Sensorless tension control method and system for a tethered unmanned aerial vehicle

Abstract

This invention relates to a sensorless tension control method and system for tethered unmanned aerial vehicles (UAVs), belonging to the field of UAV control technology. The system includes a UAV body and a tether. The UAV body incorporates a disturbance observer module, an equivalent thrust constraint calculation module, and a saturated backstepping controller module. The disturbance observer module estimates the tether tension online based on the UAV's position, velocity, and thrust, using translational motion mechanics equations, eliminating the need for force sensors or tether status sensors. The equivalent thrust constraint calculation module calculates the upper limit of thrust based on the estimated tension and preset constraints. The saturated backstepping controller module calculates thrust and angular velocity commands under thrust constraints to achieve trajectory tracking. Compared to existing technologies, this invention significantly reduces system hardware costs and engineering complexity while ensuring the tether tension does not exceed a safety threshold. It exhibits excellent tracking performance and disturbance resistance, making it suitable for tethered UAV control in kilometer-scale tethered environments and complex wind conditions.

Description

Technical Field

[0001] This invention relates to the field of unmanned aerial vehicle (UAV) control technology, and in particular to a sensorless tension control method and system for tethered UAVs. Background Technology

[0002] A tethered drone is a drone system that is connected to a ground power source via a tether. The tether continuously provides power to the drone, enabling it to remain airborne for extended periods. Tethered drones are widely used in underwater mapping, disaster search and rescue, emergency communications, forest fire fighting, and personnel guidance.

[0003] As tether lengths increase to the kilometer level, tethered drones face significant control challenges. The tether itself can weigh hundreds of kilograms, exerting a significant downward force on the drone. In complex wind conditions, the aerodynamic loads on the tether can cause large, time-varying tension fluctuations. Excessive tether tension can lead to damage to the drone's structure, tether breakage, connector failure, or loss of flight control. Therefore, tether tension must be strictly controlled within safe limits.

[0004] Currently, there are two main methods for achieving tension control in tethered unmanned aerial vehicles (UAVs): The first type of approach simplifies the tether to an ideal geometry (such as a straight segment or catenary) and designs a controller based on the simplified model. For example, Rossi et al. simplified the tether to a straight segment and used model predictive control to control the tether tension and length; Nicotra et al. also used a straight segment model to design a cascaded control scheme based on thrust vectors. However, in kilometer-scale tethering and strong wind disturbance environments, the actual shape of the tether deviates significantly from the idealized model, leading to model mismatch, decreased control performance, and inability to guarantee the satisfaction of tension constraints.

[0005] The second type of method discretizes the tether into a series of rigid links or spring-damped units, establishes a high-fidelity dynamic model, and designs a controller based on this model. For example, Lee discretizes the tether into rigid links and uses a geometric control method for UAV control. However, this requires the angle and angular velocity of each link as input, thus necessitating real-time acquisition of the position and velocity information of all nodes on the tether. The technical complexity and economic cost of deploying a complex sensor network make it difficult to implement in practical engineering. For example, Chinese patent CN119645107A discloses a control method, device, and storage medium for tethered UAVs to resist wind loads. By establishing a multi-level safety protection mechanism, real-time monitoring and mode switching, and employing a system dynamic model that fuses multi-source sensor data, combined with a discrete-time neural network controller and Hamilton-Jacobi-Bellman equations, it achieves optimal control and attitude compensation for the tension distribution of multiple tethering points of the tethered UAV.

[0006] In these methods, accurate and reliable tension measurement relies on high-precision force sensors, complex structural designs, and costly data acquisition systems. However, most existing tethered unmanned aerial vehicle (UAV) systems lack real-time tension monitoring capabilities, severely limiting their operational flexibility and reliability in complex environments.

[0007] Therefore, the existing technology has the following disadvantages: (1) the control method based on simplified model has insufficient model accuracy and poor control reliability in complex environment; (2) the control method based on high-precision model has demanding measurement requirements, high sensor cost and difficult engineering implementation; (3) there is a lack of a control framework that can achieve sufficient model accuracy and engineering feasibility and ensure system safety without directly measuring the state and tension of the tether. Summary of the Invention

[0008] The purpose of this invention is to provide a sensorless tension control method and system for tethered unmanned aerial vehicles (UAVs), which can achieve safe tension restraint of long tethers without the need for force sensors and tether status sensors.

