JP2005327596A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system accurately estimating an amount of impurities in an anode of a fuel cell, and exhausting the impurities without wasting fuel gas. <P>SOLUTION: The fuel cell system is provided with an oxidant gas channel and a fuel gas channel fitted to the fuel cell, and an exhaust valve fitted to the fuel gas channel. A first gas transmission amount estimation means estimates the amount of the impurity gas transmitted from the oxidant gas channel to the fuel gas channel through an electrolyte film of the fuel cell. The fuel cell system opens the exhaust valve when accumulated amount of the impurity gas estimated by the first gas transmission amount estimation means exceeds a given volume. This prevents the exhaust valve from wastefully being opened to exhaust fuel gas or the like. Further, since estimation of the impurity gas amount is carried out by a normal fuel cell system, the fuel cell system is made in a simple structure. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fuel cell system that estimates the amount of impurities in a fuel cell and controls gas supply / discharge.

  A fuel cell system applied to a fuel cell vehicle or the like is known. A fuel cell system is a fuel cell stack including an anode electrode (fuel electrode) to which hydrogen is supplied as a fuel gas and a cathode electrode (oxygen electrode) to which air is supplied, and a fuel such as hydrogen supplied to the anode electrode. The system is equipped with a tank for storing gas, a pump for returning exhaust gas containing unused fuel gas to the original anode, and the like. In the fuel cell stack, hydrogen and oxygen contained in air react to generate electric power.

  Here, it is known that in the fuel cell, as the reaction proceeds, nitrogen in the cathode gas (air), water produced by the reaction, etc. ooze out from the cathode electrode to the anode electrode side through the electrolyte membrane. As a result, the partial pressure of nitrogen or water vapor increases at the anode electrode, the concentration of the fuel gas (hydrogen) decreases, and the power generation capacity of the fuel cell decreases.

  For this reason, in general, a discharge valve provided in the discharge flow path of the anode electrode is opened to discharge a gas containing unused hydrogen and impurities. For example, in Patent Document 1, the impurity gas concentration is calculated from the ultrasonic propagation time of the mixed gas, the impurity gas abundance is calculated based on the impurity gas concentration, pressure, and temperature, and the impurity gas abundance is a predetermined amount. A technique of purging (opening the discharge valve) when the above is described is described. Patent Document 2 describes a technique in which the discharge valve is opened when the hydrogen concentration of the fuel gas is detected and below a predetermined concentration, and when the output of the fuel cell is reduced. Patent Document 3 describes a technique in which, when the pressure in the hydrogen circulation line becomes higher than a predetermined pressure, it is determined that the impurity gas has accumulated and the discharge valve is opened. In addition, Patent Document 4 discloses a technique for purging hydrogen using a decrease in cell voltage, a predetermined time, and a decrease in stack layer voltage as determination factors.

  However, the technique described in Patent Document 1 has a problem in that an ultrasonic transmitter / receiver is required and costs are high. Further, in the techniques described in Patent Documents 2 to 4, there is a problem in that unused hydrogen is discharged unnecessarily because the impurity concentration is not estimated in consideration of the current situation in the anode electrode. Therefore, it led to a decrease in fuel consumption.

JP 2003-317752 A JP 2003-77506 A JP 2000-58092 A Japanese Patent Laid-Open No. 2002-246045

  The present invention has been made to solve such problems, and the object of the present invention is to accurately estimate the amount of impurities in the anode electrode of a fuel cell without exhausting fuel gas wastefully. The object is to provide a fuel cell system capable of efficiently discharging impurities.

  In one aspect of the present invention, a fuel cell system includes an oxidant gas passage and a fuel gas passage provided in a fuel cell, and the fuel gas from the oxidant gas passage per unit time via the electrolyte of the fuel cell. A first gas permeation amount estimating means for estimating the amount of impurity gas permeating through the passage; and the fuel gas when an amount obtained by integrating the impurity gas amounts estimated by the first gas permeation amount estimation means is a predetermined amount or more. Control means for adjusting the amount of fuel gas in the passage.

