Tilt-rotor unmanned aerial vehicle transition section preset time switching tracking control method

Abstract

The invention belongs to the technical field of tilt-rotor unmanned aerial vehicles, and relates to a preset time switching tracking control method for a tilt-rotor unmanned aerial vehicle transition section, which comprises the following steps: establishing a longitudinal nonlinear dynamic model of the tilt-rotor unmanned aerial vehicle transition section, and dividing a nonlinear system into a plurality of nonlinear subsystems, establishing a switching nonlinear system model; designing a cost function by combining a tilt corridor, calculating an optimal transition path and resolving an ideal reference signal needing to be tracked; a preset time tracking control scheme is designed, so that the tracking error of the ideal reference trajectory is converged within preset time; stability analysis is carried out, and parameters of a preset time tracking controller are designed; according to the method, the optimal transition path of the tilt-rotor unmanned aerial vehicle can be calculated, and the tracking error with the ideal reference trajectory is converged within the preset time, so that the tilt-rotor unmanned aerial vehicle can complete the stable conversion of the flight mode within the given time.

Description

Technical Field

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

[0002] Tilt-rotor UAVs are highly innovative aircraft that combine the advantages of helicopters and fixed-wing aircraft and can quickly switch between different flight states. Using the rotatable nacelles at the wingtips, this UAV can effectively transform from helicopter mode to fixed-wing mode. This design greatly enriches its application range, especially when performing tasks in complex terrain and urban environments. Tilt-rotor UAVs can achieve vertical take-off and landing and high-speed flight, thereby completing a variety of mission requirements, such as rapid maneuvers, reconnaissance, search and rescue, etc.

[0003] Tilt-rotor drones have three main flight modes: helicopter mode, transition mode, and fixed-wing mode. In helicopter mode, the nacelle is vertically upward, and the rotor generates lift to offset the gravity of the aircraft, allowing it to hover easily; in transition mode, the nacelle will tilt, and the aircraft must precisely control its attitude to smoothly switch to fixed-wing mode; in fixed-wing mode, the nacelle is placed horizontally, and the wing provides lift combined with the forward thrust of the rotor, allowing the drone to fly at high speed.

[0004] Although tilt-rotor UAVs have excellent technical characteristics, there are still many challenges in flight dynamics modeling and control law design, especially in transition mode, where its nonlinear characteristics make modeling extremely complex and also need to consider the changes in the aerodynamic shape when the nacelle tilts. This process requires designers to take into account a variety of dynamic characteristics and deal with possible disturbances during flight, such as rotor wake, which affect flight stability. Therefore, it is particularly important to conduct in-depth research on the longitudinal control problem of tilt-rotor UAVs.

[0005] To this end, a nonlinear dynamic model is established, the system is divided into multiple nonlinear subsystems, and a switching control strategy is designed to achieve efficient and stable flight control. In addition, the flight performance of the drone can be further improved by optimizing the transition path and formulating a preset time tracking control scheme. Summary of the invention

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

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

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

[0009] S1. Assuming that there is no lateral motion in the transition section of the tilt-rotor UAV, the longitudinal nonlinear dynamic model of each component of the tilt-rotor UAV is constructed by the split modeling method; 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; wherein:

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

[0011]

[0012] In the formula, x1=[P x ,P z ,θ] T are the three states of the system in the body coordinate system, T represents matrix transposition; 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, 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, σ(t): For the switching signal, is a set of integers;

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

[0017]

[0018] C s (V,β M )=v(β M )C a (V,β M )+[1-v(β M )]C w (V,β M )

[0019] Among them, C a (V,β M ) represents the cost function of the posture, θ(V,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 p (V,β M ) represents the power cost function, P(V,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;

[0020] The objective function is minC s (V,β M );

[0021] The expression of the ideal reference signal is as follows:

[0022] x r (t) = [P xr ,P zr ,θ r ]

[0023] 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;

[0024] S3, designing a preset time tracking control scheme according to the ideal reference signal in step S2, wherein the preset time tracking control scheme can achieve the tracking error of the ideal reference trajectory to converge within a preset time; wherein:

[0025] The ideal reference trajectory is a state trajectory given by the ideal reference signal;

[0026] The coordinate transformation form of the tracking error is:

[0027] l1=x1-x r

[0028]

[0029] Where l1 and l2 represent the tracking errors of the corresponding states; is a virtual controller, and its expression is Where K 11 With K 12 is the gain matrix of the virtual controller;

[0030] 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

[0031]

[0032] In the formula, 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;

[0033] The expression of the Lyapunov function V1 is:

[0034] 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:

[0035]

[0036] In the formula, K 21 With K 22 is the gain matrix of the controller;

[0037] Wherein, the expression of the Lyapunov function V2 is:

[0038]

[0039] As a limitation of the present invention, the state trajectory is expressed in the form of coordinate transformation.

