JP2007179947A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent deterioration by suppressing fuel cell voltage rise due to hydrogen remaining in a fuel circulation passage when gas circulation between a fuel electrode and the fuel circulation passage is started in starting a fuel cell. <P>SOLUTION: A controller 30 first causes the gas circulation between an anode 4 and the fuel circulation passage 11 to be executed by starting a circulation pump 12 with a purge valve 20, an air pressure regulation valve 24 and a hydrogen supply valve 9 closed in starting this fuel cell system, and extracts a current from the fuel cell 2 to prevent a voltage value of the fuel cell 2 detected by a power manager 15 from exceeding a predetermined value. Then, the controller starts hydrogen supply from the hydrogen supply valve 9 to the anode. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fuel cell system, and more particularly to a fuel cell system suitable for a moving body driving power source that repeatedly starts and stops.

  In a fuel cell, a fuel gas such as hydrogen gas and an oxidizing gas containing oxygen are electrochemically reacted through an electrolyte, and electric energy is directly taken out between electrodes provided on both surfaces of the electrolyte. In particular, solid polymer fuel cells using solid polymer electrolytes are attracting attention as power sources for electric vehicles because of their low operating temperature and easy handling. That is, a fuel cell vehicle is equipped with a hydrogen storage device such as a high-pressure hydrogen tank, a liquid hydrogen tank, or a hydrogen storage alloy tank in the vehicle, and reacts by supplying hydrogen supplied therefrom and oxygen-containing air to the fuel cell. This is the ultimate clean vehicle that drives the motor connected to the drive wheels with the electric energy extracted from the fuel cell, and that the only exhaust material is water.

  By the way, in an operation region where the output of the fuel cell is small, there is a system in which power generation is temporarily stopped and power is supplied from a power storage device such as a secondary battery or a capacitor to a load device because power generation efficiency is low. In such a fuel cell system that performs idle stop, in an operation region where the power generation efficiency of the fuel cell is high, power is supplied from the fuel cell to the load device and charged to the power storage device, and an operation region where the power generation efficiency of the fuel cell is low is avoided. In addition, the fuel efficiency of the fuel cell system can be improved.

  However, it is known that when the fuel cell system is repeatedly started and stopped, the deterioration of the fuel cell is promoted as compared to the continuous operation state. For example, when the supply of hydrogen to the anode is started when the fuel cell system is started, an interface (hydrogen front) between the air that has entered the anode during the stop and the hydrogen that is newly supplied is formed. Then, hydrogen is ionized at the anode electrode in the first region to which hydrogen behind the hydrogen front is supplied, and hydrogen ions reach the cathode through the electrolyte membrane. At this time, electrons are not supplied to the cathode from an unconnected external circuit, and carbon dioxide, hydrogen ions, and electrons are generated by the reaction of carbon and water carrying the cathode catalyst in the second region before the hydrogen front. Is done. The electrons move from the second region to the first region in the cathode electrode and contribute to the generation of water. Hydrogen ions ionized in the second region move to the opposing anode region through the electrolyte membrane. Due to such a reaction, the carbon in the catalyst carrier in the cathode region before the hydrogen front is lost by gasification to carbon dioxide, and there is a problem that catalyst fine particles aggregate and the catalyst performance deteriorates.

In order to solve this problem, in the invention described in Patent Document 1, hydrogen is supplied to the anode in the state where the air inflow to the cathode is shut off and the circulation function of the hydrogen circulation device is stopped when the fuel cell is started. The oxygen remaining in the cathode is consumed by taking out the current from the fuel cell. Then, after the cathode oxygen is consumed, the fuel gas circulation by the hydrogen circulation device is started.
Japanese Patent Laying-Open No. 2005-158553 (page 8, FIG. 6)

  However, in the above conventional example, hydrogen is supplied without driving the hydrogen circulation device at the start-up, so that hydrogen is not supplied uniformly to each cell constituting the fuel cell stack, and the fuel cell voltage is suppressed. When current extraction for voltage limit control (VLC) is performed, a cell deficient in hydrogen causes a reversal and the stack may be deteriorated.

  In order to avoid this problem, before the hydrogen supply is started, the hydrogen circulation device is operated to form a sufficient gas flow between the fuel electrode and the fuel circulation path in advance, and then the hydrogen supply is started. It is conceivable to perform VLC control in a state where hydrogen is supplied evenly to the cells. However, in the case of starting from a state in which hydrogen remains in the fuel circulation path, when the hydrogen circulation device is started, the residual hydrogen may flow into the fuel electrode, the fuel cell voltage may rise, and the fuel cell may deteriorate. The problem that there is.

  FIG. 8 is a time chart at start-up for explaining this problem. (A) Hydrogen pressure at the anode, (b) Rotational speed of a circulation pump as a hydrogen circulation device, (c) Stack current, (d) Stack voltage Respectively. In FIG. 8, the circulation pump before hydrogen supply is started at time ta, the rotation speed of the circulation pump reaches a steady state at time tb, hydrogen is supplied up to pressure P1 at time tc, and air supply is started at time td. Suppose that normal power generation is started. However, when the operation of the circulation pump is started, if the hydrogen remaining in the fuel circulation path is supplied to the anode and current is not taken out from the fuel cell, the stack voltage will rise and the fuel cell may be deteriorated. There was a problem that there was.

