Fuel cell system

Abstract

To meet the need for technology that, while preventing a fuel cell in a fuel cell system from drying, prevents the output of the fuel cell from becoming insufficient.SOLUTION: Provided is a fuel cell system comprising a fuel cell, an air compressor, a flow sensor, a voltage sensor for acquiring an output voltage, and a control unit of the fuel cell system. The control unit executes either a pull-up drive for letting the air compressor be supplied with a cathode gas so that a first air stoichiometric ratio is reached, or a pull-down drive for letting the air compressor be supplied with the cathode gas so that a second air stoichiometric ratio lower than the first air stoichiometric ratio is reached. Meanwhile, the control unit executes the pull-up drive when a first condition is met including that the output voltage shows a value included in a first range, and does not execute the pull-up drive when a second condition is met including that the output voltage shows a value included in a second range higher than the first range.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] To prevent fuel cells from deteriorating, it is necessary to prevent the stack from drying out. The fuel cell system of Patent Document 1 prevents the stack from drying out by adjusting the amount of water generated per unit time during power generation. More specifically, the fuel cell system of Patent Document 1 reduces the amount of cathode gas supplied to the stack, thereby reducing the amount of water removed by the cathode gas. This prevents the stack from drying out.

[0003] In such a case, the air stoichiometric ratio is lower than normal. The air stoichiometric ratio is the ratio of the amount of cathode gas actually supplied to the 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 stack.

[0004] In the fuel cell system of Patent Document 1, the air stoichiometric ratio is maintained at 1.0 or higher. Therefore, the fuel cell system can generate the required power by supplying the anode gas necessary to generate the required power. If 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 provided in the fuel cell system discharges the shortage of power or charges the surplus power.

[0005] When the air stoichiometric ratio is lower than normal, moisture is likely to accumulate in the stack. When excess moisture is generated in the stack, flooding occurs. Flooding causes concentration overvoltage, which can cause the fuel cell to be unable to output the required power due to a drop in output voltage. For this reason, the fuel cell system of Patent Document 1 performs a drainage process before flooding occurs. The drainage process increases the amount of cathode gas supplied to the stack. This removes moisture that has accumulated in the stack. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2020-4675 Summary of the Invention [Problem to be solved by the invention]

[0007] However, since the wastewater treatment tends to dry out the stack, which may accelerate the deterioration of the fuel cell, the inventors have been studying ways to reduce the wastewater treatment when the air stoichiometric ratio is lower than normal.

[0008] However, the magnitude of the concentration overvoltage generated by stacks varies due to factors such as deterioration over time and variations in quality. For this reason, if wastewater treatment before flooding occurs is reduced, it is difficult to prevent concentration overvoltage caused by flooding. Therefore, there was a need for technology that could prevent the stack from drying out while also preventing a shortage of fuel cell output. [Means for solving the problem]

[0009] The present disclosure can be realized in the following forms.

