Fuel cell system and control method

Abstract

The invention discloses a fuel cell system and a control method. The fuel cell system comprises a fuel cell stack, an air pump, a humidifier, a back pressure valve, a water pump, a radiator, a hydrogen inlet valve group, a check valve and a hydrogen water segregator. The provided system comprises a plurality of humidifying branches, different humidifying modes can be adopted under different conditions, on one hand, water generated by the system can be recycled, the self-humidifying purpose of the fuel cell can be achieved, the running temperature of the fuel cell can be increased, the performance of the fuel cell can be improved, and the service life of the system can be prolonged; the performance of the fuel cell can be changed by only adjusting the opening of the three-way valve and controlling the tail gas reflux quantity, so that the fuel cell reaches the optimal performance state; and on the other hand, different humidifying branches can be selected according to different working conditions, and the system can adapt to operation under multiple working conditions.

Description

Technical Field

[0001] The present invention belongs to the field of fuel cells, and in particular relates to a fuel cell system and a control method. Background Art

[0002] A hydrogen fuel cell is an electrochemical power generation device that uses hydrogen and oxygen as raw materials to undergo an electrochemical reaction to generate water and simultaneously converts chemical energy into electrical energy. It has the advantages of high energy conversion efficiency, environmental friendliness, simple structure, and easy operation.

[0003] PEMFC generally uses perfluorosulfonic acid resin membrane as a proton exchange membrane. Experiments have shown that only under certain humidity conditions can good proton exchange be achieved. At present, it is difficult to achieve self-humidification inside the battery to stabilize the working performance of the fuel cell. Usually, a humidifier is added to the air inlet to increase the humidity of the intake air to ensure the output performance of the fuel cell. At present, membrane tube humidifiers or plate humidifiers are commonly used in fuel cell systems. The water in the air with a large water content in the reaction process is transferred to the new air side in the form of concentration difference to increase the humidity of the new air and ensure the performance output of the fuel cell. However, on the one hand, this method will lead to a complex system structure due to the usually large volume of the humidifier, and the membrane humidifier will increase the gas resistance on the cathode side, increase the power consumption of the air supply air pump or blower on the cathode side, and reduce the system efficiency. On the other hand, it is impossible to respond promptly to changes in the operating conditions and environmental conditions of the stack during operation. Summary of the invention

[0004] In view of the defects of the existing invention technology, the purpose of the present invention is to provide an operation process of a fuel cell system with multiple humidification branches. On the one hand, the liquid water generated by the anode water separation flows back to the cathode humidifier, and the liquid water is vaporized at the high-temperature outlet of the air pump to achieve humidification on the cathode side of the fuel cell, increase the operating temperature of the fuel cell, and thus improve the performance of the fuel cell; on the other hand, it is more adaptable to changes in operating conditions. To achieve the above purpose, the process scheme adopted by the present invention is: a fuel cell system is provided, including a fuel cell stack, an air pump, a humidifier, a water pump, a radiator, and a hydrogen water separator; the air pump, the humidifier, the fuel cell stack, and the hydrogen water separator are connected by pipelines The first humidification branch is formed as follows: the air pump outlet is connected to the gas inlet of the humidifier, the gas outlet of the humidifier is connected to the cathode inlet of the fuel cell, the anode outlet of the fuel cell stack is connected to the air inlet of the hydrogen water separator, and the water outlet of the hydrogen water separator is connected to the liquid inlet of the humidifier; the second humidification branch is formed as follows: the air pump outlet is connected to the gas inlet of the humidifier, the gas outlet of the humidifier is connected to the cathode inlet of the fuel cell stack, the anode outlet of the fuel cell stack is connected to the air inlet of the hydrogen water separator, the water outlet of the hydrogen water separator is connected to the liquid inlet of the humidifier, and the cathode outlet of the fuel cell stack is connected to the air pump inlet through a back pressure valve and a three-way valve.

[0005] The air pump, fuel cell stack, back pressure valve, and three-way valve are connected to form a third humidification branch through a pipeline. The air pump outlet is connected to the cathode inlet of the fuel cell stack, the cathode outlet of the fuel cell stack is connected to the back pressure valve inlet, the back pressure valve outlet is connected to the three-way valve, and the three-way valve is connected to the air pump inlet. The exhaust gas at the cathode outlet of the fuel cell stack is divided into two passages by the three-way valve, one of which is directly discharged into the atmosphere and marked as the first passage, and the other passage is connected to the air pump inlet and marked as the second passage.

