Study on the application of Four-terminal Flexible High Voltage Direct Current Transmission Technology in Nanjing Power System

Back-to-back flexible High Voltage Direct Current (HVDC) transmission technology can not only connect two or more alternating-current (AC) systems, but also connect areas supplied by different distribution networks through its DC bus. Base on this back-to-back flexible HVDC transmission technology, power transmission abilities of current AC transmission lines can be fully utilized. This technology makes full use of current AC transmission lines, taps the capacity of current AC power systems, and transfers loads through DC bus interconnection, so as to achieve balanced load distribution in the current AC power systems. At the same time, it can realize load transfer intelligently and flexibly and reduce the load shedding of the current AC systems under failure modes. With the construction of rectifier and inverter stations in the same site, back-to-back flexible HVDC transmission structure with two or more teminals can be formed and different partitions can be interconnected, with less total occupied areas and investment cost by saving its mutual DC connection lines. The challenges in Nanjing central-urban-area power systems during the 14th-Five-Year planning period will be analyzed in this paper. Afterwards the solution by using back-to-back flexible HVDC transmission technology to deal with the problem development in Nanjing central-urban-area power system will be proposed. With further study on this proposed solution, technical advantages and promotion prospects of this back-to-back flexible HVDC transmission technology utilized in the central-urban-area power systems will be summarized.