Fuel cell system and method for controlling fuel cell system

Abstract

The invention relates to a fuel cell system and a control method of the fuel cell system. A fuel cell system (10) includes a deceleration buffer (74) that is an amount of power capable of charging a power storage device (244) with surplus power ([Delta] AP) generated when an air pump (112) decelerates, in which a control device (26) changes a buffer width of the deceleration buffer (74) in accordance with a temperature (Tbat) of the power storage device (244), and changes the buffer width of the deceleration buffer (74) in accordance with the temperature (Tbat) of the power storage device (244). The FC current limit value of the fuel cell stack (12) is replaced on the basis of the buffer width of the deceleration buffer (74), and the fuel cell stack (12) is caused to generate power on the basis of the replaced FC current limit value.

Description

Technical Field

[0001] The present invention relates to a fuel cell system and a control method for a fuel cell system. Background Art

[0002] In recent years, in order to ensure that more people can access appropriate, reliable, sustainable, and advanced energy, research and development have been carried out on fuel cells that contribute to energy efficiency improvement.

[0003] A power generation system equipped with a fuel cell stack is called a fuel cell system. The fuel cell stack includes a plurality of power generation single cells. Each power generation single cell generates electricity through an electrochemical reaction between a fuel gas (hydrogen-containing gas) and an oxidant gas (oxygen-containing gas) supplied from an air pump. The electricity generated by each power generation single cell is supplied to a load and charged into a power storage device.

[0004] For example, Patent Document 1 discloses a fuel cell system that sets a limit range for the charge and discharge power amount of a power storage device.

[0005] This fuel cell system sets a buffer for the limit range of the charge and discharge power amount, and distributes the power amount of this buffer part to the drive of the air pump. When the temperature of the power storage device is low, the buffered power amount is set small. As a result, the power amount that the power storage device can discharge to devices other than the air pump increases.

[0006] Prior Art Documents

[0007] Patent Documents

[0008] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2017-152280 Summary of the Invention

[0009] Problems to be Solved by the Invention

[0010] Desirably, in a fuel cell system, the power amount range in which a power storage device can be charged and discharged is optimized.

[0011] An object of the present invention is to solve the above problems.

[0012] Means for Solving the Problems

[0013] A first aspect of the present invention relates to a fuel cell system, comprising: a fuel cell that generates electricity using a fuel gas and an oxidant gas; a pump that supplies the oxidant gas to the fuel cell; a power storage device that can supply power to the pump; a control device that controls the power generation of the fuel cell and the charge and discharge of the power storage device; and a temperature measurement device that measures the temperature of the power storage device. The control device sets a power amount range in which the power storage device can be charged and discharged, and sets a buffer within the power amount range of the power storage device. The buffer includes a deceleration buffer, and the deceleration buffer is a power amount that can charge the surplus power generated when the pump decelerates into the power storage device. In the fuel cell system, the control device changes the buffer width of the deceleration buffer according to the temperature of the power storage device, replaces the current limit value of the fuel cell based on the buffer width of the deceleration buffer, and causes the fuel cell to generate electricity according to the replaced current limit value.

[0014] A second aspect of the present invention relates to a control method for a fuel cell system. The fuel cell system comprises: a fuel cell that generates electricity using a fuel gas and an oxidant gas; a pump that supplies the oxidant gas to the fuel cell; a power storage device that can supply power to the pump; a control device that controls the power generation of the fuel cell and the charge and discharge of the power storage device; and a temperature measurement device that measures the temperature of the power storage device. The control device sets a power amount range in which the power storage device can be charged and discharged, and sets a buffer within the power amount range of the power storage device. The buffer includes a deceleration buffer, and the deceleration buffer is a power amount that can charge the surplus power generated when the pump decelerates into the power storage device. In the control method for the fuel cell system, it includes: a step of changing the buffer width of the deceleration buffer according to the temperature of the power storage device; a step of replacing the current limit value of the fuel cell based on the buffer width of the deceleration buffer; and a step of causing the fuel cell to generate electricity according to the replaced current limit value.

[0015] Effects of the Invention

[0016] According to the present invention, in a fuel cell system, it is possible to optimize the power amount range in which a power storage device can be charged and discharged.

[0017] The above objects, features, and advantages should be easily understood from the description of the following embodiments described with reference to the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic structural diagram of a fuel cell system according to an embodiment.

[0019] Figure 2It is a schematic diagram of a turbine-type air pump equipped with an air bearing mechanism.

[0020] Figure 3 It is an explanatory diagram for explaining the charge and discharge limit range of the power storage device.

[0021] Figure 4 It is a timing chart showing an example of the relationship between the actual power consumption of the air pump (AP) and the steady-state power consumption of the AP.

[0022] Figure 5 (a) thereof is an explanatory diagram showing the change in the rotational speed of the air pump over time, Figure 5 (b) thereof is an explanatory diagram showing the change in the opening degree of the bypass valve over time. Figure 5 (c) thereof is an explanatory diagram showing the change in the flow rate of the oxidant gas over time, Figure 5 (d) thereof is an explanatory diagram showing the change in the dryness inside the fuel cell stack over time.

[0023] Figure 6 It is a flowchart showing the process of setting the current limit value of the fuel cell stack.

[0024] Figure 7 It is a timing chart showing an example of the transition of the actual power consumption of the air pump (AP) and the steady-state power consumption of the AP at low temperature and normal temperature.

[0025] Figure 8 It is an explanatory diagram showing an example of the FC current limit value corresponding to the temperature of the power storage device. Detailed implementation

[0026] [Structure of fuel cell system 10]

[0027] Figure 1 It is a schematic structural diagram of the fuel cell system 10 related to the implementation mode. Here, the structure of the fuel cell system 10 mounted on the fuel cell vehicle 11 is described. However, the fuel cell system 10 can also be mounted on a moving body other than a vehicle. For example, the fuel cell system 10 can also be mounted on a ship, an aircraft, a robot, etc., and can also be used as a stationary power source in equipment, homes, etc.

[0028] In the fuel cell system 10, a fuel gas and an oxidant gas are used as reaction gases. The fuel gas is a hydrogen-containing gas. The oxidant gas is an oxygen-containing gas such as air. The fuel gas and the oxidant gas are each supplied to the fuel cell stack 12 for an electrochemical reaction. Moreover, in this specification, the fuel gas that is discharged from the fuel cell stack 12 without being used for the electrochemical reaction is also referred to as fuel exhaust. In addition, the oxidant gas that is discharged from the fuel cell stack 12 without being used for the electrochemical reaction is also referred to as oxidant exhaust.

[0029] The fuel cell system 10 includes a fuel cell stack 12, a tank 14, an anode system 16, a cathode system 18, a cooling system 20, a load 21, and a power supply system 27. In addition, the fuel cell system 10 includes a control device 26.

[0030] The fuel cell stack 12 has a positive terminal 23a and a negative terminal 23b. The electric power generated by the fuel cell stack 12 is supplied to the load 21 and the power supply system 27 via the positive terminal 23a and the negative terminal 23b.

[0031] The tank 14 is filled with high-pressure fuel gas.

[0032] The fuel cell stack 12 has a fuel gas supply port 22a and a fuel gas discharge port 22b. The fuel gas supply port 22a supplies fuel gas to the inside of the fuel cell stack 12. The fuel gas discharge port 22b discharges fuel exhaust gas from the inside of the fuel cell stack 12.

[0033] The fuel cell stack 12 has an oxidant gas supply port 22c and an oxidant gas discharge port 22d. The oxidant gas supply port 22c supplies oxidant gas to the inside of the fuel cell stack 12. The oxidant gas discharge port 22d discharges oxidant exhaust gas from the inside of the fuel cell stack 12.

[0034] The fuel cell stack 12 has a cooling medium supply port 22e and a cooling medium discharge port 22f. The cooling medium supply port 22e supplies cooling medium to the inside of the fuel cell stack 12. The cooling medium discharge port 22f discharges cooling medium from the inside of the fuel cell stack 12.

[0035] The anode system 16 includes a fuel gas supply passage 84, a fuel gas discharge passage 86, a circulation passage 88, and a drainage passage 90. The anode system 16 includes an ejector 94, an eductor 96, a gas-liquid separator 98, and a drain valve 100.

[0036] The fuel gas supply passage 84 is connected to the discharge port of the tank 14 and the fuel gas supply port 22a of the fuel cell stack 12. The ejector 94 and the eductor 96 are provided in the fuel gas supply passage 84. The inflow port of the eductor 96 is connected to the discharge port of the ejector 94, and the discharge port of the eductor 96 is connected to the fuel gas supply port 22a. The eductor 96 is disposed between the ejector 94 and the fuel gas supply port 22a.

