JP2007242408A - Fuel cell system - Google Patents

Abstract

Deterioration due to uneven distribution of hydrogen and air (oxygen) in a fuel circulation system at the time of starting of a fuel cell is prevented.
When a hydrogen concentration detected by a hydrogen concentration meter 50 is within a predetermined concentration range while power generation of a fuel cell is stopped, a hydrogen circulation pump 24 is driven to circulate a fuel gas and a catalyst for a fuel electrode 1b. Above, hydrogen and oxygen are reacted to remove hydrogen.
[Selection] Figure 1

Description

  The present invention relates to a fuel cell system, and more particularly to a fuel cell system in which deterioration at startup is suppressed.

  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.

  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 hydrogen supply is started when the fuel cell system is started, an interface (hydrogen front) between air that has entered the fuel electrode during the stop and newly supplied hydrogen is formed. In the first region of the fuel electrode to which hydrogen behind the hydrogen front is supplied, hydrogen is ionized, and hydrogen ions reach the oxidant electrode via the electrolyte membrane. At this time, electrons are not supplied from the unconnected external circuit to the oxidant electrode, and carbon dioxide and hydrogen ions are reacted by the reaction of carbon and water carrying the oxidant electrode catalyst in the second region before the hydrogen front. And electrons are generated. The electrons move from the second region to the first region side in the oxidizer electrode and contribute to the generation of water. Hydrogen ions ionized in the second region move to the opposite fuel electrode region via the electrolyte membrane. Due to such a reaction, the carbon of the catalyst support in the oxidant electrode region before the hydrogen front is lost by gasification to carbon dioxide, and the catalyst fine particles aggregate to deteriorate the catalyst performance. .

In order to solve such a problem that the deterioration of the oxidizer electrode proceeds quickly, the fuel gas at the time of startup is supplied at a pressure higher than the pressure during normal operation, so that the oxygen remaining in the fuel electrode can be reduced. There has been an invention that discharges in time and suppresses deterioration of an electrode catalyst or the like (for example, Patent Document 1).
JP 2004-139984 A (page 12, FIG. 14)

  However, in the start-up method in which the fuel gas circulation pump according to the invention described in Patent Document 1 is first rotated, the gas composition in the system is such that the fuel electrode side in the fuel cell is air and the fuel gas circulation path is fuel gas. However, depending on the transient response of the pump, there is a problem in that it takes time for the fuel gas to pass through the fuel electrode and promotes deterioration.

  In order to increase the transient response of the pump, the volume, weight, and power consumption of the pump increase, making it unsuitable for mounting on a vehicle.

  In order to solve the above problems, the present invention has a fuel electrode and an oxidant electrode that sandwich an electrolyte, and a fuel that generates electric power by receiving supply of fuel gas and oxidant gas to the fuel electrode and oxidant electrode, respectively. In a fuel cell system comprising a battery, a fuel gas circulation path for recirculating a part of the exhaust fuel gas from the fuel cell to the supply side, and a fuel gas circulation means, in the fuel electrode or the fuel gas circulation path Detecting means for detecting a value related to the hydrogen concentration in the fuel gas circulating means during a power generation stop when the hydrogen concentration based on the detection value of the detecting means is within the range of the first predetermined value to the second predetermined value. Is a fuel cell system characterized by operating the fuel cell.

  In the present invention, the concentration of hydrogen gas in the fuel system including the fuel electrode, the fuel gas circulation path, and the fuel circulation means gradually decreases while the power generation of the fuel cell is stopped. Along with this, air containing oxygen enters the fuel system from the oxidant electrode via the electrolyte. If the value related to the hydrogen gas concentration of the fuel system is detected by the detecting means, and the hydrogen gas concentration based on the detected value is not less than the first predetermined value that is the upper limit value or less than the second predetermined value that is the lower limit value, The fuel gas circulation means is not operated while the power generation is stopped. Then, the fuel gas circulation means is operated during power generation stop when the hydrogen concentration is within the range of the first predetermined value to the second predetermined value. As a result, when the hydrogen gas concentration is high enough, and conversely, when the hydrogen gas concentration is low enough, the deterioration of the oxidizer electrode catalyst due to the hydrogen front will occur when the fuel gas circulation pump is first started at the next start-up. Therefore, it is possible to save the drive energy of the fuel gas circulation means by maintaining the stopped state of the fuel gas circulation means, and to avoid noise vibration due to the drive of the fuel gas circulation means.

  Further, when the fuel gas supply is started at the next start-up, the hydrogen concentration that may cause deterioration of the oxidant electrode catalyst due to the hydrogen front is within the range of the first predetermined value to the second predetermined value, while the power generation is stopped. By operating the fuel gas circulation means, hydrogen in the fuel gas and oxygen that has entered the fuel system can be reacted on the fuel electrode catalyst and consumed.

  According to the present invention, by detecting the hydrogen concentration, the replacement state of air in the fuel electrode can be known, and the fuel gas circulation means operates according to the replacement state of air. During the stoppage, the gas in which the residual hydrogen and the air that has flowed into the fuel system (fuel electrode, fuel gas circulation path, fuel gas circulation means) are mixed non-uniformly is supplied to the fuel cell fuel electrode catalyst, so that Since it disappears, there is an effect that deterioration of the fuel cell due to the uneven distribution of fuel gas and air in the fuel electrode can be avoided under a high voltage at the time of restart.

  Next, embodiments of the present invention will be described in detail with reference to the drawings.

