Robust output feedback trajectory tracking for quadrotors

This paper focuses on robust output tracking control for quadrotors exposed to parametric uncertainties and external disturbances. Based on the back-stepping control principle, the quadrotor dynamics is decomposed into translational and rotational subsystems. To handle the limitation of traditional extended state observer that can only be effective for integral-chain systems, a high-order extended state observer with special structure is developed to estimate the unmeasurable states and the lumped disturbances in rotational subsystem simultaneously. To avoid the tedious analysis and repeated differentiation of virtual control laws in the back-stepping technique, a first-order sliding mode differentiator is introduced to compute the derivative of virtual control law at each step in the presence of disturbances. The stability analysis is established using the Lyapunov theory. Simulation results demonstrate the effectiveness of the proposed control scheme in achieving a guaranteed tracking performance with respect to an 8-shaped reference trajectory.