[0037] The fuel gas discharge passage 86 is connected to the fuel gas discharge interface 22b of the fuel cell stack 12 and the supply interface of the gas-liquid separator 98. The circulation passage 88 is connected to the exhaust interface of the gas-liquid separator 98 and the suction interface of the ejector 96. The drain passage 90 is connected to the drain interface of the gas-liquid separator 98 and the discharge passage 109. The discharge passage 109 communicates with the atmosphere through the discharge interface 109p provided in the fuel cell vehicle 11. A drain valve 100 is provided in the drain passage 90.

[0038] The cathode system 18 includes an oxidant gas supply passage 106, an oxidant gas discharge passage 108 (discharge passage), and a bypass passage 110. The cathode system 18 includes an air filter 105, a gas pump 112 (oxidant gas supply device, compressor, also simply referred to as a pump), a humidifier 114, an inlet seal valve 116, an outlet seal valve 118 as a back pressure valve, and a bypass valve 120.

[0039] The oxidant gas supply passage 106 is connected to the air intake interface 106p provided in the fuel cell vehicle 11 and the oxidant gas supply interface 22c of the fuel cell stack 12. In the oxidant gas supply passage 106, there are provided an air filter 105, a flow sensor 107, a gas pump 112, an inlet seal valve 116, and a humidifier supply passage 114A of the humidifier 114.

[0040] The portion of the oxidant gas supply passage 106 disposed upstream of the humidifier 114 is referred to as the oxidant gas supply passage 106A. The portion of the oxidant gas supply passage 106 disposed downstream of the humidifier 114 is referred to as the oxidant gas supply passage 106B.

[0041] The inlet seal valve 116 is disposed closer to the humidifier 114 than the gas pump 112. An air filter 105, a flow sensor 107, a temperature sensor 104, and a pressure sensor 266 are installed upstream of the gas pump 112 in the oxidant gas supply passage 106A. The flow sensor 107 detects the flow rate Qo of the oxidant gas flowing through the gas pump 112. The temperature sensor 104 detects the temperature (inlet temperature of the gas pump 112) Tin of the oxidant gas in the suction interface 300 of the gas pump 112. The pressure sensor 266 detects the pressure (inlet pressure of the gas pump 112) Pin on the suction interface 300 side of the gas pump 112. A pressure sensor 268 is installed downstream of the gas pump 112 in the oxidant gas supply passage 106A. The pressure sensor 268 detects the pressure (outlet pressure of the gas pump 112) Pout on the discharge interface 302 side of the gas pump 112.

[0042] Figure 2 It is a schematic diagram of a turbine-type gas pump 112 having an air bearing mechanism.

[0043] The air pump 112 has a rotor shaft 274, and an impeller 276 is fixed to one end of the rotor shaft 274. A plurality of magnets are axially embedded in the cylindrical side surface of the rotor shaft 274. Stator coils 272 of U phase, V phase, and W phase are installed in the housing of the air pump 112, and a bearing (also referred to as an air bearing) 292 is installed. The rotor shaft 274 is inserted through the bearing 292. A flow path for the oxidant gas is installed in the housing of the air pump 112, and a supercharger 294 including the impeller 276 is provided.

[0044] When the impeller 276 rotates along with the rotation of the rotor shaft 274, compressed air is supplied between the rotor shaft 274 and the inner peripheral surface of the bearing 292 at a predetermined rotational speed or higher. Thereby, an air layer is formed between the rotor shaft 274 and the inner peripheral surface of the bearing 292, and the rotor shaft 274 can rotate stably at high speed without contacting the inner peripheral surface of the bearing 292. This is called the shaft floating of the rotor shaft 274.

[0045] Preferably, during the operation of the fuel cell system 10 (from the start of operation to the stop of operation), in order to timely respond to the power generation requirements of the fuel cell stack 12, the shaft floating of the rotor shaft 274 is maintained. Basically, the rotational speed of the air pump 112 is controlled to a value above the rotational speed at which the shaft floating of the rotor shaft 274 can be achieved. That is, the rotational speed of the air pump 112 is controlled to a value above the minimum rotational speed at which the rotor shaft 274 can rotate without contacting the inner peripheral surface of the bearing 292.

[0046] Under such control, the air pump 112 sucks in external gas through the suction interface 300 and is supercharged (pressurized and compressed) by the supercharger 294. The air supercharged by the supercharger 294 is the oxidant gas, which is ejected from the ejection interface 302 to the oxidant gas supply path 106A.

[0047] Return to Figure 1 , the oxidant gas discharge path 108 is connected to the oxidant gas discharge interface 22d of the fuel cell stack 12 and the discharge path 109. In the oxidant gas discharge path 108, there are a humidifier discharge path 114B of the humidifier 114 and an outlet seal valve 118.

[0048] The part of the oxidant gas discharge path 108 disposed upstream of the humidifier 114 is referred to as the oxidant gas discharge path 108A. The part of the oxidant gas discharge path 108 disposed downstream of the humidifier 114 is referred to as the oxidant gas discharge path 108B.

[0049] A hydrogen concentration sensor 111 is installed in the oxidant gas discharge path 108A. The hydrogen concentration sensor 111 is installed near the oxidant gas discharge interface 22d. The hydrogen concentration sensor 111 detects the hydrogen concentration Dh in the oxidant exhaust gas.

[0050] The bypass flow path 110 is connected at a position between the air pump 112 and the inlet sealing valve 116 in the oxidant gas supply path 106A, and at a position downstream of the outlet sealing valve 118 in the oxidant gas discharge path 108B. A bypass valve 120 is provided in the bypass flow path 110.

[0051] The bypass valve 120 is a butterfly valve capable of linearly adjusting the opening degree. Similarly, the inlet sealing valve 116 for opening and closing the oxidant gas supply path 106B and the outlet sealing valve 118 for opening and closing the oxidant gas discharge path 108A are also butterfly valves capable of linearly adjusting the opening degree. Moreover, the inlet sealing valve 116 and the outlet sealing valve 118 may also be valves that switch between open (opening degree 100%) and closed (opening degree 0%) such as solenoid valves.

[0052] The cooling system 20 includes a cooling medium supply path 122 and a cooling medium discharge path 124. The cooling system 20 includes a water pump 126 and a radiator 128. The cooling medium supply path 122 is connected to the fluid ejection interface of the radiator 128 and the cooling medium supply interface 22e of the fuel cell stack 12. A water pump 126 is provided in the cooling medium supply path 122.

[0053] The cooling medium discharge path 124 is connected to the cooling medium discharge interface 22f of the fuel cell stack 12 and the fluid supply interface of the radiator 128. A temperature sensor 130 is installed in the cooling medium discharge path 124. The temperature sensor 130 detects the temperature of the cooling medium flowing in the cooling medium discharge path 124. The temperature of the cooling medium flowing in the cooling medium discharge path 124 corresponds to the temperature inside the fuel cell stack 12 (stack temperature).

[0054] The fuel cell stack 12 is formed by stacking a plurality of power generation single cells 24. The power generation single cell 24 includes an electrolyte membrane - electrode structure body 32, and separators 28 and 30 that sandwich the electrolyte membrane - electrode structure body 32. The electrolyte membrane - electrode structure body 32 includes an MEA (Membrane Electrode Assembly) 34 and a resin frame member (not shown) that surrounds the outer peripheral portion of the MEA.

[0055] The MEA 34 includes, for example, a thin film (solid polymer electrolyte membrane) 36 containing perfluorosulfonic acid with moisture, a cathode electrode 40 and an anode electrode 38 that sandwich the thin film 36. The cathode electrode 40 and the anode electrode 38 each have an electrode catalyst layer (not shown) and a gas diffusion layer (not shown) formed of carbon paper or the like. The electrode catalyst layer includes porous carbon particles carrying a platinum alloy on the surface. The porous carbon particles are uniformly coated on the surface of the gas diffusion layer together with an ion - conductive polymer binder. Thus, the electrode catalyst layer is formed. The electrode catalyst layer is formed on both sides of the thin film (solid polymer electrolyte membrane) 36.

[0056] On the surface of the separator 28 of one side facing the electrolyte membrane - electrode assembly 32, a cathode flow path (oxidant gas flow path) 50 is formed. The cathode flow path 50 connects the oxidant gas supply port 22c and the oxidant gas discharge port 22d. The opening degree of the outlet seal valve 118 is adjusted by the control device 26, thereby controlling the pressure of the oxidant gas flowing through the cathode flow path 50.

