Fuel cell system

Abstract

Fuel cell system (100), comprising: a fuel cell stack (11), an ejector set (16), a fuel gas supply device (12) which supplies fuel gas to the ejector set (16), a circulation flow path (14) which recovers fuel exhaust gas emitted from the fuel cell stack (11) and returns the fuel exhaust gas as circulation gas to the ejector set (16), a mixed gas supply flow path (13) which connects the ejector set (16) to the fuel cell stack (11) and enables the supply of the mixed gas, which contains the fuel gas and the circulation gas, from the ejector set (16) to the fuel electrodes of the fuel cell stack (11), a pressure detector (15) which detects pressure information on the fuel electrode side of the fuel cell stack (11), and a fuel exhaust gas outlet (19). which releases the fuel exhaust gas to the outside, wherein the concentration of the fuel gas is a predetermined concentration or less,and a control unit (17) configured to purge the gas, which differs from the fuel gas, from the electrodes of a fuel cell stack (11) in a short time at the time of starting the fuel cell system (100), wherein the ejector set (16) comprises a first ejector and a second ejector in parallel, wherein the first ejector is an ejector which supplies a first mixed gas to the fuel electrodes of the fuel cell stack (11), and the second ejector is an ejector which supplies a second mixed gas to the fuel electrodes of the fuel cell stack (11), wherein a concentration ratio of the circulating gas is greater than that of the first mixed gas; wherein for the second ejector, a supply flow rate of the mixed gas which can be supplied to the fuel electrodes of the fuel cell stack (11) is smaller than for the first ejector; wherein, as a first control, in the case,in which the pressure information detected by the pressure detector (15) exceeds a first predetermined limit, the control unit (17) makes a proportion of the second ejector greater than a proportion of the first ejector, if the total proportion of the ejectors of the ejector set (16) is determined to be 100%; and wherein, as a second control, in the case in which the pressure information detected by the pressure detector (15) exceeds a second predetermined limit, which is greater than the first limit, the control unit (17) makes the proportion of the first ejector greater than the proportion of the second ejector after the first control, if the total proportion of the ejectors of the ejector set (16) is determined to be 100%.

Description

TECHNICAL FIELDThe present invention relates to a fuel cell system.PRIOR ARTA fuel cell is a power generation device that generates electric power by electrochemical reaction between hydrogen (H 2), which serves as fuel gas, and oxygen (O 2), which serves as oxidant gas, in a fuel cell stack (hereinafter, it may be simply referred to as a "stack") composed of stacked units of fuel cells. Hereinafter, fuel gas and oxidant gas may be collectively and simply referred to as "reaction gas" or "gas".Generally, the units of the fuel cells are composed of a membrane electrode unit (MEA) and, if necessary, two separators sandwiching the membrane electrode unit.The membrane electrode unit has such a structure that a catalyst layer and a gas diffusion layer are formed in this order on both surfaces of a solid polymer electrolyte membrane having proton (H +)- conductivity (hereinafter, simply referred to as "electrolyte membrane").In general, the separators have such a structure that a groove is formed as a reaction gas flow path on a surface in contact with the gas diffusion layer. The separators function as a collector of the generated electricity.In the fuel electrode (anode) of the fuel cell, the hydrogen supplied from the flow path and the gas diffusion layer is protonated by the catalytic activity of the catalyst layer, and the protonated hydrogen passes through the electrolyte membrane to the oxidant electrode (cathode). An electron is generated at the same time, and passes through an external circuit, performs work, and then reaches the cathode. The oxygen supplied to the cathode reacts with the proton and the electron on the cathode, thereby generating water.The water produced supplies sufficient moisture to the electrolyte membrane. Excess water penetrates the gas diffusion layer, passes through the flow path, and is then discharged to the outside of the system.Such a method that, at the time of terminating the fuel cell system including the fuel cell stack, the supply of the fuel gas to the fuel electrodes of the fuel cell stack is terminated; the fuel gas in the fuel electrodes of the fuel cell stack is discharged into the air; and the fuel electrodes of the fuel cell stack are filled with gas different from fuel gas such as air and nitrogen gas (hereinafter referred to as "inert gas") is known. Accordingly, at the time of starting the fuel cell system, it is necessary to replace the inert gas in the fuel electrodes of the fuel cell stack with fuel gas.The fuel cell system capable of purging the gas other than the fuel gas from the fuel electrodes of the fuel cell stack in a short time at the start time is studied.For example, in Patent Literature 1, a fuel cell system is disclosed which uses such inverse circulation characteristics of an ejector that, by setting the supply amount of the fuel gas at the start time to the range in which the fuel gas flows inversely from an ejector through a circulation passage to a fuel cell, the fuel gas flows from the ejector to the inlet port of the fuel cell through a fuel supply passage, and at the same time flows from the ejector to the fuel cell through the circulation passage; further, by using the inverse circulation characteristics, the inert gas filling the circulation passage and the fuel supply passage can flow from the ejector to a purging pipe, thereby purging air from the pipe securely in a short time.Patent Literature 2 discloses a fuel cell system equipped with a plurality of ejectors connected in series and capable of