Fuel cell system

Abstract

To operate a fuel cell system even when the voltage of a fuel cell decreases.SOLUTION: A fuel cell system includes a fuel cell stack, a voltage measurement unit, and a control device. The fuel cell stack includes a plurality of fuel cells. The voltage measurement unit measures the voltage of the fuel cells. When the average cell voltage becomes a first threshold or less, the control device performs a flooding cancellation control to cancel flooding. If the flooding cancellation control prevents the average cell voltage from becoming more than or equal to a second threshold, which is larger than the first threshold, the control device decreases an upper limit value of an object value of the output power in the fuel cell stack.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] This disclosure relates to a fuel cell system. [Background technology]

[0002] The fuel cell system disclosed in Patent Document 1 comprises a fuel cell stack, an electric compressor, a control valve, an anode gas supply unit, and a control device. The fuel cell stack comprises a plurality of fuel cell cells. The fuel cell stack generates electricity through a chemical reaction between anode gas and cathode gas. The anode gas supply unit supplies anode gas to the fuel cell stack. The electric compressor supplies cathode gas to the fuel cell stack. The control valve adjusts the pressure of the cathode gas discharged from the fuel cell stack. The control device determines whether or not flooding is occurring in the fuel cell stack. If flooding is occurring in the fuel cell stack, the voltage of the fuel cell cells decreases. If flooding is occurring in the fuel cell stack, the control device increases the opening of the control valve. Furthermore, the control device increases the amount of cathode gas supplied by controlling the electric compressor. In this way, the control device eliminates the flooding. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2008-41625 [Overview of the project] [Problems that the invention aims to solve]

[0004] Even if the opening of the control valve is increased or the amount of cathode gas supplied from the electric compressor is increased, the voltage drop in the fuel cell may not be resolved. In such cases, it may still be necessary to operate the fuel cell system. [Means for solving the problem]

[0005] A fuel cell system that solves the above problems comprises a fuel cell stack having a plurality of fuel cell cells, a control valve for adjusting the pressure of cathode gas discharged from the fuel cell stack, a voltage measuring unit for measuring the voltage of the fuel cell cells, and a control device for setting a target value for the output power of the fuel cell stack. The control device performs flooding elimination control to eliminate flooding when the voltage of the fuel cell falls below a first threshold, and if the flooding elimination control does not cause the voltage of the fuel cell to rise above a second threshold (a value greater than the first threshold), it lowers the upper limit of the target value for the fuel cell stack.

[0006] The control unit performs flood elimination control when the fuel cell voltage falls below the first threshold. If the cause of the fuel cell voltage drop is flooding, the flood elimination control raises the fuel cell voltage to above the second threshold. If the cause of the fuel cell voltage drop is not flooding, the fuel cell voltage may not rise above the second threshold even after flood elimination control. In this case, the control unit lowers the upper limit of the target output power in the fuel cell stack. Therefore, the fuel cell system can be operated even when the fuel cell voltage is low.

[0007] With respect to the fuel cell system described above, the flooding elimination control may include an opening increase control that increases the opening of the control valve, a flow rate increase control that increases the flow rate of the cathode gas supplied to the fuel cell stack, and a prohibition control that prohibits adjusting the output power of the fuel cell stack by feedback control.

[0008] With respect to the fuel cell system described above, if the voltage of the fuel cell does not exceed the second threshold after the opening increase control has been performed, the control device may perform the flow rate increase control, and if the voltage of the fuel cell does not exceed the second threshold after the flow rate increase control has been performed, the control device may lower the upper limit of the target value of the fuel cell stack.

[0009] With respect to the fuel cell system described above, the control device may stop the flooding elimination control and return to the normal state if the voltage of the fuel cell becomes equal to or greater than the second threshold due to the flooding elimination control.

[0010] With respect to the fuel cell system described above, the control device may restore the reduced upper limit value to its original state when it receives a command to stop the operation of the fuel cell system. [Effects of the Invention]

[0011] According to the present invention, the fuel cell system can be operated even when the voltage of the fuel cell is low. [Brief explanation of the drawing]

[0012] [Figure 1] This is a schematic diagram of a fuel cell system. [Figure 2] Figure 1 is a schematic diagram of the fuel cell cell configuration of the fuel cell stack. [Figure 3] Figure 1 is a schematic diagram of the first DC / DC converter included in the fuel cell system. [Figure 4] This diagram shows the power generation modes of the fuel cell stack shown in Figure 1. [Figure 5] Figure 1 is a state transition diagram showing the states that the control device transitions through when performing flood elimination control and power generation suppression control. [Modes for carrying out the invention]

[0013] An embodiment of a fuel cell system will be described. As shown in Figure 1, the industrial vehicle 10 comprises a vehicle load 11, a key switch 12, 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 moves by the drive of this electric motor. The industrial vehicle 10 is, for example, a forklift or a towing tractor.

[0014] The key switch 12 is operated by a user of the industrial vehicle 10. The key switch 12 is switched between ON and OFF by an operation performed by the user. In the following description, turning on the key switch 12 may be referred to as key-on, and turning off the key switch 12 may be referred to as key-off.

