A modified structure for robustness enhancement of time-delay systems with communication disturbance observer

This paper presents a modified structure for robustness enhancement of time-delay systems with communication disturbance observer (CDOB). A time-delay compensation method based on network disturbance (ND) concept and CDOB has been proposed and applied to various time-delay systems. The effectiveness is the same as Smith predictor. In addition, it works even when the value of time delay is unknown, since the method compensates time-delay effects without time-delay models. However, it has a problem of the robustness on system model errors. In case there are model errors of the system, serious steady-state error occurs. In this paper, a modified structure that enhances the robustness of time-delay systems with CDOB is proposed. The structure enhances the robustness and achieves zero steady-state error. The effectiveness of the proposed structure is presented by a case study of a time-delayed motor control system. In addition, this paper addresses stability and transient characteristics of the proposed structure.