<General fuel cell system configuration>
First, with reference to FIG. 9 which is a conceptual diagram of a fuel cell system and FIG. 10 which is a conceptual diagram of a single cell of a fuel cell, the overall configuration of the fuel cell system to which the present invention is applied will be described.

Fuel cell body As shown in FIG. 10, the fuel cell body 1 of FIG. 9 includes, for example, a fuel electrode (anode) catalyst layer 103 and an oxidant electrode (on both sides of an electrolyte membrane 102 using a solid polymer electrolyte membrane). Cathode) A membrane electrode assembly (MEA) 101 having a catalyst layer 104 formed thereon, a fuel gas diffusion layer 105, an oxidant gas diffusion layer 106, and separators 107, 108 disposed on both sides of the MEA 101. The separator 107 and the fuel A plurality of fuel cell single cells 100 provided with a fuel gas flow path 109 between the gas diffusion layer 105 and an oxidant gas flow path 110 between the separator 108 and the oxidant gas diffusion layer 106 are stacked. The fuel gas (hydrogen) and the oxidant gas (air) supplied from the outside of the fuel cell main body 1 are respectively connected to the fuel gas channel 109 and the oxidant gas channel. Is supplied to the 10, it generates power through an electrochemical reaction.

Air system The air compressed by the air compressor 11 is sent to the air system humidifier 13 via the air supply path 12, and after being humidified, is sent to the oxidant electrode 1 a of the fuel cell body 1. After oxygen is consumed by the electrochemical reaction in the fuel cell main body 1, the pressure passes through the air exhaust path 14, the pressure is adjusted by the air pressure regulating valve 15, and the air is exhausted outside the system. The pressure of the air supplied to the oxidant electrode 1a is detected by an air pressure gauge 16 provided at the inlet of the oxidant electrode 1a, and the air pressure regulating valve 15 is controlled so that this pressure becomes a desired pressure. . As the air humidifier 13, a device using a water vapor exchange membrane that uses moisture in exhaust gas, a device that supplies pure water from the outside, or the like can be used.

  In addition, a hydrogen detector (not shown) for detecting hydrogen in the exhaust air is provided downstream of the air pressure regulating valve 15, and leaks from hydrogen that has permeated from the fuel electrode to the oxidizer electrode through the electrolyte membrane 102 and from the seal portion. Hydrogen can be detected.

-Hydrogen system Hydrogen supplied by the high-pressure hydrogen tank 21 passes through the hydrogen supply path 22, is adjusted to a desired pressure by the hydrogen pressure regulating valve 23, and joins with the exhausted hydrogen circulated by the hydrogen circulation pump 24. The fuel is humidified by the hydrogen humidifier 25 and sent to the fuel electrode 1b of the fuel cell main body 1. The pressure of hydrogen supplied to the fuel electrode 1b is detected by a hydrogen pressure gauge 29 provided at the inlet of the fuel electrode 1b, and the hydrogen pressure regulating valve 23 is controlled so that this pressure becomes a desired pressure. After the hydrogen is consumed by the electrochemical reaction in the fuel cell body 1, the unreacted hydrogen passes through the hydrogen circulation path 26 and is again used for power generation by the hydrogen circulation pump 24.

  Further, in the hydrogen system, nitrogen permeating from the oxidizer electrode 1a to the fuel electrode 1b during operation and impurities contained in the high-pressure hydrogen tank 21 accumulate, so that these are discharged to the outside of the system. A hydrogen exhaust path 27 and a hydrogen discharge valve (purge valve) 28 are provided. The hydrogen discharge valve 28 is a pressure release means that opens the fuel gas circulation path (hydrogen circulation path 26) to atmospheric pressure.

-Cooling water system The cooling water system is provided in order to remove the heat generated by the power generation of the fuel cell main body 1 and keep the fuel cell main body 1 at an appropriate temperature. The cooling water pumped by the cooling water pump 31 passes through the fuel cell body 1, absorbs heat, passes through the cooling water circulation path 32, exhausts heat to the outside of the system by the heat exchanger 33, and is again cooled. At 31, the fuel cell body 1 is pumped. In addition, while monitoring the cooling water temperature with the cooling water thermometer 34, the temperature is adjusted to an appropriate temperature for power generation of the fuel cell body.

-Load system The load device 40 that consumes the generated power of the fuel cell main body 1 is an inverter device that supplies power to a vehicle drive motor in a fuel cell vehicle, for example. The generated voltage of the fuel cell body 1 is detected by the voltmeter 41 and transmitted to the controller 45. In addition, a load device 40 is connected to the fuel cell main body 1 via an ammeter 42, and the generated power of the fuel cell is supplied to the load device 40. The fuel cell system includes a battery 44 as a power storage device and a battery controller 43 that controls charging and discharging thereof. The battery controller 43 discharges the battery 44 from the battery 44 to the load device 40 when the generated power of the fuel cell main body 1 is insufficient, and from the fuel cell main body 1 to the battery 44 when there is surplus in the generated power of the fuel cell main body 1. Control the charging.

  Further, the battery controller 43 detects the voltage and charge / discharge current of the battery 44, and further, if necessary, the battery temperature, etc., and detects or estimates the amount of electricity stored in the battery 44 based on these detection results, and sends it to the controller 45. Send.

