Hydrogen fuel cell system and shutdown method

Abstract

The application relates to the field of fuel cell technology and discloses a hydrogen fuel cell system and a shutdown method, which comprise a stack, a hydrogen system, a hydrogen backflow pump, an air system, a bypass path, a first electromagnetic valve, a second electromagnetic valve and an air backflow pump; the hydrogen system is connected with the stack and is used for supplying hydrogen to the stack; the hydrogen backflow pump is arranged on a pipeline of the hydrogen system; the air system is connected with the stack and is used for supplying air to the stack; the bypass path 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 path; the second electromagnetic valve is arranged on the outlet side of the bypass path; the air backflow pump is arranged on the bypass path and is arranged between the first electromagnetic valve and the second electromagnetic valve. The application comprehensively improves the performance, service life, safety and reliability of the hydrogen fuel cell in vehicle application.

Description

Technical Field

[0001] This invention relates to the field of fuel cell technology, and more specifically to a hydrogen fuel cell system and a shutdown method. Background Technology

[0002] In the field of hydrogen fuel cell vehicles, the shutdown process of fuel cell systems has always faced numerous challenges. Traditional fuel cell systems, due to technological limitations, typically only rely on a return pump to remove internal moisture during shutdown, failing to completely purge the hydrogen atmosphere. Simultaneously, the air side, constrained by onboard conditions, lacks effective nitrogen purging capabilities, often requiring the use of air to purge the air side. However, this approach leads to hydrogen and air mixing within the stack, creating a high-potential environment that corrodes the cathode carbon support, severely impacting the stack's performance and lifespan. Furthermore, while existing technologies utilize reactive gases to lower the open-circuit potential, the unevenness of the internal reaction can easily lead to insufficient gas, and the cathode chamber may not completely react to remove internal air, allowing air from other locations to diffuse into the stack, again creating a high-potential environment. These problems significantly affect the reliability and lifespan of hydrogen fuel cell vehicles. Therefore, researching and designing a novel hydrogen fuel cell system and shutdown method to overcome the existing problems in hydrogen fuel cell vehicles undoubtedly has significant practical importance and application value. Therefore, this patent proposes a novel 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 permeating from the cathode when the system is shut down. This protects the fuel cell stack, extends its service life, and improves vehicle safety. Summary of the Invention

[0003] To address the problems in the existing hydrogen fuel cell vehicle field, such as difficulty in removing hydrogen from on-board hydrogen fuel cells, easy formation of high potential inside the fuel cell, easy corrosion of the cathode carbon support, and affected lifespan, this invention provides a hydrogen fuel cell system and shutdown method.

[0004] The technical solution adopted by the present invention to achieve the above objectives is: a hydrogen fuel cell system, comprising...

[0005] fuel cell stack;

[0006] A hydrogen system connected to the fuel cell stack, the hydrogen system being used to supply hydrogen to the fuel cell stack;

[0007] A hydrogen reflux pump, wherein the hydrogen reflux pump is installed on the pipeline of the hydrogen system;

[0008] An air system connected to the fuel cell stack, the air system being used to supply air to the fuel cell stack;

[0009] A bypass passage, the bypass passage connecting the inlet of the air system to the outlet of the air system;

[0010] A first solenoid valve is disposed on the inlet side of the bypass passage;

[0011] The second solenoid valve is disposed on the bypass outlet side;

[0012] An air return pump is provided on the bypass passage and is located between the first solenoid valve and the second solenoid valve.

[0013] According to some embodiments of the present invention, a hydrogen fuel cell system is provided in which the stack is composed of multiple single-cell batteries stacked together.

[0014] 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 tailpipe, 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 via the hydrogen delivery pipeline, the hydrogen tailpipe is connected to the hydrogen outlet of the fuel cell stack via the hydrogen discharge pipeline, and the hydrogen back pressure valve is disposed on the hydrogen discharge pipeline.

[0015] According to some embodiments of the present invention, a hydrogen fuel cell system further includes a first valve and a second valve. The first valve is disposed on the hydrogen delivery pipeline. A hydrogen reflux pump is connected to the hydrogen delivery pipeline via 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 disposed on the hydrogen emission pipeline, and the second valve is disposed between the hydrogen back pressure valve and the hydrogen tailpipe. The hydrogen reflux pump is connected to the hydrogen emission pipeline via a second hydrogen reflux pipeline, and the second hydrogen reflux pipeline is connected between the hydrogen back pressure valve and the second valve.

