Asymptotic Reference Tracking and Disturbance Rejection of UDE-Based Robust Control

The uncertainty and disturbance estimation (UDE)-based robust control strategy is able to achieve good robust performance by estimating and compensating the uncertainty and disturbance in a system with a filter having the appropriate frequency characteristics. However, how to systematically design the filter and the reference system in a UDE-based control system to achieve asymptotic reference tracking and disturbance rejection is still missing in the literature. In this paper, this is solved by applying the well-known internal model principle. The conditions to guarantee the closed-loop system stability and to achieve asymptotic disturbance rejection and reference tracking are derived. Experimental results on a servo system are presented as an example to demonstrate its excellent performance, which can actually reach the hardware resolution limit, with comparisons to the disturbance-observer-based control and the active disturbance rejection control.