JP2009117056A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system capable of suppressing rise of a cathode potential after power generation stoppage of a fuel cell, and preventing degradation of the fuel cell at restarting. <P>SOLUTION: The fuel cell system 1 is provided with a fuel cell stack 10, a hydrogen tank 31 as well as a second shutoff valve 34 for supplying fuel gas to an anode flow channel 16a, a voltage sensor 23 for detecting a cathode potential of the fuel cell stack 10 for every elapse of a given time Δt1 after power generation stoppage of the fuel cell stack 10, an ECU 60 storing the cathode potentials, and the ECU 60 for calculating difference of this-time cathode potential and previous cathode potential, and, when the difference is above a given value, calculating a target supply volume of hydrogen based on the difference, and controlling the second shutoff valve 34 so that hydrogen of the target supply volume is supplied to the anode flow channel 16a. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fuel cell system.

  In recent years, the development of fuel cells such as polymer electrolyte fuel cells (PEFC) that generate electricity by supplying hydrogen (fuel gas) to the anode and oxygen (oxidant gas) to the cathode has been developed. It is thriving. Fuel cells are being applied in a wide range, such as fuel cell vehicles that run on the power generated by them, and household power supplies, and their application range is expected to expand in the future.

  When stopping the power generation of such a fuel cell, it is common to stop the hydrogen supply to the anode and the air supply to the cathode. And the technique which improves the restart property of a fuel cell is proposed (refer patent document 1).

JP 2006-139991 A

However, after a certain amount of time has elapsed after the power generation of the fuel cell is stopped, hydrogen in the anode channel passes through the electrolyte membrane (solid polymer membrane) and leaks into the cathode channel. On the other hand, the air (oxygen) in the cathode channel passes through the electrolyte membrane and leaks into the anode channel.
Here, the upstream and downstream of the anode channel are generally closed when the power generation of the fuel cell is stopped, but the upstream and downstream of the cathode channel, particularly the upstream communicating with the compressor (oxidant gas supply source) is the fuel cell. It is general that the power is communicated with the outside through the compressor even when the power generation is stopped.

(1) In this way, when the power generation of the fuel cell is stopped, if the cathode flow channel communicates with the outside, hydrogen leaked from the anode flow channel flows out to the outside, and air flows into the cathode flow channel. The cathode flow path is almost filled with air.
Then, the cathode potential based on the cathode flow path substantially filled with air becomes higher than the anode potential based on the anode flow path in which hydrogen and air are mixed. When the cathode potential is increased in this way, the cell voltage (difference between the cathode potential and the anode potential) increases. Note that the anode potential based on the anode flow path in which hydrogen and air are mixed is substantially zero.

  (2) After that, when the power generation stop state of the fuel cell continues, the air in the cathode channel passes through the electrolyte membrane and leaks into the anode channel. And when air leaks into the anode channel in this way, the oxygen in the leaked air generates an electrode reaction under the catalyst of the anode, the anode potential rises, approaches the cathode potential, and as a result, the cell voltage drops To do.

  In the situation where the cathode potential is high as described in (1) and (2), when the fuel cell system is restarted and air is supplied to the cathode flow path, the cathode potential further rises and the fuel potential increases. The battery (electrolyte membrane, anode, cathode, etc.) may be deteriorated.

  Therefore, an object of the present invention is to provide a fuel cell system that can suppress an increase in cathode potential after stopping the power generation of the fuel cell and prevent deterioration of the fuel cell at the time of restart.

  As means for solving the above problems, the present invention has a fuel gas flow path and an oxidant gas flow path, the fuel gas in the fuel gas flow path, the oxidant gas in the oxidant gas flow path, A fuel cell that generates power by being supplied, a fuel gas supply means that supplies fuel gas to the fuel gas flow path, and a cathode potential of the fuel cell every time a predetermined time elapses after power generation of the fuel cell is stopped A potential amount detection means for detecting the potential amount; a potential amount storage means for storing the potential amount detected by the potential amount detection means; and a potential amount difference which is a difference between the current potential amount and the previous potential amount. When the calculated potential amount difference is equal to or greater than the predetermined potential amount difference, the fuel gas is determined based on the current potential difference so that the cathode potential does not deteriorate even if the cathode potential rises due to restart. Calculate target supply volume , As the fuel gas calculated target supply amount is supplied to the fuel gas flow field, a fuel cell system characterized by and a control means for controlling the fuel gas supply means.

