Optimal Allocation Of Energy Storage Systems Considering Flexibility In Active Distribution Network

The global energy crisis and environmental problems are becoming more and more serious,and large-scale development and utilization of renewable energy has become one of the main solutions.In the active distribution network,grid connection is mainly achieved through distributed generation.However,renewable energy sources such as wind power and photovoltaic power are affected by environmental factors and have strong intermittentness,resulting in insufficient flexibility of the power system.The main problems faced by the active distribution network are: local voltage limits are exceeded,power is sent back to the superior power grid,local currents in the distribution network change drastically,and renewable energy cannot be completely absorbed.The energy storage system has the ability to adjust and change the charging and discharging state and power size flexibly.It is an ideal resource of flexibility.It is an ideal resource ang providing a good solution for improving the power flow distribution and voltage quality of the active distribution network,and solving the problem of source and load timing mismatch.To this end,this paper,from the perspective of active distribution network flexibility,has carried out an in-depth study on the optimal configuration of energy storage devices in active distribution networks.The completed work and the research results obtained in the paper are as follows:(1)The K-means clustering algorithm is used to integrate the output curve of photovoltaic and load in the active distribution network with distributed photovoltaic power generation connected to the grid,and then the typical photovoltaic-load joint output scenario of the active distribution network is obtained.On this basis,considering the uncertainty of the short-term forecast errors of photovoltaic and load output,based on the robust optimization theory and the typical output scenario,a set of uncertain operating scenarios considering the worst conditions is obtained.It laid the foundation for the establishment of the optimal configuration model and simplified calculation in the follow-up research.(2)Analyzed the characteristics of flexibility in the active distribution network,introduced various flexibility resources in the active distribution network,and discussed the flexibility and sufficiency of the active distribution network based on changes in the penetration rate.It lays the foundation for the later development of an optimized energy storage configuration plan that takes into account flexibility.(3)The operation flexibility in the distribution network is analyzed,and on this basis,the local distribution network flexibility constraint method and the overall distribution network flexibility quantitative calculation method are proposed.Established an optimal configuration model of double-layer energy storage devices suitable for traditional distribution networks,and the introduction of flexibility constraints and insufficient flexibility penalties in the lower-level model.The verification by calculation examples shows that the obtained planning scheme can reduce the phenomenon of light abandonment and load shedding in the distribution network,and improve the ability of the distribution network to operate safely and stably.(4)In the active distribution network,the flexibility calculation model of the source network load flexibility resource is carried out,and the interaction between the flexibility resources is considered,the flexibility supply and demand balance index and branch flexibility are proposed to integrate multiple flexibility resources.The evaluation index system is applied to the established economic and flexible multiobjective model for the optimal configuration of energy storage devices in the active distribution network.Validation by calculation examples shows that considering the interaction between various flexible resources significantly reduces the investment cost of the optimal configuration of energy storage devices,and further improves the flexibility and economy of the active distribution network.