JP2010108756A - Fuel cell system and purge control method of fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system capable of assuring power generation performance even under a low atmospheric pressure, and a purge control method of the fuel cell system. <P>SOLUTION: The fuel cell system 10 includes: a fuel cell 11; an anode off-gas piping 35 flowing an anode off-gas discharged from the fuel cell; a purge valve 52 being openable and closable in the anode off-gas piping and discharging the anode off-gas out of the gas passage; a gas-liquid separator 40 arranged in the anode off-gas piping and capable of separating water included in the anode off-gas; a drain valve 42 being openable and closable to discharge the water stored in the gas-liquid separator out of the gas passage; and an atmospheric pressure detection means 58 detecting an atmospheric pressure, wherein a purge volume discharged from the purge valve is reduced as the atmospheric pressure lowers, and further includes a discharge volume control means raising a ratio of a drain volume discharged from the drain valve to a purge volume as the atmospheric pressure detected by the atmospheric pressure detection means lowers. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a fuel cell system and a purge control method for a fuel cell system.

  Conventionally, for example, in a fuel cell mounted on a vehicle, a membrane electrode structure is formed by sandwiching a solid polymer electrolyte membrane (hereinafter referred to as an electrolyte membrane) between an anode electrode and a cathode electrode. A pair of separators are arranged on both sides of the body to form a flat unit fuel cell (hereinafter referred to as a unit cell), and a plurality of the unit cells are stacked to form a fuel cell stack (hereinafter referred to as a fuel cell). Things are known. In such a fuel cell, hydrogen gas is supplied as an anode gas (fuel gas) between the anode electrode and the separator, and air is supplied as a cathode gas (oxidant gas) between the cathode electrode and the separator. As a result, hydrogen ions generated by the catalytic reaction at the anode electrode pass through the solid polymer electrolyte membrane and move to the cathode electrode, causing an electrochemical reaction with oxygen in the air at the cathode electrode, thereby generating power. It should be noted that water is generated inside the fuel cell with this power generation.

In recent fuel cells, the electrolyte membrane is becoming thinner, and there is a phenomenon that the generated water generated on the cathode side permeates the electrolyte membrane through the osmotic pressure and concentration difference and enters the anode side. If the generated water is stored in the pipe on the anode side, a flooding phenomenon occurs, and the power generation performance may be reduced. In particular, in a place where the atmospheric pressure is low (high altitude), the amount of air that can be used to dilute the purged anode off-gas decreases, so the amount of purged anode off-gas (purge amount) decreases. Therefore, when the purge amount is small, the amount of the generated water (water vapor / water droplets) on the anode side discharged together with the purge gas is also small, so that a large amount of water remains on the anode side, which easily causes a flooding phenomenon. .
Therefore, in order to solve such a problem, a fuel cell system that provides a pressure sensor that detects the pressure downstream of the purge valve and controls the discharge amount (purge amount) discharged from the purge valve based on the downstream pressure. Has been proposed (see, for example, Patent Document 1). Specifically, control is performed such that the lower the downstream pressure, the smaller the discharge amount and the shorter the discharge interval.
JP 2007-103172 A

  By the way, according to the fuel cell system of Patent Document 1, since only the purge amount is controlled according to the atmospheric pressure, when the purge amount is reduced, a flooding phenomenon may occur and power generation performance may be reduced. .

  Therefore, the present invention has been made in view of the above circumstances, and provides a fuel cell system and a purge control method for a fuel cell system that can ensure power generation performance even in a state where the atmospheric pressure is low. .

  In order to solve the above problems, the invention described in claim 1 is a fuel cell (for example, fuel cell 11 in the embodiment) that generates electricity by supplying an anode gas to an anode electrode and a cathode gas to a cathode electrode; An anode offgas pipe through which the anode offgas discharged from the fuel cell flows (for example, the anode offgas discharge pipe 35 in the embodiment), and an anode offgas pipe disposed in the anode offgas pipe and opened and closed to discharge the anode offgas out of the flow path. A possible purge valve (for example, the purge valve 52 in the embodiment), and a gas-liquid separator (for example, the catch tank 40 in the embodiment) that is disposed in the anode off-gas pipe and can separate moisture contained in the anode off-gas. , A drain valve that can be opened and closed to discharge the water stored in the gas-liquid separator out of the flow path (eg, For example, the drain valve 42 in the embodiment and an atmospheric pressure detecting means (for example, the atmospheric pressure sensor 58 in the embodiment) for detecting the atmospheric pressure, and the purge discharged from the purge valve as the atmospheric pressure decreases. A fuel cell system (for example, the fuel cell system 10 in the embodiment) that reduces the amount of drain discharged from the drain valve with respect to the purge amount as the atmospheric pressure detected by the atmospheric pressure detecting means decreases. A discharge amount adjusting means (for example, a purge amount command value calculating unit 47 and a drain amount command value calculating unit 48 in the embodiment) for increasing the ratio of the amounts is provided.

