Design Of Function Block Based On EPA Specification And Research On Schedule Method

With the development of computer networks, communications and control technology, currently the distributed control system based on industrial Ethernet has been accepted gradually by the field of industrial control and continually improved and promoted. "EPA (Ethernet for Plant Automation) system architecture and communication standards" is our first self-owned intellectual property rights fieldbus standard. EPA function blocks as the user-level of EPA protocol, is the core component of a device which can complete the control function, the basic control unit of the entire system, and the key of the control strategy composed of field devices.By analyzing the network structure and communication model of EPA control system, on the base of establishing EPA link objects, achieve the communication between function blocks to ensure that the devices in the system can communicate with each other, so that function blocks in each device can work together to complete the control function. Based on the model of EPA function block, the structure of the function block is designed. Achieve the instantiation of function blocks when the device receives configuration information or re-start. In order to improve the efficiency of the access of function block instances, the function block instances are classified managed by using a hash table.In order to solve the problem that the use of equipment is restricted because of the algorithm within the function block cannot be changed, the composite function block is designed and developed, whose internal algorithm can be edited as needed by the user. By analyzing the overall structure of the composite function block, the variable areas are designed for data store. The implementation of the IEC61131-3 function blocks is detailed, including its structure and execution. Design the storage structure of composite function block algorithms and composite function block instances. Public areas are used to resolve the problem of data exchange due to the difference of data format between composite function block instances and algorithms, to achieve the seamless connectivity between a composite function blocks and standard function blocks. Because there are many differences between the composite function block and standard function block, the instantiation and implementation processes of the composite function block are presented.On the base of analysis of the EPA deterministic scheduling strategy for communication, a scheduling method, for the function blocks execution cooperating with the communication, is proposed. The function block execution and communication are treated as tasks, and the cycles of them are unified as macro-cycle, so that the problem of execution cycle uncertain is avoided. By studying the function block tasks and the relationship with communication task, the macro-cycle setting rules are given, and the method of combining the interrupt mode and search mode is used to achieve the function block scheduling.An actual temperature control system is developed to verify the function blocks. Under the control requirements, use the function blocks for the system configuration. Based on the function block scheduling strategy, the system scheduling parameters are determined, and record the timestamps of the function block instances execution. The results of the experiment show that the function blocks in the devices can be executed correctly in accordance with the configuration strategy, and can realize the functions of the system control.