To address the issue of the large volume and weight of offshore converter platforms

this paper conducts research on the compact design method for the valve of unidirectional-current hybrid modular multilevel converter (UC-HYB-MMC). Based on a ±500 kV/2 000 MW high voltage direct current system for offshore wind power

the parameters of the UC-HYB-MMC are designed

and based on the parameters

the structures of unidirectional-current clamp-double submodule (UC-CDSM) and unidirectional-current full-bridge submodule (UC-FBSM) are respectively designed. Thermal simulation results indicate that the heat dissipation design can limit the junction temperature of the semiconductor devices within an allowable range

and the temperature distribution is relatively uniform. Based on the submodule structural designs

the valve section designs for the UC-CDSMs and UC-FBSMs

as well as the design for the valve tower of the UC-HYB-MMC are conducted. The layout for the valve towers of the UC-HYB-MMC in a valve hall is presented. A comparison of the hall size between the conventional half-bridge submodule-based MMC and the UC-HYB-MMC is conducted

and the result shows that the UC-HYB-MMC has significant advantages in terms of compactness and lightweight.