[0057] On the surface of the separator 30 of the other side facing the electrolyte membrane - electrode assembly 32, an anode flow path (fuel gas flow path) 66 is formed. The anode flow path 66 connects the fuel gas supply port 22a and the fuel gas discharge port 22b.

[0058] A fuel gas (hydrogen) is supplied to the anode electrode 38. In the anode electrode 38, due to the electrode reaction generated by the catalyst, hydrogen ions are generated from hydrogen molecules and electrons are released from hydrogen molecules. The hydrogen ions permeate through the MEA 34 and move to the cathode electrode 40. On the other hand, the electrons released from hydrogen molecules move from the separator 30 and the negative terminal 23b through the load 21 and via the positive terminal 23a and the separator 28 to the cathode electrode 40.

[0059] An oxidant gas (oxygen) is supplied to the cathode electrode 40. In the cathode electrode 40, due to the action of the catalyst, hydrogen ions and electrons react with the oxygen contained in the supplied oxidant gas to generate water.

[0060] A single - cell voltage sensor 25 is installed in each power - generating single cell 24. The single - cell voltage sensor 25 detects the voltage between the terminals of one power - generating single cell 24 (cell unit), that is, the single - cell voltage Vcell.

[0061] The load 21 includes a motor 246 as a high - voltage load and an air pump (electric auxiliary device) 112, a battery heater 251 as a low - voltage load, and an air conditioner (not shown). The motor 246 is a driving source of the fuel - cell vehicle 11, and the fuel - cell vehicle 11 travels with the driving force of the motor 246. The air pump 112 supplies an oxidant gas to the fuel - cell stack 12. The battery heater 251 warms the power - storage device 244.

[0062] The power supply system 27 includes a low - voltage power supply that generates a low voltage Vl, that is, a power - storage device (battery) 248, and a high - voltage power supply that generates a high voltage Vh, that is, a power - storage device (battery) 244. Here, the power supply 248 uses a lead - acid battery. Alternatively, a lithium - ion secondary battery or the like can be used instead of the lead - acid battery. Here, the power - storage device 244 uses a lithium - ion secondary battery. Alternatively, a capacitor or the like can be used instead of the lithium - ion secondary battery.

[0063] The power storage device 244 is configured to be able to charge and discharge electric power, and discharges the insufficient part of the generated electric power of the fuel cell stack 12 with respect to the actual power consumption of the motor 246 and the air pump 112 (hereinafter also referred to as the AP actual power consumption) during power operation. The power storage device 244 is charged with the regenerative power of the motor 246 during regeneration. In addition, the power storage device 244 is charged with the excess part of the generated electric power of the fuel cell stack 12 with respect to the AP actual power consumption of the air pump 112.

[0064] A temperature sensor (temperature measuring device) 250, a charge amount detection sensor (SOC sensor) 245, and a battery heater 251 are installed in the power storage device 244. The temperature sensor 250 detects the temperature Tbat of the power storage device 244 and outputs it to the control device 26.

[0065] The charge amount detection sensor 245 detects the SOC of the power storage device 244 {state of charge [%] = (current remaining capacity) ÷ (fully charged capacity) × 100} and outputs it to the control device 26. SOC [%] is the remaining capacity with respect to the fully charged capacity, and the charge amount detection sensor 245 calculates SOC [%] based on the temperature Tbat, input / output current (charge / discharge current), and storage voltage of the power storage device 244.

[0066] The charge amount detection sensor 245 calculates a discharge limit value Dlim [kWh] and a charge limit value Clim [kWh] based on the calculated SOC. The discharge limit value Dlim is a threshold value that prohibits over-discharge of the power storage device 244, and the charge limit value Clim is a threshold value that prohibits over-charge of the power storage device 244.

[0067] In addition to based on the SOC of the power storage device 244, the discharge limit value Dlim and the charge limit value Clim can be calculated based on the temperature Tbat, input / output current (charge / discharge current), and storage voltage of the power storage device 244, the internal impedance of the power storage device 244, etc. Moreover, it can also be that the discharge limit value Dlim and the charge limit value Clim are not calculated by the charge amount detection sensor 245, but by the control device 26.

[0068] The charge amount detection sensor 245 notifies the calculated discharge limit value Dlim and charge limit value Clim to the control device 26. The control device 26 prohibits the use of ranges exceeding the discharge limit value Dlim and the charge limit value Clim via the buck-boost converter 243. In other words, the control device 26 uses the power storage device 244 within the charge / discharge limit range (electric power range) 68 from the discharge limit value Dlim to the charge limit value Clim.

[0069] Figure 3It is an explanatory diagram for explaining the charge-discharge limit range 68 of the power storage device 244. According to the temperature Tbat of the power storage device 244, the overall power width of the charge-discharge limit range 68 can be changed. Generally speaking, at low temperatures (including extremely low temperatures (e.g., less than 0 degrees)), compared with normal temperatures, the power width of the charge-discharge limit range 68 is smaller. The charge amount detection sensor 245 monitors the charge-discharge limit range 68 at any time and notifies it to the control device 26.

[0070] As Figure 3 shown, a buffer (also called margin) 70 for the air pump 112 is set in the charge-discharge limit range 68 of the power storage device 244. The buffer 70 includes an acceleration buffer (discharge margin) 72 set on the discharge limit value Dlim side and a deceleration buffer (charge margin) 74 set on the charge limit value Clim side.

[0071] The acceleration buffer 72 allows for the sharp power consumption, insufficient FC generation power, and excessive power fluctuations that occur along with the acceleration of the air pump 112. For example, when there is insufficient power in the air pump 112, the power storage device 244 discharges the insufficient power to the air pump 112 within the range of the acceleration buffer 72. Moreover, the acceleration of the air pump 112 means that the ratio [rpm / sec] of the rotational speed [rpm] of the air pump 112 changing with time is positive.

[0072] On the other hand, the deceleration buffer 74 allows for the sharp power surplus, excessive FC generation power, power surplus due to the regenerative power of the air pump 112 or the regenerative power of the motor 246, and excessive power fluctuations that occur along with the deceleration of the air pump 112. For example, when there is a power surplus in the air pump 112, the power storage device 244 charges with the surplus power within the range of the deceleration buffer 74. Moreover, the deceleration of the air pump 112 means that the ratio [rpm / sec] of the rotational speed [rpm] of the air pump 112 changing with time is negative.

[0073] As a result, the buffer 70 (acceleration buffer 72, deceleration buffer 74) absorbs the sharp fluctuations in the actual AP power consumption of the air pump 112 during acceleration and deceleration, preventing over-discharge and over-charge of the power storage device 244.

[0074] For example, the power width of the buffer 70 can be set based on the discharge limit value Dlim, the charge limit value Clim calculated by the charge amount detection sensor 245, and the temperature Tbat of the power storage device 244. Alternatively, the control device 26 can calculate the power width of the buffer 70 using a buffer calculation correspondence relationship (not shown) pre-stored in the storage unit 138 of the control device 26. Moreover, the power width of the buffer 70 is also simply referred to as the buffer width.

[0075] In the fuel cell system 10 according to this embodiment, the electric power amount of the acceleration buffer 72 can be changed (varied) within the power width (buffer width) of the buffer 70. For example, the minimum value (minimum necessary value) of the acceleration buffer 72 can be set based on the electric power amount required when the air pump 112 rotates at the minimum rotational speed (the minimum value of the rotational speed at which the rotor shaft 274 of the air pump 112 can be axially floated). For example, the maximum value (maximum necessary value) of the acceleration buffer 72 can be set based on the electric power amount required when the air pump 112 rotates at the maximum acceleration rate (the positive maximum value of the ratio of the rotational speed change with time).

[0076] Similarly, the electric power amount of the deceleration buffer 74 can also be changed (varied) within the power width (buffer width) of the buffer 70. For example, the minimum value (minimum necessary value) of the deceleration buffer 74 can be set in consideration of deviations such as the measurement error of the flow sensor 107 and the power error of the inverter 252. The maximum value (maximum necessary value) of the deceleration buffer 74 can be set based on the maximum deceleration rate (the negative maximum value of the ratio of the rotational speed change with time) of the air pump 112 that can avoid drying of the fuel cell stack 12 when reducing the output of the fuel cell stack 12. Here, the established rated current of the fuel cell stack 12 refers to the current value set according to the I-V characteristics (current-voltage characteristics) of the fuel cell stack 12, and can also be, for example, the maximum value of the current that the fuel cell stack 12 can stably output.

