Composite wing unmanned aerial vehicle transition process control method based on fractional order sliding mode

Abstract

The invention discloses a composite wing unmanned aerial vehicle transition process control method based on a fractional order sliding mode, and particularly relates to the field of composite wing unmanned aerial vehicle flight control. A Newton-Euler equation is adopted to carry out integrated modeling on a composite wing unmanned aerial vehicle transition process, and a longitudinal nonlinear mathematical model is deduced; designing a novel fractional order reaching law by combining a double-power reaching law and a fractional order calculus thought on the basis of a traditional exponential power reaching law, and constructing a pitch angle, air speed and four-rotor height fractional order sliding mode controller; and force and torque of the four-rotor system and the fixed-wing system are distributed by adopting an airspeed weight control distribution strategy, so that output of an actuator is solved. The sliding mode variable structure control is applied to the transition control of the composite wing unmanned aerial vehicle, and the proposed fractional order sliding mode control method improves the dynamic quality of the system, reduces the control steady state error, improves the robustness of the flight control system of the composite wing unmanned aerial vehicle, and realizes the stable control of the transition process.

Description

Technical Field

[0001] The invention relates to the field of flight control of composite wing unmanned aerial vehicles, and in particular to a composite wing unmanned aerial vehicle transition process control method based on fractional order sliding mode. Background Art

[0002] Vertical Take-off and Landing Fixed-Wing Unmanned Aerial Vehicle (VTOL-FW UAV) combines the advantages of fixed-wing UAVs and rotary-wing UAVs. It can take off and land vertically and hover, and has the speed performance, endurance performance and load-bearing advantages of fixed-wing UAVs, while avoiding the defects of the two types of UAVs to the greatest extent.

[0003] Among the types of vertical take-off and landing fixed-wing UAVs, although the compound-wing UAV (Quadplane) has the problem of large dead weight, it has the advantages of simple mechanical structure, good technical feasibility, low economic cost, high feasibility, high safety factor, and low requirements for external conditions for take-off and recovery. It is currently the vertical take-off and landing solution with the lowest engineering difficulty, the highest practicality and reliability, and has extremely broad application prospects and practical significance.

[0004] The transition process of a composite-wing UAV requires the switching between the rotor structure and the fixed-wing structure, which is difficult to control and is the key to determining the success or failure of a composite-wing UAV's flight mission.

[0005] The existing research solutions for the control law problem of the transition process of composite wing UAVs are mainly divided into two categories: ① Linear control law, including PID control, LQR control, H∞ control, etc. ② Nonlinear control law, including backstepping control, nonlinear dynamic inverse control, self-disturbance rejection control, etc. Compared with linear control, nonlinear control has the advantages of flexibility, strong adaptability and improved system stability, and has better adaptability to the control problem of the transition process of composite wing UAVs with greater control difficulty.

[0006] Sliding Mode Control (SMC) is a nonlinear control with the advantages of fast response, low dependence on system models, and strong robustness, and is widely used in industrial systems. However, the sliding mode approach stage is prone to control chattering, leading to system crash.

[0007] In view of the problems of great difficulty in controlling the transition process of composite-wing UAV and model uncertainty, the present invention provides a transition process control method of composite-wing UAV based on fractional-order sliding mode. Summary of the invention

[0008] To this end, the present invention provides a transition process control method for a composite wing UAV based on fractional-order sliding mode. Compared with traditional PID control and traditional sliding mode control, the proposed control method reduces the control tracking error, enhances the control accuracy and anti-disturbance capability, improves the robustness of the composite wing UAV flight control system, and realizes smooth control of the transition process, so as to solve the current problem of longitudinal control of the transition process of composite wing UAV.

[0009] In order to achieve the above-mentioned purpose, the present invention provides the following technical solutions: a sliding mode control solution for the transition process of a composite wing UAV, which needs to control the pitch angle, airspeed and altitude of the composite wing UAV, specifically comprising the following steps:

[0010] S1: Based on the Newton-Euler equation, the rotor and fixed-wing dynamics of the composite wing UAV during the transition process are integrated and the longitudinal nonlinear mathematical model of the composite wing UAV is derived;

[0011] S2: A new fractional-order reaching law designed based on the traditional exponential power reaching law, combining the idea of ​​double power reaching law and the idea of ​​fractional-order calculus;

[0012] S3: Based on the novel fractional-order reaching law, a fractional-order sliding mode controller for the pitch angle, airspeed and quadrotor altitude during the transition process is constructed in the longitudinal nonlinear mathematical model of the composite-wing UAV, and a fixed-wing altitude controller is constructed as the pitch angle outer loop to jointly maintain altitude stability;

[0013] S4: adopting the airspeed weight control allocation strategy, solving the output of the fractional-order sliding mode controller as the actuator output, and completing the sliding mode control method for the transition process of the composite wing UAV.

