JP2007250280A - Fuel cell system and control method for fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system suppressing deterioration of fuel cell even when the fuel cell is exposed to extremely low temperature environment. <P>SOLUTION: The fuel cell system comprises: a fuel cell provided with a film, an anode electrode, and a cathode electrode; a control apparatus 30 controlling the fuel cell, and a temperature sensor 31. The control apparatus 30 is provided with: a freezing judging means 41 judging whether minimum temperature in the electrode during a stopping period of the fuel cell has become the extremely low temperature at which moisture inside the electrode can be judged to be frozen; a thawing judging means 42 judging whether the temperature of the electrode has become 0°C at which the frozen moisture is judged to be thawed; and a power generation prohibiting means 43 prohibiting a power generation by the fuel cell until judgement is made by the thawing judging means 42 that the temperature of the electrode is 0°C or more by the thawing judging means 42 when the minimum temperature during a stopping period of the fuel cell is judged by the freezing judging means 41 to be the extremely low temperature or less even when starting of th fuel cell is requested. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fuel cell system and a fuel cell control method.

  In recent years, fuel cell systems have attracted attention as a new power source for automobiles. The fuel cell system includes, for example, a fuel cell that generates power by chemically reacting a reaction gas, a reaction gas supply device that supplies the reaction gas to the fuel cell via a reaction gas flow path, and a control that controls the reaction gas supply device An apparatus.

  The fuel cell has, for example, a stack structure in which several tens to several hundreds of cells are stacked. Here, each cell is configured by sandwiching a membrane electrode structure (MEA) between a pair of separators. The membrane electrode structure includes two electrodes, an anode electrode (anode) and a cathode electrode (cathode), and these electrodes. And a solid polymer electrolyte membrane sandwiched between the two.

  When hydrogen gas as a reaction gas is supplied to the anode electrode of the fuel cell and air containing oxygen as a reaction gas is supplied to the cathode electrode, power is generated by an electrochemical reaction. Since only harmless water is generated at the time of power generation, fuel cells are attracting attention from the viewpoint of environmental impact and utilization efficiency.

By the way, as the above fuel cell system, when starting the fuel cell from a low temperature state, a configuration is proposed in which a heat medium is circulated through the fuel cell to heat the air flow path near the discharge port of the fuel cell. (See Patent Document 1). In this fuel cell system, power generation is started after heating to a predetermined temperature.
According to the fuel cell system of Patent Document 1, by heating the air flow path, the generated water generated by the power generation of the fuel cell can be prevented from being condensed or frozen, and the power generation can be continued.
JP 2003-303607 A

  By the way, although the antifreeze water which does not freeze even at 0 degreeC is contained in the pore inside MEA, in the cryogenic environment, this antifreeze water may freeze. When antifreeze water freezes into ice, this ice behaves like normal ice. That is, even if it is non-freezing water, once it freezes in a cryogenic environment, it does not thaw until it becomes 0 degreeC or more. Therefore, when the antifreeze water freezes in a cryogenic environment, the antifreeze water is frozen inside the electrode even if the temperature of the fuel cell then rises from the cryogenic temperature to a temperature at which power generation is possible.

  When the antifreeze water freezes in this way, the pores extending from the reaction gas supply path to the inside of the MEA are closed with ice, and the supplied reaction gas cannot reach the reaction site (catalyst surface) inside the MEA. In this way, the fuel cell attempts to generate the required output voltage despite the fact that the antifreeze water inside the MEA is frozen, so that the current density locally increases in the region that can be used for power generation. Become. Therefore, the current density of a part of the MEA becomes excessive, and the deterioration of the MEA may be promoted in this part.

  The fuel cell system disclosed in Patent Document 1 starts power generation even when the temperature is below freezing (0 ° C. or lower) if the temperature of the fuel cell has reached a predetermined temperature. Therefore, when this fuel cell is once exposed to a cryogenic environment and the antifreeze water inside the MEA is in a frozen state, the area where the ice inside the MEA is formed cannot be used for power generation, and the MEA deteriorates. Will be promoted.

  An object of the present invention is to provide a fuel cell stem and a fuel cell control method capable of suppressing deterioration of the fuel cell even when the fuel cell is exposed to a cryogenic environment.

