JP2009093918A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress deterioration of a fuel cell even when decision of gas leak is executed during intermittent operation of the fuel cell. <P>SOLUTION: Upon transferring an operation mode of a fuel cell 2 from a normal operation mode to an intermittent operation mode, a control part 5 starts an open circuit voltage avoidance treatment, and executes gas leak decision treatment after an output current value of the fuel cell 2 detected with a current sensor A becomes an avoidance treatment finishing threshold value or lower. When the gas leak is decided in the decision treatment, the control part 5 starts again the supply of hydrogen gas while stopping the supply of oxidation gas and sets open circuit voltage to command voltage to a DC/DC converter 91, and executes again the gas leak decision treatment. When the gas leak is decided in the decision treatment, the control part 5 outputs a gas leak alarm. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fuel cell system.

In recent years, a fuel cell system using a fuel cell that generates electric power by an electrochemical reaction between a fuel gas, which is a reactive gas, and an oxidizing gas as an energy source has been developed. In such a fuel cell system, it is necessary to monitor whether or not the fuel gas leaks from the gas pipe or the fuel cell from the viewpoint of ensuring safety. In the fuel cell system described in Patent Document 1 described below, fuel gas leakage determination is performed not only during the power generation operation of the fuel cell but also during intermittent operation (when power generation is stopped).
JP 2006-185886 A

  By the way, when the fuel gas leakage determination is performed during intermittent operation of the fuel cell, the output current of the fuel cell is forcibly set to 0 A so that it can be easily performed without considering the fuel gas consumption. become. However, if the output current of the fuel cell is forcibly set to 0 A immediately after the transition to the intermittent operation, the state in which the output voltage of the fuel cell reaches the open circuit voltage (OCV) may be continued. In some cases, the fuel cell will deteriorate.

  The present invention has been made to solve the above-described problems caused by the prior art, and can suppress deterioration of the fuel cell even when the fuel gas leakage determination is performed during intermittent operation of the fuel cell. An object is to provide a fuel cell system.

  In order to solve the above-described problems, a fuel cell system according to the present invention is a fuel cell system having a fuel cell that is supplied with a fuel gas and an oxidizing gas and generates electric power by an electrochemical reaction between the fuel gas and the oxidizing gas. In the intermittent operation of the fuel cell, a leakage determination means for determining whether or not the fuel gas leaks in the fuel cell system, and an open circuit voltage for gradually decreasing the output current of the fuel cell by stopping the supply of the oxidizing gas Avoidance processing execution means for executing avoidance processing, wherein the leakage determination means determines whether or not there is a fuel gas leak after the open circuit voltage avoidance processing is completed.

  According to the present invention, during the intermittent operation of the fuel cell, after the open circuit voltage avoidance process in which the supply of the oxidizing gas is stopped and the output current of the fuel cell is gradually reduced is completed, the presence or absence of fuel gas leakage is determined. Since the determination can be made, it is possible to prevent the output voltage of the fuel cell from reaching the open circuit voltage. Therefore, deterioration of the fuel cell can be suppressed even when the fuel gas leak determination is executed during intermittent operation of the fuel cell.

  In the fuel cell system, the avoidance processing execution means can determine that the open circuit voltage avoidance processing has ended when the output current of the fuel cell has become equal to or less than a predetermined avoidance processing end threshold.

  By doing in this way, fuel gas leak determination can be performed without considering the amount of fuel gas pressure drop due to the flow of output current.

  A fuel cell system according to the present invention is a fuel cell system having a fuel cell that receives supply of a fuel gas and an oxidizing gas and generates electric power by an electrochemical reaction of the fuel gas and the oxidizing gas. Leak determination means for determining the presence or absence of fuel gas leakage in the fuel cell system during intermittent operation, and avoidance of executing open circuit voltage avoidance processing for gradually decreasing the output current of the fuel cell by stopping the supply of oxidizing gas Processing execution means, wherein the leakage determination means determines the presence or absence of fuel gas leakage when the open circuit voltage avoidance processing is being executed.

  According to the present invention, during the intermittent operation of the fuel cell, when the open circuit voltage avoidance process is executed in which the supply of the oxidizing gas is stopped and the output current of the fuel cell is gradually reduced, the fuel gas leaks Therefore, it is possible to prevent the output voltage of the fuel cell from reaching the open circuit voltage. Therefore, deterioration of the fuel cell can be suppressed even when the fuel gas leak determination is executed during intermittent operation of the fuel cell. Further, the fuel gas leakage determination can be performed in parallel with the execution of the open circuit voltage avoidance process.

