JPWO2013128610A1 - Fuel cell system - Google Patents

Abstract

A fuel cell system according to the present invention includes a fuel cell including a membrane-electrode assembly in which electrodes having a catalyst layer are arranged on both sides of a polymer electrolyte membrane, and a power storage device connected in parallel to the fuel cell with respect to a load And a control device that performs the performance recovery process of the catalyst layer by reducing the output voltage of the fuel cell to a predetermined voltage, and when a predetermined intermittent operation condition is satisfied, a power generation command value to the fuel cell Is set to zero and the intermittent operation in which power supply to the load is covered by the power from the power storage device can be performed, and the performance recovery process is performed during the intermittent operation. When it is necessary to perform performance recovery processing, when the remaining capacity of the power storage device is equal to or less than a predetermined amount, the execution timing of the intermittent operation is delayed and the remaining capacity exceeds the predetermined amount. Implementing charging of the collector.

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 decrease and output characteristics may deteriorate. In view of such circumstances, Patent Document 1 discloses that when the required power for the fuel cell is less than a predetermined value, the supply of air (oxidizing gas) to the fuel cell stack is stopped and the output voltage of the fuel cell stack is set to DC. / DC converter forcibly lowers the cell voltage to a reduction voltage (for example, 0.6 V or less), thereby removing the oxide film from the platinum catalyst surface and recovering the performance of the catalyst layer (hereinafter referred to as refresh process) Is referred to).

  The document also mentions that for a fuel cell vehicle using a fuel cell system as an in-vehicle power source, the refresh process is prohibited when the traveling speed of the fuel cell vehicle is traveling above a predetermined value.

JP 2008-192468 A

  During the refresh process, since the cell voltage is lower than that during normal load operation, there is a possibility that the response to an output increase request to the fuel cell, particularly a high load request, may be significantly reduced. For example, in a fuel cell vehicle, if the cell voltage is lowered by the refresh process, an output that follows the accelerator response at the time of a high load request may not be obtained, and drivability (steering performance) may be significantly reduced. .

  In order to suppress such a decrease in responsiveness, it is conceivable to perform the refresh process during intermittent operation. The intermittent operation is a fuel cell system including a fuel cell and a battery as a power supply source, for example, when a predetermined intermittent operation condition is satisfied such that a required power from a load is a predetermined value or less. The command value is set to zero, and the power supplied to the load is covered by the power from the battery.

  However, when the amount of the oxide film formed on the catalyst layer is large and it is necessary to secure a sufficient refresh processing time (refresh time), if the remaining battery capacity is low, the battery can be supplied to the drive motor. The amount of power is limited, and as a result, drivability may deteriorate. Further, if the estimation of the amount and properties of the oxide film is not accurate, the effect of the refresh process may not be sufficiently obtained.

  For example, the oxide film can be removed by reducing the output voltage of the fuel cell stack to a reduction voltage as referred to in Patent Document 1 (hereinafter referred to as the first reduction voltage) (hereinafter referred to as I-type oxidation). It is recognized that a film (hereinafter referred to as a II-type oxide film) that cannot be removed without lowering to a second reduction voltage lower than the first reduction voltage can be mixed.

  In the refresh process of Patent Document 1, since only one stage of reduction voltage (first reduction voltage) that can remove the oxide film is assumed, the output voltage of the fuel cell stack is increased to the assumed first reduction voltage. Although it is possible to remove the I-type oxide film by lowering for a certain time, it is not possible to remove the II-type oxide film. Therefore, the performance recovery of the catalyst layer may not always be sufficient.

  Accordingly, an object of the present invention is to propose a fuel cell system capable of suppressing a decrease in responsiveness after the performance recovery processing of the catalyst layer of the fuel cell or during the processing.

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 with the fuel cell with respect to a load;
A controller for performing a performance recovery process of the catalyst layer by reducing the output voltage of the fuel cell to a predetermined voltage,
When a predetermined intermittent operation execution condition is satisfied, an intermittent operation in which a power generation command value to the fuel cell is set to zero and power supply to the load is provided by power from the power storage device can be performed. A fuel cell system in which the performance recovery process is performed during operation,
When the remaining capacity of the power storage device is equal to or less than a predetermined amount when the performance recovery process needs to be performed, the control device delays the execution timing of the intermittent operation, and the remaining capacity is The power storage device is charged until a predetermined amount is exceeded.

