Method and controller for cooling a fuel cell stack

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 according to the preamble of claim 1 . [Background technology]

[0002] Cooling of the fuel cell stack of the fuel cell system can be realized by a cooling system including a pump and a radiator equipped with a fan. In mobile versions, i.e. in vehicles, the radiator is usually a vehicle cooler.

[0003] A cooling system for regulating the temperature of a fuel cell system originates, for example, from DE 10 200 03 133 A1, which has a closed cooling channel for the coolant. A pump is integrated into the cooling channel for regulating the pressure in the cooling channel. By means of the pump, the coolant is fed to the fuel cell stack to be cooled. There, the coolant absorbs the process heat of the fuel cell system. After passing through the fuel cell system, the coolant is fed to a cooler, for example a vehicle cooler, where it is cooled again by means of a fan.

[0004] Furthermore, cooling systems are known that have multiple cooling circuits with a bypass for bypassing the cooler or radiator. In this case, a directional control valve can be used to adjust the mixture ratio of the coolant flow guided via the radiator and the coolant flow guided via the bypass. A fixed target temperature of the coolant is usually adjusted by adjusting the directional 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 lifetime. It may be advantageous to adjust the coolant temperature lower than a fixed target temperature, since a lower temperature has a positive effect on the efficiency of the fuel stack. However, this results in a smaller temperature difference at the radiator relative to the surroundings. This may result in the cooling system's cooling performance being exceeded or operating within a limiting range such that energy consumption increases, since the required cooling capacity cannot be provided without increasing the coolant flow or air flow at the radiator. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] German Patent Application Publication No. 102016213533A1 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention addresses the problem of optimizing the cooling of a fuel cell stack so as to increase the efficiency of the fuel cell stack and reduce the energy costs for cooling. [Means for solving the problem]

[0008] To achieve this object, a method is proposed with the features of claim 1. Further features of the invention can be read from the dependent claims. Furthermore, a controller for carrying out the steps of the method is described.

[0009] Proposed is a method for cooling a fuel cell stack of a preferably mobile fuel cell system by means of a cooling circuit for guiding a coolant, in which a pump, a radiator with a fan and a directional control valve for opening and closing a bypass for bypassing the radiator are integrated, with 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 and / or the bypass and via the air velocity at the radiator. According to the invention, the temperature of the coolant is varied depending on the current cooling capacity of the cooling circuit and / or depending on the current energy consumption of the cooling circuit, either lowering or raising it relative to the standard value or range.

[0010] The proposed method therefore does not pre-set a fixed target value for the coolant temperature, but instead varies the coolant temperature, thereby lowering or increasing it (starting from a predefined standard value or range). Decisive for the temperature reduction or increase are the current power and / or the current energy consumption of the cooling circuit. By focusing on these two parameters, the coolant temperature can be kept as low as possible, thus increasing the efficiency of the fuel cell stack.

[0011] The proposal to make the coolant temperature variable therefore makes it possible to optimally adapt the temperature to the current situation, so that an efficiency increase can be achieved without increasing energy consumption.

[0012] In the proposed method, preferably, a standard range for the temperature of the coolant is first defined. This standard range may be, for example, 62-68°C. Below a temperature value limiting the standard range at a lower end, the cooling circuit is operated with a lower temperature range. Above a temperature value limiting the standard range at an upper end, the cooling circuit is operated with an increased temperature range. Setting a standard range instead of setting one standard value allows for greater flexibility in the design.

[0013] Advantageously, (i) When the cooling circuit is reliably prevented from exceeding its cooling capacity, and (ii) if the energy consumption of the cooling circuit can be kept below a predefined limit value; The coolant temperature is reduced compared to a standard value or range.

[0014] A reduction in the coolant temperature is therefore linked to a number of conditions, only if these conditions are met can the temperature be reduced in order to increase the efficiency of the fuel cell stack, in this way not only is it possible to avoid exceeding the limits of the cooling capacity of the cooling circuit, but at the same time also avoiding an increase in the energy consumption of the cooling circuit, in particular of the pumps and fans of the cooling circuit.

