JP2009135021A - Fuel cell system and control method of fuel cell system - Google Patents

Abstract

An object of the present invention is to provide a fuel cell system that eliminates generated water adhering to a fuel cell while suppressing deterioration of the membrane-electrode assembly, and a control method for the fuel cell system.
A fuel cell system includes a fuel cell having a membrane / electrode assembly having an electrolyte membrane sandwiched between catalyst electrodes, and water generated in the membrane / electrode assembly. The voltage application means 8, 15, 17 for applying an applied voltage equal to or higher than a predetermined first voltage required for electrolyzing the fuel cell 27, and the open circuit voltage of the fuel cell 27 to the fuel cell 27 When the voltage is lower than the voltage obtained by subtracting the predetermined first voltage from the predetermined second voltage at which the membrane / electrode assembly 24 starts to deteriorate when the voltage is applied, the voltage applying means 8, 15, 17 are controlled to the fuel cell 27. And a control means 3 for applying a voltage.
[Selection] Figure 3

Description

  The present invention relates to a fuel cell system and a control method for the fuel cell system.

  The fuel cell performs power generation by causing an electrochemical reaction between hydrogen as a fuel gas and oxygen as an oxidant gas. The electrochemical reaction between hydrogen and oxygen is performed in a fuel cell carrying a membrane / electrode assembly or a gas diffusion layer.

  The water produced by the electrochemical reaction between hydrogen and oxygen adheres to the fuel cell. When the fuel cell is frozen with a large amount of produced water attached, the frozen produced water inhibits gas diffusion and makes it difficult to start the fuel cell, or the frozen produced water destroys the fuel cell. Therefore, a technique for reducing the amount of generated water before the generated water adhering to the fuel cell freezes has been studied.

In Patent Documents 1 to 3, when a fuel cell is stopped, a voltage is applied to the fuel cell to electrolyze the water present in the membrane / electrode assembly or gas diffusion layer into hydrogen and oxygen, thereby removing the water. The technology to do is described. Patent Document 4 describes a technique in which when the fuel cell stack becomes low temperature, an electric resistance is connected, and the open circuit voltage at low temperature start is lowered to lower the withstand voltage performance of each electric circuit.
JP 2004-311348 A JP 2005-93426 A JP 2005-50749 A JP 2005-100705 A

  When electrolyzing the produced water adhering to the fuel cell into hydrogen and oxygen, it is necessary to give a potential difference of about 1.23V to 1.40V. However, in the fuel cell immediately after stopping, oxygen stays on the cathode electrode side and hydrogen stays on the anode electrode side. For this reason, a potential difference of about 1.0 V is generated between the cathode electrode and the anode electrode of the fuel cell immediately after stopping due to an electrochemical reaction between hydrogen and oxygen. For this reason, in order to electrolyze the produced water adhering to the fuel cell, a potential difference for electrolyzing the produced water between the cathode electrode and the anode electrode and a potential difference generated by an electrochemical reaction of hydrogen and oxygen It is necessary to give a potential difference of about 2.23V to 2.40V, which is the sum of.

  The catalyst layer of the membrane / electrode assembly is usually composed of carbon carrying platinum. Here, when a voltage of 1.40 V or more is applied to the fuel cell, platinum is eluted from the catalyst layer, or carbon in the catalyst layer is corroded to discharge carbon dioxide.

  In view of the above problems, the present invention has an object to provide a fuel cell system that eliminates generated water adhering to a fuel cell while suppressing deterioration of the membrane-electrode assembly, and a control method for the fuel cell system. To do.

  In order to solve the above problems, the present invention performs electrolysis of generated water when the open circuit voltage is low.

  Specifically, in a fuel cell system, it is necessary to electrolyze a fuel cell having a membrane / electrode assembly in which an electrolyte membrane is sandwiched between catalyst electrodes and water generated in the membrane / electrode assembly. A voltage applying means for applying an applied voltage equal to or higher than a predetermined first voltage to the fuel battery cell, and when the open circuit voltage of the fuel battery cell is applied to the fuel battery cell, the membrane-electrode assembly is Control means for controlling the voltage applying means to apply a voltage to the fuel cell when the voltage is less than a voltage obtained by subtracting the predetermined first voltage from a predetermined second voltage that starts to deteriorate.

  In the fuel cell system, hydrogen and oxygen are supplied to the reaction surface of the membrane / electrode assembly to cause an electrochemical reaction to generate electric power. The water produced during the electrochemical reaction adheres to the fuel cell. The fuel cell system according to the present invention is premised on electrolyzing and removing adhering product water into hydrogen and oxygen.

  In order to electrolyze the produced water into hydrogen and oxygen, it is necessary to apply a voltage to the produced water. In the present application, the voltage required to electrolyze the produced water adhering to the fuel battery cell is referred to as a predetermined first voltage. This predetermined first voltage is a voltage theoretically determined in advance by the properties of water and the structure of the fuel cell. Moreover, there is an upper limit in the voltage that can be applied to the fuel cell. This is because if the applied voltage is too high, the electrolyte membrane, the catalyst electrode, and the like constituting the membrane / electrode assembly of the fuel battery cell deteriorate. The applied voltage at which the membrane / electrode assembly of the fuel cell starts to deteriorate is referred to as a predetermined second voltage in the present application.

  In the fuel cell system immediately after the stop, hydrogen and oxygen remain on the reaction surface of the membrane-electrode assembly, so that a potential difference is generated between both electrodes of the fuel cell. Hereinafter, this potential difference generated at both electrodes of the fuel cell in the no-load state is referred to as an open circuit voltage. In order to electrolyze the generated water adhering to the fuel cell in a state where a potential difference is generated between the two electrodes, it is necessary to apply an applied voltage of a potential difference obtained by adding at least the predetermined first voltage and the open circuit voltage. . This is because a potential difference has already occurred between the two electrodes, so that a potential difference necessary for electrolysis is not added to the generated water even when a predetermined first voltage is applied. Here, in electrolyzing the produced water adhering to the fuel cell, if the open circuit voltage of the fuel cell is high, the applied voltage necessary for electrolyzing the produced water inevitably has a predetermined second voltage. It will exceed.

