FFC incorporating PI controller designed by CDM for temperature control systems

The design of a PI controller for the first order lag plus dead time process control, such as a temperature process, by the coefficient diagram method (CDM) is investigated. The factor of the dead time of the process is first approximated to be the first-order by the Pade approximation. Responses of the temperature control system designed by CDM satisfy both transient and steady state specifications. However, the transient response generally still has long rise time. In order to improve the speed of the system response, a feedforward controller (FFC) is added to the PI control system. The structure of the FFC is a phase lead structure with two designed parameters and one derivative time obtained from the reaction curve of the temperature process. The experimental results show that the performance of the PI control system with properly assigned FFC has short rise time, no overshoot and good disturbance rejection properties.