WO2006120874A1 - Fuel cell system - Google Patents

Fuel cell system Download PDF

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Publication number
WO2006120874A1
WO2006120874A1 PCT/JP2006/308497 JP2006308497W WO2006120874A1 WO 2006120874 A1 WO2006120874 A1 WO 2006120874A1 JP 2006308497 W JP2006308497 W JP 2006308497W WO 2006120874 A1 WO2006120874 A1 WO 2006120874A1
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WO
WIPO (PCT)
Prior art keywords
fuel cell
idling
fuel
stop
fuel gas
Prior art date
Application number
PCT/JP2006/308497
Other languages
French (fr)
Inventor
Hitoshi Igarashi
Mitsuhiro Kokubo
Kenichi Goto
Masatoshi Iio
Hiromasa Sakai
Original Assignee
Nissan Motor Co., Ltd.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Nissan Motor Co., Ltd. filed Critical Nissan Motor Co., Ltd.
Publication of WO2006120874A1 publication Critical patent/WO2006120874A1/en

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04082—Arrangements for control of reactant parameters, e.g. pressure or concentration
    • H01M8/04089—Arrangements for control of reactant parameters, e.g. pressure or concentration of gaseous reactants
    • H01M8/04097—Arrangements for control of reactant parameters, e.g. pressure or concentration of gaseous reactants with recycling of the reactants
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04223—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids during start-up or shut-down; Depolarisation or activation, e.g. purging; Means for short-circuiting defective fuel cells
    • H01M8/04228—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids during start-up or shut-down; Depolarisation or activation, e.g. purging; Means for short-circuiting defective fuel cells during shut-down
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04223—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids during start-up or shut-down; Depolarisation or activation, e.g. purging; Means for short-circuiting defective fuel cells
    • H01M8/04231—Purging of the reactants
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04298—Processes for controlling fuel cells or fuel cell systems
    • H01M8/04313—Processes for controlling fuel cells or fuel cell systems characterised by the detection or assessment of variables; characterised by the detection or assessment of failure or abnormal function
    • H01M8/0432—Temperature; Ambient temperature
    • H01M8/04343—Temperature; Ambient temperature of anode exhausts
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04298—Processes for controlling fuel cells or fuel cell systems
    • H01M8/04313—Processes for controlling fuel cells or fuel cell systems characterised by the detection or assessment of variables; characterised by the detection or assessment of failure or abnormal function
    • H01M8/0432—Temperature; Ambient temperature
    • H01M8/04365—Temperature; Ambient temperature of other components of a fuel cell or fuel cell stacks
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04298—Processes for controlling fuel cells or fuel cell systems
    • H01M8/04313—Processes for controlling fuel cells or fuel cell systems characterised by the detection or assessment of variables; characterised by the detection or assessment of failure or abnormal function
    • H01M8/0438—Pressure; Ambient pressure; Flow
    • H01M8/04395—Pressure; Ambient pressure; Flow of cathode reactants at the inlet or inside the fuel cell
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04298—Processes for controlling fuel cells or fuel cell systems
    • H01M8/04313—Processes for controlling fuel cells or fuel cell systems characterised by the detection or assessment of variables; characterised by the detection or assessment of failure or abnormal function
    • H01M8/0438—Pressure; Ambient pressure; Flow
    • H01M8/04425—Pressure; Ambient pressure; Flow at auxiliary devices, e.g. reformers, compressors, burners
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04298—Processes for controlling fuel cells or fuel cell systems
    • H01M8/04313—Processes for controlling fuel cells or fuel cell systems characterised by the detection or assessment of variables; characterised by the detection or assessment of failure or abnormal function
    • H01M8/0444—Concentration; Density
    • H01M8/04462—Concentration; Density of anode exhausts
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04298—Processes for controlling fuel cells or fuel cell systems
    • H01M8/04313—Processes for controlling fuel cells or fuel cell systems characterised by the detection or assessment of variables; characterised by the detection or assessment of failure or abnormal function
    • H01M8/04492—Humidity; Ambient humidity; Water content
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04298—Processes for controlling fuel cells or fuel cell systems
    • H01M8/04313—Processes for controlling fuel cells or fuel cell systems characterised by the detection or assessment of variables; characterised by the detection or assessment of failure or abnormal function
    • H01M8/04492—Humidity; Ambient humidity; Water content
    • H01M8/04514—Humidity; Ambient humidity; Water content of anode exhausts
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04298—Processes for controlling fuel cells or fuel cell systems
    • H01M8/04313—Processes for controlling fuel cells or fuel cell systems characterised by the detection or assessment of variables; characterised by the detection or assessment of failure or abnormal function
    • H01M8/04537—Electric variables
    • H01M8/04544—Voltage
    • H01M8/04552—Voltage of the individual fuel cell
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04298—Processes for controlling fuel cells or fuel cell systems
    • H01M8/04313—Processes for controlling fuel cells or fuel cell systems characterised by the detection or assessment of variables; characterised by the detection or assessment of failure or abnormal function
    • H01M8/04537—Electric variables
    • H01M8/04544—Voltage
    • H01M8/04559—Voltage of fuel cell stacks
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04298—Processes for controlling fuel cells or fuel cell systems
    • H01M8/04313—Processes for controlling fuel cells or fuel cell systems characterised by the detection or assessment of variables; characterised by the detection or assessment of failure or abnormal function
    • H01M8/04537—Electric variables
    • H01M8/04604—Power, energy, capacity or load
    • H01M8/04626—Power, energy, capacity or load of auxiliary devices, e.g. batteries, capacitors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04298—Processes for controlling fuel cells or fuel cell systems
    • H01M8/04694—Processes for controlling fuel cells or fuel cell systems characterised by variables to be controlled
    • H01M8/04746—Pressure; Flow
    • H01M8/04753—Pressure; Flow of fuel cell reactants
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04298—Processes for controlling fuel cells or fuel cell systems
    • H01M8/04694—Processes for controlling fuel cells or fuel cell systems characterised by variables to be controlled
    • H01M8/04746—Pressure; Flow
    • H01M8/04761—Pressure; Flow of fuel cell exhausts
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/50—Fuel cells

Definitions

  • the present invention relates to a fuel cell system which performs an idling-stop that is a temporary suspension of electric power generation under no-load condition or low-load condition.
  • a fuel cell is an electrochemical device to convert chemical energy of fuel gas such as hydrogen gas and oxidizing gas containing oxygen electrochemically into electric energy.
  • a typical fuel cell has an electrolyte membrane in contact with an anode and a cathode on either side. Fuel gas is continuously fed to the anode and the oxidizing gas is continuously fed to the cathode. The electrochemical reactions take place at the electrodes to produce an electric current through the electrolyte membrane, while supplying a complementally electric current to a load.
  • Polymer Electrolyte Fuel Cell using a solid polymer electrolyte has gained attention as a power source of an electrical vehicle due to low operating temperature and easy handling.
  • a fuel cell vehicle carries a fuel cell and a hydrogen storage device or a hydrogen gas generating device. Hydrogen gas is supplied from the hydrogen storage device or the hydrogen gas generating device to the fuel cell to react with air taken from outside. Electric energy produced by the reaction is taken out of the fuel cell to drive a motor connected to driving wheels . Because the emission substance from the fuel cell is only water, the fuel cell vehicle is an ultimately environmentally clean vehicle .
  • Japanese Patent Application Laid-open Publication No. 2001-307758 discloses a technology in which a fuel cell is controlled to temporarily suspend power generation thereof and a required power is supplied from a secondary battery under low-load or no-load condition where power generation efficiency of the fuel cell is low, while the fuel cell charges the secondary battery when the fuel cell generates excess power.
