Fuel cell system

Abstract

To provide a fuel cell system that can improve the speed of emitting fuel gas.SOLUTION: A fuel cell system includes a fuel cell, an oxidant gas supply pipe, a fuel gas supply pipe, a coupling pipe, a voltage sensor, and a control unit. The coupling pipe connects the oxidant gas supply pipe and the fuel gas supply pipe. A coupling valve is disposed in the coupling pipe. The voltage sensor measures the voltage of the fuel cell. The opening and closing of the coupling valve is controlled by the control unit. The control unit stores in advance a first threshold and a second threshold of the voltage of the fuel cell.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] Various technologies have been proposed for fuel cells (FCs). In Patent Document 1, a fuel cell system that discharges anode gas from the fuel cell system by supplying an inert gas is disclosed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the prior art, since the working time for connecting a cylinder for supplying an inert gas to the fuel cell system is long, the time from when a moving body such as a vehicle equipped with the fuel cell system is stored until it is shipped out becomes long.

[0005] The present disclosure has been made in view of the above circumstances, and the main object thereof is to provide a fuel cell system capable of improving the rate of discharging fuel gas.

Means for Solving the Problems

[0006] In the present disclosure, a fuel cell system having the following features is provided. A fuel cell system comprising a fuel cell, an oxidizer gas supply pipe, a fuel gas supply pipe, a connecting pipe, a voltage sensor, and a control unit, wherein the connecting pipe connects the oxidizer gas supply pipe and the fuel gas supply pipe, a connecting valve is provided in the connecting pipe, the voltage sensor measures the voltage of the fuel cell, the control unit controls the opening and closing of the connecting valve, the control unit stores a first threshold and a second threshold for the voltage of the fuel cell in advance, and when the fuel cell stops, the control unit performs a charge decharging process of the fuel cell. When the control unit is started, it supplies oxidizing gas to the cathode of the fuel cell and closes the connecting valve. When the voltage of the fuel cell drops to the first threshold, the control unit stops supplying the oxidizing gas to the cathode of the fuel cell. When the voltage of the fuel cell drops to the first threshold, the control unit opens the connecting valve to supply the oxidizing gas to the anode of the fuel cell. When the voltage of the fuel cell drops to the second threshold, the control unit closes the connecting valve.

[0007] This disclosure provides a fuel cell system having the following features. A fuel cell system comprising a fuel cell and a fuel gas supply pipe, wherein the fuel gas supply pipe has a connection port to which a cylinder for supplying inert gas can be connected.

[0008] In this disclosure, the fuel gas supply piping may have a connection port to which a cylinder for supplying inert gas can be connected. [Effects of the Invention]

[0009] The fuel cell system of this disclosure can improve the rate at which fuel gas is discharged. [Brief explanation of the drawing]

[0010] [Figure 1] This is a system configuration diagram showing an example of a fuel cell system in this disclosure. [Figure 2]This flowchart shows an example of voltage control performed by the fuel cell system of this disclosure. [Figure 3] This diagram illustrates the relationship between the state of the fuel cell, the gases present in the fuel gas system, the gases present in the anode and cathode, and the voltage of the fuel cell. [Modes for carrying out the invention]

[0011] This disclosure provides a fuel cell system having the following features. A fuel cell system comprising a fuel cell, an oxidizer gas supply pipe, a fuel gas supply pipe, a connecting pipe, a voltage sensor, and a control unit, wherein the connecting pipe connects the oxidizer gas supply pipe and the fuel gas supply pipe, a connecting valve is provided in the connecting pipe, the voltage sensor measures the voltage of the fuel cell, the control unit controls the opening and closing of the connecting valve, the control unit stores a first threshold and a second threshold for the voltage of the fuel cell in advance, and when the fuel cell stops, the control unit performs a charge decharging process of the fuel cell. When the control unit is started, it supplies oxidizing gas to the cathode of the fuel cell and closes the connecting valve. When the voltage of the fuel cell drops to the first threshold, the control unit stops supplying the oxidizing gas to the cathode of the fuel cell. When the voltage of the fuel cell drops to the first threshold, the control unit opens the connecting valve to supply the oxidizing gas to the anode of the fuel cell. When the voltage of the fuel cell drops to the second threshold, the control unit closes the connecting valve.