Control system The controller 45 controls the entire fuel cell system including the fuel cell main body 1. Further, the controller 45 sets the optimum pressure / pressure which is set in advance for the fuel cell body 1 based on the detection signals of the air pressure gauge 16, the hydrogen pressure gauge 29, the cooling water thermometer 34, the voltmeter 41 and the ammeter 42. Control signals are output to the compressor 11, the air pressure adjustment valve 15, the hydrogen pressure adjustment valve 23, the hydrogen discharge valve 28, the cooling water pump 31, the load device 40, and the battery controller 43 in order to obtain temperature, flow rate, and load.

  Note that an operation switch (key switch) (not shown) is connected to the controller 45 so that the user can input an instruction to operate or stop the fuel cell system to the controller 45 by operating the operation switch. The controller 45 may have an idle stop function for temporarily stopping power generation when the fuel cell is at a low load or no load.

  Next, the state of the fuel chamber (hydrogen supply path 22, hydrogen circulation pump 24, hydrogen-based humidifier 25, fuel electrode 1b, hydrogen circulation path 26) at the time of the next start-up after such a stop of the fuel cell system is shown in FIG. FIG. 12 and FIG. 13 are used to explain (hydrogen humidifier 25 is omitted in the figure).

(A) State immediately after operation stop (hereinafter referred to as state (A))
Immediately after the fuel cell system is stopped, the fuel chamber is filled with hydrogen when power generation is stopped.

(B) A state in which sufficient time has elapsed after the operation is stopped (hereinafter referred to as state (B)).
When a sufficient time has elapsed from the stop, air permeates from the oxidant electrode 1a to the fuel electrode 1b through the MEA 101, and the fuel chamber is filled with air by diffusion. The time until it is filled with air varies depending on the material, thickness, temperature, etc. of the MEA, but is generally several hours. When the fuel chamber is replaced with air immediately after the operation is stopped, the state (B) is obtained after the replacement.

(C) State after several minutes to several tens of minutes after stopping (hereinafter referred to as state (C))
When not much time has passed since the stop, air exists in the fuel electrode 1b with respect to the state (B), but other parts (hydrogen circulation pump 24, hydrogen humidifier 25, hydrogen circulation path) 26) is filled with hydrogen during the previous power generation, and air and hydrogen are unevenly present in the fuel chamber. Such a state varies depending on the material, thickness, temperature, etc. of the MEA, but is generally about several minutes to several tens of minutes.

<Problems of conventional technology>
In the prior art, in order to discharge the air remaining in the fuel electrode 1b in a short time, the hydrogen discharge valve 28 is opened, the operation of the hydrogen circulation pump 24 is started, and the fuel electrode 1b is set to a negative pressure. High-pressure hydrogen is supplied, and oxygen remaining in the fuel electrode 1b is quickly discharged by the suction force due to the negative pressure and the high-pressure supply force. However, as in the state (C), air and hydrogen remain in the fuel chamber. If it exists unevenly, hydrogen and oxygen are unevenly distributed in the fuel electrode 1b as soon as the operation of the hydrogen circulation pump 24 is started.

  When the transient response of the hydrogen circulation pump 24 is sufficient, the existence time of the uneven distribution of hydrogen and oxygen can be shortened and deterioration can be suppressed. However, a small and lightweight system such as a fuel cell vehicle is required. In this case, the hydrogen circulation pump 24 is also suitable to be small and light. In this case, since the transient response of the hydrogen circulation pump 24 is limited, the existence time of the uneven distribution of hydrogen and oxygen becomes long and deteriorates. There was a problem of proceeding.

  The present invention provides a control method of a fuel cell system that solves this problem.

[Constitution]
Next, the configuration of Embodiment 1 of the fuel cell system according to the present invention will be described with reference to FIG. The configuration of this embodiment is obtained by adding a hydrogen concentration meter 50 capable of measuring the hydrogen concentration in the vicinity of the outlet of the fuel electrode 1b to FIG. 9 which is a general fuel cell system. Since other configurations are the same as those in FIG. 9, the same components are denoted by the same reference numerals, and redundant description is omitted.

[Control method]
Next, the operation of this embodiment will be described with reference to the control flowchart of FIG. 2 and the time chart of FIG.

  The control flowchart of FIG. 2 is called and executed at regular time intervals (for example, every 100 [msec]) while the fuel cell is stopped. However, an execution permission condition described later may be added. . In the case of a fuel cell vehicle, the controller 45 determines that the operation of the fuel cell is being stopped based on an operation switch signal, an idle stop signal, etc. (not shown).

  In the control flowchart of FIG. 2, first, in step (hereinafter abbreviated as “S”) 61, the hydrogen concentration meter 50 is turned on to detect the hydrogen concentration. Next, in S62, it is determined whether or not the detected hydrogen concentration is within a predetermined concentration range.

  When the first predetermined concentration 211, the second predetermined concentration 212, and the hydrogen concentration management point 210 during power generation are set (210> 211> 212), the hydrogen concentration can be divided based on three conditions.

<When the concentration is not less than the first predetermined concentration (211 or more)>
Immediately after power generation is stopped, air replacement has not progressed, and a high hydrogen concentration is maintained. Therefore, even if the cathode air supply and fuel gas circulation pump rotation start at the time of restart and the fuel cell is in a high voltage state, the fuel gas and air are not unevenly distributed in the anode, so that the deterioration is promoted. Since there is no, go to S64.

