Minimum resonant capacitor design of high‐power LLC resonant converter for comprehensive efficiency improvement in battery charging application

Abstract

Here, a minimum resonant capacitor design approach is proposed for the insulated-gate bipolar transistor (IGBT)-based high-power LLC resonant converter to improve its comprehensive efficiency in the electric vehicle (EV) battery charging application. The mathematical model of LLC resonant converter is established by using the first harmonic approximation (FHA) method. Then, the switching losses of IGBT-based high-power LLC resonant converter are analysed. Also, the relationship between predominant turn-off losses and turn-off current of power device IGBT is derived. To improve the comprehensive efficiency, the minimum resonant capacitor is proposed to reduce the turn-off losses, avoiding complex control or auxiliary circuit. Finally, the proposed approach is verified by a 2 kW LLC resonant converter prototype with 690 V DC input voltage and 75–150 V DC output voltage. Experimental results show the comprehensive efficiency of the prototype is up to 93.7%.