JP2005228688A - Wet condition judging device for solid polymer fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wet condition judging device for a solid polymer fuel cell capable of judging wet condition inside a fuel cell by a simple arithmetic process. <P>SOLUTION: Voltage of each of a plurality of battery cells as constituents of the solid polymer fuel cell is measured, and a minimum voltage (an object cell voltage) V is selected out of measured voltages of the plurality of battery cells. The wet condition in the fuel cell is judged depending on the minimum voltage at the time when a factor influencing the wet condition of the fuel cell or a load of the fuel cell is changed. For example, if the minimum voltage V exceeds a first judged value V<SB>1</SB>set in advance when the factor (for example, an amount of air) is changed into a direction of decrease of an amount of moisture in the fuel cell, the wet condition of the fuel cell prior to the change of the factor is judged as an excessive wetting. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a polymer electrolyte fuel cell composed of a plurality of battery cells, and more particularly to a wet state determination device for determining a wet state inside a fuel cell.

  An electrolyte membrane (solid polymer electrolyte membrane) used in a polymer electrolyte fuel cell requires water molecules for movement of hydrogen ions therein, and exhibits high hydrogen ion conductivity only when it contains moisture. For this reason, when the moisture in the fuel cell is insufficient and the electrolyte membrane is dried, the cell performance of the polymer electrolyte fuel cell is greatly deteriorated as the conductivity decreases. On the other hand, if excessive moisture is present in the fuel cell, the gas flow to the anode and cathode is hindered by the water present in the vicinity of the electrolyte membrane. Will fall. Therefore, for the polymer electrolyte fuel cell, it is important to maintain the wet state in the fuel cell in an appropriate wet state in order to maintain high cell performance.

In order to appropriately maintain the wet state in the fuel cell, first, it is required to accurately determine the current wet state. In particular, in a fuel cell configured by laminating a plurality of battery cells, the plurality of battery cells are connected in series, so that a decrease in the battery performance of one battery cell decreases the battery performance of the entire fuel cell. . For this reason, it is necessary to accurately determine the wet state in units of battery cells. As a technique for determining the wet state of the fuel cell, for example, a technique described in Patent Document 1 is known. In this prior art, the voltage is measured for each of a plurality of battery cells (single cells) constituting the fuel cell before and after the supply amount of the oxidizing gas to the fuel cell is increased, and the variance of each voltage is calculated. Then, the dispersion of each voltage before the increase in the supply amount of the oxidizing gas is compared with the dispersion of each voltage after the increase. When the former is equal to or less than the latter, it is determined that the wet state is appropriate. Judgment. In this prior art, the evaporation of moisture in the fuel cell is promoted by the increase in the supply amount of the oxidizing gas, so that the battery cell in an excessively wet state approaches a proper wet state, and the voltage variation of each battery cell becomes small. Based on this, the wet state is determined.
JP 2000-243418 A Japanese Patent Laid-Open No. 9-245826 JP 2000-208161 A

  However, since a fuel cell is usually configured by stacking hundreds of battery cells, complicated calculation processing is required to calculate the variance of each voltage of these hundreds of battery cells. As a result, the load on the CPU increases. In the fuel cell system, various arithmetic processes related to the operation control of the fuel cell are performed by the CPU. Therefore, each arithmetic process should be as simple as possible in order to reduce the load on the CPU. The same applies to the calculation processing related to the determination of the wet state of the fuel cell. If the load on the CPU is taken into consideration, it is desired that the wet state can be determined by means that requires simpler calculation processing.

  The present invention has been made to solve the above-described problems, and provides a wet state determination device for a polymer electrolyte fuel cell that can determine the wet state in a fuel cell by simple arithmetic processing. For the purpose.

In order to achieve the above object, a first invention is a wet state determination apparatus for a polymer electrolyte fuel cell,
A polymer electrolyte fuel cell comprising a plurality of battery cells;
Measuring means for measuring each voltage of the plurality of battery cells;
A minimum voltage selecting means for selecting a minimum voltage from the measured voltages of the plurality of battery cells; and
Wet state determination means for determining a wet state in the fuel cell, or a wet state in the fuel cell based on the minimum voltage when a factor affecting the load of the fuel cell changes;
It is characterized by having.

