A simplified structure for robustness enhancement of time-delay systems

In this paper, we propose a simplified control structure for robustness enhancement of time-delay systems. We have developed a time-delay compensation method based on network disturbance (ND) concept and communication disturbance observer (CDOB). The method effectively compensates time-delay effect and stabilizes time-delay systems. It has been validated that the effectiveness of the time-delay compensation is equivalent to Smith predictor. However, a defect in robustness on model errors has been revealed. Steady-state errors depending on model errors arise in responses. In order to handle the problem, various approaches have been proposed so far. However, sufficient robustness enhancement without degradation of stability and control performance has not been achieved yet. Therefore, this paper proposes a simplified control structure of time-delay systems without CDOB. The proposed structure accomplishes robustness enhancement on model errors without significant degradation of performance. The stability and the transient characteristics are analyzed and the validity is clarified. Then, the effectiveness of the proposed structure is validated by simulation results.