Fuel cell system, control device, and program

Abstract

This fuel cell system comprises a fuel cell and a control device. The control device determines a temperature band for controlling the temperature of the fuel cell for each of a plurality of levels corresponding to states of the fuel cell and, with the current change speed determined for the temperature band being used as an upper limit, changes a current outputted by the fuel cell. The level is determined so that the level advances as a discretionary state of the fuel cell advances in one direction. The temperature band is determined so as to increase as the level advances.

Description

Fuel cell system, control device and program CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to Japanese Patent Application No. 2023-108226, filed on June 30, 2023, the entire disclosure of which is incorporated herein by reference.

[0002] The present disclosure relates to a fuel cell system, a control device, and a program.

[0003] In solid oxide fuel cells, fuel gas supplied to the fuel cell is produced from raw fuel by steam reforming. The steam reforming reaction is an endothermic reaction. The heat required for the reaction is supplied by combustion of off-gas discharged from the fuel cell and unreacted gas contained in the off-gas. In order to improve the power generation efficiency of such solid oxide fuel cells, it has been proposed to periodically correct the upper limit of the proportion of fuel gas used for power generation out of the total fuel gas supplied to the fuel cell (see Patent Document 1).

[0004] Patent No. 6758232

[0005] In one embodiment, (1) a fuel cell system comprises: a fuel cell; and a control device in which a temperature band for controlling the temperature of the fuel cell is set at a plurality of levels according to the state of the fuel cell, and which changes the current output by the fuel cell up to an upper limit of the current change rate set for the temperature band; wherein the level is set to advance as any state of the fuel cell advances in one direction, and the temperature band is set to increase as the level advances.

[0006] (2) In the fuel cell system of (1) above, the temperature band is divided into a plurality of temperature subregions, a different current change rate is defined for each of the temperature subregions, and the plurality of temperature subregions are defined to be continuous at the same level.

[0007] (3) In the fuel cell system of (1) or (2), the control device advances the level when the voltage of the fuel cell is equal to or lower than a threshold value.

[0008] (4) In the fuel cell system according to any one of (1) to (3) above, the level is determined to be only maintained or advanced.

[0009] (5) In the fuel cell system according to any one of (1) to (4) above, the temperature difference between the temperature bands for which the same current change rate is set at adjacent levels is set to be constant.

[0010] (6) In the fuel cell system of (2) above, when the level is most advanced, the control device changes the current output by the fuel cell with the minimum value of the current change rate defined for each of the temperature subranges as the upper limit.

[0011] (7) In any of the fuel cell systems (1) to (6) above, when the level has reached the maximum or has reached the next level below the maximum, the control device further reduces the temperature of the fuel cell.

[0012] In one embodiment, (8) a fuel cell system includes a fuel cell and a control device that changes the current output by the fuel cell with a current change rate as an upper limit, and when any state of the fuel cell progresses in one direction, the control device increases or decreases the current change rate according to the temperature of the fuel cell.

[0013] In one embodiment, (9) the control device is configured such that a temperature band for controlling the temperature of the fuel cell is set at a plurality of levels according to the state of the fuel cell, and the current output by the fuel cell is changed with the current change rate set for the temperature band as an upper limit, and the level is set to advance as any state of the fuel cell advances in one direction, and the temperature band is set to increase as the level advances.

[0014] In one embodiment, (10) the program causes the control device to change the current output by the fuel cell with a current change rate set for the temperature range as an upper limit, the temperature range for controlling the temperature of the fuel cell being set for a plurality of levels according to the state of the fuel cell, and the level being set to advance as any state of the fuel cell advances in one direction.

[0015] The present invention relates to a fuel cell system and a method for controlling the output current of a fuel cell system, and more particularly to a fuel cell control system for controlling a temperature range of a fuel cell.

[0016] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the following drawings, the same components are designated by the same reference numerals.

[0017] 1 , a fuel cell system 10 according to one embodiment of the present disclosure includes a fuel cell 11 and a control device 19. The fuel cell system 10 may further include a temperature sensor 12, a voltage sensor 13, a first supply device 14, a second supply device 15, a reformer 16, a third supply device 17, and a combustion unit 18.

