JP5391227B2 - Fuel cell system and control method thereof - Google Patents

Description

  The present invention relates to a fuel cell system and a control method thereof. More specifically, the present invention relates to a fuel cell system that supplies a low flow amount of oxidant gas and extracts a low current from the fuel cell during idle stop, and a control method thereof.

  In recent years, fuel cell systems have attracted attention as a new power source for automobiles. The fuel cell system includes, for example, a fuel cell that generates electric power by electrochemically reacting a reaction gas, and a reaction gas supply device that supplies the reaction gas to the fuel cell via a reaction gas channel.

  The fuel cell has, for example, a stack structure in which several tens to several hundreds of cells are stacked. Here, each cell is configured by sandwiching a membrane electrode structure (MEA) between a pair of separators. The membrane electrode structure includes an anode electrode (cathode) and a cathode electrode (anode), and a solid polymer electrolyte membrane sandwiched between these electrodes.

  When hydrogen is supplied as fuel gas to the anode electrode of the fuel cell and air is supplied as oxidant gas to the cathode electrode, an electrochemical reaction proceeds to generate electricity. As described above, the fuel cell is preferred in terms of high power generation efficiency because it directly obtains electricity through an electrochemical reaction. Further, since the fuel cell generates only harmless water during power generation, it is considered preferable from the viewpoint of environmental impact.

  By the way, in a fuel cell vehicle using such a fuel cell system as a power source, for example, when idle power generation is continuously performed when the vehicle is stopped such as waiting for a signal, the supply of the oxidant gas and the fuel gas is stopped. Idle stop for stopping idle power generation is executed. By executing this idle stop, the fuel can be used efficiently.

  However, when the idle stop is executed, hydrogen and oxygen staying in the vicinity of the electrolyte membrane react at a high concentration when the cross leak phenomenon occurs, and the electrolyte membrane may be deteriorated. Therefore, by supplying a low-flow oxidant gas to a fuel cell that is idled, the amount of oxygen staying in the vicinity of the electrolyte membrane is reduced to suppress reaction with hydrogen and to suppress deterioration of the electrolyte membrane. It has been proposed (see, for example, Patent Document 1).

JP 2005-327492 A

  By the way, when the current extraction from the fuel cell is completely stopped as in the technique of the above-mentioned Patent Document 1, the fuel cell becomes a high potential by the power generation of hydrogen and oxygen remaining in the fuel cell system, and the electrolyte membrane May deteriorate. For this reason, it is preferable to take out a low current from the fuel cell even during idling stop. Accordingly, by performing idle stop control that supplies a low-flow oxidant gas to the fuel cell and draws a low current from the fuel cell during idle stop, the electrolyte by the reaction of hydrogen and oxygen staying in the vicinity of the electrolyte membrane Both the deterioration of the membrane and the deterioration of the electrolyte membrane due to the high potential of the fuel cell can be suppressed.

  However, when the fuel cell system performing the idle stop control described above is in an environment with a low atmospheric pressure such as a high altitude, that is, in an environment with a low air density, the flow rate of the air supplied as the oxidant gas is reduced to a level. Therefore, the air pump as the oxidant gas supply means operates at a high speed. Then, the rotation speed of the air pump exceeds the upper limit value that guarantees good noise / vibration (hereinafter referred to as “NV (Noise Vibration)”) performance of the fuel cell system during idling stop, and the NV performance deteriorates. There was a problem.

  The present invention has been made in view of the above, and an object of the present invention is to provide a fuel cell system in a low-pressure environment that is performing idle stop control that extracts a low current from the fuel cell while supplying a low-flow oxidant gas. Even in such a case, it is an object of the present invention to provide a fuel cell system and a control method thereof that can suppress deterioration in NV performance.

  In order to achieve the above object, a fuel cell system (for example, a fuel cell system 1 described later) according to the present invention is supplied with an oxidant gas (for example, air described later) and a fuel gas (for example, hydrogen described later). A fuel cell (for example, a fuel cell 10 to be described later) for generating electricity, an oxidant gas supply means (for example, an air pump 21 to be described later) for supplying an oxidant gas to the fuel cell, and a fuel gas to the fuel cell And a fuel gas supply means (for example, a hydrogen tank 22, an ejector 28, and a regulator 261, which will be described later). When predetermined conditions are satisfied during idle power generation, the oxidant gas supply means causes a lower flow rate than during idle power generation. The idle stop control is started to supply the oxidant gas to the fuel cell while taking out a lower current from the fuel cell than during the idle power generation. Stop control means (for example, an idle stop control unit and VCU 15 of ECU 40 described later) and low pressure environment determination means (for example, described later) for determining whether the fuel cell system is in a low pressure environment during the idle stop control. A low pressure environment determination unit, an atmospheric pressure sensor 42 and a GPS sensor 43) of the ECU 40, and an operation restriction means for restricting the operation of the oxidant gas supply means when it is determined that the fuel cell system is in a low pressure environment. (For example, an operation restricting portion of the ECU 40 described later).

  According to the present invention, during idle stop, a fuel cell that performs idle stop control that supplies an oxidant gas having a lower flow rate than that during idle power generation to the fuel cell and extracts a lower current from the fuel cell than during idle power generation. In the system, when the fuel cell system is in a low pressure environment, the operation of the oxidant gas supply means is limited. Specifically, for example, when an air pump is used as the oxidant gas supply means, an upper limit value is set for the rotation speed of the air pump, and the air pump is operated below the upper limit value. As a result, even when the fuel cell system performing the idle stop control is in a low-pressure environment such as a high altitude, the operation of the air pump can be restricted, and the deterioration of the NV performance can be suppressed.

