Fuel cell system and control method for the system

Abstract

The present invention relates to a fuel cell system and a control method for the system. A control unit (12) estimates an amount (Qh) of discharged fuel gas that is discharged from an outlet of a cathode flow path (47) among fuel exhaust gas that is introduced into an inlet of the cathode flow path (47) from a communication flow path (156) and flows through a cathode electrode (42). An amount (Qb) of oxidant gas required for dilution at the time of discharging to the atmosphere is obtained based on the estimated amount (Qh) of discharged fuel gas, and an ejection amount of an air pump (26) is set based on the obtained amount (Qb) of oxidant gas.

Description

Technical Field

[0001] The present invention relates to a fuel cell system including a fuel cell that generates electricity using an oxidant gas supplied to a cathode electrode and a fuel gas supplied to an anode electrode, and a control method for the system. Background Art

[0002] For example, a polymer electrolyte fuel cell includes an electrolyte membrane - electrode assembly (MEA). In this electrolyte membrane - electrode assembly (MEA), an anode electrode is disposed on one surface of an electrolyte membrane formed of a polymer ion - exchange membrane, and a cathode electrode is disposed on the other surface. The electrolyte membrane - electrode assembly is sandwiched by separators, thereby forming a power - generating single cell (cell unit). Usually, a predetermined number of power - generating single cells are stacked, and thus, for example, they are assembled into a fuel cell stack and incorporated into a fuel cell vehicle (fuel cell electric vehicle) or the like.

[0003] In such a fuel cell vehicle, when discharging fuel exhaust to the atmosphere, in order to reduce the hydrogen concentration to a predetermined concentration or less and discharge it, an oxidant gas for dilution is taken in from an air pump, and the fuel exhaust is diluted by the oxidant gas for dilution to reduce the hydrogen concentration.

[0004] For example, Patent Document 1 discloses a fuel cell system in which a discharge fluid including unconsumed fuel exhaust and liquid water discharged through a drain valve of a gas - liquid separator provided on the outlet side of an anode flow path in a fuel cell stack is introduced from the inlet of a cathode flow path into a cathode electrode via a connection pipe. In this fuel cell system, the fuel gas in the fuel exhaust included in the discharge fluid undergoes a catalytic reaction at the cathode electrode (

[0049] of Patent Document 1).

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: Japanese Patent JP2019 - 114351A Summary of the Invention

[0008] Problems to be Solved by the Invention

[0009] In the fuel cell system disclosed in Patent Document 1, after the fuel gas is reduced due to the catalytic reaction, the fuel exhaust is discharged from the outlet of the cathode flow path, and the fuel gas that needs to be diluted can be reduced.

[0010] However, when diluting the fuel gas that needs to be diluted, a considerable amount of the oxidant gas for dilution is incrementally taken in from the air pump.

[0011] However, when more oxidant gas for dilution than required is taken in, the power consumption of the air pump becomes excessive, and the power efficiency of the fuel cell system deteriorates.

[0012] The present invention has been made in consideration of such a problem, and an object thereof is to provide a fuel cell system capable of making an appropriate amount of oxidant gas required for diluting fuel exhaust discharged from the outlet of a cathode flow path, and a control method for the system.

[0013] Solution to the problem

[0014] One aspect of the present invention relates to a fuel cell system including a fuel cell that generates electricity using an oxidant gas ejected from an air pump and supplied to a cathode electrode through an inlet of a cathode flow path and a fuel gas supplied to an anode electrode through an inlet of an anode flow path. In the fuel cell system, there are provided: a communication flow path that guides fuel exhaust discharged from the outlet of the anode flow path of the fuel cell to the inlet of the cathode flow path; and a control unit that controls the fuel cell system. The control unit estimates the amount of fuel gas discharged from the outlet of the cathode flow path in the fuel exhaust that is introduced from the communication flow path into the inlet of the cathode flow path and flows through the cathode electrode, obtains the amount of oxidant gas required for dilution when discharging to the atmosphere based on the estimated amount of fuel gas, and sets the ejection amount of the air pump based on the obtained amount of oxidant gas.

[0015] Another aspect of the present invention relates to a control method for a fuel cell system including a fuel cell that generates electricity using an oxidant gas ejected from an air pump and supplied to a cathode electrode through an inlet of a cathode flow path and a fuel gas supplied to an anode electrode through an inlet of an anode flow path. In the control method for the fuel cell system, fuel exhaust discharged from the outlet of the anode flow path of the fuel cell is introduced into the inlet of the cathode flow path via a communication flow path, the amount of fuel gas discharged from the outlet of the cathode flow path in the fuel exhaust that is introduced from the communication flow path into the inlet of the cathode flow path and flows through the cathode electrode is estimated, the amount of oxidant gas required for dilution when discharging to the atmosphere is obtained based on the estimated amount of fuel gas, and the ejection amount of the air pump is set based on the obtained amount of oxidant gas.

[0016] Effect of the invention

[0017] According to the present invention, the amount of fuel gas discharged from the outlet of the cathode flow path in the fuel exhaust flowing through the cathode electrode from the inlet of the cathode flow path is estimated, the amount of oxidant gas required for dilution is obtained based on the estimated amount of fuel gas, and the ejection amount of the air pump is set based on the obtained amount of oxidant gas. Therefore, the amount of oxidant gas required for dilution can be accurately grasped and made appropriate (the minimum required amount). As a result, the increase in the power of the air pump can be minimized, and a decrease in the power efficiency of the fuel cell system can be suppressed.