  (1) A membrane (for example, the solid polymer membrane 123 in the embodiment), and an anode electrode (for example, the anode electrode 121 in the embodiment) and a cathode electrode (for example, in the embodiment) provided across the membrane A fuel cell (for example, the fuel cell 10 in the embodiment) that generates electric power by reaction of the reaction gas supplied to the anode electrode and the cathode electrode, and a control unit that controls the fuel cell ( For example, a fuel cell system comprising a control device 30) in the embodiment, further comprising temperature detection means (for example, temperature sensor 31 in the embodiment) for detecting the temperature of the electrode, The minimum temperature of the electrode during the stop period of the fuel cell can be determined that the moisture inside the electrode is frozen. Freezing determination means (for example, freezing determination means 41 in the embodiment) for determining whether or not the temperature has become equal to or lower than one temperature, and the temperature of the electrode is equal to or higher than a second temperature at which it can be determined that the frozen water has thawed The thawing determination means (for example, the thawing determination means 42 in the embodiment) for determining whether or not the fuel cell has been started, and even if the start of the fuel cell is requested, the freezing determination means determines the minimum during the stop period of the fuel cell. When it is determined that the temperature is equal to or lower than the first temperature, the power generation prohibition prohibits power generation of the fuel cell until the thawing determination means determines that the temperature of the electrode is equal to or higher than the second temperature. And a fuel cell system (for example, the fuel cell system 1 in the embodiment).

  Here, examples of the reactive gas include hydrogen gas and air containing oxygen. The first temperature is, for example, an extremely low temperature of about minus 40 ° C., and the second temperature is, for example, 0 ° C.

According to the invention of (1), the fuel cell system is provided with the temperature detecting means, and the control means is further provided with the freeze determining means, the thawing determining means, and the power generation prohibiting means.
Thereby, when it is determined that the minimum temperature of the electrode during the stop period of the fuel cell is equal to or lower than the first temperature, the power generation of the fuel cell is performed until it is determined that the temperature of the electrode is equal to or higher than the second temperature. Is prohibited.
Thus, for example, even when the fuel cell is exposed to a cryogenic environment and the antifreeze water inside the electrode is frozen, the power generation of the fuel cell can be prohibited until the frozen antifreeze water thaws. It is possible to prevent the current density from becoming high and to suppress the deterioration of the fuel cell.

  (2) Warming-up means (for example, the external heater 15 in the embodiment) for warming up the fuel cell is further provided, and the control means is configured to perform the warm-up means during a period when power generation is prohibited by the power generation prohibiting means. (1) The fuel cell system according to (1), further comprising a warm-up control unit (for example, the warm-up control unit 44 in the embodiment).

According to the invention of (2), the warm-up means is provided, and the control means is further provided with the warm-up control means for operating the warm-up means during the period in which power generation is prohibited by the power generation prohibition means.
Therefore, even when the outside air temperature is low, the antifreezing water frozen by the warm-up means can be thawed without waiting for the freezing antifreeze water to naturally thaw due to the rise in the outside air temperature. The fuel cell can be activated. Further, by operating the warm-up means, the period during which the power generation of the fuel cell is prohibited can be shortened, and the fuel cell can be started early.

  (3) A control method for a fuel cell comprising a membrane, and an anode electrode and a cathode electrode provided across the membrane, and generating power by reaction of a reaction gas supplied to the anode electrode and the cathode electrode, Even if the minimum temperature of the electrode during the stop period of the fuel cell is equal to or lower than a first temperature at which it is possible to determine that the moisture inside the electrode has been frozen, the fuel cell is requested to start. When it is determined that the minimum temperature during the stop period of the fuel cell is equal to or lower than the first temperature, power generation of the fuel cell is prohibited, and the temperature of the electrode can be determined that the frozen moisture has thawed. It is determined whether or not the temperature is equal to or higher than a second temperature, and when it is determined that the temperature of the electrode is equal to or higher than the second temperature, power generation of the fuel cell is started. .

  According to the invention of (3), there is an effect similar to the above (1).

