JP2011192458A - Fuel cell system, movable body, and control method of fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To maintain accuracy of power generation control based on current-voltage characteristics, even if formation of an oxide coating is progressed in catalyst of an electrode accompanying power generation. <P>SOLUTION: The fuel cell system includes a catalyst oxide coating film derivation unit which derives a catalyst oxide coating film rate by integrating a catalyst oxide generation rate as a difference between a generation reaction speed and a reduction reaction speed by time, a current-voltage characteristics derivation unit deriving current-voltage characteristics on the basis of the catalyst oxide coating film rate, a load demand acquisition unit, an operation point setter for setting an operation point in a fuel cell consisting of an output current and an output voltage for generating power corresponding to the load demand on the basis of the current-voltage characteristics, and a control unit for making the fuel cell generate power at the set operation point. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a fuel cell system, a moving body, and a control method for the fuel cell system.

  The amount of power generated by the fuel cell may vary depending on the operating temperature of the fuel cell, the gas flow rate supplied to the fuel cell, etc., but when a sufficient amount of gas is supplied under appropriate operating temperature conditions, the output current and output voltage are Shows a certain relationship. Therefore, when performing power generation control in a fuel cell, generally, the operating point of the fuel cell is such that a desired power based on the load request is obtained based on the relationship between the output current and the output voltage obtained in advance. (Combination of output current and output voltage) is set.

JP 2008-192468 A JP 2006-147404 A JP 2007-103115 A JP 2008-226593 A JP 2000-357526 A

  However, it is known that when the fuel cell continues to generate electricity, an oxide film is formed in the catalyst provided in the electrode of the fuel cell, for example, platinum (see, for example, Patent Document 1). Thus, when an oxide film is formed in platinum of an electrode, since the progress of the electrochemical reaction on the platinum surface is suppressed, the relationship between the output current and the output voltage (current-voltage characteristics) in the fuel cell changes. Therefore, even if the current-voltage characteristic of the fuel cell to be used is obtained in advance and the power generation control is performed based on this current-voltage characteristic, if the current-voltage characteristic changes as the oxide film is formed on the platinum electrode, The accuracy of the control operation gradually decreases.

  The present invention has been made to solve the above-described conventional problems, and maintains the accuracy of power generation control based on the current-voltage characteristics even when the formation of an oxide film in the electrode catalyst proceeds with power generation. The purpose is to do.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

[Application Example 1]
A fuel cell system comprising a fuel cell,
The catalyst oxide film rate, which is the ratio of the area where the oxide film is formed on the surface of the catalyst provided in the cathode of the fuel cell, the reaction rate at which the catalyst oxide is generated, and the catalyst oxide A catalytic oxide film rate deriving unit for deriving by integrating the catalyst oxide production rate as a difference between the reduction reaction rate, which is the reaction rate to be reduced, with time;
A current-voltage characteristic deriving unit for deriving a current-voltage characteristic that is a relationship between the output current and the output voltage of the fuel cell based on the catalytic oxide film rate derived by the catalytic oxide film rate deriving unit;
A load request acquisition unit for acquiring a load request for the fuel cell;
In the fuel cell comprising the output current and the output voltage for generating electric power corresponding to the load request acquired by the load request acquisition unit based on the current-voltage characteristic derived by the current-voltage characteristic deriving unit An operation point setting section for setting operation points;
A fuel cell system comprising: a control unit that generates power at the operation point set by the operation point setting unit.

  According to the fuel cell system described in Application Example 1, the catalytic oxide film rate is derived, the current current-voltage characteristics are derived based on the obtained catalytic oxide film rate, and the operating point of the fuel cell is set. ing. Therefore, the operation point of the fuel cell can be set using the current-voltage characteristics closer to the actual state, and the accuracy of the operation for outputting the desired power from the fuel cell can be improved. Here, the catalytic oxide film rate always varies with the power generation of the fuel cell. However, the catalytic oxide film rate is derived by integrating the catalyst oxide generation rate with time to derive the catalytic oxide film rate. Can improve the accuracy.

[Application Example 2]
The fuel cell system according to Application Example 1, further including a voltage acquisition unit that acquires an output voltage of the fuel cell, a current acquisition unit that acquires an output current of the fuel cell, and a temperature of the fuel cell. A temperature acquisition unit; and an impedance deriving unit for deriving an impedance of the fuel cell, wherein the catalytic oxide film rate deriving unit is configured to obtain the voltage acquisition unit, the current acquisition unit, and the temperature acquisition unit of the fuel cell. Obtaining the voltage, current, and temperature and the impedance of the fuel cell derived by the impedance deriving unit, and based on the obtained voltage, current, temperature, and impedance, the production reaction rate and the reduction reaction rate are calculated. Derived fuel cell system. According to the fuel cell system described in Application Example 2, the rate of catalytic oxide film is determined by deriving the production reaction rate and the reduction reaction rate based on the voltage, current, temperature, and impedance, and determining the production rate of the catalyst oxide. Can be derived with high accuracy.

[Application Example 3]
The fuel cell system according to Application Example 2, wherein the current-voltage characteristic deriving unit has a plurality of values corresponding to factors that cause the output voltage of the fuel cell to decrease with respect to the theoretical electromotive force, The current-voltage characteristic is derived by expressing the output voltage of the fuel cell by expressing a value having a current as a variable as a value obtained by subtracting the value from the theoretical electromotive force as a value among the plurality of values. One of the values other than the value having the current as a variable has the catalyst oxide film ratio as a variable and is a value approximating the degree of voltage drop caused by the oxide film of the catalyst. According to the fuel cell system described in Application Example 3, the current-voltage characteristics are derived by approximating the degree of voltage drop due to the oxide film of the catalyst using the accurately obtained catalyst oxide film rate, The accuracy of estimation of current-voltage characteristics can be improved.

[Application Example 4]
The fuel cell system according to Application Example 3, wherein the current-voltage characteristic deriving unit subtracts a plurality of values corresponding to factors that cause the output voltage of the fuel cell to be lower than the theoretical electromotive force from the theoretical electromotive force. Is an expression that the value is the output voltage of the fuel cell, and each term representing the value corresponding to the factor has a coefficient, and is obtained by the catalytic oxide film rate and the voltage acquisition unit. A fuel cell system that derives the current-voltage characteristics by determining each coefficient as a value that satisfies the equation based on the output voltage obtained and the output current obtained by the current obtaining unit. According to the fuel cell system described in Application Example 4, the current-voltage characteristics are obtained by performing the fitting to obtain each coefficient as a value that satisfies the above formula based on the catalytic oxide film ratio, the voltage, and the current. Can be derived with high accuracy.

[Application Example 5]
5. The fuel cell system according to Application Example 3 or 4, wherein one of the values having the current as a variable is a value corresponding to an activation overvoltage and a value expressed as a logarithm term of the current. . According to the fuel cell system described in Application Example 5, by expressing the activation overvoltage as a logarithmic term of the current, it is possible to improve the accuracy of deriving the current-voltage characteristics.

[Application Example 6]
The fuel cell system according to any one of Application Examples 2 to 5, further comprising an impedance storage unit that stores an impedance of the fuel cell when power generation is stopped when the fuel cell stops power generation. And the temperature acquisition unit continue to acquire the voltage or temperature of the fuel cell until the voltage of the fuel cell becomes 0, even after the fuel cell stops generating power, and the catalytic oxide film The rate deriving unit includes the impedance stored in the impedance storage unit, the voltage acquired by the voltage acquisition unit, and the temperature acquisition unit until the voltage of the fuel cell becomes 0 after the fuel cell stops power generation. The catalyst oxide film rate is repeatedly derived based on the temperature acquired by the fuel cell system, and the fuel cell system further stops the power generation by the fuel cell. A catalyst oxide film rate storage unit for storing the catalyst oxide film rate when the voltage of the fuel cell becomes 0 after the current, and the current-voltage characteristic deriving unit starts the power generation again by the fuel cell. Sometimes, the fuel cell system derives the current-voltage characteristics using the catalyst oxide film ratio stored in the catalyst oxide film ratio storage unit. According to the fuel cell system described in the application example 6, in order to derive the catalytic oxide film rate even after the fuel cell generates power, when starting the power generation of the fuel cell again, a value closer to the actual value is set as the catalyst. It can be used as an oxide film rate. Therefore, when the power generation of the fuel cell is temporarily stopped during the operation of the fuel cell system, or when the power generation of the fuel cell is restarted after the fuel cell system is stopped, the accuracy of deriving the current-voltage characteristic is improved. Can do.

