Fuel cell system

Abstract

The invention provides a fuel cell system. The fuel cell system includes a fuel cell, an air compressor, a flow sensor, a voltage sensor, and a control unit. The control unit executes either a pull-up operation in which the air compressor supplies the cathode gas at a first air stoichiometric ratio or a pull-down operation in which the air compressor supplies the cathode gas at a second air stoichiometric ratio lower than the first air stoichiometric ratio. When a first condition is satisfied, the pull-up operation is executed, and when a second condition is satisfied, the pull-up operation is not executed, the first condition includes that the output voltage is a value included in a first range, and the second condition includes that the output voltage is a value included in a second range higher than the first range.

Description

Technical Field

[0001] The present disclosure relates to fuel cell systems. Background Art

[0002] To prevent degradation, fuel cells must prevent stack drying. The fuel cell system disclosed in Japanese Patent Application Laid-Open No. 2020-4675 prevents stack drying by adjusting the amount of generated water produced per unit time by power generation. More specifically, the fuel cell system disclosed in Japanese Patent Application Laid-Open No. 2020-4675 reduces the amount of water removed by the cathode gas by reducing the amount of cathode gas supplied to the stack. This prevents stack drying.

[0003] In this case, the air stoichiometric ratio is lower than usual. The air stoichiometric ratio refers to the ratio of the amount of cathode gas actually supplied to the battery stack to the minimum amount of cathode gas required to generate the power required by the load. The smaller the air stoichiometric ratio, the less cathode gas is supplied to the battery stack.

[0004] In the fuel cell system disclosed in Japanese Patent Application Laid-Open No. 2020-4675, the air stoichiometric ratio is maintained at a value of 1.0 or greater. Therefore, the fuel cell system can generate the required power by supplying the anode gas required to generate the required power. Furthermore, when the air stoichiometric ratio fluctuates, the power generated by the fuel cell also fluctuates. If the generated power exceeds or falls short of the required power, the secondary battery of the fuel cell system discharges the insufficient power or charges the excess power.

[0005] When the air stoichiometric ratio is lower than normal, moisture is more likely to accumulate in the battery stack. When excessive moisture accumulates in the battery stack, flooding occurs. This flooding can cause concentration overvoltage, potentially preventing the fuel cell from outputting the required power due to a drop in output voltage. Therefore, the fuel cell system disclosed in Japanese Patent Application Laid-Open No. 2020-4675 performs drainage before flooding occurs. This drainage process increases the amount of cathode gas supplied to the battery stack, thereby removing moisture trapped in the battery stack.

[0006] However, since the drainage process tends to dry out the stack, there is a possibility of accelerating the degradation of the fuel cell. Therefore, the inventors have studied a method of reducing the drainage process when the air stoichiometric ratio is lower than normal.

[0007] However, the magnitude of concentration overvoltage generated by battery packs varies depending on factors such as age-related degradation and quality. Therefore, even if drainage prior to overflow is reduced, preventing concentration overvoltage caused by overflow is difficult. Therefore, a technology is needed to prevent both drying out of the battery pack and insufficient fuel cell output. Summary of the Invention

[0008] The present disclosure can be implemented in the following forms.

[0009] (1) According to one aspect of the present disclosure, a fuel cell system is provided.

[0010] The fuel cell system has:

[0011] fuel cells;

[0012] an air compressor for adjusting the flow rate of cathode gas flowing into the fuel cell;

[0013] A flow sensor for obtaining the flow of the cathode gas;

[0014] a voltage sensor for obtaining an output voltage of the fuel cell; and

[0015] a control unit that controls the fuel cell system;

[0016] The control unit performs either a pull-up operation in which the air compressor supplies the cathode gas at a first air stoichiometric ratio, or a pull-down operation in which the air compressor supplies the cathode gas at a second air stoichiometric ratio, wherein the first air stoichiometric ratio is an air stoichiometric ratio of 1 or greater, and the second air stoichiometric ratio is an air stoichiometric ratio of 1 or greater and lower than the first air stoichiometric ratio.

