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Improved Unterminated Behavioral Model for Common-Mode EMI Emission of SiC Power Converters with Different Switching Frequencies

Fig. 1. GaN-based MHz totem-pole PFC rectifier
With the advent of 600V gallium-nitride (GaN) power semiconductor devices, the totem-pole bridgeless power factor correction (PFC) rectifier, which was a nearly abandoned topology, is suddenly become a popular solution for applications like a front-end converter for server and telecommunication power supply. This is mostly attributed to the significant performance im-provement of the GaN high-electron-mobility transistor (HEMT) compared to the silicon (Si) metal - oxide - semiconductor field-effect transistor (MOSFET).

Based on previous study, soft switching truly benefits the cascode GaN HEMT. As the cas-code GaN HEMT has a high turn-on loss and an extremely small turn-off loss due to the cur-rent-source turn-off mechanism, critical mode (CRM) operation is very suitable. In order to evaluate the impact and system-level benefits of high frequency, the cascode GaN HEMT is applied in the totem-pole PFC rectifier while pushing frequency to above 1MHz.

Several important high-frequency issues, which used to be less significant at low-frequency, are emphasized and the corresponding solutions are proposed. Detailed design considerations are presented in this paper including ZVS extension in order to solve switching loss caused by non-ZVS valley switching; variable on-time control to improve the power factor, particularly the zero-crossing distortion caused by negative current and traditional constant on-time control; and interleaving control for input current ripple cancellation.

Finally, a prototype of the 1.2kW 1MHz GaN-based dual-phase interleaved CRM totem-pole PFC rectifier is demonstrated. With ZVS soft switching, 99% peak efficiency is achieved at MHz frequency range. And at the same time, the volume of passive components, like the inductor and the DM filter, are shrunk dramatically so that the power density of the system increases significantly to as high as 200W/in3.

Fig. 2. Efficiency of single-phase totem-pole PFC rectifier
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