Methods for cooling fuel cell stacks, controllers

Abstract

The invention relates to a method for cooling a fuel cell stack (2) of a preferably mobile fuel cell system (1) by means of a cooling circuit (3) for guiding a coolant, in which a pump (4), a radiator (5) with a fan (6) and a directional control valve (7) for opening and closing a bypass (8) for bypassing the radiator (5) are integrated, the temperature of the coolant being adjusted to a predefined standard value or range via the mixture ratio of the coolant flows guided through the radiator (5) and / or the bypass (8) and via the air velocity at the radiator (5). Furthermore, the invention relates to a controller for carrying out the steps of the method. [Solution] According to the present invention, the temperature of the coolant is varied depending on the current cooling capacity of the cooling circuit (3) and / or depending on the current energy consumption of the cooling circuit (3) to be lowered or raised relative to the standard value or standard range.

Description

Technical Field

[0001] The present invention relates to a method for cooling a fuel cell stack of a preferably mobile fuel cell system as described in the preamble of claim 1.

Background Art

[0002] The cooling of the fuel cell stack of a fuel cell system can be implemented by a cooling system including a pump and a radiator equipped with a fan. In the case of mobile specifications, that is, in a vehicle, the radiator is usually a vehicle cooler.

[0003] A cooling system for temperature adjustment of a fuel cell system having a closed cooling pipe for a coolant is, for example, derived from Patent Document 1. A pump for adjusting the pressure in the cooling pipe is integrated in the cooling pipe. By the pump, the coolant is supplied to the fuel cell stack to be cooled. Thus, the coolant absorbs the process heat of the fuel cell system. The coolant is supplied to the aftercooler of the fuel cell system, for example, to the vehicle cooler, and is cooled again there using a fan.

[0004] Furthermore, a cooling system having a plurality of cooling circuits with a bypass for bypassing a cooler or radiator is known. In this case, by using a direction control valve, the mixing ratio of the coolant flow guided through the radiator and the coolant flow guided through the bypass can be adjusted. Usually, the fixed target temperature of the coolant is adjusted by adjusting the direction control valve in combination with the adjustment of the fan.

[0005] The coolant temperature affects the aging of the fuel cell stack and therefore its efficiency over its lifespan. Lower temperatures have a positive effect on the efficiency of the fuel stack, so it may be advantageous to adjust the coolant temperature to be lower than the fixed target temperature. However, this results in a smaller temperature difference at the radiator relative to the ambient temperature. Consequently, the cooling system may be forced to operate within limits where its cooling performance exceeds its limits, or where the required cooling capacity cannot be provided without increasing the coolant flow or airflow at the radiator, leading to increased energy consumption. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] German Patent Application Publication No. 102016213533A1 Specification [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] This invention addresses the challenge of optimizing the cooling of a fuel cell stack in order to improve the efficiency of the fuel cell stack and reduce the energy cost of cooling. [Means for solving the problem]

[0008] To solve this problem, a method having the configuration of claim 1 is proposed. Further configurations of the present invention can be read from the dependent claims. Furthermore, a controller for carrying out the steps of the method is described.

[0009] The proposed method involves cooling the fuel cell stack of a mobile fuel cell system using a cooling circuit that guides a coolant, which integrates a pump, a radiator with a fan, and a directional control valve for opening and closing a bypass to route the coolant around the radiator. The temperature of the coolant is adjusted to a predetermined standard value or range via the mixing ratio of the coolant flow guided through the radiator and / or the bypass, and via the air velocity in the radiator. According to the present invention, the temperature of the coolant is changed depending on the current cooling capacity of the cooling circuit and / or the current energy consumption of the cooling circuit to decrease or increase the standard value or standard range.

[0010] Therefore, the proposed method does not pre-set a fixed target value for the coolant temperature, but rather varies the coolant temperature. In this process, the coolant temperature is decreased or increased (starting from a predefined standard value or standard range). The decisive factors in this decrease or increase in temperature are the current power and / or current energy consumption of the cooling circuit. By focusing on these two parameters, the coolant temperature can be kept as low as possible, thus improving the efficiency of the fuel cell stack.

[0011] Therefore, by proposing to vary the temperature of the coolant, the temperature can be optimally adapted to the current conditions, and as a result, efficiency can be improved without increasing energy consumption.

[0012] In the proposed method, it is preferable to first define a standard range for the coolant temperature. This standard range may be, for example, 62 to 68°C. If the temperature falls below the lower limit of the standard range, the cooling circuit will operate by lowering the temperature range. If the temperature rises above the upper limit of the standard range, the cooling circuit will operate by raising the temperature range. Setting a standard range instead of a single standard value allows for greater flexibility during the design phase.

