JP5625495B2 - Fuel cell system and fuel cell control method - Google Patents

Description

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

  A fuel cell is a device that generally obtains electric energy using hydrogen and oxygen as fuel. Since this fuel cell is excellent in terms of environment and can realize high energy efficiency, it has been widely developed as a future energy supply system.

  In particular, since the polymer electrolyte fuel cell operates at a relatively low temperature among various types of fuel cells, it has a good startability. For this reason, research has been actively conducted for practical application in various fields. In solid polymer fuel cells, when the water content of the solid polymer electrolyte decreases, the ionic conductivity of the solid polymer electrolyte decreases. Therefore, Patent Document 1 discloses a technique for detecting the drying of the electrolyte membrane based on the amount of decrease in the pressure loss of the fuel gas and increasing the humidification amount of the humidification module.

JP 2009-009891 A

  However, in the technique of Patent Document 1, since a humidification module must be provided, the size of the apparatus is increased.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a fuel cell system and a fuel cell control method capable of suppressing drying of the electrolyte membrane while avoiding an increase in size of the apparatus. To do.

The fuel cell system according to the present invention includes a fuel cell stack in which a plurality of fuel cells are stacked, a flow rate variation obtaining means for obtaining a flow rate variation of a reaction gas between the plurality of fuel cells, and the fuel cell stack. In the case where the relative humidity of the off-gas of at least one of the reaction gases of the above is less than 100% from the state of exceeding 100%, the fuel of the fuel cell stack is obtained when the flow rate variation obtained by the flow rate variation obtaining unit exceeds a predetermined value. And a circulating water amount control means for increasing the amount of water contained in the circulating fuel gas circulating from the gas outlet to the fuel gas inlet. In the fuel cell system according to the present invention, the amount of circulating water can be controlled when the flow rate variation becomes large, so that drying of the electrolyte membrane can be suppressed. Moreover, since a humidification module becomes unnecessary, the enlargement of the apparatus can be avoided.

Before Symbol rate variation obtaining means, when exceeding a predetermined value operating temperature of the fuel cell stack is increased, the flow rate variation of the reaction gases may be determined to exceed a predetermined value. Before Symbol rate variation obtaining means, when the decrease rate for the time of the pressure loss of the fuel cell stack exceeds a predetermined value, the flow rate variation of the reaction gases may be determined to exceed a predetermined value.

The circulating water amount control means may increase the circulating water amount by increasing the fuel gas circulation amount of the fuel off-gas to the fuel gas inlet. The circulating water amount control means may increase the amount of water taken away from the fuel cell stack by the fuel gas by reducing the fuel gas pressure in the fuel cell stack. The circulating water amount control means may increase the amount of water contained in and discharged from the fuel gas by increasing the oxidant gas pressure in the fuel cell stack.

  The reaction gas in the fuel battery cell may form a counter flow in which an oxidant gas and a fuel gas flow opposite to each other. The fuel cell may be a polymer electrolyte fuel cell.

The fuel cell control method according to the present invention includes a flow rate variation acquisition step of acquiring a flow rate variation of a reaction gas between the plurality of fuel cells in a fuel cell stack in which a plurality of fuel cells are stacked, and the fuel cell. in the case where at least one of the relative humidity of the off-gas of the off-gas of the reaction gas in the stack is below 100% state of more than 100%, when the flow rate variations are Oite acquired the flow variation obtaining step exceeds a predetermined value, And a circulating water amount control step for increasing the amount of water contained in the circulating fuel gas circulating from the fuel gas outlet to the fuel gas inlet of the fuel cell stack. In the control method for the fuel cell according to the present invention, the amount of circulating water can be controlled when the flow rate variation becomes large, so that drying of the electrolyte membrane can be suppressed. Moreover, since a humidification module becomes unnecessary, the enlargement of the apparatus can be avoided.

Prior Symbol rate variation acquisition step, if exceeding a predetermined value operating temperature of the fuel cell stack is increased, the flow rate variation of the reaction gases may be determined to exceed a predetermined value. Prior Symbol rate variation acquisition step, if the reduction rate with respect to time of the pressure loss of the fuel cell stack exceeds a predetermined value, the flow rate variation of the reaction gases may be determined to exceed a predetermined value.

In the circulating water amount control step , the circulating water amount may be increased by increasing the fuel gas circulation amount of the fuel off gas to the fuel gas inlet. In the circulating water amount control step, the amount of water taken away from the fuel cell stack by the fuel gas may be increased by reducing the fuel gas pressure in the fuel cell stack. In the circulating water amount control step, the amount of water contained and discharged in the fuel gas may be increased by increasing the oxidant gas pressure in the fuel cell stack.

  The reaction gas in the fuel battery cell may form a counter flow in which an oxidant gas and a fuel gas flow opposite to each other. The fuel cell may be a polymer electrolyte fuel cell.

  According to the present invention, it is possible to provide a fuel cell system and a fuel cell control method capable of suppressing the drying of the electrolyte membrane while avoiding the enlargement of the apparatus.