[0018] The fuel cell 11 generates electricity through an electrochemical reaction using fuel gas and air. The fuel cell 11 may include a fuel cell unit. The fuel cell 11 may include a plurality of fuel cell units. The plurality of fuel cell units may form a cell stack. The cell stack may have any shape, for example, a hollow plate, a flat plate, a metal support, a cylinder, or the like. The fuel cell unit may be a solid oxide fuel cell unit. In the fuel cell 11, all of the fuel gas and oxygen gas in the air may not undergo an electrochemical reaction, and unreacted fuel gas and oxygen gas may be discharged.

[0019] The temperature sensor 12 may detect the temperature of the fuel cell 11. The temperature sensor 12 may detect the temperature of the cell stack of the fuel cell 11. The temperature sensor 12 may detect the temperature at a position of the cell stack of the fuel cell 11 that is expected to be the center in the vertical direction when the fuel cell system 10 is installed. The temperature sensor 12 is, for example, a thermocouple.

[0020] The voltage sensor 13 may measure the voltage of the fuel cell 11. The voltage sensor 13 may measure the voltage of the cell stack of the fuel cell 11.

[0021] The first supply device 14 directly or indirectly supplies fuel gas to the fuel cell 11. For example, the first supply device 14 supplies raw fuel to the reformer 16, thereby supplying fuel gas obtained by reforming the raw fuel as described below to the fuel cell 11. The first supply device 14 may directly or indirectly adjust the amount of fuel gas supplied to the fuel cell 11. The first supply device 14 may be, for example, a pump with a variable duty ratio.

[0022] The second supply device 15 may adjust the amount of water supplied to the water reformer 16. The second supply device 15 may be, for example, a pump with a variable duty ratio.

[0023] The reformer 16 is positioned in a direction that is expected to be directed vertically upward from the combustion unit 18 when the fuel cell system 10 is installed. The reformer 16 contains a reforming catalyst. The reforming catalyst may generate fuel gas by steam reforming using a raw fuel and steam. The reforming catalyst is heated by heat generated by combustion in the combustion unit 18 to carry out the steam reforming reaction. The raw fuel includes, for example, light hydrocarbons such as methane, ethane, propane, and butane. The raw fuel is, for example, city gas or LPG containing the light hydrocarbons. Steam is supplied to the reformer 16 as liquid reforming water. The liquid reforming water may be vaporized into steam in a vaporization unit provided in the reformer 16. The fuel gas includes, for example, hydrogen gas.

[0024] The third supply device 17 may adjust the amount of oxygen-containing gas supplied to the fuel cell 11. The oxygen-containing gas may be air. The third supply device 17 may be, for example, a blower with a variable duty ratio.

[0025] The combustion unit 18 burns unreacted fuel gas in the fuel cell 11 using unreacted oxygen gas. The combustion unit 18 can heat the reformer 16 using the heat generated by burning the unreacted fuel gas. The combustion unit 18 may heat the reformer 16 to provide energy for causing a steam reforming reaction in the reformer 16.

[0026] The control device 19 includes at least one processor, at least one dedicated circuit, or a combination thereof. The processor may be a general-purpose processor such as a CPU (Central Processing Unit) or a GPU (Graphics Processing Unit), or a dedicated processor specialized for a specific process. The dedicated circuit may be, for example, an FPGA (Field-Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit). The control device 19 may control the operation of the fuel cell system 10. The control device 19 stores in its memory a program describing the processing content for realizing each function of the fuel cell system 10. The processor of the control device 19 can read and execute the program.

[0027] After starting up the fuel cell system 10, the control device 19 may control each component of the fuel cell system 10, such as the voltage of the fuel cell 11 and the amount of supply from the first supply device 14, the second supply device 15, and the third supply device 17, so that the fuel cell 11 generates power of the current value of the required load. In the following description of the present application, the amount of supply may mean a flow rate, i.e., the amount that flows per short period of time.

[0028] The control device 19 determines the appropriate operating temperature of the fuel cell 11 from a predetermined temperature range depending on the state (e.g., deterioration state) of the fuel cell 11. The control device 19 controls the fuel cell 11 so that it is maintained at an appropriate temperature.

