Fuel cell system

Abstract

In the present invention, a fuel cell system includes a plurality of power generation units, a plurality of oxygen supply units that supply an -containing gas to each of the plurality of power generation units, a discharge unit, and a control device. Exhaust paths for the exhaust gas from each of the plurality of power generation units collectively constitute the discharge unit. When some of the plurality of power generation units execute an operation stop process, the control device performs control so that oxygen-containing gas is continuously supplied to some of the power generation units by some of the plurality of oxygen supply units, and performs control so that the oxygen-containing gases supplied to some of the power generation units will differ in terms of flow rate between during execution of the operation stop process of some of the power generation units and following the conclusion of the operation stop process of some of the power generation units.

Description

fuel cell system Cross-reference to related applications

[0001] This application claims priority to Japanese Patent Application No. 2024-057874, filed on March 29, 2024, the entire disclosure of which is incorporated herein by reference.

[0002] The present disclosure relates to fuel cell systems.

[0003] Fuel cell systems have been known as power generation systems that can contribute to carbon neutrality. Recently, fuel cell systems that include multiple fuel cells have become popular. In such fuel cell systems, exhaust gas from one of the multiple fuel cells may flow back into the other fuel cells.

[0004] To address this issue, a fuel cell system is known, as described in Patent Document 1. In this fuel cell system, when some of the multiple fuel cell units are operating to generate electricity and the other fuel cell units are not operating to generate electricity, the control unit of the fuel cell unit that is not operating to generate electricity operates the air supply device of that fuel cell unit.

[0005] Japanese Patent Application Laid-Open No. 2022-47085

[0006] A fuel cell system according to one embodiment of the present disclosure comprises: a plurality of power generation units; a plurality of oxygen supply units that supply an oxygen-containing gas to each of the plurality of power generation units; an exhaust unit that collectively configures exhaust gas exhaust paths for each of the plurality of power generation units; and a control device, wherein the control device, when some of the plurality of power generation units perform a shutdown process, controls the oxygen-containing gas to be continuously supplied to the some of the power generation units by some of the plurality of oxygen supply units, while controlling the flow rate of the oxygen-containing gas supplied to the some of the power generation units to be different during the shutdown process of the some of the power generation units and after the shutdown process of the some of the power generation units is completed.

[0007] It is a block diagram showing the configuration of a fuel cell system according to an embodiment of the present disclosure. It is a sequence diagram showing an example of the operation of the fuel cell system shown in Fig. 1. It is a flowchart showing an example of the operation of the fuel cell device ...

[0008] Conventional techniques for preventing backflow of exhaust gas into the power generation unit have room for improvement. According to one embodiment of the present disclosure, the techniques for preventing backflow of exhaust gas into the power generation unit can be improved.

[0009] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0010] A fuel cell system 1 as shown in Fig. 1 is installed, for example, in a customer facility. In Fig. 1, solid lines indicate the flow of fluids such as electric power or fuel gas. Dashed lines indicate the flow of control. The fuel cell system 1 is capable of supplying electric power to a group of loads 2. The group of loads 2 includes at least one load device. The load device is, for example, an electrical appliance or an electronic device.

[0011] The fuel cell system 1 includes a power conversion device 10, a plurality of fuel cell devices 20, and a discharge section 40. In this embodiment, the fuel cell system 1 includes three fuel cell devices 20, namely, fuel cell devices 20-1, 20-2, and 20-3, as the plurality of fuel cell devices 20. However, the fuel cell system 1 may include any number of fuel cell devices 20. The number of fuel cell devices 20 included in the fuel cell system 1 may be two, or may be four or more. The fuel cell device 20 includes a control device 30, as will be described later.

[0012] The fuel cell system 1 may be provided with a master control device that controls the operation of each of the plurality of fuel cell devices 20. In this case, the master control device may control the operation of each of the plurality of fuel cell devices 20 by transmitting a control signal to each of the control devices 30 of the plurality of fuel cell devices 20.

[0013] In the fuel cell system 1, a master fuel cell device 20 and a slave fuel cell device 20 may be assigned to each of the multiple fuel cell devices 20. In this case, the control device 30 of the master fuel cell device 20 may control the operation of the slave fuel cell device 20 by transmitting a control signal to the control device 30 of the slave fuel cell device 20.

[0014] In the fuel cell system 1, the control devices 30 of the plurality of fuel cell devices 20 may exchange information with each other, so that the plurality of control devices 30 may control the operation of the plurality of fuel cell devices 20, respectively.

[0015] The power conversion device 10 is also called a “power conditioner.” The power conversion device 10 includes a communication unit 11, a storage unit 12, a control unit 13, and a power conversion unit 14.

[0016] The communication unit 11 is configured to include at least one communication module capable of communicating with the fuel cell device 20. The communication module is a module that complies with the standard for communication between the power conversion device 10 and the fuel cell device 20. The communication between the power conversion device 10 and the fuel cell device 20 may be wired or wireless.

[0017] The communication unit 11 may be configured to include at least one communication module capable of communicating with an external device such as a remote controller. The communication module is a module that complies with a standard for communication between the power conversion device 10 and the external device. The communication between the power conversion device 10 and the external device may be short-range wireless communication.

[0018] The storage unit 12 includes at least one semiconductor memory, at least one magnetic memory, at least one optical memory, or a combination of at least two of these. The storage unit 12 may function as a main storage device, an auxiliary storage device, or a cache memory. The storage unit 12 stores data used in the operation of the power conversion device 10 and data obtained by the operation of the power conversion device 10. The storage unit 12 may also store a program executed by the control unit 13.

[0019] The control unit 13 is configured to include at least one processor, at least one dedicated circuit, or a combination of these. The processor is, for example, 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 is, for example, an FPGA (Field-Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit). The control unit 13 executes processes related to the operation of the power conversion device 10 while controlling each part of the power conversion device 10.

[0020] The power conversion unit 14 is configured to include, for example, at least one of a DC / DC converter and a DC / AC converter (inverter). DC power is supplied to the power conversion unit 14 from each of the plurality of fuel cell devices 20. The power conversion unit 14 converts the supplied DC power into predetermined AC power or DC power based on the control of the control unit 13. The power conversion unit 14 supplies the converted AC power or DC power to the load group 2.

[0021] The fuel cell device 20 includes a power generation unit 21, reforming water supply units 23-1 and 23-2, oxygen supply units 24-1 and 24-2, air flow meters 25-1 and 25-2, a gas supply unit 26, a gas flow meter 27, a temperature sensor 28, and a control device 30. The fuel cell device 20 includes reforming water supply lines 23L-1 and 23L-2, oxygen supply lines 24L-1 and 24L-2, and a fuel supply line 26.

