Analysis of First Order Systems with Variable Time Delay using Pi Controller and Smith Predictor

A. Saeidi and H.D. Taghirad (Iran)


PI Controller, Smith Predictor, Stability, Performance, Variable Time Delay.


Smith predictor is one of the first structures used to compensate the time delay in closed loop systems. One of the simplest controllers which are used to control the industrial systems is PID controller. Although, we know that the derivative term is rarely used for controlling the time delay systems. Subtle identification of time delay is usually impossible in reality; on the other hand, PI controller design with smith structure is practiced upon the open loop delay free system. Therefore the structural uncertainty will be existed in open loop systems which make the designing of the PI controller very difficult. In this paper, at first, we analyze the effect of difference between modeled time delay and real time delay on the PI parameters, then the performance of the closed loop system compared with a second order delay free system is investigated; and finally, we compare the tracking of variable time delay system with fixed time delay system which both of them have the same parameters. In this analysis we assume that the fixed time delay is max of variable time delay.

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