[0077] In Figure 3 In the charge-discharge limit range 68 shown, the range other than the acceleration buffer 72 and the deceleration buffer 74 is referred to as the energy management control range (EM control range) 76. The power width of the EM control range 76 is allocated to the charge and discharge of the load 21 other than the air pump 112. The load 21 other than the air pump 112 includes the motor 246, the battery heater 251, an air conditioner (not shown), etc.

[0078] Return to Figure 1 , the motor 246 is connected to the inverter 242. To the inverter 242, electric power of the high voltage Vh is supplied from the fuel cell stack 12 via the boost converter 240, and electric power of the high voltage Vh is supplied from the power storage device 244 via the buck-boost converter 243. That is, electric power is supplied to the motor 246 from both the fuel cell stack 12 and the power storage device 244 or one of them. The inverter 242 converts the direct current of the high voltage Vh supplied from both the fuel cell stack 12 and the power storage device 244 or one of them into a three-phase alternating current to drive the motor 246.

[0079] The power generation energy generated by the fuel cell stack 12 for the power storage device 244 is used for charging. The boost converter 240 boosts the power generation voltage Vfc of the fuel cell stack 12 to a high DC voltage Vh, and the boosted high voltage Vh is applied to the power storage device 244 via the buck-boost converter 243.

[0080] When the fuel cell vehicle 11 decelerates, that is, when the motor 246 regenerates, the motor 246 functions as a generator and generates a three-phase alternating current in the motor 246. The generated three-phase alternating current is converted into electric power of a high DC voltage Vh by the inverter 242 and is supplied to the high-voltage terminal of the buck-boost converter 243. The regenerative power supplied to the high-voltage terminal is charged to the power storage device 244 through the low-voltage terminal of the buck-boost converter 243.

[0081] The low-voltage loads include the control device 26, various sensors, the battery heater 251, an air conditioner (not shown), an electric power steering device, and a lighting device, etc. Electric power of a low DC voltage Vl is supplied from the power source 248 to these low-voltage loads. The electric power of the high voltage Vh supplied from the power storage device 244 is stepped down to the low voltage Vl by the buck converter 247 and is charged to the power source 248.

[0082] Three-phase alternating current power is supplied from the inverter 252 to the air pump 112. The inverter 252 converts the DC high voltage Vh supplied from the power storage device 244 into a three-phase alternating current. The inverter 252 supplies the converted three-phase alternating current to the air pump 112 to drive the air pump 112 within the range of the rated power. The rated power of the air pump 112 is, for example, the maximum power that the air pump 112 can stably output and is preset according to the specifications of the air pump 112. Any two phases of the three-phase alternating current, here, the U-phase alternating current Iu and the V-phase alternating current Iv are respectively detected by the current sensors 253 and 254.

[0083] It should be noted that in the case of driving the air pump 112 with the power generation power of the fuel cell stack 12, the power generated by the fuel cell stack 12 is not directly supplied to the air pump 112. In this case, after the power generated by the fuel cell stack 12 is charged to the power storage device 244 through the buck-boost converter 243, it is supplied from the power storage device 244 to the air pump 112 through the inverter 252.

[0084] The control device 26 is connected to a power switch (operation switch or ignition switch, not shown). The user instructs the start of operation (start of power generation) and the stop of operation (stop of power generation) of the fuel cell vehicle 11 (fuel cell system 10) through the power switch.

[0085] When the power switch is in the ON state, the power generation operation of the fuel cell stack 12 is started or continued, so that the fuel cell vehicle 11 is in a drivable state or a driving state. The drivable state of the fuel cell vehicle 11 means that the fuel cell stack 12 is in an idling power generation state with a small power generation amount and the fuel cell vehicle 11 is in a stopped driving state. When the power switch is in the OFF state, the power generation operation of the fuel cell stack 12 is ended, so that the fuel cell vehicle 11 is in a stopped state (idle state).

[0086] The control device 26 can be constituted by an ECU (Electronic Control Unit). The control device 26 includes an arithmetic unit 136 and a storage unit 138. The arithmetic unit 136 is, for example, a processor such as a CPU (Central Processing Unit) or a GPU (Graphics Processing Unit). That is, the arithmetic unit 136 can be constituted by a processing circuitry. The arithmetic unit 136 executes computer-executable instructions (programs) stored in the storage unit 138 to control each device. Alternatively, at least a part of the arithmetic unit 136 can be implemented by an integrated circuit such as an ASIC (Application-Specific Integrated Circuit) or an FPGA (Field-Programmable Gate Array). Alternatively, at least a part of the arithmetic unit 136 can be implemented by a circuit including discrete devices.

[0087] The arithmetic unit 136 includes an acquisition unit 140, a control unit 142, a timing unit (not shown), a determination unit 146, a buffer setting unit 150, and a current limit value setting unit 152. The acquisition unit 140 acquires information from electronic components (sensors, ECUs, etc.) other than the control device 26.

[0088] In addition to including Figure 1 the single cell voltage sensor 25, the temperature sensor 104, the flow sensor 107, the hydrogen concentration sensor 111, the temperature sensor 130, the current sensor 253, the current sensor 254, the pressure sensor 266, the pressure sensor 268, the charge amount detection sensor 245, and the temperature sensor 250 shown, the sensors also include sensors not shown. For example, there are a voltage sensor for detecting the power generation voltage Vfc of the fuel cell stack 12, a current sensor for detecting the power generation current Ifc of the fuel cell stack 12, a voltage sensor for detecting the high voltage Vh of the power storage device 244, a voltage sensor for detecting the low voltage Vl of the power supply 248, a flow sensor for detecting the flow rate of the oxidant gas in the fuel cell stack 12, etc.

[0089] The control unit 142 executes computer-executable instructions (programs) based on various signals acquired from sensors by the acquisition unit 140. The control unit 142 controls the operations of the injector 94, the air pump 112, the water pump 126, the motor 246, the boost converter 240, the inverter 242, the inverter 252, the buck-boost converter 243, the buck converter 247, and valves. The timing unit measures the execution time and the like by a timer (not shown). The determination unit 146 determines the appropriateness of the buffer 70 of the power storage device 244 and the like. The buffer setting unit 150 sets the buffer 70 of the power storage device 244. The current limit value setting unit 152 sets the upper limit value of the output current of the fuel cell stack 12 (hereinafter also referred to as the FC current limit value).

[0090] The storage unit 138 is composed of a computer-readable storage medium, namely a volatile memory (not shown) and a non-volatile memory (not shown). Alternatively, at least a part of the storage unit 138 may be provided in the above-mentioned processor, integrated circuit, etc.

[0091] The volatile memory is, for example, a RAM (Random Access Memory), etc. Data and the like are recorded in the volatile memory, for example. Physical quantities acquired by the control device 26 from various sensors, calculated values including the discharge limit value Dlim and the charge limit value Clim, etc. are recorded in the volatile memory.

[0092] The non-volatile memory is, for example, a ROM (Read Only Memory), a flash memory, etc. Programs, forms, mapping tables, etc. are recorded in the non-volatile memory, for example. In the non-volatile memory, a power calculation correspondence 148 capable of calculating the steady-state power consumption of the air pump 112 (AP steady-state power consumption) is recorded. In addition, a buffer calculation correspondence (not shown) and an air pump system efficiency correspondence (not shown) are recorded in the non-volatile memory.

[0093] The AP steady-state power consumption of the air pump 112 refers to the power consumed in a state where the air pump 112 rotates at a fixed rotational speed [rpm] (steady state) when the fuel cell stack 12 generates electricity with a stable power generation amount. The AP steady-state power consumption is recorded in advance in the power calculation correspondence 148 for each fixed rotational speed. The control unit 142 acquires the rotational speed of the air pump 112, and based on the acquired rotational speed and referring to the power calculation correspondence 148, the AP steady-state power consumption can be calculated.

[0094] Alternatively, the AP steady-state power consumption may be calculated based on the theoretical thermodynamic work [w] of the compressor (air pump 112) and the air pump system efficiency [%]. The air pump system efficiency can be calculated based on the air pump system efficiency correspondence.

[0095] In the air pump system efficiency correspondence, the air pump system efficiency [%] corresponding to the flow rate Qo of the oxidant gas and the pressure ratio of the air pump 112 is pre-recorded. The pressure ratio of the air pump 112 is calculated as the ratio of the inlet pressure Pin of the air pump 112 detected by the pressure sensor 266 to the outlet pressure Pout of the air pump 112 detected by the pressure sensor 268. The control unit 142 calculates the air pump system efficiency based on the flow rate Qo of the oxidant gas and the pressure ratio of the air pump 112 with reference to the air pump system efficiency correspondence.

