JP2009152131A - Fuel cell system - Google Patents

Abstract

A fuel cell system capable of optimally controlling the operation of an air bypass valve in accordance with the operating state of a fuel cell.
When the ECU determines that it is time to return the opening degree of the air bypass valve to 0% during the rapid warm-up B, the ECU starts the abutting process (step S100 → step S200). If there is an instruction to open the air bypass valve due to the necessity of quick warm-up or the like during the origin abutting process (step S200 → step S300), the ECU gives priority to this instruction and abuts the origin. The process is canceled, and the air bypass valve is controlled to open at a desired timing (step S400 → step S500). This makes it possible to prevent problems such as abnormalities in the output of the fuel cell stack due to excessive air stoichiometric ratio.
[Selection] Figure 7

Description

  The present invention relates to a fuel cell system, and more particularly to a fuel cell system that performs operation control in consideration of the charge / discharge amount with respect to the capacity component of the fuel cell.

  A fuel cell is a power generation system that directly converts energy released during an oxidation reaction into electrical energy by oxidizing fuel by an electrochemical process. Both sides of an electrolyte membrane for selectively transporting hydrogen ions Has a stack structure in which a plurality of membrane-electrode assemblies are sandwiched between a pair of electrodes made of a porous material. Among them, a solid polymer electrolyte fuel cell using a solid polymer membrane as an electrolyte is expected to be used as an in-vehicle power source because it is low-cost and easy to downsize and has a high output density. .

In general, this type of fuel cell has an optimum temperature range of 70 to 80 ° C. for power generation. However, in an environment such as a cold region, it may take a long time to reach the optimum temperature range after startup. Therefore, various warm-up systems are being studied. For example, Patent Document 1 below discloses a technique for controlling the self-heat generation amount of a fuel cell by performing low-efficiency operation with lower power generation efficiency than normal operation and warming up the fuel cell. According to this method, since the fuel cell can be self-warmed, it is not necessary to mount a warm-up device, and the convenience is excellent.
Japanese Patent Application No. 2007-541078

  By the way, the fuel cell system configured as described above is provided with a bypass passage for guiding a part of the oxidizing gas flowing through the gas supply passage to the discharge passage and an air bypass valve for adjusting the bypass amount of the oxidizing gas. It has been. By controlling the valve opening (0 to 100%) of the air bypass valve, the stoichiometric ratio (air stoichiometric ratio) of the oxidizing gas supplied to the fuel cell is adjusted. Conventionally, when an air bypass valve that has been adjusted to a certain degree of opening is fully closed, a closed state is reliably formed (that is, in order to prevent the air bypass valve from closing poorly) as follows. The origin abutting process (origin learning process) was always performed.

  FIG. 8 is a diagram for explaining the origin bypassing process of the air bypass valve. The horizontal axis indicates the number of motor driving steps and the valve opening that controls the valve opening of the air bypass valve, and the vertical axis supplies the fuel cell. Shows the flow rate of the oxidizing gas.

  When the air bypass valve is fully closed, after the motor driving step is completed at 0 step, the motor is driven further in the closing direction by 12 steps and abutting is performed (the origin abutting position shown in FIG. 8). Return to the position of 0 step by returning to the opening direction by 4 steps. When performing the abutting process, the motor driving speed during the abutting process is set slower than that during normal driving in order to prevent misalignment (so-called bounce back) due to rebound, for example, the motor during normal driving. Is set to about 250 (pps), while the driving speed of the motor during the abutting process is set to about 16.5 (pps).

  Therefore, it takes time until the air bypass valve is fully closed after it is instructed to fully close the air bypass valve. Even if there is an instruction to open the air bypass valve, the abutting process has always been prioritized, so the air bypass valve does not open at the desired timing, and the fuel cell output is abnormal due to excessive air stoichiometric ratio (overcurrent) A problem such as an abnormality) has occurred.

  The present invention has been made in view of the circumstances described above, and an object thereof is to provide a fuel cell system capable of optimally controlling the operation of the air bypass valve in accordance with the operating state of the fuel cell.

