JP2010153247A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system which can suppress excessive wet or lack of wet in a fuel cell by a simple structure. <P>SOLUTION: A dilution box 8 which dilutes a fuel gas exhausted from a circulation passage 21 with an oxidant gas is placed, and a purge valve 12 is placed between the circulation passage 21 and the dilution box 8. A concentration sensor 24 to detect a concentration of the fuel gas is placed in the downstream of the dilution black box 8. When the detected concentration is lower than a lower-limit threshold concentration relating to the excessive wet in the fuel cell 1 after opening the purge valve 12, an amount of fuel gas exhausted from the purge valve 12 is increased. In addition, when the detected concentration is higher than the upper-limit threshold concentration relating to lack of the wet in the fuel cell 1 after opening the purge valve 12, an amount of fuel gas exhausted from the purge valve 12 is decreased. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a fuel cell system that generates electricity by an electrochemical reaction between a fuel gas such as hydrogen and an oxidant gas such as oxygen, and more particularly to a fuel cell system having a function of diluting discharged fuel gas. .

Some fuel cell systems include a fuel gas containing hydrogen supplied to the anode electrode of the fuel cell and an oxidant gas such as air supplied to the cathode electrode. In this fuel cell system, hydrogen in the fuel gas is ionized and moves to the cathode electrode through the solid polymer electrolyte membrane, and electrons generated during this time are taken out to an external circuit.
The exhaust passage connected to the anode electrode is provided with a purge valve for replacing the gas around the anode electrode with fresh gas, and when the purge valve is opened at a predetermined timing, the anode off-gas that has consumed hydrogen is removed. It is discharged outside. Since the fuel gas (hydrogen) that could not be completely consumed by the fuel cell remains in the anode off gas, the anode gas is usually diluted with an oxidant gas such as air in a dilution box and then discharged outside the system.

  By the way, in such a fuel cell system, it is important to sufficiently dilute the fuel gas in the dilution box, but the fuel gas concentration in the anode off-gas passage on the fuel cell side changes depending on the operating environment of the fuel cell. For example, when the purge valve is opened periodically for a certain period of time, the concentration of the fuel gas introduced into the dilution box may change, and it may be difficult to perform stable dilution with the dilution box.

  For this reason, as a fuel cell system to cope with this, a system has been devised that obtains the concentration of the fuel gas introduced into the dilution box and controls the opening interval of the purge valve in accordance with the concentration (for example, (See Patent Documents 1 and 2).

  In the fuel cell system described in Patent Document 1, the amount of change in gas pressure before and after opening the purge valve is obtained, and the concentration of fuel gas introduced into the dilution box is determined based on the amount of change in gas pressure. It is calculated by calculation.

In the fuel cell system described in Patent Document 2, a concentration sensor is installed on the downstream side of the dilution box, and the concentration of the fuel gas in the dilution box is directly detected by the concentration sensor.
Japanese Patent Laid-Open No. 2006-164562 Japanese Patent No. 3880898

However, this conventional fuel cell system limits the amount of fuel gas discharged from the purge valve when the concentration of the fuel gas introduced into the dilution box is higher than a specified value. In the case where excessive wetting (flooding) occurred in the inside of the glass, this could not be suppressed. When excessive wetting occurs inside the fuel cell, moisture stays around the anode electrode, the reaction of the fuel gas is hindered, and the power generation of the fuel cell tends to become unstable.
On the other hand, if wetting deficiency occurs inside the fuel cell, hydrogen ionization on the solid polymer electrolyte membrane is hindered, and the power generation efficiency of the fuel cell decreases. Therefore, improvement of this point is now desired.

  Accordingly, the present invention is intended to provide a fuel cell system capable of suppressing excessive or insufficient wetting inside the fuel cell with a simple configuration.

