Fuel cell system

Abstract

In a fuel cell system, when a difference between an optimum value of an output voltage of a fuel cell corresponding to a measured value of an output current of the fuel cell measured by a current sensor and a measured value of the output voltage of the fuel cell measured by a voltage sensor is defined as an output voltage difference, a control section performs the following processing: when there is a request to stop power generation of the fuel cell, reducing a target pressure of fuel gas supplied by a fuel supply device, that is, a target fuel pressure, to stop power generation of the fuel cell, and when reducing the target fuel pressure of the fuel supply device, varying a reduction rate of the target fuel pressure of the fuel supply device based on the output voltage difference.

Description

Technical Field

[0001] This disclosure relates to a fuel cell system having a fuel cell that receives a supply of fuel gas and oxidant gas to generate electricity. Background Technology

[0002] Patent Document 1 discloses a fuel cell system having a first valve and a second valve, wherein the first valve is used to control the flow rate of oxidant gas (reaction air) supplied to the fuel cell, and the second valve is used to control the flow rate of oxidant exhaust gas (reaction air) discharged from the fuel cell.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2022-185247 Summary of the Invention

[0006] The problem the invention aims to solve

[0007] The fuel cell system disclosed in Patent Document 1 has a first valve and a second valve, which increases the number of components and thus increases the cost of manufacturing and maintenance. In addition, when the fuel cell stops generating electricity, if the flow rate of the oxidant gas supplied to the fuel cell changes, causing a sudden change in the output voltage of the fuel cell, a high load is applied to the fuel cell. Therefore, depending on the condition of the fuel cell, it may deteriorate.

[0008] Therefore, this disclosure was made to solve the above-mentioned problems, and its purpose is to provide a fuel cell system that can reduce costs and stop the fuel cell from generating electricity while suppressing the degradation of the fuel cell.

[0009] Solution for solving the problem

[0010] One aspect of this disclosure, undertaken to address the aforementioned problems, is a fuel cell system comprising: a fuel cell that receives a supply of fuel gas and an oxidant gas to generate electricity; a fuel supply passage for supplying the fuel gas to the fuel cell; a fuel supply device disposed in the fuel supply passage and driven to supply the fuel gas to the fuel cell; and an oxidant gas supply passage for supplying the oxidant gas to the fuel cell. The fuel cell system is characterized in that the output current of the fuel cell depends on the voltage of a battery charged with electricity generated by the fuel cell. The fuel cell system further comprises: a current sensor for measuring the output current of the fuel cell; and an oxidant gas supply passage for supplying the oxidant gas to the fuel cell. The fuel cell includes a pressure sensor that measures the output voltage of the fuel cell and a control unit that controls the fuel supply device. When the difference between the optimal value of the fuel cell's output voltage corresponding to the measured value of the fuel cell's output current (measured by the current sensor) and the measured value of the fuel cell's output voltage (measured by the voltage sensor) is defined as the output voltage difference, the control unit performs the following processing: when there is a request to stop the fuel cell from generating electricity, it reduces the target pressure (i.e., the target combustion pressure) of the fuel gas supplied by the fuel supply device to stop the fuel cell from generating electricity; and when the target combustion pressure of the fuel supply device is reduced, the rate at which the target combustion pressure of the fuel supply device is reduced changes based on the output voltage difference.

[0011] According to this method, the target combustion pressure of the fuel supply device is reduced to stop the fuel supply from the fuel supply device to the fuel cell, thereby stopping the fuel cell from generating electricity (e.g., intermittently stopping). Therefore, the fuel cell can stop generating electricity even without cutting off the supply of oxidant gas to the fuel cell. Consequently, there is no need for equipment (e.g., valves) to cut off the supply of oxidant gas to the fuel cell, thus reducing the number of components in the fuel cell system and lowering the cost of the fuel cell system.

[0012] Furthermore, when reducing the target combustion pressure of the fuel supply device, the rate at which the target combustion pressure of the fuel supply device is reduced is adjusted based on the magnitude of the output voltage difference (i.e., the difference between the optimal value and the measured value of the fuel cell's output voltage), which is an indicator of the fuel cell's state. Therefore, it is possible to reduce the target combustion pressure of the fuel supply device while suppressing fuel cell degradation, thereby stopping the fuel cell from generating electricity.

