Modular Multilevel Converter for Direct MVDC Connection of Offshore Wind Farms

This paper introduces a new concept for offshore wind turbine electrical architectures for wind farms with MVDC collection grids. With the proposed pre-transformer wind turbine drivetrain arrangement, the AC output of the wind turbine generator is transformed to a higher voltage by a step-up transformer and then rectified to a corresponding DC voltage by an active ac-dc converter. A modular multilevel converter (MMC) is used for the rectifier to achieve the variable frequency AC to DC power conversion. The MMC has been shown to have burdensome design constraints at low frequency. This paper demonstrates that these design constraints are not applicable for the wind turbine application and that the MMC is a good candidate for the wind turbine rectifier.