JP2007207724A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system in which a circulating amount is suitably controlled and a gas liquid separation performance is maintained in a high status. <P>SOLUTION: The fuel cell system is provided with a driving means to circulate gas in an exhaust passage to a supply passage through a circulating passage, a separator to separate water from gas to be circulated, a storing unit to store water, a calculating means to calculate a residual water amount in the system based on an operation status of the fuel cell and an environmental status in which the fuel cell is operated, an exhausting means to exhaust water in the storing unit, a calculating means to calculate an operation time to drive the driving means to reduce a residual water amount based on the operation status and environment, a calculating means to calculate an operation time to operate the exhausting means to exhaust water in the storing unit, a calculating means to calculate an water amount stored in the storing unit, and a controlling means for the driving means to be operated till the end of the operation time and for the exhausting means to be operated till the end of the operation time. The controlling means operates the gas driving means at a different driving amount in accordance with whether the water amount exceeds a threshold value or not. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fuel cell system that generates water during power generation.

  Solid polymer fuel cell (hereinafter also referred to as fuel cell) system has a problem that when water is more than necessary in the fuel cell or path when the system is stopped, the water freezes when exposed to freezing for a long time. . Therefore, in order to stably operate the fuel cell system even at a temperature below freezing point, it is necessary to discharge the water in the path of the fuel cell system when the fuel cell system is stopped. For this reason, in a fuel cell including a gas path in the circulation system, gas is circulated through a path including a gas-liquid separator (this is called scavenging) to reduce the amount of remaining water. However, if the scavenging time in the path of the fuel cell system becomes longer, the time required for stopping the fuel cell system becomes longer and the usability becomes worse. That is, since supply of scavenging and dilution air is relied on the pump, a long amount of scavenging consumes a large amount of power, and noise during driving of the pump becomes a problem. Furthermore, there is a problem in that the merchantability is impaired if it takes time to stop the fuel cell system after the ignition switch is turned off.

In addition, protons (hydrogen ions) in the electrolyte membrane in the fuel cell move by water molecules. In the operation of the fuel cell, it is necessary to wet the electrolyte membrane of the fuel cell and the vicinity thereof in order to ensure proton mobility. Therefore, in order to smoothly start the fuel cell system and achieve a stable operation state even at a temperature below freezing point, a certain amount of moisture is required inside the fuel cell.
JP 2003-297399 A JP 2004-288491 A JP 2005-141943 A

  The ability to separate moisture from the gas circulating in the fuel cell system (gas-liquid separation performance) is the amount of residual water in the fuel cell system, the amount of circulation (flow rate per unit time of gas circulating in the fuel cell system), and gas It changes depending on the water level of the tank that stores the water separated by the liquid separator. However, the above conventional technique does not control the circulation amount to an appropriate value according to the change in the gas-liquid separation performance. Therefore, the gas-liquid separation performance cannot be maintained in a high state. An object of the present invention is to provide a technique for controlling the amount of circulation to an appropriate value and maintaining a high gas-liquid separation performance.

  The present invention employs the following means in order to solve the above-described problems. That is, the present invention relates to a fuel cell main body, a gas supply passage for supplying gas to the fuel cell main body, a gas discharge passage for discharging gas from the fuel cell main body, and the gas discharge passage connected to the gas supply passage. A gas circulation passage, gas driving means for circulating the gas in the gas discharge passage through the gas circulation passage to the gas supply passage, a gas-liquid separator for separating moisture from the circulated gas, and the separated moisture A reservoir for storing; drainage means for draining the water in the reservoir to the outside of the fuel cell system; moisture amount calculating means for calculating the amount of moisture stored in the reservoir; and And a control unit that operates the gas driving unit with a different driving amount depending on whether or not it is equal to or greater than a threshold value. In the present invention, the gas driving means is operated with different driving amounts according to the amount of water stored in the reservoir. Therefore, the remaining water in the fuel cell system is scavenged with a drive amount corresponding to the amount of water stored in the reservoir. As a result, the gas-liquid separation performance of the gas-liquid separator can be maintained in a high state.