[0013] In the above-described manner, it is preferable that when the output voltage difference is less than a predetermined value, the control unit sets the decompression speed to a first speed, and when the output voltage difference is greater than or equal to the predetermined value, the control unit sets the decompression speed to a second speed that is slower than the first speed.

[0014] According to this method, a voltage difference exceeding a specified value indicates a state where the fuel cell is prone to degradation. Therefore, when stopping power generation, the target combustion pressure of the fuel cell is gradually reduced. Thus, even in a state prone to degradation, the fuel cell's output voltage will not change abruptly, allowing the fuel cell to stop generating electricity while suppressing degradation.

[0015] In the above-described manner, it is preferable that when the measured value of the output current of the fuel cell, as determined by the current sensor, becomes 0 or approximately 0, the control unit sets the target combustion pressure of the fuel supply device to atmospheric pressure or approximately atmospheric pressure.

[0016] According to this method, when the fuel cell stops generating electricity and the measured value of the fuel cell output current becomes 0 or approximately 0, it is possible to prevent the fuel supply passage from becoming negative pressure (i.e., pressure lower than atmospheric pressure). Therefore, it is possible to prevent oxidant gas from flowing from the oxidant gas supply passage through the fuel cell into the fuel supply passage. Consequently, it is possible to prevent the catalyst within the fuel cell from deteriorating due to oxidant gas.

[0017] In the above-described manner, it is preferable that when the measured value of the output current of the fuel cell, as determined by the current sensor, becomes 0 or approximately 0, the control unit controls the target combustion pressure of the fuel supply device so that the output voltage of the fuel cell becomes a target voltage lower than the voltage of the battery.

[0018] According to this method, when the fuel cell stops generating electricity, a target voltage is set for the fuel cell's output voltage to avoid overvoltage (voltage drop) or high voltage, and corresponding feedback control of the target fuel pressure of the fuel supply device is performed. Therefore, it is possible to prevent the fuel cell's output voltage from becoming overvoltage (voltage drop) or high voltage, thereby suppressing fuel cell degradation.

[0019] The effects of the invention

[0020] The fuel cell system disclosed herein can reduce costs and stop generating electricity while suppressing fuel cell degradation. Attached Figure Description

[0021] Figure 1 This is a diagram showing the general structure of the fuel cell system according to this embodiment.

[0022] Figure 2 This is a diagram showing the IV characteristics of an FC fuel cell stack.

[0023] Figure 3This is an example of a mapping diagram that specifies the relationship between measured FC current and estimated FC voltage.

[0024] Figure 4 This is an example of a mapping diagram that specifies the relationship between measured and determined FC current values.

[0025] Figure 5 This is a flowchart illustrating the content of the control performed in the first embodiment.

[0026] Figure 6 This is a flowchart illustrating the control procedures performed in the second embodiment. Detailed Implementation

[0027] The embodiments of the fuel cell system disclosed herein will be described.

[0028] <Overview of Fuel Cell Systems>

[0029] First, an overview of the fuel cell system 1 of this embodiment will be described. The fuel cell system 1 is a system that is mounted on a fuel cell vehicle and supplies electricity to its drive motor (not shown).

[0030] (Overview of the structure of a fuel cell system)

[0031] like Figure 1 As shown, the fuel cell system 1 includes an FC stack 11, a hydrogen system 12, an air system 13, a cooling system 14, and a control unit 15. Furthermore, the FC stack 11 is an example of the "fuel cell" of this disclosure.

[0032] The FC fuel cell stack 11 generates electricity by receiving a supply of fuel gas and an oxidant gas. In this embodiment, the fuel gas is hydrogen, and the oxidant gas is air. That is, the FC fuel cell stack 11 generates electricity by receiving a supply of hydrogen from the hydrogen system 12 and a supply of air from the air system 13. The electricity generated by the FC fuel cell stack 11 is then supplied to the battery 101 and the inverter 102 (or the motor).

