A Disturbance Observer Based Attitude Controller for Quadrotor Helicopters

This paper deals with the design of a robust attitude controller for a quadrotor helicopter subject to external disturbances. In order to attenuate these time varying and non-vanishing disturbances, we propose the use of a proportional integral observer to estimate and compensate for the disturbances. So, a two-stage procedure to design the robust attitude controller is proposed. First, a disturbance observer is designed. Then based on the observer, a backstepping controller is designed to stabilize the attitude of the quadrotor. Furthermore, the principle for selecting control parameters and stability analysis of the proposed composite controller are given. The observer output is used to compensate for the disturbance, and then the control law is generated by backstepping method. The observer based flight controller is able to provide robust attitude control of the quadrotor while relying only on knowledge of the bound of the disturbances. Simulations demonstrate the efficiency of the composite controller in the presence of external disturbances as well as model inaccuracy.