A Singular Perturbation Analysis of High Frequency Filter Design

This paper concerns the control design of systems with lightly damped high frequency oscillatory modes. Systems exhibiting these lightly damped modes include turbine-generators and large flexible structures. Frequently the dynamics of these high frequency modes are not known very accurately. As a result, the design objective is to improve the slow dynamics without destabilising the high frequency modes. From a classical frequency domain design viewpoint, this is in part a filtering problem requiring some kind of high frequency filters. In this paper we use the singular perturbation method to systematically develop a two-time-scale method to design these high frequency filters and provides guidelines on what kind of high frequency filters to be used. In addition, the method provides an asymptotic error analysis. The design is illustrated with an example representative of a power system model with a two-mass turbine-generator model.