A method for disturbance observation and fixed-point control of rotary-wing unmanned aerial vehicles

Abstract

This invention relates to the field of rotorcraft unmanned aerial vehicle (UAV) control, specifically a method for disturbance observation and fixed-point control of a rotorcraft UAV. The method includes setting up a position loop linear expansion state observer to observe the disturbance forces acting on the UAV and feeding the observation results back to the control loop; setting up a position loop sliding mode controller and an acceleration limiting module; and outputting the desired lift based on the deviation between the UAV's position, velocity, and desired values. This invention enables a rotorcraft UAV to adjust its lift under bounded disturbances, thereby overcoming the disturbance effect to a certain extent and allowing its trajectory to fit the desired path.

Description

Technical Field

[0001] This invention relates to the field of rotary-wing unmanned aerial vehicles (UAVs), and more particularly to a method for disturbance observation and fixed-point control of rotary-wing UAVs. Background Technology

[0002] As a type of autonomous robot, unmanned aerial vehicles (UAVs) offer a wide range of advantages, including good spatial accessibility, ease of operation, and high maneuverability. Rotary-wing UAVs, in particular, have developed rapidly over the past decade. As an excellent platform, they can integrate various payloads to achieve different mission objectives. However, the complexity of UAV operating scenarios varies. In some special environments, UAVs are subject to frequent disturbances, and the mission objectives place high demands on payload control. For example, UAVs carrying observation payloads require consistent and continuous imagery. In such cases, ensuring that the payload operates under optimal conditions is a problem that needs to be addressed.

[0003] To address the aforementioned issues, one approach is to equip the payload with support mechanisms such as gimbals. This method offers good compensation for flight trajectories with bounded deviations, enabling the payload to operate at a fixed point through the adjustment of the support mechanisms. However, this approach has several drawbacks: the additional integrated mechanisms increase the complexity of the system and reduce its reliability; the additional mechanisms also increase costs accordingly; moreover, the adjustment function of the support mechanisms is limited, and if the trajectory deviation is too large, the operational objective cannot be achieved. Summary of the Invention

[0004] This invention proposes a method for disturbance observation and fixed-point control of a rotary-wing unmanned aerial vehicle (UAV). This method can observe the disturbance acceleration experienced by the UAV during flight and compensate for it, thereby enabling fixed-point control of the rotary-wing UAV.

[0005] The technical solution adopted by this invention to achieve the above objectives is: a method for disturbance observation and fixed-point control of a rotary-wing unmanned aerial vehicle (UAV). In the position control loop of the UAV, a linear extended state observer is set up to observe the acceleration of disturbances experienced by the UAV during flight, and feeds this information back to the sliding mode controller and acceleration limiting module to compensate for the disturbances. The method outputs lift to achieve fixed-point control of the rotary-wing UAV, including the following steps:

[0006] (1) The UAV's position information is obtained by integral fusion using the inertial measurement element and GPS module installed on the UAV itself;

[0007] (2) The actual position of the UAV combined with the output control quantity of the controller is used as the input quantity of the linear extended state observer. Based on the change of position, the observed value of the disturbance acceleration of the UAV is used as the output quantity.

[0008] (3) Feed back the disturbance acceleration observation value output by the linear extended state observer to the sliding mode controller to achieve compensation for the disturbance acceleration;

[0009] (4) When the change in the observed value of the disturbance acceleration exceeds the threshold, the bias control quantity is output through the acceleration limiting module;

[0010] (5) The deviation between the desired position and the actual position of the UAV, the deviation between the desired speed and the actual speed, and the observed value of the disturbance acceleration are used as inputs to the sliding mode controller, and the lift is output in combination with the bias control quantity.

[0011] (6) Based on the layout structure of the UAV, the lift output by the sliding mode controller is converted into the rotational speed of each motor and propeller of the UAV, driving the UAV to fly along the desired path.

