JP2009140860A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system capable of reducing power consumption in scavenging. <P>SOLUTION: After the power generation of a fuel cell 10 is stopped, first scavenging predominantly scavenging a cathode 13 is performed, and then second scavenging predominantly scavenging an anode 12 is performed. Based on the system stopping time from the power generation stop of the fuel cell 10 to the first scavenging, hydrogen concentration remained in the anode 12 is predicted, and based on the predicted hydrogen concentration, the using time of a purge valve 23 and a drain valve 46 in the cathode scavenging is determined. When the system stop time is short, the using time of the purge valve 23 and the drain valve 46 is set long, and when the system stop time is long, the using time of the purge valve 23 and the drain valve 46 is set short. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fuel cell system including a scavenging method for scavenging a fuel cell.

  In a fuel cell system installed in a fuel cell vehicle, etc., if water remains in the piping including the fuel cell when the system is stopped, the water freezes in a cold environment such as a cold region or winter, and the Low temperature startability is reduced. For this reason, scavenging treatment is performed by introducing air to the anode side and the cathode side when the system is stopped.

Further, in this type of fuel cell system, since the fuel gas remains in the anode when the system is stopped, the scavenging is performed according to the remaining fuel gas concentration so that the high concentration fuel gas is not discharged outside the system. It has been proposed to obtain a flow rate (see, for example, Patent Document 1). Further, a technique has been proposed in which scavenging gas is introduced into the anode side and purged when scavenging the cathode side (see, for example, Patent Document 2).
JP 2007-35509 A (FIGS. 1 and 2) JP 2006-139939 A (FIGS. 1 and 3)

  However, in the conventional fuel cell system, when scavenging the anode, air replacement in the fuel cell is performed by using a purge valve during the previous scavenging of the anode, and this method is always performed in the same manner. It was. For this reason, even if it is not necessary to use the purge valve, there is a problem that it continues to be used and energy is wasted.

  The present invention solves the above-described conventional problems, and an object thereof is to provide a fuel cell system capable of reducing power consumption during scavenging.

  The present invention relates to a fuel cell that generates electric power by a reaction between a fuel gas supplied to an anode and an oxidant gas supplied to a cathode, a fuel gas flow passage through which fuel gas flows through the anode, and an oxidant to the cathode An oxidant gas flow passage through which gas is circulated; a communication flow path that connects the fuel gas flow passage and the oxidant gas flow passage; a communication valve that opens and closes the communication flow path; State monitoring means for monitoring a subsequent state change, and when the state change becomes a predetermined condition after stopping the power generation of the fuel cell, the communication valve is opened to scavenge the cathode with the oxidant gas. Scavenging means for performing a first scavenging and then a second scavenging for scavenging the anode, and an oxidant gas supply for determining a supply amount of the oxidant gas necessary for the first scavenging and the second scavenging Quantity calculation means In the fuel cell system, the fuel exhaust gas discharged from the anode is diluted with an oxidant gas and discharged to the outside, and the fuel exhaust gas from the anode is purged to the fuel exhaust gas dilution means. Purge control means for controlling the purge amount; fuel gas concentration prediction means for predicting the concentration of fuel gas from the anode based on the system stop time until the first scavenging after the fuel cell power generation is stopped; Based on the concentration of the fuel gas predicted by the fuel gas concentration prediction means, the purge amount purged by the purge control means during the first scavenging is set to a smaller amount as the fuel gas concentration is lower And a purge amount calculating means for calculating.

  According to the present invention, the hydrogen concentration on the anode side is predicted based on the system stop time from when the fuel cell power generation is stopped to when the automatic scavenging is performed (when the state change becomes a predetermined condition), and during the cathode scavenging accordingly. Therefore, it is possible to determine the optimum operation of the purge control means, and the purge control means is not operated wastefully, and the power consumption can be reduced.

  Further, the oxidant gas supply amount calculation means is configured so that the longer the system stop time is, the longer the system stop time is based on the system stop time until the first scavenging after the fuel cell power generation is stopped. It is preferable to set so that there is less.

  According to this, since the apparatus (for example, air compressor) which supplies oxidizing gas is not driven unnecessarily for a long time, it becomes possible to reduce power consumption.

