Isolated AC-DC Converter Using Medium Frequency Transformer for Off-Shore Wind Turbine DC Collection Grid

This paper investigates a dc collection grid architecture to process energy from offshore wind turbine generators (WTGs), which can be further interfaced with the shore via a high-voltage dc network. In the proposed approach, WTG output voltage is rectified and converted to medium frequency (MF). Then, a transformer isolation stage is used, followed by a boost rectification stage. The boost rectification stage is controlled to emulate a resistive load, forming a medium voltage dc (MVDC) interconnection. This type of control is simple for varying wind conditions. The operating principles and unique advantages of the proposed approach are documented along with comparison with a conventional benchmark, assuming the turbines are fitted with direct drive technology. System design example, loss/size analysis and transformer finite element analysis are shown in this paper. Simulation results demonstrate the functional capability of the system. Experimental results from a scaled down prototype prove the operation of proposed concept.