Direct Synthesis Controller Identification Lemma Dendena Tufa Chemical Engineering Department,Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 31750 Tronoh, Perak, Malaysia. lemma_dendena@petronas.com.my Keywords: Direct Synthesis, controller identification, controller design, inverse identification Abstract. Direct synthesis controller design approach has serious limitations when it is applied to plant models that have more complex models and models involving time delays. In such cases the design becomes more cumbersome and the time delay appears in the denominator making it difficult to realize. In order to get simple realizable controllers approximations of plant model and time delays are done. This leads to controllers with non-optimal parameters. In this paper, a new approach for designing the controller by combining direct synthesis approach and system identification is presented. The controller is identified from the plant model and the desired closed- loop without the need for approximating the plant model and the time delay and ensures that the controller parameters are optimal. Introduction Direct synthesis controller design is an established controller design approach [1-3]. It enables to design the controller structure and its tuning parameters simultaneously and follows a logical design process where the control strategy [4-6]. Chen and Seborg [7] proposed a design method for PID controllers based on the direct synthesis approach and specification of the desired closed-loop transfer function for disturbances. They derived analytical expressions for several common types of process models. Ramasamy and Sundaramoorthy [4] proposed a method of designing PID controllers using ‘impulse response’. Avoiding the need for explicit plant model for the design of PID controller parameters based on the direct synthesis approach. They used the direct synthesis approach to PID controller design using the Maclaurin series of the desired closed-loop transfer function, truncated up to the first three terms. Seshagiri, et al. [8] used the direct synthesis method for designing a PID controller in series with a lead/lag compensator together with set-point weighting to control open loop integrating processes with time delay. They reported that the method gives significant load disturbance rejection performances. In their analysis, they replaced all time delays with first order Pade' approximations. Currently, one of the most popular and effective approaches for tuning PI and PID controllers is the Skogestad approach [9]. The approach is based on approximating the plant model with either a first order plus time delay (FOPTD) or second order plus time delay (SOPTD) and then designing the controller using direct synthesis approach. In using, the direct synthesis approach the time delay in the denominator is approximated using first order Taylor's approximation. The performance of controller based on approximation, among other things, depends on the accuracy of the approximation of the plant model and the time delay. However, there is no any mathematical justification for the parameters of such controllers to be optimal for the structures proposed by the authors. Current Work In this section, a different approach to design controller in which the optimal parameters for a selected structure can be determined without the need for approximating the plant model and the time delay is proposed. Advanced Materials Research Vols. 622-623 (2013) pp 1498-1502 © (2013) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/AMR.622-623.1498 All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, www.ttp.net. (ID: 203.135.191.3-18/10/12,10:45:43)