Convex inner approximations of nonconvex semialgebraic sets applied to fixed-order controller design

Didier Henrion (1, 2) , Christophe Louembet (1)

1 LAAS - Laboratoire d'analyse et d'architecture des systèmes
2 FEL CTU - Faculty of Electrical Engineering [Prague]

We describe an elementary algorithm to build convex inner approximations of nonconvex sets. Both input and output sets are basic semialgebraic sets given as lists of defining multivariate polynomials. Even though no optimality guarantees can be given (e.g. in terms of volume maximization for bounded sets), the algorithm is designed to preserve convex boundaries as much as possible, while removing regions with concave boundaries. In particular, the algorithm leaves invariant a given convex set. The algorithm is based on Gloptipoly 3, a public-domain Matlab package solving nonconvex polynomial optimization problems with the help of convex semidefinite programming (optimization over linear matrix inequalities, or LMIs). We illustrate how the algorithm can be used to design fixed-order controllers for linear systems, following a polynomial approach.

Keywords: polynomials; nonconvex optimization; LMI; fixed-order controller design

Domains: Optimization and Control [math.OC]

Didier Henrion, Christophe Louembet. Convex inner approximations of nonconvex semialgebraic sets applied to fixed-order controller design. 2011. ⟨hal-00585633v1⟩