Method for operating fuel cell system

Abstract

The invention relates to a method for operating a fuel cell system (2), comprising: a step of detecting (100) data for determining a current membrane humidity of the fuel cell system (2) by means of a sensor unit (20); a step of determining (200), by means of a processing unit (22), a current membrane humidity of the fuel cell system (2) on the basis of the detected data; and a step of explicitly adjusting (400), by means of a control unit (24), at least one of a total pressure (PGes) of the cathode gas and a target parameter of a stoichiometric ratio (lambda) of the cathode gas on the basis of the determined current membrane humidity target.

Description

Technical Field

[0001] The invention is based on a method for operating a fuel cell system, a fuel cell system and a motor vehicle comprising such a fuel cell system. Background Art

[0002] Hydrogen-based fuel cell systems are seen as the mobility concept of the future, as they only emit water as exhaust gas and enable fast refueling times. However, there is still room for optimization in terms of the efficiency and service life of fuel cell systems.

[0003] Thus, in fuel cell systems, conflicts may arise between stack requirements and subsystem limitations. This problem exists in particular when a subsystem is to be designed for different stacks with different requirements. However, even when the subsystems are to be specifically coordinated with the respective stacks, inconsistencies may also occur between stack requirements and subsystem limitations due to the large operating ranges in the individual operating points (e.g., 5-100% oxygen consumption and corresponding air mass flow at pressures between 1 and >3 bar). The mentioned inconsistencies may lead in particular to membrane humidity that is too high or too low, which not only significantly reduces the achievable power of the fuel cell system, but also leads to irreversible damage to the fuel cell system. Summary of the invention

[0004] According to a first aspect, the subject matter of the invention is a method having the features of an independent method claim, and according to a second aspect, the subject matter of the invention is a fuel cell system having the features of an independent system claim. Further features and details of the invention are derived from the corresponding dependent claims, the description and the drawings. It goes without saying that the features and details described in connection with the method according to the invention are also associated with the fuel cell system according to the invention and vice versa, so that with respect to the disclosure of the individual inventive aspects, reference is always made to one another or can be made to one another.

[0005] The method according to the invention or the fuel cell system according to the invention is used in particular to compensate for excessive drying and excessive humidity of the membrane of the fuel cell of the fuel cell system during operation and thereby to safely avoid irreversible damage caused by overflow of the membrane or exhaustion of reactants due to excessive drying of the membrane. As a result, not only the efficiency and reliability of the fuel cell system can be improved, but also the service life of the fuel cell can be significantly extended. In addition, the advantages mentioned are achieved in a structurally simple and cost-effective manner and method by a specific method or a specific configuration according to the invention of a specific fuel cell system. By the configuration provided according to the invention, the method according to the invention can also be integrated into an existing fuel cell system in a simple and cost-effective manner.

[0006] Here, the method according to the invention for operating a fuel cell system comprises the following steps: detecting data for determining the current membrane humidity of the fuel cell system by means of a sensor unit; determining the current membrane humidity of the fuel cell system by means of a processing unit based on the detected data; and adjusting at least one of the target parameters of the total pressure of the cathode gas and the stoichiometric ratio of the cathode gas by means of a control unit based on the determined current membrane humidity. It goes without saying that the two mentioned target parameters (simultaneously or successively) can also be adjusted in a targeted manner.

[0007] In the context of the present invention, the current membrane humidity can be understood in particular as the current water content of the membrane of the fuel cell of a specific fuel cell system, which water content must not be too low, but also must not be too high, in order to achieve the most efficient and durable operation of the fuel cell system. According to the present invention, the total pressure of the cathode gas can be understood in particular as the measurable cathode outlet pressure at the cathode output, which cathode outlet pressure can in particular be variable with the amount of air supplied. Preferably, the stoichiometric ratio of the cathode gas can be understood as the inverse of the turnover of the cathode gas in the fuel cell reaction. Preferably, the cathode gas is supplied in a superstoichiometric ratio, wherein the stoichiometric ratio can in particular be between 1 and 4.

