JP5794197B2 - Fuel cell system and control method thereof - Google Patents

Description

  The present invention relates to a fuel cell.

  A polymer electrolyte fuel cell (hereinafter, also simply referred to as “fuel cell”) usually includes a membrane electrode assembly in which electrodes are disposed on both sides of an electrolyte membrane that exhibits good proton conductivity in a wet state. The electrolyte membrane repeats swelling and shrinking according to the change in the wet state inside the fuel cell. Therefore, during operation of the fuel cell, when the electrolyte membrane is extremely dried and contracts in the membrane electrode assembly, internal stress due to the deformation is generated, and cracks and microholes in the electrolyte membrane and electrode are generated. There are cases where irreversible deterioration such as occurrence occurs.

  Up to now, there has been proposed a technique for executing control for eliminating the dry state when significant dryness of the electrolyte membrane is detected during operation of the fuel cell (Patent Document 1 below). However, sufficient measures have not been taken to suppress the electrolyte membrane from becoming dry, to suppress the deterioration of the membrane electrode assembly, and thus to suppress the deterioration of the fuel cell.

JP 2008-047368 A JP 2006-351506 A

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. A first aspect of the present invention is a fuel cell system that outputs electric power according to an output request from the outside, a fuel cell including a membrane electrode assembly, a control unit that controls an output current of the fuel cell, The control unit sets a target current value It according to the output request, and executes a first control for causing the fuel cell to output a current of the target current value It. The control unit includes: In the first control, when the target current value It is within a preset limit range, the target current value It is reset to a boundary value of the limit range or a value outside the limit range. Then, a process of switching to the second control for outputting the current of the target current value It after resetting to the fuel cell is performed, and the limit range includes the current and resistance in the membrane electrode assembly during power generation. In the relationship, the membrane electrode junction Is a current value range defined with respect to a resistance value range measured in a dry state of not more than a predetermined wetness, wherein the first current value Ia and the second current value Ib (Ib> The target current value It can be smaller than the first current value Ia and can be larger than the second current value Ib. Offered as. Second embodiment of the present invention is a control method of a fuel cell system including a fuel cell having a membrane electrode assembly receives the output request from the (a) outside the target of the fuel cell in accordance with the output request A step of setting a current value It; and (b) when the target current value It is within a preset limit range, the target current value It is set to a boundary value of the limit range or outside the limit range. And (c) outputting the current of the target current value It set in the step (a) or the step (b) to the fuel cell, and the limit range is In the relationship between the current and resistance in the membrane electrode assembly during power generation, the current defined for the range of resistance values measured when the membrane electrode assembly is in a dry state below a predetermined wetness A range of values, the first The target current value It is a range between the current value Ia and the second current value Ib (Ia <IB), and can be smaller than the first current value Ia. It is provided as a control method that can take a value larger than the value Ib.

  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 that outputs electric power according to an output request from the outside, comprising a fuel cell and a control unit that controls an output current of the fuel cell, wherein the control unit is a target according to the output request A current value is set, and a first control for outputting the current of the target current value to the fuel cell is executed, and the control unit is configured to limit the target current value set in advance in the first control. If it is within the range, the target current value is reset to a boundary value of the limit range or a value outside the limit range, and the current of the target current value after reset is output to the fuel cell. The fuel cell system is switched to the second control.
With this fuel cell system, it is possible to avoid the output of a current within a preset limit range in which there is a possibility of deterioration of the fuel cell, so that deterioration of the fuel cell can be suppressed.

[Application Example 2]
The fuel cell system according to Application Example 1, wherein the fuel cell includes a membrane electrode assembly, and the restriction range is determined by the relationship between a current and a resistance in the membrane electrode assembly during power generation. A fuel cell system having a current value range defined with respect to a resistance value range measured when the joined body is in a dry state of a predetermined wetness or less.
In this fuel cell system, since the output of current in the current range corresponding to the range of the resistance value detected when the membrane electrode assembly is in a dry state can be avoided, the membrane electrode assembly is in a dry state. It can be suppressed, and deterioration due to drying of the membrane electrode assembly can be suppressed.

[Application Example 3]
The fuel cell system according to Application Example 1 or Application Example 2, further including a temperature detection unit that detects an operation temperature of the fuel cell, wherein the limit range is set in advance for each operation temperature of the fuel cell, The said control part is a fuel cell system which uses the said restriction | limiting range according to the present operating temperature of the said fuel cell in said 1st and 2nd control.
With this fuel cell system, it is possible to appropriately protect the fuel cell even when the range of the output current that may cause deterioration of the fuel cell widens as the operating temperature of the fuel cell increases. . Here, the membrane electrode assembly is easily dried as the operating temperature rises, and the relationship between the current and resistance in the membrane electrode assembly changes. Therefore, in the fuel cell system of application example 3 that cites application example 2, the limit range becomes wider as the operating temperature rises, so that the drying of the membrane electrode assembly can be more appropriately suppressed, resulting from the drying. It is possible to more appropriately suppress deterioration.

[Application Example 4]
The fuel cell system according to any one of Application Examples 1 to 3, further comprising: a secondary battery that functions as a power supply unit together with the fuel cell; and a charge that detects a value indicating a charge state of the secondary battery A state detection unit, wherein the control unit switches between charging and discharging of the secondary battery based on a detection value of the charge state detection unit, and the limiting range includes first and second current values. It is a range between Ia and Ib (Ia <Ib), and the control unit is set in the first control when executing the control for discharging the secondary battery in the second control. When the control for resetting the target current value Ic below the first current value Ia and charging the secondary battery is executed, the target current value Ic is set to the second current value Ib. Fuel cell system to be reset as above.
According to this fuel cell system, in the second control, the target current value of the fuel cell is reset according to the state of charge of the secondary battery. Therefore, it is possible to appropriately adjust the load of the secondary battery during the execution of the second control, and it is possible to suppress deterioration of the fuel cell while maintaining a good charged state of the secondary battery.

[Application Example 5]
In the fuel cell system according to Application Example 4, in the first control, the control unit may detect the target current value when the detection value of the charge state detection unit is out of a preset allowable range. Even when Ic is set within the limit range, the power generation condition of the fuel cell is changed to prevent deterioration of the fuel cell without switching to the second control. The fuel cell system executes a third control for causing the fuel cell to output a current having the target current value Ic.
According to this fuel cell system, when there is a possibility that the state of charge of the secondary battery cannot be satisfactorily maintained by executing the second control, the operating state of the fuel cell is controlled so that the deterioration of the fuel cell is suppressed. Then, the fuel cell is made to output a current according to the output request. Therefore, it can avoid that the load with respect to a secondary battery increases by switching to 2nd control, and a secondary battery can be protected with a fuel cell.

[Application Example 6]
The fuel cell system according to Application Example 5, wherein the control unit preliminarily stores information indicating an operation pattern of the fuel cell in which a detection value of the charging state detection unit is likely to be out of a preset allowable range. Based on the stored information indicating the operation pattern of the fuel cell, the charging / discharging of the secondary battery is switched when it is detected that the detection value of the charging state detection unit is out of the allowable range. A fuel cell system that changes a reference and suppresses a detection value of the charge state detection unit from being out of the allowable range.
With this fuel cell system, the state of charge of the secondary battery can be maintained in a more appropriate state, and deterioration of the secondary battery can be suppressed.

[Application Example 7]
The fuel cell system according to Application Example 5, wherein the fuel cell system is mounted on a moving body, and the fuel cell system further includes a movement information detection unit that detects movement information of the moving body, Based on the movement information, the control unit is moving toward a predetermined route that is set in advance as a route in which the detection value of the charging state detection unit is likely to be out of the allowable range. When this is detected, the fuel cell system suppresses the detection value of the charge state detection unit from being out of the allowable range by changing a reference for switching between charging and discharging of the secondary battery.
With this fuel cell system, since the state of charge of the secondary battery can be maintained in a more appropriate state based on the movement information of the moving body, deterioration of the secondary battery can be suppressed.

[Application Example 8]
The fuel cell system according to any one of Application Example 4 to Application Example 6, which refers to Application Example 3, wherein the fuel cell system is mounted on a moving body, and the fuel cell system further includes the fuel cell system described above. A movement information detection unit that detects movement information of the moving body; and a refrigerant circulation supply system that supplies a refrigerant to the fuel cell to adjust an operating temperature of the fuel cell, and the control unit includes the movement information. On the basis of the above, when it is detected that the moving body is moving toward a predetermined route set in advance as a route that is likely to have an operating temperature of the fuel cell higher than a predetermined threshold, A fuel cell system that increases a supply flow rate of the refrigerant to the fuel cell and suppresses an increase in operating temperature of the fuel cell.
With this fuel cell system, when the moving body is moving toward a path where the operating temperature of the fuel cell may increase, the increase in the operating temperature of the fuel cell is suppressed in advance. be able to. Therefore, when the moving body reaches the specific path, it is possible to suppress the operating temperature of the fuel cell from being significantly increased and the limit range of the output current of the fuel cell from being widened.

[Application Example 9]
The fuel cell system according to any one of Application Examples 2 to 8, further comprising a resistance detection unit that detects a resistance in the fuel cell, wherein the control unit is a relationship between an output current and a resistance in the fuel cell. In the fuel cell system, when the change in the relationship falls outside a preset allowable range, the range of the resistance value serving as a reference for the limit range is changed. In this fuel cell system, when the relationship between the current and the resistance in the fuel cell changes beyond the allowable range, the range of the resistance value that is the setting reference for the limit range is changed to appropriately correct the limit range. be able to. Therefore, the fuel cell can be protected more appropriately.

