Modeling Method for Mode Conversion Model of a Hybrid Power Propulsion System

Abstract

The present invention relates to the technical field of aeroengines, and particularly to a method for modeling a mode conversion model of a combined power propulsion system. The method includes establishing a polynomial nonlinear model based on the linear time-invariant models of each engine, and then establishing the NPV model of each engine respectively; establishing a common working model based on the oncoming flow rate during the mode conversion period according to the NPV models of each engine, and considering the coupling of the intake splitter plate angle to the oncoming flow rate to obtain a common working model based on the splitter plate angle; and then applying it to the smooth transition of thrust during the mode conversion period and the realization of a large range of thrusts. The matrix parameters of the NPV system adopted by this modeling method can be changed in real time according to altitude, Mach number and scheduling parameters, which can better describe the strong nonlinear and time-varying dynamic characteristics of aeroengines, effectively solve the modeling difficulty problem caused by the large span of altitude Mach number of combined power engines, and lay a foundation for problems such as the control design and instability determination of aeroengines.

Description

Technical Field

[0001] The present invention relates to the technical field of aeroengines, and particularly relates to a method for modeling a mode conversion model of a combined power propulsion system. Background Art

[0002] With the exploration of the aerospace industry by people, in order to achieve the purpose of quickly reaching long distances, major scientific and technological powers around the world have been vigorously developing high-speed propulsion systems. However, the existing mature single power forms (turbine, ramjet, rocket engine) cannot achieve the functions of a wide speed range, high specific impulse, horizontal takeoff and landing, and reusability. Thus, a combined cycle power propulsion system that makes use of the advantages of each engine in different operating spaces in stages has emerged. The combined power propulsion system has the advantages of conventional takeoff and landing, reusability, high reliability, and high low-speed performance, and is considered to be an ideal propulsion system for air-breathing hypersonic aircraft. Currently, the mainstream combined cycle power systems are mainly two categories: the turbine-based combined cycle (TBCC) and the rocket-based combined cycle (RBCC). The TBCC combined engine combines two technologies, namely, a turbine engine (including a turbojet and a turbofan engine) and a ramjet engine (including a subsonic combustion, a supersonic combustion, and a dual-mode combustion ramjet engine), and integrates their advantages within their respective applicable flight Mach number ranges.

[0003] And it is necessary to focus on reasonably organizing the working ranges of each sub-power engine so that they cooperate with each other to complete the established flight mission. Among all flight missions, the relay process of the conversion between the two sub-power engines is the key area where the coupling is the most serious and the most likely dangerous working conditions occur. Mode conversion needs to analyze the co-operation of the two-way engines and the moving mechanisms in the channel, which significantly increases the complexity of simulating the engine performance. In addition, the mode conversion process needs to consider how to avoid the thrust fluctuation from causing the flight trajectory of the aircraft to fluctuate, how to ensure the flow of the two ducts during mode conversion, how to make the ramjet engine work stably after the turbine-based engine shuts down, and how to adjust each adjustable component to make the mode conversion process as smooth as possible. Thus, it can be seen that the mode conversion process is the most difficult and important link in the control of the combined engine.

[0004] In addition, in order to conduct research on the design of the combined power propulsion system controller, the definition of the stable operating state range, etc., it is necessary to establish a model for control and instability determination. Currently, most aeroengines adopt the component-level model modeling method. After obtaining the component-level model, the engine control system model is obtained by identifying this model. However, the existing system identification methods are only applied to the modeling of a single engine, and the system identification modeling method cannot be applied to the modeling of the combined power engine state space model. Summary of the Invention

[0005] To solve one of the deficiencies in the difficult modeling of the combined power propulsion system in the above-mentioned prior art, the present invention provides a method for modeling the mode conversion model of a combined power propulsion system, including a combined power propulsion system composed of several sub-engines. The modeling method includes the following steps:

[0006] Step S10: Establish the component-level models of each sub-engine, then determine the model type required for system identification and convert it into a least squares problem; generate corresponding sequences for each working state point as the excitation of the sub-engine component-level model, so as to obtain the data source required for system identification;

[0007] Step S20: Establish the linear time-invariant models of each sub-engine according to the determined model type, identification criterion and input-output data source respectively; then, establish the polynomial non-linear models of each sub-engine by fitting;

[0008] Step S30: Establish the NPV models of the large envelope according to the polynomial non-linear models of each sub-engine; the matrix parameters of the system in the NPV model are expressions related to altitude, Mach number and scheduling parameters;

[0009] Step S40: Establish the common working model during the mode conversion period by paralleling the NPV models of each engine, and then convert the oncoming flow rate parameters and the parameters to be identified of each sub-engine into parameters related to the inlet splitter plate angle α, so as to simplify the control input matrix of the common working model and reduce the input dimension;

[0010] Step S50: According to the simplified common working model, change the oncoming flow rate of each engine by adjusting the splitter plate angle α, and then adjust the magnitude of each fuel flow rate to achieve a smooth transition of thrust and a large range of thrust during the mode conversion period.

[0011] In one embodiment, a TBCC combined engine is used as the combined power propulsion system, which includes two types: a turbine engine and a ramjet engine.

[0012] In one embodiment, in step S10, the rotational speed and total pressure of the turbine engine are selected as state variables, and the model type required for its system identification is:

[0013] ;

[0014] ;

[0015] In the formula, represents the rotational speed, represents the differential of the rotational speed, represents the total pressure of the turbine engine, represents the differential of the total pressure of the turbofan engine, represents the thrust of the turbofan engine, represents the fuel flow rate of the turbofan engine, represents the incoming flow rate of the turbofan engine, 、 、 、 、 、 、 、 、 、 are the parameters to be identified.

