Method for operating a fuel cell system, computer program product and fuel cell system

Abstract

The present invention relates to a method for operating a fuel cell system (1), according to which an introduction rate (n) of a fuel for supplying a stack (2) is changed in the event of a requested change of a supplied electrical power (P_ist) to a requested electrical power (P_soll). A transport time (TD) of the fuel between introducing the fuel and reaching the stack (2) is taken into consideration. The invention additionally relates to a computer program product for carrying out the method, and to a fuel cell system (1) operated in such a manner.

Description

[0001] R.413099

[0002] 1

[0003] Method for operating a fuel cell system, computer program product and fuel cell system

[0004] The present invention relates to a method for operating a fuel cell system comprising at least one fuel cell and a fuel supply system for supplying the fuel cell with fuel. The invention also relates to a computer program for carrying out the method. Furthermore, the invention relates to a fuel cell system operated in this manner.

[0005] To operate fuel cells, they are supplied with fuel in an associated fuel cell system. For this purpose, the fuel cell system typically includes a feed system with an injection device through which the fuel is introduced. During operation, the fuel cell delivers electrical power that can be supplied to a consumer.

[0006] A disadvantage of fuel cell systems is a reduced possible change in the delivered electrical power in order to avoid damage to the fuel cell.

[0007] The present invention addresses the objective of providing improved or at least alternative variants of a method for operating a fuel cell system of the type mentioned above, a computer program product for operating the fuel cell system, and a fuel cell system operated in this manner. In particular, the present invention addresses the objective of providing embodiments of the method, the computer program product, and the fuel cell system that are characterized by an increased service life and / or faster responses to requested electrical power. R.413099

[0008] 2

[0009] This problem is solved according to the invention by the subject matter of the independent claims. Advantageous variations are found in the dependent claims.

[0010] The core idea of ​​the present invention is therefore to take into account the transport time required by the fuel between its introduction and arrival at the fuel cells when the requested power output of a fuel cell system changes. This means that, within the framework of the inventive method for operating the fuel cell system, the delay between the introduction of the fuel and its arrival at the fuel cells is considered when the requested electrical power changes. It has been recognized according to the invention that this delay, when the requested electrical power changes, is responsible for damage to the fuel cells.For example, failing to account for the delay when increasing the requested electrical power leads to fuel depletion in the fuel cells, which can damage them. Similarly, failing to account for the delay when decreasing the requested electrical power can lead to excessive fuel saturation in the fuel cells, also causing damage. Therefore, taking this delay into account prevents or at least reduces such damage. Furthermore, it enables a faster response to changes in the requested power. These faster responses open up applications for the fuel cell system where it has previously been unsuitable due to slow response times and / or the risk of damage. R.413099.

[0011] 3

[0012] The fuel cell system comprises a stack with at least one fuel cell and a fuel supply system for supplying the stack with fuel. The fuel supply system also includes a device for introducing fuel into the fuel supply system, which is hereinafter also referred to as the injection device. During operation, the injection device introduces fuel into the fuel supply system at a rate referred to as the injection rate. Within the framework of the inventive method for operating the fuel cell system, a transport time of the fuel from the injection device to the stack is taken into account if, at any point, a change in the electrical power supplied by the stack to a requested electrical power is requested within a specified duration. The time of the change request is hereinafter also referred to as the initial time, and the duration as the change duration.The starting point is therefore the change in the requested electrical power at the initial time, whereby the change in the requested electrical power must be present after the change period has elapsed. The transport time is taken into account here.

[0013] The electrical current is particularly useful as the basis for the requested electrical power and / or the delivered electrical power. This means, in particular, that the transmission time is taken into account if, at the initial time, a change in the electrical current supplied by the stack to a requested electrical current is requested within the change timeframe.

[0014] The change in the required electrical power corresponds in particular to a load change. The solution according to the invention thus enables faster load changes while preventing or at least reducing damage to the stack. R.413099

[0015] 4

[0016] The fuel contains hydrogen and is supplied to an anode of at least one fuel cell. The fuel is typically supplied to the stack in gaseous form. Therefore, the fuel can also be referred to as anode gas. Examples of fuels include natural gas (NG), methane (CH4), H2, ammonia (NH3), and similar gases. The gas exiting the stack at the anode side is subsequently referred to as anode exhaust.

