Manufacturing process for producing a fuel cell stack and fuel cell system

Abstract

The presented invention relates to a manufacturing method (100) for producing a fuel cell stack (201, 307, 309, 311). The manufacturing process (100) comprises: - Providing (101) a fuel cell stack (201, 307, 311), - measuring (103) a design-related pressure loss (301) of the fuel cell stack (201, 307, 311), - Increasing (105) a pressure loss of the fuel cell stack (201, 307, 311) to a value which is greater than the measured value of the design-related pressure loss (301) of the fuel cell stack (201, 307, 311), wherein the increasing (105) of the pressure loss is effected by introducing a number of adjusting elements (203) into a supply system of the fuel cell stack (201, 307, 311).

Description

[0001] The presented invention relates to a manufacturing method for producing a fuel cell stack and a fuel cell system according to the appended claims. State of the art

[0002] Fuel cell systems are used to convert chemically bound energy directly into electrical energy, i.e., not via a combustion process.

[0003] For better manufacturability in terms of handling and mass production, several fuel cell stacks are typically used in a fuel cell system, all of which must be supplied with air and fuel gas as evenly as possible.

[0004] Due to tolerances and variations in manufacturing, fuel cell stacks exhibit pressure drop variations of up to 40% at the beginning of life (BoL).

[0005] When used simultaneously and coupled in a purely passive or fluidic parallel manner to form an overall system, the variation in pressure losses inevitably leads to an uneven fluid distribution between the fuel cell stacks.

[0006] To achieve equalization of the fluid distribution, a process known as "stack pairing" can be performed. This involves measuring the pressure drops of a fuel cell stack, and then only those fuel cell stacks with the same or very similar pressure drops are combined into a fuel cell system. Disclosure of the invention

[0007] Within the scope of the invention presented, a manufacturing method for producing a fuel cell stack 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 manufacturing 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.

[0008] The invention presented serves in particular to provide a possibility for a fuel-efficient and robust solid oxide fuel cell system.

[0009] Thus, according to a first aspect of the invention presented, a manufacturing method for producing a fuel cell stack is presented.

[0010] The proposed manufacturing method comprises providing a fuel cell stack, measuring a design-related pressure loss of the fuel cell stack, and increasing a pressure loss of the fuel cell stack to a value that is greater than the measured value of the design-related pressure loss of the fuel cell stack, wherein the pressure loss is increased by introducing a number of actuating elements into a supply system of the fuel cell stack.

[0011] In the context of the present invention, a supply system of a fuel cell stack is understood to be a duct system for conveying operating media required or generated during the operation of the fuel cell stack. In particular, a supply system comprises a cathode subsystem with an air supply and an exhaust path, as well as an anode subsystem with an air supply and an exhaust path.

[0012] In the context of the present invention, an actuating element is understood to be a pneumatic balancing or compensating component that is or will be introduced into a fluid path of a fuel cell stack or a line system through which fluid flows during operation of the fuel cell stack in order to adjust a pressure in the fluid path. For example, an actuating element can be a passive mechanical barrier in the form of a porous structure or an actively adjustable valve for adjusting the flow cross-section and, accordingly, for changing the pressure.

[0013] The presented invention is based on the principle of increasing the pressure loss of a particular fuel cell stack compared to the design-related pressure loss. By increasing the pressure loss, it can be controlled so that, for example, all fuel cell stacks in a fuel cell system are set to the same pressure loss, minimizing the pressure loss difference between the respective fuel cell stacks.

[0014] To adjust the pressure loss, the invention uses a number of control elements, i.e., one or more control elements, which are or will be incorporated into a supply system of the fuel cell stack. Accordingly, the control elements cause an increase in the pressure loss of a fuel cell stack.

[0015] The number of control elements that are or will be arranged in the supply system of a respective fuel cell stack is specifically tailored to the respective fuel cell stack by taking into account its design-related pressure loss and, for example, increasing it to a specified standard value.

[0016] Accordingly, pressure loss differences between the fuel cell stacks are compensated or minimized by the control elements of different fuel cell stacks.

