An Impedance-Based Digital Synchronous Rectifier Driving Scheme for Bidirectional High-Voltage SiC LLC Converter

Conventional digital
LLC
synchronous rectifier (SR) control typically uses detection circuits to sense the drain-source voltage of SR MOSFET in low output voltage applications, or gives SR duty cycle only considering the switching frequency in the microcontroller. They are difficult to be applied to the applications of 700-V high voltage and 6.6-kW high power directly due to the high
dv
/
dt
and large SR duty cycle variations, which poses serious challenge for SRs control. A bidirectional impedance-based SR driving scheme is presented for high-voltage SiC
LLC
converter. Based on the
LLC
equivalent impedance, mathematical models are built to calculate the SR on-time in the forward and reverse modes, which can be tuned timely when the switching frequency and load vary. Thus, both bidirectional
LLC
performance with high efficiency and high immunity to the switching noise can be achieved without adding auxiliary circuits. A prototype of 300-kHz 6.6-kW SiC bidirectional
LLC
charger was built. Compared to the conventional SR method, the
LLC
efficiencies improve 0.3% in the forward and reverse modes at full load by using the proposed SR driving scheme.