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

Abstract

A technology is provided that can expand the output range of a fuel cell system while suppressing deterioration of the fuel cell. [Solution] A fuel cell system includes a fuel cell and a battery that stores the power output from the fuel cell, and has a first operating mode in which the power output from the fuel cell is extracted to the outside, and a second operating mode including a discharge mode in which the power output from the battery is extracted to the outside. A control method for the fuel cell system includes switching between the first and second operating modes based on a target power of the fuel cell.

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 viewpoint of carbon neutrality, there has been a demand for power generation devices (e.g., monogeneration devices) that use fuel cell systems equipped with fuel cells. However, due to their characteristics, fuel cells tend to deteriorate more easily when the generated power is low than when the generated power is high. Therefore, from the viewpoint of suppressing fuel cell deterioration, it is desirable, for example, not to allow the fuel cell to generate power below a predetermined power. However, in this case, the output range of the fuel cell system (power generation device) is limited to above the predetermined power.

[0005] The present invention has been made to solve the above problems, and its purpose is to provide a technology that can expand the output range of a fuel cell system while suppressing deterioration of the fuel cell. [Means for solving the problem]

[0006] 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 and a battery for storing power output from the fuel cell, and having a first operating mode in which the power output from the fuel cell is extracted to the outside, and a second operating mode including a discharge mode in which the power output from the battery is extracted to the outside, and includes switching between the first operating mode and the second operating mode based on a target power of the fuel cell.

[0007] 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.

[0008] A fuel cell system according to another aspect of the present invention comprises a fuel cell and a battery for storing power output from the fuel cell, and has a first operating mode in which the power output from the fuel cell is extracted to the outside, and a second operating mode including a discharge mode in which the power output from the battery is extracted to the outside, and comprises a mode switching unit for switching between the first operating mode and the second operating mode based on a target power of the fuel cell.

[0009] A monogeneration system according to another aspect of the present invention includes the above fuel cell system. [Effects of the Invention]

[0010] According to the above configuration, it is possible to widen the output range of the fuel cell system while suppressing deterioration of the fuel cell. [Brief explanation of the drawings]

[0011] [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 3A]4 is a flowchart showing a part of the flow of switching the operation mode of the fuel cell system. [Figure 3B] 10 is a flowchart showing another part of the flow in switching the operation mode. [Figure 4] FIG. 3 is an explanatory diagram illustrating switching of the operation mode based on a target power of a fuel cell included in the fuel cell system. [Figure 5] 10 is a flowchart showing a procedure for changing a power generation instruction for the fuel cell. DETAILED DESCRIPTION OF THE INVENTION

[0012] The following describes an embodiment of the present invention with reference to the drawings.

[0013] [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.

[0014] 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.

[0015] The fuel cell system 2 also has an operation mode 2M, which is a first operation mode 2M1 and a second operation mode 2M2. The second operation mode 2M2 includes a discharge mode 2M2A and a charge mode 2M2B. These will be described in detail later.

[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 power generated by the monogeneration device 1 (fuel cell system 2) and commercial power supplied from the commercial power system 101. Note that the configuration related to power supply to the load 102 is not limited to the above. For example, the load 102 may be configured to 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 power generated by the monogeneration device 1. The configuration of the fuel cell system 2 will be described below.

[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 of 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. In other words, the battery 22 stores the power output from the fuel cell 21a.

[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 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. 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 S 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 voltage power supplied from at least one of the fuel cell 21a and the battery 22 into AC voltage power and supplies it to the load 102 (see FIG. 1). More 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 power output from the inverter 23 (at that time) 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 and data are stored in the storage unit 24b. The various programs include a control program 24b1 related to a method for switching the operation mode 2M (see FIG. 1) of the fuel cell system 2 and a power generation instruction 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 cooperate to allow the control device 24 to operate as a mode switching unit 24c and a power instruction unit 24d. That is, the fuel cell system 2 includes the mode switching unit 24c and the power instruction 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 mode switching unit 24c and the power instruction 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 mode switching unit 24c and the power instruction 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 mode switching unit 24c and the power instruction unit 24d may be realized by hardware using a dedicated IC or the like. At least one of the mode switching unit 24c and the power instruction unit 24d may also be realized by a combination of software and hardware. The mode switching unit 24c and the power instruction 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] Based on a target power TP (see FIG. 4) of the fuel cell 21a, which will be described later, the mode switching unit 24c controls switching of the operation mode 2M of the fuel cell system 2. As described above, the operation mode 2M includes a first operation mode 2M1 and a second operation mode 2M2 (see FIG. 1).