  In the fuel cell system, the gas leak determination unit determines whether or not there is a fuel gas leak after correcting a predetermined leak determination threshold for determining whether or not there is a fuel gas leak according to the output electric energy of the fuel cell. can do.

  By doing in this way, even when the fuel gas leak determination is performed in parallel with the execution of the open circuit voltage avoidance process, the fuel gas leak determination can be accurately performed.

  In the fuel cell system, the gas leak determination means can determine that there is a fuel gas leak when the pressure change in the fuel gas supply mechanism that supplies the fuel gas is larger than a leak determination threshold value.

  By doing in this way, the precision of fuel gas leak determination can be adjusted by changing the leak determination threshold value.

  In the fuel cell system, when the gas leak determination unit determines that there is a fuel gas leak, the supply of the oxidizing gas is stopped, the fuel gas is supplied to the fuel cell, and the output current of the fuel cell flows. It is possible to determine again whether or not there is a fuel gas leak after changing to a state where there is no fuel.

  By doing so, for example, even if it is erroneously determined that there is a fuel gas leak due to a failure of the current sensor or the like, the fuel gas leak determination can be performed again in a state where the output current does not flow. The accuracy of fuel gas leak determination can be further improved.

  According to the present invention, deterioration of the fuel cell can be suppressed even when the fuel gas leak determination is executed during intermittent operation of the fuel cell.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of a fuel cell system according to the invention will be described with reference to the accompanying drawings. This embodiment demonstrates the case where the fuel cell system which concerns on this invention is used as a vehicle-mounted power generation system of a fuel cell vehicle (FCHV; Fuel Cell Hybrid Vehicle).
[First embodiment]

  With reference to FIG. 1, the structure of the fuel cell system in 1st Embodiment is demonstrated. FIG. 1 is a configuration diagram schematically showing the fuel cell system according to the first embodiment.

  As shown in FIG. 1, a fuel cell system 1 includes a fuel cell 2 that generates electric power by an electrochemical reaction between an oxidizing gas that is a reactive gas and the fuel gas, and an oxidizing gas that supplies air as the oxidizing gas to the fuel cell 2. It has a piping system 3, a hydrogen gas piping system 4 that supplies hydrogen as fuel gas to the fuel cell 2, and a control unit 5 that performs overall control of the entire system. The fuel cell 2 and the hydrogen gas piping system 4 constitute a hydrogen gas supply mechanism (fuel gas supply mechanism).

  The fuel cell 2 has a stack structure in which a plurality of single cells that generate power upon receiving a reaction gas are stacked. A part of the DC power generated by the fuel cell 2 is stepped down by the DC / DC converter 91 and charged to the secondary battery 92 which is a battery. The traction inverter 93 converts DC power supplied from both or one of the fuel cell 2 and the secondary battery 92 into AC power, and supplies AC power to the traction motor 94. The fuel cell 2 is provided with a voltage sensor V that detects the output voltage of the fuel cell 2 and a current sensor A that detects the output current of the fuel cell 2.

  The oxidizing gas piping system 3 compresses air taken in through the filter 30 and sends out compressed air as oxidizing gas, and an air supply flow path 32 for supplying the oxidizing gas to the fuel cell 2. And an air discharge passage 33 for discharging the oxidizing off-gas discharged from the fuel cell 2. The air supply flow path 32 and the air discharge flow path 33 are provided with a humidifier 34 that humidifies the oxidizing gas pumped from the compressor 31 using the oxidizing off gas discharged from the fuel cell 2. The oxidizing off gas that has undergone moisture exchange or the like in the humidifier 34 is finally exhausted into the atmosphere outside the system as exhaust gas.

  The hydrogen gas piping system 4 includes a hydrogen tank 40 as a fuel supply source that stores high-pressure (for example, 70 MPa) hydrogen gas, and a fuel supply passage for supplying the hydrogen gas from the hydrogen tank 40 to the fuel cell 2. A hydrogen supply channel 41 and a circulation channel 42 for returning the hydrogen off-gas discharged from the fuel cell 2 to the hydrogen supply channel 41 are provided. The hydrogen gas piping system 4 is an embodiment of the fuel supply system in the present invention. Instead of the hydrogen tank 40 in the present embodiment, for example, a reformer that reforms a hydrocarbon-based fuel into a hydrogen-rich fuel gas using water vapor, and a fuel gas reformed in the reformer with a high pressure A high-pressure gas tank that accumulates pressure in a state can be employed as a fuel supply source. A tank having a hydrogen storage alloy can also be employed as a fuel supply source.