<When not more than second predetermined concentration (212 or less)>
It has been left for a long time since power generation was stopped, and it has been sufficiently replaced with air, maintaining a low hydrogen concentration. Therefore, even if the cathode air supply and fuel gas circulation pump rotation start at the time of restart and the fuel cell is in a high voltage state, the fuel gas and air are not unevenly distributed in the anode, so that the deterioration is promoted. Since there is no, go to S64.

<When less than the first predetermined concentration and exceeds the second predetermined concentration (from 211 to 212)>
Although it has been left for a while since the power generation was stopped, the replacement with air has progressed, but a high hydrogen concentration is maintained. Therefore, when the fuel cell enters a high voltage state by starting the cathode air supply and the fuel gas circulation pump rotation at the time of restart, the fuel gas and the air are unevenly distributed in the anode, and the deterioration can be promoted. Proceed to S63.

  In S63, it is determined that the hydrogen and the replacement air that were being generated last time are non-uniformly present in the fuel chamber (state C), the hydrogen circulation pump 24 is operated, and the gas in the fuel chamber is circulated to thereby return the fuel electrode 1b. A chemical reaction operation is performed on the catalyst. The hydrogen circulation pump is rotated at a predetermined rotational speed. This is returned as the rotational speed (240) which is suppressed to such an extent that the anode gas circulates and does not give an uncomfortable feeling to the driver or people around the vehicle experimentally.

  In S64, it is determined that there is no longer any uneven distribution of hydrogen and oxygen in the fuel electrode 1b, the hydrogen circulation pump 24 is stopped (241), the chemical reaction operation on the fuel electrode catalyst is terminated, and the process returns.

[Effect of Example 1]
(1) When it is determined that the fuel electrode 1b is filled with hydrogen, it can be started immediately after a restart request is made (time 200 to 201 in FIG. 7). Further, since the hydrogen circulation pump drive operation is not executed, no extra auxiliary power is consumed. Fuel consumption can be improved without excessive consumption of hydrogen.

  (2) When it is determined that the inside of the fuel electrode 1b is filled with air, if a restart request is made during that time, it can be started immediately (after time 202 in FIG. 7). If a restart request is made, a negative pressure is generated in the fuel electrode 1b by the hydrogen circulation pump 24, and then high-pressure hydrogen can be supplied. Therefore, the uneven distribution state of hydrogen and oxygen in the fuel electrode 1b can be shortened and deterioration can be suppressed.

  (3) When it is judged that the hydrogen in the fuel chamber and the air that has permeated from the oxidizer electrode 1a exist non-uniformly at the previous power generation, it is generated immediately after the hydrogen circulation pump is activated when a restart is requested. The uneven distribution of hydrogen and oxygen in the fuel electrode 1b to be performed cannot be avoided. However, as shown in the present embodiment, since the circulation pump drive operation is executed and hydrogen is consumed, this section can be shortened significantly (time 201 to 202 in FIG. 7). Therefore, it is possible to reduce the frequency of activation accompanied by deterioration in the number of restarts. Therefore, deterioration of the fuel cell can be suppressed.

  Here, the installation position of the hydrogen concentration meter 50 will be described. During the stop of the fuel cell operation, air permeates from the oxidant electrode 1a to the fuel electrode 1b or air flows backward from the hydrogen exhaust path 28, so that the fuel cell main body 1 has an outlet at the fuel electrode 1b. By installing the hydrogen concentration meter 50, it is possible to grasp the air replacement state of the fuel chamber. Of course, it may be the entrance.

Alternatively, a hydrogen concentration meter may be installed by experimentally measuring the hydrogen concentration in each part such as the fuel electrode 1b, the hydrogen circulation path 26, etc., specifying the part where the air replacement is most advanced and the part where the air replacement is most difficult to proceed. A plurality of hydrogen concentration meters may be installed in the fuel electrode and the circulation line. The upper and lower limits may be determined using another hydrogen concentration meter.

[Constitution]
Next, Example 2 will be described. The configuration of this embodiment is a configuration in which the hydrogen concentration meter 50 is removed from the configuration of the first embodiment shown in FIG. In this embodiment, the hydrogen concentration is estimated based on the elapsed time from the stop of the operation of the fuel cell and the pressure of the fuel electrode instead of the detected value of the hydrogen concentration meter.

[Control method]
Next, the control method of the present embodiment will be described with reference to the control flowchart of FIG. 3 and the time chart of FIG.

  The control flowchart of FIG. 3 is called and executed at regular time intervals (for example, every 100 [msec]) while the fuel cell is stopped. However, an execution permission condition to be described later may be added. . In the case of a fuel cell vehicle, the controller 45 determines that the operation of the fuel cell is being stopped based on an operation switch signal, an idle stop signal, etc. (not shown).

  In the control flowchart of FIG. 3, first, in S71, it is determined whether the operation switch is turned off or an idle stop state is entered.

  If the determination in S71 is Yes, the process proceeds to S72 to perform normal control. If the determination in S71 is No, the process proceeds to S82, the timer A is reset, and the process returns.

  In S72, the timer A is counted and the process proceeds to S73. If this control routine is repeated, for example, every 100 [msec], an integrated sum of 100 [msec] may be used each time. In that case, it is not necessary to prepare a timer outside the controller.

  In S73, it is determined whether or not the current value of the timer A is between the first predetermined time and the second predetermined time. Here, the first predetermined time and the second predetermined time are times set based on the degree of air replacement in the fuel chamber.

