JP2013243009A - Fuel battery system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel battery system which can carry out performance recovery treatment for a catalyst layer without depending on a residual capacity of an electrical storage device.SOLUTION: A fuel battery system comprises: a fuel battery including a film-electrode assembly in which an electrode having a catalyst layer is disposed on both surfaces of a polymer electrolyte film; an electrical storage device connected in parallel with the fuel battery with respect to a load, which allows discharging to the load and charging from the fuel battery; and a control device for controlling a driving point of the fuel battery on the basis of request output power to be requested for the fuel battery. The control device can carry out performance recovery treatment of the catalyst layer by decreasing an output voltage of the fuel battery up to a predetermined voltage, and when carrying out the performance recovery treatment, the control device selects a driving point having a lower output voltage among a plurality of driving points satisfying the request output power.

Description

  The present invention relates to a fuel cell system having a catalyst activation function.

  A fuel cell stack is a power generation system that directly converts energy released during an oxidation reaction into electric energy by oxidizing fuel by an electrochemical process. The fuel cell stack has a membrane-electrode assembly in which both side surfaces of a polymer electrolyte membrane for selectively transporting hydrogen ions are sandwiched by a pair of electrodes made of a porous material. Each of the pair of electrodes is mainly composed of a carbon powder carrying a platinum-based metal catalyst, and is formed on the surface of the catalyst layer in contact with the polymer electrolyte membrane and a gas having both air permeability and electronic conductivity. And a diffusion layer.

  In this type of fuel cell system, when the battery operation is continued in an operation region where the cell voltage is an oxidation voltage (approximately 0.7 V to 1.0 V), the formation of an oxide film on the platinum catalyst surface of the catalyst layer causes The effective area may be reduced, and the performance of the catalyst layer and thus the power generation performance may be reduced. In Patent Document 1, a process for recovering power generation performance by removing an oxide film from the surface of the platinum catalyst by reducing the cathode potential to a reduction voltage (for example, 0.6 V or less) (hereinafter referred to as a refresh process) is output from the fuel cell. The technology to be implemented while taking out is mentioned.

JP 2009-64681 A

In the technique disclosed in Patent Document 1, since the output of the fuel cell fluctuates due to the execution of the refresh process, surplus power is supplied (charged) to a storage battery connected in parallel to the fuel cell with respect to the load. It is necessary to stabilize the output.
However, when the remaining capacity of the storage battery is large, it is not possible to charge the storage battery with surplus power, which may cause a disadvantage that the refresh process cannot be performed.

  Therefore, an object of the present invention is to provide a fuel cell system capable of performing the performance recovery process of the catalyst layer without depending on the remaining capacity of the power storage device.

In order to achieve the above object, the fuel cell system of the present invention comprises:
A fuel cell comprising a membrane-electrode assembly in which electrodes having a catalyst layer are disposed on both sides of a polymer electrolyte membrane;
A power storage device connected in parallel to the fuel cell with respect to a load and capable of discharging to the load and charging from the fuel cell;
A control device for controlling the operating point of the fuel cell based on the required output power required for the fuel cell,
The control device can perform the performance recovery process of the catalyst layer by reducing the output voltage of the fuel cell to a predetermined voltage, and when performing the performance recovery process, the control device satisfies a plurality of requirements for the required output power. The operation point with the lower output voltage is selected from among the operation points.

  In this configuration, when performance recovery processing is required, among the operating points corresponding to the required output power required for the fuel cell, the lower output voltage, in other words, the higher output current, In other words, control at an operating point that does not belong to the normal control region will be selected daringly, but since the output power of the fuel cell is stabilized, the performance recovery process does not depend on the remaining capacity of the power storage device. It becomes possible to obtain the effect.

  In the above configuration, the control device may be configured to shift the operating point to a low voltage side on an IV curve indicating a current-voltage characteristic of the fuel cell when performing the performance recovery process. .

  In the above configuration, when the performance recovery process is performed, the control device changes the direction of decreasing the current-voltage characteristics of the fuel cell, and selects an operation point on the low voltage side on the changed IV curve. It may be configured as follows.

