Humidifier attenuation degree on-line diagnosis method, humidity adjustment method and fuel cell system

Abstract

The application discloses a humidifier attenuation degree online diagnosis method, a humidity adjusting method and a fuel cell system. The online diagnosis method comprises the following steps: S1, obtaining a high-frequency impedance value of a fuel cell stack when the fuel cell system operates at a set diagnosis current; S2, determining a cathode inlet humidity value under the diagnosis current according to the high-frequency impedance value based on a preset high-frequency impedance value and cathode inlet humidity relationship mapping table; S3, obtaining operation parameters of the fuel cell system under the diagnosis current, wherein the operation parameters at least comprise a cathode inlet total pressure, a cathode outlet total pressure, a cooling path inlet temperature, a cooling path outlet temperature and an air flow parameter; S4, calculating a water transfer coefficient of the humidifier under a current state according to the cathode inlet humidity value and the operation parameters; and S5, determining the attenuation degree of the humidifier according to the calculated water transfer coefficient based on a preset water transfer coefficient and humidifier attenuation degree relationship mapping table.

Description

Technical Field

[0001] This invention relates to the field of fuel cell technology, and in particular to a method for evaluating the heat dissipation capacity of a fuel cell system, a method for early warning of fuel cell degradation, and a fuel cell system. Background Technology

[0002] Proton exchange membrane fuel cells (PEMFCs) are a common type of fuel cell used in vehicles. They mainly consist of a proton exchange membrane, anode and cathode catalyst layers, a gas diffusion layer, and bipolar plates. The proton exchange membrane conducts protons, isolates electrons, and isolates reactants at the anode and cathode. The anode and cathode catalyst layers are the sites of electrochemical reactions. The gas diffusion layer mainly determines the transport of reactant gases and the discharge of liquid water. The bipolar plates isolate reactants and coolant.

[0003] The water content distribution in a fuel cell directly affects its output voltage and lifespan. Generally, a dry inlet reduces the proton conductivity at the inlet, leading to decreased power generation capacity and reduced performance. Furthermore, an excessively dry inlet can increase the degradation rate of the proton exchange membrane at the inlet, further shortening the fuel cell's lifespan.

[0004] The humidity at the fuel cell inlet primarily depends on the humidification capacity of the cathode inlet, and adding a humidifier at the cathode inlet is a common external humidification method. However, the humidification capacity of the humidifier significantly decreases with operating time. Current technologies include solutions that use humidity sensors for direct monitoring. This method involves installing high-precision humidity sensors at the humidifier outlet or cathode inlet to directly measure the intake air humidity. The degree of degradation is determined by comparing the current humidity value with the expected humidity value under the humidifier's rated performance, or by monitoring the humidity's decreasing trend over time. However, the on-board environment places extremely high demands on the reliability, durability, and cost of sensors. Humidity sensors exposed to high temperatures, high humidity, and the presence of chemicals over long periods are prone to drift, failure, or accuracy degradation, leading to unreliable diagnostic results. Furthermore, adding dedicated sensors increases the system's complexity and cost.

[0005] Therefore, it is necessary to propose a technical solution to overcome the shortcomings of existing technologies. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, this invention proposes an online diagnostic method for the degree of humidifier degradation, a humidity control method, and a fuel cell system. This method can accurately assess the health status of the humidifier in real time without significantly increasing the system's hardware cost and complexity.

[0007] This invention is achieved through the following technical solution: an online diagnostic method for the attenuation level of a humidifier, the method comprising the following steps:

[0008] S1. When the fuel cell system is operating at a set diagnostic current, obtain the high-frequency impedance value of the fuel cell stack;

[0009] S2. Based on a preset mapping table of high-frequency impedance values ​​and cathode inlet humidity, determine the cathode inlet humidity value under the diagnostic current according to the high-frequency impedance value;

[0010] S3. Obtain the operating parameters of the fuel cell system under the diagnostic current, the operating parameters including at least: total cathode inlet pressure, total cathode outlet pressure, cooling path inlet temperature, cooling path outlet temperature, and air flow rate;

[0011] S4. Calculate the water transfer coefficient of the humidifier in the current state based on the cathode inlet humidity value and the operating parameters;

[0012] S5. Based on the preset mapping table of the relationship between water transfer coefficient and humidifier attenuation degree, determine the attenuation degree of the humidifier according to the calculated water transfer coefficient.