[0010] (1) According to one aspect of the present disclosure, there is provided a fuel cell system including a fuel cell, an air compressor that adjusts the flow rate of a cathode gas flowing into the fuel cell, a flow rate sensor that acquires the flow rate of the cathode gas, a voltage sensor that acquires an output voltage of the fuel cell, and a controller that controls the fuel cell system, wherein the controller performs either a power-up operation that causes the air compressor to supply the cathode gas to a first air stoichiometric ratio that is equal to or greater than 1, or a power-down operation that causes the air compressor to supply the cathode gas to a second air stoichiometric ratio that is equal to or greater than 1 but lower than the first air stoichiometric ratio, and while the power-down operation is being performed, the power-up operation is performed for a predetermined first time period when a first condition is satisfied, the first condition including the output voltage being a value within a first range, and the power-up operation is not performed when a second condition is satisfied, the second condition including the output voltage being a value within a second range higher than the first range. The air stoichiometric ratio is the ratio of the amount of cathode gas actually supplied to the stack to the minimum amount of cathode gas necessary to generate the required power. For example, in order for the fuel cell to generate the required power, the air compressor is controlled so that the air stoichiometric ratio is 1 or greater. When the air stoichiometric ratio is the second air stoichiometric ratio, the flow rate of the cathode gas is reduced compared to when the air stoichiometric ratio is the first air stoichiometric ratio. This reduces the amount of water removed from the fuel cell, preventing the fuel cell from drying out. However, when the air stoichiometric ratio is the second air stoichiometric ratio, the amount of water contained in the fuel cell increases, increasing the possibility of concentration overvoltage due to flooding. The concentration overvoltage reduces the output voltage of the fuel cell. In this configuration, when the output voltage falls within the first range due to a decrease in output voltage due to concentration overvoltage, a boost operation is performed so that the air stoichiometric ratio becomes the first air stoichiometric ratio. In other words, increasing the flow rate of the cathode gas eliminates concentration overvoltage due to flooding. Therefore, the fuel cell system of the present disclosure can prevent the fuel cell from drying out by controlling the flow rate of the cathode gas in response to a decrease in output voltage due to concentration overvoltage, compared to a configuration in which the flow rate of the cathode gas is controlled to prevent concentration overvoltage in advance. Furthermore, the fuel cell system of the present disclosure can prevent insufficient output from the fuel cell by increasing the flow rate of the cathode gas in response to a decrease in output voltage. (2) In the fuel cell system of the above aspect, the first condition may include the output voltage being within the first range for a predetermined second time period. By adopting this configuration, if the output voltage drops for less than the second time, the power pull-up operation is not performed. The output voltage may drop momentarily due to, for example, a fluctuation in the required power. Therefore, the fuel cell system of the present disclosure can prevent the power pull-up operation from being erroneously performed due to a momentary drop in output voltage. (3) In the fuel cell system of the above aspect, the control unit may execute the reduction operation after the first time period has elapsed. By adopting such a configuration, the fuel cell system of the present disclosure can prevent the fuel cell from drying out after the first time period has elapsed more effectively than a configuration in which the reduction operation is not performed. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is an explanatory diagram showing the configuration of a fuel cell system according to a first embodiment. [Figure 2] 3 is a flowchart showing a control method for a fuel cell system. [Figure 3] 10 is a waveform showing the output power of a fuel cell system when the output voltage drops. DETAILED DESCRIPTION OF THE INVENTION

[0012] A. First embodiment: A-1. Fuel cell system configuration: 1 is an explanatory diagram showing the configuration of a fuel cell system 10 according to a 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 according to this embodiment is mounted on, for example, an electric vehicle and used as a driving power source or a power source for various devices.

[0013] The fuel cell stack 100 generates electricity by receiving anode gas and cathode gas as reactant gases. 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 stack structure in which multiple unit cells serving as power generation bodies are stacked. In this specification, the "fuel cell stack" is also simply referred to as a "fuel cell" or a "stack."

[0014] A single cell includes an MEA (Membrane Electrode Assembly), a pair of gas diffusion layers arranged to sandwich the MEA, and a pair of gas separators arranged on the outside of each gas diffusion layer. The MEA includes an electrolyte membrane and an anode and a cathode, which are catalytic electrode layers formed on each side of the electrolyte membrane. In each single cell, an anode gas flow channel 120 through which anode gas flows is formed on the anode side, and a cathode gas flow channel 110 through which cathode gas flows is formed on the cathode side, with the electrolyte membrane interposed therebetween. In FIG. 1, the single cell is not shown to facilitate understanding of the technology.

[0015] In the cathode, water is generated as the electrochemical reaction progresses. This increases the amount of water contained in the cathode gas flow channel 110. However, since the water in the cathode gas flow channel 110 is removed by the cathode gas, the amount of water contained in the cathode gas flow channel 110 varies depending on the amount of water generated and the flow rate of the cathode gas. Therefore, depending on the flow rate of the cathode gas, the cathode gas flow channel 110 may dry out or flood. Adjustment of the water amount in the cathode gas flow channel 110 by the fuel cell system 10 will be described in detail later. In this specification, the water amount in the fuel cell stack 100 refers to the water amount in the cathode gas flow channel 110.

