fuel cell system

Abstract

To moisturize a fuel battery stack in accordance with a dry state of the fuel battery stack.SOLUTION: A fuel battery system comprises a fuel battery stack, a control device, and an auxiliary device for moisturizing the fuel battery stack. By applying a specific AC voltage to the fuel battery stack, the control device measures an impedance of the fuel battery stack. The control device carries out moisturizing processing for adjusting an operation amount of the auxiliary device with respect to a target value of a moisturizing state in such a manner that the fuel battery stack is more moisturized when a real component in the impedance of the fuel battery stack is greater, if the real component in the impedance of the fuel battery stack is equal to or greater than a starting threshold.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to fuel cell systems. [Background technology]

[0002] The fuel cell system disclosed in Patent Document 1 includes a fuel cell stack, a cooling unit, and a control device. The fuel cell stack generates electricity through a chemical reaction between anode gas and cathode gas. The cooling unit cools the fuel cell stack. The control device strengthens the cooling by the cooling unit when the impedance of the fuel cell stack becomes equal to or greater than a first threshold. The control device continues to strengthen the cooling by the cooling unit until the impedance of the fuel cell stack becomes equal to or less than a second threshold. This allows the fuel cell stack to be moistened when it is dry. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-73587 Summary of the Invention [Problem to be solved by the invention]

[0004] In Patent Document 1, when the impedance of the fuel cell stack exceeds a first threshold, the cooling unit continues to strengthen cooling until the impedance of the fuel cell stack falls to a second threshold or less. In this case, the temperature of the fuel cell stack may drop excessively. This may reduce the power generation efficiency of the fuel cell stack, which may impair the stability of control related to power generation by the fuel cell stack. [Means for solving the problem]

[0005] A fuel cell system that solves the above problem comprises a fuel cell stack, a measuring unit that measures the impedance of the fuel cell stack, a control device, and an auxiliary device that moistens the fuel cell stack, wherein the control device obtains the impedance measured by the measuring unit by applying a specific AC voltage to the fuel cell stack, and when the real component of the impedance is equal to or greater than a start threshold, executes a moistening process that adjusts the operating amount of the auxiliary device relative to a target value for the moist state so that the larger the real component, the more moist the fuel cell stack becomes.

[0006] The control device adjusts the operation amount of the auxiliary device so that the fuel cell stack becomes wetter as the real component of the impedance increases. The fuel cell stack becomes drier as the real component of the impedance increases. By adjusting the fuel cell stack so that the fuel cell stack becomes wetter as the real component of the impedance increases, the fuel cell stack can be wetted in accordance with the dryness state of the fuel cell stack. This makes it possible to prevent the stability of the control of the fuel cell stack from being impaired.

[0007] In the above fuel cell system, the auxiliary equipment may include a circulation pump that circulates anode gas through the fuel cell stack, an adjustment valve that adjusts the pressure of cathode gas discharged from the fuel cell stack, and a coolant pump that circulates a coolant that cools the fuel cell stack, and the wetting process may adjust an operating amount of at least one of the circulation pump, the adjustment valve, and the coolant pump so that the fuel cell stack becomes wetter as the real component becomes larger.

[0008] In the fuel cell system, the control device may terminate the wetting process when the real component becomes less than a termination threshold, and the termination threshold may be smaller than the start threshold. In the above fuel cell system, the control device may measure the impedance using the measurement unit while the fuel cell stack is generating power.

[0009] In the above fuel cell system, the control device may maintain the target value at a predetermined value when the real component becomes equal to or greater than an upper threshold value, and after the target value is maintained at the predetermined value, adjust the target value when the real component becomes less than a fluctuation start threshold value so that the lower the real component is, the less humidified the fuel cell stack becomes, and the upper threshold value may be greater than the start threshold value and the fluctuation start threshold value may be smaller than the upper threshold value.

[0010] In the above fuel cell system, the control device may adjust the operating amount of the circulation pump when the real component is greater than or equal to the start threshold, adjust the operating amount of the regulating valve when the real component is greater than or equal to a pressure adjustment start threshold, and adjust the operating amount of the refrigerant pump when the real component is greater than or equal to a cooling start threshold, wherein the pressure adjustment start threshold is greater than the start threshold and the cooling start threshold is greater than the pressure adjustment start threshold. [Effects of the Invention]

[0011] According to the present invention, the fuel cell stack can be moistened in accordance with the dryness state of the fuel cell stack. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram of a fuel cell system. [Figure 2] FIG. 2 is a schematic diagram of a fuel cell; [Figure 3] 10 is a flowchart showing a wetting control. [Figure 4] 1 is a Nyquist plot of a fuel cell stack. [Figure 5] FIG. 10 is a diagram showing the relationship between the electrolyte membrane resistance and the target value for the wet state. DETAILED DESCRIPTION OF THE INVENTION

[0013] An embodiment of a fuel cell system will now be described. As shown in Fig. 1, the industrial vehicle 10 includes a vehicle load 11 and a fuel cell system 20. The vehicle load 11 is a device driven by electricity. The vehicle load 11 is, for example, an electric motor driven by electricity. The industrial vehicle 10 travels by being driven by this electric motor.

[0014] <Fuel cell system> The fuel cell system 20 includes a fuel cell stack 21 , a cathode system 40 , an anode system 60 , a diluter 71 , a cooling system 80 , an electrical system 90 , and a control device 110 .

[0015] The fuel cell stack 21 includes a plurality of fuel cell units 22. The fuel cell units 22 are polymer membrane fuel cell units. The fuel cell units 22 generate electricity through a chemical reaction between cathode gas and anode gas.

