Nonlinear robust output feedback tracking control of a quadrotor UAV using quaternion representation

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In this paper, a new quaternion-based nonlinear robust output feedback tracking controller is developed to address the attitude and altitude tracking problem of a quadrotor unmanned aerial vehicle which is subject to structural uncertainties and unknown external disturbances. By using the unit quaternion representation, the singularity associated with orientation representations can be avoided. A set of non-model-based filters are introduced to provide estimations for the unmeasurable angular velocities and translational velocity in the altitude direction of the quadrotor in the case that velocity feedback is unavailable. Approximation components based on neural network (NN) are introduced to estimate the modeling uncertainties, and robust feedback components are designed to compensate for external disturbances and NN reconstruction errors. The Lyapunov-based stability analysis is employed to prove that a semiglobally asymptotic tracking result is achieved and all the closed-loop states remain bounded. Numerical simulation results are provided to illustrate the good tracking performance of the proposed control methodologies.