  In this case, the oxidant gas supply means is preferably an air pump (for example, an air pump 21 described later).

  According to this invention, the effect of the said invention is show | played reliably. Moreover, since it is only necessary to control the rotation speed of the air pump, deterioration of NV performance can be suppressed by simple control.

  In addition, the control method of the fuel cell system of the present invention is a fuel cell (for example, a fuel cell 10 described later) that generates power by being supplied with an oxidant gas (for example, air described later) and a fuel gas (for example, hydrogen described later). ), An oxidant gas supply means (for example, an air pump 21 described later) for supplying an oxidant gas to the fuel cell, and a fuel gas supply means for supplying a fuel gas to the fuel cell (for example, a hydrogen tank 22 described later) A control method for a fuel cell system (e.g., a fuel cell system 1 described later) including an ejector 28 and a regulator 261), which starts when a predetermined condition is satisfied during idle power generation, and the oxidant gas supply means While supplying an oxidant gas having a lower flow rate than that during idle power generation to the fuel cell, a lower current is extracted from the fuel cell than during idle power generation. A low pressure environment for determining whether the fuel cell system is in a low pressure environment during an idle stop step (for example, an idle stop control step executed by an idle stop control unit of the ECU 40 described later) and the idle stop step. A determination step (for example, a step shown in step S12 of FIG. 2 described later) and an operation restriction step of restricting the operation of the oxidant gas supply means when it is determined that the fuel cell system is in a low pressure environment ( For example, it is provided with the process shown in step S14 of FIG. 2 mentioned later.

  The control method of the fuel cell system of the present invention is the above-described fuel cell system developed as a method invention, and has the same effect as the above-described fuel cell system.

  According to the present invention, a fuel capable of suppressing deterioration in NV performance even when the fuel cell system that is performing idle stop control for extracting a low current from the fuel cell while supplying a low-flow oxidant gas is in a low-pressure environment. A battery system and a control method thereof can be provided.

1 is a block diagram showing a fuel cell system according to an embodiment of the present invention. It is a flowchart which shows the procedure of the upper limit control process which restrict | limits the upper limit of an air pump rotation speed during idle stop control which concerns on the said embodiment. It is a flowchart which shows the procedure of the low voltage | pressure environment determination process which determines whether it exists in a low voltage | pressure environment during idle stop control which concerns on the said embodiment. It is a flowchart which shows the procedure of the cell voltage recovery control process which recovers a cell voltage during the upper limit control which concerns on the said embodiment. It is a time chart which shows the example of control in case the fall of a cell voltage is normal in the cell voltage recovery control which concerns on the said embodiment. It is a time chart which shows the example of control in case the fall of a cell voltage is abnormal in the cell voltage recovery control which concerns on the said embodiment.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram of a fuel cell system 1 according to this embodiment.
The fuel cell system 1 includes a fuel cell 10, a supply device 20 that supplies a reaction gas to the fuel cell 10, and an electronic control unit (hereinafter referred to as “ECU”) 40 that controls the fuel cell 10 and the supply device 20. Is provided. The fuel cell system 1 is mounted, for example, in a fuel cell vehicle (not shown) that uses electric power generated by the fuel cell 10 as a power source.

  The fuel cell 10 has a stack structure in which, for example, several tens to several hundreds of fuel cells are electrically connected in series and stacked. Each cell is configured by sandwiching a membrane electrode structure (MEA) between a pair of separators. The membrane electrode structure is composed of two electrodes, an anode electrode (cathode) and a cathode electrode (anode), and a solid polymer electrolyte membrane sandwiched between these electrodes. Usually, both electrodes are formed of a catalyst layer that performs an oxidation / reduction reaction in contact with the solid polymer electrolyte membrane and a gas diffusion layer in contact with the catalyst layer.

  In such a fuel cell 10, hydrogen as a fuel gas is supplied to an anode electrode channel 13 formed on the anode electrode (cathode) side, and oxygen is supplied to a cathode electrode channel 14 formed on the cathode electrode (anode) side. When air as an oxidant gas containing oxygen is supplied, an electrochemical reaction between hydrogen and oxygen proceeds to generate electricity.

  The fuel cell 10 is connected via a current limiter (VCU) 15 to a high voltage battery 16 as a power storage device and a drive motor 17 as an electric load. The high-voltage battery 16 and the drive motor 17 are supplied with electric power generated by the fuel cell 10.

The VCU 15 includes a DCDC converter (not shown) and controls the discharge current of the fuel cell 10 based on a current command value output from the ECU 40.
The high voltage battery 16 stores the electric power generated by the fuel cell 10 when the voltage of the high voltage battery 16 is lower than the output voltage of the fuel cell 10. On the other hand, power is supplied to the drive motor 17 as needed to assist the drive of the drive motor 17. The high voltage battery 16 is configured by, for example, a secondary battery such as a lithium ion battery, a capacitor, or the like.

  The supply device 20 includes an air pump 21 as oxidant gas supply means for supplying air to the cathode electrode flow path 14, a hydrogen tank 22 as fuel gas supply means for supplying hydrogen to the anode electrode flow path 13, an ejector 28, and a regulator. 261.

