On the robustness of adaptive controllers using relative deadzones

Abstract Recently sufficient conditions have been presented for robust stability of adaptive control algorithms. The purpose of this paper is to further examine these conditions, and to study the question of robustness and performance for adaptive and non-adaptive controllers. In particular, we compare an adaptive controller with a fixed linear controller for a representative system including structured and unstructured modelling errors. In the case of unstructured modelling errors alone, we show that the theoretical sufficient conditions for signal boundedness of the adaptive controller are comparable with those for the fixed linear controller designed to achieve equivalent performance. When structured modelling errors (i.e. parametric uncertainties) are added, then simulation studies of a second-order system suggest that the adaptive controller achieves superior performance to the fixed linear controller.