JP2008293708A - Fuel cell system and fuel cell control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To fully suppress performance degradation of a fuel cell by eliminating defects, such as, platinum dissolution and an increase in platinum particle size. <P>SOLUTION: When an OC state or an idling state occurs in the middle of operation control of a fuel cell 10, a hydrogen-gas supply pressure Ph is increased so as to control cell voltage E to a prescribed voltage E1 which is lower than OCV. By this, it is possible to suppress a performance degradation degree, by eliminating nonconformities, such as platinum dissolution and an increase in platinum particle size during at OC state or at an idling load state. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fuel cell system including a fuel cell that generates power by receiving supply of a fuel gas containing hydrogen and an oxidizing gas containing oxygen, and a fuel cell control method for controlling the fuel cell.

  In the fuel cell, the performance deteriorates according to the accumulated operation time. Conventionally, as one technique for preventing performance degradation, after the fuel cell finishes a normal stop operation, only hydrogen is supplied to the fuel cell, thereby consuming oxygen remaining on the air electrode side in the fuel cell. A configuration for reducing the voltage of the fuel cell has been proposed (for example, Patent Document 1 below). This is because the fuel cell deteriorates when left in a high potential no-load state, and the progress of the deterioration can be suppressed by reducing the voltage after the normal stop operation.

JP 2005-100820 A

  However, with the conventional technology, it is possible to suppress performance degradation caused by the state after the fuel cell has stopped operating, but when viewed from the whole fuel cell, the suppression of performance degradation is still insufficient. There wasn't.

  The problem to be solved by the present invention is to sufficiently suppress the performance deterioration of the fuel cell.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

[Application Example 1]
A fuel cell system including a fuel cell that generates power by receiving supply of a fuel gas containing hydrogen and an oxidizing gas containing oxygen, and the load is normally operated in the fuel cell system that supplies the generated power to the load. An operation control unit that executes switching between a first operation mode that is a load and a second operation mode in which the load is an unloaded or idling load; and the operation control unit includes the second operation mode. A fuel cell system comprising voltage reduction control means for performing control to reduce the voltage of the fuel cell when the mode is executed.

  In the application example 1 configured as described above, when the operation control unit enters the second operation mode during the operation control of the fuel cell, the voltage drop control unit changes the voltage of the fuel cell. Reduced. When the fuel cell is operated with no load or idling load, it causes problems such as platinum elution and an increase in platinum particle size, which causes performance deterioration, because the fuel cell voltage is high. As described above, the voltage of the fuel cell decreases in the second operation mode, so that it is possible to suppress the problem of platinum elution and an increase in the platinum particle size at the time of no load or idling load. Can be suppressed. When there is no load or idling load during the operation of the fuel cell, it frequently occurs intermittently. Therefore, when viewed from the entire operation time of the fuel cell, the effect of suppressing the performance deterioration is great. Therefore, there is an effect that the performance deterioration of the fuel cell can be sufficiently suppressed.

  In the present specification, the “idling load” means a load that minimizes the electric power extracted from the fuel cell (≠ 0). For example, when mounted on a vehicle, the drive motor is stopped and compensated. This is the load when operating only the machine. Here, the auxiliary equipment is a device in the fuel cell system that is not directly related to the travel of the vehicle but is indirectly required to assist the travel, such as a hydrogen pump for circulation and an air compressor. . In other words, the “idling load” can be said to be a load having a magnitude such that the voltage of the fuel cell is substantially equal to the no-load voltage (open circuit voltage: OCV).

[Application Example 2]
The fuel cell system according to Application Example 1, wherein the voltage reduction control unit increases the fuel gas supply pressure to reduce the voltage of the fuel cell by increasing the supply pressure of the fuel gas supplied to the fuel cell. A fuel cell system comprising means.

  According to the configuration of the application example 2, by increasing the supply pressure of the fuel gas supplied to the fuel cell, the amount of cross leak of the fuel gas to the oxidizing gas electrode side can be increased. The voltage of the fuel cell can be lowered in response to a decrease in oxygen concentration due to reaction, that is, the permeated fuel gas reacts with the oxidizing gas on the oxidizing gas electrode side. Therefore, voltage control at the time of no load or idling load can be easily performed using the existing control of controlling the supply pressure of the fuel gas.

[Application Example 3]
The fuel cell system according to Application Example 1 or 2, further comprising voltage detection means for detecting the voltage of the fuel cell, wherein the voltage drop control means controls the voltage of the fuel cell to a predetermined voltage or less. There is a fuel cell system.

