Fuel cell system

Abstract

A fuel cell system wherein, if there is a command for a control unit to establish a complete shut-off state in which the power generation of the fuel cell is shut off while in an ordinary power generation state in which a fuel cell generates power in accordance with the voltage of a battery, the control unit establishes an intermittent shut-off state in which the power generation of the fuel cell is reduced by shutting off or decreasing the supply of oxidizing gas to the fuel cell by an oxidizing gas supply unit, and then establishes a complete shut-off state by shutting off the supply of fuel gas to the fuel cell by a fuel gas supply unit.

Description

fuel cell system

[0001] The present disclosure relates to a fuel cell system having a fuel cell that generates electricity when supplied with a fuel gas and an oxidant gas.

[0002] Patent Document 1 discloses a fuel cell system having a fuel cell that receives a supply of fuel gas from a fuel gas system and a supply of oxidant gas from an oxidant gas system to generate electricity.

[0003] Japanese Patent Application Laid-Open No. 2022-185247

[0004] In a DCDC converter-less fuel cell system (described in more detail below), when a power generation stop process is performed to change the fuel cell from a state of power generation to a state of complete shutdown (i.e., a state in which power generation is completely stopped), oxidant gas (e.g., air) may remain in the fuel cell, oxidizing the fuel cell catalyst (carbon) and causing deterioration of the fuel cell.

[0005] However, Patent Document 1 does not disclose any measures to prevent the deterioration of the fuel cell from progressing due to the process of stopping power generation of the fuel cell.

[0006] Therefore, the present disclosure has been made to solve the above-mentioned problems, and aims to provide a fuel cell system that can suppress the progression of fuel cell deterioration due to the fuel cell power generation stopping process.

[0007] One aspect of the present disclosure made to solve the above problem is a fuel cell system having a fuel cell and a battery that charges with power generated by the fuel cell, wherein the output current of the fuel cell depends on the voltage of the battery, the system comprising: a fuel gas supply unit that supplies fuel gas to the fuel cell; an oxidant gas supply unit that supplies oxidant gas to the fuel cell; and a control unit that controls the fuel gas supply unit and the oxidant gas supply unit, wherein when the fuel cell is in a state of natural generation in which it generates power according to the voltage of the battery and there is a request to put the fuel cell into a complete shutdown state to stop power generation, the control unit stops or reduces the supply of oxidant gas to the fuel cell by the oxidant gas supply unit, thereby putting the fuel cell into an intermittent shutdown state in which power generation of the fuel cell is suppressed, and then stops the supply of fuel gas to the fuel cell by the fuel gas supply unit to put the fuel cell into the complete shutdown state.

[0008] According to this aspect, when the fuel cell is switched from a run-of-the-mill power generation state to a completely stopped state, the fuel cell is temporarily switched to an intermittently stopped state during this period. By switching the fuel cell to an intermittently stopped state in this manner, the supply of oxidant gas by the oxidant gas supply unit is stopped or the supply amount is reduced, and then the supply of fuel gas by the fuel gas supply unit is stopped, thereby switching the fuel cell to a completely stopped state.

[0009] This reduces the amount of oxidant gas remaining in the fuel cell when the fuel cell goes from a run-of-the-mill state to a completely shut-down state, thereby preventing the catalyst in the fuel cell from being deteriorated by the oxidant gas, and thus preventing the progression of deterioration of the fuel cell caused by the process of shutting down the power generation of the fuel cell.

[0010] In the above aspect, it is preferable that the fuel cell has a current measuring unit that measures the current value of the fuel cell, and the control unit switches the fuel cell to the completely stopped state after the measured value of the current measuring unit falls below a predetermined current value after switching the fuel cell to the intermittent stopped state.

[0011] According to this aspect, after the fuel cell enters an intermittent shutdown state, the fuel cell can be brought to a complete shutdown state after the oxidant gas has been sufficiently consumed. This reliably reduces the amount of oxidant gas remaining in the fuel cell when the fuel cell goes from an intermittent shutdown state to a complete shutdown state, more effectively preventing the fuel cell catalyst from being deteriorated by the oxidant gas. Therefore, it is possible to more effectively prevent the progression of fuel cell deterioration caused by the fuel cell power generation shutdown process.

