JP5332089B2 - FUEL CELL SYSTEM AND METHOD FOR STOPPING FUEL CELL SYSTEM - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To bring about an optimal wetting status of a fuel cell stack to start up in a temperature below zero. <P>SOLUTION: The shutdown method of a fuel cell system is to detect a shutdown trigger to shut down the fuel cell system and to measure a representing temperature of a fuel cell stack if the shutdown trigger is detected, and based on the representing temperature, a purging time is determined so that the higher the representing temperature the shorter the purging time, and gas is made to flow to a fuel cell stack to start purging, and after the purging is started up and the purging time is over, the purging is stopped to shut down the fuel cell system. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to a fuel cell system for performing purge control for the purpose of starting a fuel cell stack below zero and a method for stopping the fuel cell stack, and more particularly to a purge control technique for controlling a purge time and a flow rate from the temperature or wetness of a fuel cell. .

  A fuel cell system is a device that directly converts chemical energy of fuel into electrical energy, and supplies a fuel gas containing hydrogen to an anode of a pair of electrodes provided with an electrolyte membrane interposed therebetween, and the other cathode An oxygen agent gas containing oxygen is supplied to the electrode, and electric energy is extracted from the electrodes by using the following electrochemical reaction that occurs on the surface of the pair of electrodes on the electrolyte membrane side.

Anode reaction: H ₂ → 2H ⁺ + 2e ⁻ (1)
Cathodic reaction: 2H ⁺ + 2e ⁻ + (1/2) O ₂ → H ₂ O (2)
As the fuel gas supplied to the anode, a method of directly supplying from a hydrogen storage device, a method of supplying a hydrogen-containing gas by reforming a fuel containing hydrogen, and the like are known. Examples of the hydrogen storage device include a high-pressure gas tank, a liquefied hydrogen tank, a hydrogen storage alloy tank, and the like. As the fuel containing hydrogen, natural gas, methanol, gasoline, and the like are conceivable.

  On the other hand, air is generally used as the oxygen agent gas supplied to the cathode.

  Incidentally, in order to start the fuel cell from below freezing point, it is necessary to remove moisture from the inside of the fuel cell in advance. This is because in a sub-freezing atmosphere, the water remaining inside the fuel cell freezes, preventing the reaction gas from diffusing and making it impossible to generate power. Thus, many documents relating to techniques for purging moisture when the fuel cell is stopped are disclosed, and various methods have been proposed for the conditions for stopping the purge.

  For example, as disclosed in Japanese Patent Application Laid-Open No. 2001-332281 (Patent Document 1) and Japanese Patent Application Laid-Open No. 2002-208421 (Patent Document 2), the fuel cell is not humidified when the fuel cell is stopped. And a technique for stopping the operation by regarding the time when the output voltage of the fuel cell main body, which is lowered by drying of the electrolyte membrane, is lowered to a predetermined value or less as a predetermined wet state, is dried. It has become.

In addition, as disclosed in Japanese Patent Application Laid-Open No. 2002-246053 (Patent Document 3), the moisture state of the electrolyte membrane is grasped using a moisture sensor such as a hygrometer or a resistance meter at the outlet of the purge gas, A technique for performing moisture removal control based on the wet state is known.
JP 2001-332281 A JP 2002-208421 A JP 2002-246053 A

  However, in the conventional fuel cell systems disclosed in Patent Document 1 and Patent Document 2, the wet state of the electrolyte membrane is determined based on the decrease in the voltage of the fuel cell. In addition, there is a problem that this method cannot be used when purging using a battery or the like. In addition, when an electrolyte membrane having high robustness against humidity, that is, an electrolyte membrane that is resistant to drying is used, the wet state of the electrolyte membrane cannot always be grasped only by the cell voltage.

  Furthermore, in the conventional fuel cell system disclosed in Patent Document 3, since a hygrometer and a dew point meter are used, there are problems such as poor responsiveness, high cost, and low durability of the measuring instrument. . Even if an ohmmeter is used, an ohmmeter that is costly and can measure a full stack level AC impedance has a high technical difficulty and is not preferable for mounting in a vehicle.