[0016] In one embodiment, in step S10, the method for generating the corresponding sequence for each operating state point includes the following:

[0017] For the turbofan engine, a three-segment hybrid sequence is used to excite the model, where the first segment is a step signal, the second segment is a pseudo-random signal, and the third segment is a sine signal;

[0018] For the ramjet engine, a step signal is used to excite the model.

[0019] In one embodiment, in step S20, based on the linear time-invariant model established using multiple operating state points, with the rotational speed as the scheduling parameter, and based on the idea of gain scheduling, the polynomial nonlinear model of the sub-engine obtained by fitting is:

[0020] ;

[0021] ;

[0022] In the formula, represents the rotational speed, represents the differential of the rotational speed, represents the total pressure of the turbofan engine, represents the differential of the total pressure of the turbofan engine, represents the thrust of the turbofan engine, represents the fuel flow rate of the turbofan engine, represents the incoming flow rate of the turbofan engine, are the parameters to be identified The polynomial fitted with the rotational speed, are the parameters to be identified The polynomial fitted with the rotational speed, are the parameters to be identified The polynomial fitted with the rotational speed, are the parameters to be identified The polynomial fitted with the rotational speed, are the parameters to be identified The polynomial fitted with rotational speed, is the parameter to be identified The polynomial fitted with rotational speed, is the parameter to be identified The polynomial fitted with rotational speed, is the parameter to be identified The polynomial fitted with rotational speed, is the parameter to be identified The polynomial fitted with rotational speed, is the parameter to be identified The polynomial fitted with rotational speed.

[0023] In one embodiment, in step S40, for a turbofan engine, the NPV model of the large envelope is established as follows:

[0024] ;

[0025] ;

[0026] In the formula, the matrix parameter of the system is the parameter to be identified with respect to altitude and the scheduling parameter is an expression, is the parameter to be identified with respect to altitude and the scheduling parameter is an expression, is the parameter to be identified with respect to altitude and the scheduling parameter is an expression, is the parameter to be identified with respect to altitude and the scheduling parameter is an expression, is the parameter to be identified with respect to altitude and the scheduling parameter is an expression, is the parameter to be identified with respect to altitude and the scheduling parameter is an expression, is the parameter to be identified with respect to altitude and the scheduling parameter is an expression, is the parameter to be identified with respect to altitude and the scheduling parameter is an expression, is the parameter to be identified Regarding altitude and scheduling parameters of the formula is the parameter to be identified Regarding altitude and scheduling parameters of the formula, where represents the rotational speed represents the total pressure of the turbofan engine represents the thrust of the turbofan engine represents the fuel flow rate of the turbofan engine represents the incoming flow rate of the turbofan engine;

[0027] For a ramjet engine, the selected states are the total pressure and total temperature, and its NPV model for establishing the large envelope is as follows:

[0028] ;

[0029] ;

[0030] In the formula, the matrix parameters of the system is the parameter to be identified Regarding altitude and scheduling parameters of the formula is the parameter to be identified Regarding altitude and scheduling parameters of the formula is the parameter to be identified Regarding altitude and scheduling parameters of the formula is the parameter to be identified Regarding altitude and scheduling parameters of the formula is the parameter to be identified Regarding altitude and scheduling parameters of the formula is the parameter to be identified Regarding altitude and scheduling parameters of the formula is the parameter to be identified Regarding altitude and scheduling parameters of the formula is the parameter to be identified Regarding altitude and scheduling parameters The formula of is the parameter to be identified with respect to height and the scheduling parameter The formula of is the parameter to be identified with respect to height and the scheduling parameter The formula, where represents the total temperature, represents the total pressure of the ramjet engine, represents the thrust of the ramjet engine, represents the fuel flow rate of the ramjet engine, represents the incoming flow rate of the ramjet engine.

[0031] In one embodiment, in step S40, the common working model during the mode conversion period is established as:

[0032] ;

[0033] ;

[0034] In the formula, represents the rotational speed, represents the differential of the rotational speed, represents the total pressure of the turbofan engine, represents the differential of the total pressure of the turbofan engine, represents the total pressure of the ramjet engine, represents the differential of the total pressure of the ramjet engine, represents the total temperature of the ramjet engine, represents the differential of the total temperature of the ramjet engine, represents the thrust of the turbofan engine, represents the thrust of the ramjet engine, represents the total thrust, represents the fuel flow rate of the turbofan engine, represents the incoming flow rate of the turbofan engine, represents the fuel flow rate of the ramjet engine, represents the incoming flow rate of the ramjet engine.

[0035] In one embodiment, in step S40, the simplified common working model is obtained as:

[0036] ;

[0037] ;

[0038] Where , , , , , , , ; , , , ; The parameters in the matrix can be correspondingly transformed into , to further reduce the input dimension.

[0039] In one embodiment, in step S50, the steps to achieve a smooth transition of thrust during the mode conversion period are as follows:

[0040] First, define a flight plan by oneself, including the mode conversion time, the required range of Mach number, and the required range of altitude;

[0041] Then, at each operating point during the mode conversion period, select a series of diverter vane angles α to obtain the respective oncoming flow rates of each sub-engine at each operating point. Thus, with altitude and Mach number as independent variables and the total flow rate as the dependent variable, perform fitting, and through multiple regression, obtain the equation for the change of the total oncoming flow rate with altitude and Mach number: And an equation for the change of a diversion ratio with the diverter vane angle α: % ; % , where k is a specific constant;

[0042] Finally, according to the oncoming flow rates of each sub-engine obtained above and adjust the magnitudes of the fuel flow rates of each sub-engine to obtain the curves of the oncoming flow rate and the fuel flow rate changing with time, so that the total thrust can be smoothly transitioned.

