Control strategy of cascaded multilevel converter based on dual active bridge for wind energy conversion system

Low voltage high power wind energy conversion system (WECS) requires heavy cables and large step-up grid interfacing transformers. In recent years, power and voltage rating of offshore wind turbines have already reached 10MW and 10kV respectively, and medium voltage converters have become strongly demanded. Some scholars proposed a cascaded multilevel converter based on dual active bridge (DAB) to avoid the multi-phase generator, multi-windings transformer or large bridge inductors in traditional multilevel cascaded converter, which is suitable for medium voltage applications. However, there is little research on the strategies of current control, DC-Link voltage stability control and balance control for this topology. Thus, in this paper, the current side-split control and the voltage hierarchical control is proposed for the topology applied to medium voltage WECS. The control strategy is verified by simulation.