  It has been found that the performance degradation of the fuel cell at no load rapidly increases when a predetermined voltage is exceeded. According to the configuration of the application example 3, by controlling the voltage of the fuel cell to be equal to or lower than the predetermined voltage, it is possible to reliably suppress performance deterioration.

[Application Example 4]
The fuel cell system according to Application Example 3, comprising storage means for storing a target voltage range defined by an upper limit voltage value corresponding to the predetermined voltage and a lower limit voltage value lower than the upper limit voltage value, The voltage drop control means includes: voltage determination means for determining whether or not the voltage of the fuel cell is lower than the lower limit voltage value; and the voltage of the fuel cell is lower than the lower limit voltage value by the voltage determination means. A fuel cell system comprising: an oxidizing gas supply pressure increase control means for increasing the supply pressure of the oxidizing gas supplied to the fuel cell.

  In the configuration of the application example 4, when returning from the no-load or idling load state to the traveling state, the voltage of the fuel cell does not fall below the lower limit voltage value of the target voltage range. There is no.

[Application Example 5]
A fuel cell control method for supplying a fuel cell containing hydrogen and an oxidant gas containing oxygen to a fuel cell, and supplying the power generated by the fuel cell to a load. It is executed while switching between a first operation mode that is a load and a second operation mode in which the load is unloaded or idling, and the voltage of the fuel cell is reduced during the execution of the second operation mode. A fuel cell control method for performing control.

  Similar to the fuel cell system of the present invention, the fuel cell control method has an effect that the performance deterioration of the fuel cell can be sufficiently suppressed.

  Hereinafter, embodiments of the present invention will be described based on examples.

A. Overall configuration of the fuel cell system:
FIG. 1 is an overall configuration diagram of a fuel cell system 1 to which a first embodiment of the present invention is applied. As shown in the figure, this fuel cell system 1 includes a fuel cell 10 that generates power upon receipt of a fuel gas containing hydrogen and an oxidizing gas containing oxygen, and hydrogen gas from a hydrogen gas source (not shown). A hydrogen gas flow path system 20 for flowing in the system, an air flow path system 40 for flowing air (air) as an oxidizing gas, and an electronic control unit (hereinafter, “ ECU ”) 60). This fuel cell system 1 is used as a power supply for a drive motor of a vehicle, and supplies power generated by the fuel cell 10 to a drive motor that is a load. In addition to the drive motor, an auxiliary machine, which will be described later, is also supplied with power from the fuel cell 10 as a load.

  FIG. 2 is an explanatory diagram showing a schematic configuration of a single cell constituting the fuel cell 10. The fuel cell 10 has a stack structure in which a large number of single cells are stacked. FIG. 2 shows a part of a vertical cross section of a single cell. A single cell of the fuel cell 10 mainly includes a membrane electrode assembly (hereinafter referred to as MEA) in which electrodes 14 and 15 are disposed on both surfaces of a solid polymer electrolyte membrane (hereinafter simply referred to as “electrolyte membrane”) 13. ) 12 and a pair of separators 16 and 17 sandwiching the MEA 12 from both sides. This single cell is a DC power supply of several hundred volts by closely laminating a large number of single cells.

  The MEA 12 is obtained by sandwiching an electrolyte membrane 13 between two electrodes, that is, an anode 14 that is a fuel electrode and a cathode 15 that is an oxygen electrode. Here, the electrolyte membrane 13 is a membrane made of a solid polymer material having good proton conductivity in a wet state. Specifically, the membrane is made of a fluorine-based resin (such as a Nafion membrane manufactured by DuPont). ) And the like.

  The anode 14 and the cathode 15 are constituted by catalyst electrodes 14a and 15a and gas diffusion layers 14b and 15b, respectively. The catalyst electrodes 14a and 15a are located on the side in contact with the electrolyte membrane 13, and are made of conductive carbon black carrying platinum fine particles. On the other hand, the gas diffusion layers 14b and 15b are formed of carbon cloth laminated on the catalyst electrodes 14a and 15a and woven with yarns made of carbon fibers. The platinum contained in the catalyst electrodes 14a and 15a has an action of promoting the separation of hydrogen into protons and electrons or promoting the reaction of generating water from oxygen, protons and electrons. If it has, you may use things other than platinum. The gas diffusion layers 14b and 15b may be formed of carbon paper or carbon felt made of carbon fiber in addition to carbon cloth, and may have sufficient gas diffusibility and conductivity.

