Patent Publication Number: US-2022238899-A1

Title: Fuel cell system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2021-009441 filed on Jan. 25, 2021, the contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a fuel cell system mounted on a moving body and which generates power. 
     Description of the Related Art 
     In a fuel cell system mounted on a moving body such as a fuel cell vehicle, anode off-gas containing anode gas (hydrogen gas) not used for power generation inside a fuel cell stack is discharged to the outside of the moving body. In order to prevent the anode gas from catching fire, the fuel cell system typically has a diluter that dilutes the discharged anode gas. 
     This type of diluter causes the increased size of the fuel cell system. Therefore, J P 2020-009598 A discloses a fuel cell system without a diluter. In this fuel cell system, when power generation is stopped, the anode off-gas discharged from the fuel cell stack is returned to the anode supply path. The anode gas passes through the membrane electrode assembly, moves from the anode path to the cathode path, is diluted by the cathode gas in the cathode path, and is discharged to the outside. 
     SUMMARY OF THE INVENTION 
     In a fuel cell system, water generated at a cathode by power generation of the fuel cell stack is discharged to an anode system apparatus. However, in the fuel cell system disclosed in JP 2020-009598 A, a means for discharging the generated water discharged to the anode system apparatus is not considered. The fuel cell system needs to discharge the generated water that has flowed out to the anode system apparatus, and at the time of discharge, the anode gas is also discharged. Therefore, there is a problem that the anode gas cannot be sufficiently diluted in a situation where the moving body is traveling or stopped, only by guiding the anode gas to the cathode path at the stoppage of power generation. 
     An object of the present invention is to solve the aforementioned problem. 
     According to an aspect of the present invention, there is provided a fuel cell system provided in a moving body, including: a fuel cell stack; an air pump configured to supply cathode gas to the fuel cell stack; a cathode discharge path through which cathode off-gas is discharged from the fuel cell stack; an anode path configured to allow anode gas to flow through the fuel cell stack; one or more discharge paths configured to guide the anode gas of the anode path to the cathode discharge path; and a control device configured to control operation of the air pump, wherein the control device is configured to: while the moving body is traveling, supply the cathode gas by rotating the air pump at a low-load rotational speed and perform a low-load power generation in the fuel cell stack; and in a case where power generation of the fuel cell stack is performed while the moving body is stopped, increase a supply amount of the cathode gas by rotating the air pump at a travel-stopping rotational speed (a during-stoppage-of-traveling rotational speed), which is greater than the low-load rotational speed. 
     In the fuel cell system described above, by adjusting the supply amount of the cathode gas according to the situation, the appropriately diluted anode gas can be discharged to the outside of the moving body. 
     The above and other objects features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings, in which a preferred embodiment of the present invention is shown by way of illustrative example. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an explanatory view schematically showing an overall configuration of a fuel cell system mounted on a moving body according to an embodiment of the present invention; 
         FIG. 2  is a timing chart for explaining power generation in the fuel cell system while the moving body is traveling; 
         FIG. 3A  is a schematic side view showing discharge of anode gas and cathode gas while the moving body is traveling, and  FIG. 3B  is a schematic side view showing the discharge of the anode gas and the cathode gas while the moving body is stopped; 
         FIG. 4  is a block diagram showing a functional block for performing processing by a power generation control unit of an ECU while the moving body is traveling; 
         FIG. 5  is a block diagram showing a functional block for performing processing by the power generation control unit of the ECU while the moving body is stopped; 
         FIG. 6A  is a timing chart for explaining the power generation of the fuel cell system while the moving body is stopped, and  FIG. 6B  is a timing chart illustrating the amount of discharge of the anode gas when a drain valve is in an open failure; 
         FIG. 7  is a flowchart illustrating a process flow of a cathode gas supply method; 
         FIG. 8  is a flowchart illustrating a process flow in a service mode; and 
         FIG. 9  is an explanatory view showing the overall configuration of the fuel cell system according to a modification. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     As shown in  FIG. 1 , a fuel cell system  10  according to an embodiment of the present invention includes a fuel cell stack  12 , an anode system apparatus  14 , a cathode system apparatus  16 , and a cooling apparatus  18 . The fuel cell system  10  is mounted on a moving body  11  such as a fuel cell vehicle. The fuel cell system  10  supplies electric power generated by the fuel cell stack  12  to a battery Bt, a traction motor Mt, and the like, of the moving body  11 . Note that the moving body  11  on which the fuel cell system  10  is mounted is not limited to a fuel cell vehicle, and may be another vehicle, a ship, an aircraft, a robot, or the like. 
     In the fuel cell stack  12 , a stack body  21  in which a plurality of power generation cells  20  are stacked is housed in a stack case (not shown). Each power generation cell  20  generates power by an electrochemical reaction between an anode gas (a fuel gas such as hydrogen) and a cathode gas (an oxygen-containing gas such as air). 
     Each power generation cell  20  includes a membrane electrode assembly  22  (hereinafter referred to as a “MEA  22 ”) and a pair of separators  24  ( 24   a ,  24   b ) sandwiching the MEA  22 . The MEA  22  includes an electrolyte membrane  26 , an anode  28  provided on one surface of the electrolyte membrane  26 , and a cathode  30  provided on the other surface of the electrolyte membrane  26 . The electrolyte membrane  26  is, for example, a solid polymer electrolyte membrane (cation exchange membrane). In the separator  24   a , an anode gas flow field  32  through which the anode gas flows is formed on one surface of the MEA  22 . In the separator  24   b , a cathode gas flow field  34  through which the cathode gas flows is formed on the other surface of the MEA  22 . In addition, by stacking the plurality of power generation cells  20 , a coolant flow field  36  through which a coolant flows is formed between the surfaces of the separator  24   a  and the separator  24   b  facing each other. 
     Further, each power generation cell  20  includes a plurality of passages (an anode gas passage, a cathode gas passage, and a coolant passage) (not shown) through which the anode gas, the cathode gas, and the coolant flow along the stacking direction of the stack body  21 . The anode gas passage communicates with the anode gas flow field  32 , the cathode gas passage communicates with the cathode gas flow field  34 , and the coolant passage communicates with the coolant flow field  36 . 