[0013] As a further improved technical solution, the set diagnostic current is no greater than 100A.

[0014] As a further improved technical solution, the set diagnostic current value is between 50A and 60A.

[0015] As a further improved technical solution, in step S4, the water transfer coefficient of the humidifier in the current state is calculated according to the following formula. :

[0016] ;

[0017] in, The water vapor flow rate at the cathode inlet is calculated using the following formula:

[0018] ;

[0019] in, The water pressure at the cathode inlet is calculated using the following formula: ,in This is the humidity value at the cathode inlet. This refers to the inlet temperature of the cooling path; The airflow rate entering the fuel cell stack is calculated using the following formula: Where N is the number of fuel cell stack plates and I is the fuel cell stack generating current. , where is the excess coefficient of the cathode, 29 is the molar mass of air in g / mol, 4 is the number of electrons transferred per oxygen molecule during the reaction, 96485 is the Faraday constant in C / mol, and 0.21 is the proportion of oxygen in the air. This represents the total pressure at the cathode inlet.

[0020] in, The water vapor flow rate at the cathode outlet is calculated using the following formula:

[0021] ;

[0022] in The water pressure at the cathode outlet is calculated using the following formula: ,in The total pressure at the cathode outlet. 18 represents the outlet temperature of the cooling path, 18 represents the molar mass of water in g / mol, and 60 represents the time unit conversion parameter, with the conversion relationship being 1 g / s = 60 g / min.

[0023] This invention is also achieved through the following technical solution: a humidity regulation method for the cathode inlet of a fuel cell, the humidity regulation method comprising:

[0024] Perform the online diagnostic method described above to obtain the current level of humidifier degradation; and

[0025] S6. Based on the current attenuation level and the preset target value of cathode inlet humidity, determine the cooling path inlet temperature setting value required to meet the target value of cathode inlet humidity;

[0026] S7. Adjust the cooling system of the fuel cell to bring the inlet temperature of the cooling path to the set temperature value.

[0027] As a further improved technical solution, the humidity regulation method is achieved by keeping the cooling path outlet temperature constant and reducing the cooling path inlet temperature.

[0028] As a further improved technical solution, step S6 includes:

[0029] Based on the current attenuation level, query the pre-stored water transfer coefficient mapping table corresponding to each working current under different attenuation levels to obtain the humidifier water transfer coefficient under different working currents.

[0030] As a further improved technical solution, step S6 includes:

[0031] Based on the target operating current, the required cooling path inlet temperature setpoint is calculated using the water transfer coefficient, operating parameters, and target cathode inlet humidity value corresponding to the target operating current.

[0032] As a further improved technical solution, in step S6, the required cooling path inlet temperature setpoint is calculated using the following formula:

[0033] ;

[0034] in, This is the target humidity value at the cathode inlet.

[0035] The present invention is also achieved through the following technical solution: a fuel cell system, comprising a fuel cell stack, a humidifier, and a cooling system, wherein the fuel cell system is used to perform the humidity regulation method described above, and the fuel cell system includes:

[0036] The parameter acquisition unit is used to acquire the high-frequency impedance value of the fuel cell stack and the operating parameters of the system.

[0037] The online diagnostic unit is configured to obtain the degree of humidifier degradation based on the parameters obtained by the parameter acquisition unit.

[0038] The adjustment calculation unit is configured to determine the cooling path inlet temperature setpoint required to meet the cathode inlet humidity target value based on the attenuation degree and the preset cathode inlet humidity target value.

[0039] The adjustment execution unit is configured to control the cooling system to perform actions based on the temperature setpoint output by the adjustment calculation unit.

[0040] The online diagnostic method for humidifier performance degradation provided by this invention utilizes the inherent high-frequency impedance measurement function of the fuel cell system, combined with a preset impedance-humidity and water transport coefficient-degradation degree mapping table. This allows for online, non-destructive, and quantitative diagnosis of the humidifier's performance degradation without the need for an additional dedicated humidity sensor. This method effectively overcomes the problems of high cost, poor reliability, and insufficient durability associated with relying on external sensors in existing technologies, as well as the low accuracy and weak adaptability resulting from relying on complex mechanistic models. It achieves real-time and accurate assessment of the humidifier's health status, providing a crucial and reliable data foundation for subsequent adaptive humidity control, ensuring stable stack operation, and extending system lifespan. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the system architecture of an embodiment of the fuel cell system of the present invention.

