Application of a Robust Nonlinear Control Strategy for Disturbance-Resilient Tilt-Rotor Quadcopter Trajectory Tracking

A robust nonlinear control strategy is developed for a Tilt-Rotor Quadcopter (TRQ), which is shown to achieve reliable trajectory tracking performance in the presence of external disturbances. The control method is based on the robust integral of the sign of the error (RISE) control method, which is modified to address the control challenges inherent in TRQ dynamic model. To the best of the authors' knowledge, this is the first result that applies a RISE-based nonlinear control method to a TRQ system. A challenge in the TRQ dynamic model is that the control input is pre-multiplied by a state-dependent input gain matrix. This challenge is mitigated by endowing the control law with a robust feedback element designed to provide enhanced compensation for the resulting perturbations in the input gain matrix. A rigorous Lyapunov-based stability analysis is utilized to prove that the proposed tracking control law achieves semi-global asymptotic stability in the presence of norm-bounded external disturbances, where the region of convergence can be made arbitrarily large through judicious control gain selection. A detailed numerical comparison study is provided to demonstrate the improved disturbance-rejection capability of the proposed control law as compared to a standard non-RISE control law.