  In order to solve the above problems, a fuel cell system according to the present invention is a fuel cell system that warms up a fuel cell by performing low-efficiency operation with lower power generation efficiency than normal operation. A bypass passage for bypassing the fuel cell to a discharge passage with a part of the cathode gas flowing through the gas supply passage; a bypass valve for controlling a bypass amount of the cathode gas; and an origin when the bypass valve is fully closed If there is an instruction to open the bypass valve while the low-efficiency operation is being performed and the origin learning process is being performed, the origin learning process is forcibly terminated. And valve opening control means for adjusting the opening of the bypass valve in accordance with the instruction.

  According to such a configuration, there is an instruction to open the cathode gas (oxidizing gas) bypass valve due to the necessity of rapid warm-up while performing the origin learning process (origin butt process) during low-efficiency operation. In this case, the origin learning process is forcibly terminated (cancelled) by giving priority to this instruction, and the bypass valve is opened (see α2 and the bold line portion shown in FIG. 6). This makes it possible to prevent problems such as an abnormality in the output of the fuel cell stack due to an excessive air stoichiometric ratio or the like.

  Here, in the above configuration, the low-efficiency operation includes a first low-efficiency operation and a second low-efficiency operation having a power generation efficiency lower than that of the first low-efficiency operation. The degree control means has an instruction to switch from the first low-efficiency operation to the second low-efficiency operation during the first low-efficiency operation and performing the origin learning process, When it is determined that the bypass valve should be opened, it is preferable that the origin learning process is forcibly terminated and the opening degree of the bypass valve is adjusted according to the instruction.

  Another fuel cell system according to the present invention is a fuel cell system for warming up a fuel cell by performing a low efficiency operation having a lower power generation efficiency than a normal operation, wherein the gas supply path of the fuel cell A bypass passage that bypasses the fuel cell to the discharge passage, a bypass valve that controls the bypass amount of the cathode gas, and when the bypass valve is to be fully closed, Determining means for determining an operation state of the fuel cell and determining whether to prohibit or permit the origin learning process based on the determination result; and a learning processing means for performing the origin learning process when permitted by the determining means. It is characterized by comprising.

  As described above, by determining whether the origin learning process is prohibited or permitted depending on the operating state of the fuel cell, problems such as abnormalities in the output of the fuel cell due to excessive air stoichiometric ratio or the like may occur. It becomes possible to prevent.

  Here, in the above configuration, it is preferable that the determination unit determines that the origin learning process should be prohibited when the operating state of the fuel cell at the time is the low-efficiency operation.

  According to the present invention, it is possible to optimally control the operation of the air bypass valve in accordance with the operating state of the fuel cell.

A. First Embodiment Hereinafter, an embodiment according to the present invention will be described with reference to the drawings.
FIG. 1 shows a system configuration of a fuel cell system 10 mounted on a vehicle according to the present embodiment. In the following description, a fuel cell vehicle (FCHV) is assumed as an example of the vehicle, but the present invention can also be applied to an electric vehicle and a hybrid vehicle. Further, it can be applied not only to vehicles but also to various moving bodies (for example, ships, airplanes, robots, etc.), stationary power sources, and portable fuel cell systems.

  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, a cooling system 60 for cooling the fuel cell stack 20, and a controller (ECU) 70 for controlling the entire system are provided.

The fuel cell stack 20 is a solid polymer electrolyte cell stack formed by stacking a plurality 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. The fuel cell stack 20 as a whole undergoes an electromotive reaction of the formula (3).
_{^{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)

  A voltage sensor 71 for detecting the output voltage of the fuel cell stack 20 and a current sensor 72 for detecting the generated current are attached to the fuel cell stack 20.

