Fuel cell system control method, fuel cell system control program, fuel cell system, and single power generation device

Abstract

Provided is a technique capable of expanding the output range of a fuel cell system while suppressing deterioration of a fuel cell. The fuel cell system is provided with a fuel cell and a battery that accumulates power output from the fuel cell, and has a first operation mode in which the power output from the fuel cell is extracted to the outside, and a second operation mode including a discharge mode in which the power output from the battery is extracted to the outside. A control method of a fuel cell system includes switching a first operation mode and a second operation mode based on a target power of a fuel cell.

Description

Technical Field

[0001] This 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 single power generation device. Background Technology

[0002] As prior art, a cogeneration device equipped with a gas engine is known (see, for example, Patent Document 1).

[0003] Patent Document 1: Japanese Patent No. 6321484

[0004] In recent years, from the perspective of carbon neutrality, power generation devices (e.g., single power generation devices) equipped with fuel cells have been preferred. However, fuel cells tend to deteriorate more rapidly when generating large amounts of electricity compared to when generating large amounts. Therefore, from the perspective of suppressing fuel cell deterioration, it is preferable, for example, to prevent fuel cells from generating electricity below a specified power output. However, in this case, the output range of the fuel cell system (power generation device) is often limited to above the aforementioned specified power output. Summary of the Invention

[0005] This invention was made to solve the above-mentioned problems, and its purpose is to provide a technology that can expand the output range of a fuel cell system while suppressing the degradation of the fuel cell.

[0006] In a control method for a fuel cell system according to one aspect of the present invention, the fuel cell system includes a fuel cell and a battery for storing electricity output from the fuel cell, and has a first operating mode for extracting electricity output from the fuel cell to the outside and a second operating mode including a discharge mode for extracting electricity output from the battery to the outside. The control method for the fuel cell system includes switching the first operating mode and the second operating mode based on a target power of the fuel cell.

[0007] The control program for the fuel cell system, as described in other aspects of the present invention, causes at least one computing device to execute the control method described above.

[0008] The fuel cell system according to other aspects of the present invention includes a fuel cell and a battery for storing the power output from the fuel cell, and has a first operating mode for extracting the power output from the fuel cell to the outside and a second operating mode including a discharge mode for extracting the power output from the battery to the outside. The fuel cell system includes a mode switching unit that switches between the first operating mode and the second operating mode based on the target power of the fuel cell.

[0009] Other aspects of the present invention relate to a single power generation device that includes the aforementioned fuel cell system.

[0010] Based on the above structure, the output range of the fuel cell system can be expanded while suppressing the degradation of the fuel cell. Attached Figure Description

[0011] Figure 1 This is a block diagram schematically illustrating a simplified connection structure of a single power generation device according to one embodiment of the present invention.

[0012] Figure 2 This is a block diagram schematically representing the structure of the fuel cell system with the aforementioned single power generation device.

[0013] Figure 3A This is a flowchart illustrating part of the process of switching operating modes in the aforementioned fuel cell system.

[0014] Figure 3B This is a flowchart representing another part of the process in the switching of the above-mentioned operating modes.

[0015] Figure 4 This is an explanatory diagram illustrating the switching of the aforementioned operating modes based on the target power of the fuel cells contained in the aforementioned fuel cell system.

[0016] Figure 5 This is a flowchart illustrating the process of changing the power generation indication for the aforementioned fuel cell.

[0017] Explanation of reference numerals in the attached figures

[0018] 1…Single power generation 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 switching unit; 102…Load; PW…Specified power; S…Charging rate; TM…Specified time; TP…Target power; Th…Target power threshold. Detailed Implementation

[0019] The embodiments of the present invention will be described based on the accompanying drawings as follows.

[0020] [1. Connection structure of a single power generation unit]

[0021] Figure 1 This is a schematic block diagram illustrating a simplified connection structure of a single power generation device 1 according to one embodiment of the present invention. The single power generation device 1 includes a fuel cell system 2 and is interconnected with a commercial power system 101. Furthermore, in Figure 1The diagram illustrates a single power generation device 1 as an example, but it could also be a structure in which multiple single power generation devices 1 are interconnected with a commercial power system 101.

[0022] The fuel cell system 2 generates electricity using fuel gas and oxidant gas supplied externally from the single power generation unit 1. In this embodiment, an example using hydrogen as the fuel gas and air as the oxidant gas will be described. However, the fuel gas is not limited to hydrogen; for example, it can be a gas with methane as its main component. Furthermore, the oxidant gas is not limited to air; any oxygen-containing gas is acceptable. Therefore, the single power generation unit 1 generates electricity. More specifically, the single power generation unit 1 only has the function of generating electricity. That is, the single power generation unit 1 does not have, for example, a waste heat recovery function that recovers waste heat generated during power generation.

[0023] Furthermore, the fuel cell system 2, operating in mode 2M, has a first operating mode 2M1 and a second operating mode 2M2. The second operating mode 2M2 includes a discharge mode 2M2A and a charging mode 2M2B. Details of these modes will be described later.

