Fuel cell system

Abstract

To suppress a decrease in output voltage even when the interior of the fuel cell stack becomes high in temperature.SOLUTION: A fuel cell system 100 includes a fuel cell stack provided with an anode flow path through which a fuel gas containing hydrogen flows, and a cathode flow path through which an oxidant gas containing oxygen flows, a fuel gas supply unit 5 that supplies the fuel gas to the anode flow path, an oxidant gas supply unit 6 that supplies the oxidant gas to the cathode flow path, an oxygen partial pressure detection unit 21 that detects either the oxygen partial pressure of the oxidant gas flowing through the cathode flow path or a representative value of oxygen partial pressure, which is a physical quantity correlated with the oxygen partial pressure, and a current limiting unit 22 that, on the basis of the oxygen partial pressure or the representative value of oxygen partial pressure detected by the oxygen partial pressure detection unit 21, limits the output current from the fuel cell stack such that the output current becomes equal to or less than a predetermined value when the oxygen partial pressure falls below a predetermined pressure.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. As a technology related to such fuel cells, a device that limits the output current from a fuel cell stack is known (see, for example, Patent Document 1). The device described in Patent Document 1 calculates the delay time of air from a flow sensor until it reaches the fuel cell based on the volumetric flow rate of air, calculates the volumetric flow rate of air inside the fuel cell based on the volumetric flow rate of air and the delay time, and limits the generated current of the fuel cell so that it corresponds to the volumetric flow rate of air inside the fuel cell. [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, when the temperature inside the fuel cell stack rises, the partial pressure of water vapor in the oxidant gas (air) rises, causing a decrease in the partial pressure of oxygen. Therefore, if the output current is simply limited according to the air flow rate, as in the device described in Patent Document 1, there is a risk that the output voltage from the stack will decrease when the temperature inside the fuel cell stack rises. [Means for solving the problem]

[0005] A fuel cell system according to one aspect of the present invention comprises a fuel cell stack having an anode flow path through which a fuel gas containing hydrogen flows and a cathode flow path through which an oxidant gas containing oxygen flows, a fuel gas supply unit that supplies the fuel gas to the anode flow path, an oxidant gas supply unit that supplies the oxidant gas to the cathode flow path, an oxygen partial pressure detection unit that detects the oxygen partial pressure of the oxidant gas flowing through the cathode flow path or a representative oxygen partial pressure amount which is a physical quantity that correlates with the oxygen partial pressure, and a current limiting unit that, based on the oxygen partial pressure or representative oxygen partial pressure amount detected by the oxygen partial pressure detection unit, limits the output current output from the fuel cell stack to a predetermined value or less when the oxygen partial pressure falls below a predetermined pressure. [Effects of the Invention]

[0006] According to the present invention, it is possible to suppress a decrease in output voltage even when the temperature inside the fuel cell stack becomes high. [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] 2 is a diagram for explaining the relationship between the flow rate of the oxidant gas flowing through the cathode flow channel in FIG. 1 and the decrease in output voltage of the fuel cell stack. FIG. [Figure 4] 2 is a diagram for explaining the relationship between the oxygen partial pressure of the oxidant gas flowing through the cathode flow channel in FIG. 1 and a decrease in output voltage of the fuel cell stack. FIG. [Figure 5] 3 is a diagram for explaining the characteristics of a limit value set by a current limiting unit in FIG. 2; [Figure 6A] 3 is a flowchart showing an example of processing executed by the electronic control unit of FIG. 2; [Figure 6B] 10 is a flowchart showing another example of the 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 6B. 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 each having a solid polymer electrolyte membrane, and an electronic control unit 20 that controls each part of the fuel cell system 100. 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 moving bodies other than vehicles, such as aircraft and ships, robots, and various industrial machines.

