Method for operating a fuel cell device, fuel cell device and fuel cell vehicle

Abstract

Method for operating a fuel cell device (1) with a fuel tank (5), a fuel cell stack (2) and a fuel line (8) connecting the fuel tank (5) to the fuel cell stack (2), to which a plurality of injectors (13) is assigned, for the control of which a 2-point hysteresis controller (19) is provided, comprising the steps: a) Check whether the fuel cell stack (2) is operated in a lower load range for which the supply from only one of the injectors (13) is sufficient, b) in the event that the fuel cell stack (2) is operated in the lower load range, rolling control of the injectors, i.e. use of the first injector for the first hysteresis and successive use of one of the further injectors (13) for the further hystereses, until after all injectors (13) have been used, the first injector (13) is used again, c) temporal recording of the pressure increase for each injector (13) when it is put into use as a quality criterion for the fuel flow, d) Comparison of the pressure increases of the injectors (13), e) Issue a warning message if a difference between the pressure increases exceeds a specified or specifiable threshold.

Description

[0001] The invention relates to a method for operating a fuel cell device having a fuel tank, a fuel cell stack and a fuel line connecting the fuel tank to the fuel cell stack, to which a plurality of injectors is assigned, for the control of which a 2-point hysteresis controller is provided, comprising the steps: a) Check whether the fuel cell stack is operated in a lower load range for which the supply from only one of the injectors is sufficient, b) in the event that the fuel cell stack is operated in the lower load range, rolling control of the injectors, i.e. use of the first injector for the first hysteresis and successive use of one of the other injectors for the further hystereses, until the first injector is used again after all injectors have been used, c) temporal recording of the pressure increase for each injector at the start of its use as a quality criterion for the fuel flow, d) Comparison of the pressure increases of the injectors, e) Issue a warning message if a difference between the pressure increases exceeds a specified or specifiable threshold.

[0002] The invention further relates to a fuel cell device and a fuel cell vehicle.

[0003] Fuel cell devices are used for the chemical conversion of a fuel with oxygen to water in order to generate electrical energy. For this purpose, fuel cells contain the so-called membrane electron assembly as a core component. This assembly consists of a proton-conducting membrane and an electrode arranged on either side of the membrane, namely an anode and a cathode. To ensure that the plurality of fuel cells combined in a fuel cell stack are adequately supplied with fuel, particularly hydrogen, injectors are used between a hydrogen tank and the anode side of the fuel cell stack to regulate the hydrogen pressure. The target hydrogen pressure results from a power requirement and the associated current, which is then determined using the Faraday constant and a lambda factor.In order to control the injectors and regulate the required pressure, a 2-point hysteresis controller is used, which regulates the degree of opening of the injectors. For more precise determination of the hydrogen consumption, the injectors can also be released depending on the load point and, for example, in the lower load range the pressure is regulated with only one injector, at partial load with two injectors and at full load with three injectors.

[0004] JP 2017-91625 A describes a method for detecting malfunctions of a fuel cell system using a pressure sensor arranged downstream of a first injector and a second injector in a fuel line. The method comprises a first step of operating the first injector and detecting a first pressure measurement value with the pressure sensor, and the step of operating the second injector and detecting a second pressure measurement value with the pressure sensor. The first measurement value and the second measurement value are compared, and a sensor malfunction is determined if the measurement values ​​are inconsistent and deviate from a theoretical value.

[0005] US Pat. No. 11,177,490 B2 discloses a fuel cell system with two injectors arranged in parallel in the fuel line, which can be operated in different modes. For this purpose, a load requirement is evaluated and determined whether it is so low that the use of one injector is sufficient. The two injectors are then used alternately to compensate for wear. If the load requirement is high, both injectors are used simultaneously.

[0006] JP 2018-160363 A discloses a fuel cell system with three injectors arranged in parallel in the fuel line of a fuel cell system. A pressure sensor is arranged upstream or downstream of the injectors. A malfunction of the pressure sensor or the injectors can be determined by a suitable operating mode in which a control unit compares a pressure expected value of an adjustment pattern with the measured values ​​during sequential control of the injectors. If a measured value of an injector deviates from the expected value by an amount exceeding a threshold value, the injector in question is classified as faulty. If the measured values ​​of all injectors deviate from the expected value by an amount exceeding a threshold value during sequential control, the sensor is considered faulty.

[0007] DE 10 2005 047 972 A1 shows an anode inlet unit for a fuel cell system that uses multiple injectors to control the hydrogen throughput. At low throughput, the duty cycle of one of the injectors is controlled, and the other injectors are kept closed. As the throughput increases, the duty cycle of the injector is increased until it is fully open, and then other injectors are controlled sequentially in the same way. DE 10 2008 010 305 A1 discloses a method that detects and reduces the pressure increase caused by a defective, open injector. AT 522100 A1 discloses a method for creating an injection strategy for a fuel cell system, in which a control error is determined as a difference between the desired anode pressure and a current anode pressure in order to then determine a desired injection frequency.

