Fuel cell system

Abstract

This invention provides a fuel cell system capable of suppressing freezing blockage of the cathode channel. [Solution] A fuel cell system comprising: a fuel cell; a gas supply system for supplying a reaction gas to the fuel cell; a cooling system for circulating cooling water through the fuel cell to cool it; an ambient temperature sensor for measuring ambient temperature; a cooling water temperature sensor for measuring the temperature of the cooling water; and a control unit, wherein when the control unit receives a request to stop power generation of the fuel cell, if the value of the ambient temperature sensor is lower than a first threshold T1, it drives the cooling system to perform a cooling process to cool the fuel cell until the value of the temperature sensor is higher than 0°C and less than or equal to a threshold B; and after the cooling process is completed, the control unit executes a shutdown of the fuel cell system.

Description

Technical Field

[0001] The present disclosure relates to a fuel cell system.

Background Art

[0002] Various technologies have been proposed regarding a fuel cell (FC) system as disclosed in Patent Document 1.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a fuel cell system, in a low-temperature environment such as outdoors in a cold region, moisture in the system may freeze when the system stops. Since the freezing of moisture in the fuel cell system can cause various problems, it is desirable to suppress it. Patent Document 1 discloses a fuel cell system that pumps the fuel gas discharged from the fuel cell with a fuel gas pump after the operation of the fuel cell stops, and cools the fuel cell with cooling water after the operation of the fuel cell stops to lower the fuel cell temperature below the fuel gas pump temperature. Patent Document 1 describes that it is possible to suppress dew condensation of moisture in the fuel gas pump and prevent freezing of the fuel gas pump after the operation of the fuel cell stops. However, in the fuel cell system of Patent Document 1, generation of a temperature gradient in the fuel cell cannot be prevented. As a result, due to the difference in saturated vapor pressure, water in the fuel cell moves to the cathode flow path (oxidant gas flow path), and the cathode flow path may be frozen and blocked at the next startup. The freezing and blockage of the cathode flow path hinders the diffusion of the oxidant gas, which causes poor power generation and also leads to an increase in the exhaust hydrogen concentration due to hydrogen gas (pumping hydrogen) generated at the cathode.

[0005] This disclosure is made in view of the above circumstances and primarily aims to provide a fuel cell system capable of suppressing freezing blockage of the cathode flow path. [Means for solving the problem]

[0006] In other words, this disclosure includes the following aspects: <1> A fuel cell system, The aforementioned fuel cell system Fuel cells and A gas supply system for supplying reaction gas to the fuel cell, A cooling system that cools the aforementioned fuel cell by circulating cooling water, An ambient temperature sensor that measures the outside temperature, A cooling water temperature sensor for measuring the temperature of the cooling water, It comprises a control unit and, When the control unit receives a request to stop power generation from the fuel cell, if the value of the ambient temperature sensor is lower than the first threshold T1, it drives the cooling system and performs a cooling process to cool the fuel cell until the value of the cooling water temperature sensor is higher than 0°C and less than or equal to the threshold B. The control unit executes a shutdown of the fuel cell system after the cooling process is completed. Fuel cell system.

[0007] <2> The cooling water temperature sensor measures the fuel cell outlet temperature of the cooling water. <1> The fuel cell system described above.

[0008] <3> The control unit drives the gas supply system to perform a scavenging process to discharge any stagnant water inside the fuel cell to the outside of the fuel cell, and then performs the cooling process. <1> or <2> The fuel cell system described above.

[0009] <4> A fuel cell system, The aforementioned fuel cell system Fuel cells and A gas supply system for supplying reaction gas to the fuel cell, A cooling system that cools the aforementioned fuel cell by circulating cooling water, An ambient temperature sensor that measures the outside temperature, It comprises a control unit and, The control unit is capable of performing control to drive the gas supply system to perform a scavenging process that discharges stagnant water accumulated inside the fuel cell to the outside of the fuel cell. The control unit is capable of performing high-potential avoidance control, which controls the voltage of the fuel cell to be below a predetermined high-potential avoidance voltage. When the control unit receives a request to stop power generation of the fuel cell, if the value of the ambient temperature sensor is greater than or equal to a first threshold T1 and less than or equal to a second threshold T2, the control unit performs the scavenging process in the high potential avoidance control with the high potential avoidance voltage set to a predetermined second voltage V2 which is higher than the predetermined first voltage V1 under normal conditions. The control unit executes the scavenging process and then shuts down the fuel cell system. Fuel cell system. [Effects of the Invention]

