Coordinated control method based on air compressor and bypass valve during fuel cell load reduction process

Abstract

The application discloses a kind of fuel cell unloading process based on the collaborative control method of air compressor and bypass valve, it is related to the field of fuel cell system anti-surge, comprising: obtaining air compressor inlet air flow, air compressor speed and oxygen excess ratio;Based on air compressor speed, the surge flow lower limit of corresponding compressor is calculated;When air compressor inlet air flow is lower than the multiple of compressor surge lower limit, increase bypass valve opening degree value a on initial bypass valve opening degree value to obtain anti-surge opening degree value, simultaneously improve air compressor speed to first speed;When air compressor inlet air flow is higher than the multiple of compressor surge lower limit and oxygen excess ratio is greater than or equal to minimum oxygen excess ratio;Obtain fuel cell stack inlet cathode pressure, based on fuel cell stack inlet cathode pressure and anti-surge opening degree value, PI control bypass valve opening degree is adopted.The application can be realized in fuel cell system unloading process, based on the joint anti-surge and anti-hypoxia control of air compressor and bypass valve.

Description

Technical Field

[0001] This invention relates to the field of surge prevention in fuel cell systems, and in particular to a coordinated control method based on an air compressor and a bypass valve during fuel cell unloading. Background Technology

[0002] While existing single-loop airflow control methods based on proportional-integral (PI) regulation with bypass valves reduce the risk of compressor surge to some extent, they cannot simultaneously address both the air pressure level at the fuel cell stack front end and the fuel cell's demand for excess air. During dynamic load shedding, safety hazards such as insufficient oxygen supply to the fuel cell stack and compressor surge often still occur.

[0003] Furthermore, if the system only uses the air compressor inlet flow meter for control, it is impossible to accurately estimate the air flow rate discharged through the bypass valve; if an additional flow meter is added at the fuel cell inlet, it will significantly increase the system cost and make the system layout more complex. Summary of the Invention

[0004] The purpose of this invention is to provide a coordinated control method based on the air compressor and bypass valve during the unloading process of a fuel cell system, which aims to solve the problems of insufficient oxygen supply to the fuel cell stack and air compressor surge during the unloading process of the fuel cell system.

[0005] This invention provides a coordinated control method based on an air compressor and a bypass valve during fuel cell unloading, comprising:

[0006] Obtain the air inlet flow rate of the air compressor, the air compressor speed, and the excess oxygen ratio;

[0007] The lower limit of compressor surge flow rate is calculated based on the compressor speed.

[0008] When the air flow rate at the air compressor inlet is lower than the compressor surge limit When the speed is doubled, the bypass valve opening value 'a' is increased to the initial bypass valve opening value to obtain the anti-surge opening value, and the air compressor speed is simultaneously increased to the first speed.

[0009] When the air flow rate at the air compressor inlet is higher than the compressor surge lower limit When the oxygen excess ratio is greater than or equal to the minimum oxygen excess ratio, obtain the DC current of the fuel cell stack, calculate the air flow rate required for the fuel cell stack cathode based on the DC current of the fuel cell stack, and calculate the difference between the air flow rate at the air compressor inlet and the air flow rate required for the fuel cell stack cathode.

[0010] The inlet cathode pressure of the fuel cell stack is obtained. Based on the inlet cathode pressure of the fuel cell stack, the predicted flow rate of the bypass valve is calculated through a linearization model. The difference is subtracted from the predicted flow rate of the bypass valve to obtain the error control variable. Based on the error control variable and the anti-surge opening value, the opening of the bypass valve is controlled by PI.

[0011] By employing the embodiments of the present invention, the present invention can realize the joint anti-surge and anti-oxygen deficiency control of the air compressor and the bypass valve during the unloading process of the fuel cell system.

[0012] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and in order to make the above and other objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described below. Attached Figure Description

[0013] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0014] Figure 1 This is a flowchart of a method for coordinated control of an air compressor and a bypass valve during fuel cell unloading according to an embodiment of the present invention.