[0018] Referring to the following description of the embodiments with reference to the accompanying drawings, the above objects, features, and advantages can be easily understood. Description of the Drawings

[0019] Figure 1 It is a schematic block diagram showing the structure in which the fuel cell system according to the embodiment is incorporated into a fuel cell vehicle.

[0020] Figure 2 It is depicted with arrow lines Figure 1 in the fuel cell system in the block diagram showing the flow of current and the flow of gas.

[0021] Figure 3 It is a flowchart for explaining Figure 1 the operation of the fuel cell system in

[0022] Figure 4A It is a characteristic diagram showing the relationship between the refrigerant outlet temperature and the catalytic reaction rate.

[0023] Figure 4B It is a characteristic diagram showing the relationship between the amount of oxidant gas supplied to the stack and the catalytic reaction rate.

[0024] Figure 4C It is an explanatory diagram of the catalytic reaction rate with the amount of oxidant gas supplied to the stack and the refrigerant outlet temperature as parameters.

[0025] Figure 5 It is a block diagram of the arithmetic unit of the control unit that executes the processing of the flowchart. Detailed Embodiments

[0026] Hereinafter, embodiments will be given, and the fuel cell system according to the present invention and the control method of the system will be described in detail with reference to the accompanying drawings.

[0027] [Structure]

[0028] Figure 1 It is a schematic block diagram showing the structure in which the fuel cell system 14 according to the embodiment is incorporated into a fuel cell vehicle 10.

[0029] The fuel cell vehicle 10 is composed of a control unit 12 that controls the entire fuel cell vehicle 10, a fuel cell system 14, and an output unit 20 electrically connected to the fuel cell system 14.

[0030] The fuel cell system 14 basically consists of a fuel cell stack (simply referred to as a fuel cell) 16, a hydrogen tank 18, an oxidant gas system device 22, and a fuel gas system device 24.

[0031] The oxidant gas system device 22 includes an air pump 26 and a humidifier (HUM) 28.

[0032] The fuel gas system device 24 includes an injector (INJ) 30, an ejector (EJT) 32, and a gas-liquid separator 34.

[0033] The fuel cell stack 16 stacks a plurality of power generation single cells 40. The power generation single cell 40 includes an electrolyte membrane-electrode structure 44, and separators 45 and 46 that sandwich the electrolyte membrane-electrode structure 44.

[0034] The electrolyte membrane-electrode structure 44 includes: a solid polymer electrolyte membrane 41, for example, a thin film containing perfluorosulfonic acid with moisture; and a cathode electrode 42 and an anode electrode 43 that sandwich the solid polymer electrolyte membrane 41.

[0035] The cathode electrode 42 and the anode electrode 43 have a gas diffusion layer (not shown) formed of carbon paper or the like. Porous carbon particles carrying a platinum alloy on the surface are uniformly coated on the surface of the gas diffusion layer, thereby forming an electrode catalyst layer (not shown). Electrode catalyst layers are formed on both sides of the solid polymer electrolyte membrane 41.

[0036] On the surface of one separator 45 facing the electrolyte membrane-electrode structure 44, a cathode flow path (oxidant gas flow path) 47 that connects the oxidant gas inlet communication port 116 and the oxidant gas outlet communication port 102 is formed.

[0037] On the surface of the other separator 46 facing the electrolyte membrane-electrode structure 44, an anode flow path (fuel gas flow path) 48 that connects the fuel gas inlet communication port 146 and the fuel gas outlet communication port 148 is formed.

[0038] In the anode electrode 43, by supplying fuel gas, hydrogen ions are generated from hydrogen molecules due to an electrode reaction caused by a catalyst. The hydrogen ions permeate through the solid polymer electrolyte membrane 41 and move to the cathode electrode 42. On the other hand, electrons are released from the hydrogen molecules.

[0039] The electrons released from the hydrogen molecules move from the negative terminal 86 through the output adjuster 80 and an external load, and via the positive terminal 88 to the cathode electrode 42.

[0040] In the cathode electrode 42, due to the action of the catalyst, hydrogen ions and electrons react with oxygen contained in the supplied oxidant gas to generate water.

[0041] A voltage sensor 91 for detecting the power generation voltage is provided between the positive terminal 88 and the negative terminal 86. Also, a current sensor 93 for detecting the power generation current is provided in the wiring between the positive terminal 88 and the output adjuster 80.

[0042] The air pump 26 is composed of a mechanical supercharger or the like driven by a drive unit 25 including an inverter and a motor, and has a function of taking in atmospheric air (air), pressurizing it, and supplying it to the humidifier 28.

[0043] The humidifier 28 has: a flow path 52 through which the oxidant gas (dry air) flows; and a flow path 54 through which the exhaust gas (humidified oxidant exhaust gas and fuel exhaust gas described later) from the cathode flow path 47 of the fuel cell stack 16 flows.

[0044] Moreover, the exhaust gas from the cathode flow path 47 of the fuel cell stack 16 is supplied to the flow path 54 through the oxidant gas outlet communication port 102 of the fuel cell stack 16 and the pipe 104.

