Method for operating an electric drive system, drive system, vehicle, computer program product and storage medium

Abstract

The technology disclosed here relates to a method for operating an electric drive system (10) of a vehicle (100), wherein the electric drive system comprises at least one buffer battery (11) and a fuel cell system (12) for electrically charging the buffer battery (11), comprising the steps of: providing a target operating mode for operating the fuel cell system (12) with a predefined constant efficiency for generating a predefined constant output power by the fuel cell system (12), determining a current charge state of the buffer battery (11), and operating the fuel cell system (12) in the target operating mode depending on the determined current charge state of the buffer battery (11). The technology further relates to an electric drive system (10), a vehicle (100), a computer program product (15), and a computer-readable storage medium (16).

Description

The technology disclosed herein relates to a method of operating an electric propulsion system of a vehicle, and to a propulsion system and a vehicle for carrying out the method. The technology disclosed here further relates to a computer program product for carrying out the method and to a computer-readable storage medium on which such a computer program product is stored.Fuel cell systems for mobile applications are known in the prior art. In a vehicle, the fuel cell system is configured in particular for providing energy to at least one drive machine for the purpose of moving the vehicle. Fuel cell systems of the generic type have a fuel cell stack. The fuel cell stack generally has a plurality of fuel cells, each of which has two electrodes and a membrane arrangement between the two electrodes. In the fuel cell stack, hydrogen may react with oxygen in reverse electrolysis, thereby generating current. The hydrogen may be provided to the fuel cell stack from one or more high pressure tanks in the vehicle. The oxygen is generally taken from the ambient air.It is also known to use a so-called buffer battery in fuel cell vehicles. The current generated by the fuel cells can take two ways, depending on the current or power requirement in the specific driving situation. The current may flow directly to electrically drive the vehicle, thereby driving the vehicle. Alternatively, the current may charge the buffer battery, which serves as a buffer until the current or the electrical energy is required for the electrical drive. The backup battery in conventional systems is significantly smaller and lighter than the battery of a full electric vehicle that does not have fuel cells.Fuel cell systems of the generic type have different efficiencies depending on their operating state. As a rule, the efficiency of the fuel cell system decreases as the output power increases. Furthermore, it is known that fuel cell systems and in particular the fuel cells have increased ageing in the case of rapid and dynamic power changes.It is an object of the present invention to provide improved methods and devices for operating an electric drive system of a fuel cell vehicle.The above object is achieved by the claims. In particular, the above object is achieved by the method according to claim 1 and the electric drive system, the vehicle, the computer program product and the computer-readable storage medium according to the dependent claims. Further advantages of the disclosed technology are evident from the dependent claims, the description and the figures. Features described in connection with the method also apply in connection with the electric drive system, the fuel cell system, the vehicle, the computer program product, the storage medium and vice versa, so that with regard to the disclosure, mutual reference is and / or can always be made to the individual aspects.According to a first aspect of the present technology, a method for operating an electric drive system of a vehicle is proposed. The electric drive system includes at least a backup battery and a fuel cell system for electrically charging the backup battery. The method comprises the following steps:providing a setpoint operating mode for operating the fuel cell system with a predefined constant efficiency for generating a predefined constant output power by the fuel cell system,determining a current state of charge of the buffer battery; andoperating the fuel cell system to the desired operating mode as a function of the ascertained current state of charge of the buffer battery.The proposed method is based firstly on the finding that fuel cell systems of the generic type have different efficiencies at different load points. In a high load point where a high output is generated, the efficiency of the fuel cell system is generally lower than in a low load point where a low output is generated. In order to achieve the highest possible overall efficiency, high load points of the fuel cell system should therefore be avoided as far as possible. According to the method, therefore, firstly the desired operating mode is provided, in which the fuel cell system is operated with the predefined constant and as high an efficiency as possible, in order to generate a correspondingly constant output power in this case, which is relatively low compared to a maximum possible output power. The aim is now to operate the fuel cell system to the desired operating mode as frequently and / or for a long time as possible during a journey of the vehicle. In the context of the present technology, it has now been recognized, inter alia, that this is possible by means of a sufficiently large buffer battery, monitoring the state of charge of the buffer battery and a targeted consideration of the setpoint operating mode or an efficiency-based performance of the fuel cell system. That is, if it is detected, for example, that the state of charge of the buffer battery is sufficiently high, the fuel cell system is operated to the setpoint operating mode at which the predefined high efficiency is