Performance Preserving Frequency Weighted Controller Approximation: A Coprime Factorisation Approach

P.J. Goddard and K. Glover

Abstract

Given a stabilising controller which satisfies a prespecified H-infinity performance bound on the closed loop we derive sufficient conditions for reduced order controllers to be stabilising and satisfy the same performance bound. The conditions are expressed as norm bounds on the frequency weighted error between coprime factor representations of the given controller and the reduced order controller. Reduced order controllers are then designed by interpreting the sufficient conditions as frequency weighted model reduction problems.

Keywords Controller order reduction, Frequency weighted model reduction, Coprime factorisations, H-infinity.