[Application Example 10]
A control method for a fuel cell system, comprising:
(A) receiving an output request from the outside, and setting a target current value of the fuel cell according to the output request;
(B) when the target current value is within a preset limit range, resetting the target current value to a boundary value of the limit range or a value outside the limit range;
(C) outputting the current of the target current value set in the step (a) or the step (b) to the fuel cell;
A control method comprising:
With this control method for a fuel cell system, it is possible to avoid a preset output within a limited range where there is a possibility of deterioration of the fuel cell, so that deterioration of the fuel cell can be suppressed.

  The present invention can be realized in various forms, for example, a fuel cell system and a control method thereof, a computer program for realizing the function of the system or the control method, and the computer program recorded therein. It can be realized in the form of a recording medium or the like.

Schematic which shows the structure of a fuel cell system. Schematic which shows the electrical structure of a fuel cell system. Schematic which shows the structure of a membrane electrode assembly, and a schematic diagram for demonstrating the deformation | transformation according to the wet state of an electrolyte membrane. Explanatory drawing which shows the control procedure of the output control of a fuel cell. Explanatory drawing for demonstrating the acquisition process of the command value of the electric current and voltage of a fuel cell. Explanatory drawing for demonstrating the restriction | limiting range where the output current of a fuel cell is restrict | limited. The schematic diagram for demonstrating the "local resistance" of a fuel cell. The schematic diagram for demonstrating an example of the method of determining the limiting value of local resistance. Explanatory drawing which shows the procedure of electric power generation body protection control. Explanatory drawing which shows an example of the time change of the target electric current of a fuel cell when electric power generation body protection control is performed. Explanatory drawing which shows the procedure of the electric power generation body protection control in 2nd Example. Schematic for demonstrating the time change of the target electric current of a fuel cell when electric power generation body protection control is performed in the fuel cell system of 2nd Example. Explanatory drawing which shows the control procedure of the output control of the fuel cell in 3rd Example. Explanatory drawing which shows the process sequence of the correction process of the limit value of local resistance. Schematic for demonstrating the determination process about the change of Ir characteristic. Schematic for demonstrating the acquisition process of the limit value after correction | amendment. Explanatory drawing which shows the procedure of the electric power generation body protection control in 4th Example. The schematic diagram for demonstrating an operating condition change process. Explanatory drawing which shows the control procedure of the output control of the fuel cell in 5th Example. Explanatory drawing which shows the procedure of the electric power generation body protection control in 5th Example. Schematic for demonstrating the effect by the change of the SOC reference value. Schematic which shows the structure of the fuel cell system of 6th Example. Explanatory drawing which shows the control procedure of the output control of the fuel cell in 6th Example. The schematic for demonstrating the processing content of the change process of SOC reference value, and the effect by the processing. Explanatory drawing which shows the control procedure of the output control of the fuel cell in 7th Example. The schematic for demonstrating the processing content of the prior adjustment process of operating temperature, and the effect by the process.

A. First embodiment:
FIG. 1 is a schematic diagram showing the configuration of a fuel cell system as an embodiment of the present invention. The fuel cell system 100 is mounted on a fuel cell vehicle and outputs electric power that is a power source of the fuel cell vehicle in response to a request from a driver. The fuel cell system 100 includes a fuel cell 10, a control unit 20, a cathode gas supply system 30, a cathode gas discharge system 40, an anode gas supply system 50, an anode gas discharge system 60, and a refrigerant circulation supply system 70. .

  The fuel cell 10 is a polymer electrolyte fuel cell that generates power by receiving supply of hydrogen (anode gas) and air (cathode gas) as reaction gases. The fuel cell 10 has a stack structure in which a plurality of single cells 11 are stacked.

  Each single cell 11 is a plate-like substrate 2 that functions as a current collector plate while sandwiching a membrane electrode assembly (described later) and a flow path for a reaction gas or a refrigerant by sandwiching the membrane electrode assembly 2. Sheet separator (not shown). Further, the fuel cell 10 is formed with a manifold (not shown) for reaction gas and refrigerant as a through hole along the stacking direction.

  The control unit 20 can be configured by a microcomputer including a central processing unit and a main storage device. The control unit 20 controls each system 30, 40, 50, 60 described below, and causes the fuel cell 10 to generate electric power according to an output request for the system. Operation control of the fuel cell 10 by the control unit 20 will be described later.

  The cathode gas supply system 30 includes a cathode gas pipe 31, an air compressor 32, an air flow meter 33, an on-off valve 34, and a pressure measuring unit 35. The cathode gas pipe 31 is a pipe connected to the cathode side inlet of the fuel cell 10. The air compressor 32 is connected to the fuel cell 10 via the cathode gas pipe 31 and supplies air compressed by taking in outside air to the fuel cell 10 as cathode gas.

  The air flow meter 33 measures the amount of outside air taken in by the air compressor 32 on the upstream side of the air compressor 32, and transmits it to the control unit 20. The control unit 20 controls the amount of air supplied to the fuel cell 10 by driving the air compressor 32 based on the measured value.

  The on-off valve 34 is provided between the air compressor 32 and the fuel cell 10. The on-off valve 34 is normally closed, and opens when air having a predetermined pressure is supplied from the air compressor 32 to the cathode gas pipe 31. The pressure measurement unit 35 measures the pressure of air in the vicinity of the inlet of the supply manifold on the cathode side of the fuel cell 10 and outputs the measured pressure to the control unit 20.

  The cathode gas discharge system 40 includes a cathode exhaust gas pipe 41, a pressure regulating valve 43, and a pressure measuring unit 44. The cathode exhaust gas pipe 41 is a pipe connected to the discharge manifold on the cathode side of the fuel cell 10. The cathode exhaust gas is discharged to the outside of the fuel cell system 100 via the cathode exhaust gas pipe 41.

  The opening of the pressure regulating valve 43 is controlled by the control unit 20 and adjusts the pressure of the cathode exhaust gas in the cathode exhaust gas pipe 41 (back pressure on the cathode side of the fuel cell 10). The pressure measurement unit 44 is provided on the upstream side of the pressure regulating valve 43, measures the pressure of the cathode exhaust gas, and outputs the measurement result to the control unit 20.

  The anode gas supply system 50 includes an anode gas pipe 51, a hydrogen tank 52, an on-off valve 53, a regulator 54, a hydrogen supply device 55, and a pressure measurement unit 56. The hydrogen tank 52 is connected to the supply manifold on the anode side of the fuel cell 10 through the anode gas pipe 51, and supplies hydrogen filled in the tank to the fuel cell 10.

  The on-off valve 53, the regulator 54, the hydrogen supply device 55, and the pressure measuring unit 56 are provided in the anode gas pipe 51 in this order from the upstream side (hydrogen tank 52 side). The on-off valve 53 opens and closes according to a command from the control unit 20 and controls the inflow of hydrogen from the hydrogen tank 52 to the upstream side of the hydrogen supply device 55. The regulator 54 is a pressure reducing valve for adjusting the pressure of hydrogen on the upstream side of the hydrogen supply device 55, and its opening degree is controlled by the control unit 20.

  The hydrogen supply device 55 can be configured by, for example, an injector that is an electromagnetically driven on-off valve. The pressure measurement unit 56 measures the pressure of hydrogen on the downstream side of the hydrogen supply device 55 and transmits it to the control unit 20. The control unit 20 controls the flow rate of hydrogen supplied to the fuel cell 10 by controlling the hydrogen supply device 55 based on the measurement value of the pressure measurement unit 56.

  The anode gas discharge system 60 includes an anode exhaust gas pipe 61, an on-off valve 66, and a pressure measuring unit 67. The anode exhaust gas pipe 61 is a pipe connected to the discharge manifold on the anode side of the fuel cell 10. The anode exhaust gas containing unreacted gas (such as hydrogen and nitrogen) that has not been used for the power generation reaction is discharged to the outside of the fuel cell system 100 via the anode exhaust gas pipe 61.

  The on-off valve 66 is provided in the anode exhaust gas pipe 61 and opens and closes according to a command from the control unit 20. The pressure measuring unit 67 of the anode gas discharge system 60 is provided in the anode exhaust gas pipe 61. The pressure measurement unit 67 measures the pressure of the anode exhaust gas (back pressure on the anode side of the fuel cell 10) in the vicinity of the discharge manifold on the anode side of the fuel cell 10 and outputs the pressure to the control unit 20.

  The refrigerant circulation supply system 70 includes a refrigerant pipe 71, a radiator 72, a three-way valve 73, a refrigerant circulation pump 75, and two refrigerant temperature measuring units 76a and 76b. The refrigerant pipe 71 is a pipe for circulating a refrigerant for cooling the fuel cell 10, and includes an upstream pipe 71a, a downstream pipe 71b, and a bypass pipe 71c.

  The upstream pipe 71 a connects the refrigerant discharge manifold provided in the fuel cell 10 and the inlet of the radiator 72. The downstream pipe 71 b connects the refrigerant supply manifold provided in the fuel cell 10 and the outlet of the radiator 72. One end of the bypass pipe 71c is connected to the upstream pipe 71a via the three-way valve 73, and the other end is connected to the downstream pipe 71b. The control unit 20 controls the opening and closing of the three-way valve 73, thereby adjusting the amount of refrigerant flowing into the bypass pipe 71c and controlling the amount of refrigerant flowing into the radiator 72.