  The oxidizing gas supply system 30 includes an oxidizing gas passage 34 through which oxidizing gas supplied to the cathode electrode of the fuel cell stack 20 flows, and an oxidizing off gas passage 36 through which oxidizing off gas discharged from the fuel cell stack 20 flows. . In the oxidizing gas passage 34, an air compressor 32 that takes in the oxidizing gas from the atmosphere via the filter 31, a humidifier 33 for humidifying the oxidizing gas supplied to the cathode electrode of the fuel cell stack 20, and an oxidizing gas supply A throttle valve 35 for adjusting the amount is provided. The oxidizing off gas passage 36 is provided with a back pressure adjusting valve 37 for adjusting the oxidizing gas supply pressure. Here, the humidifier 33 exchanges moisture between the low wet state oxidizing gas flowing through the oxidizing gas passage 34 and the high wet state oxidizing off gas flowing through the oxidizing off gas passage 36, and is supplied to the fuel cell stack 20. Moderately humidify the oxidizing gas.

  Between the oxidizing gas passage 34 and the oxidizing off-gas passage 36, a bypass passage 38 for guiding a part of the oxidizing gas flowing through the oxidizing gas passage 34 to the discharge passage (not shown) bypassing the fuel cell stack 20, and the bypass passage An air bypass valve 39 that adjusts the flow rate of the oxidizing gas flowing through the valve 38 (that is, the bypass amount of the oxidizing gas) is provided. Various drive valves (such as a motor drive valve and a solenoid valve) can be applied to the air bypass valve 39. In the present embodiment, the adjustment of the opening degree of the air bypass valve 39 and the execution of the above-described origin abutting process (origin learning process) are controlled by the ECU 70 according to the operating state of the fuel cell stack 20 (detailed later).

  The fuel gas supply system 40 includes a fuel gas supply source 41, a fuel gas passage 45 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 46 for returning the off gas to the fuel gas passage 45, a circulation pump 47 that pumps the fuel off gas in the circulation passage 46 to the fuel gas passage 43, and an exhaust drainage passage 48 that is branched and connected to the circulation passage 47. Have.

  The fuel gas supply source 41 is made 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 42 is opened, the fuel gas flows out from the fuel gas supply source 41 into the fuel gas passage 45. The fuel gas is decompressed to, for example, about 200 kPa by the regulator 43 and the injector 44 and supplied to the fuel cell stack 20.

The fuel gas supply source 41 includes a reformer that generates a hydrogen-rich reformed gas from a hydrocarbon-based fuel, and a high-pressure gas tank that stores the reformed gas generated by the reformer in a high-pressure state. It may be configured.
The regulator 43 is a device that regulates the upstream side pressure (primary pressure) to a preset secondary pressure, and includes, for example, a mechanical pressure reducing valve that reduces the primary pressure. The mechanical pressure reducing valve has a housing in which a back pressure chamber and a pressure adjusting chamber are formed with a diaphragm therebetween, and the primary pressure is reduced to a predetermined pressure in the pressure adjusting chamber by the back pressure in the back pressure chamber. It has a configuration for the next pressure.

  The injector 44 is an electromagnetically driven on-off valve capable of adjusting the gas flow rate and gas pressure by driving the valve body directly with a predetermined driving cycle with an electromagnetic driving force and separating the valve body from the valve seat. The injector 44 includes a valve seat having an injection hole for injecting gaseous fuel such as fuel gas, a nozzle body for supplying and guiding the gaseous fuel to the injection hole, and an axial direction (gas flow direction) with respect to the nozzle body. And a valve body that is slidably accommodated and opens and closes the injection hole.

  An exhaust / drain valve 49 is disposed in the exhaust / drain passage 48. The exhaust / drain valve 49 is operated according to a command from the controller 70 to discharge the fuel off-gas and impurities including impurities in the circulation passage 46 to the outside. By opening the exhaust drain valve 49, the concentration of impurities in the fuel off-gas in the circulation passage 46 is lowered, and the hydrogen concentration in the fuel off-gas circulating in the circulation system can be increased.

  The fuel off gas discharged through the exhaust drain valve 49 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 47 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 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 charge / discharge of the battery 52 is controlled by these functions of the DC / DC converter 51. Further, the operation point (output voltage, output current) of the fuel cell stack 20 is controlled by voltage conversion control by the DC / DC converter 51.

