Control method for fuel cell system, control program for fuel cell system, fuel cell system, and monogeneration device

Abstract

To provide a technology that can keep a battery in a good state and can make a fuel cell generate electricity efficiently. The fuel cell system includes a fuel cell, an inverter that converts DC power supplied from the fuel cell into AC power and outputs it, and a battery that assists the power supply from the fuel cell to the inverter. The control method for the fuel cell system includes executing a target power determination process that determines a target power for the fuel cell based on the power output by the inverter and the charging rate of the battery.

Description

[Technical Field]

[0001] The present invention relates to a control method for a fuel cell system, a control program for a fuel cell system, a fuel cell system, and a monogeneration device. [Background technology]

[0002] A cogeneration system equipped with a gas engine is known as a conventional technology (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6321484 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, from the perspective of carbon neutrality, there has been a demand for power generation devices (e.g., monogeneration devices) that use fuel cell systems in which DC power generated by a fuel cell is converted to AC power by an inverter and output to the outside. However, even when a fuel cell system is used, if the power generation by the fuel cell is inefficient, fuel gas (e.g., hydrogen gas) used for power generation will be wasted, and as a result, there is a risk that it will be difficult to achieve carbon neutrality.

[0005] Furthermore, a fuel cell system may be provided with a battery to assist the power supply from the fuel cell to the inverter. In this case, it is desirable to keep the battery in a good condition (for example, at a constant charging rate) in order for the battery to perform the above-mentioned auxiliary function reliably.

[0006] The present invention has been made to solve the above problems, and its purpose is to provide a technology that can keep the battery in good condition and enable the fuel cell to generate electricity efficiently. [Means for solving the problem]

[0007] A control method for a fuel cell system according to one aspect of the present invention is a control method for a fuel cell system comprising a fuel cell, an inverter that converts DC power supplied from the fuel cell into AC power and outputs it, and a battery that assists in the supply of power from the fuel cell to the inverter, and includes executing a target power determination process that determines a target power for the fuel cell based on the power output by the inverter and the charging rate of the battery.

[0008] A control program for a fuel cell system according to another aspect of the present invention causes at least one arithmetic device to execute the above control method.

[0009] A fuel cell system according to another aspect of the present invention comprises a fuel cell, an inverter that converts DC power supplied from the fuel cell into AC power and outputs it, and a battery that assists in the supply of power from the fuel cell to the inverter, and further comprises a target power calculation unit that calculates a target power for the fuel cell based on the power output by the inverter and the charging rate of the battery.

[0010] A monogeneration system according to another aspect of the present invention includes the above fuel cell system. [Effects of the Invention]

[0011] According to the above configuration, the battery can be kept in good condition, and the fuel cell can generate electricity efficiently. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a block diagram showing a schematic connection configuration of a monogeneration device according to an embodiment of the present invention; [Figure 2] FIG. 2 is a block diagram showing a schematic configuration of a fuel cell system of the monogeneration device. [Figure 3] 4 is a flowchart showing a flow up to the start of a target power determination process in the fuel cell system. [Figure 4] 10 is a flowchart showing the flow of the target power determination process. [Figure 5] 10 is a flowchart showing a flow when the first predetermined value increases in the target power determination process. [Figure 6] 10 is a flowchart showing a flow when the second predetermined value increases in the target power determination process. [Figure 7] 5 is an explanatory diagram illustrating a method for protecting a battery included in the fuel cell system when the battery overheats. FIG. [Figure 8] 5 is an explanatory diagram illustrating a method for protecting the battery when the battery is in an overcharged state. FIG. [Figure 9] 4 is an explanatory diagram illustrating a method for protecting the battery when the battery is in an over-discharge state. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0013] The following describes an embodiment of the present invention with reference to the drawings.

[0014] [1. Connection configuration of monogeneration device] 1 is a block diagram showing a schematic connection configuration of a monogeneration apparatus 1 according to one embodiment of the present invention. The monogeneration apparatus 1 includes a fuel cell system 2 and is interconnected with a commercial power grid 101. Although only one monogeneration apparatus 1 is shown in FIG. 1 as an example, a configuration in which multiple monogeneration apparatuses 1 are interconnected with the commercial power grid 101 is also possible.

[0015] The fuel cell system 2 generates power using a fuel gas and an oxidant gas supplied from outside the monogeneration device 1. In this embodiment, an example will be described in which hydrogen gas is used as the fuel gas and air is used as the oxidant gas. However, the fuel gas is not limited to hydrogen gas and may be, for example, a gas containing methane as a main component. Furthermore, the oxidant gas is not limited to air and may be any gas containing oxygen. Therefore, the monogeneration device 1 generates power. More specifically, the monogeneration device 1 simply has a power generation function. In other words, for example, a waste heat recovery function for recovering waste heat generated during power generation is excluded from the monogeneration device 1.

[0016] The commercial power system 101 includes a commercial power source 101a and supplies commercial power generated by the commercial power source 101a. The load 102 is connected to the commercial power system 101. That is, the load 102 is electrically connected to the fuel cell system 2. The load 102 includes, for example, household electrical appliances, industrial (industrial, facility) electrical appliances, etc. Specifically, motors, pumps, etc. provided in such appliances consume power. The power demand (power consumption) of the load 102 is met by the power generated by the monogeneration device 1 (fuel cell system 2) and the commercial power supplied from the commercial power system 101. Note that the configuration related to the power supply to the load 102 is not limited to the above. For example, the load 102 may be directly connected to the monogeneration device 1 without being connected to the commercial power system 101. In this case, the power demand of the load 102 is met by the power generated by the monogeneration device 1. In this embodiment, even if the power demand of the load 102 fluctuates, the fluctuations are assumed to be gradual. The configuration of the fuel cell system 2 will now be described.

[0017] 2. Configuration of fuel cell system 2 is a block diagram that schematically shows the configuration of the fuel cell system 2. The fuel cell system 2 includes a fuel cell module 21, a battery 22, an inverter 23, and a control device 24.

[0018] In this embodiment, one fuel cell module 21, one inverter 23, and one control device 24 are provided, and multiple batteries 22 are provided. However, FIG. 2 illustrates only one battery 22 as an example. The numbers of fuel cell modules 21, batteries 22, inverters 23, and control devices 24 are not limited to those described above. For example, there may be multiple fuel cell modules 21, multiple inverters 23, and multiple control devices 24, or there may be only one battery 22. The fuel cell module 21, battery 22, inverter 23, and control device 24 are each disposed inside the monogeneration system 1.

[0019] The fuel cell module 21 has a fuel cell 21a, a boost converter 21b, a compressor 21c, and a fuel cell control unit 21d. That is, the fuel cell system 2 includes the fuel cell 21a, the boost converter 21b, the compressor 21c, and the fuel cell control unit 21d.

