Controller synthesis free of analytical model: fixed-order controllers

This paper extends the existing results on model-free approach for three-term controllers to fixed-order controllers. It is shown that knowing the frequency response of a plant is sufficient to calculate a subset of stabilising fixed-order controllers using a set of linear inequalities. The main feature of the proposed approach is that the possible lowest order stabilising controllers corresponding to any stable, unstable, minimum and non-minimum phase plants can be obtained. Also, it is shown that the performance criterion can be transformed to simultaneously stabilising problem for a family of real and complex plants derived from the nominal plant. The usefulness of the proposed approach is illustrated by some examples.