MAE Seminar Series

Multiple-Time-Scale Nonlinear Output Feedback Control of Systems With Model Uncertainties

John Valasek.

Dr. John Valasek

Professor, Aerospace Engineering, Texas A&M University

March 9, 2023 | 3:30 p.m. | 337 Bell Hall


The Geometric Singular Perturbation theory (Fenichel, 1979) is a powerful control law development tool for multiple-timescale systems because it provides physical insight into the evolution of the states in more than one timescale. The behaviour of the full-order system can be approximated by the slow subsystem, provided that the fast states can be stabilised on an equilibrium manifold. The fast subsystem describes how the fast states evolve from their initial conditions to their equilibrium trajectory or the manifold. This presentation develops two nonlinear, multiple-time-scale, output feedback tracking controllers for a class of nonlinear, nonstandard systems with slow and fast states, slow and fast actuators, and model uncertainties. The class of systems is motivated by aircraft with uncertain inertias, control derivatives, engine time-constant, and without direct measurement of angle-of-attack and sideslip angle. Each controller is synthesized using time-scale separation, lower-order reduced subsystems, and estimates of unknown parameters and unmeasured states. The update laws are so chosen that errors remain ultimately bounded for the full-order system. The controllers are simulated on a six-degree-of-freedom, F-16A Fighting Falcon model commanded to perform a demanding, combined longitudinal and lateral/directional maneuver. Even though angle-of-attack and sideslip angles are not measured, tracking is adequate and as good as a previously developed full-state feedback controller handling similar parametric uncertainties. Of the two new output feedback controllers, the slow state tracker accomplishes the maneuver with less control effort, while the simultaneous slow and fast state tracker does so with a smaller number of gains to tune.


John Valasek is Director, Vehicle Systems & Control Laboratory (, Thaman Professor of Undergraduate Teaching Excellence, Professor of Aerospace Engineering, and member of the Honors Faculty at Texas A&M University (TAMU), which he joined in 1997. He has been actively conducting autonomy and flight controls research of Unmanned Air Systems (UAS) in both Industry and Academia for 37 years. He began his career as a Flight Control Engineer for the Northrop Corporation, Aircraft Division where he worked in the Flight Controls Research Group, and on the AGM-137 Tri-Services Standoff Attack Missile (TSSAM) program. He is co-inventor on a patent for Autonomous Air Refueling (AAR) of UAS and co-inventor on a patent for the design of a UAS. John is the TAMU Site Director for the new NSF Center for Autonomous Air Mobility and Sensing (CAAMS) and has conducted more than 600 fixed-wing and rotorcraft UAS test flights over a 23 year period at TAMU. He is the recipient of the 2014 ASEE/AIAA John Leeland Atwood Award for national outstanding aerospace educator, the National Faculty Advisor Award from AIAA, and served as the National President of Sigma Gamma Tau (SGT) from 2006-2008. John is co-author / editor of four books including Nonlinear Multiple Time Scale Systems in Standard and Non-Standard Forms: Analysis and Control, (SIAM, 2014). John is a Fellow of AIAA, Chair of the AIAA Intelligent Systems Technical Committee, member of the AIAA Unmanned Systems Technical Program Committee, and an Associate Editor of the Journal of Guidance, Control, and Dynamics. He earned the B.S. degree in Aerospace Engineering from California State Polytechnic University, Pomona in 1986 and the M.S. degree with honors and the Ph.D. in Aerospace Engineering from the University of Kansas, in 1990 and 1995 respectively.

Event Date: March 9, 2023