  The radiator 72 is provided in the refrigerant pipe 71 and cools the refrigerant by exchanging heat between the refrigerant flowing through the refrigerant pipe 71 and the outside air. The refrigerant circulation pump 75 is provided on the downstream side pipe 71b on the downstream side (the refrigerant inlet side of the fuel cell 10) from the connection point of the bypass pipe 71c, and is driven based on a command from the control unit 20. The two refrigerant temperature measuring units 76 a and 76 b are provided in the upstream pipe 71 a and the downstream pipe 71 b, respectively, and output measured values to the control unit 20.

  The control unit 20 detects the operating temperature of the fuel cell 10 from the difference between the measured values of the refrigerant temperature measuring units 76a and 76b, and based on the detection result, the rotational speed of the refrigerant circulation pump 75 and the three-way valve 73. The operating temperature of the fuel cell 10 is adjusted by controlling the opening degree. Specifically, when the current operating temperature of the fuel cell 10 is higher than the set target value, the control unit 20 increases the number of revolutions of the refrigerant circulation pump 75 or the amount of refrigerant flowing into the radiator 72. The opening degree of the three-way valve 73 is reduced so that increases. On the other hand, when the current operating temperature of the fuel cell 10 is lower than the set target value, the three-way valve 73 is set so that the rotational speed of the refrigerant circulation pump 75 is reduced or the amount of refrigerant flowing into the radiator 72 is reduced. Increase the opening of the.

  FIG. 2 is a schematic diagram showing an electrical configuration of the fuel cell system 100. The fuel cell system 100 includes a secondary battery 81, a DC / DC converter 82, a DC / AC inverter 83, a current measurement unit 90, a voltage measurement unit 91, and an SOC detection unit 92. The fuel cell 10 is connected to a DC / AC inverter 83 via a DC wiring DCL, and the DC / AC inverter 83 is connected to a motor 200 that is a driving force source of the fuel cell vehicle.

  The secondary battery 81 is connected to the DC wiring DCL via the DC / DC converter 82. The secondary battery 81 functions as a power source together with the fuel cell 10. The secondary battery 81 can be composed of, for example, a lithium ion battery. The control unit 20 controls the DC / DC converter 82 to control the current / voltage of the fuel cell 10 and the charge / discharge of the secondary battery 81 to variably adjust the voltage level of the DC wiring DCL. To do.

  The DC / AC inverter 83 converts DC power obtained from the fuel cell 10 and the secondary battery 81 into AC power and supplies the AC power to the motor 200. When regenerative power is generated by the motor 200, the DC / AC inverter 83 converts the regenerative power into DC power. The regenerative power converted into direct current power is stored in the secondary battery 81 via the DC / DC converter 82.

  The current measuring unit 90 is connected to the DC wiring DCL, measures the current value output from the fuel cell 10, and outputs the current value to the control unit 20. The voltage measurement unit 91 is connected to the fuel cell 10, measures the output voltage of the fuel cell 10, and outputs it to the control unit 20. The SOC detection unit 92 is connected to the secondary battery 81. The SOC detection unit 92 detects a state of charge (SOC) that is a charged state of the secondary battery 81 and outputs the detected state to the control unit 20.

  Here, the SOC of the secondary battery 81 means the ratio of the remaining charge (charged amount) of the secondary battery 81 to the charge capacity of the secondary battery 81. The SOC detection unit 92 detects the SOC of the secondary battery 81 by measuring the temperature, power, and current of the secondary battery 81. Based on the detection value of SOC detection unit 92, control unit 20 manages the SOC of secondary battery 81 as follows.

  The control unit 20 sets the SOC reference value of the secondary battery 81, and the SOC of the secondary battery 81 is a predetermined range centered on the reference value (a limit range in which deterioration of the secondary battery 81 can be suppressed). The charging / discharging of the secondary battery 81 is controlled so as to be within. Specifically, when the detected value of the SOC is lower than the set reference value, the control unit 20 controls the secondary battery 81 to be charged, and the detected value of the SOC is higher than the set reference value. Is controlled so that the secondary battery 81 is discharged.

  FIG. 3 is a schematic diagram for explaining the membrane electrode assembly 5 provided in the fuel cell 10. FIG. 3A is a schematic diagram showing a configuration of the membrane electrode assembly 5 provided in the fuel cell 10. The membrane electrode assembly 5 has a configuration in which the electrodes 2 and 3 are disposed on both surfaces of the electrolyte membrane 1. The electrolyte membrane 1 is a solid polymer thin film that exhibits good proton conductivity when in a wet state, and can be composed of, for example, a thin film of a fluorine-based ion exchange resin.

  The electrodes 2 and 3 can be formed as a coating film of so-called catalyst ink. Here, the “catalyst ink” means a dispersion liquid in which conductive particles carrying a catalyst for promoting a power generation reaction and the same or similar ionomer that constitutes the electrolyte membrane 1 are dispersed. To do. As the catalyst, for example, platinum (Pt) can be adopted, and as the conductive particles, for example, carbon (C) particles can be adopted.

  The membrane electrode assembly 5 is disposed in each unit cell 11 of the fuel cell 10 with the outer peripheral end of the electrolyte membrane 1 held by a seal member (not shown) or the like. That is, in each single cell 11, the electrolyte membrane 1 is arranged in a state where the size in the direction along the plane (hereinafter simply referred to as “plane direction”) is fixed at a predetermined reference size S. On the other hand, as will be described below, the electrolyte membrane 1 has a property that its size changes in accordance with its wet state (hydrated state).

  FIG. 3B is a schematic view for explaining deformation according to the wet state of the electrolyte membrane 1. In the middle part of FIG. 3B, the electrolyte membrane 1 when the reference size is S is shown. Hereinafter, the wetness of the electrolyte membrane 1 is referred to as “reference wetness”. In FIG. 3B, the electrolyte membrane 1 in a state of being drier than the reference wetness is sandwiched between the electrolyte membrane 1 of the reference wetness, and the electrolyte membrane 1 in a state of being wetter than the reference wetness is shown in the upper stage. Each is illustrated in the lower part.

  Here, the reference wetness of the electrolyte membrane 1 may be the wetness at the time of factory shipment. In general, the lower the wetness of the electrolyte membrane 1, the smaller the dimension in the planar direction and the contraction (the upper stage in FIG. 3B). Then, as the wetness is higher, the dimension in the planar direction increases and expands (lower stage in FIG. 3B).

  During the operation of the fuel cell 10, the wetness of the electrolyte membrane 1 varies depending on the operation state (for example, the operation temperature of the fuel cell 10, the amount of power generation, the flow rate of the reaction gas, etc.). However, as described above, since the electrolyte membrane 1 is fixedly held in each unit cell 11 of the fuel cell 10 so that the reference size S is held, the deformation in the planar direction according to the wetness thereof. (Especially, shrinkage deformation) is suppressed.

  Therefore, during the operation of the fuel cell 10, when the electrolyte membrane 1 is in a dry state where the wetness of the electrolyte membrane 1 is lower than the reference wetness, a stress corresponding to the amount of suppression of the contraction deformation is generated in the electrolyte membrane 1. Further, since the degree of deformation of the electrodes 2 and 3 of the membrane electrode assembly 5 is different from that of the electrolyte membrane 1 according to the degree of wetness, during the operation of the fuel cell 10, the electrode 2 and 3 are not in contact with each other. In addition, a stress corresponding to a change in the wet state occurs.

  The stress fluctuation according to the change in the wet state repeatedly generated in the membrane electrode assembly 5 in the fuel cell 10 during power generation causes irreversible deterioration in the membrane electrode assembly 5. Specifically, the fluctuation of the internal stress repeatedly generated in the membrane electrode assembly 5 causes a remarkable density distribution in the structure of the electrolyte membrane 1 or increases the diameter of the minute holes of the electrolyte membrane 1, thereby causing the electrolyte membrane to This causes the airtightness of 1 to be reduced. In addition, the electrodes 2 and 3 also cause cracks. The cracks in the electrodes 2 and 3 further become a starting point of stress concentration in the electrolyte membrane 1 and cause the electrolyte membrane 1 to crack.

  Therefore, in the fuel cell system 100 of the present embodiment, the control unit 20 executes output control of the fuel cell 10 according to the control procedure described below, thereby causing stress that causes deterioration in the membrane electrode assembly 5. Suppresses fluctuations.

  FIG. 4 is a flowchart showing a control procedure of output control of the fuel cell 10 executed by the control unit 20. In step S5, the control unit 20 receives an external output request. In step S10, electric power to be output to the fuel cell 10 is determined in response to an output request from the outside, and target values (command values) of the current and voltage of the fuel cell 10 for obtaining the electric power are acquired.

FIG. 5 is an explanatory diagram for explaining a process of acquiring target values of current and voltage of the fuel cell 10 in step S10. FIG. 5 shows a graph GIP indicating the current-voltage characteristics ( _IP characteristics) of the fuel cell 10 and a graph GIV indicating the current-voltage characteristics ( _IV characteristics), with the left and right vertical axes respectively. A voltage axis and a power axis are shown, and a horizontal axis is shown as a current axis.

  Usually, the I-P characteristic of a fuel cell is represented as an upwardly convex curve graph. Further, the IV characteristic of the fuel cell is represented as a horizontal S-shaped curve graph that gently falls as the current increases. The control unit 20 stores in advance information representing the IP characteristic and the IV characteristic of the fuel cell 10 as control information for the fuel cell 10, and based on the control information, the control unit 20 Get current and voltage command values. Specifically, it is as follows.

  The control unit 20 determines the power (target power Pt) to be output by the fuel cell 10 in response to an output request from the outside. Then, based on the IP characteristic of the fuel cell 10, a target value (target current It) of the current that the fuel cell 10 should output with respect to the target power Pt is acquired.