  Further, in the above configuration, when the performance recovery process is performed, the control device changes the direction to improve the current-voltage characteristics of the fuel cell, and sets the operating point on the low voltage side on the IV curve after the change. It may be configured to select.

  In the above configuration, the control device adjusts the temperature of the fuel cell, or adjusts the supply amount or / and supply pressure of the fuel gas or / and the oxidizing gas to the fuel cell, so that the current-voltage characteristics May be configured to change.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the fuel cell system which can implement the performance recovery process of a catalyst layer, without depending on the remaining capacity of an electrical storage apparatus.

1 is a configuration diagram of a fuel cell system according to an embodiment of the present invention. It is a disassembled perspective view of the cell which comprises a fuel cell stack. It is a flowchart which shows an example of the refresh process implemented at the time of a driving | operation of a fuel cell system. It is a figure explaining the change of the operating point on the IP curve of a fuel cell stack. It is a figure explaining the change of the operating point on the IV curve of a fuel cell stack. It is a figure explaining the change of the operating point on the VP curve of a fuel cell stack. It is a flowchart which shows the other example of the refresh process implemented at the time of a driving | running of a fuel cell system. It is a figure explaining the change of the operating point on the IV curve after the IV characteristic change of a fuel cell stack. It is a figure explaining the change of the operating point on the VP curve after the IV characteristic change of a fuel cell stack. It is a figure explaining the change of the operating point on the IV curve after the IV characteristic change of a fuel cell stack. It is a figure explaining the change of the operating point on the VP curve after the IV characteristic change of a fuel cell stack.

Embodiments according to the present invention will be described below with reference to the drawings.
FIG. 1 shows a system configuration of a fuel cell system 10 according to an embodiment of the present invention.

  The fuel cell system 10 functions as an in-vehicle power supply system mounted on a fuel cell vehicle. The fuel cell stack 20 generates electric power by receiving supply of reaction gas (fuel gas, oxidant gas), and air as oxidant gas. An oxidizing gas supply system 30 for supplying the fuel cell stack 20 with hydrogen, a fuel gas supply system 40 for supplying hydrogen gas as the fuel gas to the fuel cell stack 20, and a cooling water as a refrigerant for the fuel cell stack 20 The system includes a refrigerant supply system 70 for supplying power, a power system 50 for controlling charge / discharge of power, and a controller 60 for overall control of the entire system.

The fuel cell stack 20 is a solid polymer electrolyte cell stack formed by stacking a large number of cells in series. In the fuel cell stack 20, the oxidation reaction of the formula (1) occurs at the anode electrode, and the reduction reaction of the equation (2) occurs at the cathode electrode. In the fuel cell stack 20 as a whole, the electromotive reaction of the formula (3) occurs.
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)

FIG. 2 is an exploded perspective view of the cells 21 constituting the fuel cell stack 20.
The cell 21 includes a polymer electrolyte membrane 22, an anode electrode 23, a cathode electrode 24, and separators 26 and 27. The anode electrode 23 and the cathode electrode 24 are diffusion electrodes having a sandwich structure with the polymer electrolyte membrane 22 sandwiched from both sides.

  Separators 26 and 27 made of a gas-impermeable conductive member form fuel gas and oxidizing gas flow paths between the anode electrode 23 and the cathode electrode 24 while sandwiching the sandwich structure from both sides. . The separator 26 is formed with a rib 26a having a concave cross section.

  When the anode electrode 23 comes into contact with the rib 26a, the opening of the rib 26a is closed and a fuel gas flow path is formed. The separator 27 is formed with a rib 27a having a concave cross section. When the cathode electrode 24 comes into contact with the rib 27a, the opening of the rib 27a is closed and an oxidizing gas flow path is formed.

  The anode electrode 23 is mainly composed of a carbon powder supporting a platinum-based metal catalyst (Pt, Pt—Fe, Pt—Cr, Pt—Ni, Pt—Ru, etc.), and a catalyst layer 23 a in contact with the polymer electrolyte membrane 22. And a gas diffusion layer 23b formed on the surface of the catalyst layer 23a and having both air permeability and electronic conductivity. Similarly, the cathode electrode 24 has a catalyst layer 24a and a gas diffusion layer 24b.