[0037] In the first operation mode 2M1, (all) the electric power generated by the fuel cell 21a is supplied to the load 102 via the boost converter 21b and the inverter 23. That is, in the first operation mode 2M1, the fuel cell system 2 extracts the electric power output from the fuel cell 21a to the outside of the fuel cell system 2 (monogeneration device 1).

[0038] As described above, the second operation mode 2M2 includes the discharge mode 2M2A and the charge mode 2M2B (see FIG. 1). In the discharge mode 2M2A, power generation by the fuel cell 21a is stopped, and power discharged from the battery 22 is supplied to the load 102. That is, in the discharge mode 2M2A, the fuel cell system 2 stops power generation by the fuel cell 21a, and extracts the power output from the battery 22 to the outside of the fuel cell system 2 (monogeneration device 1).

[0039] In the charging mode 2M2B, a portion of the power generated by the fuel cell 21a is supplied to the load 102, and the remainder of the power generated by the fuel cell 21a is supplied to the battery 22. That is, in the charging mode 2M2B, the fuel cell system 2 stores the power output from the fuel cell 21a in the battery 22 and extracts it outside the fuel cell system 2 (monogeneration device 1).

[0040] Furthermore, in addition to switching between the first operation mode 2M1 and the second operation mode 2M2, the mode switching unit 24c controls switching between a discharge mode 2M2A and a charge mode 2M2B in the second operation mode 2M2 based on the state of the battery 22. The power instruction unit 24d gives instructions to the fuel cell control unit 21d regarding the power to be generated by the fuel cell 21a.

[0041] [3. Method of switching the operation mode of the fuel cell system] A method for switching between operation modes 2M will be described below. When the operation mode 2M is switched, the power generation instruction to the fuel cell 21a is changed. Therefore, the power generation instruction to the fuel cell 21a will also be described below.

[0042] In this embodiment, the method for switching the operation mode 2M is realized by the arithmetic device 24a in the control device 24 executing arithmetic processing in accordance with the control program 24b1 (see FIG. 2). In this embodiment, as described above, there is one arithmetic device 24a, but there may be two or more arithmetic devices 24a. In this case, the arithmetic processing in accordance with the control program 24b1 may be realized by two or more arithmetic devices 24a. In other words, the control program 24b1 is a program that causes at least one arithmetic device 24a to execute a control method related to switching the operation mode 2M of the fuel cell system 2.

[0043] 3A and 3B are flowcharts showing the flow of switching the operation mode 2M of the fuel cell system 2. The flowchart shown in FIG. 9A and the flowchart shown in FIG. 9B are connected by connectors A and B. In step S0, the fuel cell system 2 (monogeneration device 1) is assumed to be operating in the first operation mode 2M1. Note that in step S0, the fuel cell system 2 may also be operating in the second operation mode 2M2.

[0044] As shown in FIG. 3A, in step S1, the mode switching unit 24c (see FIG. 2) determines whether or not an instruction to terminate the operation of the fuel cell system 2 has been issued. In this embodiment, the termination instruction is issued by operating an operation panel (not shown) provided in the monogeneration device 1. In this embodiment, the instruction to terminate the operation of the fuel cell system 2 and the instruction to terminate the operation of the monogeneration device 1 are the same, but they may be different. If an instruction to terminate has been issued (Yes in step S1), the operation of the fuel cell system 2 is terminated, and this flowchart ends. If an instruction to terminate has not been issued (No in step S1), the process proceeds to the next step S2.

[0045] In step S2, the mode switching unit 24c calculates the target power TP of the fuel cell 21a. In this embodiment, the target power TP is calculated by dividing the actual power output by the inverter 23 by the conversion efficiency of the inverter 23. Once the target power TP of the fuel cell 21a has been calculated, the process proceeds to the next step S3.