  According to the fuel cell system of the present invention, power consumption during scavenging can be reduced.

  FIG. 1 is an overall configuration diagram showing a fuel cell system according to the present embodiment, FIG. 2 is a flowchart showing control after the system is stopped in the present embodiment, and FIG. 3A is a relationship between the system stop time and the hydrogen concentration in the anode system. (B) is a map showing the relationship between the anode system hydrogen concentration and the purge valve and drain valve usage time during cathode scavenging, (c) is a map showing the relationship between the system stop time and scavenging time, 4 is a sub-flowchart in the scavenging step of FIG. 2, FIG. 5 is a timing chart showing the opening / closing operation of various valves when the system stop time is short in this embodiment, and FIG. 6 is a case where the system stop time is long in this embodiment It is a timing chart which shows the opening / closing operation | movement of various valves. In addition, although this embodiment demonstrates and demonstrates the fuel cell system mounted in a fuel cell vehicle as an example, it is not limited to this, The fuel cell system of this embodiment is mobile bodies, such as a ship and an aircraft. Or, it can be applied to anything such as a stationary type such as home use.

  As shown in FIG. 1, the fuel cell system 1 of this embodiment includes a fuel cell 10, an anode system 20, a cathode system 30, a control system 50, and the like.

  The fuel cell 10 is a solid polymer type PEM (Proton Exchange Membrane) type fuel cell, and an anode (fuel electrode) 12 and a cathode (oxidant electrode) 13 containing a predetermined catalyst on both surfaces of the electrolyte membrane 11. A plurality of unit cells each composed of a membrane electrode assembly (MEA) sandwiched between a pair of conductive separators 14 and 15 are stacked. An anode channel 14a through which hydrogen (fuel gas) flows is formed on the surface of the separator 14 facing the anode 12, and air (oxidant gas) flows on the surface of the separator 15 facing the cathode 13. A cathode channel 15a is formed.

  In the fuel cell 10, hydrogen is supplied to the anode 12 and air (oxygen) is supplied to the cathode 13, so that electrons are separated from hydrogen by the action of the catalyst in the anode 12, and hydrogen ions pass through the electrolyte membrane 11. The light passes through the cathode 13 and the electrons move to the cathode 13 via an external load (such as a travel motor). At the cathode 13, hydrogen ions, electrons, and oxygen in the air react with each other by the action of the catalyst to generate water.

  The anode system 20 supplies and discharges hydrogen to and from the anode 12 of the fuel cell 10, and includes an anode gas supply pipe 2a, an anode off-gas discharge pipe 2b, a high-pressure hydrogen tank 21, a cutoff valve 22, a purge valve 23, and the like. It is configured with.

  The anode gas supply pipe 2 a has one end connected to the inlet of the anode flow path 14 a of the fuel cell 10 and the other end connected to the shut-off valve 22. One end of the anode off-gas discharge pipe 2 b is connected to the outlet of the anode flow path 14 a of the fuel cell 10, and the other end is connected to the purge valve 23. Although not shown, the anode system 20 is provided with an anode gas circulation pipe for returning the unreacted hydrogen discharged from the fuel cell 10 to the anode gas supply pipe 2a for recirculation.

  The high-pressure hydrogen tank 21 is a container capable of accumulating high-purity hydrogen at a very high pressure.

  The shut-off valve 22 is, for example, an electromagnetically operated type having a solenoid, and is provided in the vicinity of the outlet of the high-pressure hydrogen tank 21. The shut-off valve 22 may be an in-tank type provided integrally with the high-pressure hydrogen tank 21.

  The purge valve 23 is, for example, an electromagnetically operated type having a solenoid and is configured to prevent the power generation performance from being lowered by opening the valve periodically, for example, in response to a decrease in cell voltage. . Incidentally, the purge valve 23 is opened because nitrogen, generated water and the like contained in the air supplied to the cathode 13 permeate the anode 12 through the electrolyte membrane 11 during power generation and the hydrogen concentration in the anode 12 Due to the decline.

  Although not shown, a regulator for reducing the pressure of the high-pressure hydrogen discharged from the high-pressure hydrogen tank 21 is provided on the downstream side of the shutoff valve 22 of the anode system 20.

