Fuel cell system and control method when fuel cell system is stopped

Abstract

To suppress deterioration of a fuel cell when a fuel cell system is stopped.SOLUTION: When a control device 26 detects an operation stop signal for a fuel cell vehicle 11 (fuel cell system 10), it gradually reduces the power generation voltage Vfc of a fuel cell stack 12 at a first voltage reduction rate Vdr1 and charges the surplus generated power to a power storage device 244. Thereafter, it suddenly reduces the power generation voltage Vfc at a second voltage reduction rate Vdr2 that is higher than the first voltage reduction rate Vdr1, thereby suppressing deterioration of the fuel cell stack 12.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a fuel cell system and a control method for a fuel cell system when the system is stopped. [Background technology]

[0002] In recent years, research and development into fuel cells has been conducted to contribute to energy efficiency in order to ensure that more people have access to affordable, reliable, sustainable and advanced energy.

[0003] A power generation system equipped with a fuel cell stack is called a fuel cell system. A fuel cell stack has multiple power generation cells. Each power generation cell generates electricity through an electrochemical reaction between fuel gas (hydrogen-containing gas) and oxidant gas (oxygen-containing gas) supplied from an air compressor.

[0004] For example, Patent Document 1 discloses a fuel cell system in which the power generated by a fuel cell stack is supplied to an external load (an inverter-driven motor), an internal load (a circulation pump), and a smoothing capacitor via a diode, and to a lithium-ion capacitor (hereinafter referred to as "capacitor") via a relay (Fig. 1 of Patent Document 1). When the relay is closed, the power of the capacitor is also supplied to the external load and the internal load (paragraph

[0039] of Patent Document 1).

[0005] In the fuel cell system disclosed in Patent Document 1, when a shutdown request is input, the control unit stops power generation in the fuel cell stack and cuts off the relay (ibid., paragraph

[0049] ). Furthermore, when a shutdown request is input, the control unit reduces the stack voltage of the fuel cell stack before the voltage of the internal load in order to suppress deterioration of the fuel cell stack (ibid., paragraphs

[0050] -

[0052] ).

[0006] By such control, the fuel cell system disclosed in Patent Document 1 prevents current from flowing from the fuel cell stack to the external load when the system is stopped (ibid., paragraph

[0053] ). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 2023-55497 Summary of the Invention [Problem to be solved by the invention]

[0008] In a fuel cell system, the amount of surplus generated power that can be charged into a power storage device when operation is stopped is fixed. However, a challenge with fuel cell systems is that when operation is stopped, it is necessary to reduce the voltage of the fuel cell stack as quickly as possible to prevent deterioration of the fuel cell stack.

[0009] However, in the fuel cell system disclosed in Patent Document 1, the relay connecting the fuel cell stack to the capacitor is cut off when operation is stopped, so the above-mentioned problem cannot be solved.

[0010] The present invention aims to solve the above-mentioned problems. [Means for solving the problem]

[0011] The first invention is a fuel cell system comprising a fuel cell that generates electricity using fuel gas and oxidant gas supplied from an air compressor, and a control device that controls the fuel cell, wherein the control device comprises an acquisition unit that acquires an operation stop signal, and a control unit that, when the acquisition unit acquires the operation stop signal, reduces the generated voltage of the fuel cell at a first voltage reduction rate, and then reduces it at a second voltage reduction rate that is higher than the first voltage reduction rate.

[0012] The second invention is a control method for shutting down a fuel cell system comprising a fuel cell that generates electricity using fuel gas and oxidant gas supplied from an air compressor, and a control device that controls the fuel cell, wherein when the control device receives an operation shutdown signal, the control device reduces the generated voltage of the fuel cell at a first voltage reduction rate, and then reduces the generated voltage at a second voltage reduction rate that is higher than the first voltage reduction rate. [Effects of the Invention]

[0013] According to this invention, when the fuel cell system is stopped, the generated voltage is reduced at a first voltage reduction rate, thereby controlling charging so that the surplus generated power does not exceed the power that can be charged to the storage device, thereby suppressing deterioration of the storage device, and after charging control, the generated voltage is reduced at a second voltage reduction rate that is higher than the first voltage reduction rate, thereby suppressing deterioration of the fuel cell. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic diagram of a fuel cell vehicle equipped with a fuel cell system according to an embodiment. [Figure 2] FIG. 2 is a schematic diagram of a turbo air compressor equipped with an air bearing mechanism. [Figure 3] FIG. 3 is a circuit diagram of a boost converter in a fuel cell system. [Figure 4] FIG. 4 is a flowchart illustrating the processing operation when the fuel cell system stops operating. [Figure 5] FIG. 5 is a time chart illustrating an example of the operation of the embodiment described with reference to the flowchart of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0015] [Configuration of fuel cell system 10] FIG. 1 is a schematic diagram of a fuel cell vehicle 11 equipped with a fuel cell system 10 according to an embodiment. The fuel cell system 10 can be installed not only in vehicles but also in ships, aircraft, robots, etc. The fuel cell system 10 can also be used as a power source for facilities, homes, etc. In the fuel cell system 10, a fuel gas and an oxidant gas are used as reactant 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 a fuel cell stack 12 (fuel cell) and subjected to an electrochemical reaction. In this specification, the fuel gas discharged from the fuel cell stack 12 without being subjected to the electrochemical reaction is also referred to as fuel off-gas. In this specification, the oxidant gas discharged from the fuel cell stack 12 without being subjected to the electrochemical reaction is also referred to as oxidant off-gas.

[0016] 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. The fuel cell system 10 also includes a controller .