[0046] In step S3, the mode switching unit 24c adjusts the target power TP of the fuel cell 21a. In this embodiment, the adjustment is calculated by adjusting the target power TP calculated in step S2 by an adjustment value corresponding to the charging rate S of the battery 22. More specifically, if the charging rate S of the battery 22 is the same as the target charging rate of the battery 22, the mode switching unit 24c maintains the target power TP before adjustment (leaving it as is). If the charging rate S of the battery 22 is lower than the target charging rate of the battery 22, the mode switching unit 24c adds a predetermined first adjustment value to the target power TP before adjustment. If the charging rate S of the battery 22 is higher than the target charging rate of the battery 22, the mode switching unit 24c subtracts a predetermined second adjustment value from the target power TP before adjustment. In this embodiment, the target charging rate of the battery 22, the first adjustment value, and the second adjustment value are set in advance and stored in the storage unit 24b (see FIG. 2).

[0047] Therefore, the target power TP of the fuel cell 21a is calculated based on the output power (actual power) of the inverter 23. Furthermore, as described above, the inverter 23 supplies, i.e., outputs, AC power in accordance with the power demand of the load 102. In other words, the target power TP of the fuel cell 21a is calculated based on the power demand of the load 102. Once the target power TP of the fuel cell 21a has been adjusted, the process proceeds to the next step S4.

[0048] In step S4, the mode switching unit 24c determines whether the operation mode 2M is the first operation mode 2M1. If the operation mode 2M is the first operation mode 2M1 (Yes in step S4), the process proceeds to the next step S5. If the operation mode 2M is not the first operation mode 2M1, that is, if the operation mode 2M is the second operation mode 2M2 (No in step S4), the process proceeds to step S8 (see FIG. 3B) (via connector A).

[0049] In step S5, the mode switching unit 24c determines whether the adjusted target power TP is less than a first target power threshold Th1 (see FIG. 4) included in the target power thresholds Th, which will be described later. In this embodiment, the first target power threshold Th1 is set in advance and stored in the storage unit 24b. Note that the target power thresholds Th include a second target power threshold Th2 (see FIG. 4), which will be described later, in addition to the first target power threshold Th1. In this embodiment, the first target power threshold Th1 and the second target power threshold Th2 are different (different values), but may be the same (the same value). If the adjusted target power TP is less than the first target power threshold Th1 (Yes in step S5), the process proceeds to the next step S6. If the adjusted target power TP is not less than the first target power threshold Th1, that is, if the adjusted target power TP is equal to or greater than the first target power threshold Th1 (No in step S5), the process proceeds to step S7.

[0050] In step S6, the mode switching unit 24c switches the operation mode 2M from the first operation mode 2M1 to the second operation mode 2M2. When the operation mode 2M is switched from the first operation mode 2M1 to the second operation mode 2M2, the process returns to step S1.

[0051] In step S7, the power instruction unit 24d (see FIG. 2) instructs the fuel cell control unit 21d (see FIG. 2) to cause the fuel cell 21a to generate power at the adjusted target power TP. 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 adjusted target power TP. As described above, the adjusted target power TP is calculated based on the power demand of the load 102. Therefore, in the first operation mode 2M1, the fuel cell 21a outputs power to follow the power demand of the load 102. That is, the control method for the fuel cell system 2 of this embodiment includes causing the power output from the fuel cell 21a to follow the power demand of the load 102 in the first operation mode 2M1.

[0052] The fuel cell 21a may generate electricity more efficiently by operating at a power lower than the rated power (also called rated output) (at a partial load) than by operating at the rated power (at a full load). Therefore, from the perspective of improving the power generation efficiency of the fuel cell system 2 by causing the fuel cell 21a to generate power at a power lower than the rated power, the following configuration is desirable. That is, as in this embodiment, the control method for the fuel cell system 2 desirably includes causing the power output from the fuel cell 21a to follow the power demand of the load 102 in the first operation mode 2M1.

[0053] As shown in FIG. 3B, in step S8, the mode switching unit 24c determines whether the pre-adjustment target power TP of the fuel cell 21a is equal to or greater than the second target power threshold Th2 and whether the charging rate S of the battery 22 is equal to or less than an upper threshold. The upper threshold is set in advance and stored in the storage unit 24b. The upper threshold is, for example, 80%. If the pre-adjustment target power TP is equal to or greater than the second target power threshold Th2 and the charging rate S of the battery 22 is equal to or less than the upper threshold (Yes in step S8), the process proceeds to step S16. If at least one of the pre-adjustment target power TP is not equal to or greater than the second target power threshold Th2 and the charging rate S of the battery 22 is not equal to or less than the upper threshold is satisfied (No in step S8), the process proceeds to step S9.

