JP2004193113A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system capable of improving fuel economy, and maintaining stable operation status, while extending the service life of the fuel cell. <P>SOLUTION: A mode determination switching part 45 determines if power generation current IFC of a fuel cell stack 12 detected by a power generation current/voltage detection part 44 is continuously generated for a predetermined period or higher, at a predetermined current level or higher, and switches the setting to stable mode or unstable mode based on the result of the determination. A pump flow rate calculation part 50, a purge parameter calculation part 46, a target air flow rate calculation part 34 and a target air pressure calculation part 36 calculate control parameters according to the set mode to control the supply gas supplied to the fuel cell stack 12 as well as to control the exhaust gas discharged from the fuel cell stack 12. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention provides a fuel cell that generates electric energy by reacting a hydrogen-containing gas supplied to an anode electrode and an oxygen-containing gas supplied to a cathode electrode, and the hydrogen-containing gas and the oxygen-containing gas for the fuel cell. The present invention relates to a fuel cell system including a supply adjustment unit that adjusts gas supply and an emission adjustment unit that adjusts emission of exhaust gas from the fuel cell.

  For example, in a polymer electrolyte fuel cell, an electrolyte membrane (electrolyte) / electrode structure in which an anode electrode and a cathode electrode are arranged on both sides of an electrolyte membrane composed of a polymer ion exchange membrane (cation exchange membrane) is separated by a separator. It is configured by pinching. This type of fuel cell is generally used as a fuel cell stack by laminating a predetermined number of electrolyte membrane / electrode structures and separators.

  In a fuel cell, a fuel gas, for example, a hydrogen-containing gas supplied to an anode electrode is hydrogen-ionized on an electrode catalyst, moves to a cathode electrode side through a moderately humidified electrolyte membrane, and during the movement. The generated electrons are taken out to an external circuit and used as DC electric energy. Since an oxidant gas, for example, an oxygen-containing gas such as air is supplied to the cathode electrode, hydrogen ions, electrons, and oxygen gas react at the cathode electrode to generate water.

  By the way, in such a fuel cell, the temperature is not sufficiently increased immediately after start-up, or impurities are accumulated due to the power generation state being continued for a long time, water is covered on the anode electrode surface, and the reaction gas is Is not supplied sufficiently, a situation occurs in which the generated voltage drops. Therefore, in order to maintain the life of the fuel cell and maintain an efficient power generation state, the flow rate and the pressure of the fuel gas and the oxidizing gas are appropriately controlled and supplied, and the exhaust gas including water is supplied at an appropriate timing. Must be discharged to the outside.

  Therefore, in the related art disclosed in Patent Document 1, a voltage generated by the fuel cell is detected, and when the generated voltage falls below the reference voltage, control is performed to discharge water or exhaust gas from the anode electrode to the outside. I have.

JP-A-2002-93438 (paragraphs [0025] to [0027])

  However, when a decrease in the power generation voltage is detected, the power generation capacity of the fuel cell has already been reduced due to the accumulation of water and impurities.If power generation is continued in this state, the life of the fuel cell is shortened, or With a delay in voltage recovery, there is a possibility that a current that can be taken out is limited.

  On the other hand, in order to quickly recover the power generation voltage, it is conceivable to quickly discharge exhaust gas or the like or to increase the supply amount of fuel gas or oxidizing gas.

  However, if the amount of exhaust gas or the like is increased, high-concentration hydrogen gas may be discharged to the outside with the discharge, and if the supply amount of the fuel gas or the oxidizing gas is increased, the fuel efficiency may be reduced. There is a possibility that it will decrease.

  The present invention is to solve this kind of problem, and to provide a fuel cell system that can extend the life of a fuel cell, improve fuel efficiency, and maintain a stable operation state. With the goal.

  According to the first aspect of the present invention, the operation state is determined by monitoring whether or not the generated current equal to or more than the reference current is continuously output for the reference time or more, and the control parameter is set according to the determination result, and By performing the supply control of the supply gas to the battery and / or the discharge control of the exhaust gas, the operation of the fuel cell can be continued in an optimum operation state without causing a decrease in the generated voltage.

  According to the second aspect of the present invention, when the generated current equal to or more than the first reference current continues for the first reference time or more, the operating state determination unit determines that the fuel cell is in a stable state, and based on the first control parameter for the stable time, The supply control of the supply gas and / or the discharge control of the exhaust gas are performed. When the generated current equal to or less than the second reference current continues for the second reference time or longer, the operation state determination unit determines that the state is unstable, and controls the supply of the supply gas to the fuel cell based on the second control parameter for the unstable time. And / or performing emission control of the exhaust gas to quickly shift the fuel cell to a stable state.

  According to the third aspect of the present invention, a control parameter, which is a flow rate of the hydrogen-containing gas, is calculated based on the determination result of the power generation state of the fuel cell. , The fuel cell can be operated in a desired state.

  According to the present invention, the supply adjusting section for controlling the flow rate of the hydrogen-containing gas is provided in the circulation loop connecting the gas supply port and the gas exhaust port of the anode electrode, and the supply control section is discharged from the gas exhaust port. The operating state of the fuel cell is optimized by adjusting the supplied hydrogen-containing gas to a desired flow rate and supplying it to the gas supply port.

  According to the fifth aspect of the present invention, a purge parameter for controlling discharge of exhaust gas to the outside and prohibition of discharge to the outside is calculated from the generated current and the determination result of the power generation state of the fuel cell. By performing exhaust gas emission control based on the exhaust gas, it is possible to operate the fuel cell in a desired state while controlling the concentration of hydrogen gas in the exhaust gas to be exhausted.

