Nonblocking supervisory control of state-tree structures with event forcing

For complex discrete-event systems, state-tree structures (STSS) have demonstrated significant advantages in terms of the modeling and supervisor synthesis. The notorious state explosion problem can be effectively managed in STS. In this paper, the STS framework is enhanced with the concept of event forcing. Intuitively, event forcing is utilized to deny permission for the occurrence of undesirable competing events, that is, such events are directly or indirectly disabled. To reflect event forcing in STS, a systematic on-the-fly procedure during supervisor synthesis is proposed, which benefits the computational effort of computer memory and time cost. In addition, an incrementally iterative algorithm is developed and the computational complexity of it is polynomial with respect to the number of binary decision diagram nodes in use. Finally, several case studies are provided for evaluating the performance of the method. The experimental results show that the proposed method is computationally efficient for supervisor synthesis of a discrete-event system imposed event forcing.