[0020] The fuel cell 21a (also called a fuel cell stack) is composed of a plurality of stacked cells. Each cell includes a solid polymer electrolyte membrane, an anode, a cathode, and a pair of separators. The anode and cathode sandwich the solid polymer electrolyte membrane. The anode is a negative electrode (fuel electrode) and includes an anode catalyst layer and a gas diffusion layer. The cathode is a positive electrode (air electrode) and includes a cathode catalyst layer and a diffusion layer. The anode, solid polymer electrolyte membrane, and cathode form a membrane electrode assembly (MEA). The pair of separators sandwich the membrane electrode assembly. Each separator has a plurality of grooves. Each groove in one separator forms a flow path for hydrogen gas. Each groove in the other separator forms a flow path for air.

[0021] At the anode, hydrogen is decomposed into hydrogen ions and electrons by a catalyst. The hydrogen ions pass through the solid polymer electrolyte membrane and move to the cathode. Meanwhile, the electrons pass through an external circuit and move to the cathode. This generates an electric current (electricity is generated). At the cathode, oxygen contained in the air combines with the electrons that have flowed through the external circuit and the hydrogen ions that have passed through the solid polymer electrolyte membrane to produce water. The produced water is contained in the exhaust gas and discharged outside the monogeneration device 1.

[0022] The electric power generated by the fuel cell 21a is boosted by the boost converter 21b and supplied to the inverter 23. Note that the electric power generated by the fuel cell 21a and boosted by the boost converter 21b may be supplied to the battery 22 in addition to the inverter 23.

[0023] The compressor 21c is provided to take in air to be supplied to the fuel cell 21a from outside the monogeneration device 1. The air taken in from outside the monogeneration device 1 by the compressor 21c flows into the fuel cell 21a via multiple filters (none of which are shown) provided inside the monogeneration device 1.

[0024] The fuel cell control unit 21d controls each part of the fuel cell module 21. For example, the fuel cell control unit 21d controls the power generation of the fuel cell 21a, the drive of the compressor 21c, etc. The fuel cell control unit 21d is connected to be able to communicate with the control device 24. Communication between the fuel cell control unit 21d and the control device 24 is performed by, for example, CAN communication, but the communication method is not limited to CAN communication.

[0025] The battery 22 is formed of, for example, a lithium ion battery, and stores the power supplied to the inverter 23. The battery 22 may be formed by unitizing a plurality of battery cells, or may be formed by a single battery cell. As described above, the battery 22 may be supplied with power generated by the fuel cell 21a. The battery 22 is charged by the power supplied from the fuel cell 21a to the battery 22.

[0026] The battery 22 is controlled by a battery control unit 22a. The battery control unit 22a is also called a BMU (Battery Management Unit), and controls, for example, the input and output of the battery 22. The battery control unit 22a also calculates a state of charge (SOC) of the battery 22 (described later) based on information (e.g., the voltage, current, temperature, etc. of the battery 22) acquired via various sensors (not shown) provided in the battery 22 (see FIGS. 7, 8, and 9). The state of charge S of the battery 22 means the ratio of the remaining charge capacity (at that time) to the charge capacity when fully charged.

[0027] The battery control unit 22a is communicably connected to the control device 24. Communication between the battery control unit 22a and the control device 24 is performed, for example, by CAN communication, but the communication method is not limited to CAN communication. The battery control unit 22a transmits, for example, information about the battery 22 (including the charging rate calculated by the battery control unit 22a) to the control device 24 via CAN communication.

[0028] The inverter 23 is configured by mounting various electrical components (e.g., diodes, capacitors, power transistors, etc.) on a substrate (none of which are shown). The inverter 23 converts DC power supplied from the fuel cell 21a into AC power and outputs it. More specifically, the inverter 23 converts DC voltage power supplied from the fuel cell 21a, or from the fuel cell 21a and the battery 22, into AC voltage power and supplies it to the load 102 (see FIG. 1). Specifically, the inverter 23 supplies AC power to the load 102 in accordance with the power demand of the load 102. For example, when the power demand of the load 102 increases, the inverter 23 increases the AC power supplied to the load 102, and when the power demand of the load 102 decreases, the inverter 23 reduces the AC power supplied to the load 102.

[0029] In the following, the voltage supplied to the inverter 23 may be referred to as the link voltage. The voltage (of power) generated by the fuel cell 21a and boosted by the boost converter 21b follows the link voltage. Therefore, the link voltage is the same as the voltage (of power) output from the battery 22.

[0030] The inverter 23 is connected to the control device 24 so as to be able to communicate with it. Communication between the inverter 23 and the control device 24 is performed, for example, by CAN communication, but the communication method is not limited to CAN communication. The inverter 23 transmits information about the inverter 23, including, for example, an actual power AP (see FIG. 3 ), which will be described later, to the control device 24 via the CAN communication.

[0031] The control device 24 controls each part of the fuel cell system 2. In addition to the fuel cell system 2, the control device 24 may also control devices other than the fuel cell system 2 that the monogeneration device 1 includes.

[0032] The control device 24 is, for example, a computer device including an arithmetic device 24a, a storage unit 24b, and an input / output unit (not shown). The arithmetic device 24a is, for example, a processor or a microprocessor. In FIG. 2, as an example, one arithmetic device 24a is illustrated in the control device 24, but the number of arithmetic devices 24a may be two or three or more.

[0033] The storage unit 24b is a main storage device such as a read-only memory (ROM) or a random access memory (RAM). The storage unit 24b may further include an auxiliary storage device such as a hard disk drive (HDD) or a solid state drive (SSD). Various programs, data, and the like are stored in the storage unit 24b. The various programs include a control program 24b1 related to power generation instructions for the fuel cell 21a. For example, the arithmetic unit 24a reads the control program 24b1 from the storage unit 24b and executes arithmetic processing in accordance with the control program 24b1. The programs stored in the storage unit 24b may be provided, for example, by a computer-readable nonvolatile recording medium. As another example, the programs may be provided from a program providing server via a communication line such as the Internet.

[0034] The above-described hardware and software work together to cause the control device 24 to operate as a target power determination unit 24c and a target charging rate update unit 24d. That is, the fuel cell system 2 includes the target power determination unit 24c and the target charging rate update unit 24d. The control device 24 may be configured as a single piece of hardware, or may be configured as multiple pieces of hardware that can communicate with each other.

[0035] The target power determination unit 24c and the target charging rate update unit 24d included in the control device 24 may be realized by causing the arithmetic device 24a to execute arithmetic processing according to a program, i.e., by software, as described above, but may also be realized by other methods. At least one of the target power determination unit 24c and the target charging rate update unit 24d may be realized using, for example, an application-specific integrated circuit (ASIC) or a field-programmable gate array (FPGA). That is, at least one of the target power determination unit 24c and the target charging rate update unit 24d may be realized by hardware using a dedicated IC or the like. At least one of the target power determination unit 24c and the target charging rate update unit 24d may also be realized by a combination of software and hardware. The target power determination unit 24c and the target charging rate update unit 24d are conceptual structures. Therefore, the functions performed by one component may be distributed among multiple components, or the functions of multiple components may be integrated into one component.