  More specifically, the catalyst layers 23a and 24a are made by dispersing carbon powder carrying platinum or an alloy made of platinum and another metal in an appropriate organic solvent, adding an appropriate amount of an electrolyte solution to form a paste, and forming a polymer electrolyte. Screen-printed on the film 22. The gas diffusion layers 23b and 24b are formed of carbon cloth, carbon paper, or carbon felt woven with carbon fiber yarns.

  The polymer electrolyte membrane 22 is a proton conductive ion exchange membrane formed of a solid polymer material, for example, a fluororesin, and exhibits good electrical conductivity in a wet state. A membrane-electrode assembly 25 is formed by the polymer electrolyte membrane 22, the anode electrode 23, and the cathode electrode 24.

  Returning to FIG. 1, a voltage sensor 57 for detecting the output voltage (FC voltage) of the fuel cell stack 20 and a current sensor 58 for detecting the output current (FC current) are attached to the fuel cell stack 20. Yes.

  The oxidizing gas supply system 30 has an oxidizing gas passage 33 through which oxidizing gas supplied to the cathode electrode of the fuel cell stack 20 flows and an oxidizing off gas passage 34 through which oxidizing off gas discharged from the fuel cell stack 20 flows. . In the oxidizing gas passage 33, an air compressor 32 that takes in the oxidizing gas from the atmosphere via the filter 31, a humidifier 35 for humidifying the oxidizing gas pressurized by the air compressor 32, and the fuel cell stack 20 are connected. A shutoff valve A1 for shutting off the oxidizing gas supply is provided.

  In the oxidizing off gas passage 34, a shutoff valve A2 for shutting off the oxidizing off gas discharge from the fuel cell stack 20, a back pressure adjusting valve A3 for adjusting the oxidizing gas supply pressure, oxidizing gas (dry gas) and oxidizing A humidifier 35 is provided for exchanging moisture with off-gas (wet gas).

  The fuel gas supply system 40 includes a fuel gas supply source 41, a fuel gas passage 43 through which fuel gas supplied from the fuel gas supply source 41 to the anode electrode of the fuel cell stack 20 flows, and fuel discharged from the fuel cell stack 20. A circulation passage 44 for returning off-gas to the fuel gas passage 43, a circulation pump 45 for pressure-feeding the fuel off-gas in the circulation passage 44 to the fuel gas passage 43, and an exhaust / drain passage 46 branched and connected to the circulation passage 44 Have.

  The fuel gas supply source 41 is composed of, for example, a high-pressure hydrogen tank or a hydrogen storage alloy, and stores high-pressure (for example, 35 MPa to 70 MPa) hydrogen gas. When the shut-off valve H1 is opened, the fuel gas flows out from the fuel gas supply source 41 into the fuel gas passage 43. The fuel gas is decompressed to about 200 kPa, for example, by the regulator H2 and the injector 42, and supplied to the fuel cell stack 20.

  The circulation passage 44 is connected to a shutoff valve H4 for shutting off the fuel off-gas discharge from the fuel cell stack 20 and an exhaust drainage passage 46 branched from the circulation passage 44. An exhaust / drain valve H5 is disposed in the exhaust / drain passage 46. The exhaust / drain valve H <b> 5 is operated according to a command from the controller 60 to discharge (purge) the fuel off-gas and impurities including impurities in the circulation passage 44 to the outside.

  The fuel off-gas discharged through the exhaust / drain valve H5 is mixed with the oxidizing off-gas flowing through the oxidizing off-gas passage 34 and diluted by a diluter (not shown). The circulation pump 45 circulates and supplies the fuel off gas in the circulation system to the fuel cell stack 20 by driving the motor.

  The refrigerant supply system 70 includes a cooling path 71 connected to the cooling water inlet / outlet of the fuel cell stack 20 and circulating the cooling water. The cooling path 71 includes a pump C1 that pressurizes and circulates the cooling water, a radiator C2 that radiates the retained heat of the cooling water to the outside, a bypass path 72 that bypasses the radiator C2, and the cooling water discharged from the fuel cell stack 20. A three-way valve C4 for switching the distribution destination is provided. The radiator C2 is provided with a cooling fan C3 that is rotationally driven by a motor.