  According to the present invention, when it is determined that the minimum temperature of the electrode during the stop period of the fuel cell is equal to or lower than the first temperature, the fuel is maintained until it is determined that the temperature of the electrode is equal to or higher than the second temperature. Prohibit battery power generation. Therefore, for example, even when the fuel cell is exposed to a cryogenic environment and the antifreeze water inside the electrode is frozen, the power generation of the fuel cell can be prohibited until the frozen antifreeze water thaws. It is possible to prevent the current density from becoming high and to suppress the deterioration of the fuel cell.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram of a fuel cell system 1 according to an embodiment of the present invention.
The fuel cell system 1 includes a fuel cell 10, a supply device 20 that supplies hydrogen gas or air as a reaction gas to the fuel cell 10, and a control device 30 that serves as a control unit that controls the fuel cell 10 and the supply device 20. Have

FIG. 2 is a cross-sectional view of the cell 11 constituting the fuel cell 10.
That is, the fuel cell 10 has a stack structure in which, for example, several tens to several hundreds of cells 11 are stacked. Each cell 11 is configured by sandwiching a membrane electrode structure (MEA) 12 between a pair of separators 13A and 13B. The MEA 12 includes a solid polymer film 123 as a film, and an anode electrode (anode) 121 and a cathode electrode (cathode) 122 that sandwich the solid polymer film 123.
Both electrodes 121 and 122 are formed of catalyst layers 121A and 122A that perform an oxidation / reduction reaction in contact with the solid polymer film 123, and gas diffusion layers 121B and 122B that are in contact with the catalyst layers 121A and 122A.
A hydrogen circulation groove 131 is formed in the separator 13A joined to the gas diffusion layer 121B, and an air circulation groove 132 is formed between the gas diffusion layer 122B and the separator 13B.

Referring back to FIG. 1, in such a fuel cell 10, hydrogen gas as a reaction gas is supplied to the anode electrode (anode) side, and air containing oxygen as a reaction gas is supplied to the cathode electrode (cathode) side. And generate electricity by electrochemical reaction.
Further, the fuel cell 10 is provided with an external heater 15 as warm-up means. Examples of the external heater 15 include a catalytic combustion heater and an electric heater.

  The supply device 20 includes a compressor 21 that supplies air to the cathode electrode side of the fuel cell 10, a hydrogen tank 22 that supplies hydrogen gas to the anode electrode side, and an ejector 28.

The compressor 21 is connected to the cathode electrode side of the fuel cell 10 via the air supply path 23.
An air discharge path 24 is connected to the cathode electrode side of the fuel cell 10, and a back pressure valve 241 is provided at the front end side of the air discharge path 24.

  The hydrogen tank 22 is connected to the anode electrode side of the fuel cell 10 through a hydrogen supply path 25. The hydrogen supply path 25 is provided with the above-described ejector 28. A pressure regulating valve 251 is provided between the hydrogen tank 22 and the ejector 28 in the hydrogen supply path 25.

  Further, a hydrogen discharge path 26 is connected to the anode electrode side of the fuel cell 10, and a purge valve 261 is provided on the front end side of the hydrogen discharge path 26. In the vicinity of the fuel cell 10 in the hydrogen discharge path 26, a temperature sensor 31 is provided as temperature detecting means. Further, in the hydrogen discharge path 26, the hydrogen discharge path 26 is branched on the anode electrode side of the purge valve 261 and connected to the above-described ejector 28.

  The ejector 28 collects the hydrogen gas that has flowed into the hydrogen discharge path 26 through the branch path of the hydrogen discharge path 26 and returns it to the hydrogen supply path 25.

  The compressor 21, the back pressure valve 241, the external heater 15, the purge valve 261, and the pressure adjustment valve 251 are controlled by the control device 30 described later. The control device 30 is connected to the temperature sensor 31 described above.

The procedure for generating power with the fuel cell 10 is as follows.
That is, the purge valve 261 is closed, the pressure adjustment valve 251 is opened, and hydrogen gas is supplied from the hydrogen tank 22 to the anode side of the fuel cell 10 through the hydrogen supply path 25. Further, by driving the compressor 21, air is supplied to the cathode side of the fuel cell 10 through the air supply path 23.
The hydrogen gas and air supplied to the fuel cell 10 are supplied to the power generation system, and then flow into the hydrogen discharge path 26 and the air discharge path 24 together with residual water such as produced water on the anode side from the fuel cell 10. At this time, since the purge valve 261 is closed, the hydrogen gas flowing into the hydrogen discharge path 26 is returned to the ejector 28 and reused.
Thereafter, by opening the purge valve 261 and the back pressure valve 241 at an appropriate opening degree, hydrogen gas, air, and residual water are discharged from the hydrogen discharge path 26 and the air discharge path 24.

FIG. 3 is a block diagram of the control device 30.
The control device 30 includes freezing determination means 41, thawing determination means 42, power generation prohibition means 43, and warm-up control means 44.