[0036] The target power determination unit 24c executes a target power determination process, and the target charging rate update unit 24d executes a target charging rate update process. The target charging rate update process will be described later. The target power determination process will be described below.

[0037] [3. Method for determining target power of fuel cell] 3 is a flowchart showing the flow up to the start of the target power determination process. Note that the order of the process of step S1 and the process of step S2 may be reversed.

[0038] In step S1, the target power determination unit 24c (see FIG. 2) acquires the actual power AP, which is the power that the inverter 23 is currently outputting. In this embodiment, the actual power AP of the inverter 23 is acquired by a power detector (not shown) provided inside the monogeneration device 1 detecting the actual power AP of the inverter 23 and outputting the detection result to the control device 24. Note that the power detector may be provided outside the monogeneration device 1, or may be provided both inside and outside the monogeneration device 1. Once the actual power AP of the inverter 23 has been acquired, the process proceeds to the next step S2.

[0039] In step S2, the target power determination unit 24c acquires the charging rate S of the battery 22 at that time. In this embodiment, the charging rate S of the battery 22 is acquired by transmitting information about the battery 22, including the charging rate S of the battery 22, from the battery control unit 22a to the control device 24. Once the charging rate S of the battery 22 is acquired, the process proceeds to the next step S3.

[0040] In step S3, the target power determination unit 24c executes the target power determination process. As described above, the target power determination unit 24c is realized by having the arithmetic device 24a of the control device 24 execute the arithmetic process in accordance with the control program 24b1. Therefore, the control method for the fuel cell system 2 related to the target power determination process executed by the target power determination unit 24c (including the processes before and after the target power determination process) is also realized by having the arithmetic device 24a execute the arithmetic process in accordance with the control program 24b1. Note that in this embodiment, as described above, one arithmetic device 24a executes the above arithmetic process. However, if there are two or more arithmetic devices 24a, the arithmetic process may be executed by two or more arithmetic devices 24a. In other words, the control program 24b1 for the fuel cell system 2 in this embodiment is a program that causes at least one arithmetic device 24a to execute the control method for the fuel cell system 2. The target power determination process will be described below. FIG. 4 is a flowchart showing the flow of the target power determination process.

[0041] In step S31, the target power determination unit 24c corrects the actual power AP of the inverter 23 by the conversion efficiency E of the inverter 23 in order to calculate the target power TP of the fuel cell 21a. As a result, a value obtained by correcting the actual power AP of the inverter 23 by the conversion efficiency E of the inverter 23 is calculated. In other words, the target power determination process includes calculating a value obtained by correcting the power output by the inverter 23 (the actual power AP of the inverter 23 in this embodiment) by the conversion efficiency E of the inverter 23 as the target power TP of the fuel cell 21a. Note that in this embodiment, the "value obtained by correcting the actual power AP of the inverter 23 by the conversion efficiency E of the inverter 23" is also referred to as the "corrected actual power AP of the inverter 23" or "corrected actual power AP."

[0042] In this embodiment, the above correction is achieved by the target power determination unit 24c dividing the actual power AP of the inverter 23 (acquired in step S1) by the conversion efficiency E of the inverter 23. The conversion efficiency E of the inverter 23 is set in advance and stored in the storage unit 24b (see FIG. 2). Note that the conversion efficiency E of the inverter 23 may be configured to change depending on the state of the inverter 23 (for example, the temperature of the inverter 23, etc.). Once the actual power AP of the inverter 23 has been corrected, the process proceeds to the next step S32.

[0043] In step S32, the target power determination unit 24c determines whether the charging rate S of the battery 22 (acquired in step S2) is the same as the target charging rate TS of the battery 22. In this embodiment, the target charging rate TS of the battery 22 is set in advance and stored in the storage unit 24b. If the charging rate S of the battery 22 is the same as the target charging rate TS of the battery 22 (Yes in step S32), the process proceeds to step S33. If the charging rate S of the battery 22 is not the same as the target charging rate TS of the battery 22 (No in step S32), the process proceeds to step S34.

[0044] In step S33, target power determination unit 24c determines the corrected actual power AP of inverter 23 (calculated in step S31) as the target power TP of fuel cell 21a. Target power determination unit 24c instructs fuel cell control unit 21d (see FIG. 2) to generate power at the determined target power TP of fuel cell 21a (corrected actual power AP of inverter 23). Based on this instruction, fuel cell control unit 21d controls fuel cell 21a so that the power output from fuel cell 21a becomes the target power TP (corrected actual power AP of inverter 23).

[0045] In this case, all of the power output from the fuel cell 21a is supplied to the inverter 23. More specifically, the power to be supplied to the inverter 23 so that the inverter 23 outputs the actual power AP to cover the power demand of the load 102 is supplied by the power generated by the fuel cell 21a. At this time, both charging and discharging of the battery 22 are stopped.

[0046] In step S34, target power determination unit 24c determines whether or not the charging rate S of battery 22 is greater than the target charging rate TS of battery 22. If the charging rate S of battery 22 is greater than the target charging rate TS of battery 22 (Yes in step S34), the process proceeds to step S35. If the charging rate S of battery 22 is not greater than the target charging rate TS of battery 22, that is, if the charging rate S of battery 22 is less than the target charging rate TS of battery 22 (No in step S34), the process proceeds to step S37.

[0047] In step S35, the target power determination unit 24c subtracts a first predetermined value X1 from the corrected actual power AP of the inverter 23. As described above, the target power determination unit 24c calculates the corrected actual power AP of the inverter 23 (a value obtained by correcting the actual power AP of the inverter 23 using the conversion efficiency E of the inverter 23) as the target power TP of the fuel cell 21a. Therefore, the target power determination process includes subtracting the first predetermined value X1 from the target power TP of the fuel cell 21a (in this embodiment, the corrected actual power AP of the inverter 23) when the charging rate S of the battery 22 is greater than the target charging rate TS of the battery 22. In this embodiment, the first predetermined value X1 is set in advance and stored in the storage unit 24b. The first predetermined value X1 is set to, for example, 500 W. However, the setting of the first predetermined value X1 is not limited to 500 W and may be, for example, 100 W or 1000 W. After the subtraction is performed, the process proceeds to the next step S36.

