Efficiency and Power Density Evaluations of Bidirectional Non-isolated DC-DC converter Based on Flying-capacitor Converters

This study carries out the efficiency and power density evaluations of a bidirectional non-isolated dc-dc converter based on flying-capacitor converters using Pareto optimization method. The converter comprises a main converter with four power devices and an auxiliary converter, each of which is formed by cascaded chopper cells. A converter design procedure based on Pareto optimization method is proposed, followed by the discussions how the carrier frequencies of the main and auxiliary converters, and the chopper-cell count affect the efficiency and power density of the converter. Consequently, it is revealed that the maximum power density can be achieved when using four cells in the auxiliary converter. The validity and effectiveness of the design method presented in this paper are verified using a 200-V, 1-kW down-scaled model. Further, the efficiency and power density evaluations of an actual dc-dc converter system rated at 100 kW are carried out using numerical analysis based on the MATLAB software package.