  Therefore, in the fuel cell system according to the present invention, the control means includes the voltage application means so that the voltage is applied to the fuel cell when the open circuit voltage is less than the voltage obtained by subtracting the predetermined first voltage from the predetermined second voltage. Control. Thereby, when electrolyzing the produced water adhering to the fuel cell, it is possible to eliminate the produced water adhering to the fuel cell while suppressing deterioration of the membrane-electrode assembly.

  Note that the open circuit voltage of the fuel cell gradually decreases with time because hydrogen and oxygen cross-leak through the electrolyte membrane. Therefore, when the open circuit voltage is equal to or higher than the voltage obtained by subtracting the predetermined first voltage from the predetermined second voltage, the control means performs control to wait for application of the voltage until the open circuit voltage decreases.

  Here, the control means may stop application of the voltage to the fuel cell by the voltage application means before the applied voltage becomes equal to or higher than the predetermined second voltage.

When a voltage is applied to the fuel cell, hydrogen and oxygen are generated on the cathode electrode side and the anode electrode side by electrolysis of the produced water. When hydrogen and oxygen are generated at both electrodes of the fuel cell, the open circuit voltage of the fuel cell increases. When the open circuit voltage of the fuel cell increases, the voltage required to electrolyze the generated water increases, so the voltage applied by the voltage applying means needs to be increased. However, as described above, if the voltage applied to the fuel cell is too high, the membrane / electrode assembly and the like deteriorate. Therefore, the control means controls the voltage application means so that the voltage application means does not apply a voltage equal to or higher than the predetermined second voltage to the fuel cell. According to this, it becomes possible to eliminate the produced water adhering to the fuel cell without substantially deteriorating the membrane / electrode assembly of the fuel cell.

  Here, the fuel cell system further includes a current detection unit that detects a current of the fuel cell, and the control unit detects that the current of the fuel cell detected by the current detection unit is the fuel cell. When a predetermined current state in which the application of the voltage to the battery is to be stopped, the application of the voltage to the fuel cell by the voltage applying means may be stopped.

  As described above, the open circuit voltage of the fuel cell gradually decreases due to the cross leak between hydrogen and oxygen. Further, as described above, when the produced water adhering to the fuel cell is electrolyzed, hydrogen and oxygen are generated at both electrodes, and the open circuit voltage is increased. Therefore, control is performed such that electrolysis is started when the open circuit voltage decreases, and electrolysis is stopped when the open circuit voltage becomes high. Thereby, it becomes possible to eliminate the generated water adhering to the fuel cell without applying a voltage that deteriorates the membrane-electrode assembly to the fuel cell.

  Here, the fuel cell system further includes a current detection unit that detects a current of the fuel cell, and the control unit detects that the current of the fuel cell detected by the current detection unit is the fuel cell. The voltage application unit may be controlled so as to stop the application of the voltage to the fuel cell when a predetermined current state in which the application of the voltage to the battery is to be stopped is reached.

  The current flowing through the fuel cell during electrolysis varies depending on the amount of produced water adhering to the fuel cell. This is because the electric resistance between both electrodes of the fuel cell varies depending on the amount of generated water. For example, if the amount of produced water adhering to the fuel battery cell is large, the electrical resistance between both electrodes of the fuel battery cell becomes small, and if the amount of produced water adhering to the fuel battery cell is small, the fuel cell The electrical resistance between the two poles increases. Therefore, the current when a voltage is applied to the fuel cell is measured, and when the current reaches a predetermined current state, the application of the voltage to the fuel cell is stopped. Thereby, for example, as soon as the generated water adhering to the fuel cell is sufficiently removed, it becomes possible to stop the application of voltage to the fuel cell. Here, the predetermined current state is a current state of the fuel battery cell detected by the current detection means, for example, a current state of the fuel battery cell in a state where the application of voltage should be stopped.

  Here, the predetermined current state may be a state in which the current of the fuel battery cell starts to change again after becoming substantially constant.

  The current of the fuel cell when electrolyzing the generated water is relatively stable unless the amount of generated water fluctuates suddenly for some reason or the membrane / electrode assembly deteriorates rapidly. Keep almost constant. On the other hand, for example, when the electrolysis of the produced water that has adhered is completed, the electrical resistance between the two electrodes of the fuel cell increases and the current decreases rapidly, and the carbon constituting the membrane / electrode assembly corrodes. If platinum or platinum is eluted, the electric resistance between both electrodes of the fuel cell decreases and the current increases rapidly.

  Accordingly, the current of the fuel cell in a state where a voltage is applied is measured, and when the current starts to change from a substantially constant state, the generated water adhering to the fuel cell is completely removed, or the membrane -Judge that the electrode assembly has started to deteriorate, and control to stop the application of voltage. As a result, it is possible to eliminate generation water adhering to the fuel cell excessively or promoting deterioration of the membrane-electrode assembly by the applied voltage.

  Here, the predetermined current state may be a state in which a change in the current of the fuel cell after a predetermined time has elapsed since the start of application of a voltage to the fuel cell is equal to or greater than a predetermined value.

