JP2008004445A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To consume oxidant gas present in an oxidant electrode in a short time and in a low deterioration state in the stop of a system. <P>SOLUTION: A control part 31 supplies hydrogen to a fuel electrode of a fuel cell stack 1 as stop control executing in the stop of the system, controls a current taking out part 30 according to a state of the fuel cell stack 1 in a state that the supply of oxidant gas to the oxidant electrode of the fuel cell stack 1 is stopped. The oxidant gas in the oxidant electrode of the fuel cell stack 1 is consumed in accordance with the current taken out by the current taking out part 30. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fuel cell system, and more particularly to stop control executed when the system is stopped.

  Conventionally, a fuel gas (for example, hydrogen) is supplied to the fuel electrode, and an oxidant gas (for example, air) is supplied to the oxidant electrode, whereby these gases are reacted electrochemically to generate power. A fuel cell system including a battery is known. In this type of fuel cell system, when air is present in both the oxidant electrode and the fuel electrode at the time of system startup, the hydrogen that is the interface between the air present on the fuel electrode side and newly supplied hydrogen The presence of the front may cause the fuel cell stack to deteriorate. Specifically, when the hydrogen front exists on the fuel electrode side, the following reaction occurs on the oxidant electrode side facing the region where no hydrogen exists on the fuel electrode side.

C + 2H ₂ O → CO ₂ + 4H ⁺ + 4e ⁻
By this reaction, corrosion of the carbon carrier carrying a catalyst such as platinum occurs and the fuel cell stack is deteriorated. For this reason, various start-up methods that suppress such deterioration have been developed. However, in view of the fact that the cause of deterioration during start-up is air in both the oxidizer electrode and the fuel electrode, stop It is also conceivable to suppress deterioration at startup by taking some measures at times.

For example, Patent Document 1 discloses a method for stopping a fuel cell. In such a method, the load connected to the fuel cell is disconnected, the flow of air to the oxidant electrode is stopped, and oxygen and hydrogen in the fuel cell are caused to react with each other, thereby allowing oxygen to flow between the fuel electrode and the oxidant electrode. In the oxidizer electrode until no gas remains in it and the gas composition in the fuel electrode and oxidant electrode reaches an equilibrium gas composition comprising at least 0.0001% hydrogen and the remainder of the fuel cell inert gas. The concentration of remaining oxygen is decreased, and the concentration of hydrogen in the fuel cell is increased. When the equilibrium gas composition is reached, a gas composition consisting of at least 0.0001% hydrogen and the balance fuel cell inert gas is maintained while the system is shut down.
JP 2005-518632 A

  By the way, consuming oxygen at the oxidizer electrode at the time of stoppage is effective as a technique for suppressing deterioration at start-up. However, even when this oxygen is consumed, deterioration caused in the fuel cell is reduced. It is important to do. From the viewpoint of energy efficiency, it is important to consume oxygen in a short time without unnecessarily consuming energy.

  The present invention has been made in view of such circumstances, and an object of the present invention is to perform an operation of consuming oxidant gas existing in the oxidant electrode in a short time and with little deterioration when the system is stopped. is there.

  In order to solve such problems, the present invention provides a fuel cell, an oxidant gas system, a fuel gas system, a fuel gas system, an oxidant system regulating means, a fuel system regulating means, a current extraction means, A fuel cell system having a control means is provided. Here, in the fuel cell, fuel gas is supplied to the fuel electrode, and oxidant gas is supplied to the oxidant electrode, whereby the fuel gas and the oxidant gas are reacted electrochemically to generate electric power. To do. The oxidant gas system includes an oxidant gas supply channel that supplies oxidant gas to the oxidant electrode of the fuel cell, and an oxidant gas discharge channel that discharges oxidant gas from the oxidant electrode. The fuel gas system includes a fuel gas discharge passage for discharging fuel gas from the fuel electrode of the fuel cell. The oxidant system restricting means is provided in the oxidant gas system, and restricts the entry of outside air from the oxidant gas system to the fuel cell according to its own operating state. The fuel system regulating means is provided in the fuel gas system and regulates the entry of outside air from the fuel gas system to the fuel cell according to its own operating state. The current extraction means extracts current from the fuel cell. The control unit controls the oxidant system regulation unit, the fuel system regulation unit, and the current extraction unit. In this case, as a stop control executed when the system is stopped, the control means supplies the fuel gas to the fuel electrode of the fuel cell and stops the supply of the oxidant gas to the oxidant electrode of the fuel cell. By controlling the current extraction means according to the state of the battery, the oxidant gas in the oxidant electrode of the fuel cell is consumed according to the current taken out by the current extraction means.

  According to the present invention, oxygen present in the oxidizer electrode can be consumed by taking out the current from the fuel cell in a state where the fuel gas is supplied to the fuel electrode. At this time, by taking out the current in accordance with the state of the fuel cell, it is possible to suppress spending of extra time and energy. The agent gas can be consumed. In addition, by consuming the oxidant gas at the oxidant electrode when the fuel cell is stopped, the amount of oxidant gas present at the oxidant electrode can be reduced when the fuel cell is started. Can do.

(First embodiment)
FIG. 1 is a block diagram showing the overall configuration of the fuel cell system according to the first embodiment of the present invention. A fuel cell system comprises a fuel cell structure (fuel cell) in which a solid polymer electrolyte membrane is sandwiched between an oxidant electrode and a fuel electrode, sandwiched by separators, and a fuel that is formed by stacking a plurality of fuel cells. A battery stack 1 is provided. In the fuel cell stack 1, fuel gas is supplied to the fuel electrode, and oxidant gas is supplied to the oxidant electrode, whereby these gases are reacted electrochemically to generate electric power. In the present embodiment, a case will be described in which hydrogen is used as the fuel gas and oxygen (specifically, air containing oxygen) is used as the oxidant gas. This fuel cell system is mounted on a vehicle and used as a power source for an electric motor that drives the vehicle, for example.

  The fuel cell system includes a hydrogen system 10 for supplying hydrogen to the fuel cell stack 1 and an air system 20 for supplying air to the fuel cell stack 1.

  In the hydrogen system 10, hydrogen, which is a fuel gas, is supplied to the fuel cell stack 1 from a fuel supply device (for example, a fuel tank 11 that is a high-pressure hydrogen cylinder) via a hydrogen supply channel L10. Specifically, a hydrogen supply valve 12 is provided in the hydrogen supply flow path L10 downstream of the fuel tank 11, and when the hydrogen supply valve 12 is opened, the high-pressure hydrogen gas from the fuel tank 11 flows downstream thereof. The pressure is mechanically reduced to a predetermined pressure by a pressure-reducing valve (not shown) provided in the. The depressurized hydrogen is further depressurized by a hydrogen pressure regulating valve 13 provided downstream of the depressurizing valve, and then supplied to the fuel cell stack 1. The open / close state of the hydrogen supply valve 12 is controlled by a control device 3 to be described later according to the necessity of hydrogen supply to the fuel cell stack 1, and the hydrogen pressure regulating valve 13 is supplied to the fuel cell stack 1. The opening degree is controlled by the control device 3 so that the hydrogen pressure becomes a desired value.