  A plurality of holes and recesses are formed in each of the pair of separators 16 and 17. A flow path for a reaction gas used for an electrochemical reaction is formed between the recess and the MEA 12. That is, a single-cell fuel gas flow channel 16a through which a fuel gas containing hydrogen passes is formed between the separator 16 on the anode 14 side and the MEA 12. In addition, between the separator 17 on the cathode 15 side and the MEA 12, an in-single cell oxidizing gas channel 17 a through which an oxidizing gas containing oxygen such as air passes is formed.

  Returning to FIG. 1, the hydrogen gas flow path system 20 extends from the discharge port of the hydrogen gas source to the supply port of the fuel cell 10 and from the discharge port of the fuel cell 10 to the hydrogen gas supply tube 22. And a hydrogen gas discharge pipe 24. The supply port and the discharge port of the fuel cell 10 are connected to the above-described intra-cell fuel gas flow path 16a (FIG. 2) via a manifold hole (not shown).

  The hydrogen gas supply pipe 22 is provided with a pressure gauge P1 and a hydrogen pressure regulating valve V1 from the supply port side of the fuel cell 10. A hydrogen storage tank as a hydrogen gas source and a regulator are connectable to the other end of the hydrogen gas supply pipe 22 so that hydrogen gas can be supplied during operation of the fuel cell 10. At this time, the supply pressure of the supplied hydrogen gas can be adjusted by controlling the open / close state of the hydrogen pressure regulating valve V1.

  The hydrogen gas discharge pipe 24 is provided with a pressure gauge P 2, a steam / water separator 32, a circulation hydrogen pump 34 and a check valve 36 from the discharge port side of the fuel cell 10. The other end of the hydrogen gas discharge pipe 24 is connected to the downstream side of the hydrogen pressure regulating valve V1 of the hydrogen gas supply pipe 22. With the hydrogen gas discharge pipe 24, the exhaust hydrogen gas that has not contributed to the cell reaction in the fuel cell 10 can be returned to the hydrogen gas supply pipe 22 through the hydrogen gas discharge pipe 24. The steam separator 32 removes excess water contained in the discharged hydrogen gas and regenerates it as supply hydrogen gas. The pressure gauge P2 detects the pressure near the discharge port of the fuel cell 10 for hydrogen gas. One end of a discharge pipe 38 provided with a valve V2 is connected between the hydrogen pump 34 for circulation in the hydrogen gas supply pipe 22 and the check valve 36. When the valve V2 is opened, the one from the other end is connected. It can be discharged.

  The air flow path system 40 includes an air supply pipe 42 that reaches the oxidizing gas supply port of the fuel cell 10 and an air discharge pipe 44 that reaches the oxidizing gas discharge port of the fuel cell 10. The oxidizing gas supply port and the oxidizing gas discharge port are connected to the above-described single cell oxidizing gas channel 17a (FIG. 2) via a manifold hole (not shown). In the middle of the air discharge pipe 44, a pressure gauge P3 and an air pressure regulating valve V3 are provided. Air can be supplied to the fuel cell 10 through the air supply pipe 42, and exhaust air and generated water whose oxygen density has been lowered by the cell reaction can be discharged through the air discharge pipe 44. The other ends of the air supply pipe 42 and the air discharge pipe 44 are connected to the humidifier 43, and supply humidified air to the fuel cell 10, and the generated water discharged through the air discharge pipe 44 to the air supply pipe 42. It is configured to be reusable and reusable. The pressure gauge P3 detects the pressure in the vicinity of the outlet of the fuel cell 10 for air.

  The humidifier 43 is further connected to one end of each of a supply pipe 47 and a discharge pipe 49 provided with an air compressor 46. Air is supplied from outside air through a filter (not shown) disposed at the other end of the supply pipe 47. In addition to suction, exhaust air and unnecessary generated water can be discharged from the other end of the discharge pipe 49 to the outside.

  The fuel cell 10 is provided with a voltage measuring device 52 that is electrically connected to a single cell constituting the fuel cell 10 and measures the voltage of the single cell. Specifically, the voltage measuring device 52 is connected to one single cell at a predetermined position (for example, near the center) of the stack structure of the fuel cell 10 and measures the voltage of one single cell at the predetermined position. . Further, the number of single cells to be measured is not limited to one, and the voltage of a plurality of (for example, two or all) single cells may be measured and the average value thereof may be obtained.

