Abstract
This paper presents novel tuning formulas for two-degree of freedom PID-family controllers. The structure of the proposed control system consists of a plant or process to be controlled, P or PI or PID controllers and a pre-filter. The tuning formulas are derived based on the CDM design method by solving CDM algebraic equations obtained from the known controllers' structures and the approximated plant model based on the experimental test. The proposed formulas are summarized in the tuning table and can be used easily. To apply the tuning rules, the plant or process is firstly tested to find the values of critical gain and critical period experimentally in the same manner as Ziegler-Nichols' second method. The parameters of P, PI or PID controller and the associated pre-filter are then obtained by substituting those values in the formulas. The experiments in controlling the level process with long pipeline controlled by the controllers tuned by the proposed rules and the well-known Ziegler-Nichols' formulas are conducted and compared. The proposed control systems result in responses with shorter settling time and considerably smaller or no overshoot. Overall, the proposed formulas are well applicable despite their simplicity.
