JP2014029801A - Fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To find a factor which can drop an open circuit voltage.SOLUTION: A fuel cell system 20 grasps transition of open circuit voltage Vocv when the open circuit voltage Vocv drops for each voltage drop factor after associating the transition with transition of a film resistance value R. Then, the open circuit voltage Vocv detected at the time of operation control of an electrolyte film 121 to a drying side which is performed after the open circuit voltage Vocv has dropped is compared with the transition state of the grasped open circuit voltage to specify the factor of voltage drop.

Description

  The present invention relates to.

  The battery cells constituting the fuel cell generate electricity by causing an electrochemical reaction utilizing the proton conductivity of the electrolyte membrane. The power generation performance of the battery cell can be grasped as an output voltage when operating the fuel cell with a load below a predetermined value, for example, an open circuit voltage that is an output voltage in a no-load state in which no current flows to an external load. . On the other hand, this open circuit voltage depends on the wet state of the electrolyte membrane. For this reason, a method for determining the presence or absence of abnormality of the electrolyte membrane based on the open circuit voltage has been proposed (Patent Document 1 and the like).

JP 2008-108612 A JP 2005-32587 A

  Although it can be inferred that the cause of the decrease in the open circuit voltage is excessive moisture in the electrolyte membrane, it is not sufficient to elucidate other factors that can cause the decrease in the open circuit voltage. Is the actual situation. For example, a cross leak in which hydrogen supplied to the anode leaks the electrolyte membrane to the cathode side can cause a decrease in open circuit voltage because the leaked hydrogen does not participate in the electrochemical reaction. In addition, since the electrolyte membrane can repeatedly swell and contract as the fuel cell is operated to cause local thinning, the short-circuit resistance of the electrolyte membrane interposed between the electrode catalyst layers on both membrane surfaces decreases. And in a battery cell having an electrolyte membrane in which this short circuit resistance drop has occurred, leakage of the open circuit voltage can occur, and thus the short circuit resistance drop can cause a drop in the open circuit voltage. However, the above method lacks consideration of the occurrence of cross leaks and the short-circuit resistance of the electrolyte membrane, and as described above, it is required to clarify the factors that can cause the open circuit voltage to decrease. It was. In addition, because the above factors are not sufficiently elucidated, an abnormality is reported when there is an abnormality in the electrolyte membrane due to a decrease in the open circuit voltage. Despite the fact that it is possible to diversify, the reality is that diversification of countermeasures after elucidating these factors has not progressed.

  In order to achieve at least a part of the above object, the present invention can be implemented as the following application examples.

  (1) According to one aspect of the present invention, there is provided a fuel cell system including a fuel cell including a plurality of battery cells each having a membrane electrode assembly in which an electrode catalyst layer is bonded to both membrane surfaces of an electrolyte membrane. The fuel cell system includes a characteristic detection unit that detects a low load output characteristic based on an output voltage of the fuel cell when the fuel cell is operated and controlled at a predetermined load or less, and a threshold voltage that is determined in advance by the output voltage. When the operating state of the fuel cell is changed to the side where the drying of the electrolyte membrane proceeds, the factor that causes the output voltage to decrease due to the detected behavior of the output characteristic at the time of low load after being changed, A voltage drop factor specifying unit that specifies one of the excess moisture of the electrolyte membrane and a plurality of factors other than the excess moisture is provided. According to the fuel cell system of the above aspect, a factor that can cause a decrease in open circuit voltage can be specified as one of excessive moisture in the electrolyte membrane or a plurality of factors other than excessive moisture. It is also possible to cope with the factors identified in this way.

  (2) In the fuel cell system of the above aspect, the voltage reduction factor specifying unit uses a voltage / resistance relationship indicating a relationship between the output voltage and a membrane resistance value of the electrolyte membrane as the low load output characteristic. Thus, the factor can be specified by the behavior of the voltage / resistance relationship. In other words, in a situation where the fuel cell is controlled so that the drying of the electrolyte membrane proceeds, the electrolyte membrane dries regardless of the type of the factor that caused the output voltage to decrease, so the membrane resistance value of the electrolyte membrane Will rise. And, if the cause of the decrease in the output voltage is excessive moisture in the electrolyte membrane, the excess moisture is eliminated, so the increase in output voltage is expected due to the influence, and this increase in output voltage is due to the membrane resistance value. Appears with the rise. On the other hand, the events that occur due to each of a plurality of factors other than excessive water content of the electrolyte membrane as factors that cause a decrease in output voltage also change as the operation of the fuel cell is controlled so that the drying of the electrolyte membrane proceeds. For each factor other than the excessive water content of the membrane, the transition of the output voltage comes with an increase in the membrane resistance value of the electrolyte membrane. In the fuel cell system of this embodiment, as described above, the voltage indicating the relationship between the output voltage and the membrane resistance value of the electrolyte membrane with respect to the excessive water content of the electrolyte membrane as a factor causing the decrease in the output voltage and other factors. By the behavior of the / resistance relationship, it is possible to elucidate the factors that can cause the output voltage to decrease, that is, the excessive water content of the electrolyte membrane as one factor and other factors.

  (3) In the fuel cell system according to the above aspect, the change in the voltage / resistance relationship detected by the voltage drop factor specifying unit as the low load output characteristic is grasped for each factor that causes the output voltage to drop. Further, the factor can be specified by comparing with the behavior of the voltage / resistance relationship. In this way, it is possible to more accurately identify factors that can cause a decrease in output voltage as excess moisture in the electrolyte membrane and other factors.

  (4) In the fuel cell system according to any one of the above aspects, the low load output characteristic can be an output voltage characteristic when the fuel cell is operated in a no-load state in which no current flows to an external load. By doing so, the output voltage characteristic can be specified as an output in a no-load state, which makes it easy to detect the output voltage characteristic.

  (5) In the fuel cell system of the above-described form, the output characteristic can be an open circuit voltage of the fuel cell detected for each battery cell. By doing so, the output characteristics can be specified as the characteristics of the open circuit voltage, which makes it easier to detect the characteristics of the output voltage.

  (6) In the fuel cell system of the above-described form, the voltage reduction factor specifying unit captures the occurrence of gas cross-leakage in the electrolyte membrane and the reduction in membrane short-circuit resistance of the electrolyte membrane as factors other than the excessive water content. Thus, the behavior of the voltage / resistance relationship is grasped in association with each of the excess moisture, the cross leak expression, and the decrease in the membrane short-circuit resistance, and the grasped behavior of the voltage / resistance and the detection Through the verification with the open circuit voltage, the factor can be specified as one of the excessive moisture, the cross leak, and the short circuit resistance. Changes in the open circuit voltage caused by excessive electrolyte membrane moisture and cross-leakage as well as a decrease in the membrane short-circuit resistance of the electrolyte membrane can be related to the membrane low resistance transition of the electrolyte membrane. It is. Therefore, in the fuel cell system of this embodiment, the cause of the decrease in the open circuit voltage is one of the excess moisture of the electrolyte membrane as one factor, the occurrence of cross leak and the decrease in membrane short-circuit resistance as other factors. Can be solved.

  (7) In the fuel cell system of the above aspect, when the factor is specified as the excess moisture by the voltage reduction factor specifying unit, the fuel cell is connected to the electrolyte until the open circuit voltage returns to the threshold voltage. Operation control can be continued on the side where the drying of the membrane proceeds. In this way, it is possible to increase the effectiveness of recovering the open circuit voltage that has decreased due to excessive moisture in the electrolyte membrane.

