5L full-scale converter with a dc-link flying-capacitor auxiliary bridge leg for large direct-drive wind turbines

A novel five-level (5L) full-scale converter is proposed for large direct-drive wind turbines. In this scheme, a 5LVienna rectifier is used as a robust generator-side converter and a 5L neutral-point-clamped inverter as a grid-side converter, a flying-capacitor auxiliary bridge leg is proposed to maintain the voltage balance of the dc capacitors. This study first discusses the neutral-point balancing method based on the flying-capacitor auxiliary bridge leg and modulation. Furthermore, it presents the control strategies for the proposed 5L converter. Finally, simulation and small-scale experiments are carried out to verify the analysis.