  Gas discharged from the fuel electrode side of the fuel cell stack 1 (exhaust gas containing unused hydrogen) is discharged to the hydrogen circulation passage L11. The other end of the hydrogen circulation flow path L11 is connected to the hydrogen supply flow path L10 on the downstream side of the hydrogen pressure regulating valve 13. The hydrogen circulation passage L11 is provided with hydrogen circulation means such as a hydrogen circulation pump 14 and an ejector 15, for example. By this hydrogen circulation means, the hydrogen discharged from the discharge side of the fuel electrode is circulated to the supply side, and the fuel consumption of hydrogen can be improved.

  By the way, when air is used as the oxidant gas, since nitrogen in the air permeates from the oxidant electrode to the fuel electrode, the nitrogen concentration of the gas in the hydrogen system 10 tends to increase and the hydrogen partial pressure tends to decrease. For this reason, the hydrogen circulation flow path L11 is connected to a hydrogen discharge flow path L12 for discharging the gas in the hydrogen system 10 to the outside (that is, a part of the hydrogen circulation flow path L11 discharges hydrogen from the fuel electrode). It also functions as a hydrogen discharge flow path L12). A purge valve 16 is provided in the hydrogen discharge flow path L12, and an exhaust gas (a gas containing nitrogen, unused hydrogen, etc.) flowing through the hydrogen circulation flow path L11 by switching the open / close state of the purge valve 16 Is discharged to the outside. The open / close state of the purge valve 16 is controlled by the control device 3 according to the operating state of the fuel cell stack 1. For example, the purge valve 16 is basically controlled to be in a closed state, but can be switched from a closed state to an open state as necessary by estimating the nitrogen concentration in the fuel electrode or at predetermined intervals. It is like that. Thereby, nitrogen is purged from the hydrogen system together with unreacted hydrogen, and a decrease in hydrogen partial pressure can be suppressed.

  Further, as one of the features of this embodiment, the purge valve 16 opens and closes the flow path according to its own operating state, that is, its open / closed state, so that the hydrogen discharge flow path L12 is connected to the fuel cell stack 1. It is responsible for regulating the entry of outside air (air). Here, in view of the presence of the hydrogen supply device upstream of the hydrogen supply flow path L10, the cause of the air entering the fuel cell stack 1 from the hydrogen system 10 is the opening of the hydrogen discharge flow path L12. Only at the edge. In other words, the purge valve 16 functions as a hydrogen system regulating unit that regulates the entry of outside air from the hydrogen system 10 into the fuel cell stack 1. In the present embodiment, the purge valve 16 is hereinafter referred to as a “hydrogen-based outlet valve 16”.

  In the air system 20, for example, when the atmospheric air is taken in and compressed by the compressor 21, the compressed air is supplied to the fuel cell stack 1 via the air supply channel L 20. Supplied. Gas discharged from the oxidant electrode side of the fuel cell stack 1 (air in which a part of oxygen is consumed) is discharged to the outside (atmosphere) through the air discharge flow path L21. An air pressure regulating valve 22 is provided in the air discharge flow path L21. The opening of the air pressure regulating valve 22 is controlled by the control device 3 together with the drive amount (rotation speed) of the compressor 21 so that the air pressure and the air flow rate supplied to the fuel cell stack 1 have desired values. The

  As one of the features of the present embodiment, the air system 20 is provided with an oxidant system restricting means for restricting the entry of outside air from the air system 20 into the fuel cell stack 1, and this oxidant system restricting means. Is composed of an air system inlet valve 23 and an air system outlet valve 24.

  The air system inlet valve 23 is provided in the air supply flow path L20, and restricts the entry of outside air from the air supply flow path L20 into the fuel cell stack 1 by opening and closing the flow path according to its open / closed state. To do. In addition, the air system outlet valve 24 is provided in the air discharge passage L21, and the outside air enters the fuel cell stack 1 from the air discharge passage L21 by opening and closing the passage according to its own open / close state. To regulate. From the viewpoint of minimizing the volume of the space between the air system inlet valve 23 and the air system outlet valve 24, the air system inlet valve 23 is provided immediately above the fuel cell stack 1 in the air supply flow path L20. The air system outlet valve 24 is provided immediately below the fuel cell stack 1 in the air discharge passage L21. For this reason, among the various elements provided in the air supply flow path L20, the air system inlet valve 23 is laid out at a position closest to the fuel cell stack 1, and this air supply flow path L20 is connected to the air system inlet valve 23 and the fuel. The battery stack 1 is not provided with any parts other than piping. Of the various elements provided in the air discharge channel L21, the air system outlet valve 24 is laid out at a position closest to the fuel cell stack 1, and the air exhaust channel L21 is connected to the air system outlet valve 24 and the fuel. The battery stack 1 is not provided with any parts other than piping.

  The control device 3 is mainly configured by a current extraction unit 30 and a control unit 31. The current extraction unit 30 is controlled by the control unit 31 and extracts current from the fuel cell stack 1. The current extracted by the current extraction unit 30 is supplied to load means such as the secondary battery 2. The control unit 31 has a function of controlling the entire system in an integrated manner, and controls the operating state of the fuel cell stack 1 by controlling each part of the system according to the control program. In relation to the present embodiment, the control unit 31 controls a current value or a voltage value when the current extraction unit 30 extracts current as stop control executed when the system is stopped, and the hydrogen-based outlet valve 16, The open / close state of the air system inlet valve 23 and the air system outlet valve 24 is controlled. Detection signals from various sensors are input to the control unit 31 in order to detect the operating state of the fuel cell system.

  2 and 3 are explanatory diagrams of the voltage sensor 32. The voltage sensor 32 is a sensor that detects the voltage of the fuel cell stack 1. As shown in FIG. 2A, the voltage sensor 32 detects the voltages of the individual power generation cells 1a constituting the fuel cell stack 1, respectively. However, as the voltage sensor 32, as shown in FIG. 2B, the voltage of each cell unit may be detected using a cell unit composed of a plurality of power generation cells 1a as a detection unit. The total voltage of the fuel cell stack 1 can also be detected from the sum of the voltage values obtained from these voltage sensors 32.

  Furthermore, in the case of accurately monitoring the voltage state of each power generation cell 1a, as shown in FIG. 3A, the flow of hydrogen as a fuel gas, for example, at a plurality of locations for each power generation cell 1a. The voltage sensors 32 may be provided at both ends (that is, the hydrogen supply side and the discharge side) opposite to each other. In this case, as the voltage sensor 32, as shown in FIG. 3B, the cell unit may be provided as a detection unit, and the voltage sensor 32 may be provided at a plurality of locations of each cell unit.

