Transformer-less five-level high-voltage full-scale converter with a self-balance auxiliary circuit for 10 MW wind turbines

A novel transformer-less five-level (5L) high-voltage full-scale converter is proposed for 10 MW wind turbines. In this scheme, a unidirectional sinusoidal 5L-Vienna rectifier is used as a variable-speed controller at the generator side, and a conventional 5L neutral-point-clamped (NPC) inverter is used as the grid-integrated converter. The intrinsic dc-link NP imbalance issue is solved only by a proposed dc-link self-balance auxiliary circuit. This study focuses on the modulation technology of the rectifier and the operational principle of the auxiliary circuit. Furthermore, it presents a control strategy for the proposed converter. Finally, the small-scale experiments are carried out to verify the analysis.