The air pump 21 is connected to one end side of the cathode electrode channel 14 via the air supply channel 23. An air discharge path 24 is connected to the other end side of the cathode electrode flow path 14, and a diluter 50 described later is connected to the front end side of the air discharge path 24. The air discharge path 24 introduces air (oxidant off-gas) discharged from the fuel cell 10 into the diluter 50.
Further, the back pressure valve 241 is provided in the air discharge path 24. The back pressure valve 241 controls the pressure in the air supply passage 23 and the cathode electrode passage 14 to a predetermined pressure.

  The air supply path 23 is provided with a diluting gas flow path 25 for introducing the air compressed by the air pump 21 into the diluter 50 as a diluting gas. The distal end side of the dilution gas channel 25 is connected to the diluter 50. The dilution gas flow path 25 is provided with a dilution gas cutoff valve (not shown) that opens and closes the dilution gas flow path 25.

  The hydrogen tank 22 is connected to one end side of the anode electrode channel 13 through a hydrogen supply channel 26. The ejector 28 is provided in the hydrogen supply path 26. A hydrogen cutoff valve (not shown) for opening and closing the hydrogen supply path 26 and a regulator 261 for controlling the flow rate of hydrogen supplied from the hydrogen tank 22 are provided between the hydrogen tank 22 and the ejector 28 in the hydrogen supply path 26. Is provided.

  Air pressure from the air pump 21 toward the hydrogen supply path 26 is input to the regulator 261 as signal pressure (pilot pressure) through a pipe 31 provided with an orifice (not shown). The regulator 261 controls the hydrogen pressure based on the input air pressure, and thereby the flow rate of the supplied hydrogen is controlled.

  A hydrogen reflux path 27 is connected to the other end side of the anode electrode flow path 13. The distal end side of the hydrogen reflux path 27 is connected to an ejector 28. The hydrogen recirculation path 27 introduces hydrogen (fuel offgas) discharged from the fuel cell 10 into the ejector 28. The ejector 28 collects the hydrogen flowing through the hydrogen reflux path 27 and returns it to the hydrogen supply path 26.

The hydrogen reflux path 27 is provided with a hydrogen discharge path 29 that branches off from the hydrogen reflux path 27 and discharges hydrogen (fuel off-gas). A diluter 50 is connected to the distal end side of the hydrogen discharge path 29.
The hydrogen discharge path 29 is provided with a purge valve 291 that opens and closes the hydrogen discharge path 29. The purge process is executed by opening the purge valve 291, and hydrogen (fuel offgas) discharged from the fuel cell 10 is introduced into the diluter 50.

  The diluter 50 introduced the fuel off-gas introduced through the hydrogen discharge passage 29 and stayed in the diluter 50 through the oxidant off-gas and dilution gas passage 25 introduced through the air discharge passage 24. Dilute with oxidant gas. The fuel off-gas is introduced into the diluter 50 when the purge valve 291 is opened and the purge process is executed, diluted in the diluter 50, and then released to the atmosphere.

  In the present embodiment, the cathode electrode flow path 14, the air supply path 23, the air discharge path 24, and the dilution gas flow path 25 are oxidant gas system flow paths through which the oxidant gas or the oxidant off-gas flows, and in FIG. This is indicated by a black arrow. Further, the anode electrode flow path 13, the hydrogen supply path 26, the hydrogen recirculation path 27, and the hydrogen discharge path 29 are fuel gas flow paths through which fuel gas or fuel off-gas flows, and are indicated by white arrows in FIG.

  The air pump 21, the back pressure valve 241, the dilution gas cutoff valve, the hydrogen cutoff valve and the purge valve 291 are electrically connected to the ECU 40 and controlled by the ECU 40.

  The ECU 40 shapes an input signal waveform from various sensors, corrects a voltage level to a predetermined level, converts an analog signal value into a digital signal value, and a central processing unit (hereinafter, referred to as a central processing unit). "CPU"). In addition, the ECU 40 outputs control signals to a storage circuit that stores various calculation programs executed by the CPU, calculation results, and the like, an air pump 21, a back pressure valve 241, a dilution gas cutoff valve, a hydrogen cutoff valve, and a purge valve 291. Output circuit.

  In addition, a cell voltage sensor 41, an atmospheric pressure sensor 42, and a GPS sensor 43 are electrically connected to the ECU 40. Detection signals from these sensors are transmitted to the ECU 40.

The cell voltage sensor 41 detects a cell voltage for each of the plurality of fuel cells constituting the fuel cell 10. The ECU 40 sets the lowest cell voltage among the detected cell voltages for each fuel cell as the lowest cell voltage.
The cell voltage sensor 41 may be configured to detect two or more of the plurality of fuel cells as one fuel cell group and detect the voltage for each of these fuel cell groups. In this case, the ECU 40 sets the lowest voltage among the voltages for each fuel cell group as the lowest cell voltage.

The atmospheric pressure sensor 42 is provided at the outside air intake port of the air pump 21 and detects the atmospheric pressure at the current position with high accuracy.
The GPS sensor 43 is provided in a navigation system (not shown), receives a GPS signal transmitted from a GPS satellite, and accurately detects the longitude, latitude, and altitude of the current position of the fuel cell vehicle.

  The ECU 40 is a module for executing idle stop control, upper limit control, and cell voltage recovery control, which will be described later, as an idle stop control unit, a low-voltage environment determination unit, an operation restriction unit, a cell voltage threshold determination unit, and a cell voltage drop time determination. And a cell voltage recovery unit.