  In this configuration, in the fuel cell system in which the performance recovery process of the catalyst layer is performed during intermittent operation, when it is determined that the performance recovery process needs to be performed and the remaining capacity of the power storage device is equal to or less than a predetermined amount Thus, the charging of the power storage device is prioritized over the performance recovery process. Thus, after the performance recovery process is performed after the transition to the intermittent operation, or the remaining capacity of the power storage device being implemented is ensured, it is possible to minimize the influence on the responsiveness.

  In the above configuration, the control device may predict the output increase request timing for the fuel cell, and determine the content of the performance recovery process based on the prediction result. For example, in the case of a fuel cell system mounted on a fuel cell vehicle as an in-vehicle power source, the control device may predict the timing of an output increase request for the fuel cell based on the running state of the vehicle. Good.

  According to this configuration, the amount of removal of the oxide film formed on the catalyst layer is not performed in accordance with the predicted output increase request timing, instead of performing uniform processing when the performance recovery processing of the catalyst layer is necessary. Can be adjusted. Therefore, it is possible to achieve both minimization of the influence on responsiveness (drivability in an in-vehicle fuel cell system) and maximum recovery of the performance of the catalyst layer.

In the above configuration,
A first oxide film that can be removed by reducing the output voltage of the fuel cell to a first film removal voltage, and an output of the fuel cell; When the second oxide film that cannot be removed without lowering the voltage to a second film removal voltage lower than the first film removal voltage is mixed,
The control device may change the predetermined voltage to be reduced according to the prediction result when the performance recovery process needs to be performed.

  In this configuration, when it is predicted that the output increase request timing to the fuel cell is close, priority is given to minimizing the influence on the responsiveness to the output increase request, and the output voltage of the fuel cell is set to the first. If performance recovery processing is performed that only reduces the film removal voltage, and it is predicted that the output increase request timing to the fuel cell is not so close, maximizing the recovery of the performance of the catalyst layer will be given top priority. It is possible to perform performance recovery processing in which the battery output voltage is lowered to the second film removal voltage.

In the above configuration,
A first oxide film that can be removed by reducing the output voltage of the fuel cell to a first film removal voltage, and an output of the fuel cell; When the second oxide film that cannot be removed without lowering the voltage to a second film removal voltage lower than the first film removal voltage is mixed,
The control device may change an execution time of the performance recovery process according to the prediction result when the performance recovery process needs to be performed.

  In this configuration, when it is predicted that the output increase request timing to the fuel cell will be close, the performance recovery process with a short execution time is performed with the highest priority given to minimizing the impact on the response to the output increase request. When it is predicted that the output increase request timing to the fuel cell is not so close, it is possible to perform a performance recovery process with a long implementation time with the highest priority given to maximizing the recovery of the performance of the catalyst layer. .

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the fuel cell system which can suppress the responsiveness fall after the performance recovery process of the catalyst layer of a fuel cell or during a process.

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 timing chart which shows the example of 1 operation control of a fuel cell system. It is a flowchart which shows the procedure which implements a refresh process on one of the conditions that the remaining capacity of a battery exceeded the predetermined threshold value. It is a figure which shows the relationship between the output current of a fuel cell, and the content rate of the type II oxide film in an oxide film. It is a figure which shows that each ratio of I-type oxide film-III-type oxide film in the oxide film formed in a catalyst layer changes with elapsed time when the output voltage of a fuel cell stack is maintained at a constant value. . It shows that each ratio of type I oxide film and type II oxide film in the oxide film formed on the catalyst layer changes as the number of times the output voltage of the fuel cell stack crosses the predetermined boundary voltage up and down FIG. It is a timing chart which shows the other example of operation control of a fuel cell system. 6 is a timing chart showing still another example of operation control of the fuel cell system.

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)

  Embodiments according to the present invention will be described below with reference to the drawings. The same device is denoted by the same reference numeral, and redundant description is omitted.