[0017] The fuel cell stack 12 has a positive electrode terminal 23a and a negative electrode terminal 23b. A voltage sensor 25 that detects the power generation voltage Vfc of the fuel cell stack 12 is attached between the power lines extending from the positive electrode terminal 23a and the negative electrode terminal 23b. Electricity generated by the fuel cell stack 12 is supplied to the load 21 and the power supply system 27 via the positive electrode terminal 23a and the negative electrode terminal 23b. The tank 14 is filled with high-pressure fuel gas.

[0018] The fuel cell stack 12 includes a fuel gas supply port 22a that supplies fuel gas to the inside of the fuel cell stack 12, and a fuel gas discharge port 22b that discharges fuel off-gas from the inside of the fuel cell stack 12. The fuel cell stack 12 also includes an oxidant gas supply port 22c that supplies oxidant gas to the inside of the fuel cell stack 12, an oxidant gas discharge port 22d that discharges oxidant off-gas from the inside of the fuel cell stack 12, and a drain port 22g that drains water produced in the fuel cell stack 12. The fuel cell stack 12 also includes a coolant supply port 22e that supplies a coolant to the inside of the fuel cell stack 12, and a coolant discharge port 22f that discharges the coolant from the inside of the fuel cell stack 12.

[0019] The anode system 16 includes a fuel gas supply channel 84, a fuel gas discharge channel 86, a circulation channel 88, and a drain channel 90. The anode system 16 also includes an injector 94, an ejector 96, a gas-liquid separator 98, and an on-off drain valve 100. The fuel gas supply channel 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 fuel gas supply channel 84 is provided with an injector 94 and an ejector 96. The inlet port of the ejector 96 is connected to the discharge port of the injector 94, and the discharge port of the ejector 96 is connected to the fuel gas supply port 22a. A pressure sensor 85 is attached to the fuel gas supply channel 84 near the fuel gas supply port 22a. The ejector 96 is disposed between the injector 94 and the fuel gas supply port 22a. The fuel gas discharge path 86 is connected to the fuel gas discharge port 22b of the fuel cell stack 12 and a supply port of the gas-liquid separator 98. The circulation path 88 is connected to the exhaust port of the gas-liquid separator 98 and the suction port of the ejector 96. The drain path 90 is connected to the drain port of the gas-liquid separator 98 and a discharge path 109. The discharge path 109 communicates with the atmosphere through a discharge port 109p provided in the fuel cell vehicle 11. A drain valve 100 is provided in the drain path 90.

[0020] The cathode system 18 includes an oxidant gas supply channel 106, an oxidant gas discharge channel 108 (discharge channel), a bypass flow path 110, and a drain channel 91. The cathode system 18 also includes an air cleaner 105, an air compressor 112 (oxidant gas supplier), a humidifier 114, an inlet seal valve 116 of an on / off valve, an outlet seal valve 118 of a valve position adjustment valve which is a back pressure valve, and a bypass valve 120 of the valve position adjustment valve. The oxidant gas supply channel 106 is connected to an air intake port 106p provided in the fuel cell vehicle 11 and an oxidant gas supply port 22c of the fuel cell stack 12. The oxidant gas supply channel 106 also includes the air cleaner 105, a flow rate sensor 107, the air compressor 112, the inlet seal valve 116, and a humidifier supply channel 114A of the humidifier 114. A portion of the oxidizing gas supply channel 106 that is arranged upstream of the humidifier 114 is referred to as the oxidizing gas supply channel 106A. A portion of the oxidizing gas supply channel 106 that is arranged downstream of the humidifier 114 is referred to as the oxidizing gas supply channel 106B. The inlet seal valve 116 is arranged closer to the humidifier 114 than the air compressor 112. A flow rate sensor 107 is attached to the oxidizing gas supply channel 106A upstream of the air compressor 112. The flow rate sensor 107 detects the flow rate of the oxidizing gas flowing through the air compressor 112.

[0021] FIG. 2 is a schematic diagram of a turbo air compressor 112 equipped with an air bearing mechanism. The air compressor 112 has a rotor shaft 274, to which an impeller 276 is fixed or rotates integrally. Multiple magnets are embedded axially on the cylindrical side surface of the rotor shaft 274. U-phase, V-phase, and W-phase stator coils 272 are attached to the casing of the air compressor 112. An air bearing 292, through which the rotor shaft 274 is inserted, is attached to the casing of the air compressor 112. An oxidizer gas flow path is attached to the casing of the air compressor 112, and a supercharger 294 including the impeller 276 is provided. When the impeller 276 rotates in accordance with the rotation of the rotor shaft 274, the air bearing 292 levitates the rotor shaft 274 using compressed air at a predetermined rotation speed or higher. Air is drawn in through an intake port 300 of the air compressor 112, which communicates with the oxidizing gas supply channel 106A, and is supercharged (compressed and compressed) by the supercharger 294. The compressed and compressed air, i.e., the oxidizing gas, is discharged from a discharge port 302 into the oxidizing gas supply channel 106A.

[0022] Air is drawn in through an intake port 300 of the air compressor 112, which is in communication with the oxidizing gas supply channel 106A, and is supercharged (compressed and compressed) by the supercharger 294. The air compressed and compressed by the supercharger 294, i.e., the oxidizing gas, is discharged from a discharge port 302 into the oxidizing gas supply channel 106A.

[0023] 3 is a circuit diagram of a switching-type boost converter 240 that boosts a generated voltage Vfc as an input voltage to a high power supply voltage Vh of a power storage device 244. The boost converter 240 includes an inductor 262, a power MOSFET 264, a diode 266 (a commutation diode), a smoothing capacitor 268, and a discharging resistor 270.