  According to a second aspect, in the first aspect, the wet state determination unit is configured to determine a first determination value in which the minimum voltage is predetermined when the factor changes in a direction in which the amount of water in the fuel cell decreases. Is exceeded, the wet state in the fuel cell before the change of the factor is determined to be overwetting.

In a third aspect based on the second aspect, the change in the factor is a temporary change,
The wet state determination means determines whether or not the fuel cell is wet when the minimum voltage falls below a second predetermined value smaller than the predetermined first determination value when the factor changes or after the change ends. It is characterized by valid results.

  A fourth invention is characterized in that in any one of the first to third inventions, a changing means for forcibly changing the factor is provided.

In a fifth aspect based on the fourth aspect, the changing means changes the factor in a direction in which the amount of water in the fuel cell decreases when the minimum cell voltage falls below a predetermined third determination value. Let
The wet state determining means is characterized in that when the factor is changed by the operation of the changing means, the wet state in the fuel cell is determined.

  According to a sixth aspect, in the fifth aspect, the third determination value is set based on a reference cell voltage selected from the voltages of the plurality of battery cells.

  According to a seventh invention, in any one of the first to sixth inventions, the wet state determination means determines the minimum voltage in advance when the factor changes in a direction in which the load of the fuel cell increases. If the value falls below the fourth determination value, the wet state in the fuel cell before the change of the factor is determined to be insufficient.

  In an eighth aspect based on the seventh aspect, the fourth determination value is set based on a reference cell voltage selected from the voltages of the plurality of battery cells.

A ninth invention further comprises a maximum voltage selecting means for selecting a maximum voltage from the voltages of the plurality of battery cells in the sixth or eighth invention,
The maximum voltage is set as the reference cell voltage.

  In a tenth aspect based on the second or third aspect, the wet state determining means is a fifth aspect in which the rate of change in unit time of the factor in the direction in which the amount of water in the fuel cell decreases is predetermined. When the determination value is exceeded, the determination result regarding the wet state in the fuel cell is validated.

  In an eleventh aspect based on the seventh or eighth aspect, the wet state determination means is a sixth determination value in which the rate of change in unit time of the factor in the direction in which the load of the fuel cell increases is predetermined. The determination result regarding the wet state in the fuel cell is validated when the value exceeds.

  A battery cell that is not in a wet state exhibits a specific voltage change when the wet state in the fuel cell or a factor that affects the load of the fuel cell changes. Specifically, a battery cell that is excessively wet exhibits a lower voltage than a battery cell that is in a proper wet state, and the voltage increases as the amount of water in the fuel cell decreases. On the other hand, in the battery cells that are deficient in wetness, the voltage decreases more greatly than the battery cells in a proper wet state as the load of the fuel cell increases. Therefore, when the wet state in the fuel cell or the factor affecting the load of the fuel cell changes, the minimum voltage is selected from the voltages of the plurality of battery cells and the change in the voltage is observed. The wet state of can be easily determined. According to the first aspect of the invention, a complicated calculation process such as calculation of variance is not required, so that the load required for the calculation process is reduced.

  Further, according to the second invention, when the factor changes in a direction in which the amount of water in the fuel cell decreases, the wet state in the fuel cell can be determined simply by comparing the minimum voltage with the predetermined first determination value. It can be easily determined whether or not it is excessively wet.

  When the wet state in the fuel cell is excessively wet, if the change of the factor is a temporary change, the minimum voltage decreases again at the time of the change of the factor or after the change is completed. According to the third invention, since the change in the minimum voltage after the change of the factor or after the change is also one of the determination conditions, it is possible to accurately determine whether or not the wet state in the fuel cell is excessively wet. Can be determined.

  According to the fourth invention, the factor can be forcibly changed to determine the wet state in the fuel cell, so that the wet state can be reliably determined at an arbitrary timing. Become.

