Fuel cell system

Abstract

This fuel cell system includes a power conversion device and a plurality of fuel cells electrically connected in parallel to the power conversion device. The power conversion device controls a combined current value that is drawn from the plurality of fuel cells to the power conversion device, on the basis of a voltage difference between a closed circuit voltage value of at least one fuel cell, among the plurality of fuel cells, that is generating power and an open circuit voltage value of at least one fuel cell that has not started to generate power.

Description

fuel cell system Cross-reference to related applications

[0001] This application claims priority to Japanese Patent Application No. 2024-044036, filed on March 19, 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 devices that can contribute to carbon neutrality. Among such fuel cell systems, those equipped with multiple fuel cells are known. For example, Patent Literature 1 (JP-A-2005-102626) describes a fuel cell system that includes electrical wiring connecting multiple fuel cells in parallel.

[0004] JP 2016-134287 A

[0005] A fuel cell system according to one embodiment of the present disclosure includes a power conversion device and a plurality of fuel cells electrically connected in parallel to the power conversion device, wherein the power conversion device controls the combined current value drawn from the plurality of fuel cells to the power conversion device based on the voltage difference between the closed circuit voltage value of at least one of the plurality of fuel cells during power generation and the open circuit voltage value of at least one of the fuel cells before power generation begins.

[0006] It is a block diagram showing the configuration of a fuel cell system according to an embodiment of the present disclosure.It is a flowchart showing an example of the operation of the power conversion device shown in Figure 1.It is a flowchart showing an example of the operation of the power conversion device shown in Figure 1.

[0007] There is room for improvement in the operation of a fuel cell system having multiple fuel cells connected in parallel. According to one embodiment of the present disclosure, the degree of degradation of the fuel cells can be reduced.

[0008] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0009] 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.

[0010] The fuel cell system 1 includes a power conversion device 10 and a plurality of fuel cell devices 20. 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 number of fuel cell devices 20 included in the fuel cell system 1 may be any number. The number of fuel cell devices 20 included in the fuel cell system 1 may be two, or may be four or more.

[0011] The power conversion device 10 is also referred to as 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. The power conversion device 10 may further include a plurality of relays 15. Each of the plurality of relays 15 is provided between each of the plurality of fuel cell devices 20 and the power conversion unit 14.

[0012] 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.

[0013] 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. For example, the storage unit 12 may store any data used to calculate the open circuit voltage value and the closed circuit voltage value described below. The storage unit 12 may store a program executed by the control unit 13.

[0014] 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.

[0015] In the case where the power conversion device 10 includes the above-mentioned multiple relays 15, when the fuel cell device 20 starts generating power, the control unit 13 controls the relays 15 between the fuel cell device 20 and the power conversion unit 14 to be in the on state. When the fuel cell device 20 stops generating power, the control unit 13 may control the relays 15 between the fuel cell device 20 and the power conversion unit 14 to be in the off state.

[0016] The control unit 13 controls the value of the current drawn by the power conversion device 10 from the plurality of fuel cell devices 20. Through this control, the DC power drawn by the power conversion device 10 is supplied to the power conversion unit 14. The control unit 13 may receive information on the temperature, generated current value, and voltage value of the fuel cell module 22 (described later) from the control device 30 (described later) via the communication unit 11.

[0017] 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.

[0018] The fuel cell device 20 includes a power generation unit 21, reforming water supply units 23-1 and 23-2, air 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, 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.

[0019] 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 air supply unit 24-1 and the air supply unit 24-2, they will also be referred to as the "air 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 is provided with two reforming water supply units 23, two air supply units 24, and two air flow meters 25. However, the number of reforming water supply units 23, two air supply units 24, and two air flow meters 25 provided in the fuel cell device 20 may be any number depending on the number of fuel cell modules 22 (described later) included in the power generation unit 21.

[0020] 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.

[0021] 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 fuel cell modules 22-1 and 22-2. However, the power generation unit 21 may also be fuel cell modules 22-1 and 22-2. The power generation unit 21 may have other shapes. The fuel cell modules may be hot modules. Hereinafter, when there is no particular distinction between the fuel cell module 22-1 and the fuel cell module 22-2, they are also referred to as "fuel cell modules 22." In FIG. 1, the number of fuel cell modules 22 included in the power generation unit 21 is two. However, the number of fuel cell modules 22 included in the power generation unit 21 may be any number. The number of fuel cell modules 22 included in the power generation unit 21 may be one or more, or may be three or more.

[0022] The plurality of 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.

[0023] 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.

[0024] Air is supplied to the fuel cell modules 22 from an air supply unit 24. In Fig. 1, air is supplied to the fuel cell module 22-1 from an air supply unit 24-1, and air is supplied to the fuel cell module 22-2 from an air supply unit 24-2.

[0025] Fuel gas is distributed and supplied to the fuel cell modules 22 from a gas supply unit 26. Distributed supply means that gas from one gas supply unit 26 is distributed and supplied to a plurality of fuel cell modules 22.

[0026] When the fuel cell module 22 starts to start up, the temperature of the fuel cell module 22 rises. When the temperature of the fuel cell module 22 reaches a temperature at which power can be generated, the fuel cell module 22 starts to generate power.

[0027] 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 is, for example, a solid oxide fuel cell (SOFC). The cell stack 22S generates an electrochemical reaction between air supplied from an air 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.

[0028] 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 on the temperature, generated current value, and voltage value of the fuel cell module 22 to the control unit 33. The temperature of the fuel cell module 22 is, for example, the temperature at the center of the fuel cell module 22. However, the temperature of the fuel cell module 22 may be the temperature of any location as long as the temperatures can be compared between multiple fuel cell modules 22.

[0029] 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-1. 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.

[0030] 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.

[0031] 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.

[0032] The air 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 air 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 air 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.

