Reasearch On AC/DC Hybrid Distribution Network Planning Considering Flexibility

In order to alleviate energy shortages and environmental pollution problems,clean energy such as wind power and photovoltaics,as well as green vehicles such as electric vehicles,have developed rapidly.However,distributed power supply and intermittent load access to the distribution network bring short-term and severe fluctuations in system load,threaten the safe and stable operation of the power distribution system,and put forward new requirements for flexible operation of the power distribution system.At present,DC components such as distributed photovoltaics and electric vehicle charging stations are mainly converted into AC distribution networks by converters,and the economics of access are poor due to the high cost of the converters.In order to take advantage of distributed power generation technology and DC technology,reduce the adverse impact of its access to the power network,rationally plan and design the future AC/DC hybrid distribution network structure,and improve the flexibility of the distribution network.The optimization planning model for the AC/DC distribution network of photovoltaic,energy storage and electric vehicle loads is carried out.The research on distributed power supply,electric vehicle charging station layout and grid layout design of AC/DC distribution network is carried out.The main research contents are as follows:Firstly,it summarizes the connotation of flexibility in existing research and the existing evaluation index of flexibility,and proposes the time-division flexibility supply-demand balance index suitable for flexible resource optimization scheduling and the flexibility evaluation applicable to scheduling scheme and planning scheme.The overall flexibility supply and demand balance indicator and the flexibility evaluation index in the distribution network grid planning.The randomness,volatility,and intermittent nature of distributed power and intermittent loads are the primary sources of uncertainty in power distribution systems.The spatio-temporal coupling characteristics of distributed photovoltaics exacerbate the uncertainty of output.This paper considers the correlation between PV station output and establishes a multi-chain Markov model to predict the power of PV stations.The prediction results preserve the PV sequence well.Spatio-temporal correlation for the generation of a flexible demand scenario.The historical flexibility requirement scenario is clustered by the neighbor propagation algorithm.The influence of the electric vehicle load on the flexibility demand is analyzed.The flexibility requirement scenario is modified for the subsequent flexible resource optimization scheduling and distribution network planning research.In terms of flexible resource optimization scheduling,this paper summarizes the main flexible resources in the distribution network,and establishes a supply model of flexible resources,and analyzes its supply capacity,operating costs and operational constraints.Considering the minimum net load volatility and the minimum operating cost,the real-time flexibility supply and demand balance constraint is added to construct an optimal scheduling model for flexible resources.A separate and unified scheduling strategy for resources is proposed.The proposed scheduling model is applied in the improved IEEE 33 example,and the ability of the two strategies to improve the flexibility of the distribution network is compared.In order to determine the layout of each DC component and the network architecture of the AC/DC distribution network,a two-level planning mathematical model integrating planning and operation is established.The lower layer is the operation layer,and the optimal operation scene of flexible resources is obtained.The upper layer is the planning layer to integrate The minimum annual cost is the target.The planning cost includes the converter installation cost,AC/DC line new and retrofit cost,network loss cost,converter loss cost,and AC/DC network interaction cost.In this paper,based on the root node fusion method,the method of networking the nodes in the corridor is designed,and the alternating current and alternating current iteration method is used to calculate the production simulation in the planning process.Finally,the proposed planning model is applied in the improved IEEE 33-node example,and the economics and flexibility of the planning scheme in the four cases are compared,and the superiority of the AC-DC hybrid distribution network structure is verified.