Operating method for avoiding anode depletion during operation of fuel cell system

Abstract

The invention relates to an operating method (100) for avoiding anode depletion during operation of a fuel cell system (200), in the operating method, a threshold value for a characteristic value of an operating variable of the fuel cell system (200) is determined as a function of a change in a current supplied by the fuel cell system (200) for adjusting a load demand that is reduced in relation to a currently adjusted load demand, and if the characteristic value reaches the threshold value, the operating variable of the fuel cell system (200) is determined as a function of the change in the current supplied by the fuel cell system (200). If so, the hydrogen content in an anode subsystem (203) of the fuel cell system (200) is increased.

Description

Technical Field

[0001] The present invention relates to an operating method for avoiding anode depletion during operation of a fuel cell system, and a fuel cell system, according to the appended claims. Background Technology

[0002] Hydrogen-based polymer electrolyte membrane fuel cells are seen as a future mobility concept because they emit only water as exhaust gas and can achieve rapid refueling times.

[0003] During the operation of a fuel cell system, inert gases (nitrogen, water vapor) accumulate in the hydrogen system. These inert gases displace hydrogen or reduce its concentration, which can lead to decreased power, especially the voltage of individual cells in the fuel cell system, or degradation due to hydrogen depletion.

[0004] To avoid these negative effects, it is known to regularly flush or “purge” the hydrogen system or anode subsystem. Here, when the purge valve is opened, some of the hydrogen mixture leaks from the hydrogen system and typically mixes into the exhaust path of the air system downstream of the cathode.

[0005] Many methods are known for controlling or regulating purge valves; however, these methods cannot prevent hydrogen depletion during large load jumps. Summary of the Invention

[0006] Within the framework of this invention, an operating method for operating a fuel cell system and a fuel cell system are proposed. Further features and details of the invention are derived from the corresponding dependent claims, description, and drawings. The features and details described herein in conjunction with the operating method according to the invention are of course also applicable to the fuel cell system according to the invention, and vice versa, so that disclosures concerning individual aspects of the invention are always mutually referenced or may be mutually referenced.

[0007] This invention is particularly applicable to providing a way to prevent hydrogen depletion during large load jumps.

[0008] Therefore, according to a first aspect of the present invention, an operating method for avoiding anode depletion during the operation of a fuel cell system is proposed.

[0009] In the proposed operating method, for this situation: a threshold value for the characteristic value of the operating parameters of the fuel cell system is determined based on the change in current provided to adjust for a load demand that has been reduced relative to the current load demand, and if the characteristic value reaches the threshold value, the hydrogen content in the anode subsystem of the fuel cell system is increased.

[0010] In the context of this invention, anode depletion is understood as a state of a fuel cell system in which the hydrogen concentration in the anode subsystem of the fuel cell system drops below a critical threshold, making degradation and / or a power drop possible.

[0011] In the context of this invention, operating parameters are understood as the trends of parameters that change during the operation of a fuel cell system, particularly the current supplied by the fuel cell system or the pressure applied to the hydrogen or air system of the fuel cell system.

[0012] The reduced load demand relative to the currently set load demand can be predetermined or provided, for example, as a response to an instruction, such as one provided by a user or automatic control system, to reduce the currently set load demand. Such an instruction could be provided by the driver of the vehicle, for example, by reducing the pressure on the accelerator pedal of the vehicle driven by the proposed fuel cell system. Alternatively, such an instruction could be provided, for example, by a control device for controlling the vehicle driven by the proposed fuel cell system, i.e., transmitted to the computing unit of the proposed fuel cell system.

[0013] The proposed operating method is based on an identification step that identifies a state in which anode depletion typically begins. According to the invention, the current supplied through the fuel cell system is analyzed and evaluated as a response to varying load demands. For example, it can be identified whether the current exhibits a particularly steep load gradient or a particularly large jump height, which typically causes anode depletion.

[0014] If a state is identified in which anode depletion typically begins, a threshold or threshold is dynamically determined from which the hydrogen concentration in the anode subsystem is actively increased, i.e., by adjusting the fuel cell system.