The invention according to claim 1, which solves the above problem, includes a fuel cell (for example, a fuel cell 1 in an embodiment described later) that generates power by reacting a fuel gas and an oxidant gas, and an anode electrode of the fuel cell. For example, a diluting means for diluting the fuel gas discharged from the anode electrode 3 (for example, an anode electrode 3 in an embodiment described later) with an oxidant gas (for example, a dilution box 8 in the embodiment described later), and fuel from the anode electrode to the diluting means A discharge valve (for example, a purge valve 12 in an embodiment described later) for adjusting gas discharge, and a concentration detection means (for example, an embodiment described later) provided in the dilution means or downstream of the dilution means for detecting the concentration of fuel gas. A fuel cell system comprising a concentration sensor 24) and a control means for controlling the exhaust valve (for example, a control device 13 in an embodiment described later). The control means, after opening the discharge valve, when the detected concentration of the concentration detecting means is lower than a threshold concentration correlated with excessive wetness in the fuel cell, It is characterized by correcting the increase in gas emission.
When the inside of the fuel cell becomes excessively wet, the partial pressure of water vapor mixed in the fuel gas increases, and as a result, the concentration of the fuel gas discharged to the dilution means through the discharge valve decreases. Therefore, when the concentration of the fuel gas on the dilution means side is lower than the threshold concentration, it can be determined that the inside of the fuel cell is excessively wet. Thus, when it is determined that there is excessive wetness, it is possible to promote the discharge of moisture in the fuel cell by increasing the discharge amount of the fuel gas.

According to a second aspect of the present invention, in the fuel cell system according to the first aspect, the control means corrects an increase in the amount of discharge of the fuel gas, and then determines the elapsed time, the frequency of opening the exhaust valve, the fuel When at least one of the accumulated gas discharge amounts exceeds a specified value, the discharge amount of the fuel gas is restored.
Elapsed time, valve opening frequency, and accumulated fuel gas emissions are all parameters related to fuel gas emissions, so it is important to accurately grasp the fuel gas emissions by paying attention to these values. be able to. Therefore, when the excess wetness in the fuel cell is sufficiently eliminated, the control of the fuel gas discharge amount is restored.

According to a third aspect of the present invention, in the fuel cell system according to the first or second aspect, the increase correction is performed according to a difference between a detected concentration of fuel gas and the threshold concentration.
As a result, the discharge amount of the fuel gas is increased and corrected in accordance with the difference between the detected concentration of the fuel gas and the threshold concentration, and the increase correction amount increases as the difference increases.

According to a fourth aspect of the present invention, there is provided a fuel cell for generating power by reacting a fuel gas and an oxidant gas, a diluting means for diluting the fuel gas discharged from the anode electrode of the fuel cell with the oxidant gas, A discharge valve for adjusting the discharge of the fuel gas from the anode electrode to the dilution means, a concentration detection means for detecting the concentration of the fuel gas provided in the dilution means or downstream of the dilution means, and a control means for controlling the discharge valve In the fuel cell system, the control means, after opening the discharge valve, the detected concentration of the fuel gas by the concentration detection means is more than a threshold concentration that correlates with insufficient wetting in the fuel cell. Is higher, the emission amount of the fuel gas is corrected to decrease in accordance with the detected concentration.
When the inside of the fuel cell becomes insufficiently wet, the electrolyte membrane inside the cell is dried, so that the fuel gas is hardly ionized. For this reason, the consumption amount of the fuel gas in the fuel cell decreases, and as a result, the concentration of the fuel gas discharged from the discharge valve increases. Therefore, when the concentration of the fuel gas on the dilution means side is higher than the threshold concentration, it can be determined that the inside of the fuel cell is insufficiently wet. Thus, when it is determined that the moisture is insufficient, the discharge of moisture in the fuel cell can be suppressed by reducing the discharge amount of the fuel gas.

According to a fifth aspect of the present invention, in the fuel cell system according to the fourth aspect of the present invention, the control means corrects a decrease in the amount of discharged fuel gas, and then the elapsed time, the opening frequency of the discharge valve, the fuel When at least one of the accumulated gas discharge amounts exceeds a specified value, the discharge amount of the fuel gas is restored.
As a result, when the shortage of wetness on the anode side is sufficiently resolved, the control of the fuel gas discharge amount is restored.

According to a sixth aspect of the present invention, in the fuel cell system according to the fourth or fifth aspect, the decrease correction is performed according to a difference between a detected concentration of fuel gas and the threshold concentration.
As a result, the amount of fuel gas discharged is corrected to decrease in accordance with the difference between the detected concentration of fuel gas and the threshold concentration, and the amount of decrease correction increases as the difference increases.

