JP4810872B2 - Fuel cell system - Google Patents

Description

  The present invention relates to a fuel cell system and an operation method thereof.

  Conventionally, since fuel cells have high power generation efficiency and do not emit harmful substances, they have been put into practical use as power generators for industrial and household use, or as power sources for artificial satellites and spacecrafts. Development is progressing as a power source for vehicles such as buses and trucks. The fuel cell may be an alkaline aqueous solution type, a phosphoric acid type, a molten carbonate type, a solid oxide type, a direct type methanol or the like, but a solid polymer type fuel cell is generally used.

  In this case, the solid polymer electrolyte membrane is sandwiched between two gas diffusion electrodes and integrated to join. When one of the gas diffusion electrodes is used as a fuel electrode (anode electrode) and hydrogen gas as fuel is supplied to the surface thereof, hydrogen is decomposed into hydrogen ions (protons) and electrons, and the hydrogen ions are converted into a solid polymer electrolyte. Permeates the membrane. Further, when the other of the gas diffusion electrodes is an oxygen electrode (cathode electrode) and air as an oxidant is supplied to the surface, oxygen in the air is combined with the hydrogen ions and electrons to generate water. The An electromotive force is generated by such an electrochemical reaction.

  In the polymer electrolyte fuel cell, since both sides of the polymer electrolyte membrane need to be kept wet, water is supplied to the fuel electrode side and the oxygen electrode side, respectively. In this case, moisture moves as proton-entrained water from the fuel electrode side toward the oxygen electrode side, and moves as back diffusion water from the oxygen electrode side toward the fuel electrode side.

By the way, it is known that when the load is high, on the fuel electrode side, dry-up, a phenomenon in which the amount of water evaporation increases and ion conductivity decreases, and the performance of the fuel cell deteriorates. (For example, refer to Patent Document 1). In addition, on the oxygen electrode side, the amount of generated water increases, flooding occurs, which is a phenomenon that the flow path of hydrogen gas and air is blocked by moisture, and the performance of the fuel cell is reduced. It is known to end up.
Japanese Patent Laid-Open No. 11-185778

  However, in the conventional fuel cell system, it is impossible to accurately detect the occurrence of dry-up or flooding, and it has not been possible to quickly take countermeasures. Therefore, the performance of the fuel cell is reduced due to the occurrence of dry-up or flooding, the fuel cell system cannot be stably operated for a long time, and the fuel cell itself is deteriorated. .

  However, it is possible to detect the occurrence of dry-up or flooding based on changes in the current density-voltage performance characteristics of the entire fuel cell stack, or to detect dry-up or flooding based on changes in the impedance (resistance) of the entire fuel cell stack. A method of detecting occurrence has been proposed. In this case, since the occurrence of dry-up or flooding is detected based on changes in the characteristics of the entire fuel cell stack, it is not possible to quickly detect dry-up or flooding that occurs locally in a part of the fuel cell stack. It was. In addition, a method has been proposed in which the occurrence of dry-up or flooding is detected by detecting changes in all voltages of the unit cells forming the fuel cell stack. In this case, it is possible to detect locally generated dry-up and flooding, but it is necessary to attach a detection device for detecting the voltage to all of the many unit cells packed in a narrow space. The cost of the apparatus becomes high, it is difficult to attach the detection apparatus, and the fuel cell stack becomes large.

The present invention solves the problems of the conventional fuel cell system, specifies in advance a unit cell located in a place with a high probability of occurrence of dry-up and a unit cell located in a place with a high probability of occurrence of flooding. By measuring the electromotive force of the unit cell and detecting the occurrence of dry-up and flooding, the cost of the detection device is low, the installation of the detection device is easy, and the fuel cell stack does not increase in size, and an object thereof is to provide a fuel cell system that can rapidly detect the dry-up and flooding.

  Therefore, in the fuel cell system of the present invention, a fuel cell in which an electrolyte layer is sandwiched between a fuel electrode and an oxygen electrode has a fuel gas flow path formed along the fuel electrode, and an air flow along the oxygen electrode. First detection for detecting an electromotive force of a fuel cell stack stacked with a separator having a path formed therein and a first fuel cell located in a place where the probability of dry-up in the fuel cell stack is high Apparatus, a second detection device for detecting an electromotive force of a second fuel cell located at a place where the occurrence probability of flooding in the fuel cell stack is high, and a probability of occurrence of dry-up and flooding in the fuel cell stack A third detection device for detecting an electromotive force of a third fuel cell located at a low position of the first fuel cell, an electromotive force of the first fuel cell, and an electromotive force of the third fuel cell If the difference between the two fuel cells exceeds a first predetermined value, it is determined that dry-up has occurred, and the difference between the electromotive force of the second fuel cell and the electromotive force of the third fuel cell is a second predetermined value. And a control device that determines that flooding has occurred.

  In another fuel cell system of the present invention, the first detection device detects an electromotive force of a fuel cell in the vicinity of a fuel gas flow path inlet in the fuel cell stack, and the second detection device The electromotive force of the fuel cell in the vicinity of the outlet of the fuel gas passage in the fuel cell stack is detected.