[0033] The air supply unit 24 includes a blower and other components. Based on a control signal from the control device 30, the air supply unit 24 supplies an oxygen-containing gas to the cell stack 22S of the fuel cell module 22 via the oxygen supply line 24L. In this embodiment, the air supply unit 24 supplies air as the oxygen-containing gas to the cell stack 22S. However, the oxygen-containing gas supplied by the air supply unit 24 to the cell stack 22S is not limited to air. For example, the air supply unit 24 may supply only oxygen as the oxygen-containing gas to the cell stack 22S, or may supply a gas containing oxygen other than air to the cell stack 22S. Based on a control signal from the control device 30, the air supply unit 24 controls the amount of air supplied to the cell stack 22S. In FIG. 1 , the air supply unit 24-1 supplies air to the cell stack 22S of the fuel cell module 22-1 via the oxygen supply line 24L-1 based on a control signal from the control device 30. Based on a control signal from the control device 30, the air supply unit 24-2 supplies air to the cell stack 22S of the fuel cell module 22-2 via the oxygen supply line 24-2.

[0034] The air 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.

[0035] 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.

[0036] 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.

[0037] The gas supply unit 26 includes a pump and other components. 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 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 fuel cell modules 22. However, two gas supply units 26 may be provided separately for the fuel cell modules 22-1 and 22-2.

[0038] 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 portion of the fuel supply line 26L between the portion connected to the gas supply unit 26 and the portion 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. However, two gas flow meters 27 may be attached to each of the two branches of the fuel supply line 26L.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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 ASIC. The control unit 33 controls each part of the fuel cell device 20 and executes processes related to the operation of the fuel cell device 20.

[0043] The control unit 33 acquires information on the temperature, generated current value, and voltage value of the fuel cell module 22 from the fuel cell module 22. The control unit 33 transmits the information on the temperature, generated current value, and voltage value of the fuel cell module 22 to the power conversion device 10 via the communication unit 31.

[0044] [Processing at Start-up of Fuel Cell System] In the fuel cell system 1, a plurality of power generation units 21 are electrically connected in parallel to the power conversion device 10. In other words, in the fuel cell system 1, a plurality of fuel cell modules 22-1 are electrically connected in parallel to the power conversion device 10. In Fig. 1, the fuel cell module 22-1 of the fuel cell device 20-1, the fuel cell module 22-1 of the fuel cell device 20-2, and the fuel cell module 22-1 of the fuel cell device 20-3 are electrically connected in parallel to the power conversion device 10. In other words, in this embodiment, three fuel cell modules 22-1 are electrically connected in parallel to the power conversion device 10.

[0045] Of the multiple fuel cell modules 22-1 electrically connected in parallel to the power conversion device 10, some of the fuel cell modules 22-1 are generating electricity, while the remaining fuel cell modules 22-1 have not yet started generating electricity. When a fuel cell module 22-1 that has not yet started generating electricity starts generating electricity, the relay 15 in the power conversion device 10, for example, is turned on, electrically connecting the fuel cell module 22-1 that has started generating electricity to the power conversion unit 14. If there is a voltage difference between the voltage of the fuel cell module 22-1 currently generating electricity and the voltage of the fuel cell module 22-1 that has started generating electricity, the voltages of the multiple fuel cell modules 22-1 electrically connected in parallel to the power conversion unit 14 are made equal. Therefore, an inrush current may flow from the fuel cell module 22-1 that has started generating electricity to the fuel cell module 22-1 currently generating electricity via the power conversion unit 14. Furthermore, the greater the generated current supplied to the power conversion device 10 from the fuel cell module 22-1 currently generating electricity, the lower the voltage of the fuel cell module 22-1 currently generating electricity. Therefore, the greater the potential difference between the fuel cell module 22-1 that is generating electricity and the fuel cell module 22-1 that has just started generating electricity, the greater the potential inrush current that may occur. If a large inrush current occurs, the cell stack 22S may be damaged by oxidation due to gas starvation or thermal shock due to the rapid generation of Joule heat.

[0046] Here, when the fuel cell module 22-1 has not yet started power generation, no generated current is supplied from the fuel cell module 22-1 to the power conversion device 10. Furthermore, if the power conversion device 10 is equipped with the above-mentioned multiple relays 15, the relays 15 between the fuel cell module 22-1 and the power conversion unit 14 before power generation starts are in the OFF state. Therefore, when the fuel cell module 22-1 has not yet started power generation, no load is applied to the fuel cell module 22-1. When the fuel cell module 22-1 has not yet started power generation, the voltage of the fuel cell module 22-1 becomes an open circuit voltage (OCV) because no load is applied to the fuel cell module 22-1.

[0047] In contrast, when the fuel cell module 22-1 is generating power, the generated current is supplied from the fuel cell module 22-1 to the power conversion unit 14. As a result, a load is applied to the fuel cell module 22-1 during power generation. As a result of the load being applied to the fuel cell module 22-1 during power generation, the voltage of the fuel cell module 22-1 during power generation becomes a closed circuit voltage.

[0048] Therefore, when the fuel cell system 1 begins to start up, the control unit 13 of the power conversion device 10 acquires the closed circuit voltage value of the fuel cell module 22-1 that is generating electricity and the open circuit voltage value of the fuel cell module 22-1 before the start of power generation, among the multiple fuel cell modules 22-1.

[0049] As an example of acquiring the open circuit voltage value, the control unit 13 may acquire the electromotive force of the fuel cell module 22-1 before the start of power generation as the open circuit voltage value. The electromotive force of the fuel cell module 22-1 before the start of power generation may be equal to the open circuit voltage value of the fuel cell module 22-1. The control unit 13 may acquire the open circuit voltage value by calculating the electromotive force of the fuel cell module 22-1 before the start of power generation using the Nernst equation.