     The fuel cell stack  12  is supplied with anode gas by the anode system apparatus  14 . In the fuel cell stack  12 , the anode gas flows through the anode gas passage (anode gas supply passage) into the anode gas flow field  32 . The anode gas is used for power generation in the anode  28 . Anode off-gas that has been used for power generation flows out from the anode gas flow field  32  to the anode gas passage (anode gas discharge passage) and is discharged from the fuel cell stack  12  to the anode system apparatus  14 . The anode off-gas contains unreacted hydrogen. 
     Cathode gas is supplied to the fuel cell stack  12  by the cathode system apparatus  16 . In the fuel cell stack  12 , the cathode gas flows through the cathode gas passage (cathode gas supply passage) into the cathode gas flow field  34 . The cathode gas is used for power generation in the cathode  30 . The cathode off-gas that has been used for power generation flows out from the cathode gas flow field  34  to the cathode gas passage (cathode gas discharge passage) and is discharged from the fuel cell stack  12  to the cathode system apparatus  16 . 
     Further, the fuel cell stack  12  is supplied with a coolant by the cooling apparatus  18 . In the fuel cell stack  12 , coolant flows through the coolant passage (coolant supply passage) into the coolant flow field  36 . The coolant cools the power generation cell  20 . The coolant that has cooled the power generation cells  20  flows out from the coolant flow field  36  to the coolant passage (coolant discharge passage) and is discharged from the fuel cell stack  12  to the cooling apparatus  18 . 
     The anode system apparatus  14  of the fuel cell system  10  has an anode path  38 . The anode path  38  includes an anode supply path  40  that supplies anode gas to the fuel cell stack  12  and an anode discharge path  42  that discharges anode off-gas from the fuel cell stack  12 . The anode path  38  has an anode circulation path  44  for returning unreacted hydrogen contained in the anode off-gas of the anode discharge path  42  to the anode supply path  40 . 
     The anode path  38  includes an anode supply path  40 , an anode discharge path  42 , and a circulation circuit  39 , which are arranged downstream of the ejector  50 . The circulation circuit  39  circulates the anode gas (anode off-gas) through the anode circulation path  44 . A bleed path  46  is connected to the anode circulation path  44 . The bleed path  46  supplies part of the anode off-gas from the circulation circuit  39  to the cathode system apparatus  16 . 
     A tank  47  for storing anode gas is disposed upstream of the anode supply path  40 . Further, an injector  48  and an ejector  50  are provided in the anode supply path  40  in order toward the downstream side in the flow direction of the anode gas. The injector  48  is opened and closed during the operation of the fuel cell system  10  to discharge the anode gas having a lower pressure than the internal pressure of the tank  47  to the downstream side. The ejector  50  supplies the anode gas discharged from the injector  48  to the fuel cell stack  12 . Further, the ejector  50  suctions the anode off-gas from the anode circulation path  44  and supplies the suctioned anode off-gas to the fuel cell stack  12 . The ejector  50  suctions the anode off-gas by a negative pressure generated by the flow of the anode gas discharged from the injector  48 . 
     A gas-liquid separator  52  is provided in the anode discharge path  42 . The gas-liquid separator  52  separates liquid water (water generated during power generation) contained in the anode off-gas from the anode off-gas. The anode circulation path  44  is connected to an upper portion of the gas-liquid separator  52 . Thus, the anode off-gas (gas) from which the liquid water has been removed flows into the anode circulation path  44 . One end of a drain path  54  for discharging the separated liquid water is connected to the bottom portion of the gas-liquid separator  52 . A drain valve  56  for opening and closing the flow path is provided in the drain path  54 . The bleed path  46  is provided with a bleed valve  58  that opens and closes a flow passage in the bleed path  46 . The drain valve  56  and the bleed valve  58  are stop valves  55  for switching between opening (opening degree 100%) and closing (opening degree 0%). As the stop valve  55 , for example, a solenoid valve is used. 
     The cathode system apparatus  16  of the fuel cell system  10  has a cathode path  60 . The cathode path  60  includes a cathode supply path  62  that supplies cathode gas to the fuel cell stack  12 , and a cathode discharge path  64  that discharges cathode off-gas from the fuel cell stack  12 . A cathode bypass passage  66  is connected between the cathode supply path  62  and the cathode discharge path  64 . As a result, the cathode gas in the cathode supply path  62  flows directly to the cathode discharge path  64  without passing through the fuel cell stack  12 . 
     An air pump (air compressor)  68  that supplies cathode gas to the fuel cell stack  12  is provided in the cathode supply path  62 . The air pump  68  rotates a fan (not shown), compresses air (outside air) on the upstream side of the air pump  68 , and supplies the compressed air to the cathode supply path  62  on the downstream side. The air pump  68  may include a compressor in the cathode supply path  62  and an expander coaxial with the compressor in the cathode discharge path  64 . 
     The cathode supply path  62  includes a temperature controller  70  (intercooler) between the air pump  68  and the cathode bypass passage  66 . The temperature controller  70  cools the cathode gas with a coolant such as air, water, or the like. The cathode supply path  62  also includes a humidifier  72  between the cathode bypass passage  66  and the fuel cell stack  12 . The above-described bleed path  46  is connected to the cathode supply path  62  downstream of the humidifier  72 . Preferably, a gas-liquid separator (not shown) is provided at the connecting portion of the bleed path  46 . 
     The humidifier  72  is provided so as to straddle the cathode supply path  62  and the cathode discharge path  64 . The humidifier  72  humidifies the cathode gas supplied from the cathode supply path  62  by moisture (water generated during power generation or the like) contained in the cathode off-gas discharged from the fuel cell stack  12  to the cathode discharge path  64 . 
     In the cathode discharge path  64 , the drain path  54  of the anode system apparatus  14  is connected to the downstream side of the cathode bypass passage  66 . If the air pump  68  includes an expander in the cathode discharge path  64 , a gas-liquid separator is preferably provided between the humidifier  72  in the cathode discharge path  64  and the cathode bypass passage  66 . The gas-liquid separator separates water contained in the cathode off-gas and discharges liquid water to the downstream side of the expander. 
     A bypass valve  74  is provided in the cathode bypass passage  66 . The bypass valve adjusts the flow rate of the cathode gas bypassing the fuel cell stack  12 . As the bypass valve  74 , a butterfly valve whose opening degree can be linearly adjusted is used. 
