Fuel cell system

Abstract

The invention relates to a fuel cell system (100) comprising a fuel cell stack (102) and a housing (104) in which the fuel cell stack (102) is housed, the housing (104) having an inflow opening (106) and an outflow opening (108) through which ambient air (110) flows through the housing (104). The device further comprises a hydrogen gas sensor (114) for detecting the H2 content of the measurement gas in the housing (104) and a control and analysis evaluation unit (122). The control and analysis evaluation unit (122) analyzes and evaluates the measurement signal output by the hydrogen gas sensor (114) and changes the amount (124) of ambient air (110) flowing through the housing (104). The functional state of the hydrogen gas sensor (114) is checked by evaluating a first measurement signal (136) in the case of a first quantity (138) of the ambient air (110) flowing through the housing (104) and a second measurement signal (140) different from the first quantity (138) in the case of a second quantity (142) of the ambient air (110) flowing through the housing (104).

Description

Technical Field

[0001] The invention relates to a fuel cell system. Background Art

[0002] A fuel cell stack can be used in a system running on hydrogen. A stack includes multiple fuel cells. Such a fuel cell stack can be a polymer electrolyte membrane (PEM) stack or a solid oxide fuel cell (SOFC-Solid Oxide Fuel Cell) stack.

[0003] These stacks are usually installed in a housing to collect H2 from leaks in the fuel cell stack and conduct it purposefully to the outside or into an exhaust line. This is achieved by exhausting the gas surrounding the stack with a ventilator or by setting an excess pressure.

[0004] The determination of hydrogen concentration, for example in an air-hydrogen mixture, plays an important role in the application of hydrogen fuel cell systems. Safety-related applications should be mentioned in particular. An air-hydrogen mixture is ignitable, for example, at a hydrogen content of 4%. For example, a sensor for detecting hydrogen can be used in a hydrogen fuel cell vehicle in order to detect hydrogen that appears due to damage or defects and trigger an alarm signal and / or protective measures by coupling to the corresponding system. Therefore, each fuel cell vehicle requires a plurality of hydrogen sensors, which are either installed in the exhaust line of the vehicle (exhaust pipe) or work under atmospheric conditions (environment), for example above the gas tank, or in the stack housing, the exhaust gas of the stack housing can be introduced into the exhaust line.

[0005] In order to detect critical H2 concentrations, a hydrogen sensor is installed in particular before the discharge point of the stack housing. The signal of the hydrogen sensor is detected by the controller and the fuel cell system is shut down if necessary to prevent further discharge of H2 from the stack housing.

[0006] Despite these advantages of the fuel cell systems known from the prior art, fuel cell systems still have potential for improvement. Hydrogen sensors measure the H2 content in a gas that is normally H2-free. If the H2 signal of the sensor drifts over time, the sensor displays too much or too little H2 despite the fact that there is an H2-free environment around the stack. Thus, in the event of a "stack leak", it can happen that a critical H2 concentration in the stack housing cannot be detected because too low an H2 concentration is measured. Summary of the invention

[0007] Within the scope of the present invention, a fuel cell system is proposed which at least largely avoids the disadvantages of known fuel cell systems and is suitable in particular for detecting whether a hydrogen sensor in a stack housing is drifting.

[0008] The fuel cell system according to the present invention includes at least one fuel cell stack. In addition, the fuel cell system includes a housing. The fuel cell stack is accommodated in the housing. The housing has an inlet opening and an outlet opening. With the help of the inlet opening and the outlet opening, ambient air can flow through the housing. The fuel cell system also includes a hydrogen sensor for detecting the H2 content of the measurement gas in the housing. The fuel cell system also includes a control and analysis evaluation unit. The control and analysis evaluation unit is configured to analyze and evaluate the measurement signal output by the hydrogen sensor. The control and analysis evaluation unit is configured to change the amount of ambient air flowing through the housing. The control and analysis evaluation unit is also configured to check the functional state of the hydrogen sensor by analyzing a first measurement signal under a first amount of ambient air flowing through the housing and a second measurement signal under a second amount of ambient air flowing through the housing, wherein the second amount is different from the first amount.

