Fuel cell system

Abstract

This fuel cell system includes a converter, a plurality of power generation units, a plurality of current sensors, and a control unit. Each of the power generation units includes a fuel cell. The plurality of power generation units are electrically connected in parallel to the converter. Each of the current sensors detects a current flowing through the power generation unit. The control unit controls the flow rates of a fuel gas, water, and air supplied to the power generation unit according to a current value of the power generation unit.

Description

fuel cell system CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to Japanese Patent Application No. 2024-057880, filed on March 29, 2024, the entire disclosure of which is incorporated herein by reference.

[0002] The present invention relates to a fuel cell system.

[0003] It has been proposed to supply fuel to a plurality of fuel cells in parallel in a configuration in which the total current flowing through the plurality of fuel cells connected in parallel is controlled by a power conditioner (see Patent Document 1).

[0004] Patent No. 6230925

[0005] A fuel cell system according to a first aspect includes a converter; a plurality of power generation units each having a fuel cell and electrically connected in parallel to the converter; a plurality of current sensors for detecting the current flowing through each of the plurality of power generation units; and a control unit for controlling the flow rates of fuel gas, water, and air supplied to each of the power generation units in accordance with the current value of each of the power generation units.

[0006] It is a configuration diagram showing the schematic configuration of a fuel cell system according to the present embodiment. It is a configuration diagram showing the schematic configuration of a power generation unit of Fig. 1. It is a flowchart for explaining a flow rate adjustment process executed by a control unit of Fig. 1.

[0007] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the following drawings, the same components are denoted by the same reference numerals.

[0008] 1 , a fuel cell system 10 according to an embodiment of the present disclosure includes a converter 11, a plurality of power generation units 12, a plurality of current sensors 13, and a control unit 14. The fuel cell system 10 may further include a plurality of temperature sensors 15. The fuel cell system 10 may further include a backflow prevention element that prevents backflow of current, and a voltmeter, between the converter 11 and the power generation unit 12.

[0009] The converter 11 may convert the voltage of the power generation unit 12 to a desired voltage. The converter 11 may constitute a power adjustment device together with a bidirectional DC / AC converter that converts DC power and AC power into each other. The converter 11 may constitute a power adjustment device together with a DC / DC converter that converts the voltage of DC current. The power adjustment device is, for example, a power conditioner. The power adjustment device may supply the converted AC power or DC current to the load device 22. The power adjustment device may adjust the current value based on the required load of the fuel cell system 10. The required load is the power value required of the fuel cell system 10 by a consumer facility that uses the fuel cell system 10.

[0010] The plurality of power generation units 12 are electrically connected in parallel to the converter 11. The plurality of power generation units 12 may also be connected to the converter 11 via relays 23. As shown in Fig. 2, the power generation unit 12 has at least one fuel cell 16. In a configuration in which the power generation unit 12 has a plurality of fuel cells 16, the plurality of fuel cells 16 may be connected in series. The power generation unit 12 may further have a combustion unit 17, a reformer 18, a first supply unit 19, a second supply unit 20, and a third supply unit 21.

[0011] The fuel cell 16 generates electricity through an electrochemical reaction using a fuel gas and air. The fuel gas may include, for example, hydrogen gas. Specifically, the fuel cell 16 performs an electrochemical reaction using oxygen gas in the air. The fuel cell 16 may include a fuel cell unit. The fuel cell 16 may include a plurality of fuel cell units. The plurality of fuel cell units may form a cell stack. The fuel cell unit may be a solid oxide fuel cell unit. In the fuel cell 16, not all of the fuel gas and oxygen gas in the air may undergo an electrochemical reaction, and unreacted fuel gas and oxygen gas may be discharged.

[0012] The combustion unit 17 may combust unreacted fuel gas in the fuel cell 16 using unreacted oxygen gas. The combustion unit 17 may heat the reformer 18 using heat generated by burning the unreacted fuel gas. The combustion unit 17 may heat the reformer 18 to provide energy for a steam reforming reaction in the reformer 18. The combustion unit 17 may be located in a direction opposite to the first direction from the reformer 18 to effectively heat the reformer 18. In the fuel cell system 10, the first direction is a direction that is assumed to be directed vertically upward when the fuel cell system 10 is installed. The combustion unit 17 may be, for example, a space in the first direction from the fuel cell 16. Unreacted fuel gas and unreacted oxygen gas injected from an outlet of the fuel cell 16 may be combusted in this space. Alternatively, the combustion unit 17 may be, for example, a burner located in the first direction from the fuel cell 16.