     The fuel cell system  10  described above includes an ECU  80  (Electronic Control Unit: control device) for controlling each components of the fuel cell system  10 . The ECU  80  is constituted by a computer having one or more processors, memories, input/output interfaces, and electronic circuits (none of which are shown). The ECU  80  controls the operation of the drain valve  56 , the bleed valve  58 , the air pump  68 , the bypass valve  74 , and the like by one or more processors executing a program (not shown) stored in the memory. 
     In the anode system apparatus  14 , when the drain valve  56  is opened, liquid water separated in the gas-liquid separator  52  and anode gas contained in the anode off-gas are discharged to the drain path  54 . The drain path  54  is connected to the cathode discharge path  64 . Therefore, the anode gas in the drain path  54  is discharged to the outside together with the cathode gas through the cathode discharge path  64 . In the anode system apparatus  14 , when the bleed valve  58  is opened, nitrogen, oxygen, and anode gas contained in the anode off-gas flow out to the cathode supply path  62 . After passing through the fuel cell stack  12 , the anode gas is discharged to the cathode discharge path  64  and discharged to the outside together with the cathode off-gas. 
     In the fuel cell system  10  according to the present embodiment, a diluter for diluting the anode gas is not provided downstream of the connection point of the drain path  54  in the cathode discharge path  64 . Thus, miniaturization of the fuel cell system  10  as a whole can be achieved. 
     When discharging the anode gas from the cathode discharge path  64  to the outside of the moving body  11 , the ECU  80  appropriately adjusts the supply amount of the cathode gas in accordance with the situation of the moving body  11 . Thus, the anode gas that has flowed into the cathode discharge path  64  is favorably diluted. A description will now be given of a method of supplying the cathode gas in each of the cases where the moving body  11  is traveling and where the moving body  11  is stopped. 
     [During Traveling of Moving Body  11 ] 
     The fuel cell system  10  generates power in the fuel cell stack  12  while the moving body  11  is traveling (during operation by an ignition or a starter switch being turned on). This power generation is based on a power generation request from the travel control ECU or the battery ECU. At this time, the ECU  80  supplies electric power corresponding to the power generation request, to the air pump  68 . In addition, the amount of the cathode gas supplied to the fuel cell stack  12  is adjusted by adjusting the opening degree of the bypass valve  74 . 
     As shown in  FIG. 2 , the fuel cell system  10  performs normal power generation in a situation where the moving body  11  is traveling on a flat road or the like. The normal power generation generates power in accordance with the power consumption of the traction motor Mt and the air pump  68  necessary for normal traveling. At this time, the ECU  80  changes the rotational speed of the air pump  68  within a predetermined rotational range RR, based on the power generation request (the rotational speed is set to be constant for convenience in  FIG. 2 ). Accordingly, an appropriate amount of cathode gas is supplied from the air pump  68  to the fuel cell stack  12 . 
     Further, in a situation where a high load is applied to the traction motor Mt, for example, when the moving body  11  is climbing a hill road, the fuel cell system  10  performs a high-load power generation. At this time, the ECU  80  rotates the air pump  68  at a high-load rotational speed HR higher than the rotational range RR for the normal traveling or at a rotational speed near the upper limit of the rotational range RR. Therefore, the supply amount of the cathode gas supplied to the fuel cell stack  12  (flow rate corresponding to the high-load rotational speed HR) is larger than the supply amount of the normal power generation. 
     Conversely, in a situation in which the traction motor Mt is subjected to a low load, such as when the user of the moving body  11  loosens the accelerator, the fuel cell system  10  performs a low-load power generation. At this time, the ECU  80  rotates the air pump  68  at a low-load rotational speed LR which is lower than the rotational range RR for the normal traveling or at a rotational speed close to the lower limit of the rotational range RR. Therefore, the supply amount (flow rate corresponding to the low-load rotational speed LR) of the cathode gas supplied to the fuel cell stack  12  is smaller than the supply amount of the normal power generation. 
     A small amount of cathode gas is supplied to the fuel cell stack  12  even when the power generation request is zero in a situation where the moving body  11  is traveling or stopped. In this case, the fuel cell system  10  rotates the air pump  68  at a low rotational speed, for example, at a rotational speed close to the low-load rotational speed LR. Thus, the fuel cell stack  12  performs idle power generation in which the generated power is lower than the power consumption of the air pump  68 . Power generated by the idle power generation is consumed by the air pump  68 . 
     While the moving body  11  is traveling, the ECU  80  also controls the auxiliary devices (such as the injector  48 ) of the anode system apparatus  14  to supply the anode gas in a supply amount corresponding to the supply amount of the cathode gas, to the fuel cell stack  12 . Thus, the fuel cell stack  12  outputs electric power corresponding to various types of power generation (normal power generation, high-load power generation, low-load power generation, idle power generation, etc.). 
     During the traveling of the moving body  11 , an anode gas (anode off-gas) corresponding to the power generation of the fuel cell stack  12  circulates in the circulation circuit  39  of the anode path  38 . The fuel cell system  10  appropriately opens the drain valve  56  and the bleed valve  58  to discharge the generated water, nitrogen, oxygen and the like flowing through the circulation circuit  39 , to the cathode discharge path  64 . The generated water, nitrogen, oxygen and the like flowing through the circulation circuit  39  are cathode gas that has passed through the electrolyte membrane  26 . In  FIG. 2 , the drain valve  56  and the bleed valve  58  are opened at different timings. However, for example, the drain valve  56  and the bleed valve  58  may be simultaneously opened during the execution of the high-load power generation. 
     When the drain valve  56  or the bleed valve  58  is opened, the anode gas also flows out. Here, as shown in  FIG. 3A , when the moving body  11  is traveling, there is no element (such as an ignition source) that causes anode gas to catch fire, near a discharge port  76   a  of a tail pipe  76  through which the cathode discharge path  64  communicates. Therefore, the cathode gas supplied along with the power generation of the fuel cell stack  12  dilutes the anode gas, thereby ensuring safety in discharging the anode gas. 
     Even if the air pump  68  is rotated at the low-load rotational speed LR by performing the low-load power generation or the idle power generation while the moving body  11  is traveling, a small supply amount of the cathode gas can sufficiently dilute the anode gas. For example, it is possible to adjust the concentration of the anode gas such that the average of the volume concentration of the anode gas calculated based on concentration data obtained every three seconds will not exceed the value of 4%, or such that the instantaneous maximum value of the concentration of the anode gas at a given time will not exceed 8%. As shown in  FIG. 4 , for example, the ECU  80  includes a during-traveling power generation control unit  81 . The during-traveling power generation control unit  81  controls the dilution of the anode gas by supplying the cathode gas while the moving body  11  is traveling. 