[0024] One end of an inductor 262 is connected to the positive terminal 23a of the fuel cell stack 12. The other end of the inductor 262 is connected to the drain terminal of a MOSFET 264 and the anode terminal of a diode 266. The cathode terminal of the diode 266 is connected to the high-voltage terminals of the inverters 242 and 252, the power storage device 244, and the step-down converter 247. The low-voltage terminals of the inverters 242 and 252, the power storage device 244, and the step-down converter 247 are connected to the negative terminal 23b of the fuel cell stack 12. A capacitor 268 and a resistor 270 are connected in parallel between the cathode terminal of the diode 266 and the negative terminal 23b of the fuel cell stack 12. The source terminal of the MOSFET 264 is connected to the negative terminal 23b of the fuel cell stack 12.

[0025] Returning to FIG. 1 , the oxidant gas discharge channel 108 is connected to the oxidant gas discharge port 22d of the fuel cell stack 12 and a discharge channel 109. The oxidant gas discharge channel 108 is provided with a humidifier discharge channel 114B of the humidifier 114 and an outlet seal valve 118. A portion of the oxidant gas discharge channel 108 that is arranged upstream of the humidifier 114 is referred to as the oxidant gas discharge channel 108A. A portion of the oxidant gas discharge channel 108 that is arranged downstream of the humidifier 114 is referred to as the oxidant gas discharge channel 108B. A pressure sensor 111 is attached to the oxidant gas discharge channel 108B. The bypass channel 110 is connected to the oxidant gas supply channel 106A between the air compressor 112 and the inlet seal valve 116 and to the oxidant gas discharge channel 108B downstream of the outlet seal valve 118. A bypass valve 120 is provided in the bypass channel 110. The drainage channel 91 is connected to the drainage port 22g and a discharge channel 109. The discharge channel 109 is provided with a drainage valve 101 which is an on / off valve.

[0026] The cooling system 20 includes a cooling medium supply path 122 and a cooling medium discharge path 124. The cooling system 20 also includes a pump 126 and a radiator 128. The cooling medium supply path 122 is connected to a cooling medium discharge port of the radiator 128 and a cooling medium supply port 22e of the fuel cell stack 12. The cooling medium supply path 122 is provided with the pump 126. The cooling medium discharge path 124 is connected to a cooling medium discharge port 22f of the fuel cell stack 12 and a fluid supply port of the radiator 128. A temperature sensor 130 is attached to the cooling medium discharge path 124. The temperature sensor 130 detects the temperature of the cooling medium circulating through the cooling medium discharge path 124. The temperature of the cooling medium circulating through the cooling medium discharge path 124 is estimated to be the internal temperature of the fuel cell stack 12 (stack temperature).

[0027] The fuel cell stack 12 is formed by stacking a plurality of power-generating cells 24. Each power-generating cell 24 includes a membrane electrode assembly 32 and separators 28, 30 that sandwich the membrane electrode assembly 32. The membrane electrode assembly 32 includes a membrane electrode assembly (MEA) 36, which is, for example, a thin film (solid polymer electrolyte membrane) of perfluorosulfonic acid containing moisture, and a cathode electrode 40 and an anode electrode 38 that sandwich the MEA 36. The cathode electrode 40 and the anode electrode 38 have gas diffusion layers (not shown) made of carbon paper or the like. An electrode catalyst layer (not shown) is formed on the surface of the gas diffusion layer by uniformly applying porous carbon particles having a platinum alloy supported on the surface. The electrode catalyst layers are formed on both sides of the MEA 36.

[0028] A cathode flow path (oxidant gas flow path) 50 that connects the oxidant gas supply port 22c and the oxidant gas discharge port 22d is formed on the surface of one separator 28 facing the membrane electrode assembly 32. The pressure of the oxidant gas flowing through the cathode flow path 50 is controlled by the control device 26 adjusting the opening of the outlet seal valve 118.

[0029] An anode flow path (fuel gas flow path) 66 that connects the fuel gas supply port 22a and the fuel gas discharge port 22b is formed on the surface of the other separator 30 facing the membrane electrode assembly 32. When fuel gas (hydrogen) is supplied to the anode electrode 38, a catalytic electrode reaction generates hydrogen ions from hydrogen molecules. The hydrogen ions permeate the MEA 36 and move to the cathode electrode 40, while electrons are released from the hydrogen molecules. The electrons released from the hydrogen molecules move from the separator 30 and the negative electrode terminal 23b through the load 21, via the positive electrode terminal 23a and the separator 28, to the cathode electrode 40. At the cathode electrode 40, the hydrogen ions and electrons react with oxygen contained in the supplied oxidant gas due to the action of the catalyst to produce water. The load 21 includes a motor 246 and an air compressor 112 as high voltage loads.

[0030] The power supply system 27 includes a power storage device 248, which is a low-voltage power supply that generates a low power supply voltage Vl, and a power storage device 244, which is a high-voltage power supply that generates a high power supply voltage Vh. A lead-acid battery is used as the power storage device 248 here. A lithium-ion secondary battery or the like may be used instead of the lead-acid battery. A lithium-ion secondary battery is used as the power storage device 244 here. A capacitor or the like may be used instead of the lithium-ion secondary battery.

[0031] The power storage devices 244, 248 are each equipped with a temperature sensor (not shown) for detecting the temperature of the power storage devices 244, 248 and an SOC sensor (not shown) for detecting the SOC, which is the remaining capacity of the power storage devices 244, 248.

