Research On Active Disturbance Rejection Sliding Mode Control For Uavs Close Formation Based On LESO

Cooperative working mode of multi-unmanned aerial vehicles(UAVs)formation flight can improve efficiency for single aircraft to some extent,so it has broad application value in military and civil fields.Considering the fact that UAV is inevitably to suffer from all kinds of uncertain disturbances such as aerodynamic coupling and wind during the flight,obviously,the tradition control method of linearization is not appropriate.For UAVs close formation system with nonlinear,under-actuated and strong coupling,an improved active disturbance rejection sliding mode control algorithm is proposed in this paper.First,extended state observer(ESO)is designed to estimate the uncertainties and compensate them in control law.Then,in order to reduce the difficulties of parameter optimization and controlling for under-actuated system,the ADRC is combined with sliding mode control to design the compound controller,which is an innovation of this paper.Finally,Lyapunov function is used to prove that the tracking error converges uniformly to zero,and simulation analysis is completed by MATLAB.The main content of this paper is as follows:First of all,the general “leader-follower” formation strategy is used,and relative kinematics equations are derived in detail.In chapter 2,these aerodynamic coupling effects are properly modeled by using horseshoe vortex model.Based on the Biot-Savart law,we calculate the aerodynamic increment and stability derivative in each direction,and the autopilot in UAV is modified.After comparing simulation results of two kinds of system,we get some significant conclusions.Secondly,in this paper,the ADRC algorithm is used to solve the problem of controller parameter setting and control accuracy decrease when suffering internal disturbances and external disturbances.In order to facilitate the design and theoretical analysis,we abandon the nonlinear part.Especially,an in-depth study of stability and convergence error analysis for LESO is made.Starting with frequency domin analysis,the rejection quality for external disturbance is analyzed.The relationship between the dynamic characteristics and the bandwidth is discussed and the method of parameter selection is proposed,which enhances the practicability of the engineering.Thirdly,the ADRC controller is designed for close formation flight system.It is mainly divided into yaw,velocity and height channels and the controller can effectively transform and keep formation configuration.Simulation results show that compared with the traditional PID method,LADRC does not need to consider the precise model of the object and all kinds of external disturbances,so it can track the target quickly and accurately.However,when the instruction is too complex,the performance of the system at initial time is unsatisfied.Therefore,we need to search a more simple and efficient way to generate nonlinear control laws.Finally,aiming at the control problem of under-actuated system,an active disturbance rejection sliding mode control method is proposed.A nonlinear smooth function is designed to be applied to the approach law,which can effectively eliminate the chattering in the control signal.A feasible autonomous formation flight control method with complete auto disturbance rejection is realized by the technology based on the LESO combined with sliding mode control.Eventually,several test cases are designed and the results show that the performance is better than LADRC in parameter setting,steady-state response and anti disturbance.