  (8) In the fuel cell system according to any one of the above-described forms, when the factor is identified as the occurrence of the cross leak by the voltage reduction factor identifying unit, the both surfaces of the electrolyte membrane in the membrane electrode assembly of the battery cell Based on the differential pressure of the gas supplied to and discharged from the electrode catalyst layer, the amount of cross leak accompanying the occurrence of the cross leak is determined for each battery cell, and the occurrence status of the cross leak determined for each battery cell For high cross-leakage battery cells that are higher than a predetermined threshold cross-leakage, notification of cell replacement can be performed. In this way, when the cause of the decrease in the open circuit voltage is the occurrence of cross leak, it is possible to report about the high cross leak battery cell that has caused the decrease in the open circuit voltage, for example, the repair or replacement of the cell. Recovery of open circuit voltage by replacement or replacement can be expected.

  (9) In the fuel cell system according to any one of the forms described above, a map first storage unit that stores a short-circuit resistance value transition map in which a transition of the short-circuit resistance value of the electrolyte membrane is associated with the voltage / resistance relationship; The short-circuit resistance value of the electrolyte membrane corresponding to the open-circuit voltage detected by the detection unit is compared with the voltage / resistance relationship and the short-circuit resistance value transition map for the open-circuit voltage detected by the voltage detection unit. The upper limit of the output voltage capable of suppressing damage to the electrolyte membrane due to heat generated due to the short-circuit resistance value of the electrolyte membrane and the output voltage of the battery cell. A second storage unit that stores a membrane damage suppression map associated with the short-circuit resistance value, and the short-circuit resistance value of the electrolyte membrane obtained by the short-circuit resistance value calculation unit is compared with the membrane damage suppression map. A voltage upper limit calculation unit for obtaining an upper limit of the output voltage capable of suppressing damage to the electrolyte membrane, and when the factor is specified as the membrane short-circuit resistance reduction by the voltage reduction factor specifying unit, the short circuit The resistance value calculation unit obtains the short-circuit resistance value of the electrolyte membrane, and the voltage upper limit calculation unit obtains the upper limit of the output voltage capable of suppressing damage to the electrolyte membrane, and then meets the external load request. The output voltage of the fuel cell based can be limited to the upper limit. In this way, when the open circuit voltage reduction factor is a reduction in membrane short-circuit resistance, the output voltage of the fuel cell based on the external load requirement is limited to an upper limit capable of suppressing damage to the electrolyte membrane, thereby It is possible to operate the fuel cell while suppressing damage to the membrane.

  (10) In the fuel cell system of the above aspect, when the factor is specified as the membrane short-circuit resistance reduction by the voltage reduction factor specifying unit, the electrolyte membrane obtained by the short-circuit resistance value calculating unit for each battery cell For the small short-circuit resistance value battery cell whose short-circuit resistance value is smaller than a predetermined threshold short-circuit resistance value, notification of cell replacement can be performed. In this way, when the cause of the decrease in the open circuit voltage is a decrease in the short circuit resistance of the membrane, it is possible to notify the small short circuit resistance battery cell that has caused the decrease in the open circuit voltage, for example, to notify the repair or replacement of the cell. Recovery of the open circuit voltage can be expected by repairing or replacing the device.

  The present invention can be realized, for example, in the form of a fuel cell operation method, a fuel cell operation abnormality determination device, a determination method, and the like in addition to the fuel cell system.

FIG. 2 is an explanatory diagram showing a block diagram showing a configuration example of a fuel cell system 20 as a first embodiment of the present invention together with a schematic enlarged view of a fuel cell 120. 4 is a flowchart showing power generation operation control of the fuel cell 100 that is repeated when the vehicle on which the fuel cell system 20 is mounted travels. 3 is a flowchart showing cell property determination control that is performed when a vehicle on which the fuel cell system 20 is mounted is started or when operation is stopped. It is explanatory drawing which shows the relationship between the open circuit voltage Vocv and the membrane resistance value R for every factor which brings about the fall of the open circuit voltage Vocv. It is explanatory drawing which shows the relationship between the open circuit voltage Vocv and the membrane resistance value R at the time of the fall degree of the short circuit resistance of the electrolyte membrane 121 differing. It is explanatory drawing of the 1st map which shows the relationship between the factor analysis parameter (dVocv / dR film | membrane) which is the inclination of the locus | trajectory for every short circuit resistance of FIG. 5, and a short circuit resistance value. It is explanatory drawing of the 2nd map which shows the relationship between the absolute value of a cell voltage, and a short circuit resistance value.

  FIG. 1 is an explanatory diagram showing a block diagram showing a configuration example of a fuel cell system 20 as a first embodiment of the present invention together with a schematic enlarged view of a fuel cell 120. This fuel cell system 20 shows a fuel cell system mounted on a vehicle as an example.

  The fuel cell system 20 includes a fuel cell 100, an anode gas (fuel gas) supply unit 200 and a cathode gas (oxidizing gas) supply unit 300, a cooling device 400, a cell characteristic measurement unit 500, a power control unit 600, And a control unit 700.

  The fuel cell 100 is formed by an electrochemical reaction between a fuel gas (hydrogen) as an anode gas supplied to an anode and an oxidizing gas (air, strictly speaking, oxygen contained in air) as a cathode gas supplied to a cathode. Generate power.

  The fuel cell 100 has a stack structure in which fuel cells 120 using a solid polymer electrolyte membrane having proton conductivity are stacked. As shown in the schematic enlarged view, the fuel battery cell 120 includes both electrode catalyst layers of an anode 122 and a cathode 123 which are catalyst electrodes on both sides of the electrolyte membrane 121. The anode 122 and the cathode 123 are formed on both membrane surfaces of the electrolyte membrane 121 and form a membrane electrode assembly (MEA) together with the electrolyte membrane 121. In addition, the fuel cell 120 includes an anode-side gas diffusion layer 124, a cathode-side gas diffusion layer 125, and gas separators 126 and 127 that sandwich the electrode-formed electrolyte membrane 121 from both sides. It is joined to the electrode.

  The electrolyte membrane 121 is a proton-conductive ion exchange membrane formed of a solid polymer material, for example, a fluorine-based resin, and exhibits good electrical conductivity in a wet state. The anode 122 and the cathode 123 include a catalyst (for example, platinum or a platinum alloy), and are formed by supporting these catalysts on a conductive carrier (for example, carbon particles). The anode-side gas diffusion layer 124 and the cathode-side gas diffusion layer 125 are manufactured using a conductive member having gas diffusibility, such as carbon paper or carbon cloth, and form a gas diffusion channel to each electrode.

  The gas separator 126 includes an in-cell fuel gas flow path (not shown) for flowing a fuel gas containing hydrogen on the anode gas diffusion layer 124 side. The gas separator 127 is provided with an in-cell oxidizing gas channel (not shown) through which an oxidizing gas containing oxygen (air in this embodiment) flows, on the cathode side gas diffusion layer 125 side. Although not shown in the figure, an inter-cell refrigerant flow path through which a refrigerant flows can be formed between adjacent fuel cells 120, for example. The gas separators 126 and 127 are made of a gas-impermeable conductive member, for example, a dense carbon made by compressing carbon and impermeable to gas, baked carbon, or a metal material such as stainless steel.

  A plurality of holes are formed at predetermined positions near the outer peripheries of the gas separators 126 and 127. The plurality of holes overlap each other when the fuel cell 120 is laminated together with other members and the fuel cell 100 is assembled to form a flow path that penetrates the fuel cell 100 in the lamination direction. That is, a manifold for supplying and discharging fuel gas, oxidizing gas, or refrigerant is formed with respect to the in-cell fuel gas channel, the in-cell oxidizing gas channel, or the inter-cell refrigerant channel.

  The fuel cell 100 of this embodiment supplies hydrogen gas from the in-cell fuel gas flow path of the gas separator 126 to the anode 122 while diffusing in the anode gas diffusion layer 124. As for air, the air from the in-cell oxidizing gas flow path of the gas separator 127 is supplied to the cathode 123 while being diffused by the cathode side gas diffusion layer 125.