[0015] <Fuel cell system> The fuel cell system 20 includes a fuel cell stack 21, a cathode system 40, an anode system 60, a diluter 69, an electrical system 80, and a control device 110.

[0016] The fuel cell stack 21 includes a plurality of fuel cells 22. The fuel cells 22 are polymer electrolyte membrane fuel cells. The fuel cells 22 generate electricity through a chemical reaction between a cathode gas and an anode gas.

[0017] As shown in FIG. 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 therebetween. The anode-side microporous layer 25 and the cathode-side microporous layer 28 sandwich the electrolyte membrane 23 and the respective catalyst layers 24, 27 therebetween. The anode-side diffusion layer 26 and the cathode-side diffusion layer 29 sandwich the electrolyte membrane 23, the respective catalyst layers 24, 27, and the respective microporous layers 25, 28 therebetween.

[0018] Each of the catalyst layers 24, 27 promotes the reaction of the anode gas and the cathode gas via a catalyst. Each of the catalyst layers 24, 27 contains a catalyst, a carrier that supports the catalyst, and an ionomer that covers these components. As the catalyst, for example, platinum, ruthenium, or the like can be used. As the carrier, for example, carbon can be used. As the ionomer, an ion-conductive polymer electrolyte can be used. As the ionomer, for example, the same material as that of the electrolyte membrane 23 may be used.

[0019] Each microporous layer 25, 28 promotes the discharge of water generated by chemical reactions during power generation, preventing it from accumulating in each catalyst layer 24, 27. Each microporous layer 25, 28 is composed of, for example, a water-repellent resin and a conductive material such as carbon.

[0020] Each diffusion layer 26, 29 serves as a pathway for electrons, anode gas, and cathode gas. Each diffusion layer 26, 29 is made of a material that is gas permeable and electron conductive. Each diffusion layer 26, 29 is made of, for example, carbon.

[0021] As shown in Figure 1, the fuel cell stack 21 comprises a cathode channel 30 and an anode channel 33. Cathode gas flows through the cathode channel 30. Anode gas flows through the anode channel 33. The cathode channel 30 comprises an inlet 31 and an outlet 32. Cathode gas flows into the cathode channel 30 from the inlet 31 and out from the outlet 32. The anode channel 33 comprises an inlet 34 and an outlet 35. Anode gas flows into the anode channel 33 from the inlet 34 and out from the outlet 35. The cathode gas is an oxidizing gas. An example of an oxidizing gas is oxygen in the air. The anode gas is a fuel gas. An example of a fuel gas is hydrogen gas.

[0022] The cathode system 40 includes an intake port 41, an electric compressor 42, an inverter 44, an intercooler 45, a cathode supply passage 46, a cathode discharge passage 49, a first valve 51, and a second valve 52.

[0023] The intake port 41 draws cathode gas into the fuel cell system 20. The intake port 41 may be open to the atmosphere. The intake port 41 may be connected to a gas cylinder. The electric compressor 42 is equipped with 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 it 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.

[0024] The inverter 44 is connected to the electric motor 43. The inverter 44 converts DC power to AC power and supplies it to the electric motor 43. This drives the electric motor 43.

[0025] The intercooler 45 is supplied with 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.

[0026] The cathode supply passage 46 connects the electric compressor 42 to the cathode flow path 30. More specifically, the cathode supply passage 46 connects the electric compressor 42 to the inlet 31 of the cathode flow path 30. The cathode supply passage 46 includes a first supply passage 47 and a second supply passage 48. The first supply passage 47 connects the electric compressor 42 to the intercooler 45. The second supply passage 48 connects the intercooler 45 to the cathode flow path 30.

[0027] The cathode discharge channel 49 connects the cathode flow path 30 and the diluent 69. More specifically, the cathode discharge channel 49 connects the outlet 32 ​​of the cathode flow path 30 to the diluent 69. The cathode discharge channel 49 is the passage through which cathode exhaust gas flows. The cathode exhaust gas is the cathode gas discharged from the fuel cell stack 21, and is cathode gas containing generated water. The generated water is water produced by power generation in the fuel cell stack 21.

[0028] The first valve 51 is located in the cathode supply passage 46. In this embodiment, the first valve 51 is located in the second supply passage 48, i.e., between the intercooler 45 and the cathode flow path 30. The first valve 51 may also be located in the first supply passage 47, i.e., between the intercooler 45 and the electric compressor 42.

[0029] The second valve 52 is located in the cathode discharge passage 49. The second valve 52 is a valve whose opening degree can be adjusted. By adjusting the opening degree of the second valve 52, the pressure of the cathode exhaust gas can be adjusted. The smaller the opening degree of the second valve 52, the higher the pressure of the cathode exhaust gas. The second valve 52 is a control valve.

[0030] The anode system 60 includes a tank 61, a pressure reducing valve 62, an anode gas supply unit 63, a supply passage 64, a circulation passage 65, a gas-liquid separator 66, a circulation pump 67, and an exhaust drain valve 68.

[0031] Tank 61 stores anode gas. Anode gas is supplied to the pressure reducing valve 62 from the tank 61. 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 the anode gas supply unit 63.

[0032] The anode gas supply unit 63 is a component 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. For example, a solenoid valve such as an injector can be used as the anode gas supply unit 63.

