Research On Modulation Strategy Of Series Resonant Dab Converter Based On Minimum Reactive Power

Dual Active Bridge(DAB)converters are widely used in electric vehicles,energy storage systems,microgrids and other fields due to their bi-directional power transmission,high modularity,ease of achieving zero voltage switching(ZVS),and electrical isolation of input and output.Compared with traditional DAB,the advantage of series resonant DAB lies in that the inductance current can approach sinusoidal by adding only one capacitor,thus reducing the dc component of transformer and further reducing eddy current loss.However,there is a problem that the reactive power is large and the system efficiency is affected.In order to improve the efficiency of the system and reduce the reactive power output of the system,reactive power optimization of series resonant DAB is thoroughly studied in this paper.Firstly,the circuit principle and basic characteristics of series resonant dual active bridge converter is analyzed.The active power expressions and reactive power expressions under three different modulation strategies of extended phase shift,dual phase shift and triple phase shift are respectively calculated.The soft switching boundary line is drawn by ZVS restriction conditions.The maximum range of ZVS is obtained by analyzing and comparing the three different modulation modes.According to the expressions of normalized active power and normalized reactive power,the curves of different normalized active power and normalized reactive power contours are drawn,and the minimum reactive power value obtained by modulation mode under different normalized active power unit is analyzed by comparing the images.Through the comparison of ZVS range of the above three modulation modes and the analysis of the minimum value exchanged between reactive power and active power under different unit values of active power,the appropriate modulation mode is selected as the modulation mode applied in this paper.Then,an extended phase shift modulation method is selected for control,and a control strategy for reactive power minimization is proposed by constructing an objective function,adding active power and soft switching constraints,and basing on the trend of variables such as inter-bridge phase shift angle,intra-bridge phase shift angle,voltage gain and normalized active power value and reactive power.The control strategy is to minimize the reactive power value at the output of the system with different active power values while realizing the ZVS of the full bridge arm.The optimal combination of phase shift angles corresponding to the minimum reactive power at different active powers is obtained by using MATLAB to perform the optimization search,and the correctness of the optimization search algorithm is verified by simulation.Finally,the hardware circuit is designed and built to experimentally validate the reactive power minimization-based optimization method designed in this paper.The experiments show that the combination of the output phase shift angles under this optimization-seeking method is the point where the reactive power value is minimized under the premise of ZVS of the full bridge arm.