Robust optimal attitude control for hexarotors with disturbances, uncertainties, and delays

A robust optimal attitude controller for hexarotor helicopters is proposed. Compared to the previous research studies on hexarotors, the current study takes account of the influences of non-linear and coupling dynamics, structured and unstructured uncertainties, external time-varying disturbances, and input time delays. A linear time-invariant system is derived for each Euler angle by considering the actual rotational dynamic model as a nominal non-linear system plus an equivalent perturbation, including non-linear and coupling dynamics, uncertainties, disturbances, and time delays. Using this approach, a Linear Quadratic Regulation controller is first designed for the nominal linear system of each angle to accomplish the desired tracking performances. Then, a robust compensator based on the robust compensation method is proposed to counteract the effects of the equivalent perturbation on the system. Moreover, the robust attitude tracking property and uniform asymptotical stability of the closed-loop hexarotor system are proved using Lyapunov stability theory. Several simulations have been performed to demonstrate the effectiveness and robustness of the proposed controller. Finally, experimental results are provided to confirm the robust performance of the proposed controller.