  The power system 50 includes a DC / DC converter 51, a battery (power storage device) 52, a traction inverter 53, a traction motor 54, and auxiliary machinery 55. The DC / DC converter 51 boosts the DC voltage supplied from the battery 52 and outputs it to the traction inverter 53, and the DC power generated by the fuel cell stack 20, or the regenerative power collected by the traction motor 54 by regenerative braking. And a function of charging the battery 52 by stepping down the voltage.

  The battery 52 functions as a surplus power storage source, a regenerative energy storage source during regenerative braking, and an energy buffer during load fluctuations associated with acceleration or deceleration of the fuel cell vehicle. As the battery 52, for example, a secondary battery such as a nickel / cadmium storage battery, a nickel / hydrogen storage battery, or a lithium secondary battery is suitable. The battery 52 is provided with an SOC sensor for detecting SOC (State of charge) which is the remaining capacity.

  The traction inverter 53 is, for example, a PWM inverter driven by a pulse width modulation method, and converts a DC voltage output from the fuel cell stack 20 or the battery 52 into a three-phase AC voltage in accordance with a control command from the controller 60. The rotational torque of the traction motor 54 is controlled. The traction motor 54 is a three-phase AC motor, for example, and constitutes a power source of the fuel cell vehicle.

  Auxiliary machines 55 are motors (for example, power sources such as pumps) arranged in each part in the fuel cell system 10, inverters for driving these motors, and various on-vehicle auxiliary machines. (For example, an air compressor, an injector, a cooling water circulation pump, a radiator, etc.) is a general term.

  The controller 60 is a computer system including a CPU, a ROM, a RAM, and an input / output interface, and controls each part of the fuel cell system 10. For example, when the controller 60 receives the start signal IG output from the ignition switch, the controller 60 starts the operation of the fuel cell system 10, and the accelerator opening signal ACC output from the accelerator sensor or the vehicle speed signal output from the vehicle speed sensor. The required power of the entire system is obtained based on VC or the like. The required power of the entire system is the total value of the vehicle running power and the auxiliary machine power.

  Auxiliary power includes power consumed by in-vehicle accessories (humidifiers, air compressors, hydrogen pumps, cooling water circulation pumps, etc.), and equipment required for vehicle travel (transmissions, wheel control devices, steering devices, and Power consumed by a suspension device or the like, and power consumed by a device (such as an air conditioner, a lighting fixture, or audio) disposed in the passenger space.

  The controller 60 determines the distribution of the output power of each of the fuel cell stack 20 and the battery 52, and the oxidizing gas supply system 30 and the fuel gas supply system 40 so that the power generation amount of the fuel cell stack 20 matches the target power. And the DC / DC converter 51 to adjust the output voltage of the fuel cell stack 20, thereby controlling the operation point (output voltage, output current) of the fuel cell stack 20.

  In the fuel cell stack 20, as shown in the above formula (1), hydrogen ions generated at the anode electrode 23 pass through the electrolyte membrane 22 and move to the cathode electrode 24, and the hydrogen ions moved to the cathode electrode 24 are As shown in the above equation (2), an electrochemical reaction is caused with oxygen in the oxidizing gas supplied to the cathode electrode 24 to cause a reduction reaction of oxygen. As a result, the platinum catalyst surface of the catalyst layer 24a is covered with an oxide film, the effective area is reduced, and power generation efficiency (output characteristics) is reduced.

  Therefore, the controller 60 reduces the oxide film by reducing the cell voltage to the reduction voltage (refresh voltage) for a predetermined time (refresh time) at a predetermined execution timing, and performs a refresh process for removing the oxide film from the catalyst surface. .

  More specifically, by decreasing the voltage of each cell, that is, the output voltage of the fuel cell stack 20 for a predetermined time, the output current is increased, and the electrochemical reaction in the catalyst layer 24a is shifted from the oxidation reaction region to the reduction reaction region. Thus, the catalyst activity is recovered.

  Thus, the refresh process is indispensable for suppressing a decrease in power generation efficiency of the fuel cell stack 20. However, the output of the fuel cell stack 20 varies depending on the execution of the refresh process. However, when the remaining capacity of the battery 52 is large, the surplus power cannot be charged in the battery 52, so the refresh process is performed. It may happen that you cannot do it.