The idle stop control unit executes idle stop control described later when a predetermined condition is satisfied during idle power generation.
Here, idle power generation, in which power generation is performed at a low stoichiometric ratio compared to normal power generation during vehicle travel, is performed, for example, when the vehicle speed is continuously zero for a predetermined time.
The case where the predetermined condition is satisfied is, for example, a case where the current hydrogen concentration in the diluter 50 is equal to or lower than the predetermined hydrogen concentration and it is determined that the dilution of the fuel off-gas in the diluter 50 is completed. . The predetermined hydrogen concentration is set to a concentration at which high concentration hydrogen is not discharged outside the vehicle when idle stop control described later is executed.
The current hydrogen concentration in the diluter 50 is, for example, the amount of diluting gas introduced into the diluter 50 from the previous purge process after the purge valve 291 is opened and the fuel off-gas is introduced into the diluter 50. Calculated based on the integrated value. That is, if the integrated value of the dilution gas amount introduced into the diluter 50 after the previous purge process is greater than or equal to a predetermined value, it can be determined that the current hydrogen concentration in the diluter 50 is less than or equal to the predetermined hydrogen concentration. is there. The integrated value of the dilution gas amount from the previous purge process is calculated based on the current integrated value from the previous purge process.
Note that whether or not the dilution has been completed may be determined based on, for example, a detection signal of a hydrogen concentration sensor that detects the hydrogen concentration in the gas discharged from the diluter 50.

The idle stop control unit supplies an air having a lower flow rate than that during idle power generation to the fuel cell 10 in response to the establishment of the predetermined condition, while taking out a lower current from the fuel cell 10 than during idle power generation. Start stop control.
Specifically, the idle stop control unit has a current command value (hereinafter referred to as “idle stop current command value”) lower than a current command value during idle power generation (hereinafter referred to as “idle power generation current command value”). Is output to the VCU 15 to control the discharge current of the fuel cell 10. As a result, the discharge current is lower than that during idle power generation. The discharge current is used for driving the air pump 21.
This idle stop control is canceled when the minimum cell voltage of the fuel cell 10 falls below the minimum cell voltage threshold, which will be described later, and the cell voltage recovery control, which will be described later, is executed, or when there is an acceleration request from the driver. Is done.

  Further, the idle stop control unit sets an air flow rate lower than that during idle power generation in accordance with the idle stop current command value, and sends a command value for the air pump rotation speed to the air pump 21 in accordance with the set air flow rate. Output. As a result, air having a lower flow rate than that during idle power generation is supplied to the fuel cell 10. Further, in the fuel cell system 1 of the present embodiment, a signal pressure corresponding to a low flow rate of air is input to the regulator 261, and a lower flow rate of hydrogen is supplied to the fuel cell 10 than during idle power generation. That is, power generation is performed at a lower stoichiometry than during idle power generation. For example, while the stoichiometric ratio is set to about 2.0 in idle power generation, the stoichiometric ratio is set to about 1.0 in the idle stop control of the present embodiment.

The low-pressure environment determination unit determines whether or not the fuel cell vehicle that is executing the idle stop control is in a low-pressure environment.
Specifically, the low-pressure environment determination unit determines whether the atmospheric pressure detected by the atmospheric pressure sensor 42 is below a predetermined atmospheric pressure threshold, or the altitude at the current position detected by the GPS sensor 43 exceeds the predetermined altitude threshold. If it falls under any of the above, it is determined that the fuel cell vehicle is in a low pressure environment.
The predetermined atmospheric pressure threshold is set, for example, to the atmospheric pressure when the rotation speed of the operating air pump 21 increases and the NV performance starts to deteriorate in order to secure the air flow rate supplied during idle stop control. Similarly, the predetermined altitude threshold is set to an altitude at the time when the rotational speed of the operating air pump 21 increases and the NV performance starts to deteriorate, for example, in order to secure the air flow rate supplied during the idle stop control.

The operation restriction unit restricts the operation of the air pump 21 when the low-pressure environment determination unit determines that the fuel cell vehicle that is executing the idle stop control is in a low-pressure environment.
Specifically, a predetermined upper limit value is set for the rotation speed of the air pump 21, and upper limit control for operating the air pump 21 below the upper limit value is executed.
The predetermined upper limit value is set to an upper limit value (for example, 700 rpm) of the rotational speed that can ensure good NV performance of the fuel cell system 1 during the idle stop control.

The cell voltage threshold determination unit determines whether or not the minimum cell voltage of the fuel cell 10 falls below a predetermined minimum cell voltage threshold during the above upper limit control.
More specifically, the cell voltage threshold determination unit acquires the lowest minimum cell voltage among the cell voltages for each fuel cell detected by the cell voltage sensor 41, and the acquired minimum cell voltage is a predetermined minimum cell voltage threshold. It is determined whether or not it falls below.
Here, the predetermined minimum cell voltage threshold is set to a value that is equal to or less than the cell voltage at which current limiting starts from the viewpoint of protection of the fuel cell 10 during normal power generation during vehicle travel, and does not become a negative voltage. Thereby, it is avoided that the discharge current command value is increased although it is necessary to start the current limitation, and a stable cell voltage is secured.

