JP2008269911A - Fuel cell system, and gas pressure control method in fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress performance degradation of a fuel cell caused by decrease in water content in an electrolyte membrane without decreasing energy efficiency caused by increase in auxiliary machine loss and suppress performance degradation of the fuel cell caused by decrease in hydrogen concentration. <P>SOLUTION: A fuel cell system 10 including a fuel cell stack 22 having a solid polymer electrolyte membrane is equipped with an anode gas pressure control part (an injector 62) controlling gas pressure on the anode side of the fuel cell stack 22; an impurity exhausting part (an exhaust gas exhausting passage 64 and a purge valve 27); and a control part 70. The control part 70, when decreasing gas pressure on the anode side from positive pressure to negative pressure, controls the impurity exhausting part and exhausts impurities in anode gas, and then controls the anode gas pressure control part and decrease gas pressure from the positive pressure to the negative pressure. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fuel cell system including a solid polymer fuel cell.

In a fuel cell that generates electricity by an electrochemical reaction between hydrogen and oxygen, it is considered that the cell performance is degraded due to various state changes in the fuel cell during operation of the fuel cell.
For example, in a fuel cell, a circulation passage for circulating the exhaust of the hydrogen electrode (hereinafter referred to as anode exhaust gas) and supplying the hydrogen electrode again is provided to effectively utilize the residual hydrogen contained in the anode exhaust gas. There is something like that. In the case of such a fuel cell, since the anode exhaust gas includes, for example, water vapor, nitrogen, etc., if the anode exhaust gas is continuously circulated for a long period of time, the concentration of these components increases, The concentration may be reduced, and the battery performance may be reduced. For this reason, conventionally, a purge valve for discharging a part of the anode exhaust gas to the outside air is provided in the circulation flow path, and the purge valve is opened periodically to reduce the concentration of nitrogen and water vapor, thereby reducing the hydrogen concentration. There has been proposed a technique for avoiding the deterioration in battery performance caused by the phenomenon (see, for example, Patent Document 1).

  In the polymer electrolyte fuel cell, when the water content of the electrolyte membrane decreases, proton conductivity in the electrolyte membrane decreases and membrane resistance increases. As a result, the output voltage decreases and the cell performance decreases. In order to suppress such inconvenience, as a countermeasure against a decrease in the water content of the electrolyte membrane, a configuration has been proposed in which the gas pressure on the cathode side is further increased (see, for example, Patent Document 2).

JP 2003-151592 A JP 2002-175821 A

  When the gas pressure on the cathode side is increased, the gas pressure on the cathode side becomes relatively higher than that on the anode side, so that water generated on the cathode side moves to the anode side. Therefore, the water content of the electrolyte membrane can be increased. However, since the gas supply to the cathode side is normally performed by pressurizing and supplying air using a pump or the like, if the gas pressure on the cathode side is increased, the power consumption of the pump or the like, that is, the loss of auxiliary equipment is reduced. Will increase. When the auxiliary machine loss increases in this way, the energy efficiency of the entire system decreases.

  Therefore, the present invention suppresses fuel cell performance degradation due to a decrease in the water content of the electrolyte membrane without causing a decrease in energy efficiency due to an increase in auxiliary machinery loss or the like, and also results from a decrease in hydrogen concentration. It aims at suppressing the performance fall of the fuel cell which carries out.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

Application Example 1 A fuel cell system including a fuel cell having a solid polymer electrolyte membrane,
An anode gas pressure adjusting unit for adjusting a gas pressure on the anode side of the fuel cell;
An impurity discharge part for discharging impurities in the anode gas;
A control unit for controlling the anode gas pressure adjusting unit and the impurity discharge unit;
Further,
The controller is
When reducing the gas pressure on the anode side from a positive pressure to a negative pressure, the impurity discharge unit is controlled to discharge impurities in the anode gas, and then the anode gas pressure adjustment unit is controlled, The gist is to reduce the gas pressure from a positive pressure to a negative pressure.

  In the fuel cell system of the present invention, when reducing the gas pressure on the anode side (hereinafter also referred to as anode internal pressure) from positive pressure to negative pressure, first, impurities in the anode gas are discharged out of the fuel cell system. . For example, after reducing the anode internal pressure to a negative pressure, even if an impurity in the anode gas is discharged into the atmosphere, the impurity cannot be discharged into the atmosphere due to a pressure difference. According to the fuel cell system of the present invention, since the impurities in the anode gas are discharged into the atmosphere before the anode internal pressure is lowered, the impurities can be discharged into the atmosphere satisfactorily. Therefore, it is possible to suppress a decrease in battery performance by discharging impurities in the anode gas to the atmosphere and increasing the hydrogen concentration in the anode gas.

  And, for example, when the output of the fuel cell decreases due to flooding, if the anode internal pressure is reduced to a negative pressure, the anode gas flow rate increases, and the anode gas flows to stay on the anode side in the fuel cell. Since it is easy to discharge the liquid water out of the fuel cell, flooding on the anode side can be suppressed. Accordingly, since the circulation of the anode gas is improved, it is possible to suppress the performance deterioration of the fuel cell. That is, according to the fuel cell system of the present invention, it is possible to comprehensively suppress a decrease in battery performance.

  Furthermore, since it is not necessary to increase energy consumption when reducing the anode internal pressure, it is possible to suppress a decrease in battery performance without reducing energy efficiency.

