Investigating Dynamic Behavior of Control Systems Including Time-Delay Smith Predictor

The problem of Time-Delay or Dead Time (DT) in control systems is an old problem which is of primary importance in process control as well. It is known as one of the main effects in attenuating the performance of control systems. The first proposed solution for this problem was the Smith predictor in 1957. It was based on the idea of removing the time-delay from the characteristic equation of the control loop, which seemed to be very attractive at the first. In this paper the dynamic behavior of the open loop transfer function of control systems with Smith dead-time compensator were investigated. The various cases resulting to limited or non-limited phase behavior were discussed. In this way the stability characteristics of such systems were discussed and revealed that it is possible to make the behavior of the closed loop system to trace the behavior of the minimum phase term available in the open loop transfer function of the system for improving the performance of the control loop.