During the upper limit control, the cell voltage decrease time determination unit starts the idle stop control until a minimum cell voltage of the fuel cell 10 falls below the minimum cell voltage threshold (hereinafter referred to as “cell It is determined whether or not the “voltage drop time” is within a predetermined time (hereinafter referred to as “cell voltage abnormal drop determination time”).
More specifically, the cell voltage decrease time determination unit measures and acquires the cell voltage decrease time with a timer, and determines whether or not the acquired cell voltage decrease time is within the cell voltage abnormal decrease determination time. judge. Here, the cell voltage abnormality decrease determination time is set by conducting an experiment in advance.

The cell voltage recovery control unit executes cell voltage recovery control for recovering the cell voltage during the upper limit control.
Specifically, the cell voltage recovery control unit determines the air to be supplied to the fuel cell 10 when the cell voltage threshold determination unit determines that the minimum cell voltage of the fuel cell 10 is lower than the minimum cell voltage threshold. Increase flow rate.
Further, when the cell voltage drop time determination unit determines that the cell voltage drop time is within the cell voltage abnormal drop determination time, the air flow rate is increased as compared with the idle power generation. Specifically, by outputting a current command value higher than the idle power generation current command value (hereinafter referred to as “abnormal cell voltage recovery current command value”) to the VCU 15, the discharge current becomes higher than during idle power generation. . In addition, an air flow rate that is higher than that during idle power generation is set according to the abnormal cell voltage recovery current command value, and a command value for the air pump speed corresponding to the set air flow rate is output to the air pump 21. As a result, air having a higher flow rate than that during idle power generation is supplied to the fuel cell 10. In addition, a signal pressure corresponding to a high flow rate of air is input to the regulator 261, and a higher flow rate of hydrogen than that during idle power generation is supplied to the fuel cell 10. That is, power generation is performed at a higher stoichiometry than during idle power generation.
In addition, when it is determined that the cell voltage drop time is within the cell voltage abnormality drop determination time, the cell voltage recovery control unit increases the air flow rate as the cell voltage drop time is shorter. That is, a current command value corresponding to the cell voltage drop time is output to the VCU 15, and a command value for the air pump rotation speed corresponding to the current command value is output to the air pump 21. Thus, the air flow rate and the hydrogen flow rate are increased according to the cell voltage drop time, that is, the degree of occurrence of the flatting phenomenon.

  Hereinafter, the procedure of the upper limit control process for limiting the upper limit value of the air pump speed during the idle stop control will be described in detail with reference to FIG.

  FIG. 2 is a flowchart showing a procedure of an upper limit control process for limiting the upper limit value of the air pump speed during the idle stop control. The process shown in FIG. 2 is started in response to the ignition switch being turned on, and is repeatedly executed by the ECU every predetermined control cycle.

  In step S11, it is determined whether or not idle stop control is being performed. If this determination is YES, the process proceeds to step S12, and if this determination is NO, this process ends.

  In step S12, after executing low pressure environment determination for determining whether or not the fuel cell vehicle is in a low pressure environment, the process proceeds to step S13. The low-pressure environment determination procedure will be described later with reference to FIG.

  In step S13, it is determined whether or not the fuel cell vehicle is in a low pressure environment based on the determination result in step S12. If this determination is YES, it is determined that it is necessary to limit the operation of the air pump in order to ensure good NV performance, and the process proceeds to step S14. If this determination is NO, it is determined that good NV performance can be ensured without restricting the operation of the air pump, and the present process is terminated.

  In step S14, the operation of the air pump is limited, and this process is terminated. Specifically, a predetermined upper limit value is set for the rotation speed of the air pump, and upper limit control for operating the air pump below the upper limit value is executed. As a result, the operation of the air pump is limited, and good NV performance is ensured.

FIG. 3 is a flowchart showing a low-pressure environment determination process for determining whether or not the vehicle is in a low-pressure environment during idle stop control by the ECU.
In step S21, the atmospheric pressure detected by the atmospheric pressure sensor falls below a predetermined atmospheric pressure threshold, or the altitude at the current position detected by the GPS sensor exceeds the predetermined altitude threshold. It is determined whether or not. If it is at least one and this determination is YES, the process proceeds to step S22, where it is determined that the fuel cell vehicle is in a low-pressure environment, and this process is terminated. If the determination is NO and the determination is NO, it is determined that the fuel cell vehicle is not in a low pressure environment, and the present process is terminated.

Here, in the upper limit control of the present embodiment, the operation of the air pump is restricted and the air flow rate is also restricted, so that a flatting phenomenon occurs in which the water in the gas passage is not completely discharged and the gas passage is blocked. To do. When the flatting phenomenon occurs, air cannot flow, so that hydrogen and oxygen react at a high concentration in the vicinity of the electrolyte membrane, and deterioration of the electrolyte membrane cannot be suppressed. Further, when the flatting phenomenon occurs, the minimum cell voltage of the fuel cell stack is greatly reduced. In this case, the cell voltage becomes unstable immediately after returning from the idle stop, and current limitation may be required.
Therefore, in the present embodiment, the cell voltage recovery control by the cell voltage recovery control unit is executed during the upper limit control. Hereinafter, the cell voltage recovery control of this embodiment will be described with reference to FIG.

FIG. 4 is a flowchart showing the procedure of the cell voltage recovery control process for recovering the cell voltage during the upper limit control.
In step S31, it is determined whether or not the minimum cell voltage of the fuel cell falls below a predetermined minimum cell voltage threshold value during the upper limit control. If this determination is YES, it is determined that a flatting phenomenon has occurred and the cell voltage needs to be recovered by eliminating the flatting phenomenon, and the process proceeds to step S33. If this determination is NO, it is determined that there is no need to recover the cell voltage, and the routine goes to Step S32.

