JP2007059120A - Fuel battery system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To restrain polar changes, consume hydrogen, and restrain degradation of a fuel battery at stopping of a fuel battery system. <P>SOLUTION: In stopping the fuel battery system, supply of hydrogen from a hydrogen gas cylinder 4 to a fuel electrode 51 of the fuel battery 1 is stopped, and exhaust hydrogen is circulated by a circulation pump 6 to electrically connect the fuel battery 1 and an electric charge consumption means 21. Afterwards, when a minimum voltage VL of a unit cell 40 gets below a given voltage V1, a first control is carried out to cut down electric connection between the fuel battery 1 and the charge consumption means 21. Later, in case either of voltages of the unit cells 40 gets higher than a given voltage V2 after an elapse of a given time T1, a second control is carried out to electrically connect the fuel battery 1 and the charge consumption means 21. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fuel cell system, and more particularly to control when the fuel cell system is stopped.

Conventionally, when the fuel cell system is stopped, in order to suppress deterioration caused by the remaining hydrogen in the fuel electrode, a charge consuming means is connected to the fuel cell to perform a power generation reaction, and the hydrogen and oxygen remaining in the fuel cell In particular, Patent Document 1 discloses that consumes hydrogen in the fuel electrode.
JP 2004-139950 A

  In the above invention, when the voltage drop of each unit cell of the fuel cell is uniform, that is, when a uniform concentration of hydrogen is supplied to each unit cell, there is a difference in the voltage drop between the unit cells. Therefore, deterioration of the fuel cell can be suppressed without leaving hydrogen.

  However, if the hydrogen concentration in each unit cell is not uniform, there is a difference in voltage drop between the unit cells, and if there is a unit cell in which the voltage of the unit cell is less than 0 V and causes reversal, the charge consuming means In order to disconnect the electrical connection between the fuel cell and the fuel cell, there is a unit cell in which hydrogen remains, and deterioration of the fuel cell cannot be sufficiently suppressed.

  The present invention was invented to solve such problems, and an object thereof is to consume hydrogen remaining in a unit cell while suppressing inversion and suppress deterioration of a fuel cell.

  In the present invention, a fuel cell having a stack part in which unit cells each composed of a fuel electrode and an oxidant electrode sandwiching an electrolyte membrane are stacked, fuel gas supply means for supplying fuel gas to the fuel electrode, and discharge from the fuel electrode Gas circulation means for circulating the discharged fuel gas, voltage detection means for detecting the voltages of a plurality of unit cells, and charge consumption for consuming the fuel gas remaining in the fuel electrode when the fuel cell system is stopped Means, switching means for switching electrical connection between the fuel cell and the charge consuming means, and fuel cell system stop control means for controlling stop of the fuel cell system. When stopping the fuel cell system, after stopping the supply of the fuel gas from the fuel gas supply means to the fuel electrode, circulating the exhaust fuel gas, and electrically connecting the fuel cell and the charge consuming means, When the lowest voltage of the unit cells is lower than the first predetermined voltage, the first control is performed to disconnect the electrical connection between the fuel cell and the charge consuming means, and after a predetermined time has elapsed from the first control. Second control for electrically connecting the fuel cell and the charge consuming means when any one of the unit cell voltages becomes higher than a second predetermined voltage higher than the first predetermined voltage. And the first control is performed again.

  When stopping the fuel cell system, the supply of the fuel gas from the fuel gas supply means to the fuel electrode is stopped, the exhausted fuel gas is circulated, and the fuel cell and the charge consuming means are electrically connected. Later, when the minimum voltage of the unit cell becomes lower than the first predetermined voltage, the first control is performed to disconnect the electrical connection between the fuel cell and the charge consuming means, and after a predetermined time has elapsed from the first control, When the voltage of the unit cell having the lowest voltage becomes higher than the second predetermined voltage higher than the first predetermined voltage, the third control for electrically connecting the fuel cell and the charge consuming means is performed, and again The first control is performed.

  According to the present invention, when the fuel cell system is stopped, when the voltage of the unit cell becomes lower than the predetermined voltage V1, the electrical connection between the fuel cell and the charge consuming means is disconnected, and the fuel electrode of each unit cell is disconnected. Make the hydrogen concentration substantially uniform. Thereafter, when the voltage of the unit cell is higher than the predetermined voltage V2, the fuel cell and the charge consuming means are electrically connected again to consume the hydrogen remaining in the fuel cell. By repeating these steps, the hydrogen concentration in the unit cell can be kept substantially uniform, the reversal can be suppressed, and the hydrogen remaining in the fuel cell can be consumed. Therefore, deterioration of the fuel cell can be suppressed.

  The configuration of the fuel cell system according to the first embodiment of the present invention will be described with reference to FIG.

