Design and operation considerations of three-phase dual active bridge converters for low-power applications with wide voltage ranges

Three-phase dual active bridge (3ph-DAB) DC/DC converters offer a flexible solution for the interconnection in DC power supply systems or DC grids. However, the topology is known to suffer from reduced overall efficiency when used for wide operating ranges. In this body of work, a novel parallel-phase operation is proposed to enable the utilization of dual phase-shift operation modes to enhance the overall efficiency. Thus far, such operation modes have been applied only in single phase DAB converters. This thesis examines the optimal combination of different operation modes and the associated design considerations. The analysis is carried out on the basis of the specifications of a DC/DC converter for an electric vehicle. The converter interconnects the high and low-voltage on-board power supply systems and has a rated power of 3 kW. It is shown that the combination of different operation modes allows for a frequency variation for specific operating ranges, which achieves an additional efficiency boost. Measurements on a converter prototype show efficiencies in the range of 92 to 98 % for the majority of operating points. In summary, the proposed operation concept offers the possibility to achieve high efficiencies for a wide voltage and power range. The approach potentially requires a higher filter and transformer effort, which can be partly compensated by the choice of operating modes or variations of the switching frequency. Ultimately, the concept enhances the suitability of 3ph-DAB converters for a wider range of applications.