[0012] In the above aspect, it is preferable that the control unit puts the motor into the completely stopped state after a predetermined time has elapsed since the motor was put into the intermittently stopped state.

[0013] According to this aspect, after the fuel cell enters an intermittent shutdown state, the fuel cell can be brought to a complete shutdown state after the oxidant gas has been sufficiently consumed. This reliably reduces the amount of oxidant gas remaining in the fuel cell when the fuel cell goes from an intermittent shutdown state to a complete shutdown state, more effectively preventing the fuel cell catalyst from being deteriorated by the oxidant gas. Therefore, it is possible to more effectively prevent the progression of fuel cell deterioration caused by the fuel cell power generation shutdown process.

[0014] In the above aspect, it is preferable that the control unit has a current measuring unit that measures the current value of the fuel cell, and when there is a request to switch to the completely stopped state while the fuel cell is in the intermittently stopped state, the control unit switches to the completely stopped state after the measured value of the current measuring unit falls below a predetermined current value.

[0015] According to this aspect, when a request is made to completely stop the fuel cell while the fuel cell is in an intermittent stop state, the fuel cell can be switched from the intermittent stop state to the completely stopped state after the oxidant gas has been sufficiently consumed. This makes it possible to reduce the amount of oxidant gas remaining in the fuel cell when the fuel cell is switched from the intermittent stop state to the completely stopped state. Therefore, when a request is made to completely stop the fuel cell while the fuel cell is in an intermittent stop state, it is possible to prevent the catalyst of the fuel cell from being deteriorated by the oxidant gas when the fuel cell is switched from the intermittent stop state to the completely stopped state.

[0016] In the above aspect, if a request to change to the completely stopped state is made when the control unit is in the intermittent stopped state, it is preferable that the control unit change to the completely stopped state after a predetermined time has elapsed since the request to change to the intermittent stopped state was made.

[0017] According to this aspect, when a request is made to completely stop the fuel cell while the fuel cell is in an intermittent stop state, the fuel cell can be switched from the intermittent stop state to the completely stopped state after the oxidant gas has been sufficiently consumed. This makes it possible to reduce the amount of oxidant gas remaining in the fuel cell when the fuel cell is switched from the intermittent stop state to the completely stopped state. Therefore, when a request is made to completely stop the fuel cell while the fuel cell is in an intermittent stop state, it is possible to prevent the catalyst of the fuel cell from being deteriorated by the oxidant gas when the fuel cell is switched from the intermittent stop state to the completely stopped state.

[0018] In the above aspect, it is preferable that the predetermined current value is changed according to the current value of the fuel cell in the state of spontaneous power generation.

[0019] According to this aspect, the amount of oxidant gas remaining in the fuel cell can be reduced when the fuel cell transitions from an intermittent shutdown state to a complete shutdown state, depending on the power generation state of the fuel cell when the fuel cell is in a run-of-the-mill power generation state, thereby more effectively reducing the deterioration of the fuel cell catalyst due to the oxidant gas.

[0020] In the above aspect, it is preferable that the predetermined time be changed in accordance with the current value of the fuel cell in the state of spontaneous power generation.

[0021] According to this aspect, the amount of oxidant gas remaining in the fuel cell can be reduced when the fuel cell transitions from an intermittent shutdown state to a complete shutdown state, depending on the power generation state of the fuel cell when the fuel cell is in a run-of-the-mill power generation state, thereby more effectively reducing the deterioration of the fuel cell catalyst due to the oxidant gas.

[0022] According to the fuel cell system of the present disclosure, the progress of deterioration of the fuel cell caused by the process of stopping power generation of the fuel cell can be suppressed.