  Further, in the invention according to claim 6, the power generation voltage is reduced by calculating the target flow rate and the target pressure from the target power generation current and the determination result of the power generation state of the fuel cell and supplying the supply gas to the fuel cell. A desired generated current can be obtained without the need.

  Furthermore, in the invention according to claim 7, the temperature of the fuel cell is detected in addition to the generated current or the target generated current, and the control parameter is calculated based on the generated current or the target generated current and the temperature of the fuel cell. By operating the battery, the fuel cell can be operated in a more appropriate state.

  In the invention according to claim 8, the operating state of the fuel cell can be determined more accurately by detecting the temperature of the fuel cell and setting the reference current and the reference time according to the detected temperature.

  Further, according to the ninth aspect of the present invention, the temperature of the fuel cell is detected, the control parameter, the reference current, and the reference time are set according to the temperature, and the operating state of the fuel cell is determined based on these. In addition, the determination accuracy can be further improved.

  According to the present invention, the operating state of the fuel cell is determined based on the generated current, and the operating conditions are set based on the determination result. Can be planned. In addition, while the operating state is determined with high accuracy, the supply gas is appropriately supplied to the fuel cell, and the exhaust gas is appropriately discharged, so that the fuel efficiency can be improved. It can be suppressed and discharged to the outside.

  In addition, by detecting the temperature of the fuel cell and determining the operation state based on the temperature, the determination accuracy can be further improved, and the fuel cell can be operated more efficiently.

  FIG. 1 shows a fuel cell system 10 of the present embodiment. In FIG. 1, a line indicated by a double line indicates a gas flow path, and a line indicated by a single line indicates an electric signal line.

The fuel cell system 10 includes a fuel cell stack 12 (fuel cell) that generates electric energy by being supplied with hydrogen gas H _{2 as} a fuel gas (anode gas) and air as an oxidant gas (cathode gas). And a control device 14 (control unit) that controls fuel gas and oxidizing gas supplied to the fuel cell stack 12 and controls exhaust gas containing water discharged from the fuel cell stack 12. Is done.

The fuel cell stack 12 is configured by connecting in series a number of cells 16 formed by connecting an anode electrode supplied with hydrogen gas H ₂ and a cathode electrode supplied with air via an electrolyte membrane. In this case, the cooling unit 17 is connected to the fuel cell stack 12 to circulate and supply the cooling water to suppress an increase in the heat generation temperature due to the power generation and to keep the fuel cell stack 12 in an optimal temperature range.

The temperature θ _{W of the} cooling water supplied to the fuel cell stack 12 is detected by a cooling water temperature detecting unit 19 connected to the cooling unit 17. Further, the temperature θ _A of the hydrogen gas H ₂ supplied to the anode electrode is detected by the anode gas temperature detection unit 21. Further, the temperature θ _C of the air supplied to the cathode electrode is detected by the cathode gas temperature detection unit 23.

Hydrogen gas H ₂ from the hydrogen tank 18 is supplied to the gas supply port of the anode electrode of the fuel cell stack 12 at a predetermined pressure adjusted by the regulator 20. Air is compressed and supplied to the gas supply port of the cathode electrode of the fuel cell stack 12 by the compressor 22. In this case, the air output from the compressor 22, is supplied to the regulator 20, the pressure ratio of hydrogen gas H ₂ is adjusted by the pressure of the air. Upstream of the compressor 22, a flow rate detection unit 24 that detects the flow rate of air supplied to the cathode electrode is connected.

A hydrogen dilution box 28 is connected to a gas outlet of the anode electrode of the fuel cell stack 12 via a purge valve 26. Hydrogen gas H ₂ , which did not contribute to power generation in the fuel cell stack 12, water generated by power generation and permeated through the electrolyte membrane from the cathode electrode, and water contained in air and permeated through the electrolyte membrane from the gas discharge port The exhausted nitrogen gas and the like are exhausted. The purge valve 26 is constituted by an on / off valve, and discharges the exhaust gas to the hydrogen dilution box 28 as needed.

The gas outlet of the anode electrode is connected to the gas supply port through the pump 29, constituting circulation loop for supplying the hydrogen gas H ₂ to the fuel cell stack 12 again discharged without contributing to the power generation .

  A hydrogen dilution box 28 is connected to a gas outlet of the cathode electrode of the fuel cell stack 12 via a pressure control valve 30. Water generated by power generation is discharged from the gas discharge port, and a part of the air supplied from the gas supply port is discharged as exhaust gas. The pressure control valve 30 controls the pressure of the air supplied to the fuel cell stack 12 by adjusting the pressure of the exhaust gas.

The hydrogen dilution box 28 dilutes an exhaust gas containing hydrogen gas H ₂ discharged from the anode electrode via the purge valve 26 with an exhaust gas containing air discharged from the cathode electrode via the pressure control valve 30 and externally dilutes it. To be discharged.

The control device 14 includes a target generation current setting unit 32 that sets a target generation current by the fuel cell stack 12 and a target air flow calculation unit 34 (target value) that calculates a target air flow (target flow) for obtaining the target generation current. Calculation unit), a target air pressure calculation unit 36 (target value calculation unit) for calculating an optimum target air pressure (target pressure) for obtaining a target power generation current, and each cell 16 constituting the fuel cell stack 12. Current / voltage detector 44 for detecting current and voltage to be supplied, pump flow calculator 50 (hydrogen-containing gas flow calculator) for calculating the flow rate of hydrogen gas H ₂ by pump 29, and hydrogen gas H by purge valve 26. A purge parameter calculating unit 46 for calculating a purge parameter for performing the discharge control of No. ₂ , and an operation state of the fuel cell stack 12 being in a stable mode or unstable. A mode determination switching unit 45 (operation state determination unit) that determines whether the mode is the mode and performs switching.

