Chapter 14 - Structure of Reliable Controllers

Abstract

In recent years, the reliable control system design has been studied. The integrity is one of the theories of the reliable control. The integrity is the property that closed-loop systems remain stable even if there exists some outages of sensors and/or actuators. Although integrity is a very important property, it may be too conservative because it ensures the stability of the open-loop systems. This chapter investigates the integrity conditions from the viewpoint of the small gain theorem and the LFT-scaling. The chapter demonstrates the effectiveness and the flexibility of the LFT-scaling approach to design reliable control systems. The numerical example, given in the chapter, shows that the method by Asai et al. achieves higher performance than that by Veillette et al. The numerical example also shows that the designed controller is not full rank.The chapter also investigates the reasons for the rank deficiency. As decentralized controllers are always full rank, rank-deficient centralized controllers might have an advantage in integrity over decentralized controllers. This conjecture might affect the motivation to use decentralized control systems. Thus, further research should be made on this topic.