[0008] The problem is that the injectors can exhibit drift on the production side, meaning they inject a different amount of hydrogen at the same load point and the same pre-pressure, or they are open for different lengths of time. This means that the injectors are not identical and have different characteristics. In the worst case, not enough hydrogen can be injected, leading to an undersupply with insufficient power delivery and possible damage to the fuel cells.

[0009] It is therefore an object of the present invention to provide an improved method for operating a fuel cell device and an improved fuel cell device as well as an improved fuel cell vehicle.

[0010] This object is achieved by a method having the features of claim 1, by a fuel cell device having the features of claim 6, and by a fuel cell vehicle having the features of claim 7. Advantageous embodiments with expedient further developments of the invention are specified in the dependent claims.

[0011] The method mentioned at the beginning offers the advantage that the operating state of the fuel cell device can be better determined without cost-intensive additional sensors, namely by exploiting the fact that in the lower load range only one injector is required, which does not always have to be identical but can also be replaced, so that as a result all injectors can be recorded and compared individually.

[0012] It is particularly preferred if at least three of the injectors are intended for rolling operation and if the injector causing the difference is identified in the warning message.

[0013] This also makes it possible for the injector causing the difference to be excluded from use during operation in the partial load range and / or the lower load range. As a result, uninterrupted operation of the fuel cell device can be ensured in these load ranges.

[0014] Even in the event of a warning message being issued in step e), the power output from the fuel cell stack can be limited to a value below the maximum power, i.e., if the third injector is also required to be used for the full load range, the detected fault can be taken into account by reducing the power, which also prevents fuel starvation.

[0015] If there is no serious fault but only an impairment that affects consumption, if a difference below the threshold is detected, the calculated fuel consumption can be corrected on the basis of this difference.

[0016] The above-mentioned advantages and effects also apply mutatis mutandis to a fuel cell device with a control unit which is configured to carry out the above-mentioned method, and to a fuel cell vehicle with such a fuel cell device, wherein with regard to the fuel cell vehicle in particular the consumption and thus the remaining range can be determined more precisely and it is also possible to advise the user to visit a workshop to replace the injectors in order to prevent damage.

[0017] The features and feature combinations mentioned above in the description, as well as the features and feature combinations mentioned below in the description of the figures and / or shown alone in the figures, can be used not only in the respective combination specified, but also in other combinations or on their own, without departing from the scope of the invention. Thus, embodiments are also to be considered encompassed and disclosed by the invention that are not explicitly shown or explained in the figures, but which emerge and can be produced from the explained embodiments through separate feature combinations.

[0018] Further advantages, features, and details of the invention will become apparent from the claims, the following description of preferred embodiments, and the drawings. Herein: Fig. 1 a schematic representation of a fuel cell device.

[0019] In the Fig. 1 schematically shows a fuel cell device 1 which has a fuel cell or a plurality of fuel cells combined to form a fuel cell stack 2.

[0020] Each of the fuel cells comprises a membrane electrode assembly consisting of an anode and a cathode, as well as a proton-conductive membrane separating the anode from the cathode.

[0021] Fuel (e.g., hydrogen) is supplied to the anodes via anode compartments within the fuel cell stack 2. In a polymer electrolyte membrane fuel cell (PEM fuel cell), fuel or fuel molecules are split into protons and electrons at the anode. The membrane allows the protons (e.g., H + ) but is impermeable to the electrons (e - ). The following reaction takes place at the anode: 2H 2 → 4H + + 4e -(Oxidation / electron release). While the protons pass through the membrane to the cathode, the electrons are conducted to the cathode or to an energy storage device via an external circuit. Cathode gas (e.g., oxygen or oxygen-containing air) can be supplied to the cathodes via cathode chambers within the fuel cell stack 2, so that the following reaction takes place on the cathode side: O 2 + 4H + + 4e - → 2H 2 O (reduction / electron uptake).

[0022] Compressed air is supplied to the fuel cell stack 2 via a cathode fresh gas line 3 by a compressor 4. Additionally, the fuel cell is connected to a cathode exhaust line 6. On the anode side, hydrogen, in particular, is supplied to the fuel cell stack 2 via a fuel line 8 from a fuel tank 5.

[0023] In the Fig. 1 shows a plurality of injectors 13, in the illustrated embodiment three injectors 13, which function as pressure regulators to achieve the desired partial pressure of fresh fuel for the given power requirement with the associated load point. At full load, all three injectors 13 are used, at partial load two of the three injectors 13 are used, and in the lower load range the use of one of the injectors 13 is sufficient. The desired partial pressure can also be present within an anode circuit, which is created by the anode recirculation line 7. With the anode recirculation line 7, the fuel not consumed in the fuel cell stack 2 can be resupplied to the anode chambers upstream of the fuel cell, so that the anode recirculation line 7 flows back into the fuel line 8. Used fuel is removed from the fuel cell via the anode exhaust line 9.To achieve recirculation, an alternative or additional method can be used in the . Fig. 1, the recirculation fan also shown can be used. A water separator 14 with a water separator valve 15 is also present in the anode recirculation line 7.

