JP5172488B2 - Fuel cell system - Google Patents

Description

  The present invention relates to a fuel cell system. Specifically, the present invention relates to a fuel cell system that performs a scavenging process during a stop period of the fuel cell.

  In recent years, fuel cell systems have attracted attention as a new power source for automobiles. The fuel cell system includes, for example, a fuel cell that generates electricity by chemically reacting a reaction gas, and a reaction gas supply device that supplies the reaction gas to the fuel cell via a reaction gas path.

  The fuel cell has, for example, a stack structure in which several tens to several hundreds of cells are stacked. Here, each cell is configured by sandwiching a membrane electrode structure (MEA) between a pair of separators. The membrane electrode structure includes two electrodes, an anode electrode (anode) and a cathode electrode (cathode), and these electrodes. And a solid polymer electrolyte membrane sandwiched between the two.

  When hydrogen gas as anode gas is supplied to the anode electrode of the fuel cell and air as cathode gas is supplied to the cathode electrode, power is generated by an electrochemical reaction. Since only harmless water is generated at the time of power generation, a fuel cell system has attracted attention from the viewpoint of environmental impact and utilization efficiency.

  Such a fuel cell system is provided with a diluter, and by this diluter, the hydrogen off-gas discharged from the anode electrode of the fuel cell is diluted with the air off-gas discharged from the cathode electrode and discharged to the outside. .

  By the way, the water generated during the power generation remains in the fuel cell, the reaction gas passage, and the like after the power generation is stopped. If the fuel cell system after power generation is stopped is left in an environment where the outside air temperature is below freezing point, such residual water freezes inside the fuel cell and the reaction gas passage, and the fuel cell system is started the next time the fuel cell system is started. There is a risk that it is difficult to ensure the power generation stability of the battery.

Therefore, during the fuel cell outage period, scavenging processing is performed that uses the power stored in the battery to circulate scavenging gas inside these fuel cells and reaction gas passages and discharge residual water to the outside of the system. (See Patent Document 1). Specifically, after the cathode scavenging is performed to scavenge the cathode gas system including the cathode electrode, the anode scavenging is performed to scavenge the anode gas system including the anode electrode.
JP 2006-139939 A

  However, when the anode scavenging is started after the cathode scavenging is performed, a high concentration of hydrogen off-gas in the anode gas system flows into the diluter, so that it takes a lot of time to dilute the hydrogen off-gas. Thus, when the time required for the scavenging process is prolonged, the scavenging energy required for the scavenging process increases, so that the electric power stored in the battery decreases, and the commercial value may decrease at the next start-up.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a fuel cell system capable of reducing the scavenging energy by completing the scavenging process in a short time.

  A fuel cell system (for example, a fuel cell system 1 described later) of the present invention includes an anode gas (for example, a hydrogen gas described later) supplied through an anode gas supply path (for example, a hydrogen supply path 33 described later), and a cathode gas. A fuel cell (for example, a fuel cell 10 described later) that generates electricity by reaction of a cathode gas (for example, air described later) supplied through a supply channel (for example, an air supply channel 22 described later), and a cathode connected to the cathode gas supply channel Cathode gas supply means (for example, an air compressor 21 described later) for supplying gas, a cathode gas discharge path (for example, an air discharge path 23 described later) through which the cathode gas discharged from the fuel cell flows, and the cathode gas A back pressure valve (for example, a back pressure valve 231 described later) provided in the discharge path and an anode gas discharged from the fuel cell An anode gas discharge passage (for example, a hydrogen recirculation passage 34, a hydrogen discharge passage 35, and a scavenging gas discharge passage 36, which will be described later), and a scavenging gas discharge valve (for example, a scavenging gas described later) provided in the anode gas discharge passage. A scavenging gas introduction path (for example, a scavenging gas introduction path 24 described later) connecting the discharge valve 361), the cathode gas supply path and the anode gas supply path, and a scavenging gas introduction provided in the scavenging gas introduction path Dilution means (for example, diluter 50 described later) for diluting the anode gas flowing through the anode gas discharge path using a valve (for example, a scavenging gas introduction valve 241 described later) and a cathode gas flowing through the cathode gas discharge path The scavenging gas introduction valve and the back pressure valve are opened, the scavenging gas discharge valve is closed, and the cathode gas supply means supplies the cathode. A cathode scavenging means (for example, a cathode scavenging unit 43 described later) for performing a cathode scavenging process for scavenging a cathode gas system including the cathode gas supply path and the cathode gas discharge path by supplying a cathode gas to The scavenging gas introduction valve and the scavenging gas discharge valve are opened, the back pressure valve is closed, and the cathode gas is supplied to the cathode supply path by the cathode gas supply means, whereby the anode gas supply path and the anode An anode scavenging means (for example, an anode scavenging unit 44 described later) that performs an anode scavenging process for scavenging an anode gas system including a gas discharge path, and a cathode scavenging process performed by the cathode scavenging means, and then the anode scavenging means A scavenging control means for executing anode scavenging processing (for example, a scavenging control unit 4 described later) 6), wherein when the scavenging control means starts the anode scavenging process, the opening of the back pressure valve is smaller than when the cathode scavenging process is executed for a predetermined time. The intermediate opening is larger than that when the anode scavenging process is executed.

