Research On Harmonic State Estimation And Harmonic Responsibility Division Of Distribution Network

The large-scale application of non-linear loads such as power electronic devices in the distribution network has led to a sharp rise of harmonics in the power grid,and the power quality of the distribution network has continued to deteriorate.In order to ensure the safe and efficient operation of distribution network,it is necessary to define the harmonic state of each node.The harmonic state estimation technology can estimate the harmonic state of the whole power grid by using the limited measurement in the system,which provides an effective help to solve the problem.Secondly,in order to ensure the reasonable implementation of the "reward and punishment scheme of harmonic control",it is necessary to make an accurate assessment of the harmonic responsibility of each harmonic source in the distribution network.Based on the above background,this paper focuses on the problem of harmonic state estimation and harmonic responsibility division in distribution network,and studies the measurement data selection,state estimation,harmonic source location,harmonic responsibility evaluation,etc.The main contents of this thesis and outstanding achievements are as follows:(1)A stepwise estimation method of harmonic state based on the mixed measurement of SCADA measurement data and PMU measurement data is proposed:A hybrid genetic algorithm is proposed to solve the nonlinear harmonic state estimation equation,which solves the problem that the traditional Newton Raphson method needs appropriate initial value on the premise of ensuring the first estimation accuracy;The first estimation result is combined with the PMU measurement data to establish the linear harmonic state estimation equation,and the second estimation is carried out by the robust least square algorithm to improve the accuracy of harmonic state estimation.(2)A method for dividing harmonic responsibilities of multiple harmonic sources in a distribution network based on continuous harmonic state estimation is proposed:Based on the harmonic voltage and current data of each node obtained by continuous harmonic state estimation,all possible harmonic sources in the system can be found by harmonic source location method.After that,the partial least square algorithm is used to divide the responsibilities of multiple harmonic sources,so as to avoid the problem of low accuracy caused by unknown harmonic sources.According to different scenarios of harmonic exceeding standard and different requirements of harmonic control,a dual responsibility index division method based on harmonic voltage and harmonic current is proposed.This measure can provide a comprehensive and reasonable basis for harmonic control.(3)The harmonic responsibility division method of distribution network including electric vehicle charging station is studied.The charging model and harmonic characteristics of EV charging station are analyzed,and the harmonic model of distribution network including EV charging station is established.Secondly,the method of dividing the harmonic responsibility by data segmentation is proposed,which can dynamically follow the change of harmonic responsibility.After that,the weight setting method is used to divide the comprehensive responsibility of the system in a long time scale,which improves the accuracy of the harmonic responsibility division when the harmonic injection current changes.