1 is a diagram for explaining a fuel cell system according to Embodiment 1. FIG. The flow direction of the fuel gas and the oxidant gas in the membrane-electrode assembly of each fuel cell will be described. (A) is a figure which shows the relationship between the operating temperature of a fuel cell, and a pressure loss, (b) is the figure which showed the flow direction of the reaction gas in the membrane-electrode assembly side view. (A) shows the cell voltage and cell resistance of the fuel cell during normal temperature operation, and (b) shows the cell voltage and cell resistance of the fuel cell during high temperature operation. It is a figure which shows the relationship between operating temperature, an anode stoichiometric ratio, and the amount of circulating water. It is a figure which shows the relationship between a cathode stoichiometric ratio and the cell voltage of a fuel cell. It is a figure which shows the relationship between the operating temperature of a fuel cell stack, and the pressure loss of the reaction gas flow path of each fuel cell. It is a figure for demonstrating the method (1). It is a figure explaining other examples of method (1). It is a figure for demonstrating a method (A). It is a figure for demonstrating the effect in the case of controlling the supply amount of circulating water. It is a figure which shows the example of a flowchart.

  Hereinafter, the best mode for carrying out the present invention will be described.

  FIG. 1 is a diagram for explaining a fuel cell system 100 according to the first embodiment. FIG. 1A is a block diagram showing the overall configuration of the fuel cell system 100. FIG.1 (b) is typical sectional drawing of the fuel battery cell 11 mentioned later. As shown in FIG. 1A, the fuel cell system 100 includes a fuel cell stack 10, a fuel gas supply means 20, a three-way valve 30, a pump 31, an oxidant gas supply means 40, a refrigerant circulation means 50, a control means 60, and the like. Is provided. The fuel cell stack 10 includes a pressure loss sensor 12, a humidity sensor 13, a resistance sensor 14, a temperature sensor 15, and a voltage sensor 16.

  The fuel cell stack 10 has a structure in which a plurality of fuel cells 11 are stacked. As shown in FIG. 1 (b), the fuel cell 11 has a structure in which the membrane-electrode assembly 110 is sandwiched between the separator 120 and the separator 130. In the membrane-electrode assembly 110, the anode catalyst layer 112 and the gas diffusion layer 113 are sequentially bonded to the separator 120 side of the electrolyte membrane 111, and the cathode catalyst layer 114 and the gas diffusion layer 115 are sequentially bonded to the separator 130 side of the electrolyte membrane 111. Has a structured. The electrolyte membrane 111 is made of a solid polymer electrolyte such as a perfluorosulfonic acid type polymer having proton conductivity.

  The anode catalyst layer 112 is composed of a conductive material supporting a catalyst, a proton conductive electrolyte, and the like. The catalyst in the anode catalyst layer 112 is a catalyst for promoting protonation of hydrogen. For example, the anode catalyst layer 112 includes platinum-supported carbon, perfluorosulfonic acid type polymer, and the like. The gas diffusion layer 113 is made of a conductive material having gas permeability such as carbon paper or carbon cloth.

  The cathode catalyst layer 114 is composed of a conductive material supporting a catalyst, a proton conductive electrolyte, and the like. The cathode catalyst layer 114 is a catalyst for promoting the reaction between protons and oxygen. For example, the cathode catalyst layer 114 includes platinum-supported carbon, perfluorosulfonic acid type polymer, and the like. The gas diffusion layer 115 is made of a conductive material having gas permeability such as carbon paper or carbon cloth.

  Separator 120,130 is comprised from electroconductive materials, such as stainless steel. On the surface of the separator 120 on the membrane-electrode assembly 110 side, a fuel gas flow path 121 for flowing the fuel gas is formed. On the surface of the separator 120 on the side opposite to the membrane-electrode assembly 110, a refrigerant flow path 122 for allowing the refrigerant to flow is formed. On the surface of the separator 130 on the membrane-electrode assembly 110 side, an oxidant gas flow path 131 is formed for the oxidant gas to flow. On the surface of the separator 130 on the side opposite to the membrane-electrode assembly 110, a refrigerant flow path 132 for allowing the refrigerant to flow is formed. The fuel gas flow path 121, the oxidant gas flow path 131, and the refrigerant flow paths 122 and 132 are, for example, concave portions formed on the surface of the separator. Further, the fuel gas channel 121 and the oxidant gas channel 131 may be collectively referred to as a reaction gas channel.

  The fuel gas supply means 20 is a device that supplies a fuel gas containing hydrogen to the fuel gas passage 121 via the fuel gas inlet of the fuel cell stack 10. The fuel gas supply unit 20 includes, for example, a hydrogen cylinder, a reformer, and the like. The fuel gas supply means 20 includes a flow rate adjustment valve and adjusts the amount of fuel gas supplied to the fuel cell stack 10.