[0024] Commercial power system 101 includes commercial power source 101a and supplies commercial power generated by commercial power source 101a. Load 102 is connected to commercial power system 101. That is, load 102 is electrically connected to fuel cell system 2. Load 102 includes, for example, household electrical equipment, industrial (engineering, facility) electrical equipment, etc. Specifically, motors, pumps, etc. installed in such equipment consume electricity. The power demand (power consumption) of load 102 is supplied by the power generated by the single power generation unit 1 (fuel cell system 2) and the commercial power supplied from commercial power system 101. Furthermore, the structure for supplying power to load 102 is not limited to the structure described above. For example, load 102 may also be directly connected to the single power generation unit 1 without being connected to commercial power system 101. In this case, the power demand of load 102 is supplied by the power generated by the single power generation unit 1. The structure of fuel cell system 2 will be described below.

[0025] [2. Structure of a fuel cell system]

[0026] Figure 2 This is a block diagram schematically representing the structure of fuel cell system 2. Fuel cell system 2 includes: fuel cell module 21, battery 22, inverter 23, and control device 24.

[0027] In this embodiment, one each of the fuel cell module 21, inverter 23, and control device 24 is provided, and multiple batteries 22 are provided. However, in Figure 2In the example shown, only one battery 22 is illustrated. Furthermore, the number of each of the fuel cell module 21, battery 22, inverter 23, and control device 24 is not limited to the numbers described above. For example, there can be multiple fuel cell modules 21, inverters 23, and control devices 24, and the number of batteries 22 can be one. Additionally, the fuel cell module 21, battery 22, inverter 23, and control device 24 are each disposed within the single power generation unit 1.

[0028] The fuel cell module 21 includes: 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: a fuel cell 21a, a boost converter 21b, a compressor 21c, and a fuel cell control unit 21d.

[0029] A fuel cell 21a (also known as a fuel cell stack) consists of multiple stacked individual cells. Each individual 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 the negative electrode (fuel electrode) and includes an anode catalyst layer and a gas diffusion layer. The cathode is the positive electrode (air electrode) and includes a cathode catalyst layer and a diffusion layer. The anode, solid polymer electrolyte membrane, and cathode constitute a membrane electrode assembly (MEA). A pair of separators sandwich the MEA. Each separator has multiple slots. The slots of one separator form a hydrogen flow path. The slots of the other separator form an air flow path.

[0030] On the anode side, hydrogen is decomposed into hydrogen ions and electrons by a catalyst. Hydrogen ions move towards the cathode through a solid polymer electrolyte membrane. Conversely, electrons move towards the cathode through an external circuit. This generates an electric current (power generation). On the cathode side, oxygen from the air combines with electrons flowing from the external circuit and hydrogen ions that have passed through the solid polymer electrolyte membrane to form water. The generated water is contained in the exhaust gas and discharged to the outside of the single power generation unit 1.

[0031] The electricity generated by fuel cell 21a is boosted by boost converter 21b and supplied to inverter 23. In addition, the electricity generated by fuel cell 21a and boosted by boost converter 21b is sometimes supplied to battery 22 in addition to inverter 23.

[0032] The compressor 21c is provided to draw in air from outside the single power generation unit 1 to supply air to the fuel cell 21a. The air drawn in from outside the single power generation unit 1 by the compressor 21c flows into the fuel cell 21a through multiple filters (not shown) provided inside the single power generation unit 1.

[0033] The fuel cell control unit 21d controls various parts of the fuel cell module 21. For example, the fuel cell control unit 21d controls the power generation of the fuel cell 21a and the drive of the compressor 21c. The fuel cell control unit 21d is communicatively connected to the control device 24. Communication between the fuel cell control unit 21d and the control device 24 is, for example, via CAN communication, but the communication method is not limited to CAN communication.

[0034] Battery 22, for example, is composed of a lithium-ion battery and stores the power supplied to inverter 23. Battery 22 can be constructed by modularizing multiple battery cells or by using a single battery cell. As described above, sometimes power generated by fuel cell 21a is supplied to battery 22. Battery 22 is charged using the power supplied from fuel cell 21a. That is, battery 22 stores the power output from fuel cell 21a.

[0035] Battery 22 is controlled by a battery control unit 22a. The battery control unit 22a, also known as a BMU (Battery Management Unit), controls the input and output of battery 22. Furthermore, the battery control unit 22a calculates the state of charge (SOC) of battery 22 based on information obtained from various sensors (not shown) installed on battery 22 (e.g., voltage, current, temperature, etc.). The state of charge (SOC) of battery 22 refers to the ratio of the remaining (at that moment) charge capacity to the charge capacity when fully charged.

[0036] The battery control unit 22a is communicatively connected to the control device 24. Communication between the battery control unit 22a and the control device 24 is, for example, via CAN communication, but is not limited to CAN communication. For example, the battery control unit 22a transmits information about the battery 22 (including the charge rate S calculated by the battery control unit 22a) to the control device 24 via CAN communication.

[0037] Inverter 23 is constructed by mounting various electrical components (such as diodes, capacitors, power transistors, etc.) on a substrate (not shown). Inverter 23 converts the DC voltage power supplied from at least one of the fuel cell 21a and battery 22 into AC voltage power and supplies it to the load 102 (see reference). Figure 1 More specifically, inverter 23 supplies AC power to load 102 according to the power demand of load 102. For example, if the power demand of load 102 increases, inverter 23 increases the AC power supplied to load 102; if the power demand of load 102 decreases, inverter 23 decreases the AC power supplied to load 102.