  In order to solve the above problems, the present invention provides a fuel cell stack in which a plurality of cells each having an electrolyte membrane sandwiched between a fuel electrode and an oxidant electrode, and a fuel that supplies fuel gas to the fuel electrode. A supply means, a fuel circulation path for circulating the fuel gas discharged from the fuel electrode to the fuel electrode again, a fuel circulation means for pumping the gas in the fuel circulation path, and a fuel gas containing impurities from the fuel circulation path. Discharge means for discharging out of the system, oxidant supply means for supplying oxidant gas to the oxidant electrode, current extraction means for extracting current from the fuel cell stack, and voltage detection for detecting the voltage of the fuel cell stack A fuel cell system comprising: means for limiting the voltage of the fuel cell stack before supplying an oxidant gas to the oxidant electrode when starting the fuel cell system. When the fuel gas is supplied and oxygen in the fuel electrode is consumed, the fuel circulation means is activated with the discharge means closed before the fuel gas supply from the fuel supply means to the fuel electrode is started. Then, the current extraction is performed from the fuel cell stack so that the voltage value detected by the voltage detection means does not exceed a predetermined voltage while performing gas circulation between the fuel electrode and the fuel circulation path. .

  The present invention also provides a fuel cell stack in which a plurality of cells each having an electrolyte membrane sandwiched between a fuel electrode and an oxidant electrode, fuel supply means for supplying fuel gas to the fuel electrode, and the fuel electrode A fuel circulation path for circulating the fuel gas discharged from the fuel electrode again, a fuel circulation means for pumping the gas in the fuel circulation path, and a discharge means for discharging the fuel gas containing impurities from the fuel circulation path to the outside of the system Oxidant supply means for supplying an oxidant gas to the oxidant electrode, current extraction means for extracting current from the fuel cell stack, voltage detection means for detecting the voltage of the fuel cell stack, and the fuel supply means And control means for controlling gas supply by the oxidant supply means, fuel circulation by the fuel circulation means, gas discharge by the discharge means, and current extraction by the current extraction means, In the obtained fuel cell system, when the fuel cell system is activated, the control means first activates the fuel circulation means with the discharge means closed, and performs gas circulation between the fuel electrode and the fuel circulation path. The current extraction means extracts current from the fuel cell stack so that the voltage value detected by the voltage detection means does not exceed a predetermined voltage, and then supplies fuel gas to the fuel electrode to The gist is to consume oxygen and then supply an oxidant gas to the oxidant electrode.

  According to the present invention, when the hydrogen circulation device is started and a sufficient gas flow is formed between the fuel circulation path and the fuel electrode, the voltage detected by detecting the voltage of the fuel cell stack exceeds the predetermined voltage. Therefore, even if the fuel circulation path is started from a state where hydrogen remains, the fuel cell voltage does not exceed a predetermined value, and it is possible to prevent deterioration of the fuel cell.

  Next, embodiments of the present invention will be described in detail with reference to the drawings. Although not particularly limited, each of the following embodiments is a fuel cell system suitable as a power source for a fuel cell vehicle.

  FIG. 1 is a system configuration diagram illustrating a schematic configuration of a first embodiment of a fuel cell system 1 according to the present invention. In FIG. 1, a fuel cell system 1 includes, for example, a polymer electrolyte fuel cell stack (hereinafter also simply referred to as a fuel cell) 2. The fuel cell 2 has a structure in which a plurality of unit cells (cells) in which an electrolyte membrane 3 is sandwiched between an anode (fuel electrode) 4 and a cathode (oxidant electrode) 5 are stacked, but only a unit cell is schematically illustrated. . Hydrogen gas is supplied as fuel to the anode 4 and air is supplied as oxidant gas to the cathode 5, and the electrode reaction shown below proceeds to generate electric power.

Anode (fuel electrode): H ₂ → 2H ⁺ + 2e ⁻ (1)
Cathode (oxidant electrode): 2H ⁺ + 2e ⁻ + (1/2) O ₂ → H ₂ O (2)
At this time, a part of the water generated at the cathode 5 becomes water vapor and permeates the electrolyte membrane 3 and enters the anode 4. Hydrogen as a fuel gas is supplied from the hydrogen tank 6 to the anode 4 through the hydrogen tank main valve 7, the pressure reducing valve 8, and the hydrogen supply valve 9. The high-pressure hydrogen supplied from the hydrogen tank 6 is mechanically reduced to a predetermined pressure by the pressure reducing valve 8 and further reduced by the hydrogen supply valve 9 so that the hydrogen pressure at the inlet of the anode 4 becomes a desired pressure. The hydrogen pressure at the anode inlet is detected by the anode inlet pressure sensor 10 a and input to the controller 30.

  A fuel circulation path 11 is provided for circulating the fuel gas that has not been consumed at the anode from the outlet of the anode 4 to the inlet of the anode 4. The circulation pump 12 is fuel circulation means for increasing the pressure of the fuel gas in the fuel circulation path 11 and circulating it. The circulation pump 12 is driven to rotate by an electric motor (not shown), and the rotation speed is detected by a rotation sensor 13. Air to the cathode 5 is supplied by a compressor 14 which is an oxidant supply means. An air pressure adjusting valve 24 is provided at the cathode outlet to control the cathode pressure.

  The power manager 15 is a current extraction unit that extracts current from the fuel cell 2 and supplies power to the load device 16 or the battery 17. The power manager 15 is also a voltage detection means for detecting the voltage (total voltage or stack voltage) of the fuel cell 2, and in response to an instruction from the controller 30, the current is extracted from the fuel cell 2 at the time of start-up. 2 has a function of limiting the voltage of 2 to a predetermined voltage or less.

  The battery controller 18 monitors the charging / discharging current of the battery 17 to calculate the state of charge (SOC) of the battery, and transmits the SOC to the controller 30. The cell voltage sensor 19 detects the voltage of each unit cell (cell) of the fuel cell 2 or each unit cell group (cell group) in which a plurality of unit cells are connected in series, and the stack voltage that is the sum of these voltages. And output to the controller 30.

