Tap changing transformer based dual active bridge bi-directional DC-DC converter

Voltage fed Dual Active Bridge (VF-DAB) is the simplest isolated bidirectional DC-DC converter topology with least number of high frequency tank elements. This paper addresses the issue of Phase Shift operated VF-DAB when used for energy storage applications due to their variable nature in terminal voltage based on the state of charge. Circulation currents and limitations in the soft-switching range are the main drawbacks of VF-DAB when operated with phase shift control within the two active bridges and widely varying voltage at one port. This affect their overall efficiencies at low and mid loads. In this paper, a modification in VF-DAB is proposed which reduces the drawbacks of the conventional phase shift controlled DAB by having variable transformer turns ratio, thereby improving the efficiency of the overall converter at medium and light loads. The analysis and design guidelines for the proposed converter are briefly explained and validated with experimental results.