Abstract: Due to the wide switching frequency range and low overall efficiency, traditional LLC resonant converters are not suitable for wide voltage gain applications. To solve the problem, a multi-mode dual LLC resonant converter is proposed. Based on the topology reconfiguration of half-bridge and full-bridge circuits as well as full-bridge and voltage-doubler rectifiers, the converter realizes an ultrawide output voltage within a limited frequency range by four modes with different voltage gain. While the efficiency of the converter is improved, the cost is reduced by multiplexing power devices. In order to achieve smooth transitions between these modes, a pulse width modulation-pulse frequency modulation (PWM-PFM) control method is designed for the converter, which is further optimized according to the characteristics of mode switching to improve the speed. To verify the feasibility of the proposed converter and control method, a SiC-based experimental prototype with an output voltage of 60~450 V and a maximum power of 900 W is designed and tested.