Fuel cell system

Abstract

To provide a fuel cell system capable of stopping power generation of a fuel cell while reducing costs and suppressing the occurrence of deterioration of the fuel cell.SOLUTION: In an embodiment of the present disclosure, when there is a request to intermittently stop power generation of an FC stack 11, a control unit 15 reduces the target fuel pressure of an injector 34 to intermittently stop power generation of the FC stack 11, and when reducing the target fuel pressure of the injector 34, the control unit changes the rate at which the target fuel pressure of the injector 34 is reduced on the basis of the FC overvoltage.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present disclosure relates to a fuel cell system having a fuel cell that generates electricity by receiving supplies of fuel gas and oxidant gas.

Background Art

[0002] Patent Document 1 discloses a fuel cell system having a first valve that controls the flow rate of oxidant gas (reaction air) supplied to the fuel cell and a second valve that controls the flow rate of oxidant off-gas (reaction air) discharged from the fuel cell.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Since the fuel cell system disclosed in Patent Document 1 has a first valve and a second valve, the number of components increases, so the costs required for manufacturing and maintenance increase. Further, when stopping the power generation of the fuel cell, if the flow rate of the oxidant gas supplied to the fuel cell fluctuates and the output voltage of the fuel cell changes suddenly, a high load is applied to the fuel cell, so there is a risk of deterioration of the fuel cell depending on the state of the fuel cell.

[0005] Therefore, the present disclosure has been made to solve the above-described problems, and an object thereof is to provide a fuel cell system that can stop the power generation of the fuel cell while reducing costs and suppressing the occurrence of deterioration of the fuel cell.

Means for Solving the Problems

[0006] One aspect of the present disclosure made to solve the above problems is a fuel cell that generates power by receiving supplies of a fuel gas and an oxidant gas, a fuel supply passage that supplies the fuel gas to the fuel cell, a fuel supply device that is provided in the fuel supply passage and drives to supply the fuel gas to the fuel cell, and an oxidant gas supply passage that supplies the oxidant gas to the fuel cell. In the fuel cell system, the fuel cell system is a system in which the output current of the fuel cell depends on the voltage of a battery that charges the power generated by the fuel cell. The fuel cell system includes 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 a control unit that controls the fuel supply device. When defining the difference between the optimum value of the output voltage of the fuel cell corresponding to the measured value of the output current of the fuel cell measured by the current sensor and the measured value of the output voltage of the fuel cell measured by the voltage sensor as the output voltage difference, when there is a request to stop the power generation of the fuel cell, the control unit reduces the target fuel pressure, which is the target pressure of the fuel gas supplied by the fuel supply device, to stop the power generation of the fuel cell, and when reducing the target fuel pressure of the fuel supply device, changes the decompression rate of the target fuel pressure of the fuel supply device based on the output voltage difference.

[0007] According to this aspect, by reducing the target fuel pressure of the fuel supply device to stop the supply of fuel from the fuel supply device to the fuel cell, the power generation of the fuel cell is stopped (for example, intermittently stopped). Therefore, the power generation of the fuel cell can be stopped without shutting off the supply of the oxidant gas to the fuel cell. Accordingly, a device (for example, a valve) for shutting off the supply of the oxidant gas to the fuel cell becomes unnecessary, so that the number of components of the fuel cell system can be reduced and the cost of the fuel cell system can be reduced.

[0008] When reducing the target fuel pressure of the fuel supply device, the decompression rate of the target fuel pressure of the fuel supply device is changed according to the magnitude of the output voltage difference (i.e., the difference between the optimum value and the measured value of the output voltage of the fuel cell), which is an index of the state of the fuel cell. Therefore, while suppressing the occurrence of deterioration of the fuel cell, the target fuel pressure of the fuel supply device can be reduced to stop the power generation of the fuel cell.

[0009] In the above aspect, it is preferable that the control unit sets the decompression rate to a first speed when the output voltage difference is less than a predetermined value, and sets the decompression rate to a second speed slower than the first speed when the output voltage difference is greater than or equal to the predetermined value.

[0010] According to this aspect, when the output voltage difference is greater than or equal to the predetermined value, it means that the fuel cell is in a state where it is likely to deteriorate. Therefore, when stopping the power generation of the fuel cell, the target fuel pressure of the fuel cell is slowly decompressed. As a result, when the fuel cell is in a state where it is likely to deteriorate, the output voltage of the fuel cell does not change suddenly, so that the power generation of the fuel cell can be stopped while suppressing the occurrence of deterioration of the fuel cell.