  In order to supply air as an oxidant to the cathode 5, non-chemically reacting nitrogen permeates the electrolyte membrane 3 and accumulates in a hydrogen circulation system including the anode 4, the fuel circulation path 11 and the circulation pump 12. If the amount of nitrogen accumulated in the hydrogen circulation system increases too much, the mass density of the gas in the hydrogen circulation system increases and the gas circulation amount by the circulation pump 12 cannot be maintained, so the amount of nitrogen in the hydrogen circulation system must be managed. There is. Therefore, the gas containing nitrogen in the hydrogen circulation system is discharged to the outside by the purge valve 20 so that the circulation performance can be maintained for the amount of nitrogen present in the hydrogen circulation system. The anode inlet pressure sensor 10 b is a sensor that measures the pressure at the anode inlet, and the detected value is input to the controller 30. Further, a signal is input to the controller 30 to the key switch 23 for the user to instruct to stop the operation of the fuel cell system 1.

  The controller 30 controls each actuator in the system using each sensor signal at the time of starting, stopping, and generating power of the fuel cell system to supply the gas of the oxidant gas and the fuel gas, the gas circulation of the fuel circulation path, and impurities. It is a control means for controlling discharge of the contained gas and current extraction from the fuel cell 2.

  In this embodiment, the controller 30 is composed of a microprocessor having a CPU, a ROM storing a control program and control parameters, a working RAM, and an input / output interface. This is achieved by executing the program.

  Next, with reference to the flowchart of FIG. 2 and the time chart of FIG. 5, the operation at the time of starting the fuel cell system by the controller 30 will be described. When the key switch 23 in FIG. 1 is switched from the off state to the on state or when the fuel cell system returns from the idle stop state at the time of low load, the start control in FIG. 2 is started.

  When the activation control is started, first, in step (hereinafter, step is abbreviated as S) 102, the controller 30 clears the control flag to zero. This flag is set to 1 when the extraction current from the fuel cell 2 exceeds the peak during start-up VLC control of the fuel cell, and takes a value of 0 otherwise. Next, in S104, the controller 30 closes the air pressure adjusting valve 24, and closes the purge valve 20 in S106. Note that, depending on the specifications of the stop state of the fuel cell system, there are those that hold the closed state of the air pressure adjusting valve 24 and the purge valve 20 during the stop, and in this case, S104 and S106 can be omitted.

  Next, in S108, the controller 30 instructs the power manager 15 to prepare for taking out the current from the fuel cell 2. When the power manager 15 is instructed to prepare for current extraction, the power manager 15 thereafter monitors the total voltage of the fuel cell 2 and performs current extraction from the fuel cell 2 so that the total voltage does not exceed the predetermined voltage Vlm. It is configured. The predetermined voltage Vlm is calculated, for example, by multiplying a cell voltage that does not corrode carbon that is an experimentally determined fuel cell catalyst carrier by the number of cells in the fuel cell stack. The current extracted at this time may be charged in the battery 17 by the power manager 15 or may be consumed in the power manager 15 or in the load device 16.

  Next, in S110, the circulation pump 12 is started to rotate at the target rotation speed r2, and the circulation of the gas in the anode 4 and the fuel circulation path 11 is started. This corresponds to time ta in FIG. This target rotational speed r2 is a target rotational speed at which the circulating gas supplied to the anode 4 is uniformly distributed to each cell constituting the fuel cell 2, and experiments with actual machines or the circulating pump 12 and the fuel cell 2 are performed. And a fluid dynamic numerical simulation of the fuel circulation path 11.

  Next, in S112, the power manager 15 detects the voltage of the fuel cell 2, performs current extraction according to the fuel cell voltage detected in S114, and performs VLC control to limit the fuel cell voltage to Vlm. When the circulation pump 12 is started in S110, if the elapsed time from the previous stop of the fuel cell is not so long, hydrogen as fuel gas may remain in the fuel circulation path 11, and the hydrogen circulates. The pump 12 starts and flows from the fuel circulation path 11 to the anode 4 of the fuel cell 2. In this embodiment, since VLC control is prepared before the circulation pump 12 is started and the voltage of the fuel cell 2 rises, current can be extracted from the fuel cell 2 based on this voltage. The voltage of 2 can be limited to Vlm as shown by the solid line in FIG. 5 (d), and there is no increase in voltage as in the prior art shown by the broken line in FIG. 5 (d).

  Next, in S116, the controller 30 determines whether or not the value of the flag is 1. If the flag is 1, the process proceeds to S122. If the flag is not 1 (flag is 0), the process proceeds to S118, and it is determined whether or not the extraction current exceeds the peak. This is because the controller 30 itself determines that the peak has been exceeded if the current extraction current is smaller than the previous current extraction with reference to the current extraction monitor value sent from the power manager 15 every control cycle. Alternatively, the power manager 15 may determine whether or not the extraction current exceeds the peak, and transmit the result to the controller 30.

  If the extraction current does not exceed the peak in the determination of S118, the process returns to S112, and the fuel cell voltage limitation by the current extraction from the fuel cell 2 is continued while monitoring the fuel cell voltage. If the extraction current exceeds the peak in the determination in S118, the process proceeds to S120, the flag is set to 1, and then it is determined whether or not the hydrogen supply is started in S122. This hydrogen supply start determination is determined to start hydrogen supply when the extraction current becomes a predetermined value or less, or when a predetermined time or more has elapsed after the extraction current exceeds the peak. If it is not determined in S122 that hydrogen supply has started, the process returns to S112.

