A Bidirectional Synchronous/Asynchronous Rectifier Control for Wide Battery Voltage Range in SiC Bidirectional LLC Chargers

Conventional pulse frequency modulation is typically adopted in the reverse
LLC
converter resulting in a low voltage gain. The output bus voltage may be lower than peak grid voltage, so that the buck-type inverter cannot output 220 Vac and poses series challenge to achieve bidirectional charger operation. A bidirectional synchronous/asynchronous rectifier control is proposed for wide battery voltage applications in the
LLC
converter. In the forward mode, a simplified model is built to calculate the synchronous rectifier (SR) on-time and achieve high efficiency by using a two-order function. In the reverse mode, the turn-
on
instants of primary side and secondary side power devices are controlled with a delay angle to obtain high voltage gain and high efficiency. A 6.6-kW silicon carbide bidirectional
LLC
charger was built. With the proposed SR control, the forward
LLC
efficiency improves 0.2% compared with the conventional SR method. The reverse
LLC
voltage gain is up to 1.33 so that the charger can output 220 Vac in the full battery voltage range of 200–500 V.