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 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 70. 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 cooling system 60 includes refrigerant passages 61, 62, 63, and 64 for flowing the refrigerant circulating in the fuel cell stack 20, a circulation pump 65 for pumping the refrigerant, and heat exchange between the refrigerant and the outside air. A radiator 66, a three-way valve 67 for switching the refrigerant circulation path, and a temperature sensor 74 for detecting the refrigerant temperature are provided. During normal operation after the warm-up operation is completed, the refrigerant flowing out of the fuel cell stack 20 flows through the refrigerant passages 61 and 64 and is cooled by the radiator 66, and then flows through the refrigerant passage 63 and flows into the fuel cell stack 20 again. Thus, the three-way valve 67 is controlled to open and close. On the other hand, during the warm-up operation immediately after system startup, the three-way valve 67 is controlled to open and close so that the refrigerant flowing out of the fuel cell stack 20 flows through the refrigerant passages 61, 62, 63 and again into the fuel cell stack 20.

  The controller 70 is a computer system including a CPU, a ROM, a RAM, an input / output interface, and the like, and each part of the fuel cell system 10 (the oxidizing gas supply system 30, the fuel gas supply system 40, the power system 50, and the cooling system 60). It functions as a control means for controlling. For example, when the controller 70 receives the start signal IG output from the ignition switch, the controller 70 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 is the 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 suspensions) Power consumed by devices, etc., and power consumed by devices (air conditioners, lighting fixtures, audio, etc.) disposed in the passenger space.
Then, the controller 70 determines the distribution of the output power of each of the fuel cell stack 20 and the battery 52, calculates the power generation command value, and oxidizes so that the power generation amount of the fuel cell stack 20 matches the target power. The gas supply system 30 and the fuel gas supply system 40 are controlled. Further, the controller 70 controls the operating point (output voltage, output current) of the fuel cell stack 20 by controlling the DC / DC converter 51 and adjusting the output voltage of the fuel cell stack 20. The controller 70 outputs, for example, each of the U-phase, V-phase, and W-phase AC voltage command values to the traction inverter 53 as a switching command so as to obtain a target torque according to the accelerator opening, and the traction motor 54 The output torque and rotational speed of the motor are controlled.

FIG. 2 shows the CV characteristic (cyclic voltammogram) of the fuel cell stack 20.
This CV characteristic indicates the dynamic electric characteristic of the fuel cell stack 20, and when the voltage of the fuel cell stack 20 is increased at a constant voltage increase rate, the CV characteristic flows into the fuel cell stack 20 from the outside ( When a current flows in the negative direction) and the voltage of the fuel cell stack is lowered at a constant voltage drop rate, the current flows in the direction of flowing from the fuel cell stack 20 to the outside (positive direction). Such dynamic electrical characteristics have been found to be due to the parasitic capacitance component of the fuel cell stack 20.

  Here, when the generated current is suddenly increased or decreased, the ohmic voltage drop caused by the ohmic resistance of the electrolyte membrane of each cell constituting the fuel cell stack 20 follows the change in the generated current with good responsiveness. The activation overvoltage generated in the electric double layer cannot follow the change in the generated current with good responsiveness, and slowly settles to an equilibrium state over a certain period of time. The reason why such a difference occurs is that the electrical characteristics of the electrolyte membrane 22 can be modeled as a resistance element, whereas the electrical characteristics of the electric double layer can be modeled as a capacitor.

FIG. 3 is an equivalent circuit diagram modeling the dynamic electrical characteristics of the fuel cell stack 20.
The fuel cell stack 20 has a circuit configuration in which an ideal fuel cell 28 and a capacitor 29 are connected in parallel. The ideal fuel cell 28 is a model of a virtual fuel cell that does not have the above-described CV characteristics, and behaves equivalent to a variable power source in terms of electrical characteristics. The capacitor 29 is obtained by modeling the electric behavior of the electric double layer formed at the interface as a capacitive element. The external load 56 is an equivalent circuit that models the power system 50. The current flowing from the ideal fuel cell 28 is Ifc, the output voltage of the ideal fuel cell 28 (the output voltage of the fuel cell stack 20) is Vfc, the current flowing into the capacitor 29 is Ic, and the current flowing from the fuel cell stack 20 to the external load 56 is Is. When the capacitance of the capacitor 29 is C and the time is t, the following equations (4) to (5) are established.
Ifc = Ic + Is (4)
Ic = C · ΔVfc / Δt (5)