  • Japanese Patent Application Laid-open Publication No. 2004-173450 discloses a control of the idling-stop in which the idling-stop is permitted or prohibited depending on a pressure of hydrogen gas supplied to a fuel cell, a cell voltage, status of an exhaust gas diluter, and the like, even when a power requirement to the fuel cell meets a condition for the idling-stop, in order to obtain a favorable ability of restarting from the idling-stop.
  • An object of the present invention is to provide a fuel cell system in which responsiveness at the time of returning from an idling-stop to a normal power generation is maintained, while sufficiently supplying hydrogen gas to the fuel cell at the time of restarting the power generation and preventing deterioration of the fuel cell.
  • An aspect of the present invention is a fuel cell system comprising: a fuel cell which generates power by a reaction of a fuel gas, the fuel cell having a fuel electrode to which the fuel gas is supplied for the reaction, an inlet through which the fuel gas is supplied to the fuel electrode, and an outlet through which the fuel gas unused in the reaction is discharged from the fuel electrode; a fuel gas circulation system for re-circulating the unused fuel gas from the outlet to the inlet; an impurity concentration detecting device which detects or estimates a value related to an impurity concentration in the fuel electrode or the fuel gas circulation system; and an idling-stop controller which controls an idling-stop of the fuel cell, in which power generation of the fuel cell is temporarily suspended, based on a power requirement to the fuel cell, wherein the idling-stop controller permits or prohibits the idling-stop based on the value detected or estimated by the impurity concentration detecting device.
  • FIG. 1 is a system configuration diagram of a fuel cell system according to a first embodiment of the present invention
  • FIG. 2 is a block diagram showing an idling-stop control function of a controller
  • FIG. 3 is a flowchart of an idling-stop control in the first embodiment
  • FIG. 4A is a flowchart of determination of idling-stop condition other than impurity concentration
  • FIG. 4B is a flowchart of performing idling-stop
  • FIG. 5 is a time chart showing a change of anode nitrogen concentration before, through and after the idling-stop
  • FIG. 6 is a flowchart showing an idling-stop control according to a second embodiment.
  • a fuel cell system 1 includes, for example, a fuel cell stack 2, a hydrogen gas system Sh for supplying hydrogen gas as fuel gas to the fuel cell stack 2, an air system Sa for supplying air as oxidizing gas to the fuel cell stack 2, and an electrical equipment and control system Se.
  • the fuel cell stack 2 is constituted of a plurality of single cells stacked on one another.
  • Each of the cells is constituted of a membrane electrode assembly MEA which is formed of a solid polymer electrolyte membrane M, an anode (fuel electrode, negative electrode) 3 provided on one side thereof, and a cathode (oxidizer electrode, positive electrode) 4 provided on the other side thereof, and a pair of separators SP sandwiching the MEA therebetween.
  • MEA membrane electrode assembly MEA which is formed of a solid polymer electrolyte membrane M, an anode (fuel electrode, negative electrode) 3 provided on one side thereof, and a cathode (oxidizer electrode, positive electrode) 4 provided on the other side thereof, and a pair of separators SP sandwiching the MEA therebetween.
  • the hydrogen gas system Sh includes a hydrogen gas supply device 5 which is a fuel reforming device, a hydrogen storage device, or the like, to supply hydrogen gas to the anode 3, a hydrogen gas cutoff valve 6, a hydrogen gas pressure regulator 7, a hydrogen gas supply flow path 8, an anode pressure sensor 9, a hydrogen gas circulation flow path 10, a hydrogen gas circulation pump 11, a purge valve 12, and a hydrogen gas discharging flow path 13.
  • the hydrogen gas system Sh further includes a exhaust hydrogen treatment device 31, a temperature sensor 32 for detecting a temperature Th of the fuel gas flowing in the hydrogen gas circulation flow path 10, and an impurity concentration detecting device 33 for detecting or estimating impurity concentration Cn inside of the hydrogen gas circulation flow path 10.
  • the air system Sa includes a filter 14, an air flow meter 15, an air compressor 16 for compressing air taken from outside, a cooler 17, a humidifier 18 for humidifying air to be supplied to the cathode 4 by adding moisture contained in air discharged from the cathode 4 , an air supply flow path 19, a cathode pressure sensor 20, an air discharging flow path 21, and an air pressure regulator 22.
  • the electrical equipment and control system Se includes a DC/DC converter 23 for converting an output voltage of the fuel cell stack 2 to a voltage of a battery 24, the battery 24 to be charged with electric current from the DC/DC converter
  • a vehicle driving motor 27 operated by the alternate current from the inverter 26
  • a total voltage sensor 28 for detecting an output voltage of the fuel cell stack 2
  • a cell voltage sensor 29 for detecting a voltage of each cell of the fuel cell stack 2 or a voltage of a group of a predetermined number of serially connected cells (both are called a cell voltage Vc herein)
  • a controller (ECU) 30 for controlling the entire fuel cell system 1, as a controlling means for carrying out an operation of increasing a fuel cell voltage during idling-stop.
  • the hydrogen gas circulation flow path 10 and the hydrogen gas circulation pump 11 constitute a fuel gas circulation system which re-circulates or re-supply hydrogen gas discharged from an outlet of the anode 3, containing hydrogen unused in the reaction with oxygen, to an inlet of the anode 3.
  • the hydrogen gas supplied from the hydrogen gas supply device 5 is supplied to the anode 3 through, the hydrogen gas pressure regulator 7.
  • a pressure Ph of hydrogen gas at the anode outlet of the fuel cell stack 2 is measured by the anode pressure sensor 9.
  • the hydrogen gas pressure regulator 7 is controlled by the controller 30 so that the pressure Ph measured by the anode pressure sensor 9 becomes a target pressure TPh corresponding to a required power Prq from the fuel cell stack 2.
  • the purge valve 12 is closed, and the hydrogen gas discharged from the anode outlet of the fuel cell stack 2 is re-supplied to the inlet of the anode 3 by the hydrogen gas circulation flow path 10 and the hydrogen gas circulation pump 11.
  • the hydrogen gas circulation flow path 10 has a temperature sensor 32 for detecting a gas temperature Th inside thereof and an impurity concentration detecting device 33 for detecting or estimating impurity concentration Cn inside thereof.
  • the impurity concentration detecting device 33 is specifically constituted of a hydrogen sensor 33a for detecting hydrogen concentration Ch and a water vapor sensor 33b for detecting water vapor concentration Cw inside of the hydrogen gas circulation flow path 10.
  • a gas composition inside of the hydrogen gas circulation flow path 10 mainly hydrogen, nitrogen, and water vapor are possible.
  • nitrogen derives from nitrogen components in the air permeating the electrolyte membrane from the cathode 4 to the anode 3 and from nitrogen components contained in the hydrogen gas supplied from the hydrogen gas supply device 5, or the like.
  • the water vapor derives from water vapor used for humidifying the air of the cathode 4 and from moisture of water generated by the chemical reaction in cathode 4 permeating from the cathode to the anode.
  • the purge valve 12 When water leakage is caused in the fuel cell stack 2, when impurities are accumulated in the anode 3 or the hydrogen gas circulation flow path 10, or when an operating pressure in the fuel cell stack 2 is lowered, the purge valve 12 is opened to discharge hydrogen gas containing the impurities from the hydrogen gas discharging flow path 13 to the exhaust hydrogen treatment device 31 in which a hydrogen gas diluter, a hydrogen combustion catalytic device, or the like is used.
  • the purge valve 12 and the hydrogen gas discharging flow path 13 collectively constitute a discharging device for discharging the hydrogen gas containing the impurities from the fuel gas circulation system to the outside of the system.
  • Dust and harmful chemical compounds in the air are removed by the filter 14 when being introduced from outside to the air system Sa, and the air is compressed by the compressor 9.
