Operating method for operating a fuel cell system

Abstract

The invention relates to an operating method (100) for operating a fuel cell system (300) for supplying electrical energy to an electrical consumer. The operating method (100) comprises activating (101) a turn-off program of the fuel cell system (300) in response to receipt of a turn-off command. The turn-off procedure comprises turning off an air supply unit (305) for supplying air to a cathode subsystem (303) of the fuel cell system (300) in order to reduce oxygen introduced into the cathode subsystem (303) and a voltage provided by the fuel cell system (300), activating (103) a reactivation program of the fuel cell system (300) as a response to receipt of the start-up command when the start-up command is received after the shut-off command within a predetermined time period, the reactivation program comprising, directly after receipt of the start-up command, activating (103) the reactivation program of the fuel cell system (300); the rotational speed of the air supply unit (305) is increased to a minimum rotational speed.

Description

Technical Field

[0001] The invention relates to an operating method, a fuel cell system and a motor vehicle according to the claims. Background Art

[0002] Fuel cells convert hydrogen and oxygen into water, producing electricity which can be supplied to electrical consumers, such as electric motors, in order to operate them.

[0003] In order to supply the fuel cell with oxygen, ambient air, which is provided by a compressor, usually flows through the cathode of the fuel cell.

[0004] The process waste heat is usually dissipated by means of liquid cooling. The cooling medium is usually conveyed by means of an electrically driven conveying pump.

[0005] In order to optimize the reaction temperature in the fuel cell system, electric heaters are used at various locations.

[0006] All these auxiliary loads can be supplied directly from the fuel cell for efficiency reasons or at another voltage level via a voltage converter.

[0007] When shutting down the fuel cell system, the voltage and the reactants need to be reduced. Advantageously, the fuel cell system is adjusted in such a way that an optimal shutdown state is provided with defined humidity, oxygen and hydrogen concentrations on the anode side and the cathode side.

[0008] Known procedures require time for regulating the fuel cell system to set the shutdown state, so that if a need for restarting arises during the regulation, the complete shutdown and regulation phase of the fuel cell system must be waited out, which is not energy efficient. Summary of the invention

[0009] Within the scope of the invention, a method for operating a fuel cell system, a fuel cell system and a motor vehicle are proposed. Further features and details of the invention are derived from the dependent claims, the description and the drawings. Features and details described in connection with the cell stack according to the invention naturally also apply to the production method according to the invention and vice versa, so that the disclosures concerning the various aspects of the invention always refer to each other or can refer to each other.

[0010] The invention serves in particular to enable a rapid restart of a fuel cell system during a shutdown procedure.

[0011] Therefore, according to a first aspect of the present invention, an operating method for operating a fuel cell system to supply electrical energy to an electrical consumer is proposed. The operating method includes activating a shutdown procedure of the fuel cell system in response to receiving a shutdown command, wherein the shutdown procedure includes shutting down an air supply unit for supplying air to a cathode subsystem of the fuel cell system so as to reduce oxygen introduced into the cathode subsystem and a voltage provided by the fuel cell system, and when a startup command is received within a predetermined time period after the shutdown command, activating a reactivation procedure of the fuel cell system in response to receiving the startup command, and wherein the reactivation procedure includes increasing the rotation speed of the air supply unit to a minimum rotation speed (minimum rotation speed) (at which the system can operate normally) directly after receiving the startup command (immediately after receiving the startup command).

[0012] In the context of the present invention, a shutdown procedure can be understood as a process in which the fuel cell system is switched under regulated conditions into an idle state, in which, for example, residual oxygen in the cathode subsystem is decomposed or converted into water by hydrogen in the anode subsystem until the voltage in the fuel cell stack drops below a predetermined threshold value due to lack of oxygen.

[0013] The proposed operating method is based on the principle that during a shutdown procedure of the fuel cell system a command for starting the fuel cell system is triggered, ie a restart is carried out which leads to a restart of the fuel cell system within a short period of time after an operating phase.