Further Oite the other fuel cell system of the present invention, further, the second predetermined value, Ru said first predetermined value greater than der.

  According to the present invention, in the fuel cell system, the fuel cell in which the electrolyte layer is sandwiched between the fuel electrode and the oxygen electrode has a fuel gas flow path formed along the fuel electrode, and an air flow along the oxygen electrode. First detection for detecting an electromotive force of a fuel cell stack stacked with a separator having a path formed therein and a first fuel cell located in a place where the probability of dry-up in the fuel cell stack is high Apparatus, a second detection device for detecting an electromotive force of a second fuel cell located at a place where the occurrence probability of flooding in the fuel cell stack is high, and a probability of occurrence of dry-up and flooding in the fuel cell stack A third detection device for detecting an electromotive force of a third fuel cell located at a low position of the first fuel cell, an electromotive force of the first fuel cell, and an electromotive force of the third fuel cell Is determined to have exceeded the first predetermined value, it is determined that dry-up has occurred, and the difference between the electromotive force of the second fuel cell and the electromotive force of the third fuel cell exceeds the second predetermined value. And a control device that determines that flooding has occurred.

  In this case, it is only necessary to use a small number of detection devices, so the cost of the detection devices is low, the installation of the detection devices is easy, the fuel cell stack is not enlarged, and dry-up and flooding can be detected quickly. can do.

  In another fuel cell system, the first detection device further detects an electromotive force of the fuel cell in the vicinity of the fuel gas flow path inlet in the fuel cell stack, and the second detection device includes: An electromotive force of the fuel cell in the vicinity of the fuel gas flow path outlet in the fuel cell stack is detected.

  In this case, it is possible to reliably and quickly detect dry-up and flooding.

  Further, in the operation method of the fuel cell system, the operation of the fuel cell system that supplies air to the air flow path of the fuel cell stack mounted on the vehicle and supplies the fuel gas to the fuel gas flow path of the fuel cell stack. A method of producing a third fuel cell located in a place where the electromotive force of the first fuel cell located in the fuel cell stack where the probability of occurrence of dry-up is high and the probability of occurrence of dry-up and flooding is low. It is determined that dry-up has occurred when the difference from the electromotive force exceeds the first predetermined value, and the electromotive force of the second fuel cell located at a place where the occurrence probability of flooding in the fuel cell stack is high When the difference from the electromotive force of the third fuel cell exceeds a second predetermined value, it is determined that flooding has occurred.

  In this case, it is only necessary to use a small number of detection devices, so the cost of the detection devices is low, the installation of the detection devices is easy, the fuel cell stack is not enlarged, and dry-up and flooding can be detected quickly. can do.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 2 is a diagram showing the configuration of the fuel cell stack in the embodiment of the present invention, FIG. 3 is a diagram showing the configuration of the cell module of the fuel cell in the embodiment of the present invention, and FIG. 4 is in the embodiment of the present invention. It is a schematic cross section which shows the structure of the unit cell of a fuel cell.

  In FIG. 2, a fuel cell stack 20 as a fuel cell (FC) is used as a power source for vehicles such as passenger cars, buses, trucks, passenger carts, and luggage carts. Here, the vehicle is equipped with a large number of auxiliary devices that consume electricity, such as lighting devices, radios, and power windows, which are used even when the vehicle is stopped. Since the output range is extremely wide, it is desirable to use the fuel cell stack 20 as a power source and a secondary battery as a power storage means (not shown) in combination.

  The fuel cell stack 20 is of an alkaline aqueous solution type (AFC), phosphoric acid type (PAFC), molten carbonate type (MCFC), solid oxide type (SOFC), direct methanol (DMFC), or the like. However, a polymer electrolyte fuel cell (PEMFC) is desirable.

  More preferably, PEMFC (Proton Exchange Membrane Fuel Cell) type fuel cell or PEM (Proton Exchange Membrane) using hydrogen gas as fuel gas, that is, anode gas, and oxygen or air as oxidant, that is, cathode gas. ) Type fuel cell. Here, the PEM fuel cell is generally a fuel cell in which a catalyst, an electrode, and a separator are combined on both sides of a solid polymer electrolyte membrane as an electrolyte layer that transmits ions such as protons. Are composed of a plurality of stacks connected in series.

  In the present embodiment, the fuel cell stack 20 includes a plurality of cell modules 10 as shown in FIG. In addition, the arrow in FIG. 2 has shown the flow of the hydrogen gas as fuel gas. As shown in FIG. 3, the cell module 10 electrically connects a unit cell (MEA) 10A as a fuel cell with the unit cells 10A and hydrogen introduced into the unit cell 10A. The separator 10B that separates the gas flow path and the air, and the unit cell 10A and the separator 10B are set as one set, and a plurality of sets are stacked in the thickness direction. In the cell module 10, the unit cells 10 </ b> A and the separators 10 </ b> B are stacked and stacked in multiple stages so that the unit cells 10 </ b> A are arranged with a predetermined gap (gap) therebetween.