[0008] In this case, the method according to the invention can be used in particular in a fuel cell-operated motor vehicle. Likewise, however, use in other fuel cell-operated transport vehicles such as cranes, ships, rail vehicles, flying objects or also in stationary fuel cell-operated objects is also conceivable. In this case, the method according to the invention can be used in particular in a PEM fuel cell, or the fuel cell system according to the invention is preferably designed as a PEM fuel cell system.

[0009] In the context of the present invention, it has been recognized that in order to ensure efficient and system-friendly operation of the fuel cell system, it is necessary to operate the fuel cell system at a predetermined target activity in a stable operating strategy. It is not sufficient to assign a combination of target parameters (such as cathode outlet pressure and / or cathode stoichiometric ratio) to each current intensity and temperature in order to ensure sufficient membrane humidity. More precisely, it has been recognized that if the target parameters (such as cathode outlet pressure and / or cathode stoichiometric ratio) cannot be set optimally, for example due to system limitations, then the optimal outlet activity will not be achieved. Deviations. Thus, in the case of too high a pressure, there is a risk of too wet operation and a risk of flooding. In addition, in the case of too low a pressure, there is a risk of too dry operation and drying out of the membrane. Likewise, too high a cathode stoichiometry can lead to too dry operation and drying out of the membrane, while too low a cathode stoichiometry can lead to too wet operation and a risk of flooding.

[0010] With regard to the structurally simple and at the same time accurate determination of the current membrane humidity of the fuel cell system, it can be provided according to the invention in particular that the current membrane humidity of the fuel cell system is determined by determining the current outlet activity at the cathode outlet of the fuel cell system, wherein a targeted adjustment of at least one of the target parameters of the total pressure of the cathode gas and the stoichiometric ratio of the cathode gas is preferably carried out based on a comparison of the current outlet activity at the cathode outlet of the fuel cell system with at least one limit value for the outlet activity at the cathode outlet of the fuel cell system. Preferably, at least two limit values ​​or limit value curves can be used here, one for a minimum outlet activity at a specific current intensity and temperature and one for a maximum outlet activity at a specific current intensity and temperature. The current outlet activity should lie between these limit values ​​or limit value curves, so that no targeted adjustment of at least one of the target parameters of the total pressure of the cathode gas and the stoichiometric ratio of the cathode gas should be carried out. However, if the current outlet activity is not within this range, an adjustment should be carried out.

[0011] According to the invention, within the framework of the most economical possible operation of a specific fuel cell system, it can be advantageously provided that a targeted adjustment of at least one of the target parameters of the total pressure of the cathode gas and the stoichiometric ratio of the cathode gas is carried out taking into account minimizing the power of the compressor for compressing the cathode gas.

[0012] According to the invention, within the framework of determining the current membrane humidity of the fuel cell system as accurately as possible and thus preventing inefficient and system-damaging operation of the fuel cell system as reliably as possible, it can also be provided that data for determining the current oxygen partial pressure at the cathode outlet of the fuel cell system are additionally detected by means of a sensor unit and the current oxygen partial pressure at the cathode outlet of the fuel cell system is determined by means of a processing unit on the basis of the detected data, wherein a targeted adjustment of at least one of the target parameters of the total pressure of the cathode gas and the stoichiometric ratio of the cathode gas is preferably additionally performed based on the determined current oxygen partial pressure at the cathode outlet of the fuel cell system by means of a control unit. It goes without saying that a specific sensor unit and / or processing unit can also be a sensor unit and / or processing unit that has already been described with respect to the detection of parameters or the determination of the current membrane humidity. Likewise, it is conceivable, for example, that (especially in stable operation) the targeted adjustment of at least one of the target parameters of the total pressure of the cathode gas and the stoichiometric ratio of the cathode gas is preferably additionally performed based on other variables such as, for example, a minimum velocity of the cathode gas for liquid water discharge or the like.