[0014] According to the above scheme, based on the transition process modeling of the composite wing UAV of S1, assuming that the UAV flies horizontally without sideslip during the transition process, the longitudinal nonlinear mathematical model of the composite wing UAV is:

[0015]

[0016] Where: H is the height; V is the airspeed; θ, α and γ are the pitch angle, angle of attack and track angle respectively; q is the pitch angular velocity; m is the mass of the UAV; I yy is the moment of inertia around the y-axis; F x w , F z w and M y They are the x-axis force, z-axis force and pitch moment in the UAV airflow coordinate system, expressed as:

[0017]

[0018] M y =Mfixed +M rotor

[0019] Where: g is the gravity acceleration of the drone; T, D, L, M fixed , F rotor and M rotor They are respectively the thrust of the engine propeller, the fixed-wing drag, the fixed-wing lift, the pitch moment generated by the fixed-wing, and the lift and pitch moment generated by the quadrotor, expressed as:

[0020]

[0021] D=0.5ρV 2 SC D

[0022] L=0.5ρV 2 SC L

[0023] M fixed =0.5ρV 2 S C M

[0024]

[0025] Where: ρ is the atmospheric density; S is the effective wing area; c is the average aerodynamic chord length of the wing; c Tf and c Tr are the thrust coefficients of the engine and the quadrotor propeller respectively; d is the distance between the quadrotor and the center of gravity of the UAV; δ t is the engine propeller speed; ω1, ω2, ω3 and ω4 are the quadrotor propeller speeds respectively; C D , C L and C M are the aerodynamic coefficients of fixed-wing drag, lift and pitching moment respectively.

[0026] Furthermore, the novel fractional-order reaching law described in S2 is as follows:

[0027]

[0028] Where: s is the sliding surface function, is the differential of the sliding surface function, ε>0, k i >0, i=1~3, 0<p<1, 1<q<2, α is the fractional calculus operator, The Riemann-Liouville fractional calculus is The general formula is defined as follows:

[0029]

[0030] Where: Γ(x) means that the Gamma function is the general formula of Γ(m-α), m-1<α<m, m is a constant, and the following The symbol is abbreviated as D α .

[0031] Furthermore, S3 constructs a fractional-order sliding mode controller for the pitch angle, airspeed and altitude of the composite wing UAV during the transition process based on the novel fractional-order reaching law, which specifically includes the following sub-steps:

[0032] S3.1, taking the total pitch moment as the virtual control quantity, construct a pitch angle fractional order sliding mode controller;

[0033] S3.2, using the engine propeller thrust as the virtual control variable, construct an airspeed fractional order sliding mode controller;

[0034] S3.3, using the lift of the quadrotor as the virtual control quantity, constructing the quadrotor altitude fractional sliding mode controller, using the fixed-wing altitude controller as the attitude outer loop, constructing the fixed-wing altitude PID controller, and jointly maintaining the altitude stability of the composite wing UAV;

[0035] S3.4. Based on Lyapunov stability theory, stability analysis is performed on the pitch angle, airspeed and quadrotor altitude fractional sliding mode controller.

[0036] According to S3.1, the sliding mode surface function form of the pitch angle fractional-order sliding mode controller is:

[0037]

[0038] Where: s θ is the pitch angle sliding surface function, e θ =θ-θ d is the pitch angle tracking error, is the differential of the pitch angle tracking error, c θ >0 is the pitch angle sliding surface coefficient, k θ >0 is the pitch fractional coefficient, D η is the fractional calculus, and η is the fractional calculus operator of the sliding surface.