  The upper limit value of the amount of generated water that can adhere to the fuel cell is determined to a certain value depending on the shape and size of the membrane / electrode assembly constituting the fuel cell. Therefore, the upper limit value of the time required for electrolyzing the produced water adhering to the fuel cell is also determined to a certain value according to the fuel cell. Therefore, even after a predetermined time has elapsed since the start of electrolysis of the produced water adhering to the fuel cell (in other words, after the voltage is applied to the fuel cell), the fluctuation of the current remains at the predetermined value. By stopping the electrolysis when it does not fall within the range, it is possible to eliminate the excessive elimination of generated water and the promotion of the deterioration of the membrane / electrode assembly. Here, the predetermined time is the time from the start of application of voltage to the fuel cell until it stops, for example, the time required to electrolyze the produced water adhering to the fuel cell. Is approximately the same time. Further, the predetermined value is a fluctuation range of the current flowing through the fuel battery cell, for example, a maximum value of a current fluctuation flowing through the fuel battery cell when the generated water is electrolyzed normally.

  Here, the predetermined current state may be a state in which the current of the fuel cell reaches a predetermined current value.

  As described above, when the carbon constituting the membrane / electrode assembly is corroded or platinum is eluted, the electrical resistance between the two electrodes of the fuel cell decreases and the current increases. Therefore, the current of the fuel cell to which the voltage is applied is measured, and when the current reaches a predetermined current value, the application of the voltage to the fuel cell is stopped to control the membrane / electrode assembly. It becomes possible to prevent deterioration. Here, the predetermined current value is a current value of a current flowing through the fuel cell when the voltage applying unit is applying a voltage to the fuel cell, for example, a deterioration of the membrane / electrode assembly of the fuel cell. It is a slightly lower current value than starting to start.

  Here, the control means stops the application of the voltage to the fuel cell, and then the open circuit voltage of the fuel cell becomes less than the voltage obtained by subtracting the predetermined first voltage from the predetermined second voltage. The voltage application to the fuel cell may be resumed by the voltage application means.

  As described above, when the generated water adhering to the fuel cell is electrolyzed, hydrogen and oxygen are generated at both electrodes, and the open circuit voltage is increased. Further, as described above, hydrogen and oxygen generated at both electrodes of the fuel battery cell cross-leak, and the open circuit voltage of the fuel battery cell eventually decreases with time. Therefore, by controlling the electrolysis to be interrupted or restarted according to the open circuit voltage of the fuel cell, the generated water adhering to the fuel cell can be eliminated without degrading the membrane-electrode assembly. It can be completed.

  Here, the fuel cell system further includes discharge means for discharging the fuel battery cell, and the control means causes the fuel battery cell to be discharged when the voltage application means is not applying a voltage to the fuel battery cell. You may discharge with the said discharge means.

  Since the cross leak between hydrogen and oxygen between both electrodes of the fuel cell is performed through the polymer electrolyte membrane, it gradually proceeds. If the progress of the cross leak is slow, it takes time for the open circuit voltage to drop, so if the open circuit voltage of the fuel cell is equal to or higher than the voltage obtained by subtracting the predetermined first voltage from the predetermined second voltage, the voltage application means It takes a long time to apply a voltage to the fuel cell. If it takes a long time for the voltage application means to apply a voltage to the fuel cell, for example, the generated water freezes when the fuel cell with the generated water attached is exposed to an extremely low temperature. Resulting in. Therefore, when the open circuit voltage of the fuel cell is high, it is desirable to quickly reduce the open circuit voltage.

Therefore, the fuel cell is discharged while the voltage application means is not applying a voltage to the fuel cell. Although generated water is generated in the fuel cell by the discharge, the open circuit voltage is immediately reduced, so that the fuel cell is not allowed to stand for a long time with the generated water attached. Thereby, electrolysis of the produced water adhering to the fuel cell can be promoted, and the produced water can be prevented from freezing.

  Here, the predetermined first voltage may be any voltage satisfying a condition of 1.24V or more and less than 1.40V. The predetermined second voltage may be a voltage of 1.40V.

  The applied voltage necessary for electrolyzing the produced water adhering to the fuel battery cell is theoretically determined to be about 1.24V or more. Further, when a potential difference of 1.40 V or more is applied between both electrodes of the fuel cell, the membrane / electrode assembly starts to deteriorate (carbon constituting the electrode of the membrane / electrode assembly is particularly corroded).

  Therefore, the membrane / electrode assembly is deteriorated by setting the predetermined first voltage to any voltage satisfying the condition of 1.24V or more and less than 1.40V, or by setting the predetermined second voltage to 1.40V. It is possible to eliminate the generated water adhering to the fuel cell without any problem.

  The present invention may be a control method for a fuel cell system that performs any of the above functions. That is, for example, in order to solve the above-described problem, a fuel cell having a membrane-electrode assembly in which an electrolyte membrane is sandwiched between catalyst electrodes and electrolyzing water generated in the membrane-electrode assembly And a voltage applying means for applying an applied voltage equal to or higher than a predetermined predetermined first voltage to the fuel cell, wherein the open circuit voltage of the fuel cell is applied to the fuel cell. When the voltage is applied, when the voltage is less than the voltage obtained by subtracting the predetermined first voltage from the predetermined second voltage at which the membrane / electrode assembly begins to deteriorate, the voltage is applied to the fuel cell by controlling the voltage applying means. You may make it have the 1st step to do.

  It is possible to provide a fuel cell system and a control method for the fuel cell system that eliminate generated water adhering to the fuel cell while suppressing deterioration of the membrane-electrode assembly.

  Hereinafter, an embodiment of the present invention will be exemplarily described. Embodiment shown below is an illustration and this invention is not limited to these.

<Configuration>
FIG. 1 is a configuration diagram of a fuel cell system 1 according to the present embodiment. In the present embodiment, the fuel cell system 1 is assumed to be mounted on a vehicle, but the present invention is not limited to this, and may be installed on the ground.

  As shown in FIG. 1, the fuel cell system 1 includes a fuel cell 2 and a control device 3 (corresponding to control means in the present invention). The fuel cell 2 is connected to a hydrogen storage tank 4 for supplying hydrogen necessary for power generation and an air compressor 5 for supplying air containing oxygen. Further, the fuel cell 2 is electrically connected to a motor 6 for moving the vehicle, an auxiliary machine 7 constituted by an air conditioner, a radiator fan, and the like, and a secondary battery 8 as a storage battery.