[0029] The control device 19 performs control to change the current of the fuel cell 11. For example, when the power demand of the user increases, the control device 19 may change the current output by the fuel cell 11 as load following control. The control device 19 may change the current of the fuel cell 11 at high speed by feedback control. The control device 19 may always perform load following control while the fuel cell 11 is in operation.

[0030] A sudden increase in the output current of the fuel cell 11 increases energy loss due to Joule loss, thereby reducing cost efficiency. From the perspective of improving cost efficiency, a current change rate is set, which is the upper limit of the rate at which the control device 19 changes the current of the fuel cell 11. Specifically, the current change rate may be set depending on the fuel cell 11.

[0031] In particular, when the temperature of the fuel cell 11 is low, the electrical resistance of the cell stack of the fuel cell 11 increases, and the voltage of the fuel cell 11 decreases. If the control device 19 suddenly increases the output current of the fuel cell 11 at this time, energy loss due to Joule loss will increase further. Therefore, from the perspective of further improving cost efficiency, the fuel cell system 10 determines a current change rate according to the temperature of the fuel cell 11. Specifically, the temperature band may be divided into multiple temperature subranges, and a current change rate may be determined for each temperature subrange. A different current change rate may be determined for each temperature subrange. The higher the temperature subrange, the greater the current change rate may be. In this embodiment, for example, the number of temperature subranges is determined to be four. The number of temperature subranges may be two or more.

[0032] Depending on the change in the state of the fuel cell 11, the rate of change in current determined according to the temperature of the fuel cell 11 may no longer be appropriate. In particular, if the fuel cell 11 deteriorates, the electrical resistance of the cell stack of the fuel cell 11 increases, causing a drop in the voltage of the fuel cell 11. If the control device 19 suddenly increases the output current of the fuel cell 11 at this time, energy loss due to Joule loss will increase further.

[0033] Therefore, from the viewpoint of improving cost efficiency, in the fuel cell system 10, a temperature band corresponding to, for example, the same current increase rate is defined for each of a plurality of levels according to the state of the fuel cell 11. The control device 19 advances the level as the state of the fuel cell 11 progresses in one direction. The control device 19 raises the temperature band as the level advances.

[0034] The state of the fuel cell 11 progressing in one direction means, for example, that the deterioration of the fuel cell 11 progresses. In the above example, the progression of the level means that the control device 19 increases the level. The level may be expressed as a natural number. When the fuel cell system 10 is shipped, the level may be level 1. In this embodiment, the number of levels is five. However, the number of levels may be two or more.

[0035] At the same level, multiple temperature sub-regions may be contiguous, in other words, the lower temperature side of two adjacent temperature sub-regions may be contiguous with the higher temperature side of the adjacent temperature sub-region.

[0036] Referring to Figure 2, multiple temperature subranges will be described using level 1 as an example. When the temperature of the fuel cell 11 is less than 600°C, the maximum allowable current change rate may be 0.04 A / s. When the temperature of the fuel cell 11 is 600°C or higher and lower than 630°C, the current change rate may be 0.08 A / s. When the temperature of the fuel cell 11 is 630°C or higher and lower than 660°C, the current change rate may be 0.16 A / s. When the temperature of the fuel cell 11 is 660°C or higher, the current change rate may be 0.35 A / s.

[0037] The control device 19 may advance the level when the voltage of the fuel cell 11 is equal to or lower than a threshold value. The control device 19 may advance the level by one when the voltage of the fuel cell 11 is equal to or lower than a threshold value. The threshold value may be a value slightly higher than the voltage of the low voltage protection function that is stopped when the voltage of the fuel cell 11 becomes too low. The threshold value may be, for example, 15 V. The level may be set to be maintained or to only advance. The level may be saved even when the fuel cell system 10 or the fast load following control is stopped. For example, the level may be saved in a non-volatile memory included in the control device 19.

[0038] The control device 19 may advance the level only when the state in which the voltage of the fuel cell 11 remains equal to or lower than the threshold continues for a certain period of time, which may be, for example, one second.

