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WO2006059776A2 - Fuel cell system - Google Patents

Fuel cell system Download PDF

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Publication number
WO2006059776A2
WO2006059776A2 PCT/JP2005/022402 JP2005022402W WO2006059776A2 WO 2006059776 A2 WO2006059776 A2 WO 2006059776A2 JP 2005022402 W JP2005022402 W JP 2005022402W WO 2006059776 A2 WO2006059776 A2 WO 2006059776A2
Authority
WO
WIPO (PCT)
Prior art keywords
fuel cell
cell system
target
power
oxidizing gas
Prior art date
Legal status (The legal status 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 status listed.)
Ceased
Application number
PCT/JP2005/022402
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French (fr)
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WO2006059776A3 (en
Inventor
Masaru Okamoto
Kotaro Akashi
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Nissan Motor Co Ltd
Original Assignee
Nissan Motor Co Ltd
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Filing date
Publication date
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Publication of WO2006059776A2 publication Critical patent/WO2006059776A2/en
Publication of WO2006059776A3 publication Critical patent/WO2006059776A3/en
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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    • 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
    • H01M8/04007—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids related to heat exchange
    • H01M8/04029—Heat exchange using liquids
    • 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
    • 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
    • H01M8/04358—Temperature; Ambient temperature of the coolant
    • 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
    • H01M8/04373—Temperature; Ambient temperature of 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
    • H01M8/0438—Pressure; Ambient pressure; Flow
    • H01M8/04388—Pressure; Ambient pressure; Flow of anode 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
    • H01M8/04395—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
    • H01M8/04417—Pressure; Ambient pressure; Flow of the coolant
    • 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
    • H01M8/04544—Voltage
    • H01M8/04567—Voltage 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
    • H01M8/04313—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
    • H01M8/04574—Current
    • H01M8/04589—Current 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
    • H01M8/04574—Current
    • H01M8/04597—Current 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
    • H01M8/04313—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
    • H01M8/04619—Power, energy, capacity or load 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
    • H01M8/04701—Temperature
    • H01M8/04708—Temperature 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
    • H01M8/04753—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
    • H01M8/04768—Pressure; Flow of the coolant
    • 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
    • H01M8/04955—Shut-off or shut-down of fuel cells
    • 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
    • H01M8/10—Fuel cells with solid electrolytes
    • H01M2008/1095—Fuel cells with polymeric electrolytes
    • 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, and particularly, to a fuel cell system with an improved starting ability at low temperatures.
  • a related art disclosing this sort of a fuel cell system is, for example, Japanese Laid- open Patent Publication No. 2002-313388.
  • the related art lowers the pressure of a hydrogen gas supplied to a fuel cell of the system lower than that for a normal-temperature starting. Then decreasing the power generating efficiency of the fuel cell increases self-generated heat of the fuel cell. In this way, the related art realizes shortening a warm-up time of the system.
  • a fuel cell system intentionally lowers the power generating efficiency of the fuel cell when starting the system at low temperatures, to increase heat generated in the fuel cell, i.e., the temperature of the fuel cell itself.
  • the temperature of reactive gases, i.e., hydrogen and air supplied to the fuel cell is also low. If the air to the fuel cell is at or below the freezing point when starting the fuel cell system, a cathode of the fuel cell that receives the air will become inactive because water produced around the cathode during power generation freezes due to the freezing-point air. As a result, the system fails to start.
  • an object of the present invention is to provide a fuel cell system capable of smoothly starting even at low temperatures.
  • An aspect of the present invention provides a fuel cell system that includes, a fuel cell arranged and configured to chemically react a fuel gas and an oxidizing gas with each other to generate electricity, accessories arranged and configured to support the fuel cell in generating electricity, a battery arranged and configured to accumulate electricity and supply the electricity to the accessories, a heating mechanism arranged and configured to heat the oxidizing gas supplied to the fuel cell, and a controller arranged and configured to set a target temperature and a target heating time for the oxidizing gas heated with the heating mechanism, said controller arranged and configured to determine, when starting the fuel cell system, operating conditions of the heating mechanism according to a power balance derived from electric power consumed by the heating mechanism, electric power consumed by the accessories, available electric power of the battery, and electric power generated by the fuel cell, and said controller arranged and configured to control the heating of the oxidizing gas supplied to the fuel cell according to the operating conditions.
  • a fuel cell system that includes a fuel cell configured to chemically react a fuel gas and an oxidizing gas with each other and generate electricity, accessories configured to support the fuel cell in generating electricity, a battery configured to accumulate electricity and supply the electricity to the accessories, a heating mechanism configured to heat the oxidizing gas supplied to the fuel cell when starting the fuel cell system, and a controller configured to set a target temperature and a target heating time for the oxidizing gas heated with the heating mechanism, determine, when starting the fuel cell system, operating conditions of the heating mechanism according to a power balance derived from electric energy consumed by the heating mechanism, electric energy consumed by the accessories, available electric energy of the battery, and electric energy generated by the fuel cell, and control the heating of the oxidizing gas supplied to the fuel cell, each piece of the electric energy being obtained by multiplying electric power by time.
  • Figure 1 shows a fuel cell system according to a first embodiment of the present invention.
  • Figure 2 is a flowchart showing a low-temperature starting operation according to the first embodiment of the present invention.
  • Figure 3 is a flowchart showing a determination operation whether or not the fuel cell system is started in a low-temperature mode or a normal mode.
  • Figure 4 shows an example of a map function stored in the memory of the controller 101 to estimate an available power of the battery 11.
  • Figure 5 shows an example of a map function representing the relationships among the target heating time, target air flow rates, target air pressures, and power consumption.
  • Figure 6 shows a sequence of calculating the minimum output power target of the fuel cell l.
  • Figure 7 is a flowchart showing determination operation whether or not the fuel cell system is to be started in the low-temperature mode.
  • Figure 8 is a flow chart showing a sequence of calculating a power balance and setting the operating conditions of the heating mechanism according to the power balance.
  • Figure 9 is a flowchart showing a sequence of changing the operating conditions of the heating mechanism.
  • Figure 10 is a flowchart showing a sequence of determining whether or not the heating operation carried out with the heating mechanism is ended.
  • Figure 11 shows a map function to estimate available electric energy of the battery 11.
  • Figure 12 shows a map function of target heating time, target air flow rate, target air pressure, and electric energy consumption.
  • Figure 13 shows a calculation operation to determine the minimum electric energy target of the fuel cell 1
  • Figure 14 is a flowchart showing a sequence of determining whether or not the fuel cell system is started according to the minimum electric energy target and upper output power limit profile of the fuel cell 1.
  • FIG. 1 shows a fuel cell system according to a first embodiment of the present invention.
  • the system includes a fuel cell 1, a fuel gas system, and an oxidizing gas system.
  • the fuel gas system includes a hydrogen supply tank 2, a hydrogen pressure regulator 3, a purge control valve 4, and a hydrogen circulating pump 5.
  • the oxidizing gas system includes an air supply unit 6 and an air pressure regulator 7.
  • the system further includes a cooling water pump 8.
  • the fuel cell 1 chemically reacts the fuel gas, i.e., the hydrogen gas with the oxidizing gas, i.e., air to generate electricity. Heat produced at this time is removed with cooling water circulated through the fuel cell 1 by the cooling water pump 8.
  • the hydrogen gas to be supplied to the fuel cell 1 is stored in the hydrogen supply tank 2.
  • the hydrogen gas in the hydrogen supply tank 2 is pressure-regulated by the hydrogen pressure regulator 3 and is supplied to the fuel cell 1.
  • An unused hydrogen gas discharged from the fuel cell 1 is partly purged through the purge control valve 4, which works to remove nitrogen when accumulated in the hydrogen circulating system. The remaining part of the discharged unused hydrogen is returned through the hydrogen circulating pump 5 to a hydrogen inlet of the fuel cell 1.
  • the returned hydrogen is mixed with hydrogen supplied from the hydrogen supply tank 2, and the mixed hydrogen is supplied to the fuel cell 1.
  • the hydrogen circulated through the hydrogen circulating system contains much water, and when mixed with dry hydrogen supplied from the hydrogen supply tank 2, humidifies the hydrogen supplied to an anode of the fuel cell 1.
  • the air supply unit 6 is an air compressor, for example, and supplies the oxidizing gas, i.e., air to the fuel cell 1. Unused air discharged from the fuel cell 1 is pressure-regulated through the air pressure regulator 7 and is discharged outside.
  • the air pressure regulator 7 works to regulate the pressure of air supplied to a cathode of the fuel cell 1.
  • the air supply unit (air compressor) 6 supplies compressed air to the fuel cell 1.
  • the pressure and flow rate of air supplied to the fuel cell 1 are determined by the number of revolutions of the air compressor 6 and an opening of the air pressure regulator 7.
  • the air supplied to the fuel cell 1 is heated when it is compressed by the air compressor 6.