  A hydrogen inlet valve 9 for controlling the flow of hydrogen is provided in the middle of the path connecting the hydrogen storage tank 4 and the fuel cell 2, and further, electric power is supplied in the fuel cell 2 downstream of the fuel cell 2. A hydrogen outlet valve 10 is provided for controlling the exhaust of hydrogen that has not chemically reacted. The hydrogen inlet valve 9 and the hydrogen outlet valve 10 open and close a path based on a control signal sent from the control device 3 to control the flow of hydrogen.

  A humidifier 11 for humidifying the air sent to the fuel cell 2 and an air inlet valve 12 for controlling the air flow are provided in the middle of the path connecting the air compressor 5 and the fuel cell 2. ing. An air outlet valve 13 for controlling the exhaust of air that has not electrochemically reacted in the fuel cell 2 is provided on the downstream side of the fuel cell 2. The air compressor 5, the humidifier 11, the air inlet valve 12, and the air outlet valve 13 operate based on a control signal sent from the control device 3. In addition, the exhaust of the air which did not electrochemically react in the fuel cell 2 is discharged out of the system after passing through the humidifier 11 after leaving the air outlet valve 13. Thereby, the produced water produced | generated by the electrochemical reaction in the fuel cell 2 is utilized effectively in the humidification of the air in the humidifier 11.

  A drive inverter 14 is provided in the middle of the circuit connecting the fuel cell 2 and the motor 6. This is because since the motor 6 is an AC motor, it is necessary to convert DC electricity output from the fuel cell 2 into AC electricity. The drive inverter 14 can control the rotation speed and torque of the motor 6 by adjusting the frequency of the AC output. The drive inverter 14 controls the motor 6 by adjusting the frequency and voltage of AC electricity based on a control signal sent from the control device 3.

  A DC-DC converter 15 is provided in the middle of the circuit connecting the fuel cell 2 and the auxiliary machine 7 or the secondary battery 8. The DC-DC converter 15 performs a role of electrically connecting the fuel cell 2 having a different rated voltage, the secondary battery 8 and the auxiliary machine 7 by converting a voltage of direct current electricity. The DC-DC converter 15 opens and closes an electric circuit based on a control signal sent from the control device 3 to electrically connect or disconnect the fuel cell 2 and the secondary battery 8 or the auxiliary machine 7. A current direction limiter 16 (diode) is provided between the fuel cell 2 and the DC-DC converter 15 in order to prevent reverse power from being applied to the fuel cell 2 during power generation due to load fluctuations of the motor 6 or the like. Is provided. In addition, the current direction limiter 16 is bypassed between the fuel cell 2 and the DC-DC converter 15 in order to apply the voltage of the secondary battery 8 to the fuel cell 2 so that the generated water can be electrolyzed. A bypass circuit is provided. On this bypass circuit, a switch 17 for opening and closing the circuit is provided. Note that the secondary battery 8, the DC-DC converter 15, and the switch 17 correspond to the voltage application means in the present invention.

  The fuel cell 2 is a polymer electrolyte fuel cell (PEFC) suitable for a moving medium such as a fuel cell vehicle, and includes a plurality of fuel cell cells 27 in a stacked state. The fuel cell 2 includes a voltage sensor 18 that detects the voltage of the fuel cell 27 disposed therein, a temperature sensor 19 that detects the temperature of the fuel cell 27, and a current sensor 20 that detects the current flowing through the fuel cell. Is provided.

  FIG. 2 is a cross-sectional view showing the configuration of the fuel cell 27 disposed inside the fuel cell 2. As shown in FIG. 2, the fuel cell 27 includes a membrane / electrode assembly 24 (MEA) in which a polymer electrolyte membrane 21 is sandwiched between an anode catalyst electrode 22 and a cathode catalyst electrode 23, and a cathode catalyst electrode. The cathode catalyst electrode side gas diffusion layer 25 joined to the anode catalyst electrode side gas diffusion layer 26 and the anode catalyst electrode side gas diffusion layer 26 joined to the anode catalyst electrode 22. The cathode catalyst electrode side gas diffusion layer 25 and the anode catalyst electrode side gas diffusion layer 26 are made of a gas-permeable material having a large number of pores inside. Therefore, oxygen (air) sent from the air compressor 5 flows on the surface of the cathode catalyst electrode side gas diffusion layer 25 and inside thereof. Further, hydrogen fed from the hydrogen storage tank 4 flows on the surface of the anode catalyst electrode side gas diffusion layer 26 and inside thereof.

The polymer electrolyte membrane 21 is made of a conductive substance having an ion exchange ability having a solid polymer such as polyfluorocarbon as a main chain and a side chain such as a sulfone group or a carboxylic acid group for carrying a charge. The The cathode catalyst electrode 23 and the anode catalyst electrode 22 are made of carbon black carrying platinum (Pt). The membrane / electrode assembly 24 generates power by causing an electrochemical reaction between hydrogen sent to the anode catalyst electrode 22 side and oxygen in the air sent to the cathode catalyst electrode 23 side, and a potential difference is generated between the two electrodes. Is generated.

  The control device 3 controls the entire fuel cell system 1 and includes a CPU (Central Processing Unit), ROM, RAM, and an input / output interface. The control device 3 receives input of measurement signals sent from the voltage sensor 18, current sensor 20, and temperature sensor 19, and receives the secondary battery 8, DC-DC converter 15, auxiliary machine 7, driving inverter 14, motor 6, opening / closing By outputting control signals to the device 17, the valves 9, 10, 12, 13, the humidifier 11, the air compressor 5, etc., each device constituting the fuel cell system 1 is controlled.