[0016] The cathode gas supply / discharge system 200 supplies cathode gas to the fuel cell stack 100 and discharges cathode gas from the fuel cell stack 100. The cathode gas supply / 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.

[0017] The cathode gas supply pipe 210 supplies cathode gas from 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 that connects the outside to the inlet of the air compressor 230, and a second cathode gas supply pipe 212 that connects the outlet of the air compressor 230 to the inlet of the cathode gas flow path 110. As a result, the cathode gas supply pipe 210 supplies the cathode gas supplied from the outside by the air compressor 230 to the cathode gas flow path 110.

[0018] The flow rate sensor 220 acquires 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 acquired flow rate to the control unit 500.

[0019] The air compressor 230 adjusts the flow rate of the cathode gas that flows 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 in accordance with a command from the control unit 500.

[0020] Adjusting the flow rate of the cathode gas adjusts the output voltage Vf of the fuel cell stack 100. The control of power of the fuel cell system 10 will be described in detail later. Furthermore, adjusting the flow rate of the cathode gas adjusts the amount of water in the fuel cell stack 100, as described above.

[0021] 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.

[0022] The anode gas supply / discharge system 300 supplies 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, and the like. The anode gas supply / discharge system 300 also includes a supply pipe and an exhaust pipe that allow the anode gas supplied from the anode gas tank to flow through the anode gas flow path 120. However, to facilitate understanding of the technology, the configuration of the anode gas supply / discharge system 300 is not shown in FIG. 1.

[0023] The output circuit 400 supplies power from the fuel cell stack 100 in accordance with the power required by the load device 440. The output circuit 400 includes a voltage sensor 410, a current sensor 420, an output adjustment unit 430, and the load device 440.

[0024] The voltage sensor 410 acquires the output voltage Vf of the fuel cell stack 100. The voltage sensor 410 sends the acquired output voltage Vf to the control unit 500.

[0025] The current sensor 420 acquires the output current If of the fuel cell stack 100. The current sensor 420 sends the acquired output current If to the control unit 500.

[0026] The output adjustment unit 430 adjusts the output power P1 of the fuel cell stack 100 in accordance with the power required by 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 in accordance with a current command value from the control unit 500. Furthermore, the output adjustment unit 430 transforms the output voltage Vf of the fuel cell stack 100 to a voltage required by the load device 440. For example, a drive device for a 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 for the motor. The control of the output adjustment unit 430 will be described in detail later. The "output adjustment unit" will also be referred to as "FDC."

[0027] The load device 440 consumes the load power P2 output from the output adjustment unit 430. The load device 440 includes, for example, a vehicle drive device including a motor and a motor drive circuit, the air compressor 230, an anode gas pump, etc. The load device 440 sends information about the required load power P2 to the control unit 500. In this specification, the load power P2 required by the load device 440 is referred to as required power.

[0028] The control unit 500 controls the fuel cell system 10. The control unit 500 is configured as a logic circuit centered around a microcomputer. More specifically, the control unit 500 includes a CPU, a ROM, a RAM, and input / output ports for inputting and outputting various signals. The CPU executes a preset control program. The ROM stores in advance control programs and control data required for the CPU to execute various arithmetic processes. The RAM temporarily reads and writes various data required for the CPU to execute various arithmetic processes. The functions of the control unit 500 are described below.

[0029] The control unit 500 performs either an operation to increase the air stoichiometric ratio or an operation to decrease the air stoichiometric ratio by controlling the flow rate of the cathode gas using the air compressor 230. The air stoichiometric ratio is the ratio of the amount of cathode gas actually supplied to the fuel cell stack 100 to the minimum amount of cathode gas necessary to generate the required power. In other words, the air stoichiometric ratio is 1.0 or greater.