rapid activation even under a low temperature environment in which there is a risk that the check valve of a circulation gas flow path is frozen.Further, Patent Literatures 3 to 5 disclose fuel cell systems of the related art.Patent Literature 1: JP 2003-157 875 APatent Literature 2: JP 2008-192 514 APatent Literature 3: US 2005 / 0 130 008 A1Patent Literature 4: DE 103 31 261 A1Patent Literature 5: DE 10 2006 019 077 A1The fuel cell system described in Patent Literature 1 uses the inverse circulation characteristics of the ejector. Accordingly, the inert gas is likely to remain particularly on the side away from the fuel gas supply port of a fuel cell stack. Consequently, there is a possibility that the inert gas cannot be entirely purged from the fuel electrodes of the fuel cell stack in a short time.Regarding purging, it is ideal to install a hydrogen pump in a circulation flow path and purge the inert gas from the fuel electrodes after the inert gas is stirred and circulated in the fuel cell stack. However, the hydrogen pump is expensive and difficult to install in the fuel cell system from the viewpoint of encouraging distribution of fuel cell-equipped vehicles.SUMMARYThe disclosed embodiments have been achieved in light of the above circumstances. A main object of the disclosed embodiments is to provide a fuel cell system configured to purge, at the time of starting the fuel cell system, the gas different from the fuel gas from the electrodes of a fuel cell stack in a short time.In a first embodiment, a fuel cell system is provided, comprising:a fuel cell stack,an ejector set,a fuel gas supply device or fuel gas source which supplies fuel gas to the ejector set,a circulation flow path that recovers the fuel off gas discharged from the fuel cell stack and returns the fuel off gas to the ejector set as a circulation gas,a mixed gas supply flow path connecting the ejector set to the fuel cell stack and allowing mixed gas containing fuel gas and the circulating gas from the ejector set to be supplied to the fuel electrodes of the fuel cell stack,a pressure detector that detects information on pressure of a fuel electrode side of the fuel cell stack,a fuel exhaust outlet which discharges the fuel exhaust gas to the outside, wherein a concentration of the fuel gas is a predetermined concentration or less; anda controller configured to purge, at the time of starting the fuel cell system, the gas different from the fuel gas from the electrodes of a fuel cell stack in a short time,wherein the ejector set comprises a first ejector and a second ejector in parallel, wherein the first ejector is an ejector that supplies the first mixed gas to the fuel electrodes of the fuel cell stack, and the second ejector is an ejector that supplies the second mixed gas to the fuel electrodes of the fuel cell stack, wherein a content ratio of the circulation gas is greater than that of the first mixed gas;wherein, for the second ejector, a supply flow amount of the mixed gas that can be supplied to the fuel electrodes of the fuel cell stack is smaller than that for the first ejector;wherein, as a first control in the case where the pressure information detected by the pressure detector exceeds a predetermined first threshold value, the control unit makes a duty ratio of the second ejector larger than a duty ratio of the first ejector when a total duty ratio of the ejectors of the ejector set is determined to be 100%; andwherein, as a second control in the case where the pressure information detected by the pressure detector exceeds a predetermined second threshold value larger than the first threshold value, the control unit, after the first control, makes the share ratio of the first ejector larger than the share ratio of the second ejector when the total share ratio of the ejectors of the ejector set is determined to be 100%.The fuel cell system of the disclosed embodiments may be a fuel cell system, wherein, as the first control, in the case where the pressure information detected by the pressure detector is the predetermined first threshold or less, the control unit makes the share ratio of the first ejector larger than the share ratio of the second ejector when the total share ratio of the ejectors of the ejector set is determined to be 100%.The fuel cell system of the disclosed embodiments may be a fuel cell system, wherein as the first control, in the case where the pressure information detected by the pressure detector exceeds the predetermined first threshold, the control unit switches from the first ejector to the second ejector and supplies the second mixed gas from the second ejector to the fuel electrodes of the fuel cell stack, and wherein as the second control, in a case where the pressure information detected by the pressure detector exceeds the predetermined second threshold larger than the predetermined first threshold, the control unit switches from the second ejector to the first ejector and supplies the first mixed gas from the first ejector to the fuel electrodes of the fuel cell stack, and in a case where the pressure information is the second threshold or less, The control unit supplies the second mixed gas from the second ejector to the fuel electrodes of the fuel cell stack.The fuel cell system of the disclosed embodiments may be a fuel cell system, wherein, as the first controller, in a case where the pressure information detected by the pressure detector is the predetermined first threshold or less, the control unit supplies the first mixed gas from the first ejector to the fuel electrodes of the fuel cell stack.According to the disclosed embodiments, there is provided a fuel cell system configured to purge, at the same start time of the fuel cell system, the gas different from the fuel gas from the fuel electrodes of the fuel cell stack in a short time.BRIEF DESCRIPTION OF THE DRAWINGSIn the accompanying drawing, FIG. 1 is a view showing an example of the structure of the fuel cell system according to the disclosed embodiments; FIG. 2 is a view