A Hybrid Flying Cascaded DC/DC Converter Topology for HVDC Interconnections

The present landscape for power transmission network is undergoing remarkable change with the significant progress made in HVDC transmission, especially the modular multilevel converter (MMC) which shows many operational advantages for high-power application. Similar to the role of AC-transformer in AC systems, there urgently needs DC/DC converter to interconnect multiple dc transmission lines with different voltage levels. This paper investigates a transformerless high-voltage DC/DC converter termed as hybrid-flying-cascaded DC/DC converter (HFC) is suitable for interconnecting high-voltage. This topology presents the merits of less amount of semiconductors, very attractive capital costs, light converter weight and high system efficiency. In this paper, operating principles of the HFC are analyzed, while the modulation and control schemes are also elaborated. Feasibility of the proposed topology is verified by simulation results based on a 300MW, 300kV/500kV HFC.