A method and system for controlling tail exhaust hydrogen concentration of a fuel cell system

Abstract

The present invention relates to the field of fuel cell technology, and discloses a method and system for controlling tail exhaust hydrogen concentration of a fuel cell system, comprising the following steps: obtaining the anode voltage of all cells in a stack, judging the state of the stack anode according to the anode voltage of all cells, the state of the stack anode including: flooded state and normal state; if the stack anode is in the flooded state, maintaining the cathode current and pressure of the stack unchanged, opening the exhaust valve and bypass valve, and exhausting the stack anode; adjusting the opening of the bypass valve, controlling the concentration of hydrogen in the exhaust gas, until the stack anode is converted to a normal state, and closing the exhaust valve and bypass valve. By maintaining the cathode current and pressure of the stack unchanged, and changing the air compression amount of the air compressor through the bypass valve, the air from the air compressor is diverted, which can not only increase the air content in the tail exhaust pipeline, but also ensure that the stack anode will not experience pressure fluctuations in the stack cathode during the exhaust process, thereby ensuring good power generation performance of the stack.

Description

Technical Field

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

[0002] A fuel cell stack is composed of multiple single cells stacked on top of each other. During the operation of the fuel cell system, cathode nitrogen will penetrate into the anode through the proton exchange membrane. The accumulation of nitrogen will reduce the hydrogen concentration, causing the overall voltage of the stack to drop. Therefore, regular exhaust is required. Since the exhaust gas discharged from the anode contains a large amount of hydrogen, it is generally necessary to mix it with the cathode exhaust gas and reduce the hydrogen concentration before discharging it into the atmosphere to ensure the safety of hydrogen discharge.

[0003] When the anode is flooded, the voltage of the single cell decreases, and it takes a long time to exhaust and purge the accumulated water to restore the voltage of the single cell. While purging the anode of the stack, a large amount of hydrogen will be discharged from the anode. The traditional treatment method is to increase the air flow of the cathode, so that the air flow discharged from the cathode outlet of the stack increases, thereby reducing the concentration of hydrogen in the tail exhaust pipeline. However, this treatment method has disadvantages. Increasing the air flow of the cathode of the stack will cause the pressure of the cathode of the stack to fluctuate, which will destroy the stability of the cathode reaction and affect the normal power generation of the fuel cell system. Therefore, in this case, it is necessary to optimize the tail exhaust hydrogen concentration control. Summary of the invention

[0004] The present invention aims to solve the above-mentioned problem and provides a method and system for controlling the tail exhaust hydrogen concentration of a fuel cell system, so as to solve the problem that when the anode of the fuel cell stack of the existing fuel cell system is flooded, the air flow to the cathode of the fuel cell stack is increased, resulting in unstable cathode voltage of the fuel cell stack and affecting the power generation stability of the fuel cell stack.

[0005] To achieve this object, the present invention adopts the following technical solutions:

[0006] A method for controlling tail exhaust hydrogen concentration of a fuel cell system comprises the following steps:

[0007] Obtaining the anode voltages of all cells in the battery stack, and determining the state of the anode of the battery stack according to the anode voltages of all cells, wherein the state of the anode of the battery stack includes: a flooded state and a normal state;

[0008] If the anode of the stack is flooded, maintain the cathode current and pressure of the stack unchanged, open the exhaust valve and bypass valve, and exhaust the anode of the stack;

[0009] Adjust the opening of the bypass valve to control the concentration of hydrogen in the exhaust gas until the anode of the stack is converted to a normal state, and then close the exhaust valve and bypass valve.

[0010] Preferably, determining whether the anode of the battery stack is in a flooded state comprises the following steps:

[0011] Set the voltage difference threshold and calculate the average anode voltage of all cells;

[0012] Obtain the maximum and minimum values ​​of the anode voltages of all single cells, defined as the maximum single voltage and the minimum single voltage;

[0013] The difference between the maximum single voltage and the average value of the anode voltage is calculated, which is defined as the first difference; the difference between the average value of the anode voltage and the minimum single voltage is calculated, which is defined as the second difference;

[0014] If and only if both the first difference and the second difference are greater than the pressure difference threshold, it is determined that the anode of the stack is in a flooded state.

[0015] Preferably, when the anode of the fuel cell stack is in a flooded state, the opening of the back pressure valve is kept unchanged, the cathode pressure of the fuel cell stack is kept unchanged, and the cathode air flow entering the fuel cell stack is kept unchanged.

[0016] Preferably, when the anode of the stack is in a flooded state, opening the exhaust valve and the bypass valve further comprises the following steps:

[0017] Set valve opening times t1 and t2, and t2>t1;

[0018] Set the minimum and maximum dilution values ​​of the bypass valve;

[0019] At time t1, the bypass valve is opened and the opening of the bypass valve is adjusted to the maximum dilution value;

[0020] Set the minimum and maximum emission values ​​of the exhaust valve;

[0021] At time t2, the exhaust valve is opened and the opening of the exhaust valve is adjusted to the minimum emission value;

[0022] The hydrogen concentration at the tail exhaust of the fuel cell system is detected, and the openings of the exhaust valve and the bypass valve are adjusted according to the detected hydrogen concentration.