  In the present invention, when it is determined that the refresh process needs to be performed, the output power requested from the fuel cell stack 20 is kept as it is, and the output voltage of the plurality of operation points having the same output power is more output. By setting the output voltage at the lower operating point to the target voltage, it is possible to perform the refresh process independent of the remaining capacity of the battery 52.

<First Control Mode and Modifications>
Next, an example of control during load operation of the fuel cell system 10 will be described with reference to the flowchart of FIG. 3 and the maps of FIGS. 4 to 6.

  The load operation refers to the operation control by calculating the power generation command value of the fuel cell stack 20 based on the accelerator opening, the vehicle speed, and the like, and the electric power required for vehicle travel and the power required for system operation are generated by the fuel cell stack 20 This is an operation that is covered only by the power generated by the fuel cell stack 20 and the power from the battery 52, and is carried out in a high load region where the power generation efficiency is high (an operation region where the power generation request exceeds a predetermined value). is there.

  During the load operation, the controller 60 determines whether or not the refresh process is necessary at a predetermined control cycle (step S1 in FIG. 3). In this step S1, for example, the elapsed time (horizontal axis) from the previously performed refresh process, the generated current (vertical axis) of the fuel cell stack 20, the total amount and breakdown of oxide films (I-type oxide film, II described later) The determination is made with reference to a map (not shown) showing the relationship with the mold oxide film.

  In addition to this map (not shown), the maps shown in FIGS. 4-6 and FIGS. 8-11 described later are created based on experiments and simulation results, and are stored in the memory in the controller 60. To do.

  If the determination result of step S1 in FIG. 3 is “No”, that is, if the refresh process is unnecessary, the controller 60 skips the process of step S3 and returns the process to the main routine.

Then, the controller 60 refers to, for example, the map (IP curve) shown in FIG. 4, and the operation points A (I ₁ , P ₁ ), B (I) satisfying the output power P ₁ required for the fuel cell stack 20. ₂ , P ₁ ) at the operation point A belonging to the normal control region that is normally selected from the viewpoint of improving fuel efficiency, specifically, at the operation point A (I ₁ , P ₁ ) with the lower output current I. The DC / DC converter 51 is controlled by setting the output voltage to the target voltage.

On the other hand, if the determination result in step S1 is “Yes”, that is, if refresh processing is required, the controller 60 refers to, for example, the map shown in FIG. Of the operating points A (I ₁ , P ₁ ) and B (I ₂ , P ₁ ) that satisfy the power P ₁ , the operating point B that does not belong to the normal control region, specifically, the one with the higher output current I The output voltage at the operation point B (I ₂ , P ₁ ) is set to the target voltage to control the DC / DC converter 51 (step S3).

This target voltage can be obtained, for example, with reference to a map (IV curve) shown in FIG. As is apparent from this IV curve, when there are a plurality of operating points A and B having the same output power P _1, the output voltage V _{2 at} the operating point B with the higher output current I is: It is lower than the output voltage V _{1 at the} operating point A belonging to the normal control region.

The output voltage V ₂ is a voltage lower than the reduction voltage (refresh voltage) described. Therefore, the refresh effect is obtained by the output control at the operation point B that does not belong to the normal control region.

  The controller 60 continues the control at the operation point B for a predetermined refresh time, and then returns to the control in the normal control region. That is, the controller 60 controls the DC / DC converter 51 by setting the output voltage at the operation point with the lower output current among the operation points corresponding to the output power required for the fuel cell stack 20 as the target voltage. To do.

  As described above, in the present embodiment, when a refresh process is required, an operation point that does not belong to the normal control region is selected from operation points corresponding to output power required for the fuel cell stack 20. The refresh process is performed. Thereby, since the output power of the fuel cell stack 20 is stabilized, it is possible to perform the refresh process and obtain the effect without depending on the remaining capacity of the battery 25.