[0048] In step S36, the target power determiner 24c determines the corrected actual power AP of the inverter 23, from which the first predetermined value X1 has been subtracted, as the target power TP of the fuel cell 21a. In this embodiment, the "corrected actual power AP of the inverter 23, from which the first predetermined value X1 has been subtracted" is also referred to as the "subtracted actual power AP of the inverter 23" or "subtracted actual power AP." The target power determiner 24c instructs the fuel cell control unit 21d to generate power at the determined target power TP of the fuel cell 21a (subtracted actual power AP of the inverter 23). Based on this instruction, the fuel cell control unit 21d controls the fuel cell 21a so that the power output from the fuel cell 21a becomes the target power TP (subtracted actual power AP of the inverter 23).

[0049] In this case, all of the power output from the fuel cell 21a is supplied to the inverter 23. However, the power generated by the fuel cell 21a is smaller than the power that should be supplied to the inverter 23 so that the inverter 23 outputs the actual power AP to cover the power demand of the load 102. Therefore, in order to cover the power that should be supplied to the inverter 23, in addition to the power generation by the fuel cell 21a, the battery 22 is discharged. In other words, in this case, the power that should be supplied to the inverter 23 is covered by the power generated by the fuel cell 21a and the power discharged by the battery 22.

[0050] In step S37, the target power determiner 24c adds a second predetermined value X2 to the corrected actual power AP of the inverter 23. That is, the target power determination process includes adding the second predetermined value X2 to the target power TP of the fuel cell 21a (in this embodiment, the corrected actual power AP of the inverter 23) when the charging rate S of the battery 22 is lower than the target charging rate TS of the battery 22. As described above, the target power determination process also includes subtracting the first predetermined value X1 from the target power TP of the fuel cell 21a when the charging rate S of the battery 22 is higher than the target charging rate TS of the battery 22. Therefore, in the target power determination process, the target power TP of the fuel cell 21a is increased or decreased depending on the result of comparing the charging rate S of the battery 22 with the target charging rate TS of the battery 22. In other words, the target power determination process includes adjusting the target power TP of the fuel cell 21a (in this embodiment, the corrected actual power AP of the inverter 23) according to the result of comparing the charging rate S of the battery 22 with the target charging rate TS of the battery 22.

[0051] In this embodiment, the second predetermined value X2 is set in advance and stored in the storage unit 24b. The second predetermined value X2 is set to, for example, 500 W. That is, in this embodiment, the setting of the second predetermined value X2 is the same as the setting of the first predetermined value X1. However, the setting of the second predetermined value X2 is not limited to 500 W, and may be, for example, 100 W or 1000 W. Furthermore, the setting of the second predetermined value X2 may be different from the setting of the first predetermined value X1. After the above addition is performed, the process proceeds to the next step S38.

[0052] In step S38, the target power determiner 24c determines the corrected actual power AP of the inverter 23 to which the second predetermined value X2 has been added as the target power TP of the fuel cell 21a. In this embodiment, the "corrected actual power AP of the inverter 23 to which the second predetermined value X2 has been added" is also referred to as the "actual power AP of the inverter 23 after addition" or "actual power AP after addition." The target power determiner 24c instructs the fuel cell control unit 21d to generate power at the determined target power TP of the fuel cell 21a (the actual power AP of the inverter 23 after addition). Based on this instruction, the fuel cell control unit 21d controls the fuel cell 21a so that the power output from the fuel cell 21a becomes the target power TP (the actual power AP of the inverter 23 after addition).

[0053] In this case, a portion of the power output from the fuel cell 21a is supplied to the inverter 23. More specifically, the power to be supplied to the inverter 23 so that the inverter 23 can output the actual power AP and cover the power demand of the load 102 is covered by a portion of the power generated by the fuel cell 21a. The remaining power output from the fuel cell 21a is supplied to the battery 22. This ensures a supply destination for the surplus power to be supplied to the inverter 23. Furthermore, the remaining power output from the fuel cell 21a is supplied to the battery 22, thereby charging the battery 22. In other words, by charging, the battery 22 functions as a supply destination for the surplus power to be supplied to the inverter 23. Furthermore, as described above, the battery 22 can make up for a shortage of power to be supplied to the inverter 23 by discharging. In other words, the battery 22 has a function of assisting the power supply from the fuel cell 21a to the inverter 23.

[0054] As described above, the target power TP of the fuel cell 21a is determined based on the actual power AP of the inverter 23 and the charging rate S of the battery 22 in the target power determination process executed by the target power determiner 24c. In other words, the control method for the fuel cell system 2 of this embodiment includes executing a target power determination process that determines the target power TP of the fuel cell 21a based on the power output by the inverter 23 (actual power AP in this embodiment) and the charging rate S of the battery 22. The fuel cell system 2 also includes a target power determiner 24c that determines the target power TP of the fuel cell 21a based on the power output by the inverter 23 (actual power AP in this embodiment) and the charging rate S of the battery 22.

[0055] According to the above configuration, for example, it is not necessary to set the rated power (also called rated output) as the target power TP of the fuel cell 21a. This makes it possible to avoid power generation at the rated power of the fuel cell 21a (full load operation). That is, the fuel cell 21a can be made to generate power (partial load operation) at a power other than the rated power, i.e., a power smaller than the rated power. The power generation efficiency of the fuel cell 21a is often higher when the fuel cell 21a generates power at a power smaller than the rated power (partial load operation) than when the fuel cell 21a generates power at the rated power (full load operation). Therefore, power can be generated more efficiently than when the fuel cell 21a generates power at the rated power.

[0056] Furthermore, for example, when the charging rate S of the battery 22 increases, the target power TP of the fuel cell 21a can be reduced. When the target power TP of the fuel cell 21a is reduced, the power output from the fuel cell 21a is reduced, and the power supplied from the fuel cell 21a to the battery 22 is reduced. Therefore, charging of the battery 22 is suppressed, and a further increase in the charging rate S of the battery 22 can be prevented. On the other hand, when the charging rate S of the battery 22 decreases, the target power TP of the fuel cell 21a can be increased. When the target power TP of the fuel cell 21a is increased, the power output from the fuel cell 21a is increased, and the power supplied from the fuel cell 21a to the battery 22 is increased. Therefore, charging of the battery 22 can be promoted, and a further decrease in the charging rate S of the battery 22 can be prevented. In other words, the charging rate S of the battery 22 can be maintained within a certain range, and the battery 22 can be maintained in a good state. As described above, the battery 22 can be maintained in a good state, and the fuel cell 21a can generate power efficiently.

[0057] In the inverter 23, power loss occurs when DC power is converted to AC power. For this reason, even if the fuel cell 21a is caused to generate power using the actual power AP of the inverter 23 as the target power TP of the fuel cell 21a, the power output from the inverter 23 will be smaller than the actual power AP. Therefore, in order to maintain the power output from the inverter 23 at the actual power AP, it is desirable to supply to the inverter 23 power that has been corrected by the conversion efficiency E of the inverter 23 (i.e., power that has been increased in advance to account for the loss). From this perspective, as in this embodiment, the target power determination process desirably includes calculating a value obtained by correcting the power output by the inverter 23 (in this embodiment, the actual power AP) by the conversion efficiency E of the inverter 23 as the target power TP of the fuel cell 21a.

