Fuel cell system

Abstract

A fuel cell system (100) is provided with: a fuel cell stack (1) 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 flows; a fuel gas supply unit (5) that supplies a fuel gas to the anode flow path (2); an oxidant gas supply unit (6) that supplies an oxidant gas to the cathode flow path (3); an oxygen partial pressure detection unit (21) that detects the oxygen partial pressure of the oxidant gas flowing through the cathode flow path (3) or an oxygen partial pressure representative quantity that is a physical quantity having a correlation with the oxygen partial pressure; and a current limiting unit (22) that, on the basis of the oxygen partial pressure or the oxygen partial pressure representative amount detected by the oxygen partial pressure detection unit (21), limits the output current such that the output current output from the fuel cell stack (1) becomes a predetermined value or less when the oxygen partial pressure becomes a predetermined pressure or less.

Description

Technical Field

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

[0002] Using fuel cells as a vehicle's power source, for example, can help improve energy efficiency. As a technology related to such fuel cells, devices for limiting the output current from a fuel cell stack are known. For example, the device described in Patent Document 1 calculates the delay time for air from a flow sensor to reach the fuel cell based on the air's volumetric flow rate. The volumetric flow rate of air within the fuel cell is calculated based on the air's volumetric flow rate and the delay time, and the fuel cell's generated current is limited so that the generated current corresponds to the volumetric flow rate of air within the fuel cell.

[0003] However, when the temperature inside the fuel cell stack reaches a high temperature, the water vapor partial pressure in the oxidant gas (air) increases, causing the oxygen partial pressure to decrease. Therefore, if the output current is limited solely based on the air flow rate, as in the device described in Patent Document 1, the output voltage from the fuel cell stack may decrease when the temperature inside the fuel cell stack reaches a high temperature.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2015-228305 (JP 2015-228305 A). Summary of the Invention

[0007] A fuel cell system according to one technical solution of the present invention comprises: a fuel cell stack provided with an anode flow channel for flowing a fuel gas containing hydrogen and a cathode flow channel for flowing an oxidant gas containing oxygen; a fuel gas supply unit for supplying fuel gas to the anode flow channel; an oxidant gas supply unit for supplying oxidant gas to the cathode flow channel; an oxygen partial pressure detection unit for detecting 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 correlated with the oxygen partial pressure; and a current limiting unit for limiting the output current in such a manner that the output current output from the fuel cell stack becomes below a specified value when the oxygen partial pressure becomes below a specified pressure based on the oxygen partial pressure or the representative amount of the oxygen partial pressure detected by the oxygen partial pressure detection unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The objects, features and advantages of the present invention will be further clarified through the following description of the embodiments in conjunction with the accompanying drawings.

[0009] Figure 1 FIG. 1 is a diagram schematically showing an example of the overall structure of a fuel cell system according to an embodiment of the present invention;

[0010] Figure 2 This is a block diagram schematically showing an example of a control structure of a fuel cell system according to an embodiment of the present invention;

[0011] Figure 3 Is used to illustrate Figure 1 a graph showing a relationship between a flow rate of an oxidant gas flowing in a cathode flow channel and a decrease in an output voltage of a fuel cell stack;

[0012] Figure 4 Is used to illustrate Figure 1 a graph showing a relationship between the oxygen partial pressure of the oxidant gas flowing in the cathode flow channel and a decrease in the output voltage of the fuel cell stack;

[0013] Figure 5 Is used to illustrate the Figure 2 A diagram showing characteristics of a limit value set by a current limiting unit;

[0014] Figure 6A It is shown by Figure 2 A flowchart of an example of a process executed by an electronic control unit;

[0015] Figure 6B It is shown by Figure 2 A flowchart of another example of the processing executed by the electronic control unit. DETAILED DESCRIPTION

[0016] Below, refer to Figures 1 to 6B Embodiments of the present invention will be described. Figure 1 1 is a diagram schematically showing an example of the overall structure of a fuel cell system 100 according to an embodiment of the present invention. Figure 1 As shown, the fuel cell system 100 primarily comprises a fuel cell stack 1, which is composed of stacked power generation cells having a solid polymer electrolyte membrane; and an electronic control unit 20, which controls various components of the fuel cell system 100. The fuel cell system 100 can be installed in, for example, a vehicle to generate power for driving the vehicle. The fuel cell system 100 can also be installed in mobile vehicles other than vehicles, such as aircraft and ships, as well as in robots and various industrial machines.

