Efficiency and power density evaluations of bidirectional non-isolated DC-DC converter based on flying-capacitor converters

This paper 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 consists of a main converter with four power devices and an auxiliary converter which is formed by cascaded chopper cells. A converter design method is proposed, and the relationship between the carrier frequencies of the main and auxiliary converters, the number of chopper cells, and the efficiency and power density of the converter are analyzed quantitatively based on Pareto optimization method. Consequently, it is revealed that the maximum power density can be achieved when the number of cells is four. The validity and effectiveness of the design method presented in this paper are verified using a 200-V, 1-kW down-scale 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 and computer simulation using the “PSCAD/EMTDC” software package. © 2021 The Institute of Electrical Engineers of Japan.