[0015] To dynamically determine the threshold, the variation in current supplied to adjust for reduced load demand is analyzed and evaluated. This can be done, for example, by analyzing and evaluating the gradient or absolute jump height of the variation, and by assigning the variation a corresponding threshold, for example, using an assignment diagram.

[0016] If it is necessary to increase the hydrogen content in the anode subsystem or to reach the corresponding operating parameters threshold, the fuel cell system can be tuned, in particular, by manipulating the purge valve and / or the hydrogen metering valve in the anode subsystem used to deliver hydrogen to the fuel cell system, so that the concentration, partial pressure, or absolute amount of hydrogen in the anode subsystem is prioritized relative to other adjustment targets.

[0017] It can be configured to determine the change in current supplied to adjust for reduced load requirements based on the change in current over time and / or the absolute change in current intensity.

[0018] In particular, the temporal variation of the current supplied by the fuel cell system, i.e., the gradient in [A / s], has proven to be a reliable measure for identifying anode depletion.

[0019] You can also set the threshold to have negative values, positive values, or to be expressed as an absolute value.

[0020] Depending on the type of eigenvalues ​​being obtained, a threshold can be selected accordingly, such that, for example, small unloading can be distinguished from large unloading, and hydrogen supply and enrichment in the anode subsystem only begin during large unloading.

[0021] Accordingly, "reaching the threshold" is understood in the context of this invention as a process in which the obtained operating parameters, such as the load gradient, have values ​​that exceed or fall below a threshold, particularly less than a negative threshold.

[0022] It can also be set that the characteristic values ​​include the change of current over time, the change of pressure in the hydrogen system of the fuel cell system over time, and / or the change of pressure in the air system of the fuel cell system over time.

[0023] Changes not only in the air system, but also in the hydrogen system or in the supplied current can indicate anode depletion.

[0024] It is also possible to increase the hydrogen content in the anode subsystem of the fuel cell system by using a hydrogen metering valve to dispense hydrogen into the anode system and opening a purge valve to discharge gas from the anode subsystem and / or reducing the electrical load of the fuel cell system and / or delaying the pressure drop in the cathode subsystem of the fuel cell system.

[0025] By opening the purge valve to discharge gas from the anode subsystem, the pressure in the anode subsystem can be reduced, thereby enabling the supply of hydrogen through the hydrogen metering valve. Specifically, the hydrogen content in the anode subsystem of the fuel cell system can be increased by closing the recirculation valve of the fuel cell system.

[0026] By reducing the electrical load until it is completely unloaded, a smaller minimum hydrogen partial pressure is required, thus minimizing the required hydrogen supply.

[0027] By delaying the pressure drop in the cathode subsystem of the fuel cell system, the pressure drop in the anode subsystem can be carried out with optimal efficiency without opening the purge valve.

[0028] You can also set it to work if one of the following conditions is met: -Since the hydrogen content in the anode subsystem began to increase after a predetermined time, - A pre-defined minimum amount of hydrogen was dispensed to increase the hydrogen content in the anode subsystem. - The hydrogen partial pressure in the anode subsystem is above a pre-defined hydrogen partial pressure threshold. This reduces the hydrogen content in the anode subsystem back to a pre-defined normal value.

[0029] Here, the hydrogen partial pressure in the anode subsystem can be estimated using a mathematical model.

[0030] Mathematical models enable the abandonment of expensive sensing devices.

[0031] According to a second aspect, the present invention relates to a fuel cell system for converting energy.

[0032] The proposed fuel cell system includes a fuel cell stack and a computing unit, wherein the computing unit is configured in a possible configuration for executing the proposed operating method.

[0033] In particular, the computing unit can be configured to determine a threshold value for a characteristic value of the operating parameters of the fuel cell system based on the change in current provided to adjust for a load demand that has been reduced relative to the current load demand, and to increase the hydrogen content in the anode subsystem of the fuel cell system if the characteristic value reaches the threshold value.

[0034] The advantages of the operating method for avoiding anode depletion during operation according to the first aspect of the present invention are also applicable to the fuel cell system for energy conversion according to the second aspect of the present invention.

