Compilation Technology For Control Program Based On Event Graph Method

Programmable Logic Controller (PLC) is the basic unit of Distributed Control Systems (DCS). In recent years, as the development of computer science, communication technology and control technology, DCS have been widely used. At present, the configuration software can only be used for single PLC programming, so it is inconvenient to design and analyze control programs with the various dispersing of PLC logic. Therefore, programming for DCS without specific devices in an unified way has great development value and application prospect.A compilation approach based on event graph is proposed referring to the dependencies among variables for FBD programs. The programs of the controlling network are mapped to Discrete Event Systems(DES). Variable transitions and instruction executions are mapped to events and scheduling activities. Create an Event Graph model for control programs according to the relationship between variables and connections. This model describes the interactions between input variables, internal variables and output variables. It put forward a new event graph traversal rule based on Depth First Search(DFS). This rule can analyze the dependencies of control programs and extract instruction sequences which don’t have coupling relationships.According to the principle of minimum communication time and load balancing, instruction sequences are assigned to different devices based on the types of I/O variables while control programs are downloaded accurately. Through analyzing the topology of DCS, the communication paths and communication instructions can be got. Then variables in different devices can be refreshed automatically.A configuration software named DConfig is developed with Visual Studio2005. It can program for DCS in an unified way. Building monitoring system is designed as an example to verify the effect of the compilation approach. The result shows that instructions can be downloaded to corresponding devices and I/O variables are refreshed automatically while the control logic is correct. The compilation approach can solve the contradiction between unified programming and distributed downloading and be applied to network-oriented programming.