[0010] The fuel cell system of this disclosure can suppress freezing blockage of the cathode channel. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 is a system configuration diagram showing an example of the fuel cell system of this disclosure. [Figure 2] Figure 2 is an illustrative diagram showing an example of the temperature distribution in a fuel cell that has been left standing after power generation has stopped and scavenging has been completed. [Figure 3] Figure 3 is a flowchart showing an example of the control of the fuel cell system (1) of this disclosure. [Figure 4] Figure 4 is a flowchart showing another example of the control of the fuel cell system (1) of this disclosure. [Figure 5] Figure 5 is a flowchart showing an example of the control of the fuel cell system (2) of this disclosure. [Figure 6]FIG. 6 is an image diagram showing an example of the power generation distribution of the current during scavenging of the fuel cell and the water content in the voids of the cathode (Ca) catalyst layer.

Embodiments for Carrying Out the Invention

[0012] Hereinafter, embodiments according to the present disclosure will be described. Matters other than those specifically mentioned in this specification and necessary for the implementation of the present disclosure (for example, the general configuration and manufacturing process of a fuel cell system that does not characterize the present disclosure) can be grasped as design matters of those skilled in the art based on the prior art in the relevant field. The present disclosure can be implemented based on the content disclosed in this specification and the common technical knowledge in the relevant field. Also, the dimensional relationships (length, width, thickness, etc.) in the drawings do not reflect the actual dimensional relationships.

[0013] In the present disclosure, there is provided a fuel cell system, the fuel cell system including a fuel cell, a gas supply system for supplying reaction gas to the fuel cell, a cooling system for circulating and cooling cooling water through the fuel cell, an outside air temperature sensor for measuring the outside air temperature, a cooling water temperature sensor for measuring the temperature of the cooling water, and a control unit. When the control unit receives a power generation stop request for the fuel cell, if the value of the outside air temperature sensor is lower than a first threshold value T1, the control unit drives the cooling system to perform a cooling process for cooling the fuel cell until the value of the cooling water temperature sensor is higher than 0°C and not more than a threshold value B. After the cooling process is completed, the control unit executes the stop of the fuel cell system.

[0014] Furthermore, the present disclosure provides a fuel cell system (2) comprising: a fuel cell; a gas supply system for supplying reaction gas to the fuel cell; a cooling system for circulating cooling water through the fuel cell to cool it; an ambient temperature sensor for measuring ambient temperature; and a control unit, wherein the control unit is capable of performing control for driving the gas supply system to perform scavenging to discharge stagnant water accumulated inside the fuel cell to the outside of the fuel cell; the control unit is capable of performing high potential avoidance control to control the voltage of the fuel cell to be below a predetermined high potential avoidance voltage; and when the control unit receives a request to stop power generation of the fuel cell, if the value of the ambient temperature sensor is above a first threshold T1 and below a second threshold T2, the control unit performs the scavenging in the high potential avoidance control with the value of the high potential avoidance voltage set to a predetermined second voltage V2 which is higher than a predetermined first voltage V1 under normal conditions; and after performing the scavenging, the control unit performs the shutdown of the fuel cell system.

[0015] The fuel cell system of this disclosure may be used mounted on a mobile body such as a vehicle. Furthermore, the fuel cell system of this disclosure may be used mounted on a stationary power generation system such as a generator that supplies power to the outside of the fuel cell system. Also, the fuel cell system of this disclosure may be used mounted on a mobile body such as a vehicle that can run on power from a secondary battery. Here, "vehicle" may refer to a fuel cell vehicle or the like. Examples of other mobile entities include trains, ships, and aircraft. The mobile entity may have a drive unit such as a motor, inverter, or hybrid control system. The hybrid control system may be capable of propelling the mobile entity by using both the output of the fuel cell and the power of a secondary battery.

[0016] Figure 1 is a system configuration diagram showing an example of a fuel cell system (fuel cell system (1) and fuel cell system (2)) of the present disclosure. The fuel cell system 100 shown in Figure 1 comprises a fuel cell 10, a cooling system 50, a control unit 60, an oxidizer gas system 70, a fuel gas system 80, and an ambient temperature sensor 90. In this disclosure, the gas supply system for supplying reaction gas to a fuel cell consists of an oxidizer gas system that supplies an oxidizer gas (cathode gas) to the cathode of the fuel cell and a fuel gas system that supplies a fuel gas (anode gas) to the anode of the fuel cell. The oxidizer gas is a gas containing oxygen, and may be oxygen, air, etc. The fuel gas is a gas mainly containing hydrogen, and may be hydrogen.

