Fuel cell system, method for operating a fuel cell system and vehicle with a fuel cell system

Abstract

The presented invention relates to a method (100) for operating a fuel cell system (301) in a vehicle (300), wherein the method (100) comprises: - Determine (101) a power requirement for the fuel cell system (300) for a future time range, - Selecting (103) an operating mode (M1.1, M1.2, M1.3) from a number of operating modes (M1.1, M1.2, M1.3), depending on the determined power requirement, in the event that the determined power requirement is less than a specified threshold value, - Setting (105) an air system pre-control and a cathode exhaust gas recirculation rate of the fuel cell system (301) according to the selected operating mode (M1.1, M1.2, M1.3), where the number of operating modes (M1.1, M1.2, M1.3) includes at least: - a first operating mode (M1.1) in which more electrical energy is provided by the fuel cell system (301) than is consumed by the fuel cell system (301) itself, - a second operating mode (M1.2) in which the fuel cell system (301) provides as much electrical energy as is consumed by the fuel cell system (301) itself, - a third operating mode (M1.3) in which less electrical energy is provided by the fuel cell system (301) than is consumed by the fuel cell system (301) itself.

Description

[0001] The presented invention relates to a method for operating a fuel cell system in a vehicle, a fuel cell system for converting energy and a vehicle, according to the attached claims. State of the art

[0002] Unlike a battery, in fuel cell systems the supplied electrical power cannot be reduced to zero, because significant degradation occurs in the range of high cell voltages, i.e., at low currents.

[0003] Accordingly, fuel cells have a predefined operating range. If the power demand falls below a lower limit of this operating range, the fuel cell system or a fuel cell stack within the system is shut down. Disclosure of the invention

[0004] Within the scope of the presented invention, a fuel cell system, a method for operating the fuel cell system, and a vehicle are introduced. Further features and details of the invention will become apparent from the respective dependent claims, the description, and the drawings. Features and details described in connection with the method according to the invention naturally also apply in connection with the fuel cell system and the vehicle according to the invention, and vice versa, so that the disclosure of the individual aspects of the invention is always, or can always be, mutually interdependent.

[0005] The presented invention serves in particular to provide a possibility for an energy-efficient and robust fuel cell system.

[0006] Thus, according to a first aspect of the presented invention, a method for operating a fuel cell system in a vehicle is presented.

[0007] The presented method comprises determining a power requirement for the fuel cell system for a future time period, selecting an operating mode from a number of operating modes depending on the determined power requirement, in the case that the determined power requirement is less than a predetermined threshold, setting an air system feedforward control and a cathode exhaust recirculation rate of the fuel cell system according to the selected operating mode, wherein the number of operating modes includes at least a first operating mode in which more electrical energy is supplied by the fuel cell system than is consumed by the fuel cell system, a second operating mode in which as much electrical energy is supplied by the fuel cell system as is consumed by the fuel cell system, and a third operating mode.includes situations where less electrical energy is supplied by the fuel cell system than is consumed by the fuel cell system.

[0008] The presented method is based on the detection of an operating situation in which there is or is expected to be a low power requirement, such as standby operation, a stop at a traffic light, stop-and-go operation in a traffic jam, a downhill run or operation with short load phases.

[0009] For this purpose, a power requirement for the fuel cell system, determined for a future time period, is compared with a threshold value that corresponds, for example, to the electrical power that can be provided without oxygen depletion in the cathode system of the fuel cell system. The power requirement or the threshold value can be specified as a characteristic value of a system parameter, such as the voltage applied to individual fuel cells or a fuel cell stack, or the amount of electrical energy provided by the fuel cell system.

[0010] In the event that the determined power requirement is less than the threshold value, an operating mode for setting an air system pre-control and a cathode exhaust gas recirculation rate of the fuel cell system is selected from a number, e.g. a list, of predefined operating modes and set on the fuel cell system.

[0011] The list of operating modes includes a first operating mode in which more electrical energy is provided by the fuel cell system than is consumed by the fuel cell system itself, i.e., by a fuel cell stack and respective auxiliary components, such as a cathode system and / or a cooling system and / or an anode system; a second operating mode in which as much electrical energy is provided by the fuel cell system as is consumed by the fuel cell system itself; and a third operating mode in which less electrical energy is provided by the fuel cell system than is consumed by the fuel cell system itself.