[0038] Furthermore, the voltage supplied to inverter 23 will sometimes be referred to as the link voltage. The voltage of the electricity generated by fuel cell 21a and boosted by boost converter 21b corresponds to the link voltage. Therefore, the link voltage is the same as the voltage of the electricity output from battery 22.

[0039] Inverter 23 is communicatively connected to control device 24. Communication between inverter 23 and control device 24 is, for example, via CAN communication, but the communication method is not limited to CAN communication. Inverter 23, for example, transmits information about the power output from inverter 23 (at that moment) to control device 24 via CAN communication.

[0040] The control device 24 controls each component of the fuel cell system 2. Furthermore, in addition to controlling the fuel cell system 2, the control device 24 can also control the equipment included in the standalone power generation unit 1, other than the fuel cell system 2.

[0041] The control device 24 is, for example, a computer device comprising an arithmetic unit 24a, a storage unit 24b, and an input / output unit (not shown). The arithmetic unit 24a is, for example, a processor or a microprocessor. Figure 2 As an example, in the control device 24, an arithmetic device 24a is illustrated, but there may be two or more arithmetic devices 24a.

[0042] Storage unit 24b is a main storage device such as ROM (Read Only Memory) or RAM (Random Access Memory). Storage unit 24b may also include auxiliary storage devices such as HDD (Hard Disk Drive) or SSD (Solid State Drive). Storage unit 24b stores various programs and data. These programs include the operating mode 2M of fuel cell system 2 (see reference). Figure 1 The switching method and the control program 24b1 regarding the 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 the arithmetic processing according to the control program 24b1. The program stored in the storage unit 24b may also be provided by a computer-readable non-volatile recording medium, for example. As another example, the program may also be provided from a program providing server via a communication line such as the Internet.

[0043] Through the cooperation of the aforementioned hardware and software, the control device 24 can operate as both the mode switching unit 24c and the power indicator unit 24d. That is, the fuel cell system 2 includes the mode switching unit 24c and the power indicator unit 24d. The control device 24 can be a single piece of hardware or multiple pieces of hardware that can communicate with each other.

[0044] Furthermore, as described above, the mode switching unit 24c and power indicator unit 24d of the control device 24 can enable the arithmetic unit 24a to perform calculations according to the program, that is, implemented through software, but can also be implemented through other methods. At least one of the mode switching unit 24c and power indicator unit 24d can also be implemented using, for example, an ASIC (Application Specific Integrated Circuit) or a FPGA (Field Programmable Gate Array). That is, at least one of the mode switching unit 24c and power indicator unit 24d can also be implemented in hardware using a dedicated IC, etc. Additionally, at least one of the mode switching unit 24c and power indicator unit 24d can also be implemented using both software and hardware. Furthermore, the mode switching unit 24c and power indicator unit 24d are conceptual structures. Therefore, the function performed by one structural element can be distributed among multiple structural elements, and the functions of multiple structural elements can be integrated into one structural element.

[0045] The mode switching unit 24c is based on the target power TP of the fuel cell 21a described later (see reference). Figure 4 This is used to control the switching of the operating mode 2M of the fuel cell system 2. As described above, the operating mode 2M includes a first operating mode 2M1 and a second operating mode 2M2 (see reference). Figure 1 ).

[0046] In the first operating mode 2M1, all the electricity 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 operating mode 2M1, the fuel cell system 2 extracts the electricity output from the fuel cell 21a to the outside of the fuel cell system 2 (single power generation unit 1).

[0047] As described above, the second operating mode 2M2 includes a discharge mode 2M2A and a charging mode 2M2B (see reference). Figure 1 In discharge mode 2M2A, the power generation of fuel cell 21a stops, and the power discharged from battery 22 is supplied to load 102. That is, in discharge mode 2M2A, fuel cell system 2 stops the power generation of fuel cell 21a and extracts the power output from battery 22 to the outside of fuel cell system 2 (single power generation device 1).

[0048] In charging mode 2M2B, a portion of the electricity generated by fuel cell 21a is supplied to load 102, and the remaining electricity generated by fuel cell 21a is supplied to battery 22. That is, in charging mode 2M2B, the fuel cell system 2 stores the electricity output from fuel cell 21a in battery 22 and extracts it to the outside of fuel cell system 2 (single power generation device 1).

[0049] In addition to controlling the switching between the first operating mode 2M1 and the second operating mode 2M2, the mode switching unit 24c also controls the switching between the discharge mode 2M2A and the charging mode 2M2B in the second operating mode 2M2 based on the state of the battery 22. The power indication unit 24d provides an indication of the power generated by the fuel cell 21a relative to the fuel cell control unit 21d.

[0050] [3. Method for switching operating modes of fuel cell systems]

[0051] The method for switching to operating mode 2M will be explained. Furthermore, if operating mode 2M is switched, the instructions for power generation from fuel cell 21a will change. Therefore, the instructions for power generation from fuel cell 21a will also be explained below.

[0052] In this embodiment, the method for switching operating mode 2M is implemented by the arithmetic unit 24a in the control device 24 performing arithmetic processing according to the control program 24b1 (see reference). Figure 2 In this embodiment, as described above, there is one computing device 24a, but there may also be two or more. In this case, the computational processing according to the control program 24b1 can be implemented by two or more computing devices 24a. That is, the control program 24b1 is a program that causes at least one computing device 24a to execute a control method for switching the operating mode 2M of the fuel cell system 2.