  As described above in detail, the hydrogen gas channel system 20 and the air channel system 40 are configured to supply and discharge hydrogen gas and supply and discharge air to and from the fuel cell 10. When the fuel cell 10 is supplied with hydrogen gas and air, the fuel cell 10 generates power by an electrochemical reaction (battery reaction).

  The aforementioned pressure gauges P1 to P3, the circulation hydrogen pump 34, the hydrogen pressure regulating valve V1, the valve V2, the air pressure regulating valve V3, the humidifier 43, the air compressor 46, the voltage measuring device 52 and the like are electrically connected to the ECU 60. Has been.

  The ECU 60 is configured by a known microcomputer including a CPU, a ROM, a RAM (not shown), and the like. Various computer programs are stored in advance in the ROM. The CPU controls the operation timing of each of the electrically connected parts by executing the computer program using the RAM as a work area. In practice, the ECU 60 functions as an operation control unit M1 that controls the output of the fuel cell 10 by adjusting the amount of hydrogen gas and air according to the magnitude of the load by executing the computer program by the CPU. Has been realized.

  The operation control unit M1 includes a normal operation mode in which the load is a normal load (hereinafter referred to as “first operation mode”), and a second in which the load is an unloaded (OC: open circuit) or an idling load. Driving is proceeding while switching the operation mode to and from the operation mode. In the present embodiment, the “normal load” is a load having a magnitude when the drive motor of the vehicle is operated, and varies depending on the traveling state of the vehicle. The “idling load” is a load when the driving motor is stopped and the auxiliary machines in the fuel cell system 1 such as the air compressor 46 and the circulation hydrogen pump 34 are operated (that is, “idling state”). Since the control process in the first operation mode by the operation control unit M1 is well known, detailed description thereof is omitted here. The control process in the second operation mode by the operation control unit M1 will be described in detail below. The voltage drop control unit M2 is realized by executing the control process in the second operation mode, that is, the second operation mode control process.

B. Software configuration:
FIG. 3 is a flowchart showing a second operation mode control process executed by the ECU 60. This process is executed by an interrupt process as part of the operation control of the fuel cell 10 in the control unit 60. That is, execution of the second operation mode control process is started by interrupting operation control for executing the first operation mode every predetermined time (for example, every 100 [ms]).

  As shown in FIG. 3, when the process is started, the CPU of the ECU 60 first determines whether or not the fuel cell 10 is in the OC state or the idling state (step S100). The OC state is an open circuit (OC) state in which the movement of electric charges between the two electrodes of the fuel cell 10 is blocked, and is an unloaded state. The idling state is a state in which an idling load having a load magnitude approximate to that of the OC state is received. In step S100, specifically, operation control of the fuel cell 10 is monitored to determine whether or not it is in the OC state or the idling state. Instead of the configuration for monitoring the operation control, the determination is made based on whether or not an accelerator operation unit (for example, an accelerator pedal, an accelerator lever, etc.) (not shown) provided in the vehicle equipped with the fuel cell system 1 is operated. It is good also as composition which performs. When the accelerator operation unit is not operated, either the OC state in which neither the drive motor nor the auxiliary machine is operating, or the idling state in which the drive motor is stopped and only the auxiliary machine is operated, the accelerator operation unit is The determination in step S100 can be made according to whether the operation is not performed or the operation is performed.

  If it is determined in step S100 that the state is neither the OC state nor the idling state, the process returns to “RETURN” and the second operation mode control process is temporarily terminated. On the other hand, if it is determined in step S100 that the state is the OC state or the idling state, the CPU advances the process to step S110.

  In step S110, the CPU takes in the voltage of a single cell (hereinafter referred to as “cell voltage”) E detected by the voltage measuring device 52, and in the subsequent step S120, the CPU takes the obtained cell voltage E as the predetermined voltage. It is determined whether or not E1 is exceeded. The predetermined voltage E1 is a target voltage that suppresses the performance deterioration of the fuel cell in the OC state, and is a value smaller than the OCV that can be taken in the conventional fuel cell system to which the present invention is not applied. The OCV is, for example, 1.0 [V], and the predetermined voltage E1 is, for example, 0.9 [V].

  If it is determined in step S120 that the cell voltage E exceeds the predetermined voltage E1, the CPU performs a process of increasing the hydrogen gas supply pressure Ph (step S130). Specifically, the hydrogen gas supply pressure Ph sent to the fuel cell 10 through the hydrogen gas supply pipe 22 is increased by opening the opening S of the hydrogen pressure regulating valve V1 by a minute opening ΔS. Here, the opening degree is a minute opening degree ΔS, and the opening degree S is gradually increased by repeatedly executing the process of step S130. After the execution of step S130, the process returns to “Return” to end the second operation mode control process.