[0012] (First Embodiment) The fuel cell system of the first embodiment of the present disclosure comprises a fuel cell, an oxidizer gas supply pipe, a fuel gas supply pipe, a connecting pipe, a voltage sensor, and a control unit. The fuel cell system of the present disclosure may also include an oxidizer gas system, a fuel gas system, and a cooling system. The fuel cell system of this disclosure may be used mounted on a mobile body such as a vehicle. Alternatively, the fuel cell system of this disclosure may be used mounted on a generator that supplies power to an external source. The vehicle may be a fuel cell vehicle, etc. Other mobile bodies include, for example, railways, ships, and aircraft. Furthermore, the fuel cell system of this disclosure may be used mounted on a mobile body such as a vehicle that can also run on the power of a secondary battery. The mobile body may be equipped with the fuel cell system of this disclosure. The mobile body may have drive units such as a motor, inverter, and hybrid control system. The hybrid control system may be capable of driving the mobile body using both the output of the fuel cell and the power of the secondary battery.

[0013] A fuel cell may consist of only one single cell, or it may be a fuel cell stack (sometimes referred to as an FC stack, stack, etc.) which is a stack of multiple single cells. In this disclosure, both a single cell and a fuel cell stack may be referred to as a fuel cell. The number of stacked single cells is not particularly limited and may range from 2 to several hundred, for example.

[0014] A single cell of a fuel cell typically comprises a membrane electrode gas diffusion layer assembly. The membrane electrode gas diffusion layer assembly comprises, in this order, an anode gas diffusion layer, an anode catalyst layer, an electrolyte membrane, a cathode catalyst layer, and a cathode gas diffusion layer.

[0015] The cathode (oxidizing electrode) includes a cathode catalyst layer and a cathode-side gas diffusion layer. The anode (fuel electrode) includes an anode catalyst layer and an anode-side gas diffusion layer. The cathode catalyst layer and the anode catalyst layer are collectively referred to as the catalyst layer. The catalyst layer may comprise, for example, a catalytic metal that promotes electrochemical reactions, a proton-conducting electrolyte, and an electronically conductive support. Examples of catalyst metals that can be used include platinum (Pt), and alloys made of Pt and other metals (for example, Pt alloys mixed with cobalt and nickel). As the electrolyte, a fluororesin or the like may be used. As the fluororesin, for example, Nafion solution or the like may be used. The above catalyst metal is supported on a carrier, and in each catalyst layer, the carrier supporting the catalyst metal (catalyst-supported carrier) and the electrolyte may be mixed. Examples of the carrier for supporting the catalyst metal include carbon materials such as commercially available carbon.

[0016] The cathode-side gas diffusion layer and the anode-side gas diffusion layer are collectively referred to as the gas diffusion layer. The gas diffusion layer may be a conductive member having gas permeability or the like. Examples of the conductive member include carbon porous bodies such as carbon cloth and carbon paper, and metal porous bodies such as metal mesh and foamed metal.

[0017] The electrolyte membrane may be a solid polymer electrolyte membrane. Examples of the solid polymer electrolyte membrane include fluorine-based electrolyte membranes such as thin films of perfluorosulfonic acid containing water, and hydrocarbon-based electrolyte membranes. As the electrolyte membrane, for example, a Nafion membrane (manufactured by DuPont) or the like may be used.

[0018] The single cell may include two separators that sandwich both sides of the membrane electrode gas diffusion layer assembly as needed. One of the two separators is the anode-side separator, and the other is the cathode-side separator. In the present disclosure, the anode-side separator and the cathode-side separator are collectively referred to as the separator. The separator may have holes that constitute a manifold such as supply holes and discharge holes for allowing fluids such as reaction gas and cooling medium to flow in the stacking direction of the single cell. As the cooling medium, cooling water such as a mixed solution of ethylene glycol and water can be used to prevent freezing at low temperatures. Also, air for cooling can be used as the cooling medium. Examples of the supply holes include a fuel gas supply hole, an oxidant gas supply hole, and a cooling medium supply hole. Examples of exhaust ports include fuel gas exhaust ports, oxidizer gas exhaust ports, and cooling medium exhaust ports. The separator may have a reaction gas channel on the side in contact with the gas diffusion layer. Alternatively, the separator may have a cooling medium channel on the side opposite to the side in contact with the gas diffusion layer to maintain a constant temperature in the fuel cell. The separator may be a gas-impermeable conductive material. Examples of conductive materials include dense carbon, which is compressed to be gas-impermeable, and press-formed metal plates (e.g., iron, aluminum, and stainless steel). The separator may also have a current-collecting function.

