Design and Experimental Verification of a Three-Phase Dual-Active Bridge Converter for Offshore Wind Turbines

This paper deals with design and experimental verification of a medium-voltage (MV) DC-DC converter intended for offshore wind. The power rating of the turbine tends to reduce the total cost. However, higher power ratings and longer distances between the turbines cause higher losses in the AC collector grid due to the required larger cable sizes. Furthermore, the need for higher voltage ratings in the AC collector grid to reduce the current rating i.e. cable sizes results in big step-up transformers. To solve these disadvantages, researchers and engineers are considering the system with a pure DC collector grid. With focus on the DC collector grid, the authors have discussed the design of a 10- MW ±25-kV DC-DC converter regarding the converter structure and topology, the semiconductor arrangement, and the transformer to increase the efficiency. Following the above considerations, this paper describes the prototype construction, the experimental verification, and the proposed design of the medium-frequency transformer. The experimental results and the loss analysis verify that the 10- MW ±25-kV DC-DC converter can achieve the efficiency of 98.5% by the three-phase DAB topology, the suitable selection of the semiconductor devices, and the revised medium-frequency transformer.