  Here, since the target current It acquired based on the IP characteristic of the fuel cell 10 is a command value used in normal control described below, it is particularly called “normal target current It”. The control unit 20 further acquires a target value (target voltage Vt) of the voltage of the fuel cell 10 necessary for outputting the normal target current It based on the IV characteristic of the fuel cell 10.

  It should be noted that the IP characteristic and the IV characteristic of the fuel cell 10 change according to the operating state such as the operating temperature of the fuel cell 10. Therefore, it is preferable that the control unit 20 stores control information for each of the operating states in advance, and appropriately select and use the control information according to the current operating state of the fuel cell 10.

  In step S20 (FIG. 4), the control unit 20 determines whether or not the normal target current It is an output in the limited range. Here, the “restricted range” refers to the output current of the fuel cell 10 in advance in order to limit the output that may cause the membrane electrode assembly 5 to generate stress due to drying and cause irreversible degradation. It is the set range.

  When the control unit 20 determines that the normal target current It is an output within the limit range, the control unit 20 executes power generator protection control that is control for protecting the membrane electrode assembly 5 (step S40). Details of the output current limit range of the fuel cell 10 and the power generator protection control will be described later.

  When it is determined that the normal target current It is not an output within the limit range, the control unit 20 executes normal output control in step S30. Specifically, the control unit 20 instructs the DC / DC converter 82 to cause the fuel cell 10 to output the target voltage Vt in order to cause the fuel cell 10 to output the normal target current It. Note that the power shortage until the output voltage of the fuel cell 10 reaches the target voltage Vt is compensated by the output of the secondary battery 81. The control unit 20 repeats the control in steps S5 to S40 until the operation of the fuel cell vehicle is stopped (step S50).

  FIG. 6 is an explanatory diagram for explaining a limit range in which the output current of the fuel cell 10 is limited in the fuel cell system 100 of the present embodiment. FIG. 6 illustrates an example of a graph showing a relationship (also referred to as “Ir characteristics”) between a current I and a local resistance (described later) r for each operating temperature T of the fuel cell 10. FIG. 6A is a three-dimensional graph in which three orthogonal axes are current I, local resistance r, and operating temperature T, respectively, and FIG. 6B is a three-dimensional graph of FIG. It is a graph which shows the relationship between the local resistance r and the electric current I when the driving | running temperature T is arbitrary temperature Ta obtained from a graph.

  In FIG. 6, a region included in the limited range is illustrated as a limited region LR, and a region outside the limited range is illustrated as an allowable region AR. Specifically, in FIG. 6A, the restriction area LR and the allowable area AR are illustrated by different hatching, and in FIG. 6B, the graph in the allowable area AR is indicated by a solid line, and the graph in the restriction area LR is indicated by two lines. It is shown by a dotted line. Here, “local resistance” shown in the graphs of FIGS. 6A and 6B will be described.

  FIG. 7 is a schematic diagram for explaining “local resistance” of the fuel cell 10. In FIG. 7, a schematic diagram of the fuel cell 10 is illustrated in the upper stage, and a schematic diagram illustrating a temperature distribution in the power generation region GA of the single cell 11 is illustrated in the lower stage. Normally, a temperature distribution is generated in the operating fuel cell 10. Specifically, in the fuel cell 10, the operating temperature is the lowest for the single cells 11 on both outer sides, and the operating temperature is higher for the single cell 11 closer to the center in the stacking direction of the single cells 11.

  Also in the power generation region GA of the single cell 11c having the highest operating temperature (hereinafter also referred to as “high temperature cell 11c”), as shown in the lower part of FIG. Occur. Hereinafter, in the power generation region GA of the high-temperature cell 11c, a portion where the operating temperature is highest is referred to as a “high-temperature region HTR”.

  In general, in a membrane electrode assembly during power generation, the higher the temperature, the lower the wetness and the higher the resistance. Therefore, in the fuel cell 10, the wetness of the membrane electrode assembly 5 is the lowest and the resistance is the highest in the high temperature region HTR of the high temperature cell 11c. In this specification, the local resistance measured in the high temperature region HTR is referred to as “local resistance”.

In the fuel cell 10, when the current is increased, the local resistance can obtain an Ir characteristic that changes upward from a rising tendency to a downward tendency with the maximum value being r _max (FIG. 6). Further, the Ir characteristic of the fuel cell 10 shows a change in which the maximum value r _max of the local resistance increases as the operating temperature T increases, and the change of the local resistance with respect to the current I becomes steeper.

  In the fuel cell system 100 of the present embodiment, the control unit 20 stores in advance a map in which the Ir characteristics for each operating temperature T as described above are represented. Hereinafter, in this specification, the map in which the Ir characteristic is expressed is also simply referred to as an “Ir map”.

Here, when the local resistance is remarkably large, the membrane electrode assembly 5 of the high-temperature cell 11c is remarkably dried, and stress that causes irreversible deterioration may be generated in the membrane electrode assembly 5. There is. Therefore, a limit value r _lim indicating a limit allowed for the partial resistance for protecting the membrane electrode assembly 5 is set on the Ir map, and the local resistance is higher than the limit value r _lim. The current range is defined as the limit range.

In the Ir map of this embodiment, the limit value r _lim of the local resistance is set as a constant value regardless of the operating temperature (illustrated by a broken line in FIG. 6A). Therefore, the limit range of the output current of the fuel cell 10 becomes wider as the operating temperature is higher due to the change in the Ir characteristic according to the operating temperature.

Thus, in this embodiment, the limit range of the output current of the fuel cell 10 is _defined by the limit value r _lim for the preset local resistance. Here, in the present embodiment, the limit value r _lim of the local resistance is determined by the following method to appropriately prevent accumulation of irreversible deterioration of the membrane electrode assembly 5.

8A to 8C are schematic diagrams for explaining an example of a method for determining the limit value r _lim of the local resistance. FIG. 8A shows an example of an SN diagram (SN curve) obtained by a fatigue test of the membrane / electrode assembly 5. This SN diagram can be obtained by the following method, for example.

  A predetermined tensile stress along the planar direction is applied to the membrane / electrode assembly 5 at a constant period, and the tensile stress when a predetermined irreversible deterioration occurs in the membrane / electrode assembly 5 is observed. Measure the number of times applied (fatigue test). The measurement results are plotted on a graph in which the vertical axis is the magnitude of the tensile stress applied to the membrane electrode assembly 5 and the horizontal axis is the number of times the tensile stress is applied (logarithmic display). A curve graph (S—N curve) is created based on the distribution of.

  In the above fatigue test, the “state in which a predetermined irreversible deterioration has occurred in the membrane electrode assembly 5” is, for example, irreversibly up to a predetermined size when the size of the membrane electrode assembly 5 is plastically expanded. It may be in a state that has been fully extended. In the membrane / electrode assembly 5, a predetermined number of lacerations may be observed, and the air permeability in the thickness direction of the membrane / electrode assembly 5 increases to a predetermined level. It is good also as what is in the state.

  In the SN diagram obtained by the fatigue test as described above, the allowable stress δa is selected as the allowable stress δa as the stress generated in the membrane electrode assembly 5. In the SN diagram, the fatigue limit (the limit of the stress that the membrane electrode assembly 5 will not reach the state where the irreversible deterioration occurs even if the stress is applied an infinite number of times) appears. If it is, the fatigue limit is preferably the allowable stress δa.

  FIG. 8B shows an example of a graph showing the relationship between the wetness (WH%) of the membrane electrode assembly 5 and the stress generated in the membrane electrode assembly 5. This graph is obtained based on the amount of swelling change (strain amount) according to the wetness of the electrolyte membrane 1. From this graph, the wetness of the membrane electrode assembly 5 when the allowable stress δa is generated is acquired as the allowable wetness Wa that is the minimum limit value of the wetness allowed for the membrane electrode assembly 5.

FIG. 8C illustrates an example of a graph showing the wetness (WH%) of the membrane electrode assembly 5 and the resistance of the membrane electrode assembly 5. Usually, the higher the wetness of the membrane electrode assembly 5, the lower the resistance of the membrane electrode assembly 5 exponentially. Based on this relationship, the resistance of the membrane electrode assembly 5 with respect to the allowable wetness Wa is acquired as a limit value r _lim of local resistance.

Thus, by setting the limit value r _lim of the local resistance based on the fatigue test of the membrane electrode assembly 5, the fuel is generated so that the generation of stress that accumulates fatigue of the membrane electrode assembly 5 is limited. A limit range of the output current of the battery 10 can be defined. Therefore, the occurrence of fatigue accumulated in the membrane electrode assembly 5 can be suppressed more appropriately.

As described above, in the operation control of the fuel cell 10 (FIG. 4), the control unit 20 determines whether or not the normal target current It is an output in the limited range in step S20. More specifically, the control unit 20 is sandwiched between the first and second current values Ia and Ib (Ia <Ib) at which the local resistance becomes the limit value r _lim on the Ir map (FIG. 6). It is determined whether or not the normal target current It is included in the current range.

  In the case where the normal target current It is within the limit range, if the fuel cell 10 outputs the normal target current It, there is a possibility that the membrane electrode assembly 5 will be extremely dry at least in the high temperature cell 11c. is there. Therefore, when the normal target current It is within the limit range in step S20, the control unit 20 executes power generator protection control described below in step S40.

  FIG. 9 is a flowchart showing a procedure of power generator protection control executed in step S40 (FIG. 4). In step S110, the control unit 20 determines which one of the first and second current values Ia and Ib is used as the target current It based on the normal target output obtained from the external request output. The selection is made according to the magnitude of the current It (FIG. 5).

