Diagnostic procedure for diagnosing the condition of a gas delivery unit of a fuel cell system and fuel cell system

Abstract

The presented invention relates to a diagnostic method (100) for diagnosing a condition of a gas delivery unit (203) of a fuel cell system (200), wherein the diagnostic method (100) comprises: - Setting (101) a predefined operating point of the fuel cell system (200), - Determining (103) a characteristic number that quantifies frictional resistance during movement of moving components of the gas delivery unit (203) during the specified operating point, - Comparing (105) the determined key figure with a reference, and - Output (107) an error message in the event that the determined key figure deviates from the reference by a value greater than a specified diagnostic threshold.

Description

[0001] The presented invention relates to a diagnostic method for diagnosing a condition of a gas delivery unit of a fuel cell system and a fuel cell system. State of the art

[0002] Polymer electrolyte membrane (PEM) fuel cell systems convert hydrogen using oxygen to electrical energy, generating waste heat and water.

[0003] A PEM fuel cell consists of an anode supplied with hydrogen, a cathode supplied with air, and the polymer electrolyte membrane placed in between.

[0004] In practical applications, several fuel cells are stacked to form a fuel cell stack in order to increase the generated voltage.

[0005] Within a fuel cell stack, or “stack,” there are supply channels that supply the individual fuel cells with hydrogen and air and transport away the depleted moist air and the depleted anode exhaust gas.

[0006] Gas delivery units used include jet pumps or hybrid solutions combining jet pumps and hydrogen blowers. Gas delivery units for conveying air, such as blowers, particularly turbines, are also known.

[0007] The electrical power consumed by a gas delivery unit is partly dissipated as power losses due to friction losses of the mechanically moving components.

[0008] Gas delivery units with ball bearings initially exhibit a slightly higher frictional loss until the bearings have run in. However, if the frictional loss then increases, especially to a significant degree, it can be concluded that parts within the component are moving against each other that shouldn't, causing the component to fail imminently.

[0009] In addition, if parts that are abrasive for chips move against each other, the resulting electrically conductive chips can electrically short-circuit a fuel cell stack on the anode side and damage it. Disclosure of the invention

[0010] Within the scope of the invention presented, a diagnostic method and a fuel cell system 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 diagnostic 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 a robust fuel cell system.

[0012] Thus, according to a first aspect of the invention presented, a diagnostic method for diagnosing a state of a gas delivery unit of a fuel cell system is presented.

[0013] The presented diagnostic method comprises setting a predefined operating point of the fuel cell system, determining a characteristic value that quantifies a frictional resistance during a movement of moving components of the gas delivery unit during the predefined operating point, comparing the determined characteristic value with a reference, and outputting an error message in the event that the determined characteristic value deviates from the reference by a value that is greater than a predefined diagnostic threshold.

[0014] In the context of the present invention, a predetermined operating point is understood to mean, in particular, an operating point of a fuel cell system at which a fuel cell stack is supplied with a predetermined volume flow of operating media and / or a predetermined power requirement is set. For example, a predetermined operating point can be a so-called "hydrogen flush" when starting a fuel cell system or flooding an anode subsystem with hydrogen when shutting down a fuel cell system.

[0015] In the context of the invention presented, a gas delivery unit is understood to mean, for example, a hydrogen blower or an air blower.

[0016] The presented invention is based on a characteristic value that quantifies frictional resistance during the movement of moving components of the gas delivery unit during the specified operating point. For this purpose, the characteristic value can, for example, include or mathematically represent the amount of electrical energy supplied to the gas delivery unit and / or the rotational speed of the gas delivery unit.

[0017] By comparing a currently determined key figure with a reference, such as a previously determined key figure, a change in the frictional resistance of the gas delivery unit can be detected. For this purpose, it can be provided, for example, that the key figure(s) is / are determined regularly and a current key figure is compared with at least one previous key figure.

[0018] Alternatively, a respective determined key figure can be compared with a reference in the form of a specified value, which changes, for example, depending on the age of the fuel cell system.

[0019] If the comparison of a respective key figure with a respective reference results in a value that exceeds a specified threshold, it can be assumed that the frictional resistance of the gas delivery unit has increased and that the gas delivery unit is showing signs of wear. An error message can be issued accordingly, for example, to prevent a failure of the gas delivery unit by scheduling early maintenance or repair.

[0020] In order to maximize the validity of the key figure provided according to the invention, disturbance variables or variances of the key figure are minimized by setting the fuel cell system to a predetermined operating point to determine the key figure, so that in particular different key figures are determined under the same or similar conditions.

[0021] It may be provided that the key figure includes the electrical power consumed by the gas production unit during a given period of time.