  Here, as the potential amount related to the cathode potential, for example, cathode potential (vs SHE), anode potential (vs SHE), cell voltage (cathode potential-anode potential), fuel gas or oxidant in the oxidant gas flow path Examples include gas concentration and elapsed time after power generation is stopped.

According to such a fuel cell system, when the potential amount difference, which is the difference between the potential amount detected this time and the potential amount detected last time and stored in the potential amount storage means, is greater than or equal to the predetermined potential amount difference. The target supply amount of fuel gas calculated based on the current potential amount difference is less than or equal to the cathode potential at which the fuel cell does not deteriorate even if the cathode potential rises due to restart. The fuel gas supply means is controlled so as to be supplied to the engine.
Then, the fuel gas supplied to the fuel gas channel passes through the electrolyte membrane and leaks to the oxidant gas channel. Then, the amount of fuel gas in the oxidant gas flow path increases, and the cathode potential decreases.

  In this way, since the increase in the cathode potential after stopping the power generation of the fuel cell is suppressed, the system is restarted after that, even if the oxidant gas is newly supplied to the cathode flow path and the cathode potential is increased, The cathode potential never reaches the potential at which the fuel cell deteriorates. As a result, deterioration of the fuel cell (MEA or the like) can be prevented.

  In the fuel cell system, the target supply amount is set to increase as the current potential difference increases.

  According to such a fuel cell system, the target supply amount of fuel gas is set (corrected) so as to increase the current potential difference. Thereby, an appropriate amount of fuel gas can be supplied to the fuel gas flow path.

  In the fuel cell system, the target supply amount is set to increase as the elapsed time from the power generation stop of the fuel cell is shorter.

  According to such a fuel cell system, the target supply amount of the fuel gas is set (corrected) as the elapsed time from the power generation stop of the fuel cell is shorter. Thereby, an appropriate amount of fuel gas can be supplied to the fuel gas flow path.

  In the fuel cell system, the target supply amount is set to increase as the temperature of the fuel cell when power generation is stopped is higher.

  According to such a fuel cell system, the target supply amount of the fuel gas is set (corrected) as the temperature of the fuel cell when power generation is stopped is higher. Thereby, an appropriate amount of fuel gas can be supplied to the fuel gas flow path.

  The fuel gas supply means includes a fuel gas source, a first shut-off valve, a pressure adjusting means, and a second shut-off valve. The fuel gas of the fuel gas source includes the first shut-off valve, the pressure When the fuel cell is supplied to the fuel gas passage through the adjusting means and the second shut-off valve in order to stop the power generation of the fuel cell, the first shut-off valve and the second shut-off valve are closed, and the fuel cell When supplying fuel gas to the fuel gas flow path after stopping power generation, the control means opens the second shutoff valve while keeping the first shutoff valve closed. .

  According to such a fuel cell system, when supplying the fuel gas to the fuel gas flow path after stopping the power generation of the fuel cell, the control means opens the second cutoff valve while keeping the first cutoff valve closed. Thereby, the fuel gas remaining between the first cutoff valve and the second cutoff valve can be supplied to the fuel gas flow path.

  ADVANTAGE OF THE INVENTION According to this invention, the fuel cell system which can suppress the raise of the cathode potential after the power generation stop of a fuel cell and can prevent deterioration of the fuel cell at the time of restart can be provided.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 to 5.

≪Configuration of fuel cell system≫
A fuel cell system 1 according to this embodiment shown in FIG. 1 is mounted on a fuel cell vehicle (moving body) (not shown). The fuel cell system 1 includes a fuel cell stack 10, a standard hydrogen electrode 21 and a voltage sensor 23 for detecting the cathode potential of the single cells 11 constituting the fuel cell stack 10, and an anode 14 of the fuel cell stack 10. An anode system (fuel gas supply means) for supplying and discharging hydrogen (fuel gas), a cathode system for supplying and discharging air containing oxygen (oxidant gas) to the cathode 15 of the fuel cell stack 10, and IG51 (ignition) And an ECU 60 (Electronic Control Unit) for electronically controlling them.