[0009] The fuel cell stack 1 is provided with an anode flow path 2 through which a fuel gas containing hydrogen flows, and a cathode flow path 3 through which an oxidant gas containing oxygen, such as air, flows. The fuel gas is supplied to the anode electrode of each power generation cell of the fuel cell stack 1 via the anode flow path 2, and the oxidant gas is supplied to the cathode electrode via the 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 by the injector 5. The fuel gas supplied to the anode flow channel 2 by the injector 5 is partially consumed 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 to the anode flow channel 2 again.

[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. A portion of the oxidant gas supplied to the cathode flow channel 3 is used at the cathode electrode and then discharged to the outside from the cathode flow channel 3 as oxidant exhaust gas. A cathode pressure sensor 7a and a cathode flow rate sensor 7b are provided in the pipe connecting the inlet of the cathode flow channel 3 to the air compressor 6. The cathode pressure sensor 7a detects the pressure (cathode pressure) P of the oxidant gas supplied to the cathode flow channel 3 by the air compressor 6. The cathode flow rate sensor 7b detects the flow rate (cathode flow rate) Q of the oxidant gas supplied to the cathode flow channel 3 by the air compressor 6. The cathode flow rate Q is, for example, a mass flow rate.

[0012] A cooling flow path 8 through which a cooling medium circulates is also provided inside the fuel cell stack 1. A water pump 9 that circulates the cooling medium via a radiator (not shown) is connected to the cooling flow path 8. A stack temperature sensor 10 is provided near the outlet of the cooling flow path 8 on the pipe connecting the cooling flow path 8 and the water pump 9, and detects the temperature of the cooling medium discharged from the cooling flow path 8. The temperature of the cooling medium discharged from the cooling flow path 8 represents the overall temperature (stack temperature) inside the fuel cell stack 1, and also represents the temperature (cathode temperature) T of the oxidant gas flowing through the cathode flow path 3. The stack temperature sensor 10 detects the cathode temperature T via the temperature of the cooling medium discharged from the cooling flow path 8.

[0013] The fuel cell stack 1 is electrically connected to a drive motor 11 via metal terminal plates that sandwich the stack of power-generating cells. A current limiter 12 is interposed between the fuel cell stack 1 and the drive motor 11, and the power generated by the fuel cell stack 1 is supplied to the drive motor 11 via the current limiter 12. The current limiter 12 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 current limiter 12 can be electrically connected to the battery 13 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 13 via the current limiter 12. Furthermore, electrical energy generated by the drive motor 11 for vehicle travel during regenerative braking of the vehicle can also be stored in the battery 13 via the current limiter 12. Furthermore, the power stored in the battery 13 can be supplied to the drive motor 11 via the current limiter 12 as needed. The battery 13 is provided with a battery voltage sensor 13a that detects the voltage of the battery 13. The charging rate (SOC (State Of Charge)) of the battery 13 can be estimated based on the battery voltage detected by the battery voltage sensor 13a.

[0015] FIG. 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 cathode pressure sensor 7a, a cathode flow rate sensor 7b, a stack temperature sensor 10, and a battery voltage sensor 13a 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 component of the fuel cell system 100, such as the injector 5, the air compressor 6, and the current limiter 12, and the electronic control unit 20 controls each component of the fuel cell system 100.

[0016] As shown in FIG. 2 , the electronic control unit 20 is also connected to a command input unit 14 that inputs various commands, such as those for starting the fuel cell system 100 and the required output. The command input unit 14 includes, for example, an ignition switch and an accelerator position sensor of a vehicle that uses the drive motor 11 as a driving source. When a start command for the fuel cell system 100 is input from the command input unit 14, 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 14, 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 12 according to the calculation results.

[0017] As shown in FIG. 2, the electronic control unit 20 has, as functional components, an oxygen partial pressure detection section 21 and a current limiting section 22, and functions as the oxygen partial pressure detection section 21 and the current limiting section 22.