[0053] Figure 3A and Figure 3B This is a flowchart illustrating the process of switching the operating mode 2M of the fuel cell system 2. Figure 3A The process shown and Figure 3B The illustrated flow is connected via connectors A and B. In step S0, the fuel cell system 2 (single power generation unit 1) operates in the first operating mode 2M1. Alternatively, in step S0, the fuel cell system 2 can also operate in the second operating mode 2M2.

[0054] like Figure 3A As shown, in step S1, the mode switching unit 24c (refer to...) Figure 2The system determines whether there is an indication to end the operation of the fuel cell system 2. In this embodiment, the indication to end the operation is obtained by operating the control panel (not shown) on the single power generation unit 1. Furthermore, in this embodiment, the indication to end the operation of the fuel cell system 2 is the same as the indication to end the operation of the single power generation unit 1, but it may also be different. If there is an indication to end the operation (yes in step S1), the operation of the fuel cell system 2 ends, and this process ends. If there is no indication to end the operation (no in step S1), the process proceeds to the next step, S2.

[0055] 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. If the target power TP of the fuel cell 21a is calculated, the process proceeds to the next step S3.

[0056] 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 using an adjustment value corresponding to the charging rate S of the battery 22. More specifically, when 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 (keeping it as is). When the charging rate S of the battery 22 is less 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. When the charging rate S of the battery 22 is greater 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. Furthermore, in this embodiment, the target charging rate of the battery 22, the first adjustment value, and the second adjustment value are preset and stored in the storage unit 24b (see reference). Figure 2 ).

[0057] Therefore, the target power TP of fuel cell 21a is calculated based on the output power (actual power) of inverter 23. Furthermore, as described above, inverter 23 supplies AC power, i.e., outputs AC power, according to the power demand of load 102. In other words, the target power TP of fuel cell 21a is calculated based on the power demand of load 102. If the target power TP of fuel cell 21a is adjusted, the process proceeds to the next step, S4.

[0058] In step S4, the mode switching unit 24c determines whether the operating mode 2M is the first operating mode 2M1. If the operating mode 2M is the first operating mode 2M1 (yes in step S4), the process proceeds to the next step S5. If the operating mode 2M is not the first operating mode 2M1, that is, if the operating mode 2M is the second operating mode 2M2 (no in step S4), the process proceeds to step S8 (see reference A) Figure 3B ).

[0059] In step S5, the mode switching unit 24c determines whether the adjusted target power TP is less than the first target power threshold Th1 included in the target power threshold Th (described later). Figure 4 In this embodiment, a first target power threshold Th1 is preset and stored in the storage unit 24b. Furthermore, in addition to the first target power threshold Th1, the target power threshold Th also includes a second target power threshold Th2 (described later). Figure 4 In this embodiment, the first target power threshold Th1 and the second target power threshold Th2 are different (different values), but they can also 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 greater than or equal to the first target power threshold Th1 (no in step S5), the process proceeds to step S7.

[0060] In step S6, the mode switching unit 24c switches the operating mode 2M from the first operating mode 2M1 to the second operating mode 2M2. If the operating mode 2M switches from the first operating mode 2M1 to the second operating mode 2M2, the process returns to step S1.

[0061] In step S7, the power indicator 24d (refer to...) Figure 2 ) Instruction for fuel cell control unit 21d (refer to) Figure 2 The fuel cell 21a is controlled by a control unit 21d to generate electricity with an adjusted target power TP. Based on this instruction, the fuel cell 21a is controlled by a control unit 21d to ensure that the power output from the fuel cell 21a is 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 operating mode 2M1, the fuel cell 21a outputs power in a manner that follows the power demand of the load 102. That is, the control method of the fuel cell system 2 in this embodiment includes ensuring that the power output from the fuel cell 21a follows the power demand of the load 102 in the first operating mode 2M1.

[0062] Compared to generating electricity at its rated power (also known as rated output) (full load operation), fuel cell 21a sometimes generates electricity at a power level less than its rated power (partial load operation) more efficiently. Therefore, from the viewpoint of improving the power generation efficiency of fuel cell system 2 by enabling fuel cell 21a to generate electricity at a power level less than its rated power, the following structure is preferred. That is, as in this embodiment, the control method of fuel cell system 2 preferably includes, in the first operating mode 2M1, making the power output from fuel cell 21a follow the power demand of load 102.

[0063] like Figure 3B As shown, in step S8, the mode switching unit 24c determines whether the target power TP of the fuel cell 21a before adjustment is above the second target power threshold Th2 and whether the charging rate S of the battery 22 is below the upper limit threshold. The aforementioned upper limit threshold is preset and stored in the storage unit 24b. The upper limit threshold is, for example, 80%. If the target power TP before adjustment is above the second target power threshold Th2 and the charging rate S of the battery 22 is below the upper limit threshold (yes in step S8), the process proceeds to step S16. If at least one of the following conditions is met (no in step S8): the target power TP before adjustment is not above the second target power threshold Th2 and the charging rate S of the battery 22 is not below the upper limit threshold, the process proceeds to step S9.