  • the air compressed by the compressor 9 is cooled by the cooler 17 to be supplied to the humidifier 18.
  • the humidifier 18 is, for example, a humidity exchange device using a polymer hollow fiber membrane that gives water vapor contained in the discharged air from the cathode 4 to the air from the cooler 17 and humidifies the air.
  • the humidified air is supplied to the cathode 4 through the air supply flow path 19.
  • An air pressure Pa at the inlet of the cathode 4 is measured by the cathode pressure sensor 20.
  • the cathode pressure sensor 20, the total voltage sensor 28, the cell voltage sensor 29, the temperature sensor 32, ,and the impurity concentration detecting device 33 is connected to an input terminal of the controller 30, and respectively detection signals detected by each sensor, that is, a hydrogen gas pressure Ph, a flow rate Qa, an air pressure Pa, a total voltage Vt, a cell voltage Vc, a hydrogen gas temperature Th, and an impurity concentration Cn, are inputted to the controller 30.
  • each of the hydrogen gas cutoff valve 6, the hydrogen gas pressure regulator 7, the hydrogen gas circulation pump 11, the purge valve 12, the air compressor 16, and the air pressure regulator 22 is connected to an output terminal of the controller 30 so as to be controlled by control signals outputted by the controller 30.
  • the controller 30 determines an operating state of the fuel cell stack 2 from the inputted signals from the respective sensors and controls the entire fuel cell system 1. In addition, the controller 30 controls idling-stop of the fuel cell stack 2 based on a target power TPW from the fuel cell system 1 required from the vehicle control system VCS. In addition, the controller 30 is an idling-stop controller for permitting or prohibiting the idling-stop of the fuel cell stack 2 based on a detected result Cn of the impurity concentration detecting device 33.
  • the controller 30 in the present embodiment is, but not limited to, constituted by a CPU, a ROM in which control parameters such as control program and control map are stored, a R ⁇ M for operation, and a microprocessor including an input/output interface.
  • This DC/DC converter 23 is, for example, a buck-boost type DC/DC converter capable of increasing or decreasing output voltage, which charges the power generated by the fuel cell stack 2 to the battery 24 after its conversion, and/or supplies the power from the fuel cell stack 2 to the vehicle driving motor 27 through the inverter 26.
  • FIG. 2 is a block diagram for describing an idling-stop control function of the controller 30.
  • the controller 30 includes a required power calculating unit 101 for calculating a required power Prq from the fuel cell stack 2, a dischargeable battery power calculating unit 102 for calculating a battery power Pbt available to be discharged from the battery 24, an impurity concentration detection unit 103 for detecting an impurity concentration Cn based on values Ch and Cw detected by the hydrogen sensor 33a and the water vapor sensor 33b, an idling-stop condition I determining unit 104 for determining an idling-stop condition other than the impurity concentration Cn, an impurity concentration determining unit 105 for determining the impurity concentration Cn, an idling-stop condition II determining unit 106 for comprehensively determining an idling-stop condition other than the impurity concentration Cn and an idling-stop condition regarding the impurity concentration Cn, and an idling-stop performing unit 107.
  • the dischargeable battery power calculating unit 102 calculates a battery power Pbt available to be discharged from the battery 24 based on the SOC detected by the SOC sensor 25. This calculation method is programmed in advance according to the type and characteristic of the battery.
  • the impurity concentration detection unit 103 calculates an impurity concentration Cn based on detected values of the hydrogen concentration Ch and the water vapor concentration Cw obtained from the impurity concentration sensor 33.
  • the idling-stop condition I determining unit 104 determines whether or not the idling-stop condition other than the impurity concentration Cn, that is, for example, a required power Prq from the fuel cell stack 2 is at or below a predetermined value and at or below a dischargeable battery power Pbt, is met.
  • the impurity concentration determining unit 105 determines as an impurity concentration condition of idling-stop whether or not the impurity concentration Cn calculated by the impurity concentration detection unit 103 is at or below a first threshold.
  • the idling-stop condition II determining unit 106 comprehensively determines the idling-stop condition other than the impurity concentration Cn and the idling-stop condition regarding the impurity concentration Cn.
  • the idling-stop performing unit 107 carries out idling-stop by stopping the air compressor 16 when the idling-stop condition II determining unit 107 determines that all of the idling-stop conditions are established. In addition, the idling-stop performing unit 107 carries out purge for discharging impurities in the anode and the hydrogen gas circulation flow path by opening the purge valve when the impurity concentration Cn of the anode increases during the idling-stop.
  • FIG. 3 is a flowchart of an idling-stop control of the controller 30 according to the first embodiment, which is to be repeatedly carried out at regular time intervals.
  • S a routine is carried out for determining whether or not the idling-stop condition other than the impurity concentration is established. Detailed description of SlO will be given later by referring to FIG. 4A.
  • S20 from the determination result of SlO, it is determined whether or not the idling-stop condition other than the impurity concentration Cn is established, and when the condition is not established, the step proceeds to S21, and when established, the step proceeds to S23.
  • the step proceeds to S22 to reset the ISF flag, and further proceeds to S40 so that a normal power generation is resumed from the idling-stop.
  • the start-up operations same as that of the normal fuel cell start-up are carried out to return to the normal power generation. Specifically, the air compressor 16 is started to supply air to the fuel cell stack 2, and the hydrogen gas circulation pump 11 is started to supply hydrogen gas to the fuel cell stack 2 through the hydrogen gas pressure regulator 7.
  • the step proceeds to S50 to continue the normal power generation and returns to the first control processing.
  • a threshold A (a first threshold) of the impurity concentration Cn for permitting the idling-stop to start and a threshold B (a second threshold) of the impurity concentration Cn for canceling the idling-stop are calculated with reference to a control table stored in advance.
  • the threshold A is a value of nitrogen concentration, that the impurity concentration Cn of the anode is estimated to remain, for a certain length of time with the idling-stop operation being performed, below a maximum allowable nitrogen concentration which is determined from the characteristics of the hydrogen gas pump 11, as long as a nitrogen concentration is at or below the threshold A.
  • the threshold B is the maximum allowable nitrogen concentration of the anode to be determined by the characteristics of the hydrogen gas pump 11, and is a value that, if a nitrogen concentration of the gas to be pumped by the hydrogen gas pump 11 exceeds the threshold B, performance of the hydrogen gas circulation pump 11 becomes deteriorated and insufficient at the time of restarting the fuel cell stack 2 (see, FIG. 5) .
  • the threshold B is set to be higher than the threshold A (the threshold B > the threshold A) in the impurity concentration Cn in order to reduce the user's sense of discomfort caused by frequently repeated start and cancellation of the idling-stop, which is caused by increasing permeation of the impurities from the cathode to the anode.
  • the control table storing these thresholds A and B of the impurity concentration Cn is a control table based on the results of measuring anode nitrogen concentration during experimental idling-stop operations under various temperature and humidity conditions carried out on an experimental instrument having the same structure as that of the fuel cell stack 2, and the simulation results.
  • a permeating flux Q [kmol/ (s*m2) ] that is a volume of permeating gas per unit time and unit area is represented by the following equation (1) by using a permeation coefficient
  • the threshold A of the impurity concentration Cn for permitting the idling-stop to start is determined based on the temperature Tc and humidity Hc of the fuel cell stack 2 like the present embodiment, even though there is no change in the thickness t of the electrolyte membrane separating the anode and the cathode and a change of the partial pressure difference of nitrogen on the both sides of the electrolyte membrane before and after nitrogen permeation is negligible small, since the permeation coefficient C of nitrogen from the cathode to the anode depends on the temperature and humidity of the electrolyte membrane.
  • thresholds A and B respectively having a fixed value can be used depending on the typical conditions of temperature and humidity of a fuel cell stack 2 during idling-stop.