[0018] During normal rated operation (normal operation) of the fuel cell stack 1, the stack temperature and cathode temperature T are in a temperature range from room temperature to a predetermined temperature Tα higher than room temperature. However, when the outside air temperature is high or when operation is performed at high load (high output) for a long period of time, the stack temperature and cathode temperature T may rise and exceed the predetermined temperature Tα (high-temperature operation). During high-temperature operation, the rise in cathode temperature T increases the water vapor partial pressure (cathode water vapor partial pressure) PHO of the oxidant gas flowing through the cathode flow path 3, which in turn reduces the oxygen partial pressure (cathode oxygen partial pressure) P0, thereby reducing the oxygen concentration at the cathode electrode interface.

[0019] When the cathode oxygen partial pressure PO2 drops, the oxygen concentration at the interface of the cathode electrode drops and may fall below the concentration required for power generation, even if the amount of oxidant gas required for power generation (electrochemical reaction) in the fuel cell stack 1 is supplied to the cathode flow path 3. In this case, to maintain the current value, it becomes necessary to consume voltage (concentration overvoltage) to increase the probability of electron exchange between the cathode electrode and oxygen, which causes the output voltage to drop below the reference IV characteristic during normal operation and makes the power generation state unstable.

[0020] FIG. 3 is a diagram illustrating the relationship between the cathode flow rate Q and the decrease in output voltage of the fuel cell stack 1, and shows the difference between the average value (average output voltage) and the minimum value (minimum output voltage) of the output voltage of the fuel cell stack 1 during normal operation and high-temperature operation. As shown in FIG. 3, the difference between the average output voltage and the minimum output voltage, i.e., the decrease in the output voltage of the fuel cell stack 1, is greater during high-temperature operation than during normal operation, making the power generation state more unstable during high-temperature operation than during normal operation. Furthermore, the decrease in the output voltage of the fuel cell stack 1 is greater on the constant flow rate side where the cathode flow rate Q is smaller, making the power generation state more unstable.

[0021] FIG. 4 is a diagram illustrating the relationship between the cathode oxygen partial pressure PO2 and the decrease in output voltage of the fuel cell stack 1. As shown in FIG. 4, the decrease in output voltage of the fuel cell stack 1 increases as the cathode oxygen partial pressure PO2 decreases, resulting in unstable power generation. The cathode oxygen partial pressure PO2 can be calculated and estimated based on the cathode pressure P, the cathode flow rate Q, and the cathode temperature T. That is, the cathode water vapor partial pressure PH2O is calculated as the saturated water vapor pressure corresponding to the cathode temperature T, and the partial pressures of oxygen and nitrogen (PO2 + PN2) contained in the oxidant gas flowing through the cathode flow path 3 are calculated by subtracting the cathode water vapor partial pressure PH2O from the cathode pressure P. The electronic control unit 20 (ROM) pre-stores the characteristics of saturated water vapor pressure with respect to temperature or temperature range. The cathode oxygen partial pressure PO2 is calculated by multiplying the calculated partial pressures of oxygen and nitrogen (PO2 + PN2) by the air stoichiometric ratio corresponding to the cathode flow rate Q. The air stoichiometric ratio is the ratio of the amount of oxygen consumed by power generation (electrochemical reaction) in the fuel cell stack 1 to the amount of oxidant gas (oxygen and nitrogen) supplied, and can be calculated based on the current value and the cathode flow rate Q. When the cathode oxygen partial pressure PO2 falls below a predetermined pressure Pα, the drop in output voltage of the fuel cell stack 1 exceeds a reference value, and the power generation state becomes unacceptably unstable.