[0039] The control law of the pitch angle fractional-order sliding mode controller is:

[0040]

[0041] Where: U θ is the virtual control variable of the pitch angle fractional-order sliding mode controller, ε θ >0,k i >0, i=1~3 is the reaching law coefficient of the pitch angle fractional order sliding mode controller, To set the second-order differential of the pitch angle, I yy is the moment of inertia about the y-axis.

[0042] Furthermore, the sliding mode surface function form of the airspeed fractional-order sliding mode controller described in S3.2 is:

[0043] s V =e V +λ V ∫e V dt+k V D η e V ,λ V >0,k V >0

[0044] Where: s V is the airspeed sliding surface function, e V =VV d is the airspeed tracking error, λ V >0 is the airspeed integral sliding surface coefficient, k V >0 is the airspeed calculus coefficient.

[0045] The control law of the airspeed fractional-order sliding mode controller is:

[0046]

[0047] Where: U V is the virtual control variable of the airspeed fractional-order sliding mode controller, ε V >0,k i >0, i=4~6 is the reaching law coefficient of the airspeed fractional sliding mode controller, Φ=-gsinγ+(F rotor sinα-D) / m, is the airspeed differential, m is the mass, g is the acceleration due to gravity, γ is the track angle, α is the angle of attack, D is the drag, and F rotor It is the lift of the quadrotor.

[0048] Furthermore, the sliding mode surface function form of the quadrotor altitude fractional sliding mode controller described in S3.3 is:

[0049]

[0050] Where: s H is the quadrotor altitude sliding surface function, e H =HH d is the height tracking error, is the height tracking error differential, c H >0 is the height sliding surface coefficient, k H >0 is the height calculus coefficient.

[0051] The control law of the quadrotor altitude fractional-order sliding mode controller is:

[0052]

[0053] Where: U H is the virtual control variable of the quadrotor altitude fractional-order sliding mode controller, ε H >0,k i >0, i=7~9 is the reaching law coefficient of the quadrotor altitude fractional order sliding mode controller, To set the second-order differential of height.

[0054] The fixed-wing altitude controller is in the form of:

[0055]

[0056] Where: k fHP , k fHI , k fHD are proportional, integral and differential coefficients respectively, θ d To set the pitch angle.

[0057] Further, according to S3.4, the Lyapunov function is defined as:

[0058]

[0059] Taking the pitch angle fractional-order sliding mode controller as an example,

[0060]

[0061] It is proved that the sliding surface s of the pitch angle fractional-order sliding mode controller θ is asymptotically stable. Similarly, it can be proved that s H and V is gradually stable.

[0062] Further, S4 designs the airspeed weight control allocation strategy based on the pitch angle, airspeed and quadrotor altitude fractional sliding mode controller and the fixed-wing altitude controller, and solves the output of the compound wing UAV actuator, which specifically includes the following sub-steps:

[0063] S4.1. Design the airspeed weight control allocation strategy and calculate the forces and torques that the fixed-wing system and the quadrotor system need to provide;

[0064] S4.2. Calculate the engine propeller speed based on the engine thrust;

[0065] S4.3. Calculate the elevator deflection angle using the fixed-wing pitch moment;

[0066] S4.4. Calculate the propeller speed of the quadrotor using the lift and pitch moment of the quadrotor.

[0067] According to S4.1, the airspeed weight control allocation strategy is:

[0068]

[0069] w rotor =1-w fixed

[0070] Where: w fixed is the fixed wing weight; w rotor is the quadrotor weight; V is the current airspeed; V min is the minimum airspeed of the transition mode; V is the maximum airspeed of the transition mode.

[0071] max

[0072] The forces and moments of the fixed-wing system and the quadrotor system are:

[0073] T=U V

[0074] M fixed =U θ w fixed

[0075] M rotor =U θ w rotor

[0076] F rotor =U H w rotor

[0077] Furthermore, the engine propeller speed described in S4.2 is calculated as:

[0078]

[0079] Furthermore, the fixed-wing pitch moment calculation formula described in S4.3 is:

[0080]

[0081] Where: is the pitch angular velocity of dimension one.

