JP5217123B2 - Fuel cell system - Google Patents

Description

  The present invention relates to a fuel battery cell that generates power by an electrochemical reaction between an oxidizing gas and a fuel gas, a fuel battery cell stack in which a plurality of fuel battery cells are stacked, and a scavenging gas supply that supplies a scavenging gas into the fuel cell stack. The present invention relates to a fuel cell system including a unit.

  The fuel cell stack is composed of a fuel cell stack obtained by laminating a plurality of sets of fuel cell units, for example, a membrane-electrode assembly (MEA) composed of an anode side electrode, an electrolyte membrane and a cathode side electrode and a separator. doing. That is, each fuel cell is configured by arranging an anode side electrode on one side of an electrolyte membrane made of a polymer ion exchange membrane, a cathode side electrode on the other side, and further providing separators on both sides. doing. A fuel cell stack in which a plurality of sets of such fuel cells are stacked is sandwiched between current collector plates, insulating plates, and end plates to constitute a fuel cell stack that generates a high voltage.

  In such a fuel cell, a fuel gas, for example, a gas containing hydrogen is supplied to the anode side electrode, and an oxidizing gas, for example, air is supplied to the cathode side electrode. As a result, the fuel gas and the oxidizing gas are supplied to the cell reaction to generate an electromotive force, and water is generated at the cathode side electrode.

  Conventionally, as described in Patent Document 1 and Patent Document 2, in the fuel cell, since water exists in the cathode side electrode, when the fuel cell is to be started below freezing point, However, it is known that there is a problem that the electrochemical reaction is difficult to occur in the fuel cell. That is, if the water remaining in the fuel cell freezes, there will be a shortage of oxidizing gas or hydrogen in the fuel cell, and the fuel cell will not be able to generate power and will not be able to exhibit its capabilities. Moreover, volume expansion may occur in a part of the flow path due to freezing of water, destroying the location where water is present, and may significantly deteriorate durability.

  On the other hand, in the case of the fuel cell systems described in Patent Literature 1 and Patent Literature 2, scavenging gas supply means for scavenging moisture in the oxidizing gas flow channel on the cathode side electrode side inside the fuel cell is provided. . Further, when the fuel cell power generation is stopped, if the residual moisture in the fuel cell is excessive, the residual moisture in the gas flow path is discharged to the outside by unhumidified air.

Further, in the case of the fuel cell systems described in Patent Document 1 and Patent Document 2, in order to estimate the residual water amount inside the fuel cell, the pressure of the oxidizing gas supplied to the fuel cell on the inlet side of the fuel cell is set. An inlet pressure sensor for detecting and an outlet pressure sensor for detecting the pressure on the outlet side are provided. Then, the inlet pressure value detected by the inlet pressure sensor P _A, and the pressure difference the inlet outlet pressure difference Pdif (= P _A -P _B) is given between the outlet pressure value P _B detected by the outlet pressure sensor Pdif It is determined whether or not “Pdif ≦ Pdif”. That is, the inlet / outlet pressure difference Pdif becomes a large value when the residual water in the oxidizing gas flow path constituting the fuel cell is large, and the inlet / outlet pressure difference Pdif becomes a small value as the residual water decreases. When the inlet / outlet pressure difference Pdif exceeds a predetermined pressure difference Pdif ′, it is estimated that the residual water in the oxidizing gas flow path is excessive, and a scavenging process (purging) with dry air is performed. On the other hand, when the inlet / outlet pressure difference Pdif is equal to or smaller than the predetermined pressure difference Pdif ′, it is estimated that water does not remain in the oxidizing gas flow path, and the scavenging process is not performed.

JP 2005-209634 A JP 2005-209635 A JP 2005-302304 A JP 2003-297399 A

In the case of the fuel cell system described in Patent Literature 1 and Patent Literature 2 as described above, the oxidation pressure is obtained by obtaining the inlet / outlet pressure difference Pdif between the inlet pressure value P _A and the outlet pressure value P _B of the oxidizing gas. It is estimated whether or not the residual water in the gas flow path is excessive. In the case of such a fuel cell system, if the amount of residual water can be accurately estimated, there is a possibility that the time for scavenging the inside of the fuel cell can be optimized. However, with such a fuel cell system, it is difficult to increase the accuracy of estimation of the residual water amount. That is, since the gas path through which the gas flows may contain water vapor, the oxidation gas inlet pressure value P _A and the outlet pressure value P _B include the gas at the inlet side and the outlet side of the fuel cell, respectively. The amount of water vapor in the path is greatly related. Therefore, the inlet / outlet pressure difference Pdif also varies greatly depending on how much water vapor is present in the gas on the inlet side of the fuel cell and in the gas on the outlet side. Further, the inlet / outlet pressure difference Pdif also changes depending on the temperature of the fuel cell. Therefore, by measuring the inlet / outlet pressure difference Pdif, it is difficult to accurately estimate the amount of residual water in the fuel cell, in other words, to sufficiently reduce the estimation error of the residual water amount. If the estimation error of the residual water amount cannot be made sufficiently small, it becomes difficult not only to optimize the time for scavenging the inside of the fuel cell, but also to restart the fuel cell well below freezing point.