[0011] In the above aspect, it is preferable that the control unit sets the target fuel pressure of the fuel supply device to atmospheric pressure or substantially atmospheric pressure when the measured value of the output current of the fuel cell measured by the current sensor becomes 0 or substantially 0.

[0012] According to this aspect, when the power generation of the fuel cell stops and the measured value of the output current of the fuel cell becomes 0 or substantially 0, it is possible to suppress the fuel supply passage from becoming a negative pressure (i.e., a pressure lower than atmospheric pressure). Therefore, it is possible to suppress the oxidant gas from flowing from the oxidant gas supply passage into the fuel supply passage through the fuel cell. Accordingly, it is possible to suppress the catalyst in the fuel cell from deteriorating due to the oxidant gas.

[0013] In the above aspect, it is preferable that the control unit controls the target fuel 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 when the measured value of the output current of the fuel cell measured by the current sensor becomes 0 or substantially 0.

[0014] According to this aspect, at the time of stopping the power generation of the fuel cell, a target voltage at which overvoltage (voltage drop) or high voltage does not occur is set for the output voltage of the fuel cell, and feedback control of the target fuel pressure of the fuel supply device is performed in accordance with it. Therefore, it is possible to avoid overvoltage (voltage drop) and high voltage with respect to the output voltage of the fuel cell. Therefore, the occurrence of deterioration of the fuel cell can be suppressed.

Effect of the Invention

[0015] According to the fuel cell system of the present disclosure, it is possible to stop the power generation of the fuel cell while reducing costs and suppressing the occurrence of deterioration of the fuel cell.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Mode for Carrying Out the Invention

[0017] An embodiment of the fuel cell system of the present disclosure will be described.

[0018] <Overview of the fuel cell system> First, the overview of the fuel cell system 1 of the present embodiment will be described. The fuel cell system 1 is a system mounted on a fuel cell vehicle and supplies power to its drive motor (not shown).

[0019] (Schematic configuration of the fuel cell system) As shown in FIG. 1, 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. Note that the FC stack 11 is an example of the "fuel cell" of the present disclosure.

[0020] The FC stack 11 generates electricity by receiving the supply of fuel gas and oxidant gas. In the present embodiment, the fuel gas is hydrogen gas and the oxidant gas is air (i.e., atmospheric air). That is, the FC stack 11 generates electricity by receiving the supply of hydrogen gas from the hydrogen system 12 and the supply of air from the air system 13. Then, the power generated by the FC stack 11 is supplied to the battery 101 and the inverter 102 (or the motor).

[0021] 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 power 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 power generated by the FC stack 11, hereinafter referred to as "FC voltage").

[0022] The hydrogen system 12 is provided on the anode side of the FC stack 11. This hydrogen system 12 includes a hydrogen filling passage 20, a hydrogen gas supply passage 21, and a hydrogen off-gas discharge passage 22.

[0023] The hydrogen filling passage 20 is a passage for filling hydrogen gas from the filling port 30 into the hydrogen tank 31. The hydrogen gas supply passage 21 is a passage for supplying hydrogen gas from the hydrogen tank 31 to the FC stack 11, and is an example of the "fuel supply passage" of the present disclosure.

[0024] The hydrogen off-gas discharge passage 22 is a passage through which hydrogen off-gas, which is hydrogen gas not used for power generation from the FC stack 11, is discharged.

[0025] The hydrogen system 12 includes a valve 32, a pressure reducing valve 33, an injector 34, and a pressure sensor 35 in this order from the hydrogen tank 31 side in the hydrogen gas supply passage 21.

[0026] The valve 32 is a valve that switches between supplying and blocking the supply of hydrogen gas from the hydrogen tank 31 to the hydrogen gas supply passage 21, or switches between supplying and blocking the supply of hydrogen gas from the filling port 30 to the hydrogen tank 31. The pressure reducing valve 33 is a pressure regulating valve for reducing the pressure of hydrogen gas.

[0027] The injector 34 is a valve that is driven to supply (i.e., inject) hydrogen gas to the FC stack 11, and is an example of the "fuel supply device" of the present disclosure. The pressure sensor 35 measures the pressure of the hydrogen gas injected from the injector 34 (i.e., the fuel pressure or the outlet pressure).