[0042] Figure 2 This is a graph showing the sensitivity of high-frequency impedance to changes in cathode inlet humidity under different currents.

[0043] Figure 3This is a quantitative relationship between cathode inlet humidity and high-frequency impedance when the stack current is 55A.

[0044] Figure 4 This is a graph showing the quantitative relationship between the water transfer coefficient of the humidifier and the degree of humidifier attenuation when the stack current is 55A.

[0045] Figure 5 The WTE curves of the humidifier water transfer coefficient at different current points under different humidifier attenuation levels are shown.

[0046] Figure 6 The WTE curves of the humidifier at different currents when the humidifier attenuation is 21%.

[0047] Figure 7 The image shows the cooling path inlet temperature curves before and after optimization of an embodiment of the humidity control method of the present invention.

[0048] Figure 8 The following are the cathode inlet humidity curves before and after optimization of an embodiment of the humidity control method of the present invention.

[0049] The following are the reference numerals: 1. Air compressor; 2. Humidifier; P2. Cathode inlet pressure sensor; P3. Cathode outlet pressure sensor; 4. Fuel cell stack; 5. DC-DC converter; 6. Cooling circuit inlet temperature sensor; 7. Cooling circuit outlet temperature sensor; 8. Cooling water pump; 9. Electric thermostatic valve; 10. Radiator; 11. Ambient temperature sensor. Detailed Implementation

[0050] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0051] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0052] This invention provides an online diagnostic method for the degradation level of a humidifier, a humidity control method, and a fuel cell system. First, please refer to... Figure 1The example illustrates a fuel cell system architecture that implements the method of the present invention. The system includes an air compressor 1 supplying air to a fuel cell stack 4. After being compressed by the air compressor 1, the air enters the dry side of a humidifier 2, where it undergoes hydrothermal exchange with the humid gas returning from the cathode outlet of the fuel cell stack 4, thereby being humidified. The humidified air, i.e., the cathode inlet gas, enters the cathode side of the fuel cell stack 4 via a pipe equipped with a cathode inlet pressure sensor P2 to participate in the electrochemical reaction. The gas after the electrochemical reaction, i.e., the cathode outlet gas, is discharged from the fuel cell stack 4 and flows through a pipe equipped with a cathode outlet pressure sensor P3. The direct current generated by the fuel cell stack 4 is voltage-converted by a DC-DC converter 5 and supplied to a load or energy storage device. It is particularly noteworthy that in this invention, the DC-DC converter 5 is not only used for power regulation, but its control unit is also configured to inject a high-frequency AC signal into the fuel cell stack 4 and detect the response, thereby measuring the high-frequency impedance (HFR) of the fuel cell stack 4. This utilizes the functionality of existing onboard power electronics equipment, eliminating the need for additional dedicated impedance measurement instruments. The heat from the fuel cell stack 4 is removed by a cooling system, which mainly includes a cooling water pump 8, an electrically operated temperature control valve 9, a radiator 10, and necessary temperature sensors. Specifically, the coolant, driven by the cooling water pump 8, flows through the cooling channels of the fuel cell stack 4 to absorb heat. The temperature of the coolant exiting the fuel cell stack 4 is measured by the cooling path outlet temperature sensor 7. Subsequently, the coolant flows through the electrically operated temperature control valve 9, which regulates the proportion of coolant flowing through the radiator 10, thereby controlling the heat dissipation intensity. After being mixed with the radiator 10 and / or bypass, the temperature of the coolant is measured by the cooling path inlet temperature sensor 6, and then it re-enters the fuel cell stack 4, forming a closed loop. The ambient temperature sensor 11 is used to monitor the ambient temperature and provides a reference for cooling control. The controller is communicatively connected to all the aforementioned sensors—cathode inlet pressure sensor P2, cathode outlet pressure sensor P3, cooling path inlet temperature sensor 6, cooling path outlet temperature sensor 7, ambient temperature sensor 11—as well as all moving parts, such as air compressor 1, cooling water pump 8, electric thermostatic valve 9, radiator 10, and DC-DC converter 5—to receive measurement data, send control commands, and execute the diagnostic and regulation algorithms described in this invention. The controller is not shown separately in the figure; its functions can be integrated into the vehicle VCU or a dedicated fuel cell controller.