  The fuel cell system of this embodiment supplies air to the fuel cell 1, a hydrogen cylinder (fuel gas supply means) 4 that supplies hydrogen (fuel gas) to a fuel electrode 51 described later, and an oxidant electrode 52 described later. A compressor 5 and a circulation pump (fuel gas circulation means) 6 for circulating the discharged hydrogen discharged from the fuel electrode 51 to the fuel electrode are provided.

  The fuel cell 1 includes a stack unit 2 in which a plurality of unit cells 40 are stacked, and current collector plates 3 provided at both ends of the stack unit 2. The electric power generated by the fuel cell 1 is supplied to the outside by two current collecting plates 3.

  Further, when the hydrogen concentration in the discharged hydrogen is reduced and the hydrogen supply flow path 10 that connects the hydrogen cylinder 4 and the fuel electrode 51, the discharged hydrogen that has not been used for the power generation reaction of the fuel cell 1 is removed from the fuel cell system. A hydrogen discharge flow path 11 for discharging to the outside, a hydrogen discharge flow path 11 and a hydrogen supply flow path 10 are connected, and a hydrogen circulation flow path 12 having a circulation pump 6 in the middle thereof is provided.

  The hydrogen supply flow path 10 is provided with a flow rate control valve 13 for controlling the flow rate of hydrogen from the hydrogen cylinder 4, and the hydrogen discharge path 11 is provided with a flow rate control valve 14 for controlling the flow rate of discharged hydrogen.

  In addition, an air supply passage 15 that communicates between the compressor 5 and the oxidant electrode 52, and an air discharge passage 16 that discharges exhaust air that has not been used in the power generation reaction of the fuel cell 1 to the outside of the fuel cell system. Prepare.

  The air supply flow path 15 is provided with a flow control valve 17 that controls the flow rate of air supplied to the oxidant electrode 52, and the air discharge flow path 16 is provided with a flow control valve 18 that controls the flow rate of exhaust air.

  Furthermore, a voltage sensor (voltage detection means) 20 that detects the voltage of each unit cell 40 of the fuel cell 1 is provided. In addition, a charge consuming means 21 for consuming hydrogen or oxygen remaining in the fuel electrode 51 and the oxidant electrode 52 when the fuel cell system is stopped is provided. The electric charge consuming means 21 can be switched in electrical connection with the fuel cell 1 by a switch (switching means) 22. In addition, the voltage sensor 20 describes one voltage sensor 20 for description in FIG. The voltage sensor 20 is preferably provided in each unit cell 40, and is provided in at least the unit cells 40 located at both ends of the stack unit 2.

  The charge consuming means 21 is, for example, a resistor, and consumes hydrogen remaining in the fuel cell 1 and oxygen in the air. A secondary battery may be used for the charge consuming means 21.

  When the fuel cell system is stopped, the flow control valves 13, 14, 17, and 18 are controlled to open and close, the compressor 5 and the circulation pump 6 are controlled, and the fuel cell 1 and the charge consuming means 21 are electrically connected by the switch 22. A controller (fuel cell system stop control means) 30 for switching the connection is provided.

  Here, the unit cell 40 will be described with reference to the schematic configuration diagram of FIG.

  The unit cell 40 includes a solid polymer electrolyte membrane (hereinafter referred to as an electrolyte membrane) 41, an anode catalyst layer 42 and a cathode catalyst layer 43 that sandwich the electrolyte membrane 41, and anode gas diffusion provided outside the anode catalyst layer 42. A layer 44 and a cathode gas diffusion layer 45 provided outside the cathode catalyst layer 43. Further, an anode separator 47 provided outside the anode gas diffusion layer 44 and having a hydrogen channel 46 and a cathode separator 49 provided outside the cathode gas diffusion layer 45 and having an air channel 48 are provided. Further, an edge seal 50 is provided so that hydrogen or air does not leak. Although not shown, a cooling water flow path through which cooling water for cooling the unit cell 40 may be provided. In addition, the voltage sensor 20 is provided between the anode separator 47 and the cathode separator 49.

  Here, the anode catalyst layer 42 and the anode gas diffusion layer 44 are the fuel electrode 51, and the cathode catalyst layer 43 and the cathode gas diffusion layer 45 are the oxidant electrode 52.

  The electrolyte membrane 41 is a polymer electrolyte membrane such as perfluorosulfonic acid such as Nafion (registered trademark) manufactured by DuPont.

  The anode catalyst layer 42 and the cathode catalyst layer 43 are carbon black carrying platinum as a catalyst. The catalyst is not limited to platinum.

  For the anode gas diffusion layer 44 and the cathode gas diffusion layer 45, for example, carbon paper or carbon cloth is used.

  With the above configuration, when the fuel cell system is stopped, the concentration of hydrogen and oxygen in the air in each unit cell 40 is made uniform, the amount of hydrogen and oxygen remaining in the unit cell 40 is reduced, and deterioration of the fuel cell 1 is suppressed. be able to.

