Synthesis of Supervisors for a PID-Controlled Industrial Process and Implementation on Foundation Fieldbus

Abstract

Abstract This paper exploits the Supervisory Control Theory for the synthesis of minimally restrictive and nonblocking discrete-event supervisors that ensure safety specifications for both the normal and non-routine operations of a PID-controlled industrial process. The discrete-event dynamics of the components of a tank level control system is modeled in such a way that supervisors may indirectly avoid undesired level thresholds by deciding on the occurrence of controllable events of a valve, pump and operator interface. A modular control and coordination scheme is used to avoid state-space growth in synthesis. The reduced supervisors are implemented in PLC that turns the pump on and off and saturates the outputs of a PID-controller on a Foundation Fieldbus only when necessary. The experimental results on a real plant shows that supervisory control may effectively assure a safe behavior during startup, steady state and shutdown with minimal intervention on the process.