  • the air supply unit (air compressor) 6 and air pressure regulator 7 form an air heating mechanism to heat air to be supplied to the fuel cell 1.
  • the warmth of air is dependent on the pressure and flow rate of the air.
  • the heating of air is controllable by controlling the pressure and flow rate of the air through the heating mechanism.
  • the fuel cell system further includes a power converter 9, a load 10, a battery 11, a battery controller 12, and sensors.
  • the power converter 9 converts electricity generated by the fuel cell 1 into electricity suitable for the specifications of the load 10 and battery 11, and the converted electricity is supplied to the load 10 and/or battery 11.
  • the load 10 may be an inverter or a motor to consume the electricity. If the load 10 is an inverter, a load such as a motor to consume the electricity is connected thereto.
  • the load 10 sets a necessary electricity value according to which the fuel cell 1 supplies a load current to the load 10.
  • the electricity converted by the power converter 9 and supplied to the battery 11 is accumulated in the battery 11.
  • the accumulated electricity is supplied to, for example, the air supply unit (air compressor) 6, which is one of accessories of the fuel cell system, at the starting of the fuel cell system.
  • the supplied electricity works as part of electricity for driving the air compressor 6.
  • the battery controller 12 is connected to the battery 11, to measure SOC (state of charge) of the battery 11.
  • SOC state of charge
  • the measured SOC from the battery controller 12 is used to estimate, for example, available electricity of the battery 11.
  • a pressure sensor 13 for measuring the pressure of hydrogen gas supplied to the fuel cell 1 and a temperature sensor 14 for measuring the temperature of the hydrogen gas are arranged at a hydrogen inlet of the fuel cell 1.
  • a temperature sensor 15 for measuring the temperature of cooling water discharged from the fuel cell 1 is arranged at a cooling water outlet of the fuel cell 1.
  • a voltage sensor 16 for measuring a voltage of the fuel cell 1 is arranged on the fuel cell 1.
  • a temperature sensor 17 for measuring the temperature of intake air to the air supply unit 6 is arranged on the upstream side of the air supply unit 6.
  • a pressure sensor 18 for measuring the pressure of air supplied to the fuel cell 1 and a temperature sensor 19 for measuring the temperature of the air are arranged at an air inlet of the fuel cell 1.
  • a current sensor 20 for measuring a load current passed from the fuel cell 1 to the power converter 9 and a voltage sensor 21 for measuring a voltage of electricity supplied from the fuel cell 1 to the power converter 9 are arranged between the fuel cell 1 and the power converter 9.
  • a voltage sensor 22 for measuring a voltage of electricity supplied from the power converter 9 to the battery 11 and a current sensor 23 for measuring a current passed from the power converter 9 to the battery 11 are arranged between the fuel cell 1 and the battery 11.
  • a temperature sensor 24 for measuring an approximate temperature of the battery 11 is arranged adjacent to the battery 11.
  • the fuel cell system has a controller 101.
  • the controller 101 serves as a control center for controlling operation of the system and is realized with, for example, a microcomputer having resources that function as a CPU, a memory, an I/O unit, and the like according to programs to control various operations.
  • the controller 101 reads signals from all sensors including those shown in Fig. 1, and according to the read signals and internal control logics (programs), issues instructions to the components such as the air supply unit 6 and air pressure regulator 7 of the fuel cell system, thereby entirely controlling operations of the system.
  • the operations include a heating operation achieved at the start of the fuel cell system and a power balance calculating operation to be explained later.
  • FIG. 2 is a flowchart showing a low-temperature starting operation according to the first embodiment of the present invention, hi Fig. 2, step S200 determines whether the fuel cell system is started in a low-temperature mode or a normal mode. According to the first embodiment, this determination is made based on the temperature of intake air to the air supply unit 6 measured with the temperature sensor 17 and the temperature of cooling water at the fuel cell outlet measured with the temperature sensor 15. The details of this determination will be explained with reference to a flowchart shown in Fig.3.
  • step S300 checks to see if the intake air temperature is lower than a threshold ThI, or if the cooling water temperature at the fuel cell outlet is lower than a threshold Th2. If any one of the conditions is met, the low-temperature mode is carried out. If none of the conditions is met, it is determined that the fuel cell system can be started in the normal mode, and step S201 carries out the normal-mode starting operation.
  • the low-temperature mode is realized with the heating mechanism including the air supply unit (air compressor) 6 and air pressure regulator 7 to heat air to the fuel cell inlet.
  • the heating mechanism heats air to the fuel cell 1 by adjusting the flow rate and pressure of the air.
  • step S202 sets a target air temperature to be measured at the fuel cell inlet.
  • the target air temperature is a variable preset according to tests or examinations. According to the first embodiment, it is, for example, 2°C at which no freezing occurs in the fuel cell 1.
  • Step S203 sets an initial target heating time to be required for attaining the target temperature, according to an intake air temperature measured with the temperature sensor 17.
  • the initial target heating time may be changed later according to a power balance to be explained later.
  • the initial target heating time is, for example, 10 seconds.
  • Step S204 estimates an available power of the battery 11.
  • relationships between SOC and available power of the battery 11 with the temperature of the battery 11 serving as a parameter are stored in advance in the memory of the controller 101.
  • Figure 4 shows an example of a map function stored in the memory of the controller 101 to estimate an available power of the battery 11.
  • the temperature of the battery 11 is difficult to directly measure.
  • the first embodiment arranges the temperature sensor 24 adjacent to the battery 11 to approximate the temperature of the battery 11. According to a battery temperature measured with the temperature sensor 24 and an SOC of the battery 11 measured with the battery controller 12, the map function of Fig. 4 is employed to estimates an available power of the battery 11.
  • step S205 finds operating conditions of the heating mechanism to heat air up to the target temperature within the target heating time.
  • the operating conditions of the heating mechanism may be a target flow rate and target pressure of air to heat.
  • To find the target flow rate and target pressure of air relationships between air pressure and the power consumption of the heating mechanism with target heating time and air flow rates serving as parameters are stored beforehand in the memory of the controller 101.
  • Figure 5 shows an example of a map function representing the relationships among the target heating time, target air flow rates, target air pressures, and power consumption. This sort of map function is prepared in advance from tests and the like.
  • the map function may provide a plurality of combinations of air pressure and air flow rate that can attain the target air temperature.
  • step S206 estimates a power consumption of the heating mechanism according to the map function of Fig. 5.
  • Step S207 estimates a power consumption of the other accessories including the hydrogen circulating pump 5, cooling water pump 8, and valves, excluding the heating mechanism.
  • Step S208 calculates a minimum output power target of the fuel cell 1 that makes a power balance equal to or greater than zero, the power balance indicating a power available at the start of the system and a power consumed to heat air.
  • the minimum output power target of the fuel cell 1 is calculated as follows:
  • P12 is the minimum output power target of the fuel cell 1
  • P13 is the power consumption of the heating mechanism obtained in step S206
  • P14 is the power consumption of the accessories other than the heating mechanism obtained in step S207
  • PTHl is a first threshold.
  • the above calculation is based on an assumption that the balance of "PIl + P12 - P13 - P14" is below zero, i.e., a negative value. In practice, the calculation may involve an error. Accordingly, even if the balance is a positive value such as +1, a true balance may be a negative value. Due to this, the threshold PTHl may be a positive value such as +1 (kW).
  • Figure 6 shows a sequence of calculating the minimum output power target of the fuel cell 1.
  • the first embodiment determines the minimum output power target P12 of the fuel cell 1 as shown in Fig. 6. Namely, P12 is calculated as follows:
  • the minimum output power target P12 is set to make the power balance equal to or greater than zero. In practice, there will be an error so that a true balance may be negative even if the balance shows a positive value of, for example, +1. Accordingly, the balance may be set to, for example, +1.5.
  • Step S209 compares the calculated minimum output power target of the fuel cell 1 with an upper output power limit of the fuel cell 1, and according to a result of the comparison, again determines whether or not the fuel cell system is to be started in the low-temperature mode. The details of this determination will be explained with reference to a flowchart of Fig.
  • the flowchart of Fig. 7 shows a sequence of determining a system starting mode according to the minimum output power target and upper output power limit of the fuel cell 1.
  • a graph in the right upper part of Fig.7 shows a relationship between a fuel cell temperature and an upper output power limit obtained from tests.
  • Step S700 sets an upper output power limit
  • Step S701 compares the minimum output power target of the fuel cell 1 with the upper output power limit PTH3. If the minimum output power target is lower than the upper output power limit, step S702 starts the fuel cell system. If the minimum output power target is greater than the upper output power limit, it is determined that the system is unable to start and steps S703 and S210 stop starting the system.
  • Step S211 calculates a power balance at present. The details of this calculation will be explained with reference to a flowchart of Fig. 8A,
  • the flowchart of Fig. 8A shows a sequence of calculating a power balance and setting the operating conditions of the heating mechanism according to the power balance.