[0050] As an example of obtaining the closed circuit voltage value, the control unit 13 may obtain the closed circuit voltage value of the fuel cell module 22-1 during power generation by calculating it using the following formula (1): Closed circuit voltage value = Open circuit voltage value (electromotive force) - R × I Formula (1) In formula (1), the resistance value R is the resistance value of the fuel cell module 22-1 during power generation when the fuel cell module 22-1 is considered as an electric circuit. The current value I is the generated current value of the fuel cell module 22-1 during power generation.

[0051] When the control unit 13 acquires the closed circuit voltage value, etc., it controls the composite current value based on the voltage difference between the closed circuit voltage value of the fuel cell module 22-1 that is generating power and the open circuit voltage value of the fuel cell module 22-1 before the start of power generation. The composite current value is the current value drawn from the multiple fuel cell modules 22-1 to the power conversion device 10. The fuel cell module 22-1 generates power with a generated current value equal to the current value drawn by the power conversion device 10. In other words, the composite current value is the sum of the generated current values ​​of the multiple fuel cell modules 22-1. When multiple fuel cell modules 22-1 are generating power, the control unit 13 may acquire the lowest closed circuit voltage value among the multiple fuel cell modules that are generating power. When one fuel cell module 22-1 is generating power, the control unit 13 may treat the closed circuit voltage value of this one fuel cell module 22-1 as the lowest closed circuit voltage value. Hereinafter, the fuel cell module 22 exhibiting the lowest closed circuit voltage value refers to the fuel cell module 22 exhibiting the lowest closed circuit voltage value when multiple fuel cell modules 22 are generating electricity, and refers to that single fuel cell module 22 when only one fuel cell module 22 is generating electricity. Here, the electromotive force of a fuel cell module 22-1 generating electricity can be equal to the open circuit voltage value of that fuel cell module 22-1. The electromotive force of a fuel cell module 22-1 generating electricity can be determined by the Nernst equation (1). Therefore, even if multiple fuel cell modules 22-1 have not yet started generating electricity, the open circuit voltage values ​​of the multiple fuel cell modules 22-1 before the start of power generation can be equal. Therefore, when multiple fuel cell modules 22-1 have not yet started generating electricity, the control unit 13 may use the open circuit voltage value of any one of the fuel cell modules 22-1 before the start of power generation.

[0052] The control unit 13 calculates the voltage difference between the lowest acquired closed circuit voltage value of the fuel cell module 22-1 and the open circuit voltage value of the fuel cell module 22-1 before the start of power generation. If the calculated voltage difference exceeds a voltage threshold, the control unit 13 controls the combined current value. By controlling the combined current value, it is possible to reduce the inrush current of the fuel cell module 22-1 that has started power generation.

[0053] The control unit 13 may control the combined current value so that the larger the calculated potential difference, the smaller the combined current value. The larger the voltage difference between the closed circuit voltage value of the fuel cell module 22-1 during power generation and the open circuit voltage value of the fuel cell module 22-1 before the start of power generation, the larger the inrush current of the fuel cell module 22-1 that has started power generation. Therefore, by controlling the combined current value so that the larger the calculated potential difference, the smaller the combined current value, the smaller the inrush current of the fuel cell module 22-1 that has started power generation can be reduced.

[0054] The control unit 13 may control the combined current value according to the temperature of the fuel cell module 22-1 with the lowest closed circuit voltage value. The control unit 13 may control the combined current value so that the lower the temperature of the fuel cell module 22-1 with the lowest closed circuit voltage value, the smaller the combined current value. The lower the temperature of the fuel cell module 22-1 during power generation, the smaller the voltage value of the fuel cell module 22-1 during power generation. As a result, the voltage difference between the closed circuit voltage value of the fuel cell module 22-1 during power generation and the open circuit voltage value of the fuel cell module 22-1 before the start of power generation becomes larger. By controlling the combined current value so that the lower the temperature of the fuel cell module 22-1 with the lowest closed circuit voltage value, the inrush current of the fuel cell module 22-1 that has started power generation can be reduced.

[0055] When the temperature of the fuel cell module 22-1 currently generating electricity, which has the lowest closed-circuit voltage among the fuel cell modules 22 currently generating electricity, is equal to or higher than the temperature threshold, the control unit 13 may execute a process to increase the electromotive force of the fuel cell module 22-1 currently generating electricity. However, the control unit 13 may also execute a process to increase the electromotive force of other fuel cell modules 22 currently generating electricity. The temperature threshold may be set according to the structure of the fuel cell module 22-1. Increasing the electromotive force of the fuel cell module 22-1 currently generating electricity can reduce the influence of the product of the resistance value R and the current value I (the term R×I in equation (1)) on the closed-circuit voltage of the fuel cell module 22-1 currently generating electricity. Reducing the influence of the product of the resistance value R and the current value I on the closed-circuit voltage can result in a reduction in the voltage difference between the closed-circuit voltage of the fuel cell module 22-1 currently generating electricity and the open-circuit voltage of the fuel cell module 22-1 before the start of power generation. This reduction in voltage difference can reduce the inrush current of the fuel cell module 22-1 that has started power generation.

[0056] The control unit 13 may control the fuel cell module 22-1 to perform at least one of a first process, a second process, and a third process as a process for increasing the electromotive force of the fuel cell module 22-1 during power generation. By performing at least one of the first process, the second process, and the third process, the electromotive force of the fuel cell module 22-1 during power generation can be increased.