  The temperature sensor 31 measures the temperature of the hydrogen gas passing through the hydrogen discharge path 26 and transmits it to the control device 30 as the temperature of the electrodes 121 and 122. The temperature sensor 31 continuously measures the temperature not only during the period when the fuel cell 10 is generating power but also during the period when it is stopped.

  Further, an ignition switch (not shown) is connected to the control device 30. This ignition switch is provided in the driver's seat of the fuel cell vehicle, and transmits an on / off signal to the control device 30 in accordance with the operation of the driver. The control device 30 performs power generation of the fuel cell 10 in accordance with ON / OFF of the ignition switch.

FIG. 4 is a diagram showing the relationship between the temperature during monitoring of the fuel cell and the power generation effective area of the electrodes 121 and 122.
As described above, the antifreeze water contained in the MEA is frozen in a cryogenic environment. If this antifreeze water freezes, the behavior of the ice made from the antifreeze water becomes the same as that of normal ice, so the frozen antifreeze water is completely until the temperature inside the MEA reaches 0 ° C or higher. Do not melt.
Specifically, as illustrated in FIG. 4, for example, when the temperature of the fuel cell 10 is decreased by stopping the fuel cell 10, the power generation effective area of the electrodes 121 and 122 is decreased along the path A. Thereafter, when the temperature of the fuel cell 10 rises by starting the fuel cell 10, the power generation effective area of the electrodes 121 and 122 increases along the paths A ′, B, C, D, E, and F.
Here, when the temperature of the fuel cell 10 starts to rise without reaching an extremely low temperature, the antifreezing water does not freeze, so that the power generation effective area increases along the path A ′. That is, the power generation effective area changes along the same path regardless of whether the temperature of the fuel cell 10 decreases or increases.
On the other hand, when the temperature of the fuel cell 10 starts to rise after reaching an extremely low temperature, the antifreezing water freezes, so that the power generation effective area increases along the paths B to F. That is, the power generation effective area varies along different paths (hysteresis characteristics) depending on whether the temperature of the fuel cell 10 decreases or increases.

  The freezing determination means 41 stores the lowest temperature of the fuel cell 10 measured by the temperature sensor 31 as the lowest temperature, and the lowest temperature of the electrodes 121 and 122 of the fuel cell 10 being monitored is the first temperature. It is determined whether or not the temperature is below an extremely low temperature, that is, whether or not the temperature is below the temperature at which the antifreezing water inside the electrodes 121 and 122 can be determined to be frozen.

  The thawing determination means 42 determines whether or not the temperature of the electrodes 121 and 122 is equal to or higher than 0 ° C. as the second temperature, that is, whether or not the temperature at which the frozen water can be determined to have been thawed.

  Even if the fuel cell 10 is requested to start up, the power generation prohibiting unit 43 uses the thawing determination unit 41 to determine whether the minimum temperature during the stop period of the fuel cell 10 has become an extremely low temperature or less. , 122 is prohibited until the temperature of 122 is 0 ° C. or higher.

  The warm-up control unit 44 operates the external heater 15 during a period in which power generation is prohibited by the power generation prohibiting unit 43.

The operation of the fuel cell system 1 will be described with reference to the flowchart of FIG.
Initially, the ignition switch (IG) is turned off (ST1). In this state, the temperature of the fuel cell 10 is measured by the temperature sensor 31, the minimum temperature of the fuel cell 10 is stored by the freezing determination means 41, and the temperature of the fuel cell 10 is monitored. (ST2).

  Thereafter, when the ignition switch (IG) is turned on (ST3), the freezing determination means 41 determines whether or not the stored minimum temperature of the monitored fuel cell 10 is extremely low (ST4). When this determination is “NO”, the process proceeds to ST8 described later.

On the other hand, when this determination is “YES”, the power generation prohibiting unit 43 prohibits the power generation of the fuel cell 10 (ST5), and the warm-up control unit 44 operates the external heater 15 (ST6).
Subsequently, it is determined whether or not the temperature of the electrodes 121 and 122 of the fuel cell 10 measured by the temperature sensor 31 is 0 ° C. or higher (ST7). When this determination is “NO”, since the frozen antifreeze water has not completely thawed, the process returns to ST5 and ST6, and the power generation of the fuel cell 10 is prohibited and the external heater 15 is operated. On the other hand, when this determination is “YES”, it is considered that the frozen antifreeze water has almost thawed, so normal power generation control is performed (ST8).

