Hydrogen fuel cell system and shutdown method

Abstract

The invention relates to the technical field of fuel cells, and discloses a hydrogen fuel cell system and a shutdown method.The hydrogen fuel cell system comprises an electric pile, a hydrogen system, a hydrogen reflux pump, an air system, a bypass, a first electromagnetic valve, a second electromagnetic valve and an air reflux pump, the hydrogen system is connected with the electric pile, and the hydrogen system is used for supplying hydrogen to the electric pile; the hydrogen reflux pump is arranged on a pipeline of the hydrogen system, the air system is connected with the galvanic pile and used for supplying air to the galvanic pile, the bypass is connected between an inlet of the air system and an outlet of the air system, the first electromagnetic valve is arranged on the inlet side of the bypass, and the second electromagnetic valve is arranged on the outlet side of the bypass. And the air reflux pump is arranged on the bypass and between the first electromagnetic valve and the second electromagnetic valve. According to the invention, the performance, the service life, the safety and the reliability of the hydrogen fuel cell in vehicle application are comprehensively improved.

Description

Technical Field

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

[0002] In the field of hydrogen fuel cell vehicles, the shutdown process of fuel cell systems has long been plagued by numerous issues. During shutdown, conventional fuel cell systems typically rely solely on a reflux pump to remove internal moisture due to technical limitations, but are unable to completely remove the hydrogen atmosphere. Furthermore, the air side, limited by onboard conditions, lacks an effective nitrogen purge function, often requiring air purge. However, this operation method causes hydrogen and air to mix within the stack, creating a high-potential environment that in turn causes corrosion of the cathode carbon support, severely impacting the stack's performance and lifespan. Furthermore, while existing methods employ reactive gases to reduce the open-circuit potential, the uneven nature of the internal reaction can easily lead to gas shortages. Furthermore, the cathode chamber struggles to completely react with the air inside, allowing air from other locations to diffuse into the stack, creating a high-potential environment once again. These issues severely impact the reliability and service life of hydrogen fuel cell vehicles. In light of these issues, the research and design of a novel hydrogen fuel cell system and shutdown method to overcome the challenges of existing hydrogen fuel cell vehicles undoubtedly possesses significant practical significance and application value. Therefore, this patent proposes a new type of hydrogen fuel cell system and shutdown method, which aims to effectively prevent the hydrogen inside the anode from forming a "hydrogen-air interface" with the oxygen penetrating from the cathode during shutdown, thereby protecting the fuel cell stack, extending the service life of the fuel cell stack, and improving the safety of the vehicle. Summary of the Invention

[0003] In order to solve the problems in the existing hydrogen fuel cell vehicle field, such as the difficulty in removing hydrogen from on-board hydrogen fuel cells, the easy formation of high potential inside the fuel cell, the easy corrosion of the cathode carbon carrier, and the shortened service life, the present invention provides a hydrogen fuel cell system and a shutdown method.

[0004] The technical solution adopted by the present invention to achieve the above-mentioned purpose is: a hydrogen fuel cell system, comprising Battery stack; a hydrogen system connected to the fuel cell stack and configured to supply hydrogen to the fuel cell stack; A hydrogen reflux pump, the hydrogen reflux pump being arranged on a pipeline of the hydrogen system; an air system connected to the fuel cell stack and configured to supply air to the fuel cell stack; a bypass passage connected between an inlet of the air system and an outlet of the air system; a first solenoid valve, the first solenoid valve being arranged at an inlet side of the bypass passage; a second solenoid valve, the second solenoid valve being arranged at an outlet side of the bypass passage; An air return pump is provided on the bypass passage and between the first solenoid valve and the second solenoid valve.

[0005] In a hydrogen fuel cell system according to some embodiments of the present invention, the fuel cell stack is formed by stacking multiple single-cell batteries.

[0006] According to some embodiments of the present invention, a hydrogen fuel cell system includes a high-pressure gas cylinder, a hydrogen delivery pipeline, a hydrogen tail exhaust, a hydrogen discharge pipeline and a hydrogen back-pressure valve. The high-pressure gas cylinder is connected to the hydrogen inlet of the fuel cell stack through the hydrogen delivery pipeline, the hydrogen tail exhaust is connected to the hydrogen outlet of the fuel cell stack through the hydrogen discharge pipeline, and the hydrogen back-pressure valve is arranged on the hydrogen discharge pipeline.