[0009] Specifically, the present invention aims to solve the following technical problems: (1) In view of the problem that the existing control methods based on simplified models have insufficient model accuracy and poor control reliability in complex wind field environments, the present invention provides a disturbance observer that can estimate the tether tension online without relying on idealized tether shape assumptions and can adapt to the actual tether dynamic characteristics in complex environments. (2) In view of the problem that existing control methods based on high-precision models require the deployment of complex sensor networks and have high engineering implementation costs, this invention provides a sensorless tension estimation method that relies only on the UAV's built-in measurement equipment (position, velocity, attitude, etc.), which significantly reduces system complexity and cost; (3) In view of the problem that existing tethered UAV systems lack real-time tension monitoring and constraint capabilities and are difficult to ensure that the tether tension does not exceed the safety threshold, this invention provides an equivalent thrust constraint method, which transforms the tension constraint that is difficult to control directly into the thrust constraint that is easy to implement, thereby ensuring the safe operation of the system; (4) To address the challenge of maintaining trajectory tracking performance under tension constraints, this invention provides a saturated backstepping controller that achieves high position and attitude tracking accuracy while satisfying thrust constraints.

[0010] This invention achieves a tethered UAV tension control scheme that requires no additional sensors, has high engineering feasibility, strong safety, and good tracking performance through the coordinated operation of a disturbance observer module, an equivalent thrust constraint calculation module, and a saturated backstepping controller module.

[0011] The objective of this invention can be achieved through the following technical solutions: A sensorless tension control method for tethered unmanned aerial vehicles (UAVs) includes the following steps: Step S1: Real-time acquisition of the current position, velocity, attitude, and thrust of the UAV body; Step S2: Based on the position, velocity, and thrust of the UAV body, estimate the tension exerted by the tether on the UAV body online based on the translational motion mechanics equation of the UAV body, and output the tension estimate. Step S3: Calculate the upper limit of the thrust of the UAV body based on the tension estimate, the thrust of the previous moment, the attitude of the UAV body, and the preset tension constraint upper limit, according to the equivalent relationship between tension and thrust. Step S4: Calculate the thrust command and angular velocity command based on the desired trajectory, the current position and velocity of the UAV body, the tension estimate, and the upper limit of thrust. Step S5: Send the thrust command and angular velocity command to the actuator of the UAV body; Step S6: Return to step S1 and repeat until the task is completed.

[0012] In step S2, the tension estimate is calculated based on the observer equation, which is: ; ; in, This is a speed estimate. The derivative of the velocity estimate, This is the tension estimate. The derivative of the tension estimate, For speed estimation error, The actual speed of the drone itself. For thrust vector, For the mass of the drone body, It is the acceleration due to gravity. The z-axis unit vector. and The observer gain matrix is ​​chosen such that the system matrix is ​​a Hurwitz matrix.

[0013] The observer gain matrix and Designed to enable augmented system matrix The eigenvalues ​​of all have negative real parts, among which It is a 3×3 identity matrix.

[0014] In step S3, the formula for calculating the upper limit of thrust is: ; in, This is the upper limit of thrust. The thrust value at the previous moment. This is the projection of the tension estimate onto the thrust direction. Here is the attitude rotation matrix of the UAV body. The z-axis unit vector. This is the tension estimate from the previous moment. For adjustment coefficient and , These are the preset design parameters. , , The square of the deviation between the tension estimate at the previous moment and the upper safety limit is... , To constrain the upper limit of the conservative tension constraint, The upper limit of the preset tension constraint, This is the upper bound of the observer error.

[0015] The design parameters The range of values ​​is .

[0016] In step S4, the step of calculating the thrust command includes: Define position error and speed error ,in The location of the drone itself. For the desired trajectory, The derivative of the desired trajectory, This refers to the actual speed of the drone itself. Calculate auxiliary variables and ,in , To control the gain, It is a saturation function; Calculate the desired thrust vector : ; in, For the mass of the drone body, It is the acceleration due to gravity. The z-axis unit vector. This is the tension estimate. To control the gain, The second derivative of the desired trajectory; Calculate the expected thrust. and the desired thrust direction ; The desired thrust magnitude is obtained by saturation treatment. ; Calculate the actual thrust ,in This is the third column of the current attitude rotation matrix of the UAV. The calculated actual thrust As a thrust command.