[0012] The linearly extended state observer is constructed as follows:

[0013]

[0014]

[0015]

[0016] z1, z2, z3 represent the state variables of the linearly extended state observer, where z1 and z2 are used as position and velocity observations, respectively, and z3 is used as the disturbance acceleration observation. β1, β2, and β3 are the observer gain coefficients, and u... p is the control quantity output by the sliding mode controller, and p is the actual altitude of the UAV.

[0017] The sliding mode controller is constructed as follows:

[0018]

[0019] in, Z is the observed value of the disturbance acceleration, i.e., z3, ρ1 and ρ2 are the controller parameters, and sgn is the sign function;

[0020] Sliding surface Where k1, k2, γ1, and γ2 are controller parameters, k1 and k2 are positive constants, γ1 and γ2 are the ratio of positive odd numbers, and γ1 < γ2, 1 < γ1 < γ2;

[0021] Δp=pp d

[0022]

[0023] Where p is the actual height, p d The desired height.

[0024] The acceleration limiting module is in the following form:

[0025]

[0026] Among them, u f This is the bias control value. a represents the actual acceleration of the UAV, i.e., the observed value of the disturbance acceleration. d k is the acceleration limit value. f This is the gain coefficient.

[0027] The present invention has the following beneficial effects and advantages:

[0028] 1. The system has a simple structure, requiring no additional components or mechanical structures, and makes full use of the state variables of the rotary-wing UAV, thus improving stability and reliability.

[0029] 2. The structure and process are clear, there are no complex parameter coupling relationships, and the meaning of each state variable is clear.

[0030] 3. The proposed method feeds the disturbance observation results back to the controller, which improves the robustness of the controller and achieves excellent control performance.

[0031] 4. The proposed method is based on a specific application scenario and takes into account the influencing factors in the actual working environment, thus having engineering significance.

[0032] 5. This invention enables a rotary-wing unmanned aerial vehicle (UAV) to adjust its lift under the influence of bounded disturbance forces, thereby overcoming the disturbance effect to a certain extent and making its motion trajectory fit the desired path. Attached Figure Description

[0033] Figure 1 This is a flowchart of the method of the present invention;

[0034] Figure 2 This is a control principle diagram of the method of the present invention;

[0035] Figure 3 This is a comparison chart of the disturbance force and observation results in an embodiment of the present invention;

[0036] Figure 4 This is a diagram showing the fixed-point control results of an embodiment of the present invention. Detailed Implementation

[0037] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0038] like Figure 1 As shown, a method for disturbance observation and fixed-point control of a rotary-wing unmanned aerial vehicle (UAV) is presented. This method enables the UAV to observe and compensate for disturbances during flight, thereby achieving fixed-point control of the rotary-wing UAV.

[0039] like Figure 2 As shown, the method includes a position loop disturbance acceleration observation module, specifically a linear extended state observer, which estimates the actual form of the disturbance force by observing and calculating various state variables during the UAV's flight; a feedback control module, specifically a sliding mode controller, which outputs a control quantity by combining the observed values ​​of the UAV's state variables and the disturbance force to achieve fixed-point control of the UAV and reduce the impact of the disturbance force on the UAV's motion to a certain extent; and an acceleration limiting module, which calculates the UAV's acceleration by observing the changes in the UAV's position and velocity state variables. When the acceleration is too large, it outputs an offset control quantity to prevent the control accuracy from being affected by the lag in disturbance observation and compensation when the disturbance force is too large.

[0040] The specific process of this method is as follows:

[0041] Set the desired flight path points for the drone;

[0042] By installing inertial measurement elements and GPS modules on the drone itself, the drone's position information is obtained through integral fusion.

[0043] The actual position of the UAV is used as the input of the linear extended state observer, and the disturbance action of the UAV observed based on the position change is used as the output.

[0044] The disturbance force observation results output by the linear extended state observer are fed back to the position loop sliding mode controller to achieve compensation for the disturbance force.

[0045] The actual position and velocity state variables of the UAV are used as inputs to the acceleration limiting module, and it is determined whether to output the bias control quantity.

[0046] The desired position and velocity information, actual position and velocity information, and disturbance force observations of the UAV are used as inputs to the sliding mode controller, and the output lift is combined with the bias control quantity as inputs to the UAV dynamics model.