According to a seventh aspect of the present invention, when the control means has a fluctuation width of the generated current of the fuel cell or a fluctuation width of the oxidant gas introduced into the fuel cell for a predetermined time, the control means is smaller than the specified width, The control according to claim 1 or 4 is started.
As a result, when the generated current or the oxidant gas fluctuates greatly during the operation of the fuel cell or the like, it is no longer necessary to determine whether or not the fuel gas emission amount needs to be corrected or to perform actual correction.

The invention according to claim 8 is characterized in that the control means starts the control according to claim 1 or 4 when the generated current of the fuel cell is not more than a predetermined value.
As a result, in a situation where the generated current becomes large due to the operation of the fuel cell, it is no longer necessary to determine whether or not to correct the fuel gas emission amount or to perform actual correction.

  According to the first aspect of the present invention, after the discharge valve is opened, the concentration of the fuel gas on the dilution means side is detected, and when the detected concentration is lower than the threshold concentration and the fuel cell is excessively wet. Since the amount of discharge of the fuel gas is increased and corrected in accordance with the detected concentration, excessive wetting inside the fuel cell can be reliably eliminated with a simple configuration. Therefore, stable power generation of the fuel cell can be obtained.

  According to the second aspect of the present invention, the fuel gas is discharged by utilizing any one of the elapsed time, the valve opening frequency, and the fuel gas discharge integrated amount that are parameters related to the fuel gas discharge amount. In order to determine the timing for returning the discharge amount, the fuel gas discharge amount can be returned to the original timing at a proper timing when the water in the fuel cell is sufficiently discharged, and the proper wet state can be maintained.

  According to the third aspect of the present invention, since the amount of discharge of the fuel gas is increased and corrected in accordance with the difference between the detected concentration of the fuel gas and the threshold concentration, an unnecessary rapid increase in the concentration of the fuel gas in the dilution means is caused. In addition, excessive wetting inside the fuel cell can be quickly eliminated.

  According to the fourth aspect of the present invention, after the discharge valve is opened, the concentration of the fuel gas on the dilution means side is detected, and when the detected concentration is higher than the threshold concentration and the fuel cell is insufficiently wet. In addition, since the discharge amount of the fuel gas is corrected to decrease in accordance with the detected concentration, it is possible to reliably eliminate deficiency in the inside of the fuel cell with a simple configuration. Therefore, the power generation efficiency of the fuel cell can be improved.

  According to the fifth aspect of the present invention, the fuel gas is discharged by utilizing any one of the elapsed time, the valve opening frequency, and the fuel gas discharge integrated amount that are parameters related to the fuel gas discharge amount. Since the timing for returning the discharge amount to the original state is determined, the discharge amount of the fuel gas can be returned to the original state at an appropriate timing when the inside of the fuel cell is sufficiently humidified, and the proper wet state can be maintained.

  According to the sixth aspect of the present invention, since the discharge amount of the fuel gas is corrected to decrease according to the difference between the detected concentration of the fuel gas and the threshold concentration, the inside of the fuel cell is not caused without insufficient purge on the anode electrode side. Insufficient wetting can be quickly resolved.

  According to the seventh and eighth aspects of the present invention, in the situation where the fuel gas and the oxidant gas are likely to fluctuate during the operation of the fuel cell or the like, it is determined whether or not the fuel gas emission amount needs to be corrected and the actual correction is performed. Therefore, appropriate control according to excess or deficiency of the wetness in the fuel cell can be performed.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
In addition, the fuel cell system of embodiment described below is an aspect mounted in a fuel cell vehicle.
FIG. 1 is a schematic configuration diagram of a fuel cell system. The fuel cell 1 is formed by stacking a plurality of battery cells (hereinafter referred to as “cells”), and each cell has an anode electrode 3 on both sides of a solid polymer electrolyte membrane 2 (hereinafter referred to as “electrolyte membrane 2”). And a cathode electrode 4, and a gas passage (not shown) for supplying a reaction gas to the outside of the anode electrode 3 and the cathode electrode 4. In FIG. 1, an image of one cell is schematically shown so that the internal structure of the cell can be grasped.

  In the fuel cell 1, a fuel gas containing hydrogen gas as a main component is supplied to the anode electrode 3, and air containing oxygen (oxidant gas) is supplied to the cathode electrode 4. In the anode electrode 3 of the fuel cell 1, hydrogen ions are generated by a catalytic reaction, and the hydrogen ions pass through the electrolyte membrane 2 and move to the cathode electrode 4. At the cathode 4, hydrogen ions generate an electric power by causing an electrochemical reaction with oxygen.

