Fuel cell system

Abstract

To suppress the decrease in an output voltage due to flooding.SOLUTION: A fuel cell system 100 includes a fuel cell stack formed by stacking power generating cells including an electrolyte film and an electrode, a temperature detection unit 9 that detects the temperature of the fuel cell stack, a warming execution unit 21 that warms the fuel cell stack at low-temperature start-up time at which the fuel cell stack is started from a predetermined low-temperature state, a water-content estimation unit 22 that estimates the water content of the power generating cell, and a current limiting unit 23 that limits the output current output from the fuel cell stack to be less than or equal to a limit value. The current limiting unit 23 sets the limit value on the basis of the temperature detected by the temperature detection unit 9 and the water content estimated by the water-content estimation unit 22, and limits the output current to be less than or equal to the limit value after the warming by the warming execution unit 21 is completed.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a fuel cell system. [Background technology]

[0002] Using fuel cells as a driving source for a vehicle can contribute to improving energy efficiency. A known technology related to such fuel cells is a device that limits the output current from a fuel cell stack when the stack is started in a low-temperature environment (see, for example, Patent Document 1). The device described in Patent Document 1 calculates a first limit value based on the average internal temperature of the stack, calculates a second limit value based on the impedance resistance value of the stack, and limits the output current to the smaller of the first limit value and the second limit value until the stack has fully warmed up. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-228305 Summary of the Invention [Problem to be solved by the invention]

[0004] However, simply limiting the output current while the stack is warming up, as in the device described in Patent Document 1, may result in a drop in the output voltage from the stack due to flooding if a relatively large output is required immediately after warm-up is complete. [Means for solving the problem]

[0005] A fuel cell system according to one aspect of the present invention includes a fuel cell stack constructed by stacking power generation cells each having an electrolyte membrane and an electrode, a temperature detection unit for detecting the temperature of the fuel cell stack, a warm-up execution unit for warming up the fuel cell stack during low-temperature startup when the fuel cell stack is started from a predetermined low-temperature state, a water content estimation unit for estimating the water content of the power generation cells, and a current limiting unit for limiting the output current output from the fuel cell stack to a limit value or less. The current limiting unit sets the limit value based on the temperature detected by the temperature detection unit and the water content estimated by the water content estimation unit, and limits the output current to the limit value or less after warm-up by the warm-up execution unit is complete. [Effects of the Invention]

[0006] According to the present invention, it is possible to suppress a drop in output voltage due to flooding. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a diagram schematically illustrating an example of the overall configuration of a fuel cell system according to an embodiment of the present invention. [Figure 2] FIG. 1 is a block diagram showing an example of a control configuration of a fuel cell system according to an embodiment of the present invention. [Figure 3] 3 is a diagram for explaining the characteristics of a limit value set by a current limiting unit in FIG. 2; [Figure 4] 3 is a flowchart showing an example of processing executed by the electronic control unit of FIG. 2; DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 to 4. FIG. 1 is a diagram schematically illustrating an example of the overall configuration of a fuel cell system 100 according to an embodiment of the present invention. As shown in FIG. 1, the fuel cell system 100 mainly includes a fuel cell stack 1 configured by stacking power-generating cells, and an electronic control unit 20 that controls each part of the fuel cell system 100. Each power-generating cell of the fuel cell stack 1 has a membrane electrode assembly (MEA) in which electrodes (electrode catalyst layers, gas diffusion layers, etc.) are provided on both sides of a solid polymer electrolyte membrane. The fuel cell system 100 is mounted, for example, on a vehicle and can generate electric power for driving the vehicle. The fuel cell system 100 can also be mounted on mobile objects other than vehicles, such as aircraft and ships, robots, and various industrial machines.

[0009] A fuel gas containing hydrogen is supplied to the anode electrode of each power generation cell of the fuel cell stack 1 via an anode flow path 2, and an oxidant gas containing oxygen, such as air, is supplied to the cathode electrode via a cathode flow path 3. This causes an electrochemical reaction to proceed at the electrode of each power generation cell, and power is generated in the fuel cell stack 1.