[0053] Based on the above fuel cell system architecture, this invention provides an online diagnostic method for the degradation level of a humidifier. The method includes the following steps:

[0054] S1. When the fuel cell system is operating at a set diagnostic current, obtain the high-frequency impedance value of the fuel cell stack;

[0055] S2. Based on a preset mapping table of high-frequency impedance values ​​and cathode inlet humidity, determine the cathode inlet humidity value under the diagnostic current according to the high-frequency impedance value;

[0056] S3. Obtain the operating parameters of the fuel cell system under the diagnostic current, the operating parameters including at least: total cathode inlet pressure, total cathode outlet pressure, cooling path inlet temperature, cooling path outlet temperature, and air flow rate;

[0057] S4. Calculate the water transfer coefficient of the humidifier in the current state based on the cathode inlet humidity value and the operating parameters;

[0058] S5. Based on the preset mapping table of the relationship between water transfer coefficient and humidifier attenuation degree, determine the attenuation degree of the humidifier according to the calculated water transfer coefficient.

[0059] The online diagnostic method for humidifier performance degradation provided by this invention utilizes the inherent high-frequency impedance measurement function of the fuel cell system, combined with a preset impedance-humidity and water transport coefficient-degradation degree mapping table. This allows for online, non-destructive, and quantitative diagnosis of the humidifier's performance degradation without the need for an additional dedicated humidity sensor. This method effectively overcomes the problems of high cost, poor reliability, and insufficient durability associated with relying on external sensors in existing technologies, as well as the low accuracy and weak adaptability resulting from relying on complex mechanistic models. It achieves real-time and accurate assessment of the humidifier's health status, providing a crucial and reliable data foundation for subsequent adaptive humidity control, ensuring stable stack operation, and extending system lifespan.

[0060] The core logic of the online diagnostic method for humidifier attenuation provided by this invention lies in establishing a recursive relationship chain between high-frequency impedance (HFR), cathode inlet humidity, water transfer coefficient (WTE), and attenuation level, thereby achieving non-destructive online diagnostics using existing vehicle signals.

[0061] Specifically, in step S1, a diagnostic current needs to be set first. The selection of this diagnostic current is based on the mechanism of the influence of fuel cell humidity distribution on high-frequency impedance. For example... Figure 2As shown, the high-frequency impedance value is affected by the overall humidity distribution inside the fuel cell stack 4, which is determined by both the inlet humidity and the water produced by the fuel cell stack 4 itself. In the lower current region, the fuel cell stack 4 produces less water, and the internal humidity level is more sensitive to changes in inlet humidity. This means that, for the same change in inlet humidity, the change in high-frequency impedance (ΔHFR) in the low current region is greater. Since high-frequency impedance measurement itself has a certain inherent error, measuring under conditions where impedance changes are more significant is beneficial to improving the accuracy of humidity change identification, i.e., obtaining a higher signal-to-noise ratio. Therefore, the diagnostic current is set within a range not exceeding 100A, preferably between 50A and 60A. In a preferred embodiment, after experimental calibration, 55A is selected as the characteristic diagnostic current. At this current, the impedance is highly sensitive to inlet humidity and is a common low-power operating point of the system, facilitating diagnosis. When the system is stably operating at the set diagnostic current (e.g., 55A), the controller obtains the high-frequency impedance value R of the fuel cell stack 4 at this time through the DC-DC converter 5.