[0023] FIG. 1 is a configuration diagram of a fuel cell system (open cathode system) of a first embodiment; FIG. 2 is a flowchart showing the content of control performed in the first embodiment; FIG. 3 is a diagram showing an example of a map that defines the relationship between the FC current value when the FC stack is in a natural power generation state and a predetermined current value when the FC stack is changed from an intermittently stopped state to a completely stopped state; FIG. 4 is a diagram showing an example of a map that defines the relationship between the FC current value when the FC stack is in a natural power generation state and a predetermined time when the FC stack is changed from an intermittently stopped state to a completely stopped state; FIG. 5 is a configuration diagram of a fuel cell system (closed cathode system) of a second embodiment; and FIG. 6 is a flowchart showing the content of control performed in the second embodiment.

[0024] An embodiment of a fuel cell system according to the present disclosure will now be described.

[0025] First Embodiment First, a fuel cell system 1 according to a first embodiment will be described.

[0026] 1, in the fuel cell system 1 of this embodiment, an FC stack 11, a battery 12, and an inverter 13 (or a motor) are connected in parallel, forming a simple system configuration that does not include a DC-DC converter. In other words, the fuel cell system 1 is a DC-DC converter-less system.

[0027] The DC-DC converter is a device that converts the FC voltage supplied to the battery 12. The FC stack 11 is an example of a "fuel cell" in the present disclosure. The FC voltage is the voltage of the power generated by the FC stack 11.

[0028] The fuel cell system 1 also includes a hydrogen system 21 and an air and cooling system 22 .

[0029] The FC stack 11 generates power by receiving a supply of fuel gas and an oxidant gas. In this embodiment, the fuel gas is hydrogen gas, and the oxidant gas is air. That is, the FC stack 11 generates power by receiving a supply of hydrogen gas from a hydrogen system 21 and a supply of air from an air / cooling system 22. The power generated by the FC stack 11 is then supplied to the battery 12 and the inverter 13.

[0030] The fuel cell system 1 is also provided with a current sensor 14. The current sensor 14 is a sensor that measures the output current value of the FC stack 11 (i.e., the current value of the power generated by the FC stack 11, hereinafter referred to as the "FC current value"). The current sensor 14 is an example of the "current measuring unit" of the present disclosure.

[0031] The battery 12 is connected to the FC stack 11 and is charged with the power generated by the FC stack 11. The battery 12 is also connected to the inverter 13 and supplies the charged power to the inverter 13.

[0032] The hydrogen system 21 is provided on the anode side of the FC stack 11. The hydrogen system 21 includes a hydrogen gas supply passage 31, a hydrogen off-gas discharge passage 32, and a hydrogen gas filling passage 33.

[0033] The hydrogen gas supply passage 31 is a passage for supplying hydrogen gas from a hydrogen tank 41 in which hydrogen gas is stored to the FC stack 11. The hydrogen off-gas discharge passage 32 is a passage for discharging hydrogen gas (i.e., hydrogen off-gas) discharged from the FC stack 11. The hydrogen gas filling passage 33 is a passage for filling hydrogen gas into the hydrogen tank 41 from a filling port 51.

[0034] The hydrogen system 21 also includes, in order from the hydrogen tank 41 side, a valve 61, a pressure reducing valve 62, an injector 63, and a pressure sensor 64 in the hydrogen gas supply passage 31. The injector 63 is an example of the "fuel gas supply unit" of the present disclosure.

[0035] The valve 61 switches between supplying and blocking hydrogen gas from the hydrogen tank 41 to the hydrogen gas supply passage 31. The pressure reducing valve 62 is a pressure regulating valve for reducing the pressure of hydrogen gas. The injector 63 is a device that injects hydrogen gas guided from the hydrogen tank 41 downstream, and supplies hydrogen gas to the FC stack 11. The pressure sensor 64 is a pressure measuring unit that measures the outlet fuel pressure of the injector 63 (i.e., the pressure of the hydrogen gas at the outlet of the injector 63). The injector 63 is an example of a "fuel gas supply unit" in this disclosure.