  The invention described in claim 2 includes drain amount threshold setting means (for example, a drain amount threshold setting unit 49 in the embodiment) for setting an upper limit threshold of the drain amount, and the drain adjusted by the discharge amount adjusting means. When the amount exceeds the drain amount threshold set by the drain amount threshold setting means, the drain amount is set to the drain amount threshold.

  The invention described in claim 3 is characterized in that the drain amount threshold is set based on a generated water generation amount and a generated water discharge amount generated in the fuel cell.

  The invention described in claim 4 is characterized in that the discharge amount adjusting means increases the ratio by increasing at least the drain amount.

  According to a fifth aspect of the present invention, there is provided a fuel cell for generating electricity by supplying an anode gas to the anode electrode and a cathode gas to the cathode electrode, an anode off-gas pipe through which the anode off-gas discharged from the fuel cell flows, and the anode A purge valve that is disposed in an off-gas pipe and is openable and closable for discharging the anode off-gas out of the flow path; a gas-liquid separator that is disposed in the anode off-gas pipe and is capable of separating moisture contained in the anode off-gas; A drain valve that can be opened and closed to discharge the water stored in the gas-liquid separator to the outside of the flow path; and an atmospheric pressure detection means that detects atmospheric pressure; and the purge valve as the atmospheric pressure decreases A purge control method for a fuel cell system for reducing the amount of purge discharged from a fuel, comprising: A purge amount correction coefficient determining step for determining a purge amount correction coefficient based on the atmospheric pressure and the outside air temperature; and a purge amount base for determining a purge amount base command value based on the current value of the fuel cell and the temperature of the anode gas A command value determining step; a purge amount command value determining step for determining a purge amount command value based on the purge amount correction coefficient and the purge amount base command value; and a drain amount correction coefficient based on the atmospheric pressure and the outside air temperature. A drain amount correction coefficient determining step; a drain amount base command value determining step for obtaining a drain amount base command value based on the current value of the fuel cell and the temperature of the anode gas; and the drain amount correction coefficient and the drain amount base command Drain amount command value determination step for obtaining a drain amount command value based on the value A drain amount threshold value calculating step for calculating a drain amount threshold value based on a generated water generation amount and a generated water discharge amount generated by the fuel cell; and whether the drain amount command value is greater than the drain amount threshold value. Drain amount determining step, and when the drain amount determining step determines that the drain amount is determined to be large, the drain amount command value is set to the drain amount threshold value, and the drain discharge is performed to discharge the moisture from the drain valve. And a step.

  According to the first aspect of the present invention, as the atmospheric pressure decreases, the amount of anode off-gas that can be purged decreases, and even if the amount of water discharged with the purge decreases, the ratio of the drain amount to the purge amount increases. Therefore, the generated water remaining on the anode side can be sufficiently discharged. Therefore, it is possible to prevent the flooding phenomenon caused by the generated water, so that the power generation performance of the fuel cell can be sufficiently ensured.

  According to the invention described in claim 2, when the upper limit threshold is set for the drainable drain amount, and when the water stored in the gas-liquid separator is discharged, the discharged water amount does not exceed the drain amount threshold. By doing so, it is possible to prevent not only moisture but also anode off gas from being discharged simultaneously. Therefore, the anode gas concentration on the anode side can be maintained.

  According to the invention described in claim 3, since the amount of water stored in the gas-liquid separator is determined based on the amount of generated water and the amount discharged, the amount of drain can be set appropriately.

  According to the fourth aspect of the present invention, even if the amount of water discharged together with the purge is reduced by reducing the purge amount, the amount of drain can be increased, so that the generated water can be sufficiently discharged. Therefore, it is possible to prevent the flooding phenomenon caused by the generated water, so that the power generation performance of the fuel cell can be sufficiently ensured.