  The fuel gas outlet of the fuel cell stack 10 is connected to the inlet of the three-way valve 30 via a pipe. One outlet of the three-way valve 30 communicates with the outside air. The other outlet of the three-way valve 30 is connected to a fuel gas inlet of the fuel cell stack 10 via a pump 31. When the other outlet of the three-way valve 30 is open, a circulation path through which fuel gas (hereinafter referred to as fuel off-gas) that has not been used for power generation in the fuel cell stack 10 is introduced into the fuel gas inlet by the pump 31. Is formed. Therefore, the amount of fuel offgas introduced into the fuel gas inlet and the fuel offgas pressure can be adjusted using the pump 31 and the three-way valve 30.

  The oxidant gas supply means 40 is a device that supplies an oxidant gas containing oxygen to the oxidant gas flow path 131 via the oxidant gas inlet of the fuel cell stack 10. The oxidant gas supply means 40 includes an air pump or the like. The oxidant gas supply means 40 includes a flow rate adjustment valve and adjusts the amount of oxidant gas supplied to the fuel cell stack 10 (oxidant gas pressure). The oxidant gas outlet of the fuel cell stack 10 communicates with the outside air. As a result, the oxidant gas that has not been used for power generation in the fuel cell stack 10 (hereinafter referred to as oxidant off-gas) is discharged to the outside air.

  The refrigerant circulation means 50 is a device that supplies refrigerant to the refrigerant flow paths 122 and 132 via the refrigerant inlet of the fuel cell stack 10. The refrigerant circulation means 50 includes a refrigerant circulation pump or the like. The refrigerant circulating means 50 circulates the refrigerant discharged from the refrigerant outlet of the fuel cell stack 10 to the refrigerant inlet.

  The pressure loss sensor 12 is a sensor that detects the difference between the pressure of the oxidant gas inlet and the pressure of the oxidant gas outlet of the fuel cell stack 10 and / or the difference between the pressure of the fuel gas inlet and the pressure of the fuel gas outlet. Yes, the detection result is given to the control means 60. Since the inside of the reaction gas flow path inside the fuel cell stack 10 is a laminar flow, the pressure loss (hereinafter also referred to as pressure loss) may be measured as a linear function of the reaction gas flow rate.

  The humidity sensor 13 is a sensor that detects the relative humidity of the oxidant off-gas and / or fuel off-gas in the fuel cell stack 10, and gives the detection result to the control means 60. Hereinafter, the oxidant offgas and the fuel offgas may be collectively referred to as a reaction offgas. In the present embodiment, the humidity sensor 13 detects the relative humidity of the oxidant off-gas as an example. The resistance sensor 14 is a sensor that detects an electrical resistance (cell resistance) of at least one fuel cell 11 of the fuel cell stack 10, and gives the detection result to the control means 60.

  The temperature sensor 15 is a sensor that detects the operating temperature of the fuel cell stack 10. In the present embodiment, the temperature sensor 15 indirectly detects the operating temperature of the fuel cell stack 10 by detecting the temperature of the refrigerant discharged from the fuel cell stack 10, and gives the detection result to the control means 60. . The voltage sensor 16 is a sensor that detects a power generation voltage (cell voltage) of at least one fuel cell 11 of the fuel cell stack 10, and gives the detection result to the control means 60.

  The control means 60 comprises a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory) and the like. The control means 60 controls each part of the fuel cell system 100 according to the detection results of the pressure loss sensor 12, the humidity sensor 13, the resistance sensor 14, the temperature sensor 15, and the voltage sensor 16.

  Next, the operation of the fuel cell system 100 during power generation will be described with reference to FIGS. 1 (a) and 1 (b). First, the control means 60 controls the fuel gas supply means 20 so that the fuel gas is supplied to the fuel gas flow path 121 and the oxidant gas so that the oxidant gas is supplied to the oxidant gas flow path 131. The supply means 40 is controlled. Thereby, power generation is started.

  The fuel gas passes through the gas diffusion layer 113 and reaches the anode catalyst layer 112. Hydrogen contained in the fuel gas is dissociated into protons and electrons via the catalyst of the anode catalyst layer 112. The protons conduct through the electrolyte membrane 111 and reach the cathode catalyst layer 114. The oxidant gas passes through the gas diffusion layer 115 and reaches the cathode catalyst layer 114. In the cathode catalyst layer 114, protons and oxygen react via the catalyst. Thereby, electric power is generated and water (hereinafter also referred to as power generation generated water) is generated. The generated water is discharged through the oxidant gas channel 131 and / or the fuel gas channel 121.

  Further, the control means 60 controls the refrigerant circulation means 50 so that the refrigerant is supplied to the refrigerant flow paths 122 and 132 at a predetermined timing. Thereby, the operating temperature of the fuel cell stack 10 is adjusted to a predetermined temperature. Further, the control means 60 controls the three-way valve 30 to control the amount of fuel off-gas discharged to the outside air and the amount of circulation to the fuel cell stack 10. By discharging the fuel off-gas to the outside air, it is possible to discharge nitrogen gas or the like remaining in the fuel cell stack 10. In addition, by circulating the fuel off gas to the fuel cell stack 10, the power generation water contained in the fuel off gas can be introduced into the fuel cell stack 10.

