JP7614912B2 - FUEL CELL SYSTEM, CONTROL METHOD FOR FUEL CELL SYSTEM, AND PROGRAM - Google Patents

Description

The present invention relates to a fuel cell system, a control method for a fuel cell system, and a program.

Conventionally, fuel cell systems have a fuel cell stack equipped with a cell structure in which multiple cell structures, each of which has a pair of electrodes sandwiched between an electrolyte membrane, are stacked. In such a fuel cell system, hydrogen gas is supplied between the anode electrode and the separator as an anode gas (fuel gas), and air is supplied between the cathode electrode and the separator as a cathode gas (oxidant gas). This allows hydrogen ions generated by a catalytic reaction at the anode electrode to permeate the electrolyte membrane and travel to the cathode electrode, where they undergo an electrochemical reaction with oxygen in the air, generating electricity. As a result of this power generation, water is produced inside the fuel cell.

In a fuel cell system equipped with such a fuel cell, if it is used in a sub-freezing environment, for example, there is a risk that the liquid water remaining inside the fuel cell system while it is stopped will freeze. Therefore, a technology has been proposed to recover the liquid water inside the fuel cell system (for example, see Patent Document 1).

JP 2005-251576 A

In the case of Patent Document 1, it is difficult to recover all the liquid water in the fuel cell system, and the remaining liquid water may freeze. In this case, the circulation of the anode gas and cathode gas is hindered during startup, resulting in issues such as reduced power generation stability and deterioration of the fuel cell.

The present invention has been made in consideration of these circumstances, and one of its objectives is to provide a fuel cell system, a control method for a fuel cell system, and a program that can recover from a drop in cell voltage while maintaining stable power generation and suppressing fuel cell degradation when used in a sub-freezing environment.

The fuel cell system, the control method for the fuel cell system, and the program according to the present invention employ the following configuration.
(1): A fuel cell system according to one aspect of the present invention includes a fuel cell stack configured by stacking a plurality of cell structures, each having a pair of electrodes disposed with an electrolyte membrane sandwiched therebetween, and which generates electricity when an oxidant gas and a fuel gas are supplied thereto; a flow passage which supplies an anode gas to the fuel cell stack and which distributes an anode off-gas discharged from the fuel cell stack; and a gas-liquid separation section which is provided in the flow passage and separates liquid water contained in the anode off-gas discharged from the fuel cell stack, discharges the anode off-gas from a gas discharge section, and discharges the liquid water from a liquid water discharge section. The fuel cell system comprises a water volume acquisition means for acquiring the volume of stored liquid water in the gas-liquid separation section, and a control unit for performing a freeze determination process for determining whether the stored liquid water is frozen or not, wherein when the freeze determination process at start-up determines that the stored liquid water is in a frozen state, the control unit starts a thawing process for the frozen stored liquid water, and at start-up, the control unit limits the output of the fuel cell stack based on the volume of frozen stored liquid water in the gas-liquid separation section acquired by the water volume acquisition means and a predetermined water storage volume in the gas-liquid separation section.

(2): In the above aspect (1), the control unit of the fuel cell system performs a process to calculate the storable volume of liquid water generated after startup of the fuel cell system in the gas-liquid separation unit based on the volume of frozen stored liquid water and the liquid water storage upper limit value of the gas-liquid separation unit, and the control unit limits the output of the fuel cell stack so that the time it takes for the volume of liquid water generated by the output of the fuel cell stack to reach the storable volume is longer than the time required for the thawing process of the frozen stored liquid water.

(3): In the above aspect (1) or (2), the water volume acquisition means of the fuel cell system calculates the volume of the stored liquid water based on temperature and humidity information of the fuel cell stack when the fuel cell system was last stopped and volume information of the anode off-gas flowing through the flow passage.

(4): In the above aspect (1) or (2), the water volume acquisition means of the fuel cell system calculates the volume of the stored liquid water based on the volume of the generated water relative to the valve opening interval of the liquid water discharge section that discharges the liquid water during the previous operation of the fuel cell system.

(5): In the above aspect (1), the fuel cell system includes a plurality of fuel cell stacks, and the control unit controls one of the plurality of fuel cell stacks, the electrode of which is in a relatively deteriorated state, to perform stable output power generation, and the other fuel cell stack, the electrode of which is in a relatively less deteriorated state, to perform transient response power generation. When the control unit determines that the stored liquid water in the gas-liquid separation unit connected to the other fuel cell stack is frozen by the freezing determination process, the control unit controls the other fuel cell stack to perform stable output power generation, the one fuel cell stack to perform transient response power generation, and the one fuel cell stack to compensate for the limited portion of the output of the other fuel cell stack.

(6): A method of controlling a fuel cell system according to another aspect of the present invention includes a fuel cell stack configured by stacking a plurality of cell structures, each having a pair of electrodes disposed across an electrolyte membrane, and supplied with an oxidant gas and a fuel gas to generate electricity; a flow passage that supplies an anode gas to the fuel cell stack and distributes an anode off-gas discharged from the fuel cell stack; a gas-liquid separation unit provided in the flow passage that separates liquid water contained in the anode off-gas discharged from the fuel cell stack, discharges the anode off-gas from a gas discharge unit, and discharges the liquid water from a liquid water discharge unit; A method for controlling a fuel cell system comprising: a water volume acquisition means for acquiring the volume of the stored liquid water stored in a gas-liquid separation unit; and a control unit for performing a freeze determination process for determining whether the stored liquid water is frozen or not, wherein the control unit starts a process for thawing the frozen stored liquid water when the freeze determination process at startup determines that the stored liquid water is frozen; and the control unit performs control at startup to limit the output of the fuel cell stack based on the volume of the frozen stored liquid water in the gas-liquid separation unit acquired by the water volume acquisition means and a predetermined water volume stored in the gas-liquid separation unit.

(7): A program according to another aspect of the present invention is a program that causes a computer to obtain the results of a freeze determination process that determines whether the stored liquid water in a gas-liquid separation unit of a fuel cell system mounted on an electrically operated electric device is frozen or not, starts a process of thawing the frozen stored liquid water, and limits the output of the fuel cell stack based on the amount of frozen stored liquid water in the gas-liquid separation unit and the amount of generated water generated after startup.

According to the above aspects (1) to (7), in a fuel cell system, when used in a sub-freezing environment, it is possible to recover from a drop in cell voltage while simultaneously achieving stable power generation and suppressing deterioration of the fuel cell.

1 is a diagram showing an example of the configuration of an electric vehicle equipped with a fuel cell system according to an embodiment; FIG. 1 is a diagram illustrating an example of the configuration of a fuel cell system. FIG. 2 is a diagram illustrating an example of a configuration of a vehicle control device. FIG. 2 is a diagram illustrating an example of a configuration of a supervisory ECU. FIG. 2 is a diagram showing a schematic configuration of a gas-liquid separator. 4 is a flowchart showing an example of a flow of processing executed by a computer of the fuel cell system according to the embodiment. 4 is a flowchart showing an example of a flow of processing executed by a computer of the fuel cell system according to the embodiment. 4 is a flowchart showing an example of a flow of processing executed by a computer of the fuel cell system according to the embodiment. 1 is a diagram showing an example of the configuration of a fuel cell system according to an embodiment;

First Embodiment
Hereinafter, with reference to the drawings, an embodiment of a fuel cell system, a control method for a fuel cell system, and a program of the present invention will be described. The fuel cell system according to the embodiment is mounted on an electric device that operates by electricity, for example. The electric device includes, for example, an electric vehicle, a railroad vehicle, an aircraft (for example, an aircraft, a drone, etc.), a ship, a robot, and other moving objects. The electric device may also include a stationary device (for example, a fuel cell system). In the following, an example in which the fuel cell system is mounted on an electric vehicle will be described. The electric vehicle is, for example, a fuel cell vehicle that uses the power generated in a fuel cell as power for running or power for operating on-board equipment. The electric vehicle is a two-wheeled, three-wheeled, four-wheeled, or other automobile. The electric vehicle may also be, for example, a large vehicle such as a bus or truck that can be equipped with a plurality of fuel cell systems described later.

