Method for heating a fuel cell system, fuel cell system, vehicle, computer program product, and storage medium

Abstract

The invention relates to a method for heating a fuel cell system (10), having the steps of: determining a starting temperature at a starting time of a heating process, determining a first threshold temperature of the fuel cell system (10), wherein the first threshold temperature is higher than the starting temperature, determining a maximum electrical load by means of which the fuel cell system (10) is to be electrically loaded in order to heat the fuel cell system (10) when the first threshold temperature is reached, determining a starting electrical load by means of which the fuel cell system (10) is to be electrically loaded at the starting time in order to heat the fuel cell system (10), determining a heating process load increase from the starting electrical load at the starting time to the maximum electrical load when the first threshold temperature is reached, and carrying out the heating process for heating the fuel cell system (10) using the determined load increase. The invention also relates to a fuel cell system (10), to a vehicle (100), to a computer program product (40) and to a computer-readable storage medium (50).

Description

[0001] Description

[0002] Method for heating a fuel cell system, fuel cell system, vehicle, computer program product and storage medium

[0003] The technology disclosed here relates to a method for heating a fuel cell system, and in particular for performing a freeze start of the fuel cell system. The technology further relates to a fuel cell system with a controller for performing the method, as well as to a vehicle with the fuel cell system. Furthermore, the technology relates to a computer program product for executing the method, as well as to a computer-readable storage medium on which such a computer program product is stored.

[0004] During operation, a fuel cell system generates water that can freeze at cold system temperatures. The frozen water can block gas supply channels to and from the fuel cells of the fuel cell system. The frozen water can therefore directly or indirectly damage the fuel cell system and must be taken into account when starting the fuel cell system under frost conditions. For this purpose, it is known to start a fuel cell system under frost conditions with a load point shift, which is achieved by reducing the oxygen supply to the fuel cells of the fuel cell system. By reducing the oxygen supply to the fuel cells, the efficiency of the fuel cells is reduced, whereby increased heat is generated to heat up the fuel cell system.Therefore, known methods attempt to operate the fuel cell at the lowest possible efficiency and with the highest possible thermal load during the heating process. However, operating the fuel cell under oxygen depletion can also lead to damage to the fuel cells or at least to accelerated aging of the fuel cells. To address this problem, it is known to monitor the load point of the fuel cell system during the heating process with reference to the water content in the fuel cell system and to adjust it if necessary. This means that if, for example, a high water content is detected in the fuel cell system, a lower load point is selected. If a lower water content is detected, a higher load point is selected.The object of the present invention is to provide an improved method and an improved device for heating a fuel cell system, in particular for carrying out a frost start.

[0005] The above object is achieved by the patent claims. In particular, the above object is achieved by the method according to claim 1 and by the fuel cell system, the vehicle, the computer program product, and the computer-readable storage medium according to the independent claims. Further advantages of the disclosed technology emerge from the dependent claims, the description, and the figures. Features described in connection with the method also apply in connection with the fuel cell system, the vehicle, the computer program product, the storage medium, and vice versa, so that with regard to the disclosure of the individual aspects, reciprocal reference is and / or can always be made.

[0006] According to a first aspect of the present technology, a method for heating a fuel cell system is proposed. The method comprises the following steps:

[0007] - Determining a starting temperature at a starting time of a heating process,

[0008] - determining a first threshold temperature of the fuel cell system, wherein the first threshold temperature is higher than the starting temperature,

[0009] - Determining a maximum electrical load by means of which the fuel cell system is to be electrically loaded when the first threshold temperature for heating the fuel cell system is reached,

[0010] - Determining an electrical starting load by means of which the fuel cell system is to be electrically loaded at the start time in order to heat up the fuel cell system,

[0011] - Determination of a load increase for the heating process from the electrical starting load at the start time to the electrical maximum load when the first threshold temperature is reached,

[0012] - Carrying out the heating process to heat the fuel cell system using the determined load increase.