showing a difference in performance between the first ejector and the second ejector; FIG. 3 is a flow diagram of an example of the method for controlling the fuel cell system according to the disclosed embodiments; FIG. 4 is a view showing an example of the relationship between time and anode pressure / hydrogen concentration in the case of simulating the control of the fuel cell system according to the disclosed embodiments; FIG. 5 is a view showing a gas concentration distribution on the fuel electrode side of the fuel cell stack at a predetermined timing in a simulation that tries to purge nitrogen gas from the fuel electrodes of the fuel cell stack using only the first ejector; and FIG. 6 is a view showing a gas concentration distribution on the fuel electrode side of the fuel cell stack at a predetermined timing in a simulation that tries to purge nitrogen gas from the fuel electrodes of the fuel cell stack by controlling the fuel cell system of the disclosed embodiments.DETAILED DESCRIPTIONThe fuel cell system of the disclosed embodiments is a fuel cell system comprising:a fuel cell stack,an ejector set,a fuel gas supply device that supplies fuel gas to the ejector set,a circulation flow path that recovers fuel off gas discharged from the fuel cell stack and returns the fuel off gas as a circulation gas to the ejector set,a mixed gas supply flow path connecting the ejector set to the fuel cell stack and allowing the mixed gas containing the fuel gas and the circulating gas from the ejector set to be supplied to the fuel electrodes of the fuel cell stack,a pressure detector that detects pressure information of a fuel electrode side of the fuel cell stack,a fuel exhaust outlet which discharges the fuel exhaust to the outside, wherein a concentration of the fuel gas is a predetermined concentration or less; anda control unit,wherein the ejector set comprises a first ejector and a second ejector in parallel, wherein the first ejector is an ejector that supplies the first mixed gas to the fuel electrodes of the fuel cell stack, and the second ejector is an ejector that supplies the second mixed gas to the fuel electrodes of the fuel cell stack, wherein a content ratio of the circulating gas is greater than that of the first mixed gas;wherein, for the second ejector, a supply flow amount of the mixed gas that can be supplied to the fuel electrodes of the fuel cell stack is smaller than that for the first ejector;wherein, as a first control, in a case where the pressure information detected by the pressure detector exceeds a predetermined first threshold value, the control unit makes a share ratio of the second ejector larger than a share ratio of the first ejector when a total share ratio of the ejectors of the ejector set is determined to be 100%; andwherein, as a second control in the case where the pressure information detected by the pressure detector exceeds a predetermined second threshold value larger than the first threshold value, the control unit after the first control makes the share ratio of the first ejector larger than the share ratio of the second ejector when the total share ratio of the ejectors of the ejector set is determined to be 100%.FIG. 1 is a view of an example of the structure of the fuel cell system of the disclosed embodiments.A fuel cell system 100 shown in FIG. 1 includes the following: a fuel cell stack 11; a fuel gas supplier 12; a mixed gas supply flow path 13; a circulation flow path 14 that circulates fuel off gas discharged as circulation gas from the fuel electrodes of the fuel cell stack 11; a pressure detector 15 that detects the pressure information of the fuel electrode side of the fuel cell stack 11; an ejector set 16 that supplies mixed gas of the fuel gas and the circulation gas to the fuel electrodes of the fuel cell stack 11; a control unit 17; a fuel gas supply flow path 18; a fuel off gas outlet 19; an oxidant gas supplier 21; an oxidant gas supply flow path 22; and an oxidant gas outlet flow path 23.The fuel cell system of the disclosed embodiments includes at least the fuel cell stack, the fuel gas supplier, the mixed gas supply flow path, the circulation flow path, the fuel off-gas outlet, the pressure detector, the ejector set, and the control unit. In general, the fuel cell system further includes a fuel gas supply flow path, an oxidant gas supply device, an oxidant gas supply flow path, an oxidant gas outlet flow path, a cooling water supply device, a cooling water circulation flow path, etc.The fuel cell stack is composed of stacked fuel cell units.The number of the stacked fuel cell units is not particularly limited. For example, 2 to 200 fuel cell units may be stacked.The fuel cell stack may include an end plate at both ends of the stacking direction of each fuel cell unit.Each individual fuel cell or fuel cell unit comprises at least one membrane electrode unit including an oxidant electrode, an electrolyte membrane and a fuel electrode. If necessary, it may include two separators sandwiching the membrane electrode unit.The separators may have such a gas flow path structure that a groove as a reaction gas flow path is formed on a surface in contact with a gas diffusion layer. Also, the separators may have such a cooling water flow path structure that a groove is formed on a surface opposite to the surface in contact with the gas diffusion layer as a cooling water flow path to maintain the stack temperature at a constant level.The separators may be a gas impervious, electrically conductive member, etc. As the electroconductive member, examples include, but are not limited to, gas-impermeable dense carbon obtained by carbon compaction and a metal plate obtained by compression molding. The separators may have a function of current collection.The oxidant electrode includes an oxidant electrode catalyst layer and a gas diffusion layer.The fuel electrode includes a fuel electrode catalyst layer and a gas diffusion layer.The oxidant electrode catalyst layer and the fuel electrode catalyst layer may