[0017] The fuel cell stack 1 is provided with an anode flow channel 2 through which a fuel gas containing hydrogen flows, and a cathode flow channel 3 through which an oxidant gas, such as air containing oxygen, flows. The fuel gas is supplied to the anode electrodes of each power generation cell in the fuel cell stack 1 via the anode flow channel 2, while the oxidant gas is supplied to the cathode electrodes via the cathode flow channel 3. This allows electrochemical reactions to proceed at the electrodes of each power generation cell, resulting in power generation in the fuel cell stack 1.

[0018] A fuel gas tank storing high-pressure fuel gas is connected to the anode channel 2 via an ejector 4 and an injector 5. The fuel gas in the fuel gas tank is supplied to the anode channel 2 via the injector 5. The fuel gas supplied to the anode channel 2 by the injector 5 is partially used by the anode electrode and then discharged from the anode channel 2 as a fuel exhaust. The fuel exhaust discharged from the anode channel 2 is separated from water by a gas-liquid separator (not shown), then sucked into the anode channel 2 via the ejector 4 and supplied again to the anode channel 2.

[0019] An air compressor 6 for supplying oxidant gas is connected to the cathode channel 3, and the oxidant gas compressed by the air compressor 6 is supplied to the cathode channel 3. After a portion of the oxidant gas supplied to the cathode channel 3 is used at the cathode electrode, it is discharged from the cathode channel 3 to the outside as oxidant exhaust. A cathode pressure sensor 7a and a cathode flow sensor 7b are provided in the piping connecting the inlet of the cathode channel 3 and the air compressor 6. The cathode pressure sensor 7a detects the pressure (cathode pressure) P of the oxidant gas supplied by the air compressor 6 to the cathode channel 3. The cathode flow sensor 7b detects the flow (cathode flow) Q of the oxidant gas supplied by the air compressor 6 to the cathode channel 3. The cathode flow Q is, for example, a mass flow rate.

[0020] A cooling channel 8 for circulating a cooling medium is also provided inside the fuel cell stack 1. A water pump 9 is connected to the cooling channel 8 to circulate the cooling medium via a radiator (not shown). A stack temperature sensor 10 is provided near the outlet of the cooling channel 8 in the piping connecting the cooling channel 8 and the water pump 9 to detect the temperature of the cooling medium discharged from the cooling channel 8. The temperature of the cooling medium discharged from the cooling channel 8 represents the overall temperature (stack temperature) inside the fuel cell stack 1 and represents the temperature (cathode temperature) T of the oxidant gas flowing through the cathode channel 3. The stack temperature sensor 10 detects the cathode temperature T by means of the temperature of the cooling medium discharged from the cooling channel 8.

[0021] The fuel cell stack 1 is electrically connected to a drive motor (motor generator) 11 via metal terminal plates that sandwich the stack of power generation cells. A current limiter (current limiting circuit) 12 is interposed between the fuel cell stack 1 and the drive motor 11. Electric 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 output current (current value) from the fuel cell stack 1 to below a specified limit value.