[0033] The supply channel 64 connects the anode gas supply unit 63 and the anode flow path 33. More specifically, the supply channel 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 channel 64.

[0034] The circulation path 65 connects the outlet 35 of the anode flow path 33 to 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 back to the supply path 64.

[0035] The gas-liquid separator 66 is installed in the circulation path 65. The gas-liquid separator 66 separates the anode exhaust gas into anode gas and generated water. The generated water separated from the anode exhaust gas is stored in the gas-liquid separator 66.

[0036] The circulation pump 67 is located in the circulation path 65. 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 circulates the anode gas to the fuel cell stack 21.

[0037] The exhaust and drain valve 68 is connected to the gas-liquid separator 66. The exhaust and drain valve 68 can be switched between an open state and a closed state. When the exhaust and drain valve 68 is open, the generated water is discharged from the gas-liquid separator 66. Also, exhaust is carried out from the circulation path 65. When the exhaust and drain valve 68 is closed, the generated water can no longer be discharged from the gas-liquid separator 66. That is, when the exhaust and drain valve 68 is closed, the generated water is stored in the gas-liquid separator 66. The exhaust and drain valve 68 is switched from the closed state to the open state at predetermined valve opening intervals.

[0038] The gas-liquid separator 66 is connected to the diluent 69. When the exhaust drain valve 68 is open, the generated water and anode exhaust gas stored in the gas-liquid separator 66 are supplied to the diluent 69. The diluent 69 dilutes the anode exhaust gas with the cathode exhaust gas and discharges it into the atmosphere.

[0039] The electrical system 80 includes a first DC / DC converter 81, a voltage measuring unit 85, a current measuring unit 86, a second DC / DC converter 95, a first energy storage device 96, a charge state detection unit 98, and a second energy storage device 99.

[0040] The first DC / DC converter 81 is connected to the fuel cell stack 21. The first DC / DC converter 81 transforms the output voltage of the fuel cell stack 21 and outputs it. For example, the first DC / DC converter 81 transforms the output voltage of the fuel cell stack 21 to 48[V] and outputs it. The output power from the first DC / DC converter 81 is supplied to the vehicle load 11.

[0041] As shown in Figure 3, the first DC / DC converter 81 comprises a positive terminal wiring Lp, a negative terminal wiring Ln, six switching elements Q1, Q2, Q3, Q4, Q5, Q6, six diodes D1, D2, D3, D4, D5, D6, three reactors 82, 83, 84, and a capacitor C.

[0042] The first switching element Q1 and the second switching element Q2 are connected in series with each other. The third switching element Q3 and the fourth switching element Q4 are connected in series with each other. The fifth switching element Q5 and the sixth switching element Q6 are connected in series with each other. The first switching element Q1, the third switching element Q3, and the fifth switching element Q5 are connected to the positive terminal wiring Lp. The second switching element Q2, the fourth switching element Q4, and the sixth switching element Q6 are connected to the negative terminal wiring Ln. The first switching element Q1, the third switching element Q3, and the fifth switching element Q5 constitute the upper arm. The second switching element Q2, the fourth switching element Q4, and the sixth switching element Q6 constitute the lower arm. MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) are used as the six switching elements Q1 to Q6. IGBTs (Insulated Gate Bipolar Transistors) may also be used as the six switching elements Q1 to Q6.

[0043] Diodes D1 to D6 are connected in parallel to each switching element Q1 to Q6. Diodes D1 to D6 are parasitic diodes of switching elements Q1 to Q6. The cathodes of diodes D1, D3, and D5, which are connected in parallel to the switching elements Q1, Q3, and Q5 that make up the upper arm, are connected to the positive terminal wiring Lp. The anodes of diodes D1, D3, and D5, which are connected in parallel to the switching elements Q1, Q3, and Q5 that make up the upper arm, are connected to the midpoint of two switching elements Q1 to Q6 that are connected in series with each other. The cathodes of diodes D2, D4, and D6, which are connected in parallel to the switching elements Q2, Q4, and Q6 that make up the lower arm, are connected to the midpoint of two switching elements Q1 to Q6 that are connected in series with each other. The anodes of diodes D2, D4, and D6, which are connected in parallel to the switching elements Q2, Q4, and Q6 that make up the lower arm, are connected to the negative terminal wiring Ln.

[0044] One reactor each, 82, 83, and 84, is connected to the midpoint between the switching elements Q1, Q3, and Q5 that make up the upper arm and the switching elements Q2, Q4, and Q6 that make up the lower arm. Reactors 82, 83, and 84 are connected to the fuel cell stack 21.

[0045] Capacitor C is connected to the positive terminal wire Lp and the negative terminal wire Ln. In the first DC / DC converter 81 described above, the voltage is boosted by the switching operation of the switching elements Q1 to Q6.

[0046] As shown in Figure 1, the voltage measurement unit 85 measures the output voltage [V] of the fuel cell stack 21. The voltage measurement unit 85 used is one that can individually measure the voltage of multiple fuel cell cells 22. For example, the voltage measurement unit 85 may have multiple ports, to which the positive and negative electrodes of the fuel cell cells 22 are connected. This allows the voltage measurement unit 85 to individually measure the voltage of the fuel cell cells 22.