In the above embodiment, the controller 60 has been described with reference to the maps (IP curve, IV curve) shown in FIGS. 4 and 5. However, the present invention is not limited to this example. Absent. For example, when the map (VP curve) shown in FIG. 6 is provided, the operation point A (V ₁ , P ₁₎ satisfying the output power P ₁ required for the fuel cell stack 20 with reference to the map. ), B (V ₂ , P ₁ ), the output voltage V ₂ at the operation point B (V ₂ , P ₁ ) not belonging to the normal control region is set to the target voltage V to control the DC / DC converter 51. May be.

<Second Control Mode and Modifications>
Next, another control example during the load operation of the fuel cell system 10 will be described with reference to the flowchart of FIG. 7 and the maps of FIGS. 8 and 9.

  During the load operation, the controller 60 determines whether or not the refresh process is necessary at a predetermined control cycle (step S11 in FIG. 7). Since the determination process performed in step S11 is the same as the determination process performed in step S1 in FIG. 3, a description thereof is omitted here.

  If the determination result in step S11 is “No”, that is, if the refresh process is unnecessary, the controller 60 skips the processes in steps S13 and S15 and returns the process to the main routine. Then, the controller 60 controls the DC / DC converter 51 by setting the output voltage at the operation point A belonging to the normal control region as the target voltage.

  On the other hand, if the determination result in step S11 is “Yes”, that is, if refresh processing is necessary, the controller 60 performs processing for changing the IV characteristics of each cell 21 (step S11). S13). Specifically, for example, as shown in FIG. 8, the IV characteristic is changed to a direction in which the IV characteristic is reduced so that the IV curve displayed with a solid line becomes an IV curve displayed with a broken line.

  The change of the IV characteristic can be realized by changing the cooling water temperature, the cooling water circulation amount, the fuel gas supply amount, the oxidizing gas supply amount, the fuel gas supply pressure, or the oxidizing gas supply pressure, for example. Specifically, it can be realized by changing the rotation speed of the pump C1 and / or the cooling fan C3, changing the rotation speed of the circulation pump 45 and / or the air compressor 32, etc., but is limited to these examples. It is not a thing.

  When the process of step S13 is performed, the IV curve in FIG. 8 changes from the solid line to the broken line, so that the controller 60 starts from the map corresponding to the IV curve indicated by the solid line. It changes to the thing corresponding to IV curve shown by.

Further, the controller 60 operates as the operation points of the fuel cell stack 20 among the operation points on the IV curve after the change, the operation points A (I ₁ , V ₁ ) and B on the IV curve before the change. It is an operating point that satisfies the same output power P ₁ as (I ₂ , V ₂ ), and the output current I ₃ satisfies I ₁ <I ₃ <I ₂ and the output voltage V ₃ satisfies V ₂ <V ₃ <V ₁ . The operation point C (I ₃ , V ₃ ) is selected, the output voltage V ₃ at the operation point C is set as a target voltage, and the DC / DC converter 51 is controlled.

As is apparent from the IV curve indicated by the broken line in FIG. 8, when there are a plurality of operation points A, B, and C having the same output power P ₁ , the output voltage V _{3 at the} operation point C is the normal control region. This is a voltage lower than the output voltage V _{1 at the} operation point A belonging to and lower than the reduction voltage (refresh voltage) described.
Therefore, the refresh effect is obtained by the output control at the operation point C that does not belong to the normal control region.

  The controller 60 continues the control at the operation point C for a predetermined refresh time, and then returns to the control in the normal control region. That is, the controller 60 controls the DC / DC converter 51 by setting the output voltage at the operation point with the lower output current among the operation points corresponding to the output power required for the fuel cell stack 20 as the target voltage. To do.

  As described above, in the present embodiment, when the refresh process is required, the IV characteristic of the cell 21 is changed so as to be lowered, and the output power required for the fuel cell stack 20 is dealt with. Among the operating points to be refreshed, the refresh process is performed at the same operating point as the output power required for the fuel cell stack 20 on the changed IV curve.

Thereby, since the output power of the fuel cell stack 20 is stabilized, it is possible to perform the refresh process and obtain the effect without depending on the remaining capacity of the battery 25. Moreover, as is apparent from FIG. 8, the operation point C (I ₃ , V ₃ ) is the operation point B (I ₂ , V ₂ ) on the IV curve before changing the IV characteristics. Since the output current I ₃ is lower than that of), fuel efficiency can be improved.