  According to this invention, when the anode scavenging process is started, the opening of the back pressure valve is set to the intermediate opening. Therefore, even when a highly concentrated anode gas flows into the diluting means at the start of the anode scavenging process, the cathode gas in the cathode gas system flows into the diluting means through the back pressure valve. This can accelerate the dilution time. As a result, the scavenging process can be completed in a short time, and the scavenging energy can be reduced.

  In this case, a purge valve (for example, a purge valve to be described later) provided in the anode gas discharge path is further provided, and the scavenging control means temporarily opens the purge valve during execution of the cathode scavenging process. It is preferable that a purge process for discharging the gas remaining in the anode gas system to the diluting means is performed and the opening of the back pressure valve is set to the intermediate opening.

  According to the present invention, when performing the purge process during the cathode scavenging process, since the opening of the back pressure valve is set to the intermediate opening, the cathode gas in the cathode gas system flows into the dilution means through the back pressure valve. Even if the anode off gas flows into the diluting means by the treatment, the dilution of the anode off gas in the diluting means is promoted, and the discharge capacity of the anode off gas can be improved.

  The fuel cell system of the present invention supplies a fuel cell that generates power by a reaction between an anode gas supplied through an anode gas supply path and a cathode gas supplied through the cathode gas supply path, and supplies the cathode gas to the cathode gas supply path. A cathode gas supply means; a cathode gas discharge passage through which the cathode gas discharged from the fuel cell flows; a back pressure valve provided in the cathode gas discharge passage; and an anode through which the anode gas discharged from the fuel cell flows. A gas discharge passage, a scavenging gas discharge valve and a purge valve provided in the anode gas discharge passage, a scavenging gas introduction passage connecting the cathode gas supply passage and the anode gas supply passage, and the scavenging gas introduction passage. The scavenging gas introduction valve provided and the cathode gas flowing through the cathode gas discharge path are used to Diluting means for diluting the anode gas flowing through the gas discharge path, the scavenging gas introduction valve and the back pressure valve are opened, the scavenging gas discharge valve is closed, and the cathode gas supply means supplies the cathode supply path to the cathode supply path. A cathode scavenging means for performing a cathode scavenging process for scavenging a cathode gas system including the cathode gas supply path and the cathode gas discharge path by supplying a cathode gas; and the scavenging gas introduction valve and the scavenging gas discharge valve; The anode gas system including the anode gas supply path and the anode gas discharge path is scavenged by opening the state, closing the back pressure valve, and supplying the cathode gas to the cathode supply path by the cathode gas supply means. Anode scavenging means for performing an anode scavenging process and a cathode scavenging means A scavenging control means for performing an anode scavenging process by the anode scavenging means after performing the scavenging process, wherein the scavenging control means performs the purge during the cathode scavenging process. The valve is temporarily opened to perform a purge process for discharging the gas remaining in the anode gas system to the diluting means, and the opening of the back pressure valve is set to the intermediate opening.

  According to the present invention, there are effects similar to those described above.

