Research On Zvs Half-bridge Three-Level DC-DC Converter With Two Transformers

Switching power supplies have already been following the trends of high-frequencyfor several years. High-frequency switching power supplies have been taken advantagedin many high-input and high-power environments. Nevertheless, power supplies withhigh-frequency also have to face the problems of switching loss. In the meantime, it isalso a challenge for power supplies to bear higher input voltage. The switching loss canbe reduced by using the soft-switching technology, and the switches voltage stress can bedecreased by adopting the three-level topology. As a result, the soft-switching has beenused in the three-level circuit to improve the power effiency. This is what would beprobed deeply in this paper.There exists some shortcomings in the conventional HB TL DC-DC converter, suchas legging switches is hard to execute soft-switching, the rectifier diodes in transformersecondary side have to suffer high spike of reverse recovery voltage and the outputvoltage waveform of conventional structure is actually two-level wave, etc. In thisproject, an improved type of HB TL DC-DC converter is proposed. Two transformers isdesigned in this new circuit structure, which would change the two-level outputwaveform into three-level, and the more leakage inductance brought by the extratransformer will make it easier to execute zero-voltage-switching through LC resonancebetween the leakage inductance and the junction capacitor of switches. Besides, thepassive buffering circuit added to the secondary side of transformer would decrease thereverse voltage spike of rectifier diodes.The working principles and modes are analysed, and the parameters andcomponents of main circuit, drive circuit, control circuit and protective circuit aredesigned. At the same time, the closed-loop control programme is designed by using thesimulation tool TMS320F2812, and the main circuit is simulated by using the tool Pspice.After this, the theory is confirmed by building up an experimental prototype.The chaos phenomenon may appears when the parameter of main circuit varies.According to the improved type HB TL converter, the accurate discrete model isestablished. According to this model, the steady output scope is concluded by using themethod of bifurcation analysis, which makes it easier to ascertain the parameters.In this project, an experiment prototype with12V rated output voltage,10A outputcurrent and80kHz frequency is build up. The result measured confirmed theory of thisimproved type HB TL DC-DC converter, and eliminate the defects existed inconventional structure. The ideal waveform is outputted and the performancerequirement is satisfied.