[0054] In step S9, the mode switching unit 24c determines whether the fuel cell system 2 is in the discharge mode 2M2A. If the fuel cell system 2 is in the discharge mode 2M2A (Yes in step S9), the process proceeds to the next step S10. If the fuel cell system 2 is not in the discharge mode 2M2A, that is, if the fuel cell system 2 is in the charge mode 2M2B (No in step S9), the process proceeds to step S13.

[0055] In step S10, the mode switching unit 24c determines whether any of the following conditions is satisfied: the charging rate S of the battery 22 is equal to or lower than a lower limit threshold, the battery 22 is in the final stage of discharge, or the link voltage is equal to or lower than a link voltage threshold. In this embodiment, the lower limit threshold and the link voltage threshold are set in advance and stored in the storage unit 24b. The lower limit threshold is, for example, 40%. The final stage of discharge of the battery 22 (also simply referred to as the end of discharge) is realized when the voltage of the battery 22 (the voltage of the power stored in the battery 22) becomes equal to or lower than a predetermined lower limit voltage. The battery control unit 22a (see FIG. 2) determines whether the battery 22 is in the final stage of discharge. The result of this determination is transmitted to the control device 24 via CAN communication.

[0056] If any one of the following conditions is satisfied (Yes in step S10): the charging rate S of the battery 22 is equal to or lower than the lower threshold, the battery 22 is in the final stage of discharge, or the link voltage is equal to or lower than the link voltage threshold, the process proceeds to the next step S11. If none of the following conditions is satisfied (No in step S10): the charging rate S of the battery 22 is equal to or lower than the lower threshold, the battery 22 is in the final stage of discharge, or the link voltage is equal to or lower than the link voltage threshold, the process proceeds to step S12.

[0057] In step S11, the mode switching unit 24c switches the fuel cell system 2 from the discharge mode 2M2A to the charge mode 2M2B. Once the mode has been switched from the discharge mode 2M2A to the charge mode 2M2B, the process returns to step S8.

[0058] In step S12, the power instruction unit 24d instructs the fuel cell control unit 21d to stop power generation by the fuel cell 21a. Based on this instruction, the fuel cell control unit 21d controls the fuel cell 21a to stop power generation by the fuel cell 21a. This stops power output from the fuel cell 21a. When the instruction to stop power generation by the fuel cell 21a is issued, the process returns to step S8.

[0059] In step S13, the mode switching unit 24c determines whether or not either the charging rate S of the battery 22 is equal to or greater than an upper limit threshold, or the battery 22 is in the final stage of charging. In this embodiment, the final stage of charging of the battery 22 (also simply referred to as the final stage of charging) is realized when the voltage of the battery 22 (the voltage of the power stored in the battery 22) becomes equal to or greater than a predetermined upper limit voltage. As with the determination of the final stage of discharging of the battery 22, the determination of whether the battery 22 is in the final stage of charging is made by the battery control unit 22a.

[0060] If either the charging rate S of the battery 22 is equal to or greater than the upper threshold or the battery 22 is in the final stage of charging (Yes in step S13), the process proceeds to the next step S14. If neither the charging rate S of the battery 22 is equal to or greater than the upper threshold or the battery 22 is in the final stage of charging (No in step S13), the process proceeds to step S15.

[0061] In step S14, the mode switching unit 24c switches the fuel cell system 2 from the charge mode 2M2B to the discharge mode 2M2A. That is, the control method for the fuel cell system 2 of this embodiment includes switching between the discharge mode 2M2A and the charge mode 2M2B based on the state of the battery 22. Specifically, the state of the battery 22 includes the charging rate S of the battery 22. As described above, the end of discharge and the end of charge of the battery 22 are determined by the voltage of the battery 22, and the link voltage is the same as the voltage of the battery 22. Therefore, the state of the battery 22 includes the voltage of the battery 22 in addition to the charging rate S of the battery 22 (see steps S10 and S13). Once the charging mode 2M2B has been switched to the discharge mode 2M2A, the process returns to step S8.

[0062] The following configuration is desirable from the viewpoint of switching between the discharge mode 2M2A and the charge mode 2M2B while maintaining a good state of the battery 22. That is, as in this embodiment, it is desirable that the control method for the fuel cell system 2 includes switching between the discharge mode 2M2A and the charge mode 2M2B based on the state of the battery 22.