Application Example 2 In the fuel cell system according to Application Example 1, the control unit determines whether the temperature inside the fuel cell is equal to or higher than a predetermined temperature, and the temperature inside the fuel cell is When it is determined that the temperature is equal to or higher than the predetermined temperature, the gas pressure on the anode side may be reduced to a negative pressure.

  When the temperature inside the fuel cell rises, the fuel cell performance may be lowered, for example, due to a decrease in the water content of the electrolyte membrane. As in Application Example 2, when the temperature inside the fuel cell is equal to or higher than a predetermined temperature, if the gas pressure on the anode side is reduced, it is relative to the gas pressure on the cathode side (hereinafter also referred to as the cathode internal pressure). In addition, since the anode gas pressure is lowered, the movement of water from the cathode to the anode is promoted, and the decrease in the water content of the electrolyte membrane can be suppressed. Therefore, a decrease in fuel cell performance based on a decrease in the water content of the electrolyte membrane can be suppressed, and as a result, a decrease in fuel cell performance when the temperature inside the fuel cell rises can be suppressed.

Application Example 3 In the fuel cell system according to Application Example 1, the control unit determines whether or not the water content in the electrolyte membrane included in the fuel cell is reduced, and the water content is reduced. When it is determined that, the gas pressure on the anode side may be reduced to a negative pressure.

  In this way, when the water content of the electrolyte membrane decreases, as described above, the anode gas pressure becomes lower relative to the cathode internal pressure, so that the movement of water from the cathode to the anode is promoted, and the electrolyte A decrease in the water content of the membrane can be suppressed. That is, it is possible to suppress a decrease in the performance of the fuel cell due to a decrease in the hydrogen concentration and to suppress a decrease in the performance of the fuel cell due to a decrease in the water content of the electrolyte membrane.

Application Example 4 In the fuel cell system according to Application Example 2, the control unit may determine whether or not the water content is reduced based on the temperature inside the fuel cell. .

  In this way, by measuring a value that reflects the internal temperature of the fuel cell or the internal temperature of the fuel cell, it is possible to easily determine whether the moisture content of the electrolyte membrane has decreased.

Application Example 5 In the fuel cell system according to any one of Application Examples 1 to 4,
A hydrogen gas supply path for supplying hydrogen gas to the anode of the fuel cell;
An anode exhaust gas path for guiding the gas discharged from the anode of the fuel cell to the hydrogen gas supply path,
A part of the hydrogen gas supply path and the anode exhaust gas path form a circulation path for circulating hydrogen between the inside of the fuel cell,
The anode gas pressure adjusting unit may set a pressure in the circulation channel as a gas pressure on the anode side.

  With such a configuration, in a fuel cell system that uses hydrogen gas as the fuel gas, it is possible to efficiently reduce the battery performance while efficiently using the hydrogen gas.

Application Example 6 In the fuel cell system according to Application Example 5,
The anode gas pressure adjusting unit is
An injector provided upstream of the circulation flow path in the hydrogen gas supply path and having a discharge port for discharging the hydrogen gas to the circulation flow path side and a valve for opening and closing the discharge port;
The controller is
The anode gas adjusting unit may be controlled so as to reduce the gas pressure on the anode side from a positive pressure to a negative pressure by adjusting the opening / closing state of the discharge port by the valve of the injector.

  With such a configuration, the gas pressure on the anode side can be easily adjusted to a desired pressure by adjusting the opening / closing state of the discharge port by the valve.

  The present invention can be realized in various forms other than those described above. For example, the present invention can be realized in a form such as a method for adjusting the gas pressure on the anode side in a fuel cell including a solid polymer electrolyte membrane.

Next, embodiments of the present invention will be described in the following order based on examples.
A. Overall configuration of the device:
B. Relationship between anode internal pressure and membrane resistance:
C. Control when membrane water content is reduced:
D. Effects of the embodiment:
E. Variation:

A. Overall configuration of the device:
FIG. 1 is an explanatory diagram showing the configuration of a fuel cell system 10 as a preferred embodiment of the present invention. As shown in FIG. 1, the fuel cell system 20 supplies a fuel cell stack 22 and hydrogen as fuel gas to the fuel cell stack 22, and exhaust gas discharged from the fuel cell stack 22 (hereinafter also referred to as anode exhaust gas). .) Is discharged to the atmosphere, and air as an oxidant gas is supplied to the fuel cell stack 22, and the exhaust gas discharged from the fuel cell stack 22 is discharged to the atmosphere. And a control unit 70 that controls the movement of each unit of the fuel cell system 10.

  The fuel cell stack 22 is a polymer electrolyte fuel cell that is relatively small and excellent in power generation efficiency. Pure hydrogen as a fuel gas and oxygen in the air as an oxidant gas cause an electrochemical reaction at each electrode. Thus, an electromotive force is obtained.

  The hydrogen supply system mainly includes a hydrogen tank 23, a hydrogen supply path 60, an anode exhaust gas path 63, and an exhaust gas discharge path 64.

  The hydrogen tank 23 is, for example, a hydrogen cylinder that stores high-pressure hydrogen. Alternatively, a tank that stores hydrogen by storing a hydrogen storage alloy inside and storing the hydrogen storage alloy in the hydrogen storage alloy may be used.

  The hydrogen supply path 60 is provided with a pressure regulating valve 61 and an injector 62. The hydrogen gas stored in the hydrogen tank 23 is discharged to the hydrogen supply path 60 connected to the hydrogen tank 23, and then adjusted (depressurized) to a predetermined pressure by the pressure adjustment valve 61, and the fuel cell is supplied via the injector 62. The fuel gas is supplied to the anode of each single cell constituting the stack 22. Although the pressure regulating valve 61 is shown as a single valve in FIG. 1, it is sufficient if the high-pressure hydrogen gas supplied from the hydrogen tank 23 can be reduced to a desired pressure and supplied to the injector 62. A valve provided with any number of pressure regulating valves may be used.