[0039] The temperature difference between the temperature bands at adjacent levels for which the same current change rate is set may be constant. More specifically, the temperature difference between the lower limit values ​​of two adjacent temperature bands may be constant, and the temperature difference between the upper limit values ​​may be constant. As a specific example, in this embodiment, the temperature difference between the temperature bands at adjacent levels for which the same current change rate is set is 20°C between levels 1 to 4. The temperature difference between the temperature bands at which the same current change rate is set between the maximum level and the level immediately preceding the maximum level may be significantly larger than that between other adjacent levels. Specifically, the temperature difference between the temperature bands at which the same current change rate is set between level 5 and level 4 may be 140°C.

[0040] When any state of the fuel cell 11 progresses in one direction, the control device 19 may increase or decrease the rate of change of current in accordance with the temperature of the fuel cell 11. For example, the control by the control device 19 to increase or decrease the rate of change of current will be described using an example in which the level progresses from level 1 to level 2. When the temperature of the fuel cell 11 is 620°C, the control device 19 maintains the rate of change of current at 0.08 A / s. When the temperature of the fuel cell 11 is 610°C, the control device 19 decreases the rate of change of current from 0.08 A / s to 0.04 A / s. In another embodiment, when any state of the fuel cell 11 progresses in one direction, the control device 19 may increase the rate of change of current based on the temperature of the fuel cell 11.

[0041] As another example, when the level is at its most advanced, the control device 19 may change the current output by the fuel cell 11 with the minimum current change rate set for each temperature band as the upper limit. For example, when there are five levels and the level is level 5, the current change rate may be 0.04 A / s regardless of the temperature of the fuel cell 11.

[0042] When the level has reached the maximum, or when it has reached the level just before the maximum, the control device 19 may further reduce the temperature of the fuel cell 11. For example, when the level is level 5, or when the level is level 4, the control device 19 may further reduce the temperature of the fuel cell 11. The control device 19 may reduce the current or voltage of the fuel cell 11, thereby reducing the temperature of the fuel cell 11. The control device 19 may also reduce the temperature of the fuel cell 11 by causing a fan or the like to blow air.

[0043] Next, the output current control of the fuel cell system 10 executed by the control device 19 in this embodiment will be described with reference to the flowchart of Fig. 3. The control device 19 starts the output current control, for example, periodically, while the fuel cell system 10 is in operation.

[0044] In step S100, the control device 19 acquires a level indicating an arbitrary state of the fuel cell 11. For example, the control device 19 may read a level stored in a non-volatile memory.

[0045] In step S101, the control device 19 determines whether the level is maximum. If the level is maximum, the control device 19 terminates the output current control. Furthermore, if the level is maximum while the load following control is being performed, the control device 19 may terminate the load following control of the fuel cell 11. If the level is not maximum, the process proceeds to step S102.

[0046] In step S102, the control device 19 determines whether or not the load following control is being executed. If the control device 19 is executing the load following control, the process proceeds to step S103. If the control device 19 is not executing the load following control, the process proceeds to step S104.

[0047] In step S103, the control device 19 changes the current output by the fuel cell 11 at the level acquired in step S100, with the current change rate set for the temperature range in which the temperature of the fuel cell 11 is controlled as the upper limit.

[0048] In step S104, the control device 19 determines whether the voltage of the fuel cell 11 is equal to or less than a threshold value. If the voltage of the fuel cell 11 is equal to or less than the threshold value, the process proceeds to step S105. If the voltage of the fuel cell 11 exceeds the threshold value, the output current control ends. As another example, in step S104, the control device 19 may determine whether the state in which the voltage of the fuel cell 11 is equal to or less than the threshold value has continued for a certain period of time.

[0049] In step S105, the control device 19 advances the level by 1. After advancing the level, the control device 19 ends the output current control.

[0050] To improve user convenience, it is preferable for the control device 19 to quickly increase the output current of the fuel cell 11 to meet the user's power demand. On the other hand, if the temperature of the fuel cell 11 is low or if the fuel cell 11 has deteriorated, and the control device 19 suddenly increases the output current of the fuel cell 11, energy loss due to Joule loss increases, and cost efficiency decreases.

[0051] The inventors have discovered that the more the condition of the fuel cell 11 progresses in one direction (for example, the more the fuel cell 11 deteriorates), the more the level corresponding to that condition is increased, and the control device 19 raises the temperature band as the level increases, thereby enabling the fuel cell system 10 to reduce the decline in cost efficiency regardless of changes in the condition of the fuel cell 11.