[0033] In addition, a current sensor 16 and a voltage sensor 17 are provided in the fuel cell system 1. The current sensor 16 is a sensor that measures the output current of the FC stack 11 (i.e., the current of the electricity generated by the FC stack 11, hereinafter referred to as "FC current"). The voltage sensor 17 is a sensor that measures the output voltage of the FC stack 11 (i.e., the voltage of the electricity generated by the FC stack 11, hereinafter referred to as "FC voltage").

[0034] The hydrogen system 12 is located on the anode side of the FC stack 11. The hydrogen system 12 includes a hydrogen filling passage 20, a hydrogen supply passage 21, and a hydrogen exhaust passage 22.

[0035] Hydrogen filling passage 20 is a passage for filling hydrogen from filling port 30 to hydrogen tank 31. Hydrogen supply passage 21 is a passage for supplying hydrogen from hydrogen tank 31 to FC stack 11, and is an example of the "fuel supply passage" of this disclosure.

[0036] Hydrogen exhaust passage 22 is a passage for discharging hydrogen, i.e. hydrogen waste gas, that is not used in power generation from FC stack 11.

[0037] The hydrogen system 12 includes, in the hydrogen supply passage 21, a valve 32, a pressure reducing valve 33, an injector 34, and a pressure sensor 35 in sequence from the hydrogen tank 31 side.

[0038] Valve 32 is used to switch the supply and cut-off of hydrogen from hydrogen tank 31 to hydrogen supply passage 21, or to switch the supply and cut-off of hydrogen from filling port 30 to hydrogen tank 31. Pressure reducing valve 33 is a pressure regulating valve used to reduce the pressure of hydrogen.

[0039] Injector 34 is a valve driven to supply (i.e., inject) hydrogen to FC stack 11, and is an example of the "fuel supply device" of this disclosure. Pressure sensor 35 measures the pressure (i.e., combustion pressure or outlet pressure) of the hydrogen injected from injector 34.

[0040] In addition, the hydrogen system 12 has a gas-liquid separator 41 and an exhaust drain valve 42 in the hydrogen exhaust passage 22.

[0041] The gas-liquid separator 41 is a device used to separate moisture from hydrogen waste gas. The exhaust drain valve 42 is a valve used to control the discharge of hydrogen waste gas from the FC stack 11 to the outside.

[0042] An air system 13 is located on the cathode side of the FC stack 11. The air system 13 includes an air supply passage 51 and an air exhaust passage 52.

[0043] Air supply passage 51 is a passage for supplying air from outside the fuel cell system 1 to the FC stack 11, and is an example of the "oxidant gas supply passage" of this disclosure. Air exhaust passage 52 is a passage for discharging air, i.e., air exhaust gas, that is not used in power generation from the FC stack 11.

[0044] The air system 13 includes an air compressor 61 in the air supply passage 51. The air compressor 61 is a device that supplies air to the FC stack 11.

[0045] The air system 13 of this embodiment does not have an inlet air valve for controlling the flow rate of air supplied from the air supply passage 51 to the FC stack 11, or an outlet air valve for controlling the flow rate of air exhaust discharged from the FC stack 11 to the air exhaust passage 52.

[0046] The cooling system 14 is a system for cooling the FC stack 11, and includes a cooling water passage 81 and a cooling fan 82. The cooling water passage 81 is a passage for the flow of cooling water. In addition, the cooling fan 82 is a device for cooling the cooling water flowing in the cooling water passage 81.

[0047] The control unit 15 is, for example, a device having a processing unit such as a CPU, a storage unit such as ROM and RAM, and an input / output interface unit. The ROM stores control programs and control data processed by the CPU, and the RAM is used as various operating areas for control processing. Furthermore, the control unit 15 performs various controls on the fuel cell system 1 according to the control programs stored in the storage unit.

[0048] Specifically, the control unit 15 performs, for example, drive control of the injector 34 and speed control of the air compressor 61. In addition, the control unit 15 also controls valves 32, pressure reducing valve 33, exhaust / drain valve 42, cooling fan 82, etc. Furthermore, the control unit 15 acquires information from the measured values ​​of current sensor 16, voltage sensor 17, and pressure sensor 35.