[0043] In one embodiment, in step S50, the steps to achieve a large range of thrust are as follows:

[0044] First, define a flight plan by oneself, including the mode conversion time, the required range of Mach number, and the required range of altitude; then obtain the respective oncoming flow rates of each sub-engine at each operating point according to the flight plan and the simplified common working model; finally, switch different operations by restricting whether the parameters and input quantities in the matrix are 0 under different operating states, and according to the total thrust requirement, adjust each input quantity to achieve a large range of thrust changes.

[0045] Based on the above, compared with the prior art, the method for modeling the mode conversion model of the combined power propulsion system provided by the present invention uses the NPV model to reflect the time-varying and non-linear characteristics of the engine, and can effectively solve the problem of modeling difficulty caused by the large span of altitude and Mach number of the combined power engine. In addition, the NPV models of each sub-engine are connected in parallel, and the coupling of the inlet splitter plate angle is considered to establish a common working model of each sub-engine system during the mode conversion period, so as to effectively achieve a smooth transition of thrust during the mode conversion and achieve a large range of thrust.

[0046] Other features and beneficial effects of the present invention will be described in the following specification, and part of them will become obvious from the specification, or be understood by implementing the present invention. The objectives and other beneficial effects of the present invention can be achieved and obtained through the structures specifically pointed out in the specification, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained according to these drawings; in the following description, regarding the positional relationship in the drawings, unless otherwise specified, the directions shown by the components in the drawings are taken as the reference.

[0048] Figure 1 It is a flowchart of the method for modeling the mode conversion model of the combined power propulsion system provided by the present invention;

[0049] Figure 2 It is a schematic diagram of the mixed sequence signal generated by the turbine engine;

[0050] Figure 3 It is a verification diagram (after normalization) of the polynomial non-linear state space model at a certain operating point;

[0051] Figure 4 It is a fitting schematic diagram of establishing the NPV model based on the polynomial non-linear model;

[0052] Figure 5 It is a verification diagram (after normalization) of the NPV state space model;

[0053] Figure 6 It is a curve showing the variation of altitude and Mach number with time;

[0054] Figure 7 It is a curve showing the variation of the splitter plate angle α with the Mach number;

[0055] Figure 8It is a curve graph showing the total incoming flow rate, the incoming flow rates of the two engines, and the fuel flow rate varying with time during the modal conversion period;

[0056] Figure 9 It is a curve graph showing the thrust of the turbofan engine, the thrust of the ramjet engine, and the total thrust varying with time during the modal conversion period;

[0057] Figure 10 It is a curve graph showing the altitude and Mach number varying with time in a large range;

[0058] Figure 11 It is a reference graph of the thrust of the turbofan engine, the thrust of the ramjet engine, the total thrust, and the total thrust requirement under a large-range flight plan. Specific implementation manners

[0059] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention; the technical features designed in different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other; based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0060] In the description of the present invention, it should be noted that all terms (including technical terms and scientific terms) used in the present invention have the same meanings as those commonly understood by those of ordinary skill in the art to which the present invention belongs, and should not be construed as a limitation of the present invention; it should be further understood that the terms used in the present invention should be understood as having meanings consistent with their meanings in the context of this specification and the relevant art, and should not be understood in an idealized or overly formal sense, unless otherwise defined explicitly in the present invention.

[0061] In the present invention, the component-level model of the combined power engine is used as the identification object. At each working state point, the least squares estimation method and a mixed sequence are used as the input to model the component model of the combined power engine into an NPV model. By transforming the modeling problem of the combined power engine into a system identification problem of the least squares estimation method and improving the signal source, the system identification accuracy can be improved while effectively reducing the computational complexity. Among them, the NPV (nonlinear parameter-varying) model can be established according to the following formula:

[0062] ;

[0063] Wherein, If it is a polynomial function of altitude and Mach number, an engine large envelope model can be obtained. The advantages of this model are as follows: it can establish a component-level model into a large envelope NPV model. Compared with other models, the NPV model can better reflect the time-varying and non-linear characteristics of the engine. The matrix parameters of the NPV system can be changed in real time according to altitude, Mach number, and scheduling parameters, which can better describe the dynamic characteristics of the strong non-linearity and time-varying characteristics of aeroengines, providing a new approach for problems such as the control design and instability determination of aeroengines, and serving as the basis for further research on the steady-state and transient control of aeroengines.

[0064] Specifically, please refer to Figure 1 , the present invention provides a method for modeling a mode conversion model of a combined power propulsion system. The combined power propulsion system includes several sub-engines, and the modeling method includes the following steps:

[0065] Step S10: Establish the component-level models of each sub-engine, then determine the model class required for system identification and convert it into a least-squares problem; generate corresponding sequences for each operating state point as the excitation of the component-level model of the sub-engine, so as to obtain the data source required for system identification;

[0066] Step S20: Establish the linear time-invariant models of each sub-engine according to the determined model class, identification criterion, and input-output data source respectively; then, establish the polynomial non-linear models of each sub-engine by fitting;

[0067] Step S30: Establish the NPV model of the large envelope according to the polynomial non-linear models of each sub-engine; the matrix parameters of the system in the NPV model are expressions related to altitude, Mach number, and scheduling parameters;

[0068] Step S40: Establish a common working model during the mode conversion period by paralleling the NPV models of each engine, and then convert the oncoming flow rate parameters and the parameters to be identified of each sub-engine into parameters related to the intake duct diverter vane angle α to simplify the control input matrix of the common working model and reduce the input dimension;

[0069] Step S50: According to the simplified common working model, change the oncoming flow rate of each engine by adjusting the diverter vane angle α, and then achieve a smooth transition of thrust and a large range of thrust during the mode conversion period by adjusting the magnitude of each fuel flow rate.

