Analysis of a Magnetically Controlled Single Stage LLC Resonant Converter

The traditional single stage AC/DC converter suffers from a variable DC bus voltage that also affects the operation of the DC/DC unit. In this paper, a magnetically controlled single stage LLC resonant converter is proposed for low power applications, and it has the following features: 1) single stage operation; 2) inherent power factor correction function; 3) almost constant DC bus voltage; 4) fixed switching frequency and duty cycle operation; 5) the LLC resonant converter is operating at the series resonant frequency point, which is the highest efficiency point, so the converter can always achieve the maximum efficiency operation; 6) soft switching operation for all semiconductors can be achieved. Finally, a 75 W experimental prototype was built to validate the proposed converter.