[0016] 2, the fuel cell 22 includes an ion-permeable electrolyte membrane 23, an anode-side catalyst layer 24, an anode-side microporous layer 25, an anode-side diffusion layer 26, a cathode-side catalyst layer 27, a cathode-side microporous layer 28, and a cathode-side diffusion layer 29. The anode-side catalyst layer 24 and the cathode-side catalyst layer 27 sandwich the electrolyte membrane 23. The anode-side microporous layer 25 and the cathode-side microporous layer 28 sandwich the electrolyte membrane 23 and the catalyst layers 24 and 27. The anode-side diffusion layer 26 and the cathode-side diffusion layer 29 sandwich the electrolyte membrane 23, the catalyst layers 24 and 27, and the microporous layers 25 and 28.

[0017] Each of the catalyst layers 24, 27 promotes the reaction between the anode gas and the cathode gas by means of a catalyst. Each of the catalyst layers 24, 27 includes a catalyst, a carrier that supports the catalyst, and an ionomer that coats the catalyst and the carrier. Examples of the catalyst that can be used include platinum and ruthenium. Examples of the carrier include carbon. Examples of the ionomer that can be used include an ion-conductive polymer electrolyte. Examples of the ionomer that can be used include the same material as the electrolyte membrane 23.

[0018] Each of the microporous layers 25, 28 facilitates the discharge of water generated by chemical reactions during power generation to the outside so that the water does not accumulate in each of the catalyst layers 24, 27. Each of the microporous layers 25, 28 is configured to include, for example, a water-repellent resin and a conductive material such as carbon.

[0019] Each of the diffusion layers 26, 29 serves as a path for electrons, anode gas, and cathode gas. Each of the diffusion layers 26, 29 is made of a material that is gas permeable and electron conductive. Each of the diffusion layers 26, 29 is made of, for example, carbon.

[0020] As shown in FIG. 1, the fuel cell stack 21 includes a cathode flow path 30 and an anode flow path 33. A cathode gas flows through the cathode flow path 30. An anode gas flows through the anode flow path 33. The cathode flow path 30 includes an inlet 31 and an outlet 32. The cathode gas flows into the cathode flow path 30 through the inlet 31 and flows out through the outlet 32. The anode flow path 33 includes an inlet 34 and an outlet 35. The anode gas flows into the anode flow path 33 through the inlet 34 and flows out through the outlet 35. The fuel cell stack 21 generates power by a reaction between the anode gas and the cathode gas. The cathode gas is an oxidant gas. An example of the oxidant gas is oxygen in the air. The anode gas is a fuel gas. An example of the fuel gas is hydrogen gas.

[0021] The cathode system 40 includes an intake port 41 , an electric compressor 42 , an inverter 44 , an intercooler 45 , a cathode supply channel 46 , a cathode discharge channel 49 , a first valve 51 , and a second valve 52 .

[0022] The inlet 41 draws the cathode gas into the fuel cell system 20. The inlet 41 may be open to the atmosphere or may be connected to a gas cylinder. The electric compressor 42 includes an electric motor 43. The electric compressor 42 is driven by the electric motor 43. The electric compressor 42 supplies cathode gas to the fuel cell stack 21. Specifically, the electric compressor 42 compresses the cathode gas supplied from the intake port 41 and supplies the compressed cathode gas to the fuel cell stack 21. The cathode gas supplied from the electric compressor 42 to the fuel cell stack 21 flows through the cathode flow path 30.

[0023] The inverter 44 is connected to the electric motor 43. The inverter 44 converts DC power into AC power and supplies it to the electric motor 43. In this way, the electric motor 43 is driven.

[0024] The intercooler 45 is supplied with the cathode gas discharged from the electric compressor 42. The intercooler 45 cools the cathode gas supplied from the electric compressor 42. The cathode gas supplied to the fuel cell stack 21 is the cathode gas that has been cooled by the intercooler 45.

[0025] The cathode supply path 46 connects the electric compressor 42 and the cathode flow path 30. More specifically, the cathode supply path 46 connects the electric compressor 42 and the inlet 31 of the cathode flow path 30. The cathode supply path 46 includes a first supply path 47 and a second supply path 48. The first supply path 47 connects the electric compressor 42 and the intercooler 45. The second supply path 48 connects the intercooler 45 and the cathode flow path 30.

[0026] The cathode discharge channel 49 connects the cathode flow path 30 and the diluter 71. More specifically, the cathode discharge channel 49 connects the outlet 32 ​​of the cathode flow path 30 and the diluter 71. The cathode discharge channel 49 is a passage through which the cathode exhaust gas flows. The cathode exhaust gas is cathode gas discharged from the fuel cell stack 21 and contains produced water. The produced water is water produced by power generation in the fuel cell stack 21.

[0027] The first valve 51 is provided in the cathode supply passage 46. In the present embodiment, the first valve 51 is provided in the second supply passage 48, i.e., between the intercooler 45 and the cathode flow passage 30. The first valve 51 may also be provided in the first supply passage 47, i.e., between the intercooler 45 and the electric compressor 42.

[0028] The second valve 52 is provided in the cathode discharge path 49. The second valve 52 is a valve whose opening is adjustable. The compression ratio of the electric compressor 42 can be controlled by adjusting the opening of the second valve 52. The pressure of the cathode exhaust gas can be adjusted by adjusting the opening of the second valve 52. The smaller the opening of the second valve 52, the higher the pressure of the cathode exhaust gas. The second valve 52 is an adjustment valve.

[0029] The anode system 60 includes a tank 61, a pressure reducing valve 62, an anode gas supply unit 63, a supply path 64, a circulation path 65, a gas-liquid separator 66, a circulation pump 67, an inverter 69, and an exhaust / drain valve .

[0030] The tank 61 stores the anode gas. The anode gas is supplied from the tank 61 to the pressure reducing valve 62. The pressure reducing valve 62 reduces the pressure of the anode gas supplied from the tank 61. The reduced pressure anode gas is supplied to an anode gas supply unit 63.

