A simple method of tuning parallel cascade controllers for unstable FOPTD systems. (November 2016)

• Record Type: Journal Article
• Authors: Santosh, Simi; Chidambaram, M.
• Is Part Of: ISA transactions. Volume 65(2016:Nov.)
• Page Start: 475
• Page End: 486
• Publication Date: 2016-11
• Subjects: Cascade control -- PI controller -- Unstable system -- FOPTD -- P/PI controllers; Engineering instruments -- Periodicals; Engineering instruments; Periodicals; Electronic journals; 629.805
• DOI: 10.1016/j.isatra.2016.08.007
• Languages: English
• ISSNs: 0019-0578

Abstract

Abstract: A simple method is proposed to design parallel cascade controllers for open loop unstable processes. A proportional (P)controller is considered for the secondary loop and a proportional integral (PI) controller is considered for the primary loop (P/PI control configuration). Coefficients of the corresponding powers of s (Laplace variable), in the numerator is matched with the coefficients of the corresponding powers of s in the denominator of a closed loop transfer function for a servo problem. Three simulation case studies are considered in this paper. The first case involves a stable secondary loop process and an unstable primary process, the second case involves both unstable primary and secondary processes and the third one, a simulation application to a nonlinear bioreactor model equations. For comparison purposes, P/PI controller design is also carried out by improved simultaneous relay autotuning method, synthesis method and minimizing ISE criterion method. It is found that the proposed method gives a better performance. Robust stability analysis using the complimentary sensitivity function is carried out. The present method is found to be more robust. Abstract : Highlights: Simple method given for designing P/PI parallel cascade controllers. Unstable FOPTD systems are considered. Performance better than the conventional tuning method. The method has robust performance. Simulation results are given for two examples.