[0082] The elevator deflection angle is calculated as:

[0083]

[0084] Furthermore, the quadrotor propeller speed described in S4.4 is calculated as:

[0085]

[0086] The present invention has the following advantages:

[0087] The sliding mode variable structure nonlinear control is applied to the transition process control of the composite wing UAV. In order to improve the shortcomings of the traditional sliding mode exponential power reaching law such as chattering and inflexible parameters, a new fractional order reaching law is proposed by combining the double power reaching law and the fractional order calculus idea, and a fractional order sliding mode controller is constructed to improve the rapid convergence of the sliding mode surface and suppress chattering. At the same time, the airspeed weight control allocation strategy is used to allocate the control quantity to realize the actuator solution. Compared with the traditional PID control and sliding mode control, the sliding mode control method reduces the control steady-state error, enhances the control accuracy, improves the robustness of the flight control system, and realizes the smooth control of the transition process, providing a new method for the transition process control of composite wing UAV. BRIEF DESCRIPTION OF THE DRAWINGS

[0088] Figure 1 This is a structural block diagram of the sliding mode control method for the transition process of a composite wing UAV provided by the present invention.

[0089] Figure 2 This is a flow chart of the sliding mode control method for the transition process of a composite wing UAV provided by the present invention.

[0090] Figure 3 This is a MATLAB / SIMULINK block diagram of the composite wing UAV fractional-order sliding mode controller provided by the present invention.

[0091] Figure 4 This is a MATLAB / SIMULINK block diagram of the longitudinal mathematical model of the composite wing UAV provided by the present invention.

[0092] Figure 5 The sliding mode control airspeed tracking curve diagram of the transition process of the composite wing UAV provided by the present invention;

[0093] Figure 6 The airspeed tracking error diagram of the sliding mode control of the composite wing UAV transition process provided by the present invention;

[0094] Figure 7 A sliding mode control pitch angle tracking curve diagram of the transition process of the composite wing UAV provided by the present invention;

[0095] Figure 8 A graph of the pitch angle tracking error of the sliding mode control during the transition process of the composite wing UAV provided by the present invention;

[0096] Fig. 9 A sliding mode control height tracking curve diagram of the transition process of the composite wing UAV provided by the present invention;

[0097] Fig.10This is a sliding mode control height tracking error diagram for the transition process of the composite wing UAV provided by the present invention.

[0098] Fig.11 This is a sliding mode control weight distribution diagram for the transition process of the composite wing UAV provided by the present invention. DETAILED DESCRIPTION

[0099] The following is a description of the implementation of the present invention by specific embodiments. People familiar with the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0100] like Figure 1-Figure 2 As shown, this embodiment provides a transition process control method for a composite wing UAV based on a fractional order sliding mode, comprising the following steps:

[0101] Step 1: Based on the Newton-Euler equation, the rotor and fixed-wing dynamics of the composite wing UAV transition process are integrated and the longitudinal nonlinear mathematical model of the composite wing UAV is derived:

[0102]

[0103] Where: H is the height; V is the airspeed; θ, α and γ are the pitch angle, angle of attack and track angle respectively; q is the pitch angular velocity; m is the mass of the UAV; I yy is the moment of inertia F about the y-axis x w , F z w and M y They are the x-axis force, z-axis force and pitch moment in the UAV airflow coordinate system, expressed as:

[0104]

[0105] M y =M fixed +M rotor

[0106] Where: g is the gravity acceleration of the drone; T, D, L, M fixed , F rotor and M rotor They are respectively the thrust of the engine propeller, the fixed-wing drag, the fixed-wing lift, the pitch moment generated by the fixed-wing, and the lift and pitch moment generated by the quadrotor, expressed as:

[0107]

[0108] D=0.5ρV 2 SC D

[0109] L=0.5ρV 2 SC L

[0110] M fixed =0.5ρV 2 S C M

[0111]

[0112] Where: ρ is the atmospheric density; S is the effective wing area; c is the average aerodynamic chord length of the wing; c Tf and c Tr are the thrust coefficients of the engine and the quadrotor propeller respectively; d is the distance between the quadrotor and the center of gravity of the UAV; δ t is the engine propeller speed; ω1, ω2, ω3 and ω4 are the quadrotor propeller speeds respectively; C D , C L and C M are the aerodynamic coefficients of fixed-wing drag, lift and pitching moment respectively.

