A preset time switching tracking control method for transition section of tilt-rotor unmanned aerial vehicle

Abstract

The present application belongs to the technical field of tilt-rotor unmanned aerial vehicle, and relates to a preset time switching tracking control method for transition section of tilt-rotor unmanned aerial vehicle, comprising the following steps: establishing a longitudinal nonlinear dynamics model for the transition section of tilt-rotor unmanned aerial vehicle, dividing the nonlinear system into multiple nonlinear subsystems, and establishing a switching nonlinear system model; combining with a tilt corridor to design a cost function, calculating an optimal transition path and solving an ideal reference signal to be tracked; designing a preset time tracking control scheme to make the tracking error of the ideal reference trajectory converge within the preset time; performing stability analysis to design preset time tracking controller parameters; the present application can calculate the optimal transition path of the tilt-rotor unmanned aerial vehicle, make the tracking error of the ideal reference trajectory converge within the preset time, and enable the tilt-rotor unmanned aerial vehicle to complete smooth conversion of flight modes within a given time.

Description

Technical Field

[0001] The present invention belongs to the technical field of tilt-rotor UAVs, and in particular relates to a preset time switching tracking control method for a transition section of a tilt-rotor UAV. Background Art

[0002] Tilt-rotor drones are highly innovative aircraft that combine the advantages of helicopters and fixed-wing aircraft, capable of rapidly switching between different flight modes. Utilizing rotatable nacelles at the wingtips, these drones can effectively transition from helicopter to fixed-wing mode. This design greatly expands their application range, particularly in complex terrain and urban environments. Tilt-rotor drones can achieve vertical takeoff and landing, as well as high-speed flight, enabling them to fulfill diverse mission requirements, such as rapid maneuvering, reconnaissance, and search and rescue.

[0003] Tilt-rotor drones have three main flight modes: helicopter mode, transition mode, and fixed-wing mode. In helicopter mode, the nacelle points vertically upward, and the rotors generate lift to offset the aircraft's gravity, allowing it to easily hover. In transition mode, the nacelle tilts, and the aircraft must precisely control its attitude to smoothly transition to fixed-wing mode. In fixed-wing mode, the nacelle is positioned horizontally, and the wings provide lift combined with the forward thrust of the rotors, enabling the drone to achieve high-speed flight.

[0004] Despite the excellent technical features of tilt-rotor UAVs, numerous challenges remain in flight dynamics modeling and control law design. This is particularly true in transition mode, where nonlinear characteristics complicate modeling and require consideration of the changes in the aerodynamic shape as the nacelle tilts. This process requires designers to balance multiple dynamic characteristics and address potential disturbances during flight, such as rotor wake turbulence, which can affect flight stability. Therefore, in-depth research on the longitudinal control of tilt-rotor UAVs is crucial.

[0005] To this end, a nonlinear dynamics model was established, the system was divided into multiple nonlinear subsystems, and a switching control strategy was designed to achieve efficient and stable flight control. Furthermore, by optimizing the transition path and developing a preset time tracking control scheme, the UAV's flight performance was further improved. Summary of the Invention

[0006] The purpose of the present invention is to overcome the deficiencies in the prior art and to provide a method and system for tracking control of a tilt-rotor UAV transition section with a preset time switching.

[0007] In order to achieve the purpose of the present invention, we will adopt the following technical solutions to implement it:

[0008] A preset time switching tracking control method for a tilt-rotor UAV transition section comprises the following steps:

[0009] S1. Assuming that there is no lateral motion in the transition section of the tilt-rotor UAV, a split-body modeling method is used to construct a longitudinal nonlinear dynamic model for each component of the tilt-rotor UAV. The nonlinear system is divided into at least two nonlinear subsystems, and at least two nonlinear subsystems are modeled as sequential switching longitudinal nonlinear dynamic models. Where:

[0010] The expression of the longitudinal nonlinear dynamic model is:

[0011]

[0012] Where, x1=[P x ,P z ,θ] T are the three states of the system in the body coordinate system, T represents the matrix transpose; P x is the position along the x-axis of the body, P z is the position along the z-axis of the body coordinate system, θ is the pitch angle; x2=[u,w,q] T Then there are three other states, u represents the forward flight speed, w is the longitudinal speed, and q is the pitch angular speed; represent β M is the tilt angle; u c =[u1,u2,u3] T is the control input, u1 is the rotor thrust, u2 is the longitudinal cyclic pitch, and u3 represents the deflection of the elevator; A1(x1), and is the parameter matrix; d represents the external disturbance;

