A fuel cell system start-up process emission valve fault diagnosis method, fuel cell system start-up process

Abstract

The application discloses a kind of fuel cell system starting process emission valve fault diagnosis method, fuel cell system starting process.For the failure that fuel cell system cannot open emission valve in starting process, this application diagnoses whether there is abnormality to emission valve before normal output power of fuel cell system, to directly avoid the failure that emission valve cannot open, directly start to cause anode hydrogen deficiency when stack runs, and thus cause system trigger cannot start.For when establishing OCV directly, stack single cell OCV voltage will be in about 0.96V high voltage state, long-term in this high voltage state can lead to carbon corrosion phenomenon of stack membrane electrode, affect stack service life, after system OCV is established without abnormality, this application applies certain current to stack simultaneously in starting process, and single cell voltage of stack is maintained at about 0.80~0.85V, and this voltage is generally considered to have less influence on membrane electrode carbon corrosion.

Description

Technical Field

[0001] This invention belongs to the field of fuel cell technology, specifically relating to a method for diagnosing faults in the discharge valve during the start-up process of a fuel cell system and the start-up process of a fuel cell system. Background Technology

[0002] During startup, the proton exchange membrane fuel cell system needs to establish the open-circuit voltage (OCV) of the stack. During this process, the system does not output power to the outside and is used to determine whether the performance of each cell in the stack is normal. Once the OCV voltage is established normally, current is applied to the stack so that the stack can output power to the outside.

[0003] Currently, during the startup and establishment of the OCV (Optical Characteristic Cell) in a fuel cell system, hydrogen is typically supplied to the anode and air to the cathode. Once the OCV voltage is normal, the system directly applies current to the stack to start operation.

[0004] For example, the invention application with publication number CN115275276A discloses the specific procedure for starting up a fuel cell stack as follows: air and hydrogen are introduced into the anode and cathode of the stack, respectively. After the stack establishes a stable OCV, the load is controlled to make the stack output 5-10 mA / cm for a period of time. 2 The current is monitored, and the subsequent startup procedure is run only after the stack voltage has risen continuously for 3-10 seconds. The process of establishing the OCV before fuel cell stack startup refers to the process from the initial introduction of reactant gas until the stack voltage reaches a stable open-circuit voltage.

[0005] The invention application with publication number CN117525497A discloses a method for starting up a high-temperature proton exchange membrane fuel cell and a fuel cell. In the first stage of startup, gas supply is started before startup to establish the OCV.

[0006] This conventional startup method has the following two drawbacks: Firstly, when establishing the OCV directly, the OCV voltage of each cell in the fuel cell stack will be at a high voltage of about 0.96V. Being in this high voltage state for a long time will cause carbon corrosion of the film electrode of the fuel cell stack, affecting the service life of the fuel cell stack.

[0007] Secondly, when the system has been shut down for a long time, air will remain in the anode of the fuel cell stack. When hydrogen is introduced into the anode during the startup process, a hydrogen-air interface will be formed at the anode of the fuel cell stack. At this time, although the OCV voltage is normal, if the discharge valve fails to open during this process and current is directly applied to the fuel cell stack, it will cause hydrogen deficiency at the anode, which will cause the system to fail to work properly. Summary of the Invention

[0008] To address the aforementioned shortcomings in the prior art, this invention provides a method for diagnosing faults in the discharge valve during the start-up process of a fuel cell system, and the start-up process of a fuel cell system.