[0017] The control gain , and All are positive numbers, among which Controlling the convergence speed of position error, Weights for controlling speed error Used to adjust thrust limits.

[0018] In step S4, the step of calculating the angular velocity command includes: Calculate the rate of change of the desired thrust direction : 1) Calculate the estimated derivative of the velocity error : ; in, It is the thrust vector; 2) Calculate the estimated derivatives of the auxiliary variables. : ; 3) Calculate the estimated derivative of the desired thrust vector. : ; in, It is a diagonal matrix. The third derivative of the desired trajectory, The derivative of the tension estimate; 4) Calculate the rate of change of the desired thrust direction. : ; in, It is a skew-symmetric matrix operator; Based on the rate of change of the desired thrust direction Calculate the angular velocity command using the following formula. : ; in, and To control the gain, Here is the attitude rotation matrix of the UAV body. This is the yaw rate command.

[0019] The control gain and All are positive numbers, among which Control the attitude convergence speed, Weights that control attitude error.

[0020] A sensorless tension control system for a tethered unmanned aerial vehicle (UAV) is used to implement the method described above. The system includes a UAV body and a tether. The UAV body is equipped with a disturbance observer module, an equivalent thrust constraint calculation module, and a saturated backstepping controller module. The disturbance observer module is used to estimate the tension exerted by the tether on the UAV body online based on the translational motion mechanics equation of the UAV body, according to the real-time acquired position, velocity and thrust of the UAV body, and output the tension estimate value. The equivalent thrust constraint calculation module is used to calculate the upper limit of the thrust of the UAV body based on the tension estimate, the thrust value at the previous moment, the attitude of the UAV body, and the preset tension constraint upper limit, and based on the equivalent relationship between tension and thrust. The saturated backstep controller module is used to calculate thrust commands and angular velocity commands based on the desired trajectory, the current position and velocity of the UAV body, the tension estimate, and the upper limit of thrust, and send them to the actuators of the UAV body.

[0021] Compared with the prior art, the present invention has the following beneficial effects: (1) Reduced system cost: This invention does not require the installation of force sensors, tether status sensors and wind field measurement equipment. It can achieve tension estimation by relying only on the position, velocity and attitude measurement of the UAV itself, which significantly reduces hardware cost; (2) Improved engineering feasibility: The disturbance observer of the present invention only uses the position, velocity and thrust information that can be measured by the UAV, and is easy to implement on the existing tethered UAV system without any modification to the tether; (3) Ensuring safety: This invention uses an equivalent thrust constraint method to transform the tension constraint, which is difficult to control directly, into a thrust constraint that is easy to implement, thereby ensuring that the tension of the tether does not exceed the safety threshold. (4) Maintaining tracking performance: The saturated backstepping controller of the present invention can still achieve high position and attitude tracking accuracy under the premise of satisfying the thrust constraint; (5) Disturbance resistance: The disturbance observer of the present invention can estimate the tension change caused by wind disturbance in real time, and the controller automatically adjusts to adapt to environmental changes; (6) Theoretical guarantee: The closed-loop system satisfies the uniformly eventually bounded (UUB) property, and the position error, velocity error and attitude error eventually converge to the bounded neighborhood near the origin. Attached Figure Description

[0022] Figure 1 This is a system structure diagram of the present invention; Figure 2This is a flowchart of the method of the present invention; Figure 3 This is a comparison curve of the tension estimate and the actual value in an embodiment of the present invention; Figure 4 This is a graph showing the changes in rope tension and position error over time in an embodiment of the present invention. Detailed Implementation

[0023] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0024] This embodiment first provides a sensorless tension control system for tethered unmanned aerial vehicles, such as... Figure 1 As shown, the system includes a drone body 10 and a tether 20.

[0025] The drone body 10 is a large tethered drone equipped with position sensors, velocity sensors, attitude sensors, and an inertial measurement unit (IMU) for real-time position measurement. ,speed Attitude rotation matrix and angular velocity .

[0026] The tether 20 is fixed at one end to a ground anchor point and connected to the drone body 10 at the other end, and is used to transmit electrical energy and signals.

[0027] The UAV body is equipped with a disturbance observer module 11, an equivalent thrust constraint calculation module 12, and a saturated backstepping controller module 13.