[0015] Figure 2 It is an air supply system for a fuel cell engine;

[0016] Explanation of reference numerals in the attached figures:

[0017] 1: Fuel cell stack; 2: Power control unit; 3: Cooling unit; 4: Hydrogen supply unit; 5: Air filter; 6: Air flow meter; 7: Air compressor; 8: Air cooler; 9: Electric inlet valve; 10: Exhaust muffler; 11: Fuel cell stack inlet pressure sensor; 12: Fuel cell stack inlet temperature sensor; 13: Humidifier; 14: Back pressure valve; 15: Ambient pressure / temperature sensor; 16: Anti-surge bypass valve; 17: Controller. Detailed Implementation

[0018] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Method Implementation Examples

[0020] According to embodiments of the present invention, a coordinated control method based on an air compressor and a bypass valve is provided during the unloading process of a fuel cell. Figure 1This is a flowchart of a method for coordinated control of an air compressor and a bypass valve during fuel cell unloading according to an embodiment of the present invention, as shown below. Figure 1 As shown, it specifically includes:

[0021] Obtain the air inlet flow rate of the air compressor, the air compressor speed, and the excess oxygen ratio;

[0022] The lower limit of compressor surge flow rate is calculated based on the compressor speed.

[0023] When the air flow rate at the air compressor inlet is lower than the compressor surge limit When the speed is doubled, the bypass valve opening value 'a' is increased to the initial bypass valve opening value to obtain the anti-surge opening value, and the air compressor speed is simultaneously increased to the first speed.

[0024] When the air flow rate at the air compressor inlet is higher than the compressor surge lower limit When the oxygen excess ratio is greater than or equal to the minimum oxygen excess ratio, obtain the DC current of the fuel cell stack, calculate the air flow rate required for the fuel cell stack cathode based on the DC current of the fuel cell stack, and calculate the difference between the air flow rate at the air compressor inlet and the air flow rate required for the fuel cell stack cathode.

[0025] The inlet cathode pressure of the fuel cell stack is obtained. Based on the inlet cathode pressure of the fuel cell stack, the predicted flow rate of the bypass valve is calculated through a linearization model. The difference is subtracted from the predicted flow rate of the bypass valve to obtain the error control variable. Based on the error control variable and the anti-surge opening value, the opening of the bypass valve is controlled by PI.

[0026] In this embodiment of the invention, the lower limit of the surge flow rate of the corresponding compressor is calculated based on the compressor speed using the following formula:

[0027] ;

[0028] in, Lower limit of surge flow rate, unit: kg / s. , and The data is fitted using a quadratic polynomial. The speed of the air compressor is expressed in r / min.

[0029] The quadratic polynomial fitting data was obtained by collecting multiple surge boundary points (flow rate, speed) on a compressor test bench. Based on these data points, a quadratic polynomial fitting was performed to obtain the coefficients. , and .

[0030] Calculation example: Assume = 20000 r / min, then:

[0031]

[0032] (6) Usage: Each time the control loop executes the following calculations: a. Read the current... b. will Substitute into the above fitting formula for calculation; c. Multiply by the safety factor. (For example, 1.05) to obtain the minimum flow rate m with margin. safe d. m safe The flow threshold is used to determine surge protection.

[0033] The value of 1.05 means that the actual inlet air flow is less than 1.05 times the compressor surge limit, indicating that the air compressor is at risk of entering surge.