[0017] To operate the fuel cell system, an oxygen-containing oxidizing agent, subsequently also referred to as cathode gas, is supplied to the cathode of at least one fuel cell. The cathode gas can be, in particular, air.

[0018] The fuel cell system can be used in any application. In particular, the fuel cell system can be used in both stationary and mobile applications. It is conceivable to use the fuel cell system in a building. Likewise, the fuel cell system can be used in a vehicle.

[0019] The fuel cell in question can be of any type.

[0020] For example, the fuel cell in question could be a solid oxide fuel cell, also known by its English name "Solid Oxide Fuel Cell" or "SOFC" for short. More specifically, the fuel cell could be a solid oxide electrolyzer cell. A solid oxide electrolyzer cell is also known by the English abbreviation "SOEC," which stands for "Solid Oxide Electrolyzer Cell."

[0021] The fuel cell system can be designed to deliver any maximum electrical power, hereinafter also referred to as total power R.413099

[0022] It could be 5. For example, the total power output could be several kilowatts. In particular, the total power output could be between 20 kW and 40 kW.

[0023] The fuel cell system is preferably modular in design, with each module comprising such a stack. This makes it possible to assemble the fuel cell system modularly, depending on the required total power output.

[0024] According to one variant of the inventive solution, the transport time is taken into account by implementing a delay in the change in the delivered electrical power, starting from the initial time. This means that the electrical power delivered by the stack is held constant for a period, hereinafter referred to as the delay period, starting from the initial time. Simultaneously, the feed rate of the fuel is adjusted from the initial time according to the change in the requested electrical power. Maintaining the delivered electrical power for the delay period allows for an adjustment of the fuel concentration in the stack, so that when the delivered electrical power subsequently changes, there is neither depletion nor excessive saturation of the fuel in the stack.In particular, maintaining the supplied electrical power for the delay period when the requested electrical power increases leads to an increase in the fuel concentration in the stack, so that the subsequent increase in electrical power does not result in fuel depletion in the stack. Thus, damage to at least one fuel cell, especially to the anode of at least one fuel cell, is prevented or at least reduced.

[0025] In this case, a change in the input rate corresponding to the change in the requested electrical power means that if the requested R.413099 is increased

[0026] 6. If the electrical power is increased, the input rate is increased, and if the electrical power is reduced, the input rate is reduced.

[0027] The delay period can, in principle, be of any length, provided it is shorter than the change period.

[0028] In preferred embodiments, the delay duration corresponds to the transport duration. This leads to the most reliable possible prevention or at least reduction of damage to the stack, while simultaneously minimizing the delay in the response to the requested change in electrical power.

[0029] The delivered electrical power is preferably modified after the delay period such that it corresponds to the requested electrical power at the end of the modification period. This can be achieved, for example, by modifying the delivered electrical power linearly with a slope after the delay period, where this slope is steeper than a direct linear slope at the initial time. This results in faster response times of the fuel cell system while simultaneously preventing or at least reducing damage to the stack.

[0030] The change in the input rate from the initial time can be arbitrary.

[0031] For example, the input rate can be continuously, and in particular linearly, changed from the initial time in accordance with the change in the requested electrical power. R.413099

[0032] 7

[0033] Alternatively, the input rate can be changed abruptly, in particular in steps, at the initial time according to the change in the requested electrical power.

[0034] A sudden change in the present sense exists in particular when the change is temporarily more pronounced than a purely linear change between the initial time and the end of the change period.

[0035] According to a further embodiment of the solution according to the invention, the transport duration is taken into account by abruptly changing the input rate at the initial time, particularly in steps, in accordance with the change in the requested electrical power, and simultaneously changing the electrical power supplied by the stack directly from the initial time in accordance with the change in the requested electrical power. The change in the supplied electrical power is such that, at the end of the change period, the supplied electrical power corresponds to the requested electrical power. In this embodiment, an immediate change in electrical power is thus implemented, which is made possible by the abrupt, particularly in steps, change in the input rate in such a way that this change in the input rate prevents or at least reduces damage to the stack.