[0070] In this embodiment, first, according to the characteristics of each sub-engine, a component-level model of each sub-engine needs to be established based on the component method. Then, the input and output data of the component-level model are processed using the method of system identification, and the model class required for system identification is determined according to the task requirements. Next, the problem of modeling the aero-engine is transformed into a least-squares problem of system identification, and a linear time-invariant model at each steady state point is identified through the L-M least-squares estimation method. In this embodiment, the least-squares problem in the system identification modeling of the aero-engine can be solved using the System identification Toolbox in Matlab.

[0071] Secondly, corresponding sequences are generated for each operating state point of the aero-engine. Among them, appropriate sequences can be selected according to the characteristics of the component-level models of each sub-engine to ensure the subsequent fitting accuracy and cross-validation accuracy. The sequences can be selected from a step input signal, a sine input signal, and a pseudo-random sequence, or a combination of multiple ones, without limitation here. Then, the corresponding sequences of each operating state point are used as the excitation of the component-level model of the sub-engine, so as to obtain the data source required for system identification.

[0072] Next, linear time-invariant models of each sub-engine are established respectively according to the determined model class, identification criterion, and input-output data source; and polynomial nonlinear models of each sub-engine are established by fitting. Among them, univariate regression analysis can be used to establish the quantitative relationship of mutual dependence between the rotational speed and the parameters of the state space matrix. Since the quantitative relationship between the two is unknown, linear regression or nonlinear regression can be selected according to the actual data. Specifically, a cost function is selected, and an optimal regression model is found to minimize the corresponding cost function. Then, based on the linear state space system established for multiple operating states, with the rotational speed of the engine as the scheduling parameter, a polynomial nonlinear model is established based on the idea of gain scheduling.

[0073] Finally, the NPV model of the large envelope is established using the polynomial nonlinear models of each sub-engine at each operating point; the matrix parameters of the system in the NPV model are expressions related to altitude, Mach number, and scheduling parameter. Then, the NPV models of each sub-engine are connected in parallel to establish a common working model during the mode conversion period, so as to embody the meaning of combined power. Further, considering the influence of the coupling of the inlet diverter flap angle on the incoming flow rate of each sub-engine, the control input matrix of the common working model is simplified to reduce the input dimension, so as to obtain a common working model describing the mode conversion process of the combined engine. This common working model can be used to achieve a smooth transition of thrust and a large range of thrust during the mode conversion period.

[0074] To better illustrate the above-mentioned modeling method for the mode conversion model of the combined power propulsion system, the present invention takes the TBCC combined engine as an example of the combined power propulsion system for corresponding illustration. The TBCC combined engine includes two types: a turbojet engine and a ramjet engine. Specifically, a common working model for its appropriate mode conversion process can be established according to the characteristics of these two types of combined engines.

[0075] Specifically, the modeling process is as follows:

[0076] I. The process of establishing the NPV model for the turbojet engine is as follows:

[0077] (1) Establish a component-level model of the turbojet engine. Using the method of system identification for the input and output data of this component-level model, select the rotational speed and total pressure as state variables according to its mission requirements, and then determine the model type required for system identification, as follows:

[0078] ;

[0079] ;

[0080] In the formula, represents the rotational speed, represents the differential of the rotational speed, represents the total pressure of the turbojet engine, represents the differential of the total pressure of the turbojet engine, represents the thrust of the turbojet engine, represents the fuel flow rate of the turbojet engine, represents the oncoming flow rate of the turbojet engine, , , , , , , , , , are the parameters to be identified.

[0081] The output variables of the model type in the identification process are the rotational speed, total pressure, and thrust. The most critical output variable of the finally established model is the thrust.

[0082] (2) Convert the modeling problem of the aeroengine into a least squares problem of system identification, and identify the actual rotational speed linear time-invariant model at each steady state point through the least squares estimation method.

[0083] Specifically, the L-M least squares method is a method that combines the steepest descent method and the Gauss-Newton (G-N) method. The steepest descent method is applicable to algorithms where the parameter estimate values are far from the optimal value at the beginning of the iteration, while the Gauss-Newton algorithm is applicable to the later stage of the iteration when the parameter estimate values are in the neighborhood of the optimal value. The L-M least squares method overcomes the limitation that the G-N algorithm requires the matrix to be full column rank when dealing with nonlinear problems. When the least squares algorithm used for identification is the L-M estimation algorithm, in some system identification cases, the values of the elements of matrix B are prone to be extremely large. Through practice, it is found that in this situation, the G-N least squares method can be used for iteration to solve the problem of extremely large values of the elements of matrix B, which reflects the characteristics that the Gauss-Newton algorithm is applicable to the later stage of the iteration and the parameter estimate values are in the neighborhood of the optimal value. Its specific calculation process can use the System identification Tool in Matlab to solve the least squares problem in the system identification modeling of aeroengines.

[0084] (3) Generate corresponding sequences for each working state point as the excitation of the sub-engine component-level model to determine the system identification input and output data sources.

[0085] At different rotational speeds of each working state point in the turbine engine system, the types and amplitudes of signals will affect the accuracy of least squares identification and the accuracy of subsequent cross-validation. Therefore, it is necessary to select appropriate sequences as the excitation of the engine component-level model.

