Decentralized Control for Multivariable Processes with Actuator Nonlinearities

Decentralized control is the most widely used control strategy in the process industries because of the simplicity to design and implement the controller, and the potential to achieve failure tolerant control. Actuator nonlinearities are often encountered in many chemical processes. This paper presents a decentralized control method for processes which have static actuator nonlinearities, such as saturation and dead zone. The proposed decentralized integral controller is designed based on feedforward passivation, which can be applied to nonminimum phase processes and/or processes of high relative degree. The concept of marginally stable positive real systems is used to analyse the stability of a closedloop system. The feedforward system is constructed to attain dynamic performance on the basis of frequency based passivity analysis. The effectiveness of the proposed approach is demonstrated using an example of a quadruple tank control problem.

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