Method and controller for operating a fuel cell system, and fuel cell system

Abstract

The invention relates to a method for operating a fuel cell system (200), wherein the fuel cell system (200) contains at least one fuel cell module (100) in the form of a proton exchange membrane fuel cell. The method comprises a step of determining the electric charge (247) of the fuel cell system (200) during a shutdown procedure of the fuel cell system (200) by integrating an electric current (235) between the anode and cathode of each fuel cell module (100) starting with a shutdown of an air supply to the at least one fuel cell module (100) over time. Shutting down the air supply has the effect of hermetically enclosing a predefined volume of air in the at least one fuel cell module (100). The method also comprises a step of generating an operating parameter (249) for operating the fuel cell system (200) by assessing the determined electric charge (247). The operating parameter (249) represents a tightness state of the fuel cell system (200). For the assessment, a comparison is carried out between the determined electric charge (247) and a predefined reference value, wherein the operating parameter (200) is generated depending on a result of the comparison.

Description

[0001] Description

[0002] title

[0003] Method and control device for operating a fuel cell system and fuel cell system

[0004] State of the art

[0005] The present invention relates to a method, to a corresponding control device and to a corresponding computer program product.

[0006] PEM fuel cell stacks (PEM = Proton Exchange Membrane) or polymer electrolyte fuel cell stacks comprise many individual cells that are stacked and held together by a clamping system. The core element of an individual cell is a membrane that separates the media on the anode and cathode sides. The tightness of the membrane can deteriorate over time due to a variety of damage mechanisms, such as mechanical, chemical, and thermal. During shutdown or maintenance, internal and external leakage between the anode and cathode can be checked using standard leakage tests, such as pressure drop tests. A complex single-cell voltage monitor (CVM = Cell Voltage Monitor) can detect membrane damage during operation.By choosing a special operating strategy, damage to the membrane during operation can be minimized.

[0007] Disclosure of the invention

[0008] Against this background, the approach presented here presents a method, a control unit that uses this method, and finally a corresponding computer program product according to the main claims. Advantageous embodiments emerge from the respective subclaims and the following description.

[0009] According to embodiments, leak detection in fuel cell modules can advantageously be implemented by evaluating the current curve during shutdown. Thus, for example, a potentially dangerous leak can be identified using on-board diagnostics each time the system is shut down. Complex individual cell voltage monitoring, for example, can be eliminated. In particular, timely leak detection can prevent the membrane's tightness from critically deteriorating due to a variety of damage mechanisms, e.g., mechanical, chemical, or thermal. For example, by detecting in good time that a membrane is about to leak, high efficiency can be maintained because oxygen in the air and hydrogen cannot reach the other side and react directly there without generating electricity.This can also prevent the leakage from becoming too high locally at one point, which could otherwise lead to greater heating at that point.

[0010] A method for operating a fuel cell system is presented, wherein the fuel cell system has at least one fuel cell module designed as a proton exchange membrane fuel cell, the method comprising the following steps:

[0011] Determining the electrical charge of the fuel cell system during a shutdown process of the fuel cell system by integrating an electrical current between the anode and cathode of each fuel cell module, starting with a shutdown of an air supply to the at least one fuel cell module over time, wherein a predefined air volume is hermetically enclosed in the at least one fuel cell module by shutting off the air supply; and

[0012] Generating an operating parameter for operating the fuel cell system by evaluating the determined electrical charge, wherein the operating parameter represents a tightness state of the fuel cell system, wherein a comparison is carried out between the determined electrical charge and a predefined reference value for the evaluation, wherein the operating parameter is generated depending on a result of the comparison.

[0013] A majority of fuel cell modules designed as proton exchange membrane fuel cells can also be referred to as a fuel cell stack or, more precisely, a PEM fuel cell stack (PEM = Proton Exchange Membrane;

[0014] Proton exchange membrane fuel cell stacks are also referred to as proton exchange membrane fuel cell stacks or polymer electrolyte fuel cell stacks. Such fuel cell stacks comprise many individual fuel cell modules or individual cells, which can be stacked and held together, for example, by a clamping system. Each individual cell can have a membrane that separates the media on the anode and cathode sides. Between the individual cells or individual cells,

[0015] Fuel cell modules can be arranged with so-called bipolar plates, through which cooling water can flow to dissipate heat loss from the chemical reaction. The method can also include a step of controlling the operation of the fuel cell system using the operating parameters. The fuel cell system can have at least one current sensor and, additionally or alternatively, at least one blocking device. The at least one blocking device can be designed to close off the air supply to the fuel cell stack or the at least one fuel cell module from the environment by means of flaps or valves when the fuel cell stack is shut off, such that a closed space is formed.

