An anti-interference control strategy for advanced configuration unmanned aerial vehicle based on fractional order sliding mode

Abstract

The application discloses an advanced layout shipborne unmanned aerial vehicle anti-interference finite time attitude control strategy based on a finite time high-order sliding mode observer and a fractional calculus nonsingular terminal sliding surface, and belongs to the field of calculation, reckoning or counting. The application is aimed at the comprehensive characteristics of an advanced layout shipborne unmanned aerial vehicle, such as strong coupling, nonlinearity and susceptibility to external environmental interference, and the shipborne aerial vehicle is prone to be disturbed by the ship stern flow during landing and is difficult to realize landing in a predicted attitude, so an interference estimation method based on a high-order sliding mode finite time observer and a finite time attitude controller based on an adaptive fractional calculus integral nonsingular terminal sliding surface are provided, the interference encountered by the shipborne aerial vehicle is effectively estimated and compensated, and fast attitude control with strong robustness and high control precision is realized.

Description

Technical Field

[0001] This invention discloses an advanced finite-time anti-interference attitude control strategy for shipborne unmanned aerial vehicles, specifically an anti-interference control method based on an observer and fractional sliding mode, belonging to the technical field of calculation, estimation, or counting. Background Technology

[0002] Modern warfare is characterized by comprehensive, multi-layered, and wide-ranging coordinated operations. Aircraft carrier battle groups, primarily composed of aircraft carriers and carrier-based aircraft, combine the advantages of large warships' ability to navigate long distances at sea and the flexible takeoff of fighter jets. They are crucial for protecting maritime routes, ensuring troop transport and mission execution, maintaining regional military superiority, conducting large-scale air and sea battles, and safeguarding national maritime rights. Carrier-based unmanned aerial vehicles (UAVs) have excelled in naval warfare, performing numerous tasks such as reconnaissance and early warning, target identification, and electronic warfare. They possess advantages such as low cost, no personnel casualties, and suitability for performing dangerous missions in various environments. Their combat effectiveness has been proven in numerous wars, and they have become a key piece of equipment for military development worldwide. Compared to conventional UAVs composed of wings, fuselages, and tail sections, advanced carrier-based UAVs eliminate horizontal and vertical stabilizers. The smoothly connected fuselage and wings have no clear boundaries, resulting in a clean, integrated wing design. This gives flying-wing aircraft unique advantages in aerodynamic efficiency, endurance, stealth performance, and payload distribution, making it an ideal configuration for long-range, long-endurance aircraft.

[0003] While advanced layout carrier-based UAVs offer the aforementioned advantages, their structure also presents several challenges for flight control. First, the blended wing-body design of advanced layout carrier-based UAVs results in inherent instability, exhibiting weak longitudinal stability. Furthermore, roll and yaw maneuvers lead to low longitudinal operational efficiency and strong lateral motion coupling. Second, the elimination of horizontal and vertical stabilizers may result in static instability in the heading direction. In addition, the six-degree-of-freedom dynamic equations of advanced layout carrier-based UAVs constitute a complex set of nonlinear equations. Their aerodynamic characteristics exhibit strong nonlinearities with altitude, airspeed, and attitude, and the parameters between different channels are interconnected, making the UAV dynamic equations nonlinear, rapidly time-varying, strongly coupled, and multi-input multi-output (MIMO) characteristics. Moreover, advanced layout carrier-based UAVs are primarily used for subsonic high-altitude reconnaissance, transport, or bombing missions, requiring extremely high accuracy in trajectory and attitude control. Decoupling based on a small disturbance assumption and designing a controller using a linearized model is insufficient to achieve ideal control performance under conditions of inaccurate model parameters and external disturbances.

[0004] The landing phase of a drone is one of the most dangerous phases. Firstly, the takeoff deck of even the largest aircraft carriers is much shorter than a land-based runway, severely limiting ground conditions for landing. When advanced carrier-based drones fly near the ground, the ground effect alters their lift, drag, and longitudinal moment. The ground effect indirectly changes the drone's lateral aerodynamic characteristics, affecting their overall lateral aerodynamic performance. Furthermore, when an aircraft carrier is at sea, wave motion causes deck movement, resulting in drift in the target landing position. Complex air turbulence at sea and the carrier's stern airflow also pose serious threats to drone landing safety. Therefore, rapid and effective anti-interference methods are crucial for protecting drones from external environmental interference. However, for advanced carrier-based drone model systems with multi-control surfaces exhibiting nonlinearity, strong coupling, and uncertainty, in addition to anti-interference measures, a high-precision, low-overshoot, and fast-convergence attitude controller is also required.