[0016] According to some embodiments of the present invention, a hydrogen fuel cell system includes an air system comprising an air compressor, an air delivery pipeline, an air exhaust pipe, an air discharge pipeline, and an air back pressure valve. The air compressor is connected to the air inlet of the fuel cell stack via the air delivery pipeline, the air exhaust pipe is connected to the air outlet of the fuel cell stack via the air discharge pipeline, and the air back pressure valve is disposed on the air discharge pipeline.

[0017] According to some embodiments of the present invention, in a hydrogen fuel cell system, the air system further includes a third valve and a fourth valve. The third valve is disposed on the air supply pipeline. The bypass passage is connected to the air supply pipeline and is connected between the third valve and the fuel cell stack. The fourth valve is disposed on the air discharge pipeline and is disposed between the air back pressure valve and the air tailpipe. The bypass passage is connected to the air discharge pipeline and is connected between the air back pressure valve and the fourth valve.

[0018] According to some embodiments of the present invention, in a hydrogen fuel cell system, when the fuel cell stack is operating normally, the first solenoid valve and the second solenoid valve are in a closed state, and the air return pump is in a closed state.

[0019] The present invention also provides a shutdown method for a hydrogen fuel cell system, characterized in that, using the hydrogen fuel cell system, the method includes the following steps:

[0020] S1. Load reduction and purging stage: During the operation of the hydrogen fuel cell system, when the voltage of a single cell of the stack is lower than 0.85V, the speed of the hydrogen return pump is increased, and the speed of the air compressor is increased at the same time;

[0021] S2. Load Reduction and Pressure Boosting Stage: Reduce the load current of the hydrogen fuel cell system to 0A, increase the hydrogen infeed pressure and air infeed pressure, increase the hydrogen infeed pressure to 0.7bar~1.0bar, and increase the air infeed pressure to 0.5bar~0.8bar. Then, close the first valve and the third valve, reduce the hydrogen infeed flow rate and the air infeed flow rate to 0L / min, close the second valve and the fourth valve, keep the hydrogen return pump running, and open the first solenoid valve and the second solenoid valve at the same time.

[0022] S3. Oxygen-consuming load-pushing stage: The air recirculation pump is turned on, and the hydrogen fuel cell system issues a small current load-pushing command to the load connected to the positive and negative terminals at both ends of the stack. The load is pulled for 1~5s and then stopped for 1~5s. This process is repeated until the voltage of a single cell of the stack drops to 0.1V~0.2V and then the load-pushing stops.

[0023] S4. Complete shutdown phase: When the hydrogen side pressure of the hydrogen fuel cell system is lower than the air side pressure by 0.4 bar to 0.6 bar, the fourth valve is opened and the air back pressure valve is opened at the same time to depressurize the air side to 0.1 bar to 0.3 bar lower than the hydrogen side pressure. After the depressurization is completed, the second valve and the fourth valve are closed, and the hydrogen fuel cell system is powered off and shut down.

[0024] According to some embodiments of the present invention, in a shutdown method for a hydrogen fuel cell system, in step S1, during the load reduction and purging stage, the rotational speed of the air compressor 16 is increased by 500 rpm / s to 1000 rpm / s, increasing the rotational speed of the air compressor 16 to 35500 rpm / s to 36000 rpm / s. After the rotational speed of the air compressor 16 is increased, the feed air volume metering ratio is increased by 1.0 to 2.0, increasing the feed air volume metering ratio to 3.0 to 4.0.

[0025] According to some embodiments of the present invention, in a shutdown method for a hydrogen fuel cell system, in step S4, before closing the fourth valve during the complete shutdown phase, the internal cavity pressure of the fuel cell stack is guaranteed to be 0.1 bar to 0.2 bar higher than atmospheric pressure.

