Research And Implementation Of Function Block Based On EPA

Distributed control system is accepted by production manufacturing and process control industry now. EPA, the distributed Ethernet fieldbus standard, is published as the fourteenth type of international standard IEC61158 fourth edition. Function block is the basic control unit of EPA fieldbus control system(FCS) and the primary part of control strategy composed of field device, therefore the research of the function block is in favor of EPA standard's extension.Followed by the structure and concept of function block provided by IEC61499 standard, the function blocks for EPA fieldbus control system are designed. In view of improving function block's self-diagnosis and self-adaptation, the transmission of parameter's state and the transition of function block's working mode are adopted to realize the detection and disposal of function block trouble, preventing integral saturation, and bumpless mode switching. According to the unreasonable usage of field device's resource because of the function block number's fixation, function block hash is designed to manage standard function block for function block's dynamic instantiation. As the executive control algorithm of function block, the time and event triggering methods proposed by IEC61499 standard are realized.Because the type of standard function blocks is single, which can't meet the requirement of engineering application, the flexible function block(FFB) is presented to realize the programmable function block. Two storage areas for the input and output parameters in FFB are applied to realize the dynamic change of the input and output parameters' type and number. And these areas defined as two special variable areas are operated with others defined in FFB algorithm synchronously. The algorithm and inner variables of FFB are edited by using the standard programming language for program logic control(PLC) defined in IEC61131-3. FFB algorithm domain is presented to manage FFB instance for the realization of FFB dynamic instantiation. The execution of FFB is realized by scanning and executing all function instructions in FFB algorithm.For the system's stability and real-time, the execution process of function block task and communication task in device is presented based on pipeline parallel technology and compact mode concept. Based on adopting event triggering method, the earliest deadline first(EDF) arithmetic is used to decide the order of event execution, which is the function block scheduling mechanism. Meanwhile, the corresponding link layer scheduling mechanism is confirmed, which includes the length of periodic message timeslice and macro cycle.The function blocks are applied in practical system, and it is indicated that the software can realize the distributed control by applied in the multi-loop control composed of several devices, and it can also realize the programmable function block by editing the FFB.