[0017] When executing the above pull-down operation,

[0018] When a first condition is satisfied, including that the output voltage is a value included in a first range, the pull-up operation is performed during a predetermined first time period.

[0019] When a second condition is satisfied, including the output voltage being a value included in a second range higher than the first range, the pull-up operation is not performed.

[0020] The air stoichiometry is the ratio of the amount of cathode gas actually supplied to the battery pack to the minimum amount of cathode gas required to generate the required power. In order for the fuel cell to generate the required power, for example, the air compressor is controlled so that the air stoichiometry is 1 or more. When the air stoichiometry becomes the second air stoichiometry, the flow rate of the cathode gas decreases compared to the case where the air stoichiometry is the first air stoichiometry. As a result, since the amount of moisture removed from the fuel cell decreases, drying of the fuel cell can be prevented. However, when the air stoichiometry is the second air stoichiometry, since the amount of moisture contained in the fuel cell increases, there is a high possibility of concentration overvoltage caused by overflow. The concentration overvoltage reduces the output voltage of the fuel cell. In this way, when the output voltage is included in the first range due to the reduction in the output voltage caused by the concentration overvoltage, a pull-up operation is performed so that the air stoichiometry becomes the first air stoichiometry. That is, the concentration overvoltage caused by overflow is eliminated by increasing the flow rate of the cathode gas. Therefore, the fuel cell system of the present disclosure can prevent drying of the fuel cell by controlling the flow rate of the cathode gas according to the reduction in the output voltage caused by the concentration overvoltage, compared to the method of controlling the flow rate of the cathode gas in order to prevent the concentration overvoltage in advance. And, the fuel cell system of the present disclosure can prevent insufficient output of the fuel cell by increasing the flow rate of the cathode gas according to the reduction in the output voltage.

[0021] (2) In the fuel cell system in the above-described manner, the first condition may also include a case where the output voltage is included in the first range during a predetermined second time period.

[0022] By being in this way, in the reduction of the output voltage for less than the second time, the pull-up operation is not performed. The output voltage may sometimes decrease instantaneously due to a change in the required power. Therefore, the fuel cell system of the present disclosure can prevent the pull-up operation from being erroneously performed due to an instantaneous decrease in the output voltage.

[0023] (3) In the fuel cell system in the above-described manner, the control unit may also perform the pull-down operation after the first time has elapsed.

[0024] By being in this way, compared to the method of not performing the pull-down operation after the first time has elapsed, the fuel cell system of the present disclosure can prevent drying of the fuel cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Hereinafter, the features, advantages, and technical and industrial importance of the embodiments of the present invention will be described with reference to the drawings, and the same reference numerals denote the same elements, where,

[0026] Figure 1 This is an explanatory diagram showing the structure of a fuel cell system according to the first embodiment.

[0027] Figure 2 This is a flowchart showing a control method of the fuel cell system.

[0028] Figure 3 This is a waveform of the output power of the fuel cell system when the output voltage decreases. Detailed Embodiments

[0029] A. First Embodiment:

[0030] A - 1. Structure of the Fuel Cell System:

[0031] Figure 1 This is an explanatory diagram showing the structure of a fuel cell system 10 according to the first embodiment. The fuel cell system 10 includes a fuel cell stack 100, a cathode gas supply / discharge system 200, an anode gas supply / discharge system 300, an output circuit 400, and a control unit 500. The fuel cell system 10 of the present embodiment is used, for example, as a driving power source and a power source for various devices by being mounted on a battery electric vehicle.

[0032] The fuel cell stack 100 receives the supply of anode gas and cathode gas as reaction gases to generate electricity. For example, the anode gas is hydrogen, and the cathode gas is air. The fuel cell stack 100 is a polymer electrolyte fuel cell and has a stacked structure in which a plurality of single cells as power generation elements are stacked. In this specification, the "fuel cell stack" is also simply referred to as a "fuel cell" or a "cell stack".

