A model-based variable-geometry cycle engine mode switching combination control method
By designing a low-pressure rotor speed cascade controller and fuzzy theory tuning, and introducing pitch angle feedforward and over-limit protection controllers, the problem of unstable mode switching in the shaft fan variable cycle engine was solved, and safe and stable mode switching was achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- NANJING UNIV OF AERONAUTICS & ASTRONAUTICS
- Filing Date
- 2024-03-28
- Publication Date
- 2026-05-08
AI Technical Summary
In the existing technology, the mode switching control method for shaft fan variable cycle engines has not been effectively studied, resulting in unstable mode switching and difficulty in achieving safe and stable mode conversion.
A low-pressure rotor speed cascade controller was designed, and the controller parameters were tuned using fuzzy theory. A pitch angle feedforward controller, an over-limit protection controller, and a tail nozzle area-engine rotor slip controller were introduced. A transient venting plan for the low-pressure compressor was designed to ensure the stability and safety of the mode switching process.
Stable switching between different modes of the shaft fan variable cycle engine was achieved, avoiding problems such as over-temperature, over-speed and surge, and ensuring the stability of key parameters during the switching process.
Smart Images
Figure CN118188177B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of aero-engine technology, specifically to a model-based combined control method for switching modes of a shaft-sector variable cycle engine. Background Technology
[0002] While conventional helicopters possess vertical takeoff and landing (VTOL) and low-altitude hovering capabilities, their maximum forward speed is limited by the compressibility of the advancing blade and the airflow separation of the retreating blade, resulting in weak long-range rapid response capabilities. Tiltrotor aircraft such as the V-22 Osprey and V-280 Warrior can compensate for the shortcomings in forward speed to some extent, but their high-speed cruise capability is limited by the rotor tip speed, making it difficult to achieve further breakthroughs in flight speed. Current fixed-wing aircraft such as the F-35 Lightning, while possessing VTOL capabilities, have low hovering efficiency during vertical takeoff, resulting in a significant reduction in mission payload and mission radius. To overcome the limitations of advancing blade tip speed, combining helicopter rotor configurations with fixed-wing jet aircraft configurations is an effective mode for achieving VTOL and high-speed long-range cruise. This approach offers superior short takeoff / vertical landing (STOVL) and high-speed cruise performance, and the corresponding power plant should ideally possess the performance characteristics of both turboshaft and turbofan engines.
[0003] In the turboshaft mode, the output shaft power of the shaft-fan variable cycle engine is used to achieve vertical takeoff and landing and hovering through the aerodynamically efficient rotor. In the turbofan mode, the engine detaches from the rotor to output jet thrust for subsonic cruise. The mode switching problem is more similar to the transient control problem of conventional engines. How to design a suitable controller and control law to coordinate the changes in various control parameters and achieve stable and safe mode switching is a key research issue. There is currently no publicly available data on mode switching control methods for shaft-fan variable cycle engines, but the mode switching control system for shaft-fan variable cycle engines can refer to conventional turbofan, turboshaft, and variable cycle engines. During mode switching, the turbine speed control scheme of turboshaft engines can be used as a reference, implementing closed-loop control of the low-pressure rotor speed. Other variable geometry parameter control schemes can also draw on the influence of variable geometry component adjustments on engine performance in conventional variable cycle engines, thereby designing corresponding mode switching control laws. Summary of the Invention
[0004] Objective of the Invention: To address the problems existing in the background technology, this invention provides a model-based combined control method for switching modes of a shaft-fan variable cycle engine. For the constant low-pressure rotor speed control requirement in the turboshaft mode of the engine, a low-pressure rotor speed cascade controller is designed, and the controller's PI parameters are tuned online based on fuzzy theory. Pitch angle feedforward, over-limit protection controller, nozzle area-engine rotor slip controller, and low-pressure compressor transient bleed-out plan are introduced to ensure stable switching between different modes of the shaft-fan variable cycle engine.
[0005] Technical solution: To achieve the above objectives, the technical solution adopted by this invention is as follows:
[0006] A model-based combined control method for mode switching of a shaft-sector variable cycle engine includes the following steps:
[0007] 1) Based on the constant low-pressure output shaft speed requirement of the vortex shaft mode of the shaft-fan variable cycle engine, a low-pressure rotor speed cascade controller is designed, and fuzzy theory is used to tune the control parameters in real time;
[0008] 2) Based on the power and thrust output requirements when the shaft fan variable cycle engine mode is switched, design the control law of the adjustable guide vane at the outer bypass duct inlet and the area control law of the outer bypass duct tail nozzle. Combine the high and low pressure rotor speed difference to design the EPR control law. Use the area of the inner bypass duct tail nozzle as an intermediate variable to adjust the remaining power and thrust of the low pressure output shaft and prevent surge.
[0009] 3) Based on the working characteristics of the clutch and rotor, design the clutch pressure open-loop law and the pitch angle feedforward compensation law when the shaft fan variable cycle engine mode is switched.
[0010] 4) Design an over-limit protection controller to ensure that the shaft fan variable cycle engine does not exceed the temperature or speed limits during the switching process;
[0011] 5) Combining the relationship between the high and low pressure rotor speed difference and the surge margin of high and low pressure compressor components, design the transient gas release law of the low pressure compressor to improve the surge margin of the low pressure compressor during the switching of the shaft fan variable cycle engine mode.