[0047] The current measuring unit 86 measures the output current [A] of the fuel cell stack 21. The second DC / DC converter 95 is connected to the first DC / DC converter 81. The second DC / DC converter 95 transforms the output voltage of the first DC / DC converter 81 and outputs it. For example, the second DC / DC converter 95 transforms the output voltage of the first DC / DC converter 81 to 12[V] and outputs it.

[0048] The first energy storage device 96 is connected to the first DC / DC converter 81. The first energy storage device 96 is connected in parallel to the first DC / DC converter 81 with the 48V auxiliary equipment 97. When the output power from the first DC / DC converter 81 exceeds the power consumption of the vehicle load 11 and the 48V auxiliary equipment 97, the first energy storage device 96 is charged with the surplus power. When the output power from the first DC / DC converter 81 is less than the power consumption of the vehicle load 11 and the 48V auxiliary equipment 97, the first energy storage device 96 discharges. Any type of chargeable and dischargeable energy storage device 96 may be used. Examples of the first energy storage device 96 include a secondary battery and a capacitor. The 48V auxiliary equipment 97 includes an electric compressor 42 and a circulation pump 67.

[0049] The charge state detection unit 98 detects the charge state of the first energy 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 energy storage device 96 from the sensor's detection result. The sensor is, for example, a current sensor and a voltage sensor. The derivation unit can derive the charge rate of the first energy storage device 96 from the sensor's detection result. Methods for deriving the charge rate include, for example, a method using the open-circuit voltage of the first energy storage device 96, a current integration method, or a combination thereof.

[0050] The second energy storage device 99 is connected to the second DC / DC converter 95. The second energy storage device 99 is connected in parallel to the second DC / DC converter 95 with the 12V auxiliary equipment 100. When the output power from the second DC / DC converter 95 exceeds the power consumption of the 12V auxiliary equipment 100, the second energy storage device 99 is charged with the surplus power. When the output power from the second DC / DC converter 95 is less than the power consumption of the 12V auxiliary equipment 100, the second energy storage device 99 discharges. Any type of device that can be charged and discharged can be used as the second energy storage device 99. Examples of the second energy storage device 99 include a secondary battery and a capacitor. The 12V auxiliary equipment 100 includes a first valve 51 and a second valve 52.

[0051] The control device 110 comprises a processor 111 and a storage unit 112. The storage unit 112 includes RAM (Random Access Memory) and ROM (Read Only Memory). The storage unit 112 stores program code or instructions configured to cause the processor 111 to execute processing. The storage unit 112, i.e., the computer-readable medium, includes any available medium accessible by a general-purpose or dedicated computer. The control device 110 may be composed of hardware circuits such as an ASIC (Application Specific Integrated Circuit) or an FPGA (Field Programmable Gate Array). 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.

[0052] <Control of the first DC / DC converter by the control unit> The control device 110 controls the first DC / DC converter 81. When the output voltage of the fuel cell stack 21 is lower than the voltage of the first energy storage device 96, the control device 110 boosts the output voltage of the fuel cell stack 21 using the first DC / DC converter 81. When the output voltage of the fuel cell stack 21 is higher than the voltage of the first energy storage device 96, the control device 110 does not perform the switching operation of the switching elements Q1 to Q6. In this case, current flows from the diodes D1, D3, and D5, which are parasitic diodes of the switching elements Q1, Q3, and Q5 that constitute the upper arm. The output voltage of the fuel cell stack 21 can be lowered by the diodes D1, D3, and D5.

[0053] <Control related to power generation performed by the control device> The control device 110 controls the output power [kW] of the fuel cell stack 21. The output power of the fuel cell stack 21 varies depending on the amount of cathode gas supplied to the fuel cell stack 21 and the amount of anode gas supplied to the fuel cell stack 21. The output power of the fuel cell stack 21 is the power generated by the fuel cell stack 21. The control device 110 controls the amount of anode gas supplied to the fuel cell stack 21 by controlling the anode gas supply unit 63. The control device 110 controls the amount of cathode gas supplied to the fuel cell stack 21 by controlling the electric compressor 42.

[0054] As shown in Figure 4, the control device 110 switches the power generation mode of the fuel cell stack 21 in stages according to the charge level of the first energy storage device 96. The power generation modes in this embodiment include a power generation stop mode ST1, a low power generation mode ST2, a medium power generation mode ST3, and a high power generation mode ST4. Each of the power generation stop mode ST1, low power generation mode ST2, medium power generation mode ST3, and high power generation mode ST4 is associated with a target value [kW] of the output power of the fuel cell stack 21. The control device 110 sets the target value of the output power of the fuel cell stack 21 by switching the power generation mode.

[0055] Power generation shutdown mode ST1 is a mode in which the fuel cell stack 21 does not generate power. The target value of output power in power generation shutdown mode ST1 is 0 [kW]. Low power generation mode ST2 is a mode in which the fuel cell stack 21 generates power. The target value of the output power of the fuel cell stack 21 in low power generation mode ST2 is defined as the low output power. The low output power is, for example, 3 kW.