[0010] A fuel gas tank storing high-pressure fuel gas is connected to the anode flow channel 2 via an ejector 4 and an injector 5, and the fuel gas in the fuel gas tank is supplied to the anode flow channel 2. A portion of the fuel gas supplied to the anode flow channel 2 is used at the anode electrode and then discharged as fuel exhaust gas from the anode flow channel 2. Water is separated from the fuel exhaust gas discharged from the anode flow channel 2 through a gas-liquid separator (not shown), after which the fuel is sucked in through the ejector 4 and supplied again to the anode flow channel 2.

[0011] An air compressor 6 for supplying oxidant gas is connected to the cathode flow channel 3, and the oxidant gas compressed by the air compressor 6 is supplied to the cathode flow channel 3. After a portion of the oxidant gas supplied to the cathode flow channel 3 is used at the cathode electrode, it is discharged to the outside from the cathode flow channel 3 as oxidant exhaust gas.

[0012] A cooling flow path 7 through which a cooling medium circulates is also provided inside the fuel cell stack 1. A water pump 8 that circulates the cooling medium via a radiator (not shown) is connected to the cooling flow path 7. A stack temperature sensor 9 is provided near the outlet of the cooling flow path 7 and detects the temperature of the cooling medium discharged from the cooling flow path 7. Since the temperature of the cooling medium discharged from the cooling flow path 7 represents the overall temperature (stack temperature) inside the fuel cell stack 1, the stack temperature sensor 9 can detect the stack temperature via the temperature of the cooling medium discharged from the cooling flow path 7.

[0013] The fuel cell stack 1 is electrically connected to a drive motor 10 via metal terminal plates that sandwich the stack of power-generating cells. A current limiter 11 is interposed between the fuel cell stack 1 and the drive motor 10, and the power generated by the fuel cell stack 1 is supplied to the drive motor 10 via the current limiter 11. The current limiter 11 limits the magnitude (current value) of the output current output from the fuel cell stack 1 to a predetermined limit value or less.

[0014] The battery 12 can be electrically connected to the current limiter 11 via a DC / DC converter (not shown). In this case, some or all of the power generated by the fuel cell stack 1 can be stored in the battery 12 via the current limiter 11. Furthermore, electrical energy generated by the drive motor 10 for vehicle travel during regenerative braking of the vehicle can also be stored in the battery 12 via the current limiter 11. Furthermore, the power stored in the battery 12 can be supplied to the drive motor 10 via the current limiter 11 as needed.

[0015] The battery 12 is provided with a battery temperature sensor 12a that detects the temperature (battery temperature) of the battery 12 and a battery voltage sensor 12b that detects the voltage (battery voltage) of the battery 12. The charging rate (SOC (State Of Charge)) of the battery 12 can be estimated based on the battery voltage detected by the battery voltage sensor 12b.

[0016] 2 is a block diagram showing an example of the control configuration of the fuel cell system 100. The electronic control unit 20 of the fuel cell system 100 includes a computer having a CPU, RAM, ROM, an I / O interface, and other peripheral circuits. As shown in FIGS. 1 and 2, sensors such as a stack temperature sensor 9, a battery temperature sensor 12a, and a battery voltage sensor 12b are connected to the electronic control unit 20, and detected values ​​from each sensor are input to the electronic control unit 20. The electronic control unit 20 is also connected to each part of the fuel cell system 100, such as the injector 5, the air compressor 6, and the current limiter 11, and the electronic control unit 20 controls each part of the fuel cell system 100.