  • a nitrogen concentration that is the impurity concentration Cn is estimated based on the hydrogen concentration Ch and the water vapor concentration Cw detected by the impurity concentration detecting device 33.
  • S26 it is determined whether or not the ISF flag i.s 1. When the ISF flag is 1 in S26, it means that the idling-stop operation has been already started. Therefore the step proceeds to S 29 to determine accumulation of impurity.
  • the step proceeds to S27 to determine whether or not the impurity concentration Cn estimated in S25 is at or below the threshold A, since that is a case where the idling-stop condition other than the impurity- concentration Cn is established during no-idling-stop.
  • the step proceeds to S50 to continue the normal power generation since the idling condition regarding the impurity concentration Cn is not established.
  • the step proceeds to S28 to set the ISF flag to be 1, and further proceeds to S60.
  • idling-stop is carried out, and the detailed description thereof will be given later by referring to FIG. 4B. In this manner, in the present embodiment, in addition to the conventional idling-stop conditions, permitting or prohibiting idling-stop of a fuel cell is controlled based on the impurity concentration Cn inside of the anode or the fuel gas circulation system.
  • S29 it is determined whether or not the impurity concentration Cn during idling-stop estimated in S25 is at or below the threshold B (> the threshold A) .
  • the step proceeds to S30 to continue the idling-stop and returns to the first control processing.
  • the step proceeds to S31 to reset the ISF to be 0, and further proceeds to S70.
  • S70 the normal power generation is resumed from the idling-stop and the purge is performed to return to the first control processing.
  • the control processing in S70 specifically includes starting the air compressor 16, opening the air pressure regulator 22 to start air supply, opening the hydrogen gas pressure regulator 7 to start hydrogen gas supply, opening the purge valve 12, and driving the hydrogen gas circulation pump 11 so that the impurities in the anode 3 and the hydrogen gas circulation flow path 10 are discharged to the exhaust hydrogen treatment device 31 to be processed.
  • FIG. 4A is a flowchart for describing the determination of an idling-stop condition other than the impurity concentration Cn.
  • FIG. 4B is a flowchart for describing the details of performing the idling-stop.
  • a required power Prq [W] from the fuel cell system is detected or calculated.
  • the required power Prq is calculated from, for example, vehicle speed Vs and amount of operation Ao of accelerator pedal (required torque) .
  • the SOC of the battery 24 is detected by the SOC sensor 25 so that a battery power Pbt [W] available to be discharged from the battery 24 is calculated in S13 based on the detected SOC referring to the control table.
  • the SOC sensor 25 detects SOC
  • the battery power Pbt available to be discharged from the battery 24 varies depending on the characteristics of the battery to be used, it is preferable that, for example, the Pbt is set to be the maximum dischargeable power when the SOC exceeds 30 [%] , and to be reduced according to the decreased amount of the SOC when the SOC is 30 [%] or below.
  • the step proceeds to S17 to set the idling-stop condition flag to be 0 to return to the first control processing.
  • the idling-stop is started in FIG. 4B, first in S61, the hydrogen gas pressure regulator 7 is closed to stop the supply of new hydrogen gas to the anode 3, and the purge valve 12 is closed if it has been opened.
  • the air compressor 16 is . stopped to stop air supply to the cathode 4, and the air pressure regulator 22 is closed.
  • FIG. 5 is a time chart for showing a change of an anode nitrogen concentration before through and after the idling-stop.
  • the idling-stop condition other than the impurity concentration Cn and the idling-stop condition regarding the impurity concentration Cn nitrogen concentration ⁇ threshold A
  • the purge control is also stopped and the nitrogen concentration of the anode is increased with the elapse of time.
  • the nitrogen concentration exceeds the threshold B at time tl after the start of idling-stop, the normal power generation is resumed from the idling-stop.
  • the purge control is started and the nitrogen concentration of the anode is decreased.
  • the idling-stop condition regarding the nitrogen concentration is fulfilled.
  • a structure of the fuel cell system according to the second embodiment is the same as that of the fuel cell system according to the first embodiment shown in FIG. 1.
  • purge of an anode and hydrogen gas circulation system is performed before returning to normal power generation, and it is determined again whether or not the idling-stop condition is established.
  • FIG. 6 is a flowchart for describing an idling-stop control of a controller 30 in the second embodiment, which is set to be repeated at regular time intervals.
  • the flowchart of the first embodiment shown in FIG. 3 in that if the impurity concentration found to exceed the threshold A when the impurity concentration Cn and the threshold A are compared in S27, the step proceeds to S32 to perform purging before normal power generation is resumed. After that, when the flowchart of FIG.
  • the impurity concentration Cn is surely at or below the threshold A in the determination this time in S27, since the purge is carried out in S32 in the previous time to reduce the impurity concentration Cn when the idling-stop conditions other than the impurity concentration Cn are established. Therefore, the determination result in S27 becomes YES, and the idling-stop is carried out by the processing of S28 and S29.
  • Other steps are the same as that of FIG. 3. Therefore, the same step numbers are given to denote the same steps, and the description thereof is omitted.
  • the impurities are discharged from the fuel circulation system to the outside of the system so that a chance to be able to performing idling-stop is increased. Therefore, a fuel consumption performance and an acoustic vibration reduction can be further improved.
  • an impurity concentration Cn inside of the anode and the hydrogen gas circulation system is set to be a nitrogen concentration.
  • the impurity concentration Cn is not limited to this. It can be a sum of a nitrogen concentration and a water vapor concentration, or a concentration of impurities contained in the hydrogen gas supplied from the hydrogen gas supply device.
  • the present disclosure relates to subject matters contained in Japanese Patent Application No.2005-140185, filed on May 12, 2005, the disclosure of which is expressly incorporated herein by reference in its entirety.
  • an impurity concentration detecting device 33 detects an impurity concentration inside of a fuel gas circulation system having a hydrogen gas circulation flow path 10 and a hydrogen gas circulation pump 11, or an impurity concentration in fuel gas inside of an anode 3. Then, a controller 30 permits idling-stop when this impurity concentration is at or below a first threshold, and prohibits it when the impurity concentration exceeds the first threshold. Therefore, it is prevented that the deterioration of catalyst in a fuel electrode due to the generation of local hydrogen shortage in the fuel cell at the time of restarting normal power generation after the idling-stop. Accordingly, the fuel cell system according to the present invention is industrially applicable.

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Abstract

A fuel cell system including: a fuel cell having an anode to which a fuel gas is supplied for power generating reaction, an inlet through which the fuel gas is supplied to the anode, and an outlet through which the fuel gas unused in the reaction is discharged from the anode; a fuel gas circulation system for re-circulating the unused fuel gas from the outlet to the inlet; an impurity concentration detecting device which detects or estimates a value related to an impurity concentration in the anode or the fuel gas circulation system; and a controller controlling an idling-stop of the fuel cell based on a power requirement to the fuel cell, wherein the idling-stop controller permits or prohibits the idling-stop based on the value detected or estimated by the impurity concentration detecting device.

Description

DESCRIPTION FUEL CELL SYSTEM
TECHNICAL FIELD The present invention relates to a fuel cell system which performs an idling-stop that is a temporary suspension of electric power generation under no-load condition or low-load condition.
BACKGROUND ART A fuel cell is an electrochemical device to convert chemical energy of fuel gas such as hydrogen gas and oxidizing gas containing oxygen electrochemically into electric energy. A typical fuel cell has an electrolyte membrane in contact with an anode and a cathode on either side. Fuel gas is continuously fed to the anode and the oxidizing gas is continuously fed to the cathode. The electrochemical reactions take place at the electrodes to produce an electric current through the electrolyte membrane, while supplying a complementally electric current to a load. In particular, Polymer Electrolyte Fuel Cell using a solid polymer electrolyte has gained attention as a power source of an electrical vehicle due to low operating temperature and easy handling.
