Fuel cell apparatus and method thereof

Abstract

The invention relates to a fuel cell device (1) having a fuel cell system (12), comprising a plurality of fuel cell stacks (10), the fuel cell system (12) being electrically connected or connectable to an output network system (20) comprising an output network (24) in order to supply the output network (24) with electrical energy generated by the operation of the fuel cell stacks (10), the fuel cell device (1) further has a load resistance network (50) which comprises a load resistor (52) for securing a load point of the fuel cell stack (10) in the event of a failure of the output network system (20), in particular a network failure (104), the fuel cell system (12) being electrically connected to the load resistance network (50), in order to supply the load resistance network (50) with electrical energy generated by the operation of the fuel cell stack (10).

Description

Technical Field

[0001] The invention relates to a fuel cell system and a method for ensuring the load point of a fuel cell stack of a fuel cell system in a fuel cell system in the fuel cell system in the event of a fault, in particular a fault of an output grid system. Background Art

[0002] Applications are known from the prior art in which the electrical energy generated by a SOFC fuel cell stack (SOFC is the abbreviation for “Solid Oxide Fuel Cell” in English) is fed into a three-phase AC grid.

[0003] The power dynamic response of this fuel cell stack is slow for a variety of reasons, such as the risk of cracking the battery cells due to the sharp temperature difference that may occur when the load changes suddenly. Therefore, the fuel cell stack cannot respond to rapid changes in electrical load.

[0004] In addition to the fuel cell stack itself, the entire fuel cell system can also be damaged by sudden unloading. The fuel gas cannot be converted into electrical energy in this case, which can lead to abnormal heating of the oxidation catalyst in the fuel cell system, or even complete destruction of the system in severe cases.

[0005] In the event of a fault in the feeder grid, there is also the danger that the fuel gas energy cannot be converted into electrical energy. The grid stability requirements imposed by the local so-called "grid regulations" also necessitate special electrical designs for these situations (such as the so-called low voltage ride-through capability). Summary of the invention

[0006] The object of the present invention is to specify a fuel cell device whose electrical design is simple, cost-effective and optimized so that in the event of a fault, in particular a grid fault and in particular a grid blackout, the fuel cell device is not damaged.

[0007] The aforementioned object is achieved by a fuel cell device having the features of claim 1 and a method having the features of claim 12. Further features and details of the invention are derived from the dependent claims, the description and the figures. Here, the features and details described with respect to the fuel cell device according to the invention are of course also applicable in connection with the method according to the invention and vice versa, so that reference is always made to each other or can be made to each other with respect to the disclosure of the individual inventive aspects.

[0008] The invention provides a fuel cell device having a fuel cell system. The fuel cell system comprises a plurality of fuel cell stacks, wherein the fuel cell system is electrically connected or electrically connectable to an output grid system so as to supply the electrical energy generated by the operation of the fuel cell stack to the output grid, wherein the output grid system comprises an output grid. The fuel cell device further comprises a load resistor network, which comprises a load resistor, wherein the load resistor is used to ensure the load point of the fuel cell stack in the event of a fault, in particular in the output grid system and in particular in the event of a grid fault in the output grid, wherein the fuel cell system is electrically connected to the load resistor network so as to supply the electrical energy generated by the operation of the fuel cell stack to the load resistor network.

[0009] Therefore, the present invention provides a fuel cell device, in which the fuel cell stack can maintain its operating point or load point in the event of a fault, in particular a grid fault, such as in particular a grid outage. The load point of the fuel cell stack does not change at least beyond a range predetermined according to its power dynamics, within which the risk of possible damage to the fuel cell system is negligible. Here, a grid fault is characterized by the fact that only a small amount of electrical energy, or in particular in the event of a grid outage, no electrical energy can flow into the output grid. Such a grid outage may occur, for example, in the case of an external short circuit in the fuel cell device. In normal operation, the electrical energy generated by the fuel cell stack is delivered to the output grid, which is therefore called the output grid. However, as an alternative, it may also be called a feeder grid, for example. Therefore, if the generated power cannot be delivered to the output grid, in particular the AC grid and / or the three-phase grid, due to a grid fault, the excess energy can be directed to the load resistor. If the grid fault is eliminated, the electrical energy can flow into the output grid again after the grid voltage is restored, and no longer into the load resistor.