  The fuel cell system includes the fuel cell main body, the gas supply passage, the gas discharge passage, and the gas circulation passage based on the operating state of the fuel cell main body and the state of the environment in which the fuel cell main body is operated. Means for calculating the amount of residual water in the fuel cell system, and an operating time for calculating an operating time for operating the gas driving means to reduce the amount of residual water to a predetermined value according to the operating state and the state of the environment A calculation means; and a drainage time calculation means for calculating a drainage operation time for operating the drainage means to drain the water in the reservoir outside the fuel cell system, and the control means includes the gas drive The means may be operated until the end of the operating time and the draining means may be operated until the end of the draining operating time. In the present invention, the remaining water in the fuel cell system can be controlled to an appropriate amount by an appropriate scavenging time corresponding to the remaining water amount in the fuel cell system. Also, drain the water in the reservoir at an appropriate time. As a result, the gas-liquid separation performance of the gas-liquid separator can be maintained in a high state.

  In the fuel cell system, when the amount of water is equal to or greater than a predetermined threshold, the control unit may operate the drainage unit until the end of a time obtained by extending the drainage operation time by a predetermined time. In the present invention, the amount of water stored in the reservoir can be maintained at an appropriate value by adjusting the time for draining the water stored in the reservoir outside the fuel cell system.

  In the fuel cell system, when the water content is equal to or greater than a predetermined threshold, the control unit may decrease the drive amount by a predetermined value. In the present invention, the driving amount of the gas driving means can be reduced, and the gas-liquid separation performance of the gas-liquid separator can be maintained in a high state.

  According to the present invention, the circulation rate can be controlled to an appropriate value, and the gas-liquid separation performance can be maintained in a high state.

  Hereinafter, a design apparatus according to the best mode (hereinafter referred to as an embodiment) for carrying out the present invention will be described with reference to the drawings. The configuration of the following embodiment is an exemplification, and the present invention is not limited to the configuration of the embodiment.

  A fuel cell system according to this embodiment will be described with reference to the drawings of FIGS. FIG. 1 is a diagram illustrating a configuration example of a fuel cell system according to the present embodiment. 1, the fuel cell system includes a fuel cell stack 1, an anode gas passage 2, an anode off gas passage 3, an anode off gas circulation passage 4, a cathode gas passage 5, a cathode off gas passage 6, a hydrogen tank 7, a hydrogen pump 8, and a pump 9. , Pressure control valves 10 and 11, filter 12, humidifier 13, gas-liquid separator 14, drain tank 15, drain valve 16, control unit 17, residual water amount calculation unit 18, purge valve 19, and water level detection unit 20.

  The fuel cell stack 1 is configured by stacking a plurality of cells. Each cell includes an electrolyte membrane, an anode (fuel electrode), a cathode (air electrode), and a separator. Between the anode and the cathode, a flow path for hydrogen and air is formed. The anode gas passage 2 is a passage for supplying an anode gas containing hydrogen to the anode of the fuel cell stack 1. The cathode gas passage 5 is a passage for supplying cathode gas containing air to the cathode of the fuel cell stack 1.

  The hydrogen tank 7 supplies anode gas to the anode gas passage 2. The anode gas supplied from the hydrogen tank 7 is adjusted to a predetermined pressure by the pressure regulating valve 10. The anode gas is supplied from the anode gas passage 2 to the anode of the fuel cell stack 1. When the pump 9 (also referred to as an air compressor) is driven, the cathode gas supplied from outside the fuel cell system is supplied to the cathode of the fuel cell stack 1.

  In the anode of the fuel cell stack 1, when anode gas is supplied, hydrogen ions are generated from hydrogen contained in the anode gas. Further, oxygen contained in the air is supplied to the cathode of the fuel cell stack 1. In the fuel cell stack 1, an electrochemical reaction between hydrogen and oxygen occurs to generate electric energy. Further, at the cathode of the fuel cell stack 1, water is generated by combining hydrogen ions generated from hydrogen and oxygen.