[0012] Preferably, the implementation process of step 1) is as follows:
[0013] 1.1): Design of a low-voltage rotor speed cascade controller:
[0014] The low-voltage rotor speed cascade controller consists of an outer loop low-voltage rotor speed controller and an inner loop high-voltage rotor speed controller. The outer loop low-voltage rotor speed controller is determined by the actual low-voltage rotor speed n. L and low-pressure rotor command speed n Lr The difference is used to calculate the commanded speed n of the high-pressure rotor. Hr The inner-loop high-voltage rotor speed controller controls the rotor speed n via high-voltage rotor commands. Hr The actual output speed n of the shaft fan variable cycle engine H Calculate the difference in fuel flow rate ΔW f :
[0015]
[0016] Where: ΔW f [k] represents the fuel flow increment at time k calculated by the inner ring high-pressure rotor speed controller, K. pHΔn represents the proportional coefficient of the inner loop high-voltage rotor speed controller. H [k] represents the high-pressure rotor command speed n at time k. Hr The actual output speed n of the shaft fan variable cycle engine H Deviation, Δn H [k-1] represents the high-pressure rotor command speed n at time k-1. Hr The actual output speed n of the shaft fan variable cycle engine H The deviation, T iH Δn represents the integral time constant of the inner loop high-voltage rotor speed controller. Hr [k] represents the increment of the high-voltage rotor command speed at time k calculated by the outer loop low-voltage rotor speed controller, K pL Δn is the proportional coefficient of the outer loop low-voltage rotor speed controller. L [k] represents the low-pressure rotor command speed n at time k. Lr The actual output speed n of the shaft fan variable cycle engine L Deviation, Δn L [k-1] represents the low-pressure rotor command speed n at time k-1. Lr The actual output speed n of the shaft fan variable cycle engine L The deviation; T is the sampling period of the low-voltage rotor speed cascade controller, T iL The integral time constant of the outer loop low-pressure rotor speed controller;
[0017] 1.2): The parameter input to the fuzzy controller is the deviation e1 = Δn L [k] and e2 = Δn H [k] and its respective rate of change of deviation ec1=Δn L [k]-Δn L [k-1] and ec2 = Δn H [k]-Δn H [k-1], converts the parameters of the input fuzzy controller to values in the fuzzy universe of discourse. Based on the discreteness or continuity of the fuzzy universe of discourse, the membership function H(x) is... i The function is taken in discrete form, and a fuzzy subset H is formed through the membership degrees of a finite number of points:
[0018]
[0019] In the formula: sub-terms Used to describe element x in a fuzzy universe i Its membership function H(x) i The correspondence between ) is shown, where the "+" sign indicates the whole of a fuzzy subset on the fuzzy domain;
[0020] The normal membership function is selected as follows:
[0021]
[0022] The triangular membership function is selected as follows:
[0023]
[0024] Where: a, b and p are all constant values, and their values are selected according to the range of the universe of discourse;
[0025] The output set is clarified using a discrete universe of discourse and the centroid method. The calculation formula for the centroid method is as follows:
[0026]
[0027] Where: the universe of discourse u = {u1, u1, ... u1} n} is a discrete universe of discourse, u j The membership degree at point H(u) is j ), where u is the abscissa corresponding to the center of the area; the fuzzy set of the output is obtained by reasoning the parameters of the input fuzzy controller through the rule base, and then the exact precise quantity is determined by the defuzzification method, and the control parameter K of the inner loop high-voltage rotor speed controller at the current time k is calculated. p The control parameter K of the outer ring low-pressure rotor speed controller i The change is input to the low-pressure rotor speed cascade controller to update the control parameters.
[0028] Preferably, the implementation process of step 2) is as follows:
[0029] 2.1): A variable geometry working mechanism analysis was conducted on the adjustable guide vane at the outer bypass duct inlet and the area of the outer bypass duct tail nozzle. The closure degree of the adjustable guide vane at the outer bypass duct inlet showed a positive correlation with the change in the residual power of the low-pressure shaft. During mode switching, the change law of the adjustable guide vane at the outer bypass duct inlet was consistent with the change law of the rotor pitch angle.
[0030]
[0031] Where: α VIGV For the angle of the adjustable guide vane at the outer bypass duct inlet, β rotor The rotor pitch angle is denoted by 'max', which represents the maximum value.
[0032] When switching from turboshaft mode to turbofan mode, the area of the outer bypass duct nozzle remains unchanged. The control law for the area of the outer bypass duct nozzle is as follows:
[0033]
[0034] A 18 =A 18d
[0035] In the formula: A18 A is the area of the outer bypass duct tailpipe. 18d The area of the tailpipe of the outer duct is to be designed.
[0036] 2.2): Based on step 2.1), the EPR control law will be adopted for the area control of the inner duct tail nozzle. r =f(Δn), Δn = n Hcor -n Lcor The EPR command value is calculated using the relative equivalent speed difference Δn between the high-pressure and low-pressure rotors, where f(·) represents the function. This function calculates the EPR command value by controlling the low-pressure rotor speed to remain constant. r The EPR instruction value is EPR. r The input to the tailpipe area controller, the control logic during mode switching is that when the relative equivalent speed difference Δn between the high and low pressure rotors increases, the EPR... r Reduced internal exhaust nozzle area to prevent high-pressure compressor surging; reduced EPR when the relative equivalent speed difference Δn between high and low pressure rotors decreases. r Increased internal exhaust nozzle area reduces low-pressure compressor intake pressure; during mode switching, the shaft fan variable cycle engine pressure ratio is simultaneously affected by fuel flow W. f The desired trend of the inner duct tail nozzle area change should conform to the change of low-pressure shaft load power, so as to compensate for the residual power of the low-pressure shaft and prevent surge.
[0037] Preferably, in step 3):
[0038] 3.1): During the process of engaging the clutch and rotating the rotor, the clutch engagement process follows the principle of "slow at first, then fast". During the idle stroke stage, the clutch does not transmit torque, and at this time the clutch does not generate impact on the transmission system. As the clutch pressure increases, the clutch is in a slipping state. In order to reduce the impact on the transmission system and the variable cycle engine, the clutch should engage slowly. As the speed difference between the main and driven discs decreases, the clutch pressure is increased to reduce the engagement time and the slipping work during the engagement process. The disengagement process is the opposite of the engagement process.