  In this case, the fuel cell further includes anode gas amount estimation means (for example, an anode gas amount estimation unit 45 described later) for estimating the anode gas amount inside the fuel cell, and the scavenging control means is based on the estimated anode gas amount. It is preferable to determine whether or not the opening of the back pressure valve is the intermediate opening.

  If the back pressure valve opening is set to an intermediate opening, the scavenging time will be prolonged, which may increase the energy consumption. However, according to the present invention, for example, when the amount of anode gas is estimated to be small, Therefore, it is determined that there is no need to positively discharge the anode off gas, and the opening of the back pressure valve is not set to the intermediate opening. Therefore, the scavenging process can be completed in a short time, and the scavenging energy can be reduced.

  According to the present invention, when the anode scavenging process is started, the opening of the back pressure valve is set to the intermediate opening. Therefore, even when a highly concentrated anode gas flows into the diluting means at the start of the anode scavenging process, the cathode gas in the cathode gas system flows into the diluting means through the back pressure valve. This can accelerate the dilution time. As a result, the scavenging process can be completed in a short time, and the scavenging energy can be reduced.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram of a fuel cell system 1 according to this embodiment.
The fuel cell system 1 includes a fuel cell 10, a supply device 20 that supplies anode gas and cathode gas to the fuel cell 10, and an electronic control unit (hereinafter referred to as "ECU") that controls the fuel cell 10 and the supply device 20. 40). The fuel cell system 1 is mounted, for example, in a fuel cell vehicle (not shown) that uses electric power generated by the fuel cell 10 as a power source.

  The fuel cell 10 has a stack structure in which, for example, several tens to several hundreds of cells are stacked. Each cell is configured by sandwiching a membrane electrode structure (MEA) between a pair of separators. The membrane electrode structure is composed of two electrodes, an anode electrode (anode) and a cathode electrode (cathode), and a solid polymer electrolyte membrane sandwiched between these electrodes. Usually, both electrodes are formed of a catalyst layer that performs an oxidation / reduction reaction in contact with the solid polymer electrolyte membrane and a gas diffusion layer in contact with the catalyst layer.

In such a fuel cell 10, hydrogen gas as an anode gas is supplied to an anode flow path 13 formed on the anode electrode (anode) side, and oxygen is supplied to a cathode flow path 14 formed on the cathode electrode (cathode) side. When air (air) as the cathode gas is supplied, power is generated by these electrochemical reactions.
A temperature sensor 15 that measures the temperature of the fuel cell 10 is provided inside the fuel cell 10.

  The supply device 20 includes an air compressor 21 as a cathode gas supply means, a hydrogen tank 31 and an ejector 32.

The air compressor 21 supplies air to one end side of the cathode flow path 14 of the fuel cell 10 via an air supply path 22 as a cathode gas supply path. The air compressor 21 can adjust the supplied air flow rate from zero to a large flow rate.
An air discharge path 23 as a cathode gas discharge path through which air discharged from the fuel cell 10 flows is connected to the other end side of the cathode flow path 14 of the fuel cell 10. A diluter 50 as a diluting means described later is connected. The air discharge path 23 is provided with a back pressure valve 231 whose opening degree can be adjusted.

  Further, a scavenging gas introduction path 24 is branched from the air supply path 22. The front end side of the scavenging gas introduction path 24 is connected to a hydrogen supply path 33 described later. The scavenging gas introduction path 24 is provided with a scavenging gas introduction valve 241. When the scavenging gas introduction valve 241 is opened, the air supply path 22 and the hydrogen supply path 33 communicate with each other, and when the scavenging gas introduction valve 241 is closed, the air supply path 22 and the hydrogen supply path 33 communicate with each other. Blocked.

  The hydrogen tank 31 supplies hydrogen gas to one end side of the anode flow path 13 of the fuel cell 10 through a hydrogen supply path 33 as an anode gas supply path. An ejector 32 is provided in the hydrogen supply path 33. In addition, between the hydrogen tank 31 and the ejector 32 in the hydrogen supply path 33, a shut-off valve and a regulator (not shown) for reducing the pressure of the hydrogen gas supplied from the hydrogen tank 31 are provided. Further, a pressure sensor 331 for measuring the pressure of the hydrogen supply path 33 is provided in the vicinity of the fuel cell 10 in the hydrogen supply path 33.

