Critical-Mode-Based Soft-Switching Modulation for High-Frequency Three-Phase Bidirectional AC-DC Converters

In this paper, a novel critical-conduction-mode-based modulation is proposed for three-phase bidirectional ac-dc converters. With this modulation, the switching frequency variation range shrinks, zero-voltage-switch soft switching is achieved, and the switching-related loss is reduced, which is especially beneficial for systems operating above hundreds of kHz high switching frequency with wide-band-gap power semiconductor devices to achieve both high power density and high efficiency. A 25 kW silicon carbide based high-frequency three-phase bidirectional ac-dc converter prototype is designed to achieve a power density of 127 W/in(3), which is at least five times higher than commercial products. All the control functions are digitally implemented with one low-cost microcontroller, and the aforementioned benefits are experimentally verified on this prototype under both inverter mode and rectifier mode operations. With the proposed soft-switching modulation, the tested peak efficiency is close to 99.0% for this prototype even at above 300 kHz high switching frequency operation.