fuel cell system

Abstract

To suppress deterioration in power generation performance of a catalyst an electrode includes by suppressing voltage fluctuation of a fuel cell caused by variations of an internal state of the fuel cell.SOLUTION: A fuel cell system comprises a fuel cell, which includes a solid polymer electrolyte film and an air electrode, and a control section. The control section performs first control for acquiring a current value of a relative humidity of the electrolyte film and controlling actuation of an actuator capable of adjusting the relative humidity so as to change the relative humidity to a side where the acquired current value is close to a preset target value and second control for acquiring a current value of an oxide coating rate of a catalyst of the air electrode and controlling the actuation of the actuator capable of adjusting the oxide coating rate so as to change the oxide coating rate to a side where the acquired current value is close to a preset target value.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a fuel cell system. [Background technology]

[0002] It has been known that voltage fluctuations in a fuel cell can cause deterioration in the power generation performance of the catalyst in the fuel cell's electrodes. Therefore, in the fuel cell system described in Patent Document 1, the control unit reduces fluctuations in the fuel cell's target power, thereby suppressing actual voltage fluctuations in the fuel cell. This makes it possible to suppress catalyst performance degradation caused by voltage fluctuations. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-149882 Summary of the Invention [Problem to be solved by the invention]

[0004] However, variations in the internal state of the fuel cell also cause voltage fluctuations in the fuel cell, which deteriorate the power generation performance of the catalyst in the electrodes.

[0005] In view of the above, the present invention aims to provide a fuel cell system that can suppress voltage fluctuations of a fuel cell caused by variations in the internal state of the fuel cell and suppress deterioration of the power generation performance of the catalyst in the electrode. [Means for solving the problem]

[0006] In order to achieve the above object, according to the invention described in claim 1, The fuel cell system a fuel cell (20) having a solid polymer electrolyte membrane (22), a fuel electrode (23) disposed on one side of the electrolyte membrane, and an air electrode (24) disposed on the other side of the electrolyte membrane; a first actuator (44) capable of adjusting a first state quantity indicating an internal state of the fuel cell; a second actuator (37, 39, 41, 43, 61) capable of adjusting a second state quantity that indicates an internal state of the fuel cell different from the first state quantity; a control unit (70) that controls the operation of the first actuator and the operation of the second actuator, The control unit acquires a current value of a first state quantity, and performs first control to control the operation of the first actuator so that the acquired current value of the first state quantity changes the first state quantity to approach a predetermined first target value, and also acquires a current value of a second state quantity, and performs second control to control the operation of the second actuator so that the acquired current value of the second state quantity changes the second state quantity to approach a predetermined second target value. stomach, when performing the first control, the control unit controls the operation of the second actuators (41, 43) so that the first state quantity is suppressed from changing to a side away from the first target value due to the operation of the second actuators; The first state quantity is the relative humidity of the electrolyte membrane or a physical quantity related to the relative humidity, and the second state quantity is the gas diffusion resistance of the air electrode. According to the invention described in claim 2, the fuel cell system comprises: a fuel cell (20) having a solid polymer electrolyte membrane (22), a fuel electrode (23) disposed on one side of the electrolyte membrane, and an air electrode (24) disposed on the other side of the electrolyte membrane; a first actuator (44) capable of adjusting a first state quantity indicating an internal state of the fuel cell; a second actuator (37, 39, 41, 43, 61) capable of adjusting a second state quantity that indicates an internal state of the fuel cell different from the first state quantity; a control unit (70) that controls the operation of the first actuator and the operation of the second actuator, the control unit acquires a current value of the first state quantity, and performs first control to control operation of the first actuator so that the acquired current value of the first state quantity changes the first state quantity to approach a predetermined first target value, and also acquires a current value of the second state quantity, and performs second control to control operation of the second actuator so that the acquired current value of the second state quantity changes the second state quantity to approach a predetermined second target value, the first state quantity is the relative humidity of the electrolyte membrane or a physical quantity related to the relative humidity, the second state quantity is a gas diffusion resistance of the air electrode, The control unit performs the first control and then the second control. . According to the invention described in claim 3, the fuel cell system comprises: a fuel cell (20) having a solid polymer electrolyte membrane (22), a fuel electrode (23) disposed on one side of the electrolyte membrane, and an air electrode (24) disposed on the other side of the electrolyte membrane; a first actuator (44) capable of adjusting a first state quantity indicating an internal state of the fuel cell; a second actuator (37, 39, 41, 43, 61) capable of adjusting a second state quantity that indicates an internal state of the fuel cell different from the first state quantity; a control unit (70) that controls the operation of the first actuator and the operation of the second actuator, the control unit acquires a current value of the first state quantity, and performs first control to control operation of the first actuator so that the acquired current value of the first state quantity changes the first state quantity to approach a predetermined first target value, and also acquires a current value of the second state quantity, and performs second control to control operation of the second actuator so that the acquired current value of the second state quantity changes the second state quantity to approach a predetermined second target value, the first state quantity is the relative humidity of the electrolyte membrane or a physical quantity related to the relative humidity, the second state quantity is an oxide film ratio of a catalyst included in the air electrode, the control unit performs the first control and then the second control, the fuel cell system includes a third actuator (41, 43) capable of adjusting the gas diffusion resistance of the air electrode as a third state quantity indicating an internal state of the fuel cell; After performing the second control, the control unit acquires a current value of the third state quantity, and performs third control to control the operation of the third actuator so that the acquired current value of the third state quantity changes the third state quantity toward a predetermined third target value.

[0007] This makes it possible to suppress voltage fluctuations in the fuel cell due to variations in the internal state of the fuel cell, thereby suppressing deterioration in the power generation performance of the catalyst in the air electrode.

[0008] The reference symbols in parentheses attached to each component indicate an example of the correspondence between the component and the specific components described in the embodiments described below. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic diagram showing the overall configuration of a fuel cell system according to a first embodiment. [Figure 2] FIG. 1 is a schematic diagram showing the internal structure of a fuel cell according to a first embodiment. [Figure 3] FIG. 2 is a schematic diagram of a control unit provided in the fuel cell system of the first embodiment. [Figure 4A] FIG. 10 is a diagram showing the relationship between the output voltage and the output current of a fuel cell under ideal characteristics. [Figure 4B] FIG. 1 is a diagram showing the relationship between the output voltage and the output current of a fuel cell, for explaining the problem to be solved by the present invention. [Figure 5] 4 is a flowchart of membrane humidity control performed by a control unit in the fuel cell system of the first embodiment. [Figure 6] 4 is a time chart of the voltage, membrane humidity, etc. of the fuel cell in the fuel cell system of the first embodiment and the fuel cell system of Comparative Example 1. [Figure 7] 4 is a flowchart of a process for permitting the start of catalytic oxide film ratio control, which is performed by a control unit in the fuel cell system of the first embodiment. [Figure 8] 4 is a flowchart of catalytic oxide film rate control performed by a control unit in the fuel cell system of the first embodiment. [Figure 9] 10 is a time chart showing the voltage and catalytic oxide film ratio of the fuel cell in the fuel cell system of the first embodiment and the fuel cell system of Comparative Example 2. [Figure 10]4 is a flowchart of operation control performed by a control unit in the fuel cell system of the first embodiment. [Figure 11] 11 is a flowchart of the intermittent operation process in step S36 of FIG. 10. [Figure 12] 10 is a time chart showing the voltage and catalytic oxide film ratio of the fuel cell in the fuel cell system of the first embodiment and the fuel cell system of Comparative Example 3. [Figure 13] 4 is a flowchart of a process for permitting the start of diffusion resistance control, which is performed by a control unit in the fuel cell system of the first embodiment. [Figure 14] 4 is a flowchart of the diffusion resistance control performed by the control unit in the fuel cell system of the first embodiment. [Figure 15] 10 is a time chart of the voltage, diffusion resistance, etc. of the fuel cell in the fuel cell system of the first embodiment and the fuel cell system of Comparative Example 4. [Figure 16] 10 is a time chart of the voltage, membrane humidity, etc. of the fuel cell in the fuel cell system of the second embodiment and the fuel cell system of Comparative Example 5. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the following embodiments, parts that are identical or equivalent to each other will be denoted by the same reference numerals.

[0011] (First embodiment) 1 is mounted on a vehicle as a power source for driving the vehicle. In addition to the fuel cell system 10, the vehicle is also equipped with a drive motor 100. The fuel cell system 10 includes a fuel cell (i.e., FC) 20, a fuel gas supply system 30, an oxidant gas supply system 40, an exhaust gas system 50, and a power circuit 60.