[0006] The radiator, water pump and fuel cell stack form a coolant loop, the water pump inlet is connected to the outlet end of the radiator, the water pump outlet is connected to the coolant inlet of the fuel cell stack, and the fuel cell stack coolant outlet is connected to the radiator inlet.

[0007] Based on the above technical solution, preferably, the gas outlet of the hydrogen water separator is connected to the anode inlet of the fuel cell stack through a check valve and a hydrogen inlet valve group to form a hydrogen circulation loop.

[0008] Based on the above technical scheme, preferably, a gas-water separation filter element and a liquid level sensor are provided in the hydrogen water separator, and a drain valve is provided at the water outlet of the hydrogen water separator. The liquid level is monitored by the liquid level sensor, and the outlet drain valve is controlled to discharge the anode water, so that the separated liquid water is discharged from the water outlet to the liquid inlet end of the humidifier through the control of the tail drain valve.

[0009] Based on the above technical solution, preferably, the humidifier includes a humidifier shell and a water-absorbing material located inside the shell, a water dividing tray is provided at the top of the humidifier shell, a drainage chamber and a drain port are provided at the bottom, and a plurality of micropores are evenly distributed on the water dividing tray; liquid water entering the humidifier flows into the micropores of the water dividing tray at the top of the humidifier and flows out into the water-absorbing material, and when the water-absorbing material is saturated with liquid water, it enters the drainage chamber and is discharged through the drain port.

[0010] Based on the above technical solution, preferably, the diameter of the liquid discharge port of the humidifier is about 0.5-1 mm, the water-absorbing material is absorbent cotton or a hydrophilic coating; and the diameter of the evenly distributed micropores in the water distribution plate of the humidifier is 2-5 mm.

[0011] On the other hand, a humidification method for a fuel cell system is provided, using the above-mentioned fuel cell system to perform humidification through the first humidification branch, the second humidification branch or the third humidification branch.

[0012] Based on the above technical scheme, preferably, the specific steps of the first humidification branch include the following: returning the liquid water separated by the hydrogen water separator to the humidifier; during the operation of the fuel cell system, increasing the speed of the air pump, increasing the air supply, and gradually increasing the outlet temperature of the air pump to pass into the humidifier; the liquid water in the humidifier is vaporized to form a low-temperature humidified mixed air that enters the fuel cell stack.

[0013] The specific steps of the third humidification branch are: by controlling the opening of the three-way valve, the air flow of the first passage and the second passage is controlled, and then the flow of the exhaust gas reflux is controlled. After mixing with the fresh air at the cathode inlet, a low-temperature humidified mixed air is formed to enter the fuel cell stack; the specific steps of the second humidification branch include the specific steps of the first humidification branch and the third humidification branch.

[0014] Based on the above technical scheme, preferably, when the first humidification branch is used, the working gauge pressure of the fuel cell stack is controlled to be 30-50kPa, the air humidity entering the cathode inlet of the fuel cell stack is 80%-100%, and the heat dissipation of the radiator is controlled to make the fuel cell coolant inlet temperature 60-70°C, the coolant outlet temperature 65-75°C, the humidification area in the humidifier is 50%-80%, and the anode side pressure of the fuel cell stack is 10-30kPa higher than the cathode side pressure.

[0015] When the third humidification branch is used, the working gauge pressure of the fuel cell stack is controlled to be 10-30kPa, the air humidity entering the cathode inlet of the fuel cell stack is 30%-50%, and the fuel cell coolant inlet temperature is 55-60°C and the coolant outlet temperature is 60-65°C by controlling the heat dissipation of the radiator; the anode side pressure of the fuel cell stack is 10-30kPa higher than the cathode side pressure, and the ratio of the exhaust gas return air flow rate to the fresh air flow rate of the second passage is 1:1~1:3.