  The unit cell 10A includes an air electrode 12 as an oxygen electrode provided on the side of the solid polymer electrolyte membrane 11 as an electrolyte layer and a fuel electrode 13 provided on the other side. The air electrode 12 is composed of an electrode diffusion layer made of a conductive material that permeates while diffusing the reaction gas, and a catalyst layer that is formed on the electrode diffusion layer and is supported in contact with the solid polymer electrolyte membrane 11. Become. Further, the air electrode side as a mesh-like current collector in which a large number of openings are formed that are in contact with the electrode diffusion layer on the air electrode 12 side of the unit cell 10A and collect a mixed flow of air and water. It has a collector 14 and a fuel electrode side collector 15 as a mesh current collector for contacting the electrode diffusion layer on the fuel electrode 13 side of the unit cell 10A and similarly leading out current.

  And in unit cell 10A, as FIG. 4 shows, water moves. In FIG. 4, 48 is a fuel chamber as a fuel gas flow path, and 49 is an oxygen chamber as an air flow path. In this case, when a fuel gas, that is, hydrogen gas as an anode gas is supplied into the fuel chamber 48 of the fuel electrode side collector 15, hydrogen is decomposed into hydrogen ions and electrons, and the hydrogen ions are accompanied by proton-entrained water. It passes through the solid polymer electrolyte membrane 11. Further, when the air electrode 12 is a cathode electrode and an oxidant, that is, air as a cathode gas is supplied into the oxygen chamber 49, oxygen in the air is combined with the hydrogen ions and electrons to generate water. Is done. Moisture permeates through the solid polymer electrolyte membrane 11 as reverse diffusion water and moves into the fuel chamber 48 of the fuel electrode side collector 15. Here, the reverse diffusion water means that the water generated in the oxygen chamber 49 diffuses into the solid polymer electrolyte membrane 11 and permeates through the solid polymer electrolyte membrane 11 in the direction opposite to the hydrogen ions. It penetrated up to 48.

  Next, the overall configuration of the fuel cell system will be described.

  FIG. 1 is a diagram showing a configuration of a fuel cell system according to an embodiment of the present invention.

  In FIG. 1, a device for supplying hydrogen gas as a fuel gas and air as an oxidant to a fuel cell stack 20 is shown. Although hydrogen gas, which is fuel taken out by reforming methanol, gasoline, or the like by a reformer (not shown), can be directly supplied to the fuel cell stack 20, it is stable and sufficient even during high-load operation of the vehicle. In order to be able to supply an amount of hydrogen gas, it is desirable to supply the hydrogen gas stored in the fuel storage means 73. Thereby, the hydrogen gas is always sufficiently supplied at a substantially constant pressure, so that the fuel cell stack 20 can follow the fluctuation of the load of the vehicle and supply a necessary current. . In this case, the output impedance of the fuel cell stack 20 is extremely low and can be approximated to zero.

  Hydrogen gas is stored in a container containing a hydrogen storage alloy, a container containing a hydrogen storage liquid such as decalin, a fuel storage means 73 such as a hydrogen gas cylinder, a first fuel supply line 21 as a fuel supply line, and The fuel is supplied to the inlet of the fuel gas flow path of the fuel cell stack 20 through a second fuel supply pipe 33 as a fuel supply pipe connected to the first fuel supply pipe 21. The first fuel supply pipe 21 is provided with a fuel storage means on-off valve 24, a pressure sensor 27, a first fuel pressure adjustment valve 25a, a second fuel pressure adjustment valve 25b, and a fuel supply electromagnetic valve 26. The The second fuel supply pipe 33 is provided with a safety valve 33a and a pressure sensor 78 for detecting the pressure in the fuel gas passage. In this case, the fuel storage means 73 has a sufficiently large capacity and is capable of always supplying sufficiently high pressure hydrogen gas.

  The hydrogen gas discharged as an unreacted component from the outlet of the fuel gas flow path of the fuel cell stack 20 is discharged to the outside of the fuel cell stack 20 through the fuel discharge pipe 31. A water recovery drain tank 60 as a recovery container is disposed in the fuel discharge line 31. The water recovery drain tank 60 is connected with a fuel discharge line 30 for discharging water and the separated hydrogen gas. The fuel discharge line 30 is provided with a suction circulation pump 36 as a pump. Yes. A hydrogen circulation electromagnetic valve 34 is disposed in the fuel discharge line 30. The end of the fuel discharge line 30 opposite to the water recovery drain tank 60 is connected to the second fuel supply line 33. Thereby, the hydrogen gas discharged to the outside of the fuel cell stack 20 can be recovered, supplied to the fuel gas flow path of the fuel cell stack 20, and reused.