[0010] The fuel cell device according to the invention is particularly concerned with protecting the load points of the fuel cell stack of the fuel cell system in the fuel cell device in the event of a grid fault in the output grid, but can also be advantageously used for load point protection of a system not connected to the grid. All features described in relation to the occurrence of a grid fault can therefore also be advantageously used for a system not connected to the grid.

[0011] The fuel cell stack can be a solid oxide fuel cell stack in particular. Thus, the fuel cell system can be a solid oxide fuel cell system or a solid oxide electrolyzer system (also a SOFC system, in English "Solid Oxide Fuel Cell System"). In addition, these fuel cell stacks can be electrically connected to each other in parallel, in particular via a (voltage) intermediate circuit described in detail later. However, it is also possible that some or all of the fuel cell stacks are electrically connected to each other in series.

[0012] Preferably, the load resistor is set up to convert electrical energy into waste heat. Therefore, the excess electrical energy that cannot be output from the fuel cell device via the output grid in the event of a grid failure can be discharged from the fuel cell device in an advantageous manner, i.e. as waste heat. Therefore, waste heat refers in particular to the heat that is dissipated after the electrical energy is converted into thermal energy. More particularly, the waste heat is discharged outside the fuel cell stack and the fuel cell system. Therefore, the waste heat is preferably not conveyed to the fuel cell stack, which can increase its efficiency, but is not a desired result, because more electrical energy must be converted into waste heat.

[0013] It is also preferred that the load resistor is arranged outside the fuel cell stack. As mentioned above, this has the advantage that the heat generated by the load resistor is not utilized in the fuel cell stack. Instead, the installation space outside the fuel cell system containing the fuel cell stack can be advantageously used for the load resistor network. In this case, the optional cooling device can also be better accommodated and its size optimized in terms of installation space technology.

[0014] It is therefore also preferred that the fuel cell device comprises a cooling unit for cooling the load resistor. The cooling unit can be an air cooling unit and / or a water cooling unit, i.e., is set up for cooling by means of air (especially ambient air) and / or water. Within the scope of the present invention, water can advantageously refer to any coolant, in particular a liquid coolant. The air can be circulated, for example, by means of a fan. The water can be actively cooled by means of a cooling unit. As a result, a large amount of electrical energy can be transferred to the load resistor without damaging it, which is particularly advantageous when the power grid is off, because at this time no electrical energy can be output via the output grid. In principle, it can also be advantageous if the cooling is carried out by natural convection.

[0015] It is also advantageous if the load resistor network comprises power electronics which are designed to enable the load resistors in the event of a grid fault. Enablement of the load resistors here means that the electrical energy generated by the fuel cell system is supplied to the load resistors so that they dissipate electrical energy, in particular convert it into waste heat, or in other words, convert and dissipate thermal energy.

[0016] It is more particularly preferred here that the power electronic device is set up to continuously measure the voltage in the intermediate circuit between the fuel cell system and the output grid system, and enable the load resistor when a voltage increase occurs in the intermediate circuit. The intermediate circuit can be a DC intermediate circuit in particular. Therefore, the power electronic device can determine the fault very quickly based on the voltage measurement and the possible voltage increase. The load resistor can therefore be enabled with the shortest delay after the fault occurs to avoid damage to the fuel cell device. The voltage increase required to enable the power electronic device can be particularly predefined here. The voltage increase can be particularly predetermined as a maximum absolute voltage value and / or a voltage change within a predetermined time period. Therefore, the load resistor can be enabled, especially when the actual voltage measured continuously is higher than a predetermined maximum absolute voltage value or a predetermined voltage change occurs within a predetermined time period.

[0017] It is also advantageous if the power electronics has a regulator for regulating the electrical energy supplied to the load resistor as a function of the voltage measured in the intermediate circuit. It is therefore advantageous that electrical energy can be delivered to the load resistor only as required by the extent of the fault, in particular if there is no complete power failure or grid failure. It is also possible to easily determine when the fault has been eliminated and when the output grid system is available again.