[0012] The FC 20 is a polymer electrolyte fuel cell. The FC 20 has a stack configuration in which a plurality of unit cells 21 shown in Fig. 2 are stacked. Each unit cell 21 has a polymer electrolyte membrane 22, a fuel electrode 23, and an air electrode 24.

[0013] The electrolyte membrane 22 is also called a PEM. PEM is an abbreviation for Polymer Electrolyte Membrane. The electrolyte membrane 22 has proton conductivity. The fuel electrode 23 is disposed on one side of the electrolyte membrane 22. Hydrogen gas is supplied to the fuel electrode 23 as a fuel gas. The fuel electrode 23 is an anode that emits electrons. The air electrode 24 is disposed on the other side of the electrolyte membrane 22. Air, i.e., oxygen gas, is supplied to the air electrode 24 as an oxidant gas. The air electrode 24 is a cathode that accepts electrons.

[0014] The fuel electrode 23 and the air electrode 24 have catalyst layers 231 and 241, water-repellent layers 232 and 242, and gas diffusion layers 233 and 243, respectively.

[0015] The catalyst layers 231 and 241 are layers containing a catalyst and are also referred to as CL. CL is an abbreviation for Catalyst Layer. More specifically, the catalyst layers 231 and 241 include catalyst particles (e.g., Pt particles) 25, support particles 26 that support the Pt particles, and a polymer material (not shown) such as an ionomer that holds the support particles 26 and is responsible for proton conduction.

[0016] The water-repellent layers 232 and 242 are layers that transmit water to the gas diffusion layers 233 and 243 so as not to condense. The water-repellent layers 232 and 242 are also called MPLs. MPL is an abbreviation for Micro Porous Layer.

[0017] The gas diffusion layers 233 and 243 are layers that diffuse gas and distribute it evenly throughout the catalyst layers 231 and 241. The gas diffusion layers 233 and 243 are also called GDLs. GDL is an abbreviation for Gas Diffusion Layer.

[0018] A hydrogen gas flow path 27 through which hydrogen gas flows is formed on the fuel electrode 23 side of the unit cell 21. An air flow path 28 through which air flows is formed on the air electrode 24 side of the unit cell 21.

[0019] Hydrogen gas and air are supplied to the fuel electrode 23 and the air electrode 24, respectively, and the following electrochemical reactions occur as shown in FIG.

[0020] (Fuel electrode) H2→2H + +2e - (air electrode) 1 / 2O2+2H + +2e - →H2O

[0021] In this embodiment, the gas diffusion layers 233, 243 and the water-repellent layers 232, 242 are provided separately, but the gas diffusion layers 233, 243 may also function as water-repellent layers.

[0022] 1 supplies hydrogen gas as a fuel gas to the FC 20. The fuel gas supply system 30 includes a fuel gas tank 31, a hydrogen supply flow path 32, a fuel gas discharge flow path 33, a circulation flow path 34, a main stop valve 35, a regulator 36, an injector 37, a gas-liquid separator 38, and a circulation pump 39.

[0023] The fuel gas tank 31 is a storage device that stores hydrogen gas, and is connected to the FC20 via a hydrogen supply flow path 32. The hydrogen supply flow path 32 is a flow path through which hydrogen gas flows to be supplied to the FC20. The hydrogen gas stored in the fuel gas tank 31 is supplied to the anode-side flow path of the FC20 after the main stop valve 35 opens and closes the hydrogen supply flow path 32, the regulator 36 reduces the pressure, and the hydrogen gas is discharged from the injector 37.

[0024] The fuel gas discharge flow path 33 is a flow path through which the anode off-gas discharged from the FC20 flows. The circulation flow path 34 is connected to the fuel gas discharge flow path 33 and a portion of the hydrogen supply flow path 32 downstream of the injector 37. The pressure of the hydrogen circulating through the circulation flow path 34 is adjusted by a circulation pump 39. The amount of fuel gas supplied to the FC20 can be adjusted by the drive amount of the injector 37 and the circulation pump 39. The gas-liquid separator 38 is provided at the connection between the fuel gas discharge flow path 33 and the circulation flow path 34. The gas-liquid separator 38 separates water and gas in the anode off-gas.

[0025] The oxidizing gas supply system 40 supplies air as an oxidizing gas to the FC 20. The oxidizing gas supply system 40 has an air compressor 41, an air supply passage 42, a flow dividing valve 43, and a humidifier 44.

[0026] The air compressor 41 compresses air and supplies it to the cathode-side flow path of the FC20 via an air supply flow path 42. The air supply flow path 42 is a flow path through which air supplied to the FC20 flows. A flow dividing valve 43 is provided in the air supply flow path 42 at a connection portion with an air bypass flow path 55, which will be described later. The humidifier 44 is provided in the air supply flow path 42 on the air inlet side of the FC20. The humidifier 44 supplies water to the air electrode 24 of the FC20.

[0027] The exhaust gas system 50 discharges off-gas from the FC 20 to the outside. The exhaust gas system 50 includes an exhaust gas flow path 51, a pressure adjusting valve 52, a hydrogen discharge flow path 53, a purge valve 54, and an air bypass flow path 55.

[0028] The exhaust gas flow path 51 is a flow path through which cathode off-gas is discharged from the FC20. A pressure regulating valve 52 is provided in the exhaust gas flow path 51 and adjusts the air pressure in the FC20. A hydrogen discharge flow path 53 connects the gas-liquid separator 38 and the exhaust gas flow path 51. A purge valve 54 is provided in the hydrogen discharge flow path 53. The purge valve 54 opens to discharge water and gas from the gas-liquid separator 38 when the nitrogen concentration in the anode off-gas becomes high or when the amount of water in the gas-liquid separator 38 becomes large. The hydrogen in the anode off-gas discharged via the purge valve 54 is diluted by the cathode off-gas as it flows through the exhaust gas flow path 51. An air bypass flow path 55 connects the air supply flow path 42 and the exhaust gas flow path 51.

[0029] The power circuit 60 is connected to the FC 20. The drive motor 100 and various accessories (not shown) are connected to the power circuit 60. The power circuit 60 has an FC boost converter (i.e., FDC) 61, an inverter 62, a battery converter 63, a battery 64, and a battery sensor 65.

[0030] The FC boost converter 61 is a DC / DC converter that boosts the output voltage of the FC 20 to a high voltage that can be used by the drive motor 100. The inverter 62 converts the DC voltage boosted by the FC boost converter 61 into an AC voltage and supplies it to the drive motor 100. The drive motor 100 is a motor that drives the wheels of the vehicle, and generates regenerative power by regenerating when the vehicle decelerates.

[0031] The battery converter 63 is a bidirectional DC / DC converter. The battery converter 63 steps down the voltage stepped up by the FC boost converter 61 and the voltage generated by the regenerative operation of the drive motor 100, and supplies the voltage to the battery 64. The battery converter 63 also steps up the voltage of the battery 64 and supplies it to the inverter 62.

[0032] The battery 64 is a chargeable and dischargeable power storage device. The battery 64 stores the power generated by the FC 20 and the line power from the drive motor 100. The battery 64 supplies power to loads including the drive motor 100. The battery sensor 65 is connected to the battery 64 and detects the voltage, current, and state of charge (i.e., SOC) of the battery 64. SOC stands for "State Of Charge."

[0033] The fuel cell system 10 includes a control unit 70 shown in Fig. 3. The control unit 70 is configured with a microcomputer and has a CPU, ROM, RAM, and input / output ports. The control unit 70 controls the power generation of the fuel cell system 10 and also controls the entire vehicle, including the power circuit 60.

[0034] The control unit 70 acquires output signals from a plurality of sensors 71 provided in the vehicle. The plurality of sensors 71 include sensors provided in various parts of the fuel cell system 10, an accelerator position sensor, a shift position sensor, an outside air temperature sensor, and a vehicle speed sensor. The sensors provided in various parts of the fuel cell system 10 include a temperature sensor 72 that detects the temperature of the FC20, a current sensor 73 that detects the current output by the FC20, and a battery sensor 65.

[0035] The control unit 70 outputs drive signals to various actuators 81 related to power generation, driving, etc. of the vehicle, thereby controlling the operation of the various actuators 81. The various actuators 81 include the injector 37, the circulation pump 39, the air compressor 41, the flow dividing valve 43, the FC boost converter 61, etc.

