| In order to reduce the input harmonics current from the power supply, the boost power factor corrector is widely used, and it leads to the increase of the DC-link voltage of the converter. The zero-voltage-switching (ZVS) three-level converter is suitable to use in high DC-link voltage and high power area, because only half of the DC-link voltage is applied on the power switch and ZVS is easy to achieve. Based on this background, this paper studies the full bridge ZVS three-level converter.The conventional full bridge ZVS three-level converter has several drawbacks, such as narrow ZVS load rang of the lagging leg, severe duty ratio loss and the voltage spike of the transformer secondary side. In order to overcome these drawbacks, an improved full bridge ZVS three-level converter is proposed in this paper. An auxiliary net, which is composed of a coupling inductor and capacitors, is introduced to wider the ZVS load rang of the converter. And a current-doubler-rectifier (CDR) is used. Taking adventage of CDR's characteristics, the output rectifying diodes can commutate naturally without duty ratio loss and the voltage spike.The operation modes of the improved converter and the conditions of ZVS and natural commutation of the output rectifying diodes are analyzed in detail. Simulation based on PSpice has been made to validate the correctness of the improved converter preliminarily.State-space-average approach is one of the most commonly used methods in modeling of switching power supply, but low precision is its drawback. In order to improve the precision, an accurate small signal model of the improved converter is present by using the state-space-average approach with parasitic parameters considered. And the correction module is designed based on it. The experimental result shows that the model with parasitic parameters considered has higher precision and is more suited to the reality.In order to validate the performance of the improved converter ulteriorly, an experimental prototype of 24V/4A, 50kHz have been designed, including the power circuit, the auxiliary circuit, and the digital control circuit based on TMS320F2812 DSP. The prototype has many virtues, such as wide load rang of ZVS, almost no voltage spike and no duty ratio loss of the transformer secondary side and high efficiency. The experimental results show the correctness of the theoretical analysis and the feasibility of the improved converter. All the performance indexes are satisfied. |
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