Method for operating a vehicle energy system

Abstract

The invention relates to a method for operating a fuel cell system (100) having a plurality of fuel cell stacks (102, 102') and at least one energy store (114) for storing electrical energy. The method has the steps of detecting an expected power deficiency, resulting from a difference between the power capacity of the vehicle energy system and the power requirement thereof, on the basis of data associated with a trajectory for operating the fuel cell system (100), charging the at least one energy store (114) before the power deficit sets in, and dividing the power of the fuel cell system (100) over the duration of the power deficit in such a way that the at least one energy store (114) is discharged at the end of the power deficit up to a specified value of the charge state.

Description

[0001] R.416590

[0002] - 1 -

[0003] Description

[0004] title

[0005] Procedures for operating a

[0006] State of the art

[0007] Hydrogen-based fuel cell systems are considered a mobility concept of the future, as they emit only water as exhaust gas and enable rapid refueling. Fuel cell systems require air and hydrogen for the chemical reaction. The only reaction product is water, which is released in varying proportions as a gas and a liquid. The water is produced at the catalyst layer on one side of the cathode and transported by a gas diffusion layer (GDL) towards the respective gas flow channels.

[0008] A key customer requirement for vehicles is the consistent delivery of specified performance. This also applies to fuel cell vehicles. A sudden and potentially noticeable reduction in maximum drive power (derating), triggered, for example, by high ambient temperatures or low ambient pressure, can be immediately perceived by the customer as a defect and can also pose a potential risk (e.g., during overtaking maneuvers). The term "derating" refers to the intentional reduction of the maximum power that a fuel cell system or fuel cell stack can deliver. This can be done for various reasons, such as extending the cell's lifespan, preventing overheating, or optimizing efficiency under specific operating conditions.In practice, this means that the fuel cell is not always operated at its full power range to avoid overloading and increase reliability. Derating may also be necessary (R.416590).

[0009] - 2 - may occur if the environmental conditions, such as temperature or humidity, are not optimal.

[0010] DE 10 2018 209 434 A1 describes a method for operating a fuel cell device assigned to a motor vehicle, using a plurality of sensors assigned to the components of the fuel cell device to monitor the operating status of the components and compliance with limit values ​​assigned to the respective components. The method includes the step of reducing the power demand of the motor vehicle when an upper limit value is exceeded or a lower limit value is not met. Based on data from a navigation system and / or a driver assistance system and / or an environmental monitoring system, a prediction is made about future power demands within a predetermined time window. The components monitored by the sensors are then operated in such a way as to avoid exceeding a limit value and / or to mitigate the necessary power reduction.The invention further relates to a motor vehicle for carrying out the method.

[0011] US Patent 11 724 706 B2 describes methods and systems for predicting a future increase in the power demand of a fuel cell based on route data from a fuel cell-powered vehicle and for reducing the fuel cell's operating temperature before the future increase in power demand. The technology can also supply the vehicle with additional energy from a battery while lowering the fuel cell's operating temperature.

[0012] Despite the advantages of established methods for operating vehicle energy systems with fuel cells, there is still room for improvement. For example, during long periods of driving up steep inclines, high power demand can meet lower cooling capacity. A lower vehicle speed on an incline, for instance, reduces the cooling capacity of the radiators. If high ambient temperatures are also present and / or heavy loads are present, or a trailer is being towed, the system can quickly reach its limits. This can lead to thermal derating. R.416590

[0013] - 3 -

[0014] As altitude increases, ambient air pressure decreases. In very high mountain passes, the high electrical power demand required for climb performance can then meet the low intake pressures of the electric air compressors. If the specified cathode pressure can no longer be provided (the compressor's technical limit), the permissible fuel cell power must be reduced. This can lead to pressure-related derating.

[0015] The vehicle described in DE 10 2018 209 434 A1 comprises only a single fuel cell stack. Furthermore, it describes both an earlier and therefore more uniform reduction in power output and the avoidance of limit violations through the prediction of future power requirements. The avoidance of derating is not addressed, only its uniformity.