contain, for example, a catalyst metal for accelerating an electrochemical reaction, a proton conductive electrolyte, or electron conductive carbon particles.As the catalyst metal, for example, platinum (Pt) or an alloy of Pt and another metal (such as a Pt alloy mixed with cobalt, nickel, or the like) can be used.The electrolyte may be a fluorine resin or the like. As the fluorine resin, for example, a Nafion solution may be used.The catalyst metal is supported on carbon particles. In each catalyst layer, the carbon particles carrying the catalyst metal (i.e., catalyst particles) and the electrolyte may be mixed.As the carbon particles for supporting the catalyst metal (i.e., supporting carbon particles), for example, water-repellent carbon particles obtained by improving the water-repellency of commercially available carbon particles (carbon powder) by heating can be used.The gas diffusion layer may be a gas permeable, electrically conductive member or the like.As the electrically conductive member, examples include, but are not limited to, a porous carbon material such as a carbon cloth and a carbon paper, and a porous metal material such as a metal mesh and a metal foam.The electrolyte membrane may be a solid polymer electrolyte membrane. As the solid polymer electrolyte membrane, examples include, but are not limited to, a hydrocarbon electrolyte membrane and a fluorine electrolyte membrane such as a perfluorosulfonic acid thin membrane containing moisture. The electrolyte membrane may be, for example, a Nafion membrane (manufactured by DuPont).The fuel gas supply device supplies fuel gas to the ejector set.The fuel gas is a gas mainly containing hydrogen. For example, it may be hydrogen gas.As the fuel gas supplier, examples include, but are not limited to, a fuel tank such as a liquid hydrogen tank and a compressed hydrogen tank.The fuel cell system may include the fuel gas supply flow path.The fuel gas supply flow path connects the fuel gas supply device to the ejector set, and enables supply of the fuel gas from the fuel gas supply device to the ejector set. The fuel gas supply flow path is not always necessary when the fuel gas supply device and the ejector set are arranged side by side, and the fuel gas can be supplied to the ejector set directly from the fuel gas supply device.The circulation flow path allows the fuel cell stack to be connected to the ejector set, recovers the fuel off gas discharged from the fuel electrodes of the fuel cell stack, and returns the fuel off gas to the ejector set as the circulation gas.The fuel off gas mainly contains fuel gas that passed through the fuel electrode without reacting and moisture that is water generated at the oxidant electrode and transmitted to the fuel electrode. In the disclosed embodiments, the fuel off-gas may further include an inert gas such as air and nitrogen gas.The ejector set supplies the mixed gas containing the fuel gas and the circulating gas to the fuel electrodes of the fuel cell stack.The ejector set includes the first ejector and the second ejector in parallel.The first ejector supplies the first mixed gas to the fuel electrodes of the fuel cell stack.The second ejector supplies the second mixed gas to the fuel electrodes of the fuel cell stack, wherein the content ratio of the circulation gas is greater than that of the first mixed gas. For the second ejector, the supply flow amount of the mixed gas that can be supplied to the fuel electrodes of the fuel cell stack is smaller than for the first ejector.The supply flow amount of the first mixed gas that can be supplied to the fuel electrodes of the fuel cell stack by the first ejector may be 2 to 20 times larger than the supply flow amount of the second mixed gas that can be supplied to the fuel electrodes of the fuel cell stack by the second ejector, or may be 3 to 10 times larger than this.In the second mixed gas, for example, the content ratio of the circulation gas may be 2 to 10 times larger than that of the first mixed gas, or may be 3 to 4 times larger than that of the first mixed gas.The ejectors of the ejector set are electrically connected to the control unit. The use of the ejectors in combination or the use of one of the ejectors can be enabled or activated by a signal from the control unit.FIG. 2 is a view showing a difference in performance between the first ejector and the second ejector.As shown in FIG. 2, the first ejector is such an ejector that the supply flow amount is large and the content ratio of the circulation gas is small (large flow amount+low circulation ratio).The second ejector is such an ejector that the supply flow amount is small and the content ratio of the circulation gas is large (small flow amount+high circulation ratio).The mixed gas supply flow path connects the ejector set to the fuel cell stack and enables the mixed gas containing the fuel gas and the circulating gas from the ejector set to be supplied to the fuel electrodes of the fuel cell stack.The fuel off-gas outlet allows the fuel off-gas to be discharged to the outside, wherein the concentration of the fuel gas is the predetermined concentration of the fuel gas or less. External means the exterior or exterior of the fuel cell system.The fuel exhaust outlet may include a fuel exhaust outlet valve. If desired, it may further comprise a fuel-exhaust outlet flow path.The fuel exhaust outlet valve controls the fuel exhaust outlet flow rate.The fuel-off-gas discharge flow path may branch from the circulation flow path.The fuel off-gas outlet may allow the fuel off-gas to be discharged to the outside when, for example, the concentration of the fuel gas such as hydrogen in the fuel off-gas is the predetermined concentration or less. Also, the fuel off-gas outlet may discharge, for example, an inert gas other than fuel gas, such as air and nitrogen gas, to the outside. The predetermined concentration of the fuel gas is not particularly limited, and may be appropriately determined in consideration of, for example, the balance between