  Connected to the other end of the anode flow path 13 of the fuel cell 10 is a hydrogen reflux path 34 as an anode gas discharge path through which hydrogen gas discharged from the fuel cell 10 flows. The distal end side of the hydrogen reflux path 34 is connected to the ejector 32. The ejector 32 collects the hydrogen gas flowing through the hydrogen reflux path 34 and returns it to the hydrogen supply path 33.

  Further, a hydrogen discharge path 35 and a scavenging gas discharge path 36 as an anode gas discharge path are branched into the hydrogen reflux path 34. The distal ends of these hydrogen discharge passage 35 and scavenging gas discharge passage 36 are connected to a diluter 50.

The hydrogen discharge path 35 is provided with a purge valve 351 that opens and closes the hydrogen discharge path 35. By opening the purge valve 351, the gas flowing through the hydrogen reflux path 34 can be discharged to the diluter 50 at a medium flow rate.
The scavenging gas discharge path 36 is provided with a scavenging gas discharge valve 361 that opens and closes the scavenging gas discharge path 36. By opening the purge valve 351, the gas flowing through the hydrogen reflux path 34 can be discharged to the diluter 50 at a large flow rate.

  The diluter 50 uses the air off gas introduced through the air discharge passage 23 as a dilution gas, and dilutes the hydrogen off gas introduced through the hydrogen discharge passage 35 and the scavenging gas discharge passage 36 with the dilution gas. And discharged to the outside of the fuel cell system 1.

In the present embodiment, the anode gas through which the hydrogen gas and the hydrogen off-gas discharged from the fuel cell 10 are circulated by the anode flow path 13, the hydrogen supply path 33, the hydrogen reflux path 34, the hydrogen discharge path 35, and the scavenging gas discharge path 36. A system is constructed.
Further, the cathode flow path 14, the air supply path 22, the air discharge path 23, and the scavenging gas introduction path 24 constitute a cathode gas system through which air and the air-off gas discharged from the fuel cell 10 circulate. In FIG. 1, the anode gas system is indicated by a white arrow, and the cathode gas system is indicated by a solid arrow.

  The air compressor 21, the back pressure valve 231, the scavenging gas introduction valve 241, the shut-off valve, the purge valve 351, and the scavenging gas discharge valve 361 are controlled by the ECU 40.

The temperature sensor 15, the pressure sensor 331, the ignition switch 41, and the timer 42 are connected to the ECU 40.
The ignition switch 41 is provided in the driver's seat of the fuel cell vehicle on which the fuel cell system 1 is mounted, and transmits an on signal for instructing start or an off signal for instructing stop to the ECU 40 according to the operation of the driver. To do. The ECU 40 starts the start of the fuel cell 10 or stops the power generation of the fuel cell 10 in accordance with the on / off signal output from the ignition switch 41.
The timer 42 measures the elapsed time after the power generation of the fuel cell 10 is stopped and outputs it to the ECU 40.

  The ECU 40 includes a cathode scavenging unit 43 as a cathode scavenging unit, an anode scavenging unit 44 as an anode scavenging unit, an anode gas amount estimating unit 45 as an anode gas amount estimating unit, and a scavenging control unit 46 as a scavenging control unit. .

  The cathode scavenging unit 43 executes a cathode scavenging process. That is, the scavenging gas introduction valve 241 and the back pressure valve 231 are opened, the scavenging gas discharge valve 361 is closed, and air is supplied to the air supply path 22 by the air compressor 21, thereby scavenging the cathode gas system.

The anode scavenging unit 44 executes an anode scavenging process. That is, the scavenging gas introduction valve 241 and the scavenging gas discharge valve 361 are opened, the back pressure valve 231 is closed, and air is supplied to the air supply path 22 by the air compressor 21, thereby scavenging the anode gas system.
This anode scavenging treatment is intended to replace the gas containing hydrogen in the anode gas system with a scavenging gas, to discharge moisture in the anode gas system, and to dry the MEA of the fuel cell 10. .

  The anode gas amount estimation unit 45 estimates the amount of hydrogen gas inside the fuel cell 10 based on the temperature of the fuel cell 10 measured by the temperature sensor 15 and the pressure of the anode gas system measured by the pressure sensor 331.

