JP6136185B2 - Fuel cell system - Google Patents

Description

  The present invention relates to a fuel cell system.

  In the conventional fuel cell system, when the required output of the fuel cell stack decreases, the fuel cell system is controlled so that the internal moisture content of the fuel cell stack increases. Thus, when the required output of the fuel cell stack is reduced, overdrying of the electrolyte membrane due to the high temperature of the fuel cell stack is suppressed (see Patent Document 1).

JP 2006-286436 A

  However, it has been found that if the fuel cell system is controlled so that the internal moisture content of the fuel cell stack increases when the required output of the fuel cell stack is small, the internal moisture content of the fuel cell stack becomes excessive.

  The present invention has been made paying attention to such problems, and an object thereof is to appropriately control the internal moisture content of the fuel cell stack when the required output of the fuel cell stack is lowered.

The present invention is a fuel cell system that generates power by supplying anode gas and cathode gas to a fuel cell. The fuel cell system includes a steady-state internal moisture amount control means for controlling a parameter affecting the internal moisture content of the fuel cell based on the target internal moisture content and the actual moisture content of the fuel cell, and a fuel cell When the required output is reduced, the parameter affecting the internal moisture content of the fuel cell set by the steady-state internal moisture content control means is corrected so that the internal moisture content of the fuel cell is increased. Correction means. Then, when the required output lowering correction means has a small amount of reduction in the required output of the fuel cell, the parameter is corrected in a transient state after the required output lowering, and the internal output corresponding to the reduced required output is corrected. a correction increment against the water content, characterized by smaller than when the output reduction amount is large.

    According to the present invention, when the required output decrease of the fuel cell is small, that is, when the temperature decrease of the fuel cell is small, the amount of internal moisture by the required output decrease correcting means increases compared to when the required decrease is large. The amount of correction was reduced. Thereby, the internal moisture content of the fuel cell when the required output of the fuel cell is reduced can be appropriately controlled.

1 is a schematic view of a fuel cell system according to a first embodiment of the present invention. It is the figure which showed the mode of the change of stack cooling water temperature when the request | requirement output power of a fuel cell stack fell. 3 is a flowchart illustrating internal water content control of the fuel cell stack according to the first embodiment of the present invention. 7 is a table for calculating a cathode flow rate, a cathode pressure, a cathode humidity, and a cooling water flow rate during a transition after the required output power is reduced based on a stack cooling water temperature fluctuation range. FIG. 5 is a map for calculating a cathode flow rate, a cathode pressure, a cathode humidity, and a cooling water flow rate during a transition after the required output power has been reduced based on a stack cooling water temperature fluctuation range and a stack inflow cooling water temperature. 6 is a flowchart illustrating internal water content control of a fuel cell stack according to a third embodiment of the present invention. It is the figure which showed a mode when the request | requirement output power of a fuel cell stack fell. It is the figure which showed a mode when the request | requirement output power of a fuel cell stack fell.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
In a fuel cell, an electrolyte membrane is sandwiched between an anode electrode (fuel electrode) and a cathode electrode (oxidant electrode), an anode gas containing hydrogen in the anode electrode (fuel gas), and a cathode gas containing oxygen in the cathode electrode (oxidant) Electricity is generated by supplying gas. The electrode reaction that proceeds in both the anode electrode and the cathode electrode is as follows.

Anode electrode: 2H ₂ → 4H ⁺ + 4e ⁻ (1)
Cathode electrode: 4H ⁺ + 4e ⁻ + O ₂ → 2H ₂ O (2)

  The fuel cell generates an electromotive force of about 1 volt by the electrode reactions (1) and (2).

  When such a fuel cell is used as a power source for automobiles, a large amount of electric power is required, so that it is used as a fuel cell stack in which several hundred fuel cells are stacked. Then, a fuel cell system that supplies anode gas and cathode gas to the fuel cell stack is configured, and electric power for driving the vehicle is taken out.

  FIG. 1 is a schematic diagram of a fuel cell system 100 according to a first embodiment of the present invention.

  The fuel cell system 100 includes a fuel cell stack 1, an anode gas supply / discharge device 2, a cathode gas supply / discharge device 3, a stack cooling device 4, and a controller 5.

  The fuel cell stack 1 is formed by stacking a plurality of fuel cells. The fuel cell stack 1 generates electric power by receiving supply of anode gas and cathode gas, and a motor (not shown) required to drive the generated electric power. Supplied to various electrical components such as

  The anode gas supply / discharge device 2 includes a high pressure tank 21, an anode gas supply passage 22, an anode pressure regulating valve 23, an anode gas discharge passage 24, an anode gas recirculation passage 25, a recycle compressor 26, a discharge valve 27, Is provided.

