IEEE Workshop on Wide Bandgap Power Devices and Applications in Asia (WiPDA Asia 2018)

294 / 2017-12-07 20:59:27

A Novel High-Frequency and High-Efficiency Synchronous Buck Converter with a Small Coupled Inductor

zero-voltage switching (ZVS),Buck converter,coupled inductor,high-effiency,GaN MOSFET

Plenary track > Very high efficiency and compact converters

Summary
A novel high-frequency and high-efficiency synchronous buck converter with a small coupled inductor is proposed in this paper. The proposed converter introduces a small coupled inductor and a ripple steering branch consisting of an inductor and a capacitor. The coupled inductor current which is bi-directional allows two GaN-MOSFETs to operate with ZVS. Moreover, the output current ripple and output filter requirement are reduced significantly with the ripple steering branch. Thus, both high frequency and efficiency promotion can be achieved. The operating principle and analysis of the proposed converter are introduced. Experimental results based on a 48-W prototype switching at 500kHz are presented to verify the performance of the proposed converter.

Motivation
To achieve high-frequency and efficiency promotion, synchronous buck converter is commonly used and easily achieved with synchronous rectification method. In an improved synchronous buck converter, the inductor current is bi-directional to ensure that both switches have ZVS conditions . But, the inductor current ripple increases a lot due to the bi-directional current and the large ripple raises higher requirement of output filter inductor. To solve this problem, a novel high-efficiency and high-frequency synchronous buck converter with a coupled inductor and reduced output filter requirement is proposed (see Fig. 1). In PLECS simulation software, the simulation result indicates that the output current ripple cancellation can be achieved(see Fig. 2).

Results
Compared with the traditional converter, a prototype using GaN-MOSFETs and switching at 500kHz has been done. The output current ripple can be significantly reduced with the help of the ripple steering branch(see Fig. 3). The output filter requirement is reduced and the output filter inductor and capacitor can be selected with a very small value. The main switch can be operated with ZVS(see Fig.4). Therefore, the improved converter can operate with very high efficience (see Fig. 5) to further increase the power density.