[0023] Preferably, adjusting the opening of the exhaust valve and the bypass valve comprises the following steps:

[0024] Set the minimum and maximum values ​​of hydrogen concentration;

[0025] Reduce the opening of the bypass valve and increase the opening of the exhaust valve at the same time until the hydrogen concentration at the tail exhaust reaches the maximum hydrogen concentration;

[0026] Set the exhaust end time t3, and t3 is greater than t2;

[0027] The exhaust valve is closed at exhaust end time t3, and the anode of the stack is converted from a flooded state to a normal state.

[0028] Preferably, if it is detected that the hydrogen concentration is greater than the upper limit of the hydrogen concentration at any time between time t2 and time t3, the opening of the back pressure valve is increased until the hydrogen concentration is less than the upper limit of the hydrogen concentration.

[0029] Preferably, the conversion of the anode of the stack from the flooded state to the normal state further includes the following control steps:

[0030] The valve closing time t4 is set, and t4 is greater than t3. At the valve closing time t4, the hydrogen concentration in the tail exhaust pipeline is reduced to the minimum hydrogen concentration;

[0031] The bypass valve is closed at valve closing time t4.

[0032] Preferably, when the anode of the battery stack is converted from a flooded state to a normal state, the restriction on the unchanged cathode current and pressure of the battery stack is released.

[0033] A fuel cell system tail exhaust hydrogen concentration control system, including the above control method, comprises: a fuel cell stack, an oxygen supply module, a hydrogen supply module, an exhaust module, a back pressure valve and a bypass valve;

[0034] The oxygen supply module is connected to the cathode inlet of the fuel cell stack, and the oxygen supply module is used to provide oxygen to the fuel cell stack;

[0035] The hydrogen supply module is connected to the anode inlet of the fuel cell stack, and the hydrogen supply module is used to provide hydrogen to the fuel cell stack;

[0036] The discharge module is connected to the anode outlet of the fuel cell stack, and the discharge module is used to discharge gas and liquid from the anode of the fuel cell stack;

[0037] The back pressure valve is connected to the cathode outlet of the stack, and the back pressure valve is used to control the pressure of the cathode of the stack;

[0038] The bypass valve is connected between the supply module and the back pressure valve, and is used to divert the air from the oxygen supply module to the tail exhaust pipeline.

[0039] Preferably, the oxygen supply module comprises an air flow sensor, an air compressor and an air pressure sensor which are sequentially connected to the cathode of the fuel cell stack, and the output end of the air compressor is connected to the air inlet end of the bypass valve;

[0040] The hydrogen supply module comprises a hydrogen bottle, a proportional valve and an ejector connected in sequence, and the proportional valve controls the hydrogen in the hydrogen bottle to enter the anode of the stack through the ejector;

[0041] The emission module includes a gas-water separator, a drain valve and an exhaust valve. The input end of the gas-water separator is connected to the cathode outlet of the fuel cell stack, and the output end is respectively connected to the input ends of the ejector, the drain valve and the exhaust valve. The output ends of the drain valve and the exhaust valve are connected to the tail exhaust pipeline.

[0042] The contribution of the present invention is that by maintaining the cathode current and pressure of the fuel cell stack unchanged and changing the air compression volume of the air compressor through the bypass valve, the air from the air compressor is diverted, which can not only increase the air content in the tail exhaust pipe, but also ensure that during the exhaust process of the fuel cell stack anode, there will be no pressure fluctuation at the fuel cell stack cathode, thereby ensuring good power generation performance of the fuel cell stack. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is a schematic flow chart of a method for controlling tail exhaust hydrogen concentration of a fuel cell system of the present invention;

[0044] Figure 2 Schematic diagram of the changes of the bypass valve and the exhaust valve of the present invention;

[0045] Figure 3 It is a structural schematic diagram of the tail exhaust hydrogen concentration system of the fuel cell system of the present invention;

[0046] Figure 4 is a schematic flow chart of a cathode humidification method according to Embodiment 2 of the present invention;

[0047] Figure 5 is a schematic diagram of the relationship between the back pressure valve, air pressure, air flow rate and oxygen partial pressure in Example 2 of the present invention;

[0048] Figure 6 is a schematic diagram of the structure of Embodiment 3 of the present invention;

[0049] Figure 7 It is a schematic structural diagram of the tail gas collection device of the present invention;

[0050] Wherein: fuel cell stack 10, oxygen supply module 20, hydrogen supply module 30, exhaust module 40, back pressure valve 50, bypass valve 60, tail exhaust pipeline 70, tail gas collection device 80;