  Air is supplied to the cathode electrode 4 of the fuel cell 1 through an air supply path 6 from an air compressor 5 which is an oxidant supply means. The air supplied to the cathode 4 is supplied from the fuel cell 1 through the air discharge path 7 to a dilution box 8 (dilution means) described later after oxygen in the air is supplied as an oxidant.

  On the other hand, the fuel gas is supplied to the anode electrode 3 of the fuel cell 1 from the fuel tank 9 as a fuel gas supply means through the fuel gas supply path 10. The fuel gas supply path 10 is provided with an ejector 20 that joins the anode off gas of the fuel cell 1 to the fuel gas supply path 10 and returns it to the anode electrode 3. A circulation passage 21 connected to the discharge side of the anode electrode is connected to the ejector 20. The circulation passage 21 is provided with a purge passage 22 for discharging unnecessary gas in the circulation passage 21 to the outside. Is connected to the dilution box 8. The purge passage 22 is provided with a purge valve 12 (discharge valve) comprising an electromagnetic on-off valve. By opening / closing the purge valve 12, an anode off-gas (including fuel gas) from the circulation passage 21 to the dilution box 8 is provided. ) Discharge is adjusted. The purge valve 12 is controlled by the control device 13 (control means) together with the air compressor 5 and other valves.

The dilution box 8 is provided with a retention chamber in which the anode off gas introduced from the purge passage 22 is retained, and an air discharge path 7 is connected to the retention chamber. The anode off gas introduced from the purge passage 22 into the residence chamber is diluted by air (oxidant gas) introduced from the air discharge passage 7 and then discharged from the discharge passage 23 to the outside of the system. The discharge passage 23 is provided with a concentration sensor 24 (concentration detection means) for detecting the fuel gas concentration (hydrogen concentration) in the exhaust gas. A detection signal detected by the concentration sensor 24 is input to the control device 13.
In FIG. 1, reference numeral 14 denotes a current sensor that detects a current generated by the fuel cell 1.

By the way, the control device 13 controls the purge valve 12 so that the purge valve 12 is opened at regular intervals or at a preset timing during the operation of the fuel cell 1 (hereinafter, the purge valve 12 is opened by this control). The valve is called “normal purge”).
Further, the control means 13 monitors the fuel gas concentration in the gas discharged from the dilution box 8 using the concentration sensor 24 while performing this normal purge. Then, the control device 13 increases the discharge amount of the fuel gas when the fuel gas concentration detected by the concentration sensor 24 after the normal purge is lower than the lower limit threshold concentration C1 that correlates with excessive wetness in the fuel cell 1. Thus, the opening time of the purge valve 12 is corrected for extension. Here, the extension correction time is set according to the detected concentration of the fuel gas.
The lower limit threshold concentration C1 is a concentration at which the inside of the fuel cell 1 becomes excessively wet when the fuel gas concentration in the dilution box 8 falls below the threshold concentration. This lower threshold concentration is obtained by experiments or the like.

Further, the control device 13 opens the purge valve 12 so as to reduce the discharge amount of the fuel gas when the concentration detected by the concentration sensor 24 is higher than the upper limit threshold concentration C2 correlated with insufficient wetting in the fuel cell 1. Correct the valve time. Here, the shortening correction time is a time corresponding to the detected concentration of the fuel gas.
The upper limit threshold concentration C2 is a concentration at which the inside of the fuel cell 1 becomes insufficiently wet when the fuel gas concentration in the dilution box 8 rises above the threshold concentration. This upper threshold density C2 is obtained by experiments or the like, similarly to the lower threshold density C1.

Next, specific purge control in this fuel cell system will be described along the flowchart of FIG. 2 with reference to the timing chart of FIG. In this fuel cell system, normal purge is executed separately from the processing of this flowchart. Further, the timing chart of FIG. 3 shows control when the inside of the fuel cell is excessively wet.
In step S101, the fluctuation range of the generated current of the fuel cell 1 is checked on the basis of the detection value of the current sensor 14, and the fluctuation range of the generated current during a predetermined time T1 (see FIG. 3) is set in advance. It is determined whether or not it falls below W1. Here, if YES, that is, if the load fluctuation of the fuel cell 1 is small and stable, the process proceeds to step S102. If NO, the process is terminated and intermittent normal purge is continued.