[0009] This invention first provides a method for diagnosing faults in the discharge valve during the start-up process of a fuel cell system. The fuel cell system includes a fuel cell stack and a hydrogen subsystem. The fuel cell stack includes several individual cells, and the hydrogen subsystem includes a discharge valve. During the start-up process of the fuel cell system, the voltage of each individual cell decreases. The method for diagnosing faults in the discharge valve during the start-up process of the fuel cell system includes the following steps: S1, set the hydrogen inlet pressure, establish the pressure in the hydrogen chamber of the fuel cell stack, and determine whether the absolute value error between the hydrogen inlet pressure detection value and the set value is greater than the set first threshold. If it is not greater than the set first threshold, wait for the pressure to meet the condition; if it is greater than the set first threshold, open the discharge valve. S2, after a certain delay, determine whether the pressure difference between the hydrogen inlet pressure detection values ​​before and after the discharge valve opens is greater than the set second threshold. If it is greater than the set second threshold, the discharge valve is normal, indicating that the voltage drop of the single cell during the fuel cell system startup process is not caused by the discharge valve. If it is not greater than the set second threshold, it indicates that the discharge valve cannot open normally, and the voltage drop of the single cell during the fuel cell system startup process is caused by the discharge valve.

[0010] Preferably, the first threshold is 1~10 kPa; the second threshold is 20~45 kPa.

[0011] Preferably, in step S1, the hydrogen inlet pressure is set to 130~150 kPa.a.

[0012] Preferably, in step S2, the delay time is 2~5s.

[0013] To address the issue of the emission valve failing to open during the startup of a fuel cell system, this application diagnoses whether the emission valve is abnormal before the fuel cell system outputs power normally. This directly avoids the situation where the system fails to start due to hydrogen deficiency at the anode during stack operation caused by the emission valve failing to open.

[0014] This invention also provides a start-up process for a fuel cell system. The fuel cell system includes a fuel cell stack, a hydrogen subsystem, an air subsystem, and a cooling subsystem. The fuel cell stack includes several individual cells. The hydrogen subsystem includes an exhaust valve. The air subsystem includes an air compressor, a shut-off valve, and a back pressure valve. The cooling subsystem includes a circulating water pump. The start-up process of the fuel cell system includes the following steps: Step 1: The vehicle requests the fuel cell system to start. After receiving the start command, the hydrogen inlet pressure is set and the exhaust valve is opened. After a certain delay, the hydrogen pressure is established. Step 2: Close the discharge valve, turn on the circulating water pump and air compressor, and fully open the shut-off valve and back pressure valve to establish an open-circuit voltage for the fuel cell stack. Step 3: Determine if the open-circuit voltage is greater than the preset threshold. If it is not greater, the fuel cell system fails to start and the system malfunctions. If it is greater, set the fuel cell stack current so that the single cell voltage is 0.80~0.85V. Step 4: Determine if the minimum single cell voltage is greater than the preset single cell threshold. If it is, it indicates that the exhaust valve is normal, hydrogen pressure is established, the fuel cell system starts successfully, and it waits for the vehicle to request power. If it is not, it indicates that the exhaust valve may be abnormal. Further judgment is made, the current of the fuel cell stack is set to 0, and all steps are repeated from the hydrogen inlet pressure set in Step 1. If the fuel cell system still cannot start successfully after the number of cycles exceeds the set number of cycles, the exhaust valve diagnosis process is activated, and the exhaust valve fault diagnosis method for the fuel cell system startup process described in any one of claims 1 to 4 is performed.

[0015] Preferably, in step 1, the hydrogen inlet pressure is set to 110~150 kPa.a; and the delay time is 1~10 s.

[0016] Preferably, in step 2, the speed of the circulating water pump is 1000~3000 rpm; the speed of the air compressor is 30000~50000 rpm.

[0017] Preferably, in step 3, the preset threshold for the open-circuit voltage is 0.8V×N~0.96V×N, where N is the number of single cells and V represents the voltage unit.

[0018] Preferably, in step 4, the preset single-cell threshold is 0.1~0.7V; and the set number of cycles is 1~5.

[0019] When directly establishing the OCV, the OCV voltage of each cell in the fuel cell stack is at a high voltage of approximately 0.96V. Prolonged exposure to this high voltage can lead to carbon corrosion of the membrane electrode assembly (MEA) and affect the lifespan of the fuel cell stack. This application addresses this by applying a certain current to the fuel cell stack during startup after the OCV establishment is normal, thereby maintaining the voltage of each cell at approximately 0.80~0.85V. This voltage is generally considered to have a relatively small impact on the carbon corrosion of the MEA. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of a fuel cell system.