  The cathode system 30 supplies and discharges air to and from the cathode 13 of the fuel cell 10, and includes a cathode gas supply pipe 3a, a cathode offgas discharge pipe 3b, an air compressor 31, a back pressure valve 32, and the like. ing.

  One end of the cathode gas supply pipe 3a is connected to the inlet of the cathode flow path 15a of the fuel cell 10, and the other end is connected to an air compressor 31 described later. The cathode offgas discharge pipe 3b has one end connected to the outlet of the cathode flow path 15a of the fuel cell 10 and the other end connected to a back pressure valve 32 described later.

  The air compressor 31 is composed of, for example, a supercharger driven by a motor, and has a function of supplying compressed air to the fuel cell 10. The air compressor 31 can adjust the amount of air supplied to the fuel cell 10 by changing the rotational speed of the motor.

  The back pressure valve 32 is configured by a butterfly valve or the like, and the valve opening degree can be adjusted as appropriate. By changing the valve opening, the air pressure (air amount) supplied to the cathode 13 of the fuel cell 10 can be changed.

  Although not shown, the cathode system 30 is provided with a humidifier that humidifies the air supplied to the fuel cell 10. A cathode off gas discharged from the cathode 13 of the fuel cell 10 is used as a humidification source in a humidifier (not shown).

  The fuel cell system 1 according to the present embodiment includes a diluter 35, an air introduction pipe 41, an air introduction valve 42, an air discharge pipe 43, an air discharge valve 44, a drain pipe 45, a drain valve 46, a power storage device 60, and the like. ing.

  The diluter 35 has a space where the anode off gas stays and dilutes, and the anode off gas (fuel exhaust gas) discharged from the anode 12 of the fuel cell 10 is diluted with air (oxidant gas) to the outside (outside the vehicle). Has the function of discharging. In this embodiment, the anode off-gas is diluted with the cathode off-gas, but air (oxidant gas) before being supplied to the fuel cell 10 may be further introduced and diluted.

  The air introduction pipe 41 connects the anode gas supply pipe 2 a and the cathode gas supply pipe 3 a on the upstream side of the fuel cell 10. The air introduction valve 42 is, for example, an electromagnetically operated type having a solenoid, and is provided on the air introduction pipe 41.

  The air discharge pipe 43 connects the anode offgas discharge pipe 2 b and the cathode offgas discharge pipe 3 b on the downstream side of the fuel cell 10. The air discharge valve 44 is an electromagnetically operated type having a solenoid, for example, and is provided on the air discharge pipe 43.

  The drain pipe 45 connects the anode off-gas discharge pipe 2b and the cathode off-gas discharge pipe 3b further downstream of the air discharge pipe 43. The drain valve 46 is an electromagnetically operated type having a solenoid, for example, and is provided on the drain pipe 45.

  The drain valve 46 is formed to have a smaller flow path diameter than the purge valve 23. The purge valve 23 is formed to have a smaller flow path diameter than the air discharge valve 44. That is, a small flow rate gas flows through the drain valve 46, a medium flow rate gas flows through the purge valve 23, and a large flow rate gas flows through the air exhaust valve 44.

  The power storage device 60 is a high voltage system composed of a battery, a capacitor, and the like, and can store power generated by the fuel cell 10. The power storage device 60 is used as a power source after the power generation of the fuel cell 10 is stopped, a power source at the time of restart, and the like. The battery is selected from lithium ions, nickel hydrogen, and the like, and the capacitor is selected from an electric double layer capacitor, an electrolytic capacitor, and the like. Moreover, you may make it mount both a battery and a capacitor.

  The air introduction pipe 41 constitutes the communication channel of this embodiment, and the air introduction valve 42 constitutes the communication valve of this embodiment. The purge valve 23 constitutes the purge control means of this embodiment. The drain valve 46 has a function of discharging moisture (product water) during normal operation, and also functions as a purge control means during scavenging.

  The control system 50 includes an ECU (Electronic Control Unit) 51, an ignition switch (IGSW) 52, a timer 53, a temperature sensor 54, a hydrogen concentration sensor 55, and the like.