[0022] Hereinafter, when there is no particular distinction between the reforming water supply unit 23-1 and the reforming water supply unit 23-2, they will also be referred to as the "reforming water supply unit 23." When there is no particular distinction between the oxygen supply unit 24-1 and the oxygen supply unit 24-2, they will also be referred to as the "oxygen supply unit 24." When there is no particular distinction between the air flow meter 25-1 and the air flow meter 25-2, they will also be referred to as the "air flow meter 25." The fuel cell device 20 includes two reforming water supply units 23, two oxygen supply units 24, and two air flow meters 25. However, the fuel cell device 20 may include any number of reforming water supply units 23, two oxygen supply units 24, and two air flow meters 25 depending on the number of fuel cell modules 22 (described later) included in the power generation unit 21. The number of gas supply units 26 may also be two.

[0023] Hereinafter, when there is no particular distinction between the reforming water supply line 23L-1 and the reforming water supply line 23L-2, they will also be referred to as the "reforming water supply line 23L." Furthermore, when there is no particular distinction between the oxygen supply line 24L-1 and the oxygen supply line 24L-2, they will also be referred to as the "oxygen supply line 24L." The fuel cell device 20 is provided with two reforming water supply lines 23L and two oxygen supply lines 24L. However, the fuel cell device 20 may be provided with any number of reforming water supply lines 23L and oxygen supply lines 24L.

[0024] The power generation unit 21 is electrically connected to the power conversion unit 14 of the power conversion device 10. The power generation unit 21 includes at least one fuel cell module 22. A fuel cell module is also called a "hot module." In this embodiment, the power generation unit 21 includes fuel cell modules 22-1 and 22-2 as the at least one fuel cell module 22. However, the number of fuel cell modules 22 included in the power generation unit 21 is not limited to two. The number of fuel cell modules 22 included in the power generation unit 21 may be one, or three or more.

[0025] When the power generation unit 21 includes multiple fuel cell modules 22, these multiple fuel cell modules 22 are electrically connected in series. In Fig. 1, fuel cell module 22-1 and fuel cell module 22-2 are electrically connected in series. The positive side of fuel cell module 22-1 is electrically connected to the power conversion unit 14. The negative side of fuel cell module 22-2 is electrically connected to the power conversion unit 14.

[0026] The fuel cell module 22 is supplied with reforming water from a reforming water supply unit 23. In Fig. 1, the fuel cell module 22-1 is supplied with reforming water from a reforming water supply unit 23-1, and the fuel cell module 22-2 is supplied with reforming water from a reforming water supply unit 23-2.

[0027] Air is supplied to the fuel cell modules 22 from an oxygen supply unit 24. In Fig. 1, air is supplied to the fuel cell module 22-1 from an oxygen supply unit 24-1, and air is supplied to the fuel cell module 22-2 from an oxygen supply unit 24-2.

[0028] The fuel cell module 22 is supplied with fuel gas from a gas supply unit 26 .

[0029] The fuel cell module 22 includes a reformer 22R and a cell stack 22S. The reformer 22R generates hydrogen and / or carbon monoxide using reforming water supplied from a reforming water supply unit 23 and fuel gas supplied from a gas supply unit 26. The cell stack 22S may be a solid oxide fuel cell (SOFC). However, the cell stack 22S is not limited to an SOFC. The cell stack 22S may be any fuel cell. The cell stack 22S generates an electrochemical reaction between air supplied from an oxygen supply unit 24 and the hydrogen and / or carbon monoxide generated by the reformer 22R. The cell stack 22S generates DC power by generating an electrochemical reaction.

[0030] The fuel cell module 22 maintains power generation efficiency by keeping the temperature of the entire system, including the reformer 22R and the cell stack 22S, within a predetermined range. The fuel cell module 22 outputs information about the temperature of the fuel cell module 22 to the control unit 33.

[0031] The reforming water supply unit 23 and the reformer 22R of the fuel cell module 22 are connected by a reforming water supply line 23L. The reforming water supply line 23L may be configured to include piping, valves, etc. In FIG. 1, the reforming water supply unit 23-1 and the reformer 22R of the fuel cell module 22-1 are connected by a reforming water supply line 23L-. The reforming water supply unit 23-2 and the reformer 22R of the fuel cell module 22-2 are connected by a reforming water supply line 23L-2.

[0032] The reforming water supply unit 23 includes a pump and the like. Based on a control signal from the control device 30, the reforming water supply unit 23 supplies reforming water to the reformer 22R of the fuel cell module 22 via a reforming water supply line 23L. Based on the control signal from the control device 30, the reforming water supply unit 23 controls the amount of reforming water supplied to the reformer 22R. In FIG. 1 , based on the control signal from the control device 30, the reforming water supply unit 23-1 supplies reforming water to the reformer 22R of the fuel cell module 22-1 via a reforming water supply line 23L-1. Based on the control signal from the control device 30, the reforming water supply unit 23-2 supplies reforming water to the reformer 22R of the fuel cell module 22-2 via a reforming water supply line 23L-2.

[0033] The reforming water supply unit 23 may generate reforming water using, as a raw material, water recovered from the exhaust gas of the cell stack 22S of the fuel cell module 22. The exhaust heat of the cell stack 22S may be used as a heat source for generating the reforming water.

[0034] The oxygen supply unit 24 and the cell stack 22S of the fuel cell module 22 are connected by an oxygen supply line 24L. The oxygen supply line 24L may be configured to include piping, valves, etc. In FIG. 1, the oxygen supply unit 24-1 and the cell stack 22S of the fuel cell module 22-1 are connected by an oxygen supply line 24L-1. The oxygen supply unit 24-2 and the cell stack 22S of the fuel cell module 22-2 are connected by an oxygen supply line 24L-2.

[0035] The oxygen supply unit 24 includes a blower and the like. Based on a control signal from the control device 30, the oxygen supply unit 24 supplies an oxygen-containing gas to the cell stack 22S of the fuel cell module 22 via the oxygen supply line 24. In this embodiment, the oxygen supply unit 24 supplies air as the oxygen-containing gas to the cell stack 22S. However, the oxygen-containing gas supplied by the oxygen supply unit 24 to the cell stack 22S is not limited to air. For example, the oxygen supply unit 24 may supply only oxygen to the cell stack 22S, or may supply an oxygen-containing gas other than air to the cell stack 22S.