The scavenging control unit 46 executes the anode scavenging process by the anode scavenging unit 44 after performing the cathode scavenging process by the cathode scavenging unit 43.
Here, the scavenging control unit 46 performs a purge process in which the purge valve 351 is temporarily opened to discharge the gas remaining in the anode gas system to the diluter 50 during the cathode scavenging process, and the back pressure valve The opening of 231 is the intermediate opening. The intermediate opening degree of the back pressure valve 231 is an opening degree that is smaller than that when the cathode scavenging process is executed and larger than that when the anode scavenging process is executed.
Further, when the scavenging control unit 46 starts the anode scavenging process, the opening of the back pressure valve 231 is set to an intermediate opening.

  Further, the scavenging control unit 46 determines whether or not the opening of the back pressure valve 231 is set to an intermediate opening based on the hydrogen gas amount estimated by the anode gas amount estimating unit 45.

  The above scavenging process is executed during the stop period of the fuel cell 10. More specifically, the timing of executing the scavenging process is determined when the system is started every predetermined time based on the timer 42 after the stop of power generation by the fuel cell 10 and after the stop of power generation by the fuel cell 10. Depending on the case, the temperature of the fuel cell system 1 may be monitored after the power generation by the fuel cell 10 is stopped, and may be executed when the temperature of the fuel cell system 1 falls below a predetermined value.

  Hereinafter, the operation of the fuel cell system 1 will be described with reference to FIGS.

FIG. 2 is a flowchart showing the operation of the fuel cell system 1.
First, in step S1, it is detected that the ignition switch 41 has been turned off, that is, a power generation stop request by the ignition switch.
In step S2, the system temperature is monitored by the temperature sensor 15, and in step S3, the power generation stop period of the fuel cell 10 is monitored by the timer.

  In step S4, it is determined whether or not the temperature of the fuel cell system 1 is equal to or lower than a predetermined value. If this determination is YES, the process proceeds to step S5, and if NO, the process returns to step S2.

In step S5, a scavenging process is executed. This scavenging process will be described in detail later.
In step S6, it is determined whether or not the scavenging process is completed. If this determination is YES, the process ends. If NO, the process returns to step S6.

Next, the scavenging process in step S5 will be described.
FIG. 3 is a flowchart showing the procedure of the scavenging process.
First, in step S11, based on the fuel cell power generation stop period, the temperature of the fuel cell 10 measured by the temperature sensor 15, and the pressure of the hydrogen supply path 33 measured by the pressure sensor 331, the inside of the fuel cell 10 according to FIG. Estimate the amount of hydrogen gas.
FIG. 4 is a diagram showing the relationship between the power generation stop period of the fuel cell and the estimated value of the hydrogen gas amount inside the fuel cell.
As shown by the solid line in FIG. 4, the estimated value of the amount of hydrogen gas inside the fuel cell decreases as the power generation stop period of the fuel cell becomes longer.
The curve indicating the relationship between the power generation stop period and the estimated value of the hydrogen gas amount is the temperature of the fuel cell 10 measured by the temperature sensor 15 and the hydrogen measured by the pressure sensor 331, as shown by the broken line in FIG. It fluctuates up and down based on the pressure in the supply path 33.

In step S12, it is determined whether or not the estimated hydrogen gas amount is equal to or greater than a first predetermined value. If this determination is NO, the process moves to step S13, and if YES, the process moves to step S14.
In step S13, it is determined using the second predetermined value that is lower than the first predetermined value whether the estimated hydrogen gas amount is equal to or greater than the second predetermined value. If this determination is YES, the process proceeds to step S14, and if NO, the process proceeds to step S15.

In step S14, since the estimated hydrogen gas amount is equal to or greater than the first predetermined value, the scavenging process is performed in the first pattern, and the process ends.
In step S15, since the estimated hydrogen gas amount is greater than or equal to the second predetermined value and less than the first predetermined value, the scavenging process is performed in the second pattern, and the process ends.
In step S16, since the estimated hydrogen gas amount is less than the second predetermined value, the scavenging process is performed in the third pattern, and the process ends.