  The humidifier 13 humidifies the air supplied to the fuel cell stack 1. In order for an electrochemical reaction to be appropriately performed in the fuel cell stack 1, the electrolyte membrane in the fuel cell stack 1 needs to be in a wet state containing moisture, and thus humidifies the air. In addition, the water in the electrolyte membrane is separated into fine clusters and is combined with sulfonic acid groups in the electrolyte membrane, so that the water in the electrolyte membrane hardly freezes.

  Of the anode gas supplied to the anode, a gas containing unreacted hydrogen and nitrogen permeating from the cathode (hereinafter referred to as anode off gas) is sent from the fuel cell stack 1 to the anode off gas passage 3.

  Further, unreacted gas (hereinafter referred to as cathode offgas) among the cathode gas supplied to the cathode is discharged from the fuel cell stack 1 to the cathode offgas passage 6. The cathode off gas discharged from the cathode passes through the cathode off gas passage 6 and is discharged out of the fuel cell system.

  The anode off gas discharged from the anode of the fuel cell stack 1 passes through the anode off gas passage 3 and the anode off gas circulation passage 4 and is supplied again to the anode of the fuel cell stack 1 together with the anode gas from the hydrogen tank 7. Therefore, the anode off gas passage 3 supplies the anode off gas discharged from the anode of the fuel cell stack 1 to the gas-liquid separator 14.

  The gas-liquid separator 14 separates water and hydrogen contained in the anode offgas discharged from the anode of the fuel cell stack 1. The hydrogen from which the water has been separated by the gas-liquid separator 14 is supplied to the anode gas passage 2 through the anode off-gas circulation passage 4 as the anode gas by the hydrogen pump 8. The anode off-gas circulation passage 4 is a passage for circulating the anode gas delivered from the hydrogen pump 8 to the anode gas passage 2. The anode off gas circulation passage 4 constitutes a circulation path on the anode side.

  The drain tank 15 stores the water separated by the gas-liquid separator 14. By opening and closing the drain valve 16, the water stored in the drain tank 15 is discharged out of the circulation path. Further, the drain valve 16 is appropriately opened and closed so that the water stored in the drain tank 15 does not overflow.

  The control unit 17 is electrically connected to the hydrogen pump 8 and the drain valve 16 and controls the driving of the hydrogen pump 8 and the drain valve 16. The control unit 17 can control the opening / closing time of the drain valve 16 by controlling the driving of the drain valve 16.

  The remaining water amount calculation unit 18 estimates the remaining water amount in the fuel cell system. The amount of remaining water in the fuel cell system is the amount of water present in the fuel cell stack 1, the anode gas passage 2, the anode offgas passage 3, the anode offgas circulation passage 4, the hydrogen pump 8, the gas-liquid separator 14, and the drain tank 15. The amount of water that affects freezing and dry-up of residual water in the fuel cell system.

When impurities such as nitrogen increase in the anode off gas discharged from the anode, the purge valve 19 passes the anode off gas (and the anode gas circulated by the hydrogen pump 8) through a diluter (not shown) outside the circulation path. To discharge. The water level detection unit 20 detects and measures the water level of the water stored in the drain tank 15.

  FIG. 2 is a flowchart for explaining the operation of the fuel cell system according to the present embodiment. The fuel cell system according to the present embodiment executes the process of FIG. 2 when the power generation stop process is performed on the fuel cell system. For example, when the ignition switch is turned off, it is determined that there has been a command to stop the fuel cell system, and the process of FIG. 2 is performed.

  First, power generation stop processing of the fuel cell stack 1 is performed (S01). Specifically, a shut valve (not shown) provided in the hydrogen tank 7 is closed, and the supply of anode gas from the hydrogen tank 7 is shut off to stop power generation. In the fuel cell system according to the present embodiment, anode gas and anode off gas circulate in the fuel cell system in order to scavenge residual water in the fuel cell system. Even after the power generation stop processing of the fuel cell stack 1 is performed, the remaining water in the fuel cell system is scavenged by driving the hydrogen pump 8.