  The hydrogen pressure sensor 33 is provided in the hydrogen supply flow path L10, and is a sensor that detects the pressure of hydrogen supplied to the fuel electrode of the fuel cell stack 1. The air pressure sensor 34 is a sensor that is provided in the air supply flow path L <b> 20 and detects the pressure of air supplied to the oxidant electrode of the fuel cell stack 1. The air flow rate sensor 35 is a sensor that detects the flow rate of air flowing through the air supply flow path L20.

  Hereinafter, stop control executed in the fuel cell system having such a configuration will be described. FIG. 4 is a flowchart showing a stop control procedure according to the first embodiment of the present invention. The process shown in this flowchart is executed by the control unit 31 in response to an input of a signal that instructs to stop the system, such as turning off the ignition switch of the vehicle. As a premise for starting the stop control, hydrogen supply and air supply to the fuel cell stack 1 are continued. Therefore, various devices necessary for hydrogen / air supply such as the hydrogen circulation pump 14 and the compressor 21 remain in operation.

  First, in step 1 (S1), the control unit 31 stops air supply to the oxidant electrode of the fuel cell stack 1. Specifically, the control unit 31 stops the operation of the compressor 21.

  In step 2 (S2), the control unit 31 closes the hydrogen-based outlet valve 16. Therefore, after the process of step 2 is executed, the entry of outside air (air) from the hydrogen discharge flow path L12 to the fuel cell stack 1 is restricted as the hydrogen outlet valve 16 is closed.

  In step 3 (S3), the control unit 31 performs load extraction control. The load extraction control is to control the current value (or voltage value) when the current extraction unit 30 extracts current. By this load extraction control, air (oxygen) in the oxidant electrode (in a broad sense, including the air system 20 communicating with the oxidant electrode) of the fuel cell stack 1 is consumed. Note that, in the process of step 3, as a precondition, since the hydrogen supply valve 12 and the hydrogen pressure regulating valve 13 remain open, the load takeout control continues to supply hydrogen to the fuel cell stack 1. Executed in state. The control unit 31 appropriately determines a current setting value, which is a control command value for the current extracted by the current extraction unit 30, and controls the current extraction unit 30 based on the current setting value, thereby supplying current from the fuel cell stack 1. Take out.

  By the way, in view of the point that oxygen present in the oxidizer electrode is consumed in a short time in the load extraction control, it is preferable to set the current set value to a large value. However, when an excessive current is taken out from the fuel cell stack 1, hydrogen supply delay or supply variation to the individual power generation cells 1a occurs on the fuel electrode side, and hydrogen necessary for the reaction is insufficient. As a result, the fuel cell stack 1 may be deteriorated. Therefore, the control unit 31 performs load extraction control in consideration of both shortening of the time required for oxygen consumption and suppression of hydrogen shortage at the fuel electrode.

  FIG. 5 is a flowchart showing a detailed procedure of the load take-out control according to the first embodiment. First, in step 30 (S30), the current extraction speed Is is set to an initial value Isint. The current extraction speed Is indicates an increase amount of the current setting value per unit time, and the control unit 31 increases the current setting value at a constant speed according to the current extraction speed Is. The initial value Isint is a fixed value set in advance through experiments and simulations, and oxygen existing in the oxidant electrode in consideration of the characteristics of the fuel cell stack 1 and the flow rate and pressure of the supplied oxidant gas. The optimal value is set from the viewpoint of consuming the product in a short time. The control unit 31 determines a current setting value based on the set current extraction speed Is, and then controls the current extraction unit 30 based on the current setting value. Thereby, the current value extracted from the current extraction unit 30 increases linearly according to the current extraction speed Is.

  In step 31 (S31), the voltage detected by the voltage sensor 32 is read.

  As shown in step 30 described above, when the current extraction speed Is is set, the control unit 31 thereafter increases the current set value at a constant speed in accordance with the current extraction speed Is. At this time, the control unit 31 refers to the voltage detected by the voltage sensor 32 and increases the current extracted from the current extraction unit 30, that is, the current set value within a range where the voltage of the fuel cell stack 1 does not become negative. And When the voltage of the fuel cell stack 1 is predicted to be negative, the current set value is decreased from the current value, and the processing from step 30 is started again.

  In step 32 (S32), the voltage change rate Vs is calculated. The voltage change speed Vs is a voltage decrease amount per predetermined (unit) time, and can be specified based on a time-series transition of the voltage detected by the voltage sensor 32. The voltage change speed Vs may be calculated for each detection value of the voltage sensor 32 provided in each power generation cell 1a. However, from the viewpoint of reducing the processing load, a specific power generation is possible. You may selectively process the detected value from the voltage sensor 32 which detects the voltage of the cell 1a (or cell unit). Alternatively, the voltage change rate Vs may be calculated using the overall voltage of the fuel cell stack 1 specified by the individual voltage sensors 32.

  In step 33 (S33), it is determined whether or not the calculated voltage change speed Vs is equal to or higher than a determination value Vsth. In the case where oxygen is consumed in the oxidizer electrode by extracting current from the fuel cell stack 1, if the hydrogen in the fuel electrode is insufficient due to excessive current extraction, the voltage of the fuel cell stack 1 is Decreases rapidly. Therefore, through experiments and simulations, a voltage decrease range that can be regarded as deficient in hydrogen at the fuel electrode is acquired in advance, and the determination value Vsth is set based on this. If an affirmative determination is made in step 33, that is, if the voltage change speed Vs is equal to or greater than the determination value Vsth (Vs ≧ Vsth), the process proceeds to step 34. On the other hand, if a negative determination is made in step 33, that is, if the voltage change speed Vs is smaller than the determination value Vsth (Vs <Vsth), the process proceeds to step 35.

  In step 34 (S34), the control unit 31 changes the current extraction speed Is. Specifically, the control unit 31 decreases the current extraction speed Is by a predetermined amount ΔIs based on the currently set current extraction speed Is. The control unit 31 appropriately determines a current set value based on the changed current extraction speed Is, and then controls the current extraction unit 30 based on the current set value.

  In step 35 (S35), the control unit 31 changes the current extraction speed Is. Specifically, the control unit 31 increases the current extraction speed Is by a predetermined amount ΔIs based on the currently set current extraction speed Is. The changed current extraction speed Is may have an initial value Isint as an upper limit, and the current extraction speed Is may not be larger than the initial value Isint. The control unit 31 appropriately determines a current set value based on the changed current extraction speed Is, and then controls the current extraction unit 30 based on the current set value.

  In step 36 (S36), it is determined whether to end the load take-out control. Specifically, the control unit 31 determines whether air (oxygen) existing in the oxidizer electrode has been consumed. Due to the fact that the air supply is stopped in step 1, by performing the load extraction control, the oxygen amount at the oxidizer electrode tends to decrease. Therefore, in step 36, the end timing of the load extraction control is determined by determining whether or not oxygen present in the air system 20 (mainly the oxidant electrode) has been consumed. When an affirmative determination is made in step 36, that is, when oxygen in the oxidizer electrode is consumed, current extraction by the current extraction unit 30 is stopped, and this routine is terminated. On the other hand, if a negative determination is made in step 36, that is, if oxygen in the oxidizer electrode is not consumed, the load extraction control is continued, and the process returns to step 31 described above.

