Fuel cell system and method for converting energy

Abstract

The presented invention relates to a fuel cell system (100, 200) for converting energy, the fuel cell system (100, 200) comprising: - a fuel cell stack (101) which comprises a cathode subsystem and an anode subsystem, - an air compression system (103) for supplying air to the cathode subsystem, - a cathode bypass path (105) which is configured to conduct at least a portion of air provided by the air compression system (103) past the fuel cell stack (101) into an exhaust gas path (107), - a first air mass sensor (109) which is arranged upstream of the air compression system (103) in the direction of flow, - a second air mass sensor (111) which is arranged on the cathode bypass path (105), - a computer unit (113) which is configured to determine an air mass flow flowing through the fuel cell stack (101) on the basis of a difference between first values ascertained by the first air mass sensor (109) and second values ascertained by the second air mass sensor (111).

Description

[0001] Description

[0002] title and methods for converting

[0003] The presented invention relates to a fuel cell system and a method for converting energy according to the appended claims.

[0004] State of the art

[0005] In vehicles where energy for propulsion is also supplied by a fuel cell system, the oxidizing agent oxygen from the ambient air is usually used to react with hydrogen in the fuel cell to form water or water vapor and thus to supply electrical power through electrochemical conversion.

[0006] The ambient air is fed to the fuel cell stack by means of an air conveying system or air compression system, which requires a corresponding variable air mass flow and a corresponding pressure level.

[0007] Known fuel cell systems are based on a hot-film air mass sensor that measures the air mass flow upstream of the air compression system. Furthermore, the air mass flow flowing through a fuel cell stack is measured with a pressure-based air mass sensor.

[0008] The advantage of the pressure-based air mass sensor compared to the hot-film air mass sensor is that it can also be used in high-pressure ranges and at higher temperatures, allowing it to measure in close proximity to the fuel cell stack. The disadvantage of a pressure-based air mass sensor compared to a hot-film air mass sensor is that, due to its design, it has a significantly higher measurement tolerance, particularly in the partial-load range and can drift significantly over its service life.

[0009] Disclosure of the invention

[0010] Within the scope of the invention presented, a fuel cell system and a method for converting energy are presented. Further features and details of the invention emerge from the respective subclaims, the description, and the drawings. Features and details described in connection with the method according to the invention naturally also apply in connection with the fuel cell system according to the invention, and vice versa, so that with regard to the disclosure of the individual aspects of the invention, reference is always made to each other.

[0011] The invention presented serves in particular to provide an efficient and robust fuel cell system.

[0012] Thus, according to a first aspect of the invention presented, a fuel cell system for converting energy is presented.

[0013] The presented fuel cell system comprises a fuel cell stack comprising a cathode subsystem and an anode subsystem, an air compression system for supplying the cathode subsystem with air, a cathode bypass path configured to direct at least a portion of air provided by the air compression system past the fuel cell stack into an exhaust gas path, a first air mass sensor arranged upstream of the air compression system in the flow direction, a second air mass sensor arranged on the cathode bypass path, and a computing unit configured to determine an air mass flow flowing through the fuel cell stack based on a difference between first values ​​determined by the first air mass sensor and second values ​​determined by the second air mass sensor.In the context of the present invention, an air compression system is understood to be a system for conveying, in particular for compressing, air. For example, an air compression system may comprise a compressor or a blower.

[0014] The presented invention is based on the principle that a first air mass sensor is arranged upstream of an air compression system and a second air mass sensor is arranged in a cathode bypass path, in particular downstream of a valve or throttle valve for adjusting an air flow through the cathode bypass path.

[0015] Since the first air mass sensor detects the total air mass flow introduced into a respective cathode subsystem and the second air mass sensor detects the part of the total air mass flow that is guided past the fuel cell stack, an air mass flow flowing through a fuel cell stack can be determined according to the invention based on the difference between first values ​​determined by the first air mass sensor and second values ​​determined by the second air mass sensor.

[0016] The arrangement of air mass sensors provided according to the invention enables a particularly precise and, over the lifetime of the fuel cell system, particularly robust determination of the air flow through the fuel cell stack. Accordingly, the proposed fuel cell system can be controlled particularly precisely, i.e., with particularly low control tolerances. This results in particularly energy-efficient and low-wear operation of the proposed fuel cell system.

[0017] It can further be provided that the first air mass sensor and the second air mass sensor are of the hot film air mass meter type.

