Abstract：High-frequency power DC-DC converters are widely used in consumer electronics for their smaller size and higher power density. Under high-frequency conditions, the rectifiers use Schottky diodes with extremely fast switching speed. However, the forward voltage drop of Schottky diodes is still high, which limits efficiency. Due to the small switching period, the synchronous rectification control methods are no longer suitable for high-frequency conditions. Therefore, the method to realize synchronous rectification accurately and efficiently at tens of megahertz helps to improve the efficiency of high-frequency power converters. The key to realizing synchronous rectification is the accuracy of a given driving signal. Due to the high-frequency conditions, the traditional synchronous rectification control method can easily generate the error driving signal, which will cause a straight through in the arm in severe cases. To avoid the error of the driving signal, the method of providing the same driving signal for the switches on the primary and secondary sides is adopted. Therefore, there is no inductive component on the non-resonant branch side of the transformer, so the output voltage of the inverter and the input voltage of the rectifier maintain the characteristic of zero phase difference. Meanwhile, the resonant branch is constructed in another side of the transformer, which consists of the leakage inductance and resonant capacitance. In addition, it is necessary to carry out precise parameter design to ensure that the switch works under soft-switching conditions. The difficulty in realizing the abovementioned zero-phase-difference synchronous driving is constructing an air-core transformer with single-side leakage inductance. The nested toroidal air-core transformer without leakage inductance in the inner winding is designed by the outer winding completely wrapping the inner winding. The magnetic flux generated by the inner winding acts as the common magnetic flux of the inner and outer windings. That is, there is almost no leakage inductance on the secondary side. Further, this paper analyzes the modeling and design method of the nested toroidal air-core transformer. By synthesizing the relationship between the reluctance, the magnetic flux, and the transformer inductance matrix, the numerical relationship between the physical structure parameters of the nested toroidal air-core transformer and the transformer parameters is derived from the precise design of the air-core transformer. Moreover, the calculation and Maxwell simulation of the nested toroidal air-core transformer verify the feasibility of the modeling method of the nested toroidal air-core transformer. Based on the nested toroidal air-core transformer manufactured with the combination of multiple PCBs, an experimental prototype with 48 V input and 12 V/28 W output is built. The experimental results verify the effectiveness of the design method of the nested toroidal air-core transformer and the improved frequency synchronous rectification control method. The nested toroidal 3D transformer can optimize to achieve single-side leakage inductance characteristics, further decreasing the small leakage inductance. Additionally, the inductance of the power loop needs to be optimized to reduce the switch voltage oscillation. The parasitic parameters of the circuits affecting synchronous rectification must be considered.
管乐诗, 程怡, 施震宇, 王懿杰, 徐殿国. 一种10 MHz高频DC-DC功率变换器及其同步整流技术[J]. 电工技术学报, 2023, 38(18): 5029-5038.
Guan Yueshi, Cheng Yi, Shi Zhenyu, Wang Yijie, Xu Dianguo. A 10 MHz High Frequency DC-DC Power Converter and Its Synchronous Rectification Technology. Transactions of China Electrotechnical Society, 2023, 38(18): 5029-5038.
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