  In order to solve the above-described problems, a fuel cell system according to the present invention is a fuel cell system that generates power using a fuel cell stack, and includes a trigger detection unit that detects a stop trigger for stopping the fuel cell system, and a fuel cell stack. Based on the representative temperature measured by the representative temperature measuring means when the stop trigger is detected, the purge time is set such that the higher the representative temperature, the shorter the purge time when the representative temperature is measured. Purge time determining means to be determined, purge means for purging by flowing a gas to the fuel cell stack, and system stopping means for stopping the fuel cell system by stopping the purge after the purge time has elapsed since the purge was started. It is characterized by.

  The fuel cell system stop method of the present invention is a fuel cell system stop method for generating power by a fuel cell stack, and when a stop trigger for stopping the fuel cell system is detected and this stop trigger is detected. Measure the representative temperature of the fuel cell stack, and based on this representative temperature, set the purge time so that the purge time becomes shorter as the representative temperature is higher, start the purge by flowing gas into the fuel cell stack, and start the purge Then, after the purge time has elapsed, the purge is stopped and the fuel cell system is stopped.

  According to the fuel cell system and the stopping method thereof of the present invention, by measuring the representative temperature of the fuel cell stack when stopping the fuel cell system, and setting the purge time so that the purge time becomes shorter as the representative temperature becomes higher The fuel cell stack can be in a wet state that is optimal for starting below zero.

(First embodiment)
DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, a first embodiment of the invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the fuel cell system according to this embodiment.

  As shown in FIG. 1, the fuel cell system of this embodiment includes a fuel cell stack 2 that is supplied with a fuel gas and an oxygen agent gas to generate electric power through an electrochemical reaction, and a fuel cell based on detection values from various sensors. A control unit 3 that controls the system, a hydrogen tank 4 that stores hydrogen gas that is a fuel gas, a compressor 5 that pressurizes air that is an oxygen agent gas and supplies the pressurized air to the cathode of the fuel cell stack 2, and the fuel cell stack 2 A cooling water pump 6 that circulates the cooling water, a radiator 7 that dissipates the cooling water and cools it, a cooling water flow path 8 that connects the fuel cell stack 2, the cooling water pump 6 and the radiator 7 to circulate the cooling water, and A three-way valve 9 for switching between a flow path to the radiator 7 side and a flow path to the short circuit side that bypasses the radiator 7, and a plurality of units constituting the fuel cell stack 2 The stack temperature sensor 10 disposed in at least one unit cell of the Le, and a cooling water outlet temperature sensor 11 for detecting the temperature of cooling water flowing out from the fuel cell stack 2.

  Here, in the fuel cell system described above, the fuel cell stack 2 is a solid polymer membrane type fuel cell in which a pair of electrodes are provided on both sides of the solid polymer electrolyte membrane, and hydrogen gas as a fuel gas is supplied to the anode. Then, the cathode is supplied with air, which is an oxygen agent gas, to generate power by an electrochemical reaction.

  In the hydrogen supply system that supplies hydrogen gas, which is fuel gas, hydrogen gas is supplied from the hydrogen tank 4 to the anode of the fuel cell stack 2 through a pressure reducing valve and a hydrogen supply valve (not shown). The high-pressure hydrogen supplied from the hydrogen tank 4 is mechanically reduced to a predetermined pressure by a pressure reducing valve, and then the pressure of the hydrogen gas in the fuel cell stack 2 is adjusted to a desired pressure by adjusting the opening of the hydrogen supply valve. It is controlled to become.

  On the other hand, in the air supply system for supplying air as oxygen agent gas, the air sucked from the outside is compressed and sent out by the compressor 5 and supplied to the cathode of the fuel cell stack 2. The air pressure at the cathode is detected by an air pressure sensor (not shown), and the detected value is fed back to the control unit 3. Based on the detected value, the control unit 3 rotates the rotational speed of the compressor 5 and the opening area of an air pressure regulating valve (not shown). Is adjusted to control the air pressure at the cathode.

