1-kV Input 1-MHz GaN Modular Multilevel LLC Converters

A modular multilevel LLC converter suitable for high input voltage applications is proposed to reduce the voltage stress of the primary devices by half. The 650 V eGaN HEMTs with much lower R
ds(on)
can be applied instead of 1700 V SiC MOSFETs at 1 kV input voltage and 1 MHz frequency. With lower Q
g
, the eGaN HEMTs produces less switching loss and drive loss. The split resonant inductor solution is proposed to reduce the distortion of the resonant current to maintain ZVS realization. The matrix transformer is also employed to realize high step-down ratio conversion with the secondary-side current sharing and even thermal capability. To reduce the transformer parasitic capacitance, the non-interleaving type windings are proposed to minimize the displacement current from the primary-side to secondary-side. A prototype with 1 kV input and 32 V/ 3 kW output at 1 MHz was built. It achieves the peak efficiency of 95.18% (0.8% higher than the diode prototype) and power density of 107 W/in
³
, an improvement of 69% compared to the 300 kHz SiC counterpart.