[0022] The oxygen partial pressure detection unit 21 detects the cathode oxygen partial pressure PO2 or physical quantities correlating with the cathode oxygen partial pressure PO2, namely, the cathode temperature T, the cathode pressure P, and the cathode flow rate Q (oxygen partial pressure representative quantity). More specifically, the cathode oxygen partial pressure PO2 is detected by calculating the cathode oxygen partial pressure PO2 based on the cathode pressure P detected by the cathode pressure sensor 7a, the cathode flow rate Q detected by the cathode flow rate sensor 7b, and the cathode temperature T detected by the stack temperature sensor 10. In this case, the cathode water vapor partial pressure PH2O is calculated based on the cathode temperature T detected by the stack temperature sensor 10, and the cathode oxygen partial pressure PO2 is calculated based on the calculated cathode water vapor partial pressure PH2O, the cathode pressure P detected by the cathode pressure sensor 7a, and the cathode flow rate Q detected by the cathode flow rate sensor 7b. Alternatively, the oxygen partial pressure detection unit 21 detects the cathode pressure P, cathode flow rate Q, and cathode temperature T as representative quantities of oxygen partial pressure based on signals from the cathode pressure sensor 7a, the cathode flow rate sensor 7b, and the stack temperature sensor 10.

[0023] When the cathode oxygen partial pressure PO2 detected by the oxygen partial pressure detection unit 21 becomes equal to or lower than a predetermined pressure Pα, the current limiting unit 22 controls the current limiter 12 so that the output current output from the fuel cell stack 1 becomes equal to or lower than a limit value, thereby limiting the output current.

[0024] FIG. 5 is a diagram for explaining the characteristics (characteristics map) of the limiting value set by the current limiting unit 22, showing the characteristics representing the relationship between predetermined cathode pressure P, cathode flow rate Q, cathode temperature T, and limiting value. Such limiting value characteristics are determined in advance through testing and stored in the electronic control unit 20 (ROM). The limiting value characteristics are the characteristics of the limiting value for the cathode pressure P and the cathode flow rate Q, which are determined corresponding to each of a plurality of temperature ranges of the cathode temperature T. The plurality of temperature ranges of the cathode temperature T include, for example, a temperature range below a predetermined temperature Tα corresponding to the temperature range during normal operation, and a temperature range equal to or higher than the predetermined temperature Tα corresponding to the temperature range during high-temperature operation. The temperature range during high-temperature operation may further include a plurality of temperature ranges (for example, a first temperature range equal to or higher than Tα and lower than Tβ, and a second temperature range equal to or higher than Tβ). The limiting value is set to a smaller current value as the temperature range of the cathode temperature T is higher.

[0025] When limiting the output current based on the oxygen partial pressure representative quantity, the current limiting unit 22 first selects a temperature range to which the cathode temperature T belongs based on the cathode temperature T detected by the stack temperature sensor 10. The current limiting unit 22 may select the temperature range in real time according to the detection period of the cathode temperature T by the stack temperature sensor 10, or may select the temperature range at predetermined intervals longer than the detection period. When the current limiting unit 22 selects the temperature range at predetermined intervals longer than the detection period, the temperature range may be selected based on the most recently detected value of the cathode temperature T, or may be selected based on the average or maximum value over the predetermined period. In this case, the frequency of switching the characteristic map due to changes in the temperature range can be reduced, and the calculation load on the electronic control unit 20 can be reduced.

[0026] 5, the limit value is set to a smaller current value as the cathode oxygen partial pressure PO2 is lower. The current limiting unit 22 sets the limit value based on a characteristics map corresponding to a temperature range selected based on the cathode temperature T, the cathode pressure P detected by the cathode pressure sensor 7a, and the cathode flow rate Q detected by the cathode flow rate sensor 7b. Once the limit value is set, the current limiting unit 22 controls the current limiter 12 so that the output current output from the fuel cell stack 1 is equal to or less than the limit value, thereby limiting the output current.

[0027] While the output current is being limited by the current limiting unit 22, it may not be possible to satisfy the required output input from the command input unit 14. In this case, power may be supplied from the battery 13 to the drive motor 11 on the condition that the SOC based on the battery voltage detected by the battery voltage sensor 13a is equal to or greater than a predetermined threshold.