[0057] The first process is a process of increasing the flow rate of fuel gas supplied to the fuel cell module 22-1 that is generating power by a first amount. The first amount may be set depending on the structure of the fuel cell module 22-1. To execute the first process, the control unit 13 transmits a signal instructing the execution of the first process via the communication unit 11 to the fuel cell device 20 including the fuel cell module 22-1 that is generating power. In the control device 30 of the fuel cell device 20, the control unit 33 receives a signal instructing the execution of the first process from the power conversion device 10 via the communication unit 31. Upon receiving the signal instructing the execution of the first process, the control unit 33 controls the gas supply unit 26 to increase the flow rate of fuel gas supplied to the fuel cell module 22-1 that is generating power by a first amount. Here, when the power generation unit 21 includes the fuel cell module 22-2 connected in series to the fuel cell module 22-1, i.e., when the fuel cell modules 22-1 and 22-2 are electrically connected in series, the relay 15 is in the off state during startup. However, when one of the fuel cell modules 22-1, 22-2 reaches a temperature at which power can be generated, the relay 15 is turned off, and power generation begins simultaneously. Therefore, the control unit 13 may control one gas supply unit 26 to increase the flow rate of the fuel gas supplied to both the fuel cell module 22-1 and the fuel cell module 22-2 by a first amount.

[0058] The second process is a process of increasing the flow rate of the oxygen-containing gas supplied to the fuel cell module 22-1 that is generating electricity by a second amount. The second amount may be set depending on the structure of the fuel cell module 22-1. To execute the second process, the control unit 13 transmits a signal instructing the execution of the second process to the fuel cell device 20 including the fuel cell module 22-1 that is generating electricity via the communication unit 11. In the control device 30 of the fuel cell device 20, the control unit 33 receives a signal instructing the execution of the second process from the power conversion device 10 via the communication unit 31. Upon receiving the signal instructing the execution of the second process, the control unit 33 controls the air supply unit 24-1 to increase the flow rate of air supplied to the fuel cell module 22-1 that is generating electricity by a second amount. Here, as described above, when the fuel cell module 22-1 is generating electricity, the fuel cell module 22-2 is also generating electricity. Therefore, the control unit 33 may control both the air supply unit 24-1 and the air supply unit 24-2 so that the flow rate of air supplied to each of the fuel cell modules 22-1 and 22-2 increases by a second amount.

[0059] The third process is a process of reducing the flow rate of reforming water supplied to the fuel cell module 22-1 that is generating power by a third amount. The third amount may be set depending on the structure of the fuel cell module 22-1. To execute the third process, the control unit 13 transmits a signal instructing the execution of the third process via the communication unit 11 to the fuel cell device 20 including the fuel cell module 22-1 that is generating power. In the control device 30 of the fuel cell device 20, the control unit 33 receives a signal instructing the execution of the third process from the power conversion device 10 via the communication unit 31. Upon receiving the signal instructing the execution of the third process, the control unit 33 controls the reforming water supply unit 23-1 to increase the flow rate of reforming water supplied to the fuel cell module 22-1 that is generating power by a third amount. Here, as described above, when the fuel cell module 22-1 is generating power, the fuel cell module 22-2 is also generating power. Therefore, the control unit 33 may control both the reforming water supply unit 23-1 and the reforming water supply unit 23-2 so that the flow rate of the reforming water supplied to each of the fuel cell modules 22-1 and 22-2 increases by a third amount.

[0060] When the temperature of the fuel cell module 22-1 currently generating electricity, which exhibits the lowest closed-circuit voltage among the fuel cell modules 22 currently generating electricity, is below the temperature threshold, the control unit 13 may execute a process to reduce the resistance of the fuel cell module 22-1 currently generating electricity. However, the control unit 13 may also execute a process to reduce the resistance of other fuel cell modules 22 currently generating electricity. The resistance of the fuel cell module 22-1 currently generating electricity is the resistance of the fuel cell module 22-1 when the fuel cell module 22-1 is considered as an electrical circuit. Reducing the resistance of the fuel cell module 22-1 currently generating electricity reduces the influence of the product of the resistance R and the current I (the term R×I in equation (1)) on the closed-circuit voltage of the fuel cell module 22-1 currently generating electricity. As a result, as described above, the voltage difference between the closed-circuit voltage of the fuel cell module 22-1 currently generating electricity and the open-circuit voltage of the fuel cell module 22-1 before the start of power generation can be reduced. Reducing this voltage difference reduces the inrush current of the fuel cell module 22-1 that has started power generation.

[0061] The control unit 13 may control the execution of at least one of the fourth process, the fifth process, and the sixth process as a process for reducing the resistance value of the fuel cell module 22-1 during power generation. By executing at least one of the fourth process, the fifth process, and the sixth process, the resistance value of the fuel cell module 22-1 during power generation can be reduced, as described below.

[0062] The fourth process is a process of increasing the flow rate of fuel gas supplied to the fuel cell module 22-1 that is generating power by a fourth amount. The fourth amount may be set depending on the structure of the fuel cell module 22-1. To execute the fourth process, the control unit 13 transmits a signal instructing the execution of the fourth process via the communication unit 11 to the fuel cell device 20 including the fuel cell module 22-1 that is generating power. In the control device 30 of the fuel cell device 20, the control unit 33 receives a signal instructing the execution of the fourth process from the power conversion device 10 via the communication unit 31. Upon receiving the signal instructing the execution of the fourth process, the control unit 33 controls the gas supply unit 26 to increase the flow rate of fuel gas supplied to the fuel cell module 22-1 that is generating power by a fourth amount. Here, as described above, when the fuel cell module 22-1 is generating power, the fuel cell module 22-2 is also generating power. Therefore, the control unit 13 may control one gas supply unit 26 so that the flow rate of the fuel gas supplied to both the fuel cell module 22-1 and the fuel cell module 22-2 increases by a fourth amount.