[0013] The reformer 18 may generate fuel gas by steam reforming raw fuel and water. The raw fuel may include light hydrocarbons such as methane. The reformer 18 may contain a reforming catalyst. The reforming catalyst may generate fuel gas from the raw fuel and water. Steam may be supplied to the reformer 18 as liquid reforming water and vaporized into steam in a vaporizer provided in the reformer 18.

[0014] The first supply unit 19 may supply the fuel gas directly or indirectly to the fuel cell 16. For example, the first supply unit 19 may supply the fuel gas indirectly to the fuel cell 16 by supplying raw fuel to the reformer 18. In the following description, the fuel gas will be described as being supplied to the fuel cell 16 indirectly via the reformer 18. The first supply unit 19 may adjust the amount of fuel gas supplied. The first supply unit 19 may be, for example, a pump whose duty ratio is changeable.

[0015] The second supply unit 20 may supply water to the reformer 18. The second supply unit 20 may adjust the amount of water supplied to the reformer 18. The second supply unit 20 may be, for example, a pump whose duty ratio is changeable.

[0016] The third supply unit 21 may supply air to the fuel cell 16. The third supply unit 21 may adjust the amount of air supplied to the fuel cell 16. The third supply unit 21 may be, for example, a blower whose rotation speed is adjustable.

[0017] A current sensor 13 is provided in each of the plurality of power generating units 12. The current sensor 13 detects the current flowing through the power generating unit 12. The current sensor 13 is, for example, a resistance detection type current sensor or a ground field detection type current sensor.

[0018] A temperature sensor 15 is provided in each of the plurality of power generation units 12. The temperature sensor 15 detects the temperature of the power generation unit 12. The temperature sensor 15 is, for example, a temperature sensor such as a thermocouple or a thermistor. The temperature sensor 15 may be disposed inside the power generation unit 12.

[0019] The control unit 14 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 unit 14 may control the operation of the fuel cell system 10. The control unit 14 may be a single control unit that collectively controls all of the power generation units 12. Alternatively, the control unit 14 may be configured to include multiple sub-controllers that are provided in each of the multiple power generation units 12 and control each of the multiple power generation units 12. The control unit 14 may be configured to include a central control unit in addition to a plurality of sub-control units, which issues commands to the plurality of sub-control units.

[0020] The control unit 14 may further include a storage unit. The storage unit may include any storage device, such as a random access memory (RAM) or a read-only memory (ROM). The storage unit may store various programs that cause the control unit 14 to function and various information used by the control unit 14. For example, the storage unit may store correspondence relationships between the flow rates of fuel gas, water, and air, which are predetermined for appropriate operation, for multiple control elements including the current value of the power generation unit 12. The correspondence relationships may be, for example, a relational expression or a correspondence table.

[0021] The control unit 14 acquires the current value of each power generation unit 12 as information from the current sensor 13. The control unit 14 controls the flow rates of the fuel gas, water, and air according to the acquired current value. Hereinafter, the control of the flow rates of the fuel gas, water, and air according to the current value will be referred to as first control. Specifically, the control unit 14 may determine the flow rates of the fuel gas, water, and air according to the acquired current value. The determination of the flow rates may be based on a correspondence relationship stored in the memory unit. The control unit 14 may control the first supply unit 19, the second supply unit 20, and the third supply unit 21 so that the flow rates of the fuel gas, water, and air become the determined flow rates.

[0022] The control unit 14 may calculate the difference between the maximum current value and the minimum current value among the multiple power generation units 12. The maximum current value is the maximum value among the current values ​​of the multiple power generation units 12 acquired as information. The minimum current value is the minimum value among the current values ​​of the multiple power generation units 12 acquired as information.

[0023] If the difference exceeds a first difference, the control unit 14 may determine a target current range for the multiple power generation units 12. The first difference is, for example, a difference in the current values ​​of the power generation units 12 connected in parallel that is allowable from the standpoint of the durability of the entire fuel cell system 10, etc.

[0024] The control unit 14 may determine the target current range using any method. The control unit 14 may determine the median value and width of the target current range. For example, the control unit 14 may determine the median value of the target current range as the value obtained by dividing the current value required for the entire fuel cell system 10 by the number of power generation units 12. Alternatively, the control unit 14 may determine the median value of the target current range as the average value of each current value obtained as information from the current sensor 13. Furthermore, for example, the control unit 14 may determine the width of the target current range to be the first difference.