achieved. Short load peaks, for example during an overtaking procedure, can be intercepted by the sufficiently charged buffer battery. In this way, the fuel cell system can be operated not only particularly efficiently, but also with particularly low component wear.If it is detected that the state of charge of the buffer battery is relatively low and / or lower than a predefined lower reference value, the fuel cell system can be operated to or change over to a power-increasing mode of operation in which, although the efficiency decreases, a higher output power for charging the buffer battery can be generated. The fuel cell system can therefore be operated for the desired operating mode or for the power increase operating mode, depending on the ascertained current state of charge of the buffer battery. The power-increasing mode of operation can have different modes of operation. Depending on how low the state of charge of the buffer battery is and depending on how high the current power demand is in the vehicle, the power increasing mode of operation for generating output powers of different levels can be carried out. The different power boost operations result in different efficiencies, which is why the power boost operation is preferably carried out with a sufficiently high and nevertheless as low an output power as possible. The fuel cell system can accordingly be operated depending on the state of charge of the buffer battery and / or depending on a currently determined power requirement for the power increase operating mode. The transition between the desired operating mode in the power-increasing operating mode can be carried out phlegmatically and / or in attenuated fashion. That is, for example, a desired reduction in efficiency and / or increase in output power may be carried out with a predefined ramp, a damping factor and / or a corresponding gradient.According to the method, depending on the state of charge of the buffer battery and possibly depending on a power requirement in the vehicle, the desired operating mode with the highest possible efficiency, an alternative operating mode with a different efficiency and / or a switch-off process for a standby operation can be carried out. The aim here is to operate the fuel cell system as frequently as possible and / or for a long time to the desired operating mode. In the proposed manner, the buffer memory should be available not only in the case of particularly high power requirements, such as, for example, in the case of an overtaking procedure, but should be used as frequently and as long as possible at least during the desired operating mode. As buffer memory, therefore, a buffer memory with a sufficiently high capacity, for example above 5 kWh or above 8 kWh, is preferably used.The operation of the fuel cell system to the desired operating mode can be carried out by means of a characteristic diagram which, via the state of charge and possibly also via the power demand, pilot controls the desired and as constant as possible output power of the fuel cell system. The output power may result from a correspondingly adjusted efficiency. Within the framework of the proposed technology, it is possible to set the desired and as constant as possible efficiency for the desired operating mode, resulting in the output power. Furthermore, it is possible to set the desired and as constant as possible output power, which is achieved with as high an efficiency as possible and as constant as possible. In addition, it is possible, for example using a suitable computing method, to set a compromise, suitable for the respective individual case, of the highest possible efficiency at the highest possible output power. Specific efficiency values and output power values may differ from one another depending on the application.Providing the setpoint operating mode can be understood to mean ascertaining and / or calculating the setpoint operating mode on the basis of various ascertained measured values and / or operating parameters of the fuel cell system, of the buffer battery and / or of the vehicle. Furthermore, providing the desired operating mode can be understood to mean reading a predefined and / or pre-definable desired operating mode from a computer-readable memory.The current state of charge of the battery can be understood to mean a current SOC (State of Charge) and / or a current RCI (Relative Charge Indicator). The determination of the current state of charge can be understood to mean a calculation of the current state of charge on the basis of measured values and / or on the basis of operating parameters.The fuel cell system is preferably configured for mobile applications such as vehicles, in particular for providing energy to at least one drive machine such as an electric motor for moving the vehicle. The fuel cell system may include at least one fuel cell or a fuel cell stack including a plurality of fuel cells. In its simplest form, the fuel cell is an electrochemical energy converter which converts fuel and oxidant into reaction products and generates electricity and heat in the process. The anode and cathode of the respective fuel cell can be separated from one another by an ion-selective or ion-permeable separator. The efficiency of the fuel cell system can also be understood to mean an efficiency of the at least one fuel cell or an efficiency of the fuel cell stack. Depending on the efficiency, it can be of different levels. The highest possible efficiency for the at least one fuel cell and / or for the fuel cell stack is, for example, generally higher than the highest possible efficiency for the entire fuel cell system.According to a further embodiment of the present technology, it is possible for the setpoint operating mode to be provided for operating the fuel cell system with a maximum efficiency or with the highest possible efficiency described above. As already described, the method is intended to ensure that the vehicle is operated for as long as possible and / or frequently in the desired operating mode. In this way, the