A Novel Scheme for DRU-HVDC Transmitted Offshore Wind Farm.

The diode rectifier unit-based high voltage direct current (DRU-HVDC) transmission is increasingly considered a cost-effective alternative to the modular multilevel converter (MMC)-HVDC transmission for the integration of large-scale offshore wind farms (OWFs). However, only the case where the onshore MMC controls the DC voltage has been studied. There, a novel scheme for DRU-HVDC transmitted OWF is proposed in this paper. The DC voltage of the HVDC is controlled at the DRU side. Thus, the onshore MMC can operate more flexibly. The classical power system nodal theory is used to classify the wind turbines (WTs), auxiliary convertor, and the DRU as the $V\theta$, PV, and PQ nodes respectively. Then, the new grid-forming (GFM) control strategy and grid-following (GFL) control strategy for the WTs and auxiliary convertor are proposed correspondingly. Finally, the PSCAD/EMTDC simulation results are presented to validate the effectiveness of the proposed scheme for DRU-HVDC transmitted OWFs.