[0017] As shown in FIG. 2 , the electronic control unit 20 is also connected to a command input unit 13 that inputs various commands, such as those for starting the fuel cell system 100 and the required output. The command input unit 13 includes, for example, an ignition switch and an accelerator position sensor of a vehicle that uses the drive motor 10 as a driving source. When a start command for the fuel cell system 100 is input from the command input unit 13, the electronic control unit 20 controls the injector 5 and the air compressor 6 to supply fuel gas and oxidant gas to the fuel cell stack 1 so that power is generated in the fuel cell stack 1. The electronic control unit 20 also calculates the flow rates of the fuel gas and oxidant gas to be supplied to the fuel cell stack 1 based on the detection values ​​of each sensor and the required output input from the command input unit 13, and controls the injector 5 and the air compressor 6 according to the calculation results. The electronic control unit 20 also calculates a limit value for the output current from the fuel cell stack 1 based on the detection values ​​of each sensor, and controls the current limiter 11 according to the calculation results.

[0018] As shown in FIG. 2, the electronic control unit 20 has, as its functional configuration, a warm-up execution unit 21, a moisture content estimation unit 22, and a current limiting unit 23, and functions as the warm-up execution unit 21, the moisture content estimation unit 22, and the current limiting unit 23.

[0019] The warm-up execution unit 21 warms up the fuel cell stack 1 during low-temperature startup, which starts the fuel cell stack 1 from a predetermined low-temperature state. The predetermined low-temperature state is a state in which the stack temperature detected by the stack temperature sensor 9 is below a temperature at which warm-up is required. An ambient temperature sensor may be provided to detect the ambient temperature around the fuel cell stack 1, for example, the ambient temperature, and the state in which the ambient temperature detected by the ambient temperature sensor is below a temperature at which warm-up is required may be defined as the predetermined low-temperature state. In particular, below freezing temperatures may cause the water generated in each power-generating cell of the fuel cell stack 1 to freeze. Therefore, when the stack temperature or the ambient temperature is below freezing, the fuel cell stack 1 is warmed up until the stack temperature is raised to at least 0°C or above. However, the predetermined low-temperature state may include not only a state in which the stack temperature or the ambient temperature is below freezing, but also a state in which the stack temperature or the ambient temperature is above 0°C but below a temperature at which warm-up is required.

[0020] When a start-up command for the fuel cell system 100 is input from the command input unit 13, the warm-up execution unit 21 determines whether the stack temperature detected by the stack temperature sensor 9 (or the outside air temperature detected by the outside air temperature sensor) is equal to or lower than the temperature required for warm-up. If the stack temperature is equal to or lower than the temperature required for warm-up, the warm-up execution unit 21 executes warm-up of the fuel cell stack 1, and if the stack temperature exceeds the temperature required for warm-up, the warm-up execution unit 21 does not execute warm-up of the fuel cell stack 1.

[0021] When warming up the fuel cell stack 1, the warm-up execution unit 21 sets the stack temperature at which to end the warm-up (warm-up completion temperature) or the time for which to perform the warm-up (warm-up time) based on the stack temperature detected by the stack temperature sensor 9 at the start of the warm-up.

[0022] The warm-up completion temperature is set to at least 0°C or higher depending on the stack temperature at the start of warm-up. The characteristics of an appropriate warm-up completion temperature depending on the stack temperature at the start of warm-up are determined in advance by testing and stored in the electronic control unit 20 (ROM). The lower the stack temperature at the start of warm-up, the higher the appropriate warm-up completion temperature is set to. More specifically, if the stack temperature at the start of warm-up is a relatively low temperature even below freezing (for example, about -30°C), the appropriate warm-up completion temperature is set to a relatively high temperature (for example, about 50°C) that is close to the stack temperature during normal operation of the fuel cell stack 1 (for example, about 50°C to 90°C). On the other hand, if the stack temperature at the start of warm-up is a relatively high temperature even below freezing (for example, about -10°C to -5°C), the appropriate warm-up completion temperature is set to a relatively low temperature above 0°C (for example, about 20°C to 30°C).

[0023] The appropriate warm-up time according to the stack temperature at the start of warm-up is the time required to raise the temperature of the fuel cell stack 1 from the stack temperature at the start of warm-up to the corresponding warm-up completion temperature. The characteristics of the appropriate warm-up time according to the stack temperature at the start of warm-up can also be determined in advance by testing and stored in the electronic control unit 20. Both the characteristics of the appropriate warm-up completion temperature according to the stack temperature at the start of warm-up and the characteristics of the appropriate warm-up time according to the stack temperature at the start of warm-up may be stored in the electronic control unit 20, or only one of them may be stored in the electronic control unit 20.

