Abstract
This paper is concerned with disturbance rejection and stability of Smith predictor control system. It is shown that there are two type of disturbance compensators, which are proper and strictly proper. Smith predictor control system with a proper disturbance compensator has better disturbance rejection, but less stability than the ordinary Smith predictor. By using a strictly proper compensator, it is possible to improve the characteristics of disturbance rejection without damaging the stability of Smith predictor. Moreover, Smith's system which is not robustly stable can be stabilized robustly by the strictly proper compensator.
