**5. Conclusions**

This study proposed installation of a DR-HVDC for the new 100 OWF in the Jeju Island power system. To confirm the impact of the DR-HVDC, the simulation model of the present Jeju Island power system was conducted and compared with the actual power system operating history in the first case. From the analysis results of the second case, its power system had been linked with the OWF by using the DR-HVDC. And it was able to operate a steady state when the DR-HVDC transferred the output power of the OWF. In addition, this study also checked on the DR-HVDC in transient state. Although the disconnection fault of the DC transmission line, which is one of the common incidents of an HVDC, occurred, the unidirectional HVDC in the Jeju Island power system was able to compensate for the dropped active power of the OWF by a fast response characteristic in the third case. This study also analyzed the ground fault impact of an o ffshore AC grid in the last case. Then, the analysis confirmed that the DR-HVDC can be helpful in reducing fault impact. From the results in steady and transient states, although the DR-HVDC was operated by using an uncontrolled rectifier at the o ffshore station and only one MMC at the onshore side, it was able to play a role as a conventional HVDC even in the small and isolated power system. Consequently, the application of the DR-HVDC in a small power system is reasonable to reduce costs and increase the reliability of an OWF instead of a conventional HVDC. If in the future, the new OWF in the Jeju Island power system is connected with a DR-HVDC, the power system will be more stable than the AC connection method and save costs than conventional HVDC topology.

**Author Contributions:** Conceptualization: S.-H.S. and E.-H.K. Methodology: S.H.C. and M.H.K. Resources: S.H.C., S.-H.S., and E.-H.K. Writing—original draft preparation: S.H.C. and M.H.K. Writing—review and editing: S.H.C. and E.-H.K. Supervision: S.-H.S. and E.-H.K.

**Funding:** This research was funded by KETEP and KEPCO, respectively.

**Acknowledgments:** This work was supported by the Korea Institute of Energy Technology Evaluation and Planning (KETEP) and the Ministry of Trade, Industry & Energy (MOTIE) of the Republic of Korea (No. 20173010024890) and Korea Electric Power Corporation (Grant number: R18XA03), respectively.

**Conflicts of Interest:** The authors declare no conflict of interest.
