Robust, fragile, or optimal? Academic Article uri icon


  • In this paper, we show by examples that optimum and robust controllers, designed by using the H 2, H , 1, and formulations, can produce extremely fragile controllers, in the sense that vanishingly small perturbations of the coefficients of the designed controller destabilize the closed-loop control system. The examples show that this fragility usually manifests itself as extremely poor gain and phase margins of the closed-loop system. The calculations given here should raise a cautionary note and draw attention to the larger issue of controller sensitivity which may be important in other nonoptimal design techniques as well.

published proceedings

  • IEEE Transactions on Automatic Control

author list (cited authors)

  • Keel, L. H., & Bhattacharyya, S. P.

citation count

  • 615

complete list of authors

  • Keel, LH||Bhattacharyya, SP

publication date

  • January 1997