[0028] Also, the hydrogen system 12 includes a gas-liquid separator 41 and an exhaust drain valve 42 in the hydrogen off-gas discharge passage 22.

[0029] The gas-liquid separator 41 is a device that separates moisture in the hydrogen off-gas. The exhaust drain valve 42 is a valve that controls the discharge of the hydrogen off-gas discharged from the FC stack 11 to the outside.

[0030] The air system 13 is provided on the cathode side of the FC stack 11. This air system 13 includes an air supply passage 51 and an air off-gas discharge passage 52.

[0031] The 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 the present disclosure. The air off-gas discharge passage 52 is a passage through which air off-gas, which is air that has not been used for power generation from the FC stack 11, is discharged.

[0032] 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.

[0033] The air system 13 of the present embodiment does not include an inlet air valve that controls the flow rate of air supplied from the air supply passage 51 to the FC stack 11, or an outlet air valve that controls the flow rate of air off-gas discharged from the FC stack 11 to the air off-gas discharge passage 52.

[0034] The cooling system 14 is a system that cools the FC stack 11, and includes a cooling water passage 81 and a cooling fan 82. The cooling water passage 81 is a passage through which cooling water flows. The cooling fan 82 is a device that cools the cooling water flowing through the cooling water passage 81.

[0035] The control unit 15 is a device having, for example, an arithmetic processing unit such as a CPU, a storage unit such as a ROM that stores a control program and control data processed by the CPU, and a RAM used as various work areas for control processing, and an input / output interface unit. Then, the control unit 15 performs various controls of the fuel cell system 1 according to the control program stored in the storage unit.

[0036] Specifically, the control unit 15 controls, for example, the driving of the injector 34 and the rotation speed of the air compressor 61. In addition, the control unit 15 also controls other valves such as the valve 32, the pressure reducing valve 33, the exhaust and drainage valve 42, and the cooling fan 82. The control unit 15 also acquires information on the measured values of the current sensor 16, the voltage sensor 17, and the pressure sensor 35.

[0037] (Regarding the operation of the fuel cell system) In the fuel cell system 1 configured as described above, in the hydrogen system 12, the hydrogen gas supplied from the hydrogen gas supply passage 21 to the FC stack 11 is discharged to the outside as hydrogen off-gas through the hydrogen off-gas discharge passage 22 after being used for power generation in the FC stack 11. Also, in the air system 13, the air supplied from the air supply passage 51 to the FC stack 11 is discharged to the outside as air off-gas through the air off-gas discharge passage 52 after being used for power generation in the FC stack 11.

[0038] (Regarding the system without a DCDC converter) As shown in FIG. 1, in the fuel cell system 1 of the present embodiment, the FC stack 11, the battery 101, and the inverter 102 (or motor) are connected in parallel, forming a simple system configuration without a DCDC converter. That is, the fuel cell system 1 is a system without a DCDC converter. Note that the DCDC converter is a device that converts the FC voltage. Also, the battery 101 is connected to the FC stack 11 and charges the power generated by the FC stack 11. Further, the battery 101 is connected to the inverter 102 and supplies the charged power to the inverter 102.

[0039] Thus, the fuel cell system 1 of the present embodiment is a system without a DCDC converter, and since the FC voltage becomes 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, for the power generated by the FC stack 11 in the fuel cell system 1, the fuel cell system 1 supplies it to the battery 101 and the inverter 102 without converting the FC voltage.

[0040] In the fuel cell system 1, since the FC voltage thus becomes equal to the voltage of the battery 101, the FC stack 11 performs natural power generation according to the voltage of the battery 101 during power generation. When the SOC (i.e., the charge rate) of the battery 101 increases, the FC voltage is lowered below the voltage of the battery 101 to intermittently stop the natural power generation of the FC stack 11.

[0041] <Control performed during intermittent stop of power generation of the FC stack> When intermittently stopping the power generation of the FC stack 11, it is conceivable to block the supply of air to the FC stack 11 and the discharge of air off-gas from the FC stack 11 by an air valve (not shown). However, having an air valve increases the number of components, so the cost of the fuel cell system 1 (i.e., the cost required for manufacturing and maintenance) increases.

[0042] Therefore, in the present embodiment, when intermittently stopping the power generation of the FC stack 11, the supply of hydrogen gas from the injector 34 to the FC stack 11 is stopped to intermittently stop the power generation of the FC stack 11.