[0064] In step S9, the mode switching unit 24c determines whether the fuel cell system 2 is in discharge mode 2M2A. If the fuel cell system 2 is in discharge mode 2M2A (yes in step S9), the process proceeds to the next step S10. If the fuel cell system 2 is not in discharge mode 2M2A, that is, if the fuel cell system 2 is in charging mode 2M2B (no in step S9), the process proceeds to step S13.

[0065] In step S10, the mode switching unit 24c determines whether any one of the following conditions is met: the charging rate S of the battery 22 is below a lower threshold, the battery 22 is at the end of its discharge phase, and the link voltage is below a link voltage threshold. In this embodiment, each of the aforementioned lower threshold and link voltage threshold is preset and stored in the storage unit 24b. The lower threshold is, for example, 40%. Furthermore, the end of the discharge phase of the battery 22 (also simply referred to as the end of discharge) is achieved when the voltage of the battery 22 (the voltage of the electricity stored in the battery 22) becomes below a predetermined lower threshold voltage. The determination of whether the battery 22 is at the end of its discharge phase is performed by the battery control unit 22a (see reference 24b). Figure 2 The determination is performed via CAN communication. The result is then transmitted to the control device 24.

[0066] If any one of the following conditions is met (yes in step S10): the charging rate S of battery 22 is below the lower threshold, battery 22 is in the final stage of discharge, and link voltage is below the link voltage threshold, the process proceeds to step S11. If any one of the following conditions is not met (no in step S10): the process proceeds to step S12.

[0067] In step S11, the mode switching unit 24c switches the fuel cell system 2 from discharge mode 2M2A to charging mode 2M2B. If the switch is from discharge mode 2M2A to charging mode 2M2B, the process returns to step S8.

[0068] In step S12, the power indicator 24d instructs the fuel cell control unit 21d to stop the power generation of the fuel cell 21a. Based on this instruction, the fuel cell control unit 21d controls the fuel cell 21a to stop the power generation of the fuel cell 21a. Therefore, power is no longer output from the fuel cell 21a. If the instruction to stop the power generation of the fuel cell 21a is executed, the process returns to step S8.

[0069] In step S13, the mode switching unit 24c determines whether the charging rate S of the battery 22 is above the upper limit threshold or whether 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 end of charging) is achieved when the voltage of the battery 22 (the voltage of the electricity stored in the battery 22) reaches or exceeds a predetermined upper limit voltage. Similar to 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 performed by the battery control unit 22a.

[0070] If either the charging rate S of battery 22 is above the upper limit threshold or battery 22 is in the final stage of charging (yes in step S13), the process proceeds to step S14. If neither the charging rate S of battery 22 is above the upper limit threshold nor battery 22 is in the final stage of charging (no in step S13), the process proceeds to step S15.

[0071] In step S14, the mode switching unit 24c switches the fuel cell system 2 from charging mode 2M2B to discharging mode 2M2A. That is, the control method for the fuel cell system 2 in this embodiment includes switching between discharging mode 2M2A and charging 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. Furthermore, as described above, the end of discharging and the end of charging 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 not only the charging rate S of the battery 22 but also the voltage of the battery 22 (refer to steps S10 and S13). If switching from charging mode 2M2B to discharging mode 2M2A, the process returns to step S8.

[0072] From the viewpoint of maintaining the state of the battery 22 well and switching between discharge mode 2M2A and charging mode 2M2B, the following structure is preferred. That is, as in this embodiment, the control method of the fuel cell system 2 preferably includes switching between discharge mode 2M2A and charging mode 2M2B based on the state of the battery 22.

[0073] If the battery 22 is in an overcharged state where the charging rate S of the battery 22 is above the upper threshold, or in an over-discharged state where the charging rate S of the battery 22 is below the lower threshold, then the degradation of the battery 22 will be aggravated. Therefore, from the viewpoint of suppressing the aggravation of the degradation of the battery 22, as in this embodiment, the state of the battery 22 preferably includes the charging rate S of the battery 22.

[0074] As described above, the battery control unit 22a calculates the charge rate S of the battery 22 based on information obtained from various sensors installed on the battery 22 (e.g., the voltage, current, temperature, etc. of the battery 22). That is, the charge rate S of the battery 22 is an estimated value. In contrast, the voltage of the battery 22 is obtained using a voltage sensor included in the aforementioned sensors. Therefore, the deviation between the voltage of the battery 22 and the actual value is often smaller than the charge rate S of the battery 22. Therefore, from the viewpoint of reliably avoiding the battery 22 from becoming overcharged or over-discharged, as in this embodiment, the state of the battery 22 preferably includes the voltage of the battery 22.

[0075] In step S15, the power indicator 24d instructs the fuel cell control unit 21d to cause the fuel cell 21a to generate electricity with a predetermined power PW. Based on this instruction, the fuel cell control unit 21d controls the fuel cell 21a to ensure that the power output from the fuel cell 21a is the predetermined power PW. In this embodiment, the predetermined power PW is preset and stored in the storage unit 24b. That is, the control method of the fuel cell system 2 in this embodiment includes causing the fuel cell 21a to output (generate electricity) with the predetermined power PW in 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. Thus, the fuel cell system 2 can simultaneously charge the battery 22 and extract power from the outside.