[0017] The fuel cell 10 generates electricity through the reaction of hydrogen and oxygen. The fuel cell may be a single cell or a fuel cell stack consisting of multiple single cells stacked on top of each other. The number of single cells stacked in the fuel cell stack is not particularly limited and may range from 2 to several hundred. The power generation section of the fuel cell may be a membrane electrode assembly (MEA) including an electrolyte membrane and two electrodes. The electrolyte membrane may be a solid polymer electrolyte membrane. Examples of solid polymer electrolyte membranes include fluorine-based electrolyte membranes such as a thin film of perfluorosulfonic acid containing water, and hydrocarbon-based electrolyte membranes. The electrolyte membrane may also be, for example, a Nafion membrane (manufactured by DuPont). The two electrodes are an anode (fuel electrode) and a cathode (oxidizer electrode). The electrodes are equipped with at least a catalyst layer. The catalyst layer contains a catalyst, which may include a catalytic metal that promotes an electrochemical reaction, a proton-conducting electrolyte, and an electron-conducting support. Examples of catalyst metals that can be used include platinum (Pt) and alloys of Pt with other metals (for example, Pt alloys mixed with cobalt and nickel). The catalyst metal used as the cathode catalyst and the catalyst metal used as the anode catalyst may be the same or different. The electrolyte constituting the catalyst may be a fluororesin or the like. For example, a Nafion solution may be used as the fluororesin. The catalyst metal is supported on a support. Examples of the support include commercially available carbon materials such as carbon. In each catalyst layer, the catalyst metal is supported on the support (catalyst-supporting support) and the electrolyte may be mixed. The electrodes may include a gas diffusion layer as needed, in which case the power generation unit becomes a membrane electrode gas diffusion layer assembly (MEGA). The gas diffusion layer may be a conductive material having pores. Examples of conductive materials include carbon porous materials such as carbon cloth and carbon paper, and metal porous materials such as metal mesh and foamed metal. A fuel cell single cell may include a separator. The separator collects the current generated by power generation and functions as a partition. In a fuel cell, the separator is usually arranged on both sides of the stacking direction of the power generation unit so that a pair of separators sandwiches the power generation unit. One of the separators is the anode separator and the other is the cathode separator. The anode separator may have a groove on the side facing the power generation section that serves as a fuel gas passage. The cathode separator may have a groove on the side facing the power generation section that serves as an oxidant gas passage. Each separator may have a groove on the side opposite to the power generation section that serves as a cooling water passage. The separator may have holes that constitute a manifold, such as supply holes and discharge holes, for circulating the fluid in the stacking direction of the cells. The separator may be, for example, dense carbon that has been compressed to be gas-impermeable, or press-formed metal (for example, iron, titanium, and stainless steel). The fuel cell stack may have current collector plates, pressure plates, etc., at its ends in the stacking direction. The single cell may include an insulating resin frame positioned on the outer (outer) side in the planar direction of the film electrode assembly between the anode separator and the cathode separator.

[0018] The cooling system 50 comprises a cooling water pump 51, a radiator 52, a radiator fan 53, a cooling water temperature sensor 54, and a cooling water passage 55. The cooling system 50 supplies cooling water to the fuel cell 10 as a cooling medium. The cooling water may be water, ethylene glycol, or a mixture thereof. The cooling water passage 55 is a passage for circulating the cooling water inside and outside the fuel cell 10, and is provided with a cooling water pump 51 and a radiator 52. The cooling water pump 51 can pressurize and pump the cooling water, and the fuel cell 10 can be cooled by circulating the cooling water with the cooling water pump 51. Starting and stopping the cooling water pump 51 is performed based on the control of the control unit 60. The radiator 52 is provided with a radiator fan 53, which can promote heat dissipation from the radiator 52. A cooling water temperature sensor 54 for measuring the cooling water temperature is provided on the cooling water passage 55. The cooling water temperature sensor 54 is a means for measuring the fuel cell outlet temperature of the cooling water, and the measured cooling water temperature data is sent to the control unit 60.

