Design of output filter in LLC resonant converters for ripple current reduction in battery charging applications

In this paper, a filter design guideline to reduce the ripple current in LLC resonant converters for the battery charger is proposed. The effect of filter inductor on the resonant network is mathematically analyzed, and a filter inductor is designed considering capacitance of the battery. The voltage gain of LLC resonant converter with filter inductor is analyzed through fundamental harmonic approximation (FHA) method. This research verifies performance of ripple current reduction compared with conventional LLC resonant converter without output filter inductor through mathematical analysis, simulation and experimental results.