[0036] The oxygen supply unit 24 controls the amount of air supplied to the cell stack 22S based on a control signal from the control device 30. In Fig. 1, the oxygen supply unit 24-1 supplies air to the cell stack 22S of the fuel cell module 22-1 via an oxygen supply line 24L-1 based on a control signal from the control device 30. The oxygen supply unit 24-2 supplies air to the cell stack 22S of the fuel cell module 22-2 via an oxygen supply line 24-2 based on a control signal from the control device 30.

[0037] The oxygen supply unit 24 may preliminarily heat air taken in from the outside and supply it to the cell stack 22S of the fuel cell module 22.

[0038] The air flow meters 25 are attached to the oxygen supply line 24L. In FIG. 1, the air flow meter 25-1 is attached to the oxygen supply line 24L-1. The air flow meter 25-2 is attached to the oxygen supply line 24L-2. The air flow meters 25 measure the flow rate of air flowing through the oxygen supply line 24L. The air flow meter 25 transmits the measurement result of the air flow rate to the control device 30.

[0039] The gas supply unit 26 and the reformers 22R of each of the plurality of fuel cell modules 22 are connected by a fuel supply line 26L. The fuel supply line 26L may include piping, valves, and the like. In FIG. 1, the fuel supply line 26 branches into two. The gas supply unit 26 and the reformers 22R of the fuel cell module 22-1 and 22-2 are connected by the fuel supply line 26L.

[0040] The gas supply unit 26 includes a pump and the like. Based on a control signal from the control device 30, the gas supply unit 26 supplies fuel gas to the reformers 22R of each of the plurality of fuel cell modules 22 via a fuel supply line 26L. Based on the control signal from the control device 30, the gas supply unit 26 controls the amount of fuel gas supplied to each of the plurality of fuel cell modules 22.

[0041] The gas flow meter 27 is attached to the fuel supply line 26L. In FIG. 1 , the gas flow meter 27 is attached to any part of the fuel supply line 26L, from the part connected to the gas supply unit 26 to the part before the line is split into two. The gas flow meter 27 measures the flow rate of the fuel gas flowing through the fuel supply line 26L. The gas flow meter 27 transmits the measurement result of the fuel gas flow rate to the control device 30.

[0042] The temperature sensor 28 is located at a position where it can detect the outlet temperature of the power generation unit 21. The temperature sensor 28 detects the outlet temperature of the power generation unit 21. The outlet temperature of the power generation unit 21 is, for example, the temperature of a combustion catalyst. The combustion catalyst burns unreacted carbon monoxide and the like. The temperature sensor 28 transmits the detection result of the outlet temperature of the power generation unit 21 to the control device 30.

[0043] The control device 30 controls the operation of the fuel cell device 20 based on a control signal from the power conversion device 10. The control device 30 includes a communication unit 31, a storage unit 32, and a control unit 33.

[0044] The communication unit 31 includes at least one communication module that can communicate with the power conversion device 10. The communication module is a module that complies with the standard for communication between the power conversion device 10 and the fuel cell device 20.

[0045] The communication unit 31 may be configured to include at least one communication module capable of communicating with the control devices 30 of other fuel cell devices 20. The communication module is a module that complies with a standard for communication between the plurality of control devices 30. The communication between the plurality of control devices 30 may be wired or wireless.

[0046] The storage unit 32 is configured to include at least one semiconductor memory, at least one magnetic memory, at least one optical memory, or a combination of at least two of these. The storage unit 32 may function as a main storage device, an auxiliary storage device, or a cache memory. The storage unit 32 stores data used in the operation of the fuel cell device 20 and data obtained by the operation of the fuel cell device 20. The storage unit 32 may also store programs executed by the control unit 33.

[0047] The control unit 33 is configured to include at least one processor, at least one dedicated circuit, or a combination of these. The processor is, for example, a general-purpose processor such as a CPU or GPU, or a dedicated processor specialized for a specific process. The dedicated circuit is, for example, an FPGA or an ASIC. The control unit 33 executes processes related to the operation of the fuel cell device 20 while controlling each part of the fuel cell device 20. The control unit 33 may send and receive any signal, such as a control signal, to and from another control device 30 via the communication unit 31. The control unit 33 may send and receive any signal, such as a control signal, to and from the power conversion device 10 via the communication unit 31.

[0048] The discharge unit 40 includes a plurality of discharge paths 41. The discharge unit 40 is configured by collecting the plurality of discharge paths 41. In the present embodiment, the discharge unit 40 is configured by collecting three discharge paths 41, namely, discharge paths 41-1, 41-2, and 41-3, as the plurality of discharge paths 41. However, the discharge unit 40 may be configured by collecting any number of discharge paths 41 corresponding to the number of power generation units 21 included in the fuel cell system 1.

[0049] The exhaust section 40 includes a plurality of exhaust paths 41 , as well as a connecting section 42 and an exhaust port 43 .

[0050] The discharge path 41 is configured to include, for example, a pipe or the like. The discharge path 41 includes two ends. Of the two ends included in the discharge path 41, one end is connected to the power generation unit 21, and the other end is connected to the connecting unit 42. In FIG. 1 , of the two ends included in the discharge path 41-1, one end is connected to the power generation unit 21 of the fuel cell device 20-1, and the other end is connected to the connecting unit 42. Furthermore, of the two ends included in the discharge path 41-2, one end is connected to the power generation unit 21 of the fuel cell device 20-2, and the other end is connected to the connecting unit 42. Furthermore, of the two ends included in the discharge path 41-3, one end is connected to the power generation unit 21 of the fuel cell device 20-3, and the other end is connected to the connecting unit 42.

[0051] The connecting portion 42 is configured to include, for example, piping etc. A plurality of discharge paths 41 are connected to the connecting portion 42. By connecting the plurality of discharge paths 41 to the connecting portion 42, the discharge portion 40 according to the present embodiment is configured by collectively configuring the plurality of discharge paths 41.

[0052] The exhaust port 43 is provided in the connecting portion 42. Exhaust gas is discharged from the exhaust port 43. If the fuel cell system 1 includes a housing, the exhaust port 43 may be configured to discharge the exhaust gas to the outside of the housing.

[0053] [Processing of the control device] The fuel cell system 1 includes a plurality of power generation units 21. In Fig. 1, the fuel cell system 1 includes the power generation unit 21 of the fuel cell device 20-1, the power generation unit 21 of the fuel cell device 20-2, and the power generation unit 21 of the fuel cell device 20-3 as the plurality of power generation units 21.

