Design of Cascade Equivalent-Input-Disturbance Estimator for Control System Under High-Frequency Noise

Abstract

This article presents a cascade equivalent-input-disturbance (EID) estimator to handle the control problem of disturbance rejection in the presence of measurement noise. The standard EID estimator faces a challenge when the output of a system suffers from high-frequency noise, i.e., the estimator tuned to achieve high disturbance-rejection performance is usually extremely sensitive to measurement noise. A new estimator is developed in this study to address the issue by combining EID estimators in a unique cascade form. The sensitivity reduction of a cascade EID (CEID) estimator with p levels, which is related to disturbance rejection, is p times larger than that of a standard EID estimator at low frequencies. Meanwhile, the Bode magnitude curve of the transfer function related to noise suppression is shifted up only by $20\lg p$ dB at high frequencies compared to that of a standard one. This improves disturbance-rejection performance and prevents measurement noise from being over-amplified. The design of a CEID estimator-based control system is provided and the stability criterion of the system is derived. The validity and superiority of the presented method are demonstrated by a deep analysis and simulation and experimental results.