  The fuel cell system is mounted on a fuel cell vehicle or the like. The fuel cell system has an oxidant gas passage and a fuel gas passage provided in the fuel cell. Furthermore, the fuel cell system includes first gas permeation amount estimation means for estimating the amount of impurity gas permeating from the oxidant gas passage per unit time through the fuel cell electrolyte (for example, electrolyte membrane) to the fuel gas passage. Have. The fuel cell system adjusts the amount of fuel gas in the fuel gas passage when the amount obtained by integrating the impurity gas amounts estimated by the first gas permeation amount estimating means is a predetermined amount or more. That is, if there are more than a predetermined amount of impurities in the fuel cell, stable power generation cannot be performed, and the amount of fuel gas in the fuel gas passage is increased. Thereby, the fall of power generation efficiency can be prevented. In addition, since the above estimation of the amount of impurity gas can use an apparatus included in a normal fuel cell system, the fuel cell system can be simplified.

  One aspect of the above fuel cell system includes a supply hydrogen amount detecting means for detecting the amount of hydrogen supplied to the fuel gas passage per unit time under a constant pressure, and hydrogen consumed by the fuel cell per unit time. And a second gas permeation amount estimating means for estimating a gas permeation amount permeating from the fuel gas passage through the fuel cell electrolyte to the oxidant gas passage per unit time. The first gas permeation amount estimation means includes a hydrogen amount detected by the hydrogen consumption amount detection means and a second gas permeation amount from the hydrogen amount detected by the supply hydrogen amount detection means. The value obtained by subtracting the gas permeation amount estimated by the estimation means is estimated as the amount of impurity gas permeating from the oxidant gas passage through the fuel cell electrolyte to the fuel gas passage per unit time.

  In this aspect, the fuel cell system transmits the amount of hydrogen supplied to the fuel gas passage at a constant pressure, the amount of hydrogen consumed by the fuel cell, and the oxidant gas passage from the fuel gas passage through the electrolyte of the fuel cell. The amount of impurity gas is estimated based on the amount of gas (fuel gas etc.) to be performed. The estimation of the amount of permeated fuel gas, that is, the amount of permeated hydrogen, has higher estimation accuracy than directly estimating the amount of permeated impurity gas, that is, the amount of permeated nitrogen. This is because the amount of nitrogen permeating from the oxidant gas passage to the fuel gas passage is smaller than the amount of hydrogen permeating from the fuel gas passage to the oxidant gas passage, so the nitrogen permeation amount is estimated by a direct means such as a map. This is because the estimation accuracy tends to be low. Therefore, the estimation accuracy of the impurity gas amount is improved by estimating the impurity gas amount using the permeated fuel gas amount. Furthermore, also in this case, since the apparatus which a normal fuel cell system has can be utilized, a fuel cell system can be made a simple structure.

  In one aspect of the above fuel cell system, the second gas permeation amount estimation unit is configured to increase the gas permeation as the temperature of the fuel cell, the humidity in the fuel cell, and the power generation amount of the fuel cell increase. The gas permeation amount is estimated so as to increase the amount.

  In this aspect, the second gas permeation amount estimation means includes the temperature of the fuel cell, the humidity in the fuel cell, the amount of power generated by the fuel cell, and the oxidant gas passage from the fuel gas passage through the electrolyte of the fuel cell. Estimation is performed based on a map showing the relationship with the amount of gas that permeates. Therefore, it is possible to accurately estimate the amount of gas that permeates the oxidant gas passage.

  In the fuel cell system, preferably, the first gas permeation amount estimation means estimates the amount of nitrogen and water vapor as the impurities. In the fuel gas passage of the fuel cell, nitrogen that enters from the oxidant passage side, water vapor generated by a reaction for power generation, and the like accumulate as impurities, and these amounts are estimated to adjust the fuel gas amount.

  In one aspect of the above fuel cell system, the fuel cell system includes a discharge valve provided in the fuel gas passage, and the control means opens the discharge valve when an amount obtained by integrating the amount of the impurity gas is a predetermined amount or more. To do. In this aspect, the fuel cell system opens the discharge valve and discharges the gas in the fuel gas passage only when the accumulated amount of the impurity gas is equal to or greater than the predetermined amount. The fuel gas used is not discharged. Therefore, it is possible to prevent a decrease in power generation efficiency without reducing fuel consumption.

  In one aspect of the fuel cell system, the control means increases the amount of fuel gas in the fuel gas passage when the amount obtained by integrating the amount of impurity gas is equal to or greater than a predetermined amount. In this aspect, instead of opening the discharge valve and discharging the impurity gas, the amount of fuel gas in the fuel gas passage is increased to prevent a decrease in power generation efficiency.