  The high-pressure tank 21 stores the anode gas supplied to the fuel cell stack 1 while maintaining the high-pressure state.

  The anode gas supply passage 22 is a passage through which the anode gas supplied to the fuel cell stack 1 flows. One end of the anode gas supply passage 22 is connected to the high-pressure tank 21 and the other end is connected to the anode gas inlet hole 11 of the fuel cell stack 1.

  The anode pressure regulating valve 23 is provided in the anode gas supply passage 22. The anode pressure regulating valve 23 is controlled to be opened and closed by the controller 5 and adjusts the pressure of the anode gas flowing out from the high-pressure tank 21 to the anode gas supply passage 22 to a desired pressure.

  The anode gas discharge passage 24 is a passage through which the anode off gas discharged from the fuel cell stack 1 flows. One end of the anode gas discharge passage 24 is connected to the anode gas outlet hole 12 of the fuel cell stack 11 and the other end is an open end. The anode off gas is a mixed gas of excess anode gas that has not been used in the electrode reaction and an inert gas such as nitrogen that has leaked from the cathode side.

  The anode gas recirculation passage 25 is a passage for returning the anode off gas discharged to the anode gas discharge passage 24 to the anode gas supply passage 22. One end of the anode gas recirculation passage 25 is connected to the anode gas discharge passage 24 upstream of the discharge valve 27, and the other end is connected to the anode gas supply passage 22 downstream of the anode pressure regulating valve 23.

  The recycle compressor 26 is provided in the anode gas recirculation passage 25. The recycle compressor 26 returns the anode off gas discharged to the anode gas discharge passage 24 to the anode gas supply passage 22.

  The discharge valve 27 is provided in the anode gas discharge passage 24 on the downstream side of the connection portion between the anode gas discharge passage 24 and the anode gas recirculation passage 25. The discharge valve 27 is controlled to be opened and closed by the controller 5, and discharges anode off gas and condensed water to the outside of the fuel cell system 100.

  The cathode gas supply / discharge device 3 includes a cathode gas supply passage 31, a cathode gas discharge passage 32, a filter 33, a cathode compressor 34, an air flow sensor 35, and a water recovery device (hereinafter referred to as “WRD”). ) 36, a WRD bypass passage 37, a humidification control valve 38, a pressure sensor 39, and a cathode pressure regulating valve 40.

  The cathode gas supply passage 31 is a passage through which the cathode gas supplied to the fuel cell stack 1 flows. The cathode gas supply passage 31 has one end connected to the filter 33 and the other end connected to the cathode gas inlet hole 13 of the fuel cell stack 1.

  The cathode gas discharge passage 32 is a passage through which the cathode off gas discharged from the fuel cell stack 1 flows. One end of the cathode gas discharge passage 32 is connected to the cathode gas outlet hole 14 of the fuel cell stack 1, and the other end is an open end. The cathode off gas is a mixed gas of the cathode gas and water vapor generated by the electrode reaction.

  The filter 33 removes foreign matters in the cathode gas taken into the cathode gas supply passage 31.

  The cathode compressor 34 is provided in the cathode gas supply passage 31. The cathode compressor 34 takes air (outside air) as cathode gas into the cathode gas supply passage 31 through the filter 33 and supplies the air to the fuel cell stack 1.

  The air flow sensor 35 is provided in the cathode gas supply passage 31 downstream of the cathode compressor 34. The air flow sensor 35 detects the flow rate of the cathode gas flowing through the cathode gas supply passage 31 (hereinafter referred to as “cathode flow rate”).

  The WRD 36 is a device that collects moisture in the cathode off-gas and humidifies the cathode gas with the collected moisture, and includes a humidifying unit 361 and a dehumidifying unit 362.

  The humidifying unit 361 is provided in the cathode gas supply passage 31 downstream of the air flow sensor 35. The humidification unit 361 humidifies the cathode gas supplied to the fuel cell stack 1.

  The dehumidifying unit 362 is provided in the cathode gas discharge passage 32. The dehumidifying unit 362 dehumidifies the cathode off gas flowing through the cathode gas discharge passage 32 and supplies the recovered water vapor to the humidifying unit 361.

  The WRD bypass passage 37 is connected to the cathode gas supply passage 31 so as to bypass the humidifying part 361 of the WRD 36.

