High-Frequency Three-Phase Interleaved LLC Resonant Converter With GaN Devices and Integrated Planar Magnetics

The LLC converter is deemed the most widely used topology as dc/dc converter in server and telecom applications. To increase the output power and reduce the input and output current ripples, three-phase interleaved LLC converter is becoming more and more popular. It has been demonstrated that three interleaved LLC converter can achieve further efficiency improvement at the 3-kW power level. However, the magnetic components for multiphase LLC converter are complex, bulky, and difficult to manufacture in a cost-effective manner. In this paper, a high-frequency gallium nitride (GaN)-based three-phase LLC converter is employed to address these aforementioned challenges. With GaN operating at 1 MHz, all magnetic components, namely, three inductors and three transformers, can be integrated into one common structure while all magnetic windings implemented in a compact four-layer PCB with 3-oz copper. The proposed structure can be easily manufactured cost-effectively in high quality. Furthermore, shielding techniques for full-bridge secondary have been investigated, and additional two-layer shielding has been integrated to reduce common-mode noise. A 1-MHz 3-kW 400 V/48 V three-phase LLC converter is demonstrated, and the peak efficiency of 97.7% and power density of 600 W/in(3) (37 kW/L) are achieved.