[0013] During tests using the technology described here, it was discovered that an excessively steep increase in power or a correspondingly strong increase in electrical load during the heating process can lead to increased wear and tear, even to the point of damage, in the fuel cell system and in particular in the fuel cells of the fuel cell system. Furthermore, it was discovered that it is not necessarily the maximum electrical load itself that causes the disproportionately high level of wear. Rather, it is the maximum electrical load at an unsuitable time, particularly too early in the heating process, when the temperature of the fuel cell system is still too low. The method therefore proposes determining a threshold temperature for the fuel cell system or components of the fuel cell system.and, if possible, only load the fuel cell system with the maximum electrical load when or after this threshold temperature has been reached. This means that only when the previously defined threshold temperature has been reached in the fuel cell system should the fuel cell system, and in particular at least one fuel cell of the fuel cell system, be operated with such inefficient performance that the resulting heat loss achieves the highest possible heating rate while simultaneously operating the fuel cell system with as little wear as possible.

[0014] The operation to generate the desired waste heat can be achieved by oxygen depletion in the fuel cell system and in particular by oxygen depletion of individual fuel cells of the fuel cell system. The maximum electrical load of the fuel cell system can be understood as an electrical load of the fuel cell system or at least one component of the fuel cell system. The maximum load can, but does not have to, be understood as the maximum possible electrical load of the fuel cell system. For example, the maximum electrical load can be understood as an electrical load that at least approximately corresponds to the maximum possible electrical load or that at least corresponds to the highest electrical load during the heating process.The maximum electrical load can also be understood as an electrical load that results in a maximum thermal load. The maximum thermal load can, but does not necessarily, refer to the maximum possible thermal load of the fuel cell system. For example, the maximum thermal load can be understood as a thermal load that at least approximately corresponds to the maximum possible thermal load or that at least corresponds to the highest thermal load during the heating process.

[0015] The load increase for the heating process can be determined using mathematical methods and / or models. For example, the load increase can be calculated using mathematical methods and / or models. The load increase can be determined using suitable calculation methods and / or estimation methods based on measured values ​​and / or calculated values.

[0016] Carrying out the heating process for heating the fuel cell system using the determined load increase can be understood as carrying out the heating process at least temporarily according to the predetermined load increase. In this way, after the start of the heating process, the fuel cell system is heated with the deliberately reduced electrical load, which is lower than the maximum electrical load and which is continuously increased until the maximum electrical load is reached at a time when the fuel cell system has reached the first threshold temperature.

[0017] The term "determining" in this case can include determining, setting, measuring, specifying, calculating, estimating and / or defining. For example, determining the starting temperature can be understood as meaning that the starting temperature is determined, set and / or specified based on a temperature measurement, a temperature estimate and / or a temperature forecast for a temperature at a start time of the heating process. Determining the first threshold temperature can accordingly be understood as meaning, for example, calculating and / or determining the first threshold temperature, for example based on a previously determined starting temperature. Determining the threshold temperature can further be understood as meaning reading out and / or receiving a predefined threshold temperature from a computer-readable memory.Determining the maximum electrical load can be understood, for example, as calculating and / or determining the maximum electrical load, for example based on the starting temperature, the threshold temperature and / or other factors and / or parameters. Determining the electrical starting load can be understood, for example, as calculating and / or determining the electrical starting load, for example based on the starting temperature, the threshold temperature, the maximum electrical load and / or other factors and / or parameters. Determining the electrical starting load can also be understood as reading out and / or receiving a predefined starting load from a computer-readable memory. The starting temperature can be understood as the temperature of the fuel cell system, the temperature of a part of the fuel cell system and / or the temperature in the environment of the fuel cell system.The electrical load of the fuel cell system can be understood as the electrical requirements and stresses to which the fuel cell system is exposed when electrical energy is generated by the fuel cell system or an electrochemical conversion takes place. The electrical load can therefore also be understood as a resulting thermal load on the fuel cell system and / or a thermal load on a component of the fuel cell system, for example at least one fuel cell of the fuel cell system. The thermal load can correspond to a thermal load and / or a thermal load point which results from the electrical load. The maximum electrical load can, for example, be set to a value orThis results in a thermal power value in a range between 10% and 70%, between 20% and 60%, or between 40% and 60% of the maximum power of the fuel cell system. This means that if the maximum power of the fuel cell system is 120 kW, for example, the maximum electrical load can be set or determined to a value that results in a maximum thermal load of 50 kWth.