A fuel cell vehicle carries a fuel cell and a hydrogen storage device or a hydrogen gas generating device. Hydrogen gas is supplied from the hydrogen storage device or the hydrogen gas generating device to the fuel cell to react with air taken from outside. Electric energy produced by the reaction is taken out of the fuel cell to drive a motor connected to driving wheels . Because the emission substance from the fuel cell is only water, the fuel cell vehicle is an ultimately environmentally clean vehicle .
Even in such a fuel cell vehicle, an idling-stop operation is performed in order to improve energy efficiency, as in the case of an internal combustion engine vehicle. Japanese Patent Application Laid-open Publication No. 2001-307758 discloses a technology in which a fuel cell is controlled to temporarily suspend power generation thereof and a required power is supplied from a secondary battery under low-load or no-load condition where power generation efficiency of the fuel cell is low, while the fuel cell charges the secondary battery when the fuel cell generates excess power.
Japanese Patent Application Laid-open Publication No. 2004-173450 discloses a control of the idling-stop in which the idling-stop is permitted or prohibited depending on a pressure of hydrogen gas supplied to a fuel cell, a cell voltage, status of an exhaust gas diluter, and the like, even when a power requirement to the fuel cell meets a condition for the idling-stop, in order to obtain a favorable ability of restarting from the idling-stop.
DISCLOSURE OF INVENTION
However, in the above technologies, nitrogen in the air moves from an oxidizer electrode (cathode) to a fuel electrode
(anode) , permeating through an electrolyte membrane during the idling-stop. Therefore partial pressure of nitrogen at the fuel electrode increases. In addition, weight per unit volume of hydrogen gas in a hydrogen gas circulation system increases, which results in a decrease of circulating ability of a hydrogen gas circulation pump. As a result, there is a problem that an excess supply ratio of hydrogen gas in a fuel cell (that is, the ratio of a mass flow rate of excessively supplied hydrogen gas to a mass flow rate of hydrogen gas theoretically required to obtain an output current from the fuel cell) decreases at the time of restarting after the idling-stop which causes a local hydrogen shortage in the fuel cell and a deterioration of catalyst in the fuel electrode.
The present invention was made in the light of the problem. An object of the present invention is to provide a fuel cell system in which responsiveness at the time of returning from an idling-stop to a normal power generation is maintained, while sufficiently supplying hydrogen gas to the fuel cell at the time of restarting the power generation and preventing deterioration of the fuel cell.
An aspect of the present invention is a fuel cell system comprising: a fuel cell which generates power by a reaction of a fuel gas, the fuel cell having a fuel electrode to which the fuel gas is supplied for the reaction, an inlet through which the fuel gas is supplied to the fuel electrode, and an outlet through which the fuel gas unused in the reaction is discharged from the fuel electrode; a fuel gas circulation system for re-circulating the unused fuel gas from the outlet to the inlet; an impurity concentration detecting device which detects or estimates a value related to an impurity concentration in the fuel electrode or the fuel gas circulation system; and an idling-stop controller which controls an idling-stop of the fuel cell, in which power generation of the fuel cell is temporarily suspended, based on a power requirement to the fuel cell, wherein the idling-stop controller permits or prohibits the idling-stop based on the value detected or estimated by the impurity concentration detecting device. BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described with reference to the accompanying drawings wherein:
FIG. 1 is a system configuration diagram of a fuel cell system according to a first embodiment of the present invention;
FIG. 2 is a block diagram showing an idling-stop control function of a controller; FIG. 3 is a flowchart of an idling-stop control in the first embodiment;
FIG. 4A is a flowchart of determination of idling-stop condition other than impurity concentration;
FIG. 4B is a flowchart of performing idling-stop; FIG. 5 is a time chart showing a change of anode nitrogen concentration before, through and after the idling-stop;
FIG. 6 is a flowchart showing an idling-stop control according to a second embodiment.
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiments of the present invention will be explained below with reference to the drawings, wherein like members are designated by like reference characters. It should be noted that the embodiments are, but are not limited to, the cases where the present invention is applied to a fuel cell vehicle. In these embodiments, impurity concentration in an anode of a fuel cell and a hydrogen gas circulation system is set to be nitrogen concentration . [First Embodiment] A fuel cell system 1 includes, for example, a fuel cell stack 2, a hydrogen gas system Sh for supplying hydrogen gas as fuel gas to the fuel cell stack 2, an air system Sa for supplying air as oxidizing gas to the fuel cell stack 2, and an electrical equipment and control system Se. The fuel cell stack 2 is constituted of a plurality of single cells stacked on one another. Each of the cells is constituted of a membrane electrode assembly MEA which is formed of a solid polymer electrolyte membrane M, an anode (fuel electrode, negative electrode) 3 provided on one side thereof, and a cathode (oxidizer electrode, positive electrode) 4 provided on the other side thereof, and a pair of separators SP sandwiching the MEA therebetween.
The hydrogen gas system Sh includes a hydrogen gas supply device 5 which is a fuel reforming device, a hydrogen storage device, or the like, to supply hydrogen gas to the anode 3, a hydrogen gas cutoff valve 6, a hydrogen gas pressure regulator 7, a hydrogen gas supply flow path 8, an anode pressure sensor 9, a hydrogen gas circulation flow path 10, a hydrogen gas circulation pump 11, a purge valve 12, and a hydrogen gas discharging flow path 13. The hydrogen gas system Sh further includes a exhaust hydrogen treatment device 31, a temperature sensor 32 for detecting a temperature Th of the fuel gas flowing in the hydrogen gas circulation flow path 10, and an impurity concentration detecting device 33 for detecting or estimating impurity concentration Cn inside of the hydrogen gas circulation flow path 10.
The air system Sa includes a filter 14, an air flow meter 15, an air compressor 16 for compressing air taken from outside, a cooler 17, a humidifier 18 for humidifying air to be supplied to the cathode 4 by adding moisture contained in air discharged from the cathode 4 , an air supply flow path 19, a cathode pressure sensor 20, an air discharging flow path 21, and an air pressure regulator 22.
The electrical equipment and control system Se includes a DC/DC converter 23 for converting an output voltage of the fuel cell stack 2 to a voltage of a battery 24, the battery 24 to be charged with electric current from the DC/DC converter
23 and discharging to compensate the shortage in the output power from the fuel cell stack 2 when the output power thereof is less than a required power, a state-of-charge (SOC) detector
25 for detecting a state of charge of the battery 24, an inverter
26 for converting the direct current from the DC/DC converter 23 and/or the battery 24 into an alternate current, a vehicle driving motor 27 operated by the alternate current from the inverter 26, a total voltage sensor 28 for detecting an output voltage of the fuel cell stack 2, a cell voltage sensor 29 for detecting a voltage of each cell of the fuel cell stack 2 or a voltage of a group of a predetermined number of serially connected cells (both are called a cell voltage Vc herein) , and a controller (ECU) 30 for controlling the entire fuel cell system 1, as a controlling means for carrying out an operation of increasing a fuel cell voltage during idling-stop.
The hydrogen gas circulation flow path 10 and the hydrogen gas circulation pump 11 constitute a fuel gas circulation system which re-circulates or re-supply hydrogen gas discharged from an outlet of the anode 3, containing hydrogen unused in the reaction with oxygen, to an inlet of the anode 3.
