JP2011048922A - Fuel cell system, and operation stop method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To surely prevent an exhaust valve mechanism which exhausts fluid in a fuel gas passage outside a fuel cell from freezing in a simple structure and a process, and to possibly prevent a fuel cell stack from being damaged at the next starting at a temperature under the freezing point. <P>SOLUTION: A fuel cell system 10 is equipped with the fuel cell stack 12 generating power by electrochemical reaction of air and hydrogen gas, a purge valve 44 exhausting the fluid in a hydrogen passage 22 outside the fuel cell stack 12, and a controller 18. The controller 18 is equipped with a freezing determination part 58 which determines beforehand whether a purge line 40 including the purge valve 44 periodically controlled after stopping the fuel gas stack 12 is in a state of freezing or not. When determination of freezing is made by the freezing determination portion 58 after a stop command of the fuel cell stack 12, operation of the fuel cell stack 12 is made to continue until determination of non-freezing is made by the freezing determination portion 58. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a fuel cell that generates electric power by an electrochemical reaction between a fuel gas supplied to a fuel gas flow channel and an oxidant gas supplied to an oxidant gas flow channel, and a fluid in the fuel gas flow channel The present invention relates to a fuel cell system including a discharge valve mechanism that discharges to the outside of a battery, and a control mechanism that periodically controls the discharge valve mechanism after the fuel cell is stopped, and an operation stop method thereof.

  A fuel cell supplies direct current electricity by supplying a fuel gas (mainly containing hydrogen) and an oxidant gas (mainly containing oxygen) to an anode electrode and a cathode electrode to cause an electrochemical reaction. It is a system for obtaining energy.

  For example, a polymer electrolyte fuel cell has a power generation cell in which an electrolyte membrane / electrode structure (MEA) provided with an anode electrode and a cathode electrode on both sides of an electrolyte membrane made of a polymer ion exchange membrane is sandwiched by separators. I have. This type of power generation cell is normally configured as a fuel cell stack by alternately stacking a predetermined number of electrolyte membrane / electrode structures and separators, and is used, for example, in a vehicle.

  In this type of fuel cell stack, warm-up processing is usually performed at low temperature startup. For example, in the fuel cell system disclosed in Patent Document 1, warm-up power generation is continued when the temperature of the fuel cell stack is equal to or higher than a first predetermined temperature and the temperature increase rate of the fuel cell stack is lower than a predetermined threshold. Thereafter, the warm-up power generation is terminated when it is detected that the temperature rise rate of the fuel cell stack has become larger than a predetermined threshold value.

  Thereby, the warm-up power generation of the fuel cell stack is performed at the start-up, and at the timing at which partial freezing does not remain inside the fuel cell stack based on the change in the temperature rise rate of the fuel cell stack. The warm-up power generation can be terminated.

JP 2007-122911 A

  Generally, in a fuel cell stack, water generated during power generation is discharged from the fuel cell stack to a purge line (scavenging line) or a drain line, so that the water remains in the purge line or the drain line. Easy to do.

  Therefore, in Patent Document 1 described above, when the fuel cell stack is soaked (leaned) particularly at a freezing point, a purge line or a drain line is started at the start of RTC (Real Time Clock) scavenging periodically performed during the soak. May freeze.

  At this time, if the purge line freezes, there is a problem that power generation is stopped due to a shortage of purge processing that occurs in conjunction with an OCV (open circuit voltage) check at the next start of below freezing point. Moreover, the RTC scavenging process in the soak becomes insufficient, and the fuel cell stack may be damaged at the next start-up below freezing point.

  On the other hand, when the drain line is frozen, there is a problem that the power generation stability is lowered and power generation is stopped at the next start of below freezing point. Moreover, the RTC scavenging process in the soak becomes insufficient, and the fuel cell stack may be damaged at the next start-up below freezing point.

