Research On Underactuated Quadrotor Control System With Uncertainties

Quadrotor is a new pattern of unmanned rotorcrafts that could take off and land vertically.It adjusts its position and attitude by varying four symmetrical propellers' speeds,with various merits such as high flexibility,strong maneuverability and simple structure.Therefore,it is widely used in military,civil and scientific research fields.Quadrotor's model contains uncertainties such as the change of quality or moment of inertia and external disturbance.It is a typical underactuated system which controls six degrees of freedom by four inputs.It is also a multi-variable,strong coupling nonlinear system.So it is difficult to control and research it,which makes quadrotor become one of hotspots among many research fields in the world today.The main task of this paper is to develop active disturbance rejection sliding mode control and linear active disturbance rejection control based the theory of differential flatness after analyzing dynamic characteristics of quadrotor.The proposed control methods can make underactuated quadrotor with uncertainties keep stable flight states quickly and achieve fixed hovering and desired trajectory tracking of position and attitude.The main contents are listed as follows:Firstly,in view of the problem that altitude and attitude fully-actuated channels of quadrotor are sensitive to parameter uncertainty and external disturbance,this paper designs an active disturbance rejection sliding mode controller.The basic idea is to design a linear extended state observer to estimate the generalized disturbance,and then introduce a sliding surface and an exponential reaching law to generate control signal,and furthermore compensate them actively in real time.Secondly,for the underactuated problem of quadrotor's horizontal position channel,this paper applies the theory of differential flatness to find virtual control inputs.Then a linear active disturbance rejection controller is designed.Thirdly,this paper studies the estimation ability of linear extended state observer and makes use of Lyapunov stability theory to prove the sense of Lyapunov stability of active disturbance rejection sliding mode controller and bounded input bounded output stability of linear active disturbance rejection controller's tracking error.Finally,a series of simulations illustrate that the designed controllers can realize fixed hovering and desired trajectory tracking for underactuated quadrotor in the presence of uncertainties.They have good dynamic response and strong robustness and disturbance rejection.