[0062] Next, step S2 is executed, which involves adjusting the preset high-frequency impedance value R and the cathode inlet humidity. The relationship mapping table determines the cathode inlet humidity value under the set diagnostic current based on the high-frequency impedance value R. This mapping table is a pre-established database that allows for direct measurement of real cathode inlet humidity values ​​under different operating conditions using a humidity sensor in the laboratory. Simultaneously, the high-frequency impedance value R under the corresponding operating condition is measured using a DC-DC converter 5. By fitting a large number of experimental data points, the relationship between the high-frequency impedance value R and the cathode inlet humidity under this specific current can be obtained. The quantitative relationship between them. For example... Figure 3 As shown, this relationship can be highly approximated as linear within a certain humidity range, that is... =-a*R+b, where a and b are constants determined through linear regression. This fitted curve, or a lookup table composed of its data points, is stored in the storage module as a preset mapping table of the relationship between high-frequency impedance values ​​and cathode inlet humidity, and can be read by the controller. In actual vehicle applications, after measuring the high-frequency impedance value R, the controller can calculate the cathode inlet humidity value under the current operating conditions by looking up this mapping table. .

[0063] Obtain the cathode inlet humidity value Next, step S3 is executed to obtain other necessary operating parameters of the fuel cell system under the current diagnostic current. These operating parameters include parameters monitored by the conventional control system, including but not limited to: the total cathode inlet pressure measured by the cathode inlet pressure sensor P2. The total pressure at the cathode outlet, measured by cathode outlet pressure sensor P3. The cooling path inlet temperature measured by cooling path inlet temperature sensor 6 The cooling path outlet temperature measured by cooling path outlet temperature sensor 7 These operating parameters also include airflow parameters, which are typically not directly measured values. In this embodiment, airflow is... It can be calculated using electrochemical stoichiometry based on the number of plates N in the fuel cell stack 4, the current power generation current I of the fuel cell stack, and the cathode excess coefficient stoic.

[0064] Then, proceed to step S4, which involves determining the cathode inlet humidity value. Based on the aforementioned operating parameters, the water transfer coefficient (WTE) of humidifier 2 in its current state is calculated. The water transfer coefficient (WTE) is a core parameter characterizing humidifier performance, defined as the ratio of the water vapor flow rate transferred from the wet side to the dry side of the humidifier to the available water vapor flow rate on the wet side. Its calculation involves the derivation of physical quantities such as gas composition, partial pressure, and flow rate. Specifically, in step S4, the water transfer coefficient of the humidifier in its current state is calculated according to the following formula. : ;in, The water vapor flow rate at the cathode inlet is calculated using the following formula: ;in, The water pressure at the cathode inlet is calculated using the following formula: ,in This is the humidity value at the cathode inlet. This refers to the inlet temperature of the cooling path; The airflow rate entering the fuel cell stack is calculated using the following formula: Where N is the number of fuel cell stack plates and I is the fuel cell stack generating current. , where is the excess coefficient of the cathode, 29 is the molar mass of air in g / mol, 4 is the number of electrons transferred per oxygen molecule during the reaction, 96485 is the Faraday constant in C / mol, and 0.21 is the proportion of oxygen in the air. The total pressure at the cathode inlet; where, The water vapor flow rate at the cathode outlet is calculated using the following formula: ;in The water pressure at the cathode outlet is calculated using the following formula: ,in The total pressure at the cathode outlet. 18 represents the outlet temperature of the cooling path, 18 represents the molar mass of water in g / mol, and 60 represents the time unit conversion parameter, with the conversion relationship being 1 g / s = 60 g / min.

[0065] After obtaining the current humidifier water transfer coefficient (WTE) value, the diagnostic process proceeds to step S5, which determines the degree of humidifier degradation based on a preset mapping table showing the relationship between WTE and humidifier degradation. This preset mapping table is a pre-established database, and its creation can also rely on prior laboratory calibration. The table clearly defines which WTE value corresponds to which degree of degradation under specific diagnostic conditions. It is important to note that the humidity value used in establishing this mapping table is a high-precision value directly measured by laboratory sensors, while the humidity value used in on-board diagnostics is indirectly estimated by high-frequency impedance. However, the formula used to calculate WTE in both cases is consistent and based on physical laws. Figure 4 As shown, this is a graph illustrating the quantitative relationship between the humidifier's water transfer coefficient and its attenuation level when the fuel cell current is 55A. Therefore, as long as the model for estimating humidity using high-frequency impedance values ​​is accurate enough, the WTE value calculated on-board can be reliably mapped to this calibration mapping table, thereby allowing the deduction of the current humidifier's attenuation level D. hum Thus, this invention completes the online quantitative diagnosis of the performance degradation of humidifier 2 without relying on a dedicated vehicle-mounted humidity sensor.