[0056] Medium power generation mode ST3 is a mode in which the output power of the fuel cell stack 21 is greater than that of low power generation mode ST2. The target value of the output power of the fuel cell stack 21 in medium power generation mode ST3 is defined as medium output power. Medium output power is a value greater than low output power. For example, medium output power is 6 kW.

[0057] High power generation mode ST4 is a mode in which the fuel cell stack 21 generates the power required when the industrial vehicle 10 is operating at maximum load. The target value of the output power of the fuel cell stack 21 in high power generation mode ST4 is defined as high output power. High output power is a value greater than medium output power. For example, high output power is 12 kW.

[0058] When the fuel cell stack 21 is in power generation stop mode ST1, the charge rate of the first energy storage device 96 reaches the power generation start threshold V. D If the following conditions are met, the control device 110 will transition the fuel cell stack 21 to low power generation mode ST2. Power generation start threshold V D For example, one could give 50%.

[0059] When the fuel cell stack 21 is in low power generation mode ST2, the charge rate of the first energy storage device 96 reaches the medium power generation switching threshold V. M If the following conditions are met, the control device 110 will transition the fuel cell stack 21 to the medium power generation mode ST3. Medium power generation switching threshold V M For example, one could cite 45%.

[0060] When the fuel cell stack 21 is in medium power generation mode ST3, the charge rate of the first energy storage device 96 reaches the high power generation switching threshold V. HWhen the condition below is satisfied, the control device 110 causes the fuel cell stack 21 to transition to the high power generation mode ST4. High power generation switching threshold V H For example, 30[%] can be mentioned.

[0061] When the fuel cell stack 21 is in the high power generation mode ST4, the state of charge of the first power storage device 96 reaches the medium power generation switching threshold V M When the above condition is satisfied, the control device 110 causes the fuel cell stack 21 to transition to the medium power generation mode ST3.

[0062] When the fuel cell stack 21 is in the medium power generation mode ST3, the state of charge of the first power storage device 96 reaches the low power generation switching threshold V L When the above condition is satisfied, the control device 110 causes the fuel cell stack 21 to transition to the low power generation mode ST2. Low power generation switching threshold V L For example, 60[%] can be mentioned.

[0063] When the fuel cell stack 21 is in the low power generation mode ST2, the state of charge of the first power storage device 96 reaches the power generation stop threshold V S When the above condition is satisfied, the control device 110 causes the fuel cell stack 21 to transition to the power generation stop mode ST1. Power generation stop threshold V S For example, 70[%] can be mentioned.

[0064] The control device 110 controls the output power of the fuel cell stack 21 by using both feedforward control and feedback control. A case where PI control is used as the feedback control will be described as an example, but PID control may alternatively be used as the feedback control.

[0065] After setting a target value for the output power of the fuel cell stack 21 according to the above-described power generation mode, the control device 110 calculates a first current command value [A]. The first current command value is calculated, for example, from the current-voltage characteristics of the fuel cell stack 21 and a feedforward gain.

[0066] The control device 110 calculates the output power of the fuel cell stack 21 from the output voltage and output current of the fuel cell stack 21. The control device 110 calculates the deviation between the output power of the fuel cell stack 21 and the target value of the output power of the fuel cell stack 21. The control device 110 calculates the second current command value [A] from the deviation, proportional gain, and integral gain. The control device 110 sets the sum of the first current command value and the second current command value as the current command value [A]. The control device 110 controls the fuel cell system 20 so that the output current of the fuel cell stack 21 follows the current command value. As a result, the fuel cell stack 21 is controlled so that the output power of the fuel cell stack 21 follows the target value.

[0067] <Flooding elimination control and power generation suppression control> The control device 110 performs flood elimination control and power generation suppression control. Flooding elimination control is a control performed to eliminate flooding when there is a risk of flooding occurring in the fuel cell stack 21. Flooding is a phenomenon in which the supply of cathode gas to the cathode-side catalyst layer 27 is obstructed by the cathode-side catalyst layer 27, cathode-side microporous layer 28, and cathode-side diffusion layer 29 being covered with liquid water. Power generation suppression control is a control that lowers the upper limit of the target value of the output power in the fuel cell stack 21.

[0068] As shown in Figure 5, the control device 110 can be in one of the following states: normal state ST10, first elimination state ST11, second elimination state ST12, mode down state ST13, or stopped state ST14. While the fuel cell system 20 is operating, the control device 110 can be in one of the following states: normal state ST10, first elimination state ST11, second elimination state ST12, or mode down state ST13. The control device 110 performs control according to the state. The control device 110 performs in the first elimination state ST11 and the second elimination state ST12 is flooding elimination control. The control device 110 performs in the mode down state ST13 is power generation suppression control.

[0069] Normal state ST10 is the state in which the control device 110 performs normal control according to the target value of the output power of the fuel cell stack 21. The control device 110 adjusts the supply amount of anode gas, the supply amount of cathode gas, and the pressure of the cathode gas by feedback control so that the output power of the fuel cell stack 21 follows the target value.

