Research On Half-Bridge LLC Resonant DC-DC Converter

With the rapid development of switching power supply technology and the continuous improvement of human requirements for power supply technology,hard switching power supply has been unable to meet the requirements.In order to effectively improve the power density and efficiency of the converter and reduce the volume and weight of the converter,LLC resonant converter has gradually received extensive attention and research.LLC resonant converter not only has low switching loss,but also has a voltage input range.It has the advantages of wide width,light weight,small volume and high efficiency.The working principle of LLC resonant converter and the specific working process in different frequency range are introduced in detail.The half-bridge LLC resonant converter is modeled by FHA(fundamental approximation method),and its steady-state characteristics are analyzed in depth.Through drawing and analyzing the gain curve,the specific design method of LLC resonant converter is given and verified by simulation.The small signal model of LLC resonant converter is established by using the extended description function method,and the detailed derivation process is given.Then the small signal model is verified and analyzed,its steady state analysis and frequency domain analysis are carried out.Aiming at the problem of open-loop instability,a reasonable compensator is designed,and the rationality of compensator design is carried out by simulating the dynamic performance of compensated LLC resonant converter with Matlab Verification.The parameters design of LLC resonant converter and the selection of main circuit elements are analyzed and calculated in detail,and the design of transformer is analyzed and verified.According to the designed parameters,the circuit simulation is carried out to verify the rationality of the parameter design,and the open-loop simulation and closed-loop simulation of the circuit are given.The stability of the output voltage under sudden start-up and load changes is analyzed,and the closed-loop circuit is verified.The hardware parts,such as the front-stage PFC circuit,half-bridge LLC main circuit,STM32 peripheral circuit,sampling circuit,driving circuit and auxiliary power supply circuit are carried out.Design and analysis.The prototype is debugged and the experimental data are measured.The ZVS state and output voltage waveform under different loads,load switching waveform,ripple waveform under different loads,dead zone analysis waveform and secondary rectifier waveform are analyzed.The rationality of the circuit design is verified.