[0016] According to embodiments, in particular an internal leakage of fuel cell modules between the anode and cathode, as well as additional external leaks of the cathode, can be detected without complex individual cell voltage monitoring and independently of the operating strategy by means of on-board diagnostics, for example so that maintenance or servicing can be planned at an early stage.

[0017] According to one embodiment, a first operating parameter can be generated in the generating step, representing an internal seal between the anode and cathode, as well as an external seal between the cathode and the environment, if the comparison shows that the determined electrical charge corresponds to the reference value within a predefined tolerance range. Seal can be understood as a sealed state. The internal seal can represent a seal between the anode side and the cathode side. This makes it easy to determine whether the fuel cell system is properly sealed.

[0018] In the generating step, a second operating parameter can also be generated that represents an internal leak between the anode and cathode if the comparison shows that the determined electrical charge falls below the reference value by more than a predefined tolerance range. This allows an internal leak in the at least one fuel cell module to be reliably detected.

[0019] Furthermore, a third operating parameter can be generated in the generating step, representing an external leakage between the cathode and the environment, if the comparison shows that the detected electrical charge exceeds the reference value by more than a predefined tolerance range. In this way, an external leakage can be easily and reliably detected.

[0020] Furthermore, the generation step can be performed taking into account variable boundary conditions, where the boundary conditions include temperature and, additionally or alternatively, pressure. For comparison purposes, the predefined reference value for the reference boundary conditions or the determined electrical charge can be scaled depending on the currently measured boundary conditions. Thus, different environmental conditions can be taken into account in the comparison, ensuring precise and accurate results.

[0021] The method may also include a step of controlling at least one shutoff device of the fuel cell system to shut off the air supply to the at least one fuel cell module. In this way, each fuel cell module can be reliably hermetically sealed with respect to air. The method may also include a step of reading the electrical current via an interface of at least one current sensor of the fuel cell system. This allows the measured values ​​for determining the electrical charge to be obtained in a simple manner.

[0022] The approach presented here further provides a control unit configured to perform or implement the steps of a variant of a method presented here in corresponding devices. This embodiment of the invention in the form of a control unit also allows the problem underlying the invention to be solved quickly and efficiently.

[0023] In this context, a control unit can be understood as an electrical device that processes sensor signals and outputs control and / or data signals depending on them. The control unit can have an interface that can be implemented in hardware and / or software. In a hardware implementation, the interfaces can, for example, be part of a so-called system ASIC, which contains a wide variety of functions of the control unit. However, it is also possible for the interfaces to be separate integrated circuits or to consist at least partially of discrete components. In a software implementation, the interfaces can be software modules that are present, for example, on a microcontroller alongside other software modules.

[0024] Furthermore, a fuel cell system is presented, which has the following features: at least one fuel cell module designed as a proton exchange membrane fuel cell; and an embodiment of a control unit mentioned herein.

[0025] The fuel cell system can have at least one current sensor and, additionally or alternatively, at least one blocking device. The control unit can be connected to the at least one current sensor and, additionally or alternatively, to the at least one blocking device in a signal-transmitting manner. A computer program product with program code, which can be stored on a machine-readable medium such as a semiconductor memory, a hard disk memory, or an optical memory, and is used to carry out the method according to one of the embodiments described above, is also advantageous when the program product is executed on a computer or device.

[0026] The approach presented here is explained in more detail below using the attached drawings. They show:

[0027] Fig. 1 is a schematic representation of a fuel cell module;

[0028] Fig. 2 is a schematic representation of an embodiment of a fuel cell system;

[0029] Fig. 3 is a schematic diagram of a shutdown process of an embodiment of a fuel cell system;

[0030] Fig. 4 is a schematic diagram of pressure curves during a shutdown process of an embodiment of a fuel cell system; and

[0031] Fig. 5 is a flowchart of an embodiment of a method for operating a fuel cell system.

[0032] In the following description of advantageous embodiments of the present invention, the same or similar reference numerals are used for the elements shown in the various figures and having a similar effect, whereby a repeated description of these elements is omitted.