  Here, a method for determining whether or not oxygen in the oxidizer electrode has been consumed will be described. For example, the control unit 31 determines oxygen consumption by the following method.

  First, as a first method, the control unit 31 determines that oxygen in the air system 20 is consumed when the voltage value obtained from the voltage sensor 32 is equal to or less than the determination value. When oxygen is consumed, the reaction required for power generation does not occur, so the voltage of the fuel cell stack 1 becomes zero. Therefore, the consumption of oxygen can be determined by presetting a value that can be considered that the voltage of the fuel cell stack 1 is substantially zero as a determination value through experiments and simulations.

  Note that, as shown in FIG. 2A, all voltages in the individual power generation cells 1a may be targeted as voltages to be compared with the judgment values, or as shown in FIG. All of the cell units may be targeted. In addition, as a voltage value to be compared with the judgment value, as shown in FIGS. 3A and 3B, voltages at a plurality of locations detected in each power generation cell 1a or cell unit may be used. Good.

  As a second method, the control unit 31 integrates the amount of current extracted by the current extraction unit 30 in response to the start of the load extraction control, and calculates the amount of charge obtained thereby as needed. In addition, the control unit 31 calculates the number of moles of oxygen from the capacity of the flow paths L20 and 21 of the air system 20, the pressure and temperature of the air, and the number of moles of oxygen based on the previously calculated charge amount. However, it is determined that the oxygen in the air system 20 has been consumed by determining that the electric charge has been consumed until the concentration sufficiently reduces the voltage.

  As a third technique, the control unit 31 consumes oxygen in the air system 20 based on a temporal change amount of current actually taken out by the current extraction unit 30 (hereinafter referred to as “current change rate”). It may be determined whether or not it has been done. When oxygen in the oxidizer electrode is consumed, the current actually taken out from the fuel cell stack 1 rapidly decreases and then tends to converge to a certain value. Therefore, the control unit 31 monitors the current change rate, and if the current change rate is stable even after a predetermined time has elapsed (specifically, substantially becomes “0”), the oxygen of the air system 20 is detected. Is determined to be consumed.

  As a fourth method, the control unit 31 calculates the frequency of the hydrogen supply command to the fuel electrode (the number of hydrogen supply commands per unit time) in response to the start of the load extraction control. And the control part 31 determines with the oxygen of the oxidizer electrode having been consumed, when the frequency of this supply command becomes below a predetermined number of determinations. For example, in the case where the hydrogen pressure at the fuel electrode is controlled to be constant as a premise for load extraction control, when oxygen is no longer present at the oxidizer electrode, the hydrogen consumed at the fuel electrode is correspondingly reduced. For this reason, the frequency of the hydrogen supply command also decreases. Therefore, by appropriately setting the determination value through experiments and simulations, it can be determined from the frequency of the hydrogen supply command that oxygen in the air system 20 has been consumed.

  As a fifth method, on the premise that a flow rate sensor for detecting the flow rate of hydrogen is provided on the inlet side and the outlet side of the fuel cell stack 1, the control unit 31 determines the difference in hydrogen flow rate between the inlet side and the outlet side. Whether or not oxygen in the air system 20 is consumed may be determined based on (hereinafter referred to as “inlet / outlet flow rate difference”). In general, when oxygen is no longer present in the oxidizer electrode due to load extraction control, the hydrogen consumed in the fuel electrode is correspondingly reduced, so the flow rate difference between the inlet and outlet is substantially “0”. Therefore, it is possible to determine that oxygen in the air system 20 is consumed from a comparison between the inlet / outlet flow rate difference and the determination value by appropriately setting the determination value through experiments and simulations.

  From the viewpoint of determining whether or not oxygen in the air system 20 has been consumed from the flow rate, the detection value of the air flow sensor 35 is monitored, and the air flow rate in the air system 20 becomes substantially “0”. It may be determined that oxygen in the air system 20 has been consumed on the condition.

  Furthermore, as a sixth method, on the assumption that the cooling water flow path circulating in the fuel cell stack 1 is provided with temperature sensors on the inlet side and the outlet side of the power generation cell 1a, the control unit 31 has the respective temperatures. Based on the difference in temperature detected by the sensor, it may be determined whether or not oxygen in the air system 20 has been consumed. In general, when oxygen is no longer present in the oxidizer electrode by load extraction control, the redox reaction in the power generation cell 1a does not occur correspondingly. Therefore, since there is no reaction heat from the power generation cell 1a, there is no temperature difference in the cooling water between the inlet side and the outlet side, and the temperature difference detected by the sensor is almost “0”. Therefore, by appropriately setting the determination value through experiments and simulations, it is possible to determine that oxygen in the air system 20 is consumed from a comparison between the temperature difference between the inlet and outlet and the determination value.

  Referring to FIG. 4 again, in step 4 (S4), the control unit 31 stops the hydrogen supply. Specifically, the control unit 31 stops the hydrogen circulation pump 14, closes the hydrogen supply valve 12, and fully closes the hydrogen pressure regulating valve 13.

  In step 5 (S5), the control unit 31 closes the air system inlet valve 23 and the air system outlet valve 24. This restricts the entry of outside air (air) from the air supply flow path L20 and the air discharge flow path L21 into the fuel cell stack 1. The process shown in step 5 may be executed on the premise that the load extraction control shown in step 3 is performed.

  Thus, the fuel cell system of the present embodiment includes the fuel cell stack 1, the air system 20, the hydrogen system 10, the air system inlet valve 23, the air system outlet valve 24, the hydrogen system outlet valve 16, It has a current extraction unit 30 and a control unit 31. Here, the fuel cell stack 1 generates electric power by electrochemically reacting these gases by supplying hydrogen to the fuel electrode and supplying air to the oxidant electrode. The air system 20 includes an air supply flow path L20 that supplies air to the oxidant electrode of the fuel cell stack 1 and an air discharge flow path L21 that discharges air from the oxidant electrode. The hydrogen system 10 includes a hydrogen discharge passage L12 that discharges hydrogen from the fuel electrode of the fuel cell stack 1. The air system inlet valve 23 and the air system outlet valve 24 are provided in the air system 20, and an oxidant system regulation that regulates the entry of outside air from the air system 20 into the fuel cell stack 1 according to its own operating state. Means. The hydrogen system outlet valve 16 is provided in the hydrogen system 10 and is fuel system regulation means that regulates the entry of outside air from the hydrogen system 10 into the fuel cell stack 1 according to its own operating state. The current extraction unit 30 extracts current from the fuel cell stack 1. The control unit 31 controls the air system inlet valve 23, the air system outlet valve 24, the hydrogen system outlet valve 16, and the current extraction unit 30. Here, the control unit 31 supplies hydrogen to the fuel electrode of the fuel cell stack 1 and stops supplying the oxidant gas to the oxidant electrode of the fuel cell stack 1 as stop control executed when the system is stopped. In this state, by controlling the current extraction unit 30 according to the state of the fuel cell stack 1, the oxidant gas in the oxidant electrode of the fuel cell stack 1 is consumed according to the current taken out by the current extraction unit 30.

