A novel soft starting strategy of an LLC resonant DC/DC converter for plug-in hybrid electric vehicles

Usually a high-efficiency Level 1~2 battery charger consists of an AC/DC (PFC) part and a DC/DC part, which in this paper is a CoolMOS based 97%-efficiency full-bridge LLC resonant DC/DC converter. Due to the existence of the output capacitance and high input voltage (usually 400VDC), the inrush current of the DC/DC converter in the starting process is inevitable, which requires an effective soft starting strategy. This paper proposed an effective soft starting strategy to gradually charge the output capacitor, decrease the inrush current and, more importantly, avoid the hard switching in the starting process, which is a must to the CoolMOS. The proposed starting strategy has been experimentally validated on a 10kW LLC resonant DC/DC converter.