[0019] The oxidizer gas system 70 includes an air compressor 71, an air supply passage 72, an air exhaust passage 73, a bypass passage 74, an intercooler 75, a fuel cell inlet valve 76, a pressure regulating valve 77, and a control valve 78. In this embodiment, air is used as the oxidizer gas. The air compressor 71 compresses air and supplies it to the fuel cell 10 through the air supply passage 72. An intercooler 75 and a fuel cell inlet valve 76 are provided on the air supply passage 72. The intercooler 75 performs heat exchange so that the air temperature, which has risen due to compression by the air compressor 71, is approximately the same as the temperature of the fuel cell 10. The fuel cell inlet valve 76 is a valve for turning the supply of air to the fuel cell 10 on and off. A thermometer T for measuring the temperature of the air flowing in the air supply passage 72 and a pressure gauge P for measuring the pressure of the air may be provided near the outlet of the intercooler 75. The air exhaust passage 73 guides the air discharged from the fuel cell 10 to the outside of the fuel cell and discharges it. A pressure regulating valve 77 is provided on the air exhaust passage 73. The pressure regulating valve 77 adjusts the pressure of the air inside the fuel cell 10. Water generated by the power generation of the fuel cell 10 is also discharged into the air exhaust passage 73. The bypass passage 74 connects the upstream portion of the air supply passage 72 above the fuel cell inlet valve 76 with the downstream portion of the air exhaust passage 73 above the pressure regulating valve 77, and is a passage for bypassing air to the air exhaust passage 73 without passing through the fuel cell 10. The bypass passage 74 is equipped with a control valve 78, and the flow rate of air flowing through the bypass passage 74 is adjusted by opening and closing the control valve 78 or by adjusting its opening degree. A pipe connected to the discharge valve 89 of the fuel gas system 80 (described later) joins the air exhaust passage 73, and the liquid component discharged from the discharge valve 89 via the gas-liquid separator 88 is also discharged.

[0020] The fuel gas system 80 includes a fuel gas tank 81, a fuel gas supply passage 82, a fuel gas exhaust passage 83, a fuel gas circulation passage 84, an injector 85, a linear solenoid valve 86, an ejector 87, a gas-liquid separator 88, and a discharge valve 89. The fuel gas tank 81 is a fuel gas supply source and is composed of a high-pressure hydrogen tank or a hydrogen storage alloy, etc., and stores high-pressure hydrogen gas. It may also consist of a reformer that generates reformed gas and a tank that stores the reformed gas at high pressure. The fuel gas tank 81 may be equipped with a pressure gauge. The fuel gas supply passage 82 supplies fuel gas from the fuel gas tank 81 to the fuel cell 10. An injector 85, a linear solenoid valve 86, and an ejector 87 are provided on the fuel gas supply passage 82. The injector 85 and the linear solenoid valve 86 control the amount of fuel gas supplied from the fuel gas tank 81 to the fuel cell 10. The ejector 87 is located between the injector 85 and the linear solenoid valve 86 and the fuel cell 10, and is provided at the connection point between the fuel gas supply passage 82 and the fuel gas circulation passage 84. The ejector 87 uses the dynamic pressure effect of the fuel gas supplied from the injector 85 and the linear solenoid valve 86 to draw up the fuel exhaust gas flowing through the fuel gas circulation passage 84 and recirculate it back to the fuel cell 10. The fuel gas exhaust passage 83 discharges fuel exhaust gas from the fuel cell 10. A gas-liquid separator 88 is provided above the fuel gas exhaust passage 83. Since the fuel exhaust gas contains gaseous components such as fuel gas not consumed by the fuel cell 10 and liquid components such as water, the gas-liquid separator 88 separates the gas and liquid components. As previously described, the separated gaseous components are supplied back to the fuel cell 10 via the fuel gas circulation passage 84 and ejector 87. Meanwhile, the separated liquid components are stored in the gas-liquid separator 88 as needed and discharged outside the fuel cell system via the discharge valve 89.

[0021] The fuel cell system 100 is equipped with an ambient temperature sensor 90. The ambient temperature sensor 90 functions as a temperature measuring means for measuring the ambient air temperature. For example, a thermocouple can be used as the ambient temperature sensor 90. The ambient air temperature data measured by the ambient temperature sensor 90 is sent to the control unit 60.

[0022] The control unit 60 controls the operation of the fuel cell system 100, including the fuel cell 10, the gas supply system (oxidizer gas system 70, fuel gas system 80), the cooling system 50, etc. The control unit also performs, for example, power generation control of the fuel cell 10 and control of other auxiliary equipment. For power generation control of the fuel cell, for example, based on information from various sensors inside and outside the fuel cell system 100, it controls the operation of various actuators within the system (e.g., air compressor 71, intercooler 73, various valves and valves, etc.) so that the fuel cell 10 generates the necessary power. Physically, the control unit includes, for example, a processing unit such as a CPU (Central Processing Unit), a ROM (Read-Only Memory) for storing control programs and control data processed by the CPU, a storage device such as a RAM (Random Access Memory) used primarily as various work areas for control processing, and an input / output interface. It may also be an ECU (Electronic Control Unit).

