Research On Wide Input Range LLC Resonant Converter

LLC resonant converter is widely used in SMPS system as its high power density and high efficiency.LLC resonant converter achieves soft-switching in all load conditions,which largely reduced the size and improve the efficiency.Additionally,soft-switching mode can provide better EMC performance.The advantages has made LLC resonant converter uniquely qualified for battery charging application.However,the DC gain range of the LLC resonant converter is very small,resulting in a small input voltage range,which is not suitable for a large area of input.A novel variable LLC was presented on the purpose of expending the grid input voltage range in new energy.The variable LLC varies between full bridge LLC(FBLLC)and half bridge LLC(HBLLC)with the step of input voltage.The topology is FBLLC when the input voltage is low;the topology will change to HBLLC automatically by digital signal processor(DSP)controller while the input voltage is high.The circuit does not add any additional component and with simple software control.A new topology switching strategy was also presented to optimize efficiency.Analysis and experimental result showed that the input voltage was expended to twice to that of the traditional LLC.The topology is suitable for applications with ultra-wide input voltage range such as solar and wind energy.In this thesis,the working principle of the general LLC resonant converter is introduced,and its DC steady state characteristics are analyzed.On this basis,the implementation of wide range input LLC and topology switching strategy are described in detail.After that,the small signal dynamic model of the LLC resonant converter is analyzed,and the closed loop parameter is designed through the SISOTOOL tool in MATLAB,and the Simulink model is built to complete the simulation.Finally,according to the study of a wide range of input LLC resonant converter in this paper,a 500 W prototype was designed and manufactured,given the detailed design process,including driving circuit,sampling circuit,protection circuit,control circuit design,but also completed the calculation parameters of magnetic components.Finally,the feasibility of the wide range input LLC resonant converter is verified through the analysis of the experimental waveform.