High Efficiency Ac/dc Conversion Technique Based On Llc Resonant Circuit

With the rapid development of power electronics, high-frequency switching power supply has been widely applied to national defense, industrial, civil and other fields because of its many advantages, and closely related to people's work and life. But the harmonic pollution of switching power supply caused by more and more attention has been paid, the demands of its performance, size, efficiency, power density become higher and higher. Therefore, the study of high power factor, high efficiency AC/DC conversion technology has important practical significance to harmonic suppression, energy conservation and achieve green power conservation.By analyzing the research situation of power factor correction (PFC) technology and DC conversion (DC/DC) technology, two-stage structure AC/DC conversion Technique has been used, the PFC control technology and soft-switching realization has been studied. The front part use the advanced one cycle control technique, by studying its application principle, stability and performance advantages, achieved the design and optimization of the parameters for main circuit and control circuit, simplified the control circuit structure. According to the control circuit characteristics and loop stability requirements, realized the design of current loop and the control loop, ensured the system stability, and improved the system dynamic response. By establishing the circuit closed-loop simulation model, Verified the performance advantages of one cycle control to suppress input voltage and load disturbance, the advantages of continuous power factor correction, optimized the circuit parameters.LLC resonant circuit has been chosen for main circuit topology, through the frequency control achieved the DC link soft-switching characteristics. Analyzed the circuit working principles in different frequency range, established the fundamental equivalent circuit, the LLC resonant circuit voltage gain characteristics, input impedance characteristics has been analyzed through fundamental analysis method, determined the soft-switching working range. Optimized the circuit parameters based on fundamental analysis, ensured the part of DC conversion to achieve zero-voltage switch(ZVS) of primary switch in the whole input voltage range and full load range, zero-current switch(ZCS) of output rectifier diodes in larger range, and minimized the voltage and current stress in resonant circuit, greatly improved system efficiency. In order to improve the system power density, selected the optimized structure of the magnetic components, achieved the integrated of resonant inductance and transformer, greatly reduced the converter volume. Based on the theoretical analysis and parameter design, build the experimental prototype, verified and analyzed part of PFC and DC/DC through the experiment. The experimental verification, power factor more than 0.988, LLC resonant circuit achieved a full range of soft switching, the system with high efficiency.