[0031] The anode gas supply unit 63 is a member for adjusting the amount of anode gas supplied to the fuel cell stack 21. The amount of anode gas supplied to the fuel cell stack 21 can be adjusted by controlling the anode gas supply unit 63. As the anode gas supply unit 63, for example, a solenoid valve such as an injector can be used.

[0032] The supply path 64 connects the anode gas supply unit 63 and the anode flow path 33. More specifically, the supply path 64 connects the anode gas supply unit 63 and the inlet 34 of the anode flow path 33. The anode gas injected from the anode gas supply unit 63 is supplied to the fuel cell stack 21 through the supply path 64.

[0033] The circulation path 65 connects the anode flow path 33 and the supply path 64. More specifically, the circulation path 65 connects the outlet 35 of the anode flow path 33 and the supply path 64. Anode exhaust gas flows through the circulation path 65. The anode exhaust gas contains unreacted anode gas and generated water. The circulation path 65 is a passage for returning the unreacted anode gas contained in the anode exhaust gas to the supply path 64.

[0034] The gas-liquid separator 66 is provided in the circulation path 65. The gas-liquid separator 66 separates the anode exhaust gas into anode gas and produced water. The produced water separated from the anode exhaust gas is stored in the gas-liquid separator 66.

[0035] The circulation pump 67 is provided in the circulation path 65. The circulation pump 67 includes an electric motor 68. The circulation pump 67 is driven by the electric motor 68. The circulation pump 67 supplies the anode gas separated from the anode exhaust gas by the gas-liquid separator 66 to the supply path 64. This causes the anode gas to circulate through the fuel cell stack 21.

[0036] The inverter 69 is connected to the electric motor 68. The inverter 69 converts DC power into AC power and supplies it to the electric motor 68. In this way, the electric motor 68 is driven.

[0037] The exhaust / drain valve 70 is connected to the gas-liquid separator 66. The exhaust / drain valve 70 can be switched between an open state and a closed state. When the exhaust / drain valve 70 is in the open state, the produced water is discharged from the gas-liquid separator 66. In addition, exhaust is performed from the circulation path 65. When the exhaust / drain valve 70 is in the closed state, the produced water cannot be discharged from the gas-liquid separator 66. In other words, when the exhaust / drain valve 70 is in the closed state, the produced water accumulates in the gas-liquid separator 66. The exhaust / drain valve 70 is switched from the closed state to the open state at predetermined valve opening intervals.

[0038] The gas-liquid separator 66 is connected to a diluter 71. When the exhaust / drain valve 70 is opened, the produced water stored in the gas-liquid separator 66 and the anode exhaust gas are supplied to the diluter 71. The diluter 71 dilutes the anode exhaust gas with the cathode exhaust gas and discharges it into the atmosphere.

[0039] The cooling system 80 includes a refrigerant circulation path 81 , a heat exchanger 82 , a fan 83 , a refrigerant pump 84 , an inverter 86 , and a temperature measurement unit 87 . The refrigerant circulation path 81 connects the fuel cell stack 21 and a heat exchanger 82. The heat exchanger 82 is, for example, a radiator. A refrigerant circulates through the refrigerant circulation path 81. The refrigerant may be, for example, water, antifreeze, or air.

[0040] The fan 83 blows air toward the heat exchanger 82. The air blown from the fan 83 cools the refrigerant inside the heat exchanger 82. The refrigerant pump 84 circulates the refrigerant through the refrigerant circulation path 81. The refrigerant pump 84 includes an electric motor 85. The refrigerant pump 84 is driven by the electric motor 85. The refrigerant cooled in the heat exchanger 82 is supplied to the fuel cell stack 21 through the refrigerant circulation path 81, thereby cooling the fuel cell stack 21.

[0041] The inverter 86 is connected to the electric motor 85. The inverter 86 converts DC power into AC power and supplies it to the electric motor 85. In this way, the electric motor 85 is driven.

[0042] The temperature measurement unit 87 measures the temperature of the refrigerant. The temperature measurement unit 87 may be configured to measure the temperature of the refrigerant before heat exchange with the fuel cell stack 21, or may be configured to measure the temperature of the refrigerant after heat exchange with the fuel cell stack 21.

[0043] The electrical system 90 includes a first DC / DC converter 91, a current sensor 93, a voltage sensor 94, a second DC / DC converter 95, a first power storage device 96, a charge state detection unit 98, and a second power storage device 99.

[0044] The first DC / DC converter 91 is connected to the fuel cell stack 21. The first DC / DC converter 91 is a DC / DC converter that transforms the output power of the fuel cell stack 21 and outputs the transformed power. For example, the first DC / DC converter 91 transforms the output power of the fuel cell stack 21 to 48 V and outputs the transformed power. The output power from the first DC / DC converter 91 is supplied to the vehicle load 11. The first DC / DC converter 91 includes a switching element 92. The first DC / DC converter 91 performs transformation by controlling the switching of the switching element 92.

[0045] The current sensor 93 measures the output current of the fuel cell stack 21 . The voltage sensor 94 measures the output voltage of the fuel cell stack 21. The voltage sensor 94 used is one that can measure the voltages of the multiple fuel cell cells 22 individually. For example, the voltage sensor 94 used is one that has multiple ports, with the positive and negative electrodes of the fuel cell cells 22 connected to each of the multiple ports. This allows the voltage sensor 94 to measure the voltages of the fuel cell cells 22 individually.

[0046] The second DC / DC converter 95 is connected to the first DC / DC converter 91. The second DC / DC converter 95 transforms and outputs the output power of the first DC / DC converter 91. For example, the second DC / DC converter 95 transforms and outputs the output power of the first DC / DC converter 91 to 12 V.