[0039] 3.2): During pitch angle adjustment, the feedforward controller approximates a gain, and the relationship between the changing gain and the pitch angle during mode switching is solved. The increment during pitch angle adjustment is transmitted to the feedforward control logic to calculate the high-voltage rotor command speed n. Hr The change in speed is then transmitted to the inner high-voltage rotor speed controller.
[0040] Preferably, in step 4):
[0041] Three over-limit protection modules are designed: a high-pressure rotor speed over-limit protection controller, a low-pressure turbine inlet total temperature over-limit protection controller, and a high-pressure compressor outlet pressure over-limit protection controller. All three over-limit protection controllers are incremental PI controllers, based on the limiting parameter high-pressure rotor speed n. Hmax Low-pressure turbine inlet total temperature T 45max and the outlet pressure P of the high-pressure compressor t3max The difference between the maximum value and the current measured value is used to calculate the corresponding fuel flow rate. The minimum value selector selects the lowest value among the fuel flow rates output by the three over-limit protectors, the maximum fuel flow rate, and the fuel flow rate calculated by the low-pressure rotor speed cascade controller, ensuring that the limiting parameters do not exceed the limit values during the entire mode switching process.
[0042] Preferably, in step 5):
[0043] By analyzing the relationship between the surge margin of the low-pressure compressor and the relative equivalent speed difference Δn between the high-pressure and low-pressure rotors during mode switching, a transient bleed-out plan for the low-pressure compressor is introduced. The bleed-out valve is located at the cross-section of the intermediate stage of the low-pressure compressor, where the relative equivalent speed difference Δn between the high-pressure and low-pressure rotors is Δn = n Hcor -n Lcor When the slip is less than 0.8%, the low-pressure compressor performs intermediate stage venting, and the venting volume is 4% of the cross-sectional flow rate. This part of the air is discharged into the atmosphere.
[0044] The rationality and effectiveness of the obtained control law for the switching mode of the shaft-fan variable cycle engine were verified by simulation of the engine component-level model.
[0045] Beneficial effects:
[0046] This invention provides a model-based combined control method for mode switching of a shaft-fan variable cycle engine. For the constant low-pressure rotor speed control requirement in turboshaft mode, a low-pressure rotor speed cascade controller is designed, and the controller's PI parameters are tuned online based on fuzzy theory. Pitch angle feedforward, over-limit protection controller, nozzle area-engine rotor slip controller, and low-pressure compressor bleed schedule are introduced to ensure stable engine mode switching. Based on this, a mode switching control law for the shaft-fan engine is proposed. The effectiveness of the mode switching control law is verified through mode switching simulation. During the switching process, key engine parameters do not exceed limits, the low-pressure rotor speed fluctuation is small, and the high-pressure rotor speed change is stable. Attached Figure Description
[0047] Figure 1 A flowchart is designed for the model-based combined control law of mode switching of a shaft-sector variable cycle engine.
[0048] Figure 2 A schematic diagram of a low-pressure rotor speed fuzzy cascade controller with pitch feedforward;
[0049] Figure 3 A schematic diagram of the dual-loop closed-loop control system for an engine.
[0050] Figure 4 A schematic diagram of a shaft-sector variable cycle engine;
[0051] Figure 5 Engine pressure ratio - slip EPR r =f(Δn) control law diagram;
[0052] Figure 6 This is a logic diagram of the over-limit protection controller;
[0053] Figure 7 (a) is a simulation diagram of the relative converted speed of the low-pressure rotor when switching from turbofan mode to turboshaft mode;
[0054] Figure 7 (b) is a simulation diagram of the relative converted speed of the high-pressure rotor when switching from turbofan mode to turboshaft mode;
[0055] Figure 7 (c) Switching between turbofan and turboshaft modes: pitch angle and α VIGV Simulation diagram;
[0056] Figure 7 (d) is a diagram showing the gas venting pattern of the intermediate stage of the low-pressure compressor when switching from turbofan mode to turboshaft mode.
[0057] Figure 7 (e) is a simulation diagram of main fuel flow rate when switching from turbofan mode to turboshaft mode;
[0058] Figure 7 (f) is a simulation diagram of the inner and outer bypass nozzle areas when switching from turbofan mode to turboshaft mode;
[0059] Figure 7 (g) is a simulation diagram of clutch pressure when switching from turbofan mode to turboshaft mode;
[0060] Figure 7 (h) is a simulation diagram of the thrust of the inner and outer bypass nozzles when switching from turbofan mode to turboshaft mode.
[0061] Figure 7 (i) is a simulation diagram of the airflow rate of the inner and outer bypass when switching from turbofan mode to turboshaft mode;
[0062] Figure 7 (j) is a simulation diagram of the power of the Flade fan switching from turbofan mode to turboshaft mode;
[0063] Figure 7 (k) is a simulation diagram of the low-pressure turbine power switching between turbofan mode and turboshaft mode;
[0064] Figure 7(l) is a simulation diagram of the engine and clutch output torque when switching from turbofan mode to turboshaft mode;
[0065] Figure 7 (m) is a simulation diagram of the total outlet pressure of the high-pressure compressor when switching from turbofan mode to turboshaft mode;
[0066] Figure 7 (n) is a simulation diagram of the total inlet temperature of the low-pressure turbine switching from turbofan mode to turboshaft mode;
[0067] Figure 7 (o) is a simulation diagram of the pressure ratio of an engine switching between turbofan mode and turboshaft mode;
[0068] Figure 7 (p) is a simulation diagram of the surge margin of the high and low pressure compressor switching from turbofan mode to turboshaft mode;
[0069] Figure 8 (a) is a simulation diagram of rotor torque switching between turbofan mode and turboshaft mode;
[0070] Figure 8 (b) is a simulation diagram of rotor power switching between turbofan mode and turboshaft mode;
[0071] Figure 8 (c) K of the inner and outer loops of the controller for switching between turbofan mode and turboshaft mode p Simulation curves;
[0072] Figure 8 (d) is the inner and outer loop K of the controller for switching between turbofan mode and turboshaft mode. i Simulation curves;
[0073] Figure 9 (a) is a simulation diagram of the relative converted speed of the low-pressure rotor when switching from turboshaft mode to turbofan mode;
[0074] Figure 9 (b) is a simulation diagram of the relative converted speed of the high-voltage rotor when switching from turboshaft mode to turbofan mode;
[0075] Figure 9 (c) Pitch angle and α for switching between turboshaft mode and turbofan mode VIGV Simulation diagram;
[0076] Figure 9 (d) is a diagram showing the gas venting pattern of the intermediate stage of the low-pressure compressor when switching from turboshaft mode to turbofan mode.