  According to the fifth aspect of the present invention, even if the amount of anode off-gas that can be purged (purge amount command value) decreases as the atmospheric pressure decreases and the amount of water discharged along with the purge decreases, Since the ratio of the amount (drain amount command value) is increased, the generated water remaining on the anode side can be sufficiently discharged. Therefore, it is possible to prevent the flooding phenomenon caused by the generated water, so that the power generation performance of the fuel cell can be sufficiently ensured.

Next, an embodiment of the present invention will be described with reference to FIGS. In the present embodiment, a case where the fuel cell system is mounted on a vehicle will be described.
(Fuel cell system)
FIG. 1 is a schematic configuration diagram of a fuel cell system.
As shown in FIG. 1, the fuel cell 11 of the fuel cell system 10 is a solid polymer membrane fuel cell that generates electric power by an electrochemical reaction between an anode gas such as hydrogen gas and a cathode gas such as air. An anode gas supply pipe 23 is connected to the anode gas supply communication hole 13 (inlet side of the anode gas passage 21) formed in the fuel cell 11, and a hydrogen tank 30 is connected to the upstream end thereof. A cathode gas supply pipe 24 is connected to the cathode gas supply communication hole 15 (inlet side of the cathode gas flow path 22) formed in the fuel cell 11, and an air compressor 33 is connected to the upstream end thereof. Yes. An anode off-gas exhaust pipe 35 (cathode gas flow path 22) is connected to the anode off-gas discharge communication hole 14 (exit side of the anode gas flow path 21) formed in the fuel cell 11. Is connected to a cathode offgas discharge pipe 38.

  Further, the hydrogen gas supplied from the hydrogen tank 30 to the anode gas supply pipe 23 is decompressed by a regulator (not shown), then passes through the ejector 26 and is supplied to the anode gas flow path 21 of the fuel cell 11. An electromagnetically driven solenoid valve 25 is provided in the vicinity of the downstream side of the hydrogen tank 30 so that the supply of hydrogen gas from the hydrogen tank 30 can be shut off.

  The anode off gas discharge pipe 35 is connected to the ejector 26 so that the anode off gas passing through the fuel cell 11 can be reused as the anode gas of the fuel cell 11 again. Further, the anode off-gas discharge pipe 35 is branched in the middle, and a purge gas discharge pipe 37 is provided. The purge gas discharge pipe 37 is connected to the dilution box 31. Further, the purge gas discharge pipe 37 is provided with an electromagnetically driven purge valve 52.

  Furthermore, a catchon tank 40 is provided in the middle of the anode off gas discharge pipe 35. The catchon tank 40 is configured to separate a gas (anode offgas) and a liquid (product water) mixed in the anode offgas flowing through the anode offgas discharge pipe 35 and store only the produced water. ing. A generated water discharge pipe 41 is connected to the catch tank 40. The generated water discharge pipe 41 is connected to the dilution box 31 so that the generated water stored in the catch tank 40 can be discharged outside the vehicle through the dilution box 31. Further, the generated water discharge pipe 41 is provided with an electromagnetically driven drain valve 42.

  Next, air (cathode gas) is pressurized by the air compressor 33, passes through the cathode gas supply pipe 24, and is then supplied to the cathode gas flow path 22 of the fuel cell 11. After this oxygen in the air is used as an oxidizing agent for power generation, it is discharged from the fuel cell 11 to the cathode offgas discharge pipe 38 as cathode offgas. The cathode offgas discharge pipe 38 is connected to the dilution box 31 and then exhausted to the outside of the vehicle. A back pressure valve 34 is provided in the cathode off gas discharge pipe 38.

  A temperature sensor 55 is provided upstream of the anode gas supply communication hole 13 in the anode gas supply pipe 23. The temperature sensor 55 can detect the hydrogen temperature in the anode gas supply pipe 23. A detection result (sensor output) from the temperature sensor 55 is transmitted to a control unit (ECU) 45 so that a base command value for obtaining a command value for the purge amount and the drain amount can be calculated based on the detection result. (It will be described in detail later).