[0036] In this case, a change in the supplied electrical power corresponding to the change in the requested electrical power means that if the requested electrical power increases, the supplied electrical power increases, and if the requested electrical power decreases, the supplied electrical power decreases.

[0037] The abrupt change in the input rate at the time of integration can, in principle, be of any magnitude. R.413099

[0038] 8

[0039] In preferred embodiments, the injection rate at the initial time is changed so abruptly that it corresponds to the injection rate of a linear change over the course of the transport period. This means that the abrupt change at the initial time is so pronounced that, after this abrupt change, the injection rate is the same as that of a linear change after the transport period has elapsed. Thus, the immediate change in the delivered electrical power is combined with the prevention or at least reduction of any impending depletion or oversaturation of fuel in the stack. This means that very fast response times are achieved, and damage to the stack is prevented or at least reduced.

[0040] Preferably, the injection rate is modified after the abrupt change such that the amount of fuel injected between the initial time and the end of the change period corresponds to the amount resulting from a linear change in the injection rate between the initial time and the end of the change period. This prevents, or at least reduces, an undesirable reduction in the O / C ratio within the stack, particularly at the anode of at least one fuel cell. This, in turn, prevents or at least reduces damage to the stack caused by such O / C ratios.

[0041] The introduction of such quantities of fuel can be achieved, for example, by keeping the abruptly changed injection rate constant for a certain period and then changing it again. Alternatively, this can be achieved by subsequently changing the abruptly changed injection rate linearly, whereby this linear change R.413099

[0042] 9 is less pronounced, i.e., has a lower slope than a linear change between the initial time and the end of the change period.

[0043] Preferred embodiments provide for an increase in the recirculation of the anode exhaust gas to the stack when an increase in the electrical power supplied by the stack is required. This prevents undesirable reductions in the O / C ratio within the stack, particularly at the anode of at least one fuel cell, or at least reduces the extent of such a reduction. The result is the prevention or at least a reduction of damage to the stack caused by such O / C ratios.

[0044] For this purpose, the fuel cell system includes a device also referred to below as a recirculation device. During operation, the recirculation device returns anode exhaust gas to the stack. The rate of the returned anode exhaust gas, i.e., the recirculation rate, is increased from the initial time within the change period, and is particularly maximized if an increase in the electrical power supplied by the stack is required.

[0045] The return of the anode exhaust gas to the stack can be implemented in particular by means of a return of the anode exhaust gas to the fuel supply system.

[0046] The method for operating the fuel cell system can be implemented using a computer program. This computer program comprises instructions which, when executed on the fuel cell system, cause it to execute the method. R.413099

[0047] 10

[0048] The computer program product is appropriately stored on a non-volatile storage system, in particular, stored there.

[0049] It is understood that, in addition to the method for operating the fuel cell system, a fuel cell system operated in this manner is also part of the scope of this invention. The fuel cell system may include a suitably designed control unit for carrying out the method. For example, the computer program may be at least partially stored in the control unit.

[0050] Further important features and advantages of the invention will become apparent from the dependent claims, the drawings and the associated description of the figures based on the drawings.

[0051] It is understood that the features mentioned above and those to be explained below can be used not only in the combinations specified, but also in other combinations or on their own, without leaving the scope of the present invention.

[0052] Preferred embodiments of the invention are shown in the drawings and are explained in more detail in the following description, wherein identical reference numerals refer to identical or similar or functionally identical components.

[0053] They show, schematically, each one

[0054] Fig. 1 shows a highly simplified, circuit diagram-like representation of a fuel cell system, R.413099

[0055] 11

[0056] Figures 2 and 3 each show a diagram to illustrate a method for operating the fuel cell system.

[0057] Figures 4 and 5 each show a diagram to illustrate the method for operating the fuel cell system in a different embodiment.

[0058] Fig. 6 shows the diagram from Figure 5 in a further embodiment.