[0063] When the battery 22 is in an overcharged state where the charging rate S of the battery 22 is equal to or higher than an upper threshold, or in an overdischarged state where the charging rate S of the battery 22 is equal to or lower than a lower threshold, deterioration of the battery 22 progresses. Therefore, from the viewpoint of suppressing the progression of deterioration of the battery 22, it is desirable that the state of the battery 22 include the charging rate S of the battery 22, as in this embodiment.

[0064] As described above, the charging rate S of the battery 22 is calculated by the battery control unit 22a based on information (e.g., the voltage, current, temperature, etc. of the battery 22) acquired via various sensors provided in the battery 22. That is, the charging rate S of the battery 22 is an estimated value. In contrast, the voltage of the battery 22 is acquired by a voltage sensor included in the various sensors. For this reason, the voltage of the battery 22 often deviates less from the actual value than the charging rate S of the battery 22. Therefore, from the viewpoint of reliably preventing the battery 22 from becoming overcharged or overdischarged, it is desirable that the state of the battery 22 include the voltage of the battery 22, as in this embodiment.

[0065] In step S15, the power instruction unit 24d instructs the fuel cell control unit 21d to cause the fuel cell 21a to generate power at a predetermined power PW. 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 predetermined power PW. In this embodiment, the predetermined power PW is set in advance and stored in the storage unit 24b. That is, the control method for the fuel cell system 2 of this embodiment includes causing the fuel cell 21a to output (generate) power at the predetermined power PW in the charging mode 2M2B. In this case, the power generated by the fuel cell 21a (the predetermined power PW) is boosted by the boost converter 21b and supplied to the battery 22 and the inverter 23. This allows the fuel cell system 2 to extract power externally while charging the battery 22.

[0066] In step S16, the mode switching unit 24c switches the operation mode 2M from the second operation mode 2M2 to the first operation mode 2M1. That is, the control method for the fuel cell system 2 of this embodiment includes switching between the first operation mode 2M1 and the second operation mode 2M2 based on the target power TP of the fuel cell 21a (in this embodiment, the target power TP before adjustment and the target power TP after adjustment). The fuel cell system 2 also includes a mode switching unit 24c that switches between the first operation mode 2M1 and the second operation mode 2M2 based on the target power TP of the fuel cell 21a (in this embodiment, the target power TP before adjustment and the target power TP after adjustment).

[0067] According to the above configuration, for example, when the target power TP of the fuel cell 21a (in this embodiment, the target power TP before adjustment) is greater than the low power range in which degradation of the fuel cell 21a is likely to progress, the fuel cell system 2 can be switched to the first operation mode 2M1. In the first operation mode 2M1, the fuel cell 21a generates power at the target power TP (in this embodiment, the target power TP after adjustment), and therefore the fuel cell 21a can be prevented from generating power in the low power range in which degradation of the fuel cell 21a is likely to progress. On the other hand, when the target power TP of the fuel cell 21a (in this embodiment, the target power TP after adjustment) is within the low power range in which degradation of the fuel cell 21a is likely to progress, the fuel cell system 2 can be switched to the second operation mode 2M2. The second operation mode 2M2 includes a discharge mode 2M2A in which power output from the battery 22 is extracted outside the fuel cell system 2 (monogeneration device 1). Therefore, by switching to the discharge mode 2M2A in the second operation mode 2M2, power generation by the fuel cell 21a is unnecessary, and it is possible to prevent the fuel cell 21a from generating power in the low power range in which degradation of the fuel cell 21a is likely to progress. Also, the output range of the fuel cell system 2 can be widened compared to a configuration in which the second operation mode 2M2 is excluded. As a result, it is possible to widen the output range of the fuel cell system 2 while suppressing degradation of the fuel cell 21a.

[0068] The following configuration is desirable from the viewpoint of suppressing deterioration of the fuel cell 21a while reliably covering the power demand of the load 102 with the power output from the fuel cell system 2. That is, as in this embodiment, it is desirable that the target power TP of the fuel cell 21a (in this embodiment, the target power TP before adjustment and the target power TP after adjustment) be calculated based on the power demand of the load 102 electrically connected to the fuel cell system 2.

[0069] It is desirable to avoid the battery 22 becoming unable to output power in the discharge mode 2M2A due to an insufficient charging rate S of the battery 22. It is also desirable for the fuel cell system 2 to extract power to the outside even when the battery 22 is being charged. From this perspective, as in this embodiment, it is desirable for the second operation mode 2M2 to include a charge mode 2M2B in which the power output from the fuel cell 21a is extracted to the outside while being stored in the battery 22.

