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

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_c requires knowledge of the desired output for all future time [t_c, ∞]. 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_c, t_c + T_p] should be sufficient to compute the output-tracking input (at current time (t_c)) with an arbitrarily-small prescribed err-or if the preview time T_p is sufficiently large. The contribution of this article is the quantification of the required preview time T_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.