Preview-based stable-inversion for nonlinear nonminimum-phase aircraft tracking: VTOL example

In this article, we demonstrate the use of the preview-based stable-inversion technique in online ouput-tracking of nonlinear nonminimum-phase aircraft systems. Although exact output tracking of nonlinear nonminimum-phase systems can be achieved by using the stable-inversion techniques, challenges exist to implement this technique to track online-generated output trajectory. This is because the computation of the bounded, exact-output-tracking Input (at the current time instant t_c) requires the knowledge of the entire future desired output for time [t _c, ∞), restricting the stable-inversion technique to trajectory-planning applications (e.g., aircraft take-off operation). However, it is intuitive that the previewed information of the desired output within a finite-time window [t_c, t_c + T_p] should be sufficient to compute the inverse input (at current time (t_c)) with an arbitrarily-small error if the preview time T_p is sufficiently large. In this paper, we present a preview-based stable-inversion technique on a VTOL aircraft model. We illustrate the procedure to quantify the preview time T_p that guarantees the desired accuracy in the inverse input for VTOL aircraft. Simulation results are presented and discussed to demonstrate the efficacy of the proposed approach in achieving precision tracking of online-generated trajectory.