[0077] Figure 9 (e) is a simulation diagram of main fuel flow rate when switching from turboshaft mode to turbofan mode;
[0078] Figure 9 (f) is a simulation diagram of the inner and outer bypass nozzle areas when switching from turboshaft mode to turbofan mode;
[0079] Figure 9 (g) is a simulation diagram of clutch pressure when switching from turboshaft mode to turbofan mode;
[0080] Figure 9 (h) is a simulation diagram of the thrust of the inner and outer bypass nozzles when switching from turboshaft mode to turbofan mode;
[0081] Figure 9 (i) is a simulation diagram of the airflow rate of the inner and outer bypass when switching from turboshaft mode to turbofan mode;
[0082] Figure 9 (j) is a simulation diagram of the Flade fan power switching between turboshaft mode and turbofan mode;
[0083] Figure 9 (k) is a simulation diagram of the low-pressure turbine power switching between turboshaft mode and turbofan mode;
[0084] Figure 9 (l) is a simulation diagram of the engine and clutch output torque when switching from turboshaft mode to turbofan mode;
[0085] Figure 9 (m) is a simulation diagram of the total outlet pressure of the high-pressure compressor switching from turboshaft mode to turbofan mode;
[0086] Figure 9 (n) is a simulation diagram of the total inlet temperature of the low-pressure turbine switching from turboshaft mode to turbofan mode;
[0087] Figure 9 (o) is a simulation diagram of the pressure ratio of the engine switching between turboshaft mode and turbofan mode;
[0088] Figure 9 (p) is a simulation diagram of the surge margin of the high and low pressure compressor switching from turboshaft mode to turbofan mode; Detailed Implementation
[0089] The invention will now be further described with reference to the accompanying drawings.
[0090] This invention provides a model-based combined control method for mode switching of a shaft-sector variable cycle engine, specifically as follows: Figure 1 As shown.
[0091] Step S1: Design a low-pressure rotor speed cascade controller and tune the controller's PI parameters online based on fuzzy theory;
[0092] Step S2: Design the control law of the adjustable guide vane at the inlet of the bypass duct and the area control law of the exhaust nozzle of the bypass duct, and design the EPR control law in combination with the speed difference between high and low pressure rotors, and then design the exhaust nozzle area-slip controller.
[0093] Step S3: Design the clutch pressure open-loop law and the pitch angle feedforward compensation law when switching engine modes.
[0094] Step S4: Design an over-limit protection controller;
[0095] Step S5: Low-pressure compressor venting plan during design mode switching.
[0096] Based on the design of the shaft-sector variable cycle engine mode switching in step S1, the nonlinear common working equation system is solved; specifically,
[0097] Step S1.1: The low-voltage rotor speed cascade controller includes an outer loop low-voltage rotor speed controller and an inner loop high-voltage rotor speed controller. The outer loop low-voltage rotor speed controller is determined by the actual low-voltage rotor speed n. L and low-pressure rotor command speed n Lr The difference is used to calculate the commanded speed n of the high-pressure rotor. Hr The inner-loop high-voltage rotor speed controller controls the rotor speed n via high-voltage rotor commands. Hr and the actual engine output speed n H Calculate the difference in fuel flow rate ΔW f :
[0098]
[0099] Where: ΔW f [k] represents the fuel flow increment at time k calculated by the inner ring high-pressure rotor speed controller, K. pH Δn represents the proportional coefficient of the inner loop high-voltage rotor speed controller. H [k] represents the high-pressure rotor command speed n at time k. Hr The actual output speed n of the shaft fan variable cycle engine H Deviation, Δn H [k-1] represents the high-pressure rotor command speed n at time k-1. Hr The actual output speed n of the shaft fan variable cycle engine H The deviation, T iH Δn represents the integral time constant of the inner loop high-voltage rotor speed controller. Hr [k] represents the increment of the high-voltage rotor command speed at time k calculated by the outer loop low-voltage rotor speed controller, K pL Δn is the proportional coefficient of the outer loop low-voltage rotor speed controller. L [k] represents the low-pressure rotor command speed n at time k. Lr The actual output speed n of the shaft fan variable cycle engine L Deviation, Δn L [k-1] represents the low-pressure rotor command speed n at time k-1. Lr The actual output speed n of the shaft fan variable cycle engine L The deviation; T is the sampling period of the low-voltage rotor speed cascade controller, T iLThe integral time constant of the outer loop low-pressure rotor speed controller;
[0100] Step S1.2: Input the fuzzy controller parameter as the deviation e1 = Δn L [k] and e2 = Δn H [k] and its respective rate of change of deviation ec1=Δn L [k]-Δn L [k-1] and ec2 = Δn H [k]-Δn H [k-1], converts the parameters of the input fuzzy controller to values in the fuzzy universe of discourse. Based on the discreteness or continuity of the fuzzy universe of discourse, the membership function H(x) is... i The function is taken in discrete form, and a fuzzy subset H is formed through the membership degrees of a finite number of points:
[0101]
[0102] In the formula: sub-terms Used to describe element x in a fuzzy universe i Its membership function H(x) i The correspondence between ) is shown in the figure, where the "+" sign represents the whole of fuzzy subsets on the fuzzy domain.