  The present invention solves this type of problem, and with a simple configuration and process, the discharge valve mechanism for discharging the fluid in the fuel gas flow path to the outside of the fuel cell is surely frozen during RTC scavenging. It is an object of the present invention to provide a fuel cell system that can be prevented and to prevent the fuel cell stack from being damaged as much as possible at the next start of sub-freezing, and a method for shutting down the fuel cell system.

  The present invention relates to a fuel cell that generates electric power by an electrochemical reaction between a fuel gas supplied to a fuel gas flow channel and an oxidant gas supplied to an oxidant gas flow channel, and a fluid in the fuel gas flow channel The present invention relates to a fuel cell system including a discharge valve mechanism that discharges to the outside of a battery, and a control mechanism that periodically controls the discharge valve mechanism after the fuel cell is stopped, and an operation stop method thereof.

  In the fuel cell system, the control mechanism includes a freezing determination unit that preliminarily determines whether or not the discharge valve mechanism that is periodically controlled after the fuel cell is stopped is in a state of freezing at the time of control. When the freezing determination by the freezing determination unit is made after the command, the operation of the fuel cell is continued until the non-freezing determination is made by the freezing determination unit.

  The freezing determination unit includes a temperature sensor that detects a startup temperature of the fuel cell and a power generation related value detection unit that detects a power generation related value of the fuel cell, and the detected startup temperature and the detected power generation It is preferable to determine whether or not the discharge valve mechanism is in a frozen state based on the related value.

  Furthermore, the freezing determination unit determines whether or not the discharge valve mechanism is in a frozen state depending on whether or not the detected power generation related value is within a power generation related value range set according to the detected starting temperature. Is preferably determined.

  Furthermore, the power generation related value is preferably at least one of a current integrated value, a power integrated value, and a power generation time.

  The operation stop method includes a step of determining whether or not a fuel cell stop command has been issued, and a state in which the discharge valve mechanism that is periodically controlled after the fuel cell stop command is issued is frozen during control. A step of pre-determining whether or not there is, a step of continuing the operation of the fuel cell until a non-freezing determination is made when a freezing determination is made after the stop command of the fuel cell, and the non-freezing determination are made The system is stopped.

  Further, the operation stop method is based on the step of detecting the starting temperature of the fuel cell, the step of detecting the power generation related value of the fuel cell, the detected starting temperature and the detected power generation related value, And determining whether or not the discharge valve mechanism is in a frozen state.

  Furthermore, in the operation stop method, whether or not the discharge valve mechanism is in a frozen state depending on whether or not the detected power generation related value is within a power generation related value range set according to the detected starting temperature. It is preferable to determine whether or not.

  In the present invention, when the freezing determination is made after the stop command of the fuel cell, the operation of the fuel cell is continued until the non-freezing determination is made. For this reason, after the fuel cell is stopped, the periodically controlled discharge valve mechanism does not freeze. Therefore, even in a low-temperature environment, after the fuel cell is stopped, the discharge valve mechanism can be regularly and reliably controlled, and the fluid in the fuel gas flow path can be discharged well to the outside of the fuel cell. Is possible.

  As a result, the discharge valve mechanism for discharging the fluid in the fuel gas flow channel to the outside of the fuel cell can be reliably prevented from freezing during the RTC scavenging with a simple configuration and process. It becomes possible to prevent the battery stack from being damaged as much as possible.

1 is a schematic configuration diagram of a fuel cell system to which an operation stop method according to the present invention is applied. It is a flowchart explaining the said operation stop method. FIG. 5 is an explanatory diagram of a relationship between a purge line temperature and a current integrated value. It is explanatory drawing of the relationship between the said electric current integrated value, starting temperature, and freezing generation | occurrence | production presence / absence conditions.