[Electric vehicles]
FIG. 1 is a diagram showing an example of the configuration of an electric vehicle equipped with a fuel cell system according to an embodiment. As shown in FIG. 1, an electric vehicle 10 includes, for example, a motor 12, drive wheels 14, a brake device 16, a vehicle sensor 20, a converter 32, a BTVCU (Battery Voltage Control Unit) 34, a battery system 40, a display device 50, a vehicle control device 80, a supervisory ECU (Electronic Control Unit) 100, a storage unit 150, and one or more FC (Fuel Cell) systems (fuel cell systems) 200. In the example shown in FIG. 1, a plurality of FC systems 200A and 200B are shown, but when they are not individually distinguished from each other, they may be simply referred to as "FC systems 200". The FC system 200 is an example of a "fuel cell system". When the first control unit 246A and the second control unit 246B of each FC system are not individually distinguished from each other, they may be simply referred to as the "control unit 246."

The motor 12 is, for example, a three-phase AC motor. The rotor of the motor 12 is connected to the drive wheels 14. The motor 12 outputs the driving force used to run the electric vehicle 10 to the drive wheels 14 using at least one of the power generated by the FC system 200 and the power stored in the battery system 40. The motor 12 also generates power using the kinetic energy of the vehicle when the vehicle decelerates.

The brake device 16 includes, for example, a brake caliper, a cylinder that transmits hydraulic pressure to the brake caliper, and an electric motor that generates hydraulic pressure in the cylinder. The brake device 16 may include a backup mechanism that transmits hydraulic pressure generated by operating the brake pedal to the cylinder via a master cylinder. The brake device 16 may also be an electronically controlled hydraulic brake device that transmits hydraulic pressure from the master cylinder to the cylinder.

The vehicle sensor 20 includes, for example, an accelerator opening sensor, a vehicle speed sensor, and a brake depression sensor. The accelerator opening sensor is attached to an accelerator pedal, which is an example of an operator that accepts an acceleration command from the driver, detects the amount of operation of the accelerator pedal, and outputs the accelerator opening to the vehicle control device 80. The vehicle speed sensor includes, for example, wheel speed sensors attached to each wheel and a speed calculator, and combines the wheel speeds detected by the wheel speed sensors to derive the vehicle speed (vehicle speed), which is output to the vehicle control device 80 and the display device 50. The brake depression sensor is attached to the brake pedal, detects the amount of operation of the brake pedal, and outputs the brake depression to the vehicle control device 80.

The vehicle sensor 20 may include an acceleration sensor that detects the acceleration of the electric vehicle 10, a yaw rate sensor that detects the angular velocity around a vertical axis, a direction sensor that detects the orientation of the electric vehicle 10, and the like. The vehicle sensor 20 may also include a position sensor that detects the position of the electric vehicle 10. The position sensor acquires position information of the electric vehicle 10 from, for example, a GNSS (Global Navigation Satellite System) receiver or a GPS (Global Positioning System) device mounted on the electric vehicle 10. The vehicle sensor 20 may also include a temperature sensor that measures the temperature of the FC system 200. Various information detected by the vehicle sensor 20 is output to the vehicle control device 80.

The converter 32 is, for example, an AC-DC converter. The DC side terminal of the converter 32 is connected to the DC link DL. The battery system 40 is connected to the DC link DL via the BTVCU 34. The converter 32 converts the AC voltage generated by the motor 12 into a DC voltage and outputs it to the DC link DL.

The BTVCU 34 is, for example, a step-up DC-DC converter. The BTVCU 34 steps up the DC voltage supplied from the battery system 40 and outputs it to the DC link DL. The BTVCU 34 outputs the regenerative voltage supplied from the motor 12 or the FC voltage supplied from the FC system 200 to the battery system 40.

The battery system 40 includes, for example, a battery 42 and a battery sensor 44. The battery 42 is, for example, a secondary battery such as a lithium-ion battery. The battery 42 stores, for example, the electric power generated by the motor 12 or the FC system 200, and discharges the electric power to drive the electric vehicle 10 or to operate on-board equipment.

The battery sensor 44 includes, for example, a current sensor, a voltage sensor, and a temperature sensor. The battery sensor 44 detects, for example, the current value, voltage value, and temperature of the battery 42. The battery sensor 44 outputs the detected current value, voltage value, temperature, etc. to the vehicle control device 80.

The battery system 40 may be connected, for example, to an external charging facility to charge the battery 42 with power supplied from a charging/discharging device.

The display device 50 includes, for example, a display unit 52 and a display control unit 54. The display unit 52 is, for example, a display unit provided in a meter or an instrument panel, or a head-up display (HUD). The display unit 52 displays various information according to the control of the display control unit 54. The display control unit 54 causes the display unit 52 to display an image based on the information output by the battery system 40 or the information output by the FC system 200. The display control unit 54 also causes the display unit 52 to display an image based on the information output by the vehicle sensor 20 or the vehicle control device 80. The display control unit 54 also causes the display unit 52 to display an image indicating the vehicle speed, etc., output by the vehicle sensor 20. The display device 50 also includes a speaker that outputs sound, and may output a sound or an alarm, etc., associated with the image displayed on the display unit 52.

The vehicle control device 80 controls the traveling of the electric vehicle 10 and the operation of the on-board equipment. For example, the vehicle control device 80 controls the supply of power charged in the battery system 40 and power generated by the FC system 200 according to the power required by the electric vehicle 10. The power required by the electric vehicle 10 is, for example, the total load power required for the load of the electric vehicle 10 to drive or operate. The load includes, for example, the motor 12, the brake device 16, the vehicle sensor 20, the display device 50, and auxiliary equipment such as other on-board equipment. The vehicle control device 80 may also control the traveling of the electric vehicle 10. The functions of the vehicle control device 80 will be described in detail later.

The supervisory ECU 100 performs overall control of the power generation amount of each of the multiple FC systems (FC systems 200A, 200B, ...) based on, for example, control information from the vehicle control device 80. The functions of the supervisory ECU 100 will be described in detail later.

The memory unit 150 is realized, for example, by a HDD (Hard Disk Drive), flash memory, EEPROM (Electrically Erasable Programmable Read Only Memory), ROM (Read Only Memory), or RAM (Random Access Memory). The memory unit 150 stores, for example, information about the cell voltage state of the fuel cell stack of the FC system 200, programs, and various other information.

Each FC system 200 has a similar configuration. The first FC system 200A will be described as an example. The FC system 200 includes, for example, a fuel cell. The fuel cell is a cell that generates electricity by, for example, reacting a fuel at the anode with an oxidant at the cathode. The fuel cell generates electricity by, for example, reacting hydrogen contained as fuel in the fuel gas with oxygen contained as an oxidant in the air. The FC system 200 generates an instructed amount of electricity under the control of the integrated ECU 100, and supplies the generated electricity, for example, to a DC link DL between the converter 32 and the BTVCU 34. As a result, the electricity supplied by the FC system 200 is supplied to the motor 12 via the converter 32 or to the battery system 40 via the BTVCU 34 under the control of the vehicle control device 80, etc., and is stored in the battery 42, or is supplied as necessary to other auxiliary devices, etc.

[FC system]
The FC system 200 will be described in detail. Fig. 2 is a diagram showing an example of the configuration of the FC system 200 according to the embodiment. The configuration shown in Fig. 2 is applicable to each of the multiple FC systems 200 mounted on the electric vehicle 10. The FC system 200 according to the present embodiment is not limited to the following configuration, and may have any system configuration as long as it generates power using an anode and a cathode, for example. 2 includes, for example, an FC stack 210, a compressor 214, a sealing inlet valve 216, a humidifier 218, a gas-liquid separator 220 (gas-liquid separation section), an exhaust circulation pump (P) 222, a hydrogen tank 226, a hydrogen supply valve 228, a hydrogen circulation section 230, a gas-liquid separator 232 (gas-liquid separation section), a flow path, a temperature sensor (T), a contactor 242, an FCVCU (Fuel Cell Voltage Control Unit) 244, a control section 246, and an FC cooling system 280. The FC system 200 includes a flow path from the hydrogen tank 226 and the compressor 214 through the FC stack 210 to an exhaust gas recirculation path 254 or an oxidizing gas discharge path 252. The flow passages include an anode gas flow passage (e.g., a fuel gas supply passage 256) that supplies anode gas to the FC stack 210, and an anode off-gas flow passage (e.g., an exhaust recirculation passage 254, a fuel gas supply passage 256) that discharges gas from the cathode exhaust port 212b of the FC stack 210.