<Fuel cell stack>
The fuel cell stack 10 is a stack formed by stacking a plurality of (for example, 200 to 400) solid polymer type single cells 11, and the plurality of single cells 11 are electrically connected in series. In FIG. 1, only one single cell 11 is shown.
The single cell 11 includes an MEA 12 (Membrane Electrode Assembly) and two conductive anode separators 16 and a cathode separator 17 sandwiching the MEA 12. The MEA 12 includes an electrolyte membrane 13 (solid polymer membrane) made of a monovalent cation exchange membrane or the like, and an anode 14 and a cathode 15 (electrode) sandwiching the membrane.

  The anode 14 and the cathode 15 are mainly composed of a conductive porous material such as carbon paper, and contain a catalyst (Pt, Ru, etc.) for causing an electrode reaction in the anode 14 and the cathode 15. .

The anode separator 16 is formed with grooves and through holes for supplying and discharging hydrogen to and from the anode 14 of each MEA 12, and these grooves and through holes function as an anode flow path 16a (fuel gas flow path). ing.
The cathode separator 17 is formed with grooves and through holes for supplying and discharging air to and from the cathode 15 of each MEA 12, and these grooves and through holes function as a cathode channel 17a (oxidant gas channel). is doing.

  Then, when hydrogen is supplied to each anode 14 through the anode flow channel 16a and air is supplied to each cathode 15 through the cathode flow channel 17a, an electrode reaction occurs, and a potential difference (OCV (OCV ( Open Circuit Voltage) is generated. Next, when the fuel cell stack 10 and an external circuit such as a travel motor are electrically connected and a current is taken out, the fuel cell stack 10 generates power.

<Standard hydrogen electrode>
As the standard hydrogen electrode 21 (Standard Hydrogen Electrode: SHE), for example, a reversible hydrogen electrode (RHE) made of a porous hydrogen diffusion layer can be used. This is a reference electrode for detecting the cathode potential (potential amount related to the cathode potential). Hydrogen for constituting the standard hydrogen electrode 21 is introduced from, for example, a hydrogen tank 31 described later via a normally closed on-off valve (not shown) that is opened in accordance with a command from the ECU 60 when a cathode potential is detected.

  Further, a part of the cathode 15 is immersed in the liquid path filled with the electrolyte solution constituting the standard hydrogen electrode 21 and is conducted. Furthermore, the electrode body of the standard hydrogen electrode 21 is connected to the cathode 15 via a switch 22 and a voltage sensor 23 (potential amount detection means) that are turned on when the cathode potential is detected.

  When the cathode potential is detected, when the on-off valve is opened and the switch 22 is turned on, the voltage sensor 23 detects the cathode potential (vs SHE) and outputs it to the ECU 60.

<Anode system>
The anode system includes a hydrogen tank 31 (fuel gas source), a first shut-off valve 32, a pressure reducing valve 33 (pressure adjusting means), a second shut-off valve 34, an ejector 35, a purge valve 36, and a temperature sensor 37. And.
The hydrogen tank 31 is connected to the inlet of the anode flow path 16a via the pipe 31a, the first shutoff valve 32, the pipe 32a, the pressure reducing valve 33, the pipe 33a, the second shutoff valve 34, the pipe 34a, the ejector 35, and the pipe 35a. Has been. Then, when the first cutoff valve 32 and the second cutoff valve 34 are opened in accordance with a command from the ECU 60, hydrogen is supplied from the hydrogen tank 31 to the anode flow path 16a via the first cutoff valve 32 and the like. It has become. The pressure reducing valve 33 is for reducing the pressure of hydrogen from the hydrogen tank 31 toward the anode flow path 16a to a predetermined pressure.

  That is, in this embodiment, the hydrogen supply flow path (fuel gas supply flow path) of hydrogen (fuel gas) supplied to the anode flow path 16a is configured by the pipes 31a, 32a, 33a, 34a, and 35a.

  A pipe 36a, a purge valve 36, and a pipe 36b are sequentially connected to the outlet of the anode flow path 16a. The middle of the pipe 36a is connected to the ejector 35 via the pipe 36c.

The purge valve 36 is a normally closed electromagnetic valve. When the purge valve 36 is closed, the anode off-gas containing unreacted hydrogen discharged from the anode flow path 16a is returned to the ejector 35. As a result, the hydrogen Has come to circulate.
On the other hand, when impurities such as water vapor accompanying the circulating hydrogen increase and the voltage (cell voltage) of the single cell 11 becomes lower than a predetermined cell voltage via a cell voltage monitor (not shown), the ECU 60 causes the purge valve 36 to Is opened, and impurities such as water vapor are discharged outside the vehicle through the pipe 36b.