  As shown in the equations (4) to (5), when the output voltage Vfc is boosted, the current Ic flowing into the capacitor 29 increases according to the amount of change ΔVfc / Δt per unit time. The current Is flowing out to the load 56 decreases. On the other hand, when the output voltage Vfc is stepped down, the current Ic flowing into the capacitor 29 decreases according to the change amount ΔVfc / Δt per unit time, so that the current Is flowing from the fuel cell stack 20 to the external load 56 increases. Thus, by controlling the amount of step-up / step-down of the output voltage Vfc per unit time, the current Is flowing from the fuel cell stack 20 to the external load 56 can be adjusted (hereinafter referred to as ΔV control for convenience).

  As an application example of ΔV control, for example, there is a method of absorbing surplus power in the capacitor 29 by controlling the output voltage Vfc when the power generation demand to the fuel cell stack 20 rapidly decreases during low-efficiency operation. Low-efficiency operation refers to, for example, operating with low power generation efficiency by increasing the power loss by setting the air stoichiometric ratio to less than 1.0 and controlling the amount of reactant gas supplied to the fuel cell stack 20. The air stoichiometric ratio is an oxygen surplus ratio and indicates how much surplus oxygen is supplied to oxygen necessary for reacting with hydrogen without excess or deficiency. When the air stoichiometric ratio is set to be low and the low efficiency operation is performed, the concentration overvoltage becomes larger than that in the normal operation, so that the heat loss (power loss) increases in the energy that can be extracted by the reaction between hydrogen and oxygen.

  The low-efficiency operation is, for example, as a means for rapidly warming up the fuel cell stack 20 by intentionally increasing heat loss at low temperature startup (when the stack temperature is below a predetermined temperature). This is performed when the vehicle is started, when the vehicle is stopped, or while the vehicle is running. In the following description, rapid warm-up by low-efficiency operation that is performed as necessary when the vehicle is started or stopped is referred to as “rapid warm-up A”, and low-efficiency operation that is performed as necessary during vehicle travel is referred to as “rapid warm-up”. The rapid warm-up is called “rapid warm-up B”.

  Rapid warm-up A by low-efficiency operation (second low-efficiency operation) performed when the vehicle is started or stopped, adjusts the amount of oxidant gas to the fuel cell stack 20 so as to obtain a small amount of power such as auxiliary machinery However, it is carried out until the stack temperature rises to a predetermined temperature (for example, 70 ° C.). When the stack temperature reaches a predetermined temperature, the operation is switched to normal operation.

  On the other hand, the rapid warm-up B by the low-efficiency operation (first low-efficiency operation) performed while the vehicle is traveling is performed until the stack temperature is raised to a predetermined temperature (for example, 70 ° C.). Is different from the rapid warm-up A in that a large voltage needs to be secured in order to drive the traction motor 54 since it is performed while the vehicle is running (for example, shift position D).

FIG. 4 is a diagram showing IV characteristics of the fuel cell stack 20.
During normal operation, operation control is performed so that the operation point (output current Ifc, output voltage Vfc) is positioned on the IV characteristic curve (current vs. voltage characteristic curve) 200 in order to increase power generation efficiency.
On the other hand, the operation point of the rapid warm-up A by the low-efficiency operation performed when the vehicle is started or stopped is an operation point that is considerably lower than the IV characteristic curve 200, for example, output voltage Vfc = V1, output current Ifc = On the other hand, the operating point of the rapid warm-up B due to the low-efficiency operation performed when the vehicle is traveling is lower than the IV characteristic curve 200 but higher than the operating point of the rapid warm-up A, for example, output The voltage Vfc = V2 and the output current Ifc = I2 are set. As described above, the reason why the operating point of the rapid warm-up B is set higher than the operating point of the rapid warm-up A as described above is the request from the load (traction motor, various auxiliary devices, etc.) during traveling of the vehicle. This is because the voltage or the like is set higher than the required voltage when the vehicle is started or when the vehicle is stopped.