  When it is determined in S122 that hydrogen supply is started, the process proceeds to S124, where the controller 30 opens the hydrogen supply valve 9 and increases the anode pressure to P1. This corresponds to time tc in FIG. When the hydrogen thus started to reach the anode 4 of the fuel cell 2, the circulation pump 12 has already continued to circulate at a rotational speed at which the circulation gas is evenly distributed to each cell. Are evenly distributed to each cell and the voltage of each cell begins to rise evenly. However, since the voltage monitoring of the fuel cell 2 by the power manager 15 and the extraction of the current corresponding to the voltage are continued, the fuel cell voltage is suppressed and the oxygen in the air remaining at the cathode 5 is consumed. The current extraction continues. When the cathode residual oxygen is exhausted, the extraction current decreases to 0, but in reality, it is slightly due to the leakage air of the compressor 14 that has stopped rotating and the leakage air of the closed air pressure adjusting valve 24. Oxygen is supplied and may not be completely zero.

  Next, in S126, the controller 30 determines whether or not to end the VLC control. This determination is made, for example, when the current taken out from the fuel cell 2 by the power manager 15 is less than or equal to a predetermined value that can be regarded as substantially zero, or the remaining oxygen of the cathode 5 is consumed after the start of hydrogen supply in S122. Judgment is made based on whether or not a VLC termination condition has been established, such as the passage of a predetermined time required for reluctance. If it is not determined in S126 that the VLC control is to be terminated, S126 is repeated until the VLC termination condition is satisfied.

  In S126, the predetermined current value at which the extraction current can be regarded as substantially zero is experimentally determined in consideration of the airtightness performance when the compressor 14 stops rotating, for example, several tens [mA]. can do.

  If it is determined in S126 that VLC control is to be terminated, the process proceeds to S128, where the controller 30 starts the compressor 14 and starts supplying air to the cathode 5, and then in S130, sends a control signal to the hydrogen supply valve 9. Then, the hydrogen pressure of the anode 4 is increased to P2 which is the operating pressure (time td in FIG. 5), the start-up control is completed, and the normal power generation state is thereafter performed.

  According to the present embodiment described above, when the hydrogen circulation device is started and a sufficient gas flow is formed between the fuel circulation path and the fuel electrode, the detected voltage is detected by detecting the voltage of the fuel cell stack. Since control is performed so as not to exceed a predetermined voltage, the fuel cell voltage does not exceed a predetermined value even when starting from a state in which hydrogen remains in the fuel circulation path, and deterioration of the fuel cell can be prevented. effective.

  Next, a second embodiment of the fuel cell system according to the present invention will be described. The schematic configuration of the second embodiment is the same as the schematic configuration of the first embodiment shown in FIG. In the second embodiment, when the fuel cell system is started, the circulation pump 12 that is a fuel circulation device is first driven at a first rotational speed that is a relatively low rotational speed, and hydrogen remaining in the fuel circulation path is used as fuel. Suppressing the rate of flow into the anode of the battery, the current extraction device can control the voltage of the fuel cell in a responsive manner, and then driving the circulation pump at a second rotational speed higher than the first rotational speed, It is characterized in that the supply of hydrogen to the anode is started.

  Next, referring to the flowchart of FIG. 3 and the time chart of FIG. 6, the operation at the time of starting the fuel cell system by the controller 30 will be described. When the key switch 23 in FIG. 1 is switched from the off state to the on state, or when the fuel cell system returns from the idle stop state at the time of low load, the start control in FIG. 3 is started.

  When the activation control is started, first, in S202, the controller 30 clears the control flag to zero. This flag is set to 1 when the extraction current from the fuel cell 2 exceeds the peak during start-up VLC control of the fuel cell, and takes a value of 0 otherwise. Next, in S204, the controller 30 closes the air pressure adjusting valve 24, and closes the purge valve 20 in S206. Note that, depending on the specifications of the stop state of the fuel cell system, there are those that hold the closed state of the air pressure adjusting valve 24 and the purge valve 20 during the stop. In this case, S204 and S206 can be omitted.

  Next, in S208, the controller 30 instructs the power manager 15 to prepare for taking out the current from the fuel cell 2. When the power manager 15 is instructed to prepare for current extraction, the power manager 15 thereafter monitors the total voltage of the fuel cell 2 and performs current extraction from the fuel cell 2 so that the total voltage does not exceed the predetermined voltage Vlm. It is configured. The predetermined voltage Vlm is calculated, for example, by multiplying the cell voltage that does not corrode the fuel cell catalyst carrier obtained experimentally by the number of cells of the fuel cell stack. The current extracted at this time may be charged in the battery 17 by the power manager 15 or may be consumed in the power manager 15 or in the load device 16.

  Next, in S210, a stop time that is an elapsed time from when the previous fuel cell operation was stopped is calculated. This stop time is obtained by incorporating a clock indicating the current time in the controller 30, storing the time when the previous fuel cell operation was stopped, and subtracting the time at the previous operation stop from the current time. can get. Next, in S212, it is determined whether or not the stop time is equal to or shorter than a predetermined time T1. Here, the predetermined time T1 is a stop time in which hydrogen does not remain in the anode 4 or the fuel circulation path 11, and varies depending on the shape, volume, catalyst performance, etc. of the gas flow path of the fuel cell. Actually, it can be obtained by an experiment with an actual machine or a numerical simulation of gas flow and catalytic reaction of the fuel cell 2 and the fuel circulation path 11.

  If it is determined in S212 that the stop time is equal to or shorter than the predetermined time T1, the circulation pump 12 is started at the two-stage rotation speed on the assumption that hydrogen gas may remain at least in the fuel circulation path 11. Then, the process proceeds to S214. If the stop time exceeds the predetermined time T1 in the determination of S212, the activation of the circulation pump 12 at the two-stage rotation speed is omitted, and the process proceeds to S228 to start at the second target rotation speed from the beginning. .