[0016] US11 724 706 B2 describes a deliberate discharge of the battery before a mountain drive, which is counterproductive, however, as using the battery during the mountain drive is more advantageous.

[0017] Disclosure of the invention

[0018] Within the scope of the present invention, a method for operating a vehicle energy system, a vehicle energy system, a motor vehicle and a computer program product are therefore proposed, which largely avoid the disadvantages of known methods for operating a vehicle energy system, a vehicle energy system, a motor vehicle and a computer program product, and which in particular avoid or at least reduce derating.

[0019] A method according to the invention for operating a fuel cell system comprises the following steps, wherein individual or all steps can be repeated: R.416590

[0020] - 4 -

[0021] Identifying an expected performance deficit resulting from a difference between the performance capability and the performance requirement of the vehicle energy system based on data assigned to a trajectory for operating the fuel cell system,

[0022] Charging the at least one energy storage device before a power deficit occurs, and

[0023] Dividing the power output of the fuel cell system over the duration of the power deficit in such a way that the at least one energy storage device is discharged to a predetermined state of charge at the end of the power deficit.

[0024] The prediction, based on data assigned to a fuel cell system's operating trajectory, such as performance and environmental data, identifies a future performance deficit that would lead to derating, for example, due to high predicted ambient temperatures, low predicted driving speeds, low predicted ambient pressures, high payload, and / or trailer operation. Thus, data is used to estimate future performance requirements, such as peak load during uphill driving, and environmental conditions, such as temperature, pressure, and humidity. Based on this prediction, the energy storage device, such as a battery, is pre-charged over a period of time, even an extended period like 5 to 10 minutes, by shifting the operating points of the fuel cell stack to higher performance points.This puts the vehicle energy system into a state of optimized conditioning at the start of the increased power demand event or power deficit. Optimized in this context means maximum battery charge. During the increased power demand event or power deficit, the power of the fuel cell stacks is evenly distributed, with the amount calculated such that the energy storage is exactly discharged at the end of the predicted high-load event. A safety factor can be included to account for uncertainties in the prediction and to protect the battery. Thus, the theoretical performance of the system can be fully utilized, and the design can be less conservative. This eliminates the need for worst-case conditioning of fuel cell systems and batteries according to R.416590.

[0025] - 5 -

[0026] The start of a high-load event, such as an uphill climb, must meet certain requirements; however, the presented operating strategy can guarantee advantageous conditioning. This can potentially lead to savings in the design of the cooling system and the battery. The operating strategy can either comprise sequential phases or implement their objectives in parallel.

[0027] The data can be provided by at least one information source, either within and / or outside the fuel cell system. The data can include at least one piece of information selected from the following: map data, GPS data, vehicle-to-vehicle communication, vehicle-to-infrastructure communication, past driver behavior, and weather report information. Such data allows for a high degree of reliability in predicting a performance deficit.

[0028] The process can further include lowering the temperature of the fuel cell system before a power deficit occurs. This puts the fuel cell system into a state of optimal conditioning at the moment the power deficit begins, such as when climbing or driving uphill. Optimal in this context means maximum battery charge and minimum temperature of the fuel cell system. Predictive cooling allows, for example, the targeted use of airflow during driving uphill to reduce the use of the fan, thus increasing efficiency and performance.

[0029] The temperature of the fuel cell system can be lowered by increasing the amount of heat dissipated to the environment, maximizing the cooling capacity of the fuel cell system's cooling system, and / or reducing the amount of heat generated by the fuel cell system. Increasing the amount of heat dissipated to the environment, maximizing the cooling capacity of the fuel cell system's cooling system, and / or reducing the amount of heat generated by the fuel cell system can be achieved by operating all fuel cell stacks at their efficiency-optimized operating points, or by individually operating a predetermined proportion of the fuel cell stacks at R.416590.