electric drive system can be operated particularly efficiently and in a component-saving manner. The maximum efficiency or the predefined maximum efficiency can be understood to mean a highest possible efficiency and / or an approximately highest possible efficiency with which the fuel cell system can still be or is to be operated during travel. If the fuel cell system has, for example, a maximum efficiency of 63%, the fuel cell system is, according to the present understanding, operated with a constant maximum efficiency even if the efficiency is at times slightly below 63%. The maximum efficiency of the fuel cell system may have a value in a range between 60% and 70%, for example. As already mentioned above, however, it should be taken into account that efficiency details can turn out to be different for the same system depending on the way in which they are viewed with respect to the entire fuel cell system or, for example, only with respect to the fuel cell stack.In the technology proposed here, it is also possible for the setpoint operating mode to be provided for operating the fuel cell system with the predefined constant efficiency for generating a constant output power which is in a range between 5% and 20% of the maximum possible output power of the fuel cell system. This means that during the desired operating mode, a relatively low output power is intentionally generated as constantly as possible. As a result, the fuel cell system can be operated not only in a particularly efficient manner, but also in a particularly low-wear manner. A fuel cell system with a maximum possible output power of 150 kW can be operated during the desired operating mode, for example, in such a way that only 10 kW output power is generated as constantly as possible. By means of a buffer battery selected to be sufficiently large, the desired operating mode can be selected relatively frequently and / or long without there being the risk of the buffer battery being discharged excessively. In particular at medium drive loads and at a sufficiently high state of charge, the fuel cell system can be operated in this way in a particularly efficient manner and as close as possible to the optimum efficiency. Only when the current state of charge falls below a predefined or predeterminable value is the output power increased or can a change be made to a power-increasing operating mode.Furthermore, in the method described here, it is possible for the fuel cell system to be operated to the desired operating mode if the state of charge of the buffer battery is in a range between 50% and 100%. This means that a state of charge range can be defined in which the fuel cell system is operated as far as possible at optimum efficiency. In this way, the buffer battery can be prevented from dropping to an undesirably low state of charge, which could result in supply bottleneck and / or increased wear of the buffer battery. By defining a state of charge range, the fuel cell system can nevertheless be operated relatively long and / or frequently particularly efficiently. According to one embodiment, the range of the state of charge can be selected to be even narrower, for example between 60% and 98% or between 70% and 95%. The upper limit can be deliberately chosen to be below 100%. For a range of, for example, more than 95%, a standby mode can be selected in which the fuel cell system can be switched to a standby mode. That is, it is possible that during the standby mode, no or substantially no power for vehicle propulsion is generated by the fuel cell system.In addition, it is possible that in a method a current power demand of the vehicle is determined and the fuel cell system is operated depending on the determined current power demand. As already described above, for the operation of the fuel cell system, for example, a current passing maneuver and / or a current hill climbing can be taken into account, each of which results in an at least temporary increase in the power demand. If such an increase occurs, the fuel cell system can be operated in a power-up mode. If such an increase is not present and the buffer battery is also in a predefined state of charge, the fuel cell system can be operated to the desired operating mode. As a result, the fuel cell system can always be operated for as long as possible and / or frequently to the desired desired operating mode. The setpoint operating mode can therefore be changed to a power increase operating mode in which the fuel cell system is operated with an increased output power if a predefined increase in the power demand is detected when the current power demand is ascertained. The transition between the desired operating mode and the power-increasing mode of operation can take place phlegmatically. This means that if it is detected, for example, that the state of charge of the buffer battery falls to a value below a predefined lower limit of 70%, for example, and / or a current particularly high power demand is present, the output power does not have to be increased abruptly. Rather, it can be advantageous if the output power and / or the efficiency are increased or decreased with a predefined gradient and in this way a smooth transition between the desired operating mode and the power-increasing operating mode is made possible.Another aspect of the presently described technology relates to an electric drive system having a backup battery, a fuel cell system for electrically charging the backup battery, and a controller, wherein the controller is configured to perform a method according to any one of the preceding claims. Thus, the electric drive system provides the same advantages as described in detail with respect to the method. The fuel cell system may be configured in the manner defined above.A further aspect of the proposed technology relates to a vehicle having an electric drive system as described above and an electric motor for driving the vehicle, wherein the buffer battery and the fuel cell system are configured to supply power to the at least one electric