Improving the conversion efficiency of converters in battery energy storage systems is of great significance to save energy and enhance economic value. In order to improve the efficiency of isolated step-up DC-DC converters in the system, resonant converters fixed at the switching frequency are widely used (DCX), which are mainly responsible for providing voltage gain and power, supplemented by a voltage regulation circuit (R). In DCX circuit, device conduction loss and winding loss (i.e., copper loss) account for the majority. Both can essentially be seen as conduction loss, with the difference being that the material through which the current flows. Device loss is the flow of current through the semiconductor, while winding loss is the flow of current through the copper. In this work, a circuit design method that comprehensively considers the device conduction loss and winding loss is proposed, and a combined conduction loss model suitable for DCX circuit is given by using the finite element simulation tool with the physical and mathematical model derivation. The circuit design can reach the highest efficiency point at the present level of devices and planar transformers, and the expected efficiency results are in good agreement with the experimental results, reflecting the high accuracy of the loss model. Experiments have verified that the DCX part of prototype has a full-load efficiency of 98.7% at the rated point of 48V input, which is basically in line with the expected full-load efficiency of 98.8%. In addition, at 40V input, the full-load efficiency is 98.5%; At 60V input, the full-load efficiency is 98.7%.

Fig. 1 Combined Conduction Loss Model with Device and Winding

Fig. 2 Topology of Cellular DC-DC.

Fig. 3 Efficiency Test of DCX Part