JP2009266426A - Fuel cell system - Google Patents

Abstract

To keep a moisture state in a fuel cell constant when power generation is stopped, and to prevent a user from feeling uncomfortable due to a variation in time required for a scavenging process.
When power generation of a fuel cell stack is stopped, an air compressor is operated to supply scavenging gas to the fuel cell stack. While scavenging, the impedance value of the fuel cell stack 2 is measured, and the completion of scavenging is determined by comparing the impedance value with a predetermined threshold value. If the time required from the start to completion of scavenging is shorter than the preset scheduled scavenging time, the bypass valve 42 is switched to the bypass path 40 side to bypass the fuel cell stack 2 from the scavenging gas blowing path. In this state, the operation of the air compressor 22 is continued until the scheduled scavenging time has elapsed.
[Selection] Figure 1

Description

  The present invention relates to a fuel cell system having a fuel cell, and more particularly to a fuel cell system that scavenges the inside of a fuel cell with scavenging gas when power generation of the fuel cell is stopped.

  During power generation of the fuel cell, water is generated on the cathode side by the reaction between the oxidant gas and the fuel gas via the membrane electrode assembly. If this water remains inside the fuel cell even after power generation of the fuel cell is stopped, when the outside air temperature drops below freezing point, the remaining water freezes and closes the reaction gas flow path. In such a state, since sufficient reaction gas cannot be supplied to the membrane electrode assembly, it takes a long time to start the fuel cell.

  In order to keep the startability of the fuel cell below the freezing point, only the moisture necessary for the power generation reaction is left, and other unnecessary moisture may be removed in advance when the power generation is stopped. As a method for removing moisture from the fuel cell, for example, as described in Patent Documents 1 to 3 listed below, scavenging by flowing dry gas into the fuel cell is effective. . As the means, it is convenient to use an air compressor originally mounted on the system in terms of simplification of the system.

  Here, whether or not moisture removal by scavenging is completed can be determined from the impedance value of the fuel cell. In the prior art described in Patent Document 2 and Patent Document 3, scavenging by the air compressor is continued until the impedance value of the fuel cell reaches a predetermined value. By doing so, the moisture state of the fuel cell when power generation is stopped can be made constant, and stable startability can be ensured even below freezing.

  However, the amount of water remaining in the fuel cell when power generation is stopped varies depending on the history of operating conditions until power generation is stopped. Since the time required for the impedance value to reach a predetermined value after the start of scavenging varies depending on the amount of residual water, the operation time of the air compressor for the scavenging process also varies each time. The fact that the operation time of the air compressor is different every time is a strange phenomenon for a user who does not know the situation, and may feel uncomfortable. In particular, when the operation time becomes long, the user may be mistaken for a system failure. However, if the operating time of the air compressor is simply fixed, the moisture state inside the fuel cell varies every time, which leads to problems such as variations in starting time and inability to start.

  Regarding the above problems, Patent Documents 1 and 2 describe a technique for reducing the uncomfortable feeling given to the user by the scavenging operation of the air compressor. In the technique described in Patent Document 1, first, scavenging is performed at a large flow rate, then scavenging is stopped for a while, and then scavenging is performed at a small flow rate. That is, in this technique, the scavenging process is divided into two stages, and a waiting time is provided between them, thereby reducing the user's uncomfortable feeling caused by the continued scavenging.

On the other hand, in the technique described in Patent Document 2, a scavenging process is in progress and the scavenging is completed is notified to the user by a text message, a voice message, or the like. In other words, in this technique, information regarding scavenging is actively disclosed to the user, thereby reducing the user's uncomfortable feeling.
JP 2007-73328 A JP 2007-305346 A JP 2007-149572 A

  However, the effects obtained by the techniques described in Patent Documents 1 and 2 are all limited effects obtained only when certain preconditions are satisfied. In the thing of patent document 1, it is a precondition of an effect that a user leaves | separates from a system during the waiting time which has stopped scavenging. In the thing of patent document 2, it is a prerequisite for an effect that a user recognizes the message which a system emits. If these preconditions are not satisfied, the user still feels uncomfortable with the variation in the scavenging operation time of the air compressor.

  As described above, each of the techniques described in Patent Documents 1 and 2 can make the moisture state inside the fuel cell constant by scavenging processing at an appropriate time, but the variation in the scavenging operation time of the air compressor and the user It was not a sufficient solution to the problem of uncomfortable feelings.