[0036] Furthermore, the hydrogen system 21 is provided with an exhaust drain valve 71 in the hydrogen off-gas discharge passage 32, which switches between discharging and blocking the hydrogen off-gas and moisture.

[0037] On the other hand, the air and cooling system 22 is provided on the cathode side of the FC stack 11. The air and cooling system 22 includes an air supply passage 81, an air off-gas discharge passage 82, and a fan 83. The fan 83 is an example of the "oxidant gas supply unit" of the present disclosure.

[0038] The air supply passage 81 is a passage for supplying air from outside the fuel cell system 1 to the FC stack 11. The air off-gas discharge passage 82 is a passage for discharging air (i.e., air off-gas) discharged from the FC stack 11.

[0039] The fan 83 supplies air to the FC stack 11 through the air supply passage 81 and discharges air off-gas from the FC stack 11 through the air off-gas discharge passage 82 .

[0040] In this embodiment, the fan 83 not only serves to supply air to the FC stack 11 via the air supply passage 81, thereby causing the FC stack 11 to generate electricity using that air, but also serves to cool the FC stack 11. In this way, the fuel cell system 1 of this embodiment is an open cathode system in which the air supplied to the FC stack 11 by the fan 83 is used as a cooling gas for the FC stack 11.

[0041] The fuel cell system 1 further includes a control unit 15. The control unit 15 is a device having, for example, an arithmetic processing unit such as a CPU, a memory unit such as a ROM for storing control programs and control data processed by the CPU and a RAM used as various work areas for control processing, and an input / output interface unit. The control unit 15 performs various controls of the fuel cell system 1 in accordance with the control programs stored in the memory unit.

[0042] In this embodiment, the control unit 15 controls various components of the fuel cell system 1, such as the inverter 13, the valve 61, the pressure reducing valve 62, the injector 63, the exhaust drain valve 71, and the fan 83. The control unit 15 also obtains the measured value of the outlet fuel pressure of the injector 63 from the pressure sensor 64 and the measured value of the FC current value from the current sensor 14.

[0043] (Operation of Fuel Cell System) In the fuel cell system 1 configured as described above, the hydrogen gas supplied from the hydrogen gas supply passage 31 to the FC stack 11 is used for power generation in the FC stack 11, and then discharged from the FC stack 11 as hydrogen off-gas via the hydrogen off-gas discharge passage 32 to the outside of the fuel cell system 1. In addition, the air supplied from the air supply passage 81 to the FC stack 11 is used for power generation in the FC stack 11, and then discharged from the FC stack 11 as air off-gas via the air off-gas discharge passage 82 to the outside of the fuel cell system 1.

[0044] The electric power generated by the FC stack 11 is supplied to the battery 12 to charge the battery 12, or is supplied to the inverter 13 to drive the inverter 13. The inverter 13 is also supplied with electric power from the battery 12.

[0045] (Regarding a DCDC converter-less system) As shown in FIG. 1 , the fuel cell system 1 of this embodiment is a so-called DCDC converter-less system in which a DCDC converter is not disposed between the FC stack 11 and the battery 12. Therefore, in the fuel cell system 1, the FC voltage is equal to (or approximately equal to) the battery voltage, and the FC current depends on the battery voltage. In other words, the fuel cell system 1 supplies the power generated in the FC stack 11 to the battery 12 and the inverter 13 without converting the FC voltage. The FC current is the current of the power generated in the FC stack 11. The battery voltage is the voltage of the battery 12.

[0046] In the fuel cell system 1, the FC voltage is equal to the battery voltage in this way, so the FC stack 11 generates power in a natural manner according to the battery voltage.

[0047] (Regarding control performed when processing to stop power generation of FC stack) In a DCDC converter-less fuel cell system 1, when processing to stop power generation of the FC stack 11 is performed to change the FC stack 11 from a state of uninterrupted power generation (i.e., a state in which power generation is being performed uninterrupted) to a state of complete stop (i.e., a state in which power generation of the FC stack 11 is completely stopped), air may remain in the FC stack 11, and this remaining air may oxidize the catalyst (carbon) in the FC stack 11, accelerating deterioration of the FC stack 11. Note that a specific example of a situation in which the FC stack 11 is brought to a complete stop state is when the key switch is turned off in a vehicle equipped with the fuel cell system 1.

