Research And Design Of Input Series Output Parallel Llc Resonant Converter Based On Digital Hybrid Control

DC/DC converters with high-voltage input and large-current output are widely used in DC distribution network,locomotive traction system and non-vehicular charging post power modules.The traditional DC/DC converters mostly use single module,hard switch,single control strategy and analog controller,which cause the voltage and current stress of the components to be too large and the system efficiency is low.The input-series output-parallel LLC resonant converter based on digital hybrid control strategy has the advantages of strong anti-interference,easy maintenance,low voltage stress on the switch,soft switch and high system efficiency,and in line with the trend of high frequency,standardization,modularity and intelligence of DC/DC converters.Therefore,the input-series output-parallel LLC resonant converter based on digital hybrid control strategy has been studied in this paper.Firstly,the details of the operating modes of the resonant converter in a full-bridge LLC resonant converter with pulse width modulation(PWM)strategy and pulse frequency modulation(PFM)strategy are given separately.Then based on the different energy transfer modes of the converter under the two control strategies,the converter is modeled based on the First Harmonic Approximation(FHA)and the time domain analysis method respectively.Finally,by studying the mathematical models and working characteristics of resonant converters under two control strategies,combined with the characteristics of ISOP converters,a hybrid ISOP LLC resonant converter is proposed.Secondly,the problem that the output current ripple factor in DC/DC converter is too large and the power between ISOP combination converter modules is difficult to balance is described.Then the influence of staggered angle on the output current ripple coefficient and the relationship between input voltage sharing,output current sharing and power balance are analyzed.Finally,the interleaved control can effectively suppress ripple,and the input voltage sharing can ensure the output current sharing and the power balance,so the interleaved control and input voltage sharing are introduced into the control of the ISOP combined converter.Thirdly,in the controller design of LLC resonant converter,it is difficult to establish the small signal model.Firstly,the small signal modeling methods of DC/DC converter is introduced.Based on the analysis of various small signal modeling methods,the small signal model of LLC resonant converter based on the Extended Description Function(EDF)method is finally selected.Finally,the equivalent circuit of the small signal model of the resonant converter is obtained.Finally,based on the above analysis,the control part and the hardware part of the system are designed.The control part mainly includes the selection of mode switching point,the calculation of resonant network parameters and the design of control flow in hybrid control.The hardware part of the system mainly designs the resonant transformer,resonant inductor and resonant capacitor parameters.Finally,through the systematic prototype,the control strategy is verified.