[0017] To determine the design-related pressure loss, this is measured during the manufacturing process, for example using a manufacturer's pressure sensor.

[0018] It can be provided that the value which is greater than the value of the design-related pressure loss is a predetermined standard value or is a setpoint value determined specifically for a respective fuel cell stack, wherein the setpoint value is selected depending on an operating situation intended for the respective fuel cell stack in a fuel cell system with several fuel cell stacks.

[0019] A specified standard value as the pressure drop to be set ensures a homogeneous pressure drop across all manufactured fuel cell stacks. This is achieved by a number of specifically designed or selected control elements that increase a design-related pressure drop precisely enough to match the standard value.

[0020] A predetermined setpoint, which is selected depending on an operating situation intended for the respective fuel cell stack in a fuel cell system with several fuel cell stacks, enables a direct adaptation of a respective fuel cell stack to its later operating situation by taking into account, for example, a length of supply lines and a corresponding pressure loss in a respective fuel cell system.

[0021] Accordingly, by using different setpoints for different fuel cell stacks of a fuel cell system, a particularly homogeneous distribution of the pressures and, consequently, the wear of the fuel cell stacks can be achieved.

[0022] It can further be provided that the manufacturing method comprises assembling a plurality of fuel cell stacks to form a fuel cell system, wherein the actuating elements in the supply systems of the respective fuel cell stacks are configured such that the fuel cell stacks differ from one another in their pressure loss by at most a predetermined differential value.

[0023] By combining and jointly designing the pressure losses of fuel cell stacks of a fuel cell system in a so-called “pneumatic adjustment”, the following advantages are achieved: 1. Simplification of the necessary intervention options / control range in a fuel cell system. 2. Optimized operational control with a narrower bandwidth for the affected controlled variables, thereby increasing the control speed. This therefore means an improvement in dynamic behavior. 3. Compliance with / minimization of the specified limits for degradation by reducing / minimizing the fluctuation range of the pressure losses during production and thus enabling control to set values ​​(voltage, current) over the entire lifetime of the fuel cell stack. 4. Standardization of degradation among fuel cell stacks in a fuel cell system, since all fuel cell stacks receive the same fluid flow on the cathode side or anode side, which is crucial for degradation. Lower volume flows on the cathode side result in lower contaminant input, particularly lower chromium input and correspondingly lower chromium poisoning, as well as lower temperature stress due to reduced cooling. This same degradation results in the fuel cell stacks behaving homogeneously or uniformly to a certain extent, requiring fewer intervention options and / or reducing the fluctuation range to be covered. Ultimately, this simplifies control, saves costs, and maximizes efficiency. The homogenization of pressure losses means that the additional intervention / control options on a fuel cell stack are sufficient to utilize or convert the provided fuel gas to the maximum permissible conversion rate. 5. Reduction of the delivered flow rate, since all fuel cell stacks are at the same temperature level. Otherwise, the control system would always have to react to the "hottest" fuel cell stack, and the remaining fuel cell stacks would be overcooled.

[0024] It can further be provided that the number of adjusting elements are arranged in the inlet path and / or in the outlet path of a cathode path and / or an anode path.

[0025] Especially in the outlet path of the cathode path, control elements have proven to be particularly effective for adjusting or increasing a pressure loss.

[0026] It can further be provided that the number of control elements comprises a number of resistance elements which are configured to increase a flow resistance in the supply system compared to a design-related flow resistance.

[0027] An adjusting element can comprise a resistance element, such as a porous material, in particular a ceramic or a metal foam, which reduces the cross-section of a supply line, in particular in the flow direction downstream of a cell stack, and increases the flow resistance for fluid flowing through the supply line. Thus, the proportions of the total volume flow are shifted or distributed among the various parallel cell stacks based on the pressure losses per cell stack and the flow resistance, thus maximizing the pressure loss. Accordingly, adjusting elements can be provided in different lengths and / or thicknesses or pore structures.

[0028] It can be provided that the number of resistance elements in the supply system is formed until a measured pressure loss of the fuel cell stack corresponds to a predetermined target value of the pressure loss.