  During the first predetermined time, the amount of air that has permeated from the oxidant electrode 1a into the fuel chamber or has flowed back from the exhaust air passage 27 has reached an upper limit at which deterioration at startup can be ignored as a mixture of hydrogen and air. The time is set. During the second predetermined time, hydrogen at the time of the previous power generation and air that has permeated from the oxidizer electrode 1a or backflowed from the air exhaust path 27 are mixed unevenly in the fuel chamber, and the deterioration is remarkable at the time of restart. The upper limit time during which air replacement is not sufficient and hydrogen remains is set to such an extent that it is determined that the process proceeds to the time. Here, the value is experimentally set in advance. However, if the second predetermined time is set under the condition that the hydrogen is most likely to remain, and the first predetermined time is set under the condition that the hydrogen is hardly remaining, the first non-uniformity is obtained. Where it is difficult to think that the process will occur, control can be bypassed here.

  If the determination in S73 is No (below the first predetermined time), the air replacement in the fuel chamber has hardly progressed, and therefore there is sufficient hydrogen, so the process returns. This section is before time 300 in FIG.

  If the determination in S73 is No (second predetermined time or longer), the air replacement in the fuel chamber is sufficiently advanced and there is almost no hydrogen, so the process returns. This section is after time 309 in FIG.

  If the determination in S73 is Yes (when the first predetermined time is exceeded and less than the second predetermined time), the air replacement is progressing, but hydrogen is still remaining, and the fuel chamber is in the previous power generation. Since hydrogen is permeated from the oxidant electrode 1a at the time or air that has flowed back from the exhaust air passage 27 is unevenly mixed and the deterioration proceeds at the time of restart, the process proceeds to S74. This section is from time 300 to time 309 in FIG.

  The air replacement state in the fuel chamber is based on the elapsed time from the previous stop to the start, but an oxygen concentration sensor or hydrogen concentration sensor is installed in each part of the fuel chamber in advance, and the elapsed time and concentration change are obtained experimentally. Thus, the time until the fuel chamber becomes oxygen concentration lower than the hydrogen concentration (higher than hydrogen concentration) where deterioration does not proceed even if the routine shifts to the normal routine immediately after startup is the first predetermined time, and the hydrogen circulation pump 24 is first operated in the fuel chamber. It is possible to set the second predetermined time as the time until the oxygen concentration is not deteriorated even if it is reduced (the hydrogen concentration is below).

  Moreover, since the time ratio of the air which permeate | transmits from the oxidizer electrode 1a to the fuel electrode 1b depends on the temperature of the fuel cell body 1 (the higher the temperature, the faster the permeation speed), the temperature measured by the cooling water thermometer 34 is The experiment can be performed while changing, measuring the elapsed time and the concentration change in the fuel chamber, obtaining a correction formula (may be a map or a table), and correcting the result by multiplying the basic elapsed time.

  Here, the second predetermined time is provided because the hydrogen concentration is estimated in S74, but even if a sufficiently long time has passed, if the estimation is incorrect, the hydrogen circulation pump will malfunction. Is to prevent in advance.

  In S74, the hydrogen concentration is estimated, and the process proceeds to S75. Here, the hydrogen concentration is calculated based on the hydrogen partial pressure. First, from the atmospheric pressure Pamb (320), the hydrogen circulation pump is operated and the anode pressure begins to drop due to a chemical reaction. When the pressure Pa (321) is reached, the hydrogen circulation pump is stopped.

Here, the differential pressure ΔPa is represented by ΔPa = Pamb (320) −Pa (321).
The chemical reaction formula is 2H ₂ + O ₂ = 2H ₂ O.
Assuming that the fuel gas in the anode contains water vapor up to the saturated water vapor pressure, 2/3 of the differential pressure ΔPa corresponds to the disappearance of hydrogen (ΔPh2).

ΔPh2 = 2 / 3ΔPa
Each time the operation is repeated, the estimated hydrogen concentration can be estimated by subtracting the estimated hydrogen concentration from the initial hydrogen concentration by 2 / 3ΔPa integrated sum.

ΔPh2 = P (310) −P (312)
= P (312) -P (313)
= P (313) -P (314)
= P (314) -P (315)
In S75, it is determined whether or not the estimated hydrogen concentration is between the first predetermined concentration and the second predetermined concentration. When the first predetermined concentration 310 and the second predetermined concentration 311 are used, the hydrogen concentration can be divided based on three conditions.

  When the determination in S75 is No (when the concentration is not less than the first predetermined concentration (310 or more)), it is immediately after the power generation is stopped, the replacement of air inside the fuel system has not yet progressed, and a high hydrogen concentration is maintained. . Therefore, even if air is supplied to the cathode at the time of restart and a high voltage state is reached, since the fuel gas and air are not unevenly distributed in the anode, the deterioration is not promoted and the process returns.

  When the determination of S75 is No (when the second predetermined concentration or less (311 or less)), the power generation has been left for a long time and the replacement with air is sufficiently advanced, and the low hydrogen concentration is maintained. ing. Therefore, even if air is supplied to the cathode at the time of restart and a high voltage state is reached, since the fuel gas and air are not unevenly distributed in the anode, the deterioration is not promoted and the process returns.

  If the determination in S75 is Yes (less than the first predetermined concentration and exceeds the second predetermined concentration (from 311 to 310)), it is in a state of being left a little after the power generation stop, and the replacement with air proceeds. However, it maintains a high hydrogen concentration. Therefore, if air is supplied to the cathode at the time of restart and a high voltage state is reached, the fuel gas and air are unevenly distributed in the anode and the deterioration can be promoted, so the process proceeds to S76.