[0024] The warm-up execution unit 21 sets the warm-up completion temperature or warm-up time based on the stack temperature at the start of warm-up and the characteristics stored in the electronic control unit 20, and performs warm-up of the fuel cell stack 1 until the warm-up time or stack temperature reaches the warm-up completion temperature.

[0025] Warming up the fuel cell stack 1 is performed, for example, as low-efficiency power generation, in which the amount of oxidant gas supplied to the cathode flow path 3 is reduced compared to normal operation of the fuel cell stack 1. In low-efficiency power generation, the amount of oxidant gas supplied to the cathode flow path 3 is reduced compared to normal operation, and the ratio of the air supply amount to the theoretical air consumption amount required for power generation (electrochemical reaction) in the fuel cell stack 1 (air stoichiometric ratio) is reduced compared to normal operation. In this case, the oxygen concentration at the interface of the cathode electrode is lower than during normal operation. Therefore, to maintain the current value, it is necessary to consume voltage (concentration overvoltage) to increase the probability of electron exchange between the cathode electrode and oxygen. This concentration overvoltage reduces the output voltage compared to normal operation, resulting in low-efficiency power generation with an output voltage lower than the IV characteristic (reference IV characteristic) during normal operation. This results in greater power generation loss compared to normal operation. The power generation loss is converted into thermal energy and heats up the fuel cell stack 1. Therefore, low-efficiency power generation allows the fuel cell stack 1 to heat up more quickly than during normal operation.

[0026] When warming up the fuel cell stack 1, the warm-up execution unit 21 controls the injector 5 and the air compressor 6 to supply fuel gas and oxidant gas to the fuel cell stack 1 so as to reduce the air stoichiometric ratio and perform low-efficiency power generation in the fuel cell stack 1. A heater may be provided around the fuel cell stack 1, and the heater may be used to warm up the fuel cell stack 1 in addition to performing low-efficiency power generation.

[0027] The water content estimation unit 22 estimates the water content of each power-generating cell (mainly the MEA) based on the operation history of the fuel cell stack 1. The operation history includes, for example, the current value and stack temperature at the last shutdown of the fuel cell stack 1, the operation time, whether warming up, scavenging, or draining of each flow path 2, 3 was performed after the last shutdown, the elapsed time from the last shutdown to the current startup, the stack temperature at the current startup, and the outside air temperature. Because the flow paths 2, 3 are sealed while the fuel cell stack 1 is shut down, the water content at the current startup can be accurately estimated based on the operation history from the last shutdown to the current startup. Furthermore, estimating the water content based on the operation history of the fuel cell stack 1 does not require additional sensors such as an impedance sensor, unlike estimating the water content based on the resistance of the power-generating cells, thereby simplifying the overall system configuration.

[0028] When the warm-up by the warm-up execution unit 21 is complete, the current limiting unit 23 controls the current limiter 11 to limit the output current output from the fuel cell stack 1 to a limit value or less for a predetermined time (for example, about 15 seconds) from the time the warm-up is complete. When the warm-up of the fuel cell stack 1 is complete, the supply amounts of fuel gas and oxidant gas are calculated according to the reference IV characteristic so as to satisfy the required output input from the command input unit 13, and the injector 5 and air compressor 6 are controlled according to the calculation results. If the fuel cell stack 1 has not yet reached the stack temperature during normal operation (for example, about 50°C to 90°C) when the warm-up is complete, and a relatively large output is required immediately after the warm-up is complete, the output voltage may drop due to flooding, resulting in unstable power generation.