[0033] A single cell includes a membrane electrode assembly (MEA: Membrane Electrode Assembly), a pair of gas diffusion layers arranged to sandwich the MEA, and a pair of gas separators arranged outside each gas diffusion layer. The MEA includes an electrolyte membrane, and an anode and a cathode as catalyst electrode layers formed on each surface of the electrolyte membrane. In each single cell, an anode gas flow path 120 through which anode gas flows is formed on the anode side via the electrolyte membrane, and a cathode gas flow path 110 through which cathode gas flows is formed on the cathode side. In Figure 1 , for ease of understanding the technology, the illustration of the single cell is omitted.

[0034] In addition, in the cathode, water is generated as the electrochemical reaction proceeds. As a result, the amount of moisture contained in the cathode gas flow path 110 increases. However, since the moisture in the cathode gas flow path 110 is removed by the cathode gas, the amount of moisture contained in the cathode gas flow path 110 varies according to the amount of generated water and the flow rate of the cathode gas. Therefore, depending on the flow rate of the cathode gas, drying of the cathode gas flow path 110 and overflow in the cathode gas flow path 110 are likely to occur. The adjustment of the moisture content in the cathode gas flow path 110 in the fuel cell system 10 will be described in detail later. In addition, in this specification, the moisture content of the fuel cell stack 100 refers to the moisture content of the cathode gas flow path 110.

[0035] The cathode gas supply and discharge system 200 supplies the cathode gas to the fuel cell stack 100 and discharges the cathode gas from the fuel cell stack 100. The cathode gas supply and discharge system 200 includes a cathode gas supply pipe 210, a flow rate sensor 220, an air compressor 230, and a cathode gas discharge pipe 240.

[0036] The cathode gas supply pipe 210 supplies the cathode gas outside the fuel cell system 10 to the fuel cell stack 100. The cathode gas supply pipe 210 is composed of a first cathode gas supply pipe 211 connecting the outside to the inlet of the air compressor 230 and a second cathode gas supply pipe 212 connecting the outlet of the air compressor 230 to the inlet of the cathode gas flow path 110. Thus, the cathode gas supply pipe 210 supplies the cathode gas supplied from the outside through the air compressor 230 to the cathode gas flow path 110.

[0037] The flow rate sensor 220 obtains the flow rate of the cathode gas. More specifically, the flow rate sensor 220 measures the flow rate of the cathode gas flowing from the first cathode gas supply pipe 211 toward the air compressor 230. The flow rate sensor 220 sends the obtained flow rate to the control unit 500.

[0038] The air compressor 230 adjusts the flow rate of the cathode gas flowing into the fuel cell stack 100. More specifically, the air compressor 230 compresses the cathode gas from the first cathode gas supply pipe 211 and discharges the cathode gas to the second cathode gas supply pipe 212. The air compressor 230 adjusts the flow rate of the cathode gas by compressing the cathode gas according to the instruction of the control unit 500.

[0039] The output voltage Vf of the fuel cell stack 100 is adjusted by adjusting the flow rate of the cathode gas. Later, the control of the power of the fuel cell system 10 will be described in detail. And, by adjusting the flow rate of the cathode gas, the moisture content of the fuel cell stack 100 is adjusted as described above.

[0040] The cathode gas discharge pipe 240 discharges the cathode gas discharged from the fuel cell stack 100 to the outside of the fuel cell system 10.

[0041] The anode gas supply / discharge system 300 supplies the anode gas to the fuel cell stack 100 and discharges the anode gas from the fuel cell stack 100. The anode gas supply / discharge system 300 includes an anode gas tank, an anode gas pump, etc. Also, the anode gas supply / discharge system 300 includes a supply pipe, an exhaust pipe, etc. that cause the anode gas supplied from the anode gas tank to flow in the anode gas flow path 120. However, for ease of understanding the technology, in Figure 1 the illustration of the structure of the anode gas supply / discharge system 300 is omitted.