[0014] In order to minimize the time of using the fuel cell system until restart, the present invention is provided that the air supply unit of the fuel cell system is controlled in such a way that the rotational speed of the air supply unit is increased to a minimum rotational speed and fresh air with additional oxygen is blown into the cathode subsystem of the fuel cell system accordingly, so that the voltage provided by the fuel cell stack of the fuel cell system can be increased, and the air supply unit and all other auxiliary units of the fuel cell system can be supplied with a voltage sufficient for operation through the fuel cell stack.

[0015] By increasing the speed of the air supply unit directly after receiving the start command, the shutdown procedure is interrupted and the reactivation procedure is started, so that the time until the fuel cell system or the electrical consumers supplied by the fuel cell system are put into operation again is reduced compared to a procedure in which the fuel cell system is completely deactivated and reactivated. The proposed operating method utilizes the inertia of the air mass flow, which still moves through the fuel cell system after the air supply unit is shut down, in order to increase the voltage applied to the fuel cell stack and restart the air supply unit.

[0016] In particular, it can be provided that the rotational speed of the air supply unit is increased by means of electrical energy generated by the fuel cell stack of the fuel cell system during the shutdown procedure.

[0017] Because a residual voltage is applied to the fuel cell stack of the fuel cell system due to the air flow that still flows through the fuel cell system after the air supply unit is shut down, this voltage can be used to activate the air supply unit and deliver fresh air into the fuel cell system, so that the voltage applied to the fuel cell stack is increased to the voltage set for operating the fuel cell system and the fuel cell system transitions to control operation or normal operation.

[0018] It can also be provided that the rotational speed of the air supply unit is increased by means of electrical energy in a battery storage device electrically coupled to the fuel cell system.

[0019] In the event that the voltage applied to the fuel cell stack is insufficient to activate the air supply unit, a battery storage device, for example a battery from the onboard power supply of a motor vehicle containing the fuel cell system, can be used to supply electrical energy to the air supply unit for a long period of time until a sufficient voltage is applied to the fuel cell stack and the air supply unit is operated via the fuel cell stack.

[0020] It can also be provided that the electrical energy for the air supply unit is supplied via a DC / DC converter (direct current / direct current converter) of the fuel cell system, the current direction of which is reversed compared to the shutdown procedure.

[0021] In the case where the air supply unit is supplied with electrical energy via a DC / DC converter and is connected in parallel with a fuel cell stack, for example, a DC / DC converter can be used to supply the air supply unit with electrical energy, for example from a battery, and to adapt the voltage accordingly to the voltage required by the air supply unit.

[0022] It can also be provided that, in response to receiving a shutdown command, a cathode shutoff valve of the fuel cell system is closed and, in response to receiving a startup command, the cathode shutoff valve is opened.

[0023] If the cathode shut-off valve was closed during the shutdown sequence, it must be opened during the reactivation sequence in order to supply the fuel cell stack with fresh air.

[0024] It can also be provided that, during the increase in the rotation speed of the air supply unit, the gross power of the fuel cell system is greater than the net power of the fuel cell system.

[0025] Since energy is supplied to auxiliary units of the fuel cell system, in particular the air supply unit, during the reactivation process, the net power of the fuel cell system is usually negative during the reactivation process, so that the fuel cell system consumes more energy than it provides.

[0026] According to a second aspect, the invention relates to a fuel cell system for supplying electrical energy to an electrical consumer. The proposed fuel cell system comprises a fuel cell stack, a cathode subsystem, an air supply unit for supplying air to the cathode subsystem, a computing unit and a user interface. The computing unit is configured to implement a possible configuration of the proposed operating method.

[0027] In the context of the present invention, a computing unit may be understood as a computer, a processor, a controller or any other programmable switching circuit.