[0030] - 6 - their efficiency-optimal operating points and deactivation of the remaining fuel cell stacks, by deactivating all fuel cell stacks, or by increasing the speed of a cooling fan and / or radiator fan in a cooling system of the fuel cell system. To maximize cooling capacity, thermal couplings between the (sub)systems can be utilized. If such a multi-system exhibits thermal coupling between the cooling circuits or even shares a common cooling circuit, all heat sinks can be used to their best advantage to dissipate initially inhomogeneously generated and / or existing thermal energy. In addition to the cooling circuits for the fuel cell stacks, other cooling circuits of the BoP systems (BoP = Balance of Plant), e.g., air system cooling circuits such as intercoolers, can also be preconditioned.Operating all fuel cell stacks at their efficiency-optimized points generates minimal waste heat while simultaneously providing electrical power. This also applies to operating only individual fuel cell stacks at their efficiency-optimized points without operating the other fuel cell stacks. Increasing the cooling fan speed to achieve a lower temperature level can be implemented if a time-compensated approach is necessary. The thermal coupling between cooling circuits can be fully activated and utilized here, especially in cases of asymmetrical power distribution, such as when operating individual fuel cell stacks at their efficiency-optimized points without operating the other fuel cell stacks. This allows for the use of radiators in cooling circuits without heat input to dissipate heat.

[0031] Lowering the temperature of the fuel cell system can occur simultaneously with or after charging the at least one energy storage device. This allows the timing of the temperature reduction to be determined as needed.

[0032] The temperature of the fuel cell system can be reduced to a temperature below its optimal operating point. This ensures that even during prolonged or intense periods of increased power demand, the temperature does not exceed an upper threshold. R.416590

[0033] - 7 -

[0034] If it is determined that a predetermined temperature threshold would be exceeded during the power deficit despite lowering the temperature of the fuel cell system, the power output of the fuel cell system can be reduced.

[0035] The fuel cell system's power output can be reduced uniformly or in stages if it is determined that, despite lowering the fuel cell system's temperature, a predetermined temperature threshold would be exceeded during the power deficit. In principle, temperatures during the power deficit may rise to the limit. If it is predicted that the temperature limit would be exceeded despite these precautions, the power delivered to the electric motors can be reduced just enough to avoid exceeding the temperature and battery limits. This derating could be achieved either through a uniform reduction over the entire uphill climb or through gradual ramps, so that the driver experiences minimal disruption and only notices slight derating gradients.

[0036] The predetermined state of charge value can be set so that it is no greater than 20%, preferably no greater than 15%, and even more preferably no greater than 10%. This provides a sufficient safety factor to account for uncertainties in the prediction and to protect the battery.

[0037] The procedure can be carried out analogously in the case of predicted pressure-related derating. Since the humidity management of the fuel cell membrane involves a relationship between temperature and pressure level to prevent drying out or flooding, the system can be operated at lower pressure levels by reducing the fuel cell temperatures. Thus, preconditioning through predictive cooling and precharging of the battery can also prevent derating due to pressure limitation. However, lower pressure levels can also lead to problematic, depleted conditions by reducing the oxygen partial pressure. A pre-charged battery, however, allows the current supplied by the fuel cell systems during uphill travel to be reduced, thereby keeping the partial pressure limit within limits. Due to the additional battery support, the drive power also needs to be derated significantly later in this context. R.416590

[0038] - 8 -

[0039] Furthermore, a vehicle energy system is proposed comprising a fuel cell system with at least one fuel cell stack, at least one energy storage device, and at least one control unit. The control unit is configured to perform a method according to one of the embodiments described above or below.

[0040] Furthermore, a motor vehicle is proposed that incorporates such a vehicle energy system.

[0041] Finally, a computer program product is proposed with program code means which, when the computer program product is executed on a computer, configure the computer to perform a method according to one of the embodiments described above or below.

[0042] The proposed computer program product could be, for example, a file to be downloaded from a server or a data carrier, such as a CD-ROM or a USB stick.