[0113] Step 2: According to the longitudinal nonlinear mathematical model of the composite wing UAV, based on the novel fractional-order reaching law, a fractional-order sliding mode controller for pitch angle, airspeed and quadrotor altitude is constructed, and a fixed-wing altitude controller is constructed as the pitch angle outer loop to jointly maintain altitude stability, including the following sub-steps:

[0114] Step 2.1, based on the traditional exponential power reaching law, the new fractional order reaching law is designed by combining double power terms and fractional order calculus, which is in the following form:

[0115]

[0116] Where: s is the sliding surface function, is the differential of the sliding surface function, ε>0, k i >0, i=1~3, 0<p<1, 1<q<2, α is the fractional calculus operator, The Riemann-Liouville fractional calculus is The general formula is defined as follows:

[0117]

[0118] Where: Γ(x) means that the Gamma function is the general formula of Γ(m-α), m-1<α<m, m is a constant, and the following The symbol is abbreviated as D α .

[0119] Step 2.2: Taking the pitch moment of the composite wing UAV as the virtual control quantity, construct the pitch angle fractional order sliding mode controller. The sliding mode surface function of the pitch angle fractional order sliding mode controller is:

[0120]

[0121] Where: s θ is the pitch angle sliding surface function, e θ =θ-θ d is the pitch angle tracking error, is the differential of the pitch angle tracking error, c θ >0 is the pitch angle sliding surface coefficient, k θ >0 is the pitch fractional coefficient, D η is the fractional calculus, η is the sliding surface fractional calculus operator;

[0122] The control law of the pitch angle fractional-order sliding mode controller is:

[0123]

[0124] Where: U θ is the virtual control variable of the pitch angle fractional-order sliding mode controller, ε θ >0,k i >0, i=1~3 is the reaching law coefficient of the pitch angle fractional order sliding mode controller, To set the second order differential of the pitch angle.

[0125] Step 2.3, using the engine propeller thrust as the virtual control variable, construct the airspeed fractional order sliding mode controller. The sliding mode surface function of the airspeed fractional order sliding mode controller is:

[0126] s V =e V +λ V ∫e V dt+k V D η e V ,λ V >0,k V >0

[0127] Where: s V is the airspeed sliding surface function, e V =VV d is the airspeed tracking error, λ V >0 is the airspeed integral sliding surface coefficient, k V >0 is the airspeed calculus coefficient.

[0128] The control law of the airspeed fractional-order sliding mode controller is:

[0129]

[0130] Where: Φ = -gsinγ + (F rotor sinα-D) / m, U V is the virtual control variable of the airspeed fractional-order sliding mode controller, ε V >0,k i >0, i=4~6 is the reaching law coefficient of the airspeed fractional order sliding mode controller, is the airspeed differential, m is the mass, g is the acceleration due to gravity, γ is the track angle, α is the angle of attack, D is the drag, and F rotor It is the lift of the quadrotor.

[0131] Step 2.4: Take the lift of the quadrotor as the virtual control quantity and construct the quadrotor altitude fractional sliding mode controller. The sliding mode surface function of the quadrotor altitude fractional sliding mode controller is:

[0132]

[0133] Where: s H is the quadrotor altitude sliding surface function, e H =HH d is the height tracking error, is the height tracking error differential, c H >0 is the height sliding surface coefficient, k H >0 is the high calculus coefficient;

[0134] The control law of the quadrotor altitude fractional-order sliding mode controller is:

[0135]

[0136] Where: U H is the virtual control variable of the quadrotor altitude fractional-order sliding mode controller, ε H >0,k i >0, i=7~9 is the reaching law coefficient of the quadrotor altitude fractional order sliding mode controller, To set the second-order differential of height.

[0137] The fixed-wing altitude controller is in the form of:

[0138]

[0139] Where: k fHP , k fHI , k fHD are proportional, integral and differential coefficients respectively, θ d To set the pitch angle.

[0140] Step 3: Based on the pitch angle, airspeed and quadrotor altitude fractional sliding mode controller and the fixed-wing altitude controller, an airspeed weight control allocation strategy is designed to solve the output of the compound wing UAV actuator, which specifically includes the following sub-steps:

[0141] Step 3.1, design the airspeed weight control allocation strategy, and calculate the forces and moments of the fixed-wing system and the quadrotor system.

[0142] The airspeed weight control allocation strategy is:

[0143]

[0144] w rotor =1-w fixed

[0145] Where: w fixed is the fixed wing weight; w rotor is the quadrotor weight; V is the current airspeed; V min is the minimum airspeed of the transition mode; V max is the maximum airspeed of the transition mode.

