Bahram Shafai


Hanoch Lev-Ari, Nader Jalili

Date of Award


Date Accepted


Degree Grantor

Northeastern University

Degree Level


Degree Name

Master of Science

Department or Academic Unit

College of Engineering. Department of Electrical & Computer Engineering.


Nonlinear Control, Parameteric Uncertainty, Robust Control, SDRE


Controls and Control Theory | Electrical and Computer Engineering | Engineering


We consider analysis of nonlinear systems that can be brought into a state dependent representation known as extended linearization. Under this formulation, conventional linear analysis techniques may be adapted to study the stability, optimality, and robustness properties of nonlinear systems. When subject to system uncertainty, estimating the radius of stability for systems under extended linearizationis difficult since the closed-loop system equations are not available explicitly. A method for obtaining the upper bound for the radius of stability in this class of systems is proposed. It is shown that the stability radius around a suitable domain can be obtained by computing the largest singular value of an overvalued matrix with special properties.

Additionally, a property of extended linearization is that it relies on a non-unique factorization of the system dynamics to bring the nonlinear system into a psuedo-linear form referred to as the State Dependent Coefficient (SDC) parametrization. Under system uncertainty, each SDC parametrization will produce its own radius ofstability in a region of interest in the state space. We propose a method to obtainthe SDC parametrization which results in the maximum radius of stability for the original nonlinear system in the region of interest. It is shown that the problem of obtaining the maximum radius of stability from a hyperplane of SDC parametrizations can be reduced to constrained minimization of the spectral norm of a comparison system.

Document Type

Master's Thesis

Rights Holder

Sam Nazari

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