  As shown in FIG. 1, a fuel cell system 10 to which an operation stop method according to the present invention is applied includes an oxidant gas (hereinafter also simply referred to as air) and fuel gas (hereinafter also simply referred to as hydrogen gas) electrochemical. A fuel cell stack 12 that generates electricity by reaction, an air supply device 14 that supplies air to the fuel cell stack 12, a hydrogen supply device 16 that supplies hydrogen gas to the fuel cell stack 12, and a cooling device that cools the fuel cell stack 12 A refrigerant supply device (not shown) for supplying a medium and a controller (control mechanism) 18 are provided.

  Although not shown, the fuel cell stack 12 includes, for example, a fuel cell that sandwiches a solid polymer electrolyte membrane in which a thin film of perfluorosulfonic acid is impregnated with water between a cathode electrode and an anode electrode, and a predetermined number of the fuel cells Batteries are stacked. In the fuel cell stack 12, an air flow path (oxidant gas flow path) 20 for supplying air to the cathode electrode of each fuel cell and a hydrogen flow path (fuel gas flow) for supplying hydrogen to the anode electrode of each fuel cell. Road) 22 is provided.

  The air supply device 14 includes an air pump (or supercharger) 24, and the compressed air output from the air pump 24 is supplied to the air flow path 20 of the fuel cell stack 12 via the air supply path 26. One end of an air discharge passage 28 is connected to the outlet side of the air flow path 20, and the other end of the air discharge passage 28 communicates with a diluter 30.

  The hydrogen supply device 16 includes a hydrogen tank 32 that stores high-pressure hydrogen. Hydrogen gas is supplied from the hydrogen tank 32 through the hydrogen supply passage 34 to the hydrogen flow path 22 of the fuel cell stack 12. An ejector 36 is disposed in the middle of the hydrogen supply passage 34.

  One end of a hydrogen discharge passage 38 is connected to the outlet side of the hydrogen flow path 22, and the other end of the hydrogen discharge passage 38 is connected to an ejector 36. The ejector 36 supplies hydrogen gas supplied from the hydrogen tank 32 to the fuel cell stack 12, and sucks exhaust gas containing unused hydrogen gas that has not been used in the fuel cell stack 12 from the hydrogen discharge passage 38. Then, the fuel cell stack 12 is again supplied as hydrogen gas.

  A purge line 40 and a drain line 42 are branched from the hydrogen discharge passage 38. The purge line 40 communicates with the diluter 30 via a purge valve 44, while the drain line 42 communicates with the diluter 30 via a drain valve 46. The purge line 40 including the purge valve 44 and the drain line 42 including the drain valve 46 constitute a discharge valve mechanism.

  The fuel cell stack 12 is provided with a temperature sensor 48 for detecting the starting temperature of the fuel cell stack 12 and a current sensor 50 for measuring the output current of the fuel cell stack 12.

  The controller 18 includes a valve control unit 52 that controls the purge valve 44 and the drain valve 46, a temperature detection unit 54 that receives temperature information from the temperature sensor 48, and a current integration that integrates the measurement output current from the current sensor 50. Freezing for preliminarily determining whether or not the purge valve 44 and the drain valve 46, which are periodically controlled after the fuel cell stack 12 is stopped, is in a frozen state based on a power generation related value (described later). The determination unit 58 and an RTC (Real Time Clock) control unit 60 that controls the purge valve 44 and the drain valve 46 at regular intervals (periodically) after the fuel cell stack 12 is stopped.

  The controller 18 is connected to an ignition switch 62 that starts and stops the fuel cell system 10 when operated by an operator. A stop command is input to the controller 18 via the ignition switch 62.

  The operation of the fuel cell system 10 configured as described above will be described below along the flowchart shown in FIG. 2 in relation to the operation stop method according to the present embodiment.

  First, when the ignition switch 62 is turned on (step S1), a start signal for the fuel cell system 10 is input to the controller 18. In the controller 18, the starting temperature of the fuel cell stack 12 input from the temperature sensor 48 to the temperature detection unit 54 is detected (step S2). Next, based on the detected starting temperature, a necessary current integrated value and a freezing generation current integrated value are calculated (step S3).