[0032] The inverter 242 that drives the motor 246 is supplied with high-voltage electricity (power supply voltage Vh) from the fuel cell stack 12 via the boost converter 240. The inverter 242 that drives the motor 246 is also supplied with high-voltage electricity (power supply voltage Vh) from the power storage device 244. That is, the motor 246 is supplied with electricity from the fuel cell stack 12 and / or the power storage device 244. The inverter 242 converts the supplied high-voltage DC current into three-phase AC current to drive the motor 246.

[0033] The power storage device 244 is charged with the energy generated by the fuel cell stack 12 when a high DC voltage obtained by boosting the power generation voltage Vfc of the fuel cell stack 12 by the boost converter 240 is applied to the power storage device 244. When the fuel cell vehicle 11 is decelerating and the motor 246 is in regeneration mode, the motor 246 generates a three-phase AC current as a generator. This three-phase AC current is converted by the inverter 242 into high-voltage DC electrical energy, and charges the power storage device 244.

[0034] The control device 26 and various sensors as low-voltage loads, as well as an air conditioner, an electric power steering device, and lighting devices (not shown), are supplied with DC low-voltage electricity (power supply voltage Vl) from the power storage device 248. The power storage device 248 is charged with electrical energy obtained by stepping down the high voltage (power supply voltage Vh) of the power storage device 244 to the low voltage (power supply voltage Vl) by the step-down converter 247.

[0035] The air compressor 112 is supplied with a three-phase alternating current obtained by converting a high voltage from the power storage device 244 by an inverter 252 .

[0036] The control device 26 may be configured by an ECU (Electronic Control Unit). The control device 26 includes a calculation unit 136 and a storage unit 138. The calculation unit 136 is, for example, a processor such as a CPU (Central Processing Unit) or a GPU (Graphics Processing Unit). That is, the calculation unit 136 may be configured by processing circuitry. The calculation unit 136 controls each device by executing computer-executable instructions (programs) stored in the storage unit 138. At least a portion of the calculation unit 136 may be realized by an integrated circuit such as an ASIC (Application Specific Integrated Circuit) or an FPGA (Field-Programmable Gate Array). At least a portion of the calculation unit 136 may be realized by an electronic circuit including discrete devices.

[0037] The calculation unit 136 includes an acquisition unit 140, a control unit 142, a timer unit 144, and a determination unit 146. The acquisition unit 140 acquires information from electronic components other than the control device 26 (sensors, ECUs, etc.).

[0038] In addition to the voltage sensor 25, pressure sensors 85, 111, and temperature sensor 130 shown in the figure, the sensors include a current sensor that detects the generated current Ifc, a voltage sensor that detects the power supply voltage Vh, and a voltage sensor that detects the power supply voltage Vl, which are not shown.

[0039] The control unit 142 executes computer-executable commands (programs) based on various signals acquired from the sensors via the acquisition unit 140, and controls the operations of the injector 94, air compressor 112, pump 126, motor 246, boost converter 240, inverters 242 and 252, step-down converter 247, valves, etc. The timing unit 144 measures execution time, etc., using a timer (not shown). The determination unit 146 performs various determination processes.

[0040] The storage unit 138 is configured by a volatile memory (not shown) and a non-volatile memory (not shown), which are computer-readable storage media. The volatile memory is, for example, a random access memory (RAM). The non-volatile memory is, for example, a read-only memory (ROM), a flash memory, etc. Data, etc., are recorded in the volatile memory. Programs, tables, maps, etc., are recorded in the non-volatile memory. At least a part of the storage unit 138 may be provided in the above-mentioned processor, integrated circuit, etc.

[0041] The control device 26 is connected to a power switch 280 (operation switch) that allows the user to instruct the fuel cell automobile 11 (fuel cell system 10) to start operation (start power generation) and stop operation (stop operation or stop power generation).

[0042] [Fluid flow in fuel cell system 10] (1) Fluid flow in the anode system 16 The injector 94 is pulse-width modulated (PWM) controlled by the control device 26 so that the pressure in the anode flow path 66 of the fuel cell stack 12, detected by the pressure sensor 85, becomes a set pressure. The injector 94 injects fuel gas supplied from the tank 14 downstream of the fuel gas supply path 84 for a time period specified by an on-duty INJod (INJod = valve open time / control period) of the PWM control. The fuel gas injected from the injector 94 is supplied to the anode flow path 66 from the fuel gas supply port 22a of the fuel cell stack 12 via the fuel gas supply path 84. The fuel gas that does not react inside the fuel cell stack 12 is discharged as fuel off-gas from the fuel gas discharge port 22b of the fuel cell stack 12. The fuel off-gas contains hydrogen that did not react with oxygen, nitrogen in the oxidant gas that has permeated the MEA 36, and moisture produced by the reaction of oxygen and hydrogen.

[0043] The fuel off-gas is supplied to the gas-liquid separator 98 via the fuel gas discharge path 86. The gas-liquid separator 98 separates the fuel off-gas into a gas component (fuel off-gas) and a liquid component (water). The fuel off-gas discharged from the gas-liquid separator 98 is supplied to the suction port of the ejector 96 via the circulation path 88. The ejector 96 combines the fuel off-gas supplied from the suction port with the fuel gas supplied from the input port. The ejector 96 supplies the combined gas as fuel gas from the discharge port to the anode flow path 66 of the fuel cell stack 12 via the fuel gas supply path 84 and the fuel gas supply port 22a.