[0029] That is, when the stack temperature is low and the saturated water vapor pressure is low, water generated by the power generation (electrochemical reaction) in the fuel cell stack 1 is not properly discharged, and flooding may occur, where water accumulates at the cathode electrode interface. In this case, the oxygen concentration at the cathode electrode interface is insufficient, slowing down the electrochemical reaction, causing the output voltage to drop rapidly, making it impossible to operate at the standard IV characteristic and resulting in unstable power generation. In particular, when the fuel cell stack 1 is warmed up using low-efficiency power generation, water is generated even during warm-up when the stack temperature is low, making flooding more likely to occur.

[0030] The current limiting unit 23 sets a limiting value based on the stack temperature detected by the stack temperature sensor 9 and the water content estimated by the water content estimating unit 22, and limits the output current from the fuel cell stack 1 to below the limiting value. The limiting value is determined in advance through testing as the maximum current value in the range in which a drop in output voltage due to flooding does not occur, depending on the stack temperature and water content. The characteristics of the limiting value depending on the stack temperature and water content are stored in the electronic control unit 20 (ROM).

[0031] FIG. 3 is a diagram illustrating the characteristics of the limit value set by the current limiting unit 23. As shown in FIG. 3, the limit value is set to a smaller current value as the stack temperature decreases and as the water content increases. After warm-up is complete and the stack temperature reaches the stack temperature during normal operation of the fuel cell stack 1 (e.g., approximately 50°C to 90°C), a decrease in output voltage due to flooding does not occur as long as operation is performed in accordance with the reference IV characteristic, and output current limiting is not necessary. After warm-up is complete and before the stack temperature during normal operation is reached, a decrease in output voltage due to flooding may occur depending on the amount of water present inside the fuel cell stack 1. In such a range, a decrease in output voltage due to flooding can be suppressed by setting a limit value according to the stack temperature and water content and limiting the output current. By setting the limit value to the maximum current value within a range in which a decrease in output voltage due to flooding does not occur depending on the stack temperature and water content, excessive output limiting can be suppressed and the output performance of the fuel cell stack 1 can be ensured.

[0032] Even if the stack temperature after warm-up is completed is relatively low, it gradually rises as the fuel cell stack 1 operates, and after a predetermined time (for example, about 15 seconds), it reaches a temperature range for normal operation where there is no risk of a drop in output voltage due to flooding. When a predetermined time has elapsed since the warm-up execution unit 21 completed warm-up, the current limiting unit 23 ends (cancels) the output current limiting and controls the current limiter 11 to perform normal operation in accordance with the reference IV characteristic of the fuel cell stack 1. In this way, by ending the output current limiting after a necessary and sufficient predetermined time, excessive output limiting can be suppressed, and the output performance of the fuel cell stack 1 can be ensured.

[0033] While the output current is being limited by the current limiting unit 23, it may not be possible to satisfy the required output input from the command input unit 13. In this case, power may be supplied from the battery 12 to the drive motor 10 on the condition that the SOC based on the battery temperature detected by the battery temperature sensor 12a and the battery voltage detected by the battery voltage sensor 12b is equal to or greater than a predetermined threshold.

[0034] FIG. 4 is a flowchart showing an example of processing executed by the electronic control unit 20. The processing in FIG. 4 is started when a startup command for the fuel cell system 100 is input from the command input unit 13. As shown in FIG. 4, first, in step S1, it is determined whether the stack temperature detected by the stack temperature sensor 9 is equal to or lower than the temperature required for warming up. If the result in step S1 is negative, the processing ends, and if the result in step S1 is positive, the processing proceeds to step S2. In step S2, a warm-up completion condition (warm-up completion temperature or warm-up time) is set based on the stack temperature detected by the stack temperature sensor 9 in step S1, and the processing proceeds to step S3, where warm-up of the fuel cell stack 1 is started. Next, in step S4, it is determined whether the warm-up completion condition set in step S2 is satisfied. If the result in step S4 is negative, the processing returns to step S3 to continue warming up the fuel cell stack 1, and if the result in step S4 is positive, the warm-up is terminated and the processing proceeds to step S5.

