Modeling And Evaluation Of Three-phase Unbalanced Stochastic Time Series In Distribution Network

The distribution network contains a large number of single-phase residential load.Affected by living habits,the residential load power has random fluctuations at various moments.This randomness will cause the three-phase load asymmetry in the distribution network and cause three-phase unbalance.With the development of the "rooftop photovoltaic" project,a large number of photovoltaic power sources are connected to the distribution network,which further exacerbates the three-phase unbalance problem.In order to reasonably evaluate the impact of photovoltaic power supply and residents' random uncertainty on the three-phase unbalance of the distribution network,this paper establishes a low voltage from three aspects: three-phase unbalance calculation,behavioral random process,and input random variable sample sampling.Three-phase unbalance evaluation model for distribution network.Firstly,aiming at the situation that the traditional algorithm solves the low-voltage distribution network power flow convergence is not ideal,the node-branch correlation matrix is introduced into the low-voltage distribution network,and the relationship between the total feeder current and the injected current phasor of each node is derived.At the same time,the photovoltaic power supply is processed,and a three-phase unbalance calculation model of the low-voltage distribution network containing photovoltaic is established.Secondly,for the random characteristics of residential load and photovoltaic power output in the time series,the EM algorithm(Expectation Maximization Algorithm)is used to divide the state of residential electricity consumption,and the cloud state is divided based on the cloud cover index.Based on the original Markov chain,a transition matrix that changes with time is established,combined with sequential Monte Carlo state duration sampling,a system state stochastic model is established.Finally,Latin Hypercube Sampling(LHS)is used to combine the system state stochastic model with the three-phase unbalance calculation,and a three-phase unbalance evaluation model for the low-voltage distribution network is established based on Monte Carlo simulation.The rural distribution network in a certain area is used as a test system to verify the rationality and effectiveness of the proposed model.Through simulation analysis,the effect of residential load and photovoltaic power on the three-phase unbalance of the distribution network is studied.