[0036] As shown in Figure 4A, in the ideal characteristics of the FC20, there is a one-to-one relationship between the output current and output voltage of the FC20. However, if the present invention is not applied, there is variation in the magnitude of the output voltage of the FC20 relative to the output current of the FC20, as shown in Figure 4B. In other words, there is variation in the value of the output voltage when the output current has a certain value. One of the causes of this variation is variation in the internal state of the FC20.

[0037] The internal state of the FC20 includes the dry / wet state of the electrolyte membrane 22, the state of the oxide film covering the catalyst of the air electrode 24, and the state of gas diffusion of air (i.e., oxygen gas) in the air electrode 24. Fluctuations in the humidity of the electrolyte membrane 22 cause fluctuations in the output voltage of the FC20. Fluctuations in the ratio of the oxide film covering the surface area to the surface area of ​​the catalyst of the air electrode 24 cause fluctuations in the output voltage of the FC20. Fluctuations in the diffusibility of air due to condensed water formed on the air electrode 24 cause fluctuations in the output voltage of the FC20.

[0038] Here, when the load is low, such as when the output current of the FC20 is 100 A or less, the cell voltage becomes a high potential of 0.8 V or more. When the cell voltage is high, an oxide film (i.e., PtO) is formed on the surface of the catalytic platinum (i.e., Pt) particles in the air electrode 24. Furthermore, when the cell voltage is high, elution occurs due to ionization of Pt. On the other hand, when the cell voltage is low, such as 0.6 V or less, the oxide film is reduced and disappears.

[0039] If the FC20 output voltage fluctuates widely due to variations in the internal state of the FC20, the cell voltage will become low, the oxide film on the catalyst will disappear, and the cell voltage will remain high for a long time in this state. Repeated elution and deposition will cause the particles to coarsen, reducing the effective surface area of ​​the catalyst and decreasing power generation performance. This causes the elution of Pt to reduce the ECSA of the catalyst, accelerating the deterioration of power generation performance. ECSA is an abbreviation for electrochemically active surface area.

[0040] Therefore, in this embodiment, the control unit 70 detects the internal state of the FC 20 and performs control to make the internal state of the FC 20 a target state.

[0041] First, detection of the internal state of the FC 20 will be described. The control unit 70 acquires multiple state quantities that indicate the internal state of the FC 20. One of the multiple state quantities is the relative humidity of the electrolyte membrane 22. Hereinafter, the relative humidity of the electrolyte membrane 22 will also be referred to as the membrane humidity. Another of the multiple state quantities is the oxide film ratio of the catalyst of the air electrode 24. Hereinafter, the oxide film ratio of the catalyst of the air electrode 24 will also be referred to as the catalyst oxide film ratio. Another of the multiple state quantities is the gas diffusion resistance of the air electrode 24. Hereinafter, the gas diffusion resistance of the air electrode 24 will also be referred to as the diffusion resistance.

[0042] [Calculation of membrane humidity] The control unit 70 calculates the model formula of the resistance overvoltage shown in the following formulas (1-1) to (1-4), the value of the resistance overvoltage, the value of the sensor, and a constant, and calculates σ, which is an unknown parameter in the model formula. PEMref Calculate.

[0043]

number

[0044] The symbols in these formulas are as shown in Table 1.

[0045] [Table 1]

[0046] The resistance overvoltage value can be calculated from the impedance. Specifically, by measuring the AC impedance of the FC20, the ohmic resistance R that constitutes the internal resistance of the FC20 can be calculated. ohm , reaction resistance R act , diffusion resistance R gas It is known that the values ​​of the resistance overvoltage ΔV can be derived as shown in the following equation (1-5). ohm and ohmic resistance R ohm There is a certain relationship between the ohmic resistance R ohm The product of this and the FC current i is the resistance overvoltage ΔV ohmUsing this relationship, the derived ohmic resistance R ohm Resistance overvoltage ΔV ohm The value of can be calculated.

[0047]

number

[0048] The sensor value is the value of the FC current i during FC operation measured by the current sensor 73. The values ​​of each constant in the formula are stored in advance in a memory unit included in the control unit 70. Note that constants that are likely to change due to degradation (for example, PEM thickness, GDL / MPL resistance) tend to change slowly over time. For this reason, a value obtained by learning the amount of degradation from the difference in the detection results of resistance overvoltage detected under operating conditions where the membrane humidity and sensor values ​​are fixed may be used as the constant value.

[0049] σ PEMref After calculating σ PEMref Calculate the film humidity from σ PEMref There is a predetermined relationship between the temperature and the film humidity. A map showing this relationship is obtained by experiment. The map showing this relationship is stored in the memory unit, and the control unit 70 uses the map showing this relationship to calculate σ PEMref The membrane humidity can be calculated from the calculated value.

[0050] [Calculation of catalytic oxide film rate] After the membrane humidity is known by the above calculation, the control unit 70 calculates ECSA, which is an unknown parameter in the model equation, using the model equations for the cathode activation overvoltage, Equations (2-1) and (2-2) shown below, the value of the cathode activation overvoltage, the sensor value, and the value of a constant.

[0051]

number

[0052] The symbols in these formulas are as shown in Table 2.

[0053] [Table 2]

[0054] The cathodic activation overvoltage value can be calculated from the impedance. As mentioned above, the reaction resistance R can be calculated by measuring the AC impedance of FC20. act The value of the cathodic activation overvoltage ΔV can be derived as shown in the following equation (2-3). act and reaction resistance R act There is a predetermined relationship between the cathode activation overvoltage ΔV and the cathode activation overvoltage ΔV. This predetermined relationship is a relationship under various conditions such as the FC current and the FC temperature. A map showing this relationship is obtained by experiment. The map showing this relationship is stored in the memory unit, and the control unit 70 uses the map showing this relationship to calculate the cathode activation overvoltage ΔV act The value of can be calculated.

[0055]

number

[0056] The sensor values ​​are the FC current value measured by the current sensor 73 during FC operation and the FC temperature value measured by the temperature sensor 72 during FC operation. ECSA temperature and humidity dependency coefficient C RH ECSA is calculated from the film humidity using a physical formula or a map. The values ​​of the constants in the formula are stored in advance in a memory unit included in the control unit 70.

[0057] After calculating ECSA, the control unit 70 calculates the catalytic oxide film ratio from ECSA. The catalytic oxide film ratio is calculated as the ratio of the calculated ECSA value to the initial value of ECSA. Note that ECSA changes reversibly due to the influence of the oxide film and also changes gradually over time due to degradation. For this reason, the amount of degradation learned from the difference between the detection results of activation overvoltages detected under conditions where there is no oxide film and each parameter is fixed may be used as a learned value instead of the initial value.

[0058] [Calculation of gas diffusion resistance] After the membrane humidity is known by the calculation of the membrane humidity and the catalytic oxide film ratio is known by the calculation of the catalytic oxide film ratio, the control unit 70 calculates the gas diffusion resistance, which is an unknown parameter in the formula, using the model formulas of the cathodic concentration overvoltage, the following formulas (3-1) to (3-4), the sensor value, and constants.

[0059]

number

[0060] The symbols in these formulas are as shown in Table 3.

[0061] [Table 3]

[0062] The value of the cathodic concentration overvoltage can be calculated from the impedance. As mentioned above, the diffusion resistance R gas The value of the cathode concentration overvoltage ΔV can be derived as shown in the following equation (3-5). cnc and diffusion resistance R gas There is a predetermined relationship between the cathode concentration overvoltage ΔV and the cathode concentration overvoltage ΔV. This predetermined relationship is a relationship under various conditions such as the FC current and the FC temperature. A map showing this relationship is obtained by experiment. The map showing this relationship is stored in the memory unit, and the control unit 70 uses the map showing this relationship to calculate the cathode concentration overvoltage ΔV cnc The value of can be calculated.

[0063]

number

[0064] The sensor values ​​are the FC current value measured by the current sensor 73 during FC operation, the FC temperature value measured by the temperature sensor 72 during FC operation, and the air flow rate (i.e., air flow rate) supplied to the FC 20 during FC operation measured by the flow rate sensor. o2 is calculated from the value of the air flow rate using a physical formula or a map. The values ​​of the constants in the formula are stored in advance in a storage unit included in the control unit 70.