[0049] (Regarding the role of fuel cell systems)

[0050] In the fuel cell system 1 with the structure described above, in the hydrogen system 12, the hydrogen supplied to the FC stack 11 from the hydrogen supply passage 21 is used by the FC stack 11 to generate electricity, and then discharged to the outside as hydrogen exhaust gas from the FC stack 11 via the hydrogen exhaust gas discharge passage 22. Similarly, in the air system 13, the air supplied to the FC stack 11 from the air supply passage 51 is used by the FC stack 11 to generate electricity, and then discharged to the outside as air exhaust gas from the FC stack 11 via the air exhaust gas discharge passage 52.

[0051] (Regarding systems without DC-DC converters)

[0052] like Figure 1As shown, in the fuel cell system 1 of this embodiment, the FC stack 11, the battery 101, and the inverter 102 (or motor) are connected in parallel, forming a simple system structure without a DC-DC converter. That is, the fuel cell system 1 is a system without a DC-DC converter. Furthermore, the DC-DC converter is a device that converts the FC voltage. Additionally, the battery 101 is connected to the FC stack 11 and is charged with electricity generated by the FC stack 11. Furthermore, the battery 101 is connected to the inverter 102, supplying the charged electricity to the inverter 102.

[0053] Thus, the fuel cell system 1 of this embodiment is a system without a DC-DC converter. Since the FC voltage is equal to (or approximately equal to) the voltage of the battery 101, the FC current depends on the voltage of the battery 101. In other words, the fuel cell system 1 supplies the power generated by the FC stack 11 to the battery 101 and the inverter 102 without converting the FC voltage.

[0054] Furthermore, in the fuel cell system 1, since the FC voltage is equal to the voltage of the battery 101, the FC stack 11 generates electricity on demand in accordance with the voltage of the battery 101 during power generation. In addition, when the SOC (i.e., charge rate) of the battery 101 increases, the FC voltage decreases relative to the voltage of the battery 101, thereby intermittently stopping the on-demand power generation of the FC stack 11.

[0055] <Regarding control measures implemented during intermittent shutdowns of FC stack power generation>

[0056] When the power generation of the FC stack 11 is intermittently stopped, it is considered to cut off the air supply to the FC stack 11 and exhaust the air from the FC stack 11 through an air valve (not shown). However, the number of components increases due to the presence of the air valve, thus increasing the cost of the fuel cell system 1 (i.e., the cost required for manufacturing and maintenance).

[0057] Therefore, in this embodiment, when the power generation intermittent of the FC stack 11 is stopped, the supply of hydrogen from the injector 34 to the FC stack 11 is stopped, thereby stopping the power generation intermittent of the FC stack 11.

[0058] Specifically, when there is a request to stop the power generation of the FC stack 11, the control unit 15 reduces the target pressure of the hydrogen supplied (i.e., injected) by the injector 34, i.e. the target combustion pressure (hereinafter referred to as "target combustion pressure of injector 34"), to stop the power generation of the FC stack 11.

[0059] Moreover, although reducing the target combustion pressure of the injector 34 in this way can stop the intermittent power generation of the FC stack 11, if the flow rate of hydrogen supplied from the injector 34 to the FC stack 11 changes and the FC voltage changes abruptly, a high load will be placed on the FC stack 11. Therefore, depending on the condition of the FC stack 11, the FC stack 11 may deteriorate.

[0060] Therefore, when the control unit 15 reduces the target combustion pressure of the injector 34, it changes the rate of reduction of the target combustion pressure of the injector 34 based on the FC overvoltage, which is an indicator of the state of the FC stack 11.

[0061] Here, "FC overvoltage" is the difference between the estimated value of the FC voltage corresponding to the measured value of the FC current (hereinafter referred to as "FC current measured value") measured by the current sensor 16 and the measured value of the FC voltage (hereinafter referred to as "FC voltage measured value") measured by the voltage sensor 17, which is an example of the "output voltage difference" of this disclosure. Furthermore, the FC voltage estimated value is the FC voltage value that is most suitable for improving the power generation efficiency of the FC stack 11 with respect to the FC current measured value, which is an example of the "optimal value of the fuel cell output voltage" of this disclosure.