[0018] The electrical load of a fuel cell system, and in particular of a fuel cell in the fuel cell system, can be expressed in different units and depends on various factors. Examples of the different units include the current, voltage, power, and operating time of the fuel cell system. The current is the amount of electricity that the fuel cell system must or should supply. The electrical load increases when the fuel cell system has to provide higher currents. The voltage can be understood as the electrical voltage supplied by the fuel cell system. The higher the required output voltage, the greater the electrical load. The electrical power is the product of the current and voltage. The electrical power indicates how much electrical work the fuel cell must perform per unit of time.The operating time can be understood as the duration for which the fuel cell system must operate continuously. A longer operating time may require higher energy generation and thus a higher electrical load. The electrical load of the fuel cell system can be understood as an electrical load point of the fuel cell system. The electrical load point can correspond to the conversion of fuel, for example, hydrogen. This means that the load point changes according to the release of thermal and electrical energy by the fuel cell system. The temperature of the fuel cell system, and in particular of the fuel cells, can be determined in various ways.For example, the temperature of the fuel cell system can be determined based on a measured temperature of a temperature control medium and / or a coolant of the fuel cell system and / or correspond to the temperature of the temperature control medium. The temperature of the temperature control medium can be measured, for example, at a temperature control medium outlet of a heat exchanger or at a location where the temperature control medium has its maximum temperature and / or a particularly high temperature. Alternatively or additionally, the temperature can be determined based on a component temperature of a component of the fuel cell system, which is measured directly or determined indirectly.

[0019] The fuel cell system is preferably configured for mobile applications such as vehicles, in particular for providing electrical energy for at least one drive unit, such as an electric motor, for propelling the vehicle. The fuel cell system can comprise at least one fuel cell or a fuel cell stack comprising multiple fuel cells. In its simplest form, the fuel cell is an electrochemical energy converter that converts fuel and oxidant into reaction products, generating electricity and heat in the process. The generated heat can be used to heat the fuel cell system. The anode and cathode of the at least one fuel cell can each be separated from one another by an ion-selective or ion-permeable separator, for example the membrane described above.To carry out the method, the fuel cell system can have a suitable determination and / or computing unit, for example, as part of at least one computer and / or at least one controller. The computer and / or the controller can have determination units for carrying out the respective method steps. In this case, a controller can be understood as a control unit.

[0020] The aforementioned process steps do not have to be performed in the described order. Rather, the respective process steps can be performed at least partially in reverse order and / or at least partially simultaneously.

[0021] According to a further embodiment of the present technology, it is possible for the first threshold temperature to be determined from a temperature range below freezing. It has been shown that the described method can be particularly advantageous for a so-called frost start, in which the fuel cell system is to be started at an ambient temperature below freezing. The first threshold temperature can therefore be selected and / or determined accordingly within a temperature range between 0 °C and -20 °C, between -5 °C and -20 °C, between -10 °C and -20 °C, and / or between -10 °C and -15 °C, for example with a value of approximately -10 °C.If the starting temperature, i.e. the temperature of the fuel cell system and / or the temperature in the environment of the fuel cell system, is -25 °C, for example, and the first threshold temperature is set to -10 °C, the load increase can be selected such that the fuel cell system is loaded with a specifically reduced but over time increasing electrical load until -10 °C is reached, until finally the maximum electrical load is reached when -10 °C is reached.

