Research On The Supportability Of Distribution Network Considering The Large-scale Access Of Electric Vehicles

In recent years,environmental pollution and energy crisis have become increasingly serious.As a new energy vehicle,electric vehicles(EV)can effectively reduce greenhouse gas emissions and dependence on fossil fuels,and have received wide attention.However,with the high proportion of electric vehicles integration in the power system,the charging load of electric vehicles is bound to have many adverse effects on the safe and stable operation of the distribution network.On the premise of ensuring safety and reliability,the existing distribution capacity of the distribution network is limited,and the charging load forecast of electric vehicles is the basis for studying the carrying capacity.Therefore,it is of great significance to predict accurately the spatial-temporal distribution of the charging demand of electric vehicles and then further study the carrying capacity of distribution network for electric vehicles.Firstly,this paper introduces the development status and prospects of electric vehicles in the background of distribution network,as well as the research status of load forecasting and carrying capacity of distribution network,and explains the necessity of research on spatial-temporal distribution and carrying capacity of charging load.In addition,the complex traff-ic network simplification method and basic path search method are explained,which provides a theoretical basis for the determination of electric vehicle travel route.Secondly,the spatial-temporal distribution probability model of electric vehicle swapping demand is established.The Depth First Search(DFS)and the random travel chains are used to determine the actual travel route of the electric vehicle for one day,and the spatial distribution pattern of the electric vehicle travel is completed.According to the travel time,parking time,etc.,the random distribution of electric vehicles in time dimension is determined.Through the combination of spatial-temporal dimension,the simulation of the electric vehicle travel process provides a basis for the determination of the electric vehicle's swapping time,location and quantity.The Monte Carlo method is used to verify the effectiveness of the proposed model and algorithm via a practical example.Then,based on the premise that the development of the swapping mode is blocked,the spatial-temporal distribution probability model of the electric vehicle charging demand is established.Considering the flexibility of the charging time and the high electricity price when the driver returns from work in the evening,the spatial-temporal distribution model of charging power is proposed based on certain time-delay characteristics.For the electric vehicle in the swapping mode,the replaced battery is subjected to centralized charging,and this paper elaborates a spatial-temporal distribution model of the electric energy.Through the combination of charging mode and swapping mode,the spatial-temporal distribution of electric vehicle in hybrid mode is studied,which lays a foundation for the research of the carrying capacity of the distribution network.Finally,the carrying capacity of the distribution network for charging load of large-scale electric vehicles is studied.The evaluation indicators of the carrying capacity of the distribution network are summarized.Considering regional electricity consumption characteristics,the basic power load of different functional areas is determined,and the corresponding total capacity of the distribution transformer is calculated according to the relevant technical guidelines.The carrying capacity of the distribution network in 500 residential districts in a specific network is studied by connecting the electric vehicle load with spatial-temporal distribution characteristics.By establishing the distribution transformer overload rate evaluation model,the influences of key factors such as the penetration rate of the electric vehicles,the spatial-temporal distribution of the charging load,the charging control strategy and the electric energy replenishment form on the carrying capacity of the distribution network are analyzed.The research results show that the higher the penetration rate of electric vehicles and the grade of residential areas,the greater the overload rate of transformers,and the weaker the load capacity of distribution networks.We can also obtain that the less the distribution of charging load of nodes,the less overload rate of transformers,the stronger the distribution network carrying capacity.Meanwhile,we can get the conclusion that the delayed charging strategy and the hybrid mode can reduce the impact of the charging load of the electric vehicle on the distribution network,which have a positive effect on delaying the upgrading of the distribution network.