  Here, as shown in FIG. 1, in the purge line 40 and the drain line 42, a freezing portion that is easily frozen at a low temperature between the purge valve 44 and the diluter 30 and between the drain valve 46 and the diluter 30. 64 exists. For example, the temperature of the purge line 40 and the current integrated value of the output current value of the fuel cell stack 12 have the relationship shown in FIG.

  In FIG. 3, a range H1 indicates a range in which the purge line 40 does not freeze when performing purge processing (scavenging processing) at regular intervals during soaking (leaving) of the fuel cell stack 12, while the range H2 indicates The range in which the purge line 40 is frozen during the purge process is shown.

  When the integrated current value is small, the amount of generated water is small and freezing does not occur even when the temperature of the purge line 40 is lowered. On the other hand, if the current integrated value increases, the temperature of the purge line 40 also becomes high, and the amount of heat is sufficiently supplied to the place where the heat is required, so that it does not freeze.

  Thus, the temperature of the purge line 40 and the current integrated value maintain a certain relationship. Therefore, instead of observing the temperature of the purge line 40, the current integrated value can be monitored, and the presence or absence of freezing in the purge line 40 during the purge process can be determined based on the current integrated value.

  Therefore, as shown in FIG. 4, the relationship between whether or not the purge line 40 is frozen is set in the starting temperature of the fuel cell stack 12 and the integrated current value when the ignition switch 62 is turned off. Here, the range H1a is a range where the purge line 40 is not frozen, and the range H2a is a range where the purge line 40 is frozen.

  The range H1a and the range H2a are partitioned by the freeze generation current integrated value La and the necessary current integrated value Ld. The freeze generation current integrated value La is an integrated current value at which freezing starts to occur in the purge line 40. If the freeze generation current integrated value La is less than the freeze generation current integrated value La, the purge line 40 does not freeze. On the other hand, the required current integrated value Lb is the maximum current integrated value at which freezing occurs in the purge line 40. When the required current integrated value Lb is exceeded, the freezing of the purge line 40 is avoided.

  The freeze generation current integrated value La and the necessary current integrated value Lb are set according to the starting temperature. When the starting temperature is relatively low, if the integrated current value is relatively small, the amount of generated water is reduced and the purge line 40 is prevented from freezing. If the integrated current value is relatively large, a desired amount of heat is sufficiently supplied regardless of the starting temperature, so that the purge line 40 does not freeze.

  In addition, when the starting temperature is relatively high, even if the current integrated value increases and the amount of generated water increases, the fuel cell stack 12 is quickly warmed up and is not easily frozen. Therefore, in step S3, the required current integrated value and the freezing generation current integrated value are calculated according to the detected starting temperature.

  Furthermore, it progresses to step S4 and step S5, and electric power generation by the fuel cell stack 12 is performed until the ignition switch 62 is turned off. Specifically, the compressed air led out to the air supply passage 26 under the driving action of the air pump 24 constituting the air supply device 14 passes through the air flow path 20 provided in each fuel cell of the fuel cell stack 12. And is supplied to the cathode electrode. On the other hand, the hydrogen gas led out from the hydrogen tank 32 constituting the hydrogen supply device 16 to the hydrogen supply passage 34 is supplied from the hydrogen flow path 22 of each fuel cell of the fuel cell stack 12 to the anode electrode.

  Thereby, oxygen in the air supplied to the cathode electrode and hydrogen supplied to the anode electrode react electrochemically to generate power. The air supplied to the cathode electrode is discharged from the air flow path 20 to the air discharge passage 28 and sent to the diluter 30. Further, the hydrogen gas used in the anode electrode is discharged from the hydrogen flow path 22 to the hydrogen discharge passage 38, and mixed with new hydrogen gas under the suction action of the ejector 36, from the hydrogen supply passage 34 to the fuel cell stack 12. To be supplied.