[0076] In step S16, the mode switching unit 24c switches the operating mode 2M from the second operating mode 2M2 to the first operating mode 2M1. That is, the control method of the fuel cell system 2 in this embodiment includes switching the first operating mode 2M1 and the second operating 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). Furthermore, the fuel cell system 2 includes a mode switching unit 24c that switches the first operating mode 2M1 and the second operating 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).

[0077] Based on the above structure, for example, when the target power TP of fuel cell 21a (in this embodiment, the target power TP before adjustment) is greater than the low power range where fuel cell 21a is prone to degradation, the fuel cell system 2 can be switched to a first operating mode 2M1. In the first operating mode 2M1, fuel cell 21a generates electricity at the target power TP (in this embodiment, the target power TP after adjustment), thus preventing fuel cell 21a from generating electricity within the low power range where fuel cell 21a is prone to degradation. On the other hand, when the target power TP of fuel cell 21a (in this embodiment, the target power TP after adjustment) is within the low power range where fuel cell 21a is prone to degradation, the fuel cell system 2 can be switched to a second operating mode 2M2. The second operating mode 2M2 includes a discharge mode 2M2A where the power output from battery 22 is extracted to the outside of fuel cell system 2 (single power generation device 1). Therefore, in the second operating mode 2M2, the discharge mode 2M2A is used, thus eliminating the need for fuel cell 21a to generate electricity, preventing fuel cell 21a from generating electricity within the low power range where fuel cell 21a is prone to degradation. Furthermore, compared to a structure lacking a second operating mode 2M2, the output range of the fuel cell system 2 can be expanded. As described above, the output range of the fuel cell system 2 can be expanded while suppressing the degradation of the fuel cell 21a.

[0078] From the viewpoint of reliably supplying the power demand of the load 102 by means of the power output from the fuel cell system 2 while suppressing the degradation of the fuel cell 21a, the following structure is preferred. That is, as in this embodiment, it is preferable to calculate 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) based on the power demand of the load 102 which is electrically connected to the fuel cell system 2.

[0079] It is preferable to avoid the battery 22 failing to output power in discharge mode 2M2A due to insufficient charging rate S of battery 22. Furthermore, it is preferable that the fuel cell system 2 extracts power to the outside even when battery 22 is charging. From this perspective, as in this embodiment, the second operating mode 2M2 preferably includes a charging mode 2M2B in which power output from fuel cell 21a is stored in battery 22 and extracted to the outside.

[0080] In charging mode 2M2B, unlike discharging mode 2M2A, although fuel cell 21a generates electricity, for example, if fuel cell 21a generates electricity with a predetermined power PW that is greater than the low power range that easily exacerbates the degradation of fuel cell 21a, then the aggravation of the degradation of fuel cell 21a is avoided. Therefore, in charging mode 2M2B, from the viewpoint of suppressing the degradation of fuel cell 21a, the following structure is also preferred. That is, as in this embodiment, the control method of fuel cell system 2 preferably includes enabling fuel cell 21a to output with a predetermined power PW in charging mode 2M2B.

[0081] If the operating mode 2M switches from the second operating mode 2M2 to the first operating mode 2M1, then (via connector B) the process returns to step S1.

[0082] See steps S5 and S6 (refer to...) Figure 3A As shown in Figure 1, the conditions for the target power TP of fuel cell 21a used to switch operating mode 2M from the first operating mode 2M1 to the second operating mode 2M2 are as follows. That is, in the case of the first operating mode 2M1, the adjusted target power TP is less than the first target power threshold Th1 in the target power threshold Th. On the other hand, as shown in steps S8 and S16, the conditions for the target power TP of fuel cell 21a used to switch operating mode 2M from the second operating mode 2M2 to the first operating mode 2M1 are as follows. That is, in the case of the second operating mode 2M2, the target power TP before adjustment is greater than or equal to the second target power threshold Th2 in the target power threshold Th. In other words, the target power threshold Th becomes the criterion for determining whether to switch between the first operating mode 2M1 and the second operating mode 2M2. More specifically, as follows. Figure 4 This is an explanatory diagram used to illustrate the switching of the operation mode 2M based on the target power TP.

[0083] For example, when the operating mode 2M is the first operating mode 2M1, if the target power TP (in this embodiment, the adjusted target power TP) decreases and falls below the first target power threshold Th1, then the operating mode 2M switches to the second operating mode 2M2 (refer to...). Figure 4 (Point P1 in the diagram). On the other hand, when the operating mode 2M is the second operating mode 2M2, if the target power TP (in this embodiment, the target power TP before adjustment) rises and becomes above the second target power threshold Th2, then the operating mode 2M switches to the first operating mode 2M1 (refer to point P1 in the diagram). Figure 4(Point P2 in the diagram). That is, the target power threshold Th, which serves as the criterion for switching operating mode 2M, becomes the first target power threshold Th1 when operating mode 2M is the first operating mode 2M1, and becomes the second target power threshold Th2 when operating mode 2M is the second operating mode 2M2. In other words, the target power threshold Th has hysteresis.

[0084] From the viewpoint of improving the stability of control in the fuel cell system 2 by preventing frequent switching (also known as oscillation) of the first operating mode 2M1 and the second operating mode 2M2 within a short period of time, the following structure is preferred. That is, as in this embodiment, the target power threshold Th, which serves as the criterion for determining whether to switch between the first operating mode 2M1 and the second operating mode 2M2, preferably has hysteresis.

