Research on efficiency optimisation of DAB converters considering current stress and soft-switching

To solve the problem of low efficiency of the dual active bridge (DAB) converter under the traditional single-phase-shift control, a natural soft-switching current stress optimisation (NSS-CSO) method is proposed by considering the current stress optimisation and soft-switching operation under dual-phase-shift (DPS) control. This study establishes the current stress and the soft-switching analytical models of the DPS control global mode. Based on these models, the Karush-Kuhn-Tucker (KKT) condition is used to analyse the influence of the current stress optimisation methods on the efficiency when all switches achieve controlled soft-switching or some switches achieve natural soft-switching. It is found that the NSS-CSO method is more efficient. Furthermore, the optimal phase-shift ratio combinations and the corresponding current stress extremums of the NSS-CSO method under various ranges of transmission power and voltage conversion ratio are deduced completely. The results of this study show that the NSS-CSO method can effectively improve the operation efficiency of the DAB converter over the entire power range when the voltage conversion ratio does not match. Finally, experimental results confirm the accuracy of the theoretical analysis and the effectiveness of the proposed optimisation method.