Design And Development Of LLC Resonant DC/DC Converter

With the development of power electronics technology, Power supply technologyhave a increasingly high demand For the size of the power supply technology,efficiency, switching losses and switching frequencies and other technicalcharacteristics. Compared with the PWM converter(hard-switching technology), LLCresonant converters have a high switching frequency, low switching loss, highefficiency and low volume weight characteristics. So LLC resonant converter markethas an increasingly important share in the Power Market. Aiming to the coretechnologies of LLC resonant converter, mainly as follows:(1)This thesis describes the deficiencies and defective of the hard switchingcircuits, analyzed the losses when soft switching circuit turn on or turn off, describessome types of the resonant circuit, then analyze their differences, leads to theadvantages and characteristics of LLC resonant converter. In this paper, a5kWhalf-bridge LLC resonant converter has been designed to verify the correctness of theproposed method.(2)Based on the fundamental analysis method (FHA), a modeling and analysis ofthe half-bridge LLC resonant circuit has been built to analysis the relationship of theswitching network model, the resonant cavity model and rectifier filter model. Thenthe unified model is built to derive the relational expression of the input voltage andoutput voltage. This essay analyses the influence of inductance and quality factor tothe DC voltage gain according to the DC voltage gain equation. Using software ofengineering software which is named MathCAD, this thesis analyzes the DC voltagegain and then get the range of inductance and quality factor.(3)Then the thesis analyzes the characteristics of the short about circuit LLCresonant half-bridge circuit, and knows that when the resonant circuit is short, thenormalized frequency should stay away from1, and then the characteristic impedanceof the resonant circuit is analyzed to obtain the maximum and minimum values of thenormalized frequency. The range of the quality factor is drawn based on the analysisof circuit soft switching characteristics.(4)According to the technical requirements of Xiamen Kehuahengsheng Limitedby Share Ltd, this essay designs the parameters of LLC resonant circuit, and thenusing Saber to simulation and verification, gets the waveform. The waveform meets the requirements of this essay.In the end, according to the simulation results, a5kW prototype is designed. Thisessay analyzes PFM modulation circuit diagram, and then analyzes the enhancementdriving circuits and introduces the soft-start hardware circuit, and the protectioncircuit of overvoltage. Finally, the essay uses an oscilloscope and a power tester toolto test the prototype, obtains the waveforms to verify the correctness of the results.