An LLC-LC Type Bidirectional Control Strategy for an LLC Resonant Converter in Power Electronic Traction Transformer

An LLC-LC type bidirectional control strategy for an LLC resonant converter is proposed in this paper. It can achieve bidirectional power flow automatically without any power flow detection procedures. Meanwhile, the soft-switching can be always guaranteed all the time. In order to adapt to the proposed control strategy, a no-load-point-based design method is put forward in this paper, which can rapidly obtain optimal parameters of an LLC resonant converter. What is more, by using the proposed control strategy, the starting characteristic in no-load condition can be improved, output voltage rising and current surge risk can be avoided. Finally, an experimental platform of power electronic traction transformer power cell (consisting of a single-phase rectifier and a bidirectional LLC resonant converter) is built to verify the validity of the proposed control strategy.