  The anode gas supply unit 200 includes a hydrogen gas tank 210 that stores high-pressure hydrogen gas as an anode gas (fuel gas), an anode gas supply channel 220 for supplying the hydrogen gas in the hydrogen gas tank 210 to the fuel cell 100, And an anode gas circulation passage 230 for returning hydrogen offgas as anode offgas (fuel offgas) discharged from the fuel cell 100 to the anode gas supply passage 220. The anode gas supply channel 220 includes an open / close valve 222 that blocks or allows the supply of hydrogen gas from the hydrogen gas tank 210, a regulator 224 that adjusts the pressure of the hydrogen gas, and a hydrogen supply unit 226 that adjusts the flow rate of the hydrogen gas. The hydrogen gas is guided to the in-cell fuel gas flow path of the fuel battery cell 120. The anode gas supply unit 200 includes a pressure sensor 227 for detecting a supply gas pressure in the anode gas supply flow path 220 and a pressure sensor 239 for detecting an exhaust gas pressure in the anode gas circulation flow path 230, respectively. The pressure (supply gas pressure and exhaust gas pressure) is output to the control unit 700 described later.

  The anode gas circulation channel 230 is provided with a hydrogen gas pump 232 that sends out hydrogen off-gas as the anode off-gas in the anode gas circulation channel 230 to the anode gas supply channel 220 side. Further, a discharge flow path 238 connected to the exhaust port 350 is connected to the anode gas circulation flow path 230 via a gas-liquid separation unit 234 and an exhaust drainage valve 236. The gas-liquid separator 234 collects moisture contained in the hydrogen off gas. The exhaust / drain valve 236 discharges the hydrogen off-gas containing moisture collected by the gas-liquid separator 234 and impurities in the anode gas circulation channel 230. The hydrogen off-gas discharged from the exhaust / drain valve 236 is exhausted from the exhaust port 350 to the atmosphere as exhaust gas. The open / close valve 222, the regulator 224, the hydrogen supply unit 226, the hydrogen gas pump 232, the gas-liquid separation unit 234, and the exhaust / drain valve 236 operate according to instructions from the control unit 700.

  The cathode gas supply unit 300 takes in air as cathode gas (oxidizing gas) through the intake port 310 and compresses and sends the air, and cathode gas supply for supplying air (air) to the fuel cell 100. A flow path 330 and a cathode off gas discharge flow path 340 for discharging the cathode off gas (oxidation off gas) discharged from the fuel cell 100 from the exhaust port 350 are provided. The cathode off gas discharge channel 340 is provided with a back pressure adjustment valve 342 for adjusting the pressure of the cathode gas (oxidizing gas) in the fuel cell 100. In the cathode gas supply channel 330 and the cathode offgas discharge channel 340, a humidification unit 360 that humidifies the cathode gas (oxidation gas) pumped from the compressor 320 using the cathode offgas (oxidation offgas) discharged from the fuel cell 100. Is provided. The cathode gas supply channel 330 guides air to the in-cell oxidizing gas channel of the fuel cell 120 through the humidification unit 360. The cathode off-gas that has passed through the humidifying unit 360 is exhausted from the exhaust port 350 to the atmosphere as exhaust gas. The compressor 320, the back pressure adjustment valve 342, and the humidification unit 360 operate according to instructions from the control unit 700. The cathode gas supply unit 300 includes a pressure sensor 332 for detecting a supply gas pressure in the cathode gas supply channel 300 and a pressure sensor 344 for detecting an exhaust gas pressure in the cathode off-gas discharge channel 340. The pressure (supply gas pressure and exhaust gas pressure) is output to the control unit 700 described later.

  The cooling device 400 includes a cooling circulator 410, a refrigerant supply passage 420 that supplies a refrigerant to the fuel cell 100, and a refrigerant discharge passage 430 that returns the refrigerant discharged from the fuel cell to the fuel cell 100. The cooling circulator 410 supplies the refrigerant to the fuel cell 100 via the refrigerant supply flow path 420 and receives the refrigerant after being supplied for cooling of the fuel cell 100 via the refrigerant discharge flow path 430, thereby Circulation is performed to cool the fuel cell 100. As the refrigerant, water, antifreeze, or the like can be used. The cooling device 400 cools the fuel cell 100 by operating the cooling circulator 410 in accordance with an instruction from the control unit 700 to achieve refrigerant circulation.

  The cell characteristic measuring unit 500 includes a cell characteristic measuring instrument 510 that measures the cell characteristics described later of the fuel cell 120, a voltage sensor 520 that measures the output voltage of the fuel cell 100, and a current sensor 530 that measures the output current. I have.

  The cell characteristic measuring instrument 510 measures cell characteristics for each fuel cell, and includes a voltage measuring unit 512 and a resistance measuring unit 514. The voltage measuring unit 512 measures the open circuit voltage (Vovv), which is an output voltage in a no-load state where no current flows to an external load, for each fuel cell 120. The resistance measurement unit 514 measures the hydrogen ion (proton) movement resistance and DC resistance at the cathode-side catalyst electrode of each fuel cell 120 as membrane resistance (R membrane) using the AC impedance method. These measured values are cell characteristics reflecting the properties of the electrolyte membrane 121 of each fuel cell, and the cell characteristic measuring instrument 510 outputs the measurement results to the control unit 700 described later. Note that the above open circuit voltage and membrane resistance measurement by the cell characteristic measuring instrument 510 can be performed for each of the fuel cells 120, and several fuel cells included in a plurality of battery cell groups located in the center of the stack. It is also possible to measure the cell 120 and some fuel cells 120 included in a plurality of battery cell groups located at both ends of the stack, and apply the measurement results to the fuel cells 120 included in each battery cell group. .

  The power control unit 600 includes a secondary battery control unit 620, a motor control unit 640, various auxiliary machine control units (not shown), and the like. The secondary battery control unit 620 controls charging / discharging of the secondary battery 610. The motor control unit 640 controls the supply of electric power from the fuel cell 100 or the secondary battery 610 to the motor 630. For example, when the motor 630 is a three-phase AC motor, the motor control unit 640 includes a three-phase inverter that converts direct current into three-phase alternating current. The accessory control unit controls the supply of electric power for driving the devices such as the hydrogen gas pump 232 and the compressor 320, for example. The motor 630 constitutes a main power source of a vehicle on which the fuel cell system 20 is mounted.

  The control unit 700 is configured as a computer system mainly including a CPU 710, a memory 720, and an input / output unit 730. The input / output unit 730 connects various actuators, various sensors, various switches, and the like via control signal lines (not shown). Various actuators include the above-described opening / closing valve 222, regulator 224, hydrogen supply unit 226, hydrogen gas pump 232, compressor 320, back pressure adjustment valve 342, cooling pump and cooling fan (not shown) included in the cooling circulator 410, and motor 630. There is an accelerator 750 for controlling the amount of rotation. Examples of the various sensors include the voltage sensor 520, the pressure sensor such as the current sensor 530 and the pressure sensor 227, a temperature sensor (not shown), a pressure sensor, a humidity sensor, and a flow rate sensor. Examples of the various switches include a start switch 740 that starts an electric vehicle on which the fuel cell system 20 is mounted.

  The memory 720 stores various computer programs (not shown) mainly for controlling the fuel cell system 20, and the CPU 710 operates as each functional block by executing these computer programs. For example, the CPU 710 functions as a battery output control unit 710a and a cell property determination unit 710b by executing a computer program of a power generation operation control routine and a cell property determination routine of the fuel cell 100. The battery output control unit 710a controls the operation of the fuel cell 100 and the secondary battery 610. The cell property determination unit 710b manages the current cell characteristics measured by the cell property measuring instrument 510 with the stored contents of the memory 720, and controls the later-described device control based on the specified cell properties and the specified properties. The stored contents of the memory 720 include various maps and characteristic diagrams described later.