  A pressure sensor 56 is provided on the anode off gas discharge pipe 35 on the downstream side of the catchon tank 40. An internal pressure in the anode off-gas discharge pipe 35 can be detected by the pressure sensor 56. The detection result (sensor output) from the pressure sensor 56 is transmitted to a control unit (ECU) 45 so that the amount of generated water discharged from the purge gas discharge pipe 37 and the generated water discharge pipe 41 can be calculated based on the detection result. (It will be described in detail later).

  Further, the fuel cell system 10 is provided with an outside air temperature sensor 57 that can detect the outside air temperature and an atmospheric pressure sensor 58 that can detect the atmospheric pressure. The detection results (sensor output) from the outside air temperature sensor 57 and the atmospheric pressure sensor 58 are transmitted to the control unit (ECU) 45, and based on the detection results, correction coefficients for obtaining the command value for the purge amount and the drain amount Can be calculated (detailed later).

  Further, the control device 45 can control the electromagnetic valve 25 according to the output required for the fuel cell 11 to supply a predetermined amount of hydrogen gas from the hydrogen tank 30 to the fuel cell 11. . The control device 45 drives the air compressor 33 according to the output required for the fuel cell 11 to supply a predetermined amount of air to the fuel cell 11 and controls the back pressure valve 34 to control the cathode gas flow path. It is comprised so that the supply pressure of the air to 22 can be adjusted.

  FIG. 2 is a schematic block diagram of the control device 45. As shown in FIG. 2, the control device 45 includes a highland control execution determination unit 46 that determines whether to execute highland control (control performed when the atmospheric pressure is low), and a purge amount that calculates a purge amount command value. A command value calculation unit 47, a drain amount command value calculation unit 48 that calculates a drain amount command value, a drain amount threshold setting unit 49 that sets a drain amount threshold (upper limit threshold), and a calculated drain amount command value and drain amount A drain amount determining unit 50 that determines the drain amount actually discharged from the threshold value.

(Purge control method for fuel cell system)
Next, a purge control method of the fuel cell system 10 in the present embodiment will be described.
FIG. 3 is a flowchart showing a purge control method of the fuel cell system 10.
As shown in FIG. 3, in S1, during the start-up of the fuel cell system 10, the value of the atmospheric pressure sensor 58 is detected every predetermined time to determine whether or not the atmospheric pressure is below a predetermined value. This is determined by the unit 46. If it is determined that the atmospheric pressure is equal to or lower than the predetermined value, that is, the altitude is located at a high altitude, the process proceeds to step S2 to execute the high altitude control. On the other hand, when atmospheric pressure is larger than a predetermined value, it progresses to Step S4.

  In step S2, a purge amount correction coefficient is determined. Specifically, the correction value is determined by applying the atmospheric pressure value detected in step S1 and the outside air temperature detected by the outside air temperature sensor 57 to the graph shown in FIG. 4, and the process proceeds to step S3. In addition, since cathode gas (air) can be supplied to the dilution box 31 so that external temperature is low, even if purge amount is increased, cathode gas corresponding to purge amount can be ensured. Therefore, when the atmospheric pressure is the same, the purge amount correction coefficient can be set larger when the outside air temperature is lower.

  In step S3, a drain amount correction coefficient is determined. Specifically, the value of the atmospheric pressure detected in step S1 and the outside air temperature detected by the outside air temperature sensor 57 are applied to the graph shown in FIG. 6 to determine a correction coefficient, and the process proceeds to step S6. Note that the higher the outside air temperature, the greater the amount of generated water that permeates from the cathode side to the anode side. Therefore, in the case of the same atmospheric pressure, the drain amount correction coefficient is set to be larger when the outside air temperature is higher.

In step S4, since it is not necessary to correct the purge amount, the correction coefficient is set to 1 and the process proceeds to step S5.
In step S5, since it is not necessary to correct the drain amount, the correction coefficient is set to 1 and the process proceeds to step S6.

  In step S6, a purge command base command value is determined. Specifically, the base command value is determined by applying the current value of the fuel cell 11 (detected by a current sensor not shown) and the hydrogen temperature in the anode system detected by the temperature sensor 55 to the graph shown in FIG. Then, the process proceeds to step S7. Note that the higher the hydrogen temperature, the lower the amount of water per volume, so the gas becomes dry. Therefore, when the current value is the same, the higher the hydrogen temperature, the lower the amount of water to be discharged, so the base command value for the purge amount can be set low.