  In step S102, it is determined whether or not the next normal purge is completed and then a predetermined time T2 (see FIG. 3) has elapsed. If YES, the process proceeds to step S103. If NO, Proceed to step S104. In step S104, the maximum value Cmax of the detected fuel gas concentration is updated, and in step S105, the minimum value Cmin of the detected fuel gas concentration is updated, and then the process returns to step S102. Therefore, the maximum value Cmax and the minimum value Cmin of the fuel gas concentration are continuously updated until the predetermined time T2 elapses.

When the process proceeds to step S103, it is determined whether or not the maximum value Cmax of the fuel gas concentration is smaller than the lower threshold concentration C1, and if YES here, the process proceeds to step S106, and if NO, Proceed to step S107.
In step S107, it is determined whether or not the minimum value Cmin of the fuel gas concentration is larger than the upper limit threshold concentration C2. If YES here, the process proceeds to step S108. If NO, the process ends. And continue normal purge.

When the process proceeds to step S106 (when it is determined that the fuel cell 1 is excessively wet), the purge correction amount (purge valve 12) is based on the absolute value of the difference between the maximum value Cmax of the fuel gas concentration and the lower limit threshold concentration C1. The valve opening extension time) is calculated.
In the subsequent step S109, it is determined whether or not a predetermined time T3 (see FIG. 3) has elapsed after the completion of the normal purge. If NO, the process proceeds to step S110 to correct the purge correction amount calculated and purge. Execute. The process in step S110 is continued until a predetermined time T3 has elapsed. When the predetermined time T3 has elapsed, the process is terminated and the normal purge is resumed.
Therefore, when it is determined that the inside of the fuel cell 1 is excessively wet, the opening time of the purge valve 12 is extended and corrected in accordance with the detected concentration of the fuel gas, and the purge process (hereinafter, referred to as the opening time) is corrected. (Referred to as “correction purge process”) is executed for a predetermined time T3. During this time, the amount of fuel gas discharged from the circulation passage 21 is increased by the correction purge process, the moisture in the fuel cell 1 and the circulation passage 21 is quickly discharged to the outside, and excessive wetting in the fuel cell 1 is eliminated. As a result, the fuel cell 1 can stably generate power.

On the other hand, when the process proceeds to step S108 (when the inside of the fuel cell 1 is determined to be insufficiently wet), the purge correction amount (purge) is based on the absolute value of the difference between the minimum value Cmin of the fuel gas concentration and the upper limit threshold concentration C2. The valve opening shortening time of the valve 12) is calculated.
In step S111, it is determined whether or not a predetermined time T3 has elapsed after completion of the normal purge. If NO, the process proceeds to step S112, and the purge is corrected with the calculated purge correction amount, and the purge is executed. The process in step S112 is continued until a predetermined time T3 has elapsed. When the predetermined time T3 has elapsed, the process is terminated and the normal purge is resumed.
Therefore, when it is determined that the inside of the fuel cell 1 is insufficiently wet, the opening time of the purge valve 12 is corrected to be shortened according to the detected concentration of the fuel gas, and the purge processing (hereinafter, referred to as the opening time) is corrected. (Referred to as “correction purge process”) is executed for a predetermined time T3. During this time, the discharge amount of the anode off-gas from the circulation passage 21 is reduced by the correction purge process, and moisture tends to stay in the fuel cell 1 and the circulation passage 21. As a result, insufficient dampness in the fuel cell 1 is resolved, and the power generation efficiency of the fuel cell 1 is improved.

Further, in this fuel cell system, after the correction purge process is started in step S110 or step S112, the normal purge is resumed when a predetermined time T3 elapses, so that the water in the fuel cell 1 is sufficiently discharged. Alternatively, the fuel cell 1 can be returned to the normal purge at an early stage at an appropriate timing when the inside of the fuel cell 1 is appropriately moistened.
In this embodiment, the elapsed time (T3) is managed to return to the normal purge after the start of the correction purge process. However, after the correction purge process is started, the frequency of opening the exhaust valve and the fuel gas The integrated amount of discharge may be managed and returned to normal purge. In any of these cases, parameters related to the fuel gas discharge amount are managed, so that the normal purge process can be restored at an appropriate timing.

