Research And Implementation Of FBD Program Model And Optimization Technology

In recent years, Fieldbus Control System (FCS) composed of Programmable Logic Controller (PLC) has been widely used in the industrial control field. PLC control system model is helpful for analyzing the control algorithms, real-time performance, reliability performance as well as providing optimization method for the control program.Aiming at standard IEC61131-3 Function Block Diagram (FBD) programming language, a modeling method of PLC program based on state space model is proposed in this paper. The method defines the mapping mechanism which includes transforming the DI, AI points to input vector, DO, AO points to output vector and internal storage data to state vector. Thus, the state space model of PLC program including hybrid variables is established according to the model of Function Blocks and the connection relation among the Function Blocks. The interaction relationship among input, output and internal state is described in the model. Then the controller scan cycle, the network communication cycle and cycles of particular function blocks in control system are analyzed and unified into a whole, served as the scan cycle of the model. In configuration software, algorithm is designed in order to develop and show FBD program model. This part achieves functional block model mapping, network modeling and whole model establishment.Using dimensionality reduction, logic algebra formula, Karnaugh map, timer and counter merging and other rules, the state space model of the PLC program can be simplified, which in turn can provide guidance for program generation. In this way, the control program is optimized. In configuration software, algorithm is designed in order to simplify program model and generate FBD program. Model optimization part reduces model dimensionality through iterative nested. Then use regular expression to parsing the model expressions, so the model can be simplified. Finally, according to the number of equations the model includes, the same quantities of networks are generated. Each equation is divided into several sub-expressions, from which the key information is extracted and the relevant function block type is deterrnined. Based on logical relations among these subs, these Function Blocks can be configured into a whole program.The establishment of program model and the proof of the optimization effects are illustrated by the running lights control program in the configuration software PLC_Config. The result shows, the occupancy rate of memory resources is decreased, and the amount of program code is reduced. Thus the scanning cycle is shortened, and the efficiency of the control system is improved. It proves that the establishment of program model can exploit a new way for program optimization with good reference significance.