[0042] The output circuit 400 supplies power from the fuel cell stack 100 according to the required power of the load device 440. The output circuit 400 includes a voltage sensor 410, a current sensor 420, an output adjustment unit 430, and a load device 440.

[0043] The voltage sensor 410 obtains the output voltage Vf of the fuel cell stack 100. The voltage sensor 410 sends the obtained output voltage Vf to the control unit 500.

[0044] The current sensor 420 obtains the output current If of the fuel cell stack 100. The current sensor 420 sends the obtained output current If to the control unit 500.

[0045] The output adjustment unit 430 adjusts the output power P1 of the fuel cell stack 100 according to the required power of the load. Specifically, the output adjustment unit 430 is a DC / DC converter. The output adjustment unit 430 is connected to the power output unit of the fuel cell stack 100. The output adjustment unit 430 extracts current from the fuel cell stack 100 according to the command value of the current from the control unit 500. Also, the output adjustment unit 430 transforms the output voltage Vf of the fuel cell stack 100 into the voltage required by the load device 440. For example, the drive device of the motor included in the load device 440 requires a voltage higher than the output voltage Vf of the fuel cell stack 100. Therefore, the output adjustment unit 430 boosts the output voltage Vf of the fuel cell stack 100 to the voltage required by the drive device of the motor. Thereafter, the control of the output adjustment unit 430 will be described in detail. In addition, the "output adjustment unit" is also referred to as "FDC".

[0046] The load device 440 consumes the load power P2 output from the output adjustment unit 430. The load device 440 includes, for example, a drive device of a vehicle including a motor and a drive circuit of the motor, an air compressor 230, an anode gas pump, etc. The load device 440 sends information on the required load power P2 to the control unit 500. In addition, in this specification, the load power P2 required by the load device 440 is referred to as the required power.

[0047] The control unit 500 controls the fuel cell system 10. It is constructed as a logic circuit centered around a microcomputer. More specifically, the control unit 500 includes a CPU, ROM, RAM, and input / output ports for inputting and outputting various signals. The CPU executes a pre-set control program. The ROM stores control programs and control data required for various computations performed by the CPU. The RAM temporarily reads and writes various data required for various computations performed by the CPU. The functions of the control unit 500 are described below.

[0048] The controller 500 controls the flow rate of the cathode gas using the air compressor 230 to perform either an increase operation or a decrease operation of the air stoichiometric ratio. The air stoichiometric ratio refers to the ratio of the amount of cathode gas actually supplied to the fuel cell stack 100 to the minimum amount of cathode gas required to generate the required power. Specifically, the air stoichiometric ratio is 1.0 or greater.

[0049] The operation to increase the air stoichiometric ratio is an operation in which the air compressor 230 supplies cathode gas at a first air stoichiometric ratio. Specifically, the first air stoichiometric ratio is 1.5. The first air stoichiometric ratio is based on the air stoichiometric ratio that maximizes the power consumption of the vehicle's drive system. In other words, the first air stoichiometric ratio is based on the air stoichiometric ratio that maximizes power, obtained by subtracting the power consumption of the air compressor 230, cathode pump, etc. from the output power P1 of the fuel cell stack 100.

[0050] The air stoichiometric ratio reduction operation is an operation in which the air compressor 230 supplies cathode gas so that the air stoichiometric ratio reaches a second air stoichiometric ratio that is lower than the first air stoichiometric ratio. For example, when the first air stoichiometric ratio is 1.5, the second air stoichiometric ratio is a value within the range of 1.2 to 1.3.