  FIG. 2A and FIG. 2B show the flow directions of the fuel gas and the oxidant gas in the membrane-electrode assembly 110 of each fuel cell 11. FIG. 2A is a diagram showing the flow direction of the reaction gas in the side view of the membrane-electrode assembly 110. FIG. 2B is a diagram showing the flow direction of the reaction gas in the plan view of the membrane-electrode assembly 110. In FIG. 2 (b), the fuel gas side surface of the membrane-electrode assembly 110 is depicted. As shown in FIGS. 2A and 2B, the fuel gas and the oxidant gas flow in opposite directions with the membrane-electrode assembly 110 interposed therebetween. Therefore, the fuel gas and the oxidant gas form a counter flow.

  Next, the relationship between the operating temperature of the fuel cell 11 and the pressure loss in the fuel gas channel 121 and the oxidant gas channel 131 of the fuel cell 11 will be described. FIG. 3A is a diagram showing the relationship between the operating temperature of the fuel cell 11 and the pressure loss. In FIG. 3A, the horizontal axis represents the operating temperature, and the vertical axis represents the pressure loss (anode pressure loss) in the fuel gas channel 121 and the pressure loss (cathode pressure loss) in the oxidant gas channel 131. In the example of FIG. 3 (a), the result when the operating temperature is gradually increased is shown. The relative humidity (outlet) at the outlet of the oxidant gas flow path 131 on the low temperature side with the operating temperature near 75 ° C. is shown. RH) is 100% or more, and less than 100% on the high temperature side.

  At the operating temperature at which the outlet RH is 100% or more, the pressure loss is high on both the anode side and the cathode side. This is considered to be because the power generation generated water stays inside the membrane-electrode assembly 110 with power generation. On the other hand, when the operating temperature rises and the outlet RH becomes less than 100%, the pressure loss is reduced on both the anode side and the cathode side. This is presumably because the water in the fuel gas channel 121 and the oxidant gas channel 131 decreases as the operating temperature rises as the operation temperature evaporates.

  Next, the evaporation location (dry location) in the membrane-electrode assembly 110 will be described. FIG. 3B is a diagram showing the flow direction of the reaction gas in the side view of the membrane-electrode assembly 110. As shown in FIG. 3 (b), if each reaction gas is not particularly humidified, the generated water in the membrane-electrode assembly 110 is likely to evaporate in the vicinity of the inlet of each reaction gas flow path, and is easily dried. In particular, when air is used as the oxidant gas, the flow rate of the oxidant gas increases, so that the region near the inlet of the oxidant gas channel 131 is most easily dried. In this case, the electric resistance of the electrolyte membrane 111 is increased at the dried portion, resulting in power generation failure. As a result, the electrode effective area in the electrolyte membrane 111 decreases. By repeating this process, the drying proceeds in order from the vicinity of the inlet of the reaction gas channel. Therefore, it can be seen that power generation failure can be suppressed if the vicinity of the inlet of the reaction gas channel can be humidified.

  Problems associated with the increase in operating temperature will be further described. FIG. 4A shows the cell voltage and cell resistance of the fuel cell 11 during operation at the normal temperature. FIG. 4B shows the cell voltage and cell resistance of the fuel cell 11 during high temperature operation. 4A and 4B, the horizontal axis indicates the stoichiometric ratio of the oxidant gas, and the vertical axis indicates the cell voltage and cell resistance of the fuel cell 11.

  As shown in FIG. 4A and FIG. 4B, when the stoichiometric ratio of the oxidant gas is excessively small, the contribution of the concentration overvoltage is large, so that the cell voltage is lowered. When the stoichiometric ratio of the oxidant gas is excessively large, the electric resistance of the electrolyte membrane 111 increases with drying, and the contribution of resistance overvoltage increases, so that the cell voltage decreases. If the stoichiometric ratio of the oxidant gas is within a preferable range, the contribution of the concentration overvoltage and the resistance overvoltage becomes small, so that the electrolyte membrane 111 maintains a low electrical resistance and the cell voltage becomes high. A region where such a stoichiometric ratio of the oxidant gas is preferable is referred to as a stable operation region.

  However, when the operating temperature changes, the width of the stable operation region changes. As shown in FIG. 4A, during normal operation, a high cell voltage and low electrical resistance are maintained even when the stoichiometric ratio of the oxidant gas is high. Therefore, the stable operation region is wide during normal operation. On the other hand, as shown in FIG. 4B, during the high temperature operation, the electrolyte membrane 111 is easily dried, so that the stable operation region is narrowed.

  Next, the operating temperature and anode stoichiometry in the operation of the anode side discharged water amount (the discharged water amount from the fuel gas flow channel 121) = the anode side supplied water amount (the supplied water amount to the fuel gas flow channel 121) = the circulation equivalent water amount. The relationship between the ratio and the amount of supplied water will be described. FIG. 5A is a diagram showing the relationship among the operating temperature, the anode stoichiometric ratio, and the amount of supplied water. In FIG. 5A, the horizontal axis represents the anode stoichiometric ratio, and the vertical axis represents the amount of water supplied on the anode side (mol / min / 4 cell).