  In step S32, the idle stop current command value is output to the VCU, and the supply of air and hydrogen at a low flow rate according to the idle stop current command value is continued. That is, the idle stop control is continued and this process is terminated.

  In step S33, it is determined whether or not the cell voltage drop time is within a predetermined cell voltage abnormality drop determination time. If this determination is YES, it is determined that an abnormal drop in the cell voltage is observed due to the occurrence of the flatting phenomenon, and the flatting phenomenon cannot be resolved unless the air flow rate is increased as compared with the idle power generation, and the process proceeds to step S35. If this determination is NO, a normal drop in the cell voltage is recognized, and it is determined that the flatting phenomenon can be eliminated by increasing the air flow rate to the same amount as during idle power generation, and the process proceeds to step S34.

  In step S34, the idle power generation current command value is output to the VCU, and air and hydrogen having a flow rate higher than the flow rate corresponding to the idle stop current command value and corresponding to the idle power generation current command value are supplied. As a result of the higher flow rate of air and hydrogen being supplied, the flatting phenomenon is eliminated, the deterioration of the electrolyte membrane is suppressed, and the cell voltage is recovered. As a result, the idle stop control and the upper limit control are canceled, and this process ends.

  In step S35, the abnormal cell voltage recovery current command value is output to the VCU, and air and hydrogen at a flow rate corresponding to the abnormal cell voltage recovery current command value, which is higher than the flow rate corresponding to the idle power generation current command value. Supply. As a result of supplying higher flow rates of air and hydrogen, the flatting phenomenon is more reliably eliminated, the deterioration of the electrolyte membrane is suppressed, and the cell voltage is recovered. As a result, the idle stop control and the upper limit control are canceled, and this process ends.

FIG. 5 is a time chart showing an example of control in the case where the cell voltage drop is normal in the cell voltage recovery control according to the present embodiment. The control example shown in FIG. 5 executes idle stop control for a fuel cell vehicle in a low pressure environment.
As described above, in the fuel cell system of the present embodiment, the air flow rate is set according to the current command value, and the hydrogen flow rate is set according to the air pressure based on the set air flow rate. (Pressure, stoichiometry), hydrogen flow rate (pressure, stoichiometry), and output current all show similar changes. Therefore, FIG. 5 shows only the air flow rate among them (the same applies to FIG. 6 described later).

First, at time _t 10 _{~t 11,} it executes the idling power generation. Specifically, the idle power generation current command value is output to the VCU, and the command value of the air pump speed corresponding to the idle power generation current command value is output to the air pump. As a result, air and hydrogen are supplied at a lower flow rate than during normal operation during vehicle travel, and the discharge current is reduced compared to during normal power generation. At this time, the average cell voltage and the minimum cell voltage are substantially equal, and no abnormality in the cell voltage is confirmed.

Next, at times t _{11 to} t ₁₃ , the idle stop control of this embodiment is executed. Specifically, as described above, the idle stop current command value is output to the VCU, and the command value of the air pump speed corresponding to the idle stop current command value is output to the air pump. At this time, since the fuel cell vehicle is in a low pressure environment, upper limit control for limiting the operation of the air pump is also executed.
Thereby, in a state where the NV performance is ensured, air and hydrogen having a lower flow rate than that during idle power generation are supplied, and the air flow rate decreases as shown in FIG. Further, it reduces the discharge current than during idling power generation, both at time t ₁₁ the average cell voltage and the lowest cell voltage is slightly higher. Thereafter, between times t _13, whereas no significant change was observed in the average cell voltage has decreased minimum cell voltage gradually.
Incidentally, from the time t ₁₁ that initiated the idling stop control, at a time t ₁₂ that the cell voltage abnormality drop determination time has elapsed, the minimum cell voltage is not below a minimum cell voltage threshold. Therefore, it is determined that the recovery time t ₁₂ in the cell voltage is still required to continue the supply of low flow air (see step S2 of FIG. 2).

Next, at time t _13, since the minimum cell voltage is below the highest unit cell voltage threshold, flooding phenomenon occurs, it is determined that it is necessary to recover the cell voltage by eliminating the flooding phenomenon, the flow rate of air Increase to restore cell voltage. At this time, since the time t ₁₁ that initiated the idling stop control has passed the cell voltage abnormality drop determination time has already determined that by increasing until the air flow rate during idling power generation can be resolved flooding phenomenon, idle The power generation current command value is output to the VCU, and the command value for the air pump speed corresponding to the idle power generation current command value is output to the air pump (see step S4 in FIG. 2). As a result, the idle stop control and the upper limit control are canceled, and the air flow rate increases to the same amount as during idle power generation as shown in FIG. 5, and the minimum cell voltage is immediately recovered.

  FIG. 6 is a time chart showing a control example when the cell voltage drop is abnormal in the cell voltage recovery control according to the present embodiment. The control example shown in FIG. 6 executes idle stop control for a fuel cell vehicle in a low pressure environment.

First, idle power generation is executed at times t _{20 to} t ₂₁ . Specifically, the idle power generation current command value is output to the VCU, and the command value of the air pump speed corresponding to the idle power generation current command value is output to the air pump. As a result, air and hydrogen are supplied at a lower flow rate than during normal operation during vehicle travel, and the discharge current is reduced compared to during normal power generation. At this time, the lowest cell voltage is slightly lower than the average cell voltage, and some abnormality is confirmed in the cell voltage.