  The hydrogen gas is circulated to the hydrogen supply passage 34 via the ejector 36, and is periodically discharged to the diluter 30 via the purge line 40 when the purge valve 44 is opened. This is because impurities such as nitrogen gas mixed in the hydrogen gas increase. Further, moisture mixed in the circulating hydrogen gas is discharged to the diluter 30 via the drain valve 46 under the opening action of the drain valve 46.

  The current output during the operation of the fuel cell stack 12 is detected via the current sensor 50, and the current integration value is calculated by the current integration unit 56 of the controller 18. Therefore, when the ignition switch 62 is turned off (YES in step S5), the process proceeds to step S6, where the current integrated value integrated by the current integrating unit 56 is calculated from the pre-calculated freezing generation current integrated value and the necessary current. It is determined whether or not it is between the integrated values.

  If it is determined that the current integrated value is within the range H2a (YES in step S6), power generation by the fuel cell stack 12 is continued until the current integrated value exceeds the necessary current integrated value (steps S7 and S7). Step S8).

  If it is determined that the current integrated value exceeds the necessary current integrated value (YES in step S8), the fuel cell system 10 stops the power generation of the fuel cell stack 12 (step S9).

  In the controller 18, under the action of the RTC control unit 60, during the soak (leaving) after the stop of the fuel cell stack 12, a purge process is performed periodically mainly at predetermined time intervals. In this purge process, compressed air is supplied to the air flow path 20 and the hydrogen flow path 22 by driving the air pump 24. The hydrogen gas remaining in the hydrogen flow path 22 and the introduced air are discharged to the diluter 30 through the purge line 40 when the purge valve 44 is opened under the action of the valve control unit 52. The air remaining in the air flow path 20 and the compressed air are discharged to the diluter 30 via the air discharge passage 28.

  In this case, in the present embodiment, after the stop command for the fuel cell stack 12, based on the starting temperature and the current integrated value calculated by the current integrating unit 56, the freezing determination unit 58 determines whether or not the purge line 40 is frozen during the RTC process. Judgment is made. When it is determined that the purge line 40 is frozen, the operation (operation) of the fuel cell stack 12 is continued until the non-freezing determination is made regardless of the stop command for the fuel cell stack 12. ing.

  Therefore, when the purge process is periodically performed through the RTC control unit 60 after the fuel cell stack is stopped, in particular, the freezing portion 64 of the purge line 40 is prevented from freezing. can do. Thus, even in a low temperature environment, the purge valve 44 can be controlled periodically after the fuel cell stack 12 is stopped, and the remaining fluid in the hydrogen flow path 22 is diverted from the fuel cell stack 12 to the diluter 30. The effect that it becomes possible to discharge well is obtained.

  Therefore, with a simple configuration and process, the discharge valve mechanism that discharges the fluid in the hydrogen flow path 22 to the outside of the fuel cell stack 12, for example, the purge valve 44 can be reliably prevented from freezing. It becomes possible to prevent the fuel cell stack 12 from being damaged as much as possible at the time of starting below the freezing point.

  For example, the purge line 40 is not frozen at the time of starting below the freezing point, the shortage of the purging process performed along with the OCV (open circuit voltage) check at the next starting of the freezing point is avoided, and the scavenging process in the soak is sufficiently performed. The advantage of being carried out is obtained.

  On the other hand, when the drain valve 46 is operated and the drain treatment of the hydrogen flow path 22 is performed during the sub-freezing soak, the freezing of the drain line 42 is avoided. Accordingly, it is possible to reliably avoid the problem that the power generation stability is lowered and the power generation is stopped at the next start of below freezing point. Moreover, the scavenging process in the soak is sufficiently performed, and it is possible to satisfactorily prevent the fuel cell stack 12 from being damaged at the next start-up below freezing point.

  In the present embodiment, the freeze determination unit 58 uses the current integrated value obtained from the current sensor 50 as the power generation related value, but is not limited to this. For example, a power integrated value obtained by integrating the output power of the fuel cell stack 12 or a power generation time of the fuel cell stack 12 may be used as a power generation related value. Further, at least two of the current integrated value, the power integrated value, and the power generation time may be used together as the power generation related value.

