New power electronic interface combining DC transmission, a medium-frequency bus and an AC-AC converter to integrate deep-sea facilities with the AC grid

A new bidirectional dc-ac power electronic interface (PEI) consisting of a dc link, an HVdc terminal based on modular multilevel converters (MMCs), medium-frequency transformers (MF-XFMRs) - higher frequencies are also possible - and ac-ac converters is proposed for interconnecting two ac systems, or dc and ac systems. The advantages of each component make the proposed topology convenient for applications that require compactness, flexibility, and reliability. For example, integration of offshore and onshore wind farms with the power grid, ac and/or dc grids interconnections, and supplying power to conventional and future deep-sea oil and gas facilities. The PEI main overall topology, operating principles and design equations are described. Size and efficiency are evaluated for the proposed topology for different operating frequencies and compared with the conventional approach. A case study of a deep-sea electric power system (DEPS) is illustrated through timedomain simulations for different operating conditions to demonstrate the feasibility of the proposed ideas.