[0005] Aircraft control methods have evolved to encompass two main categories: linear control methods, including PID control, pole placement methods, linear quadratic optimal control (LQR), traditional H∞ robust control, and μ-synthetic control; and nonlinear control methods, including feedback linearization, backstepping control, and sliding mode control. Linear control is simple in structure, reliable in operation, and easy to adjust. However, for highly nonlinear, strongly coupled, and highly uncertain aircraft systems, when operating conditions change due to external disturbances or uncertainties in model parameters, traditional linear control methods struggle to achieve the desired control performance. Furthermore, finite-time convergence is also a performance requirement for UAV control, as the time-varying nature of the controlled object necessitates the closed-loop system reaching the desired state within a finite time. Currently, research on finite-time control algorithms for aircraft is still in its early stages, with relatively few mature control results. While related nonlinear control methods can guarantee strictly finite-time convergence, the resulting nonlinear control laws often contain multiple nonlinear terms (such as exponential, power, and sign functions) and many parameters, increasing the design complexity of the control laws. Under the constraints of the above-mentioned realities, achieving the speed, accuracy, and robustness of the aircraft attitude control system within a limited timeframe will have significant practical implications and application value.

[0006] To address the structural characteristics of advanced multi-operation-face shipborne unmanned aerial vehicles (UAVs) with rudder surface coupling, high nonlinearity, and weak stability, fractional-order calculus is introduced to construct sliding mode surfaces. Compared to traditional sliding mode control methods, fractional-order integral sliding mode surfaces offer better control performance. The definition of fractional-order integrals allows for a certain "memory property" in integrating a quantity, effectively reducing overshoot and improving control accuracy during control. Therefore, fast, stable, and high-precision finite-time attitude control of advanced-layout UAVs can be achieved. A finite-time disturbance observer is designed to estimate the external disturbance airflow encountered by the UAV during landing. The estimated value is then used for disturbance compensation in the controller, enhancing the controller's robustness, i.e., its ability to cope with external disturbances. The disturbance estimation error of this observer can also converge within a finite time.

[0007] Therefore, the present invention aims to provide an advanced anti-interference control strategy for unmanned aerial vehicles (UAVs) based on fractional sliding mode, which takes into account the structural characteristics and control surface coupling of UAVs with multiple operating surfaces, and estimates and compensates for external interference. Summary of the Invention

[0008] The purpose of this invention is to address the shortcomings of the aforementioned background technology by proposing an anti-interference finite-time attitude control strategy. This method, designed for advanced layout shipborne UAVs, uses fractional integral and adaptive gain to design an adaptive fractional integral non-singular terminal sliding mode control law to achieve high-precision tracking control within a finite time. Based on a finite-time disturbance observer, it estimates the external disturbances that may be encountered during landing, ensuring the robustness of the tracking process.

[0009] To achieve the above-mentioned objectives, the present invention employs the following technical solution:

[0010] An affine nonlinear mathematical model was established for a multi-control-surface advanced layout carrier-based UAV—a flying-wing UAV. Based on the time-scale separation principle, the attitude control state variables were divided into inner and outer loops according to their rate of change. A fixed-time interference observer was designed to perform online estimation of external interference, mainly the aircraft carrier wake, and to obtain the estimated value of external interference within a pre-set estimation time.

[0011] Based on the concept of fractional calculus, the integral sliding surface is extended to the fractional order. By combining the tracking errors of the inner and outer loops, a fractional integral non-singular terminal sliding surface is constructed, and the equivalent control law is derived. An adaptive double power fast approach law is designed to obtain the switching control law, thereby deriving the complete fractional integral non-singular terminal sliding surface control law. Then, the estimated value of external disturbance is compensated to achieve anti-disturbance control.