[0028] 6A and 6B are flowcharts showing an example of processing executed by the electronic control unit 20. These processing are started when a start-up command for the fuel cell system 100 is input from the command input unit 14, and are repeated at predetermined intervals.

[0029] In the example of FIG. 6A, first, in step S1, the cathode pressure P detected by the cathode pressure sensor 7a, the cathode flow rate Q detected by the cathode flow rate sensor 7b, and the cathode temperature T detected by the stack temperature sensor 10 are read. Next, in step S2, the cathode oxygen partial pressure PO2 is calculated based on the cathode pressure P, cathode flow rate Q, and cathode temperature T read in step S1. Next, in step S3, it is determined whether the cathode oxygen partial pressure PO2 calculated in step S2 is equal to or less than a predetermined pressure Pα. If the result in step S3 is affirmative, the process proceeds to step S4, where a limit value is set and output current limiting is performed. On the other hand, if the result in step S3 is negative, the process ends without limiting the output current.

[0030] In the example of FIG. 6B, first, in step S1, the cathode pressure P detected by the cathode pressure sensor 7a, the cathode flow rate Q detected by the cathode flow rate sensor 7b, and the cathode temperature T detected by the stack temperature sensor 10 are read. Next, in step S5, it is determined whether the cathode temperature T read in step S1 is equal to or lower than a predetermined temperature Tα. If the result in step S5 is affirmative, the process proceeds to step S4, where a limiting value is set based on the cathode pressure P, cathode flow rate Q, and cathode temperature T read in step S1 and the predetermined characteristics of FIG. 5 to limit the output current. On the other hand, if the result in step S5 is negative, the process ends without limiting the output current.

[0031] According to this embodiment, the following effects can be achieved. (1) A fuel cell system 100 includes a fuel cell stack 1 having an anode flow path 2 through which a fuel gas containing hydrogen flows and a cathode flow path 3 through which an oxidizer gas containing oxygen flows, an injector 5 that supplies the fuel gas to the anode flow path 2, an air compressor 6 that supplies the oxidizer gas to the cathode flow path 3, an oxygen partial pressure detection unit 21 that detects the oxygen partial pressure (cathode oxygen partial pressure) PO2 of the oxidizer gas flowing through the cathode flow path 3 or an oxygen partial pressure representative quantity (cathode temperature T, cathode pressure P, cathode flow rate Q) that is a physical quantity that correlates with the cathode oxygen partial pressure PO2, and a current limiting unit 22 that, based on the cathode oxygen partial pressure PO2 or the oxygen partial pressure representative quantity detected by the oxygen partial pressure detection unit 21, limits the output current output from the fuel cell stack 1 so that it is below a limited value when the cathode oxygen partial pressure PO2 falls below a predetermined pressure Pα (FIGS. 1, 2, 4, 6A, and 6B). When the cathode oxygen partial pressure PO2 falls below a predetermined pressure Pα, the output current from the fuel cell stack 1 is limited, thereby making it possible to suppress a drop in output voltage even if the temperature inside the fuel cell stack 1 rises.

[0032] (2) The fuel cell system 100 further includes a cathode pressure sensor 7a that detects the pressure (cathode pressure) P of the oxidant gas supplied by the air compressor 6, a cathode flow rate sensor 7b that detects the flow rate (cathode flow rate) Q of the oxidant gas supplied by the air compressor 6, and a stack temperature sensor 10 that detects the temperature of the oxidant gas flowing through the cathode flow path 3 or a cathode temperature T that is a temperature that has a correlation with such a temperature (FIGS. 1 and 2).

[0033] (3) The oxygen partial pressure detection unit 21 detects the cathode oxygen partial pressure PO2 by calculating the cathode oxygen partial pressure PO2 based on the cathode pressure P detected by the cathode pressure sensor 7a, the cathode flow rate Q detected by the cathode flow rate sensor 7b, and the cathode temperature T detected by the stack temperature sensor 10 (step S2 in FIG. 6A). This makes it possible to accurately detect the cathode oxygen partial pressure PO2 with a simple configuration.