[0007] According to a hydrogen fuel cell system of some embodiments of the present invention, the hydrogen system also includes a first valve and a second valve, the first valve is arranged on the hydrogen delivery pipeline, the hydrogen reflux pump is connected to the hydrogen delivery pipeline through the first hydrogen reflux pipeline, and the first hydrogen reflux pipeline is connected between the first valve and the fuel cell stack, the second valve is arranged on the hydrogen exhaust pipeline, and the second valve is arranged between the hydrogen back pressure valve and the hydrogen tail exhaust, the hydrogen reflux pump is connected to the hydrogen exhaust pipeline through the second hydrogen reflux pipeline, and the second hydrogen reflux pipeline is connected between the hydrogen back pressure valve and the second valve.

[0008] According to some embodiments of the present invention, a hydrogen fuel cell system comprises an air system including an air compressor, an air delivery pipeline, an air tail exhaust, an air discharge pipeline and an air back-pressure valve. The air compressor is connected to the air inlet of the fuel cell stack through the air delivery pipeline, the air tail exhaust is connected to the air outlet of the fuel cell stack through the air discharge pipeline, and the air back-pressure valve is arranged on the air discharge pipeline.

[0009] According to a hydrogen fuel cell system of some embodiments of the present invention, the air system also includes a third valve and a fourth valve, the third valve is arranged on the air delivery pipeline, the bypass passage is connected to the air delivery pipeline, and the bypass passage is connected between the third valve and the fuel cell stack, the fourth valve is arranged on the air exhaust pipeline, and the fourth valve is arranged between the air back pressure valve and the air tail exhaust, the bypass passage is connected to the air exhaust pipeline, and the bypass passage is connected between the air back pressure valve and the fourth valve.

[0010] According to a hydrogen fuel cell system of some embodiments of the present invention, when the fuel cell stack operates normally, the first solenoid valve and the second solenoid valve are in a closed state, and the air recirculation pump is in a closed state.

[0011] The present invention further provides a method for shutting down a hydrogen fuel cell system, characterized in that the method uses the hydrogen fuel cell system according to claim 7 and comprises the following steps: S1 load reduction purge stage: During the operation of the hydrogen fuel cell system, when the voltage of a single battery of the stack is lower than 0.85V, the speed of the hydrogen reflux pump is increased, while the speed of the air compressor is increased; S2. Load reduction and pressure increase phase: Reduce the hydrogen fuel cell system's load current to 0A, increase the hydrogen inlet pressure and the air inlet pressure to 0.7 bar to 1.0 bar, and the air inlet pressure to 0.5 bar to 0.8 bar. Then, close the first and third valves, reduce the hydrogen inlet flow rate and the air inlet flow rate to 0 L / min, close the second and fourth valves, keep the hydrogen reflux pump running, and open the first and second solenoid valves. S3. Oxygen consumption loading phase: The air recirculation pump is turned on, and the hydrogen fuel cell system issues a small current loading instruction to the load connected to the positive and negative terminals of the stack. The load is loaded for 1 to 5 seconds and then stopped for 1 to 5 seconds. This process is repeated until the voltage of a single cell in the stack drops to 0.1V to 0.2V and the load is stopped. S4. Complete shutdown stage: When the hydrogen side pressure of the hydrogen fuel cell system is 0.4 bar to 0.6 bar lower than the air side pressure, the fourth valve is opened, and the air back pressure valve is opened at the same time to release the air side pressure to 0.1 bar to 0.3 bar lower than the hydrogen side pressure. After the pressure relief is completed, the second valve and the fourth valve are closed, and the hydrogen fuel cell system is powered off and shut down.

[0012] According to some embodiments of the present invention, a method for shutting down a hydrogen fuel cell system comprises: in step S1, during the load reduction and purge phase, increasing the speed of the air compressor 16 by 500 rpm / s to 1000 rpm / s, and increasing the speed of the air compressor 16 to 35500 rpm / s to 36000 rpm / s; after the speed of the air compressor 16 is increased, the metering ratio of the air entering the stack is increased by 1.0 to 2.0, and increasing the metering ratio of the air entering the stack to 3.0 to 4.0.

