Improvement of Robustness of Discrete-Time MRACS by Using Low-Pass Filters

Landau and Lozano proposed a design scheme of discrete-time model reference adaptive control system (MRACS) using low-pass filters to alleviate the influence of noises. We also presented an alternative scheme which is obtained by modifying their scheme regarding to the synthesis of control input in order to improve the robustness to parasitics.This paper discusses the robustness of above two schemes in the presence of parasitics and makes clear the following properties. The scheme by Landau and Lozano does not always contribute to improvement of the robustness to parasitics, because it needs inverse operation of low-pass filters to generate the control input. On the other hand, since our scheme does not require such inverse filter operation, it is superior to the one by Landau and Lozano with respect to the robustness to parasitics. These results are verified by the use of linearization technique and also confirmed by simple examples and simulation studies.