[0045] A cathode outlet pressure sensor 69 is provided in the pipe 104, and the cathode outlet pressure sensor 69 detects the pressure of the oxidant gas flowing in the pipe 104 as the cathode outlet pressure Pco [kPa].

[0046] The humidifier 28 has a function of humidifying the oxidant gas supplied from the air pump 26. That is, the humidifier 28 causes the moisture contained in the exhaust gas to move to the supply gas (oxidant gas) through the porous membrane.

[0047] The intake side of the air pump 26 communicates with the atmosphere through the pipe 106, an air flow sensor (AFS) (flow sensor) 56, and the pipe 108.

[0048] The air flow sensor 56 measures the mass flow rate M [g / min] of the oxidant gas supplied from the air pump 26 to the cathode flow path 47 of the fuel cell stack 16 and outputs it to the control unit 12.

[0049] The discharge side of the air pump 26 communicates with one end side of the flow path 52 of the humidifier 28 through the pipe 110 and the pipe 112. The other end side of the flow path 52 of the humidifier 28 communicates with one end side of the pipe 114, and the other end side of the pipe 114 communicates with the cathode flow path 47 in the fuel cell stack 16 through the oxidant gas inlet communication port 116.

[0050] A discharge pressure sensor 64 is provided in the pipe 110, and the discharge pressure sensor 64 detects the pressure of the oxidant gas discharged from the air pump 26 as the oxidant discharge pressure Po [kPa].

[0051] A cathode inlet pressure sensor 67 is provided in the pipe 114, and the cathode inlet pressure sensor 67 detects the pressure of the oxidant gas flowing in the pipe 114 as the cathode inlet pressure Pci [kPa].

[0052] On the ejection side of the flow path 54 of the humidifier 28, it is communicated with one inlet side of the diluter 66 through the pipeline 117 and the pipeline 118.

[0053] The pipeline 110 on the ejection port side of the air pump 26 branches, one is communicated with the pipeline 112, and the other is communicated with the pipeline 118 through the bypass pipeline 120 and the bypass valve 122.

[0054] A diluter inlet pressure sensor 62 is provided in the pipeline 118, and the diluter inlet pressure sensor 62 detects the pressure of the gas flowing through the pipeline 118 as the dilution inlet pressure Pd [kPa].

[0055] The hydrogen tank 18 is equipped with an electromagnetic operation type cut-off valve, and the hydrogen tank 18 is a container that compresses and stores high-purity hydrogen at a high pressure.

[0056] The fuel gas ejected from the hydrogen tank 18 passes through the pipeline 140, the injector 30, the pipeline 142, the ejector 32, the pipeline 144, and is supplied to the inlet of the anode flow path 48 of the fuel cell stack 16 through the fuel gas inlet communication port 146.

[0057] An anode inlet pressure sensor 68 is provided in the pipeline 144, and the anode inlet pressure sensor 68 detects the pressure of the fuel gas flowing through the pipeline 144 as the anode inlet pressure Pai [kPa].

[0058] The outlet of the anode flow path 48 is communicated with the inlet 151 of the gas-liquid separator 34 through the fuel gas outlet communication port 148 and the pipeline 150, and the fuel exhaust gas (anode exhaust gas) as a hydrogen-containing gas is supplied from the anode flow path 48 to the gas-liquid separator 34.

[0059] An anode outlet pressure sensor 70 and an anode outlet temperature sensor 72 are provided in the pipeline 150.

[0060] The anode outlet pressure sensor 70 detects the pressure of the fuel exhaust gas flowing through the pipeline 150 as the anode outlet pressure Poa [kPa]. The anode outlet temperature sensor 72 detects the temperature of the fuel exhaust gas flowing through the pipeline 150 as the anode outlet temperature To [°C].

[0061] The gas-liquid separator 34 separates the fuel exhaust gas into a gas component and a liquid component (liquid water). The gas component of the fuel exhaust gas (fuel exhaust gas) is discharged from the gas discharge port 152 of the gas-liquid separator 34 and is supplied to the ejector 32 through the pipeline 154. On the other hand, when needed, when the relief valve 158 is opened, the fuel exhaust gas is also supplied to the pipeline 114 of the oxidant gas through the connection pipeline 156 (connection flow path) and the relief valve 158.

[0062] Further, in order to prevent deterioration of the anode electrode 43 due to a decrease in the hydrogen concentration in the anode flow path 48 caused by nitrogen existing in the cathode flow path 47 permeating through the electrolyte membrane - electrode assembly 44, the bleed valve 158 is opened. That is, during normal power generation such as during driving, when it is determined that the hydrogen concentration in the anode flow path 48 has decreased, the bleed valve 158 is opened.

[0063] The fuel exhaust gas supplied to the pipe 114 for the oxidant gas is mixed with the oxidant gas supplied from the air pump 26 within the pipe 114 and is supplied to the cathode flow path 47 of the fuel cell stack 16 through the oxidant gas inlet communication port 116.