  Next, stop control of the fuel cell system performed by the controller 30 will be described using the flowchart of FIG.

  In step S100, when the stop signal of the fuel cell system is received, the compressor 5 is stopped and the flow control valves 13, 14, 17, and 18 are fully closed. As a result, the supply of new hydrogen from the hydrogen cylinder 4 to the fuel electrode 51 is stopped, and the supply of new air from the compressor 5 to the oxidant electrode 52 is stopped. Further, the communication between the fuel electrode 51 or the oxidant electrode 52 and the outside of the fuel cell system 1 is blocked. The circulation pump 6 is continuously operated, and only the discharged hydrogen is circulated to the fuel electrode 51.

  In step S101, the switch 22 is turned ON to electrically connect the fuel cell 1 and the charge consuming means 21. As a result, the hydrogen and oxygen remaining in the unit cell 40 are consumed.

  In step S102, the voltage of each unit cell 40 is detected by the voltage sensor 20, and the lowest voltage VL of the unit cell 40 having the lowest voltage among the detected voltages is compared with a predetermined voltage (first predetermined voltage) V1. When the lowest voltage VL becomes lower than the predetermined voltage V1, the process proceeds to step S103. In this embodiment, the predetermined voltage V1 is 0V <V1 ≦ 0.2V. Details of the predetermined voltage V1 will be described later.

  In step S103, the switch 22 is turned OFF, and the electrical connection between the fuel cell 1 and the charge consuming means 21 is cut off. That is, the power generation reaction in the fuel cell 1 is stopped, and the exhaust hydrogen is circulated to the fuel electrode 51 by the circulation pump 6. When the switch 22 is turned off, no hydrogen is consumed at the fuel electrode 51, and the exhaust hydrogen is circulated by the circulation pump 6. Therefore, when the hydrogen concentration in the fuel electrode 51 of each unit cell 40 varies, The hydrogen concentration in the fuel electrode 51 becomes substantially uniform. Therefore, in the unit cell 40 having a low hydrogen concentration among the unit cells 40, the voltage of the unit cell 40 increases (steps S102 and 103 constitute the first control).

  In step S102 and step S103, when the minimum voltage VL of the unit cell 40 becomes smaller than the predetermined voltage V1, the switch 22 is turned OFF and the power generation reaction is stopped in the fuel cell 1. Then, by circulating the discharged hydrogen to the fuel electrode 51 by the circulation pump 6, the hydrogen concentration of the fuel electrode 51 can be made substantially uniform, and the unit cell 40 can prevent inversion due to hydrogen shortage. Therefore, deterioration of the unit cell 40 can be suppressed.

  In step S104, the voltage V of each unit cell 40 is detected by the voltage sensor 20 after a lapse of a predetermined time T1 since the switch 22 is turned OFF, and the voltage V and the predetermined voltage (second predetermined voltage) V2 of all the unit cells 40 are detected. Compare If the voltage V of all the unit cells 40 is V ≦ V2, the process proceeds to step S105. If the voltage V of any one unit cell 40 is not V ≦ V2, the process returns to step S102. The above control is repeated. The predetermined voltage V2 is a voltage that satisfies V2 = V1 + 0.1V. The predetermined time T1 is a time obtained in advance through experiments or the like. In this embodiment, the predetermined time T1 is set to 100 ms (steps S104 and S101 constitute the second control).

  In step S105, the switch 22 is turned ON to electrically connect the fuel cell 1 and the charge consuming means 21 to consume hydrogen remaining in the fuel cell 1 and oxygen in the air. Here, since the voltages V of all the unit cells 40 satisfy V ≦ V2, the difference in the hydrogen concentration at the fuel electrode 51 of each unit cell 40 is small, and the hydrogen remaining in the fuel electrode 51 is also small. Therefore, since there is a low possibility that the unit cell 40 will cause inversion, the fuel cell 1 and the charge consuming means 21 are electrically connected to further consume the hydrogen remaining in the fuel cell 1 to operate the fuel cell system. Stop control ends.

  With the above control, when the minimum voltage VL of the unit cell 40 detected by the voltage sensor 20 when the fuel cell system is stopped is lower than the predetermined voltage V1, the electrical connection between the fuel cell 1 and the charge consuming means 21 is achieved. The connection is disconnected, and the exhaust hydrogen is circulated to the fuel electrode 51 by the circulation pump 6. Thereby, the hydrogen concentration of the unit cell 40 can be made substantially uniform, and deterioration due to the reversal of the unit cell 40 is suppressed. Further, when all the voltages V of the unit cell 40 become lower than the predetermined voltage V2 after the predetermined time T1 has elapsed, that is, when the hydrogen remaining in the fuel electrode 51 is sufficiently reduced, the fuel cell 1 and the charge consuming means 21 are electrically connected. , The hydrogen remaining in the fuel electrode 51 is consumed, and the stop control of the fuel cell system is terminated. Thereby, deterioration of the unit cell 40 due to inversion is suppressed, and hydrogen is consumed in the fuel electrode 51, whereby deterioration of the fuel cell 1 can be suppressed.