[0034] In this embodiment of the invention, when selecting α and β, α should be less than β to form a hysteresis loop for entering / exiting protection, avoiding frequent switching of the valve near the boundary and reducing the compressor surge lower limit. Double The value is 1.15. 1.15 means that the inlet airflow has significantly recovered to more than 1.15 times the lower limit of surge, and the excess oxygen ratio of the fuel cell stack air supply has recovered to λ. min The requirement indicates that the system has moved out of danger. The bypass valve opening value should be increased sufficiently to quickly move the compressor operating point out of the surge region, but not so large as to exceed the valve's physical opening range. Therefore, the bypass valve opening value 'a' is 0.25. After entering rapid protection mode, continuous monitoring of airflow and excess oxygen ratio is still necessary to prevent misjudgments leading to unnecessary control actions.

[0035] In this embodiment of the invention, the calculation of the air flow rate required for the cathode of the fuel cell stack based on the DC current of the fuel cell stack specifically includes:

[0036] ;

[0037] This indicates the airflow rate required for the cathode of the fuel cell stack, expressed in kg / s. The average molar mass of air divided by 4 times the Faraday constant. This refers to the DC current of the fuel cell stack, in amperes (A). This represents the minimum excess oxygen ratio, with a value ranging from 1.6 to 1.8.

[0038] k = M air / (4F) = 2.45×10⁻ 4 kg·A⁻¹·s⁻¹;M air= 28.97 g / mol (average molar mass of air); F = 96485 C / mol (Faraday constant). "4F" means that 4 mol of electrons are required to consume 1 mol of O2, corresponding to 4F coulombs of charge.

[0039] The principle for calculating k is as follows:

[0040] a. Pile current Converted to electron flow rate: / F (mol e⁻ per second). b. Every 4 mol e⁻ corresponds to the consumption of 1 mol O₂, therefore the O₂ consumption rate = / (4F) (mol O2 per second). c. Convert the O2 molar consumption rate to air mass flow rate: / (4F)×M air (kg / s). d. To ensure a sufficient excess of oxygen, multiply the above theoretical requirement by a coefficient. .

[0041] In this embodiment of the invention, the significance of calculating the difference between the air flow rate at the air compressor inlet and the air flow rate required for the fuel cell stack cathode is as follows:

[0042] A difference greater than 0 indicates that there is excess air supply. The excess air can be discharged through the bypass valve to maintain the oxygen excess ratio at the target level. ;

[0043] A difference of less than 0 indicates insufficient air supply, meaning that the air compressor's air supply is lower than the fuel cell stack's demand, and the fuel cell stack may face the risk of oxygen deficiency.

[0044] In this embodiment of the invention, the calculation of the predicted flow rate of the bypass valve based on the inlet cathode pressure of the fuel cell stack and using a linearized model specifically includes:

[0045] Estimate the cathode pressure at the outlet of the fuel cell stack, calculate the cathode-to-outlet pressure difference based on the cathode pressure at the inlet of the fuel cell stack, and record the cathode-to-outlet pressure difference as 0 if it is less than 0 to prevent false reverse flow.

[0046] The predicted flow rate of the bypass valve is calculated based on the pressure difference using the following formula:

[0047] ;

[0048] in, This indicates the predicted flow rate of the bypass valve. Indicates valve opening degree and pressure difference The bypass valve flow rate calibration reference value at that time. This represents the anti-surge opening value, which ranges from 0 to 1 and is dimensionless. Indicates pressure difference. This indicates the reference value for the bypass valve opening calibration (e.g., 0.5, which is 50% opening). This indicates the differential pressure calibration reference value. The sensitivity coefficient of the bypass valve flow rate to the pressure difference indicates the increase in bypass valve flow rate when the pressure difference across the valve increases by 1 kPa (unit: kg / s). The sensitivity coefficient (unit: kg / s) represents the flow rate of the bypass valve to the opening degree of the bypass valve, indicating the change in flow rate when the opening degree of the bypass valve changes by 1.0.