[0040] As a limiting scheme of the present invention, the preset time tracking control scheme is based on the coordinate transformation form of the tracking error, and by selecting the corresponding Lyapunov function to design the virtual control law and the preset time tracking controller, so that the tracking error can converge within the preset time.

[0041] As a preferred solution of the present invention, the design process of the preset time tracking controller parameters includes the following steps:

[0042] S21. Introduce the following lemma: If there exists a Lyapunov function V that satisfies

[0043]

[0044] 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;

[0045] S22. Select the Lyapunov function V1 as follows:

[0046]

[0047] The derivative is obtained as:

[0048]

[0049] S23. Design virtual controller for:

[0050]

[0051] It can be obtained that the derivative of V1 becomes:

[0052]

[0053] S23. Select the Lyapunov function V2 as:

[0054]

[0055] S24. Design preset time tracking controller u c The form is as follows:

[0056]

[0057] Among them, K 21 With K 22 is the controller gain matrix;

[0058] It can be obtained that the derivative of V2 becomes:

[0059]

[0060] 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.

[0061] 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:

[0062] 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 direction of the body coordinate z and pitch angle θ;

[0063] 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 direction 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;

[0064] The reference trajectory generation module is composed of a cost function and an objective function, and its input is the airspeed V and the tilt angle β M , the output is an ideal reference signal, which is used to generate an ideal reference trajectory.

[0065] Beneficial Effects

[0066] 1. The present invention models the tilt-rotor UAV in the transition stage 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;

[0067] 2. The present invention can ensure that the tracking error converges within the preset time by designing a preset time tracking control scheme, so that the tilt-rotor UAV can complete the smooth conversion of the flight mode within a given time;

[0068] 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

[0069] Figure 1 A schematic diagram of the tilting corridor and transition path of a tilt-rotor UAV;

[0070] Figure 2 It is a structural diagram of the present invention;

[0071] Figure 3 The present invention provides response curves of various states and ideal trajectories of a transition section of a tilt-rotor UAV obtained by the preset time switching tracking control method of the present invention, wherein (a) is a forward position response curve of a transition section of a tilt-rotor UAV obtained by the preset time switching tracking control method of the present invention; (b) is a longitudinal position response curve of a transition section of a tilt-rotor UAV obtained by the preset time switching tracking control method of the present invention; and (c) is a pitch angle response curve of a transition section of a tilt-rotor UAV obtained by the preset time switching tracking control method of the present invention. DETAILED DESCRIPTION

[0072] The present invention will be further described below in conjunction with specific embodiments and drawings.

[0073] During the transition process of the tilt-rotor UAV, the rotation of the nacelle causes the aerodynamic shape to change continuously, and this change shows strong nonlinear characteristics, and the aerodynamic parameters will also fluctuate violently. This makes it very difficult to accurately describe the dynamic behavior of the aircraft with a single model. Using a switching nonlinear system for modeling can effectively address this challenge by dividing the system into multiple subsystems. Compared with traditional nonlinear modeling methods, the modeling technology based on switching nonlinear systems can maintain the high accuracy of the model while simplifying the controller design. This method not only improves the ability to handle nonlinear characteristics in the modeling process, but also provides a good foundation for the subsequent control strategy design.

[0074] The preset time switching tracking control method of the tilt-rotor UAV transition section of the present invention specifically comprises the following steps:

[0075] Step 1: Establish the longitudinal nonlinear dynamic model of the transition section of the tilt-rotor UAV.

[0076] The modeling process adopts the split modeling method to model each part of the tilt-rotor UAV separately. Furthermore, assuming that there is no lateral motion in the process, it is simplified to a longitudinal dynamic model. The longitudinal nonlinear dynamic model of the transition section of the tilt-rotor UAV is expressed as follows:

[0077]

[0078] In the formula, x1=[P x ,P z ,θ] Tare the three states of the system in the body coordinate system, T represents matrix transposition; 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, 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;

[0079] 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:

[0080]

[0081] Where, σ(t): For the switching signal, is a set of integers.

[0082] Step 2: The specific form of the cost function is as follows:

[0083]

[0084] C s (V,β M )=v(β M )C a (V,β M )+[1-v(β M )]C w (V,β M )

[0085] Among them, C a (V,β M ) represents the cost function of the posture, θ(V,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 p (V,β M ) represents the power cost function, P(V,β M ) represents the power required by the current rotor, P min represents the minimum power required by the rotor, P xyis the available power of the engine; v(β M ) is the weight coefficient of the posture cost function;

[0086] After that, solve the objective function minC s (V,β M ) to obtain the optimal transition path, and further calculate the pitch angle and position information of the tilt-rotor UAV according to the obtained speed and tilt angle to obtain the ideal reference signal required for tracking.

