An Adaptive Robust Nonlinear Control Approach of a Quadcopter with Disturbance Observer

Unmanned aerial vehicles (UAVs, drones) have become one of the key machines/tools of the modern world in which they are widely employed to effectively enhance working performances in many fields of daily social life and manufacturing such as delivery, protecting wildlife, agricultural activities, academy, searching, rescue missions and military applications. To accomplish the given mission, the systems are required precise controllers with strong ability of adaptation and robustness. In this article, we present an adaptive robust nonlinear controller for position tracking control problems of a quadcopter system. The controller is structured with two control loops. In the inner loop, the attitude of the system is adjusted following desired signals using a proper combination of sliding-mode-backstepping control framework under nonlinear disturbance observers. The position control mission is realized by another nonlinear altitude control method. A new gain-learning mechanism is then proposed to improve both transient and steady-state control performances. Stability of the closed-loop system under time-varying disturbances is governed by Lyapunov theories. Effectiveness and feasibility of the proposed control approach were verified by comparative simulations.