Analyzing a bridgeless single stage LLC resonant PFC converter controlled by frequency and pulse width modulations techniques

Abstract

In this paper, a bridgeless single stage LLC resonant PFC converter is analyzed in time domain. This converter is simultaneously controlled by frequency and pulse width modulations techniques. Soft switching is greatly achieved thanks to the LLC resonant converter. Consequently, switching losses and EMI noises are significantly decreased and switching frequency is increased to reduce cost and volume, and increase power density. Bridgeless structure decreases conduction losses by eliminating two bridge diodes. DCM boost PFC is used because of its inherent power factor correction feature and its simple control scheme. Frequency modulation and pulse width modulation techniques are simultaneously used to control the proposed AC/DC converter that gives the designers one more degree of freedom. Here, exact time domain analysis and iteration approach are used to analyse and design the converter. To confirm its performance and the given analyses, it has been simulated. The given results are in good agreement with the mathematical analyses. 50 Hz, 220±10% Vac input voltage is applied to the simulated converter, and its output power varies between 50 and 100 W. Its switching frequency and duty cycle vary between 370 and 403 kHz and 0.29 and 0.36, respectively, to regulate its 100 V dc output voltage.