  Further, a startup fuel discharge conduit 56 is connected to the water recovery drain tank 60, and a hydrogen startup exhaust solenoid valve 62 is disposed in the startup fuel discharge pipeline 56, so that the fuel cell stack 20 is started up. The hydrogen gas discharged from the fuel gas channel can be discharged into the atmosphere. The outlet end of the starting fuel discharge line 56 is connected to the exhaust manifold 71. In addition, a hydrogen combustor may be provided in the startup fuel discharge line 56 as necessary. The hydrogen gas discharged by the hydrogen combustor can be combusted to form water, and then discharged into the atmosphere.

  Here, the first fuel pressure regulating valve 25a and the second fuel pressure regulating valve 25b are those of a butterfly valve, a regulator valve, a diaphragm type valve, a mass flow controller, a sequence valve, etc., but the first fuel pressure regulating valve Any type of hydrogen gas may be used as long as the pressure of the hydrogen gas flowing out from the outlets of 25a and the second fuel pressure regulating valve 25b can be adjusted to a preset pressure. The pressure adjustment may be performed manually, but is preferably performed by an actuator including an electric motor, a pulse motor, an electromagnet, or the like.

  The fuel supply solenoid valve 26, the hydrogen circulation solenoid valve 34, and the hydrogen activation exhaust solenoid valve 62 are so-called on-off types, and are operated by an actuator including an electric motor, a pulse motor, an electromagnet, and the like. The fuel storage means original opening / closing valve 24 is operated manually or automatically using an electromagnetic valve. Further, the suction circulation pump 36 may be of any type as long as it can forcibly discharge the reverse diffusion water together with the hydrogen gas and can bring the inside of the fuel gas passage into a negative pressure state. Good.

  On the other hand, air as an oxidant is supplied from an oxidant supply source 75 such as an air supply fan, an air cylinder, or an air tank to an air flow path of the fuel cell stack 20 through an oxidant supply line 77 and an intake manifold 74. Supplied. In this case, the pressure of the supplied air is a normal pressure of about atmospheric pressure. Note that oxygen can be used as the oxidizing agent instead of air. And the air discharged | emitted from an air flow path is discharged | emitted in air | atmosphere through the exhaust manifold 71 as a manifold, the condenser 72, the exit side exhaust manifold 22, and the exhaust port 22a.

  The oxidant supply pipe 77 is provided with a water supply nozzle 76 for spraying water to maintain the air electrode 12 of the fuel cell stack 20 in a wet state. Further, the air electrode 12 and the fuel electrode 13 can be cooled by the sprayed water. Further, the condenser 72 disposed at the end of the exhaust manifold 71 is for condensing and removing moisture contained in the air discharged from the fuel cell stack 20, and is condensed by the condenser 72. The water thus collected is collected in the water tank 52 through the condensed water discharge pipe 79. A drainage pump 51 is disposed in the condensed water discharge conduit 79, and a level gauge (water level gauge) 52a is disposed in the water tank 52.

  The water in the water tank 52 is supplied to the water supply nozzle 76 through the water supply pipe 53. A water supply pump 54 and a water filter 55 are disposed in the water supply line 53. Here, the drainage pump 51 and the water supply pump 54 may be of any kind as long as they can suck and discharge water. The water filter 55 may be of any kind as long as it removes dust, impurities, etc. contained in water.

  Furthermore, in the fuel cell stack 20, the first unit cell 10A located at a place where the probability of occurrence of dry-up is high, that is, the unit cell 10A that is likely to cause dry-up, and the second unit cell located at a place where the probability of occurrence of flooding is high. The unit cell 10A, that is, the unit cell 10A that is likely to cause flooding, and the third unit cell 10A that is located in a place where the probability of occurrence of dry-up and flooding is low, that is, the normal unit cell 10A include the corresponding unit cell A voltmeter 58 is attached as first to third detection devices for measuring the electromotive force of 10A. Then, if the difference in electromotive force between the unit cell 10A that tends to cause dry-up and the normal unit cell 10A exceeds the first predetermined value, it is determined that dry-up has occurred, and the dry-up countermeasure process Is executed. When the difference in electromotive force between the unit cell 10A that is likely to cause flooding and the normal unit cell 10A exceeds the second predetermined value, it is determined that flooding has occurred, and flooding countermeasure processing is executed. The

  The secondary battery as the power storage means is a so-called battery (storage battery), and a lead storage battery, a nickel cadmium battery, a nickel hydrogen battery, a lithium ion battery, a sodium sulfur battery, and the like are generally used. The power storage means does not necessarily have to be a battery, and electrically stores and discharges energy, such as a capacitor (capacitor) such as an electric double layer capacitor, a flywheel, a superconducting coil, and a pressure accumulator. Any form may be used as long as it has a function. Furthermore, any of these may be used alone, or a plurality of them may be used in combination.

  The fuel cell stack 20 is connected to a load (not shown) and supplies the generated current to the load. Here, the load is generally an inverter device that is a drive control device, and converts a direct current from the fuel cell stack 20 or the power storage means into an alternating current to rotate a vehicle wheel. To supply. Here, the drive motor also functions as a generator, and generates a so-called regenerative current when the vehicle is decelerated. In this case, since the drive motor is rotated by the wheel to generate electric power, the wheel is braked, that is, functions as a vehicle braking device (brake). Then, the regenerative current is supplied to the power storage means, and the power storage means is charged.