  A battery cell that is excessively wet has a lower voltage than a battery cell that is in a proper wet state. According to the fifth aspect of the invention, it is assumed that the minimum cell voltage is lower than the third determination value in the wet state determination. Therefore, unnecessary determination is prevented and the wet state in the fuel cell becomes excessively wet. It can be accurately determined whether or not.

  According to the sixth invention, since the reference cell voltage selected from the voltages of the plurality of battery cells is used for setting the third determination value, the minimum cell voltage and the voltage of the battery cell in an appropriate wet state are used. It is possible to accurately determine whether or not the wet state in the fuel cell is excessively wet.

  According to the seventh aspect of the invention, since the minimum voltage is only compared with the predetermined fourth determination value when the factor changes in the direction in which the load of the fuel cell increases, the wet state in the fuel cell is reduced. It can be easily determined whether or not the wetness is insufficient.

  According to the eighth invention, since the reference cell voltage selected from the voltages of the plurality of battery cells is used for setting the fourth determination value, the minimum cell voltage and the voltage of the battery cell in an appropriate wet state are used. It is possible to accurately determine whether or not the wet state in the fuel cell is insufficiently wet.

  According to the ninth invention, the maximum voltage selected from each voltage of the plurality of battery cells is set as the reference cell voltage, thereby minimizing the influence of the fluctuation of each voltage on the determination result. This makes it possible to determine the wet state more accurately. In addition, since the selection of the maximum voltage does not require complicated arithmetic processing such as calculation of variance, an increase in load required for the arithmetic processing can be suppressed.

  According to the tenth invention, the determination result is valid only in a situation where the change in the factor clearly appears in the change in the voltage of the battery cell that is excessively wet. Therefore, the wet state in the fuel cell becomes excessively wet. It can be determined more accurately whether or not.

  According to the eleventh aspect of the invention, the determination result is valid only in a situation where the change in the factor clearly appears in the change in the voltage of the battery cell in the insufficiently wet state. It can be determined more accurately whether or not.

Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 3.
FIG. 1 is a schematic configuration diagram showing an entire fuel cell system to which a wet state determination device for a polymer electrolyte fuel cell according to the present invention is applied. This fuel cell system is suitable as a fuel cell system for vehicles mounted on a fuel cell vehicle. However, it is of course possible to apply the fuel cell system to other uses.

  The fuel cell system includes a polymer electrolyte fuel cell (hereinafter referred to as a fuel cell) 2. The fuel cell 2 has a structure in which a plurality of battery cells are stacked. Although not shown, each battery cell is configured such that both sides of the electrolyte membrane are sandwiched between an anode electrode and a cathode electrode, which are catalyst electrodes, and further, both sides are sandwiched between conductive separators. A hydrogen flow path through which hydrogen flows is formed between the separator and the anode electrode, and an air flow path through which air flows is formed between the separator and the cathode electrode.

  The fuel cell 2 is connected with a hydrogen supply pipe 4 for supplying hydrogen to the hydrogen flow path and an off-gas exhaust pipe 6 for discharging the anode off-gas from the hydrogen flow path. An upstream end of the hydrogen supply pipe 4 is connected to a hydrogen supply device 10, and a pressure regulator 12 is disposed between the hydrogen supply device 10 and the fuel cell 2. Hydrogen supplied from the hydrogen supply device 10 is depressurized by the pressure adjusting device 12 and adjusted to a desired pressure, and then supplied to the fuel cell 2. As the hydrogen supply device 10, a reformer that reforms a hydrocarbon-based raw material such as gasoline and supplies a hydrogen-rich fuel gas may be used, or a high-pressure hydrogen tank that compresses and stores hydrogen may be used. Good.