[0019] The fuel cell stack may have manifolds such as an inlet manifold through which each supply port is connected, and an outlet manifold through which each discharge port is connected. Inlet manifolds include anode inlet manifolds, cathode inlet manifolds, and cooling medium inlet manifolds. Outlet manifolds include anode outlet manifolds, cathode outlet manifolds, and cooling medium outlet manifolds.

[0020] In this disclosure, the fuel gas and the oxidizer gas are collectively referred to as the reaction gas. The reaction gas supplied to the anode is the fuel gas (sometimes referred to as the anode gas), and the reaction gas supplied to the cathode is the oxidizer gas (sometimes referred to as the cathode gas). The fuel gas is mainly a gas containing hydrogen, but may also be hydrogen. The oxidizer gas is a gas containing oxygen, and may also be oxygen, air, dry air, etc.

[0021] The fuel cell system may also include an oxidizer gas system. The oxidizer gas system supplies oxidizer gas to the fuel cell. The oxidizer gas system may include an oxidizer gas supply unit, oxidizer gas supply piping, oxidizer off-gas discharge piping, bypass piping, etc.

[0022] The oxidizer gas supply unit may be an air compressor or the like. The air compressor is electrically connected to the control unit, and the rotational speed of its rotor is controlled according to a control signal from the control unit. The air compressor may be located in the oxidizer gas supply piping.

[0023] The oxidizer gas supply piping connects the outside of the fuel cell system to the cathode inlet of the fuel cell. The oxidizer gas supply piping enables the supply of oxidizer gas from the oxidizer gas supply section to the cathode of the fuel cell. The cathode inlet may be an oxidizer gas supply port, a cathode inlet manifold, or the like. An oxidizer gas inlet sealing valve may be located downstream of the oxidizer gas supply section in the oxidizer gas supply piping. The oxidizer gas inlet sealing valve is electrically connected to the control unit, and the control unit opens the oxidizer gas inlet sealing valve to supply oxidizer gas to the cathode of the fuel cell. The flow rate of oxidizer gas supplied to the cathode may also be adjusted by adjusting the opening degree of the oxidizer gas inlet sealing valve.

[0024] The oxidizer off-gas exhaust piping connects the cathode outlet of the fuel cell to the outside of the fuel cell system. The oxidizer off-gas exhaust piping allows the oxidizer off-gas, which is the oxidizer gas emitted from the cathode of the fuel cell, to be discharged to the outside of the fuel cell system. The cathode outlet may be an oxidizer gas discharge port, a cathode outlet manifold, or the like. A pressure regulating valve may be installed in the oxidizer off-gas exhaust piping. The pressure regulating valve is electrically connected to the control unit, and when the control unit opens the pressure regulating valve, the reacted oxidant gas, or oxidant off-gas, is discharged to the outside of the fuel cell system through the oxidant off-gas discharge pipe. The pressure of the oxidant gas supplied to the cathode (cathode pressure) may also be adjusted by adjusting the opening degree of the pressure regulating valve. The oxidant off-gas may have the same components as the oxidant gas, or it may be oxygen, air, dry air, etc., or it may contain water vapor, etc.

[0025] The bypass piping connects the oxidizer gas supply piping and the oxidizer off-gas discharge piping, bypassing the fuel cell. The bypass piping branches off from the oxidizer gas supply piping at a branching point downstream of the oxidizer gas supply section, bypasses the fuel cell, and merges with the oxidizer off-gas discharge piping at a confluence point downstream of the pressure regulating valve of the oxidizer off-gas discharge piping. Bypass valves may be installed in the bypass piping. The bypass valve may be a valve with an adjustable opening degree, or it may be a three-way valve for oxidizer gas. In the case of a three-way valve for oxidizer gas, it may be installed at the branching point of the oxidizer gas supply piping, which is the uppermost point of the bypass piping, and it also serves as an oxidizer gas inlet sealing valve. The bypass valve is electrically connected to the control unit, and when the control unit opens the bypass valve, at least a portion of the oxidizer gas can be supplied to the oxidizer off-gas discharge pipe, bypassing the fuel cell. If the bypass valve is a three-way valve for oxidizer gas, when it is not necessary to supply oxidizer gas to the fuel cell, the control unit can close the valve on the downstream side of the bypass valve to the oxidizer gas supply pipe and open the valve on the bypass pipe side, so that the flow of oxidizer gas goes from the oxidizer gas supply pipe to the bypass pipe, thereby supplying the entire amount of oxidizer gas to the oxidizer off-gas discharge pipe.