  In S214, the circulation pump 12 is started to rotate at the first target rotational speed r1 which is relatively slow, and the circulation of the gas in the anode 4 and the fuel circulation path 11 is started. This corresponds to time ta in FIG. This first target rotational speed r1 is higher than the speed at which the hydrogen remaining in the fuel circulation path 11 is supplied to the anode 4 by the rotational speed r1 of the circulation pump 12 and the voltage of the fuel cell 2 rises. Detects a voltage change of the fuel cell 2, takes out a take-out current corresponding to this voltage change from the fuel cell 2, and controls the voltage of the fuel cell 2 to be equal to or lower than the predetermined voltage Vlm at a higher rotational speed. is there.

  Next, in S216, the power manager 15 detects the voltage of the fuel cell 2, performs current extraction according to the fuel cell voltage detected in S218, and performs VLC control to limit the fuel cell voltage to Vlm. When the circulation pump 12 is activated in S214, hydrogen as fuel gas may remain in the fuel circulation path 11 if the elapsed time since the last stop of the fuel cell operation is not so long. The pump 12 starts and flows from the fuel circulation path 11 to the anode 4 of the fuel cell 2. In this embodiment, since VLC control is prepared before the circulation pump 12 is started and the voltage of the fuel cell 2 rises, current can be extracted from the fuel cell 2 based on this voltage. The voltage of 2 can be limited to Vlm as shown by the solid line in FIG. 6 (d), and there is no increase in voltage as in the prior art shown by the broken line in FIG. 6 (d).

  Next, in S220, the controller 30 determines whether or not the value of the flag is 1. If the flag is 1, the process proceeds to S226. If the flag is not 1 (flag is 0), the process proceeds to S222, and it is determined whether or not the extraction current exceeds the peak. This is because the controller 30 itself determines that the peak has been exceeded if the current extraction current is smaller than the previous current extraction with reference to the current extraction monitor value sent from the power manager 15 every control cycle. Alternatively, the power manager 15 may determine whether or not the extraction current exceeds the peak, and transmit the result to the controller 30.

  If the extraction current does not exceed the peak in the determination of S222, the process returns to S216, and the fuel cell voltage limitation by the current extraction from the fuel cell 2 is continued while monitoring the fuel cell voltage. If the extraction current exceeds the peak in the determination in S222, the process proceeds to S224, and 1 is set in the flag. Next, in S226, it is determined whether or not the extraction current from the fuel cell 2 has become equal to or less than a predetermined current value I1. If the extraction current is not less than or equal to the predetermined current value I1, the process returns to S216 and current extraction according to the fuel cell voltage is continued. If it is determined in S226 that the extraction current is equal to or less than the predetermined current value I1, the process proceeds to S228, and the rotational speed of the circulation pump 12 is increased to the second target rotational speed r2 (r1 <r2) (time in FIG. 6). te). The second target rotational speed r2 is a target rotational speed at which the circulating gas supplied to the anode 4 is uniformly distributed to each cell constituting the fuel cell 2, and is used for experiments with actual machines or the circulation pump 12 and It can be obtained by a hydrodynamic numerical simulation of the fuel cell 2 and the fuel circulation path 11.

  Next, in S230, it is determined whether or not to start hydrogen supply. This hydrogen supply start determination is determined to start hydrogen supply when the extraction current becomes a predetermined value or less, or when a predetermined time or more has elapsed after the extraction current exceeds the peak.

  When it is determined in S230 that hydrogen supply is started, the process proceeds to S232, and the controller 30 opens the hydrogen supply valve 9 and increases the anode pressure to P1. This corresponds to time tc in FIG. When the hydrogen thus started to reach the anode 4 of the fuel cell 2, the circulation pump 12 has already continued to circulate at a rotational speed at which the circulation gas is evenly distributed to each cell. Are evenly distributed to each cell and the voltage of each cell begins to rise evenly. However, since the voltage monitoring of the fuel cell 2 by the power manager 15 and the extraction of the current corresponding to the voltage are continued, the fuel cell voltage is suppressed and the oxygen in the air remaining at the cathode 5 is consumed. The current extraction continues. When the cathode residual oxygen is exhausted, the extraction current decreases to 0, but in reality, it is slightly due to the leakage air of the compressor 14 that has stopped rotating and the leakage air of the closed air pressure adjusting valve 24. Oxygen is supplied and may not be completely zero.

  Next, in S234, the controller 30 determines whether or not to end the VLC control. This determination is made, for example, when the current value taken out from the fuel cell 2 by the power manager 15 is equal to or less than a predetermined value that can be regarded as substantially zero, or the residual oxygen of the cathode 5 is consumed after the start of hydrogen supply in S232. Judgment is made based on whether or not a VLC termination condition has been established, such as the passage of a predetermined time required for reluctance. If it is not determined in S234 that VLC control is to be terminated, S234 is repeated until the VLC termination condition is satisfied.

  In S234, the predetermined current value at which the extraction current can be regarded as substantially zero is experimentally determined in consideration of the airtightness performance when the compressor 14 stops rotating, for example, several tens [mA]. can do.

  If it is determined in S234 that the VLC control is to be terminated, the process proceeds to S236, where the controller 30 starts the compressor 14 and starts supplying air to the cathode 5, and then in S238, sends a control signal to the hydrogen supply valve 9. Then, the hydrogen pressure of the anode 4 is increased to P2 which is the operating pressure (time td in FIG. 6), the start-up control is completed, and the normal power generation state is thereafter performed.