[0034] (4) The oxygen partial pressure detection unit 21 calculates the water vapor partial pressure (cathode water vapor partial pressure) PH2O of the oxidant gas flowing through the cathode flow path 3 based on the cathode temperature T detected by the stack temperature sensor 10, and calculates the cathode oxygen partial pressure PO2 based on the calculated cathode water vapor partial pressure PH2O, the cathode pressure P detected by the cathode pressure sensor 7a, and the cathode flow rate Q detected by the cathode flow rate sensor 7b (step S2 in FIG. 6A). This makes it possible to appropriately calculate the cathode oxygen partial pressure PO2 during high-temperature operation of the fuel cell stack 1.

[0035] (5) The oxygen partial pressure detection unit 21 detects the cathode pressure P, the cathode flow rate Q, and the cathode temperature T as oxygen partial pressure representative quantities (step S1 in FIG. 6B). The current limiting unit 22 sets the limiting value based on a characteristic that indicates the relationship between a predetermined cathode pressure P, a cathode flow rate Q, a cathode temperature T, and a limiting value, the cathode pressure P detected by the cathode pressure sensor 7a, the cathode flow rate Q detected by the cathode flow rate sensor 7b, and the cathode temperature T detected by the stack temperature sensor 10. This makes it possible to accurately detect the oxygen partial pressure representative quantity with a simple configuration, and to set the limiting value so that the output current is limited when the cathode oxygen partial pressure PO2 corresponding to the detected oxygen partial pressure representative quantity becomes equal to or lower than a predetermined pressure Pα.

[0036] (6) The predetermined characteristics are characteristics of limit values ​​for the cathode pressure P and the cathode flow rate Q that are predetermined for each of a plurality of temperature ranges of the cathode temperature T (Fig. 5). For example, the output current is not limited in the temperature range during normal operation of the fuel cell stack 1 (below a predetermined temperature Tα), but is limited in the temperature range during high-temperature operation (above the predetermined temperature Tα). This limits the output current from the fuel cell stack 1 during high-temperature operation, when there is a high probability that the output voltage will decrease due to a decrease in the cathode oxygen partial pressure PO2, thereby making it possible to suppress a decrease in output voltage.

[0037] (7) Based on the cathode temperature T detected by the stack temperature sensor 10, the current limiting unit 22 sets a limiting value that decreases as the cathode temperature T increases (FIG. 5). This allows for stricter output current limiting during high-temperature operation when there is a high probability that the output voltage will decrease due to a decrease in the cathode oxygen partial pressure PO2.

[0038] (8) The current limiting unit 22 sets a limiting value that is smaller the lower the cathode oxygen partial pressure PO2 is based on the cathode oxygen partial pressure PO2 or the oxygen partial pressure representative quantity (cathode temperature T, cathode pressure P, cathode flow rate Q) detected by the oxygen partial pressure detecting unit 21 (step S4 in FIGS. 6A and 6B). This allows for stricter output current limitation when operating under conditions where the cathode oxygen partial pressure PO2 is low and there is a high probability of a drop in output voltage.

[0039] 1 and the like, the above embodiment has described an example in which the temperature of the cooling medium discharged from the cooling flow path 8 is detected as the cathode temperature T, but the temperature detection unit that detects the cathode temperature 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 a physical quantity representing the cathode temperature, or the temperature of the fuel cell stack 1 itself (for example, each power generation cell) may be detected.

[0040] In the above embodiment, an example has been described in which the limit value is set using a characteristic map defined for each temperature range of the cathode temperature T, such as in Fig. 5, but the characteristic for setting the predetermined value when limiting the output current is not limited to this. For example, the characteristic may be defined for each range of the cathode pressure, or may be defined for each range of the cathode flow rate.