[0066] This invention also provides a method for regulating the cathode inlet humidity of a fuel cell using the above-mentioned online diagnostic results as input. The purpose of this method is to proactively address humidifier degradation by adjusting relevant system parameters, especially the cooling circuit temperature, to ensure that the cathode inlet humidity remains above a preset target value under different load currents, thereby guaranteeing the performance and lifespan of the fuel cell stack.

[0067] Specifically, the humidity adjustment method first executes the aforementioned online diagnostic method to obtain the current attenuation level D_hum of the humidifier 2. This forms the basis for the adjustment decision, making the adjustment strategy adaptive and capable of personalized compensation based on the actual health status of the humidifier 2. After obtaining the current attenuation level D_hum of the humidifier 2, step S6 is performed: based on this attenuation level and the preset target humidity value at the cathode inlet. The required cooling path inlet temperature setpoint to meet the humidity target was determined. The purpose of this setup is that, since the capacity of humidifier 2 decreases due to degradation, in order to achieve the same inlet humidity target, it is necessary to create a more favorable thermodynamic condition for humidification, namely, reducing the inlet air temperature on the dry side of humidifier 2, corresponding to the inlet temperature of the cooling path. This increases the humidification potential of the air within the humidifier.

[0068] To calculate the temperature setpoint across the entire current range, the controller needs to know the water transfer coefficient WTE_i of the humidifier 2 at different operating current points i under the current attenuation level. Therefore, step S6 includes: based on the current attenuation level, querying a pre-stored mapping table of water transfer coefficients corresponding to different operating currents under different attenuation levels to obtain the humidifier's water transfer coefficient at different operating currents. The pre-stored mapping table of water transfer coefficients corresponding to different operating currents under different attenuation levels is another pre-established database. This database was created during the laboratory calibration phase, where humidifier samples with different attenuation levels were tested at a series of current points using direct humidity measurement and physical calculations to obtain their water transfer coefficient WTE. The data is then organized as follows... Figure 5 The diagram shows a set of curves, each corresponding to a specific attenuation level. The horizontal axis represents current, and the vertical axis represents water transfer coefficient (WTE). It can be observed that as attenuation intensifies, the WTE curve shifts downwards overall. The vehicle controller can store a data table corresponding to these curves. When the current attenuation level D_hum is diagnosed online, the controller queries this database. Since the stored attenuation levels are discrete (e.g., 0%, 10%, 20%, 30%, etc.), an interpolation algorithm can be used to estimate the water transfer coefficient WTE_i corresponding to each operating current point i under the current actual attenuation level D_hum. For example, in one embodiment, the diagnosed attenuation level of humidifier 2 is 21%. Figure 6 The graph shows the water transfer coefficient (WTE) curves of the humidifier at different currents when the humidifier degradation level is 21%. It should also be noted that the humidifier degradation level refers to the degree of decrease in cathode inlet humidity when the humidifier is operating at the system's highest current point. For example, a humidifier with 0% degradation has a cathode inlet humidity of 100% when operating at the highest current point. A humidifier with 18% degradation is defined as having a cathode inlet humidity of 82% when operating at the highest current point.

[0069] Next, for the target operating current point where humidity needs to be guaranteed, based on the estimated WTE corresponding to that current point, the operating parameters at that current, and the given target value for cathode inlet humidity, The required cooling path inlet temperature setpoint is obtained by reverse engineering. The mathematical principle is to perform an inverse transformation on the forward formula for calculating humidity in step S4. Specifically, for example, in one embodiment, a target humidity value at the cathode inlet is required. If ≥80%, the following relationship can be established:

[0070] ; among them By transforming the formula and solving for the unknown, the required cooling path inlet temperature setpoint can be obtained. The calculation formula is as follows:

[0071] ;

[0072] The physical meaning of this formula is that, in order to ensure the cathode inlet humidity is not lower than the target value when the humidifier performance is WTE (Wide-Temperature Efficiency), the humidifier must achieve this. Cooling path inlet temperature It must not exceed a certain critical value. Calculations may be performed for multiple current points, and the corresponding cooling path inlet temperature will be adjusted based on current variations. Adjustment. The final result is as follows: Figure 7 The cooling path inlet temperature shown Operating conditions.