[0103] The normal membership function is selected as follows:
[0104]
[0105] The triangular membership function is selected as follows:
[0106]
[0107] Where: a, b and p are all constant values, and their values are selected according to the range of the universe of discourse;
[0108] Using a discrete universe of discourse and the centroid method, the output set, i.e., output K, is calculated. p and K i The changes are now clear, and the formula for calculating the center of gravity method is as follows:
[0109]
[0110] Where: the universe of discourse u = {u1, u1, ... u1} n} is a discrete universe of discourse, u j The membership degree at point H(u) is j ), u is the x-coordinate corresponding to the center of the area; the fuzzy set of the output is obtained by reasoning the input quantity through the rule base, and then the exact precise quantity is determined by the defuzzification method. The control parameters K of the inner and outer loops of the low-pressure rotor speed controller at the current time k are calculated. p and Ki The change is input to the low-pressure rotor speed cascade controller to update the control parameters.
[0111] Step S2.1: A variable geometry working mechanism analysis was conducted on the adjustable guide vane at the outer bypass duct inlet and the area of the outer bypass duct tail nozzle. The closure degree of the adjustable guide vane at the outer bypass duct inlet showed a positive correlation with the change in the residual power of the low-pressure shaft. During mode switching, the change pattern of the adjustable guide vane at the outer bypass duct inlet was consistent with the change pattern of the rotor pitch angle.
[0112]
[0113] Where: α VIGV For the adjustable guide vane angle at the outer bypass duct inlet, β rotor The rotor pitch angle is denoted by 'max', which represents the maximum value.
[0114] When switching from turboshaft mode to turbofan mode, the area of the outer bypass nozzle remains unchanged. The control law for the area of the outer bypass nozzle is as follows:
[0115]
[0116] A 18 =A 18d
[0117] In the formula: A 18 A is the area of the outer bypass nozzle. 18d The area of the nozzle outside the duct at the design point.
[0118] Step S2.2, the area control of the inner duct tailpipe is proposed to be as follows: Figure 5 The EPR control law shown is EPR r =f(Δn), Δn = n Hcor -n Lcor This represents the relative equivalent speed difference between the high-pressure and low-pressure rotors. With the low-pressure rotor speed kept constant, Δn is closely related to the remaining power of the low-pressure shaft and the compressor surge margin. The engine pressure ratio command value EPR is calculated using the high-pressure and low-pressure rotor slip Δn. r The input is given to the nozzle area controller. The control logic during mode switching is that when the slip increases, the EPR... r The slip should be reduced to prevent the high-pressure compressor from experiencing upward pressure; when the slip decreases, the EPR... r The pressure ratio (EPR) should be increased, and the pressure of A8 should be decreased to prevent the low-pressure compressor from surging. During mode switching, the engine pressure ratio (EPR) is affected by both the fuel flow rate and the internal nozzle area (A8). The desired trend of A8 change should conform to the change in low-pressure shaft load power, so as to compensate for the residual power of the low-pressure shaft and prevent surging.
[0119] Step S3.1: During the clutch engagement process with the rotating rotor, the clutch engagement process should follow the principle of "slow at first, then fast." During the idle stroke, the clutch does not transmit torque, and at this time, the clutch does not impact the transmission system. As the clutch pressure increases, the clutch is in a slipping state. To reduce the impact on the transmission system and engine, the clutch should engage slowly. As the speed difference between the driving and driven discs decreases, the clutch pressure should be increased to reduce engagement time and slipping work during engagement. The open-loop control law of clutch pressure during disengagement is the opposite of that during engagement. The open-loop control law of clutch pressure is as follows: Figure 7 (g) and Figure 9 As shown in (g).
[0120] Step S3.2: During the pitch angle adjustment process, the feedforward controller can be approximated as a gain. The feedforward control is a gain value for the control command, which is merely a series of numbers in the control process. Then, the relationship between the changing gain and the pitch angle during the mode switching process is solved. The increment during the pitch angle adjustment process is transmitted to the feedforward control logic, and the change in the high-pressure rotor command speed is calculated and transmitted to the inner loop control loop of the engine cascade controller.
[0121] Step S4: Design three over-limit protection modules: a high-pressure rotor speed over-limit protection controller, a low-pressure turbine inlet total temperature over-limit protection controller, and a high-pressure compressor outlet pressure over-limit protection controller. All three over-limit protection controllers are incremental PI controllers, based on the limiting parameter high-pressure rotor speed n. Hmax Low-pressure turbine inlet total temperature T 45max and the outlet pressure P of the high-pressure compressor t3max The difference between the maximum value and the current measured value is used to calculate the corresponding fuel flow rate. The minimum value selector selects the lowest value among the fuel flow rates output by the three over-limit protectors, the maximum fuel flow rate, and the fuel flow rate calculated by the low-pressure rotor speed cascade controller, ensuring that the limiting parameters do not exceed the limit values throughout the entire mode switching process. A schematic diagram of the over-limit protection controller is shown below. Figure 6 As shown.
[0122] Step S5: By analyzing the relationship between the surge margin and slip of the low-pressure compressor during mode switching, a transient venting plan for the low-pressure compressor is introduced. The venting valve is located at section 224 of the intermediate stage of the low-pressure compressor. The relative equivalent speed difference between the high-pressure and low-pressure rotors is Δn = n Hcor -n Lcor When the slip is less than 0.8%, the low-pressure compressor performs intermediate stage venting, with the venting volume being 4% of the cross-sectional flow rate. This portion of the air is discharged into the atmospheric environment.
