Decentralized Control System Design for Multivariable ProcessesA Novel Method Based on Effective Relative Gain Array

Abstract

In this paper, a novel method for design of a decentralized control system for multivariable processes is proposed. On the basis of a new interaction measure, effective relative gain array (ERGA), in terms of energy transmission ratio, loop interactions are quantified by two elements, i.e., relative gain and relative critical frequency. The interaction effects for a particular loop from all other closed loops are analyzed through both steady-state gain and critical frequency variations. Consequently, appropriate detuning factors for decentralized controllers under different interaction conditions can be derived based on the effective relative gain, relative gain, and relative critical frequency. The design method can be effectively used for both normal processes as well as process-loop transfer functions containing unstable zeros resulted from other closed loops. This design method is simple, straightforward, and effective and can be easily understood and implemented by field engineers. Several multivariable industrial processes with different interaction characteristics are employed to demonstrate the effectiveness and simplicity of the design method.