[0022] In a method according to the described technology, it is possible for the first threshold temperature to be determined depending on a membrane state of at least one fuel cell of the fuel cell system. For example, it is possible for the first threshold temperature to be determined depending on a water content of at least one fuel cell of the fuel cell system. This allows a particularly suitable first threshold temperature to be determined quickly and easily. The membrane state can be determined using suitable sensors and / or a suitable computing unit. The water content can also be determined using suitable sensors and / or a computing unit. The membrane state and / or the water content can be determined directly or indirectly.An indirect determination can be understood as meaning that, for example, a certain membrane state and / or a certain water content can be inferred based on a determined preconditioning of the fuel cell system, based on a determined operating state of the fuel cell system and / or based on determined operating values ​​of the fuel cell system. Furthermore, it is possible for the first threshold temperature to be determined and / or selected depending on material properties and / or a material design of the fuel cells, for example a membrane thickness of at least one fuel cell of the fuel cell system. The water content can be understood as a moisture state. The membrane state can be determined and / or selected based on a state factor such as the water content or based on various state factors.

[0023] Furthermore, with a method according to the technology described here, it is possible for the load increase to be determined as a linear load increase or as an at least predominantly and / or as linear a load increase as possible. In this way, the desired maximum load can be reached relatively accurately and reliably at the time of the first threshold temperature. The method for determining the appropriate load increase can also be carried out relatively simply, quickly, and with correspondingly low computing power. A linear load increase can be understood as a ramp-like load increase between the initial load and the maximum load.The fact that the load increase is determined as a linear load increase or as at least a predominantly linear load increase can be understood as meaning that the load increase is set and / or defined as a linear load increase or as at least a predominantly linear load increase. The load increase can, but does not have to, correspond to a linear load increase immediately after the start time. For example, the load increase can briefly correspond to an exponential load increase immediately after the start time and then transition to the determined and / or set linear load increase.

[0024] In the method described here, it may further be possible for a final temperature of the fuel cell system to be determined at the end of the heating process, and for the heating process to be subjected to the maximum electrical load after the first threshold temperature has been reached and until the second threshold temperature of the fuel cell system has been reached, wherein the first threshold temperature is determined from a temperature range below freezing and the second threshold temperature is determined from a temperature range above freezing. In other words, as soon as the fuel cell system has reached the first threshold temperature below freezing, the fuel cell system is subjected to the maximum electrical load until the second threshold temperature, which is above freezing, is reached.Tests carried out within the scope of the present invention have shown that the heating process can be carried out with relatively little wear and tear at the maximum load once the fuel cell system has reached a certain temperature. The method thus makes it possible to achieve a heating process that is as short as possible and yet relatively free of wear. Determining a temperature from a temperature range above or below freezing can be understood to mean that the respective threshold temperature is set to a value that is above or below freezing. The second threshold temperature can be determined from a temperature range between 0°C and 20°C, between 5°C and 15°C, for example with a value of 10°C, or set accordingly. Furthermore, with a method according to the present technology, it is possible for the load increase to be determined as a function of the determined starting temperature.By taking the starting temperature into account, the desired load increase can be calculated particularly quickly and easily. The load increase can also be determined or calculated based on the determined starting time, the determined starting load, the determined threshold temperature, the determined maximum electrical load, as well as other factors and / or parameters, and used accordingly. Determining the increase value can be understood as calculating and / or setting the increase value.

[0025] With the method described here, the load increase can be determined between the electrical starting load at the time of start-up and the maximum electrical load upon reaching the first threshold temperature, with an average increase value in a range between 3 A / s and 50 A / s. This value is below a previously common increase value used in conventional fuel cell systems to attempt to heat the fuel cell system as quickly as possible without regard to wear on the fuel cell system. With an increase value from the proposed range, rapid heat-up and yet relatively low wear can be achieved. The average increase value can also be in a range between 5 A / s and 4 A / s, for example in a range between 5 A / s and 30 A / s and / or between 15 A / s and 25 A / s, or can be set accordingly.Instead of the current intensity, a corresponding electrical power and / or a corresponding thermal power per unit of time can also be determined for the increase value.

