Robust flight-path control system design with multiple-delay model approach

Robust control system design with a multiple-delay model approach is applied to a flight-path and velocity control problem. The approach is based on concepts of multiple models, linear quadratic regulator, and proportional output feedback. Multiple-delay models are used to represent uncertain dynamics in the high-frequency range. The performance index is defined with a quadratic function presenting the design goal in a natural manner, and the control law is obtained by minimizing the performance index. The control law obtained by the multiple-delay model approach is robust against unstructured uncertainty and is a natural extension of the linear quadratic regulator to increase the robustness without performing complicated adjustments of the quadratic performance-index weighting matrices. A flight-path and velocity control problem for a lightweight transport is studied to examine feasibility of the approach. Crossover frequency and phase margin, frequency-response matrix singular values, control performance change due to the parameters’ variation, and command input time responses including nonlinear dynamics effects are studied to demonstrate the robustness of the control laws. Numerical results show the feasibility and usefulness of the approach.