[0026] The oxidizer gas system may include a cooler (intercooler) downstream of the oxidizer gas supply section of the oxidizer gas supply piping. The cooler may be located downstream of the oxidizer gas supply section of the oxidizer gas supply piping and upstream of the branching point with the bypass piping. A cooler may perform its cooling function by circulating the cooling medium of the cooling system inside and outside the cooler.

[0027] The oxidizing gas system may include a humidifier downstream of the oxidizing gas supply section of the oxidizing gas supply piping. The humidifier may be located downstream of the oxidizing gas supply section of the oxidizing gas supply piping and downstream of the branching point with the bypass piping. The humidifier may be positioned across the oxidizer gas supply piping and the oxidizer off-gas discharge piping.

[0028] A fuel cell system may also be equipped with a fuel gas system. The fuel gas system supplies fuel gas to the fuel cell. The fuel gas system may include a fuel gas supply unit, fuel gas supply piping, fuel off-gas discharge piping, circulation piping, ejectors, etc. Examples of fuel gas supply units include fuel tanks, specifically liquid hydrogen tanks and compressed hydrogen tanks. The fuel gas supply piping connects the fuel gas supply unit to the anode inlet of the fuel cell. The fuel gas supply piping enables the supply of hydrogen-containing fuel gas to the anode of the fuel cell. The anode inlet may be a fuel gas supply port, an anode inlet manifold, or the like. The fuel off-gas exhaust piping connects the anode outlet of the fuel cell to the outside of the fuel cell system. The anode outlet may be a fuel gas exhaust port, an anode outlet manifold, or the like. The fuel off-gas may include fuel gas that has passed through the anode unreacted, and water generated at the cathode that has reached the anode. The fuel off-gas may also include corrosive substances generated in the catalyst layer and electrolyte membrane, and oxidizing gases that may be supplied to the anode during scavenging. The circulation piping branches off from the fuel off-gas discharge piping at its branching point and merges with the fuel gas supply piping at its junction point, circulating the fuel off-gas as circulating gas within the fuel gas system. The circulation piping may include a circulation pump that circulates the circulating gas within the fuel gas system. An anode gas-liquid separator and an exhaust drain valve may be located at the branching point of the fuel off-gas exhaust piping. The exhaust drain valve is electrically connected to the control unit, and its opening and closing are controlled by the control unit.

[0029] The fuel gas supply piping of the fuel cell system in the first embodiment may have a connection port to which a cylinder for supplying inert gas can be connected. In this disclosure, the inert gas may be nitrogen gas, argon gas, etc. The cylinder may be a nitrogen cylinder, an argon gas cylinder, etc. The connection port is not particularly limited as long as it is a component that can connect the fuel gas supply piping and the cylinder. A tube for supplying inert gas may be connected to the connection port, and the fuel gas supply piping and the cylinder may be connected via the tube. The tube may be equipped with an inert gas injection device and a regulator. The inert gas injection device may be equipped with a valve that controls the on / off switching of the inert gas injection.

[0030] Downstream of the fuel gas supply section of the fuel gas supply piping, a fuel gas inlet sealing valve, a connection port, a connection to the connecting piping, a regulator, an injector, an ejector, etc., may be arranged in this order. The connection port may be located downstream of the connection to the connecting piping. The ejector may be placed at the junction of the fuel gas supply piping. The fuel gas inlet sealing valve is electrically connected to the control unit, and the control unit opens the fuel gas inlet sealing valve to supply fuel gas to the anode of the fuel cell. The flow rate of fuel gas supplied to the anode may also be adjusted by adjusting the opening degree of the fuel gas inlet sealing valve. The fuel gas inlet sealing valve may also be a linear solenoid valve or the like.