[0065] The diffusion resistance changes reversibly due to the influence of condensed water in the air flow path, and also changes gradually over time due to deterioration caused by mechanical changes in the GDL / MPL. Therefore, the initial and deteriorated diffusion resistance may be learned from the difference in the detection results of concentration overvoltages detected under conditions where there is no influence of condensed water and each parameter is fixed.

[0066] Next, the control performed by the control unit 70 to set the internal state of the FC 20 to a target state will be described.

[0067] [Membrane humidity control] When the system required output is greater than the load operation reference value, the fuel cell system 10 is operated under load. The load operation reference value is a value greater than 0 and close to 0. During load operation, the control unit 70 performs membrane humidity control to bring the membrane humidity closer to the target membrane humidity value. Specifically, the control unit 70 executes the control process shown in FIG. 5. The control process shown in FIG. 5 is repeated until its execution is stopped. The steps shown in FIG. 5 correspond to functional units that realize various functions. This also applies to other figures.

[0068] 5, in step S11, the control unit 70 acquires the current value of the membrane humidity. At this time, the current value of the membrane humidity is calculated by the calculation method described above.

[0069] Next, in step S12, the control unit 70 calculates Δmembrane humidity, which is the difference between the current membrane humidity value and the target membrane humidity value, using the current membrane humidity value acquired in step S11 and the target membrane humidity value stored in the control unit 70. The target membrane humidity value is an ideal value, for example, a value around 80%.

[0070] Next, in step S13, the control unit 70 determines whether the absolute value of the Δ film humidity calculated in step S12 is equal to or greater than a predetermined value. If the determination in step S13 is NO, the control unit 70 temporarily ends this process. If the determination in step S13 is YES, the control unit 70 proceeds to step S14.

[0071] In step S14, the control unit 70 determines whether the Δ film humidity calculated in step S12 is a negative value.

[0072] If the current value of the membrane humidity is greater than the target value of the membrane humidity and Δ membrane humidity is a negative value, the control unit 70 makes a YES determination in step S14. In this case, the control unit 70 proceeds to step S15 and reduces the humidification amount of the humidifier 44 so as to decrease the membrane humidity. This causes the membrane humidity to change so that the current value of the membrane humidity approaches the target value of the membrane humidity. Thereafter, the control unit 70 temporarily terminates this process.

[0073] On the other hand, if the current value of the membrane humidity is smaller than the target value of the membrane humidity and Δ membrane humidity is a positive value, the control unit 70 determines NO in step S14. In this case, the control unit 70 proceeds to step S16 and increases the humidification amount of the humidifier 44 so as to increase the membrane humidity. As a result, the membrane humidity changes so that the current value of the membrane humidity approaches the target value of the membrane humidity. Thereafter, the control unit 70 temporarily terminates this process.

[0074] In this way, the control unit 70 acquires the current value of the membrane humidity. The control unit 70 controls the operation of the humidifier 44 so as to change the membrane humidity so that the acquired current value of the membrane humidity approaches a preset target value of the membrane humidity. In this embodiment, the membrane humidity corresponds to the first state quantity. The target value of the membrane humidity corresponds to the first target value. The humidifier 44 corresponds to the first actuator capable of adjusting the first state quantity. The above-mentioned control of the operation of the humidifier 44 corresponds to the first control.

[0075] Here, the present embodiment is compared with Comparative Example 1. In Comparative Example 1, when the control unit 70 determines that the electrolyte membrane 22 is in an over-dried state based on the operating conditions of the FC 20, it performs control to increase the membrane humidity by increasing the air pressure in the air electrode 24, for example.

[0076] In this case, as shown by the wavy line in Figure 6, from time t11 to time t12, the membrane humidity decreases over time, causing the voltage of FC20 to decrease over time. Time t12 is the time when it is determined that the state is overdry. After time t12, the membrane humidity increases over time, causing the voltage of FC20 to increase over time. Therefore, as can be seen by comparing the voltage values ​​of FC20 at times t11 and t12, the fluctuation range of the voltage of FC20 is large.

[0077] In contrast, in this embodiment, the control unit 70 performs the above-described membrane humidity control. In this case, as shown in FIG. 6, the amount of humidification of the inlet air of the air electrode 24 of the FC20 is adjusted. As a result, the membrane humidity is maintained at a value close to the target membrane humidity value, as shown by the solid line in FIG. 6. Therefore, the voltage of the FC20 fluctuates as shown by the solid line in FIG. 6. Therefore, according to this embodiment, the fluctuation range of the voltage of the FC20 can be made smaller than that of Comparative Example 1.

[0078] In this manner, according to this embodiment, the membrane humidity is controlled to approach the target value. This reduces voltage fluctuations due to variations in membrane humidity, thereby suppressing deterioration of the power generation performance of the catalyst in the air electrode 24.

[0079] In addition to the humidifier 44, an air compressor 41 and a pressure regulating valve 52 may also be used as actuators capable of adjusting the membrane humidity. The membrane humidity can be adjusted by adjusting the air flow rate using the air compressor 41 and the pressure regulating valve 52. The membrane humidity can be adjusted by adjusting the air pressure (i.e., air pressure) using the pressure regulating valve 52. When the air pressure increases, the air flow rate decreases, making it difficult for the membrane humidity to decrease. When the air pressure decreases, the air flow rate increases, and the membrane humidity decreases. When the FC20 is operating under load, it is preferable to use the humidifier 44 and the pressure regulating valve 52 as actuators capable of adjusting the membrane humidity so that the amount of air necessary for power generation is supplied to the FC20.

[0080] [Control of catalytic oxide film rate] During load operation, the control unit 70 adjusts the output of the FC 20 (i.e., the FC output) according to the magnitude of the system required output. In addition, the control unit 70 performs catalytic oxide film ratio control to bring the catalytic oxide film ratio closer to the target value of the catalytic oxide film ratio.

[0081] In this embodiment, the control unit 70 performs the process shown in Fig. 7 before performing catalytic oxide film ratio control. In step S101, the control unit 70 acquires the current value of the film humidity, similar to step S11 in Fig. 5. Subsequently, in step S102, the control unit 70 calculates Δ film humidity, similar to step S12 in Fig. 5.

[0082] Next, in step S103, the control unit 70 determines whether the absolute value of the calculated Δ film humidity is less than a predetermined value. At this time, if film humidity control has already been performed, the absolute value will be less than the predetermined value, so the control unit 70 determines YES and proceeds to step S104. If film humidity control has not been performed, the absolute value will not be less than the predetermined value, so the control unit 70 determines NO and returns to step S101.

[0083] In step S104, the control unit 70 permits the start of catalytic oxide film rate control. When the start of catalytic oxide film rate control is permitted, the control unit 70 performs catalytic oxide film rate control. That is, the control unit 70 performs the film humidity control and then the catalytic oxide film rate control.

[0084] In the catalytic oxide film ratio control, the control unit 70 executes the control process shown in Fig. 8. The control process shown in Fig. 8 is repeated until the execution thereof is stopped.

[0085] As shown in Fig. 8, in step S21, the control unit 70 acquires the current value of the catalytic oxide film ratio. At this time, the current value of the catalytic oxide film ratio is calculated by the calculation method described above. The control process shown in Fig. 8 is repeated at predetermined intervals, so that the current value of the catalytic oxide film ratio is acquired periodically (for example, every 1 second).

[0086] Next, in step S22, the control unit 70 calculates a Δ-coating ratio, which is the difference between the target value of the catalytic oxide film ratio and the current value of the catalytic oxide film ratio, using the current value of the catalytic oxide film ratio calculated in step S21 and the target value of the catalytic oxide film ratio stored in the control unit 70.

[0087] Subsequently, in step S23, the control unit 70 determines whether the absolute value of the Δ coating ratio calculated in step S22 is equal to or greater than a predetermined value. If the determination in step S23 is NO, the control unit 70 temporarily ends this process. If the determination in step S23 is YES, the control unit 70 proceeds to step S24.

[0088] In step S24, the control unit 70 determines whether the Δ coating ratio calculated in step S22 is a negative value.

[0089] In step S24, if the current value of the catalytic oxide film ratio is greater than the target value of the catalytic oxide film ratio and the Δ film ratio is a negative value, the control unit 70 makes a YES determination. In this case, the control unit 70 proceeds to step S25 and determines whether the SOC of the battery 64 is less than a predetermined value. If the determination is NO, the control unit 70 temporarily ends this process. If the determination is YES, the control unit 70 proceeds to step S26 and corrects the output of the FC20 (i.e., the FC output) so that the voltage of the FC20 becomes the film reduction voltage, and corrects the output of the battery 64 (i.e., the BAT output) so that the battery 64 is in a charged state.