[0047] The first power storage device 96 is connected to the first DC / DC converter 91. The first power storage device 96 is connected in parallel with the 48V auxiliary equipment 97 relative to the first DC / DC converter 91. When the output power from the first DC / DC converter 91 exceeds the power consumption of the vehicle load 11 and the 48V auxiliary equipment 97, the first power storage device 96 is charged with the surplus power. When the output power from the first DC / DC converter 91 is lower than the power consumption of the vehicle load 11 and the 48V auxiliary equipment 97, the first power storage device 96 discharges. Any device that can be charged and discharged may be used as the first power storage device 96. Examples of the first power storage device 96 include a secondary battery and a capacitor. The 48V auxiliary equipment 97 includes the electric compressor 42, the circulation pump 67, and the refrigerant pump 84.

[0048] The charge state detection unit 98 detects the charge state of the first power storage device 96. The charge state detection unit 98 is, for example, a battery management system. The charge state detection unit 98 includes a sensor and a derivation unit that derives the state of the first power storage device 96 from the detection result of the sensor. The sensor is, for example, a current sensor and a voltage sensor. The derivation unit can derive the charge rate of the first power storage device 96 from the detection result of the sensor. Examples of methods for deriving the charge rate include a method that uses the open circuit voltage of the first power storage device 96, a current integration method, or a combination of these.

[0049] The second power storage device 99 is connected to the second DC / DC converter 95. The second power storage device 99 is connected in parallel with the 12V auxiliary device 100 with respect to the second DC / DC converter 95. When the output power from the second DC / DC converter 95 exceeds the power consumption of the 12V auxiliary device 100, the second power storage device 99 is charged with the surplus power. When the output power from the second DC / DC converter 95 is lower than the power consumption of the 12V auxiliary device 100, the second power storage device 99 discharges. Any device that can be charged and discharged may be used as the second power storage device 99. Examples of the second power storage device 99 include a secondary battery and a capacitor. The 12V auxiliary device 100 includes a fan 83, a first valve 51, and a second valve 52.

[0050] The control device 110 includes a processor 111 and a memory unit 112. The memory unit 112 includes a random access memory (RAM) and a read-only memory (ROM). The memory unit 112 stores program code or instructions configured to cause the processor 111 to execute processes. The memory unit 112, i.e., a computer-readable medium, includes any available medium accessible by a general-purpose or special-purpose computer. The control device 110 may be configured with a hardware circuit such as an ASIC or FPGA. The control device 110, which is a processing circuit, may include one or more processors that operate according to a computer program, one or more hardware circuits such as an ASIC or FPGA, or a combination thereof.

[0051] The control device 110 controls the fuel cell system 20 . The control device 110 controls the power generation of the fuel cell stack 21. The control device 110 switches the fuel cell stack 21 between a power generation state and a power generation stop state according to the charging rate of the first power storage device 96. The power generation states include a low power generation state, a medium power generation state, and a high power generation state. The power generated in the low power generation state is lower than the power generated in the medium power generation state. The power generated in the medium power generation state is lower than the power generated in the high power generation state. By transitioning the power generation state, the control device 110 can change the power generation in stages according to the charging rate of the first power storage device 96. For example, the control device 110 controls the power generation of the fuel cell stack 21 so that the higher the charging rate of the first power storage device 96, the lower the power generation.

[0052] <Wetness control> The control device 110 performs humidity control. The humidity control is performed to prevent the fuel cell stack 21 from becoming over-dried. Over-dryness of the fuel cell stack 21 means that the electrolyte membrane 23 becomes over-dried. The electrolyte membrane 23 requires a certain amount of moisture to ensure ionic conductivity. If the electrolyte membrane 23 becomes over-dried, the ionic conductivity decreases. For this reason, the control device 110 performs humidity control to prevent the electrolyte membrane 23 from becoming over-dried, thereby ensuring ionic conductivity.

[0053] As shown in Fig. 3, in step S1, the control device 110 determines whether or not to permit wetting of the fuel cell stack 21. Wetting of the fuel cell stack 21 refers to wetting of the electrolyte membrane 23. When the fuel cell stack 21 is in a power generating state, the control device 110 permits wetting of the fuel cell stack 21. When the determination result in step S1 is positive, the control device 110 performs processing in step S2. When the determination result in step S2 is negative, the control device 110 ends wetting control.

[0054] In step S2, the control device 110 measures the impedance of the fuel cell stack 21. As a result, the control device 110 obtains the impedance of the fuel cell stack 21. The impedance of the fuel cell stack 21 can be measured by impedance spectroscopy. The control device 110 applies an AC voltage to the fuel cell stack 21 by controlling the first DC / DC converter 91. As a result, the AC voltage is superimposed on the DC voltage of the fuel cell stack 21. The control device 110 controls the switching element 92 of the first DC / DC converter 91 to superimpose the AC voltage on the DC voltage of the fuel cell stack 21. The control device 110 obtains detection results from the current sensor 93 and the voltage sensor 94. The control device 110 extracts AC components from the output current and output voltage of the fuel cell stack 21. The control device 110 measures the impedance of the fuel cell stack 21 using an AC impedance method. The frequency of the AC voltage applied to the fuel cell stack 21 by the control device 110 is set so that the electrolyte membrane resistance can be measured. The control device 110 is a measurement unit. A detailed explanation will be given below.

[0055] Figure 4 is a Nyquist plot showing the impedance characteristics of the fuel cell stack 21. The Nyquist plot is a plot of the impedance characteristics of the fuel cell stack 21 on a complex plane using impedance spectroscopy. The horizontal axis of Figure 4 represents the real component of the impedance. The vertical axis of Figure 4 represents the imaginary component of the impedance. The vertical axis of Figure 4 is inverted in positive and negative, and the larger the value along the vertical axis, the smaller the imaginary component. The "large" and "small" on the vertical axis can also be said to represent "large" and "small" in the negative direction.

