On robust PIλDμ control for time-delay non-integer order plants

This paper deals with the robust control of time-delay non-integer order plants by means of standard noninteger order controllers. Precisely, a method for determining the parameter regions where a PI^λD^μ controller ensures a given modulus margin (inverse of the H_∞ norm of the sensitivity function) is presented. This method, which is conceptually simple and intuitive, extends to the aforementioned general classes of controllers and plants the approach recently followed by the present authors in the integer-order case. A Matlab^® program to plot the loci of constant modulus margin and those of constant crossover frequency has been written and applied to some numerical examples taken from the literature.