  As shown in FIG. 5A, when the outlet RH is 100% or more, the discharged water amount = the supplied water amount = 0 when the anode stoichiometric ratio is “1.0”. As the outlet RH decreases to the 100% side, the slope of the supplied water amount with respect to the anode stoichiometric ratio becomes smaller. This means that the amount of discharged water is reduced when the anode stoichiometric ratio is not large.

  If the outlet RH is less than 100%, the power generation water is insufficient unless the anode stoichiometric ratio exceeds “1.0”. Thereby, in order for the amount of discharged water to be positive, the anode stoichiometric ratio needs to exceed “1.0”. This tendency becomes more prominent as the operating temperature increases. In this case, if the anode stoichiometric ratio is not sufficiently higher than “1.0”, the amount of power generation generated water near the outlet of the fuel gas channel 121 is insufficient. As a result, as shown in FIG. 5B, drying proceeds near the outlet of the fuel gas channel 121 (near the inlet of the oxidant gas channel 131).

  On the other hand, even when the outlet RH is less than 100%, the drying near the outlet of the fuel gas channel 121 (near the inlet of the oxidant gas channel 131) is suppressed by increasing the amount of supplied water. be able to. Specifically, as shown in FIG. 5C, the anode stoichiometric ratio is increased, and the fuel off-gas discharged from the outlet of the fuel gas passage 121 is introduced into the inlet of the fuel gas passage 121 to circulate the circulation path. Form. In this case, since water vapor or liquid water reaches the vicinity of the outlet of the fuel gas channel 121, drying near the outlet of the fuel gas channel 121 (near the inlet of the oxidant gas channel 131) is suppressed.

  Next, the cathode stoichiometric ratio will be described. FIG. 6 is a diagram showing the relationship between the cathode stoichiometric ratio and the cell voltage of the fuel battery cell 11. In FIG. 6, the horizontal axis indicates the cathode stoichiometric ratio, and the vertical axis indicates the cell voltage. As shown in FIG. 6, when the high temperature operation is performed in the state shown in FIG. 5B where the amount of circulating water is small, the cathode stoichiometric ratio is increased and the cell voltage is greatly reduced. This is because the electric resistance of the electrolyte membrane 111 increases rapidly. Therefore, when the high temperature operation is performed in the state of FIG. 5C where the circulating water amount is sufficient, an increase in the electric resistance of the electrolyte membrane 111 is suppressed. In this case, the cell voltage peak shifts to the high cathode stoichiometric ratio side.

  Next, the relationship between the operating temperature of the fuel cell stack 10 and the pressure loss of the reaction gas flow path of each fuel cell 11 will be described. FIG. 7 is a diagram showing the relationship between the operating temperature of the fuel cell stack 10 and the pressure loss of the reaction gas flow path of each fuel cell 11. In FIG. 7, the horizontal axis indicates the elapsed time, and the vertical axis indicates the operating temperature of the fuel cell stack 10 and (average pressure loss−minimum pressure loss). FIG. 7 shows an example in which the operating temperature increases with time.

  Here, the average pressure loss is an average value of the pressure loss of each fuel cell 11 included in the fuel cell stack 10. The minimum pressure loss is the minimum value of the pressure loss of each fuel cell 11 included in the fuel cell stack 10. Here, the pressure loss may be the pressure loss of the oxidant gas passage 131, the pressure loss of the fuel gas passage 121, or the pressure loss of both.

  As shown in FIG. 7, when the operating temperature is low, the power generation generated water stays in the reaction gas flow path, and the pressure loss increases in any fuel cell 11. Thereby, (average pressure loss−minimum pressure loss) maintains a low value. When the operating temperature rises and the outlet RH falls below 100%, evaporation of accumulated water starts in any of the fuel cells 11. In this case, the accumulated water does not start to evaporate in all the fuel cells 11 at the same time, so the pressure loss of the fuel cells 11 where the accumulated water begins to evaporate is significantly reduced. Thereby, (average pressure loss−minimum pressure loss) rapidly increases. Thereafter, when stable power generation continues, the pressure loss in any fuel cell 11 decreases with time, and (average pressure loss−minimum pressure loss) also decreases.

  Therefore, in this embodiment, when the operating temperature rises with the power generation of the fuel cell stack 10, the variation in the pressure loss of each fuel cell 11 is estimated. When the variation in pressure loss exceeds a predetermined value, the supply amount of circulating water is increased. Thereby, in each fuel cell 11, drying of the electrolyte membrane 111 in the vicinity of the outlet of the fuel gas channel 121 (near the inlet of the oxidant gas channel 131) can be suppressed. In this case, since an apparatus for humidifying the reaction gas is not required, an increase in size of the fuel cell system 100 can be avoided.