[0070] The first resolution state ST11 is a state in which the control device 110 performs opening degree increase control and prohibition control. Opening degree increase control is a control that resolves flooding by increasing the opening degree of the second valve 52. The control device 110 increases the opening degree of the second valve 52 to a value greater than the maximum opening degree that the second valve 52 can take when the control device 110 is in the normal state ST10. In this embodiment, the control device 110 fully opens the second valve 52. Prohibition control is a control that prohibits adjusting the output power of the fuel cell stack 21 by feedback control. In this case, the control device 110 calculates the current command value by feedforward control.

[0071] The second elimination state ST12 is a state in which the control device 110 performs flow rate increase control and prohibition control. Flow rate increase control is a control that eliminates flooding by increasing the flow rate of cathode gas supplied to the fuel cell stack 21. The control device 110 increases the flow rate of cathode gas compared to the normal state ST10 by controlling the electric compressor 42. In this embodiment, opening degree increase control is also performed in the second elimination state ST12.

[0072] Mode-down state ST13 is a state in which the fuel cell stack 21 sets an upper limit on the power generation modes to which it can transition. When the control device 110 transitions to mode-down state ST13 while no upper limit is set on the power generation modes, medium power generation mode ST3 is set as the upper limit on the power generation modes. When the control device 110 transitions to mode-down state ST13 while medium power generation mode ST3 is set as the upper limit on the power generation modes, low power generation mode ST2 is set as the upper limit on the power generation modes. As a result, the target value of output power associated with the power generation mode set as the upper limit becomes the upper limit of the target value of the output power. For example, when medium power generation mode ST3 is set as the upper limit on the power generation modes from a state where no upper limit is set on the power generation modes, the upper limit of the target value of the output power in the fuel cell stack 21 changes from high output power to medium output power. In this way, by setting an upper limit on the power generation modes, the upper limit of the target value of the output power in the fuel cell stack 21 can be lowered. In mode-down state ST13, no power generation mode lower than low power generation mode ST2 is set as the upper limit on the power generation modes. When the control device 110 transitions to a mode down state ST13 while the low power generation mode ST2 is set as the upper limit of the power generation mode, the low power generation mode ST2 is maintained. In this embodiment, in the mode down state ST13, opening degree increase control, flow rate increase control, and prohibition control may be performed.

[0073] The stopped state ST14 is a state in which the fuel cell system 20 is stopped. In the stopped state ST14, no power is generated by the fuel cell stack 21. When the control device 110 transitions to the stopped state ST14, it restores the target value of the upper limit of the output power of the fuel cell stack 21, which had decreased due to the transition to the mode down state ST13. This releases the upper limit set for the power generation mode.

[0074] When the control device 110 is in the normal state ST10, if the average cell voltage falls below the first threshold, the control device 110 transitions to the first resolution state ST11. The average cell voltage is the average value of the voltages of multiple fuel cell cells 22. The average cell voltage may be the average value of the voltages of all fuel cell cells 22, or it may be the average value of the voltage of a representative fuel cell cell 22 among all fuel cell cells 22. The average cell voltage is an example of the voltage of a fuel cell cell 22.

[0075] The first threshold is a threshold used to determine whether flooding may be occurring in the fuel cell stack 21. If flooding is occurring in the fuel cell stack 21, the voltage of the fuel cell cells 22 decreases. The first threshold is determined based on the possible values ​​that the voltage of the fuel cell cells 22 can take when flooding is occurring in the fuel cell stack 21. The first threshold is, for example, 0.4[V].

[0076] When the control device 110 transitions to the first elimination state ST11, the control device 110 maintains the first elimination state ST11 for a first predetermined time. The first predetermined time is the time required to determine whether or not flooding is eliminated by the first elimination state ST11. The first predetermined time can be arbitrarily set between 4 and 10 seconds. After the first predetermined time has elapsed, if the average cell voltage is greater than or equal to the second threshold, the control device 110 transitions to the normal state ST10. The second threshold is a value greater than the first threshold. The second threshold is a value used to determine whether or not flooding in the fuel cell stack 21 has been eliminated. The second threshold is, for example, 0.6 V. If the average cell voltage becomes greater than or equal to the second threshold due to the flooding elimination control, the control device 110 stops the flooding elimination control and transitions to the normal state ST10. After the first predetermined time has elapsed, if the average cell voltage is less than the second threshold, the control device 110 transitions to the second elimination state ST12. As a result, if the average cell voltage does not exceed the second threshold after the opening degree increase control is performed, the control device 110 performs a flow rate increase control.

[0077] When the control device 110 transitions to the second resolution state ST12, the control device 110 maintains the second resolution state ST12 for a second predetermined time. The second predetermined time is the time required to determine whether or not flooding is resolved by the second resolution state ST12. The second predetermined time can be arbitrarily set between 4 and 10 seconds, for example. The second predetermined time may be the same as the first predetermined time, or it may be a different time. After the second predetermined time has elapsed, if the average cell voltage is above the second threshold, the control device 110 transitions to the normal state ST10. If the average cell voltage becomes above the second threshold due to flooding resolution control, the control device 110 will stop flooding resolution control and transition to the normal state ST10. After the second predetermined time has elapsed, if the average cell voltage is below the second threshold, the control device 110 transitions to the mode down state ST13. As a result, if the average cell voltage does not exceed the second threshold after flow rate increase control, the control device 110 lowers the target value of the output power in the fuel cell stack 21.