[0049] , as well as calibration calculation and The limit handling is as follows:

[0050] a. Maintain on the platform = Change the opening of the bypass valve Measure the corresponding airflow data and obtain linear fitting results. and b. Maintain on the stand =θ0, change ΔP, measure the corresponding airflow data, and obtain the same result as a by linear fitting. and c. For higher accuracy, multiple different (θ, ΔP) working conditions can be selected for testing, and multiple linear regression can be performed to improve model accuracy. d. If the predicted... If the flow rate exceeds the physical range (e.g., <0 or exceeds the valve's maximum flow rate), it needs to be saturated and limited.

[0051] In this embodiment of the invention, the temperature compensation for the pressure difference is as follows:

[0052] In this invention, "based on the pressure difference" refers to calculating the predicted flow rate of the bypass valve based on the equivalent pressure difference after temperature conversion. Specifically, the controller selects a reference temperature. (e.g., 293.15 K), for the measured pressure and corresponding gas temperature (Absolute temperature), according to the ideal gas approximation First, calculate the equivalent pressure at the reference temperature:

[0053]

[0054] Therefore, for the inlet side and the outlet side respectively:

[0055]

[0056] The equivalent pressure difference is obtained as follows:

[0057]

[0058] The pressure difference used in the subsequent linearized flow model of the bypass valve is In this way, the effects of temperature on gas density and pressure drop can be reflected in the pressure difference without changing the original flow formula structure, thus achieving temperature compensation.

[0059] For example, when the reference temperature Inlet pressure ,

[0060] Inlet temperature Export pressure ,

[0061] outlet temperature Sometimes,

[0062]

[0063] thereby The pressure difference used in the subsequent linearized flow model of the bypass valve is In this way, the effects of temperature on gas density and pressure drop can be factored into the pressure difference without changing the original flow formula structure, thus achieving temperature compensation.

[0064] In this embodiment of the invention, estimating the outlet cathode pressure of the fuel cell stack specifically includes:

[0065] Obtain the ambient atmospheric pressure, and estimate the fuel cell stack outlet cathode pressure based on the following formula;

[0066] ;

[0067] Where P represents the outlet cathode pressure of the fuel cell stack, P0 represents the ambient atmospheric pressure, and m in k1 represents the air flow rate at the air compressor inlet, k2 represents the calibration coefficient of the tailpipe, and k2 represents the calibration coefficient of the silencer.

[0068] k1 and k2 were obtained through experimental calibration, as follows:

[0069] 1) On a test bench or prototype, run the system under multiple different steady-state conditions and obtain a series of different air compressor inlet air flow rates (min) by adjusting the air compressor speed.

[0070] 2) Under each steady-state condition, record three types of data: fuel cell stack outlet cathode pressure P, ambient atmospheric pressure P0, and air compressor inlet air flow rate min, and calculate the exhaust pressure drop ΔP under that condition. tail = P− P0.

[0071] 3) This yields multiple sets of data points (min, ΔP_tail), assuming the tail discharge pressure drop and flow rate satisfy a quadratic relationship: ΔP tail ≈k1·min + k2·min².

[0072] 4) Use the least squares method (e.g., using Excel or Matlab to fit) to perform a quadratic polynomial fitting on the above data to obtain a set of optimal k1 and k2, and write them into the controller as calibration coefficients for the tailpipe and the silencer.

[0073] In simple terms, k1 and k2 are empirical parameters obtained by fitting a quadratic polynomial based on multiple sets of "measured flow-pressure drop" data.

[0074] In this embodiment of the invention, the bypass valve opening is controlled by PI based on the error control variable and the anti-surge opening value. Specifically, the valve opening increment is calculated using the following formula according to the error control variable.

[0075] ;

[0076] in, k3 represents the valve opening increment, k4 represents the proportional coefficient, and e represents the error control variable.

[0077] Add the anti-surge opening value to the valve opening increment. Obtain the bypass valve opening θ cmd .