  On the other hand, if the cell voltage E is equal to or lower than the predetermined voltage E1 in step S120, the CPU proceeds to “return” without executing step S130, and temporarily ends the second operation mode control process. In addition, the process of step S110 thru | or S130 respond | corresponds to the voltage drop control part M2 (FIG. 1).

C. Action / Effect:
FIG. 4 is a timing chart showing the operation of the second operation mode control process. As shown in the upper part of the figure, it is assumed that the vehicle on which the fuel cell system 1 of this embodiment is mounted is operated to switch between the traveling state and the OC state. That is, the time t0 to t1 is in the running state, the time t1 to t2 is in the OC state, and after the time t2, it is in the running state.

  In the middle of the figure, the cell voltage XE, the hydrogen gas supply pressure XPh, and the air supply pressure XPa for the conventional example are shown. The hydrogen gas supply pressure XPh and the air supply pressure XPa are supply pressures of hydrogen gas or air supplied to the fuel cell. Cell voltage XE rises to OCV when switching from the running state to the OC state (time t1). At times t0 to t1 before switching to the OC state, the hydrogen gas supply pressure XPh gradually increases with time. This is because the consumption of hydrogen gas in the fuel cell 10 is reduced and the hydrogen gas supply pressure XPh is gradually increased in response to the deceleration toward the stop of the vehicle.

  The increased hydrogen gas supply pressure XPh gradually decreases after time t1. This is because in the OC state, a part of the hydrogen gas supplied to the anode 14 is not consumed for power generation, but a cross leak phenomenon occurs through the electrolyte membrane 13 to the cathode 15. Note that the hydrogen gas supply pressure XPh in the OC state is a low value by a predetermined degree. This is because the hydrogen gas and air supplied by the increased hydrogen gas supply pressure XPh are consumed by the power generation reaction. In addition, the cell voltage XE gradually decreases from the OCV in response to a power generation reaction due to cross leak, that is, a decrease in oxygen concentration caused by the permeated hydrogen gas reacting with oxygen in the air on the cathode 15 side.

  After time t2 when the OC state is restored to the traveling state, the hydrogen gas supply pressure XPh and the air supply pressure XPa are restored, and the cell voltage XE is also restored to a low value.

  The lower part of the figure shows the cell voltage E, the hydrogen gas supply pressure Ph, and the air supply pressure Pa for the first embodiment. Similar to the conventional example, when the traveling state is switched to the OC state (time t1), the cell voltage E rises to the same voltage as the OCV in the conventional example. As a result, the cell voltage E exceeds the predetermined voltage E1 (time t11), and thereafter, the hydrogen gas supply pressure Ph gradually increases by the processing of steps S120 and S130 described above. In the figure, the time t11 when the cell voltage E is determined to have exceeded the predetermined voltage E1 and the hydrogen gas supply pressure Ph starts to increase is when the cell voltage E has increased to near OCV. This is because the cell voltage E rapidly increases when the OC state is reached, and the control of steps S120 and S130 cannot catch up. As the hydrogen gas supply pressure Ph gradually increases, the amount of cross leak toward the cathode 15 increases, and the cell voltage E rapidly decreases from around the OCV (L1 in the figure). Until the cell voltage E becomes equal to or lower than the predetermined voltage E1 (time t12), the hydrogen gas supply pressure Ph increases and the cell voltage E also decreases. The cell voltage E gradually decreases due to the cross leak after time t12.

  As shown by the broken line L2 in the figure, when the increase rate of the hydrogen gas supply pressure Ph is increased (that is, when the minute opening ΔS that increases in step S130 is increased), the cross leak amount can be further increased. Thus, as indicated by a broken line L3 in the figure, the cell voltage E can be decreased more rapidly (= in a shorter time).

  After the time t2 when the traveling state is returned from the OC state, the hydrogen gas supply pressure Ph and the air supply pressure Pa are restored in the first embodiment as well as the conventional example, and the cell voltage E is completely reduced to a low value. Return. Note that the OC state shown in this timing chart can be changed to an idling state.