[0022] The battery 13 can be electrically connected to the current limiter 12 via a DC / DC converter (not shown). In this case, a part or all of the electricity generated by the fuel cell stack 1 can be stored in the battery 13 via the current limiter 12. In addition, the electric energy generated by the drive motor 11 for driving the vehicle during regenerative braking of the vehicle can also be stored in the battery 13 via the current limiter 12. In addition, as needed, the electric power stored in the battery 13 can be supplied to the drive motor 11 via the current limiter 12. A battery voltage sensor 13a for detecting the voltage of the battery 13 (battery voltage) is provided in the battery 13. Based on the battery voltage detected by the battery voltage sensor 13a, the SOC (State Of Charge) of the battery 13 can be estimated.

[0023] Figure 2 This is a block diagram schematically showing an example of a control structure of the fuel cell system 100. The electronic control unit 20 of the fuel cell system 100 is composed of a computer having a CPU (Central Processing Unit), RAM (Random Access Memory), ROM (Read Only Memory), an I / O interface, and other peripheral circuits. Figure 1 and Figure 2 As shown, the electronic control unit 20 is connected to sensors such as the cathode pressure sensor 7a, cathode flow rate sensor 7b, stack temperature sensor 10, and battery voltage sensor 13a, and detection values from each sensor are input to the electronic control unit 20. Furthermore, the electronic control unit 20 is connected to various components of the fuel cell system 100, such as the injector 5, air compressor 6, and current limiter 12, and controls these components of the fuel cell system 100.

[0024] like Figure 2 As shown, the electronic control unit 20 is also connected to a command input unit 14 for inputting various commands, such as starting the fuel cell system 100 and output requirements. The command input unit 14 includes, for example, the ignition switch of a vehicle driven by the drive motor 11, an accelerator position sensor, and the like. When a command to start 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, thereby generating electricity within the fuel cell stack 1. Furthermore, the electronic control unit 20 calculates the flow rates of fuel gas and oxidant gas to be supplied to the fuel cell stack 1 based on the detection values of the various sensors and the output requirements input from the command input unit 14, and controls the injector 5 and the air compressor 6 based on the calculation results. Furthermore, the electronic control unit 20 calculates a limit value for the output current from the fuel cell stack 1 based on the detection values of the various sensors, and controls the current limiter 12 based on the calculation results.

[0025] like Figure 2As shown, the electronic control unit 20 includes an oxygen partial pressure detecting unit 21 and a current limiting unit 22 as functional components, and functions as the oxygen partial pressure detecting unit 21 and the current limiting unit 22 .

[0026] During normal rated operation (normal operation) of the fuel cell stack 1, the stack temperature and cathode temperature T are within a temperature range from room temperature to a specified temperature Tα higher than room temperature. However, in situations where the outside air temperature is high or the system is operated at high load (high power) for a long time, the stack temperature and cathode temperature T rise, sometimes reaching above the specified temperature Tα (high-temperature operation). During high-temperature operation, due to the increase in cathode temperature T, the water vapor partial pressure (cathode water vapor partial pressure) PH2O of the oxidant gas flowing through the cathode flow channel 3 increases, and the oxygen partial pressure (cathode oxygen partial pressure) PO2 decreases accordingly, thereby reducing the oxygen concentration at the interface of the cathode electrode.

[0027] When the cathode oxygen partial pressure PO2 decreases, 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 channel 3, the oxygen concentration at the interface of the cathode electrode will decrease, sometimes falling below the concentration required for power generation. In this case, in order to maintain the current value, a voltage consumption (concentration overvoltage) is required to increase the probability of electron exchange between the cathode electrode and oxygen, resulting in an output voltage lower than the baseline IV characteristic during normal operation, and the power generation state becomes unstable.

[0028] Figure 3 This is a diagram for explaining the relationship between the cathode flow rate Q and the reduction in the output voltage of the fuel cell stack 1, showing 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. Figure 3 As shown, the difference between the average output voltage and the minimum output voltage, that is, the drop in the output voltage of the fuel cell stack 1, is greater during high-temperature operation than during normal operation, and the power generation state is more unstable during high-temperature operation than during normal operation. In addition, the lower the cathode flow rate Q, the greater the drop in the output voltage of the fuel cell stack 1, and the more unstable the power generation state.

