Performance improvement of output-feedback tracking control in an augmented ADRC system with a fixed-bandwidth LESO

Robust output-feedback with active disturbance rejection control (ADRC) proved to be a very effective control paradigm for highly uncertain perturbed systems. The main practical limitation of the ADRC results from an application of a conventional high-gain observer which may cause significant amplification of a high-frequency noise corrupting the output measurements. We show that this main limitation can be significantly reduced by augmenting a conventional ADRC system with an auxiliary on-line estimator of the closed-loop tracking error dynamics which contains key residual information, useful for improving a resultant tracking control performance in the augmented ADRC system. It is shown that the tracking control improvement, resulting from an application of the proposed augmentation mechanism, prevents an excessive amplification of feedback noises and keeps a control cost on an acceptable level, especially for systems with higher-order dynamics. The proposed concept has been illustrated by selected results of extensive numerical simulations.