[0026] This invention discloses a hydrogen fuel cell system and shutdown method that effectively protects the fuel cell stack and extends its service life. By employing a load reduction purging-load reduction pressurization-oxygen-consuming load adjustment during shutdown, it avoids the formation of a hydrogen-air interface between hydrogen inside the anode and oxygen permeation at the cathode, thereby preventing reverse current generation due to increased cathode potential. This reduces the risk of carbon carrier corrosion and mitigates the performance degradation and shortened lifespan issues associated with traditional shutdown methods. This invention also optimizes gas distribution and reaction. Utilizing hydrogen and air recirculation pumps not only ensures a more uniform distribution of hydrogen and air within the stack, reducing localized gas shortages, but also improves the utilization rate of reactant gases and enhances power generation efficiency. Simultaneously, the accelerated removal of liquid water during purging helps maintain good stack operation and reduces corrosion and mass transfer resistance caused by liquid water accumulation. Furthermore, this invention significantly improves the safety and reliability of the shutdown process. Through reasonable pressure regulation and control strategies, it avoids external air ingress and high potential formation due to pressure changes during shutdown, reducing the risk of stack damage. The pulsed load-bearing method effectively prevents excessive voltage drop in any single cell, ensuring the stability and safety of the entire fuel cell stack during shutdown. Overall, the hydrogen fuel cell system and shutdown method of this invention comprehensively improve the performance, lifespan, safety, and reliability of hydrogen fuel cells in vehicle applications, and are of great significance for the promotion and application of hydrogen fuel cell vehicles. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of a hydrogen fuel cell system according to an embodiment of the present invention.

[0028] In the diagram: 1. Fuel cell stack; 2. Hydrogen reflux pump; 3. High-pressure gas cylinder; 4. Hydrogen delivery pipeline; 5. Hydrogen tailpipe; 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 tailpipe; 19. Air discharge pipeline; 20. Air back pressure valve; 21. Third valve; 22. Fourth valve. Detailed Implementation

[0029] The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and should not be construed as limiting the scope of the invention.

[0030] In the description of this invention, it should be noted that the terms "upper," "lower," "front," "rear," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. The terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two elements. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances. Furthermore, in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0031] This embodiment provides a hydrogen fuel cell system, such as... Figure 1 As shown, the system includes a fuel cell stack 1, a hydrogen system, a hydrogen reflux pump 2, an air system, a bypass 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 is used to supply hydrogen to the fuel cell stack 1. The hydrogen reflux pump 2 is installed on the pipeline of the hydrogen system. The air system is connected to the fuel cell stack 1 and is used to supply air to the fuel cell stack 1. The bypass 12 is connected between the inlet and outlet of the air system. The first solenoid valve 13 is installed on the inlet side of the bypass 12, the second solenoid valve 14 is installed on the outlet side of the bypass 12, and the air reflux pump 15 is installed on the bypass 12 and is located between the first solenoid valve 13 and the second solenoid valve 14.

[0032] As a preferred embodiment, and more specifically, the fuel cell stack 1 is composed of multiple stacked single-cell batteries. During normal operation of the fuel cell stack 1, the first solenoid valve 13 and the second solenoid valve 14 are in the closed state, and the air recirculation pump 15 is in the closed state. More specifically, the first solenoid valve 13 is in the closed state before the hydrogen fuel cell system operates, so that the air recirculation pump 15 does not participate in the power generation of the fuel cell stack 1, and the second solenoid valve 14 is also in the closed state before the hydrogen fuel cell system operates, so that the bypass passage 12 also does not participate in the power generation of the fuel cell stack.

[0033] As a preferred embodiment, and more specifically, the hydrogen system includes a high-pressure gas cylinder 3, a hydrogen delivery pipeline 4, a hydrogen tailpipe 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, and 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 tailpipe 5 is connected to the hydrogen outlet of the fuel cell stack 1 through the hydrogen discharge pipeline 6, and the hydrogen tailpipe 5 can timely discharge unreacted hydrogen. The hydrogen back pressure valve 7 is installed on the hydrogen discharge pipeline 6 and can adjust the discharge pressure to regulate the internal hydrogen gas pressure of the fuel cell stack 1. The hydrogen system also includes a first valve 8 and a second valve 9. The first valve 8 is located on the hydrogen delivery pipeline 4 and controls the flow rate of hydrogen. The first valve 8 is opened before the hydrogen fuel cell system starts working to supply hydrogen to the stack 1. It is closed after pressurization during the depressurization and pressurization phase during shutdown. The hydrogen return pump 2 is connected to the hydrogen delivery pipeline 4 through the first hydrogen return pipeline 10, which is connected between the first valve 8 and the stack 1. The second valve 9 is located on the hydrogen discharge pipeline 6, which is located between the hydrogen back pressure valve 7 and the hydrogen tailpipe 5. Before a complete shutdown, the hydrogen side is depressurized through the second valve 9. After a complete shutdown, the second valve 9 is closed to prevent external air from re-entering the stack. The hydrogen return pump 2 is connected to the hydrogen discharge pipeline 6 through the second hydrogen return pipeline 11, which is connected between the hydrogen back pressure valve 7 and the second valve 9. The hydrogen return pump 2 promotes hydrogen recycling and helps optimize hydrogen distribution.