  When the normal target current It is smaller than the predetermined reference current Ith, the control unit 20 sets the target current Ita of the fuel cell 10 in the power generator protection control to the first current value Ia (step S120). On the other hand, when the normal target current It is greater than or equal to the predetermined reference current Ith, the target current Ita of the fuel cell 10 is set to the second current value Ib (step S130).

In this embodiment, the reference current Ith, which is a reference for setting the target current of the fuel cell 10 in the power generator protection control, can be obtained from the Ir map shown in FIG. The current is the maximum value r _max . The reference current Ith may be another current value within the limit range, for example, a current value at the center of the limit range (Ith = (Ia + Ib) / 2).

  In step S140, the control unit 20 sets the target voltage Vta for causing the fuel cell 10 to output the target current Ita based on a map representing the IV characteristic of the fuel cell 10 similar to that described with reference to FIG. get. Then, the DC / DC converter 82 is commanded to cause the fuel cell 10 to output the target voltage Vta. In this power generator protection control, the power shortage with respect to the output request from the outside is compensated by the output of the secondary battery 81.

  FIG. 10 is a graph showing an example of a temporal change in the target current of the fuel cell 10 when the power generator protection control is executed. In this example, it is assumed that the operating temperature of the fuel cell 10 is constant.

In this example, at time t ₁ and time t ₄ , the output control of the fuel cell 10 is switched from the normal output control at step S30 to the power generator protection control at step S40, and again at time t ₃ and time t ₄ . Return to normal output control. In the first power generator protection control (time t _{1 to} t ₃ ), the target current of the fuel cell 10 is the first current during the time t _{1 to} t ₂ because the normal target current It is smaller than the reference current Ith. It is set to the value Ia. In addition, during the time t _{2 to} t ₃ , the normal target current It is equal to or higher than the reference current Ith, and the target current of the fuel cell 10 is set to the second current value Ib.

In the second power generating body protection control (time t ₄ ~t _6), between the times t ₄ ~t _5, since normal target current It is the reference current Ith or more, the target current of the fuel cell 10 of the second The current value Ib is set. Further, since the normal target current It is smaller than the reference current Ith between times t ₅ and t ₆ , the target current of the fuel cell 10 is set to the first current value Ia.

  As described above, in the fuel cell system 100 of the present embodiment, the control unit 20 appropriately switches the output control of the fuel cell 10 from the normal output control to the power generator protection control, and the output current of the fuel cell 10 It is avoided that the electrode assembly 5 falls within a limit range that may deteriorate the electrode assembly 5. Therefore, in the fuel cell 10, it is possible to suppress deterioration from being accumulated in the membrane electrode assembly 5 by repeating the operation in which the membrane electrode assembly 5 is remarkably dried.

B. Second embodiment:
FIG. 11 is a flowchart showing a control procedure of power generator protection control executed in the fuel cell system as the second embodiment of the present invention. 11 is substantially the same as FIG. 9 except that step S111 is provided instead of step S110. The configuration of the fuel cell system of the second embodiment is the same as that of the fuel cell system 100 of the first embodiment (FIGS. 1 and 2).

  Here, as described in the first embodiment, the control unit 20 sets the SOC reference value, and switches charging / discharging of the secondary battery 81 based on the reference value. Specifically, the control unit 20 charges the secondary battery 81 when the current SOC of the secondary battery 81 measured by the SOC detection unit 92 (FIG. 2) is smaller than the set reference value. To control. When the current SOC of the secondary battery 81 is equal to or higher than the reference value, the secondary battery 81 is controlled to be discharged.

  In the power generation protection control of the second embodiment, the control unit 20 sets the target current Ita of the fuel cell 10 based on the current SOC of the secondary battery 81 (step S111). Specifically, when the current SOC of the secondary battery 81 is equal to or higher than the reference value, the target current Ita in the power generation protection control is set to the first current value Ia that is insufficient in output current with respect to the normal target current It. To promote discharge of the secondary battery 81 (step S120). On the other hand, when the current SOC of the secondary battery 81 is lower than the reference value, the target current Ita in the power generation protection control is set to the second current value Ib in which the output current is greater than the normal target current It. Charge of the secondary battery 81 is promoted (step S130).

  FIG. 12 is a schematic diagram for explaining the temporal change of the target current of the fuel cell 10 when the power generator protection control is executed in the fuel cell system of the second embodiment. In the upper and lower stages of FIG. 12, a graph showing an example of the time change of the SOC of the secondary battery 81 and a graph showing an example of the time change of the target current of the fuel cell 10 are associated with each time axis. It is illustrated.

In the upper graph of FIG. 12, the SOC reference value Cs of the secondary battery 81 and the upper limit value C _max and the lower limit value C _{lim of} the SOC centering on the reference value Cs are shown. In this example, it is assumed that the operating temperature of the fuel cell 10 is constant.

In this example, at time t ₁ and time t ₄ , the output control of the fuel cell 10 is switched from the normal output control at step S30 to the power generator protection control at step S40, and again at time t ₃ and time t ₄ . Return to normal output control. In the first power generator protection control (time t _{1 to} t ₃ ), since the SOC of the secondary battery 81 is smaller than the reference value Cs during the time t _{1 to} t ₂ , the target current of the fuel cell 10 is the second value. Current value Ib. In addition, during time t _{2 to} t ₃ , the SOC is equal to or higher than the reference value Cs, and the target current of the fuel cell 10 is set to the first current value Ia.

On the other hand, in the second power generator protection control (time t _{4 to} t ₆ ), the SOC of the secondary battery 81 is equal to or higher than the reference value Cs during the time t _{4 to} t _5. Is set to the first current value Ia. Further, since the SOC is smaller than the reference value Cs between the times t ₅ and t ₆ , the target current of the fuel cell 10 is set to the second current value Ib.

  As described above, in the fuel cell system according to the second embodiment, by controlling the target current Ita in the power generator protection control according to the SOC of the secondary battery 81, in the power generator protection control, the secondary battery It can suppress that SOC of 81 falls remarkably or increases.

C. Third embodiment:
FIG. 13 is a flowchart showing a control procedure of output control of the fuel cell 10 executed by the control unit 20 in the fuel cell system as the third embodiment of the present invention. FIG. 13 is substantially the same as FIG. 4 except that step S15 and step S45 are added. The configuration of the fuel cell system of the third embodiment is the same as that of the fuel cell system of the second embodiment (FIGS. 1 and 2).

  As described in the first embodiment, in the power generator protection control, the limit range for the output current of the fuel cell 10 based on the Ir map (FIG. 6) representing the relationship between the current I and the local resistance r. Is set. However, the Ir characteristic in the fuel cell 10 may change according to the operating state of the fuel cell 10 or may change over time.

Therefore, when the Ir characteristic changes, it is preferable that the limit value r _lim of the local resistance set in the Ir map is corrected according to the change. In the fuel cell system of the third embodiment, the control unit 20 detects a change in the Ir characteristic of the fuel cell 10 and corrects the limit value r _lim of the local resistance in step S15.

FIG. 14 is a flowchart showing a processing procedure of the correction process of the local resistance limit value r _lim executed in step S15 (FIG. 13) of the output control of the fuel cell 10. In step S200, the control unit 20 uses the current of the fuel cell 10 measured by the current measurement unit 90 and the voltage of the fuel cell 10 measured by the voltage measurement unit 91 to determine the overall resistance ( Hereinafter, an actual measurement value Rm of “stack resistance” is calculated. In step S210, the control unit 20 determines whether or not the change in the Ir characteristic is within the allowable range, using the calculated actual measurement value Rm of the stack resistance.

  FIG. 15 is a schematic diagram for explaining a determination process for a change in the Ir characteristic in step S210. FIG. 15 shows a graph similar to the graph representing the Ir map described in FIG. The control unit 20 reads an Ir map corresponding to the current operating temperature Tc of the fuel cell 10 to execute the determination process of step S20, and uses the Ir map to determine the current state of the fuel cell 10. The local resistance rc with respect to the current Ic is acquired.

  Here, the control unit 20 of the present embodiment stores in advance a map (hereinafter, simply referred to as “r-R map”) representing the relationship between the local resistance and the stack resistance acquired in advance through experiments. Yes. The control unit 20 reads an r-R map corresponding to the current operating temperature Tc of the fuel cell 10, and uses the r-R map to obtain a stack resistance Rc with respect to the local resistance rc obtained from the Ir map. .

The control unit 20 compares the actual stack resistance value Rm acquired in step S200 with the stack resistance Rc acquired from the Ir map, and determines whether or not the difference is within a preset allowable range. To do. When the difference is equal to or smaller than a predetermined reference value and within the allowable range, the control unit 20 controls the operation of the fuel cell 10 without correcting the limit value r _lim of the local resistance (FIG. 12). Returning to step S20, the determination process of step S20 is executed.

When the difference between the measured value Rm of the stack resistance and the stack resistance Rc is larger than a predetermined threshold and is outside the allowable range, the control unit 20 corrects the limit value r _lim of the local resistance. Specifically, the control unit 20 acquires the corrected limit value cr _lim by the following method.

FIGS. 16A and 16B are schematic diagrams for explaining the process of acquiring the corrected limit value cr _lim in step S220. FIG. 16A is an explanatory diagram showing a local resistance distribution graph used in step S220.

  In this local resistance distribution graph, in the fuel cell 10 in various power generation states, the stack resistance and the local resistance are measured. It can be obtained by. In FIG. 16A, the dispersion region of the plot is schematically shown by hatching.