  Hydrogen that has not been consumed in the fuel cell 2 is exhausted from the hydrogen flow path to the off-gas exhaust pipe 6 as an anode off-gas along with impurities such as nitrogen that have permeated from the cathode electrode side. A shutoff valve 16 is disposed in the offgas exhaust pipe 6, and an offgas circulation pipe 8 is branched from the offgas exhaust pipe 6 on the upstream side of the shutoff valve 16. The off-gas circulation pipe 8 is connected to the downstream side of the pressure regulator 12 in the hydrogen supply pipe 4 via an ejector or the like. The off-gas circulation pipe 8 is provided with a circulation device 14 that draws the anode off-gas from the hydrogen flow path and sends it to the hydrogen supply pipe 4. The shut-off valve 16 is opened at a predetermined timing, and when the shut-off valve 16 is opened, impurities such as nitrogen staying in the circulation system are released to the outside together with hydrogen.

  The fuel cell 2 is connected to an air supply pipe 20 for supplying air to the air flow path and an off-gas exhaust pipe 22 for discharging cathode off-gas from the air flow path. An air supply device 24 such as an air compressor is disposed in the air supply pipe 20, and air is taken into the air supply pipe 20 from the outside by the operation of the air supply device 24 and supplied to the air flow path. The off-gas exhaust pipe 22 is opened to the atmosphere, and a pressure adjusting device 30 for adjusting the air pressure is provided in the middle of the pipe line.

  The upstream side of the pressure adjusting device 30 of the off-gas exhaust pipe 22 and the downstream side of the air supply device 24 of the air supply pipe 20 are connected by a water vapor exchange device 28. Part of the moisture contained in the cathode offgas is recovered by the water vapor exchange device 28 and applied to the air supplied to the air flow path. A bypass pipe 26 that bypasses the water vapor exchange device 28 is connected to the air supply pipe 20 in parallel with the water vapor exchange device 28. The air supply pipe 20 and the upstream end of the bypass pipe 26 are connected by a three-way valve 32. By switching the port of the three-way valve 32, the supply destination of air from the air supply apparatus 24 is changed between the steam exchange apparatus 28 side and the bypass pipe 26 side. You can switch between them.

  This fuel cell system includes an ECU (Electronic Control Unit) 40 as a control device for controlling the operation of the fuel cell 2. The ECU 40 controls the operation of the fuel cell 2 by comprehensively controlling devices such as the hydrogen supply device 10, the pressure adjustment device 12, the circulation device 14, the shutoff valve 16, the air supply device 24, the three-way valve 32, and the pressure adjustment device 30. doing. A cell voltage monitoring device 42 is connected to the input side of the ECU 40 as means for detecting information for controlling the operation of the fuel cell 2. The cell voltage monitoring device 42 measures the voltages of all the battery cells constituting the fuel cell 2 in real time, and supplies the measured voltages of all the battery cells to the ECU 40.

  One of the control modes in which the ECU 40 controls the operation of the fuel cell 2 is a wet state determination mode that is executed when the wet state of the fuel cell 2 is determined. The electrolyte membrane of the fuel cell 2 is a solid polymer membrane, and during power generation, hydrogen ions move from the anode side to the cathode side in the electrolyte membrane in a state of being coupled with water molecules. When the water content in the electrolyte membrane is insufficient, the conductivity of hydrogen ions is greatly reduced. Therefore, sufficient water is required in the electrolyte membrane to maintain battery performance, and humidification is performed so that the fuel cell 2 does not become damp enough. There is a need to. However, if the inside of the fuel cell 2 is excessively moistened due to excessive humidification, the supply of gas to the cathode electrode or the anode electrode is hindered by water present in the vicinity of the electrolyte membrane, and the cell performance deteriorates. Therefore, in order to continuously obtain high battery performance, the electrolyte membrane is sufficiently wetted, and the fuel cell 2 is appropriately wetted so that the gas can sufficiently flow through the air flow path and the hydrogen flow path. Therefore, it is important to accurately determine the current wet state of the fuel cell 2. The wet state determination mode is a control mode set based on such a request.

