Research On The Method Of Medium Voltage Distribution State Estimation

The distribution network master station is one of the main parts of the distribution network automation system.State estimation in the master station of transmission grid has already been mature and used widily.The limitation of measurements of distribution network that gained by distribution network automation system and the different structure with transmission grid lead the state methods in master sation of transmission grid cannot be directly applied to distribution network master station. Medium voltage distribution network is one of the most important parts of the distribution network and its states estimation is the fundamental function of the master station of distributiob network automation system and the basis of comprehensive analysis and other calculations. A large amount of research has been done on the methods of of distribution network state estimation, but the study of the method of medium voltage distribution network state estimation are deficient and have not been applied practically and widely.The research on the methods of medium voltage distribution network state estimation is necessary.In this paper, firstly, the research status and the challenge of state estimation of medium voltage distribution network have been analyzed.The three-phase mathematical model of medium voltage distribution network is established by the primary connecton mode of medium voltage distribution network and the elements three-phase models.The applications and functions, and the configuration situation of measurement equipment in the measurement system of medium voltage distribution network have been explained.In order to resolve the deficiency of measuremens,the pseudo-measurements are added.The pseudo-measurements are the load power and gained by the combination of short-term load forecasting and ultra-short term load forecasting.The disadvantages of Weighted Least Squares method applied to the state estimation methods of medium voltage distribution network are listed.The feeders of medium voltage distribution network are decoupled by comprehensive nodes to form subregions.The current amplitudes that pass through the edge nodes of the subregion are chose as state variables.The subregions of feeder are generalize nodes. Finally,the current amplitudes of the comprehensive nodes in the whole feeder are estimated by the KCL based on the load current amplitudes that evaluated by the result of the load forecasting results.The reasonability and validity of the method that used to the estimation of the current amplitudes of medium voltage distribution network are verified by practical example.The proposed method is simple and can estimate the current amplitudes of the comprehensive nodes in the feeder of medium voltage distribution network.