  Next, various controls performed by the control unit 700 of the fuel cell system 20 of the present embodiment will be described. FIG. 2 is a flowchart showing power generation operation control of the fuel cell 100 repeated when the vehicle on which the fuel cell system 20 is mounted, and FIG. 3 is a cell property determination control performed when the vehicle on which the fuel cell system 20 is mounted is started or stopped. It is a flowchart which shows.

  In the power generation operation control of FIG. 2, first, the control unit 700 reads the required load based on the amount of depression of the accelerator 750 (step S100), and outputs the fuel cells 120 corresponding to the read required load ( Cell voltage Sv) is calculated (step S110). In the fuel cell system 20 of the present embodiment, the drive rotation of the motor 630 is covered by the battery output and the output of the secondary battery 610, so the control unit 700 determines the amount of stored power and the amount of discharged power of the secondary battery 610. In consideration, the cell voltage Sv of each fuel cell 120 is calculated in step S110. In this case, a so-called current / voltage characteristic diagram (IV diagram) that determines the output characteristics of the fuel cell 120 is used, but the description thereof is omitted because it is not directly related to the gist of the present invention. .

  Following the calculation of the cell voltage Sv, the control unit 700 determines whether or not the output of the fuel cell 120 is limited by a cell property determination control (FIG. 3) described later (step S120). Here, if a negative determination is made that there is no output limitation, the control unit 700 supplies the fuel gas and the oxidizing gas so as to obtain the cell voltage Sv calculated in step S110 and sets each fuel cell 120 of the fuel cell 100. The power generation operation is controlled (step S130).

  On the other hand, if an affirmative determination is made in step S120 that there is an output restriction, control unit 700 restricts cell voltage Sv calculated in step S110 to output restriction voltage Vmax, and each fuel cell of fuel cell 100 120 is subjected to power generation operation control (step S140). Specifically, if the cell voltage Sv is within the limit range of the output limit voltage Vmax, the fuel cell and the oxidizing gas are supplied so that the cell voltage Sv is obtained, and each fuel cell 120 of the fuel cell 100 is set. Control power generation operation. However, if the cell voltage Sv exceeds the output limit voltage Vmax, the cell voltage Sv is limited to the output limit voltage Vmax, and the fuel gas and the oxidizing gas are supplied so as to obtain the output limit voltage Vmax. The power generation operation of each of the 100 fuel cells 120 is controlled.

  The cell property determination control of FIG. 3 that imposes such output restriction is performed at the time of start when the start switch 740 (see FIG. 1) is turned on, when the operation is stopped when the start switch 740 is turned off, or when the fuel cell system 20 is mounted. It is executed when the vehicle is stopped in the P range or in an idling state. In the cell property determination control of FIG. 3, first, the control unit 700 supplies the fuel gas and the oxidizing gas (step S <b> 200), and performs the power generation operation of each fuel cell 120 of the fuel cell 100. The gas supply amount at this time is approximately the same as the rated output (voltage) obtained when the fuel cell 120 is operated for power generation in a no-load state, or the supply amount at which 80 to 90% of the output is obtained. Is done.

  Next, the control unit 700 reads the outputs of the voltage measuring unit 512 and the resistance measuring unit 514 of the cell characteristic measuring instrument 510, and calculates the open circuit voltage Vocv and the membrane resistance value R for each fuel cell 120 (step) In step S210, the open circuit voltage Vocv obtained by the calculation is compared with the threshold voltage Vth (step S220). This threshold voltage Vth was obtained by subjecting the lower limit side voltage of the output range that is normally obtained when the fuel cell 120 is operated for power generation by supplying gas in step S200, for example, by subjecting the output voltage to statistical processing. It is defined as the voltage near the lower end of the histogram. In other words, since the output obtained when the power supply operation of the fuel cell 120 is performed by supplying the gas in step S200, the output is obviously low, so that there is an abnormality that has caused such a decrease in output. A threshold voltage Vth is defined as a voltage that can be assumed.

  If the controller 700 makes a positive determination in step S220 that the open circuit voltage Vocv exceeds the threshold voltage Vth, there is no abnormality in the power generation operation of the fuel cell 120, that is, a factor that causes a decrease in the open circuit voltage Vocv occurs. If not, this routine is terminated. On the other hand, if a negative determination is made in step S220, it is assumed that the open circuit voltage Vocv has decreased due to some factor, and a dry purge of gas is performed as a specific pretreatment of the factor (step S230). Due to the dry purge, the fuel cell 120 is controlled to operate so that the drying of the electrolyte membrane 121 proceeds, and moisture is removed from the electrolyte membrane 121 and the drying proceeds. In this case, in the dry purge, the gas itself can be dried and supplied without being humidified by the humidifying unit 360, and the discharge of generated water by the gas can be promoted by increasing the gas flow rate to dry the electrolyte membrane 121. Alternatively, the electrolyte membrane 121 may be dried while cooling by the cooling circulator 410 is refrained.

  The controller 700 repeatedly calculates the open circuit voltage Vocv and the membrane resistance value R in the same manner as in step S210 while the dry purge is performed in step S230. Then, the controller 700 divides the change amount (dVocv) of the open circuit voltage Vocv by the change amount (dR film) of the membrane resistance value R (dVovv / dR film), that is, the change amount of the membrane resistance value R ( The change amount (dVocv) of the open circuit voltage Vocv with respect to the (dR film) is calculated, and the calculated value is set as the factor analysis parameter (dVocv / dR film), and the factor is specified by this factor analysis parameter as follows. Proceed. In this case, since the open circuit voltage Vocv and the membrane resistance value R are calculated for each fuel cell 120 (step S210), the factor analysis parameter (dVovv / dR membrane) is calculated for each fuel cell 120. Is done.

  The drying purge in step S230 is executed when the open circuit voltage Vocv is lowered to a voltage equal to or lower than the threshold voltage Vth due to some factor in step S220, and the electrolyte membrane 121 is dried by drying the electrolyte membrane 121. The membrane resistance value R increases regardless of the above factors. Regarding the open circuit voltage Vocv while causing such an increase in the membrane resistance value R, the factors that caused the decrease in the open circuit voltage Vocv, specifically, excessive moisture in the electrolyte membrane 121, the occurrence of cross leak in the electrolyte membrane 121, or The transition state of the open circuit voltage Vocv during the dry purge is different for each factor of the short circuit resistance reduction of the electrolyte membrane 121. That is, if the decrease in the open circuit voltage Vocv occurs due to excess moisture in the electrolyte membrane 121, the excess moisture tends to be eliminated by drying the electrolyte membrane 121 by the dry purge, and the anode 122, cathode 123, and anode side gas The clogging of the pores of the diffusion layer 124 and the cathode side gas diffusion layer 125 due to moisture is also resolved. As a result, the diffusion of the gas to the electrolyte membrane 121 progresses and the shortage of gas supply is also resolved, so that the open circuit voltage Vocv changes so as to recover from the reduced voltage.

  If the decrease in the open circuit voltage Vocv occurs due to the occurrence of the cross leak of the electrolyte membrane 121, the amount of hydrogen gas cross leak increases due to the drying of the electrolyte membrane 121 due to the dry purge, resulting in an electrochemical reaction. Since the amount of gas not involved increases, recovery of the open circuit voltage Vocv cannot be expected, and a further decrease in the open circuit voltage Vocv is expected. If the decrease in the short-circuit resistance of the electrolyte membrane 121 is a factor, leakage of the open circuit voltage corresponding to the decreased short-circuit resistance may occur, so that the recovery of the open circuit voltage Vocv cannot be expected, and the open circuit voltage Vocv further decreases. Transition is expected. On the other hand, the decrease transition state of the open circuit voltage Vocv due to the occurrence of the cross leak and the decrease transition state of the open circuit voltage Vocv due to the short circuit resistance decrease do not coincide with each other and are clearly different.