  The humidification control valve 38 is provided in the WRD bypass passage 37. The humidification control valve 38 is controlled to be opened and closed by the controller 5 and adjusts the humidity of the cathode gas supplied to the fuel cell stack 1 (hereinafter referred to as “cathode humidity”) to a desired humidity.

  The pressure sensor 39 is provided in the cathode gas supply passage 31 downstream of the humidifying unit 361 of the WRD 36. The pressure sensor 39 detects the pressure of the cathode gas supplied to the fuel cell stack 1 (hereinafter referred to as “cathode pressure”).

  The cathode pressure regulating valve 40 is provided in the cathode gas discharge passage 32 downstream of the dehumidifying part 362 of the WRD 36. The cathode pressure regulating valve 40 is controlled to be opened and closed by the controller 5, and adjusts the pressure of the cathode gas (cathode pressure) supplied to the fuel cell stack 1 to a desired pressure.

  The stack cooling device 4 is a device that cools the fuel cell stack 1 and maintains the fuel cell stack 1 at a temperature suitable for power generation. The stack cooling device 4 includes a cooling water circulation passage 41, a radiator 42, a bypass passage 43, a three-way valve 44, a cooling water circulation pump 45, a first water temperature sensor 46, and a second water temperature sensor 47.

  The cooling water circulation passage 41 is a passage through which cooling water for cooling the fuel cell stack 11 circulates.

  The radiator 42 is provided in the cooling water circulation passage 41. The radiator 42 cools the cooling water discharged from the fuel cell stack 1.

  The bypass passage 43 has one end connected to the coolant circulation passage 41 and the other end connected to the three-way valve 44 so that the coolant can be circulated by bypassing the radiator 42.

  The three-way valve 44 is provided in the cooling water circulation passage 41 on the downstream side of the radiator 42. The three-way valve 44 switches the cooling water circulation path according to the temperature of the cooling water. Specifically, when the temperature of the cooling water is relatively high, the cooling water circulation path is such that the cooling water discharged from the fuel cell stack 1 is supplied again to the fuel cell stack 1 via the radiator 42. Switch. On the contrary, when the temperature of the cooling water is relatively low, the cooling water discharged from the cooling water discharged from the fuel cell stack 1 flows through the bypass passage 43 without passing through the radiator 42 and is again returned to the fuel cell stack 1. The cooling water circulation path is switched so as to be supplied.

  The cooling water circulation pump 45 is provided in the cooling water circulation passage 41 on the downstream side of the three-way valve 44 and circulates the cooling water.

  The first water temperature sensor 46 is provided in the cooling water circulation passage 41 on the upstream side of the radiator 42. The first water temperature sensor 46 detects the temperature of the cooling water discharged from the fuel cell stack 1 (hereinafter referred to as “stack outlet water temperature”). In this embodiment, the stack outlet water temperature is used as the temperature of the fuel cell stack 1.

  The second water temperature sensor 47 is provided in the cooling water circulation passage 41 on the downstream side of the radiator 46. The second water temperature sensor 47 detects the temperature of cooling water cooled by the radiator and flowing into the fuel cell stack 1 (hereinafter referred to as “stack inlet water temperature”).

  The controller 5 includes a microcomputer having a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM), and an input / output interface (I / O interface). In addition to the air flow sensor 35, the pressure sensor 37, the first water temperature sensor 46, and the second water temperature sensor 47 described above, the controller 5 includes a current sensor 51 that detects the output current of the fuel cell stack 1, and the fuel cell stack 1 Signals from various sensors necessary for controlling the fuel cell system 100, such as a voltage sensor 52 for detecting the output voltage of the engine, an accelerator stroke sensor 53 for detecting the depression amount of the accelerator pedal, and an outside air temperature sensor 54 for detecting the outside air temperature Is entered.

  The controller 5 calculates electric power necessary for driving the vehicle (hereinafter referred to as “required output power”) based on detection signals of various sensors, and the cathode flow rate is required to output at least the output power of the fuel cell stack 1 as required output. The cathode flow rate is controlled so that it does not fall below the flow rate required for electric power.

  The controller 5 also causes the fuel cell stack 1 to be in a predetermined wet state in which the electrolyte membrane of each fuel cell constituting the fuel cell stack 1 is appropriately humidified in order to efficiently generate power. To control the amount of moisture inside.