[0018] Although the fuel cell system advantageously remains at the load point when a grid fault occurs, it is also advantageous that the fuel cell system is set up to reduce the load point of the operating fuel cell stack when a fault occurs, especially a grid fault. In other words, the operating point of the fuel cell stack can be reduced when a fault occurs, especially a grid fault. This reduces the electrical energy generated by the fuel cell stack in the fuel cell device to reduce the load of the load resistor and reduce the resource consumption of the fuel cell stack. Here, the aforementioned regulator or another regulator can also be used to adjust the load point of the fuel cell stack based on the voltage measured in particular by the power electronics. The power dynamics of the fuel cell stack can be taken into account here, so that when the load point of the fuel cell stack is reduced, it does not exceed its power dynamic range to avoid damage to the fuel cell stack. The power dynamics indicate how quickly the load of the fuel cell stack can be reduced without causing damage. Therefore, it is an operating parameter and can be represented, for example, by the rate of change of current.

[0019] It is also advantageous that the load resistor network is arranged in the intermediate circuit between the DC / DC converter of the fuel cell stack and the DC / AC converter of the output grid system. Therefore, the aforementioned voltage measurement can be carried out in the intermediate circuit, especially the DC intermediate circuit. The voltage in the intermediate circuit is advantageously adjusted to a constant voltage by the output grid system. Advantageously, the at least one DC / AC converter therefore has a working mode of maintaining a constant voltage in the intermediate circuit. Here, the load resistor network, the DC / DC converter of the fuel cell stack and the DC / AC converter can be arranged in parallel with each other. It is possible to assign a DC / DC converter to each fuel cell stack, that is, to be electrically connected to it. It is also possible to provide multiple output grids, wherein each output grid can have a DC / AC converter. It is also particularly possible that the DC / AC converter can work bidirectionally, or two DC / AC converters connected in series are provided, which can work unidirectionally but in opposite directions to each other. Therefore, electrical energy can be drawn from the output grid as needed, especially for supplying power to the auxiliary facility grid to operate the fuel cell device during the heating and cooling stages of the fuel cell stack.

[0020] It is also advantageous that the fuel cell device includes an auxiliary facility grid, which includes auxiliary facilities for supporting the operation of the fuel cell system, wherein the fuel cell system is electrically connected to the auxiliary facility grid so as to supply the auxiliary facility grid with the electrical energy generated by the operation of the fuel cell stack. The auxiliary facility grid can also be connected to the intermediate circuit and in particular in parallel with the load resistor network, the fuel cell system and the output grid system. Auxiliary facilities are also referred to as "supporting facilities", which is "Balance of Plant" in English. In particular, the auxiliary facilities can include multiple or all components in the fuel cell system except the fuel cell stack itself. The components can, for example, include pumps, sensors, heat exchangers, seals, air compressors, circulating fans, charge air coolers and humidifiers. They obtain the electrical energy required for operation through the auxiliary facility grid, so that the components can generate electrical energy by utilizing the normal operation of the fuel cell stack. Accordingly, the aforementioned bidirectional function of the DC / AC converter in the output grid system is advantageous when the fuel cell stack is started and shut down (i.e., heated and cooled), because the fuel cell stack itself generally does not generate electrical energy or no longer generates enough electrical energy at this stage, so as to reliably supply electrical energy to the auxiliary facilities. Although it is possible to choose to set up an accumulator, this is a cost-intensive investment because of the large required capacity.

[0021] The subject matter of the invention is also a method for securing the load point of a fuel cell stack of a fuel cell system in a fuel cell system in the event of a fault, in particular a grid fault in an output grid system which is supplied with electrical energy generated by the operation of the fuel cell stack. The method comprises the following steps:

[0022] - a fault occurs, in particular a grid fault of the output grid system,

[0023] - identify faults that occur, in particular network faults, and

[0024] - The electrical energy in the fuel cell device is converted into waste heat by means of a load resistor between the fuel cell system and the output grid system.

[0025] The method according to the invention thus brings about the same advantages as explicitly described with respect to the fuel cell device according to the invention.

[0026] In particular, the fuel cell device according to the invention can be set up or designed to carry out the method according to the invention. In turn, the method according to the invention can also be carried out in particular in or by the fuel cell device according to the invention.