[0023] The fuel cell system of this disclosure may include, although not shown in the figures, a voltage sensor for measuring the voltage output from the fuel cell 10, a current sensor for measuring the current of the fuel cell 10, and a converter such as a DC / DC converter for controlling the output voltage of the fuel cell 10. Furthermore, although not shown in the figures, the fuel cell system of this disclosure may also include a secondary battery. The secondary battery can be any type that is rechargeable and dischargeable, and examples include conventionally known secondary batteries such as nickel-metal hydride secondary batteries and lithium-ion secondary batteries. The secondary battery may also include an energy storage element such as an electric double-layer capacitor. Multiple secondary batteries may be connected in series. The secondary battery supplies power to an air compressor or the like. The secondary battery may be rechargeable from an external power source of the fuel cell system, such as a household power supply, or it may be charged by the output of the fuel cell. The charging and discharging of the secondary battery may be controlled by a control unit.

[0024] The fuel cell systems (1) and (2) will be described below. [Fuel cell system (1)] Figure 2 is an illustrative diagram showing an example of the temperature distribution in a fuel cell that has been left idle after power generation has stopped and scavenging has been performed. When a fuel cell is left idle after power generation has stopped and scavenging has been performed to discharge any remaining water inside, the temperature of the fuel cell decreases from the outside inward, resulting in the temperature distribution shown in Figure 2. When such a temperature distribution is formed, water moves from the higher temperature areas to the lower temperature areas within the fuel cell due to differences in saturated water vapor volume. In other words, a relatively large amount of residual water moves into the cathode channel on the cathode side where water is generated during power generation. As a result, in low-temperature environments, the cathode channel may freeze and become blocked by the freezing of residual water before the next start-up of the fuel cell.

[0025] Therefore, in the fuel cell system (1) of this disclosure, when the ambient temperature is low and there is a possibility that it will fall below freezing while the fuel cell system is stopped, that is, when the ambient temperature is lower than a first threshold T1, the cooling system is activated to rapidly cool the fuel cell, and the fuel cell system is stopped after the temperature of the cooling water is higher than 0°C and below a threshold B. Here, the first threshold T1 is the upper limit of ambient temperature at which, while the fuel cell system is shut down, the ambient temperature is expected to fall below freezing point, causing freezing blockage of the cathode channel, and at which point the fuel cell can be cooled by the cooling water to a temperature range higher than 0°C and below threshold B. Threshold B is the upper limit of the cooling water temperature at which no water movement occurs within the fuel cell after the fuel cell system is shut down, or the upper limit of the cooling water temperature at which water movement does not occur to the extent that it would block the cathode channel. These first thresholds T1 and B can be obtained in advance through experiments or simulations. The first threshold T1 may be set to, for example, 5°C. Since the cooling water temperature can be considered as the temperature inside the fuel cell, if the fuel cell is cooled until the cooling water temperature is higher than 0°C and below threshold B, water movement within the fuel cell can be suppressed. That is, water movement toward the cathode channel can be suppressed, and freezing blockage of the cathode channel can be suppressed. As a result, at the next start-up, power generation on the cathode side can proceed normally, and the exhaust hydrogen concentration can also be kept low.

[0026] In the fuel cell system (1), the cooling water temperature sensor for measuring the cooling water temperature may be installed near the fuel cell outlet on the cooling water channel 55 (see Figure 1) to measure the cooling water temperature at the fuel cell outlet, from the viewpoint of high accuracy in estimating the temperature inside the fuel cell. The installation location of the cooling water temperature sensor is not limited as long as it is possible to estimate the temperature inside the fuel cell.

[0027] In the fuel cell system (1), when the control unit 60 receives a request to stop power generation of the fuel cell 10, it determines whether the value of the ambient temperature sensor 90 is lower than a first threshold T1. If the control unit 60 determines that the value of the ambient temperature sensor 90 is lower than the first threshold T1, it drives the cooling system 50 to rapidly cool the fuel cell 10. Then, if the control unit 60 determines that the value of the cooling water temperature sensor 54 is higher than 0°C and below threshold B, it executes a shutdown of the fuel cell system 100. A request to stop power generation of the fuel cell is, for example, when an instruction to shut down the fuel cell system 100 is input, specifically when the start switch is turned off.

[0028] In this embodiment, the cooling process is performed based on whether or not the ambient temperature is lower than a first threshold T1. However, in the case of a mobile vehicle equipped with a fuel cell system (1), the cooling process may be performed based on a determination of the change in ambient temperature during the trip from the start to the end of operation. In this case, the determination may be based not only on the trip in the current operation, but also on the change in ambient temperature during multiple trips, including the current trip. Furthermore, the feasibility of performing the cooling process may be determined based on the location information and date of the fuel cell system.