the fuel efficiency of the fuel cell system and the inert gas purging time.The method for detecting the concentration of the fuel gas in the fuel off-gas is not particularly limited. For example, a well-known concentration sensor may be used.A gas-liquid separator for reducing the moisture in the fuel off gas may be installed in the circulation flow path. Also, a drain flow path branching from the circulation flow path through the gas-liquid separator may be disposed in the circulation flow path, and a drain valve may be disposed in the drain flow path.The moisture separated from the fuel off gas in the gas-liquid separator can be discharged by opening the outflow valve of the outflow flow path branching off from the circulation flow path.The fuel exhaust gas subjected to moisture separation may be sucked from the circulation flow path through the ejector while being in the state containing a small amount of remaining mist.The pressure detector acquires the pressure information of the fuel electrode side of the fuel cell stack.As the pressure detector, examples include, but are not limited to, a pressure sensor.The installation position of the pressure detector is not particularly limited as long as the pressure information of the fuel electrode side of the fuel cell stack can be acquired. The pressure detector may be installed in the mixed gas supply flow path or may be installed in the circulation flow path. In view of increasing the accuracy of the pressure information detection, the pressure detector may be installed in the mixed gas supply flow path.The pressure information may be a gas pressure applied to the fuel cell stack.The oxidant gas supply device supplies oxidant gas to at least the oxidant electrodes of the fuel cell stack.As the oxidant gas supply device, for example, an air compressor may be used.The oxidant gas supply flow path allows the oxidant gas supply device to be connected to the fuel cell stack, and supplies oxidant gas from the oxidant gas supply device to the oxidant electrodes of the fuel cell stack.The oxidant gas is an oxygen-containing gas. It may be air, dry air, pure oxygen or the like.The oxidant gas discharge flow path enables discharge of the oxidant gas from the oxidant electrodes of the fuel cell stack.The fuel cell system may include a cooling water supply device and a cooling water circulation flow path.The cooling water circulation flow path allows it to communicate between the cooling water inlet port communication hole and the cooling water outlet port communication hole disposed in the fuel cell stack, circulates the cooling water supplied from the cooling water supply device in and out of the fuel cell stack, and cools the fuel cell stack.As the cooling water supply device, examples include, but are not limited to, a cooling water pump.The control unit controls the fuel cell system.The control unit may be connected to the pressure detector, the ejector set, the fuel gas supplier, the oxidant gas supplier, and so on through an input-output interface.The control unit makes a judgment as to whether or not the pressure information of the fuel electrode side of the fuel cell stack detected by the pressure detector exceeds the predetermined first limit value and whether or not the pressure information exceeds the predetermined second limit value. Also, the control unit controls the content ratio of the first and second ejectors of the ejector set, etc.The control unit physically includes, for example, a processing unit such as a central processing unit (CPU), a storage device such as a read-only memory (ROM) and a random access memory (RAM), and an input-output interface. The ROM is used to store a control program, control data, and so on processed by the CPU, and the RAM is mainly used as various work areas for the control processes.(1) acquiring the pressure information of the fuel electrode side of the fuel cell stackThe pressure detector acquires the pressure information of the fuel electrode side of the fuel cell stack at predetermined timings.The method for acquiring the pressure information of the fuel electrode side of the fuel cell stack is not particularly limited. For example, the pressure information of the fuel electrode side of the fuel cell stack may be acquired by installing a well-known pressure sensor in the fuel cell system and using the pressure sensor.The timing for acquiring the pressure information of the fuel electrode side of the fuel cell stack is not particularly limited. The pressure information of the fuel electrode side of the fuel cell stack may be acquired every time a predetermined time has elapsed after the operation of the fuel cell stack is started; may be acquired when the operation of the fuel cell stack is started; or may be constantly acquired. The detection timing can be determined appropriately.(2) evaluating whether or not the pressure information of the fuel electrode side of the fuel cell stack exceeds the predetermined first thresholdThe control unit judges whether or not the fuel electrode side pressure information of the fuel cell stack detected by the pressure detector exceeds the predetermined first threshold value.The first threshold value of the pressure information may be appropriately determined, for example, as follows: a data group prepared beforehand by an experiment, etc., shows a relationship between the pressure information of the fuel electrode side of the fuel cell stack and the time to complete the purging of the inert gas from the fuel electrodes of the fuel cell stack, and the first threshold value is appropriately determined by the performance, etc., of the fuel cell stack included in the data group.