  The present invention has been made in order to solve the above-described problems, so that the moisture state inside the fuel cell when power generation is stopped is kept constant, and the user does not feel uncomfortable due to variations in the time required for the scavenging process. An object of the present invention is to provide a fuel cell system.

In order to achieve the above object, a fuel cell system according to a first invention comprises:
A fuel cell;
Scavenging gas blowing means for blowing scavenging gas toward the fuel cell when power generation of the fuel cell is stopped;
Bypass means for bypassing the fuel cell from the air flow path of the scavenging gas;
Determination means for determining completion of scavenging based on a predetermined physical quantity related to the moisture state of the fuel cell;
When the time required from the start to completion of scavenging is shorter than the scheduled scavenging time, the fuel cell is bypassed by the bypass means, and the air blown by the scavenging gas blowing means until the scheduled scavenging time elapses in that state. Control means for continuing
It is characterized by having.

The fuel cell system of the second invention is the first invention,
A learning means for learning the time required from the start to completion of scavenging;
A scheduled scavenging time setting means for setting the scheduled scavenging time based on the longest required time learned by the learning means;
It is characterized by having.

  According to 1st invention, even if it is a case where the time required from the start of scavenging to completion changes every time, the ventilation time by the scavenging gas blowing means can be made constant. Therefore, it is possible to prevent the user from feeling uncomfortable due to the variation in time required for scavenging while preventing the variation in the moisture state inside the fuel cell by the scavenging process at an appropriate time.

  According to the second aspect of the present invention, by setting the scheduled scavenging time based on the longest time required for the completion of scavenging, the blowing time is shortened to the minimum necessary time within a range that does not give the user a sense of incongruity. can do. According to this, it is possible to improve the fuel efficiency of the system by suppressing waste of energy for blowing.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram schematically showing the configuration of a fuel cell system according to an embodiment of the present invention. Usually, the fuel cell is used as a fuel cell stack 2 formed by stacking a plurality of unit cells 30 as shown in FIG. Although not shown, each unit battery 30 is configured by sandwiching both sides of a membrane electrode assembly with separators. Each unit cell 30 receives fuel gas supplied to the anode side of the membrane electrode assembly and receives oxidant gas supplied to the cathode side to generate power. An impedance measuring device 32 for measuring the impedance value of the entire fuel cell stack is attached to the fuel cell stack 2.

  A hydrogen supply path 6 for supplying hydrogen as a fuel gas is connected to the fuel cell stack 2. The upstream end of the hydrogen supply path 6 is connected to a hydrogen supply source 4 such as a high-pressure hydrogen tank. In the middle of the hydrogen supply path 6, a pressure regulating valve 8 and a shut valve 10 are arranged. Hydrogen is depressurized by the pressure regulating valve 8 and adjusted to a desired pressure before being supplied to the fuel cell stack 2. Hydrogen supplied to the fuel cell stack 2 is distributed to the anode of each unit cell 30 by a supply manifold formed in the fuel cell stack 2. The outlet side of the anode of each unit cell 30 is connected to a discharge manifold formed in the fuel cell stack 2. This discharge manifold is connected to a purge valve 14 disposed outside the fuel cell stack 2. The purge valve 14 is controlled to open only when a predetermined purge condition is satisfied with the closed state as its basic state.

  The fuel cell stack 2 is connected to an air supply path 20 for supplying air as an oxidant gas. An air compressor 22 is disposed in the air supply path 20. Air is taken into the air supply path 20 by the rotation of the air compressor 22 and supplied to the fuel cell stack 2. Air supplied to the fuel cell stack 2 is distributed to the cathode of each unit cell 30 by a supply manifold formed in the fuel cell stack 2. The air that has passed through the cathode of each unit cell 30 is collected in a discharge manifold formed in the fuel cell stack 2 and discharged to the air discharge path 24. A pressure regulating valve 26 is disposed in the air discharge path 24.

  Furthermore, the fuel cell system of the present embodiment includes a bypass path 40 that bypasses the fuel cell stack 2 and connects the air supply path 20 to the air discharge path 24, and an air supply destination from the fuel cell stack 2 to the bypass path 40. And a bypass valve 42 for switching to.

  The switching operation of the bypass valve 42 is controlled by the control device 16. The control device 16 is a device that controls the operation of the entire system, and also controls the operation of the air compressor 22. In addition to the signal from the impedance measuring instrument 32 described above, signals from various sensors and measuring instruments are input to the control device 16. The control device 16 switches the bypass valve 42 when power generation of the fuel cell stack 2 is stopped, and the control device 16 uses the impedance value measured by the impedance measuring instrument 32 as an index for measuring the switching timing. Refers.