[0026] A further aspect of the present invention relates to a fuel cell system with a controller configured to carry out a method according to one of the preceding claims. Thus, the fuel cell system provides the same advantages as have been described in detail with reference to the method. The fuel cell system and / or the controller may comprise a determination unit configured to

[0027] - Determining a starting temperature at a starting time of a heating process,

[0028] - determining a first threshold temperature of the fuel cell system, wherein the first threshold temperature is higher than the starting temperature,

[0029] - Determining a maximum electrical load by means of which the fuel cell system is to be electrically loaded when the first threshold temperature is reached in order to heat up the fuel cell system, - Determining a starting electrical load by means of which the fuel cell system is to be electrically loaded at the start time in order to heat up the fuel cell system,

[0030] - Determination of a load increase for the heating process from the electrical starting load at the start time to the electrical maximum load when the first threshold temperature is reached.

[0031] The fuel cell system and / or the controller may further comprise a heating unit for performing the heating process for heating the fuel cell system using the determined load increase.

[0032] The determination unit can further be configured to determine the first threshold temperature from a temperature range below freezing, to determine the load increase as a linear load increase or as an at least predominantly or as far as possible linear load increase, to determine the second threshold temperature of the fuel cell system at the end time of the heating process and / or to determine the load increase, in particular depending on the determined starting temperature.

[0033] The fuel cell system and / or the controller can be configured such that the heating process is subjected to the maximum electrical load after the first threshold temperature is reached and until the second threshold temperature of the fuel cell system is reached, wherein the first threshold temperature is determined from a temperature range below freezing and the second threshold temperature is determined from a temperature range above freezing. The fuel cell system and / or the controller can also be configured such that the load increase between the electrical start load at the start time and the maximum electrical load upon reaching the threshold temperature has an average increase value in a range between 3 A / s and 25 A / s or is set to a corresponding value.

[0034] A further aspect of the invention relates to a vehicle having a fuel cell system as described above and at least one electric motor for driving the vehicle, wherein the fuel cell system is configured to supply power to the at least one electric motor. The vehicle thus offers the same advantages as have been described in detail with reference to the fuel cell system. The vehicle can be understood to mean a motor vehicle such as a motor-driven two-wheeler, a car, and a truck. The vehicle can also be understood to mean a road vehicle, an aircraft, a watercraft, a rail vehicle, a spacecraft, and a robot. The vehicle can also be understood to mean a purely electric vehicle and a hybrid electric vehicle, which, in addition to the at least one electric motor, has an internal combustion engine for driving the vehicle.The vehicle can be understood as a so-called FCEV (Fuel Cell Electric Vehicle).

[0035] Furthermore, the technology disclosed here comprises a computer program product and a computer-readable, in particular non-volatile, storage medium on which the computer program product is stored. Thus, the computer program product and the computer-readable storage medium also provide the advantages described above. The computer program product can include instructions that, when the computer program product is executed by a computer, for example, a vehicle control unit, cause the computer to execute the proposed method in a fuel cell system and / or vehicle as described above. In a broader sense, the computer-readable storage medium can also be understood to mean a control unit or controller, for example, a vehicle control unit, with the computer program product installed therein.

[0036] The computer program product may be implemented as computer-readable instruction code in any suitable programming language and / or machine language, such as JAVA, C++, C#, and / or Python. The computer program product may be stored on a computer-readable storage medium, such as a data disk, a removable drive, volatile or non-volatile memory, or a built-in memory / processor. The instruction code may program a computer and other programmable devices, such as a controller, to perform the desired functions. Furthermore, the computer program product may be provided and / or be provided on a network, such as the Internet, from which it can be downloaded by a user on demand.The computer program product can be and / or be implemented by means of software as well as by means of one or more special electronic circuits, i.e. in hardware or in any hybrid form, i.e. by means of software components and hardware components.