[0021] Figure 2 This is a flowchart of the fuel cell system startup process. In the decision steps, "Y" represents "yes" and "N" represents "no".

[0022] Figure 3 This is a flowchart for diagnosing discharge valve malfunctions.

[0023] Figure 4This is a sequence diagram showing the normal operation of the discharge valve during the startup process of a fuel cell system.

[0024] Figure 5 This is a sequence diagram showing the operation of a fuel cell system during startup when the discharge valve malfunctions.

[0025] Figure 6 A schematic diagram showing the internal gas distribution after hydrogen has been fully established at the anode of a fuel cell stack.

[0026] Figure 7 This is a schematic diagram of the internal gas distribution at the hydrogen-air interface of the anode in a fuel cell stack.

[0027] Figure 8 This is a diagnostic timing diagram for a fuel cell system where the discharge valve cannot be opened.

[0028] Figure 9 This is a timing diagram illustrating the diagnostic process for the normal opening of the exhaust valve in a fuel cell system.

[0029] Figure 10 This is a diagnostic data graph showing the failure of the emission valve to open in an actual fuel cell system.

[0030] Figure 11 This is a diagnostic data graph showing the normal opening of the discharge valve in an actual fuel cell system. Detailed Implementation

[0031] like Figure 1 The diagram shown is a schematic representation of the fuel cell system structure of this application. Figure 2 The diagram shown is a flowchart of the fuel cell system startup process of this application. Figure 3 The diagram shown is a flowchart for diagnosing the fault of the discharge valve in this application.

[0032] I. Structure of the fuel cell system in this application: The structure of the fuel cell system in this application is as follows: Figure 1 As shown, the fuel cell system 70 mainly includes a fuel cell hydrogen subsystem 10, a fuel cell cooling subsystem 20, a fuel cell air subsystem 30, a fuel cell stack 40, a single cell inspection controller (CVM controller) 50, and a fuel cell controller (FCU controller) 60.

[0033] The fuel cell hydrogen subsystem 10 of this application includes a high-pressure storage cylinder 11, a pressure reducing valve 12, a hydrogen pressure and flow regulating valve 13, an ejector 14, a hydrogen inlet pressure sensor 15, a pressure relief valve 16, a water separator 17, and a discharge valve 18. The high-pressure storage cylinder 11 stores hydrogen, which is reduced to the permissible operating pressure of the fuel cell system by the pressure reducing valve 12. The reduced-pressure hydrogen is then supplied with the flow rate and pressure for operation of the fuel cell stack 40 by the hydrogen pressure and flow regulating valve 13. The hydrogen inlet pressure sensor 15 detects the inlet pressure of the fuel cell stack 40. During operation, unreacted hydrogen is discharged from the anode tail and separated from the liquid water (generated during the stack reaction) by the water separator 17. The remaining wet hydrogen is recycled back into the fuel cell stack 40 via the ejector 14, and the separated liquid water is discharged into the atmosphere through the discharge valve 18. The pressure relief valve 16 is used to open and release pressure when the hydrogen inlet pressure sensor 15 detects that the pressure exceeds the set range, so that some hydrogen is released into the atmosphere through the pressure relief valve 16, ensuring that the pressure inside the fuel cell stack 40 will not be overloaded.

[0034] The fuel cell cooling subsystem 20 in this application includes a circulating water pump 21, a coolant inlet temperature sensor 22, a coolant outlet temperature sensor 23, an electronic thermostat 24, a radiator 25 (including a cooling fan), a particulate filter 26, and a water tank 27. During the reaction process of the fuel cell stack 40, the circulating water pump 21 provides a certain flow rate of coolant to the fuel cell stack 40 to remove the heat generated inside the fuel cell stack 40. The coolant inlet temperature sensor 22 and the coolant outlet temperature sensor 23 detect whether the coolant temperatures at the inlet and outlet are within a reasonable range. The electronic thermostat 24 is mainly used during the initial startup process when rapid heating is required. The coolant circulates briefly through the electronic thermostat 24. After reaching the optimal temperature of the stack, the coolant flows through the electronic thermostat 24 and then through the radiator 25. The radiator 25 dissipates the heat generated by the stack to the atmosphere, ensuring the stack operates at its optimal temperature. The coolant exiting from the radiator 25 passes through the particulate filter 26 to remove solid particles. The main function of the water tank 27 is to replenish the cooling system with coolant to prevent insufficient coolant due to thermal expansion and contraction.