motor. Thus, the vehicle also has the same advantages as described in detail above. The vehicle can be understood to mean a motor vehicle such as an engine-driven two-wheeled vehicle, a passenger 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 pure 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 to mean a so-called FCEV (Fuel Cell Electric Vehicle). The buffer battery may have a capacity of more than 3 kWh, for example in a range between 3 kWh and 20 kWh or in a range between 5 kWh and 15 kWh. The buffer battery can be understood to mean a drive battery, a traction battery and / or a high-voltage battery for supplying power to the electric motor for driving the vehicle.In addition, the technology disclosed here comprises a computer program product and a computer-readable, in particular non-transitory, 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 may comprise instructions which, when the computer program product is executed by a computer, for example a control device of the vehicle, cause the latter to execute the proposed method in a vehicle as described above. The computer-readable storage medium can also be understood to mean a control device, for example a vehicle control device, with the computer program product installed therein. The method described herein may be performed, at least in part, as a computer-implemented method.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 can be stored on a computer-readable storage medium such as a data disk, a removable drive, a 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. Further, the computer program product may be provided and / or reside on a network such as the Internet from which it may be downloaded by a user as needed. The computer program product can be realized and / or be realized both by means of software and by means of one or more special electronic circuits, that is to say in hardware or in any hybrid form, that is to say by means of software components and hardware components.Further measures will become apparent from the following description of various exemplary embodiments, which are schematically illustrated in the figures. All features and / or advantages emerging from the claims, the description or the figures, including structural details and spatial arrangements, can be essential both individually and in the various combinations.They show in each case schematically: FIG. 1 is a vehicle including an electric drive system according to an embodiment of the present technology, FIG. 2 is a flow chart for explaining a method according to an embodiment of the present technology, FIG. 3 is a diagram for explaining a method according to another embodiment of the present technology; and FIG. 4 illustrates a computer readable storage medium having stored thereon a computer program product according to an embodiment of the present technology.Elements with the same function and mode of operation are provided with the same reference numerals in each of the figures.FIG. 1 shows a vehicle 100 with an electric drive system 10. the electric drive system 10 comprises a backup battery 11 and a fuel cell system 12 for electrically charging the backup battery 11. the electric drive system 10 further comprises a controller 13 configured to execute a method described below. The controller 13 can be designed as part of a vehicle control device or can be understood as a vehicle control device. The vehicle 100 also has two electric motors 14 for driving the vehicle 100, and the backup battery 11 and the fuel cell system 12 are configured to supply power to the electric motors 14. For this purpose, the fuel cell system 12 and in particular a fuel cell stack of the fuel cell system 12 are in electrical connection with the buffer battery 11. The vehicle 100 also has a pressure vessel 17 for fuel, for example hydrogen. The pressure vessel 17 is in fluid communication with the fuel cell system 12 for a fuel supply of the fuel cell stack. The vehicle 100 shown is designed in the form of a passenger car.FIG. 2 shows a flow chart for explaining a method for operating an electric drive system 10 of the vehicle 100. The method can be basically described as follows. In a step S 1, a setpoint operating mode for operating the fuel cell system 12 with a predefined maximally constant efficiency for generating a predefined maximally constant output power by the fuel cell system 12 is provided. In a second step S 2, a current state of charge of the buffer battery 11 is determined. Steps S 1 and S 2 may be performed sequentially or at least partially simultaneously. Steps S 1 and S 2 do not have to be performed in the illustrated order. In a third step S 3, the fuel cell system 12 is or is not operated to the desired operating mode depending on the ascertained current state of charge of the buffer battery 11.In the example shown, the desired mode of operation is provided for operating the fuel cell system 12 with maximum efficiency. That is, during the target operation mode, the fuel cell system 12 is to be operated at the highest efficiency. Furthermore, the fuel cell system 12 is operated in a setpoint operating mode in which an output power having a value in a range between 5% and 20% of the maximum possible output power of the fuel cell system 12, in the present case 10 kW, is generated as constantly as possible by the fuel cell system 12. The fuel cell system 12 is operated in the target operation mode as long as the state of charge of the backup battery 11 is in a range between 50% and 100%.With reference to FIG. 3, a method of operating the electric drive system 10 according to another embodiment will be described. In the method, the current state of charge of the buffer battery 11 and a current power demand of the vehicle 100 are ascertained. The current power demand is composed of the current power demand of the driver and an existing basic power demand, for example for electrical auxiliary devices of the vehicle. Furthermore, a desired operating mode and a power-increasing operating mode are provided. Which