[0054] When the fuel cell system 1 includes multiple power generation units 21, some of the power generation units 21 may undergo shutdown processing. Here, the shutdown processing requires lowering the temperature of the cell stack 22S of the power generation unit 21 to room temperature. When the cell stack 22S is an SOFC, the high power generation temperature of the SOFC increases the time required to shut down the power generation units 21. Therefore, when some of the power generation units 21 undergo shutdown processing, there may be power generation units 21 in progress, power generation units 21 undergoing shutdown processing, and power generation units 21 that have completed shutdown processing. In this case, exhaust gas from the power generation units 21 may flow back via the exhaust unit 40 to the power generation units 21 undergoing shutdown processing or the power generation units 21 that have completed shutdown processing.

[0055] Therefore, when some of the multiple power generation units 21 are undergoing operation shutdown processing, the control device 30 controls the supply of air continuously to those some of the power generation units 21. With this configuration, air is continuously supplied by the oxygen supply unit 24 to the power generation units 21 undergoing operation shutdown processing. Therefore, exhaust gas that flows back from the exhaust path 41 to the power generation units 21 can be pushed out of the power generation units 21 by the air supplied to the power generation units 21 by the oxygen supply unit 24. As a result, the possibility of exhaust gas flowing back into the power generation units 21 can be reduced.

[0056] Furthermore, the control device 30 controls the supply of air continuously to some of the power generation units 21 for which the operation shutdown process is being performed, while controlling the flow rate of air supplied to those some of the power generation units 21 to be different during the operation shutdown process of those some of the power generation units 21 and after the operation shutdown process of those some of the power generation units 21 is completed. By making the flow rate of air supplied to the power generation units 21 different during the operation shutdown process and after the completion of the operation shutdown process, as will be described later, it is possible to reduce the possibility that exhaust gas from the power generation units 21 that are generating electricity will flow back into the power generation units 21 via the exhaust unit 40 during or after the operation shutdown process is completed.

[0057] Here, the control device 30 may receive a control signal via the communication unit 31 from an external device or the like, instructing the stopping of operation of some of the power generation units 21. Furthermore, this control signal may be a signal instructing the power generation units 21 to continue to be supplied with air, while varying the flow rate of air supplied to the power generation units 21 during the execution of the operation stopping process of the power generation units 21 and after the operation stopping process is completed. The control device 30 may control the operation of the fuel cell device 20 including those some of the power generation units 21 based on the control signal. As an example, if a master control device is provided or if a master fuel cell device 20 is assigned, the master control device or the control device 30 of the master fuel cell device 20 may receive the control signal. In this case, the master control device or the control device 30 of the master fuel cell device 20 may control the operation of the fuel cell device 20 including those some of the power generation units 21 based on the control signal. The master control device or the control device 30 of the master fuel cell device 20 may control the operation of the fuel cell device 20 including those some of the power generation units 21 by transmitting a control signal to the fuel cell device 20 including those some of the power generation units 21. As another example, the plurality of control devices 30 may control the operation of each of the plurality of fuel cell devices 20 by transmitting and receiving information on the operating status of each of the plurality of fuel cell devices 20. When a control device 30 receives a control signal instructing it to stop operation, it may send a notification indicating that it has received the control signal instructing it to stop operation to the master control device or the control device 30 of the fuel cell device 20 that will be the master.

[0058] Hereinafter, the control device 30 of the fuel cell device 20 including the power generation unit 21 for which the operation shutdown process is executed among the multiple power generation units 21 will also be referred to as a "first control device." The first control device may control the flow rate of air supplied to the power generation unit 21 so that the flow rate is different between when the operation shutdown process of the power generation unit 21 is being executed and after the operation shutdown process of the power generation unit 21 is completed, depending on the intended use of the fuel cell system 1, etc.

[0059] As an example, the first control device may control the flow rate of air supplied to the power generation unit 21 so that it is greater after the completion of the operation shutdown process of the power generation unit 21 than during the execution of the operation shutdown process of the power generation unit 21. The temperature of the power generation unit 21 may be higher during the execution of the operation shutdown process than after the completion of the operation shutdown process. Therefore, the internal pressure of the power generation unit 21 may be higher during the execution of the operation shutdown process than after the completion of the operation shutdown process. Because the internal pressure of the power generation unit 21 is higher during the execution of the operation shutdown process, backflow of exhaust gas is less likely to occur in the power generation unit 21 during the execution of the operation shutdown process than in the power generation unit 21 after the completion of the operation shutdown process. In contrast, the temperature of the power generation unit 21 is lower after the completion of the operation shutdown process than during the execution of the operation shutdown process. Therefore, the internal pressure of the power generation unit 21 may be lower after the completion of the operation shutdown process than during the execution of the operation shutdown process. Because the internal pressure of the power generation unit 21 is lower after the completion of the shutdown process, backflow of exhaust gas is more likely to occur in the power generation unit 21 after the completion of the shutdown process than in the power generation unit 21 during the shutdown process. Therefore, by increasing the flow rate of air supplied to the power generation unit 21 after the completion of the shutdown process of the power generation unit 21 compared to during the shutdown process of the power generation unit 21, it is possible to more reliably reduce the possibility of backflow of exhaust gas into the power generation unit 21. The degree to which the air flow rate is increased may be set according to the structure of the power generation unit 21.

[0060] When the flow rate of air supplied to the power generation unit 21 is to be larger after the completion of the operation shutdown process of the power generation unit 21 than during the process, the first control device may control the flow rate of air supplied to the power generation unit 21 to gradually increase during the process. During the process of shutting down the operation of the power generation unit 21, the temperature of the power generation unit 21 gradually decreases, and the internal pressure of the power generation unit 21 gradually decreases. Therefore, by gradually increasing the flow rate of air supplied to the power generation unit 21 during the process of shutting down the operation, it is possible to more reliably reduce the possibility of exhaust gas backflowing into the power generation unit 21 than, for example, when the flow rate of air supplied to the power generation unit 21 is constant. The degree to which the flow rate of air is gradually increased may be set according to the structure of the power generation unit 21.

[0061] As another example, the first control device may control the flow rate of air supplied to the power generation unit 21 so that it is greater while the power generation unit 21 is shut down than after the shutdown process of the power generation unit 21 is completed. By increasing the flow rate of air supplied to the power generation unit 21 while the shutdown process is being executed, the temperature of the cell stack 22S can be quickly reduced. By quickly reducing the temperature of the cell stack 22S, the time required for the shutdown process of the power generation unit 21 can be further shortened. The degree to which the air flow rate is increased may be set according to the structure of the power generation unit 21.