  The wet state determination mode is executed when the output voltage of the fuel cell 2 decreases, for example, when the output voltage falls below a predetermined determination value. Alternatively, it may be executed when the operation time of the fuel cell 2 reaches a predetermined time. However, as will be described later, since the determination of the wet state is affected by the change in the load of the fuel cell 2, for example, the situation in which the load of the fuel cell 2 fluctuates as during acceleration of the vehicle, or the fluctuation range is Execution of the wet state determination mode is prohibited in a situation exceeding the allowable range.

  In the wet state determination mode, the ECU 40 controls the air supply device 24 to execute control for temporarily increasing the air supply amount to the fuel cell 2. When a specific battery cell is excessively wet, excess moisture is carried away with the air due to a temporary increase in the air supply amount, so that the excessive wetness is temporarily eliminated and the cell voltage increases. Then, when the air supply amount is reduced to the original flow rate, it becomes excessively wet again and the cell voltage decreases. On the other hand, when a specific battery cell is insufficiently wet, the shortage of wetness further proceeds with a temporary increase in the air supply amount, and the voltage decreases. This phenomenon is mainly caused by an increase in the load (generated power) of the fuel cell 2 accompanying an increase in the air supply amount. The amount of movement of hydrogen ions in the electrolyte membrane increases as the load increases. At this time, water molecules in the electrolyte membrane also move from the cathode electrode side to the outside of the electrolyte membrane together with hydrogen ions. For this reason, as the load of the fuel cell 2 increases, the amount of moisture transferred to the outside of the electrolyte membrane also increases, and drying of the electrolyte membrane proceeds. When the air supply amount is reduced to the original flow rate, the load of the fuel cell 2 is also reduced, the wet state of the electrolyte membrane is recovered, and the cell voltage is increased.

  As described above, the behavior of the cell voltage when the air supply amount is temporarily increased is completely different between the case where the battery cell is excessively wet and the case where the battery cell is insufficiently wet. Therefore, the wet state in the fuel cell 2 can be determined by examining the behavior of the cell voltage at this time. The ECU 40 determines the wet state in the fuel cell 2 based on the voltages of all the battery cells measured by the cell voltage monitoring device 42. In the present embodiment, the air supply device 24 functions as a changing unit that forcibly changes a factor affecting the wet state in the fuel cell 2 or the load on the fuel cell 2.

  The ECU 40 selects a minimum voltage and a maximum voltage (minimum value and maximum value among all voltages at each measurement time) from among the measured voltages of all battery cells. The selected minimum voltage is the target cell voltage to be determined, and the maximum voltage is the reference cell voltage that is a reference for evaluating the target cell voltage. A battery cell that is excessively wet or insufficiently wet has a lower cell voltage than a battery cell that is in a proper wet state. Therefore, by selecting the minimum voltage in this way, it is possible to easily identify a battery cell that may be excessively wet or insufficiently wet from among a large number (several hundreds) of battery cells. Also, when focusing on one battery cell, the cell voltage varies, but by setting the maximum voltage as the reference cell voltage, the influence of the cell voltage variation on the determination result can be minimized. . In the present embodiment, the “minimum voltage selection means” according to the first invention and the “maximum voltage selection means” according to the ninth invention are realized by the functions of the ECU 40 described above.

  The ECU 40 determines the wet state in the fuel cell 2 using the target cell voltage and the reference cell voltage set as described above. Here, FIG. 2 is a graph showing the change in the target cell voltage that occurs when the air flow rate is temporarily increased in the presence of battery cells that are excessively wet, together with the change in the reference cell voltage. is there. FIG. 3 also shows the change in the target cell voltage that occurs when the generated power of the fuel cell 2 is temporarily increased when there is a battery cell that is insufficiently wetted, along with the change in the reference cell voltage. It is a graph. Hereinafter, the wet state determination method performed by the ECU 40 will be described in detail with reference to FIGS. 2 and 3. In the present embodiment, the “wet state determination means” according to the first aspect of the invention is realized by the function of the ECU 40 described below.