  The injector 62 is a device that includes a discharge port and a valve that is an electromagnetic valve that opens and closes the discharge port, and injects hydrogen gas from the discharge port according to the differential pressure applied before and after the injector 62 when the valve is opened. Therefore, the amount of hydrogen gas supplied to the anode side can be adjusted by the valve opening time of the valve provided in the injector 62. Specifically, a drive signal (pulse signal) is sent from the control unit 70 to be described later to the injector 62. When the drive signal input to the injector 62 is ON, the valve of the injector 62 is opened and turned OFF. Sometimes the valve is closed. By adjusting the pulse width (that is, duty ratio) of this drive signal, the amount of hydrogen gas injected from the injector 62 is adjusted, and the amount of hydrogen gas supplied to the anode is adjusted.

  Further, the anode internal pressure can be controlled by controlling the open / close state of the valve of the injector 62. FIG. 2 is an explanatory diagram showing the relationship between the anode internal pressure and the operation of the injector 62. The valve opening / closing control in the injector 62 can be performed, for example, by changing the pulse width at a constant frequency f in the drive signal input to the injector 62. As shown in FIG. 2, the anode internal pressure increases while the discharge port is opened by the valve, and the anode internal pressure is consumed by the consumption of hydrogen in the circulation flow path for power generation while the discharge port is closed. Will decline. Therefore, by opening and closing the valve, the anode internal pressure pulsates within the range of the pressure difference ΔP shown in FIG. Therefore, by controlling the duty ratio in the injector 62, the anode internal pressure is maintained at a desired pressure as a whole while finely pulsating. In addition, the injector 62 in a present Example is equivalent to the anode gas pressure adjustment part in a claim.

  A hydrogen pump 65 is provided in the anode exhaust gas path 63, and the anode exhaust gas discharged from the anode of the fuel cell stack 22 is caused to flow again downstream of the position where the injector 62 is disposed in the hydrogen supply path 60. Therefore, the remaining hydrogen in the anode exhaust gas is contained in a flow path (hereinafter referred to as a circulation flow path) composed of the anode exhaust gas path 63, a part of the hydrogen supply path 60, and the flow path in the fuel cell stack 22. It is used again for the electrochemical reaction. At this time, the duty ratio in the injector 62 is adjusted in accordance with the amount of hydrogen consumed by the electrode reaction (determined based on the amount of power generation and load demand), and hydrogen corresponding to the amount of hydrogen consumed passes through the injector 62 to the hydrogen tank 23 is replenished to the circulation channel. Further, the duty ratio in the injector 62 is feedback controlled based on the anode internal pressure, and the anode internal pressure is maintained at a predetermined substantially constant value. In addition, the anode internal pressure sensor 50 for measuring the anode internal pressure is provided in the hydrogen supply path 60 constituting the circulation channel.

  The exhaust gas discharge path 64 is branched from the anode exhaust gas path 63. A purge valve 27 is provided in the exhaust gas discharge path 64, and when the purge valve 27 is opened, part of the anode exhaust gas flowing in the anode exhaust gas path 63 is discharged to the outside through the exhaust gas discharge path 64. As a result, a part of the circulating hydrogen-containing gas is discharged to the outside, and the impurity concentration in the hydrogen-containing gas (the concentration of nitrogen in the air, which is the oxidizing gas that has moved to the anode side through the electrolyte membrane) The rise can be suppressed. In addition, the purge valve 27 and the exhaust gas discharge path 64 in the present embodiment correspond to the impurity discharge portion in the claims.

  Normally, the opening and closing of the purge valve 27 is controlled based on the nitrogen concentration in the anode exhaust gas in the anode exhaust gas path 63. The nitrogen concentration in the anode exhaust gas is determined as follows, for example. The temperature of cooling water (described later) flowing through the fuel cell stack 22 and the nitrogen concentration corresponding to the output of the fuel cell stack 22 are measured in advance, and the relationship is stored as a map in the control unit 70 (described later). Keep it. And the nitrogen concentration at that time can be calculated | required by measuring the said water temperature and output during the driving | operation of the fuel cell stack 22, and referring the said map.

  The exhaust gas discharge path 64 is connected to the diluter 26. The diluter 26 is provided to dilute the hydrogen in the anode exhaust gas with the cathode exhaust gas before discharging the anode exhaust gas to the outside.

  The air supply / exhaust system mainly includes an air compressor 24, an oxidizing gas supply path 67, and a cathode exhaust gas path 68.

  The air compressor 24 pressurizes air taken from the outside via the air cleaner 28, and supplies this pressurized air as an oxidizing gas to the cathode of the fuel cell stack 22 via the oxidizing gas supply path 67.

  The cathode exhaust gas path 68 discharges the cathode exhaust gas discharged from the cathode to the outside. The cathode exhaust gas path 68 and the oxidizing gas supply path 67 pass through the humidification module 25. In the humidification module 25, the oxidizing gas supply path 67 and the cathode exhaust gas path 68 are separated from each other by a water vapor permeable membrane, and the pressurized air supplied to the cathode is humidified using the cathode exhaust gas containing water vapor. ing. Further, the cathode exhaust gas path 68 is connected to the diluter 26 described above. Therefore, in the diluter 26, the anode exhaust gas and the cathode exhaust gas are mixed, and the anode exhaust gas is diluted and discharged to the outside.