[0037] Further measures emerge from the following description of various exemplary embodiments, which are schematically illustrated in the figures. All features and / or advantages arising from the claims, the description, or the figures, including procedural aspects, design details, and spatial arrangements, may be significant both individually and in various combinations.

[0038] They show schematically:

[0039] Fig. 1 is a diagram for explaining a method according to a first embodiment of the present technology,

[0040] Fig. 2 is a diagram for explaining a method according to a second embodiment of the present technology,

[0041] Fig. 3 shows a vehicle with a fuel cell system according to an embodiment of the present technology and

[0042] Fig. 4 shows a computer-readable storage medium having a computer program product stored thereon according to an embodiment of the present technology.

[0043] Elements with the same function and mode of operation are provided with the same reference symbols in the figures.

[0044] Fig. 1 shows a diagram for explaining a method according to a first embodiment of the present technology. The method is carried out for heating a fuel cell system 10 of a vehicle 100, shown in Fig. 3. Figure 1 shows a graph for the temperature profile 12 of the fuel cell system 10 during the heating process and during normal operation, a graph for the electrical load profile 13 of the fuel cell system 10 during the heating process and during normal operation, and a graph for the thermal load profile 14 of the fuel cell system 10 during the heating process and during normal operation. Furthermore, a dashed graph for a conventional thermal load profile 15 is shown, according to which the fuel cell system 10 would be heated unconditionally as quickly as possible. The heating process begins at time t1 and ends at time t3.At time t2, a first threshold temperature of the fuel cell system 10 is reached. At time t3, or at the end of the heating process, a second threshold temperature of the fuel cell system 10 is reached. The second threshold temperature corresponds to a temperature of the fuel cell system 10 at which the fuel cell system 10 is warm enough for normal operation and the heating process can therefore be or will be completed.

[0045] In the example shown in Fig. 1, the heating process begins at a starting temperature of -30 °C. The starting temperature is determined by a suitable temperature measurement in the fuel cell system 10. Alternatively, the starting temperature can also be determined by a temperature measurement outside the fuel cell system 10 and / or based on weather data. The first threshold temperature is then set to -10 °C. As soon as the fuel cell system 10 has reached a temperature of -10 °C, the fuel cell system 10 should be heated up with a maximum electrical load or with a corresponding maximum thermal load. In the example shown, the maximum electrical load should result in a maximum thermal load of approximately 50 kWth. An electrical starting load is then determined. The electrical starting load determined in the example and subsequently set accordingly should result in a thermal starting load of approximately25 kWth. A linear load increase for the heating process is then determined, from the electrical starting load at time t1 to the maximum electrical load upon reaching the first threshold temperature at time t2. The heating process for heating the fuel cell system 10 is then carried out using the determined load increase. This means that the rate of increase of the electrical load is adjusted depending on the starting temperature so that the maximum electrical load is reached upon reaching the first threshold temperature.

[0046] As can be seen from Fig. 1, the electrical load according to electrical load curve 13 and the thermal load according to thermal load curve 14 increase linearly between time t1 and time t2 until the fuel cell system 10 reaches the first threshold temperature of -10 °C at time t2 and the maximum electrical load is reached, resulting in a thermal load of just over 50 kWth. In the example shown, the load increase has an average rate of approximately 6 A / s.

[0047] After reaching the first threshold temperature at time t2 and until reaching the second threshold temperature at time t3, the fuel cell system 10 is uniformly loaded with the maximum electrical load and the resulting maximum thermal load, or operated accordingly. After time t2, the heating process is completed, and the fuel cell system 10 is operated in normal mode with the highest possible power efficiency.

[0048] Fig. 2 shows a diagram for explaining a method according to a second embodiment of the present technology. As shown in Fig. 2, the frost start in this example begins at -20 °C rather than -30 °C. This allows the heating process to be carried out more quickly. Therefore, a steeper ramp is selected for the load increase. In the example shown, the load increase has an average rate of approximately 16 A / s.