First, a method for determining whether or not the wet state in the fuel cell 2 is excessively wet (overwetting determination) will be described. As shown in FIG. 2, the ECU 40 sets three determination values V ₁ , V ₂ , and V ₃ as a reference for evaluating the target cell voltage V. The second determination value V ₂ is a value smaller than the first determination value V ₁ , and the third determination value V ₃ is also set to a value smaller than the first determination value V ₁ . However, the first determination value V ₁ and the second determination value V ₂ which is a fixed value, the third determination value V ₃ is a relative value to the reference cell voltage V _ref, the reference cell voltage V _ref predetermined value ΔV than It is set to _a lower value by a.

The ECU 40 first compares the target cell voltage V with the third determination value V ₃ . Then, if the target cell voltage V is lower than the third determination value V ₃ , the excessive wetness determination is started, and the air supply device 24 is controlled to temporarily increase the air flow rate. The comparison between the target cell voltage V and the third determination value V ₃ is to prevent erroneous determination, and the voltage difference ΔV _a between the reference cell voltage V _ref and the third determination value V ₃ decreases due to excessive wetting. It is set to a value that can be sufficiently estimated.

When the target cell voltage V increases due to the increase in the air flow rate, the ECU 40 compares the target cell voltage V with the first determination value V ₁ . When the target cell voltage V exceeds the first determination value V ₁ , a provisional determination is made that the target cell voltage V is excessively wet (for example, a provisional determination flag is set).

When the air flow rate starts to decrease due to the end of the operation of the air supply device 24, the target cell voltage V that has risen decreases again. If the tentative determination that the overhydration is being performed (e.g., if the temporary determination flag is set), ECU 40 performs the comparison between the target cell voltage V and the second determination value V _2. When the target cell voltage V falls below the second determination value V ₂ , the provisional determination is validated, and the wet state in the fuel cell 2 is determined to be excessively wet. One of the determination conditions is that the target cell voltage V falls below the second determination value V ₂ as described above, and it is accurately determined whether or not the wet state in the fuel cell 2 is truly excessively wet. Because. Since it may be possible that the cell voltage is temporarily lowered for some reason, such as clogging of the gas flow path, erroneous determination can be prevented by performing double determination in this way.

The third determination value V ₃ may be a value obtained by multiplying the reference cell voltage V _ref by a predetermined coefficient less than 1. Here, the first determination value V ₁ and the second determination value V ₂ are fixed values, but may be relative values to the reference cell voltage V _ref as with the third determination value V ₃ .

Next, a method for determining whether or not the wet state in the fuel cell 2 is insufficiently wet (determination of wetness) will be described. As shown in FIG. 3, the ECU 40 sets a fourth determination value V ₄ as a reference for evaluating the target cell voltage V. Fourth determination value V ₄ are relative values with respect to the reference cell voltage V _ref, is set to a value lower by a predetermined value [Delta] V _b than the reference cell voltage V _ref. Similar to the third determination value V ₃ , the fourth determination value V ₄ may be a value obtained by multiplying the reference cell voltage V _ref by a predetermined coefficient less than 1.

As can be seen by comparing the target cell voltage V in FIG. 2 and FIG. 3, in the case of insufficient wetting, the decrease in cell voltage during normal operation is not as great as in the case of excessive wetting. For this reason, it is difficult to predict whether or not the battery cell is deficient in moisture from the target cell voltage V during normal operation. Therefore, in the determination of insufficient dampness, the ECU 40 first increases the generated power of the fuel cell 2 by controlling the air supply device 24 to temporarily increase the air flow rate. When the target cell voltage V decreases due to an increase in generated power, the ECU 40 compares the target cell voltage V with the fourth determination value V ₄ . As a result of the comparison, if the target cell voltage V is lower than the fourth determination value V ₄ , the wet state in the fuel cell 2 is determined to be insufficient. The voltage difference ΔV _b between the reference cell voltage V _ref and the fourth determination value V ₄ is set to a value that can sufficiently estimate that the cell voltage has decreased due to insufficient wetting.

  According to the determination method of the wet state as described above, the main calculation process is to select the minimum voltage and the maximum voltage from the cell voltages of all the battery cells, and complicated calculation processes such as calculation of dispersion are not possible. do not need. For this reason, the load of the ECU 40 required for the arithmetic processing is reduced, and the time from the determination start to the output of the determination result can be shortened. In addition, since the load on the ECU 40 is reduced, it is possible to prevent delays in other controls than the wet state determination.

