| With the development of science and technology,the electric power equipment becomes smaller and lighter,and it should produce less pollution to power grid.The voltage stress of the three-level converter is low,and the output voltage harmonic of it is small.So it is suitable for high input/output power transformation.The usage of softswitching technique in the three-level converter can improve its performance and efficiency.So it is important to do the research on the three-level converter and its softswitching technique.Therefore,the ZVS three-level converter is researched on this paper.At first,the basic ZVS three-level DC-DC converter is analyzed.It has the following problems: high voltage spike and surge of the transformer secongdary side,duty ratio loss and hardly achieving ZVS of the lagging swithes at light load.In order to resolve the above problems,an improved ZVS three-level converter is proposed in this paper.The transformer secongdary side of the proposed converter uses the current-doubler-rectifier circuit,which can resolve the high voltage spike and surge of the transformer secongdary side and duty ratio loss.To widen the range of achieving ZVS switching of the converter,an auxiliary net in the transformer primary side of the improved converter is added.The operation principle of the converter,the condition of ZVS and the condition of the natural commutation of the output rectifying diodes are analyzed in detail in the paper.Based on the analysis of the operation principle of the improved converter,the hardware of the converter is designed,such as the main circuit,the driving circuit and the protection circuit etc.And also the software based on DSP2812 is designed.Simulation about the proposed converter has been made with PSpice.The result validates the correctness and feasibility of the improving topology preliminarily.In order to research the chaos phenomena in the three-level DC-DC converter,the precise discrete model of the converter has been established in the paper.According to the model,the influence on the operation state caused by the variation of the parameters of the converter is analyzed by ploting the bifurcation figure,and the range of the variational parameters when the onverter is operating stably is founded.At last,in order to validate the performance of the proposed converter further,an experimental prototype of 24V/10 A,80kHz is designed according to the designed hardware and software parameters.The experiment result proves the improved currentdoubler-rectifier ZVS three-level converter can realize ZVS in the wide load range,there is no voltage spike and surge of the transformer secongdary side of the proposed converter,and there is no duty ratio loss in the the transformer secongdary side of the proposed converter.All performance indexes are achieved.It shows the correctness and feasibility of the improved converter. |
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