[0016] When the second humidification branch is used, the working gauge pressure of the fuel cell stack is increased to 60-100kPa, the air humidity entering the cathode inlet of the fuel cell stack is 60%-80%, and the fuel cell coolant inlet temperature is 75-80°C and the coolant outlet temperature is 80-85°C by controlling the heat dissipation of the radiator. The humidification area in the humidifier is 50%-80%. The anode side pressure of the fuel cell stack is 10-30kPa higher than the cathode side pressure. The exhaust gas return air flow rate of the second passage is 1:1~1:3 to the fresh air flow rate.

[0017] Based on the above technical scheme, preferably, when the operating power of the fuel cell stack is less than 10kW and the ambient temperature is lower than 55°C, the third humidification branch is used; when the operating power of the fuel cell stack is greater than 10kW and the ambient temperature is lower than 40°C, the first humidification branch is used; when the operating power of the fuel cell stack is greater than 10kW and the ambient temperature is 40-55°C, the second humidification branch is used. The system provided in the present application includes multiple humidification branches, which can adopt different humidification methods under different conditions. On the one hand, it can recycle the water generated by itself to achieve the self-humidification purpose of the fuel cell, which can increase the operating temperature of the fuel cell, improve the performance of the fuel cell, and increase the life of the system. On the other hand, it can change the performance of the fuel cell to achieve the best performance state by simply adjusting the opening of the three-way valve to control the exhaust gas reflux volume; on the other hand, different humidification branches can be selected according to different operating conditions to adapt to operation under multiple operating conditions.

[0018] The humidification system provided in the present application can use the first humidification method under low temperature and high power conditions (when the operating power of the fuel cell stack is greater than 10kW and the ambient temperature is lower than 40°C), and use the water generated at the anode to reflux, thereby controlling the performance of the fuel cell stack to reach the optimal state. The process is simple, easy to implement, and the system efficiency is high. When the operating power of the fuel cell stack is greater than 10kW and the ambient temperature is 40-55°C, the second humidification method is used. In a high temperature environment, the back pressure valve is controlled to increase the working pressure of the fuel cell stack to increase the amount of water generated at the anode. As the power of the fuel cell stack increases, the air supply is increased by adjusting the air pump speed, the air pump outlet temperature gradually increases, and the high-temperature air It is passed into the humidifier to vaporize the liquid water in the humidifier to form a low-temperature humidified mixed air that enters the fuel cell. When the amount of water generated at the anode is insufficient to reach the required air humidity, the cathode gas tail gas is refluxed by controlling the opening of the three-way valve on the cathode side to increase the humidity of the cathode air entering the fuel cell stack, thereby controlling the fuel cell stack performance to reach the best state. The process is simple, easy to implement, and the system efficiency is high. Under low power conditions, the anode generates less water, and the third humidification method is used. By controlling the opening of the three-way valve, the reflux amount of the cathode gas is increased, and the humidity of the cathode air entering the fuel cell stack is increased, thereby controlling the fuel cell stack performance to reach the best state. The process is simple, easy to implement, and the system efficiency is high.

[0019] The humidifier used in the system of the present invention can make liquid water evenly distributed in the humidifier through the design of the water distribution plate and the water-absorbing material. The liquid water vaporizes and cools down in the humidifier, reduces the cathode gas temperature, and increases the gas humidity. The use of an optimized humidifier can reduce the air resistance of the humidifier, reduce the energy consumption of the air pump, and prevent the humidifier from being flooded by liquid water. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0021] Figure 1 It is the operating process of humidification on the cathode side of the fuel cell system.

[0022] Figure 2 It is a structural diagram of the cathode humidifier of the fuel cell system. DETAILED DESCRIPTION