  Specifically, the control unit 17 controls the drive of the hydrogen pump 8 to circulate the anode gas in the anode gas path 2 and the fuel cell stack 1. Then, water and hydrogen contained in the anode off-gas discharged from the anode of the fuel cell stack 1 are separated by the gas-liquid separator 14. And the control part 17 controls the drive of the drain valve 16, and discharges the isolate | separated water out of a circulation path. In the present embodiment, the process for discharging the remaining water in the fuel cell system after the power generation stop of the fuel cell stack 1 from the gas-liquid separator 14 is referred to as a scavenging / circulation process.

  Next, the remaining water amount calculation unit 18 estimates the remaining water amount in the fuel cell system when power generation is stopped from the state amount immediately before the power generation stop processing is performed (S02). For example, the remaining water amount calculation unit 18 calculates the remaining water amount Qini as a process of estimating the remaining water amount in the fuel cell system when power generation is stopped. The remaining water amount Qini is an estimated value of the remaining water amount in the fuel cell system when power generation is stopped, which is obtained from the state amount immediately before the power generation stop process is performed.

  The state quantity includes impedance between the electrodes of the fuel cell stack 1 (membrane resistance), load integrated value (current integrated value), operation time, refrigerant temperature or amount of change in refrigerant temperature, outside air temperature, humidity, and the like. By measuring the impedance between the electrodes of the fuel cell stack 1, the wet state of the electrolyte membrane in the fuel cell stack 1 can be known. Impedance can be measured from the response when an alternating current of a certain frequency is applied from the high voltage electrical system between the electrodes of the fuel cell stack 1. As the impedance, the value immediately before the power generation stop processing is used. By always measuring the impedance until immediately before the power generation stop process, the impedance value immediately before the power generation stop process can be used.

  The load integrated value (current integrated value) is the total power generation amount, and the total amount of generated water in the fuel cell can be known by measuring the load integrated value. The operation time is the power generation time of the fuel cell system. In the case where the power generation of the fuel cell system is a short time and the case where the power generation of the fuel cell system is a long time, the temperature in the path is lower when the power generation of the fuel cell system is short even if the power generation amount is about the same. For this reason, in the case of short-time power generation, the amount of water that is liquid is larger than in the case of long-time power generation.

As for the refrigerant temperature or the amount of change in the refrigerant temperature, the relative amount of change of how much the temperature has risen rather than the absolute value is important. When the temperature in the fuel cell stack 1 is high, the water in the fuel cell stack 1 becomes vapor and tends to go out of the fuel cell system. On the other hand, when the temperature in the fuel cell stack 1 is low, the water in the fuel cell stack 1 does not become vapor but tends to stay in the fuel cell system.

  Since the heat radiation from the fuel cell stack 1 varies depending on the outside air temperature, the outside air temperature affects the refrigerant temperature or the amount of change in the refrigerant temperature. Further, the humidity of the outside air affects the humidity in the path, and thus affects the amount of remaining water. As the state quantity, a state quantity within a predetermined time immediately after stopping power generation can be used. In addition, the remaining amount of water in the fuel cell system when power generation is stopped can be estimated by combining a plurality of the state quantities.

  3 and 4 are diagrams showing examples of the relationship between the state quantity and the remaining water amount in the fuel cell system. In FIG. 3, when the load integrated value is small, the remaining water amount in the fuel cell system shows a small value, and when the load integrated value is large, the remaining water amount in the fuel cell system shows a large value. In FIG. 4, when the refrigerant temperature is high, the remaining water amount in the fuel cell system shows a small value, and when the refrigerant temperature is low, the remaining water amount in the fuel cell system shows a large value.

  Such an impedance (membrane resistance) between electrodes of the fuel cell stack 1, load integrated value (current integrated value), operation time, refrigerant temperature or refrigerant temperature change amount, outside air temperature, humidity and the like in the fuel cell system The relationship with the remaining water amount can be obtained as an empirical formula. Further, the impedance (membrane resistance) between the electrodes of the fuel cell stack 1, the load integrated value (current integrated value), the operation time, the refrigerant temperature or the change amount of the refrigerant temperature, the outside air temperature, the humidity, etc., and the remaining water amount in the fuel cell system And the remaining water amount in the fuel cell system may be obtained by referring to the map (table). The remaining water amount calculation unit 18 calculates the remaining water amount Qini according to this empirical formula or map. For example, among the state quantities, the impedance between the electrodes of the fuel cell stack 1 (membrane resistance), the load integrated value (current integrated value), the operation time, the refrigerant temperature or the amount of change in the refrigerant temperature, etc. are also called the operation history or the operation state. . Further, among the state quantities, the outside air temperature, the humidity, and the like are also called a use environment or an operating environment.