[0043] The advantages which have been described in detail with regard to the operating method for operating a fuel cell system according to the invention apply equally to the vehicle according to the invention and to the computer program product according to the invention.

[0044] Within the scope of the present invention, a vehicle energy system can be understood to be a system comprising at least one fuel cell system with at least one fuel cell stack and an energy storage device. The vehicle energy system can also include a motor.

[0045] Within the scope of the present invention, a fuel cell system can be understood to be a system comprising at least one fuel cell stack, at least one anode path comprising an anode, an anode gas supply line and an anode gas return line, at least one cathode path comprising a cathode, a cathode gas supply line and a cathode gas discharge line, and at least one thermal system comprising a radiator, R.416590

[0046] - 9 - comprises a sensor unit for acquiring data to determine a power deficit of the fuel cell system, a processing unit for determining a power deficit of the fuel cell system, and a control unit. The control unit is designed to regulate the operation of the fuel cell system or the fuel cell stack. A fuel cell stack comprises at least two fuel cells, preferably at least 10 fuel cells, and more preferably at least 100 fuel cells. A fuel cell consists of electrodes between which an electrolyte (ion conductor) is located. The electrodes are the aforementioned anode and cathode. A liquid, for example alkalis or acids, or molten alkali carbonate can be used as the electrolyte. In high-temperature fuel cells, a solid is used as the electrolyte, such as ion-conducting ceramic, which then forms a solid electrolyte. Membranes are also used.They are semipermeable membranes that are permeable to only one type of ion, e.g., protons. A membrane can also separate two different liquid electrolytes. The energy is supplied by a reaction of oxygen with the fuel. This is often hydrogen, but organic compounds such as methane or methanol are also used. Both reactants are continuously supplied via the electrodes. The fuel cell system can also include a housing in which at least one fuel cell stack is contained. The fuel cell system can further include a control unit for activating a device for the targeted adjustment of the water loading of a membrane of the fuel cell system, as well as a device for the targeted adjustment of the water loading of a membrane of the fuel cell system.

[0047] The fuel cell system has several subsystems, such as the anode subsystem, which includes the anode path and one or more hydrogen tanks; the cathode subsystem, which includes the cathode path, an air compressor, and a humidifier; the electrical subsystem, which includes electrical components such as electrical connections; and the thermal system, which includes the heating system, cooling system, coolant, coolant pump, and fan or blower. R.416590

[0048] - 10 -

[0049] Within the scope of the present invention, an increased power demand event can be understood as an event in which the fuel cell system must deliver increased electrical power. This increase in electrical power can be a rise compared to a predetermined normal operating level. Such an event can occur due to high predicted ambient temperatures, such as driving in a high-temperature region, and / or low predicted driving speeds, such as driving uphill or in a traffic jam, and / or low predicted ambient pressures, such as driving in a high-altitude region, and / or a heavy payload and / or trailer operation. A power deficit in the energy system must be detected. Data is required for this purpose.Firstly, sensor units of the fuel cell system can determine its operating state, which, together with environmental conditions, determines its performance. To determine the latter, sensor units on the vehicle and information exchange with an external information source, such as a cloud, can be used. The power demand on the fuel cell system can be predicted from traffic data, route information, ambient temperature / pressure, etc. As soon as the predicted power demand exceeds the predicted performance capacity, a power deficit occurs. A power deficit can therefore be understood as a difference between the predicted performance capacity and the power demand. This is the triggering event for the increased power demand function.

[0050] Brief description of the drawings

[0051] Further optional details and features of the invention will become apparent from the following description of preferred embodiments, which are shown schematically in the figures.

[0052] They show:

[0053] Figure 1 shows a schematic representation of a vehicle energy system according to an embodiment of the present invention in a vehicle, and R.416590

[0054] - 11 -

[0055] Figure 2 shows a schematic representation of a possible embodiment of a method for operating a vehicle energy system according to an embodiment of the present invention.