[0013] According to the invention, within the framework of the most economical operation of a specific method for operating a fuel cell, it can also be provided that, before a targeted adjustment of at least one of the target parameters of the total pressure of the cathode gas and the stoichiometric ratio of the cathode gas is made based on the determined current membrane humidity, an evaluation of the current membrane humidity and / or the current oxygen partial pressure is performed, wherein the evaluation of the current membrane humidity and / or the current oxygen partial pressure is preferably performed with respect to the level of the deviation from the limit value for the membrane humidity and / or the level of the current oxygen partial pressure and / or with respect to the current state of the fuel cell system and / or with respect to the field of application of the fuel cell system. By means of the advantageously provided evaluation, it is possible that an adjustment only has to be made when an adjustment is actually necessary. If the deviation of the value of the membrane humidity is still acceptable or the system has not yet aged, then in the case of small deviations, no immediate intervention is necessary.

[0014] With regard to the possibility of targeted compensation of subsystem limitations, it can also be specifically provided that, before a targeted adjustment of at least one of the target parameters of the total pressure of the cathode gas and the stoichiometric ratio of the cathode gas is made based on the determined current membrane humidity, an evaluation of the current membrane humidity and / or the current oxygen partial pressure is performed, wherein the evaluation is preferably performed with respect to a limitation of the adjustability of one of the target parameters of the total pressure of the cathode gas and the stoichiometric ratio of the cathode gas, wherein, based on the evaluation, in particular, the total pressure of the cathode gas or the stoichiometric ratio of the cathode gas is adjusted in order to compensate for the limitation of the adjustability of the respective other component. Possible subsystem limitations can be, for example, a minimum or maximum air mass flow that can be supplied, which can be limited, for example, by a pump limit of a compressor, which can be set either not small enough or not large enough. Thus, for example, a settable minimum mass flow through the air system can already result in too small an outlet activity without additional correction of the pressure, so that a too dry membrane state can occur. If such subsystem limitations are identified within the framework of the evaluation advantageously provided according to the invention, the limitation of the adjustability of one component (cathode stoichiometric ratio) can be compensated by targeted adjustment of other components (total pressure), so that the desired activity or is continued to be maintained. Here, a possible subsystem limitation can also be the maximally achievable minimum pressure, without which adjustment a very wet membrane state can occur until the membrane overflows. By specifically adjusting the stoichiometric ratio of the cathode gas, the desired target humidity or targeted membrane humidity can be set despite the pressure limitations. Other variants for possible limitations in the air system can be the minimum and / or maximum compressor speed, the maximum electrical drive power of the compressor and the maximum temperature of the compressor impeller.

[0015] According to the invention, within the framework of a method for operating a fuel cell system that can be controlled in a simple, preferably automated manner, it can also be advantageously provided that the method is implemented in a self-learning manner, wherein within the framework of the implementation of the self-learning, after an initial learning phase, changes caused by aging can preferably be compensated. Advantageously, it can be provided that changes caused by aging can involve changed pressure losses of components, changed operating limits, restarting operation after repair or replacement of components.

[0016] In the context of the present invention, it can also be advantageously provided that individual, multiple or all mandatory and / or optional steps of the method according to the invention can be carried out in the proposed sequence, but can also be carried out in a sequence different from the proposed sequence. In this case, individual, multiple or all mandatory and / or optional steps of the method according to the invention can in particular be carried out cyclically, for example periodically repeatedly.

[0017] Furthermore, it goes without saying that individual, several or all of the mandatory and optional steps of the method according to the invention can also be implemented specifically by a computer.

[0018] Furthermore, the subject of the invention is a fuel cell system, in particular a fuel cell system for implementing the method described above. Here, the fuel cell system according to the invention comprises an anode path with an anode, an anode gas supply pipe and an anode gas return pipe, the fuel cell system comprises a cathode path with a cathode, a cathode gas supply pipe and a cathode gas outlet pipe, the fuel cell system comprises a sensor unit for detecting data for determining the current membrane humidity of the fuel cell system, a processing unit for determining the current membrane humidity of the fuel cell system, and a control unit for targeted adjustment of at least one of the total pressure of the cathode gas and the target parameter of the stoichiometric ratio of the cathode gas. The fuel cell system thus has the same advantages as those already described in detail in connection with the method according to the invention.

[0019] With regard to a fast and structurally uncomplicated possibility for exact and targeted adjustment of the target parameters, it is advantageously possible to specifically provide valves and compressors for targeted adjustment of at least one of the target parameters of the total pressure of the cathode gas and the stoichiometric ratio of the cathode gas.