[0078] When e > 0, the compressor supplies more air than the actual consumption of the fuel cell stack, and the excess air needs to be discharged by increasing the opening of the bypass valve. When e < 0, the air compressor supplies less air than the fuel cell stack requires, indicating that the fuel cell stack is not supplying enough oxygen. In this case, the opening of the bypass valve should be reduced (or the power of the air compressor should be increased) to increase the amount of air entering the fuel cell stack.

[0079] In this embodiment of the invention, a PI control law is used to reduce the opening degree of the bypass valve, as follows:

[0080] A proportional-integral controller is used to calculate the valve opening increment based on the error:

[0081] .

[0082] Where k3 is the proportional coefficient (which determines the response strength to instantaneous errors) and k4 is the integral coefficient (used to eliminate steady-state errors).

[0083] The calculated opening increment is added to the anti-surge opening value to obtain the bypass valve opening θ. cmd .

[0084] In this embodiment of the invention, the calculated θ is transmitted via the CAN bus. cmd The bypass valve actuator drives the valve to operate.

[0085] To prevent integral saturation, when the calculated bypass valve opening reaches the upper or lower limit (0 or θ)... max When the rate of change of the integral term is limited, the accumulation of the integral term should be paused (anti-integral saturation treatment) to avoid overshoot in the control.

[0086] In this embodiment of the invention, the opening range is limited to: 0 ≤ θ cmd ≤θ max , where θ max = 30% (the maximum opening degree of the bypass valve is approximately 30%). Rate of change limit: |θ cmd −θ bp，last | ≤θ lim ·Δt, where θ lim = 3 s⁻¹ (maximum rate of change of valve opening, 3 units per second).

[0087] In this embodiment of the invention, when the error control variable exceeds a first threshold and the duration exceeds a first time value, an alarm signal for abnormal bypass valve flow is recorded and issued.

[0088] In this embodiment of the invention, fault diagnosis is performed simultaneously during the operation of the method: if the error |e| exceeds the threshold e th If the flow rate is 0.01 kg / s and lasts for more than 2 seconds, record and alarm "Abnormal bypass valve flow rate" to indicate a possible sensor or valve malfunction.

[0089] In this embodiment of the invention, an apparatus is provided for implementing the method of the invention on this apparatus, such as... Figure 2 As shown, the device includes:

[0090] Fuel cell stack, power control unit, cooling unit, hydrogen supply unit, air filter, air compressor, air cooler, electric inlet valve, exhaust muffler, fuel cell stack inlet pressure sensor, fuel cell stack inlet temperature sensor, humidifier, back pressure valve, ambient pressure / temperature sensor, anti-surge bypass valve.

[0091] The fuel cell stack serves as the core of the electrochemical reaction, outputting DC power; it is connected to the cooling unit and the hydrogen supply unit.

[0092] The power control unit manages voltage, current, and power flow to achieve energy scheduling for the entire vehicle.

[0093] The cooling unit controls the operating temperature of the fuel cell stack and maintains the optimal reaction range.

[0094] The hydrogen supply unit enables hydrogen storage, pressure reduction, and stable hydrogen supply.

[0095] Air filters remove dust particles from the air, preventing damage to air compressors and fuel cell stacks;

[0096] An air flow meter measures the mass flow rate of air at the air compressor inlet in real time, providing a basis for subsequent differential pressure estimation.

[0097] An air compressor compresses ambient air to the required pressure, thereby increasing the oxygen supply capacity to the fuel cell stack.

[0098] Air cooler (intercooler) reduces compressed air temperature, improves fuel cell stack efficiency, and prevents membrane drying;

[0099] Electric inlet valve controls the on / off of air entering the reactor and is used for safety interlocking such as emergency shutdown;

[0100] Exhaust muffler, a muffler at the air outlet of the fuel cell stack, used to reduce exhaust noise;

[0101] The fuel cell stack inlet pressure sensor measures the pressure at the cathode air inlet of the fuel cell stack for differential pressure calculation.

[0102] The fuel cell stack inlet temperature sensor measures the temperature at the cathode air inlet of the fuel cell stack, which serves as a temperature compensation reference for differential pressure calculation.

