Research On Robust Sliding Mode Flight Control And Formation Technology Of Quadrotor UAV

Robust fast terminal sliding mode control theory is studied based on a quadrotor UAV's flight control system,and the formation flight control is studied further more based on improved artificial potential field method.Firstly,the development background and research status of quadrotor at home and abroad are introduced,and the flight principle is analyzed.The ground coordinate system and the body coordinate system are established,and the state space model of quadrotor is established which provides the model basis for the control laws design and formation flight research in the following part.The attitude algorithm is studied before the control laws design.The quaternion algorithm is used to describe the UAV's attitudes,and the first order Runge-Kutta method is used to update the quaternion states.In order to obtain more accurate attitude and position data,extended Kalman filtering is designed in the time domain and adaptive complementary filtering is designed in the frequency domain respectively to filter and fuse the UAV's sensor data.In the design of sliding mode control laws,the quadrotor UAV system is divided into two parts:the fully-actuation subsystem and the underactuation subsystem.The sliding mode control laws for the fully-actuation subsystem are designed by using the backstepping method,and the underactuation subsystem is analyzed to design the sliding mode control laws.The stability of the system is proved by Lyapunov method,and the simulation results show that the proposed control algorithm is feasible to some extent.In order to solve the problems that the system status errors in traditional sliding mode method cannot converge into zero in finite time,and there is chattering phenomenon,a fast terminal sliding mode control law is designed.The quadrotor model is divided into attitude subsystem and position subsystem,and a dual closed-loop control structure is designed.An adaptive law is designed to estimate the uncertainties and disturbances of the system,which enhances the robustness of the system.The fast terminal sliding mode control laws are designed for the attitude inner loop and the position outer loop respectively,and the ideal switching function sgn(s)is replaced by the saturation function sat(s).A boundary layer is set to eliminate chattering phenomenon,and the stability of the system is proved by the Lyapunov method.By analyzing the convergence time,it is proved that the system state can converge in a short time.Compared with the simulation results of traditional sliding mode control,the proposed method is better.Formation flight in three-dimensional space is further studied based on the attitude control and position control of a single UAV.By analyzing the defects of the traditional artificial potential field method and improving the potential field function,the problem of goal nonreachable with obstacle nearby(GNRON)is solved fundamentally.A mechanism of judging whether get into local minimum point is introduced,and a method of "move along the 90°direction of the target" is proposed to escape from the local minima.Finally,regression search method is used to optimize the path globally.The convictive simulation results show that the proposed method is feasible.Taking the optimized path as the desired position input of each quadrotor,the adaptive fast terminal sliding mode control designed above can be used to control each quadrotor to fly to their respective target points along an obstacle-free optimal path.