[0059] A fuel cell system 1, shown in Figure 1 in an exemplary and highly simplified manner, comprises a stack 2 with at least one fuel cell 3. For the sake of simplicity, only one fuel cell 3 of the stack 2 is visible in Figure 1. Furthermore, for the sake of simplicity, it is assumed below that the stack 2 has a single fuel cell 3. The fuel cell 3 typically has an anode 4, a cathode 5, and an electrolyte 6 between them. The fuel cell 3 could, for example, be a solid oxide fuel cell 7, also known as a "solid oxide fuel cell" or "SOFC" for short, or a solid oxide electrolyzer cell 8, also known as a "solid oxide electrolyzer cell" or "SOEC" for short.

[0060] During operation of the fuel cell 3, the anode 4 is supplied with a hydrogen-containing fuel or anode gas, which can be, for example, natural gas (NG), methane (CH₄), H₂, ammonia (NH₃), and the like. The fuel supply to the stack 2, and thus to the anode 4, is provided by a unit 9 of the fuel cell system 1, which is hereinafter also referred to as the fuel supply unit 9. The fuel supply unit 9 has a device 10 for introducing the fuel, which is hereinafter also referred to as the injection unit 10. During operation, the injection unit 10 introduces fuel into the R.413099 at a rate n (see, for example, Figure 3).

[0061] 12

[0062] Fuel supply system 9, which is also referred to below as the injection rate n, is introduced. Due to the distance between the injection device 10 and the stack 2, the introduced fuel requires a duration TD (see Figures 2 to 6) before it reaches the stack 2 or the anode 3. This duration TD is also referred to below as the transport duration TD. The gas leaving the stack 2 on the anode side is also referred to below as the anode exhaust.

[0063] Furthermore, during operation of fuel cell 3, the cathode 5 is supplied with an oxygen-containing oxidizing agent, which is hereinafter also referred to as cathode gas. The cathode gas can be, for example, air. To supply the cathode 5 with the cathode gas, the fuel cell system 1 has a system 11, which is hereinafter also referred to as the cathode gas supply system 11.

[0064] During operation, the stack 2, and thus at least one fuel cell 3, delivers an electrical power output P_actual (see, for example, Figure 2), which is subsequently also referred to as the delivered electrical power output P_actual. If a change in the delivered electrical power output P_actual is requested, this request is met by adjusting the fuel supply accordingly. Advantageously, the electrical current serves as the basis for consideration during operation, so that the electrical current delivered by the stack 2 and / or the requested electrical current are taken into account. This means that if an increase in the delivered electrical power output P_actual is requested, the input rate n is increased. Furthermore, if a decrease in the delivered electrical power output P_actual is requested, the input rate n is reduced.The requested electrical power P_sol I (see, for example, Figure 2) in the present sense therefore differs from the delivered electrical power P_ist. The request to change the delivered power P_ist to the requested electrical power P_soll occurs at a time t_int (see, for example, Figure 2), which is subsequently also referred to as the initial time t_int R.413099.

[0065] 13. Furthermore, it is required that the requested electrical power P_target be available after a certain duration AT (see, for example, Figure 2). This duration AT is subsequently also referred to as the change time AT.

[0066] In the illustrated embodiment, the fuel cell system 1 also includes a device 12 for returning the anode exhaust gas to the stack 2 and thus to the anode 4. This device 12 is hereinafter also referred to as the recirculation device 12. In the illustrated embodiment, the recirculation device 12 returns the anode exhaust gas to the fuel supply system 9. The recirculation of the anode exhaust gas occurs during operation of the recirculation device 12 at a rate that is hereinafter also referred to as the recirculation rate. To adjust the recirculation rate, the recirculation device 12 includes a conveying device 13 in the illustrated embodiment.

[0067] The fuel cell system can be operated by means of a computer program containing commands such that, when the computer program is executed on the fuel cell system 1, the fuel cell system 1 operates accordingly. The operation of the fuel cell system 1 can be carried out by means of a suitably equipped control unit 14, which for this purpose is connected, for example, to the injection unit 10 and the delivery unit 13, as indicated by dashed lines in Figure 1. In particular, the computer program can be at least partially stored in the control unit 14.