[0028] The disturbance observer module 11 is used to estimate the tension exerted by the tether on the UAV body online based on the translational motion mechanics equation of the UAV body, according to the position, velocity and thrust of the UAV body acquired in real time, and output the tension estimate. The equivalent thrust constraint calculation module 12 is used to calculate the upper limit of the thrust of the UAV body based on the tension estimate, the thrust value at the previous moment, the attitude of the UAV body and the preset tension constraint upper limit, and the equivalent relationship between tension and thrust. The saturated backstep controller module 13 is used to calculate thrust commands and angular velocity commands based on the desired trajectory, the current position and velocity of the UAV body, the tension estimate, and the upper limit of thrust, and send them to the actuators of the UAV body.

[0029] Based on the above system, this embodiment provides a sensorless tension control method for tethered unmanned aerial vehicles (UAVs), such as... Figure 2 As shown, it includes the following steps: Step S1: Real-time acquisition of the current position, velocity, attitude, and thrust of the UAV body; Step S2: The disturbance observer module 11 estimates the tension exerted on the UAV body by the tether online based on the position, velocity and thrust of the UAV body and the translational motion mechanics equation of the UAV body, and outputs the tension estimate. Step S3: The equivalent thrust constraint calculation module 12 calculates the upper limit of the thrust of the UAV body based on the tension estimate, the thrust at the previous moment, the attitude of the UAV body and the preset tension constraint upper limit, according to the equivalent relationship between tension and thrust. Step S4: The saturated backstepping controller module 13 calculates the thrust command and angular velocity command based on the desired trajectory, the current position and velocity of the UAV body, the tension estimate, and the upper limit of thrust. Step S5: Send the thrust command and angular velocity command to the actuator of the UAV body; Step S6: Return to step S1 and repeat until the task is completed.

[0030] The disturbance observer module 11 is designed based on the translational motion mechanics equations of the UAV body. The translational motion mechanics equations of the UAV body are: ; in, For the mass of the drone body, For drone speed, The derivative of the drone's speed. For thrust vector ( For the magnitude of thrust, (This refers to the attitude matrix of the UAV itself). The tension of the tether (an unknown disturbance to be estimated). It is the acceleration due to gravity. It is the unit vector along the z-axis.

[0031] The physical meaning of this equation is: the net force (thrust, tether tension, gravity) acting on the UAV is equal to its mass multiplied by its acceleration. Due to the tether tension... Since it cannot be directly measured, this invention treats it as an unknown disturbance and estimates it online using a disturbance observer.

[0032] The observer equations for disturbance observer module 11 are designed as follows: ; ; in, This is a speed estimate. The derivative of the velocity estimate, This is the tension estimate. The derivative of the tension estimate, For speed estimation error, The actual speed of the drone itself. and The observer gain matrix is ​​chosen such that the system matrix is ​​a Hurwitz matrix.

[0033] In this embodiment, the observer gain matrix and Designed to enable augmented system matrix The eigenvalues ​​of all have negative real parts, among which It is a 3×3 identity matrix. At this point, the observer error system is asymptotically stable, and the tension estimation error is bounded.

[0034] The operation of the disturbance observer module 11 is as follows: In each control cycle, it reads the current position of the UAV. ,speed ,attitude ,thrust Calculate the thrust vector Update the observer state and output the tension estimate. .

[0035] The core idea of ​​the equivalent thrust constraint calculation module 12 is to transform the tether tension constraint, which is difficult to control directly, into the thrust constraint of the UAV, which is easy to implement.

[0036] The equivalent relationship between tension and thrust can be established through the following analysis: Rope tension satisfy: ; in, Let be the projected component of tension in the thrust direction. This represents the component of tension in the direction perpendicular to the thrust.

[0037] When the tension constraint is Then, the formula for calculating the upper limit of thrust can be derived: ; in, This is the upper limit of thrust. The thrust value at the previous moment. This is the projection of the tension estimate onto the thrust direction. This is the tension estimate from the previous moment. For adjustment coefficient and , The preset design parameters and To prevent the accumulation of observer errors from causing tension exceedances, this embodiment introduces a conservative upper limit for tension constraints. : ; in, The upper limit of the preset tension constraint, Let this be a pre-defined upper bound for the observer error. Then: ; ; in, The square of the deviation between the tension estimate at the previous moment and the upper safety limit is... .

[0038] The saturated backstep controller module 13 includes a position controller unit 131 and an attitude controller unit 132.