<Processing flow>
Next, control of the generated water in the fuel cell system 1 according to this embodiment will be described. FIG. 3 is a diagram showing a control flow of the fuel cell system 1. 4 to 6 are diagrams showing the distribution of generated water adhering to the fuel cell 27 in each step. Hereinafter, the drainage control of the fuel cell system 1 will be described with reference to the control flow of FIG. 3 and FIGS.

  (Step S <b> 101) When the power generation of the fuel cell 2 stops, the control device 3 monitors the temperature of the fuel cell 2 with the temperature sensor 19. And if the control apparatus 3 detects that the temperature of the fuel cell 2 is 0 degrees C or less, it will transfer to the following process. In addition, the adhesion state of the produced water to the fuel cell 27 in this step is shown in FIG. As shown in FIG. 4, hydrogen and oxygen are present in the polymer electrolyte membrane 21, the cathode catalyst electrode 23, the cathode catalyst electrode side gas diffusion layer 25, and the cathode catalyst electrode side gas flow path of the fuel cell 27 after power generation is stopped. The produced water produced by the electrochemical reaction with is attached.

  (Step S102) Upon confirming that the temperature of the fuel cell 2 is 0 ° C. or lower, the control device 3 starts the air compressor 5 with the valves 12 and 13 opened, and supplies air to the fuel cell 2. To do. The cathode catalyst electrode side gas diffusion layer 25 and the cathode catalyst electrode side gas flow path of the fuel battery cell 27 are configured such that air supplied from the air compressor 5 flows. For this reason, by flowing air through this portion, the generated water adhering to the cathode catalyst electrode side gas diffusion layer 25 and the cathode catalyst electrode side gas flow passage is gradually drained. In addition, the control apparatus 3 supplies air in the state which stopped the humidifier 11. Thereby, dry air which is not damp is sent to the cathode side of the fuel cell 27.

  (Step S <b> 103) When the control device 3 starts draining the generated water by the air compressor 5, electricity flows from the secondary battery 8 to the fuel cell 2 through the DC-DC converter 15, and the resistance value of the fuel cell 27. Is detected. The resistance value of the fuel battery cell 27 is calculated by dividing the current detected by the current sensor 20 from the voltage detected by the voltage sensor 18. Then, the resistance value of the fuel battery cell 27 is acquired in advance by an experiment or the like, and the predetermined resistance value stored in the ROM or the like, that is, the cathode catalyst electrode side gas diffusion layer 25 or the cathode catalyst electrode side gas flow path is drained. When the resistance value of the fuel battery cell 27 at the state is reached, the process proceeds to the next step. The control device 3 continues air supply by the air compressor 5 until the resistance value of the fuel battery cell 27 reaches a predetermined resistance value.

  (Step S104) When the resistance value of the fuel cell 27 reaches the predetermined resistance value, the control device 3 closes the valves 9, 10, 12, and 13 and stops the air compressor 5. In addition, the adhesion state of the produced water to the fuel cell 27 in this step is shown in FIG. As shown in FIG. 5, the generated water adhering to the fuel cell 27 is removed from the cathode catalyst electrode side gas diffusion layer 25 and the cathode catalyst electrode side gas flow path, and the polymer electrolyte membrane is removed. Only the produced water adhering to 21 and the cathode catalyst electrode 23 remains.

  (Step S105) When the control device 3 stops the air compressor 5, the voltage sensor 18 monitors the voltage of the fuel cell 27. At this time, since the motor 6 and the auxiliary machine 7 are in a stopped state, the detected voltage of the fuel cell 27 is an open circuit voltage. In the control device 3, the open circuit voltage of the fuel battery cell 27 detected by the voltage sensor 18 is 1.40V (corresponding to a predetermined second voltage in the present invention) to 1.24V (predetermined in the present invention). In the case of 0.16 V or more obtained by subtracting 1), the voltage of the fuel cell 27 is continuously monitored. On the other hand, when the open circuit voltage of the fuel battery cell 27 becomes less than 0.16 V, the control device 3 proceeds to the next step. In addition, when the open circuit voltage of the fuel cell 27 becomes less than 0.16 V, the control device 3 does not need to immediately move to the next step, and moves to the next step after the open circuit voltage further decreases. You may make it do.

  (Step S106) When the open circuit voltage of the fuel cell 27 becomes less than 0.16 V, the control device 3 controls the DC-DC converter 15 to apply a voltage from the secondary battery 8 to the fuel cell 2 (this book). This corresponds to the first step in the invention). When applying a voltage to the fuel cell 2, the control device 3 adjusts the output of the DC-DC converter 15 so that a voltage of 1.24 V or more is applied to the fuel cell 27 of the fuel cell 2. Note that the control device 3 may monitor the output voltage of the DC-DC converter 15 and control the application of the voltage to stop before the voltage applied to the fuel cell 2 becomes 1.40 V or higher. (This corresponds to the second step in the present invention).

  Here, when a voltage is applied to the fuel cell 2 to electrolyze the generated water adhering to the fuel cell 27, oxygen is generated on the cathode catalyst electrode 23 side of the fuel cell 27, and the anode of the fuel cell 27 is Hydrogen is generated on the catalyst electrode 22 side. The reaction when the produced water is electrolyzed is as follows.