[0029] Figure 4 1 is a diagram for explaining the relationship between the cathode oxygen partial pressure PO2 and the decrease in the output voltage of the fuel cell stack 1. Figure 4As shown, the lower the cathode oxygen partial pressure PO2, the greater the drop in the output voltage of the fuel cell stack 1, and the more unstable the power generation state. 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. Specifically, the cathode water vapor partial pressure PH2O, which is the saturated water vapor pressure corresponding to the cathode temperature T, is calculated. By subtracting the cathode water vapor partial pressure PH2O from the cathode pressure P, the partial pressures of oxygen and nitrogen contained in the oxidant gas flowing through the cathode flow channel 3 (PO2 + PN2) are calculated. The electronic control unit 20 (ROM) pre-stores the characteristics of the saturated water vapor pressure corresponding to temperature or temperature range. The calculated oxygen and nitrogen partial pressures (PO2 + PN2) are multiplied by the air stoichiometric ratio corresponding to the cathode flow rate Q to calculate the cathode oxygen partial pressure PO2. It should be noted that the air stoichiometric ratio is the ratio of the oxygen consumption caused by power generation (electrochemical reaction) in the fuel cell stack 1 to the supply of the oxidant gas (oxygen and nitrogen), and can be calculated based on the current value and the cathode flow rate Q. When the cathode oxygen partial pressure PO2 becomes lower than the predetermined pressure Pα, the output voltage of the fuel cell stack 1 decreases to a value exceeding a reference value, and the power generation state becomes unstable to an unacceptable degree.

[0030] The oxygen partial pressure detection unit 21 detects the cathode oxygen partial pressure PO2 or the cathode temperature T, cathode pressure P, and cathode flow rate Q (a proxy for oxygen partial pressure), which are physical quantities correlated with the cathode oxygen partial pressure PO2. 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 a proxy for oxygen partial pressure based on signals from the cathode pressure sensor 7a, the cathode flow rate sensor 7b, and the stack temperature sensor 10.

[0031] The current limiting unit 22 controls the current limiter 12 to limit the output current so that the output current output from the fuel cell stack 1 becomes less than a limit value when the cathode oxygen partial pressure PO2 detected by the oxygen partial pressure detecting unit 21 becomes less than a predetermined pressure Pα.

[0032] Figure 5This is a diagram for explaining the characteristics (characteristic map) of the limit value set by the current limiting unit 22, showing the characteristics representing the relationship between the predetermined cathode pressure P, cathode flow rate Q, cathode temperature T, and the limit value. Such a limit value characteristic is determined in advance through experiments and stored in the electronic control unit 20 (ROM). The limit value characteristic is a characteristic of the limit value for the cathode pressure P and cathode flow rate Q, which is determined corresponding to each of the multiple temperature ranges of the cathode temperature T. The multiple temperature ranges of the cathode temperature T include, for example, a temperature range below the specified temperature Tα corresponding to the temperature range during normal operation and a temperature range above the specified temperature Tα corresponding to the temperature range during high temperature operation. The temperature range during high temperature operation may also include multiple temperature ranges (for example, a first temperature range above Tα and below Tβ and a second temperature range above Tβ). The limit value is set to a smaller current value in the temperature range with a higher cathode temperature T (that is, it is set so that the output current limit is more strictly applied in the temperature range with a higher cathode temperature T).

[0033] When the current limiting unit 22 limits the output current based on the representative value of the oxygen partial pressure, it first selects the 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 can select the temperature range in real time according to the detection cycle of the cathode temperature T by the stack temperature sensor 10, or it can be selected in units of a specified period longer than the detection cycle. When the current limiting unit 22 selects the temperature range in units of a specified period longer than the detection cycle, the temperature range can be selected based on the most recent detection value of the cathode temperature T, or it can be selected based on the average value or maximum value of the specified period. In this case, the switching frequency of the characteristic map caused by the change of the temperature range can be suppressed, and the computational load of the electronic control unit 20 can be suppressed.