[0062] For example, in the IV characteristics of FC stack 11, the measured FC current, estimated FC voltage, and measured FC voltage are respectively as follows: Figure 2 As shown in the diagram. Furthermore, at this time, the FC overvoltage is as follows: Figure 2 As shown, this is expressed as the difference between the estimated FC voltage and the measured FC voltage, i.e., the FC voltage difference. Furthermore, the estimated FC voltage is the value of the FC voltage estimated based on the measured FC current when the FC stack 11 is new, for example, using... Figure 3 The mapping diagram is used to estimate the FC voltage based on the measured FC current.

[0063] (First Embodiment)

[0064] Here, the control performed during the intermittent cessation of power generation in the FC stack 11 will first be described in the first embodiment. In this embodiment, the control unit 15 performs... Figure 5 The flowchart shows the control of the content.

[0065] like Figure 5 As shown, the control unit 15 determines whether there is a switching request from on-demand power generation to intermittent shutdown (step S1).

[0066] Furthermore, in the event of a request to switch from on-demand power generation to intermittent shutdown (i.e., during intermittent shutdown) (step S1: "Yes"), the control unit 15 stops the air compressor 61 (step S2).

[0067] Next, the control unit 15 determines whether the FC overvoltage is less than the judgment value (step S3).

[0068] In addition, for example, using Figure 4 The mapping diagram is used to calculate the judgment value based on the FC current measurement. Additionally, in Figure 4 In the mapping diagram, the judgment value varies proportionally to the measured FC current value; for example, the judgment value is 3V when the measured FC current is 10A, and the judgment value is 5V when the measured FC current is 30A. Furthermore, the judgment value is an example of the "prescribed value" of this disclosure.

[0069] Return to Figure 5 As explained, when the FC overvoltage is less than the determination value (step S3: "Yes"), the control unit 15 causes the target combustion pressure of the injector 34 to decrease significantly (i.e., rapidly) (step S4).

[0070] In this way, when the FC overvoltage is small, it is assumed that even if the flow rate of hydrogen supplied from the injector 34 to the FC stack 11 changes and the FC voltage changes suddenly, the FC stack 11 will be in a state that is not easily deteriorated. Therefore, the control unit 15 sets the decompression rate of the target combustion pressure of the injector 34 to a first speed SP1 (e.g., a decompression rate of 5 kPa per second) which is faster than the second speed SP2 described later.

[0071] On the other hand, if the FC overvoltage is above the determination value (step S3: "No"), the control unit 15 slightly (i.e., slowly) reduces the target combustion pressure of the injector 34 (step S5).

[0072] In this way, when the FC overvoltage is large, it is assumed that if the flow rate of hydrogen supplied from the injector 34 to the FC stack 11 changes and the FC voltage changes suddenly, the FC stack 11 will be in a state that is prone to deterioration. Therefore, the control unit 15 sets the decompression rate of the target combustion pressure of the injector 34 to a second speed SP2 (e.g., a decompression rate of 1 kPa per second) that is slower than the first speed SP1.

[0073] Next, the control unit 15 determines whether the FC current measurement value is approximately 0A, that is, whether the FC current measurement value is 0A or approximately 0A (step S6).

[0074] Furthermore, when the FC current measurement value is approximately 0A (step S6: "Yes"), that is, when the FC current measurement value is 0A or approximately 0A, it is considered that the power generation of the FC stack 11 is intermittently stopped. Therefore, the control unit 15 sets the target combustion pressure of the injector 34 to atmospheric pressure (0 kPaG) or a slight negative pressure (e.g., -5 kPaG) (step S7).

[0075] In this way, when the FC current measurement value becomes 0A or approximately 0A, the control unit 15 sets the target combustion pressure of the injector 34 to atmospheric pressure or approximately atmospheric pressure (more specifically, slightly negative pressure).

[0076] On the other hand, if the FC current measurement value is not approximately 0A (step S5: "No"), that is, if the FC current measurement value is not 0A or approximately 0A, it is assumed that the power generation of the FC stack 11 has not been intermittently stopped, and therefore the control unit 15 performs the processing of step S3.

[0077] Furthermore, if there is no request to switch from on-demand power generation to intermittent stop in step S1 (i.e., on-demand power generation) (step S1: "No"), the control unit 15 performs the processing in step S6.