[0013] According to a shutdown method of a hydrogen fuel cell system in some embodiments of the present invention, in step S4, during the complete shutdown phase, before closing the fourth valve, ensure that the pressure in the internal cavity of the fuel cell stack is 0.1 bar to 0.2 bar higher than the atmospheric pressure.

[0014] The present invention discloses a hydrogen fuel cell system and shutdown method that can effectively protect the stack and extend its service life. By adopting a load reduction purge-load reduction and pressure increase-oxygen consumption load pull-up process during shutdown, the hydrogen inside the stack anode and the oxygen permeating the cathode are prevented from forming a hydrogen-air interface, thereby preventing the cathode potential from rising and generating reverse current, reducing the risk of carbon carrier corrosion, and reducing the performance degradation and life shortening of the stack caused by traditional shutdown methods. The present invention also optimizes gas distribution and reaction. The use of a hydrogen reflux pump and an air reflux pump not only makes the hydrogen and air inside the stack more evenly distributed, reducing local gas shortages, but also improves the utilization rate of the reaction gas and enhances power generation efficiency. At the same time, the accelerated discharge of liquid water during the purge process is conducive to maintaining the good operating state of the stack and reducing problems such as corrosion and mass transfer resistance caused by liquid water accumulation. The present invention further significantly improves the safety and reliability of the shutdown process. Through reasonable pressure regulation and control strategies, the ingress of external air and the formation of high potential caused by pressure changes during shutdown are avoided, reducing the risk of damage to the stack. The use of a pulsed loading method effectively prevents excessive voltage drops in individual cells, ensuring the stability and safety of the entire stack during shutdown. Overall, the hydrogen fuel cell system and shutdown method of the present invention comprehensively improve the performance, lifespan, safety, and reliability of hydrogen fuel cells in vehicle applications, and are of great significance to the promotion and application of hydrogen fuel cell vehicles. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a schematic structural diagram of a hydrogen fuel cell system according to an embodiment of the present invention.

[0016] In the figure: 1. Fuel cell stack, 2. Hydrogen reflux pump, 3. High-pressure gas cylinder, 4. Hydrogen delivery pipeline, 5. Hydrogen tail exhaust, 6. Hydrogen discharge pipeline, 7. Hydrogen back-pressure valve, 8. First valve, 9. Second valve, 10. First hydrogen reflux pipeline, 11. Second hydrogen reflux pipeline, 12. Bypass, 13. First solenoid valve, 14. Second solenoid valve, 15. Air reflux pump, 16. Air compressor, 17. Air delivery pipeline, 18. Air tail exhaust, 19. Air discharge pipeline, 20. Air back-pressure valve, 21. Third valve, 22. Fourth valve. DETAILED DESCRIPTION

[0017] The following embodiments of the present invention are described in further detail with reference to the accompanying drawings and examples. The following examples are used to illustrate the present invention but are not intended to limit the scope of the present invention.

[0018] In the description of the present invention, it should be noted that the terms "upper", "lower", "front", "rear", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention. The terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be internal communication between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances. In addition, in the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0019] A hydrogen fuel cell system of this embodiment, such as Figure 1 As shown, it includes a fuel cell stack 1, a hydrogen system, a hydrogen reflux pump 2, an air system, a bypass passage 12, a first solenoid valve 13, a second solenoid valve 14 and an air reflux pump 15. The hydrogen system is connected to the fuel cell stack 1, and the hydrogen system is used to supply hydrogen to the fuel cell stack 1. The hydrogen reflux pump 2 is arranged on the pipeline of the hydrogen system. The air system is connected to the fuel cell stack 1, and the air system is used to supply air to the fuel cell stack 1. The bypass passage 12 is connected between the inlet and the outlet of the air system. The first solenoid valve 13 is arranged on the inlet side of the bypass passage 12, and the second solenoid valve 14 is arranged on the outlet side of the bypass passage 12. The air reflux pump 15 is arranged on the bypass passage 12 and is arranged between the first solenoid valve 13 and the second solenoid valve 14.

