Research On Optimal Modulation Strategy Of Modified Dual Active Bridge

With the development of renewable energy,Dual active bridge converter has been attracted more and more attention.It has many advantages such as high power density,low cost,electrical isolation,soft-switching,and so on,so it has been widely applied in energy storage system,solid state transformer and back-to-back system.However the present modulation schemes have the problems of large backflow power and narrow actual soft-switching and high current stress,which lead to higher loss of converter.In order to improve the efficiency,a triple phase-shifting optimization modulation strategy is proposed to improve the existing modulation strategy in this paper,based on the modified dual active bridge.The optimization modulation strategy achieves the goal of minimum backflow power,on the basis of actual zero-voltage Switching(ZVS)and minimum total root mean square current.Accordingly,the optimization modulation strategy can reduce the converter switching loss and conduction loss,improve work efficiency,reduce the electromagnetic interference at the same time and improve reliability of the converter.This paper analyzes the characters of the modified dual active bridge under the single phase-shift,extended phase-shift and triple phase-shift modulation strategy,the characters include of backflow power characters,soft-switching characters and root mean square current characters,then points out the existing problem in the present modulation schemes that the single phase-shift and extended phase-shift modulation strategy are at a disadvantage of backflow power and actual soft-switching characters and results in high loss.In order to improve the efficiency,the relationship between backflow power and phase angle of high voltage side is analyzed,as well as the relationship between root mean square current and phase angle of high voltage side,on the basis of the above analysis,the relationship between phase angle of high voltage side and phase angle of bridges is analyzed.In the precondition of actual ZVS and mode boundary,optimization modulation curves of different modes are achieved by selecting phase angle of high voltage side appropriately.Then the optimization modulation strategy is compared with the original schemes,and the proposed strategy proves to reduce backflow power,achieve actual ZVS and reduce current stress.Secondly,through the modeling of the system,a close-loop regulator is designed to reduce the effect on the system when the load and the input voltage are changed,and improving dynamic performance which are all verified by simulation,and the control strategy of the converter is given.Finally,hardware design methods is given,and the theoretical analysis is verified by experiments.