Current Sharing Method Using Secondary Voltage Ripple for an Interleaved LLC Resonant Converter

A circuit topology and its control for an interleaved LLC resonant converter are proposed. In general, the LLC converter achieves high efficiency, but the ripple current of the output capacitor is large, so a number of interleaving methods for the ripple current cancellation of LLC converters have been proposed. Output of the LLC converter is basically controlled by switching frequency modulation; therefore, the interleaving requires current sharing while operating at the same switching frequency. In the present study, a common LC filter is connected to the rectification outputs of two parallel-connected LLC modules and passively achieves the current sharing by the output voltage ripple of each other's modules. The switching phase difference between the two LLC modules is slightly shifted from 90 degrees for further improvement of the current balance. The proposed method is evaluated by simulation under the condition of a resonant inductances mismatch of the two LLC modules. The simulated results show that the appropriate value of the proposed common filter prevents the current imbalance due to the inductances mismatch.