Design Of Robust Controller For Four Rotor Unmanned Aerial Vehicle

Quadrotor is a kind of 6 Degree of Freedom UAV which could vertically take-off and land. It is characterized by its low cost, simple structure and special way of flight, which makes it widely used in both military and civilian region. Based on the summary of the research status quo and the key technologies, the mathematical model is established according to its dynamic characteristics and kinematic characteristics. In this paper, different kinds of flight control algorithms are applied to quadrotor on the basis of system characteristics which consist of nonlinear, multivariate, coupled and underactuated. Various simulations and experiments are carried out to analyze and validate the control schemes proposed in this paper. Some important theoretical analysis and research results are as follows:Firstly, based on the analysis of the dynamic characteristics, the dynamics equations are established according to the Newton’s law of motion and Euler Equations. On the basis of the motor model and related device parameters, the equations of the Qball-X4 experiment platform are established.Secondly, the indoor automatic flight process of quadrotor is analyzed and divided into three parts:take-off, point-to-point trajectory and landing. The logic monitoring program for the indoor automatic flight control is designed according to the finite state machine theory.Thirdly, the double-loop PID controller is designed based on the model, which consists of two parts:an inner-loop attitude controller and an outer-loop position controller. On the basis of the coupling between attitude and position, a new method of rectifying control variable is presented to improve the accuracy of the double-loop controller.PID controller is designed by MATLAB/Simulink, and the result of simulation experiment demonstrates the effectiveness and accuracy of this control approach. The controller is applied to the Qball-X4 quadrotor to realize indoor hovering successfully.Finally, considering the environmental disturbance and uncertainty during actual flight process, sliding mode controller which consists of roll, pitch, yaw and height channel is designed and analyzed by Lyapunov stability theory. Then the simulation experiments of hover and robustness analysis are implemented to validate the control effect. The experiment result shows that the response speed and robustness of sliding mode controller are improved obviously compared to the classic PID controller.