A nonsmooth, nonconvex optimization approach to Robust Stabilization by static output feedback and Low-order controllers

James V. Burke, Adrian S. Lewis, Michael L. Overton

Research output: Contribution to journalConference articlepeer-review

Abstract

Stabilization by static output feedback {SOF) is a long-standing open problem in control: given an n by n matrix A and rectangular matrices B and C, find a p by q matrix K such that A + BKC is stable. Low-order controller design is a practically important problem that can be cast in the same framework, with {p+k)(q + k) design parameters instead of pq, where k is the order of the controller, and k << n. Robust stabilization further demands stability in the presence of perturbation and satisfactory transient as well as asymptotic system response. We formulate two related nonsmooth, nonconvex optimization problems over K, respectively with the following objectives: minimization of the ϵ-pseudospeetral abscissa of A + BKC, for a fixed ϵ ≥ 0, and maximization of the complex stability radius of A + BKC. Finding global optimizers of these functions is hard, so we use a recently developed gradient sampling method that approximates local optimizers. For modest-sized systems, local optimization can be carried out from a large number of starting points with no difficulty. The best local optimizers may then be investigated as candidate solutions to the static output feedback or low-order controller design problem. We show results for two problems published in the control literature. The first is a turbo-generator example that allows us to show how different choices of the optimization objective lead to stabilization with qualitatively different properties, conveniently visualized by pseudospectral plots. The second is a well known model of a Boeing 767 aircraft at a flutter condition, For this problem, we are not aware of any SOF stabilizing K published in the literature. Our method was not only able to find an SOF stabilizing K, but also to locally optimize the complex stability radius of A + BKC. We also found locally optimizing order-1 and order-2 controllers for this problem. All optimizers are visualized using pseudospectral piots.

Original languageEnglish (US)
Pages (from-to)175-181
Number of pages7
JournalIFAC Proceedings Volumes (IFAC-PapersOnline)
Volume36
Issue number11
DOIs
StatePublished - 2003
Event4th IFAC Symposium on Robust Control Design, ROCOND 2003 - Milan, Italy
Duration: Jun 25 2003Jun 27 2003

Keywords

  • H-infinity norm
  • Low-order controller
  • Nonsmooth optimization
  • Pseudospectra
  • Spectral abscissa
  • Stability radius
  • Static output feedback

ASJC Scopus subject areas

  • Control and Systems Engineering

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