  In the present embodiment, paying attention to the transition of the open circuit voltage Vocv for each of the factors under the situation where the increase in the membrane resistance value R accompanying the drying of the electrolyte membrane 121 occurs, the amount of change in the membrane resistance value R (dR) A factor analysis parameter (dVocv / dR film), which is a calculated value of the change amount (dVocv) of the open circuit voltage Vocv with respect to the film), was introduced. Then, in order to perform the factor analysis with this factor analysis parameter (dVocv / dR membrane), an excessive amount of water in the electrolyte membrane 121 causing the decrease in the open circuit voltage Vocv, the occurrence of cross leak in the electrolyte membrane 121, by an experimental method, Alternatively, for each factor of the short-circuit resistance reduction of the electrolyte membrane 121, the transition of the open circuit voltage Vocv is examined in association with the membrane resistance value R accompanying the drying of the electrolyte membrane 121, and the control unit 700 performs factor analysis parameters that correspond to this correspondence relationship. By grasping (dVocv / dR film), the factor is specified by the parameter as described later. Note that the factor analysis parameter (dVocv / dR film) may be stored in the memory 720 in association with each factor that causes the open circuit voltage Vocv to decrease. In this case, the decrease in the open circuit voltage Vocv does not always occur for each of the above-mentioned factors, but also occurs due to the simultaneous occurrence of a plurality of factors. In this case, the voltage transition for each factor should be taken into consideration. Thus, it is possible to analyze a plurality of factors. FIG. 4 is an explanatory diagram showing the relationship between the open circuit voltage Vocv and the membrane resistance value R for each factor that causes a decrease in the open circuit voltage Vocv.

  The locus fa in FIG. 4 shows the transition of the open circuit voltage Vocv when the decrease in the open circuit voltage Vocv occurs due to excessive moisture in the electrolyte membrane 121, with the membrane resistance value R as the horizontal axis. Then, according to the locus fa, the factor analysis parameter (dVocv / dR film) obtained by calculating the change amount (dVocv) of the open circuit voltage Vocv with respect to the change amount (dR film) of the film resistance value R has the sign Positive and almost constant value. In the dry purge in step S230 performed after the open circuit voltage Vocv is lowered to a voltage equal to or lower than the threshold voltage Vth due to excessive moisture in the electrolyte membrane 121, the excess moisture tends to be eliminated by drying the electrolyte membrane 121. As described above, the open circuit voltage Vocv recovers and transitions as indicated by the locus fa by the dry purge in step S230.

  The trajectory of the trajectory fa can be obtained as follows. First, a fuel cell 120 having an electrolyte membrane 121 in which no cross leak or reduction in the short circuit resistance value of the membrane has occurred is prepared as a measurement cell. Then, the fuel cell 100 shown in FIG. 1 is replaced with the fuel cell 120 which is the measurement cell, and the gas supply / exhaust pressure is adjusted to the fuel cell 120 so that cross-leak does not occur with excessively humidified gas. Then, supply and generate electricity. If a decrease in the open circuit voltage Vocv is observed in this state, the decrease in the open circuit voltage Vocv is due to excessive moisture in the electrolyte membrane 121. Thereafter, a dry purge is performed, and the film resistance value R and the open circuit voltage Vocv during the dry purge are measured and plotted by the voltage measurement unit 512 and the resistance measurement unit 514. In this way, the locus fa of FIG. 4 is obtained. In this case, since the situation of excessive moisture in the electrolyte membrane 121 is not necessarily uniform, the state of recovery of the open circuit voltage Vocv by the dry purge may be different from the locus defined by the locus fa in FIG. The factor analysis parameter (dVocv / dR film) has a positive sign and a substantially constant value. In other words, the trajectory fa in FIG. 4 is a linear curve with a positive slope, although the slope is positive and the slope values are different.

  The locus fb in FIG. 4 shows the transition of the open circuit voltage Vocv when the decrease in the open circuit voltage Vocv occurs due to the decrease in the short circuit resistance of the electrolyte membrane 121, with the membrane resistance value R as the horizontal axis. According to the locus fb, the factor analysis parameter (dVocv / dR film) has a negative sign and a substantially constant value. In the dry purge of step S230 performed after the open circuit voltage Vocv is lowered to a voltage equal to or lower than the threshold voltage Vth due to the short circuit resistance decrease of the electrolyte membrane 121, the fuel cell 120 reduces the short circuit resistance of the electrolyte membrane 121. Since the corresponding open circuit voltage can leak, the recovery of the open circuit voltage Vocv cannot be expected, and a further decrease in the open circuit voltage Vocv is expected. For this reason, the open circuit voltage Vocv when the decrease in the open circuit voltage Vocv occurs due to the decrease in the short-circuit resistance of the electrolyte membrane 121 changes as shown by the locus fb by the dry purge in step S230.

  The trajectory fb can be obtained as follows. First, a fuel cell 120 having an electrolyte membrane 121 that is capable of a rated output (voltage) obtained when a power generation operation is performed in a no-load state and that does not cause cross leakage is prepared. Then, the electrolyte membrane 121 of the fuel cell 120 is repeatedly swollen and contracted to intentionally reduce the short-circuit resistance value of the electrolyte membrane 121. In this way, the fuel cell 120 having the electrolyte membrane 121 with the short-circuit resistance lowered is prepared as a measurement cell. Then, the fuel cell 100 shown in FIG. 1 is replaced with the fuel cell 120 which is the above-described measurement cell, and the gas supplied to the fuel cell 120 is properly wetted with a gas supply / discharge pressure so that cross leak does not occur. After adjustment, supply and generate electricity. If a decrease in the open circuit voltage Vocv is observed in this state, the decrease in the open circuit voltage Vocv is due to a decrease in the short-circuit resistance of the electrolyte membrane 121. Thereafter, a dry purge is performed, and the film resistance value R and the open circuit voltage Vocv during the dry purge are measured and plotted by the voltage measurement unit 512 and the resistance measurement unit 514. In this way, the locus fb of FIG. 4 is obtained. The trajectory fb shown in FIG. 4 shows a decrease in the open circuit voltage Vocv for the fuel cell 120 having the electrolyte membrane 121 whose short-circuit resistance has decreased to a certain resistance value, and the short-circuit resistance is different from the certain resistance value described above. When the resistance value is lowered, the above-described factor analysis parameter (dVocv / dR film) is different although it has a negative sign and a substantially constant value. FIG. 5 is an explanatory diagram showing the relationship between the open circuit voltage Vocv and the membrane resistance value R when the degree of decrease in the short-circuit resistance of the electrolyte membrane 121 is different.

  In FIG. 5, for the fuel cell 120 having the electrolyte membrane 121 adjusted to various short-circuit resistance values shown in the figure, as described above, the membrane resistance value R and the open circuit voltage Vocv during the dry purge are short-circuit resistance values. Each is plotted. As shown in FIG. 5, if the short-circuit resistance value is large, there is no voltage leakage or very little, so that the open circuit voltage Vocv is not reduced. However, as the short-circuit resistance value decreases, the open circuit voltage Vocv decreases greatly as the film resistance value R increases, and the inclination of each locus, that is, the factor analysis parameter (dVovv / dR film) described above increases. . In each short-circuit resistance value in which the open circuit voltage Vocv is decreased, the factor analysis parameter (dVovv / dR film) that is the inclination of the locus is different, but in both cases, the sign is negative and almost constant. Become. In other words, the trajectory fb in FIG. 4 is a linear curve with a negative slope, although the slope is negative and the slope values are different.