(3) First Controller(3-1) The case where the pressure information of the fuel electrode side of the fuel cell stack exceeds the predetermined first thresholdAs the first control, in the case where the pressure information detected by the pressure detector exceeds the first predetermined threshold, the control unit makes the share ratio of the second ejector larger than the share ratio of the first ejector when the total share ratio of the ejectors of the ejector set is determined to be 100%.Before the first control, the supply flow amount of the first mixed gas is increased to pressure-fill the fuel electrodes of the fuel cell stack with the fuel gas, and the content ratio of the fuel gas is large. The gas different from the fuel gas and containing large amounts of nitrogen, etc. is pushed out by the pressure filling, and the gas circulates and re-enters the fuel electrodes of the fuel cell stack through the ejector set. At this time, the content ratio of the second ejector in which the supply flow amount of the mixed gas is small and the content ratio of the circulation gas is larger than the fuel gas is increased compared to the first ejector, thereby decreasing the supply flow amount of the mixed gas from the ejector set. Accordingly, it is considered that the first mixed gas in which the content ratio of the fuel gas is large can be diffused quickly in the fuel electrodes of the fuel cell stack. Consequently, it is considered that the fuel gas can be quickly introduced into the fuel electrodes of the fuel cells located on the side away from the fuel gas supply port of the fuel cell stack. Accordingly, it can be said that the use of the second ejector is suitable for uniformly purging the inert gas from the fuel electrodes.The content ratio of the ejectors of the ejector set is not particularly limited in the case where the pressure information of the fuel electrode side of the fuel cell stack exceeds the predetermined first threshold value as long as the content ratio of the second ejector is larger than the content ratio of the first ejector when the total content ratio is determined to be 100%. With regard to completing the purging of the inert gas in a shorter time, the content ratio of the second ejector may be 100%. In other words, in the case where the pressure information of the fuel electrode side of the fuel cell stack detected by the pressure detector exceeds the predetermined first threshold value, the control unit may switch from the first ejector to the second ejector and supply the second mixed gas from the second ejector to the fuel electrodes of the fuel cell stack.The method for controlling the content ratio of the ejectors is not particularly limited. The share ratio may be controlled by electrically connecting the controller to the ejectors and transmitting a signal from the controller to the ejectors.(3-2) The case where the pressure information of the fuel electrode side of the fuel cell stack is the predetermined first threshold value or lessOn the other hand, as the first control, in the case where the pressure information of the fuel electrode side of the fuel cell stack detected by the pressure detector is the predetermined first threshold value or less, the control unit makes the content ratio of the first ejector larger than the content ratio of the second ejector when the total content ratio of the ejectors of the ejector set is determined to be 100%. At the start time of the fuel cell system, regarding the rapid pressure filling of the fuel electrodes of the fuel cell stack with the first mixed gas in which the fuel gas ratio is large, the control unit makes the content ratio of the first ejector larger than the content ratio of the second ejector when the total content ratio of the ejectors of the ejector set is determined to be 100%.The content ratio of the ejectors of the ejector set is not particularly limited in the case where the fuel electrode side pressure information of the fuel cell stack detected by the pressure detector is the predetermined first threshold value or less as long as the content ratio of the first ejector is larger than the content ratio of the second ejector when the total content ratio of the ejectors is determined to be 100%. Regarding the rapid pressure filling of the fuel electrodes of the fuel cell stack with the first mixed gas in which the fuel gas ratio is large, the content ratio of the first ejector may be 100%. In other words, in the case where the pressure information of the fuel electrode side of the fuel cell stack detected by the pressure detector is the predetermined first threshold value or less, the control unit may switch from the second ejector to the first ejector and supply the first mixed gas from the first ejector to the fuel electrodes of the fuel cell stack.(4) acquiring the pressure information of the fuel electrode side of the fuel cell stackAfter the first control, the pressure detector acquires the pressure information of the fuel electrode side of the fuel cell stack at predetermined timings.The timing for acquiring the pressure information of the fuel electrode side of the fuel cell stack is not particularly limited. The pressure information of the fuel electrode side of the fuel cell stack may be acquired at each time a predetermined time has elapsed after the first control, or may be constantly acquired. The time of the detection can be determined appropriately.(5) determining whether or not the fuel electrode side pressure information of the fuel cell stack exceeds the predetermined second thresholdAfter the first control, the control unit judges whether or not the pressure information of the fuel electrode side of the fuel cell stack detected by the pressure detector exceeds the predetermined second threshold value.The second threshold value of the pressure information may be appropriately determined, for example, as follows: a data group prepared beforehand by an experiment, etc., shows a relationship between the pressure information of the fuel electrode side of the fuel cell stack and the time to finish purging the inert gas from the fuel electrodes of the fuel cell stack, and the second threshold value may be appropriately determined by the performance, etc., of the fuel cell stack included in the data group.