Feasibility Study On Replacing AC With DC For Load In Restricted City Center Of Power Supply Corridor

With the gradual implementation of the State Grid Corporation of China’s "Carbon peak and carbon neutral" action plan,it has become an inevitable trend to develop clean energy both centrally and distributed,and maximize the development and utilization of wind power,solar power and other new energy.In this energy transition period of low carbonization and decarbonization,after large-scale distributed new energy and flexible loads such as electric vehicles are connected,a large number of power electronic energy conversion equipment are introduced into power supply,power grid and load links,and a large number of source load is transformed from AC to DC,which lays a foundation for the formation of DC distribution network.This paper studies and analyzes the dc transformation of key load in urban center limited by power supply corridor.The main contents are as follows:Elaborated the current ac/dc power distribution network development background,development present situation,and drive of its power to continue to develop,research,analysis of the ac/dc hybrid power feasible solutions of power flow calculation,the application of power distribution network and operation characteristics,space truss structure of the distribution network and equipment type selection,comprehensive evaluation scheme and the current research status of domestic and foreign typical application cases.Analysis studies the characteristics of ac/dc mixed steady-state distribution network,including the trend of the data and network loss,respectively for ac and dc part modeling,and then using the alternate iteration method for power flow calculation,using hand type ac/dc hybrid power distribution system,the simulation calculation to prove the effectiveness of the proposed calculation method,the transform of ac/dc distribution network to provide support.Analyze and study the transient characteristics of the modified AC-DC hybrid distribution network,mainly aiming at the bipolar short-circuit fault and single-pole short-circuit fault that are prone to occur on the DC side,analyze and study the current characteristics after the failure,and carry out the simulation calculation of the fault characteristics on digsilent/powerfactory software platform.According to its current characteristics and existing research data,a relay protection scheme for AC-DC hybrid distribution network is proposed.Finally,three schemes are proposed to upgrade the key load areas of the city.The comprehensive performance evaluation model of distribution network is established based on the indicators of economy,power supply capacity,network loss,power supply reliability and short-circuit current margin,and the entropy weight method and the improved TOPSIS method are used to comprehensively evaluate each scheme model.The results show that the scheme of simultaneous DC transformation on both sides of transmission lines has the best comprehensive benefits.As an important trend of future power system development,ac-DC hybrid distribution network is still in the development stage,and many technologies are not yet mature.It is necessary to further study the planning and design standards of AC-DC hybrid distribution network,including the selection standards of voltage level and network architecture,selection standards of DC power supply equipment,and engineering construction standards,so as to lay a foundation for the engineering application and demonstration of AC-DC hybrid distribution network.