[0063] By executing the fourth process in this manner, it is possible to increase the flow rate of fuel gas supplied to the fuel cell module 22-1 during power generation. By increasing the flow rate of fuel gas supplied to the fuel cell module 22-1 during power generation, it is possible to increase the temperature of the electrodes of the cell stack 22S. By increasing the temperature of the electrodes of the cell stack 22S, it is possible to reduce the resistance value of the fuel cell module 22-1 during power generation. By reducing the resistance value of the fuel cell module 22-1 during power generation, current flows more easily in the fuel cell module 22-1, and Joule heat increases. By increasing Joule heat, it is possible to increase the power generation temperature of the cell stack 22S. As a result, it is possible to further increase the temperature of the fuel cell module 22-1 during power generation.

[0064] The fifth process is a process of reducing the flow rate of the oxygen-containing gas supplied to the fuel cell module 22-1 that is generating electricity by a fifth amount. The fifth amount may be set depending on the structure of the fuel cell module 22-1. To execute the fifth process, the control unit 13 transmits a signal instructing the execution of the fifth process to the fuel cell device 20 including the fuel cell module 22-1 that is generating electricity via the communication unit 11. In the control device 30 of the fuel cell device 20, the control unit 33 receives a signal instructing the execution of the fifth process from the power conversion device 10 via the communication unit 31. Upon receiving the signal instructing the execution of the fifth process, the control unit 33 controls the air supply unit 24-1 to reduce the flow rate of air supplied to the fuel cell module 22-1 that is generating electricity by a fifth amount. Here, as described above, when the fuel cell module 22-1 is generating electricity, the fuel cell module 22-2 is also generating electricity. Therefore, the control unit 33 may control both the air supply unit 24-1 and the air supply unit 24-2 so that the flow rate of air supplied to each of the fuel cell modules 22-1 and 22-2 is reduced by a fifth amount.

[0065] By executing the fifth process in this manner, the flow rate of air supplied to the fuel cell module 22-1 that is generating electricity is reduced. By reducing the flow rate of air supplied to the fuel cell module 22-1 that is generating electricity, it is possible to reduce the likelihood that the temperature of the fuel cell module 22-1 that is generating electricity will be lost by air. By reducing the likelihood that the temperature of the fuel cell module 22-1 that is generating electricity will be lost by air, it is possible to increase the temperature of the fuel cell module 22-1 that is generating electricity. By increasing the temperature of the fuel cell module 22-1 that is generating electricity, it is possible to reduce the resistance value of the fuel cell module 22-1 that is generating electricity, as described above in the fourth process.

[0066] The sixth process is a process of reducing the flow rate of reforming water supplied to the fuel cell module 22-1 that is generating power by a sixth amount. The sixth amount may be set depending on the structure of the fuel cell module 22-1. To execute the sixth process, the control unit 13 transmits a signal instructing the execution of the sixth process via the communication unit 11 to the fuel cell device 20 including the fuel cell module 22-1 that is generating power. In the control device 30 of the fuel cell device 20, the control unit 33 receives a signal instructing the execution of the sixth process from the power conversion device 10 via the communication unit 31. Upon receiving the signal instructing the execution of the sixth process, the control unit 33 controls the reforming water supply unit 23-1 to reduce the flow rate of reforming water supplied to the fuel cell module 22-1 that is generating power by a sixth amount. Here, as described above, when the fuel cell module 22-1 is generating power, it is highly likely that the fuel cell module 22-2 is also generating power. Therefore, the control unit 33 may control both the reforming water supply unit 23-1 and the reforming water supply unit 23-2 to reduce the flow rate of the reforming water supplied to each of the fuel cell modules 22-1 and 22-2 by a sixth amount.

[0067] By performing the sixth process in this manner, the flow rate of the reforming water supplied to the fuel cell module 22-1 during power generation is reduced. Reducing the flow rate of the reforming water supplied to the fuel cell module 22-1 reduces the likelihood that the temperature of the fuel cell module 22-1 during power generation will be lost due to an endothermic reaction caused by the heat of vaporization of the reforming water. This configuration allows the temperature of the fuel cell module 22-1 during power generation to increase, thereby reducing the resistance of the fuel cell module 22-1 during power generation, as described above in the fourth process.

[0068] If the voltage difference between the lowest closed circuit voltage value of the fuel cell module 22-1 and the open circuit voltage value of the fuel cell module 22-1 before the start of power generation exceeds a voltage threshold, the control unit 13 may execute a process to lower the open circuit voltage value of the fuel cell module 22-1 before the start of power generation. Lowering the open circuit voltage value reduces the potential difference, thereby reducing the inrush current of the fuel cell module 22-1 that has started power generation.

[0069] The control unit 13 may control the execution of at least one of the seventh process, the eighth process, and the ninth process as a process for lowering the open circuit voltage value of the fuel cell module 22-1 before the start of power generation. By executing at least one of the seventh process, the eighth process, and the ninth process, it is possible to lower the electromotive force of the fuel cell module 22-1 before the start of power generation, as can be seen from the Nernst equation. As a result, it is possible to lower the open circuit voltage value of the fuel cell module 22-1 before the start of power generation.

[0070] The seventh process is a process of reducing the flow rate of fuel gas supplied to the fuel cell module 22-1 before the start of power generation by a seventh amount. The seventh amount may be set depending on the structure of the fuel cell module 22-1. To execute the seventh process, the control unit 13 transmits a signal instructing the execution of the seventh process to the fuel cell device 20 including the fuel cell module 22-1 before the start of power generation via the communication unit 11. In the control device 30 of the fuel cell device 20, the control unit 33 receives a signal instructing the execution of the seventh process from the power conversion device 10 via the communication unit 31. Upon receiving the signal instructing the execution of the seventh process, the control unit 33 controls the gas supply unit 26 to reduce the flow rate of fuel gas supplied to the fuel cell module 22-1 before the start of power generation by a seventh amount. Here, as described above, it is assumed that the temperatures of the fuel cell module 22-1 and the fuel cell module 22-2 are the same or similar. Therefore, if the fuel cell module 22-1 has not yet started power generation, it is highly likely that the fuel cell module 22-2 has not yet started power generation either. Therefore, the control unit 13 may control one gas supply unit 26 to reduce the flow rate of the fuel gas supplied to both the fuel cell module 22-1 and the fuel cell module 22-2 by a seventh amount.

