Fixed low-order controller design and H optimization for large-scale dynamical systems

Tim Mitchell, Michael L. Overton

Research output: Contribution to journalConference articlepeer-review


Large-scale linear time-invariant dynamical systems with inputs and outputs present major challenges for controller design. Model-order reduction has become popular in recent years, but controllers designed for reduced-order models may result in unstable closed-loop plants when applied to the larger-scale system. We investigate the practicality of fixed low-order controller design applied directly to large-scale continuous-time sparse systems. We assume that it is practical to compute the eigenvalues with largest real part of such systems using Matlab's eigs, which requires only matrix-vector products, but that it is not possible to compute the H,x norm using Matlab's getPeakGain or SLlCOT's slinorm, which use the Boyd-Balakrishnan-Bruinsma-Steinbuch algorithm, requiring both Hamiltonian eigenvalue decompositions and singular value decompositions. Instead, we employ a recently developed efficient algorithm called Hybrid-Expansion-Contraction (HEC), which while not guaranteed to correctly compute the H norm, finds, under certain assumptions, at least a local maximizer of the associated transfer function. Our controller design code uses nonsmooth optimization techniques first to attempt to stabilize the closed-loop system and then to minimize its H norm proxy as computed by HEC. It is implemented in a new experimental MATLAB code HIFOOS, based on the public-domain HIFOO toolbox first presented in ROCOND 2006, and will be made available for public use after further investigation and development.

Original languageEnglish (US)
Pages (from-to)25-30
Number of pages6
Issue number14
StatePublished - Jul 1 2015
Event8th IFAC Symposium on Robust Control Design, ROCOND 2015 - Bratislava, Slovakia
Duration: Jul 8 2015Jul 11 2015


  • H control
  • Low-order controller design
  • Robust stabilization

ASJC Scopus subject areas

  • Control and Systems Engineering


Dive into the research topics of 'Fixed low-order controller design and H optimization for large-scale dynamical systems'. Together they form a unique fingerprint.

Cite this