  In another aspect of the present invention, a method for estimating the amount of impurity gas in a fuel cell having an oxidant gas passage and a fuel gas passage is used to calculate the amount of hydrogen supplied to the fuel gas passage at a constant pressure per unit time. A supply hydrogen amount detection step for detecting, a hydrogen consumption amount detection step for detecting the amount of hydrogen consumed by the fuel cell per unit time, and the fuel gas passage from the fuel gas passage per unit time through the electrolyte of the fuel cell. A permeate gas amount estimation step for estimating a permeate gas amount permeating the oxidant gas passage; a hydrogen amount detected by the hydrogen consumption amount detection step from a hydrogen amount detected by the supply hydrogen amount detection step; A value obtained by subtracting the amount of permeated gas estimated by the gas amount estimating step from the oxidant gas passage per unit time through the fuel cell electrolyte to the fuel gas passage. And a step of estimating the object gas amount.

  According to the above impurity gas amount estimation method, the amount of hydrogen supplied to the fuel gas passage at a constant pressure, the amount of hydrogen consumed by the fuel cell, and the oxidant gas passage from the fuel gas passage through the electrolyte of the fuel cell The amount of impurity gas is estimated based on the amount of gas (such as fuel gas) that permeates the gas. The estimation of the amount of permeated fuel gas, that is, the amount of permeated hydrogen, has higher estimation accuracy than directly estimating the amount of permeated impurity gas, that is, the amount of permeated nitrogen. Therefore, the estimation accuracy of the impurity gas amount is improved by estimating the impurity gas amount using the permeated fuel gas amount. Furthermore, also in this case, since the apparatus which a normal fuel cell system has can be utilized, a fuel cell system can be made a simple structure.

  Preferred embodiments of the present invention will be described below with reference to the drawings.

[Configuration of fuel cell system]
FIG. 1 is a block diagram showing a schematic configuration of a fuel cell system according to one embodiment of the present invention.

  The fuel cell system 50 mainly includes a pressure regulating valve 3, a temperature sensor 5, a current sensor 6, a discharge valve 8, an ECU (Engine Control Unit) 10, supply channels 11 and 12, and a discharge channel 13. , 14. The fuel cell system 50 is a system that is mounted on a fuel cell vehicle (hereinafter simply referred to as a “vehicle”) and performs various controls on the fuel cell (fuel cell stack) 1.

  The fuel cell 1 is formed by laminating battery cells in which electrodes having a structure such as a porous layer capable of diffusing gas are formed on both surfaces of an electrolyte membrane 1c with a conductive separator interposed between the layers. The output voltage corresponding to In the drawing, for convenience of explanation, only the structure of a battery cell in which a cathode electrode (air electrode) 1a and an anode electrode (fuel electrode) 1b are formed on the surface of the electrolyte membrane 1c is shown. As shown in the figure, air as an oxidant gas is supplied to the cathode electrode 1 a from the supply channel 11, and hydrogen as a fuel gas is supplied to the anode electrode 1 b from the supply channel 12. Thereby, electric power is generated.

  The fuel cell 1 is a power supply for a motor for driving a vehicle, and generates a high DC voltage of about 300V. Further, the generated voltage of the fuel cell 1 passes through the power cable 15 and is supplied to an inverter that supplies a current corresponding to a command torque to the motor, various auxiliary devices mounted on the vehicle, and for supplying power to the auxiliary devices. The output is output to a battery which is a secondary battery (all of these are indicated as “load 7”).

  Air circulates in the supply channel 11, and hydrogen circulates in the supply channel 12. A gas discharged from the cathode electrode 1a circulates in the discharge channel 13, and a gas discharged from the anode electrode 1b (unused hydrogen, water as an impurity, nitrogen, etc.) Is included). As described above, the supply flow path 11 and the discharge flow path 13 function as the oxidant gas passage described above, and the supply flow path 12 and the discharge flow path 14 function as the fuel gas passage described above. Note that the oxidant gas passage and the fuel gas passage include a passage (for example, a passage provided on the separator) through which the gas provided in the fuel cell 1 flows.

  A flow meter 2 and a pressure regulating valve 3 are disposed on the supply flow path 12 described above. The flow meter 2 is a device that detects the flow rate of hydrogen flowing through the supply flow path 12 (hereinafter also referred to as “supply hydrogen amount”). That is, the flow rate detected by the flow meter 2 corresponds to the amount of hydrogen supplied to the anode 1b. A signal S1 corresponding to the flow rate detected by the flow meter 2 is output to the ECU 10.