  Here, the wet state of the electrolyte membrane is known to correlate with the internal high frequency resistance (HFR) (hereinafter referred to as “internal resistance”) of the fuel cell stack 1, When the amount of water is small and the electrolyte membrane is dry, the internal resistance increases and the output voltage of the fuel cell decreases. On the other hand, when the internal water content of the fuel cell is excessive, the electrode of the fuel cell is covered with water, so that the diffusion of the anode gas and the cathode gas is hindered and the output voltage is lowered.

  The amount of water in the fuel cell stack 1 varies depending on the amount of water generated by the electrode reaction and the amount of water generated as water vapor and discharged to the outside of the fuel cell stack 1 together with the cathode offgas. The amount of water generated by the electrode reaction decreases as the output power of the fuel cell stack 1 is lower. The amount of generated water discharged to the outside of the fuel cell stack 1 as water vapor varies depending on the cathode flow rate, cathode pressure, cathode humidity, and stack outlet water temperature.

  Specifically, the smaller the cathode flow rate, the smaller the amount of water that is discharged together with the cathode off gas, so the amount of generated water that is discharged to the outside of the fuel cell stack 1 decreases. The higher the cathode pressure and the lower the stack outlet water temperature, the smaller the proportion of generated water that becomes water vapor, so that the amount of generated water discharged to the outside of the fuel cell stack 1 decreases. The lower the cathode humidity, the smaller the amount of water produced outside the fuel cell stack 1 because the water vapor originally contained in the cathode gas is reduced.

  Therefore, the controller 5 basically controls the cathode flow rate, the cathode pressure, the cathode humidity, and the stack outlet water temperature according to the required output power so that the internal resistance of the fuel cell stack 1 becomes a predetermined internal resistance. Is controlled to a predetermined wet state that is moderately humidified.

  However, it has been found that when the cathode flow rate and the cathode pressure are controlled according to the required output power, the following problems occur at the time of transition after the required output power decreases.

  FIG. 2 is a diagram illustrating a change in the stack outlet water temperature when, for example, the accelerator pedal is returned and the required output power of the fuel cell stack 1 decreases.

  As shown in FIG. 2, when the required output power is reduced at time t1, the stack outlet water temperature is the required output from the stack outlet water temperature T1 in the steady state before the required output power is reduced (hereinafter referred to as “before load change”). It gradually changes to the stack outlet water temperature T2 in a steady state after the power is reduced (hereinafter referred to as “after load change”).

  At this time, the cathode flow rate, the cathode pressure, and the like are simultaneously controlled in order to control the electrolyte membrane to a predetermined moistened state. However, the change rate of the stack outlet water temperature is slower than the change rate of the cathode flow rate and the cathode pressure.

  When the required output power is greatly reduced, the difference between the stack outlet water temperature T1 in the steady state before the load change and the stack outlet water temperature T2 in the steady state after the load change (hereinafter referred to as “stack outlet water temperature fluctuation range”). ) ΔT1 increases. Then, when the stack outlet water temperature is in the transient state from the stack outlet water temperature T1 in the steady state before the load change to the stack outlet water temperature T2 in the steady state after the load change, the time of the transient state becomes long.

  Therefore, when the stack outlet water temperature fluctuation range ΔT1 is large, only the stack outlet water temperature is less than the optimum value after the load change, even though the cathode flow rate and the cathode pressure are controlled to the optimum values after the load change. It will remain high temporarily. As a result, the amount of generated water that becomes steam and is discharged to the outside of the fuel cell stack 1 together with the cathode off-gas temporarily increases, the internal moisture content of the fuel cell stack 1 decreases, and the inside of the fuel cell stack 1 temporarily Becomes overdried.

  On the other hand, when the stack outlet water temperature fluctuation width ΔT1 is small, the amount of generated water due to the electrode reaction decreases due to a decrease in the required output power, but the cathode flow rate also decreases. The amount of generated water discharged outside the stack 1 is reduced. As a result, the moisture remaining in the fuel cell stack 1 before the load change becomes difficult to be discharged, the amount of moisture inside the fuel cell stack 1 increases, and the inside of the fuel cell stack 1 is temporarily overhumid. It becomes.

  Therefore, in the present embodiment, in the transient state after the required output power is reduced, the cathode flow rate, the cathode pressure, the cathode humidity, and the stack outlet water temperature are controlled according to the stack outlet water temperature fluctuation range ΔT1. Hereinafter, the internal water content control of the fuel cell stack 1 according to this embodiment will be described.

  FIG. 3 is a flowchart for explaining the internal water content control of the fuel cell stack 1 according to the present embodiment.

  In step S <b> 1, the controller 5 reads detection signals of various sensors such as the stack outlet water temperature detected by the first water temperature sensor 46, and detects the operating state of the fuel cell system 100.

