Mixed-structure control system for an unconventional coaxial-ducted fan aircraft with input saturation

This paper presents a mixed-structure control system for a novel ducted fan aircraft in the presence of input constraint, system uncertainty and external disturbance. The control system includes mainly two parts: a robust nominal controller and a L1 adaptive augmentation. The robust nominal controller architecture consists of two loops. The inner-loop is designed as a static state feedback control matrix via H-infinity synthesis. This loop mainly provides state decoupling and external disturbance rejection. The outer-loop is defined as a series of PD controllers. This loop ensures the nominal tracking performance. Unlike tradition robust controller solution, the design constraints are expressed in terms of a series of closed-loop transfer functions. Both inner and outer loop controller elements are calculated by a non-smooth H-infinity optimizer at the same time. The L1 adaptive augmentation is mainly responsible for large uncertainty estimation and compensation. The simulation results prove that the L1 adaptive structure is able to provide a relative better performance for system with input saturation and large uncertainty.