Fuel cell system

Abstract

To set appropriate limit values according to the water content and temperature of the power generation cell to prevent excessive current limiting.SOLUTION: A fuel cell system 100 includes: a fuel cell stack constructed by stacking power generation cells each having an electrolyte membrane and an electrode; a warm-up determination unit 21 that determines whether to warm up the fuel cell stack when performing low-temperature startup operation to start the fuel cell stack from a predetermined low-temperature state; and a current control unit 24 that controls the output current output from the fuel cell stack in accordance with the required power. When the warm-up determination unit 21 determines that warm-up should be performed, the current control unit 24 limits the output current to a first limit value or less, and when the warm-up determination unit 21 determines that warm-up should not be performed, the current control unit limits the output current to a second limit value or less that is smaller than the first limit value.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 vehicles, etc., 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 up in a low-temperature environment (see, for example, Patent Document 1). In the device described in Patent Document 1, if the stack temperature at start-up is below a predetermined freezing temperature, the device limits the output current from the stack so as to constantly increase the sweep current value from the fuel cell to the power supply destination, and raises the stack temperature until it reaches or exceeds the predetermined freezing temperature. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-42566 Summary of the Invention [Problem to be solved by the invention]

[0004] In the device described in Patent Document 1, whenever the stack temperature is below a predetermined freezing point, the fuel cell stack is heated up, i.e., warmed up, while generating electricity. However, even when starting a fuel cell stack in a low-temperature environment, there are cases where warming up is performed and cases where it is not, resulting in different water contents and temperatures in the power-generating cells. In such cases, limiting the output current as in the device described in Patent Document 1 could result in excessive current limitation. [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 generating cells each having an electrolyte membrane and an electrode, a warm-up determination unit that determines whether to warm up the fuel cell stack when performing low-temperature startup operation to start the fuel cell stack from a predetermined low-temperature state, and a current control unit that controls the output current output from the fuel cell stack in accordance with the required power. When the warm-up determination unit determines that warm-up should be performed, the current control unit limits the output current to a first limit value or less, and when the warm-up determination unit determines that warm-up should not be performed, the current control unit limits the output current to a second limit value or less that is smaller than the first limit value. [Effects of the Invention]

[0006] According to the present invention, an appropriate limit value can be set depending on the water content and temperature of the power generating cell, thereby preventing excessive current limiting. [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 determination unit 21, a scavenging determination unit 22, a water content estimation unit 23, and a current control unit 24, and functions as the warm-up determination unit 21, the scavenging determination unit 22, the water content estimation unit 23, and the current control unit 24.

[0019] The warm-up determination unit 21 determines whether to warm up the fuel cell stack 1 when performing low-temperature startup operation to start 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 at or below a temperature at which warm-up may be necessary. An ambient temperature sensor may be provided to detect the ambient temperature around the fuel cell stack 1, for example, the ambient air temperature, and the state in which the ambient temperature detected by the ambient air temperature sensor is at or below a temperature at which warm-up may be necessary may be defined as the predetermined low-temperature state. In particular, below freezing temperatures may cause the water produced in each power-generating cell of the fuel cell stack 1 to freeze. However, the predetermined low-temperature state includes not only states in which the stack temperature or the ambient air temperature is below freezing but also states in which the stack temperature or the ambient air temperature is above freezing but below a temperature at which warm-up may be necessary, for example, even if the temperature is above 0°C.

[0020] When a startup command for the fuel cell system 100 is input from the command input unit 13, the warm-up determination 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 at which warm-up may be required. If the stack temperature is equal to or lower than the temperature at which warm-up may be required, the warm-up determination unit 21 determines that low-temperature startup operation of the fuel cell stack 1 will be performed, and if the stack temperature exceeds the temperature at which warm-up may be required, the warm-up determination unit 21 determines that low-temperature startup operation will not be performed. When it determines that low-temperature startup operation will be performed, the warm-up determination unit 21 determines whether or not scavenging and drying have been performed to discharge moisture from the flow paths 2, 3 to the outside since the previous shutdown of the fuel cell stack 1, the elapsed time from the previous shutdown to the current startup, the stack temperature at the time of the current startup, the outside air temperature, etc.

[0021] The warm-up of the fuel cell stack 1 is performed 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.

