Smooth Saturation Function-based Position and Attitude Tracking of a Quad-Rotorcraft Avoiding Singularity

A nonlinear hierarchical framework is proposed to design a smooth saturation function-based position and attitude tracking control of a quad-rotorcraft. The design is based on full state space Euler-Lagrange (E-L) model of the vehicle. A rigorous stability analysis proves that the overall closed-loop system is semi-globally asymptotically stable (SGAS). In addition, a strategically designed smooth saturated position controller extracts singularity-free attitude reference while a smooth saturated attitude controller guarantee non-singular attitude tracking. Numerical simulation shows the performance of the proposed controller.