Research On Photovoltaic Source Access Capacity Of Low Voltage Distribution Network Considering Power Quality Constraints

With the increasingly serious environmental problems and the increasing awareness of environmental protection in the world,traditional energy has not been able to meet the needs of sustainable green development of human society,and the development and utilization of renewable clean energy has become an important direction of current and future social energy development.In the renewable clean energy,photovoltaic power has the advantages of abundant resources,safety and reliability,and not subject to regional restrictions,which has been widely concerned and valued by all countries in the world.When photovoltaic power injects clean energy into the power grid,its active and reactive power output also changes the power distribution network trend,which has a significant impact on the operation of the distribution network.In particular,when the access capacity of large-scale photovoltaic power distribution network reaches a certain degree,it will bring huge challenges to the power quality,operation and protection control of the distribution network.China has introduced many policies to encourage distributed power grid connection,and the photovoltaic capacity of low-voltage grid connection is growing rapidly.However,there is no effective access capacity guidance for low-voltage photovoltaic grid connection,which leads to the aggravation of three-phase imbalance and over-voltage in the distribution network,and seriously affects the power supply quality of low-voltage distribution network.In this background,based on the analysis of the influence mechanism of low-voltage photovoltaic access on the power quality of distribution network,this thesis studies the acceptable limit access capacity of single/three-phase photovoltaic,and a practical calculation method of low-voltage photovoltaic access capacity suitable for 380 V distribution network is proposed,and a photovoltaic access capacity scheme is obtained.It can provide capacity guidance for low-voltage photovoltaic access,improve the operation power quality of photovoltaic access to the distribution network,and improve the absorption capacity of low-voltage photovoltaic.The research contents of this thesis include:(1)modeling the branch components and terminal components of low-voltage active distribution network,and studying the three-phase power flow calculation method of low-voltage active distribution network;(2)based on theoretical formula derivation and modeling simulation,the influence mechanism of low-voltage photovoltaic on voltage quality and three-phase unbalance of distribution network after it is connected to the 380 V distribution network is studied,and the possible problems caused by the high-capacity access of low-voltage photovoltaic in the distributionnetwork are revealed.(3)analyze the influencing factors of photovoltaic access limit capacity of distribution network.Under the constraints of voltage constraint,current constraint and three-phase unbalance degree,the calculation method of photovoltaic access limit capacity of380 V distribution network that meets the constraints of safe operation of distribution network is studied.