[0022] A heater may be provided around the fuel cell stack 1, and instead of or in addition to low-efficiency power generation, the heater may be used to warm up the fuel cell stack 1. In this case, the warm-up determination unit 21 determines whether to warm up the fuel cell stack 1, and also whether to warm up the fuel cell stack 1 using only low-efficiency power generation, only the heater, or a combination of low-efficiency power generation and the heater.

[0023] The scavenging determination unit 22 determines whether scavenging has been performed to discharge moisture from inside the fuel cell stack 1 (each flow path 2, 3) to the outside before low-temperature startup operation is performed, more specifically, after the fuel cell stack 1 was last shut down and before the current startup.

[0024] The water content estimation unit 23 estimates the water content of each power generation cell (mainly the MEA) based on the determination results by the warm-up determination unit 21 and the scavenging determination unit 22. More specifically, when the warm-up determination unit 21 determines that low-efficiency power generation for warm-up will be performed, the water content estimation unit 23 estimates the water content as a first predetermined value, and when the warm-up determination unit 21 determines that low-efficiency power generation for warm-up will not be performed, the water content estimation unit 23 estimates the water content as a second predetermined value smaller than the first predetermined value. In other words, when low-efficiency power generation in which water is produced by an electrochemical reaction is performed, the water content is estimated to be a larger value than when low-efficiency power generation is not performed.

[0025] Furthermore, the water content (first predetermined value, second predetermined value) when the scavenging determination unit 22 determines that scavenging has been performed is estimated (corrected) to be smaller than the water content when the scavenging determination unit 22 determines that scavenging has not been performed. The water content estimation unit 23 may further correct the water content based on the operation history, such as the current value and stack temperature at the last shutdown of the fuel cell stack 1, the operation time, the elapsed time from the last shutdown to the current startup, the stack temperature at the current startup, and the outside air temperature. That is, because the flow paths 2 and 3 are sealed while the fuel cell stack 1 is shut down, the water content at the current startup can be accurately estimated (corrected) based on the operation history from the last shutdown to the current startup. When the water content is estimated based on the presence or absence of warm-up or scavenging and the operation history, unlike when the water content is estimated based on the resistance (membrane resistance) of the electrolyte membrane, there is no need to provide additional sensors such as an impedance sensor, which simplifies the overall system configuration.

[0026] The current control unit 24 controls the output current output from the fuel cell stack 1 in accordance with the required power. More specifically, it calculates the supply amounts of fuel gas and oxidant gas according to the reference IV characteristic of the fuel cell stack 1 so as to satisfy the required output input from the command input unit 13, and controls the injector 5 and the air compressor 6 in accordance with the calculation results.

[0027] The current control unit 24 further controls the current limiter 11 to limit the output current from the fuel cell stack 1 to a limit value or less. Specifically, during low-temperature startup, the stack temperature is low and the saturated water vapor pressure is low, so water generated by the power generation (electrochemical reaction) in the fuel cell stack 1 is not properly discharged, resulting in flooding, 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 a rapid drop in output voltage, making operation at the reference IV characteristic impossible and resulting in unstable power generation. Furthermore, during low-temperature startup, for example, when the fuel cell stack 1 has been scavenged and dried after a previous shutdown but is not warmed up during the current startup, drying out the MEA may occur. In this case, the proton conductivity of the electrolyte membrane may decrease or the effective catalyst area of ​​the electrode catalyst layer may decrease, slowing down the electrochemical reaction, causing a rapid drop in output voltage, making operation at the reference IV characteristic impossible and resulting in unstable power generation.

[0028] The current control unit 24 sets a 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 23, and limits the output current from the fuel cell stack 1 to below the limit value. The limit 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 or drying up does not occur, depending on the stack temperature and water content. The characteristics of the limit value depending on the stack temperature and water content are stored in the electronic control unit 20 (ROM).