  Next, the voltage change of the unit cell 40 when the controller 30 performs stop control of the fuel cell system will be described with reference to the time chart of FIG. In FIG. 4, the voltage of the unit cell 40 having the lowest voltage among the unit cells 40 is indicated by a solid line, and the voltages of the other unit cells 40 are indicated by broken lines.

  When stop control of the fuel cell system is started at time t0, supply of new hydrogen from the hydrogen cylinder 4 to the fuel electrode 51 is stopped, and supply of new air to the oxidant electrode 52 by the compressor 5 is stopped. (Step S100). Further, the switch 22 is turned on to electrically connect the fuel cell 1 and the charge consuming means 21 to consume hydrogen remaining in the fuel cell 1 and oxygen in the air (step S101). As a result, the voltage V of the unit cell 40 gradually decreases.

  When the lowest voltage VL of the unit cell 40 having the lowest voltage reaches the predetermined voltage V1 at time t1, the switch 22 is turned off to disconnect the electrical connection between the fuel cell 1 and the charge consuming means 21 (steps S102 and S103). . At this time, the discharged hydrogen discharged from the fuel electrode 51 by the circulation pump 6 circulates, and the power generation reaction is not performed in the fuel cell 1, so that the hydrogen concentration of the fuel electrode 51 of each unit cell 40 becomes substantially uniform. Therefore, the voltage of the unit cell 40 that has the lowest minimum voltage VL among the voltages V of the unit cell 40 is increased.

  At time t2 when the predetermined time T1 has elapsed from time t1, the voltage V of all the unit cells 40 satisfies the condition of V ≦ V2, and the amount of hydrogen remaining in the fuel cell 1 has decreased. As a result, the fuel cell 1 and the charge consuming means 21 are electrically connected to complete the stop control of the fuel cell system (steps S104 and S105).

  Further, a change in the voltage of the unit cell 40 when the controller 30 performs the stop control of the fuel cell system will be described with reference to the time chart of FIG. FIG. 5 shows a voltage change in the case where any one of the voltages V of the unit cell 40 does not satisfy V ≦ V2 in step S104. Also in FIG. 5, the voltage of the unit cell 40 having the lowest voltage among the unit cells 40 is indicated by a solid line, and the voltages of the other unit cells 40 are indicated by broken lines.

  When stop control of the fuel cell system is started at time t0, supply of new hydrogen from the hydrogen cylinder 4 to the fuel electrode 51 is stopped, and supply of new air to the oxidant electrode 52 by the compressor 5 is stopped. (Step S100). Further, the switch 22 is turned on to electrically connect the fuel cell 1 and the charge consuming means 21 to consume hydrogen remaining in the fuel cell 1 and oxygen in the air (step S101). As a result, the voltage of the unit cell 40 gradually decreases.

  At time t1, when the lowest minimum voltage VL among the voltages V of the unit cell 40 becomes the predetermined voltage V1 (step S102), the switch 22 is turned off to electrically connect the fuel cell 1 and the charge consuming means 21. Disconnect (step S103). At this time, the hydrogen discharged from the fuel electrode 51 is circulated by the circulation pump 6 and no power generation reaction is performed in the fuel cell 1, so in the gas containing hydrogen supplied to the fuel electrode 51 of each unit cell 40. The difference in hydrogen concentration between the two becomes smaller.

  However, when the hydrogen concentration of the fuel electrode 51 varies widely, any of the voltages V of the unit cell 40 may not satisfy the condition of V ≦ V2 at the time t2 when the predetermined time T1 has elapsed from the time t1. . That is, there may be a relatively large amount of hydrogen remaining in the fuel cell 1 (step S104). In this case, in order to prevent inversion in the unit cell 40, the switch 22 is turned on to consume the hydrogen remaining in the fuel cell 1 again (step S101).

  At time t3, when the minimum voltage VL becomes equal to or lower than the predetermined voltage V1 similarly to time t1, the switch 22 is turned off (steps S102 and 103).

  If the voltage V of all the unit cells 40 satisfies the condition of V ≦ V2 at the time t4 when the predetermined time T1 has elapsed from the time t3, the fuel cell system stop control is terminated (steps S104 and S105).

