Abstract：LLC resonant converters have become a research hotspot in wide-voltage DC-DC converters with superior soft-switching characteristics, high efficiency, and high power density. Due to the wide switching operating frequency range and low overall efficiency, traditional LLC resonant converters are unsuitable for wide voltage gain applications. Designing an LLC resonant converter is imperative. This paper proposes a variable-mode ultra-wide LLC resonant converter based on the topology reconfiguration concept, achieving an ultra-wide output voltage gain range of up to 121. By reconfiguring half-bridge/full-bridge circuits and full-bridge/voltage-doubler rectifiers, the converter contains four operating modes with different voltage gain ranges: series-connected half-bridges (SCHB), single half-bridge (SHB), dual half-bridge (DHB), and mixed bridge (MB). The converter’s efficiency is improved while the cost is reduced through the multiplexing of power devices. The equivalent circuits are presented for its four operating modes, and the operating stages and waveforms of the MB mode are analyzed. The voltage and current relationship equations in the MB mode are derived. Subsequently, the voltage-gain expressions for each operating mode are deduced, the voltage gain curve of the converter is plotted, and the voltage gain range is determined. The converter contains five power MOSFETs, and each can achieve zero voltage switching (ZVS) turn-on in all operating modes. To further enhance the overall efficiency of the proposed converter under the operating conditions of a wide output voltage gain range, a hybrid control strategy tailored to this converter is proposed. The hybrid control strategy introduces pulse width modulation (PWM) based on the traditional pulse frequency modulation (PFM). The converter operates with PFM in SCHB, SHB, and DHB modes and PWM in MB mode. The converter determines the operating mode according to the load conditions and then determines the MOSFETs’ operating frequency and duty cycle. In practice, the converter must operate in a continuous gain range, and mode switching is required when the output voltage reaches the switching point. Considering the existence of ripple and jitter in the output voltage, adding a hysteresis loop comparison in the switching process is necessary. Adding PWM simplifies the design of the resonant parameters and minimizes the variations in output voltage gain caused by load changes.
张俊涛, 林国庆. 多模态超宽输出双LLC谐振变换器拓扑及控制策略[J]. 电工技术学报, 2025, 40(24): 8052-8065.
Zhang Juntao, Lin Guoqing. A Variable-Mode Ultra-Wide Output Voltage Gain Dual LLC Resonant Converter and Control Method. Transactions of China Electrotechnical Society, 2025, 40(24): 8052-8065.
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2025, Vol. 40 