  The control unit 70 is configured as a logic circuit centered on a microcomputer. Specifically, a CPU 74 that executes predetermined calculations in accordance with a preset control program, a ROM 75 that stores in advance control programs and control data necessary for executing various calculation processes by the CPU 74, and various types of CPUs 74. A RAM 76 for temporarily reading and writing various data necessary for arithmetic processing, an input / output port 78 for inputting and outputting various signals, and the like are provided. The control unit 70 acquires measurement signals from various sensors (for example, the anode internal pressure sensor 50, the temperature sensor 52, and the voltage sensor 54) provided in the fuel cell system 10, information related to a load request for the fuel cell stack 22, and the like. In addition, a drive signal is output to each part related to power generation of the fuel cell stack 22, such as the injector 62, the air compressor 24, the hydrogen pump 65, or the purge valve 27 provided in the fuel cell system 10.

  Further, the fuel cell stack 22 includes a cooling water flow path (not shown) through which cooling water circulates. By circulating the cooling water between the cooling water flow path formed inside the fuel cell stack 22 and a radiator (not shown), the internal temperature of the fuel cell stack 22 is maintained within a predetermined temperature range. Here, a temperature sensor 52 for measuring the outlet temperature of the cooling water is provided as a temperature sensor for measuring the internal temperature of the fuel cell stack 22 in the vicinity of the outlet from the fuel cell stack 22 in the cooling water flow path. ing. As a temperature sensor for measuring the internal temperature of the fuel cell stack 22, a sensor other than a sensor for measuring the outlet temperature of the cooling water may be provided. For example, as a thermocouple for directly measuring the temperature of the fuel cell stack 22. Also good. Further, the fuel cell system 10 is provided with a voltage sensor 54 for measuring the output voltage from the fuel cell stack 22.

  The anode internal pressure in the fuel cell system 10 of the present embodiment is sufficient when the fuel cell stack 22 is in steady operation, even when the load demand on the fuel cell stack 22 fluctuates and the hydrogen consumption is maximized. It is a value that can ensure the amount, and is set as a positive pressure value considering the balance with the gas pressure on the cathode side. Here, when the fuel cell stack 22 is in steady operation, the temperature of the fuel cell stack 22 is sufficiently raised, the water content of the electrolyte membrane is sufficient, and it is necessary according to the load demand. A state in which a large amount of electric power can be generated by the fuel cell stack 22 without hindrance.

B. Relationship between anode internal pressure and membrane resistance:
In the fuel cell system 10 of the present embodiment, when the water content in the solid polymer electrolyte membrane is reduced, the anode internal pressure is different from that during steady operation in order to suppress the reduction in battery performance due to the reduction in water content. Control is performed to set a value (negative pressure) lower than the atmospheric pressure. Prior to the description of the control in the fuel cell system 10 of this embodiment, the relationship between the internal resistance (cell resistance) and the anode internal pressure in the fuel cell will be described below.

  FIG. 3 is a diagram showing the results of examining the relationship between anode internal pressure, cell resistance, and cell voltage. Here, a single cell (a pair of separators sandwiching an MEA (membrane electrode assembly)) is used as a fuel cell, and hydrogen gas as a fuel gas is not circulated. Then, while connecting the single cell to a constant load, that is, while maintaining the output current value at a constant value, the pressure of the hydrogen gas supplied to the anode side (anode internal pressure) is gradually changed, and the cell resistance and the cell voltage are changed. It was measured. Further, air is used as the oxidizing gas supplied to the cathode, and the pressure of the air flowing through the oxidizing gas flow path in the single cell, that is, the cathode internal pressure is constant. Moreover, the cooling water flow path through which cooling water flows was provided in the single cell, and the temperature in the single cell was maintained substantially constant by adjusting the outlet temperature of the cooling water. In addition, the humidification conditions of the fuel gas and the oxidizing gas were set such that the water content of the electrolyte membrane was lowered when the anode internal pressure was set to a pressure balanced with the cathode internal pressure.

  Here, the internal resistance in the fuel cell includes a resistance caused by contact resistance between the constituent members of the fuel cell and a resistance possessed by each constituent member of the fuel cell itself. Although it is difficult to measure these individual resistances, the value of these resistances can vary greatly depending on the power generation conditions of the fuel cell during power generation of the fuel cell. Fluctuating electrolyte membrane resistance, ie membrane resistance. This membrane resistance increases as the water content of the electrolyte membrane decreases and the proton conductivity in the electrolyte membrane decreases. Therefore, in the result shown in FIG. 3, the increase in the membrane resistance due to the decrease in the water content of the electrolyte membrane is measured as the increase in the internal resistance of the fuel cell stack 22.

  The cell resistance, which is the internal resistance of the fuel cell, was determined by the AC impedance method. That is, a weak AC constant current having a relatively high frequency (for example, 10 kHz) is applied to a single cell, and an AC component caused by the AC current is separated from the output voltage using a filter (capacitor). The AC impedance, which is the voltage value of the AC component, was determined as the cell resistance.

  As shown in FIG. 3, the lower the internal pressure of the anode, the lower the cell resistance in the single cell and the higher the cell voltage.

  As described above, the cell resistance decreases as the anode internal pressure decreases. By reducing the anode internal pressure, the anode internal pressure becomes relatively lower than the cathode internal pressure, and the differential pressure between the two increases. This is probably because of this. When the pressure difference between the anode internal pressure and the cathode internal pressure increases, the movement of water in the electrolyte membrane from the cathode side to the anode side is promoted, resulting in an increase in the water content of the electrolyte membrane and a decrease in membrane resistance. This is probably because of this.