  In step S <b> 2, the controller 5 calculates the required output power according to the operating state of the fuel cell system 100.

  In step S3, the controller 5 determines whether or not the required output power has decreased. Specifically, it is determined whether or not the requested output power calculated this time (hereinafter referred to as “required output power current value”) is smaller than the previously calculated requested output power (hereinafter referred to as “required output power previous value”). judge. If the requested output power has not decreased, the controller 5 performs the process of step S4. On the other hand, if the required output power is reduced, the process of step S6 is performed.

  In step S4, the controller 5 determines whether or not it is a transient state after the required output power is reduced. Specifically, it is determined whether or not the transient state determination flag is set to 1. When it is determined that the controller 5 is in a transient state after the required output power is reduced, the controller 5 performs the process of step S10, and if not, performs the process of step S5.

  In step S5, the controller 5 adjusts the cathode flow rate and the like by normal control. Specifically, feedback control of the cathode flow rate, the cathode pressure, and the stack outlet water temperature is performed based on the actual internal resistance and target internal resistance of the fuel cell stack 1 so that the actual internal resistance becomes the target internal resistance. The cathode flow rate and the cathode pressure are adjusted by controlling the cathode compressor 34 and the cathode pressure regulating valve 40. The stack outlet water temperature is adjusted by controlling the cooling water circulation pump 45.

  In step S6, the controller 5 sets the transient state determination flag to 1.

  In step S7, the controller 5 calculates the estimated stack outlet water temperature T2 based on the required output power current value. The estimated stack outlet water temperature T2 is the stack outlet water temperature in the steady state after the load change. The relationship between the output power in the steady state and the stack outlet water temperature is obtained in advance by experiments or the like, and stored in the controller 5 as a map. Thus, the required output power can be calculated based on the current value.

  In step S8, the controller 5 calculates the difference between the previous value T1 of the stack outlet water temperature and the estimated stack outlet water temperature T2, that is, the stack outlet water temperature fluctuation width ΔT1. The previous value T2 of the stack outlet water temperature is the stack outlet water temperature in the steady state before the load change.

  In step S9, the controller 5 refers to each table in FIG. 4 and controls the cathode flow rate, the cathode pressure, the cathode humidity, and the stack outlet water temperature during the transition based on the stack outlet water temperature fluctuation width ΔT1. FIG. 4 will be described later.

  In step S10, the controller 5 calculates a difference ΔT2 between the current value T3 of the stack outlet water temperature and the estimated stack outlet water temperature T2.

  In step S11, the controller 5 determines whether or not the difference ΔT2 between the current value T3 of the stack outlet water temperature and the estimated stack outlet water temperature T2 is equal to or lower than the transient state end determination value. The controller 5 performs the process of step S12 if the difference ΔT2 between the current value T3 of the stack outlet water temperature and the estimated stack outlet water temperature T2 is equal to or lower than the transient state end determination value, otherwise ends the current process. To do. The transition end determination value is a value determined in advance in consideration of the cathode flow rate, the response speed of the cathode pressure, and the like.

  In step S12, the transient state determination flag is set to 0, and it is determined that the transient state has ended.

  FIG. 4 is a table for calculating the cathode flow rate, the cathode pressure, the cathode humidity, and the cooling water flow rate at the time of transition after the required output power is reduced based on the stack outlet water temperature fluctuation range ΔT1.

  FIG. 4A is a table for calculating the cathode flow rate based on the stack outlet water temperature fluctuation range ΔT1.

  As shown in FIG. 4A, when the stack outlet water temperature fluctuation range ΔT1 is smaller than a predetermined dry / wet determination value, the cathode flow rate is set in a steady state after the load change to suppress overwetting of the fuel cell stack 1. More than the flow rate to be made. On the other hand, when the stack outlet water temperature fluctuation range ΔT1 is larger than the dry / wet determination value, the cathode flow rate is made smaller than the flow rate set in the steady state after the load change in order to suppress overdrying of the fuel cell stack 1. The dry / wet determination value is a value determined in advance by experiments or the like.

  FIG. 4B is a table for calculating the cathode pressure based on the stack outlet water temperature fluctuation range ΔT1.

  As shown in FIG. 4B, when the stack outlet water temperature fluctuation range ΔT1 is smaller than the dry / wet determination value, the cathode pressure is set in a steady state after the load fluctuation in order to suppress overwetting of the fuel cell stack 1. Lower than pressure. On the other hand, when the stack outlet water temperature fluctuation range ΔT1 is larger than the dry / wet determination value, the cathode pressure is made lower than the pressure set in the steady state after the load fluctuation in order to suppress overdrying of the fuel cell stack 1.