[0058] It is desirable to maintain the charging rate S of the battery 22 within a certain range, and particularly to maintain the charging rate S of the battery 22 at the target charging rate TS of the battery 22. From this perspective, as in this embodiment, it is desirable that the target power determination process includes adjusting the target power TP of the fuel cell 21a in accordance with the result of comparing the charging rate S of the battery 22 with the target charging rate TS of the battery 22.

[0059] When the corrected actual power AP of the inverter 23, from which the first predetermined value X1 has been subtracted, is set as the target power TP of the fuel cell 21a, the power generated by the fuel cell 21a is reduced compared to when the corrected actual power AP of the inverter 23 is set as the target power TP of the fuel cell 21a. When the power generated by the fuel cell 21a is reduced, as described above, charging of the battery 22 is suppressed, and the charging rate S of the battery 22 is likely to decrease. That is, for example, when the charging rate S of the battery 22 is higher than the target charging rate TS of the battery 22, it is easy to maintain the charging rate S of the battery 22 at the target charging rate TS of the battery 22. Therefore, the following configuration is desirable from the perspective of easily maintaining the charging rate S of the battery 22, which is higher than the target charging rate TS of the battery 22, at the target charging rate TS of the battery 22. That is, as in the present embodiment, the target power determination process desirably includes subtracting the first predetermined value X1 from the target power TP of the fuel cell 21a when the charging rate S of the battery 22 is higher than the target charging rate TS of the battery 22.

[0060] When the corrected actual power AP of the inverter 23 to which the second predetermined value X2 has been added is set as the target power TP of the fuel cell 21a, the power generated by the fuel cell 21a is increased compared to when the corrected actual power AP of the inverter 23 is set as the target power TP of the fuel cell 21a. When the power generated by the fuel cell 21a is increased, as described above, charging of the battery 22 is promoted, and the charging rate S of the battery 22 is more likely to increase. That is, for example, when the charging rate S of the battery 22 is lower than the target charging rate TS of the battery 22, it is more likely that the charging rate S of the battery 22 is maintained at the target charging rate TS of the battery 22. Therefore, from the perspective of easily maintaining the charging rate S of the battery 22, which is lower than the target charging rate TS of the battery 22, at the target charging rate TS of the battery 22, the following configuration is desirable. That is, as in the present embodiment, the target power determination process desirably includes adding the second predetermined value X2 to the target power TP of the fuel cell 21a when the charging rate S of the battery 22 is lower than the target charging rate TS of the battery 22.

[0061] However, when the charging rate S of the battery 22 is greater than the target charging rate TS of the battery 22, there are cases where the charging rate S of the battery 22 continues to increase (or is maintained) even if the actual power AP of the inverter 23 after subtraction is set as the target power TP of the fuel cell 21a. In this case, the first predetermined value X1 is increased in the target power determination process. More specifically, this is as follows. Figure 5 is a flowchart showing the flow when the first predetermined value X1 is increased.

[0062] In step S351, the target power determination unit 24c determines whether the charging rate S of the battery 22 is greater than the target charging rate TS of the battery 22. If the charging rate S of the battery 22 is greater than the target charging rate TS of the battery 22 (Yes in step S351), the process proceeds to the next step S352. If the charging rate S of the battery 22 is not greater than the target charging rate TS of the battery 22 (No in step S351), this flowchart ends.

[0063] In step S352, the target power determination unit 24c determines whether the increase in the charging rate S of the battery 22 has continued for a first predetermined time TM1. In this embodiment, an increase in the charging rate S of the battery 22 includes maintaining the charging rate S of the battery 22. An increase in the charging rate S of the battery 22 also includes a slight decrease in the charging rate S of the battery 22. That is, for example, even if the charging rate S of the battery 22 has decreased, if the decrease is slight (for example, 1%), the target power determination unit 24c determines that the charging rate S of the battery 22 has increased. The first predetermined time TM1 is set in advance and stored in the storage unit 24b. The first predetermined time TM1 is set to, for example, 5 minutes. However, the setting of the first predetermined time TM1 is not limited to 5 minutes and may be, for example, 1 minute or 10 minutes. If the increase in the charging rate S of the battery 22 has continued for the first predetermined time TM1 (Yes in step S352), the process proceeds to the next step S353. If the increase in the charging rate S of the battery 22 has not continued for the first predetermined time TM1 (No in step S352), the process returns to step S351.

[0064] In step S353, the target power determiner 24c increases the first predetermined value X1. For example, the target power determiner 24c increases the first predetermined value X1 by the first predetermined value X1. That is, the value obtained by adding the first predetermined value X1 to the first predetermined value X1 is set to the increased first predetermined value X1. Note that the increase in the first predetermined value X1 is not limited to the above configuration. For example, the value obtained by adding a value different from the first predetermined value X1 (for example, 100 W) to the first predetermined value X1 may be set to the increased first predetermined value X1.

[0065] When the first predetermined value X1 increases, the process returns to step S351. Note that when the first predetermined value X1 increases, the time during which the charging rate S of the battery 22 continues to increase is reset (returned to zero). Therefore, when the charging rate S of the battery 22 continues to be higher than the target charging rate TS of the battery 22, the process of step S353 is repeated every time the charging rate S of the battery 22 continues to increase for the first predetermined time TM1. In other words, the target power determination process includes increasing the first predetermined value X1 every time the charging rate S of the battery 22 continues to increase for the first predetermined time TM1 when the charging rate S of the battery 22 is higher than the target charging rate TS of the battery 22.

[0066] When the first predetermined value X1 increases, the corrected actual power AP of the inverter 23, i.e., the target power TP of the fuel cell 21a, resulting from subtraction of the first predetermined value X1, decreases. This reduces the power generated by the fuel cell 21a, making it easier to maintain the charging rate S of the battery 22, which is higher than the target charging rate TS of the battery 22, at the target charging rate TS of the battery 22. Therefore, from the perspective of reliably realizing a configuration that maintains the charging rate S of the battery 22, which is higher than the target charging rate TS of the battery 22, at the target charging rate TS of the battery 22, the following configuration is desirable. That is, as in this embodiment, the target power determination process desirably includes increasing the first predetermined value X1 each time the charging rate S of the battery 22 continues to increase for the first predetermined time TM1 when the charging rate S of the battery 22 is higher than the target charging rate TS of the battery 22.

