Research And Design Of PLC Simulation System Based On IEC 61131-3 Standard

IEC 61131-3 standard is the first international standard that provide standardized programming languages for the industrial control system. The software design concepts and models elaborated from this standard adapt to the development of software and industrial control system. It plays an important role in promoting the development of the programmable logic controller software technology, and even the industrial control software.The main topic of this subject is designing a PLC simulation system met the IEC 61131-3 standard. This system depends on neither the specific PLC nor other control system hardware. It constructs an open programming and simulation environment realizing many functions, such as programming, transformation, simulation, and so on. With the simulation system, users can not only design and program PLC ladder diagram, but also compile instruction list language control program. Meanwhile, they transform freely between the two languages. If the ladder diagram program is finished, the simulation function support users with verifying the program for further modification and perfection.First, this paper introduces the recent research status and developing trends of the PLC simulation system and IEC 61131-3 standard. Second, a general design of the simulation system with object-oriented programming and modular ideas are given. The XML language is used to describe the ladder structure to follow the IEC 61131-3 standard. On this basis, the programming system is designed, which support two kinds of programming languages including ladder diagram and instruction list. Users can demonstrate and edit both the ladder diagram and instruction list program that met IEC 61131-3 standard. Moreover, control procedures can be transplanted between different programming and simulation systems as long as they support standard programming languages. In view of the conversion between ladder diagram and instruction list programs, the transformation algorithm is presented based on XML and binary tree. Compared with the traditional algorithm based on AOV diagraph, the presented algorithm significantly reduces the complexity of the algorithm. In addition, it can be used for the complex ladder conversion because it describes the logic relations between instructions in the ladder program with binary trees. Simulation module is the core content of this design. The simulation system supports off-line program simulation and provides a variety of monitoring modes, such as intuitive ladder status display, variable monitor and sequence diagram. It also supports varied simulation modes including the continuous and single step simulation. Test results show that the function of simulation system meets the designing requirements, and can be used in the design of practical PLC control program. Finally, summary of this subject is made and the prospect of future work is suggested.