[0018] Because the second air mass sensor is arranged in the cathode bypass path, it is spatially spaced from the fuel cell stack and is therefore subject to little thermal stress. Accordingly, the second air mass sensor can be designed as a hot-film air mass sensor (HFM). Since an HFM delivers particularly accurate measured values, the air flow flowing through the cathode bypass path can be determined particularly precisely, and the difference to the total air mass flow, or the air flow flowing through the fuel cell stack, can be calculated with corresponding precision. This results in a particularly low control tolerance when controlling the fuel cell system depending on the respective air flows flowing through the fuel cell system. The measure according to the invention can significantly improve the tolerance of mass flow detection and mass flow control across the entire operating range.The HFM sensors can ensure high accuracy even at small mass flows.

[0019] Furthermore, the use of two HFM sensors enables mutual checking of the sensors, for example by checking for plausibility or drift of measured values ​​from a respective sensor.

[0020] It can further be provided that the second air mass sensor is arranged in a region of the cathode bypass path in which a lower pressure is present during operation of the fuel cell system than in the cathode subsystem.

[0021] By arranging the second air mass sensor in a low-pressure area, it is exposed to particularly low mechanical stress, so that it has a correspondingly long service life and particularly stable measurements.

[0022] It can further be provided that the second air mass sensor is arranged in the flow direction behind a bypass valve for adjusting an air flow flowing through the cathode bypass path.

[0023] By arranging the second air mass sensor downstream of a bypass valve for adjusting an air flow flowing through the cathode bypass path, the second air mass sensor can detect the part of the total air mass flow that is directed into the cathode bypass path.

[0024] It can further be provided that the cathode bypass path runs in the flow direction between a region in front of the fuel cell stack and a region in an exhaust gas path of the fuel cell system in front of an inlet point for flushed fluids, in particular flushed fluids from the anode path or anode subsystem and after respective pressure-reducing components

[0025] Since the introduction of fluids into a line changes an air mass flow flowing in the line, a course of the cathode bypass path in the flow direction between an area in front of the fuel cell stack and an area in an exhaust path of the fuel cell system protects against an inlet point for purged fluids and after respective pressure-reducing components against an influence of such fluids on the determination of the air flow flowing through the fuel cell stack.

[0026] It can further be provided that the second air mass sensor is configured to measure a smaller air mass flow than the first air mass sensor.

[0027] By using a second air mass sensor that is configured to measure a smaller air mass flow than the first air mass sensor, a tolerance range or variance of second values ​​determined by the second air mass sensor is minimized.

[0028] It can further be provided that the computing unit is further configured to take into account a bearing air flow which is used to cool at least one bearing, in particular a gas bearing, of a component arranged in the air supply path of the fuel cell system when determining the air mass flow flowing through the fuel cell stack.

[0029] Since a bearing air flow may be guided past the fuel cell stack and / or the cathode bypass path, situations may arise in which the bearing air flow as such is not detected separately. In such a case, neither the first air mass sensor nor the second air mass sensor can precisely determine an air mass flow supplied to the fuel cell stack. Accordingly, an air mass flow flowing through the fuel cell stack can be precisely determined by a computing unit that is configured to take into account a bearing air flow that is used to cool at least one bearing, in particular a gas bearing, of a component arranged in the air supply path of the fuel cell system when determining the air mass flow flowing through the fuel cell stack.

[0030] It can further be provided that the fuel cell system comprises a bearing air sensor which is configured to measure an air flow flowing through a bearing air path for cooling the at least one bearing of the component arranged in the air supply path of the fuel cell system, or the computing unit is configured to calculate the air flow flowing through the bearing air path by means of a mathematical model.

[0031] Using a bearing air sensor, a bearing air flow can be measured, i.e., precisely determined. Accordingly, the values ​​determined by the bearing air sensor can be used to precisely determine the profile of the entire air flow introduced by the air compression system and, consequently, the air flow flowing through the fuel cell stack.

[0032] As an alternative to a bearing air sensor, the part of an entire air flow introduced by the air compression system that flows through the bearing air path can be mathematically modeled, so that a bearing air sensor can be dispensed with.

[0033] It can further be provided that the fuel cell system comprises a bearing air path for guiding a bearing air flow for cooling at least one bearing of a component arranged in the air supply path of the fuel cell system, wherein the bearing air path runs in the flow direction between a region downstream of the air compressor system or downstream of the air compression and a region in the cathode bypass path and upstream of the second air mass sensor.

[0034] Through a bearing air path that runs between a region downstream of the air compression and a region in the cathode bypass path and upstream of the second air mass sensor, the bearing air flow is diverted from the bearing air pad in a region upstream of the second air mass flow sensor, so that the air flow detected by the second air mass flow sensor includes the bearing air flow. Accordingly, the bearing air flow does not lead to a change in the overall detected air flow. This variant is particularly advantageous because the bearing air path or the bearing air flow has no influence on the determination of the stack mass flow.