[0029] FIG. 3 is a diagram illustrating the characteristics of the limit value set by the current control unit 24. As shown in FIG. 3, the limit value is set to a smaller current value as the stack temperature decreases. Furthermore, the limit value (current value) when the water content is less than a predetermined water content is set to a smaller value than the limit value when the water content is equal to or greater than the predetermined water content. After the fuel cell stack 1 is started and reaches a stack temperature during normal operation (for example, approximately 50°C to 90°C), as long as operation is performed in accordance with the reference IV characteristic, there is no need to limit the output current, as there is no decrease in output voltage due to flooding or dry-up. During start-up until the fuel cell stack 1 reaches the stack temperature during normal operation, particularly during low-temperature start-up, the amount of water present inside the fuel cell stack 1 may cause a decrease in output voltage due to flooding or dry-up.

[0030] In such a region, a decrease in output voltage due to flooding or drying up 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 or drying up does not occur according to the stack temperature and water content, excessive output restriction can be suppressed and the output performance of the fuel cell stack 1 can be ensured.

[0031] When the warm-up determination unit 21 determines that low-efficiency power generation for warm-up will be performed, the water content estimation unit 23 estimates the water content as a relatively high first predetermined value, and the current control unit 24 sets the limit value to a relatively large (low) first limit value corresponding to the first predetermined value. When the warm-up determination unit 21 determines that low-efficiency power generation for warm-up will not be performed, the water content estimation unit 23 estimates the water content as a relatively low second predetermined value, and the current control unit 24 sets the limit value to a relatively small (high) second limit value corresponding to the second predetermined value. In other words, when the warm-up determination unit 21 determines that low-efficiency power generation for warm-up will be performed, the current control unit 24 limits the output current to a first limit value or less, and when the warm-up determination unit 21 determines that low-efficiency power generation for warm-up will not be performed, the current control unit 24 limits the output current to a second limit value or less that is smaller than the first limit value. Note that the limit values ​​(first limit value and second limit value) may include the current value in a state where no current limit is performed (i.e., the maximum current value during normal operation).

[0032] When the fuel cell stack 1 is warmed up only by the heater, the warm-up determination unit 21 determines that low-efficiency power generation will not be performed as warm-up, the water content estimation unit 23 estimates the water content as a relatively low second predetermined value, and the current control unit 24 sets the second limit value. When warming up by the heater, power generation starts after the stack temperature has become higher than when no warm-up is performed, so the second limit value when warming up by the heater is set larger (looser) than the second limit value when no warm-up is performed.

[0033] Furthermore, when the scavenging determination unit 22 determines that scavenging has been performed, the water content estimation unit 23 estimates the water content (first predetermined value, second predetermined value) to be smaller than when it is determined that scavenging has not been performed, and the current control unit 24 sets the limit values ​​(first limit value, second limit value) to be smaller (stricter). In other words, the current control unit 24 sets the limit values ​​when the scavenging determination unit 22 determines that scavenging has been performed to be smaller than the limit values ​​when the scavenging determination unit 22 determines that scavenging has not been performed.

[0034] While the output current is being limited by the current control unit 24, 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.

[0035] FIG. 4 is a flowchart showing an example of processing executed by the electronic control unit 20. The processing in FIG. 4 is initiated 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 below a temperature at which warm-up may be necessary and whether low-temperature startup operation should be performed. If the result in step S1 is negative, the processing ends. If the result in step S1 is positive, the processing proceeds to step S2. In step S2, it is determined whether warm-up of the fuel cell stack 1 should be performed based on whether scavenging and drying were performed after the previous shutdown of the fuel cell stack 1, the elapsed time from the previous shutdown to the current startup, the stack temperature at the time of the current startup, the outside air temperature, etc. If the result in step S2 is positive, the processing proceeds to step S3, where a limit value (first limit value) is set based on the stack temperature detected by the stack temperature sensor 9 and the water content estimated by the water content estimation unit 23, and the output current limit is limited to or below the first limit value. If the result in step S2 is negative, the process proceeds to step S4, where a limit value (second limit value) is set based on the stack temperature detected by the stack temperature sensor 9 and the moisture content estimated by the moisture content estimation unit 23, and the output current limit is limited to less than or equal to the second limit value.