[0078] As described above, according to this embodiment, when there is a request to stop the intermittent power generation of the FC stack 11, the control unit 15 reduces the target combustion pressure of the injector 34 to stop the intermittent power generation of the FC stack 11. Moreover, when reducing the target combustion pressure of the injector 34, the control unit 15 changes the rate of reduction of the target combustion pressure of the injector 34 based on the FC overvoltage.

[0079] In this embodiment, by reducing the target combustion pressure of the injector 34, the supply of hydrogen from the injector 34 to the FC stack 11 is stopped, thereby stopping the intermittent power generation of the FC stack 11. Therefore, even without cutting off the air supply to the FC stack 11, the intermittent power generation of the FC stack 11 can be stopped. Consequently, no device (e.g., a valve) is needed to cut off the air supply to the FC stack 11, thus reducing the number of components in the fuel cell system 1 and lowering its cost.

[0080] Furthermore, when reducing the target combustion pressure of the injector 34, the rate of reduction of the target combustion pressure of the injector 34 is varied according to the magnitude of the FC overvoltage, which is an indicator of the state of the FC stack 11. Therefore, the target combustion pressure of the injector 34 can be reduced while suppressing the degradation of the FC stack 11, thereby stopping the intermittent power generation of the FC stack 11.

[0081] Specifically, when the FC overvoltage is less than the determination value, the control unit 15 sets the decompression rate of the target combustion pressure of the injector 34 to a first speed SP1, which is faster than the second speed SP2. On the other hand, when the FC overvoltage is greater than or equal to the determination value, the control unit 15 sets the decompression rate of the target combustion pressure of the injector 34 to a second speed SP2, which is slower than the first speed SP1.

[0082] In this way, when the FC overvoltage is above the threshold value, i.e., when the FC stack 11 is in a state prone to degradation, the target combustion pressure of the injector 34 is slowly reduced when the power generation interval of the FC stack 11 is stopped. Therefore, when the FC stack 11 is in a state prone to degradation, the FC voltage will not change abruptly, and thus the power generation interval of the FC stack 11 can be stopped while suppressing the degradation of the FC stack 11.

[0083] In addition, when the FC current measurement value becomes 0A or approximately 0A, the control unit 15 sets the target combustion pressure of the injector 34 to atmospheric pressure or a slight negative pressure.

[0084] Therefore, when the power generation of the FC stack 11 stops intermittently and the FC current measurement value becomes 0A or approximately 0A, it is possible to prevent the hydrogen supply passage 21 from becoming negative pressure (i.e., pressure lower than atmospheric pressure). Therefore, it is possible to prevent air from flowing from the air supply passage 51 through the FC stack 11 into the hydrogen supply passage 21. Therefore, it is possible to prevent the catalyst (not shown) within the FC stack 11 from deteriorating due to air; more specifically, it is possible to prevent the reduction in the power generation performance of the FC stack 11 due to oxidation of the catalyst within the FC stack 11 by air.

[0085] (Second Embodiment)

[0086] Next, the control measures performed during intermittent shutdowns of power generation in the FC stack 11 will be described in the second embodiment. In this embodiment, the differences from the first embodiment will be described, while the differences from the first embodiment will be omitted.

[0087] In this embodiment, the control unit 15 performs... Figure 6 The flowchart shows the control of the content.

[0088] like Figure 6 As shown, as with Figure 5 At different points, when the FC current measurement value is approximately 0A (step S16: "Yes"), the control unit 15 feeds back the target combustion pressure of the injector 34, making the FC voltage a target voltage lower than the battery voltage (i.e., the voltage of the battery 101) (step S17). Furthermore, regarding the target voltage of the FC voltage, for example, it is set as (target voltage of FC voltage) = (battery voltage) - 10V, and when the battery voltage is 40V, the target voltage of the FC voltage is set to 30V.

[0089] As described above, according to this embodiment, when the FC current measurement value becomes 0A or approximately 0A, the control unit 15 controls the target combustion pressure of the injector 34 so that the FC voltage becomes a target voltage lower than the battery voltage.