The target air flow rate calculation unit 34 includes a target power generation current IFC _OB from the target power generation current setting unit 32, the coolant temperature θ _W detected by the coolant temperature detection unit 19, and a mode switching from the mode determination switching unit 45. The target air flow rate Q _O2 is calculated based on the signal. The calculated target air flow rate Q _O2 is supplied to the air flow rate adjustment unit 40. The air flow adjustment unit 40 is connected to the compressor 22 and adjusts the compressor 22 according to the air flow detected by the flow detection unit 24 and the target air flow Q _O2 supplied from the target air flow calculation unit 34.

Target air-pressure calculating unit 36, a target generated current IFC _OB from target generated current setting unit 32, and the temperature theta _W of the cooling water detected by the coolant temperature detecting section 19, the mode switching from the mode determination switching unit 45 The target air pressure P _O2 is calculated based on the signal. The calculated target air pressure P _O2 is supplied to the pressure control valve adjustment unit 42. The pressure control valve adjustment unit 42 is connected to the pressure control valve 30, and adjusts the pressure of the air supplied to the fuel cell stack 12 by adjusting the pressure control valve 30 according to the target air pressure P _O2 .

The pump flow rate calculation unit 50 determines the temperature θ _{W of the} cooling water detected by the cooling water temperature detection unit 19, the generation current IFC detected by the generation current / voltage detection unit 44, and the mode switching from the mode determination switching unit 45. The pump flow rate Q _H2 is calculated based on the signal. The calculated pump flow rate Q _H2 is supplied to the pump flow rate adjusting unit 43. The pump flow rate adjusting unit 43 adjusts the pump 29, adjusts the flow rate of the hydrogen gas H ₂ discharged from the discharge port of the fuel cell stack 12, and supplies the hydrogen gas H ₂ to the supply port of the fuel cell stack 12.

The purge parameter calculation unit 46 determines the temperature θ _{W of the} cooling water detected by the cooling water temperature detection unit 19, the generation current IFC detected by the generation current / voltage detection unit 44, and the mode switching from the mode determination switching unit 45. Based on the signal, an exhaust gas discharge time (purge time) during which the purge valve 26 is open and a discharge inhibition time (purge interval time) during which the purge valve 26 is closed are calculated.

The mode determination switching unit 45 includes a cooling water temperature θ _W detected by the cooling water temperature detection unit 19, a temperature θ _A of the hydrogen gas H ₂ detected by the anode gas temperature detection unit 21, and a cathode gas temperature detection unit 23. Whether the fuel cell stack 12 is operating in a stable state (stable mode) based on the detected air temperature θ _C , the generated current IFC and the minimum cell voltage Vcmin detected by the generated current / voltage detection unit 44, It is determined whether the apparatus is operating in an unstable state (unstable mode), and the determination result is used as a mode switching signal by the pump flow rate adjustment unit 43, the target air pressure calculation unit 36, the purge parameter calculation unit 46, and the pump flow rate calculation unit 50. Output.

The air flow rate adjusting unit 40 and the compressor 22, the pressure control valve adjusting unit 42, the pressure control valve 30, the pump flow rate adjusting unit 43, and the pump 29 adjust the supply of air and hydrogen gas H _{2 to} the fuel cell stack 12. Make up the part. Further, the purge valve adjustment unit 48 and the purge valve 26 constitute an emission adjustment unit that adjusts the discharge of exhaust gas including water discharged from the fuel cell stack 12.

  The fuel cell system 10 according to the present embodiment is basically configured as described above. Next, the operation thereof will be described with reference to the flowcharts shown in FIGS.

  First, in the control device 14, prior to the start of the power generation operation by the fuel cell stack 12, the unstable mode is set to the mode determination switching unit 45 (step S1). That is, at the beginning of power generation, the temperature of the fuel cell stack 12 has not risen to the optimum power generation temperature, and the previous state is always an operation stop state. When water is collected in a certain place in a stopped state, the water is concentrated in a part of the fuel cell stack 12 and the power generation becomes unstable, The unstable mode is set as the default.

Next, the target generation current IFC _OB is set in the target generation current setting unit 32 (step S2), and the cooling water temperature detection unit 19 detects the cooling water temperature θ _W of the fuel cell stack 12 controlled by the cooling unit 17. (Step S3).

Target air flow rate calculating section 34, a mode switching signal from the mode determination switching unit 45, and the coolant temperature theta _W detected by the coolant temperature detecting section 19, a target generated current IFC _OB from target generated current setting unit 32 Based on the above, a target air flow rate Q _O2 that can obtain the target power generation current IFC _OB is calculated using the target power generation current-target air flow rate map shown in FIG. 5 (step S4).

Here, the target generation current-target air flow rate map shown in FIG. 5 refers to a map indicated by a solid line when the operation of the fuel cell stack 12 is in the stable mode, and when the operation is in the unstable mode, the power generation efficiency is low. Therefore, a map indicated by a dotted line in which the increased target air flow rate Q _O2 can be supplied and power generation can be actively performed is referred to. If the cooling water temperature θ _W is high, power can be efficiently generated with a small air supply amount and a small hydrogen supply amount. Therefore, the target power generation current-target air flow rate map shows that the cooling water temperatures θ _W1 and θ _W 2 It is referred in accordance with the _{θ W 3 (θ W 1 <} θ W 2 <θ W 3).

In this case, the mode switching signal is set to the unstable mode in step S1, and the target air flow rate Q _O2 is calculated with reference to the target generated current-target air flow rate map shown by the dotted line in FIG.