     The during-traveling power generation control unit  81  includes a reference cathode gas amount calculation unit  82 , a valve selection unit  84 , a dilution cathode gas amount calculation unit  86 , a pump control unit  88 , a valve opening judgment unit  90 , a valve control unit  92 , a during-traveling failure detection unit  94 , and a service mode control unit  96 . 
     The reference cathode gas amount calculation unit  82  calculates a target supply amount of the cathode gas to be supplied to the fuel cell stack  12 . The calculation of the target supply amount is based on a power generation request signal transmitted from another ECU, for example, a travel control ECU for controlling the traction motor Mt, a battery ECU for monitoring the battery level of the battery Bt, or the like. The ECU  80  may have a function of the travel control ECU or the battery ECU. The ECU  80  may also calculate a power generation request based on signals from sensors such as an accelerator opening sensor and a wheel speed sensor. 
     The valve selection unit  84  selects a valve to be opened, from among the drain valve  56  and the bleed valve  58 . The selection of the valve is based on a hydrogen concentration adjustment request of an ECU (not shown) that monitors the hydrogen concentration, or a drainage request of an ECU (not shown) that monitors the amount of accumulated water of the gas-liquid separator  52  (or other gas-liquid separator), or a detection signal of a sensor that detects the amount of accumulated water of the gas-liquid separator  52  (or other gas-liquid separator). 
     The dilution cathode gas amount calculation unit  86  calculates an amount of cathode gas (dilution cathode gas amount) necessary for dilution of the anode gas. The calculation of the dilution cathode gas amount is based on the valve opening request of the drain valve  56  or the bleed valve  58  selected by the valve selection unit  84 . For example, the dilution cathode gas amount calculation unit  86  calculates the discharge amount of the anode gas. The calculation of the discharge amount is based on the pressure difference between the upstream and the downstream of the bleed path  46  or the drain path  54 , the estimated temperature of the anode gas, the estimated concentration of the anode gas, the catalytic reaction effect, and the like. The pressure difference between upstream and the downstream of the bleed path  46  or the drain path  54  is obtained from an ECU or a sensor (not shown). Further, the dilution cathode gas amount calculation unit  86  calculates the dilution cathode gas amount based on the calculated anode gas discharge amount. 
     The pump control unit  88  calculates the rotational speed of the air pump  68 . The calculation of the rotational speed is based on the target supply amount calculated by the reference cathode gas amount calculation unit  82  and the dilution cathode gas amount calculated by the dilution cathode gas amount calculation unit  86 . The pump control unit  88  controls the rotation of the air pump  68  based on the calculated rotational speed. There are cases in which the rotational speed of the air pump  68  may become greater than a value necessary for power generation of the fuel cell stack  12 , by setting the rotational speed to a value at which the anode gas can be diluted. In this case, the ECU  80  changes the opening degree of the bypass valve  74  to adjust the amount of cathode gas flowing through the cathode bypass passage  66 . Thus, the amount of the cathode gas supplied to the fuel cell stack  12  is adjusted to an appropriate amount corresponding to a power-generation electric power. 
     The valve opening judgment unit  90  permits opening of the valve. The valve opening permission is based on the timing at which the actual flow rate detected by a flow rate sensor (not shown) of the cathode gas provided in the cathode supply path  62  exceeds the dilution cathode gas amount calculated by the dilution cathode gas amount calculation unit  86 . 
     The valve control unit  92  opens the selected stop valve  55  (one of the drain valve  56  and the bleed valve  58 ). The opening of the stop valve  55  is based on selection information of the drain valve  56  and the bleed valve  58  selected by the valve selection unit  84 , and valve opening permission by the valve opening judgment unit  90 . In addition, the valve control unit  92  may open both the drain valve  56  and the bleed valve  58  during the high-load power generation. 
     Thus, the ECU  80  discharges the anode gas from the circulation circuit  39  in accordance with the rotational speed of the air pump  68 . The discharge of the anode gas is performed by opening one of the drain valve  56  and the bleed valve  58 , or by opening both the drain valve  56  and the bleed valve  58 . Both the drain valve  56  and the bleed valve  58  are opened during the high-load power generation. For example, even in the case of performing the low-load power generation in which the air pump  68  is rotated at the low-load rotational speed LR or the idle power generation, an amount of the cathode gas capable of diluting the anode gas is supplied to the cathode discharge path  64 . Accordingly, the fuel cell system  10  can safely discharge the anode gas and the cathode gas while the moving body  11  is traveling. 
     While the moving body  11  is traveling, the during-traveling failure detection unit  94  detects a failure of each stop valve  55  (drain valve  56 , bleed valve  58 ) of the fuel cell system  10  and a leakage of the anode gas. For example, the during-traveling failure detection unit  94  monitors an opening/closing command of the drain valve  56  and a voltage of the drain valve  56 . Then, when a voltage is being applied to the drain valve  56  despite the valve closing command of the drain valve  56 , it is determined that the drain valve  56  is opened by mistake. According to this detection method (hereinafter referred to as a command operation mismatch detection method), the during-traveling failure detection unit  94  can detect an open failure in which the drain valve  56  is kept open without being closed and a leakage of the anode gas. The same applies to the bleed valve  58 . This detection method has the advantage that the abnormality of each stop valve  55  can be detected in a short time. Alternatively, in a state of giving a command for closing the valve to the drain valve  56 , the during-traveling failure detection unit  94  calculates the amount of hydrogen leakage from the detected pressure of the pressure sensor (not shown in the circulation circuit  39 ) and the value of the power generation electric current. When the leakage amount is large, it can be determined that the drain valve  56  is opened by mistake. Also in this detection method (hereinafter referred to as a pressure drop detection method), the during-traveling failure detection unit  94  can detect an open failure in which the drain valve  56  fails to close and a leakage of anode gas. The same applies to the bleed valve  58 . Although the pressure drop detection method requires a longer time than the command operation mismatch detection method, the detection accuracy can be improved. 