[0043] Specifically, when there is a request to intermittently stop the power generation of the FC stack 11, the control unit 15 reduces the target fuel pressure, which is the target pressure of the hydrogen gas supplied (i.e., injected) by the injector 34 (hereinafter referred to as the "target fuel pressure of the injector 34") to intermittently stop the power generation of the FC stack 11.

[0044] Then, when the power generation of the FC stack 11 is intermittently stopped by reducing the target fuel pressure of the injector 34 in this way, if the flow rate of the hydrogen gas supplied from the injector 34 to the FC stack 11 fluctuates and the FC voltage changes suddenly, a high load is applied to the FC stack 11. Therefore, depending on the state of the FC stack 11, there is a risk of deterioration of the FC stack 11.

[0045] Therefore, when reducing the target fuel pressure of the injector 34, the control unit 15 changes the decompression rate of the target fuel pressure of the injector 34 based on the FC overvoltage, which is an index of the state of the FC stack 11.

[0046] Here, the "FC overvoltage" is the difference between the estimated value of the FC voltage (hereinafter referred to as the "FC voltage estimated value") corresponding to the measured value of the FC current measured by the current sensor 16 (hereinafter referred to as the "FC current measured value") and the measured value of the FC voltage measured by the voltage sensor 17 (hereinafter referred to as the "FC voltage measured value"), and is an example of the "output voltage difference" in the present disclosure. Note that the FC voltage estimated value is the value of the FC voltage that is optimal for improving the power generation efficiency of the FC stack 11 with respect to the FC current measured value, and is an example of the "optimal value of the output voltage of the fuel cell" in the present disclosure.

[0047] For example, in the I-V characteristics of the FC stack 11, the FC current measured value, the FC voltage estimated value, and the FC voltage measured value are each represented as shown in FIG. 2. And at this time, as shown in FIG. 2, the FC overvoltage is represented as the FC voltage difference, which is the difference between the FC voltage estimated value and the FC voltage measured value. Also, the FC voltage estimated value is the value of the FC voltage estimated with respect to the FC current measured value when the FC stack 11 is new, and is estimated from the FC current measured value using, for example, the map in FIG. 3.

[0048] (First Embodiment) Therefore, regarding the control performed during the intermittent stop of power generation of the FC stack 11, first, the first embodiment will be described. In this embodiment, the control unit 15 performs the control shown in the flowchart in FIG. 5.

[0049] As shown in FIG. 5, the control unit 15 determines whether there is a request to switch from continuous power generation to intermittent stop (step S1).

[0050] And when there is a request to switch from continuous power generation to intermittent stop (that is, during intermittent stop) (step S1: YES), the control unit 15 stops the air compressor 61 (step S2).

[0051] Next, the control unit 15 determines whether the FC overvoltage is less than the determination value (step S3).

[0052] The determination value is calculated from the measured FC current value using, for example, the map of FIG. 4. In the map of FIG. 4, the determination value changes in proportion to the measured FC current value. For example, when the measured FC current value is 10 A, the determination value is 3 V, and when the measured FC current value is 30 A, the determination value is 5 V. The determination value is an example of the "predetermined value" of the present disclosure.

[0053] Returning to the description of FIG. 5, when the FC overvoltage is less than the determination value (step S3: YES), the control unit 15 greatly (i.e., quickly) reduces the target combustion pressure of the injector 34 (step S4).

[0054] In this way, when the FC overvoltage is small, the control unit 15 considers that the FC stack 11 is less likely to deteriorate even if the flow rate of the hydrogen gas supplied from the injector 34 to the FC stack 11 fluctuates and the FC voltage changes rapidly. Therefore, the decompression rate of the target combustion pressure of the injector 34 is set to a first speed SP1 (for example, a speed of decompressing by 5 kPa per second) that is faster than a second speed SP2 described later.

[0055] On the other hand, when the FC overvoltage is equal to or greater than the determination value (step S3: NO), the control unit 15 slowly (i.e., slowly) reduces the target combustion pressure of the injector 34 (step S5).

[0056] In this way, when the FC overvoltage is large, the control unit 15 considers that the FC stack 11 is likely to deteriorate when the flow rate of the hydrogen gas supplied from the injector 34 to the FC stack 11 fluctuates and the FC voltage changes rapidly. Therefore, the decompression rate of the target combustion pressure of the injector 34 is set to a second speed SP2 (for example, a speed of decompressing by 1 kPa per second) that is slower than the first speed SP1.