[0027] Advantageously, an occurring fault, in particular a grid fault, can be determined by measuring a voltage increase in an intermediate circuit between the fuel cell system and the output grid system.

[0028] It is also advantageous if the electrical energy converted by the load resistor can be regulated as a function of the voltage measured in the intermediate circuit.

[0029] Finally, the load point of the operating fuel cell stack can advantageously be reduced within the power dynamic range available on the fuel cell stack side after a fault, in particular a grid fault, has been detected. If the load resistor is designed to be sufficiently large, it may also be advantageous for the load point to remain unchanged. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Further advantages, features and details of the invention are derived from the following description of an embodiment described in detail with reference to the drawings, which schematically show:

[0031] Figure 1 A circuit diagram showing a fuel cell device of the present invention,

[0032] Figure 2 Show Figure 1 A partial circuit diagram of a fuel cell device.

[0033] Figure 3 Show Figure 1 The power variation process in the fuel cell device,

[0034] Figure 4 A circuit diagram showing an alternative embodiment of a fuel cell device according to the invention.

[0035] The same or functionally equivalent parts Figures 1 to 4 They are respectively indicated by the same reference numerals. DETAILED DESCRIPTION

[0036] Figure 1 FIG. 1 shows a circuit diagram of a fuel cell device 1 according to an embodiment of the present invention. The fuel cell device 1 includes a plurality of fuel cell stacks 10, which are respectively connected in parallel to an intermediate circuit 40. Figure 4 As shown, Figure 1 As an alternative to the fuel cell device 1 , the fuel cell stacks 10 can also be connected in series.

[0037] In addition to the fuel cell stack 10 , the output grid system 20 , the auxiliary facility grid 30 , and the load resistor network 50 are also connected in parallel with each other and connected in parallel with the fuel cell stack 10 via the intermediate circuit 40 .

[0038] Figure 2 Show Figure 1 The fuel cell device 1 is Figure 1 The part marked with the letter A in FIG. 1 includes, for example, ten fuel cell stacks 10, but as an alternative, there may be more or fewer fuel cell stacks 10. Therefore, Figure 2 Only three fuel cell stacks 10 are shown in detail. Figure 1 The other fuel cell stacks 10 in the embodiment are not shown here or may be omitted.

[0039] The fuel cell stack 10 is part of a fuel cell system 12, which also includes a DC / DC converter 14, wherein each fuel cell stack 10 is assigned a DC / DC converter 14. By means of the respective DC / DC converter 14, each of the fuel cell stacks 10 is electrically connected to an intermediate circuit 40, which is a DC intermediate circuit (DC means "direct current" in English).

[0040] The output grid system 20 itself has an AC / DC converter 22, which is connected to the output grid 24. The AC / DC converter 22 can be a bidirectional AC / DC converter 22, or alternatively, two unidirectional AC / DC converters 22 can be used, which work in opposite directions to each other (AC means "alternating current (current / voltage)", which is "Alternating Current" in English). Thus, according to the operating direction of the AC / DC converter 22, electrical energy (i.e., current) can be output from the intermediate circuit 40 to the output grid 24, or fed into the intermediate circuit 40 from the output grid 24.

[0041] The auxiliary equipment grid 30 itself has auxiliary equipment 34, such as pumps, sensors, heat exchangers, seals, air compressors, circulation fans, charge air coolers and / or humidifiers, for assisting the operation of the fuel cell system 12. The auxiliary equipment 34 is connected to the intermediate circuit 40 via a converter 32. The converter 32 is designed here as a DC / AC converter, but can also be designed as a DC / DC converter.

[0042] The load resistor network 50 has a power electronics 54 electrically connected to the intermediate circuit 40 and a load resistor 52. The power electronics 54 itself can have different components, such as, in particular, a voltage meter for measuring the voltage in the intermediate circuit 40 and / or a regulator for regulating the electrical energy fed from the intermediate circuit 40 into the load resistor 52.

[0043] Figure 3 The process of the exemplary method 100 of an embodiment of the present invention is illustrated by a fuel cell system power curve 120 of the power (in kW) of the fuel cell system 12 and an auxiliary facility grid power curve of the power (in kW) of the auxiliary facility grid 30 over time.