Hereinafter, the scavenging process of each pattern in steps S14 to S16 will be described with reference to FIGS.
In the following description, the opening degree of the back pressure valve, the opening degree zero fully closed state, the opening d ₄ fully open. Then, the intermediate opening between the opening zero and the opening d ₄ is set as an intermediate opening d ₁ , an intermediate opening d ₂ , and an intermediate opening d _{3 in} order from the smallest.
In addition, the amount of air supplied by the air compressor is three stages of f ₁ , f ₂ , f ₃ and f ₄ in order from the smallest, f ₁ and f ₂ are small flow rates, and f ₃ and f ₄ are large flow rates. is there.

FIG. 5 is a time chart illustrating a control example of the first pattern scavenging process.
Further, in the time chart shown in FIG. 5, in order from the top, the air flow supplied by the air compressor, the pressure in the anode gas system, the state of the purge valve, the scavenging gas discharge valve, and the back pressure valve, and the diluter It shows the concentration of discharged hydrogen.
It is assumed that the scavenging gas introduction valve is always open during the scavenging process.

As shown in FIG. 5, the scavenging process includes a “cathode scavenging process” (time t _{0 to} t ₂ ), a “fuel cell internal pressure lowering process” (time t _{2 to} t ₃ ), and a “first anode scavenging process”. ”(Time t _{3 to} t ₅ ) and“ second anode scavenging process ”(time t _{5 to} t ₆ ).

First, in the period t ₂ from time t _0, it executes the cathode scavenging. That is, the back pressure valve open state, the scavenging exhaust valve with the closed state, by driving the air compressor, and f ₃ of the large flow of air flow. As a result, the gas in the cathode gas system is pushed out into the diluter by the scavenging gas together with the moisture in the cathode gas system, and is discharged.

  In the cathode scavenging process, a purge process is performed at a predetermined timing. Specifically, the purge valve is opened for a certain time. Thereby, the gas in the anode gas system containing hydrogen is pushed out into the diluter by the scavenging gas together with the moisture in the anode gas system, diluted with the scavenging gas, and discharged. Since the gas containing hydrogen is discharged by this purge process, the discharged hydrogen concentration gradually increases.

Further, in the cathode scavenging process period t ₂ from time t ₁ immediately before the completion, it performs the purge process, the opening of the back pressure valve was much smaller, the intermediate opening d _1. As a result, scavenging gas is introduced into the anode gas system, and the pressure of the anode gas system increases, so that a large amount of hydrogen off-gas can be discharged in a short time when the purge process is executed. Moreover, since the gas in the cathode gas system flows into the diluter through the back pressure valve, the dilution of the hydrogen off gas is promoted.

In the period t ₃ from time t _2, the run the fuel cell internal pressure drop process. That is, the opening of the back pressure valve is slightly increased to the intermediate opening d ₃ , the purge valve is opened, and the air flow rate is set to f ₁ . Then, since the anode gas system gas flows into the diluter through the purge valve, the anode gas system pressure decreases. Thereby, when performing an anode scavenging process, a scavenging gas discharge valve can be opened and closed easily.

In the period t ₅ from time t _3, to perform the first anode scavenging. That is, the back pressure valve closed, as well as the scavenging exhaust valve with the open state, by driving the air compressor, the air flow rate and f ₄ of the high flow rate. As a result, the scavenging gas is introduced into the anode gas system, and the gas in the anode gas system is pushed into the diluter by the scavenging gas together with the moisture in the anode gas system, and is discharged.

Here, in the period t ₄ from time t ₃ immediately after the start of the anode scavenging, the opening of the back pressure valve, a little smaller than the fuel cell internal pressure reduction step, the intermediate opening d _2. Thereby, since the gas in the cathode gas system flows into the diluter through the back pressure valve, the dilution of the hydrogen gas in the diluter is promoted.

In the period t ₆ from the time t _5, to perform a second anode scavenging. That is, by reducing the air flow rate by the air compressor, and f ₂ of the low flow. As a result, anode scavenging is executed subsequent to the second anode scavenging process, but the pressure of the anode gas system is lower than that in the second anode scavenging process.