  The pressure regulating valve 3 is a valve that adjusts the flow rate (hydrogen amount) of hydrogen supplied to the anode 1b. The pressure regulating valve 3 supplies hydrogen to the anode 1b while keeping the pressure constant. The pressure regulating valve 3 is controlled by a control signal S2 from the ECU 10. If the pressure regulating valve 3 is a valve that can accurately adjust the opening amount, the opening amount of the supply valve 3 to the anode 1b is not used without using the flow meter 2 that directly detects the flow rate as described above. The amount of supplied hydrogen may be obtained. Further, when the pressure regulating valve 3 is constituted by an injector or the like (that is, when a valve whose opening / closing is controlled by the duty ratio of the energized control pulse is used), the upstream pressure and the upstream temperature are not used. And the supply hydrogen amount may be obtained based on the valve opening signal.

  A temperature sensor 5 is disposed in the fuel cell 1. That is, the temperature sensor 5 detects the temperature of the fuel cell 1. A signal S4 corresponding to the temperature detected by the temperature sensor 5 is output to the ECU 10. Note that the method for detecting the temperature of the fuel cell 1 is not limited to directly disposing the temperature sensor 5 on the fuel cell 1. For example, the temperature of the coolant supplied to the fuel cell 1 may be used as the temperature of the fuel cell 1. That is, a temperature that accurately reflects the temperature of hydrogen in the fuel cell 1 may be used without directly detecting the temperature of the fuel cell 1.

  The power cable 15 is provided with a current sensor 6. The current sensor 6 is a sensor that detects a current value generated by the fuel cell 1. A signal S5 corresponding to the current value detected by the current sensor 6 is output to the ECU 10. The output signal S5 of this current sensor corresponds to the power generation amount of the fuel cell 1. Further, a discharge valve 8 is disposed in the discharge flow path 14. The discharge valve 8 is a valve capable of discharging a gas containing unused hydrogen or impurities (nitrogen, water, etc.) from the anode 1b. The discharge valve 8 is controlled by a control signal S6 from the ECU 10.

  The ECU 10 includes a CPU, a ROM, a RAM, an A / D converter, an input / output interface, and the like (not shown). As described above, the ECU 10 controls the pressure regulating valve 3 and the discharge valve 8 based on the detection signals S1, S4, and S5 from the flow meter 2, the temperature sensor 5, and the current sensor 6. That is, the control signals S2 and S6 are supplied to the pressure regulating valve 3 and the discharge valve 8. In the present embodiment, the ECU 10 estimates the amount of impurities (impurity gas amount) that has passed through the electrolyte membrane 1c and moved from the cathode electrode 1a to the anode electrode 1b, and the estimated impurity gas amount is a predetermined amount or more. In such a case, the discharge valve 8 is controlled to be opened.

  Here, the significance of the ECU 10 performing the above control will be described with reference to FIG. FIG. 2 is a diagram showing how impurities in the fuel cell 1 increase with the duration of operation of the fuel cell 1. In the figure, the horizontal axis indicates time, and the vertical axis indicates the flow rate of hydrogen. Further, a straight line B1 represented by a broken line represents a predicted required flow rate of hydrogen, and a curve B2 represented by a solid line represents an actual flow rate of hydrogen. From this, it can be seen that the actual flow rate of hydrogen deviates from the predicted required flow rate as the duration of operation of the fuel cell 1 increases. This is because impurities (such as nitrogen and water vapor) that have passed through the electrolyte membrane 1c from the cathode electrode 1a accumulate in the anode electrode 1b. That is, the hatched area B3 representing the difference between the predicted required flow rate and the actual flow rate indicates the amount of impurities.