  The present invention can be realized in various forms other than those described above. For example, a mobile body equipped with a fuel cell system, a control method for the fuel cell system, or a method for learning a current-voltage characteristic of the fuel cell. Can be realized.

1 is a block diagram illustrating a schematic configuration of an electric vehicle 10. 2 is an explanatory diagram illustrating an outline of a configuration of a fuel cell system 20. FIG. It is a flowchart showing an output control processing routine. 6 is an explanatory diagram of an operation point determination operation in the fuel cell 60. FIG. It is a conceptual diagram for demonstrating the influence of the platinum oxide film with respect to an electric current-voltage characteristic. It is a flowchart showing an IV characteristic estimation processing routine.

A. Overall configuration of the device:
FIG. 1 is a block diagram showing a schematic configuration of an electric vehicle 10 equipped with a fuel cell system 20 as an embodiment of the present invention. The electric vehicle 10 includes a drive motor 32, a high-voltage auxiliary machine 40, and a low-voltage auxiliary machine 46 as loads that consume electric power. A power supply system 15 is provided as a power supply for supplying power to these loads. A wiring 50 is provided between the power supply system 15 and the load, and power is exchanged between the power supply system 15 and the load via the wiring 50.

  The power supply system 15 includes a fuel cell system 20 and a secondary battery 26. The fuel cell system 20 includes a fuel cell 60 that is a main body of power generation, and a control unit 48. In the present embodiment, the control unit 48 not only functions as a component of the fuel cell system 20 for controlling the fuel cell system 20, but also controls the entire power supply system 15 including the secondary battery 26, and an electric vehicle. 10 parts are controlled. The fuel cell system 20 further includes a voltage sensor 52 for measuring the output voltage of the fuel cell 60, a current sensor 53 for detecting the output current of the fuel cell 60, and an impedance for detecting the impedance of the fuel cell 60. AC impedance measurement unit 54. The AC impedance measurement unit 54 detects the AC current flowing between the bipolar terminals when the AC voltage is input to the bipolar terminals of the fuel cell 60 while sweeping the frequency thereof, whereby the AC impedance between the positive and negative bipolar terminals is detected. It is a well-known device for measuring. The secondary battery 26 is connected to the wiring 50 via the DC / DC converter 28, and the DC / DC converter 28 and the fuel cell 60 are connected in parallel to the wiring 50.

  FIG. 2 is an explanatory diagram showing the outline of the configuration of the fuel cell system 20 and related to the supply and discharge of gas to the fuel cell 60. First, the fuel cell system 20 will be described with reference to FIG. The fuel cell system 20 includes a fuel cell 60, a fuel gas supply unit 61, and a blower 64. Although various types of fuel cells 60 can be applied, in this embodiment, a polymer electrolyte fuel cell is used as the fuel cell 60. The fuel cell 60 has a stack configuration in which a plurality of single cells are stacked. In this embodiment, the single cell includes an MEA (Membrane Electrode Assembly), a gas diffusion layer, and a gas separator. Here, the MEA includes an electrolyte membrane and an anode and a cathode that are electrodes formed on each surface of the electrolyte membrane. The MEA is sandwiched between gas diffusion layers, and the sandwich structure composed of MEA and gas diffusion layers is sandwiched between gas separators from both sides.

  The electrolyte membrane constituting the MEA is a proton conductive ion exchange membrane formed of a solid polymer material, for example, a fluorine-based resin, and exhibits good electrical conductivity in a wet state. The cathode and the anode are layers formed on the electrolyte membrane, and include carbon particles supporting a catalytic metal (for example, platinum) that progresses an electrochemical reaction, and a polymer electrolyte having proton conductivity. In order to form the cathode and the anode, for example, carbon particles supporting a catalyst metal such as platinum are prepared, and the catalyst supporting carbon is mixed with an electrolyte similar to the electrolyte constituting the electrolyte membrane to form a catalyst paste. The prepared catalyst paste may be applied on the electrolyte membrane.

  The gas diffusion layer is formed of a member having gas permeability and electronic conductivity, and may be formed of, for example, a metal member such as foam metal or metal mesh, or a carbon member such as carbon cloth or carbon paper. it can. The gas separator is formed of a gas-impermeable conductive member, for example, a carbon-made member such as dense carbon that has been made gas-impermeable by compressing carbon, or a metal member such as press-formed stainless steel. The gas separator forms a flow path of fuel gas containing hydrogen (intra-cell fuel gas flow path) between the anode of the MEA and the flow path of oxidizing gas containing oxygen between the cathode of the MEA. (In-cell oxidizing gas flow path) is formed. The surface of the gas separator may have irregularities for forming the above-described gas flow path in the cell, or for forming the gas flow path in the cell between the gas separator and the gas diffusion layer. A porous body may be disposed.

  An inter-cell refrigerant flow path is further formed inside the fuel cell 60. Such a refrigerant flow path can be formed, for example, between all the stacked single cells, specifically, between adjacent gas separators constituting different single cells. Alternatively, an inter-cell refrigerant flow path may be formed between gas separators every time a predetermined number of single cells are stacked.

  Further, the fuel cell 60 is formed with a plurality of flow paths that penetrate the fuel cell 60 in the stacking direction. Specifically, a fuel gas supply manifold for distributing fuel gas to each in-cell fuel gas flow path, and a fuel gas discharge manifold for collecting exhaust fuel gas discharged from each in-cell fuel gas flow path are formed. Has been. In addition, an oxidizing gas supply manifold for distributing the oxidizing gas to the in-cell oxidizing gas flow paths and an oxidizing gas discharge manifold for collecting the exhaust oxidizing gases discharged from the in-cell oxidizing gas flow paths are formed. . Furthermore, a refrigerant supply manifold for distributing the refrigerant to the inter-cell refrigerant flow paths and a refrigerant discharge manifold for collecting the refrigerant discharged from the inter-cell refrigerant flow paths are formed.

  In the fuel cell 60 described above, when the fuel gas is supplied to the anode side and the oxidizing gas is supplied to the cathode side, the electrochemical reactions shown in the following formulas (1) to (3) proceed. Formula (1) indicates a reaction that proceeds at the anode, Formula (2) indicates a reaction that proceeds at the cathode, and in the fuel cell 60 as a whole, the reaction expressed by Formula (3) proceeds.

H ₂ → 2H ⁺ + 2e ⁻ (1)
(1/2) O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O (2)
H ₂ + (1/2) O ₂ → H ₂ O (3)

  Further, the fuel cell 60 is provided with a temperature sensor 67 for measuring the internal temperature of the fuel cell 60. The temperature sensor 67 can be, for example, a refrigerant temperature sensor provided at the outlet portion of the refrigerant passage described above (an end portion of the refrigerant discharge manifold). Alternatively, the temperature sensor 67 may be configured by a sensor that directly measures the internal temperature of the fuel cell 60, for example, a thermocouple.

