Critical-mode-based soft-switching modulation for three-phase rectifiers

Abstract

In this paper, a novel critical-conduction-mode (CRM)-based soft-switching modulation is applied into three-phase rectifier application. With this modulation, zero-voltage-switching (ZVS) soft switching turn-on is achieved and the efficiency of the rectifier is improved, especially for high frequency operation with SiC MOSFETs, whose turn-on energy is large while the turn-off energy is negligible. In three-phase electric vehicle (EV) charging station applications, by operating at above 300 kHz switching frequency, system power density is estimated to be at least five times higher than commercial products, while efficiency is estimated to be 98% ∼ 99% with soft switching. Non-zero-voltage-switching (Non-ZVS) issue and instability issue are solved and good performance of the proposed modulation under rectifier mode operation is verified with simulation analysis. A 25kW SiC-based three-phase bi-directional AC/DC converter prototype is built with 80W/in3 power density. All the control functions are digitally implemented and experimentally verified on this prototype, and 99% peak efficiency is achieved for both inverter mode and rectifier mode operations at above 300 kHz high switching frequency.