  In S76, the anode pressure is read from the hydrogen pressure gauge 29. Next, in S77, it is determined whether or not the anode pressure is less than a predetermined pressure. The predetermined pressure for determination (321) is set in a safe range to such an extent that the membrane in the stack is not damaged, and an excessive pressure difference between the anode and the cathode is prevented.

If it is determined in S77 that the anode pressure is less than the predetermined pressure, the process proceeds to S83.
If it is determined in S77 that the anode pressure is equal to or higher than the predetermined pressure, the process proceeds to S78.
In S78, the timer B is counted and the process proceeds to S79. In S79, it is determined whether the timer B has elapsed a predetermined time. Here, air replacement is promoted by returning the anode pressure to atmospheric pressure (320).

  If it is determined in S79 that the timer B exceeds the predetermined time, it is determined that the anode pressure has returned to the atmospheric pressure, and the process proceeds to S80 to start the chemical reaction.

  If it is determined in S79 that the timer B is equal to or shorter than the predetermined time, it is determined that the anode pressure has not returned to the atmospheric pressure, and the process proceeds to S84.

  In S80, the hydrogen circulation pump is started at a predetermined rotational speed (330), and the hydrogen discharge valve (purge valve) is closed (340). This is the rotational speed at which the anode gas circulates and is experimentally set so as not to cause a driver or a person around the vehicle to feel uncomfortable. These sections are 300 to 301, 302 to 303, 304 to 305, 306 to 307, and 308 to 309 in FIG. Then, the process returns to the main routine.

In S83, the timer B is reset, and the process proceeds to S84.
In S84, if the hydrogen circulation pump is further driven to continue the chemical reaction, the transmembrane pressure difference in the stack continues to increase. Therefore, the hydrogen circulation pump is stopped and the hydrogen discharge valve is opened to perform air replacement. The rotation of the hydrogen circulation pump is stopped (331), and the purge valve is controlled to open (340).

These sections are 301 to 302, 303 to 304, 305 to 306, and 307 to 308 in FIG. Then, the process returns to the main routine.

[Effect of Example 2]
(1) By estimating the hydrogen concentration, the air replacement state in the anode can be determined, and the fuel gas circulation means operates according to the air replacement state. Because the gas in which the residual hydrogen and the air that has flowed into the fuel chamber (fuel electrode, fuel gas circulation path, fuel gas circulation means) are mixed inhomogeneously during the stop is supplied to the fuel electrode catalyst, hydrogen disappears quickly. The deterioration of the fuel cell due to the uneven distribution of fuel gas and air in the fuel chamber can be avoided under the high voltage at the time of restart.

  (2) Since it is a system that measures the pressure in the fuel chamber, it can memorize the pressure when the fuel gas circulation means starts operating, and continue to read the pressure during operation. You can see the passage of time. Since the amount of hydrogen disappearance can be determined from the degree of pressure drop, the time course of the amount of hydrogen disappearance can be determined. The above can be realized without using the hydrogen concentration detecting means.

  (3) If hydrogen disappears too much after a single operation of the fuel gas circulation means, the pressure difference between the hydrogen pressure and air pressure increases across the membrane, leading to physical deterioration of the stack, but the pressure is released. Since the anode pressure reaches a predetermined value or less (or the differential pressure of the anode pressure with respect to the cathode pressure exceeds the predetermined value), the fuel gas circulation means is stopped and the opening operation is executed. There is no differential pressure to the extent that the membrane is physically degraded.

  (4) The fuel gas circulation means is operated based on the air replacement state in the anode, and the pressure release means is operated based on the pressure difference between the anode and the cathode. Since each operation is repeated alternately, air replacement can be promoted to a state where there is almost no hydrogen without damaging the stack due to differential pressure.

[Constitution]
Next, the configuration of the third embodiment will be described with reference to FIG. The configuration of this embodiment is obtained by adding an oxygen concentration meter 51 that can measure the oxygen concentration in the vicinity of the outlet of the fuel electrode 1b to FIG. 9 which is a general fuel cell system. Since other configurations are the same as those in FIG. 9, the same components are denoted by the same reference numerals, and redundant description is omitted.

[Control method]
Next, the control method of the present embodiment will be described with reference to the control flowchart of FIG.

  The control flowchart of FIG. 5 is called and executed at regular time intervals (for example, every 100 [msec]) while the fuel cell is stopped. However, an execution permission condition described later may be added. . In the case of a fuel cell vehicle, the controller 45 determines that the operation of the fuel cell is being stopped based on an operation switch signal, an idle stop signal, etc. (not shown).

  In the control flowchart of FIG. 5, first, in S86, the oxygen concentration meter 51 is turned on to detect the oxygen concentration. Next, in S87, it is determined whether or not the oxygen concentration is between the third predetermined concentration and the fourth predetermined concentration. When the third predetermined concentration> the fourth predetermined concentration, the oxygen concentration can be divided based on three conditions.

  When the determination in S87 is No (when the concentration is equal to or lower than the fourth predetermined concentration), it is immediately after the power generation is stopped, the air replacement has not progressed yet, and a low oxygen concentration is maintained. For this reason, even if air is supplied to the cathode at the time of restart and a high voltage state is reached, since the fuel gas and air are not unevenly distributed in the anode, the deterioration does not accelerate, and the process proceeds to S89.