[0064] A part of the fuel exhaust gas supplied to the cathode flow path 47 is ionized by the catalytic reaction of the cathode electrode 42, and the hydrogen ions react with the oxidant gas to generate water. The remaining unreacted part of the fuel exhaust gas is discharged from the oxidant gas outlet communication port 102 and is supplied to the diluter 66 through the pipe 104, the flow path 54, the pipe 117, and the pipe 118. When discharged from the diluter 66, it is diluted by the oxidant gas supplied from the bypass pipe 120 and is discharged to the outside (atmosphere) of the fuel cell vehicle 10 via the pipe 118, the diluter 66, and the pipe 124.

[0065] Fuel gas is supplied to the ejector 32 via the pipe 142 from the ejector 30 provided on the upstream side of the ejector 32. Therefore, the fuel exhaust gas (the gas component) supplied via the gas - liquid separator 34 is attracted by the ejector 32 and is supplied to the anode flow path 48 of the fuel cell stack 16 through the pipe 144 of the fuel cell stack 16 via the fuel gas inlet communication port 146 in a state of being mixed with the fuel gas.

[0066] The liquid component of the fuel exhaust gas passes through the pipe 162, the drain valve 164, and the pipe 166 from the liquid discharge port 160 of the gas - liquid separator 34 and is discharged to the outside of the fuel cell vehicle 10 from the pipe 124 via the diluter 66.

[0067] Actually, a part of the fuel exhaust gas is discharged to the pipe 166 together with the liquid component from the drain valve 164. In order to dilute and discharge the hydrogen in this fuel exhaust gas to the outside, a part of the oxidant gas ejected from the air pump 26 is supplied to the diluter 66 through the bypass pipe 120 and the pipe 118.

[0068] As a result, the hydrogen in the fuel exhaust gas is diluted in the diluter 66 and is discharged to the outside.

[0069] Regarding the fuel cell stack 16, a cooling medium supply flow path 74a for supplying a cooling medium and a cooling medium discharge flow path 74b for discharging the cooling medium are also provided in a cooling medium flow path (not shown) provided in the fuel cell stack 16. A temperature sensor 76 is provided in the cooling medium discharge flow path 74b, and the temperature sensor 76 measures the temperature Ts [°C] of the cooling medium flowing in the cooling medium discharge flow path 74b as the temperature of the fuel cell stack 16.

[0070] The control unit 12 is configured including a microcomputer, and this microcomputer includes a CPU (not shown), a storage unit (ROM and RAM) 78, etc.

[0071] In the storage unit 78, in addition to storing control programs for the fuel cell vehicle 10 and the fuel cell system 14, characteristics 201 and 202 ( Figure 4A , Figure 4B ) etc. described later are also stored.

[0072] The CPU of the control unit 12 performs calculations according to the control program, thereby controlling the operation of the fuel cell vehicle 10 and the fuel cell system 14. In addition, the control unit 12 outputs control signals such as an open valve instruction and a close valve instruction to each component such as the bypass valve 122 based on detection signals received from various sensors such as the injection pressure sensor 64, the temperature sensor 76, and an accelerator opening sensor (not shown), for example.

[0073] [Operation]

[0074] Then, the operation of the fuel cell system 14 configured basically as described above will be described in the following order: [1] The operation during normal power generation such as when the fuel cell vehicle 10 is running, [2] The calculation operation of the amount of diluted oxidant gas when the hydrogen concentration in the anode flow path 48 decreases.

[0075] [1] Description of the operation during normal power generation such as when the fuel cell vehicle 10 is running.

[0076] Refer to Figure 2 The operation during normal power generation will be described below (during running etc. when the hydrogen concentration on the anode electrode 43 side is above the threshold value that does not require the relief valve 158 to be opened).

[0077] Moreover, in Figure 2 , the solid arrow lines indicate the flow of fuel gas, oxidant gas, and electric power, and the dashed arrow lines indicate the flow of gas for explaining the calculation operation of the amount of diluted oxidant gas described later.

[0078] During normal power generation, the relief valve 158 is closed, and the bypass valve 122 is opened mainly for dilution when the purge valve 164 is opened.

[0079] On the side of the oxidant gas system device 22, under the control of the control unit 12, the air pump 26 is driven by a drive unit 25 that operates using the high-voltage power of the capacitor 82 as a power source. The oxidant gas ejected from the driven air pump 26 is humidified by the pipeline 110, the pipeline 112, and the humidifier 28, and then supplied to the oxidant gas inlet communication port 116 of the fuel cell stack 16 through the pipeline 114.

[0080] Moreover, in the humidifier 28, the moist exhaust gas discharged from the oxidant gas outlet communication port 102 of the fuel cell stack 16 flows through the flow path 54, and the moisture in the exhaust gas moves from the flow path 54 to the supply gas (oxidant gas) flowing through the flow path 52 via the porous membrane.

[0081] On the other hand, on the side of the fuel gas system device 24, under the valve opening action of the injector 30, fuel gas (hydrogen) is supplied from the high-pressure hydrogen tank 18 to the pipeline 142. The fuel gas is mixed with the fuel exhaust gas sucked into the ejector 32 through the pipeline (circulation path) 154 and then supplied to the fuel gas inlet communication port 146 of the fuel cell stack 16 after passing through the ejector 32.

