A new approach to multivariable system design for controller integrity

Integrity refers to the property that a system remains functional despite failures of certain subsystems. In multivariable systems controller integrity means that stability is preserved despite failures of certain sensors or actuators. In this paper we first show by examples that typically multivariable controllers designed by the standard state feedback observer approach lack integrity even when plant and controller are open loop stable. With this background as motivation we develop a technique of designing controllers that do possess integrity. The main mathematical tools are our recent results on computation of sets of stabilizing PID controllers and the Mapping Theorem of Robust Control Theory. The method can be extended beyond PID control and also to the plant integrity problem. Illustrative examples are included and areas for further research are indicated.