  If the determination in S87 is No (when the concentration is greater than or equal to the third predetermined concentration), the state has been left for a long time after power generation is stopped, and the replacement with air is sufficiently advanced, and a high oxygen concentration is maintained. For this reason, even if air is supplied to the cathode at the time of restart and a high voltage state is reached, since the fuel gas and air are not unevenly distributed in the anode, the deterioration does not accelerate, and the process proceeds to S89.

  If the determination in S87 is Yes (less than the third predetermined concentration and exceeds the fourth predetermined concentration), it is in a state of being left a little after the power generation is stopped, and hydrogen is mixed while maintaining a high oxygen concentration. ing. Therefore, if air is supplied to the cathode at the time of restart and a high voltage state is reached, the fuel gas and air are unevenly distributed in the anode and the deterioration can be promoted, so the process proceeds to S88.

  In S88, it is determined that hydrogen and replacement air that were being generated last time are unevenly present in the fuel chamber (state C), the hydrogen circulation pump is operated, and a chemical reaction operation is performed on the fuel electrode catalyst. The hydrogen circulation pump is rotated at a predetermined rotational speed and returned. The predetermined number of revolutions is a number of revolutions that is suppressed to such an extent that the anode gas circulates and does not experimentally cause a driver or a person around the vehicle to feel uncomfortable.

  In S89, it is determined that hydrogen and oxygen are not unevenly distributed in the fuel electrode 1b, the hydrogen circulation pump is stopped, the chemical reaction operation is terminated on the fuel electrode catalyst, and the process returns.

[Effect of Example 3]
(1) When it is determined that the inside of the fuel electrode 1b is filled with hydrogen, it can be started immediately when a restart request is made. Further, since the circulation pump drive operation is not executed, no extra auxiliary power is consumed. Fuel consumption can be improved without excessive consumption of hydrogen.

  (2) When it is determined that the fuel electrode 1b is filled with air, if a restart request is made during that time, the fuel electrode 1b can be started immediately. If a restart request is made, a negative pressure is generated in the fuel electrode 1b by the hydrogen circulation pump 24, and then high-pressure hydrogen can be supplied. Therefore, the uneven distribution state of hydrogen and oxygen in the fuel electrode 1b can be shortened and deterioration can be suppressed.

  (3) When it is determined that the hydrogen in the fuel chamber and the air that has permeated from the oxidizer electrode 1a exist non-uniformly in the fuel chamber, this occurs immediately after the hydrogen circulation pump is activated when a restart is requested. The uneven distribution of hydrogen and oxygen in the fuel electrode 1b to be performed cannot be avoided. However, as shown in the present embodiment, since the circulation pump driving operation is executed and hydrogen is consumed, this section can be significantly shortened. Therefore, it is possible to reduce the frequency of activation accompanied by deterioration in the number of restarts, and to suppress deterioration.

  Next, a supplementary explanation will be given regarding the installation position of the oximeter. During the stop, air permeates from the oxidant electrode 1a to the fuel electrode 1b, or air flows backward from the hydrogen exhaust path 28. Therefore, an oxygen concentration meter is installed at the outlet of the fuel cell body 1 to The air replacement state of the chamber can be grasped. Of course, it may be the entrance.

  Alternatively, the oxygen concentration of each part of the fuel electrode and the circulation line may be experimentally measured to identify the part where the air replacement is most advanced and the part where the air replacement is most difficult to proceed. A plurality of oxygen concentration meters may be installed in the fuel electrode and the circulation line. Further, the upper and lower limits may be determined by another oxygen concentration meter.

[Permission determination of Example 1 to Example 3]
Prior to the control method of each embodiment, it is preferable to determine whether to permit anode gas circulation. This permission determination will be described with reference to the flowchart of FIG.

  First, in S91, the stack voltage is read from the voltmeter 41, and the battery storage amount (SOC amount) is read from the battery controller 43. Next, in S92, the stack voltage and the battery SOC amount are determined. As for the stack voltage, the stop voltage and the deterioration tendency at the time of restart are experimentally investigated, and an allowable range of the stack voltage is determined within an allowable deterioration range.

Further, the battery SOC amount may be determined by experimentally investigating the power consumption amount at the time of restart, obtaining the minimum SOC amount, and using this as the determination value.

  If it is determined in S92 that the stack voltage is less than the predetermined voltage (220) and the battery SOC amount exceeds the predetermined SOC amount (230), the process proceeds to S93. In S93, the anode gas circulation is permitted and the process returns.

  If it is determined in S92 that the stack voltage is equal to or higher than the predetermined voltage (220) or the battery SOC amount is equal to or lower than the predetermined SOC amount (230), the process proceeds to S94. In S94, the anode gas circulation is prohibited and the process returns.

  In this way, the battery SOC amount is monitored, and if it is less than the predetermined amount, the operation for shifting to the air replacement state in the anode is prohibited. By prescribing the predetermined amount as the amount of power consumed by auxiliary equipment at the time of startup, there is an effect that it is possible to avoid a situation in which the system cannot be restarted due to insufficient SOC.

  Also, since the fuel cell voltage is monitored and the operation to shift to the air replacement state in the anode is prohibited in the high voltage state, the fuel gas and air are unevenly distributed in the anode under the high voltage at the time of restart. It is possible to avoid the deterioration of the fuel cell due to the above.