  Further, the control unit 17 calculates a target remaining water amount Qreq (S03). The target remaining water amount Qreq is the remaining water amount in the fuel cell system that is necessary for the electrolyte membrane in the fuel cell stack 1 to be in a moderately wet state in operating the fuel cell system. This is the amount of residual water that can avoid water freezing. Accordingly, the target residual water amount Qreq is required to be an appropriate value in order to avoid freezing and dry-up of residual water in the fuel cell system.

  In addition, the target residual water amount Qreq depends on MEA (Mebrane Electrode Assembly) and components. Furthermore, the value of the target remaining water amount Qreq is a value at which the operating environment of the fuel cell system according to the present embodiment varies depending on the destination such as a cold region or a warm region.

  Next, the control unit 17 calculates the necessary scavenging time T, the circulation amount initial value Q, and the drain valve opening time initial value Tv (S04). The necessary scavenging time T is a value obtained by estimating the execution time of the scavenging / circulation processing necessary for reducing the remaining water amount in the fuel cell system to the target remaining water amount Qreq. That is, this is the estimated time of the scavenging / circulation processing necessary for the remaining water amount Qini in the fuel cell system to reach the target remaining water amount Qreq. This estimated time may be obtained in seconds. Specifically, the relationship between the remaining water amount Qini in the fuel cell system and the scavenging / circulation processing time required to scavenge the remaining water in the fuel cell system to the target remaining water amount Qreq is previously mapped. Then, the necessary scavenging time T corresponding to the value of the remaining water amount Qini in the fuel cell system is obtained from the map.

The circulation amount initial value Q is a value of the circulation amount (L / min) when power generation is stopped. The circulation amount can be increased by increasing the number of revolutions of the hydrogen pump 8 or by pulsing the drive of the hydrogen pump 8. Further, the circulation rate can be reduced by reducing the rotation speed of the hydrogen pump 8 or returning the drive of the hydrogen pump 8 from pulsation to normal drive. The value of the circulation amount initial value Q can be obtained by actual measurement (or simulation).

  The drain valve opening time initial value Tv is the opening time of the drain valve 16 when power generation is stopped. The opening time of the drain valve 16 is a time during which the drain valve 16 is opened in order to discharge water stored in the drain tank 15. The time during which the drain valve 16 is opened is controlled by the control unit 17. The drain valve 16 is opened and closed for a predetermined time when the buffer water level is not less than a predetermined value not only during power generation but also after power generation is stopped.

  The opening time of the drain valve 16 is preset at the start of power generation. Therefore, if the opening time of the drain valve 16 is not changed during power generation, the time set at the start of power generation becomes the opening time of the drain valve 16 when power generation is stopped. The opening time of the drain valve 16 can be changed during power generation. Therefore, if there is a change in the opening time of the drain valve 16 during power generation, the time after the change becomes the opening time of the drain valve 16 when power generation is stopped. The opening time of the drain valve 16 when power generation is stopped is stored, and the control unit 17 acquires and calculates the stored opening time of the drain valve 16 when power generation is stopped. The opening time of the drain valve 16 is determined based on the buffer capacity (L), the gas-liquid separation performance of the gas-liquid separator 14, the circulation amount, and the like. The buffer capacity is the capacity of water that can be stored in the drain tank 15. Further, the buffer capacity is determined by design requirements. Further, the value of the opening time of the drain valve 16 can be obtained by actual measurement (or simulation).

  And the control part 17 acquires a buffer water level from the water level detection part 20 (S05). The buffer water level is the water level (mm) of water stored in the drain tank 15. The water level detection unit 20 measures the buffer water level with reference to the time when no water is present in the drain tank 15. The water level detection unit 20 always measures the buffer water level. Here, the buffer water level acquired by the control unit 17 from the water level detection unit 20 is defined as a buffer water level a.

