Research On AC/DC Hybrid Distribution Network And The Control Strategy

In recent years,with the rapid development of modern city and the social economy,the size and type of load in distribution network is increasing,the traditional AC power distribution network is facing various problems such as the decline of power quality,lake of the power supply corridor,and a large number of converts.At the same time,the DC distribution network has attracted the attention of expers and scholars all over the world because of its advantages such as improving the power supply capacity,improving the power quality and be convenient for DC load and distributed generation to connect.And developing DC distribution technology in traditional AC distribution network has become the trend of the construction of distribution network in the future.Therefore,the research of AC/DC hybrid distribution network work which has the advantages of DC distribution network and the basis of AC distribution network is of great significance and application value.This paper put forward a kind of hybrid AC/DC distribution network based on the traditional “hand in hand” AC distribution network.It use flexible DC technology to build a DC link in the AC distribution network to get the advantages of DC distribution network and consider the AC basis at the same time.The analysis shows that the AC / DC hybrid power distribution network can effectively improve the overall power supply quality of the distribution network,reduce the process of power converting in the distribution network,and save the corridor of the power supply line.Then,this paper studied the economic analysis of the AC/DC hybrid distribution network was carried out from the primary equipment investment and the operation loss.And a power supply region of Liaoning Province has been analyzed as an example to compare the AC/DC hybrid distribution network transformation and the expansion of AC distribution in AC and DC.Among them,the investment of equipment including converter and substation,cable lines,circuit breaker,transformer,rectifier and inverter;the operation loss including substation loss,power converting loss and transmission loss.The comparison results show that when the distribution network has a long life cycle,the AC.DC hybrid distribution network has the best economic performance because of its lower operating loss.After that,the control strategy of AC/DC hybrid distribution network is analyzed,and the study is focused on the VSC control which is directly related to the operation of DC link.This paper proposed a new improved combined control strategy based on the combined control strategy which has good integrated performance after analyzing the existing VSC control strategysapplied to MTDC system.The analysis shows that the improved combination control strategy can control the DC voltage in a better and more stable level after the VSC which is used to control the DC bus voltage break down.Therefore,the improved combination control has better control performance than the existing combined control.Finally,this paper used Matlab/Simulink simulation platform to build a simplified simulation model of AC/DC hybrid distribution network.By running the model after setting different systemsituation,the proposed structure and control strategy of the AC/DC hybrid distribution network.has been tested and verified.The simulation results showed that the voltage distribution and the quality of power supply in AC lines can be improved by the VSC which is connected with the AC lines providing appropriate reactive power compensation.And The improved combination control strategy can control the the bus voltage and the power balance of the DC system very well in the normal operation and during the breaking down of the VSC which is used to control the DC bus voltage.