  According to the present embodiment described above, when the fuel cell system is started, the circulation pump 12 as the fuel circulation device is first driven at the first rotational speed that is a relatively low rotational speed, and remains in the fuel circulation path. This suppresses the rate at which hydrogen that flows into the anode of the fuel cell is suppressed, and the current extraction device can control the voltage of the fuel cell with good response.

  Next, a third embodiment of the fuel cell system according to the present invention will be described. The schematic configuration of the third embodiment is the same as the schematic configuration of the first embodiment shown in FIG. In the third embodiment, when the fuel cell system is started, the rotational speed of the circulation pump 12 that is the fuel circulation device is first increased at the first rotational acceleration, and then the second rotation larger than the first rotational acceleration. It is characterized in that it is raised by acceleration.

  Next, referring to the flowchart of FIG. 4 and the time chart of FIG. 7, the operation at the time of starting the fuel cell system by the controller 30 will be described. When the key switch 23 in FIG. 1 is switched from the OFF state to the ON state or when the fuel cell system returns from the idle stop state at the time of low load, the start control in FIG. 4 is started.

  When the start control is started, first, in S302, the controller 30 clears the control flag to zero. This flag is set to 1 when the extraction current from the fuel cell 2 exceeds the peak during start-up VLC control of the fuel cell, and takes a value of 0 otherwise. Next, in S304, the controller 30 closes the air pressure adjusting valve 24, and closes the purge valve 20 in S306. Note that, depending on the specifications of the stop state of the fuel cell system, there are those that hold the closed state of the air pressure adjusting valve 24 and the purge valve 20 during the stop, in which case S304 and S306 can be omitted.

  Next, in step S308, the controller 30 instructs the power manager 15 to prepare for current extraction from the fuel cell 2. When the power manager 15 is instructed to prepare for current extraction, the power manager 15 thereafter monitors the total voltage of the fuel cell 2 and performs current extraction from the fuel cell 2 so that the total voltage does not exceed the predetermined voltage Vlm. It is configured. The predetermined voltage Vlm is calculated, for example, by multiplying the cell voltage that does not corrode the fuel cell catalyst carrier obtained experimentally by the number of cells of the fuel cell stack. The current extracted at this time may be charged in the battery 17 by the power manager 15 or may be consumed in the power manager 15 or in the load device 16.

  Next, in S310, a stop time that is an elapsed time since the previous stop of the fuel cell operation is calculated. This stop time is obtained by incorporating a clock indicating the current time in the controller 30, storing the time when the previous fuel cell operation was stopped, and subtracting the time at the previous operation stop from the current time. can get. Next, in S312, it is determined whether or not the stop time is equal to or shorter than a predetermined time T1. Here, the predetermined time T1 is a stop time in which hydrogen does not remain in the anode 4 or the fuel circulation path 11, and varies depending on the shape, volume, catalyst performance, etc. of the gas flow path of the fuel cell. Actually, it can be obtained by an experiment with an actual machine or a numerical simulation of gas flow and catalytic reaction of the fuel cell 2 and the fuel circulation path 11.

  If it is determined in S312 that the stop time is equal to or shorter than the predetermined time T1, hydrogen gas may remain at least in the fuel circulation path 11, and the rotational speed of the circulation pump 12 is increased by two-stage rotational acceleration. To do so, go to S314. If it is determined in S312 that the stop time exceeds the predetermined time T1, the acceleration of the circulating pump 12 by the two-stage rotational acceleration is omitted, and the process proceeds to S328 to start from the beginning with the second target rotational acceleration. .

  In S314, the circulation pump 12 is started to rotate at a relatively slow first target rotational acceleration α1, and the circulation of gas in the anode 4 and the fuel circulation path 11 is started. This corresponds to time ta in FIG. The first target rotational acceleration α1 is higher than the speed at which the hydrogen remaining in the fuel circulation path 11 is supplied to the anode 4 due to the rotational speed increase rate of the circulation pump 12 and the voltage of the fuel cell 2 rises. 15 detects the voltage change of the fuel cell 2, takes out a take-out current corresponding to the voltage change from the fuel cell 2, and controls the voltage of the fuel cell 2 to be equal to or lower than the predetermined voltage Vlm. It is.

  Next, in S316, the power manager 15 detects the voltage of the fuel cell 2, performs current extraction according to the detected fuel cell voltage in S318, and performs VLC control to limit the fuel cell voltage to Vlm. When the circulation pump 12 is activated in S314, if the elapsed time from the previous stop of the fuel cell is not so long, hydrogen as fuel gas may remain in the fuel circulation path 11, and the hydrogen circulates. The pump 12 starts and flows from the fuel circulation path 11 to the anode 4 of the fuel cell 2. In this embodiment, since VLC control is prepared before the circulation pump 12 is started and the voltage of the fuel cell 2 rises, current can be extracted from the fuel cell 2 based on this voltage. The voltage of 2 can be limited to Vlm as shown by the solid line in FIG. 7 (d), and there is no increase in voltage as in the prior art shown by the broken line in FIG. 7 (d).

  Next, in S320, the controller 30 determines whether or not the value of the flag is 1. If the flag is 1, the process proceeds to S326. If the flag is not 1 (flag is 0), the process proceeds to S322, and it is determined whether or not the extraction current exceeds the peak. This is because the controller 30 itself determines that the peak has been exceeded if the current extraction current is smaller than the previous current extraction with reference to the current extraction monitor value sent from the power manager 15 every control cycle. Alternatively, the power manager 15 may determine whether or not the extraction current exceeds the peak, and transmit the result to the controller 30.