Next, an operation control method of the fuel cell stack 20 when normal operation, rapid warm-up A, and rapid warm-up B are performed will be described with reference to FIG.
FIG. 5 is a state transition diagram showing transition of the operation state of the fuel cell stack 20.
As shown in FIG. 5, IV control is performed in normal operation, warm-up voltage control is performed in rapid warm-up A, and ΔV control and fixed voltage control are performed in rapid warm-up B. Each operation control will be described. First, “IV control” performed during normal operation means that the operation is controlled so that the operation point is located on the IV characteristic curve 200, and the DC / DC converter. The output voltage Vfc of the fuel cell stack 20 is controlled by 51, and the output current Ifc is adjusted by controlling the amount of oxidizing gas supplied to the fuel cell stack 20.

  On the other hand, the “warm-up voltage control” performed during the rapid warm-up A is set to an operating point that is considerably lower than the IV characteristic curve 200 as described above, for example, the output voltage Vfc = V1 and the output current Ifc = I1. And controlling the output voltage Vfc of the fuel cell stack 20 by the DC / DC converter 51 and greatly reducing the amount of oxidizing gas supplied to the fuel cell stack 20 (for example, reducing the air stoichiometric ratio). The output current Ifc is adjusted by adjusting the output current to 1.0 or less.

  “Fixed control” performed during the rapid warm-up B is to fix the output voltage Vfc of the fuel cell stack 20 to the rapid warm-up target voltage (that is, to be fixed) and to be supplied to the fuel cell stack 20. Controlling the output power from the fuel cell stack 20 by controlling the oxidizing gas flow rate and adjusting the output current Ifc (that is, power control).

  Furthermore, “ΔV control” performed during the rapid warm-up B is performed by controlling the amount of step-up / step-down of the output voltage Vfc per unit time in consideration of the capacity component of the fuel cell stack 20 shown in FIG. By adjusting the current Is flowing from the fuel cell stack 20 to the external load 56, the electric power supplied from the fuel cell stack 20 to the external load 56 (the sum of the power generated by the fuel cell stack 20 and the discharge power from the capacitor 29) ) Is controlled.

  FIG. 6 is a timing chart showing operation control of the fuel cell stack 20 when the rapid warm-up B is switched to the rapid warm-up A.

  For example, when the temperature of the fuel cell stack 20 detected by the temperature sensor 74 does not satisfy the threshold temperature Tth (for example, 70 ° C.), the rapid warm-up B by the low efficiency operation is performed even while the vehicle is traveling. Here, when the warm-up B is being performed, for example, when the driver switches from accelerator on to accelerator off, and the power generation demand for the fuel cell stack 20 decreases rapidly, the ECU 70 fixes the operation control of the fuel cell stack 20. In addition to switching from voltage control to ΔV control, control is performed to open the valve opening of the air bypass valve 39 from 0% (fully closed) to 25% in order to lower the air stoichiometric ratio as the output voltage Vfc increases (see FIG. 6). See t1). At this time, the rotational speed of the air compressor 32 is also adjusted.

  When the surplus power is absorbed by the ΔV control, the ECU 70 switches the operation control of the fuel cell stack 20 from the ΔV control to the fixed voltage control again, and the valve opening of the air bypass valve 39 is set to 25 to increase the air stoichiometric ratio. Control to close from 0% to 0% (that is, full close control) is performed (see t2 shown in FIG. 6).

When the fully closed control is started for the air bypass valve 39, the ECU 70 starts the abutting process of the air bypass valve 39 as described above.
Here, in the conventional fuel cell system, once the air bypass valve 39 is instructed to be fully closed and the home position abutting process is started, even if the warm-up process is required during the home position abutting process, etc. Even if there is an instruction to open the air bypass valve 39, the origin abutting process has always been prioritized (see α1 and the one-dot chain line portion shown in FIG. 6). For this reason, the air bypass valve 39 is not opened at a desired timing, and problems such as abnormalities in the output of the fuel cell stack 20 (abnormality of overcurrent, etc.) have occurred due to excessive air stoichiometric ratio. (See the section of the problem and FIG. 8).