Cathode side: 2H ₂ O → 4H ⁺ + O ₂ + 4e ⁻
Anode side: 4H ⁺ + 4e ⁻ → 2H ₂

  The open circuit voltage of the fuel cell 27 is increased by hydrogen and oxygen generated by the electrolysis. Therefore, the control device 3 stops applying the voltage to the fuel cell 2 when a certain time (for example, several seconds) has elapsed since the start of applying the voltage to the fuel cell 2, and returns to the control of step S105. (This corresponds to the fourth step in the present invention). Thereby, when hydrogen and oxygen generated in both electrodes cross-leak and the open circuit voltage of the fuel cell 27 is lowered, the control of applying the voltage again to the fuel cell 2 is repeated, and the electrolysis of the generated water gradually proceeds. To do. In addition, the adhesion state of the produced water of the fuel battery cell 27 in this step is shown in FIG. As shown in FIG. 6, after electrolysis of the produced water, the produced water adhering to the fuel cell 27 remains in the vicinity of the polymer electrolyte membrane 21 only. The control device 3 performs control so as to stop the voltage application after a certain time has elapsed since the start of voltage application. However, the present invention is not limited to this, for example, the fuel cell 2 flows. The voltage application may be stopped when the current exceeds a certain value (predetermined current value).

  Here, the control device 3 returns to the control of step S105 after the end of step S106, but the present invention is not limited to this, and may not return to the control of step S105.

  In addition, when the fuel cell 2 is started by a user operation or the like (when power generation of the fuel cell 2 is started), the control device 3 performs any of the processes in steps S101 to S106. Even so, the process is interrupted and the process proceeds to a process for starting the fuel cell 2.

<Effect>
As described above, it is possible to eliminate the generated water adhering to the fuel cell 27 while suppressing the deterioration of the membrane-electrode assembly 24. In addition, since electrolysis is performed while monitoring the open circuit voltage, the voltage increase during electrolysis is mistaken as an abnormal voltage, and the electrolysis process is stopped even though the generated water remains. That disappears. In addition, since the electrolysis is performed while monitoring the open circuit voltage, the electrolysis process is not terminated while the generated water remains attached. Since the generated water adhering to the fuel cell 27 is reliably electrolyzed, the generated water is not frozen when the fuel cell 2 is exposed to a sub-freezing environment, and the fuel gas or oxidant is not activated when the fuel cell 2 is started. Gas diffusion is not hindered. Thereby, it becomes possible to start the fuel cell 2 smoothly. Further, since the generated water is removed by electrolysis, the fuel battery cells 27 can be dried without unevenness. Thereby, the fall of the output of the fuel cell 27 by the local dry-up of the polymer electrolyte membrane 21 can be prevented.

<Modification 1>
Hereinafter, modified examples of the fuel cell system 1 according to the embodiment will be described. In the fuel cell system 1 according to the above-described embodiment, the application of voltage to the fuel cell 2 is stopped after a certain time has elapsed. However, the fuel cell system 1 according to the present modification monitors the current when the voltage is applied, and controls the applied voltage based on the change in the current. For convenience of explanation, the same components and control flow as those of the fuel cell system 1 according to the above embodiment are denoted by the same reference numerals, description thereof is omitted, and only differences from the above embodiment will be described. FIG. 7 shows a control flow according to this modification. Hereinafter, this modification will be described with reference to the control flowchart of FIG.

  (Step S201) The configuration of the fuel cell system 1 according to this modification is the same as that of the above embodiment. The control device 3 according to the present modification performs the processing from step S101 to S105, and then applies the voltage from the secondary battery 8 to the fuel cell 2 by controlling the DC-DC converter 15 as in the above-described embodiment. To do. Here, the control device 3 according to the above-described embodiment has stopped applying the voltage after a lapse of a certain time from the start of applying the voltage to the fuel cell 2. On the other hand, if the control apparatus 3 which concerns on this modification starts application of the voltage to the fuel cell 2, it will transfer to the following process (step S202).

  (Step S <b> 202) When the control device 3 starts to apply a voltage to the fuel cell 2, the control device 3 acquires the current value of the fuel cell 27 from the current sensor 20. The control device 3 obtains the rate of change of the acquired current value, and once this rate of change becomes constant and then starts to change again, the application of the voltage to the fuel cell 2 is stopped. FIG. 8 shows a detailed flow of processing in this step. A detailed processing flow in step S202 will be described below with reference to FIG.

  (Step S <b> 202-1) The control device 3 calculates the current temporal change rate (ΔI / ΔT) from the current sensor 20.

(Step S202-2) Next, the control device 3 checks whether or not the calculated fluctuation range of the time change rate (ΔI / ΔT) of the current is within a predetermined threshold value (ε). If the fluctuation range of the current temporal change rate (ΔI / ΔT) is within the predetermined threshold value (ε), the current flows constantly, so it is determined that the electrolysis of the generated water has not started. Return to step S201-1. On the other hand, if the fluctuation range of the time change rate (ΔI / ΔT) of the current deviates from the range of the predetermined threshold value (ε), it is determined that the electrolysis of the generated water has started, and the next step S202-3 Migrate to The predetermined threshold value (ε) is a preset value stored in advance in the control device 3, for example, a current time when electrolysis of generated water adhering to the fuel cell 27 is being performed. The time change rate is substantially the same as the maximum value of the change rate.

  (Step S <b> 202-3) The control device 3 calculates again the current temporal change rate (ΔI / ΔT) from the current sensor 20.

  (Step S202-4) Next, the control device 3 prevents the membrane / electrode assembly from deteriorating if the current change rate (ΔI / ΔT) is equal to or greater than a predetermined threshold value (ε). The application of the voltage to the fuel cell 2 is interrupted, and the process proceeds to step S105. FIG. 9 is a graph showing the change in current at this time. As shown in FIG. 9, the voltage application is interrupted when the electric current electrolyzing the produced water once rises again and then begins to rise again. In addition, if the time change rate ((DELTA) I / (DELTA) T) of an electric current is not more than a predetermined threshold value ((epsilon)), the control apparatus 3 will transfer to following step S202-5.