[0090] The film reduction voltage is a voltage at which the catalytic oxide film is reduced by reduction, and is, for example, a voltage lower than 0.7 V when the cell voltage is 0.7 V. Correcting the FC output to achieve the film reduction voltage means increasing the FC output. To increase the FC output, the control unit 70 controls the operation of the injector 37, circulation pump 39, air compressor 41, flow dividing valve 43, and FC boost converter 61 so that the current command from the FC boost converter 61 increases and the supply amounts of hydrogen gas and air increase. As a result, the catalytic oxide film ratio changes so that the current value of the catalytic oxide film ratio approaches the target value of the catalytic oxide film ratio.

[0091] Furthermore, the control unit controls the operation of the battery converter 63 so that the surplus of the FC output relative to the system required output is charged to the battery 64. After that, the control unit 70 temporarily ends this process.

[0092] Furthermore, in step S24, if the current value of the catalytic oxide film ratio is smaller than the target value of the catalytic oxide film ratio and the Δ film ratio is a positive value, the control unit 70 makes a NO determination. In this case, the control unit 70 proceeds to step S27 and determines whether the SOC of the battery 64 is equal to or greater than a predetermined value. If the determination is NO, the control unit 70 temporarily ends this process. If the determination is YES, the control unit 70 proceeds to step S28 and corrects the FC output so that the voltage of the FC 20 becomes the film generation voltage, and corrects the BAT output so that the BAT output becomes a shortage compensation output.

[0093] The film formation voltage is the voltage at which a catalytic oxide film is formed, and is, for example, a cell voltage higher than 0.8 V. Correcting the FC output to achieve the film formation voltage means lowering the FC output. To lower the FC output, the control unit 70 controls the operation of the injector 37, circulation pump 39, air compressor 41, flow dividing valve 43, and FC boost converter 61 so that the current command from the FC boost converter 61 decreases and the supply amounts of hydrogen gas and air decrease. As a result, the catalytic oxide film ratio changes so that the current value of the catalytic oxide film ratio approaches the target value of the catalytic oxide film ratio.

[0094] The shortage compensation output is an output that compensates for the shortage of the FC output relative to the system required output. The control unit 70 controls the operation of the battery converter 63 so that the battery 64 outputs power of an amount that compensates for the shortage relative to the system required output. Thereafter, the control unit 70 temporarily ends this process.

[0095] In this manner, the control unit 70 acquires the current value of the catalytic oxide film ratio. The control unit 70 controls the operation of the injector 37, the circulation pump 39, the air compressor 41, the flow dividing valve 43, and the FC boost converter 61 so as to change the catalytic oxide film ratio so that the acquired current value approaches a preset target value of the catalytic oxide film ratio. In this embodiment, the catalytic oxide film ratio corresponds to the second state quantity. The target value of the catalytic oxide film ratio corresponds to the second target value. The injector 37, the circulation pump 39, the air compressor 41, the flow dividing valve 43, and the FC boost converter 61 correspond to a second actuator capable of adjusting the second state quantity. Control of the operation of the injector 37 and the like corresponds to the second control.

[0096] Here, this embodiment will be compared with Comparative Example 2. In the time chart of Fig. 9, the dashed line represents Comparative Example 2, and the solid line represents this embodiment. The period from time t20 to time t22 is a low load period in which the system required output is lower than the high load reference value. The period from time t22 to time t24 is a high load period in which the system required output is higher than the high load reference value. The period after time t24 is a low load period.

[0097] 9, in Comparative Example 2, during low load from time t20 to time t22, the control unit 70 sets the FC output to a low output value corresponding to the system required output. During high load from time t22 to time t24, the control unit 70 sets the FC output to a high output value corresponding to the system required output. During low load after time t24, the control unit 70 sets the FC output to a low output value corresponding to the system required output.

[0098] In Comparative Example 2, under low load, the FC output is low and the cell potential is high, above 0.8 V. This causes the catalyst oxide film to grow, and as shown in Figure 9, the catalyst oxide film ratio increases over time. Also, in Comparative Example 2, under high load, the FC output is high and the cell potential is low, below 0.7 V. This causes the catalyst oxide film to decrease due to reduction, and the catalyst oxide film ratio decreases over time. In Comparative Example 2, when switching from low to high load, the FC outputs the desired power with the catalyst oxide film increased, resulting in a significant drop in voltage. Therefore, as shown in Figure 9, there is a large difference in voltage between low and high loads, i.e., the voltage fluctuation range is large.

[0099] In this embodiment, as shown in the period from time t20 to t21 in Fig. 9, basically, as in Comparative Example 2, the control unit 70 sets the FC output to a low output value corresponding to the system required output during low load. When the current value of the catalytic oxide film ratio exceeds the target value and the battery 64 is in a chargeable state, the control unit 70 performs step S26 in Fig. 8 in the catalytic oxide film ratio control. As a result, during the period from time t21 to time t22 in Fig. 9, the control unit 70 increases the FC output so that the voltage of the FC 20 becomes the film reduction voltage, and charges the battery 64 with the surplus FC output at that time.

[0100] 9, when the load changes from low to high, the control unit 70 increases the FC output, which is on the low voltage side, to a high output value according to the system required output. At this time, the control unit 70 stops charging the battery 64 with the surplus FC output.

[0101] When the current value of the catalytic oxide film ratio falls below the target value under high load and the battery 64 is in a state where it can output power, the control unit 70 performs step S28 in Fig. 8 in the catalytic oxide film ratio control. As a result, during the period from time t23 to time t24 in Fig. 9, the control unit 70 reduces the FC output so that the voltage of the FC 20 becomes the film generation voltage, and increases the output of the battery 64 to compensate for the power shortage.

[0102] Then, at the timing of the change from high load to low load at time t24 in Fig. 9, the control unit 70 reduces the FC output, which is on the higher voltage side, to a low output value according to the system required output, and stops output from the battery 64. After that, at time t25 in Fig. 9, the same thing as at time t21 is done.

[0103] As explained above, according to this embodiment, the catalytic oxide film ratio can be reduced compared to Comparative Example 2 during the period from time t21 to time t22 under low load conditions. Since the load is switched from low to high under these conditions, the power generation efficiency under high load conditions can be increased compared to Comparative Example 2. As a result, as shown in region A1 in FIG. 9 , when the FC output is the same, the voltage of the FC20 under high load conditions can be increased compared to Comparative Example 2. Therefore, the difference in voltage between low load and high load conditions can be reduced compared to Comparative Example 2. In other words, the voltage fluctuation range can be reduced.

[0104] As described above, according to this embodiment, the catalytic oxide film ratio is controlled to approach the target value. This reduces voltage fluctuations due to variations in the catalytic oxide film ratio, thereby suppressing deterioration of the power generation performance of the catalyst in the air electrode 24.

[0105] Furthermore, according to this embodiment, the control unit 70 performs the catalytic oxide film ratio control after performing the membrane humidity control. When the membrane humidity is low, the accuracy of detecting the catalytic oxide film ratio is low. During the catalytic oxide film ratio control, the control unit 70 detects the catalytic oxide film ratio when the membrane humidity is close to its target value. This improves the accuracy of detecting the catalytic oxide film ratio.

[0106] [Intermittent operation processing] Furthermore, the control unit 70 performs intermittent operation of the fuel cell system 10 when the system required output is smaller than the load operation reference value and power supply from the FC20 is not necessary. For example, intermittent operation is performed when the accelerator is off and the system required output is zero. Intermittent operation is an operation in which air is supplied to the FC20 intermittently. Intermittent operation is an operation in which the FC20 is made to generate power while suppressing the FC output low in order to maintain the voltage of the FC20 at a predetermined level. Intermittent operation is not limited to an operation in which power generation is limited while a small amount of power generation continues, but may also be an operation mode in which power generation by the FC20 is completely stopped.

[0107] Unlike the present embodiment, when the system required output is smaller than the load operation reference value, the supply of hydrogen gas and air to the FC20 is stopped, and power generation by the FC20 is stopped. When the system required output becomes larger than the load operation reference value from this state, startup operation is required, and it takes time to transition to load operation. Therefore, in this embodiment, when the system required output is smaller than the load operation reference value, intermittent operation is performed. This makes it possible to switch to load operation without startup operation when the system required output switches from 0 to a state larger than the load operation reference value.