     The service mode control unit  96  performs the operation of the fuel cell system  10  when an operation by a service person is performed during inspection operation, maintenance operation, or the like. For example, the service mode control unit  96  operates after the abnormality of the drain valve  56  or the bleed valve  58  has been detected. Then, the rotational speed of the air pump  68  is set to a rotational speed (service mode rotational speed) which is greater than the low-load rotational speed LR. At this time, the service mode control unit  96  adjusts the supply amount of the cathode gas to the fuel cell stack  12  in accordance with the opening degree of the bypass valve  74 , thereby performing the normal power generation or low-load power generation. As a result, in the service mode, it is possible to take measures such as recheck of a failure location, initialization of each auxiliary device (stop valve  55  or the like) in which a failure has occurred, reset of each ECU, start and stop, or the like. 
     The service mode control unit  96  may output a valve closing command to the drain valve  56  or the bleed valve  58  after the abnormality of the drain valve  56  or the bleed valve  58  has been detected, thereby preventing the discharge of the anode gas. For example, even if the drain valve  56  is in an open failure state in which the valve cannot be closed, the discharge amount of the anode gas discharged to the cathode discharge path  64  can be suppressed by closing the bleed valve  58  by the valve closing command. 
     [During Stoppage of Traveling of Moving Body  11 ] 
     Next, a method of supplying the cathode gas during power generation while the moving body  11  is stopped will be described. The fuel cell system  10  determines a state in which power generation should be performed even when traveling of the moving body  11  is stopped (during non-operation by an ignition or a starter switch being turned off), and automatically performs power generation of the fuel cell stack  12 . Situations in which power generation should be performed include avoidance of freezing of the fuel cell system  10 , remote activation of the air conditioning system, external power supply, charging of the battery Bt, and the like. Even during the stop of traveling, the ECU  80  adjusts the supply amount of the cathode gas to the fuel cell stack  12  by adjusting the operation of the air pump  68  and the opening degree of the bypass valve  74 . 
     Here, the discharge amount of the anode gas discharged from the anode path  38  is determined in accordance with the flow path cross-sectional area of the drain valve  56  or the flow path cross-sectional area of the bleed valve  58 . Therefore, the fuel cell system  10  opens either the drain valve  56  or the bleed valve  58  to discharge the anode gas even in the power generation during the stoppage of traveling. At this time, if the air pump  68  supplies the cathode gas at the same rotational speed as when the vehicle is traveling, the anode gas can be sufficiently diluted. 
     However, when an open failure occurs in which the drain valve  56  does not close or an open failure occurs in which the bleed valve  58  does not close, the anode gas is not sufficiently diluted. For example, if the bleed valve  58  is opened in the event of an open failure of the drain valve  56 , anode gas will be discharged from both the drain path  54  and the bleed path  46 . Therefore, the discharge amount of the anode gas increases as a whole of the anode system apparatus  14  (see also  FIG. 6B ). As shown in  FIG. 3B , when the moving body  11  is not traveling, there is a possibility that there exists a factor causing anode gas to catch fire, in the vicinity of the discharge port  76   a  of the tail pipe  76 . The cause of catching fire is, for example, the existence of a kind of ignition source whose temperature is higher than the hydrogen ignition point temperature, such as the work of throwing sparks in a garage. 
     Therefore, during the stoppage of traveling of the moving body  11 , the ECU  80  has a during-stoppage-of-traveling power generation control unit  100  as shown in  FIG. 5 . The during-stoppage-of-traveling power generation control unit  100  performs control to dilute the anode gas. The control for diluting the anode gas supplies a larger amount of cathode gas than an amount of cathode gas supplied in the low-load power generation or the idle power generation. 
     Specifically, the during-stoppage-of-traveling power generation control unit  100  has a valve selection unit  84 , a pump control unit  88 , a valve opening judgment unit  90 , and a valve control unit  92 , as in the case of the during-traveling power generation control unit  81 . Further, the during-stoppage-of-traveling power generation control unit  100  has a cathode gas amount setting unit  102  in place of the reference cathode gas amount calculation unit  82  and the dilution cathode gas amount calculation unit  86 . Further, the during-stoppage-of-traveling power generation control unit  100  has a during-stoppage-of-traveling failure detection unit  104  in place of the during-traveling failure detection unit  94 . 
     The cathode gas amount setting unit  102  stores a predetermined value of the rotational speed of the air pump  68  used in the power generation during the stoppage of traveling (hereinafter referred to as a during-stoppage-of-traveling rotational speed (a travel-stopping rotational speed) SR). The during-stoppage-of-traveling rotational speed SR is the rotational speed of the air pump  68  corresponding to the dilution of the total amount of the anode gas when the anode gas is discharged from the plurality of stop valves  55  (the drain valve  56  and the bleed valve  58 ). That is, the during-stoppage-of-traveling rotational speed SR is calculated as follows. First, the total amount of the discharged anode gas is calculated based on the cross-sectional areas of the flow paths of the plurality of stop valves  55 . Next, the rotational speed at which the cathode gas can be surely supplied at such an amount as to sufficiently dilute the total amount of the anode gas is determined in advance by the manufacturer through experiments or the like. When there are three or more stop valves  55  for discharging the anode gas from the anode path  38 , the during-stoppage-of-traveling rotational speed SR may correspond to dilution of the discharge amounts of the anode gas of two stop valves  55  or may correspond to dilution of the discharge amounts of the anode gas of the three or more stop valves  55 . 
     Specifically, as shown in  FIG. 6A , the during-stoppage-of-traveling rotational speed SR is greater than the low-load rotational speed LR. The low-load rotational speed LR is the rotational speed of the air pump  68  used when performing the low-load power generation or the idle power generation while the moving body  11  is traveling. It should be noted that the during-stoppage-of-traveling rotational speed SR may be lower than the high-load rotational speed HR. The high-load rotational speed HR is the rotational speed of the air pump  68  used when the high-load power generation is performed while the moving body  11  is traveling. As a result, power consumption due to excessive supply of cathode gas in the fuel cell system  10  can be suppressed during the stoppage of traveling. 
     Upon receiving a power generation request transmitted from another ECU during the stoppage of traveling, the cathode gas amount setting unit  102  automatically sets the during-stoppage-of-traveling rotational speed SR stored by itself and outputs it to the pump control unit  88 . The pump control unit  88  controls the rotation of the air pump  68  on the basis of the during-stoppage-of-traveling rotational speed SR set by the cathode gas amount setting unit  102 . The operations of the valve selection unit  84 , the valve opening judgment unit  90 , and the valve control unit  92  are the same as those of the during-traveling power generation control unit  81 . That is, the valve selection unit  84  selects one of the drain valve  56  and the bleed valve  58 . The valve control unit  92  opens the selected valve based on the permission of opening given by the valve opening judgment unit  90 . 