[0044] (2) Fluid flow in the cathode system 18 The air compressor 112 heats and compresses the oxidant gas (air) drawn in from outside the fuel cell vehicle 11, and discharges it downstream of the oxidant gas supply channel 106. The oxidant gas discharged from the air compressor 112 is supplied to the cathode flow path 50 from the oxidant gas supply port 22c of the fuel cell stack 12 via the oxidant gas supply channel 106, which is equipped with a cooler (not shown). The oxidant gas that has not reacted inside the fuel cell stack 12 is discharged as oxidant off-gas from the oxidant gas discharge port 22d of the fuel cell stack 12. The oxidant off-gas contains components contained in the oxidant gas, mainly nitrogen, and moisture produced by the reaction between oxygen and hydrogen.

[0045] The oxidant off-gas is discharged to the outside of the fuel cell vehicle 11 through the oxidant gas discharge channel 108. The oxidant off-gas contains moisture. In the humidifier 114, some of the moisture contained in the oxidant off-gas is used through a hollow fiber membrane in the humidifier 114 to humidify the oxidant gas flowing through the humidifier supply channel 114A.

[0046] (3) Fluid flow in the cooling system 20 The pump 126 discharges the cooling medium toward the cooling medium supply port 22e of the fuel cell stack 12. The cooling medium discharged from the pump 126 is supplied to the cooling medium supply port 22e of the fuel cell stack 12 via the cooling medium supply path 122. The cooling medium that has circulated inside 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 path 124. The cooling medium that has dissipated heat in the radiator 128 is drawn into the pump 126.

[0047] [Operation explanation using flowchart] The fuel cell system 10 is basically configured as described above. Next, the operation (operation shutdown process) of the fuel cell system 10 (fuel cell stack 12) when the operation is stopped will be described with reference to the flowchart of FIG.

[0048] In step S1, the determination unit 146 determines whether or not the acquisition unit 140 has detected an operation stop signal output from the power switch 280 and / or whether or not an operation stop request to stop the power generation operation has occurred. The operation stop signal is output from the power switch 280 when the power switch 280 is switched from an on state to an off state. Even when the power switch 280 is in an on state, a power generation stop request may occur depending on the situation.

[0049] When the power switch 280 is on and the fuel cell vehicle 11 is stopped (vehicle speed 0) and in power generation operation (fuel cell stack 12 is idling and generating power), the control unit 142 controls each component as follows.

[0050] The control unit 142 drives the air compressor 112 at a normal rotation speed. The control unit 142 sets the power generation voltage Vfc to a predetermined voltage command value (power generation voltage command value) Vfccom. The control unit 142 sets the on-duty INJod of the injector 94 to a normal on-duty so that the fuel gas pressure (anode pressure) Fh detected by the pressure sensor 85 and acquired by the acquisition unit 140 becomes a predetermined pressure. The control unit 142 closes the bypass valve 120, opens the inlet seal valve 116, opens the outlet seal valve 118 to a predetermined opening degree, closes the drain valve 100, and opens the drain valve (cathode drain valve) 101. The control unit 142 detects the opening degrees of the bypass valve 120 and the outlet seal valve 118 via the acquisition unit 140.

[0051] If the determination unit 146 determines that an operation stop request has not been issued (step S1: NO), the control unit 142 continues idling power generation by the fuel cell stack 12 at a vehicle speed of 0 (parked) of the fuel cell automobile 11 in step S1.

[0052] On the other hand, when the determining unit 146 determines that an operation stop request has been issued (step S1: YES), the control unit 142 shifts the processing by the control unit 142 to step S2.

[0053] In step S2, the control unit 142 performs initial settings for when the operation is stopped. At the stage of controlling the operation of the fuel cell system 10 to stop, the SOC (remaining capacity) of the power storage device 244 is generally high. Therefore, in this initial setting, the control unit 142 sets the voltage reduction rate Vdr [V / sec], which is the rate at which the voltage command value Vfccom of the fuel cell stack 12 decreases, to a first voltage reduction rate Vdr1 [V / sec] so that the power storage device 244 receives or is not supplied with power. The first voltage reduction rate Vdr1 is set to a gentle charging rate that the power storage device 244 can tolerate (does not deteriorate), taking into account the high residual oxygen concentration in the cathode flow path 50. This setting allows the power storage device 244 to be charged with the reduced power generated by the fuel cell stack 12. This control allows the power storage device 244 to be charged with surplus power generated by the fuel cell stack 12 during operation stoppage, without exceeding the power that can be charged to the power storage device 244.

[0054] Here, the boost ratio (Vh / Vfc) of the boost converter 240 that sets the voltage drop rate Vdr is given by the following equation (1).

[0055] (Vh / Vfc)={1 / (1-D)} …(1) On-duty D is the ratio of on-time ton of MOSFET 264 to the control period (constant PWM period) T of boost converter 240, and is calculated as D=(ton / T). Control unit 142 gradually increases on-time ton (approaching control period T) while maintaining first voltage drop rate Vdr1. Since power supply voltage Vh of power storage device 244 hardly changes, the power generation voltage Vfc can be reduced at the first voltage drop rate Vdr1 by increasing the boost ratio at the absolute value of first voltage drop rate Vdr1.

[0056] In step S2, the control unit 142 sets the rotation speed Nac [rpm] of the air compressor 112 to a predetermined rotation speed Nacpd that is slightly higher than the rotation speed at which the rotor shaft 274 can be lifted by the air bearings 292 and lower than the normal rotation speed during running. Meanwhile, in step S2, the control unit 142 reduces the on-duty INJod of the injector 94 and controls it to be close to the predetermined on-duty INJodpd so that the anode pressure Ph becomes a specified hydrogen partial pressure.