  If a large amount of impurities accumulates in the anode 1b, the power generation efficiency of the fuel cell 1 decreases. Therefore, it is necessary to open the discharge valve 8 to discharge the impurities. However, when the discharge valve 8 is opened, the utilization efficiency of the fuel cell 1 is lowered even though impurities are not accumulated in a large amount (an amount that adversely affects the power generation efficiency of the fuel cell 1). From this point of view, in this embodiment, the amount of impurity gas in the anode 1b is accurately estimated and the discharge valve 8 is appropriately controlled. In this embodiment, in order to estimate the amount of impurity gas with high accuracy, the amount of gas (such as hydrogen) that has passed through the electrolyte membrane 1c and moved from the anode 1b to the cathode 1a is estimated, and the amount of this gas Based on the above, the amount of impurity gas is estimated. Details of processing performed by the ECU 10 will be described later. As described above, the ECU 10 includes the first gas permeation amount estimation unit that estimates the impurity gas amount, the second gas permeation amount estimation unit that estimates the gas amount (the amount of gas moved to the cathode electrode 1a), It functions as a control means for opening the discharge valve 8 based on the amount of impurity gas.

[Method of estimating the amount of impurity gas]
Below, the estimation method of the impurity gas amount which ECU10 performs, and the control method of the discharge valve 8 based on this estimation result are demonstrated concretely.

  FIG. 3 is a flowchart showing a process performed by the ECU 10. This process is repeatedly executed at a predetermined cycle while the fuel cell 1 is in use. For example, it is preferable to perform processing at a cycle of 1 Hz or more. Furthermore, although the process for estimating the “impurity gas amount” is shown below, the present invention is not limited to this, and the “impurity concentration” may be estimated. This is because, since the volume of the fuel cell 1 is constant, the concentration and amount of gas correspond one-on-one. In the following description, it is assumed that the impurity consists only of nitrogen. This is because nitrogen most affects the power generation stability of the fuel cell 1.

  First, in step S11, the ECU 10 sets an initial value (nitrogen amount (initial value)) of the nitrogen amount in the anode 1b and an integrated value of the permeated hydrogen amount. The processing in step S11 is mainly performed when the fuel cell 1 is started. The nitrogen concentration in the fuel cell 1 after stopping for a certain time is approximately 100%. Therefore, the initial value of the nitrogen amount is determined based on the volume of the anode 1b. The initial value of the nitrogen amount may be set to a pressure value detected by a pressure gauge or the like provided on the supply flow path 12 or the discharge flow path 14. On the other hand, the permeated hydrogen amount is the amount of hydrogen that has passed through the electrolyte membrane 1c and moved from the anode 1b to the cathode 1a, and is set to “0” when the fuel cell 1 is started. When the above process ends, the process proceeds to step S12.

  In step S <b> 12, the ECU 10 obtains the amount of hydrogen consumed for power generation in the fuel cell 1 (hereinafter, also simply referred to as “amount of consumed hydrogen”). The ECU 10 determines the amount of hydrogen consumption based on a signal S5 (which is an output signal of the current sensor 6) corresponding to the power generation amount of the fuel cell 1. Then, the process proceeds to step S13.

  In step S13, the ECU 10 obtains an integrated value of the permeated hydrogen amount per unit time that has passed through the electrolyte membrane 1c from the anode 1b and moved to the cathode 1a. A method of calculating the permeated hydrogen amount will be described with reference to FIG.

  FIG. 4 shows a specific example of a map used when obtaining the permeated hydrogen amount. Specifically, FIG. 4A shows the relationship between the temperature in the fuel cell 1 and the amount of permeated hydrogen (map A11), and FIG. 4B shows the humidity in the fuel cell 1 and the amount of permeated hydrogen. FIG. 4C shows the relationship between the power generation amount of the fuel cell 1 and the amount of permeated hydrogen (map A13). FIG. 4A shows that the amount of permeated hydrogen increases as the temperature in the fuel cell 1 increases. Further, FIG. 4B shows that the permeated hydrogen amount increases as the humidity in the fuel cell 1 increases. Further, FIG. 4C shows that the amount of permeated hydrogen increases as the amount of power generation in the fuel cell 1 increases. Since the humidity of the fuel cell 1 can be obtained from the temperature and the power generation amount, the permeated hydrogen amount may be obtained using only the map A11 and the map A13 without using the map A12. Therefore, the ECU 10 can obtain the output signal S4 from the temperature sensor 5 and the output signal S5 from the current sensor 6 and obtain the permeated hydrogen amount using the map A11 and the map A13.

  The ECU 10 integrates the permeated hydrogen amount obtained in this way to the integrated value of the permeated hydrogen amount up to the previous time. When the above process ends, the process proceeds to step S14. The above-described maps A11 to A13 are stored in a memory or the like in the ECU 10.

