On the linear control of the quad-rotor system

In this article, a robust linear output feedback control scheme is proposed for the efficient regulation, and trajectory tracking tasks, in the nonlinear, multivariable, quad-rotor system model. The proposed linear feedback scheme is based on the use of a classical linear feedback controllers and suitably extended, high gain, linear Generalized Proportional Integral (GPI) observers; aiding the linear feedback controllers in two important tasks: 1) accurate estimation of the input-output system model nonlinearities, 2) accurate estimation of the unmeasured phase variables associated with the flat, or linearizing, output variables. These two key pieces of information are used in the proposed feedback controller in a) approximate, yet close, cancelation, as a lumped unstructured time-varying term, of the influence of the highly coupled nonlinearities and b) devising proper linear output feedback control laws based on the approximate estimates of the string of phase variables associated with the flat outputs simultaneously provided by the disturbance observers.