  If the extraction current does not exceed the peak in the determination of S322, the process returns to S316, and the fuel cell voltage limitation by the current extraction from the fuel cell 2 is continued while monitoring the fuel cell voltage. If the extraction current exceeds the peak in the determination of S322, the process proceeds to S324 and 1 is set in the flag. Next, in S326, it is determined whether or not the extraction current from the fuel cell 2 has become equal to or less than a predetermined current value I1. If the extraction current is not less than or equal to the predetermined current value I1, the process returns to S316 and the current extraction according to the fuel cell voltage is continued. If it is determined in S326 that the extraction current is less than or equal to the predetermined current value I1, the process proceeds to S328, and the rate of increase in the rotational speed of the circulation pump 12 is set to the second rotational acceleration α2 (α1 <α2) (time in FIG. 7). tf), the rotational speed of the circulating pump 12 is increased to the target rotational speed r2 by the second rotational acceleration α2 (time tg in FIG. 7). This target rotational speed r2 is a target rotational speed at which the circulating gas supplied to the anode 4 is uniformly distributed to each cell constituting the fuel cell 2, and experiments with actual machines or the circulating pump 12 and the fuel cell 2 are performed. And a fluid dynamic numerical simulation of the fuel circulation path 11.

  Next, in S330, it is determined whether or not to start hydrogen supply. This hydrogen supply start determination is determined to start hydrogen supply when the extraction current becomes a predetermined value or less, or when a predetermined time or more has elapsed after the extraction current exceeds the peak.

  When it is determined in S330 that the hydrogen supply is started, the process proceeds to S332, where the controller 30 opens the hydrogen supply valve 9 and increases the anode pressure to P1. This corresponds to time tc in FIG. When the hydrogen thus started to reach the anode 4 of the fuel cell 2, the circulation pump 12 has already continued to circulate at a rotational speed at which the circulation gas is evenly distributed to each cell. Are evenly distributed to each cell and the voltage of each cell begins to rise evenly. However, since the voltage monitoring of the fuel cell 2 by the power manager 15 and the extraction of the current corresponding to the voltage are continued, the fuel cell voltage is suppressed and the oxygen in the air remaining at the cathode 5 is consumed. The current extraction continues. When the cathode residual oxygen is exhausted, the extraction current decreases to 0, but in reality, it is slightly due to the leakage air of the compressor 14 that has stopped rotating and the leakage air of the closed air pressure adjusting valve 24. Oxygen is supplied and may not be completely zero.

  Next, in S334, the controller 30 determines whether or not to end the VLC control. This determination is made, for example, when the current value taken out from the fuel cell 2 by the power manager 15 is equal to or less than a predetermined value that can be regarded as substantially zero, or the remaining oxygen of the cathode 5 is consumed after the start of hydrogen supply in S332. Judgment is made based on whether or not a VLC termination condition has been established, such as the passage of a predetermined time required for reluctance. If it is not determined in step S334 that the VLC control is to be ended, step S334 is repeated until the VLC end condition is satisfied.

  In S334, the predetermined current value at which the extraction current can be regarded as substantially zero is determined experimentally in consideration of the airtightness performance when the compressor 14 stops rotating, for example, several tens [mA]. can do.

  If it is determined in S334 that VLC control is to be terminated, the process proceeds to S336, where the controller 30 starts the compressor 14 and starts supplying air to the cathode 5, and then in S338, sends a control signal to the hydrogen supply valve 9. Then, the hydrogen pressure of the anode 4 is increased to P2 that is the operating pressure (time td in FIG. 7), the start-up control is completed, and the normal power generation state is thereafter performed.

  According to the present embodiment described above, when the fuel cell system is started, the rotational speed of the circulation pump 12 that is the fuel circulation device is first increased by the first rotational acceleration, and then larger than the first rotational acceleration. When there is residual hydrogen in the fuel circulation path by increasing at the second rotational acceleration, the response speed of the VLC control in which the power manager controls the voltage of the fuel cell with the extraction current according to the voltage of the fuel cell. Since the residual hydrogen is supplied to the fuel cell at a low speed, there is an effect that the VLC control of the fuel cell voltage by the residual hydrogen can be surely performed even when the response speed of the power manager is low.

  Next, a fourth embodiment of the fuel cell system according to the present invention will be described. The schematic configuration of the fourth embodiment is the same as the schematic configuration of the first embodiment shown in FIG. The fourth embodiment is a combination of the second embodiment and the third embodiment. When the fuel cell system is started, the rotational speed of the circulation pump 12 that is the fuel circulation device is first set to the first rotational acceleration. It is characterized in that it is increased to the first rotational speed and then increased to the second rotational speed at a second rotational acceleration that is greater than the first rotational acceleration.

  The flowchart of the present embodiment can be easily realized by combining FIG. 3 of the second embodiment and FIG. According to the present embodiment, the effects of the second embodiment and the third embodiment can be obtained simultaneously.

1 is a system configuration diagram showing a basic configuration of a fuel cell system according to the present invention. 2 is a flowchart at the time of starting the fuel cell system in Example 1. 6 is a flowchart when starting a fuel cell system according to a second embodiment. 6 is a flowchart at the time of starting a fuel cell system in Example 3. It is a time chart explaining operation | movement, an effect | action, and an effect of Example 1, and is a figure which respectively shows (a) anode hydrogen pressure, (b) circulating pump rotational speed, (c) stack current, and (d) stack voltage. It is a time chart explaining the operation | movement of the Example 2, an effect | action, and an effect, (a) Anode hydrogen pressure, (b) Circulation pump rotational speed, (c) Stack current, (d) It is a figure which respectively shows a stack voltage. It is a time chart explaining the operation | movement of the Example 3, an effect | action, and an effect, (a) Anode hydrogen pressure, (b) Circulation pump rotational speed, (c) Stack current, (d) It is a figure which respectively shows a stack voltage. It is a time chart explaining the problem of a prior art, and is a figure which respectively shows (a) anode hydrogen pressure, (b) circulating pump rotational speed, (c) stack current, and (d) stack voltage.