  FIG. 4C is a table for calculating the cathode humidity based on the stack outlet water temperature fluctuation range ΔT1.

  As shown in FIG. 4C, when the stack outlet water temperature fluctuation range ΔT1 is smaller than the dry / wet determination value, the cathode humidity is set in a steady state after the load fluctuation in order to suppress overwetting of the fuel cell stack 1. Lower than humidity. On the other hand, when the stack outlet water temperature fluctuation range ΔT1 is larger than the dry / wet determination value, the cathode humidity is set lower than the humidity set at the steady state after the load change in order to suppress overdrying of the fuel cell stack 1.

  FIG. 4D is a table for calculating the coolant flow rate based on the stack outlet water temperature fluctuation range ΔT1.

  As shown in FIG. 4D, when the stack outlet water temperature fluctuation range ΔT1 is smaller than the dry / wet determination value, the cooling water flow rate is set at a steady time after the load fluctuation in order to suppress overwetting of the fuel cell stack 1. Less than the flow rate. On the other hand, when the stack outlet water temperature fluctuation range ΔT1 is larger than the dry / wet determination value, the cooling water flow rate is set to be larger than the flow rate set in the steady state after the load change in order to suppress overdrying of the fuel cell stack 1.

  According to the present embodiment described above, in the transient state after the required output power is reduced, the cathode flow rate, the cathode pressure, the cathode humidity, and the cooling water flow rate are controlled according to the stack outlet water temperature fluctuation range ΔT1. did.

  Specifically, when the stack outlet water temperature fluctuation range ΔT1 is larger than a predetermined dry / wet determination value, in order to suppress overdrying of the fuel cell stack, the internal water content of the fuel cell stack 1 is higher than that in the steady state after the load fluctuation. The cathode flow rate, cathode pressure, cathode humidity, and cooling water flow rate were controlled so that the amount increased.

  On the other hand, when the stack outlet water temperature fluctuation range ΔT1 is equal to or less than a predetermined dry / wet determination value, the internal moisture content of the fuel cell stack 1 is lower than that in the steady state after the load change in order to suppress overwetting of the fuel cell stack. Thus, the cathode flow rate, cathode pressure, cathode humidity, and cooling water flow rate were controlled.

  Thereby, since the internal moisture content of the fuel cell stack 1 in the transient state after the required output power is reduced can be maintained in an optimal state, overdrying and overwetting inside the fuel cell stack 1 can be suppressed. .

  Further, in this embodiment, when the overdrying of the fuel cell stack 1 is suppressed, the output power is not temporarily increased in order to increase the amount of water generated by the electrode reaction, so that the generation of unnecessary power is suppressed. be able to. Further, when such unnecessary power is generated, it is necessary to charge the battery with the power, and control itself for suppressing overdrying cannot be performed depending on the charging rate of the battery. On the other hand, in this embodiment, overdrying of the fuel cell stack 1 can be suppressed regardless of the charging rate of the battery.

(Second Embodiment)
Next, a second embodiment of the present invention will be described. This embodiment is different from the first embodiment in that the wet / dry determination value is corrected according to the stack outlet water temperature. Hereinafter, the difference will be mainly described. In the following embodiments, the same reference numerals are used for portions that perform the same functions as those in the first embodiment described above, and repeated descriptions are omitted as appropriate.

  As the cooling water temperature (stack inlet water temperature) flowing into the fuel cell stack 1 increases, the inside of the fuel cell stack 1 tends to dry. Therefore, when the stack inlet water temperature increases, the internal moisture content of the fuel cell stack 1 decreases even when the stack outlet water temperature fluctuation range ΔT1 is smaller than the predetermined wet / dry determination value described in the first embodiment. There is a fear.

  Therefore, in this embodiment, the wet / dry determination value is corrected according to the stack inlet water temperature. Specifically, correction is made so that the wet / dry determination value decreases as the stack inlet water temperature increases.

  FIG. 5 is a map for calculating the cathode flow rate, the cathode pressure, the cathode humidity, and the cooling water flow rate at the time of transition after the required output power is reduced based on the stack outlet water temperature fluctuation range ΔT1 and the stack inlet water temperature. is there. In the present embodiment, the cathode flow rate, the cathode pressure, the cathode humidity, and the cooling water flow rate at the time of transition after the required output power is reduced with reference to this map in step S8 of the flowchart of FIG. 3 described in the first embodiment. Is calculated.