  According to this configuration, oxygen present in the oxidizer electrode can be consumed by taking out the current from the fuel cell stack 1 while supplying hydrogen to the fuel electrode. At this time, by taking out the current according to the state of the fuel cell stack 1, it is possible to avoid spending extra time and energy, and in a state where the deterioration of the fuel cell stack 1 is difficult to occur in a short time, the oxygen in the oxidizer electrode Can be consumed. In addition, by consuming oxygen at the oxidant electrode when the fuel cell stack 1 is stopped, the amount of oxygen present at the oxidant electrode can be reduced when the fuel cell stack 1 is activated, so that deterioration during activation can be effectively suppressed. .

  In the present embodiment, the fuel cell system further includes a voltage sensor 32 that detects the voltage of the fuel cell stack 1. In this case, the control unit 31 sets an increase rate of the current set value, which is a control instruction value of the current extracted by the current extraction unit 30, as a current extraction rate, and the fuel cell stack 1 based on the set current extraction rate. The current set value is increased within a range in which the voltage of N is not negative. Here, the control unit 31 determines the voltage change rate when the voltage change rate, which is the voltage decrease rate of the fuel cell stack 1, is equal to or higher than a determination value for determining a voltage decrease due to a shortage of fuel gas at the fuel electrode. The current extraction speed is decreased so as to be smaller than the value.

  According to such a configuration, since the current set value is gradually increased according to the current extraction speed, it is possible to suppress fuel gas distribution variation and supply delay, particularly when current extraction is started. Further, since the current taken out from the fuel cell stack 1 is gradually increased, the oxygen consumption rate can be increased. Thereby, deterioration of the fuel cell stack 1 at the start of current extraction can be suppressed, and the time required for oxygen consumption can be shortened. Furthermore, by monitoring the voltage change rate Vs, determining the hydrogen deficiency state in the fuel electrode, and reducing the current change rate accordingly, the hydrogen deficiency in the fuel electrode can be suppressed. As a result, it is possible to effectively consume oxygen at the oxidant electrode while suppressing deterioration of the fuel cell stack 1.

(Second Embodiment)
The fuel cell system according to the second embodiment will be described below. The difference between the fuel cell system according to the second embodiment and that according to the first embodiment is a method of load extraction control in stop control. The fuel cell system according to the second embodiment is the same as that of the first embodiment in its configuration, and the same reference numerals are used to omit the detailed description thereof, and the difference regarding the load extraction control. The explanation will be focused on.

  FIG. 6 is a flowchart illustrating a detailed procedure of load take-out control according to the second embodiment. In step 30 to step 33, as in the first embodiment, when the current extraction speed Is is set, the voltage from the voltage sensor 32 is read, and the voltage change speed Vs is calculated, the voltage change speed Vs is calculated. It is determined whether or not the determination value is equal to or greater than Vsth.

  In step 34a (S34a) following the affirmative determination in step 33, the control unit 31 changes the rotation speed N of the hydrogen circulation pump 14. Specifically, the control unit 31 newly sets the rotation speed (N + ΔN) increased by a predetermined amount ΔN as the rotation speed N of the hydrogen circulation pump 14 based on the currently set rotation speed N. Then, the control unit 31 controls the hydrogen circulation pump 14 based on the newly set rotation speed N. Thereby, the hydrogen circulation pump 14 rotates according to the changed rotation speed N.

  On the other hand, in step 35a (S35a) following the negative determination in step 33, the control unit 31 changes the rotational speed N of the hydrogen circulation pump 14. Specifically, the rotation speed (N−ΔN) decreased by a predetermined amount ΔN based on the currently set rotation speed N is newly set as the rotation speed N of the hydrogen circulation pump 14. Then, the control unit 31 controls the hydrogen circulation pump 14 based on the newly set rotation speed N. Thereby, the hydrogen circulation pump 14 rotates according to the changed rotation speed N. The changed rotation speed N of the hydrogen circulation pump 14 may be set so that the initial value Nint preset for stop control is a lower limit and the rotation speed N does not become a value smaller than the initial value Nint.

  Then, in step 36, as in the first embodiment, it is determined whether or not the load extraction control is to be ended, and the load extraction control is continued or ended according to the determination result.

  As described above, according to the present embodiment, the fuel cell system is provided in the hydrogen sensor 10 and the voltage sensor 32 that detects the voltage of the fuel cell stack 1, and the hydrogen discharged from the fuel electrode is rotated by itself. Depending on the number, a hydrogen circulation pump 14 is further circulated to the hydrogen supply side of the fuel electrode. In this case, the control unit 31 sets an increase rate of the current set value, which is a control instruction value of the current extracted by the current extraction unit 30, as a current extraction rate, and the fuel cell stack 1 based on the set current extraction rate. The current set value is increased within a range in which the voltage of N is not negative. Here, when the voltage change rate Vs, which is the voltage decrease rate of the fuel cell stack 1, is equal to or higher than the determination value Vsth for determining the voltage decrease due to the shortage of fuel gas at the fuel electrode, the control unit 31 determines the voltage change rate. The rotation speed N of the hydrogen circulation pump 14 is increased so that Vs becomes smaller than the determination value Vsth.

  According to such a configuration, since the current set value is gradually increased according to the current extraction speed, it is possible to suppress fuel gas distribution variation and supply delay, particularly when current extraction is started. Further, since the current taken out from the fuel cell stack 1 is gradually increased, the oxygen consumption rate can be increased. Thereby, deterioration of the fuel cell stack 1 at the start of current extraction can be suppressed, and the time required for oxygen consumption can be shortened. Further, the voltage change rate Vs is monitored, the hydrogen deficiency state in the fuel electrode is determined, and the number of rotations of the hydrogen circulation pump 14 is increased accordingly, thereby suppressing the hydrogen deficiency in the fuel electrode. it can. Therefore, it is possible to effectively consume oxygen at the oxidant electrode while suppressing deterioration of the fuel cell stack 1.

(Third embodiment)
The fuel cell system according to the third embodiment will be described below. The fuel cell system according to the third embodiment is different from that of the first embodiment in the load take-out control technique in the stop control. The fuel cell system according to the third embodiment is the same as that of the first embodiment in its configuration, and by using the same reference numerals, the detailed description thereof is omitted, and the difference regarding the load take-out control. The explanation will be focused on.