[0029] When a request is received to stop power generation from the fuel cell 10, the control unit 60 may normally drive the gas supply system (oxidizer gas system 70 and / or fuel gas system 80) to perform a scavenging process to discharge any stagnant water remaining inside the fuel cell 10 to the outside of the fuel cell 10. The scavenging process involves injecting at least one of the oxidizer gas and fuel gas into the fuel cell 10 as a scavenging gas to scavenge the gas flow path inside the fuel cell. The scavenging gas may be either the oxidizer gas or the fuel gas, both, or only the oxidizer gas. The timing of the scavenging process is not particularly limited, but the cooling process may be performed after the scavenging process. Performing the cooling process after the scavenging process is expected to further enhance the effectiveness of the cooling process.

[0030] Next, an example of the operation of the fuel cell system (1) will be explained using the flowchart shown in Figure 3. Figure 3 is a flowchart showing an example of the control of the fuel cell system (1) of this disclosure. Upon receiving a power generation stop request (step S100), the control unit drives the gas supply system to perform scavenging (step S110). After scavenging, the control unit determines whether the value of the ambient temperature sensor is lower than the first threshold T1, that is, whether the ambient temperature falls below freezing point during the shutdown of the fuel cell system, and whether the system is in a low-temperature environment where freezing blockage of the cathode flow path is expected to occur (step S120). If it is determined that the system is not in a low-temperature environment (step S120: NO), the control unit proceeds to shut down the fuel cell system (step S150). If it is determined that the system is in a low-temperature environment (step S120: YES), the control unit drives the cooling system, specifically the cooling pump, and performs a cooling process (rapid cooling) of the fuel cell (step S130). The control unit then obtains the cooling water temperature from the cooling water temperature sensor and determines whether the cooling water temperature is higher than 0°C and within the range of threshold B, that is, whether the fuel cell has been cooled to the target temperature (step S140). If it is determined that the fuel cell has not been cooled, the control unit continues the cooling process (step S140: NO). If it is determined that the fuel cell has been cooled (step S140: YES), the control unit proceeds to shut down the fuel cell system (step S150).

[0031] When the fuel cell system (1) is mounted on a moving object such as a vehicle, the control unit 60 may, in cooperation with the car navigation system and using location information, execute the cooling process only in response to a request to stop power generation at a pre-registered designated location such as a home parking lot, i.e., at a location where a long period of shutdown of the fuel cell system is expected. This is because executing the cooling process for short-term shutdowns may require warming up during restart, potentially reducing the starting efficiency of the fuel cell system. An example of the specific operation of a fuel cell system in cooperation with a car navigation system will be explained using the flowchart shown in Figure 4. Figure 4 is a flowchart showing another example of the control of the fuel cell system (1) of this disclosure. Upon receiving a power generation stop request (step S300), the control unit drives the gas supply system to perform scavenging (step S310). After scavenging, the control unit determines whether the value of the outside temperature sensor is lower than the first threshold T1, and at the same time acquires car navigation information to determine whether the parking position of the mobile vehicle equipped with the fuel cell system is a pre-registered designated location such as a home parking lot (step S320). If it is determined that the environment is not low temperature and / or the parking position is not a designated location (step S320: NO), the control unit proceeds to stop the fuel cell system (step S350). If it is determined that the environment is low temperature and the parking position is a designated location (step S320: YES), the control unit drives the cooling system to perform a cooling process (rapid cooling) of the fuel cell (step S330). The control unit then determines whether the cooling water temperature is higher than 0°C and within the range of threshold B, that is, whether the fuel cell has been cooled to the target temperature (step S340). If it determines that the fuel cell has not been cooled, the control unit continues the cooling process (step S340: NO). If it determines that the fuel cell has been cooled (step S340: YES), the control unit proceeds to shut down the fuel cell system (step S350).

[0032] [Fuel cell system (2)] The fuel cell system (2) of this disclosure is primarily intended to suppress freezing blockage of the cathode flow path due to the freezing of residual water when, although rapid cooling of the fuel cell by a cooling system like that of fuel cell system (1) is difficult at present because the ambient temperature is not low, there is a possibility that the ambient temperature will fall below freezing by the time the fuel cell system is started again, that is, when the ambient temperature is above the first threshold T1 and below the second threshold T2.

