Generation of Optimal Linear Parametric Models for LFT-based Robust Stability Analysis and Control Design

Abstract

We present a general approach to generate a linear parametric state-space model, which approximates a nonlinear system with high accuracy. It is optimally suited for LFT-based robust stability analysis and control design. At the beginning a Jacobian-based linearization is applied to gernerate a set of linearized state-space systems describing the local behavior of the nonlinear plant about the corresponding equilibrium points. These models are then approximated using multivariable polynominal fitting techniques in combination with global optimization. Tthe objective is to find a linear parametric model, which allows the transformation into a Linear Fractional Representation (LFR) of least possible order. A gab metric constraint is included during the optimization in order to guarantee a specified accuracy of the tarnsfer function of the linear parametric model. The effectiveness of the proposed method is demonstrated by a robust stability analysis for a nonlinear generic missile model.