[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 warm-up determination unit 21 that determines whether to warm up the fuel cell stack 1 when performing a low-temperature startup operation to start the fuel cell stack 1 from a predetermined low-temperature state, and a current control unit 24 that controls the output current output from the fuel cell stack 1 in accordance with the required power (FIGS. 1 and 2). When the warm-up determination unit 21 determines that warm-up is to be performed, the current control unit 24 limits the output current to a first limit value or less, and when the warm-up determination unit 21 determines that warm-up is not to be performed, the current control unit 24 limits the output current to a second limit value or less that is smaller than the first limit value (FIG. 4). In this way, by setting the limit value depending on whether or not warm-up is to be performed, which affects the water content and temperature of the power-generating cells, it is possible to set an appropriate limit value depending on the water content and temperature of the power-generating cells, thereby preventing excessive current limitation.

[0037] (2) The fuel cell system 100 further includes a scavenging determination unit 22 that determines whether scavenging has been performed to discharge moisture inside the fuel cell stack 1 to the outside before the cold start-up operation is performed (FIG. 2). The current control unit 24 sets the limit values ​​(first limit value, second limit value) when the scavenging determination unit 22 determines that scavenging has been performed to be smaller than the limit values ​​when the scavenging determination unit 22 determines that scavenging has not been performed. In this way, by setting the limit values ​​depending on whether scavenging has been performed, which affects the moisture content of the power generation cells, it is possible to set more appropriate limit values ​​depending on the moisture content of the power generation cells, and it is possible to further prevent excessive current limitation.

[0038] (3) The fuel cell system 100 further includes a stack temperature sensor 9 that detects the temperature (stack temperature) of the fuel cell stack 1 (FIGS. 1 and 2). The current control unit 24 sets limit values ​​(first limit value, second limit value) based on the stack temperature detected by the stack temperature sensor 9 (steps S3 and S4 in FIGS. 3 and 4). The limit values ​​are set smaller as the stack temperature decreases (FIG. 3). By setting an appropriate limit value according to the stack temperature, excessive output restrictions can be appropriately suppressed.

[0039] (4) The fuel cell system 100 further includes a water content estimation unit 23 that estimates the water content of the power generation cell based on the determination results of the warm-up determination unit 21 and the scavenging determination unit 22 (FIGS. 1 and 2). The current control unit 24 further sets limit values ​​(first limit value, second limit value) based on the water content estimated by the water content estimation unit 23 (steps S3 and S4 in FIGS. 3 and 4). The limit value when the water content is less than a predetermined water content is set smaller than the limit value when the water content is equal to or greater than the predetermined water content (FIG. 3). By setting the limit value to the maximum current value within a range that does not cause a drop in output voltage due to flooding or drying up, depending on the stack temperature and water content, excessive output restriction can be more appropriately suppressed.

[0040] 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 gas flowing through each of the flow paths 2 and 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.

[0041] 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]

[0042] 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 scavenging determination section, 23 water content estimation section, 24 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 warm-up determination unit that determines whether to warm up the fuel cell stack when performing a low-temperature startup operation in which the fuel cell stack is started from a predetermined low-temperature state; a current control unit that controls an output current output from the fuel cell stack in accordance with a required power; The current control unit limits the output current to a first limit value or less when the warm-up determination unit determines that the warm-up is to be performed, and limits the output current to a second limit value or less that is smaller than the first limit value when the warm-up determination unit determines that the warm-up is not to be performed.

2. 2. The fuel cell system according to claim 1, a scavenging determination unit that determines whether scavenging for discharging moisture from inside the fuel cell stack to the outside has been performed before the low-temperature startup operation is performed; a current control unit that sets the first limit value and the second limit value when the scavenging determination unit determines that the scavenging has been performed to be smaller than the first limit value and the second limit value when the scavenging determination unit determines that the scavenging has not been performed.

3. 3. The fuel cell system according to claim 1, a temperature detector for detecting the temperature of the fuel cell stack; the current control unit sets the first limit value and the second limit value based on the temperature detected by the temperature detection unit; A fuel cell system, characterized in that the first limit value and the second limit value are set to be smaller as the temperature is lower.

4. 4. The fuel cell system according to claim 3, a water content estimation unit that estimates the water content of the power generating cell based on the determination result by the warm-up determination unit, the current control unit further sets the first limit value and the second limit value based on the water content estimated by the water content estimation unit; A fuel cell system characterized in that the first limit value and the second limit value when the water content is less than a predetermined water content are set to be smaller than the first limit value and the second limit value when the water content is equal to or greater than the predetermined water content.

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