  As described above, from the results shown in FIG. 3, when the water content of the electrolyte membrane is reduced, if the anode internal pressure is lowered, the cell resistance can be lowered as the anode pressure is lowered. As a result, the cell voltage is increased. The knowledge that it can be made was obtained. Therefore, in the fuel cell system 10 of the present embodiment, by utilizing the above knowledge, when the water content of the electrolyte membrane is reduced, control is performed to reduce the anode internal pressure to a negative pressure, thereby maintaining the battery performance. Yes.

  In general, when operating a fuel cell using hydrogen gas as the fuel gas and air having a relatively low oxygen concentration as the oxidizing gas, the anode internal pressure is set in consideration of the balance with the cathode internal pressure. Therefore, it is excessive as compared with a value necessary for obtaining a desired power. Therefore, by reducing the anode internal pressure to a negative pressure within a sufficient range to generate power according to the load demand, it is possible to reduce cell resistance and increase cell voltage while obtaining desired power.

C. Control when membrane water content is reduced:
FIG. 4 is a flowchart showing a membrane water content lowering processing routine executed by the CPU 74 of the control unit 70 provided in the fuel cell system 10. This routine is repeatedly executed at predetermined intervals during the power generation of the fuel cell stack 22.

  When this routine is started, the CPU 74 first lowers the flag (step S100) and determines whether or not the fuel cell stack 22 satisfies a predetermined high temperature condition (step S110). In this embodiment, the temperature measured by the temperature sensor 52 is used as the internal temperature of the fuel cell stack 22, and when the internal temperature is 90 ° C. or higher, it is determined that the fuel cell stack 22 meets a predetermined high temperature condition. The reason why the criterion for the high temperature condition is 90 ° C. is that it is considered that the water content of the electrolyte membrane is lowered due to the increase of the saturated vapor pressure. In step S110, the reduced state of the water content of the electrolyte membrane is determined based on the internal temperature of the fuel cell stack 22. Thus, when executing the process of step S110, the CPU 74 functions as a control unit in the claims.

  When it is determined in step S110 that the predetermined high temperature condition is met, the CPU 74 determines whether or not the flag is lowered (step S120), and if the flag is lowered, the impurities in the anode exhaust gas are discharged. (Step S130). Specifically, by outputting a drive signal from the CPU 74 to the purge valve 27, the purge valve 27 is opened, a part of the anode exhaust gas is discharged, and after a predetermined time has elapsed, the purge valve 27 is closed. Thus, when executing the process of step S130, the CPU 74 functions as a control unit in the claims.

  As described in the section “B. Relationship between anode internal pressure and membrane resistance”, when the water content of the electrolyte membrane is reduced, the water content of the electrolyte membrane is increased by reducing the anode internal pressure. As a result, a decrease in fuel cell performance can be suppressed. Therefore, in step S110, when it is determined that the predetermined high temperature condition is satisfied (that is, the water content of the electrolyte membrane is reduced), control for reducing the anode internal pressure described later is performed (step S140). In the present embodiment, the control for exhausting the anode exhaust gas is performed prior to step S140 (step S130). This is because, when the anode internal pressure is reduced to a negative pressure, the pressure in the circulation path is lower than the outside air pressure even if the anode exhaust gas is exhausted after that, so that outside air flows into the circulation path. This is because the anode exhaust gas cannot be exhausted.

  Conventionally, the exhaust of the anode exhaust gas is controlled based on the impurity concentration (for example, nitrogen concentration) in the anode gas. However, when the anode internal pressure is set to a negative pressure, there are the above-described problems. Therefore, in this embodiment, when the anode internal pressure is decreased from the positive pressure to the negative pressure, the anode internal pressure is related to the timing. The anode exhaust gas is discharged before the pressure decreases.

  When the purge valve 27 is closed in step S130, the CPU 74 performs control to reduce the set value of the anode internal pressure to a negative pressure (step S140). In step S150, the flag is raised, and the process returns to step S110 again. As described above, the anode internal pressure is a constant positive value considering the balance with the gas pressure on the cathode side when the fuel cell stack 22 is in steady operation (that is, until the process of step S140 is executed). It is set as a pressure value. Specifically, the control for setting the anode internal pressure to a negative pressure is performed by outputting a drive signal from the control unit 70 to the injector 62, whereby the measured value in the anode internal pressure sensor 50 becomes a predetermined value lower than the atmospheric pressure. In this manner, the duty ratio in the injector 62 is adjusted. Thus, when executing the process of step S140, the CPU 74 functions as a control unit in the claims.

  When it is determined that the fuel cell stack 22 does not meet the predetermined high temperature condition when returning to step S110, the CPU 74 proceeds to step S160 and performs control during steady operation as control of the anode internal pressure ( That is, it is controlled to a predetermined positive pressure value) and the flag is lowered (step S170). And it returns to step S110 again. As described above, when it is determined in step S110 that the fuel cell stack 22 does not satisfy the predetermined high temperature condition, the saturated vapor pressure in the gas flow path in the fuel cell is not so high, and the fuel gas and the oxidizing gas are discharged from the electrolyte membrane. It is considered that the water content reduction state of the electrolyte membrane is within the allowable range because the vaporization of moisture into the water is suppressed. Therefore, since it is not necessary to control the anode internal pressure to a negative pressure, the control is returned to the control during steady operation.

