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

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 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.