Investigation of Soft-Switching QSW Technique in DC/DC SiC-Based Flying Capacitor Converter With Q2L Control

This article investigates the soft-switching quasi-square-wave (QSW) technique in dc/dc SiC-based flying capacitor converter with quasi-two-level (Q2L) control establishing design guidelines for constructing high-efficiency soft-switched bidirectional converters with low-voltage power transistors. The general idea behind the soft-switching in the proposed system is based on near critical conduction mode operation using TCM (triangular current mode) and Q2L control with the addition of auxiliary transistor capacitances. The soft-switching process is based on a resonance between the capacitances in parallel to each transistor, and the main inductor—ZVS at turn
on
is ensured through proper modulation pattern according to TCM-Q2L control, and the turn-
off
soft-switching mechanism is assured through the novelty in the form of adding auxiliary capacitance in parallel to each of the SiC power
mosfet
s according to the QSW operation. Thus, the converter can reach very high efficiency (peak at 99.5%), maintaining soft-switching for a wide operating range, using only small auxiliary SMD capacitors and a low-volume flying capacitor, leading to high power density. The presented study is based on experimental tests using a 1.5 kV model at up to 15 kW and includes the impact of various auxiliary capacitance values and optimal capacitor value selection for maximizing the converter efficiency.