Research On ZVS Three-Level DC-DC Converter With Passive Auxiliary Net

The voltage stress of the switches in the three-level DC-DC converter's three-level leg is half of the input voltage. As a result, the three-level DC-DC converter is applied to the situation with high input voltage widely. Moreover, applying the soft-switching technique to the converter can increase its efficiency and reduce its cubage. It is an important way to improve the converter's performance. So it's very significant to do the research on three-level DC-DC converter and its soft-switching technique. Therefore, zero-voltage-switching (ZVS) three-level DC-DC converter is researched in this paper.The basic ZVS three-level DC-DC converter topology using chopping plus phase-shift control is researched thoroughly in theory at first. It is found that the basic topology has problem to realize ZVS for lagging switches in light load. And it also has great voltage rush in the secondary side of the transformer. To solve these problems, a ZVS three-level DC-DC converter with passive auxiliary net is proposed.According to the requested performance index, a DSP2812 controlled ZVS three-level DC-DC converter system is designed on the basis of theoretic analysis. The parameters of the power circuit, hardware of the control circuit and the program of the DSP are designed in detail.In order to study the influence of parameter variation on system's output and analyze the chaotic phenomena in the converter, precise discrete model of the system is established. The bifurcation figures with appointed parameter variation are plotted using Matlab. These figures are used to analyze the chaotic phenomena in the converter. It can supply references to the choice of system parameters. To verify the validity of this chaotic analyzing method, a converter in which the chaotic phenomena are known is analyzed using this method.The correctness of theoretic analysis and advantages of the proposed topology are validated through the Pspice simulation of proposed topology and basic topology which adopt the same parameters. The parameters are optimized according to the simulation result.At last, experiments are conducted on the designed converter system. The experimental results prove that this ZVS three-level DC-DC converter with passive auxiliary net can widen the load range for lagging switches to realize ZVS, restrain the voltage rush in the secondary side of transformer and increase the converter's efficiency. The proposed converter has good performance.