  On the other hand, in the present embodiment, there is an instruction to open the air bypass valve 39 due to the necessity of rapid warm-up or the like during the origin abutting process even after the origin abutting process is started. In this case (here, an instruction to switch from the rapid warm-up B to the rapid warm-up A; see t3 in FIG. 6), the home position abutting process is canceled (forced termination) by giving priority to this instruction, and the desired timing The air bypass valve 39 is controlled to open (see α2 and the thick line portion shown in FIG. 6). This makes it possible to prevent problems such as abnormalities in the output of the fuel cell stack 20 due to excessive air stoichiometric ratio.

Hereinafter, the operation in the case where there is an instruction to open the bypass valve 39 (here, the full opening instruction) by switching from the rapid warming B to the rapid warming A after the full-closed control is started will be described in detail.
After the fully closed control is started, the ECU 70 performs an operation from the shift position D range to the P range, for example, by the driver. When the ECU 70 receives an operation stop instruction of the fuel cell stack 20 in response to the operation, the ECU 70 Switching from rapid warm-up B due to low-efficiency operation to rapid warm-up A due to low-efficiency operation when stopped More specifically, the control of the operating point of the fuel cell stack 20 is switched from the fixed warm-up B fixed voltage control to the warm-up voltage control, while the air bypass valve 39 is already started with the abutting process. Cancel (see α2 shown in FIG. 6), and control is performed to switch the opening degree of the air bypass valve 39 from 0% to 100%. The process of canceling the origin abutting process (origin abutting control process) will be described with reference to the flow shown in FIG.

FIG. 7 is a flowchart showing an origin abutting control process executed by the ECU 70.
When the ECU (learning processing means) 70 determines that the timing for returning the opening degree of the air bypass valve 39 to 0% during the rapid warm-up B (that is, the timing for the fully closed control) has arrived, the home position abutting process is performed. Start (step S100 → step S200).
Thereafter, the ECU 70 determines whether or not the timing for changing the opening degree of the air bypass valve 39 (that is, the timing at which the opening degree of the air bypass valve 39 should be set to a value larger than 0%) has arrived (step S300). ). Specifically, an operation from the shift position D range to the P range is performed by the driver, and an instruction to stop the operation of the fuel cell stack 20 is received in response to the operation. When switching to rapid warm-up A due to low-efficiency operation during stoppage, the ECU 70 has reached the timing for changing the opening of the air bypass valve 39 (here, the timing at which the opening should be changed from 0% to 100%). to decide.

  When the ECU (valve opening control means) 70 determines that the change timing of the opening of the air bypass valve 39 has arrived (step S300; YES), the control of the operating point of the fuel cell stack 20 is performed by the rapid warm-up B. While switching from fixed voltage control to warm-up voltage control, for the air bypass valve 39, the already-started origin abutting process is canceled (step S400), and the opening degree of the air bypass valve 39 is changed from 0% to 100%. After performing control (adjustment) to switch to (step S500), the process is terminated.

  On the other hand, when the ECU 70 determines that the change timing of the air bypass valve 39 has not yet arrived (step S300; NO), the ECU 70 determines whether or not the origin abutting process has ended (step S600). If the ECU 70 determines that the origin abutting process has not been completed yet (step S600; NO), the ECU 70 returns to step S300 and repeatedly executes the above routine, while determining that the origin abutting process has ended (step S600; NO) Step S600; YES), the process ends.

  As described above, according to the present embodiment, when there is an instruction to open the air bypass valve due to the necessity of quick warm-up or the like during the home position abutting process, this instruction is given priority. The home position abutting process is canceled (forced termination), and control is performed to open the air bypass valve at a desired timing (see α2 and the bold line portion shown in FIG. 6). This makes it possible to prevent problems such as abnormalities in the output of the fuel cell stack due to excessive air stoichiometric ratio.

B. Modified Example (1) In the above-described embodiment, the origin abutting process is canceled when the origin abutting process is performed at the time of switching from the rapid warm-up B to the rapid warm-up A. When the origin abutting process is being performed during low-efficiency operation, such as when the origin abutting process is being performed during A or when the origin abutting process is being performed during rapid warm-up B, The origin abutting process may be canceled.