[0057] In step S3, the control unit 142 performs processing at the first voltage reduction rate Vdr1, and ends processing at the first voltage reduction rate Vdr1 when the residual oxygen concentration is equal to or lower than a predetermined value or the time has elapsed during which the residual oxygen concentration remains equal to or lower than the predetermined value.

[0058] In step S4, the determination unit 146 detects the power generation voltage Vfc of the fuel cell stack 12 via the voltage sensor 25 and the acquisition unit 140, and determines whether the detected power generation voltage Vfc has dropped to the threshold power generation voltage Vfcth. If the power generation voltage Vfc has not dropped to the threshold power generation voltage Vfcth (step 4: NO), the control unit 142 repeats the processes of steps S3 and S4. If the power generation voltage Vfc has dropped to the threshold power generation voltage Vfcth (step 4: YES), the process proceeds to step S5.

[0059] Here, the threshold power generation voltage Vfcth is a voltage obtained by adding a margin voltage to the lower limit voltage at which degradation of the fuel cell stack 12 does not occur. In the fuel cell stack 12, it is preferable that the time during which the power generation voltage Vfc stays in the degradation voltage range between this lower limit voltage and zero is as short as possible from the viewpoint of suppressing and preventing degradation.

[0060] In step S5, the control unit 142 performs the following control processes related to the process of preparing to discharge cathode-produced water: The inlet seal valve 116 is controlled to remain open. The outlet seal valve 118 is controlled to remain closed. The drain valve 101 is controlled to remain open. The rotation speed Nac of the air compressor 112 (rotor shaft 274) is controlled to remain at the predetermined rotation speed Nacpd set in step S2. The on-duty INJod [%] of the injector 94 is controlled to remain at the predetermined on-duty INJodpd [%] that maintains the hydrogen partial pressure set in step S2.

[0061] In step S6, the control unit 142 performs a forced drainage process of liquid water, including produced water, stored in the cathode flow path 50 for a predetermined time while timing with the timer 144. To achieve this, during the predetermined time, the control unit 142 slightly increases the rotation speed Nac of the air compressor 112 from the predetermined rotation speed Nacpd that was set when the air compressor 112 was being reduced at the first voltage reduction rate Vdr1. Furthermore, with the outlet seal valve 118 closed, the control unit 142 consumes the oxidant gas remaining in the cathode flow path 50 of the fuel cell stack 12. To consume the oxidant gas, the control unit 142 slightly increases the predetermined on-duty INJodpd [%] of the injector 94 for the predetermined time to maintain the hydrogen partial pressure. In this way, during the predetermined time period in which the rotation speed Nac [rpm] of the air compressor 112 is slightly increased from the predetermined rotation speed Nacpd, the cathode produced water stored in the cathode flow path 50 is discharged from the fuel cell stack 12 by the pressure of the oxidant gas supplied from the air compressor 112. That is, compressed air discharged from the air compressor 112 flows through the cathode flow path 50 via the oxidant gas supply path 106. The compressed air that has flowed through the cathode flow path 50 is discharged to the outside of the fuel cell vehicle 11 via the drain port 22g, the drain path 91, the drain valve 101, the discharge path 109, and the discharge port 109p, together with liquid water including the cathode produced water stored in the cathode flow path 50 of the fuel cell stack 12.

[0062] After the drainage process in step S6, the control unit 142 closes the drainage valve 101 and returns the rotation speed Nac of the air compressor 112 to the predetermined rotation speed Nacpd.

[0063] In step S7, the control unit 142 performs an end-of-operation setting for the shutdown. In the end-of-operation setting, the control unit 142 drives the inlet shutoff valve 116 to a closed state. At the same time, the control unit 142 changes (sets) the voltage reduction rate Vdr [V / sec], which is the rate at which the voltage command value Vfccom of the fuel cell stack 12 is reduced, to a second voltage reduction rate Vdr2 [V / sec] that is higher than the first voltage reduction rate Vdr1 [V / sec]. The second voltage reduction rate Vdr2 is a reduction rate at which the power generation voltage Vfc is reduced toward 0 [V] at a faster voltage reduction rate Vdr [V / sec] to avoid deterioration of the fuel cell stack 12 because the outlet shutoff valve 118 is already closed, the residual oxygen concentration in the cathode flow path 50 is low, and the electrochemical reaction is not progressing.

[0064] Here, the voltage reduction rate Vdr is a negative value, so it is set so that Vdr2 > Vdr1 and the relationship |Vdr1| < |Vdr2| is satisfied. With this setting, the control unit 142 continues the process of reducing the generated voltage Vfc at the second voltage reduction rate Vdr2 until the generated voltage Vfc falls below a predetermined voltage in step 8. The predetermined voltage may be continued until the determination process of the generated voltage Vfc being approximately 0 [V] is satisfied. Alternatively, the predetermined voltage may be the lower limit voltage that the boost converter 240 can control. After the voltage falls below the predetermined voltage, the voltage may be reduced. In the process of reducing the generated voltage Vfc at the second voltage reduction rate Vdr2, the control unit 142 increases the on-duty D in the above equation (1) to 100 [%] {D = 1: Vfc = Vh(1 - D)} in proportion to the absolute value of the second voltage reduction rate Vdr2, which is a high rate. That is, when the on-duty D is increased, the power supply voltage Vh does not change, and therefore the generated voltage Vfc decreases toward 0 [V].

[0065] In step S8, the determination unit 146 detects the power generation voltage Vfc of the fuel cell stack 12 via the acquisition unit 140, and if the detected power generation voltage Vfc has not dropped to a sufficiently low predetermined voltage, for example, 0 [V] (step S8: NO), the processes of steps S7 and S8 are repeated. In step S8, when the determination unit 146 detects that the power generation voltage Vfc has dropped to the predetermined voltage (step S8: YES), the control unit 142 ends the operation-stop processing.

