A method for attitude control of a quadrotor aircraft in a strong gust interference environment on Mars

Abstract

The present invention discloses a method for attitude control of a quadrotor aircraft in a strong gust interference environment on Mars. An attitude dynamics model of the quadrotor aircraft is constructed and its inherent characteristics are analyzed. On this basis, a dual-loop anti-disturbance nonlinear controller is designed. External disturbances are compensated through expanded state observers of inner and outer loops, so that the quadrotor aircraft can accurately track a set desired attitude angle, thereby completing the attitude control of the quadrotor aircraft.

Description

Technical Field

[0001] The present invention belongs to the technical field of unmanned aerial vehicles and anti-disturbance control, and specifically relates to a method for controlling the attitude of a quadrotor aircraft in a strong interference environment of Martian gusts. Background Art

[0002] Multi-rotor UAVs are very flexible aircrafts. Due to their special advantages of hovering and vertical take-off and landing, they are widely used in military reconnaissance, agricultural surveying and mapping, aerial photography, etc. In the past few decades, how to effectively control UAVs has been a hot topic in industry and academia.

[0003] The current scientific goals of Mars exploration mainly include determining whether there is life on Mars, understanding the evolution and history of the Martian climate, and understanding the origin and evolution of Mars as a geological system. Even though humans have spent more than half a century exploring Mars and studying the universe, the current level of exploration is still far from a clear understanding of Mars exploration.

[0004] The harsh flight conditions and drastic flow field changes on the surface of Mars place high demands on the performance indicators of drones. In order to ensure that the Mars drone completes the Mars exploration mission, it is urgent to solve the technical problems of flight control and navigation of drones without GPS and system integration of drones. In the flight control of rotary-wing Mars drones, the thin Martian atmosphere will cause the amplitude of the change of the rotor lift of the drone with the rotor speed to be much smaller than the amplitude of the change in the earth environment, so the flight attitude adjustment process of the Mars drone will be very slow. However, phenomena such as Martian wind and dust storms will seriously affect the stability of the flight of the Mars drone, which requires the Mars drone to make rapid adjustments to environmental changes to ensure the flight safety of the drone. At present, the control of the rotary-wing Mars drone is mainly achieved by adjusting the relative position of the tip path plane (TPP) and the center of mass of the drone to achieve the steering control and attitude adjustment of the Mars drone.

[0005] In particular, quadrotors have attracted widespread attention from multiple industries due to their small size, simple mechanical design, and convenient flight operations. However, a quadrotor is a nonlinear system with strong coupling and underactuated characteristics. It has six degrees of freedom but only four control inputs. At the same time, due to its small size and weight, it is greatly affected by external disturbances such as gusts. Therefore, designing a reliable control strategy for the stable attitude of a quadrotor system is a challenging task. Summary of the invention

[0006] In view of this, the present invention provides a method for attitude control of a quadrotor aircraft in an environment with strong interference from Martian gusts, thereby realizing attitude control of a quadrotor aircraft in a simulated environment with strong interference from Martian gusts.

[0007] The present invention provides a method for controlling the attitude of a quadrotor aircraft in a strong gust interference environment on Mars, comprising the following steps:

[0008] Step 1: Establish the attitude dynamics model of the quadrotor aircraft;

[0009] Step 2: construct an outer loop controller and an inner loop controller, wherein the outer loop controller includes an outer loop nonlinear extended state observer and an outer loop nonlinear controller, and the inner loop controller includes an inner loop nonlinear extended state observer and an inner loop nonlinear controller;

[0010] Step 3: In actual control, the outer-loop nonlinear extended state observer takes the angular velocity expected value output by the outer-loop nonlinear controller and the angle feedback value output by the quadrotor as input, and calculates the output state estimate value The outer loop nonlinear controller directly inputs the desired angle, the angle output by the quadrotor, and the state estimate. As input, calculate the expected value of angular velocity v j As output; the inner loop nonlinear extended state observer takes the angular velocity feedback value output by the quadrotor aircraft and the control quantity output by the inner loop nonlinear controller as input, and calculates the output state estimate The inner loop linear controller is based on the angular velocity expected value output by the outer loop controller, the angular velocity feedback value output by the quadrotor aircraft, and the state estimation value output by the inner loop nonlinear extended state observer. As input, the control quantity u of the quadrotor aircraft is calculated as the output i ; The control quantity u i The input is then fed into the attitude dynamics model of the quadrotor to realize the control of the quadrotor.