[0057] Next, the control unit 15 determines whether the measured FC current ≒ 0 A, that is, whether the measured FC current is 0 A or approximately 0 A (step S6).

[0058] And when the measured FC current ≒ 0 A (step S6: YES), that is, when the measured FC current is 0 A or approximately 0 A, it is considered that the power generation of the FC stack 11 has been intermittently stopped. Therefore, the control unit 15 sets the target fuel pressure of the injector 34 to atmospheric pressure (0 kPaG) or slightly negative pressure (for example, -5 kPaG) (step S7).

[0059] In this way, when the measured FC current becomes 0 A or approximately 0 A, the control unit 15 sets the target fuel pressure of the injector 34 to atmospheric pressure or approximately atmospheric pressure (specifically, slightly negative pressure).

[0060] On the other hand, when the measured FC current ≒ 0 A is not satisfied (step S5: NO), that is, when the measured FC current is not 0 A or approximately 0 A, it is considered that the power generation of the FC stack 11 has not been intermittently stopped. Therefore, the control unit 15 performs the process of step S3.

[0061] In step S1, when there is no request to switch from power generation as it comes to intermittent stop (that is, during power generation as it comes) (step S1: NO), the control unit 15 performs the process of step S6.

[0062] As described above, according to this embodiment, when there is a request to intermittently stop the power generation of the FC stack 11, the control unit 15 reduces the target fuel pressure of the injector 34 to intermittently stop the power generation of the FC stack 11. And when the control unit 15 reduces the target fuel pressure of the injector 34, it changes the decompression rate of the target fuel pressure of the injector 34 based on the FC overvoltage.

[0063] In this way, in this embodiment, by reducing the target fuel pressure of the injector 34 and stopping the supply of hydrogen gas from the injector 34 to the FC stack 11, the power generation of the FC stack 11 is intermittently stopped. Therefore, even without shutting off the supply of air to the FC stack 11, the power generation of the FC stack 11 can be intermittently stopped. Thus, since a device (for example, a valve) for shutting off the supply of air to the FC stack 11 becomes unnecessary, the number of components of the fuel cell system 1 can be reduced, and the cost of the fuel cell system 1 can be reduced.

[0064] And when reducing the target fuel pressure of the injector 34, the decompression rate of the target fuel pressure of the injector 34 is changed according to the magnitude of the FC overvoltage, which is an index of the state of the FC stack 11. Therefore, while suppressing the occurrence of deterioration of the FC stack 11, the target fuel pressure of the injector 34 can be reduced to intermittently stop the power generation of the FC stack 11.

[0065] Specifically, when the FC overvoltage is less than the determination value, the control unit 15 sets the decompression rate of the target fuel pressure of the injector 34 to a first speed SP1 that 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 fuel pressure of the injector 34 to a second speed SP2 that is slower than the first speed SP1.

[0066] In this way, when the FC overvoltage is greater than or equal to the determination value, that is, when the FC stack 11 is in a state where it is likely to deteriorate, when intermittently stopping the power generation of the FC stack 11, the target fuel pressure of the injector 34 is slowly reduced. Therefore, when the FC stack 11 is in a state where it is likely to deteriorate, the FC voltage does not change suddenly, so the power generation of the FC stack 11 can be intermittently stopped while suppressing the occurrence of deterioration of the FC stack 11.

[0067] Further, when the measured value of the FC current becomes 0 A or approximately 0 A, the control unit 15 sets the target fuel pressure of the injector 34 to atmospheric pressure or slightly negative pressure.

[0068] This makes it possible to suppress the hydrogen gas supply passage 21 from becoming negative pressure (i.e., a pressure lower than atmospheric pressure) when the power generation of the FC stack 11 stops intermittently and the measured FC current value becomes 0 A or approximately 0 A. Therefore, it is possible to suppress air from flowing from the air supply passage 51 into the hydrogen gas supply passage 21 through the FC stack 11. Accordingly, it is possible to suppress the catalyst (not shown) in the FC stack 11 from deteriorating due to air, and more specifically, it is possible to suppress the power generation performance of the FC stack 11 from deteriorating due to the catalyst in the FC stack 11 being oxidized and deteriorated by air.

[0069] (Second Embodiment) Next, the control performed during the intermittent stop of the power generation of the FC stack 11 will be described with reference to the second embodiment. In this embodiment, differences from the first embodiment will be described, and descriptions of points common to the first embodiment will be omitted.

[0070] In this embodiment, the control unit 15 performs control according to the content shown in the flowchart in FIG. 6.