  The fuel gas supply unit 61 is a device for supplying a hydrogen-containing gas as a fuel gas to the fuel cell 60, and stores hydrogen therein. For example, the fuel gas supply unit 61 may include a hydrogen cylinder or a hydrogen tank having a hydrogen storage alloy inside. The stored hydrogen gas is supplied to the anode of the fuel cell 60 through the hydrogen gas supply path 62, and the anode offgas discharged from the anode is guided to the anode offgas path 63 and flows into the hydrogen gas supply path 62 again. . In this way, the remaining hydrogen gas in the anode off-gas circulates in the flow path and is used again for the electrochemical reaction. The anode off gas passage 63 is provided with a gas-liquid separator 21, and an opening / closing valve 22 is provided in a flow path for discharging water separated by the gas-liquid separator 21 to the outside. By opening the on-off valve 22 at a predetermined timing, impurities (such as water vapor and nitrogen) other than hydrogen in the fuel gas circulating in the flow path can be discharged out of the flow path and supplied to the fuel cell 60. An increase in impurity concentration in the generated hydrogen gas can be suppressed. Further, the anode off gas passage 63 is provided with a hydrogen pump 69 that generates a driving force for circulating the fuel gas in a circulation passage constituted by the hydrogen gas supply passage 62 and the anode off gas passage 63.

  The blower 64 is a device for supplying pressurized air as an oxidizing gas to the cathode side of the fuel cell 60 via the oxidizing gas supply path 65. The cathode exhaust gas discharged from the cathode side of the fuel cell 60 is guided to the cathode exhaust gas channel 66 and discharged to the outside. In the hydrogen gas supply path 62 and the oxidizing gas supply path 65, a humidifier that humidifies hydrogen gas or air may be further provided.

  Returning to FIG. 1, the secondary battery 26 can be composed of various secondary batteries such as a lead storage battery, a nickel-cadmium storage battery, a nickel-hydrogen storage battery, and a lithium secondary battery. Further, as shown in FIG. 1, the secondary battery 26 is provided with a remaining capacity monitor 27 for detecting the remaining capacity (SOC) of the secondary battery 26. In the present embodiment, the remaining capacity monitor 27 is configured as an SOC meter that integrates the charging / discharging current value and time in the secondary battery 26. Alternatively, the remaining capacity monitor 27 may be configured by a voltage sensor instead of the SOC meter. Since the secondary battery 26 has the property that the voltage value decreases as the remaining capacity thereof decreases, the remaining capacity of the secondary battery 26 can be detected by measuring the voltage.

  When the remaining capacity of the secondary battery 26 falls below a predetermined value, the secondary battery 26 is charged by the fuel cell 60. Further, when the electric vehicle 10 is braked (when the driver depresses the brake when the vehicle is running), the kinetic energy of the axle is converted into electric energy by using the drive motor 32 as a generator. The secondary battery 26 can be charged with the obtained electric energy.

  The DC / DC converter 28 adjusts the voltage in the wiring 50 by setting a target voltage value on the output side, thereby adjusting the output voltage from the fuel cell 60 and controlling the output power of the fuel cell 60. The DC / DC converter 28 also serves as a switch for controlling the connection state between the secondary battery 26 and the wiring 50, and when the secondary battery 26 does not need to be charged / discharged, The connection with the wiring 50 is disconnected.

  The drive motor 32, which is one of the loads that receive power from the power supply system 15, is a synchronous motor and includes a three-phase coil for forming a rotating magnetic field. The drive motor 32 is supplied with power from the power supply system 15 via the drive inverter 30. The drive inverter 30 is a transistor inverter provided with a transistor as a switching element corresponding to each phase of the drive motor 32. An output shaft 36 of the drive motor 32 is connected to a vehicle drive shaft 38 via a reduction gear 34. The reduction gear 34 transmits the power output from the drive motor 32 to the vehicle drive shaft 38 after adjusting the rotational speed.

  The high-voltage auxiliary machine 40 is a device that uses the power supplied from the power supply system 15 with a voltage of about 300V. In FIG. 1, the high-voltage auxiliary machine 40 is shown outside the power supply system 15 as a load supplied with power from the power supply system 15, but the high-voltage auxiliary machine 40 includes a fuel cell that constitutes the fuel cell system 20. Auxiliary equipment is also included. Specific examples of the fuel cell auxiliary device included in the high-pressure auxiliary device 40 include a blower 64 and a hydrogen pump 69 (see FIG. 2). Further, a cooling pump (not shown) for circulating cooling water inside the fuel cell 60 in order to cool the fuel cell 60 is also included in the fuel cell auxiliary machine. Or when using a radiator in order to cool the said cooling water, the radiator fan with which a radiator is provided is also contained in a fuel cell auxiliary machine. Examples of the high-pressure auxiliary machine 40 not included in the fuel cell system 20 include vehicle auxiliary machines such as air-conditioning equipment (air conditioner) provided in the electric vehicle 10.

  The low-voltage auxiliary machine 46 is a load having a low drive voltage unlike the drive motor 32 and the high-voltage auxiliary machine, and is supplied with electric power whose voltage is reduced to about 12 V by the step-down DC / DC converter 44 connected to the wiring 50. In FIG. 1, the low-pressure auxiliary machine 46 is shown outside the power supply system 15 as a load supplied with power from the power supply system 15, but the low-pressure auxiliary machine 46 includes a fuel cell constituting the fuel cell system 20. Auxiliary equipment is also included. Specifically, the fuel cell auxiliary machine included in the low pressure auxiliary machine 46 includes a flow rate adjusting valve provided in a flow path for supplying and discharging fuel gas, oxidizing gas, and cooling water to the fuel cell 60, and the on-off valve 22 (see FIG. 2). When the voltage of the wiring 50 fluctuates, the step-down DC / DC converter 44 is driven based on the detection signal of the voltage sensor 52, and the voltage when supplying power to the low-voltage auxiliary machine 46 is kept substantially constant.

  In addition, the control unit 48 described above is configured as a logic circuit centered on a microcomputer, and more specifically, a CPU that executes predetermined calculations in accordance with a preset control program, and various arithmetic processes performed by the CPU. A ROM in which control programs and control data necessary for data storage are stored in advance, a RAM in which various data necessary for various calculation processes by the CPU are temporarily read and written, and an input / output device for inputting and outputting various signals. An output port is provided. As described above, the control unit 48 not only functions as a component of the fuel cell system 20 for controlling the fuel cell system 20, but also controls the entire power supply system 15 including the secondary battery 26, Each part of the electric vehicle 10 is controlled. Specifically, the control unit 48 acquires signals output from the voltage sensor 52, the remaining capacity monitor 27, and the temperature sensor 67 described above. Furthermore, the control part 48 acquires the information regarding driving | operation of vehicles, such as an accelerator opening degree and a vehicle speed (not shown). The control unit 48 outputs a drive signal to each unit of the power supply system 15 and each unit related to the operation in the vehicle. Specifically, the DC / DC converter 28, the drive inverter 30, the high voltage auxiliary machine 40, the step-down DC / DC converter 44, and each part of the fuel cell system 20 (fuel gas supply unit 61, blower 64, hydrogen pump 69, opening and closing A drive signal is output to the valve 22) and the like. Note that the control unit 48 that performs the above-described function does not need to be configured as a single control unit. For example, the control unit 48 is configured by a plurality of control units such as a control unit related to the operation of the fuel cell system 20, a control unit related to driving of the electric vehicle 10, and a control unit that controls vehicle auxiliary equipment not related to driving. However, necessary information may be exchanged between the plurality of control units.

B. Outline of operation point determination:
FIG. 3 shows an output control processing routine repeatedly executed at predetermined intervals by the CPU of the control unit 48 while a predetermined start switch is operated in the electric vehicle 10 and operation using the power supply system 15 is performed. It is a flowchart showing.

