Diode-Rectifier-Based Offshore Platform for Wind Power Collection and HVDC Transmission System: Implementation and Hierarchical Control

The DR-based offshore platform has been accepted as a preferable solution for wind power collection from large-scale offshore wind farms (WF) and exporting to the high-voltage direct-current (HVDC) transmission system. In this paper, for the promising implementation in the all-DC offshore wind power transmission system (OWPTS) in future, a novel design of DR-based offshore platform is proposed, based on the new conceptual frame of multi-terminal DC substation (MTDCS). The proposed offshore platform could provide interconnections between the distributed DCWFs and HVDC transmission system, with a high voltage boosting ratio. For those external terminals of the proposed offshore platform, a detailed hierarchical control scheme is presented to realize a strong DC-link voltage regulation function. Since each individual converter in the MTDCS works coordinately, both the reactive power distribution optimization and operation frequency restoration could be obtained. Moreover, a stability analysis of the MTDCS under the wide working range is conducted with utilization of the impedance-based model. Additionally, the fault protection method has been proposed for the MTDCS under DC fault occurrence. Under different working scenarios, a comprehensive simulation is carried out, and all theoretical results are validated.