  (Step S202-5) Next, if the time change rate (ΔI / ΔT) of the current is equal to or less than a value obtained by inverting the predetermined threshold value (ε) negatively, the control device 3 adheres to the fuel cell 27. It is determined that the electrolysis of the produced water has been completed, the application of voltage to the fuel cell 2 is stopped, and the process proceeds to step S107. FIG. 10 is a graph showing changes in current at this time. As shown in FIG. 10, the application of voltage is stopped when the electric current for electrolyzing the generated water once flattenes and then starts to decrease again. Note that the control device 3 returns to the next step S202-3 unless the current temporal change rate (ΔI / ΔT) is equal to or less than a value obtained by inverting the predetermined threshold value (ε) negatively.

  The processing flow in step S202 is as described above. Step S202 corresponds to the third step in the present invention.

  As described above, according to the fuel cell system 1 according to the present modification, the voltage is applied to the fuel cell while monitoring the change in the current. The generated water adhering to the fuel cell 27 can be eliminated without excessively electrolyzing the water.

  In addition, the control device 3 is, in other words, when the current does not become constant even after a lapse of a certain time (corresponding to a predetermined time in the present invention) after the application of the voltage to the fuel cell 2 is started. If step S202-3 is not executed even after a certain time has elapsed, the application of voltage to the fuel cell 2 may be stopped. Note that the case where the current does not become constant is a case where the fluctuation of the current does not fall within a predetermined value range (corresponding to a predetermined value in the present invention) even after a predetermined time has elapsed.

<Modification 2>
Hereinafter, modified examples of the fuel cell system 1 according to the embodiment and the modified examples will be described. In the fuel cell system 1 described above, when the open circuit voltage of the fuel cell 27 is high, the fuel cell system 1 waits for the voltage to drop due to hydrogen-oxygen cross-leakage via the membrane / electrode assembly 24, and the open circuit voltage is natural. The voltage was applied to the fuel cell 2 after waiting for the voltage to drop. However, in the fuel cell system 1 according to this modification, when the open circuit voltage of the fuel cell 27 is high, the power of the fuel cell 2 is actively consumed, and the open circuit voltage of the fuel cell 27 is quickly reduced. Let Note that, for convenience of explanation, the same components and control flow as those of the fuel cell system 1 according to the above-described embodiment are denoted by the same reference numerals and description thereof is omitted, and the differences from the above-described embodiments are the same as in the above modification. Only the point will be described. FIG. 11 shows a control flow according to this modification. Hereinafter, this modification will be described with reference to the control flowchart of FIG.

(Step S301) The configuration of the fuel cell system 1 according to this modification is the same as that of the above embodiment. The control device 3 according to the present modification performs the same processing as in the above-described embodiment from step S101 to step S105. In step S105, the control device 3 according to the present modification detects that the open circuit voltage of the fuel cell 27 detected by the voltage sensor 18 is 0.16V or more obtained by subtracting 1.24V from 1.40V. In this case, the switch 17 is inserted to control the DC-DC converter 15, and power is consumed from the fuel cell 2 to the auxiliary device 7 and the secondary battery 8. When power is consumed by the auxiliary machine 7, for example, a radiator fan or the like is activated to consume power. When the secondary battery 8 consumes power, the voltage of the power supplied from the DC-DC converter 15 to the secondary battery 8 side is made higher than the voltage of the secondary battery 8, so that the secondary battery 8 Power is consumed by charging. The control device 3 controls the DC-DC converter 15 and the like to supply power from the fuel cell 2 to the auxiliary device 7 and the like after a certain time has elapsed since the start of power consumption by the auxiliary device 7 and the secondary battery 8. Stop supplying. And the control apparatus 3 transfers control to step S105. This step S301 corresponds to the fifth step in the present invention.

  As described above, according to the fuel cell system 1 according to the present modification, since the power is actively consumed when the open circuit voltage is high, the decrease in the open circuit voltage depends on the cross leak of hydrogen and oxygen. In comparison with the above, the generated water adhering to the fuel battery cell 27 can be removed very quickly.

The figure which shows the structure of a fuel cell system. Sectional drawing which shows the structure of a fuel cell. The figure which shows the control flow of a fuel cell system. The figure which shows distribution of the produced water adhering to the fuel cell. The figure which shows distribution of the produced water adhering to the fuel cell. The figure which shows distribution of the produced water adhering to the fuel cell. The figure which shows the control flow of the fuel cell system which concerns on a modification. The figure which shows the detailed flow of the process in step S202 of the fuel cell system which concerns on a modification. The graph which shows the change of the electric current at the time of the voltage application of the fuel cell system which concerns on a modification. The graph which shows the change of the electric current at the time of the voltage application of the fuel cell system which concerns on a modification. The figure which shows the control flow of the fuel cell system which concerns on a modification.

Explanation of symbols

1 ... Fuel cell system 2 ... Fuel cell 3 ... Control device 4 ...・ ・ ・ ・ ・ ・ ・ ・ ・ Hydrogen storage tank 5 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Air compressor 6 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Motor 7 ・ ・ ・ ・ ・ ・... Auxiliary machine 8 ... Secondary battery 9 ... Hydrogen inlet valve 10 ...・ Hydrogen outlet valve 11 ・ ・ ・ ・ ・ ・ Humidifier 12 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Air inlet valve 13 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Air outlet valve 14 ・............ Drive inverter 15 ... DC-DC converter 16 ... Current direction limiter 17 ... .... Switch 18 ......... Voltage sensor 19 ...・ ・ ・ ・ ・ ・ Temperature sensor 20 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Current sensor 21 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Polymer electrolyte membrane 22 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・Anode catalyst electrode 23 ... Cathode catalyst electrode 24 ... Membrane / electrode assembly 25 ... Cathode catalyst electrode Side gas diffusion layer 26 ··········· Anode catalyst electrode side gas diffusion layer 27 ········ Fuel cell

Claims (22)