  The locus fc in FIG. 4 shows the transition of the open circuit voltage Vocv when the decrease in the open circuit voltage Vocv occurs due to the occurrence of cross leak in the electrolyte membrane 121, with the membrane resistance value R as the horizontal axis. According to this trajectory fc, the above-described factor analysis parameter (dVocv / dR film) has a negative sign, and the value gradually decreases after the film resistance value R slightly decreases and then gradually decreases. Decreases and does not reach a constant value. In the dry purge of step S230 performed after the open circuit voltage Vocv is lowered to a voltage equal to or lower than the threshold voltage Vth due to the occurrence of cross leak in the electrolyte membrane 121, in the fuel cell 120, the electrolyte membrane 121 is dried by the dry purge. The amount of cross leak of hydrogen gas increases, and the amount of leak is expected to increase greatly at the beginning of drying when the film turns into a dry state, and to increase thereafter. Since the amount of gas not involved in the electrochemical reaction increases corresponding to the increase in the amount of cross leak, the recovery of the open circuit voltage Vocv cannot be expected, and a further decrease in the open circuit voltage Vocv is expected. . Therefore, the open circuit voltage Vocv when the decrease in the open circuit voltage Vocv occurs due to the occurrence of cross leak in the electrolyte membrane 121 decreases as shown by the locus fc by the dry purge in step S230.

  The locus of the locus fc can be obtained as follows. First, a fuel cell 120 having an electrolyte membrane 121 that is capable of a rated output (voltage) obtained when a power generation operation is performed in a no-load state and that does not have a short circuit resistance is prepared as a measurement cell. Then, the fuel cell 100 shown in FIG. 1 is replaced with the fuel cell 120 which is the measurement cell described above, and the gas supply / discharge pressure is set to the fuel cell 120 so that the gas is properly wetted so that cross leak occurs. After intentionally adjusting it to a higher level, supply it to generate electricity. If a decrease in the open circuit voltage Vocv is observed in this state, the decrease in the open circuit voltage Vocv is due to the occurrence of cross leak in the electrolyte membrane 121. Thereafter, a dry purge is performed, and the film resistance value R and the open circuit voltage Vocv during the dry purge are measured and plotted by the voltage measurement unit 512 and the resistance measurement unit 514. In this way, the locus fc of FIG. 4 is obtained. In this case, since the appearance of the cross leak and the amount of cross leak of the electrolyte membrane 121 are not necessarily uniform, the state of the decrease in the open circuit voltage Vocv due to the dry purge is different from the locus defined by the locus fc in FIG. However, the factor analysis parameter (dVocv / dR film) described above has a negative sign and does not have a constant value.

  In the present embodiment, the above-described factor analysis parameter (dVocv / dR film) for each factor is subjected to the comparison in step S240 subsequent to step S230 in FIG. 3 and the comparison in step S280 thereafter, so that the open circuit voltage Vocv. The factor that caused the decrease is specified as one of excessive moisture in the electrolyte membrane 121, the occurrence of cross leak in the electrolyte membrane 121, or a decrease in short circuit resistance of the electrolyte membrane 121. First, in step S240 following step S230, the control unit 700 determines whether or not the factor analysis parameter (dVocv / dR film) is a positive value. If an affirmative determination is made here, the factor analysis parameter (dVocv / dR film) matches the locus fa in FIG. 4, the control unit 700 determines that the cause of the decrease in the open circuit voltage Vocv is that of the electrolyte membrane 121. It is specified that there is excessive water (step S250), and processing from step S260 onward is performed to eliminate this excessive water. That is, the controller 700 continues the dry purge similar to step S230, and continues this dry purge until the open circuit voltage Vocv is recovered to exceed the threshold voltage Vth in the subsequent step S270. Then, when the open circuit voltage Vocv is recovered until it exceeds the threshold voltage Vth, this routine is finished.

  On the other hand, if it is determined in step S240 that follows step S230 that the factor analysis parameter (dVocv / dR film) is not a positive value, the controller 700 determines in step S280 that the factor analysis parameter (dVocv / dR). It is determined whether or not the film is a constant value. If a negative determination is made here, the factor analysis parameter (dVocv / dR film) matches the locus fc in FIG. 4, the control unit 700 determines that the cause of the decrease in the open circuit voltage Vocv is that of the electrolyte membrane 121. The cross leak expression is specified (step S290), and the subsequent process deals with the cross leak expression. In dealing with this, the control unit 700 calculates a cross leak amount (step S300). That is, the control unit 700 includes the pressure sensor 227 and the pressure sensor 239 for the gas supply / discharge system in the anode gas supply unit 200 and the pressure sensor 332 and the pressure sensor 344 for the gas supply / discharge system in the cathode gas supply unit 300 in FIG. , And the cross leak amount is calculated based on the pressure difference between the supply and discharge of the fuel gas and the oxidizing gas. In this case, since the factor analysis parameter (dVocv / dR film) is calculated for each of the fuel cells 120 as described above, the cross leak amount calculated in step S300 crosses the decrease in the open circuit voltage Vocv. This is for the fuel battery cell 120 brought about by the leak.

  When the cross leak amount is calculated in this way, the control unit 700 informs the cell replacement of the fuel cell 120 whose open circuit voltage Vocv has decreased (step S320), and ends this routine. The cell replacement notification in step S320 can be performed in various ways, such as lighting notification with a lamp in the passenger compartment of the vehicle on which the fuel cell system 20 is mounted, or sounding the cell replacement from an audio device attached to the vehicle. it can. In addition to these, a signal indicating cell exchange and cell identification information to be exchanged can be transmitted to the vehicle maintenance destination together with vehicle identification information such as a chassis number. At this time, the position of the fuel cell 120 or the number of the fuel cell 120 from the end plate of the fuel cell 100 is also notified. The vehicle operator who has received the cell replacement notification takes the vehicle to a maintenance destination to perform cell replacement and travels, but the travel distance is expected to be relatively short. Therefore, the control unit 700 can be configured not to particularly limit the output of the fuel cell 100 during this carry-in traveling. Note that a map in which the travelable distance after the cell replacement notification in step S320 is targeted as the cross leak amount is stored in the memory 720 in advance, and the control unit 700 determines the travel possible distance according to the calculated cross leak amount, Notification that the travel distance is limited may be performed together with the cell replacement notification. By doing so, it is possible to prompt the vehicle operator to perform maintenance for cell replacement.

  Then, in step S280 following the negative determination in step S240, if an affirmative determination is made that the factor analysis parameter (dVocv / dR film) is a constant value, the factor analysis parameter (dVovv / dR film) is represented by the locus fb in FIG. Therefore, the control unit 700 specifies that the cause of the decrease in the open circuit voltage Vocv is a decrease in the short-circuit resistance of the electrolyte membrane 121 (step S330). deal with. In dealing with this, the control unit 700 refers to the first map and calculates a short circuit resistance reduction value (step S340). FIG. 6 is an explanatory diagram of a first map showing the relationship between the factor analysis parameter (dVocv / dR film) which is the inclination of the locus for each short-circuit resistance in FIG. 5 and the short-circuit resistance value. In FIG. 6, the factor analysis parameter (dVocv / dR film) is set on the horizontal axis, and the short-circuit resistance value corresponding to the parameter is determined. Since the control unit 700 stores in advance in the memory 720 the first map corresponding to FIG. 6, that is, the map in which the factor analysis parameter (dVocv / dR film) is associated with the short-circuit resistance value, it is obtained in step S210. The short circuit resistance value is calculated by comparing the factor analysis parameter (dVocv / dR film) calculated from the open circuit voltage Vocv and the film resistance value R with the first map of FIG. In this case, since the factor analysis parameter (dVocv / dR membrane) is calculated for each of the fuel cells 120 as described above, the short-circuit resistance value calculated in step S340 short-circuits the decrease in the open circuit voltage Vocv. This is for the fuel cell 120 brought about by the decrease in resistance.