[0035] The fuel cell air subsystem of this application includes an air filter 31, an air mass flow meter 32, an air compressor 33, an intercooler 34, a humidifier 35, a shut-off valve 36, an air inlet temperature sensor 37, an air inlet pressure sensor 38, and a back pressure valve 39. The air compressor 33 compresses ambient air into high-temperature, high-pressure compressed air. The ambient air first passes through the air filter 31 to remove harmful gases and particulate matter, and then passes through the air mass flow meter 32 to monitor the airflow rate. The compressed high-temperature, high-pressure air is cooled to a low-temperature state (high pressure) that meets the requirements of the fuel cell stack by the intercooler 34. The cooled air is then humidified by the humidifier 35 to meet the requirements of the fuel cell stack. The humidified air flows through the shut-off valve 36, and the air inlet temperature sensor 37 and air inlet pressure sensor 38 detect the air pressure and temperature values. The exhaust air from the cathode tail of the fuel cell stack 40 first passes through a humidifier 35 for heat and moisture exchange with the incoming air, and then passes through a back pressure valve 39 to be discharged into the atmosphere; the back pressure valve 39 is used to control the pressure of the air inlet of the fuel cell stack.

[0036] The fuel cell stack 40 in this application uses a low-temperature proton exchange membrane fuel cell. The fuel cell stack consists of multiple single cells connected in series. Each single cell is mainly composed of key components such as a proton exchange membrane, a catalyst layer, a diffusion layer, bipolar plates, and sealing rings. The proton exchange membrane (PEM) is used to conduct protons, isolate hydrogen at the anode and oxygen at the cathode, block electron conduction, and provide structural support for the membrane electrode assembly. The catalyst layer (CL) is loaded with a catalyst to accelerate the oxidation of hydrogen at the anode and the reduction of oxygen at the cathode, constructing a gas-liquid-solid three-phase reaction interface and achieving preliminary electron collection and transport. The gas diffusion layer (GDL) is used to uniformly distribute the reaction gases, remove the water generated by the reaction, conduct electrons, and buffer assembly pressure to protect the core components. The bipolar plates (BPP) are used to collect the output current, distribute the reaction gases and cooling medium, connect the single cells in series, remove water and heat, and provide mechanical support for the stack. The sealing rings are used to seal the anode, cathode, and coolant chamber to prevent gas crosstalk, medium leakage, and component short circuits, ensuring the stack's airtightness and operational safety.

[0037] The fuel cell controller (FCU controller) 60 monitors the operating status of components in each subsystem, coordinates the operation of system components synchronously, and handles fault diagnosis of the emission valve. The dashed lines in the diagram indicate communication connections between each component and the fuel cell controller (FCU controller) 60.

[0038] The single cell inspection controller (CVM controller) 50 is used to detect the voltage of multiple single cells connected in series in the fuel cell stack 40.

[0039] II. Working principle of the fuel cell system in this application: The main objective of this application is to reduce the duration of the OCV voltage during the startup process of a fuel cell system (which is also the process of the fuel cell system outputting electricity to the outside world) by applying a small current to the fuel cell stack (maintaining the voltage of a single cell in the stack at 0.80~0.85V, preferably 0.82V); in addition, it directly diagnoses whether there is any abnormality in the discharge valve during the startup process. If the discharge valve cannot open, it will not be able to operate normally after the system has been shut down for a long time, causing abnormal operation of the fuel cell system.