  In the present embodiment, the fuel cell system has an FC control ECU (Electronic Control Unit) (not shown) as a control device. The control device includes arithmetic means such as a CPU and MPU, storage means such as a magnetic disk and semiconductor memory, an input / output interface, and the like, and the fuel gas flow of the fuel cell stack 20 from various sensors including a hydrogen concentration detector (not shown). The oxidant supply source 75, the first fuel pressure adjustment valve 25a, and the second fuel pressure adjustment valve 25b are detected by detecting the flow rate, temperature, output voltage and the like of hydrogen, oxygen, air, etc. supplied to the passage and the air passage. The operation of the fuel supply solenoid valve 26, the hydrogen circulation solenoid valve 34, the suction circulation pump 36, the drainage pump 51, the feed water pump 54, the hydrogen activation exhaust solenoid valve 62, and the like is controlled. Further, the FC control ECU cooperates with other sensors provided in the vehicle and an EV (Electric Vehicle) control ECU (not shown) as a vehicle control means to supply fuel and oxidant to the fuel cell stack 20. Centrally control the operation of all equipment supplied. When the FC control ECU determines that dry-up has occurred in the fuel cell stack 20 based on the output of the voltmeter 58, the FC control ECU executes dry-up countermeasure processing, and flooding has occurred in the fuel cell stack 20. If it is determined that it is, the countermeasure against flooding is executed.

  Next, a method for specifying the unit cell 10A that is likely to cause dry-up in the fuel cell system having the above-described configuration will be described.

  FIG. 5 is a schematic diagram showing the flow of hydrogen in the fuel cell stack according to the embodiment of the present invention, FIG. 6 is a diagram showing a change in average cell voltage of each cell module in the embodiment of the present invention, and FIG. It is a figure which shows the comparison of the voltage of the unit cell which is easy to raise | generate dry-up in embodiment of invention, and the voltage of a normal unit cell.

  Here, a set of 10 unit cells 10A and a separator 10B is stacked to form one cell module 10, and 10 cell modules 10 are stacked to form one fuel cell stack 20. I will explain. In this case, the flow of hydrogen gas in the fuel cell stack 20 is in a serpentine shape that is folded for each cell module 10, that is, in a serpentine shape, as indicated by arrows in FIG. In FIG. 5, 1M to 10M indicate the order of the cell modules 10 from the inlet side to the outlet side of the hydrogen gas flow path in the fuel cell stack 20, and in the first to tenth cell modules 10 It means that there is. Moreover, the thickness of the arrow in FIG. 5 has shown the flow velocity and pressure of hydrogen gas.

  From FIG. 5, it can be seen that the flow rate and pressure of hydrogen gas are higher in the cell module 10 on the inlet side of the hydrogen gas flow path, and the flow rate of hydrogen gas is lower as it approaches the outlet side. And it can be considered that the higher the flow rate and pressure of the hydrogen gas, the easier it is to remove moisture from the fuel electrode 13, so that the cell module 10 closer to the inlet side of the hydrogen gas flow path is more likely to dry up.

  And when the inventor of the present invention conducted an experiment and measured the change of the average cell voltage in each of the first to tenth cell modules 10, the result as shown in FIG. 6 can be obtained. It was. In FIG. 6, the vertical axis represents the average cell voltage [V], and the horizontal axis represents time [seconds]. In FIG. 6, A is a line indicating a change in average cell voltage in each of the second to tenth cell modules 10, and B is a change in average cell voltage in each of the first cell modules 10. It is a line which shows.

  From FIG. 6, the average cell voltage in the second to tenth cell modules 10 is almost constant over time, whereas the average cell voltage in the first cell module 10 passes over time. It turns out that it falls as it goes. A decrease in the average cell voltage in the first cell module 10 indicates a decrease in performance due to the occurrence of dry-up. From this, it was confirmed that dry-up occurred in the first cell module 10 closest to the inlet side of the hydrogen gas flow path.

  Subsequently, the inventor of the present invention measures the electromotive force of each unit cell 10 </ b> A in the first cell module 10, that is, the change in voltage, and the first cell module 10 has a high probability of occurrence of dry-up. Which unit cell 10A is located at the place, that is, which unit cell 10A is likely to cause dry-up is specified. When viewed finely, the flow of hydrogen gas inside the first cell module 10 is not necessarily uniform, and the flow velocity and pressure change locally. The flow of the hydrogen gas varies depending on the structure, shape, etc. of the first cell module 10. Therefore, in the first cell module 10, it cannot be said that the unit cell 10 </ b> A closer to the inlet side of the hydrogen gas flow path is likely to cause dry-up, and which unit cell 10 </ b> A is likely to cause dry-up. This differs depending on the structure, shape, etc. of the first cell module 10. Therefore, as described above, it is necessary to determine which unit cell 10A is likely to cause dry-up by measuring the change in voltage of each unit cell 10A in the first cell module 10.

