Research On Control Strategy And Fault-tolerant Technique Of New DCS Field Control Station

DCS (Distributed Control System) is a control system of centralized management and decentralized control. Since DCS was born in 1975, along with the development of computer technology and microelectronic technology, DCS is being developed towards Information and Integration. Nowadays, DCS is widely used in various fields, such as chemical industry, metallurgical industry, textile industry and pharmacy.This new control system based on industrial Ethernet and Fieldbus is brought forward from the traditional DCS. Industrial Ethernet is used in the communication between FCS (Field Control Station) and the upper supervisory computer, and CAN (Controller Area Network) Fieldbus is used in the communication inside FCS.FCS is the kernel of control system. The main functions of system are performed by FCS, so system performance and reliability depend on it. FCS consists of master controller module and intelligent measuring and controlling modules. Master controller module is the bridge between the upper computer and intelligent modules. Data communication between them must pass master controller module. Also, master controller module performs control algorithms configed by the upper computer. In order to improve reliability of the entire system, fault-tolerant technique is used in master controller module. Redundant module is appended to master controller module to serve as a hot backup.Embedded motherboard PC/104 of industrial grade is used as the hardware platform of master controller module, on which portable embedded operating systemμC/OS-II works.μC/OS-II is a preemptive multi-tasking real-time kernel which is provided in source form, and it has got certified by Federal Aviation Administration.Various functions of master controller module are accomplished by specific tasks ofμC/OS-II. CAN bus driver is embedded inμC/OS-II to realize communication between master controller module and intelligent modules, while uIP TCP/IP stack is embedded inμC/OS-II to realize communication between upper computer and master controller module. Control algorithms configed in upper computer are downloaded to master controller module. Master controller module executes these algorithms before it outputs the operation results. Redundancy function is also accomplished by a task.Every task inμC/OS-II is assigned a distinct priority. Any time, one task at most is running. The highest priority task ready to run is always given control of CPU (Central Processing Unit). Tasks run at their own periods. Correct use of semaphores is the crux of continuous normal running without stop ofμC/OS-II.Control algorithms are the core of system control. PID controllers are widely applied in industrial control fields, as a result of simple structure and easy regulation. Besides, every parameter of PID controllers has a definite physical significance. According to different objects, PID controllers can be improved to help system achieve better results.In real industrial control, real time and reliability are the key indicators of system performance. So, on the premise of real time, more efforts should be made to study system reliability in various areas.