  On the other hand, if it is determined in step S140 that the fuel cell stack 22 meets the predetermined high temperature condition after returning to step S110 after controlling the anode internal pressure to a negative pressure, the process proceeds to step S120. Since the internal pressure is controlled to a negative pressure and the flag is raised, the process returns to step S110 without exhausting the anode exhaust gas.

  As described above, when the anode internal pressure is controlled to decrease from the positive pressure value to the negative pressure value, the anode exhaust gas is controlled to be exhausted before the negative pressure is controlled. On the other hand, when the anode internal pressure is controlled during steady operation (that is, controlled to a predetermined positive pressure value) or controlled to a constant negative pressure value, the exhaust gas of the anode exhaust gas is Regardless of the routine, it is controlled based on the nitrogen concentration in the anode gas.

D. Effects of the embodiment:
FIG. 5 is a graph showing the influence of control by the processing routine when the membrane water content is reduced. 5A shows the internal temperature of the fuel cell stack 22, FIG. 5B shows the open / close state of the purge valve 27, FIG. 5C shows the nitrogen concentration in the anode exhaust gas, FIG. 5D shows the anode internal pressure, and FIG. The output power (current x voltage) is shown respectively. In FIG. 5, all the graphs (a) to (e) are shown on the same time axis with the horizontal axis representing time. FIG. 5 shows a state in which the fuel cell system 10 is operated at a constant high load by simulating a state where a vehicle equipped with the fuel cell system 10 continues to climb a hill.

  When the internal temperature of the fuel cell stack 22 shown in FIG. 5A exceeds a high temperature determination criterion (for example, 90 ° C.) (that is, when it is determined in step S110 that the predetermined high temperature condition is satisfied). As shown in FIG. 5B, the purge valve 27 is opened. Then, a part of the anode exhaust gas in the anode exhaust gas passage 63 is discharged to the outside through the exhaust gas discharge passage 64. When a part of the anode exhaust gas is discharged, pure hydrogen is supplied from the hydrogen tank 23 accordingly, and as shown in FIG. 5C, the nitrogen concentration in the anode gas decreases. At this time, the anode internal pressure of the fuel cell stack 22 is controlled during steady operation (FIG. 5D). Then, after a predetermined time has elapsed since the purge valve 27 was opened, the valve is closed, and then the open / close state of the valve of the injector 62 is adjusted so that the anode internal pressure becomes a constant negative pressure value lower than the atmospheric pressure. (FIG. 5D). Note that after the purge valve 27 is closed, the nitrogen concentration in the anode gas gradually increases (FIG. 5C).

  In general, when the fuel cell starts operation and the internal temperature of the fuel cell increases, the electrolyte membrane gradually dries and the resistance of the electrolyte membrane gradually increases as the internal temperature of the fuel cell increases. Therefore, the output voltage with respect to a constant output current becomes small. Therefore, if the load demand is constant and the output current is constant, the output becomes small. However, when the water content of the electrolyte membrane is within an allowable range, a constant output can be obtained from the fuel cell by performing control such as increasing the output current.

  In the fuel cell system 10 in the present embodiment, when it is determined that the high temperature condition is satisfied, it is determined that the water content of the electrolyte membrane is lower than the allowable range. In the operation state of the fuel cell stack 22 shown in FIG. 5, the internal temperature of the fuel cell stack 22 continues to rise gradually even after it is determined that the high temperature condition is satisfied by continuing the high load operation. If not adjusted, the water content of the electrolyte membrane further decreases.

  Therefore, after it is determined that the high temperature condition is satisfied, the anode internal pressure is decreased, and the pressure on the anode side is decreased relative to the cathode side, thereby promoting the movement of water from the anode side and the electrolyte. Suppressing a decrease in the water content of the membrane (ie, maintaining the water content of the electrolyte membrane). As a result, the output of the fuel cell stack 22 is maintained at a constant high output (FIG. 5 (e)).

  In order to clarify the effect of the present embodiment, a control for exhausting the anode exhaust gas after reducing the anode internal pressure to a negative pressure will be described as a comparative example to the present embodiment. FIG. 6 is a graph showing the influence on the output by controlling the anode pressure in the comparative example. Also in FIG. 6, the fuel cell stack 22 is operated in a constant high load state similar to FIG.

  First, when the internal temperature of the fuel cell stack 22 exceeds a predetermined reference value (FIG. 6 (a)), the anode internal pressure is controlled to a predetermined negative pressure value lower than the atmospheric pressure (FIG. 6 (d)). . Thereafter, when the nitrogen concentration in the anode gas reaches a predetermined high concentration determination reference value (FIG. 6C), the purge valve 27 is opened, and after a predetermined time has elapsed, the valve is closed (FIG. 6B). ). When the purge valve 27 is opened, if the anode internal pressure remains lower than the atmospheric pressure, the anode exhaust gas is not discharged into the atmosphere due to the pressure difference even if the purge valve 27 is opened. The anode internal pressure is once returned to the pressure (positive pressure) at the time of normal operation control in accordance with the valve timing, and the anode internal pressure is controlled to be lowered in accordance with the timing at which the purge valve 27 is closed.

  Since it is determined that the high temperature condition is satisfied and the anode internal pressure is set to a negative pressure, the water content of the electrolyte membrane of the fuel cell stack 22 is maintained without further decrease. As shown, the output is also maintained. However, as described above, when the control to return the anode internal pressure to the positive pressure is performed in accordance with the timing when the purge valve 27 is opened, the water content of the electrolyte membrane decreases because the water on the cathode side hardly moves to the anode side. As a result, the membrane resistance increases, and as a result, the output voltage decreases and the output of the fuel cell stack 22 decreases (FIG. 6 (e)).