  As shown in FIG. 5, each map is created so that the wet / dry determination value decreases as the stack inlet water temperature increases.

  According to the present embodiment described above, the internal moisture content of the fuel cell stack 1 in the transient state after the required output power is reduced can be maintained in a more optimal state. Overwetting can be suppressed.

(Third embodiment)
Next, a third embodiment of the present invention will be described. This embodiment is different from the first embodiment in the method of controlling the cathode flow rate at the time of transition. Hereinafter, the difference will be mainly described.

  FIG. 6 is a flowchart for explaining the internal water content control of the fuel cell stack 1 according to the present embodiment.

  In step S31, the controller 5 determines whether or not the stack outlet water temperature fluctuation range ΔT1 is equal to or greater than the drying determination value. The controller performs the process of step S32 if the stack outlet water temperature fluctuation range ΔT1 is equal to or greater than the drying determination value, and performs the process of step S33 if it is less than the predetermined value.

  In step S <b> 32, the controller 5 implements measures against overdrying. Specifically, the cathode flow rate at the time of transition is made smaller than the cathode flow rate set by the normal control in step S5. This is because if the cathode output is controlled to the cathode flow rate set by the normal control when the required output power is greatly reduced and the stack outlet water temperature fluctuation width ΔT1 is equal to or greater than the dry determination value, the fuel cell stack This is because overdrying may occur due to the temperature of 1 remaining high. As a measure against overdrying, the cathode pressure, cathode humidity, and stack outlet water temperature may be controlled in addition to the cathode flow rate.

  In step S33, the controller 5 restricts the above-mentioned measures against overdrying. Specifically, the amount of decrease in the cathode flow rate during the transition is made smaller than in the case of step S32. That is, in this step, the cathode flow rate at the time of transition is made smaller than the cathode flow rate set by the normal control in step S5, but larger than the cathode flow rate set by the overdrying countermeasure in step S32. This is because if the above-mentioned countermeasure against overdrying is carried out as it is when the required output power decrease width is small and the stack outlet water temperature fluctuation range ΔT1 is less than the dryness determination value, the cathode flow rate becomes too small and the moisture in the fuel cell stack 1 is reduced. This is because there is a possibility that flooding may occur. The amount of decrease in the cathode flow rate when limiting overdrying measures may be determined by adaptation or the like, and the cathode flow rate may be made larger than the cathode flow rate set by normal control in order to completely prevent flooding. In the stub S33, the above-mentioned measures against overdrying may be prohibited.

  7 and 8 are time charts for explaining the operation of controlling the internal water content of the fuel cell stack 1 according to the present embodiment. FIG. 7 is a view showing a state when the stack outlet water temperature fluctuation range ΔT1 is equal to or larger than the drying determination value. FIG. 8 is a view showing a state when the stack outlet water temperature fluctuation range ΔT1 is less than the drying determination value.

  As shown in FIG. 7 and FIG. 8, the cathode flow rate is made smaller in the transient state than in the steady state, but when the stack outlet water temperature fluctuation range ΔT1 is less than the drying determination value, the stack outlet water temperature fluctuation range ΔT1 is determined to be dry. Reduce the amount of decrease in cathode flow rate compared to when the value is higher than the value. By doing in this way as well as the first embodiment, overdrying and overwetting of the fuel cell stack 1 can be suppressed.

  Note that the present invention is not limited to the above-described embodiment, and it is obvious that various modifications can be made within the scope of the technical idea.

  For example, in each of the above embodiments, the stack outlet water temperature (estimated stack outlet water temperature) in a steady state after load change is calculated based on the required output power after load change.

  However, the method for calculating the estimated stack outlet water temperature is not limited to such a method, and may be calculated based on the required output power and the outside air temperature. Specifically, the estimated stack cooling water temperature is decreased as the required output power is smaller. Since the stack inlet water temperature changes according to the outside air temperature, the estimated stack cooling water temperature is decreased as the outside air temperature is lower.

  In each of the above embodiments, the stack outlet water temperature in the steady state after the load change (estimated stack outlet water temperature) is calculated based on the required output power after the load change, and the estimated stack outlet is calculated from the stack outlet water temperature before the load change. The stack outlet water temperature fluctuation range ΔT1 was calculated by subtracting the water temperature. Based on the stack outlet water temperature fluctuation range ΔT1, the cathode flow rate, the cathode pressure, the cathode humidity, and the cooling water flow rate during the transition after the required output power is reduced are controlled.

