Comparative evaluation of capacitor-coupled and transformer-coupled dual active bridge converters

Dual Active Bridge (DAB) converters are emerging to become the preferred high power DC-DC conversion topology to satisfy the requirements of modularity, high voltage transfer ratio, high efficiency and bidirectional power transfer capability. However transformer design for DAB converters remains a challenging problem, especially for high voltage conversion ratio and higher switching frequencies. Capacitor-coupled transformer-less DC-DC converters capable of arbitrary high voltage transfer ratio with reasonable efficiency have been recently introduced. The voltage gain in this case is achieved by series combination of capacitor coupled active bridge modules. This paper introduces the capacitor-coupled dual active bridge converter and compares it with the traditional transformer-coupled dual active bridge converter. A brief overview of the analytical models of both transformer-coupled and capacitor-coupled DAB converters is presented and the important design factors of both topologies are identified, followed by a comparative evaluation of a published benchmark design with details of all the power circuit components.