Research On High Frequency LLC Charger With SiC MOSFET

Among the currently available charging solutions,the two stage power architecture consisting of a PFC and an isolated dc-dc converter is the most common charger architecture.The output voltage of the PFC converter is about 800V,the voltage stress devices of traditional Si MOSFET is 600V,so three-level DC/DC converter is a choice,it can use low voltage stress devices with two series-connected.But it needs complicated control and driver for at least eight switches used.In this paper,a new 1200V SiC MOSFET is used to design a high frequency full bridge LLC converter.In order to achieve high efficiency and high power density,soft switching techniques are preferred for the isolated second stage to increase the switching frequency and reduce the switching losses.Among a lot of soft switching topologies,the multi resonance LLC topology has several advantages.The most important is that the switches can achieve ZVS turn-on over wide load range.According to the characteristic of charging profile of lithium-ion battery pack,a design methodology based on fundamental harmonic approximation is proposedThe interleaving structure helps to reduce the ac winding loss effectively,especially in the condition of high frequency.Although low conduction loss and low leakage inductance can be achieved,the parasitic capacitance is considerably increased,thereby deteriorating the converter's EMI and soft-switching performance.The distribution of inter-winding capacitances and the distribution of voltage potentials on windings are the two critical factors that determine the CM current of the converter in switching frequency ranges.CM current reduction method by adjusting connection of inductor is proposed.According to the characteristic of Charging profile of lithium-ion battery pack,a design methodology based on fundamental harmonic approximation is proposed and validated through experiments on a prototype converting 800 V from the input to an output voltage range of 300V-450 V at 6.6 kW a peak efficiency of 98.4%.The design and key experimental results are provided to improve the power density.