Research On Hybrid Modulation Strategy Of Bidirectional CLLC Resonant Converter Based On PFM-EPS

The pace of new energy development is striding forward,and the energy revolution is the theme of this era.Photovoltaic,wind energy,electric vehicles and energy storage industries are developing at a high speed in parallel.Because storage battery has the advantages of making up for the intermittence of new energy generation,it plays an important role in various new energy systems,and bidirectional DC-DC converter is a bridge connecting storage batteries and systems,so it is of great significance to study high-performance bidirectional DC-DC converter.This paper takes the bidirectional CLLC resonant converter as the research object,focusing on the gain characteristics and soft-switching characteristics of Pulse frequency modulation(PFM)and Extended phase shift modulation(EPS).From the perspective of optimizing voltage regulation performance and efficiency,the modulation strategy and overall control method of the system are discussed.Firstly,on the basis of expounding the operation mode of bidirectional CLLC resonant converter during PFM modulation,the circuit gain model and the conditions of soft switching are deduced according to FHA.By analyzing the gain characteristics and soft switching characteristics,the resonant parameters are optimized and designed.In order to further improve the operation efficiency of the converter under PFM modulation,a simplified synchronous rectification strategy is adopted in the under-resonance operation state,and a load segment synchronous rectification strategy(LSSR)is designed in the over-resonance operation state,which simplifies the control difficulty.Secondly,in view of the difficulty and low efficiency of PFM modulation in step-down light load operation,PFM-EPS hybrid modulation is designed to make up for the defects of PFM modulation by using the characteristics of EPS modulation.On the basis of expounding the operation mode of EPS modulation,the gain characteristics and soft-switching characteristics are deduced in the time domain model,the soft-switching conditions are quantitatively analyzed,and the switching conditions of the two modulations are solved.On this basis,the overall control strategy of the converter system under hybrid modulation is designed to ensure the voltage regulation ability and high efficiency of the bidirectional CLLC resonant converter in a wide load range.Finally,based on Matlab/Simulink software,the circuit simulation model is established and verified,and a low-power experimental platform is built for experimental verification.The simulation and experimental results fully prove that the hybrid modulation strategy based on PFM-EPS described in this paper can effectively realize the wide range voltage regulation and high efficiency operation of the converter.The theoretical correctness and experimental feasibility of the hybrid modulation strategy designed in this paper are proved from steady state,dynamics,soft switching characteristics,modulation switching and efficiency.