[0123] Table 1: Definition of Cross Sections of Shaft-Fan Variable Cycle Engine
[0124]
[0125] To ensure the effectiveness of the model-based mode switching combination control law for the variable cycle engine designed in this invention, a specific embodiment is provided below, which designs the mode switching combination control law based on the component-level model dynamic simulation for a certain type of variable cycle engine.
[0126] First, taking the turbofan engine switching from turbofan mode to turboshaft mode at the mode switching point (H=1.5km, Ma=0.4) as an example, we design the control law for the engine's turbofan to turboshaft mode switching.
[0127] The physical constraint is: the total temperature T at the low-pressure turbine outlet. t6 For compressors with a pressure rating of ≤1600K, the surge margins for high-pressure and low-pressure compressors are set at SMC≥8% and SMC≥5%, respectively.
[0128] The simulation time was 140 seconds, and the simulation results of the low-pressure rotor relative conversion are as follows: Figure 7 As shown in (a), the low-pressure rotor command speed is set to 96%. In the first stage, as the clutch pressure increases, the output torque increases, and the low-pressure rotor speed decreases. The clutch driving and driven ends engage and lock. The first stage lasts for 10 seconds. The rotor accelerates from the windmill speed to the maximum speed. The maximum relative equivalent speed of the low-pressure rotor is 96.47%, and the minimum is 94.8%. The speed change in the first stage does not exceed 0.7%. In the first half of the second stage, after the clutch locks, the rotor pitch angle begins to increase, and the VIGV follows suit. It stops operating at 80 seconds. The low-pressure speed change in this stage is less than 0.3%. In the second half of the second stage, due to the combined effects of A8 continuously expanding to its maximum area and BV venting, a certain disturbance is generated to the control system. The speed fluctuation in this stage does not exceed 0.2%.
[0129] Simulation results of relative converted speed of high-voltage rotor are as follows Figure 7 As shown in (b), the high-pressure rotor speed change trend is positively correlated with the fuel flow rate change trend. The overall transition process is smooth. The increase in high-pressure rotor speed at 80s is caused by the BV bleed disturbance. Overall, the high-pressure rotor speed transition process is stable. The points where the speed change is more obvious during the control process are caused by disturbances generated at the moment of clutch engagement and the moment of BV bleed. The controller response to these two disturbances is relatively lagging. The model inputs for the mode switching simulation process are: paddle pitch angle, VIGV angle, fuel flow rate, A8, and A. 18 and clutch pressure, such as Figure 7 As shown in (c), 7(d), 7(e), 7(f), and 7(g), the pitch angle and VIGV angle change linearly. The clutch pressure follows the principle of "slow first, then fast". Before the pitch angle changes, the clutch pressure increases rapidly to the maximum value to prevent the clutch from disengaging due to the increase in load torque during the pitch angle increase.
[0130] The thrust provided by the outer bypass nozzle continuously decreases to near zero after the VIGV closes. The thrust provided by the inner bypass nozzle also continuously decreases as the core engine's state decreases and the tailpipe area increases, with a minimum thrust of 2.6 kN. The engine thrust cannot be completely reduced to zero; this portion of thrust is generated by the core engine and can be considered for attitude control during near-ground vertical takeoff. Simultaneously, the Flade fan power and outer bypass airflow continuously decrease during mode switching. After the Flade fan is unloaded, this power is used to drive the rotor load connected to the low-pressure shaft. The engine pressure ratio fluctuates with the core engine's state, but the overall trend is a continuous decrease, eventually reaching an EPR of 1.06. This means that most of the high-temperature gas internal energy, after conversion by the low-pressure turbine, is used to drive the compression components and loads on the low-pressure shaft. The turboshaft mode possesses the power characteristics of a turboshaft engine's aerodynamic and thermodynamic cycle. With the continuous enhancement of the low-pressure turbine's power-saving capability, the output power provided by the low-pressure turbine continuously increases. The engine output torque and clutch output torque remain consistent after the clutch is engaged. Throughout the mode switching process, due to the reduced core engine state, the total pressure at the high-pressure compressor outlet and the total temperature at the low-pressure turbine inlet continuously decrease and do not exceed limits. Regarding the surge margins of the high and low-pressure compressors, the BV bleed-out program effectively improves the surge margin of the low-pressure compressor. Although the bleed-out process reduces engine efficiency to some extent, compared to nearly doubling the lower limit of the low-pressure compressor surge margin, BV bleed-out is a necessary anti-surge measure during the mode switching process. No over-temperature, over-revving, or surge-related exceedances occurred during the entire mode switching process.
[0131] Simulation results of the rotor load end and main loop fuzzy cascade controller are as follows: Figure 8 (a) Figure 8 As shown in (b), the rotor torque and power gradually increase with clutch engagement and pitch angle. The PI controller parameters are updated in real time according to the fuzzy rules as the engine state changes. Simulation verification shows that the proposed combined control law for switching from turbofan mode to turboshaft mode of the shaft-fan variable cycle engine is effective. The engine state fluctuation is small throughout the switching process, and the steady-state control error of each state does not exceed 0.01%.
[0132] Under the same simulated flight conditions, the combined control law for switching between turboshaft and turbofan modes of the engine was designed in reverse. The simulation results of the turboshaft-turbofan mode switching of the variable cycle engine are as follows: Figure 9 (a)- Figure 9 As shown in (p), the curve of the relative equivalent speed of the low-pressure rotor during the switching process is as follows: Figure 9As shown in (a), at the initial stage of the engine variable geometry mechanism adjustment, the decrease in pitch angle leads to an increase in the residual power of the low-pressure output shaft, and the low-pressure rotor speed increases accordingly. During the first stage of pitch angle, A8, and VIGV operation, the maximum low-pressure rotor speed is 95.2%, the minimum is 94.8%, and the overall fluctuation does not exceed 0.4%. During the second stage of clutch disengagement, due to the large transient torque disturbance caused by the clutch plate changing from static friction to dynamic friction, the maximum low-pressure rotor speed is 94.8%, the minimum is 95.4%, and the overall fluctuation does not exceed 0.8%. The low-pressure rotor speed is relatively stable in both stages.