The target air-pressure calculating unit 36, a mode switching signal from the mode determination switching unit 45, and the coolant temperature theta _W detected by the coolant temperature detecting unit 19, set by the target generated current setting unit 32 target based on the generated current IFC _OB, target generated current shown in FIG. 6 - using the target air pressure map, calculates a target air pressure P _O2 capable of obtaining the target generated current IFC _OB (step S5).

The target generation current-target air pressure map shown in FIG. 6 refers to a map indicated by a solid line when the operation of the fuel cell stack 12 is in the stable mode, and indicates that the power generation efficiency is in a low state when the operation is in the unstable mode. For this reason, a map indicated by a dotted line that can set the target air pressure P _O2 high is referred to. If the cooling water temperature θ _W is high, power can be efficiently generated with a small air supply amount and a small hydrogen supply amount. Therefore, the target power generation current-target air pressure map indicates that the cooling water temperatures θ _W1 and θ _W 2. Reference is made in accordance with θ _W 3 (θ _W 1 <θ _W 2 <θ _W 3).

In this case, the mode switching signal is set to the unstable mode in step S1, and the target air pressure P _O2 is calculated with reference to the target generated current-target air pressure map indicated by the dotted line in FIG.

Next, the air flow adjusting unit 40 controls the compressor 22 in accordance with the target air flow Q _O2 supplied from the target air flow calculating unit 34 and the air flow detected by the flow detecting unit 24, and adjusts the pressure control valve. The unit 42 controls the pressure control valve 30 according to the target air pressure P _O2 supplied from the target air pressure calculation unit 36 (Step S6).

By controlling the compressor 22 according to the target air flow rate Q _O2 , a predetermined amount of air is supplied to the cathode electrode of the fuel cell stack 12 via the flow rate detection unit 24. Further, the pressure of the air supplied to the fuel cell stack 12 is adjusted by controlling the pressure control valve 30 in accordance with the target air pressure P _O2 .

Part of the air output from the compressor 22 is supplied to the regulator 20 at a predetermined pressure. Therefore, the pressure ratio of the hydrogen gas H ₂ output from the hydrogen tank 18 to the air is adjusted by the regulator 20 and supplied to the anode electrode of the fuel cell stack 12. As a result, the oxygen gas contained in the air supplied to the cathode electrode, and the hydrogen gas H ₂ was supplied to the anode electrode reacts, electrical energy is generated (step S7).

When power generation by the fuel cell stack 12 is started, hydrogen gas H _{2 that} has not contributed to the reaction is discharged from the anode electrode. The hydrogen gas H ₂ is reused for power generation by being circulated to the gas supply port of the anode electrode by the pump 29 whose flow rate has been adjusted by the pump flow rate adjusting unit 43, as described later. In addition, water generated by the reaction is discharged from the cathode electrode of the fuel cell stack 12, and nitrogen gas contained in the air and oxygen gas that has not contributed to the reaction are discharged. In addition, a part of the water and the exhaust gas generated at the cathode electrode pass through the electrolyte membrane constituting the cell 16 and is also exhausted from the gas exhaust port of the anode electrode.

Here, in the fuel cell system 10, in order to maintain a stable power generation state, the cooling water temperature θ _W which is the temperature of the fuel cell stack 12, and the anode gas temperature θ which is the temperature of the hydrogen gas H ₂ supplied to the anode electrode. _A , the cathode gas temperature θ _C , which is the temperature of the air supplied to the cathode electrode, the generated current IFC, and the minimum cell voltage Vcmin of the cell 16 are monitored to control the flow rate and pressure of the supplied air and hydrogen gas H _2. Then, a process of discharging generated water, nitrogen gas not contributing to the reaction, extra air, and the like to the outside is performed.

  Therefore, the mode determination switching unit 45 determines whether the power generation state of the fuel cell stack 12 is in a stable state according to the flowchart shown in FIG. 3, and outputs the determination result as a mode switching signal (step S8).

For example, at the beginning of power generation, the power generation state of the fuel cell stack 12 is set to the unstable mode in step S1 (step S11). The mode determination switching unit 45 determines whether the cooling water temperature θ _W detected by the cooling water temperature detecting unit 19 is lower than the reference temperature θ _W0 (step S12), or the anode gas detected by the anode gas temperature detecting unit 21. When the temperature θ _A is lower than the reference temperature θ _A0 (step S13), or when the cathode gas temperature θ _C detected by the cathode gas temperature detector 23 is lower than the reference temperature θ _C0 (step S14), the fuel cell It is determined that the power generation state of the stack 12 is unstable, and the unstable mode is maintained and set (step S15).

The cooling water temperature θ _W , the anode gas temperature θ _A and the cathode gas temperature θ _C are provided for a certain period of time or longer, and on condition that the state where the temperature is lower than the reference temperature θ _W0 , θ _A0 or θ _C0 continues. The power generation state of the fuel cell stack 12 can be determined with high accuracy without being affected by noise.

On the other hand, when θ _W ≧ θ _W0 , θ _A ≧ θ _A0 , and θ _C ≧ θ _C0 due to the heat generation of the fuel cell stack 12 itself and an increase in the environmental temperature, the mode determination switching unit 45 sets the power generation current / It is determined whether or not the generated current IFC of the fuel cell stack 12 detected by the voltage detector 44 is equal to or more than the reference current i1 (step S16). If no current equal to or more than the reference current i1 is output, the reference time TM1 Is set to the timer time tm1 (step S17). Then, the unstable mode is maintained and set as the power generation state of the fuel cell stack 12 (step S15).