[0067] Furthermore, when the charging rate S of the battery 22 is lower than the target charging rate TS of the battery 22, even if the actual power AP of the inverter 23 after the addition is set as the target power TP of the fuel cell 21a, the charging rate S of the battery 22 may continue to decrease (or be maintained). In this case, in the target power determination process, the second predetermined value X2 is increased. More specifically, this is as follows. Figure 6 is a flowchart showing the flow when the second predetermined value X2 is increased.

[0068] In step S371, the target power determination unit 24c determines whether the charging rate S of the battery 22 is lower than the target charging rate TS of the battery 22. If the charging rate S of the battery 22 is lower than the target charging rate TS of the battery 22 (Yes in step S371), the process proceeds to the next step, S372. If the charging rate S of the battery 22 is not lower than the target charging rate TS of the battery 22 (No in step S371), this flowchart ends.

[0069] In step S372, the target power determination unit 24c determines whether the decrease in the charging rate S of the battery 22 has continued for a second predetermined time TM2. In this embodiment, a decrease in the charging rate S of the battery 22 includes maintaining the charging rate S of the battery 22. A decrease in the charging rate S of the battery 22 also includes a slight increase in the charging rate S of the battery 22. That is, for example, even if the charging rate S of the battery 22 has increased, if the increase is slight (for example, 1%), the target power determination unit 24c determines that the charging rate S of the battery 22 has decreased. The second predetermined time TM2 is set in advance and stored in the storage unit 24b. The second predetermined time TM2 is set to, for example, 5 minutes. That is, in this embodiment, the setting of the second predetermined time TM2 is the same as the setting of the first predetermined time TM1. However, the setting of the second predetermined time TM2 is not limited to 5 minutes and may be, for example, 1 minute or 10 minutes. Furthermore, the second predetermined time TM2 may be set differently from the first predetermined time TM1.

[0070] If the decrease in the charging rate S of the battery 22 has continued for the second predetermined time TM2 (Yes in step S372), the process proceeds to the next step S373. If the decrease in the charging rate S of the battery 22 has not continued for the second predetermined time TM2 (No in step S372), the process returns to step S371.

[0071] In step S373, the target power determiner 24c increases the second predetermined value X2. For example, the target power determiner 24c increases the second predetermined value X2 by the second predetermined value X2. That is, the value obtained by adding the second predetermined value X2 to the second predetermined value X2 is set to the increased second predetermined value X2. Note that the increase in the second predetermined value X2 is not limited to the above configuration. For example, the increased second predetermined value X2 may be set to a value obtained by adding a value different from the second predetermined value X2 (for example, 100 W) to the second predetermined value X2.

[0072] When the second predetermined value X2 increases, the process returns to step S371. Note that when the second predetermined value X2 increases, the time during which the decrease in the charging rate S of the battery 22 continues is reset. Therefore, when the charging rate S of the battery 22 continues to be lower than the target charging rate TS of the battery 22, the process of step S373 is repeated every time the decrease in the charging rate S of the battery 22 continues for the second predetermined time TM2. In other words, the target power determination process includes increasing the second predetermined value X2 every time the decrease in the charging rate S of the battery 22 continues for the second predetermined time TM2 when the charging rate S of the battery 22 is lower than the target charging rate TS of the battery 22.

[0073] As the second predetermined value X2 increases, the actual power AP of the inverter 23 after correction to which the second predetermined value X2 has been added, i.e., the target power TP of the fuel cell 21a, increases. This increases the power generated by the fuel cell 21a, making it easier to maintain the charging rate S of the battery 22, which is lower than the target charging rate TS of the battery 22, at the target charging rate TS of the battery 22. Therefore, from the perspective of reliably realizing a configuration that maintains the charging rate S of the battery 22, which is lower than the target charging rate TS of the battery 22, at the target charging rate TS of the battery 22, the following configuration is desirable. That is, as in this embodiment, the target power determination process desirably includes increasing the second predetermined value X2 each time a decrease in the charging rate S continues for the second predetermined time TM2 when the charging rate S of the battery 22 is lower than the target charging rate TS of the battery 22.

[0074] If it becomes impossible to maintain the charging rate S of the battery 22 constant, for example, the charging rate S of the battery 22 may rise too much, i.e., the battery 22 may be in an overcharged state. Also, the charging rate S of the battery 22 may fall too much, i.e., the battery 22 may be in an overdischarged state. If the battery 22 is in an overcharged state or an overdischarged state, the deterioration of the battery 22 will progress. Moreover, the deterioration of the battery 22 will also progress if the battery 22 overheats. Therefore, in such cases, it is necessary to appropriately protect the battery 22. A method for protecting the battery 22 will be described below.

[0075] [4. Battery protection method] First, a method for protecting the battery 22 when the battery 22 overheats will be described. Fig. 7 is an explanatory diagram illustrating a method for protecting the battery 22 when the battery 22 overheats. Fig. 7 shows an example of changes over time in the temperature T of the battery 22, the charging rate S of the battery 22, and the target charging rate TS of the battery 22. In Fig. 7, the temperature T of the battery 22 is indicated by a two-dot chain line, the charging rate S of the battery 22 is indicated by a dot-dash line, and the target charging rate TS of the battery 22 is indicated by a solid line. Note that after time t1, the dot-dash line indicating the charging rate S of the battery 22 and the solid line indicating the target charging rate TS of the battery 22 overlap, as will be described below.

[0076] During the period from time t0 to time t1, the charging rate S of the battery 22 is lower than the target charging rate TS of the battery 22, so for example, the actual power AP of the inverter 23 after the addition is set as the target power TP of the fuel cell 21a (see step S38 in FIG. 4). As a result, charging of the battery 22 progresses and the charging rate S of the battery 22 gradually increases. Note that the target charging rate TS of the battery 22 is set in advance to, for example, a first target charging rate TS1. Therefore, the target charging rate TS of the battery 22 is maintained constant at the first target charging rate TS1. Meanwhile, as charging of the battery 22 progresses, the temperature T of the battery 22 gradually increases.

[0077] At time t1, the temperature T of the battery 22 reaches the temperature threshold value Tt (see point P1 in FIG. 7). Then, the target charging rate update unit 24d (see FIG. 2) updates the target charging rate TS of the battery 22 from the first target charging rate TS1 to the first charging rate S1, which is the charging rate S of the battery 22 at time t1 (executes the target charging rate update process). That is, the control method for the fuel cell system 2 of this embodiment includes updating the target charging rate TS of the battery 22 to the charging rate S of the battery 22 at that time when the temperature T of the battery 22 reaches the temperature threshold value Tt.

[0078] When the target charging rate TS of the battery 22 is updated to the first charging rate S1, the target charging rate TS of the battery 22 and the charging rate S of the battery 22 at time t1 coincide (see point P2 in FIG. 7). As a result, the target power TP of the fuel cell 21a is changed from the actual power AP of the inverter 23 after the addition to the corrected actual power AP of the inverter 23. Then, as described above, both charging and discharging of the battery 22 stop, and the charging rate S of the battery 22 stops increasing (see the period after time t1). Furthermore, as both charging and discharging of the battery 22 stop, the temperature T of the battery 22 also stops increasing (see the period after time t1).