[0012] Accordingly, the presented method utilizes an operating situation of a fuel cell system with a very low power requirement, such as standby operation, to prepare the fuel cell system for further operation by either providing electrical energy to charge a buffer battery, for example, or simply providing electrical energy to supply respective consumers when the buffer battery is already charged, or to consume energy to relieve the load on the friction brake and / or the buffer battery and / or the vehicle electrical system, for example, during downhill driving in recuperation mode.

[0013] In particular, oxygen depletion is achieved by means of a cathode exhaust gas recirculation system or a cathode exhaust gas recirculation rate in order to implement various objectives specified by the operating modes.

[0014] In particular, the cathode system remains open and permeated with air or inert gas during each of the three predefined operating modes, while an anode system and a cooling system continue to operate. Accordingly, the presented method results in improved dynamics when switching from one of the predefined operating modes to a high-power operating mode.

[0015] Furthermore, the presented method avoids or at least delays the shutdown of the fuel cell system in the event of low power demand.

[0016] Furthermore, the presented method improves homogenization and reduces the number of start-stop cycles, as well as the load profiles of fuel cell system components such as the fuel cell stack, throttle valves, and / or air compressor. This reduces the degradation of various components.

[0017] It may be provided that in the first operating mode the air system pre-control and the cathode exhaust gas recirculation rate are set in such a way that a maximum permissible voltage is established at a fuel cell stack of the fuel cell system.

[0018] An operating mode in which a maximum permissible voltage is established can be used to supply the vehicle with electrical energy, for example, to charge a buffer battery. This can be achieved, for instance, by adjusting the exhaust gas recirculation rate and the air system feedforward or control so that the oxygen partial pressure, mass flow rate, pressure, and EGR rate generate a predetermined power output or maximum permissible voltage at the fuel cell stack for a given current. Conversely, the air system feedforward or control can be adjusted to regulate the stack current or the current applied to the fuel cell stack, resulting in a maximum permissible voltage at the fuel cell stack.

[0019] In the context of the presented invention, a maximum permissible voltage is to be understood as a voltage in a high voltage range, which essentially corresponds to a maximum permissible voltage.

[0020] It may also be provided that in the second operating mode the air system pre-control and the cathode exhaust gas recirculation rate are set in such a way that fuel consumption is minimized and / or that a voltage is established at a fuel cell stack of the fuel cell system which corresponds at most to a maximum permissible voltage.

[0021] In particular, the second operating mode is designed so that no electrical energy is supplied to charge the buffer battery, meaning that, for example, the supplied electrical energy corresponds to the amount of energy currently consumed. This can be achieved, for instance, by selecting a voltage at the fuel cell stack that is lower than a maximum possible voltage.

[0022] The voltage set on the fuel cell stack can be lower than the maximum permissible voltage.

[0023] It may also be provided that in the third operating mode the air system pre-control and the cathode exhaust gas recirculation rate are set in such a way that a blower is operated to introduce an airflow into the fuel cell system with a predetermined power consumption and an oxygen mass flow into a fuel cell stack of the fuel cell system is minimized to a predetermined reduction value and / or the fuel cell stack is completely inerted.

[0024] By operating the blower or air compressor with a predetermined power consumption, electrical energy is converted into thermal energy and discharged from the fuel cell system, thus preventing an overload of the buffer battery and / or the friction brake and / or the vehicle electrical system.

[0025] To prevent an unacceptably high oxygen mass flow through the fuel cell stack caused by the operation of the blower with its power consumption, the oxygen mass flow into the fuel cell stack of the fuel cell system is throttled to a predetermined reduction value. This can be achieved by setting a correspondingly high cathode exhaust gas recirculation and / or by diverting a portion of the air mass flow compressed by the air compression system around the stack via the stack bypass. In particular, this allows the fuel cell stack to be inerted and the oxygen content in the cathode system to be minimized, thereby reducing the electrical current supplied and, consequently, the power supplied by the fuel cell system, and ensuring that a maximum permissible stack voltage is maintained.

[0026] It is specifically intended that the air system pre-control is set by adjusting the following parameters: oxygen partial pressure, mass flow rate, inlet humidity stack pressure, fuel cell stack outlet humidity, temperature and / or temperature difference of a coolant.

[0027] It may further be provided that the procedure includes a fourth operating mode, which is activated in the event that, when determining the power requirement for the fuel cell system for the future time range, it is determined that the fuel cell system must be deactivated for a maximum of a predetermined period, whereby in the fourth operating mode the cathode system is closed and inerted and an anode system of the fuel cell system remains filled with fuel or is refilled.

[0028] By filling the anode system with fuel, the fuel cell system can quickly provide high power after a low-power operating situation, allowing the fuel cell system to react particularly dynamically to load changes.