  When the wet state determination result is obtained, the ECU 40 ends the wet state determination mode and executes a control mode (cell voltage recovery mode) according to the determination result. If the determination result is excessively wet, control suitable for eliminating the excessive wetness is performed, and if the determination result is insufficient wetness, control suitable for eliminating the insufficient wetness is performed to recover the cell voltage. . As a control suitable for eliminating overwetting, for example, the air supply device 24 is controlled to increase the air supply amount. Alternatively, dry air that does not pass through the water vapor exchanger 28 by switching the three-way valve 32 may be supplied to the fuel cell 2. It is also effective to control the pressure regulators 12 and 30 to reduce the gas pressure in the fuel cell 2 or to increase the operating temperature of the fuel cell 2. As a control suitable for eliminating deficiency of wetness, for example, the air supply device 24 is controlled to reduce the air supply amount. It is also effective to control the pressure regulators 12 and 30 to increase the gas pressure in the fuel cell 2 or to reduce the operating temperature of the fuel cell 2.

  Note that during the execution of the wet state determination mode and the cell voltage recovery mode, the request cannot be met when a request for increasing the generated power is made. Therefore, in this case, necessary power is supplied from a power supply source different from the fuel cell 2 such as a secondary battery.

Others.
Although the embodiments of the present invention have been described above, 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, the following modifications may be made.

  In the above-described embodiment, the air supply device 24 is controlled to change the air amount in the wet state determination mode, but any factor that affects the wet state in the fuel cell 2 or the load of the fuel cell 2 can be used. Other factors other than the air amount may be changed. In particular, the determination of excess wetness may be any factor that affects the wet state of the fuel cell 2. For example, the gas pressure in the fuel cell 2 or the operating temperature of the fuel cell 2 may be changed. Further, the discharge amount of the anode off gas controlled by opening and closing the shutoff valve 16 may be changed. Further, regarding the deficiency of wetness determination, any factor that affects the load of the fuel cell 2 may be used. May be changed.

Furthermore, the change in the factor affecting the wet state in the fuel cell 2 or the load on the fuel cell 2 is not necessarily a forced change as in the above-described embodiment. When the factor changes due to the normal operation of the fuel cell 2, the wet state may be determined if the change satisfies a predetermined requirement. The predetermined requirement here means that in the case of excessive wetness determination, the factor changes in a direction in which the amount of water in the fuel cell 2 decreases. For example, if the amount of air is increased, the amount of air increases. That is. Thereby, the comparison with the first determination value V ₁ becomes possible. Preferably, after that, the factor changes in the direction in which the amount of water in the fuel cell 2 increases, for example, the amount of air decreases, is added to the requirement. As a result, the comparison with the second determination value V ₂ becomes possible, and a more accurate determination of the wet state can be realized. In the case of insufficient wetting determination, it is a predetermined requirement that the factor changes in the direction in which the load of the fuel cell 2 increases. For example, if the amount of air is increased, the amount of air increases. Thereby, the comparison with the fourth determination value V ₄ becomes possible. Thereafter, it is not always necessary that the factor changes in the direction in which the load of the fuel cell 2 decreases, for example, the amount of air decreases.

  When the wet state is determined based on the change of the factor due to the course, it is desirable to determine the validity of the determination result based on the rate of change of the factor in unit time. This is because when the change in the factor is small, the change in the cell voltage is small and the determination system is lowered. In the case of overwetting determination, if the rate of change in the unit time of the factor in the direction in which the amount of water in the fuel cell 2 decreases exceeds a predetermined fifth determination value, the determination result of overwetting determination is obtained. It may be valid. In the case of dampness deficiency determination, if the rate of change in the unit time of the factor in the direction in which the load on the fuel cell 2 increases exceeds the predetermined sixth determination value, the damp deficiency determination result is valid. do it.