  As described above, when the minimum voltage VL of the unit cell 40 becomes equal to or lower than the predetermined voltage V1 during the stop control of the fuel cell system, the electrical connection between the fuel cell 1 and the charge consuming means 21 is disconnected, and after a predetermined time T1 has elapsed. When the voltage V of all the unit cells 40 satisfies the condition of V ≦ V2, the stop control of the fuel cell system is finished. As a result, inversion by the unit cell 40 is prevented and hydrogen remaining in the fuel cell 1 is consumed, so that deterioration of the fuel cell 1 can be suppressed.

  Here, the relationship between the hydrogen concentration in the gas supplied to the fuel electrode 51 of the unit cell 40, the voltage V of the unit cell 40, and the degree of deterioration of the unit cell 40 when the fuel cell system is stopped is shown in FIG. Show.

  According to FIG. 6, when the hydrogen concentration in the gas supplied to the fuel electrode 51 becomes low, the voltage V of the unit cell 40 becomes low. That is, by detecting the voltage of the unit cell 40, the hydrogen concentration in the gas of the fuel electrode 51 can be estimated. In addition, when the hydrogen concentration in the gas supplied to the fuel electrode 51 is lower than about 30%, the rate of deterioration of the unit cell 40 when the fuel cell system is stopped decreases. In this embodiment, the voltage V of the unit cell 40 that changes corresponding to the hydrogen concentration of the unit cell 40 is detected, and the stop control of the fuel cell system is performed based on the voltage V of the unit cell 40, whereby the fuel cell 1. Suppresses deterioration.

  In FIG. 6, when the voltage V of the unit cell 40 is 0.3 V or less, the deterioration of the unit cell 40 is small. In this embodiment, the fuel cell 1 and the charge consuming means 21 are electrically connected to quickly consume the hydrogen remaining in the fuel electrode 51 and suppress the deterioration of the fuel cell 1. Therefore, the predetermined voltage V1 is set to 0 <V1 ≦ 0.2V. Further, it is desirable that the predetermined voltage V2 be 0.3 V or less, and in this embodiment, the predetermined voltage V2 = V1 + 0.1V. The predetermined voltage V2 may be 0.4V. Even if the predetermined voltage V2 is set to 0.4V, deterioration of the fuel cell 1 can be relatively suppressed.

  In addition, as shown in FIG. 10, exhaust air discharged from the oxidant electrode 52 may be circulated by the air circulation pump 60, and the exhaust air may be circulated to the oxidant electrode 52 during stop control of the fuel cell system. Further, stop control of the fuel cell system may be performed by supplying air to the oxidant electrode 52.

  The effect of 1st Embodiment of this invention is demonstrated.

  In this embodiment, when the fuel cell system is stopped, the supply of hydrogen from the hydrogen cylinder 4 to the fuel electrode 51 is stopped and the exhaust hydrogen is circulated by the circulation pump 6, and then the minimum voltage V of the unit cell 40 is reached. When VL becomes lower than the predetermined voltage V1, the switch 22 disconnects the electrical connection between the fuel cell 1 and the charge consuming means 21. Then, when any one of the voltages V of the unit cell 40 is higher than the predetermined voltage V2 after the predetermined time T1 has elapsed, the fuel cell 1 and the charge consuming means 21 are electrically connected by the switch 22 and the fuel electrode The hydrogen remaining in 51 is consumed. Thereafter, the minimum voltage VL is compared with the predetermined voltage V1 again. By repeating this control, the hydrogen remaining in the fuel electrode 51 can be consumed while the hydrogen concentration in the fuel electrode 51 is kept substantially uniform. In addition, inversion of the unit cell 40 caused by variation in the hydrogen concentration of the fuel electrode 51 can be prevented, and deterioration of the unit cell 40 due to inversion can be suppressed.

  When all the voltages V of the unit cells 40 are equal to or lower than the predetermined voltage V2, the fuel cell 1 and the charge consuming means 21 are electrically connected by the switch 22, and the stop control of the fuel cell system is terminated. When all the voltages V of the unit cells 40 are equal to or lower than the predetermined voltage V2, the variation in the hydrogen concentration of the fuel electrode 51 is small, and the hydrogen remaining in the fuel electrode 51 is sufficiently consumed, so that inversion is difficult to occur. Therefore, deterioration of the unit cell 40 can be suppressed and the fuel cell system can be stopped.

  Next, a second embodiment of the present invention will be described. Since the configuration of the fuel cell system of this embodiment is the same as that of the first embodiment, description thereof is omitted here.

  In this embodiment, the stop control of the fuel cell system is different, and the stop control of the fuel cell system will be described with reference to the flowchart of FIG.

  Since the control from step S200 to step S203 is the same as the control from step S100 to step S103 of the first embodiment, description thereof is omitted here.

  After the elapse of the predetermined time T1 from the control in step S203, in step S204, the voltage V of the unit cell 40 that has become the lowest voltage VL in step S202 is detected again by the voltage sensor 20, and the voltage V is compared with the predetermined voltage V2. Then, it is determined whether or not the voltage V is V ≦ V2. If the voltage V is V ≦ V2, the process proceeds to step S205. If V2 <V, the process returns to step S201 and the above control is repeated (steps S204 and S201 perform the third control). Constitute).