[0082] In the fuel cell stack 16, the oxidant gas is supplied from the oxidant gas inlet communication port 116 to the cathode electrode 42 via the cathode flow path 47 of each power generation single cell 40. On the other hand, hydrogen is supplied from the fuel gas inlet communication port 146 to the anode electrode 43 via the anode flow path 48 of each power generation single cell 40. Therefore, in each power generation single cell 40, the oxygen contained in the air supplied to the cathode electrode 42 and the hydrogen supplied to the anode electrode 43 are consumed by an electrochemical reaction (fuel cell reaction) in the electrode catalyst layer to generate electricity.

[0083] Then, the cathode exhaust gas formed by the air supplied to the cathode electrode 42 and consumed and the reaction-generated water are discharged to the oxidant gas outlet communication port 102, and after passing through the pipeline 104, the flow path 54, and the pipeline 117, they merge with the oxidant gas supplied from the bypass pipeline 120 and are supplied to the diluter 66 via the pipeline 118. It is discharged to the outside of the fuel cell vehicle 10 via the pipeline 124 from the diluter 66.

[0084] The hydrogen supplied to the anode electrode 43 and consumed is discharged as fuel exhaust gas (a part of the consumed fuel gas) to the fuel gas outlet communication port 148.

[0085] The fuel exhaust gas is introduced into the gas-liquid separator 34 from the pipeline 150 and the liquid component (liquid water) is removed, and then sucked by the ejector 32 through the pipeline 154 and used for the power generation reaction in the fuel cell stack 16.

[0086] The power of the high voltage of the generated power voltage generated by the fuel cell stack 16 formed by connecting a plurality of power generation single cells 40 in series is stored in the capacitor 82 via the output regulator 80.

[0087] According to the load state such as the accelerator opening degree and the set temperature of the air conditioner (not shown), the motor 84 is driven by the power of the capacitor 82 and / or the fuel cell stack 16 under the control of the output regulator 80, whereby the fuel cell vehicle 10 travels.

[0088] [2] Explanation of the calculation operation of the dilution oxidant gas amount

[0089] Then, with reference to Figure 3 The flowchart shown explains the calculation process of the amount Qb of the dilution oxidant gas supplied to the diluter 66 side from the bypass valve 122 when the hydrogen concentration on the anode electrode 43 (anode flow path 48) side decreases.

[0090] Execute Figure 3 The control unit 12 (CPU thereof) performs the processing (control program) of the flowchart of, but it is cumbersome to refer to the control unit 12 (CPU thereof) every time, so it is referred to as needed.

[0091] First, before explaining the detailed processing of the flowchart of Figure 3 explain the background and outline of the processing for calculating the dilution oxidant gas amount Qb.

[0092] <Background and outline of the calculation process of the dilution oxidant gas amount>

[0093] In the above normal power generation, when nitrogen present in the cathode flow path 47 permeates through the electrolyte membrane - electrode structure 44 and enters the anode flow path 48, the hydrogen concentration in the anode flow path 48 decreases. There is a concern that the anode electrode 43 may deteriorate due to the decrease in hydrogen concentration.

[0094] To prevent or suppress such deterioration, when the control unit 12 detects a sign that the hydrogen concentration will drop below a preset threshold, the relief valve 158 is opened. As a result, in the fuel cell stack 16, the fuel exhaust gas including nitrogen permeating from the cathode flow path 47 side to the anode flow path 48 passes through the fuel gas outlet communication port 148, the gas - liquid separator 34, the connection pipe 156, the pipe 114, and the oxidant gas inlet communication port 116, and flows through the cathode electrode 42 in the cathode flow path 47.

[0095] In this case, the hydrogen in the fuel exhaust gas flowing through the cathode electrode 42 is ionized in the cathode electrode catalyst layer, and the hydrogen ions are consumed by the catalytic reaction (cathode catalyst humidification reaction) of reacting with oxygen to form water.

[0096] That is, the hydrogen gas flowing through the cathode electrode 42 is consumed in the cathode electrode 42 according to the catalytic reaction rate Rc of the cathode electrode 42.

[0097] Moreover, a predetermined amount of hydrogen gas in the fuel exhaust is consumed, and the fuel exhaust formed by the remaining hydrogen gas and nitrogen after consumption is introduced into the pipeline 118 from the cathode flow path 47 through the oxidant gas outlet communication port 102 via the pipeline 104, the flow path 54, and the pipeline 117.

[0098] The oxidant gas can be made to merge into this pipeline 118 through the bypass pipeline 120.

[0099] In order to dilute the hydrogen gas in the fuel exhaust introduced from the pipeline 117 to a concentration below a specified value in the pipeline 118 and discharge it to the outside, it is necessary to increase the amount Qo of the ejected oxidant gas ejected from the air pump 26.

[0100] In order to increase the amount Qo of the ejected oxidant gas, it is necessary to increase the power consumption of the drive unit 25 and the air pump 26. In order to minimize the increase in the power consumption of the drive unit 25 and the air pump 26, it is necessary to minimize the equivalent amount of the increase in the amount Qo of the ejected oxidant gas.

[0101] Therefore, it is necessary to correctly calculate the minimum required amount of the diluted oxidant gas (bypass oxidant gas) Qb. The above description is an explanation of the background and the outline of the process.

