A Bidirectional Synchronous/Asynchronous Rectifier Control for Wide Battery Voltage Range in SiC Bidirectional <i>LLC</i> Chargers
Haoran Li, Shengdong Wang, Zhiliang Zhang, Jingfei Zhang, Wenjie Zhu, Xiaoyong Ren, Cungang Hu
Abstract
Conventional pulse frequency modulation is typically adopted in the reverse <i>LLC</i> 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 <i>LLC</i> 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-<small>on</small> 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 <i>LLC</i> charger was built. With the proposed SR control, the forward <i>LLC</i> efficiency improves 0.2% compared with the conventional SR method. The reverse <i>LLC</i> 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.