[0034] like Figure 5 As shown, the smaller the cathode flow rate Q and the lower the cathode oxygen partial pressure PO2, the smaller the limit value is set to a current value (i.e., the smaller the cathode flow rate Q and the lower the cathode oxygen partial pressure PO2, the stricter the output current limit is). The current limiter 22 sets the limit value based on a characteristic 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 sensor 7b. When the limit value is set, the current limiter 22 controls the current limiter 12 so that the output current from the fuel cell stack 1 remains below the limit value, thereby limiting the output current.

[0035] The output current limitation of the current limiting unit 22 may not satisfy the required output input from the command input unit 14. In this case, the power from the battery 13 may be supplied to the drive motor 11 under 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.

[0036] Figure 6A and Figure 6B 2 is a flowchart showing an example of processing executed by the electronic control unit 20. These processes are started when a startup command for the fuel cell system 100 is input from the command input unit 14, and are repeatedly performed in a predetermined cycle.

[0037] exist Figure 6A In the example, first, in S1 (S: processing step), 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 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 S1. Next, in S3, it is determined whether the cathode oxygen partial pressure PO2 calculated in S2 is below the specified pressure Pα. If S3 is affirmative (S3: Yes), the process proceeds to S4, where a limit value is set and output current is limited. On the other hand, if S3 is negative (S3: No), the process ends without output current limitation.

[0038] exist Figure 6B In the example, first, in S1, the cathode pressure P detected by the cathode pressure sensor 7a, the cathode flow Q detected by the cathode flow sensor 7b, and the cathode temperature T detected by the stack temperature sensor 10 are read. Then, in S5, it is determined whether the cathode temperature T read in S1 is above the predetermined temperature Tα. When S5 is affirmative (S5: No), the process proceeds to S4, and the cathode pressure P, cathode flow Q, cathode temperature T read in S1, and the predetermined temperature Tα are determined. Figure 5 On the other hand, if S5 is negative (S5: No), the output current is not limited and the process ends.

[0039] According to this embodiment, the following effects can be achieved.

[0040] (1) The fuel cell system 100 comprises: a fuel cell stack 1 provided with an anode flow path 2 for flowing a fuel gas containing hydrogen and a cathode flow path 3 for flowing an oxidant gas containing oxygen; an injector 5 for supplying fuel gas to the anode flow path 2; an air compressor 6 for supplying oxidant gas to the cathode flow path 3; an oxygen partial pressure detection unit 21 for detecting the oxygen partial pressure (cathode oxygen partial pressure) PO2 of the oxidant 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) which is a physical quantity correlated with the cathode oxygen partial pressure PO2; and a current limiting unit 22 for limiting the output current (in accordance with the cathode oxygen partial pressure PO2 or the oxygen partial pressure representative quantity detected by the oxygen partial pressure detection unit 21) in such a manner that the output current output from the fuel cell stack 1 becomes less than a limit value when the cathode oxygen partial pressure PO2 becomes less than a predetermined pressure Pα. Figure 1 、 Figure 2 、 Figure 4 、 Figure 6A 、 Figure 6B When the cathode oxygen partial pressure PO2 becomes equal to or lower than the predetermined pressure Pα, the output current from the fuel cell stack 1 is limited, thereby suppressing a decrease in the output voltage even if the temperature inside the fuel cell stack 1 reaches a high temperature.

[0041] (2) The fuel cell system 100 also includes: a cathode pressure sensor 7a, which detects the pressure (cathode pressure) P of the oxidant gas supplied by the air compressor 6; a cathode flow sensor 7b, which detects the flow (cathode flow) Q of the oxidant gas supplied by the air compressor 6; and a stack temperature sensor 10, which detects the temperature of the oxidant gas flowing through the cathode flow path 3 or a temperature correlated with such a temperature, namely, the cathode temperature T.

