Research Of Sampled Data Synchronization Algorithm For Digital Traction Substation

Information synchronization is one of the key problems of digital substation technologies. Application of IEC61850in digital substation exceeds the range of conventional substation communication with further application of network communication technique in multivariate information including substation automation protection, measurement and telecontrol. Based on this background, the synchronous transmission of sampled data which is an important part of substation information can be realized in many forms, of which the algorithm based on software has the advantage of flexible realization and saving hardware investment.The synchronous problem of sampled data is analyzed in this paper. Under the independent circumstance of clock synchronous system, the main study focuses on the algorithm with synchronous processing of the data from different Merging Units (MU) in SMV networking mode.Firstly, according to the basic characteristics of digital substation, sampled data and main equipments in process level based on IEC61850-9-2are introduced in this paper. Clock synchronization of digital substation and synchronization mode of sampled data are analyzed in this paper. Besides, two transmission modes in process level are introduced and aiming at networking mode, combined with the characteristics of digital traction substation, several networking modes in process level are discussed and six preliminary feasible schemes are provided in this paper.In order to further analyze the feasibility of networking schemes when clock synchronous system fails, equipment simulation model in networking mode is built by using OPNET Modeler to simulate transformer bay and feeder bay in separated network and combined network of SMV and GOOSE. By comparing the end-to-end transmission delay characteristics of sampled data, four feasible networking schemes are given, and transmission delay characteristics of PTP messages are verified.Secondly, linear interpolation and parabola interpolation of the basic Lagrange interpolation algorithm and their errors are analyzed in this paper. Based on algorithm complexity theory, it is verified that accelerated over-relaxation Lagrange interpolation algorithm can reduce time complexity effectively. Besides, this paper derives formulas on the basis of transmission delay analysis for synchronous processing of sampled data interpolation algorithm without clock synchronous system, gets extreme cases of maximum errors in sampled value, and research preprocessing for abnormal sampled data.Finally, applications of synchronization algorithm in both effective and ineffective clock synchronization systems are introduced. Especially when the clock synchronization system fails, combined with digital traction substation process level networking mode and transmission delay characteristics of sampled data obtained by simulation. RMS errors of sampled data obtained by using synchronization algorithm in extreme condition are analyzed quantitatively and the impact and adaptation of synchronization algorithm on differential protection are discussed qualitatively in this paper.