[0108] When the start switch ST is turned ON, the control unit 70 starts the control process of Fig. 10. First, in step S31, the control unit 70 performs intermittent operation at startup. In performing intermittent operation, the control unit 70 controls the operation of the air compressor 41 so that the supply and stop of air to the FC20 is alternately repeated. The control unit 70 controls the operation of the injector 37, etc. so that hydrogen gas is continuously supplied with a minimum amount of hydrogen gas consumption.

[0109] Next, in step S32, the control unit 70 determines whether the system required output is equal to or greater than the load operation reference value. If the determination is NO, the control unit 70 returns to step S31 and continues the intermittent operation that was performed at startup. If the determination is YES, the control unit 70 proceeds to step S33 and performs load operation. During load operation, the control unit 70 controls the operation of the injector 37, air compressor 41, etc. so that the FC output becomes an output value corresponding to the system required output.

[0110] Subsequently, in step S34, the control unit 70 acquires the catalytic oxide film rate during load operation, which is calculated by the above-described calculation method.

[0111] Next, in step S35, the control unit 70 determines whether the system required output is less than the load operation reference value. If the determination is NO, the control unit 70 returns to step S33 and continues the load operation. As a result, when the system required output is equal to or greater than the load operation reference value, the load operation is continued and the catalyst oxide film ratio is periodically acquired.

[0112] If the determination in step S35 is YES, the control unit 70 proceeds to step S36 and performs intermittent operation processing.

[0113] After performing the intermittent operation process, the control unit 70 proceeds to step S37 and determines whether the system required output is less than the load operation reference value. If the determination is NO, the control unit 70 proceeds to step S33 and performs load operation. As a result, if the required output increases during intermittent operation, the operation is switched from intermittent operation to load operation.

[0114] If the determination in step S37 is YES, the control unit 70 proceeds to step S38 and determines whether the start switch ST is OFF. If the determination in step S38 is NO, the control unit 70 returns to step S36 and performs intermittent operation processing. If the determination in step S38 is YES, the control unit 70 proceeds to step S39 and stops operation of the fuel cell system 10.

[0115] Next, the intermittent operation process of step S36 will be described. First, in step S41 of Fig. 11, the control unit 70 determines whether the SOC of the battery 64 is less than a predetermined value. In other words, the control unit 70 determines whether the battery 64 is in a chargeable state.

[0116] In step S41, if the SOC is equal to or greater than the predetermined value and the battery 64 is in a non-chargeable state, the control unit 70 makes a NO determination and proceeds to step S42. In step S42, the control unit 70 sets the FC voltage for normal intermittent operation. Thereafter, the control unit 70 proceeds to step S45.

[0117] In step S41, if the SOC is less than the predetermined value and the battery 64 is in a chargeable state, the control unit 70 makes a YES determination and proceeds to step S43. In step S43, the control unit 70 adjusts the FC voltage before intermittent operation. After the FC voltage adjustment is completed, the control unit 70 proceeds to step S44. In step S44, the control unit 70 sets the FC voltage during intermittent operation. Thereafter, the control unit 70 proceeds to step S45.

[0118] In step S45, the control unit 70 performs intermittent operation. That is, the control unit 70 controls the operation of the air compressor 41 and the flow dividing valve 43 so that the air flow rate alternates between 0 and a predetermined value greater than 0. At this time, the control unit 70 adjusts the air flow rate supplied to the FC 20 so that the FC voltage becomes the FC voltage set in step S42 or step S44. After performing intermittent operation, the control unit 70 ends the intermittent operation process.

[0119] Here, the present embodiment will be compared with Comparative Example 3. Comparative Example 3 differs from the present embodiment in the intermittent operation processing performed in step S36 of the control processing in FIG. 10. Furthermore, in Comparative Example 3, step S34 of the control processing in FIG. 10 is not performed. The other parts of the control processing in FIG. 10 are the same as those of the first embodiment.

[0120] In the time chart of Fig. 12, the dashed line represents Comparative Example 3, and the solid line represents this embodiment. Fig. 12 shows an example in which the system required output is lower than the load operation reference value at the beginning of operation of the fuel cell system 10. The beginning of operation is a predetermined period that begins immediately after the start switch ST is turned ON and operation of the fuel cell system 10 is started. At time t40, the start switch ST is turned ON. The period from time t40 to time t41 is the beginning of operation. At the beginning of operation, the system required output is 0 or close to 0, and is lower than the load operation reference value.

[0121] In both this embodiment and Comparative Example 3, after time t40, the control unit 70 executes step S31 to perform intermittent operation at startup. That is, the air flow rate supplied to the FC20 (i.e., the stack supply air flow rate) alternates between a predetermined value greater than 0 and 0. During intermittent operation at startup, the average voltage V2 is high, and the cell voltage is at a high potential of 0.7 V to 0.8 V. As a result, the oxide film on the catalyst grows over time, and the catalyst oxide film ratio increases.

[0122] After time t41, when the system required output becomes higher than the load operation reference value, the control unit 70 executes steps S32 and S33 to perform load operation in both this embodiment and Comparative Example 3. Air is continuously supplied, and the FC output is set to an output value according to the system required output.

[0123] After time t43, when the system required output becomes a value lower than the load operation reference value, in Comparative Example 3, the control unit 70 executes step S36 to perform intermittent operation after load operation. In this intermittent operation after load operation, the air supply is stopped and the FC output is set to 0. Thereafter, similar to the intermittent operation at startup, a state in which the air flow rate is a predetermined value greater than 0 and a state in which the air flow rate is 0 are alternately repeated.

[0124] After time t45, when the system required output becomes a value higher than the load operation reference value, in Comparative Example 3, the control unit 70 executes steps S37 and S33 to perform load operation. That is, air is continuously supplied at an air flow rate according to the system required output. The FC output is set to an output value according to the system required output.

[0125] Thus, in Comparative Example 3, when the system required output switches from a value higher than the load operation reference value to a value lower than the load operation reference value, the FC output is immediately set to 0, and intermittent operation is performed. When the FC output drops suddenly, the inside of the FC20 is in a rich state with both hydrogen gas and air, so the voltage of the FC20 rises sharply, and the cell voltage reaches a high potential of 0.7V to 0.8V. Therefore, during intermittent operation, the catalytic oxide film ratio increases over time. Thereafter, the system required output switches from a value lower than the load operation reference value to a value higher than the load operation reference value, and load operation is performed. At this time, load operation is performed with a high catalytic oxide film ratio, so the voltage of the FC20 drops significantly. Therefore, the difference in voltage between when the system required output is lower and when it is higher than the load operation reference value is large. In other words, the voltage fluctuation range is large.

[0126] In this embodiment, unlike Comparative Example 3, during load operation at time t42, etc., the control unit 70 periodically acquires the catalytic oxide film ratio by executing step S34. After time t43, if the system required output becomes lower than the load operation reference value, the control unit 70 performs intermittent operation processing in step S36. In this intermittent operation processing, if the battery 64 is in a chargeable state, the control unit 70 performs step S43 to adjust the FC voltage before intermittent operation.

[0127] In adjusting the FC voltage before intermittent operation, the control unit 70 compares the current value of the catalyst oxide film ratio acquired in step S34 with the target value of the catalyst oxide film ratio, and adjusts the FC output and air flow rate according to the difference between the current value and the target value so that the FC voltage becomes the target voltage. The target voltage is the voltage at which the oxide film is reduced, and is a cell potential lower than 0.7 V. The reduction becomes faster as the cell potential is lowered from 0.7 V.

[0128] Specifically, if the current value of the catalytic oxide film ratio is greater than the target value, the control unit 70 gradually reduces the FC output so that the voltage reaches a level at which the catalytic oxide film is reduced, and causes the surplus FC output to charge the battery 64. The gradual reduction in FC output is achieved by gradually reducing the hydrogen gas flow rate and air flow rate supplied to the FC 20 and by reducing the current command from the FC boost converter 61. The hydrogen gas flow rate is adjusted by the injector 37 and circulation pump 39. The air flow rate is adjusted by the air compressor 41 and flow dividing valve 43.

[0129] By gradually reducing the FC output, it is possible to suppress sudden voltage rises. By gradually reducing the air flow rate, there is a shortage of air inside the FC20, which deteriorates the IV performance. By deliberately deteriorating the IV performance, it is possible to prevent excessive voltage.

