Preview-based inversion of nonlinear nonminimum-phase systems: VTOL example

Abstract

This article quantifies the importance of future desired output trajectory in determining system-inversion-based inputs used in precision output tracking. For minimum-phase systems, only information at the current time instant is needed to compute the current value of the exact-output-tracking input when using system inversion. In contrast, for nonminimum-phase systems, computing the bounded exact-output-tracking input at time instant t/sub c/ requires knowledge of the desired output for all future time [t/sub c/, /spl infin/]. However, it is intuitive that the effect of the desired output's distant-future values, on the output-tracking input at the current time instant, should be small. Therefore, preview information of the desired output for a finite-time window [t/sub c/, t/sub c/ + T/sub p/] should be sufficient to compute the output-tracking input (at current time (t/sub c/)) with an arbitrarily-small prescribed err-or if the preview time T/sub p/ is sufficiently large. The contribution of this article is the quantification of the required preview time T/sub p/ for nonlinear nonminimum-phase systems in terms of the desired accuracy in the computing the output-tracking input, and the characteristics of the system's internal dynamics. The proposed preview-based technique is applied to a benchmark VTOL aircraft model in simulation and results are presented.