Abstract：In the DC microgrid, a bidirectional isolated DC-DC converter with a wide range of input voltage is required to ensure the safety and efficiency of power conversion. The CLLLC converter was selected by discussing the advantages and disadvantages of various DC-DC converters. Aiming at the problem of large secondary switch loss and limited step-down range of variable-frequency phase-shift modulated CLLLC converter, this paper proposes a variable-frequency dual-phase-shift (VF-DPS) modulation strategy. The proposed VF-DPS modulation strategy can enhance the voltage gain and efficiency of the CLLLC converter by simultaneously adjusting the switching frequency, phase-shift angle in the primary side full bridge, and phase-shift angle between the primary and secondary sides. The proposed strategy operates in two modes: the buck mode and the boost mode. In the buck mode, when the input voltage exceeds the rated input voltage, adjustments in the phase-shift angle in the primary side full bridge achieve a voltage gain of less than 1. In the boost mode, when the input voltage is below the rated input voltage, adjustments in the phase-shift angle in the secondary side full bridge result in a voltage gain greater than 1. According to these two modes, VF-DPS modulation is adopted for the CLLLC converter. The waveform shapes of the resonant inductor current and excitation inductor current are changed by VF-DPS modulation, achieving zero voltage switching (ZVS) for all switches. The modal analysis of the VF-DPS modulated CLLLC converter is conducted. Time domain analysis method is used to solve the voltage gain and resonant inductor current. Furthermore, the influence of different frequencies and phase-shift angles on the voltage gain and root mean square of the resonant inductor current is analyzed. An experimental prototype was designed with an input voltage of 100~300 V and an output of 400 W/ 48V. The experiments tested the wide input range, working mode, soft switching, and efficiency of the CLLLC converter. The peak efficiency is 95.1% in the buck mode and 94.4% in the boost mode, confirming soft switching in both operating modes. The VF-DPS modulated CLLLC converter has a wider gain range and higher efficiency than the variable-frequency phase-shift modulation. The proposed VF-DPS modulated CLLLC converter addresses challenges of wide switching frequency variations and ZVS losses in the wide input voltage of the variable-frequency modulated CLLLC converter and the phase-shift modulated CLLLC converter, respectively. The VF-DPS modulated CLLLC converter realizes the soft switching of all switches. Moreover, the converter achieves a voltage gain range of 3 times and a peak efficiency of 95.1%. Future research will focus on integrated magnetic design to further enhance efficiency and reduce the volume of the converter.
周国华, 王淇, 邓伦博. 宽增益高效率CLLLC变换器的变频双移相调制策略[J]. 电工技术学报, 2024, 39(8): 2511-2522.
Zhou Guohua, Wang Qi, Deng Lunbo. Variable-Frequency Dual-Phase-Shift Modulation Strategy for CLLLC Converter with Wide Voltage Gain and High Efficiency. Transactions of China Electrotechnical Society, 2024, 39(8): 2511-2522.
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