[0033] Fig. 1 shows a schematic representation of a fuel cell module 100. The fuel cell module 100 comprises a proton exchange membrane fuel cell. In other words, Fig. 1 schematically shows the structure of such a fuel cell. A fuel cell system comprises a plurality of fuel cell modules, such as the fuel cell module 100 shown here, which are arranged in a so-called fuel cell stack.

[0034] Such fuel cell stacks comprise many individual fuel cell modules or single cells, such as the fuel cell module 100 shown here, which are stacked and held together, for example, by a clamping system. Each individual cell or each fuel cell module 100 comprises a membrane 101 that separates the media on an anode side 103 or anode and a cathode side 105 or cathode. So-called bipolar plates 107 are arranged between adjacent individual cells or fuel cell modules, such as the fuel cell module 100, through which cooling water can flow to dissipate heat loss from the chemical reaction. Seals 109 are arranged between the membrane 101 and the bipolar plates 107 to seal the anode side 103 and the cathode side 105, respectively.

[0035] If the membrane is leaking, a pressure difference between the anode side 103 (anode) and the cathode side 105 (cathode) can cause hydrogen to flow from the anode side 103 to the cathode side 105, where it can react directly with the oxygen without generating electricity. This scenario is symbolically illustrated in Fig. 1 by an arrow X, which represents an internal leakage of hydrogen to the air.

[0036] Fig. 2 shows a schematic representation of an embodiment of a fuel cell system 200. The fuel cell system 200 comprises at least one fuel cell module 100 embodied as a proton exchange membrane fuel cell, which corresponds to or is similar to the fuel cell module of Fig. 1. In the illustration of Fig. 2, the fuel cell system 200 comprises, by way of example, only four fuel cell modules 100. The fuel cell system 200 can have any suitable, deviating number of fuel cell modules 100. A plurality of fuel cell modules 100 are arranged in the fuel cell system 200 in a so-called stack 210.

[0037] The fuel cell system 200 further comprises at least one shut-off device 220 configured to shut off the air supply to the at least one fuel cell module 100. The fuel cell system 200 also comprises at least one current sensor 230 configured to detect an electrical current 235 between the anode and cathode of each fuel cell module 100 and to provide it in the form of measurement data.

[0038] The fuel cell system 200 further comprises a control unit 240 configured to operate the fuel cell system 200 or to control its operation. The control unit 240 is connected in a signal-transmitting manner to the at least one fuel cell module 100 or the stack 210, or more precisely, to at least one current sensor 230 associated with the at least one fuel cell module 100 or the stack 210.

[0039] According to one embodiment, the control unit 240 comprises a control device 242 configured to control the at least one blocking device 220 using a control signal 225 in order to shut off the air supply to the at least one fuel cell module 100. Furthermore, according to one embodiment, the control unit 240 comprises a reading device 244 configured to read the electrical current 235 from the at least one current sensor 230 via an interface 241.

[0040] The control unit 240 comprises a determination device 246 configured to determine the electrical charge 247 of the fuel cell system 200 or of the stack 210 during a shutdown process of the fuel cell system 100 by integrating the electrical current 235 over time, beginning with the shutdown of an air supply to the at least one fuel cell module 100. By shutting off the air supply, a predefined air volume is hermetically sealed in the at least one fuel cell module 100. This can be achieved, in particular, by controlling the at least one blocking device 220.

[0041] The control unit 240 also includes a generating device 248 configured to generate an operating parameter 249 for operating the fuel cell system 200 by evaluating the determined electrical charge 247. To evaluate the electrical charge 247, the generating device 248 is configured to perform a comparison between the determined electrical charge 247 and a predefined reference value and to generate the operating parameter 249 depending on the result of the comparison. The operating parameter 249 represents a leak-tightness state of the fuel cell system 200.

[0042] For example, the generating device 248 is designed to generate a first operating parameter 249 or the operating parameter 249 with a first value, which represents an internal tightness between the anode and cathode and an external tightness between the cathode and the environment, if the comparison carried out shows that the determined electrical charge 247 corresponds to the reference value within a predefined tolerance range. The generating device 248 is thus designed to generate the first operating parameter 249 or the operating parameter 249 with the first value, if internal and external tightness is present. Furthermore, the generating device 248 is designed, for example, to generate a second operating parameter 249 orto generate the operating parameter 249 with a second value that represents an internal leakage between the anode and cathode if the comparison carried out shows that the determined electrical charge 247 falls below the reference value by more than a predefined tolerance range. Accordingly, the generating device 248 is also designed, for example, to generate a third operating parameter 249 or the operating parameter 249 with a third value that represents an external leakage between the cathode and the environment if the comparison carried out shows that the determined electrical charge 247 exceeds the reference value by more than a predefined tolerance range. The generating device 248 is thus designed to generate the second or third operating parameter 249 or operating parameter 249 with the second or third value if internal or external tightness is present.