[0085] As in step S15 (refer to...) Figure 3B As shown, in charging mode 2M2B, battery 22 is charged using a portion of the power output from fuel cell 21a. However, if the power output from fuel cell 21a is insufficient to charge battery 22, charging of battery 22 may not continue; that is, the charging rate S of battery 22 may not increase. The power generation indication for fuel cell 21a under this condition will be explained below. Figure 5 This is a flowchart illustrating the process of changing the power generation indication of fuel cell 21a when charging of battery 22 has stopped in charging mode 2M2B.

[0086] In step S21, the power indicator 24d (refer to...) Figure 2 Determine whether fuel cell system 2 is in charging mode 2M2B. If fuel cell system 2 is in charging mode 2M2B (yes in step S21), proceed to the next step S21. If fuel cell system 2 is not in charging mode 2M2B (no in step S21), end this process.

[0087] In step S22, the power indicator unit 24d determines whether the cessation of charging of the battery 22 has lasted for a predetermined time TM. In this embodiment, the determination of whether charging of the battery 22 has stopped is achieved by comparing the charging rate S of the battery 22 at the current moment with the charging rate S of the battery 22 immediately preceding that moment. Specifically, if the charging rate S of the battery 22 at the current moment is the same as or less than the charging rate S of the battery 22 immediately preceding that moment, the power indicator unit 24d determines that charging of the battery 22 has stopped. Conversely, if the charging rate S of the battery 22 at the current moment is greater than the charging rate S of the battery 22 immediately preceding that moment, the power indicator unit 24d determines that charging of the battery 22 is continuing (has not stopped). Furthermore, a predetermined time TM is preset and stored in the storage unit 24b (see reference 1). Figure 2 The specified time TM is set to, for example, 5 minutes. However, the specified time TM is not limited to 5 minutes; for example, it can be 1 minute or 10 minutes.

[0088] If the charging of battery 22 has stopped for a predetermined time TM (yes in step S22), the process proceeds to the next step S23. If the charging of battery 22 has not stopped for a predetermined time TM (no in step S22), the process returns to step S21.

[0089] In step S23, the power indicator 24d increases the specified power PW indicated to the fuel cell 21a in charging mode 2M2B by a specified correction power (e.g., 500W). That is, the control method of the fuel cell system 2 in this embodiment includes increasing the specified power PW when the charging of the battery 22 stops for a specified time TM in charging mode 2M2B. The specified correction power is not limited to 500W; for example, it could be 100W or 1000W. Thus, the fuel cell control unit 21d outputs an instruction to cause the fuel cell 21a to generate electricity with the specified power PW increased by the specified 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 specified power PW increased by the specified correction power.

[0090] If the specified power PW increases, the process returns to step S21. Furthermore, if the specified power PW increases, the duration of the charging halt for battery 22 is reset (reset to zero). Therefore, while charging mode 2M2B continues, the process of step S23 is repeated every specified time interval TM until charging of battery 22 resumes. That is, the specified power PW is repeatedly increased, and the power output from fuel cell 21a gradually increases.

[0091] In charging mode 2M2B, if the power output (prescribed power PW) from fuel cell 21a increases, the power supplied from fuel cell 21a to battery 22 also increases. This increased power supply to battery 22 promotes charging of battery 22. Therefore, from the viewpoint of reliably charging battery 22, the following structure is preferred. That is, as in this embodiment, the control method of fuel cell system 2 preferably includes increasing the prescribed power PW output from fuel cell 21a when the charging of battery 22 is stopped for a predetermined time in charging mode 2M2B.

[0092] [4. Supplement]

[0093] In this embodiment, an example of a single power generation device 1 with a fuel cell system 2 that only has power generation function has been described. However, the fuel cell system 2 can also be applied to devices other than the single power generation device 1. For example, the fuel cell system 2 can also be applied to a combined heat and power (CHP) device that generates electricity and recovers the waste heat generated during power generation for use in applications such as hot water supply and heating. The fuel cell 21a included in the fuel cell system 2 generates heat during power generation, therefore the fuel cell system 2 is suitable for CHP devices.

[0094] In this embodiment, a structure is described in which, when the charging rate S of battery 22 is less than the target charging rate of battery 22, the power obtained by adding the first adjustment value to the target power TP before adjustment is used as the adjusted target power TP (see reference). Figure 3A (Step S3). Thus, charging of battery 22 continues (the charging rate S of battery 22 increases), but in this case, charging of battery 22 may also stop. To reliably continue charging of battery 22 even in this state, if the charging stop of battery 22 lasts for a predetermined time, the first adjustment value can be increased.

[0095] In this embodiment, a structure is described in which the power obtained by subtracting the second adjustment value from the target power TP before adjustment is used as the adjusted target power TP when the charging rate S of battery 22 is greater than the target charging rate of battery 22 (see reference). Figure 3A (Step S3). Thus, charging of battery 22 stops, but in this case, battery 22 may continue to charge. To reliably stop charging of battery 22 in this state and prevent battery 22 from becoming overcharged, the second adjustment value is reduced if battery 22 continues to charge for a predetermined time.

