Abstract：Aiming at the problem that the unidirectional magnetization of the basic forward conversion topology will lead to the saturation of the transformer, a variety of magnetic reset measures have been proposed. Among them, the primary side magnetic reset can only consume the excitation energy on the resistance or feed back to the input side, so that the excitation energy can not be fully utilized, therefore, it is not beneficial to improving the energy transmission efficiency of the converter. The secondary-side reset forward-flyback conversion topology composed of four diodes on secondary side can not only transfer forward energy, but also transfer excitation energy to the load, thereby, the energy efficiency can be effectively improved. However, the excitation inductor and the forward inductor can affect the power transmission and distribution characteristics and the switch current stress of the conversion topology. Therefore, the relationship between the power transmission characteristics, switch current stress and the magnetic components parameters is deeply studied in this paper, and through comprehensively considering the influence of forward and flyback transmission power ratio on the electrical performance of the conversion topology, the design method of magnetic components parameters is proposed. For the forward-flyback converter, the forward inductor can only work in DCM. Comparing the minimum excitation inductor current in one cycle with zero, its working mode can be divided into Magnetizing current Continuous Conduction Mode (MCCM) and Magnetizing current Discontinuous Conduction Mode (MDCM). Through analyzing its power transmission characteristics and its relationship with load resistance RL under different modes, it is obtained that both the forward power PFW and flyback power PFB increases with the decrease of the RL when the conversion topology works in the MDCM. When the RL is reduced to make the conversion topology enter the MCCM, the PFW increases to the maximum value, and no longer increases with the decrease of the RL, while the PFB still increases with the decrease of the RL. Through analyzing the influence of excitation inductance on the power transmission and distribution characteristics of the conversion topology, the critical excitation inductance Lmc corresponding to PFW=PFB is defined, and it is obtained that for the given output power, with the increase of excitation inductance, the PFW increases and the PFB decreases, and when the excitation inductor equals Lmc and the conversion topology works in MDCM, the PFW is equal to PFB. Through analyzing the influence of the transformer turn ratio on the transmission power ratio of the conversion topology, it is concluded that for the given output power, with the increase of the transformer turn ratio, the PFB increases and the PFW decreases. Through analyzing the influence of power transmission distribution on the switch current stress, it is concluded that for the given output power, the switch current stress decreases with the decrease of PFW, therefore, reducing the PFW is beneficial to reducing the switch current stress. However, reducing the PFW will result in the increase of the PFB, while increasing the PFB requires increasing the transformer air gap to reduce the magnetizing inductance, which will result in the increase of the transformer loss. Therefore, reducing the PFW is not beneficial to improving the efficiency of the conversion topology. Through analyzing the influence of the distribution of PFW and PFB on the electrical performance of the conversion topology, it is obtained that reducing the PFW is beneficial to reducing the current stress of the switch, while reducing the PFB is beneficial to improving the efficiency of the conversion topology. Therefore, in order to improve the efficiency of the conversion topology and not cause the current stress of the switch to be too high, a component parameter design method is proposed to guarantee that PFW=PFB when the output power reaches the maximum within the given load range. Experimental results verify the correctness of the theoretical analysis and the feasibility of the proposed design method. The proposed components parameters design method of the forward-flyback conversion topology in this paper is helpful to the development of high-performance forward-flyback conversion topology and promote its popularization and application.
刘树林, 沈一君, 刘旭, 庹汉宇, 王成, 王文强, 吴星. 正-反激变换拓扑的功率传输分配特性及设计考虑[J]. 电工技术学报, 0, (): 64-64.
Liu Shulin, Shen Yijun, Liu Xu, Tuo Hanyu, Wang Cheng, Wang Wenqiang, Wu Xing. Power Transmission Distribution Characteristics and Design Considerations of Forward-Flyback Conversion Topology. Transactions of China Electrotechnical Society, 0, (): 64-64.
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