Hierarchical supervisory control systems

This thesis presents two approaches to the hierarchical supervisory control of discrete event systems (DES) modelled as finite deterministic automata.; First, a hierarchical control theory based on the aggregation of states is presented that differs from the standard approach to hierarchical supervision which mainly employs formal language methods. A high-level (i.e. aggregated) deterministic automaton model is defined that uses notions of dynamical consistency (DC) in the definition of high-level transitions. A Trace-DC condition is then defined on any given state-space partition which ensures that (i) trajectories in the low-level system are always represented in the high-level system, and (ii) trajectories in the high-level model are realized by trajectories in the low-level system. It is also shown that the Trace-DC condition ensures low-level controllable behaviours (languages) are represented as high-level controllable behaviours.; The (Non-Blocking) In-Block-Controllability condition on partitions is then defined that ensures that behaviours that are expressly controllable in the high-level model can be achieved through the control of high-level transitions between blocks combined with local state - feedback controls in each block. A so-called vocalised lifting algorithm is proposed for the construction of Trace-DC partitions. It is shown that this formulation of hierarchical supervision satisfies conditions of hierarchical consistency from the literature on formal language-based hierarchical supervisory control theory.; The approach is illustrated with several examples of manufacturing production lines, including a re-entrant transfer line and a line with two sequential queues. An application to the embedded control of home appliances (washing machines) which motivates the approach is summarised.; Second, a notion of systems of interacting finite deterministic automata is formulated via a newly proposed multi-agent ( MA) product. The transition relation of the MA product is shown to be the intersection of the transition relations of two associated products, the vector state-dependent synchronous product and the simultaneous product. It is shown also that the language accepted by the MA product is the intersection of the so-called embedded constraint language of each agent.; The supervision of one agent by another is then considered and it is shown that the standard finite automata realization for a supervisor can be employed as the model for the supervising agent.; A line of research is then initiated on the centralised, decentralised and hierarchical supervision of MA product systems. It is shown that the MA product of behaviours that are individually and independently controllable with respect to each agent forms a controllable behaviour in the MA product system.