  The ECU 51 includes a CPU (Central Processing Unit), a RAM, a ROM storing programs, various circuits, and the like, and includes scavenging means, oxidant gas supply amount calculating means, fuel gas concentration predicting means, and purge amount calculating means. Yes. The ECU 51 also includes a shutoff valve 22, a purge valve 23, an air compressor 31, a back pressure valve 32, an air introduction valve 42, an air discharge valve 44, a drain valve 46, an ignition switch 52, a timer 53, a temperature sensor 54, and a hydrogen concentration sensor. 55 is connected. Under the control of the ECU 51, the shut-off valve 22, the purge valve 23, the air introduction valve 42, the air discharge valve 44, and the drain valve 46 are opened and closed, the rotational speed of the motor of the air compressor 31 is controlled, and the back pressure valve 32 is opened. The degree is adjusted.

  The ignition switch 52 is switched between ignition off (IG-OFF) and ignition on (IG-ON) by the driver, and outputs an IG-OFF signal and an IG-ON signal to the ECU 51.

  The timer 53 detects an elapsed time (system stop time) after the IG-OFF and the power generation of the fuel cell 10 stop (system stop).

  The temperature sensor 54 is a state monitoring unit having a function of detecting the temperature of the fuel cell 10 (monitoring a state change). For example, the temperature sensor 54 is provided in the anode gas supply pipe 2 a near the inlet of the anode 12 of the fuel cell 10. Yes. The position of the temperature sensor 54 is not limited to the inlet of the anode 12 as long as the temperature of the fuel cell 10 can be detected. The anode offgas discharge pipe 2b near the outlet of the anode 12 and the vicinity of the inlet of the cathode 13 are not limited. The cathode gas supply pipe 3a, the cathode offgas discharge pipe 3b on the outlet side of the cathode 13, the pipe through which the cooling system refrigerant flows, or the temperature of the fuel cell 10 may be directly measured.

  The hydrogen concentration sensor 55 is provided in the anode offgas discharge pipe 2 b downstream of the anode 12 of the fuel cell 10 and has a function of detecting the hydrogen concentration in the anode system 20. The hydrogen concentration in the anode system 20 means the hydrogen concentration remaining in the anode gas supply pipe 2a, the anode offgas discharge pipe 2b, the anode flow path 14a, and the anode gas circulation pipe (not shown).

  Next, scavenging control in the fuel cell system 1 of the present embodiment will be described with reference to FIGS. 2 to 5 (refer to FIG. 1 as appropriate). During the operation of the fuel cell system 1, the shutoff valve 22 is opened, hydrogen is supplied from the high-pressure hydrogen tank 21 to the anode 12 of the fuel cell 10, and the air compressor 31 is driven to drive the cathode of the fuel cell 10. The air compressed and humidified at 13 is supplied, and power generation is performed in the fuel cell 10. The electric power generated by the fuel cell 10 is supplied to an auxiliary machine such as a travel motor (not shown) and the air compressor 31 and the power storage device 60 is charged.

  As shown in FIG. 2, when the ignition switch 52 is turned off (IG-OFF) by the driver, the ECU 51 determines the hydrogen concentration (initial value) in the anode system 20 by the hydrogen concentration sensor 55 in step S100. To do. In step S110, the ECU 51 stops the operation of the fuel cell system 1 (system stop). In this system stop, the shutoff valve 22 is closed to stop the supply of hydrogen to the anode 12, and the supply of power to the air compressor 31 is stopped to stop the supply of air to the cathode 13. 10 power generation is stopped.

  After the system is stopped, in step S120, the ECU 51 starts automatic monitoring of the temperature (system temperature) of the fuel cell 10 obtained from the temperature sensor 54. In step S130, the ECU 51 starts the timer 53 and starts the time (from the system stop). Automatic monitoring of (system downtime) starts. Note that the automatic monitoring of the system temperature and the system stop time is performed using, for example, electric power stored in a low voltage battery (not shown).

  In step S140, the ECU 51 determines whether or not the system temperature has become a predetermined value or less. In step S140, when the ECU 51 determines that the system temperature is not lower than the predetermined value (No), the ECU 51 returns to step S120 to continue the automatic monitoring of the system temperature and the system stop time, and the system temperature is lower than the predetermined value. If it is determined that there is (Yes), the process proceeds to step S150. The predetermined value of the system temperature is set to a temperature (for example, 5 ° C.) before the temperature drops and the water freezes.