[0146] Based on the airspeed weight control allocation strategy, the forces and moments of the fixed-wing system and the quadrotor system are calculated as:

[0147] T=U V

[0148] M fixed =U θ w fixed

[0149] M rotor =U θ w rotor

[0150] F rotor =U H w rotor

[0151] Step 3.2: Calculate the actuator outputs, including the elevator deflection angle, the engine propeller speed, and the quadrotor propeller speed, according to the forces and moments of the fixed-wing system and the quadrotor system.

[0152] The engine propeller speed is calculated as:

[0153]

[0154] The fixed-wing pitch moment calculation formula is:

[0155]

[0156] Where: is the pitch angular velocity of dimension one.

[0157] The elevator deflection angle is calculated as:

[0158]

[0159] The quadrotor propeller speed is calculated as:

[0160]

[0161] Figure 3 The MATLAB / SIMULINK block diagram of the composite wing UAV fractional order sliding mode controller is shown in Figure 1. Based on this, the S-Function module function is written according to the above steps to establish a fractional order sliding mode controller (FOSMC). Figure 4 It is a MATLAB / SIMULINK block diagram of the mathematical model of the composite wing UAV. The fractional order sliding mode controller is applied to the mathematical model of the composite wing UAV to perform simulation control test on the transition process of the composite wing UAV.

[0162] In order to verify the control effect, a certain type of composite wing UAV is selected as the object in the simulation test example of the present invention, the simulation time is set to 20s, and V max 21m / s, V min The speed is 6m / s, and the drone is set to a height of H d is 50m, set the airspeed V d for:

[0163]

[0164] Figure 5-Figure 10 The simulation results of sliding mode control of the composite wing UAV transition process are given by Figure 5 and Figure 6 It can be seen that the airspeed of the composite wing UAV has smaller overshoot, smaller tracking error and better control effect under the fractional order sliding mode controller. Figure 7 and Figure 8 It can be seen that the pitch angle tracking error is smaller and the control accuracy is higher under the fractional order sliding mode controller. Fig. 9 and Fig.10 It can be seen that during the transition process, the quadrotor altitude fractional-order sliding mode controller can better maintain altitude stability.

[0165] Fig.11 This is the control weight distribution diagram of the transition process of the composite wing UAV. It can be seen that during the simulation process, the airspeed weight control distribution strategy can be correctly executed, verifying the effectiveness of the strategy.

[0166] Based on the above simulation tests, the composite wing UAV transition process control method based on fractional-order sliding mode proposed in the present invention reduces control tracking error, improves the robustness of the composite wing UAV flight control system, and realizes smooth control of the transition process.

[0167] Although the present invention has been described in detail above by general description and specific embodiments, it is obvious to those skilled in the art that some modifications or improvements can be made to the present invention. Therefore, these modifications or improvements made without departing from the spirit of the present invention all belong to the scope of protection claimed by the present invention.

Claims

1. A transient process control method for composite wing UAV based on fractional order sliding mode, characterized in that: The transition process of the composite wing UAV is controlled based on sliding mode variable structure control, including: Step S-1: Integrate the rotor and fixed-wing dynamics of the composite-wing UAV during the transition process and derive the longitudinal nonlinear mathematical model of the composite-wing UAV; Step S-2: A new fractional-order reaching law is designed based on the traditional exponential power reaching law by combining the idea of ​​double power reaching law and the idea of ​​fractional-order calculus; Step S-3: Based on the novel fractional-order reaching law, a fractional-order sliding mode controller for the pitch angle, airspeed and quadrotor altitude during the transition process is constructed in the longitudinal nonlinear mathematical model of the composite-wing UAV, and a fixed-wing altitude controller is constructed as a pitch angle outer loop to jointly maintain altitude stability; Step S-4: Based on the pitch angle, airspeed and quadrotor altitude fractional sliding mode controller and the fixed-wing altitude controller, an airspeed weight control allocation strategy is designed to allocate the control quantity and solve the actuator output.