[0022] Since the electrical power consumed by a gas delivery unit increases proportionally to the frictional resistance of the gas delivery unit, the frictional resistance of a gas delivery unit can be determined based on the electrical power consumed.

[0023] The specified period can be during activation of the specified operating point or can be selected depending on the specified operating point.

[0024] It can further be provided that the predetermined operating point is a hydrogen flooding of an anode subsystem of the fuel cell system during a start-up process or during a shutdown process of the fuel cell system.

[0025] The power absorbed by a gas delivery unit depends not only on the condition of the bearings but also on the condition of the medium being conveyed, the support provided by a jet pump, for example, and the speed of the gas delivery unit. Gas composition, temperature, and pressure play a role in the medium.

[0026] The gas composition cannot be measured during operation, but rather models can be used which can be used to draw conclusions about the gas composition from the power consumption of the gas delivery unit. For this purpose, operating points can be specified for which as many influencing variables as possible are known or have no influence on the operation of the gas delivery unit. One of these operating points is a so-called hydrogen flush or hydrogen flooding during the start-up process of a fuel cell system. In this case, an anode subsystem of the fuel cell system is flooded with hydrogen by opening purge and drain valves, while power production by the fuel cell stack approaches zero, so that a passive influence of a jet pump is negligible or has only a minor influence from the inflowing hydrogen due to the discharge via the purge and drain valves.

[0027] Additionally, during hydrogen purging, the gas delivery unit is kept at a constant speed to distribute the hydrogen throughout the anode subsystem. The gas composition in the anode subsystem after hydrogen purging depends on the initial condition, such as pressure and shutdown duration, which define a residual amount of hydrogen in the anode subsystem. However, over a sufficiently long hydrogen purging duration, a reproducible gas composition can be provided in the anode subsystem, so that this condition can be used as a predefined operating point, for example, to analyze the power consumption of the gas delivery unit, i.e., to determine the key figure.

[0028] If the power consumption increases continuously from one hydrogen purge process to the next with otherwise constant boundary conditions, bearing wear in the gas delivery unit can be assumed.

[0029] It may further be provided that the gas delivery unit is operated at a constant speed during the specified operating point.

[0030] By operating at a constant speed, a particularly comparable key figure can be determined based on a variable that depends on the speed, such as power consumption.

[0031] It can further be provided that a speed of the gas delivery unit is changed during the specified operating point and the characteristic value is determined on the basis of a speed curve of the gas delivery unit during and / or after the change in the speed.

[0032] By changing the speed of the gas delivery unit, for example, speed ranges can be identified in which a gas delivery unit shows particularly high frictional resistance, so that a fault in the gas delivery unit can be detected particularly early.

[0033] To change the speed of the gas delivery unit, the speed can be specified, i.e., increased to a specified value or reduced to a specified value. Alternatively, the gas delivery unit can be deactivated so that the gas delivery unit rotates or coasts to a stop, exhibiting a characteristic speed curve, in particular a characteristic speed gradient.

[0034] It may also be provided that a key figure determined for a previous operating point or a specified value is selected as the reference.

[0035] By comparing a respective determined first key figure with a previously determined second key figure, a trend in the key figures and, consequently, the frictional resistance can be determined. Accordingly, a fault can be detected if the key figures change slowly but steadily or if the key figures change rapidly and significantly. For this purpose, for example, a gradient of the changes in the key figures can be compared with a gradient threshold as a diagnostic threshold.

[0036] It may further be provided that the specified operating point is only set if an existing pressure in an environment and / or a previous shutdown period are within specified limits.

[0037] In order to minimize the influence of environmental conditions on the determination of a key figure and, as a result, to maximize the validity of the key figure, it can be provided that the key figure is only determined when comparable conditions exist, ie, an existing pressure in an environment and / or a previous shutdown duration are within specified limits.

[0038] It can further be provided that the predetermined operating point comprises supplying a fuel cell stack of the fuel cell system with a constant media flow at a constant power requirement.

[0039] Constant media flows of, for example, hydrogen and / or air and / or coolant create comparable conditions for determining a respective key figure.

[0040] It may further be provided that the error message is output on an output unit and includes an indication of a mechanical defect in the gas delivery unit.

[0041] By means of an error message output on an output unit, such as a display and / or a loudspeaker, a user is informed about the internal state of a respective fuel cell system, in particular of a gas feed unit of the fuel cell system, and can, if necessary, initiate countermeasures to an impending failure, such as a repair.

[0042] It may further be provided that the error message includes control instructions that switch the fuel cell system into emergency operation in which mechanical stress on the fuel cell system is minimized.