[0086] Through analysis and practice, it is found that for a turbine engine, if only a step signal is used as the input, better identification and verification results can be achieved, but the accuracy is not as high as the fitting degree of the mixed signal, and the dynamic process effect of the thrust curve is average. When using the commonly used step signal in engineering for cross-validation, the state variables will diverge. When only using the non-linear input and output data source obtained from the sine input signal for system identification, better identification and verification results can be achieved, but the fitting degree and verification accuracy are not as high as those of the mixed signal, and the dynamic process fluctuates. If only using the pseudo-random sequence as the input can fully excite the component system, better results can be obtained when solving the non-linear least squares problem, but the generalization performance of this model is not good, and in cross-validation, the state variables of the system diverge.

[0087] To address the above problems, the present invention uses a hybrid sequence as the excitation for the component-level model of a turbofan engine to obtain the data source required for system identification. That is, for any operating state, a corresponding hybrid sequence is generated, and a set of hybrid sequences suitable for that operating state point is used as the input to the component-level model to obtain the data source for system identification. The hybrid sequence used is divided into three segments: The first segment is a step signal. The second segment is a pseudo-random signal with strong dynamic performance at a certain amplitude, and its pseudo-random sequence is an M sequence, which is generated by Matlab. For different operating points, M sequences with different amplitudes can be selected to improve the accuracy of the least squares method. The third segment is a sine signal at a certain amplitude and frequency. The hybrid sequence generated according to the above method is specifically as shown in Figure 2 shown below.

[0088] (4) Based on the three elements of the model class, identification criterion, and input-output data source determined according to the above steps, a linear time-invariant model with the rotational speed and total pressure of the turbofan engine as state variables is established for each operating state point. Specifically, the toolbox System identification Tool provided by Matlab can be used to solve the least squares problem, and the component-level system can be quickly linearized and identified in combination with the hybrid sequence. This method can complete the calculation in one step without designing complex optimization algorithms and selecting the model order, effectively simplifying the calculation process.

[0089] (5) Using the linear time-invariant systems established at multiple operating state points, with the rotational speed as the scheduling parameter, based on the idea of gain scheduling, a polynomial nonlinear model of the turbofan engine at each operating point is established by fitting, as shown below:

[0090] ;

[0091] ;

[0092] In the formula, represents the rotational speed, represents the differential of the rotational speed, represents the total pressure of the turbofan engine, represents the differential of the total pressure of the turbofan engine, represents the thrust of the turbofan engine, represents the fuel flow rate of the turbofan engine, represents the incoming flow rate of the turbofan engine, are the parameters to be identified is a polynomial fitted with the rotational speed, are the parameters to be identified is a polynomial fitted with the rotational speed, are the parameters to be identified is a polynomial fitted with the rotational speed, are the parameters to be identified The polynomial fitted with rotational speed, is the parameter to be identified The polynomial fitted with rotational speed, is the parameter to be identified The polynomial fitted with rotational speed, is the parameter to be identified The polynomial fitted with rotational speed, is the parameter to be identified The polynomial fitted with rotational speed, is the parameter to be identified The polynomial fitted with rotational speed, is the parameter to be identified The polynomial fitted with rotational speed.

[0093] According to the above polynomial nonlinear model, the verification image of the polynomial nonlinear state space model at a certain operating point can be obtained. For details, please refer to Figure 3 as shown, where the left figure represents the verification curve of rotational speed and the component-level model, and the right figure represents the verification curve of thrust and the component-level model.

[0094] (6) Using the polynomial nonlinear models of the turbine engine at each operating point obtained in step (5), establish the NPV (nonlinear parameter-varying) model of the large envelope. The fitting schematic diagram is as Figure 4 shown, and its model is as follows:

[0095] ;

[0096] ;

[0097] In the formula, the matrix parameter of the system is the parameter to be identified is a formula about altitude and the scheduling parameter , is the parameter to be identified is a formula about altitude and the scheduling parameter , is the parameter to be identified is a formula about altitude and the scheduling parameter , is the parameter to be identified is a formula about altitude and the scheduling parameter , is the parameter to be identified is a formula about altitude and the scheduling parameter , is the parameter to be identified Regarding altitude and scheduling parameters of the formula is the parameter to be identified Regarding altitude and scheduling parameters of the formula is the parameter to be identified Regarding altitude and scheduling parameters of the formula is the parameter to be identified Regarding altitude and scheduling parameters of the formula is the parameter to be identified Regarding altitude and scheduling parameters of the formula, where represents the rotational speed represents the total pressure of the turbofan engine represents the thrust of the turbofan engine represents the fuel flow rate of the turbofan engine represents the incoming flow rate of the turbofan engine

[0098] II. The process of establishing the NPV model for a ramjet engine is as follows:

[0099] Establish the NPV model of the ramjet engine according to the same idea and process as establishing the NPV model of the turbofan engine above, which will not be elaborated here. It should be noted that considering the characteristics of the component-level model of the ramjet engine, a relatively simple step signal can be used to excite the model. In addition, the state variables selected for the ramjet engine are the total pressure and total temperature. The NPV model of the ramjet engine is as follows:

[0100] ;

[0101] ;

[0102] In the formula, the matrix parameters of the system are the parameters to be identified Regarding altitude and scheduling parameters of the formula are the parameters to be identified Regarding altitude and scheduling parameters of the formula are the parameters to be identified Regarding altitude and scheduling parameters The formula of is the parameter to be identified with respect to height and scheduling parameter The formula of is the parameter to be identified with respect to height and scheduling parameter The formula of is the parameter to be identified with respect to height and scheduling parameter The formula of is the parameter to be identified with respect to height and scheduling parameter The formula of is the parameter to be identified with respect to height and scheduling parameter The formula of is the parameter to be identified with respect to height and scheduling parameter The formula of is the parameter to be identified with respect to height and scheduling parameter The formula, where represents the total temperature, represents the total pressure of the ramjet engine, represents the thrust of the ramjet engine, represents the fuel flow rate of the ramjet engine, represents the incoming flow rate of the ramjet engine.