[0096] Moreover, it can also be that, regarding the flow rate Qo of the oxidant gas, instead of the measured value of the flow sensor 107, a corrected value of the measured value of the flow sensor 107 is used. The control unit 142 can correct the measured value of the flow sensor 107 by considering, for example, the specifications of the air pump 112 and the pressure loss inside the air pump 112. When correcting the measured value of the flow sensor 107, the inlet temperature Tin of the air pump 112, the inlet pressure Pin of the air pump 112, or other values can also be considered.

[0097] The control device 26 obtains the changes in the U-phase alternating current Iu and the V-phase alternating current Iv detected by the current sensors 253 and 254 through the acquisition unit 140, and thus the control unit 142 can calculate the rotational speed of the air pump 112.

[0098] The control device 26 performs feedback control based on vector control on the three-phase alternating currents supplied from the inverter 242 to the motor 246 respectively based on the torque command value of the motor 246. In addition, the control device 26 performs feedback control based on vector control on the three-phase alternating currents Iu, Iv, and Iw supplied from the inverter 252 to the air pump 112 respectively based on the torque command value of the motor 246.

[0099] The control device 26 calculates the actual power consumption (AP actual power consumption) of the air pump 112 based on the DC terminal voltage of the air pump 112 and the three-phase alternating currents detected by the current sensors 253 and 254.

[0100] [Difference between AP actual power consumption and AP steady-state power consumption]

[0101] Here, the difference between the AP actual power consumption and the AP steady-state power consumption is described. Figure 4 It is a timing chart showing an example of the relationship between the AP actual power consumption and the AP steady-state power consumption of the air pump 112.

[0102] Basically, the fuel cell system 10 uses the electric power generated by the fuel cell stack 12 to supply the electric power required for the load 21 of the fuel cell vehicle 11. The control device 26 calculates the electric power consumed by the entire fuel cell vehicle 11. Hereinafter, the electric power consumed by the entire fuel cell vehicle 11 is referred to as the vehicle required electric power. The control device 26 calculates the target power generation power of the FC (FC power generation required power) based on this vehicle required electric power. The control device 26 calculates the target rotational speed of the air pump 112 based on the flow rate Qo of the oxidant gas corresponding to the FC power generation required power and the pressure ratio (the ratio of the inlet pressure Pin of the air pump 112 to the outlet pressure Pout of the air pump 112). The control device 26 calculates the steady-state power consumption of the AP based on the target rotational speed and referring to the power calculation correspondence 148. The calculated steady-state power consumption of the AP is fed back as the electric power required to drive the air pump 112 to the calculation of the next vehicle required electric power.

[0103] From the time point t2 to the time point t3 in Figure 4 , the fuel cell stack 12 generates electricity stably with a fixed power generation amount (FC power generation power), and the air pump 112 is driven at a fixed rotational speed. In this case, the actual power consumption of the AP is substantially the same as the steady-state power consumption of the AP.

[0104] However, when the air pump 112 accelerates or decelerates, a difference may occur between the actual power consumption of the AP and the steady-state power consumption of the AP.

[0105] Figure 4 From the time point t1 to the time point t2 in

[0106] shows the acceleration of the air pump 112. The power generation amount (FC power generation power) of the fuel cell stack 12 increases, and the rotational speed of the air pump 112 rises. In this case, the increase in the electric power (steady-state power consumption of the AP) supplied from the fuel cell stack 12 to the air pump 112 cannot catch up with the rise in the actual power consumption of the AP, and the actual power consumption of the AP is greater than the steady-state power consumption of the AP. In this specification, the difference between the actual power consumption of the AP and the steady-state power consumption of the AP (= actual power consumption of the AP - steady-state power consumption of the AP) during the transitional operation of the air pump 112 is referred to as "ΔAP".

[0107] Figure 4When the air pump 112 decelerates from time point t3 to time point t4, the power generation amount (FC power generation power) of the fuel cell stack 12 decreases and the rotational speed of the air pump 112 decreases. In this case, the decrease in the power supplied from the fuel cell stack 12 to the air pump 112 (AP steady-state power consumption) cannot catch up with the decrease in the actual power consumption of the AP, and the actual power consumption of the AP is less than the AP steady-state power consumption.

[0108] When the air pump 112 decelerates, the power storage device 244 is charged with the power of the ΔAP part to make up for the excessive power generation of the FC power generation. The deceleration buffer 74 that can be charged is set in the charge-discharge limit range 68 in advance, so that the power storage device 244 can absorb the sharp power excess and power surplus generated along with the deceleration of the air pump 112.

[0109] [Flow of Fluids in the Fuel Cell System 10]

[0110] (1) Flow of Fluids in the Anode System 16

[0111] The ejector 94 injects the fuel gas supplied from the tank 14 downstream of the fuel gas supply path 84 under the pulse width modulation (PWM) control of the control device 26. The fuel gas ejected from the ejector 94 is supplied to the fuel gas supply port 22a of the fuel cell stack 12 via the fuel gas supply path 84. The fuel gas that has not reacted inside the fuel cell stack 12 is discharged as fuel exhaust from the fuel gas discharge port 22b of the fuel cell stack 12. The fuel exhaust includes hydrogen that has not reacted with oxygen and nitrogen in the oxidant gas that has permeated through the membrane (solid polymer electrolyte membrane) 36.

[0112] In the cathode electrode 40, water is generated by the reaction of oxygen and hydrogen, and a part of the generated water moves to the anode electrode 38 side through the membrane (solid polymer electrolyte membrane) 36. The fuel exhaust includes, in addition to hydrogen and nitrogen, the water that has moved to the anode electrode 38 side through the membrane (solid polymer electrolyte membrane) 36.

[0113] The fuel exhaust is supplied to the gas-liquid separator 98 via the fuel gas discharge path 86. The gas-liquid separator 98 separates the fuel exhaust into a gas component (fuel exhaust) and a liquid component (liquid water). The fuel exhaust discharged from the gas-liquid separator 98 is supplied to the ejector 96 via the circulation path 88. In the ejector 96, the fuel exhaust sucked from the gas-liquid separator 98 merges with the fuel gas ejected from the ejector 94.

[0114] (2) Flow of Fluids in the Cathode System 18

[0115] The air pump 112 compresses the oxidant gas (air) inhaled from the outside of the fuel cell vehicle 11 and ejects it to the downstream of the oxidant gas supply passage 106. The oxidant gas ejected from the air pump 112 is supplied to the oxidant gas supply port 22c of the fuel cell stack 12 via the oxidant gas supply passage 106 provided with a cooler (not shown). The oxidant gas that has not reacted inside the fuel cell stack 12 is discharged as oxidant exhaust from the oxidant gas discharge port 22d of the fuel cell stack 12. The oxidant exhaust includes each component contained in the oxidant gas and moisture generated by the reaction of oxygen and hydrogen.

[0116] The oxidant exhaust is discharged to the outside of the fuel cell vehicle 11 via the oxidant gas discharge passage 108. The oxidant exhaust includes moisture. A part of the moisture contained in the oxidant exhaust is used to humidify the oxidant gas flowing through the humidifier supply passage 114A in the humidifier 114.

[0117] Alternatively, in the cathode system 18, the inlet seal valve 116 may be in a fully closed state and the bypass valve 120 may be in a fully open state. In this case, the oxidant gas ejected from the air pump 112 does not flow into the oxidant gas supply passage 106B but flows into the bypass flow path 110. The oxidant gas flowing into the bypass flow path 110 is discharged to the outside of the fuel cell vehicle 11 via the oxidant gas discharge passage 108.

[0118] (3) Flow of the fluid in the cooling system 20

[0119] The water pump 126 ejects the cooling medium toward the cooling medium supply port 22e of the fuel cell stack 12. The cooling medium ejected from the water pump 126 is supplied to the cooling medium supply port 22e of the fuel cell stack 12 via the cooling medium supply passage 122. The cooling medium that has flowed through the inside of the fuel cell stack 12 is discharged from the cooling medium discharge port 22f of the fuel cell stack 12. The cooling medium discharged from the cooling medium discharge port 22f is supplied to the radiator 128 via the cooling medium discharge passage 124. The cooling medium that has released heat in the radiator 128 is sucked into the water pump 126.

