Research On Optimal Start-up Control Strategy Of High Frequency LLC Resonant Converter

Contemporary society has less energy,so it is necessary to reduce energy loss and save energy in engineering.The LLC resonant converter has the advantages of high switching frequency,high power density,soft switching in the full load range,and good voltage regulation performance.It meets the needs of modern power electronic technology for switching power supplies.It is widely used in various occasions.First,the basic topology and steady-state operation mode of the half-bridge LLC resonant converter are explained in detail.The converter has different operation modes at different switching frequencies.The switching of the switching tube and the switching tube bypass in a single cycle are analyzed in detail.The pre-charge and discharge of the capacitor.The steady-state operation of the half-bridge LLC resonant converter is analyzed by the FHA method,and the equivalent model of the converter is constructed,the DC gain is calculated and the impedance characteristic is analyzed.Then,the LLC resonant converter is analyzed in detail through the time domain analysis method,which serves as the basis for soft start-up using the control plane state trajectory.The operating modes of the LLC resonant converter are divided into three,and the operating modes are various combinations of the three modes,which is convenient for analysis,and the plane state trajectory diagrams under several different operating modes are drawn.Then the soft start-up method of the common LLC resonant converter is briefly introduced.A new type of soft start method is designed.In the first stage,an asymmetric resonant current limit band is used,and then the resonant current control band is changed to a symmetric resonant current limit band.Finally,the boundary value of the resonant current limit band is reduced to the steady state operation.The peak value of the resonant current.Finally,the feasibility of parameter design is verified by simulation,and the feasibility of the proposed soft-start method and the correctness of the plane state trajectory analysis under time domain analysis are verified.Finally,an experimental platform with an output power of 750 W is constructed to verify the feasibility of the design.