  The control unit 3 controls the pressure and flow rate of hydrogen gas supplied to the anode and the pressure and flow rate of air supplied to the cathode based on detection values from various sensors (not shown). Further, the temperature of the cooling water is controlled by controlling the number of rotations of the cooling water pump 6 and switching of the three-way valve 9 based on the detection value of the cooling water outlet temperature sensor 11.

  The cooling water flow path 8 is connected to the fuel cell stack 2, the cooling water pump 6 and the radiator 7 to circulate the cooling water (radiator side flow path), and bypasses the radiator 7 to the fuel cell stack 2 and the cooling water. A flow path (short circuit) for connecting the water pump 6 and circulating the cooling water is included. The three-way valve 9 switches the flow of cooling water between the radiator-side flow path and the short circuit. When the coolant flows through a short circuit that bypasses the radiator 7 and circulates through the fuel cell stack 2, the temperature rises due to heat generation of the fuel cell stack 2 without being cooled.

  Note that the fuel cell system of the present embodiment shown in FIG. 1 shows only the parts related to the present invention, and other general equipment for establishing the system is omitted.

  The fuel cell stack 2 is configured by disposing a unit cell by disposing a cathode separator and an anode separator on both surfaces of a membrane electrode assembly, and laminating a plurality of unit cells. The stack temperature sensor 10 is installed in at least one of the unit cells stacked in this way. As the stack temperature sensor 10 and the cooling water outlet temperature sensor 11, for example, a thermocouple, a resistance temperature detector, a thermistor, or the like may be used.

  Next, a purge control process optimal for starting below zero of the fuel cell system of FIG. 1 will be described based on the flowchart of FIG.

  (A) In step 101 (S101), the trigger detection means in the control unit 3 determines whether or not a stop trigger for stopping the fuel cell system is turned on. When the stop trigger is turned on (positive determination in step 101), the process proceeds to step 102 (S102), and the representative temperature of the fuel cell stack is measured. Here, the “representative temperature of the fuel cell stack” may be a stack temperature measured using the stack temperature sensor 10 of FIG. 1. If the stack temperature sensor 10 is not provided, the coolant outlet temperature sensor 11 may be used. It may be the cooling water temperature measured using That is, the stack temperature sensor 10 or the cooling water outlet temperature sensor 11 can be used as the representative temperature measuring means.

  (B) Proceeding to step 103 (S103), the purge time determining means in the control unit 3 determines the purge time t1 based on the representative temperature of the fuel cell stack 2 measured by the representative temperature measuring means. At this time, according to the relationship between the stack representative temperature and the purge time t1 shown in the map A of FIG. 3, the purge time t1 is determined so that the purge time t1 becomes shorter as the representative temperature of the fuel cell stack 2 becomes higher. Since map A in FIG. 3 differs depending on the specifications of fuel cell stack 2, operating conditions, and the configuration of auxiliary equipment, the relationship between the purge time t1 and the stack representative temperature that are optimal for starting below zero is experimentally measured beforehand. Map A will be created.

  (C) Proceeding to step 104 (S104), gas (air) is supplied to the fuel cell stack 2 by the compressor 5 (purge means) to start purging. After purge time t1 from the start of purge (affirmative determination in step 105 (S105)), the system stop means in the control unit 3 stops the gas supply and stops the fuel cell system (step 106 (S106)). .

  FIG. 4 is a graph showing the results of an experiment on the relationship between the amount of water evaporated from the unit cell and the output of the fuel cell when starting below zero. If the amount of water that evaporates from the unit cell is small, the catalyst layer is blocked with ice when starting below zero, so that gas diffusion is hindered and output cannot be obtained. On the other hand, if the amount of water evaporated from the unit cell is too large, the polymer membrane will be dried too much, and proton conductivity at the time of start-up cannot be ensured, and output cannot be obtained. Therefore, it can be seen that there is an optimum value of the amount of water to be evaporated from the unit cell. FIG. 5 is a graph showing the change over time in the amount of water evaporated from the unit cell, and shows how the time required to reach the optimum amount of evaporation (purge time t1) varies depending on the representative temperature T of the stack. As shown in the figure, since the time (purge time t1) required to reach the optimum evaporation amount differs depending on the representative temperature T of the stack, the fuel cell only for the purge time t1 that achieves the optimum evaporation amount depending on the stack representative temperature T. By purging the stack 2, the inside of the fuel cell stack 2 can be brought into an optimum wet state for starting below zero.