[0042] (3) The oxygen partial pressure detection unit 21 calculates 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, thereby detecting the cathode oxygen partial pressure PO2 ( Figure 6A Thus, the cathode oxygen partial pressure PO2 can be detected with high accuracy using a simple structure.

[0043] (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 channel 3 based on the cathode temperature T detected by the stack temperature sensor 10, and calculates the cathode oxygen partial pressure PO2 ( Figure 6A Thus, the cathode oxygen partial pressure PO2 of the fuel cell stack 1 during high-temperature operation can be appropriately calculated.

[0044] (5) The oxygen partial pressure detection unit 21 detects the cathode pressure P, cathode flow rate Q and cathode temperature T as the representative amount of oxygen partial pressure ( Figure 6B The current limiting unit 22 sets the limit value based on a characteristic representing the relationship between a predetermined cathode pressure P, cathode flow rate Q, cathode temperature T, and the limit value, and 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 allows for highly accurate detection of the representative oxygen partial pressure with a simple configuration, and sets the limit value so that the output current is limited when the cathode oxygen partial pressure PO2 corresponding to the detected representative oxygen partial pressure falls below a predetermined pressure Pα.

[0045] (6) The predetermined characteristic is a characteristic of the limit values of the cathode pressure P and the cathode flow rate Q that is predetermined corresponding to each of the plurality of temperature ranges of the cathode temperature T ( Figure 5 For example, in the temperature range of normal operation of the fuel cell stack 1 (less than the predetermined temperature Tα), output current limitation is not performed, whereas in the temperature range of high-temperature operation (above the predetermined temperature Tα), output current limitation is performed. Thus, during high-temperature operation, where there is a high likelihood that the output voltage will decrease due to a decrease in the cathode oxygen partial pressure PO2, the output current from the fuel cell stack 1 can be limited, thereby suppressing a decrease in the output voltage.

[0046] (7) The current limiting unit 22 sets the limiting value smaller based on the cathode temperature T detected by the stack temperature sensor 10. The higher the cathode temperature T is, the smaller the limiting value is. Figure 5 Thus, during high-temperature operation, when there is a high possibility that the output voltage will decrease due to a decrease in the cathode oxygen partial pressure PO2, stricter output current limitation can be performed.

[0047] (8) The current limiting unit 22 sets the limiting value smaller as the cathode oxygen partial pressure PO2 is lower, based on the cathode oxygen partial pressure PO2 or the oxygen partial pressure representative value (cathode temperature T, cathode pressure P, cathode flow rate Q) detected by the oxygen partial pressure detecting unit 21. Figure 6A and Figure 6B Thus, when the operation is performed under the condition that the cathode oxygen partial pressure PO2 is low and the possibility of output voltage reduction is high, the output current limitation can be more strictly performed.

[0048] In the above embodiment, Figure 1 , etc., describe an example in which the temperature of the coolant discharged from the cooling flow channel 8 is detected as the cathode temperature T. However, the temperature detection unit for detecting the cathode temperature is not limited to this. For example, as a physical quantity representing the cathode temperature, the temperature of the oxidant exhaust gas discharged from the cathode flow channel 3 may be detected, or the temperature of the fuel cell stack 1 itself (e.g., each power generation cell) may be detected.

[0049] In the above embodiment, Figure 5 , etc., describe an example of setting a limit value using a characteristic map defined for each temperature range of the cathode temperature T. However, the characteristic used to set the prescribed value when limiting the output current is not limited thereto. For example, a characteristic defined for each range of the cathode pressure or a characteristic defined for each range of the cathode flow rate may be used.

[0050] One or more of the above-described embodiments and modifications may be arbitrarily combined, and modifications may be combined with each other.

[0051] According to the present invention, even if the temperature inside the fuel cell stack reaches a high temperature, a decrease in the output voltage can be suppressed.

[0052] The present invention has been described above with reference to preferred embodiments. However, it should be understood by those skilled in the art that various modifications and changes can be made without departing from the scope of the claims.