[0015] The energy consumption is preferably detected based on the current ambient temperature and / or the current air speed at the radiator, and an evaluation is then preferably performed based on this detection, i.e. it is advantageous to evaluate the energy consumption. In mobile versions, the evaluation may also be based on the vehicle speed, since the air speed at the radiator is dependent on the vehicle speed.

[0016] Even more advantageously, (i) When the cooling circuit is about to reach its cooling capacity, and (ii) If the operating temperature of the fuel cell stack can be maintained below the maximum allowable limit, The temperature of the coolant is increased relative to a standard value or range.

[0017] The increase in the coolant temperature is thus likewise linked to a number of conditions. Only if these conditions are met can the temperature be increased beyond a standard value or range. Maintenance of the conditions ensures that neither the cooling capacity of the cooling circuit nor the maximum permissible operating temperature of the fuel cell stack is exceeded.

[0018] Furthermore, it is proposed to terminate operation of the cooling circuit when the temperature of the coolant is increased, provided that the cooling performance of the cooling circuit is guaranteed to be sufficient for operation when the coolant temperature corresponds to a standard value or range, i.e., if the cooling performance of the cooling circuit allows it, to reduce the temperature of the coolant again, thereby increasing the efficiency of the fuel cell stack, since this presupposes the lowest possible coolant temperature.

[0019] In an advantageous embodiment, the operation of the cooling circuit is temporarily limited when the temperature is increased. The temporary limitation can be effected per result and / or for the entire life of the fuel cell stack, i.e. each individual increase and / or all increases in total are temporarily limited. If the temporary limit is exceeded, a further increase in the coolant temperature is no longer permitted. A reduction in the power of the fuel cell stack is then likewise necessary in order to reduce the cooling capacity of the cooling circuit to the maximum possible cooling capacity.

[0020] Furthermore, a controller is proposed which is provided for implementing the steps of the method according to the invention, by means of which it is possible, for example, to realize the control or regulation of directional control valves and / or fans integrated in the cooling circuit in order to lower or raise the temperature of the coolant.

[0021] The invention and its advantages will now be explained in more detail with the aid of the accompanying drawings. [Brief description of the drawings]

[0022] [Figure 1] FIG. 2 is a schematic diagram of a fuel cell stack of a fuel cell system connected to a cooling circuit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] The illustrated fuel cell stack 2 of the fuel cell system 1 comprises an anode 2.1 and a cathode 2.2. During operation of the fuel cell system 1, the anode 2.1 is supplied with hydrogen via an anode circuit (not shown). The cathode 2.2 is supplied with ambient air as oxygen supply via an air supply (not shown). In the fuel cells of the fuel cell stack 2, the hydrogen and oxygen are converted into electrical energy, heat and water.

[0024] The heat generated in this process is discharged via the cooling circuit 3, which is for this purpose partially guided through the fuel cell stack 2. Outside the fuel cell stack 2, a pump 4, a radiator 5 with a fan 6 and a directional control valve 7 are integrated in the cooling circuit 3. The pump 4 is used to circulate the coolant in the cooling circuit 3. When the coolant reaches the fuel cell stack 2, it absorbs heat, which is then released by the radiator 5 and the fan 6 to the surroundings. The directional control valve 7 can be used to control the coolant flow guided through the radiator 5, since depending on the switching position of the directional control valve 7, at least a partial flow of the coolant is not fed to the radiator 5, but is instead diverted into a bypass 8 which bypasses the radiator 5. This means that the coolant can release less heat. The temperature of the coolant can therefore be adjusted via the mixture ratio of the coolant flow guided through the radiator 5 and the coolant flow guided through the bypass 8. Furthermore, the air velocity at the radiator 5 influences the coolant temperature. This can be influenced via the operation of the fan 6. In addition, in mobile versions the air velocity is dependent on the speed of the vehicle.