  When this routine is executed, the CPU of the controller 48 determines whether or not it is during braking (step S100). When determining that it is not during braking, the CPU of the control unit 48 acquires detection signals from various sensors provided in the electric vehicle 10 (step S110). In step S100, in addition to a detection signal related to a load request related to driving of the vehicle (hereinafter also simply referred to as a load request), a signal related to a load request related to the vehicle auxiliary equipment (for example, the vehicle auxiliary equipment is currently consuming). A signal related to the amount of electric power or a signal related to an instruction input by the user to change the operation of the vehicle auxiliary machine is also acquired. Specific examples of the detection signal related to the load request relating to the driving of the vehicle include detection signals output from an accelerator opening sensor and a vehicle speed sensor.

  Thereafter, the CPU of the control unit 48 calculates power to be supplied to the drive motor 32 (hereinafter referred to as drive motor required power) based on the detection signal related to the load request acquired in step S110 (step S120). Specifically, the required drive torque in the drive motor 32 is derived based on the accelerator opening (accelerator acceleration). Then, by integrating the derived required drive torque and the rotation speed of the drive motor 32 derived from the vehicle speed, the drive motor power requirement can be obtained.

  After calculating the drive motor power requirement, the control unit 48 next calculates the power system target power that is the power that the power system 15 should output (step S130). The power system target power is obtained by adding the required power in the load (for example, vehicle auxiliary machine) other than the fuel cell auxiliary machine to the required power of the driving motor, and the total amount of power to be output by the power supply system 15 It is. The controller 48 of this embodiment functions as a load request acquisition unit that acquires a load request for the fuel cell in the above-described steps S110 to S130.

  After calculating the power supply system target power, the CPU of the control unit 48 next determines the operating point of the fuel cell 60 based on the value of the power supply system target power (step S140). That is, in this embodiment, the control is performed on the assumption that the power system target power is output only from the fuel cell system 20, and in step S140, the fuel cell 60 for outputting the power system target power from the fuel cell system 20 is used. Determine the operating point (output current and output voltage). At this time, the control unit 48 functions as an operation point setting unit that sets an operation point of the fuel cell for generating electric power corresponding to the load request based on the current-voltage characteristic of the fuel cell 60. Then, the control unit 48 outputs a drive signal to each part of the power supply system 15 so that the operation point in the fuel cell 60 becomes the point determined in step S140 (step S150), and ends this routine.

FIG. 4 is an explanatory diagram for conceptually explaining the operation of determining the operating point of the fuel cell 60 in step S140. FIG. 4 shows the relationship between the output current and the output power in the fuel cell 60 and the relationship between the output current and the output voltage. In the following description, the property that the output current and the output voltage have a certain relationship as shown in FIG. 4 in the fuel cell 60 is referred to as a current-voltage characteristic (IV characteristic). As shown in FIG. 4, the fuel cell 60, if Sadamare power P _FC to be output, the magnitude I _FC of the output current at that time is determined. Further, if the output current I _FC is determined from the current-voltage characteristics of the fuel cell 60, the output voltage V _{FC at} that time is determined. In step S140, the CPU of the control unit 48 determines the output current and output voltage of the fuel cell 60 as the operating point of the fuel cell 60 that can output the power system target power determined in step S130 from the fuel cell system 20. Yes. In step S150, the CPU of the control unit 48 outputs a drive signal to the DC / DC converter 28 so that the output voltage determined in step S140 becomes the output-side target voltage.

In addition, when the fuel cell 60 generates power, the fuel cell auxiliary machine described above consumes electric power. The electric power output by the fuel cell system 20 is electric power obtained by subtracting the electric power consumed by the fuel cell auxiliary machine from the power generation amount of the fuel cell 60. Since the power consumption in the fuel cell auxiliary machine is determined according to the power generation amount of the fuel cell 60, in step S140, the output of the fuel cell 60 is output based on the power system target power in consideration of the power consumption in the fuel cell auxiliary machine. Power and operating points are defined. In step S150, the CPU of the control unit 48 causes the blower 64, the hydrogen pump 69, and the fuel gas supply unit to supply the fuel cell 60 with an amount of gas corresponding to the power to be generated by the fuel cell 60. A drive signal is output to 61 etc. Thus, by driving the DC / DC converter 28 so that the voltage of the wiring 50 (the output voltage of the fuel cell 60) becomes the output voltage V _FC, and supplying a sufficient amount of gas to the fuel cell 60, The fuel cell system 20 outputs the power determined in step S130.

As shown in FIG. 4, the fuel cell 60 exhibits a constant current-voltage characteristic, but this current-voltage characteristic varies depending on various factors. For example, the current-voltage characteristic varies depending on the temperature, and the control unit 48 stores the current-voltage characteristic for each temperature and appropriately detects the temperature according to the detection signal of the temperature sensor 67. Control is performed by selecting the corresponding current-voltage characteristics. When such a control is performed, for example, when an error in the temperature detection operation increases, the current-voltage characteristic used for the control is deviated from the actual current-voltage characteristic. Further, as will be described later, an error may occur in the current-voltage characteristics used by the oxidation reaction that proceeds with the electrode catalyst in the fuel cell 60. As described above, when an error occurs in the current-voltage characteristics used for the control, even if the output voltage of the fuel cell 60 is controlled to V _FC by the DC / DC converter 28, the output power from the fuel cell 60 is desired. The power system target power will not be reached. Thus, when an error occurs between the output power from the fuel cell 60 and the power supply system target power, the generated error is absorbed by the secondary battery 26 connected in parallel with the fuel cell 60. . That is, when the power generation amount of the fuel cell 60 is insufficient, the secondary battery 26 outputs the shortage amount. When the power generation amount of the fuel cell 60 is excessive, the secondary battery 26 is charged by the excess amount. The

  When it is determined in step S100 that the vehicle is braking, the control unit 48 selects the regenerative operation mode (step S160) and ends this routine. Here, the regenerative operation mode is an operation mode in which the kinetic energy of the axle is converted into electric energy by using the drive motor 32 as a generator, thereby charging the secondary battery 26. In the regenerative operation mode, power is supplied from the drive motor 32 side to the wiring 50 via the drive inverter 30, and this power is further supplied to the secondary battery 26 via the DC / DC converter 28. Is charged.

  In the above-described embodiment, the operating point of the fuel cell 60 is set so that all the power supply system target power calculated in step S130 is output from the fuel cell system 20, but a different configuration may be used. For example, the operation point of the fuel cell 60 may be set by outputting a part of the power system target power from the secondary battery 26.

  Further, when the remaining capacity of the secondary battery 26 detected by the remaining capacity monitor 27 is lower than the reference value, control for charging the secondary battery 26 by the fuel cell 60 may be performed. In this case, in step S130, the power for charging the secondary battery 26 may be further added to set the power supply system target power.

C. Behavior for estimating changing VI characteristics:
As described above, the setting of the operating point of the fuel cell 60 for controlling the output from the power supply system 15 is performed based on the current-voltage characteristics of the fuel cell 60. It varies depending on factors. In the fuel cell system 20 of the present embodiment, the current current-voltage characteristic is always estimated, and the operating point of the fuel cell 60 is set based on the estimated current-voltage characteristic. In particular, in this embodiment, the ratio of the area where the oxide film is formed (platinum oxide film ratio θ) to the surface area of platinum, which is the catalyst included in the cathode of the fuel cell 60, was repeatedly estimated over time and estimated. It is characterized in that current-voltage characteristics are derived (learned) based on the platinum oxide film ratio θ.

  When the fuel cell generates electric power, a reaction in which an oxide film is formed on the platinum surface and a reaction in which the oxide film is reduced progress in platinum (Pt) included in the cathode. When the oxide film formation reaction proceeds faster than the oxide film reduction reaction, the oxide film increases on the platinum surface, and when the oxide film reduction reaction proceeds faster than the oxide film formation reaction, the platinum film The oxide film is reduced on the surface. Factors affecting the rate at which each of these oxide film formation reaction and reduction reaction proceeds mainly include the output voltage, output current, temperature, and impedance of the fuel cell. Below, as a formula (4), a typical example of the oxidation-reduction reaction which advances in platinum with which a cathode is provided is shown.

