Research Of Bidirectional DC-AC Converter Based On Dual Power Flowing Paths

Bidirectional DC-AC converter plays an important role in bidirectional DC-AC energy storage system as the key device connecting energy storage equipment with AC grid.With the wide voltage range of energy storage equipment,how to achieve efficient energy conversion between DC energy storage system and AC grid is still a problem.Due to the multiple power losses during energy transformation and the wide input voltage range of front-end DC-DC converter,the totally efficiency of conventional two-stage DC-AC converter is low.In order to solve these two problems,DDPCs which are composed of dual DC ports and one AC port are obtained by building another power path on traditional full-bridge DC-AC converter.Based on the requirement of isolation,two constructions with dual power flowing paths are anlazed.Firstly,the non-isolated DC-AC converter is taken as an example to analyze the operating principle,characteristic,modulatin and control method in detail.Theoretical analysis indicates that most of the power can be directly transferred between the energy storage equipment and AC grid within single-stage power conversion,which means equivalent conversion stage can be reduced.In addition,the power losses,switches' voltage and current stresses of the front-end DC-DC converter can also be reduced significantly.Secondly,the isolated DC-AC converter is introduced.With the optimized voltage regulation strategy,the voltage of two DC-buses can be controlled by the down-stream DC-AC converter.Thus,there is no voltage regulation requirement for the front-end DC-DC stage and unregulated DC-transformer(DCX)can be used with working at its optimized conditions.Meanwhile,the adaptive CBSPWM is researched to ensure the smooth mode transition.Design methods for the critical paraments in two constructions are analyzed.The feasibility and effectiveness of the researched converter is fully verified by the experimental results from a 2kW prototype.