[0035] It can further be provided that the computing unit is further configured to infer a state of the fuel cell system based on a difference between the first values ​​and the second values ​​when the cathode shut-off valves of the fuel cell stack are closed and / or to check the plausibility or calibrate the first air mass sensor or the second air mass sensor.

[0036] When the cathode shutoff valves are closed, air flow through the fuel cell stack is prevented, so that all air introduced by the air compressor system flows through the cathode bypass path, possibly also through a bearing air path. Accordingly, a second value determined by the second air mass sensor should correspond to a first value determined by the first air mass sensor, so that the running mass sensors can be checked for plausibility or calibrated based on the difference between the respective first values ​​and the respective second values.

[0037] Furthermore, a model for calculating a bearing air flow or a bearing air sensor can be validated for the case of a bearing air path leading past the second air mass sensor, since with the cathode shutoff valves closed, the bearing air flow should then correspond to a difference between the first values ​​determined by the first air mass sensor and the second values ​​determined by the second air mass sensor. For the case of a bearing air path leading to the second air mass sensor with the cathode shutoff valves closed, a model for calculating a bearing air flow or a bearing air sensor can be validated under the assumption that the bearing air flow corresponds to the respective second values ​​detected by the second air mass sensor when the cathode bypass path is tightly closed.

[0038] Furthermore, in the case of a bearing air path leading to the second air mass sensor when the cathode shut-off valves are closed, the plausibility of the first air mass sensor or the second air mass sensor can be checked under the assumption that an average value of first values ​​determined by the first air mass sensor or second values ​​determined by the second air mass sensor corresponds to an average value of an air quantity conveyed by the air compression system.

[0039] Furthermore, in the case of a bearing air path leading past the second air mass sensor when the cathode shut-off valves are closed, the plausibility of the first air mass sensor or the second air mass sensor can be checked under the assumption that a sum of second bearing air values ​​determined by the second air mass sensor and bearing air values ​​determined by a model or a bearing air sensor corresponds to an average value of an air quantity conveyed by the air compression system.

[0040] According to a second aspect, the presented invention relates to a method for converting energy by means of a possible embodiment of the presented fuel cell system.

[0041] The presented method comprises determining an air mass flow through the fuel cell stack based on a difference between first values ​​determined by the first air mass sensor and second values ​​determined by the second air mass sensor, and adjusting the fuel cell system depending on the determined air flow through the fuel cell stack. It can be provided that a state of the fuel cell system is determined and / or verified based on the determined air flow through the fuel cell stack.

[0042] Further advantages, features, and details of the invention will become apparent from the following description, which describes exemplary embodiments of the invention 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.

[0043] They show:

[0044] Figure 1 shows a possible design of the presented fuel cell system,

[0045] Figure 2 shows another possible design of the presented fuel cell system,

[0046] Figure 3 shows a possible design of the presented procedure.

[0047] Figure 1 shows a fuel cell system 100 for converting energy.

[0048] The fuel cell system 100 comprises a fuel cell stack 101, which comprises a cathode subsystem and an anode subsystem, an air compression system 103 for supplying the cathode subsystem with air, a cathode bypass path 105, which is configured to guide at least a portion of the air provided by the air compression system 103 past the fuel cell stack 101 into an exhaust gas path 107, a first air mass sensor 109, which is arranged upstream of the air compression system 103 in the flow direction, a second air mass sensor 111, which is arranged on the cathode bypass path 105, and a computing unit 113, which is configured to determine an air mass flow flowing through the fuel cell stack 101 based on a difference between first values ​​determined by the first air mass sensor 109 and second values ​​determined by the second air mass sensor 111.In Figure 1, a bearing air path 115 is provided, which discharges bearing air from the fuel cell system 100, bypassing the second air mass flow sensor 111. Accordingly, in order to determine a loss flow or a bearing air mass flowing through the bearing air path 115 and, if necessary, to correct second values ​​determined by the second air mass flow sensor 111 or to take the bearing air mass into account when calculating the air mass flow flowing through the fuel cell stack 101, the bearing air mass can be determined using a mathematical model or measured using a bearing air sensor arranged in the bearing air path.

[0049] Furthermore, it can be clearly seen in Figure 1 that the cathode bypass path 105 runs in the flow direction between a region 117 upstream of the fuel cell stack 101 and a region in the exhaust gas path 107 upstream of an inlet point 119 for purged fluids and downstream of respective pressure-reducing components.

[0050] At the inlet point 119, purge fluids are introduced into the exhaust path 107 through a purge / drain valve.

[0051] Figure 2 shows a fuel cell system 200. The fuel cell system 200 differs in its structure from the fuel cell system 100 shown in Figure 1 essentially in that the bearing air path 115 opens into a region 201 upstream of the second air mass sensor 111, so that air flowing through the bearing air path 115 is also detected by the second air mass sensor 111. Accordingly, a model for calculating or an additional air mass sensor for detecting the air flow flowing through the bearing air path 115 can be dispensed with.

