Clarification of relationship between current ripple and power density in bidirectional DC-DC converter

This paper clarifies the relationship between the current ripple and the power density in bidirectional DC-DC converters. In the conventional power density design method, in order to obtain the pareto-front curve of the power density and the efficiency, the current ripple is designed as constant value, whereas the switching frequency is varied. As a result, the possibilities of higher power density or higher efficiency at different current ripple are not considered. Therefore, in this paper, the current ripple is also varied in order to evaluate all the designable power density. Specifically, a design flow chart is introduced to show step-by-step how to express all the losses and the volume of the converter as functions of the current ripple. Several 1-kW prototypes are constructed in order to confirm the validity of the design flow chart. By varying the current ripple, the highest power density of 10.1 kW/dm3 with the efficiency of 98.55% is achieved at the current ripple of 60%. Furthermore, the maximum error between the calculated and experimental power density and efficiency are 19.5% and 0.22 pt. respectively.