Review and comparison of single and dual active bridge converters for MVDC-connected wind turbines

A key component for all-DC wind farms is the DC/DC converter. The converter must have multi-megawatt power capability, a high step-up ratio, provide galvanic isolation, and operate efficiently while being able to fit in the wind turbine nacelle. The single active bridge (SAB) and dual active bridge (DAB) converters in standalone or cascaded configuration are promising topologies that have the potential to meet these requirements. This paper reviews the operation and control of these converters, and compares their volume, weight, and efficiency for a 15 MW wind turbine with 80 kV DC connection. The results show that the standalone topologies are significantly smaller and lighter than their cascaded counterparts. However, all topologies fit inside the wind turbine nacelle. The SAB designs are the most efficient and robust, as they use diodes in the output bridge. The DAB topologies have the advantage of bidirectional power flow at the cost of additional switches and losses. The standalone DAB requires series-connected switches in the output bridge, which may difficult to implement. The cascaded topologies offer higher reliability without significantly increasing losses, making them the most attractive option for future DC wind turbines.