It is a block diagram of Example 1 of the fuel cell system according to the present invention. It is a flowchart explaining Example 1 of the fuel cell system by this invention. It is a flowchart explaining Example 2 of the fuel cell system by this invention. It is a block diagram of Example 3 of the fuel cell system according to the present invention. It is a flowchart explaining Example 3 of the fuel cell system by this invention. It is a flowchart explaining the permission determination of Example 1- Example 3 of the fuel cell system by this invention. BRIEF DESCRIPTION OF THE DRAWINGS It is a time chart explaining Example 1 of the fuel cell system by this invention, (a) Hydrogen partial pressure, (b) The rotation speed of a hydrogen circulation pump, (c) Total voltage of a fuel cell main body, (d) Battery The amount of SOC. FIG. 5 is a time chart for explaining Example 2 of the fuel cell system according to the present invention, where (a) hydrogen partial pressure, (b) anode pressure, (c) rotation speed of hydrogen circulation pump, (d) hydrogen discharge valve (purge) Valve). It is a block diagram of a general fuel cell system. It is a conceptual diagram of the single cell of a fuel cell. It is a figure explaining the state immediately after the stop of a fuel cell system. It is a figure explaining the state which time passed fully after the stop of a fuel cell system. It is a figure explaining the state after several minutes-several tens of minutes have passed since the stop of the fuel cell system.

Explanation of symbols

1: Fuel cell body (1a: oxidizer electrode, 1b: fuel electrode)
11: Air compressor 12: Air supply path 13: Air humidifier 14: Air exhaust path 15: Air pressure control valve 16: Air pressure gauge 21: High-pressure hydrogen tank 22: Hydrogen supply path 23: Hydrogen pressure control valve 24: Hydrogen circulation system 25: Hydrogen humidifier 26: Hydrogen circulation path 27: Hydrogen exhaust path 28: Hydrogen discharge valve 29: Hydrogen pressure gauge 31: Cooling water pump 32: Cooling water circulation path 33: Heat exchanger 34: Cooling water thermometer 40: Load Device 41: Voltmeter 42: Ammeter 43: Battery controller 44: Battery 45: Controller 50: Hydrogen concentration meter 51: Oxygen concentration meter

Claims (10)

A fuel cell that has a fuel electrode and an oxidant electrode that sandwich the electrolyte, and that generates power by receiving supply of fuel gas and oxidant gas to the fuel electrode and oxidant electrode, respectively, and part of the exhaust fuel gas from the fuel cell In a fuel cell system comprising a fuel gas circulation path for recirculating fuel to the supply side, and a fuel gas circulation means,
Detecting means for detecting a value relating to a hydrogen concentration in the fuel electrode or in the fuel gas circulation path;
A fuel cell system, wherein the fuel gas circulating means is operated during power generation stop when a hydrogen concentration based on a detection value of the detection means is within a range of a first predetermined value to a second predetermined value.   The detecting means is a fuel electrode pressure detecting means for detecting a pressure in the fuel electrode or the fuel gas circulation path, and a hydrogen concentration for estimating a hydrogen concentration based on the fuel gas pressure detected by the fuel electrode pressure detecting means. The fuel cell system according to claim 1, further comprising an estimation unit.   The hydrogen concentration estimating means stores a pressure when the fuel gas circulation means starts operation, and is based on a pressure difference between a pressure when the fuel gas circulation means is operated and a pressure during operation of the fuel gas circulation means. The fuel cell system according to claim 2, wherein the hydrogen concentration is estimated. Pressure release means for releasing the pressure in the fuel gas circulation path to atmospheric pressure;
4. The fuel cell according to claim 3, wherein when the fuel electrode pressure reaches a predetermined pressure or less, the pressure release means is operated to supply air into the fuel electrode and the fuel gas circulation path. system.   The operations of the fuel gas circulation means and the pressure release means are alternately operated, the pressure difference for each drive of the fuel gas circulation means is stored, and the hydrogen concentration is estimated from an integrated sum of the pressure differences. The fuel cell system according to claim 4. A fuel cell that has a fuel electrode and an oxidant electrode that sandwich the electrolyte, and that generates power by receiving supply of fuel gas and oxidant gas to the fuel electrode and oxidant electrode, respectively, and part of the exhaust fuel gas from the fuel cell In a fuel cell system comprising a fuel gas circulation path for recirculating fuel to the supply side, and a fuel gas circulation means,
Oxygen concentration detection means for detecting the oxygen concentration in the fuel electrode or the fuel gas circulation path is provided, and the fuel gas circulation is performed when power generation is stopped when the oxygen concentration is within a range of a third predetermined value to a fourth predetermined value. A fuel cell system characterized by operating the means. An operation switch is provided to instruct to stop the operation of the fuel cell system,
The fuel cell system according to any one of claims 1 to 6, wherein the fuel gas circulation means is operated while an instruction of the operation switch is stopped.   The fuel cell system according to any one of claims 1 to 7, wherein the fuel gas circulation means is operated during an idle stop.   9. A voltage detection means for detecting a fuel cell voltage is provided, and when the fuel cell voltage is equal to or higher than a predetermined value, operation of the fuel gas circulation means during power generation stop is prohibited or stopped. The fuel cell system according to any one of the above. Power storage means for supplying power to the load device of the fuel cell during power generation stop of the fuel cell;
A power storage amount detecting means for detecting a power storage amount of the power storage means,
The fuel cell system according to any one of claims 1 to 9, wherein when the amount of stored electricity is equal to or less than a predetermined value, the operation of the fuel gas circulation means during power generation stop is prohibited or stopped.

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