  FIG. 5 is a conceptual diagram for explaining the influence of the platinum oxide film on the current-voltage characteristics of the fuel cell. In FIG. 5, the output when the output current from the fuel cell is varied between 0 and a predetermined value while supplying a sufficient amount of fuel gas and oxidizing gas to the fuel cell while keeping the temperature of the fuel cell constant. The relationship between current and output voltage is shown. As shown in FIG. 5, the operating point of the fuel cell comprising a combination of current and voltage is to gradually increase the output current from the fuel cell from 0 to a predetermined value, and then gradually decrease the output current to 0 again. It falls within the range surrounded by the current-voltage curve. That is, the operating point that is a combination of the output current and output voltage of the fuel cell exhibits hysteresis. Such hysteresis at the operating point of the fuel cell is due to the property that the platinum oxide film ratio θ in the current cathode catalyst is determined by the past power generation history. Specifically, the current platinum oxide film production rate (reduction rate) is determined by the current operating point, but the current platinum oxide film rate θ is the current platinum oxide film production rate (reduction rate). Since it is an integrated value, the platinum oxide film ratio θ shows hysteresis. In this example, the current platinum oxidation-reduction reaction rate is obtained over time based on the output voltage, output current, temperature, and impedance of the fuel cell, and the obtained platinum oxidation-reduction reaction rate is integrated over time. Thus, the current platinum oxide film ratio θ is obtained.

  FIG. 6 is a flowchart illustrating an IV characteristic estimation processing routine that is repeatedly executed at predetermined intervals by the CPU of the control unit 48 while the electric vehicle 10 is being operated using the power supply system 15.

  When this routine is executed, the CPU of the control unit 48 acquires the output current, output voltage, temperature, and impedance of the fuel cell 60 (step S200). Here, the output current, the output voltage, the temperature, and the impedance are acquired as detection signals of the current sensor 53, the voltage sensor 52, the temperature sensor 67, and the AC impedance measurement unit 54, respectively. Thereafter, the CPU of the control unit 48 obtains a platinum oxide film ratio θ in platinum included in the cathode of the fuel cell 60 based on the output current, output voltage, temperature, and impedance of the fuel cell 60 acquired in Step S200 (Step S200). S210).

Here, in the platinum provided in the cathode, the rate r [mol / s / cm ² ] of the platinum oxidation-reduction reaction that proceeds per unit time per platinum unit area can be expressed by the following formula (5). Further, the relationship between the platinum oxidation-reduction reaction rate r and the platinum oxide film ratio θ can be expressed by the following equation (6).

In Expression (5), k represents a conversion coefficient. αa and αc represent charge transfer coefficients in the rightward (oxidation) or leftward (reduction) reaction in Formula (4), respectively. n represents the number of reaction electrons in the reaction shown in Formula (4). F represents a Faraday constant, and R represents a gas constant. U ₂ represents an equilibrium potential in the oxidation-reduction reaction of platinum represented by the formula (4). These values are stored in the control unit 48 in advance. In Formula (6), Γ _max represents the number of moles of platinum used for the reaction per unit platinum surface area (the number of moles of the total amount of platinum that can contribute to the reaction). In this embodiment, Γ _max is stored in the control unit 48 as a value obtained experimentally in advance. C _{H +} represents the proton concentration, specifically, the proton concentration in the polymer electrolyte provided in the cathode. Also, T is represents the temperature, V is representative of the output voltage, R _Omega represents the impedance, I is representative of the output current.

Equation (5) is based on the well-known Butler-Volmer equation representing the relationship between potential and current density. In equation (5), the first term on the right side represents the reaction rate of the oxidation reaction of platinum that proceeds to the right in equation (4), and the second term on the right side represents the reduction of platinum oxide that proceeds to the left in equation (4). The reaction rate of the reaction is shown. In the Butler-Volmer equation, the rate of the oxidation reaction or the reduction reaction is represented by the current density. Therefore, in the equation (5), the reaction rate represented by the current density is expressed in [mol / s / cm ² ] as a unit. The conversion factor k is used to convert the reaction rate into the reaction rate. In addition, in the oxidation-reduction reaction of platinum, the ease of the rightward oxidation reaction in formula (4) and the ease of the leftward reduction reaction in formula (4) depend on the platinum oxide film ratio in platinum provided in the cathode. Influenced by θ. Specifically, the reaction rate of the leftward reduction reaction in the equation (4) increases as the platinum oxide film rate θ increases, and the reaction of the rightward oxidation reaction in the equation (4) decreases as the platinum oxide film rate θ decreases. Increases speed. Therefore, in equation (5), in order to reflect the influence of the platinum oxide film rate θ at each reaction rate, (1-θ) is added as a coefficient to the first term on the right side representing the reaction rate of the platinum oxidation reaction. In the second term on the right side representing the reduction reaction of platinum oxide, θ is given as a coefficient. The oxidation-reduction reaction of platinum is affected by the proton concentration at the cathode. Specifically, the higher the proton concentration at the cathode, the greater the reaction rate of the leftward reduction reaction in equation (4). Therefore, in the formula (5), the proton concentration C _{H +} is added as a coefficient to the second term on the right side representing the reduction reaction of platinum oxide.

Formula (6) shows that the rate of change of the platinum oxide film ratio θ is a value obtained by dividing the rate r of the platinum redox reaction by the number of moles Γ _max of the total amount of platinum that can contribute to the reaction per unit platinum surface area. It represents. That is, it represents that the platinum oxide film ratio θ is obtained by integrating the value on the right side of the equation (6) on the time axis. More specifically, when the platinum oxide film rate θ is repeatedly derived, the current platinum oxidation-reduction reaction rate r (the current amount or decrease of the platinum oxide film produced) is reduced with respect to the previously derived platinum oxide film rate θ. This indicates that the current platinum oxide film ratio θ can be obtained by adding (quantity).

In step S210, the platinum oxide film ratio θ is derived based on the above formulas (5) and (6). Specifically, I of equation (5), V, to T, R _Omega, respectively, by substituting the output current of the obtained fuel cell 60, output voltage, temperature, and the impedance in step S200, equation (5) and The platinum oxide film ratio θ is calculated as a value satisfying the formula (6). In equation (5), the value of proton concentration C _{H +} may be calculated sequentially after obtaining the water transfer amount in the electrolyte based on the water vapor concentration in the gas supplied or exhausted and the amount of power generation. In this embodiment, however, constants that are derived by fitting based on actually measured data and stored in the control unit 48 in advance are used.

  When the platinum oxide film ratio θ is calculated, the CPU of the control unit 48 estimates the current IV characteristics based on the platinum oxide film ratio θ, the output current I, and the output voltage V (step S220). Exit. An equation representing the IV characteristic derived in step S220 is shown as equation (7) below.

U ₁ which is the first term on the right side of Equation (7) represents the theoretical electromotive force in the electrochemical reaction represented by Equation (3). “R _Ω · I”, which is the second term on the right side of Equation (7), represents a resistance overvoltage. “A · ln (1-θ)”, which is the third term on the right side of Equation (7), is a term that approximates the degree to which the voltage decreases due to the platinum oxide film ratio θ. “C · ln (I)”, which is the fifth term on the right side of Equation (7), represents an activation overvoltage. “B · I” that is the fourth term on the right side of Equation (7) and “d” that is the sixth term on the right side, that is, the portion expressed as the primary equation is caused by the overvoltage and the platinum oxide film described above. This represents a voltage drop caused by a different factor from the voltage drop. For example, in the fuel cell 60, if the power generation is continued, the irreversible deterioration of the electrode due to the gradual oxidation of carbon carrying platinum proceeds, but the equation (7) in this embodiment Then, the voltage drop due to such carbon oxidation is represented by the above-mentioned primary expression portion.