  The flowchart of FIG. 2 shows a routine executed by the control device 16 when the fuel cell stack 2 stops generating power. In the first step S2 of this routine, it is determined whether or not the system operation switch is turned off (or the system stop switch is turned on). The determination process in step S2 is repeatedly executed until the system operation switch is turned off.

  When the operation switch of the system is turned off, the processes after step S4 are performed. First, in step S4, the rotational speed of the air compressor 22 is set to a predetermined scavenging rotational speed. By continuing the operation of the air compressor 22 at this rotational speed, the inside of the fuel cell stack 2 is scavenged with air.

  In the next step S6, the impedance value of the fuel cell stack 2 measured by the impedance measuring device 32 is taken. In step S8, it is determined whether or not the impedance value acquired in step S6 is greater than or equal to a predetermined threshold value. This threshold value is an impedance value that appears when scavenging of the fuel cell stack 2 is completed, and a value obtained in advance by experiment is used. The impedance value is one of physical quantities related to the moisture state of the fuel cell stack 2. The processes in steps S6 and S8 are repeatedly executed until the impedance value becomes equal to or greater than the threshold value.

  When the impedance value is equal to or higher than the threshold value, scavenging is completed. In that case, in the next step S10, it is determined whether or not the elapsed time from the start of scavenging is equal to or longer than a predetermined scheduled scavenging time. The scheduled scavenging time is a fixed value, and is set to, for example, a time obtained by adding a certain margin time to the required scavenging time obtained in an experiment.

  When the elapsed time from the start of scavenging has not reached the scheduled scavenging time, the process of step S12 is executed. In step S12, the bypass valve 42 is operated to switch the air supply destination from the fuel cell stack 2 to the bypass path 40. Thereby, the supply of the scavenging gas into the fuel cell stack 2 is stopped. However, the operation of the air compressor 22 is continued while maintaining the above-described scavenging speed. The determination process in step S10 is repeatedly executed until the scheduled scavenging time has elapsed.

  Then, when the elapsed time from the start of scavenging is equal to or longer than the scheduled scavenging time, the process of step S14 is executed. In step S14, the operation of the air compressor 22 is stopped. Further, the bypass valve 42 is operated to switch the air supply destination from the bypass path 40 to the fuel cell stack 2 again. As a result, air can be supplied to the inside of the fuel cell stack 2 at the next startup of the system.

  By executing the routine described above when the power generation of the fuel cell stack 2 is stopped, the operating time of the air compressor 22 can be made constant even if the time required from the start to completion of scavenging changes each time. Therefore, according to the fuel cell system of the present embodiment, the variation in the time required for scavenging gives a sense of incongruity to the user while preventing the variation in the moisture state in the fuel cell stack 2 by the scavenging process at an appropriate time. Can also be prevented.

  In the present embodiment, as described above, the air compressor 22 functions as the “scavenging gas blowing means” according to the present invention, and air is used as the scavenging gas. Further, the bypass path 40 and the bypass valve 42 constitute a “bypass means” according to the present invention. The control device 16 functions as “determination means” and “control means” of the present invention. Specifically, the processing of steps S6 and S8 of the routine shown in FIG. 2 corresponds to the function as “determination means”, and the processing of steps S10, S12, and S14 corresponds to the function as “control means”.

  By the way, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. For example, a dedicated scavenging gas blowing means may be provided separately from the air compressor. The gas used as the scavenging gas is not necessarily air as long as it is a dry gas.

  Although the impedance measuring instrument is provided in the above-described embodiment, an ammeter and a voltmeter may be provided instead. The impedance value can be calculated from the signal from the ammeter and the signal from the voltmeter. Further, the humidity of the gas discharged from the fuel cell stack to the air discharge path can also be used as the physical quantity related to the moisture state of the fuel cell acquired for determining the completion of scavenging.

  Further, in the above-described embodiment, the scavenging scheduled time is a fixed value, but the time required to complete scavenging is learned every time, and the longest time or a little longer than the longest time is set as the scheduled scavenging time. Also good. According to this, the operation time of the compressor can be shortened to the minimum necessary time within a range in which the user does not feel uncomfortable. That is, it is possible to improve the fuel efficiency of the system by suppressing unnecessary operation of the compressor.