[0039] The position controller unit 131 adopts a saturated backstepping control strategy, and its design steps are as follows: Step 1: Define position error and speed error ,in The location of the drone itself. For the desired trajectory, The derivative of the desired trajectory; Step 2: Calculate auxiliary variables and ,in , To control the gain, This is a saturation function used to handle actuator constraints; Step 3: Calculate the desired thrust vector based on Lyapunov stability theory. : ; in, For the mass of the drone body, It is the acceleration due to gravity. The z-axis unit vector. This is the tension estimate. To control the gain, The second derivative of the desired trajectory; Step 4: Calculate the desired thrust. and the desired thrust direction ; Step 5: Saturate the desired thrust magnitude to obtain... Ensure that the actual thrust does not exceed the upper limit of thrust; Step 6: Calculate the actual thrust ,in The third column of the current attitude rotation matrix of the UAV body; the calculated actual thrust As a thrust command.

[0040] Among them, control gain , and All are positive numbers, among which Controlling the convergence speed of position error, Weights for controlling speed error Used to adjust thrust limits.

[0041] The attitude controller unit 132 is designed based on the geometric control method, and the angular velocity command is calculated as follows: Step 1: Calculate the rate of change of the desired thrust direction : 1) Calculate the estimated derivative of the velocity error : ; in, It is the thrust vector; 2) Calculate the estimated derivatives of the auxiliary variables. : ; 3) Calculate the estimated derivative of the desired thrust vector. : ; in, It is a diagonal matrix. The third derivative of the desired trajectory, The derivative of the tension estimate; 4) Calculate the rate of change of the desired thrust direction. : ; in, It is a skew-symmetric matrix operator.

[0042] Step 2: Based on the rate of change of the desired thrust direction Calculate the angular velocity command using the following formula. : ; in, and To control the gain, all values ​​are positive, where Control the attitude convergence speed, Weights that control attitude error Here is the attitude rotation matrix of the UAV body. This is the yaw rate command.

[0043] This embodiment was simulated and verified on the MATLAB 2025a / Simulink platform. The integration algorithm adopted the fourth-order Runge-Kutta method (ode45) with a maximum step size of 5 ms. The wind field adopted a gust model with a maximum wind speed of 20 m / s.

[0044] Table 1 Simulation Parameter Settings Table 2 Controller Parameter Settings The initial position of the drone is m, the desired destination position is m. The desired trajectory is generated using a minimum-jitter fifth-order polynomial path.

[0045] Simulation Result Analysis: like Figure 3 As shown, the disturbance observer module can quickly and accurately estimate the tether tension. The observer convergence time is approximately 0.5 s, the steady-state estimation error generally does not exceed 2 N, and the maximum estimation error is 230 N (occurring at the 31 s strong wind disturbance moment).

[0046] like Figure 4 As shown, the tether tension remained below the preset upper limit of 4000N, with an actual maximum tension of approximately 3950N, and no exceedances occurred. The positional error converged rapidly after strong wind disturbances, with a maximum positional error of approximately 21m. For a 2000m tether length, the relative error was approximately 1%, which is within an acceptable range.

[0047] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A sensorless tension control method for tethered unmanned aerial vehicles (UAVs), characterized in that, Includes the following steps: Step S1: Real-time acquisition of the current position, velocity, attitude, and thrust of the UAV body; Step S2: Based on the position, velocity, and thrust of the UAV body, estimate the tension exerted by the tether on the UAV body online based on the translational motion mechanics equation of the UAV body, and output the tension estimate. Step S3: Calculate the upper limit of the thrust of the UAV body based on the tension estimate, the thrust of the previous moment, the attitude of the UAV body, and the preset tension constraint upper limit, according to the equivalent relationship between tension and thrust. Step S4: Calculate the thrust command and angular velocity command based on the desired trajectory, the current position and velocity of the UAV body, the tension estimate, and the upper limit of thrust. Step S5: Send the thrust command and angular velocity command to the actuator of the UAV body; Step S6: Return to step S1 and repeat until the task is completed.

2. The sensorless tension control method for a tethered unmanned aerial vehicle according to claim 1, characterized in that, In step S2, the tension estimate is calculated based on the observer equation, which is: ； ； in, This is a speed estimate. The derivative of the velocity estimate, This is the tension estimate. The derivative of the tension estimate, For speed estimation error, The actual speed of the drone itself. For thrust vector, For the mass of the drone body, It is the acceleration due to gravity. The z-axis unit vector. and The observer gain matrix is ​​chosen such that the system matrix is ​​a Hurwitz matrix.