  On the other hand, the present inventor, as the amount of residual water inside the fuel cell decreases, the fuel cell stack in which a plurality of fuel cells are stacked rises to a point in time when there is a voltage in a state where no power generation is performed (so-called open circuit state). I found that there is a relationship. In addition, from this, when the residual water amount inside the fuel cell decreases, the present inventors also have a relationship that the voltage difference between the fuel cells, which is the voltage difference between the plurality of fuel cells, increases until a certain point in time. I found out. Therefore, the present inventor has come to consider that the residual water amount inside the fuel cell can be accurately estimated by measuring the voltage of the fuel cell stack or the voltage difference between the fuel cells.

  The present invention estimates that the amount of residual water in the fuel cell has reached the target residual water amount without using the pressure difference between the portions of the gas path that are separated from each other, and sets the time for scavenging the inside of the fuel cell. It is an object of the present invention to provide a fuel cell system that can be optimized and that can successfully restart the fuel cell even under freezing.

A fuel cell system according to the present invention includes a fuel cell that generates power by an electrochemical reaction between an oxidizing gas and a fuel gas, a fuel cell stack in which a plurality of fuel cells are stacked, and a voltage value of the plurality of fuel cells. A voltage measuring means for measuring, a scavenging gas supply unit for supplying a scavenging gas into the fuel cell stack, and a control unit; the control unit operates the scavenging gas supply unit to scavenge the gas into the fuel cell stack; After the fuel cell voltage difference between the two fuel cells of the plurality of fuel cells measured by the voltage measuring means is greater than or equal to a predetermined value, A fuel cell system comprising scavenging gas supply control means for stopping the operation of the scavenging gas supply unit.

If the fuel cell system according to the present invention, after supplying a scavenging gas to the fuel cell by the scavenging gas supply unit, fuel cell voltage difference of the scavenging gas supply unit on condition that a predetermined value or more operating Therefore, it can be estimated that the residual water amount in the fuel cell has reached the target residual water amount without using the pressure difference between the portions of the gas path that are separated from each other. For this reason, the time for scavenging the inside of the fuel cell can be optimized, and the fuel cell can be restarted satisfactorily even under freezing. That is, according to the present invention, the residual water volume of the fuel cell as described above is decreased, the residual water volume target residual in the fuel cell by utilizing the relationship that rises to the point where there is a voltage difference between the fuel cell It can be estimated that the amount of water has been reached.

  On the other hand, it has been conventionally considered to estimate the residual water amount by measuring the membrane resistance value of the electrolyte membrane of the fuel cell, but in this case, fuel is consumed for resistance measurement. In contrast, the voltage measurement consumes less fuel. For this reason, according to the present invention, fuel consumption can be reduced. In addition, when fuel consumption is acceptable, the accuracy of estimation of the residual water amount can be further improved by adding a resistance measuring means for the membrane resistance value in the present invention.

Patent Document 3 describes a fuel cell system in which a hydrogen circulation channel is provided on the fuel gas discharge side of the fuel cell stack so that hydrogen not consumed in the fuel cell stack is returned to the fuel gas supply path. ing. In addition, when the concentration of impurities in the fuel cell stack increases during operation or when water is clogged, the voltage of the fuel cell drops, so the fuel cell voltage is monitored and the fuel cell voltage is set to a predetermined value. When the pressure is lowered, the purge valve provided on the fuel gas discharge side is opened to discharge hydrogen and impurities to the outside. Such a fuel cell system described in Patent Document 3, unlike the present invention, that the voltage difference between the fuel battery cells to stop the operation of the scavenging gas supply unit on condition that a predetermined value or more Not considered. Further, unlike the case of the present invention, the fuel cell system described in Patent Document 3 does not consider optimizing the time for scavenging the inside of the fuel cell.

  In Patent Document 4, a bypass path that bypasses the humidifier and the humidifier is provided on the fuel gas supply side of the fuel cell stack, and the fuel gas passes through either the humidifier or the bypass path by the humidifier bypass valve. There is described a fuel cell system adapted to select one of these. In addition, when the fuel cell stop sequence was started, the fuel gas was supplied to the fuel cell stack as dry hydrogen that passed through the bypass path, and the measured value of the power generation voltage of the fuel cell was below the specified value. The supply of dry hydrogen is stopped on the condition. In the invention described in Patent Document 4, the condition for stopping the supply of dry hydrogen is different from the case of the present invention in that the measured voltage value is not more than a specified value. The conditions are completely different. In the case of such a fuel cell system described in Patent Document 4, there is a possibility that the amount of water in the fuel cell stack is excessively reduced and the electrode and the electrolyte membrane are excessively dried, as will be described in detail later.

