Simulation of robust controllers for disturbance rejection in ouad-copter

Abstract

In this work kinematics and dynamics of a quad-copter were presented, the quad-copter is studied in two frames: inertial or earth frame and body frame, the first is attached to the ground and the latter is attached to the aircraft's center. Forces and moments acting on the drone were studied as well as aerodynamic effects and rotor dynamics. From this information, a state space model was derived which was used to design three controllers to stabilize the system. When building the model the quad-copter and propellers are assumed to be rigid. One controller was a PID and the others followed Backstepping and Gain-scheduling methods. PID is a linear controller that minimizes the error between actual and desired states through proportional; integral and derivative terms. Backstepping is a method developed for nonlinear systems that can be decomposed into smaller subsystems and then controlling inputs are derived based on Lyapunov theory of stability. As for Gain-scheduling, it is an expansion of the PID method to be suitable for nonlinear systems where multiple PID controllers are used, switching between controllers is based on a scheduling variable, in this thesis the scheduling variable was chosen to be the desired state. In all these controllers parameters are tuned using repetitive trials until satisfactory outcome is achieved. In the end, simulation results were presented and discussed. Additionally, advantages and disadvantage of each method are highlighted to conclude with a comparison between the three controllers.