[0056] The Nyquist plot shows two arcs C1 and C2. The diameter of arc C1, which is the lower frequency of the two arcs C1 and C2, represents mass transfer resistance. Mass transfer resistance is a resistance value resulting from oxygen transfer in the diffusion layers 26 and 29. The diameter of arc C2, which is the higher frequency of the two arcs C1 and C2, represents charge transfer resistance. Charge transfer resistance is a resistance value resulting from electron transfer in the catalyst layers 24 and 27. The area higher than arc C2 represents electrolyte membrane resistance. Electrolyte membrane resistance is a resistance value resulting from ion transfer in the electrolyte membrane 23. As mentioned above, the electrolyte membrane 23 requires a certain amount of water to ensure ionic conductivity. The electrolyte membrane resistance can also be said to represent ionic conductivity. The inventors used impedance spectroscopy to determine the impedance characteristics of the fuel cell stack 21 and found that the impedance of the fuel cell stack 21 deviates from arc C2 at a frequency of 250 Hz. Therefore, by applying AC power of 250 Hz or higher to the fuel cell stack 21, the control device 110 can measure the electrolyte membrane resistance. The specific AC voltage is an AC voltage in a frequency band of 250 Hz or higher. The specific AC voltage can be said to be an AC voltage in a frequency band that allows the electrolyte membrane resistance to be measured. In the following description, impedance refers to the real component of impedance.

[0057] 3, next, in step S3, the control device 110 determines whether the impedance measured in step S2 is equal to or greater than a start threshold Imp1. The start threshold Imp1 is a predetermined value. The start threshold Imp1 is set to a value at which it is assumed that the electrolyte membrane 23 needs to be wetted, based on the correlation between the wet state of the electrolyte membrane 23 and the impedance.

[0058] Next, in step S4, the control device 110 performs a wetting treatment. The wetting treatment includes a first wetting treatment, a second wetting treatment, and a third wetting treatment. The first wetting process is a process for increasing the rotation speed of the circulation pump 67. By performing the first wetting process, the amount of anode gas circulating through the fuel cell stack 21 increases. When the amount of anode gas circulating increases, water vapor can be taken in from the cathode side by reverse diffusion from the cathode side. This makes it possible to wet the electrolyte membrane 23. The circulation pump 67 is an auxiliary device that wets the fuel cell stack 21. The operating amount of the circulation pump 67 is the rotation speed of the circulation pump 67. The higher the rotation speed of the circulation pump 67, the wetter the fuel cell stack 21 becomes.

[0059] The second moistening process is a process of reducing the opening of the second valve 52. Reducing the opening of the second valve 52 increases the pressure of the cathode exhaust gas. The higher the pressure of the cathode exhaust gas, the less water vapor is carried away from the fuel cell stack 21 as the cathode gas passes through the fuel cell stack 21. By increasing the pressure of the cathode exhaust gas through the second moistening process, the amount of water vapor carried away by the cathode can be reduced. This allows the electrolyte membrane 23 to be moistened. The second valve 52 is an auxiliary device that moistens the fuel cell stack 21. The operation amount of the second valve 52 is the opening. The smaller the opening of the second valve 52, the more moist the fuel cell stack 21 becomes. In the second moistening process, the compression ratio of the electric compressor 42 increases. In order to ensure a sufficient flow rate of the cathode gas, the electric compressor 42 is controlled so that the discharge volume increases as the compression ratio increases.

[0060] The third wetting process is a process of increasing the rotation speed of the refrigerant pump 84. Increasing the rotation speed of the refrigerant pump 84 reduces the temperature of the refrigerant. As the temperature of the fuel cell stack 21 decreases, the saturated water vapor pressure of the cathode gas decreases. The amount of water vapor carried away by the cathode gas passing through the fuel cell stack 21 decreases as the saturated water vapor pressure of the cathode gas decreases. By lowering the saturated water vapor pressure of the cathode gas through the third wetting process, the amount of water vapor carried away by the cathode gas can be reduced. This makes it possible to wet the electrolyte membrane 23. The refrigerant pump 84 is an auxiliary device that wets the fuel cell stack 21. The operation amount of the refrigerant pump 84 is the rotation speed of the refrigerant pump 84. The higher the rotation speed of the refrigerant pump 84, the more wet the fuel cell stack 21 becomes. In the third wetting process, in addition to the rotation speed of the refrigerant pump 84, the rotation speed of the fan 83 may be adjusted. Increasing the rotation speed of the fan 83 reduces the temperature of the refrigerant. As the temperature of the fuel cell stack 21 decreases, it is possible to wet the fuel cell stack 21. The circulation pump 67, the second valve 52, and the refrigerant pump 84 are collectively referred to as wet accessories as appropriate.

[0061] In FIG. 5, the vertical axis represents the target value and the horizontal axis represents the impedance. The target value when no wetting treatment is performed is set to 0. In other words, the target values ​​shown in FIG. 5 indicate the increase or decrease from the target value when no wetting treatment is performed. Line L1 represents the target value set by the first wetting treatment. The target value set by the first wetting treatment is the circulation rate [NL / min] of anode gas circulating through the fuel cell stack 21. The control device 110 controls the rotation speed of the circulation pump 67 so that the circulation rate of anode gas follows the target value of the circulation rate of anode gas. Line L2 represents the target value set by the second wetting treatment. The target value set by the second wetting treatment is the pressure [kPa] of the cathode exhaust gas. The control device 110 controls the aperture of the second valve 52 so that the pressure of the cathode exhaust gas follows the target value of the pressure of the cathode exhaust gas. Line L3 represents the target value set by the third wetting treatment. The target value set by the third wetting treatment is the refrigerant temperature [deg]. The control device 110 controls the rotation speed of the coolant pump 84 so that the coolant temperature follows the target value for the coolant temperature. The target values ​​for the anode gas circulation amount, the cathode exhaust gas pressure, and the coolant temperature are target values ​​for the wet state. The target values ​​for the wet state are target values ​​for parameters related to the wetness of the fuel cell stack 21. The control device 110 wets the fuel cell stack 21 by adjusting the operation amount of the wet auxiliary equipment according to the target values ​​for the wet state.