[ Reference example ]
Hereinafter, embodiments and reference examples according to the present invention will be described in detail with reference to the drawings. 1 to 4 show a reference example . FIG. 1 is a schematic configuration diagram of a reference example .

  The fuel cell system 10 includes a fuel cell stack 12. The fuel cell stack 12 is a fuel cell stack in which a plurality of fuel cells are stacked, and a current collector plate and an end plate are provided at both ends in the stacking direction of the fuel cell stack. The fuel cell stack, the current collector plate, and the end plate are fastened with tie rods, nuts, and the like. An insulating plate can also be provided between the current collector plate and the end plate.

  Although a detailed view of each fuel cell is omitted, it is assumed that, for example, a membrane assembly in which an electrolyte membrane is sandwiched between an anode side electrode and a cathode side electrode and separators on both sides thereof are provided. Further, hydrogen gas that is a fuel gas can be supplied to the anode side electrode, and air that is an oxidizing gas can be supplied to the cathode side electrode. Then, hydrogen ions generated by the catalytic reaction at the anode side electrode are moved to the cathode side electrode through the electrolyte membrane, and water is generated by causing a cell chemical reaction with oxygen at the cathode side electrode. An electromotive force is generated by moving electrons from the anode side electrode to the cathode side electrode through an external circuit.

  In addition, a refrigerant flow path is provided in the fuel cell stack 12 near the separator. By flowing cooling water, which is a refrigerant, in the refrigerant flow path, even if the temperature rises due to heat generated by the power generation of the fuel cell stack 12, the temperature does not rise excessively.

  The air that is the oxidizing gas is pressurized by the air compressor 14 that is also a scavenging gas supply unit, is humidified by the humidifier 16, and then is supplied to the oxidizing gas channel on the cathode side electrode side of the fuel cell stack 12. . Further, a bypass path 20 is provided in parallel with the main path 18 separately from the main path 18 for supplying air to the fuel cell stack 12 after passing the humidifier 16. The air passing through the bypass path 20 is supplied to the fuel cell stack 12 without passing through the humidifier 16. A humidifier bypass valve 21 is provided in the middle of the bypass path 20.

  Along with the humidifier bypass valve, a valve may be provided at a position indicated by broken lines 22a and 22b in FIG. 1 to control the opening degree of the humidifier bypass valve 21 and the valve 22a (or 22b). Further, without providing the humidifier bypass valve, it is also possible to provide a three-way valve at a position indicated by point a or point b in FIG. 1 and to select a flow path that allows the three-way valve to communicate with each other.

  The air after being supplied to the fuel cell stack 12 and subjected to the cell chemical reaction in each fuel cell is discharged from the fuel cell stack 12, passes through the humidifier 16, and then is returned to the atmosphere via the pressure control valve 23. Released. The pressure control valve 23 is controlled so that the supply pressure of the air sent to the fuel cell stack 12 becomes an appropriate pressure value according to the operating state of the fuel cell stack 12.

  The humidifier 16 serves to humidify the moisture obtained from the air discharged from the fuel cell stack 12 to the air before being supplied to the fuel cell stack 12. For example, the humidifier 16 allows the moisture in the gas having a high moisture content to pass through the hollow fiber membrane when a gas having a different moisture content is supplied to the inside and the outside of many hollow fiber membranes. Moisture gas with low moisture content.

  Further, hydrogen gas that is fuel gas is supplied to the fuel cell stack 12 from a hydrogen gas supply device (not shown) such as a high-pressure hydrogen tank that is a fuel gas supply device via a fuel control valve 24 that is a pressure control valve. The hydrogen gas supplied to the fuel gas flow path on the anode side electrode side of the fuel cell stack 12 and subjected to the cell chemical reaction is discharged from the fuel cell stack 12, and then the moisture is removed by the gas-liquid separator 26. After that, the hydrogen gas supplied from the hydrogen gas supply device passes through the circulation path 28 and is supplied to the fuel cell stack 12 again. The hydrogen gas supplied to the fuel cell stack 12 is pressurized by a hydrogen pump 30 provided in the circulation path 28.

  In addition, cooling water that is a refrigerant for cooling the fuel cell stack 12 flows through the cooling water path 32. The cooling water path 32 is connected to the cooling water inlet 34 and the cooling water outlet 36 of the fuel cell stack 12. The cooling water path 32 includes a cooling water feed path 40 that connects the cooling water outlet 36 and the branch portion 38, and a main path 42 and a bypass path 44 that branch from the branch portion 38. Further, a three-way valve 46 is provided at the junction of the main path 42 and the bypass path 44, and the three-way valve 46 and the cooling water pump 48 are connected by an intermediate path 50. Further, the cooling water pump 48 and the cooling water inlet 34 of the fuel cell stack 12 are communicated by a cooling water feed path 52. The cooling water pump 48 can change the discharge flow rate.