(2) In the above-described embodiment, when switching from the rapid warm-up B to the rapid warm-up A, if the home position abutting process is performed at the switching time, the home position abutting process is canceled. When there is a possibility of transition from the rapid warm-up B to the rapid warm-up A, the origin abutting process may be prohibited. Specifically, when the timing for returning the opening degree of the air bypass valve 39 to 0% arrives during the rapid warm-up B (when the air bypass valve 39 should be fully closed), the ECU 70 determines the fuel at that time. The operation state of the battery stack 20 is grasped.

  Here, when the operating state of the fuel cell stack 20 is in the rapid warm-up B, the ECU (determination means) 70 determines that there is a possibility that the rapid warm-up B may shift to the rapid warm-up A. Judgment should be prohibited. On the other hand, the ECU (determination means) 70 determines that the home position abutting process should be permitted when the operating state of the fuel cell stack 20 is normal operation. Based on the determination result, the ECU (learning processing means) 70 prohibits the origin abutting process when the operating state of the fuel cell stack 20 is in the rapid warm-up B, while the operating state of the fuel cell stack 20 Is the normal operation, the origin abutting process is permitted and the origin abutting process is performed. Thus, even if it is determined whether to prohibit or allow the origin abutting process according to the operating state of the fuel cell stack 20, an abnormality in the output of the fuel cell stack 20 may occur due to excessive air stoichiometric ratio. Problems can be prevented in advance.

1 is a system configuration diagram of a fuel cell system according to a first embodiment. It is a CV characteristic figure of a fuel cell stack. It is an equivalent circuit diagram of a fuel cell stack. It is explanatory drawing of the operating point of a fuel cell stack. It is a state transition diagram which shows the transition of the driving | running state of a fuel cell stack. 6 is a timing chart showing operation control of the fuel cell stack when the rapid warm-up B is switched to the rapid warm-up A. It is a flowchart which shows an origin butting control process. It is a figure explaining the origin butting process of an air bypass valve.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Fuel cell system, 20 ... Fuel cell stack, 30 ... Oxidation gas supply system, 40 ... Fuel gas supply system, 50 ... Electric power system, 60 ... Cooling system, 70 * ··controller.

Claims (4)

A fuel cell system that warms up a fuel cell by performing low-efficiency operation with lower power generation efficiency than normal operation,
A bypass passage for guiding a part of the cathode gas flowing through the gas supply passage of the fuel cell to the discharge passage by bypassing the fuel cell;
A bypass valve for controlling a bypass amount of the cathode gas;
Learning processing means for performing origin learning processing when the bypass valve is fully closed;
If there is an instruction to open the bypass valve during the low-efficiency operation and the origin learning process, the origin learning process is forcibly terminated and the bypass valve is opened according to the instruction. And a valve opening degree control means for adjusting the degree of the fuel cell system. The low-efficiency operation includes a first low-efficiency operation and a second low-efficiency operation that has lower power generation efficiency than the first low-efficiency operation.
The valve opening control means is instructed to switch from the first low-efficiency operation to the second low-efficiency operation during the first low-efficiency operation and while performing the origin learning process. 2. The fuel cell according to claim 1, wherein when it is determined that the bypass valve should be opened, the origin learning process is forcibly terminated and the valve opening of the bypass valve is adjusted according to the instruction. system. A fuel cell system that warms up a fuel cell by performing low-efficiency operation with lower power generation efficiency than normal operation,
A bypass passage for guiding a part of the cathode gas flowing through the gas supply passage of the fuel cell to the discharge passage by bypassing the fuel cell;
A bypass valve for controlling a bypass amount of the cathode gas;
When the bypass valve is to be fully closed, a determination unit that determines the operating state of the fuel cell at the time point and determines whether to prohibit or allow the origin learning process based on the determination result;
A fuel cell system comprising: learning processing means for performing the origin learning processing when permitted by the determination means.   The fuel cell system according to claim 3, wherein the determination unit determines that the origin learning process should be prohibited when the operation state of the fuel cell at the time is the low-efficiency operation.

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