[0056] Embodiments of the invention

[0057] Figure 1 shows a schematic representation of a vehicle energy system according to an embodiment of the present invention. The vehicle energy system comprises a fuel cell system 100. The fuel cell system 100 is arranged by way of example in a vehicle 200. The vehicle 200 can be a passenger car, although other types of vehicles are conceivable in principle.

[0058] The fuel cell system 100 comprises several fuel cell stacks 102, 102'. Each fuel cell stack 102, 102' includes several fuel cells, which are not shown in detail for clarity. Each fuel cell stack 102, 102' is connected to further subsystems. Specifically, each fuel cell stack 102, 102' is connected to an electrical system 104, 104', an air system 106, 106', a hydrogen system 108, 108', and a thermal system 110, 110'. Each fuel cell stack 102, 102' is connected via the electrical subsystems to at least one electric motor 112 of the vehicle and an energy storage device 114, such as a battery.

[0059] The fuel cell system 100 further comprises a sensor unit (not shown) for acquiring operating parameters of the fuel cell stacks 102, 102'. The sensor unit may also be configured to acquire data for determining a power deficit of the fuel cell system 100. The fuel cell system may include a processing unit (not shown) for determining a load change of the fuel cell system 100. The fuel cell system 100 further comprises a control unit 116. The control unit 116 is configured for controlling the operation of the fuel cell system 100 or the fuel cell stacks 102, 102'. R.416590

[0060] - 12 -

[0061] Figure 2 shows a schematic representation of a possible embodiment of a method for operating a vehicle energy system according to an embodiment of the present invention.

[0062] In Figure 2, the temperature T of the fuel cell stacks 102 and 102' is plotted on the Y-axis in the upper part, and time t is plotted on the X-axis. Curve 118 shows the temperature profile over time of the first fuel cell stack 102. Curve 120 shows the temperature profile over time of the second fuel cell stack 102'.

[0063] In the central part of Figure 2, the state of charge (SOC) of the energy storage device 114 is plotted on the Y-axis and time t on the X-axis. Curve 122 shows the time course of the state of charge (SOC).

[0064] In the lower part of Figure 2, the electrical power P is plotted on the Y-axis and the time t on the X-axis. Curve 124 shows the time course of the electrical power of the first fuel cell stack 102. Curve 126 shows the time course of the electrical power of the second fuel cell stack 102'. Curve 128 shows the time course of the electrical power of the energy storage device 114. Curve 130 shows the time course of the electrical power of the motor 112.

[0065] At a given time tO, the procedure includes detecting or predicting an expected performance deficit resulting from a difference between the vehicle energy system's capacity and power demand, based on data assigned to a trajectory for operating the fuel cell system. A prediction identifies a high power demand that would lead to derating, for example, due to high predicted ambient temperatures and / or low predicted driving speeds and / or low predicted ambient pressures and / or high payload and / or trailer operation. A low driving speed initially means a lower power demand. The low driving speed initially only results in lower passive cooling capacity at the radiator. The effect is therefore a potential reduction in performance. As with the ambient R.416590

[0066] - 13 - Temperature and lower ambient pressures do not directly affect the power requirement; rather, these are boundary conditions that can reduce performance. The data is provided by at least one information source within and / or outside the fuel cell system. This data is used to estimate future power requirements, such as peak load during ascent / hill climbing, and environmental conditions, such as temperature, pressure, and humidity. The data can include map data, GPS data, vehicle-to-vehicle communication, vehicle-to-infrastructure communication, past driver behavior, and weather report information.

[0067] If such an increased power demand event or power deficit is detected or predicted, the procedure comprises, in a first phase, charging the at least one energy storage device 114 before the power deficit occurs. The energy storage device 114 is pre-charged over a longer period, such as 5 to 10 minutes, by shifting the operating points of the fuel cell stacks 102, 102' to higher power points. Optionally, the system temperatures are simultaneously lowered by increasing the amount of heat dissipated to the environment, even below an optimal operating point of the fuel cell system 100.Accordingly, in the first phase 132, the temperature of the fuel cell stacks 118, 120 shows a slight decrease over time, the state of charge 122 shows a steady increase over time, the electrical power of the first and second fuel cell stacks 124, 126 shows a constant, slightly increased value over time, the electrical power of the energy storage device 128 shows a value of approximately 0 W over time, and the electrical power of the motor 130 shows a constantly low value over time.