[0030] The air stoichiometric ratio raising operation is an operation in which the air compressor 230 is caused to supply cathode gas so that the air stoichiometric ratio becomes 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 at which the power consumption of the vehicle's drive device is maximized. In other words, the first air stoichiometric ratio is based on the air stoichiometric ratio at which the power obtained by subtracting the power consumption of the air compressor 230, the cathode pump, etc. from the output power P1 of the fuel cell stack 100 is maximized.

[0031] The operation of decreasing the air stoichiometric ratio is an operation in which the air compressor 230 supplies cathode gas so that the air stoichiometric ratio becomes 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 included in the range of 1.2 to 1.3.

[0032] By operating the air stoichiometric ratio downward, the flow rate of the cathode gas is reduced compared to the case of the first air stoichiometric ratio. The reduction in the flow rate of the cathode gas reduces the amount of water removed from the fuel cell stack 100. In other words, the amount of water contained in the fuel cell stack 100 increases, preventing the fuel cell stack 100 from drying out. However, the increased amount of water in the fuel cell stack 100 makes flooding more likely to occur. Note that the "air stoichiometric ratio raising operation" is also simply referred to as the "raising operation," and the "air stoichiometric ratio lowering operation" is also simply referred to as the "lowering operation."

[0033] Even in the case of 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 become partially dry. In particular, the inlet portion of the cathode gas flow path 110 may become dry. In such a case, by performing operation to decrease the air stoichiometric ratio, the fuel cell stack 100 is prevented from drying out.

[0034] The control unit 500 further controls the output power P1 of the fuel cell stack 100 in accordance with the power required by the load device 440. More specifically, the control unit 500 acquires information about the required power from the load device 440. The control unit 500 controls the air compressor 230 based on a predetermined reference value for the output voltage Vf in accordance with the required power. When cathode gas is supplied to the fuel cell stack 100, the fuel cell stack 100 starts to generate power, thereby generating the output voltage Vf. The control unit 500 also controls the output adjustment unit 430 based on a predetermined reference value for the output current If in accordance with the required power. That is, 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 the output current If in accordance with the reference value for the output current If. Furthermore, the control unit 500 acquires the output current If and the output voltage Vf from the voltage sensor 410 and the current sensor 420. The control unit 500 calculates the output power P1 based on the acquired output current If and output voltage Vf. The control unit 500 calculates the output current If to be extracted by the output adjustment unit 430 based on the difference between the calculated output power P1 and the required power. Therefore, the output adjustment unit 430 causes the fuel cell stack 100 to output the output power P1 of the fuel cell stack 100 that corresponds to the required power.

[0035] A-2. Control method of fuel cell system: 2 is a flowchart showing a control method for the fuel cell system 10. The control method for the fuel cell system 10 will be described below. The control unit 500 repeatedly executes the following process while the fuel cell system 10 is in operation.

[0036] 2, it is determined whether or not an operation to decrease the air stoichiometric ratio is being performed. That is, if the air stoichiometric ratio is not the second air stoichiometric ratio, the control unit 500 advances the process to step S150. If the air stoichiometric ratio is the second air stoichiometric ratio, the control unit 500 advances the process to step S110.

[0037] In step S110 of FIG. 2, the control unit 500 determines whether the output voltage Vf of the fuel cell stack 100 has decreased. If the output voltage Vf has decreased, this occurs when a concentration overvoltage has occurred due to flooding. Specifically, the control unit 500 proceeds to step S120 when a first condition is satisfied, including that the voltage sensor 410 determines that the output voltage Vf of the fuel cell stack 100 is a value included in a first range. The control unit 500 proceeds to step S160 when the voltage sensor 410 determines that a second condition is satisfied, including that the output voltage Vf of the fuel cell stack 100 is a value included in a second range higher than the first range.

[0038] The "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 second range is equal to or greater than the threshold, and the first range is equal to or less than the threshold. The threshold is experimentally set based on, for example, the minimum value of the output voltage Vf that can be reached by a sudden increase in the load power P2.

