Abstract: With the development of long-distance and large-capacity offshore wind power, voltage source converter based high voltage direct current transmission (VSC-HVDC) has become an inevitable choice. However, the huge conversion platform in the prevailing centralized conversion solution results in great difficulties in transportation and construction. In this study, a novel VSC-HVDC solution for integrating offshore wind farms using series-connected distributed converters and medium-frequency AC accumulation was proposed. Within this architecture, each distributed modular multilevel converter (MMC) was installed on the existing distributed AC substation, thereby avoiding the construction of a centralized converter platform. The distributed MMCs could be designed with relatively low rated voltage because a series DC network was adopted. The cost, size, and loss of different MMCs were analyzed and compared in detail. Analysis results show that the size and cost of distributed MMC can be greatly reduced on the basis of the novel medium-frequency unidirectional-current H-bridge MMC, which makes the installation of the proposed MMC on the offshore AC substation feasible. The control schemes for the HVDC system based on series-connected distributed MMCs were also proposed. Simulation results verify the feasibility of the proposed scheme and control strategy.