Next, the inventor of the present invention measured the change in the voltage of the unit cell 10A, which tends to cause the specified dry-up, and the change in the voltage of the normal unit cell 10A. As a result, the result shown in FIG. Could get. In FIG. 7, the vertical axis represents the cell voltage [V], and the horizontal axis represents the time [second]. In FIG. 7, C is a line indicating a change in the cell voltage in the normal unit cell 10A, D is a line indicating a change in the cell voltage in the unit cell 10A that easily causes dry-up, and the lines C and D are The measurement result when the current density is 0.5 [A / cm ² ] is shown. Here, the normal unit cell 10A is a unit cell 10A located in a place where the occurrence probability of dry-up is low, that is, a unit cell 10A that hardly causes dry-up, and the second to tenth cell modules 10 Is selected from the unit cells 10A.

  From FIG. 7, the cell voltage in the normal unit cell 10A is substantially constant over time, whereas the cell voltage in the unit cell 10A that is prone to dry-up decreases with time. I understand. The decrease in the cell voltage in the unit cell 10A that easily causes the dry-up indicates a decrease in performance due to the occurrence of the dry-up. From this, when the difference between the cell voltage in the normal unit cell 10A and the cell voltage in the unit cell 10A that easily causes dry-up exceeds a preset value, it may be determined that dry-up has occurred. I understand that.

  Next, a method for identifying the unit cell 10A that is likely to cause flooding in the fuel cell system having the above-described configuration will be described.

  FIG. 8 is a diagram showing a comparison between the voltage of a unit cell that is likely to cause flooding and the voltage of a normal unit cell in the embodiment of the present invention.

  In the fuel cell stack 20, in the oxygen chamber 49 of each unit cell 10A, water generated by combining oxygen in the air, hydrogen ions, and electrons, that is, generated water is generated. Further, water sprayed from the water supply nozzle 76 is supplied into the oxygen chamber 49 in order to maintain the air electrode 12 in a wet state. When viewed finely, the distribution of moisture in the gas phase and the liquid phase in the oxygen chamber 49 is not necessarily uniform, and the amount of moisture, the flow rate, and the like vary locally. For this reason, a large amount of moisture is concentrated locally, and flooding that inhibits the flow of air in the oxygen chamber 49 may occur. Although flooding may occur in the fuel chamber 48, in the present embodiment, only the case where it occurs in the oxygen chamber 49 will be described for convenience of explanation.

  And it can be considered that the cell module 10 closer to the outlet side of the hydrogen gas flow path is more likely to be flooded. However, the probability of occurrence of flooding varies depending on the amount of generated water, the amount of water sprayed from the water supply nozzle 76, the amount of air supplied from the oxidant supply source 75, etc. Whether the unit cell 10A is likely to be flooded depends on the structure, shape, and the like of the fuel cell stack 20. Therefore, it is necessary to specify which unit cell 10A in the fuel cell stack 20 is likely to cause flooding. When flooding occurs, the air electrode 12 is covered with moisture and cannot come into contact with air, and the cell voltage of the unit cell 10A that causes flooding decreases. By measuring the change in the voltage of the unit cell 10A, the unit cell 10A that easily causes each flooding can be specified.

Next, the inventor of the present invention measured the change in the voltage of the unit cell 10A that is likely to cause the specified flooding and the change in the voltage of the normal unit cell 10A. The result shown in FIG. 8 was obtained. I was able to get it. In FIG. 8, the vertical axis represents the cell voltage [V], and the horizontal axis represents the time [second]. In FIG. 8, E is a line indicating a change in the cell voltage in the normal unit cell 10A, F is a line indicating a change in the cell voltage in the unit cell 10A that easily causes flooding, and lines E and F are currents. The measurement results when the density is 0.5 [A / cm ² ] are shown. Here, the normal unit cell 10A is a unit cell 10A located in a place where the probability of occurrence of flooding is low, that is, a unit cell 10A that hardly causes flooding. In addition, as the unit cell 10A that hardly causes flooding, the same unit cell 10A as the unit cell 10A that hardly causes dry-up can be selected, or a different unit cell 10A can be selected.

  From FIG. 8, the cell voltage in the normal unit cell 10A is substantially constant over time, whereas the cell voltage in the unit cell 10A that is prone to flooding is in the range below the cell voltage in the normal unit cell 10A. It can be seen that there is a large fluctuation in. The decrease in the cell voltage in the unit cell 10A that easily causes flooding indicates a decrease in performance due to the occurrence of flooding. Further, the rise in cell voltage in the unit cell 10A that is likely to cause flooding is temporarily caused by some factor such as that the water covering the air electrode 12 is blown away by the air supplied from the oxidant supply source 75, for example. Shows the performance recovery due to the removal. From this, it may be determined that flooding has occurred when the difference between the cell voltage in the normal unit cell 10A and the cell voltage in the unit cell 10A that easily causes flooding exceeds a preset value. I understand. 7 and 8, it can be seen that the amount of voltage decrease is greater when flooding occurs than when dry-up occurs.