[0029] Alternatively, it can be provided that the number of resistance elements is formed based on a mathematical relationship between a shape of the number of resistance elements, a material-specific constant and a predetermined target value of the pressure loss.

[0030] The mathematical relationship can be expressed, for example, as formula (1): Δpsoll=Δpcathode+Δpcalibration

[0031] This means that by selecting a shape and structure of an actuating element, e.g. by sawing or material removal, a pressure loss of a fuel cell stack can be adjusted or calibrated according to formula (2). ΔpAdjustment∼K∗l

[0032] Where "K" is a material-specific constant, e.g., a function of porosity, and "I" is the thickness of the control element. Alternatively, the pressure drop can be adjusted or increased by selecting different materials with different porosities, for example, or by other methods, such as cross-sectional constrictions in general.

[0033] It can further be provided that the number of control elements comprises a number of active control elements which are configured to set a variable additional pressure loss in the supply system.

[0034] Using active control elements, such as valves, a respective pressure loss can be adjusted quickly and easily without material adjustments.

[0035] Furthermore, active control elements can be used to adjust a pressure loss over the course of a fuel cell stack's service life, for example to react to leaks in a particular fuel cell system and to maintain homogenization of the pressure losses.

[0036] According to a second aspect, the presented invention relates to a fuel cell system for converting energy.

[0037] The presented fuel cell system comprises a plurality of fuel cell stacks produced according to a possible embodiment of the presented manufacturing method, wherein the number of actuating elements of respective fuel cell stacks in at least one selection of the plurality of fuel cell stacks is selected such that the respective fuel cell stacks of the selection of fuel cell stacks differ from one another in their respective pressure loss by at most a differential value that is smaller than a predetermined threshold value.

[0038] Due to the large number of fuel cell stacks manufactured according to the presented manufacturing process, pressure loss is distributed very homogeneously across the different fuel cell stacks, so that local differences in power output and aging or wear are minimal.

[0039] It can be provided that the threshold value is between 1 mbar and 50 mbar, in particular less than 10 mbar, preferably less than 2 mbar.

[0040] While in known fuel cell systems the pressure loss difference is usually above 50 mbar, the presented fuel cell system enables significantly smaller pressure loss differences.

[0041] It may further be provided that the fuel cell system is a solid oxide fuel cell system.

[0042] The presented fuel cell system is particularly suitable as a solid oxide fuel cell system, since such systems are particularly large and cause correspondingly high pressure losses.

[0043] It can further be provided that the number of control elements of a respective fuel cell stack comprises a number of active control elements which are configured to set a variable additional pressure loss in the supply system.

[0044] An active control element can be, for example, a valve or a slide that can dynamically change a pressure loss.

[0045] An active actuator can be used as a standard component for pneumatic balancing, which can be permanently and consistently installed in the supply system of a fuel cell stack, thus standardizing and simplifying the production of different fuel cell stacks.

[0046] Furthermore, an active control element enables pressure loss adjustment and readjustment depending on a load by changing the pressure loss setting depending on the load of a respective fuel cell stack or fuel cell system in order to be able to react to changed operating conditions and to achieve a permanently homogeneous pressure distribution.

[0047] It can further be provided that the fuel cell system comprises a computing unit which is configured to adjust the number of active control elements of at least one selection of fuel cell stacks in such a way that the respective fuel cell stacks of the selection of fuel cell stacks differ from one another in their respective pressure loss by at most a differential value which is smaller than the predetermined threshold value.

[0048] In the context of the invention presented, a computing unit is understood to mean a computer, a processor, a control unit or any other programmable circuit.

[0049] It can further be provided that respective fuel cell stacks further comprise a further number of active actuating elements in an anode path and the computing unit is configured to execute a machine learner or a machine learning method for adjusting the active actuating elements of the respective fuel cell stacks, wherein the machine learner is trained to adjust the active actuating elements such that the respective fuel cell stacks of the selected fuel cell stacks differ from one another in their respective pressure loss by at most a differential value that is smaller than the predetermined threshold value.