[0087] Step 3: The expression of the ideal reference signal is as follows:

[0088] x r (t) = [P xr ,P zr ,θ r ]

[0089] 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;

[0090] Furthermore, a preset time tracking control scheme is designed to obtain the following coordinate transformation form:

[0091] l1=x1-x r

[0092]

[0093] 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.

[0094] Step 4: Perform stability analysis and controller parameter design. First, introduce the following lemma: If there exists a Lyapunov function V that satisfies

[0095]

[0096] 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;

[0097] Further, the Lyapunov function V1 is selected as follows:

[0098]

[0099] The derivative is obtained as:

[0100]

[0101] Design of virtual control law for:

[0102]

[0103] It can be obtained that the derivative of V1 becomes:

[0104]

[0105] Further, the Lyapunov function V2 is selected as:

[0106]

[0107] Design controller u c The form is as follows:

[0108]

[0109] Among them, K 21 With K 22 is the controller gain matrix;

[0110] It can be obtained that the derivative of V2 becomes:

[0111]

[0112] By designing the above virtual control law With controller u c , it can be further proved that the tracking error l1 can be f ≤2τ c Internal convergence.

[0113] In order to verify the effectiveness of the present invention in the preset time switching tracking control of the tilt-rotor transition section, the following simulation experiment was conducted.

[0114] exist Figure 1 In the tilt corridor shown, the nacelle angle is the complementary angle of the tilt angle; and in combination with the tilt corridor, a cost function is further designed to optimize the transition path of the tilt-rotor UAV; and a structural diagram of the control method used in this example is constructed, as shown in FIG. Figure 2 shown.

[0115] Assuming that the entire tilting process takes 15 seconds, the switching signal σ(t) is designed as follows: when t∈[0,5), σ(t)=1; when t∈[5,10), σ(t)=2; when t∈[10,15), σ(t)=3.

[0116] Figure 3 (a) Figure 3 (b) and Figure 3 (c) shows the relationship between the system state x1 and the ideal reference trajectory x given by the ideal reference signal after applying the preset time switching tracking control method. r By performing simulation, a comparison diagram of the response curves of each state of the present invention is obtained, such as Figure 3 (a) Figure 3 (b) and Figure 3 (c) as shown.

[0117] It can be seen that in Figure 3 (a) Figure 3 (b) with 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 can be well tracked within the transition section, and the tilt-rotor UAV has a good control effect, thereby ensuring that the tilt-rotor UAV can complete the smooth transition of the flight mode within a given time. The above simulation results fully demonstrate that the preset time switching tracking control method of the transition section of the tilt-rotor UAV can effectively solve the problem of flight mode conversion of the tilt-rotor aircraft.

[0118] 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 changes and substitutions without departing from the principle of the present invention. These equivalent changes and substitutions should also be regarded as belonging to the protection scope of the present invention.

Claims

1. A preset time switching tracking control method for a transition section of a tilt-rotor UAV, characterized in that: The steps include: S1. Assuming that there is no lateral motion in the transition section of the tilt-rotor UAV, the longitudinal nonlinear dynamic model of each component of the tilt-rotor UAV is constructed by the split modeling method; 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; wherein: The expression of the longitudinal nonlinear dynamic model is: In the formula, x1=[P x ,P z ,θ] T are the three states of the system in the body coordinate system, T represents matrix transposition; 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: In the formula, For the switching signal, is a set of integers; S2. Based on step S1, a cost function is designed in combination with the tilting corridor, and the transition path is optimized by solving the objective function. The pitch angle and position information of the tilt-rotor UAV are calculated according to the obtained speed and tilting angle to obtain the ideal reference signal required for tracking; wherein: the expression of the cost function is: C s (V,β M )=v(β M )C a (V,β M )+[1-v(β M )]C w (V,β M ) Among them, C a (V,β M ) represents the cost function of the posture, θ(V,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 p (V,β M ) represents the power cost function, P(V,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,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 according to the ideal reference signal in step S2, wherein the preset time tracking control scheme can achieve the tracking error of the ideal reference trajectory to converge 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: l1=x1-x r Where l1 and l2 represent the tracking errors of the corresponding states; is a virtual controller, and its expression is Where 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 In the formula, 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: In the formula, 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 of 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 of the transition section of a tilt-rotor UAV according to claim 1 is 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 the preset time.

4. The preset time switching tracking control method of a tilt-rotor UAV transition section according to claim 1 is 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: It can be obtained that 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; It can be obtained that 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.

5. A preset time switching tracking control system for a transition section of a tilt-rotor UAV, characterized in that: The preset time switching tracking control system comprises a sequential switching nonlinear system model, a preset time switching control module and a reference trajectory generation module, wherein: 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 z and pitch angle θ; 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 direction 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; The reference trajectory generation module is composed of a cost function and an objective function, and its input is the airspeed V and the tilt angle β M , the output is an ideal reference signal, which is used to generate an ideal reference trajectory.

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