[0103] Based on the establishment of the above two NPV models, the verification images of the NPV state-space model can be obtained, specifically as Figure 5 shown, where (a) represents the verification curve of the thrust of the incoming flow rate and fuel flow rate at a certain operating point of the turbofan engine and the component-level model, (b) represents the verification curve of the rotational speed of the incoming flow rate and fuel flow rate at a certain operating point of the turbofan engine and the component-level model, (c) represents the error curve of the thrust in Figure (a) and the component model, (d) represents the error curve of the rotational speed in Figure (b) and the component model, (e) represents the verification curve of the total pressure of the ramjet engine at a certain operating point with the incoming flow rate and fuel flow rate of and the component-level model, (f) represents the verification curve of the total pressure of the ramjet engine at a certain operating point with the incoming flow rate and fuel flow rate of and the component-level model, (g) represents the incoming flow rate of the ramjet engine at a certain operating point, and the fuel flow rate changes from to Total pressure verification curve, (h) represents the incoming flow rate at a certain operating point of the ramjet engine, and the fuel flow rate ranges from to Thrust verification curve (where and are specific constants, and is less than ).

[0104] III. Establish a common working model of the two engines during the mode transition period based on the established NPV models of the two sub-engines, thereby reflecting the meaning of the combined power.

[0105] During the mode transition period, the turbine engine and the ramjet engine work simultaneously to provide thrust for the aircraft. Combine the two NPV models into one through a parallel connection to obtain the common working model as follows:

[0106] ;

[0107] ;

[0108] In the formula, represents the rotational speed, represents the differential of the rotational speed, represents the total pressure of the turbine engine, represents the differential of the total pressure of the turbine engine, represents the total pressure of the ramjet engine, represents the differential of the total pressure of the ramjet engine, represents the total temperature of the ramjet engine, represents the differential of the total temperature of the ramjet engine, represents the thrust of the turbine engine, represents the thrust of the ramjet engine, represents the total thrust, represents the fuel flow rate of the turbine engine, represents the incoming flow rate of the turbine engine, represents the fuel flow rate of the ramjet engine, represents the incoming flow rate of the ramjet engine.

[0109] Next, considering that the incoming flow rates of the two engines are determined by the angle α of the inlet splitter plate, further, it can be simplified into the following model, reducing the input variables to three:

[0110] ;

[0111] ;

[0112] In the formula, , that is, = , , , , , , , , , that is , , , ; indicates the opening of the diverter plate.

[0113] By comparing the above two equations, it can be known that the co - working model one can be converted into model two, but only the matrix parameters in the B matrix that affect the oncoming flow rate need to be changed accordingly.

[0114] The specific change process is as follows: → , where ; It can be seen that the parameters and that affect the fuel size are equal before and after the conversion, and for the corresponding change in the oncoming flow rate, the equation can be obtained: , that is ; In the equation, = , is the total oncoming flow rate, is the undetermined coefficient. Similarly, by completing the conversion of the other three rows of the B matrix, we can get , that is ; In the equation, = , is the total oncoming flow rate, is the undetermined coefficient. In particular, when , define .

[0115] Thus, the conversion from the co - working model one to the co - working model two is completed, reducing the input dimension.

[0116] IV. To achieve a smooth transition of thrust during the modal conversion, the air oncoming flow rates of the two engines are changed by controlling the diverter plate angle. In addition, the fuel flow rate needs to be adjusted, so as to achieve the effect that the thrust of the turbofan engine gradually decreases to 0 and the thrust of the ramjet engine continuously increases during the modal conversion, while the total thrust remains basically unchanged.

[0117] Specifically, first define a flight plan, such as the curve showing the variation of altitude and Mach number with time as shown in Figure 6 . Assume that the modal conversion time is 60 seconds and is approximated by the simplest linear variation. The Mach number changes from to , and the corresponding altitude changes from to , where , , , are specific constants representing the altitude and Mach number values at the start and end states of the mode conversion process. is less than , is less than . Assuming that the total flow rate is constant after fixing the altitude and Mach number, the diverter vane angle is then adjusted to change the proportion of the oncoming flow distributed to the turbofan engine and the ramjet engine.

[0118] Secondly, at each operating point during the mode conversion period, a series of diverter vane angles are selected to obtain the corresponding oncoming flow rates of the turbofan engine and the ramjet engine respectively, and further obtain the total flow rate and the proportions of the two flow paths;

[0119] Next, after obtaining the total oncoming flow rate at each operating point, with altitude and Mach number as independent variables and total flow rate as the dependent variable, a fitting is performed, and a multiple regression is used to obtain an equation for how the total oncoming flow rate changes with altitude and Mach number: ; In this way, the total oncoming flow rate can be obtained from the altitude and Mach number. Since the total flow rate varies with altitude and Mach number, considering whether the curve of the diversion ratio changing with the diverter vane angle is also different at different altitude - Mach number combinations, it is obtained through fitting of experimental data that the fitting equations of the curve of the diversion ratio changing with the diverter vane angle are the same at different operating points.

[0120] The fitting equation is: % ; % ; where k is a specific constant.