[0062] Here, when another of the multiple power generation units 21 is generating power, the control unit 13 of the power conversion device 10 may adjust the required amount of power so as to reduce the amount of power generated by the other power generation unit 21. The required amount of power is the amount of power generated required of the power generation unit 21 that is generating power. The control unit 13 may change the value of current drawn from the power generation unit 21 of the fuel cell device 20 to the power conversion unit 14. The power generation unit 21 generates an amount of power corresponding to the value of the current drawn by the power conversion unit 14. Therefore, the control unit 13 may control the amount of power generated by the other power generation unit 21 to be reduced by reducing the value of current drawn from the other power generation unit 21 that is generating power to the power conversion unit 14. Reducing the amount of power generated by the power generation unit 21 that is generating power can reduce the total amount of exhaust gas in the fuel cell system 1. Reducing the total amount of exhaust gas in the fuel cell system 1 can more reliably reduce the possibility of exhaust gas flowing back into the power generation unit 21 via the exhaust unit 40 during or after the operation shutdown process is being performed.

[0063] Hereinafter, the control device 30 of the fuel cell device 20 that has one of the multiple power generation units 21 that is generating power will also be referred to as a "second control device." The second control device may receive an alert signal, which will be described later, from the master control device, the control device 30 of the master fuel cell device 20, or the first control device 30. In this case, the second control device may control the power generation unit 21 of its own device to execute an operation shutdown process. If there are multiple second control devices, the master control device, the control device 30 of the master fuel cell device 20, or the first control device 30 may send a signal to all of the multiple second control devices 30 instructing them to shut down their operations.

[0064] The control unit 33 of the control device 30 can receive the above-mentioned control signal from an external device or the like via the communication unit 31. Upon receiving the control signal, the control unit 33 starts processing to stop the operation of the power generation unit 21. Furthermore, the control unit 33 controls the oxygen supply unit 24 so that air is continuously supplied to the power generation unit 21, while controlling the flow rate of air supplied to the power generation unit 21 to be different during processing to stop the operation of the power generation unit 21 and after the processing to stop the operation of the power generation unit 21 is completed. The control unit 33 may control both the oxygen supply units 24-1 and 24-2, or may control only one of the oxygen supply units 24-1 and 24-2.

[0065] When the power generation unit 21 of the own device executes the operation shutdown process, the control unit 33 may control the oxygen supply unit 24 of the own device based on the detection result of the temperature sensor 28 of the own device. It is possible to detect that the exhaust gas is flowing back into the power generation unit 21 of the own device based on the outlet temperature of the power generation unit 21. Therefore, by the control unit 33 controlling the oxygen supply unit 24 based on the detection result of the temperature sensor 28, it is possible to reduce the possibility of the exhaust gas flowing back into the power generation unit 21 of the own device.

[0066] <During Execution of Operation Shutdown Process> During execution of the operation shutdown process for the power generation unit 21 of the own device, if the rate of decrease in the outlet temperature of the power generation unit 21 of the own device is smaller than the first rate threshold, the control unit 33 may control the flow rate of air supplied to the power generation unit 21 of the own device to be increased. The rate of decrease in temperature may be the magnitude of the temperature decrease per unit time. The degree to which the air flow rate is increased may be set according to the structure of the power generation unit 21. If the rate of decrease in the outlet temperature of the power generation unit 21 is small, there is a high possibility that exhaust gas is flowing back from another power generation unit 21 to the power generation unit 21 of the own device. Therefore, by increasing the flow rate of air supplied to the power generation unit 21 of the own device when the rate of decrease in the outlet temperature of the power generation unit 21 of the own device is small, the possibility of exhaust gas flowing back to the power generation unit 21 of the own device can be reduced. The first rate threshold may be set taking into account the normal rate of decrease in the outlet temperature of the power generation unit 21 during execution of the operation shutdown process for the power generation unit 21.

[0067] When the outlet temperature of the power generation unit 21 is higher than the temperature of the fuel cell module 22, the control unit 33 may control the flow rate of air supplied to the power generation unit 21 of the own device to be increased. The degree to which the air flow rate is increased may be set according to the structure of the power generation unit 21. The temperature of the fuel cell module 22 is, for example, the central temperature of the fuel cell module 22. When the outlet temperature of the power generation unit 21 is higher than the temperature of the fuel cell module 22, there is a high possibility that exhaust gas from another power generation unit 21 is flowing back into the power generation unit 21 of the own device. Therefore, when the outlet temperature of the power generation unit 21 is higher than the temperature of the fuel cell module 22, the control unit 33 may increase the flow rate of air supplied to the power generation unit 21 of the own device to further reduce the possibility of exhaust gas flowing back into the power generation unit 21 of the own device. Here, when the outlet temperature of the power generation unit 21 is higher than the temperature of the fuel cell module 22 by a temperature threshold, the control unit 33 may control the flow rate of air supplied to the power generation unit 21 of the own device to be increased. The temperature threshold value may be set taking into consideration the difference between the outlet temperature of the power generation unit 21 and the temperature of the fuel cell module 22 when exhaust gas flows back to the power generation unit 21 of the device itself.

[0068] The control unit 33 may increase the flow rate of air supplied to the power generation unit 21 of the fuel cell system 1, and then transmit an alert signal via the communication unit 31 if the rate of decrease in the outlet temperature of the power generation unit 21 of the fuel cell system 1 is smaller than the second rate threshold. The control unit 33 may transmit the alert signal to the master control unit, the control unit 30 of the master fuel cell system 20, or the second control unit 30. If the rate of decrease in the outlet temperature of the power generation unit 21 is small despite the increase in the air flow rate, it is highly likely that exhaust gas continues to flow back to the power generation unit 21 of the fuel cell system 1. Therefore, the control unit 33 transmits the alert signal. As described above, when the alert signal is transmitted, the second control unit 30 controls the power generation unit 21 to perform the operation shutdown process. By all of the second control units controlling the power generation units 21 to perform the operation shutdown process, all of the multiple power generation units 21 included in the fuel cell system 1 perform the operation shutdown process. This configuration more reliably reduces the possibility of exhaust gas flowing back to the power generation unit 21. The second rate threshold may be set taking into consideration the outlet temperature of the power generation unit 21 when exhaust gas flows back into the power generation unit 21 despite the increased air flow rate.

