Attenuation of periodic disturbances via customized ADRC solution: a case of highly oscillatory 3DOF torsional plant

In this work, the problem of estimating and suppressing periodic disturbances in feedback control systems is addressed. The problem is formulated and solved here in the framework of active disturbance rejection control (ADRC). The new, custom ADRC-based solution uses a a special modified version of a resonant extended state observer, a recently introduced tool dedicated to reconstructing harmonic-type uncertainties. The controller synthesis is performed in the absence of a detailed plant mathematical model, with only a rough value of disturbance frequency needed. In order to make the proposed observer-based control structure more practically appealing, it is expressed here in an alternative, error-driven form, which makes it resemble industry-proven feedback controller forms (like PID). The effectiveness of the proposed scheme is validated through laboratory experiments conducted on a 3DOF torsional plant, in which trajectory tracking task has to be realized despite the presence of periodic disturbance coming from the underactuated, unmodeled, compliant plant dynamics.