Decentralised design of robust controllers

The paper presents a procedure for improving the feedback properties, including robustness, of a decentralised multivariable feedback system designed by a quadratic index optimisation methodology. The procedure allows the possibility of adding extra controllers which can be used to fine-tune the closed-loop behaviour of the nominal control system. Although attention is focused on the quadratic index methodology, the basic approach can be applied to adjust the design parameters of any decentralised design methods. The methodology and design procedure are illustrated by considering two numerical examples, including a 9th-order power system with a five-terminal DC network configuration.