[0069] <After Completion of Operation Shutdown Process> After completion of the operation shutdown process for the power generation unit 21 of the own device, if the rate of increase in the outlet temperature of the power generation unit 21 of the own device is greater than the third rate threshold, the control unit 33 may control the flow rate of air supplied to the power generation unit 21 of the own device to be increased. The rate of increase in temperature may be the magnitude of the temperature increase per unit time. Here, if the cell stack 22S is an SOFC, the outlet temperature of the power generation unit 21 after completion of the operation shutdown process is, for example, 80°C or less. In contrast, the temperature of the exhaust gas from the power generation unit 21 during power generation is, for example, approximately 250°C. Therefore, if the rate of increase in the outlet temperature of the power generation unit 21 of the own device is large, there is a high possibility that exhaust gas from another power generation unit 21 is flowing back into the power generation unit 21 of the own device. Therefore, by increasing the air flow rate when the rate of increase in the outlet temperature of the power generation unit 21 of the own device is large, the possibility of exhaust gas flowing back into the power generation unit 21 of the own device can be further reduced. The third rate threshold may be set based on the rate of increase in the outlet temperature of the power generation unit 21 when exhaust gas flows back into the power generation unit 21 after the shutdown process is completed. The degree to which the air flow rate is increased may be set according to the structure of the power generation unit 21.

[0070] The control unit 33 may transmit an alert signal via the communication unit 31 if the rate of decrease in the outlet temperature of the power generation unit 21 of the fuel cell system 1 is smaller than a fourth rate threshold after controlling the flow rate of air supplied to the power generation unit 21 of the fuel cell system 1 to increase. The control unit 33 may transmit the alert signal to the master control unit, the control unit 30 of the master fuel cell system 20, or the second control unit 30. As described above, if the rate of decrease in the outlet temperature of the power generation unit 21 is small despite increasing the air flow rate, there is a high possibility that exhaust gas continues to flow back to the power generation unit 21 of the fuel cell system 1. Therefore, the control unit 33 transmits the alert signal. As described above, when the alert signal is transmitted, the second control unit 30 controls the power generation unit 21 to perform the operation shutdown process. By all of the second control units controlling the power generation units 21 to perform the operation shutdown process, all of the multiple power generation units 21 included in the fuel cell system 1 perform the operation shutdown process. This configuration more reliably reduces the possibility of exhaust gas flowing back to the power generation unit 21. The fourth rate threshold may be set taking into consideration the outlet temperature of the power generation unit 21 when exhaust gas flows back into the power generation unit 21 despite the air flow rate being increased.

[0071] (Operation of Fuel Cell System) FIG. 2 is a sequence diagram showing an example of the operation of the fuel cell system 1 shown in FIG.

[0072] In the control device 30 of the master fuel cell device 20, the control unit 33 receives a control signal from an external device via the communication unit 31 instructing the shutdown of some of the power generation units 21 (step S1). The control unit 33 then transmits a notification to the power conversion device 10 indicating that the shutdown process for the some of the power generation units 21 has been executed (step S2).

[0073] In the power conversion device 10, the control unit 13 receives a notification from the control device 30 of the master fuel cell device 20, indicating that operation of some of the power generation units 21 is to be stopped, via the communication unit 11 (step S3). The control unit 13 controls the remaining power generation units 21 that are generating power to reduce the amount of power generated (step S4).

[0074] In the process of step S5, the control unit 33 of the control device 30 of the master fuel cell device 20 transmits a control signal to the first control device via the communication unit 31. In the process of step S6, the control unit 33 of the first control device 30 receives the control signal via the communication unit 31. However, when the first control device 30 corresponds to the control device 30 of the master fuel cell device 20 and executes the process of step S1, i.e., when it receives a control signal from an external device, the processes of steps S5 and S6 do not need to be executed.

[0075] In the process of step S7, the control unit 33 of the first control device starts processing to stop the operation of the power generation unit 21. In the process of step S8, the control unit 33 controls the oxygen supply unit 24 so that air is continuously supplied to the power generation unit 21, while controlling the flow rate of air supplied to the power generation unit 21 to be different during the processing to stop the operation of the power generation unit 21 and after the processing to stop the operation of the power generation unit 21 is completed.

[0076] 3 and 4 are flowcharts showing an example of the operation of the fuel cell device 20 shown in Fig. 1. After executing the process of step S7, the control unit 33 of the control device 30 of the fuel cell device 20 may start the process of step S11.

[0077] The control unit 33 receives the detection result of the outlet temperature of the power generation unit 21 from the temperature sensor 28 (step S11). The control unit 33 determines whether the rate of decrease in the outlet temperature of the power generation unit 21 received in the process of step S11 is smaller than a first rate threshold (step S12). If the control unit 33 determines that the rate of decrease in the outlet temperature of the power generation unit 21 is smaller than the first rate threshold (step S12: YES), the control unit 33 proceeds to the process of step S13. On the other hand, if the control unit 33 determines that the rate of decrease in the outlet temperature of the power generation unit 21 is equal to or greater than the first rate threshold (step S12: NO), the control unit 33 proceeds to the process of step S16.

[0078] In the process of step S13, the control unit 33 controls the oxygen supply unit 24 to increase the flow rate of air supplied to the power generation unit 21.

[0079] In the process of step S14, the control unit 33 receives the detection result of the outlet temperature of the power generation unit 21 from the temperature sensor 28. The control unit 33 determines whether the rate of decrease in the outlet temperature of the power generation unit 21 received in the process of step S14 is smaller than the second rate threshold (step S15). If the control unit 33 determines that the rate of decrease in the outlet temperature of the power generation unit 21 is equal to or greater than the second rate threshold (step S15: NO), the control unit 33 proceeds to the process of step S16. If the control unit 33 determines that the rate of decrease in the outlet temperature of the power generation unit 21 is smaller than the second rate threshold (step S15: YES), the control unit 33 proceeds to the process of step S17.

[0080] In the process of step S16, the control unit 33 determines whether or not the operation shutdown process of the power generation unit 21 has been completed. If the control unit 33 determines that the operation shutdown process of the power generation unit 21 has been completed (step S16: YES), the control unit 33 proceeds to the process of step S18 shown in Fig. 4. If the control unit 33 does not determine that the operation shutdown process of the power generation unit 21 has been completed, that is, if the control unit 33 determines that the operation shutdown process is currently being executed (step S16: NO), the control unit 33 returns to the process of step S11.

[0081] In the process of step S17 , the control unit 33 transmits an alert signal via the communication unit 31 .

[0082] In the process of step S18 shown in Fig. 4, the control unit 33 receives the detection result of the outlet temperature of the power generation unit 21 from the temperature sensor 28. The control unit 33 determines whether the rate of increase of the outlet temperature of the power generation unit 21 received in the process of step S18 is greater than a third rate threshold (step S19). If the control unit 33 determines that the rate of increase of the outlet temperature of the power generation unit 21 is greater than the third rate threshold (step S19: YES), the control unit 33 proceeds to the process of step S20. If the control unit 33 determines that the rate of increase of the outlet temperature of the power generation unit 21 is equal to or less than the third rate threshold (step S19: NO), the control unit 33 ends the process shown in Fig. 4.