[0020] As a preferred embodiment of this invention, more specifically, the fuel cell stack 1 is formed by stacking multiple single-cell batteries. When the fuel cell stack 1 is operating normally, the first solenoid valve 13 and the second solenoid valve 14 are in a closed state, and the air recirculation pump 15 is in a closed state. More specifically, the first solenoid valve 13 is in a closed state before the hydrogen fuel cell system is operated, so that the air recirculation pump 15 does not interfere with the power generation of the fuel cell stack 1. The second solenoid valve 14 is also in a closed state before the hydrogen fuel cell system is operated, so that the bypass path 12 also does not interfere with the power generation of the fuel cell stack.

[0021] As a preference of this embodiment, more specifically, the hydrogen system includes a high-pressure gas cylinder 3, a hydrogen delivery pipeline 4, a hydrogen tail exhaust 5, a hydrogen discharge pipeline 6 and a hydrogen back-pressure valve 7. The high-pressure gas cylinder 3 is connected to the hydrogen inlet of the fuel cell stack 1 through the hydrogen delivery pipeline 4. The high-pressure gas cylinder 3 can stably supply hydrogen to the fuel cell stack 1 to ensure the operation of the fuel cell stack 1. The hydrogen tail exhaust 5 is connected to the hydrogen outlet of the fuel cell stack 1 through the hydrogen discharge pipeline 6. The hydrogen tail exhaust 5 can discharge unreacted hydrogen in time. The hydrogen back-pressure valve 7 is arranged on the hydrogen discharge pipeline 6 and can adjust the discharge pressure to adjust the hydrogen gas pressure inside the fuel cell stack 1. The hydrogen system also includes a first valve 8 and a second valve 9. The first valve 8 is arranged on the hydrogen delivery pipeline 4 and can control the delivery flow of hydrogen. The first valve 8 is opened before the hydrogen fuel cell system works to supply hydrogen to the fuel cell stack 1, and is closed after pressure replenishment during the load reduction and pressure increase stage of shutdown. The hydrogen reflux pump 2 is connected to the hydrogen delivery pipeline 4 through the first hydrogen reflux pipeline 10, and the first hydrogen reflux pipeline 10 is connected between the first valve 8 and the fuel cell stack 1. The second valve 9 is arranged on the hydrogen discharge pipeline 6, and the second valve 9 is arranged between the hydrogen back pressure valve 7 and the hydrogen tail exhaust 5. Before complete shutdown, the hydrogen side is depressurized through the second valve 9. After complete shutdown, the second valve 9 is closed to prevent external air from re-entering the fuel cell stack. The hydrogen reflux pump 2 is connected to the hydrogen discharge pipeline 6 through the second hydrogen reflux pipeline 11, and the second hydrogen reflux pipeline 11 is connected between the hydrogen back pressure valve 7 and the second valve 9. The hydrogen reflux pump 2 can promote the recycling of hydrogen and help optimize hydrogen distribution.

[0022] As a preferred embodiment of the present invention, more specifically, the air system includes an air compressor 16, an air delivery pipeline 17, an air tail exhaust 18, an air discharge pipeline 19, and an air back pressure valve 20. The air compressor 16 is connected to the air inlet of the fuel cell stack 1 through the air delivery pipeline 17. The air compressor 16 can stably supply air to the fuel cell stack 1. The air tail exhaust 18 is connected to the air outlet of the fuel cell stack 1 through the air discharge pipeline 19. The air tail exhaust 18 can discharge the air after the reaction in time. The air back pressure valve 20 is arranged on the air discharge pipeline 19. The air back pressure valve 20 can adjust the discharge pressure to adjust the air gas pressure inside the fuel cell stack 1. The air system also includes a third valve 21 and a fourth valve 22. The third valve 21 is arranged on the air delivery pipeline 17. The third valve 21 is opened before the hydrogen fuel cell system works, connecting the air compressor 16 and the air inlet of the fuel cell stack 1, i.e., the cathode inlet, and pumping air into the fuel cell stack. It is closed after the pressure is replenished during the load reduction and pressure increase phase of the shutdown. The bypass passage 12 is connected to the air delivery line 17 and is connected between the third valve 21 and the fuel cell stack 1. The fourth valve 22 is provided on the air discharge line 19 and between the air back pressure valve 20 and the air tail exhaust 18. Before a complete shutdown, the air side is depressurized through the fourth valve 22. After a complete shutdown, the fourth valve 22 is closed to prevent external air from re-entering the fuel cell stack. The bypass passage 12 is connected to the air discharge line 19 and is connected between the air back pressure valve 20 and the fourth valve 22. The bypass passage 12 and the air return pump 15 can perform gas disturbance and mixing during shutdown, optimizing air flow and concentration distribution.