  The cooling water is boosted by the cooling water pump 48 and supplied to the fuel cell stack 12, and then flows through the internal cooling water flow path 54 of the fuel cell stack 12, whereby the temperature of the fuel cell stack 12 rises due to the power generation operation. If so, the fuel cell stack 12 is cooled. The cooling water that has passed through the fuel cell stack 12 is sent to a radiator 56 provided in the middle of the main path 42, and is radiated when the temperature rises. The cooling water after passing through the radiator 56 passes through the three-way valve 46 and then is sent to the cooling water pump 48 again. On the other hand, the cooling water flowing through the bypass path 44 is sent to the three-way valve 46 without passing through the radiator 56.

  Further, a part of the cooling water sent out from the cooling water pump 48 passes through the ion exchange resin 58 and then is sent to the branch portion 38 between the main path 42 and the bypass path 44. Ions such as metal ions are removed from the cooling water after passing through the ion exchange resin 58.

  On the other hand, a voltage monitor 60 is connected to the fuel cell stack 12 to measure the voltage of the fuel cell stack. A voltage signal that is a signal representing a measured value of the voltage is input to the control unit (ECU) 62. The control unit 62 includes a residual water amount estimation unit that estimates the residual water amount inside the fuel cell stack 12, and an air compressor control unit that controls an operation state that is the rotation speed and rotation time of the air compressor 14, that is, a scavenging air supply control unit. And have. The control unit 62 is connected to a start switch (not shown) that functions as an ignition switch of the fuel cell system, and is subjected to power generation start processing on condition that a power generation start signal corresponding to the ON state is received from the start switch. The power generation stop process is performed on condition that a power generation stop signal corresponding to the OFF state is received.

  The control unit 62 also receives input signals such as a signal from the start switch, a voltage signal from the voltage monitor 60, a detection signal from a temperature sensor (not shown) provided near the cooling water inlet or near the cooling water outlet. Corresponding to the given condition, the operating state of the air compressor 14, the humidifier bypass valve 21, the pressure control valve 23, the fuel control valve 24, the three-way valve 46, and the like are controlled.

  As described above, the control unit 62 includes means for estimating the amount of residual water inside the fuel cell stack 12, which is calculated based on the voltage value of the fuel cell stack of the fuel cell stack 12 measured by the voltage monitor 60. The amount of residual water inside the battery stack 12 is estimated. This will be described with reference to FIG. FIG. 2 shows the amount of residual water in the fuel cell stack 12 (FIG. 1) and the fuel cell stack when air is supplied as scavenging gas to the fuel cell stack 12 by the air compressor 14 after the fuel supply of the fuel cell is stopped. The example which this inventor discovered about the relationship with a voltage is shown.

  In FIG. 2, the horizontal axis represents time, and the vertical axis represents the residual water amount and the voltage of the fuel cell stack. Curve a represents the relationship between the amount of residual water and time, and curve b represents the relationship between voltage and time. The supply flow rate of air to the fuel cell stack 12 is constant. As can be seen from FIG. 2, as the air is supplied to the fuel cell stack 12, the residual water amount (curve a) gradually decreases, whereas the voltage (curve b) gradually increases as time passes. After rising, it gradually decreases due to a decrease in power generation efficiency at a certain point.

This reference example was invented based on such knowledge, and utilizes the relationship in the case where the voltage increases as the residual water amount decreases. That is, the relationship of the range shown by the arrow a in FIG. 2 is used. On the other hand, in the case of the fuel cell system described in the above-mentioned Patent Document 4, the voltage of the fuel cell decreases as the residual water amount in the fuel cell stack decreases. The basic focus is greatly different from the present invention. Further, in the case of the fuel cell system described in Patent Document 4, the supply of dry hydrogen to the fuel cell stack is stopped when the amount of residual water falls below the specified value within the range indicated by the arrow b in FIG. . In the case of such a fuel cell system described in Patent Document 4, there is a possibility that the amount of residual water is excessively reduced.

This reference example uses the relationship that the voltage of the fuel cell increases as the residual water amount that has not been focused on conventionally decreases, so that the residual water amount estimation means of the control unit 62 measures the fuel cell stack. The amount of residual water in the fuel cell stack 12 is estimated from the voltage. The air compressor control means of the control unit 62 supplies air to the fuel cell stack 12 by the air compressor 14 until the measured voltage becomes equal to or higher than the target voltage corresponding to the target residual water amount. Further, the air compressor control means stops the operation of the air compressor 14 when the measured voltage becomes equal to or higher than the target voltage.

Next, a method for scavenging residual water after stopping the power generation operation of the fuel cell will be described using the flowchart shown in FIG. 3 and the time chart shown in FIG. In FIG. 4, the horizontal axis represents time, (A) shows the amount of residual water in the fuel cell stack 12, (B) shows the power generation amount of the fuel cell stack 12, and (C) shows the fuel cell stack. Represents the body voltage. First, in step S1 (FIG. 3), when the start switch is stopped (turns OFF), the control unit 62 receives a signal indicating a fuel supply stop command, and a power generation stop process is executed. In this case, in step S2, the fuel control valve 24 that controls the supply of hydrogen gas from the hydrogen gas supply device is closed, the new supply of hydrogen gas is stopped, and the power generation is stopped (t _{0 in} FIG. 4). .