[0068] With reference to Figures 2 to 6, a method for operating the fuel cell system 1 is explained below, which occurs when the electrical power P_actual supplied by the stack changes to a requested electrical power P_target. For the sake of simplicity, it is assumed below that R.413099

[0069] 14. This change involves an increase, meaning that the delivered power P_actual is increased to a requested electrical power P_sol I. As explained below, the transport duration TD is taken into account in such a change.

[0070] Figures 2 and 3 show two diagrams for a first embodiment of the method for operating the fuel cell system 1. Figure 2 shows a diagram with a time course of the delivered power P_actual, where time t is plotted on the abscissa and power P on the ordinate. The prior art course of the delivered power P_actual is indicated by a dashed line. Figure 3 shows a diagram with a time course of the injection rate n, where time t is plotted on the abscissa and injection rate n on the ordinate.

[0071] As can be seen from a comparison of Figures 2 and 3, in this embodiment, starting from the initial time t_int, the electrical power P_actual supplied by the stack is held unchanged for a duration TK (see Figure 2). This duration TK is subsequently also referred to as the delay duration TK. As can be seen particularly in Figure 2, the delay duration TK is shorter than the change duration AT. In the illustrated embodiment, the delay duration TK corresponds to the transport duration TD. At the same time, as can be seen in Figure 3, the input rate n is changed from the initial time t_int according to the change in the requested electrical power P_target, i.e., increased in the illustrated embodiment. After the delay duration TK has elapsed, the delivered electrical power P_actual is changed according to the requested change, i.e., increased in this case.In the illustrated embodiment, this is achieved by means of a linear and therefore continuous increase in the delivered electrical power P_ist. This increase is such that the delivered electrical power P_ist during the change period AT of R.413099.

[0072] The requested electrical power P_sol I corresponds to 15, as can be seen in Figure 2. In contrast to the prior art (compare the dashed line in Figure 2), in which the delivered electrical power P_ist is increased directly and linearly from the initial time t_int, after the delay period TK the delivered electrical power P_ist increases with a steeper slope.

[0073] Figures 4 and 5 show diagrams for a second embodiment of the method for operating the fuel cell system 1. Figure 4 shows a time course of the delivered electrical power P_actual, with time t plotted on the abscissa and power P on the ordinate. Figure 5 shows a time course of the injection rate n, with time t plotted on the abscissa and injection rate n on the ordinate. For comparison, the injection rate n according to the prior art is indicated by a dashed line in Figure 5.

[0074] As a comparison of Figures 4 and 5 shows, in the illustrated embodiment, the electrical power P_actual supplied by Stack 2 is changed from the initial time t_int according to the change in the requested electrical power P_target, i.e., increased in the illustrated embodiment, so that the supplied electrical power P_actual corresponds to the requested electrical power P_target I at the end of the change period AT (see Figure 4). This increase is linear and therefore continuous in the illustrated embodiment. At the same time, as can be seen in Figure 5, the input rate n is changed abruptly at the initial time t_int according to the change in the requested electrical power P_target, i.e., increased abruptly in the illustrated embodiment. In the illustrated embodiment, this abrupt change occurs in steps.In contrast to the linear progression of the injection rate n shown with dashed lines according to the state of the art, a sudden change occurs at the initial time t_int and R.413099.

[0075] 16. Stepwise increase of the injection rate n. As can further be seen in Figure 4, the injection rate n is increased abruptly at the initial time t_int such that it corresponds to the injection rate n of the linear change shown with dashed lines as the transport duration TD elapses. Figure 4 also shows that, in the illustrated embodiment, the injection rate n is changed after the abrupt increase such that, at the elapsed time AT, it corresponds to the injection rate n of a completely linear change shown with dashed lines.

[0076] Figure 6 shows a further embodiment of the method for operating the fuel cell system 1, which differs from the embodiment shown in Figures 4 and 5 in the profile of the injection rate n. Accordingly, Figure 6 shows the diagram depicted in Figure 5 with this profile of the injection rate n. As can be seen in Figure 6, in this embodiment, the injection rate n is changed after the abrupt increase such that the quantity of fuel injected between the initial time t_int and the end of the change period AT corresponds to the quantity of the perfectly linear change in the injection rate n shown with dashed lines. This is achieved in this case by initially keeping the injection rate n constant after the abrupt increase and then abruptly increasing it again, so that from this abrupt increase onward it follows the perfectly linear increase.

