Design of DOB-Based Control System in the Presence of Uncertain Delays for Low-Order Processes

This brief is concerned with the design of the disturbance observer (DOB) in the presence of uncertain delay. The stability, robustness, and output performance of the DOB-based control system are studied. First, the zero exclusion criterion is used to study the stability of the characteristic equation with uncertain delay, and a method is proposed to determine the range of the uncertain delay that a given DOB-based control system can tolerate. The effect of the DOB on the stability is analyzed, and some guidelines are proposed to design a DOB-based control system for a process with a given range of uncertain delay. In addition, the disturbance rejection performance and robustness are analyzed. As a result, the method to design a DOB-based control system satisfying multiple objectives in the presence of uncertain delay and disturbance is proposed. Simulation examples show the effectiveness and merits of the proposed method, and the method is successfully used to control the fuel flow of a glass furnace.