[0013] To have an advantage, (i) When it is certain that the cooling performance limit of the cooling circuit will not be exceeded, (ii) If the energy consumption of the cooling circuit can be kept below a predetermined limit, Lower the temperature of the coolant to a standard value or standard range.

[0014] Therefore, lowering the coolant temperature is linked to several conditions. Only when these conditions are met can the temperature be lowered to increase the efficiency of the fuel cell stack. In this way, not only is it avoided that the cooling performance limit of the cooling circuit is exceeded, but at the same time, an increase in the energy consumption of the cooling circuit, especially the pump and fan of the cooling circuit, is avoided.

[0015] It is preferable to detect energy consumption based on the current ambient temperature and / or the current air velocity in the radiator, and in this case, to perform an evaluation based on this detection. That is, it is advantageous to evaluate energy consumption. In mobile specifications, since the air velocity in the radiator depends on the vehicle speed, the evaluation may be performed based on the vehicle speed.

[0016] To further advantage, (i) When the cooling performance limit of the cooling circuit is about to be exceeded, (ii) When the operating temperature of the fuel cell stack can be kept below the maximum permissible limit, Raise the temperature of the coolant to a standard value or standard range.

[0017] Therefore, increasing the coolant temperature is similarly tied to several conditions. Only when these conditions are met can the temperature be increased beyond the standard value or standard range. Maintaining these conditions ensures that neither the cooling performance of the cooling circuit nor the maximum allowable operating temperature of the fuel cell stack is exceeded.

[0018] Furthermore, it is proposed to terminate the operation of the cooling circuit when the temperature of the coolant rises, provided that the cooling performance of the cooling circuit is guaranteed to be sufficient for the operation when the temperature of the coolant corresponds to a standard value or a standard range. That is, if the cooling performance of the cooling circuit permits, the efficiency of the fuel cell stack can be improved by reducing the temperature of the coolant again. This is because it is premised on the lowest possible coolant temperature.

[0019] In an advantageous aspect, the operation of the cooling circuit is temporarily restricted when the temperature is raised. The temporary restriction may be carried out for each result and / or over the entire life of the fuel cell stack. That is, each individual rise and / or all rises in total are temporarily restricted. Beyond the temporary restriction, a rise in the coolant temperature is no longer permitted. At this time, in order to reduce the cooling capacity of the cooling circuit to the maximum possible cooling capacity, a reduction in the power of the fuel cell stack is similarly required.

[0020] Furthermore, a controller installed to carry out the steps of the method according to the invention is proposed. Using this controller, for example, control or adjustment of the direction control valve and / or fan integrated in the cooling circuit can be realized in order to lower or raise the temperature of the coolant.

[0021] Next, the present invention and its advantages will be explained in more detail with reference to the accompanying drawings.

Brief Description of the Drawings

[0022] <_{ } [Figure 1] It is a schematic diagram of a fuel cell stack of a fuel cell system connected to a cooling circuit.

Embodiments for Carrying Out the Invention

[0023] The illustrated fuel cell stack 2 of fuel cell system 1 has an anode 2.1 and a cathode 2.2. During operation of fuel cell system 1, hydrogen is supplied to anode 2.1 via an anode circuit (not shown). Ambient air is supplied to cathode 2.2 as an oxygen source via an air supply passage (not shown). Hydrogen and oxygen are converted into electrical energy, heat, and water within the fuel cell of fuel cell stack 2.

[0024] The heat generated in this process is discharged through the cooling circuit 3, which is therefore partially guided through the fuel cell stack 2. Outside the fuel cell stack 2, a pump 4, a radiator 5 equipped with a fan 6, and a directional control valve 7 are integrated into the cooling circuit 3. The pump 4 is used to circulate the coolant within the cooling circuit 3. Once the coolant reaches the fuel cell stack 2, it absorbs heat, and then the radiator 5 and fan 6 release the heat to the surroundings. The directional control valve 7 can be used to control the coolant flow guided through the radiator 5. This is because, depending on the switching position of the directional control valve 7, at least a portion of the coolant flow is diverted to a bypass 8 that bypasses the radiator 5, rather than being supplied to the radiator 5. In other words, the coolant can release less heat. Therefore, the temperature of the coolant can be adjusted by the mixing ratio of the coolant flow guided through the radiator 5 and the coolant flow guided through the bypass 8. Furthermore, the air velocity in the radiator 5 also affects the coolant temperature. This can be influenced through the operation of fan 6. In addition, in the mobile version, the air velocity depends on the vehicle's speed.