  In step S14, ECU10 calculates | requires permeated nitrogen amount using the hydrogen amount calculated | required by the above step S12 and step S13. This amount of permeated nitrogen is the amount of nitrogen per unit time (that is, the amount of impurity gas) that has passed through the electrolyte membrane 1c from the cathode 1a and moved to the anode 1b. Specifically, the permeated nitrogen amount is obtained using the following equation (1).

(Amount of permeated nitrogen) = (Amount of supplied hydrogen) − (Amount of hydrogen consumed) − (Amount of permeated hydrogen) Equation (1)
The “supply hydrogen amount” in the equation (1) is the amount of hydrogen supplied to the anode 1b per unit time under a constant pressure, and is obtained from the output signal S1 from the flow meter 2. The “hydrogen consumption amount” is the hydrogen amount obtained in step S12, and the “permeated hydrogen amount” is the hydrogen amount obtained in step S13. That is, since the supply of hydrogen is performed at a constant pressure, the value obtained by subtracting the amount of hydrogen used for power generation and the amount of hydrogen transferred to the cathode 1a from the amount of supplied hydrogen is the amount of nitrogen that has entered the anode 1b. It is none other than. When the process for obtaining the permeated nitrogen amount is completed, the process proceeds to step S15.

  In step S15, the ECU 10 obtains the current amount of nitrogen existing in the anode 1b. The current amount of nitrogen is a value obtained by adding the amount of permeated nitrogen obtained in step S14 to the amount of nitrogen obtained in the previous processing of this routine. Then, the process proceeds to step S16.

  In step S16, the ECU 10 obtains an allowable maximum nitrogen amount. This allowable maximum nitrogen amount is the maximum value of the nitrogen amount that can stably generate power in the anode 1b. That is, if the amount of nitrogen exceeding the maximum allowable nitrogen amount exists in the anode 1b, the power generation of the fuel cell 1 becomes unstable. A method of calculating the allowable maximum nitrogen amount will be described with reference to FIG.

  In FIG. 5, the horizontal axis indicates the power generation amount of the fuel cell 1, and the vertical axis indicates the temperature of the fuel cell 1. In FIG. 5, a plurality of curves A2 represent characteristic curves (hereinafter also referred to as “map A2”) showing the relationship among the power generation amount, the temperature of the fuel cell 1, and the allowable maximum nitrogen amount. This permissible maximum nitrogen amount is indicated by concentration (concentrations of 40%, 30%, 20% and 10% are shown). As shown in the figure, the allowable maximum nitrogen amount depends on the power generation amount and temperature of the fuel cell 1. Specifically, the larger the power generation amount, the larger the required amount of fuel gas (hydrogen), and therefore the allowable maximum nitrogen amount tends to decrease. It can also be seen that the lower the temperature of the fuel cell 1, the less likely it is that a reaction for power generation occurs, so that the required amount of fuel gas (hydrogen) increases and the allowable maximum nitrogen amount tends to decrease. As described above, in step S16, the ECU 10 acquires the power generation amount of the fuel cell 1 from the current sensor 6, acquires the temperature of the fuel cell 1 from the temperature sensor 5, and uses the acquired value and the map A2 to allow the maximum allowable value. Determine the amount of nitrogen. Then, the process proceeds to step S17. The map A2 described above is also stored in a memory or the like in the ECU 10.

  In step S17, the ECU 10 determines whether or not the current nitrogen amount is greater than or equal to the allowable maximum nitrogen amount. The current nitrogen amount is the amount obtained in step S15, and the allowable maximum nitrogen amount is the amount obtained in step S16. In the processing in step S17, it is determined whether or not the current amount of nitrogen in the anode 1b exists so that the power generation of the fuel cell 1 becomes unstable. Therefore, when the current nitrogen amount is smaller than the allowable maximum nitrogen amount (step S17; No), the process returns to step S12 and the process is performed again. That is, since there is not enough nitrogen in the anode 1 to make the power generation of the fuel cell 1 unstable, the discharge valve 8 is not opened.