[0025] The control unit 14 may perform a second control, instead of the first control, on a power generation unit 12 whose current value is outside the target current range. In the second control, the control unit 14 may control the flow rates of fuel gas, water, and air supplied to the power generation unit 12 that is the target of the second control, in accordance with an arbitrary current value within the target current range. The arbitrary current value may be, for example, the upper limit of the target current range for a power generation unit 12 whose current value exceeds the upper limit of the target current range. Furthermore, the arbitrary current value may be, for example, the lower limit of the target current range for a power generation unit 12 whose current value is below the lower limit of the target current range.

[0026] When the difference between the maximum current value and the minimum current value among the plurality of power generation units 12 exceeds the first difference, the control unit 14 may set a target current value for each of the power generation units 12 for at least some of the plurality of power generation units 12, instead of setting a target current range. This set may include, for example, power generation units 12 with a current value outside the above-mentioned target current range. This set may also include power generation units 12 with a current value within the target current range. The target current value may be the same for all power generation units 12, may be different for each, or may be divided into a plurality of groups and set to the same value for each group.

[0027] In a configuration in which the target current value is the same for all power generation units 12 for which the target current value is set, the target current value may be, for example, the median value of the target current range. In a configuration in which the target current value is different for each of the power generation units 12 for which the target current value is set, the target current value may be, for example, any value within a partial range obtained by dividing the target current range into the number of power generation units 12. In a configuration in which the power generation units 12 for which the target current value is set are divided into a plurality of groups and the target current value is the same for each group, the target current value may be any value within a partial range obtained by dividing the target current range into the number of groups.

[0028] The control unit 14 may perform a third control, instead of the first control, on the power generation units 12 for which a target current value has been set. In the third control, the control unit 14 may control the flow rates of the fuel gas, water, and air supplied to each power generation unit 12 in accordance with the target current value set for each power generation unit 12.

[0029] In the third control, the control unit 14 may perform at least one of increasing the flow rate of fuel gas and reducing the flow rate of water supplied to the power generation unit 12 whose current value detected by the current sensor 13 is smaller than the target current value. Furthermore, in the third control, the control unit 14 may change the flow rates of fuel gas, air, and water supplied to the power generation unit 12 whose current value detected by the current sensor 13 is larger than the target current value, based on the temperature detected by the temperature sensor 15 provided in the power generation unit 12. Specifically, when the temperature of the power generation unit 12 whose current value detected by the current sensor 13 is larger than the target current value is equal to or higher than a predetermined temperature reference value, the control unit 14 may perform at least one of reducing the flow rate of fuel gas, increasing the flow rate of air, and increasing the flow rate of water supplied to the power generation unit 12. The temperature reference value may be determined from the perspective of protecting the power generation unit 12. In addition, specifically, when the temperature of the power generation unit 12 in which the current value detected by the current sensor 13 is greater than the target current value is less than a predetermined temperature reference value, the control unit 14 may perform at least one of reducing the flow rate of fuel gas supplied to the power generation unit 12, reducing the flow rate of air, and increasing the flow rate of water.

[0030] In the first to third controls, when the control unit 14 changes the flow rates of the fuel gas, air, and water supplied to the power generation unit 12, it may store the changed flow rate values, and when restarting the power generation unit 12, it may supply the stored flow rates of the fuel gas, air, and water.

[0031] Next, the flow rate adjustment process executed by the control unit 14 in this embodiment will be described with reference to the flowchart of Fig. 3. The supply rate adjustment process is started periodically, for example.

[0032] In step S100, the control unit 14 extracts the maximum current value and the minimum current value from the current values ​​of the power generation unit 12 acquired as information. After extraction, the process proceeds to step S101.

[0033] In step S101, the control unit 14 calculates the difference between the maximum current value and the minimum current value. After the calculation, the process proceeds to step S102.

[0034] In step S102, the control unit 14 determines whether the difference calculated in step S101 is equal to or greater than a first difference. If the difference is not equal to or greater than the first difference, the process proceeds to step S103. If the difference is equal to or greater than the first difference, the process proceeds to step S104.