     As a result, the fuel cell system  10 , while discharging anode gas from the circulation circuit  39 , rotates the air pump  68  in accordance with the during-stoppage-of-traveling rotational speed SR to supply cathode gas to the fuel cell stack  12 . The supply amount of the anode gas supplied from the anode system apparatus  14  to the fuel cell stack  12  during the stoppage of traveling is set to, for example, the same supply amount as that at the time of the low-load power generation during traveling. Therefore, the fuel cell stack  12  performs the low-load power generation based on the inflow of the anode gas and the cathode gas, and outputs the generated power. The cathode gas supplied in excess of the necessary amount for power generation by the fuel cell stack  12  is guided from the cathode bypass passage  66  to the cathode discharge path  64  in accordance with the opening degree of the bypass valve  74 . 
     Accordingly, the cathode gas supplied from the rotating air pump  68  dilutes the anode gas. Even if one or both of the drain valve  56  and the bleed valve  58  is subjected to an open failure and anode gas consequently flows out from both the bleed path  46  and the drain path  54 , the anode gas discharged from the two stop valves  55  can be diluted. Therefore, the fuel cell system  10  can sufficiently dilute the anode gas in the power generation during the stoppage of traveling. For example, it is possible to adjust the concentration of the anode gas such that the average of the volume concentration of the anode gas calculated based on concentration data obtained every three seconds will not exceed the value of 4%, or such that the instantaneous maximum value of the concentration of the anode gas at a given time will not exceed 8%. 
     The during-stoppage-of-traveling failure detection unit  104  detects a failure of each valve (the drain valve  56  and the bleed valve  58 ) of the fuel cell system  10  and a leakage of the anode gas while the moving body  11  is stopped. For example, during the stoppage of traveling of the moving body, the failure detection unit  104  acquires a detected pressure of a pressure sensor (not shown) of the circulation circuit  39 , and constantly calculates an outflow amount of anode gas for each of the drain valve  56  and the bleed valve  58 . The during-stoppage-of-traveling failure detection unit  104  commands the drain valve  56  or the bleed valve  58  to open and close in order. When the outflow amount of the anode gas is large in spite of the valve closing command, it can be determined that the drain valve  56  or the bleed valve  58  is erroneously opened. According to this detection method (hereinafter referred to as an outflow amount estimation detection method), the during-stoppage-of-traveling failure detection unit  104  can detect an open failure of the valve and a leakage of the anode gas. Further, although the outflow estimation detection method takes longer time than the command operation mismatch detection method or the pressure drop detection method described above, the outflow estimation detection method can perform highly accurate detection. Further, since no voltage sensor or current sensor is provided, the cost can be reduced. 
     The fuel cell system  10  according to the present embodiment is basically configured as described above. The processing flow will be described below with reference to  FIG. 7 . 
     When performing power generation in the fuel cell stack  12 , the ECU  80  of the fuel cell system  10  first determines whether the moving body  11  is traveling or stopped, based on a signal of the ignition or the starter switch (step S 1 ). If it is determined that the moving body  11  is traveling (step S 1 : YES), the process proceeds to step S 2  where a cathode-gas supply process by the during-traveling power generation control unit  81  is performed. 
     Specifically, the during-traveling power generation control unit  81  first determines whether to execute the service mode for maintenance of the fuel cell system  10  (step S 2 ). As described above, the service mode is executed when an operation is performed by a serviceperson (car technician) or the like, and is not executed in other cases. If the service mode is not executed in step S 2  (step S 2 : YES), the during-traveling power generation control unit  81  executes power generation of the fuel cell stack  12  based on the power generation request (step S 3 ). 
     In power generation control during traveling, the ECU  80  appropriately performs the normal power generation, the high-load power generation, the low-load power generation, the idle power generation, or the like, and adjusts the rotational speed of the air pump  68  according to the type of power generation. Thus, an amount of the cathode gas corresponding to the rotational speed of the air pump  68  flows through the cathode path  60 , and the anode gas discharged from the anode system apparatus  14  is diluted. For example, the anode gas flowing out to the drain path  54  by opening the drain valve  56  flows into the cathode discharge path  64 , and is diluted by the cathode gas. Then, it is discharged to the outside of the moving body  11  together with the cathode gas. Similarly, the anode gas flowing out to the bleed path  46  due to the opening of the bleed valve  58  flows into the cathode supply path  62  and is mixed with the cathode gas. Then, the anode gas flows through the fuel cell stack  12 , is discharged into the cathode discharge path  64 , and is discharged to the outside of the moving body  11  together with the cathode gas. 
     The during-traveling failure detection unit  94  determines whether or not the drain valve  56  or the bleed valve  58  has failed during power generation of the fuel cell stack  12  (step S 4 ). At this time, the during-traveling failure detection unit  94  detects failures of the drain valve  56  and the bleed valve  58  by the above-described command operation mismatch detection method without spending a long time. Thus, it is possible to quickly check that the drain valve  56  or the bleed valve  58  has failed. 
     If it is determined that the drain valve  56  or the bleed valve  58  has failed (step S 4 : YES), the during-traveling failure detection unit  94  proceeds to step S 5 , and stores a failure code of the failed valve. In case of the open failure of the drain valve  56  or the bleed valve  58 , the during-traveling failure detection unit  94  stops the supply of the anode gas to the anode system apparatus  14 . In addition, a valve closing command is issued to the drain valve  56  and the bleed valve  58  (step S 6 ). Further, the during-traveling failure detection unit  94  notifies the user of the moving body  11  that an abnormality has occurred in the anode system apparatus  14  via a notification unit (not shown) of the moving body  11  (step S 7 ). 
     When the drain valve  56  or the bleed valve  58  has not failed in step S 4  and after the end of step S 7 , the ECU  80  determines whether or not the traveling of the moving body  11  has ended (step S 8 ). When the traveling of the moving body  11  is continued (step S 8 : NO), the process returns to step S 3 , and the same processing flow is repeated. 
     If it is determined in step S 1  that the moving body  11  is in the stoppage of traveling (step S 1 : NO), the process proceeds to step S 9 , and the during-stoppage-of-traveling power generation control unit  100  performs a cathode-gas supply process. 