[0043] According to one embodiment, the generating device 248 is configured to generate the operating parameter 249 taking into account variable boundary conditions. Such boundary conditions include a temperature and / or a pressure. For comparison purposes, the generating device 248 is configured to scale a predefined reference value for reference boundary conditions or the determined electrical charge depending on the currently measured boundary conditions.

[0044] Fig. 3 shows a schematic diagram of a shutdown process of an exemplary embodiment of a fuel cell system. The shutdown process relates to the fuel cell system from one of the figures described herein or a similar fuel cell system. The diagram plots the curves of various variables over time t, more specifically the curves of an electrical voltage 351, an air flow 352, a hydrogen flow 353, and the electrical current 235, with a current setpoint 354 also shown. Furthermore, the electrical charge 247 is shown as an area between the graph of the air flow 352 and the graph of the electrical current 235.

[0045] The shutdown process is thus shown in Fig. 3. To shut down, first the air supply or air flow 352 is stopped and valves that prevent air from flowing in are closed. Since less oxygen is available for the chemical reaction, the electric current 235 and the electric voltage 351 drop over time. Then the hydrogen supply or hydrogen flow 353 is also turned off. In the enclosed volume on the cathode side, an oxygen atom O reacts with two hydrogen ions H+ and two electrons e- to form a water molecule H2O. There is therefore a direct relationship between the electric charge 247 and the amount of oxygen that was in the enclosed space. The area between the graph of the air flow 352 and the graph of the electric current 235 after the air supply has been stopped therefore describes the number of electrons and thus the charge that were required for the reaction with oxygen.

[0046] Fig. 4 shows a schematic diagram of pressure curves during a shutdown process of an embodiment of a fuel cell system. The shutdown process relates to the fuel cell system from one of the figures described herein or a similar fuel cell system. In the diagram, curves of the pressure p for air 452 (pi_uft) and for hydrogen 453 (PH2) are plotted against time t, with a time 455 at which the air supply is shut off also being shown. Fig. 4 thus shows the pressure curve after the air is shut off, here from time 455 onwards. While the hydrogen pressure 453 remains constant due to the supply, the pressure on the cathode side or the air pressure 452 collapses because the gaseous oxygen reacts with hydrogen to form water.

[0047] Fig. 5 shows a flowchart of an embodiment of a method 540 for operating a fuel cell system. The method 540 for operating can be executed to operate a fuel cell system or to control the operation of a fuel cell system. The method 540 for operating can be carried out in connection with the fuel cell system from one of the figures described herein or a similar fuel cell system. The steps of the method 540 for operating can be executed using a control unit from one of the figures described herein or a similar control unit.

[0048] The operating method 540 comprises a determining step 546 and a generating step 548. In determining step 546, the electrical charge of the fuel cell system is determined during a shutdown process of the fuel cell system by integrating an electrical current between the anode and cathode of each fuel cell module over time, beginning with the shutting off of an air supply to the at least one fuel cell module. By shutting off the air supply, a predefined air volume is hermetically enclosed in the at least one fuel cell module. Subsequently, in generating step 548, an operating parameter for operating the fuel cell system is generated by evaluating the determined electrical charge. The operating parameter represents a tightness state of the fuel cell system.For evaluation, a comparison is made between the determined electrical charge and a predefined reference value. The operating parameter is generated based on the result of the comparison.

[0049] According to one embodiment, the operating method 540 further comprises a step 542 of controlling at least one blocking device of the fuel cell system to shut off the air supply to the at least one fuel cell module. Additionally or alternatively, the operating method 540 further comprises a step 544 of reading the electrical current via an interface from at least one current sensor of the fuel cell system.

[0050] With reference to the figures described herein, an embodiment is summarized again below and, in other words, briefly explained.

[0051] According to exemplary embodiments, in particular, a diagnosis of a leakage state of a fuel cell system 200 is enabled. The electrical charge 247 is determined by means of the control unit 240 and / or the method 540 each time the fuel cell system 200 is shut down by integrating the current profile or the profile of the electrical current 235 after the air has been shut down over time. An evaluation of the electrical charge 247 is then performed. If the electrical charge 247 decreases over the running time under the same boundary conditions, this means that less oxygen was available for power generation. A reduction in the electrical charge 247 is therefore an indication of internal leakage of hydrogen to the cathode side 105. An increase in the electrical charge 247 means that more oxygen is available.This is an indication that the cathode side 105 is leaking to the outside and additional air is flowing onto the cathode side 105 from the outside.