  When it is determined that the generated current IFC of the fuel cell stack 12 detected by the generated current / voltage detection unit 44 is equal to or more than the reference current i1 (step S16), the timer time tm1 set in step S17 becomes zero. It is determined whether or not it has been performed (step S18). As a result of the determination, when the timer time tm1 is not 0, after subtracting the time ΔT1 from the previous determination time in step S18 to the current determination time in step S18 from the timer time tm1 (step S19), Since the generated current IFC equal to or greater than the current i1 does not continue for the reference time TM1 or more, the unstable mode is maintained and set (step S15).

  When it is determined that the generated current IFC of the fuel cell stack 12 detected by the generated current / voltage detector 44 is equal to or more than the reference current i1 (step S16), and when the timer time tm1 = 0 (step S18), This means that the generated current IFC equal to or greater than the reference current i1 (first predetermined current) has continued for the reference time TM1 (first reference time).

  Therefore, based on the generated current IFC detected by the generated current / voltage detection unit 44, the mode determination switching unit 45 calculates the reference voltage V1 using the generated current-reference voltage map shown in FIG. 7 (Step S20). Next, it is determined whether or not the minimum cell voltage Vcmin of each cell 16 detected by the generated current / voltage detector 44 is higher than the reference voltage V1 (step S21). Is maintained (step S15). If it is determined that the minimum cell voltage Vcmin is higher than the reference voltage V1 (step S21), the power generation state of the fuel cell stack 12 is shifted to the stable state, and the stable mode is set (step S22). .

  On the other hand, when the power generation state of the fuel cell stack 12 has shifted to the stable mode (step S11), the power generation current IFC detected by the power generation current / voltage detection unit 44 is compared with the reference current i2 (i1> i2), When the generated current IFC is larger than the reference current i2 (step S23), the reference time TM2 (TM1 <TM2) is set to the timer time tm2 (step S24).

  Next, based on the generated current IFC detected by the generated current / voltage detection unit 44, the mode determination switching unit 45 calculates a reference voltage V2 (V1> V2) using a generated current-reference voltage map shown in FIG. (Step S25). Next, it is determined whether or not the minimum cell voltage Vcmin of each cell 16 detected by the generated current / voltage detection unit 44 is higher than the reference voltage V2 (step S26), and the state of the reference voltage V2 or lower continues for a predetermined time or longer. If not, the stable mode is maintained and set (step S22). If the time during which the minimum cell voltage Vcmin becomes equal to or higher than the reference voltage V2 has continued for a predetermined time or more (step S26), it is determined that the power generation state of the fuel cell stack 12 has transitioned to the unstable state, and the unstable mode is set. Is set (step S27).

  When it is determined that the generated current IFC of the fuel cell stack 12 detected by the generated current / voltage detection unit 44 is equal to or smaller than the predetermined current i2 (step S23), the timer time tm2 set in step S24 becomes zero. It is determined whether or not it has been performed (step S28). As a result of the determination, when the timer time tm2 is not 0, after subtracting the time ΔT2 from the previous determination time in step S28 to the current determination time in step S28 from the timer time tm2 (step S29), the generation current IFC Is calculated and compared with the minimum cell voltage Vcmin (steps S25 and S26). If the state below the reference voltage V2 has not continued for a predetermined time or more, the stable mode is maintained and set (step S22). If the time during which the minimum cell voltage Vcmin becomes equal to or higher than the reference voltage V2 continues for a predetermined time or longer, the unstable mode is set assuming that the power generation state of the fuel cell stack 12 has transitioned to the unstable state ( Step S27).

It should be noted that the reference currents i1 and i2 and the reference times TM1 and TM2 for determining the power generation state are set in a relationship of i1> i2 and TM1 <TM2. That is, when the fuel cell stack 12 is set to the unstable mode, the lower limit reference current i1, which is the determination criterion, is set higher, while the lower limit reference time during which the generated current IFC higher than the reference current i1 continues. By setting TM1 to be short, the criterion for switching the fuel cell stack 12 to the operation in the stable mode is strict, and the life of the fuel cell stack 12 can be extended. When the fuel cell stack 12 is set to the stable mode, the lower limit reference current i2 is set lower, while the lower limit reference time TM2 during which the generated current IFC lower than the reference current i2 continues is set longer. it allows loosely criteria for switching the fuel cell stack 12 in operation in the unstable mode, thereby improving the fuel economy, it is possible to suppress the increase in the concentration of the hydrogen gas H ₂ to be discharged to the outside.

  Next, the target air flow rate calculating section 34, the target air pressure calculating section 36, the purge parameter calculating section 46, and the pump flow rate calculating section 50 execute the mode obtained by the mode determination switching section 45 according to the flowchart shown in FIG. Based on the switching signal, the operating conditions of the air flow adjustment unit 40, the pressure control valve adjustment unit 42, the purge valve adjustment unit 48, and the pump flow adjustment unit 43 are set (step S9).

  First, a case where the power generation state of the fuel cell stack 12 is set to the stable mode will be described (step S41).

The pump flow rate calculating section 50 is based on the generated current IFC detected by the generated current / voltage detecting section 44 and the coolant temperature θ _W of the fuel cell stack 12 by the cooling section 17 detected by the coolant temperature detecting section 19. A required pump flow rate Q _H2 is calculated using the generated current-pump flow rate map shown in FIG. 8 and supplied to the pump flow rate adjusting unit 43 (step S42). In this case, since the operation of the fuel cell stack 12 is in the stable mode, the pump flow rate Q _H2 (first control parameter) is calculated using the generated current-pump flow rate map shown by the solid line.