[0035] In step S103, the control unit 14 controls the flow rates of the fuel gas, air, and water supplied to each power generation unit 12 in accordance with the current value of each power generation unit 12. After the control, the flow rate adjustment process ends.

[0036] In step S104, the control unit 14 sets target current values ​​for at least some of the power generation units 12. After setting, the process proceeds to step S105.

[0037] In step S105, the control unit 14 selects the power generation unit 12 that has a current value smaller than the target current value set in step S104. After the selection, the process proceeds to step S106.

[0038] In step S106, the control unit 14 controls the first supply unit 19 to increase the flow rate of the fuel gas, and the control unit 14 controls the second supply unit 20 to decrease the flow rate of the water. After this control, the process proceeds to step S107.

[0039] In step S107, the control unit 14 selects one unselected power generation unit 12 from among the power generation units 12 having a current value equal to or greater than the target current value set in step S104. After the selection, the process proceeds to step S108.

[0040] In step S108, the control unit 14 determines whether the temperature of each power generation unit 12 selected in step S107 is equal to or greater than the reference temperature value. If the temperature is equal to or greater than the reference temperature value, the process proceeds to step S109. If the temperature is not equal to or greater than the reference temperature value, the process proceeds to step S110.

[0041] In step S109, the control unit 14 controls the first supply unit 19 to reduce the flow rate of fuel gas. The control unit 14 also controls the third supply unit 21 to increase the flow rate of air. The control unit 14 also controls the second supply unit 20 to increase the flow rate of water. After this control, the process proceeds to step S111.

[0042] In step S110, the control unit 14 controls the first supply unit 19 to reduce the flow rate of fuel gas. The control unit 14 also controls the third supply unit 21 to reduce the flow rate of air. The control unit 14 also controls the second supply unit 20 to increase the flow rate of water. After this control, the process proceeds to step S111.

[0043] In step S111, the control unit 14 determines whether all power generation units 12 having a current value equal to or greater than the target current value have been selected in step S107. If all have been selected, the process proceeds to step S112. If not all have been selected, the process proceeds to step S107.

[0044] In step S112, the control unit 14 determines whether there is any power generation unit 12 for which a target current value was not set in step S104. If there is any power generation unit 12 for which a target current value was not set, the process proceeds to step S113. If there is no power generation unit 12 for which a target current value was not set, the flow rate adjustment process ends.

[0045] In step S113, the control unit 14 controls the flow rates of the fuel gas, air, and water supplied to each power generation unit 12 in accordance with the current value of each power generation unit 12 for which it was determined in step S112 that the target current value has not been set. After the control, the flow rate adjustment process ends.

[0046] When the control unit 14 changes the flow rates of fuel gas, air, and water supplied to each power generation unit 12 at each step of the flow rate adjustment process, it stores these changed flow rates, and when each power generation unit 12 is restarted, it may supply the fuel gas, air, and water at the stored flow rates.

[0047] The fuel cell system 10 of this embodiment, configured as described above, includes a converter 11, multiple power generation units 12, each having a fuel cell 16 and electrically connected in parallel to the converter 11, multiple current sensors 13 that detect the current flowing through each of the multiple power generation units 12, and a control unit 14 that controls the flow rates of fuel gas, water, and air supplied to each of the power generation units 12 in accordance with the current value of each power generation unit 12. Typically, from the standpoint of durability and efficiency, each fuel cell is designed to supply fuel gas, air, and water at a predetermined target flow rate relative to the current value. However, in a fuel cell system with multiple fuel cells connected in parallel, currents may flow at different values ​​due to variations in the performance of each fuel cell. Therefore, if fuel gas or the like is supplied at a flow rate that assumes the same current value in a fuel cell system configured as described above, durability and efficiency may be reduced. On the other hand, the fuel cell system 10 having the above-described configuration controls the supply amount of fuel gas, etc. according to the current value actually measured in each power generation unit 12, thereby improving the operating efficiency of each fuel cell 16 in the power generation unit 12 connected in parallel.

[0048] Furthermore, when the difference between the maximum current value and the minimum current value among the plurality of power generation units 12 exceeds a first difference, the fuel cell system 10 determines a target current range, and controls the flow rates of fuel gas, water, and air supplied to the power generation units 12 whose current values ​​are outside the target current range according to any current value within the target current range. With this configuration, the fuel cell system 10 can suppress extreme variations in current values ​​among the plurality of power generation units 12 while improving the overall durability of the fuel cell system 10.