[0102] <Calculation process of the diluted oxidant gas amount>

[0103] During the power generation of the fuel cell stack 16, with the shut-off valves of the relief valve 158 and the bypass valve 122 closed, the Figure 3 processing of the flowchart is started.

[0104] In step S1, it is determined whether the hydrogen concentration in the anode flow path 48 decreases.

[0105] Based on the temperature of the anode electrode 43 (replaced by the temperature Ts of the cooling medium), the anode inlet pressure Pai, and the cathode inlet pressure Pci, the amount of nitrogen permeating from the cathode electrode 42 side through the electrolyte membrane-electrode structure 44 to the anode electrode 43 side is estimated, and thus the hydrogen concentration in the anode flow path 48 can be estimated.

[0106] When it is determined that the hydrogen concentration will decrease below a preset threshold value (step S1: Yes), in step S2, the catalytic reaction rate Rc is calculated using the stack supply oxidant gas amount Qs and the refrigerant temperature Ts and referring to Figure 4A the characteristic 201 shown in Figure 4B and / or the characteristic 202 shown in

[0107] AsFigure 4A As shown in characteristic 201, the catalytic reaction rate Rc increases as the refrigerant temperature Ts measured by the temperature sensor 76 increases. Additionally, as Figure 4B shown in characteristic 202, the catalytic reaction rate Rc decreases as the amount of oxidant gas Qs supplied to the stack increases.

[0108] When considering the synthesis of Figure 4A characteristic 201 and Figure 4B characteristic 202, the relationship shown in Figure 4C is obtained. That is, the higher the refrigerant outlet temperature Ts and the lower the amount of oxidant gas Qs supplied to the stack (the smaller the value), the higher the catalytic reaction rate Rc.

[0109] Moreover, characteristics 201 and 202 are pre-measured according to the model of the fuel cell stack 16 and stored in the storage unit 78.

[0110] Here, when the bypass valve 122 and the bleed valve 158 are closed (Qb = 0, Qe = 0), the amount of oxidant gas Qs supplied to the stack is equal to the amount of oxidant gas Qo ejected by the air pump 26, which is obtained as the measured value of the air flow sensor 56.

[0111] Moreover, in the case where the drain valve 164 is opened and the bypass valve 122 is opened to dilute the hydrogen contained in the fuel exhaust in the liquid water, the amount of oxidant gas Qs supplied to the stack is estimated as shown in the following formula (1) (refer to Figure 2 ).

[0112] Qs = Qo - Qb…(1)

[0113] Here, Qo is the amount of oxidant gas ejected by the air pump 26, and Qb is the amount of oxidant gas flowing in the bypass line 120.

[0114] Moreover, the amount of oxidant gas Qb flowing in the bypass line 120 can be detected by inserting a gas flow sensor in the bypass line 120, or can also be estimated based on the pressure difference between the pressure values measured by the ejection pressure sensor 64 and the diluter inlet pressure sensor 62.

[0115] Then, in step S3, the amount of discharged fuel gas Qh that is not reacted in the catalytic reaction and discharged from the cathode flow path 47 of the fuel cell stack 16 is calculated based on the following formula (2), that is, the fuel exhaust introduction amount Qe introduced into the cathode flow path 47 when the bleed valve 158 is opened is multiplied by the unreacted ratio. Moreover, the unit of the catalytic reaction rate Rc in formula (2) is the converted value in percentage [%].

[0116] Qh = Qe × (1 - Rc)…(2)

[0117] In formula (2), the amount of fuel exhaust gas Qe flowing through the relief valve 158 can be detected by inserting a gas flow sensor in the communication pipeline 156, or can be estimated based on the pressure difference between the pressure values measured by the anode outlet pressure sensor 70 and the cathode inlet pressure sensor 67.

[0118] Then, in step S4, based on the discharged fuel gas amount Qh, the amount of dilution oxidant gas Qb (equivalent increment) required to maintain a value below the target exhaust concentration Dtar is calculated according to the following formula (3).

[0119] Qb = {(100 [%] - Dtar [%]) × Qh} / Dtar [%] … (3)

[0120] Then, in step S5, the air pump 26 is driven by the drive unit 25 so that the required amount of dilution oxidant gas Qb calculated according to formula (3) flows through the bypass pipeline 120, and thus the amount of dilution oxidant gas Qb (equivalent increment) is supplied to the bypass pipeline 120. Moreover, when the bypass valve 122 is opened, an amount equivalent to the amount of dilution oxidant gas Qb is increased and supplied to the bypass pipeline 120.

[0121] Then, in step S6, the relief valve 158 is opened, and the fuel exhaust gas containing nitrogen is introduced from the anode electrode 43 side to the cathode electrode 42 side of the fuel cell stack 16.

[0122] In this case, a part of the fuel gas in the fuel cell stack 16 is consumed due to the catalytic reaction of the cathode electrode 42, and the amount of dilution oxidant gas Qb (equivalent increment) is mixed with the discharged fuel gas amount Qh ejected from the oxidant gas outlet communication port 102. Thus, the discharged fuel gas is diluted via the diluter 66 while being maintained below the target exhaust concentration Dtar and is discharged to the atmosphere.

[0123] Figure 5 A block diagram of the arithmetic unit of the control unit 12 that executes the processing of the flowchart is shown.

