A different look at output tracking: Control of a VTOL aircraft

In this paper we propose a scheme for output tracking of nonminimum phase Aat systems. The technique, which is applicable even in the minimum phase case, uses an inverse trajectory for feedforward which is stabilized by a state tracker built using the hat output. In contrast to approximate-linearization based control [Hauser, J., S. Sastry and G. Meyer (1992). Nonlinear control design for slightly nonminimum phase systems: application to v/stol aircraft. Automatica, 28, 665-679], which yields good performance in slightly nonminimum phase systems, our approach applies equally well to slightly and strongly nonminimum phase systems. The proposed control scheme and the approximate-linearization based controller are applied to a Vertical Take Off and Landing (VTOL) aircraft example and the performances are compared.