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Mathematical Problems in Engineering
Volume 2014 (2014), Article ID 521460, 7 pages
Research Article

Enhanced PID Controllers Design Based on Modified Smith Predictor Control for Unstable Process with Time Delay

School of Mechanical and Automobile Engineering, Liaocheng University, Liaocheng 252059, China

Received 1 July 2014; Revised 30 August 2014; Accepted 1 September 2014; Published 29 September 2014

Academic Editor: Hongli Dong

Copyright © 2014 Chengqiang Yin et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


A two-degree-of-freedom control structure is proposed for a class of unstable processes with time delay based on modified Smith predictor control; the superior performance of disturbance rejection and good robust stability are gained for the system. The set-point tracking controller is designed using the direct synthesis method; the IMC-PID controller for disturbance rejection is designed based on the internal mode control design principle. The controller for set-point response and the controller for disturbance rejection can be adjusted and optimized independently. Meanwhile, the two controllers are designed in the form of PID, which is convenient for engineering application. Finally, simulation examples demonstrate the validity of the proposed control scheme.