[0133] During the switching process, the relative equivalent speed of the high-pressure rotor shows a positive correlation with fuel flow. As the load power decreases, the remaining power of the low-pressure shaft increases, and the high-pressure rotor speed decreases with fuel flow. Then, the Falde fan is loaded, and the high-pressure rotor speed increases with fuel flow. Throughout the switching process, the high-pressure rotor speed changes smoothly without drastic fluctuations. The clutch pressure follows the principle of "fast first, slow later." At 80s, the VIGV and pitch angle stop operating, and at 89s, the inner duct exhaust nozzle stops operating. As the Falde fan is loaded, the airflow in the outer bypass duct increases, and the thrust provided gradually increases. The thrust provided by the inner duct gradually increases with the change in core engine state and the reduction in exhaust nozzle area. After the pitch angle becomes 0°, the rotor disengages at 88s, and the low-pressure rotor naturally reverses and locks after being loaded, completing the mode switch. Throughout the switching process, during the phases with small slip, the low-pressure compressor intermediate stage bleed program is engaged, such as... Figure 9 As shown in (p), BV venting can significantly improve the surge margin of the low-pressure compressor and reduce the risk of low-pressure compressor surge during mode switching.
[0134] In summary, the designed mode switching combination control law for the shaft-fan variable cycle engine exhibits small fluctuations in low-pressure rotor speed and stable changes in various engine state variables during the fully digital simulation. Furthermore, the key engine parameters do not exceed temperature, speed limits, or surge during the mode switching process. The simulation results verify the effectiveness of the designed mode switching control law.
[0135] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.
Claims
1. A model-based combined control method for mode switching of a shaft-sector variable cycle engine, characterized in that, Includes the following steps: 1) Based on the constant low-pressure output shaft speed requirement of the vortex shaft mode of the shaft-fan variable cycle engine, a low-pressure rotor speed cascade controller is designed, and fuzzy theory is used to tune the control parameters in real time; 2) Based on the power and thrust output requirements when the shaft fan variable cycle engine mode is switched, design the control law of the adjustable guide vane at the outer bypass duct inlet and the area control law of the outer bypass duct tail nozzle. Combine the high and low pressure rotor speed difference to design the EPR control law. Use the area of the inner bypass duct tail nozzle as an intermediate variable to adjust the remaining power and thrust of the low pressure output shaft and prevent surge. 3) Based on the working characteristics of the clutch and rotor, design the clutch pressure open-loop law and the pitch angle feedforward compensation law when the shaft fan variable cycle engine mode is switched. 4) Design an over-limit protection controller to ensure that the shaft fan variable cycle engine does not exceed the temperature or speed limits during the switching process; 5) Combining the relationship between the high and low pressure rotor speed difference and the surge margin of the high and low pressure compressor components, design the transient gas release law of the low pressure compressor to improve the surge margin of the low pressure compressor during the switching of the shaft fan variable cycle engine mode. The implementation process of step 1) is as follows: 1.1): Design of a low-voltage rotor speed cascade controller: The low-voltage rotor speed cascade controller consists of an outer loop low-voltage rotor speed controller and an inner loop high-voltage rotor speed controller. The outer loop low-voltage rotor speed controller is determined by the actual low-voltage rotor speed n. L and low-pressure rotor command speed n Lr The difference is used to calculate the commanded speed n of the high-pressure rotor. Hr The inner-loop high-voltage rotor speed controller controls the rotor speed n via high-voltage rotor commands. Hr The actual output speed n of the shaft fan variable cycle engine H Calculate the difference in fuel flow rate ΔW f : Where: ΔW f [k] represents the fuel flow increment at time k calculated by the inner ring high-pressure rotor speed controller, K. pH Δn represents the proportional coefficient of the inner loop high-voltage rotor speed controller. H [k] represents the high-pressure rotor command speed n at time k. Hr The actual output speed n of the shaft fan variable cycle engine H Deviation, Δn H [k-1] represents the high-pressure rotor command speed n at time k-1. Hr The actual output speed n of the shaft fan variable cycle engine H The deviation, T iH Δn represents the integral time constant of the inner loop high-voltage rotor speed controller. Hr [k] represents the increment of the high-voltage rotor command speed at time k calculated by the outer loop low-voltage rotor speed controller, K pL Δn is the proportional coefficient of the outer loop low-voltage rotor speed controller. L [k] represents the low-pressure rotor command speed n at time k. Lr The actual output speed n of the shaft fan variable cycle engine L Deviation, Δn L [k-1] represents the low-pressure rotor command speed n at time k-1. Lr The actual output speed n of the shaft fan variable cycle engine L The deviation; T is the sampling period of the low-voltage rotor speed cascade controller, T iL The integral time constant of the outer loop low-pressure rotor speed controller; 1.2): The parameter input to the fuzzy controller is the deviation e1 = Δn L [k] and e2 = Δn H [k] and its respective rate of change of deviation ec1=Δn L [k]-Δn L [k-1] and ec2 = Δn H [k]-Δn H [k-1], converts the parameters of the input fuzzy controller to values in the fuzzy universe of discourse. Based on the discreteness or continuity of the fuzzy universe of discourse, the membership function H(x) is... i The function is taken in discrete form, and a fuzzy subset H is formed through the membership degrees of a finite number of points: In the formula: sub-terms Used to describe element x in a fuzzy universe i Its membership function H(x) i The correspondence between ) is shown, where "+" sign represents the whole of fuzzy subsets on the fuzzy domain; The normal membership function is selected as follows: The triangular membership function is selected as follows: Where: a, b and p are all constant values, and their values are selected according to the range of the universe of discourse; The output set is clarified using a discrete universe of discourse and the centroid method. The calculation formula for the centroid method is as follows: Where: the universe of discourse u = {u1, u1, L u} n } is a discrete universe of discourse, u j The membership degree at point H(u) is j ), where u is the abscissa corresponding to the center of the area; the fuzzy set of the output is obtained by reasoning the parameters of the input fuzzy controller through the rule base, and then the exact precise quantity is determined by the defuzzification method, and the control parameter K of the inner loop high-voltage rotor speed controller at the current time k is calculated. p The control parameter K of the outer ring low-pressure rotor speed controller i The change is input to the low-pressure rotor speed cascade controller to update the control parameters.