[0013] The expression of the sequential switching longitudinal nonlinear dynamic model is:

[0014]

[0015] Where, For the switching signal, is a set of integers;

[0016] S2. Based on step S1, a cost function is designed in combination with the tilt corridor. The transition path is optimized by solving the objective function. The pitch angle and position information of the tilt-rotor UAV are calculated based on the obtained speed and tilt angle to obtain the ideal reference signal required for tracking. The expression of the cost function is:

[0017]

[0018] Among them, V a is the airspeed, C a (V a ,β M ) represents the cost function of the posture, θ(V a ,β M ) represents the current pitch angle, θ0 is the pitch angle in the hovering state, |θ| max is the maximum absolute value of the pitch angle within the feasible range; C w (V a ,β M ) represents the power cost function, P(V a ,β M ) represents the power required by the current rotor, P min Represents the minimum power required by the rotor, P xy is the available power of the engine; v(β M ) is the weight coefficient of the posture cost function;

[0019] The objective function is minC s (V a ,β M );

[0020] The expression of the ideal reference signal is as follows:

[0021] x r (t)=[P xr ,P zr ,θ r ];

[0022] Where, P xr is the ideal position along the x-axis of the body, P zr is the ideal longitudinal position along the z-axis of the body coordinate, θ r is the ideal pitch angle;

[0023] S3. Designing a preset time tracking control scheme based on the ideal reference signal in step S2, wherein the preset time tracking control scheme can achieve convergence of the tracking error of the ideal reference trajectory within a preset time; wherein:

[0024] The ideal reference trajectory is a state trajectory given by the ideal reference signal;

[0025] The coordinate transformation form of the tracking error is:

[0026]

[0027] Where l1 and l2 represent the tracking errors of the corresponding states; is a virtual controller, and its expression is Among them, K 11 With K12 is the gain matrix of the virtual controller;

[0028] Wherein: the virtual controller The expression is designed by introducing the lemma and selecting the Lyapunov function V1 through derivation; wherein, the lemma: if there exists a Lyapunov function V that satisfies

[0029]

[0030] Where, 0<α<1, τ c >0 is a given constant, then V is stable for a practical preset time; in addition, V can be stable within a preset time τ f ≤2τ c Converges to the neighborhood Inside;

[0031] The expression of the Lyapunov function V1 is:

[0032] S4, the virtual controller in step S3 Perform stability analysis to design the controller parameter K 21 With K 22 , combined with the selected Lyapunov function V2 to design the preset time tracking controller u c , the preset time tracking controller u c The expression is:

[0033]

[0034] Where K 21 With K 22 is the controller gain matrix;

[0035] Wherein, the expression of the Lyapunov function V2 is:

[0036]

[0037] As a limitation of the present invention, the state trajectory is expressed in a coordinate transformation form.

[0038] As a limiting solution of the present invention, the preset time tracking control solution is to design a virtual controller and a preset time tracking controller by selecting a corresponding Lyapunov function based on the coordinate transformation form of the tracking error, so that the tracking error can converge within the preset time.

[0039] As a limiting solution of the present invention, the design process of the preset time tracking controller includes the following steps:

[0040] S21. Introduce the following lemma: If there exists a Lyapunov function V that satisfies:

[0041]

[0042] Among them, 0<α<1, τ c >0 is a given constant, then V is stable for a practical preset time; in addition, V can be stable within a preset time τ f ≤2τ c Converges to the neighborhood Inside;

[0043] S22. Select the Lyapunov function V1 as follows:

[0044]

[0045] The derivative is obtained as:

[0046]

[0047] S23. Design virtual controller for:

[0048]

[0049] So the derivative of V1 becomes:

[0050]

[0051] S23. Select the Lyapunov function V2 as:

[0052]

[0053] S24. Design preset time tracking controller u c The form is as follows:

[0054]

[0055] Among them, K 21 With K 22 is the controller gain matrix;

[0056] So the derivative of V2 becomes:

[0057]

[0058] S25, through the virtual controller and preset time tracking controller u c , it can be proved that the tracking error l1 can be f ≤2τ c Internal convergence.