  In order to start the fuel cell system from below zero, in the fuel cell system in which purging is performed when operation is stopped, the representative temperature T of the fuel cell stack 2 is monitored during purging, and the purge time t1 is determined based on the temperature T. Thereby, for example, by performing purge for a normal time when the stack temperature is higher than normal, it is possible to prevent a problem that power generation cannot be performed at the next start-up because the film is too dry. Further, deterioration due to excessive drying of the film can also be prevented.

(Second Embodiment)
A second embodiment of the present invention will be described with reference to the drawings.

  The configuration of the fuel cell system according to the second embodiment is the same as the configuration shown in FIG.

  A purge control process optimum for starting below zero of the fuel cell system will be described with reference to the flowchart of FIG.

  (A) In step 201 (S201), the control unit 3 (trigger detection means) determines whether or not a stop trigger for stopping the fuel cell system is turned on. When the stop trigger is turned on (positive determination in step 201), the process proceeds to step 202 (S202), and gas (air) is supplied to the fuel cell stack 2 by the compressor 5 to start purge. At the same time, a very small amount of cooling water is supplied to the fuel cell stack 2 by the cooling water pump 6. At this time, it is desirable to switch the three-way valve 9 to the short circuit side and supply a relatively high temperature cooling water that is not cooled by the radiator 7.

  (B) Proceeding to step 203 (S203), the coolant temperature is measured using the coolant outlet temperature sensor 11. Until the counter C is counted up to a predetermined value Cx (positive determination in step 204 (S204)), the coolant temperature is measured repeatedly at regular intervals. Thereby, the temperature change rate of cooling water temperature can be calculated | required. Thereafter, the process proceeds to step 206 (S206), and the wet state inside the fuel cell stack 2 is obtained from the temperature change rate of the cooling water temperature. At this time, since the gas is supplied to the fuel cell stack 2, the control unit 3 (wetting degree detection unit) causes the coolant outlet temperature sensor 11 (cooling water temperature measurement unit) to flow the gas to the fuel cell stack 2. The degree of wetness in the fuel cell stack 2 can be detected based on the time change rate of the cooling water temperature measured by the above.

  (C) Proceeding to step 207 (S207), the control unit 3 (purge time determining means) determines the purge time t1 based on the degree of wetness in the fuel cell stack 2 and the representative temperature of the fuel cell stack 2. At this time, according to the relationship between the purge time t1 and the wetness degree shown in FIG. 9, the purge time t1 is determined so that the purge time becomes longer as the wetness degree becomes higher. In FIG. 9, when the stack representative temperature T is different, the inclination angle is different, and T1 <T2 <T3.

  (D) Proceeding to step 208 (S208), after purging is started in step 202, and after the purge time t1 (affirmative determination in step 208), the control unit 3 (system stop means) stops the gas supply and stops the fuel cell. The system is stopped (step 209 (S209)).

  FIG. 7 shows a time-series change in the stack temperature in the fuel cell stack 2. When the inside of the fuel cell stack 2 is relatively wet (Wet), the inside of the fuel cell stack 2 is cooled by the latent heat of vaporization, so the temperature change rate dT per unit time dt as shown by “wet” in the figure. / Dt increases. Further, when the inside of the fuel cell stack 2 is relatively dry (Dry), the amount of evaporation is small, so that the temperature change rate is small as indicated by “dry” in the figure. Therefore, by obtaining the temperature change rate dT / dt per unit time, it is possible to grasp the wet state inside the fuel cell stack 2 as shown in FIG. In FIG. 8, the relationship between the time change rate of the temperature and the wet state changes depending on the purge start temperature TS. Here, T1 <T2 <T3.