  In step S7, the purge amount command value is determined by multiplying the purge amount base command value by the correction coefficient. Based on this purge amount command value, the valve opening time of the purge valve 52 is determined. Note that the processing of steps S2, S4, S6, and S7 is executed by the purge amount command value calculation unit 47 of the control device 45.

  In step S8, a drain command base command value is determined. Specifically, the base command value is determined by applying the current value of the fuel cell 11 (detected by a current sensor not shown) and the hydrogen temperature in the anode system detected by the temperature sensor 55 to the graph shown in FIG. Then, the process proceeds to step S9. Note that the higher the hydrogen temperature, the greater the amount of generated water that permeates from the cathode side to the anode side. Therefore, in the case of the same current value, the base command value for the drain amount is set to be larger when the hydrogen temperature is higher.

  In step S9, the drain amount command value is determined by multiplying the drain amount base command value by the correction coefficient. Note that the processing of steps S3, S5, S8, and S9 is executed by the drain amount command value calculation unit 48 of the control device 45.

  In step S10, the drain amount threshold setting unit 49 calculates a drain amount threshold (upper limit threshold). Specifically, it is calculated by executing a subroutine shown in FIG.

In step S101, the amount of water produced by the fuel cell 11 is calculated. The amount of generated water is calculated based on the current integrated value of the fuel cell 11.
In step S102, the amount of generated water discharged from the purge gas discharge pipe 37 and the generated water discharge pipe 41 so far is calculated. The amount of discharged water is calculated from the valve opening time of the purge valve 52 and the drain valve 42 and the internal pressure at that time (detected value of the pressure sensor 56). By calculating the discharged water amount, the remaining water amount can be estimated.
In step S103, the amount of generated water remaining in the system can be estimated from the numerical values calculated in steps S101 and S102. A drain amount threshold that can be discharged from the generated water discharge pipe 41 within a range not exceeding this residual water amount is calculated, and the process returns to S11 of the main routine.

  In step S11, the drain amount determination unit 50 compares the drain amount command value obtained in step S9 with the drain amount threshold obtained in step S10. When the drain amount command value is larger than the drain amount threshold value, the process proceeds to step S12. When the drain amount command value is equal to or smaller than the drain amount threshold value, the valve opening time is determined based on the drain amount command value.

  In step S12, the drain amount command value is changed to the drain amount threshold value, and the valve opening time is determined based on the drain amount command value.

  By causing the purge valve 52 and the drain valve 42 to open for a predetermined time based on the purge amount command value and the drain amount command value determined as described above, a flooding phenomenon due to generated water is generated in a high altitude where the atmospheric pressure is low. Can be prevented.

  According to the present embodiment, as the atmospheric pressure decreases, the amount of anode off-gas that can be purged decreases, and even if the amount of water discharged along with the purge decreases, the ratio of the drain amount to the purge amount increases. The generated water remaining in the water can be sufficiently discharged. Therefore, it is possible to prevent the flooding phenomenon due to the generated water, so that the power generation performance of the fuel cell 11 can be sufficiently ensured.

  In addition, by setting an upper limit threshold (drain amount threshold) for the drainable drain amount, when the moisture stored in the catch tank 40 is discharged, the discharged moisture amount does not exceed the drain amount threshold, In addition, the anode off gas can be prevented from being discharged at the same time. Therefore, the anode gas concentration on the anode side can be properly maintained.

  Further, since the amount of water stored in the catch tank 40 is determined based on the amount of generated water and the amount discharged, the amount of drain can be set appropriately.

Note that the present invention is not limited to the above-described embodiment, and includes various modifications made to the above-described embodiment without departing from the spirit of the present invention. That is, the specific structure and configuration described in the embodiment are merely examples, and can be changed as appropriate.
For example, in the present embodiment, the temperature sensor for detecting the hydrogen temperature in the anode system is configured to be attached to the anode gas supply pipe at only one place, but the temperature sensor may be attached not only to one place but also to a plurality of places. In that case, either temperature may be detected, or an average value of each temperature sensor may be obtained.

