Metro substation automation based real-time embedded system

Metro substation automation system (MSAS) manages many intelligent electronic devices (IEDs) and performs online control, data acquisition, information retrieving and communication with remote control center (CC). A MSAS based real-time embedded system is designed in this paper. It consists of station management level, network communication level and field level. In network communication level an embedded real-time PC-104 system with 2 WMbps fiber-Ethernet ports is employed as network communication device (NCD). NCDs provide different field-bus interfaces to IEDs. In MSAS many policies have been adopted to optimize its real-time response ability, reliability and flexibility. Firstly, optical fiber media is used for Ethernet connection. Secondly, no matter network-bridge PC or embedded PC-104 system adopt real-time operating system QNX. Thirdly, publish-subscribe architecture instead of client-server is adopted to lower the LAN load. Fourthly, two data queues owning different transfer priority and QoS policy are separately established for control & status data and analog data. At last, the high-precision time synchronization in MSAS is realized through network time protocol (NTP).