  Next, the control part 17 determines whether the buffer water level a acquired from the water level detection part 20 is more than the predetermined threshold value A (S06). The anode off gas delivered from the anode enters the gas-liquid separator 14 and is separated into hydrogen and water. When the water level is high, there is a high possibility that the water near the water surface stored in the drain tank 15 is sent again to the anode offgas passage 3 together with the separated hydrogen. Therefore, when the water level of the water stored in the drain tank 15 is high, the gas-liquid separation performance of the gas-liquid separator 14 is lowered. Here, the value obtained by dividing the amount of recovered water (the amount of water stored in the drain tank 15) of the gas-liquid separator 14 by the amount of introduced water (the amount of water entering the inlet portion of the gas-liquid separator 14) is the gas-liquid separation rate (%). That's it.

  FIG. 5 is a diagram showing the relationship between the buffer water level and the gas-liquid separation rate. The horizontal axis in FIG. 5 indicates the buffer water level (mm), and the vertical axis in FIG. 5 indicates the gas-liquid separation rate (%). Curve X in FIG. 5 shows changes in the gas-liquid separation rate with respect to the buffer water level when the circulation rate is small. Curve Y in FIG. 5 shows the change in the gas-liquid separation rate with respect to the buffer water level when the circulation amount is large. As shown in FIG. 5, the gas-liquid separation rate is maintained at a higher value in the curve X (when the circulation amount is small) than in the curve Y (when the circulation amount is large).

  When the amount of circulation is large, the gas-liquid separation rate tends to drop sharply when the buffer water level exceeds a certain value (A in FIG. 5). In this embodiment, when the buffer water level increases, the gas-liquid separation rate starts to decrease. The predetermined threshold A may be obtained by actual measurement (or simulation).

When the buffer water level a is equal to or greater than the predetermined threshold A, the control unit 17 controls the driving of the hydrogen pump 8 and decreases the circulation amount by a predetermined value from the current value (S07). Specifically, the control unit 17 controls the driving of the hydrogen pump 8 and decreases the rotational speed of the hydrogen pump 8 from the current value by a predetermined value. When the drive of the hydrogen pump 8 is switched to pulsation, the control unit 17 controls the drive of the hydrogen pump 8. Then, the control unit 17 switches the driving of the hydrogen pump 8 from pulsation to normal driving. Thereby, the circulation amount can be decreased from the current value by a predetermined value.

  In this case, the circulation amount is set to a value at which the rotation efficiency is high. Rotational efficiency is a percentage of the number of times liquid water (liquid water) circulates in the fuel cell system compared to when gas circulates in the fuel cell system once. FIG. 6 is a diagram showing the relationship between the circulation amount and the rotation efficiency. The horizontal axis in FIG. 6 indicates the circulation amount (L / min), and the vertical axis indicates the rotation efficiency (%). FIG. 6 shows the lowest rotation efficiency when the circulation amount is near zero. The circulation rate increases to the value B in FIG. 6 and the rotation efficiency also increases. However, even if the circulation amount increases from the value B in FIG. 6 to the value C in FIG. 6, the rotation efficiency maintains a constant high value. The amount of circulation when the rotation efficiency maintains a constant high value is called a high efficiency region. The value at which the circulation amount is in the high efficiency region is obtained by actual measurement (or simulation). In addition, a predetermined value for reducing the rotation speed of the hydrogen pump 8 (that is, the difference between the current value of the rotation speed of the hydrogen pump 8 and the rotation speed value of the hydrogen pump 8 in which the circulation amount is in the high efficiency region) is actually measured ( Alternatively, it may be obtained by simulation.

  In addition, when the drive of the hydrogen pump 8 is controlled so as to reduce the rotation speed of the hydrogen pump 8, the control unit 17 may calculate the necessary scavenging time T after reducing the rotation speed of the hydrogen pump 8 again. Good. Further, when the driving of the hydrogen pump 8 is controlled to be switched from the pulsation to the normal driving, the control unit 17 recalculates the necessary scavenging time T after the driving of the hydrogen pump 8 is switched from the pulsation to the normal driving. May be. In these cases, subsequent processing (processing from S08 to S10 in FIG. 2) may be performed using the necessary scavenging time T calculated again.