[0078] When the control device 110 is in mode-down state ST13, if the average cell voltage is below the second threshold, the control device 110 transitions to the first resolution state ST11. When the control device 110 is in mode-down state ST13, if the average cell voltage is above the second threshold, the control device 110 transitions to the normal state ST10.

[0079] When the control device 110 is in the normal state ST10, if the key is turned off, the control device 110 transitions to the stopped state ST14. The control device 110 also transitions to the stopped state ST14 when it receives a stop command, which is a stop command, such as a key being turned off.

[0080] [Operation of this embodiment] The control device 110 performs flooding elimination control when the average cell voltage is below a first threshold. If the voltage drop of the fuel cell cell 22 is caused by flooding, the flooding elimination control brings the average cell voltage above a second threshold. In this embodiment, the control device 110 performs opening increase control and prohibition control in the first elimination state ST11. If the average cell voltage does not reach the second threshold even in the first elimination state ST11, the control device 110 performs flow rate increase control and prohibition control in the second elimination state ST12.

[0081] If the voltage drop in the fuel cell 22 is not caused by flooding, the average cell voltage may not reach the second threshold even with flood elimination control. For example, when an organic solvent is supplied to the fuel cell stack 21 along with the cathode gas from the electric compressor 42, chemiadsorption may occur, where the organic solvent adheres to the cathode-side catalyst layer 27. Chemiadsorption causes a voltage drop in the fuel cell 22. Chemiadsorption cannot be eliminated even with flood elimination control. Chemiadsorption is resolved when the voltage of the fuel cell 22 is repeatedly reduced. Therefore, by operating the fuel cell system 20, the voltage fluctuations of the fuel cell 22 are repeated, and chemiadsorption is resolved naturally.

[0082] If the average cell voltage does not exceed the second threshold even after flooding elimination control is performed, it is highly likely that a voltage drop in the fuel cell 22 is occurring due to chemiadsorption. Therefore, if the average cell voltage does not exceed the second threshold even after flooding elimination control is performed, the control device 110 lowers the upper limit of the target value of the output power in the fuel cell stack 21 by setting an upper limit in the power generation mode.

[0083] [Effects of this embodiment] (1) If the average cell voltage does not exceed the second threshold due to flooding elimination control, the control device 110 lowers the upper limit of the target value of the output power in the fuel cell stack 21. If the target value of the output power is set high despite the average cell voltage not exceeding the second threshold, it may cause deterioration of the fuel cell cells 22. By lowering the upper limit of the target value of the output power in the fuel cell stack 21, the fuel cell system 20 can be operated even if the average cell voltage is below the first threshold.

[0084] (2) Flooding elimination control includes opening degree increase control, flow rate increase control, and prohibition control. When the valve opening is increased, the opening of the second valve 52 increases. When the opening of the second valve 52 is small, it is difficult for liquid water to pass through the second valve 52. The amount of cathode gas supplied from the electric compressor 42 increases with the number of fuel cell cells 22. On the other hand, the cathode gas pressure required for the fuel cell stack 21 does not change with the number of fuel cell cells 22. In a fuel cell stack 21 with a small number of fuel cell cells 22, the amount of cathode gas supplied is small, so it is necessary to reduce the opening of the second valve 52 to increase the cathode gas pressure. For this reason, the fewer the number of fuel cell cells 22, the more likely drainage problems are to occur in the fuel cell system 20. When the valve opening is increased, the opening of the second valve 52 increases, making it easier for liquid water to pass through the second valve 52. Therefore, flooding can be eliminated.

[0085] When flow rate increase control is performed, the flow rate of cathode gas supplied from the electric compressor 42 to the fuel cell stack 21 increases. This makes it easier for liquid water to be discharged from the fuel cell stack 21. As a result, flooding can be eliminated.

[0086] When the disable control is activated, the feedback control is disabled. If feedback control is activated when the average cell voltage is low, the current command value may become excessively large in order to maintain output power. By activating the disable control, it is possible to suppress the current command value from becoming excessively large.

[0087] Furthermore, the first DC / DC converter 81 steps down the output voltage of the fuel cell stack 21 using diodes D1, D3, and D5. If the cathode gas flow rate increases due to flow rate increase control, the output voltage of the fuel cell stack 21 will increase, which may increase the step-down ratio of the first DC / DC converter 81. A higher step-down ratio leads to a larger current, which in turn increases the amount of water produced in the fuel cell stack 21. By disabling feedback control, further increases in current are suppressed, thereby preventing an increase in the amount of water produced in the fuel cell stack 21.

[0088] (3) If the average cell voltage does not exceed the second threshold after the opening degree increase control, the control device 110 performs flow rate increase control. If the average cell voltage does not exceed the second threshold after the flow rate increase control, the control device 110 lowers the upper limit of the target value of the output power in the fuel cell stack 21. If the average cell voltage exceeds the second threshold due to the opening degree increase control, flow rate increase control is not performed. Performing flow rate increase control increases the noise generated by the electric compressor 42, thus reducing quietness. By performing opening degree increase control before flow rate increase control, if flooding is resolved by opening degree increase control, flow rate increase control does not need to be performed. Therefore, the reduction in quietness can be suppressed.