[0047] Based on the layout and structure of the drone, the control output of the controller is converted into the rotational speed of each motor and propeller of the drone, driving the drone to fly along the desired path.

[0048] The linearly extended state observer includes three observation variables, representing the observed values ​​of position, velocity, and disturbance acceleration, respectively.

[0049] The desired location information, i.e., the flight path points, is pre-designed, and the location is a function of time; the desired speed information is calculated based on the location information.

[0050] The acceleration limiting module takes the observed disturbance acceleration value as input and performs proportional control to output an offset control value. The purpose is to prevent the control accuracy from being affected by the lag in disturbance observation and compensation when the disturbance force is too large.

[0051] The position loop sliding mode controller selects position and velocity errors as state variables and designs a suitable sliding surface so that the state variables satisfy a certain relationship.

[0052] The design control law, as a function of the sliding surface, forces the system to move on the designed sliding surface in order to obtain the desired motion characteristics.

[0053] The UAV layout structure is based on the following requirements: the rotor UAV is symmetrical, the four propellers are coplanar, the lift provided by rotation is in the same direction, and the mass and moment of inertia remain unchanged.

[0054] like Figure 4 As shown in Table 1, this embodiment uses the height channel as an example, and the desired path points are as follows:

[0055] Table 1

[0056] Location 3m 5m 7m

[0057] The disturbance dynamics observation module employs a linear extended state observer, which treats the system's unmodeled dynamics and unknown external disturbances as a composite disturbance and performs real-time estimation.

[0058] For this embodiment, the linearly extended state observer structure is designed as follows:

[0059] Let the altitude of the UAV be p, then the position estimation error is:

[0060] e p =z1-p

[0061] The specific structure of the observer is as follows:

[0062]

[0063]

[0064]

[0065] Where z1, z2, and z3 are the observer state variables, and z3 is the observed disturbance acceleration. β1, β2, and β3 are the observer gain coefficients, and u p This refers to the control quantity output by the controller.

[0066] After obtaining the observed results of the disturbance acceleration, it is used as the input of the feedback control module to achieve the compensation effect of the disturbance force.

[0067] The feedback control module employs a sliding mode controller. Sliding mode control is characterized by strong robustness, good dynamic performance, and insensitivity to internal system parameters, making it suitable for UAV control. The key to sliding mode control lies in selecting a suitable sliding surface, which affects the system's dynamic performance.

[0068] For unmanned aerial vehicle (UAV) systems, position error and velocity error can be selected as the state vector:

[0069] Δp=pp d

[0070]

[0071] Where p is the actual height, p d The desired height.

[0072] The sliding surface is designed as follows:

[0073]

[0074] Where k1, k2, γ1, γ2 are controller parameters, k1 and k2 are positive constants, γ1 and γ2 are the ratio of positive odd numbers, and γ1 < γ2, 1 < γ1 < γ2.

[0075] The control law, as a function of the sliding surface, forces the system to move on the constructed sliding surface in order to obtain the desired motion characteristics.

[0076] Sliding mode controllers can eliminate disturbances, but only if the disturbance has an upper bound. If the disturbance is too large, the control quantity will also increase in order to force the system to reach the sliding surface, causing system chattering. In actual systems, frequent switching of control quantity may also damage the actuator. Therefore, the design of sliding mode controllers needs to take into account the estimation of external disturbances.

[0077] The controller is designed as follows:

[0078]

[0079] in, is the observed value of the disturbance acceleration, and the rest are controller parameters. sgn is the sign function.

[0080] The acceleration limiting module calculates the UAV's acceleration by analyzing changes in its position and velocity state variables. When the acceleration is too large, it outputs an offset control value to prevent lag in interference observation and compensation when the interference force is too large.

[0081] In this embodiment, the acceleration limiting module takes the following form:

[0082]

[0083] Among them, uf This is the bias control value. For the observed value of the perturbation acceleration, a d k is the acceleration limit value. f This is the gain coefficient.

