An Integrated Charging Equalizer Based on LLC Resonant DC-DC Converter for Series-Connected Battery String in Plug-in Hybrid Electric Vehicle

The LLC resonant DC-DC converter has the advantage of high-efficient and high-power density. It is widely used as the battery charger in the plug-in hybrid electric vehicle. In order to ensure charging safety, a zero-voltage switching (ZVS) integrated charging equalizer based on LLC resonant is proposed, which can charge and balance the battery string simultaneously. And the integrated voltage equalizer reuses the LLC converter's magnetic element, and the automatic voltage balance function is achieved without cell monitoring. The working principle of the LCC converter-based integrated equalizer is analyzed. Simulation results show that the proposed integrated equalizer can realize charging and balance functions under the condition of ZVS. An experimental prototype is designed to charge and balance 4 series-connected battery cells. The function of LLC converter stage is validated and the measured results fit the theoretical analysis.