  Next, the control unit 17 increases the drain valve opening time initial value Tv for a predetermined time (S08). This predetermined time is determined based on the buffer capacity, the gas-liquid separation performance of the gas-liquid separator 14, the current circulation amount (circulation amount reduced by the processing of S07), and the like. Further, the value of the predetermined time for increasing the drain valve opening time initial value Tv can be obtained by actual measurement (or simulation).

  Moreover, in this embodiment, the example in the case of increasing the drain valve opening time initial value Tv for a predetermined time was shown. However, the implementation of the present invention is not limited to such a configuration. For example, the process shown in FIG. 2 may be performed without increasing the drain valve opening time initial value Tv for a predetermined time. In that case, after controlling the drive of the hydrogen pump 8 and performing the process of reducing the circulation amount (process of S07), the process of increasing the drain valve opening time initial value Tv for a predetermined time (the process of S08) is not performed. The process of S09 may be performed.

  On the other hand, when the buffer water level a is not equal to or greater than the predetermined threshold A (when it is determined negative in S06), the process of S09 is performed.

  Then, the control unit 17 determines whether or not the scavenging / circulation processing time has reached the necessary scavenging time T (S09). Specifically, the control unit 17 acquires the elapsed time of the scavenging / circulation process from a timer (not shown) that counts the time of the scavenging / circulation process, and compares it with the required scavenging time T. Then, the control unit 17 determines whether the acquired elapsed time of the scavenging / circulation process is the same value as the necessary scavenging time T or a value greater than that.

  When it is determined that the scavenging / circulation processing time has not reached the required scavenging time T, the control unit 17 continues the scavenging / circulation processing and returns control to the processing of S05. Then, the processes from S05 to S09 are performed again.

On the other hand, when it is determined that the scavenging / circulation processing time has reached the required scavenging time T, the control unit 17 controls to stop driving the hydrogen pump 8 and to stop driving the drain valve 16. (S10). When the control unit 17 performs control so as to stop the driving of the drain valve 16, the opening and closing of the drain valve 16 is stopped. In the above case, the opening / closing of the drain valve 16 may be stopped simultaneously with the stop of the driving of the hydrogen pump 8. In addition, the opening / closing of the drain valve 16 may be stopped separately from stopping the driving of the hydrogen pump 8. For example, when the control unit 17 stops driving the hydrogen pump 8 and the opening time of the drain valve 16 has not ended, the opening and closing of the drain valve 16 may be stopped after the opening time of the drain valve 16 ends. Good. And when the control part 17 controls to stop the drive of the hydrogen pump 8, and it controls to stop the drive of the drain valve 16, the operation | movement of a fuel cell system is stopped.

  According to the present embodiment, when the buffer water level a is equal to or greater than the predetermined threshold A, the control unit 17 controls the driving of the hydrogen pump 8 to reduce the circulation amount. Further, the circulation amount is set as a high efficiency region. Therefore, the gas-liquid separation performance of the gas-liquid separator 14 can be maintained in a high state. Then, scavenging / circulation processing in the fuel cell system can be performed with the gas-liquid separator 14 having high gas-liquid separation performance. As a result, the scavenging / circulation processing time in the fuel cell system can be shortened. In addition, freezing of residual water in the fuel cell system can be prevented. Furthermore, it is possible to reduce both the time for scavenging and circulation processing in the fuel cell system and the prevention of freezing of the remaining water in the fuel cell system. In addition, freezing of residual water in the fuel cell system can inhibit the stable power generation of the fuel cell and reduce the possibility of loss of auxiliary equipment.

<Modification>
In the above embodiment, the fuel cell system has the hydrogen pump 8 and the gas-liquid separator 14. For example, the cathode-side pump 9 may be used to scavenge residual water in the fuel cell system, like the hydrogen pump 8. Further, the gas-liquid separator 14 of the anode off gas passage 3 may be provided in the cathode off gas passage 6. Further, a drain tank 15 and a drain valve 16 may be provided in the gas-liquid separator 14 in that case.