  Next, the operation of the fuel cell system having the above configuration will be described. First, the operation in steady operation will be described.

  During steady operation in the fuel cell system of the present embodiment, after adjusting the pressure of hydrogen gas flowing out from the outlets of the first fuel pressure adjustment valve 25a and the second fuel pressure adjustment valve 25b to a predetermined constant pressure, The first fuel pressure adjustment valve 25a and the second fuel pressure adjustment valve 25b are not adjusted during operation of the fuel cell system, and are maintained as they are. The oxidant supply source 75 operates so that air set in advance according to the output current of the fuel cell is supplied. In this case, the amount of air supplied is an amount sufficiently larger than the amount of air necessary for the output of the fuel cell stack 20 to be maximized. In the present embodiment, the pressure of the air supplied to the unit cell 10A of the fuel cell stack 20 is a normal pressure of about atmospheric pressure and does not need to be particularly pressurized. Therefore, since the oxidant supply source 75, the oxidant supply pipe 77, the intake manifold 74, the exhaust manifold 71, the condenser 72, the outlet side exhaust manifold 22 and the like do not need to have pressure resistance, the configuration is simplified. Can do.

  When the fuel cell stack 20 starts operation, reverse diffusion water is generated in each unit cell 10A constituting the fuel cell stack 20, and the reverse diffusion water permeates the solid polymer electrolyte membrane 11 to flow the fuel gas. Then, the fuel electrode 13 side of the solid polymer electrolyte membrane 11 is humidified. Thereby, the fuel electrode 13 side of the solid polymer electrolyte membrane 11 is in a wet state, and hydrogen ions generated from hydrogen by an electrochemical reaction can move smoothly in the solid polymer electrolyte membrane 11.

  Further, the hydrogen gas as an unreacted component that is supplied to the fuel gas flow path and surplus is mixed with the back-diffused water that has permeated into the fuel gas flow path and becomes surplus, and a gas-liquid mixture Become. The hydrogen gas that has become the gas-liquid mixture is sucked by the suction circulation pump 36 and discharged to the outside of the fuel cell stack 20 through the fuel discharge pipe 31 connected to the fuel cell stack 20. The gas-liquid mixture passes through the fuel discharge pipe 31 and is introduced into the water recovery drain tank 60. Then, by staying in the water recovery drain tank 60 having a relatively wide space, heavy moisture falls downward due to gravity, and the reverse diffusion water is separated from the hydrogen gas. The hydrogen gas in a state where the reverse diffusion water is separated and dried is discharged out of the water recovery drain tank 60 from the fuel discharge pipe 30.

  In steady operation, the hydrogen gas discharged from the fuel discharge line 30 passes through the open hydrogen circulation electromagnetic valve 34, is introduced into the second fuel supply line 33, and again. Then, it is supplied to the fuel gas flow path of the fuel cell stack 20 and reused.

  Next, the operation when dry-up or flooding occurs in the fuel cell stack 20 will be described.

  FIG. 9 is a flowchart showing an operation when dry-up or flooding of the fuel cell system according to the embodiment of the present invention occurs.

  First, the FC control ECU determines the voltage of the normal unit cell 10A based on the voltage measured by the voltmeter 58 attached to the normal unit cell 10A and the voltmeter 58 attached to the unit cell 10A that easily causes dry-up. It is determined whether or not the difference ΔEd between the voltage of the unit cell 10A that easily causes dry-up exceeds a preset first predetermined value (step S1). Here, the first predetermined value is a reference value for determining that dry-up has occurred, and is, for example, about 50 to 100 [mV], but can be set to an arbitrary value. In addition, the first predetermined value may not be constant, and may change according to the load of the fuel cell stack 20, for example.

  When the difference ΔEd exceeds the first predetermined value, the FC control ECU determines that dry-up has occurred in the fuel cell stack 20, and executes dry-up countermeasure processing (step S2). The dry-up countermeasure process is a process for eliminating the generated dry-up. For example, the operation temperature of the fuel cell stack 20 is decreased, the pressure of the air supplied to the fuel cell stack 20 is increased, and the fuel cell stack 20 For example, an increase in the pressure of hydrogen gas supplied to the tank.

  When the difference ΔEd does not exceed the first predetermined value, the FC control ECU measures the voltmeter 58 attached to the normal unit cell 10A and the voltmeter 58 attached to the unit cell 10A that easily causes flooding. Based on the determined voltage, it is determined whether or not the difference ΔEf between the voltage of the normal unit cell 10A and the voltage of the unit cell 10A that is likely to cause flooding exceeds a preset second predetermined value (step S3).

  The normal unit cell 10A for detecting the difference ΔEf may be the same as or different from the normal unit cell 10A for detecting the difference ΔEd. That is, the same unit cell 10A may be used as the normal unit cell 10A in the case of detecting the occurrence of dry-up and the case of detecting the occurrence of flooding, or different unit cells 10A may be used as normal unit cells. It may be used as 10A.