[0051] Air flow sensor 21, air compressor 22, air pressure sensor 23, hydrogen cylinder 31, proportional valve 32, ejector 33, air-water separator 41, drain valve 42, exhaust valve 43, box body 81, inlet 82, outlet 83, air guide port 84, baffle 85, and L-shaped channel 86. DETAILED DESCRIPTION

[0052] The following examples are provided to further explain and supplement the present invention and do not constitute any limitation to the present invention. Example

[0053] To facilitate understanding of the fuel cell system tail exhaust hydrogen concentration control method, the fuel cell system tail exhaust hydrogen concentration control system is first explained here. Figure 3 As shown:

[0054] The tail exhaust hydrogen concentration control system includes a fuel cell stack 10, an oxygen supply module 20, a hydrogen supply module 30, an exhaust module 40, a back pressure valve 50 and a bypass valve 60;

[0055] Furthermore, the oxygen supply module 20 includes an air flow sensor 21, an air compressor 22 and an air pressure sensor 23 which are sequentially connected to the cathode of the fuel cell stack 10, and the output end of the air compressor 22 is connected to the air inlet end of the bypass valve 60;

[0056] The hydrogen supply module 30 includes a hydrogen bottle 31, a proportional valve 32 and an ejector 33 connected in sequence, wherein the proportional valve 32 controls the hydrogen in the hydrogen bottle 31 to enter the anode of the fuel cell stack 10 through the ejector 33;

[0057] The emission module 40 includes a gas-water separator 41, a drain valve 42 and an exhaust valve 43. The input end of the gas-water separator 41 is connected to the cathode outlet 83 of the fuel cell stack 10, and the output end is respectively connected to the input ends of the ejector 33, the drain valve 42 and the exhaust valve 43. The output ends of the drain valve 42 and the exhaust valve 43 are connected to the tail exhaust pipeline 70.

[0058] Specifically, the air compressor 22 is used to control the air flow entering the fuel cell system. The air compressor 22 can compress and heat the air (70°-80°). The compressed and heated air enters the cathode inlet 82 of the fuel cell stack 10, and is discharged from the cathode outlet 83 of the fuel cell stack 10 after reaction. A back pressure valve 50 is connected to the cathode outlet 83 of the fuel cell stack 10. The back pressure valve 50 is used to control the pressure of the cathode of the fuel cell stack 10 to ensure that the pressure of the cathode of the fuel cell stack 10 does not fluctuate greatly. The exhaust gas from the cathode of the fuel cell stack 10 passes through the back pressure valve 50 and enters the tail exhaust pipeline 70 for discharge. The back pressure valve 50 and the air compressor 22 are connected by a bypass valve 60. The bypass valve 60 can divert part of the air from the air compressor 22 to the tail exhaust pipeline 70, thereby diluting the hydrogen concentration.

[0059] For further explanation, the proportional valve 32 in the hydrogen supply module 30 can control the pressure of hydrogen entering the anode of the fuel cell stack 10, and introduce the high-pressure hydrogen into the anode of the fuel cell stack 10 through the ejector 33. The gas-water separator 41 can separate the gas and liquid (liquid water, nitrogen and hydrogen) discharged from the anode of the fuel cell stack 10. The drain valve 42 and the exhaust valve 43 respectively connected to the gas-water separator 41 will be opened periodically to discharge the liquid and gas in the gas-water separator 41 to the tail exhaust pipeline 70. Since the cathode outlet 83 of the fuel cell stack 10 will continuously discharge unreacted air to the tail exhaust pipeline 70, the periodic drainage and exhaust of the gas-water separator 41 will not cause the hydrogen concentration in the tail exhaust pipeline 70 to exceed the standard, but when When the anode of the fuel cell stack 10 is in a flooded state, it is necessary to purge the anode of the fuel cell stack 10 for a long time, that is, the exhaust valve 43 needs to be continuously opened. At this time, the unreacted hydrogen passing through the anode of the fuel cell stack 10 will continuously enter the tail exhaust pipe 70 through the exhaust valve 43, resulting in an increase in the hydrogen concentration in the tail exhaust pipe 70. The air from the cathode outlet 83 of the fuel cell stack 10 alone cannot effectively reduce the hydrogen concentration in the tail exhaust pipe 70. The present invention sets a bypass valve 60 between the air compressor 22 and the back pressure valve 50. Under the premise of ensuring that the air flow and pressure at the cathode of the fuel cell stack 10 do not change, additional air is introduced to increase the air content in the tail exhaust pipe 70, thereby reducing the hydrogen concentration.

[0060] In order to better apply to the above control system, this embodiment also provides a Figure 1-2 The fuel cell system tail exhaust hydrogen concentration control method shown includes the following steps:

[0061] The anode voltages of all cells in the battery stack 10 are obtained, and the state of the anodes of the battery stack 10 is determined based on the anode voltages of all cells, wherein the state of the anodes of the battery stack 10 includes: a flooded state and a normal state; when the anodes of the battery stack 10 are in a flooded state, the voltages of the cells in the battery stack 10 will decrease, thereby reducing the overall power generation performance of the battery stack 10 and causing the battery stack 10 to age and decay prematurely.