The temperature sensor 37 (fuel cell temperature detection means) is arranged in the pipe 36a, detects the temperature of the anode off gas discharged from the anode flow path 16a as the temperature of the fuel cell stack 10, and outputs it to the ECU 60. It has become.
However, the position of the temperature sensor 37 that detects the temperature of the fuel cell stack 10 is not limited to this, and a pipe 42a through which the cathode off-gas flows, a pipe (not shown) through which the refrigerant discharged from the fuel cell stack 10 flows, It is good also as a structure arrange | positioned in the housing | casing of the fuel cell stack 10. FIG. A plurality of temperature sensors 37 may be provided to prevent erroneous detection.

<Cathode system>
The cathode system includes a compressor 41 (oxidant gas supply means) and a back pressure valve 42 (pressure adjustment means).
The compressor 41 is connected to the inlet of the cathode channel 17a via the pipe 41a. When the compressor 41 operates according to a command from the ECU 60, the compressor 41 takes in air containing oxygen and supplies it to the cathode channel 17a. The pipe 41a is provided with a humidifier (not shown) that appropriately humidifies the air toward the cathode flow path 17a.

  A pipe 42a, a back pressure valve 42, and a pipe 42b are connected to the outlet of the cathode flow path 17a, and the cathode off gas discharged from the cathode flow path 17a is discharged to the outside (outside) through the pipe 42a and the like. It is like that. The back pressure valve 42 adjusts the back pressure, that is, the gas pressure in the cathode flow path 17a, in accordance with a command from the ECU 60.

<IG>
The IG 51 is a start switch for the fuel cell vehicle and the fuel cell system 1 and is provided around the driver's seat. Further, the IG 51 is connected to the ECU 60, and the ECU 60 detects an ON / OFF signal of the IG 51.

<ECU>
The ECU 60 (control means, potential amount storage means) is a control device that electronically controls the fuel cell system 1, and includes a CPU, a ROM, a RAM, various interfaces, an electronic circuit, and the like, and is stored therein. Various devices are controlled and various processes are executed in accordance with the programmed programs.
The specific control contents by the ECU 60 will be described in detail below with reference to the flowchart of FIG.

≪Operation of fuel cell system≫
Next, mainly referring to FIG. 2, the operation of the fuel cell system 1 will be described together with the flow of a program (flow chart) set in the ECU 60.
Note that when the IG 51 is turned off, the processing shown in FIG. 2 starts. In the initial state (before the IG 51 is turned off), the first cutoff valve 32 and the second cutoff valve 34 are opened, the compressor 41 is operating, and the fuel cell stack 10 is generating power.

In step S101, the ECU 60 closes the first cutoff valve 32 and the second cutoff valve 34, and stops the supply of hydrogen to the anode flow path 16a. Further, the ECU 60 stops the compressor 41 and stops the supply of air to the cathode flow path 17a. Further, the ECU 60 turns off the connection between the fuel cell stack 10 and an external circuit including a travel motor and stops the power generation of the fuel cell stack 10.
Further, here, the case where the back pressure valve 42 is opened after the power generation of the fuel cell stack 10 is stopped is illustrated.

  In step S102, the ECU 60 detects the temperature of the fuel cell stack 10 when power generation is stopped via the temperature sensor 37, and stores this in an internal memory (RAM or the like).

In step S103, the ECU 60 uses the internal clock to determine whether the determination result in step S101, step S105 described later is No, or whether a predetermined time Δt has elapsed after step S109 described later. The predetermined time Δt1 (for example, 5 minutes) is a time for periodically detecting the cathode potential after power generation of the fuel cell stack 10 is stopped, and is obtained by an incident test or the like and stored in the ECU 60 in advance. Has been.
Note that the predetermined time Δt1 may be variable, for example, the predetermined time Δt1 may be gradually increased as time elapses after the fuel cell stack 10 stops generating power.

  When it is determined that the predetermined time Δt1 has elapsed (S103: Yes), the process of the ECU 60 proceeds to step S104. On the other hand, when it is determined that the predetermined time Δt1 has not elapsed (S103 · No), the ECU 60 repeats the determination in step S103.