  In step S150, the ECU 51 predicts the hydrogen concentration in the anode system 20 based on the system stop time. The means for predicting the hydrogen concentration is determined based on, for example, the map of FIG. Note that FIG. 3A is obtained in advance by experiments and the like, and as shown in the figure, the hydrogen concentration in the anode system 20 has the highest initial value and gradually decreases as the system shutdown time becomes longer. . Incidentally, the hydrogen concentration in the anode system 2 becomes lower as the system stop time becomes longer. This is because nitrogen contained in the air in the cathode 13 is transferred to the anode 12 through the electrolyte membrane 11 by so-called cross leak. This is because the hydrogen that permeates and the residual hydrogen in the anode 12 permeates to the cathode 13 through the electrolyte membrane 11. Note that step S150 corresponds to the processing performed by the fuel gas concentration prediction means in the present embodiment.

  In step S160, the ECU 51 determines the movement of the valve necessary for cathode priority scavenging. The required valve movement is the usage time (opening time) of the purge valve 23 and the drain valve 46 used during the cathode-weighted scavenging, and is determined based on the map of FIG. FIG. 3B is obtained in advance by experiments or the like, and is set so that the use time becomes shorter as the hydrogen concentration in the anode system 20 becomes lower. Note that step S160 corresponds to the processing performed by the purge amount calculation means in the present embodiment.

  In step S170, the ECU 51 calculates a scavenging time. Here, the scavenging time is the scavenging time of the first scavenging (cathode-weighted scavenging) for scavenging the cathode 13 of the fuel cell 10 and the scavenging time of the second scavenging (anode-weighted scavenging) for scavenging the anode 12. And the total time. Further, the scavenging time is determined based on the map of FIG. 3C, and is set to a shorter time as the system stop time from the power generation stop of the fuel cell 10 to the first scavenging (cathode priority scavenging) becomes longer. Is done. In addition, this step S170 corresponds to the process which the oxidizing agent gas supply amount calculation means in this embodiment implements.

  And in step S180, ECU51 implements scavenging based on the subflow shown in FIG. That is, in step S181 in FIG. 4, the ECU 51 starts the air compressor 31 using the electric power of the power storage device 60, and opens the air introduction valve 42, the purge valve 23, and the drain valve 46 in step S182. At this time, the opening degree of the back pressure valve 32 is set to a valve opening degree (for example, fully open) by the ECU 51 so that the cathode 13 side is preferentially scavenged. The timing of starting the air compressor 31 and opening the air introduction valve 42 may be simultaneous, or the air introduction valve 42 is started after the air compressor 31 is started first to increase the pressure on the cathode 13 side. May be opened. Further, the opening timing of the air introduction valve 42 and the opening timing of the purge valve 23 and the drain valve 46 may be simultaneous, or the purge valve 23 and the drain after the air introduction valve 42 is opened first. The valve 46 may be opened.

  As a result, the air from the air compressor 31 is introduced into the anode 12 of the fuel cell 10 via the air introduction pipe 41, so that hydrogen remaining on the anode 12 side is pushed out from the purge valve 23 and pushed out. Hydrogen is discharged to the diluter 35. Further, the hydrogen remaining on the anode 12 side is gradually pushed out from the drain valve 46, and the pushed-out hydrogen merges with the air flowing on the cathode 13 side and is diluted and then discharged toward the diluter 35. That is, in this scavenging process (first scavenging), scavenging is mainly performed on the cathode 13 side and residual hydrogen on the anode 12 side is diluted. Scavenging mainly on the cathode 13 side dilutes the hydrogen on the anode 12 side and discharges the generated water remaining in the cathode gas supply pipe 3a, cathode channel 15a, and cathode offgas discharge pipe 3b on the cathode 13 side. It is to be.

  In step S183, the ECU 51 determines whether or not the scavenging time calculated in step S170 (the scavenging time necessary for the first scavenging) has elapsed. In step S183, if the ECU 51 determines that the scavenging time has not elapsed (No), it repeats the process of step S183, and if it is determined that the scavenging time has elapsed (Yes), it proceeds to step S184. .

