Direct connection of WECS system to the MV grid with multilevel converters

A medium voltage power interface for a variable speed Wind Turbine is presented in this paper. The converter topology consists on the Back-to-Back connection of two medium voltage Diode Clamped Multilevel Inverters (DCMI) in the full power path. This mitigates traditional tradeoffs around the low voltage connection between the generator and the grid on the megawatt range. Also, this configuration allows for higher control versatility for grid codes compliance. The converter controllers are based on a Finite-States Model Predictive Control approach, leading to fast dynamic response and DC bus voltage equalization. The control scheme can be used with converters of an arbitrary number of levels with reduced computational effort. This is based on necessary switching restrictions which allow the reliable operation of converter legs. The performance of the control scheme is evaluated through computer simulations.

► Multilevel Converters in Wind Energy Conversion Systems.
► The back to back converter topology enhances grid codes compliance.
► Multilevel converters allows for transformerless connection to the grid and present low current distortion.
► The conversion system addresses high power wind turbine design tradeoffs.