[0130] At time t44, when the FC output becomes 0 and the adjustment of the FC voltage is completed, the control unit 70 sets the FC voltage during intermittent operation in step S44. At this time, the air flow rate during intermittent operation is set to be smaller than that during intermittent operation at startup, so that the average voltage V1 during intermittent operation is maintained at the voltage during FC voltage adjustment.

[0131] After time t44, the control unit 70 executes step S45, thereby performing intermittent operation. That is, the air flow rate alternates between 0 and a predetermined value. As described above, the predetermined value of the air flow rate at this time is lower than that of the intermittent operation at startup. Note that the control unit 70 may adjust the air supply timing as necessary so that the average voltage during intermittent operation is maintained at the voltage during FC voltage adjustment.

[0132] After that, when the system required output becomes larger than the load operation reference value after time t45, the load operation is performed as in the third comparative example.

[0133] Thus, in this embodiment, when the system required output switches from a value higher than the load operation reference value to a value lower than the load operation reference value, the FC output is gradually reduced to 0, and then intermittent operation is performed. By gradually reducing the FC output, the cell potential is set to a low potential lower than 0.7 V. In this intermittent operation, the air flow rate is reduced compared to intermittent operation at startup, so the cell potential is maintained at a low potential. This reduces the oxide film on the catalyst, and the catalyst oxide film rate decreases.

[0134] Thereafter, the system required output switches from a value lower than the load operation reference value to a value higher than the load operation reference value, and load operation is performed. At this time, load operation is performed with a low catalyst oxide film ratio, so power generation efficiency at high loads can be increased compared to Comparative Example 3. As a result, as shown in area A2 in FIG. 12, when compared assuming the same FC output, the voltage of the FC 20 can be increased compared to Comparative Example 3. Therefore, the difference in voltage between intermittent operation at startup and load operation can be reduced compared to Comparative Example 3. In other words, the voltage fluctuation range can be reduced. Therefore, deterioration of the power generation performance of the catalyst in the air electrode 24 can be suppressed.

[0135] [Diffusion resistance control] The control unit 70 performs diffusion resistance control to bring the diffusion resistance closer to the target value of the diffusion resistance when the FC 20 is generating electricity, such as during load operation.

[0136] In this embodiment, the control unit 70 performs the process shown in FIG. 13 before performing the diffusion resistance control. In step S201, the control unit 70 acquires the current value of the catalytic oxide film ratio, similar to step S21 in Fig. 8. Subsequently, in step S202, the control unit 70 calculates the Δ film ratio, similar to step S22 in Fig. 8.

[0137] Next, in step S203, the control unit 70 determines whether the absolute value of the calculated Δ coating ratio is less than a predetermined value. If catalytic oxide film ratio control has already been performed, the absolute value will be less than the predetermined value, so the control unit 70 makes a YES determination and proceeds to step S204. If catalytic oxide film ratio control has not been performed, the absolute value will not be less than the predetermined value, so the control unit 70 makes a NO determination and returns to step S201.

[0138] In step S204, the control unit 70 permits the start of diffusion resistance control. When the start of diffusion resistance control is permitted, the control unit 70 performs diffusion resistance control. That is, the control unit 70 performs the coating ratio control and then the diffusion resistance control.

[0139] In the diffusion resistance control, the control unit 70 executes the control process shown in Fig. 14. The control process shown in Fig. 14 is repeated until its execution is stopped.

[0140] 14, in step S51, the control unit 70 acquires the current value of the diffusion resistor. At this time, the current value of the diffusion resistor is calculated by the calculation method described above.

[0141] Subsequently, in step S52, the control unit 70 calculates a Δ diffusion resistance value, which is the difference between the current value of the diffusion resistance and the target value of the diffusion resistance, using the current value of the diffusion resistance acquired in step S51 and the target value of the diffusion resistance stored in the control unit 70.

[0142] Next, in step S53, the control unit 70 determines whether the absolute value of the Δ diffusion resistance value calculated in step S52 is equal to or greater than a predetermined value. If the determination in step S53 is NO, the control unit 70 temporarily ends this process. If the determination in step S53 is YES, the control unit 70 proceeds to step S54.

[0143] In step S54, the control unit 70 determines whether the Δ diffusion resistance value calculated in step S52 is a negative value.

[0144] If the current value of the diffusion resistance is greater than the target value of the diffusion resistance and the Δdiffusion resistance value is a negative value, the control unit 70 makes a YES determination in step S14. In this case, the control unit 70 proceeds to step S55 and controls the operation of at least one of the air compressor 41 and the flow dividing valve 43 to increase the air flow rate so as to decrease the diffusion resistance value. This causes the current value of the diffusion resistance to change toward the target value of the diffusion resistance. Thereafter, the control unit 70 temporarily terminates this process.

[0145] On the other hand, if the current value of the diffusion resistance is smaller than the target value of the diffusion resistance and the Δdiffusion resistance value is a positive value, the control unit 70 makes a NO determination in step S54. In this case, the control unit 70 proceeds to step S56 and controls the operation of at least one of the air compressor 41 and the flow dividing valve 43 to reduce the air flow rate so as to increase the diffusion resistance value. This causes the current value of the diffusion resistance value to change toward the target value of the diffusion resistance value. Thereafter, the control unit 70 temporarily terminates this process.

[0146] In this manner, the control unit 70 acquires the current value of the diffusion resistance. The control unit 70 controls the operation of at least one of the air compressor 41 and the flow dividing valve 43 so as to change the diffusion resistance so that the acquired current value of the diffusion resistance approaches a preset target value of the diffusion resistance. In this embodiment, the diffusion resistance corresponds to the third state quantity. The target value of the diffusion resistance corresponds to the third target value. The air compressor 41 and the flow dividing valve 43 correspond to a third actuator capable of adjusting the third state quantity. The control of the air compressor 41 and the like corresponds to the third control.

[0147] Here, the present embodiment is compared with Comparative Example 4. Unlike the present embodiment, Comparative Example 4 increases the air flow rate when it is determined from the operating state of the FC20 that flooding (i.e., water clogging inside the air electrode 24) has occurred.

[0148] In this case, as shown in FIG. 15, when the FC output is a predetermined value greater than 0, before time t51, water is produced by the power generation of the FC20, and the diffusion resistance increases as time passes. At time t51, it is determined that flooding has occurred, and the air flow rate is increased. After time t51, the air stoichiometric ratio becomes larger than before time t51. In Comparative Example 4, the diffusion resistance increases until it is determined that flooding has occurred. The increase in diffusion resistance causes the voltage of the FC20 to decrease. As a result, the voltage fluctuation range of the FC20 is large.

[0149] In contrast, in this embodiment, the control unit 70 performs the above-described diffusion resistance control. In this case, as shown in FIG. 15, the air flow rate is adjusted, and the diffusion resistance is maintained at a value close to the target value. Because the air flow rate is constantly adjusted during power generation by the FC20, the air stoichiometric ratio constantly fluctuates. Because the diffusion resistance is maintained at a value close to the target value, the voltage fluctuation range of the FC20 can be made smaller than that of Comparative Example 4, as shown in region A3 in FIG. 15.

[0150] In this manner, according to this embodiment, the diffusion resistance is controlled to approach the target value. This reduces voltage fluctuations due to variations in the diffusion resistance. This in turn reduces deterioration of the power generation performance of the catalyst in the air electrode 24.

[0151] Furthermore, according to this embodiment, the control unit 70 performs the diffusion resistance control after performing the membrane humidity control and the catalytic oxide film ratio control. Therefore, during the diffusion resistance control, the control unit 70 detects the diffusion resistance when the membrane humidity and the catalytic oxide film ratio are close to their respective target values. This improves the detection accuracy of the diffusion resistance.

[0152] (Second embodiment) In this embodiment, the control unit 70 performs the diffusion resistance control after performing the membrane humidity control. The control contents of the membrane humidity control and the diffusion resistance control are the same as those in the first embodiment. In this embodiment, the membrane humidity corresponds to the first state quantity. The membrane humidity control corresponds to the first control. The humidifier 44 corresponds to the first actuator. The diffusion resistance corresponds to the second state quantity. The diffusion resistance control corresponds to the second control. The air compressor 41 and the flow dividing valve 43 correspond to the second actuator.

[0153] Here, this embodiment will be compared with Comparative Example 5. In the time chart of Fig. 16, the dashed line represents Comparative Example 5, and the solid line represents this embodiment. The membrane humidity corresponds to the first state quantity. The diffusion resistance corresponds to the second state quantity.