The FC stacks 210A and 210B each include a stack (not shown) of multiple fuel cell cells, and a pair of end plates (not shown) that sandwich the stack from both sides in the stacking direction. The stack is configured by stacking multiple cell structures in which a pair of electrodes are arranged with an electrolyte membrane sandwiched between them, and includes multiple fuel cell stacks that generate electricity when oxidant gas and fuel gas are supplied. The fuel cell includes a membrane electrode assembly (MEA) and a pair of separators that sandwich the membrane electrode assembly from both sides in the joining direction. The membrane electrode assembly includes, for example, an anode consisting of an anode catalyst and a gas diffusion layer, a cathode consisting of a cathode catalyst and a gas diffusion layer, and a solid polymer electrolyte membrane consisting of a cation exchange membrane or the like sandwiched between the anode and the cathode from both sides in the thickness direction.

The anode is supplied with fuel gas containing hydrogen as fuel from a hydrogen tank 226. The cathode is supplied with air, which is an oxidant gas (reactant gas) containing oxygen as an oxidant, from a compressor 214. The hydrogen supplied to the anode is ionized by a catalytic reaction on the anode catalyst, and the hydrogen ions move to the cathode through a suitably humidified solid polymer electrolyte membrane. Electrons generated as the hydrogen ions move can be extracted as direct current to an external circuit (such as the FCVCU 244). The hydrogen ions that move from the anode to the cathode catalyst of the cathode react with the oxygen supplied to the cathode and the electrons on the cathode catalyst to produce water.

The compressor 214 is equipped with a motor and other components that are driven and controlled by the control unit 246. The compressor 214 takes in air from the outside using the driving force of the motor, compresses it, and sends the compressed air to the oxidant gas supply path 250 connected to the cathode, thereby pressurizing the oxidant gas to the fuel cell.

The sealed inlet valve 216 is provided in an oxidant gas supply passage 250 that connects the compressor 214 and a cathode supply port 212a that can supply air to the cathode of the FC stack 210A, and is opened and closed under the control of the control unit 246. The sealed inlet valve 216 is an example of a flow rate adjustment means.

The humidifier 218 humidifies the air sent from the compressor 214 to the oxidant gas supply path 250. For example, the humidifier 218 has a water-permeable membrane such as a hollow fiber membrane, and adds moisture to the air from the compressor 214 by contacting the air through the water-permeable membrane, thereby humidifying the air.

An air supply circulation pump 223 is provided between the sealed inlet valve 216 and the cathode supply port 212a. The air supply circulation pump 223 supplies air that has flowed into the oxidant gas supply path 250 from the compressor 214 from the sealed inlet valve 216 toward the cathode supply port 212a. The air supply circulation pump 223 is an example of an air supply means.

A flow rate control valve 270 is provided in the oxidant gas supply path 250 between the compressor 214 and the humidifier 218. The flow rate control valve 270 is opened and closed under the control of the control unit 246.

The gas-liquid separator 220 discharges the cathode exhaust gas and liquid water discharged from the cathode exhaust port 212b to the oxidant gas discharge path 252 into the atmosphere via the cathode exhaust path 262 without being consumed by the cathode. The gas-liquid separator 220 may also separate the cathode exhaust gas and liquid water discharged to the oxidant gas discharge path 252 and allow only the separated cathode exhaust gas to flow into the exhaust gas recirculation path 254. The gas-liquid separator 220 has a configuration similar to that of the gas-liquid separator 232 described later.

The exhaust circulation pump 222 is provided in the exhaust recirculation path 254, and mixes the cathode exhaust gas that has flowed into the exhaust recirculation path 254 from the gas-liquid separator 220 with air flowing through the oxidant gas supply path 250 from the sealed inlet valve 216 toward the cathode supply port 212a, and supplies the gas again to the cathode. The exhaust circulation pump 222 is an example of an air supply means.

The hydrogen tank 226 stores hydrogen in a compressed state. The hydrogen supply valve 228 is provided in a fuel gas supply path 256 that connects the hydrogen tank 226 to an anode supply port 212c that can supply hydrogen to the anode of the FC stack 210. When the hydrogen supply valve 228 is opened under the control of the control unit 246, it supplies hydrogen stored in the hydrogen tank 226 to the fuel gas supply path 256. An injector 271 and an ejector 236 are provided in the fuel gas supply path 256.

The hydrogen circulation unit 230 is, for example, a pump that circulates and supplies fuel gas to the fuel cell. The hydrogen circulation unit 230 circulates, for example, anode exhaust gas that is not consumed at the anode and is discharged from the anode exhaust port 212d to the fuel gas discharge path 258, via the gas-liquid separator 232 to the fuel gas supply path 256.

The gas-liquid separator 232 separates the anode exhaust gas and liquid water circulated from the fuel gas exhaust passage 258 to the fuel gas supply passage 256 by the action of the hydrogen circulation section 230. FIG. 5 is a schematic diagram showing the configuration of the gas-liquid separator 232. The gas-liquid separator 232 includes a storage section 91, an inlet 92, an exhaust port 93 (gas exhaust section), a liquid water exhaust port (liquid water exhaust port) 98, a drain heater 95, and an anode drain valve 96. The anode exhaust gas separated from the liquid water in the storage section 91 is supplied from the exhaust port 93 to the anode supply port 212c of the FC stack 210. Specifically, the anode exhaust gas separated from the liquid water flows from the exhaust port 93 to the exhaust recirculation passage 254 and is supplied to the anode supply port 212c of the FC stack 210. In the gas-liquid separator 220, the anode gas flows to the fuel gas supply passage 256. The liquid water discharge port 98 is provided at the bottom of the storage section 91. A drainage channel 971 is provided between the liquid water discharge port 98 and the anode drain valve 96. When the anode drain valve 96 is closed, liquid water is stored in the drainage channel 971 and at the bottom of the storage section 91. The stored liquid water is called stored liquid water. When the anode drain valve 96 is opened, the liquid water discharged from the inlet 92 to the storage section 91 and separated into gas and liquid flows out from the liquid water discharge port 98 to the drain pipe 264 and is discharged into the atmosphere. The drain heater 95 is disposed at the bottom end of the storage section 91 and near the liquid water discharge port 98. The drain heater 95 is a heater that can be energized via a cable 951. The anode drain valve 96 is a valve that opens and closes the drainage channel 971. The anode drain valve 96 is, for example, a solenoid valve.

The temperature sensor detects the temperature of the anode and cathode of the FC stack 210 and outputs a detection signal (temperature information) to the control unit 246.

The contactor 242 is provided between the anode and cathode of the FC stack 210 and the FCVCU 244. The contactor 242 electrically connects or disconnects the FC stack 210 and the FCVCU 244 based on control from the control unit 246.

The FCVCU 244 is, for example, a step-up DC-DC converter. The FCVCU 244 is disposed between the anode and cathode of the FC stack 210 and the electrical load via the contactor 242. The FCVCU 244 boosts the voltage of the output terminal 248 connected to the electrical load to a target voltage determined by the control unit 246. The FCVCU 244 boosts, for example, the voltage output from the FC stack 210 to the target voltage and outputs it to the output terminal 248.

The control unit 246 controls the start and end of power generation in the FC system 200, the amount of power generation, and the start and end of power generation by the drain heater 95, in accordance with the power generation control by the integrated ECU 100. The control unit 246 controls the temperature adjustment of the FC system 200 using the FC cooling system 280. The control unit 246 may be replaced with a control device such as an FC-ECU. The control unit 246 may control the power supply to the electric vehicle 10 in cooperation with the integrated ECU 100 and the vehicle control device 80.

The FC cooling system 280 cools the FC system 200 according to the control of the control unit 246, for example, when the temperature of the FC stack 210 detected by the temperature sensor is equal to or higher than a threshold value. For example, the FC cooling system 280 cools the temperature of the FC stack 210 by circulating a coolant through a flow path provided in the FC stack 210 to discharge heat from the FC stack 210. In addition, when the FC system 200 is generating power, the FC cooling system 280 may control the heating or cooling of the FC stack 210 so that the temperature detected by the temperature sensor is maintained within a predetermined temperature range.

[Vehicle control device]
3 is a diagram showing an example of the configuration of the vehicle control device 80. The vehicle control device 80 includes, for example, a motor control unit 82, a brake control unit 84, a power control unit 86, and a driving control unit 88. The motor control unit 82, the brake control unit 84, the power control unit 86, and the driving control unit 88 are each realized by, for example, a hardware processor such as a CPU (Central Processing Unit) executing a program (software). In addition, some or all of these components may be realized by hardware (including circuitry) such as an LSI (Large Scale Integration), an ASIC (Application Specific Integrated Circuit), an FPGA (Field-Programmable Gate Array), or a GPU (Graphics Processing Unit), or may be realized by cooperation between software and hardware. The program may be stored in advance in a storage device (storage device having a non-transient storage medium) such as an HDD or flash memory of the electric vehicle 10, or may be stored in a removable storage medium such as a DVD or CD-ROM, and the storage medium (non-transient storage medium) may be installed in the HDD or flash memory of the electric vehicle 10 by mounting the storage medium (non-transient storage medium) in a drive device. The storage device is, for example, the storage unit 150 .