     In step S 9 , the during-stoppage-of-traveling power generation control unit  100  rotates the air pump  68  based on the during-stoppage-of-traveling rotational speed SR set by the cathode gas amount setting unit  102 . Then, the cathode gas is supplied at a supply amount larger than the supply amount of the cathode gas for the low-load power generation during traveling. The supply amount of the cathode gas depends on the sum of the discharge amount of the anode gas from the drain valve  56  and the discharge amount of the anode gas from the bleed valve  58 . Thus, even if the anode gas is discharged from a plurality of discharge paths (the bleed path  46 , the drain path  54 ) due to an open failure in which the drain valve  56  or the bleed valve  58  does not close, the anode gas can be sufficiently diluted by the cathode gas. 
     The during-stoppage-of-traveling failure detection unit  104  determines whether the drain valve  56  or the bleed valve  58  has failed during power generation of the fuel cell stack  12  (step S 10 ). At this time, the during-stoppage-of-traveling failure detection unit  104  detects the failure of the drain valve  56  and the bleed valve  58  over time longer than the outflow amount estimation detection method described above. Thus, the failure of the drain valve  56  or the bleed valve  58  can be detected with high accuracy. Even if a long time is required for failure detection, ignition of anode gas or the like can be avoided because the anode gas continues to be diluted by the cathode gas having a large supply amount. 
     If it is determined in step S 10  that the valve has failed (step S 10 : YES), the during-stoppage-of-traveling failure detection unit  104  proceeds to step S 11 , and stores a failure code of the valve that has failed. Further, the during-stoppage-of-traveling failure detection unit  104  notifies the user of the moving body  11  that an abnormality has occurred in the anode system apparatus  14  via a notification unit (not shown) of the moving body  11  (step S 12 ). 
     When the drain valve  56  or the bleed valve  58  has not failed in step S 10  (step S 10 : NO) or after the end of step S 12 , the ECU  80  determines whether or not power generation during the stoppage of traveling of the moving body  11  ends (step S 13 ). When the power generation of the fuel cell stack  12  is continued while the moving body  11  is stopped (step S 13 : NO), the ECU  80  returns to step S 9  and repeats the same processing flow. 
     On the other hand, when it is determined that the service mode should be executed in step S 2  shown in  FIG. 7  (step S 2 : NO), the service mode control unit  96  starts the control of the fuel cell system  10  as shown in  FIG. 8 . The service mode control unit  96  may prohibit the traveling of the moving body  11  during the service mode. 
     In the service mode, the service mode control unit  96  sets a service mode rotational speed greater than the low-load rotational speed LR of the air pump  68  for the low-load power generation. Thus, the increased supply amount of the cathode gas is supplied downstream of the air pump  68  (step S 21 ). The during-traveling failure detection unit  94  determines whether the drain valve  56  or the bleed valve  58  has failed even in the service mode (step S 22 ). In the service mode, the supply amount of the cathode gas is large and the anode gas is diluted. Therefore, the during-traveling failure detection unit  94  takes a time and detects a failure of the drain valve  56  and the bleed valve  58 , by using the outflow amount estimation detection method (or the pressure drop detection method) described above, for example. 
     If it is determined in step S 22  that a failure has occurred (step S 22 : YES), the during-traveling failure detection unit  94  proceeds to step S 23  and stores a failure code for the valve that has failed. Further, the during-traveling failure detection unit  94  notifies the user of the moving body  11  that an abnormality has occurred in the anode system apparatus  14  via a notification unit (not shown) of the moving body  11  (step S 24 ). 
     If it is determined in step S 22  that the drain valve  56  and the bleed valve  58  have not failed (step S 22 : NO) and after the end of step S 24 , the ECU  80  determines whether to end the service mode (step S 25 ). 
     If the service mode is continued (step S 25 : NO), the service mode control unit  96  returns to step S 21  and repeats the same processing flow. By implementing the service mode in this manner, the fuel cell system  10  can check the failure of the stop valve  55  and quickly take necessary measures when the moving body  11  is traveling. It should be noted that the moving body  11  may be allowed to travel in the service mode, whereby the moving body can be easily transported to a maintenance factory or the like. 
     The present invention is not limited to the embodiments described above, and various modifications can be made in accordance with the essence and gist of the invention. For example, the air pump  68  is not limited to a compressor, and a device capable of supplying an oxygen-containing gas such as a blower may be used. 
     For example, in the processing flow described above, the ECU  80  outputs a valve closing command to the stop valve  55  when a failure of the stop valve  55  (the drain valve  56 , the bleed valve  58 ) is detected while the moving body  11  is traveling (step S 6  in  FIG. 7 ). Alternatively, when detecting a failure of the stop valve  55  while the moving body  11  is traveling, the ECU  80  may perform control to increase the rotational speed of the air pump  68  to a value greater than the rotational speed of the air pump  68  in a state in which the stop valve  55  is not in failure. As a result, a sufficient supply amount of cathode gas can be led to the cathode discharge path  64  to dilute the anode gas. 
     For example, as shown in  FIG. 9 , in the fuel cell system  10 , a purge path  110  is connected to the anode circulation path  44 . Further, a purge valve  112  for opening and closing the flow passage of the purge path  110  may be provided. In this case, the purge path  110  has the same function as the bleed path  46 , and the purge valve  112  has the same function as the bleed valve  58 . Alternatively, the fuel cell system  10  includes a drain pipe (not shown) for directly discharging the produced water accumulated in the fuel cell stack  12 . Further, a stop valve  55  for opening and closing the flow passage of the drain pipe may be provided. The number of discharge paths for discharging anode gas from the anode system apparatus  14  and the number of stop valves  55  included in the fuel cell system  10  are not particularly limited, and three or more may be provided. 
     As another modification, the fuel cell system  10  includes only one discharge path (e.g., the drain path  54 ) for discharging anode gas from the anode path  38 . Further, one stop valve  55  (e.g., a drain valve  56 ) for opening and closing the discharge path may be provided. Thus, even if there is only one discharge path, setting the rotational speed of the air pump  68  during the stoppage of traveling to the during-stoppage-of-traveling rotational speed SR set based on the cross-sectional area of the flow path of the drain valve  56  makes it possible to sufficiently dilute the anode gas with the cathode gas. In addition, the during-stoppage-of-traveling rotational speed SR in this case is set to a value greater than the low-load rotational speed LR of the air pump  68  used when the low-load power generation is performed while the moving body  11  is traveling. 