[0079] Therefore, from the viewpoint of suppressing an increase in the temperature T of the battery 22 and protecting the battery 22 (avoiding the progression of deterioration of the battery 22) when the battery 22 overheats, the following configuration is desirable: That is, as in this embodiment, the control method for the fuel cell system 2 desirably includes updating the target charging rate TS of the battery 22 to the charging rate S of the battery 22 at that time when the temperature T of the battery 22 reaches the temperature threshold value Tt.

[0080] Next, a method for protecting the battery 22 when the battery 22 is in an overcharged state or an overdischarged state will be described. First, a method for protecting the battery 22 when the battery 22 is in an overcharged state will be described. FIG. 8 is an explanatory diagram illustrating a method for protecting the battery 22 when the battery 22 is in an overcharged state. FIG. 8 shows an example of time variations in the voltage V of the battery 22, the charging rate S of the battery 22, and the target charging rate TS of the battery 22. In FIG. 8, the voltage V of the battery 22 is indicated by a two-dot chain line, the charging rate S of the battery 22 is indicated by a dashed dotted line, and the target charging rate TS of the battery 22 is indicated by a solid line. Note that after time t1A, the dashed dotted line indicating the charging rate S of the battery 22 and the solid line indicating the target charging rate TS of the battery 22 overlap, as will be described below.

[0081] Moreover, the change over time in the charging rate S of the battery 22 during the period from time t0A to time t1A shown in Fig. 8 is similar to the change over time in the charging rate S of the battery 22 during the period from time t0 to time t1 shown in Fig. 7. Furthermore, the change over time in the target charging rate TS of the battery 22 during the period from time t0A to time t1A shown in Fig. 8 is similar to the change over time in the target charging rate TS of the battery 22 during the period from time t0 to time t1 shown in Fig. 7.

[0082] 7, during the period from time t0A to time t1A, the charging rate S of the battery 22 is lower than the target charging rate TS of the battery 22, and therefore the charging of the battery 22 progresses, and the charging rate S of the battery 22 and the voltage V of the battery 22 gradually increase. Note that the target charging rate TS of the battery 22 is set in advance to, for example, a second target charging rate TS2. Therefore, the target charging rate TS of the battery 22 is maintained constant at the second target charging rate TS2.

[0083] At time t1A, the voltage V of the battery 22 reaches the upper threshold Vt1 of the voltage thresholds Vt (see point P3 in FIG. 8). Then, the target charging rate update unit 24d updates the target charging rate TS of the battery 22 from the second target charging rate TS2 to the second charging rate S2, which is the charging rate S of the battery 22 at time t1A (executes the target charging rate update process).

[0084] When the target charging rate TS of the battery 22 is updated to the second charging rate S2, the target charging rate TS of the battery 22 and the charging rate S of the battery 22 at time t1A will match (see point P4 in FIG. 8). As a result, the target power TP of the fuel cell 21a is changed from the actual power AP of the inverter 23 after the addition to the corrected actual power AP of the inverter 23. Then, as described above, both charging and discharging of the battery 22 stop, and the increase in the charging rate S of the battery 22 and the increase in the voltage V of the battery 22 stop (see the period after time t1A).

[0085] Next, a method for protecting the battery 22 when the battery 22 is in an over-discharged state will be described. Fig. 9 is an explanatory diagram illustrating a method for protecting the battery 22 when the battery 22 is in an over-discharged state. Fig. 9 shows an example of time variations in the voltage V of the battery 22, the charging rate S of the battery 22, and the target charging rate TS of the battery 22. In Fig. 9, similar to Fig. 8, the voltage V of the battery 22 is indicated by a two-dot chain line, the charging rate S of the battery 22 is indicated by a dashed dotted line, and the target charging rate TS of the battery 22 is indicated by a solid line. Note that after time t1B, the dashed dotted line indicating the charging rate S of the battery 22 and the solid line indicating the target charging rate TS of the battery 22 overlap, as will be described below.

[0086] During the period from time t0B to time t1B, the charging rate S of the battery 22 is greater than the target charging rate TS of the battery 22, so for example, the actual power AP of the inverter 23 after the subtraction is set as the target power TP of the fuel cell 21a (see step S36 in FIG. 4). As a result, charging of the battery 22 is suppressed, and the charging rate S of the battery 22 and the voltage V of the battery 22 gradually decrease. Note that the target charging rate TS of the battery 22 is set in advance to, for example, a third target charging rate TS3. Therefore, the target charging rate TS of the battery 22 is maintained constant at the third target charging rate TS3.

[0087] At time t1B, the voltage V of the battery 22 reaches the lower limit threshold Vt2 of the voltage thresholds Vt (see point P5 in FIG. 9). Then, the target charging rate update unit 24d updates the target charging rate TS of the battery 22 from the third target charging rate TS3 to the third charging rate S3, which is the charging rate S of the battery 22 at time t1B (executes the target charging rate update process). In other words, the control method for the fuel cell system 2 of this embodiment includes updating the target charging rate TS of the battery 22 to the charging rate S of the battery 22 at that time when the voltage V of the battery 22 reaches the voltage thresholds Vt (in this embodiment, the upper limit threshold Vt1 and the lower limit threshold Vt2).

[0088] When the target charging rate TS of the battery 22 is updated to the third charging rate S3, the target charging rate TS of the battery 22 and the charging rate S of the battery 22 at time t1B will match (see point P6 in FIG. 9). As a result, the target power TP of the fuel cell 21a is changed from the actual power AP of the inverter 23 after the subtraction to the corrected actual power AP of the inverter 23. Then, as described above, both charging and discharging of the battery 22 stop, and the decrease in the charging rate S of the battery 22 and the decrease in the voltage V of the battery 22 stop (see the period after time t1B).

[0089] Therefore, in order to protect the battery 22 (avoiding the progression of deterioration of the battery 22) by stopping the increase or decrease in the voltage V of the battery 22 when the battery 22 is in an overcharged state or an overdischarged state, the following configuration is desirable: That is, as in this embodiment, the control method for the fuel cell system 2 desirably includes updating the target charging rate TS of the battery 22 to the charging rate S of the battery 22 at that time when the voltage V of the battery 22 reaches the voltage threshold Vt.

[0090] [5. Supplementary Information] In this embodiment, an example has been described in which a monogeneration device 1 simply having a power generation function is equipped with a fuel cell system 2, but the fuel cell system 2 may be applied to devices other than the monogeneration device 1. For example, the fuel cell system 2 may be applied to a cogeneration device that generates power and recovers waste heat generated during the power generation, making it possible to use the heat for, for example, hot water supply or heating. Because the fuel cell 21a included in the fuel cell system 2 generates heat during power generation, the fuel cell system 2 is suitable for a cogeneration device.