The motor control unit 82 calculates the driving force required of the motor 12 based on the output of the vehicle sensor 20, and controls the motor 12 to output the calculated driving force.

The brake control unit 84 calculates the braking force required of the brake device 16 based on the output of the vehicle sensor 20, and controls the brake device 16 to output the calculated braking force.

The power control unit 86 calculates the amount of power required for the battery system 40 and the FC system 200 based on the output of the vehicle sensor 20. For example, the power control unit 86 calculates the torque to be output by the motor 12 based on the accelerator opening and the vehicle speed, and calculates the amount of power required by adding up the drive shaft load power calculated from the torque and the rotation speed of the motor 12 and the power required by the auxiliary equipment. The power control unit 86 also manages the charging status (electricity storage status) of the battery system 40. For example, the power control unit 86 calculates the SOC (State of Charge) of the battery 42 based on the output of the battery sensor 44. For example, when the SOC of the battery 42 is less than a predetermined value, the power control unit 86 executes control to charge the battery 42 by power generation by the FC system 200, or outputs information to the display device 50 that prompts the occupant to charge the battery 42 by power supply from an external charging facility. The power control unit 86 may stop charging control when the SOC of the battery 42 is greater than a predetermined value, or may perform control to cause surplus power generated by the FC system 200 to be consumed by auxiliary equipment, etc.

The driving control unit 88 executes driving control of the electric vehicle 10 based on, for example, information acquired by the vehicle sensor 20. The driving control unit 88 may also execute driving control of the electric vehicle 10 based on map information and information acquired from a monitoring unit (not shown) in addition to the information acquired by the vehicle sensor 20. The monitoring unit includes, for example, a camera that captures an image of the space outside the electric vehicle 10, a radar or LIDAR (Light Detection and Ranging) that has a detection range outside the electric vehicle 10, and an object recognition device that performs sensor fusion processing based on the output of these. The monitoring unit estimates the type of object (particularly, a vehicle, a pedestrian, and a bicycle) that exists in the vicinity of the electric vehicle 10, and outputs it to the driving control unit 88 together with information on its position and speed. Driving control is, for example, controlling one or both of the steering and acceleration/deceleration of the electric vehicle 10 to drive the electric vehicle 10. Driving control includes, for example, driving assistance control such as ADAS (Advanced Driver Assistance System). ADAS includes, for example, LKAS (Lane Keeping Assistance System), ACC (Adaptive Cruise Control System), CMBS (Collision Mitigation Brake System), etc.

[Control ECU]
4 is a diagram showing an example of the configuration of the master ECU 100. The master ECU 100 includes, for example, a flow control unit 102, a required power acquisition unit 104, an output control unit 106, an air supply control unit 107, a water volume acquisition unit 103, a defrosting control unit 105, and a power generation control unit 108. The flow control unit 102, the required power acquisition unit 104, the output control unit 106, and the power generation control unit 108 are each realized by, for example, a hardware processor such as a CPU executing a program (software). Some or all of these components may be realized by hardware (including circuitry) such as an LSI, an ASIC, an FPGA, or a GPU, or may be realized by cooperation between software and hardware. The program may be stored in advance in a storage device (a storage device having a non-transient storage medium) such as an HDD or flash memory of the electric vehicle 10, or may be stored in a removable storage medium such as a DVD or CD-ROM, and installed in the HDD or flash memory of the electric vehicle 10 by mounting the storage medium (non-transient storage medium) in a drive device. The above-mentioned storage device is, for example, the storage unit 150.

The power requirement acquisition unit 104 acquires the amount of power required from the electric vehicle 10. For example, the power requirement acquisition unit 104 acquires the amount of power required to be generated by the multiple FC systems 200 by the vehicle control device 80 (i.e., the amount of power required by the entire electric vehicle excluding the amount of power supplied by the battery system 40).

The flow control unit 102 controls one of the FC stacks 210A, 210B of the multiple FC systems 200A, 200B to perform stable output power generation in one FC system having an FC stack with a relatively large deterioration state of the electrodes, and to perform transient response power generation in the other fuel cell system having the other FC stack with a relatively small deterioration state of the electrodes.

The air supply control unit 107 controls the operating state of an air supply means such as the air supply circulation pump 223. For example, the air supply control unit 107 can control the flow rate and flow speed of the air in the oxidant gas supply path 250 by increasing or decreasing the output of the air supply circulation pump 223. The air supply control unit 107 is an example of an air supply control means.

The water volume acquisition unit 103 acquires the volume of the stored liquid water stored in the lower part of the storage section 91 of the gas-liquid separator 220, 232. The water volume acquisition unit 103 may include either one or both of a means for detecting the volume of the stored liquid water using a sensor or the like and a means for calculating an estimated volume of the stored liquid water. When the water volume acquisition unit 103 is a means for measuring the volume of the stored liquid water, for example, a water level sensor or a temperature sensor may be provided in the gas-liquid separator 220, 232. When the water volume acquisition unit 103 is a means for estimating the volume of the stored liquid water, for example, the estimated volume of the stored liquid water may be calculated from the operating status before the FC system is stopped (hereinafter, sometimes referred to as the "previous operating status"). When the water volume acquisition unit 103 is a means for estimating the volume of the stored liquid water, for example, production volume information indicating the production volume of liquid water corresponding to the output of the FC stack 210 may be stored in advance, and the volume of the stored liquid water may be acquired based on the stored production volume information.

An example of calculation is shown below in which the water volume acquisition unit 103 calculates an estimated amount of stored liquid water based on the previous operating status. For example, when the FC system is operating, the amount of stored liquid water in the gas-liquid separator is calculated based on the output of the FC stack 210 and the interval of time the anode drain valve is open. For example, during the previous operation, the pressure drop characteristics of one cycle from when the drain valve is opened to when it is closed are acquired. Specifically, the pressure of the FC stack 210 is acquired by the anode pressure sensor. The difference ΔP per unit time of the acquired pressure values is calculated.

In formula 1, Q is mass flow rate (unit: Kg/s), C is flow coefficient, ΔP is orifice differential pressure (unit: kPA), and Y is fluid density (unit: kg/m ³ ).
By applying ΔP to the orifice equation shown in (Equation 1), the amount of liquid water flowing out during one drain cycle from when the drain valve is opened to when it is closed is calculated. The value of the liquid water amount is integrated to calculate the amount of liquid water generated per drain cycle. Next, the current density of the FC stack 210 is measured. An estimated value of the membrane permeability characteristic of the FC stack 210 is obtained by acquiring multiple relationship values between the amount of liquid water generated per drain cycle and the current density of the FC stack 210. The water amount acquisition unit 103 estimates the amount of stored liquid water at the time of low-temperature startup based on the current density of the FC stack 210 acquired during low-temperature startup and the estimated value of the membrane permeability characteristic of the FC stack 210. It is assumed that the estimated amount of stored liquid water is all frozen, and a thawing process is performed.

The membrane permeability characteristics of the FC stack 210 differ for each FC stack 210. Therefore, the membrane permeability characteristics are estimated for each of the FC stacks 210, and the amount of liquid water generated in the anode system of each FC stack 210 is obtained individually. During low-temperature startup, the current density is obtained for each of the FC stacks 210, and the amount of liquid water generated in each FC stack 210 is estimated based on the obtained current density value, and the amount of liquid water stored in the gas-liquid separator is calculated. The trend of power generation during normal operation may be obtained, and the amount of water generated in the anode system for each current density may be estimated and learned. By estimating the amount of liquid water generated in each FC stack 210, the accuracy of the estimated value of the amount of stored liquid water is improved. As a result, the thawing process can be performed optimally for the actual amount of stored liquid water.

If the temperature drops after the FC system is shut down, condensation water will form in the flow path. The condensation water will also freeze. In this case, the estimated amount of stored liquid water can be calculated by adding the amount of stored liquid water remaining in the gas-liquid separator to the calculated amount of liquid water produced.