[0071] The eighth process is a process for increasing the flow rate of reforming water supplied to the fuel cell module 22-1 before the start of power generation by an eighth amount. The eighth amount may be set depending on the structure of the fuel cell module 22-1. To execute the eighth process, the control unit 13 transmits a signal instructing the execution of the eighth process via the communication unit 11 to the fuel cell device 20 including the fuel cell module 22-1 before the start of power generation. In the control device 30 of the fuel cell device 20, the control unit 33 receives a signal instructing the execution of the eighth process from the power conversion device 10 via the communication unit 31. Upon receiving the signal instructing the execution of the eighth process, the control unit 33 controls the reforming water supply unit 23-1 to increase the flow rate of reforming water supplied to the fuel cell module 22-1 during power generation by an eighth amount. Here, as described above, when the fuel cell module 22-1 has not yet started power generation, the fuel cell module 22-2 has also not yet started power generation. Therefore, the control unit 33 may control both the reforming water supply unit 23-1 and the reforming water supply unit 23-2 to increase the flow rate of the reforming water supplied to each of the fuel cell modules 22-1 and 22-2 by an eighth amount.

[0072] The ninth process is a process for delaying the timing at which the fuel cell module 22-1 starts generating power before the start of power generation. The extent to which the timing at which the power generation start is delayed may be set depending on the structure of the fuel cell module 22-1. To execute the ninth process, the control unit 13 transmits a signal instructing the execution of the ninth process to the fuel cell device 20 including the fuel cell module 22-1 before the start of power generation via the communication unit 11. In the control device 30 of the fuel cell device 20, the control unit 33 receives a signal instructing the execution of the ninth process from the power conversion device 10 via the communication unit 31. Upon receiving the signal instructing the execution of the ninth process, the control unit 33 controls the fuel cell module 22-1 to delay the timing at which the power generation start is initiated. The control unit 13 may also delay the timing at which the relay 15 between the fuel cell module 22-1 and the power conversion unit 14 is turned on. Delaying the timing at which the fuel cell module 22-1 starts generating power allows the central temperature of the fuel cell module 22-1 and the temperature of the cell stack 22S to increase before the fuel cell module 22-1 starts generating power. By raising these temperatures, the electromotive force of fuel cell module 22-1 can be lowered. By lowering the electromotive force of fuel cell module 22-1 before the start of power generation, the open circuit voltage value of fuel cell module 22-1 before the start of power generation can be lowered. Here, as described above, when fuel cell module 22-1 has not yet started power generation, it is highly likely that fuel cell module 22-2 has not yet started power generation either. Therefore, the control unit 13 may delay the power generation start timing of each of fuel cell module 22-1 and fuel cell module 22-2.

[0073] Figures 2 and 3 are flowcharts showing an example of the operation of the power conversion device 10 shown in Figure 1. The operation shown in Figures 2 and 3 corresponds to the operation at the time of startup of the fuel cell system 1. When the fuel cell system 1 starts startup, the control unit 13 starts the process of step S1 shown in Figure 2.

[0074] The control unit 13 acquires the closed circuit voltage value of at least one fuel cell module 22-1 that is generating electricity among the plurality of fuel cell modules 22-1 (step S1). As described above, the control unit 13 may acquire the electromotive force of the fuel cell module 22-1 before the start of power generation as the open circuit voltage value. The control unit 13 may acquire any data used to calculate the closed circuit voltage value from the memory unit 12, or may receive the data via the communication unit 11 from the control device 30 of the fuel cell device 20 that includes the fuel cell module 22-1 that is generating electricity.

[0075] The control unit 13 obtains the open circuit voltage value of at least one of the fuel cell modules 22-1 before the start of power generation (step S2). As described above, the control unit 13 may obtain the closed circuit voltage value of the fuel cell module 22-1 during power generation by calculating it using equation (1). The control unit 13 may obtain any data used to calculate the open circuit voltage value from the storage unit 12, or may receive it via the communication unit 11 from the control device 30 of the fuel cell device 20 including the fuel cell module 22-1 before the start of power generation.

[0076] The control unit 13 calculates the voltage difference between the lowest closed circuit voltage value of the fuel cell module 22-1 and the open circuit voltage value of the fuel cell module 22-1 before the start of power generation (step S3).

[0077] The control unit 13 determines whether the potential difference calculated in the process of step S3 exceeds the voltage threshold (step S4). If the potential difference is less than the voltage threshold (step S4: NO), the control unit 13 proceeds to the process of step S5. If the control unit 13 determines that the potential difference exceeds the voltage threshold (step S4: YES), the control unit 13 proceeds to the process of step S6.

[0078] In the process of step S5, the control unit 13 determines whether all of the plurality of fuel cell modules 22-1 electrically connected in parallel to the power conversion device 10 have started power generation. If the control unit 13 determines that all of the plurality of fuel cell modules 22-1 have started power generation (step S5: YES), the control unit 13 ends the flow shown in Fig. 2. After ending the flow shown in Fig. 2, the fuel cell system 1 continues power generation. If the control unit 13 does not determine that all of the plurality of fuel cell modules 22-1 have started power generation (step S5: NO), the control unit 13 returns to the process of step S1.

[0079] In the process of step S6, the control unit 13 controls the combined current value. As described above, the control unit 13 may control the combined current value so that the greater the potential difference calculated in the process of step S3, the smaller the combined current value. Alternatively, the control unit 13 may control the combined current value according to the temperature of the fuel cell module 22-1 with the lowest closed circuit voltage value. In this case, the control unit 13 may control the combined current value so that the smaller the temperature of the fuel cell module 22-1 with the lowest closed circuit voltage value, the smaller the combined current value.