[0024] To provide fresh hydrogen, the injectors 13 can be repeatedly opened and closed to provide the desired hydrogen pressure. Downstream of the injectors 13 and upstream of the fuel cell stack 2, the prevailing pressure can be detected by means of a hydrogen pressure sensor 16. In addition to the desired hydrogen pressure 17, the measured value of the hydrogen pressure sensor 16 can also be fed as a control signal 18 to a 2-point hysteresis controller 19. Due to the hysteresis pressure control performed by the control unit with a maximum hysteresis and a minimum hysteresis, a sawtooth curve of the fuel pressure results. Each injector 13 not only has an open or closed position, but can also assume any intermediate position between the open and closed positions.

[0025] To control the state of the injectors 13, a method for operating a fuel cell device 1 with a fuel tank 5, a fuel cell stack 2 and a fuel line 8 connecting the fuel cell tank 5 to the fuel cell stack 2, to which a plurality of injectors 13 is assigned, for the control of which a 2-point hysteresis controller 19 is provided, can be used, which comprises the steps: a) Check whether the fuel cell stack 2 is operated in a lower load range for which the supply from only one of the injectors 13 is sufficient, b) in the event that the fuel cell stack 2 is operated in the lower load range, rolling control of the injectors 13, i.e. use of the first injector 13 for the first hysteresis and successive use of one of the other injectors 13 for the further hysteresis, until after all injectors 13 have been used, the first injector 13 is used again, c) temporal recording of the pressure increase for each injector 13 at the start of its use as a quality criterion for the flow of the fuel, d) Comparison of the pressure increases of the injectors 13, e) Issue a warning message if a difference between the pressure increases exceeds a specified or specifiable threshold.

[0026] It is therefore exploited that in the lower load range only one injector 13 is required, the characteristics of which can thus be observed in isolation from the behavior of the other injectors 13.

[0027] In the exemplary embodiment, at least three of the injectors 13 are provided for rolling operation, so that the injector 13 causing the difference can be identified in the warning message. This then also results in the possibility that the injector 13 causing the difference is excluded from use during operation in the partial load range.

[0028] In order to avoid fuel starvation, the power that can be delivered by the fuel cell stack 2 can then be limited to a value below the maximum power, particularly in the event of a warning message being issued in step e).

[0029] However, the method also offers advantages if the difference is below the threshold value, since the calculated fuel consumption can be corrected based on this difference.

[0030] The advantages of the invention are particularly evident when a fuel cell device 1 having a control unit configured to carry out the above-mentioned method is assigned to a fuel cell vehicle, since its reliability and utility value are increased and the consumption and thus also the remaining range can be determined more accurately. LIST OF REFERENCE SYMBOLS: 1 fuel cell device 2 fuel cell stacks 3 Cathode fresh gas line 4 compressors 5 Fuel tank 6 Cathode exhaust line 7 Anode recirculation line 8 Fuel line 9 Anode exhaust line 10 Fresh gas supply line 11 Cathode exhaust line 13 Injector 14 water separators 15 Water separator valve 16 Hydrogen pressure sensor 17 Hydrogen target pressure 18 Control signal 19 2-point hysteresis controller

Claims

[1] Method for operating a fuel cell device (1) with a fuel tank (5), a fuel cell stack (2) and a fuel line (8) connecting the fuel tank (5) to the fuel cell stack (2), to which a plurality of injectors (13) is assigned, for the control of which a 2-point hysteresis controller (19) is provided, comprising the steps: a) Check whether the fuel cell stack (2) is operated in a lower load range for which the supply from only one of the injectors (13) is sufficient, b) in the event that the fuel cell stack (2) is operated in the lower load range, rolling control of the injectors, i.e. use of the first injector for the first hysteresis and successive use of one of the further injectors (13) for the further hystereses, until after all injectors (13) have been used, the first injector (13) is used again, c) temporal recording of the pressure increase for each injector (13) when it is put into use as a quality criterion for the fuel flow, d) Comparison of the pressure increases of the injectors (13), e) Issue a warning message if a difference between the pressure increases exceeds a specified or specifiable threshold. [2] Method according to claim 1, characterized by that at least three of the injectors (13) are intended for rolling operation, and that the injector (13) causing the difference is identified in the warning message. [3] Method according to claim 2, characterized by that the injector (13) causing the difference is excluded from use during operation in the partial load range. [4] Method according to one of claims 1 to 3, characterized bythat in the event of a warning message being issued in step e), the power that can be delivered by the fuel cell stack (2) is limited to a value below the maximum power. [5] Method according to one of claims 1 to 4, characterized by that if a difference below the threshold is detected, the calculated fuel consumption is corrected on the basis of this difference. [6] Fuel cell device (1) with a control unit which is configured to carry out the method according to one of claims 1 to 5. [7] Fuel cell vehicle with a fuel cell device (1) according to claim 6.

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