[0120] [Current limit value of the fuel cell stack 12]

[0121] For the fuel cell system 10 according to this embodiment, in order to control the power generation current Ifc of the fuel cell stack 12, an upper limit value is set for the power generation current Ifc. This upper limit value is referred to as the current limit value of the fuel cell stack 12, or simply the FC current limit value.

[0122] Normally, the maximum output of the fuel cell stack 12, i.e., the rated current, is set for the FC current limit value. However, when the deceleration buffer 74 is insufficient and the deceleration rate of the air pump 112 (the time change rate of the rotational speed during deceleration) cannot meet the established conditions, sometimes a small current during idling power generation is set for the FC current limit value. In this specification, the established conditions that the deceleration rate of the air pump 112 should meet are referred to as the water content control conditions of the fuel cell stack 12.

[0123] [Water Content Control Conditions of Fuel Cell Stack 12]

[0124] Use Figure 5 of (a) to (d) to illustrate the water content control conditions of the fuel cell stack 12.

[0125] Figure 5 of (a) shows the change in the rotational speed (AP rotational speed) [rpm] of the air pump 112 over time during deceleration of the air pump 112, i.e., the deceleration rate [rpm / sec] of the air pump 112. Figure 5 of (b) shows the change in the opening degree [%] of the bypass valve 120 over time, Figure 5 of (c) shows the change in the flow rate of the oxidant gas (stack air flow rate) [g / sec] flowing through the fuel cell stack 12 over time. Figure 5 of (d) shows the change in the dryness (stack dryness) inside the fuel cell stack 12 over time.

[0126] At Figure 5 of (a) to (d), the time point t30 is the initial state. In the initial state, the fuel cell stack 12 outputs a predetermined rated current, and the air pump 112 rotates at a rotational speed corresponding to the rated current of the fuel cell stack 12. In each figure, the time from the time point t30 to the time point t32 is referred to as the excess air allowable time.

[0127] The excess air allowable time refers to the time during which excess oxidant gas is allowed to flow through the fuel cell stack 12 when the rotational speed of the air pump 112 is reduced to a rotational speed corresponding to the current during idling power generation.

[0128] The current during idling power generation is, for example, a small current that can drive the air pump 112 at the minimum rotational speed at which the rotor shaft 274 of the air pump 112 can float. Alternatively, the current during idling power generation can be a small current such that the power generated by the fuel cell stack 12 is approximately equal to the power consumed by the air pump 112.

[0129] The excess air allowable time is set within a range of, for example, several seconds according to the specifications of the fuel cell system 10 including the fuel cell stack 12, etc.

[0130] When the rotational speed of the air pump 112 is reduced within the excess air allowable time to a rotational speed corresponding to the current during idling power generation, drying inside the fuel cell stack 12 can be avoided. In this case, the deceleration rate satisfies the water content control condition. On the other hand, when the rotational speed of the air pump 112 is not reduced within the excess air allowable time to a rotational speed corresponding to the current during idling power generation, the inside of the fuel cell stack 12 dries out. In this case, the deceleration rate does not satisfy the water content control condition.

[0131] In Figure 5 the solid line curve in (a) is an example of a deceleration rate that satisfies the water content control condition. The rotational speed of the air pump 112 gradually decreases from time point t30 and reaches a rotational speed corresponding to the current during idling power generation at time point t31.

[0132] Figure 5 The solid line curve in (b) shows that the bypass valve 120 starts to be driven from time point t30 toward the fully open state (opening degree 100%). The bypass valve 120 reaches the fully open state before reaching time point t31.

[0133] Figure 5 The solid line curve in (c) shows that an oxidant gas with a flow rate corresponding to the rated current is flowing inside the fuel cell stack 12 at time point t30. The oxidant gas flowing inside the fuel cell stack 12 gradually decreases and reaches a flow rate corresponding to the current during idling power generation at time point t31. The flow rate of the oxidant gas flowing inside the fuel cell stack 12 also remains at a flow rate corresponding to the current during idling power generation after time point t31.

[0134] Figure 5 The solid line curve in (d) shows that the dryness inside the fuel cell stack 12 is low at time point t30. When the air pump 112 starts to decelerate, the power generation of the fuel cell stack 12 decreases, and the amount of moisture generated inside the fuel cell stack 12 decreases. On the other hand, the oxidant gas also flows inside the fuel cell stack 12 after time point t30. The dryness inside the fuel cell stack 12 gradually rises. However, the dryness inside the fuel cell stack 12 also remains at a value lower than the dryness threshold after time point t31.

[0135] On the other hand, Figure 5 the dashed line curves in (a), (c), and (d) show an example of a case where the water content control condition is not satisfied.

[0136] As Figure 5 shown in (a), the deceleration rate in the case where the water content control condition is not satisfied is smaller than the deceleration rate in the case where the water content control condition is satisfied. Therefore, at time point t32, the rotational speed of the air pump 112 exceeds the rotational speed corresponding to the current during idling power generation. In Figure 5At the time point t32 in (c), the flow rate of the oxidant gas flowing in the fuel cell stack 12 exceeds the flow rate corresponding to the current during idling power generation. As a result, as shown in Figure 5 (d) at the time point t32, the stack dryness exceeds the dryness threshold. That is, when the deceleration rate does not satisfy the water content control condition, the fuel cell stack 12 will be dried.

[0137] In this way, the fuel cell system 10 can be controlled using the water content control condition including the relationship between the rotation speed of the air pump 112 corresponding to the FC current limit value (usually the rated current), the rotation speed of the air pump 112 corresponding to the current during idling power generation, and the excess air allowable time, so as to avoid drying inside the fuel cell stack 12 when the air pump 112 decelerates.

[0138] Moreover, the following points should be noted: The fuel cell system 10 is provided with a bypass valve 120. The rotation speed of the air pump 112 corresponding to the current during idling power generation can be changed according to the opening degree of the bypass valve 120. If the opening degree of the bypass valve 120 is increased, the flow rate of the oxidant gas toward the fuel cell stack 12 will decrease. Therefore, the rotation speed of the air pump 112 corresponding to the current during idling power generation can also be a large value. In this case, there is the following advantage: The remaining power ΔAP generated in the air pump 112 when the air pump 112 decelerates is reduced, and it is sufficient to set a small buffer width for the deceleration buffer 74.

[0139] [Setting of Current Limit Value]

[0140] The fuel cell system 10 according to the present embodiment is basically configured as described above. Then, with reference to Figure 6 the flowchart of to illustrate the process of the control device 26 setting the current limit value (FC current limit value) of the fuel cell stack 12.

[0141] In step S21, the control device 26 obtains the temperature Tbat of the power storage device (battery) 244 from the temperature sensor 250.

[0142] In step S22, the control device 26 compares the temperature Tbat with the threshold temperature Tthr1. The threshold temperature Tthr1 is the threshold between extremely low temperature (for example, less than 0 °C) and low temperature (for example, above 0 °C and less than 5 °C), and is set to 0 °C, for example.

[0143] When the temperature Tbat is less than the threshold temperature Tthr1 (step S22: Yes), the control device 26 determines that there is not enough power width in the charge and discharge limit range 68 of the power storage device 244. The control device 26 does not set the buffer 70 (acceleration buffer 72, deceleration buffer 74) and proceeds to step S23.

[0144] In step S23, the control device 26 sets the current (idle current) during idle power generation for the FC current limit value. The control device 26 waits for a predetermined time to warm up the power storage device 244.

[0145] Return to step S21, and the control device 26 obtains the temperature Tbat of the power storage device (battery) 244 from the temperature sensor 250 again.

[0146] In step S22, the control device 26 compares the temperature Tbat with the threshold temperature Tthr1. When the temperature Tbat is equal to or higher than the threshold temperature Tthr1 (step S22: No), the charge and discharge limit range 68 of the power storage device 244 expands slightly compared to the case of extremely low temperature. The control device 26 determines that it is possible to set the buffer 70 (deceleration buffer 74, acceleration buffer 72) within the charge and discharge limit range 68 of the power storage device 244, and proceeds to step S24.

[0147] In step S24, the control device 26 compares the temperature Tbat with the threshold temperature Tthr2. The threshold temperature Tthr2 is the threshold between low temperature (e.g., above 0°C and less than 5°C) and normal temperature (e.g., above 5°C), and is, for example, 5°C.

[0148] When the temperature Tbat is less than the threshold temperature Tthr2 (step S24: Yes), the control device 26 determines that it is possible to set the minimum buffer 70 (deceleration buffer 74, acceleration buffer 72) within the charge and discharge limit range 68 of the power storage device 244, and proceeds to step S25.