[0051] By operating the fuel cell stack 100 at a lower air stoichiometric ratio, the cathode gas flow rate is reduced compared to the first air stoichiometric ratio. The reduction in the cathode gas flow rate reduces the amount of moisture removed from the fuel cell stack 100. In other words, since the amount of moisture contained in the fuel cell stack 100 increases, drying out of the fuel cell stack 100 can be prevented. However, the increased moisture content in the fuel cell stack 100 makes flooding more likely to occur. Furthermore, the "operation to increase the air stoichiometric ratio" will also be simply referred to as "pull-up operation," and the "operation to decrease the air stoichiometric ratio" will also be simply referred to as "pull-down operation."

[0052] Even during an operation to increase the air stoichiometric ratio, the cathode gas supplied from the air compressor 230 is dry, so the fuel cell stack 100 may partially dry out. In particular, the inlet of the cathode gas flow path 110 may partially dry out. In this case, by performing an operation to decrease the air stoichiometric ratio, it is possible to prevent the fuel cell stack 100 from drying out.

[0053] The control unit 500 further controls the output power P1 of the fuel cell stack 100 based on the power required by the load device 440. More specifically, the control unit 500 obtains information about the power required from the load device 440. Based on the power required, the control unit 500 controls the air compressor 230 based on a predetermined reference value for the output voltage Vf. By supplying cathode gas to the fuel cell stack 100, the fuel cell stack 100 begins generating electricity, thereby generating an output voltage Vf. Furthermore, based on the power required, the control unit 500 controls the output adjustment unit 430 based on a predetermined reference value for the output current If. Specifically, the output adjustment unit 430 extracts the output current If from the fuel cell stack 100 based on the reference value for the output current If, thereby outputting an output current If corresponding to the reference value for the output current If. Based on this, the control unit 500 obtains the output current If and the output voltage Vf via the voltage sensor 410 and the current sensor 420. Based on the obtained output current If and output voltage Vf, the control unit 500 calculates the output power P1. The controller 500 calculates the output current If to be taken out by the output regulator 430 based on the difference between the calculated output power P1 and the required power. Therefore, the output regulator 430 causes the fuel cell stack 100 to output the output power P1 of the fuel cell stack 100 corresponding to the required power.

[0054] A-2. Fuel cell system control method:

[0055] Figure 2 1 is a flowchart showing a method for controlling the fuel cell system 10. The following describes a method for controlling the fuel cell system 10. The control unit 500 repeatedly executes the following processing during operation of the fuel cell system 10.

[0056] exist Figure 2 In S100, it is determined whether the pull-down operation of the air stoichiometric ratio is being executed. That is, if the air stoichiometric ratio is not the second air stoichiometric ratio, the control unit 500 advances the process to S150. If the air stoichiometric ratio is the second air stoichiometric ratio, the control unit 500 advances the process to S110.

[0057] exist Figure 2In S110, the control unit 500 determines whether the output voltage Vf of the fuel cell stack 100 is decreasing. If the output voltage Vf is decreasing, a concentration overvoltage may occur due to flooding. Specifically, if the voltage sensor 410 determines that a first condition is satisfied, including that the output voltage Vf of the fuel cell stack 100 is within a first range, the control unit 500 advances the process to S120. If the voltage sensor 410 determines that a second condition is satisfied, including that the output voltage Vf of the fuel cell stack 100 is within a second range higher than the first range, the control unit 500 advances the process to S160.

[0058] "A second range higher than the first range" means that the lower limit of the second range is higher than the upper limit of the first range. The first and second ranges are defined by a predetermined threshold. More specifically, the range above the threshold is the second range, and the range below the threshold is the first range. The threshold is set experimentally, for example, based on the minimum value of the output voltage Vf achievable in response to a sudden increase in load power P2.