[0066] [Operation explanation using time chart] An example of the operation (processing during shutdown) described with reference to the flowchart in Fig. 4 will be described with reference to the time chart in Fig. 5. In the time chart in Fig. 5, the waveform at the top shows an example of the time change state of the generated power Wfc of the fuel cell stack 12.

[0067] 5, the control unit 142 detects a request to stop operation based on the transition of the power switch 280 from the on state to the off state through the determination unit 146 (step S1: YES). Note that the time at which the power switch 280 turns off may be before time t0, in which case power generation continues until time t0 is reached, and a request to stop the fuel cell system 10 is detected at time t0.

[0068] At the detected time t0, the control unit 142 performs initial settings including a process of setting the first voltage reduction rate Vdr1 of the boost converter 240 (corresponding to step S2).

[0069] In the initial setting, the inlet seal valve 116 is set to an open (continuous) state, the outlet seal valve 118 is set to an opening degree of a number [%] corresponding to the idling power generation, the drain valve (cathode drain valve) 101 is set to an open (continuous) state, the rotation speed Nac of the air compressor 112 is set to a predetermined rotation speed Nacpd, and the on-duty INJod of the injector 94 is set to a predetermined on-duty INJodpd.

[0070] With this setting, between time t0 and time t1, the power storage device 244 is charged with the suppressed generated power of about several [kW] by the fuel cell stack 12. Since the generated voltage Vfc is gradually reduced at the first voltage reduction rate Vdr1, the surplus generated power of the fuel cell stack 12 when operation is stopped can be used to charge the power storage device 244 without deteriorating it (corresponding to step S3).

[0071] The control unit 142 reduces the power generation voltage Vfc from time t0 in accordance with the voltage command value Vfccom, which reduces the power generation voltage Vfc at a first voltage reduction rate Vdr1. When it detects at time t1 that the power generation voltage Vfc has decreased to the threshold power generation voltage Vfcth (step S4: YES), it maintains the power generation voltage Vfcth at the threshold power generation voltage Vfcth until time t5.

[0072] Between time t1 and time t3, the control unit 142 performs a learning process for the outlet sealing valve 118 by varying the opening degree of the outlet sealing valve 118 from several [%] to 100 [%] and then returning it to 0 [%] (corresponding to step S5).

[0073] Between time t3 and time t4, the control unit 142 increases the on-duty INJod [%] of the injector 94 slightly from the predetermined on-duty INJodpd and maintains it at that value. Using the generated power between time t3 and time t4, the rotation speed Nac [rpm] of the air compressor 112 is increased slightly from the predetermined rotation speed Nacpd that was set when the generated voltage Vfc was being reduced at the first voltage reduction rate Vdr1. Increasing the rotation speed Nac of the air compressor 112 increases the pressure of the oxidant gas discharged from the air compressor 112 and circulating in the cathode flow path 50. This oxidant gas pressure causes the cathode-produced water stored in the cathode flow path 50 to be discharged from the fuel cell stack 12 and to the outside via the drain valve 101 and the discharge path 109 (corresponding to step S6).

[0074] At time t4, after the drainage process, the control unit 142 closes the drainage valve 101 and returns the rotation speed Nac of the air compressor 112 to the predetermined rotation speed Nacpd. The on-duty INJod of the injector 94 is set to the predetermined on-duty INJodpd.

[0075] At time t5, the control unit 142 drives the inlet shutoff valve 116 from an open state to a closed state, and sets the voltage reduction rate Vdr, which reduces the generated voltage Vfc from the threshold generated voltage Vfcth to zero, to a second voltage reduction rate Vdr2 higher than the first voltage reduction rate Vdr1 (corresponding to step S7).

[0076] With this setting, between time t5 and time t6, the power generation voltage Vfc drops rapidly from the threshold power generation voltage Vfcth to 0 in accordance with the voltage command value Vfccom set at the second voltage drop rate Vdr2 (step S8: YES). At time t6, driving of the air compressor 112 is stopped, causing the rotation speed Nac to become 0. Also at time t6, the on-duty INJod of the injector 94 is set to 0 [%], and the stop process is terminated.

[0077] [Explanation of the effects of the embodiment] When the control device 26 detects a signal to stop operation of the fuel cell vehicle 11 (fuel cell system 10), it gently (gradually) reduces the power generation voltage Vfc of the fuel cell stack 12 at a first voltage reduction rate Vdr1, and charges the surplus generated power to the power storage device 244. Thereafter, it suddenly reduces the power generation voltage Vfc at a second voltage reduction rate Vdr2 that is higher than the first voltage reduction rate Vdr1, thereby suppressing deterioration of the fuel cell stack 12 and stopping power generation.

[0078] In the process according to the comparative example prior to the process according to this embodiment, the rate of decrease (decrease rate) of the power generation voltage Vfc during shutdown was constant and not variable. Therefore, setting a low voltage decrease rate (corresponding to the first voltage decrease rate Vdr1) that prioritizes charging the power storage device 244 resulted in deterioration of the fuel cell stack 12. On the other hand, setting a high (fast) voltage decrease rate (corresponding to the second voltage decrease rate Vdr2) that prioritizes preventing degradation of the fuel cell stack 12 limited the amount of charge to the power storage device 244 to a small amount. Taking into account this trade-off in the comparative example, this embodiment changes the voltage decrease rate Vdr in two stages, from low to high, during shutdown, thereby achieving both charging the power storage device 244 and preventing degradation of the fuel cell stack 12.

