High-Efficiency High-Density MHz Cellular DC/DC Converter for On-Board Charger

In this article, a high efficiency and high power density Regulated dc Transformer (RDCX) is proposed for on-board charger (OBC). In this circuit, high input and output voltages are undertaken by series connected low-voltage devices. Owing to the low new figure of merit (NFoM, Rdson×Coss)(Il-Jung et al., 1995), (Wu and Shi, 2020) characteristic of low-voltage devices, the conduction loss of switches can be reduced. Mathematical modeling and verification are also carried out. In addition, by applying cascaded buck as the regulation part of RDCX, the volt-second of buck inductor can be reduced compared with the traditional two-level buck circuit. As a result, the size of the inductor can be reduced. Furthermore, since all dc buses of the cascaded buck converter are from the rectifiers whose windings are coupled to the same transformer, those bus voltages can be naturally balanced. A 2.3 kW prototype based on 60V device with 388–412 V input and 250–450 V output voltage range is built up to verify the analysis, achieving 98% peak efficiency and 910 W/in3 power density.