[0040] like Figure 2 The diagram shown is a flowchart of the fuel cell system startup process of this application. The main working principle of this application is as follows: Step S101: As Figure 4 As shown, when the vehicle is stationary, the fuel cell system is in an inactive state, and the vehicle key switch is turned on.

[0041] Step S102: The vehicle requests the fuel cell system to start. If the start command is "Yes", proceed to step S103; if the start command is "No", proceed to step S201 to wait for the vehicle start command.

[0042] Step S103: Set the hydrogen inlet first pressure Pset1 and open the discharge valve, as follows. Figure 4 During the OCV setup phase of the system, the first hydrogen inlet pressure Pset1 can be selected as 140 kPa.a. This pressure can be selected according to the actual situation of the system. The selectable value range is 110~150 kPa.a. It is necessary to control the difference between the hydrogen pressure and the fuel cell stack air inlet pressure to be less than or equal to 50 kPa.

[0043] Step S104: Delay time Δt1; Δt1 can be selected as 6s. This delay time Δt1 can be selected according to the actual situation of the system. The range of selectable values ​​is 1~10s. Its main purpose is to purge the air in the anode of the fuel cell stack during the startup process and establish hydrogen pressure.

[0044] Step S105: Close the discharge valve, set the first speed of the circulating water pump (WCP), set the first speed of the air compressor (RCP), fully open the shut-off valve, and fully open the back pressure valve. The first speed of the circulating water pump (WCP) can be selected as 2000 rpm. This speed can be selected according to the actual system conditions, with a selectable range of 1000~3000 rpm. It is necessary to control the inlet pressure of the fuel cell coolant to not exceed the inlet pressure of the air side. The first speed of the air compressor (RCP) can be selected as 45000 rpm. This speed can be selected according to the actual system conditions, with a selectable range of 30000~50000 rpm. It is necessary to control the inlet pressure of the air to not exceed the inlet pressure of the hydrogen. Fully open the shut-off valve; fully open the back pressure valve; set the air compressor speed. The purpose of opening the shut-off valve and the back pressure valve is to establish the open-circuit voltage (OCV) of the fuel cell stack.

[0045] Step S106: Determine whether the open-circuit voltage (OCV) of the fuel cell stack is greater than a preset first threshold Vst1. The preset first threshold Vst1 can be set to 0.9V×N, where N is the number of individual cells in the fuel cell stack. The first threshold Vst1 can be selected according to the actual system conditions, with a selectable value range of 0.8×N~0.96×N (unit: V), as long as it can be determined that the performance of the individual cells in the fuel cell stack is normal. If step S106 determines "no", proceed to step S202: Fuel cell system startup failure, troubleshooting system malfunction. The OCV voltage cannot be established successfully, which may be due to damage to the membrane electrode assembly leading to performance degradation.

[0046] Step S107: If the determination in step S106 is "yes", that is, the open-circuit voltage OCV of the fuel cell stack is greater than the preset first threshold Vst1, the first current Crst1 of the fuel cell stack is set, such as... Figure 4 During the high-potential elimination phase, the initial current Crst1 of the fuel cell stack can be selected as 37A to maintain the voltage of each individual cell at approximately 0.82V. The initial current Crst1 can be selected at other values ​​depending on the actual system conditions to maintain the voltage of each individual cell within a selectable range of 0.80~0.85V. The purpose is to reduce the voltage of each individual cell during startup and minimize carbon corrosion.

[0047] Step S108: Determine whether the lowest single-cell voltage of the single cell is greater than the preset first single-cell threshold Vcell1. The first single-cell threshold Vcell1 can be selected as 0.6V. This value can be selected according to the actual system conditions, with a range of 0.1~0.7V. Any value that can determine an abnormal single-cell voltage is acceptable, as long as the condition is met. The purpose of this step is to determine if a shutdown during a long stack operation, resulting in the vent valve failing to open and the anode becoming filled with air, leads to a hydrogen-air interface forming at the anode after hydrogen pressure is established in step S103. Figure 7 During this process, the individual cell will not exhibit any abnormalities. However, with the instantaneous application of current, hydrogen deficiency occurs at the anode, causing a sudden drop in the cell voltage. Figure 5 High potential elimination stage; if the judgment in step S108 is "yes", it means that there is no abnormality in the discharge valve. After the hydrogen pressure is established in step S103, the hydrogen chamber of the fuel cell stack is completely filled with hydrogen gas. Figure 6 The fuel cell has started successfully and is waiting for the vehicle to request power.