[0049] Furthermore, when the difference between the maximum current value and the minimum current value in the plurality of power generation units 12 exceeds a first difference, the fuel cell system 10 sets a target current value for each of the plurality of power generation units 12 and controls the flow rates of the fuel gas, water, and air supplied to the plurality of power generation units 12 according to the target current value. With this configuration, the fuel cell system 10 can suppress extreme variations in the current value among the plurality of power generation units 12 while improving the durability of the fuel cell system 10 as a whole.

[0050] The fuel cell system 10 also includes a plurality of temperature sensors 15 that detect the temperatures of the plurality of power generation units 12, respectively, and the control unit 14 changes the flow rates of fuel gas, water, and air supplied to the power generation units 12 that have current values ​​greater than the target current value based on the temperatures detected by the temperature sensors 15. With this configuration, the fuel cell system 10 can maintain the temperatures of the power generation units 12 at appropriate temperatures while suppressing a decrease in operating efficiency and suppressing extreme variations in current values ​​among the plurality of power generation units 12.

[0051] Furthermore, when the temperature of the power generation unit 12 is equal to or higher than a predetermined temperature reference value, the fuel cell system 10 performs at least one of reducing the flow rate of fuel gas supplied to the power generation unit 12, increasing the flow rate of air, and increasing the flow rate of water. With this configuration, the fuel cell system 10 reduces the temperature of the power generation unit 12, increasing the internal resistance of the power generation unit 12 and, as a result, reducing the current value of the power generation unit 12. Because the fuel cell system 10 reduces the current value of the power generation unit 12, extreme variations in current value among the multiple power generation units 12 can be suppressed. Furthermore, when the temperature of the power generation unit 12 is equal to or higher than a predetermined temperature reference value, the fuel cell system 10 increases the flow rate of air supplied to the power generation unit 12, thereby cooling the temperature of the fuel cell 16 and improving power generation efficiency.

[0052] The current value of the power generation unit 12 can be adjusted by adjusting the voltage (closed circuit voltage). Here, the closed circuit voltage is calculated by the following formula (1): Closed circuit voltage = Open circuit voltage + IR (1) In formula (1), I is the current value, and R is the internal resistance. The open circuit voltage of the power generation unit 12 is calculated by the Nernst equation. Specifically, the open circuit voltage is calculated by the following formula (2).

[0053] Open circuit voltage = -ΔG / nF + (RT / nF) × ln{P(H ２ ) x P ０．５ (O ２ ) / P (H ２ 0) (2)

[0054] In equation (2), ΔG is the Gibbs free energy change [kJ / mol], n is the number of electrons involved in the reaction, T is the battery temperature (temperature between cells) [°C], F is the Faraday constant (= 96484.56 [C / mol]), R is the gas constant (8.3145 [J / (mol × K)]), and P (mol) is the partial pressure of each gas.

[0055] When the temperature of the power generation unit 12 is below a predetermined reference temperature value, the fuel cell system 10 performs at least one of reducing the flow rate of fuel gas, reducing the flow rate of air, and increasing the flow rate of water supplied to the power generation unit 12. With this configuration, the fuel cell system 10 can reduce the flow rate of fuel gas, air, and water supplied to the power generation unit 12 by adjusting {P(H ２ ) x P ０．５(O ２ ) / P (H ２ 0)} is reduced, thereby reducing the open circuit voltage generated in the power generation unit 12. Therefore, the fuel cell system 10 reduces the closed circuit voltage, and can therefore reduce the current value of the power generation unit 12. As a result, the fuel cell system 10 lowers the maximum current value, and can therefore suppress extreme variations in current value among the multiple power generation units 12. Furthermore, when the temperature of a power generation unit 12 is below a predetermined temperature reference value, the fuel cell system 10 reduces the flow rate of air supplied to that power generation unit 12, thereby increasing the temperature of the fuel cell 16 and improving power generation efficiency.

[0056] Furthermore, the fuel cell system 10 performs at least one of increasing the flow rate of fuel gas supplied to the power generation unit 12, which has a current value smaller than the target current value, and reducing the flow rate of water. ２ ) x P ０．５ (O ２ ) / P (H ２ 0)} increases, the open circuit voltage generated in the power generation unit 12 increases. Therefore, the fuel cell system 10 increases the closed circuit voltage, and can increase the current value of the power generation unit 12. Furthermore, by having the above-mentioned configuration, the fuel cell system 10 increases the temperature of the fuel cell 16, which can contribute to an increase in the current value of the power generation unit 12.

