Battery Charging Resonant Converter with a Secondary Side PFC

A single-phase supplied Li-ion battery charger with a maximum voltage of 60 V, power of 600 W and with a PFC functionality is under development currently. The industrial partner especially accents EMI minimizing, which is a common problem of high-power switching supplies. Small size is required as well, therefore a relatively high switching frequency of approx. 150 kHz was chosen. To ensure a satisfactory efficiency and low EMI a resonant converter is used. The proposed novel design ensures lowering the dv/dt slope on the primary side of the resonant converter independently of the load to minimize EMI significantly. The resonant converter is supplied from a passive rectifier with a soft DC link (low capacitance in the DC link). This converter serves only for galvanic separation and voltage/current transformation, there is no voltage control and therefore ideal conditions for soft switching are ensured (both ZCS and ZVS). The output voltage control as well as the input phase current shaping (PFC functionality) are provided by an additional secondary step-up converter. Important aspects, simulations and design details are included in this contribution.