[0012] The affine nonlinear mathematical model of the flying-wing UAV system is: ,in, For a relatively slow-changing state vector of an affine nonlinear dynamic system, For an affine nonlinear dynamic system, the state vector changes relatively rapidly. These are the three attitude angles of the UAV: ​​angle of attack, sideslip angle, and roll angle. These are the three angular velocity components corresponding to the attitude angle in the body coordinate system. It is the wake interference that acts on the angle of attack and sideslip angle. These are the state functions and control functions for the outer loop and inner loop, respectively.

[0013] In mathematical models These are indirect control quantities, including three control torques. The specific expression is as follows:

[0014]

[0015] in For the unfolded area of ​​the flying wing For air density, Scalar airspeed, Wingspan length For the chord length, To control the torque coefficient, the control torque coefficient is as follows:

[0016]

[0017]

[0018] in, For the deflection of the control surface, These are the left and right elevons, respectively. These are the left and right side drag rudders, respectively. The first Roll and pitch control torque coefficients of each control surface These are the three-channel control torque coefficients, which are the cross-coupled third elevators on the left and right sides and the drag rudder on the same side.

[0019] Inner loop for attitude angle control with external wake interference The design of a high-order sliding mode fixed-time disturbance observer is as follows:

[0020]

[0021] in ,parameter satisfy and For two sufficiently small positive numbers Observer gain Requires satisfying the matrix , If it is Hurwitz stable, then the variables in the observer They are External interference and its infinitesimal components The estimated value.

[0022] Interference estimation error By performing a differential operation, we can obtain:

[0023]

[0024] The disturbance error can converge to a very small neighborhood around the equilibrium point in a finite time, and the convergence time will be as follows:

[0025] in , It is a positive number, a symmetric matrix. and satisfy , and These represent the maximum and minimum values ​​among the eigenvalues ​​of the matrix, respectively.

[0026] According to the definition of fractional calculus of the Caputo type:

[0027] Defined as from arrive For a function of Fractional calculus of order, where , satisfy Represents the order, This refers to the Gamma function with the following definition.

[0028]

[0029] Applying the definition of Caputo fractional calculus to the sliding mode surface construction, taking the inner loop as an example, the inner and outer loop tracking errors are first defined as follows: Design a fractional integral nonsingular terminal sliding surface:

[0030]

[0031] in , and They are two positive definite diagonal matrices. , Fractional order satisfies , satisfy For tracking error and and scalar , express in The function that represents positive and negative signs.

[0032] Differentiating the sliding surface yields

[0033] The sliding mode control law consists of two parts: Through solution Obtain the equivalent control quantity .

[0034] To achieve rapid system convergence and enhance controller tracking performance during chattering, this project employs a novel double-power-law approaching law combined with an adaptive law algorithm when the state variables are far from the sliding surface.

[0035]

[0036] in , and , and It is a positive definite diagonal matrix. This represents the adaptive time-varying approach law, from which the switching control law is derived:

[0037]

[0038] Based on the concept of sliding mode control law, the complete adaptive fractional-order nonsingular terminal sliding mode control law is obtained:

[0039]

[0040] The outer-loop control law is derived through a similar derivation, and combined with the disturbance estimation value mentioned above, the outer-loop adaptive fractional-order non-singular terminal sliding mode anti-disturbance control law is obtained:

[0041]

[0042] The present invention, by adopting the above technical solution, has the following beneficial effects:

[0043] (1) This invention designs an interference estimation method based on a fixed-time interference observer to estimate the external wake interference encountered by advanced multi-control surface layout shipborne UAVs during landing online, providing interference information for the subsequent controller's anti-interference. The observer has a fast observation speed and high estimation accuracy, and can realize the reconstruction and estimation of interference within a limited time.

[0044] (2) This invention utilizes the integral memory function of fractional calculus to extend and improve the original integer integral, designing a fractional integral non-singular terminal sliding surface. The resulting equivalent control law can significantly reduce overshoot during convergence. Combined with an adaptive double power-law approach, it improves the convergence speed of tracking error and reduces chattering and overshoot. It has high applicability and effectiveness for attitude control of advanced layout shipborne UAVs that are strongly coupled, highly nonlinear, and susceptible to external interference. Attached Figure Description

[0045] Figure 1 This is an architecture diagram of the advanced layout of the fractional-order nonsingular terminal sliding mode anti-interference control for shipborne unmanned aerial vehicles according to the present invention.