  In step S184, the ECU 51 opens the air discharge valve 44 while keeping the purge valve 23 and the drain valve 46 open. Note that the opening degree of the back pressure valve 32 at this time is set by the ECU 51 so that the anode 12 side is preferentially scavenged. Thereby, the air from the air compressor 31 flows through the air introduction pipe 41 to the anode gas supply pipe 2a, the anode flow path 14a, and the anode offgas discharge pipe 2b, and passes through the air discharge pipe 43 and the cathode offgas discharge pipe 3b. And discharged to the diluter 35. Thereby, produced water and the like are discharged together with the diluted hydrogen remaining on the anode 12 side.

  In step S185, the ECU 51 determines whether scavenging has been completed. The condition for the completion of the scavenging is determined based on the predetermined time (the scavenging time necessary for the second scavenging) calculated in step S170. However, it is preferable to make a determination within a range in which the power storage device 60 does not fall below a voltage value that can secure power necessary for the next startup or the like. In step S185, if the ECU 51 determines that scavenging has not been completed (No), the process of step S185 is repeated. If it is determined that scavenging has been completed (Yes), the process returns to the flow of FIG. In step S190, the automatic monitoring of the system temperature is stopped.

  Further description will be made with reference to the time charts of FIGS. FIG. 5 is a time chart in the case where the system stop time is short until the start of the cathode important scavenging (first scavenging) after the fuel cell 10 stops generating power, and FIG. 6 is a long system stop time. It is a time chart in the case.

  As shown in FIG. 5, after the power generation of the fuel cell 10 is stopped, the time during which the system temperature decreases to a predetermined value (time t2, Yes at S140) is early, that is, from when the ignition switch 52 is turned off (time t1). When the system stop time (time t1 to t2) is short, the hydrogen concentration in the anode system 20 can be predicted to be high at time t2 (S150). In this case, the valve opening time (T1 + T2 + T3 + T4) The movements of the purge valve 23 and the drain valve 46 are determined so as to be longer (S160). At time t2, the air compressor 31 is driven using the electric power of the power storage device 60, the air introduction valve 42 is opened, and the purge valve 23 and the drain valve 46 are intermittently opened. Incidentally, in the opening / closing control of the purge valve 23 and the drain valve 46, when it is considered that the hydrogen concentration discharged first is high, the first valve opening time T1 may be set short as shown in FIG. The predetermined interval (valve opening time) may be divided into a predetermined number of times. Thereby, the cathode 13 side is scavenged for a predetermined time Tc, and the hydrogen remaining on the anode 12 side is diluted.

  Then, after the end of the cathode important scavenging (time t3), the air introduction valve 42, the purge valve 23 and the drain valve 46 are kept open, and the air discharge valve 44 is opened using the electric power of the power storage device 60. Anode-focused scavenging is performed (time t3 to t4). In the anode important scavenging, Ta scavenging is performed for a predetermined time, and generated water and condensed water mainly remaining on the anode 12 side are discharged by the air introduced from the air introduction pipe 41.

  On the other hand, as shown in FIG. 6, after the power generation of the fuel cell 10 is stopped, the time during which the system temperature decreases to a predetermined value (time t2, Yes in S140) is long, that is, the ignition switch 52 is turned off (time t1). ) Is long (time t1 to t2), the hydrogen concentration in the anode system 20 can be predicted to be low at time t2 (S150). In this case, the valve opening time ( The movements of the purge valve 23 and the drain valve 46 are determined so that T5) becomes shorter (S160). At time t2, the air compressor 31 is driven using the electric power of the power storage device 60, the air introduction valve 42 is opened, and the purge valve 23 and the drain valve 46 are determined (opening time) ).

  As described above, in this embodiment, when the system stop time is short, the cathode-focused scavenging is performed with the purge valve 23 and the drain valve 46 opened for a long time (see FIG. 5), and the system stop time is long. In this case, the cathode intensive scavenging is performed with the purge valve 23 and the drain valve 46 open for a short time (see FIG. 6). Therefore, when the system stop time is long and the concentration of hydrogen remaining on the anode 12 side is low, the purge valve 23 and the drain valve 46 are not opened unnecessarily, so that power consumption can be reduced. .