[0068] In a second phase 134 following the first phase 132, the method comprises lowering the temperature of the fuel cell system before the onset of a power deficit. Such pre-cooling of the fuel cell system 100, and in particular the fuel cell stacks 102, 102', can be achieved by increasing the amount of heat dissipated to the environment, maximizing the cooling capacity of the fuel cell system's cooling system, and / or reducing the amount of heat generated by the fuel cell system by operating all R.416590

[0069] - 14 -

[0070] Fuel cell stacks at their efficiency-optimal operating points, by individually operating a predetermined proportion of the fuel cell stacks at their efficiency-optimal operating points and not operating the remaining fuel cell stacks, by not operating all fuel cell stacks, or by increasing a cooling fan and / or cooling fan speed of a cooling system of the fuel cell system.

[0071] To maximize cooling capacity, thermal couplings between the subsystems can be utilized. If the fuel cell system 100 has thermal coupling between the cooling circuits or even shares a common cooling circuit, all heat sinks can be used optimally to dissipate initially inhomogeneous and / or existing thermal energy. In addition to the cooling circuits for the fuel cell stacks 102 and 102', further cooling circuits of the BoP systems (BoP = Balance of Plant), such as air system cooling circuits like intercoolers, can also be preconditioned.

[0072] Accordingly, in the second phase 134, the temperature of the fuel cell stacks 118, 120 shows a significant decrease over time, the state of charge 122 shows an approximately constant high value over time, the electrical power of the first and second fuel cell stacks 124, 126 shows a constant lower value than in the first phase 132 over time, the electrical power of the energy storage 128 shows a constant low value over time, and the electrical power of the motor 130 shows a constant low value over time.

[0073] The procedure for predicted pressure-induced derating is analogous. Since the membrane's humidity management system uses a relationship between temperature and pressure level to prevent drying out or flooding, the system can be operated at lower pressure levels by reducing the temperatures of the fuel cell stacks 102, 102'. Thus, preconditioning through predictive cooling and precharging of the battery can also prevent derating due to pressure limitation. However, lower pressure levels can also lead to problematic, depleting conditions by reducing the oxygen partial pressure. A pre-charged battery, however, can mitigate the effects of R.416590.

[0074] - 15 - The electricity supplied to the fuel cell systems during uphill travel is reduced, thus ensuring compliance with the partial pressure limit. Due to the additional battery support, the drive power must also be derated significantly later in this context.

[0075] In a third phase 136 following the second phase 134, the increased power demand event or power deficit occurs. The method involves distributing the power of the fuel cell system over the duration of the power deficit such that the at least one energy storage device 114 is discharged to a predetermined state of charge at the end of the power deficit. The predetermined state of charge is not greater than 20%, preferably not greater than 15%, and even more preferably not greater than 10%. The power of the fuel cell stacks 102, 102' is, for example, distributed equally. Its value can be calculated in such a way that the battery is exactly discharged at the end of the predicted high-load event. A safety factor can be provided to account for uncertainties in the prediction and to protect the battery.

[0076] The cooling capacity remains at its maximum, as in the second phase 134. Temperatures are allowed to rise to their limit. Accordingly, in the third phase 136, the temperature profile of the fuel cell stacks 118, 120 shows an increase over time, the state of charge profile 122 shows a gradual decrease over time, the electrical power profile of the first and second fuel cell stacks 124, 126 shows a constant high value over time, the electrical power profile of the energy storage system 128 shows a constant high value over time, and the electrical power profile of the motor 130 shows a constant high value over time.