[0090] In this way, in this embodiment, when the power generation of the FC stack 11 is intermittently stopped, a target voltage is set for the FC voltage to prevent it from becoming overvoltage (voltage drop) or high voltage, and feedback control of the target combustion pressure of the injector 34 is performed accordingly. Therefore, it is possible to avoid the FC voltage becoming overvoltage (voltage drop) or high voltage. Consequently, it is possible to suppress the degradation of the FC stack 11.

[0091] Furthermore, the above-described embodiments are merely illustrative and do not limit the scope of this disclosure in any way. Of course, various modifications and variations can be made without departing from its spirit.

[0092] For example, in the hydrogen supply passage 21, an ejector may be installed downstream of the injector 34, i.e., between the injector 34 and the FC stack 11 (specifically, the pressure sensor 35). Furthermore, in this case, the ejector is an example of the "fuel supply device" of this disclosure. Moreover, the control unit 15 reduces the target combustion pressure of the ejector to stop the intermittent power generation of the FC stack 11. Furthermore, when reducing the target combustion pressure of the ejector, the control unit 15 changes the rate of reduction of the target combustion pressure of the ejector based on the FC overvoltage.

[0093] Furthermore, while the above description describes a closed cathode system in which the cooling system 14 and the air system 13 are separate, this disclosure can also be applied to an open cathode system in which the cooling system 14 and the air system 13 are shared.

[0094] Explanation of reference numerals in the attached figures

[0095] 1: Fuel Cell System

[0096] 11: FC fuel cell stack

[0097] 12: Hydrogen System

[0098] 13: Air system

[0099] 14: Cooling System

[0100] 15: Control Department

[0101] 16: Current sensor

[0102] 17: Voltage sensor

[0103] 21: Hydrogen supply pathway

[0104] 34: Injector

[0105] 35: Pressure sensor

[0106] 51: Air supply passage

[0107] 61: Air compressor

[0108] 101: Storage battery

[0109] 102: Inverter (or motor)

[0110] SP1: First Speed

[0111] SP2: Second speed.

Claims

1. A fuel cell system, comprising: A fuel cell generates electricity by accepting a supply of fuel gas and oxidant gas. A fuel supply passage for supplying the fuel gas to the fuel cell; A fuel supply device, disposed in the fuel supply passage, is driven to supply the fuel gas to the fuel cell; and An oxidant gas supply passage is provided for supplying the oxidant gas to the fuel cell. The fuel cell system is characterized in that, The fuel cell system is a system in which the output current of the fuel cell depends on the voltage of a battery that is charged with electricity generated by the fuel cell. The fuel cell system also has: A current sensor that measures the output current of the fuel cell; A voltage sensor that measures the output voltage of the fuel cell; and The control unit controls the fuel supply device. in, When the difference between the optimal value of the fuel cell's output voltage corresponding to the measured value of the fuel cell's output current determined by the current sensor and the measured value of the fuel cell's output voltage determined by the voltage sensor is defined as the output voltage difference, the control unit performs the following processing: When a request is made to stop the fuel cell from generating electricity, the target pressure (target combustion pressure) of the fuel gas supplied by the fuel supply device is reduced to stop the fuel cell from generating electricity. When the target combustion pressure of the fuel supply device is reduced, the rate at which the target combustion pressure of the fuel supply device is reduced is changed based on the output voltage difference.

2. The fuel cell system according to claim 1, characterized in that, If the output voltage difference is less than a specified value, the control unit sets the pressure reduction speed to a first speed. When the output voltage difference is above the specified value, the control unit sets the decompression speed to a second speed that is slower than the first speed.

3. The fuel cell system according to claim 1 or 2, characterized in that, When the measured value of the output current of the fuel cell, as determined by the current sensor, becomes 0 or approximately 0, the control unit sets the target combustion pressure of the fuel supply device to atmospheric pressure or approximately atmospheric pressure.

4. The fuel cell system according to claim 1 or 2, characterized in that, When the measured value of the output current of the fuel cell, as determined by the current sensor, becomes 0 or approximately 0, the control unit controls the target combustion pressure of the fuel supply device to make the output voltage of the fuel cell a target voltage lower than the voltage of the battery.

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