[0046] Figure 2 This is a graph showing the external ship wake interference and interference estimation based on a fixed-time observer, as presented in this invention.

[0047] Figure 3 The graph shows the fractional integral nonsingular terminal sliding mode control curve of the present invention under the presence of external disturbances.

[0048] Figure 4 The curve represents the anti-interference finite-time control strategy curve of the advanced layout UAV based on observer and fractional sliding mode of the present invention. Detailed Implementation

[0049] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to the accompanying drawings.

[0050] This invention proposes an anti-interference sliding mode control method for advanced layout shipborne unmanned aerial vehicles (UAVs) to solve the problem of anti-interference and fast attitude tracking control during landing of aircraft with multiple coupled, highly nonlinear, and easily disturbed operating surfaces. The method includes the following five steps.

[0051] Step 1: Establish an affine nonlinear mathematical model for the flying-wing UAV. Based on the time-scale separation principle, divide the control quantity into inner and outer control loops. The mathematical model of the flying-wing UAV affine nonlinear system is expressed as follows:

[0052]

[0053] in, For a relatively slow-changing state vector of an affine nonlinear dynamic system, For an affine nonlinear dynamic system, the state vector changes relatively rapidly. These are the three attitude angles of the UAV: ​​angle of attack, sideslip angle, and roll angle. These are the three angular velocity components corresponding to the attitude angle in the body coordinate system. It is the wake interference that acts on the angle of attack and sideslip angle. These are the state functions and control functions for the outer loop and inner loop, respectively. In the mathematical model... These are indirect control quantities, including three control torques. The specific expression is as follows:

[0054]

[0055] in For the unfolded area of ​​the flying wing For air density, Scalar airspeed, Wingspan length For the chord length, To control the torque coefficient.

[0056] Step 2: Considering the effects of control surface deflection nonlinearity and cross-coupling nonlinearity, the nonlinear dynamic efficiency model of the control surface is fitted as follows:

[0057]

[0058] in, For the deflection of the control surface, These are the left and right elevons, respectively. These are the left and right side drag rudders, respectively. The first Roll and pitch control torque coefficients of each control surface These are the three-channel control torque coefficients, which are the cross-coupled third elevators on the left and right sides and the drag rudder on the same side.

[0059] Step 3: Inner loop for attitude angle control with external wake interference. The design of a high-order sliding mode fixed-time disturbance observer is as follows:

[0060]

[0061] in ,parameter satisfy and For two sufficiently small positive numbers Observer gain Requires satisfying the matrix , If it is Hurwitz stable, then the variables in the observer They are External interference and its infinitesimal components The estimated value.

[0062] Interference estimation error It can converge to a very small neighborhood around the equilibrium point in a finite amount of time. Convergence time:

[0063] in , It is a positive number, a symmetric matrix. and satisfy , and These represent the maximum and minimum values ​​among the eigenvalues ​​of the matrix, respectively.

[0064] Step 4: Applying the definition of Caputo fractional calculus to the construction of a sliding surface, and taking an inner loop as an example, design a non-singular terminal sliding surface for fractional integrals:

[0065]

[0066] in , and They are two positive definite diagonal matrices. , Fractional order satisfies , satisfy For tracking errors in inner and outer loops and and scalar , express ( ) in This represents a function indicating positive and negative signs. It is solved... Obtain the equivalent control quantity

[0067] Step 5: Propose a novel double-power-order reaching law that combines an adaptive law algorithm.

[0068]

[0069] in , and , and It is a positive definite diagonal matrix. This represents the adaptive time-varying approach law, from which the switching control law is derived:

[0070]

[0071] Based on the concept of sliding mode control law, the complete adaptive fractional-order nonsingular terminal sliding mode control law is obtained:

[0072]

[0073] Step 6: Combining the disturbance estimation values ​​from the previous section, obtain the adaptive fractional-order nonsingular terminal sliding mode anti-disturbance control law for the outer loop:

[0074]

[0075] This invention simulates anti-interference attitude control for a flying-wing UAV. The simulation establishes a fixed-time disturbance observer based on high-order sliding mode and an adaptive fractional-order non-singular terminal sliding mode controller based on fractional calculus and adaptive reaching law. The simulation process is carried out in MATLAB. Figure 2 This demonstrates that the fixed-time observer designed in this invention can estimate external ship wake interference in a timely and effective manner; Figure 3 The fractional-order nonsingular terminal sliding mode controller of the present invention has certain robust attitude tracking control performance. Figure 4 The anti-interference control strategy of the present invention has a good anti-interference robust attitude tracking control effect.