1 is a schematic configuration diagram illustrating an entire fuel cell system to which a wet state determination device for a polymer electrolyte fuel cell according to the present invention is applied. It is a graph for demonstrating the excess wet determination performed in embodiment of this invention. It is a graph for demonstrating the deficiency of dampness performed in embodiment of this invention.

Explanation of symbols

2 Fuel cell 4 Hydrogen supply pipe 6 Off-gas exhaust pipe 8 Off-gas circulation pipe 10 Hydrogen supply apparatus 12 Pressure regulator 14 Circulation apparatus 16 Shut-off valve 20 Air supply pipe 22 Off-gas exhaust pipe 24 Air supply apparatus 26 Bypass pipe 28 Water vapor exchange apparatus 30 Pressure device 32 Three-way valve 40 ECU
42 Cell voltage monitoring device

Claims (11)

A polymer electrolyte fuel cell comprising a plurality of battery cells;
Measuring means for measuring each voltage of the plurality of battery cells;
A minimum voltage selecting means for selecting a minimum voltage from the measured voltages of the plurality of battery cells; and
Wet state determination means for determining a wet state in the fuel cell, or a wet state in the fuel cell based on the minimum voltage when a factor affecting the load of the fuel cell changes;
An apparatus for determining a wet state of a polymer electrolyte fuel cell, comprising:   When the factor changes in a direction in which the amount of water in the fuel cell decreases, the wet state determination means determines that the fuel before the change of the factor when the minimum voltage exceeds a predetermined first determination value. 2. The apparatus for determining a wet state of a polymer electrolyte fuel cell according to claim 1, wherein the wet state in the battery is determined to be excessively wet. The change in the factor is a temporary change,
The wet state determination means determines whether or not the fuel cell is wet when the minimum voltage falls below a second predetermined value smaller than the predetermined first determination value when the factor changes or after the change ends. 3. The wet polymer state determination device for a polymer electrolyte fuel cell according to claim 2, wherein the result is validated.   The wet state determination apparatus for a polymer electrolyte fuel cell according to any one of claims 1 to 3, further comprising changing means for forcibly changing the factor. The changing means changes the factor in a direction in which the amount of water in the fuel cell decreases when the minimum cell voltage falls below a predetermined third determination value,
The wet state of the polymer electrolyte fuel cell according to claim 4, wherein the wet state determination unit makes a determination regarding the wet state in the fuel cell when the factor is changed by the operation of the changing unit. Judgment device.   6. The wet state determination device for a polymer electrolyte fuel cell according to claim 5, wherein the third determination value is set based on a reference cell voltage selected from each voltage of the plurality of battery cells. .   When the factor changes in the direction in which the load of the fuel cell increases, the wet state determination means determines that the wet state determination means has a value within the fuel cell before the change of the factor when the minimum voltage falls below a predetermined fourth determination value. The wet state determination device for a polymer electrolyte fuel cell according to any one of claims 1 to 6, wherein the wet state is determined as insufficient wetness.   8. The wet state determination apparatus for a polymer electrolyte fuel cell according to claim 7, wherein the fourth determination value is set based on a reference cell voltage selected from each voltage of the plurality of battery cells. . Further comprising a maximum voltage selection means for selecting a maximum voltage from each voltage of the plurality of battery cells;
The wet state determination device for a polymer electrolyte fuel cell according to claim 6 or 8, wherein the maximum voltage is set as the reference cell voltage.   The wet state determination means determines that the wet state in the fuel cell when the rate of change in the unit time of the factor in the direction in which the amount of water in the fuel cell decreases exceeds a predetermined fifth determination value. 4. The wet state determination device for a polymer electrolyte fuel cell according to claim 2, wherein the determination result regarding the state is validated. The wet state determination means relates to a wet state in the fuel cell when the rate of change in unit time of the factor in the direction in which the load of the fuel cell increases exceeds a predetermined sixth determination value. 9. The apparatus for determining a wet state of a polymer electrolyte fuel cell according to claim 7, wherein the determination result is validated.

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