[0048] Therefore, in this embodiment, measures are taken to suppress the progression of deterioration of the FC stack 11 due to the process of stopping power generation of the FC stack 11.

[0049] Specifically, when a request is made to put the FC stack 11 into a completely stopped state while the FC stack 11 is in a state of natural power generation, the control unit 15 puts the FC stack 11 into an intermittent stopped state and then into a completely stopped state.

[0050] Here, when the FC stack 11 is put into an intermittent stop state, the supply of hydrogen gas into the FC stack 11 by the injector 63 continues, but the supply of air to the FC stack 11 by the fan 83 is stopped, or the amount of air supplied to the FC stack 11 by the fan 83 is reduced, thereby suppressing the power generation of the FC stack 11 more than when it is in a continuous power generation state.

[0051] In addition, when the FC stack 11 is brought to a completely stopped state, the supply of hydrogen gas into the FC stack 11 by the injector 63 is stopped, and the supply of air to the FC stack 11 by the fan 83 is stopped, thereby stopping power generation by the FC stack 11.

[0052] More specifically, the control unit 15 performs control as shown in Fig. 2. As shown in Fig. 2, when there is an FC stop request (i.e., a request to completely stop power generation by the FC stack 11) (step S1: YES), the control unit 15 determines whether there is a request for flow-through power generation (step S2).

[0053] Then, if there is a request for flow-through power generation (i.e., the FC stack 11 is in a flow-through power generation state) (step S2: YES), the control unit 15 puts the FC stack 11 into an intermittent stop state (also called a low current mode state) (step S3).

[0054] Here, in step S3, when the control unit 15 puts the FC stack 11 into an intermittent stop state, it stops the supply of air to the FC stack 11 by the fan 83 or reduces the amount of air supplied to the FC stack 11 by the fan 83. Note that the hydrogen pressure when the FC stack 11 is in a state of continuous power generation is, for example, 50 kPaG.

[0055] In this way, when the FC stack 11 is in an intermittent stop state, the control unit 15 stops the supply of air to the FC stack 11 by the fan 83, or reduces the amount of air supplied to the FC stack 11 by the fan 83, thereby making the FC current value smaller than when the FC stack 11 is in a natural power generation state.

[0056] In this way, when the FC stack 11 is in a state of natural power generation and there is a request to put the FC stack 11 into a completely stopped state, the control unit 15 first puts the FC stack 11 into an intermittently stopped state.

[0057] 2, next, the control unit 15 determines whether the FC current value measured by the current sensor 14 is equal to or less than a predetermined current value PC (step S4). Here, the predetermined current value PC is set to, for example, 10% of the FC current value when the FC stack 11 is in a state of natural power generation. For example, if the FC current value when the FC stack 11 is in a state of natural power generation is 50 A, the predetermined current value PC is set to 5 A.

[0058] If the FC current measured by the current sensor 14 is equal to or less than the predetermined current value PC (step S4: YES), the control unit 15 stops the injection of hydrogen gas from the injector 63 and brings the FC stack 11 to a complete stop state (step S5). At this time, the fan 83 remains stopped.

[0059] In this way, in this embodiment, when there is a request to put the FC stack 11 into a completely stopped state while the FC stack 11 is in a state of natural power generation, the control unit 15 puts the FC stack 11 into an intermittently stopped state, and then puts the FC stack 11 into a completely stopped state after the FC current value becomes equal to or less than a predetermined current value PC.

[0060] At this time, the predetermined current value PC is changed according to the power generation state of the FC stack 11 when the FC stack 11 is in a state of uninterrupted power generation, for example, the FC current value. Specifically, the larger the FC current value when the FC stack 11 is in a state of uninterrupted power generation, the larger the predetermined current value PC is set to. Therefore, for example, the control unit 15 uses the map shown in FIG. 3 to determine the predetermined current value PC based on the FC current value when the FC stack 11 is in a state of uninterrupted power generation.