[0044] In the first step 102 of the method, the fuel cell system 12 is operated at full power and provides, for example, 60 kW (see fuel cell system power curve 120 for the time range of the first step 102 ). A portion of the power of the fuel cell system 12 is provided to the auxiliary system grid 30 , as can be seen from the auxiliary system power curve 130 .

[0045] It is now assumed that a grid fault 104, in particular a grid fault of the output grid 24, occurs in the second step of the method 100, resulting in the output grid 24 no longer being able to draw electrical energy from the intermediate circuit 40. The occurrence of the grid fault 104 can advantageously be detected by the power electronics 54, which determines by means of its voltage measuring device whether the voltage in the intermediate circuit 40 is higher than a maximum voltage predefined for the grid fault 104, and thereby detects the grid fault 104.

[0046] Then, in a third step 106 of the method 100, the power electronics 54 activates the load resistor 52. In the intermediate circuit 40, the electrical energy generated successively by the fuel cell system 12 and fed into the intermediate circuit 40 is now input to the load resistor 52, which converts it into waste heat. This conversion takes place outside the fuel cell system 12. The load resistor 52 is preferably cooled during its operation, particularly preferably water-cooled.

[0047] In parallel with or after the third step 106, the fourth step 108 of the method 100 is initiated, in which, after the grid fault 104 is detected, the load point of the operating fuel cell stack 10 is lowered within the power dynamic range available to the fuel cell stack 10. The electrical energy generated thereby decreases over time, as can be seen from the fuel cell system power curve 120 within the time range of the third step 106. The electrical energy that needs to be delivered from the intermediate circuit 40 to the load resistor 52 is thereby reduced.

[0048] Once the grid fault 104 has been eliminated, a grid restoration 110 of the output grid 24 takes place at a certain point in time as a fifth step of the method 100 . At this point, the output grid 24 can again receive an electrical energy feed from the intermediate circuit 40 .

[0049] Accordingly, according to the sixth step 112 of the method 100, the electrical energy is again fed to the output grid 24 instead of the load resistor 52. In this case, the load resistor 52 can be disconnected from the power electronics 54. The determination of the grid restoration 110 can also be realized here by voltage measurement at the power electronics 54. In parallel with the sixth step 112 or after it, the seventh step 114 of the method 100 is performed, in which, after the grid restoration 110 is detected, the load point of the operating fuel cell stack 10 is increased again within the power dynamic range available to the fuel cell stack 10.

[0050] Figure 4 An alternative embodiment of a fuel cell system 1 is shown, in which the fuel cell stacks 10 of a fuel cell system 12 are connected in series with one another, for example. Furthermore, the output grid 24 and the auxiliary system 34 share a common DC / AC converter 22 .

[0051] However, it is important that the load resistor 52 is not located in the intermediate circuit 40 but between the DC connection of the fuel cell stack 10 and the DC / AC converter 22. The power electronics 54 responsible for controlling and / or regulating the load resistor 52 is preferably part of the DC / AC converter 22.

[0052] The load resistor 52 can therefore be connected directly to the DC terminals of the fuel cell stack 10 or to the intermediate circuit 40, such as Figure 1 and Figure 2 The control loop of the control device can be realized on a separate control unit with a load resistor transistor switch or on a central control device.

[0053] The above explanations of the embodiments describe the present invention only within the scope of examples.

[0054] Reference numerals list

[0055] 1 Fuel cell equipment

[0056] 10 Fuel Cell Stack

[0057] 12 Fuel Cell System

[0058] 14 DC / DC Converter

[0059] 20 Output grid system

[0060] 22 DC / AC converter (for output grid system)

[0061] 24 Output grid

[0062] 30 Auxiliary facilities power grid

[0063] 32 Converter (for auxiliary utility grid)