  The wet state inside the fuel cell stack 2 is predicted, and the purge time t1 is determined based on the wet state and the representative temperature of the fuel cell stack 2 at the time of purging. Thus, for example, when the electrolyte membrane is dry at the same temperature, the purge time t1 is shortened, and when the electrolyte membrane is wet, the purge time t1 is increased. Can be in a state.

  A minute amount of the cooling water of the fuel cell stack 2 is flowed at the time of purging, and the wet state inside the fuel cell stack 2 is predicted from the temperature change rate of the cooling water outlet temperature of the fuel cell stack 2, so that a highly accurate wet state prediction can be realized. .

(First modification)
In the second embodiment, the example in which the cooling water temperature is measured using the cooling water outlet temperature sensor 11 and the wet state inside the fuel cell stack 2 is obtained from the temperature change rate of the cooling water temperature has been described. The means for predicting the wet state inside the fuel cell stack 2 is not limited to the temperature change rate of the cooling water temperature, but may be the temperature change rate inside the fuel cell stack 2 measured by the stack temperature sensor 10. That is, the control unit 3 (wetting degree detecting means) detects the degree of wetting in the fuel cell 2 based on the time rate of change of the stack temperature measured by the stack temperature sensor 10 while flowing gas into the fuel cell stack 2. It doesn't matter. Also in this case, as in the second embodiment, when the inside of the fuel cell stack 2 is wet, the latent heat cooling is performed by the evaporation and the temperature change rate inside the fuel cell stack 2 is increased. When the amount of water in the battery stack 2 is small, the amount of evaporation is small and the rate of temperature change is small. Therefore, the wet state inside the fuel cell stack 2 can be grasped by measuring the temperature change rate inside the fuel cell stack 2.

(Second modification)
Further, the flowchart of FIG. 6 shows an example in which the wetness degree is obtained from the time change rate of the cooling water temperature (step 206) and the purge time t1 is obtained from the wetness degree (step 207). However, without obtaining the purge time t1 in advance, as shown in FIG. 10, the purge may be stopped when the rate of change of the cooling water temperature with time becomes a predetermined value or less.

  With reference to FIG. 10, the purge control process according to the second modification will be described.

  In Step 301 (S301) to Step 303 (S303), in the same manner as in Step 201 to Step 203 of FIG. 6, when the stop trigger is turned on, a small amount of cooling water is flowed at the same time as gas supply is started. The coolant temperature is measured using the outlet temperature sensor 11. Thereby, the wet state inside the fuel cell stack 2 is grasped. Thereafter, in step 304 (S304), it is monitored whether or not the time change rate of the cooling water temperature becomes a predetermined value or less, and during that time, the cooling water temperature is repeatedly measured. Then, when the rate of change of the cooling water temperature with time is below a predetermined value (affirmative determination at step 304), that is, when the wet state inside the fuel cell stack 2 is below a predetermined value, gas supply (purging) is performed. Stop and stop the system (step 305 (S305)). Accordingly, the purge can be stopped in a wet state optimal for starting below zero inside the fuel cell stack 2. That is, it is possible to prevent a problem that the electrolyte membrane is too dry and cannot generate power at the next start-up, and it is possible to prevent deterioration due to excessive drying of the electrolyte membrane.

(Third embodiment)
A third embodiment of the present invention will be described with reference to the drawings.

  The configuration of the fuel cell system according to the third embodiment is the same as the configuration shown in FIG.

  Next, a purge control process optimal for starting below zero of the fuel cell system will be described based on the flowchart of FIG. The flowchart of FIG. 11 has a configuration in which Step 403 (S403) is added to the flowchart of FIG. 2, and Step 401 (S401), Step 402 (S402), and Step 404 (S404) to Step 407 (S407) are The processing contents are the same as those in steps 101 to 106 in FIG.