2. The model-based combined control method for switching modes of a shaft-sector variable cycle engine as described in claim 1, characterized in that, The implementation process of step 2) is as follows: 2.1): A variable geometry working mechanism analysis was conducted on the adjustable guide vane at the outer bypass duct inlet and the area of the outer bypass duct tail nozzle. The closure degree of the adjustable guide vane at the outer bypass duct inlet showed a positive correlation with the change in the residual power of the low-pressure shaft. During mode switching, the change law of the adjustable guide vane at the outer bypass duct inlet was consistent with the change law of the rotor pitch angle. Where: α VIGV For the angle of the adjustable guide vane at the outer bypass duct inlet, β rotor The rotor pitch angle is denoted by max, which represents the maximum value. When switching from turboshaft mode to turbofan mode, the area of the outer bypass duct nozzle remains unchanged. The control law for the area of the outer bypass duct nozzle is as follows: A 18 =A 18d In the formula: A 18 A is the area of the outer bypass duct tailpipe. 18d The area of the tailpipe of the outer duct is to be designed. 2.2): Based on step 2.1), the EPR control law will be adopted for the area control of the inner duct tail nozzle. r =f(Δn), Δn = n Hcor -n Lcor f(g) represents the relative equivalent speed difference between the high-pressure and low-pressure rotors, and f(g) represents a function. Under the condition that the low-pressure rotor speed is kept constant, the EPR command value EPR is calculated using the relative equivalent speed difference Δn between the high-pressure and low-pressure rotors. r The EPR instruction value is EPR. r The input to the tailpipe area controller, the control logic during mode switching is that when the relative equivalent speed difference Δn between the high and low pressure rotors increases, the EPR... r Reduced internal exhaust nozzle area to prevent high-pressure compressor surging; reduced EPR when the relative equivalent speed difference Δn between high and low pressure rotors decreases. r Increased internal exhaust nozzle area reduces low-pressure compressor intake pressure; during mode switching, the shaft fan variable cycle engine pressure ratio is simultaneously affected by fuel flow W. f The desired trend of the inner duct tail nozzle area change should conform to the change of low-pressure shaft load power, so as to compensate for the residual power of the low-pressure shaft and prevent surge.
3. The model-based combined control method for switching modes of a shaft-sector variable cycle engine as described in claim 1, characterized in that, In step 3): 3.1): During the process of engaging the clutch and rotating the rotor, the clutch engagement process follows the principle of "slow at first, then fast". During the idle stroke stage, the clutch does not transmit torque, and at this time the clutch does not generate impact on the transmission system. As the clutch pressure increases, the clutch is in a slipping state. In order to reduce the impact on the transmission system and the variable cycle engine, the clutch should engage slowly. As the speed difference between the main and driven plates decreases, the clutch pressure is increased to reduce the engagement time and the slipping work during the engagement process. The disengagement process is the opposite of the engagement process. 3.2): During pitch angle adjustment, the feedforward controller approximates a gain, and the relationship between the changing gain and the pitch angle during mode switching is solved. The increment during pitch angle adjustment is transmitted to the feedforward control logic to calculate the high-voltage rotor command speed n. Hr The change in speed is then transmitted to the inner high-voltage rotor speed controller.
4. The model-based combined control method for switching modes of a shaft-sector variable cycle engine as described in claim 1, characterized in that, In step 4): Three over-limit protection modules are designed: a high-pressure rotor speed over-limit protection controller, a low-pressure turbine inlet total temperature over-limit protection controller, and a high-pressure compressor outlet pressure over-limit protection controller. All three over-limit protection controllers are incremental PI controllers, based on the limiting parameter high-pressure rotor speed n. Hmax Low-pressure turbine inlet total temperature T 45max and the outlet pressure P of the high-pressure compressor t3max The difference between the maximum value and the current measurement value is used to calculate the corresponding fuel flow rate; The minimum value selector selects the lowest value among the fuel flow outputs of the three over-limit protectors, the maximum fuel flow, and the fuel flow calculated by the low-pressure rotor speed cascade controller, ensuring that the limiting parameters do not exceed the limit values throughout the entire mode switching process.
5. The model-based combined control method for switching modes of a shaft-sector variable cycle engine as described in claim 2, characterized in that, In step 5): By analyzing the relationship between the surge margin of the low-pressure compressor and the relative equivalent speed difference Δn between the high-pressure and low-pressure rotors during mode switching, a transient bleed-out plan for the low-pressure compressor is introduced. The bleed-out valve is located at the cross-section of the intermediate stage of the low-pressure compressor, where the relative equivalent speed difference Δn between the high-pressure and low-pressure rotors is Δn = n Hcor -n Lcor When the slip is less than 0.8%, the low-pressure compressor performs intermediate stage venting, and the venting volume is 4% of the cross-sectional flow rate. This part of the air is discharged into the atmosphere. The rationality and effectiveness of the obtained control law for the switching mode of the shaft-fan variable cycle engine were verified by simulation of the engine component-level model.