[0050] In the partial load range, the flow rates are significantly lower, and an optimized passive pressure compensation for the nominal operating state at full load with a fixed value would potentially lead to uneven pressure compensation at partial load, so that the various fuel cell stacks in a fuel cell system would no longer exhibit approximately the same pressure drop at partial load. Self-adapting pressure compensation within a fuel cell system using a processing unit, e.g., running a machine learning engine, can be used to dynamically adjust the active control elements.

[0051] For this purpose, when commissioning a fuel cell system, the machine learner can be independently trained on the pressure loss that can be achieved in the supply system for each fuel cell stack. The advantage of this is that no individual, manual human intervention is required, thus providing a cost-effective process.

[0052] Furthermore, it is advantageous that the absolute worst performing fuel cell stack from the entire production run is not used to adjust the active control elements, but rather the worst performing fuel cell stack in a fuel cell system represents the reference to which all other fuel cell stacks must be adjusted.

[0053] This allows for a lower pressure loss overall for the fuel cell system, which leads to an increase in the efficiency of the fuel cell system.

[0054] Advantages detailed in the manufacturing method for producing a fuel cell stack 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.

[0055] 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.

[0056] They show schematically: Fig. 1 a possible design of the presented manufacturing process, Fig. 2 a possible design of the presented fuel cell system, and Fig. 3 a detailed representation of a possible operation of the fuel cell system according to Fig. 2.

[0057] In Fig. 1 shows a manufacturing method 100 for producing a fuel cell stack.

[0058] The manufacturing method 100 comprises a provision step 101 in which a fuel cell stack is provided, ie, for example, manufactured on a production line, a measuring step 103 in which a design-related pressure loss of the fuel cell stack is measured, and an increasing step 105 in which a pressure loss of the fuel cell stack is increased to a value that is greater than the value of the design-related pressure loss of the fuel cell stack measured in the measuring step 103.

[0059] The pressure drop is increased by incorporating a number of control elements into the fuel cell stack's supply system. For example, a foam can be injected into the supply system's lines and / or a number of tapered discs can be inserted to reduce the cross-section of the lines.

[0060] Alternatively or in addition to reducing the cross-section of the respective lines, a number of active control elements, such as a valve, can be used.

[0061] In Fig. 2 shows a fuel cell system 200 for converting energy.

[0062] The fuel cell system 200 comprises a plurality of fuel cell stacks 201, which were manufactured according to the manufacturing method and each comprise a number of actuating elements 203.

[0063] Due to the adjusting elements 203, a pressure loss of the fuel cell stacks 201 is homogeneous among each other, so that the same operating conditions are established at the fuel cell stacks 201.

[0064] In Fig. 3 shows a diagram 300 which spans a pressure loss on its ordinate and an ordinal number of fuel cell stacks of a fuel cell system on its abscissa.

[0065] When comparing the various fuel cell stacks, it can be seen that they differ in their design-related pressure loss 301, as shown by area 301, so that different additional pressure losses are set by adjusting elements, as shown by area 303, in order to equalize the total pressure losses of the fuel cell stacks.

[0066] In this case, a value to which the control elements set the total pressure loss can be determined based on a reference fuel cell stack 305, which corresponds to the batch reference fuel cell stack of an entire production batch with a highest design-related pressure loss.

[0067] Alternatively, the value to which the control elements set the total pressure loss can be determined based on a reference fuel cell stack 307, which corresponds to the fuel cell stack among the fuel cell stacks of the fuel cell system with the highest design-related pressure loss. This requires that the value to which the control elements set the total pressure loss is smaller than the value determined in relation to the batch reference fuel cell stack, as indicated by the difference range 309.

[0068] For comparison, the fuel cell stack 311 represents a fuel cell stack with the lowest design-related pressure loss of a production batch.