[0062] Judging whether the anode of the battery stack 10 is flooded according to the anode voltages of all the cells in the battery stack 10 includes the following steps:

[0063] Set the voltage difference threshold and calculate the average anode voltage of all cells;

[0064] Obtain the maximum and minimum values ​​of the anode voltages of all single cells, defined as the maximum single voltage and the minimum single voltage;

[0065] The difference between the maximum single voltage and the average value of the anode voltage is calculated, which is defined as the first difference; the difference between the average value of the anode voltage and the minimum single voltage is calculated, which is defined as the second difference;

[0066] If and only if both the first difference and the second difference are greater than the pressure difference threshold, it is determined that the anode of the fuel cell stack 10 is in a water-flooded state.

[0067] Specifically, the detector in the fuel cell system will detect the anode voltage of all single cells in the stack 10 in real time, and feed back the detected voltage signal to the control processor of the fuel cell system. The control processor will calculate the average anode voltage of all single cells according to the received anode voltage signal. At the same time, the control processor will screen out the maximum and minimum anode voltages of all single cells, and define them as the maximum single voltage and the minimum single voltage respectively, and then calculate the first difference and the second difference, wherein the first difference is the difference between the maximum single voltage and the average anode voltage, and the second difference is the difference between the average anode voltage and the minimum single voltage. After calculating the first difference and the second difference, the first difference and the second difference are compared with the pressure difference threshold respectively, so as to determine whether the anode of the stack 10 is in a flooded state. Further explanation: if and only if the first difference and the second difference are both greater than the pressure difference threshold (the pressure difference threshold value range is 0.03V-0.05V), it is determined that the anode of the stack 10 is in a flooded state, and a subsequent purge process is performed.

[0068] After determining that the anode of the stack 10 is flooded through the anode voltages of all cells, the cathode current and pressure of the stack 10 need to be maintained constant, and the exhaust valve 43 and the bypass valve 60 are opened to exhaust the anode of the stack 10.

[0069] Further explanation, when the anode of the stack 10 is flooded, the traditional treatment method is to increase the air flow of the cathode, so that the gas flow discharged from the cathode outlet 83 of the stack 10 increases, thereby reducing the concentration of hydrogen in the tail exhaust pipe 70. However, this treatment method has disadvantages, that is, increasing the air flow of the cathode of the stack 10 will cause the pressure of the cathode of the stack 10 to fluctuate, which will destroy the stability of the cathode reaction and thus affect the normal power generation of the fuel cell system. In order to avoid changes in the cathode pressure of the stack 10, which will affect the power generation performance of the stack 10, this embodiment first maintains the cathode pressure when the anode of the stack 10 is in a flooded state. The cathode current and pressure of the stack 10 remain unchanged (the cathode current and pressure of the stack 10 remain unchanged by maintaining the opening of the back pressure valve 50 unchanged), and then the bypass valve 60 and the exhaust valve 43 are opened in sequence. The exhaust valve 43 is opened to allow hydrogen to purge the anode of the stack 10, thereby reducing the amount of water in the anode of the stack 10. The bypass valve 60 changes the air compression amount of the air compressor 22, thereby diverting the air from the air compressor 22, which can increase the air content in the tail exhaust pipe 70 and ensure that the cathode of the stack 10 will not experience pressure fluctuations during the exhaust process of the anode of the stack 10, thereby ensuring good power generation performance of the stack 10.

[0070] To further illustrate, opening the exhaust valve 43 and the bypass valve 60 also includes the following steps:

[0071] Set valve opening times t1 and t2, and t2 is greater than t1;

[0072] Setting a minimum dilution value and a maximum dilution value of the bypass valve 60 (the minimum dilution value corresponds to an opening degree of the bypass valve 60 of 10%, and the maximum dilution value corresponds to an opening degree of the bypass valve 60 of 30%);

[0073] At time t1, the bypass valve 60 is opened and the opening of the bypass valve 60 is adjusted to the maximum dilution value;

[0074] Setting the minimum emission value and the maximum emission value of the exhaust valve 43 (the minimum emission value corresponds to an opening degree of the exhaust valve 43 of 80%, and the maximum emission value corresponds to an opening degree of the exhaust valve 43 of 100%);

[0075] At time t2, the exhaust valve 43 is opened and the opening of the exhaust valve 43 is adjusted to the minimum emission value;

[0076] The hydrogen concentration at the tail exhaust of the fuel cell system is detected, and the openings of the exhaust valve 43 and the bypass valve 60 are adjusted according to the detected hydrogen concentration.