For example, if the cooling water temperature theta _W was _{θ W 1 <θ W 2 <} θ W 3, the higher the cooling water temperature theta _W is, power generation because the efficiency is considered to be high, a small pump flow rate Q _H2 pump flow rate adjustment This is set in the section 43. When the cooling water temperature θ _W is low, the power generation efficiency is considered to be low, and therefore, a larger pump flow rate Q _H2 is set in the pump flow rate adjusting unit 43.

In addition, the purge parameter calculation unit 46 determines the generation current shown in FIG. 9 based on the generation current IFC detected by the generation current / voltage detection unit 44 and the cooling water temperature θ _W detected by the cooling water temperature detection unit 19. Using the purge time map and the generated current-purge interval time map shown in FIG. 10, the purge time T _ON with the purge valve 26 open and the purge interval time T _OFF with the purge valve 26 closed are calculated. Then, the power is supplied to the purge valve adjustment unit 48 (Steps S43 and S44). In this case, since the operation of the fuel cell stack 12 is in the stable mode, the purge time T _ON (first control) is calculated using the generated current-purge time map shown by the solid line and the generated current-purge interval time map shown by the solid line. And a purge interval time T _OFF (first control parameter).

For example, when the cooling water temperature θ _{W is set} to θ _W 1 <θ _W 2 <θ _W 3, if the cooling water temperature θ _W is high, the power generation efficiency is high and a small amount of supply gas is supplied to the fuel cell stack 12. It is considered that the power generation can be efficiently performed and the amount of the exhaust gas including the discharged water is also small. Therefore, the short purge time T _ON and the long purge interval time T _OFF are set. Further, when the cooling water temperature theta _W is low, the power generation efficiency is low, it is necessary to supply a large amount of feed gas to the fuel cell stack 12, thus, considered to exhaust gas containing a large amount of water is also discharged Therefore, a long purge time T _ON and a short purge interval time T _OFF are set.

Further, the target air flow rate calculation unit 34 and the target air pressure calculation unit 36 determine the generation current IFC detected by the generation current / voltage detection unit 44 and the cooling water temperature detection unit 19 in the same manner as in steps S4 and S5. Based on the detected cooling water temperature θ _W , a target air flow rate is calculated using a target power generation current-target air flow map shown by a solid line in FIG. 5 and a target power generation current-target air pressure map shown by a solid line in FIG. Q _O2 (first control parameter) and target air pressure P _O2 (first control parameter) are calculated (steps S45 and S46).

Next, when there is a switch from the unstable mode to the stable mode between the previous operation condition setting and the current operation condition setting (step S47), the target air in the stable mode calculated in step S45 is calculated. Using the flow rate Q _O2ST , the target air flow rate Q _O2UN in the unstable mode calculated in step S50 described later, and the air flow rate switching time Δt, an air flow rate change rate ΔQ / Δt is calculated, for example,
ΔQ / Δt = F · (Q _O2ST −Q _O2UN ) / Δt
(Step S48). Note that F is set to plus (+) when the mode is switched from the unstable mode to the stable mode, and is set to minus (-) when the mode is switched from the stable mode to the unstable mode.

  After each operating condition in the stable mode is set as described above, power generation by the fuel cell stack 12 is continued according to the operating condition (steps S10 and S7).

That is, the air flow adjusting unit 40 adjusts the compressor 22 and supplies the air having the target air flow rate Q _O2 calculated in step S45 to the cathode electrode of the fuel cell stack 12. Further, the pressure control valve adjustment unit 42 adjusts the pressure control valve 30 and controls the discharge of the air composed of the target air pressure P _O2 calculated in step S46. At this time, the regulator 20 supplies the hydrogen gas H ₂ from the hydrogen tank 18 to the anode electrode of the fuel cell stack 12 according to the air pressure controlled by the pressure control valve 30. As a result, the oxygen gas reacts with the hydrogen gas H ₂ in the fuel cell stack 12 to generate electric energy.

In addition, when switching from the unstable mode to the stable mode is performed between the time of setting the previous operation condition and the time of setting the current operation condition, the target air flow rate Q _O2 may greatly fluctuate. Therefore, the air flow rate adjusting section 40, a compressor 22 is driven in accordance with an air flow rate variation rate Delta] Q / Delta] t calculated in step S48, the the target air flow rate Q _O2ST in a stable mode from the target air flow rate Q _O2UN in unstable modes Then, the flow rate is gradually switched (see FIG. 11). Thereby, a sense of incongruity due to a sudden change in the flow rate can be suppressed.

Along with the operation of the fuel cell stack 12, a part of the air and water generated by the reaction are discharged from the cathode electrode of the fuel cell stack 12. From the anode electrode, hydrogen gas H ₂ not contributing to the reaction and water and nitrogen gas permeating from the cathode side through the electrolyte membrane are discharged. Among these, the hydrogen gas H _{2 that} has not contributed to the reaction is reused by being returned to the fuel cell stack 12 by the pump 29 via the circulation loop. In this case, the pump flow rate adjusting unit 43 adjusts the pump 29, controls the supply of the hydrogen gas H ₂ by the pump flow rate Q _H2 supplied from the pump flow rate calculating unit 50 is calculated in step S42.

On the other hand, the purge valve adjustment unit 48 controls the purge valve 26 to be ON / OFF according to the purge time T _ON and the purge interval time T _OFF calculated in steps S43 and S44, and discharges the exhaust gas including the hydrogen gas H ₂ from the fuel cell stack 12. Discharge to the outside.