Further, since the operation point C (I ₃ , V ₃ ) has an output voltage V ₃ higher than that of the operation point B (I ₂ , V ₂ ), the operation point C (I ₁ , V ₁ ) to the operation point C (I _3, V ₃ when changing to) the voltage fluctuation width _{ΔV AC (= V 1 -V 3} ) , when changed from the operation point a (I _1, V ₁₎ to the operating point B (I _2, V ₂₎ Voltage fluctuation range ΔV _AB (= V ₁ −V ₂ ). As a result, the voltage fluctuation width during the refresh process is reduced, and the deterioration of the cell 21 can be suppressed.

In addition, although the controller 60 demonstrated the example which refers the map (IV curve) shown in FIG. 8 in the said embodiment, this invention is not limited to this example. For example, when a map of the VP curve as shown in FIG. 9 is provided, the fuel cell stack 20 is required with reference to the map of the VP curve (broken line) after the IV characteristic change. Even if the output voltage V ₃ at the operation point C (V ₃ , P ₁ ) that does not belong to the normal control region among the operation points satisfying the output power P ₁ is set to the target voltage V, the DC / DC converter 51 is controlled. Good.

<Third Control Mode and Modifications>
Next, another control example during the load operation of the fuel cell system 10 will be described with reference to the maps of FIGS. 10 and 11 with reference to the flowchart of FIG.

  During the load operation, the controller 60 determines whether or not the refresh process is necessary at a predetermined control cycle (step S11 in FIG. 7). Since the determination process performed in step S11 is the same as the determination process performed in step S1 in FIG. 3, a description thereof is omitted here.

  If the determination result in step S11 is “No”, that is, if the refresh process is unnecessary, the controller 60 skips the processes in steps S13 and S15 and returns the process to the main routine. Then, the controller 60 controls the DC / DC converter 51 by setting the output voltage at the operation point X belonging to the normal control region as the target voltage.

  On the other hand, if the determination result in step S11 is “Yes”, that is, if refresh processing is necessary, the controller 60 performs processing for changing the IV characteristics of each cell 21 (step S11). S13). Specifically, for example, as shown in FIG. 10, the IV curve is changed from the IV curve displayed as a solid line to the IV curve displayed as a broken line in the direction of improving the IV characteristic.

  The change of the IV characteristic can be realized by changing the cooling water temperature, the cooling water circulation amount, the fuel gas supply amount, the oxidizing gas supply amount, the fuel gas supply pressure, or the oxidizing gas supply pressure, for example. Specifically, it can be realized by changing the rotation speed of the pump C1 and / or the cooling fan C3, changing the rotation speed of the circulation pump 45 and / or the air compressor 32, etc., but is limited to these examples. It is not a thing.

  When the process of step S13 is performed, the IV curve in FIG. 10 changes from the solid line to the broken line, so that the controller 60 changes from the one corresponding to the IV curve indicated by the solid line to the broken line. It changes to the thing corresponding to IV curve shown by.

Further, the controller 60 is the same as the operation point X (I ₁ , V ₁ ) on the IV curve before the change among the operation points on the IV curve after the change as the operation point of the fuel cell stack 20. The operating points Y (I ₂ , V ₂ ) and Z (I ₃ , V ₃ ) satisfying the output power P ₁ , the output current I ₃ is I ₂ <I ₁ <I ₃ and the output voltage V ₃ is V _3. The operation point Z (I ₃ , V ₃ ) satisfying <V ₁ <V ₂ is selected, the output voltage V ₃ at the operation point Z is set as the target voltage, and the DC / DC converter 51 is controlled.

As is clear from the I-V curve shown by the broken line in FIG. 10, the output power P ₁ is equal to a plurality of operating points X, Y, in the case where Z is present, the output voltage V ₃ at the operating point Z is, I-V The voltage is lower than the output voltages V ₁ and V _{2 at the} operation points X and Y belonging to the respective normal control regions before and after the characteristic change, and lower than the reduction voltage (refresh voltage) described.
Therefore, the refresh effect is obtained by the output control at the operation point Z that does not belong to the normal control region.