[0061] If the FC current value is greater than the predetermined current value PC in step S4 (step S4: NO), the control unit 15 returns to the process in step S3.

[0062] Furthermore, if there is no request for continuous power generation in step S2 (step S2: NO), that is, if there is a request for intermittent stop (i.e., power generation by the FC stack 11 is in an intermittent stop state), the control unit 15 proceeds to processing in step S4.

[0063] In this way, when the control unit 15 receives a request to put the FC stack 11 into a completely stopped state while the FC stack 11 is in an intermittently stopped state, it proceeds to step S4 and puts the FC stack 11 into a completely stopped state after the FC current value becomes equal to or less than the predetermined current value PC.

[0064] As a variant, in step S4, the control unit 15 may determine whether a predetermined time PT has elapsed since the FC stack 11 was put into an intermittent stop state (or since a request to put it into an intermittent stop state) (step S4).

[0065] At this time, the predetermined time PT is changed according to the power generation state of the FC stack 11 when the FC stack 11 is in a run-of-the-mill power generation state, for example, the FC current value. Specifically, the larger the FC current value when the FC stack 11 is in a run-of-the-mill power generation state, the longer the predetermined time PT is made. Therefore, for example, the control unit 15 uses the map shown in Figure 4 to determine the predetermined time PT based on the FC current value when the FC stack 11 is in a run-of-the-mill power generation state (denoted as "current value (A) during run-of-the-mill power generation" in the figure).

[0066] Then, when the predetermined time PT has elapsed (step S4: YES), the control unit 15 stops the injection of hydrogen gas from the injector 63, and puts the FC stack 11 into a completely stopped state (step S5).

[0067] In this way, when there is a request to put the FC stack 11 into a completely stopped state while the FC stack 11 is in a state of natural power generation (step S2: YES), the control unit 15 may, as a variant, put the FC stack 11 into a completely stopped state after a predetermined time PT has elapsed since the FC stack 11 was put into an intermittent stopped state.

[0068] In addition, if there is a request to put the FC stack 11 into a completely stopped state when the FC stack 11 is in an intermittently stopped state (step S2: NO), as a variant, the control unit 15 may put the FC stack 11 into a completely stopped state after a predetermined time PT has elapsed since the request to put the FC stack 11 into an intermittently stopped state.

[0069] (Effects of this embodiment) As described above, according to this embodiment, when the FC stack 11 is in a state of natural power generation and there is a request to put the FC stack 11 into a completely stopped state, the control unit 15 puts the FC stack 11 into an intermittent stopped state and then puts it into a completely stopped state.

[0070] In this way, when the FC stack 11 is changed from a state of power generation as it goes along to a state of complete shutdown, the FC stack 11 is temporarily put into an intermittent shutdown state during that time. By putting the FC stack 11 into an intermittent shutdown state in this way, the supply of air by the fan 83 is stopped or the amount of supply is reduced, and then the supply of hydrogen gas by the injector 63 is stopped, and the FC stack 11 is put into a complete shutdown state.

[0071] As a result, when the FC stack 11 goes from a going-around state to a completely stopped state, the supply of air to the FC stack 11 by the fan 83 can be stopped, or the amount of air supplied to the FC stack 11 by the fan 83 can be reduced, thereby reducing the amount of air remaining in the FC stack 11 and preventing the catalyst in the FC stack 11 from being deteriorated by the air. Therefore, the progression of deterioration of the FC stack 11 caused by the process of stopping power generation of the FC stack 11 can be prevented.

[0072] In addition, the control unit 15 puts the FC stack 11 into a completely stopped state after the measurement value of the current sensor 14 falls below a predetermined current value PC after the FC stack 11 is put into an intermittently stopped state, or after a predetermined time PT has elapsed after the FC stack 11 is put into an intermittently stopped state.

