Adaptive Output-Feedback Control with Closed-Loop Reference Models and Applications to Very Flexible Aircraft

Abstract

This paper proposes an adaptive controller for a class of multi-input multi-output (MIMO) plants where the number of outputs is larger than the number of inputs, an example of which is very-flexible aircraft (VFA). A dominant presence of model uncertainties and actuator anomalies necessitates an adaptive approach for control of VFA. The proposed controller, denoted as the adaptive SPR/LTR controller, combines a baseline observer-based design with loop transfer recovery (LTR) properties and an adaptive design based on strictly positive real (SPR) transfer functions. In addition to accommodating the absence of full state measurements, the controller includes a reference model that also plays the role of an observer through a closed-loop component. Conditions are delineated under which this controller, can guarantee asymptotic reference tracking, and the control design is validated using a VFA model around a single equilibrium flight condition with 707 states, 12 outputs and 2 control inputs. Simulation results show that the adaptive controller not only ensures stability but also recovers a nominal performance both in time domain and in frequency domain despite the presence of varying wing shape and actuator anomalies.