The hydrogen gas supplied from the hydrogen gas supply device 5 is supplied to the anode 3 through, the hydrogen gas pressure regulator 7. A pressure Ph of hydrogen gas at the anode outlet of the fuel cell stack 2 is measured by the anode pressure sensor 9. The hydrogen gas pressure regulator 7 is controlled by the controller 30 so that the pressure Ph measured by the anode pressure sensor 9 becomes a target pressure TPh corresponding to a required power Prq from the fuel cell stack 2. Generally, the purge valve 12 is closed, and the hydrogen gas discharged from the anode outlet of the fuel cell stack 2 is re-supplied to the inlet of the anode 3 by the hydrogen gas circulation flow path 10 and the hydrogen gas circulation pump 11.
In addition, the hydrogen gas circulation flow path 10 has a temperature sensor 32 for detecting a gas temperature Th inside thereof and an impurity concentration detecting device 33 for detecting or estimating impurity concentration Cn inside thereof.
The impurity concentration detecting device 33 is specifically constituted of a hydrogen sensor 33a for detecting hydrogen concentration Ch and a water vapor sensor 33b for detecting water vapor concentration Cw inside of the hydrogen gas circulation flow path 10. As a gas composition inside of the hydrogen gas circulation flow path 10, mainly hydrogen, nitrogen, and water vapor are possible. Here, nitrogen derives from nitrogen components in the air permeating the electrolyte membrane from the cathode 4 to the anode 3 and from nitrogen components contained in the hydrogen gas supplied from the hydrogen gas supply device 5, or the like. The water vapor derives from water vapor used for humidifying the air of the cathode 4 and from moisture of water generated by the chemical reaction in cathode 4 permeating from the cathode to the anode. When water leakage is caused in the fuel cell stack 2, when impurities are accumulated in the anode 3 or the hydrogen gas circulation flow path 10, or when an operating pressure in the fuel cell stack 2 is lowered, the purge valve 12 is opened to discharge hydrogen gas containing the impurities from the hydrogen gas discharging flow path 13 to the exhaust hydrogen treatment device 31 in which a hydrogen gas diluter, a hydrogen combustion catalytic device, or the like is used. Here, the purge valve 12 and the hydrogen gas discharging flow path 13 collectively constitute a discharging device for discharging the hydrogen gas containing the impurities from the fuel gas circulation system to the outside of the system.
Dust and harmful chemical compounds in the air are removed by the filter 14 when being introduced from outside to the air system Sa, and the air is compressed by the compressor 9. The air compressed by the compressor 9 is cooled by the cooler 17 to be supplied to the humidifier 18. The humidifier 18 is, for example, a humidity exchange device using a polymer hollow fiber membrane that gives water vapor contained in the discharged air from the cathode 4 to the air from the cooler 17 and humidifies the air. The humidified air is supplied to the cathode 4 through the air supply flow path 19. An air pressure Pa at the inlet of the cathode 4 is measured by the cathode pressure sensor 20.
Each of the anode pressure sensor 9, the air flow meter
15, the cathode pressure sensor 20, the total voltage sensor 28, the cell voltage sensor 29, the temperature sensor 32, ,and the impurity concentration detecting device 33 is connected to an input terminal of the controller 30, and respectively detection signals detected by each sensor, that is, a hydrogen gas pressure Ph, a flow rate Qa, an air pressure Pa, a total voltage Vt, a cell voltage Vc, a hydrogen gas temperature Th, and an impurity concentration Cn, are inputted to the controller 30.
In addition, each of the hydrogen gas cutoff valve 6, the hydrogen gas pressure regulator 7, the hydrogen gas circulation pump 11, the purge valve 12, the air compressor 16, and the air pressure regulator 22 is connected to an output terminal of the controller 30 so as to be controlled by control signals outputted by the controller 30.
The controller 30 determines an operating state of the fuel cell stack 2 from the inputted signals from the respective sensors and controls the entire fuel cell system 1. In addition, the controller 30 controls idling-stop of the fuel cell stack 2 based on a target power TPW from the fuel cell system 1 required from the vehicle control system VCS. In addition, the controller 30 is an idling-stop controller for permitting or prohibiting the idling-stop of the fuel cell stack 2 based on a detected result Cn of the impurity concentration detecting device 33.
The controller 30 in the present embodiment is, but not limited to, constituted by a CPU, a ROM in which control parameters such as control program and control map are stored, a RΔM for operation, and a microprocessor including an input/output interface.
In addition, power to be taken from the fuel cell stack 2 is controlled by the DC/DC converter 23. This DC/DC converter 23 is, for example, a buck-boost type DC/DC converter capable of increasing or decreasing output voltage, which charges the power generated by the fuel cell stack 2 to the battery 24 after its conversion, and/or supplies the power from the fuel cell stack 2 to the vehicle driving motor 27 through the inverter 26.
FIG. 2 is a block diagram for describing an idling-stop control function of the controller 30. The controller 30 includes a required power calculating unit 101 for calculating a required power Prq from the fuel cell stack 2, a dischargeable battery power calculating unit 102 for calculating a battery power Pbt available to be discharged from the battery 24, an impurity concentration detection unit 103 for detecting an impurity concentration Cn based on values Ch and Cw detected by the hydrogen sensor 33a and the water vapor sensor 33b, an idling-stop condition I determining unit 104 for determining an idling-stop condition other than the impurity concentration Cn, an impurity concentration determining unit 105 for determining the impurity concentration Cn, an idling-stop condition II determining unit 106 for comprehensively determining an idling-stop condition other than the impurity concentration Cn and an idling-stop condition regarding the impurity concentration Cn, and an idling-stop performing unit 107. The required power calculating unit 101 calculates a required power Prq from the fuel cell stack 2 based on, for example, an accelerator operating amount Ao and a vehicle speed Vs.
The dischargeable battery power calculating unit 102 calculates a battery power Pbt available to be discharged from the battery 24 based on the SOC detected by the SOC sensor 25. This calculation method is programmed in advance according to the type and characteristic of the battery.
. The impurity concentration detection unit 103 calculates an impurity concentration Cn based on detected values of the hydrogen concentration Ch and the water vapor concentration Cw obtained from the impurity concentration sensor 33.
The idling-stop condition I determining unit 104 determines whether or not the idling-stop condition other than the impurity concentration Cn, that is, for example, a required power Prq from the fuel cell stack 2 is at or below a predetermined value and at or below a dischargeable battery power Pbt, is met.
The impurity concentration determining unit 105 determines as an impurity concentration condition of idling-stop whether or not the impurity concentration Cn calculated by the impurity concentration detection unit 103 is at or below a first threshold.
The idling-stop condition II determining unit 106 comprehensively determines the idling-stop condition other than the impurity concentration Cn and the idling-stop condition regarding the impurity concentration Cn.
The idling-stop performing unit 107 carries out idling-stop by stopping the air compressor 16 when the idling-stop condition II determining unit 107 determines that all of the idling-stop conditions are established. In addition, the idling-stop performing unit 107 carries out purge for discharging impurities in the anode and the hydrogen gas circulation flow path by opening the purge valve when the impurity concentration Cn of the anode increases during the idling-stop.
FIG. 3 is a flowchart of an idling-stop control of the controller 30 according to the first embodiment, which is to be repeatedly carried out at regular time intervals. First, in step (hereinafter abbreviated as S) 10, a routine is carried out for determining whether or not the idling-stop condition other than the impurity concentration is established. Detailed description of SlO will be given later by referring to FIG. 4A. Next in S20, from the determination result of SlO, it is determined whether or not the idling-stop condition other than the impurity concentration Cn is established, and when the condition is not established, the step proceeds to S21, and when established, the step proceeds to S23.
At S21, it is determined whether or not a value of ISF flag (it takes 1 while idling-stop operation is performed, and 0 while idling-stop operation is not performed) is 1. Here, the idling-stop condition is not established. Therefore, in the case of ISF=I, the idling-stop cannot be continued any longer. In this case, the step proceeds to S22 to reset the ISF flag, and further proceeds to S40 so that a normal power generation is resumed from the idling-stop. At S40, the start-up operations same as that of the normal fuel cell start-up are carried out to return to the normal power generation. Specifically, the air compressor 16 is started to supply air to the fuel cell stack 2, and the hydrogen gas circulation pump 11 is started to supply hydrogen gas to the fuel cell stack 2 through the hydrogen gas pressure regulator 7.