[0062] The first wetting process, the second wetting process, and the third wetting process are performed according to multiple thresholds set for the impedance. The first wetting process is started when the impedance becomes equal to or greater than the start threshold Imp1. As shown by line L1, in the first wetting process, the target value for the circulation amount of anode gas increases as the impedance increases. As the impedance becomes greater than the start threshold Imp1, the rotation speed of the circulation pump 67 increases. An upper limit is set for the target value for the circulation amount of anode gas. The upper limit is a predetermined value. The upper limit set for the target value for the circulation amount of anode gas can also be said to be the upper limit for the rotation speed of the circulation pump 67.

[0063] When the impedance becomes equal to or greater than the pressure adjustment start threshold Imp2, the second wetting process is initiated. The pressure adjustment start threshold Imp2 is a value greater than the start threshold Imp1. The pressure adjustment start threshold Imp2 is set as a threshold for initiating the second wetting process when the wetting condition of the electrolyte membrane 23 does not improve even after the first wetting process is performed. In the second wetting process, the target value for the pressure of the cathode exhaust gas increases as the impedance increases. The opening of the second valve 52 decreases as the impedance increases above the pressure adjustment start threshold Imp2. An upper limit is set for the target value of the cathode exhaust gas. The upper limit is a predetermined value. The upper limit set for the target value of the cathode exhaust gas can also be considered a lower limit for the opening of the second valve 52.

[0064] When the impedance becomes equal to or greater than the cooling start threshold Imp3, the third wetting process is initiated. The cooling start threshold Imp3 is a value greater than the pressure adjustment start threshold Imp2. The cooling start threshold Imp3 is set as a threshold for initiating the third wetting process when the wetting state of the electrolyte membrane 23 does not improve even after performing the first and second wetting processes. In the third wetting process, the target value of the refrigerant temperature decreases as the impedance increases. A lower limit is set for the target value of the refrigerant temperature. The cooling start threshold Imp3 is also the value at which the target value of the anode gas circulation rate reaches its upper limit. When the impedance is equal to or greater than the cooling start threshold Imp3, the target value of the anode gas circulation rate is set to its upper limit.

[0065] When the impedance reaches the upper pressure threshold Imp4, the target value for the cathode exhaust gas pressure reaches its upper limit. The upper pressure threshold Imp4 is greater than the cooling start threshold Imp3. If the impedance is equal to or greater than the upper pressure threshold Imp4, the target value for the cathode exhaust gas pressure is set to the upper limit.

[0066] When the impedance reaches the upper threshold Imp5, the target value of the refrigerant temperature reaches the lower limit. The lower limit is a predetermined value. The upper threshold Imp5 is greater than the pressure upper limit threshold Imp4. Therefore, the upper threshold Imp5 is greater than the start threshold Imp1. When the impedance reaches the upper threshold Imp5, it can be said that maximum wetting by the wetting accessories is being achieved.

[0067] When the impedance is equal to or greater than the upper threshold Imp5, the target value of the anode gas circulation rate is maintained at the upper limit even if the impedance falls below the upper threshold Imp5. When the impedance is less than the start threshold Imp1, the target value of the anode gas circulation rate is adjusted according to the impedance. The target value of the anode gas circulation rate decreases as the impedance approaches the end threshold Imp0 from the start threshold Imp1. As the target value of the anode gas circulation rate decreases, the fuel cell stack 21 becomes less humidified. When the impedance is less than the start threshold Imp1, the control device 110 controls the rotation speed of the circulation pump 67 so that the fuel cell stack 21 is less humidified as the impedance decreases. The start threshold Imp1 is a fluctuation start threshold. The fluctuation start threshold is a value that starts fluctuation of the target value of the humidification state, which is maintained at a predetermined value. The end threshold Imp0 is a value smaller than the start threshold Imp1. The end threshold Imp0 is set, for example, based on the impedance value of the fuel cell stack 21 when the electrolyte membrane 23 is not overdried.

[0068] When the impedance becomes equal to or greater than the upper threshold Imp5, the target value for the cathode exhaust gas pressure is maintained at the upper limit until the impedance becomes less than the start threshold Imp1, even if the impedance falls below the upper threshold Imp5. The target value for the cathode exhaust gas pressure decreases as the impedance approaches the end threshold Imp0 from the start threshold Imp1. As the target value for the cathode exhaust gas pressure decreases, it becomes more difficult to moisten the fuel cell stack 21. When the impedance becomes less than the start threshold Imp1, the controller 110 controls the aperture of the second valve 52 so that the fuel cell stack 21 is not moistened as the impedance becomes lower.

[0069] When the impedance becomes equal to or greater than the upper threshold Imp5, the target value of the coolant temperature is maintained at the lower limit even if the impedance falls below the upper threshold Imp5. When the impedance becomes less than the start threshold Imp1, the target value of the coolant temperature is adjusted according to the impedance. The target value of the coolant temperature increases as the impedance approaches the end threshold Imp0 from the start threshold Imp1. As the target value of the coolant temperature increases, it becomes more difficult to moisten the fuel cell stack 21. When the impedance becomes less than the start threshold Imp1, the controller 110 controls the rotation speed of the coolant pump 84 so that the fuel cell stack 21 is not moistened as the impedance becomes lower.