[0023] In order to make the technical solutions and advantages of the present invention more clear, the technical solutions in the embodiments of the present invention are clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention: like Figure 1 A fuel cell system shown in the figure includes a fuel cell stack, an air pump, a humidifier, a back pressure valve, a water pump, a radiator, a hydrogen intake valve group, a check valve, and a hydrogen water separator. The air pump inlet is connected to the atmospheric environment, the air pump outlet is connected to the inlet of the humidifier, the humidifier outlet is connected to the cathode inlet of the fuel cell stack, the cathode outlet end of the fuel cell stack is connected to the inlet of the back pressure valve, the back pressure valve outlet is connected to the inlet of the three-way valve, and the three-way valve outlet is connected to the air pump inlet and the atmospheric environment respectively; the water pump inlet is connected to the radiator outlet, the water pump outlet is connected to the coolant inlet of the fuel cell stack, and the coolant outlet of the fuel cell stack is connected to the radiator inlet; the fuel cell anode includes an anode intake inlet, which is connected to the outlet of the hydrogen intake valve group, the intake valve group inlet is connected to the hydrogen source, and the fuel cell stack anode outlet The outlet is connected with the air inlet of the anode hydrogen water separator, the anode hydrogen water separator has an air inlet, an air outlet and a water outlet, the water outlet is located below the air inlet and the air outlet, a gas-water separation filter element and a liquid level sensor are arranged in the anode hydrogen water separator, the filter element is used to separate the water in the gas entering the anode hydrogen water separator to the water outlet, the water outlet is provided with a drain valve, the liquid level sensor is used to determine the liquid level height in the anode hydrogen water separator, and control the water outlet drain valve to discharge the anode water, the water outlet is connected with the liquid inlet of the humidifier, and the water at the water outlet is discharged to the liquid inlet of the cathode humidifier by controlling the drain valve, the air outlet of the anode hydrogen water separator is connected with the reflux port of the hydrogen inlet valve group of the fuel cell stack, so as to form a complete fuel cell system.

[0024] In the fuel cell system, an air pump is used to pump fresh air into the fuel cell stack at a certain flow rate. The air pump outlet is connected to a humidifier. The humidifier includes an air inlet and an outlet and a liquid water inlet and an outlet. The liquid water inlet is connected to the discharge port of the anode hydrogen water separator. The liquid water discharged from the anode water separator enters the humidifier. During the operation of the fuel cell system, as the power of the fuel cell stack increases, the air pump increases the air supply by adjusting the speed. At the same time, the outlet temperature of the air pump gradually increases, and the anode liquid water enters the humidifier, mixes with the high-temperature air at the outlet of the air pump and vaporizes to form a low-temperature humidified mixed air that enters the fuel cell, which can increase the operating temperature of the fuel cell, thereby making the performance of the fuel cell stack reach the optimal state.

[0025] In view of the defects of the existing invention technology, the purpose of the present invention is to provide an optimized fuel cell humidifier, which returns the liquid water generated by the anode water separation to the cathode humidifier, and evenly distributes the liquid water through the humidifier. At the high-temperature outlet of the air pump, the liquid water is vaporized to achieve cooling and humidification of the fuel cell cathode gas, thereby improving the performance of the fuel cell. To achieve the above purpose, the humidifier used in the present invention is: the humidifier includes a humidifier housing, a cathode gas inlet and outlet, a liquid water reflux port, a liquid water drain port and a water-absorbing material. The water-absorbing material used is water-absorbing cotton, which is distributed in a ring shape on the inner surface of the humidifier housing, wherein the liquid inlet reflux port is on the upper part of the water-absorbing cotton. The humidifier mainly returns the liquid water separated by the anode water separator to the humidifier on the cathode side under the action of the pressure difference between the anode and the cathode.

[0026] The liquid flows into the water distribution plate at the top of the humidifier at the liquid inlet. The water distribution plate is distributed with multiple micropores. Liquid water flows out into the water-absorbing material through the micropores of the water distribution plate and is evenly distributed in the water-absorbing material. A liquid water drainage chamber is arranged at the bottom of the humidifier and is connected to the liquid water outlet. When the water-absorbing material is saturated, the excess liquid water flows to the bottom drainage chamber. During the operation of the fuel cell system, the air pump pumps a certain flow of fresh air into the fuel cell stack. As the power of the fuel cell stack increases, the air pump increases the air supply by adjusting the speed. The outlet temperature of the air pump gradually increases, and the high-temperature air is passed into the humidifier to vaporize the liquid water in the humidifier to form a low-temperature humidified mixed air that enters the fuel cell, thereby making the fuel cell stack performance reach the best state. At the same time, the excess liquid water is discharged from the drainage port under the action of air pressure.

[0027] like Figure 2As shown, the water outlet diameter of the humidifier is about 0.5-1mm; the water-absorbing material in the humidifier can be absorbent cotton or a hydrophilic coating. At the liquid inlet of the humidifier, the anode side pressure of the fuel cell system is 10-30kPa higher than the cathode side pressure. The stoichiometric ratio of the cathode gas flow in the humidifier is 1.5-3 times. The diameter of the uniformly distributed micropores in the water distribution plate of the humidifier is 2-5mm.