  • the controller 101 reads measurements from the current sensor 20 and voltage sensor 21 and calculates a generating power of the fuel cell 1 based on the measurements.
  • the control unit 101 reads measurements from the voltage sensor 22 and current sensor 23 and calculates an available power of the battery 11 based on the measurements.
  • Step S801 determines whether or not the following condition is satisfied:
  • P15 is the available power of the battery 11
  • P16 is the generating power of the fuel cell 1
  • P13 is the power consumption of the heating mechanism obtained in step S206
  • P14 is the power consumption of the accessories other than the heating mechanism obtained in step S207
  • PHT2 is a second threshold
  • PTHl is the first threshold.
  • the second threshold PTH2 is set based on an assumption that the power balance has a margin so that the accessories may consume much electricity.
  • the second threshold PTH2 may be equal to or greater than "the power balance + 5" PcW).
  • step S802 sets an operating condition change flag FLAG_CHANGE to 1. This flag indicates whether or not the operating conditions of the heating mechanism is changed. Thereafter, a target heating time shortening mode is executed. If step S801 determines that the above-mentioned condition is not met, step S803 determines whether or not the following condition is met: P15 + P16 - P13 - P14 ⁇ PTH1 ... (4)
  • step S212 changes the operating conditions of the heating mechanism according to the operating condition change flag FLAG_CHANGE set according to the power balance calculated in step S211.
  • the details of the operating condition changing process will be explained with reference to a flowchart of Fig. 9.
  • the threshold PTH4 is set based on an assumption that the power balance is sufficient and the accessories may consume more power. Accordingly, the threshold PTH4 may be 50% or greater of the full SOC of the battery 11.
  • a target power instruction to the load 10 that takes power from the fuel cell 1 may be oscillated around the minimum output power target of the fuel cell 1 obtained in step S208. Namely, the target power instruction to the load 10 may alternately become above and below the minimum output power target of the fuel cell 1.
  • An example of a technique of shortening the target heating time is to refer to the map function of Fig. 5, calculate usable power values according to the present SOC and temperature of the battery 11, find combinations of air flow rate and air pressure achievable with the calculated power values, select a combination of air flow rate and air pressure that realizes a minimum heating time from among the combinations, and set the selected heating time as a new target heating time.
  • An example of a technique of extending the target heating time is to refer to the map function of Fig. 5, calculate usable power values according to the present SOC and temperature of the battery 11, find combinations of air flow rate and air pressure achievable with the calculated power values, select a combination of air flow rate and air pressure that realizes a maximum heating time from among the combinations, and set the selected heating time as a new target heating time. After changing the target heating time, step S905 is carried out.
  • step S905 the controller 101 reads measurements from the current sensor 20 and voltage sensor 21, calculates an output power of the fuel cell 1 according to the measurements, reads measurements from the voltage sensor 22 and current sensor 23, and calculates an available power of the battery 11 according to the measurements.
  • step S906 uses the map function of Fig.5 and finds the operating conditions, Le., air flow rate and air pressure of the heating mechanism to realize the new target heating time. This target heating time is realized with a power derived by subtracting the power consumption of the accessories from the sum of the available power of the battery 11 and the output power of the fuel cell 1.
  • steps S206 to S212 are carried out.
  • step S213 drives the cooling water pump 8 to pass a small quantity of cooling water through the fuel cell 1 and measures, with the temperature sensor 15, the temperature of the cooling water at the outlet of the fuel cell 1. Based on the measured temperature, it is determined whether or not the fuel cell 1 has been heated. If cooling water is left in the fuel cell 1, it is difficult to correctly measure the temperature of cooling water. Accordingly, a small quantity of cooling water is passed through the fuel cell 1. In connection with this, the number of revolutions of the cooling water pump 8 and a cooling water flow rate are determined according to, for example, test data.
  • Step S214 determines whether or not the fuel cell system has been warmed up, the heating operation is finished, and the low-temperature mode is ended. The details of this determination will be explained with reference to a flowchart of Fig. 10.
  • Step SlOOO checks to see if "the present SOC of the battery 11 ⁇ PTH8" and "the present power output of the fuel cell 1 ⁇ the minimum output power target P12 of the fuel cell 1.” If the conditions are met, it is determined that no power is available for the air compressor 6 to supply a minimum quantity of air to start the fuel cell system. Then, step SlOOl sets a heating end flag FLAGJHEAT END to 1, and step S1002 stops the starting of the system.
  • the threshold PTH8 may be set according to power consumption estimated from, for example, test data. The threshold PTH8 presumes that the SOC of the battery 11 is insufficient to continue the starting of the fuel cell system, and therefore, may be about 35% SOC of the battery 11.
  • the thresholds Th5, Th6, and FTH9 may be estimated and set according to, for example, test data.
  • the threshold PTH9 may be set to continuously generate a power of "a maximum among minimum output power targets + margin" so that the warm-up operation is continued.
  • a minimum output power target is determined to realize a positive power balance.
  • the available power of the battery 11 decreases, and therefore, a power generation requirement for the fuel cell 1, i.e., the minimum output power target of the fuel cell 1 increases. Due to this, the minimum output power target of the fuel cell 1 has a maximum value.
  • the minimum output power target of the fuel cell 1 may be, for example, about 12 kW, and the margin may be about 3 kW.
  • the first embodiment finds a power balance among the power consumption of the heating mechanism, the available power of the battery 11, and the output power of the fuel cell 1, and according to the power balance, controls the heating of air supplied to the fuel cell 1. Namely, the first embodiment can properly control the heating of air to the fuel cell 1 according to available electric power. This prevents the air supplied to the fuel cell 1 from cooling the fuel cell 1 and freezing water produced in the fuel cell 1.
  • the first embodiment extends a target heating time and sets operating conditions of the heating mechanism that are achievable with presently available power. This results in decreasing power consumption and starting the fuel cell system without causing a shortage of power. If the power balance is positive, the first embodiment sets a short target heating time that is achievable by the heating mechanism with presently available power. This results in starting the fuel cell system in a shortest time without causing a shortage of power.
  • the first embodiment charges the battery 11 while starting the fuel cell system. This increases a battery assistance power after the completion of the starting of the fuel cell system and prevents a power shortage during the acceleration of a vehicle in which the fuel cell system is installed.
  • the first embodiment sets a minimum output power target for the fuel cell 1 before starting the fuel cell system, to prevent a power shortage during the starting of the system.
  • the first embodiment checks to see if the fuel cell 1 can generate power that is equal to or greater than the minimum output power target and determines whether or not the system can be started. If it is determined that the system cannot be started, the first embodiment does not start the system and saves the power of the battery 11.
  • the first embodiment passes a small quantity of cooling water through the fuel cell 1 and measures the temperature of the cooling water at the outlet of the fuel cell 1. This technique is to correctly grasp the temperature of the fuel cell 1. If the cooling water temperature at the fuel cell outlet is high, the first embodiment determines that the fuel cell 1 can continue power generation with serf-generating heat. In this case, the first embodiment stops the heating of air and saves power.
  • the first embodiment determines that there is a shortage of power for heating and supplying air to the fuel cell 1. In such a power shortage occasion, the first embodiment stops heating air and terminates the starting of the fuel cell system, thereby saving power.
  • the saved power is reserved for handling a system stopping request. Namely, if there is a system stopping request, lhe reserved power is used to drive the air supply unit 6 to dilute hydrogen discharged from the fuel cell 1 for safety.
  • the first embodiment determines that the fuel cell 1 can maintain power generation with serf-generating heat. Then, the first embodiment stops heating air, to save power. This increases a battery assistance power after the completion of the starting of the fuel cell system and prevents a power shortage during the acceleration of the vehicle.
  • the first embodiment may oscillate a target generating power instructed to the fuel cell 1 around a minimum output power target of the fuel cell 1. This results in repeating the charging and discharging of the battery 11 and increasing the temperature of the battery 11, thereby improving an available power of the battery 11. As a consequence, a battery assistance power after the completion of the starting of the fuel cell system is increased to prevent a power shortage during the acceleration of the vehicle.
  • FIG. 11 shows a map function to estimate available electric energy of the battery 11.
  • the first embodiment refers to the map function of Fig. 4 and estimates available power of the battery 11.
  • the second embodiment refers to the map function of Fig. 11 (not Fig. 4) showing electric energy (Wh) and estimates, in step S204, available electric energy of the battery 11 that can be supplied through a target heating time. According to the second embodiment, electric energy is handled in units of Wh.
  • Figure 12 shows a map function of target heating time, target air flow rate, target air pressure, and electric energy consumption.
  • the first embodiment obtains power consumption of the heating mechanism.
  • the second embodiment refers to the map function of Fig. 12 and finds, in step S206, electric energy (Wh) consumed by the heating mechanism through the target heating time. This electric energy consumption is obtained according to a product of a power consumed by the heating mechanism and the target heating time.