[0009] The control and evaluation unit can be designed to check the functional state of the hydrogen sensor by comparing the first measurement signal and the second measurement signal.

[0010] The second amount may be greater than the first amount.

[0011] The control and evaluation unit may be designed to detect leaks in the fuel cell stack and / or drift of the hydrogen sensor.

[0012] The control and evaluation unit may be designed to detect a leak in the fuel cell stack if the first measurement signal has a value that deviates from a hydrogen content of 0% and the second measurement signal has a value that is smaller than the first measurement signal.

[0013] The control and evaluation unit may be designed to detect a drift of the hydrogen sensor if the first measurement signal has a value which deviates from a hydrogen content of 0% and the second measurement signal has the same value as the first measurement signal.

[0014] Furthermore, the fuel cell system can include a ventilation device and / or an overpressure line. The control and evaluation unit is designed to change the amount of ambient air flowing through the housing by changing the power of the ventilation device and / or the pressure of the overpressure line.

[0015] The control and evaluation unit can be designed to change the pressure in the excess pressure line by changing a throttling of the excess pressure line or by changing the power of a compressor of the excess pressure line.

[0016] The ventilation device can be arranged in an inlet opening of the housing.

[0017] The control and evaluation unit can be designed to output a fault message if the evaluation of the first measurement signal and the second measurement signal results in a deviation from a setpoint value which exceeds a predetermined threshold value.

[0018] In the context of the present invention, a fuel cell stack can be understood as an arrangement consisting of up to hundreds of individual fuel cells, which are stacked on top of each other and electrically connected in series. In each of these fuel cells connected in series, in the so-called "cold combustion", the chemical reaction energy of the continuously supplied hydrogen and air oxygen is converted into electrical energy. This is achieved by catalytically decomposing hydrogen into electrons and protons. Protons diffuse through the polymer membrane toward the cathode, while electrons flow from the anode to the cathode via an electrical circuit and supply current to the electrical consumer. Protons, air and electrons eventually react at the cathode to form the final product, water. In addition, no pollutants such as particles or nitrogen oxides are produced. The stack generates electrical energy, which, for example, drives a fuel cell vehicle.

[0019] In the context of the present invention, a hydrogen sensor is understood to be a sensor having at least one sensor element which is designed to detect the H2 content in a gas mixture and to output a measurement signal indicating the H2 content. The H2 content can be detected as an absolute value, i.e., as a concentration expressed in volume percent or mass percent, and / or as a partial pressure. A large number of measuring principles can be used for such hydrogen sensors. This includes in particular the following measuring principles: thermal conductivity, catalytic oxidation sensor (katalytischer pellistor), electrochemical cell, semiconductive metal oxide, chemical resistor, field effect transistor.

[0020] The sensor element is designed, for example, as a sensor chip with a heatable measuring membrane. The sensor chip comprises, for example, a chip surface. The chip surface has a measuring surface that can be acted upon by a fluid medium and an island surface. Conductor tracks of a sensor circuit with at least one heating element are mounted on the measuring surface. Conductor tracks of a sensor circuit with at least one temperature sensor are mounted on the base island surface.

[0021] The sensor chip can be arranged on a base, in particular a glass base or a silicon base. The connection between the sensor chip and the base can be achieved by means of anodic bonding. An access channel can also be constructed in the base. For example, the access channel is implemented in the form of a hole. The access channel can be manufactured by a scratching or sawing process or an etching process. In this implementation, it is possible to form a chamber on the side of the measuring surface facing the base, that is, on the lower side of the measuring surface. The chamber can be constructed similarly to a cavity, for example.

[0022] In the context of the present invention, a membrane is understood to be a thin structure which, like a skin or a film, has a large surface retardation dimension in comparison with its thickness.

[0023] Within the scope of the present invention, the amount of ambient air is understood to mean the volume flow or the mass flow of the ambient air.

[0024] Unless otherwise expressly stated, the percentages mentioned here relate to volume percentages or mass percentages. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Further optional details and features of the invention emerge from the following description of preferred exemplary embodiments which are schematically illustrated in the drawings.