(6) Second Controller(6-1) The case where the pressure information of the fuel electrode side of the fuel cell stack exceeds the predetermined second thresholdAs the second control, in the case where the pressure information detected by the pressure detector exceeds the predetermined second threshold value, which is larger than the first threshold value, the control unit after the first control may make the share ratio of the first ejector larger than the share ratio of the second ejector when the total share ratio of the ejectors of the ejector set is determined to be 100%, and then the control unit may end the control.In the case where the pressure information exceeds the predetermined second threshold, it is assumed that the first mixed gas in which the fuel gas ratio is large is sufficiently diffused in the fuel electrodes of the fuel cell stack and the fuel gas is introduced into the fuel electrodes of the fuel cells located on the side away from the fuel gas supply port of the fuel cell stack. Accordingly, by the second control, the content ratio of the first ejector in which the supply flow amount of the mixed gas is large and the content ratio of the fuel gas is larger than the circulation gas is increased, thereby increasing the supply flow amount of the mixed gas from the ejector set, as compared with the second ejector. Accordingly, the pressure information of the fuel electrode side of the fuel cell stack can reach the predetermined target value for operating the fuel cell stack in a short time. Accordingly, it can be said that the use of the first ejector is suitable for purging the inert gas from the fuel electrodes in a short time.The content ratio of the ejectors of the ejector set is not particularly limited in the case where the pressure information of the fuel electrode side of the fuel cell stack exceeds the predetermined second threshold value as long as the content ratio of the first ejector is larger than the content ratio of the second ejector when the total content ratio of the ejectors is determined to be 100%. In view that the pressure information of the fuel electrode side of the fuel cell stack may reach the predetermined target value for operating the fuel cell stack in a shorter time, the content ratio of the first ejector may be 100%. In other words, in the case where the pressure information of the fuel electrode side of the fuel cell stack detected by the pressure detector exceeds the predetermined second threshold, the control unit may switch from the second ejector to the first ejector and supply the first mixed gas from the first ejector to the fuel electrodes of the fuel cell stack.(6-2) The case where the pressure information of the fuel electrode side of the fuel cell stack is the second threshold value or lessMeanwhile, as the second control, in the case where the pressure information of the fuel electrode side of the fuel cell stack detected by the pressure detector is the predetermined second threshold value or less, the control unit may continue, after the first control, to make the content ratio of the second ejector larger than the content ratio of the first ejector when the total content ratio of the ejectors of the ejector set is determined to be 100%, or the control unit may switch from the first ejector to the second ejector and supply the second mixed gas from the second ejector to the fuel electrodes of the fuel cell stack.FIG. 3 is a flow diagram of an example of the method of controlling the fuel cell system according to the disclosed embodiments. The disclosed embodiments are not limited to this typical example.In the control method shown in FIG. 3, first, at the start time of the fuel cell system, the control unit supplies the first mixed gas to the fuel electrodes of the fuel cell stack using the first ejector.Next, the pressure detector acquires the pressure information of the fuel electrode side of the fuel cell stack.Subsequently, in the case where the acquired pressure information of the fuel electrode side of the fuel cell stack is the predetermined first threshold value or less, the control unit continues to supply the first mixed gas to the fuel electrodes of the fuel cell stack using the first ejector.On the other hand, in the case where the pressure information exceeds the first threshold value, the control unit switches from the first ejector to the second ejector and supplies the second mixed gas to the fuel electrodes of the fuel cell stack.Then, the pressure detector detects the pressure information of the fuel electrode side of the fuel cell stack again.Then, in the case where the acquired pressure information of the fuel electrode side of the fuel cell stack is the predetermined second threshold value or less, the control unit continues to supply the second mixed gas to the fuel electrodes of the fuel cell stack using the second ejector.On the other hand, in the case where the pressure information exceeds the second threshold value, the control unit switches from the second ejector to the first ejector and supplies the first mixed gas to the fuel electrodes of the fuel cell stack. Then, the control unit terminates the control.FIG. 4 is a view showing an example of the relationship between time and anode pressure / hydrogen concentration in the case of simulating the control of the fuel cell system according to the disclosed embodiments.In FIG. 4, "High" represents the use of the first ejector, and "Low" represents the use of the second ejector.As can be seen from FIG. 4, by executing the two-step control (the first control and the second control), the anode pressure increases in two steps, and the anode pressure and the hydrogen concentration of the anode can be increased to target values in a short time of 0.75 seconds.FIG. 5 is a view showing a gas concentration distribution on the fuel electrode side of the fuel cell stack at a predetermined timing in a simulation that tries to purge nitrogen gas from the fuel electrodes of the fuel cell stack using only the first ejector.In FIG. 5, "inlet port" represents the fuel gas supply port; "outlet port" represents the