[0031] A fuel cell system may be equipped with a cooling system. The cooling system regulates the temperature of the fuel cell. The cooling system may include piping for the cooling medium. The cooling medium piping allows the cooling medium to circulate inside and outside the fuel cell. The cooling medium piping communicates with the cooling medium supply port and cooling medium discharge port provided in the fuel cell, enabling the cooling medium to circulate inside and outside the fuel cell. A cooling medium supply unit may be provided in the cooling medium piping. The cooling medium supply unit is electrically connected to the control unit. The cooling medium supply unit is driven according to a control signal from the control unit. The control unit controls the flow rate of the cooling medium supplied from the cooling medium supply unit to the fuel cell. This controls the temperature of the fuel cell. The cooling medium supply unit may be, for example, a cooling water pump. The cooling medium piping may be equipped with a radiator to dissipate the heat from the cooling medium. The cooling medium piping may be equipped with a reserve tank for storing the cooling medium.

[0032] A fuel cell system may also be equipped with a battery. The battery (secondary battery) can be any type that is capable of charging and discharging, such as conventionally known secondary batteries like 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 in the vehicle, such as a household power supply. The secondary battery may also be charged by the output of a fuel cell. The charging and discharging of the secondary battery may be controlled by a control unit.

[0033] The voltage sensor measures the voltage of the fuel cell. The voltage sensor is electrically connected to the control unit. The control unit detects the voltage of the fuel cell obtained by the voltage sensor.

[0034] The connecting piping connects the oxidizer gas supply piping and the fuel gas supply piping. A connecting valve is installed in the connecting piping. The connecting valve is electrically connected to the control unit. The control unit controls the opening and closing of the connecting valve. By opening the connecting valve, oxidizer gas can be supplied from the oxidizer gas system to the fuel gas system.

[0035] Physically, the control unit comprises, 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) primarily used as various work areas for control processing, and an input / output interface. Alternatively, the control unit may also be a control device such as a Power Control Unit (PCU) or an Electronic Control Unit (ECU). The control unit may be electrically connected to an ignition switch, which may be mounted on the vehicle. The control unit may also be able to operate using an external power source even when the ignition switch is turned off.

[0036] The control unit pre-stores a first threshold and a second threshold for the fuel cell voltage. The first and second thresholds may be the same value or they may be different values. When the fuel cell is shut down and the control unit initiates the decharge process, the control unit supplies oxidizing gas to the fuel cell cathode and closes the coupling valve. When the fuel cell voltage drops to a first threshold, the control unit stops supplying oxidant gas to the fuel cell cathode. When the fuel cell voltage drops to a first threshold, the control unit opens the coupling valve to supply oxidant gas to the fuel cell anode. When the fuel cell voltage drops to the second threshold, the control unit closes the coupling valve. In the first embodiment of this disclosure, by installing connecting piping, it is possible to introduce oxidizer gas into the fuel gas system, thereby improving the rate at which fuel gas is discharged from the fuel cell system. As a result, in the first embodiment of this disclosure, although the degradation of the fuel cell will progress slightly, nitrogen cylinders will not be required, and the time from when a mobile vehicle or other vehicle equipped with the fuel cell system enters the depot until when it leaves the depot can be shortened.

[0037] (Second Embodiment) A fuel cell system according to a second embodiment of the present disclosure comprises a fuel cell and a fuel gas supply piping. The fuel gas supply piping has a connection port to which a cylinder for supplying inert gas can be connected. The fuel cell system of the second embodiment of this disclosure may have the same configuration as the fuel cell system of the first embodiment, except that it has a connection port as an essential component. The cylinder and connection port may be the same as those described in the first embodiment. Furthermore, the fuel cell system of the first embodiment and the fuel cell system of the second embodiment may be combined. In conventional technology, time is required to connect the nitrogen cylinder to the FC system. In the second embodiment of this disclosure, the work time can be reduced by providing a port for connecting a cylinder for supplying inert gas to the fuel gas system.

[0038] Figure 1 is a system configuration diagram showing an example of the fuel cell system of this disclosure. For convenience, the cooling system is omitted in Figure 1. The fuel cell system 100 comprises a fuel cell 10, a fuel gas system, an oxidizer gas system, connecting piping 40, a voltage sensor 50, a control unit 60, and a connection port 70. The fuel gas system includes a fuel gas supply unit 20, fuel gas supply piping 21, fuel off-gas discharge piping 22, circulation piping 23, fuel gas inlet sealing valve 24, anode gas-liquid separator 25, exhaust drain valve 26, and circulation pump 27. The oxidizer gas system includes an oxidizer gas supply unit 30, an oxidizer gas supply pipe 31, an oxidizer off-gas discharge pipe 32, a bypass pipe 33, an oxidizer gas inlet sealing valve 34, a pressure regulating valve 35, and a bypass valve 36. The connecting pipe 40 connects the fuel gas supply pipe 21 and the oxidizer gas supply pipe 31. A connecting valve 41 is located in the connecting pipe 40.