  In the first embodiment configured as described above, the cell voltage E is controlled to be equal to or lower than the predetermined voltage E1 when the fuel cell 10 is in the OC state or idling state during the operation control. When the fuel cell is operated in the OC state or the idling state, it causes problems such as elution of platinum and an increase in the particle size of the platinum, resulting in performance deterioration. However, as described above, the cell voltage E is set to the OCV in the conventional example. By controlling to a predetermined voltage E1 lower than the above, it is possible to eliminate the above-described problems of elution of platinum and increase in the particle size of platinum and suppress the degree of performance deterioration. When the fuel cell 10 is in the OC state or idling state during the operation, it frequently occurs intermittently. Therefore, when viewed from the entire operation time of the fuel cell 10, the effect of suppressing the performance deterioration is great. Therefore, there is an effect that the performance deterioration of the fuel cell 10 can be sufficiently suppressed.

D. Second embodiment:
Next, a second embodiment of the present invention will be described. The second embodiment is different from the first embodiment only in the configuration of the second operation mode control process executed by the ECU 60, and the other software and hardware configurations are the same.

  FIG. 5 is a flowchart showing a second operation mode control process executed by the ECU 60. Compared with the second operation mode control process of the first embodiment, this process is identical in steps S100, S120, and S130, but differs in steps S210, S240, and S250.

  In step S210, the CPU, in addition to the cell voltage E, each pressure near the discharge port of the fuel cell 10 for the hydrogen gas and air detected by the pressure gauges P2 and P3, that is, the hydrogen gas discharge pressure SPh and the air discharge. The outlet pressure SPa is taken in.

  If it is determined in step S120 that the cell voltage E is equal to or lower than a predetermined voltage (hereinafter referred to as “first predetermined voltage” in this embodiment) E1, the CPU proceeds to step S240 and proceeds to step S240. It is determined whether or not the cell voltage E captured in S210 is lower than the second predetermined voltage E2. The second predetermined voltage E2 is a value smaller than the first predetermined voltage E1. That is, the first predetermined voltage E1 and the second predetermined voltage E2 are for defining the upper limit voltage value and the lower limit voltage value of the target voltage range when the cell voltage E is lowered. For example, the first predetermined voltage E1 is, for example, 0.9 [V] as described above, while the second predetermined voltage E2 is, for example, 0.8 [V].

  The values of the first predetermined voltage E1 and the second predetermined voltage E2 are stored in the ROM as numerical values described in the computer program. Instead, E1 and E2 are stored as separate data in the ROM. Each value may be stored, and each value may be read according to a computer program.

  When it is determined in step S240 that the cell voltage E is lower than the second predetermined voltage E2, the CPU controls the air pressure regulating valve V3 provided on the downstream side of the fuel cell 10 to the closed side. Thus, the process of increasing the supply pressure Pa of the air sent to the fuel cell 10 through the air supply pipe 42 is performed (step S250). Specifically, the opening degree of the air pressure regulating valve V3 is adjusted so that the hydrogen gas outlet pressure SPh and the air outlet pressure SPa taken in step S210 are the same. The fact that the hydrogen gas outlet pressure SPh and the air outlet pressure SPa are equal is equivalent to the fact that the hydrogen gas supply pressure Ph and the air supply pressure Pa are the same. The air supply pipe 42 is also provided with a pressure gauge, and the opening of the air pressure regulating valve V3 is adjusted so that the detection result of this pressure gauge and the pressure gauge P1 of the hydrogen gas supply pipe 22 is the same pressure. The configuration may be changed.

  After execution of step S250, the CPU proceeds to “return” and temporarily ends the second operation mode control process. On the other hand, if it is determined in step S240 that the cell voltage E is equal to or higher than the second predetermined voltage E2, the process proceeds to “RETURN” without executing step S130, and the second operation mode control process is temporarily terminated. To do.

  FIG. 6 is a timing chart showing the operation of the second operation mode control process in the second embodiment. The chart showing the upper running state shown in the figure is the same as that of the first embodiment (see FIG. 4). The chart showing the cell voltage E in the middle stage is the same as that of the broken line L3 in the first embodiment (see FIG. 4) (however, until t13 described later). That is, the chart showing the cell voltage E is obtained by increasing the increase rate of the hydrogen gas supply pressure Ph so that the cell voltage E decreases more rapidly.

  As shown in the figure, similarly to the first example, at times t11 to t12, the hydrogen gas supply pressure Ph gradually increases and the cell voltage E rapidly decreases. After time t12, the cell voltage E gradually decreases, but when the cell voltage E falls below the second predetermined voltage E2 (time t13), the air supply pressure Pa is reduced to hydrogen by the processing of steps S240 and S250 described above. The pressure is increased to the same pressure as the gas supply pressure Ph. If the hydrogen gas supply pressure Ph and the air supply pressure Pa are the same, the cross leak phenomenon does not occur, so that the decrease in the cell voltage E is suppressed, and the cell voltage E maintains the second predetermined voltage E2 until time t2. .