[0059] A preset time switching tracking control system for a transition section of a tilt-rotor UAV comprises a sequential switching nonlinear system model, a preset time switching control module, and a reference trajectory generation module, wherein:

[0060] The sequential switching nonlinear system model is composed of a sequential switching longitudinal nonlinear dynamic model, which is used to design a preset time switching control scheme. Its input is the switching signal σ(t), the controller u c and external disturbance d, the output is the position P along the x-axis of the body x , the position P along the z-axis of the body coordinate z and pitch angle θ;

[0061] The preset time switching control module is composed of a preset time tracking control scheme, and its input is the switching signal σ(t), the position P along the x-axis direction of the body x , the position P along the z-axis of the body coordinate z and pitch angle θ and the ideal reference signal, the output is the preset time tracking controller u c , so that the tracking error of the ideal reference trajectory converges within a preset time;

[0062] The reference trajectory generation module is composed of a cost function and an objective function, and its input is the airspeed V a and tilt angle β M , the output is an ideal reference signal, which is used to generate an ideal reference trajectory.

[0063] Beneficial effects

[0064] 1. The present invention models the tilt-rotor UAV in the transition phase as a switching nonlinear system. Compared with the nonlinear system model, it can simplify the control law design while ensuring the accuracy of the model.

[0065] 2. The present invention ensures that the tracking error converges within a preset time by designing a preset time tracking control scheme, so that the tilt-rotor UAV can complete a smooth transition of flight modes within a given time;

[0066] 3. The present invention optimizes the transition path of the tilt-rotor UAV by designing a cost function, which is more reasonable than the ideal path selected based on experience. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Figure 1 This is a schematic diagram of the tilt corridor and transition path of the tilt-rotor UAV;

[0068] Figure 2 It is a structural diagram of the present invention;

[0069] Figure 3The response curve diagram of each state and ideal trajectory of the tilt-rotor unmanned aerial vehicle transition section obtained by the preset time switching tracking control method of the application is shown in the drawings, wherein (a) is the forward position response curve diagram of the tilt-rotor unmanned aerial vehicle transition section obtained by the preset time switching tracking control method of the application; (b) is the longitudinal position response curve diagram of the tilt-rotor unmanned aerial vehicle transition section obtained by the preset time switching tracking control method of the application; (c) is the pitch angle response curve diagram of the tilt-rotor unmanned aerial vehicle transition section obtained by the preset time switching tracking control method of the application. DETAILED DESCRIPTION

[0070] The application will be further described below in combination with specific embodiments and drawings.

[0071] In the transition process of the tilt-rotor unmanned aerial vehicle, the rotation of the nacelle causes the aerodynamic shape to change continuously, and the change shows strong nonlinear characteristics, and the aerodynamic parameters also appear violent fluctuations. This makes it very difficult to accurately describe the dynamics behavior of the aircraft with a single model. The modeling by using the switching nonlinear system can effectively cope with this challenge by dividing the system into multiple subsystems. Compared with the traditional nonlinear modeling method, the modeling technology based on the switching nonlinear system can simplify the controller design while maintaining high accuracy of the model. This method not only improves the processing capability of nonlinear characteristics in the modeling process, but also provides a good foundation for the subsequent control strategy design.

[0072] The preset time switching tracking control method of the tilt-rotor unmanned aerial vehicle transition section of the application specifically comprises the following steps:

[0073] Step 1, establishing a longitudinal nonlinear dynamics model of the tilt-rotor unmanned aerial vehicle transition section.

[0074] The modeling process adopts a split modeling method, and each part of the tilt-rotor unmanned aerial vehicle is modeled. Further, it is assumed that there is no lateral motion in the process, which is simplified as a longitudinal dynamics model. The longitudinal nonlinear dynamics model of the tilt-rotor unmanned aerial vehicle transition section has the following expression:

[0075]

[0076] In the formula, x1=[P x ,P z ,θ] T are three states of the system in the body coordinate system, T represents matrix transposition; P x is the position along the x-axis direction of the body, P z is the position along the z-axis direction of the body, and θ is the pitch angle; x2=[u,w,q] T are other three states, u represents the forward flight speed, w is the longitudinal speed, and q is the pitch angular velocity; represent β M is the tilt angle; u c =[u1,u2,u3] T is the control input, u1 is the rotor thrust, u2 is the longitudinal cyclic pitch, and u3 represents the deflection of the elevator; A1(x1), and is the parameter matrix; d represents the external disturbance;

[0077] Furthermore, the nonlinear system is divided into multiple nonlinear subsystems and modeled as a switching nonlinear system. The specific form of the sequentially switched nonlinear system is:

[0078]

[0079] in, For the switching signal, is a set of integers.