  • step S207 of Fig. 2 the first embodiment finds power consumption of the accessories. Instead, the second embodiment finds, in step S207, electric energy (Wh) consumed by the accessories through the target heating time. This electric energy consumption is calculated from a product of a power consumed by the accessories and the target heating time.
  • Wh electric energy
  • step S208 of Fig.2 the first embodiment calculates a minimum output power target of the fuel cell 1 that makes a power balance equal to or greater than zero. Instead, the second embodiment calculates, in step S208, a minimum electric energy target of the fuel cell 1 that makes a power balance equal to or greater than zero as follows:
  • P21 is electric energy to be supplied from the battery 11 during the target heating time, obtained in step S204
  • P22 is the minimum electric energy target of the fuel cell 1 for the target heating time
  • P23 is electric energy consumed by the heating mechanism during the target heating time
  • P24 is electric energy consumed by the accessories other than the heating mechanism during the target heating time, obtained in step S207
  • PTH3 is a third threshold.
  • a minimum electric energy target profile of the fuel cell 1 is calculated to satisfy the above-mentioned condition.
  • the second embodiment determines the minimum electric energy target of the fuel cell 1 as shown in Fig. 13 and as follows:
  • An integration time is from the present time to the end of the target heating time.
  • the controller 101 carries out this calculation with the use of discrete values, and therefore, the integration will be ⁇ i.
  • the second embodiment expresses the minimum electric energy target P22 of the fuel cell 1 with the expression (6), and therefore, minimum output power target values of the fuel cell 1 take the form of a time-series profile shown in Fig. 13.
  • the first embodiment compares the minimum output power target of the fuel cell 1 obtained in step S208 with an upper output power limit.
  • the second embodiment compares, in step S209, the minimum output power target profile (electric energy based on minimum output power target values) of the fuel cell 1 obtained in step S208 with an upper output power limit profile (electric energy based on upper output power limit values), and according to a result of the comparison, again determines whether or not the low- temperature mode is carried out to start the fuel cell system. The details of this determination will be explained with reference to a flowchart of Fig. 14.
  • step S1400 refers to heating profile data obtained in advance from tests, the operating conditions (air flow rate and air pressure) of the heating mechanism, and a difference between an ambient temperature and a fuel cell inlet temperature, and according to these data pieces, estimates a heating profile of air to be supplied to the fuel cell inlet, like a graph shown in the right part of Fig. 14.
  • Step S1401 refers to data about upper output power limit profiles (each indicating a relationship between fuel cell inlet temperature and upper available output power limit) obtained in advance from tests, and according to the data and the estimated heating profile, sets an upper output power limit profile (PTH3) as shown in the graph in the right part of Fig. 14.
  • PTH3 upper output power limit profile
  • Step S1402 compares the upper output power limit profile with the minimum output power target profile of the fuel cell 1 obtained in step S208. If the minimum output power target profile of the fuel cell 1 is smaller than the upper output power limit profile, step S1403 achieves the starting of the fuel cell system. If the minimum output power target profile of the fuel cell 1 is greater than the upper output power limit profile, step S1404 stops starting the system.
  • the second embodiment provides the same effect as the first embodiment.
  • the second embodiment introduces electric energy, i.e., a temporal factor to estimate future energy output and control the air heating process accordingly.
  • the second embodiment can stop the starting of the fuel cell system before consuming the power of the battery 11 for the air heating process, thereby preserving the power of the battery 11. Information about the battery 11 necessary for calculating a power balance is frequently given as electric energy, and therefore, using the electric energy for controlling the heating of air supplied to the fuel cell 1 makes it easy to conduct related calculations.
  • the present invention controls the heating of air supplied to a fuel cell according to a power balance of a fuel cell system, thereby properly using available power.
  • the present invention can prevent air supplied to the fuel cell from freezing water produced in the fuel cell, thereby smoothly starting the fuel cell system even at low temperatures.

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Abstract

A fuel cell chemically reacts a fuel gas and an oxidizing gas with each other to generate electricity. Accessories is for supporting the fuel cell in generating electricity. A battery for accumulates electricity and supplying the electricity to the accessories. A heating mechanism heats the oxidizing gas supplied to the fuel cell A controller sets a target temperature and a target heating time for the oxidizing gas heated with the heating mechanism, determines, when starting the fuel cell system, operating conditions of the heating mechanism according to a power balance derived from electric power consumed by the heating mechanism, electric power consumed by the accessories, available electric power of the battery, and electric power generated by the fuel cell, and controls the heating of the oxidizing gas supplied to the fuel cell according to the operating conditions.

Description

DESCRIFΠON
FUELCELLSYSTEM
TECHNICALHELD The present invention relates to a fuel cell system, and particularly, to a fuel cell system with an improved starting ability at low temperatures.
BACKGROUND AET
A related art disclosing this sort of a fuel cell system is, for example, Japanese Laid- open Patent Publication No. 2002-313388. When starting the fuel cell system at low temperatures, the related art lowers the pressure of a hydrogen gas supplied to a fuel cell of the system lower than that for a normal-temperature starting. Then decreasing the power generating efficiency of the fuel cell increases self-generated heat of the fuel cell. In this way, the related art realizes shortening a warm-up time of the system.
DISCLOSURE OFTHE INVENTION
A fuel cell system according to the related art intentionally lowers the power generating efficiency of the fuel cell when starting the system at low temperatures, to increase heat generated in the fuel cell, i.e., the temperature of the fuel cell itself. When an ambient temperature is low, the temperature of reactive gases, i.e., hydrogen and air supplied to the fuel cell is also low. If the air to the fuel cell is at or below the freezing point when starting the fuel cell system, a cathode of the fuel cell that receives the air will become inactive because water produced around the cathode during power generation freezes due to the freezing-point air. As a result, the system fails to start. To avoid the problem, there is a technique of heating air and supplying the warm air to a fuel cell when starting a fuel cell system at or below the freezing point. To heat air, electricity is needed. At the starting of the system, the fuel cell is insufficiently activated, and therefore, is unable to supply sufficient electricity for heating air. Accordingly, a battery (secondary battery) provided for the system is needed to supply electricity for heating air. If the battery has an insufficient accumulation of electricity, the battery is unable to supply electricity sufficient to heat air. Without hot air, the fuel cell system is unable to start generating electricity. In consideration of these problems, an object of the present invention is to provide a fuel cell system capable of smoothly starting even at low temperatures.
An aspect of the present invention provides a fuel cell system that includes, a fuel cell arranged and configured to chemically react a fuel gas and an oxidizing gas with each other to generate electricity, accessories arranged and configured to support the fuel cell in generating electricity, a battery arranged and configured to accumulate electricity and supply the electricity to the accessories, a heating mechanism arranged and configured to heat the oxidizing gas supplied to the fuel cell, and a controller arranged and configured to set a target temperature and a target heating time for the oxidizing gas heated with the heating mechanism, said controller arranged and configured to determine, when starting the fuel cell system, operating conditions of the heating mechanism according to a power balance derived from electric power consumed by the heating mechanism, electric power consumed by the accessories, available electric power of the battery, and electric power generated by the fuel cell, and said controller arranged and configured to control the heating of the oxidizing gas supplied to the fuel cell according to the operating conditions.
Another aspect of the present invention provides a fuel cell system that includes a fuel cell configured to chemically react a fuel gas and an oxidizing gas with each other and generate electricity, accessories configured to support the fuel cell in generating electricity, a battery configured to accumulate electricity and supply the electricity to the accessories, a heating mechanism configured to heat the oxidizing gas supplied to the fuel cell when starting the fuel cell system, and a controller configured to set a target temperature and a target heating time for the oxidizing gas heated with the heating mechanism, determine, when starting the fuel cell system, operating conditions of the heating mechanism according to a power balance derived from electric energy consumed by the heating mechanism, electric energy consumed by the accessories, available electric energy of the battery, and electric energy generated by the fuel cell, and control the heating of the oxidizing gas supplied to the fuel cell, each piece of the electric energy being obtained by multiplying electric power by time.
BRIEF DESCRIPTION OFTHE DRAWINGS Figure 1 shows a fuel cell system according to a first embodiment of the present invention.
Figure 2 is a flowchart showing a low-temperature starting operation according to the first embodiment of the present invention. Figure 3 is a flowchart showing a determination operation whether or not the fuel cell system is started in a low-temperature mode or a normal mode.
Figure 4 shows an example of a map function stored in the memory of the controller 101 to estimate an available power of the battery 11.
Figure 5 shows an example of a map function representing the relationships among the target heating time, target air flow rates, target air pressures, and power consumption.
Figure 6 shows a sequence of calculating the minimum output power target of the fuel cell l.
Figure 7 is a flowchart showing determination operation whether or not the fuel cell system is to be started in the low-temperature mode. Figure 8 is a flow chart showing a sequence of calculating a power balance and setting the operating conditions of the heating mechanism according to the power balance.