[0029] It may further be provided that the procedure includes a fifth operating mode, which is activated in the event that, when determining the power requirement for the fuel cell system for the future time range, it is determined that the fuel cell system will be deactivated for at least a predetermined period, wherein in the fifth operating mode the cathode system is closed and inerted and an anode system of the fuel cell system is also inerted.

[0030] By inerting the cathode system and the anode system, the fuel cell system is prepared for a long standstill, e.g. in response to a detected system error or a predictively announced long shutdown phase.

[0031] It may also be possible to select and set an operating mode of the fuel cell system depending on the determined power requirement. In particular, the fourth, fifth, and sixth operating modes can be selected directly or set in a cascaded manner.

[0032] The first, second and third operating modes can, for example, be selected as sub-operating modes of a superior sixth operating mode, whereby these operating modes can be selected in any order, i.e., they are not limited to the order first operating mode, second operating mode, third operating mode.

[0033] According to a second aspect, the presented invention relates to a fuel cell system for converting energy.

[0034] The presented fuel cell system comprises a fuel cell stack, a recirculation system for recirculating cathode exhaust gas into a cathode system of the fuel cell system, and a computing unit, wherein the computing unit is configured to control the recirculation system in order to carry out a possible embodiment of the presented method.

[0035] According to a third aspect, the presented invention relates to a vehicle. The presented vehicle comprises a possible embodiment of the presented fuel cell system.

[0036] The vehicle presented could be, for example, a car, a truck, or a ship.

[0037] Advantages described in detail in relation to the method for operating a fuel cell system in a vehicle according to the first aspect of the invention apply equally to the fuel cell system for converting energy according to the second aspect of the invention and to the vehicle according to the third aspect of the invention, and vice versa.

[0038] Further advantages, features, and details of the invention will become apparent from the following description, in which exemplary embodiments of the invention are described in detail with reference to the drawings. The features mentioned in the claims and in the description can each be essential to the invention individually or in any combination.

[0039] They each show schematically: Fig. 1. A possible design of the presented procedure, Fig. 2 a detailed description of the procedure according to Fig. 1, and Fig. 3 a possible embodiment of the presented vehicle with a possible embodiment of the presented fuel cell system.

[0040] In Fig. Figure 1 shows a method 100 for operating a fuel cell system in a vehicle.

[0041] The procedure 100 comprises a determination step 101, in which a power requirement for the fuel cell system is determined for a future time range, a selection step 103, in which an operating mode is selected from a number of operating modes, depending on the determined power requirement, in the event that the determined power requirement is less than a predetermined threshold, and a setting step 105, in which an air system feedforward control and a cathode exhaust gas recirculation rate of the fuel cell system are set according to the selected operating mode.

[0042] It is planned that the number of operating modes will include at least: - a first operating mode in which more electrical energy is provided by the fuel cell system than is consumed by the fuel cell system, - a second operating mode in which the fuel cell system provides as much electrical energy as is consumed by the fuel cell system, - a third operating mode in which less electrical energy is provided by the fuel cell system than is consumed by the fuel cell system.

[0043] In Fig. 2 is a possible sequence of procedure 100 according to Fig. 1 shown.

[0044] If, in a request step 35, a fuel cell system with, for example, several fuel cell stacks 110, 120, and 130 requests a power output that is less than a minimum power output that can be set under normal oxygen concentration, then in a selection step 30, a choice is made between operating modes four (M2), five (M3), and six (M1), and the selected operating mode is set in a setting step 40. The sixth operating mode (M1) comprises three sub-operating modes M1.1, M1.2, and M1.3, which can only be activated if the sixth operating mode (M1) is activated.

[0045] In particular, the power requirement is predictively determined in prediction step 6 for a future time period, since the duration of the respective stop or shutdown phases in that future time period is relevant for selection step 30. All data available in a vehicle can be used for this purpose.

[0046] In higher-level system control levels 10 and 11, target trajectories for various quantities, in particular electrical power (PelReq) and energy flows, are determined, and a battery charge level is taken into account.

[0047] If a significant power reduction is requested in a request step 15, a determination step 20 determines which fuel cell stack 110, 120, 130 should be switched off and / or operated at reduced power under oxygen-deficient conditions. Optionally, determination step 20 can be repeated in a repetition step 25 for each fuel cell stack 110, 120, 130.

[0048] In a further selection step 50, if the sixth operating mode M1 was selected in selection step 30, a sub-mode is selected from the respective sub-operating modes M1.1, M1.2, M1.3.