  In step S203, the switch 22 is turned OFF, and the gas containing hydrogen is circulated to the fuel electrode 51 by the circulation pump 6, so that the hydrogen concentration in each unit cell 40 becomes substantially uniform. At this time, since the hydrogen concentration in the unit cell 40 that has reached the minimum voltage VL in step S204 becomes high, the voltage of the unit cell 40 that has reached the minimum voltage VL increases. In step S204, if the voltage V of the unit cell 40 that has reached the lowest voltage VL becomes greater than the predetermined voltage V2 after the elapse of the predetermined time T1, it is determined that a large amount of hydrogen remains in the entire fuel cell 1, and step S204 is performed. Returning to S201, the charge consuming means 21 consumes the hydrogen remaining in the fuel cell 1 again.

  As described above, when the voltage V of the unit cell 40 that has reached the minimum voltage VL after the elapse of the predetermined time T1 becomes higher than the predetermined voltage V2, the hydrogen remaining in the fuel cell 1 by the charge consuming means 21 is unitized. It is possible to suppress the deterioration of the fuel cell 1 by consuming so that no reversal occurs in the cell 40.

  In step S205, the voltage change amount dV of the unit cell 40 that has become the lowest voltage VL in step S202 is calculated. If dV> 0, that is, if the voltage of the unit cell 40 is increased, the voltage V is then increased. Since there is a possibility that the voltage is higher than the predetermined voltage V2, the process returns to step S204 and the above control is repeated. If dV ≦ 0, that is, if the voltage of the unit cell 40 has not increased, the process proceeds to step S206.

  In step S206, the switch 22 is turned on to electrically connect the fuel cell 1 and the charge consuming means 21, and the hydrogen and oxygen remaining in the fuel cell 1 are consumed. Here, since the voltage V of the unit cell 40 that has reached the minimum voltage VL in step S202 satisfies V ≦ V2, and the voltage V has not increased, the amount of hydrogen remaining in the fuel cell 1 is small. For this reason, since there is a low possibility of occurrence of inversion in the unit cell 40, the fuel cell 1 and the charge consuming means 21 are electrically connected to further consume hydrogen remaining in the fuel cell 1 and stop the fuel cell system. End control.

  With the above control, when the minimum voltage VL of the unit cell 40 detected by the voltage sensor 20 when the fuel cell system is stopped is lower than the predetermined voltage V1, the electrical connection between the fuel cell 1 and the charge consuming means 21 is achieved. The connection is disconnected, and the exhaust hydrogen is circulated to the fuel electrode 51 by the circulation pump 6. Thereby, the hydrogen concentration of the unit cell 40 can be made substantially uniform, and deterioration due to the reversal of the unit cell 40 is suppressed. Further, when the voltage V of the unit cell 40 that has become the minimum voltage VL becomes equal to or lower than the predetermined voltage V2 after the predetermined time T1 has elapsed, and the voltage increase dV becomes equal to or lower than zero, the fuel cell 1 and the charge consuming means 21 are electrically , The hydrogen remaining in the fuel electrode 51 is consumed, and the stop control of the fuel cell system is terminated. Thereby, deterioration of the unit cell 40 due to inversion is suppressed, and hydrogen is consumed in the fuel electrode 51, whereby deterioration of the fuel cell 1 can be suppressed.

  Next, the voltage change of the unit cell 40 when the controller 30 performs stop control of the fuel cell system will be described with reference to the time chart of FIG. FIG. 8 shows the voltage change of the unit cell 40 having the lowest voltage among the unit cells 40.

  When the stop control of the fuel cell system is started at time t0, supply of new hydrogen from the hydrogen cylinder 3 to the fuel electrode 51 is stopped, and supply of new air to the oxidant electrode 52 by the compressor 4 is stopped. (Step S200). Further, the switch 22 is turned on to electrically connect the fuel cell 1 and the charge consuming means 21 to consume the hydrogen remaining in the fuel cell 1 and the oxygen in the air (step S201). As a result, the voltage of the unit cell 40 gradually decreases.

  At time t1, when the lowest minimum voltage VL among the voltages V of the unit cell 40 becomes the predetermined voltage V1 (step S202), the switch 22 is turned off to electrically connect the fuel cell 1 and the charge consuming means 21. Disconnect (step S203). At this time, the discharged hydrogen discharged from the fuel electrode 51 by the circulation pump 6 circulates, and the power generation reaction is not performed in the fuel cell 1, so that the hydrogen concentration of the fuel electrode 51 of each unit cell 40 becomes substantially uniform. Therefore, the voltage of the unit cell 40 that has the lowest minimum voltage VL among the voltages V of the unit cell 40 is increased.