[0023] More specifically, the first valve 8 , the second valve 9 , the third valve 21 and the fourth valve 22 are solenoid valves, and the hydrogen back-pressure valve 7 and the air back-pressure valve 20 are proportional valves.

[0024] The present invention also provides a method for shutting down a hydrogen fuel cell system, characterized in that the method uses the hydrogen fuel cell system of claim 7 and comprises the following steps: S1. Load-Reduced Purge Phase: During operation of the hydrogen fuel cell system, when the voltage of a single cell in the fuel cell stack 1 falls below 0.85V, the speed of the hydrogen reflux pump 2 is increased to accelerate the circulation of liquid water on the hydrogen side. The liquid water is discharged from the fuel cell stack through the water separator. Simultaneously, the speed of the air compressor 16 is increased to increase the amount of air entering the stack, thereby accelerating the discharge of water from the air side. As a preferred embodiment of this embodiment, more specifically, during the load-reduced purge phase, the speed of the air compressor 16 is increased by 500 rpm / s to 1000 rpm / s, bringing the speed of the air compressor 16 to 35,500 rpm / s to 36,000 rpm / s. After the speed increase, the air flow rate ratio of the air flow rate to the stack is increased by 1.0 to 2.0, bringing the air flow rate ratio to 3.0 to 4.0. The purge phase is crucial for draining liquid water from the fuel cell stack 1, slowing bipolar plate corrosion, and reducing cold start time.

[0025] S2. Load reduction and pressure increase stage: Reduce the load current of the hydrogen fuel cell system to 0A, increase the hydrogen inlet pressure and air inlet pressure, increase the hydrogen inlet pressure to 0.7bar~1.0bar, and increase the air inlet pressure to 0.5bar~0.8bar, and increase the volume concentration of air and hydrogen inside the fuel cell stack 1 in advance to prepare for the following oxygen consumption load, prevent the reverse polarity phenomenon after oxygen consumption load, which may cause aging of the catalyst part of the fuel cell stack 1, and prevent the vacuum generated during oxygen consumption load from causing mechanical damage to the fuel cell stack 1 and thus shortening the life of the fuel cell stack 1. After the pressure of the hydrogen and air entering the stack reaches the preset pressure, close the first valve 8 and the third valve 21, reduce the hydrogen inlet flow rate and the air inlet flow rate to 0L / min, close the second valve 9 and the fourth valve 22 to close the hydrogen tail exhaust 5 and the air tail exhaust 18, keep the hydrogen reflux pump 2 running, open the first solenoid valve 13 and the second solenoid valve 14, switch the air side to the bypass pipe 12 containing the air reflux pump 15, due to the increase in the space inside the hydrogen fuel cell system, the pressure in the hydrogen fuel cell system pipe will drop slightly, at this time the hydrogen side and the air side of the stack are in a closed state.

[0026] S3. Oxygen-consuming loading stage: The air reflux pump 15 is turned on, and the hydrogen reflux pump 2 also works synchronously. The hydrogen fuel cell system issues a small current loading instruction to the load connected to the positive and negative poles of the fuel cell stack 1. At this time, the voltage of each cell in the fuel cell stack 1 begins to drop. The load is loaded for 1 to 5 seconds and then stopped for 1 to 5 seconds. The disturbance of the gas by the operation of the air reflux pump 15 and the hydrogen reflux pump 2 is achieved to mix the reaction gases. This process is repeated until the voltage of a single cell in the fuel cell stack 1 drops to 0.1V~0.2V and the loading is stopped. At this time, the air side of the fuel cell stack 1 contains extremely high-concentration nitrogen, while the hydrogen side of the fuel cell stack 1 contains pure hydrogen.