[0124] The refrigerant temperature (refrigerant outlet temperature) Ts or the stack supply oxidant gas amount Qs is converted into the catalytic reaction rate Rc (corresponding to step S2) through the catalytic reaction rate conversion correspondence 220 (having the Figure 4A and Figure 4B characteristics 201, 202).

[0125] Then, the unreacted ratio (1 - Rc) is calculated by subtracting the catalytic reaction rate Rc from the value 1 by the subtractor 222. In addition, the discharged fuel gas amount Qh is calculated by the multiplier 224 as shown in formula (2) (corresponding to step S3).

[0126] Then, the dilution oxidant gas amount calculation unit 226 calculates the dilution oxidant gas amount Qb (increment equivalent amount) described above using Equation (3) (corresponding to step S4). The calculated dilution oxidant gas amount Qb is added to the stack supply oxidant gas amount Qs calculated separately to adjust the ejected oxidant gas amount Qo (Qo = Qb + Qs), thereby driving the air pump 26 (corresponding to step S5).

[0127] [Invention that can be grasped according to the embodiment]

[0128] Here, the invention that can be grasped according to the above embodiment is described as follows. Moreover, for ease of understanding, reference numerals used in the embodiment are attached to the structural elements, but the structural elements are not limited to the elements to which the reference numerals are attached.

[0129] The fuel cell system according to the present invention includes a fuel cell that generates electricity using an oxidant gas ejected from the air pump 26 and supplied to the cathode electrode 42 through the inlet of the cathode flow path 47 and a fuel gas supplied to the anode electrode 43 through the inlet of the anode flow path 48. In the fuel cell system 14, there are provided: a communication pipe 156 that guides fuel exhaust discharged from the outlet of the anode flow path 48 of the fuel cell to the inlet of the cathode flow path 47; and a control unit 12 that controls the fuel cell system 14. The control unit 12 estimates the amount of fuel gas (discharged fuel gas amount) Qh discharged from the outlet of the cathode flow path 47 among the fuel exhaust that is introduced into the inlet of the cathode flow path 47 from the communication pipe 156 and flows through the cathode electrode 42, obtains the amount of oxidant gas Qb required for dilution when discharging to the atmosphere based on the estimated discharged fuel gas amount Qh, and sets the ejection amount of the air pump 26 based on the obtained oxidant gas amount Qb.

[0130] In the present invention, the discharged fuel gas amount Qh discharged from the outlet of the cathode flow path 47 among the fuel exhaust that flows from the inlet of the cathode flow path 47 to the cathode electrode 42 is estimated, and thus the amount of oxidant gas (dilution oxidant gas amount) Qb required for dilution is obtained based on the estimated discharged fuel gas amount Qh, and the ejection amount of the air pump 26 is set based on the obtained dilution oxidant gas amount Qb. Therefore, the amount of oxidant gas Qb required for dilution can be accurately grasped, and the ejection increment of the air pump 26 can be set in such a way as to increase the amount of oxidant gas Qb required for dilution. As a result, the amount of oxidant gas Qb required for dilution is made appropriate, the increase in the power of the air pump 26 is minimized, and a decrease in the power efficiency of the fuel cell system 14 can be suppressed.

[0131] Further, in the fuel cell system, the control unit 12 estimates the amount of discharged fuel gas Qh discharged from the outlet of the cathode flow path 47 as follows: based on the amount of fuel exhaust gas introduced from the outlet of the anode flow path 48 to the cathode electrode 42 via the communication pipe 156 and the catalytic reaction rate of the catalytic reaction occurring at the cathode electrode.

[0132] According to this structure, the amount of discharged fuel gas Qh discharged from the outlet of the cathode flow path 47 is estimated based on the amount of fuel exhaust gas introduced Qe from the outlet of the anode flow path 48 to the cathode electrode 42 via the communication pipe 156 and the catalytic reaction rate Rc of the catalytic reaction occurring at the cathode electrode 42.

[0133] According to this structure, the amount of discharged fuel gas Qh discharged from the outlet of the cathode flow path 47 can be easily obtained as "the amount of discharged fuel gas Qh discharged from the outlet of the cathode flow path 47 = the amount of fuel exhaust gas introduced Qe into the cathode electrode × (1 - catalytic reaction rate Rc)".

[0134] Furthermore, in the fuel cell system, the control unit 12 estimates the catalytic reaction rate Rc based on the temperature of the fuel cell or the amount of oxidant gas Qs supplied from the air pump 26 to the cathode electrode 42.

[0135] In this way, since the catalytic reaction rate Rc is estimated based on the temperature of the fuel cell or the amount of oxidant gas Qs supplied to the cathode electrode 42 of the stack from the air pump 26, the catalytic reaction rate Rc can be estimated in real time and easily, and the amount of oxidant gas Qb required for dilution can be accurately and appropriately set without excess.