[0052] Figure 3 illustrates a method 300 for converting energy using a fuel cell system 100 or 200 according to Figure 1 or 2. The method 300 includes a determination step 301 in which an air mass flow flowing through the fuel cell stack 101 is determined based on a difference between first values ​​determined by the first air mass sensor 109 and second values ​​determined by the second air mass sensor 111.

[0053] Furthermore, the method 300 comprises an adjustment step 303 in which the fuel cell system is adjusted as a function of the determined air flow flowing through the fuel cell stack 101.

Claims

Claims 1. A fuel cell system (100, 200) for converting energy, the fuel cell system (100, 200) comprising: a fuel cell stack (101) comprising a cathode subsystem and an anode subsystem, an air compression system (103) for supplying the cathode subsystem with air, a cathode bypass path (105) configured to direct at least a portion of air provided by the air compression system (103) past the fuel cell stack (101) into an exhaust gas path (107), a first air mass sensor (109) arranged upstream of the air compression system (103) in the flow direction, a second air mass sensor (111) arranged on the cathode bypass path (105), a computing unit (113) configured toto determine an air mass flow flowing through the fuel cell stack (101) based on a difference between first values ​​determined by the first air mass sensor (109) and second values ​​determined by the second air mass sensor (111).

2. Fuel cell system (100, 200) according to claim 1, characterized in that the first air mass sensor (109) and the second air mass sensor (111) are of the hot-film air mass meter type.

3. Fuel cell system (100, 200) according to claim 1 or 2, characterized in that the second air mass sensor (111) is arranged in a region of the cathode bypass path (105) in which, during operation of the fuel cell system (100, 200) a lower pressure is applied than in the cathode subsystem.

4. Fuel cell system (100, 200) according to one of the preceding claims, characterized in that the second air mass sensor (111) is arranged in the flow direction behind a bypass valve for adjusting an air flow flowing through the cathode bypass path (105).

5. Fuel cell system (100, 200) according to one of the preceding claims, characterized in that the cathode bypass path (105) runs in the flow direction between a region upstream of the fuel cell stack (101) and a region in an exhaust gas path (107) of the fuel cell system (100, 200) upstream of an inlet point for purged fluids and downstream of respective pressure-reducing components.

6. Fuel cell system (100, 200) according to one of the preceding claims, characterized in that the second air mass sensor (111) is configured to measure a smaller air mass flow than the first air mass sensor (109).

7. Fuel cell system (100, 200) according to one of the preceding claims, characterized in that the computing unit (113) is further configured to take into account a bearing air flow which is used to cool at least one bearing in a bearing air path (115) of a component arranged in the air supply path of the fuel cell system (100, 200) when determining the air mass flow flowing through the fuel cell stack (101).

8. Fuel cell system (100, 200) according to claim 7, characterized in that the fuel cell system (100, 200) comprises a bearing air sensor which is configured to measure an air flow flowing through a bearing air path (115) for cooling the at least one bearing of the component arranged in the air supply path of the fuel cell system (100, 200), or the computing unit (113) is configured to calculate the air flow flowing through the bearing air path (115) by means of a mathematical model.

9. Fuel cell system (100, 200) according to one of claims 1 to 6, characterized in that the fuel cell system (100, 200) comprises a bearing air path (115) for guiding a bearing air flow for cooling at least one bearing of a component arranged in the air supply path of the fuel cell system (100, 200), wherein the bearing air path (115) runs in the flow direction between a region downstream of the air compression system (103) and a region in the cathode bypass path (105) and upstream of the second air mass sensor (111).

10. Fuel cell system (100, 200) according to one of the preceding claims, characterized in that the computing unit (113) is further configured to infer a state of the fuel cell system (100, 200) based on a difference between the first values ​​and the second values ​​when the cathode shut-off valves of the fuel cell stack (101) are closed and / or to check the plausibility or calibrate the first air mass sensor (109) or the second air mass sensor (111).

11. A method (300) for converting energy by means of a fuel cell system (100, 200) according to any one of claims 1 to 10, wherein the method (300) comprises: Determining (301) an air mass flow flowing through the fuel cell stack (101) based on a difference between first values ​​determined by the first air mass sensor (109) and second values ​​determined by the second air mass sensor (111), - setting (303) the fuel cell system (100, 200) in Dependence of the determined air flow flowing through the fuel cell stack (101).

12. Method (300) according to claim 11, characterized in that a state of the fuel cell system (100, 200) is determined and / or verified based on the determined air flow flowing through the fuel cell stack (101).

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