[0035] Other advantages, features, and details of the invention will become apparent from the following description, in which embodiments of the invention are described in detail with reference to the accompanying drawings. Herein, the features mentioned in the claims and the description are substantially important to the invention, individually or in any combination. Attached Figure Description

[0036] The attached diagram shows: Figure 1 : A possible configuration of the proposed operating method Figure 2 : A possible configuration of the proposed fuel cell system. Detailed Implementation

[0037] exist Figure 1The diagram illustrates an operation method 100 for operating a fuel cell system. The operation method 100 includes an identification step 101, in which the state of the fuel cell system at which anode depletion begins can be identified. This can be done, for example, by analyzing and evaluating trends in the current supplied by the fuel cell system or the load demand and comparing them to pre-given thresholds.

[0038] If a state is identified in identification step 101, in which anode depletion typically begins, for example, a change in the supplied current of -300 A / s or a load jump of -300 A, then hydrogen is supplied to the anode subsystem of the fuel cell system by activating the hydrogen metering valve and / or the purge valve of the fuel cell system.

[0039] exist Figure 2 The diagram shows a fuel cell system 200. The fuel cell system 200 includes a fuel cell stack 201 having an anode subsystem 203 and a cathode subsystem 205, and a computing unit 207.

[0040] The computing unit 207 is configured to execute the running method 100 and may be, for example, a computer, processor, control device or any other programmable circuit.

Claims

1. Operating method (100) for avoiding anode starvation when a fuel cell system (200) is operated, in which operating method: - a threshold value for a characteristic value of an operating variable of the fuel cell system (200) is determined as a function of a change in the current provided for setting a reduced load demand relative to a currently set load demand, and - the hydrogen content in an anode subsystem (203) of the fuel cell system (200) is increased if the characteristic value reaches the threshold value.

2. Operating method (100) according to claim 1, characterized in that the change in the current provided for setting the reduced load demand is determined as a function of a change in time of the current and / or an absolute change in the intensity of the current.

3. Operating method (100) according to claim 1 or 2, characterized in that the threshold value has a negative value, has a positive value or is expressed as an absolute value.

4. Operating method (100) according to any of the preceding claims, characterized in that the characteristic value comprises a change in time of the current, a change in time of a pressure in a hydrogen system of the fuel cell system (200) and / or a change in time of a pressure in an air system of the fuel cell system (200).

5. Operating method (100) according to any of the preceding claims, characterized in that the hydrogen content in the anode subsystem (203) of the fuel cell system (200) is increased in such a way that hydrogen is dosed into the anode subsystem (203) by means of a hydrogen metering valve and a purge valve for discharging gas from the anode subsystem (203) is opened and / or the electrical load of the fuel cell system (200) is reduced and / or a pressure drop in a cathode subsystem (205) of the fuel cell system (200) is delayed.

6. Operating method (100) according to any of the preceding claims, characterized in that the hydrogen content in the anode subsystem (203) of the fuel cell system (200) is increased in such a way that a recirculation valve of the fuel cell system (200) is closed.

7. Operating method (100) according to any of the preceding claims, characterized in that if one of the following conditions occurs: - a predefined time has elapsed since the hydrogen content in the anode subsystem (203) was increased, - a predefined minimum amount of hydrogen has been dosed for increasing the hydrogen content in the anode subsystem (203), - the hydrogen partial pressure in the anode subsystem (203) is above a predefined hydrogen partial pressure threshold value, the hydrogen content in the anode subsystem (203) is again reduced to a predefined normal value.

8. Operating method (100) according to claim 7, characterized in that the hydrogen partial pressure in the anode subsystem (203) is estimated by means of a mathematical model.

9. Fuel cell system (200) for converting energy, wherein the fuel cell system (200) comprising: - a fuel cell stack (201), - a computing unit (207), wherein the computing unit (207) is configured to perform the operating method (100) according to any of the preceding claims 1 to 8.

10. The fuel cell system (200) according to claim 9, characterized in that the computing unit (207) is configured to - determine a threshold value for a characteristic value of an operating parameter of the fuel cell system (200) depending on a change of the current provided for setting a reduced load demand relative to a currently set load demand, and - increase a hydrogen content in the anode subsystem (203) of the fuel cell system (200) if the characteristic value reaches the threshold value.

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