[0149] In step S25, the control device 26 sets the minimum buffer width (minimum necessary value) for the deceleration buffer 74. The minimum buffer width of the deceleration buffer 74 can also be, for example, the minimum amount of electric power required to absorb deviations such as the measurement error of the flow sensor 107 and the power error of the inverter 252.

[0150] In step S25, when the control device 26 sets the deceleration buffer 74, it also sets the acceleration buffer 72. For the acceleration buffer 72, for example, the minimum buffer width (minimum necessary value) is set. The minimum buffer width of the acceleration buffer 72 can also be, for example, the amount of electric power required to rotate the air pump 112 at the minimum rotational speed (the minimum value of the rotational speed at which the rotor shaft 274 of the air pump 112 can float).

[0151] Then, in step S26, the control device 26 changes the FC current limit value to a value larger than the current (idle current) during idle power generation according to the temperature Tbat. The current value intermediate between the current during idle power generation and the rated current is set for the FC current limit value. Hereinafter, this current value intermediate between the current during idle power generation and the rated current is referred to as the intermediate current value.

[0152] When the FC current limit value is increased from the current during idling power generation to an intermediate current value, the fuel cell stack 12 can generate a current larger than the current during idling power generation. For example, if the power generated by the fuel cell stack 12 is supplied to the battery heater 251, the battery heater 251 can warm the power storage device 244. The control device 26 waits for a predetermined time to warm the power storage device 244.

[0153] When the temperature Tbat is equal to or higher than the threshold temperature Tthr2 (step S24: No), the control device 26 determines that a large buffer 70 (deceleration buffer 74, acceleration buffer 72) can be set within the charge / discharge limit range 68 of the power storage device 244, and proceeds to step S27.

[0154] In step S27, the control device 26 sets the maximum buffer width (maximum necessary value) for the deceleration buffer 74. Alternatively, the maximum buffer width of the deceleration buffer 74 can be calculated based on the deceleration rate when reducing the output of the fuel cell stack 12 from the rated current to the current during idling power generation within the excess air allowable time.

[0155] When setting the deceleration buffer 74, the control device 26 alternates the buffer width of the acceleration buffer 72 according to the temperature Tbat. Alternatively, the buffer width of the acceleration buffer 72 can be set based on the amount of power required when the air pump 112 rotates at the maximum acceleration rate.

[0156] Then, in step S28, the control device 26 alternates the FC current limit value from the intermediate current value to the rated current. Thereby, the fuel cell stack 12 can generate power at the rated current, and in addition to being able to supply power to low-voltage loads such as the battery heater 251, it can also supply power to high-voltage loads such as the motor 246.

[0157] [Explanation of the operation of the timing diagram]

[0158] Omit the repetition of the operation explanation, and refer to Figure 7 of the timing diagram to explain an example of the operation described in the Figure 6 flowchart.

[0159] Figure 7 is a timing diagram showing an example of the transition of the actual power consumption and steady-state power consumption of the AP of the air pump 112 at low temperature and normal temperature.

[0160] At time point t40, it is determined that the temperature Tbat of the power storage device 244 is low (step S24: Yes). The minimum buffer width is set for the deceleration buffer 74, and also the minimum buffer width is set for the acceleration buffer 72 (step S25). The intermediate current value is set for the FC current limit value (step S26). At this time, the upper limit (FC power limit value) of the FC power is limited to the FC power upper limit value based on the intermediate current value.

[0161] In addition, at time point t40, the control device 26 receives the target power generation power (FC power command) of the fuel cell stack 12. When the control device 26 instructs the target rotation speed to the air pump 112, the air pump 112 starts to accelerate, and the AP actual power consumption and the AP steady-state power consumption start to rise.

[0162] From time point t40 to time point t41, the AP steady-state power consumption is allocated to the deceleration buffer 74, and the deceleration buffer 74 rises slightly. After time point t41, the upper limit of the deceleration buffer 74 is maintained at the minimum buffer width set in step S25.

[0163] At time point t42, the acceleration of the air pump 112 ends, and the air pump 112 is in a steady state. At this time, the AP actual power consumption and the AP steady-state power consumption are substantially the same. The fuel cell stack 12 can supply power to low-voltage loads such as the battery heater 251, for example.

[0164] At time point t43, the air pump 112 starts to decelerate. The minimum value is set for the deceleration buffer 74. Here, the control device 26 decelerates the air pump 112 at a deceleration rate such that no surplus power (the difference between the AP actual power consumption and the AP steady-state power consumption) ΔAP is generated in the air pump 112. At time point t44, the deceleration of the air pump 112 ends.

[0165] At time point t45, it is determined that the temperature Tbat of the power storage device 244 is normal temperature (step S24: No). The maximum buffer width is set for the deceleration buffer 74 (step S27), and also an appropriate buffer width is set for the acceleration buffer 72. The control device 26 replaces the FC current limit value from the intermediate current value with the rated current (step S28). At this time, the upper limit value (FC power limit value) of the FC power generation power is opened to the upper limit value based on the FC rated current.

[0166] At time point t45, the control device 26 receives the target power generation power (FC power command) of the fuel cell stack 12. When the control device 26 instructs the target rotation speed to the air pump 112, the air pump 112 starts to accelerate, and the AP actual power consumption and the AP steady-state power consumption start to rise.

[0167] During the period from time point t45 to time point t46, the AP steady-state power consumption is allocated to the deceleration buffer 74, and the upper limit of the deceleration buffer 74 is maintained at the maximum buffer width set in step S27.

[0168] At time point t47, the air pump 112 starts to decelerate. Since the maximum necessary value is set for the deceleration buffer 74 (step S27), the power storage device 244 can be charged with the surplus power ΔAP generated between the actual AP power consumption and the AP steady-state power consumption. At time point t48, the deceleration of the air pump 112 ends.

[0169] [Comparative Example]

[0170] Figure 8 It is an explanatory diagram showing an example of the FC current limit value corresponding to the temperature Tbat of the power storage device 244.

[0171] Figure 8 The dashed line in shows the comparative example. In the comparative example, at extremely low temperatures and low temperatures, the FC current limit value is fixed at the current during idling power generation. When the temperature Tbat of the power storage device 244 reaches the threshold between low temperature and normal temperature (threshold temperature Tthr2), the FC current limit value is first increased to the rated current.

[0172] In this comparative example, the rotational speed of the air pump 112 corresponding to the current during idling power generation is small, so the deceleration rate that satisfies the water content control condition increases. A large surplus power ΔAP may be generated when the air pump 112 decelerates. Therefore, the deceleration buffer 74 needs to ensure a large buffer width corresponding to the deceleration rate. Thus, in this comparative example, the FC current limit value is fixed at the current during idling power generation without increasing the FC current limit value to the rated current until the buffer width required for the deceleration buffer 74 can be ensured.

[0173] Figure 8 The solid line in shows an example of the FC current limit value in the fuel cell system 10. In this fuel cell system 10, when the temperature Tbat of the power storage device 244 is extremely low, the current during idling power generation is set for the FC current limit value (step S23). When the temperature Tbat of the power storage device 244 reaches the threshold between extremely low temperature and low temperature (threshold temperature Tthr1), the FC current limit value is replaced with an intermediate current value (step S26). When the temperature Tbat of the power storage device 244 reaches the threshold between low temperature and normal temperature (threshold temperature Tthr2), the FC current limit value is increased to the rated current (step S28).

[0174] In this way, even when the fuel cell system 10 cannot ensure sufficient deceleration buffering 74 for the power storage device 244 at low temperatures, the FC current limit value is changed from the current during idling power generation to an intermediate current value to cause the fuel cell stack 12 to generate power. For example, power can be supplied to a low-voltage load such as the battery heater 251, and the battery heater 251 can be used to heat the power storage device 244. As a result, a moving body such as a fuel cell vehicle 11 equipped with the fuel cell stack 12 can be quickly transferred to a drivable state (operable state).

[0175] Regarding the above disclosure, the following First Addendum to Fourth Addendum are also disclosed.

[0176] (First Addendum)

[0177] The fuel cell system 10 includes: a fuel cell (fuel cell stack) 12 that generates power using a fuel gas and an oxidant gas; a pump 112 that supplies the oxidant gas to the fuel cell; a power storage device 244 that can supply power to the pump; a control device 26 that controls the power generation of the fuel cell and the charge and discharge of the power storage device; and a temperature measurement device 250 that measures the temperature Tbat of the power storage device. The control device sets a power amount range 68 in which the power storage device can be charged and discharged, and sets a buffer 70 within the power amount range of the power storage device. The buffer includes a deceleration buffer 74, and the deceleration buffer is a power amount that can charge the surplus power ΔAP generated when the pump decelerates into the power storage device. In the fuel cell system, the control device changes the buffer width of the deceleration buffer according to the temperature of the power storage device, replaces the current limit value (FC current limit value) of the fuel cell based on the buffer width of the deceleration buffer, and causes the fuel cell to generate power according to the replaced current limit value (intermediate current value).