[0028] It can be set that the computing unit is configured to activate a shutdown program of the fuel cell system in response to a shutdown command triggered by a user interface, wherein the shutdown program configures the computing unit to transmit a control command to the air supply unit, which control command causes the air supply unit to shut down in order to reduce the oxygen introduced into the cathode subsystem and the voltage provided by the fuel cell stack, and wherein the computing unit is also configured to activate a reactivation program of the fuel cell system in response to a start command triggered by the user interface within a predetermined time period after the shutdown command, wherein the reactivation program configures the computing unit to transmit a control command to the air supply unit directly after the start command is triggered, which control command causes the rotational speed of the air supply unit to be increased to a minimum rotational speed.

[0029] It may also be provided that the reactivation program configures the computer unit to supply the air supply unit with electrical energy from the energy storage device directly after the start command has been triggered if the voltage provided by the fuel cell stack is less than a predefined threshold value.

[0030] The energy storage device for supplying the air supply unit with electrical energy may be, for example, a battery of the motor vehicle comprising the proposed fuel cell system or a battery of the fuel cell system itself.

[0031] According to a third aspect, the invention relates to a motor vehicle having a possible embodiment of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Further advantages, features and details of the invention are 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 the description may be essential to the invention individually or in any combination.

[0033] The accompanying drawings show:

[0034] Figure 1 : Schematic diagram of a possible configuration of the proposed operating method,

[0035] Figure 2 :according to Figure 1 Detailed view of the run method,

[0036] Figure 3 : Possible configuration of the proposed fuel cell system in a possible configuration of the proposed motor vehicle. DETAILED DESCRIPTION

[0037] exist Figure 1 Detailed description is given of an operating method 100 for operating a fuel cell system to provide electrical energy to an electrical consumer.

[0038] The operating method 100 includes a first activation step 101, in which a shutdown procedure of the fuel cell system is activated in response to receiving a shutdown command. The shutdown procedure includes shutting down an air supply unit for supplying air to a cathode subsystem of the fuel cell system so as to reduce oxygen introduced into the cathode subsystem and reduce a voltage provided by the fuel cell system.

[0039] The operating method 100 further comprises a second activation step 103, in which, when a start command is received within a predetermined time period after the shutdown command, a reactivation procedure of the fuel cell system is activated as a response to receiving the start command. The reactivation procedure comprises a control step 105, in which, directly after receiving the start command, the air supply unit is controlled in such a way that the rotational speed of the air supply unit is increased to a minimum rotational speed (at which the system can operate normally). For this purpose, the air supply unit can be supplied with electrical energy from the fuel cell stack of the fuel cell system and / or from a battery, for example.

[0040] exist Figure 2 2 shows a diagram 200 which depicts a temporal profile 201 of a voltage present at a fuel cell stack, a temporal profile 203 of a rotational speed of an air supply unit and a temporal profile 205 of a current provided by the fuel cell stack.

[0041] From time T0 to time T1 , the normal operation of the fuel cell system is performed, during which the voltage, the rotational speed and the current are adjusted to constant values.

[0042] At time T1, a shutdown command is triggered by the user and the shutdown procedure of the fuel cell system is activated, so that, for example, the cathode shutoff valve of the fuel cell system is closed and the speed of the air supply unit is reduced. Accordingly, the voltage applied to the fuel cell stack and the current provided during the so-called "bleeddown", i.e., the conversion of the remaining oxygen in the fuel cell system into water, also decrease.

[0043] At time T2, the user triggers a start command as a result of a so-called "change of mind" after time T1 within a predetermined time period and activates the reactivation procedure of the fuel cell system, so that the air supply unit is supplied with current or voltage and the rotation speed of the air supply unit is increased accordingly, thereby increasing the current provided and the voltage applied to the fuel cell stack, until the so-called "optimal operation" is reached at time T3, that is, the operation has the optimal operating conditions for starting the fuel cell system. At time T4, if there is sufficient control reserve for the cathode air quantity, the control strategy of the normal power control is activated.

[0044] Trend 207 shows that according to Figure 1 The current flowing through the DC / DC converter of the operating method 100 shown in FIG.

[0045] Curve 209 shows the current flowing through the DC / DC converter during normal operation when the fuel cell system is completely shut down.