  (A) In step 401, the control unit 3 (trigger detection means) determines whether or not a stop trigger for stopping the fuel cell system is turned on. When the stop trigger is turned on (positive determination in step 401), the process proceeds to step 402, and the representative temperature of the fuel cell stack 2 is measured.

  (B) Proceeding to step 403 (S403), the control unit 3 (purge flow rate determining means) obtains the optimum purge flow rate from the representative temperature of the fuel cell stack 2 according to the map B in FIG.

  (C) Proceeding to step 404, the control unit 3 (purge time determining means) determines the purge time t1 based on the representative temperature of the fuel cell stack 2. At this time, according to the relationship between the stack representative temperature and the purge time t1 shown in the map A of FIG. 3, the purge time t1 is determined so that the purge time t1 becomes shorter as the representative temperature of the fuel cell stack 2 becomes higher.

  (D) Proceeding to step 405 (S405), the purge gas is supplied to the fuel cell stack 2 by the compressor 5 and the purge is started. After the purge time t1 from the start of purge (affirmative determination in step 406 (S406)), the control unit 3 (system stop means) stops the gas supply and stops the fuel cell system (step 407).

  FIG. 12 is a graph showing the relationship between the purge flow rate and the relative humidity of the fuel cell stack 2 outlet gas at the time of purging at each temperature. When the temperature is T1, which is relatively high, the evaporation rate is fast, so that the outlet gas comes out at a relative humidity of 100% even if the purge flow rate is increased to some extent. However, when the temperature is T3, the evaporation rate is slow, so even if the purge flow rate is increased, the water in the fuel cell stack 2 does not evaporate in time and comes out unsaturated. Therefore, even if the purge flow rate is increased, the ability to dry is small, and the capability is the same as when the flow rate is small, and even if the flow rate is increased, it is wasted. FIG. 13 is a map B created by obtaining the most efficient purge flow rate at each temperature from FIG. 12. The map B is used to determine the purge flow rate. In this way, the representative temperature of the fuel cell stack 2 is monitored at the time of purging, and the purge flow rate is determined based on the temperature. As a result, a large amount of gas does not flow unnecessarily at low temperatures where the evaporation rate is not in time, and the inside of the fuel cell stack 2 can be brought into a wet state suitable for sub-zero startup with less power consumption and sound vibration. .

(Fourth embodiment)
A fourth embodiment of the present invention will be described with reference to the drawings.

  The configuration of the fuel cell system according to the fourth embodiment is the same as the configuration shown in FIG.

  Next, a purge control process optimal for starting below zero of the fuel cell system will be described with reference to the flowchart of FIG. The flowchart of FIG. 14 has a configuration in which step 507 (S507) is added to the flowchart of FIG. 11, and step 501 (S501) to step 506 (S506) and step 508 (S508) are steps 401 to 401 in FIG. The processing contents are the same as those in step 407.

  (A) In step 501, the trigger detection means in the control unit 3 determines whether or not a stop trigger for stopping the fuel cell system is turned on. When the stop trigger is turned on (positive determination in step 501), the process proceeds to step 502 (S502), and the representative temperature of the fuel cell stack 2 is measured.

  (B) Proceeding to step 503 (S503), the optimum purge flow rate is obtained from the representative temperature of the fuel cell stack 2 according to the map B in FIG. Proceeding to step 504 (S504), the purge time t1 is determined from the representative temperature of the fuel cell stack 2 according to the map A in FIG.

  (C) Proceeding to step 505 (S505), the purge gas is supplied to the fuel cell stack 2 by the compressor 5 and the purge is started. In step 507, the purge flow rate is decreased as time elapses from the start of the purge to the purge time t1 according to the map C in FIG. After purge time t1 from the start of purge (affirmative determination in step 506), control unit 3 (system stop means) stops gas supply and stops the fuel cell system (step 508).