  Thus, in Expression (7), the output voltage V is represented as a value obtained by subtracting the voltage drop due to various factors from the theoretical electromotive force. The right side of Expression (7) has an output current I as a variable. In this embodiment, the current-voltage characteristic of the fuel cell 60 is expressed by Expression (7). a, b, c, d are parameters for enabling the output voltage V to be expressed based on the above-described concept.

  In step S220, the platinum oxide film ratio θ derived in step S210 and the output current I and output voltage V acquired in step S200 are substituted into equation (7), thereby expressing the current current-voltage characteristics. a, b, c, d are obtained. In order to derive the parameters a, b, c, and d in step S220, a sequential parameter estimation algorithm, for example, a sequential least square method is used. Sequential least squares method is a method of acquiring past data repeatedly in time series and correcting the previous parameter estimated value by fitting based on the new data each time new data is obtained. This is a well-known online (real-time) estimation algorithm that attempts to obtain the same effect as fitting to all data.

  When setting the operation point of the fuel cell 60 in step S140 of the output control processing routine described above, the value derived in step S220 of the IV characteristic estimation processing routine is set as the parameter a, the current-voltage characteristic of the fuel cell 60. Equation (7) substituted for b, c, and d is used. Specifically, the driving point may be obtained as follows. Expression (8) shown below is an expression obtained by multiplying both sides of Expression (7) by the output current I. In Expression (8), W represents the output power of the fuel cell 60.

As shown in Expression (8), the output from the fuel cell 60 can represent the output current I as a variable. In step S140, the power system target power calculated in step S130 is substituted as the output power W in the equation (8), the value derived in step S210 is substituted as the platinum oxide film ratio θ, and the impedance _RΩ is obtained. The obtained latest impedance value is substituted, and the values derived in step S220 are substituted for the parameters a, b, c, and d. Thereby, the target output current I of the fuel cell 60 for outputting the power system target power from the fuel cell 60 can be calculated. Based on the power system target power and the target output current I, the target output voltage V of the fuel cell 60 for outputting the power system target power from the fuel cell 60 can be calculated. Thereby, the operating point of the fuel cell 60 can be set.

  Note that when the regenerative operation mode is selected in step S160 shown in FIG. 3, if the amount of regenerative power is sufficient, the fuel cell 60 does not generate power. However, the learning operation for deriving the platinum oxide film ratio θ shown in FIG. 6 continues even when the fuel cell 60 does not generate power, that is, when the operating point of the fuel cell is not set. Just do it. In this case, in Expression (5), 0 is substituted for the output current I, and newly detected values are substituted for the output voltage V and the fuel cell temperature T, as in step S210. It is only necessary to continue to derive the platinum oxide film ratio θ. Thus, when the load demand increases again and the power generation of the fuel cell 60 is resumed, the current-voltage characteristics can be derived using the platinum oxide film ratio θ that has been continuously derived, and the operating point can be set. It becomes possible.

  According to the power supply system 15 including the fuel cell system 20 of the present embodiment configured as described above, the current-voltage is calculated based on the platinum oxide film rate θ obtained by deriving the platinum oxide film rate θ. The characteristics are estimated, and the operating point of the fuel cell 60 is set based on the estimated current-voltage characteristics. Therefore, it becomes possible to set the operating point of the fuel cell using current-voltage characteristics that are closer to the actual state, and the accuracy of the operation of outputting desired power from the fuel cell can be improved.

  In particular, the platinum oxide film ratio θ is not uniquely determined based merely on the current output voltage or the like, but is a value determined by the past history of fuel cell output. Therefore, the platinum oxide film ratio θ can be derived with high accuracy for the first time by continuously performing the operation of deriving the platinum oxide film ratio θ using the value reflecting the fuel cell output. In this example, when the platinum oxide film ratio θ is determined, the platinum oxidation-reduction reaction speed r, which is the difference between the reaction speed of the platinum oxidation reaction and the reaction speed of the reduction reaction, is integrated over time to obtain the platinum oxide film ratio. θ is obtained. Thereby, the hysteresis resulting from the platinum oxide film in the current-voltage characteristics of the fuel cell is accurately reflected, and the current current-voltage characteristics can be accurately derived.

  For example, a configuration in which the current-voltage characteristic of the fuel cell is approximated by a linear expression and the approximate expression is continuously corrected by learning based on the output current and output voltage of the fuel cell is also conceivable. However, the influence of the platinum oxide film ratio θ due to the platinum oxidation-reduction reaction rate r as the difference between the constantly changing platinum oxidation reaction rate and the reduction reaction rate cannot be sufficiently expressed by the linear equation. Therefore, if an attempt is made to approximate the entire current-voltage characteristic with a linear expression, the error due to the platinum oxide film ratio θ may become very large. In this example, when reflecting the influence of the platinum oxide film ratio θ on the current-voltage characteristics, as shown in the equation (7), (1−θ), that is, the region not covered with the platinum oxide film. Since the logarithmic term of the ratio is used, the accuracy of deriving the current-voltage characteristic in consideration of the platinum oxide film ratio θ can be further increased.

  As described above, the oxidation reaction rate and the reduction reaction rate of platinum always change with the change in the operating state of the fuel cell, and the resulting platinum oxide film ratio θ also always changes. Thus, the influence of the platinum oxide film ratio θ on the fuel cell operating point setting is influenced by other factors that affect the current-voltage characteristics of the fuel cell (for example, the temperature of the fuel cell, the amount of gas supplied, or the carbon content of the catalyst). Compared with the influence of (oxidation), it can be said that it is extremely large in a relatively short time. Therefore, when the output control of the fuel cell is repeatedly performed at short time intervals according to the load requirement, the improvement in the accuracy of the current-voltage characteristic derivation by considering the influence of the platinum oxide film ratio θ is In the output control accuracy, it has a great effect.

  As described above, the accuracy with which the derived current-voltage characteristic approaches a true value is increased, and the power closer to the desired power can be output from the fuel cell depending on the set operation point. Charging / discharging for absorbing the error can be suppressed. Here, when the secondary battery 26 is charged and discharged, heat loss occurs as a loss associated with charging and discharging. By suppressing charging / discharging of the secondary battery 26 due to the control error, heat loss in the secondary battery 26 can be suppressed, and the energy efficiency of the entire power supply system 15 can be increased. As a result, in the electric vehicle 10, fuel consumption can be improved.

  In this embodiment, the activation overvoltage is expressed as a logarithmic term of the output current I when the current-voltage characteristic is derived based on the equation (7). Thereby, the accuracy of deriving the current-voltage characteristic in consideration of the activation overvoltage can be greatly improved as compared with, for example, a configuration in which the current-voltage characteristic is approximated by a linear expression.

D. Variations:
The present invention is not limited to the above-described examples and embodiments, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.

D1. Modification 1:
In the embodiment, the current-voltage characteristics of the fuel cell 60 are derived based on the formula (7), but different configurations may be used. For example, overvoltage that lowers the output voltage with respect to the theoretical electromotive force includes concentration overvoltage in addition to resistance overvoltage and activation overvoltage. Since the concentration overvoltage has a relatively small relative influence except in the power generation state where the output current is large, the equation (7) in the embodiment does not take the concentration overvoltage into consideration. That is, the influence of the concentration overvoltage is included in the primary equation portion as a result. However, in Equation (7), a term representing the concentration overvoltage may be further provided as a term representing the voltage drop from the theoretical electromotive force U ₁ . An expression representing a current-voltage characteristic in consideration of the concentration overvoltage in Expression (7) is shown below as Expression (9). In equation (9), e is a parameter for fitting similar to a to d. The smaller the catalyst partial oxygen partial pressure (oxygen partial pressure in the vicinity of the cathode catalyst), the greater the concentration overvoltage, and the seventh term on the right side of equation (9) becomes smaller.