In this case, the exhaust gas mainly composed of the air discharged from the cathode electrode of the fuel cell stack 12 is supplied to the hydrogen dilution box 28 via the pressure control valve 30. The exhaust gas including the hydrogen gas H ₂ discharged from the anode electrode of the fuel cell stack 12 is supplied to the hydrogen dilution box 28 during the purge time T _{ON when} the purge valve 26 is open, and the exhaust gas from the cathode electrode is exhausted. The gas dilutes the concentration of the hydrogen gas H ₂ and is discharged to the outside. After the purge time T _ON has elapsed, the purge valve 26 is closed for the purge interval time T _OFF . Then, the exhaust gas containing the hydrogen gas H ₂ discharged from the anode electrode is returned to the supply side by the pump 29, and the power generation is continued.

  Next, a case where the power generation state of the fuel cell stack 12 is set to the unstable mode will be described (step S41).

The pump flow rate calculating unit 50 calculates a required pump flow rate Q _H2 (second control parameter) using the generated current-pump flow rate map shown by the dotted line in FIG. 8 and supplies the calculated pump flow rate Q _H2 to the pump flow rate adjusting unit 43 (step S49). ). In this case, the pump flow rate Q _H2 is increased as compared with the case where the stable mode is set, so that more hydrogen gas H ₂ is supplied to the fuel cell stack 12, which is expected to increase the generated current. The operation of the fuel cell stack 12 shifts from an unstable state to a stable state without a situation in which the generated voltage decreases.

Further, the purge parameter calculation unit 46 uses the generated current-purge time map and the generated current-purge interval time map shown by the dotted lines in FIGS. 9 and 10 to generate the necessary purge time T _ON (second control parameter) and purge. An interval time T _OFF (second control parameter) is calculated and supplied to the purge valve adjustment unit 48 (Steps S50 and S51). For example, as shown in FIG. 12, when the power generation current IFC _ST in the stable mode becomes the power generation current IFC _UN (IFC _UN <IFC _ST ) in the unstable mode, a large amount of water generated by the reaction in the fuel cell stack 12 becomes large. The power generation efficiency may be reduced, and the generated voltage may also be reduced. Therefore, by setting the purge time T _ONUN , which is the opening time of the purge valve 26 in the unstable mode, longer than the purge time T _ONST in the stable mode, water can be discharged to the outside as much as possible. Similarly, the purge interval time T _OFFUN a closure time of the purge valve 26 in an unstable mode, short to set than the purge interval time T _offst in a stable mode. As a result, an increase in the generated current is expected, and the operation of the fuel cell stack 12 shifts from an unstable state to a stable state.

The target air flow rate calculating section 34 and the target air pressure calculating section 36 use the target generated current-target air flow rate map and the target generated current-target air pressure map shown by the dotted lines in FIGS. Q _O2 (second control parameter) and target air pressure P _O2 (second control parameter) are calculated (steps S52 and S53).

  Further, when the mode is switched from the stable mode to the unstable mode (Step S47), the air flow rate change rate ΔQ / Δt is calculated in the same manner as described above (Step S48).

After each operating condition in the unstable mode is set as described above, power generation by the fuel cell stack 12 is continued according to the operating condition (steps S10 and S7). In this case, the reaction by the flow of air and hydrogen gas H ₂ is supplied to the fuel cell stack 12 is increased is accelerated transition to a stable state from the operation unstable state of the fuel cell stack 12 generated current is increased It is expected to be.

When the mode is switched from the stable mode to the unstable mode, the air flow adjusting unit 40 drives the compressor 22 according to the air flow rate change rate ΔQ / Δt calculated in step S48, and sets the target air flow rate in the stable mode. gradually carry out the switching of the flow rate from the Q _O2ST to the target air flow rate Q _O2UN of an unstable mode (see Figure 11). As a result, it is possible to suppress the generation of noise due to a rapid change in the flow rate.

In the above-described embodiment, the reference current i1 and the reference time TM1 are set as fixed values to determine the operating state of the fuel cell stack 12 (steps S16 to S19). However, as shown in the flowchart of FIG. it may be these parameters to be set according to the coolant temperature theta _W.

That is, when the power generation state of the fuel cell stack 12 is set to the unstable mode (step S11), based on the coolant temperature θW detected by the coolant temperature detector 19, the coolant temperature _−W shown in FIG. The reference current i1 is calculated using the reference current map (step S61). In this case, the reference current i1 is, the higher the cooling water temperature theta _W is, the fuel cell stack 12 is considered to be stable, it is set to a small value.

Further, based on the coolant temperature theta _W detected by the coolant temperature detecting section 19, the coolant temperature is shown in Figure 15 - to calculate the reference time TM1 with a reference current map (step S62). In this case, the reference time TM1 is, the higher the cooling water temperature theta _W is, the fuel cell stack 12 is considered to be stable, is set to be shorter.

Then, the coolant temperature theta _W reference current i1 and the reference time TM1 which is set in accordance with the using the generated current IFC detected by the power generation current / voltage detecting unit 44, in step S16~S19 shown in FIG. 3 By performing the processing, the operation state of the fuel cell stack 12 is determined, and the unstable mode or the stable mode is set (steps S15 and S22).

In this case, since the reference current i1 and the reference time TM1 is a parameter for the mode determination can be set according to the coolant temperature theta _W, it is possible to further improve the mode determination accuracy.

  On the other hand, when the power generation state of the fuel cell stack 12 is set to the stable mode (step S11), the processing of steps S23 to S26, S28, and S29 shown in FIG. The determination is made, and the unstable mode or the stable mode is set (steps S22 and S27).

