Research On Power Quality Evaluation And Inprovement Of Low-Voltage Distribution Network Considering Three-phase Unbalance

With the increasing proportion of distributed power in the distribution network,the grid connection of distributed power has had an important impact on the power quality of the distribution network.In order to get the power quality improvement method of distribution network,this paper mainly studies the power quality evaluation of distribution network and the power quality optimization allocation scheme of distributed power connected to the grid.This paper briefly introduces the characteristics of distributed power supply,explores the influence mechanism of distributed power supply on distribution network,and analyzes the influence of grid connection of distributed power supply on line loss and power quality by simulating a 12-node low-voltage distribution network in a certain area.Aiming at the power quality evaluation problem of distribution network with distributed power supply,the voltage deviation and three-phase unbalance degree of power quality are analyzed,and the power quality index is classified according to the national standard.In order to avoid subjective factors affecting the evaluation results,a comprehensive evaluation method of power quality based on BP(Back Propagation)neural network algorithm is proposed.Considering the voltage deviation and threephase unbalance in power quality,a comprehensive power quality evaluation system is constructed to evaluate the power quality of distribution network with distributed power supply.In view of the influence of grid-connected distributed power supply,the optimal allocation model of phase selection location and capacity of distributed power supply based on whale algorithm is established by taking power quality and network loss as comprehensive objective functions.Taking a 28-node low-voltage distribution network in a certain area as an example,four different grid-connection methods were selected to optimize the configuration,and the optimal location,capacity and phase configuration scheme of distributed power supply was obtained.The results show that the optimal configuration effect of single-phase and three-phase hybrid grid-connection of distributed power supply in this example is the best.Aiming at the power quality improvement problem of the joint configuration of SVG and distributed power supply,the basic principle of SVG is briefly introduced,and the influence of SVG access on the distribution network is analyzed.Using isometric sampling method and pseudo-reverse learning strategy to generate population,introducing threshold control method and nonlinear convergence factor improvement strategy,an optimized power quality allocation method based on improved whale algorithm is proposed.Whale algorithm,genetic algorithm and improved whale algorithm were used to optimize the configuration of 28-node distribution network in a certain region,and the distributed power access location,capacity and phase,and SVG access location and capacity configuration schemes were obtained.Compared with the results of the three algorithms,it is verified that the proposed improved whale algorithm is superior to genetic algorithm and whale algorithm in improving power quality and reducing line loss in distributed distribution network.