[0083] In the process of step S20, the control unit 33 controls the oxygen supply unit 24 to increase the flow rate of air supplied to the power generation unit 21.

[0084] In the process of step S21, the control unit 33 receives the detection result of the outlet temperature of the power generation unit 21 from the temperature sensor 28. The control unit 33 determines whether the outlet temperature of the power generation unit 21 received in the process of step S21 is smaller than a fourth threshold value (step S22). If the control unit 33 determines that the rate of decrease in the outlet temperature of the power generation unit 21 is smaller than the fourth rate threshold value (step S22: YES), the control unit 33 proceeds to the process of step S23. If the control unit 33 determines that the rate of decrease in the outlet temperature of the power generation unit 21 is equal to or greater than the fourth rate threshold value (step S22: NO), the control unit 33 ends the process shown in FIG. 4 .

[0085] In the process of step S23, the control unit 33 transmits an alert signal via the communication unit 31.

[0086] Here, in the process of step S12, the control unit 33 may determine whether the outlet temperature of the power generation unit 21 received in the process of step S11 is higher than the temperature of the fuel cell module 22. In this case, if the control unit 33 determines that the outlet temperature of the power generation unit 21 is higher than the temperature of the fuel cell module 22 (step S12: YES), the control unit 33 may proceed to the process of step S13. If the control unit 33 determines that the outlet temperature of the power generation unit 21 is equal to or lower than the temperature threshold of the fuel cell module 22 (step S12: NO), the control unit 33 may proceed to the process of step S16.

[0087] Furthermore, the control unit 33 may execute the processes of steps S11 to S23 while satisfying the instructions of the control signal received in the process of step S4. For example, the control unit 33 may execute the processes of steps S11 to S23 while air is continuously supplied to the power generation unit 21 and while controlling the flow rate of air supplied to the power generation unit 21 to be different during the process of stopping the operation of the power generation unit 21 and after the process of stopping the operation of the power generation unit 21 is completed.

[0088] Furthermore, when the processing of step S17 or step S23 is executed, the control unit 33 of the second control device may receive an alert signal from the master control device, the control device 30 of the master fuel cell device 20, or the first control device via the communication unit 31. In this case, the control unit 33 of the second control device may control the power generation unit 21 of the second control device to execute the operation shutdown processing.

[0089] As described above, when some of the multiple power generation units 21 are undergoing shutdown processing, the control device 30 according to this embodiment controls the supply of air continuously to those power generation units 21, while controlling the flow rate of air supplied to those power generation units 21 to be different during and after the shutdown processing of those power generation units 21. With this configuration, as described above, it is possible to further reduce the possibility that exhaust gas from the power generation unit 21 that is generating electricity will flow back into the power generation unit 21 during or after the shutdown processing has been completed via the exhaust unit 40. Therefore, according to this embodiment, it is possible to improve the technology for preventing the backflow of exhaust gas into the power generation unit.

[0090] Furthermore, in this embodiment, the cell stack 22S may be an SOFC. As described above, when the cell stack 22S is an SOFC, the time required to shut down the power generation unit 21 increases due to the high power generation temperature of the SOFC. In this embodiment, as described above, air is supplied to the power generation unit 21 even during the shutdown process of the power generation unit 21. This configuration can further reduce the possibility of exhaust gas flowing back through the exhaust unit 40 into the power generation unit 21 during the shutdown process.

[0091] While the present disclosure has been described based on various drawings and examples, it should be noted that those skilled in the art would easily be able to make various modifications and alterations based on the present disclosure. Therefore, it should be noted that these modifications and alterations are within the scope of the present disclosure. For example, the functions included in each functional unit can be rearranged so as not to cause logical inconsistencies. Multiple functional units may be combined into one or divided. The above-described embodiments of the present disclosure are not limited to faithful implementation of each of the described embodiments, but may be implemented by combining features or omitting some features as appropriate. In other words, those skilled in the art can make various modifications and alterations to the contents of the present disclosure based on the present disclosure. Therefore, these modifications and alterations are within the scope of the present disclosure. For example, in each embodiment, each functional unit, each means, or each step can be added to other embodiments so as not to cause logical inconsistencies, or can be replaced with each functional unit, each means, or each step of other embodiments. Furthermore, in each embodiment, multiple functional units, each means, or each step can be combined into one or divided. Furthermore, each of the above-described embodiments of the present disclosure is not limited to being implemented faithfully according to each of the described embodiments, but can also be implemented by combining each feature or omitting some of them as appropriate.

[0092] For example, an embodiment is also possible in which a general-purpose computer functions as at least one of the power conversion device 10 and the fuel cell device 20 according to the above-described embodiments. Specifically, a program describing the processing content for realizing each function of at least one of the power conversion device 10 and the fuel cell device 20 according to the above-described embodiments is stored in the memory of the general-purpose computer, and the program is read and executed by a processor. Therefore, the present disclosure can also be realized as a program executable by a processor, or a non-transitory computer-readable medium storing the program.

[0093] In one embodiment, (1) a fuel cell system includes: a plurality of power generation units; a plurality of oxygen supply units that supply oxygen-containing gas to each of the plurality of power generation units; an exhaust unit that collectively configures exhaust gas exhaust paths for each of the plurality of power generation units; and a control device, wherein when some of the plurality of power generation units perform a shutdown process, the control device controls some of the plurality of oxygen supply units to continuously supply the oxygen-containing gas to the some of the power generation units, while controlling the flow rate of the oxygen-containing gas supplied to the some of the power generation units to be different during the shutdown process of the some of the power generation units and after the shutdown process of the some of the power generation units is completed.

[0094] (2) In the fuel cell system described in (1) above, the control device may control the flow rate of the oxygen-containing gas supplied to the partial power generation unit so that it is greater after the operation shutdown process of the partial power generation unit is completed than during the operation shutdown process of the partial power generation unit.

[0095] (3) In the fuel cell system described in (2) above, the control device may control the flow rate of the oxygen-containing gas supplied to the power generation unit to gradually increase while the operation shutdown process for the power generation unit is being performed.

[0096] (4) In the fuel cell system described in (1) above, the control device may control the flow rate of the oxygen-containing gas supplied to the partial power generation unit so that it is greater while the partial power generation unit is being shut down than after the shutdown process for the partial power generation unit has been completed.