[0103] In this embodiment of the invention, the temperature compensation reference scheme is as follows:

[0104] Considering that gas density changes with temperature, to avoid flow prediction errors caused by directly using pressure differences under different temperature conditions, the controller preferably performs temperature-based pressure conversion. Specifically, the controller selects a reference temperature. Regarding the measured pressure and the corresponding gas temperature Calculate the equivalent pressure at the reference temperature:

[0105] ;

[0106] For example, for fuel cell stack inlet pressure With inlet temperature And pressure on the reactor outlet (or environment). With temperature ,available:

[0107] ;

[0108] And further calculate the equivalent pressure difference:

[0109] ;

[0110] The pressure difference subsequently used in the linearized flow prediction model for the bypass valve is the equivalent pressure difference. This allows for temperature-pressure compensation, improving the accuracy of bypass valve flow estimation under different operating conditions.

[0111] The humidifier uses the exhaust gas from the fuel cell stack to humidify the air entering the fuel cell stack, thus maintaining the water content of the membrane electrolyte.

[0112] Back pressure valve, which regulates the back pressure of the fuel cell cathode, optimizes the reaction pressure and stabilizes the air flow;

[0113] An ambient pressure / temperature sensor measures ambient atmospheric pressure and temperature as a reference for differential pressure estimation and temperature compensation.

[0114] In this embodiment of the invention, in addition to providing the ambient atmospheric pressure P0 as the starting point for estimating the tailpipe pressure difference, the ambient pressure / temperature sensor measures the ambient temperature T_amb as the reference for temperature compensation. The controller selects a fixed reference temperature T_ref (e.g., 293.15 K, corresponding to 20°C) and converts the pressure difference under the current operating conditions to the reference temperature.

[0115] Specifically, regarding the pressure difference between the reactor outlet side and the environment;

[0116] Assuming the exhaust gas temperature is close to the ambient temperature, the controller operates based on the ideal gas law. Convert it to the equivalent pressure difference at the reference temperature:

[0117]

[0118] Where T_amb is measured by an ambient temperature sensor, and T_ref is a pre-set reference temperature. The pressure difference used subsequently in the bypass valve flow estimation model is the equivalent pressure difference mentioned above. This allows us to use ambient temperature as a benchmark to incorporate the effects of temperature on gas density and pressure drop into the pressure difference, thereby achieving temperature compensation.

[0119] The anti-surge bypass valve allows excess air to be discharged directly to the atmosphere, preventing surge in the air compressor.

[0120] The controller is used to acquire ambient atmospheric pressure and temperature, pressure at the cathode air inlet of the fuel cell stack, temperature at the cathode air inlet of the fuel cell stack, mass flow rate of air at the air compressor inlet, air compressor speed, DC current of the fuel cell stack, anti-surge opening value, and execute the method proposed in this invention.

[0121] The entire device operates as follows:

[0122] Airflow direction:

[0123] Outside air first passes through an air filter to remove dust, particles and other impurities; clean air is then drawn in and pressurized by an air compressor; the high-temperature, high-pressure air enters an intercooler and is cooled to a temperature suitable for entering the fuel cell stack; the cooled air flows into the dry side of a humidifier to exchange humidity with the humid, hot air from the fuel cell stack exhaust gas; the humidified air then enters the fuel cell stack cathode through an electric inlet valve to participate in the electrochemical reaction.

[0124] Bypass and exhaust passage:

[0125] When the air flow provided by the air compressor is higher than the actual demand of the fuel cell stack, or when the operating point of the air compressor is close to the surge boundary, the controller will open the anti-surge bypass valve to release the excess air directly into the atmosphere. This will prevent the air compressor from entering the surge condition and prevent too much air from being diverted, thus affecting the normal oxygen supply of the fuel cell stack.