[0043] To avoid significant damage to a fuel cell system, for example due to a defective gas delivery unit, an error message can include control instructions that automatically switch the fuel cell system to emergency mode when the error message is issued.

[0044] According to a second aspect, the presented invention relates to a fuel cell system for converting energy.

[0045] The fuel cell system comprises a fuel cell stack, a gas delivery unit for supplying the fuel cell stack with an operating medium and a computing unit.

[0046] The computing unit is configured to execute a possible embodiment of the presented diagnostic procedure.

[0047] Advantages described in detail with respect to the diagnostic method for diagnosing a state of a gas feed unit of a fuel cell system according to the first aspect of the invention equally apply to the fuel cell system for converting energy according to the second aspect of the invention.

[0048] 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.

[0049] They show: Fig. 1 a possible design of the presented diagnostic procedure, Fig. 2 a possible design of the presented fuel cell system.

[0050] In Fig. 1 shows a diagnostic method 100 for diagnosing a condition of a gas delivery unit of a fuel cell system.

[0051] The diagnostic method 100 comprises a setting step 101 in which a predetermined operating point is set on the fuel cell system, a determination step 103 in which a characteristic value is determined that quantifies a frictional resistance during a movement of movable components of the gas delivery unit during the predetermined operating point, a comparison step 105 in which the determined characteristic value is compared with a reference, and an output step 107 in which an error message is output in the event that the determined characteristic value deviates from the reference by a value that is greater than a predetermined diagnostic threshold value.

[0052] In Fig. 2 shows a fuel cell system 200 for converting energy.

[0053] The fuel cell system 200 comprises a fuel cell stack 201, a gas delivery unit 203 for supplying the fuel cell stack 201 with an operating medium, and a computing unit 205.

[0054] The computing unit 205 is configured to set a predetermined operating point on the fuel cell system 200, to determine a characteristic value that quantifies a frictional resistance during a movement of movable components of the gas delivery unit 203 during the predetermined operating point, to compare the determined characteristic value with a reference, and to output an error message in the event that the determined characteristic value deviates from the reference by a value that is greater than a predetermined diagnostic threshold.

Claims

[1] Diagnostic method (100) for diagnosing a condition of a gas delivery unit (203) of a fuel cell system (200), the diagnostic method (100) comprising: - setting (101) a predetermined operating point of the fuel cell system (200), - determining (103) a characteristic value which quantifies a frictional resistance during a movement of movable components of the gas delivery unit (203) during the predetermined operating point, - comparing (105) the determined key figure with a reference, and - Outputting (107) an error message in the event that the determined key figure deviates from the reference by a value that is greater than a predetermined diagnostic threshold value. [2] Diagnostic method (100) according to claim 1, characterized by that the characteristic number comprises an electrical power absorbed by the gas conveying unit (203) during a predetermined period of time. [3] Diagnostic method (100) according to claim 1 or 2, characterized by that the predetermined operating point is a hydrogen flooding of an anode subsystem of the fuel cell system (200) during a start-up process or during a shutdown process of the fuel cell system (200). [4] Diagnostic method (100) according to one of the preceding claims, characterized by that the gas delivery unit (203) is operated at a constant speed during the predetermined operating point. [5] Diagnostic method (100) according to claim 3, characterized by that a speed of the gas delivery unit (203) is changed during the predetermined operating point and the characteristic number is determined on the basis of a speed curve of the gas delivery unit (203) during and / or after the change in the speed. [6] Diagnostic method (100) according to one of the preceding claims, characterized bythat a key figure determined for a previous operating point or a specified value is selected as the reference. [7] Diagnostic method (100) according to one of the preceding claims, characterized by that the specified operating point is only set if the existing pressure in an environment and / or a previous shutdown time are within specified limits. [8] Diagnostic method (100) according to one of the preceding claims, characterized by that the predetermined operating point comprises supplying a fuel cell stack (201) of the fuel cell system (200) with a constant media flow at a constant power requirement. [9] Diagnostic method (100) according to one of the preceding claims, characterized by that the error message is output on an output unit and includes an indication of a mechanical defect in the gas delivery unit (203). [10] Diagnostic method (100) according to one of the preceding claims, characterized by , that the error message comprises control instructions which switch the fuel cell system (200) into an emergency mode in which a mechanical load on the fuel cell system (200) is minimized. [11] Fuel cell system (200) for converting energy, wherein the fuel cell system (200) comprises: - a fuel cell stack (201), - a gas delivery unit (203) for supplying the fuel cell stack (201) with an operating medium, - a computing unit (205), wherein the computing unit (205) is configured to execute a diagnostic method (100) according to one of claims 1 to 10.

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