In addition, the amount of stored liquid water may be calculated based on the temperature and humidity information of the FC stack when it was last stopped and the volume information of the anode off-gas flowing through the flow passage.

The thawing control unit 105 performs control to thaw the stored liquid water. For example, it controls the time that the anode heater is energized based on the amount of stored liquid water at the time the FC system is started. For example, in addition to controlling the time that the anode heater is energized, during the thawing control, the output control unit 106 and the air supply control unit 107 perform control to send control information to each FC system to perform stable output power generation or transient response power generation.

The integrated ECU 100 is not limited to a configuration including all of the flow control unit 102, the required power acquisition unit 104, the output control unit 106, the air supply control unit 107, and the power generation control unit 108. For example, the integrated ECU 100 may not include the output control unit 106, the air supply control unit 107, or the required power acquisition unit 104.

In the following explanation, an example is shown in which the deterioration state of the electrodes of the first FC stack 210A of the first FC system 200 is relatively greater than that of the electrodes of the second FC stack 210B. In other words, the first FC stack 210A is an example of a deteriorated fuel cell stack.

The cell voltage of each cell structure of each FC stack 210 is detected by the cell voltage sensor 201. The cell voltage sensor 201 constantly or periodically detects the cell voltage of the cell structure. The detection result of the cell voltage of the cell structure is recorded in the memory unit 150. If the detection result of the cell voltage of the cell structure by the cell voltage sensor 201 falls below a predetermined value, the flow control unit 102 determines that the cell voltage of the cell structure has decreased. When a decrease in cell voltage is determined, the flow control unit 102 controls the decreased fuel cell stack (first FC stack 210A), which is a fuel cell stack having at least a cell structure with a decreased cell voltage, to perform stable output power generation, and performs flow control to increase the flow rate of either the oxidant gas or the fuel gas supplied to the decreased fuel cell stack 210A compared to the flow rate before the cell voltage decrease.

Stable output power generation refers to a power generation state in which the output of the FC stack 210A having a cell structure with a reduced cell voltage is reduced and power generation continues. Stable output power generation includes a power generation state in which the thaw control unit 105 reduces the output of the FC stack 210A having a cell structure and power generation continues during the unfreezing process.

Transient response power generation refers to a power generation state in which the other FC system 200B compensates for the reduced output as a result of switching the degraded fuel cell stack to stable output power generation, and the system as a whole can generate the requested amount of power acquired by the requested power acquisition unit 104. The other FC system 200B increases its power generation amount so that it is equivalent to the reduction in the power generation amount of the FC system 200A targeted for stable output power generation, or is less than the reduction but is still capable of generating the requested amount of power. During transient response power generation, for example, the flow control unit 102 increases the power generation amount of the other FC system 200B. Transient response power generation includes a power generation state in which, when performing unfreezing processing, the power generation amount is increased at the end of the unfreezing processing or at the end of the thawing processing described below to compensate for the reduced output during the thawing processing, so that the power generation amount can be generated to be capable of generating the requested amount of power.

For example, the flow control unit 102 controls the open/close state of the flow control valve 270 based on the detection result of the cell voltage sensor 201 to adjust the amount of oxidant gas supplied. The flow control adjusts the open/close state and opening amount of the valves provided in each flow path of the fuel gas and oxidant gas, or adjusts the output of the pump to control the flow rate in the fuel distribution path. The method of controlling the flow rate is selected depending on the state of the cell voltage of the cell structure.

For example, when performing flow control to increase the flow rate of the oxidant gas, the flow control unit 102 also increases the flow rate of the fuel gas supplied to the first FC stack 210A, which is the degraded fuel cell stack, compared to the flow rate before the cell voltage decreased.

After the flow control unit 102 starts flow control, if the cell voltage sensor 201 detects that the cell voltage of the cell structure of the first FC stack 210A, which is a low fuel cell stack, has risen to or above a predetermined cell voltage, the flow control unit 102 cancels the increased state of the flow rate of the oxidizer gas and/or fuel gas, and simultaneously controls each of the multiple FC stacks 210A, 210B stacks to generate power in the power generation state before the detection of the drop in cell voltage.

The output control unit 106 controls the output of the multiple FC stacks 210A, 210B. When the cell voltage sensor 201 detects that the cell voltage of the cell structure of the degraded fuel cell stack 210A does not rise above a predetermined cell voltage, the output control unit 106 performs output limitation to limit the output of the degraded fuel cell stack 210A to a predetermined value or less, and performs output complementation control to increase the output of the second FC stack 210B, which performs transient response power generation, compared to the output before the output limitation.

If the cell voltage sensor 201 detects that the cell voltage of the cell structure of the degraded fuel cell stack 210A continues to decrease even after the output limit is imposed, the output control unit 106 stops power generation by the degraded fuel cell stack 210A and controls the output of the other FC cell stack 210B that is performing transient response power generation to be increased compared to the output when the output was limited.

[Processing flow]
The flow of processing executed by the computer of the fuel cell system according to the embodiment will be described below with reference to a flowchart. The following processing will be mainly described with a focus on the processing of power supply control by the multiple FC systems mounted on the electric vehicle 10. Fig. 6 is a flowchart showing an example of the flow of processing executed by the computer of the fuel cell system according to the embodiment. The processing in Fig. 6 is executed repeatedly at a predetermined timing or at a predetermined cycle, for example, while the electric vehicle 10 is running.

In the example of FIG. 6, first, for example, when the electric vehicle 10 is started and the fuel cell system is started, the supervisory ECU 100 acquires temperature information in the vicinity of the fuel cell system. The temperature information is acquired, for example, from the outside air temperature of the electric vehicle 10, the temperature of the fuel cell system housing of the electric vehicle 10, a temperature sensor provided in the vicinity of the gas-liquid separator, etc. The supervisory ECU 100 judges whether the stored liquid water is frozen or not based on the acquired temperature information (step S10). If the temperature information is higher than zero degrees Celsius, the freezing and unfreezing process (step S11) described later is not performed, and the FC systems 200A and 200B are operated normally. The supervisory ECU 100 performs the freezing and unfreezing process based on the temperature information (step S11). When the freezing and unfreezing process is started, the supervisory ECU 100 judges whether the stored liquid water in the gas-liquid separator is frozen or not (step S12). The method of judging whether the stored liquid water is frozen or not is, for example, by detecting the opening and closing of the anode drain valve provided in each FC system 200. The upstream end of the anode drain valve is connected to the gas-liquid separator and is in contact with the stored liquid water. Therefore, if the stored liquid water is frozen, the anode drain valve will not open. Therefore, for example, the integrated ECU 100 performs a valve drive process to open the anode drain valve provided in each FC system 200. If the valve drive process does not detect that the anode drain valve is open, the integrated ECU 100 determines that the stored liquid water is frozen. The determination means used to determine whether the stored liquid water is frozen is not limited to this example. For example, a sensor capable of detecting the freezing of the stored liquid water may be provided in the gas-liquid separator to detect whether the stored liquid water is frozen.

If the supervisory ECU 100 determines that the stored liquid water is frozen in the freezing determination process (step S12) (YES), it performs a process of thawing the frozen stored liquid water (step S13). Specifically, it energizes the anode heater to increase the temperature of the anode heater. The anode heater is disposed near the drain outlet and at the lower end of the gas-liquid separator. Therefore, when the stored liquid water is frozen, it is buried in or in contact with the frozen stored liquid water. When the anode heater is heated, the stored liquid water gradually thaws from the periphery of the anode heater. The anode heater is heated until the thawing of the stored liquid water is completed. If the supervisory ECU 100 determines that the stored liquid water is frozen in the freezing determination process (step S12) (NO), it ends the unfreezing process and the FC systems 200A and 200B are switched to normal operation.

The general ECU 100 acquires the amount of liquid water stored in the gas-liquid separator at the same time as the start of the thawing process (step S14). The amount of stored liquid water includes a means for detecting the amount of liquid water using a sensor and a means for calculating an estimated amount of water. For example, when a sensor is used, a sensor for detecting the amount of liquid may be provided in the gas-liquid separator. When calculating the estimated amount of water, the estimated amount of water may be calculated from the previous operating status. Specifically, when the fuel cell system is started, the amount of stored liquid water in the gas-liquid separator may be calculated based on the output of the FC stack 210 and the interval between the opening times of the anode drain valve 96 immediately before the fuel cell system is stopped and the output of the FC stack 210. In this case, the amount of liquid water generated may be calculated based on the interval between the opening times of the anode drain valve 96 immediately before the fuel cell system is stopped and the output of the FC stack 210. In this case, the amount of stored liquid water may be calculated by adding the amount of stored liquid water remaining in the gas-liquid separator to the calculated amount of liquid water generated. As another example, production volume information indicating the amount of liquid water produced corresponding to the output of the FC stack 210 may be stored in advance, and the amount of stored liquid water may be obtained based on the stored production volume information.