[0028] Example 1 A 260-cell fuel cell stack is used to provide air to the cathode inlet of the fuel cell through an air pump. The absolute air pressure is about 1.3 bar. When the anode liquid water does not flow back to the cathode side, the fuel cell power is 35kW, the air pump outlet temperature is 70 degrees Celsius, the cathode side gas temperature entering the fuel cell stack is 70°C, the humidity is about 2%, the air flow metering ratio is about 2.5 times, the fuel cell stack coolant outlet temperature is 60°C, the working current is 220A, and the voltage is 159V. When the anode liquid water flows back to the cathode humidifier, the fuel cell power is 40kW, the air pump outlet temperature is 80 degrees Celsius, and the humidification area of ​​the humidifier is about 60%. After passing through the humidifier, the cathode side gas temperature entering the fuel cell stack is 50°C, the humidity is 70%, the air flow metering ratio is about 2 times, the fuel cell stack coolant outlet temperature is 70°C, the working current is 250A, and the voltage is 160V. It can be seen that by adopting the method of anode liquid water reflux, the performance of the fuel cell stack can be significantly improved.

[0029] Example 2 A 110-cell fuel cell stack is used, and air is provided to the cathode inlet of the fuel cell through an air pump. The air flow metering ratio is about 4 times, the air absolute pressure is about 1.15 bar, and the fuel cell stack coolant outlet temperature is about 50°C. The flow of the first passage and the second passage can be controlled by adjusting the three-way valve at the cathode outlet of the fuel cell. When the flow of the second passage is 0, that is, the cathode outlet exhaust gas does not reflux, at this time, the fuel cell operating power is 3kW and the voltage is about 78V. When the flow rate of the first passage and the flow rate of the second passage are controlled to be 1:2, at this time, the fuel cell voltage is about 83V and the power is about 3.3kW. It can be seen that by adopting the cathode exhaust gas reflux, the performance of the fuel cell stack can be significantly improved.

[0030] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A fuel cell system, characterized in that include: Fuel cell stack, air pump, humidifier, water pump, radiator, hydrogen intake valve group, hydrogen water separator; The air pump, humidifier, fuel cell stack, and hydrogen water separator are connected to form a first humidification branch or a second humidification branch through pipelines; the first humidification branch is as follows: the air pump outlet is connected to the humidifier gas inlet, the humidifier gas outlet is connected to the cathode inlet of the fuel cell stack, the fuel cell stack anode outlet is connected to the air inlet of the hydrogen water separator, and the water outlet of the hydrogen water separator is connected to the liquid inlet of the humidifier; the second humidification branch is as follows: the air pump outlet is connected to the humidifier gas inlet, the humidifier gas outlet is connected to the cathode inlet of the fuel cell stack, the fuel cell stack anode outlet is connected to the air inlet of the hydrogen water separator, the water outlet of the hydrogen water separator is connected to the liquid inlet of the humidifier, and the fuel cell stack cathode outlet is connected to the air pump inlet through a back pressure valve and a three-way valve; The air pump, the fuel cell stack, the back pressure valve, and the three-way valve are connected to form a third humidification branch through a pipeline, the air pump outlet is connected to the cathode inlet of the fuel cell stack, the cathode outlet of the fuel cell stack is connected to the back pressure valve inlet, the back pressure valve outlet is connected to the three-way valve, the three-way valve is connected to the air pump inlet, and the exhaust gas at the cathode outlet of the fuel cell stack is divided into two passages by the three-way valve, one of which is directly discharged into the atmosphere and marked as the first passage, and the other passage is connected to the air pump inlet and marked as the second passage; The radiator, water pump and fuel cell stack form a coolant loop, the water pump inlet is connected to the outlet end of the radiator, the water pump outlet is connected to the coolant inlet of the fuel cell stack, and the fuel cell stack coolant outlet is connected to the radiator inlet; The humidifier includes a humidifier housing and a water absorbing material located within the housing.

2. The fuel cell system according to claim 1, characterized in that: The gas outlet of the hydrogen water separator is connected to the anode inlet of the fuel cell stack through a check valve and a hydrogen inlet valve group to form a hydrogen circulation loop.

