LLC Resonant Converter With Semiactive Variable-Structure Rectifier (SA-VSR) for Wide Output Voltage Range Application

A semiactive variable-structure rectifier (SA-VSR) is proposed for the LLC resonant converter to achieve wide output voltage range power conversion. The SA-VSR is composed of two active switches and two diodes. The SA-VSR is operated as a voltage-doubler rectifier when the duty cycle of the active switches is 0.25, whereas it is a voltage-quadrupler rectifier when the duty cycle of the active switches is 0.5. Hence, the output voltage range is extended by adaptively changing the operation mode of the rectifier, which results in reduced switching frequency range, circulating current, and conduction losses of the LLC resonant converter. The switches' switching frequency of the SA-VSR is halved in comparison with the switches on the primary side of the LLC resonant converter, and zero voltage switching and zero current switching are achieved for all the active switches and diodes, respectively, to reduce the switching losses. The operation principles are analyzed and a 1.5-kW prototype with 400-V input voltage and 100-500-V output voltage is built and tested to verify the feasibility of the proposed method.