[0034] As a preferred embodiment, and more specifically, the air system includes an air compressor 16, an air supply pipeline 17, an air 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 via the air supply pipeline 17, and can stably supply air to the fuel cell stack 1. The air exhaust 18 is connected to the air outlet of the fuel cell stack 1 via the air discharge pipeline 19, and can promptly discharge the air after the reaction. The air back pressure valve 20 is installed on the air discharge pipeline 19, and can regulate the discharge pressure to regulate the internal air pressure of the fuel cell stack 1. The air system also includes a third valve 21 and a fourth valve 22. The third valve 21 is installed on the air supply pipeline 17. The third valve 21 is opened before the hydrogen fuel cell system starts working, connecting the air compressor 16 and the air inlet (cathode inlet) of the fuel cell stack 1, pumping air into the fuel cell stack. It is closed after pressurization during the depressurization and pressurization phase during shutdown. Bypass 12 is connected to air supply line 17 and is also connected between third valve 21 and fuel cell stack 1. Fourth valve 22 is located on air discharge line 19 and is also located between air back pressure valve 20 and air tailpipe 18. Before a complete shutdown, the air side is depressurized through fourth valve 22. After a complete shutdown, fourth valve 22 is closed to prevent external air from re-entering the fuel cell stack. Bypass 12 is connected to air discharge line 19 and is also connected between air back pressure valve 20 and fourth valve 22. Bypass 12 and air return pump 15 can turbulently mix the gas during shutdown, optimizing airflow and concentration distribution.

[0035] 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.

[0036] The present invention also provides a shutdown method for a hydrogen fuel cell system, characterized in that, using a hydrogen fuel cell system, the method includes the following steps:

[0037] S1. Load Reduction and Purging Stage: During the operation of the hydrogen fuel cell system, when the voltage of a single cell in stack 1 is below 0.85V, the speed of the hydrogen return pump 2 is increased to accelerate the circulation of liquid water on the hydrogen side. The liquid water is discharged from the stack through the water distributor. 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 on the air side. As a preferred embodiment, more specifically, during the load reduction and purging stage, the speed of the air compressor 16 is increased by 500 rpm / s to 1000 rpm / s, raising 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, raising the metering ratio of the air entering the stack to 3.0 to 4.0. The purging stage is of great significance for the discharge of liquid water inside stack 1, the slowing down of bipolar plate corrosion rate, and the reduction of cold start time.

[0038] S2. Load Reduction and Pressure Increase Stage: The load current of the hydrogen fuel cell system is reduced to 0A, and the hydrogen infeed pressure and air infeed pressure are increased. The hydrogen infeed pressure is increased to 0.7 bar to 1.0 bar, and the air infeed pressure is increased to 0.5 bar to 0.8 bar. This pre-increases the volume concentration of air and hydrogen inside stack 1, preparing for the subsequent oxygen-consuming load. This prevents reverse polarity after oxygen-consuming load, which could cause aging of the catalyst in stack 1, and also prevents mechanical damage to stack 1 caused by vacuum during oxygen-consuming load, thus affecting the lifespan of stack 1. Hydrogen infeed pressure... After the air inlet pressure reaches the preset pressure, close the first valve 8 and the third valve 21 to 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 to close the hydrogen tail vent 5 and the air tail vent 18. Keep the hydrogen return pump 2 running. Open the first solenoid valve 13 and the second solenoid valve 14 to switch the air side to the bypass passage 12 containing the air return pump 15. Due to the increased internal space of the hydrogen fuel cell system, the pressure inside the hydrogen fuel cell system pipe will decrease slightly. At this time, both the hydrogen side and the air side of the stack are in a closed state.