[0048] Step S203: If the result in step S108 is "No", it indicates that there may be an abnormality in the discharge valve, and further judgment is required. At this time, the fuel cell current is set to 0.

[0049] Step S204: Determine if the number of executions is greater than n. If the result is "no", proceed to step S103 and repeat the process. If the number of executions is greater than n, it can be further determined that the probability of the discharge valve failing to open has increased. Here, the number of executions n can be selected as 3. This value can be selected according to the actual situation of the system. The range of selectable values ​​is 1 to 5.

[0050] Step S205: If the determination in step S204 is "yes", then the discharge valve diagnostic process is activated to perform fault diagnosis for the inability to open the discharge valve.

[0051] III. Diagnostic methods for discharge valves like Figure 3 The diagram shown is a flowchart for diagnosing a discharge valve malfunction. The steps for diagnosing a discharge valve malfunction are as follows: Step S301: Set the second hydrogen inlet pressure Pset2 to establish the pressure of the hydrogen chamber in the fuel cell stack. The second hydrogen inlet pressure Pset2 can be selected as 145 kPa.a. This value can be selected according to the actual situation of the system. The selectable value range is 130~150 kPa.a, as long as the pressure difference between the hydrogen chamber and the air chamber does not exceed the hydrogen-air pressure difference allowed by the fuel cell stack.

[0052] Step S302: Determine whether the absolute error between the hydrogen inlet pressure sensor detected pressure Pc and the set hydrogen inlet second pressure Pset2 is greater than the set first threshold ΔP1; the set first threshold ΔP1 can be 5 kPa or other values, and the range of selectable values ​​is 1~10 kPa, as long as the actual hydrogen pressure meets the target pressure; if the determination in step S302 is "no", then wait for the pressure to reach the target pressure.

[0053] Step S303: If the determination in step S302 is "yes", then the discharge valve opens.

[0054] Step S304: Delay time Δt2, Δt2 can be selected as 3s, or other times can be selected according to the actual situation. The selectable value range is 2~5s. The purpose is to have enough time to determine whether the hydrogen pressure has changed after the discharge valve is opened.

[0055] Step S305: Determine whether the pressure difference between the hydrogen pressure (Pc) before the discharge valve is opened and the hydrogen pressure after the delay time Δt2 is greater than the set second threshold ΔP2; ΔP2 can be selected as 25kPa or other values, and the selectable value range is 20~45kPa.

[0056] Step S306: If the determination in step S305 is "yes", it indicates that the discharge valve is not abnormal; if Figure 8 As shown in the t2~t3 stage, Figure 10The data is from actual testing in the fuel cell system. The initial hydrogen pressure was 140.2 kPa.a. After 3 seconds, the hydrogen pressure was 102.2 kPa.a. The ΔP2 value was 40 kPa. This indicates that the voltage drop in the single cell during system startup was not caused by the exhaust valve, and other aspects of the system need to be checked.

[0057] Step S401: If the result in step S305 is "No", it means the discharge valve cannot be opened; Figure 9 As shown in the t2~t3 stage, Figure 11 The data is from actual testing in a fuel cell system. The initial hydrogen pressure was 140.6 kPa.a. After 3 seconds, the hydrogen pressure was 139.8 kPa.a, and the ΔP2 value was 0.8 kPa. This indicates that the exhaust valve could not open, and the voltage drop in a single cell during system startup was caused by the exhaust valve.

