This study presents the topology of a three-phase LLC resonant converter with matrix transformers. The three-phase LLC resonant converter has the advantages of conventional LLC resonant converters, including zero-voltage switching at the primary side, zero-current switching at the secondary side, high-frequency feasibility, and high efficiency. Moreover, it has additional advantages that differ from conventional LLC, including low output capacitor current ripple, natural current sharing in three resonant currents, and a high power level. As a result of the above mentioned characteristics, LLC topology has been used in many electric vehicle charging systems, server power systems, and other high-power applications. However, as the power level becomes higher and higher, the input voltage is usually too high to reduce conduction loss, and the output current also increases. This situation makes transformer design more difficult. The increasing current means more core and copper loss, and the heat dissipation of the transformer becomes more difficult. Matrix transformer technology can improve this problem directly and simply. By utilizing matrix transformers, which are primary series connected and secondary parallel connected, the primary voltage stress and secondary current stress of the transformers can be reduced, and the output current can be distributed. The analysis of the proposed converter in this study includes a circuit operation introduction, a time-domain analysis, calculation of the transfer ratio curve in the frequency domain, and a loss analysis. The theoretical analysis and performance of the proposed converter are verified. A three-phase LLC resonant converter with matrix transformers prototype is built with a high input voltage of 800-VDC and high output current of 200-A. The output voltage is 100-VDC. The waveform and efficiency data will be shown in the experimental results.

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This paper presents the designed method and the implementation of stepped air-gap ferrite inductor applied in power factor correction (PFC). Conventionally, the input inductor of the PFC has a designed consideration on the maximum output power; thus, designing the PFC for peak-power-load conditions results in a very large inductor. The proposed designed method improves the load-carrying capability without increasing the volume of the inductor when the PFC is operating in peak-power-load conditions. The stepped air-gap ferrite inductor maintains the inductance in the rated-full-load and sustains the peak-power-load conditions with the lower inductance. Compared with the convectional ferrite inductor, the proposed method can maintain the size and the efficiency of the power supply, and promote the powercarrying ability. The detailed analysis and the design of the proposed method are described. Experimental results are recorded and evaluated by a prototype PFC with an AC input voltage of 110-264 VAC and a DC output voltage of 384 VDC. Finally, the volume of input inductor is kept with 40950 mm 2 , the efficiency is also same compared with the conventional inductor, and the load-carrying capability of the converter is promoted from the normal rated power of 1 kW to the peak power load of 2 kW.

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