[0039] The first condition further includes a condition that the output voltage Vf falls within the first range for 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 configuration, if the output voltage Vf drops for less than the second time, the pull-up operation is not performed. The output voltage Vf may drop momentarily due to fluctuations in the load power P2. Therefore, the fuel cell system 10 of the present disclosure can prevent the pull-up operation from being erroneously performed due to a momentary drop in the output voltage Vf. In this specification, the "second time" is also referred to as the "determination time for preventing erroneous determination."

[0040] 2, the control unit 500 executes an operation to increase the air stoichiometric ratio. That is, the control unit 500 increases the flow rate of the cathode gas by the air compressor 230 so that the air stoichiometric ratio becomes the first air stoichiometric ratio.

[0041] In step S130 of FIG. 2, the control unit 500 continues to perform the pull-up operation for a predetermined first time period so that the air stoichiometric ratio is maintained at the first air stoichiometric ratio. The first time period is the time required to resolve flooding. In this specification, the "first time period" is also referred to as the "drainage time period." The drainage time period is experimentally set according to the specifications of the fuel cell stack 100. For example, the drainage time period is 30 minutes.

[0042] 2, the control unit 500 executes an operation to decrease the air stoichiometric ratio after the first time period has elapsed. That is, the control unit 500 controls the air compressor 230 to decrease the flow rate of the cathode gas so that the air stoichiometric ratio becomes the second air stoichiometric ratio.

[0043] 2, the control unit 500 continues operation so as to achieve the conventional air stoichiometric ratio. That is, the control unit 500 continues operation so as to maintain the air stoichiometric ratio at step S100.

[0044] In step S160 of FIG. 4, the control unit 500 continues operation with the air stoichiometric ratio reduced.

[0045] The above process is repeated while the fuel cell stack 100 outputs the output power P1. That is, after the process of any one of steps S140 to S160 in Fig. 3, the control unit 500 starts the process of step S100.

[0046] Regarding the above, when the air stoichiometric ratio becomes the second air stoichiometric ratio, the flow rate of the cathode gas is reduced compared to when the air stoichiometric ratio is the first air stoichiometric ratio. This reduces the amount of water removed from the fuel cell, preventing the fuel cell from drying out. However, when the air stoichiometric ratio becomes the second air stoichiometric ratio, the amount of water contained in the fuel cell increases, increasing the possibility of concentration overvoltage due to flooding. Concentration overvoltage reduces the output voltage Vf of the fuel cell.

[0047] Fig. 3 shows a waveform illustrating the output power P1 of the fuel cell system 10 when the output voltage Vf decreases. In the waveform of Fig. 3, the horizontal direction of the drawing indicates the passage of time, and the vertical direction of the drawing indicates the magnitude of the value. In the fuel cell system 10 of the present disclosure, when the output voltage Vf decreases due to concentration overvoltage and becomes less than the threshold value, a boost operation is performed so that the air stoichiometric ratio becomes the first air stoichiometric ratio. In other words, the flow rate of the cathode gas is increased.

[0048] As a result, the air stoichiometric ratio changes from the second air stoichiometric ratio to the first air stoichiometric ratio, as shown in Figure 3. Therefore, the concentration overvoltage caused by flooding is eliminated, and the output voltage Vf increases. However, the condition for determining a decrease in the output voltage Vf is that the decrease in the output voltage Vf continues beyond the determination time for preventing erroneous determination.

[0049] 3, the output current If fluctuates with fluctuations in the output voltage Vf because the output adjustment unit 430 causes the fuel cell stack 100 to output an output power P1 that satisfies the required power, thereby keeping the output power P1 constant.

[0050] Therefore, 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 flow rate of the cathode gas is controlled to prevent concentration overvoltage by controlling the flow rate of the cathode gas in accordance with a decrease in output voltage Vf due to concentration overvoltage. Furthermore, the fuel cell system 10 of the present disclosure can prevent insufficient output from the fuel cell by increasing the flow rate of the cathode gas in accordance with a decrease in output voltage Vf.

[0051] Furthermore, by adopting this configuration, if the output voltage Vf drops below the determination time for preventing erroneous determination, the power-up operation is not executed. The output voltage Vf may drop momentarily due to, for example, a fluctuation in the required power. Therefore, the fuel cell system 10 of the present disclosure can prevent the power-up operation from being erroneously executed due to a momentary drop in the output voltage Vf.