[0097] (5) In the fuel cell system described in any one of (1) to (4) above, the system may include a plurality of temperature sensors capable of detecting the outlet temperatures of the plurality of power generation units, and the control device may control the portion of the oxygen supply unit based on the detection results of some of the plurality of temperature sensors when some of the power generation units perform a shutdown process.

[0098] (6) In the fuel cell system described in (5) above, the control device may control the flow rate of the oxygen-containing gas supplied to the power generation unit to be increased when the rate of decrease in the outlet temperature of the power generation unit is smaller than a first rate threshold during the execution of the operation shutdown process of the power generation unit.

[0099] (7) In the fuel cell system described in (5) above, the control device may control the flow rate of the oxygen-containing gas supplied to the partial power generation unit to be increased when the outlet temperature of the partial power generation unit is higher than the temperature of the fuel cell module of the partial power generation unit during the execution of the operation shutdown process of the partial power generation unit.

[0100] (8) In the fuel cell system described in any one of (5) to (7) above, the control device may control the flow rate of the oxygen-containing gas supplied to the power generation unit to be increased, and then send an alert signal if the rate of decrease in the outlet temperature of the power generation unit is smaller than a second rate threshold.

[0101] (9) In the fuel cell system described in any one of (5) to (7) above, the control device may control the flow rate of the oxygen-containing gas supplied to the power generation unit to be increased when the rate of increase in the outlet temperature of the power generation unit is greater than a third rate threshold after the operation shutdown process of the power generation unit is completed.

[0102] (10) In the fuel cell system described in (9) above, the control device may control the flow rate of the oxygen-containing gas supplied to the power generation unit to be increased, and then send an alert signal if the rate of decrease in the outlet temperature of the power generation unit is smaller than a fourth rate threshold.

[0103] (11) In the fuel cell system described in (8) or (10) above, the control device may control all of the plurality of power generation units to perform an operation stop process when the alert signal is transmitted.

[0104] (12) The fuel cell system according to any one of (1) to (11) above may further include a power conversion device electrically connected to each of the plurality of power generation units, and the power conversion device may be controlled so that when another power generation unit among the plurality of power generation units is generating power, the amount of power generated by the other power generation unit that is generating power is reduced.

[0105] 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, the first process can exchange the identifiers "first" and "second" with the second process. The exchange of identifiers is performed simultaneously. The configurations remain distinguished even after the exchange of identifiers. 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.

[0106] REFERENCE SIGNS LIST 1 fuel cell system 10 power conversion device 11 communication unit 12 memory unit 13 control unit 14 power conversion unit 2 load group 20, 20-1, 20-2, 20-3 fuel cell device 21 power generation unit 22, 22-1, 22-2 fuel cell module 22R reformer 22S cell stack 23, 23-1, 23-2 reforming water supply unit 23L, 23L-1, 23L-2 reforming water supply line 24, 24-1, 24-2 air supply unit 25, 25-1, 25-2 air flow meter 24L, 24L-1, 24L-2 oxygen supply line 26 gas supply unit 26L fuel supply line 27 gas flow meter 30 control device 31 communication unit 32 memory unit 33 control unit 40 discharge unit 41, 41-1, 41-2, 41-3 Exhaust passage 42 Connection part 43 Exhaust port

Claims

1. A fuel cell system comprising: a plurality of power generation units; a plurality of oxygen supply units that supply oxygen-containing gas to each of the plurality of power generation units; an exhaust unit that collectively configures exhaust gas exhaust paths for each of the plurality of power generation units; and a control device, wherein when some of the plurality of power generation units perform a shutdown process, the control device controls the oxygen-containing gas to be continuously supplied to the some of the power generation units by some of the plurality of oxygen supply units, while controlling the flow rate of the oxygen-containing gas supplied to the some of the power generation units to be different during the shutdown process of the some of the power generation units and after the shutdown process of the some of the power generation units is completed.

2. The fuel cell system of claim 1, wherein the control device controls the flow rate of the oxygen-containing gas supplied to the power generation unit so that it is greater after the operation shutdown process of the power generation unit is completed than during the operation shutdown process of the power generation unit.

3. The fuel cell system according to claim 2, wherein the control device controls the flow rate of the oxygen-containing gas supplied to the partial power generation unit so as to gradually increase while the operation shutdown process for the partial power generation unit is being executed.

4. A fuel cell system as described in claim 1, wherein the control device controls the flow rate of the oxygen-containing gas supplied to the power generation unit so that it is greater while the power generation unit is being shut down than after the shutdown process for the power generation unit has been completed.

5. A fuel cell system as described in any one of claims 1 to 4, comprising a plurality of temperature sensors capable of detecting the outlet temperatures of each of the plurality of power generation units, and wherein the control device controls some of the oxygen supply units based on the detection results of some of the plurality of temperature sensors when some of the power generation units perform operation shutdown processing.

6. A fuel cell system as described in claim 5, wherein the control device controls the flow rate of the oxygen-containing gas supplied to the power generation unit to be increased when the rate of decrease in the outlet temperature of the power generation unit is smaller than a first rate threshold while the operation shutdown process of the power generation unit is being performed.

7. A fuel cell system as described in claim 5, wherein the control device controls the flow rate of the oxygen-containing gas supplied to the partial power generation unit to be increased when the outlet temperature of the partial power generation unit is higher than the temperature of the fuel cell module of the partial power generation unit during execution of the operation shutdown process of the partial power generation unit.

8. A fuel cell system as described in any one of claims 5 to 7, wherein the control device controls the flow rate of the oxygen-containing gas supplied to the part of the power generation unit to be increased, and then sends an alert signal if the rate of decrease in the outlet temperature of the part of the power generation unit is smaller than a second rate threshold.

9. A fuel cell system as described in any one of claims 5 to 7, wherein the control device controls the flow rate of the oxygen-containing gas supplied to the power generation unit to be increased if, after completion of the operation shutdown process for the power generation unit, the rate of increase in the outlet temperature of the power generation unit is greater than a third rate threshold.

10. The fuel cell system of claim 9, wherein the control device controls the flow rate of the oxygen-containing gas supplied to the portion of the power generation unit to be increased, and then transmits an alert signal if the rate of decrease in the outlet temperature of the portion of the power generation unit is smaller than a fourth rate threshold.

11. The fuel cell system according to claim 8 or 10, wherein the control device controls all of the plurality of power generation units to perform operation shutdown processing when the alert signal is transmitted.

12. A fuel cell system as described in any one of claims 1 to 11, further comprising a power conversion device electrically connected to each of the plurality of power generation units, wherein when another power generation unit among the plurality of power generation units is generating electricity, the power conversion device controls the amount of power generated by the other power generation unit that is generating electricity to decrease.

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