[0079] [Note] In addition to the above disclosure, the following additional notes are also disclosed. (Appendix 1) The first disclosure is a fuel cell system 10 comprising a fuel cell (fuel cell stack 12) that generates electricity using fuel gas and oxidant gas supplied from an air compressor 112, and a control device 26 that controls the fuel cell, wherein the control device comprises an acquisition unit 140 that acquires an operation stop signal, and a control unit 142 that, when the acquisition unit acquires the operation stop signal, reduces the power generation voltage Vfc of the fuel cell at a first voltage reduction rate Vdr1 and then reduces the power generation voltage Vfc at a second voltage reduction rate Vdr2 that is higher than the first voltage reduction rate.

[0080] The second disclosure is a control method for shutting down a fuel cell system that includes a fuel cell that generates electricity using fuel gas and oxidant gas supplied from an air compressor, and a control device that controls the fuel cell, in which, when an operation shutdown signal is received, the control device reduces the generated voltage of the fuel cell at a first voltage reduction rate, and then reduces the generated voltage at a second voltage reduction rate that is higher than the first voltage reduction rate.

[0081] According to the first and second disclosures above, when the fuel cell system is stopped, by reducing the generated voltage at a first voltage reduction rate, charging control can be performed so that the surplus generated power does not exceed the power that can be charged to the storage device, thereby suppressing deterioration of the storage device, and by reducing the generated voltage at a second voltage reduction rate after charging control, deterioration of the fuel cell can be suppressed.

[0082] (Appendix 2) The fuel cell system described in Supplementary Note 1 includes a boost converter 240 that boosts the power generation voltage of the fuel cell to a power supply voltage Vh, and a load 21 and a power storage device 244 to which the power supply voltage is applied, and when the control unit is reducing the power generation voltage at the first voltage reduction rate, the boost converter boosts the power generation voltage to the power supply voltage and charges the power storage device. In this way, by using the boost converter to boost the power generation voltage to the power supply voltage of the power storage device, the power storage device can be charged with the generated power.

[0083] (Appendix 3) In the fuel cell system described in Supplementary Note 1, after reducing the generated voltage at the first voltage reduction rate, the control unit increases the rotation speed Nac of the air compressor for a predetermined time period higher than the rotation speed when the generated voltage is reduced at the first voltage reduction rate before reducing the generated voltage at a second voltage reduction rate higher than the first voltage reduction rate. With this configuration, liquid water accumulated in the cathode flow path of the fuel cell, such as water generated by power generation when operation is stopped, can be drained in a short time.

[0084] (Appendix 4) In the fuel cell system described in Supplementary Note 3, the control unit increases the fuel gas pressure of the fuel cell by a predetermined amount during the predetermined time period in which the rotation speed of the air compressor is kept high. With this configuration, the power required for the air compressor to drain generated water and the like that is generated when operation is stopped can be provided by the power generated by the fuel cell, rather than by the power of a power storage device that has finished charging.

[0085] The present invention is not limited to the above disclosure, and various configurations can be adopted without departing from the gist of the present invention. [Explanation of symbols]

[0086] 10...Fuel cell system 11...Fuel cell vehicle 12...Fuel cell stack 16...Anode system 18...Cathode system 101...Drain valve 106 (106A)...oxidant gas supply path 108 (108A)...Oxidant gas discharge path 109...discharge channel 110...bypass channel 112...Air compressor 116...Inlet sealing valve 118...Outlet sealing valve 120...Bypass valve 240...Boost converter 242, 252...Inverter 244…Electricity storage device (power supply)

Claims

1. a fuel cell that generates electricity using fuel gas and oxidant gas supplied from an air compressor; a control device for controlling the fuel cell; A fuel cell system comprising: The control device includes an acquisition unit that acquires an operation stop signal; a control unit that, when the acquisition unit acquires the operation stop signal, reduces the power generation voltage of the fuel cell at a first voltage reduction rate, and then reduces the power generation voltage of the fuel cell at a second voltage reduction rate that is higher than the first voltage reduction rate; the control unit, after reducing the generated voltage at the first voltage reduction rate, and before reducing the generated voltage at the second voltage reduction rate higher than the first voltage reduction rate, increases the rotation speed of the air compressor for a predetermined time period higher than the rotation speed when the generated voltage is reduced at the first voltage reduction rate. Fuel cell system.

2. 2. The fuel cell system according to claim 1, a boost converter that boosts the generated voltage of the fuel cell to a power supply voltage; a load to which the power supply voltage is applied and a power storage device, When the control unit is reducing the generated voltage at the first voltage reduction rate, the control unit causes the boost converter to boost the generated voltage to the power supply voltage and charges the power storage device. Fuel cell system.

3. 2. The fuel cell system according to claim 1, the control unit increases the fuel gas pressure of the fuel cell by a predetermined amount during the predetermined time period during which the rotation speed of the air compressor is kept high. Fuel cell system.

4. a fuel cell that generates electricity using fuel gas and oxidant gas supplied from an air compressor; a control device for controlling the fuel cell; A control method for a fuel cell system during operation shutdown, comprising: When the control device receives an operation stop signal, when the control device reduces the power generation voltage of the fuel cell at a first voltage reduction rate and then at a second voltage reduction rate higher than the first voltage reduction rate, after reducing the power generation voltage at the first voltage reduction rate and before reducing the power generation voltage at the second voltage reduction rate higher than the first voltage reduction rate, the control device increases the rotation speed of the air compressor for a predetermined time higher than the rotation speed when the power generation voltage was reduced at the first voltage reduction rate. A control method for a fuel cell system when the system is stopped.

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