[0064] 34 Auxiliary facilities

[0065] 40 Intermediate circuit

[0066] 50 Load resistor network

[0067] 52 Load resistance

[0068] 54 Power Electronics

[0069] 100 Methods

[0070] 102 First Step

[0071] 104 Grid failure

[0072] 106 Step 3

[0073] 108 Step 4

[0074] 110 Power grid restored

[0075] 112 Step 6

[0076] 114 Step 7

[0077] 120 Fuel Cell System Power Curve

[0078] 130 Auxiliary facilities power grid power curve

Claims

1. A fuel cell device (1) having a fuel cell system (12), comprising a plurality of fuel cell stacks (10), in, The fuel cell system (12) is electrically connected or can be electrically connected to an output grid system (20) including an output grid (24) so ​​as to supply the output grid (24) with electrical energy generated by the operation of the fuel cell stack (10). It is characterized in that The fuel cell device (1) also has a load resistor network (50), which includes a load resistor (52) for ensuring the load point of the fuel cell stack (10) when a fault occurs in the output grid system (20), in particular a grid fault (104), wherein the fuel cell system (12) is electrically connected to the load resistor network (50) so as to supply the load resistor network (50) with electrical energy generated by the operation of the fuel cell stack (10).

2. The fuel cell device (1) as claimed in claim 1, It is characterized in that The load resistor (52) is designed to convert electrical energy into waste heat.

3. The fuel cell device (1) according to claim 1 or 2, It is characterized in that The load resistor (52) is arranged outside the fuel cell stack (12).

4. The fuel cell device (1) as claimed in any one of the preceding claims, It is characterized in that The fuel cell device (1) comprises a cooling unit for cooling the load resistor (52).

5. The fuel cell device (1) as claimed in any one of the preceding claims, It is characterized in that The load resistor network (50) comprises power electronics (54) which are designed to enable the load resistor (52) when the grid fault (104) occurs.

6. The fuel cell device (1) as claimed in claim 5, It is characterized in that The power electronics (54) is designed to continuously measure the voltage in an intermediate circuit (40) between the fuel cell system (12) and the output grid system (20) and to activate the load resistor (52) when a voltage increase occurs in the intermediate circuit (40).

7. The fuel cell device (1) according to claim 6, It is characterized in that The power electronics (54) has a regulator for regulating the electrical energy supplied to the load resistor (52) as a function of a voltage measured in the intermediate circuit (40).

8. The fuel cell device (1) as claimed in any one of the preceding claims, It is characterized in that The fuel cell system (12) is designed to reduce the load point of the operating fuel cell stack (10) in the event of a fault.

9. The fuel cell device (1) as claimed in any one of the preceding claims, It is characterized in that The load resistor network (50) is arranged in an intermediate circuit (40) between a DC / DC converter (16) of the fuel cell stack (10) and a DC / AC converter (22) of the output grid system (20).

10. The fuel cell device (1) according to any one of claims 1 to 8, It is characterized in that The load resistor network (50) is arranged between the DC connection terminal of the fuel cell stack (10) and the DC / AC converter (22) of the output grid (24).

11. The fuel cell device (1) as claimed in any one of the preceding claims, It is characterized in that The fuel cell device (1) includes an auxiliary facility grid (30), which contains auxiliary facilities (34) for assisting the operation of the fuel cell system (12), wherein the fuel cell system (12) is electrically connected to the auxiliary facility grid (30) so as to supply the auxiliary facility grid (30) with electrical energy generated by the operation of the fuel cell stack (10).

12. A method (100) for securing a load point of a fuel cell stack (10) of a fuel cell system (12) of a fuel cell device (1) in the event of a fault in an output grid system (20) supplied with electrical energy generated by the operation of the fuel cell stack (10), in, The method (100) is characterized by the following steps: - a fault occurs, in particular a grid fault (104) of the output grid system (20), - determining the fault that has occurred, in particular a network fault (104), and - The electrical energy of the fuel cell system (1) is converted into waste heat between the fuel cell system (12) and an output grid system (20) by means of a load resistor (52).

13. The method (100) of claim 12, It is characterized in that An occurring fault, in particular the grid fault (104), is determined by measuring a voltage increase in an intermediate circuit (40) between the fuel cell system (12) and the output grid system (20).

14. The method (100) of claim 13, It is characterized in that The electrical energy converted by the load resistor (52) is regulated according to the voltage measured in the intermediate circuit (40).

15. The method (100) according to any one of claims 12 to 14, It is characterized in that After the fault, in particular the grid fault (104), has been detected, the load point of the operating fuel cell stack (10) is reduced within the load dynamic range available for the fuel cell stack (10).

Images