[0121] Given again a simple curve of the diverter vane angle α changing with time, as Figure 7 shown, where , , , are specific constants, is less than , is less than , according to the above - mentioned method, the oncoming flow rates of the turbofan engine and the ramjet engine can be obtained respectively. By adjusting the magnitudes of their respective fuel flow rates, as Figure 8 shown as the curve of the oncoming flow rate and fuel flow rate changing with time during the mode conversion period, so that the total thrust can be smoothly transitioned, specifically as Figure 9The figure shows a graph of the thrust of the turbine engine, the thrust of the ramjet engine, and the total thrust varying with time during the mode conversion period.

[0122] V. To achieve a large range of thrust, first define a flight plan, such as Figure 10 The figure shows a graph of the large range of altitude and Mach number varying with time, where , , , , are specific constants, is less than is less than , is less than is less than . During the mode conversion period, all fuel values and oncoming flow rates can be directly used with the values described in the thrust process during the above-mentioned mode conversion. The model uses a common working model, and only by restricting whether the parameters and input quantities of the matrix are 0 in different working states can different working states be reflected, achieving the effect of switching working states. According to the total thrust requirement, by adjusting each input quantity, a large range of thrust changes can be achieved. For example, Figure 11 The figure shows a reference line graph of the thrust of the turbine engine, the thrust of the ramjet engine, the total thrust, and the total thrust requirement under a large range of flight plans. It can be seen that the total thrust fluctuates less during the mode conversion period, meeting the requirements.

[0123] In summary, compared with the prior art, the method for modeling the mode conversion model of the combined power propulsion system provided by the present invention has the following advantages:

[0124] I. Adopting the NPV modeling method, compared with other models, the NPV model can better reflect the time-varying and non-linear characteristics of the engine, laying a foundation for subsequent work such as instability determination of the combined power engine and controller design;

[0125] II. The present invention can effectively solve the problem of modeling difficulty caused by the large span of altitude and Mach number of the combined power engine, and provides a modeling method for describing the mode conversion process of the combined engine;

[0126] III. During the mode conversion period, each engine works simultaneously. The NPV models of each sub-power engine are connected in parallel, and the coupling of the inlet splitter plate angle is considered to establish a common working model for each engine subsystem during the mode conversion period, thus reflecting the meaning of combined power;

[0127] IV. During the system identification process, aiming at the characteristics of the output curve of the specific engine, a mixed excitation signal composed of a step signal, a pseudo-random signal, and a sine signal is used as the input of the component model, which can fully stimulate the dynamic characteristics of the system, and its comprehensive performance is also better than other single input signals.

[0128] In addition, those skilled in the art should understand that although there are many problems in the prior art, each embodiment or technical solution of the present invention can be improved in only one or several aspects, and it is not necessary to solve all the technical problems listed in the prior art or the background art at the same time. Those skilled in the art should understand that the content not mentioned in a claim should not be regarded as a limitation to that claim.

[0129] Although terms such as component-level model, linear time-invariant model, polynomial nonlinear model, NPV model, co-working model, etc. are used more frequently herein, the possibility of using other terms is not excluded. These terms are used only to more conveniently describe and explain the essence of the present invention; interpreting them as any additional limitation is contrary to the spirit of the present invention.

[0130] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A modeling method for the mode conversion model of a combined power propulsion system, characterized in that, A combined power propulsion system including several sub-engines, using a TBCC combined engine as the combined power propulsion system, which includes two types: a turbine engine and a ramjet engine. Its modeling method includes the following steps: Step S10, establish the component-level models of each sub-engine, then determine the model type required for system identification and convert it into a least squares problem; generate corresponding sequences for each operating state point as the excitation of the sub-engine component-level model, so as to obtain the data source required for system identification; in step S10, select the rotational speed and total pressure of the turbine engine as state variables, and the model type required for its system identification is: ； ； wherein, represents the rotational speed, represents the differential of the rotational speed, represents the total pressure of the turbine engine, represents the differential of the total pressure of the turbine engine, represents the thrust of the turbine engine, represents the fuel flow rate of the turbine engine, represents the oncoming flow rate of the turbine engine, , , , , , , , , , are the parameters to be identified; Step S20, establish the linear time-invariant models of each sub-engine according to the determined model type, identification criterion, and input-output data source respectively; then, establish the polynomial nonlinear models of each sub-engine by fitting; Step S30, establish the NPV models of the large envelope for each sub-engine respectively; the matrix parameters of the system in the NPV model are expressions related to altitude, Mach number, and scheduling parameters; Step S40, establish the common working model during the mode conversion period by paralleling the NPV models of each engine, and then convert the oncoming flow rate parameters and the parameters to be identified of each sub-engine into parameters related to the intake splitter plate angle α, so as to simplify the control input matrix of the common working model and reduce the input dimension; Step S50, according to the simplified common working model, change the oncoming flow rate of each engine by adjusting the splitter plate angle α, and then achieve a smooth transition of thrust and a large range of thrust during the mode conversion period by adjusting the magnitude of each fuel flow rate.

2. The method for modeling the mode conversion model of the combined power propulsion system according to claim 1, characterized in that, In step S10, generating corresponding sequences for each operating state point includes the following methods: For the turbine engine, a three-segment hybrid sequence is used to excite the model, where the first segment is a step signal, the second segment is a pseudo-random signal, and the third segment is a sine signal; For the ramjet engine, a step signal is used to excite the model.