[0011] Furthermore, the outer loop nonlinear extended state observer in step 2 is constructed as follows:

[0012]

[0013] Among them, y 1 =η=[φ,θ,ψ] T =[y 1j ] 3×1 ∈R 3×1 ,j=φ,θ,ψandy 2 =[y 2j ] 3×1 ∈R 3×1, j = φ, θ, ψ represent the external disturbance values, φ is the pitch angle of the quadrotor, θ is the roll angle of the quadrotor, and ψ is the yaw angle of the quadrotor. and Respectively represent y 1 and 2 The corresponding state estimate, v j represents the output value of the outer loop nonlinear controller, is the estimated value of the state The first-order derivative of is the estimated value of the state The first-order derivative value, β 1j and ε 1j are all positive adjustable constants, It is a nonlinear function and its expression is:

[0014]

[0015] Where σ is a positive adjustable constant.

[0016] Furthermore, the outer loop nonlinear controller is constructed as follows:

[0017]

[0018] Among them, e η =η-η d =[e ηj ] 3×1 ∈R 3×1 ,j=φ,θ,ψ are the error values ​​of pitch angle, roll angle and yaw angle; k 0j ,k 1j ,k 2j All are normal numbers; is an adjustable positive constant; v j is the expected value of the angular velocity output by the outer loop nonlinear controller.

[0019] Furthermore, the inner loop nonlinear extended state observer is constructed as follows:

[0020]

[0021] Among them, α 1i , α 2i and ε 0i are all non-negative constants, is a nonlinear function, and x 1i and x 2i The estimated values ​​of the two states, b iis the inverse of the moment of inertia of each channel, and p, q, and r are the angular velocities of the quadrotor in the body coordinate system.

[0022] Furthermore, the inner loop nonlinear controller is constructed as follows:

[0023]

[0024] Among them, e Ω =ω-ω r =[e ωi ] 3×1 ∈R 3×1 is the error value of the angular velocity of the three channels, k pi ,k di ,k Ni are positive constants of proportional term, differential term and nonlinear term respectively, is the inverse of the moment of inertia of each channel, is a non-linear function.

[0025] Beneficial effects:

[0026] The present invention constructs an attitude dynamics model of a quadrotor aircraft, analyzes its inherent characteristics, and designs a dual-loop anti-disturbance nonlinear controller on this basis. Through the expanded state observers of the inner and outer loops, external disturbances are compensated, and the quadrotor aircraft can accurately track the set desired attitude angle, thereby completing the control of the quadrotor aircraft's attitude. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A control schematic diagram of a method for controlling the attitude of a quadrotor aircraft in a strong gust interference environment on Mars provided by the present invention. DETAILED DESCRIPTION

[0028] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0029] Active disturbance rejection control technology has the ability to handle a wide range of problems such as unknown dynamics within the system and external disturbances, and has become an emerging technology in control engineering. The active disturbance rejection controller consists of a tracking differentiator, an extended state observer, and a nonlinear control law. Among them, the extended state observer is the most important part of the entire controller, which estimates the state of the system through the output of the system. Therefore, in the case of strong gust interference simulating Mars, applying active disturbance rejection control technology to the quadcopter attitude system will help resist the influence of external uncertain interference on the flight effect of the quadcopter, thereby achieving stable flight of the drone.

[0030] Based on the above considerations, the present invention provides an attitude control method for a quadrotor aircraft in a strong interference environment of Martian gusts, the core idea of ​​which is: first, the desired attitude angle is input into the quadrotor aircraft, and then the errors of the three attitude angles are controlled and calculated respectively through the outer loop angle controller, and the disturbance of the angle is compensated through the outer loop nonlinear expanded state observer, so as to solve the desired angular velocity; further, the obtained desired angular velocity and the angular velocity feedback value obtained from the system are input into the inner loop angular velocity controller, the angular velocity of the aircraft is controlled by the inner loop anti-disturbance controller, and the disturbance of the angle is compensated by the inner loop nonlinear expanded state observer, so as to obtain three torque forces that need to be input into the aircraft, and the pitch angle, roll angle and yaw angle of the aircraft system are controlled respectively through the torques of the three channels, and the obtained output values ​​are fed back to the controller, so as to realize closed-loop attitude control of the entire aircraft system.

[0031] It can be seen that, unlike the prior art which only uses the anti-disturbance rejection control algorithm in the inner loop of the aircraft attitude control, the present invention adds an outer loop anti-disturbance rejection controller and an outer loop nonlinear state observer to cope with the situation of strong gusts and strong interference under the background of Mars.

[0032] The present invention provides a method for controlling the attitude of a quadrotor aircraft in a strong gust interference environment on Mars. Figure 1 As shown, the specific steps include:

[0033] Step 1: Establish the attitude dynamics model of the quadrotor.

