Research On The Advanced Control Method Of Three-phase Dual Active Bridge Based Bidirectional DC-DC Converter With Wide Power Range

With the application of large-scale energy storage devices in smart grid,the development of DC microgrid,and the planning of electric vehicle grid supporting functions,the demand for high power density bidirectional DC-DC converters is increasing.Compared with the traditional single-phase dual active bridge(SP-DAB),three-phase dual active bridge(TP-DAB)has the advantages of higher power density and lower filter volume,etc.However,due to the limitation of the topology of TP-DAB,through the traditional three-phase mode under light load,the efficiency of the TP-DAB can be as low as 70%.Therefore,based on the TP-DAB with Δ-Δ configuration of threephase high frequency transformer winding(Δ-Δ TP-DAB),a novel two-phase mode is proposed in this paper to improve the operation efficiency of the three-phase dual active bridge in light load,and the efficiency can reach more than 80%.The corresponding model predictive control is proposed for three-phase and two-phase modes.The specific research contents are as follows:(1)Taking the Δ-Δ TP-DAB as the research object,in the traditional three-phase mode,through the analysis of the high-frequency square wave voltage on both sides of the highfrequency transformer and the high-frequency current of the power transfer inductor,the ZVS area of the Δ-Δ TP-DAB is obtained,and the zero-reactive-power area of the threephase mode is analyzed for the first time.At the same time,the power density of SP-DAB and TP-DAB are compared.(2)In order to solve the problem of low efficiency of Δ-Δ TP-DAB under light load,a two-phase mode is proposed in this paper.In two-phase mode,there are two control degrees of freedom,and only two phases of high-frequency transformer are in operation.Therefore,under light load,the ZVS area and zero-reactive-power area of Δ-Δ TP-DAB are increased,which greatly improves the operation efficiency of Δ-Δ TP-DAB.(3)For the three-phase and two-phase modes,a hybrid optimal modulation strategy is proposed.In heavy load,three-phase mode is adopted;in light load,two-phase mode is adopted,so as to realize high efficiency operation in a wide power range.At the same time,according to the zero-reactive-power and the minimum current stress,the overall operation state of the Δ-Δ TP-DAB is optimized.(4)In order to improve the dynamic response speed of Δ-Δ TP-DAB,model predictive control is proposed for three-phase mode and two-phase mode respectively,and the influence of internal parameters of battery is considered in the overall modeling.Through the proposed model predictive control,the dynamic response speed of the Δ-Δ TP-D AB can reach 20 ms,which is far better than the traditional PI control.