  The hydrogen supply channel 41 includes a main stop valve 43 that shuts off or allows the supply of hydrogen gas from the hydrogen tank 40, a regulator 44 that adjusts the hydrogen gas pressure to a preset secondary pressure, and a hydrogen supply channel. A first shut-off valve 45 that shuts off or allows the supply of hydrogen gas from the fuel cell 2 to the fuel cell 2, and a second shut-off valve 46 that shuts off or allows the hydrogen off-gas flow from the fuel cell 2 to the circulation flow path 42. Is provided. A pressure sensor P that detects the pressure of hydrogen gas in the hydrogen gas supply mechanism is provided downstream of the first shutoff valve 45.

  The circulation channel 42 is provided with a hydrogen pump 47 that pressurizes the hydrogen off-gas in the circulation channel 42 and sends it to the hydrogen supply channel 41 side. Further, a discharge flow path 50 is connected to the circulation flow path 42 via a gas-liquid separator 48 and an exhaust drain valve 49. The gas-liquid separator 48 recovers moisture from the hydrogen off gas. The exhaust / drain valve 49 discharges (purges) the water collected by the gas-liquid separator 48 and the hydrogen off-gas containing impurities in the circulation flow path 42 in accordance with a command from the control unit 5. The hydrogen off-gas discharged from the exhaust / drain valve 49 is diluted by the diluter 51 and merges with the oxidizing off-gas in the air discharge passage 33.

  The control unit 5 detects an operation amount of an acceleration operation member (accelerator or the like) provided in the fuel cell vehicle, and controls information such as an acceleration request value (for example, a required power generation amount from a power consuming device such as the traction motor 94). In response, the operation of various devices in the system is controlled. In addition to the traction motor 94, the power consuming device includes, for example, auxiliary equipment required for operating the fuel cell 2 (for example, the motor of the compressor 31 and the hydrogen pump 47), and various types of vehicles involved in traveling of the vehicle. This includes actuators used in devices (transmissions, wheel control devices, steering devices, suspension devices, etc.), air conditioning devices (air conditioners) for passenger spaces, lighting, audio, and the like.

  When the operation mode of the fuel cell 2 shifts from the normal operation mode to the intermittent operation mode, the control unit 5 starts an open circuit voltage avoidance process to be described later, and after the open circuit voltage avoidance process ends, the fuel cell 2 A gas leak determination process is performed to determine whether or not hydrogen gas leaks in the system.

  In the intermittent operation mode, for example, the power generation of the fuel cell 2 is temporarily stopped during low load operation such as idling, low-speed traveling or regenerative braking, and a load (vehicle motor or the like) is stored from the power storage means such as the secondary battery 92. ) Is an operation mode in which power is supplied.

  The open circuit voltage avoiding process is a process of gradually decreasing the output current of the fuel cell 2 by stopping the supply of the oxidizing gas to the fuel cell 2. By performing such processing at the time of transition to the intermittent operation mode, it is possible to output while gradually decreasing the output current of the fuel cell 2, so that an increase in the output voltage can be suppressed and the output voltage can be opened. The situation of reaching the circuit voltage can be avoided.

  Whether or not the open circuit voltage avoidance process has ended is determined by whether or not the output current of the fuel cell 2 has become equal to or less than a predetermined avoidance process end threshold. That is, when the output current of the fuel cell 2 is equal to or less than the predetermined avoidance process end threshold, it is determined that the open circuit voltage avoidance process has ended, and the gas leakage determination process is executed. This avoidance process end threshold value is a threshold value used for determining whether or not the open circuit voltage avoidance process has ended. In order to further improve the accuracy of the gas leak determination, it is preferable to set the avoidance process end threshold value to 0A. However, it is not necessarily set to 0 A, and the avoidance process end threshold value can be set within a range in which the pressure drop amount that can be generated by the output current at the set threshold value is a pressure drop amount that does not affect the gas leak determination. .

  As the gas leak determination process, various gas leak determination processes employed in conventional fuel cell systems can be applied. For example, the following gas leak determination process can be applied. First, by closing the first shut-off valve 45 and the second shut-off valve 46, a pressure change in the closed space formed between the first shut-off valve 45 and the second shut-off valve 46 is detected by the pressure sensor P. The amount of gas leakage is measured using the result. When the measured gas leak amount is larger than a predetermined leak determination threshold value registered in advance, it is determined that a hydrogen gas leak has occurred in the hydrogen gas piping system 4. On the other hand, when the amount of gas leakage is equal to or less than the leakage determination threshold value, it is determined that no hydrogen gas leakage has occurred in the hydrogen gas piping system 4.