  After time t2 when returning from the OC state to the traveling state, the hydrogen gas supply pressure Ph and the air supply pressure Pa return and the cell voltage E also completely returns to a low value, as in the first embodiment.

  In the second embodiment configured as described above, the cell voltage E is a target voltage lower than the OCV in the conventional example when the fuel cell 10 is in the OC state or the idling state during the operation control. Control is performed in the areas E1 to E2. Therefore, in the second embodiment, as in the first embodiment, the degree of deterioration of the performance of the fuel cell in the second operation mode that is in the OC state or the idling state can be suppressed. There is an effect that the performance degradation of 10 can be sufficiently suppressed. In the second embodiment, the cell voltage E does not fall below the target voltage range E1 to E2 when returning from the OC state or idling state to the traveling state (time t2). The effect is that there is no loss. That is, as compared with the first embodiment, there is an effect peculiar to the second embodiment that the startability can be improved when returning to the running state.

  In the second embodiment, the hydrogen gas supply pressure Ph and the air supply pressure Pa are configured to be the same by increasing the air supply pressure Pa. Instead, the air supply pressure Pa changes. Alternatively, the hydrogen gas supply pressure Ph may be reduced so that the two are the same. That is, the hydrogen gas may be released by controlling the valve V2 to the open side so that the hydrogen gas supply pressure Ph and the air supply pressure Pa are the same.

E. Other embodiments:
The present invention is not limited to the first and second embodiments and modifications described above, and can be carried out in various modes without departing from the scope of the invention. Embodiments are possible.

(1) In each of the above-described embodiments, the cell voltage E is reduced by increasing the supply pressure of the hydrogen gas at the time of OC or idling load. Instead, the supply of air, that is, the oxidizing gas is performed. It is good also as a structure which implement | achieves the fall of the cell voltage E by reducing a pressure. Alternatively, in FIG. 1, the exhaust from the discharge pipe 49 may be returned to the supply pipe 47 so that the amount of oxygen supplied to the fuel cell 10 is reduced and the cell voltage E is reduced. That is, any means may be used as long as the cell voltage can be lowered at the time of OC or idling load.

(2) In each of the above embodiments, the control for lowering the voltage of the fuel cell is performed while observing the cell voltage E measured by the voltage measuring device 52. Instead, the control is switched to the second operation mode. In this case, the fuel cell voltage may be decreased by increasing the hydrogen gas supply pressure by a predetermined magnitude without detecting the fuel cell voltage. The configuration for reducing the voltage of the fuel cell can be replaced with various means as in the above (1). Also with this configuration, the performance deterioration of the fuel cell 10 in the OC state or idling state can be suppressed to some extent.

(3) The solid polymer electrolyte membrane 13 used in each of the above examples has a typical film thickness of about 30 [μm], but the film thickness is thinner than about 30 [μm]. Such a thinned structure may be used. FIG. 7 is a graph showing the relationship between the thickness of the electrolyte membrane and the permeation amount of hydrogen gas. The horizontal axis represents the film thickness, and the vertical axis represents the transmission amount. The permeation amount is the permeation amount of hydrogen gas in the electrolyte membrane when the hydrogen gas supply pressure is 100 [kPa (G)] and the air supply pressure is 0 [kPa (G)]. As shown in the figure, the amount of transmission increases as the film thickness decreases. When the film thickness is made thinner than about 30 [μm], the transmission amount is large. The large amount of transmission means that the amount of cross leakage at the time of OC or idling load is large, and the cell voltage E can be reduced in a shorter time. Therefore, according to this modification, the period during which the cell voltage E is OCV can be further reduced, and therefore, the performance deterioration of the fuel cell can be suppressed more effectively.

  The film thickness of about 30 [μm] or less is one application example, and the film thickness is not necessarily about 30 [μm] or less. Even if the film thickness is greater than 30 [μm], any film structure may be used as long as the amount of transmission is large and the cell voltage can be reduced.

(4) In each of the above embodiments, the pressure of the hydrogen gas or air is detected by a pressure gauge, and the hydrogen gas supply pressure or the air supply pressure is controlled according to the detected pressure. It is good also as a structure which controls the flow velocity of hydrogen gas or air.