Claims

1. A fuel cell system (100), characterized in that: have: A fuel cell stack (1) is provided with an anode flow channel (2) for flowing a fuel gas containing hydrogen and a cathode flow channel (3) for flowing an oxidant gas containing oxygen; a fuel gas supply unit (5) for supplying the fuel gas to the anode flow channel (2); an oxidant gas supply unit (6) for supplying the oxidant gas to the cathode flow channel (3); an oxygen partial pressure detecting section (21) for detecting the oxygen partial pressure of the oxidant gas flowing through the cathode flow channel (3) or a representative amount of the oxygen partial pressure as a physical quantity correlated with the oxygen partial pressure; as well as A current limiting unit (22) limits the output current in a manner such that the output current output from the fuel cell stack (1) becomes below a specified value when the oxygen partial pressure becomes below a specified pressure, based on the oxygen partial pressure or the oxygen partial pressure representative amount detected by the oxygen partial pressure detecting unit (21).

2. The fuel cell system (100) according to claim 1, characterized in that Also features: a pressure detecting section (7a) for detecting the pressure of the oxidant gas supplied by the oxidant gas supply section (6); a flow rate detection unit (7b) for detecting the flow rate of the oxidant gas supplied by the oxidant gas supply unit (6); and a temperature detection unit (10) for detecting the temperature of the oxidant gas flowing through the cathode flow channel (3) or a temperature correlated with the temperature, namely, the cathode temperature; The oxygen partial pressure detecting unit (21) calculates the oxygen partial pressure based on the pressure detected by the pressure detecting unit (7a), the flow rate detected by the flow rate detecting unit (7b), and the cathode temperature detected by the temperature detecting unit (10), thereby detecting the oxygen partial pressure, or detecting the pressure, the flow rate, and the cathode temperature as representative quantities of the oxygen partial pressure.

3. The fuel cell system (100) according to claim 2, characterized in that The oxygen partial pressure detecting unit (21) detects the oxygen partial pressure by calculating the oxygen partial pressure based on the pressure detected by the pressure detecting unit (7a), the flow rate detected by the flow rate detecting unit (7b), and the cathode temperature detected by the temperature detecting unit (10).

4. The fuel cell system (100) according to claim 3, characterized in that The oxygen partial pressure detection unit (21) calculates the water vapor partial pressure of the oxidant gas flowing through the cathode flow channel (3) based on the cathode temperature detected by the temperature detection unit (10), and calculates the oxygen partial pressure based on the calculated water vapor partial pressure, the pressure detected by the pressure detection unit (7a), and the flow rate detected by the flow detection unit (7b).

5. The fuel cell system (100) according to claim 2, characterized in that The oxygen partial pressure detection unit (21) detects the pressure, the flow rate, and the cathode temperature as the oxygen partial pressure representative amount. The current limiting unit (22) sets the prescribed value based on a characteristic indicating a relationship among the predetermined pressure, the flow rate, the cathode temperature, and the prescribed value, the pressure detected by the pressure detection unit (7a), the flow rate detected by the flow rate detection unit (7b), and the cathode temperature detected by the temperature detection unit (10).

6. The fuel cell system (100) according to claim 5, characterized in that The predetermined characteristics are characteristics for the prescribed values of the pressure and the flow rate, which are determined in advance corresponding to each of a plurality of temperature ranges of the cathode temperature.

7. The fuel cell system (100) according to any one of claims 2 to 6, characterized in that The current limiting unit (22) sets the predetermined value to be smaller as the cathode temperature is higher, based on the cathode temperature detected by the temperature detecting unit (10).

8. The fuel cell system (100) according to any one of claims 1 to 6, characterized in that The current limiting unit (22) sets the prescribed value to be smaller as the oxygen partial pressure is lower, based on the oxygen partial pressure or the oxygen partial pressure representative amount detected by the oxygen partial pressure detecting unit (21).

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