  When it is determined in the gas leak determination process that a hydrogen gas gas leak has occurred, the control unit 5 performs the gas leak redetermination process according to the following procedure. First, the supply of hydrogen gas is restarted while the supply of the oxidizing gas to the fuel cell 2 is stopped. Subsequently, the state is changed so that the output current of the fuel cell 2 does not flow. And the gas leak determination process mentioned above is performed again. As a state where the output current of the fuel cell 2 does not flow, for example, the output voltage of the fuel cell 2 is changed to an open circuit voltage (open end voltage) that becomes the maximum output voltage of the fuel cell, and the output of the fuel cell This corresponds to physically stopping the current. Thereby, for example, even when it is erroneously determined that the gas leak is caused by the failure of the current sensor A, the gas leak determination can be performed again in a state in which no current flows. Can be increased.

  With reference to FIG. 2, the timing for executing the above-described open circuit voltage avoidance processing and gas leakage determination processing will be described. The upper graph shown in FIG. 2 is a graph representing the transition of the output voltage value of the fuel cell 2, the middle graph is a graph representing the transition of the output current value of the fuel cell 2, and the lower graph is a hydrogen graph. 4 is a graph showing the transition of the pressure value of hydrogen gas supplied from a tank 40. 2 is a timing when the operation mode of the fuel cell 2 is shifted from the normal operation mode to the intermittent operation mode, and t2 is a timing when the output current of the fuel cell 2 is equal to or lower than a predetermined avoidance processing end threshold value. is there. That is, the open circuit voltage avoidance process is executed during the period indicated by reference numeral 200, and the gas leak determination process is executed during the period indicated by reference numeral 100.

  Here, the control unit 5 physically includes, for example, a CPU, a ROM and an HDD that store control programs and control data processed by the CPU, and a RAM that is mainly used as various work areas for control processing. And an input / output interface. These elements are connected to each other via a bus. Various sensors such as a pressure sensor P, a current sensor A, and a voltage sensor V are connected to the input / output interface, as well as a compressor 31, a main stop valve 43, a first shut-off valve 45, a second shut-off valve 46, a hydrogen pump. Various drivers for driving 47 and the exhaust drain valve 49 are connected.

  The CPU receives detection results from the pressure sensor P, current sensor A, and voltage sensor V via the input / output interface according to a control program stored in the ROM, and processes them using various data in the RAM. The gas leak determination process during intermittent operation of the fuel cell system 1 is controlled. Further, the CPU controls the entire fuel cell system 1 by outputting control signals to various drivers via the input / output interface.

  Next, the gas leakage determination process during intermittent operation of the fuel cell system according to the first embodiment will be described using the flowchart shown in FIG.

  First, when the operation mode of the fuel cell 2 shifts from the normal operation mode to the intermittent operation mode (step S101), the control unit 5 executes an open circuit voltage avoidance process (step S102). Thereby, supply of oxidizing gas is stopped and the output current of the fuel cell 2 gradually decreases.

  Subsequently, the control unit 5 determines whether or not the output current value of the fuel cell 2 detected by the current sensor A is equal to or less than the avoidance process end threshold (step S103). If this determination is NO (step S103; NO), the determination in step S103 is repeated.

  On the other hand, when it is determined in step S103 that the output current value of the fuel cell 2 is equal to or smaller than the avoidance process end threshold value (step S103; YES), the control unit 5 executes a gas leak determination process (step S104). Then, it is determined whether or not a gas leak has occurred (step S105). If this determination is NO (step S105; NO), the intermittent operation gas leakage determination process is terminated.

  On the other hand, when it is determined in step S105 that a gas leak has occurred (step S105; YES), the control unit 5 restarts the supply of hydrogen gas while stopping the supply of the oxidizing gas (step S106). An open circuit voltage is set as a command voltage to the DC / DC converter 91 and sent to the DC / DC converter 91 (step S107).

  Subsequently, the control unit 5 executes a gas leak determination process (step S108) and determines whether or not a gas leak has occurred (step S109). If this determination is NO (step S109; NO), the intermittent operation gas leakage determination process is terminated.

  On the other hand, when it is determined in step S109 that a gas leak has occurred (step S109; YES), the control unit 5 outputs a gas leak alarm (step S110).