The control unit 20 stores in advance the relationship between the local resistance and the stack resistance represented by the curve graph DA in the local resistance distribution graph of FIG. In step S220, using the relationship between the local resistance and the stack resistance, the lower value of the stack resistance with respect to the current local resistance limit value r _lim is obtained as the correction reference resistance Rs. Using the current output voltage of the fuel cell 10 and the correction reference resistance Rs, the control unit 20 acquires the current of the fuel cell 10 when the stack resistance becomes the correction reference resistance Rs as the correction reference current Is.

FIG. 16B is an explanatory diagram for explaining a process of obtaining a corrected limit value r _lim using the corrected reference current Is. FIG. 16B is almost the same as FIG. 15 except that the description content of the processing is different. The control unit 20 reads the Ir map corresponding to the current operating temperature Tc of the fuel cell 10 again, and based on the Ir map, the local resistance with respect to the corrected reference current Is is set as the corrected limit value cr _lim. get.

When the corrected limit value cr _lim is obtained as a value larger than the original limit value r _lim (cr _lim > r _lim ), the current limit range of the fuel cell 10 is changed to become narrower. become. Therefore, in this case, from the viewpoint of preventing the deterioration of the membrane electrode assembly 5, the original limit value r _lim is maintained without correction, and the current limit range of the fuel cell 10 is maintained as it is. Also good.

When the corrected limit value cr _lim is acquired, in step S20 (FIG. 13), the normal target current It is determined based on the limit range _defined by the corrected limit value cr _lim . In step S40, the power generator protection control is executed using the boundary values Ia and Ib of the limit range _defined by the corrected limit value cr _lim .

In step S45, the control unit 20 discards the corrected limit value cr _lim and sets the original limit value r _{lim to} be used in the subsequent processing. However, the control unit 20 stores the number of executions in which the correction process of the local resistance limit value r _lim in step S15 is repeatedly executed, and the correction limit value after correction is repeated when the correction process is repeated a predetermined number of times. cr _lim is set as an initial value of the limit value r _lim . As a result, it is possible to suppress irreversibly updating the limit value r _lim of the local resistance every time a temporary change of the Ir characteristic occurs.

As described above, in the fuel cell system of the third embodiment, even if the Ir characteristic of the fuel cell 10 changes and a difference from the previously stored Ir map occurs, By changing the limit value r _lim of the local resistance, the limit range can be changed appropriately. Therefore, the membrane electrode assembly 5 can be protected more appropriately.

D. Fourth embodiment:
FIG. 17 is a flowchart showing a control procedure of the power generator protection control executed in the fuel cell system as the fourth embodiment of the present invention. FIG. 17 is almost the same as FIG. 11 except that three steps (steps S105, S150, and S151) are added. The configuration of the fuel cell system of the fourth embodiment is the same as that of the fuel cell system of the third embodiment (FIGS. 1 and 2). Further, the control procedure of the operation control of the fuel cell 10 by the control unit 20 is the same as that in the third embodiment (FIG. 13).

Here, the control unit 20 sets predetermined limit ranges (upper limit value C _max , lower limit value C _lim ) for the SOC of the secondary battery 81, and the secondary battery so that the SOC is within the limit range. 81 charge / discharge is controlled. This limit range is a range set so as to be able to suppress deterioration due to overcharging or undercharging of the secondary battery 81.

  However, in the control after step S111, since the output current of the fuel cell 10 is forcibly offset from the limit range, the load on the secondary battery 81 is likely to increase. Therefore, in the power generator protection control of the fourth embodiment, the process of offsetting the output current of the fuel cell 10 is executed only when the secondary battery 81 has the SOC within an allowable range having a margin beyond the limit range. . If the SOC of the secondary battery 81 is out of the allowable range, the operating condition of the fuel cell 10 is changed to protect the membrane electrode assembly 5 and avoid an increase in the load of the secondary battery 81. Perform possible output control. Specifically, it is as follows.

In step S105, the control unit 20 determines whether or not the current SOC of the secondary battery 81 is a value within the allowable range. Specifically, the control unit 20 presets first and second threshold values Ca and Cb that are values within the limit range and are values in the vicinity of the upper limit value C _max and the lower limit value C _lim , respectively. Then, it is determined whether or not the SOC is equal to or less than the first threshold value Ca and equal to or greater than the second threshold value Cb. When the current SOC of the secondary battery 81 is within the allowable range, the control unit 20 executes control after step S111. When the current SOC of the secondary battery 81 is outside the allowable range, the control unit 20 performs step S150. The subsequent control is executed.

  FIG. 18 is a schematic diagram for explaining the operating condition changing process in step S150. The upper part of FIG. 18 shows a three-dimensional graph representing the same Ir characteristic as described in FIG. In the lower part of FIG. 18, a three-dimensional graph showing the Ir characteristic of the fuel cell 10 after changing the operating conditions is shown so that it can be compared with the upper part of FIG. 18.

In step S150, the control unit 20 changes the operating condition of the fuel cell 10 and changes the Ir characteristic of the fuel cell 10 so that the maximum value of the local resistance is lower than the limit value _rlim . Specifically, the wetness of the membrane electrode assembly 5 can be increased by increasing the back pressure on the cathode side of the fuel cell 10 more than usual or increasing the stoichiometric ratio of the anode gas of the fuel cell 10 more than usual. Change to the operating conditions that can be used.

  In step S151, in a state where the Ir characteristic of the fuel cell 10 is changed, the DC / DC converter 82 is controlled to output the target voltage Vt to the fuel cell 10 in the same manner as in the normal operation control, and the normal target The current It is output. Hereinafter, the control in steps S150 and S151 is referred to as “Ir characteristic change control”.

  As described above, in the fuel cell system of the fourth embodiment, when there is a possibility that the secondary battery 81 may be deteriorated by the control for forcibly offsetting the output current of the fuel cell 10 from the limit range, the I− Execution of such control is avoided by the r characteristic change control. Therefore, the secondary battery 81 can be protected together with the membrane electrode assembly 5.

E. Example 5:
FIG. 19 is a flowchart showing a control procedure of output control of the fuel cell 10 executed by the control unit 20 in the fuel cell system as the fifth embodiment of the present invention. FIG. 19 is substantially the same as FIG. 13 except that steps S12 and S13 are added. FIG. 20 is a flowchart showing a control procedure of power generator protection control executed by the control unit 20 in the fuel cell system of the fifth embodiment. FIG. 20 is substantially the same as FIG. 17 except that step S149 is added.

  The configuration of the fuel cell system of the fifth embodiment is the same as that of the fuel cell system of the fourth embodiment (FIGS. 1 and 2). In the fuel cell system of the fifth embodiment, the control unit 20 executes the operation control while recording the history of control data during operation. The history of the control data to be recorded includes, for example, a time change in externally requested output, a time change in the output power of the fuel cell 10, and a time change in the SOC of the secondary battery 81.

  In the power generator protection control of the fifth embodiment, as described in the fourth embodiment, when the SOC of the secondary battery 81 is not within the allowable range (step S105), the Ir characteristic change control is performed. This is executed (steps S150 and S151). However, since the execution of the Ir characteristic change control may reduce the system efficiency and the fuel consumption of the fuel cell vehicle, the execution frequency is preferably reduced.

  Therefore, when the controller 20 of the fifth embodiment detects the possibility that the Ir characteristic change control is executed in the power generator protection control, the SOC of the secondary battery 81 is within an allowable range in advance. Control for adjustment is executed (steps S12 and S15 in FIG. 19). Specifically, it is as follows. For convenience of explanation, first, a case where Ir characteristic control is executed in the power generator protection control (FIG. 20) will be described.

  When it is determined in the power generator protection control that the SOC of the secondary battery 81 is outside the allowable range (step S105), the control unit 20 obtains the control data history in the predetermined period immediately before the sample history. Data is recorded in a nonvolatile manner (step S149). The control unit 20 sets the sample history data as data when the SOC of the secondary battery 81 is too low and out of the allowable range, and data when the SOC of the secondary battery 81 is too high and out of the allowable range. It is classified and accumulated. After recording the sample history data of the operation control, the control unit 20 executes the Ir characteristic change control (steps S150 and S151), and returns to the operation control of the fuel cell 10 (FIG. 19).

  In the operation control of the fuel cell 10, the control unit 20 receives a request for output from the outside (step S <b> 10), and then determines to detect the possibility that the Ir characteristic change control is executed in the power generator protection control. Processing is executed (step S12). Specifically, the sample history data accumulated by repeating the execution of the Ir characteristic change control of the power generator protection control (FIG. 20) is compared with the history of the control data in the immediately preceding predetermined period. And verify the similarity.

  When the control unit 20 detects that the accumulated sample history data includes data having a predetermined similarity with the history of the control data in a predetermined period up to the present, in the future operation, It is determined that the SOC of the secondary battery 81 may be out of the allowable range. In this case, the control unit 20 executes a process for changing the reference value for controlling the SOC of the secondary battery 81 (step S13).

  FIGS. 21A and 21B are schematic diagrams for explaining the effect of changing the SOC reference value in step S13. FIGS. 21A and 21B are graphs showing the time change of the SOC after the execution of the process of step S13. 21A and 21B, as a comparative example, a broken line graph showing the time change of the SOC when the process of step S13 is not executed is illustrated.

  In step S13, the control unit 20 increases the SOC reference value Cs when the sample history data having a predetermined similarity is data when the SOC falls outside the allowable range due to excessive decrease. Thus, in the subsequent operation control, the frequency of charging the secondary battery 81 can be increased, so that it is possible to avoid the SOC from being out of the allowable range due to the shortage of the SOC (FIG. 21A).