[0035] In step S5, a limiting value is set based on the stack temperature detected by the stack temperature sensor 9 and the water content estimated by the water content estimator 22, and output current limiting is initiated. Next, in step S6, it is determined whether a predetermined time has elapsed since warm-up was completed (output current limiting was initiated). If the result in step S6 is negative, the process returns to step S5 to continue output current limiting, and if the result in step S6 is positive, the process proceeds to step S7 to end (cancel) output current limiting and terminate the process. When the process in FIG. 4 is completed, the process transitions to normal operation in accordance with the reference IV characteristic of the fuel cell stack 1.

[0036] According to this embodiment, the following effects can be achieved. (1) A fuel cell system 100 includes a fuel cell stack 1 configured by stacking power-generating cells each having an electrolyte membrane and an electrode, a stack temperature sensor 9 for detecting the temperature (stack temperature) of the fuel cell stack 1, a warm-up execution unit 21 for warming up the fuel cell stack 1 during low-temperature startup when the fuel cell stack 1 is started from a predetermined low-temperature state, a water content estimation unit 22 for estimating the water content of the power-generating cells, and a current limiting unit 23 for limiting the output current output from the fuel cell stack 1 to a limit value or less (FIGS. 1 and 2). The current limiting unit 23 sets the limit value based on the stack temperature detected by the stack temperature sensor 9 and the water content estimated by the water content estimation unit 22, and limits the output current to a limit value or less after the warm-up by the warm-up execution unit 21 is completed (steps S5 to S7 in FIGS. 3 and 4).

[0037] By limiting the output current after the warm-up of the fuel cell stack 1 is completed in this way, it is possible to suppress a drop in output voltage due to flooding, even if a relatively large output is required immediately after the warm-up is completed. Furthermore, by setting the limit value based on the stack temperature and water content, it is possible to accurately set an appropriate limit value. Furthermore, by setting the limit value to the maximum current value within a range in which a drop in output voltage due to flooding does not occur, depending on the stack temperature and water content, it is possible to suppress excessive output limiting and ensure the output performance of the fuel cell stack 1.

[0038] (2) The limit value is set smaller the lower the stack temperature and the higher the water content (Figure 3). If a relatively large output is required when the stack temperature is relatively low immediately after the fuel cell stack 1 has finished warming up, flooding may occur depending on the amount of water present inside the fuel cell stack 1, and the output voltage output from the stack may decrease. After the fuel cell stack 1 has finished warming up, by limiting the output current to a necessary level based on the stack temperature and water content, it is possible to prevent a decrease in output voltage due to flooding while maintaining the output performance of the fuel cell stack 1.

[0039] (3) The current limiting unit 23 limits the output current to a limit value or less for a predetermined time from the point at which the warm-up by the warm-up execution unit 21 is completed (steps S5 to S7 in FIG. 4). Even if the stack temperature is relatively low at the point at which the warm-up is completed, it gradually rises as the fuel cell stack 1 operates, and after the predetermined time it reaches a temperature range during normal operation where there is no risk of a drop in output voltage due to flooding. By ending the output current limiting after such a predetermined time, excessive output limitation can be suppressed, and the output performance of the fuel cell stack 1 can be ensured.

[0040] (4) The warm-up execution unit 21 sets the warm-up time or warm-up completion temperature based on the stack temperature detected at the start of warm-up, and continues warming up the fuel cell stack 1 for the warm-up time or until the stack temperature reaches the warm-up completion temperature (steps S3 to S4 in FIG. 4). By setting an appropriate warm-up time or warm-up completion temperature according to the stack temperature at the start of warm-up, it is possible to minimize the decrease in energy efficiency due to warm-up, which is accompanied by power generation loss.

[0041] (5) The warm-up completion temperature is set to 0°C or higher, and the warm-up time is set so that the stack temperature detected at the completion of warm-up is 0°C or higher. In a predetermined low-temperature state where the outside air temperature or stack temperature is below the temperature required for warm-up, there is a risk that the water generated in each power generation cell of the fuel cell stack 1 will freeze. Therefore, when the outside air temperature or stack temperature is below the temperature required for warm-up, the fuel cell stack 1 is warmed up until the stack temperature is raised to at least 0°C or higher.