3. The fuel cell system according to claim 1, characterized in that: The hydrogen water separator is provided with a gas-water separation filter element and a liquid level sensor. The water outlet of the hydrogen water separator is provided with a drain valve. The liquid level is monitored by the liquid level sensor, and the outlet drain valve is controlled to discharge the anode water, so that the separated liquid water is discharged from the water outlet to the liquid inlet end of the humidifier through the control of the tail drain valve.

4. The fuel cell system according to any one of claims 1 to 3, characterized in that: A water distribution tray is arranged at the top of the humidifier shell, and a drainage chamber and a liquid discharge port are arranged at the bottom.

5. The fuel cell system according to claim 4, characterized in that: The water separation plate has multiple micropores evenly distributed thereon; the liquid water entering the humidifier flows into the micropores of the water separation plate at the top of the humidifier and flows out to the water absorbing material; when the water absorbing material is saturated with liquid water, it enters the drainage chamber and is discharged through the drainage port.

6. The fuel cell system according to claim 4, characterized in that: The diameter of the liquid discharge port of the humidifier is 0.5-1mm, and the water-absorbing material is water-absorbing cotton or a hydrophilic coating; the diameter of the evenly distributed micropores of the water distribution plate of the humidifier is 2-5mm.

7. A control method for a fuel cell system, characterized in that: Using the fuel cell system according to any one of claims 1 to 5, humidification is performed through the first humidification branch, the second humidification branch or the third humidification branch.

8. The control method according to claim 7, characterized in that: The humidification step of the first humidification branch includes the following: (1) Return the liquid water separated by the hydrogen water separator to the humidifier; (2) During the operation of the fuel cell system, the speed of the air pump is increased, the air supply is increased, and the outlet temperature of the air pump is gradually increased and passed into the humidifier; (3) The liquid water in the humidifier vaporizes to form low-temperature humidified mixed air that enters the fuel cell stack; The humidification step of the third humidification branch is: by controlling the opening of the three-way valve, the air flow of the first passage and the second passage is controlled, and then the flow of the exhaust gas reflux is controlled, and after being mixed with the fresh air at the cathode inlet, the low-temperature humidified mixed air is formed and enters the fuel cell stack; The specific steps of the second humidification branch include the specific steps of the first humidification branch and the third humidification branch.

9. The control method according to claim 7, characterized in that: When the first humidification branch is used, the working gauge pressure of the fuel cell stack is controlled to be 30-50 kPa, the air humidity entering the cathode inlet of the fuel cell stack is 80%-100%, the fuel cell coolant inlet temperature is 60-70°C, the coolant outlet temperature is 65-75°C, the humidification area in the humidifier is 50%-80%, and the anode side pressure of the fuel cell stack is 10-30 kPa higher than the cathode side pressure; When the third humidification branch is used, the working gauge pressure of the fuel cell stack is controlled to be 10-30 kPa, the air humidity entering the cathode inlet of the fuel cell stack is 30%-50%, the fuel cell coolant inlet temperature is 55-60°C, and the coolant outlet temperature is 60-65°C. The anode side pressure of the fuel cell stack is 10-30 kPa higher than the cathode side pressure. The ratio of the exhaust gas return air flow rate to the fresh air flow rate of the second passage is 1:1~1:3; When the second humidification branch is used, the working gauge pressure of the fuel cell stack is increased to 60-100kPa, the air humidity entering the cathode inlet of the fuel cell stack is 60%-80%, the fuel cell coolant inlet temperature is 75-80℃, the coolant outlet temperature is 80-85℃, the humidification area in the humidifier is 50%-80%, the anode side pressure of the fuel cell stack is 10-30kPa higher than the cathode side pressure, and the exhaust gas return air flow rate of the second passage is 1:1~1:3 to the fresh air flow rate.

10. The control method according to claim 7, characterized in that: When the operating power of the fuel cell stack is less than 10kW and the ambient temperature is lower than 55°C, the third humidification branch is used; When the operating power of the fuel cell stack is greater than 10kW and the ambient temperature is lower than 40°C, the first humidification branch is used; When the operating power of the fuel cell stack is greater than 10kW and the ambient temperature is 40-55°C, the second humidification branch is used.

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