  When the short circuit resistance value is calculated in this way, the control unit 700 compares the calculated short circuit resistance value (R short circuit) with the threshold short circuit resistance Rth (step S350). The threshold short-circuit resistance th is defined as a short-circuit resistance value that serves as a guide for cell replacement in terms of power generation efficiency and capacity maintenance. If the controller 700 makes an affirmative determination in step S350 that the calculated short-circuit resistance value (R short-circuit) is smaller than the threshold short-circuit resistance Rth, the control unit 700 proceeds to step S320 described above to promote cell replacement, and ends this routine.

  On the other hand, if it is determined in step S350 that the calculated short circuit resistance value (R short circuit) has not decreased to the threshold short circuit resistance Rth, the control unit 700 sets the output voltage limit value for the fuel cell 120 to the second value. This is determined with reference to the map (step S360). FIG. 7 is an explanatory diagram of a second map showing the relationship between the absolute value of the cell voltage and the short-circuit resistance value. FIG. 7 is a map in which the horizontal axis represents the short-circuit resistance value of the electrolyte membrane 121 and the vertical axis represents the output voltage value (absolute value) of the fuel cell 120, and the output voltage of the fuel cell 120 relative to the short-circuit resistance value ( The upper limit of (absolute value) is determined by the boundary locus fvm in the figure. The short circuit resistance reduction of the electrolyte membrane 121 does not occur in the entire area of the electrolyte membrane 121, but the short circuit resistance decreases at a local site where swelling and contraction are repeated. Thus, when a current corresponding to the cell output voltage flows through a local part where the short circuit resistance is reduced, Joule heat is generated in the local part based on the resistance (short circuit resistance) and current, and the heat is transferred to the electrolyte. It is possible that the decomposition temperature of the membrane 121 is exceeded. As a result, pinholes are generated at the local site, and the electrolyte membrane 121 is irreparably damaged. Due to Joule's law, the Joule heat generated at a local site increases in heat even at low voltages if the resistance (short-circuit resistance) is small. For these reasons, it is desirable to limit the output voltage of the fuel cell 120 having the electrolyte membrane 121 with a reduced short-circuit resistance in order to avoid pinholes. The boundary locus fvm in FIG. 7 is a diagram in which the upper limit of the output voltage (absolute value) of the fuel cell 120 with respect to the short-circuit resistance of the electrolyte membrane 121 is determined from avoiding pinholes, and is stored in the memory 720 in advance. . Then, the control unit 700 collates the short-circuit resistance decrease value calculated in step S340 with the boundary locus fvm in the second map of FIG. 7, thereby obtaining the upper limit value Vmax (absolute value) of the output voltage for the fuel cell 120. And finishes this routine. The control unit 700 uses the upper limit value Vmax determined in this way as the limiting voltage of the cell voltage Sv of the fuel cell 120 in step S140 in FIG. 2 and limits the cell voltage Sv of the fuel cell 120. As a result, not only the fuel cell 120 whose short circuit resistance has been lowered, but also the cell voltages Sv of all the fuel cells 120 are limited by the upper limit value Vmax.

  As described above, in the fuel cell system 20 of the first embodiment, the cause of the decrease in the open circuit voltage Vocv is excessive moisture in the electrolyte membrane 121, occurrence of cross leak in the electrolyte membrane 121, or short circuit of the electrolyte membrane 121. Assuming that the resistance is reduced, the transition of the open circuit voltage Vocv is grasped in association with the membrane resistance value R of the electrolyte membrane 121 for each factor (FIG. 4). When the open circuit voltage Vocv of each fuel battery cell 120 constituting the fuel cell 100 falls below a predetermined threshold voltage Vth (step S220), a dry purge is performed (step S230), and the factors during this dry purge The analysis parameter (dVocv / dR film) identifies the cause of the decrease in the open circuit voltage Vocv as one of excessive moisture in the electrolyte film 121, cross leak in the electrolyte film 121, or a decrease in the short circuit resistance of the electrolyte film 121. (Step S240, Step S280). For this reason, excess moisture is eliminated, cell replacement notification is performed for each of the excess moisture in the electrolyte membrane 121, the occurrence of cross leakage in the electrolyte membrane 121, or the short-circuit resistance reduction in the electrolyte membrane 121 specified as the factors causing the decrease in the open circuit voltage Vocv. It is possible to deal with output restrictions.

  Further, in the fuel cell system 20 of the present embodiment, when it is specified that the cause of the decrease in the open circuit voltage Vocv is excessive moisture in the electrolyte membrane 121 (step S250), the open circuit voltage Vocv returns to the threshold voltage Vth. Until the drying of the electrolyte membrane 121 proceeds, operation control is continued (steps S260 to 270). For this reason, since the open circuit voltage Vocv decreased due to excessive water content in the electrolyte membrane 121 can be recovered, the fuel cell 120 and, moreover, the fuel cell 100 composed of the plurality of the fuel cells can be controlled, so that the power generation performance can be maintained. And recovery.

  Further, when the fuel cell system 20 according to the present embodiment specifies that the cause of the decrease in the open circuit voltage Vocv is the occurrence of cross leak in the electrolyte membrane 121 (step S290), the supply / discharge pressure of the fuel gas or the oxidizing gas is increased. Based on this, the amount of cross leak is calculated for each cell of the fuel cell 120 (step S300). In addition, if the calculated cross leak amount has increased to such an extent that cell replacement is desired, notification is made to prompt cell replacement (step S320). For this reason, recovery of the open circuit voltage Vocv by cell replacement and maintenance or recovery of the power generation capability of the fuel cell 100 as a stack of the fuel cells 120 can be achieved.

  Further, when the fuel cell system 20 of the present embodiment specifies that the cause of the decrease in the open circuit voltage Vocv is the short circuit resistance decrease of the electrolyte membrane 121 (step S330), the amount of change in the membrane resistance value R (dR membrane) ) With reference to the first map (FIG. 6) showing the relationship between the factor analysis parameter (dVovv / dR film) that is the calculated value of the change amount (dVoccv) of the open circuit voltage Vocv and the short-circuit resistance value. Is determined (step S340). In addition, in order to avoid the occurrence of pinholes due to Joule heat generated due to the short-circuit resistance value of the electrolyte membrane 121 and the cell output voltage, the upper limit of the cell voltage Sv of the fuel cell 120 is set to an electrolyte. The upper limit of the output voltage (absolute value) of the fuel cell 120 with respect to the short-circuit resistance of the membrane 121 is obtained with reference to a second map (FIG. 7) determined from avoiding pinholes, and each fuel cell of the fuel cell 100 is obtained. The cell voltage Sv of 120 is limited (FIG. 2: step S140). For this reason, when the cause of the decrease in the open circuit voltage Vocv is a decrease in the short-circuit resistance of the electrolyte membrane 121, the output voltage of the fuel cell 100 based on an external load requirement can be reduced to prevent damage to the electrolyte membrane 121. By limiting to the upper limit, it is possible to control the operation of the fuel cell 100 while suppressing damage to the electrolyte membrane 121.

  Further, the fuel cell system 20 of the present embodiment is obtained with reference to the first map (FIG. 6) when it is specified that the factor causing the decrease in the open circuit voltage Vocv is a decrease in the short circuit resistance of the electrolyte membrane 121. If the short-circuit resistance value of the electrolyte membrane 121 has decreased to such an extent that cell replacement is desired, a notification is made to prompt cell replacement (step S320). For this reason, recovery of the open circuit voltage Vocv by cell replacement and maintenance or recovery of the power generation capability of the fuel cell 100 as a stack of the fuel cells 120 can be achieved.

