Partition Variable Frequency and EPS Hybrid Control to Achieve Full Load Range ZVS for Dual Active Bridge Converters

Zero -voltage switching (ZVS) is of great importance for high-efficiency dc/dc converters. In the dual active bridge (DAB) converter with the extended phase shift (EPS) control, however, due to the junction capacitance of switches, the ZVS region splits into two separated parts according to its load degree. It has been found that applying the variable frequency modulation (VFM) simply to the EPS can move rather than fill the gap between the ZVS areas. In this article, a partition VFM is proposed, which increases the switching frequency at heavy loads and decreases it at light loads. The partition VFM extends the ZVS regions of EPS toward each other and connects them finally. A hybrid control law combining the partition VFM and EPS has been developed. The minimum rms current optimization is carried out to determine the relationship between duty cycle and phase shift. Some frequency-dependent characteristics are analyzed to establish loss model. Minimum switching frequency is calculated to obtain high efficiency while ensuring ZVS. Finally, the effectiveness of the proposed control method is experimentally verified on a 100-300-kHz, 1-kW DAB prototype.