Attitude Control Of Quadrotor UAV Based On Linear Active Disturbance Rejection

The Unmanned Aerial Vehicle（UAV）is a highly mobile,low-cost micro-drone that has attracted the close attention of many researchers around the world and has made some important advances.With the development of science and technology,more requirements are put forward,namely,improving control accuracy,reducing energy consumption and prolonging service life.This makes the quadrotor widely used in military surveillance,search-and-rescue missions,and cooperative operation.As a typical nonlinear dynamic object,four-rotor UAVs often have serious coupling problems.Therefore,how to solve these complex coupling relationships has gradually become the focus of researchers’ academic research.Attitude control of quadrotor is very important in its position and attitude system,because attitude control determines the stability of the quadrotor,so it is the key of the entire quadrotor control system.Therefore,the stability of the attitude system is the key to the realization of the entire four-rotor control system.The main research contents and work of this paper are as follows:Firstly,considering the air resistance and the moment acting on the quadrotor,the dynamics model of the ordinary quadrotor UAV is established,and the conversion relationship between the body coordinates and the inertia coordinates is deduced.In addition,for the quadrotor load UAV with time-varying mass,the position of the center of mass after the mass change of the quadrotor UAV is fully considered,and the position of the center of mass is correlated with the mass,and the dynamics model of the quadrotor load UAV is established.Secondly,a linear active disturbance control（LADRC）strategy with fewer adjustable parameters is proposed for attitude control of ordinary four-rotor UAVs.This method has good tracking ability and strong anti-disturbance,and does not depend on the specific mathematical model.The three attitude and altitude channels of the quadrotor UAV are controlled by LADRC.A linear extended state observer（LESO）is used to estimate the total disturbance of the system in real time and compensated by a proportional-derivative（PD）controller.In order to make parameter adjustment more convenient,adaptive control is introduced in LADRC to adjust the parameters.When the quadrotor is disturbed,the designed adaptive law can adjust the parameters of the controller in real time according to the changes of the system dynamic characteristics and the disturbance.In addition,the tracking error caused by the deviation of the controller parameters can also be compensated,which not only enhances the anti-disturbance capability of the system,but also provides a new method to prove the stability of the controller.Finally,the stability analysis of the four-rotor control system is carried out using Lyapunov stability theory.Simulation results show that it can be seen that the scheme is feasible,and it can track the reference input stably and quickly.Thirdly,in view of the existence of external disturbances and internal unmodeled dynamics in ordinary quadrotor UAV,an attitude control scheme combining sliding mode control（SMC）and LADRC is designed,the scheme combines the advantages of both.SMC can enhance the robustness of the controller.Internal unmodeled dynamics and external disturbances of the system were estimated using LESO,the PD controller compensates for the total disturbance.In addition,in order to simplify the parameter setting,adaptive control is introduced in the PD control,which can adjust the parameters in real time according to the input and output data,which makes the whole controller only have three adjustable parameters,which greatly simplifies the parameter setting process,and provides.The stability analysis of the controller provides a new method,which enables the entire controller to prove its stability using Lyapunov theory.The simulation results show that the proposed scheme has good anti-disturbance capability and fast response speed even in the presence of external and internal disturbance of quadrotor.Fourthly,for the quadrotor load UAV with time-varying mass,the problem of mass change is fully considered,and a composite control scheme combining SMC and LADRC is adopted,which combines the advantages of the two control algorithms and is complementary.SMC can improve the anti-disturbance performance of the controller and overcome the problem of low control accuracy caused by the limited bandwidth of LADRC,which further improves the performance of the quadrotor control system.LESO can estimate the external disturbance of the system and the internal unmodeled dynamics excited by SMC chattering in real time,and then compensate for the total disturbance by the PD controller.For the mass change of the quadrotor load UAV,a mass adaptive law is designed,which can effectively eliminate the influence of mass change on the system.The stability analysis of the whole control system is carried out by using Lyapunov stability theory.The simulation results are compared with LADRC and dynamic surface active disturbance rejection control（DSADRC）.The results show that this scheme has the advantages of small overshoot and fast response.In addition,the designed mass adaptive law is also effective,which can eliminate the influence of parameter bias,so that the proposed scheme can track the reference signal stably even in the presence of disturbance.