Stable Sub-Optimum Controllers for the Smith Dead Time Compensation

Dahlin and Dead-Beat controllers are analyzed in connection with the Smith Dead Time compensation scheme. It is well known that the Smith configuration needs explicit knowledge of the process dead time. This paper proposes modifications in the Dahlin and the Dead Beat controllers in such a way that the explicit knowledge of the dead time is not needed in the controller. This is a desirable feature in real life applications due to the fact that the reliable estimation of the process dead time is not always easy to obtain. Stability and the steady state performance of these algorithms are analyzed theoretically. It was proved that a low pass filter in the feedback path can be used to stabilize the system. Furthermore, it was also shown that this filter does not effect the steady state performance of the control system.