H∞ identification for robust control

In this paper, the role that frequency domain model identification performs in the controller design for single input, single output systems is developed. H_∞ control design methods can guarantee the stability of a closed loop system with the plant only partially known, provided the controlled nominal plant as well as the uncertainty are stable and the frequency response of the plant uncertainty can be bounded. The nominal performance of such a closed loop system is critically dependent on the class of uncertainty that must be designed for, as well as the actual (but often unknown) accuracy of the model. Thus it is a primary aim of this paper to address conservatism in the modelling error bounds in order to enhance the ultimate performance of the controlled plant. The techniques for experiment design, frequency response estimation, model identification, estimation of priors and bound calculation that are developed are demonstrated in the case study which identified a model and bound for the vertical plasma dynamics of a tokamak fusion reactor.