When the determination result of S21 is ISF≠l (= 0) , the idling-stop condition is not established, that is, the idling-stop operation is not being performed. Therefore, the step proceeds to S50 to continue the normal power generation and returns to the first control processing.
At S23, temperature Tc and humidity Hc.inside of the fuel cell stack 2 are detected by the temperature sensor 34 and the humidity sensor 35, respectively. Next, in S24, based on the detected temperature Tc and humidity Hc, a threshold A (a first threshold) of the impurity concentration Cn for permitting the idling-stop to start and a threshold B (a second threshold) of the impurity concentration Cn for canceling the idling-stop are calculated with reference to a control table stored in advance.
Here, the threshold A is a value of nitrogen concentration, that the impurity concentration Cn of the anode is estimated to remain, for a certain length of time with the idling-stop operation being performed, below a maximum allowable nitrogen concentration which is determined from the characteristics of the hydrogen gas pump 11, as long as a nitrogen concentration is at or below the threshold A. The threshold B is the maximum allowable nitrogen concentration of the anode to be determined by the characteristics of the hydrogen gas pump 11, and is a value that, if a nitrogen concentration of the gas to be pumped by the hydrogen gas pump 11 exceeds the threshold B, performance of the hydrogen gas circulation pump 11 becomes deteriorated and insufficient at the time of restarting the fuel cell stack 2 (see, FIG. 5) . The threshold B is set to be higher than the threshold A (the threshold B > the threshold A) in the impurity concentration Cn in order to reduce the user's sense of discomfort caused by frequently repeated start and cancellation of the idling-stop, which is caused by increasing permeation of the impurities from the cathode to the anode.
The control table storing these thresholds A and B of the impurity concentration Cn is a control table based on the results of measuring anode nitrogen concentration during experimental idling-stop operations under various temperature and humidity conditions carried out on an experimental instrument having the same structure as that of the fuel cell stack 2, and the simulation results.
A permeating flux Q [kmol/ (s*m2) ] that is a volume of permeating gas per unit time and unit area is represented by the following equation (1) by using a permeation coefficient
C [kmol#m/ (s*m2'kPa) ] , a partial pressure difference of gas ΔP[kPa] on the both sides of the electrolyte membrane, and a thickness of the membrane t [m] . Q = C x ΔP/t ••• (1) Here, it is desirable that the threshold A of the impurity concentration Cn for permitting the idling-stop to start is determined based on the temperature Tc and humidity Hc of the fuel cell stack 2 like the present embodiment, even though there is no change in the thickness t of the electrolyte membrane separating the anode and the cathode and a change of the partial pressure difference of nitrogen on the both sides of the electrolyte membrane before and after nitrogen permeation is negligible small, since the permeation coefficient C of nitrogen from the cathode to the anode depends on the temperature and humidity of the electrolyte membrane. However, by simplifying the controlling steps, thresholds A and B respectively having a fixed value can be used depending on the typical conditions of temperature and humidity of a fuel cell stack 2 during idling-stop. Next in S25, a nitrogen concentration that is the impurity concentration Cn is estimated based on the hydrogen concentration Ch and the water vapor concentration Cw detected by the impurity concentration detecting device 33. In S26, it is determined whether or not the ISF flag i.s 1. When the ISF flag is 1 in S26, it means that the idling-stop operation has been already started. Therefore the step proceeds to S 29 to determine accumulation of impurity.
When the ISF is not 1 in S26, the step proceeds to S27 to determine whether or not the impurity concentration Cn estimated in S25 is at or below the threshold A, since that is a case where the idling-stop condition other than the impurity- concentration Cn is established during no-idling-stop.
When the impurity concentration Cn is not at or below the threshold A in the determination in S27, the step proceeds to S50 to continue the normal power generation since the idling condition regarding the impurity concentration Cn is not established.
When the impurity concentration Cn is at or below the threshold A in the determination in S27, the idling-stop condition regarding the impurity concentration Cn is established. Therefore, the step proceeds to S28 to set the ISF flag to be 1, and further proceeds to S60. In S60, idling-stop is carried out, and the detailed description thereof will be given later by referring to FIG. 4B. In this manner, in the present embodiment, in addition to the conventional idling-stop conditions, permitting or prohibiting idling-stop of a fuel cell is controlled based on the impurity concentration Cn inside of the anode or the fuel gas circulation system. Therefore, there is an effect that a time required for the system to be ready to restart power generation can be reduced when returning from the idling-stop to the normal power generation, securing responsiveness thereof, and the shortage of circulating hydrogen gas volume at the time of restarting power generation is avoided whereby the deterioration of fuel cell due to the shortage of the hydrogen gas can be prevented.
In S29, it is determined whether or not the impurity concentration Cn during idling-stop estimated in S25 is at or below the threshold B (> the threshold A) . When the impurity concentration Cn is at or below the threshold B, the step proceeds to S30 to continue the idling-stop and returns to the first control processing. When the impurity concentration Cn exceeds the threshold B in the determination in S29, the step proceeds to S31 to reset the ISF to be 0, and further proceeds to S70. In S70, the normal power generation is resumed from the idling-stop and the purge is performed to return to the first control processing. The control processing in S70 specifically includes starting the air compressor 16, opening the air pressure regulator 22 to start air supply, opening the hydrogen gas pressure regulator 7 to start hydrogen gas supply, opening the purge valve 12, and driving the hydrogen gas circulation pump 11 so that the impurities in the anode 3 and the hydrogen gas circulation flow path 10 are discharged to the exhaust hydrogen treatment device 31 to be processed. FIG. 4A is a flowchart for describing the determination of an idling-stop condition other than the impurity concentration Cn. FIG. 4B is a flowchart for describing the details of performing the idling-stop.
In FIG. 4A, when the determination of an idling-stop condition is started, first in SIl, a required power Prq [W] from the fuel cell system is detected or calculated. In the case of fuel cell vehicles, the required power Prq is calculated from, for example, vehicle speed Vs and amount of operation Ao of accelerator pedal (required torque) . Next in S12, the SOC of the battery 24 is detected by the SOC sensor 25 so that a battery power Pbt [W] available to be discharged from the battery 24 is calculated in S13 based on the detected SOC referring to the control table. The SOC sensor 25 detects SOC
[%] as a ratio of, for example, the amount of charge of the battery 24 to the maximum capacity of the battery 24. Though the battery power Pbt available to be discharged from the battery 24 varies depending on the characteristics of the battery to be used, it is preferable that, for example, the Pbt is set to be the maximum dischargeable power when the SOC exceeds 30 [%] , and to be reduced according to the decreased amount of the SOC when the SOC is 30 [%] or below.
Next in S14, it is determined whether or not the required power Prq is less than a predetermined value Pl. When the required power Prq is less than Pl, it is determined in S15 whether or not the required power Prq is smaller than the dischargeable battery power Pbt. When Prq is smaller than Pbt, the step proceeds to S16 so as to set an idling-stop condition flag to be 1 to return to the first control processing since the required power can be taken from the battery 24 even when the idling-stop operation is performed on the fuel cell system 1.
When it is determined No in S 14 or S15, the step proceeds to S17 to set the idling-stop condition flag to be 0 to return to the first control processing. When the idling-stop is started in FIG. 4B, first in S61, the hydrogen gas pressure regulator 7 is closed to stop the supply of new hydrogen gas to the anode 3, and the purge valve 12 is closed if it has been opened. In S62, the air compressor 16 is. stopped to stop air supply to the cathode 4, and the air pressure regulator 22 is closed. This saving of the power of driving the compressor during the idling-stop greatly contributes to comprehensive improvement of the efficiency of the fuel cell system by idling-stop.