[0039] In mobile vehicles equipped with fuel cell systems, such as fuel cell vehicles, it is anticipated that the stack will be lowered and fuel cell system components removed at service centers. During this removal, it is necessary to (1) discharge the fuel gas, such as hydrogen, from the fuel cell system and (2) reduce the remaining voltage of the stack to make it ready for work. Decharging is a pre-treatment for safely removing components from the fuel cell system and includes the processes described in (1) and (2) above. The following is an example using air as the oxidizing gas and hydrogen as the fuel gas.

[0040] Figure 2 is a flowchart showing an example of voltage control performed by the fuel cell system of this disclosure. Figure 3 illustrates the relationship between the state of the fuel cell, the gas present in the fuel gas system, the gas present in the anode, the gas present in the cathode, and the voltage of the fuel cell. The charge decharge flow of the stack shown in Figure 2 and the hydrogen emission conditions shown in Figure 3 are explained below as examples. From the voltage behavior from (i) to (iii) in the standing state (hydrogen present at both electrodes), (ii) with the cathode replaced with air, and (iii) with the anode replaced with air, it is possible to confirm (1) the emission of hydrogen from within the fuel cell system to the outside of the system and (2) the voltage drop.

[0041] Step (a) When the fuel cell is shut down, the control unit starts the charge decharging process. At the start of the decharge process, hydrogen and air are not being supplied to the fuel cell, and the fuel cell is being left idle. When hydrogen and air are not supplied to the fuel cell, the gas near the electrodes permeates the electrolyte membrane over time. Then, the hydrogen that has moved from the anode to the cathode reacts with the oxygen present in the cathode. Therefore, as shown in Figure 3, at the start of the decharge process, the cathode contains hydrogen that has moved from the anode and nitrogen from the air that remains in the cathode as a result of the reaction between hydrogen and oxygen. The anode contains hydrogen and nitrogen that has moved from the cathode. Hydrogen that was supplied to the fuel cell until the fuel cell's power generation was stopped is present in the piping of the fuel gas system and in the anode inlet manifold of the fuel cell. The control unit may start the charge decharging process when it receives a start signal. The start signal may be input by an operator from outside the fuel cell system, for example.

[0042] Step (b) During the decharge process, the control unit opens the oxidizer gas inlet sealing valve, the pressure regulating valve, and the bypass valve, controls the air compressor to supply air to the fuel cell cathode, and closes the coupling valve. In step (b), the hydrogen and nitrogen in the cathode are replaced with air. When the air supply is started, the hydrogen in the anode reacts with the supplied air. As a result, in step (b), the fuel cell voltage rises from 0V to the first open-circuit voltage. The first open-circuit voltage may be the open-circuit voltage (OCV) multiplied by a value between 0.9 and 1.0.

[0043] Step (c) Subsequently, in step (c), the hydrogen present in the anode is consumed by reacting with the air present in the cathode, and the anode is filled with nitrogen. In step (c), the fuel cell voltage decreases from the first open-circuit voltage to the first threshold V1. The first voltage V1 is lower than the first open-circuit voltage. The first voltage V1 is the voltage value obtained by experiment or simulation when no fuel gas is present near the electrodes of the fuel cell. The first voltage V1 may also be the value obtained by multiplying the number of single cells in the fuel cell by 0.1V. The control unit determines whether the fuel cell voltage obtained from the voltage sensor is below the first threshold V1.

[0044] Step (d) When the fuel cell voltage drops to the first threshold V1, the control unit closes the oxidizer gas inlet sealing valve, the pressure regulating valve, and the bypass valve, stopping the supply of air to the fuel cell cathode. When the fuel cell voltage drops to the first threshold V1, the control unit opens the connecting valve to supply air to the fuel cell anode. In step (d), the hydrogen present in the fuel gas system piping is replaced by air. The hydrogen that was present in the fuel gas system piping moves to the anode. The hydrogen that has moved to the anode reacts with the air at the cathode. Therefore, in step (d), the fuel cell voltage rises from the first threshold V1 to the second open-circuit voltage. The second open-circuit voltage may be the open-circuit voltage multiplied by a value between 0.9 and 1.0. On the other hand, if the fuel cell voltage obtained from the voltage sensor exceeds the first threshold V1, the control unit continues to supply air to the fuel cell cathode.