Explanation of symbols

1: Fuel cell system 2: Fuel cell 3: Electrolyte membrane 4: Anode 5: Cathode 6: Hydrogen tank 7: Hydrogen tank original valve 8: Pressure reducing valve 9: Hydrogen supply valve 10a, 10b: Pressure sensor 11: Fuel circuit 12 : Circulation pump 13: Rotation sensor 14: Compressor 15: Power manager 16: Load device 17: Battery 18: Battery controller 19: Cell voltage sensor 20: Purge valve 23: Key switch 30: Controller

Claims (9)

A fuel cell stack in which a plurality of cells each having an electrolyte membrane sandwiched between a fuel electrode and an oxidant electrode are stacked;
Fuel supply means for supplying fuel gas to the fuel electrode;
A fuel circulation path for recirculating the fuel gas discharged from the fuel electrode to the fuel electrode;
A fuel circulation means for pumping the gas in the fuel circulation path;
Discharging means for discharging fuel gas containing impurities from the fuel circulation path out of the system;
An oxidant supply means for supplying an oxidant gas to the oxidant electrode;
Current extraction means for extracting current from the fuel cell stack;
Voltage detection means for detecting the voltage of the fuel cell stack;
In a fuel cell system comprising:
When starting the fuel cell system, before supplying the oxidant gas to the oxidant electrode, supplying the fuel gas to the fuel electrode while limiting the voltage of the fuel cell stack to consume oxygen in the fuel electrode In addition,
Before starting the supply of fuel gas from the fuel supply means to the fuel electrode, the fuel circulation means is started with the discharge means closed, and the gas circulation between the fuel electrode and the fuel circulation path is started. A fuel cell system wherein current is taken out from the fuel cell stack so that the voltage value detected by the voltage detection means does not exceed a predetermined voltage. A fuel cell stack in which a plurality of cells each having an electrolyte membrane sandwiched between a fuel electrode and an oxidant electrode are stacked;
Fuel supply means for supplying fuel gas to the fuel electrode;
A fuel circulation path for recirculating the fuel gas discharged from the fuel electrode to the fuel electrode;
A fuel circulation means for pumping the gas in the fuel circulation path;
Discharging means for discharging fuel gas containing impurities from the fuel circulation path out of the system;
An oxidant supply means for supplying an oxidant gas to the oxidant electrode;
Current extraction means for extracting current from the fuel cell stack;
Voltage detection means for detecting the voltage of the fuel cell stack;
Control means for controlling gas supply by the fuel supply means and the oxidant supply means, fuel circulation by the fuel circulation means, gas discharge by the discharge means, and current extraction by the current extraction means;
In a fuel cell system comprising:
When the fuel cell system is started, the control means starts the fuel circulation means with the discharge means closed, and performs the gas detection between the fuel electrode and the fuel circulation path, while detecting the voltage. The current extraction means extracts current from the fuel cell stack so that the voltage value detected by the means does not exceed a predetermined voltage, then supplies fuel gas to the fuel electrode to consume oxygen in the fuel electrode, and then An oxidant gas is supplied to the oxidant electrode.   3. The fuel cell system according to claim 1, wherein the predetermined voltage is a potential at which corrosion of carbon of the catalyst carrier on the hydrogen flow front surface of the fuel cell does not occur.   When driving the fuel circulation means, it is first driven at a first rotational speed, then driven at a second rotational speed higher than the first rotational speed, and during driving at a second rotational speed, 3. The fuel cell system according to claim 2, wherein supply of fuel gas from the fuel supply means is started.   While the fuel circulating means is driven at the first rotational speed, the rotational speed of the fuel circulating means is increased to the second rotational speed when the current value taken out from the fuel cell becomes a predetermined current value or less. The fuel cell system according to claim 4. When restarting the fuel cell system when the fuel circulation system is restarted when the stop time of the fuel cell system does not exceed a predetermined time in which almost all the residual hydrogen in the anode is considered to be replaced with air, the fuel circulation system is first driven at the first rotational speed. Drive, and then drive at a second rotational speed higher than the first rotational speed, and during the driving at the second rotational speed, start supplying fuel gas from the fuel supply means,
At the time of restart after the stop time of the fuel cell system exceeds a predetermined time, the fuel circulation means is driven at the second rotation speed from the beginning without increasing the stepwise rotation speed. The fuel cell system according to claim 2.   The increase in the rotation speed of the fuel circulation means is first performed at a first rotation acceleration equal to or lower than the response speed of the current extraction function for extracting current from the fuel cell stack, and then the second rotation faster than the first rotation acceleration. The fuel cell system according to any one of claims 4 to 6, wherein the fuel cell system is performed at an acceleration.   8. The fuel cell system according to claim 7, wherein the switching from the first rotational acceleration to the second rotational acceleration is performed when a current value taken out from the fuel cell stack becomes a predetermined current value or less. . When the fuel cell system is not restarted for a predetermined time in which almost all of the residual hydrogen in the anode has been replaced with air, the increase in the rotational speed of the fuel circulation means is first from the fuel cell stack. Performing at a first rotational acceleration equal to or lower than the response speed of the current extraction function for extracting current, and then performing at a second rotational acceleration greater than the first rotational acceleration;
When restarting after the stop time of the fuel cell system exceeds the predetermined time, the rotational speed of the fuel circulation means is increased at the second rotational acceleration from the beginning without switching the rotational acceleration. The fuel cell system according to any one of claims 4 to 6.

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