  In the fuel cell system 10 of the present embodiment, when it is determined that the water content of the electrolyte membrane has decreased, the purge valve 27 is opened before the anode internal pressure is reduced to a negative pressure, and the anode exhaust gas Exhaust is being performed. Therefore, as in the comparative example, the output concentration is not reduced, the nitrogen concentration in the anode exhaust gas is reduced, and the decrease in the water content of the electrolyte membrane is suppressed, thereby suppressing the overall decrease in battery performance. be able to.

  Furthermore, since the anode internal pressure is reduced by adjusting the opening / closing time of the valve of the injector 62, there is no need to increase energy consumption. Therefore, it is possible to suppress a decrease in battery performance due to a decrease in water content of the electrolyte membrane without reducing energy efficiency.

  In this embodiment, the anode internal pressure can be easily controlled to a desired value by a simple operation of opening / closing control of the valve of the injector 62. The anode internal pressure may be adjusted by a method other than the method of adjusting the opening / closing time of the valve of the injector 62. For example, the anode internal pressure may be adjusted by adjusting the opening of the valve.

E. Variation:
The present invention is not limited to the above-described examples and embodiments, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.

  (1) In the above-described embodiment, the reduction in the water content of the electrolyte membrane has been described as an example of one of the factors that deteriorate the cell performance of the fuel cell stack 22, but the cell performance is affected by various other factors. When decreasing, the anode internal pressure may be decreased to a negative pressure.

  For example, when it is considered that flooding occurs on the anode side, control may be performed to reduce the anode internal pressure to a negative pressure. Specifically, in step S110, it is determined whether or not a low temperature condition (for example, 80 ° C. or lower) that can be in a flooding state. If the low temperature condition is satisfied, a decrease state of the output voltage is determined, If it is lower than a predetermined rate, it is determined that a flooding state has occurred.

  As a method for determining the output voltage drop state, for example, it can be determined as follows. The output voltage value of the fuel cell stack 22 measured by the voltage sensor 54 is acquired, and the output current value of the fuel cell stack 22 measured by a current sensor (not shown) is acquired. In general, a fuel cell performing steady operation has a property that an output voltage value is uniquely determined according to an output current value, and there is a certain relationship between the output current value and the output voltage value. (Current-voltage characteristics) Based on the acquired output current value and the current-voltage characteristics of the fuel cell stack 22 stored in advance in the control unit 70, the CPU 74 determines a reference voltage value that is a reference value of the output voltage value during steady operation. Ask. Then, the obtained reference voltage value is compared with the measured value of the output voltage value acquired from the voltage sensor 54 to determine the output voltage drop state.

  If it is determined in step S110 that the flooding state has occurred, the exhaust control of the anode exhaust gas is performed (step S130), and then the anode internal pressure reduction control is performed (step S140).

  When the anode internal pressure is reduced to a negative pressure, the flow rate of the anode gas is increased, so that water staying in the fuel cell stack 22 can be easily discharged, and flooding can be suppressed.

  (2) In the above-described embodiment, the water content reduction state of the electrolyte membrane is determined based on the internal temperature of the fuel cell stack 22 in step S110 of FIG. 4, but the water content of the electrolyte membrane is based on different criteria. You may determine a fall state.

  For example, it may be determined based on the output voltage of the fuel cell stack 22 whether or not the water content of the electrolyte membrane is reduced. For example, as described in (1), the reference voltage value is compared with the measured value of the output voltage value acquired from the voltage sensor 54, and the actual measured value is lower than the reference voltage value by a predetermined rate or more. If it is, it may be determined that the moisture content of the electrolyte membrane is in a reduced state.

  Alternatively, the reduced water content of the electrolyte membrane may be determined based on the membrane resistance of the electrolyte membrane. As described above, when the water content of the electrolyte membrane decreases, the membrane resistance of the electrolyte membrane increases. Therefore, when the membrane resistance increases to a predetermined value or more, it can be determined that the water content is in a reduced state.

  Moreover, it is good also as determining the moisture content fall state of an electrolyte membrane based on the pressure loss (cathode pressure loss) in the oxidizing gas supplied to a cathode. When the water content of the membrane is low, the amount of water is also low in the oxidizing gas flow path, and the pressure loss is reduced by reducing the obstruction of the oxidizing gas flow by the liquid water. The state can be determined. Similarly, the water content reduction state of the electrolyte membrane may be determined based on the pressure loss (anode pressure loss) in the fuel gas supplied to the anode.

  Further, the moisture content reduction state of the electrolyte membrane may be determined based on the humidity of the exhaust gas (cathode exhaust gas or anode exhaust gas). In a fuel cell, when the temperature is relatively low, the water vapor pressure in the exhaust gas is a saturated vapor pressure. However, when the temperature of the fuel cell rises and the electrolyte membrane can be in a reduced water content state, the water vapor pressure in the exhaust gas falls below the saturated vapor pressure. Therefore, an exhaust gas humidity serving as a reference for determining a moisture content lowering state is determined in advance, and when the exhaust gas humidity determined based on the measured value is lower than the exhaust gas humidity serving as the reference, the electrolyte membrane has a reduced moisture content. It can be determined that it is in a state.

  (3) In the above-described embodiment, the injector 62 is used to replenish the circulation flow path with hydrogen gas. However, a different configuration may be used. For example, a pressure reducing valve may be provided in place of the injector 62, and the pressure inside the anode may be controlled by adjusting the fuel gas pressure supplied to the fuel cell stack 22 with the pressure reducing valve.