[0080] Step 2: The specific form of the cost function is as follows:

[0081]

[0082] Among them, V a is the airspeed, C a (V a ,β M ) represents the cost function of the posture, θ(V a ,β M ) represents the current pitch angle, θ0 is the pitch angle in the hovering state, |θ| max is the maximum absolute value of the pitch angle within the feasible range; C w (V a ,β M ) represents the power cost function, P(V a ,β M ) represents the power required by the current rotor, P min Represents the minimum power required by the rotor, P xy is the available power of the engine; v(β M ) is the weight coefficient of the posture cost function;

[0083] After that, solve the objective function minC s (V a ,β M ) to obtain the optimal transition path, and further calculate the pitch angle and position information of the tilt-rotor UAV based on the obtained speed and tilt angle to obtain the ideal reference signal required for tracking.

[0084] Step 3: The expression of the ideal reference signal is as follows:

[0085] x r (t)=[P xr ,P zr ,θ r ];

[0086] Among them, P xr is the ideal position along the x-axis of the body, P zr is the ideal longitudinal position along the z-axis of the body coordinate, θ r is the ideal pitch angle;

[0087] Furthermore, a preset time tracking control scheme is designed to obtain the following coordinate transformation form:

[0088]

[0089] Among them, l1 and l2 represent the tracking errors of the corresponding states; is a virtual controller, and its specific form is where K 11 With K 12 is the controller gain matrix.

[0090] Step 4: Perform stability analysis and controller parameter design. First, introduce the following lemma: If there exists a Lyapunov function V that satisfies:

[0091]

[0092] Among them, 0<α<1, τ c >0 is a given constant, then V is stable for a practical preset time. In addition, V can be stable for a preset time τ f ≤2τ c Converges to the neighborhood Inside;

[0093] Furthermore, the Lyapunov function V1 is selected as follows:

[0094]

[0095] The derivative is obtained as:

[0096]

[0097] Design of virtual control laws for:

[0098]

[0099] It can be obtained that the derivative of V1 becomes:

[0100]

[0101] Further, a Lyapunov function V2 is selected as:

[0102]

[0103] The controller u is designed c The form is as follows:

[0104]

[0105] Wherein, K 21 And K 22 is a controller gain matrix;

[0106] It can be obtained that the derivative of V2 becomes:

[0107]

[0108] By designing the above virtual control law And the controller u c It can be further proved that the tracking error l1 can converge within a preset time τ f ≤2τ c .

[0109] In order to verify the effectiveness of the preset time switching tracking control of the tilt rotor transition section, the following simulation experiment is carried out.

[0110] In the tilt corridor shown in Figure 1 , the nacelle angle is the complementary angle of the tilt angle; in combination with the tilt corridor, a cost function is further designed to optimize the transition path of the tilt rotor unmanned aerial vehicle; and a structure diagram of the control method used in the present example is constructed, as shown in Figure 2 .

[0111] It is assumed that the entire tilt process is completed in 15s, and the switching signal σ(t) is designed as: when t∈[0,5), σ(t)=1; when t∈[5,10), σ(t)=2; when t∈[10,15), σ(t)=3.

[0112] Figure 3 (a)、 Figure 3 (b) and Figure 3 (c) show the curve diagram of the system state x1 and the ideal reference trajectory x r given by the ideal reference signal after applying the preset time switching tracking control method. By simulation, the comparison diagram of the state response curves of the present application is obtained, as shown in Figure 3 (a)、 Figure 3 (b) and Figure 3 (c).

[0113] It can be seen that in Figure 3 (a)、 Figure 3 (b) and Figure 3 In (c), after applying the preset time switching tracking control method, the method proposed in the present invention can make the system state within the preset time τ f The ideal state trajectory given by the reference signal is well tracked within the transition phase, providing good control effect on the tiltrotor UAV, thereby ensuring that the tiltrotor UAV can complete a smooth transition in flight mode within a given time. The above simulation results fully demonstrate that the preset time switching tracking control method for the transition phase of the tiltrotor UAV can effectively solve the problem of tiltrotor aircraft flight mode transition.

[0114] The technical solution of the present invention is described in detail above in conjunction with the embodiments / drawings, but the present invention is not limited to the above technical solution. For ordinary technicians in this technical field, after knowing the contents recorded in the present invention, they can make several equivalent transformations and substitutions without departing from the principles of the present invention. These equivalent transformations and substitutions should also be regarded as falling within the scope of protection of the present invention.

