Research On Optimal Operation Of Distribution Network Considering Electric Vehicles And Soft Open Points

With the support and promotion of the electric vehicle industry,the future large number of electric vehicle access will challenge the safe operation of the distribution network.At the same time,the source network load presents the development trend of power electronics: on the load side,electric vehicles are connected to the distribution network through the converter interface of charging pile.The charging pile has the characteristics of flexible and fast control,and the active control of electric vehicles can effectively improve the voltage distribution of the distribution network;on the grid side,as a controllable power electronic device,soft open point can replace the conventional tie switch,which can effectively improve the negative impact of centralized charging on the distribution network and ensure the stable operation of the distribution network.Therefore,this paper focuses on the optimization operation of the distribution network considering the access of electric vehicles and soft open points.The main research contents are as follows:(1)The factors affecting charging characteristics are analyzed,and the power model of electric vehicle is established.According to the soft open point power control characteristics of normal state and fault state,the soft open point power model is established.The load curve of charging station is simulated by Monte Carlo method,and the influence of electric vehicle charging station on node voltage of distribution network is analyzed.An example of distribution network system with the soft open point is simulated,and the influence of the soft open point on node voltage of distribution network is analyzed.The simulation results show that the reactive power compensation of charging station and the soft open point can improve the node voltage of distribution network.(2)Due to the slow response speed of traditional voltage regulators,it is difficult to follow the rapid voltage changes caused by the charging load of electric vehicles.Coordinated day-ahead and real-time optimization model for distribution network considering reactive power compensation of charging stations is proposed.Taking the model of on load voltage regulation,day-ahead power model of charging station and the distribution network power flow equation as the constraint conditions,and the operation cost is the lowest as the optimization objective.The day-ahead optimization model is established.The real-time optimization model takes the results of day-ahead optimization as the operating reference point,and realizes the effective distribution of power among the power distribution network,charging stations and electric vehicles through the coordination and complementarity between the multi-layer optimization models.In order to ensure that each electric vehicle can reach the target state of charge when it leaves,in real-time optimization,the state of charge of the electric vehicle at the previous moment is considered to dynamically adjust its current state of charge boundary.The effectiveness of the proposed method is tested in the IEEE 33 node system.(3)Aiming at the problem that the potential of soft open point in distribution network voltage regulation and network loss optimization has not been tapped,a distribution network optimization operation method considering orderly charging and soft open point is proposed.According to the change of distribution network load curve,the membership function is used to classify the time of use price,and the constraints of orderly charging of electric vehicles are proposed.First of all,take the user’s minimum charging cost as the optimization goal,and formulate a corresponding charging plan for each user.Then,by controlling the power of the intelligent soft switch,combined with the reactive power compensation of the charging station,the distribution network loss is minimized.Finally,on this basis,a distribution network optimization model based on rolling optimal dispatch is established.Aiming at the original nonlinear optimization problem,the linearization principle of circle constraint and quadratic term is used to realize the linearization of the optimization model.The effectiveness and feasibility of the proposed method are verified through the analysis of a numerical example.