Research On Tracking And Fault Tolerant Control For Quadrotor

Quadrotor has become quite a hot topic nowadays.The brushless DC motors(BLDCM),used as the actuators,are rotating at high speed for a long time,so that they are easy to have faults.In order that the quadrotor is capable of completing the mission independently whether it has faults or not,it is particularly necessary to conduct research on its tracking control and fault tolerant control.In this paper,the control structure of inner and outer loops is used,and the position controller and attitude controllers are get by backstepping method,so that the quadrotor can achieve stable trajectory tracking.Furthermore,the condition that actuating motor has bias fault is taken into account,and the fault tolerant controller is designed based on the sliding mode observer to tolerate the fault.At last,the fault tolerant controller is optimized with seeker optimization algorithm(SOA).Specific research contents are as follows:(1)Tracking control design.First,the position and the attitude models of the quadrotor are established by Newton's second law and Euler equation respectively.Because the quadrotor is a typical under-actuated system,in order to avoid the complex design of under-actuated control law under indirect-driven control structure,three position control inputs along three axes in space are designed by backstepping separately based on the inner and outer loop control structure in this paper,and the the position controller(under-actuated control law)for the outer loop is obtained by calculation.The desired trajectories of roll angle and pitch angle for the inner loop are calculated by the position control inputs.The attitude controllers of inner loop are also designed by backstepping method.The advantages of simpler expression and faster tracking of under-actuated control law under inner and outer loop structure are highlighted by comparison of theory and simulation.(2)Fault tolerant control.The change of position and attitude for quadrotor are produced by the rotation of four propellers respectively driven by four brushless DC motors serving as the actuators.When the actuating motor rotates at high speed for along time,it is extremely prone to have faults.Therefore,the problem of fault tolerant control for quadrotor in case of actuator fault is further studied in this chapter.First,the dynamics of four brushless DC motors with bias faults are added to the model of quadrotor,which realizes the improvement of quadrotor's model.Next,the fault is detected and reconstructed by sliding mode observer,and then the fault tolerant controller is designed to compensate the fault,so as to ensure that the quadrotor can still achieve stable position and attitude tracking in the case of actuator fault.The simulation results verify the effectiveness of the designed sliding mode observer and fault tolerant controller.Fault tolerant control design based on Seeker Optimization Algorithm.In order to optimize the parameters of relevant controllers in fault tolerant control design,first,the population is initialized and the appropriate fitness function is selected,and the new position of the next iteration is determined by calculating the search direction and step size of each individual.After finite iterations,a set of optimal control parameters can be found to make the speeds of motors in four propellers of a quadrotor have better dynamic characteristics and improve the comprehensive performance of its actuators.