DESCRIPTION OF SYMBOLS 10 ... Fuel cell system 12 ... Fuel cell stack 14 ... Air supply device 16 ... Hydrogen supply device 18 ... Controller 20 ... Air flow path 22 ... Hydrogen flow path 24 ... Air pump 28 ... Air discharge passage 30 ... Diluter 32 ... Hydrogen tank 34 ... Hydrogen supply passage 36 ... Ejector 38 ... Hydrogen discharge passage 40 ... Purge line 42 ... Drain line 44 ... Purge valve 46 ... Drain valve 48 ... Temperature sensor 50 ... Current sensor 52 ... Valve control unit 54 ... Temperature detection unit 56 ... Current integration Unit 58 ... Freezing determination unit 60 ... RTC control unit 62 ... Ignition switch

Claims (8)

A fuel cell that generates electricity by an electrochemical reaction of a fuel gas supplied to the fuel gas flow path and an oxidant gas supplied to the oxidant gas flow path;
A discharge valve mechanism for discharging the fluid in the fuel gas flow path to the outside of the fuel cell;
A control mechanism for periodically controlling the discharge valve mechanism after the fuel cell is stopped;
A fuel cell system comprising:
The control mechanism includes a freezing determination unit that preliminarily determines whether or not the discharge valve mechanism that is periodically controlled after the fuel cell is stopped is in a state of freezing at the time of control,
The fuel cell system is characterized in that the operation of the fuel cell is continued until the non-freezing determination is made by the freezing determination unit when the freezing determination unit makes a freezing determination after the fuel cell stop command. 2. The fuel cell system according to claim 1, wherein the freezing determination unit includes a temperature sensor that detects a startup temperature of the fuel cell;
A power generation related value detection unit for detecting a power generation related value of the fuel cell;
With
A fuel cell system that determines whether or not the exhaust valve mechanism is frozen based on the detected starting temperature and the detected power generation related value.   3. The fuel cell system according to claim 2, wherein the freezing determination unit determines whether the detected power generation related value is within a power generation related value range set according to the detected starting temperature. A fuel cell system for determining whether or not the discharge valve mechanism is in a frozen state.   4. The fuel cell system according to claim 2, wherein the power generation related value is at least one of a current integrated value, a power integrated value, and a power generation time. A fuel cell that generates electricity by an electrochemical reaction of a fuel gas supplied to the fuel gas flow path and an oxidant gas supplied to the oxidant gas flow path;
A discharge valve mechanism for discharging the fluid in the fuel gas flow path to the outside of the fuel cell;
A control mechanism for periodically controlling the discharge valve mechanism after the fuel cell is stopped;
A method for stopping operation of a fuel cell system comprising:
Determining whether a stop command for the fuel cell has been issued; and
Pre-determining whether or not the discharge valve mechanism, which is periodically controlled after the fuel cell stop command is issued, is frozen during control;
A step of continuing operation of the fuel cell until a non-freezing determination is made when a freezing determination is made after the fuel cell stop command;
A step of stopping the system when the non-freezing determination is made; and
A method for stopping the operation of the fuel cell system. 6. The operation stop method according to claim 5, wherein a step of detecting a start temperature of the fuel cell;
Detecting a power generation related value of the fuel cell;
Determining whether or not the discharge valve mechanism is in a frozen state based on the detected starting temperature and the detected power generation related value;
A method for stopping the operation of the fuel cell system.   7. The operation stop method according to claim 6, wherein the discharge valve mechanism freezes depending on whether or not the detected power generation related value is within a power generation related value range set according to the detected startup temperature. A method for stopping the operation of a fuel cell system, comprising: determining whether or not the fuel cell system is in a state.   The operation stop method according to claim 6 or 7, wherein the power generation related value is at least one of an integrated current value, an integrated power value, and a generation time.

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