  Then, at time t2 when the predetermined time T1 has elapsed from time t1, the voltage V of the unit cell 40 that has reached the lowest voltage VL becomes V ≦ V2 (step S204), and when the voltage increase dV becomes dV ≦ 0 (step S204). In step S205, the switch 22 is turned on to electrically connect the fuel cell 1 and the charge consuming means 21 to end the stop control of the fuel cell system (step S206).

  Next, the voltage change when it is determined once in step S204 that V2 <V will be described with reference to the time chart of FIG. FIG. 9 shows the voltage change of the unit cell 40 having the lowest voltage among the unit cells 40.

  Since the voltage change from time t0 to time t1 is the same as that in the time chart shown in FIG. 8, the description thereof is omitted here.

  At time t2 when the predetermined time T1 has elapsed from time t1, if the voltage V of the unit cell 40 that has reached the lowest voltage VL is V> V2 (step S204), the switch 22 is turned ON and the fuel cell 1 and the charge consuming means 21 And hydrogen remaining in the fuel cell 1 is consumed (step S201). As a result, the voltage of the unit cell 40 is lowered.

  At time t3, the voltage of the unit cell 40 that has become the lowest voltage VL is detected again. When the voltage V becomes lower than the predetermined voltage V1 (step S202), the switch 22 is turned off and the fuel cell 1 and the charge consuming means 21 are turned off. The electrical connection is disconnected (step S203).

  At time t4 when the predetermined time T1 has elapsed from time t3, the voltage V of the unit cell 40 that has reached the minimum voltage VL becomes V ≦ V2 (step S204), and further, the voltage increase dV becomes dV ≦ 0 (step S205). Then, the switch 22 is turned on to electrically connect the fuel cell 1 and the charge consuming means 21 to end the stop control of the fuel cell system (step S206).

  As described above, when the lowest minimum voltage VL of the unit cells 40 becomes equal to or lower than the predetermined voltage V1 during the stop control of the fuel cell system, the electrical connection between the fuel cell 1 and the charge consuming means 21 is cut off for a predetermined time. When the voltage V of the unit cell 40 that has reached the lowest voltage VL after T1 is V ≦ V2, and the voltage increase dV satisfies the condition of dV ≦ 0, the stop control of the fuel cell system is terminated. As a result, inversion by the unit cell 40 is prevented and hydrogen remaining in the fuel cell 1 is consumed, so that deterioration of the fuel cell 1 can be suppressed.

  The effect of 2nd Embodiment of this invention is demonstrated.

  In this embodiment, when the fuel cell system is stopped, the supply of hydrogen from the hydrogen cylinder 4 to the fuel electrode 51 is stopped and the discharged hydrogen is circulated by the circulation pump 6, and then the voltage V of the unit cell 40 is When the lowest voltage VL becomes lower than the predetermined voltage V1, the switch 22 disconnects the electrical connection between the fuel cell 1 and the charge consuming means 21. When the voltage V of the unit cell 40 that has reached the minimum voltage VL is greater than the predetermined voltage V2 after the predetermined time T1 has elapsed, the fuel cell 1 and the charge consuming means 21 are electrically connected by the switch 22; The hydrogen remaining in the fuel cell 51 is consumed. Thereafter, the minimum voltage VL is compared with the predetermined voltage V1 again. By repeating this control, the hydrogen remaining in the fuel electrode 51 can be consumed while the hydrogen concentration in the fuel electrode 51 is kept substantially uniform. In addition, inversion of the unit cell 40 caused by variation in the hydrogen concentration of the fuel electrode 51 can be prevented, and deterioration of the unit cell 40 due to inversion can be suppressed.

  When the voltage V of the unit cell 40 that has reached the minimum voltage VL becomes equal to or lower than the predetermined voltage V2 and the voltage increase dV becomes equal to or lower than zero, the fuel cell 1 and the charge consuming means 21 are electrically connected by the switch 22 to The stop control of the battery system is terminated. When the voltage V becomes the predetermined voltage V2 or less and the voltage increase dV becomes zero or less, the variation in the hydrogen concentration in the fuel electrode 51 is small, and the hydrogen remaining in the fuel electrode 51 is sufficiently consumed. It becomes difficult to occur. Therefore, deterioration of the unit cell 40 can be suppressed and the fuel cell system can be stopped.

  It goes without saying that the present invention is not limited to the above-described embodiments, and includes various modifications and improvements that can be made within the scope of the technical idea.

  The fuel cell system can be used for a fuel cell vehicle having a large number of times of starting and stopping.