[0089] (4) If the average cell voltage does not rise above the second threshold due to flooding elimination control, the control device 110 lowers the voltage of the fuel cell 22. For example, when the control device 110 is turned off and enters the stopped state ST14, the power generation of the fuel cell stack 21 stops, causing the voltage of the fuel cell 22 to drop. This promotes the elimination of chemiadsorption.

[0090] (5) When the key is turned off, the control device 110 restores the upper limit of the target value of the output power in the fuel cell stack 21 to its original value. If chemiadsorption has not been resolved, after the key is turned on, the upper limit of the target value of the output power in the fuel cell stack 21 is lowered again, allowing the fuel cell system 20 to be operated even if the average cell voltage is below the first threshold. If chemiadsorption has been resolved, after the key is turned on, the fuel cell system 20 can be operated with the upper limit of the target value of the output power in the fuel cell stack 21 restored to its original value.

[0091] (6) Flooding is eliminated by performing flooding elimination control. Therefore, it is possible to suppress the enlargement of auxiliary equipment such as the electric compressor 42 in order to eliminate flooding.

[0092] [Example of changes] The embodiment can be implemented with the following modifications. The embodiment and the following modifications can be combined with each other to the extent that they do not contradict each other technically.

[0093] The trigger for the control device 110 to restore the upper limit of the target value of the output power in the fuel cell stack 21 can be arbitrarily set. For example, the control device 110 may restore the upper limit of the target value of the output power in the fuel cell stack 21 at regular intervals.

[0094] ○If the average cell voltage does not exceed the second threshold due to flooding elimination control, the control device 110 may lower the voltage of the fuel cell cell 22 by adjusting the amount of anode gas supplied to the fuel cell stack 21 and the amount of cathode gas supplied.

[0095] ○The opening degree increase control and the flow rate increase control may be executed at the same time. Alternatively, the flow rate increase control may be performed before the opening degree increase control. ○Flooding elimination control may be a control that performs flow rate increase control and prohibition control. Flooding elimination control may also be a control that performs opening degree increase control and prohibition control.

[0096] ○The control device 110 may be configured to continuously change the target value of the output power in the fuel cell stack 21. ○The power generation mode may have four or more modes. The power generation mode may have three modes.

[0097] ○The control device 110 may set a target value for the output power in the fuel cell stack 21 according to the power requirements of the vehicle load 11, the 48V auxiliary equipment 97, and the 12V auxiliary equipment 100. ○The voltage of the fuel cell 22 used for comparison with the first threshold and the second threshold may be the lowest cell voltage, the highest cell voltage, or the central cell voltage. The lowest cell voltage is the voltage of the fuel cell 22 with the lowest voltage among the multiple fuel cell 22. The highest cell voltage is the voltage of the fuel cell 22 with the highest voltage among the multiple fuel cell 22. The central cell voltage is the voltage of the fuel cell 22 whose voltage is the median value among the multiple fuel cell 22.

[0098] ○The stop command can be any command that is output when stopping the fuel cell system 20, such as a command to forcibly stop the fuel cell system 20 when an abnormality occurs in the fuel cell system 20.

[0099] ○The fuel cell system 20 may be installed in passenger cars, ships, trains, etc. ○The fuel cell system 20 may also be used as a stationary power generation device. [Explanation of Symbols]

[0100] 20...Fuel cell system, 21...Fuel cell stack, 22...Fuel cell cell, 52...Second valve which is a control valve, 85...Voltage measurement unit, 110...Control device.

Claims

1. A fuel cell stack having multiple fuel cell cells, A control valve for adjusting the pressure of the cathode gas discharged from the fuel cell stack, A voltage measuring unit for measuring the voltage of the fuel cell, The system includes a control device for setting a target value for the output power of the fuel cell stack, The control device is When the voltage of the fuel cell falls below a first threshold, flooding elimination control is performed to eliminate flooding. If the voltage of the fuel cell does not become greater than or equal to a second threshold value, which is greater than the first threshold value, due to the flooding elimination control, the upper limit of the target value of the fuel cell stack is reduced. The flooding elimination control described above is: An opening degree increasing control that increases the opening degree of the aforementioned control valve, Flow rate increase control that increases the flow rate of the cathode gas supplied to the fuel cell stack, The system includes a prohibition control that prohibits adjusting the output power of the fuel cell stack by feedback control, When the aforementioned prohibition control is performed, the control device calculates a current command value by feedforward control to bring the output power of the fuel cell stack to track the target value, in a fuel cell system.

2. The control device is If the voltage of the fuel cell does not exceed the second threshold after the opening degree increase control has been performed, the flow rate increase control will be performed. The fuel cell system according to claim 1, wherein if the voltage of the fuel cell does not exceed the second threshold after the flow rate increase control has been performed, the upper limit of the target value of the fuel cell stack is reduced.

3. The fuel cell system according to claim 1, wherein the control device stops the flooding elimination control and returns to the normal state when the voltage of the fuel cell becomes equal to or greater than the second threshold due to the flooding elimination control.

4. The fuel cell system according to claim 1, wherein the control device, upon receiving a command to stop the operation of the fuel cell system, restores the reduced upper limit to its original value.

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