3. The modeling method of the combined power propulsion system mode conversion model according to claim 2, characterized in that In step S20, using the linear time-invariant models established by multiple operating state points, with the rotational speed as the scheduling parameter, based on the idea of gain scheduling, the polynomial nonlinear model of the turbine engine is obtained by fitting as: ; ; In the formula, represents the rotational speed, represents the differential of the rotational speed, represents the total pressure of the turbofan engine, represents the differential of the total pressure of the turbofan engine, represents the thrust of the turbofan engine, represents the fuel flow rate of the turbofan engine, represents the incoming flow rate of the turbofan engine, is the parameter to be identified is a polynomial fitted with the rotational speed, is the parameter to be identified is a polynomial fitted with the rotational speed, is the parameter to be identified is a polynomial fitted with the rotational speed, is the parameter to be identified is a polynomial fitted with the rotational speed, is the parameter to be identified is a polynomial fitted with the rotational speed, is the parameter to be identified is a polynomial fitted with the rotational speed, is the parameter to be identified is a polynomial fitted with the rotational speed, is the parameter to be identified is a polynomial fitted with the rotational speed, is the parameter to be identified is a polynomial fitted with the rotational speed, is the parameter to be identified is a polynomial fitted with the rotational speed.

4. The method for modeling the mode conversion model of the combined power propulsion system according to claim 3, characterized in that: In step S40, for the turbine engine, the NPV model of the large envelope is established as follows: ； ； In the formula, the matrix parameters of the system are the parameters to be identified with respect to the height and the scheduling parameters is an expression are the parameters to be identified with respect to the height and the scheduling parameters is an expression are the parameters to be identified with respect to the height and the scheduling parameters is an expression are the parameters to be identified with respect to the height and the scheduling parameters is an expression are the parameters to be identified with respect to the height and the scheduling parameters is an expression are the parameters to be identified with respect to the height and the scheduling parameters is an expression are the parameters to be identified with respect to the height and the scheduling parameters is an expression are the parameters to be identified with respect to the height and the scheduling parameters is an expression are the parameters to be identified with respect to the height and the scheduling parameters is an expression are the parameters to be identified with respect to the height and the scheduling parameters is an expression, where represents the rotational speed represents the total pressure of the turbofan engine represents the thrust of the turbofan engine represents the fuel flow rate of the turbofan engine represents the incoming flow rate of the turbofan engine; For the ramjet engine, the selected states are total pressure and total temperature, and the NPV model of the large envelope is established as follows: ； ； In the formula, the matrix parameters of the system are the parameters to be identified with respect to the altitude and the scheduling parameters of the formula, are the parameters to be identified with respect to the altitude and the scheduling parameters of the formula, are the parameters to be identified with respect to the altitude and the scheduling parameters of the formula, are the parameters to be identified with respect to the altitude and the scheduling parameters of the formula, are the parameters to be identified with respect to the altitude and the scheduling parameters of the formula, are the parameters to be identified with respect to the altitude and the scheduling parameters of the formula, are the parameters to be identified with respect to the altitude and the scheduling parameters of the formula, are the parameters to be identified with respect to the altitude and the scheduling parameters of the formula, are the parameters to be identified with respect to the altitude and the scheduling parameters of the formula, are the parameters to be identified with respect to the altitude and the scheduling parameters of the formula, where represents the total temperature, represents the total pressure of the ramjet, represents the thrust of the ramjet, represents the fuel flow rate of the ramjet, represents the incoming flow rate of the ramjet.

5. The modeling method of the combined power propulsion system mode conversion model according to claim 4, characterized in that: In step S40, the common working model during the mode conversion period is established as: ； ； In the formula, represents the rotational speed, represents the differential of the rotational speed, represents the total pressure of the turbine engine, represents the differential of the total pressure of the turbine engine, represents the total pressure of the ramjet engine, represents the differential of the total pressure of the ramjet engine, represents the total temperature of the ramjet engine, represents the differential of the total temperature of the ramjet engine, represents the thrust of the turbine engine, represents the thrust of the ramjet engine, represents the total thrust, represents the fuel flow rate of the turbine engine, represents the incoming flow rate of the turbine engine, represents the fuel flow rate of the ramjet engine, represents the incoming flow rate of the ramjet engine.

6. The method for modeling the mode conversion model of the combined power propulsion system according to claim 5, characterized in that: In step S40, the simplified common working model is obtained as: ； ； Among them, , , , , , , , ; , , , ; The parameters in the matrix can be correspondingly transformed into: , to further reduce the input dimension.

7. The method for modeling the mode conversion model of the combined power propulsion system according to claim 1, characterized in that: In step S50, the steps to achieve a smooth transition of thrust during the mode conversion period are: First, define a flight plan by yourself, including the mode conversion time, the required range of Mach number, and the required range of altitude; Next, at each operating point during the modal conversion period, a series of diverter plate angles α are selected to obtain the respective oncoming flow rates of each sub-engine at each operating point. Then, using altitude and Mach number as independent variables and total flow rate as the dependent variable, fitting and multiple regression are performed to obtain an equation for the variation of the total oncoming flow rate with altitude and Mach number: and an equation for the variation of a diversion ratio with the diverter plate angle α: % ; % , where k is a specific constant; Finally, according to the oncoming flow rate of each sub-engine obtained above and adjust the magnitude of the fuel flow rate of each sub-engine, obtain the curves of the oncoming flow rate and fuel flow rate changing with time, so that the total thrust can be smoothly transitioned.

8. The method for modeling the mode conversion model of the combined power propulsion system according to claim 1, wherein In step S50, the steps to achieve a large range of thrust are: First, define a flight plan by yourself, which includes the modal conversion time, the required Mach number range, and the required altitude range. Then, obtain the respective incoming flow rates of each sub-engine at each operating point according to the flight plan and the simplified common working model. Finally, switch different operations based on whether the parameters and input quantities in the constraint matrix are 0 under different operating states, and achieve a large range of thrust changes by adjusting each input quantity according to the total thrust requirement.

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