[0025] Since a low coolant temperature during operation of the fuel cell system 1 has a positive effect on the ageing and thus on the efficiency of the fuel cell stack 2, it is sought to obtain the lowest possible coolant temperature. However, this results in a small temperature difference with respect to the surroundings at the radiator 5. It may be assumed that if the surroundings temperature is low enough, the heat absorbed by the coolant can be released without a significant increase in the energy required for this. However, to be able to fulfill this same cooling capacity, the coolant flow and / or the air flow in the radiator 5 would generally have to be increased. This means that the power of the pump 4 and / or the fan 6 would have to be increased, which would increase the energy consumption of the cooling circuit 3.

[0026] Similarly, if the coolant temperature is increased, the temperature difference with respect to the surroundings at the radiator 5 will be larger, thereby providing more cooling capacity for a given coolant and air flow at the radiator 5. However, it is less desirable to increase the coolant temperature in order to increase the efficiency of the fuel cell stack 2.

[0027] In order to resolve this objective conflict, the method according to the invention proposes a variable adjustment of the coolant temperature, the adjustment being made as a function of the current cooling capacity and / or the current energy consumption of the cooling circuit 3, in particular of the pump 4 integrated in the cooling circuit 3 and of the fan 6 integrated in the cooling circuit 3.

[0028] According to the method according to the invention, the coolant temperature is lowered or increased compared to a predefined standard value or range, the lowering or increasing of the coolant temperature being linked to specific conditions.

[0029] A reduction of the coolant temperature compared to the standard value or range is only to be considered if it is ensured that the cooling performance of the cooling circuit 3, i.e. the maximum permissible cooling capacity, is not exceeded and that the energy consumption remains below a predefined limit value. This operating mode leads to an increase in the efficiency of the fuel cell stack 2 and is therefore advantageously selected, provided that the two aforementioned conditions are met.

[0030] Increasing the coolant temperature compared to the standard value or standard range is only permissible if the cooling capacity of the cooling circuit 3 is insufficient, so that the limits of the cooling performance of the cooling circuit 3 are imminent, while at the same time ensuring that the maximum permissible operating temperature of the fuel cell stack 2 is not exceeded.

[0031] The method according to the invention makes it possible to configure an operating strategy in such a way that the fuel cell system 1 is operated as often as possible at a low coolant temperature. However, if this leads to a significant increase in energy consumption and / or operation of the cooling circuit 3 in the limiting region, with the result that there is a risk of exceeding the limits of the cooling capacity of the cooling circuit 3, the coolant temperature can be increased. By increasing the temperature, energy consumption is reduced and exceeding the limits of the cooling capacity of the cooling circuit 3 is ensured to be avoided. [Explanation of symbols]

[0032] 1. Fuel cell system 2. Fuel cell stack 3 Cooling circuit 4. Pump 5. Radiator 6 Fans 7. Directional Control Valve 8. Bypass

Claims

1. 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), Method, characterized in that the temperature of the coolant is varied in dependence on the current cooling capacity of the cooling circuit (3) and / or in dependence on the current energy consumption of the cooling circuit (3) to be lowered or raised relative to the standard value or standard range.

2. (iii) the cooling circuit (3) is reliably prevented from exceeding its cooling capacity limit, and (iv) if the energy consumption of the cooling circuit (3) can be kept below a predefined limit value, 2. The method of claim 1, further comprising reducing the temperature of the coolant relative to the standard value or range.

3. 3. The method according to claim 1 or 2, characterized in that the energy consumption is detected, preferably evaluated, on the basis of a current ambient temperature and / or a current air speed at the radiator (5).

4. (iii) when the cooling capacity of the cooling circuit (3) is about to be exceeded; and (iv) the operating temperature of the fuel cell stack (2) can be kept below a maximum allowable limit, 4. The method according to claim 1, wherein the temperature of the coolant is increased compared to the standard value or range.

5. 5. The method according to claim 1, further comprising terminating operation of the cooling circuit (3) when the temperature of the coolant is increased if the cooling performance of the cooling circuit (3) is guaranteed to be sufficient for operation when the temperature of the coolant corresponds to the standard value or to the standard range.

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

7. A controller arranged to carry out the steps of the method according to any one of claims 1 to 6.

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