[0077] The bypass valve 60 opens at time t1 before the exhaust valve 43. The opening of the bypass valve 60 can increase the air content in the tail exhaust pipe 70, so that the concentration of hydrogen in the anode of the subsequent fuel cell stack 10 will not be too high when entering the tail exhaust pipe 70. After the air flow in the tail exhaust pipe 70 increases, the exhaust valve 43 is opened at time t2 (the interval between t2 and t1 is between 0.5s-1s), and hydrogen enters the tail exhaust pipe 70 through the exhaust valve 43, resulting in a gradual increase in the hydrogen concentration in the tail exhaust pipe 70. Further explanation, in order to ensure that the concentration of hydrogen does not exceed the standard when entering the tail exhaust pipe 70, in this embodiment, the initial opening of the bypass valve 60 is set to the maximum dilution value, and the initial opening of the exhaust valve 43 is set to the minimum emission value, to ensure that the concentration of hydrogen entering the tail exhaust pipe 70 is not too high.

[0078] After the hydrogen enters the tail exhaust pipe 70, the exhaust valve 43 and the bypass valve 60 need to be adjusted to ensure that the hydrogen concentration does not exceed the standard and the anode of the stack 10 can be purged to the greatest extent, which specifically includes the following steps:

[0079] Setting the minimum and maximum values ​​of hydrogen concentration (in this embodiment, the minimum value of hydrogen concentration is 3000 ppm, and the maximum value of hydrogen concentration is 10000 ppm, where the minimum and maximum values ​​of hydrogen concentration refer to the range of explosion critical values ​​of hydrogen in the tail exhaust pipeline 70);

[0080] Reduce the opening of the bypass valve 60 and increase the opening of the exhaust valve 43 at the same time (the amount of hydrogen discharged per unit time increases, and the anode purge time of the fuel cell stack 10 is shortened) until the hydrogen concentration at the tail exhaust reaches the maximum hydrogen concentration (at this time, it is at the explosion critical value of hydrogen. Under the premise of ensuring safety, the opening of the exhaust valve 43 is as large as possible, and the opening of the bypass valve 60 is as small as possible). Reducing the opening of the bypass valve 60 means reducing the flow of the air compressor 22, thereby reducing the burden on the air compressor 22 and avoiding premature damage to the air compressor 22;

[0081] Set the exhaust end time t3, and t3 is greater than t2;

[0082] The exhaust valve 43 is closed at the exhaust end time t3, and the anode of the fuel cell stack 10 is converted from the flooded state to the normal state.

[0083] Specifically, at time t3, the anode of the fuel cell stack 10 is converted from a flooded state to a normal state. The method for judging whether the anode of the fuel cell stack 10 is converted to a normal state is similar to the method for judging whether the anode of the fuel cell stack 10 is in a flooded state. Specifically, the anode of the fuel cell stack 10 is judged to be in a normal state when and only when the first difference and the second difference are both less than the pressure difference threshold.

[0084] For further explanation of this embodiment, if the hydrogen concentration detected at any time between time t2 and time t3 is greater than the upper limit of the hydrogen concentration, the opening of the back pressure valve 50 is increased until the hydrogen concentration is less than the upper limit of the hydrogen concentration. Specifically, the hydrogen concentration detected between time t2 and time t3 is greater than the upper limit of the hydrogen concentration, indicating that the bypass valve 60 is very likely to be blocked, resulting in the air from the bypass valve 60 not being able to smoothly enter the tail exhaust pipe 70. The air from the cathode outlet 83 of the stack 10 alone cannot effectively reduce the hydrogen concentration in the tail exhaust pipe 70 to the maximum value of the hydrogen concentration. In order to avoid the tail exhaust pipe 70 from discharging excessive hydrogen, the opening of the back pressure valve 50 is increased at this time, thereby increasing the air flow entering the cathode of the stack 10, which plays a role in diluting the hydrogen.

[0085] To further illustrate this embodiment, when the anode of the stack 10 is converted from the flooded state to the normal state, the following control steps are also included:

[0086] A valve closing time t4 is set, and the bypass valve 60 is closed at the valve closing time t4, t4 is greater than t3 (the interval between t4 and t3 is between 0.5s-1s), and the hydrogen concentration in the tail exhaust pipeline 70 is reduced to the minimum hydrogen concentration at the valve closing time t4;

[0087] When the anode of the stack 10 is converted from a flooded state to a normal state, the restriction on the cathode current and pressure of the stack 10 is released.

[0088] Specifically, the valve closing time t4 is set after the exhaust end time t3, ensuring that the hydrogen concentration in the tail exhaust pipe 70 is reduced to the minimum critical value of hydrogen explosion (the minimum hydrogen concentration). At this time, the air at the cathode outlet 83 of the fuel cell stack 10 can continue to dilute the residual hydrogen in the tail exhaust pipe 70, and there is no need to open the bypass valve 60, thereby reducing the working pressure of the air compressor 22. Further explanation, when the anode of the fuel cell stack 10 is converted from a flooded state to a normal state, the restriction on the unchanged cathode current and pressure of the fuel cell stack 10 is released, so that the fuel cell stack 10 can adjust the air flow at the inlet 82 according to the actual required power generation power to adapt to the different power requirements of the vehicle. Example

[0089] When the anode of the stack 10 is flooded, the fuel cell system is in a low-power state. Since the current of the stack 10 is small at this time, the amount of water generated at the cathode of the stack 10 is small, and the anode purge of the stack 10 lasts for a long time. A large amount of air is passed through the cathode of the stack 10 for a long time, resulting in a large amount of water being carried away from the cathode of the stack 10. The longer the purge time, the greater the possibility of drying of the cathode membrane of the stack 10. Drying of the cathode membrane of the stack 10 will greatly reduce the proton conductivity of the membrane, resulting in reduced power generation performance of the cathode of the stack 10.