[0136] In the control method of the fuel cell system according to the present invention, the fuel cell system 14 includes a fuel cell that generates electricity using an oxidant gas ejected from the air pump 26 and supplied to the cathode electrode 42 through the inlet of the cathode flow path 47 and a fuel gas supplied to the anode electrode 43 through the inlet of the anode flow path 48. In the control method of the fuel cell system, the fuel exhaust gas discharged from the outlet of the anode flow path 48 of the fuel cell is introduced into the inlet of the cathode flow path 47 via the communication pipe 156, and the amount of fuel gas (discharged fuel gas amount) Qh discharged from the outlet of the cathode flow path 47 in the fuel exhaust gas introduced into the inlet of the cathode flow path 47 from the communication pipe 156 and flowing through the cathode electrode 42 is estimated. Based on the estimated discharged fuel gas amount Qh, the amount of oxidant gas Qb required for dilution when discharging to the atmosphere is obtained, and the ejection amount of the air pump 26 is set based on the obtained amount of oxidant gas Qb.

[0137] Based on this structure, the amount of exhaust fuel gas Qh discharged from the outlet of the cathode flow path 47 among the fuel exhaust gas flowing from the inlet of the cathode flow path 47 to the cathode electrode 42 is estimated. Then, based on the estimated amount of exhaust fuel gas Qh, the amount of oxidant gas Qb required for dilution is obtained, and the ejection amount of the air pump 26 is set based on the amount of oxidant gas Qb. Therefore, the amount of oxidant gas Qb required for dilution can be accurately grasped, and the ejection increment of the air pump 26 is set in such a way as to increase the amount of oxidant gas Qb required for dilution. As a result, the amount of oxidant gas Qb required for dilution is made appropriate, the increase in the power of the air pump 26 is minimized, and a decrease in the power efficiency of the fuel cell system 14 can be suppressed.

[0138] Moreover, the present invention is not limited to the above-described embodiments, and of course, various structures can be adopted based on the content described in this specification.

Claims

1. A fuel cell system includes a fuel cell that generates electricity using an oxidant gas ejected from an air pump and supplied to a cathode electrode through an inlet of a cathode flow path and a fuel gas supplied to an anode electrode through an inlet of an anode flow path. In the fuel cell system, there are provided: A communication flow path that introduces fuel exhaust discharged from an outlet of the anode flow path of the fuel cell into an inlet of the cathode flow path; A bypass pipe that connects an ejection port of the oxidant gas of the air pump to a pipe communicating with an outlet of the cathode flow path, and dilutes the fuel exhaust discharged from the outlet of the cathode flow path with the oxidant gas supplied from the air pump; and A control unit that controls the fuel cell system, The control unit estimates the amount of fuel gas discharged from the outlet of the cathode flow path in the fuel exhaust introduced into the inlet of the cathode flow path from the communication flow path and flowing through the cathode electrode; The control unit obtains the amount of oxidant gas required for dilution when discharging to the atmosphere based on the estimated amount of fuel gas; The control unit sets the ejection amount of the air pump based on the obtained amount of oxidant gas.

2. The fuel cell system according to claim 1, Characterized in that, The control unit estimates the amount of fuel gas discharged from the outlet of the cathode flow path as follows: Based on the amount of fuel exhaust introduced into the cathode electrode from the outlet of the anode flow path via the communication flow path and the catalytic reaction rate of the catalytic reaction occurring at the cathode electrode.

3. The fuel cell system according to claim 2, Characterized in that, The control unit estimates the catalytic reaction rate based on the temperature of the fuel cell or the amount of oxidant gas supplied from the air pump to the cathode electrode.

4. A fuel cell system includes a fuel cell that generates electricity using an oxidant gas ejected from an air pump and supplied to a cathode electrode through an inlet of a cathode flow path and a fuel gas supplied to an anode electrode through an inlet of an anode flow path. In the fuel cell system, there are provided: A communication flow path that introduces fuel exhaust discharged from an outlet of the anode flow path of the fuel cell into an inlet of the cathode flow path; and A control unit that controls the fuel cell system, The control unit estimates the amount of fuel gas discharged from the outlet of the cathode flow path in the fuel exhaust introduced into the inlet of the cathode flow path from the communication flow path and flowing through the cathode electrode as follows: Based on the amount of fuel exhaust introduced into the cathode electrode from the outlet of the anode flow path via the communication flow path and the catalytic reaction rate of the catalytic reaction occurring at the cathode electrode; The control unit obtains the amount of oxidant gas required for dilution when discharging to the atmosphere based on the estimated amount of fuel gas; The control unit sets the ejection amount of the air pump based on the obtained amount of oxidant gas.

5. A control method for a fuel cell system, the fuel cell system including a fuel cell that generates electricity using an oxidant gas ejected from an air pump and supplied to a cathode electrode through an inlet of a cathode flow path and a fuel gas supplied to an anode electrode through an inlet of an anode flow path. In the control method of the fuel cell system, the fuel exhaust gas discharged from an outlet of the anode flow path of the fuel cell is introduced into the inlet of the cathode flow path via a connection flow path, the fuel exhaust gas discharged from an outlet of the cathode flow path is diluted by the oxidant gas supplied from the air pump through a bypass line that connects an ejection port of the oxidant gas of the air pump to a line communicating with the outlet of the cathode flow path; estimating an amount of fuel gas discharged from an outlet of the cathode flow path in the fuel exhaust gas introduced from the connection flow path into the inlet of the cathode flow path and flowing through the cathode electrode, calculating an amount of oxidant gas required for dilution when discharging to the atmosphere based on the estimated amount of fuel gas, setting an ejection amount of the air pump based on the calculated amount of oxidant gas.

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