A Platform-less Voltage-Sourced Wind Energy Collection System for Offshore Wind Farms Using Single Active Bridge (SAB) Converters

The cost of installation of offshore wind farms (OWFs) can be reduced significantly if the large offshore platform can be eliminated. Thus, a platform-less series-connected DC offshore wind farm structure is adopted in this work, with single active bridges (SAB) acting as dc/dc converters on each wind turbine (WT). SABs are considered a suitable option for isolated DC-DC converters due to their compact size and galvanic isolation feature. Since wind turbines in a real offshore wind farm experience varying wind power inputs, the series-connected structure often faces the issue of voltage mismatch among the DC/DC converters. To address this, the inputs terminals of the series-connected SABs are connected in parallel in this work, and appropriate control strategies are developed to balance the output voltages of the SABs in spite of the variations in wind speed or failures in the wind turbines or converters. Unlike existing voltage balancing strategies, the proposed method does not require any fast communication between the wind turbines or between the onshore grid and the turbines. The effectiveness of the proposed structure and control strategy is validated through simulations and experimental results on a laboratory prototype.