  (4) In the above-described embodiment, the hydrogen supply / discharge system has a configuration in which the circulation flow path is configured to return the anode exhaust gas to the hydrogen supply path 60. However, the anode exhaust gas may not be circulated. For example, the anode exhaust gas path 63 may not be provided, and the exhaust gas exhaust path 64 may be directly connected to the fuel cell stack 22. Even in such a configuration, the impurities in the anode gas in the fuel cell stack 22 can be discharged by opening the purge valve 27. Such a configuration is suitable, for example, when all of the supplied hydrogen is used for the electrode reaction.

  (5) In the above-described embodiment, the hydrogen gas stored in the hydrogen tank 23 is used as the fuel gas containing hydrogen. However, a different configuration may be used. For example, a hydrogen-rich reformed gas obtained by using a reforming reaction such as a steam reforming reaction from a fuel such as alcohol or hydrocarbon may be used as the fuel gas. Also in this case, when the water content of the electrolyte membrane is reduced, the same effect can be obtained by controlling the reduction of the anode internal pressure to suppress an increase in resistance in the electrolyte membrane and securing the output voltage.

1 is an explanatory diagram illustrating an outline of a configuration of a fuel cell system 10. FIG. FIG. 6 is an explanatory diagram showing a relationship between anode internal pressure and operation of an injector 62. It is a figure which shows the result of having investigated the relationship between anode internal pressure, cell resistance, and cell voltage. 3 is a flowchart showing a membrane water content reduction processing routine executed in the fuel cell system 10. It is a graph which shows the influence of control by the processing routine at the time of membrane water content fall. It is a graph which shows the influence on the output by control of the anode internal pressure of a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Fuel cell system 22 ... Fuel cell stack 23 ... Hydrogen tank 24 ... Air compressor 25 ... Humidification module 26 ... Diluter 27 ... Purge valve 28 ... Air cleaner 50 ... Anode internal pressure sensor 52 ... Temperature sensor 54 ... Voltage sensor 60 ... Hydrogen supply path DESCRIPTION OF SYMBOLS 61 ... Pressure regulating valve 62 ... Injector 63 ... Anode exhaust gas path 64 ... Exhaust gas exhaust path 65 ... Hydrogen pump 67 ... Oxidation gas supply path 68 ... Cathode exhaust gas path 70 ... Control part 74 ... CPU
78 ... I / O port

Claims (7)

A fuel cell system comprising a fuel cell having a solid polymer electrolyte membrane,
An anode gas pressure adjusting unit for adjusting a gas pressure on the anode side of the fuel cell;
An impurity discharge part for discharging impurities in the anode gas;
A control unit for controlling the anode gas pressure adjusting unit and the impurity discharge unit;
Further,
The controller is
When reducing the gas pressure on the anode side from a positive pressure to a negative pressure, the impurity discharge unit is controlled to discharge impurities in the anode gas, and then the anode gas pressure adjustment unit is controlled, A fuel cell system, wherein the gas pressure is reduced from a positive pressure to a negative pressure. The fuel cell system according to claim 1,
The controller is
It is determined whether or not the temperature inside the fuel cell is equal to or higher than a predetermined temperature, and when it is determined that the temperature inside the fuel cell is equal to or higher than the predetermined temperature, the gas pressure on the anode side is set. A fuel cell system, wherein the fuel cell system is reduced to a negative pressure. The fuel cell system according to claim 1,
The controller is
It is determined whether or not the water content in the electrolyte membrane included in the fuel cell is reduced, and when it is determined that the water content is in a reduced state, the gas pressure on the anode side is reduced to a negative pressure. A fuel cell system. The fuel cell system according to claim 3, wherein
The controller is
A fuel cell system that determines whether or not the water content is reduced based on the temperature inside the fuel cell. The fuel cell system according to any one of claims 1 to 4, further comprising:
A hydrogen gas supply path for supplying hydrogen gas to the anode of the fuel cell;
An anode exhaust gas path for guiding the gas discharged from the anode of the fuel cell to the hydrogen gas supply path;
With
A part of the hydrogen gas supply path and the anode exhaust gas path form a circulation path for circulating hydrogen between the inside of the fuel cell,
The fuel gas system according to claim 1, wherein the anode gas pressure adjusting unit sets a pressure in the circulation channel as a gas pressure on the anode side. The fuel cell system according to claim 5, wherein
The anode gas pressure adjusting unit is
An injector provided upstream of the circulation flow path in the hydrogen gas supply path and having a discharge port for discharging the hydrogen gas to the circulation flow path side and a valve for opening and closing the discharge port;
The controller is
A fuel cell comprising: controlling the anode gas adjusting unit so as to reduce the gas pressure on the anode side from a positive pressure to a negative pressure by adjusting an opening / closing state of the discharge port by the valve of the injector. system. A gas pressure adjusting method for adjusting a gas pressure on an anode side of the fuel cell in a fuel cell system including a fuel cell having a solid polymer electrolyte membrane,
A first step of determining that the gas pressure on the anode side is reduced to a negative pressure when the gas pressure on the anode side of the fuel cell is a positive pressure;
A second step of discharging impurities in the anode gas out of the fuel cell when it is determined in the first step that the gas pressure on the anode side is reduced to a negative pressure;
After the second step, a third step of setting the gas pressure on the anode side to a negative pressure;
A gas pressure adjusting method comprising:

Images