  The controller 60 continues the control at the operation point Z for a predetermined refresh time, and then returns to the control in the normal control region. That is, the controller 60 controls the DC / DC converter 51 by setting the output voltage at the operation point with the lower output current among the operation points corresponding to the output power required for the fuel cell stack 20 as the target voltage. To do.

  As described above, in the present embodiment, when the refresh process is necessary, after changing the cell 21 to improve the IV characteristic, the output power required for the fuel cell stack 20 is handled. Of the operating points, the refresh process is performed at the operating point that is the same as the output power required for the fuel cell stack 20 on the changed IV curve and at the lower operating point. .

Thereby, since the output power of the fuel cell stack 20 is stabilized, it is possible to perform the refresh process and obtain the effect without depending on the remaining capacity of the battery 25. Moreover, the operating point Z (I _3, V _3), as is clear from FIG. 10, I-V characteristics before changing the I-V curves are operating point ride on X (I _1, V ₁ ) for low output voltage V ₃ of having a high output current I ₃ than would be greater refreshing effect can be obtained, it is possible to improve the substantial performance comprehensively.

At this time, ΔV _XZ (= V) between the operation point X (I ₁ , V ₁ ) before the IV characteristic change and the operation point Z (I ₃ , V ₃ ) after the IV characteristic change. ₁₋ V ₃ ), there is a voltage difference corresponding to ₁₋ V ₃ ), and the voltage fluctuation width during the refresh process increases by that difference after changing the IV characteristics. However, as described, a larger refresh effect is obtained. As a result, overall performance can be greatly improved.

In addition, in the said embodiment, although the controller 60 demonstrated the example which refers to the map (IV curve) shown in FIG. 10, this invention is not limited to this example. For example, when a map of the VP curve as shown in FIG. 11 is provided, the fuel cell stack 20 is required with reference to the map of the VP curve (broken line) after the IV characteristic change. Even if the output voltage V ₃ at the operation point Z (V ₃ , P ₁ ) that does not belong to the normal control region among the operation points satisfying the output power P ₁ is set to the target voltage V, the DC / DC converter 51 is controlled. Good.

  In each of the above-described embodiments, the form in which the fuel cell system 10 is used as an in-vehicle power supply system has been illustrated. However, the form of use of the fuel cell system 10 is not limited to this example. For example, the fuel cell system 10 may be mounted as a power source of a mobile body (robot, ship, aircraft, etc.) other than the fuel cell vehicle. Further, the fuel cell system 10 according to the present embodiment may be used as a power generation facility (stationary power generation system) such as a house or a building.

DESCRIPTION OF SYMBOLS 11 Fuel cell system 12 Fuel cell 24a Catalyst layer 25 Membrane-electrode assembly 52 Battery (power storage device)
60 controller (control device)

Claims (5)

A fuel cell comprising a membrane-electrode assembly in which electrodes having a catalyst layer are disposed on both sides of a polymer electrolyte membrane;
A power storage device connected in parallel to the fuel cell with respect to a load and capable of discharging to the load and charging from the fuel cell;
A control device for controlling the operating point of the fuel cell based on the required output power required for the fuel cell,
The control device can perform the performance recovery process of the catalyst layer by reducing the output voltage of the fuel cell to a predetermined voltage, and when performing the performance recovery process, the control device satisfies a plurality of requirements for the required output power. A fuel cell system that selects an operation point having a lower output voltage among the operation points. The fuel cell system according to claim 1, wherein
The control device shifts the operation point to a low voltage side on an IV curve indicating a current-voltage characteristic of the fuel cell when performing the performance recovery process. The fuel cell system according to claim 1, wherein
When performing the performance recovery process, the control device changes the current-voltage characteristics of the fuel cell in a direction to decrease, and selects a low-voltage side operation point on the changed IV curve. . The fuel cell system according to claim 1, wherein
When the performance recovery process is performed, the control device changes in a direction to improve the current-voltage characteristics of the fuel cell, and selects a low-voltage side operation point on the changed IV curve. . The fuel cell system according to claim 3 or 4,
The control device changes the current-voltage characteristic by adjusting the temperature of the fuel cell, or adjusting the supply amount or / and supply pressure of fuel gas or / and oxidizing gas to the fuel cell, Fuel cell system.

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