[0049] In setting step 55, a signal is generated to activate settings 60 according to the sub-mode selected in selection step 50.

[0050] Selection steps 20, 30 and 50 can be cascaded or performed together, with the option of evaluating in an assessment step 35 which fuel cell stack is shut down.

[0051] In Fig. Figure 3 shows a vehicle 300. The vehicle 300 comprises a fuel cell system 301, which includes a fuel cell stack 303, a recirculation system 305 for recirculating cathode exhaust gas into the fuel cell stack 303, and a computing unit 307 configured to control the recirculation system 305 to carry out the procedure 100 according to Fig. 1. To be carried out includes.

Claims

[1] Method (100) for operating a fuel cell system (301) in a vehicle (300), the method (100) comprising: - Determine (101) a power requirement for the fuel cell system (301) for a future time range, - Selecting (103) an operating mode (M1.1, M1.2, M1.3) from a number of operating modes (M1.1, M1.2, M1.3), depending on the determined power requirement, in the case that the determined power requirement is less than a specified threshold value, - Setting (105) an air system feedforward control and a cathode exhaust gas recirculation rate of the fuel cell system (301) according to the selected operating mode (M1.1, M1.2, M1.3), wherein the number of operating modes (M1.1, M1.2, M1.3) includes at least: - a first operating mode (M1.1) in which more electrical energy is provided by the fuel cell system (301) than is consumed by the fuel cell system (301) itself, - a second operating mode (M1.2) in which as much electrical energy is provided by the fuel cell system (301) as is consumed by the fuel cell system (301) itself, - a third operating mode (M1.3) in which less electrical energy is provided by the fuel cell system (301) than is consumed by the fuel cell system (301) itself. [2] Method (100) according to claim 1, characterized by , that in the first operating mode (M1.1) the air system pre-control and the cathode exhaust gas recirculation rate are set such that a maximum permissible voltage is established at a fuel cell stack (110, 120, 130, 303) of the fuel cell system (301). [3] Method (100) according to claim 1 or 2, characterized by , that in the second operating mode (M1.2) the air system pre-control and the cathode exhaust gas recirculation rate are set such that fuel consumption by the fuel cell system (301) is minimized and / or that a voltage is established at a fuel cell stack (303) of the fuel cell system (301) which corresponds at most to a maximum permissible voltage. [4] Method (100) according to any of the preceding claims, characterized by, that in the third operating mode (M1.3) the air system pre-control and the cathode exhaust gas recirculation rate are set such that a blower for introducing an airflow into the fuel cell system (301) is operated with a predetermined power consumption and an oxygen mass flow into a fuel cell stack (303) of the fuel cell system (301) is minimized to a predetermined reduction value and / or the fuel cell stack (110, 120, 130, 303) is completely inerted. [5] Method (100) according to any one of the preceding claims, characterized by , that the air system pre-control is set by adjusting the following parameters: oxygen partial pressure, mass flow rate, pressure, inlet humidity of the stack, outlet humidity of the fuel cell stack (110, 120, 130, 303), temperature and / or temperature difference of a coolant [6] Method (100) according to any one of the preceding claims, characterized by, that the method (100) further comprises a fourth operating mode (M2) which is activated in the event that, when determining the power requirement to the fuel cell system (301) for the future time range, it is determined that the fuel cell system (301) is to be deactivated for at most a predetermined period, wherein in the fourth operating mode (M2) the cathode system is closed and inerted and an anode system of the fuel cell system (301) remains filled with fuel or is refilled. [7] Method (100) according to any of the preceding claims, characterized by , that the procedure (100) further includes a fifth operating mode (M3) which is activated in the event that, after the selected operating mode (M1.1, M1.2, M1.3), the power requirement for the fuel cell system is determined for the future time range, and that the fuel cell system (301) is deactivated for at least a predetermined period. in the fifth operating mode (M3) the cathode system is closed and inerted and an anode system of the fuel cell system (301) is also inerted. [8] Method (100) according to any one of the preceding claims, characterized by , that depending on the determined power requirement for the fuel cell system, an operating mode of the fuel cell system (301) is selected and set. [9] Fuel cell system (301) for converting energy, the fuel cell system (301) comprises: - a fuel cell stack (303), - a recirculation system (305) for recirculating cathode exhaust gas in a cathode system of the fuel cell system (301), - a computing unit (307), wherein the computing unit (307) is configured to control the recirculation system (305) to perform a method (100) according to any one of claims 1 to 8. [10] Vehicle (300), wherein the vehicle (300) comprises a fuel cell system (301) according to claim 9.

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