[0045] Step (e) After step (d), in step (e), the hydrogen present at the anode is consumed by reacting with the air present at the cathode, and the cathode is filled with air that has moved in from the fuel gas system piping. In step (e), the fuel cell voltage drops from the second open-circuit voltage to the second threshold V2. The control unit determines whether the fuel cell voltage obtained from the voltage sensor is below the second threshold V2. The second voltage V2 is lower than the second open-circuit voltage. The second voltage V2 is the voltage at which components can be safely removed from the fuel cell system. The second voltage V2 may be the voltage value obtained when the fuel gas in the anode of the fuel cell is consumed, which has been determined in advance by experiment or simulation. The second voltage V2 may be lower than the first voltage V1, or it may be equal to the first voltage V1. The second threshold voltage may be 25V. When the fuel cell voltage drops to the second threshold, the control unit closes the coupling valve and stops the gas supply to the fuel cell. This allows the fuel gas system and oxidizer gas system of the fuel cell system to be filled with air, completing the charge decharging process. Meanwhile, if the fuel cell voltage obtained from the voltage sensor exceeds the second threshold V2, the control unit continues to supply air to the fuel cell anode.

[0046] Step (d') If the fuel cell system has a connection port, the control unit may perform the following processing in step (d): When the fuel cell voltage drops to a first threshold V1, the control unit connects a nitrogen cylinder to the connection port instead of opening the coupling valve, supplying nitrogen from the nitrogen cylinder to the fuel cell anode. In step (d'), hydrogen present in the fuel gas system piping is replaced with nitrogen.

[0047] Step (e') After step (d'), in step (e'), the hydrogen present at the anode is consumed by reacting with the air present at the cathode, and the area is filled with nitrogen that has moved in from the fuel gas system piping.

[0048] The voltage change of the fuel cell in the fuel cell system of this disclosure allows us to determine the point at which fuel gas discharge is complete in the fuel cell system. Therefore, the time required to discharge fuel gas from the fuel cell system can be shortened. According to the fuel cell system of this disclosure, components can be safely removed from the fuel cell system. Furthermore, since the completion of fuel gas emission can be determined from the change in the fuel cell voltage, component removal from the fuel cell system can be started earlier compared to cases where the completion of fuel gas emission cannot be determined. [Explanation of Symbols]

[0049] 10 fuel cell 20 Fuel Gas Supply Unit 21 Fuel gas supply piping 22 Fuel off-gas discharge piping 23 Circulation piping 24 Fuel gas inlet sealing valve 25 Anode gas-liquid separator 26 Exhaust and drain valve 27 Circulation pump 30 Oxidizer gas supply unit 31 Oxidizer gas supply piping 32 Oxidizer off-gas discharge piping 33 Bypass piping 34 Oxidizer gas inlet sealing valve 35 Pressure Regulating Valve 36 Bypass valve 40 Connecting piping 41. Connecting valve 50 Voltage Sensors 60 Control Unit 70 connection ports 100 Fuel Cell Systems

Claims

1. A fuel cell system, The fuel cell system comprises a fuel cell, an oxidizer gas supply pipe, a fuel gas supply pipe, a connecting pipe, a voltage sensor, and a control unit. The aforementioned connecting pipe connects the oxidizer gas supply pipe and the fuel gas supply pipe. A connecting valve is provided in the aforementioned connecting piping. The voltage sensor measures the voltage of the fuel cell. The control unit controls the opening and closing of the connecting valve. The control unit stores in advance the first and second threshold values ​​of the voltage of the fuel cell. When the control unit starts the decharge process of the fuel cell when the fuel cell is stopped, the control unit supplies oxidizing gas to the cathode of the fuel cell and closes the connecting valve. When the voltage of the fuel cell drops to the first threshold, the control unit stops supplying the oxidizer gas to the cathode of the fuel cell, and when the voltage of the fuel cell drops to the first threshold, the control unit opens the connecting valve to supply the oxidizer gas to the anode of the fuel cell. A fuel cell system characterized in that the control unit closes the coupling valve when the voltage of the fuel cell drops to the second threshold.

2. The fuel cell system according to claim 1, wherein the fuel gas supply piping has a connection port to which a cylinder for supplying inert gas can be connected.

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