Next in S63, power extraction by the DC/DC converter 23 is stopped, and in S64, the hydrogen gas circulation pump 11 is stopped. Next in S65, a coolant pump and a radiator fan, which are not shown in FIG. 1, are stopped.
FIG. 5 is a time chart for showing a change of an anode nitrogen concentration before through and after the idling-stop.
For example, at time t0 in FIG. 5, it is assumed that the idling-stop condition other than the impurity concentration Cn and the idling-stop condition regarding the impurity concentration Cn (nitrogen concentration ≤ threshold A) are established and the idling-stop is started. After that, the purge control is also stopped and the nitrogen concentration of the anode is increased with the elapse of time. When the nitrogen concentration exceeds the threshold B at time tl after the start of idling-stop, the normal power generation is resumed from the idling-stop. At the same time, the purge control is started and the nitrogen concentration of the anode is decreased. After that, at time t2, the idling-stop condition regarding the nitrogen concentration is fulfilled. [Second Embodiment] Next, a second embodiment of a fuel cell system according to the present invention will be described below. A structure of the fuel cell system according to the second embodiment is the same as that of the fuel cell system according to the first embodiment shown in FIG. 1. In the second embodiment when idling stop conditions other than an impurity concentration are established and idling-stop condition regarding the impurity- concentration is not established, purge of an anode and hydrogen gas circulation system is performed before returning to normal power generation, and it is determined again whether or not the idling-stop condition is established.
FIG. 6 is a flowchart for describing an idling-stop control of a controller 30 in the second embodiment, which is set to be repeated at regular time intervals. There is a difference from the flowchart of the first embodiment shown in FIG. 3, in that if the impurity concentration found to exceed the threshold A when the impurity concentration Cn and the threshold A are compared in S27, the step proceeds to S32 to perform purging before normal power generation is resumed. After that, when the flowchart of FIG. 6 is invoked, the impurity concentration Cn is surely at or below the threshold A in the determination this time in S27, since the purge is carried out in S32 in the previous time to reduce the impurity concentration Cn when the idling-stop conditions other than the impurity concentration Cn are established. Therefore, the determination result in S27 becomes YES, and the idling-stop is carried out by the processing of S28 and S29. Other steps are the same as that of FIG. 3. Therefore, the same step numbers are given to denote the same steps, and the description thereof is omitted.
As described above, in the present embodiment, it is possible that when idling-stop cannot be carried out since the idling-stop conditions other than the impurity concentration Cn are established and the impurity concentration Cn exceeds the threshold A, the impurities are discharged from the fuel circulation system to the outside of the system so that a chance to be able to performing idling-stop is increased. Therefore, a fuel consumption performance and an acoustic vibration reduction can be further improved.
While the present invention has been described in terms of the preferred embodiments described above, it is not limited to these and those skilled in the art will recognize that other embodiments or modifications in accordance with the technical scope of the present invention can be variously practiced. For example, in the first and second embodiments, an impurity concentration Cn inside of the anode and the hydrogen gas circulation system is set to be a nitrogen concentration. However, the impurity concentration Cn is not limited to this. It can be a sum of a nitrogen concentration and a water vapor concentration, or a concentration of impurities contained in the hydrogen gas supplied from the hydrogen gas supply device. The present disclosure relates to subject matters contained in Japanese Patent Application No.2005-140185, filed on May 12, 2005, the disclosure of which is expressly incorporated herein by reference in its entirety.
INDUSTRIAL APPLICABILITY
In a fuel cell system according to the present invention, an impurity concentration detecting device 33 detects an impurity concentration inside of a fuel gas circulation system having a hydrogen gas circulation flow path 10 and a hydrogen gas circulation pump 11, or an impurity concentration in fuel gas inside of an anode 3. Then, a controller 30 permits idling-stop when this impurity concentration is at or below a first threshold, and prohibits it when the impurity concentration exceeds the first threshold. Therefore, it is prevented that the deterioration of catalyst in a fuel electrode due to the generation of local hydrogen shortage in the fuel cell at the time of restarting normal power generation after the idling-stop. Accordingly, the fuel cell system according to the present invention is industrially applicable.

Claims

1. A fuel cell system comprising: a fuel cell which generates power by a reaction of a fuel gas, the fuel cell having a fuel electrode to which the fuel gas is supplied for the reaction, an inlet through which the fuel gas is supplied to the fuel electrode, and an outlet through which the fuel gas unused in the reaction is discharged from the fuel electrode; a fuel gas circulation system for re-circulating the unused fuel gas from the outlet to the inlet; an impurity concentration detecting device which detects or estimates a value related to an impurity concentration in the fuel electrode or the fuel gas circulation system; and an idling-stop controller which controls an idling-stop of the fuel cell, in which power generation of the fuel cell is temporarily suspended, based on a power requirement to the fuel cell, wherein the idling-stop controller permits or prohibits the idling-stop based on the value detected or estimated by the impurity concentration detecting device.
2. The fuel cell system according to claim 1, wherein the idling-stop controller uses in permitting the idling-stop an idling-stop condition that the value detected or estimated by the impurity concentration detecting device is at or below a first threshold.
3. The fuel cell system according to claim 2, further comprising: a discharging device which discharges the fuel gas containing impurities in the fuel electrode or the fuel gas circulation system to the outside, wherein the discharging device is controlled to start discharging the fuel gas containing impurities, or increase a flow rate of discharging the fuel gas containing impurities, when the idling-stop condition is not met.
4. The fuel cell system according to claim 3, further comprising: at least one of a temperature sensor for detecting a temperature of the fuel cell and a humidity sensor for detecting a humidity of the fuel cell, wherein the first threshold is calculated based on at least one of the temperature and humidity detected.
5. The fuel cell system according to claim 3, wherein the power generation of the fuel cell is controlled to resume from the idling-stop, and the discharging device is controlled to discharge the fuel gas containing impurities to the outside, when the value detected or estimated by the impurity concentration detecting device exceeds a second threshold which is larger than the first threshold.
6. The fuel cell system according to claim 5, further comprising: a temperature sensor for detecting a temperature of the fuel cell; a humidity sensor for detecting a humidity of the fuel cell; and a pressure sensor for detecting a pressure of the fuel gas in the fuel electrode, wherein the second threshold is calculated based on at least one of the temperature, humidity, and pressure detected.
7. The fuel cell system according to claim 3, further comprising: a exhaust hydrogen treatment device which combusts or dilutes the fuel gas containing impurities to be discharged to the outside; and a compressor which supplies air to an oxidizer electrode of the fuel cell and the exhaust hydrogen treatment device, wherein the compressor is controlled to supply air at least to the exhaust hydrogen treatment device at the time of discharging the fuel gas containing impurities from the discharging device.
8. A method of controlling an idling-stop of a fuel cell system which includes: a fuel cell for generating power by a reaction of a fuel gas, the fuel cell having a fuel electrode to which the fuel gas is supplied for the reaction, an inlet through which the fuel gas is supplied to the fuel electrode, and an outlet through which the fuel gas unused in the reaction is discharged from the fuel electrode; and a fuel gas circulation system for re-circulating the unused fuel gas from the outlet to the inlet; the method comprising: detecting or estimating a value related to an impurity concentration in the fuel electrode or the fuel gas circulation system; and permitting or prohibiting the idling-stop of the fuel cell based on the detected or estimated value related to the impurity concentration.
PCT/JP2006/308497 2005-05-12 2006-04-18 Fuel cell system WO2006120874A1 (en)

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