Design and control of a direct drive wind turbine equipped with multilevel converters

This paper concentrates on the design and control of a three-level grid side converter (GSC) for direct drive high power wind turbines. The three-level, neutral point clamped (NPC) topology was investigated. The proposed control scheme, based on vector current control, offers very satisfying performances regarding to structure stability and grid connection requirements (GCR). In order to have an accurate evaluation of grid voltage source, two grid synchronization methods are developed and their performances are compared. The GSC performances are evaluated under both normal and grid fault conditions. Simulation results show that stability is maintained during voltage dips and that the proposed direct drive wind turbine satisfies completely GCR.