[0039] S3. Oxygen-consuming load-pushing stage: The air reflux pump 15 is turned on, and the hydrogen reflux pump 2 also works synchronously. The hydrogen fuel cell system sends a small current load-pushing command to the load connected to the positive and negative terminals at both ends of the stack 1. At this time, the voltage of each cell in the stack 1 begins to drop. The load is pulled for 1~5 seconds and then stopped for 1~5 seconds. The operation of the air reflux pump 15 and the hydrogen reflux pump 2 disturbs the gas to achieve the purpose of mixing the reaction gases. This process is repeated until the voltage of a single cell in the stack 1 drops to 0.1V~0.2V and then the load-pushing stops. At this time, the air side of the stack 1 contains extremely high concentration of nitrogen gas, while the hydrogen side of the stack 1 contains pure hydrogen gas.

[0040] S4. Complete Shutdown Phase: To reduce the hydrogen-air pressure difference inside stack 1, 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 simultaneously to depressurize the air side to 0.1 bar to 0.3 bar lower than the hydrogen-side pressure. After depressurization 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. As a preferred embodiment, more specifically, before closing the fourth valve 22 during the complete shutdown phase, the internal cavity pressure of stack 1 is ensured to be 0.1 bar to 0.2 bar higher than atmospheric pressure.

[0041] In this embodiment, during the startup process of the hydrogen fuel cell system, the first valve 8, the second valve 9, and the hydrogen back pressure valve 7 are opened, hydrogen is supplied to 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 turned on, the first solenoid valve 13 and the second solenoid valve 14 are closed, and the air compressor 16 is powered to supply air to the fuel cell stack 1.

[0042] Because the cathode of fuel cell stack 1 uses air, in which oxygen is a reactant, the high concentration of oxygen at the cathode leads to a high potential, causing corrosion of the cathode carbon support. In the on-board environment, high-purity nitrogen cannot be used for purging, resulting in the constant presence of oxygen at the cathode, inevitably leading to localized high potentials. While the voltage can be zero in either the anode chamber (without hydrogen) or the cathode chamber (without air), the disappearance of hydrogen at the anode creates a negative pressure, which is detrimental to the stability of the fuel cell's internal mechanical structure. Furthermore, after prolonged shutdown, external air can enter the anode, while the cathode is composed of air, with an oxygen volume fraction of 21% and the remainder being nitrogen. Nitrogen exhibits inert electrochemical reactions. Therefore, when the vehicle is shut down, a very small discharge current is established by connecting loads to both sides of the fuel cell stack. This significantly increases the nitrogen content, preventing air from permeating to the anode and forming a hydrogen-air interface, and greatly reducing the open-circuit potential of the fuel cell stack after shutdown.

[0043] The function of the air recirculation pump is to rapidly agitate the cathode gas, reduce the polarity of the cells during load testing, and prevent the voltage of a single cell or several single cells from dropping too quickly, thus ensuring complete oxygen consumption. If the air recirculation pump is not used, and a small current is directly controlled at both ends of the stack for load testing, the randomness of the gas diffusion electrode reaction and the edge effect of the stack will lead to inconsistent voltage drop rates for each single cell. Furthermore, if load testing is forced when the reactive gas is insufficient, other structures may react and damage the stack. After the oxygen-consuming load testing ends, the concentrations of hydrogen and air inside the flow field are low, while the concentration of active gas inside the pipelines is high. After the load testing stops, due to the interconnected pipelines and the concentration difference, oxygen from other locations outside the flow channels will diffuse back into the flow field of stack 1, establishing an open-circuit potential with the hydrogen in the anode. Therefore, air and hydrogen recirculation pumps are needed on both the air and hydrogen sides to ensure that the reacting and unreacted gases are thoroughly mixed and maintain uniform concentration.

[0044] The following points should be noted:

[0045] Regarding the risk of reverse polarity that may occur during oxygen-consuming load testing, reverse polarity mainly refers to the corrosion of the carbon support in the anode area when there is insufficient hydrogen gas, while the cathode gains electrons. During forced load testing, water will be electrolyzed, generating hydrogen gas and increasing the temperature. Because the load current is low, there is only a very low probability of membrane perforation, which will not cause serious damage to the fuel cell stack 1 itself. This can be resolved by circulating coolant. Therefore, during oxygen-consuming load testing, as long as the hydrogen supply to the anode is sufficient, the performance of fuel cell stack 1 will not degrade.