[0090] like Figure 4-5 As shown, this embodiment provides a method for humidifying the cathode of a stack 10, which is applied to the case where the cathode of the stack 10 is excessively dry after the anode of the stack 10 is purged, and specifically includes the following humidification steps:

[0091] S1: Setting a purge time threshold. If the purge time of the anode of the stack 10 is greater than the purge time threshold, it is determined that the cathode of the stack 10 is in a dry state (the anode continues to purge and removes a large amount of moisture from the membrane electrode, causing part of the moisture on the membrane electrode on the cathode side of the stack 10 to be absorbed by the membrane electrode on the anode side of the stack 10, causing the cathode membrane electrode of the stack 10 to dry out);

[0092] S2: Obtain the current air pressure P1 and air flow Q1 of the cathode of the fuel cell stack 10, increase the air pressure P1 to P2 within T1, and maintain the air flow Q1 unchanged;

[0093] S3: When the air pressure rises to P2, the air flow rate Q1 is reduced to Q2 within T2 to maintain the air pressure P2 unchanged;

[0094] S4: When the air flow rate is reduced to Q2, the air pressure P2 is reduced to P1 within T3, and the air flow rate Q2 is increased to Q1 at the same time;

[0095] S5: Repeat steps S2-S4 within a preset number of times to complete cathode humidification of the fuel cell stack 10.

[0096] Among them, T1 is 1s-2s, T2 is 3s-6s, T3 is 3s-6s, the preset number of times is 10-15 times, Q1=2Q2, P2=1.4P1.

[0097] To further explain, in step S2, increasing the air pressure from P1 to P2 is achieved by adjusting the back-pressure valve 50, specifically by reducing the opening of the back-pressure valve 50, thereby increasing the air pressure while keeping the air flow rate Q1 unchanged. The increased air pressure at the cathode of the fuel cell stack 10 will cause an increase in the oxygen partial pressure at the cathode (higher than the target oxygen partial pressure at the cathode of the fuel cell stack 10), which is beneficial to the electrochemical reaction at the cathode of the fuel cell stack 10 to generate water, thereby wetting the cathode membrane of the fuel cell stack 10.

[0098] It should be noted here that the oxygen partial pressure is mainly determined by two factors: air pressure and air flow, and the oxygen partial pressure is directly proportional to the air pressure and air flow. The cathode reaction of the fuel cell stack 10 needs to be maintained at the corresponding target oxygen partial pressure, so as to maintain a certain excess ratio of oxygen participating in the reaction to prevent the single cell from lacking oxygen and being unable to generate electricity stably.

[0099] In step S3, the air flow rate Q1 is reduced to Q2. In order to maintain the air pressure P2 unchanged, it is necessary to further reduce the opening of the back pressure valve 50. At this time, due to the reduction in air flow, the oxygen partial pressure at the cathode will decrease (slightly lower than the target oxygen partial pressure of the fuel cell stack 10, with a decrease of 3%-5%). The air flow rate is reduced without affecting the normal power generation of the cathode of the fuel cell stack 10, thereby reducing the moisture carried away by the cathode of the fuel cell stack 10 and inhibiting the drying of the cathode membrane of the fuel cell stack 10.

[0100] In step S4, the air pressure P2 is reduced to P1, and the air flow Q2 is increased to Q1, so that the cathode of the stack 10 returns to its initial state, and the oxygen partial pressure at the cathode of the stack 10 also returns to the initial target oxygen partial pressure, thereby completing a cycle of humidification process.

[0101] Through 10-15 times of repeated humidification, the cathode membrane of the fuel cell stack 10 can be restored to a better wet state, thereby preventing the cathode membrane of the fuel cell stack 10 from drying out and failing to generate electricity normally.

[0102] This embodiment adjusts the air pressure and air flow at the cathode of the fuel cell stack 10 to change the oxygen partial pressure at the cathode of the fuel cell stack 10. This can ensure the normal operation of the cathode of the fuel cell stack 10 while humidifying the cathode of the fuel cell stack 10, thereby avoiding drying of the cathode of the fuel cell stack 10 due to long-term purging of the anode of the fuel cell stack 10 in a low-power environment of the fuel cell system. Example

[0103] During the anode purging process of the fuel cell stack 10, hydrogen will continue to be discharged into the external environment. If it is in an open environment, the discharged hydrogen will quickly disperse into the atmosphere and will not affect the environment. If it is in a tunnel or an environment with poor air circulation, the hydrogen discharged by the anode purging of the fuel cell stack 10 is prone to accumulation. When the hydrogen concentration reaches a certain range, combustion or even explosion accidents are prone to occur, which brings great safety hazards to the application of fuel cell vehicles. Therefore, the purged hydrogen cannot be directly discharged into the atmosphere in the tunnel.