[0026] The accompanying drawings show:

[0027] Figure 1 : a schematic cross-sectional view of a fuel cell system according to an embodiment of the present invention, and

[0028] Figures 2A to 2D : Exemplary measurement signal curves and air supply curves. DETAILED DESCRIPTION

[0029] Figure 1 1 is a schematic cross-sectional view of a fuel cell system 100 according to an embodiment of the present invention. The fuel cell system 100 can be configured in particular for use in a hydrogen fuel cell vehicle. However, in principle, other applications are also possible. The fuel cell system 100 has at least one fuel cell stack 102. In addition, the fuel cell system 100 has a housing 104. The fuel cell stack 102 is accommodated in the housing 104. In other words, the housing 104 surrounds the fuel cell stack 102. The housing 104 has an inlet opening 106 and an outlet opening 108. With the aid of the inlet opening 106 and the outlet opening 108, ambient air 110 can flow through the housing 104, as shown by arrows 110. Here, the flow is carried out from the inlet opening 106 to the outlet opening 108. The outlet opening 108 can be fluidically connected to an exhaust pipe 112. The exhaust pipe 112 can be introduced into the surrounding environment of the housing 104 or into the exhaust line of the fuel cell vehicle.

[0030] The fuel cell system 100 further comprises a hydrogen sensor 114 for detecting the H2 content of the measurement gas in the housing 104. For this purpose, the hydrogen sensor 114 comprises a sensor element 116, which can be located in a wall 118 of the housing 104 or outside the wall 118. In order to allow the sensor element 116 to be supplied with measurement gas, the hydrogen sensor 114 can have a gas supply 120, which is designed, for example, in the form of a tube.

[0031] The fuel cell system 100 further has a control and analysis unit 122. The control and analysis unit 122 is configured to analyze and evaluate the measurement signal output by the hydrogen sensor 114. For this purpose, the control and analysis unit 122 can be integrated in the hydrogen sensor 114. Alternatively, the control and analysis unit 122 can be arranged separately from the hydrogen sensor 114 and electrically connected to the hydrogen sensor 114. The control and analysis unit 122 is configured to change the amount of ambient air 110 flowing through the housing 104.

[0032] For this purpose, the fuel cell system 100 also has a ventilation device 126. The ventilation device 126 is arranged in the inflow opening 106 of the housing 104. The control and analysis evaluation unit 122 is configured to change the amount 124 of the ambient air 110 flowing through the housing 104 by changing the power of the ventilation device 126. Accordingly, less ambient air 110 flows through the housing 104 when the ventilation device 126 is low power than when the ventilation device 126 is high power. Alternatively or additionally, the ambient air 110 can be supplied from the cathode path of the fuel cell system 100, which is not shown in more detail, via the overpressure pipeline. The control and analysis evaluation unit 122 can be configured here to change the pressure of the overpressure pipeline by changing the throttling of the overpressure pipeline or changing the compressor power of the overpressure pipeline. In other words, the ambient air 110 can be supplied by the throttling portion of the overpressure pipeline, so that the air supply can be changed by changing the throttling or by changing the air compressor power.

[0033] Figures 2A to 2D Exemplary measurement signal curves and air supply curves are shown. Figures 2A to 2D Possible scenarios of the functional state of the fuel cell system 100 and possible scenarios of the detectability of the function of the hydrogen sensor 114 are shown. Figures 2A to 2D In each case, time 128 is plotted on the X-axis. On the left Y-axis, a measurement signal 130 of the hydrogen sensor 114 is plotted. On the right Y-axis, the amount of ambient air 110 supplied to the interior of the housing 104 or the power of the ventilation device 126 is plotted. In this case, curve 132 shows the variation of the measurement signal of the hydrogen sensor 114 over time. Curve 134 shows the variation of the amount of air 124 supplied to the housing 104 over time.