[0034] The existing quadrotor attitude dynamics model is adopted, and the model is expressed as follows:

[0035]

[0036]

[0037] Where ω=[p,q,r] T ∈R 3 is the angular velocity of the aircraft in the body coordinate system, η=[φ,θ,ψ] T ∈R 3 is the Euler angle of the aircraft in the inertial coordinate system, φ is the pitch angle of the aircraft, θ is the roll angle of the aircraft, and ψ is the yaw angle of the aircraft, W -1 The rotation matrix is ​​as follows:

[0038]

[0039] τ is the input (torque) of the aircraft as follows:

[0040]

[0041] Among them, k 1 is the thrust factor, k 2 is the tension factor, ω i is the angular velocity of the i-th motor, i is a positive integer, l 1 and l 2 Represent the distance from the rotor to the x and y axes respectively.

[0042] Step 2: construct an outer loop controller and an inner loop controller, wherein the outer loop controller includes an outer loop nonlinear extended state observer and an outer loop nonlinear controller, and the inner loop controller includes an inner loop nonlinear extended state observer and an inner loop nonlinear controller.

[0043] Different from the existing linear state observer, the present invention adds nonlinear terms to the calculation of the two state estimates on the basis of linearity, and achieves better anti-disturbance effect by adjusting the parameter σ of the nonlinear function. The outer loop nonlinear extended state observer constructed by the present invention is constructed as follows:

[0044]

[0045] Among them, y 1 =η=[φ,θ,ψ] T =[y 1j ] 3×1 ∈R 3×1 ,j=φ,θ,ψandy 2 =[y 2j ] 3×1 ∈R 3×1 ,j=φ,θ,ψ represent the external disturbance values ​​respectively, and Respectively represent y 1 and 2 The corresponding state estimate, v j represents the output value of the outer loop controller, is the estimated value of the state The first-order derivative of is the estimated value of the state The first-order derivative value, β 1j and ε 1j are all positive adjustable constants, It is a nonlinear function and its expression is:

[0046]

[0047] Among them, σ is a positive adjustable constant. By adjusting the value of σ, the tracking effect of the entire system on the desired attitude angle can be improved.

[0048] Different from the existing linear anti-disturbance controller, the outer loop controller further adds a nonlinear control law on the basis of the linear PI controller and the state feedback quantity in order to make the error value tend to 0 within a limited time. At the same time, the PI control rate and the nonlinear control rate complement each other. On the one hand, it has a good anti-disturbance effect, and on the other hand, it accelerates convergence. The outer loop nonlinear controller constructed by the present invention is constructed as follows:

[0049]

[0050] Among them, e η =η-η d =[e ηj ] 3×1 ∈R 3×1 ,j=φ,θ,ψ, represents the error value of pitch angle, roll angle and yaw angle; k 0j ,k 1j ,k 2j is a positive constant; is an adjustable positive constant; v j is the output of the outer loop nonlinear controller, that is, the expected value of the angular velocity, and also the input value of the inner loop controller.

[0051] In addition, the attitude dynamics model of the quadrotor can also be expressed as follows:

[0052]

[0053] It is further transformed into the state space expression:

[0054]

[0055]

[0056] Among them, x 1 (t) = ω, x 2 (t) = f(t), and is bounded.

[0057] On this basis, the present invention makes the following improvements to the representation method of the three channels, and represents the posture dynamics model as follows:

[0058]

[0059] On this basis, the inner loop nonlinear extended state observer constructed by the present invention is constructed as follows:

[0060]

[0061] Among them, α 1i , α 2i and ε0i are all non-negative constants, is a nonlinear function, and x 1i and x 2i The estimated values ​​of the two states, b i is the inverse of the moment of inertia of each channel. It is input into the inner loop nonlinear controller as the inner loop disturbance compensation term.

[0062] The inner loop nonlinear controller constructed by the present invention adds a nonlinear term with a nonlinear function as the control rate on the basis of the PI control law and the state feedback quantity, so that the controller has better adaptability and robustness, wherein the control rate is expressed as follows:

[0063]

[0064] Among them, e Ω =ω-ω r =[e ωi ] 3×1 ∈R 3×1 is the error value of the angular velocity of the three channels, k pi ,k di ,k Ni are positive constants of proportional term, differential term and nonlinear term respectively, is the inverse of the moment of inertia of each channel, u i is the control quantity of the quadrotor aircraft.