[0070] In charge mode 2M2B, unlike discharge mode 2M2A, the fuel cell 21a generates power, but if the fuel cell 21a generates power at a predetermined power PW that is higher than the low power range in which degradation of the fuel cell 21a is likely to progress, the progression of degradation of the fuel cell 21a can be avoided. Therefore, in charge mode 2M2B as well, the following configuration is desirable from the perspective of suppressing degradation of the fuel cell 21a. That is, as in this embodiment, the control method for fuel cell system 2 desirably includes causing the fuel cell 21a to output the predetermined power PW in charge mode 2M2B.

[0071] When the operation mode 2M is switched from the second operation mode 2M2 to the first operation mode 2M1, the process returns to step S1 (via connector B).

[0072] As shown in steps S5 and S6 (see FIG. 3A), the condition related to the target power TP of the fuel cell 21a for switching the operation mode 2M from the first operation mode 2M1 to the second operation mode 2M2 is as follows: In other words, when in the first operation mode 2M1, the adjusted target power TP must be less than the first target power threshold Th1 of the target power thresholds Th. On the other hand, as shown in steps S8 and S16, the condition related to the target power TP of the fuel cell 21a for switching the operation mode 2M from the second operation mode 2M2 to the first operation mode 2M1 is as follows: In other words, when in the second operation mode 2M2, the pre-adjustment target power TP must be equal to or greater than the second target power threshold Th2 of the target power thresholds Th. In other words, the target power threshold Th serves as a criterion for determining whether to switch between the first operation mode 2M1 and the second operation mode 2M2. More specifically, the condition is as follows. FIG. 4 is an explanatory diagram for explaining switching of the operation mode 2M based on the target power TP.

[0073] For example, when the operation mode 2M is the first operation mode 2M1, the target power TP (in this embodiment, the adjusted target power TP) decreases, and when it becomes less than the first target power threshold Th1, the operation mode 2M switches to the second operation mode 2M2 (see point P1 in FIG. 4). On the other hand, when the operation mode 2M is the second operation mode 2M2, the target power TP (in this embodiment, the pre-adjustment target power TP) increases, and when it becomes equal to or greater than the second target power threshold Th2, the operation mode 2M switches to the first operation mode 2M1 (see point P2 in FIG. 4). That is, the target power threshold Th used as a criterion for switching the operation mode 2M is the first target power threshold Th1 when the operation mode 2M is the first operation mode 2M1, and the second target power threshold Th2 when the operation mode 2M is the second operation mode 2M2. That is, the target power threshold Th has hysteresis.

[0074] The following configuration is desirable from the viewpoint of preventing frequent switching between the first operation mode 2M1 and the second operation mode 2M2 in a short period of time (also called hunting) and improving the stability of control in the fuel cell system 2. That is, as in this embodiment, it is desirable for the target power threshold Th, which is the criterion for determining whether or not to switch between the first operation mode 2M1 and the second operation mode 2M2, to have hysteresis.

[0075] As shown in step S15 (see FIG. 3B), in the charging mode 2M2B, the battery 22 is charged by (a portion of) the power output from the fuel cell 21a. However, if (a portion of) the power output from the fuel cell 21a is insufficient (insufficient) for charging the battery 22, the charging of the battery 22 may not progress, i.e., the charging rate S of the battery 22 may not increase. The power generation instruction to the fuel cell 21a in this case will be described below. FIG. 5 is a flowchart showing the flow of changing the power generation instruction to the fuel cell 21a when charging of the battery 22 is stopped in the charging mode 2M2B.

[0076] In step S21, the power instruction unit 24d (see FIG. 2) determines whether the fuel cell system 2 is in the charging mode 2M2B. If the fuel cell system 2 is in the charging mode 2M2B (Yes in step S21), the process proceeds to the next step S21. If the fuel cell system 2 is not in the charging mode 2M2B (No in step S21), this flowchart ends.