[0080] 3, the control unit 13 obtains the temperature of the fuel cell module 22-1 having the lowest closed circuit voltage value. The control unit 13 may receive, via the communication unit 11, information on the temperature of the fuel cell module 22-1 from the control device 30 of the fuel cell device 20 that includes the fuel cell module 22-1.

[0081] In the process of step S8, the control unit 13 determines whether the temperature of the fuel cell module 22-1 with the lowest closed circuit voltage value acquired in step S7 is equal to or higher than the temperature threshold value. If the control unit 13 determines that the temperature of the fuel cell module 22-1 with the lowest closed circuit voltage value is equal to or higher than the temperature threshold value (step S8: YES), the control unit 13 proceeds to the process of step S9. If the control unit 13 determines that the temperature of the fuel cell module 22-1 with the lowest closed circuit voltage value is lower than the temperature threshold value (step S8: NO), the control unit 13 proceeds to the process of step S10.

[0082] In the process of step S9, the control unit 13 executes a process to increase the electromotive force of the fuel cell module 22-1 that is generating electricity. As described above, the control unit 13 may control the execution of at least one of the first process, the second process, and the third process as the process to increase the electromotive force of the fuel cell module 22-1 that is generating electricity. If multiple fuel cell modules 22-1 are generating electricity, the control unit 13 may execute the process of step S9 for all or some of the multiple fuel cell modules 22-1 that are generating electricity.

[0083] In the process of step S10, the control unit 13 executes a process to reduce the resistance value of the fuel cell module 22-1 that is generating power. As described above, the control unit 13 may control the execution of at least one of the fourth process, the fifth process, and the sixth process as the process to reduce the resistance value of the fuel cell module 22-1 that is generating power. If multiple fuel cell modules 22-1 are generating power, the control unit 13 may execute the process of step S10 for all or some of the multiple fuel cell modules 22-1 that are generating power.

[0084] In the process of step S11, the control unit 13 executes a process to lower the open circuit voltage value of the fuel cell module 22-1 before the start of power generation. As described above, the control unit 13 may control so that at least one of the seventh process, the eighth process, and the ninth process is executed as the process to lower the open circuit voltage value of the fuel cell module 22-1 before the start of power generation. When multiple fuel cell modules 22-1 have not yet started power generation, the control unit 13 may execute the process of step S11 for all or some of the multiple fuel cell modules 22-1 before the start of power generation.

[0085] Here, if the control unit 13 determines that the potential difference exceeds the voltage threshold (step S4: YES), it may execute the process of step S11 without executing the processes of steps S6 to S10. After executing the process of step S11, the control unit 13 may execute the processes of steps S6 to S10, or may not execute the processes of steps S6 to S10. Furthermore, before executing the process of step S11, the control unit 13 may re-calculate the voltage difference between the lowest closed circuit voltage value of the fuel cell module 22-1 and the open circuit voltage value of the fuel cell module 22-1 before the start of power generation. In this case, the control unit 13 may execute the process of step S11 if the calculated voltage difference exceeds the voltage threshold.

[0086] In the processing of steps S1 to S11, the control unit 13 may cause the control unit 30 to transmit information on the temperature, generated current value, and voltage value of the fuel cell module 22 to the power conversion device 10 by sending a control signal to the control device 30 via the communication unit 11 at any timing.

[0087] As described above, in the fuel cell system 1 according to this embodiment, multiple fuel cell modules 22-1 are electrically connected in parallel to the power conversion device 10. The power conversion device 10 controls a combined current value based on the voltage difference between the closed-circuit voltage value of at least one of the multiple fuel cell modules 22-1 during power generation and the open-circuit voltage value of at least one of the fuel cell modules 22-1 before power generation begins. Controlling the combined current value reduces the inrush current of the fuel cell module 22-1 that has started power generation. As described above, if a large inrush current occurs in the fuel cell module 22-1, the cell stack 22S may be damaged due to oxidation of the cell stack 22S caused by gas starvation or thermal shock due to rapid Joule heat generation. In this embodiment, the reduced inrush current reduces the likelihood of damage to the cell stack 22S. Therefore, this embodiment reduces the degree of degradation of the fuel cell module.

[0088] 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.

[0089] 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.

[0090] In one embodiment, (1) a fuel cell system includes a power conversion device and a plurality of fuel cells electrically connected in parallel to the power conversion device, and the power conversion device controls the combined current value drawn from the plurality of fuel cells to the power conversion device based on the voltage difference between the closed circuit voltage value of at least one of the plurality of fuel cells during power generation and the open circuit voltage value of at least one of the fuel cells before power generation begins.

[0091] (2) In the fuel cell system described in (1) above, the power conversion device may control the composite current value when the voltage difference between the lowest closed circuit voltage value among the fuel cells generating power and the open circuit voltage value of the at least one fuel cell before power generation starts exceeds a voltage threshold.

[0092] (3) In the fuel cell system described in (2) above, the power conversion device may control the combined current value in accordance with the temperature of the fuel cell having the lowest closed circuit voltage value.

[0093] (4) In the fuel cell system described in any one of (1) to (3) above, the power conversion device may execute a process to increase the electromotive force of the fuel cell currently generating electricity when the temperature of the fuel cell currently generating electricity that has the lowest closed circuit voltage value among the fuel cells currently generating electricity is equal to or higher than a temperature threshold value.

