The Research On Probability Evaluation Of Voltage Quality In The Rural Distribution Network With Photovoltaic

In recent years,the large-scale access of distributed photovoltaics,the increasing random fluctuation of agricultural production load and the impact of natural weather have brought many uncertainties to the operation of the power grid,and also provided safe and stable operation,prediction and analysis of the power system.Control has had a huge impact.Probabilistic load flow analysis can comprehensively consider various factors to analyze the probability distribution characteristics of the system state quantity,so as to more fully reveal the operating characteristics of the power system.This paper analyzes the flow probability distribution and static voltage stability of low-voltage distribution networks in the context of distributed photovoltaic access to rural low-voltage distribution networks.In order to accurately reveal the influence of distributed photovoltaic on probabilistic load flow analysis in the low-voltage distribution network,this thesis introduces a probabilistic load flow analysis method based on combining cumulant and Laplace transform techniques.Firstly,according to the sensitivity matrix of the input variables(photovoltaic output and load power)to the output variables(voltage amplitude and phase angle,active output)and the branch current matrix are derived.Secondly,based on the sensitivity matrix,a cumulant probability power flow model is established considering photovoltaic.Then,the Laplace transform technique with the cumulant method introduced into the probabilistic load flow calculation.The Laplacian transform method is used to estimate the cumulative probability density of the output random variable.The simulation analysis of the network is carried out as an example,and bying the IEEE-14 bus system and the actual distribution a certain area of Gansu to performe.The results show that the method has high computational efficiency and simulation accuracy.A probabilistic load flow calculation method based on cumulant and hybrid Copula is used to analyze the influence of the random variation of distributed photovoltaic in the distribution network.Firstly,the edge probability density of photovoltaic output is constructed by non-parametric kernel density estimation method,and the hybrid Copula is used to establish the probability model of the relevant random variables.Then according to the photovoltaic output in different periods,single or hybrid Copula function is selected to construct the joint distribution of photovoltaicoutput.Finally,the hybrid Copula dependent structure is combined with the linearized AC flow equation to obtain the probability distributions of bus voltage and branch power flow.The applicability of the proposed method in distributed photovoltaic distribution network is verified by taking the IEEE-33 bus of photovoltaic as the test system.In order to effectively analyze the fluctuation of voltage during photovoltaic access to the distribution network,based on describing the characteristics of voltage distribution,the probabilistic load flow calculation results based on cumulant method define voltage offset index and voltage over-limit index respectively.Finally,an actual distribution network in Gansu Province is taken as an example to verify the proposed method.The results show that the proposed method can better reflect the probability distribution of voltage when distributed photovoltaic is connected to rural distribution network as a whole,and qualitatively analyze the impact of distributed photovoltaic on the voltage of distribution network.