Optimal Design of Guard Conditions of Nonlinear Hybrid Automata

Application to PLC-based ControlSystems

Abstract

Programmable Logic Controllers (PLCs) have been widely used in industry. This class of systems is characterized by its use of low-resolution (typically ON/OFF) sensors and actuators. In PLC-based control systems, the design of sensor parameters is crucial since the sensor parameters as well as the outputs of the plant determine the sensors ON/OFF states, with the parameters finally affecting overall control performance.
In this paper, first, a method for transforming PLC-based control systems into hybrid automata is presented. Here, the sensor parameter design problem can be formulated as the optimal design of guard conditions in hybrid automata. Secondly, the optimal method for designing of guard conditions is proposed. This method is basically based on a graph search method, and can be applied to nonlinear plants. Finally, the usefulness of the proposed method is demonstrated through a numerical example.