[0020] Under the framework of simple, preferably automated control of the fuel cell system according to the present invention, it can be specifically provided that the fuel cell system is constructed in the form of a self-learning system. Here, the self-learning system can be constructed, for example, to learn from the logic and independently input the set value or target value and improve the subsystem regulation in this way. For this purpose, the fuel cell system can be equipped with an initial target parameter group, for example. In the first stage, the fuel cell system can, for example, at the first start, from the initial parameterization, by means of a reactive regulation path, especially in consideration of the subsystem limitations currently occurring, derive new set value pre-set parameters. Then, the new set value can preferably be fed back and used as data input for self-learning optimization. Then, in the second stage, the fuel cell system can preferably be improved at each operation until the optimal state is reached. In the third stage (within the service life of the system), the frequency of the change of the set value can then preferably be significantly reduced and can, for example, be performed only once a month. If the fuel cell system is relevantly changed during a larger maintenance (for example, when replacing / replacing a component), re-initialization and training can be performed.

[0021] The subject matter of the invention is also a motor vehicle, which comprises the fuel cell system described above. The motor vehicle according to the invention thus has the same advantages as those already described in detail with respect to the method according to the invention or the fuel cell system according to the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] 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 in the description may be essential to the invention individually or in any combination.

[0023] The accompanying drawings show:

[0024] Figure 1 A schematic diagram showing individual steps of the method according to the invention for operating a fuel cell system,

[0025] Figure 2 A schematic diagram shows a fuel cell system according to the invention according to a first exemplary embodiment,

[0026] Figure 3 Further schematic illustrations show individual steps of the method according to the invention for operating a fuel cell system within the context of carrying out a self-learning process. DETAILED DESCRIPTION

[0027] Figure 1The schematic diagram shows individual steps of the method according to the invention for operating a fuel cell system 2 .

[0028] As per Figure 1 As can be seen, the method according to the invention comprises: a step of detecting 100 data for determining the current membrane humidity of the fuel cell system 2 by means of the sensor unit 20; a step of determining 200 the current membrane humidity of the fuel cell system 2 by means of the processing unit 22 based on the detected data; and a step of specifically adjusting 400 the total pressure P of the cathode gas based on the determined current membrane humidity by means of the control unit 24. Ges and a step of determining at least one of a target parameter of a stoichiometric λ of the cathode gas.

[0029] Here, it can be advantageously provided that the current membrane humidity of the fuel cell system 2 is determined 200 by determining the current outlet activity a at the cathode outlet 42 of the fuel cell system 2, wherein the total pressure P of the cathode gas is Ges The targeted adjustment 400 of at least one of the target parameters of the stoichiometric ratio λ of the cathode gas is preferably based on a comparison of the current outlet activity a at the cathode outlet 42 of the fuel cell system 2 with at least one limit value for the outlet activity a at the cathode outlet 42 of the fuel cell system 2 .

[0030] Here, according to the present exemplary embodiment of the method according to the invention for operating the fuel cell system 2, it is further provided that the total pressure P of the cathode gas is reduced with a view to minimizing the power of the compressor 36 for compressing the cathode gas. Ges A target of at least one of a target parameter of a stoichiometric ratio λ of the cathode gas is explicitly adjusted 400 .

[0031] Furthermore, according to the present exemplary embodiment of the method according to the invention for operating the fuel cell system 2, provision can be made that, in addition, a measurement is carried out by means of the sensor unit 20′ (or the sensor unit 20) for determining the current oxygen partial pressure pO at the cathode outlet 42 of the fuel cell system 2. 2 The data of the detection 100 ', and based on the detected data, with the help of the processing unit 22 '(or the processing unit 22) to perform the current oxygen partial pressure pO at the cathode outlet 42 of the fuel cell system 2 2 Determination 200', wherein the total pressure P of the cathode gas Ges The target-specific adjustment 400 of at least one of the target parameters of the stoichiometric ratio λ of the cathode gas can additionally be based on the determined current oxygen partial pressure pO at the cathode outlet 42 of the fuel cell system 2. 2 This is done with the aid of the control unit 24 .