[0027] S4. Complete Shutdown: To reduce the hydrogen-air pressure differential within fuel cell stack 1, when the hydrogen-side pressure of the hydrogen fuel cell system is 0.4-0.6 bar lower than the air-side pressure, fourth valve 22 is opened. Simultaneously, air backpressure valve 20 is opened to relieve the air-side pressure to 0.1-0.3 bar lower than the hydrogen-side pressure. After pressure relief is complete, second valve 9 and fourth valve 22 are closed, and the hydrogen fuel cell system is powered down and shut down. As a preferred embodiment of this embodiment, more specifically, during the complete shutdown phase, before closing fourth valve 22, the internal cavity pressure of fuel cell stack 1 is maintained at 0.1-0.2 bar higher than atmospheric pressure.

[0028] During the startup process of the hydrogen fuel cell system of this embodiment, the first valve 8, the second valve 9 and the hydrogen back-pressure valve 7 are opened, hydrogen is passed through the fuel cell stack 1, the air compressor 16, the third valve 21, the fourth valve 22 and the air back-pressure valve 20 are opened, the first solenoid valve 13 and the second solenoid valve 14 are closed, the air compressor 16 works and air is passed through the fuel cell stack 1.

[0029] Since the cathode of stack 1 uses air, in which oxygen is a reactive substance, the high concentration of oxygen at the cathode of stack 1 will lead to the formation of a high potential, causing corrosion of the cathode carbon carrier. High-purity nitrogen cannot be used for purging in the vehicle environment, resulting in the constant presence of oxygen in the cathode, and the inevitable formation of a high potential locally inside. If there is no hydrogen in the anode chamber or no air in the cathode chamber, the voltage can be zero. However, after the hydrogen at the anode disappears, a negative pressure will form inside, which is not conducive to the stability of the mechanical structure inside the stack. Moreover, after a long period of shutdown, external air will enter the anode, while the cathode is air, in which the volume fraction of oxygen is 21%, and the remaining main component is nitrogen. The electrochemical reaction of nitrogen is inert. Therefore, when the entire vehicle is shut down, a load is connected on both sides of the stack to establish an extremely small discharge current, which greatly increases the volume fraction of nitrogen gas as an inert gas inside the stack, so that air will not penetrate into the anode to form a hydrogen-air interface, and greatly reduces the open circuit potential of the stack after shutdown.

[0030] The air recirculation pump rapidly stirs the cathode gas, minimizing the extreme variation of cells during loading inspections and preventing a rapid voltage drop in a single cell or cells, which could lead to complete oxygen consumption. Without an air recirculation pump, directly applying loading to the stack by controlling a small current across the stack will result in inconsistent voltage drop rates for each cell due to the random nature of the gas diffusion electrode reaction and stack edge effects. Furthermore, forced loading in the absence of reactant gas can cause other structures to react instead and damage the stack. After oxygen-consuming loading ends, the hydrogen and air concentrations within the flow field are low, while the reactive gas concentration within the pipeline is high. After loading ceases, the interconnected pipelines create a concentration difference, and oxygen from locations outside the flow channel can diffuse back into the flow field of the stack 1, establishing an open-circuit potential with the hydrogen in the anode. Therefore, air and hydrogen recirculation pumps are required on the air and hydrogen sides to ensure thorough mixing of the reacting and unreacted gases and maintain uniform concentrations.

[0031] The following points should be noted: Regarding the reverse polarity risk that may be caused by oxygen-consuming loading, the reverse polarity is mainly caused by the lack of hydrogen, which may lead to corrosion of the carbon carrier in the anode area, while the cathode gains electrons. During forced loading, water will be electrolyzed to generate hydrogen and increase the temperature. Due to the low loading current, there is only an extremely low probability of membrane perforation, and it will not cause serious damage to the stack 1 itself. It can be solved by circulating coolant. Therefore, when performing oxygen-consuming loading, as long as the hydrogen supply at the anode is guaranteed to be sufficient, the performance of the stack 1 can be guaranteed not to decline.

[0032] To prevent a continuous drop in the voltage of a single cell, a pulsed loading method is required. This gradually reduces the oxygen concentration on the air side while increasing the nitrogen concentration. If the pressure is not increased beforehand, the consumption of the air return pump will cause a negative pressure to form inside the stack cavity. If the pipeline is not tightly sealed, air will enter the cathode and may generate a high potential, damaging the stack. Therefore, it is necessary to increase the internal pressure in advance when shutting down and loading. When the air pressure drops, it will be greater than atmospheric pressure, avoiding the formation of a negative pressure, which would draw in outside air.

