Abstract: Wide gain and high performance are the keys for the LLC resonant converter applications in electric vehicles, renewable energy systems, etc., while there are problems of wide switching frequency ranges and poor voltage regulation performances under the conventional pulse frequency modulation. To this end, an improved topology of the Common resonant branches is proposed based on the voltage doubling rectifier structure, and the fixed frequency variable duty ratio modulation strategy is designed. Firstly, the topology introduction and operating principle of the converter are given; secondly, the effects of the inductance ratio and quality factor on the gain are analyzed with the gain characteristics, and the parameters are constrained according to the ZVS condition; finally, the converter performance is compared with the conventional ones. Simulations and experiments show that the converter is able to achieve the wide output voltage regulation, haing good soft switching performance. Compared with conventional pulse frequency modulation, the proposed control here always works at the optimal resonant frequency point with the small circulating current in the circuit.