[0025] Low coolant temperatures during operation of the fuel cell system 1 have a positive effect on the aging of the fuel cell stack 2 and thus on efficiency, so efforts are made to achieve the lowest possible coolant temperature. However, as a result, the temperature difference between the radiator 5 and the surroundings becomes small. If the ambient temperature is sufficiently low, it can be assumed that the heat absorbed by the coolant can be released without significantly increasing the energy required for heat dissipation. However, in order to achieve the same cooling capacity, it is generally necessary to increase the coolant flow and / or air flow in the radiator 5. That is, the power of the pump 4 and / or fan 6 must be increased, which increases the energy consumption of the cooling circuit 3.

[0026] Similarly, if the coolant temperature rises, the temperature difference between the radiator 5 and the surroundings will increase, and as a result, if the coolant flow and airflow in the radiator 5 remain unchanged, it can provide greater cooling capacity. However, raising the coolant temperature to increase the efficiency of the fuel cell stack 2 is not very desirable.

[0027] To resolve this objective contradiction, the method according to the present invention proposes variable adjustment of the coolant temperature. In this case, the adjustment is made depending on the current cooling capacity and / or current energy consumption of the cooling circuit 3, in particular the pump 4 and the fan 6 integrated within the cooling circuit 3.

[0028] According to the method of the present invention, the coolant temperature is lowered or raised compared to a predetermined standard value or standard range. In this case, the decrease or increase in the coolant temperature is linked to specific conditions.

[0029] Lowering the coolant temperature compared to the standard value or standard range should only be considered if it is guaranteed that the cooling performance of the cooling circuit 3, i.e., the maximum allowable cooling capacity, is not exceeded, and that energy consumption remains below a predetermined limit. Since this operating mode leads to an improvement in the efficiency of the fuel cell stack 2, it is advantageous to select it assuming that the two conditions mentioned above are met.

[0030] Raising the coolant temperature beyond the standard value or standard range is permitted only if the cooling capacity of cooling circuit 3 is insufficient, resulting in an imminent exceedance of the cooling performance limit of cooling circuit 3, while simultaneously ensuring that the maximum allowable operating temperature of fuel cell stack 2 is not exceeded.

[0031] The method according to the present invention allows the fuel cell system 1 to be configured to operate at the lowest possible coolant temperature as often as possible. However, if this leads to a significant increase in energy consumption and / or operation of the cooling circuit 3 in a critical region, and as a result there is a risk of exceeding the cooling performance limit of the cooling circuit 3, the coolant temperature may be increased. By increasing the temperature, energy consumption is reduced and exceeding the cooling performance limit of the cooling circuit 3 is reliably avoided. [Explanation of Symbols]

[0032] 1. Fuel cell system 2 Fuel cell stack 3 Cooling circuit 4 pumps 5. Radiator 6 Fans 7 Directional control valve 8 Bypass

Claims

1. A method for cooling a fuel cell stack (2) of a mobile fuel cell system (1) mounted on a vehicle using a cooling circuit (3) for guiding a coolant, the circuit having an integrated pump (4), a radiator (5) equipped with a fan (6), and a directional control valve (7) for opening and closing a bypass (8) to bypass the radiator (5), wherein the method adjusts the temperature of the coolant to a predetermined standard value or standard range via the mixing ratio of the coolant flow guided through the radiator (5) and / or the bypass (8), and via the air velocity in the radiator (5), The current energy consumption of the cooling circuit (3) is evaluated based on the vehicle speed of the moving vehicle. A method characterized by changing the temperature of the coolant in accordance with the current cooling capacity of the cooling circuit (3) and the current energy consumption of the cooling circuit (3) to lower or raise it relative to the standard value or standard range.

2. The cooling performance limit of the aforementioned cooling circuit (3) is reliably prevented from being exceeded, and If the energy consumption of the cooling circuit (3) can be kept below a predetermined limit, The method according to claim 1, characterized in that the temperature of the coolant is reduced compared to the standard value or the standard range.

3. The method according to claim 1 or 2, characterized in that the energy consumption is detected and evaluated based on the current ambient temperature and / or the current air velocity in the radiator (5).

4. The cooling performance limit of the aforementioned cooling circuit (3) is about to be exceeded, and When the operating temperature of the fuel cell stack (2) can be kept below the maximum permissible limit, The method according to claim 1 or 2, characterized in that the temperature of the coolant is increased compared to the standard value or the standard range.

5. The method according to claim 1 or 2, characterized in that, if it is guaranteed that the cooling performance of the cooling circuit (3) is sufficient for operation when the temperature of the coolant corresponds to the standard value or standard range, the operation of the cooling circuit (3) is terminated when the temperature of the coolant is increased.

6. The method according to claim 1 or 2, characterized in that when the temperature is increased, the operation of the cooling circuit (3) is temporarily restricted for each result and / or over the entire lifespan of the fuel cell stack (2).

7. A controller installed for carrying out a step of the method according to claim 1 or 2.

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