In the above-described embodiment, whether the operating state of the fuel cell stack 12 is stable or unstable is determined by the generated current IFC, the minimum cell voltage Vcmin, the cooling water temperature θ _W , the anode gas temperature θ _A and Judgment is made based on the cathode gas temperature θ _C, and the operating conditions are set according to the judgment result. For example, three or more operation states such as a stable state, a metastable state, and an unstable state are set. The determination may be made separately for each state, and the operating condition may be set according to each determination result.

1 is a configuration block diagram of a fuel cell system according to an embodiment of the present invention. 2 is a processing flowchart in a control device in the fuel cell system shown in FIG. 1. 3 is a flowchart of a mode determination switching process in the flowchart shown in FIG. 3 is a flowchart of an operating condition setting process in the flowchart shown in FIG. 2. FIG. 4 is an explanatory diagram of a target generated current-target air flow rate map. FIG. 5 is an explanatory diagram of a target generated current-target air pressure map. FIG. 4 is an explanatory diagram of a generated current-reference voltage map. FIG. 4 is an explanatory diagram of a generated current-pump flow rate map. FIG. 4 is an explanatory diagram of a generated current-purge time map. FIG. 4 is an explanatory diagram of a generated current-purge interval time map. FIG. 8 is an explanatory diagram of an air flow rate adjustment process at the time of mode switching. FIG. 4 is a diagram illustrating a relationship among a generated current, a pump flow rate, and an open / closed state of a purge valve. It is a flow chart of mode judgment change processing in other embodiments. FIG. 4 is an explanatory diagram of a cooling water temperature-reference current map. It is explanatory drawing of a cooling water temperature-reference time map.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 10 ... Fuel cell system 12 ... Fuel cell stack 14 ... Control device 17 ... Cooling part 18 ... Hydrogen tank 19 ... Cooling water temperature detecting part 20 ... Regulator 21 ... Anode gas temperature detecting part 22 ... Compressor 23 ... Cathode gas temperature detecting part 24 ... Flow detection unit 26 ... Purge valve 28 ... Hydrogen dilution box 30 ... Pressure control valve 32 ... Target power generation current setting unit 34 ... Target air flow calculation unit 36 ... Target air pressure calculation unit 40 ... Air flow adjustment unit 42 ... Pressure control valve adjustment Unit 43: Pump flow adjusting unit 44: Generated current / voltage detecting unit 45: Mode determination switching unit 46: Purge parameter calculating unit 48: Purge valve adjusting unit 50: Pump flow calculating unit

Claims (9)

A fuel cell that generates electric energy by reacting a hydrogen-containing gas supplied to an anode electrode with an oxygen-containing gas supplied to a cathode electrode; and supplying the hydrogen-containing gas and the oxygen-containing gas to the fuel cell. In a fuel cell system including a supply adjustment unit that adjusts and an emission adjustment unit that adjusts emission of exhaust gas from the fuel cell,
A generated current detection unit that detects a generated current output from the fuel cell,
An operation state determination unit that determines an operation state of the fuel cell by whether or not the generated current equal to or more than a reference current is continuously output for a reference time or more;
A control unit that sets a control parameter according to a determination result by the operation state determination unit and controls the supply adjustment unit and / or the discharge adjustment unit based on the control parameter;
A fuel cell system comprising: The system according to claim 1,
The operation state determination unit determines that the stable state is established when the generated current equal to or greater than the first reference current continues for the first reference time, and the output state of the generated current equal to or less than the second reference current is equal to or greater than the second reference time If it continues, it is judged as unstable,
The control unit, when determined to be in the stable state, sets a first control parameter for a stable time according to the generated current, and based on the first control parameter, the supply control unit and / or the discharge control unit Controlling the supply control unit and the discharge control unit based on the second control parameter based on the second control parameter. A fuel cell system comprising: The system according to claim 1,
The control unit has a hydrogen-containing gas flow rate calculation unit that calculates the flow rate of the hydrogen-containing gas that is the control parameter according to the determination result of the generated current and the operating state,
The fuel cell system according to claim 1, wherein the supply adjusting unit adjusts the supply of the hydrogen-containing gas based on the calculated flow rate. The system according to claim 3,
The supply adjusting unit is disposed in a circulation loop connecting a gas supply port and a gas exhaust port of an anode electrode in the fuel cell, and based on the flow rate calculated by the hydrogen-containing gas flow rate calculation unit, the gas exhaust rate A fuel cell system, wherein the hydrogen-containing gas discharged from a port is circulated and supplied to the gas supply port. The system according to claim 1,
The control unit has a purge parameter calculation unit that calculates a purge parameter that is the control parameter that controls emission of the exhaust gas, according to the determination result of the generated current and the operation state,
The fuel cell system according to claim 1, wherein the discharge adjusting unit controls the discharge of the exhaust gas to the outside and the prohibition of the discharge of the exhaust gas based on the calculated purge parameter. The system according to claim 1,
The control unit has a target value calculation unit that calculates a target flow rate and a target pressure of the supply gas, which are the control parameters, according to the target power generation current and the determination result of the operation state.
The fuel cell system according to claim 1, wherein the supply adjusting unit controls supply of the supply gas based on the calculated target flow rate and the target pressure. The system according to any one of claims 1 to 6,
A temperature detecting unit that detects a temperature of the fuel cell,
The fuel cell system according to claim 1, wherein the control unit calculates the control parameter according to the generated current or the target generated current and the temperature. The system according to any one of claims 1 to 6,
A temperature detecting unit that detects a temperature of the fuel cell,
The fuel cell system according to claim 1, wherein the operation state determination unit determines an operation state of the fuel cell according to the reference current and the reference time set according to the temperature of the fuel cell. 9. The system according to claim 8, wherein
The fuel cell system according to claim 1, wherein the control unit calculates the control parameter according to the generated current or the target generated current and the temperature.

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