[0032] Likewise, it can be provided that, based on the determined current membrane humidity, the total pressure P of the cathode gas Ges Before at least one of the target parameters of the stoichiometric ratio λ of the cathode gas is adjusted 400, the current membrane humidity and / or the current oxygen partial pressure pO is adjusted. 2 The evaluation 300 is preferably for the total pressure P of the cathode gas. Ges and the limitation of the adjustability of one of the target parameters of the stoichiometric ratio λ of the cathode gas, wherein, based on the evaluation 300 , in particular the total pressure P of the cathode gas is determined. Ges Or the stoichiometric ratio λ of the cathode gas is set in a targeted manner in order to compensate for the limitations of the adjustability of the respective other components.

[0033] Finally, it can also be provided that the method is carried out in a self-learning manner, wherein within the scope of the implementation of the self-learning, after an initial learning phase, changes caused by aging can preferably be compensated.

[0034] Figure 2 A schematic illustration of a fuel cell system 2 according to the invention is shown according to a first exemplary embodiment.

[0035] As per Figure 2 It can be seen that the fuel cell system 2 according to the present invention includes an anode path, which has an anode 8, an anode gas supply pipe 12 and an anode gas return pipe or an outlet pipe 16, and the fuel cell system includes a cathode path, which has a cathode 10, a cathode gas supply pipe 14 and a cathode gas outlet pipe 18. The fuel cell system includes a sensor unit 20 for detecting 100 data for determining the current membrane humidity of the fuel cell system 2, a processing unit 22 for determining 200 the current membrane humidity of the fuel cell system 2, and a control unit 24 for specifically adjusting at least one of the target parameters of the total pressure of the cathode gas and the stoichiometric ratio of the cathode gas.

[0036] To control the gas flows, the fuel cell system 2 has various valves 28 .

[0037] For targeted adjustment of at least one of the target parameters of the total pressure of the cathode gas and the stoichiometric ratio of the cathode gas, the sensor unit 22 , the processing unit 24 and the control unit 26 can be connected to each other and to the compressor 36 via a control cable 40 or wirelessly.

[0038] In order to detect 100 data for determining the current membrane moisture of the fuel cell system 2 , the sensor unit 20 can also preferably be connected to the cathode output 42 .

[0039] Furthermore, it can be seen that a water separator 30 is arranged for separating water in the anode gas return line 16 , which is connected to a water tank 32 for storing the separated water.

[0040] Figure 3 Further schematic illustrations show individual steps of the method according to the invention for operating a fuel cell system 2 within the context of carrying out a self-learning process.

[0041] As per Figure 3 It can be seen that the method according to the invention in a first phase initially comprises an initial parameterization 500a (preferably taking into account currently occurring subsystem limitations) from the first start, wherein new setpoints are used as data input for subsequent self-learning optimization.

[0042] In the second phase, the fuel cell system can then preferably be improved in each operation until the optimal state is reached. Here, optimization according to new setpoints 600a, adjustment of target variables 600b and feedback of new target values ​​600c are successively carried out, which can be stored within the framework of subsystem control 500f.

[0043] In the third phase (during the service life of the system), the frequency of changes of the setpoint 700a can then preferably be significantly reduced and carried out, for example, only once a month.

[0044] If the fuel cell system is relevantly changed in the event of major maintenance (eg, when replacing / changing a component), a re-initialization and training 800a may be performed.

Claims

1. A method for operating a fuel cell system (2), the method comprising the following steps: - detecting (100) data for determining the current membrane moisture of the fuel cell system (2) by means of a sensor unit (20), - determining (200) the current membrane humidity of the fuel cell system (2) by means of a processing unit (22) based on the detected data, - targeted regulation (400) of the total pressure (P Ges ) and at least one of the target parameters of the stoichiometric ratio (λ) of the cathode gas.

2. The method according to claim 1, characterized in that The current membrane humidity of the fuel cell system (2) is determined (200) by determining the current outlet activity (a) at the cathode outlet (42) of the fuel cell system (2), wherein the total pressure (P Ges ) and the stoichiometric ratio (λ) of the cathode gas is preferably based on a comparison of a current outlet activity (a) at the cathode outlet (2) of the fuel cell system (2) with at least one limit value for the outlet activity (c) at the cathode outlet (42) of the fuel cell system (2).