[0052] In addition, in the fuel cell system 10 of this embodiment, the temperature band is divided into multiple temperature subranges, a different current change rate is set for each of the temperature subranges, and the multiple temperature subranges are set to be continuous at the same level. With this configuration, the fuel cell system 10 can achieve both user convenience and cost efficiency based on the temperature of the fuel cell 11 and the level corresponding to the state of the fuel cell 11.

[0053] Furthermore, the fuel cell system 10 of this embodiment advances the level when the voltage of the fuel cell 11 is equal to or lower than a threshold value. When the cell stack of the fuel cell 11 deteriorates, the electrical resistance increases and the voltage of the fuel cell 11 decreases. Therefore, the fuel cell system 10 can determine that the fuel cell 11 has deteriorated when the voltage of the fuel cell 11 is equal to or lower than a threshold value.

[0054] Furthermore, in the fuel cell system 10 of this embodiment, the level is determined in accordance with the progression of deterioration of the fuel cell 11, and is therefore set to only be maintained or increased, and will not decrease, so the fuel cell system 10 can more accurately recognize the state of the fuel cell 11.

[0055] In addition, in the fuel cell system 10 of this embodiment, the temperature difference between the temperature bands at adjacent levels for which the same current change rate is set is constant. This configuration allows the temperature bands to more appropriately reflect the state of the fuel cell 11.

[0056] Furthermore, in the fuel cell system 10 of this embodiment, when the level is at its most advanced, the current output by the fuel cell 11 is changed using the minimum current change rate set for each temperature band as an upper limit. If the current change rate is increased when the level is at its most advanced, the temperature of the fuel cell 11 may become too high. This may result in a decrease in the power generation efficiency of the fuel cell 11, a decrease in the durability of the fuel cell 11, and so on. In response to this, the control device 19 changes the current output by the fuel cell 11 using the minimum current change rate set for each temperature band as an upper limit, thereby gradualing the change in current and enabling the fuel cell system 10 to maintain an appropriate temperature of the fuel cell 11.

[0057] Furthermore, the fuel cell system 10 of this embodiment lowers the temperature of the fuel cell 11 when the level reaches the maximum or when the level reaches just before the maximum. With this configuration, the fuel cell system 10 can further protect the fuel cell 11 while further ensuring the power generation efficiency of the fuel cell 11.

[0058] In the fuel cell system 10 of this embodiment, when any state of the fuel cell 11 progresses in one direction, the control device 19 increases or decreases the current change rate in accordance with the temperature of the fuel cell 11. When the control device 19 increases the current change rate, the output current of the fuel cell 11 increases rapidly in response to the user's power demand. As a result, the fuel cell system 10 can improve user convenience. On the other hand, when the control device 19 decreases the current change rate, Joule loss caused by the control device 19 abruptly increasing the output current of the fuel cell 11 can be reduced. As a result, the fuel cell system 10 can improve cost efficiency. Therefore, with this configuration, the fuel cell system 10 can switch between operating in a state that pursues user convenience and operating in a state that pursues cost efficiency based on the temperature of the fuel cell 11, in other words, the usage state of the fuel cell system 10.

[0059] The above has described an embodiment of the fuel cell system 10, but the present disclosure can also be embodied as a method or program for implementing the device, as well as a storage medium on which a program is recorded (for example, an optical disk, a magneto-optical disk, a CD-ROM, a CD-R, a CD-RW, a magnetic tape, a hard disk, or a memory card).

[0060] Furthermore, the implementation form of the program is not limited to application programs such as object code compiled by a compiler or program code executed by an interpreter, but may also be in the form of a program module incorporated into an operating system. Furthermore, the program may or may not be configured so that all processing is performed solely by the CPU on the control board. The program may also be configured so that part or all of it is executed by another processing unit mounted on an expansion board or expansion unit added to the board as needed.

[0061] The drawings illustrating the embodiments of the present disclosure are schematic, and the dimensional ratios and the like in the drawings do not necessarily correspond to the actual ones.