  FIG. 16A is a graph showing the relationship between the elapsed time from the start of the purge and the outlet gas relative humidity when the purge flow rate is constant, and FIG. 16B is a graph in which the purge flow rate is decreased with time. It is a graph which shows the relationship between the elapsed time from the purge start in this case, and outlet gas relative humidity. As the inside of the fuel cell stack 2 is dried by purging, the amount of water evaporated from the inside of the fuel cell stack 2 decreases. For this reason, when the same constant flow rate as that at the beginning of the purge is kept flowing, the outlet gas relative humidity decreases with time from the start of the purge as shown in FIG. That is, in the second half of the purge, useless gas is flowing. Therefore, by decreasing the flow rate with the purge time in the second half of the purge, the outlet gas relative humidity can always be maintained at 100% as shown in FIG. 16 (b), exceeding the amount necessary for evaporation in the second half of the purge. Thus, the inside of the fuel cell stack 2 can be brought into a wet state suitable for starting below zero with less power consumption and sound vibration.

  The fuel cell system and the stopping method thereof according to the present invention have been described based on the illustrated embodiment. However, the present invention is not limited to this, and the configuration of each part is an arbitrary configuration having a similar function. Can be replaced with something.

1 is a block diagram showing a configuration of a fuel cell system according to a first embodiment of the present invention. The flowchart which shows the purge control process optimal for subzero starting of the fuel cell system of FIG. Graph showing the relationship between the stack representative temperature and the purge time t1 (Map A) A graph showing the results of experiments on the relationship between the amount of water evaporated from a unit cell and the output of a fuel cell at subzero start-up A graph showing the change over time in the amount of water evaporated from a unit cell The flowchart which shows the purge control processing of the fuel cell system concerning 2nd Embodiment. Graph showing time-series change of stack temperature in fuel cell stack 2 Graph showing the relationship between the rate of change of temperature over time and the wet state A graph showing the relationship between the purge time t1 and the wetness in the fuel cell stack 2 The flowchart which shows the purge control processing of the fuel cell system concerning a 2nd modification. Flowchart showing the purge control process of the fuel cell system according to the third embodiment. A graph showing the relationship between the purge flow rate and the relative humidity of the fuel cell stack outlet gas during purging A graph (map B) showing the relationship between the representative temperature of the fuel cell stack 2 and the optimum purge flow rate for starting below zero The flowchart which shows the purge control processing of the fuel cell system concerning 4th Embodiment. Graph showing the relationship between the elapsed time from the start of purge and the purge flow rate (Map C) Graph showing the relationship between the elapsed time from the start of purge and the relative humidity of the outlet gas

Explanation of symbols

2 Fuel cell stack 3 Control unit 4 Hydrogen tank 5 Compressor 6 Cooling water pump 7 Radiator 8 Cooling water flow path 9 Three-way valve 10 Stack temperature sensor 11 Cooling water outlet temperature sensor

Claims (16)

