Sequential Design Method for Multivariable Decoupling and Multiloop PID Controllers

Abstract

Underlying algorithms for designing multivariable decoupling and multiloop PI/PID controllers in a sequential fashion are addressed. A single-loop technique, composed of biased relay identification schemes and tuning formulae leading to the minimum weighted integral of square error, is developed to tune each loop in the predetermined sequence of loop closing. The proposed tuning technique is appropriate for a wide range of process dynamics in a multivariable environment. A method is then proposed to design decouplers to compensate for the effect of interactions and tune the resultant weakly interacting, single-loop PI/PID controllers sequentially. The decouplers, together with the single-loop controllers, constitute the multivariable decoupling controller. If the interactions are not significant, multiloop PI/PID controllers, which do not incorporate decouplers, could be employed. Simulation and comparative results are shown for one 2 × 2 and one 3 × 3 multivariable system from the literature. Despite its simplicity, the proposed design method yields superior multivariable designs on the basis of performance, robust stability, and integrity.

Inter-Communicative Decentralized Multi-Scale Control (ICD-MSC) Scheme: A New Approach to Overcome MIMO Process Interactions

“…The performance/robustness of the ICD-MSC scheme is compared with the decentralized control scheme of Shiu and Hwang [8] with partial decoupling structures. In the Shiu and Hwang partial decoupling scheme, three decouplers are used.…”

“…In the Shiu and Hwang partial decoupling scheme, three decouplers are used. Thus, in this case the proposed ICD-MSC scheme is much simpler than the Shiu and Hwang [8] decoupling multi-loop control scheme.…”

“…The sequential design approach was introduced in 1970s [6] and has been quite extensively studied, e.g. Shiu and Hwang [7], Hovd and Skogestad [8], and Loh et al [9]. One of the common disadvantages of the sequential loop closing is that the final control system performance might not be satisfactory because the order of the loop closing often affects the control performance overall.…”

Decoupling Multivariable Processes using Partial Least Squares for Decentralized Control

“…Gagnon et al (1998) provided guidelines and summary of advantages & limitations of decoupling methods for 2×2 systems [10]. Shiu & Hwang (1998) presented sequential tuning of MIMO control system based on ultimate frequency that ranks each loop from fast to slow [11]. Gjosaeter & Foss (1997) argued that discarding the use of decouplers for ill conditioned process is not essential [12].…”

Design of decentralized IMC‐PID controller based on dRI analysis

“…However, the design procedures for obtaining the less conservative detuning factors are complex and require higher calculation load. In the sequential loop closing method, 9,10 by taking interactions from the closed loops into account in a sequential fashion, multiple single-loop design strategies can be directly employed. The main drawback of this method is that the design must proceed in a very ad hoc manner.…”