Si-IGBT versus SiC-MOSFET — An isolated bidirectional resonant LLC DC-DC converter for distributed power systems

This report discusses using the new SiC-MOSFETs in a front-end DC-DC converter for distributed power systems. In such an application, high efficiency and high power density are the major driving factors that naturally require a high switching frequency. The SiC-MOSFET is widely considered a desirable switching device for the high-frequency power conversion/inversion circuits due to its high voltage, low on-resistance, and fast switching speed. Here a 700-V 40-kW isolated bidirectional resonant LLC DC-DC converter is designed and fabricated using both the conventional Si-IGBTs and SiC-MOSFETs. The experimental results show the DC-DC converter using SiC-MOSFETs can reach a system efficiency around 98%, about 2% higher than that of the DC-DC converter using the conventional Si-IGBTs at rated power. It is also found that high-power and high-frequency transfer such as working at 100 kHz is now not commercially available. The optimized design and fabrication of the high-frequency transformer is crucial to promote the application of SiC-MOSFETs in high-power isolated DC-DC converters. Besides, accurate modeling of the SiC-MOSFET, high-precision simulation of the converter, and cost-performance evaluation/prediction are also important.