  FIG. 7 is a flowchart illustrating a detailed procedure of load take-out control according to the third embodiment. In step 30 to step 33, as in the first embodiment, when the current extraction speed Is is set, the voltage from the voltage sensor 32 is read, and the voltage change speed Vs is calculated, the voltage change speed Vs is calculated. It is determined whether or not the determination value is equal to or greater than Vsth.

  In step 34b (S34b) following the affirmative determination in step 33, the control unit 31 changes the hydrogen pressure Ph supplied to the fuel electrode. Specifically, the control unit 31 newly sets the hydrogen pressure (Ph + ΔPh) increased by a predetermined amount ΔPh as the hydrogen pressure Ph supplied to the fuel electrode based on the currently set hydrogen pressure Ph. . Then, the control unit 31 controls the hydrogen pressure regulating valve 13 based on the newly set hydrogen pressure Ph.

  On the other hand, in step 35b (S35b) following the negative determination in step 33, the hydrogen pressure Ph supplied to the fuel electrode is changed. Specifically, the control unit 31 newly sets the hydrogen pressure (Ph−ΔPh) reduced by a predetermined amount ΔPh as the hydrogen pressure Ph supplied to the fuel electrode based on the currently set hydrogen pressure Ph. Set. Then, the control unit 31 controls the hydrogen pressure regulating valve 13 based on the newly set hydrogen pressure Ph. The hydrogen pressure Ph supplied to the fuel electrode after the change may have an initial value Phint preset for stop control as a lower limit so that the hydrogen pressure Ph does not become smaller than the initial value Phint. .

  Then, in step 36, as in the first embodiment, it is determined whether or not the load extraction control is to be ended, and the load extraction control is continued or ended according to the determination result.

  As described above, according to the present embodiment, the fuel cell system is provided in the hydrogen sensor 10 and the voltage sensor 32 that detects the voltage of the fuel cell stack 1, and adjusts the hydrogen pressure Ph supplied to the fuel electrode. And a hydrogen pressure regulating valve 13. In this case, the control unit 31 sets an increase rate of the current set value, which is a control instruction value of the current extracted by the current extraction unit 30, as a current extraction rate, and the fuel cell stack 1 based on the set current extraction rate. The current set value is increased within a range in which the voltage of N is not negative. Here, when the voltage change rate Vs, which is the voltage decrease rate of the fuel cell stack 1, is equal to or higher than the determination value Vsth for determining the voltage decrease due to the shortage of fuel gas at the fuel electrode, the control unit 31 determines the voltage change rate. The hydrogen pressure supplied to the fuel electrode by the hydrogen pressure regulating valve 13 is increased so that Vs becomes smaller than the determination value Vsth.

  According to such a configuration, since the current set value is gradually increased according to the current extraction speed, it is possible to suppress fuel gas distribution variation and supply delay, particularly when current extraction is started. Further, since the current taken out from the fuel cell stack 1 is gradually increased, the oxygen consumption rate can be increased. Thereby, deterioration of the fuel cell stack 1 at the start of current extraction can be suppressed, and the time required for oxygen consumption can be shortened. Furthermore, the voltage change speed Vs is monitored, the hydrogen deficiency state in the fuel electrode is determined, and the hydrogen pressure supplied to the fuel electrode is increased accordingly, thereby suppressing the hydrogen deficiency in the fuel electrode. Can do. Therefore, it is possible to effectively consume oxygen at the oxidant electrode while suppressing deterioration of the fuel cell stack 1.

(Fourth embodiment)
The fuel cell system according to the fourth embodiment will be described below. The difference of the fuel cell system according to the fourth embodiment from that of the first embodiment is a method of load extraction control in stop control. The fuel cell system according to the fourth embodiment is the same as that of the first embodiment in the configuration, and the same reference numerals are used to omit the detailed description thereof, and the difference regarding the load extraction control. The explanation will be focused on.

  In the fourth embodiment, the control unit 31 monitors the lowest voltage among the plurality of power generation cells 1 a based on the detection value from the voltage sensor 32. And the electric current taken out by the electric current extraction part 30 is controlled so that this minimum voltage may approach 0V. For example, the control unit 31 sets the current set value by a control method such as feedback according to the difference between the minimum voltage and 0V.

  According to such a configuration, the maximum amount of current that can be taken out at that time can be taken out from the fuel cell stack 1, so that the consumption time of oxygen can be shortened. In addition, since the voltage does not rise in the power generation cell 1a in a state where hydrogen in the fuel electrode is insufficient, by monitoring the minimum voltage, current can be taken out in a state where hydrogen in the fuel electrode is not insufficient. As a result, oxygen in the oxidant electrode can be effectively consumed while suppressing deterioration of the fuel cell stack 1.

(Fifth embodiment)
FIG. 8 is a block diagram showing an overall configuration of a fuel cell system according to the fifth embodiment. The fuel cell system according to the fifth embodiment will be described below. The difference of the fuel cell system according to the fifth embodiment from that of the first embodiment is a method of load extraction control in stop control. The fuel cell system according to the fifth embodiment has basically the same configuration as that of the first embodiment. The same reference numerals are used for the same configurations, and detailed descriptions thereof are omitted. An explanation will be given focusing on the differences regarding the load extraction control. In the fuel cell system of this embodiment, a hydrogen pressure sensor 36 that detects the pressure of hydrogen discharged from the fuel electrode of the fuel cell stack 1 is provided in the hydrogen circulation passage L11.

  FIG. 9 is a flowchart illustrating a detailed procedure of load take-out control according to the fifth embodiment. In this load extraction control, the control unit 31 starts to extract current from the fuel cell stack 1 by controlling the current extraction unit 30 in accordance with a preset current setting value. The control unit 31 controls the hydrogen circulation pump 14 so that the flow rate of hydrogen supplied to the fuel cell stack 1 is constant.

  Under such a premise, first, in step 40 (S40), the pressure detected by the hydrogen pressure sensor 33 provided on the upstream side of the fuel cell stack 1 (hereinafter referred to as "upstream pressure"), the fuel cell The pressure (hereinafter referred to as “downstream pressure”) detected by the hydrogen pressure sensor 36 provided on the downstream side of the stack 1 is read. In step 41 (S41), the pressure difference ΔP is calculated by subtracting the downstream pressure from the upstream pressure.

  In step 42 (S42) following step 41, it is determined whether or not the calculated pressure difference ΔP is not less than the lower limit determination value ΔPmin and not more than the upper limit determination value ΔPmax. When the flow rate of hydrogen supplied to the fuel electrode is constant, the pressure difference ΔP between the upstream side and the downstream side via the fuel cell stack 1 tends to increase when the hydrogen necessary for the reaction is deficient in the fuel electrode. Indicates. Therefore, the calculated pressure difference ΔP deviates from the range defined by the lower limit determination value ΔPmin and the upper limit determination value ΔPax, so that it can be determined whether or not hydrogen is deficient in the fuel electrode. For this reason, the lower limit determination value ΔPmin and the upper limit determination value ΔPmax are set in advance through experiments and simulations from the viewpoint of hydrogen deficiency in the fuel electrode.