Claims

1. A method for diagnosing a fault in a discharge valve during the start-up process of a fuel cell system, the fuel cell system comprising a fuel cell stack and a hydrogen subsystem, the fuel cell stack comprising several individual cells, and the hydrogen subsystem comprising a discharge valve, characterized in that, The startup process of a fuel cell system causes a drop in the voltage of a single cell. The method for diagnosing a fault in the discharge valve during the startup process of the fuel cell system includes the following steps: S1, set the hydrogen inlet pressure, establish the pressure in the hydrogen chamber of the fuel cell stack, and determine whether the absolute value error between the hydrogen inlet pressure detection value and the set value is greater than the set first threshold. If it is not greater than the set first threshold, wait for the pressure to meet the condition; if it is greater than the set first threshold, open the discharge valve. S2, after a certain delay, determine whether the pressure difference between the hydrogen inlet pressure detection values ​​before and after the discharge valve opens is greater than the set second threshold. If it is greater than the set second threshold, the discharge valve is normal, indicating that the voltage drop of the single cell during the fuel cell system startup process is not caused by the discharge valve. If it is not greater than the set second threshold, it indicates that the discharge valve cannot open normally, and the voltage drop of the single cell during the fuel cell system startup process is caused by the discharge valve.

2. The method for diagnosing exhaust valve faults during the start-up process of a fuel cell system according to claim 1, characterized in that, The first threshold is 1~10 kPa; The second threshold is 20~45kPa.

3. The method for diagnosing exhaust valve faults during the start-up process of a fuel cell system according to claim 1, characterized in that, In step S1, the hydrogen inlet pressure is set to 130~150 kPa.a.

4. The method for diagnosing exhaust valve faults during the start-up process of a fuel cell system according to claim 1, characterized in that, In step S2, the delay time is 2~5s.

5. A start-up process for a fuel cell system, the fuel cell system comprising a fuel cell stack, a hydrogen subsystem, an air subsystem, and a cooling subsystem, the fuel cell stack comprising a plurality of individual cells, the hydrogen subsystem comprising an exhaust valve, the air subsystem comprising an air compressor, a shut-off valve, and a back pressure valve, and the cooling subsystem comprising a circulating water pump, characterized in that, The startup process of the fuel cell system includes the following steps: Step 1: The vehicle requests the fuel cell system to start. After receiving the start command, the hydrogen inlet pressure is set and the exhaust valve is opened. After a certain delay, the hydrogen pressure is established. Step 2: Close the discharge valve, turn on the circulating water pump and air compressor, and fully open the shut-off valve and back pressure valve to establish an open-circuit voltage for the fuel cell stack. Step 3: Determine if the open-circuit voltage is greater than the preset threshold. If it is not greater, the fuel cell system fails to start and the system malfunctions. If it is greater, set the fuel cell stack current so that the single cell voltage is 0.80~0.85V. Step 4: Determine if the minimum single cell voltage is greater than the preset single cell threshold. If it is, it indicates that the exhaust valve is normal, hydrogen pressure is established, the fuel cell system starts successfully, and it waits for the vehicle to request power. If it is not, it indicates that the exhaust valve may be abnormal. Further judgment is made, the current of the fuel cell stack is set to 0, and all steps are repeated from the hydrogen inlet pressure set in Step 1. If the fuel cell system still cannot start successfully after the number of cycles exceeds the set number of cycles, the exhaust valve diagnosis process is activated, and the exhaust valve fault diagnosis method for the fuel cell system startup process described in any one of claims 1 to 4 is performed.

6. The fuel cell system start-up process according to claim 5, characterized in that, In step 1, the hydrogen inlet pressure is set to 110~150 kPa.a; the delay time is 1~10 s.

7. The fuel cell system start-up process according to claim 5, characterized in that, In step 2, the speed of the circulating water pump is 1000~3000 rpm; the speed of the air compressor is 30000~50000 rpm.

8. The fuel cell system start-up process according to claim 5, characterized in that, In step 3, the preset threshold for open-circuit voltage is 0.8V×N~0.96V×N, where N is the number of single cells.

9. The fuel cell system start-up process according to claim 5, characterized in that, In step 4, the preset single-cell threshold is 0.1~0.7V; the set number of cycles is 1~5.

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