Robust backstepping control for attitude tracking of a quadrotor based on integral linear extended state observer under input saturation

In this paper, a novel and robust backstepping controller is introduced for a quadrotor system by combining an integral linear extended state observer (ILESO), an auxiliary dynamic system, and a sliding mode differentiator. The ILESO is specifically designed to observe unmeasured states and address the challenges posed by the 'lump disturbance', encompassing unknown external disturbances and modeling uncertainties, while also mitigating measurement noise effects. To contend with input saturation in the quadrotor, an auxiliary dynamic system is implemented. Additionally, a sliding mode differentiator is employed to counteract the differential explosion issue inherent in traditional backstepping controllers. The controller's efficacy is established through the assurance of the quadrotor's capability to accurately track desired attitudes. The uniform ultimate boundedness of all signals in the closed-loop system is demonstrated using the Lyapunov theory. Simulation results further illustrate the effectiveness and superiority of the proposed controller.