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. Gas supply system 30 for supplying the fuel cell stack 20 with hydrogen, fuel gas supply system 40 for supplying hydrogen gas as the fuel gas to the fuel cell stack 20, and power for controlling charge and discharge of power A system 50 and a controller 60 that performs overall control of the entire system are provided.

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)

  The fuel cell stack 20 is provided with a voltage sensor 71 for detecting the output voltage (FC voltage) of the fuel cell stack 20 and a current sensor 72 for detecting the output current (FC current).

  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, thereby discharging the fuel off-gas containing impurities in the circulation passage 44 and moisture 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 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.

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.

FIG. 3 is a timing chart showing operation control of the fuel cell system 10.
The fuel cell system 10 improves power generation efficiency by switching the operation mode of the fuel cell stack 20 according to the operation load.

  For example, the fuel cell system 10 calculates the power generation command value of the fuel cell stack 20 based on the accelerator opening and the vehicle speed in a high load region where the power generation efficiency is high (an operation region where the power generation request is equal to or greater than a predetermined value). Operation control is performed, and normal load operation is performed in which the power required for vehicle travel and the power required for system operation are covered only by the power generated by the fuel cell stack 20 or by the power generated by the fuel cell stack 20 and the power from the battery 52.

  On the other hand, the fuel cell system 10 sets the power generation command value of the fuel cell stack 20 to zero in the low load region where the power generation efficiency is low (the operation region that satisfies the intermittent operation execution condition where the power generation request is less than a predetermined value). Operation control is performed, and intermittent operation is performed in which the power required for vehicle travel and the power required for system operation are covered by the power from the battery 52. Note that if the cell voltage is low when there is a high load request (output increase request) during intermittent operation, the drivability deteriorates, so the cell voltage during intermittent operation is kept high.

  Further, the fuel cell system 10 depresses the brake when parked or stopped immediately after startup or when waiting for a signal, in other words, when the shift lever is in the P range or N range, or in the D range. When the vehicle speed is zero, the fuel cell stack 20 generates power at the power generation voltage necessary for ensuring drivability, and the idle operation for charging the generated power to the battery 52 is performed.

  In the case where the voltage of the cathode electrode 24 is kept high during the idling operation, in the fuel cell stack 20, the platinum catalyst of the catalyst layer 24a may be eluted. High potential avoidance control (OC avoidance operation) is performed to control the fuel cell stack 20 so as to maintain the durability of the fuel cell stack 20 by controlling it to the use upper limit voltage V1 or lower. The use upper limit voltage V1 is set so that the voltage is about 0.9 V per cell, for example.

  FIG. 4 is a flowchart showing a procedure for performing the refresh process under one condition that the remaining capacity of the battery 52 exceeds a predetermined threshold. Hereinafter, this flowchart will be described with reference to FIG. 3 as necessary.

When the controller 60 detects a signal instructing idle operation during normal load operation (step S1), the controller 60 shifts the operation state of the fuel cell system 10 from normal load operation to idle operation (step S3). During this idle operation, the OC avoidance operation is performed.
As an example of the signal for instructing the idling operation, the accelerator opening signal ACC output from the accelerator sensor indicates that the accelerator opening is zero (accelerator OFF), or the brake opening signal output from the brake sensor. Corresponds to the case where indicates that the brake opening is fully open.

  Next, it is determined whether or not the total amount of oxide film formed on the platinum catalyst surface of the catalyst layer 24a exceeds a predetermined amount α (step S5, timing t2 in FIG. 3). The total amount of the oxide film is estimated by referring to, for example, a map shown in FIG. The map of FIG. 5 shows the elapsed time (horizontal axis) from the refresh process performed last time, the generated current (vertical axis) of the fuel cell stack 20, the total amount and breakdown of the oxide film (solid line and broken line in FIG. 5), These are created based on experiments and simulation results and stored in the memory in the controller 60.

  From FIG. 5, the generation current of the fuel cell stack 20 decreases as the elapsed time from the previously performed refresh process increases, and the type II oxide film in the oxide film (denoted as film 2 in FIG. 5). It is clear that the rate of decrease in the generated current of the fuel cell stack 20 with respect to the elapsed time since the last refresh process, in other words, the effect on the performance degradation of the catalyst layer 24a increases. .

