A modified IMC design for Second Order Plus Time Delayed Processes

Abstract

This paper considers the design of modified internal model control (m-IMC) for a second order plus time delayed (SOPTD) processes. m-IMC has recently been proposed wherein an additional controller is introduced in the control loop of the basic IMC structure. The additional controller can take any form such as a PD, PI, PID controller, a lead-lag compensator, or a transfer function. In this work, the additional controller is considered as a PD controller which introduces an additional tuning parameter and simultaneously enhances the close loop bandwidth of the system and hence the transient performance can be improved. The overall controller has two tuning parameters as compared to the basic IMC which has only one. The controller parameters of m-IMC are tuned to satisfy phase margin (φ m ) and gain cross-over frequency (ω g ) independently. However, for the basic IMC with only one tuning parameter, either φ m or ω g can be chosen. The controller design is validated through simulation results and compared with some well known controllers in IMC. The performance of controllers is verified for transient parameters such as rise time (T r ), settling time (T s ), and maximum overshoot (%M p ). The effectiveness of controllers is evaluated in terms of integral absolute error (IAE), and integral of the time weighted absolute error (ITAE).