  In the fuel cell stack 10, the reaction gas is supplied from the common manifold to the reaction gas channel inlet of each fuel cell 11, and the reaction off gas is discharged from the reaction gas channel outlet to the common manifold. In such a configuration, even if the pressure loss is different in each fuel battery cell 11, the reaction gas flow rate changes for each fuel battery cell 11, and thus the pressure loss value in each fuel battery cell 11 is the same. Therefore, the “variation in pressure loss” of each fuel cell 11 is synonymous with the variation in the flow rate of the reaction gas.

  The variation in the flow rate of the reaction gas in each fuel cell 11 can be detected using a flow meter or the like, but an alternative method may be used for cost reduction. For example, (1) When the evaporation of stagnant water in each fuel cell 11 is active or expected to increase, (2) When the relative humidity of the reaction off-gas becomes a predetermined value (for example, 100%) or less (3) When the reduction rate of the pressure loss of the entire fuel cell stack 10 becomes high, it can be determined that the variation in the flow rate of the reaction gas in each fuel cell 11 exceeds a predetermined value. In addition, when any of the conditions (1) to (3) is satisfied, it may be determined that the flow rate variation exceeds a predetermined value, and when two or more conditions (1) to (3) are satisfied. It may be determined that the flow rate variation exceeds a predetermined value.

  FIG. 8 is a diagram for explaining the method (1). In FIG. 8, the horizontal axis indicates the operating temperature of the fuel battery cell 11, and the vertical axis indicates the amount of evaporation from the fuel battery cell 11. As shown in FIG. 8, below the low operating temperature, the amount of evaporation from the fuel cell 11 is small. Thereby, in the reaction gas flow path of the fuel cell 11, the power generation generated water stays. When the amount of evaporation from the fuel battery cell 11 increases as the operating temperature rises and exceeds a predetermined temperature, the fuel battery cell 11 begins to dry. By using this predetermined temperature as a threshold value, it can be expected that the accumulated water in the fuel battery cell 11 is vigorously or actively evaporated. This predetermined temperature is determined according to the supply amount of the reaction gas, the reaction gas pressure, and the like. The operating temperature can be detected using the temperature sensor 15 of FIG.

FIG. 9 is a diagram for explaining another example of the method (1). In the fuel cell stack 10, a low-pressure loss fuel cell 11 (hereinafter referred to as a sensor cell) is examined in advance. In the sensor cell, since the amount of reaction gas flowing in increases, it is easy to dry and the cell resistance (mΩ · cm ² ) is likely to increase. Therefore, by detecting the cell resistance of the sensor cell (hereinafter referred to as R sensor), it can be expected that the evaporation of the accumulated water in each fuel cell 11 is or will be increased.

Specifically, when the R sensor exceeds a specified value, it can be expected that the accumulated water in each fuel battery cell 11 evaporates or increases. An example of the specified value in this case is about 120 mΩ · cm ² . Further, the relationship between the R sensor and the resistance of the entire fuel cell stack 10 (hereinafter referred to as R stack) may be used. For example, even if {(R sensor)-(R stack)} / (R stack)> specified value, even if it is expected that the accumulated water in each fuel cell 11 evaporates or increases. Good. An example of the specified value in this case is “1.6”, for example. Further, when (R sensor) / (R stack)> specified value, it may be expected that the accumulated water in each fuel cell 11 evaporates or increases. An example of the specified value in this case is “1.8”, for example. The R sensor and the R stack can be detected by using the resistance sensor 14 of FIG.

  Further, by detecting the cell voltage of the sensor cell (hereinafter referred to as a V sensor), it can be expected that the accumulated water in each fuel cell 11 evaporates or increases. Since the pressure loss in the sensor cell is low, the reaction gas flow rate in the sensor cell increases. Thereby, the cell voltage of the sensor cell becomes high during low temperature operation. However, during high temperature operation, if the reaction gas flow rate is high, drying proceeds, so that the cell voltage of the sensor cell decreases. Therefore, when the V sensor falls below the specified value, it can be expected that the accumulated water in each fuel cell 11 evaporates or increases. Further, when the V sensor falls below the average cell voltage of each fuel cell 11, it can be expected that the accumulated water in each fuel cell 11 evaporates or increases.

  Next, the method (2) will be described. As the reaction off gas, either a fuel off gas or an oxidant off gas may be used. Moreover, when the relative humidity of both off-gas is less than 100%, it can be determined that the variation in the flow rate of the reaction gas in each fuel cell 11 exceeds a predetermined value. The relative humidity of the reaction off gas can be detected using the humidity sensor 13.

  Next, the method (3) will be described. As described above, the accumulated water decreases as the amount of evaporation from the fuel cell 11 increases, so the pressure loss of the fuel cell stack 10 decreases. Since the rate of decrease in pressure loss increases immediately after the start of evaporation, when the rate of decrease in pressure loss of the entire fuel cell stack 10 exceeds a specified value, the flow rate variation of the reaction gas in each fuel cell 11 is predetermined. It can be determined that the value has been exceeded.