[0046] To prevent a continuous drop in the voltage of a single cell, a pulsed load-bearing method is required. This method gradually reduces the oxygen concentration on the air side while continuously increasing the nitrogen concentration. If the pressure is not increased beforehand, the consumption of the air return pump will create a negative pressure inside the stack cavity. If the pipeline is not properly sealed after the negative pressure is formed, air may enter the cathode, potentially creating a high potential and damaging the stack. Therefore, it is necessary to increase the internal pressure before the shutdown load-bearing process. Even after the air pressure drops, it should still be greater than atmospheric pressure to avoid creating a negative pressure and drawing in outside air.

[0047] After oxygen consumption load, the hydrogen in the anode and the oxygen in the cathode drop to a certain concentration, and the pressure decreases. However, since the pressure has been increased in advance, the pressure on the side where the oxygen is consumed is still greater than the external atmospheric pressure, which can ensure that no new air enters the stack. Alternatively, the stack pressure can be released to be slightly greater than the ambient pressure, but both methods must ensure the pressure balance of the hydrogen cavity to avoid damage to the membrane electrode.

[0048] The hydrogen recirculation pump is used to save hydrogen consumption during the operation of the fuel cell system, to discharge liquid water during purging, and to ensure the uniformity of hydrogen distribution in the flow field inside the stack during voltage consumption before shutdown, so as to avoid local gas shortage. In contrast, the air recirculation pump in this embodiment is only used to ensure the flow and uniformity of fluid in the cathode chamber while the system is closed during shutdown.

[0049] In this embodiment, the shutdown process can be completed by the driver giving the command to turn off the engine and then leaving the vehicle. After the shutdown operation is completed, the vehicle's central control system will automatically control the hydrogen fuel cell system to completely shut down. Alternatively, after the driver gives the command to turn off the engine and the engine system is completely powered down, the driver can be prompted that the engine has completely stopped before leaving the vehicle.

[0050] The hydrogen fuel cell system of the present invention can be used in the components of new energy vehicles.

[0051] The embodiments of the present invention are given for illustrative and descriptive purposes only, and are not intended to be exhaustive or to limit the invention to the forms disclosed. Many modifications and variations will be apparent to those skilled in the art. The embodiments were chosen and described in order to better illustrate the principles and practical application of the invention, and to enable those skilled in the art to understand the invention and to design various embodiments with various modifications suitable for a particular purpose.

Claims

1. A hydrogen fuel cell system, characterized in that, include fuel cell stack (1); A hydrogen system connected to the fuel cell stack (1) and used to supply hydrogen to the fuel cell stack (1); Hydrogen reflux pump (2), the hydrogen reflux pump (2) is installed on the pipeline of the hydrogen system; An air system connected to the fuel cell stack (1) and used to supply air to the fuel cell stack (1); A bypass (12) is provided, which connects the inlet of the air system to the outlet of the air system. The first solenoid valve (13) is disposed on the inlet side of the bypass passage (12); The second solenoid valve (14) is disposed on the 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); The hydrogen system includes a hydrogen delivery pipeline (4), a hydrogen discharge pipeline (6), a first valve (8), and a second valve (9). The first valve (8) is installed on the hydrogen delivery pipeline (4), and the second valve (9) is installed on the hydrogen discharge pipeline (6). The air system includes an air compressor (16), an air delivery pipeline (17), an air discharge pipeline (19), an air back pressure valve (20), a third valve (21), and a fourth valve (22). The third valve (21) is installed on the air delivery pipeline (17), the fourth valve (22) is installed on the air discharge pipeline (19), and the air back pressure valve (20) is installed on the air discharge pipeline (19). The shutdown method for the hydrogen fuel cell system includes the following steps: S1. Load reduction and purging stage: During the operation of the hydrogen fuel cell system, when the voltage of a single cell of the stack (1) is lower than 0.85V, the speed of the hydrogen return pump (2) is increased, and the speed of the air compressor (16) is increased at the same time. S2. Load reduction and pressure increase stage: Reduce the load current of the hydrogen fuel cell system to 0A, increase the hydrogen infeed pressure and air infeed pressure, increase the hydrogen infeed pressure to 0.7bar~1.0bar, and increase the air infeed pressure to 0.5bar~0.8bar. Then close the first valve (8) and the third valve (21), reduce the hydrogen infeed flow rate and the air infeed flow rate to 0L / min, close the second valve (9) and the fourth valve (22), keep the hydrogen return pump (2) running, and open the first solenoid valve (13) and the second solenoid valve (14). S3. Oxygen-consuming load-pushing stage: The air reflux pump (15) is turned on, and the hydrogen fuel cell system issues a small current load-pushing command to the load connected to the positive and negative poles at both ends of the stack (1). The load is pulled for 1~5s and then stopped for 1~5s. This process is repeated until the voltage of a single cell of the stack (1) drops to 0.1V~0.2V and then the load-pushing stops. S4. Complete shutdown phase: When the hydrogen side pressure of the hydrogen fuel cell system is lower than the air side pressure by 0.4 bar to 0.6 bar, the fourth valve (22) is opened and the air back pressure valve (20) is opened at the same time to depressurize the air side to 0.1 bar to 0.3 bar lower than the hydrogen side pressure. After the depressurization 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.