[0046] exist Figure 3 4 shows a motor vehicle 400 having a fuel cell system 300 . The fuel cell system 300 comprises a fuel cell stack 301 , a cathode subsystem 303 , an air supply unit 305 for supplying air to the cathode subsystem 303 , a computing unit 307 and a user interface 309 .

[0047] The computer unit 307 is configured to execute the operating method 100 if, after the command to shut down the fuel cell system, within a predefined time period a start command is issued via the user interface 309 for restarting or activating a restart procedure of the fuel cell system 300 .

Claims

1. An operating method (100) for operating a fuel cell system (300) to provide electrical energy to an electrical consumer, in, The operating method (100) comprises: - in response to receiving a shutdown command, activating (101) a shutdown procedure of the fuel cell system (300), The shut-down procedure includes shutting down an air supply unit (305) for supplying air to a cathode subsystem (303) of the fuel cell system (300), so as to reduce oxygen introduced into the cathode subsystem (303) and a voltage provided by the fuel cell system (300), - when a start-up command is received within a predetermined time period after the shut-down command, activating (103) a reactivation procedure of the fuel cell system (300) in response to receiving the start-up command, The reactivation procedure includes: - Directly after receiving the start command, the rotational speed of the air supply unit (305) is increased to a minimum rotational speed.

2. The operating method (100) according to claim 1, It is characterized in that The rotational speed of the air supply unit (305) is increased by means of electrical energy generated by a fuel cell stack (301) of the fuel cell system (300) during the shutdown procedure.

3. The operating method (100) according to claim 1, It is characterized in that The rotational speed of the air supply unit (305) is increased using electrical energy in a battery storage device electrically coupled to the fuel cell system (300).

4. The operating method (100) according to claim 3, It is characterized in that The electric energy of the air supply unit (305) is supplied via a DC / DC converter of the fuel cell system (300), the current direction of the DC / DC converter being reversed compared to the shutdown procedure.

5. The operating method (100) according to any one of the preceding claims, It is characterized in that In response to receiving the shutdown command, closing the cathode shutoff valve of the fuel cell system (300), and In response to receiving the start command, the cathode cutoff valve is opened.

6. The operating method (100) according to any one of the preceding claims, It is characterized in that During the increase in the rotation speed of the air supply unit (305), the gross power of the fuel cell system (300) is greater than the net power of the fuel cell system (300).

7. A fuel cell system (300) for providing electrical energy to an electrical appliance, in, The fuel cell system (300) comprises: - a fuel cell stack (301), - cathode subsystem (303), - an air supply unit (305) for supplying the cathode subsystem (303) with air, - a calculation unit (307), - user interface (309), Therein, the computing unit (307) is configured to carry out the operating method (100) according to any one of claims 1 to 6.

8. The fuel cell system (300) according to claim 7, It is characterized in that The computing unit (307) is configured to: activate a shutdown procedure of the fuel cell system (300) in response to a shutdown command triggered via the user interface (309), wherein the shutdown program configures the computing unit (307) to transmit a control instruction to the air supply unit (305), the control instruction causing the air supply unit (305) to shut down in order to reduce the oxygen introduced into the cathode subsystem (303) and the voltage provided by the fuel cell stack (301), and The computing unit (307) is further configured to: activate a reactivation program of the fuel cell system (300) in response to a start-up command triggered by the user interface (309) within a predetermined time period after the shut-down command, The reactivation program configures the computing unit (307) to transmit a control command to the air supply unit (305) directly after the start command is triggered, the control command causing the rotational speed of the air supply unit (305) to be increased to a minimum rotational speed.

9. The fuel cell system (300) according to claim 8, It is characterized in that The reactivation program configures the computing unit (307) to supply the air supply unit (305) with electrical energy from an energy storage device directly after the start command is triggered if the voltage provided by the fuel cell stack (301) is below a predetermined threshold value.

10. A motor vehicle (400) comprising a fuel cell system (300) according to any one of claims 7 to 9.

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