[0065] Step 3: In actual control, the outer-loop nonlinear extended state observer takes the expected angular velocity value output by the outer-loop nonlinear controller and the angle feedback value output by the quadrotor as input, and calculates the output state estimate value The outer loop nonlinear controller directly inputs the desired angle, the angle output by the quadrotor, and the state estimate. As input, calculate the expected value v of the output angular velocity i The inner loop nonlinear extended state observer takes the angular velocity feedback value output by the quadrotor and the angular acceleration value output by the inner loop nonlinear controller as input, and calculates the output state estimate value The inner loop linear controller is based on the angular velocity expected value output by the outer loop controller, the angular velocity feedback value output by the quadrotor aircraft, and the state estimation value output by the inner loop nonlinear extended state observer. As input, the control quantity u of the quadrotor aircraft is calculated as the output i ; The control quantity u i The input is then fed into the attitude dynamics model of the quadrotor to realize the control of the quadrotor.

[0066] Among them, in actual control, the quadrotor aircraft is equivalent to an aircraft attitude dynamics system.

[0067] In the above-mentioned aircraft architecture, under the control of the inner and outer loops, compared with the general anti-disturbance rejection controller, the dual-loop anti-disturbance rejection controller in the present invention can make the aircraft have better anti-disturbance capability, and can also make the error value converge more quickly, so that the aircraft system can quickly and accurately reach the desired attitude angle, and realize effective attitude control of the aircraft in a strong interference environment.

[0068] In summary, the above are only preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for attitude control of a quadrotor aircraft in a strong gust interference environment on Mars, characterized in that: The following steps are involved: Step 1: Establish the attitude dynamics model of the quadrotor aircraft; Step 2: construct an outer loop controller and an inner loop controller, wherein the outer loop controller includes an outer loop nonlinear extended state observer and an outer loop nonlinear controller, and the inner loop controller includes an inner loop nonlinear extended state observer and an inner loop nonlinear controller; Step 3: In actual control, the outer-loop nonlinear extended state observer takes the angular velocity expected value output by the outer-loop nonlinear controller and the angle feedback value output by the quadrotor as input, and calculates the output state estimate value The outer loop nonlinear controller uses the desired angle directly input, the angle feedback value output by the quadrotor aircraft, and the state estimation value As input, calculate the expected value of angular velocity v j As output; the inner loop nonlinear extended state observer takes the angular velocity feedback value output by the quadrotor aircraft and the control quantity output by the inner loop nonlinear controller as input, and calculates the output state estimate The inner loop nonlinear controller is based on the angular velocity expected value output by the outer loop controller, the angular velocity feedback value output by the quadrotor aircraft, and the state estimation value output by the inner loop nonlinear extended state observer. As input, the control quantity u of the quadrotor aircraft is calculated as the output i ; The control quantity u i Input into the attitude dynamics model of the quadrotor to realize the control of the quadrotor; The construction form of the outer loop nonlinear extended state observer in step 2 is as follows: Where y1 = η = [φ, θ, ψ] T =[y 1j ] 3×1 ∈R 3×1 ,j=φ,θ,ψ and y2=[y 2j ] 3×1 ∈R 3×1 , j = φ, θ, ψ represent the external disturbance values, φ is the pitch angle of the quadrotor, θ is the roll angle of the quadrotor, and ψ is the yaw angle of the quadrotor. and Respectively represent the state estimates corresponding to y1 and y2, v j is the expected value of the angular velocity output by the outer loop nonlinear controller, is the estimated value of the state The first-order derivative of is the estimated value of the state The first-order derivative value, β 1j and ε 1j are all positive adjustable constants, It is a nonlinear function and its expression is: Where σ is a positive adjustable constant.

2. The posture control method according to claim 1, characterized in that: The outer loop nonlinear controller is constructed as follows: Among them, e η =η-η d =[e ηj ] 3×1 ∈R 3×1 ,j=φ,θ,ψ are the error values ​​of pitch angle, roll angle and yaw angle; k 0j ,k 1j ,k 2j All are normal numbers; is an adjustable positive constant; v j is the expected value of the angular velocity output by the outer loop nonlinear controller.

3. The posture control method according to claim 1, characterized in that: The construction form of the inner loop nonlinear extended state observer is as follows: Among them, α 1i , α 2i and ε 0i are all non-negative constants, is a nonlinear function, and x 1i and x 2i The estimated values ​​of the two states, b i is the inverse of the moment of inertia of each channel, and p, q, and r are the angular velocities of the quadrotor in the body coordinate system.

4. The posture control method according to claim 1, characterized in that: The construction form of the inner loop nonlinear controller is as follows: Among them, e ω =ω-ω r =[e ωi ] 3×1 ∈R 3×1 is the error value of the angular velocity of the three channels, k pi ,k di ,k Ni are positive constants of proportional term, differential term and nonlinear term respectively, is the inverse of the moment of inertia of each channel, is a nonlinear function.

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