Distributed Power Generation Planning Problem Considering Alleviating Three-phase Imbalance In Distribution Networ

With the systematic deployment of regional major strategic ecological environment and the continuous improvement of new energy generation technology,a large number of distributed power sources represented by wind power and photovoltaic are integrated into the distribution system.At the same time,the rapid popularity of high-power devices and electric vehicles makes it difficult for the current distribution grid distributed power planning methods to meet the needs of ensuring the quality of electricity consumption and the economics of grid operation for users.Especially in rural areas with rapid economic development,the quality of life of farmers has improved,and various high-power appliances have become daily necessities for farmers after the transformation of the rural network,which has led to a dramatic increase in single-phase load.The rural power grid with mainly one-way lines did not consider forward-looking from a long-term perspective at the early stage of construction,and the design contains many unscientific points,which makes it difficult for users to ensure simultaneous electricity consumption and similar capacity,leading to the emergence of three-phase imbalance in the low-voltage distribution network.In addition,many users install PV panels independently,their respective models and power generation power are not consistent,and the power generation process is characterized by volatility and uncertainty,which further aggravates the severity of threephase imbalance.In this paper,we systematically analyze the problem of distributed power planning for active distribution networks from the perspectives of electricity safety and economy of operation cost,taking the active distribution network under the access of a large number of household photovoltaic devices as the background.The following work is mainly accomplished:Firstly,based on the relevant domestic and foreign literature,the tide calculation,modeling of controllable devices,correlation processing of distributed power supply,consideration of three-phase unbalance situation and planning problems of distribution network in active distribution network are considered and summarized under the condition of ensuring the optimal power quality and economy,which lay the foundation and theoretical support for this paper to solve the work of distributed power supply planning under three-phase unbalance situation.Secondly,a three-phase optimal tidal model for active distribution network based on Distflow model is proposed.Since the distribution network tide calculation is a nonconvex nonlinear problem,the original model is transformed into a linear model by using the second-order cone relaxation technique,which can be solved quickly by using a linear solver,and it has been confirmed in the literature that the method has good accuracy for such models.It is verified by arithmetic examples that the established model can be optimized by using coordinated active components such as energy storage devices and reactive power compensation in the case of three-phase imbalance,thus ensuring the node voltage quality within the allowable range while ensuring the minimum network loss.Subsequently,the uncertainty and correlation problems among distributed power sources are further considered.Based on the historical data of scenery output,the probability distribution of each generation equipment is obtained by using the nonparametric kernel density estimation method,and then the Frank-Copula function is used to establish the correlation link between them.Different from simple random sampling,to avoid repeated sampling,a large number of samples can be generated by using Latin hypercube stratified sampling technique combined with cholesky decomposition method.Due to the large computational volume,scenes are reduced and classified by K-means clustering method,and the relationship between classification number and classification effect is discussed by introducing DBI index,and finally five classes of classical scenes with their occurrence probabilities are obtained.Finally,based on the active distribution grid optimal tide model and scenario generation considering scenery correlation,a two-tier distributed power planning model is established with energy storage devices and active management components determined.The upper layer model aims at the lowest investment cost,including investment cost,operation and maintenance cost,network loss cost,etc.,and considers the problem of siting and capacity setting of distributed power supply;the lower operation layer uses the established three-phase optimal tide model with the goal of minimizing network loss.The proposed two-layer model greatly reduces the computational effort while ensuring the accuracy of the results.The effectiveness of the proposed method is confirmed by the improved IEEE 33-node model for a rural area in southwest China,where the optimal configuration of distributed power supply considering the degree of three-phase imbalance in the distribution network is obtained.By comparing the experimental results,it can be concluded that the three-phase unbalance situation and reactive power compensation device affect the planning results of distributed power supply to a larger extent.