  Furthermore, this is because the oxide film contains a type II oxide film rather than a type I oxide film (denoted as film 1 in FIG. 5) alone. The influence on the performance degradation of the layer 24a is large, and when the type II oxide film is included in the oxide film, the higher the content ratio of the type II oxide film, the lower the performance of the catalyst layer 24a. It shows that the effect of.

Here, it supplements about an I type oxide film, a II type oxide film, and a III type oxide film. These oxide films can be mixed in one oxide film. For example, as shown in FIG. 6, when the output voltage of the fuel cell stack 20 is maintained at a constant oxide film formation voltage (oxidation voltage). It is known that the ratio in the oxide film gradually changes as the holding time increases, and that the respective reduction voltage magnitude relationships satisfy the following relationship.
Type I oxide film (for example, 0.65 V to 0.9 V)> Type II oxide film (for example, 0.4 V to 0.6 V)> Type III oxide film (for example, 0.05 V to 0.4 V)

  In addition, the I-type oxide film, the II-type oxide film, and the III-type oxide film, for example, as shown in FIG. 7 (however, the III-type oxide film is not shown), the output voltage of the fuel cell stack 20 has a predetermined boundary. It is also known that the ratio in the oxide film gradually changes with an increase in the number of times (eg, the number of cycles) over which a voltage (for example, 0.8 V) is straddled up and down.

  During the idling operation, as shown in FIG. 3, the fuel cell stack 20 performs constant voltage power generation, and the generated voltage is an oxidation voltage, so that an oxide film is formed on the catalyst layer 24a. Therefore, the controller 60 starts from a certain point during idling, and the rate of decrease in the generated current from the amount of decrease in the generated current of the fuel cell stack 20 after a predetermined time has elapsed (from the linear slope in FIG. 5). In step S5, the reduction rate of the generated current is applied to the map of FIG. 5 to obtain the total amount of oxide film and the breakdown of the oxide film (for example, the content ratio of type II oxide film) ( In FIG. 3, timing at time t1).

  When the total amount of the oxide film thus obtained exceeds the predetermined amount α (step S5: YES), the idle operation is continued as it is (timing at time t3 in FIG. 3), and the power generation of the fuel cell stack 20 is performed. Electric power is charged in the battery 52 (step S7). When the remaining capacity of the battery is equal to or less than a predetermined amount β (for example, 50%) (step S9: NO), the process returns to step S7 and the idle operation is continued to generate the power generated by the fuel cell stack 20 to the battery 52. Continue charging.

  On the other hand, when the remaining capacity of the battery (shown as SOC in FIG. 4) exceeds the predetermined amount β (step S9: YES), the operation state of the fuel cell system 10 is shifted from the idle operation to the intermittent operation (step S9). S11). And if the controller 60 detects the signal which instruct | indicates completion | finish of an intermittent operation, it will be determined whether the total amount of an oxide film exceeds predetermined amount (alpha) '(step S13).

The determination in step S13 is the same as the determination in step S5 except that the predetermined amount α ′ as a threshold value is different from the predetermined amount α, and thus description thereof is omitted here.
An example of a signal instructing the end of intermittent operation corresponds to a case where the accelerator opening signal ACC output from the accelerator sensor indicates an accelerator opening (accelerator ON) that is equal to or greater than a predetermined opening.

  If the total amount of the oxide film exceeds the predetermined amount α ′ (step S13: YES), a refresh process is performed (step S15, timing at time t4 in FIG. 3), and then the fuel cell system 10 The operation state is shifted from intermittent operation to normal load operation (step S17). On the other hand, when the total amount of the oxide film is equal to or less than the predetermined amount α ′ (step S13: NO), the operation state of the fuel cell system 10 is shifted from the intermittent operation to the normal load operation without performing the refresh process ( Step S17).

Here, it supplements about a refresh process.
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.