[0178] According to such a structure, for example, even when sufficient deceleration buffering 74 cannot be ensured at low temperatures, the FC current limit value of the fuel cell stack 12 is replaced with an intermediate current value to cause the fuel cell to generate power.

[0179] As a result, for example, power is supplied to a low-voltage load such as the battery heater 251, and the battery heater 251 can be used to heat the power storage device 244. The charge and discharge limit range 68 in which the power storage device can be charged and discharged is expanded due to the heating of the power storage device 244, and the power amount range in which the power storage device 244 can be charged and discharged is optimized. As a result, a moving body such as a fuel cell vehicle 11 equipped with the fuel cell stack 12 can be quickly transferred to a drivable state (operable state). In addition, when the outside air temperature is low, the occupants of the fuel cell vehicle 11 can use the air conditioner. The occupants can also use power inside the fuel cell vehicle 11.

[0180] (Second Supplementary Note)

[0181] In the fuel cell system described in the first supplementary note, it is also possible that the control device replaces the current limit value of the fuel cell based on the buffer width of the deceleration buffer and the time change rate of the rotational speed of the pump, and causes the fuel cell to generate power according to the replaced current limit value.

[0182] According to such a structure, in addition to the buffer width of the deceleration buffer 74, the time change rate (deceleration rate) of the rotational speed of the air pump 112 is also added to replace the FC current limit value. Thereby, for example, power can be supplied to low-voltage loads such as the battery heater 251 as soon as possible.

[0183] (Third Supplementary Note)

[0184] In the fuel cell system described in the first supplementary note or the second supplementary note, it is also possible that it further includes: an oxidant gas supply path 106 that supplies the oxidant gas to the fuel cell; an inlet seal valve 116 that is provided between the pump and the fuel cell in the oxidant gas supply path; a discharge path 109 that discharges the oxidant gas discharged from the fuel cell to the outside; a bypass flow path 110 that allows the oxidant gas supplied to the oxidant gas supply path to flow from the upstream side of the inlet seal valve to the discharge path; and a bypass valve 120 that is provided between the oxidant gas supply path and the discharge path in the bypass flow path, and the control device replaces the current limit value of the fuel cell based on the buffer width of the deceleration buffer and the opening degree of the bypass valve, and causes the fuel cell to generate power according to the replaced current limit value.

[0185] According to such a structure, in addition to the buffer width of the deceleration buffer 74, the opening degree of the bypass valve 120 is also added to replace the FC current limit value. Thereby, for example, power can be supplied to low-voltage loads such as the battery heater 251 as soon as possible.

[0186] (Fourth Supplementary Note)

[0187] A control method for a fuel cell system, the fuel cell system 10 comprising: a fuel cell 12 that generates electricity using a fuel gas and an oxidant gas; a pump 112 that supplies the oxidant gas to the fuel cell; a power storage device 244 that can supply power to the pump; a control device 26 that controls the power generation of the fuel cell and the charge and discharge of the power storage device; and a temperature measurement device 250 that measures the temperature Tbat of the power storage device. The control device sets a power range 68 in which the power storage device can be charged and discharged, and sets a buffer 70 within the power range of the power storage device. The buffer includes a deceleration buffer 74, and the deceleration buffer is a power amount that can charge the surplus power ΔAP generated when the pump decelerates into the power storage device. In the control method of the fuel cell system, it includes: a step of changing the buffer width of the deceleration buffer according to the temperature of the power storage device (steps S25, S27); a step of replacing the current limit value of the fuel cell based on the buffer width of the deceleration buffer (steps S23, S26, S28); and a step of generating electricity from the fuel cell according to the replaced current limit value.

[0188] According to such a structure, for example, even when it is impossible to ensure a sufficient deceleration buffer 74 at low temperatures, the FC current limit value of the fuel cell stack 12 is replaced with an intermediate current value to generate electricity from the fuel cell.

[0189] Thereby, for example, power is supplied to a low-voltage load such as a battery heater 251, and the battery heater 251 can be used to warm the power storage device 244. Due to the warming of the power storage device 244, the power range in which the power storage device can be charged and discharged (charge and discharge limit range 68) is expanded, and the power range in which the power storage device 244 can be charged and discharged is optimized. Thereby, a moving body such as a fuel cell vehicle 11 equipped with a fuel cell stack 12 can be quickly transferred to a drivable state (operable state). Also, in the case of low external air temperature, the occupants of the fuel cell vehicle 11 can use the air conditioner. The occupants can also use electricity inside the fuel cell vehicle 11.

[0190] Moreover, the present invention is not limited to the above disclosure, and various structures can be adopted without departing from the gist of the present invention.

[0191] For example, the opening degree of the bypass valve 120 is not limited to Figure 5 the example shown in (b) of. The opening degree of the bypass valve 120 may not be in a fully open state (opening degree 100%). The opening degree of the bypass valve 120 can be appropriately changed. It may also be that, in addition to controlling the bypass valve 120, the inlet seal valve 116 and the outlet seal valve 118 are also controlled to adjust the flow rate of the oxidant gas flowing in the fuel cell stack 12.

[0192] For example,Figure 8 The intermediate current value shown is an example, and multiple intermediate current values can also be set between the rated current and the current during idling power generation. It can also be that, according to the temperature Tbat of the power storage device 244, the intermediate current value is set in a manner of monotonically increasing in a stepped, stepped or curved manner as shown in Figure 8 the curve graph.

Claims

1. A fuel cell system, comprising: A fuel cell that generates electricity using fuel gas and oxidant gas; A pump that supplies the oxidant gas to the fuel cell; A power storage device that can supply power to the pump; A control device that controls the power generation of the fuel cell and the charge and discharge of the power storage device; and A temperature measurement device that measures the temperature of the power storage device, The control device sets a power amount range in which the power storage device can be charged and discharged, and sets a buffer within the power amount range of the power storage device, The buffer includes a deceleration buffer, and the deceleration buffer is a power amount that can charge the surplus power generated when the pump decelerates into the power storage device, In the fuel cell system, The control device changes the buffer width of the deceleration buffer according to the temperature of the power storage device, Based on the buffer width of the deceleration buffer, the current limit value of the fuel cell is replaced, and the fuel cell generates electricity according to the replaced current limit value.

2. The fuel cell system according to claim 1, wherein The control device replaces the current limit value of the fuel cell based on the buffer width of the deceleration buffer and the time change rate of the rotation speed of the pump, The fuel cell generates electricity according to the replaced current limit value.

3. The fuel cell system according to claim 1 or 2, characterized in that, It further comprises: An oxidant gas supply path that supplies the oxidant gas to the fuel cell; A shut-off valve that is provided between the pump and the fuel cell in the oxidant gas supply path; A discharge path that discharges the oxidant gas discharged from the fuel cell to the outside; A bypass flow path that allows the oxidant gas supplied to the oxidant gas supply path to flow from the upstream side of the shut-off valve to the discharge path; And A bypass valve that is provided between the oxidant gas supply path and the discharge path in the bypass flow path, The control device replaces the current limit value of the fuel cell based on the buffer width of the deceleration buffer and the opening degree of the bypass valve, The fuel cell generates electricity according to the replaced current limit value.

4. A control method for a fuel cell system, the fuel cell system comprising: A fuel cell that generates electricity using fuel gas and oxidant gas; A pump that supplies the oxidant gas to the fuel cell; A power storage device that can supply power to the pump; A control device that controls the power generation of the fuel cell and the charge and discharge of the power storage device; And A temperature measurement device that measures the temperature of the power storage device, The control device sets a power amount range in which the power storage device can be charged and discharged, and sets a buffer within the power amount range of the power storage device, The buffer includes a deceleration buffer, and the deceleration buffer is a power amount that can charge the surplus power generated when the pump decelerates into the power storage device, In the control method for the fuel cell system, it includes: The step of changing the buffer width of the deceleration buffer according to the temperature of the power storage device; The step of replacing the current limit value of the fuel cell based on the buffer width of the deceleration buffer; and The step of generating electricity of the fuel cell according to the replaced current limit value.

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