  In addition, according to the present embodiment, as shown in FIG. 3C, the scavenging time, in particular, the predetermined time 1 in FIG. Since the predetermined time 2 can be shortened, the driving time of the air compressor 31 during the cathode-weighted scavenging can be shortened, and the power consumption by the air compressor 31 can be reduced. That is, when the system stop time is long, the hydrogen permeation amount from the anode 12 to the cathode 13 due to so-called cross leak is large, and when the system stop time is short, the hydrogen permeation amount from the anode 12 to the cathode 13 is small. I can judge. Therefore, when the system shutdown time is extended for a long time, the residual hydrogen concentration is reduced due to natural diffusion, so that it is possible to prevent the cathode-focused scavenging from being performed in an unnecessarily long time. Therefore, since the power supplied to the air compressor 31 can be reduced, the power consumption can be reduced.

  In this embodiment, the determination condition for scavenging completion (S183, S185) is based on time. However, the determination is not limited to time, and a flow rate sensor is provided downstream of the air compressor 31 so that the air You may judge based on flow volume.

It is a whole lineblock diagram showing the fuel cell system of this embodiment. It is a flowchart which shows the scavenging control after the system stop in this embodiment. (A) is a map showing the relationship between the system stop time and the hydrogen concentration in the anode system, (b) is a map showing the relationship between the hydrogen concentration in the anode system and the purge valve and drain valve usage time during cathode scavenging, (c) ) Is a map showing the relationship between the system stop time and the scavenging time. FIG. 3 is a sub-flowchart in a scavenging execution step of FIG. 2. It is a timing chart which shows the opening / closing operation | movement of various valves when the system stop time in this embodiment is short. It is a timing chart which shows the opening / closing operation | movement of various valves when the system stop time in this embodiment is long.

Explanation of symbols

1 Fuel cell system 2a Anode gas supply pipe (fuel gas flow passage)
2b Anode off-gas discharge pipe (fuel gas flow passage)
3a Cathode gas supply pipe (oxidant gas flow passage)
3b Cathode off-gas discharge pipe (oxidant gas flow passage)
12 Anode 13 Cathode 23 Purge valve 31 Air compressor 32 Back pressure valve 35 Diluter (Fuel exhaust gas dilution means)
41 Air introduction piping (communication flow path)
42 Air introduction valve (communication valve)
43 Air exhaust pipe 44 Air exhaust valve 45 Drain pipe 46 Drain valve 51 ECU (scavenging means, oxidant gas supply amount calculating means, fuel gas concentration predicting means, purge amount calculating means)
54 Temperature sensor (status monitoring means)
FC fuel cell

Claims (2)

A fuel cell that generates power by a reaction between a fuel gas supplied to the anode and an oxidant gas supplied to the cathode;
A fuel gas flow passage through which fuel gas flows through the anode;
An oxidant gas flow passage for flowing an oxidant gas to the cathode;
A communication flow path for communicating the fuel gas flow passage and the oxidant gas flow passage;
A communication valve for opening and closing the communication channel;
State monitoring means for monitoring a change in state of the fuel cell after power generation is stopped;
When the change in state becomes a predetermined condition after the power generation of the fuel cell is stopped, the communication valve is opened to perform a first scavenging to scavenge the cathode with the oxidant gas, and then the anode is scavenged. Scavenging means for performing second scavenging,
An oxidant gas supply amount calculating means for obtaining a supply amount of the oxidant gas required for the first scavenging and the second scavenging, and a fuel cell system comprising:
A fuel exhaust gas dilution means for diluting the fuel exhaust gas discharged from the anode with an oxidant gas and discharging it to the outside;
A purge control means for controlling a purge amount for purging the fuel exhaust gas from the anode to the fuel exhaust gas dilution means;
Fuel gas concentration predicting means for predicting the concentration of fuel gas from the anode based on a system stop time until the first scavenging after power generation stop of the fuel cell;
The purge amount purged by the purge control means during the first scavenging is smaller as the fuel gas concentration is lower based on the fuel gas concentration predicted by the fuel gas concentration prediction means. And a purge amount calculation means for calculating as a fuel cell system.   The oxidant gas supply amount calculation means is configured to reduce the supply amount of the oxidant gas as the system stop time is longer, based on the system stop time until the first scavenging after the fuel cell power generation is stopped. The fuel cell system according to claim 1, wherein the fuel cell system is set to be

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