| With the development of the high-voltage converter technology and high-power electronic devices in recent years,the flexible HVDC technology has been constantly improved.Research in domestic and overseas shows that:the flexible HVDC can independently control the active and reactive power,and it is suitable for connection of non-synchronous power grids.The flexible HVDC also has the advantage of no commutation failure and less need of the land than the AC transmission.Therefore,flexible DC technology is becoming a new mean to solve the city electricity load growth,improve the power quality,improve the utilization of urban power channels,and enhance the intelligence and automation of the grid.The study of flexible HVDC in the city grid is not only the need of flexible DC technology,but also the need of safe of AC/DC hybrid power grid.This paper studies on the flexible HVDC.First of all,the research status of flexible HVDC project is summarized and the basic situation of flexible HVDC project in Xiamen is introduced.Then the wiring type of flexible HVDC project is studied,the characteristics of bipolar connection mode and pseudo bipolar connection mode has also been discussed.Compared the two wiring types in reliability,power supply capacity,investment and time,the research shows that,the investment of bipolar connection mode is bigger,but the reconstruction of the first power channel can be delayed and the fifth power channel can be delayed to build.Therefore bipolar connection mode is proposed for the flexible HVDC project in Xiamen.And then research in domestic and overseas of HVDC cable project and the AC and DC cable laying is summarized,while introducing the main factor affects the AC and DC cable laying..The calculation method of AC and DC cable laying is deduced through the classical electromagnetic theory,while the AC and DC cable laying in different situation of flexible HVDC project in Xiamen is detailed calculated.The result shows that the method is feasible.The suggestion of DC cable grounding mode is presented.The DC cable of flexible HVDC project in Xiamen is studied in the aspects including insulation,metal jacket,outer sheath and core.Finally the research of flexible HVDC project in this paper is summarized,while pointing out issues which still need to be studied like the control strategy of flexible HVDC project and DC breaker. |