Next, at times t _{21 to} t ₂₂ , the idle stop control of this embodiment is executed. Specifically, as described above, the idle stop current command value is output to the VCU, and the command value of the air pump speed corresponding to the idle stop current command value is output to the air pump. At this time, since the fuel cell vehicle is in a low pressure environment, upper limit control for limiting the operation of the air pump is also executed.
Thereby, in a state where the NV performance is ensured, air having a lower flow rate than that during idle power generation is supplied, and the air flow rate decreases as shown in FIG. Moreover, since the discharge current than during idling power generation is decreased, both at time t ₂₁ the average cell voltage and the lowest cell voltage is slightly higher. Thereafter, between times t _22, whereas no significant change was observed in the average cell voltage, a minimum cell voltage is rapidly decreased.

Next, at time t _22, since the minimum cell voltage is below the highest unit cell voltage threshold, flooding phenomenon occurs, it is determined that it is necessary to recover the cell voltage by eliminating the flooding phenomenon, increase air flow Then, the cell voltage is recovered. At this time, since the time from the time t ₂₁ that initiated the idling stop control is a cell voltage abnormality drop determination time, the flooding phenomenon is that the excessive reduction of the cell voltage and abnormalities, than during idling power generation If the air flow rate is not increased, it is determined that the flatting phenomenon cannot be sufficiently resolved, the abnormal cell voltage recovery current command value is output to the VCU, and the command value of the air pump speed according to the abnormal cell voltage recovery current command value Is output to the air pump (see step S5 in FIG. 2). As a result, the idle stop control and the upper limit control are canceled, the air flow rate is increased as compared with that during idle power generation, and the minimum cell voltage is immediately recovered as shown in FIG.
In this case also, the amount of increase in air flow rate (increase amount A of FIG. 6) is, from the time t ₂₁ after starting the execution of the idle stop control, until time t ₂₂ to the lowest cell voltage is below the highest unit cell voltage threshold time ( It is set according to the cell voltage drop time T) in FIG. Specifically, the shorter the cell voltage drop time T is, the more noticeable the occurrence of the flatting phenomenon is, and it is judged that the cell voltage drop is abnormal. Therefore, the increase amount A is set large.

According to this embodiment, the following effects are produced.
(1) According to the present embodiment, during idling stop, the oxidant gas having a lower flow rate than that during idling power generation is supplied to the fuel cell 10 and the idling stop for taking out a lower current from the fuel cell 10 than during idling power generation. In the fuel cell system 1 that executes control, when the fuel cell system 1 is in a low-pressure environment, the operation of the air pump 21 is limited. Specifically, an upper limit value is set for the number of rotations of the air pump 21, and upper limit control for operating the air pump 21 below the upper limit value is executed. Thereby, even when the fuel cell system 1 that is executing the idle stop control is in a low-pressure environment such as a high altitude, the operation of the air pump 21 can be restricted, and the deterioration of the NV performance can be suppressed. Moreover, since it is only necessary to control the rotation speed of the air pump 21, the deterioration of the NV performance can be suppressed by simple control.

  (2) Further, according to the present embodiment, when the minimum cell voltage of the fuel cell 10 falls below a predetermined minimum cell voltage threshold value during the upper limit control, it is determined that a flatting phenomenon has occurred, and the fuel The flow rate of air supplied to the battery 10 is increased. Thereby, since the flatting phenomenon is eliminated, the deterioration of the electrolyte membrane can be suppressed, the cell voltage can be recovered, and a stable cell voltage can be secured immediately after returning from the idle stop.

(3) Also, during the upper limit control, if the minimum cell voltage falls below the predetermined minimum cell voltage threshold within a predetermined time (cell voltage abnormality drop determination time) after starting the idle stop control, The abnormal decrease is considered to be caused by the occurrence of excessive flatting and a large amount of water blocking the air supply path 23 and the cathode electrode flow path 14. For this reason, when the flow rate of air supplied to the fuel cell 10 is low, the flatting phenomenon may not be sufficiently eliminated.
Therefore, according to the present embodiment, when the cell voltage drop time is within a predetermined time, the air flow rate is increased as compared with the idle power generation. As a result, the flatting phenomenon is surely eliminated, so that the deterioration of the electrolyte membrane can be suppressed, the cell voltage can be recovered, and a stable cell voltage can be secured immediately after returning from the idle stop.

  (4) Further, according to the present embodiment, when the minimum cell voltage rapidly decreases during the upper limit control, the air flow rate is increased as the cell voltage decrease time is shorter. That is, the flow rate of air supplied to the fuel cell 10 is increased in accordance with the degree of occurrence of the flatting phenomenon. As a result, the flatting phenomenon is more reliably eliminated, so that the deterioration of the electrolyte membrane can be suppressed, the cell voltage can be recovered, and a stable cell voltage can be secured immediately after returning from the idle stop.

It should be noted that the present invention is not limited to the above-described embodiment, and modifications, improvements, etc. within a scope that can achieve the object of the present invention are included in the present invention.
For example, in the above-described embodiment, low flow rate air and hydrogen are supplied during the idle stop control. However, only low flow rate air may be supplied without supplying hydrogen.