2. The hydrogen fuel cell system according to claim 1, characterized in that, In 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 feed air volume metering ratio is increased by 1.0 to 2.0, and the feed air volume metering ratio is increased to 3.0 to 4.

0.

3. A hydrogen fuel cell system according to claim 1, characterized in that, In step S4, before closing the fourth valve (22) during the complete shutdown phase, the pressure inside the fuel cell stack (1) is guaranteed to be 0.1 bar to 0.2 bar higher than atmospheric pressure.

4. A hydrogen fuel cell system according to claim 1, characterized in that, The stack (1) is composed of multiple single-cell batteries stacked together.

5. A hydrogen fuel cell system according to claim 4, characterized in that, The hydrogen system also includes a high-pressure gas cylinder (3), a hydrogen tailpipe (5), 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 a hydrogen delivery pipeline (4). The hydrogen tailpipe (5) is connected to the hydrogen outlet of the fuel cell stack (1) through a hydrogen discharge pipeline (6). The hydrogen back pressure valve (7) is installed on the hydrogen discharge pipeline (6).

6. A hydrogen fuel cell system according to claim 5, characterized in that, The hydrogen reflux pump (2) in the hydrogen system 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), and the second valve (9) is located between the hydrogen back pressure valve (7) and the hydrogen tail discharge (5). 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).

7. A hydrogen fuel cell system according to claim 6, characterized in that, The air system also includes an air exhaust (18), the air compressor (16) is connected to the air inlet of the fuel cell stack (1) through an air delivery pipeline (17), and the air exhaust (18) is connected to the air outlet of the fuel cell stack (1) through an air discharge pipeline (19).

8. A hydrogen fuel cell system according to claim 7, characterized in that, The bypass passage (12) in the air system 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 located between the air back pressure valve (20) and the air 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).

9. A hydrogen fuel cell system according to claim 8, characterized in that, When the fuel cell stack (1) is operating normally, the first solenoid valve (13) and the second solenoid valve (14) are closed, and the air return pump (15) is closed.

10. A method for shutting down a hydrogen fuel cell system, characterized in that, Using the hydrogen fuel cell system of claim 9 includes the following steps: S1. Load reduction and purging stage: During the operation of the hydrogen fuel cell system, when the voltage of a single cell of the stack (1) is lower than 0.85V, the speed of the hydrogen return pump (2) is increased, and the speed of the air compressor (16) is increased at the same time. S2. Load reduction and pressure increase stage: Reduce the load current of the hydrogen fuel cell system to 0A, increase the hydrogen infeed pressure and air infeed pressure, increase the hydrogen infeed pressure to 0.7bar~1.0bar, and increase the air infeed pressure to 0.5bar~0.8bar. Then close the first valve (8) and the third valve (21), reduce the hydrogen infeed flow rate and the air infeed flow rate to 0L / min, close the second valve (9) and the fourth valve (22), keep the hydrogen return pump (2) running, and open the first solenoid valve (13) and the second solenoid valve (14). S3. Oxygen-consuming load-pushing stage: The air reflux pump (15) is turned on, and the hydrogen fuel cell system issues a small current load-pushing command to the load connected to the positive and negative poles at both ends of the stack (1). The load is pulled for 1~5s and then stopped for 1~5s. This process is repeated until the voltage of a single cell of the stack (1) drops to 0.1V~0.2V and then the load-pushing stops. S4. Complete shutdown phase: When the hydrogen side pressure of the hydrogen fuel cell system is lower than the air side pressure by 0.4 bar to 0.6 bar, the fourth valve (22) is opened and the air back pressure valve (20) is opened at the same time to depressurize the air side to 0.1 bar to 0.3 bar lower than the hydrogen side pressure. After the depressurization 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.

Images