Power loss estimation for three-port DC/DC converter for 12-V/48-V dual-voltage hybrid electric vehicle subsystem

The 12-V/48-V dual-voltage subsystem using a three-port DC/DC converter is proposed for hybrid electric vehicles. The new subsystem design can reduce the number of circuit components and volume by using the three-port DC/DC converter, which integrates a dual active bridge and a multiphase DC/DC converter. The total losses are also expected to decrease as two-circuit topologies share the components and their losses. In order to clarify the advantage of conversion efficiency, this study developed a loss estimation technique for the three-port DC/DC converter, and the total losses are compared with that of conventional converters. A geometrical loss calculation as a function of both 12-V and 48-V load is proposed, and the soft switching condition is also studied. A 1.0-kW, 50-kHz prototype converter was constructed, and power losses were measured to verify the accuracy of the loss estimation technique. The measured and calculated efficiencies show very good agreement, and the prototype achieves high efficiency of more than 92% over a wide output power for 12-V, with a maximum efficiency of 94.1%. The calculation results show smaller losses of the three-port converter in all output power ranges of 12-V than that of conventional converters. The proposed 12-V/48-V subsystem using the three-port DC/DC converter has attempted to realize compact, lower-cost, and higher fuel efficiency. Finally, efficiency improvement is also estimated using GaN FET to identify the compassable higher efficiency.