[0077] If it is predicted that the temperature limit will be exceeded despite these precautions, the power delivered to the electric motors can be reduced just enough to avoid exceeding the temperature and battery limits. This derating could be achieved either through a uniform reduction throughout the entire uphill climb or by using slow ramps, so that the driver experiences minimal disruption and only feels slight derating gradients. R.416590

[0078] - 16 -

[0079] It is explicitly emphasized that the described procedure is merely an example of a three-phase division and only one example of how the procedure can be implemented. Changes to the sequence, combining, or subdividing the phases or procedural steps are also conceivable.

Claims

R.416590 - 1 7 - Claims 1. Method for operating a vehicle energy system with a fuel cell system (100) having multiple fuel cell stacks (102, 102') and with at least one energy storage device (114) for storing electrical energy, comprising the steps: Identifying an expected performance deficit resulting from a difference between the performance capability and the performance requirement of the vehicle energy system based on data assigned to a trajectory for operating the fuel cell system (100), Charging the at least one energy storage device (114) before the onset of a power deficit, and Dividing the power of the fuel cell system (100) over a duration of the power deficit such that the at least one energy storage device (114) is discharged to a predetermined value of a state of charge at the end of the power deficit.

2. Method according to the preceding claim, wherein the data are provided by at least one information source inside and / or outside the fuel cell system (100).

3. Method according to any of the preceding claims, wherein the data comprise at least one piece of information selected from the group consisting of: map data, GPS data, vehicle-to-vehicle communication, vehicle-to-infrastructure communication, past driver behavior, and weather report information.

4. Method according to one of the preceding claims, further comprising lowering the temperature of the fuel cell system (100) before the power deficit occurs. R.416590 - 18 - 5. Method according to the preceding claim, wherein the temperature reduction of the fuel cell system (100) is achieved by increasing the amount of heat dissipated to the environment, maximizing the cooling capacity of a cooling system of the fuel cell system (100) and / or reducing the amount of heat generated by the fuel cell system (100).

6. Method according to the preceding claim, wherein increasing the amount of heat dissipated to the environment, maximizing the cooling capacity of the cooling system of the fuel cell system (100) and / or reducing the amount of heat generated by the fuel cell system (100) is achieved by operating all fuel cell stacks at their efficiency-optimal operating points, by individually operating a predetermined proportion of the fuel cell stacks at their efficiency-optimal operating points and not operating the remaining fuel cell stacks, by not operating all fuel cell stacks, or by increasing a cooling fan and / or cooling fan speed of a cooling system of the fuel cell system (100).

7. Method according to one of the three preceding claims, wherein the lowering of a temperature of the fuel cell system (100) takes place simultaneously with or after the charging of the at least one energy storage device (114).

8. Method according to one of the four preceding claims, wherein the temperature of the fuel cell system (100) is reduced to a temperature below an optimal operating point of the fuel cell system (100).

9. Method according to one of the five preceding claims, wherein the power output of the fuel cell system (100) is reduced if it is determined that, despite lowering the temperature of the fuel cell system (100), a predetermined temperature threshold would be exceeded during the power deficit.

10. Method according to the preceding claim, wherein the power of the fuel cell system (100) is reduced uniformly or in stages, R.416590 - 19 - if it is determined that despite lowering the temperature of the fuel cell system (100), a predetermined temperature threshold would be exceeded during the power deficit.

11. Method according to one of the preceding claims, wherein the predetermined value of the state of charge of the energy storage device is not greater than 20%, preferably not greater than 15% and more preferably not greater than 10%.

12. Vehicle energy system comprising a fuel cell system (100) with multiple fuel cell stacks (102, 102') and with at least one energy storage device (114) and further comprising at least one control unit (116), wherein the control unit (116) is configured to perform a method according to one of the preceding claims.

13. Vehicle (200), comprising a vehicle energy system according to the preceding claim.

14. Computer program product comprising program code means which, when the computer program product is executed on a computer, configure the computer to perform a method according to any one of claims 1 to 11.

Images