[0077] In step S22, the power instruction unit 24d determines whether the suspension of charging of the battery 22 has continued for a predetermined time TM. In this embodiment, the determination of whether charging of the battery 22 has suspended is achieved by comparing the charging rate S of the battery 22 at that time with the charging rate S of the battery 22 immediately before that time. Specifically, the power instruction unit 24d determines that charging of the battery 22 has suspended if the charging rate S of the battery 22 at that time is the same as or lower than the charging rate S of the battery 22 immediately before that time. Furthermore, the power instruction unit 24d determines that charging of the battery 22 is progressing (not suspended) if the charging rate S of the battery 22 at that time is higher than the charging rate S of the battery 22 immediately before that time. The predetermined time TM is set in advance and stored in the storage unit 24b (see FIG. 2). The predetermined time TM is set to, for example, five minutes. However, the setting of the predetermined time TM is not limited to 5 minutes, but may be, for example, 1 minute or 10 minutes.

[0078] If the suspension of charging of the battery 22 has continued for the predetermined time TM (Yes in step S22), the process proceeds to the next step S23. If the suspension of charging of the battery 22 has not continued for the predetermined time TM (No in step S22), the process returns to step S21.

[0079] In step S23, the power instruction unit 24d increases the predetermined power PW instructed to the fuel cell 21a in the charging mode 2M2B by a predetermined correction power (for example, 500 W). That is, the control method for the fuel cell system 2 of this embodiment includes increasing the predetermined power PW when charging of the battery 22 is stopped for a predetermined time TM in the charging mode 2M2B. The predetermined correction power is not limited to 500 W and may be, for example, 100 W or 1000 W. As a result, an instruction is output to the fuel cell control unit 21d to cause the fuel cell 21a to generate power at the predetermined power PW increased by the predetermined correction power. Therefore, the fuel cell control unit 21d controls the fuel cell 21a so that the power output from the fuel cell 21a becomes the predetermined power PW increased by the predetermined correction power.

[0080] When the predetermined power PW increases, the process returns to step S21. When the predetermined power PW increases, the duration of the suspension of charging of the battery 22 is reset (returned to zero). Therefore, if the charging mode 2M2B continues, the process of step S23 is repeated every predetermined time TM until charging of the battery 22 progresses. That is, the predetermined power PW is repeatedly increased, and the power output from the fuel cell 21a gradually increases.

[0081] In the charging mode 2M2B, when the power output from the fuel cell 21a (predetermined power PW) increases, the power supplied from the fuel cell 21a to the battery 22 increases. Increasing the power supplied to the battery 22 promotes charging of the battery 22. Therefore, from the perspective of reliably charging the battery 22, the following configuration is desirable. That is, as in this embodiment, the control method for the fuel cell system 2 desirably includes increasing the predetermined power PW output from the fuel cell 21a when charging of the battery 22 is stopped for a predetermined time in the charging mode 2M2B.

[0082] [4. 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.

[0083] In the present embodiment, a configuration has been described in which, when the charging rate S of the battery 22 is lower than the target charging rate of the battery 22, the pre-adjustment target power TP plus the first adjustment value is set as the adjusted target power TP (see step S3 in FIG. 3A). As a result, charging of the battery 22 progresses (the charging rate S of the battery 22 increases), but even in this case, charging of the battery 22 may be stopped. Even in this state, in order to ensure that charging of the battery 22 progresses, the first adjustment value may be increased when the stoppage of charging of the battery 22 continues for a predetermined time.

[0084] In the present embodiment, a configuration has been described in which, when the charging rate S of the battery 22 is higher than the target charging rate of the battery 22, the pre-adjustment target power TP is set to the adjusted target power TP by subtracting the second adjustment value (see step S3 in FIG. 3A). This stops the charging of the battery 22, but even in this case, the charging of the battery 22 may continue. Even in this state, the second adjustment value may be reduced when the charging of the battery 22 continues for a predetermined time in order to reliably stop the charging of the battery 22 and prevent the battery 22 from becoming overcharged.

[0085] [5. 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.

[0086] The control method of the fuel cell system of appendix (1) is A fuel cell; a battery that stores the power output from the fuel cell; a first operation mode in which the power output from the fuel cell is extracted to the outside; a second operation mode including a discharge mode in which power output from the battery is extracted to the outside, The method includes switching between the first operating mode and the second operating mode based on a target power of the fuel cell.

[0087] A control method for a fuel cell system according to claim (2) is the control method according to claim (1), The target power of the fuel cell is calculated based on the power demand of a load electrically connected to the fuel cell system.

[0088] The control method for a fuel cell system according to Supplementary Note (3) is the control method according to Supplementary Note (2), In the first operating mode, the power output from the fuel cell is made to follow the power demand of the load.