  In the refresh process, the oxide film is reduced by lowering the cell voltage to a reduction voltage (hereinafter sometimes referred to as refresh voltage) for a predetermined time (hereinafter sometimes referred to as refresh time), and the oxide film is removed from the catalyst surface. It is a removal process. More specifically, the output current is increased by dropping the voltage of each cell, that is, the output voltage of the fuel cell stack 20 for a predetermined time, and the electrochemical reaction in the catalyst layer 24a is transitioned from the oxidation reaction region to the reduction reaction region. To recover the catalytic activity.

  As is clear from the above description, the predetermined amount α ′ used for the determination in step S13 is a threshold for determining whether or not the refresh process is necessary, whereas the predetermined amount used for the determination in step S5. α is a value larger than the predetermined amount α ′, and when the remaining capacity of the battery 52 is equal to or less than the predetermined amount β, even when refresh processing necessary and sufficient for recovering the performance of the catalyst layer 24a is performed, This is a threshold value that can secure a sufficient remaining capacity of the battery 52 necessary and sufficient to suppress the decrease.

  Therefore, when the total amount of the oxide film is equal to or less than the predetermined amount α (step S5: NO), it is not necessary to continue the idle operation and charge the generated power of the fuel cell stack 20 to the battery 52. The processing of step S7 and step S9 is skipped, and the operation state of the fuel cell system 10 is shifted from idle operation to intermittent operation (step S11).

  As described above, in the present embodiment, there are main features in steps S5, S7, and S9 in FIG. 4, and thus the description of steps S5, S7, and S9 will be supplemented below.

  When the total amount of the oxide film exceeds the predetermined amount α (step S5: YES), the operation state of the fuel cell system 10 is shifted from the idle operation to the intermittent operation without executing the processing of step S7 and step S9 ( If step S11) is performed, the remaining capacity of the battery 52 after the execution of the refresh process is insufficient, and drivability may be deteriorated. That is, when the total amount of the oxide film is large, the time required for the refresh process (refresh time) becomes long and the discharge amount of the battery 52 increases, so that the remaining capacity of the battery 52 becomes insufficient when a sudden high load is requested. There is a risk of inviting.

  However, in this embodiment, in order to avoid such a situation, when the total amount of the oxide film is large (that is, exceeds the predetermined amount α) (step S5: YES), the remaining capacity of the battery 52 is always increased. If the remaining capacity of the battery 52 is insufficient (that is, not more than the predetermined amount β) (step S9: NO), even if the total amount of the oxide film performs the refresh process (step S9). Even when the power amount has been reached (step S5: YES), the battery 52 in the idle operation state is charged by deliberately delaying the transition timing without immediately shifting to the intermittent operation (step S11). Continue (step S7).

  That is, in this embodiment, when the total amount of the oxide film is large (that is, exceeds the predetermined amount α) (step S5: YES), priority is given to securing the remaining capacity of the battery 52 over the execution of the refresh process. I have to. Therefore, even when a refresh process with a long refresh time is performed during intermittent operation and a high load request is made thereafter, the remaining capacity of the battery 52 is sufficiently secured, so that drivability is ensured. .

  In the embodiment illustrated in FIG. 3, the example in which the refresh process is performed after the operation state of the fuel cell system 10 has shifted from the intermittent operation to the normal load operation has been described. The timing of the refresh process is illustrated in FIG. 8, for example. Thus, the timing (time t5) immediately after the operating state of the fuel cell system 10 shifts from idle operation to intermittent operation or a predetermined timing (time t6) during intermittent operation may be used.

  Note that the broken lines in FIG. 8 indicate changes in the cell voltage when the refresh process is performed. Further, in FIG. 8, for convenience of explanation, a case where the refresh process is performed at a timing (time t5) immediately after the operation state of the fuel cell system 10 shifts from the idle operation to the intermittent operation, and a predetermined timing during the intermittent operation. Both cases where the refresh process is performed at (time t6) are shown in one drawing.

  When the refresh process is performed during intermittent operation, the refresh voltage may be changed according to the vehicle speed, for example, as shown in FIG.