  As described above, according to the fuel cell system 1 in the first embodiment, during the intermittent operation of the fuel cell 2, the supply of the oxidizing gas is stopped and the output current of the fuel cell 2 is gradually decreased. Since the presence or absence of gas leakage can be determined after the circuit voltage avoidance process is completed, the output voltage of the fuel cell 2 can be prevented from continuing to reach the open circuit voltage, and the output current Gas leakage determination can be performed without considering the amount of hydrogen gas pressure drop due to the flow of gas. Thereby, even if it is a case where gas leak determination is performed at the time of the intermittent operation of the fuel cell 2, degradation of the fuel cell 2 can be suppressed, and the accuracy of the gas leak determination can be further improved.

In addition, since the gas leak re-determination process can be performed, for example, even if it is erroneously determined that there is a gas leak due to a failure of the current sensor or the like, the gas leak determination is performed again without the output current flowing. Therefore, the accuracy of the gas leak determination can be further improved.
[Second Embodiment]

  A second embodiment of the present invention will be described. The second embodiment is different from the first embodiment in that, in the first embodiment, the gas leakage determination process is performed after the open circuit voltage avoidance process is completed, whereas in the second embodiment, the open circuit is opened. The difference is that the gas leakage determination process is performed when the voltage avoidance process is executed. This will be specifically described with reference to FIG. In the first embodiment, the open circuit voltage avoidance process is executed in the period indicated by reference numeral 200 and the gas leak determination process is executed in the period indicated by reference numeral 100, whereas in the second embodiment, the reference numeral 200 indicates Are different in that both the open circuit voltage avoidance process and the gas leakage determination process are executed during the period indicated by.

  The configuration of the fuel cell system according to the second embodiment is the same as the configuration of the fuel cell system according to the first embodiment shown in FIG. In the following, differences from the first embodiment will be mainly described.

  When the operation mode of the fuel cell 2 shifts from the normal operation mode to the intermittent operation mode, the control unit 5 starts the open circuit voltage avoidance process and executes the gas leak determination process.

  The control unit 5 corrects the leak determination threshold for determining the presence or absence of hydrogen gas leak according to the output current of the fuel cell 2 and then determines whether or not hydrogen gas leaks. Specifically, the amount of hydrogen gas consumption is calculated using the output current, and the amount of hydrogen gas pressure drop due to the flow of the output current is calculated using this consumption amount. Then, the leak determination threshold value is corrected using the pressure drop amount. Specifically, the leak determination threshold value is corrected by adding a pressure value corresponding to the pressure drop amount by the calculated output current to a predetermined leak determination threshold value registered in advance.

  The control unit 5 determines that hydrogen gas leakage has occurred when the amount of pressure drop in the hydrogen gas supply mechanism that supplies hydrogen gas is greater than the corrected leak determination threshold value.

  Next, the gas leakage determination process during intermittent operation of the fuel cell system according to the second embodiment will be described using the flowchart shown in FIG. Note that the processes in steps S207 to S211 shown in FIG. 4 are the same processes as the processes in steps S106 to S110 described in the first embodiment (see FIG. 3), and are therefore unique to the second embodiment. Processing in steps S201 to S206, which is processing, will be described below.

  First, when the operation mode of the fuel cell 2 shifts from the normal operation mode to the intermittent operation mode (step S201), the control unit 5 executes an open circuit voltage avoidance process (step S202). Thereby, supply of oxidizing gas is stopped and the output current of the fuel cell 2 gradually decreases.

  Subsequently, the control unit 5 calculates the consumption amount of hydrogen gas by using the output current value of the fuel cell 2 detected by the current sensor A, and causes the output current value by using the consumption amount of hydrogen gas. The pressure drop amount of the hydrogen gas to be calculated is calculated (step S203). The control unit 5 corrects the leak determination threshold using the pressure drop amount (step S204).

  Subsequently, the control unit 5 executes a gas leak determination process (step S205) and determines whether or not a gas leak has occurred (step S206). If this determination is NO (step S206; NO), the intermittent operation gas leakage determination process is terminated.

  On the other hand, if it is determined in step S206 that a gas leak has occurred (step S206; YES), a gas leak re-determination process is performed in the same manner as in the processes in steps S106 to S110 described above (steps S207 to S211). ).