[0059] The first condition is a condition that also includes the case where the output voltage Vf is included in the first range during a predetermined second time. Specifically, the second time is a time based on the response speed of the air compressor 230. For example, the second time is 4 seconds. By adopting this method, the pull-up operation is not performed when the output voltage Vf decreases for less than the second time. The output voltage Vf sometimes decreases instantaneously due to fluctuations in the load power P2. Therefore, the fuel cell system 10 disclosed in the present invention can prevent the pull-up operation from being erroneously performed due to a momentary decrease in the output voltage Vf. In this specification, the "second time" is also referred to as the "determination time for preventing erroneous determination."

[0060] exist Figure 2 In S120 , the control unit 500 performs an operation to increase the air stoichiometric ratio. That is, the control unit 500 increases the flow rate of the cathode gas through the air compressor 230 so that the air stoichiometric ratio becomes the first air stoichiometric ratio.

[0061] exist Figure 2 In S130 , the controller 500 continues the pull-up operation, maintaining the air stoichiometric ratio at the first air stoichiometric ratio for a predetermined first time period. The first time period is the time required to eliminate flooding. In this specification, the "first time period" is also referred to as the "drainage time period." The drainage time period is set experimentally based on the specifications of the fuel cell stack 100. For example, the drainage time period is 30 minutes.

[0062] exist Figure 2In S140, after the first period of time has elapsed, the control unit 500 performs a pull-down operation of the air stoichiometric ratio. That is, the control unit 500 reduces the flow rate of the cathode gas through the air compressor 230 such that the air stoichiometric ratio becomes the second air stoichiometric ratio.

[0063] In Figure 2 S150, the control unit 500 continues to operate such that the existing air stoichiometric ratio is achieved. That is, the control unit 500 continues to operate in a manner that maintains the air stoichiometric ratio in S100.

[0064] In Figure 2 S160, the control unit 500 continues to operate in a state where the air stoichiometric ratio has been pulled down.

[0065] During the period when the fuel cell stack 100 outputs the output power P1, the above processing is repeated. That is, after any one of the processes in Figure 3 S140 to S160, the control unit 500 starts the process of S100.

[0066] As described above, when the air stoichiometric ratio becomes the second air stoichiometric ratio, the flow rate of the cathode gas decreases compared to the case where the air stoichiometric ratio is the first air stoichiometric ratio. As a result, since the amount of water removed from the fuel cell decreases, drying of the fuel cell can be prevented. However, when the air stoichiometric ratio is the second air stoichiometric ratio, since the amount of water contained in the fuel cell increases, the possibility of concentration overvoltage due to overflow is high. The concentration overvoltage reduces the output voltage Vf of the fuel cell.

[0067] Figure 3 is a waveform showing the output power P1 of the fuel cell system 10 when the output voltage Vf decreases. In Figure 3 the waveform, the horizontal axis of the drawing represents the passage of time, and the vertical axis of the drawing represents the magnitude of the value. In the fuel cell system 10 of the present disclosure, when the output voltage Vf is less than the threshold value due to the decrease in the output voltage Vf caused by the concentration overvoltage, a pull-up operation is performed such that the air stoichiometric ratio becomes the first air stoichiometric ratio. That is, the flow rate of the cathode gas increases.

[0068] As a result, as Figure 3 shown, the air stoichiometric ratio, which is the second air stoichiometric ratio, becomes the first air stoichiometric ratio. Therefore, the concentration overvoltage caused by overflow is eliminated, and the output voltage Vf increases. However, the determination of the decrease in the output voltage Vf is based on the condition that the output voltage Vf continues to decrease beyond the determination time for preventing misjudgment.

[0069] In addition, as Figure 3As shown, since the output adjustment unit 430 outputs the output power P1 that satisfies the required power from the fuel cell stack 100, the output current If varies with the variation in the output voltage Vf.

[0070] Therefore, by adopting this method, the fuel cell system 10 of the present disclosure controls the cathode gas flow rate in response to a decrease in output voltage Vf caused by concentration overvoltage. This prevents fuel cell drying compared to methods that control the cathode gas flow rate to prevent concentration overvoltage. Furthermore, by increasing the cathode gas flow rate in response to a decrease in output voltage Vf, the fuel cell system 10 of the present disclosure can prevent insufficient fuel cell output.