[0049] Fig. 3 shows a vehicle 100 in the form of a passenger car. The vehicle 100 has a fuel cell system 10 as described above, comprising a fuel cell stack 11 and two electric motors 30 for driving the vehicle 100. The fuel cell stack 11 has a plurality of fuel cells. The fuel cell system 10 is configured to supply power to the electric motors 30. The vehicle 100 also has a pressure vessel 60 for storing a fuel such as hydrogen, which can be converted into electrical energy in the fuel cell system 10 and in particular in the fuel cell stack 11. In addition, the vehicle 100 has a controller 20 configured to carry out a method as described above.

[0050] Fig. 4 shows a computer-readable and non-volatile storage medium 50 on which a computer program product 40 is stored. The storage medium 50 is configured in the form of a flash drive. The computer program product 40 includes instructions that, when executed by a computer, for example, a computer of the controller 20, cause the computer to perform a method for heating the fuel cell system 10 or parts thereof in the illustrated vehicle 100.

[0051] The technology disclosed here allows for further design principles in addition to the embodiments shown. This means that the technology should not be considered limited to the embodiments explained with reference to the figures.

[0052] Fuel cell system

[0053] Fuel cell stack

[0054] Temperature curve Electrical load curve Thermal load curve Thermal load curve (conventional)

[0055] Controller

[0056] electric motor

[0057] computer program product

[0058] storage medium

[0059] pressure vessel

[0060] vehicle

Claims

Patent claims 1. A method for heating a fuel cell system (10), comprising: - Determining a starting temperature at a starting time of a heating process, - determining a first threshold temperature of the fuel cell system (10), wherein the threshold temperature is higher than the starting temperature, - determining a maximum electrical load by means of which the fuel cell system (10) is to be electrically loaded when the threshold temperature for heating the fuel cell system (10) is reached, - determining an electrical starting load by means of which the fuel cell system (10) is to be electrically loaded at the start time for heating the fuel cell system (10), - Determination of a load increase for the heating process from the electrical starting load at the start time to the maximum electrical load when the threshold temperature is reached, - Carrying out the heating process for heating the fuel cell system (10) using the determined load increase.

2. The method according to claim 1, wherein the first threshold temperature is determined from a temperature range below freezing.

3. Method according to one of the preceding claims, wherein the first threshold temperature is determined as a function of a membrane state of at least one fuel cell of the fuel cell system (10).

4. Method according to one of the preceding claims, wherein the first threshold temperature is determined as a function of a water content of at least one fuel cell of the fuel cell system (10).

5. Method according to one of the preceding claims, wherein the load increase is determined as a linear load increase or as an at least predominantly linear load increase.

6. Method according to one of the preceding claims, wherein a second Threshold temperature of the fuel cell system (10) is determined at an end time of the heating process and the heating process is stopped after reaching the first Threshold temperature and until the second threshold temperature of the fuel cell system (10) is reached, the first threshold temperature is determined from a temperature range below the freezing point and the second threshold temperature is determined from a temperature range above the freezing point.

7. Method according to one of the preceding claims, wherein the load increase is determined as a function of the determined starting temperature.

8. Method according to one of the preceding claims, wherein the load increase between the electrical starting load at the start time and the maximum electrical load upon reaching the first threshold temperature is determined with an average increase value in a range between 3 A / s and 50 A / s.

9. A fuel cell system (10) comprising a controller (20) configured to perform a method according to any one of the preceding claims.

10. A vehicle (100) comprising a fuel cell system (10) according to claim 9 and at least one electric motor (30) for driving the vehicle (100), wherein the fuel cell system (10) is configured to supply power to the at least one electric motor (30).

11. A computer program product (40) comprising instructions which, when the computer program product (40) is executed by a computer, cause the computer to carry out the method according to one of claims 1 to 8 in a fuel cell system (10) according to claim 9.

12. A computer-readable storage medium (50) having stored thereon a computer program product (40) according to claim 11.

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