[0089] The control method for a fuel cell system according to Supplementary Note (4) is the control method according to any one of Supplementary Note (1) to (3), The target power threshold, which is the criterion for determining whether or not to switch between the first operation mode and the second operation mode, has hysteresis.

[0090] The control method for a fuel cell system according to Supplementary Note (5) is the control method according to any one of Supplementary Note (1) to (4), The second operation mode includes a charge mode in which the power output from the fuel cell is stored in the battery and extracted to the outside.

[0091] The control method for a fuel cell system according to claim 6 further comprises the steps of: Switching between the discharging mode and the charging mode based on a state of the battery.

[0092] A control method for a fuel cell system according to claim (7) is the control method according to claim (6), The battery status includes the charge rate of the battery.

[0093] The control method for a fuel cell system according to claim (8) is the control method according to claim (6) or (7), The battery condition includes the voltage of the battery.

[0094] The control method for a fuel cell system according to Supplementary Note (9) is the control method according to any one of Supplementary Note (5) to (8), In the charging mode, the fuel cell is caused to output a predetermined amount of power.

[0095] A control method for a fuel cell system according to claim 10, wherein the control method according to claim 9, In the charging mode, when the suspension of charging of the battery continues for a predetermined time, the predetermined power is increased.

[0096] The control program for the fuel cell system of supplementary note (11) causes at least one arithmetic device to execute the control method according to any one of supplementary notes (1) to (10).

[0097] The fuel cell system of appendix (12) A fuel cell; a battery that stores the power output from the fuel cell; a first operation mode in which the power output from the fuel cell is extracted to the outside; a second operation mode including a discharge mode in which power generation by the fuel cell is stopped and power output from the battery is extracted to the outside, The fuel cell includes a mode switching unit that switches between the first operating mode and the second operating mode based on a target power of the fuel cell.

[0098] The monogeneration device of appendix (13) includes the fuel cell system of appendix (12).

[0099] 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]

[0100] The present invention can be used in monogeneration systems for industrial and home use, for example. [Explanation of symbols]

[0101] 1. Monogeneration device 2. Fuel cell system 2M1 First operating mode 2M2 Second operating mode 2M2A discharge mode 2M2B charging mode 21a fuel cell 22 Battery 24c Mode switch 102 Load PW Predetermined power S charging rate TM specified time TP target power Th Target power threshold

Claims

1. A fuel cell; a battery that stores the power output from the fuel cell; a first operation mode in which the power output from the fuel cell is extracted to the outside; a second operation mode including a discharge mode in which power output from the battery is extracted to the outside, A control method for a fuel cell system, comprising switching between the first operating mode and the second operating mode based on a target power of the fuel cell.

2. 2. The control method for a fuel cell system according to claim 1, wherein the target power of the fuel cell is calculated based on a power demand of a load electrically connected to the fuel cell system.

3. 3. The method of controlling a fuel cell system according to claim 2, further comprising: in the first operation mode, causing the power output from the fuel cell to follow the power demand of the load.

4. 2. The control method for a fuel cell system according to claim 1, wherein the target power threshold, which is used as a criterion for determining whether to switch between the first operating mode and the second operating mode, has hysteresis.

5. 2. The control method for a fuel cell system according to claim 1, wherein the second operation mode includes a charge mode in which the power output from the fuel cell is stored in the battery and extracted to an external device.

6. The method for controlling a fuel cell system according to claim 5 , further comprising switching between the discharge mode and the charge mode based on the state of the battery.

7. 7. The method for controlling a fuel cell system according to claim 6, wherein the state of the battery includes a charging rate of the battery.

8. The method for controlling a fuel cell system according to claim 6 , wherein the state of the battery includes a voltage of the battery.

9. 6. The method for controlling a fuel cell system according to claim 5, further comprising causing the fuel cell to output a predetermined power in the charging mode.

10. 10. The control method for a fuel cell system according to claim 9, further comprising increasing the predetermined electric power when charging of the battery is stopped for a predetermined time in the charging mode.

11. 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 10.

12. A fuel cell; a battery that stores the power output from the fuel cell; a first operation mode in which the power output from the fuel cell is extracted to the outside; a second operating mode including a discharge mode in which power output from the battery is extracted to the outside, A fuel cell system comprising: a mode switching unit that switches between the first operating mode and the second operating mode based on a target power of the fuel cell.

13. A monogeneration device comprising the fuel cell system of claim 12.

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