[0104] like Figure 6-7 As shown, this embodiment designs an exhaust gas collection device 80, which is connected to the tail exhaust pipe 70, and the exhaust gas collection device 80 includes a box 81, an inlet 82, an outlet 83, an air guide port 84 and a baffle 85;

[0105] The box 81 is provided with accumulated water;

[0106] The inlet 82 and the outlet 83 are respectively arranged on both sides of the box body 81, and the inlet 82 is located above the outlet 83;

[0107] The gas guide port 84 is disposed at the top of the box body 81 , and the gas guide port 84 is connected to the ejector 33 , and is used to guide the hydrogen accumulated in the box body 81 into the ejector 33 ;

[0108] One end of the baffle 85 is connected to one end of the box body 81 close to the outlet 83, and the other end of the baffle 85 is inserted into the accumulated water and located below the outlet 83. An L-shaped channel 86 is provided between the other end of the baffle 85 and the box body 81 for the accumulated water to enter the outlet 83.

[0109] The bottom plane of the outlet 83 is at the same vertical height as the top plane of the accumulated water.

[0110] Specifically, when the fuel cell system is in the tunnel, the hydrogen purged from the anode of the stack 10 is diluted and reduced in concentration through the tail exhaust pipeline 70 and then enters the box 81 from the inlet 82 of the tail gas collection device 80. Liquid water is provided at the bottom of the box 81. The tail exhaust gas entering the box 81 contains water vapor, oxygen, nitrogen and hydrogen. The water vapor will liquefy and accumulate at the bottom of the box 81 after contacting the liquid water. The water near the outlet 83 will be discharged into the tunnel along the outlet 83 under the pressure of the gas in the box 81. The oxygen, nitrogen and hydrogen will be stored in the accumulation. To further illustrate, above the water, oxygen, nitrogen and hydrogen will be stratified in the box 81. Hydrogen, due to its lightest mass, will accumulate at the top of the box 81, and oxygen and nitrogen will be closer to the accumulated water. When the tail exhaust gas enters the box 81, in addition to water vapor turning into accumulated water and being discharged from the box 81, oxygen and nitrogen will be pushed out of the box 81 by the hydrogen accumulated above and discharged from the box 81 together with the accumulated water. As the purge continues, more and more hydrogen will be stored in the box 81, and oxygen, nitrogen and water vapor will be continuously discharged from the box 81 to avoid hydrogen accumulation in the tunnel.

[0111] When the fuel cell system leaves the tunnel with the vehicle, the inlet 82 of the exhaust gas collection device 80 is closed, and the hydrogen purged from the anode of the fuel cell stack 10 is diluted by the air in the tail exhaust pipe 70 and discharged to the outside after the concentration is reduced (refer to the emission control method of Example 1). On the other hand, while closing the inlet 82 of the exhaust gas collection device 80, the air guide port 84 is opened, so that the hydrogen stored in the box 81 re-enters the anode of the fuel cell stack 10 through the ejector 33, so that the hydrogen can be reused repeatedly, saving resources.

[0112] Further explanation, the setting of the baffle 85 in this embodiment can increase the pressure at the L-shaped channel 86, so that the accumulated water, oxygen and nitrogen can be quickly discharged from the box 81. At the same time, the setting of the baffle 85 can effectively prevent hydrogen from bypassing the accumulated water and being discharged directly from the outlet 83.

[0113] In this embodiment, a tail gas collection device 80 is provided on the tail exhaust pipeline 70, and by utilizing the low density of hydrogen, hydrogen is stored in the tail gas collection device 80 when the anode of the fuel cell stack 10 is purged, thereby avoiding hydrogen discharge, improving the safety performance of the fuel cell system in the tunnel, and reusing the hydrogen in the tail gas collection device 80 after leaving the tunnel, thereby saving hydrogen resources.

[0114] Although the present invention is disclosed through the above embodiments, the protection scope of the present invention is not limited thereto. Without departing from the concept of the present invention, any deformation, replacement, etc. made to the above components shall fall within the scope of the claims of the present invention.

Claims

1. A method for controlling tail exhaust hydrogen concentration of a fuel cell system, characterized in that: The steps include: Obtaining the anode voltages of all cells in the battery stack, and determining the state of the anode of the battery stack according to the anode voltages of all cells, wherein the state of the anode of the battery stack includes: a flooded state and a normal state; If the anode of the stack is flooded, keep the back pressure valve open, maintain the cathode current and pressure of the stack and the cathode air flow entering the stack unchanged, open the exhaust valve and bypass valve, and exhaust the anode of the stack; Adjust the opening of the bypass valve to control the concentration of hydrogen in the exhaust gas until the anode of the stack is converted to a normal state, and then close the exhaust valve and bypass valve.