[0042] In the above embodiment, an example has been described in which the temperature of the cooling medium discharged from the cooling flow path 7 is detected as the stack temperature in Fig. 1 etc., but the physical quantity representing the temperature of the fuel cell stack is not limited to this. For example, the temperature of the oxidant exhaust gas discharged from the cathode flow path 3 may be detected as the physical quantity representing the temperature of the fuel cell stack, or the temperature of the fuel cell stack 1 itself (for example, each power generation cell) may be detected.

[0043] In the above embodiment, an example has been described in which the water content is estimated based on the operation history of the fuel cell stack 1 and the output current limit value is set according to the stack temperature and water content, as shown in FIG. 3 and elsewhere. However, the characteristics for setting the limit value are not limited to this. That is, the limit value, which is the maximum current value within the range in which a drop in output voltage due to flooding does not occur, varies depending on the amount of water present inside the fuel cell stack 1, more specifically, on the cathode side, and the stack temperature. The amount of water varies depending on the operation history of the fuel cell stack 1 from shutdown to startup. Furthermore, the water content of the power-generating cells (mainly the MEA) and the relative humidity of the oxidant exhaust gas discharged from the cathode flow path 3 vary in response to the amount of water. Therefore, the characteristics of the limit value may be determined based on the relative humidity of the oxidant exhaust gas discharged from the cathode flow path 3 and the stack temperature. Alternatively, the characteristics of the limit value according to the stack temperature may be determined for each pattern of the operation history, such as the presence or absence of scavenging and drainage, from shutdown to startup of the fuel cell stack 1.

[0044] The above description is merely an example, and the present invention is not limited to the above-described embodiment and modifications as long as the features of the present invention are not impaired. One or more of the above-described embodiment and modifications can be arbitrarily combined, and modifications can also be combined with each other. [Explanation of symbols]

[0045] 1 fuel cell stack, 2 anode flow path, 3 cathode flow path, 4 ejector, 5 injector, 6 air compressor, 7 cooling flow path, 8 water pump, 9 stack temperature sensor, 10 drive motor, 11 current limiter, 12 battery, 12a battery temperature sensor, 12b battery voltage sensor, 13 command input section, 20 electronic control unit, 21 warm-up execution section, 22 water content estimation section, 23 current limiting section, 100 fuel cell system

Claims

1. a fuel cell stack formed by stacking power generation cells each having an electrolyte membrane and an electrode; a temperature detection unit that detects the temperature of the fuel cell stack; a warm-up execution unit that warms up the fuel cell stack during low-temperature startup, in which the fuel cell stack is started from a predetermined low-temperature state; a water content estimation unit that estimates the water content of the power generating cell; a current limiting unit that limits the output current output from the fuel cell stack to a limit value or less, a current limiting unit that sets the limit value based on the temperature detected by the temperature detection unit and the water content estimated by the water content estimation unit, and limits the output current to less than or equal to the limit value after warm-up by the warm-up execution unit is completed.

2. 2. The fuel cell system according to claim 1, A fuel cell system, characterized in that the limit value is set to be smaller as the temperature is lower and as the water content is higher.

3. 3. The fuel cell system according to claim 1, The fuel cell system is characterized in that the current limiting unit limits the output current to the limit value or less for a predetermined time from the point in time when the warm-up by the warm-up execution unit is completed.

4. 3. The fuel cell system according to claim 1, The warm-up execution unit sets a warm-up time or a warm-up completion temperature based on the temperature detected by the temperature detection unit at the start of warm-up, and continues warming up the fuel cell stack until the warm-up time or the temperature detected by the temperature detection unit reaches the warm-up completion temperature.

5. 5. The fuel cell system according to claim 4, The warm-up completion temperature is set to 0°C or higher, The fuel cell system is characterized in that the warm-up time is set so that the temperature detected by the temperature detection unit is 0° C. or higher when the warm-up is completed.

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