Research Of Key Technologies For Network Power Quality Monitoring System

It is an inevitable future trend of power quality monitoring system (PQMS) to realize network, informatization, standardization and intelligent. Rapid development of embedded system and network communication technology creates an opportunity for putting forward the network monitoring scheme of power quality, which can realize continuous on-line monitoring of multiple-spots. With abundant and overall information centralized and various intelligent diagnostic softwares configured, those advanced functions such as tendency judgment, probability statistic, comprehensive evaluation, disturbance event identification and Web services can be achieved in the center workstation. The network PQMS provides advanced supervision and service methods for power quality in distribution network, with increasing incomparable advantages compared to the traditional single-point monitoring scheme.The network PQMS is a new research field of power quality monitoring. This paper summarizes multifaceted challenges for the first time, such as function algorithms, technical realization, economical costs, etc., which are existing in the process of research and application extending of the network PQMS. Several key technologies have been in-depth studied, mainly including disturbance identification of dynamic power quality, comprehensive evaluation of regional power quality, automatic location of disturbance event source, construction of low-cost and high-performance communications network, etc. The creative works of this paper mainly include the following aspects:1.A new system construction scheme of the network PQMS is proposed, which is composed by high-speed distribution line carrier communication (DLCC) network, power quality workstation and a large number of power quality monitors (PQM). Then, structure and functions of the network PQMS are carried out a detailed analysis, design and planning.2.According to the idea of"disturbances generation→characteristics extraction→pattern classification→result analysis", an identification algorithm for dynamic power quality disturbances (PQD) based on Generalized S-transform (GST) and multi-level support vector machines (SVMs) is presented. The PQD signals are transformed into phase space by GST firstly, then, multiple characteristic curves are defined and characteristics are extracted. After that, a pattern classifier is constructed and trained, with the structure of classification decision tree based on multi-level SVMs. Simulation results show that, for dynamic PQD signals with the features such as instantaneity, randomness and nonstationarity, the algorithm has the ability to identify them flexibly, quickly and accurately.3.Based on matter-element and extension theory, a multi-stage extension method is suggested to realize the comprehensive evaluation (CE) of power quality from single-point to various levels of regional. In single-point CE process, a new objective weighting method with time-varying characteristic based on correlation degree is designed, and the traditional subjective weighting method is been improved for its difficulties to determine consistency. In regional CE process, a new index system is established, which's characteristic items include voltage level, load capacity, number of users, importance of the user, user sensitivity, quality performance of the subregions. Based on this, the subjective and objective weighting algorithms for regional CE are developed respectively. Case studies validate the effectiveness of the multi-stage CE method of power quality.4.The location problem of PQD event source in distribution network is explored, and one kind of three-level automatic location algorithm basing on linked-list and matrix algorithm is put forward. Firstly, rapid predict for the feeder sub-regional with PQD is achieved using linked-list method. Secondly, preliminary judgment for PQD event source is realized according to the monitoring coverage matrix and direction information matrix. Thirdly, after the concept of virtual PQM defined, accurate location for PQD event source is implemented with extension matrix algorithm. It shows that the proposed algorithm has many advantages, such as simple and intuitive, low computational complexity, fast and accurate, suitable for computer programming, and etc.5.To reduce construction costs of the network PQMS, a type of high-speed DLCC network scheme with the OFDM technology is adopted. After analyzing the requirement of communication rate to each PQM, the performance of communication rate of the DLCC network is discussed. Then, with the improved analysis method for channel attenuation and the simulation model of the DLCC system based on the OFDM technology, the performance of communication quality is researched, under the influence of three factors including channel characterization, base-band modulation and signal output power. By combining with means of signal broadcasting and transfer matrix, communication link dynamic topology of the DLCC network can be determined. Aiming to minimization of the relay hops, a novel routing optimization method for the DLCC network is proposed. Simulation and analysis verified the feasibility of the DLCC network scheme, and it is able to meet the communication requirements of the network PQMS.