[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, 7a cathode pressure sensor, 7b cathode flow rate sensor, 8 cooling flow path, 9 water pump, 10 stack temperature sensor, 11 drive motor, 12 current limiter, 13 battery, 13a battery voltage sensor, 14 command input section, 20 electronic control unit, 21 oxygen partial pressure detection section, 22 current limiting section, 100 fuel cell system

Claims

1. a fuel cell stack provided with an anode flow path through which a fuel gas containing hydrogen flows and a cathode flow path through which an oxidant gas containing oxygen flows; a fuel gas supply unit that supplies the fuel gas to the anode flow channel; an oxidant gas supply unit that supplies the oxidant gas to the cathode flow path; an oxygen partial pressure detection unit that detects the oxygen partial pressure of the oxidant gas flowing through the cathode flow channel or a representative amount of the oxygen partial pressure, which is a physical quantity that has a correlation with the oxygen partial pressure; a current limiting unit that limits the output current output from the fuel cell stack to a predetermined value or less when the oxygen partial pressure falls below a predetermined pressure, based on the oxygen partial pressure or the representative amount of oxygen partial pressure detected by the oxygen partial pressure detection unit.

2. 2. The fuel cell system according to claim 1, a pressure detection unit that detects the pressure of the oxidant gas supplied by the oxidant gas supply unit; a flow rate detection unit that detects the flow rate of the oxidant gas supplied by the oxidant gas supply unit; a temperature detection unit that detects the temperature of the oxidant gas flowing through the cathode flow channel or a cathode temperature that is a temperature that has a correlation with the temperature of the oxidant gas flowing through the cathode flow channel, The oxygen partial pressure detection unit detects the oxygen partial pressure by calculating the oxygen partial pressure based on the pressure detected by the pressure detection unit, the flow rate detected by the flow rate detection unit, and the cathode temperature detected by the temperature detection unit, or detects the pressure, the flow rate, and the cathode temperature as the oxygen partial pressure representative quantity.

3. 3. The fuel cell system according to claim 2, a fuel cell system characterized in that the oxygen partial pressure detection unit detects the oxygen partial pressure by calculating the oxygen partial pressure based on the pressure detected by the pressure detection unit, the flow rate detected by the flow rate detection unit, and the cathode temperature detected by the temperature detection unit.

4. 4. The fuel cell system according to claim 3, the oxygen partial pressure detection unit calculates a water vapor partial pressure of the oxidant gas flowing through the cathode flow path based on the cathode temperature detected by the temperature detection unit, and calculates the oxygen partial pressure based on the calculated water vapor partial pressure, the pressure detected by the pressure detection unit, and the flow rate detected by the flow rate detection unit.

5. 3. The fuel cell system according to claim 2, the oxygen partial pressure detection unit detects the pressure, the flow rate, and the cathode temperature as the oxygen partial pressure representative quantities; a current limiting unit that sets the predetermined value based on a characteristic that represents a predetermined relationship between the pressure, the flow rate, the cathode temperature, and the predetermined value, the pressure detected by the pressure detection unit, the flow rate detected by the flow rate detection unit, and the cathode temperature detected by the temperature detection unit.

6. 6. The fuel cell system according to claim 5, The fuel cell system is characterized in that the predetermined characteristics are characteristics of the predetermined values ​​for the pressure and the flow rate that are determined in advance corresponding to each of a plurality of temperature ranges of the cathode temperature.

7. The fuel cell system according to any one of claims 2 to 6, The fuel cell system according to claim 1, wherein the current limiting unit sets the predetermined value smaller as the cathode temperature increases based on the cathode temperature detected by the temperature detecting unit.

8. The fuel cell system according to any one of claims 1 to 6, The fuel cell system is characterized in that the current limiting unit sets the predetermined value smaller as the oxygen partial pressure is lower, based on the oxygen partial pressure or the representative amount of oxygen partial pressure detected by the oxygen partial pressure detection unit.

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