[0096] [5. Postscript]

[0097] The control method, control program 24b1, fuel cell system 2, and single power generation device 1 described in this embodiment can also be described as the control method, control program, fuel cell system, and single power generation device of the fuel cell system shown in the following notes.

[0098] A control method for a fuel cell system as described in Appendix (1), wherein the fuel cell system includes a fuel cell and a battery for storing electricity output from the fuel cell, and has a first operating mode for extracting electricity output from the fuel cell to the outside, and a second operating mode including a discharge mode for extracting electricity output from the battery to the outside.

[0099] The control method for the aforementioned fuel cell system includes switching between the first operating mode and the second operating mode based on the target power of the fuel cell.

[0100] The control method for the fuel cell system in Appendix (2) is as follows: based on the control method described in Appendix (1),

[0101] The target power of the fuel cell is calculated based on the power demand of the load electrically connected to the fuel cell system.

[0102] The control method for the fuel cell system in Appendix (3) is as follows: based on the control method described in Appendix (2),

[0103] This includes ensuring that, in the first operating mode described above, the power output from the fuel cell follows the power demand of the load.

[0104] The control method for the fuel cell system in Appendix (4) is based on the control method described in any of Appendix (1) to (3).

[0105] The target power threshold, which serves as the criterion for determining whether to switch between the first and second operating modes, exhibits hysteresis.

[0106] The control method for the fuel cell system in Appendix (5) is based on the control method described in any of Appendix (1) to (4).

[0107] The second operating mode mentioned above includes a charging mode in which the electricity output from the fuel cell is stored in the battery and then taken out to the outside.

[0108] The control method for the fuel cell system in Appendix (6) is as follows: based on the control method described in Appendix (5),

[0109] It includes switching between the discharge mode and the charging mode based on the state of the battery.

[0110] The control method for the fuel cell system in Appendix (7) is as follows: based on the control method described in Appendix (6),

[0111] The state of the battery mentioned above includes the battery's charge rate.

[0112] The control method for the fuel cell system in Appendix (8) is as follows: based on the control method described in Appendix (6) or (7),

[0113] The state of the battery mentioned above includes its voltage.

[0114] The control method for the fuel cell system in Appendix (9) is based on the control method described in any of Appendix (5) to (8).

[0115] The above charging mode enables the fuel cell to output a specified amount of electricity.

[0116] The control method for the fuel cell system in Appendix (10) is as follows: based on the control method described in Appendix (9),

[0117] This includes increasing the specified power when the charging of the battery stops for a specified period of time under the above charging mode.

[0118] A control program for a fuel cell system, as described in Appendix (11), causes at least one computing device to execute the control method described in any one of Appendices (1) to (10).

[0119] A fuel cell system as described in Appendix (12) includes a fuel cell and a battery for storing electricity output from the fuel cell, and has a first operating mode for extracting electricity from the fuel cell to the outside, and a second operating mode including a discharge mode that stops the power generation of the fuel cell and extracts electricity from the battery to the outside.

[0120] The aforementioned fuel cell system includes a mode switching unit that switches between the first operating mode and the second operating mode based on the target power of the fuel cell.

[0121] A single power generation device as described in Appendix (13) includes the fuel cell system described in Appendix (12).

[0122] The embodiments of the present invention have been described above, but the scope of the present invention is not limited thereto, and can be extended or modified within the scope of the spirit of the invention.

[0123] Industrial availability

[0124] This invention can be used, for example, in single-power generation devices for industrial or household applications.

Claims

1. A control method for a fuel cell system, the fuel cell system comprising a fuel cell and a battery for storing electricity output from the fuel cell, and having a first operating mode for extracting electricity from the fuel cell to an external environment, and a second operating mode including a discharge mode for extracting electricity from the battery to an external environment, wherein, The control method for the fuel cell system includes switching between a first operating mode and a second operating mode based on the target power of the fuel cell.

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 the power demand of the load electrically connected to the fuel cell system.

3. The control method for a fuel cell system according to claim 2, wherein, This includes ensuring that, in the first operating mode, the power output from the fuel cell follows the power demand of the load.

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

5. The control method for a fuel cell system according to claim 1, wherein, The second operating mode includes a charging mode in which the electricity output from the fuel cell is stored in the battery and then extracted to the outside.

6. The control method for a fuel cell system according to claim 5, wherein, It includes switching the discharge mode and the charging mode based on the state of the battery.

7. The control method for a fuel cell system according to claim 6, wherein, The state of the battery includes the battery's charge rate.

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

9. The control method for a fuel cell system according to claim 5, wherein, The charging mode includes enabling the fuel cell to output a specified amount of electricity.

10. The control method for a fuel cell system according to claim 9, wherein, Includes increasing the specified power when the charging of the battery stops for a specified period of time during the charging mode.

11. A control program for a fuel cell system, wherein, The control method described in any one of claims 1 to 10 is executed by at least one computing device.

12. A fuel cell system comprising a fuel cell and a battery for storing electricity output from the fuel cell, and having a first operating mode for extracting electricity from the fuel cell to an external environment, and a second operating mode including a discharge mode for extracting electricity from the battery to an external environment, wherein, The device includes a mode switching unit that switches between a first operating mode and a second operating mode based on the target power of the fuel cell.

13. A single power generation device, wherein, The fuel cell system as described in claim 12 is provided.

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