High Efficiency Dual-Bridge LLC Resonant Converter with Adaptive Frequency Control for On-Board Charger Applications

This paper proposes an adaptive frequency control strategy for the unidirectional DC/DC converter based on Dual-bridge LLC (DBLLC) resonant converter to eliminate the circulating interval (CI), which causes high conduction loss. The LLC resonant converters are the preferred choice to select of DC/DC converter topology for on-board charger (OBC) due to it provides many advantages such as high efficiency, high power density. The DBLLC resonant converter operating with variable frequency and the pulse width-modulated (PWM) control will be applied as an isolated stage (DC/DC converter) of 400V-7.4 kW to improve the power density and efficiency of the whole system. The advantage of operating at the adaptive frequency is that the conduction loss in all devices will be reduced, while the soft switching technique is still achieved over the full load range. Furthermore, the detailed CI characteristic along with losses analysis is presented. The topology is designed for 400 VDC input to 220-380VDC output conversion, in the power range from 3.3 kW to 7.4kW. All theoretical analysis and the experimental results on the proposed converter are provided to verify the system performance.