  In step S104, the ECU 60 (potential amount storage means) detects the cathode potential (current cathode potential) via the voltage sensor 23. Then, the ECU 60 stores the detected current cathode potential in an internal memory (RAM or the like).

  After that, even if the determination result in step S105 described later is No, or after step S109, the determination result in step S103 is Yes and the process proceeds to step S104, the ECU 60 again detects the cathode potential, Remember.

  That is, the process of step S104 is executed every time the predetermined time Δt1 elapses after the fuel cell stack 10 stops generating power. Then, except for the first time, the ECU 60 stores the cathode potential detected in the current step S104 (current cathode potential) and the cathode potential detected in the previous step S104 (previous cell voltage).

In step S105, the ECU 60 determines whether or not the difference between the current cathode potential and the previous cathode potential stored in the internal memory is equal to or greater than a predetermined value (predetermined potential amount difference).
If it is determined that the difference between the current cathode potential and the previous cathode potential is greater than or equal to a predetermined value (S105, Yes), the process of the ECU 60 proceeds to step S106. On the other hand, when it is determined that the difference between the current cathode potential and the previous cathode potential is not equal to or greater than the predetermined value (No in S105), the process of the ECU 60 proceeds to step S103.
In the initial determination in step S105, the determination result is set to No.

Here, the movement of the anode potential (vs SHE), the cathode potential (vs SHE), and the cell voltage (cathode potential−anode potential) after power generation stop of the fuel cell stack 10 will be described with reference to FIG.
The anode potential is substantially zero when power generation is stopped. After the power generation is stopped, air leaks from the cathode channel 17a to the anode channel 16a, but the anode potential continues to be substantially zero.

  The cathode potential is about 0.7 to 0.9 V, for example, depending on the specifications of the MEA 12, the set pressure of the cathode channel 17a, and the like when power generation is stopped. Thereafter, as time elapses, hydrogen remaining in the anode flow channel 16a permeates the electrolyte membrane 13 and leaks to the cathode flow channel 17a. When the leaked hydrogen undergoes an electrode reaction under a catalyst contained in the cathode 15, The potential and cell voltage are reduced.

Since the upstream and downstream sides of the cathode channel 17a are opened to the outside (external) via the back pressure valve 42 and the like that remain open, the leaked hydrogen flows out of the vehicle and the cathode channel 17a from the outside of the vehicle. Air flows into the. When air flows into the cathode channel 17a in this way, oxygen in the air undergoes an electrode reaction under the catalyst of the cathode 15, and the cathode potential and cell voltage tend to increase (see symbols A and B in FIG. 5).
Next, the air in the cathode channel 17a passes through the electrolyte membrane 13 and begins to leak into the anode channel 16a.

  When air leaks into the anode flow path 16a, oxygen in the leaked air undergoes an electrode reaction under the catalyst of the anode 14, and the anode potential tends to increase (see symbol C in FIG. 5). On the other hand, since the cathode potential remains increased, the cell voltage tends to decrease as the anode potential increases (see symbol D in FIG. 5).

Then, the IG 51 is turned on in the state in which the cathode potential is increased in this way, and the ECU 60 that detects this ON signal operates the compressor 41 to restart the fuel cell system 1 to the cathode flow path 17a. When air is newly introduced, oxygen in the introduced air undergoes an electrode reaction, the cathode potential rises (see symbol E in FIG. 5), and the upper limit cathode potential that was planned when the fuel cell stack 10 and MEA 12 were designed. It becomes higher than V1.
On the other hand, hydrogen is newly supplied to the anode flow path 16a, and this hydrogen undergoes an electrode reaction, so that the anode potential decreases (see reference F in FIG. 5).

  As a result, the cell voltage greatly increases (see symbol G in FIG. 5), and becomes higher than the upper limit cell voltage ΔV1 scheduled at the time of design. If a current is taken out in such a state, a current larger than planned flows and the MEA 12 or the like may be deteriorated.

  Further, the degree of increase in the cathode potential is related to the degree of activity of the catalyst contained in the cathode 15, and the higher the activity of the catalyst, that is, the higher the temperature of the catalyst, the more the cathode potential tends to increase. Therefore, the higher the temperature of the fuel cell stack 10 when power generation is stopped and the shorter the elapsed time since power generation is stopped, the more the cathode potential tends to increase.