     A description will be given below concerning technical concepts and effects that are capable of being grasped from the above-described embodiment. 
     According to an aspect of the present invention, there is provided a fuel cell system  10  provided in a moving body  11 , including: a fuel cell stack  12 ; an air pump  68  configured to supply cathode gas to the fuel cell stack  12 ; a cathode discharge path  64  through which cathode off-gas is discharged from the fuel cell stack  12 ; an anode path  38  configured to allow anode gas to flow through the fuel cell stack  12 ; one or more discharge paths (the bleed path  46 , the drain path  54 ) configured to guide the anode gas of the anode path  38  to the cathode discharge path  64 ; and a control device (ECU  80 ) configured to control operation of the air pump  68 , wherein the control device is configured to: while the moving body  11  is traveling, supply the cathode gas by rotating the air pump  68  at a low-load rotational speed LR and perform a low-load power generation in the fuel cell stack  12 ; and in a case where power generation of the fuel cell stack  12  is performed while the moving body  11  is stopped, increase a supply amount of the cathode gas by rotating the air pump  68  at a during-stoppage-of-traveling rotational speed (a travel-stopping rotational speed) SR, which is greater than the low-load rotational speed LR. 
     With the above configuration, in the fuel cell system  10 , adjusting the supply amount of the cathode gas in accordance with a situation of the moving body  11 , e.g., during traveling or during stoppage of traveling, makes it possible to discharge the appropriately diluted anode gas to the outside of the moving body  11 . In particular, when the moving body  11  is stopped, there is a possibility that an element that causes anode gas to catch fire exists outside the moving body  11 . In this case, the fuel cell system  10  rotates the air pump  68  at the during-stoppage-of-traveling rotational speed SR which is greater than the low-load rotational speed. Thus, the cathode gas discharged to the cathode discharge path  64  can sufficiently dilute the anode gas. As a result, the fuel cell system  10  does not require a diluter, and the overall size of the system can be reduced. 
     The fuel cell system  10  further includes one or more stop valves  55  (drain valve  56 , bleed valve  58 ) configured to switch between a state of allowing flow of the anode gas in the one or more discharge paths (bleed path  46 , drain path  54 ) and a state of stopping flow of the anode gas in the one or more discharge paths. The during-stoppage-of-traveling rotational speed SR of the air pump  68  is set based on a flow path cross-sectional area of the one or more stop valves  55 . Thus, setting the during-stoppage-of-traveling rotational speed SR in accordance with the flow path cross-sectional area of the stop valve  55  makes it possible to adjust the supply amount of the cathode gas of the air pump  68  so as to be appropriate for the amount necessary for dilution of the anode gas. Thus, since the fuel cell system  10  does not need to rotate the air pump  68  more than necessary, the efficiency of power generation can be improved. 
     A plurality of discharge paths (bleed path  46 , drain path  54 ) are provided. Further, each of the plurality of discharge paths is provided with the stop valve  55 . The during-stoppage-of-traveling rotational speed SR is set so as to achieve a supply amount of the cathode gas corresponding to a total amount of the anode gas discharged from the plurality of stop valves  55 . Thus, even if the plurality of stop valves  55  are opened simultaneously, the supply amount of cathode gas supplied correspondingly to the total amount of anode gas discharged from the plurality of stop valves  55  enables the anode gas to be sufficiently diluted. 
     The anode path  38  includes an anode supply path  40 , an anode discharge path  42 , and an anode circulation path  44 . The anode supply path  40  supplies anode gas to the fuel cell stack  12 . The anode discharge path  42  discharges anode off-gas from the fuel cell stack  12 , and further includes a gas-liquid separator  52 . The anode circulation path  44  allows the anode off-gas discharged from the gas-liquid separator  52  to circulate to the anode supply path  40 . The plurality of stop valves  55  include a drain valve  56  and a bleed valve  58 . The drain valve  56  opens and closes a drain path  54 , which is one of the discharge paths connected to the gas-liquid separator  52 , to discharge the separated water. The bleed valve  58  opens and closes a bleed path  46 , which is another one of the discharge paths connected to the anode circulation path  44 , to discharge the anode off-gas. Thus, in the fuel cell system  10 , even when both the drain valve  56  and the bleed valve  58  are opened due to the abnormality of both the valves, the supply of an appropriate amount of cathode gas enables sufficient dilution of the anode gas. 
     Further, the control device (ECU  80 ) can implement a first detection method for detecting a failure of the stop valves  55  while the moving body  11  is traveling and a second detection method for detecting a failure of the stop valves  55  while the moving body  11  is stopped. The detection time required for the first detection method is shorter than the detection time required for the second detection method. As a result, the fuel cell system  10  detects a failure in a short detection time by the first detection method while the moving body  11  is traveling, so that the abnormality of the stop valve  55  can be detected early and the user can be prompted to take necessary measures. On the other hand, the fuel cell system  10  can accurately detect the abnormality of the stop valve  55  by the second detection method which requires a longer time, during the stoppage of traveling of the moving body  11 , and can enhance safety while the moving body  11  is traveling. 
     When a failure of the one or more stop valves  55  is detected while the moving body  11  is traveling, the control device (ECU  80 ) increases a rotational speed of the air pump  68  after the detection of the failure, to a value greater than a rotational speed of the air pump  68  before the detection of the failure. Thus, even when the fuel cell system  10  detects a failure of the stop valve  55  while the moving body  11  is traveling, the increase in the supply amount of the cathode gas enables the anode gas to be sufficiently diluted. 
     When a failure of the stop valves  55  is detected, the control device (ECU  80 ) outputs a valve closing command to the stop valves  55 . As a result, the fuel cell system  10  can immediately reduce the discharge of the anode gas when a failure of the stop valves  55  is detected. 
     Further, while the moving body  11  is traveling after the failure of the stop valves  55  has been detected during stoppage of traveling of the moving body  11 , the control device (ECU  80 ) increases a rotational speed of the air pump  68  after the failure has been detected, to a value greater than a rotational speed of the air pump  68  in a state where the stop valves  55  are not in failure. Thus, the fuel cell system  10  enables the anode gas to be sufficiently diluted even when the stop valve  55  fails while the moving body  11  is traveling, and enables the moving body  11  to be moved as necessary.