operating mode is carried out can be determined by means of the diagram shown in FIG. 3 and accordingly as a function of the current state of charge and of the current power demand.Referring to FIG. 3, the target operation is performed when the power demand is less than 100 kW and the state of charge of the backup battery 11 is in a range between 70% and 95%. The fuel cell system 12 is operated as constantly as possible with the maximum efficiency, for example 63%, during the desired operating mode. This results in a correspondingly constant output power of approximately 10 kW. The range of the desired operating mode is shown shaded in FIG. 3. If the state of charge of the buffer battery 11 falls below 70%, the setpoint operating mode changes to a power generation operating mode. If the power demand exceeds 100 kW and / or a predefined power demand increase is detected or determined, the power increase mode is likewise changed over. That is, below the hatched area and right next to the hatched area, the fuel cell system 12 is operated in the power generation mode. During the power generation mode, the fuel cell system 12 is operated at a lower efficiency than during the target mode. This results in an increased output power. If a power demand is below 100 kW and the state of charge of the buffer battery 11 is above 95%, the fuel cell system 12 can be operated in a standby mode. Here, exclusively or at least approximately exclusively, the buffer battery 11 is used for supplying power to the electric motors 14 and / or to other electronic components of the vehicle 100. The fuel cell system 12 may or may not generate power for driving the vehicle 100 at this time. Accordingly, there is no power trajectory within the shaded region, but rather an efficiency-based power point of the fuel cell system 12 of, for example, 10 kW. In other words, in the shaded area, the efficiency or the efficiency of the fuel cell system 12 is considered exclusively or at least approximately exclusively and not the currently required drive power. Between the operating modes, a transition which is as soft or phlegmatic as possible is produced. That is, the transitions between the operations need not be as direct as represented by the lines.FIG. 4 shows a computer-readable and non-transitory storage medium 16 on which a computer program product 15 is stored. The storage medium 16 is configured in the form of a flash drive. The computer program product 15 comprises instructions which, when the computer program product 15 is executed by a computer, for example the controller 13, cause the computer program product to execute, in the illustrated vehicle 100, a method for operating the electric drive system 10.The technology disclosed here allows further design principles in addition to the embodiments shown. That is, the technology should not be considered limited to the embodiments explained with reference to the figures. For example, the performance values with respect to a truck mentioned above by way of example with respect to the passenger car can be correspondingly higher.List of reference characters10 Electric drive system 11 Buffer battery 12 Fuel cell system 13 Controller 14 Electric motor 15 Computer program product 16 Storage medium 17 Pressure vessel 100 Vehicle

Claims

Method for operating an electric drive system (10) of a vehicle (100), wherein the electric drive system comprises at least one buffer battery (11) and a fuel cell system (12) for electrically charging the buffer battery (11), having: - providing a setpoint operating mode for operating the fuel cell system (12) with a predefined constant efficiency for generating a predefined constant output power by the fuel cell system (12), - determining a current state of charge of the buffer battery (11), and - operating the fuel cell system (12) to the setpoint operating mode as a function of the determined current state of charge of the buffer battery (11).The method of claim 1, wherein the desired mode of operation is provided for operating the fuel cell system (12) with maximum efficiency.Method according to one of the preceding claims, wherein the setpoint operating mode is provided for operating the fuel cell system (12) with the predefined constant efficiency for generating a constant output power which is in a range between 5% and 20% of the maximum possible output power of the fuel cell system (12).Method according to one of the preceding claims, wherein the fuel cell system (12) is operated in the desired operating mode if the state of charge of the buffer battery (11) is in a range between 50% and 100%.Method according to one of the preceding claims, wherein a current power demand of the vehicle (100) is determined and the fuel cell system (12) is operated as a function of the determined current power demand.Method according to Claim 5, wherein the setpoint operating mode is changed to a power-increasing operating mode in which the fuel cell system (12) is operated with an increased output power if a predefined increase in the power demand is detected when the current power demand is ascertained.An electric drive system (10) comprising a backup battery (11), a fuel cell system (12) for electrically charging the backup battery (11), and a controller (13), wherein the controller (13) is configured to perform a method according to any of the preceding claims.Vehicle (100) comprising an electric drive system (10) according to claim 7 and an electric motor (14) for driving the vehicle (100), wherein the buffer battery (11) and the fuel cell system (12) are configured to power the at least one electric motor (14).A computer program product (15) comprising instructions which, when the computer program product (15) is executed by a computer, cause the computer program product to execute, in a vehicle (100) according to claim 8, the method according to any one of claims 1 to 6.A computer readable storage medium (16) having stored thereon a computer program product (15) according to claim 9.

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