[0077] In particular, in the embodiments shown in Figures 4 to 6, it can also be provided that the recirculation rate of the recirculated anode exhaust gas is increased and, in particular, maximized from the initial time t_int within the change period AT (not shown).

[0078] With the method according to the invention, changes in the supplied electrical power P_ist and thus load changes are both R.413099

[0079] 17

[0080] Depletion and supersaturation of the fuel in stack 2 are prevented or at least reduced, thus preventing or at least reducing corresponding damage to stack 2. At the same time, the method according to the invention allows such changes to be addressed more quickly, thereby shortening the reaction times of the fuel cell system 1.

Claims

R.413099 18 Claims 1. Method for operating a fuel cell system (1) comprising a stack (2) comprising at least one fuel cell (3) and a fuel supply system (9) for supplying the stack (2) with fuel, wherein the fuel supply system (9) has an injection device (10) which, during operation, introduces fuel into the fuel supply system (9) at an injection rate (n), - where, within the procedure, a transport time (TD) of the fuel from the injection device (10) to the stack (2) is taken into account if, at an initial time (t_int), a change from an electrical power (P_ist) supplied by the stack (2) to a requested electrical power (P_soll) is requested within a change time (AT).

2. Method according to claim 1, characterized in that the electrical power (P_ist) supplied by the stack (2) is kept unchanged from the initial time (t_int) for a delay period (TK) and at the same time the injection rate (n) of the injected fuel is changed according to the change in the requested electrical power (P_sol I).

3. Method according to claim 2, characterized in that the delay time (TK) corresponds to the transport time (TD).

4. Method according to claim 2 or 3, characterized in that, R.413099 19 that the supplied electrical power (P_is) is changed after the delay period (TK) in such a way that the supplied power (P_is) corresponds to the requested electrical power (P_should) at the end of the change period (AT).

5. Method according to one of claims 2 to 4, characterized in that the injection rate (n) is changed continuously, in particular linearly, starting from the initial time (t_int) according to the change in the requested electrical power (P_soll).

6. Method according to one of claims 1 to 4, characterized in that the injection rate (n) at the initial time (t_int) is changed abruptly, in particular in steps, according to the change in the requested electrical power (P_soll).

7. Method according to claim 6, characterized in that the electrical power (P_ist) supplied by the stack (2) is changed from the initial time (t_int) according to the change in the requested electrical power (P_sol I), in particular continuously, so that the supplied electrical power (P_ist) corresponds to the requested electrical power (P_sol I) at the end of the change period (AT).

8. Method according to claim 6 or 7, characterized in that the injection rate (n) is changed abruptly at the initial time (t_int) such that it corresponds to the injection rate (n) of a linear change R.413099 20 corresponds to the end of the transport duration (TD).

9. Method according to one of claims 6 to 8, characterized in that the injection rate (n) is changed after the abrupt change such that an injected quantity of fuel between the initial time (t_int) and the expiry of the change period (AT) corresponds to that quantity of a linear change in the injection rate (n).

10. Method according to any one of claims 1 to 9, characterized in that the fuel cell system (1 ) has a recirculation device (12) which, during operation, returns an anode exhaust gas from the stack (2) to the stack (2), wherein a recirculation rate of the returned anode exhaust gas is increased, in particular maximized, from the initial time (t_int) within the change period (AT) if an increase in the electrical power (P_ist) supplied by the stack (2) is requested.

11. Computer program product comprising instructions which, when the computer program product is executed on a fuel cell system according to any one of claims 1 to 10, cause the fuel cell system to execute the method according to any one of claims 1 to 10.

12. Fuel cell system (1) - with a stack (2) comprising at least one fuel cell (3), - with a fuel supply system (9) for supplying the stack (2) with fuel, R.413099 21 - wherein the fuel supply system (9) has an injection device (10) which, during operation, introduces fuel into the fuel supply system (9) at an injection rate (n), - with a control device (14) designed to operate the fuel cell system (1) according to the method of any one of claims 1 to 10.

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