[0071] Furthermore, by adopting this configuration, the pull-up operation is not executed when the output voltage Vf decreases by less than the determination time required to prevent erroneous determinations. The output voltage Vf may drop momentarily due to, for example, fluctuations in required power. Therefore, the fuel cell system 10 of the present disclosure can prevent the pull-up operation from being erroneously executed due to a momentary drop in the output voltage Vf.

[0072] And, as Figure 3 As shown, after the drain time has elapsed, the fuel cell system 10 performs a pull-down operation to change the air stoichiometric ratio from the first air stoichiometric ratio to the second air stoichiometric ratio.

[0073] By adopting this configuration, the fuel cell system 10 of the present disclosure can prevent the fuel cell from drying out, compared to a configuration in which the pull-down operation is not performed after the first time has elapsed.

[0074] B. Modification:

[0075] (1) In the above embodiment, the first air stoichiometric ratio is 1.5. However, the first air stoichiometric ratio may be 1.5 or greater. Furthermore, in the above embodiment, the second air stoichiometric ratio is a value within the range of 1.2 or greater and 1.3 or less. However, the second air stoichiometric ratio may be 1.0 or greater and less than 1.5.

[0076] (2) In the above embodiment, the control unit 500 does not perform the pull-up operation when the output voltage Vf decreases for a period shorter than the determination time for preventing erroneous determination. However, the control unit 500 may also perform the pull-up operation when the output voltage Vf decreases for a period shorter than the determination time for preventing erroneous determination. This makes control easier.

[0077] (3) In the above embodiment, the control unit 500 performs the pull-down operation after the first time has elapsed. However, the control unit 500 may not perform the pull-down operation after the first time has elapsed. Even if the pull-down operation is not performed, the dryness of the fuel cell stack 100 is reduced because the pull-down operation has already been performed.

[0078] (4) In the above embodiment, the control unit 500 may be composed of a plurality of microcomputers. More specifically, the functions of the control unit 500, such as performing an increase or decrease operation of the air stoichiometric ratio or controlling the output adjustment unit 430, may not be implemented by a single microcomputer.

[0079] The present disclosure is not limited to the above-mentioned embodiments and can be implemented in various structures without departing from its main purpose. For example, the technical features of the embodiments corresponding to the technical features in each method described in the invention summary can be appropriately replaced or combined in order to solve part or all of the above-mentioned problems or to achieve part or all of the above-mentioned effects. In addition, if the technical feature is not described as being necessary in this specification, it can be appropriately removed.

Claims

1. A fuel cell system, wherein, Comprising: A fuel cell; An air compressor that adjusts the flow rate of the cathode gas flowing into the fuel cell; A flow sensor that obtains the flow rate of the cathode gas; A voltage sensor that obtains the output voltage of the fuel cell; And A control unit that controls the fuel cell system, The control unit performs either a pull-up operation in which the air compressor supplies the cathode gas so as to achieve a first air stoichiometric ratio or a pull-down operation in which the air compressor supplies the cathode gas so as to achieve a second air stoichiometric ratio. The first air stoichiometric ratio is an air stoichiometric ratio of 1 or more, and the second air stoichiometric ratio is an air stoichiometric ratio of 1 or more and lower than the first air stoichiometric ratio. When performing the pull-down operation, When a first condition including the case where the output voltage is a value included in a first range is satisfied, the pull-up operation is performed during a predetermined first time period. When a second condition including the case where the output voltage is a value included in a second range higher than the first range is satisfied, the pull-up operation is not performed.

2. The fuel cell system according to claim 1, wherein The first condition includes the case where the output voltage is included in the first range during a predetermined second time period.

3. The fuel cell system according to claim 2, wherein The control unit performs the pull-down operation after the first time period has elapsed.

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