Disturbance Rejection and Noise Suppression for Control System Using Cascade Equivalent-Input-Disturbance Approach

Measurement noise poses a challenge in the disturbance-rejection control of industrial systems. In particular, the parameters of a control system chosen to achieve high disturbance-rejection performance make the system sensitive to measurement noise. This article presents a cascade equivalent-input-disturbance (EID) approach to address the tradeoff between disturbance rejection and noise suppression by combining state observers and EID estimators in a cascade form. The configuration and the design of a cascade EID-based control system are provided. The performance of disturbance rejection and noise suppression is analyzed in the frequency domain. It is shown that increasing the number of cascade levels improves disturbance-rejection performance without amplifying measurement noise. It is proven that noise-suppression performance is mainly determined by the parameters in the first level of the cascade form. A stability criterion is derived by dividing the system into several subsystems. The validity and effectiveness of the presented method are demonstrated by simulation and experimental results.