  On the other hand, when the current nitrogen amount is greater than or equal to the allowable maximum nitrogen amount (step S17; Yes), the process proceeds to step S18. In step 18, the ECU 10 opens the discharge valve 8. In this case, since the impurity amount is equal to or greater than the allowable maximum nitrogen amount, the ECU 10 opens the discharge valve 8, and the fluid in the anode 1b (hydrogen, nitrogen, water present in the anode 1b (including gas and liquid) Etc.). This is because the impurities are discharged to ensure the power generation stability of the fuel cell 1. The ECU 10 controls the discharge valve 8 based on the pressure value in the anode 1b (for example, determines the valve opening time (or duty ratio) of the discharge valve 8). When the above process ends, the process proceeds to step S19.

  In step S19, the ECU 10 resets the initial value of the nitrogen amount (nitrogen amount (initial value)) and the integrated value of the permeated hydrogen amount. Specifically, the ECU 10 sets the initial value of the nitrogen amount to “(current nitrogen amount) − (exhausted nitrogen amount)”, and sets the integrated value of the permeated hydrogen amount to “0”. The “exhausted nitrogen amount” at the initial value of the nitrogen amount is determined by, for example, how to open the discharge valve 8 during the processing of step S18. When the above process ends, the process returns to step S12 and is performed again.

  As described above, in this embodiment, since the amount of impurity gas is estimated based on the current state of the anode 1b of the fuel cell 1, the estimation accuracy is improved. Further, since the supply / discharge of the gas from the anode 1b is controlled based on the estimation result, it is possible to ensure the power generation stability of the fuel cell 1 and to reduce unnecessary fuel gas discharge. . Furthermore, since the impurity gas amount estimation method according to the present embodiment can be performed using a sensor / control device included in a normal fuel cell system, it is not necessary to provide a new device, and thus a simple configuration is used. Can be executed. Therefore, the cost does not increase.

  Furthermore, since the amount of discharged hydrogen can be calculated in the same way as the amount of exhausted nitrogen, the amount of hydrogen to be supplied can be increased when the amount of air supplied to the hydrogen processor is insufficient. It is possible to make the best use of the ability.

[Modification]
Below, the modification regarding embodiment mentioned above is demonstrated.

  In the above description, when the current nitrogen amount is equal to or larger than the allowable maximum nitrogen amount, the discharge valve 8 is opened. Instead, the hydrogen supply pressure to the anode 1b may be increased. That is, the pressure regulating valve 3 is further opened while the discharge valve 8 is closed to increase the amount of hydrogen to be supplied. In the above embodiment, since the pressure in the anode 1b is kept constant, when the amount of impurity gas in the anode 1b is increased, the amount of hydrogen is relatively decreased and the power generation efficiency is lowered. Therefore, instead of discharging the impurities, if the supply pressure of hydrogen is temporarily increased and sufficient hydrogen is supplied to the anode 1b, a decrease in power generation efficiency can be prevented. In addition, when increasing the amount of hydrogen, it is necessary to control in consideration of the mechanical strength of the fuel cell 1 and the like.

  Furthermore, although the method using the “nitrogen amount” for the estimation of the impurity gas amount has been described above, the present invention is not limited to this, and the “nitrogen concentration” may be used. This is because the amount of nitrogen and the nitrogen concentration are in a corresponding relationship because the pressure in the anode electrode is kept constant.

  Moreover, although the example which estimates only the amount of nitrogen as an impurity and performs control was shown, you may consider not only nitrogen but a water vapor | steam amount as an impurity. In this case, the amount of water vapor can be obtained from a map of the separation rate of the gas-liquid separator provided in the fuel cell system 50, the outlet temperature of the hydrogen system, or a substitute value thereof. In this case, the ECU 10 estimates the current amount of nitrogen and water vapor in the anode 1b, and determines whether or not the estimated amount is equal to or greater than the maximum amount of impurity gas that the fuel cell 1 can stably generate power. A determination may be made. As a specific example, in the above example, in step S16 for obtaining the maximum allowable nitrogen amount in FIG. 3, the amount of water vapor determined as described above is subtracted from the maximum allowable nitrogen amount determined with reference to FIG. The process of step S17 may be performed using the value as a new allowable maximum nitrogen amount.

  Furthermore, although the fuel cell system 50 shown in FIG. 1 is configured with a system in which discharged hydrogen is not circulated, the fuel cell system is reused in a hydrogen circulation system (reused unused gas is recycled). System) may be used to estimate the amount of impurity gas and control hydrogen discharge / supply.