[0126] After the fuel cell stack reaction, the cathode exhaust gas is discharged from the stack outlet. It first passes through the wet side of the humidifier, where moisture and some heat are transferred to the fresh air entering the dry side. Then, the exhaust gas is discharged into the environment after the pressure is regulated by the back pressure valve.

[0127] Sensing and Control: Key sensors in the system include the air compressor inlet air flow meter and the fuel cell stack inlet pressure sensor. The controller (ECU) reads the signals from these sensors in real time, as well as data such as air compressor speed and stack current, and then executes two types of control actions:

[0128] Adjust the air compressor speed to ensure that the air supply follows the load demand of the fuel cell stack and keep the air compressor operating point away from the surge line;

[0129] Adjust the bypass valve opening to quickly release excess air and prevent the instantaneous pressure at the air compressor outlet from becoming too high, while ensuring that the excess oxygen entering the fuel cell stack is not lower than the safety lower limit.

[0130] Functional Collaboration:

[0131] The entire air supply loop forms a parallel structure of "main air path + bypass air path". The main air path ensures that the fuel cell stack receives stable air with suitable temperature and humidity; the bypass air path quickly releases excess air when the system is unloaded, and works in conjunction with the air compressor speed regulation to achieve the dual control objectives of anti-surge and anti-oxygen deficiency.

[0132] The beneficial effects of this invention are as follows:

[0133] The key sensors employed in this invention include an air compressor inlet air flow meter and a fuel cell stack inlet pressure sensor. A collaborative control strategy using these two minimal sensors enables joint control of the air compressor and bypass valve. During rapid load reduction in the fuel cell system, this strategy simultaneously prevents both air compressor surge and fuel cell stack oxygen deficiency, avoiding the cost and complexity of adding extra flow sensors. This invention provides an air compressor-bypass valve joint control algorithm, a complete air management control algorithm. It includes calculating theoretical air demand using fuel cell stack current, determining the oxygen surplus coefficient, and then calculating excess air flow. A linearized model is used to predict the current flow of the bypass valve, and the error is obtained by comparing the two results before using PI control to adjust the bypass valve opening. This algorithm can dynamically allocate air flow, quickly discharging excess air while ensuring sufficient oxygen supply to the fuel cell stack, significantly improving the system's safety and response speed under power slump conditions.

[0134] Rapid Anti-Surge Response Mechanism: To address the risk of transient surge in air compressors, a rapid protection mechanism based on threshold judgment is designed. When the air compressor inlet flow rate is detected to be below the surge margin (e.g., below 105%), the control strategy immediately increases the bypass valve opening by a predetermined amount (e.g., 25% stroke) and simultaneously requests the air compressor to increase its speed to quickly improve air supply and move away from the surge region. Once the air flow rate recovers and exceeds the surge lower limit by a certain margin (e.g., 115%) and the excess oxygen ratio returns to normal, the controller smoothly switches back to conventional PI control. This rapid response mechanism ensures stable operation of the air compressor even under extreme descent conditions, preventing surge.

[0135] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the present invention.

Claims

1. A method for coordinated control of an air compressor and a bypass valve during a fuel cell load reduction, the method comprising: The method comprises the following steps: acquiring the air flow at the inlet of the air compressor, the rotating speed of the air compressor and the excess oxygen ratio; calculating the lower limit of the surge flow of the compressor based on the rotating speed of the air compressor; the calculation of the lower limit of the surge flow of the compressor based on the rotating speed of the air compressor adopts the following formula: ； wherein, is the surge flow lower limit, , and is a quadratic polynomial fit to the data, is the air compressor rotational speed; When the air flow at the inlet of the air compressor is lower than the lower limit of the compressor surge When the air flow at the inlet of the air compressor is lower than the lower limit of the compressor surge The value of a is 1.05, and the value of the bypass valve opening degree a is 0.