  Next, in step S3 (FIG. 3), the control unit 62 causes the cooling water discharge flow rate of the cooling water pump 48 to be a predetermined flow rate Qcw, and the air supply flow rate of the air into the fuel cell stack 12 by the air compressor 14. The cooling water pump 48 and the air compressor 14 are controlled so that becomes a predetermined flow rate Qca. Then, air is supplied into the oxidizing gas flow path in the fuel cell stack 12 to perform scavenging, that is, purging. In this case, the air sent out from the air compressor 14 may pass through the bypass path 20 where the humidifier 16 is not provided, or may pass through the main path 18. Preferably, the air passes through the bypass path 20. In this case, the cooling water discharge flow rate and the air supply flow rate are not limited to constant predetermined values, but may be changed.

  The three-way valve 46 provided in the cooling water passage 32 controls the position of the valve so that the cooling water passes through the bypass passage 44. The reason for this is to prevent the fuel cell stack 12 from being cooled more than necessary and to keep the temperature of the fuel cell stack 12 high to some extent. If the fuel cell stack 12 is excessively cooled, the time for removing moisture from the inside of the fuel cell stack 12 becomes long, and the scavenging time may become excessively long. By passing the cooling water through the bypass path 44, such inconvenience can be eliminated.

  Next, in step S4, it is determined whether or not the residual water amount in the fuel cell stack 12 is the target residual water amount. This determination process is performed to reduce or substantially eliminate residual water when the power generation operation of the fuel cell system 10 is stopped, and to ensure good startability at the time of restart. That is, it is possible to facilitate quick start even in an environment below freezing. Then, when the residual water amount reaches the target residual guess, the supply of cooling water and the supply of air to the oxidizing gas channel are stopped, and the scavenging, that is, the purge is stopped.

That is, as described with reference to FIG. 2 above, there is a correlation between the residual water amount in the fuel cell stack 12 and the voltage of the fuel cell stack, that is, the voltage decreases as the residual water amount decreases. Since it is known that it rises, it is possible to control the residual water amount to become the target residual water amount by measuring the voltage. More specifically, in step S4 described above, as shown in FIGS. 4A and 4C, a target voltage value Vt corresponding to the target residual water amount is obtained in advance, and the air compressor control means is measured. It is determined whether or not the voltage value V has reached or exceeded the target voltage value Vt. If the voltage value V does not reach the target voltage value Vt or more, the air compressor control means determines that the target residual water amount has not been reached, that is, the amount of residual water is large, and continues to supply air. On the other hand, if the voltage value V reaches the target voltage value Vt or more, the air compressor control means estimates that the target residual water amount has been reached, and in step S5, the cooling water pump 48 and the air compressor 14 The operation is stopped (t _{1 in} FIG. 4).

Thus, according to the present reference example , it can be estimated that the remaining water amount in the fuel cell stack 12 has reached the target residual water amount after the power generation operation is stopped. In particular, in the case of this reference example , after the air is supplied into the fuel cell stack 12 by the air compressor 14, the measured value of the voltage of the fuel cell stack is not less than a predetermined value Vt. Since the operation is stopped, it can be estimated that the residual water amount in the fuel cell stack 12 has reached the target residual water amount without using the pressure difference between the portions of the gas path that are separated from each other. For this reason, the time for scavenging the inside of the fuel cell stack 12 can be optimized, and the fuel cell can be restarted satisfactorily even below the freezing point.

In the case of this reference example , resistance measuring means such as a resistance measuring device is not required, and a low-cost system configuration can be achieved with a simple configuration. In addition, after the fuel control valve 24 (FIG. 1) is closed, resistance measurement is not required during scavenging, so that fuel shortage can be effectively prevented. In particular, in the conventional fuel cell system, if fuel is consumed by resistance measurement or the like, fuel shortage tends to occur near the fuel gas outlet of the fuel cell stack, but in the case of this reference example where resistance measurement is not performed. Eliminates such inconvenience. Furthermore, it is possible to effectively prevent the occurrence of problems that may cause damage or deterioration by forcibly driving an auxiliary machine such as the hydrogen pump 30 (FIG. 1) in a fuel-deficient state. In addition, it is possible to effectively prevent deterioration of the electrolyte membrane due to fuel shortage. Further, even if the fuel is not consumed or consumed when scavenging, the consumption amount can be sufficiently reduced, so that the hydrogen pressure in the hydrogen supply path after the fuel supply stop command can be easily maintained at a predetermined pressure.

  In addition, since it is known that the relationship between the residual water amount in the fuel cell stack 12 and the voltage of the fuel cell stack is as shown in FIG. 5, the target residual water amount is given a wide range as the target residual water amount. And the target voltage value of the fuel cell stack is set to a target voltage range corresponding to the target residual water amount range, and the control unit 62 controls the air compressor when the measured voltage of the fuel cell stack is within the target voltage range. The operation of 14 can also be stopped.