  Note that the broken lines in FIG. 9 indicate changes in the cell voltage when the refresh process is performed. For convenience of explanation, FIG. 9 shows a first refresh process (in FIG. 9, it is shown that the refresh voltage is set to V2), and the refresh voltage is set to V2. Both of the second refresh processes set to lower V3 (shown in FIG. 9 to be performed at the timing of time t8) are shown in one figure.

(First refresh process)
When the vehicle speed detected based on the vehicle speed signal VC output from the vehicle speed sensor exceeds the predetermined value ε, in other words, when it is determined that there is a possibility that the accelerator is further depressed to accelerate (output increase request is In the case of being predicted), for example, by setting the refresh voltage to the voltage V2 necessary for removing the I-type oxide film, the decrease in the cell voltage is suppressed as much as possible to ensure drivability.

(Second refresh process)
On the other hand, when the vehicle speed detected based on the vehicle speed signal VC output from the vehicle speed sensor is equal to or less than the predetermined value ε, in other words, when it is determined that the possibility of acceleration by further depression of the accelerator is low (output increase request is When it is not predicted), it is not necessary to consider ensuring drivability, so that the refresh voltage is lowered to, for example, the voltage V3 necessary for removing the II-type oxide film or the III-type oxide film, thereby reducing the catalyst layer 24a. Sufficient performance recovery.

(Modification of second refresh process)
The refresh process for reducing the refresh voltage to the voltage V3 is not only performed when the vehicle speed falls below the predetermined value ε, but, for example, the shift lever is in the P range (parking), the N range (neutral), It may be in the range of any one of the B range (engine brake). This is because the case where the shift lever is in such a range corresponds to a case where it is determined that the possibility of acceleration is low (when an output increase request is not predicted).

In the above-described embodiment, the mode in which the refresh voltage is changed according to the vehicle speed and the state of the shift lever has been described. However, the refresh time may be changed.
For example, when the vehicle speed is a predetermined value ε or less, or when the shift lever is in the P range, N range, or B range, the vehicle speed exceeds the predetermined value ε or the shift lever is in the P range, N range, For example, the refresh time may be longer than that in the D range other than the B range.

  Moreover, in each above-mentioned embodiment, although the usage form which uses the fuel cell system 10 as a vehicle-mounted power supply system was illustrated, the usage form of the fuel cell system 10 is not restricted 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.

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 with the fuel cell with respect to a load;
A controller for performing a performance recovery process of the catalyst layer by reducing the output voltage of the fuel cell to a predetermined voltage,
When a predetermined intermittent operation execution condition is satisfied, an intermittent operation in which a power generation command value to the fuel cell is set to zero and power supply to the load is provided by power from the power storage device can be performed. A fuel cell system in which the performance recovery process is performed during operation,
When the remaining capacity of the power storage device is equal to or less than a predetermined amount when the performance recovery process needs to be performed, the control device delays the execution timing of the intermittent operation, and the remaining capacity is A fuel cell system that performs charging of the power storage device until a fixed amount is exceeded. The fuel cell system according to claim 1, wherein
The said control apparatus is a fuel cell system which estimates the timing of the output increase request | requirement with respect to the said fuel cell, and determines the content of the said performance recovery process based on the prediction result. The fuel cell system according to claim 2, wherein the fuel cell system is mounted on a fuel cell vehicle as an in-vehicle power source.
The said control apparatus is a fuel cell system which estimates the timing of the output increase request | requirement with respect to the said fuel cell based on the driving state of the said vehicle. The fuel cell system according to claim 2, wherein
A first oxide film that can be removed by reducing the output voltage of the fuel cell to a first film removal voltage, and an output of the fuel cell; A second oxide film that cannot be removed unless the voltage is lowered to a second film removal voltage lower than the first film removal voltage,
When the performance recovery process needs to be performed, the control device changes the predetermined voltage to be reduced according to the prediction result. The fuel cell system according to claim 2, wherein
A first oxide film that can be removed by reducing the output voltage of the fuel cell to a first film removal voltage, and an output of the fuel cell; A second oxide film that cannot be removed unless the voltage is lowered to a second film removal voltage lower than the first film removal voltage,
The control device changes the execution time of the performance recovery process according to the prediction result when the performance recovery process needs to be performed.

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