Adaptive Attitude Tracking of a Quad-Rotorcraft Using Nonlinear Control Hierarchy

摘要

Adaptive control of a quad-rotorcraft is designed to estimate unknown plant parameters online in order to improve the robustness of the system against parametric uncertainties. Using the hierarchical structure of a quadrotor a nonlinear position and an adaptive attitude control law is proposed that can asymptotically track a command signal without the knowledge of inertia matrix. A projection based adaptive law estimates the unknown inertia parameters and ensures that the estimate always stay inside a pre-defined compact set. Adaptive design obeys the underlying principle behind hierarchical control where the vehicle tracks the desired position and compute guided attitudes from a thrust input so that designed rotor torques drives the vehicle towards desired orientation. A rigorous stability analysis proves that the overall system is stable by considering the effect of strong nonlinear coupling between the position and attitude subsystem. Closed-loop error dynamics is asymptotically converging and ensure all signals are bounded in the cascaded control structure. Simulation results demonstrate the theoretical conjecture of the proposed controller.