[0057] Furthermore, in the fuel cell system 10, when the control unit 14 changes the flow rates of the fuel gas, air, and water supplied to the power generation unit 12, it stores the changed flow rates of the fuel gas, air, and water, and supplies the fuel gas, air, and water at those flow rates when the power generation unit 12 is restarted. During operation of the fuel cell system 10, the power generation unit 12 may be stopped and restarted for some reason. If the fuel gas, air, and water are supplied at preset flow rates during restart, it is expected that the current value will need to be adjusted again. In response to such an assumption, the fuel cell system 10 having the above-described configuration can reduce the need for repeated current value adjustments by supplying the fuel gas, air, and water at the stored flow rates during restart of the power generation unit 12. Therefore, the fuel cell system 10 can reduce the number of changes in the flow rates of the fuel gas, air, and water supplied to the power generation unit 12 during restart. In addition, the control unit 14 may store the changed current value instead of the flow rate of the fuel gas, air, and water supplied to the power generation unit 12, and adjust the flow rate of the fuel gas, air, and water so that the changed current value is achieved when the power generation unit 12 is restarted.

[0058] 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).

[0059] 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.

[0060] 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.

[0061] 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.

[0062] All of the features described in this disclosure and / or all steps of all 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.

[0063] 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.

[0064] In this disclosure, descriptions such as "first" and "second" are identifiers for distinguishing the configuration. In this disclosure, configurations distinguished by descriptions such as "first" and "second" can have their numbers exchanged. For example, a first supply unit can exchange the identifiers "first" and "second" with a second supply unit. 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.

[0065] REFERENCE SIGNS LIST 10 fuel cell system 11 converter 12 power generation unit 13 current sensor 14 control unit 15 temperature sensor 16 fuel cell 17 combustion unit 18 reformer 19 first supply unit 20 second supply unit 21 third supply unit 22 load device 23 relay

Claims

1. A fuel cell system comprising: a converter; a plurality of power generation units each having a fuel cell and electrically connected in parallel to the converter; a plurality of current sensors that detect the current flowing through each of the plurality of power generation units; and a control unit that controls the flow rates of fuel gas, water, and air supplied to each of the power generation units in accordance with the current value of each of the power generation units.

2. A fuel cell system according to claim 1, wherein the control unit determines a target current range when the difference between the maximum current value and the minimum current value in the plurality of power generation units exceeds a first difference, and controls the flow rates of fuel gas, water, and air to be supplied to the power generation units whose current values ​​are outside the target current range in accordance with any current value within the target current range.

3. A fuel cell system according to claim 1, wherein, when the difference between the maximum current value and the minimum current value in the plurality of power generation units exceeds a first difference, the control unit sets a target current value for each of the plurality of power generation units, and controls the flow rates of fuel gas, water, and air supplied to the plurality of power generation units in accordance with the target current value.

4. A fuel cell system according to claim 3, further comprising a plurality of temperature sensors for detecting the temperatures of the plurality of power generation units, respectively, and wherein the control unit changes the flow rates of fuel gas, water, and air supplied to the power generation units having current values ​​greater than the target current value based on the temperatures detected by the temperature sensors.

5. A fuel cell system according to claim 4, wherein the control unit, when the temperature of the power generation unit is equal to or higher than a predetermined reference temperature value, performs at least one of reducing the flow rate of fuel gas supplied to the power generation unit, increasing the flow rate of air, and increasing the flow rate of water.

6. A fuel cell system according to claim 4, wherein, when the temperature of the power generation unit is below a predetermined temperature reference value, the control unit performs at least one of reducing the flow rate of fuel gas, reducing the flow rate of air, and increasing the flow rate of water supplied to the power generation unit.

7. A fuel cell system according to any one of claims 3 to 6, wherein the control unit performs at least one of increasing the flow rate of fuel gas supplied to the power generation unit, the flow rate of which is smaller than the target current value, and reducing the flow rate of water.

8. A fuel cell system according to any one of claims 3 to 7, wherein when the control unit changes the flow rates of fuel gas, air, and water supplied to the power generation unit, the control unit stores the changed flow rates of fuel gas, air, and water, and supplies fuel gas, air, and water at those flow rates when the power generation unit is restarted.

Images