Inversion-free decentralised quantitative feedback design of large-scale systems

In this paper, a new method for robust decentralised control of multi-input multi-output (MIMO) systems using quantitative feedback theory (QFT) is suggested. The proposed method does not need inversion of the plant transfer function matrix in the design process. For a given system, an equivalent descriptor system representation is defined. By using this representation, sufficient conditions for closed-loop diagonal dominance over the uncertainty space are obtained. These conditions transform the original MIMO system into a set of isolated multi-input single-output (MISO) subsystems. Then, the local controllers are designed by using the typical MISO QFT technique for each isolated subsystem to satisfy the predefined desired specifications and the closed-loop diagonal dominance sufficient conditions. The proposed technique is less conservative in comparison to the approaches using the over-bounding concept in the design procedure. The effectiveness of the proposed technique is finally assessed on a MIMO Scara robot.