[Embodiment of the Invention ]
Next, FIGS. 6 to 7 show an embodiment of the present invention . In the case of the fuel cell system 10 according to the present embodiment, in the reference example shown in FIGS. 1 to 4 described above, the voltage of the fuel cell stack of the fuel cell stack 12 is not measured. A plurality of voltage monitors that measure the voltages of all the fuel cells constituting the battery stack 12 are provided. And the control part 62 calculates | requires the voltage difference between fuel cells which is a difference between the voltage values of two fuel cells of a some fuel cell, and a fuel cell stack by the calculated voltage difference between fuel cells The amount of residual water in 12 is estimated, and the operation of the air compressor 14 is controlled so as to reach the target amount of residual water.

That is, in the present embodiment, unlike the above-described reference example , the air compressor control means of the control unit 62 determines the inter-fuel cell voltage that is the difference between the measured voltage values of the two fuel cells. The operation of the air compressor 14 is stopped on condition that the difference is equal to or greater than a predetermined value. This embodiment has been invented based on the inventor's knowledge that there is a relationship in which the voltage difference between fuel cells increases as the amount of residual water in the fuel cell stack 12 decreases. . In this case, the relationship between the residual water amount and the voltage difference between the fuel cells is in the range of the arrow a between the residual water amount (curve a) and the fuel cell stack voltage (curve b) shown in FIG. In relation, the vertical axis in FIG. 2 is changed to a voltage difference between fuel cells by changing the magnification, and the curve b in FIG. 2 is the same as the curve showing the voltage difference between fuel cells.

The relationship between the residual water amount and the voltage difference between the fuel cells is such a reason as follows. That is, as described in the above reference example , the voltage of the fuel cell stack increases as the residual water amount in the fuel cell stack 12 decreases. Therefore, the voltage of one fuel cell increases as the residual water amount decreases. It is derived that there is a relationship that increases. Further, a high voltage of one fuel battery cell leads to an increase in the value of voltage variation, which is a voltage difference inevitably generated between the two fuel battery cells. For this reason, it is considered that there is a relationship in which the residual water amount decreases as the voltage difference between the two fuel cells increases.

  In the present embodiment, in the fuel cell system 10 shown in FIG. 1 described above, instead of omitting the voltage monitor 60 that measures the voltage of the fuel cell stack, a plurality of voltage values that measure the voltage values of all fuel cells are measured. The voltage monitor is provided. And the control part 62 is calculating | requiring the voltage difference between fuel cells between the measurement voltages of two fuel cells of a some fuel cell. For example, a minimum voltage value and a maximum voltage value are selected from the voltage values of a plurality of fuel cells, and a difference between the minimum voltage value and the maximum voltage value is obtained as a voltage difference between fuel cells. Since the configuration of the other fuel cell system 10 is the same as the configuration shown in FIG. 1, the description of the present embodiment will be made using the reference numerals in FIG.

  The control unit 62 has a residual water amount estimation means inside the fuel cell stack 12 and an air compressor control means for controlling the operating state that is the rotation speed and rotation time of the air compressor 14. Of these, the residual water amount estimation means estimates the residual water amount inside the fuel cell stack 12 from the voltage difference between the fuel cells between the measured voltages of the two fuel cells.

  Then, when scavenging the residual water in the fuel cell stack 12 after stopping the power generation operation of the fuel cell, whether or not the residual water amount in the fuel cell stack 12 is the target residual water amount in step S4 shown in FIG. The determination process is performed. In particular, in the case of the present embodiment, there is a correlation between the amount of residual water in the fuel cell stack 12 and the voltage difference between fuel cells, that is, the voltage difference between fuel cells increases as the amount of residual water decreases. 7 (A) and 7 (C), the target fuel cell voltage difference difVt corresponding to the target residual water amount is obtained, and the fuel cell measured by the air compressor control means is obtained. It is determined whether or not the cell voltage difference difV has reached the target fuel cell voltage difference difVt or more. The air compressor control means determines that the target residual water amount has not been reached, that is, the amount of residual water is large unless the inter-fuel cell voltage difference difV has reached the target inter-fuel cell voltage difference difVt. Continue to do. On the other hand, the air compressor control means estimates that the target residual water amount has been reached if the fuel cell voltage difference difV reaches or exceeds the target fuel cell voltage difference difVt. The operations of the water pump 48 and the air compressor 14 are stopped.

In the case of this embodiment, after air is supplied into the fuel cell stack 12 by the air compressor 14, the operation of the air compressor 14 is stopped on condition that the obtained voltage difference between the fuel cells becomes equal to or greater than a predetermined value difVt. Therefore, it can be estimated that the residual water amount in the fuel cell stack 12 has reached the target residual water amount without using the pressure difference between the portions of the gas path that are separated from each other. For this reason, the time for scavenging the inside of the fuel cell stack 12 can be optimized, and the fuel cell can be restarted satisfactorily even below the freezing point. In addition, when the voltage of one fuel cell rises excessively, the deterioration of the fuel cell may be promoted. In the case of the present embodiment, between the fuel cells between two fuel cells. Since the voltage difference can be reduced, the voltage of each fuel cell can be easily reduced, and deterioration of the fuel cell can be easily suppressed.
Since the remaining structure and the scavenging method of the remaining water after stopping the power generation operation of the fuel cell system 10 are the same as in the case of the above-described reference example , redundant description is omitted.