[0071] As shown in FIG. 6, as a difference from FIG. 5, when the measured FC current value ≒ 0 A (step S16: YES), the control unit 15 feedback-controls the target fuel injection pressure of the injector 34 so that the FC voltage becomes a target voltage lower than the battery voltage (i.e., the voltage of the battery 101) (step S17). For the target voltage of the FC voltage, for example, (target voltage of FC voltage) = (battery voltage) - 10 V, and when the battery voltage is 40 V, the target voltage of the FC voltage is set to 30 V.

[0072] As described above, according to this embodiment, when the measured FC current value becomes 0 A or approximately 0 A, the control unit 15 controls the target fuel injection pressure of the injector 34 so that the FC voltage becomes a target voltage lower than the battery voltage.

[0073] In this way, in this embodiment, when the power generation of the FC stack 11 is intermittently stopped, a target voltage at which overvoltage (voltage drop) or high voltage does not occur is set for the FC voltage, and feedback control of the target fuel pressure of the injector 34 is performed accordingly. Therefore, it is possible to avoid overvoltage (voltage drop) and high voltage for the FC voltage. Accordingly, the occurrence of deterioration of the FC stack 11 can be suppressed.

[0074] Note 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 can be made without departing from the gist thereof.

[0075] For example, in the hydrogen gas supply passage 21, an ejector may be provided at a position downstream of the injector 34, that is, at a position between the injector 34 and the FC stack 11 (specifically, the pressure sensor 35). In this case, the ejector is an example of the "fuel supply device" of the present disclosure. Then, the control unit 15 reduces the target fuel pressure of the ejector to intermittently stop the power generation of the FC stack 11. And when the control unit 15 reduces the target fuel pressure of the ejector, it changes the decompression rate of the target fuel pressure of the ejector based on the FC overvoltage.

[0076] Also, although the closed cathode system in which the cooling system 14 and the air system 13 are separated has been described above, the present disclosure can also be applied to an open cathode system in which the cooling system 14 and the air system 13 are common.

Explanation of Reference Numerals

[0077] 1 Fuel cell system 11 FC stack 12 Hydrogen system 13 Air system 14 Cooling system 15 Control unit 16 Current sensor 17 Voltage sensor 21 Hydrogen gas supply passage 34 Injector 35 Pressure sensor 51 Air supply passage 61 Air compressor 101 Battery 102 Inverter (or motor) SP1 First speed SP2 Second speed

Claims

1. A fuel cell that generates electricity by receiving a supply of fuel gas and oxidant gas, A fuel supply passage that supplies the fuel gas to the fuel cell, A fuel supply device that is provided in the fuel supply passage and drives to supply the fuel gas to the fuel cell, An oxidant gas supply passage that supplies the oxidant gas to the fuel cell, In a fuel cell system having: The fuel cell system is a system in which the output current of the fuel cell depends on the voltage of a battery that charges the electric power generated by the fuel cell, 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 a control unit that controls the fuel supply device, When defining the difference between the optimum value of the output voltage of the fuel cell corresponding to the measured value of the output current of the fuel cell measured by the current sensor and the measured value of the output voltage of the fuel cell measured by the voltage sensor as the output voltage difference, The control unit: When there is a request to stop the power generation of the fuel cell, the target fuel pressure, which is the target pressure of the fuel gas supplied by the fuel supply device, is depressurized to stop the power generation of the fuel cell, When depressurizing the target fuel pressure of the fuel supply device, the depressurization rate of the target fuel pressure of the fuel supply device is changed based on the output voltage difference, A fuel cell system characterized by the above.

2. In the fuel cell system according to Claim 1, The control unit: When the output voltage difference is less than a predetermined value, the depressurization rate is set as a first rate, When the output voltage difference is greater than or equal to the predetermined value, the depressurization rate is set as a second rate slower than the first rate, A fuel cell system characterized by the above.

3. In the fuel cell system according to claim 1 or 2, when the measured value of the output current of the fuel cell measured by the current sensor becomes 0 or substantially 0, the control unit sets the target fuel pressure of the fuel supply device to atmospheric pressure or substantially atmospheric pressure; A fuel cell system characterized by the above.

4. In the fuel cell system according to claim 1 or 2, when the measured value of the output current of the fuel cell measured by the current sensor becomes 0 or substantially 0, the control unit controls the target fuel 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; A fuel cell system characterized by the above.

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