[0062] Although the embodiments of the present disclosure have been described based on the drawings and examples, it should be noted that those skilled in the art could make various modifications or alterations based on the present disclosure. Therefore, it should be noted that these modifications or alterations are included in the scope of the present disclosure. For example, the functions included in each component can be rearranged so as not to cause logical inconsistencies, and multiple components can be combined or divided into one.

[0063] All of the features described in this disclosure and / or all steps of all of the disclosed methods or processes may be combined in any combination except combinations in which these features are mutually exclusive. Furthermore, each feature described in this disclosure may be replaced by an alternative feature serving the same, equivalent, or similar purpose, unless expressly denied. Thus, unless expressly denied, each disclosed feature is only one example of a generic series of identical or equivalent features.

[0064] Furthermore, embodiments of the present disclosure are not limited to the specific configurations of any of the above-described embodiments, but rather extend to any novel feature or combination thereof described herein, or any novel method or process step or combination thereof described herein.

[0065] In this disclosure, descriptions such as "first" and "second" are identifiers for distinguishing the configuration. Configurations distinguished by descriptions such as "first" and "second" in this disclosure can have their numbers exchanged. For example, a first supply device can exchange the identifiers "first" and "second" with a second supply device. The exchange of identifiers is performed simultaneously. The configurations remain distinguished even after the identifier exchange. Identifiers may be deleted. A configuration from which an identifier has been deleted is distinguished by a symbol. The descriptions of identifiers such as "first" and "second" in this disclosure should not be used solely to interpret the order of the configurations or to justify the existence of an identifier with a smaller number.

[0066] REFERENCE SIGNS LIST 10 fuel cell system 11 fuel cell 12 temperature sensor 13 voltage sensor 14 first supply device 15 second supply device 16 reformer 17 third supply device 18 combustion section 19 control device

Claims

1. Fuel cells and The temperature range for controlling the temperature of the fuel cell is defined for each of several levels corresponding to the state of the fuel cell, and the control device changes the current output by the fuel cell up to a current change rate defined for each temperature range, The level is set to advance as any state of the fuel cell progresses in one direction. The aforementioned temperature range is defined to increase as the aforementioned level progresses. Fuel cell system.

2. In the fuel cell system according to claim 1, The temperature range is divided into multiple sub-temperature regions, and a different current change rate is defined for each of the sub-temperature regions. At the same level, multiple temperature sub-regions are defined to be continuous. Fuel cell system.

3. In the fuel cell system according to claim 1 or 2, The control device advances the level when the voltage of the fuel cell is below a threshold. Fuel cell system.

4. In the fuel cell system according to claim 1 or 2, The aforementioned levels are defined to be maintained or advanced only. Fuel cell system.

5. In the fuel cell system according to claim 1 or 2, The temperature difference between adjacent temperature zones where the same current change rate is defined is constant. Fuel cell system.

6. In the fuel cell system according to claim 2, When the level is at its most advanced, the control device changes the current output by the fuel cell, with the minimum value among the current change rates defined for each of the temperature ranges as the upper limit. Fuel cell system.

7. In the fuel cell system according to claim 1 or 2, If the aforementioned level has reached its maximum, or one level below the maximum, the control device further lowers the temperature of the fuel cell. Fuel cell system.

8. Fuel cells and A control device that changes the current output by the fuel cell, with the current change rate being the upper limit, Equipped with, When any state of the fuel cell progresses in one direction, the control device increases or decreases the rate of current change according to the temperature of the fuel cell. Fuel cell system.

9. A temperature range for controlling the temperature of the fuel cell is defined for each of several levels corresponding to the state of the fuel cell, and the current output by the fuel cell is changed up to a current change rate defined for that temperature range. The level is set to advance as any state of the fuel cell progresses in one direction. The aforementioned temperature range is defined to increase as the aforementioned level progresses. Control device.

10. The control device changes the current output by the fuel cell, up to a current change rate defined for each temperature range. The temperature range for controlling the temperature of the fuel cell is defined for each of several levels corresponding to the state of the fuel cell. The level is set to advance as any state of the fuel cell progresses in one direction. The aforementioned temperature range is defined to increase as the aforementioned level progresses. program.