A High Frequency High Efficiency GaN Based Bi-Directional 48V/12V Converter with PCB Coupled Inductor for Mild Hybrid Vehicle

The commercialization of the mild hybrid is impeded by the demands of a lightweight, compact yet efficient bidirectional DC/DC converter between 48V system and the conventional 12V system. With conventional Si-based design, the converter operating frequency is typically less than 70 kHz, resulting in a bulky system with 1-2kW/L power density and no more than 95% efficiency. In this paper, a bi-directional 3.5kW 48V/12V converter is designed using low voltage GaN devices from EPC. Due to the superior performance of GaN devices, the switching frequency of the converter can be pushed to over 200kHz and the whole converter volume and weight are significantly reduced. In the meantime, thanks to the high frequency operation, PCB winding coupled inductors with −0.6 coupling coefficient are adopted to further shrink the system size and simplify the manufacture process. As a result, the converter reaches over 8.7kW/L power density with 97.5% peak efficiency, which are far beyond the current Si practice.