[0033] If the output voltage of a fuel cell rises excessively, the deterioration of constituent materials such as catalysts may progress. Therefore, a high-potential avoidance voltage is set in advance as an acceptable voltage, and high-potential avoidance control is implemented to control the output voltage of the fuel cell so that it does not exceed this high-potential avoidance voltage. For example, when the power generation of a fuel cell is stopped, the supply of oxidizer gas and fuel gas to the fuel cell is stopped, but oxidizer gas and fuel gas remain inside the fuel cell. If the power generation of the fuel cell is stopped while residual gas is present, the cathode potential can become extremely high. Therefore, high-potential avoidance control is implemented to suppress an excessive rise in the cathode potential by sweeping a small current from the fuel cell and generating a small amount of power. When stopping power generation in a fuel cell, a scavenging process is also performed to discharge any stagnant water inside the fuel cell to the outside. When scavenging is performed by driving the gas supply system, particularly the oxidizer gas system, the power generation distribution within the cell surface in the above-mentioned minute power generation with high-potential avoidance control is biased towards the cathode outlet side. This is because the cathode inlet side tends to dry out due to the scavenging process, causing power generation to concentrate on the cathode outlet side. As a result, the amount of residual water after scavenging increases on the cathode outlet side. Consequently, in low-temperature environments, freeze blockage is likely to occur in the flow path on the cathode outlet side.

[0034] Therefore, in the fuel cell system (2) of this disclosure, when a power generation stop request is received, if the ambient temperature is above a first threshold T1 and below a second threshold T2, the high potential avoidance control raises the value of the high potential avoidance voltage to a predetermined second voltage V2, which is higher than the predetermined first voltage V1 under normal conditions, and performs scavenging. By raising the high potential avoidance voltage from the first voltage V1 to the second voltage V2, it is possible to lower the sweep current of the fuel cell, thereby suppressing the amount of power generated. Figure 6 is an illustrative diagram showing an example of the power generation distribution of the current during scavenging of the fuel cell and the water content of the voids in the cathode (Ca) catalyst layer. As shown in Figure 6, as the sweep current during scavenging is reduced, the water content of the voids on the oxidant gas outlet side of the cathode catalyst layer decreases. Thus, according to the fuel cell system (2) of this disclosure, by reducing the amount of water generated during scavenging, especially the amount of water generated on the cathode outlet side, it is possible to suppress freezing and closure of the cathode flow path.

[0035] Here, the first threshold T1 is the same as T1 described in fuel cell system (1). The second threshold T2 is higher than the first threshold T1 and is the upper limit of ambient temperature at which freezing and blockage of the cathode flow path are expected to occur when the ambient temperature falls below freezing during shutdown of the fuel cell system. The first voltage V1 is the value of the high potential avoidance voltage under normal conditions. "Under normal conditions" here refers to the case when the ambient temperature is lower than the first threshold T1 or higher than the second threshold T2 when a power generation shutdown request is received. The first voltage V1 is usually set to a value lower than the open-circuit voltage of the fuel cell (e.g., 0.8V). The second voltage V2 is a voltage that allows for a reduction in the amount of water produced by a lower sweep current (second current value) compared to the normal high potential avoidance control (first voltage V1, first current value) as described above. For example, it can be set to a voltage at which a sweep current of 5A is possible or a voltage at which a sweep current of 0A is possible. These first threshold T1, second threshold T2, first voltage V1, and second voltage V2 can be obtained in advance through experiments, simulations, etc.

[0036] In the fuel cell system (2), the control unit 60 can perform high-potential avoidance control, which involves driving a converter or the like based on information from sensors such as a voltage sensor and a current sensor, and controlling the voltage of the fuel cell 10 to be below the high-potential avoidance voltage. When the control unit 60 receives a request to stop power generation from the fuel cell 10, it determines whether the value of the ambient temperature sensor 90 is greater than or equal to a first threshold T1 and less than or equal to a second threshold T2. If it is determined that the value of the ambient temperature sensor 90 is greater than or equal to the first threshold T1 and less than or equal to the second threshold T2, the control unit 60 executes control to change the value of the high potential avoidance voltage from the first voltage V1 to the second voltage V2. Then, it drives the gas supply system to perform scavenging while sweeping with a low current (second current value) corresponding to the second voltage V2. After the scavenging process, the control unit 60 executes a shutdown of the fuel cell system 100. In this embodiment, scavenging is performed with an increased high-potential avoidance voltage based on whether the ambient temperature is above a first threshold T1 and below a second threshold T2. However, in the case of a mobile device equipped with a fuel cell system (2), similar to the fuel cell system (1), the scavenging may be performed based on a determination of the change in ambient temperature during the trip from the start to the end of operation. Alternatively, the feasibility of performing the scavenging may be determined based on the location information and date of the fuel cell system 100. The scavenging process is the same as in fuel cell system (1).