1 is a schematic configuration diagram of a fuel cell system in an embodiment of the present invention. It is a schematic block diagram of the control part in embodiment of this invention. It is a flowchart which shows the purge control method of the fuel cell system in embodiment of this invention. It is a map image which calculates | requires the correction coefficient of the purge amount in embodiment of this invention. It is a map image which calculates | requires the base command value of the purge amount in embodiment of this invention. It is a map image which calculates | requires the correction coefficient of the drain amount in embodiment of this invention. It is a map image which calculates | requires the base command value of the drain amount in embodiment of this invention. It is a flowchart which shows the subroutine of drain amount threshold value calculation in embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Fuel cell system 11 ... Fuel cell 35 ... Anode off gas discharge piping (anode off gas piping) 40 ... Catch tank (gas-liquid separator) 42 ... Drain valve 47 ... Purge amount command value calculation part (discharge amount adjustment means) 48 ... Drain amount command value calculating section (discharge amount adjusting means) 49 ... Drain amount threshold setting section (drain amount threshold setting means) 52 ... Purge valve 58 ... Atmospheric pressure sensor (atmospheric pressure detecting means)

Claims (5)

A fuel cell for generating electricity by supplying an anode gas to the anode electrode and a cathode gas to the cathode electrode; and
An anode offgas pipe through which the anode offgas discharged from the fuel cell flows;
A purge valve that is disposed in the anode offgas pipe and is openable and closable for discharging the anode offgas out of the flow path;
A gas-liquid separator disposed in the anode off-gas pipe and capable of separating moisture contained in the anode off-gas;
A drain valve that can be opened and closed to discharge the moisture stored in the gas-liquid separator out of the flow path;
An atmospheric pressure detecting means for detecting atmospheric pressure,
A fuel cell system that reduces a purge amount discharged from the purge valve as the atmospheric pressure decreases,
A fuel cell system comprising discharge amount adjusting means for increasing the ratio of the drain amount discharged from the drain valve to the purge amount as the atmospheric pressure detected by the atmospheric pressure detecting means decreases. . A drain amount threshold setting means for setting an upper limit threshold of the drain amount;
The drain amount is set to the drain amount threshold when the drain amount adjusted by the discharge amount adjusting unit exceeds the drain amount threshold set by the drain amount threshold setting unit. Item 4. The fuel cell system according to Item 1.   The fuel cell system according to claim 2, wherein the drain amount threshold is set based on a generated water generation amount and a generated water discharge amount generated in the fuel cell.   The fuel cell system according to any one of claims 1 to 3, wherein the discharge amount adjusting means increases the ratio by increasing at least the drain amount. A fuel cell for generating electricity by supplying an anode gas to the anode electrode and a cathode gas to the cathode electrode; and
An anode offgas pipe through which the anode offgas discharged from the fuel cell flows;
A purge valve that is disposed in the anode offgas pipe and is openable and closable for discharging the anode offgas out of the flow path;
A gas-liquid separator disposed in the anode off-gas pipe and capable of separating moisture contained in the anode off-gas;
A drain valve that can be opened and closed to discharge the moisture stored in the gas-liquid separator out of the flow path;
An atmospheric pressure detecting means for detecting atmospheric pressure,
A purge control method for a fuel cell system that reduces a purge amount discharged from the purge valve as the atmospheric pressure decreases,
An atmospheric pressure determination step for determining whether or not the atmospheric pressure is a predetermined value or less;
A purge amount correction coefficient determination step for obtaining a purge amount correction coefficient based on the atmospheric pressure and the outside air temperature;
A purge amount base command value determining step for obtaining a purge amount base command value based on the current value of the fuel cell and the temperature of the anode gas;
A purge amount command value determining step for obtaining a purge amount command value based on the purge amount correction coefficient and the purge amount base command value;
A drain amount correction coefficient determination step for obtaining a drain amount correction coefficient based on the atmospheric pressure and the outside air temperature;
A drain amount base command value determining step for obtaining a drain amount base command value based on the current value of the fuel cell and the temperature of the anode gas;
A drain amount command value determining step for obtaining a drain amount command value based on the drain amount correction coefficient and the drain amount base command value;
A drain amount threshold value calculating step for calculating a drain amount threshold value based on a generated water generation amount and a generated water discharge amount generated in the fuel cell;
A drain amount determination step of determining whether or not the drain amount command value is larger than the drain amount threshold;
A drain discharge step of setting the drain amount command value to the drain amount threshold value and discharging the moisture from the drain valve when it is determined that the drain amount determination step is large. A purge control method for a fuel cell system.

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