Next, the integrated ECU 100 performs output restriction processing for the fuel cell stack (step S15). If the stored liquid water in the gas-liquid separator is frozen, the anode drain valve will not open even if valve opening control is performed, or the frozen stored liquid water will not be drained. In this state, when the fuel cell system is started, liquid water will accumulate in the gas-liquid separator, and the liquid water level in the gas-liquid separator will rise. If the amount of liquid water in the gas-liquid separator exceeds the allowable water storage capacity, it will reach the outlet for the anode exhaust gas from the FC stack 210, reducing the power generation efficiency. It will also cause deterioration of the electrodes. Therefore, the integrated ECU 100 restricts the output of the FC stack 210 so that the stored liquid water in the gas-liquid separator does not exceed the allowable water storage capacity until the stored liquid water thaws and can be drained from the anode drain valve.

In the output limiting process (step S15), the general ECU 100 calculates the amount of liquid water that can flow into the gas-liquid separator. As shown in FIG. 5, the amount of water W3 obtained by subtracting the amount of stored liquid water W2 obtained in step S14 from the allowable water storage amount W1 of the gas-liquid separator at the allowable water level L1 is the amount of liquid water that can newly flow into the gas-liquid separator during low-temperature startup. During low-temperature startup, the general ECU 100 performs output limiting control while the thawing process (step S13) is being performed. The output limiting control is performed in the same manner as the output limiting control (S108) described below. For example, during the unfreezing process, the output of each FC stack 210 is limited to a predetermined value or less by back-calculating from the current density corresponding to the amount of liquid water that can newly flow in.

While the thawing process (step S13) and the output limiting process (step S15) are being performed, the supervisory ECU 100 performs the freezing determination process (step S16) in the same manner as in step S12. If the freezing determination process (step S16) determines that the stored liquid water is frozen (YES), the thawing process (step S13) through the output limiting process (step S15) are repeated. In the freezing determination process (step S16), the supervisory ECU 100 determines that the stored liquid water has thawed when the anode drain valve 96 is opened and the stored liquid water can be drained. If the freezing determination process (step S16) determines that the stored liquid water is not frozen (non-frozen), i.e., thawed (NO), the unfreezing process is terminated and the FC systems 200A, 200B are switched to normal operation.

In the above example, the thawing process (step S13), the water volume acquisition process (step S14), and the output restriction process (step S15) are started in sequence, but each process (steps S13, S14, S15) may be started simultaneously to perform parallel processing. Also, after the water volume acquisition process (step S14), the thawing process (step S13) and the output restriction process (step S15) may be performed.

Figure 7 is a flowchart showing an example of the processing of the fuel cell system. The fuel cell system includes a plurality of FC systems 200A, 200B, and the integrated ECU 100 controls the FC stack 210A, 200B, one of which has a relatively large deterioration state of the electrodes, to perform stable output power generation, and the other FC stack 210B, one of which has a relatively small deterioration state of the electrodes, to perform transient response power generation. In addition, when the integrated ECU 100 determines that the stored liquid water in the gas-liquid separator connected to the other FC stack 210A of the plurality of FC stacks 210 is frozen by the freezing determination process (step S12), the integrated ECU 100 controls the other FC stack 210A to perform stable output power generation, the one FC stack 210B to perform transient response power generation, and the one fuel cell stack to compensate for the limited portion of the output of the other fuel cell stack.

First, the determination of the deterioration state of the electrodes of the multiple FC stacks 210A, 200B and the control of the central ECU 100 in the normal operation mode will be described. Based on the cell voltage information acquired in step S100, the central ECU 100 determines whether the cell voltage of each FC stack 210 has decreased, and detects the cell voltage decrease (step S101). If a cell voltage decrease is detected in the first FC stack 210A, the flow control unit 102 adjusts the opening amount of the air supply circulation pump 223 and the flow control valve 270 of the first FC system 200A to increase the flow rate of air supplied from the oxidizing gas supply path 250 (step S102).

The integrated ECU 100 determines whether the cell voltage drop in the first FC stack 210A has recovered from the result of step S102 (step S103). If it is determined that the cell voltage drop in the first FC stack 210A has recovered (YES), the flow control is returned to normal control (step S104). When normal control is returned to, the cell voltage monitoring in step S100 is continued. If it is determined in step S103 that the cell voltage drop in the first FC stack 210A has not recovered (NO), the flow control unit 102 opens the purge valve 279 of the first FC system 200A and controls to increase the flow rate of the fuel gas (step S105).

The supervisory ECU 100 judges whether the cell voltage drop of the first FC stack 210A has recovered from the result of step S105 (step S106). If it is judged that the cell voltage drop of the first FC stack 210A has recovered (YES), the flow control is returned to normal control (step S104). When normal control is resumed, the cell voltage monitoring of step S100 is continued. If it is judged in step S106 that the cell voltage drop of the first FC stack 210A has not recovered (NO), the cell voltage drop is not caused by gas flow path blockage due to condensed water, and another fault diagnosis needs to be performed. The supervisory ECU 100 judges that there is a system abnormality and transmits a signal to the vehicle control device 80 to notify the system abnormality and to prompt repair (step S107). The vehicle control device 80 transmits information on the system abnormality and repair via the display device 50 or audio system of the electric vehicle 10.

Next, the first control unit 246A performs output limiting control (S108). The output control unit 106 controls the output of the multiple FC stacks 210A, 210B. When the cell voltage sensor 201 detects that the cell voltage of the cell structure of the degraded fuel cell stack 210A does not rise above a predetermined cell voltage, the output control unit 106 performs output limiting to limit the output of the degraded fuel cell stack 210A to a predetermined value or less. At the same time, the output control unit 106 performs output supplementary control to increase the output of the second FC stack 210B, which performs transient response power generation, compared to the output before the output limiting.

When deposits in the fuel gas and/or oxidant gas flow paths are removed as a result of limiting the output of the first FC system 200A, the cell voltage drop may be resolved. The supervisory ECU 100 determines whether the cell voltage drop of the first FC stack 210A has stopped decreasing (step S109). If it is determined that the cell voltage drop of the first FC stack 210A has recovered (YES), the process returns to cell voltage monitoring (step S100). In this case, the next time the FC system 200 is started, the power generation state is returned to the power generation state before the cell voltage drop was detected. If it is determined in step S109 that the cell voltage drop of the first FC stack 210A has not recovered (NO), the supervisory ECU 100 determines that a system abnormality has occurred, and stops power generation only in the first FC system 200A, while the other FC systems 200 continue power generation (step S110). At this time, the supervisory ECU 100 may control the output of the FC stack 210B in the other FC system 200B to be increased. This completes the processing in this flowchart.

If it is determined that the cell voltage drop in the first FC stack 210A has recovered (YES), the flow control may be returned to normal control (step S104). When normal control is returned to, the cell voltage monitoring in step S100 continues.

According to the embodiment described above, when a cell voltage drop occurs in one of the multiple FC stacks 210, recovery control from the cell voltage drop can be performed while suppressing the effects of the cell voltage drop.

The processing flow is not limited to the example shown in FIG. 7. For example, the processing flow may be a flowchart shown in FIG. 8. FIG. 8 is a flowchart showing another example of the processing flow executed by the computer of the fuel cell system. The processing of FIG. 8 is executed repeatedly at a predetermined timing or at a predetermined cycle, for example, while the electric vehicle 10 is running.

In the example of FIG. 8, first, the supervisory ECU 100 monitors the cell voltage (step S200). Specifically, the supervisory ECU 100 acquires the cell voltage value of the cell structure detected by the cell voltage sensor 201 provided in each FC system 200. In the process of step S200, the supervisory ECU 100 may store the acquired cell voltage information in the memory unit 150.