[0073] according to Figure 7 The modified current-temperature relationship shown is used to control the inlet temperature of the cooling circuit. You can eventually obtain such Figure 8 The result is that the cathode inlet humidity at all current points is ≥80%. Specifically, to achieve the following: Figure 7 The cooling path inlet temperature shown After determining the operating conditions, proceed to step S7, which involves adjusting the fuel cell's cooling system to bring the cooling path inlet temperature to the calculated setpoint. The cooling system of the fuel cell can be adjusted by controlling actuators such as the cooling water pump 8, the electric temperature control valve 9, and the radiator 10 to maintain the outlet temperature of the cooling path. Without changing the temperature, actively reduce the inlet temperature of the cooling path. To achieve this. When After the temperature decreases, the air temperature entering the dry side of humidifier 2 also decreases, and its saturated water vapor partial pressure decreases. Under the same humidifier water transfer capacity (WTE), the cooler air can be humidified to a higher relative humidity, thus compensating for the humidification loss due to humidifier degradation, ultimately resulting in... Figure 8 The optimized cathode inlet humidity curve shown can maintain above the target value (e.g., 80%) across the entire current range, effectively alleviating the problem of excessively dry inlet caused by humidifier attenuation and improving the economy and reliability of system operation.

[0074] Corresponding to the above-described humidity control method, the present invention also provides a fuel cell system for implementing the humidity control method. This system... Figure 1Based on the hardware architecture, it includes multiple functional units, such as a parameter acquisition unit, an online diagnostic unit, an adjustment calculation unit, and an adjustment execution unit. The parameter acquisition unit is responsible for integrating high-frequency impedance data from the DC-DC converter 5, as well as operating parameters from various sensors. The online diagnostic unit integrates the algorithms of steps S1-S5 of the aforementioned diagnostic method. It receives data from the parameter acquisition unit, calls two key mapping tables stored in memory, performs calculations, and finally outputs the current attenuation level D_hum of the humidifier 2. The adjustment calculation unit integrates the algorithms of the humidity adjustment steps. It takes the attenuation level D_hum and the preset humidity target value as input, queries the pre-stored attenuation level-current-WTE three-dimensional mapping table, and outputs the cooling path inlet temperature setpoint required to compensate for attenuation through interpolation and inverse calculation. The regulating actuator is the controller of the cooling system; it receives... The system uses a closed-loop control algorithm (such as PID control) to drive actuators such as the cooling water pump 8, electric temperature control valve 9, and radiator 10, ultimately stabilizing the cooling circuit inlet temperature near the set value. These functional units can be physically integrated into one or more electronic control units (ECUs) and their functions can be implemented through software programming. This invention, through this systematic hardware and software collaborative solution, achieves intelligent sensing of the humidifier's degradation state and adaptive closed-loop control of the cathode inlet humidity.

[0075] In summary, this invention creatively establishes and utilizes a recursive diagnostic chain of high-frequency impedance, inlet humidity, water transport coefficient, and attenuation level to achieve online diagnosis of humidifier attenuation. Based on the diagnostic results and combined with system operating parameters, it executes a cooling circuit inlet temperature adjustment and compensation strategy. This successfully achieves online, quantitative, and non-destructive diagnosis and effective compensation for the performance degradation of on-board fuel cell humidifiers without the need for expensive and easily damaged dedicated humidity sensors. This not only reduces system cost and complexity but also significantly improves the intelligence level of fuel cell system water and thermal management and its operational robustness throughout its entire lifecycle, possessing significant engineering application value.

[0076] This invention has been illustrated through several specific embodiments. Those skilled in the art will understand that various modifications and equivalent substitutions can be made to this invention without departing from its scope. Furthermore, various modifications can be made to this invention for specific situations or circumstances without departing from its scope. Therefore, this invention is not limited to the specific embodiments disclosed, but should include all embodiments falling within the scope of the claims.