[0091] In this embodiment, the case where the power demand of the load 102 fluctuates gradually has been described, but the power demand of the load 102 may also fluctuate suddenly. As described above, the target power TP of the fuel cell 21a is determined based on the actual power AP of the inverter 23. Therefore, for example, if the power demand of the load 102 suddenly increases, the power generated by the fuel cell 21a will be insufficient to supply to the inverter 23 so that the inverter 23 outputs power equal to the power demand of the load 102. For this reason, in this case, the battery 22 discharges to make up for the shortage of power to be supplied to the inverter 23.

[0092] On the other hand, if the power demand of the load 102 suddenly decreases, the power generated by the fuel cell 21a will be in excess of the power that should be supplied to the inverter 23 so that the inverter 23 can output the same power as the power demand of the load 102. For this reason, in this case, the battery 22 is charged to ensure a supply destination for the surplus power that should be supplied to the inverter 23. In other words, the function of the battery 22 to assist the power supply from the fuel cell 21a to the inverter 23 is exerted even when the power demand of the load 102 suddenly changes.

[0093] [6. Notes] The control method, control program 24b1, fuel cell system 2, and monogeneration device 1 of the fuel cell system 2 described in this embodiment can also be expressed as the control method, control program, fuel cell system, and monogeneration device of the fuel cell system shown in the following appendix.

[0094] The control method of the fuel cell system of appendix (1) is A fuel cell; an inverter that converts DC power supplied from the fuel cell into AC power and outputs the AC power; a battery that assists power supply from the fuel cell to the inverter, The method includes executing a target power determination process for determining a target power for the fuel cell based on the power output by the inverter and the charging rate of the battery.

[0095] A control method for a fuel cell system according to claim (2) is the control method according to claim (1), The target power determination process includes calculating the target power of the fuel cell as a value obtained by correcting the power with the conversion efficiency of the inverter.

[0096] The control method for a fuel cell system according to claim (3) is the control method according to claim (1) or (2), The target power determination process includes adjusting the target power of the fuel cell in accordance with a result of comparing the charging rate with a target charging rate of the battery.

[0097] A control method for a fuel cell system according to claim 4, wherein the control method according to claim 3, The target power determination process includes: When the charging rate is greater than the target charging rate, subtracting a first predetermined value from the target power of the fuel cell; When the charging rate is lower than the target charging rate, adding a second predetermined value to the target power of the fuel cell.

[0098] The control method for a fuel cell system according to claim 5 further comprises the steps of: The target power determination process includes: When the charging rate is higher than the target charging rate, increasing the first predetermined value every time the increase in the charging rate continues for a first predetermined time; When the charging rate is lower than the target charging rate, the second predetermined value is increased every time the decrease in the charging rate continues for a second predetermined time.

[0099] The control method for a fuel cell system according to Supplementary Note (6) is the control method according to any one of Supplementary Note (3) to (5), When the temperature of the battery reaches a temperature threshold, the target charging rate is updated to the charging rate at that time.

[0100] The control method for a fuel cell system according to Supplementary Note (7) is the control method according to any one of Supplementary Note (3) to (6), When the voltage of the battery reaches a voltage threshold, the target charging rate is updated to the charging rate at that time.

[0101] The control program for the fuel cell system of supplementary note (8) causes at least one arithmetic device to execute the control method according to any one of supplementary notes (1) to (7).

[0102] The fuel cell system of Appendix (9) is A fuel cell; an inverter that converts DC power supplied from the fuel cell into AC power and outputs the AC power; a battery that assists in the supply of power from the fuel cell to the inverter, The system further includes a target power determination unit that determines a target power for the fuel cell based on the power output by the inverter and the charging rate of the battery.

[0103] The monogeneration device of appendix (10) includes the fuel cell system of appendix (9).

[0104] Although the embodiments of the present invention have been described above, the scope of the present invention is not limited to these, and the invention can be expanded or modified without departing from the spirit of the invention. [Industrial Applicability]

[0105] The present invention can be used in monogeneration systems for industrial and home use, for example. [Explanation of symbols]

[0106] 1. Monogeneration device 2. Fuel cell system 21a fuel cell 22 Battery 23 Inverter 24a Arithmetic unit 24b1 control program 24c Target power determination section E conversion efficiency S charging rate T temperature TM1 First scheduled time TM2 2nd predetermined time TP target power TS target charging rate Tt temperature threshold V Voltage Vt Voltage Threshold X1 1st predetermined value X2 Second predetermined value

Claims

1. Fuel cells and an inverter that converts DC power supplied from the fuel cell into AC power and outputs the AC power; a battery that assists power supply from the fuel cell to the inverter, A control method for a fuel cell system, comprising: executing a target power determination process for determining a target power for the fuel cell based on the power output by the inverter and the charging rate of the battery.

2. 2. The control method for a fuel cell system according to claim 1, wherein the target power determination process includes calculating the target power of the fuel cell as a value obtained by correcting the power with a conversion efficiency of the inverter.

3. 2. The control method for a fuel cell system according to claim 1, wherein the target power determination process includes adjusting the target power of the fuel cell in accordance with a result of comparing the charging rate with a target charging rate of the battery.

4. The target power determination process is as follows: When the charging rate is greater than the target charging rate, subtracting a first predetermined value from the target power of the fuel cell; 4. The control method for a fuel cell system according to claim 3, further comprising adding a second predetermined value to the target power of the fuel cell when the charging rate is lower than the target charging rate.

5. The target power determination process is as follows: In a case where the charging rate is higher than the target charging rate, increasing the first predetermined value every time the increase in the charging rate continues for a first predetermined time; 5. The control method for a fuel cell system according to claim 4, further comprising: when the charging rate is lower than the target charging rate, increasing the second predetermined value each time the decrease in the charging rate continues for a second predetermined time.

6. 4. The method for controlling a fuel cell system according to claim 3, further comprising updating the target charging rate to the charging rate at the time when the temperature of the battery reaches a temperature threshold.

7. 4. The method for controlling a fuel cell system according to claim 3, further comprising updating the target charging rate to the charging rate at the time when the voltage of the battery reaches a voltage threshold.

8. A control program for a fuel cell system, which causes at least one arithmetic device to execute the control method according to any one of claims 1 to 7.

9. Fuel cells and an inverter that converts DC power supplied from the fuel cell into AC power and outputs the AC power; a battery that assists in the supply of power from the fuel cell to the inverter, A fuel cell system comprising a target power determination unit that determines a target power for the fuel cell based on the power output by the inverter and the charging rate of the battery.

10. A monogeneration device comprising the fuel cell system according to claim 9.

Images