[0154] In Comparative Example 5, at time t61, the control unit 70 simultaneously starts membrane humidity control and diffusion resistance control. At time t61, the current value of membrane humidity is lower than the target value. Therefore, the control unit 70 increases the amount of humidification to bring the current value of membrane humidity closer to the target value. When the amount of humidification increases, condensed water is generated inside the air electrode 24, and the diffusion resistance increases. When the current value of diffusion resistance becomes larger than the target value, the control unit 70 increases the air flow rate to bring the current value of diffusion resistance closer to the target value. When the air flow rate increases, the amount of water removed from the electrolyte membrane increases, and the membrane humidity decreases.

[0155] Thus, in Comparative Example 5, when an actuator capable of adjusting one state quantity is operated, the operated quantity affects another state quantity. In other words, the other state quantity fluctuates away from the target value. As a result, the state quantities of the film humidity and the diffusion resistance repeatedly fluctuate, approaching and deviating from the target value. It takes time for each state quantity to approach the target value. Furthermore, fluctuations in the state quantities of the film humidity and the diffusion resistance cause fluctuations in the output voltage of the FC20.

[0156] In contrast, in this embodiment, the control unit 70 starts membrane humidity control at time t61. Then, at time t62, after the membrane humidity has approached the target value through membrane humidity control, the control unit 70 starts diffusion resistance control. In other words, when performing membrane humidity control, the control unit 70 controls the operation of the humidifier and the actuator that adjusts the air flow rate so as to minimize the effect of the actuator that adjusts the air flow rate on the membrane humidity. In other words, when performing membrane humidity control, the control unit 70 controls the operation of the actuator that adjusts the air flow rate so as to prevent the membrane humidity from changing away from the target value due to the operation of the actuator that adjusts the air flow rate.

[0157] This prevents the diffusion resistance control from interfering with the membrane humidity control. Fluctuations in the membrane humidity approaching or deviating from the target value can be reduced. This reduces the time it takes for the membrane humidity to approach the target value after the membrane humidity control is started.

[0158] Furthermore, when controlling diffusion resistance, the previously adjusted membrane humidity is close to the target value, so fluctuations in membrane humidity due to the influence of diffusion resistance control are small. Therefore, the influence of membrane humidity control on diffusion resistance control is small. Fluctuations in the diffusion resistance approaching or deviating from the target value can be reduced.

[0159] 16, by reducing the fluctuations in the membrane humidity and the diffusion resistance, the present embodiment can reduce the voltage fluctuations of FC20 compared to Comparative Example 5. Therefore, the deterioration of the power generation performance of the catalyst in the air electrode 24 can be suppressed.

[0160] In this embodiment, the control unit 70 detects the membrane humidity and performs membrane humidity control to bring the current value of the membrane humidity closer to the target value. However, the control unit 70 may use H + Conductivity (i.e., proton conductivity) is detected and H + The current conductivity value may be controlled to approach the target value. +The conductivity has a predetermined relationship with the film humidity and is a physical quantity related to the film humidity.

[0161] (Other embodiments) (1) In the above-described embodiment, the calculation of the membrane humidity, catalytic oxide film ratio, and diffusion resistance is performed using a model formula. However, the calculation may be performed using a multidimensional map that inputs variables such as sensor values.

[0162] (2) The present invention is not limited to the above-described embodiments, and can be modified as appropriate within the scope of the claims, including various modifications and modifications within the scope of equivalents. Furthermore, the above-described embodiments are not unrelated to each other and can be combined as appropriate, except in cases where the combination is clearly impossible. Furthermore, in the above-described embodiments, it goes without saying that the elements constituting the embodiments are not necessarily essential, except in cases where they are specifically stated as essential or where they are clearly considered essential in principle.

[0163] (3) The control unit and the method described herein may be implemented by a special-purpose computer configured by configuring a processor and memory programmed to perform one or more functions embodied in a computer program. Alternatively, the control unit and the method described herein may be implemented by a special-purpose computer configured by configuring a processor with one or more dedicated hardware logic circuits. Alternatively, the control unit and the method described herein may be implemented by one or more special-purpose computers configured by combining a processor and memory programmed to perform one or more functions with a processor configured with one or more hardware logic circuits. Furthermore, the computer program may be stored in a computer-readable non-transitory tangible recording medium as instructions executed by a computer. [Explanation of symbols]

[0164] 20 Fuel Cell 22 Electrolyte membrane 24 Air electrode 37 Injector 39 Circulation Pump 41 Air Compressor 43 Diverter valve 44 Humidifier 61 FC boost converter 70 Control Unit

Claims

1. 1. A fuel cell system, comprising: a fuel cell (20) having a solid polymer electrolyte membrane (22), a fuel electrode (23) disposed on one side of the electrolyte membrane, and an air electrode (24) disposed on the other side of the electrolyte membrane; a first actuator (44) capable of adjusting a first state quantity indicating an internal state of the fuel cell; a second actuator (37, 39, 41, 43, 61) capable of adjusting a second state quantity that indicates an internal state of the fuel cell and that is different from the first state quantity; a control unit (70) that controls the operation of the first actuator and the operation of the second actuator, the control unit acquires a current value of the first state quantity, and performs first control to control operation of the first actuator so that the acquired current value of the first state quantity changes the first state quantity to approach a predetermined first target value, and also acquires a current value of the second state quantity, and performs second control to control operation of the second actuator so that the acquired current value of the second state quantity changes the second state quantity to approach a predetermined second target value, when performing the first control, the control unit controls the operation of the second actuators (41, 43) so that the first state quantity is suppressed from changing to a side away from the first target value due to the operation of the second actuators; The fuel cell system, wherein the first state quantity is a relative humidity of the electrolyte membrane or a physical quantity related to the relative humidity, and the second state quantity is a gas diffusion resistance of the air electrode.

2. 1. A fuel cell system, comprising: a fuel cell (20) having a solid polymer electrolyte membrane (22), a fuel electrode (23) disposed on one side of the electrolyte membrane, and an air electrode (24) disposed on the other side of the electrolyte membrane; a first actuator (44) capable of adjusting a first state quantity indicating an internal state of the fuel cell; a second actuator (37, 39, 41, 43, 61) capable of adjusting a second state quantity that indicates an internal state of the fuel cell and that is different from the first state quantity; a control unit (70) that controls the operation of the first actuator and the operation of the second actuator, the control unit acquires a current value of the first state quantity, and performs first control to control operation of the first actuator so that the acquired current value of the first state quantity changes the first state quantity to approach a predetermined first target value, and also acquires a current value of the second state quantity, and performs second control to control operation of the second actuator so that the acquired current value of the second state quantity changes the second state quantity to approach a predetermined second target value, the first state quantity is a relative humidity of the electrolyte membrane or a physical quantity related to the relative humidity, the second state quantity is a gas diffusion resistance of the air electrode, The control unit performs the first control and then the second control.

3. 1. A fuel cell system, comprising: a fuel cell (20) having a solid polymer electrolyte membrane (22), a fuel electrode (23) disposed on one side of the electrolyte membrane, and an air electrode (24) disposed on the other side of the electrolyte membrane; a first actuator (44) capable of adjusting a first state quantity indicating an internal state of the fuel cell; a second actuator (37, 39, 41, 43, 61) capable of adjusting a second state quantity that indicates an internal state of the fuel cell and that is different from the first state quantity; a control unit (70) that controls the operation of the first actuator and the operation of the second actuator, the control unit acquires a current value of the first state quantity, and performs first control to control operation of the first actuator so that the acquired current value of the first state quantity changes the first state quantity to approach a predetermined first target value, and also acquires a current value of the second state quantity, and performs second control to control operation of the second actuator so that the acquired current value of the second state quantity changes the second state quantity to approach a predetermined second target value, the first state quantity is a relative humidity of the electrolyte membrane or a physical quantity related to the relative humidity, the second state quantity is an oxide film ratio of a catalyst included in the air electrode, the control unit performs the first control and then the second control, the fuel cell system includes a third actuator (41, 43) capable of adjusting the gas diffusion resistance of the air electrode as a third state quantity indicating an internal state of the fuel cell; the control unit, after performing the second control, acquires a current value of the third state quantity, and performs third control to control the operation of the third actuator so that the acquired current value of the third state quantity changes the third state quantity toward a predetermined third target value.

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