DESCRIPTION OF SYMBOLS 1 ... Fuel cell system 10 ... Fuel cell 15 ... VCU (idle stop control means)
21 ... Air pump (oxidant gas supply means)
22 ... Hydrogen tank (fuel gas supply means)
28 ... Ejector (fuel gas supply means)
261 ... Regulator (fuel gas supply means)
40. ECU (idle stop control means, low-pressure environment determination means, operation restriction means, cell voltage threshold value determination means, cell voltage drop time determination means, cell voltage recovery means)
41 ... Cell voltage sensor (cell voltage threshold determination means)
42 ... Atmospheric pressure sensor (low pressure environment determination means)
43 ... GPS sensor (low pressure environment determination means)

Claims (4)

A fuel cell that generates electricity by being supplied with an oxidant gas and a fuel gas; and
An oxidant gas supply means for supplying an oxidant gas to the fuel cell;
A fuel cell system comprising fuel gas supply means for supplying fuel gas to the fuel cell,
When a predetermined condition is established during idle power generation, the oxidant gas supply means supplies an oxidant gas having a flow rate lower than that during idle power generation to the fuel cell, while lowering the current than during idle power generation. Idle stop control means for starting idle stop control to be taken out from the fuel cell;
Low pressure environment determination means for determining whether the fuel cell system is in a low pressure environment during the idle stop control;
An operation restricting means for restricting the operation of the oxidant gas supply means when it is determined that the fuel cell system is in a low pressure environment ,
The oxidant gas supply means is an air pump for supplying air to the fuel cell;
The low-pressure environment determining means is configured such that the rotational speed of the air pump that operates to ensure the amount of air supplied to the fuel cell during the idle stop control is equal to or higher than a predetermined rotational speed at which noise vibration performance starts to deteriorate. And determining that the fuel cell system is in a low-pressure environment,
The operation limiting means executes an upper limit control for limiting the rotation speed of the air pump below the upper limit value of the rotation speed at which good noise vibration performance can be ensured,
The fuel cell system includes:
Cell voltage threshold determination means for determining whether or not the minimum cell voltage of the fuel cell is lower than a predetermined minimum cell voltage threshold during the upper limit control;
During the upper limit control, when it is determined that the minimum cell voltage is lower than the minimum cell voltage threshold, the upper limit is increased by increasing the flow rate of air supplied to the fuel cell to be higher than the air flow rate during idle power generation. by releasing the control, the fuel cell system further comprising said Rukoto and a cell voltage recovery control means for recovering the cell voltage of the fuel cell.   A cell that determines whether or not a cell voltage drop time, which is a time from when the idle stop control is started until the lowest cell voltage falls below the lowest cell voltage threshold, is within a predetermined cell voltage abnormality drop determination time Further comprising a voltage drop time determination means,
  When it is determined that the cell voltage drop time is within the cell voltage abnormality drop determination time, the cell voltage recovery control means sets the flow rate of air supplied to the fuel cell to be higher than the air flow rate during idle power generation. And when it is determined that the cell voltage drop time is not within the cell voltage abnormality drop determination time, the flow rate of air supplied to the fuel cell is increased to the same amount as the air flow rate during idle power generation. The fuel cell system according to claim 1, wherein A fuel cell that generates electricity by being supplied with an oxidant gas and a fuel gas; and
An oxidant gas supply means for supplying an oxidant gas to the fuel cell;
A fuel cell system control method comprising: a fuel gas supply means for supplying fuel gas to the fuel cell;
Starting when a predetermined condition is satisfied during idle power generation, the oxidant gas supply means supplies an oxidant gas having a lower flow rate than during idle power generation to the fuel cell, while lower current than during idle power generation. An idle stop step of removing the fuel cell from the fuel cell;
A low pressure environment determination step for determining whether the fuel cell system is in a low pressure environment during the idle stop step;
An operation limiting step of limiting the operation of the oxidant gas supply means when it is determined that the fuel cell system is in a low-pressure environment ,
The oxidant gas supply means is an air pump for supplying air to the fuel cell;
In the low-pressure environment determination step, when the rotation speed of the air pump that operates to secure the amount of air supplied to the fuel cell during the idle stop step is equal to or higher than a predetermined rotation number at which noise vibration performance starts to deteriorate. And determining that the fuel cell system is in a low-pressure environment,
In the operation limiting step, an upper limit control is performed to limit the rotation speed of the air pump below the upper limit value of the rotation speed at which good noise vibration performance can be ensured,
The control method of the fuel cell system includes:
A cell voltage threshold determination step for determining whether or not the minimum cell voltage of the fuel cell is lower than a predetermined minimum cell voltage threshold during the upper limit control;
During the upper limit control, when it is determined that the minimum cell voltage is lower than the minimum cell voltage threshold, the upper limit is increased by increasing the flow rate of air supplied to the fuel cell to be higher than the air flow rate during idle power generation. by releasing the control, the control method of the fuel cell system, characterized in further comprising Rukoto a cell voltage recovery control step of recovering the cell voltage, of the fuel cell.   A cell for determining whether or not a cell voltage drop time that is a time from the start of the idle stop process until the lowest cell voltage falls below the lowest cell voltage threshold is within a predetermined cell voltage abnormality drop determination time A voltage drop time determination step;
  In the cell voltage recovery control step, when it is determined that the cell voltage drop time is within the cell voltage abnormality drop determination time, the flow rate of air supplied to the fuel cell is set to be higher than the air flow rate during idle power generation. And when it is determined that the cell voltage drop time is not within the cell voltage abnormality drop determination time, the flow rate of air supplied to the fuel cell is increased to the same amount as the air flow rate during idle power generation. The control method of a fuel cell system according to claim 3, wherein

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