(5) In each of the above embodiments, the fuel cell stack is a solid polymer fuel cell, but it can also be applied to different types of fuel cells such as a solid oxide fuel cell and a phosphoric acid fuel cell. . In each of the above-described embodiments, the fuel cell system is mounted on a vehicle. Alternatively, the fuel cell system can be mounted on other transportation means such as a ship and an aircraft, and other various industrial machines. is there.

1 is an overall configuration diagram of a fuel cell system 1 to which a first embodiment of the present invention is applied. 2 is an explanatory diagram showing a schematic configuration of a single cell constituting the fuel cell 10. FIG. 7 is a flowchart showing a second operation mode control process executed by the ECU 60. It is a timing chart which shows operation of the 2nd operation mode control processing. It is a flowchart which shows the 2nd operation mode control process in 2nd Example. It is a timing chart which shows operation of the 2nd operation mode control processing in the 2nd example. It is a graph which shows the relationship between the film thickness of an electrolyte membrane, and the permeation | transmission amount of hydrogen gas.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Fuel cell system 10 ... Fuel cell 13 ... Solid polymer electrolyte membrane 13 ... Electrolyte membrane 14 ... Anode 14a ... Catalyst electrode 14b ... Gas diffusion layer 15 ... Cathode 15a ... Catalyst electrode 15b ... Gas diffusion layer 16 ... Separator 16a ... Single In-cell fuel gas flow path 17 ... Separator 17a ... Single-cell oxidizing gas flow path 20 ... Hydrogen gas flow path system 22 ... Hydrogen gas supply pipe 24 ... Hydrogen gas discharge pipe 32 ... Air / water separator 34 ... Hydrogen hydrogen pump 36 ... check valve 38 ... discharge pipe 40 ... air flow path system 42 ... air supply pipe 43 ... humidifier 44 ... air discharge pipe 45 ... discharge pipe 46 ... air compressor 47 ... supply pipe 49 ... discharge pipe 52 ... voltage measuring instrument 60 ... Control unit (ECU)
M1 ... Operation control unit M2 ... Voltage drop control unit P1, P2, P3 ... Pressure gauge V1 ... Hydrogen pressure regulating valve V2 ... Valve V3 ... Air pressure regulating valve E ... Cell voltage E1 ... First predetermined voltage E2 ... Second Predetermined voltage Ph ... Hydrogen gas supply pressure Pa ... Air supply pressure

Claims (6)

In a fuel cell system that includes a fuel cell that generates power by receiving supply of a fuel gas containing hydrogen and an oxidizing gas containing oxygen, and that supplies the generated power to a load,
An operation control means for performing the operation of the fuel cell while switching between a first operation mode in which the load is a normal load and a second operation mode in which the load is an unloaded or idling load;
The operation control means includes
A fuel cell system comprising voltage reduction control means for performing control to reduce the voltage of the fuel cell during execution of the second operation mode. The fuel cell system according to claim 1,
The voltage drop control means includes
A fuel cell system comprising fuel gas supply pressure increasing means for decreasing the voltage of the fuel cell by increasing the supply pressure of the fuel gas supplied to the fuel cell. The fuel cell system according to claim 1 or 2,
Voltage detecting means for detecting the voltage of the fuel cell;
The voltage drop control means includes
A fuel cell system configured to control a voltage of the fuel cell to a predetermined voltage or less. The fuel cell system according to claim 3,
Storage means for storing a target voltage range defined by an upper limit voltage value corresponding to the predetermined voltage and a lower limit voltage value lower than the upper limit voltage value;
The voltage drop control means includes
Voltage determination means for determining whether or not the voltage of the fuel cell is lower than the lower limit voltage value;
Oxidant gas supply pressure increase control means for increasing the supply pressure of the oxidant gas supplied to the fuel cell when the voltage determination means determines that the voltage of the fuel cell is lower than the lower limit voltage value; Fuel cell system. A fuel cell control method for supplying a fuel gas containing hydrogen and an oxidizing gas containing oxygen to a fuel cell, and supplying the power generated by the fuel cell to a load,
Executing the operation of the fuel cell while switching between a first operation mode in which the load is a normal load and a second operation mode in which the load is an unloaded or idling load;
A fuel cell control method that performs control to reduce the voltage of the fuel cell when executing the second operation mode. The fuel cell control method according to claim 5,
The control for reducing the voltage of the fuel cell is as follows:
A fuel cell control method, comprising increasing a supply pressure of fuel gas supplied to the fuel cell.

Images