According to this embodiment, there are the following effects.
(1) The temperature sensor 31 is provided in the fuel cell system 1, and the freezing determination means 41, the thawing determination means 42, and the power generation prohibition means 43 are further provided in the control device 30.
As a result, when it is determined that the minimum temperature of the electrodes 121 and 122 during the stop period of the fuel cell 10 has become an extremely low temperature or lower, the fuel until the temperature of the electrodes 121 and 122 has been determined to be 0 ° C. or higher. The power generation of the battery 10 is prohibited.
Therefore, for example, even when the fuel cell 10 is exposed to a cryogenic environment and the antifreeze water inside the electrodes 121 and 122 is frozen, power generation of the fuel cell 10 can be prohibited until the frozen antifreeze water is thawed. It is possible to prevent the current density of a part of the electrodes 121 and 122 from becoming high, and to suppress deterioration of the fuel cell 10.

(2) The external heater 15 is provided, and the control device 30 is further provided with a warm-up control unit 44 that operates the external heater 15 during a period in which power generation is prohibited by the power generation prohibiting unit 43.
Therefore, even when the outside air temperature is low, the antifreeze water frozen by the external heater 15 can be thawed without waiting for the freezing antifreeze water to naturally thaw due to the rise in the outside air temperature. The fuel cell 10 can be activated. In addition, by operating the external heater 15, the period during which the power generation of the fuel cell 10 is prohibited can be shortened, and the fuel cell 10 can be started early.

  It should be noted that the present invention is not limited to the above-described embodiment, and modifications, improvements, etc. within a scope that can achieve the object of the present invention are included in the present invention.

1 is a block diagram of a fuel cell system according to an embodiment of the present invention. It is sectional drawing of the cell which comprises the fuel battery | cell which concerns on the said embodiment. It is a block diagram of a control device constituting the fuel cell system according to the embodiment. It is a figure which shows the relationship between the temperature under monitoring of the fuel cell which concerns on the said embodiment, and the power generation effective area of an electrode. 4 is a flowchart of the fuel cell system according to the embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Fuel cell system 10 ... Fuel cell 15 ... External heater 30 ... Control apparatus (control means)
31 ... Temperature sensor (temperature detection means)
41 ... Freezing determination means 42 ... Defrosting determination means 43 ... Power generation prohibiting means 44 ... Warm-up control means 121 ... Anode electrode 122 ... Cathode electrode 123 ... Solid polymer membrane (membrane)

Claims (3)

A fuel cell that includes a membrane, and an anode electrode and a cathode electrode provided across the membrane, and that generates power by reaction of a reaction gas supplied to the anode electrode and the cathode electrode, and a control means for controlling the fuel cell A fuel cell system comprising:
A temperature detecting means for detecting the temperature of the electrode;
The control means includes
Freezing determination means for determining whether or not the minimum temperature of the electrode during the stop period of the fuel cell is equal to or lower than a first temperature at which it is possible to determine that moisture inside the electrode is frozen;
Thawing determination means for determining whether the temperature of the electrode is equal to or higher than a second temperature at which it can be determined that the frozen moisture has been thawed;
Even if the start of the fuel cell is requested, when the freezing determination means determines that the minimum temperature during the stop period of the fuel cell is equal to or lower than the first temperature, the thawing determination means determines the temperature of the electrode. A fuel cell system, comprising: a power generation prohibiting unit that prohibits power generation of the fuel cell until it is determined that the temperature is equal to or higher than the second temperature. Further comprising warming-up means for warming up the fuel cell;
2. The fuel cell system according to claim 1, wherein the control unit includes a warm-up control unit that operates the warm-up unit during a period in which power generation is prohibited by the power generation prohibiting unit. A control method for a fuel cell comprising a membrane, and an anode electrode and a cathode electrode provided between the membrane, and generating power by reaction of a reaction gas supplied to the anode electrode and the cathode electrode,
Determining whether the minimum temperature of the electrode during the stop period of the fuel cell is equal to or lower than a first temperature at which it is possible to determine that the moisture inside the electrode has been frozen;
When it is determined that the minimum temperature during the stop period of the fuel cell is equal to or lower than the first temperature even when the fuel cell is requested to start,
Determining whether the temperature of the electrode is equal to or higher than a second temperature at which the frozen moisture can be determined to have been thawed;
A fuel cell control method, comprising: starting power generation of the fuel cell when it is determined that the temperature of the electrode has become equal to or higher than the second temperature.

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