[0033] After the oxygen consumption load, the hydrogen in the anode and the oxygen in the cathode drop to a certain concentration, and the pressure drops. However, since the pressure has been increased in advance, the pressure on this side is greater than the external atmospheric pressure after the oxygen is consumed, which can ensure that no new air enters the stack. It is also possible to continue to release the stack pressure to a pressure slightly greater than the ambient pressure, but both must ensure the pressure balance of the hydrogen cavity to avoid damage to the membrane electrode.

[0034] The hydrogen reflux pump is used to save hydrogen consumption when the fuel cell system is working, to discharge liquid water during purging, and to ensure the uniformity of hydrogen distribution in the flow field inside the fuel cell stack during voltage consumption before shutdown to avoid local gas shortage; the air reflux pump in this embodiment is only used during the shutdown process to ensure the flow and uniformity of the fluid in the cathode chamber while the system is closed.

[0035] The shutdown process of this embodiment allows the driver to leave the vehicle after giving the shutdown command. After the shutdown operation is completed, the car's central control system automatically controls the hydrogen fuel cell system to completely power down. The driver can also give the shutdown command, and after the engine system is completely powered down, the driver is prompted that the engine has been completely shut down before leaving the vehicle.

[0036] The hydrogen fuel cell system of the present invention can be used in accessories of new energy vehicles.

[0037] The embodiments of the present invention are presented for purposes of illustration and description and are not intended to be exhaustive or to limit the invention to the disclosed forms. Many modifications and variations will be apparent to those skilled in the art. The embodiments are chosen and described in order to better illustrate the principles of the invention and its practical application and to enable those skilled in the art to understand the invention and design various embodiments with various modifications as suited for specific applications.

Claims

1. A hydrogen fuel cell system, characterized in that: include Battery stack (1); A hydrogen system, the hydrogen system being connected to the fuel cell stack (1), and the hydrogen system being used to supply hydrogen to the fuel cell stack (1); A hydrogen reflux pump (2), the hydrogen reflux pump (2) being arranged on a pipeline of the hydrogen system; An air system, the air system being connected to the fuel cell stack (1), and the air system being used to supply air to the fuel cell stack (1); a bypass passage (12), the bypass passage (12) being connected between an inlet of the air system and an outlet of the air system; a first solenoid valve (13), the first solenoid valve (13) being arranged at an inlet side of the bypass passage (12); a second solenoid valve (14), the second solenoid valve (14) being arranged at an outlet side of the bypass passage (12); An air return pump (15) is provided on the bypass passage (12) and between the first solenoid valve (13) and the second solenoid valve (14).

2. A hydrogen fuel cell system according to claim 1, characterized in that: The battery stack (1) is formed by stacking multiple single-cell batteries.

3. A hydrogen fuel cell system according to claim 2, characterized in that: The hydrogen system comprises a high-pressure gas cylinder (3), a hydrogen delivery pipeline (4), a hydrogen tail exhaust (5), a hydrogen discharge pipeline (6) and a hydrogen back-pressure valve (7); the high-pressure gas cylinder (3) is connected to the hydrogen inlet of the fuel cell stack (1) via the hydrogen delivery pipeline (4); the hydrogen tail exhaust (5) is connected to the hydrogen outlet of the fuel cell stack (1) via the hydrogen discharge pipeline (6); and the hydrogen back-pressure valve (7) is arranged on the hydrogen discharge pipeline (6).

4. A hydrogen fuel cell system according to claim 3, characterized in that: The hydrogen system further includes a first valve (8) and a second valve (9), wherein the first valve (8) is arranged on the hydrogen delivery pipeline (4), the hydrogen reflux pump (2) is connected to the hydrogen delivery pipeline (4) through a first hydrogen reflux pipeline (10), and the first hydrogen reflux pipeline (10) is connected between the first valve (8) and the fuel cell stack (1), the second valve (9) is arranged on the hydrogen discharge pipeline (6), and the second valve (9) is arranged between the hydrogen back pressure valve (7) and the hydrogen tail exhaust (5), the hydrogen reflux pump (2) is connected to the hydrogen discharge pipeline (6) through a second hydrogen reflux pipeline (11), and the second hydrogen reflux pipeline (11) is connected between the hydrogen back pressure valve (7) and the second valve (9).