[0034] As explained further below, the control and analysis and evaluation unit 122 is also configured to check the functional state of the hydrogen sensor 114 by analyzing a first measurement signal 136 in the case of a first quantity 138 of ambient air 110 flowing through the housing 104 and a second measurement signal 140 in the case of a second quantity 142 of ambient air 110 flowing through the housing 104, the second quantity 142 being different from the first quantity 138. The second quantity 142 is greater than the first quantity 138. The control and analysis and evaluation unit 122 is particularly configured to check the functional state of the hydrogen sensor 114 by comparing the first measurement signal 136 and the second measurement signal 140. The control and analysis and evaluation unit 122 is therefore configured to identify a leak 144 of the fuel cell stack 102 and / or a drift of the hydrogen sensor 114. Such a leak 114 Figure 1 In the figure, this is exemplarily indicated by arrows.

[0035] Here Figure 2A The situation is shown in which the hydrogen sensor 114 is in a normal state and there is no hydrogen leak 144 in the housing 104. If the hydrogen sensor 114 is in a normal state and there is no hydrogen leak 144 in the housing 104, then at a first amount 138 of supplied ambient air 110, a first measurement signal 136 is detected by the control and evaluation unit 122, which first measurement signal shows an H2 content of 0%. If the amount of supplied ambient air 110 is then increased, the hydrogen sensor 114 detects a second measurement signal 140, which shows the same H2 content as the first measurement signal 136. Thus, the value of the measurement signal 130 does not change when the flow through the housing 104 and thus the dilution of the measured gas in the housing 104 changes. Accordingly, a comparison of the first measurement signal 136 and the second measurement signal 140 results in a normal functional state of the hydrogen sensor 114.

[0036] Here Figure 2B The situation is shown in which the hydrogen sensor 114 is not in a normal state because there is a drift and there is no hydrogen leak 144 in the housing 104. The control and evaluation unit 122 is designed to detect the drift of the hydrogen sensor 114 if the first measurement signal 136 has a value that shows a deviation from a 0% hydrogen content and the second measurement signal has the same value as the first measurement signal 136. In other words, in the absence of an H2 leak 144, instead of a signal showing 0% H2, an H2 value of the hydrogen sensor 114 is determined or calculated, which H2 value shows a positive or negative deviation, i.e. a drift, compared to the 0% signal. This H2 value does not change when the flow through the housing 104 changes, and thus the dilution changes.

[0037] Here Figure 2CThe situation is shown in which the hydrogen sensor 114 is in a normal state and there is a hydrogen leak 144 in the housing 104. The control and evaluation unit 122 is designed to detect a leak 144 in the fuel cell stack 102 if the first measurement signal 136 has a value that is displayed as deviating from a 0% hydrogen content and the second measurement signal has a value that is less than the first measurement signal 136. In the case of a normal functioning of the hydrogen sensor 114 and the presence of an H2 leak 144, a positive H2 value is displayed. However, if the flow through the housing 104 or the fuel cell stack 102 now increases, the displayed H2 value decreases due to the increased dilution with air and it can be assumed that there is a real H2 leak 144.

[0038] Here Figure 2D The situation is shown in which the hydrogen sensor 114 is not in a normal state because there is a drift and there is a hydrogen leak 144 in the housing 104. In this case, the first measurement signal 136 has a value that shows no deviation from the 0% hydrogen content and a particularly significant deviation, and the second measurement signal has a value that is less than the value of the first measurement signal. In other words, in the case of an increased flow rate, the H2 value shown by the measurement signal decreases due to the increased degree of dilution with air. However, this H2 value of the second measurement signal 140 deviates from the signal showing 0% H2 due to the drift and due to the leak. For the general drift detection situation, it is necessary to change the amount of air supplied regularly, for example once per driving cycle, in order to safely detect the H2 drift of the sensor without an H2 leak. In the special H2 leak detection situation, it is not possible to determine how large the contribution of the leak and how large the contribution of the drift is. In this case, it can be checked by greatly increasing the amount of air supplied whether the H2 value can be reduced to close to 0% in order to exclude the drift contribution. If the measured H2 value in this case is greater than 0%, the measured value corresponds to the drift and the value measured without dilution can be corrected accordingly.