Claims

1. A method for online diagnosis of humidifier degradation, characterized in that, The method includes the following steps: S1. When the fuel cell system is operating at a set diagnostic current, obtain the high-frequency impedance value of the fuel cell stack, wherein the set diagnostic current is not greater than 100A; S2. Based on a preset mapping table of high-frequency impedance values ​​and cathode inlet humidity, determine the cathode inlet humidity value under the diagnostic current according to the high-frequency impedance value; S3. Obtain the operating parameters of the fuel cell system under the diagnostic current, the operating parameters including at least: total cathode inlet pressure, total cathode outlet pressure, cooling path inlet temperature, cooling path outlet temperature, and air flow rate; S4. Calculate the water transfer coefficient of the humidifier in the current state based on the cathode inlet humidity value and the operating parameters. , ,in, The water vapor flow rate at the cathode inlet. The water vapor flow rate at the cathode outlet; S5. Based on the preset mapping table of the relationship between water transfer coefficient and humidifier attenuation degree, determine the attenuation degree of the humidifier according to the calculated water transfer coefficient.

2. The online diagnostic method as described in claim 1, characterized in that, The set diagnostic current is between 50A and 60A.

3. The online diagnostic method as described in claim 1, characterized in that, In step S4, Calculated using the following formula: ； in, The water pressure at the cathode inlet is calculated using the following formula: ,in This is the humidity value at the cathode inlet. This refers to the inlet temperature of the cooling path; The airflow rate entering the fuel cell stack is calculated using the following formula: Where N is the number of fuel cell stack plates and I is the fuel cell stack generating current. , where is the excess coefficient of the cathode, 29 is the molar mass of air in g / mol, 4 is the number of electrons transferred per oxygen molecule during the reaction, 96485 is the Faraday constant in C / mol, and 0.21 is the proportion of oxygen in the air. This represents the total pressure at the cathode inlet. Calculated using the following formula: ； in The water pressure at the cathode outlet is calculated using the following formula: ,in The total pressure at the cathode outlet. 18 represents the outlet temperature of the cooling path, 18 represents the molar mass of water in g / mol, and 60 represents the time unit conversion parameter, with the conversion relationship being 1 g / s = 60 g / min.

4. A method for humidity control at the cathode inlet of a fuel cell, characterized in that, The humidity regulation method includes: Perform the online diagnostic method as described in any one of claims 1 to 3 to obtain the current degradation level of the humidifier; and S6. Based on the current attenuation level and the preset target value of cathode inlet humidity, determine the cooling path inlet temperature setting value required to meet the target value of cathode inlet humidity; S7. Adjust the cooling system of the fuel cell to bring the inlet temperature of the cooling path to the set temperature value.

5. The humidity control method as described in claim 4, characterized in that, The humidity regulation method achieves this by keeping the outlet temperature of the cooling path constant and reducing the inlet temperature of the cooling path.

6. The humidity control method as described in claim 4, characterized in that, Step S6 includes: Based on the current attenuation level, query the pre-stored water transfer coefficient mapping table corresponding to each working current under different attenuation levels to obtain the humidifier water transfer coefficient under different working currents.

7. The humidity control method as described in claim 6, characterized in that, Step S6 includes: Based on the target operating current, the required cooling path inlet temperature setpoint is calculated using the water transfer coefficient, operating parameters, and target cathode inlet humidity value corresponding to the target operating current.

8. The humidity control method as described in claim 7, characterized in that, In step S6, the required cooling path inlet temperature setpoint is calculated using the following formula. : ； in, This is the target humidity value at the cathode inlet.

9. A fuel cell system, comprising a stack, a humidifier, and a cooling system, characterized in that, The fuel cell system is used to perform the humidity regulation method as described in any one of claims 4 to 8, the fuel cell system comprising: The parameter acquisition unit is used to acquire the high-frequency impedance value of the fuel cell stack and the operating parameters of the system. The online diagnostic unit is configured to obtain the degree of humidifier degradation based on the parameters obtained by the parameter acquisition unit. The adjustment calculation unit is configured to determine the cooling path inlet temperature setpoint required to meet the cathode inlet humidity target value based on the attenuation degree and the preset cathode inlet humidity target value. The adjustment execution unit is configured to control the cooling system to perform actions based on the temperature setpoint output by the adjustment calculation unit.

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