  Finally, a fuel cell system (a fuel cell system of a different invention from the present invention) that has been devised in the inventive process and that has technical characteristics different from those of the above-described embodiments will be described.

First, the first invention is
A fuel cell;
Scavenging gas blowing means for blowing scavenging gas toward the fuel cell when power generation of the fuel cell is stopped;
A flow rate adjusting means for adjusting a flow rate of air blown by the scavenging gas blowing means;
Determination means for determining completion of scavenging based on a predetermined physical quantity related to the moisture state of the fuel cell;
When the time required from the start to completion of scavenging is shorter than the preset scheduled scavenging time, the flow rate of the scavenging gas is reduced by the flow rate adjusting means, and the scavenging scheduled time elapses in that state. Control means for continuing blowing by the scavenging gas blowing means;
A fuel cell system comprising:

  Such a fuel cell system can be realized by using the configuration shown in FIG. In this case, the air compressor 22 serves as “scavenging gas blowing means”, and the control device 16 that controls the rotation speed of the air compressor 22 functions as “flow rate adjusting means”. The control device 16 can also function as “determination means” and “control means”. In the fuel cell system of the first different invention, the bypass valve 42 and the bypass passage 40 need not be provided.

  According to the first alternative invention, even when the time required from the start to completion of scavenging changes every time, the blowing time by the scavenging gas blowing means can be made constant. Further, by reducing the flow rate of the scavenging gas, further drying inside the fuel cell can be suppressed. Therefore, it is possible to prevent the user from feeling uncomfortable due to the variation in time required for scavenging while preventing the variation in the moisture state inside the fuel cell.

In addition, the second separate invention is
A fuel cell;
Scavenging gas blowing means for blowing scavenging gas toward the fuel cell when power generation of the fuel cell is stopped;
Back pressure adjusting means for adjusting the back pressure of the scavenging gas discharged from the fuel cell;
Determination means for determining completion of scavenging based on a predetermined physical quantity related to the moisture state of the fuel cell;
When the time required from the start to completion of scavenging is shorter than the preset scheduled scavenging time, the back pressure adjusting means increases the back pressure of the scavenging gas, and the scheduled scavenging time elapses in that state. Control means for continuing blowing by the scavenging gas blowing means,
A fuel cell system comprising:

  Such a fuel cell system can also be realized using the configuration shown in FIG. In that case, the air compressor 22 becomes “scavenging gas blowing means”, and the pressure regulating valve 26 becomes “back pressure adjusting means”. Further, the control device 16 can function as “determination means” and “control means”. In the fuel cell system of the second different invention, the bypass valve 42 and the bypass passage 40 do not have to be provided.

  According to the second invention, even when the time required from the start to the completion of scavenging changes every time, the blowing time by the scavenging gas blowing means can be made constant. Further, by further increasing the back pressure of the scavenging gas, further drying inside the fuel cell can be suppressed. Therefore, it is possible to prevent the user from feeling uncomfortable due to the variation in time required for scavenging while preventing the variation in the moisture state inside the fuel cell.

It is a figure which shows the structure of the fuel cell system as embodiment of this invention. It is a flowchart which shows the routine performed by a control apparatus at the time of the electric power generation stop of a fuel cell stack.

Explanation of symbols

2 Fuel cell stack 4 Hydrogen supply source 6 Hydrogen supply path 8 Pressure regulating valve 10 Shut valve 14 Purge valve 16 Controller 20 Air supply path 22 Air compressor 24 Air discharge path 26 Pressure regulating valve 30 Unit battery 32 Impedance measuring instrument 40 Bypass path 42 Bypass valve

Claims (2)

A fuel cell;
Scavenging gas blowing means for blowing scavenging gas toward the fuel cell when power generation of the fuel cell is stopped;
Bypass means for bypassing the fuel cell from the air flow path of the scavenging gas;
Determination means for determining completion of scavenging based on a predetermined physical quantity related to the moisture state of the fuel cell;
When the time required from the start to completion of scavenging is shorter than a preset scheduled scavenging time, the fuel cell is bypassed by the bypass means, and the scavenging gas is used until the scheduled scavenging time elapses in that state. Control means for continuing blowing by the blowing means;
A fuel cell system comprising: A learning means for learning the time required from the start to completion of scavenging;
A scheduled scavenging time setting means for setting the scheduled scavenging time based on the longest required time learned by the learning means;
The fuel cell system according to claim 1, further comprising:

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