Abstract：Aiming at the problem that the unidirectional magnetization of the single-switch forward conversion topology will lead to the saturation of the transformer, a variety of magnetic reset measures have been proposed. These measures can be broadly categorized as primary side magnetic reset and secondary side magnetic reset. 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 magnetic reset can transfer the excitation energy to the load during the switch-off period. However, the dual-winding structure on the secondary side increases the volume of the transformer and complicates the winding process. Additionally, the secondary side of the transformer with additional LCD (representing inductor, capacitor, and diode, respectively) different combinations of the structure of the converter, although it has a certain performance advantage, but it also increases the complexity of the circuit, so that its application has been limited to some extent. In contrast, the secondary-side additional-capacitor magnetically reset forward converter has a simple structure, requiring only one capacitor to achieve magnetic reset and transfer excitation energy to the load. Moreover, it facilitates enhancements in multiple electrical performances, effectively improving the performance and efficiency of the converter. This simplicity and performance enhances the application prospects. However, currently, there has been no research report addressing the impact of the additional capacitor on electrical performance and its associated parameter design methods. Therefore, this paper conducts a thorough analysis of the influence of the additional capacitor Cb on the energy transfer process and electrical performance of the converter. Additionally, a parameter design method is proposed to fully exploit the electrical performance advantages of the converter. There are four combinations of operating modes for the secondary additional capacitance magnetic reset forward converter, among which the optimal mode is when the excitation inductor Lm operates in discontinuous current mode (DCM), and the forward inductor L operates in continuous current mode (CCM). When the converter operates in this mode, it achieves zero-current turn-off for the freewheeling diode and low-voltage turn-on of the switch under light load conditions. This prevents issues associated with diode reverse recovery and reduces the conduction losses of the switch, thereby enhancing the efficiency and system reliability of the converter. Analyzing the relationship between the additional capacitor and the voltage stress on the switch under the operation of the excitation inductor in CCM and DCM, respectively. Based on the principle of energy conservation (i.e., the excitation energy generated by the transformer equals the energy stored in the additional capacitor within one cycle), an expression for the relationship between the additional capacitor Cb and the voltage stress on the switch was derived. It was concluded that the voltage stress on the switch can be adjusted through the additional capacitor Cb, and as Cb increases, the voltage stress on the switch decreases. Through a thorough analysis of the zero current switching (ZCS) characteristics of the freewheeling diode and the low-voltage turn-on of the switch, it was pointed out that achieving ZCS for the diode requires the excitation inductor to operate in DCM, and the discharge current of the additional capacitor needs to rise to equal the freewheeling current of the forward inductor. Achieving low-voltage turn-on of the switch requires ZCS for the diode and the voltage across the additional capacitor VCb to be less than the output voltage Vo. However, these conditions necessitate that the current in the forward inductor not be too large, implying that these performance characteristics are only viable under light load conditions. Combining the conditions for achieving ZCS for the diode and low-voltage turn-on of the switch, a design approach for the additional capacitor and the forward inductor was proposed. This method ensures that the converter operates in the optimal combination mode and fully leverages the electrical performance advantages of the converter. Experimental results validated the correctness of the theoretical analysis and the feasibility of the proposed design method. The research in this paper indicates that the secondary-side additional-capacitor magnetically reset forward converter holds broad prospects for widespread application.
刘树林, 庹汉宇, 张元昌. 二次侧附加电容磁复位正激变换器电气性能分析及参数设计[J]. 电工技术学报, 2024, 39(19): 6008-6017.
Liu Shulin, Tuo Hanyu, Zhang Yuanchang. Electrical Performance Analysis and Parameter Design of the Secondary-Side Capacitor Magnetic Reset Forward Converter. Transactions of China Electrotechnical Society, 2024, 39(19): 6008-6017.
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