Active disturbance rejection control assisted by a cascade connection of repetitive and data-driven observers

This paper presents a novel estimator that utilizes a cascade connection of a repetitive observer (RO) and a data-driven observer (DDO). The composite estimator is integrated into an active disturbance rejection control (ADRC) scheme, which employs an error-based framework for tracking and rejecting periodic and non-periodic signals. The DDO is responsible for enforcing the reference model of the plant and attenuating disturbances at low and intermediate frequencies. Meanwhile, the RO enhances the disturbance rejection capability specifically at frequencies where harmonic disturbances manifest. The cascade structure enables the multiplication of the sensitivity functions of the DDO and RO, resulting in improved overall performance. Furthermore, the proposed design features a reduced number of tuning parameters, facilitating practical implementation. To demonstrate the advantages of the introduced method, a simulation study is conducted on the current control of a grid-connected converter. This study serves to illustrate the superior characteristics of the proposed approach over conventional resonant control.