  In the present embodiment, in consideration of the movement of the anode potential, the cathode potential, and the cell potential, when the difference between the current cathode potential and the previous cathode potential is equal to or greater than a predetermined value (Yes in S105), Hydrogen is supplied to the anode flow path 16a, hydrogen is leaked to the cathode flow path 17a, and an increase in cathode potential is suppressed.

Then, even when the system is restarted and air is newly supplied to the cathode flow path 17a and the cathode potential rises, the cathode potential becomes lower than the upper limit cathode potential V1, that is, after the power generation is stopped and before the restart. The cathode potential is controlled so that the cathode potential becomes equal to or lower than the upper limit cathode potential V2 before restarting after power generation is stopped.
Note that the upper limit cathode potential V2 after the power generation is stopped and before the restart is set to, for example, a potential obtained by subtracting the increase amount (ΔV5) of the cathode potential at the time of restart from the upper limit cathode potential V1.

  Therefore, the predetermined value that becomes the determination criterion in step S105 is related to the predetermined time Δt1 in step S103 (the predetermined value becomes smaller as the predetermined time Δt1 becomes shorter), and related to the specifications of the MEA 12, etc., and the IG 51 is turned on. Even when the system is restarted and the cathode potential rises by ΔV5, the cathode potential after the rise becomes the upper limit cathode potential V1 or less, and the MEA 12 and the like are set to values that do not deteriorate. Such a predetermined value is obtained by a preliminary test or the like and stored in advance in the ECU 60.

Returning to FIG. 2, the description will be continued.
In step S106, the ECU 60 supplies the anode flow path 16a with the difference between the current cathode potential and the previous cathode potential (potential amount difference), the temperature of the fuel cell stack 10 when power generation is stopped, and the map of FIG. The amount of hydrogen (target supply amount) to be calculated and the open time Δt2 (hydrogen supply time, target supply amount) of the second shut-off valve 34 are calculated. Next, the correction coefficient X is obtained based on the time from the stop of power generation and the map of FIG.

3 and 4 are obtained by a preliminary test or the like and stored in the ECU 60 in advance.
As shown in FIG. 3, the larger the difference between the current cathode potential and the previous cathode potential, and the higher the temperature of the fuel cell stack 10 at the time of power generation stop, the longer the open time Δt2 of the second shutoff valve 34. That is, the amount of hydrogen supplied to the anode channel 16a and leaking to the cathode channel 17a is set to be large.

  As shown in FIG. 4, the correction coefficient X is 1 when power generation is stopped, and is set to gradually increase as time elapses from the stop of power generation. As a result, the opening time Δt2 of the second shut-off valve 34 becomes longer and the hydrogen leaking to the cathode flow path 17a increases as time elapses from the stop of power generation.

In step S107, the ECU 60 opens the second cutoff valve 34 while keeping the first cutoff valve 32 closed.
Here, since the residual hydrogen in the anode channel 16a permeates the electrolyte membrane 13 and leaks to the cathode channel 17a, the pressure downstream of the second shutoff valve 34 including the anode channel 16a is The pressure is lower than the pressure between the first shutoff valve 32 and the pressure reducing valve 33 (primary pressure of the pressure reducing valve 33).

In such a situation, when the second shut-off valve 34 is opened, the pressure reducing valve 33 is opened, the residual hydrogen in the pipe 32a flows downstream of the pressure reducing valve 33, and hydrogen is supplied to the anode flow path 16a.
That is, in the present embodiment, the pipe 32a functions as a buffer unit for temporarily storing the hydrogen supplied to the anode flow path 16a after the fuel cell stack 10 stops generating power. Therefore, for example, the pipe 32a may be partially thickened to increase the amount of hydrogen stored.

  Next, the hydrogen supplied to the anode channel 16a passes through the electrolyte membrane 13 and leaks to the cathode channel 17a. As a result, the hydrogen concentration in the cathode channel 17a increases, and a part of the hydrogen reacts under the catalyst of the cathode 15, and as a result, the cathode potential and the cell voltage decrease (see symbols H and I in FIG. 5). .