  Furthermore, when the permeated hydrogen amount of the electrolyte membrane used in the fuel cell stack is small, the permeated hydrogen amount may be ignored and the permeated nitrogen amount may be obtained using the following equation (2). Formula (2) is preferably used for the fuel cell 1 having a relatively small amount of permeated hydrogen due to its properties, such as a hydrocarbon electrolyte membrane.

(Amount of permeated nitrogen) = (Amount of supplied hydrogen) − (Amount of hydrogen consumed) Equation (2)
Further, the nitrogen permeation amount may be integrated using a map of the nitrogen permeation amount per unit time without calculating the permeated nitrogen amount from the supply hydrogen amount, the hydrogen consumption amount, or the like. In this case, the amount of permeated nitrogen is the time (such as the time since the discharge valve 8 was last opened), the temperature of the fuel cell 1, the amount of power generated per unit time of the fuel cell 1, the It can be determined based on humidity.

1 is a block diagram showing a schematic configuration of a fuel cell system according to an embodiment of the present invention. It is the figure which showed a mode that the impurity accumulated in the fuel cell. It is a flowchart which estimates the amount of impurity gas which concerns on embodiment of this invention. The map for calculating | requiring permeated hydrogen amount is shown. The map for calculating | requiring the allowable maximum nitrogen amount is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel cell 1a Cathode pole 1b Anode pole 2 Flowmeter 3 Pressure regulating valve 5 Temperature sensor 6 Ammeter 8 Discharge valve 10 ECU
11, 12 Supply flow path 13, 14 Discharge flow path 50 Fuel cell system

Claims (7)

An oxidant gas passage and a fuel gas passage provided in the fuel cell;
First gas permeation amount estimation means for estimating an amount of impurity gas per unit time permeating from the oxidant gas passage through the fuel cell electrolyte to the fuel gas passage;
Control means for adjusting the amount of fuel gas in the fuel gas passage when the amount obtained by integrating the impurity gas amounts estimated by the first gas permeation amount estimating means is a predetermined amount or more. A fuel cell system. Supply hydrogen amount detection means for detecting the amount of hydrogen supplied to the fuel gas passage at a constant pressure per unit time;
Hydrogen consumption detecting means for detecting the amount of hydrogen consumed by the fuel cell per unit time;
Second gas permeation amount estimating means for estimating a gas permeation amount per unit time permeating from the fuel gas passage through the fuel cell electrolyte to the oxidant gas passage;
The first gas permeation amount estimation means includes the hydrogen amount detected by the hydrogen consumption amount detection means and the gas estimated by the second gas permeation amount estimation means from the hydrogen amount detected by the supply hydrogen amount detection means. The value obtained by subtracting the permeation amount is estimated as the amount of impurity gas permeating from the oxidant gas passage through the fuel cell electrolyte to the fuel gas passage per unit time. Fuel cell system. The second gas permeation amount estimation means is configured to increase the gas permeation amount as the temperature of the fuel cell, the humidity in the fuel cell, and the power generation amount of the fuel cell increase. The fuel cell system according to claim 2, wherein The fuel cell system according to any one of claims 1 to 3, wherein the first gas permeation amount estimation means estimates the amount of nitrogen and water vapor as the impurities. A discharge valve provided in the fuel gas passage;
The fuel cell system according to any one of claims 1 to 4, wherein the control means opens the discharge valve when an amount obtained by integrating the impurity gas amounts is a predetermined amount or more. 5. The control unit according to claim 1, wherein the control unit increases the amount of fuel gas in the fuel gas passage when an amount obtained by integrating the impurity gas amounts is a predetermined amount or more. Fuel cell system. An impurity gas amount estimation method in a fuel cell having an oxidant gas passage and a fuel gas passage,
A supply hydrogen amount detection step for detecting the amount of hydrogen supplied to the fuel gas passage at a constant pressure per unit time;
A hydrogen consumption detection step for detecting the amount of hydrogen consumed by the fuel cell per unit time;
A permeated gas amount estimating step of estimating a permeated gas amount per unit time permeating from the fuel gas passage through the fuel cell electrolyte to the oxidant gas passage;
A value obtained by subtracting the hydrogen amount detected by the consumed hydrogen amount detecting step and the permeated gas amount estimated by the permeated gas amount estimating step from the hydrogen amount detected by the supplied hydrogen amount detecting step is a unit time. A method for estimating the amount of impurity gas permeated from the oxidant gas passage to the fuel gas passage through the fuel cell electrolyte.

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