[0070] As described above, in the wetting process, the electrolyte membrane 23 is wetted according to the impedance. As shown in FIG. 3, next, in step S5, the control device 110 determines whether or not the impedance is less than the termination threshold Imp0. When the wetting condition of the electrolyte membrane 23 is improved by the wetting process, the impedance becomes less than the termination threshold Imp0. Step S5 can be said to be a process for determining whether or not the wetting condition of the electrolyte membrane 23 has been improved by the wetting process. If the determination result of step S5 is negative, the control device 110 performs the process of step S4. As a result, the control device 110 repeatedly performs the wetting process until the determination result of step S5 is positive. If the determination result of step S5 is positive, the control device 110 performs the process of step S6.

[0071] In step S6, the control device 110 ends the wetting process. [Operation of this embodiment] When the impedance becomes equal to or greater than the start threshold Imp1, the control device 110 starts the wetting process. In the wetting process, the higher the impedance, the more the fuel cell stack 21 becomes wet. In detail, the control device 110 adjusts the operation amount of the wetting accessories until the impedance becomes from the start threshold Imp1 to the upper limit threshold Imp5, thereby enabling wetting of the fuel cell stack 21 according to the impedance.

[0072] [Effects of this embodiment] (1) The control device 110 adjusts the operation amount of the wetting auxiliary device so that the fuel cell stack 21 becomes wetter as the impedance increases. The fuel cell stack 21 becomes drier as the impedance increases. By adjusting the fuel cell stack 21 so that the fuel cell stack 21 becomes wetter as the impedance increases, the fuel cell stack 21 can be wetted in accordance with the dryness state of the fuel cell stack 21. This makes it possible to prevent the stability of the control of the fuel cell stack 21 from being impaired.

[0073] (2) In the wetting process, the control device 110 adjusts the operation amounts of the circulation pump 67, the second valve 52, and the refrigerant pump 84. The control device 110 can wet the electrolyte membrane 23 by adjusting the operation amounts of these wetting accessories.

[0074] (3) The end threshold Imp0 is smaller than the start threshold Imp1. Once the wetting process is started, it continues until the impedance reaches the end threshold Imp0. This prevents the wetting process from being restarted in a short time after it has finished.

[0075] (4) The control device 110 measures the impedance while the fuel cell stack 21 is generating electricity. When the fuel cell stack 21 is not generating electricity, the accuracy of the impedance measurement decreases. By measuring the impedance while the fuel cell stack 21 is generating electricity, the accuracy of the impedance measurement can be improved.

[0076] (5) When the impedance becomes equal to or greater than the upper threshold Imp5, the control device 110 maintains the target value of the wet state at a predetermined value. When the impedance becomes less than the start threshold Imp1 after the target value of the wet state has been maintained at a predetermined value, the control device 110 adjusts the target value of the wet state so that the fuel cell stack 21 becomes less wet as the impedance becomes lower. When the impedance becomes equal to or greater than the upper threshold Imp5 despite having performed the first wetting process, the second wetting process, and the third wetting process, it is necessary to protect the fuel cell stack 21. Therefore, when the impedance becomes equal to or greater than the upper threshold Imp5, the control device 110 wets the fuel cell stack 21 by maintaining the target value of the wet state until the impedance becomes less than the start threshold Imp1. This makes it possible to protect the fuel cell stack 21.

[0077] (6) The pressure adjustment start threshold Imp2 is greater than the start threshold Imp1. The cooling start threshold Imp3 is greater than the pressure adjustment start threshold Imp2. The circulation pump 67 is less likely to make noise even when its rotation speed is increased. Reducing the opening of the second valve 52 requires an increase in the discharge rate of the electric compressor 42, which tends to increase noise compared to when the rotation speed of the circulation pump 67 is increased. By performing the first wetting process before the second wetting process, the second wetting process is not performed if the impedance during the first wetting process is less than the end threshold Imp0. This suppression of noise leads to improved sensory performance. Increasing the rotation speed of the refrigerant pump 84 reduces the temperature of the fuel cell stack 21. A decrease in the temperature of the fuel cell stack 21 may reduce the power generation efficiency of the fuel cell stack 21. Furthermore, this may impair the stability of control by the control device 110. By performing the first and second wetting processes before the third wetting process, the third wetting process is not performed if the impedance during the first and second wetting processes is less than the end threshold Imp0. This can prevent the power generation efficiency of the fuel cell stack 21 from decreasing and the control stability of the fuel cell stack 21 from being impaired.

[0078] [Example of change] The embodiment can be modified as follows: The embodiment and the following modifications can be combined with each other within the scope of technical compatibility.

[0079] The magnitude relationship between the pressure adjustment start threshold Imp2 and the cooling start threshold Imp3 may be changed as appropriate. The pressure adjustment start threshold Imp2 and the cooling start threshold Imp3 may be the same value. The cooling start threshold Imp3 may be smaller than the pressure adjustment start threshold Imp2.

[0080] When the impedance becomes equal to or greater than the initiation threshold Imp1, the control device 110 may simultaneously start the first wetting process, the second wetting process, and the third wetting process. The fluctuation start threshold may be any value smaller than the upper limit threshold Imp5 and may be different from the start threshold Imp1. The fluctuation start threshold may be a value larger than or smaller than the start threshold Imp1. Furthermore, different fluctuation start thresholds may be set for the first, second, and third wetting processes.

[0081] A circulation start threshold may be set for the impedance. The circulation start threshold is the impedance at which the first wetting process is initiated. The circulation start threshold is a value greater than the initiation threshold Imp1. In this case, when the impedance reaches or exceeds the initiation threshold Imp1, at least one of the second wetting process and the third wetting process may be performed. In other words, the order in which the first wetting process, the second wetting process, and the third wetting process are initiated may be changed as appropriate.

[0082] The control device 110 may measure the impedance when the fuel cell stack 21 is not generating electricity. The start threshold Imp1 and the end threshold Imp0 may be set to the same value.