[0073] In this way, after the FC stack 11 has entered an intermittent stop state, the amount of air supplied to the FC stack 11 can be reliably reduced before the FC stack 11 is placed in a completely stopped state. This reliably reduces the amount of air remaining in the FC stack 11 when the FC stack 11 goes from an intermittent stop state to a completely stopped state, making it possible to more effectively prevent the catalyst in the FC stack 11 from being deteriorated by air. Therefore, it is possible to more effectively prevent the progression of deterioration of the FC stack 11 caused by the process of stopping power generation of the FC stack 11.

[0074] In addition, if there is a request to put the FC stack 11 into a completely stopped state when the FC stack 11 is in an intermittent stopped state, the control unit 15 puts the FC stack 11 into a completely stopped state after the measurement value of the current sensor 14 falls below a predetermined current value PC, or after a predetermined time PT has elapsed since the request to put the FC stack 11 into an intermittent stopped state.

[0075] In this way, if there is a request to put the FC stack 11 into a completely stopped state when the FC stack 11 is in an intermittent stopped state, the FC stack 11 can be changed from an intermittently stopped state to a completely stopped state after the amount of air supplied to the FC stack 11 has decreased. This makes it possible to reduce the amount of air remaining in the FC stack 11 when the FC stack 11 changes from an intermittently stopped state to a completely stopped state. Therefore, if there is a request to put the FC stack 11 into a completely stopped state when the FC stack 11 is in an intermittently stopped state, it is possible to prevent the catalyst in the FC stack 11 from being deteriorated by air when the FC stack 11 is changed from an intermittently stopped state to a completely stopped state.

[0076] Furthermore, the predetermined current value PC or the predetermined time PT is changed according to the FC current value when the FC stack 11 is in a state of natural power generation. Specifically, the larger the FC current value when the FC stack 11 is in a state of natural power generation, the larger the predetermined current value PC or the longer the predetermined time PT.

[0077] In this way, the amount of air remaining in the FC stack 11 can be reduced when the FC stack 11 changes from an intermittent stop state to a complete stop state, depending on the power generation state of the FC stack 11 when the FC stack 11 is in a continuous power generation state. As a result, deterioration of the catalyst in the FC stack 11 due to air can be more effectively reduced.

[0078] Second Embodiment Next, a fuel cell system 2 of a second embodiment will be described. Differences from the fuel cell system 1 of the first embodiment will be described, and descriptions of commonalities with the fuel cell system 1 will be omitted.

[0079] (General Configuration of Fuel Cell System) The fuel cell system 2 of this embodiment is a closed cathode system, and as shown in FIG. 5, the fuel cell system 2 has an air system 122 and a cooling system 123.

[0080] The air system 122 is provided on the cathode side of the FC stack 11. The air system 122 includes an air supply passage 181 and an air off-gas discharge passage 182.

[0081] The air supply passage 181 is a passage for supplying air to the FC stack 11 from outside the fuel cell system 1. The air off-gas discharge passage 182 is a passage for discharging air off-gas, which is air not used for power generation, from the FC stack 11.

[0082] The air system 122 includes an air compressor 191 and an inlet air valve 192 in the air supply passage 181. The air compressor 191 is a device that supplies air to the FC stack 11. The inlet air valve 192 is provided downstream of the air compressor 191 in the air flow, and is a valve that controls the flow rate of air supplied to the FC stack 11. The air compressor 191 is an example of the "oxidant gas supply unit" of this disclosure.

[0083] The air system 122 also includes an outlet air valve 193 in the air off-gas discharge passage 182. The outlet air valve 193 is a valve that controls the flow rate of air off-gas discharged from the FC stack 11 to the air off-gas discharge passage 182.

[0084] The cooling system 123 is a system that cools the FC stack 11, and includes a cooling water passage 201 and a cooling fan 202. The cooling water passage 201 is a passage through which cooling water flows. The cooling fan 202 is a device that cools the cooling water flowing through the cooling water passage 201.

[0085] In this embodiment, the control unit 15 controls the air compressor 191 , the inlet air valve 192 , the outlet air valve 193 , and the cooling fan 202 .