  On the other hand, when the sample history data having a predetermined similarity is data when the SOC is excessively increased and deviates from the allowable range, the control unit 20 decreases the SOC reference value Cs. Accordingly, in the subsequent operation control, the frequency of discharging to the secondary battery 81 can be increased, so that it is possible to avoid the SOC from being out of the allowable range due to excessive SOC (FIG. 21B).

  As described above, in the fuel cell system of the fifth embodiment, the control unit 20 learns the operation pattern in which the SOC is out of the allowable range based on the operation control history, and the SOC is out of the allowable range in advance. A state can be avoided. Therefore, the frequency with which the Ir characteristic change control is executed can be reduced, and the reduction in system efficiency and fuel cell vehicle fuel consumption can be suppressed while protecting the membrane electrode assembly 5 and the secondary battery 81. it can.

F. Example 6:
FIG. 22 is a schematic diagram showing the configuration of a fuel cell system 100A as a sixth embodiment of the present invention. FIG. 22 is substantially the same as FIG. 1 except that a travel route detection unit 93 is added. The electrical configuration of the fuel cell system 100A of the sixth embodiment is the same as that of the fuel cell system of the fifth embodiment (FIG. 2).

  The travel route detection unit 93 can be configured by a navigation device having a GPS function, for example, and can detect the current travel route of the fuel cell vehicle on which the fuel cell system 100A is mounted. The travel route detection unit 93 outputs information on the detected travel route to the control unit 20.

  FIG. 23 is a flowchart showing a control procedure of operation control of the fuel cell 10 executed by the control unit 20 in the fuel cell system 100A of the sixth embodiment. FIG. 23 is substantially the same as FIG. 19 except that step S12A is provided instead of step S12.

  In the fuel cell system 100A of the sixth embodiment, after receiving an output request from the outside (step S10), the control unit 20 determines the SOC of the secondary battery 81 based on the current travel route information of the fuel cell vehicle. A process of changing the reference value is executed (steps S12A, S13). Specifically, it is as follows.

  In step S <b> 12 </ b> A, the control unit 20 acquires altitude information of a place away from the current location by a predetermined distance in the traveling direction of the fuel cell vehicle based on the information on the travel route acquired from the travel route detection unit 93. When there is a predetermined altitude difference between the current location and the location ahead of the traveling direction of the fuel cell vehicle, the control unit 20 will drive the fuel cell vehicle uphill or downhill from now on. Judge that there is a possibility.

  On the other hand, if there is no such altitude difference between the current location and the location ahead of the traveling direction of the fuel cell vehicle, it is determined that the fuel cell vehicle continues to travel on a relatively flat route, The process after step S20 is executed. In the fuel cell system 100A of the sixth embodiment, the power generator protection control in step S40 is executed in the same control procedure as that of the fuel cell system of the fourth embodiment (FIG. 17).

  If it is determined in step S12A that the fuel cell vehicle is likely to travel uphill or downhill, the control unit 20 performs the same SOC as described in the fifth embodiment. A reference value changing process (step S13) is executed. Specifically, it is as follows.

  FIGS. 24A to 24D are schematic diagrams for explaining the processing contents of the SOC reference value changing process in step S13 and the effects of the process. FIGS. 24A and 24B each show a graph showing an example of the time change of the altitude of the fuel cell vehicle and an example of the time change of the SOC of the secondary battery 81 when the vehicle approaches a downhill in the middle of traveling. The graph shown is shown in association with the time axis.

  FIGS. 24C and 24D show graphs similar to the graphs of FIGS. 24A and 24B when the vehicle is approaching an uphill in the middle of traveling. FIGS. 24B and 24D show the SOC reference value Cs by a one-dot chain line, and show the time variation of the SOC when the SOC reference value is not changed, as a comparative example. Is indicated by a broken line.

  If a downhill is detected in the traveling direction of the fuel cell vehicle at time tp, the control unit 20 decreases the SOC reference value Cs in step S13 (FIGS. 24A and 24B). When the SOC reference value Cs is lowered, the frequency of discharge of the secondary battery 81 can be increased, so that the secondary battery 81 can be brought into a relatively low SOC state. Therefore, even when the fuel cell vehicle travels downhill after time t, it is possible to sufficiently store the surplus output of the fuel cell 10.

  On the other hand, when an uphill is detected in the traveling direction of the fuel cell vehicle at time tp, the control unit 20 increases the SOC reference value Cs in step S13 (FIGS. 24C and 24D). . When the SOC reference value Cs is increased, the frequency of charging the secondary battery 81 can be increased, so that the secondary battery 81 can be brought into a relatively high SOC state. Therefore, even when the fuel cell vehicle travels uphill after time t and the output of the fuel cell 10 is insufficient, the shortage can be reliably compensated for by the secondary battery 81.

  In addition, when the control unit 20 detects that the fluctuation range of the altitude information of the fuel cell vehicle is within a predetermined range and the downhill or the uphill is completed, the control unit 20 returns the SOC reference value Cs to the initial value again. It is good as a thing.

  As described above, in the fuel cell system of the sixth embodiment, the SOC of the secondary battery 81 is adjusted in advance based on the travel route of the fuel cell vehicle. Therefore, it is possible to suppress the SOC of the secondary battery 81 from being out of the allowable range, and it is possible to reduce the execution frequency of the Ir characteristic change control (FIG. 17).

G. Seventh embodiment:
FIG. 25 is a flowchart showing a control procedure of output control of the fuel cell 10 executed by the control unit 20 in the fuel cell system as the seventh embodiment of the present invention. FIG. 25 is substantially the same as FIG. 23 except that the determination condition in the determination process of step S12A is different and that step S14 is provided instead of step S13.

  The configuration of the fuel cell system of the seventh embodiment is the same as that of the fuel cell system of the sixth embodiment (FIGS. 22 and 2). Further, the control procedure of the power generator protection control (step S40) executed in the fuel cell system of the seventh embodiment is the same as that of the fuel cell system of the sixth embodiment (FIG. 17).

  In the fuel cell system of the seventh embodiment, when the control unit 20 detects an increase in the predetermined altitude in the traveling direction of the fuel cell vehicle from the output information of the travel route detection unit 93 in step S12A, the fuel cell vehicle. It is determined that there is a possibility of traveling uphill. In this case, the control unit 20 executes pre-processing for adjusting the operating temperature of the fuel cell 10 in step S14. As a result, the operating temperature of the fuel cell 10 is prevented from rising excessively as the fuel cell vehicle climbs, and the output current of the fuel cell 10 is increased as the operating temperature of the fuel cell 10 increases. Suppressing expansion of the limit range. Specifically, it is as follows.

  FIGS. 26A to 26C are schematic diagrams for explaining the processing contents of the pre-adjustment processing of the operating temperature of the fuel cell 10 in step S14 and the effects of the processing. FIG. 26 (A) shows a graph showing an example of the time change of the altitude of the fuel cell vehicle when the vehicle is going uphill during traveling.

  FIG. 26B shows a graph showing a change over time in the operating temperature of the fuel cell 10 whose time axis corresponds to the graph of FIG. In the graph of FIG. 26B, the target value Tt of the store temperature of the fuel cell 10 set by the control unit 20 is shown by a one-dot chain line. In FIG. 26B, as a comparative example, a graph showing a change over time in the operating temperature of the fuel cell 10 when the process of step S140 is not executed is shown by a broken line.

  FIG. 26C shows a graph showing the change over time of the limit range of the fuel cell 10 whose time axis corresponds to the graph of FIG. In FIG. 26C, changes in the two current values Ia and Ib that are the boundary values of the limit range are shown by solid lines, and the limit range sandwiched between the two current values Ia and Ib is hatched. . Further, in FIG. 26B, as a comparative example, a graph showing changes in the two current values Ia and Ib when the process of step S140 is not executed is illustrated by broken lines.

  When the control unit 20 detects a downhill in the traveling direction of the fuel cell vehicle at time tp, the control unit 20 decreases the target value Tt of the operating temperature of the fuel cell 10 as the operating temperature pre-adjustment process in step S14. Execute the process. As a result, before the fuel cell vehicle approaches an uphill at a subsequent time t, an increase in the operating temperature of the fuel cell 10 is suppressed and the operating temperature is kept relatively low (FIG. 26B).

  Here, as described in FIG. 6, the limit range of the output current of the fuel cell 10 is set so as to become narrower as the operating temperature of the fuel cell 10 becomes higher. Therefore, after execution of the process of step S14, the expansion of the limit range of the output current of the fuel cell 10 is suppressed to the extent that the increase in the operating temperature of the fuel cell 10 is suppressed (FIG. 26 (C )).

  As described above, according to the fuel cell system of the seventh embodiment, when an increase in the output of the fuel cell 10 is predicted, control for suppressing an increase in the operating temperature of the fuel cell 10 is executed in advance. Therefore, the expansion of the limit range of the output current of the fuel cell 10 accompanying the increase in the operating temperature of the fuel cell 10 is suppressed, and the load on the secondary battery 81 is reduced.

H. Variation:
The present invention is not limited to the above-described examples and embodiments, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.

H1. Modification 1:
In the above embodiment, in the power generator protection control, the target current Ita of the fuel cell 10 is set to the current value Ia or Ib that is the boundary value of the limit range. However, the target current Ita of the fuel cell 10 in the power generator protection control may not be set to the limit values boundary values Ia and Ib, and the target current Ita may be set to a value outside the limit range. That is, the target current Ita of the fuel cell 10 may be set to a value not more than the first boundary value Ia of the limit range or not less than the second boundary value Ib.

H2. Modification 2:
In the above embodiment, the limit range of the output current of the fuel cell 10 for each operating temperature of the fuel cell 10 is set in the Ir map. However, the output current limit range of the fuel cell 10 may be set to a certain range regardless of the operating temperature of the fuel cell 10.