  An example of how to determine the catalyst partial oxygen partial pressure in equation (9) will be described below. When generating power in a steady state where the fuel cell 60 is sufficiently heated and supplied with a sufficient amount of gas, the oxygen flow rate from the in-cell oxidizing gas flow path to the vicinity of the catalyst is equal to the amount of oxygen consumed by power generation. it is conceivable that. The oxygen flow rate from the in-cell oxidizing gas channel to the vicinity of the catalyst is considered to be proportional to the difference between the oxygen partial pressure in the in-cell oxidizing gas channel (channel oxygen partial pressure) and the oxygen concentration in the vicinity of the catalyst. Therefore, when the proportionality constant is D, the following formula (10) is established. Therefore, from equation (10), equation (11) for determining the catalyst partial oxygen partial pressure is obtained. The proportional constant D between the oxygen diffusion rate and the oxygen partial pressure difference may be experimentally determined in advance and stored in the control unit 48.

  When obtaining the catalyst vicinity oxygen partial pressure based on the equation (11), the oxygen consumption amount by power generation can be calculated based on the current power generation amount in the fuel cell 60 and the equation (2). Further, the channel oxygen partial pressure can be obtained based on the following equation (12). In equation (12), the pressure of the oxidizing gas in the oxidizing gas flow channel in the cell is “air pressure”, the oxygen flow rate at the outlet of the oxidizing gas discharge manifold is “FC outlet oxygen flow rate”, and the discharge at the outlet of the oxidizing gas discharge manifold The flow rate of the oxidizing gas is described as “FC outlet air flow rate”, and the flow rate of the oxidizing gas flowing into the oxidizing gas supply manifold is described as “FC inlet air flow rate”.

  When the current-voltage characteristic is derived based on the equation (9) in step S220, a pressure sensor is further provided in the in-cell oxidizing gas channel or the channel communicating with the in-cell oxidizing gas channel. ", And the" FC inlet air flow rate "is always detected repeatedly by the flow rate sensor provided in the oxidizing gas flow path communicating with the fuel cell. Then, using these values, the flow channel oxygen partial pressure and the catalyst vicinity oxygen partial pressure are obtained based on the equations (12) and (11), and the equation (9) is obtained in the same manner as in the embodiment based on the equation (7). ) To derive the current-voltage characteristics.

D2. Modification 2:
In the derivation of the current-voltage characteristics based on the expression (7) in the embodiment, further different modifications may be made. For example, in equation (7), at least one of the resistance overvoltage and the activation overvoltage is not separately approximated as a term representing the voltage drop, but may be included in the primary equation portion for fitting. .

  The resistance overvoltage and the activation overvoltage are not values that change linearly in the same manner as the influence of the platinum oxide film ratio. Thus, by separately approximating the terms representing the voltage drop, the current-voltage characteristics can be derived. Accuracy can be improved. However, it is considered that the influence of the platinum oxide film ratio θ is the greatest to the extent that the influence of the change deviates from the linear expression among the factors that cause the voltage to drop. Therefore, in the expression representing the current-voltage characteristic as shown in Expression (7), the voltage drop caused by at least one of the three overvoltages, that is, the concentration overvoltage, the resistance overvoltage, and the activation overvoltage, As a result of inclusion in “b · I + d”, a term approximating the overvoltage may not be provided. Also in this case, among the voltage drop factors from the theoretical electromotive force, the voltage drop due to the platinum oxide film ratio θ is represented by a logarithmic term using the platinum oxide film ratio θ, and the voltage drop due to other factors. By representing at least one of these by a term having a current as a variable, it is possible to obtain the same effect as that of the embodiment in which the accuracy of deriving the current-voltage characteristic is improved.

D3. Modification 3:
Further, when deriving the current-voltage characteristics, a term different from the examples and the modifications already described may be used as a term that approximates an overvoltage that causes the voltage to drop from the theoretical electromotive force. For example, in the expression (7), the fifth term on the right side “c · lnI” is provided in order to express the influence caused by the activation overvoltage, but instead of the fifth term on the right side, “c · ln ( The term “I + i_n)” may be provided.

  The above “i_n” is an internal current. During power generation of the fuel cell, a phenomenon occurs in which hydrogen permeates through the electrolyte membrane from the anode side to the cathode side, and the permeated hydrogen reacts with oxygen at the cathode. When such a reaction is treated as an internal current and the hydrogen permeation amount is n “mol / s”, the internal current i_n can be expressed by the following equation (13).

i_n = n / (2F) [A] (13)
Where F is a Faraday constant.

  Therefore, the term representing the activation overvoltage can be “c · ln (I + i_n)”. The internal current i_n can be obtained, for example, by storing the hydrogen permeation amount in advance in the control unit 48 as a map of temperature and impedance and referring to the map using the detected temperature and impedance. Further, the hydrogen permeation amount varies depending on the degree of deterioration of the fuel cell (degree of deterioration of the electrolyte membrane). For this reason, the hydrogen permeation amount is obtained while learning so as to match the detected values of the output current, output voltage, etc. of the fuel cell, similarly to the equation (7) for fitting the parameters a, b, c, d. It is also good.

D4. Modification 4:
In the embodiment, the platinum oxide film ratio θ is sequentially derived, and the current current-voltage characteristics are derived based on the formula (7) using the derived platinum oxide film ratio θ. The operation for deriving the current-voltage characteristic using the coating rate θ may be different. For example, an IV curve as a current-voltage characteristic as shown in FIG. 4 (actually, several sequences as a combination of current and voltage) is obtained for each platinum oxide film ratio θ and for each temperature of the fuel cell. Prepared and stored in the control unit 48. In step S220, the current IV curve is selected from the stored IV curves according to the detected fuel cell temperature and the platinum oxide film ratio θ obtained in step S210, and the selected I-V curve is selected. The operation point setting may be controlled using the −V curve. If the operation point is set based on the current-voltage characteristic obtained from the sequentially derived platinum oxide film ratio θ, the operation point follows the short-term change in the current-voltage characteristic caused by the increase or decrease of the platinum oxide film. The same effect that improves the setting accuracy can be obtained.

D5. Modification 5:
In the embodiment, the operation for deriving the platinum oxide film ratio θ shown in FIG. 6 is continuously performed even during the period in which the regenerative operation mode is selected in step S160 and the power generation of the fuel cell 60 is not performed. Similarly, the operation for deriving the platinum oxide film ratio θ may be continued even when the power supply system 15 is stopped.

  That is, in the electric vehicle 10, when a predetermined stop switch is operated, the power supply from the power supply system 15 is stopped until the predetermined start switch is operated next time. After the electric vehicle 10 is instructed to stop in this way, in Expression (5), 0 is substituted for the output current I, and newly detected values are used for the output voltage V and the fuel cell temperature T. By substituting, it is sufficient to continue to derive the platinum oxide film ratio θ in the same manner as in step S210. After the fuel cell stops generating power, the voltage of the fuel cell gradually decreases from the open circuit voltage (OCV) to 0, but until the voltage reaches 0, it is affected by the voltage and temperature. The oxide film ratio θ varies. As described above, by continuously deriving the platinum oxide film rate θ even after the fuel cell stops power generation, the platinum oxide film rate θ when the voltage of the fuel cell becomes zero can be obtained. Thus, when the electric vehicle 10 is restarted and the power generation of the fuel cell 60 is resumed, the current-voltage characteristic is derived using the platinum oxide film ratio θ when the voltage becomes 0, and the operation point is accurately performed. Can be set.

