Research Of Medium Voltage AC-DC Hybrid Distribution Network Planning Based On Converter Siting

Due to the increasing demand for energy and environmental protection,DC distributed generators and DC loads,such as distributed photovoltaic,battery energy storage systems,electric vehicles,cell phones and other electronic devices and so on,are growing fast in distribution network.These DC generators and loads need power electronic devices which transfer power between AC and DC to connect to the AC network,undoubtedly bringing the loss of energy conversion and the need to build more power electronic devices.Under this background more and more people begin to pay attention to DC distribution network.However,the dominant generators and loads in the current networks are still in AC form and need to be powered by AC network.If completely transforming the existing AC distribution networks to DC distribution networks,there will be severe waste of manpower and resources.By using AC-DC hybrid distribution network and with proper planning according to local conditions,the AC-DC hybrid distribution network can not only meet the power demand but also take advantages of both AC and DC distribution network.There will be scenarios where large amounts of AC and DC distributed generators and loads exist simultaneously in the future so the research on planning of AC-DC distribution network is very realistic and important.This paper made a research on the planning of medium voltage AC-DC hybrid distribution network,and the siting of inverters and converters were especially considered.The main work are as follows:(1)Summarized the typical structures,application scenarios and components of the medium voltage AC-DC hybrid distribution network in current researches and proposed a power flow model for AC-DC hybrid distribution network based on the Distflow method referring to the existing research on AC distribution network.Since the model contains the battery energy storage system,constraints of mixed integers are needed and because of the Distflow method used in the calculation of the distribution network power flow,it is necessary to bring in the second-order cone relaxation for some constraints.(2)Proposed a cost-benefit model for the planning of medium-voltage AC-DC hybrid distribution network,and a genetic algorithm based on the elite strategy to optimize the planning scheme.The cost-benefit model consists of two elements of construction and operation,and the construction cost of each equipment in the distribution network is divided through its whole life cycle.During the planning process,both the capacity allocation of photovoltaic and battery energy storage system when the connecting point and total capacity are given,and the AC and DC boundary division of the distribution network are considered.And the boundary division problem is transferred into the converter siting problem in the distribution network.(3)Verified the source-network coordinated medium-voltage AC-DC hybrid distribution network planning method proposed in this paper by simulation experiments.A simulation test system is built based on the IEEE 33-node system.Using MATLAB and its toolkit Yalmip and solver Cplex,the power flow calculation of the AC-DC hybrid distribution network and the optimization process of genetic algorithm for the planning scheme can be achieved.At last the simulation results are analyzed.