Figure 9 is a flowchart showing a sequence of changing the operating conditions of the heating mechanism.
Figure 10 is a flowchart showing a sequence of determining whether or not the heating operation carried out with the heating mechanism is ended.
Figure 11 shows a map function to estimate available electric energy of the battery 11. Figure 12 shows a map function of target heating time, target air flow rate, target air pressure, and electric energy consumption.
Figure 13 shows a calculation operation to determine the minimum electric energy target of the fuel cell 1
Figure 14 is a flowchart showing a sequence of determining whether or not the fuel cell system is started according to the minimum electric energy target and upper output power limit profile of the fuel cell 1.
BEST MODE FOR CARRYING OUT THE INVENTION Various embodiments of the present invention will be described with reference to the accompanying drawings. It is to be noted that same or similar reference numerals are applied to the same or similar parts and elements throughout the drawings, and the description of the same or similar parts and elements will be omitted or simplified. Figure 1 shows a fuel cell system according to a first embodiment of the present invention. The system includes a fuel cell 1, a fuel gas system, and an oxidizing gas system. The fuel gas system includes a hydrogen supply tank 2, a hydrogen pressure regulator 3, a purge control valve 4, and a hydrogen circulating pump 5. The oxidizing gas system includes an air supply unit 6 and an air pressure regulator 7. The system further includes a cooling water pump 8.
The fuel cell 1 chemically reacts the fuel gas, i.e., the hydrogen gas with the oxidizing gas, i.e., air to generate electricity. Heat produced at this time is removed with cooling water circulated through the fuel cell 1 by the cooling water pump 8. The hydrogen gas to be supplied to the fuel cell 1 is stored in the hydrogen supply tank 2. The hydrogen gas in the hydrogen supply tank 2 is pressure-regulated by the hydrogen pressure regulator 3 and is supplied to the fuel cell 1. An unused hydrogen gas discharged from the fuel cell 1 is partly purged through the purge control valve 4, which works to remove nitrogen when accumulated in the hydrogen circulating system. The remaining part of the discharged unused hydrogen is returned through the hydrogen circulating pump 5 to a hydrogen inlet of the fuel cell 1. The returned hydrogen is mixed with hydrogen supplied from the hydrogen supply tank 2, and the mixed hydrogen is supplied to the fuel cell 1. The hydrogen circulated through the hydrogen circulating system contains much water, and when mixed with dry hydrogen supplied from the hydrogen supply tank 2, humidifies the hydrogen supplied to an anode of the fuel cell 1.
The air supply unit 6 is an air compressor, for example, and supplies the oxidizing gas, i.e., air to the fuel cell 1. Unused air discharged from the fuel cell 1 is pressure-regulated through the air pressure regulator 7 and is discharged outside. The air pressure regulator 7 works to regulate the pressure of air supplied to a cathode of the fuel cell 1. The air supply unit (air compressor) 6 supplies compressed air to the fuel cell 1. The pressure and flow rate of air supplied to the fuel cell 1 are determined by the number of revolutions of the air compressor 6 and an opening of the air pressure regulator 7. The air supplied to the fuel cell 1 is heated when it is compressed by the air compressor 6. Namely, the air supply unit (air compressor) 6 and air pressure regulator 7 form an air heating mechanism to heat air to be supplied to the fuel cell 1. The warmth of air is dependent on the pressure and flow rate of the air. Namely, the heating of air is controllable by controlling the pressure and flow rate of the air through the heating mechanism.
The fuel cell system further includes a power converter 9, a load 10, a battery 11, a battery controller 12, and sensors. The power converter 9 converts electricity generated by the fuel cell 1 into electricity suitable for the specifications of the load 10 and battery 11, and the converted electricity is supplied to the load 10 and/or battery 11. The load 10 may be an inverter or a motor to consume the electricity. If the load 10 is an inverter, a load such as a motor to consume the electricity is connected thereto. The load 10 sets a necessary electricity value according to which the fuel cell 1 supplies a load current to the load 10.
The electricity converted by the power converter 9 and supplied to the battery 11 is accumulated in the battery 11. The accumulated electricity is supplied to, for example, the air supply unit (air compressor) 6, which is one of accessories of the fuel cell system, at the starting of the fuel cell system. The supplied electricity works as part of electricity for driving the air compressor 6. The battery controller 12 is connected to the battery 11, to measure SOC (state of charge) of the battery 11. The measured SOC from the battery controller 12 is used to estimate, for example, available electricity of the battery 11. The sensors will be explained. A pressure sensor 13 for measuring the pressure of hydrogen gas supplied to the fuel cell 1 and a temperature sensor 14 for measuring the temperature of the hydrogen gas are arranged at a hydrogen inlet of the fuel cell 1. A temperature sensor 15 for measuring the temperature of cooling water discharged from the fuel cell 1 is arranged at a cooling water outlet of the fuel cell 1. A voltage sensor 16 for measuring a voltage of the fuel cell 1 is arranged on the fuel cell 1. A temperature sensor 17 for measuring the temperature of intake air to the air supply unit 6 is arranged on the upstream side of the air supply unit 6. A pressure sensor 18 for measuring the pressure of air supplied to the fuel cell 1 and a temperature sensor 19 for measuring the temperature of the air are arranged at an air inlet of the fuel cell 1. A current sensor 20 for measuring a load current passed from the fuel cell 1 to the power converter 9 and a voltage sensor 21 for measuring a voltage of electricity supplied from the fuel cell 1 to the power converter 9 are arranged between the fuel cell 1 and the power converter 9. A voltage sensor 22 for measuring a voltage of electricity supplied from the power converter 9 to the battery 11 and a current sensor 23 for measuring a current passed from the power converter 9 to the battery 11 are arranged between the fuel cell 1 and the battery 11. A temperature sensor 24 for measuring an approximate temperature of the battery 11 is arranged adjacent to the battery 11.
The fuel cell system has a controller 101. The controller 101 serves as a control center for controlling operation of the system and is realized with, for example, a microcomputer having resources that function as a CPU, a memory, an I/O unit, and the like according to programs to control various operations. The controller 101 reads signals from all sensors including those shown in Fig. 1, and according to the read signals and internal control logics (programs), issues instructions to the components such as the air supply unit 6 and air pressure regulator 7 of the fuel cell system, thereby entirely controlling operations of the system. The operations include a heating operation achieved at the start of the fuel cell system and a power balance calculating operation to be explained later.
Figure 2 is a flowchart showing a low-temperature starting operation according to the first embodiment of the present invention, hi Fig. 2, step S200 determines whether the fuel cell system is started in a low-temperature mode or a normal mode. According to the first embodiment, this determination is made based on the temperature of intake air to the air supply unit 6 measured with the temperature sensor 17 and the temperature of cooling water at the fuel cell outlet measured with the temperature sensor 15. The details of this determination will be explained with reference to a flowchart shown in Fig.3.
In Fig.3, step S300 checks to see if the intake air temperature is lower than a threshold ThI, or if the cooling water temperature at the fuel cell outlet is lower than a threshold Th2. If any one of the conditions is met, the low-temperature mode is carried out. If none of the conditions is met, it is determined that the fuel cell system can be started in the normal mode, and step S201 carries out the normal-mode starting operation. The thresholds ThI and Th2 are obtained in advance from tests or examinations. According to the first embodiment, the thresholds are, for example, ThI = 2°C, and Th2 = 2°C. Returning to Fig. 2, the low-temperature mode is realized with the heating mechanism including the air supply unit (air compressor) 6 and air pressure regulator 7 to heat air to the fuel cell inlet. The heating mechanism heats air to the fuel cell 1 by adjusting the flow rate and pressure of the air. To achieve this, step S202 sets a target air temperature to be measured at the fuel cell inlet. The target air temperature is a variable preset according to tests or examinations. According to the first embodiment, it is, for example, 2°C at which no freezing occurs in the fuel cell 1.
Step S203 sets an initial target heating time to be required for attaining the target temperature, according to an intake air temperature measured with the temperature sensor 17. The initial target heating time may be changed later according to a power balance to be explained later. According to the first embodiment, the initial target heating time is, for example, 10 seconds.
Step S204 estimates an available power of the battery 11. For this purpose, relationships between SOC and available power of the battery 11 with the temperature of the battery 11 serving as a parameter are stored in advance in the memory of the controller 101. Figure 4 shows an example of a map function stored in the memory of the controller 101 to estimate an available power of the battery 11. The temperature of the battery 11 is difficult to directly measure. Accordingly, the first embodiment arranges the temperature sensor 24 adjacent to the battery 11 to approximate the temperature of the battery 11. According to a battery temperature measured with the temperature sensor 24 and an SOC of the battery 11 measured with the battery controller 12, the map function of Fig. 4 is employed to estimates an available power of the battery 11.