  Also, a cathode offgas circulation passage is provided so that air discharged to the cathode offgas passage 6 passes through the cathode offgas circulation passage and is supplied again to the cathode of the fuel cell stack 1 together with the cathode gas supplied from outside the fuel cell system. May be. A cathode-side circulation path is configured by the cathode off-gas circulation path. By controlling the driving of the pump 9 and the gas-liquid separator 14, the remaining water in the fuel cell system can be discharged out of the circulation path.

  Further, for example, in a state where the hydrogen pump 8 and the gas-liquid separator 14 are provided in the anode gas passage 2, the pump 9 is used for scavenging the remaining water in the fuel cell system, and the cathode off-gas passage 6 is provided with the cathode gas. A liquid separator may be provided. Further, a drain tank 15 and a drain valve 16 may be provided in the cathode gas-liquid separator in that case.

  Also, a cathode offgas circulation passage is provided so that air discharged to the cathode offgas passage 6 passes through the cathode offgas circulation passage and is supplied again to the cathode of the fuel cell stack 1 together with the cathode gas supplied from outside the fuel cell system. May be. A cathode-side circulation path is configured by the cathode off-gas circulation path. By controlling any or all of the hydrogen pump 8, the pump 9, the gas / liquid separator 14, and the cathode gas / liquid separator, the remaining water in the fuel cell system can be discharged out of the circulation path.

It is a figure which shows the structural example of the fuel cell system which concerns on this embodiment. It is a flowchart explaining operation | movement of the fuel cell system which concerns on this embodiment. It is the figure which showed the example of the relationship between a state quantity and the amount of residual water in a fuel cell system. It is the figure which showed the example of the relationship between a state quantity and the amount of residual water in a fuel cell system. It is the figure which showed the relationship between a buffer water level and a gas-liquid separation rate. It is the figure which showed the relationship between circulation amount and rotation efficiency.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel cell stack 2 Anode gas passage 3 Anode off gas passage 4 Anode off gas circulation passage 5 Cathode gas passage 6 Cathode off gas passage 7 Hydrogen tank 8 Hydrogen pump 9 Pump 10, 11 Pressure regulating valve 12 Filter 13 Humidifier 14 Gas-liquid separator 15 Drain Tank 16 Drain valve 17 Control unit 18 Remaining water amount calculation unit 19 Purge valve 20 Water level detection unit

Claims (4)

A fuel cell body;
A gas supply passage for supplying gas to the fuel cell body;
A gas discharge passage for discharging gas from the fuel cell body;
A gas circulation passage connecting the gas discharge passage to the gas supply passage;
Gas driving means for circulating the gas in the gas discharge passage through the gas circulation passage to the gas supply passage;
A gas-liquid separator for separating moisture from the circulating gas;
A reservoir for storing the separated water;
Drainage means for draining the water in the reservoir outside the fuel cell system;
Moisture amount calculating means for calculating the amount of moisture stored in the reservoir;
And a control unit that operates the gas driving unit with a different driving amount depending on whether or not the water content is equal to or greater than a predetermined threshold value. The remaining in the fuel cell system including the fuel cell body, the gas supply passage, the gas discharge passage, and the gas circulation passage based on the operating state of the fuel cell body and the state of the environment in which the fuel cell body is operated. Means for calculating the amount of water;
An operation time calculating means for calculating an operation time for operating the gas driving means in order to reduce the residual water amount to a predetermined value according to the operating state and the environmental state;
Drainage time calculating means for calculating drainage operation time for operating the drainage means to drain the water in the reservoir outside the fuel cell system; and
2. The fuel cell system according to claim 1, wherein the control unit operates the gas driving unit until the end of the operation time and operates the drainage unit until the end of the drainage operation time.   3. The fuel cell system according to claim 2, wherein the control unit operates the drainage unit until the end of a time obtained by extending the drainage operation time by a predetermined time when the moisture amount is equal to or greater than a predetermined threshold.   4. The fuel cell system according to claim 1, wherein the control unit decreases the drive amount by a predetermined value when the moisture amount is equal to or greater than a predetermined threshold value. 5.

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