  Here, the second predetermined value is a reference value for determining that flooding has occurred, and is, for example, about 300 to 900 [mV], but can be set to an arbitrary value. Further, the second predetermined value may not be constant, and may change according to the load of the fuel cell stack 20, for example.

  When the difference ΔEf exceeds the second predetermined value, the FC control ECU determines that flooding has occurred in the fuel cell stack 20, and executes flooding countermeasure processing (step S4). The flooding countermeasure process is a process for eliminating the generated flooding, for example, a process of increasing the flow rate of air supplied to the fuel cell stack 20 or the like.

  If the difference ΔEf does not exceed the second predetermined value, the FC control ECU again determines whether or not the difference ΔEd exceeds the first predetermined value, and repeats the above operation.

  As described above, in the present embodiment, the fuel cell system specifies in advance the unit cell 10A that easily causes dry-up and the unit cell 10A that easily causes flooding, and the normal unit cell 10A and the unit cell 10A that easily causes dry-up. A voltmeter 58 is attached to each of the unit cells 10A that are likely to cause flooding, and the electromotive force of each is measured. Then, if the difference ΔEd between the voltage of the normal unit cell 10A and the voltage of the unit cell 10A that easily causes dry-up exceeds the first predetermined value, it is determined that dry-up has occurred, and measures for dry-up are taken. Execute the process. Further, when the difference ΔEf between the voltage of the normal unit cell 10A and the voltage of the unit cell 10A that easily causes flooding exceeds the second predetermined value, it is determined that flooding has occurred, and flooding countermeasure processing is executed. To do.

  Therefore, the occurrence of dry-up and flooding can be detected by a small number of voltmeters 58, and the cost of the detection device for detecting the occurrence of dry-up and flooding can be reduced. Further, since only a small number of voltmeters 58 need be attached to a small number of unit cells 10A, the voltmeter 58 can be easily attached. Furthermore, since only a small number of voltmeters 58 need be attached, the fuel cell stack 20 does not increase in size. Further, since the occurrence of dry-up and flooding is detected based on the state of the unit cell 10A that is prone to dry-up and the unit cell 10A that is prone to flooding, the occurrence of dry-up and flooding is reliably and promptly detected. be able to.

  In addition, this invention is not limited to the said embodiment, It can change variously based on the meaning of this invention, and does not exclude them from the scope of the present invention.

It is a figure which shows the structure of the fuel cell system in embodiment of this invention. It is a figure which shows the structure of the fuel cell stack in embodiment of this invention. It is a figure which shows the structure of the cell module of the fuel cell in embodiment of this invention. It is a schematic cross section which shows the structure of the unit cell of the fuel cell in embodiment of this invention. It is a schematic diagram which shows the flow of the hydrogen in the fuel cell stack in embodiment of this invention. It is a figure which shows the change of the average cell voltage of each cell module in embodiment of this invention. It is a figure which shows the comparison with the voltage of the unit cell which is easy to raise | generate dry-up in embodiment of this invention, and the voltage of a normal unit cell. It is a figure which shows the comparison with the voltage of the unit cell which is easy to raise | generate flooding in embodiment of this invention, and the voltage of a normal unit cell. 4 is a flowchart showing an operation when dry-up or flooding of the fuel cell system according to the embodiment of the present invention occurs.

Explanation of symbols

10A Unit cell 10B Separator 11 Solid polymer electrolyte membrane 12 Air electrode 13 Fuel electrode 20 Fuel cell stack 48 Fuel chamber 49 Oxygen chamber 58 Voltmeter

Claims (3)

A fuel cell in which an electrolyte layer is sandwiched between a fuel electrode and an oxygen electrode is stacked with a fuel gas flow path formed along the fuel electrode and a separator formed with an air flow path formed along the oxygen electrode. A fuel cell stack,
A first detection device for detecting an electromotive force of a first fuel cell located at a place where the probability of occurrence of dry-up in the fuel cell stack is high;
A second detection device for detecting an electromotive force of a second fuel cell located at a place where the occurrence probability of flooding is high in the fuel cell stack;
A third detection device for detecting an electromotive force of a third fuel cell located in a place where the probability of occurrence of dry-up and flooding is low in the fuel cell stack;
When the difference between the electromotive force of the first fuel cell and the electromotive force of the third fuel cell exceeds a first predetermined value, it is determined that dry-up has occurred, and the start of the second fuel cell is determined. A fuel cell system comprising: a control device that determines that flooding has occurred when a difference between electric power and an electromotive force of the third fuel cell exceeds a second predetermined value.   The first detection device detects an electromotive force of a fuel cell in the vicinity of the fuel gas flow path inlet in the fuel cell stack, and the second detection device is in the vicinity of a fuel gas flow path outlet in the fuel cell stack. The fuel cell system according to claim 1, wherein an electromotive force of the fuel cell is detected. 3. The fuel cell system according to claim 1, wherein the second predetermined value is larger than the first predetermined value.

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