Discrete Event Dynamic System Monitoring Using Supervisory Control Theory

Abstract Using the supervisory control concepts, some extensions are proposed in this paper to synthesize a Monitoring Module (MM) within operational safety context. The MM, added to an existing nominal supervisory control, is based on fault-tolerance techniques and contains three main subtasks: detection, compensation and recovery. When there is no failure, the MM is inactive or in a waking state. At the detection of a critical failure, the compensation is activated to replace the nominal functioning by a degraded one. During the degraded behaviour, the compensator may need to authorize events which are disabled by the nominal supervisor S. To overcome this problem, the control of S is masked when the MM is active. The compensation remains active until the beginning of the recovery whose task is to bring the system back to a “legal” state of nominal supervisory control. After recovery, S is liberated and the MM is again in the waking state. The proposed fonnalization introduces the concept of activation at a high level, the concept of masking a supervisor and the switching function of a supervisor. A mechanism of forcing states is presented. An example illustrates the proposed approach.