  As described above, according to the fuel cell system 1 in the second embodiment, during the intermittent operation of the fuel cell 2, the supply of the oxidizing gas is stopped and the output current of the fuel cell 2 is gradually decreased. Since the presence or absence of gas leakage can be determined when the circuit voltage avoidance process is executed, it is possible to prevent the output voltage of the fuel cell 2 from continuously reaching the open circuit voltage. The gas leak determination can be started immediately after shifting to intermittent operation. Thereby, even if it is a case where gas leak determination is performed at the time of the intermittent operation of the fuel cell 2, deterioration of the fuel cell 2 can be suppressed, and gas leak determination can be started earlier.

  In the second embodiment described above, when the leak determination threshold is corrected, the pressure drop amount is calculated based on the output current. However, the pressure drop amount may be calculated based on the output voltage. That is, the pressure drop amount can be calculated based on the output power amount.

  Further, in each of the above-described embodiments, the case where the fuel cell system according to the present invention is mounted on a fuel cell vehicle has been described. However, various mobile bodies (robots, ships, aircrafts, etc.) other than the fuel cell vehicle are also described. The fuel cell system according to the present invention can be applied. Moreover, the fuel cell system according to the present invention can also be applied to a stationary power generation system used as a power generation facility for buildings (houses, buildings, etc.).

It is a lineblock diagram showing typically the fuel cell system in each embodiment. It is a graph for demonstrating the timing which performs the open circuit voltage avoidance process and gas leak determination process in each embodiment. It is a flowchart for demonstrating the gas leak determination process at the time of the intermittent operation of the fuel cell in 1st Embodiment. It is a flowchart for demonstrating the gas leak determination process at the time of the intermittent operation of the fuel cell in 2nd Embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Fuel cell system, 2 ... Fuel cell, 3 ... Oxidation gas piping system, 4 ... Hydrogen gas piping system, 5 ... Control part, 30 ... Filter, 31 ... Compressor, 32 ... Air supply flow path, 33 ... Air exhaust flow 34, humidifier, 40 ... hydrogen tank, 41 ... hydrogen supply flow path, 42 ... circulation flow path, 43 ... main stop valve, 44 ... regulator, 45 ... first shut-off valve, 46 ... second shut-off valve, 47 DESCRIPTION OF SYMBOLS ... Hydrogen pump, 48 ... Gas-liquid separator, 49 ... Exhaust drain valve, 50 ... Discharge flow path, 51 ... Diluter, 91 ... DC / DC converter, 92 ... Secondary battery, 93 ... Traction inverter, 94 ... Traction motor , V: voltage sensor, A: current sensor, P: pressure sensor.

Claims (6)

A fuel cell system having a fuel cell that receives supply of a fuel gas and an oxidizing gas and generates electric power by an electrochemical reaction of the fuel gas and the oxidizing gas,
Leak determination means for determining the presence or absence of fuel gas leakage in the fuel cell system during intermittent operation of the fuel cell;
An avoidance process executing means for executing an open circuit voltage avoidance process for stopping the supply of the oxidizing gas and gradually decreasing the output current of the fuel cell;
The fuel cell system according to claim 1, wherein the leak determination means determines whether or not there is a fuel gas leak after the open circuit voltage avoidance process is completed.   The said avoidance process execution means determines with the said open circuit voltage avoidance process having been complete | finished when the output current of the said fuel cell becomes below a predetermined avoidance process completion threshold value. Fuel cell system. A fuel cell system having a fuel cell that receives supply of a fuel gas and an oxidizing gas and generates electric power by an electrochemical reaction of the fuel gas and the oxidizing gas,
Leak determination means for determining the presence or absence of fuel gas leakage in the fuel cell system during intermittent operation of the fuel cell;
An avoidance process executing means for executing an open circuit voltage avoidance process for stopping the supply of the oxidizing gas and gradually decreasing the output current of the fuel cell;
The fuel cell system characterized in that the leakage determination means determines whether or not there is a fuel gas leakage when the open circuit voltage avoidance process is being executed.   The gas leakage determination means corrects a predetermined leakage determination threshold for determining the presence or absence of the fuel gas leakage according to the output power amount of the fuel cell, and then determines the presence or absence of the fuel gas leakage. The fuel cell system according to claim 3, wherein   The said gas leak determination means determines with the said fuel gas leak having existed when the pressure change in the fuel gas supply mechanism which supplies the said fuel gas is larger than the said leak determination threshold value. The fuel cell system described.   When the gas leakage determination means determines that the fuel gas leakage is present, the supply of the oxidizing gas is stopped, the fuel gas is supplied to the fuel cell, and the output current of the fuel cell does not flow. The fuel cell system according to any one of claims 1 to 5, wherein the presence or absence of leakage of the fuel gas is determined again after changing to a state.

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