[0037] Next, an example of the operation of the fuel cell system (2) will be explained using the flowchart shown in Figure 5. Figure 5 is a flowchart showing an example of the control of the fuel cell system (2) of this disclosure. Upon receiving a power generation stop request (step S200), the control unit determines whether the value of the ambient temperature sensor is greater than or equal to a first threshold T1 and less than or equal to a second threshold T2, that is, whether the ambient temperature falls below freezing point during the shutdown of the fuel cell system, and whether the system is in a low-temperature environment where freezing and blockage of the cathode flow path is expected to occur (step S210). If it is determined that the system is in a low-temperature environment (step S210: YES), the control unit increases the value of the high-potential avoidance voltage in the high-potential avoidance control from the first voltage V1 to the second voltage V2, and then drives the gas supply system to perform scavenging (step S220). At this time, as the high-potential avoidance voltage increases to the second voltage V2, the sweep current decreases to a second current value (for example, 0A). On the other hand, if it is determined that the environment is not low temperature (step S210: NO), the control unit drives the gas supply system to perform scavenging by keeping the high potential avoidance voltage value in the high potential avoidance control at the state of the first voltage V1 (the current value also remains at the first current value, for example, 20A) (step S230). After the scavenging process, the control unit proceeds to shut down the fuel cell system (step S240). [Explanation of Symbols]

[0038] 10...fuel cell 50...Cooling system 51 ... Cooling water pump 52 ... Radiator 53 ...Radiator fan 54 ... Cooling water temperature sensor 55…Cooling channel 60 ... Control Unit 70... Oxidizing gas system 71 ... Air compressor 72 ... Air supply path 73 ... Air exhaust passage 74 ... Bypass 75...Intercooler 76…Fuel cell inlet valve 77... Pressure regulating valve 78 ... Adjustment valve 80... Fuel gas system 81... Fuel gas tank 82 ... Fuel gas supply lines 83 ... Fuel gas exhaust passage 84 ... Fuel gas circulation path 85... Injector 86... Linear solenoid valve 87... Ejector 88…gas-liquid separator 89 ... Discharge valve 90... Outdoor temperature sensor 100… Fuel cell system P... Pressure sensor T...Temperature sensor

Claims

1. A fuel cell system, The aforementioned fuel cell system Fuel cells and A gas supply system for supplying reaction gas to the fuel cell, A cooling system that cools the aforementioned fuel cell by circulating cooling water, An ambient temperature sensor that measures the outside temperature, A cooling water temperature sensor for measuring the temperature of the cooling water, It comprises a control unit and, When the control unit receives a request to stop power generation from the fuel cell, if the value of the ambient temperature sensor is lower than the first threshold T1, it drives the cooling system and performs a cooling process to cool the fuel cell until the value of the cooling water temperature sensor is higher than 0°C and less than or equal to the threshold B. The control unit executes a shutdown of the fuel cell system after the cooling process is completed. Fuel cell system.

2. The fuel cell system according to claim 1, wherein the cooling water temperature sensor measures the fuel cell outlet temperature of the cooling water.

3. The fuel cell system according to claim 1, wherein the control unit drives the gas supply system to perform a scavenging process to discharge stagnant water accumulated inside the fuel cell to the outside of the fuel cell, and then performs the cooling process.

4. A fuel cell system, The aforementioned fuel cell system Fuel cells and A gas supply system for supplying reaction gas to the fuel cell, A cooling system that cools the aforementioned fuel cell by circulating cooling water, An ambient temperature sensor that measures the outside temperature, It comprises a control unit and, The control unit is capable of performing control to drive the gas supply system to perform a scavenging process that discharges stagnant water accumulated inside the fuel cell to the outside of the fuel cell. The control unit is capable of performing high-potential avoidance control, which controls the voltage of the fuel cell to be below a predetermined high-potential avoidance voltage. When the control unit receives a request to stop power generation of the fuel cell, if the value of the ambient temperature sensor is greater than or equal to a first threshold T1 and less than or equal to a second threshold T2, the control unit performs the scavenging process in the high potential avoidance control with the high potential avoidance voltage set to a predetermined second voltage V2 which is higher than the predetermined first voltage V1 under normal conditions. The control unit executes the scavenging process and then shuts down the fuel cell system. Fuel cell system.

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