Returning to Fig. 2, step S205 finds operating conditions of the heating mechanism to heat air up to the target temperature within the target heating time. The operating conditions of the heating mechanism may be a target flow rate and target pressure of air to heat. To find the target flow rate and target pressure of air, relationships between air pressure and the power consumption of the heating mechanism with target heating time and air flow rates serving as parameters are stored beforehand in the memory of the controller 101. Figure 5 shows an example of a map function representing the relationships among the target heating time, target air flow rates, target air pressures, and power consumption. This sort of map function is prepared in advance from tests and the like. The map function may provide a plurality of combinations of air pressure and air flow rate that can attain the target air temperature. Among the combinations, one with a minimum power consumption is selected to find a target air flow rate and a target air pressure. After obtaining the target air flow rate and target air pressure, the controller 101 calculates the number of revolutions of the air compressor 6 and an opening of the air pressure regulator 7 that can achieve the target air flow rate and target air pressure. This calculation is carried out with the use of data that is prepared in advance from tests and the like and indicates a relationship between the number of revolutions and valve opening and the air pressure and air flow rate. Returning to Fig. 2, step S206 estimates a power consumption of the heating mechanism according to the map function of Fig. 5. Step S207 estimates a power consumption of the other accessories including the hydrogen circulating pump 5, cooling water pump 8, and valves, excluding the heating mechanism. The first embodiment carries out this estimation according to power consumption data prepared in advance from tests. Step S208 calculates a minimum output power target of the fuel cell 1 that makes a power balance equal to or greater than zero, the power balance indicating a power available at the start of the system and a power consumed to heat air. The minimum output power target of the fuel cell 1 is calculated as follows:
PIl + P12 - P13 - P14 > PTHl ... (1) where PIl is the available power of the battery 11 obtained in step S204, P12 is the minimum output power target of the fuel cell 1, P13 is the power consumption of the heating mechanism obtained in step S206, P14 is the power consumption of the accessories other than the heating mechanism obtained in step S207, and PTHl is a first threshold.
The above calculation is based on an assumption that the balance of "PIl + P12 - P13 - P14" is below zero, i.e., a negative value. In practice, the calculation may involve an error. Accordingly, even if the balance is a positive value such as +1, a true balance may be a negative value. Due to this, the threshold PTHl may be a positive value such as +1 (kW).
Figure 6 shows a sequence of calculating the minimum output power target of the fuel cell 1. To satisfy the above-mentioned condition, the first embodiment determines the minimum output power target P12 of the fuel cell 1 as shown in Fig. 6. Namely, P12 is calculated as follows:
P12 = G x coefficient ... (2) where G = P13 + P14 + PTHl - PIl and the coefficient is an optional value equal to or greater than l. If G > 0, electric power is insufficient. E G <= 0, electric power is sufficient. If electric power is sufficient, the first embodiment advances to a shortening mode to shorten the target heating time, as will be explained later.
The minimum output power target P12 is set to make the power balance equal to or greater than zero. In practice, there will be an error so that a true balance may be negative even if the balance shows a positive value of, for example, +1. Accordingly, the balance may be set to, for example, +1.5.
Step S209 compares the calculated minimum output power target of the fuel cell 1 with an upper output power limit of the fuel cell 1, and according to a result of the comparison, again determines whether or not the fuel cell system is to be started in the low-temperature mode. The details of this determination will be explained with reference to a flowchart of Fig.
7.
The flowchart of Fig. 7 shows a sequence of determining a system starting mode according to the minimum output power target and upper output power limit of the fuel cell 1.
A graph in the right upper part of Fig.7 shows a relationship between a fuel cell temperature and an upper output power limit obtained from tests. Step S700 sets an upper output power limit
PTEB according to the graph. Step S701 compares the minimum output power target of the fuel cell 1 with the upper output power limit PTH3. If the minimum output power target is lower than the upper output power limit, step S702 starts the fuel cell system. If the minimum output power target is greater than the upper output power limit, it is determined that the system is unable to start and steps S703 and S210 stop starting the system.
If the system can be started, the procedure returns to Fig. 2. Step S211 calculates a power balance at present. The details of this calculation will be explained with reference to a flowchart of Fig. 8A,
The flowchart of Fig. 8A shows a sequence of calculating a power balance and setting the operating conditions of the heating mechanism according to the power balance. In step S800 of Fig. 8A, the controller 101 reads measurements from the current sensor 20 and voltage sensor 21 and calculates a generating power of the fuel cell 1 based on the measurements. Also in step S800, the control unit 101 reads measurements from the voltage sensor 22 and current sensor 23 and calculates an available power of the battery 11 based on the measurements. Step S801 determines whether or not the following condition is satisfied:
P15 + P16 - P13 - P14 > PTH2 > PTH1 ... (3) where P15 is the available power of the battery 11, P16 is the generating power of the fuel cell 1, P13 is the power consumption of the heating mechanism obtained in step S206, P14 is the power consumption of the accessories other than the heating mechanism obtained in step S207, PHT2 is a second threshold, and PTHl is the first threshold. The second threshold PTH2 is set based on an assumption that the power balance has a margin so that the accessories may consume much electricity. The second threshold PTH2 may be equal to or greater than "the power balance + 5" PcW).
If the above-mentioned condition is satisfied, it is determined that the power balance is enough and has a surplus, and step S802 sets an operating condition change flag FLAG_CHANGE to 1. This flag indicates whether or not the operating conditions of the heating mechanism is changed. Thereafter, a target heating time shortening mode is executed. If step S801 determines that the above-mentioned condition is not met, step S803 determines whether or not the following condition is met: P15 + P16 - P13 - P14 < PTH1 ... (4)
If this conditions is met, it is determined that power is tight, and step S804 sets FIAG_CHANGE = 2. Thereafter, a power saving mode is executed to extend the target heating time and save power. If the condition (4) is unsatisfied, step S805 sets FLAG_CHANGE = 3, to maintain the present operating conditions. In this way, the power balance calculating step S211 examines whether or not the fuel cell 1 generates electricity equal to or greater than the minimum output power target during the starting of the fuel cell system.
Returning to Fig. 2, step S212 changes the operating conditions of the heating mechanism according to the operating condition change flag FLAG_CHANGE set according to the power balance calculated in step S211. The details of the operating condition changing process will be explained with reference to a flowchart of Fig. 9.
The flowchart of Fig. 9 shows a sequence of changing the operating conditions of the heating mechanism. Ih Fig. 9, if the operating condition change flag FLAG_CHANGE = 1 in step S900 and if the SOC of the battery 11 is greater than a threshold PTH4 in step S901, step S902 shortens the target heating time and starts a short mode. The threshold PTH4 is set based on an assumption that the power balance is sufficient and the accessories may consume more power. Accordingly, the threshold PTH4 may be 50% or greater of the full SOC of the battery 11.
Instead of shortening the target heating time, a target power instruction to the load 10 that takes power from the fuel cell 1 may be oscillated around the minimum output power target of the fuel cell 1 obtained in step S208. Namely, the target power instruction to the load 10 may alternately become above and below the minimum output power target of the fuel cell 1.
An example of a technique of shortening the target heating time is to refer to the map function of Fig. 5, calculate usable power values according to the present SOC and temperature of the battery 11, find combinations of air flow rate and air pressure achievable with the calculated power values, select a combination of air flow rate and air pressure that realizes a minimum heating time from among the combinations, and set the selected heating time as a new target heating time.
If FLAG_CHANGE = 1 in step S900 and the SOC of the battery 11 is smaller than the threshold PTH4 in step S901, the target heating time is unchanged and the next step is carried out.
If FLAG_CHANGE = 2 in step S903, the target heating time is extended in step S904. If FLAG_CHANGE = 3 in step S903, the target heating time is unchanged and the next step is carried out. An example of a technique of extending the target heating time is to refer to the map function of Fig. 5, calculate usable power values according to the present SOC and temperature of the battery 11, find combinations of air flow rate and air pressure achievable with the calculated power values, select a combination of air flow rate and air pressure that realizes a maximum heating time from among the combinations, and set the selected heating time as a new target heating time. After changing the target heating time, step S905 is carried out. In step S905, the controller 101 reads measurements from the current sensor 20 and voltage sensor 21, calculates an output power of the fuel cell 1 according to the measurements, reads measurements from the voltage sensor 22 and current sensor 23, and calculates an available power of the battery 11 according to the measurements. like step S205, step S906 uses the map function of Fig.5 and finds the operating conditions, Le., air flow rate and air pressure of the heating mechanism to realize the new target heating time. This target heating time is realized with a power derived by subtracting the power consumption of the accessories from the sum of the available power of the battery 11 and the output power of the fuel cell 1. Thereafter, steps S206 to S212 are carried out.