25. When the air flow at the inlet of the air compressor is higher than the lower limit of compressor surge When the air flow at the inlet of the air compressor is higher than the lower limit of compressor surge is greater than or equal to the minimum excess air ratio, obtaining the direct current of the fuel cell stack, calculating the air flow required by the cathode of the fuel cell stack based on the direct current of the fuel cell stack, and calculating the difference between the air flow at the inlet of the air compressor and the air flow required by the cathode of the fuel cell stack; wherein, is greater than or equal to the minimum excess air ratio, obtaining the direct current of the fuel cell stack, calculating the air flow required by the cathode of the fuel cell stack based on the direct current of the fuel cell stack, and calculating the difference between the air flow at the inlet of the air compressor and the air flow required by the cathode of the fuel cell stack; wherein, is greater than or equal to the minimum excess air ratio, obtaining the direct current of the fuel cell stack, acquiring the inlet cathode pressure of the fuel cell stack, calculating the predicted flow of the bypass valve based on the inlet cathode pressure of the fuel cell stack through a linearization model, subtracting the predicted flow of the bypass valve from the difference to obtain an error control variable, and adopting PI control on the opening of the bypass valve based on the error control variable and the anti-surge opening value; the calculation of the predicted flow of the bypass valve based on the inlet cathode pressure of the fuel cell stack and through a linearization model comprises the following steps: estimating the outlet cathode pressure of the fuel cell stack, calculating the outlet-inlet cathode pressure difference of the fuel cell stack based on the inlet cathode pressure of the fuel cell stack, and setting the outlet-inlet cathode pressure difference as 0 if the outlet-inlet cathode pressure difference is less than 0; calculating the predicted flow of the bypass valve based on the pressure difference adopts the following formula: ； wherein, represents a predicted flow rate of the bypass valve, represents a valve opening and a pressure difference when a bypass valve flow rate calibration reference value, represents an anti-surge opening value, represents a pressure difference, represents a bypass valve opening calibration reference value, represents a pressure difference calibration reference value, represents a bypass valve flow rate to pressure difference sensitivity coefficient, represents an increase in bypass valve flow rate when the pressure difference across the valve increases by 1 kPa, represents a bypass valve flow rate to bypass valve opening sensitivity coefficient, represents a change in flow rate when the bypass valve opening changes by 1.0; the PI control on the opening of the bypass valve based on the error control variable and the anti-surge opening value specifically comprises the following steps: calculating the valve opening increment based on the error control variable by using the following formula; ； wherein, represents the valve opening increment, k3 represents the proportional coefficient, k4 represents the integral coefficient, and e represents the error control variable. adding the valve opening increment to the anti-surge opening value to obtain the opening of the bypass valve.

2. The method of claim 1, wherein, the calculation of the required air flow of the cathode of the fuel cell stack based on the direct current of the fuel cell stack specifically comprises the following steps: ； Qair represents the air flow required for the cathode of the fuel cell stack, Qair represents the air flow required for the cathode of the fuel cell stack, I represents the direct current of the fuel cell stack, Qair represents the air flow required for the cathode of the fuel cell stack, 3. The method of claim 1, wherein, the estimation of the outlet cathode pressure of the fuel cell stack specifically comprises the following steps: acquiring the ambient atmospheric pressure, and estimating the outlet cathode pressure of the fuel cell stack based on the ambient atmospheric pressure by using the following formula; ； where P represents the fuel cell stack outlet cathode pressure, P0represents the ambient atmospheric pressure, m in where m represents the air flow rate at the air compressor inlet, k1represents the calibration coefficient of the tail pipe, and k2represents the calibration coefficient of the muffler.

4. The method of claim 1, wherein, when the error control variable exceeds the first threshold value and the duration exceeds the first time value, an alarm signal of the abnormal flow of the bypass valve is recorded and sent.

5. The method of claim 1, wherein, the opening of the bypass valve is provided with an opening range and a change rate constraint.

Images