  Then, the method to increase the supply amount of circulating water is demonstrated. Specifically, the supply of circulating water is increased by techniques such as (A) increasing the amount of fuel off-gas circulation, (B) reducing the fuel gas pressure, and (C) increasing the oxidant gas pressure. Can be made. Note that any one of the methods (A) to (C) may be used, and two or more methods (A) to (C) may be used simultaneously.

  FIG. 10 is a diagram for explaining the method (A). In FIG. 10, when the horizontal axis represents the fuel gas outlet of the fuel cell stack 10 when pure hydrogen gas or a mixed gas of nitrogen and hydrogen is introduced into the fuel gas flow path 121 in the fuel cell stack 10 in a state where power generation is stopped. The discharge amount of the discharged gas is shown, and the vertical axis shows the dew point (° C.) of the discharged gas.

  As shown in FIG. 10, it was found that the amount of water vapor discharged is determined by the amount of gas discharged from the fuel gas outlet of the fuel cell stack 10 regardless of whether pure hydrogen or a mixed gas is used. Therefore, the amount of circulating water supplied to the fuel gas channel 121 of the fuel cell stack 10 can be increased by increasing the circulation amount of the fuel off gas.

  Next, the method (B) will be described. Here, the power generation water generated by the power generation is mainly discharged to the outside through the oxidant gas flow path 131, but also moves to the fuel gas flow path 121 side through the electrolyte membrane 111. When the fuel gas pressure supplied to the fuel gas channel 121 of the fuel cell stack 10 decreases, water easily evaporates on the anode side, so that the amount of power generation generated water that moves the electrolyte membrane 111 from the cathode side to the anode side increases. . Thereby, the supply amount of circulating water can be increased.

  Next, the method (C) will be described. If the oxidant gas pressure supplied to the oxidant gas flow path 131 of the fuel cell stack 10 increases, the evaporation of water on the cathode side is suppressed, so that power generation moves the electrolyte membrane 111 from the cathode side to the anode side. The amount of water produced increases. Thereby, the supply amount of circulating water can be increased.

  Fig.11 (a) and FIG.11 (b) are the figures for demonstrating the effect in the case of controlling the supply amount of circulating water. A region surrounded by a dotted line in FIGS. 11A and 11B is the above-described stable operation region. In the example of FIG. 11A, when the operating temperature exceeds 77 ° C., the circulating water inside the fuel cell 11 is insufficient regardless of the operating temperature. However, the operation in the stable operation region can be performed by increasing the discharge amount (= circulation amount) on the anode side by the methods (A) to (C). From the above, it is possible to easily realize the operation in the stable operation region by controlling the discharge amount on the anode side regardless of the operation temperature.

  In addition, if the staying water evaporates uniformly in each fuel battery cell 11, the flow volume variation between each fuel battery cell 11 will become small. In this case, the reaction gas flow rate in the specific fuel battery cell 11 is suppressed from protruding. Therefore, if the flow rate variation among the fuel cells 11 is reduced, it is not necessary to increase the supply amount of the circulating water. For example, when the rate of decrease in the pressure loss of the entire fuel cell stack 10 is equal to or less than a specified value, it may be determined that the variation in the flow rate of the reaction gas in each fuel cell 11 has decreased.

  Hereinafter, examples of flowcharts of the above-described control are shown in FIGS. 12A shows the control of the method (1), FIG. 12B shows the control of the method (2), and FIG. 12C shows the control of the method (3). 12A to 12C are executed at a predetermined cycle.

  As shown in FIG. 12 (a), in the process of increasing the operating temperature of the fuel cell stack 10, the control means 60 is or is expected to evaporate stagnant water in each fuel cell 11. It is determined whether or not (step S1). As described above, the determination can be made based on the detection result of the resistance sensor 14, the temperature sensor 15, or the voltage sensor 16. When it determines with "Yes" in step S1, the control means 60 increases the amount of circulating water (step S2). When it is determined “No” in step S1 and after execution of step S2, the control unit 60 ends the execution of the flowchart. As described above, the amount of circulating water can be increased by controlling at least one of the fuel gas supply means 20, the three-way valve 30, and the oxidant gas supply means 40.

  As shown in FIG. 12B, the control means 60 determines whether or not the off-gas relative humidity of the fuel cell stack 10 falls below 100% in the process of increasing the operating temperature of the fuel cell stack 10 (step S11). . As described above, the determination can be made based on the detection result of the humidity sensor 13. When it determines with "Yes" in step S11, the control means 60 increases the amount of circulating water (step S12). When it is determined as “No” in Step S11 and after execution of Step S12, the control unit 60 ends the execution of the flowchart.

  As shown in FIG. 12C, the control means 60 determines whether or not the rate of decrease in the pressure loss of the fuel cell stack 10 exceeds a specified value in the process of increasing the operating temperature of the fuel cell stack 10 (step S21). ). As described above, the determination can be made based on the detection result of the pressure loss sensor 12. When it determines with "Yes" in step S21, the control means 60 increases the amount of circulating water (step S22). When it is determined as “No” in Step S21 and after execution of Step S22, the control unit 60 ends the execution of the flowchart.