[0083] The wetting treatment may involve at least one of the first wetting treatment, the second wetting treatment, and the third wetting treatment. The term "at least one" used in this embodiment means "one or more" of the desired options. As an example, the term "at least one" used in this specification means "only one option" or "both of two options" if the number of options is two. As another example, the term "at least one" used in this specification means "only one option" or "any combination of two or more options" if the number of options is three or more.

[0084] The fuel cell system 20 may be installed in a passenger vehicle, a ship, a train, or the like. The fuel cell system 20 may be used as a stationary power generation device. The measurement unit may be a control unit that controls the first DC / DC converter 91.

[0085] The fuel cell system 20 may be provided with a dedicated device for measuring impedance. [Note] The technical ideas that can be understood from the embodiments and modified examples will be described.

[0086] [1] A fuel cell system comprising a fuel cell stack, a measuring unit that measures the impedance of the fuel cell stack, a control device, and an auxiliary device that moistens the fuel cell stack, wherein the control device obtains the impedance measured by the measuring unit by applying a specific AC voltage to the fuel cell stack, and when the real component of the impedance is equal to or greater than a start threshold, performs a moistening process that adjusts the operation amount of the auxiliary device relative to a target value for a moist state so that the larger the real component, the more moist the fuel cell stack becomes.

[0087] [2] The auxiliary equipment includes a circulation pump that circulates anode gas through the fuel cell stack, a regulating valve that adjusts the pressure of cathode gas discharged from the fuel cell stack, and a coolant pump that circulates a coolant that cools the fuel cell stack, and the wetting process adjusts the operating amount of at least one of the circulation pump, the regulating valve, and the coolant pump so that the fuel cell stack becomes wetter as the real component becomes larger. [1] The fuel cell system described in [1]

[0088] [3] The fuel cell system according to [1] or [2], wherein the control device terminates the wetting process when the real component becomes less than a termination threshold, and the termination threshold is smaller than the start threshold.

[0089] [4] The fuel cell system according to any one of [1] to [3], wherein the control device measures the impedance using the measuring unit while the fuel cell stack is generating electricity. [5] The control device maintains the target value at a predetermined value when the real component becomes equal to or greater than an upper threshold value, and after the target value is maintained at the predetermined value, adjusts the target value when the real component becomes less than a fluctuation start threshold value so that the lower the real component is, the less humidified the fuel cell stack becomes, and the upper threshold value is greater than the start threshold value, and the fluctuation start threshold value is less than the upper threshold value. The fuel cell system described in any one of [1] to [4]. [Explanation of symbols]

[0090] 20... fuel cell system, 21... fuel cell stack, 52... second valve as auxiliary equipment and adjustment valve, 67... circulation pump as auxiliary equipment, 84... refrigerant pump as auxiliary equipment, 110... control device as measurement unit.

Claims

1. a fuel cell stack; a measurement unit for measuring the impedance of the fuel cell stack; a control device; an accessory for wetting the fuel cell stack; The control device acquiring the impedance measured by the measuring unit by applying a specific AC voltage to the fuel cell stack; If the real component of the impedance is equal to or greater than a start threshold, a wetting process is performed to adjust the operation amount of the auxiliary device relative to a target value for a wetting state so that the larger the real component, the wetter the fuel cell stack becomes; When the real component is equal to or greater than an upper threshold, the target value is maintained at a predetermined value; After the target value is maintained at the predetermined value, when the real component becomes less than a fluctuation start threshold, the target value is adjusted so that the lower the real component is, the less the fuel cell stack becomes wet; the upper threshold is greater than the start threshold; A fuel cell system, wherein the fluctuation start threshold is smaller than the upper limit threshold.

2. a fuel cell stack; a measurement unit for measuring the impedance of the fuel cell stack; a control device; an accessory for wetting the fuel cell stack; The auxiliary machine is a circulation pump that circulates an anode gas through the fuel cell stack; a regulator valve for regulating the pressure of the cathode gas discharged from the fuel cell stack; a coolant pump that circulates a coolant that cools the fuel cell stack, The control device acquiring the impedance measured by the measuring unit by applying a specific AC voltage to the fuel cell stack; If the real component of the impedance is equal to or greater than a start threshold, a wetting process is performed to adjust the operation amount of the auxiliary device relative to a target value for a wetting state so that the larger the real component, the wetter the fuel cell stack becomes; When the real component is equal to or greater than the start threshold, adjusting the operation amount of the circulation pump; When the real number component is equal to or greater than a pressure adjustment start threshold, an operation amount of the adjustment valve is adjusted; When the real number component is equal to or greater than a cooling start threshold, adjusting an operation amount of the refrigerant pump; the pressure adjustment start threshold is greater than the start threshold; A fuel cell system, wherein the cooling start threshold is greater than the pressure adjustment start threshold.

3. The auxiliary machine is a circulation pump that circulates an anode gas through the fuel cell stack; a regulator valve for regulating the pressure of the cathode gas discharged from the fuel cell stack; a coolant pump that circulates a coolant that cools the fuel cell stack, 2. The fuel cell system according to claim 1, wherein the wetting process adjusts an operation amount of at least one of the circulation pump, the adjustment valve, and the coolant pump so that the fuel cell stack is wetter as the real component increases.

4. the control device terminates the wetting process when the real component becomes less than a termination threshold; 3. The fuel cell system according to claim 1, wherein the end threshold is smaller than the start threshold.

5. 3. The fuel cell system according to claim 1, wherein the control device measures the impedance using the measuring unit while the fuel cell stack is generating power.

6. The control device When the real component is equal to or greater than an upper threshold, the target value is maintained at a predetermined value; After the target value is maintained at the predetermined value, when the real component becomes less than a fluctuation start threshold, the target value is adjusted so that the lower the real component is, the less the fuel cell stack becomes wet; the upper threshold is greater than the start threshold; The fuel cell system according to claim 2 , wherein the fluctuation start threshold is smaller than the upper limit threshold.

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