Bidirectional Synchronous Rectification on-Line Calculation Control for High Voltage Applications in SiC Bidirectional LLC Portable Chargers

With 700 V bus voltage in the SiC bidirectional
LLC
converters, high
dv/dt
is up to 35 kV/
μ
s with 20 ns switching speed, which causes high common mode noise and poses serious challenge for synchronous rectification (SRs) control. A digital bidirectional SR online calculation control is proposed for 700 V high voltage at 300 kHz. It not only achieves bidirectional operation with high efficiency, but also applies to high voltage since it owns high immunity to the switching noise without any detection circuits. The mathematical model is built to calculate the SR conduction time online in the forward and reverse modes, and determine the SR turn
off
instant considering the switching frequency and load. The transformer dc bias is analyzed in the reverse mode. A 6.6-kW SiC bidirectional portable charger was built. The
LLC
efficiency of forward and reverse modes is improved by 0.3% and 0.2% over the conventional SR control at full load, respectively.