Research On LLC Resonant Converter With Series-Parallel Auto Regulated Rectifier

Resonant converters have been applied to kinds of power supply systems for the features of excellent soft switching performance and high power density.However,resonant converters cannot maintain high efficiency in the wide operation range for the increased circulating loss.Based on this background,the thesis focuses on the resonant converter with an overall high efficiency in the wide operation range.A new type of series-parallel auto regulated hybrid rectifier with inherent wide voltage gain range is studied and employed to the LLC resonant converter to harvest a family of series-parallel auto regulated LLC resonant converter.The proposed converters can operate in a wide voltage range with an overall high efficiency under narrow frequency variation by the implementation of variable-frequency(VF)plus phase-shift(PS)control.Firstly,the series-parallel auto regulated LLC resonant converter with paralleled primary structure is studied.The operation principles under VF control and PS control are analyzed.The basic characteristics are achieved and the voltage gain equation and curve are derived by state-panel analysis.A 3.5kW prototype is built and tested in the laboratory.The experimental results verify that the proposed converter has gorgeous soft switching performance in the full load and voltage range and can be a good candidate for wide output voltage range application.Then,the series-parallel auto regulated LLC resonant converter with series primary structure is studied.The operation principles under steady state and hold up mode are analyzed and the basic characteristics are introduced briefly.A 12V/300 W prototype is built and tested in the laboratory.The experimental results verify that the proposed converter inherits the excellent characteristics of traditional LLC converter in the steady state and can maintain the output voltage with 20 ms in the hold-up mode.