H3. Modification 3:
In the above embodiment, the limit range of the output current of the fuel cell 10 is _defined by setting the limit value r _lim for the local resistance of the fuel cell 10 on the previously prepared Ir map. However, the limit range of the output current of the fuel cell 10 may be defined by other standards without using the limit map _rlim for the Ir map or the local resistance. The limit range of the output current of the fuel cell 10 may be defined based on, for example, stack resistance. Alternatively, the first and second current values Ia and Ib for defining the limit range may simply be set in advance for each operating temperature.

H4. Modification 4:
The Ir characteristic in the above embodiment can also be interpreted as one aspect of the characteristic representing the relationship between the current and the resistance in the fuel cell. In the above embodiment, the local resistance is an arbitrary value in the power generation region GA. It is possible to replace with the resistance of the place, the average resistance in the entire power generation area GA, the resistance in an arbitrary single cell 11, and the stack resistance. Therefore, the limit range in the above embodiment is the range of the resistance value measured when the membrane electrode assembly is in a dry state of a predetermined wetness or less in the relationship between the current and resistance in the membrane electrode assembly during power generation. It can also be interpreted as a current value range defined for. Further, in the third embodiment, the control unit 20 detects a change in the relationship between the output current and the resistance in the fuel cell 10, and when the change in the relationship deviates from a preset allowable range, It can be interpreted that the range of the resistance value serving as a reference for the change is changed.

H5. Modification 5:
In the fifth embodiment, the control unit 20 may cause the SOC to deviate from the allowable value based on the similarity between the sample history data recorded when the SOC is out of the allowable range and the history of the immediately previous control data. I was detecting sex. However, the control unit 20 does not need to detect the possibility that the SOC is out of tolerance based on the similarity between the sample history data and the history of the immediately preceding control data. The control unit 20 may detect the possibility that the SOC is out of tolerance when a predetermined operation pattern is detected in the history of the immediately preceding control data. The sample history data may not be data acquired in actual operation of the fuel cell system, but may be data prepared in advance.

H6. Modification 6:
In the sixth embodiment, when the control unit 20 detects a hill ahead of the traveling direction of the fuel cell vehicle based on the output information of the travel route detection unit 93, the SOC is likely to be out of the allowable range. The SOC reference value has been changed on the assumption that the fuel cell vehicle is facing the vehicle. However, the control unit 20 does not have to change the SOC when detecting a slope ahead of the traveling direction of the fuel cell vehicle, and the control unit 20 sets a predetermined route that is likely to be out of the allowable range. The SOC reference value may be changed when it is detected that the vehicle is moving. Similarly, in the seventh embodiment, the control unit 20 is moving toward a predetermined route that is set in advance as a route that is likely to have the operating temperature of the fuel cell 10 higher than a predetermined threshold value. Is detected, the coolant supply flow rate to the fuel cell 10 may be increased.

H7. Modification 7:
In the above embodiment, the fuel cell system is mounted on the vehicle. However, the fuel cell system of the above embodiment may be mounted on a moving body other than a vehicle, or may be fixedly installed in a building or facility.

DESCRIPTION OF SYMBOLS 1 ... Electrolyte membrane 2, 3 ... Electrode 5 ... Membrane electrode assembly 10 ... Fuel cell 11 ... Single cell 11c ... High temperature cell 20 ... Control part 30 ... Cathode gas supply system 31 ... Cathode gas piping 32 ... Air compressor 33 ... Air flow meter 34 ... On-off valve 35 ... Pressure measuring part 40 ... Cathode gas discharge system 41 ... Cathode exhaust pipe 43 ... Pressure regulating valve 44 ... Pressure measuring part 50 ... Anode gas supply system 51 ... Anode gas pipe 52 ... Hydrogen tank 53 ... Open / close valve 54 ... Regulator 55 ... Hydrogen supply device 56 ... Pressure measuring unit 60 ... Anode gas discharge system 61 ... Anode exhaust gas piping 66 ... Open / close valve 67 ... Pressure measuring unit 70 ... Refrigerant circulation supply system 71 ... Refrigerant piping 71a ... Upstream side piping 71b ... Downstream Side piping 71c ... Bypass piping 72 ... Radiator 73 ... Three-way valve 75 ... Refrigerant circulation pumps 76a, 76 ... Refrigerant temperature measurement part 81 ... Secondary battery 82 ... DC / DC converter 83 ... DC / AC inverter 90 ... Current measurement part 91 ... Voltage measurement part 92 ... SOC detection part 93 ... Travel route detection part 100, 100A ... Fuel cell system 200 ... Motor AR ... Allowable region LR ... Limited region DA ... Curve graph DCL ... DC wiring GA ... Power generation region HTR ... High temperature region

Claims (9)

A fuel cell system that outputs electric power according to an output request from the outside,
A fuel cell comprising a membrane electrode assembly ;
A control unit for controlling the output current of the fuel cell,
With
The controller sets a target current value It according to the output request, and executes a first control for causing the fuel cell to output a current of the target current value It ,
In the first control, when the target current value It is within a preset limit range, the control unit sets the target current value It as a boundary value of the limit range or outside the limit range. reconfigure the value, the target current value it of the current after resetting running toggle its processing to the second control to output to the fuel cell,
The limit range is a relationship between a resistance value measured when the membrane electrode assembly is in a dry state of a predetermined wetness or less in a relationship between current and resistance in the membrane electrode assembly during power generation. A range of defined current values, a range between a first current value Ia and a second current value Ib (Ib>Ia);
The target current value It can take a value smaller than the first current value Ia and can take a value larger than the second current value Ib . The fuel cell system according to claim 1 , wherein
A temperature detector for detecting the operating temperature of the fuel cell;
The limit range is set in advance for each operating temperature of the fuel cell,
The said control part is a fuel cell system which uses the said restriction | limiting range according to the present operating temperature of the said fuel cell in said 1st and 2nd control. The fuel cell system according to claim 1 or 2 , further comprising:
A secondary battery that functions as a power source together with the fuel cell;
A charge state detection unit for detecting a value indicating a charge state of the secondary battery;
With
The control unit switches between charging and discharging of the secondary battery based on a detection value of the charging state detection unit ,
In the second control, when the control is performed to cause the secondary battery to discharge, the control unit uses the target current value It set in the first control as the first current value Ia. The fuel cell system, which is reset to the following and resets the target current value It to be equal to or higher than the second current value Ib when the control for charging the secondary battery is being executed. The fuel cell system according to claim 3 , wherein
When the detection value of the charging state detection unit is out of a preset allowable range, the control unit
In the first control, even if the target current value It is set within the limit range, the power generation condition of the fuel cell is changed without switching to the second control, and the fuel cell A fuel cell system that executes a third control for outputting the current of the target current value It to the fuel cell in a state where deterioration of the fuel is suppressed. The fuel cell system according to claim 4 , wherein
The control unit stores in advance information indicating an operation pattern of the fuel cell, in which the detection value of the charging state detection unit is likely to be out of a preset allowable range,
Based on the information indicating the operation pattern of the fuel cell, when the possibility that the detection value of the charging state detection unit is out of the allowable range is detected, the reference for switching between charging and discharging of the secondary battery is changed. A fuel cell system that suppresses a detection value of the charging state detection unit from being out of the allowable range. The fuel cell system according to claim 4 , wherein
The fuel cell system is mounted on a moving body,
The fuel cell system further includes a movement information detection unit that detects movement information of the moving body,
Based on the movement information, the control unit is moving toward a predetermined route that is set in advance as a route in which the detection value of the charging state detection unit is likely to be out of the allowable range. When this is detected, the fuel cell system suppresses the detection value of the charge state detection unit from being out of the allowable range by changing a reference for switching between charging and discharging of the secondary battery. A fuel cell system according to any one of claims 3 to 5 dependent on claim 2 ,
The fuel cell system is mounted on a moving body,
The fuel cell system further includes:
A movement information detection unit for detecting movement information of the mobile body;
A refrigerant circulation supply system for supplying a refrigerant to the fuel cell and adjusting an operating temperature of the fuel cell;
With
Based on the movement information, the control unit is moving toward a predetermined route that is set in advance as a route that is likely to cause the operating temperature of the fuel cell to be higher than a predetermined threshold. When this is detected, a fuel cell system that increases a supply flow rate of the refrigerant to the fuel cell and suppresses an increase in operating temperature of the fuel cell. The fuel cell system as claimed in any one of claims 1 to 7,
Comprising a resistance detector for detecting resistance in the fuel cell;
The control unit detects a change in power generation characteristics represented by a relationship between output current and resistance in the fuel cell,
The fuel cell system, wherein when the change in the power generation characteristics deviates from a preset allowable range, a resistance value range serving as a reference for the limit range is changed. A control method for a fuel cell system comprising a fuel cell having a membrane electrode assembly ,
(A) receiving the output request from the outside, and a step of setting a target current value It of the fuel cell in accordance with the output request,
(B) when the target current value It is within a preset limit range, resetting the target current value It to a boundary value of the limit range or a value outside the limit range;
(C) outputting the current of the target current value It set in the step (a) or the step (b) to the fuel cell;
With
The limit range is a relationship between a resistance value measured when the membrane electrode assembly is in a dry state of a predetermined wetness or less in a relationship between current and resistance in the membrane electrode assembly during power generation. A range of defined current values, a range between a first current value Ia and a second current value Ib (Ia <IB);
The control method, wherein the target current value It can take a value smaller than the first current value Ia and can take a value larger than the second current value Ib.

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