Claims

1. An advanced layout UAV anti-interference control strategy based on fractional sliding mode, characterized in that, Force and torque analysis were performed on a class of advanced shipborne UAVs—flying wing UAVs—and an affine nonlinear model of the UAV was established. The attitude control state variables were divided into inner and outer loops. The wake interference of the aircraft carrier was considered as the main external interference encountered by the UAV in the working environment and a mathematical model was established. A finite fixed interference observer with high-order sliding mode was designed and constructed to observe the wake interference and obtain its estimated value. The time taken for the observation process can also be estimated. By applying the principles of fractional calculus to the design of sliding surfaces, a fractional integral non-singular terminal sliding surface is constructed. Based on the concept of sliding mode control, an equivalent control law is obtained. Then, an adaptive algorithm is applied to the design of the approach law, and an adaptive double power approach law is proposed to obtain the switching control law. Thus, a complete adaptive fractional integral non-singular terminal sliding mode control law is obtained, which realizes fast convergence, small overshoot, and high precision attitude control of flying wing UAVs. Combined with the obtained wake interference estimation value, robust anti-interference control is achieved. The affine nonlinear mathematical model of the flying wing UAV is as follows: ,in For an affine nonlinear dynamic system, the state vector changes relatively rapidly. To simulate a state vector that changes relatively quickly. These are the three attitude angles of the UAV: ​​angle of attack, sideslip angle, and roll angle. These are the three angular velocity components corresponding to the attitude angles in the body coordinate system. These are the state functions and control functions for the outer loop and the inner loop, respectively; Applying the principles of fractional calculus to sliding surface design, specifically: taking the control inner loop as an example, and combining the tracking errors of the inner and outer loops, a fractional integral nonsingular terminal sliding surface is designed: ,in , and They are two positive definite diagonal matrices of fractional order. , satisfy , satisfy For tracking error and and scalar , express in The function representing positive and negative signs is solved by... Obtain the equivalent control quantity , Design an adaptive double power-law approach law: ,in , , and It is a positive definite diagonal matrix. This represents the adaptive time-varying approach law, from which the switching control law is derived: .

2. The advanced layout UAV anti-interference control strategy based on fractional sliding mode according to claim 1, characterized in that, In mathematical models These are indirect control quantities, including three control torques. The specific expression is as follows: ,in For the unfolded area of ​​the flying wing For air density, Scalar airspeed, Wingspan length For the chord length, To control the torque coefficient, the control torque coefficient is as follows: in and These are the deflection values ​​of the eight control surfaces. As an allocation coefficient These are the three-channel control torque coefficients, which are the cross-coupled third elevators on the left and right sides and the drag rudder on the same side.

3. The advanced layout UAV anti-interference control strategy based on fractional sliding mode according to claim 2, characterized in that, Design a fixed-time disturbance observer that employs a higher-order sliding mode: ,in ,parameter satisfy and For two sufficiently small positive numbers Observer gain Requires satisfying the matrix , If it is Hurwitz stable, then the variables in the observer They are External interference and its infinitesimal components The estimated value.

4. The advanced layout UAV anti-interference control strategy based on fractional sliding mode according to claim 3, characterized in that, Interference estimation error It can converge to a very small neighborhood around the equilibrium point in a finite amount of time, and the convergence time will be as follows: ,in , It is a positive number, a symmetric matrix. and satisfy , and Represent matrices respectively The maximum and minimum values ​​among the eigenvalues.

5. The advanced layout UAV anti-interference control strategy based on fractional sliding mode according to claim 4, characterized in that, Based on the concept of sliding mode control law, the complete adaptive fractional-order nonsingular terminal sliding mode control law is obtained: Through similar derivation, the outer-loop control law is obtained, and combined with the disturbance estimation value in claim 4, an adaptive fractional-order non-singular terminal sliding mode anti-disturbance control law is derived. 。

Images