Design and comparison of LQG/LTR and H-infinity controllers for a VSTOL flight control system

In this paper two robust controllers for a multivariable vertical short take-off and landing (VSTOL) aircraft system are designed and compared. The aim of these controllers is to achieve robust stability margins and good performance in step response of the system. LQG/LTR method is a systematic design approach based on shaping and recovering open-loop singular values while mixed-sensitivity H-infinity method is established by defining appropriate weighting functions to achieve good performance and robustness. Comparison of the two controllers show that LQG method requires rate feedback to increase damping of closed-loop system, while H-infinity controller by only proper choose the weighting functions, meets the same performance for step response. Output robustness of both controllers is good but H-infinity controller has poor input stability margin. The net controller order of H-infinity is higher than the LQG/LTR method and the control effort of them is in the acceptable range. (c) 2006 The Franklin Institute. Published by Elsevier Ltd. All rights reserved