[0086] (Operation of the fuel cell system) In the fuel cell system 2 configured as described above, in the air system 122, the air supplied from the air supply passage 181 to the FC stack 11 is used for power generation in the FC stack 11, and then discharged from the FC stack 11 as air off-gas to the outside via the air off-gas discharge passage 182.

[0087] (Control Performed When Processing to Stop Power Generation of FC Stack) In this embodiment, the control unit 15 performs control shown in FIG. 6 as control performed when processing to stop power generation of the FC stack 11 .

[0088] As shown in Figure 6, in step S13, the control unit 15 puts the FC stack 11 into an intermittent stop state, at which time the supply of air to the FC stack 11 by the air compressor 191 is stopped or the amount of air supplied to the FC stack 11 by the air compressor 191 is reduced.

[0089] In step S15, the control unit 15 stops the injector 63 and closes the inlet air valve 192 and the outlet air valve 193 to completely stop the FC stack 11. At this time, the air compressor 191 stops supplying air.

[0090] In this embodiment, as in the first embodiment, the progress of deterioration of the FC stack 11 can be suppressed by performing the process of stopping power generation of the FC stack 11 .

[0091] It should be noted that the above-described embodiments are merely examples and do not limit the present disclosure in any way. It goes without saying that various improvements and modifications are possible within the scope of the gist of the present disclosure.

[0092] REFERENCE SIGNS LIST 1 fuel cell system 2 fuel cell system 11 FC stack 12 battery 13 inverter 14 current sensor 15 control unit 21 hydrogen system 22 air system / cooling system 31 hydrogen gas supply passage 63 injector 81 air supply passage 83 fan 122 air system 123 cooling system 181 air supply passage 182 air off-gas discharge passage 191 air compressor 192 inlet air valve 193 outlet air valve PC predetermined current value PT predetermined time

Claims

1. A fuel cell system having a fuel cell and a battery that charges with power generated by the fuel cell, wherein the output current of the fuel cell depends on the voltage of the battery, comprising: a fuel gas supply unit that supplies fuel gas to the fuel cell; an oxidant gas supply unit that supplies oxidant gas to the fuel cell; and a control unit that controls the fuel gas supply unit and the oxidant gas supply unit, wherein when the fuel cell is in a state of natural power generation in which it generates power according to the voltage of the battery and there is a request to put the fuel cell into a complete shutdown state to stop power generation, the control unit stops or reduces the supply of oxidant gas to the fuel cell by the oxidant gas supply unit to put the fuel cell into an intermittent shutdown state that suppresses power generation, and then stops the supply of fuel gas to the fuel cell by the fuel gas supply unit to put the fuel cell into the complete shutdown state.

2. A fuel cell system according to claim 1, further comprising a current measuring unit that measures the current value of the fuel cell, and wherein the control unit switches the fuel cell to the complete stop state after the measured value of the current measuring unit falls below a predetermined current value after switching the fuel cell to the intermittent stop state.

3. A fuel cell system according to claim 1, wherein the control unit switches the system to the complete stop state after a predetermined time has elapsed since the system was switched to the intermittent stop state.

4. A fuel cell system according to claim 1, further comprising a current measuring unit that measures the current value of the fuel cell, and wherein, when a request is made to switch to the complete stop state while the fuel cell is in the intermittent stop state, the control unit switches to the complete stop state after the measured value of the current measuring unit falls below a predetermined current value.

5. A fuel cell system according to claim 1, wherein, when a request to switch to the complete stop state is made while the fuel cell system is in the intermittent stop state, the control unit switches to the complete stop state after a predetermined time has elapsed since the request to switch to the intermittent stop state was made.

6. A fuel cell system according to claim 2 or 4, characterized in that the predetermined current value is changed according to the current value of the fuel cell in the state of spontaneous power generation.

7. A fuel cell system according to claim 3 or 5, wherein the predetermined time is changed according to the current value of the fuel cell in the state of spontaneous power generation.

Images