Interleaved LLC Resonant Converter Based On Vraiable-Inductor

With the rapid development of modern science and technology,energy conservation,high efficiency and intelligence are regarded as important indicators to measure the performance of power electronic equipment in various fields such as communication,energy,chemical industry and so on.With the innovation of power electronic devices,various traditional circuit optimization and the emergence of new topologies are promoting the power electronic equipment system in the direction of improving efficiency and increase power output through module parallel mode.Because of its superior performance such as soft switching,the LLC resonant converter has low switching noise,high efficiency and high power density.However,in the case of high current output,the conduction loss of LLC increases sharply and the stress requirement of each power device increases,which reduces the efficiency of the equipment.In order to solve this problem,the interleaved parallel LLC resonant converter is studied in this thesis.The interleaved parallel LLC converter can not only avoid the influence of the conduction loss of each power device on the overall efficiency of the converter under high current,but also reduce the output ripple,the capacity of output filter capacitor and the volume of output filter capacitor by interleaved parallel technology.However,since LLC converter operates in variable frequency modulation mode,it is impossible to keep the switching signals of LLC in fixed phase shift with each other.This will make it difficult to realize parallel interleaving operation of multiple LLC converters to reduce output ripple,and make the current sharing problem of parallel modules caused by device differences prominent.In this thesis,variable inductance is applied to interleaved parallel multichannel LLC converters.By controlling the variable inductance,the frequency synchronization of multichannel LLC converter can be realized.At the same time,the interleaving and parallel operation of each module of LLC can be achieved,and the basic requirement of current sharing of each module can be satisfied.The contents of this thesis are as follows:(1)The principle and working mode of LLC resonant converter are analyzed in detail.The soft switching failure principle of LLC resonant converter is discussed.Based on the First Harmonic Approximation method,the equivalent steady-state model of LLC converter is established and the gain characteristics are analyzed.LLC resonant network and transformer parameters are designed to complete device selection.(2)Drawing the equivalent magnetic circuit of variable inductance and introducing the working principle of VI.Variable inductance is applied to LLC converter for analysis.The effect of variable inductance on output gain of LLC converter under different switching frequencies and loads is discussed.(3)The operating mode of interleaved parallel LLC converter is analyzed in detail.The control method of interleaving parallel LLC based on variable inductance is proposed,and the control principle of interleaving parallel operation of variable inductance in LLC converter is analyzed.(4)Build the experimental platform,complete the design of hardware circuit including signal acquisition and conditioning circuit and driving circuit of LLC converter,and winding variable inductance and power transformer.Write the control program based on variable inductance interleaved parallel LLC in the controller of DSP28335.Complete the experiment and analysis of the experimental results.