FIG. 6 is a time chart illustrating a control example of the second pattern scavenging process.
The second pattern is different from the first pattern in that the opening of the back pressure valve is not set to the intermediate opening d _{1 in} the period immediately before the completion of the cathode scavenging process.
This is because in the second pattern, it is estimated that the amount of hydrogen gas remaining in the anode gas system is smaller than that in the first pattern, and therefore it is not necessary to promote the discharge of hydrogen off-gas.

FIG. 7 is a time chart showing a control example of the third pattern scavenging process.
In the third pattern, that in the period immediately after the start of the anode scavenging is not the opening of the back pressure valve and the intermediate opening d ₂ is different from the second pattern.
This is because it is estimated that the amount of hydrogen gas remaining in the anode gas system is smaller in the third pattern than in the second pattern, and therefore it is not necessary to promote the discharge of hydrogen off-gas.

According to this embodiment, there are the following effects.
(1) when performing the purge process in the cathode scavenging, since the opening of the back pressure valve 231 and the intermediate opening d _1, that by introducing a scavenging gas to the anode gas system, increasing the pressure of the anode gas system Can do. Therefore, when the purge process is executed, a large amount of hydrogen off-gas can be discharged in a short time.
Further, since the gas in the cathode gas system flows into the diluter 50 through the back pressure valve 231, even if hydrogen offgas flows into the diluter 50 by the purge process, the dilution of the hydrogen offgas in the diluter 50 is promoted. The hydrogen off gas discharge capacity can be improved.

(2) Conventionally, when the pressure of the anode gas system is high, the pressure difference between the upstream side and the downstream side of the scavenging gas discharge valve 361 increases, and the scavenging gas discharge valve 361 that is an electromagnetic valve cannot be easily opened and closed.
Thus, since the pressure of the anode gas system is reduced in the fuel cell internal pressure reduction step, the scavenging gas discharge valve 361 can be easily opened and closed when the anode scavenging is executed.

(3) when starting the anode scavenging process, the opening of the back pressure valve 231 and the intermediate opening d _2. Therefore, even if hydrogen gas having a high concentration flows into the diluter 50 at the start of the anode scavenging process, the gas in the cathode gas system flows into the diluter 50 through the back pressure valve 231. Therefore, the hydrogen gas in the diluter 50 Dilution is facilitated and the dilution time can be shortened. As a result, the scavenging process can be completed in a short time, and the scavenging energy can be reduced.

(4) When it is estimated that the amount of hydrogen gas is small, it is determined that it is not necessary to positively discharge the hydrogen off gas, and the opening of the back pressure valve 231 is not set to the intermediate opening. Therefore, the scavenging process can be completed in a short time, and the scavenging energy can be reduced.

  It should be noted that the present invention is not limited to the above-described embodiment, and modifications, improvements, etc. within a scope that can achieve the object of the present invention are included in the present invention.

1 is a block diagram of a fuel cell system according to an embodiment of the present invention. It is a flowchart which shows operation | movement of the fuel cell system which concerns on the said embodiment. It is a flowchart which shows the scavenging process of the fuel cell system which concerns on the said embodiment. It is a figure which shows the relationship between the electric power generation stop period of the fuel cell which concerns on the said embodiment, and the estimated amount of hydrogen gas inside a fuel cell. It is a time chart which shows the example of control of the scavenging process of the 1st pattern concerning the above-mentioned embodiment. It is a time chart which shows the example of control of the scavenging process of the 2nd pattern concerning the above-mentioned embodiment. It is a time chart which shows the example of control of the scavenging process of the 3rd pattern concerning the above-mentioned embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Fuel cell system 10 ... Fuel cell 21 ... Air compressor (cathode gas supply means)
22. Air supply path (cathode gas supply path)
23. Air discharge path (cathode gas discharge path)
24 ... Scavenging gas introduction path 33 ... Hydrogen supply path (anode gas supply path)
34 ... Hydrogen reflux path (anode gas discharge path)
35 ... Hydrogen discharge passage (anode gas discharge passage)
36. Scavenging gas discharge path (anode gas discharge path)
43 ... Cathode scavenging section (cathode scavenging means)
44 ... Anode scavenging section (anode scavenging means)
45 ... Anode gas amount estimation unit (anode gas amount estimation means)
46. Scavenging control unit (scavenging control means)
50 ... Dilutor (dilution means)
231 ... Back pressure valve 241 ... Scavenging gas introduction valve 351 ... Purge valve 361 ... Scavenging gas discharge valve