  Further, in this fuel cell system, in order to correct the fuel gas discharge amount (opening time of the purge valve 12) according to the difference between the detected concentration of the fuel gas and the upper limit threshold concentration C2 and the lower limit threshold concentration C2, The wet state in the fuel cell 1 can be quickly adjusted without causing a sudden increase in exhaust fuel gas concentration or insufficient purge.

Further, in this fuel cell system, in step S101, only when the fluctuation range of the generated current of the fuel cell 1 is smaller than the specified width W1, the necessity for the correction purge process is determined and executed, and the fluctuation range of the generated current is determined. Therefore, it is possible to perform appropriate control in accordance with the actual wet state in the fuel cell 1 because the determination or execution of the necessity for the correction purge process is not performed in a situation where the exhaust fuel gas concentration is likely to fluctuate.
In this embodiment, when the fluctuation range of the generated current of the fuel cell 1 is smaller than the specified width W1, whether or not the correction purge process is necessary is determined and executed, but is introduced into the fuel cell 1. When the fluctuation range of the oxidant gas is smaller than the specified range, or when the absolute value of the generated current of the fuel cell 1 is smaller than a predetermined value, it may be determined whether or not the correction purge process is necessary. .

  In addition, this invention is not limited to said embodiment, A various design change is possible in the range which does not deviate from the summary. For example, in the above embodiment, the concentration sensor is installed on the downstream side of the dilution box, but the concentration sensor may be installed in the dilution box.

1 is a schematic configuration diagram of a fuel cell system according to an embodiment of the present invention. The flowchart which shows the flow of the purge process of one Embodiment of this invention. The timing chart for demonstrating the purge process of one Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Fuel cell 3 ... Anode electrode 8 ... Dilution box (dilution means)
12 ... Purge valve (discharge valve)
13. Control device (control means)
24 ... Concentration sensor (concentration detection means)

Claims (8)

A fuel cell that generates electricity by reacting a fuel gas and an oxidant gas; and
Dilution means for diluting the fuel gas discharged from the anode of the fuel cell with an oxidant gas;
A discharge valve for adjusting the discharge of fuel gas from the anode electrode to the dilution means;
A concentration detection means for detecting the concentration of fuel gas provided in the dilution means or downstream of the dilution means;
A fuel cell system comprising: control means for controlling the discharge valve;
The control means, after opening the discharge valve, when the detected concentration of the concentration detecting means is lower than a threshold concentration correlated with excessive wetness in the fuel cell, A fuel cell system that corrects an increase in emissions.   The control means, after correcting the increase in the fuel gas discharge amount, when at least one of the elapsed time, the valve opening frequency of the discharge valve, and the fuel gas discharge integrated amount exceeds a specified value. The fuel cell system according to claim 1, wherein the discharge amount of the fuel gas is restored.   3. The fuel cell system according to claim 1, wherein the increase correction is performed according to a difference between a detected concentration of fuel gas and the threshold concentration. A fuel cell that generates electricity by reacting a fuel gas and an oxidant gas; and
Dilution means for diluting the fuel gas discharged from the anode of the fuel cell with an oxidant gas;
A discharge valve for adjusting the discharge of fuel gas from the anode electrode to the dilution means;
A concentration detection means for detecting the concentration of fuel gas provided in the dilution means or downstream of the dilution means;
A fuel cell system comprising: control means for controlling the discharge valve;
When the detected concentration of the concentration detecting means is higher than a threshold concentration that correlates with insufficient wetting in the fuel cell after opening the discharge valve, the control means determines the amount of fuel gas according to the detected concentration. A fuel cell system, wherein emission is reduced and corrected.   The control means, after correcting the decrease in the fuel gas discharge amount, when at least one of the elapsed time, the valve opening frequency, and the fuel gas discharge integrated amount exceeds a specified value The fuel cell system according to claim 4, wherein the discharge amount of the fuel gas is restored.   6. The fuel cell system according to claim 4, wherein the decrease correction is performed according to a difference between a detected concentration of fuel gas and the threshold concentration.   5. The control according to claim 1, wherein the control unit is configured to control when the fluctuation range of the generated current of the fuel cell or the fluctuation range of the oxidant gas introduced into the fuel cell during a predetermined time is smaller than the specified width. A fuel cell system.   5. The fuel cell system according to claim 1, wherein the control means starts the control according to claim 1 or 4 when the generated current of the fuel cell is equal to or less than a predetermined value.

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