  However, the present invention is not limited to this method, and the cathode flow rate, cathode pressure, cathode humidity, and cooling water flow rate at the time of transition after the required output power decreases are directly controlled based on the fluctuation range of the required output power. May be.

  Further, in each of the above embodiments, the determination as to whether or not the transient state after the reduction of the required output power has ended is made based on the difference between the current value of the stack outlet water temperature and the estimated stack outlet water temperature being the transient state end determination value. Judgment was made based on whether or not:

  However, the determination of whether or not the transient state has ended is not limited to such a method. For example, it may be determined that the transition has ended after a predetermined time has elapsed since the required output power has decreased. Further, the predetermined time may be changed in accordance with the stack outlet water temperature fluctuation width ΔT1 and the fluctuation width of the required output power.

  In each of the above embodiments, the WRD bypass passage 37 is provided in the cathode gas supply passage 31, but it may be provided in the cathode gas discharge passage 32 so as to bypass the dehumidifying part 362 of the WRD 36.

  In the second embodiment, the dry / wet determination value is corrected based on the stack inlet water temperature. However, the present invention is not limited to this. The stack inlet water temperature is cooled to a temperature equivalent to the outside air temperature by the radiator. Therefore, the wet / dry determination value may be corrected based on the outside air temperature instead of the stack inlet water temperature.

1 Fuel cell stack (fuel cell)
100 Fuel cell system S6 Estimated temperature calculation means S8 Internal moisture content control means

Claims (9)

A fuel cell system for generating power by supplying anode gas and cathode gas to a fuel cell,
Based on the target internal moisture content and the actual moisture content of the fuel cell, a steady-state internal moisture content control means for controlling a parameter that affects the internal moisture content of the fuel cell;
When the required output of the fuel cell decreases, a parameter that is set by the steady-state internal moisture amount control means that affects the internal moisture amount of the fuel cell is set so that the internal moisture amount of the fuel cell increases. A correction means at the time of required output reduction to correct,
With
The required output reduction correction means is
If the amount of decrease in required output of the fuel cell is small, in transient after required output decreased, by correcting the parameters, the correction amount of increase against the internal water content in accordance with the required output after reduction, the A fuel cell system characterized in that the fuel cell system is smaller than when the output reduction amount is large. A fuel cell system for generating power by supplying anode gas and cathode gas to a fuel cell,
Estimated temperature calculation means for calculating an estimated temperature of the fuel cell in a steady state after a decrease in the required output when the required output of the fuel cell decreases;
When the difference between the temperature of the fuel cell before the decrease in the required output and the estimated temperature of the fuel cell is equal to or less than a predetermined value, the internal moisture content of the fuel cell is decreased as compared with the steady state after the decrease in the required output. And an internal water content control means for controlling a parameter that affects the internal water content of the fuel cell;
A fuel cell system comprising: The internal moisture content control means includes:
When the difference between the temperature of the fuel cell before the decrease in the required output and the estimated temperature of the fuel cell is larger than a predetermined value, the internal moisture amount of the fuel cell increases more than in the steady state after the decrease in the required output. And controlling parameters that affect the internal moisture content of the fuel cell,
The fuel cell system according to claim 2. The internal moisture content control means includes:
The lower the cooling water temperature flowing into the fuel cell, the smaller the predetermined value,
The fuel cell system according to claim 2 or claim 3, wherein The internal moisture content control means includes:
The lower the outside temperature is, the smaller the predetermined value is.
The fuel cell system according to claim 2 or claim 3, wherein The estimated temperature calculating means includes
The lower the required output and the lower the outside air temperature, the lower the estimated temperature of the fuel cell.
The fuel cell system according to any one of claims 2 to 5, wherein The parameter that affects the internal moisture content of the fuel cell is at least one of a cathode gas flow rate, a cathode gas pressure, a cathode gas humidity, and a temperature of the fuel cell.
The fuel cell system according to any one of claims 2 to 6, wherein The temperature of the fuel cell is a temperature of cooling water discharged from the fuel cell.
The fuel cell system according to any one of claims 2 to 7, characterized in that: A fuel cell system for generating power by supplying anode gas and cathode gas to a fuel cell,
When the required output of the fuel cell is reduced, when the reduction width of the required output is equal to or less than a predetermined value, the fuel cell has a lower internal moisture content than the steady state after the reduction of the required output. An internal water content control means for controlling a parameter that affects the internal water content of
A fuel cell system.

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