  The present invention is not limited to the above-described embodiment, and can be realized with various configurations without departing from the spirit of the present invention. For example, the technical features of the embodiments corresponding to the technical features in each embodiment described in the summary section of the invention are intended to solve part or all of the above-described problems, or part of the above-described effects. Or, in order to achieve the whole, it is possible to replace or combine as appropriate. Further, if the technical feature is not described as essential in the present specification, it can be deleted as appropriate.

  In the above embodiment, the fuel cell system 20 is described as a vehicle. However, the fuel cell system 100 can be applied as a power generation system that generates power using a stationary type. In addition, in the above-described embodiment, the voltage drop factor is specified based on each locus in FIG. 4 in which the open circuit voltage Vocv and the membrane resistance value R are associated. However, the physical properties of the electrolyte membrane 121 other than the membrane resistance value R It is also possible to grasp the relationship between the value and the open circuit voltage Vocv for each voltage drop factor and specify each factor.

DESCRIPTION OF SYMBOLS 20 ... Fuel cell system 100 ... Fuel cell 120 ... Fuel cell 121 ... Electrolyte membrane 122 ... Anode 123 ... Cathode 124 ... Anode side gas diffusion layer 125 ... Cathode side gas diffusion layer 126 ... Gas separator 127 ... Gas separator 200 ... Anode gas Supply part 210 ... Hydrogen gas tank 220 ... Anode gas supply flow path 222 ... Open / close valve 224 ... Regulator 226 ... Hydrogen supply part 227 ... Pressure sensor 230 ... Anode gas circulation flow path 232 ... Hydrogen gas pump 234 ... Gas-liquid separation part 236 ... Exhaust drainage Valve 238 ... Exhaust flow path 239 ... Pressure sensor 300 ... Cathode gas supply section 310 ... Intake port 320 ... Compressor 330 ... Cathode gas supply flow path 332 ... Pressure sensor 340 ... Cathode off-gas discharge flow path 342 ... Back pressure adjustment bar 344 ... Pressure sensor 350 ... Exhaust port 360 ... Humidifying unit 400 ... Cooling device 410 ... Cooling circulator 420 ... Refrigerant supply channel 430 ... Refrigerant discharge channel 500 ... Cell characteristic measuring unit 510 ... Cell characteristic measuring unit 512 ... Voltage measurement Unit 514 ... Resistance measurement unit 520 ... Voltage sensor 530 ... Current sensor 600 ... Power control unit 610 ... Secondary battery 620 ... Secondary battery control unit 630 ... Motor 640 ... Motor control unit 700 ... Control unit 710 ... CPU
710a: Battery output control unit 710b ... Cell property determination unit 720 ... Memory 730 ... Input / output unit 740 ... Start switch 750 ... Accelerator

Claims (10)

A fuel cell system,
A fuel cell comprising a plurality of battery cells each having a membrane electrode assembly in which an electrode catalyst layer is bonded to both membrane surfaces of the electrolyte membrane;
A characteristic detection unit for detecting an output characteristic at low load based on an output voltage of the fuel cell when the fuel cell is operated and controlled at a load below a predetermined value;
When the output voltage falls below a predetermined threshold voltage, the output of the fuel cell is changed according to the behavior of the detected output characteristic at low load after changing the operation state of the fuel cell to the side where the drying of the electrolyte membrane proceeds. A fuel cell system, comprising: a voltage reduction factor specifying unit that specifies a factor that causes a decrease in voltage as one of excessive moisture in the electrolyte membrane and a plurality of factors other than the excessive moisture.   2. The fuel cell system according to claim 1, wherein the voltage reduction factor specifying unit uses a voltage / resistance relationship indicating a relationship between the output voltage and a membrane resistance value of the electrolyte membrane as the low load output characteristic. The fuel cell system according to claim 2, wherein
The voltage drop factor specifying unit collates the change in the voltage / resistance relationship detected as the output characteristic at the time of low load with the behavior of the voltage / resistance relationship grasped for each factor that causes the output voltage to drop. The fuel cell system that identifies the factor.   4. The fuel cell system according to claim 2, wherein the low-load output characteristic is a characteristic of an output voltage when the fuel cell is operated in a no-load state in which no current flows to an external load.   The fuel cell system according to claim 4, wherein the output characteristic is an open circuit voltage of a fuel cell detected for each battery cell. The fuel cell system according to claim 5, wherein
The voltage lowering factor specifying unit captures the behavior of the voltage / resistance relationship as a factor other than the excessive moisture, considering the occurrence of gas cross-leakage in the electrolyte membrane and the membrane short-circuit resistance reduction of the electrolyte membrane. Grasp the excess moisture, the cross-leakage expression, and the membrane short-circuit resistance drop in association with each other, and by comparing the grasped behavior of the voltage / resistance relationship with the detected open circuit voltage, the factor is determined. The fuel cell system is specified as one of the excessive water, the cross leak, and the short circuit resistance.   When the factor is specified as the excess moisture by the voltage reduction factor specifying unit, the fuel cell is continuously operated to the side where the drying of the electrolyte membrane proceeds until the open circuit voltage returns to the threshold voltage. The fuel cell system according to claim 6. The fuel cell system according to claim 6 or 7, wherein
When the voltage lowering factor specifying unit specifies the occurrence of the cross leak, the differential pressure of the gas supplied to and discharged from the electrode catalyst layers on both surfaces of the electrolyte membrane in the membrane electrode assembly of the battery cell Based on the above, the amount of cross leak accompanying the occurrence of the cross leak is determined for each battery cell, and the high cross leak battery cell in which the occurrence status of the cross leak determined for each battery cell is higher than a predetermined threshold cross leak level A fuel cell system that provides information about the fuel cell system. A fuel cell system according to any one of claims 6 to 8, wherein
A map first storage unit for storing a short-circuit resistance value transition map in which a transition of a short-circuit resistance value of the electrolyte membrane is associated with the voltage / resistance relationship;
For each battery cell, the short-circuit resistance value of the electrolyte membrane corresponding to the detected open-circuit voltage is compared with the voltage / resistance relationship for the detected open-circuit voltage and the short-circuit resistance value transition map. A short-circuit resistance value calculation unit to be obtained;
Film damage associated with the upper limit of the output voltage capable of suppressing damage to the electrolyte film due to heat generated due to the short circuit resistance value of the electrolyte film and the output voltage of the battery cell, and the short circuit resistance value of the electrolyte film A map second storage unit for storing the suppression map;
A voltage upper limit calculation unit that obtains an upper limit of the output voltage capable of suppressing damage to the electrolyte membrane by comparing the short-circuit resistance value of the electrolyte membrane obtained by the short-circuit resistance value calculation unit with the membrane damage suppression map. ,
When the factor is specified as the membrane short-circuit resistance reduction by the voltage reduction factor specifying unit, the short-circuit resistance value calculating unit obtains a short-circuit resistance value of the electrolyte membrane, and the voltage upper limit calculating unit is A fuel cell system that obtains an upper limit of the output voltage capable of suppressing damage and then limits the output voltage of the fuel cell based on an external load request to the upper limit. The fuel cell system according to claim 9, wherein
When the factor is specified as the membrane short-circuit resistance drop by the voltage reduction factor specifying unit, the short-circuit resistance value of the electrolyte membrane obtained by the short-circuit resistance value calculation unit for each battery cell is a predetermined threshold short-circuit resistance value A fuel cell system that provides information about smaller small short-circuit resistance battery cells.

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