A Startup Strategy for the Parallel-type All-DC Offshore Wind Power System

With the increase in the configured capacity of wind turbine generators (WTGs) and the length of submarine transmission cable, the conventional AC collection scheme of the offshore wind farm (OWF) suffers from high power losses and over-voltage problems in the collection lines. An all-DC OWF with DC collection lines is a feasible solution. This paper presents a startup method for a parallel all-DC offshore wind power system with the centralized step-up platform, which is aimed at eliminating the inrush current and obtaining a smooth transition in the absence of the auxiliary power supply. In this work, the startup strategies of the hybrid modular multilevel converter (MMC), the modular multilevel DC-DC converter (MMDC), and the DC WTG are first introduced, respectively, and then the startup process of the whole system is described in detail. Time-domain simulation results validate the feasibility of the proposed startup strategy.