2. The transition process control method of composite wing UAV based on fractional order sliding mode according to claim 1 is characterized in that: In step S-2, the novel fractional-order reaching law is in the form of: Where: s is the sliding surface function, is the differential of the sliding surface function, ε>0, k i >0, i=1~3, 0<p<1, 1<q<2, α is the fractional calculus operator, The Riemann-Liouville fractional calculus is The general formula is defined as follows: Where: Γ(x) means that the Gamma function is the general formula of Γ(m-α), m-1<α<m, m is a constant, and the subsequent 0D t α The symbol is abbreviated as D α .

3. The transition process control method of composite wing UAV based on fractional order sliding mode according to claim 1 is characterized in that: Step S-3 includes the following sub-steps: Step S-3-1: Taking the pitch moment as the virtual control variable, construct a pitch angle fractional order sliding mode controller; Step S-3-2: Using the engine propeller thrust as the virtual control variable, construct an airspeed fractional order sliding mode controller; Step S-3-3: Use the quadrotor lift as the virtual control quantity to construct a quadrotor altitude fractional-order sliding mode controller, use the fixed-wing altitude controller as the attitude outer loop, and construct a fixed-wing altitude PID controller to jointly maintain the altitude stability of the composite wing UAV.

4. The transition process control method of composite wing UAV based on fractional order sliding mode according to claim 3 is characterized in that: In step S-3-1, the sliding mode surface function form of the pitch angle fractional-order sliding mode controller is: Where: s θ is the pitch angle sliding surface function, e θ =θ-θ d is the pitch angle tracking error, is the differential of the pitch angle tracking error, c θ >0 is the pitch angle sliding surface coefficient, k θ >0 is the pitch fractional coefficient, D η is the fractional calculus, η is the sliding surface fractional calculus operator; The control law of the pitch angle fractional-order sliding mode controller is: Where: U θ is the virtual control variable of the pitch angle fractional-order sliding mode controller, ε θ >0,k i >0, i=1~3 is the reaching law coefficient of the pitch angle fractional order sliding mode controller, To set the second-order differential of the pitch angle, I yy is the moment of inertia about the y-axis.

5. The transition process control method of composite wing UAV based on fractional order sliding mode according to claim 3 is characterized in that: In step S-3-2, the sliding mode surface function form of the airspeed fractional-order sliding mode controller is: s V =e V +λ V ∫e V dt+k V D η e V ,λ V >0,k V >0 Where: s V is the airspeed sliding surface function, e V =VV d is the airspeed tracking error, λ V >0 is the airspeed integral sliding surface coefficient, k V >0 is the airspeed calculus coefficient; The control law of the airspeed fractional-order sliding mode controller is: Where: U V is the virtual control variable of the airspeed fractional-order sliding mode controller, ε V >0,k i >0, i=4~6 is the reaching law coefficient of the airspeed fractional sliding mode controller, Φ=-gsinγ+(F rotor sinα-D) / m, is the airspeed differential, m is the mass, g is the acceleration due to gravity, γ is the track angle, α is the angle of attack, D is the drag, and F rotor It is the lift of the quadrotor.

6. The transition process control method of composite wing UAV based on fractional order sliding mode according to claim 3 is characterized in that: In step S-3-3, the sliding mode surface function of the quadrotor altitude fractional sliding mode controller is: Where: s H is the quadrotor altitude sliding surface function, e H =HH d is the height tracking error, is the height tracking error differential, c H >0 is the height sliding surface coefficient, k H >0 is the high calculus coefficient; The control law of the quadrotor altitude fractional-order sliding mode controller is: Where: U H is the virtual control variable of the quadrotor altitude fractional-order sliding mode controller, ε H >0,k i >0, i=7~9 is the reaching law coefficient of the quadrotor altitude fractional order sliding mode controller, To set the height second order differential; The fixed-wing altitude controller is in the form of: Where: k fHP , k fHI , k fHD are proportional, integral and differential coefficients respectively, θ d To set the pitch angle.

7. The transition process control method of composite wing UAV based on fractional order sliding mode according to claim 1 is characterized in that: Step S-4 includes the following sub-steps: Step S-4-1: Design the airspeed weight control allocation strategy to calculate the forces and moments of the fixed-wing system and the quadrotor system; Step S-4-2: According to the forces and moments of the fixed-wing system and the quadrotor system, the actuator outputs are solved, including the elevator deflection angle, the engine propeller speed and the quadrotor propeller speed.

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