Returning to Fig. 2, step S213 drives the cooling water pump 8 to pass a small quantity of cooling water through the fuel cell 1 and measures, with the temperature sensor 15, the temperature of the cooling water at the outlet of the fuel cell 1. Based on the measured temperature, it is determined whether or not the fuel cell 1 has been heated. If cooling water is left in the fuel cell 1, it is difficult to correctly measure the temperature of cooling water. Accordingly, a small quantity of cooling water is passed through the fuel cell 1. In connection with this, the number of revolutions of the cooling water pump 8 and a cooling water flow rate are determined according to, for example, test data.
Step S214 determines whether or not the fuel cell system has been warmed up, the heating operation is finished, and the low-temperature mode is ended. The details of this determination will be explained with reference to a flowchart of Fig. 10.
The flowchart of Fig. 10 shows a sequence of determining whether or not the heating operation carried out wilh the heating mechanism is ended. Step SlOOO checks to see if "the present SOC of the battery 11 < PTH8" and "the present power output of the fuel cell 1 < the minimum output power target P12 of the fuel cell 1." If the conditions are met, it is determined that no power is available for the air compressor 6 to supply a minimum quantity of air to start the fuel cell system. Then, step SlOOl sets a heating end flag FLAGJHEAT END to 1, and step S1002 stops the starting of the system. The threshold PTH8 may be set according to power consumption estimated from, for example, test data. The threshold PTH8 presumes that the SOC of the battery 11 is insufficient to continue the starting of the fuel cell system, and therefore, may be about 35% SOC of the battery 11.
If step SlOOO determines that the conditions are unsatisfied, step S1003 checks to see if "the cooling water temperature at the fuel cell outlet measured in step S213 > Th5," or "a present air temperature at the fuel cell inlet > Th6," or "the present power output of the fuel cell 1 > FIΗ9." If the conditions are met, step S1004 sets FIAG_HEAT_END = 2, determines that the present output power is sufficient to generate heat and power, and stops the low- temperature mode. If step S1003 determines that the conditions are unsatisfied, step S1005 sets FLAG_HEAΓ_END = 3, and continues the heating operation under the present conditions. The thresholds Th5, Th6, and FTH9 may be estimated and set according to, for example, test data. The threshold PTH9 may be set to continuously generate a power of "a maximum among minimum output power targets + margin" so that the warm-up operation is continued. A minimum output power target is determined to realize a positive power balance. When the battery 11 is used to start the fuel cell system, the available power of the battery 11 decreases, and therefore, a power generation requirement for the fuel cell 1, i.e., the minimum output power target of the fuel cell 1 increases. Due to this, the minimum output power target of the fuel cell 1 has a maximum value. The minimum output power target of the fuel cell 1 may be, for example, about 12 kW, and the margin may be about 3 kW.
Returning to Fig. 2, step S215 determines whether or not a vehicle in which the fuel cell system is installed is ready to run according to the heating end flag FLAG_HEAT_END. If FLAG_EEAT_END = 1, the starting of the fuel cell system is terminated. If
FlAGJEffiAT_END = 2, the starting control is finished and the vehicle is allowed to run. If
FLAG_HEAT_END = 3, the process returns to step S211 to continue the system starting control.
As explained above, the first embodiment finds a power balance among the power consumption of the heating mechanism, the available power of the battery 11, and the output power of the fuel cell 1, and according to the power balance, controls the heating of air supplied to the fuel cell 1. Namely, the first embodiment can properly control the heating of air to the fuel cell 1 according to available electric power. This prevents the air supplied to the fuel cell 1 from cooling the fuel cell 1 and freezing water produced in the fuel cell 1.
If the power balance is negative, the first embodiment extends a target heating time and sets operating conditions of the heating mechanism that are achievable with presently available power. This results in decreasing power consumption and starting the fuel cell system without causing a shortage of power. If the power balance is positive, the first embodiment sets a short target heating time that is achievable by the heating mechanism with presently available power. This results in starting the fuel cell system in a shortest time without causing a shortage of power.
If a power balance during the heating of air is equal to or greater than a predetermined value, the first embodiment charges the battery 11 while starting the fuel cell system. This increases a battery assistance power after the completion of the starting of the fuel cell system and prevents a power shortage during the acceleration of a vehicle in which the fuel cell system is installed.
The first embodiment sets a minimum output power target for the fuel cell 1 before starting the fuel cell system, to prevent a power shortage during the starting of the system. The first embodiment checks to see if the fuel cell 1 can generate power that is equal to or greater than the minimum output power target and determines whether or not the system can be started. If it is determined that the system cannot be started, the first embodiment does not start the system and saves the power of the battery 11.
The first embodiment passes a small quantity of cooling water through the fuel cell 1 and measures the temperature of the cooling water at the outlet of the fuel cell 1. This technique is to correctly grasp the temperature of the fuel cell 1. If the cooling water temperature at the fuel cell outlet is high, the first embodiment determines that the fuel cell 1 can continue power generation with serf-generating heat. In this case, the first embodiment stops the heating of air and saves power.
If the SOC (state of charge) of the battery 11 reaches a predetermined lower limit and the output power of the fuel cell 1 decreases below the minimum output power target during the starting of the fuel cell system, the first embodiment determines that there is a shortage of power for heating and supplying air to the fuel cell 1. In such a power shortage occasion, the first embodiment stops heating air and terminates the starting of the fuel cell system, thereby saving power. The saved power is reserved for handling a system stopping request. Namely, if there is a system stopping request, lhe reserved power is used to drive the air supply unit 6 to dilute hydrogen discharged from the fuel cell 1 for safety. If the fuel cell 1 outputs a power greater than a predetermined value and if such a state continues for a predetermined time, the first embodiment determines that the fuel cell 1 can maintain power generation with serf-generating heat. Then, the first embodiment stops heating air, to save power. This increases a battery assistance power after the completion of the starting of the fuel cell system and prevents a power shortage during the acceleration of the vehicle.
The first embodiment may oscillate a target generating power instructed to the fuel cell 1 around a minimum output power target of the fuel cell 1. This results in repeating the charging and discharging of the battery 11 and increasing the temperature of the battery 11, thereby improving an available power of the battery 11. As a consequence, a battery assistance power after the completion of the starting of the fuel cell system is increased to prevent a power shortage during the acceleration of the vehicle.
Next, a fuel cell system according to a second embodiment of the present invention will be explained. The first embodiment mentioned above controls the heating of air based on the power of the fuel cell 1 and battery 11 and the power consumption of the accessories. On the other hand, the second embodiment controls the heating of air based on electric energy (electric power multiplied by time). The structure and operation sequences of the second embodiment are substantially the same as those of the first embodiment. Differences of the second embodiment from the first embodiment will be explained. Figure 11 shows a map function to estimate available electric energy of the battery 11.
In step S204 of Fig. 2, the first embodiment refers to the map function of Fig. 4 and estimates available power of the battery 11. Instead, the second embodiment refers to the map function of Fig. 11 (not Fig. 4) showing electric energy (Wh) and estimates, in step S204, available electric energy of the battery 11 that can be supplied through a target heating time. According to the second embodiment, electric energy is handled in units of Wh.
Figure 12 shows a map function of target heating time, target air flow rate, target air pressure, and electric energy consumption. In step S206 of Fig. 2, the first embodiment obtains power consumption of the heating mechanism. Instead, the second embodiment refers to the map function of Fig. 12 and finds, in step S206, electric energy (Wh) consumed by the heating mechanism through the target heating time. This electric energy consumption is obtained according to a product of a power consumed by the heating mechanism and the target heating time.
In step S207 of Fig. 2, the first embodiment finds power consumption of the accessories. Instead, the second embodiment finds, in step S207, electric energy (Wh) consumed by the accessories through the target heating time. This electric energy consumption is calculated from a product of a power consumed by the accessories and the target heating time.
In step S208 of Fig.2, the first embodiment calculates a minimum output power target of the fuel cell 1 that makes a power balance equal to or greater than zero. Instead, the second embodiment calculates, in step S208, a minimum electric energy target of the fuel cell 1 that makes a power balance equal to or greater than zero as follows:
P21 + P22 - P23 - P24 > FIΗ3 ... (5) where P21 is electric energy to be supplied from the battery 11 during the target heating time, obtained in step S204, P22 is the minimum electric energy target of the fuel cell 1 for the target heating time, P23 is electric energy consumed by the heating mechanism during the target heating time, obtained in step S206, P24 is electric energy consumed by the accessories other than the heating mechanism during the target heating time, obtained in step S207, and PTH3 is a third threshold.
At each timing, a minimum electric energy target profile of the fuel cell 1 is calculated to satisfy the above-mentioned condition. To satisfy the above-mentioned condition, the second embodiment determines the minimum electric energy target of the fuel cell 1 as shown in Fig. 13 and as follows:
P22 =
(electric energy inclination A x target heating time + present electric energy) =
{j*(P13 + P14 - PIl) + PTH3} x coefficient
... (6) where the coefficient is an optional value equal to or greater than 1.