In step S108, the ECU 60 uses the internal clock to determine whether or not the corrected open time Δt2 calculated in step S106 has elapsed after opening the second shut-off valve 34 in step S107.
When it is determined that the corrected open time Δt2 has elapsed (S108, Yes), the process of the ECU 60 proceeds to step S109. When it is determined that the corrected open time Δt2 has not elapsed (NO at S108), the ECU 60 repeats the determination at step S108.

In step S109, the ECU 60 closes the second cutoff valve 34.
Thereafter, the processing of the ECU 60 proceeds to step S103.

≪Effect of fuel cell system≫
According to such a fuel cell system 1, the following effects are obtained.
After the power generation of the fuel cell stack 10 is stopped, the current cathode potential is repeatedly detected every predetermined time Δt1. If the difference between the current cathode potential and the previous cathode potential is equal to or greater than a predetermined value, the anode channel 16a Hydrogen is supplied and hydrogen is leaked to the cathode channel 17a, so that an increase in cathode potential can be suppressed.
As a result, even after the IG 51 is turned on, the fuel cell system 1 is restarted, and new air is supplied to the cathode flow path 17a, the cathode potential and the cell voltage are the upper limit cathode potential V1 at which the MEA 12 and the like deteriorate. Further, it is prevented that the voltage becomes higher than the upper limit cell voltage ΔV1.

  Further, the opening time Δt2 of the second shutoff valve 34, that is, the amount of hydrogen leaked to the cathode flow path 17a is the difference between the current cathode potential and the previous cathode potential, the temperature of the fuel cell stack 10 when power generation is stopped, and power generation stop. Based on the time from, it can be determined appropriately.

  Furthermore, since the fuel cell system 1 includes the first shut-off valve 32, the pressure reducing valve 33, and the second shut-off valve 34 in order from the hydrogen tank 31 that is a fuel gas source toward the anode flow path 16a, the second shut-off valve 34 is provided. Can be supplied to the anode channel 16a.

  As mentioned above, although one Embodiment of this invention was described, this invention is not limited to the said embodiment, For example, it can change as follows in the range which does not deviate from the meaning of this invention.

In the embodiment described above, the back pressure valve 42 is opened after the fuel cell stack 10 stops generating power (after the fuel cell system 1 stops). However, after the fuel cell stack 10 stops generating power, the back pressure valve 42 is turned off. The present invention may be applied to a configuration that is closed and reduces the inflow of air into the cathode channel 17a from the outside via the pipe 42b or the like.
In the case of this configuration, since the air flowing into the cathode flow path 17a is reduced, the rise in the cathode potential is delayed. However, if the back pressure valve 42 is exposed to a low temperature environment such as below freezing during the stop, it is preferable to keep the back pressure valve 42 open at a small opening in order to prevent the back pressure valve 42 from being frozen completely. .

In the above-described embodiment, when the cathode potential rises after power generation is stopped, the second shut-off valve 34 is opened, and the residual hydrogen in the pipe 32a is supplied to the anode flow path 16a. It is good also as a structure which opens 32 and supplies the hydrogen in the hydrogen tank 31. FIG.
Further, for example, a tank for temporarily storing hydrogen may be provided so as to branch from the pipe 35a, and hydrogen may be supplied from the tank to the anode flow path 16a.

  In the above-described embodiment, after power generation is stopped, hydrogen is supplied to the anode flow path 16a, and hydrogen is leaked to the cathode flow path 17a to suppress the increase in cathode potential. Alternatively, hydrogen may be directly supplied to the cathode channel 17a via a simple pipe.

In the above-described embodiment, the hydrogen supply to the anode flow path 16a after the power generation is stopped is controlled based on the open time (hydrogen supply time) of the second shut-off valve 34. And may be controlled based on the pressure change. When the first shut-off valve 32 is opened and hydrogen is supplied also from the hydrogen tank 31, for example, a pressure sensor may be provided in the pipe 31a.
Further, a pressure sensor for detecting the pressure of the anode flow path 16a is provided, and when the pressure of the anode flow path 16a reaches a predetermined pressure (when the pressure increases), it is predicted that hydrogen has been supplied and hydrogen supply is performed. It is good also as a structure which stops.

  In the above-described embodiment, the cathode potential is detected after power generation is stopped, and hydrogen is supplied based on the amount of change in the cathode potential. For example, air leaks into the anode flow path 16a after power generation stops, and the anode When the potential rises, the cathode potential is also expected to rise. Therefore, when the amount of change in the anode potential, that is, when the anode potential rises, hydrogen may be supplied.