2. A method for controlling tail exhaust hydrogen concentration of a fuel cell system according to claim 1, characterized in that: Determining whether the anode of the battery stack is flooded includes the following steps: Set the voltage difference threshold and calculate the average anode voltage of all cells; Obtain the maximum and minimum values ​​of the anode voltages of all single cells, defined as the maximum single voltage and the minimum single voltage; The difference between the maximum single voltage and the average value of the anode voltage is calculated, which is defined as the first difference; the difference between the average value of the anode voltage and the minimum single voltage is calculated, which is defined as the second difference; If and only if both the first difference and the second difference are greater than the pressure difference threshold, it is determined that the anode of the stack is in a flooded state.

3. A method for controlling tail exhaust hydrogen concentration of a fuel cell system according to claim 1, characterized in that: When the anode of the stack is flooded, opening the exhaust valve and bypass valve also includes the following steps: Set valve opening times t1 and t2, and t2 is greater than t1; Set the minimum and maximum dilution values ​​of the bypass valve; At time t1, the bypass valve is opened and the opening of the bypass valve is adjusted to the maximum dilution value; Set the minimum and maximum emission values ​​of the exhaust valve; At time t2, the exhaust valve is opened and the opening of the exhaust valve is adjusted to the minimum emission value; The hydrogen concentration at the tail exhaust of the fuel cell system is detected, and the openings of the exhaust valve and the bypass valve are adjusted according to the detected hydrogen concentration.

4. A method for controlling tail exhaust hydrogen concentration of a fuel cell system according to claim 3, characterized in that: Adjusting the opening of the exhaust valve and the bypass valve comprises the following steps: Set the minimum and maximum values ​​of hydrogen concentration; Reduce the opening of the bypass valve and increase the opening of the exhaust valve at the same time until the hydrogen concentration at the tail exhaust reaches the maximum hydrogen concentration; Set the exhaust end time t3, and t3 is greater than t2; The exhaust valve is closed at exhaust end time t3, and the anode of the stack is converted from a flooded state to a normal state.

5. A method for controlling tail exhaust hydrogen concentration of a fuel cell system according to claim 4, characterized in that: If it is detected that the hydrogen concentration is greater than the upper limit of the hydrogen concentration at any time between time t2 and time t3, the opening of the back pressure valve is increased until the hydrogen concentration is less than the upper limit of the hydrogen concentration.

6. A method for controlling tail exhaust hydrogen concentration of a fuel cell system according to claim 4, characterized in that: The conversion of the stack anode from the flooded state to the normal state also includes the following control steps: The valve closing time t4 is set and the bypass valve is closed at the valve closing time t4, t4 is greater than t3, and the hydrogen concentration in the tail exhaust pipeline is reduced to the minimum hydrogen concentration at the valve closing time t4.

7. A method for controlling tail exhaust hydrogen concentration of a fuel cell system according to claim 6, characterized in that: When the anode of the stack is converted from a flooded state to a normal state, the restrictions on the cathode current and pressure of the stack are released.

8. A fuel cell system tail exhaust hydrogen concentration control system, comprising the control method according to any one of claims 1 to 7, characterized in that: include: Fuel stack, oxygen supply module, hydrogen supply module, exhaust module, back pressure valve and bypass valve; The oxygen supply module is connected to the cathode inlet of the fuel cell stack, and the oxygen supply module is used to provide oxygen to the fuel cell stack; The hydrogen supply module is connected to the anode inlet of the fuel cell stack, and the hydrogen supply module is used to provide hydrogen to the fuel cell stack; The discharge module is connected to the anode outlet of the fuel cell stack, and the discharge module is used to discharge gas and liquid from the anode of the fuel cell stack; The back pressure valve is connected to the cathode outlet of the stack, and the back pressure valve is used to control the pressure of the cathode of the stack; The bypass valve is connected between the supply module and the back pressure valve, and is used to divert the air from the oxygen supply module to the tail exhaust pipeline.

9. A fuel cell system tail exhaust hydrogen concentration control system according to claim 8, characterized in that: The oxygen supply module includes an air flow sensor, an air compressor and an air pressure sensor which are sequentially connected to the cathode of the fuel cell stack, and the output end of the air compressor is connected to the air inlet end of the bypass valve; The hydrogen supply module comprises a hydrogen bottle, a proportional valve and an ejector connected in sequence, and the proportional valve controls the hydrogen in the hydrogen bottle to enter the anode of the stack through the ejector; The emission module includes a gas-water separator, a drain valve and an exhaust valve. The input end of the gas-water separator is connected to the cathode outlet of the fuel cell stack, and the output end is respectively connected to the input ends of the ejector, the drain valve and the exhaust valve. The output ends of the drain valve and the exhaust valve are connected to the tail exhaust pipeline.

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