[0052] 3, after the drainage time has elapsed, the fuel cell system 10 operates to decrease the air stoichiometric ratio from the first air stoichiometric ratio to the second air stoichiometric ratio, thereby again operating to prevent the fuel cell stack 100 from drying out.

[0053] By adopting such a configuration, the fuel cell system 10 of the present disclosure can prevent the fuel cell from drying out after the first time period has elapsed more effectively than a configuration in which the reduction operation is not performed.

[0054] B. Variations: (1) In the above embodiment, the first air stoichiometric ratio is 1.5. However, the first air stoichiometric ratio may be any value as long as it is 1.5 or greater. Furthermore, in the above embodiment, the second air stoichiometric ratio is a value within the range of 1.2 to 1.3. However, the second air stoichiometric ratio may be any value as long as it is 1.0 or greater and less than 1.5. (2) In the above embodiment, the control unit 500 does not perform the power-up operation when the output voltage Vf drops below the time limit for preventing erroneous determination. However, the control unit 500 may perform the power-up operation when the output voltage Vf drops below the time limit for preventing erroneous determination. This configuration facilitates control. (3) In the above embodiment, the control unit 500 executes the reduction operation after the first time has elapsed. However, the control unit 500 does not have to execute the reduction operation after the first time has elapsed. Even if the reduction operation is not executed, the drying of the fuel cell stack 100 is reduced because the reduction operation has already been executed. (4) In the above embodiment, the control unit 500 may be configured with a plurality of microcomputers. More specifically, the function of the control unit 500 to increase or decrease the air stoichiometric ratio or to control the output adjustment unit 430 does not have to be realized by a single microcomputer.

[0055] The present disclosure is not limited to the above-described embodiments and can be realized in various configurations without departing from the spirit thereof. For example, the technical features of the embodiments corresponding to the technical features in each aspect described in the Summary of the Invention section can be appropriately replaced or combined to solve some or all of the above-described problems or achieve some or all of the above-described effects. Furthermore, if a technical feature is not described as essential in this specification, it can be appropriately deleted. [Explanation of symbols]

[0056] 10... fuel cell system, 100... fuel cell stack, 110... cathode gas flow path, 120... anode gas flow path, 200... cathode gas supply / discharge system, 210... cathode gas supply pipe, 211... first cathode gas supply pipe, 212... second cathode gas supply pipe, 220... flow rate sensor, 230... air compressor, 240... cathode gas discharge pipe, 300... anode gas supply / discharge system, 400... output circuit, 410... voltage sensor, 420... current sensor, 430... output adjustment unit, 440... load device, 500... control unit, If... output current, P1... output power, P2... load power, Vf... output voltage

Claims

1. 1. A fuel cell system, comprising: A fuel cell; an air compressor for adjusting the flow rate of the cathode gas flowing into the fuel cell; a flow rate sensor for acquiring a flow rate of the cathode gas; a voltage sensor for acquiring an output voltage of the fuel cell; a control unit that controls the fuel cell system, The control unit performing either a raising operation in which the air compressor is caused to supply the cathode gas so as to achieve a first air stoichiometric ratio that is equal to or greater than 1, or a lowering operation in which the air compressor is caused to supply the cathode gas so as to achieve a second air stoichiometric ratio that is equal to or greater than 1 and is lower than the first air stoichiometric ratio; When the lowering operation is being performed, When a first condition is satisfied, the first condition including the output voltage being a value included in a first range, the pull-up operation is performed for a predetermined first time period; The fuel cell system does not perform the boost operation when a second condition is satisfied, the second condition including the output voltage being a value included in a second range higher than the first range.

2. 2. The fuel cell system according to claim 1, The first condition includes the output voltage being within the first range for a second predetermined time period.

3. 3. The fuel cell system according to claim 2, The control unit executes the reduction operation after the first time period has elapsed.

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