A fuel cell having a membrane-electrode assembly in which an electrolyte membrane is sandwiched between catalyst electrodes;
Voltage applying means for applying an applied voltage equal to or higher than a predetermined first voltage necessary for electrolyzing the generated water generated in the membrane-electrode assembly to the fuel cell;
When the open circuit voltage of the fuel cell is less than a voltage obtained by subtracting the predetermined first voltage from a predetermined second voltage at which the membrane-electrode assembly starts to deteriorate when a voltage is applied to the fuel cell. Control means for controlling the voltage application means to apply a voltage to the fuel cell, a fuel cell system. The control means stops application of voltage to the fuel cell by the voltage application means before the applied voltage becomes equal to or higher than the predetermined second voltage.
The fuel cell system according to claim 1. Further comprising voltage detection means for detecting the voltage of the fuel cell,
The control means includes
When the open circuit voltage of the fuel cell detected by the voltage detection means becomes less than a voltage obtained by subtracting the predetermined first voltage from the predetermined second voltage, application of the voltage to the fuel cell is started. Controlling the voltage applying means,
Controlling the voltage application means so as to stop the application of the voltage to the fuel cell before the voltage of the fuel cell detected by the voltage detection means becomes equal to or higher than the predetermined second voltage;
The fuel cell system according to claim 1 or 2. Further comprising current detection means for detecting the current of the fuel cell,
When the current of the fuel cell detected by the current detection unit reaches a predetermined current state in which the application of voltage to the fuel cell is to be stopped, the control unit supplies the fuel cell to the fuel cell by the voltage application unit. Stop applying the voltage of
The fuel cell system according to any one of claims 1 to 3. The fuel cell system according to claim 4, wherein the predetermined current state is a state in which the current of the fuel cell starts to change again after becoming substantially constant. 5. The fuel according to claim 4, wherein the predetermined current state is a state in which a change in current of the fuel battery cell after a predetermined time has elapsed since the start of voltage application to the fuel battery cell is greater than or equal to a predetermined value. Battery system. The fuel cell system according to claim 4, wherein the predetermined current state is a state in which the current of the fuel battery cell has reached a predetermined current value. The control means stops the application of the voltage to the fuel cell, and then when the open circuit voltage of the fuel cell becomes less than the voltage obtained by subtracting the predetermined first voltage from the predetermined second voltage, the voltage Resuming the application of voltage to the fuel cell by the application means;
The fuel cell system according to any one of claims 1 to 7. Further comprising discharge means for discharging the fuel cell,
The control means discharges the fuel cell with the discharge means when the voltage application means is not applying a voltage to the fuel cell.
The fuel cell system according to any one of claims 1 to 8.   The fuel cell system according to any one of claims 1 to 9, wherein the predetermined first voltage is any voltage satisfying a condition of 1.24V or more and less than 1.40V.   The fuel cell system according to any one of claims 1 to 10, wherein the predetermined second voltage is a voltage of 1.40V. A fuel cell having a membrane-electrode assembly in which an electrolyte membrane is sandwiched between catalyst electrodes;
Voltage applying means for applying an applied voltage equal to or higher than a predetermined first voltage necessary for electrolyzing the generated water generated in the membrane-electrode assembly to the fuel cell;
A control method for a fuel cell system comprising:
When the open circuit voltage of the fuel cell is less than a voltage obtained by subtracting the predetermined first voltage from a predetermined second voltage at which the membrane-electrode assembly starts to deteriorate when a voltage is applied to the fuel cell. Having a first step of controlling the voltage application means to apply a voltage to the fuel cell,
Control method of fuel cell system. The method of controlling a fuel cell system according to claim 12, further comprising a second step of stopping application of a voltage to the fuel cell by the voltage application means before the applied voltage becomes equal to or higher than the predetermined second voltage. The fuel cell system further comprises voltage detection means for detecting the voltage of the fuel cell,
The first step includes
When the open circuit voltage of the fuel cell detected by the voltage detection means becomes less than a voltage obtained by subtracting the predetermined first voltage from the predetermined second voltage, application of the voltage to the fuel cell is started. Controlling the voltage applying means,
The second step includes
Controlling the voltage application means so as to stop the application of the voltage to the fuel cell before the voltage of the fuel cell detected by the voltage detection means becomes equal to or higher than the predetermined second voltage;
The method for controlling a fuel cell system according to claim 12 or 13. The fuel cell system further comprises current detection means for detecting a current of the fuel cell,
When the current of the fuel battery cell detected by the current detection means reaches a predetermined current state where the application of voltage to the fuel battery cell should be stopped, the voltage application means applies the voltage to the fuel battery cell. Further comprising a third step of stopping,
The method for controlling a fuel cell system according to any one of claims 12 to 14. The control method for a fuel cell system according to claim 15, wherein the predetermined current state is a state in which the current of the fuel cell starts to change again after becoming substantially constant. The fuel according to claim 15, wherein the predetermined current state is a state in which a change in current of the fuel battery cell after a predetermined time has elapsed after starting application of a voltage to the fuel battery cell is greater than or equal to a predetermined value. Battery system control method. The control method of the fuel cell system according to claim 15, wherein the predetermined current state is a state in which the current of the fuel cell reaches a predetermined current value. After stopping the application of the voltage to the fuel cell, when the open circuit voltage of the fuel cell becomes less than the voltage obtained by subtracting the predetermined first voltage from the predetermined second voltage, the fuel by the voltage applying means A fourth step of resuming the application of voltage to the battery cell;
The method for controlling a fuel cell system according to any one of claims 12 to 18. The fuel cell system further comprises discharge means for discharging the fuel cell,
A fifth step of discharging the fuel cell by the discharging means when the voltage applying means is not applying a voltage to the fuel cell;
The method for controlling a fuel cell system according to any one of claims 12 to 19.   21. The fuel cell system control method according to claim 12, wherein the predetermined first voltage is any voltage satisfying a condition of 1.24V or more and less than 1.40V.   The method of controlling a fuel cell system according to any one of claims 12 to 21, wherein the predetermined second voltage is a voltage of 1.40V.

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