Claims

[1] Manufacturing method (100) for producing a fuel cell stack (201, 307, 311), the manufacturing method (100) comprising: - providing (101) a fuel cell stack (201, 307, 311), - measuring (103) a design-related pressure loss (301) of the fuel cell stack (201, 307, 311), - Increasing (105) a pressure loss of the fuel cell stack (201, 307, 311) to a value which is greater than the measured value of the design-related pressure loss (301) of the fuel cell stack (201, 307, 311), wherein the increasing (105) of the pressure loss is effected by introducing a number of adjusting elements (203) into a supply system of the fuel cell stack (201, 307, 311). [2] Manufacturing method (100) according to claim 1, characterized bythat the value which is greater than the value of the design-related pressure loss (301) is a predetermined standard value or is a setpoint value determined specifically for a respective fuel cell stack (201, 307, 311), wherein the setpoint value is selected as a function of an operating situation intended for the respective fuel cell stack (201, 307, 311) in a fuel cell system (200) with a plurality of fuel cell stacks (201, 307, 311). [3] Manufacturing method (100) according to claim 1 or 2, characterized by that the manufacturing process (100) further comprises: - assembling a plurality of fuel cell stacks (201) to form a fuel cell system (200), wherein the actuating elements (203) in the supply systems of the respective fuel cell stacks (201) are configured such that the fuel cell stacks (201) differ from one another in their pressure loss by at most a predetermined differential value. [4] Manufacturing method (100) according to one of the preceding claims, characterized by that the number of adjusting elements (203) are arranged in the inlet path and / or in the outlet path of a cathode path and / or an anode path. [5] Manufacturing method (100) according to one of the preceding claims, characterized by in that the number of actuating elements (203) comprises a number of resistance elements which are configured to increase a flow resistance in the supply system compared to a design-related flow resistance. [6] Manufacturing method (100) according to claim 5, characterized by that the number of resistance elements is determined based on a mathematical relationship between a shape of the number of resistance elements, a material-specific constant and a predetermined target value of the pressure loss. [7] Manufacturing method (100) according to claim 5 or 6, characterized bythat the number of resistance elements in the supply system is formed until a measured pressure loss of the fuel cell stack (201, 307, 311) corresponds to a predetermined target value of the pressure loss. [8] Manufacturing method (100) according to one of the preceding claims, characterized by in that the number of actuating elements (203) comprises a number of active actuating elements (203) configured to adjust a variable additional pressure loss in the supply system. [9] Fuel cell system (200) for converting energy, the fuel cell system (200) comprising: - a plurality of fuel cell stacks (201, 307, 311) produced according to a manufacturing method (100) according to one of claims 1 to 8, wherein the number of actuating elements (203) of respective fuel cell stacks (201, 307, 311) in at least one selection of the plurality of fuel cell stacks (201, 307, 311) is selected such that the respective fuel cell stacks (201, 307, 311) of the selection of fuel cell stacks (201, 307, 311) differ from one another in their respective pressure loss by at most a differential value which is smaller than a predetermined threshold value. [10] Fuel cell system (200) according to claim 9, characterized by that the threshold value is between 1 mbar and 50 mbar, in particular less than 10 mbar, preferably less than 2 mbar. [11] Fuel cell system (200) according to claim 9 or 10, characterized by that the fuel cell system (200) is a solid oxide fuel cell system. [12] Fuel cell system (200) according to one of claims 9 to 11, characterized by in that the number of actuating elements (203) of a respective fuel cell stack (201, 307, 311) comprises a number of active actuating elements (203) which are configured to set a variable additional pressure loss in the supply system. [13] Fuel cell system (200) according to claim 12, characterized by in that the fuel cell system (200) comprises a computing unit which is configured to set the number of active actuating elements (203) of at least one selection of fuel cell stacks (201, 307, 311) in such a way that the respective fuel cell stacks (201, 307, 311) of the selection of fuel cell stacks (201, 307, 311) differ from one another in their respective pressure loss by at most a differential value which is smaller than the predetermined threshold value. [14] Fuel cell system (200) according to claim 12 or 13, characterized byin that respective fuel cell stacks (201, 307, 311) further comprise a further number of active actuating elements (203) in an anode path, and the computing unit is configured to execute a machine learner for adjusting the active actuating elements (203) of the respective fuel cell stacks (201, 307, 311), wherein the machine learner is trained to adjust the active actuating elements (203) such that the respective fuel cell stacks (201, 307, 311) of the selection of fuel cell stacks (201, 307, 311) differ from one another in their respective pressure loss by at most a difference value which is smaller than the predetermined threshold value.

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