  In the present embodiment, the voltage of all the fuel cells constituting the fuel cell stack 12 is measured. If the voltage can be measured by a plurality of fuel cells, the number of fuel cells that measure the voltage is determined. It is not limited. However, as a matter of course, the estimation accuracy of the residual guess can be improved as the number of fuel cells for measuring the voltage is increased. For example, the fuel cells that measure the voltage may be every other fuel cell of the fuel cell stack 12.

  Further, the relationship between the residual water amount in the fuel cell stack 12 and the voltage difference between the fuel cells is the relationship between the residual water amount and the voltage of the fuel cell stack shown in FIG. It turns out that it becomes the same as what made the voltage difference between fuel cells by changing magnification. For this reason, the target residual water amount is widened to obtain a target residual water amount range, and the target voltage difference of the inter-fuel cell voltage difference is set to a target voltage range corresponding to this target residual water amount range, and the control unit 62 (FIG. 1). By referring to FIG. 1, the operation of the air compressor 14 (see FIG. 1) can also be stopped when the voltage difference between fuel cells based on the measured voltage is within the target voltage difference range.

As a reference example of the present invention, in the reference example shown in FIGS. 1 to 4 above, the air compressor control unit of the control unit 62, the time rate of change of the measured voltage of the fuel cell stack of the fuel cell stack 12 However, when the air compressor 14 causes air to be supplied to the fuel cell stack 12 until the target value is less than or equal to the target predetermined value, and the time rate of change of the measured voltage is equal to or lower than the target predetermined value, the operation of the air compressor 14 is stopped. You can also.

That is, as shown in FIG. 2 above, as air is supplied to the fuel cell stack 12, the amount of residual water in the fuel cell stack 12 (curve a) gradually decreases, but the voltage (curve b) is As the time elapses, it gradually rises in the area a, and then gradually decreases in the area b after a certain point in time. Therefore, in the vicinity of the boundary between the area A and area B in FIG. 2 where the residual water amount has decreased to some extent, the time change rate of the voltage of the curve b decreases with a positive value, and after 0, becomes a negative value. I understand. This reference example uses such a relationship, and estimates the amount of residual water from the time change rate of the voltage and optimizes the time for scavenging the inside of the fuel cell stack 12. That is, in the case of this reference example , when the rate of change of voltage with time is below a predetermined value (for example, 0 or less) after the fuel supply to the fuel cell is stopped by the residual water amount estimation means of the control unit 62, 12, it is estimated that the remaining water amount has reached the target residual water amount, and the operation of the air compressor 14 is stopped by the air compressor control means of the control unit 62.

According to this reference example, it can be estimated that the residual water amount in the fuel cell stack 12 has reached the target residual water amount after the power generation operation is stopped. In particular, in the case of this reference example , after supplying air into the fuel cell stack 12 by the air compressor 14, the time change rate of the measured value of the voltage of the fuel cell stack is not more than a predetermined value. Since the operation of the compressor 14 is stopped, it can be estimated that the residual water amount in the fuel cell stack 12 has reached the target residual water amount without using the pressure difference between the portions of the gas path that are separated from each other. Other configurations and operations are the same as those in the case of the reference example shown in FIG. 1 to FIG.

Moreover, although illustration is abbreviate | omitted, said embodiment and reference example can also be combined with the following structures.
(1) Membrane resistance measuring means for measuring the membrane resistance value of the electrolyte membrane of the fuel battery cell is provided, and the control unit 62 (see FIG. 1) determines that the voltage of the fuel cell stack or the voltage difference between the fuel battery cells is a predetermined value. On the condition that the membrane resistance value of the electrolyte membrane of the fuel cell becomes equal to or greater than a predetermined value, the operation of the air compressor 14 (see FIG. 1) is stopped, and the fuel cell stack 12 (see FIG. 1) is reached. Stop the air supply. With this configuration, the estimation accuracy of the residual water amount in the fuel cell stack 12 can be improved. That is, it is known that there is a relationship in which the residual water amount decreases as the membrane resistance value increases, and the residual water amount increases as the membrane resistance value decreases, so that the voltage of the fuel cell stack or the voltage difference between fuel cells The estimation accuracy of the residual water amount can be further improved by combining the correlation between the membrane resistance value and the residual water amount with the correlation with the residual water amount. However, in this case, unlike the case of each of the above-described embodiments, fuel is consumed as much as the membrane resistance is measured.
(2) Since the correlation between the voltage value of the fuel cell stack or the voltage difference between fuel cells and the amount of residual water may change due to deterioration of the fuel cell or the like, for example, the control unit 62 (see FIG. 1) The fuel cell load (vehicle drive motor) 64 (see FIG. 1) and the fuel cell stack, such as voltage, temperature, and humidity, are constant when the fuel cell is started and operated. It is also possible to correct the curve representing the correlation between the voltage and the impedance obtained in advance by correlating the voltage and the impedance of the battery cell stack. And the residual water amount estimation means of the control unit 62 can also estimate the impedance corresponding to the voltage and the residual water amount correlated with the impedance from the voltage of the fuel cell stack measured after the power generation is stopped. Then, the air compressor control means of the control unit 62 stops the operation of the air compressor 14 (see FIG. 1) when the voltage reaches or exceeds the target voltage corresponding to the target residual water amount, and the supply of air to the fuel cell stack 12 is stopped. Stop. With this configuration, the accuracy of the correlation between the voltage and the residual water amount can be further improved, and the estimation accuracy of the residual water amount can be further improved. The above-mentioned constant condition is, for example, a condition that is the same as the power generation stop condition or a condition that can be correlated with the power generation stop condition.

