flow is set through the selected fuel cell stack by directing at least part of the coolant flow to another fuel cell stack of the plurality of fuel cell stacks.so that the temperature in the selected fuel cell stack remains within a specified temperature range, and wherein, during the second drying phase, the coolant flow is cooled by a cooler and passed through the selected fuel cell stack with an increased volume flow compared to the first drying phase.

[0049] Of course, procedure 100 is also applicable to a fuel cell system with only one fuel cell stack, in which case selection step 101 is omitted.

[0050] Fig. 2 shows a flowchart 200 of the process 100 according to Fig. 1.

[0051] In initialization step 201, a command to deactivate the fuel cell system is provided via a user interface.

[0052] Subsequently, in a calibration step 203, an ambient temperature is compared to a predefined threshold value, e.g., 0°C. If the ambient temperature is higher than the threshold value, the process 100 is terminated, and in an activation step 205, an alternative process for the symmetrical drying of the fuel cell stacks is activated. Finally, the alternative process is terminated in a termination step 207.

[0053] In the event that the ambient temperature is less than or equal to the threshold, in selection step 209 a fuel cell stack is selected for preconditioning for a freeze start and another fuel cell stack for gentle drying.

[0054] Subsequently, in an introductory step 211, a first drying phase is initiated by completely directing a coolant flow through the fuel cell system to the further fuel cell stack.

[0055] In a gentle drying step 213, the next fuel cell stack is rapidly cooled by diverting the coolant flow through it via a cooler, such as a vehicle radiator. Furthermore, the next fuel cell stack is dried with a reduced air mass.

[0056] Furthermore, by completely diverting the coolant flow to the other fuel cell stack, a first drying phase 215 of the selected fuel cell stack is activated, in which the selected fuel cell stack is held without coolant flow.

[0057] After the gentle drying of the next fuel cell stack, it is deactivated in a deactivation process 217.

[0058] Following the deactivation process 217, the first drying phase of the selected fuel cell stack ends, and the entire coolant flow is diverted into the selected fuel cell stack in a rerouting step 219. By diverting the entire coolant flow into the selected fuel cell stack, the second drying phase 221 of the selected fuel cell stack is initiated, during which it is rapidly cooled by the coolant flow.

[0059] In deactivation step 223, the selected fuel cell stack is deactivated.

[0060] Figure 3 shows a fuel cell system 300 for providing electrical energy.

[0061] The fuel cell system 300 comprises a first fuel cell stack 301, a second fuel cell stack 303, a common coolant pump 305 and a cooler 307.

[0062] A first valve 309 can be used to switch or split the coolant flow between the first fuel cell stack 301 and the second fuel cell stack 303.

[0063] A second valve 313 can be used to activate a bypass to circumvent the cooler 307.

[0064] Furthermore, the fuel cell system 300 includes a computing unit 311, which is configured to perform the procedure according to Fig. 1 or 2.

[0065] Figure 4 shows a first diagram 401 and a second diagram 403, each spanning time on its abscissa and depicting both temperature and a coolant flow on its ordinate.

[0066] Diagram 401 shows a temperature curve (405) of a selected fuel cell stack and a coolant flow curve (407) through the selected fuel cell stack. Diagram 403 shows a temperature curve (409) of another fuel cell stack and a coolant flow curve (411) through another fuel cell stack. Comparing curves 405 and 409, and 407 and 411, it is evident that the coolant flow initially passes through the other fuel cell stack, and the temperature in the selected fuel cell stack remains high.

[0067] At a switching point T1, the coolant flow is diverted from the other fuel cell stack to the selected fuel cell stack, causing the temperature in the selected fuel cell stack to drop.

[0068] Arrow 413 indicates a potential for cooling the temperature of the next fuel cell stack by pre-cooling the coolant flow within that stack using a cooler. This pre-cooling leads to faster cooling of the selected fuel cell stack after the switchover time T1.

Claims

Claims 1. Method (100) for deactivating a fuel cell system (300) comprising at least one fuel cell stack (301) and a temperature control system, wherein the method (100) comprises: Initiating (103) a first drying phase in response to a command to deactivate the fuel cell system (300), Initiation (105) of a second drying phase after the first drying phase, wherein during the first drying phase a coolant flow is set through the at least one fuel cell stack (301) such that a temperature in the at least one fuel cell stack (301) remains within a specified temperature range, wherein during the second drying phase the coolant flow is cooled by a cooler (307) and passed through the at least one fuel cell stack (301) with an increased volume flow compared to the first drying phase.

2. Method (100) according to claim 1, wherein the fuel cell system (300) comprises a plurality of fuel cell stacks (301, 303) and a temperature control system connecting the fuel cell stacks (301, 303), wherein the method (100) further comprises: Selecting (101) a fuel cell stack (301) to be activated first for a subsequent start of the fuel cell system (300) from the plurality of fuel cell stacks (301, 303), wherein during the first drying phase a coolant flow is set through the selected fuel cell stack (301) by directing at least part of the coolant flow to another fuel cell stack (303) of the plurality of fuel cell stacks (301, 303), such that a temperature in the selected fuel cell stack (301) remains within a specified temperature range, wherein during the second drying phase the coolant flow is cooled by a cooler (307) and passed through the selected fuel cell stack (301) with an increased volume flow compared to the first drying phase.

3. Method (100) according to claim 2, characterized in that during the first drying phase, coolant flows and / or air mass flows directed into different fuel cell stacks (301 , 303) of the fuel cell system (300) differ from each other.

4. Method (100) according to claim 2 or 3, characterized in that in the first drying phase the coolant flow is directed completely to the further fuel cell stack (303).

5. Method (100) according to one of the preceding claims, characterized in that the first drying phase is carried out for a predetermined duration.

6. Method (100) according to one of claims 2 to 5, characterized in that the coolant flow is pre-cooled by the further fuel cell stack (303) before the introduction of the second drying phase.

7. Method (100) according to one of claims 2 to 6, characterized in that during the first drying phase the selected fuel cell stack (301) is kept in a predetermined temperature range and the further fuel cell stack (303) is continuously cooled.

8. Method (100) according to any one of the preceding claims, characterized in that, in order to increase the coolant flow through the selected fuel cell stack (301) in the second drying phase, the coolant flow is increased according to a predetermined transition function.

9. Method (100) according to one of the preceding claims, characterized in that the method (100) is only carried out when the ambient temperature is below a predetermined threshold.

10. Fuel cell system (300) for providing electrical energy, wherein the fuel cell system (300) comprises: a number of fuel cell stacks (301, 303), a temperature control system, a computing unit (311), wherein the computing unit (311) is configured to perform a method (100) according to any one of claims 1 to 9.

11. Fuel cell system (300) according to claim 10, characterized in that the fuel cell system (300) comprises a valve (309) configured to provide, in a first position, a coolant flow to a selected fuel cell stack (301) which is reduced relative to a coolant flow to a further fuel cell stack (303), and, in a second position, to provide a coolant flow to the selected fuel cell stack (301) which is increased relative to a coolant flow to the further fuel cell stack (303).

12. Fuel cell system (300) according to claim 10 or 11, characterized in that the temperature control system comprises only a coolant pump (305).

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