  In addition, although the example of the counter flow has been described in the above embodiment, it is not limited thereto. For example, even if the fuel gas and the oxidant gas flow in the same direction, if the conditions for evaporating the accumulated water are satisfied and the reaction gas flow rate varies, a region that is easily dried appears in the electrolyte membrane 111. Even in this case, local drying of the electrolyte membrane 111 can be suppressed by increasing the supply amount of the circulating water.

DESCRIPTION OF SYMBOLS 10 Fuel cell stack 11 Fuel cell 12 Pressure loss sensor 13 Humidity sensor 14 Resistance sensor 15 Temperature sensor 16 Voltage sensor 20 Fuel gas supply means 30 Three-way valve 40 Oxidant gas supply means 50 Refrigerant circulation means 60 Control means 100 Fuel cell system 110 Membrane -Electrode assembly 111 Electrolyte membrane 121 Fuel gas flow path 131 Oxidant gas flow path

Claims (16)

A fuel cell stack in which a plurality of fuel cells are stacked;
A flow rate variation obtaining means for obtaining a flow rate variation of the reaction gas between the plurality of fuel cells;
When the flow rate variation acquired by the flow rate variation acquisition means exceeds a predetermined value when the relative humidity of the off-gas of at least one of the reaction gases of the fuel cell stack is less than 100% from a state where it exceeds 100% , the fuel A fuel cell system comprising: a circulating water amount control means for increasing the amount of water contained in the circulating fuel gas circulating from the fuel gas outlet to the fuel gas inlet of the battery stack. 2. The fuel according to claim 1, wherein the flow rate variation obtaining unit determines that the flow rate variation of the reaction gas exceeds a predetermined value when an operating temperature of the fuel cell stack rises and exceeds a predetermined value. Battery system. The flow rate variation obtaining means, when the decrease rate for the time of the pressure loss of the fuel cell stack exceeds a predetermined value, according to claim 1, wherein the variation in the flow rate of the reaction gas and determines that exceeds a predetermined value Fuel cell system. The fuel cell system according to any one of claims 1 to 3, wherein the circulating water amount control means increases the circulating water amount by increasing the amount of fuel gas circulating to the fuel gas inlet of the fuel off gas. . The circulating water quantity control means, by reducing the fuel gas pressure in the fuel cell stack, the fuel gas in any one of claims 1 to 3, characterized in that increasing the amount of water carried away from the fuel cell stack The fuel cell system described. The circulating water quantity control means, by increasing the oxidant gas pressure in the fuel cell stack, any one of the preceding claims, characterized in that increasing the amount of moisture contained in the fuel gas discharged The fuel cell system described in 1. The fuel cell system according to any one of claims 1 to 6, wherein the reaction gas in the fuel cell forms a counter flow in which an oxidant gas and a fuel gas flow opposite to each other. The fuel cell system according to claim 1 , wherein the fuel cell is a polymer electrolyte fuel cell. In a fuel cell stack in which a plurality of fuel cells are stacked, a flow rate variation obtaining step for obtaining a flow rate variation of the reaction gas between the plurality of fuel cells, and
In the case below 100 percent state of at least the relative humidity of any of the off-gas is above 100% of the off-gas of the reaction gas in the fuel cell stack, the flow rate variations are Oite acquired the flow variation obtaining step exceeds a predetermined value And a circulating water amount control step for increasing the amount of water contained in the circulating fuel gas circulating from the fuel gas outlet to the fuel gas inlet of the fuel cell stack. 10. The fuel according to claim 9, wherein in the flow rate variation obtaining step, when the operating temperature of the fuel cell stack rises and exceeds a predetermined value, it is determined that the flow rate variation of the reaction gas exceeds a predetermined value. Battery control method. In the flow variation acquisition step, if the reduction rate with respect to time of the pressure loss of the fuel cell stack exceeds a predetermined value, according to claim 9, wherein the variation in the flow rate of the reaction gas and determines that exceeds a predetermined value Fuel cell control method. 12. The fuel cell according to claim 9, wherein in the circulating water amount control step , the circulating water amount is increased by increasing a fuel gas circulation amount of the fuel off-gas to the fuel gas inlet. Control method. In the circulating water quantity control step, by reducing the fuel gas pressure in the fuel cell stack, the fuel gas in any one of claims 9-12, characterized in that increasing the amount of water carried away from the fuel cell stack The fuel cell control method described. In the circulating water quantity control step, by increasing the oxidant gas pressure in the fuel cell stack, claim 9-12, characterized in that increasing the amount of moisture contained in the fuel gas discharged The control method of the fuel cell as described in any one of. The method for controlling a fuel cell according to any one of claims 9 to 14, wherein the reaction gas in the fuel cell forms a counter flow in which an oxidant gas and a fuel gas flow opposite to each other. The fuel cell control method according to claim 9, wherein the fuel cell is a polymer electrolyte fuel cell.

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