[0094] (5) In the fuel cell system described in (4) above, the power conversion device controls to execute at least one of a first process, a second process, and a third process as a process for increasing the electromotive force of the fuel cell during power generation, the first process being a process for increasing the flow rate of fuel gas supplied to the fuel cell during power generation by a first amount, the second process being a process for increasing the flow rate of oxygen-containing gas supplied to the fuel cell during power generation by a second amount, and the third process being a process for decreasing the flow rate of reforming water supplied to the fuel cell during power generation by a third amount.

[0095] (6) In the fuel cell system described in any one of (1) to (5) above, the power conversion device may execute a process to reduce the resistance value of the fuel cell currently generating electricity when the temperature of the fuel cell currently generating electricity that exhibits the lowest closed circuit voltage value among the fuel cells currently generating electricity is below the temperature threshold value.

[0096] (7) In the fuel cell system described in (6) above, the power conversion device controls at least one of a fourth process, a fifth process, and a sixth process to be performed as a process for reducing the resistance value of the fuel cell during power generation, the fourth process being a process for increasing the flow rate of fuel gas supplied to the fuel cell during power generation by a fourth amount, the fifth process being a process for decreasing the flow rate of oxygen-containing gas supplied to the fuel cell during power generation by a fifth amount, and the sixth process being a process for decreasing the flow rate of reforming water supplied to the fuel cell during power generation by a sixth amount.

[0097] (8) In the fuel cell system described in (2) above or any one of (3) to (7) above that is dependent on (2) above, the power conversion device may execute a process to lower the open circuit voltage value of the fuel cell before the start of power generation when the voltage difference between the lowest closed circuit voltage value and the open circuit voltage value of the at least one fuel cell before the start of power generation exceeds a voltage threshold.

[0098] (9) In the fuel cell system described in (8) above, the power conversion device controls to execute at least one of a seventh process, an eighth process, and a ninth process as a process for lowering the open circuit voltage value of the fuel cell before the start of power generation, the seventh process is a process for lowering the flow rate of fuel gas supplied to the fuel cell before the start of power generation by a seventh amount, the eighth process is a process for increasing the flow rate of reforming water supplied to the fuel cell before the start of power generation by an eighth amount, and the ninth process may be a process for delaying the power generation start timing at which power generation of the fuel cell begins before the start of power generation.

[0099] 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.

[0100] REFERENCE SIGNS LIST 1 fuel cell system 10 power conversion device 11 communication unit 12 memory unit 13 control unit 14 power conversion unit 15 relay 2 load group 20, 20-1, 20-2, 20-3 fuel cell device 21 power generation unit 22, 22-1, 22-2 fuel cell 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

Claims

1. A fuel cell system comprising: a power conversion device; and a plurality of fuel cells electrically connected in parallel to the power conversion device, wherein the power conversion device controls the combined current value drawn from the plurality of fuel cells to the power conversion device based on the voltage difference between the closed circuit voltage value of at least one of the plurality of fuel cells during power generation and the open circuit voltage value of at least one of the fuel cells before power generation begins.

2. The fuel cell system according to claim 1, wherein the power conversion device controls the combined current value when a voltage difference between the lowest closed circuit voltage value among the fuel cells generating power and the open circuit voltage value of the at least one fuel cell before power generation starts exceeds a voltage threshold.

3. The fuel cell system according to claim 2, wherein the power conversion device controls the combined current value in accordance with the temperature of the fuel cell having the lowest closed circuit voltage value.

4. A fuel cell system as described in any one of claims 1 to 3, wherein the power conversion device executes a process to increase the electromotive force of the fuel cell during power generation when the temperature of the fuel cell during power generation that exhibits the lowest closed circuit voltage value among the fuel cells during power generation is equal to or higher than a temperature threshold value.

5. The fuel cell system of claim 4, wherein the power conversion device controls to execute at least one of a first process, a second process, and a third process as a process for increasing the electromotive force of the fuel cell during power generation, the first process being a process for increasing the flow rate of fuel gas supplied to the fuel cell during power generation by a first amount, the second process being a process for increasing the flow rate of oxygen-containing gas supplied to the fuel cell during power generation by a second amount, and the third process being a process for decreasing the flow rate of reforming water supplied to the fuel cell during power generation by a third amount.

6. A fuel cell system as described in any one of claims 1 to 5, wherein the power conversion device executes a process to reduce the resistance value of the fuel cell currently generating electricity when the temperature of the fuel cell currently generating electricity that exhibits the lowest closed circuit voltage value among the fuel cells currently generating electricity is below the temperature threshold value.

7. The fuel cell system of claim 6, wherein the power conversion device controls to execute at least one of a fourth process, a fifth process, and a sixth process as a process for reducing the resistance value of the fuel cell during power generation, the fourth process being a process for increasing the flow rate of fuel gas supplied to the fuel cell during power generation by a fourth amount, the fifth process being a process for decreasing the flow rate of oxygen-containing gas supplied to the fuel cell during power generation by a fifth amount, and the sixth process being a process for decreasing the flow rate of reforming water supplied to the fuel cell during power generation by a sixth amount.

8. A fuel cell system as described in claim 2 or any one of claims 3 to 7 dependent on claim 2, wherein the power conversion device executes a process to lower the open circuit voltage value of the fuel cell before the start of power generation when the voltage difference between the lowest closed circuit voltage value and the open circuit voltage value of the at least one fuel cell before the start of power generation exceeds a voltage threshold.

9. The fuel cell system described in claim 8, wherein the power conversion device controls to execute at least one of a seventh process, an eighth process, and a ninth process as a process for lowering the open circuit voltage value of the fuel cell before the start of power generation, the seventh process is a process for lowering the flow rate of fuel gas supplied to the fuel cell before the start of power generation by a seventh amount, the eighth process is a process for increasing the flow rate of reforming water supplied to the fuel cell before the start of power generation by an eighth amount, and the ninth process is a process for delaying the power generation start timing at which power generation of the fuel cell begins before the start of power generation.

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