  If an affirmative determination is made in step 42, that is, if the pressure difference ΔP is not less than the lower limit determination value ΔPmin and not more than the upper limit determination value ΔPmax, the process proceeds to step 46. On the other hand, if a negative determination is made in step 42, that is, if the pressure difference ΔP is smaller than the lower limit determination value ΔPmin or larger than the upper limit determination value ΔPmax, the process proceeds to step 43 (S43).

  In step 43, it is determined whether or not the calculated pressure difference ΔP is larger than an upper limit determination value ΔPmax. If the determination in step 43 is affirmative, that is, if the calculated pressure difference ΔP is larger than the upper limit determination value ΔPmax, the process proceeds to step 44. On the other hand, if a negative determination is made in step 43, that is, if the calculated pressure difference ΔP is smaller than the upper limit determination value ΔPmax (more specifically, smaller than the lower limit determination value ΔPmin), the process proceeds to step 45. .

  In step 44, the control unit 31 receives an affirmative determination in step 43, determines the lack of hydrogen in the fuel electrode, and decreases the current set value. On the other hand, in step 45, the control unit 31 receives a negative determination in step 43, determines that there is sufficient hydrogen that can be consumed in the fuel electrode, and increases the current set value.

  In step 46 (S46), it is determined whether or not the load take-out control is to be terminated, as in step 36 shown in the first embodiment. If an affirmative determination is made in step 46, this routine is terminated. On the other hand, if a negative determination is made in step 46, the load take-out control is continued, and the process returns to step 40 described above.

  As described above, according to the present embodiment, in addition to monitoring the voltage of the fuel cell stack 1, the state of hydrogen actually supplied to the fuel electrode (specifically, the pressure) The shortage of hydrogen associated with the consumption operation can be suppressed. In addition, by reducing the current set value as necessary, hydrogen supply delays, supply variations to the individual power generation cells 1a, and the like tend to be suppressed, so that hydrogen shortage at the fuel electrode can be suppressed. . Further, since the maximum amount of current that can be taken out at that time can be taken out from the fuel cell stack 1, it is possible to achieve both the suppression of deterioration of the fuel cell stack 1 and the reduction of oxygen consumption time.

  In the above-described embodiment, the hydrogen pressure sensors 33 and 36 are provided in the hydrogen supply flow path L10 and the hydrogen circulation flow path L11, respectively, thereby detecting the upstream pressure and the downstream pressure. However, the pressure is not limited to this, and the pressure upstream and downstream of the power generation surface of the fuel cell stack 1 may be detected, or the pressure may be detected in a manifold that distributes and merges hydrogen into the individual power generation cells 1a. That is, the pressure of hydrogen supplied to the fuel cell stack 1 (specifically, the hydrogen electrode) and the pressure of hydrogen discharged from the fuel cell stack 1 (specifically, the hydrogen electrode) should be detected. For example, the form is not limited.

(Sixth embodiment)
FIG. 10 is a block diagram showing the overall configuration of the fuel cell system according to the sixth embodiment. The fuel cell system according to the sixth embodiment will be described below. The difference of the fuel cell system according to the sixth embodiment from that of the fifth embodiment is a method of load extraction control in stop control. The fuel cell system according to the sixth embodiment is basically the same as that of the fifth embodiment. The same reference numerals are used for the same components, and detailed description thereof is omitted. An explanation will be given focusing on the differences regarding the load extraction control. In the fuel cell system of this embodiment, a hydrogen flow rate sensor 37 that detects the flow rate of hydrogen supplied to the fuel cell stack 1 (hereinafter referred to as “upstream flow rate”) is provided in the hydrogen supply flow path L10, and the fuel A hydrogen flow rate sensor 38 for detecting the flow rate of hydrogen discharged from the battery stack 1 (hereinafter referred to as “downstream flow rate”) is provided in the hydrogen discharge flow path L12.

  The detailed procedure of the load extraction control performs basically the same processing as the flowchart of FIG. 9 shown in the fifth embodiment. Specifically, in this load take-out control, the control unit 31 starts taking out current from the fuel cell stack 1 by controlling the current take-out unit 30 in accordance with a preset current setting value.

  Under such a premise, first, the upstream flow rate detected by the upstream hydrogen flow rate sensor 37 and the downstream flow rate detected by the downstream hydrogen flow rate sensor 38 are read. The flow rate difference ΔQ is calculated by subtracting the downstream flow rate from the upstream flow rate.

  Next, it is determined whether or not the calculated flow rate difference ΔQ is not less than the lower limit determination value ΔQmin and not more than the upper limit determination value ΔQmax. When the fuel electrode is depleted of hydrogen during the oxygen consumption operation, the flow rate difference ΔQ between the upstream side and the downstream side via the fuel cell stack 1 tends to increase. Therefore, it is possible to determine whether or not the fuel electrode is deficient in hydrogen by deviating the calculated flow rate difference ΔQ from the range defined by the lower limit determination value ΔQmin and the upper limit determination value ΔQax. For this reason, the lower limit determination value ΔQmin and the upper limit determination value ΔQmax are set in advance through experiments and simulations from the viewpoint of hydrogen deficiency in the fuel electrode.

  When the flow rate difference ΔQ is not less than the lower limit determination value ΔQmin and not more than the upper limit determination value ΔQmax, as shown in FIG. 9, the process proceeds to step 46 to determine the end of the load take-out control.

  On the other hand, when the calculated flow rate difference ΔQ is larger than the upper limit determination value ΔQmax, the lack of hydrogen in the fuel electrode is determined and the current set value is decreased. On the other hand, when the calculated flow rate difference ΔQ is smaller than the lower limit determination value ΔQmin, it is determined that there is sufficient hydrogen that can be consumed in the fuel electrode, and the current set value is increased.

  As described above, according to the present embodiment, in addition to monitoring the voltage of the fuel cell stack 1, the state of hydrogen actually supplied to the fuel electrode (specifically, the flow rate) can be monitored to The shortage of hydrogen associated with the consumption operation can be suppressed. In addition, by reducing the current set value as necessary, hydrogen supply delays, supply variations to the individual power generation cells 1a, and the like tend to be suppressed, so that hydrogen shortage at the fuel electrode can be suppressed. . Further, since the maximum amount of current that can be taken out at that time can be taken out from the fuel cell stack 1, it is possible to achieve both the suppression of deterioration of the fuel cell stack 1 and the reduction of oxygen consumption time.

  In the above-described embodiment, the hydrogen flow rate sensors 37 and 38 are provided in the hydrogen supply flow path L10 and the hydrogen circulation flow path L11, respectively, thereby detecting the upstream flow rate and the downstream flow rate. However, the present invention is not limited to this, and the flow rate upstream and downstream of the power generation surface of the fuel cell stack 1 may be detected, or the flow rate may be detected in a manifold that distributes and merges hydrogen into the individual power generation cells 1a. That is, if the flow rate of hydrogen supplied to the fuel cell stack 1 (specifically, the fuel electrode) and the flow rate of hydrogen discharged from the fuel cell stack 1 (specifically, the fuel electrode) are detected, The form is not limited.