[0039] The control and analysis and evaluation unit 122 can be configured to output a fault report if the analysis of the first measurement signal 136 and the second measurement signal 140 shows that the deviation from the expected value exceeds a predetermined threshold value. If the analysis of the first measurement signal 136 and the second measurement signal 140 shows, for example, that the drift of the hydrogen sensor 114 exceeds a previously determined threshold value and is therefore no longer tolerable for safety reasons, a fault report can be output. In this case, it may be necessary to replace or repair the hydrogen sensor 114. If on the other hand, the analysis of the first measurement signal 136 and the second measurement signal 140 shows that the leakage 144 of the fuel cell stack 102 exceeds a previously determined threshold value and is therefore no longer tolerable for safety reasons, a fault report can be output. In this case, the fuel cell system 100 can be shut down to prevent H2 from continuing to be discharged from the stack housing 104.

[0040] The invention can be used in packaged systems in which H2 is processed and these systems are cleaned to remove possible H2 leaks 144 from the system. The drift of hydrogen sensors 114 installed in these systems can be checked by the invention. The invention can be verified by checking whether the air flow supplied to the stack housing 104 (via a ventilator or a pressure drop) is changed in a targeted manner.

Claims

1. A fuel cell system (100), comprising: at least one fuel cell stack (102), A housing (104), wherein the fuel cell stack (102) is accommodated in the housing (104), wherein the housing (104) has an inlet opening (106) and an outlet opening (108), wherein ambient air (110) can flow through the housing (104) via the inlet opening (106) and the outlet opening (108), a hydrogen sensor (114) for detecting the H2 content of the measurement gas in the housing (104), and A control and analysis evaluation unit (122), wherein the control and analysis evaluation unit (122) is configured to evaluate a measurement signal output by the hydrogen sensor (114), wherein the control and analysis evaluation unit (122) is configured to change a quantity (124) of ambient air (110) flowing through the housing (104), wherein the control and analysis evaluation unit (122) is further configured to check a functional state of the hydrogen sensor (114) by analyzing a first measurement signal (136) in the case of a first quantity (138) of ambient air (110) flowing through the housing (104) and a second measurement signal (140) in the case of a second quantity (142) of ambient air (110) flowing through the housing (104), wherein the second quantity (142) is different from the first quantity (138).

2. The fuel cell system (100) according to claim 1, wherein: The control and evaluation unit (122) is designed to check the functional state of the hydrogen sensor (114) by comparing the first measurement signal (136) and the second measurement signal (140).

3. The fuel cell system (100) according to one of the preceding claims, wherein: The second amount (142) is greater than the first amount (138).

4. The fuel cell system (100) according to the preceding claim, wherein: The control and evaluation unit (122) is designed to detect a leak (144) of the fuel cell stack (102) and / or a drift of the hydrogen sensor (114).

5. The fuel cell system (100) according to the preceding claim, wherein: The control and evaluation unit (122) is designed to detect a leak (144) in the fuel cell stack (102) if the first measurement signal (136) has a value that deviates from a hydrogen content of 0% and the second measurement signal (140) has a value that is smaller than the first measurement signal (136).

6. The fuel cell system (100) according to claim 4 or 5, wherein: The control and evaluation unit (122) is designed to detect a drift of the hydrogen sensor (114) if the first measurement signal (136) has a value that deviates from a hydrogen content of 0% and the second measurement signal (140) has the same value as the first measurement signal (136).

7. The fuel cell system (100) according to one of the preceding claims, further comprising a ventilation device (126) and / or an overpressure line, wherein: The control and evaluation unit (122) is designed to change a quantity (124) of ambient air (110) flowing through the housing (104) by changing the output of the ventilation device (126) and / or the pressure of the excess pressure line.

8. The fuel cell system (100) according to the preceding claim, wherein: The control and evaluation unit (122) is designed to change the pressure in the excess pressure line by changing a throttling of the excess pressure power or by changing a compressor power of the excess pressure line.

9. The fuel cell system (100) according to claim 7 or 8, wherein: The ventilation device (126) is arranged in an inlet opening (106) of the housing (104).

10. The fuel cell system (100) according to one of the preceding claims, wherein: The control and evaluation unit (122) is designed to output a fault message if an analysis of the first measurement signal (136) and the second measurement signal (140) results in a deviation from a setpoint value that exceeds a predetermined threshold value.

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