3. The method according to claim 1 or 2, characterized in that: The total pressure (P) of the cathode gas is controlled in such a way that the power of the compressor used to compress the cathode gas is minimized. Ges ) and a target parameter of the stoichiometric ratio (λ) of the cathode gas are explicitly adjusted (400).

4. The method according to any one of the preceding claims, characterized in that Additionally, data for determining a current oxygen partial pressure (pO2) at a cathode outlet (42) of the fuel cell system (2) are detected (100') by means of a sensor unit (20'), and based on the detected data, the current oxygen partial pressure (pO2) at the cathode outlet (42) of the fuel cell system (2) is determined (200') by means of a processing unit (22'), wherein the total pressure (P Ges ) and the stoichiometric ratio (λ) of the cathode gas is additionally adjusted (400) on the basis of a determined current oxygen partial pressure (pO2) at the cathode outlet (42) of the fuel cell system (2) with the aid of the control unit (24).

5. The method according to any one of the preceding claims, characterized in that Based on the determined current membrane humidity, the total pressure of the cathode gas (P Ges ) and the stoichiometric ratio (λ) of the cathode gas, an evaluation (300) of the current membrane humidity and / or the current oxygen partial pressure (pO2) is performed before a targeted adjustment (400) of at least one of the target parameters of the cathode gas stoichiometric ratio (λ) and the cathode gas stoichiometric ratio (λ) is performed, wherein the evaluation of the current membrane humidity and / or the current oxygen partial pressure (pO2) is performed with respect to the height of the deviation from the limit values ​​for the membrane humidity and / or the current oxygen partial pressure (pO2) and / or with respect to the current state of the fuel cell system (2) and / or with respect to the field of use of the fuel cell system (2).

6. The method according to any one of the preceding claims, characterized in that Based on the determined current membrane humidity, the total pressure of the cathode gas (P Ges ) and the target parameters of the stoichiometric ratio (λ) of the cathode gas, an evaluation (300) of the current membrane humidity and / or the current oxygen partial pressure (pO2) is performed before a targeted adjustment (400) of at least one of the target parameters of the stoichiometric ratio (λ) of the cathode gas is carried out, wherein the evaluation (300) is preferably based on the total pressure (P Ges ) and the limit of the adjustability of one of the target parameters of the stoichiometric ratio (λ) of the cathode gas, wherein based on the evaluation (300) in particular the total pressure (P Ges ) or the stoichiometric ratio (λ) of the cathode gas is specifically adjusted in order to compensate for the limitations of the adjustability of the respective other components.

7. The method according to any one of the preceding claims, characterized in that The method is carried out in a self-learning manner, wherein within the scope of the self-learning implementation, after an initial learning phase, changes caused by aging are preferably compensated.

8. A fuel cell system (2), in particular a fuel cell system for carrying out the method according to any one of claims 1 to 7, comprising: - an anode path, the anode path having an anode (8), an anode gas supply pipe (12) and an anode gas return pipe (16), - a cathode path, the cathode path comprising a cathode (10), a cathode gas supply pipe (14) and a cathode gas outlet pipe (18), a sensor unit (20) for detecting (100) data for determining a current membrane humidity of the fuel cell system (2), a processing unit (22) for determining (200) a current membrane humidity of the fuel cell system (2), a control unit (24) for targeted regulation (400) of the total pressure (P Ges ) and at least one of the target parameters of the stoichiometric ratio (λ) of the cathode gas.

9. The fuel cell system (2) according to claim 8, characterized in that: A method for specifically adjusting (400) the total pressure (P) of the cathode gas is provided. Ges ) and a valve (28) and a compressor (36) for controlling at least one of a target parameter of a stoichiometric ratio (λ) of the cathode gas.

10. The fuel cell system (2) according to any one of claims 8 to 9, characterized in that: The fuel cell system (2) is designed as a self-learning system.

11. A motor vehicle comprising a fuel cell system (2) according to any one of claims 8 to 10.

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