Improvement technique for Power Efficiency of DAB DC-DC Converters by Reducing Hard Switching and Copper Losses in Light Loads

Dual active bridge (DAB) converters have many advantages, such as bidirectional power transfer, and are becoming popular in energy storage systems such as microgrids. However, if the input-output voltage conversion ratio is not equal to the turn ratio of the magnetic transformer, the power efficiency at light loads deteriorates. While hard switching has attracted attention as a cause of this power efficiency deterioration, this paper shows that in addition to hard switching, part of the copper loss during conventional operation becomes a fixed loss, causing efficiency deterioration at light loads. As for the solution technique of this problem, we propose the control switching technique using triangular current control in buck mode and trapezoidal current control in boost mode, respectively. The experimental results have confirmed that power efficiency can be improved by up to 25% with triangular current control at an input-output voltage conversion ratio of 100V/75V and by up to 20% with trapezoidal current control at an input-output voltage conversion ratio of 100V/125V.