[0084] The input to the UAV dynamics model is:

[0085] u = u p +u f

[0086] Finally, by combining the UAV dynamics model, the lift and propeller speed are output as the actual inputs for UAV flight.

[0087] like Figure 3 As shown, to demonstrate the function of the disturbance force observation module in the embodiment, a combined disturbance force, including a fused step signal and an oscillation signal, was added during the simulation. d Let f be the expected value, and f be the observed value. The observed value of the disturbance force is the product of the observed value of the disturbance acceleration and the mass of the UAV.

[0088] Simulation results show that the designed observer can observe the disturbance force.

[0089] like Figure 4 As shown, for a given desired point, the proposed method can achieve rapid approach and hovering at a fixed point under the working conditions corresponding to the embodiment. The sway amplitude of the UAV is very small and within an acceptable range in terms of the influence of disturbance force, which can achieve fixed-point operation under normal conditions.

Claims

1. A method for disturbance observation and spot control of a rotor unmanned aerial vehicle, characterized in that, In the position control loop of a rotary-wing UAV, a linear extended state observer is set up to observe the acceleration of disturbances experienced by the UAV during flight, and feeds it back to the sliding mode controller and acceleration limiting module to compensate for the disturbances. The output lift is used to achieve fixed-point control of the rotary-wing UAV, including the following steps: (1) The UAV's position information is obtained by integral fusion using the inertial measurement element and GPS module installed on the UAV itself; (2) The actual position of the UAV combined with the output control quantity of the controller is used as the input quantity of the linear extended state observer. Based on the change of position, the observed value of the disturbance acceleration of the UAV is used as the output quantity. (3) Feed back the disturbance acceleration observation value output by the linear extended state observer to the sliding mode controller to achieve compensation for the disturbance acceleration; (4) When the change in the observed value of the disturbance acceleration exceeds the threshold, the bias control quantity is output through the acceleration limiting module; (5) The deviation between the desired position and the actual position of the UAV, the deviation between the desired speed and the actual speed, and the observed value of the disturbance acceleration are used as inputs to the sliding mode controller, and the lift is output in combination with the bias control quantity. (6) Based on the layout structure of the UAV, the lift output by the sliding mode controller is converted into the rotational speed of each motor and propeller of the UAV, driving the UAV to fly along the desired path.

2. The method of claim 1, wherein, The linearly extended state observer is constructed as follows: z1, z2, z3 represent linear extended state observer state variables, wherein z1, z2 are used as position observation values, speed observation values respectively, z3 is used as disturbance acceleration observation value, β1, β2, β3 are observer gain coefficients, u p is a control amount output by the sliding mode controller, and p is the actual height of the UAV.

3. The method of claim 1, wherein, The sliding mode controller is constructed as follows: wherein is the disturbance acceleration observation, i.e. z3, and p1, p2 are controller parameters and sgn is the sign function. Slip surface wherein k1, k2, γ1, γ2 are controller parameters, k1, k2 are normal numbers, γ1, γ2 are positive odd numbers, and γ1<γ2, 1<γ1<γ2. Δp = p - p d where p is the actual height, p d is the desired height.

4. The method for disturbance observation and fixed-point control of a rotary-wing unmanned aerial vehicle according to claim 1, characterized in that, The acceleration limiting module is in the following form: Among them, u f This is the bias control value. a represents the actual acceleration of the UAV, i.e., the observed value of the disturbance acceleration. d k is the acceleration limit value. f This is the gain coefficient.

5. A disturbance observation and fixed-point control device for a rotary-wing unmanned aerial vehicle, characterized in that, It includes a memory and a processor; the memory is used to store a computer program; the processor is used to implement, when executing the computer program, a method for disturbance observation and fixed-point control of a rotary-wing unmanned aerial vehicle as described in any one of claims 1-4.

6. A computer-readable storage medium, characterized in that, The storage medium stores a computer program, which, when executed by a processor, implements a method for disturbance observation and fixed-point control of a rotary-wing unmanned aerial vehicle as described in any one of claims 1-4.

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