To satisfy this condition, the electric energy inclination A is adjusted. An integration time is from the present time to the end of the target heating time. In practice, the controller 101 carries out this calculation with the use of discrete values, and therefore, the integration will be ∑i.
The second embodiment expresses the minimum electric energy target P22 of the fuel cell 1 with the expression (6), and therefore, minimum output power target values of the fuel cell 1 take the form of a time-series profile shown in Fig. 13. In step S209 of Fig. 2, the first embodiment compares the minimum output power target of the fuel cell 1 obtained in step S208 with an upper output power limit. Instead, the second embodiment compares, in step S209, the minimum output power target profile (electric energy based on minimum output power target values) of the fuel cell 1 obtained in step S208 with an upper output power limit profile (electric energy based on upper output power limit values), and according to a result of the comparison, again determines whether or not the low- temperature mode is carried out to start the fuel cell system. The details of this determination will be explained with reference to a flowchart of Fig. 14.
The flowchart of Fig. 14 shows a sequence of deteπnining whether or not the fuel cell system is started according to the minimum electric energy target and upper output power limit profile of the fuel cell 1. In Fig. 14, step S1400 refers to heating profile data obtained in advance from tests, the operating conditions (air flow rate and air pressure) of the heating mechanism, and a difference between an ambient temperature and a fuel cell inlet temperature, and according to these data pieces, estimates a heating profile of air to be supplied to the fuel cell inlet, like a graph shown in the right part of Fig. 14. Step S1401 refers to data about upper output power limit profiles (each indicating a relationship between fuel cell inlet temperature and upper available output power limit) obtained in advance from tests, and according to the data and the estimated heating profile, sets an upper output power limit profile (PTH3) as shown in the graph in the right part of Fig. 14.
Step S1402 compares the upper output power limit profile with the minimum output power target profile of the fuel cell 1 obtained in step S208. If the minimum output power target profile of the fuel cell 1 is smaller than the upper output power limit profile, step S1403 achieves the starting of the fuel cell system. If the minimum output power target profile of the fuel cell 1 is greater than the upper output power limit profile, step S1404 stops starting the system. In this way, the second embodiment provides the same effect as the first embodiment. In addition, the second embodiment introduces electric energy, i.e., a temporal factor to estimate future energy output and control the air heating process accordingly. The second embodiment can stop the starting of the fuel cell system before consuming the power of the battery 11 for the air heating process, thereby preserving the power of the battery 11. Information about the battery 11 necessary for calculating a power balance is frequently given as electric energy, and therefore, using the electric energy for controlling the heating of air supplied to the fuel cell 1 makes it easy to conduct related calculations.
As mentioned above, the present invention controls the heating of air supplied to a fuel cell according to a power balance of a fuel cell system, thereby properly using available power. The present invention can prevent air supplied to the fuel cell from freezing water produced in the fuel cell, thereby smoothly starting the fuel cell system even at low temperatures.
The entire contents of Japanese patent applications P2004-351166 filed December 3rd, 2004 and P2005-338488 filed November 24th, 2005 are hereby incorporated by reference.
The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims

1. Afuel cell system comprising: a fuel cell arranged and configured to chemically react a fuel gas and an oxidizing gas with each other to generate electricity; accessories arranged and configured to support the fuel cell in generating electricity; a battery arranged and configured to accumulate electricity and supply the electricity to the accessories; a heating mechanism arranged and configured to heat the oxidizing gas supplied to the fuel cell; and a controller arranged and configured to set a target temperature and a target heating time for the oxidizing gas heated with the heating mechanism, said controller arranged and configured to determine, when starting the fuel cell system, operating conditions of the heating mechanism according to a power balance derived from electric power consumed by the heating mechanism, electric power consumed by the accessories, available electric power of the battery, and electric power generated by the fuel cell, and said controller arranged and configured to control the heating of the oxidizing gas supplied to the fuel cell according to the operating conditions.
2. The fuel cell system of claim 1, wherein: if the power balance becomes equal to or lower than a first value after the start of the fuel cell system, said controller extends the target heating time and again sets the operating conditions of the heating mechanism according to the power balance, said operating conditions are set to reach the target temperature of the oxidizing gas within the extended target heating time.
3. The fuel cell system of claim 2, wherein: the first value is equal to or lower than 1 kW.
4. The fuel cell system of claim 1, wherein: if the power balance is equal to or greater than a second value and a state of charge of the battery is equal to or greater than a third value after the start of the fuel cell system, said controller shortens the target heating time and again sets the operating conditions of the heating mechanism according to the power balance, said the operating conditions are set to reach the target temperature of the oxidizing gas within the shortened target heating time.
5. The fuel cell system of claim 4, wherein: the second value is equal to or greater than 5 KW.
6. The fuel cell system of claim 4, wherein: the third value is equal to or greater than a 50% charged state of the battery.
7. The fuel cell system of claim 1, wherein: if the power balance is equal to or greater than a fourth value and a state of charge of the battery is equal to or lower than a fifth value after the start of the fuel cell system, said controller maintains the operating conditions of the heating mechanism and accumulates electricity generated by the fuel cell in the battery.
8. The fuel cell system of claim 1, wherein: said controller sets, before starting the fuel cell system, a minimum output power target of the fuel cell so that the power balance become equal to or greater than the first value, and if the set minimum output power target is greater than an upper output power limit of the fuel cell, does not start the fuel cell system, the power balance being obtained by subtracting the sum of an estimated power consumption of the heating mechanism to heat the oxidizing gas up to the target temperature within the target heating time and an estimated power consumption of the accessories from the sum of an estimated power supply of the battery and the minimum output power target of the fuel cell.
9. The fuel cell system of claim 1, wherein: if the temperature of cooling water circulated through the fuel cell is equal to or greater than a seventh value after the start of the fuel cell system, the controller stops the heating of the oxidizing gas by the heating mechanism.
10. The fuel cell system of claim 9, wherein: if the temperature of the cooling water at an outlet of the fuel cell is equal to or greater than 15°C, the controller stops the heating of the oxidizing gas by the heating mechanism.
11. The fuel cell system of claim 1, wherein: if a state of charge of the battery becomes equal to or lower than an eighth value and an output of the fuel cell becomes equal to the minimum output power target after the start of the fuel cell system, the controller stops the fuel cell system.
12. The fuel cell system of claim 11, wherein: the eighth value is equal to or lower than a 35% charged state of the battery.
13. The fuel cell system of claim 1, wherein: if an output power of the fuel cell maintains a tenth value or greater for a predetermined period or longer after the start of the fuel cell system, the controller terminates the heating of the oxidizing gas by the heating mechanism.
14. The fuel cell system of claim 1, wherein: if the power balance is more than zero (0) after the start of the fuel cell system, the controller sets a target generating power value, which is set for a load that receives a load current from the fuel cell, periodically exceed and fall below a minimum output power target of the fuel cell.
15. The fuel cell system of claim 1, wherein: the heating mechanism comprises a compressor arranged and configured to compress the oxidizing gas and a pressure regulator configured to regulate the pressure of the oxidizing gas passed through the fuel cell; the heating mechanism controls the heating of the oxidizing gas based on the pressure and flow rate of the oxidizing gas; and the controller controls the number of revolutions of the compressor and an opening of the pressure regulator, to control the pressure and flow rate of the oxidizing gas so as to heat the oxidizing gas up to the target temperature.
16. A fuel cell system comprising: a fuel cell configured to chemically react a fuel gas and an oxidizing gas with each other and generate electricity; accessories configured to support the fuel cell in generating electricity; a battery configured to accumulate electricity and supply the electricity to the accessories; a heating mechanism configured to heat the oxidizing gas supplied to the fuel cell when starting the fuel cell system; and a controller configured to set a target temperature and a target heating time for the oxidizing gas heated with the heating mechanism, determine, when starting the fuel cell system, operating conditions of the heating mechanism according to a power balance derived from electric energy consumed by the heating mechanism, electric energy consumed by the accessories, available electric energy of the battery, and electric energy generated by the fuel cell, and control the heating of the oxidizing gas supplied to the fuel cell, each piece of the electric energy being obtained by multiplying electric power by time.
17. A fuel cell system comprising: a fuel cell for chemically reacting a fuel gas and an oxidizing gas with each other to generate electricity; accessories for supporting the fuel cell in generating electricity; a battery for accumulating electricity and supplying the electricity to the accessories; a heating mechanism for heating the oxidizing gas supplied to the fuel cell; and a controller for setting a target temperature and a target heating time for the oxidizing gas heated with the heating mechanism, said controller for determining, when starting the fuel cell system, operating conditions of the heating mechanism according to a power balance derived from electric power consumed by the heating mechanism, electric power consumed by the accessories, available electric power of the battery, and electric power generated by the fuel cell, and said controller for controlling the heating of the oxidizing gas supplied to the fuel cell according to the operating conditions.
PCT/JP2005/022402 2004-12-03 2005-11-30 Fuel cell system Ceased WO2006059776A2 (en)

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