[0052] Relevant influencing parameters and fundamental principles are explained below: The relevant value for the electrical charge 247 is the amount of oxygen n. The electrical charge 247 is proportional to the amount of oxygen n. The dependence of the amount of oxygen n on pressure p and temperature T is described by the general gas equation n = (p * V) / (R * T). The electrical charge 247 is therefore determined for a reference temperature and a reference pressure. If the engine is switched off, for example, at a higher temperature T*, the electrical charge 247 can be calculated from the lower electrical charge 247* determined during this switching off process using the general gas equation, and this switching off process can also be evaluated. The evaluation is part of the software of the control unit 240. The at least one current sensor 230 is designed to evaluate the electrical current 235 during switching off until the electrical current 235 has become zero.

[0053] The exemplary embodiments described and shown in the figures are selected only as examples. Different exemplary embodiments can be combined with one another in their entirety or with regard to individual features. One exemplary embodiment can also be supplemented by features of another exemplary embodiment. Furthermore, the method steps presented here can be repeated and performed in a different order than the one described.

[0054] If an embodiment comprises an “and / or” link between a first feature and a second feature, this is to be read as meaning that the embodiment according to one embodiment has both the first feature and the second feature and according to another embodiment has either only the first feature or only the second feature.

Claims

Claims 1. A method (540) for operating a fuel cell system (200), wherein the fuel cell system (200) comprises at least one fuel cell module (100) designed as a proton exchange membrane fuel cell, the method (540) comprising the following steps: Determining (546) the electrical charge (247) of the fuel cell system (200) during a shutdown process of the fuel cell system (200) by integrating an electrical current (235) between the anode (103) and cathode (105) of each fuel cell module (100), beginning with a shutdown of an air supply to the at least one fuel cell module (100) over time, wherein a predefined air volume is hermetically enclosed in the at least one fuel cell module (100) by shutting off the air supply; and Generating (548) an operating parameter (249) for operating the fuel cell system (200) by evaluating the determined electrical charge (247), wherein the operating parameter (249) represents a tightness state of the fuel cell system (200), wherein a comparison is carried out between the determined electrical charge (247) and a predefined reference value for the evaluation, wherein the operating parameter (200) is generated depending on a result of the comparison.

2. Method (540) according to claim 1, wherein in the generating step (548) a first operating parameter (249) is generated which represents an internal tightness between the anode (103) and the cathode (105) and an external tightness between the cathode (105) and the environment, if the comparison shows that the determined electrical charge (247) agrees with the reference value within a predefined tolerance range.

3. Method (540) according to one of the preceding claims, wherein in the generating step (548) a second operating parameter (249) is generated which represents an internal leakage between the anode (103) and the cathode (105) if the comparison shows that the determined electrical charge (247) falls below the reference value by more than a predefined tolerance range.

4. Method (540) according to one of the preceding claims, wherein in the generating step (548) a third operating parameter (249) is generated which represents an external leakage between the cathode (105) and the environment if the comparison shows that the determined electrical charge (247) exceeds the reference value by more than a predefined tolerance range.

5. Method (540) according to one of the preceding claims, wherein the step (548) of generating is carried out taking into account variable boundary conditions, wherein the boundary conditions comprise a temperature and / or a pressure, wherein for the comparison the reference value predefined for reference boundary conditions or the determined electrical charge (247) is scaled depending on currently measured boundary conditions.

6. Method (540) according to one of the preceding claims, comprising a step (542) of controlling at least one blocking device (220) of the fuel cell system (200) in order to shut off the air supply to the at least one fuel cell module (100).

7. Method (540) according to one of the preceding claims, comprising a step (544) of reading the electrical current (235) via an interface (241) from at least one current sensor (230) of the fuel cell system (200).

8. Control device (240) which is designed to carry out the steps of a method (540) according to one of the preceding claims in corresponding devices (242, 244, 246, 248).

9. A fuel cell system (200) comprising: at least one fuel cell module (100) configured as a proton exchange membrane fuel cell; and a control unit (240) according to claim 8.

10. Computer program product with program code for carrying out the method (540) according to one of claims 1 to 7, when the program product is executed on a device.

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