  Further, as an invention related to the present invention, since the relationship between the voltage of the fuel cell stack or the voltage difference between the fuel cells and the residual water amount can be inferred from the above FIG. 2 or FIG. Prior to the start of power generation, the state of the fuel cell before power generation can be determined by measuring the voltage of the fuel cell stack or the voltage difference between fuel cells. Since the state of the fuel cell can be determined before power generation, for example, when the amount of residual water in the fuel cell stack 12 (see FIG. 1) is large, the control unit 62 (FIG. 1) is configured to supply more air after power generation is started. The control of the operation of the air compressor 14 (see FIG. 1) can be controlled by the reference), or the driver can be informed that the power cannot be generated when the temperature is below freezing by warning sound, warning display lighting, or the like.

  The present invention does not limit the structure of the fuel cell stack, and various structures such as a conventionally known structure can be adopted.

It is a figure which shows the basic composition of the fuel cell system of a reference example . It is a figure which shows one example of the relationship between the amount of residual water and the voltage of a fuel cell laminated body at the time of supplying air to a fuel cell stack with a fixed flow rate after a power generation operation stop. 5 is a flowchart for explaining a method of scavenging residual water in a fuel cell stack after stopping a power generation operation in a fuel cell system of a reference example . Similarly, when scavenging residual water, the cooling water supply flow rate, the air supply flow rate (air flow rate) to the fuel cell stack, the residual water amount inside the fuel cell stack, the power generation amount, and the voltage of the fuel cell stack It is a time chart which shows. It is a figure which shows one example of the relationship between the amount of residual water and the voltage of a fuel cell laminated body. 4 is a flowchart for explaining a method of scavenging residual water in the fuel cell stack after stopping the power generation operation in the embodiment of the invention . Similarly, when scavenging residual water, the cooling water supply flow rate, the air supply flow rate (air flow rate) to the fuel cell stack, the residual water amount inside the fuel cell stack, the power generation amount, and the voltage difference between the fuel cell cells It is a time chart which shows a voltage.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Fuel cell system, 12 Fuel cell stack, 14 Air compressor, 16 Humidifier, 18 paths, 20 Bypass path, 21 Humidifier bypass valve, 22a, 22b Valve, 23 Pressure control valve, 24 Fuel control valve, 26 Gas liquid Separator, 28 Circulation path, 30 Hydrogen pump, 32 Cooling water path, 34 Cooling water inlet, 36 Cooling water outlet, 38 Branch part, 40 Cooling water feed path, 42 Main path, 44 Bypass path, 46 Three-way valve, 48 Cooling Water pump, 50 intermediate path, 52 cooling water feed path, 54 internal cooling water flow path, 56 radiator, 58 ion exchange resin, 60 voltage monitor, 62 control unit, 64 load.

Claims (2)

A fuel cell that generates electricity by an electrochemical reaction between an oxidizing gas and a fuel gas;
A fuel cell stack in which a plurality of fuel cells are stacked;
Voltage measuring means for measuring voltage values of a plurality of fuel cells;
A scavenging gas supply unit for supplying a scavenging gas into the fuel cell stack;
A control unit,
The control unit operates the scavenging gas supply unit to supply the scavenging gas into the fuel cell stack, and then between the voltage values of two fuel cells of the plurality of fuel cells measured by the voltage measuring unit. A fuel cell system comprising scavenging gas supply control means for stopping the operation of the scavenging gas supply unit on condition that the voltage difference between fuel cells, which is the difference, is a predetermined value or more. The fuel cell system according to claim 1, wherein
The voltage measuring means measures the voltage value of all the fuel cells of the fuel cell stack,
The control unit selects a minimum voltage value and a maximum voltage value from the measured voltage value, and obtains a difference between the minimum voltage value and the maximum voltage value as a voltage difference between fuel cells.

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