3. The sensorless tension control method for a tethered unmanned aerial vehicle according to claim 2, characterized in that, The observer gain matrix and Designed to enable augmented system matrix The eigenvalues ​​of all have negative real parts, among which It is a 3×3 identity matrix.

4. The sensorless tension control method for a tethered unmanned aerial vehicle according to claim 1, characterized in that, In step S3, the formula for calculating the upper limit of thrust is: ； in, This is the upper limit of thrust. The thrust value at the previous moment. This is the projection of the tension estimate onto the thrust direction. Here is the attitude rotation matrix of the UAV body. The z-axis unit vector. This is the tension estimate from the previous moment. For adjustment coefficient and , These are the preset design parameters. , , The square of the deviation between the tension estimate at the previous moment and the upper safety limit is... , To constrain the upper limit of the conservative tension constraint, The upper limit of the preset tension constraint, This is the upper bound of the observer error.

5. The sensorless tension control method for a tethered unmanned aerial vehicle according to claim 4, characterized in that, The design parameters The range of values ​​is .

6. The sensorless tension control method for a tethered unmanned aerial vehicle according to claim 1, characterized in that, In step S4, the step of calculating the thrust command includes: Define position error and speed error ,in The location of the drone itself. For the desired trajectory, The derivative of the desired trajectory, This refers to the actual speed of the drone itself. Calculate auxiliary variables and ,in , To control the gain, It is a saturation function; Calculate the desired thrust vector : ； in, For the mass of the drone body, It is the acceleration due to gravity. The z-axis unit vector. This is the tension estimate. To control the gain, The second derivative of the desired trajectory; Calculate the expected thrust. and the desired thrust direction ; The desired thrust magnitude is obtained by saturation treatment. ; Calculate the actual thrust ,in This is the third column of the current attitude rotation matrix of the UAV. The calculated actual thrust As a thrust command.

7. The sensorless tension control method for a tethered unmanned aerial vehicle according to claim 6, characterized in that, The control gain , and All are positive numbers, among which Controlling the convergence speed of position error, Weights for controlling speed error Used to adjust thrust limits.

8. The sensorless tension control method for a tethered unmanned aerial vehicle according to claim 6, characterized in that, In step S4, the step of calculating the angular velocity command includes: Calculate the rate of change of the desired thrust direction : 1) Calculate the estimated derivative of the velocity error : ； in, It is the thrust vector; 2) Calculate the estimated derivatives of the auxiliary variables. : ； 3) Calculate the estimated derivative of the desired thrust vector. : ； in, It is a diagonal matrix. The third derivative of the desired trajectory, The derivative of the tension estimate; 4) Calculate the rate of change of the desired thrust direction. : ； in, It is a skew-symmetric matrix operator; Based on the rate of change of the desired thrust direction Calculate the angular velocity command using the following formula. : ； in, and To control the gain, Here is the attitude rotation matrix of the UAV body. This is the yaw rate command.

9. A sensorless tension control method for a tethered unmanned aerial vehicle according to claim 8, characterized in that, The control gain and All are positive numbers, among which Control the attitude convergence speed, Weights that control attitude error.

10. A sensorless tension control system for a tethered unmanned aerial vehicle (UAV), used to implement the method according to any one of claims 1 to 9, characterized in that, The system includes a drone body and a tether. The drone body is equipped with a disturbance observer module, an equivalent thrust constraint calculation module, and a saturated backstep controller module. The disturbance observer module is used to estimate the tension exerted by the tether on the UAV body online based on the translational motion mechanics equation of the UAV body, according to the real-time acquired position, velocity and thrust of the UAV body, and output the tension estimate value. The equivalent thrust constraint calculation module is used to calculate the upper limit of the thrust of the UAV body based on the tension estimate, the thrust value at the previous moment, the attitude of the UAV body, and the preset tension constraint upper limit, and based on the equivalent relationship between tension and thrust. The saturated backstep controller module is used to calculate thrust commands and angular velocity commands based on the desired trajectory, the current position and velocity of the UAV body, the tension estimate, and the upper limit of thrust, and send them to the actuators of the UAV body.

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