  In each of the above-described embodiments, the individual embodiments are described according to the characteristics thereof. However, it is also possible to perform load take-out control by applying these embodiments in combination.

1 is a block diagram showing the overall configuration of a fuel cell system according to a first embodiment. Illustration of voltage sensor 32 Illustration of voltage sensor 32 The flowchart which shows the procedure of the stop control concerning 1st Embodiment. The flowchart which shows the detailed procedure of the load extraction control concerning 1st Embodiment. The flowchart which shows the detailed procedure of the load extraction control concerning 2nd Embodiment. The flowchart which shows the detailed procedure of the load extraction control concerning 3rd Embodiment. The block diagram which shows the whole structure of the fuel cell system concerning 5th Embodiment. The flowchart which shows the detailed procedure of the load extraction control concerning 5th Embodiment The block diagram which shows the whole structure of the fuel cell system concerning 6th Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel cell stack 1a Power generation cell 3 Control apparatus 10 Hydrogen system 11 Fuel tank 12 Hydrogen supply valve 13 Hydrogen pressure regulating valve 14 Hydrogen circulation pump 15 Ejector 16 Hydrogen system outlet valve (purge valve)
DESCRIPTION OF SYMBOLS 20 Air system 21 Compressor 22 Air pressure regulation valve 23 Air system inlet valve 24 Air system outlet valve 30 Current extraction part 31 Control part 32 Voltage sensor 33 Hydrogen pressure sensor 34 Air pressure sensor 35 Air flow sensor 36 Hydrogen pressure sensor 37 Hydrogen flow sensor 38 Hydrogen flow sensor L10 Hydrogen supply flow path L11 Hydrogen circulation flow path L12 Hydrogen discharge flow path L20 Air supply flow path L21 Air discharge flow path

Claims (7)

In the fuel cell system,
A fuel cell that generates electric power by electrochemically reacting the fuel gas and the oxidant gas by supplying a fuel gas to the fuel electrode and supplying an oxidant gas to the oxidant electrode;
An oxidant gas system including an oxidant gas supply channel for supplying an oxidant gas to the oxidant electrode of the fuel cell; and an oxidant gas discharge channel for discharging the oxidant gas from the oxidant electrode;
A fuel gas system including a fuel gas discharge passage for discharging the fuel gas from the fuel electrode of the fuel cell;
An oxidant system regulating means provided in the oxidant gas system, for regulating the entry of outside air from the oxidant gas system to the fuel cell according to its own operating state;
A fuel system regulating means that is provided in the fuel gas system and regulates the entry of outside air from the fuel gas system to the fuel cell according to its own operating state;
Current extraction means for extracting current from the fuel cell;
Control means for controlling the oxidant system regulating means, the fuel system regulating means, and the current extraction means;
The control means, as stop control executed when the system is stopped, supplies the fuel gas to the fuel electrode of the fuel cell, and stops the supply of the oxidant gas to the oxidant electrode of the fuel cell. A fuel cell system characterized in that the oxidant gas in the oxidant electrode of the fuel cell is consumed according to the current taken out by the current extraction means by controlling the current extraction means according to the state of the fuel cell. Voltage detection means for detecting the voltage of the fuel cell;
The control means sets, as a current extraction speed, an increase rate of a current setting value that is a control instruction value of the current extracted by the current extraction means, and the voltage of the fuel cell is negative based on the set current extraction speed. While increasing the current setting value in a range that does not become,
When the voltage change rate, which is the voltage decrease rate of the fuel cell, is equal to or higher than a determination value for determining a voltage decrease due to a shortage of fuel gas at the fuel electrode of the fuel cell, the voltage change rate is higher than the determination value. The fuel cell system according to claim 1, wherein the current extraction speed is decreased so as to be reduced. Voltage detecting means for detecting the voltage of the fuel cell;
A circulation means provided in the fuel gas system, for circulating the fuel gas discharged from the fuel electrode to the fuel gas supply side of the fuel electrode according to its own operation amount;
The control means sets, as a current extraction speed, an increase rate of a current setting value that is a control instruction value of the current extracted by the current extraction means, and the voltage of the fuel cell is negative based on the set current extraction speed. While increasing the current setting value in a range that does not become,
When the voltage change rate, which is the voltage decrease rate of the fuel cell, is equal to or higher than a determination value for determining a voltage decrease due to a shortage of fuel gas at the fuel electrode of the fuel cell, the voltage change rate is higher than the determination value. 2. The fuel cell system according to claim 1, wherein an operation amount of the circulation unit is increased so as to be reduced. Voltage detecting means for detecting the voltage of the fuel cell;
Pressure adjusting means that is provided in the fuel gas system and adjusts the pressure of the fuel gas supplied to the fuel electrode;
The control means sets, as a current extraction speed, an increase rate of a current setting value that is a control instruction value of the current extracted by the current extraction means, and the voltage of the fuel cell is negative based on the set current extraction speed. While increasing the current setting value in a range that does not become,
When the voltage change rate, which is the voltage decrease rate of the fuel cell, is equal to or higher than a determination value for determining a voltage decrease due to a shortage of fuel gas at the fuel electrode of the fuel cell, the voltage change rate is higher than the determination value. 2. The fuel cell system according to claim 1, wherein the pressure of the fuel gas supplied to the fuel electrode is increased by the pressure adjusting means so as to decrease. Voltage detection means for detecting the voltage of the fuel cell;
2. The control unit according to claim 1, wherein the control unit sets a current set value, which is a control instruction value of a current taken out by the current extraction unit, so that a voltage detected by the voltage detection unit is maintained at zero volts. The described fuel cell system. A first pressure sensor for detecting the pressure of the fuel gas supplied to the fuel electrode of the fuel cell;
A second pressure sensor for detecting the pressure of the fuel gas discharged from the fuel electrode of the fuel cell;
The control means calculates a pressure difference between a pressure detected by the first pressure sensor and a pressure detected by the second pressure sensor, and based on the calculated pressure difference, the current extraction 2. The fuel cell system according to claim 1, wherein the current setting value which is a control instruction value of the current taken out from the fuel cell is set by the means. A first flow rate sensor for detecting a flow rate of the fuel gas supplied to the fuel electrode of the fuel cell;
A second flow rate sensor for detecting the flow rate of the fuel gas discharged from the fuel electrode of the fuel cell;
The control means calculates a flow rate difference between a flow rate detected by the first flow rate sensor and a flow rate detected by the second flow rate sensor, and based on the calculated flow rate difference, the current extraction 2. The fuel cell system according to claim 1, wherein the current setting value which is a control instruction value of the current taken out from the fuel cell is set by the means.

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