  In addition, after power generation stops, the cell voltage decreases as the cathode potential decreases, and then the cell voltage increases as the cathode potential increases. It is good also as a structure which supplies hydrogen in anticipation of having risen.

  Furthermore, after the hydrogen concentration in the cathode channel 17a once increases due to leakage to the cathode channel 17a, hydrogen flows out of the vehicle, and when the hydrogen concentration decreases, the cathode potential rises. A configuration may be adopted in which a hydrogen sensor for detecting the hydrogen concentration is provided at an appropriate place and the hydrogen supply is controlled based on a change in the hydrogen concentration.

  Furthermore, after power generation stops, the cathode potential once decreases and then rises. Therefore, after a predetermined time has elapsed since power generation stopped, the cathode potential is expected to increase, and hydrogen is supplied based on the elapsed time since power generation stopped. It is good also as a structure which controls.

It is a figure which shows the structure of the fuel cell system which concerns on this embodiment. It is a flowchart which shows operation | movement of the fuel cell system which concerns on this embodiment. 6 is a map showing the relationship between the difference between the current cathode potential and the previous cathode potential, the open time Δt2 of the second shut-off valve, and the temperature of the fuel cell stack when power generation is stopped. 3 is a map showing a relationship between an elapsed time from power generation stop of a fuel cell stack and a correction coefficient X. It is a time chart which shows one operation example of the fuel cell system concerning this embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel cell system 10 Fuel cell stack 11 Single cell 12 MEA
13 Electrolyte membrane 14 Anode 15 Cathode 16a Anode flow path (fuel gas flow path)
17a Cathode channel (oxidant gas channel)
21 Standard hydrogen electrode 23 Voltage sensor (potential detection means)
31 Hydrogen tank (fuel gas source, fuel gas supply means)
32 1st shut-off valve (fuel gas supply means)
33 Pressure reducing valve (pressure adjusting means, fuel gas supplying means)
34 Second shut-off valve (fuel gas supply means)
37 Temperature sensor (Fuel cell temperature detection means)
60 ECU (potential amount storage means, control means)
V1 Upper limit cathode potential at start-up V2 Upper limit cathode potential at power generation stop ΔV1 Upper limit cell voltage at start-up Δt2 Second shut-off valve 34 open time (hydrogen supply time, target supply amount)

Claims (5)

A fuel cell having a fuel gas channel and an oxidant gas channel, wherein fuel gas is generated by supplying fuel gas to the fuel gas channel and oxidant gas to the oxidant gas channel;
Fuel gas supply means for supplying fuel gas to the fuel gas flow path;
A potential amount detection means for detecting a potential amount related to the cathode potential of the fuel cell every predetermined time after power generation of the fuel cell is stopped;
A potential amount storage means for storing the potential amount detected by the potential amount detection means;
When the potential difference, which is the difference between the current potential amount and the previous potential amount, is calculated and the calculated potential amount difference is equal to or greater than the predetermined potential amount difference, the fuel cell The target supply amount of the fuel gas is calculated based on the current potential difference so that the cathode potential does not deteriorate or less, and the calculated target supply amount of fuel gas is supplied to the fuel gas flow path. Control means for controlling the fuel gas supply means;
A fuel cell system comprising: The fuel cell system according to claim 1, wherein the target supply amount is set to increase as the current potential difference increases. 3. The fuel cell system according to claim 1, wherein the target supply amount is set to increase as the elapsed time from the power generation stop of the fuel cell is shorter. The fuel cell system according to any one of claims 1 to 3, wherein the target supply amount is set to increase as the temperature of the fuel cell at the time of stopping power generation increases. The fuel gas supply means includes a fuel gas source, a first cutoff valve, a pressure adjustment means, and a second cutoff valve,
The fuel gas of the fuel gas source is supplied to the fuel gas flow path through the first cutoff valve, the pressure adjusting means, and the second cutoff valve in this order,
When stopping the power generation of the fuel cell, the first cutoff valve and the second cutoff valve are closed,
When supplying fuel gas to the fuel gas flow path after stopping the power generation of the fuel cell, the control means opens the second shutoff valve while keeping the first shutoff valve closed. The fuel cell system according to any one of claims 1 to 4.

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