  When the electric vehicle 10 is stopped, the platinum oxide film rate θ when the power generation of the fuel cell 60 is stopped is stored without repeating the above-described operation of deriving the platinum oxide film rate θ, and is stored when the electric vehicle 10 is restarted. The current-voltage characteristic deriving unit may be derived using the value. When the value at the time of stopping the power generation of the fuel cell 60 is used as the platinum oxide film ratio θ at the time of restarting, compared with the case where the platinum oxide film ratio θ is derived even after the power generation of the fuel cell 60 is stopped. There is a possibility that the operation point setting accuracy at the time of start-up is insufficient. However, the operation for repeatedly deriving the platinum oxide film ratio θ is started with the start of power generation, and learning control for fitting the current-voltage characteristics is started. Therefore, even when the platinum oxide film ratio θ when power generation of the fuel cell 60 is stopped is used, the accuracy of deriving the current-voltage characteristics is sufficiently increased during the warm-up operation of the fuel cell system after restarting. It becomes possible.

D6. Modification 6:
In the embodiment, platinum is used as the catalyst provided in the cathode, but a different configuration may be used. For example, a noble metal other than platinum may be used as the catalyst. Even when a catalyst other than platinum is used, depending on the electrode potential, battery performance may be reduced due to the formation of an oxide film on the catalyst. Therefore, the same effect as that of the embodiment can be obtained by deriving the catalytic oxide film ratio and estimating the current-voltage characteristics in the same manner as in the embodiment.

D7. Modification 7:
In the embodiment, the fuel cell system 20 is included in the power supply system 15 including the secondary battery 26, but may have a different configuration. For example, instead of the secondary battery 26 or in addition to the secondary battery 26, another type of battery (for example, a capacitor) may be provided. Alternatively, a power supply system that uses only a fuel cell as a power supply without providing a capacitor may be used.

D8. Modification 8:
In the embodiment, the fuel cell system 20 is used as a power source for driving an electric vehicle, but a different configuration may be used. A power source for driving a moving body other than the vehicle may be used, and the fuel cell system may be used as a stationary power source.

DESCRIPTION OF SYMBOLS 10 ... Electric vehicle 15 ... Power supply system 20 ... Fuel cell system 21 ... Gas-liquid separator 22 ... On-off valve 27 ... Remaining capacity monitor 28 ... DC / DC converter 30 ... Drive inverter 32 ... Drive motor 34 ... Reduction gear 36 ... Output shaft DESCRIPTION OF SYMBOLS 38 ... Vehicle drive shaft 40 ... High voltage auxiliary machine 44 ... Step-down DC / DC converter 46 ... Low voltage auxiliary machine 48 ... Control part 50 ... Wiring 52 ... Voltage sensor 53 ... Current sensor 54 ... AC impedance measurement part 60 ... Fuel cell 61 ... Fuel Gas supply part 62 ... Hydrogen gas supply path 63 ... Anode off gas path 64 ... Blower 65 ... Oxidation gas supply path 66 ... Cathode exhaust gas path 67 ... Temperature sensor 69 ... Hydrogen pump

Claims (8)

A fuel cell system comprising a fuel cell,
The catalyst oxide film rate, which is the ratio of the area where the oxide film is formed on the surface of the catalyst provided in the cathode of the fuel cell, the reaction rate at which the catalyst oxide is generated, and the catalyst oxide A catalytic oxide film rate deriving unit for deriving by integrating the catalyst oxide production rate as a difference between the reduction reaction rate, which is the reaction rate to be reduced, with time;
A current-voltage characteristic deriving unit for deriving a current-voltage characteristic that is a relationship between the output current and the output voltage of the fuel cell based on the catalytic oxide film rate derived by the catalytic oxide film rate deriving unit;
A load request acquisition unit for acquiring a load request for the fuel cell;
In the fuel cell comprising the output current and the output voltage for generating electric power corresponding to the load request acquired by the load request acquisition unit based on the current-voltage characteristic derived by the current-voltage characteristic deriving unit An operation point setting section for setting operation points;
A fuel cell system comprising: a control unit that generates power at the operation point set by the operation point setting unit. The fuel cell system according to claim 1, further comprising:
A voltage acquisition unit for acquiring an output voltage of the fuel cell;
A current acquisition unit for acquiring an output current of the fuel cell;
A temperature acquisition unit for acquiring the temperature of the fuel cell;
An impedance deriving unit for deriving the impedance of the fuel cell;
With
The catalytic oxide film rate deriving unit includes the voltage, current, and temperature of the fuel cell acquired by the voltage acquiring unit, the current acquiring unit, and the temperature acquiring unit, and the impedance of the fuel cell derived by the impedance deriving unit. The fuel cell system derives the production reaction rate and the reduction reaction rate based on the obtained voltage, current, temperature, and impedance. The fuel cell system according to claim 2, wherein
The current-voltage characteristic deriving unit has a plurality of values corresponding to factors that reduce the output voltage of the fuel cell with respect to the theoretical electromotive force, and some of the plurality of values have a current as a variable. Deriving the current-voltage characteristic by representing the output voltage of the fuel cell, with the value subtracted from the theoretical electromotive force,
Of the plurality of values, one of the values other than the value having the current as a variable has the catalyst oxide film ratio as a variable, and approximates the degree of voltage drop due to the oxide film of the catalyst. Is a fuel cell system. The fuel cell system according to claim 3, wherein
In the current-voltage characteristic deriving unit, a value obtained by subtracting a plurality of values corresponding to a factor for reducing the output voltage of the fuel cell from the theoretical electromotive force from the theoretical electromotive force is the output voltage of the fuel cell. Wherein each term representing a value corresponding to the factor has a coefficient, and the catalytic oxide film rate, the output voltage acquired by the voltage acquisition unit, and the current acquisition unit A fuel cell system that derives the current-voltage characteristic by determining each of the coefficients as a value that satisfies the equation based on an output current. The fuel cell system according to claim 3 or 4, wherein
One of the values having the current as a variable is a value corresponding to the activation overvoltage, and is a value expressed as a logarithmic term of the current. 6. The fuel cell system according to claim 2, further comprising:
When the fuel cell stops power generation, an impedance storage unit that stores the impedance of the fuel cell at the time of power generation stop,
Each of the voltage acquisition unit and the temperature acquisition unit continues to acquire the voltage or temperature of the fuel cell until the voltage of the fuel cell becomes 0, even after the fuel cell stops generating power,
The catalytic oxide film rate deriving unit, after the fuel cell stops generating power, until the voltage of the fuel cell becomes 0, the impedance stored by the impedance storage unit, the voltage acquired by the voltage acquisition unit, Based on the temperature acquired by the temperature acquisition unit, the derivation of the catalytic oxide film rate is repeated,
The fuel cell system further includes a catalyst oxide film rate storage unit that stores the catalyst oxide film rate when the voltage of the fuel cell becomes 0 after the fuel cell stops power generation,
The current-voltage characteristic deriving unit derives the current-voltage characteristic using the catalytic oxide film rate stored in the catalytic oxide film rate storage unit when the fuel cell starts power generation again. . A moving body that uses electrical energy as a driving force,
A fuel cell system according to any one of claims 1 to 6,
The moving body uses the fuel cell system as at least one of driving power sources. A control method for a fuel cell system comprising a fuel cell,
The catalyst oxide film rate, which is the ratio of the area where the oxide film is formed on the surface of the catalyst provided in the cathode of the fuel cell, the reaction rate at which the catalyst oxide is generated, and the catalyst oxide A first step of deriving by integrating the catalyst oxide production rate as a difference between the reduction reaction rate, which is a reaction rate to be reduced, with time;
A second step of deriving a current-voltage characteristic that is a relationship between an output current and an output voltage of the fuel cell based on the catalytic oxide film ratio;
A third step of obtaining a load request for the fuel cell;
Based on the current-voltage characteristics derived in the second step, the operation in the fuel cell comprising the output current and the output voltage for generating electric power corresponding to the load request acquired in the third step A fourth step of setting points;
And a fifth step of generating the fuel cell at the operating point set in the fourth step.

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