Claims (4)

A fuel cell that generates electricity by a reaction between an anode gas supplied through an anode gas supply path and a cathode gas supplied through a cathode gas supply path;
A cathode gas supply means for supplying a cathode gas to the cathode gas supply path;
A cathode gas discharge passage through which the cathode gas discharged from the fuel cell flows;
A back pressure valve provided in the cathode gas discharge path;
An anode gas discharge path through which the anode gas discharged from the fuel cell flows;
A scavenging gas discharge valve provided in the anode gas discharge path;
A scavenging gas introduction path connecting the cathode gas supply path and the anode gas supply path;
A scavenging gas introduction valve provided in the scavenging gas introduction path;
Diluting means for diluting the anode gas flowing through the anode gas discharge passage with the cathode gas flowing through the cathode gas discharge passage;
The scavenging gas introduction valve and the back pressure valve are opened, the scavenging gas discharge valve is closed, and cathode gas is supplied to the cathode gas supply path by the cathode gas supply means. A cathode scavenging means for performing a cathode scavenging process for scavenging a cathode gas system including the cathode gas discharge path;
The scavenging gas introduction valve and the scavenging gas discharge valve are opened, the back pressure valve is closed, and the cathode gas is supplied to the anode gas supply path by the cathode gas supply means. Anode scavenging means for performing an anode scavenging process for scavenging an anode gas system including the anode gas discharge path;
A scavenging control means for performing an anode scavenging process by the anode scavenging means after performing a cathode scavenging process by the cathode scavenging means, and a fuel cell system comprising:
When the scavenging control means starts the anode scavenging process, the opening of the back pressure valve is lower than the case where the cathode scavenging process is executed for a predetermined time and is larger than the case where the anode scavenging process is executed. A fuel cell system characterized by a degree. A purge valve provided in the anode gas discharge path;
The scavenging control means performs a purging process in which the purge valve is temporarily opened during the execution of the cathode scavenging process to discharge gas remaining in the anode gas system to the diluting means, and the back pressure valve The fuel cell system according to claim 1, wherein the opening degree is set to the intermediate opening degree. A fuel cell that generates electricity by a reaction between an anode gas supplied through an anode gas supply path and a cathode gas supplied through a cathode gas supply path;
A cathode gas supply means for supplying a cathode gas to the cathode gas supply path;
A cathode gas discharge passage through which the cathode gas discharged from the fuel cell flows;
A back pressure valve provided in the cathode gas discharge path;
An anode gas discharge path through which the anode gas discharged from the fuel cell flows;
A scavenging gas discharge valve and a purge valve provided in the anode gas discharge path;
A scavenging gas introduction path connecting the cathode gas supply path and the anode gas supply path;
A scavenging gas introduction valve provided in the scavenging gas introduction path;
Diluting means for diluting the anode gas flowing through the anode gas discharge passage with the cathode gas flowing through the cathode gas discharge passage;
The scavenging gas introduction valve and the back pressure valve are opened, the scavenging gas discharge valve is closed, and cathode gas is supplied to the cathode gas supply path by the cathode gas supply means. A cathode scavenging means for performing a cathode scavenging process for scavenging a cathode gas system including the cathode gas discharge path;
The scavenging gas introduction valve and the scavenging gas discharge valve are opened, the back pressure valve is closed, and the cathode gas is supplied to the anode gas supply path by the cathode gas supply means. Anode scavenging means for performing an anode scavenging process for scavenging an anode gas system including the anode gas discharge path;
A scavenging control means for performing an anode scavenging process by the anode scavenging means after performing a cathode scavenging process by the cathode scavenging means, and a fuel cell system comprising:
The scavenging control means performs a purging process in which the purge valve is temporarily opened during the execution of the cathode scavenging process to discharge gas remaining in the anode gas system to the diluting means, and the back pressure valve The fuel cell system is characterized in that the opening degree is set to the intermediate opening degree. An anode gas amount estimating means for estimating an anode gas amount inside the fuel cell;
The scavenging control means determines whether or not the opening of the back pressure valve is set to the intermediate opening based on the estimated anode gas amount. Fuel cell system.

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