An Integrated Approach to Controls and Diagnostics: The 4-Parameter Controller

In this paper we present a theoretical basis for an integrated approach to the design of reliable control systems. In this approach, the control and diagnostic modules of a reliable control system are designed together, instead of independently, thereby accounting for the interactions which occur between these two modules in a functioning reliable control system. The approach makes use of a significant generalisation of the familiar 2-parameter controller known as the 4-parameter controller. This controller has two vector inputs and not one, but two vector outputs; correspondingly, this controller is comprised of not two, but four matrix parameters. The additional controller output is monitored to detect and isolate sensor and actuator faults, thereby providing the controller with diagnostic capabilities, or "intelligence," in addition to its control capabilities. Using a parameterization of all stabilising 4-parameter controllers, the fundamental limitations and inherent tradeoffs governing the design of reliable control systems are clarly delineated, with special attention given the issues of uncertainty and control/diagnostic interaction. Several means for resolving these desig tradeoffs are proposed, and illustrated by way of non-trivial examples. These results are expected to pave the way for the achievement of improved overall control/dignostic performance in reliable control systems, and also to pave the way for the achivement of significant complexity reductions in both the design and implementation of reliable control systems.