1 is a schematic configuration diagram of a fuel cell system according to a first embodiment of the present invention. It is a schematic block diagram of the unit cell of 1st Embodiment of this invention. It is a flowchart which shows stop control of the fuel cell system of 1st Embodiment of this invention. It is a time chart which shows the voltage change of the unit cell of 1st Embodiment of this invention. It is a time chart which shows the voltage change of the unit cell of 1st Embodiment of this invention. It is a figure which shows the relationship between the hydrogen concentration and voltage in the unit cell of 1st Embodiment of this invention, or the relationship between hydrogen concentration and the deterioration degree of a unit cell. It is a flowchart which shows stop control of the fuel cell system of 2nd Embodiment of this invention. It is a time chart which shows the voltage change of the unit cell of 2nd Embodiment of this invention. It is a time chart which shows the voltage change of the unit cell of 2nd Embodiment of this invention. It is a schematic block diagram which shows the example of a change of the fuel cell system in 1st Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel cell 2 Stack part 4 Hydrogen cylinder (fuel gas supply means)
5 Compressor 6 Circulation pump (fuel gas circulation means)
20 Voltage sensor (voltage detection means)
22 Switch (switching means)
30 controller (fuel cell system stop control means)
40 unit cell 41 polymer electrolyte membrane (electrolyte membrane)
51 Fuel electrode 52 Oxidant electrode

Claims (8)

A fuel cell having a stack portion in which unit cells composed of a fuel electrode and an oxidant electrode sandwiching an electrolyte membrane are stacked;
Fuel gas supply means for supplying fuel gas to the fuel electrode;
Fuel gas circulation means for circulating the exhaust fuel gas discharged from the fuel electrode;
Voltage detecting means for detecting voltages of the plurality of unit cells;
Charge consuming means for consuming the fuel gas remaining in the fuel electrode when stopping the fuel cell system;
Switching means for switching electrical connection between the fuel cell and the charge consuming means;
Fuel cell system stop control means for performing stop control of the fuel cell system,
The fuel cell system stop control means includes
After stopping the supply of the fuel gas from the fuel gas supply means to the fuel electrode, circulating the exhaust fuel gas, and electrically connecting the fuel cell and the charge consuming means,
First control for disconnecting the electrical connection between the fuel cell and the charge consuming means when the lowest voltage of the plurality of unit cells detected by the voltage detecting means is lower than a first predetermined voltage. And
When any one of the voltages of the unit cells becomes higher than a second predetermined voltage higher than the first predetermined voltage after a predetermined time has elapsed from the first control, the fuel cell and the Performing a second control to electrically connect the charge consuming means,
Thereafter, the first control is performed again. The fuel cell system stop control means includes
When all the voltages of the unit cells are lower than the second predetermined voltage after a predetermined time has elapsed from the first control, the fuel cell and the charge consuming means are electrically connected,
The fuel cell system according to claim 1, wherein stop control of the fuel cell system is terminated. A fuel cell having a stack portion in which unit cells composed of a fuel electrode and an oxidant electrode sandwiching an electrolyte membrane are stacked;
Fuel gas supply means for supplying fuel gas to the fuel electrode;
Fuel gas circulation means for circulating the exhaust fuel gas discharged from the fuel electrode;
Voltage detecting means for detecting voltages of the plurality of unit cells;
Charge consuming means for consuming the fuel gas remaining in the fuel electrode when stopping the fuel cell system;
Switching means for switching electrical connection between the fuel cell and the charge consuming means;
Fuel cell system stop control means for performing stop control of the fuel cell system,
The fuel cell system stop control means includes
After stopping the supply of the fuel gas from the fuel gas supply means to the fuel electrode, circulating the exhaust fuel gas, and electrically connecting the fuel cell and the charge consuming means,
Performing a first control to disconnect an electrical connection between the fuel cell and the charge consuming means when a minimum voltage of the plurality of unit cells is lower than a first predetermined voltage;
The fuel cell and the charge consuming means when the voltage of the unit cell that has become the lowest voltage becomes higher than a second predetermined voltage higher than the first predetermined voltage after a predetermined time has elapsed since the first control. And third control to electrically connect
Thereafter, the first control is performed again. The fuel cell system stop control means includes
The fuel cell when the voltage of the unit cell that has reached the lowest voltage is lower than the second predetermined voltage after a predetermined time has elapsed from the first control, and the voltage increase amount of the unit cell is less than or equal to zero. And the electric charge consuming means are electrically connected,
The fuel cell system according to claim 3, wherein the stop control of the fuel cell system is terminated.   5. The fuel cell system according to claim 1, wherein the voltage detection unit is provided in the unit cells located at both ends of the stack.   The fuel cell system according to any one of claims 1 to 4, wherein the first predetermined voltage is 0 V or more and 0.2 V or less.   The fuel cell system according to claim 6, wherein the second predetermined voltage is 0.1 V greater than the first predetermined voltage.   The fuel cell system according to claim 6, wherein the second predetermined voltage is 0.4 V or less.

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