fuel gas outlet port; "stacking direction" indicates the direction of stacking the fuel cell units of the fuel cell stack; and "rear" indicates the side farthest from the fuel gas supply port of the fuel cell stack. The same applies to FIG. 6 described below.As can be seen from FIG. 5, when the nitrogen gas purging is performed by using only the first ejector, there is a large change in the concentration in the stacking direction of the fuel cell units of the fuel cell stack.FIG. 6 is a view showing a gas concentration distribution on the fuel electrode side of the fuel cell stack at a predetermined timing in a simulation that tries to purge nitrogen gas from the fuel electrodes of the fuel cell stack by controlling the fuel cell system of the disclosed embodiments.As is apparent from FIG. 6, according to the fuel cell system of the disclosed embodiments, the change in concentration in the stacking direction of the fuel cell units of the fuel cell stack is small.From the above results, it is considered that according to the fuel cell system of the disclosed embodiments, even when a hydrogen pump is not installed in the circulation flow path, the gas other than the fuel gas can be purged from the fuel electrodes of the fuel cell stack in a short time by using the second ejector capable of uniformly purging and having high circulation characteristics and the first ejector capable of purging in a short time and having a large flow amount depending on the time point differently.LIST OF REFERENCE NUMERALS11 Fuel cell stack 12 Fuel gas supplier 13 Mixed gas supply flow path 14 Circulation flow path 15 Pressure detector 16 Ejector set 17 Control unit 18 Fuel gas supply flow path 19 Fuel exhaust gas outlet 21 Oxidant gas supplier 22 Oxidant gas supply flow path 23 Oxidant gas outlet flow path 100 Fuel cell system

Claims

A fuel cell system (100) comprising: a fuel cell stack (11); an ejector set (16); a fuel gas supplier (12) that supplies fuel gas to the ejector set (16); a circulation flow path (14) that recovers fuel off gas discharged from the fuel cell stack (11) and returns the fuel off gas as a circulation gas to the ejector set (16); a mixed gas supplier flow path (13) that connects the ejector set (16) to the fuel cell stack (11) and allows the mixed gas containing the fuel gas and the circulation gas to be supplied from the ejector set (16) to the fuel electrodes of the fuel cell stack (11); and a pressure detector (15) that detects pressure information of the fuel electrode side of the fuel cell stack (11), and a fuel off-gas outlet (19) that discharges the fuel off-gas to the outside, wherein a concentration of the fuel gas is a predetermined concentration or less, and a control unit (17) configured to, at the time of starting the fuel cell system (100), purge the gas different from the fuel gas from the electrodes of a fuel cell stack (11) in a short time, wherein the ejector set (16) includes a first ejector and a second ejector in parallel, wherein the first ejector is an ejector that supplies a first mixed gas to the fuel electrodes of the fuel cell stack (11), and the second ejector is an ejector that supplies a second mixed gas to the fuel electrodes of the fuel cell stack (11), wherein a content ratio of the circulating gas is greater than that of the first mixed gas; wherein, for the second ejector, a supply flow amount of the mixed gas that can be supplied to the fuel electrodes of the fuel cell stack (11) is smaller than that for the first ejector; wherein, as a first control, in the case where the pressure information detected by the pressure detector (15) exceeds a first predetermined threshold value, the control unit (17) makes a ratio of the second ejector larger than a ratio of the first ejector when a total ratio of the ejectors of the ejector set (16) is determined to be 100%; and wherein, as a second control, in the case where the pressure information detected by the pressure detector (15) exceeds a second predetermined threshold value larger than the first threshold value, the control unit (17) after the first control makes the share ratio of the first ejector larger than the share ratio of the second ejector when the total share ratio of the ejectors of the ejector set (16) is determined as 100%.The fuel cell system (100) according to claim 1, wherein as the first control, in the case where the pressure information detected by the pressure detector (15) is the predetermined first threshold value or less, the control unit (17) makes the content ratio of the first ejector larger than the content ratio of the second ejector when the total content ratio of the ejectors of the ejector set (16) is determined to be 100%.The fuel cell system (100) according to claim 1, wherein as the first control, in the case where the pressure information detected by the pressure detector (15) exceeds the predetermined first threshold, the control unit (17) switches from the first ejector to the second ejector and supplies the second mixed gas from the second ejector to the fuel electrodes of the fuel cell stack (11), and wherein as the second control, in the case where the pressure information detected by the pressure detector (15) exceeds the predetermined second threshold, the control unit (17) switches from the second ejector to the first ejector and supplies the first mixed gas from the first ejector to the fuel electrodes of the fuel cell stack (11), and in the case where the pressure information is the second threshold or less, the control unit ( 17) supplies the second mixed gas from the second ejector to the fuel electrodes of the fuel cell stack ( 11).The fuel cell system (100) according to claim 1, wherein as the first controller, in the case where the pressure information detected by the pressure detector (15) is the predetermined first threshold value or less, the control unit (17) supplies the first mixed gas from the first ejector to the fuel electrodes of the fuel cell stack (11).

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