Next, the general ECU 100 determines whether or not the cell voltage of each FC stack 210 has decreased based on the cell voltage information acquired in step S200, and detects the cell voltage decrease (S201). When a cell voltage decrease is detected in the first FC stack 210A, the flow control unit 102 adjusts the opening amount of the supply air circulation pump 223 and the flow control valve 270 of the first FC system 200A to increase the flow rate of air supplied from the oxidant gas supply path 250, and opens the purge valve 279 of the first FC system 200A to increase the flow rate of hydrogen, which is the fuel gas (step S202). In this way, the flow control unit 102 can eliminate the cell voltage decrease in a short time by simultaneously increasing the flow rate of the fuel gas and the flow rate of the oxidant gas. As a result, the output stability of the entire fuel cell system can be further improved.

Next, the supervisory ECU 100 judges whether the cell voltage drop of the first FC stack 210A has recovered from the result of step S202 (step S203). If it is judged that the cell voltage drop of the first FC stack 210A has recovered (YES), the flow control is returned to normal control (step S204). When normal control is resumed, the cell voltage monitoring of step S200 is continued. If it is judged in step S203 that the cell voltage drop of the first FC stack 210A has not recovered (NO), the cell voltage drop is not caused by gas flow path blockage due to condensed water, and another fault diagnosis needs to be performed. The supervisory ECU 100 judges that there is a system abnormality and transmits a signal to the vehicle control device 80 to notify the system abnormality and to prompt repair (step S205). The vehicle control device 80 transmits information on the system abnormality and repair via the display device 50 or audio system of the electric vehicle 10.

Next, the first control unit 246A performs output limiting control (S206). The output control unit 106 limits the output of the first FC system 200A. For example, the output control unit 106 performs control to reduce the output of the air supply circulation pump 223 and control to reduce the flow rate of the hydrogen circulation unit 230, thereby reducing the flow rate of the fuel gas and oxidant gas and limiting the output of the first FC system 200A. At this time, the general ECU 100 may control the second control unit 246B to perform transient response power generation in the second FC system 200B.

When deposits in the flow path of the fuel gas and/or oxidant gas are removed as a result of limiting the output of the first FC system 200A, the cell voltage drop may be resolved. The supervisory ECU 100 determines whether the cell voltage drop of the first FC stack 210A has stopped decreasing (step S207). If it is determined that the cell voltage drop of the first FC stack 210A has recovered (YES), the process returns to cell voltage monitoring (step S200). In this case, the next time the FC system 200 is started, the power generation state is returned to the power generation state before the cell voltage drop was detected. If it is determined in step S207 that the cell voltage drop of the first FC stack 210A has not recovered (NO), the supervisory ECU 100 determines that a system abnormality has occurred, and stops power generation only in the first FC system 200A, while the other FC systems 200 continue power generation (step S208). At this time, the supervisory ECU 100 may control the output of the FC stack 210B in the other FC system 200B to be increased. This completes the processing in this flowchart.

If it is determined that the cell voltage drop in the first FC stack 210A has been restored (YES), the flow control may be returned to normal control (step S204). When normal control is returned to, the cell voltage monitoring in step S200 continues.

In such a fuel cell system, if the stored liquid water is determined to be frozen by the freeze determination process at startup (step S11), a process to thaw the frozen stored liquid water (step S13) is initiated. At startup, the general ECU 100 performs control to limit the output of each FC stack 210A, 210B based on the amount of frozen stored liquid water in the gas-liquid separator obtained by the water amount acquisition process (step S14) and the predetermined amount of water stored in the gas-liquid separator.

When the integrated ECU 100 determines that the stored liquid water in the gas-liquid separator connected to the other FC stack 210B is frozen by the freezing determination process (step S11), the integrated ECU 100 controls the other FC stack 210B to perform stable output power generation, the one FC stack 210A to perform transient response power generation, and the one FC stack 210A to compensate for the limited output of the other FC stack 210B. As a result, the FC system 200B with the frozen gas-liquid separator is subjected to the unfreezing process intensively, and the FC system 200A with the unfrozen gas-liquid separator performs transient response power generation, thereby shortening the time required to make the electric vehicle 10 operable.

According to the embodiment described above, when a cell voltage drop occurs in one of the multiple FC stacks 210, recovery control from the cell voltage drop can be performed while suppressing the effects of the cell voltage drop.

Second Embodiment
Next, a second embodiment of the fuel cell system will be described with reference to Fig. 9. In the description of this embodiment, the same components as those in the first embodiment will be denoted by the same reference numerals and description thereof will be omitted. In this embodiment, each FC system 200A is an example in which a plurality of FC stacks 210 are arranged in series. In this fuel cell system, two FC stacks 210 are arranged in series. Three or more FC stacks 210 may be arranged in series.

The fuel cell system, the schematic configuration of which is shown in FIG. 7, comprises multiple FC systems 200A, 200B and a power conversion unit. The multiple FC systems 200A, 200B each have the same configuration. The first FC system 200A will be used as an example. The FC system 200 comprises two FC stacks 210, a fuel gas supply unit, an oxidizer gas supply unit, and a cooling mechanism. The fuel gas supply unit is supplied from a hydrogen tank 226. The fuel gas separated by the gas-liquid separator is supplied to each of the FC stacks 210 arranged in series. The oxidizer gas supply unit also supplies the oxidizer gas to each of the FC stacks 210 arranged in series. As in the first embodiment, the fuel gas flow path is provided with a fuel gas flow rate adjustment means (e.g., hydrogen circulation unit 230, injector 231, purge valve 279, etc.), and the oxidizer gas flow path is provided with an oxidizer gas flow rate adjustment means (e.g., air supply circulation pump 223, flow rate adjustment valve 270, sealed inlet valve 216, etc.) that are independent of each other. A cell voltage sensor 201 is provided individually for each FC stack 210.

The cooling mechanism 202 includes a radiator 203, a refrigerant tank 204, a refrigerant pump 206, a fan (not shown), and a thermostat. The radiator 203 is a heat exchanger for dissipating heat from the high-temperature refrigerant that flows out of the refrigerant flow path 205. The refrigerant is, for example, water. The refrigerant may also be, for example, water containing ethylene glycol, or another refrigerant. The radiator 203 dissipates heat from the refrigerant that flows out of the refrigerant flow path 205 by heat exchange with air. The refrigerant pump 206 compresses the refrigerant that flows in from the upstream of the refrigerant flow path 205. The temperature of the FC stack 210A is adjusted by circulating the refrigerant through the refrigerant flow path 205.

In the fuel cell system, the first control unit 246A and the second control unit 246B of each FC system 200 control the operation of the FC system 200 under the control of the integrated ECU 100.

For example, when the flow control unit 102 increases the flow rate of the oxidant gas supplied to each FC stack 210 during flow control, it also increases the flow rate of the fuel gas supplied to each FC stack 210 of the first FC system 200A, which is a degraded fuel cell system, compared to the flow rate before the cell voltage was degraded. With this flow control, the degraded first FC stack 210A increases the flow rates of the oxidant gas and fuel gas, so that blockage of the gas flow path caused by condensed water can be eliminated. As a result, blockages in each gas flow path can be eliminated, and an effective attempt can be made to restore the cell voltage.

For example, when the cell voltage sensor 201 detects that the cell voltage of the cell structure of the first FC stack 210A, which is a degraded fuel cell stack, has risen to a predetermined cell voltage or higher due to an increase in the flow rate of the oxidant gas and/or fuel gas, the flow rate control unit 102 controls to cancel the increase in the flow rate of the oxidant gas and/or fuel gas, and controls each FC system 200 to generate power in the power generation state before the cell voltage drop was detected. With this flow rate control, when the cell voltage drop of the first FC stack 210A is resolved, the gas flow rate is quickly reduced to the state before the drop. As a result, waste of fuel gas can be prevented.

For example, if the cell voltage sensor 201 detects that the cell voltage of the cell structure of the first FC stack 210A, which is a degraded fuel cell stack, does not rise above a predetermined cell voltage, the output control unit 106 performs control to limit the output of the first FC stack 210A to a predetermined value or less, and also performs output complement control to increase the output of the FC stack 210B of the second FC system 200B, which performs transient response power generation, compared to the output before the output limit. With this type of output complement control, the output reduction of the first FC system 200A can be stored in the second FC system 200B. Therefore, even if the output of the first FC stack 210A decreases, the fuel cell system can continue to operate.

For example, if the cell voltage sensor detects that the cell voltage of the cell structure of the first FC stack 210A, which is a degraded fuel cell stack, continues to decrease even after the output limit is imposed, the output control unit 106 performs control to stop power generation by the first FC stack 210A, and also performs output complement control to increase the output of the second FC stack 210B of the second FC system 200B, which performs transient response power generation, compared to the output at the time of the output limit. This output complement control allows the fuel cell system to continue operating even if the output of the first FC stack 210A is stopped. Furthermore, the output complement control makes it possible to perform various recovery operations for the first FC stack 210A while maintaining operation of the fuel cell system.