5. A hydrogen fuel cell system according to claim 4, characterized in that: The air system comprises an air compressor (16), an air delivery pipeline (17), an air tail exhaust (18), an air discharge pipeline (19) and an air back pressure valve (20); the air compressor (16) is connected to the air inlet of the fuel cell stack (1) through the air delivery pipeline (17); the air tail exhaust (18) is connected to the air outlet of the fuel cell stack (1) through the air discharge pipeline (19); and the air back pressure valve (20) is arranged on the air discharge pipeline (19).

6. A hydrogen fuel cell system according to claim 5, characterized in that: The air system further includes a third valve (21) and a fourth valve (22), wherein the third valve (21) is arranged on the air delivery pipeline (17), the bypass passage (12) is connected to the air delivery pipeline (17), and the bypass passage (12) is connected between the third valve (21) and the fuel cell stack (1), the fourth valve (22) is arranged on the air exhaust pipeline (19), and the fourth valve (22) is arranged between the air back pressure valve (20) and the air tail exhaust (18), the bypass passage (12) is connected to the air exhaust pipeline (19), and the bypass passage (12) is connected between the air back pressure valve (20) and the fourth valve (22).

7. A hydrogen fuel cell system according to claim 6, characterized in that: When the fuel cell stack (1) operates normally, the first solenoid valve (13) and the second solenoid valve (14) are in a closed state, and the air return pump (15) is in a closed state.

8. A method for shutting down a hydrogen fuel cell system, characterized in that: The hydrogen fuel cell system according to claim 7 comprises the following steps: S1. Load reduction and purge phase: During the operation of the hydrogen fuel cell system, when the voltage of a single battery of the stack (1) is lower than 0.85V, the speed of the hydrogen reflux pump (2) is increased, and the speed of the air compressor (16) is increased; S2. Load reduction and pressure increase stage: reduce the load current of the hydrogen fuel cell system to 0A, increase the hydrogen inlet pressure and the air inlet pressure, increase the hydrogen inlet pressure to 0.7 bar~1.0 bar, and increase the air inlet pressure to 0.5 bar~0.8 bar, close the first valve (8) and the third valve (21), reduce the hydrogen inlet flow rate and the air inlet flow rate to 0 L / min, close the second valve (9) and the fourth valve (22), keep the hydrogen reflux pump (2) running, and open the first solenoid valve (13) and the second solenoid valve (14); S3. Oxygen consumption loading stage: the air recirculation pump (15) is turned on, and the hydrogen fuel cell system issues a small current loading instruction to the load connected to the positive and negative electrodes of the stack (1). The load is loaded for 1 to 5 seconds and then stopped for 1 to 5 seconds. This process is repeated until the voltage of a single battery cell of the stack (1) drops to 0.1V to 0.2V and the loading is stopped; S4. Complete shutdown stage: When the hydrogen side pressure of the hydrogen fuel cell system is 0.4 bar to 0.6 bar lower than the air side pressure, the fourth valve (22) is opened, and the air back pressure valve (20) is opened at the same time to release the air side pressure to 0.1 bar to 0.3 bar lower than the hydrogen side pressure. After the pressure relief is completed, the second valve (9) and the fourth valve (22) are closed, and the hydrogen fuel cell system is powered off and shut down.

9. A hydrogen fuel cell system according to claim 8, characterized in that: In the step S1, during the load reduction and purging stage, the speed of the air compressor (16) is increased by 500 rpm / s to 1000 rpm / s, and the speed of the air compressor (16) is increased to 35500 rpm / s to 36000 rpm / s. After the speed of the air compressor (16) is increased, the metering ratio of the air entering the stack is increased by 1.0 to 2.0, and the metering ratio of the air entering the stack is increased to 3.0 to 4.

0.

10. A hydrogen fuel cell system according to claim 8, characterized in that: In the step S4, during the complete shutdown phase, before closing the fourth valve (22), it is ensured that the pressure in the internal cavity of the fuel cell stack (1) is 0.1 bar to 0.2 bar higher than the atmospheric pressure.

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