Research On Trajectory Tracking Control For Quadrotor Based On Disturbance Rejection Observer

Quadrotors have been widely used in various fields due to theirs low cost,small size and vertical take-off and landing.However,the quadrotors are complex and self-instable systems,which are accompanied by nonlinear,coupled and underactuated model characteristics.In addition,the quadrotors during specific missions are usually affected by environment disturbances which are difficult to estimate.All of these will have negative effects on attitude,position and cooperative tracking controls of the quadrotors.Based on extended state observers which are kind of disturbance rejection observers,following aspects are studies in this paper.Firstly,for the uncertainty and disturbance of the attitude control system,a time-varying prescribed-time extended state observer is designed to estimate the total disturbance.Convergence time of the prescribed-time extended state observer is fixed and set as a observer parameter.The time-varying parameters will increase over time.This control method with small gains effectively alleviates peak phenomenon in convergence process.In addition,a terminal sliding mode controller is used to track desired attitude angles,which can reduce the chattering phenomenon of traditional sliding mode controller.The effectiveness of the proposed attitude control strategy is verified by simulation in roll,pitch and yaw directions.Furthermore,in order to improve the control accuracy and response speed,a double closed-loop finite-time altitude control strategy is designed for the quadrotor.In this strategy,a height dynamic model of the quadrotor is divided into a inner velocity loop and a outer height loop.A finite-time extended state observer is designed for the inner speed loop to estimate the external disturbance and compensate it in a finite-time super-twisting controller.An integral sliding mode controller is constructed for the outer loop height loop to generate a desired speed.The feasibility and stability of the proposed control strategy are guaranteed by appropriate Lyapunov functions.Numerical simulations of step and periodic functions for the quadrotor verify the effectiveness of the double closed-loop finite-time altitude control strategy.Finally,a leader-follower cooperative control strategy is proposed to deal with a multiple quadrotors cooperative control problem under the disturbances.This scheme constructs a cooperative subsystem and a position subsystem.A nonlinear extended state observer is designed for the cooperative subsystem to estimate the external disturbance and compensate it in a nonlinear feedback controller.In the position subsystem,an adaptive sliding mode controller is designed to ensure the position tracking of the multiple quadrotors.A simulation and a experiment verify the applicability and effectiveness of the proposed control strategy.