For example, when switching the first FC stack 210 from transient response power generation to stable output power generation, the air supply control unit 107 can control the air supply means to supply a flow rate of oxidant gas and/or fuel gas that can compensate for the difference in the amount of power generated by stable output power generation before and after switching the power generation state with transient response power generation.

According to the embodiment described above, each FC system 200 is equipped with a cell voltage sensor 201 and a control unit 246. Therefore, the FC system 200A having the degraded fuel cell stack 210A and the other FC system 200B can be controlled independently.

According to the embodiment described above, when the fuel cell system is restarted at a temperature where liquid water freezes, such as below freezing, it determines whether the stored liquid water in the storage section 91 of the gas-liquid separator is frozen, and if it is determined that the stored liquid water is frozen, it performs a thawing process (step S103). Therefore, when restarting a fuel cell system that has been stopped due to low temperatures, such as in cold regions, even if liquid water is frozen in the gas-liquid separator, the thawing process allows for smooth startup. Furthermore, the water volume acquisition means acquires the amount of stored liquid water in the storage section 91, and the output of the fuel cell stack is limited based on the acquired amount of stored liquid water and the specified amount of water stored in the gas-liquid separator, so that when used in a sub-freezing environment, it is possible to recover from a drop in cell voltage while achieving both power generation stability and suppression of fuel cell deterioration.

According to the embodiment described above, the control unit performs a process to calculate the storage capacity of the liquid water generated after the fuel cell system is started in the gas-liquid separator based on the amount of frozen stored liquid water and the liquid water storage upper limit value of the gas-liquid separator, and the control unit limits the output of the fuel cell stack so that the time it takes for the amount of liquid water generated by the output of the FC stacks 210A and 210B to reach the storage capacity is longer than the time required for the thawing process of the frozen stored liquid water. Therefore, the fuel cell system can start the output of the fuel cell stack in parallel with the thawing process of the frozen stored liquid water. Furthermore, even if the thawing process and the output of the fuel cell stack are performed in parallel, it is possible to prevent liquid water from accumulating in excess of the upper limit value in the storage section 91 of the gas-liquid separator. Therefore, it is possible to recover from a drop in cell voltage while achieving both power generation stability and suppression of fuel cell deterioration.

According to the embodiment described above, the acquisition means calculates and acquires the amount of stored liquid water based on the temperature and humidity information of the fuel cell stack when the fuel cell system was last stopped and the volume information of the anode off-gas circulating through the flow passage, so that the amount of stored liquid water can be calculated quickly and appropriate fuel cell stack restriction processing can be started in a short time. In addition, because the amount of stored liquid water is calculated based on the previous operating results, it is possible to calculate an amount of water that is close to the actual amount of stored liquid water.

According to the embodiment described above, the amount of stored liquid water can be calculated based on the amount of water produced relative to the valve opening interval in the liquid water discharge section that discharges liquid water during the previous operation of the fuel cell system, so the amount of stored liquid water can be calculated quickly and appropriate fuel cell stack restriction processing can be started in a short time. In addition, because the amount of stored liquid water is calculated based on the previous operating results, it is possible to calculate an amount of water that is close to the actual amount of stored liquid water.

According to the embodiment described above, if the cell voltage drop does not recover even after flow control by the flow control unit 102, further cell voltage drop is avoided by limiting only the output taken from the degraded fuel cell stack 210A. This makes it possible to minimize the output drop of the entire system.

The above describes the form for carrying out the present invention using an embodiment, but the present invention is not limited to such an embodiment, and various modifications and substitutions can be made without departing from the spirit of the present invention.

In the above embodiment, an example with multiple FC systems and an example with multiple FC stacks in an FC system have been described, but the above system can also be applied to a single FC system with a single FC stack.

93...exhaust port (gas exhaust section), 98...liquid water exhaust port (liquid water exhaust section), 100...general ECU, 106...output control section, 107...air supply control section (air supply control means), 200A, 200B...FC system (fuel cell system), 201...cell voltage sensor, 210...FC stack, 220, 232...gas-liquid separator (gas-liquid separation section)

Claims (7)

a fuel cell stack including a plurality of cell structures each including a pair of electrodes sandwiching an electrolyte membrane therebetween, the cell structures being stacked together and supplied with an oxidant gas and a fuel gas to generate electricity;
a flow passage for supplying an anode gas to the fuel cell stack and for circulating an anode off-gas discharged from the fuel cell stack;
a gas-liquid separation section provided in the flow passage, which separates liquid water contained in the anode off-gas discharged from the fuel cell stack, discharges the anode off-gas from a gas discharge section, and discharges the liquid water from a liquid water discharge section;
a water amount acquiring means for acquiring the amount of liquid water stored in the gas-liquid separation section;
a control unit that performs a freezing determination process to determine whether the stored liquid water is in a frozen state or a non-frozen state,
the control unit, when determining that the stored liquid water is frozen by the freezing determination process at the time of startup, starts a thawing process of the frozen stored liquid water;
The control unit limits the output of the fuel cell stack at the time of startup based on the amount of frozen liquid water in the gas-liquid separation unit obtained by the water amount acquisition means and a predetermined amount of water stored in the gas-liquid separation unit. the control unit performs a process of calculating a storage capacity of the liquid water generated after startup of the fuel cell system in the gas-liquid separation unit based on the amount of frozen stored liquid water and a liquid water storage upper limit value of the gas-liquid separation unit;
2. The fuel cell system according to claim 1, wherein the control unit limits the output of the fuel cell stack so that the time required for the amount of liquid water generated by the output of the fuel cell stack to reach the storage capacity is longer than the time required for the thawing process of the frozen stored liquid water. The fuel cell system according to claim 1 or 2, wherein the water volume acquisition means calculates the volume of the stored liquid water based on temperature and humidity information of the fuel cell stack when the fuel cell system was last stopped and volume information of the anode off-gas flowing through the flow passage. The fuel cell system according to claim 1 or 2, wherein the water volume acquisition means calculates the volume of the stored liquid water based on the volume of water generated relative to the valve opening interval of a liquid water discharge section that discharges the liquid water during the previous operation of the fuel cell system. A plurality of the fuel cell stacks are provided,
the control unit controls one of the plurality of fuel cell stacks, the one having an electrode in a relatively deteriorated state, to perform stable output power generation, and controls the other of the fuel cell stacks, the other having an electrode in a relatively less deteriorated state, to perform transient response power generation;
2. The fuel cell system of claim 1, wherein when the control unit determines through the freezing determination process that the stored liquid water in the gas-liquid separation unit connected to the other fuel cell stack has frozen, the control unit controls the other fuel cell stack to perform stable output power generation, the one fuel cell stack to perform transient response power generation, and the one fuel cell stack to compensate for the limited amount of output from the other fuel cell stack. a fuel cell system comprising: a fuel cell stack constructed by stacking a plurality of cell structures, each having a pair of electrodes disposed across an electrolyte membrane, and which generates electricity when an oxidant gas and a fuel gas are supplied thereto; a flow passage which supplies an anode gas to the fuel cell stack and distributes an anode off-gas discharged from the fuel cell stack; a gas-liquid separation section which is provided in the flow passage and separates liquid water contained in the anode off-gas discharged from the fuel cell stack, discharges the anode off-gas from a gas discharge section, and discharges the liquid water from a liquid water discharge section; and a water amount acquisition means which acquires the amount of liquid water stored in the gas-liquid separation section;
A control unit that performs a freezing determination process to determine whether the stored liquid water is frozen or not.
the control unit, when determining that the stored liquid water is frozen by the freezing determination process at the time of startup, starts a thawing process of the frozen stored liquid water;
A control method for a fuel cell system in which the control unit performs control to limit the output of the fuel cell stack based on the amount of frozen liquid water in the gas-liquid separation unit obtained by the water amount acquisition means and a predetermined amount of water stored in the gas-liquid separation unit at the time of startup. On the computer,
obtaining a result of a freezing determination process for determining whether or not the stored liquid water in a gas-liquid separation unit of a fuel cell system mounted on an electrically operated electric device;
A thawing process of the frozen stored liquid water is started,
limiting the output of a fuel cell stack of the fuel cell system based on the amount of stored liquid water frozen in the gas-liquid separation unit and the amount of generated water generated after startup;
program.

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