Claims

1. A preset time switching tracking control method for a tilt-rotor UAV transition section, characterized in that: The steps include: S1. Assuming that there is no lateral motion in the transition section of the tilt-rotor UAV, a split-body modeling method is used to construct a longitudinal nonlinear dynamic model for each component of the tilt-rotor UAV. The nonlinear system is divided into at least two nonlinear subsystems, and at least two nonlinear subsystems are modeled as sequential switching longitudinal nonlinear dynamic models. Where: The expression of the longitudinal nonlinear dynamic model is: Where, x1=[P x ,P z ,θ] T are the three states of the system in the body coordinate system, T represents the matrix transpose; P x is the position along the x-axis of the body, P z is the position along the z-axis of the body coordinate system, θ is the pitch angle; x2=[u,w,q] T Then there are three other states, u represents the forward flight speed, w is the longitudinal speed, and q is the pitch angular speed; represent β M is the tilt angle; u c =[u1,u2,u3] T is the control input, u1 is the rotor thrust, u2 is the longitudinal cyclic pitch, and u3 represents the deflection of the elevator; A1(x1), and is the parameter matrix; d represents the external disturbance; The expression of the sequential switching longitudinal nonlinear dynamic model is: Where: For switching signals, is a set of integers; S2. Based on step S1, a cost function is designed in combination with the tilt corridor. The transition path is optimized by solving the objective function. The pitch angle and position information of the tilt-rotor UAV are calculated based on the obtained speed and tilt angle to obtain the ideal reference signal required for tracking. The expression of the cost function is: C s (V a ,b M )=v(β M )C a (V a ,b M )+[1-v(β M )]C w (V a ,b M ) Among them, V a is the airspeed, C a (V a ,β M ) represents the cost function of the posture, θ(V a ,β M ) represents the current pitch angle, θ0 is the pitch angle in the hovering state, |θ| max is the maximum absolute value of the pitch angle within the feasible range; C w (V a ,β M ) represents the cost function of power, P(V a ,β M ) represents the power required by the current rotor, P min Represents the minimum power required by the rotor, P xy is the available power of the engine; v(β M ) is the weight coefficient of the posture cost function; The objective function is minC s (V a ,β M ); The expression of the ideal reference signal is as follows: x r (t)=[P xr ,P zr ,θ r ]; Where: P xr is the ideal position along the x-axis of the body, P zr is the ideal longitudinal position along the z-axis of the body coordinate, θ r is the ideal pitch angle; S3. Designing a preset time tracking control scheme based on the ideal reference signal in step S2, wherein the preset time tracking control scheme can achieve convergence of the tracking error of the ideal reference trajectory within a preset time; wherein: The ideal reference trajectory is a state trajectory given by the ideal reference signal; The coordinate transformation form of the tracking error is: Where: l1 and l2 represent the tracking errors of the corresponding states; is a virtual controller, and its expression is Among them, K 11 With K 12 is the gain matrix of the virtual controller; Wherein: the virtual controller The expression is designed by introducing the lemma and selecting the Lyapunov function V1 through derivation; wherein, the lemma: if there exists a Lyapunov function V that satisfies Where: 0<α<1, τ c >0 is a given constant, then V is stable for a practical preset time; in addition, V can be stable within a preset time τ f ≤2τ c Converges to the neighborhood Inside; The expression of the Lyapunov function V1 is: S4, the virtual controller in step S3 Perform stability analysis to design the controller parameter K 21 With K 22 , combined with the selected Lyapunov function V2 to design the preset time tracking controller u c , the preset time tracking controller u c The expression is: Where: K 21 With K 22 is the controller gain matrix; Wherein, the expression of the Lyapunov function V2 is:

2. The preset time switching tracking control method for the transition section of a tilt-rotor UAV according to claim 1 is characterized in that: The state trajectory is expressed in the form of coordinate transformation.

3. The preset time switching tracking control method for the transition section of a tilt-rotor UAV according to claim 1, characterized in that: The preset time tracking control scheme is to design a virtual controller and a preset time tracking controller by selecting a corresponding Lyapunov function according to the coordinate transformation form of the tracking error, so that the tracking error can converge within a preset time.

4. The preset time switching tracking control method for a tilt-rotor UAV transition section according to claim 1, characterized in that: The design process of the preset time tracking controller includes the following steps: S21. Introduce the following lemma: If there exists a Lyapunov function V that satisfies: Among them, 0<α<1, τ c >0 is a given constant, then V is stable for a practical preset time; in addition, V can be stable within a preset time τ f ≤2τ c Converges to the neighborhood Inside; S22. Select the Lyapunov function V1 as follows: The derivative is obtained as: S23. Design virtual controller for: So the derivative of V1 becomes: S23. Select the Lyapunov function V2 as: S24. Design preset time tracking controller u c The form is as follows: Among them, K 21 With K 22 is the controller gain matrix; So the derivative of V2 becomes: S25, through the virtual controller and preset time tracking controller u c , it can be proved that the tracking error l1 can be f ≤2τ c Internal convergence.

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