A fuel cell system for generating power by a fuel cell stack,
Trigger detecting means for detecting a stop trigger for stopping the fuel cell system;
Representative temperature measuring means for measuring a representative temperature of the fuel cell stack;
Purge means for purging by flowing a gas to the fuel cell stack;
When the trigger detection means detects the stop trigger, the wetness degree is determined based on the time rate of change of the representative temperature measured by the representative temperature measurement means while flowing gas to the fuel cell stack by the purge means. A purge time determining means for calculating and determining the purge time such that the higher the wetness, the longer the purge time;
A fuel cell system comprising system stop means for stopping the purge and stopping the fuel cell system after the purge time has elapsed since the start of the purge. The representative temperature measuring means is a cooling water temperature measuring means for measuring the temperature of the cooling water flowing out of the fuel cell stack,
The purge time determining means calculates the degree of wetness in the fuel cell stack based on the time change rate of the cooling water temperature measured by the cooling water temperature measuring means while flowing gas into the fuel cell stack. The fuel cell system according to claim 1, wherein: The representative temperature measuring means is a stack temperature measuring means for measuring the temperature inside the fuel cell stack,
The purge time determining means calculates the degree of wetness in the fuel cell based on the time change rate of the stack temperature measured by the stack temperature measuring means while flowing gas into the fuel cell stack. The fuel cell system according to claim 1 . Based on the representative temperature measured by the representative temperature measuring means, further comprising a purge flow rate determining means for determining a purge flow rate such that the purge flow rate increases as the representative temperature increases;
2. The fuel cell system according to claim 1, wherein the purge unit performs purge by flowing a gas having a purge flow rate determined by the purge flow rate determining unit to the fuel cell stack. 3. The fuel cell system according to claim 4 , wherein the purge unit decreases the purge flow rate as time elapses after the purge is started. A fuel cell system for generating power by a fuel cell stack,
Trigger detecting means for detecting a stop trigger for stopping the fuel cell system;
Representative temperature measuring means for measuring a representative temperature of the fuel cell stack;
Purge means for purging by flowing a gas to the fuel cell stack;
A wetness degree detection means for detecting a wetness degree in the fuel cell stack based on a temporal change rate of the representative temperature measured by the representative temperature measurement means while flowing gas to the fuel cell stack by the purge means ;
A fuel cell system comprising: system stop means for stopping the purge and stopping the fuel cell system when the wetness degree detected by the wetness degree detection means falls below a predetermined value. 3. The fuel cell according to claim 2 , wherein when detecting the degree of wetness in the fuel cell, the cooling water circulates in the fuel cell stack bypassing a radiator for cooling the cooling water. system.   2. The purge time determining means determines the purge time based on the representative temperature measured by the representative temperature measuring means so that the purge time becomes shorter as the representative temperature is higher. The fuel cell system described. A method for stopping a fuel cell system that generates power using a fuel cell stack,
A first step of detecting a stop trigger for stopping the fuel cell system;
A second step of measuring a representative temperature of the fuel cell stack when detecting the stop trigger;
A third step of starting a purge by flowing a gas through the fuel cell stack;
A fourth step of calculating the degree of wetting based on the time rate of change of the representative temperature while flowing gas through the fuel cell stack, and determining the purge time so that the purge time becomes longer as the degree of wetness is higher;
And a fifth step of stopping the fuel cell system by stopping the purge after elapse of the purge time from the start of the purge. In the second step, the temperature of the cooling water flowing out of the fuel cell stack is measured,
The fourth step is, claim based on the time rate of change of the temperature of the cooling water measured while flowing a gas to the fuel cell stack, and calculating the wetting degree within the fuel cell 9 The fuel cell system stop method described. In the second step, the temperature inside the fuel cell stack is measured,
The fourth step is, claim wherein the fuel cell based on the time rate of change of temperature inside the stack which is measured while flowing a gas to the stack, and calculates the wetting degree within the fuel cell stack 9 The fuel cell system stop method described. A seventh step of determining the purge flow rate based on the representative temperature so that the purge flow rate increases as the representative temperature increases;
10. The method of stopping a fuel cell system according to claim 9, wherein the third step starts the purge by flowing a gas at the purge flow rate to the fuel cell stack. 13. The fuel cell system stop method according to claim 12, wherein the third step decreases the purge flow rate as time elapses after the purge is started. A method for stopping a fuel cell system that generates power using a fuel cell stack,
A first step of detecting a stop trigger for stopping the fuel cell system;
A second step of measuring a representative temperature of the fuel cell stack when detecting the stop trigger;
A third step of starting a purge by flowing a gas through the fuel cell stack;
A fourth step of detecting the degree of wetting in the fuel cell based on the time rate of change of the representative temperature measured while flowing gas through the fuel cell stack;
And a fifth step of stopping the fuel cell system by stopping the purge when the wetness level is equal to or lower than a predetermined value. The method further comprises an eighth step of circulating the fuel cell stack by bypassing a radiator that cools the cooling water when detecting the degree of wetness in the fuel cell. the method of stopping the fuel cell system according 10. 10. The fuel cell system stopping method according to claim 9, wherein the fourth step determines the purge time based on the representative temperature so that the purge time becomes shorter as the representative temperature is higher.

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