Abstract
This paper proposes a new variable-mode control strategy that is applicable for LLC resonant converters operating in a wide input voltage range. This control strategy incorporates advantages from full-bridge LLC resonant converters, half-bridge LLC resonant converters, variable-frequency control mode, and phase-shift control mode. Under this control strategy, different input voltages determine the different operating modes of the circuit. When the input voltage is very low, it works in a full-bridge circuit and variable frequency mode (FB_VF mode). When the input voltage rises to a certain level, it shifts to a full-bridge circuit and phase-shifting control mode (FB_PS mode). When the input voltage further increases, it shifts into a half-bridge circuit and variable frequency mode (HB_VF mode). Such shifts are enabled by the digital signal processor (DSP), which means that no auxiliary circuit is needed, just a modification of the software. From light load to heavy load, the primary MOSFET for the LLC resonant converter can realize zero-voltage switching (ZVS), and the secondary rectifier diode can realize zero-current switching (ZCS). With an LLC resonant converter prototype with a 300 W rated power and a 450 V output voltage, as well as a resonant converter with 20–120 V input voltage, the experiments verified the proposed control strategy. Experimental results showed that under this control strategy, the maximum converter efficiency reaches 95.7% and the range of the input voltage expands threefold.
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Project supported by the National Natural Science Foundation of China (Nos. 51177148 and 51407151)
ORCID: Zheng-yu LU, http://orcid.org/0000-0003-1032-2938
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Lin, Hp., Jin, Xg., Xie, L. et al. A new variable-mode control strategy for LLC resonant converters operating in a wide input voltage range. J. Zhejiang Univ. - Sci. C 18, 410–422 (2017). https://doi.org/10.1631/FITEE.1600029
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DOI: https://doi.org/10.1631/FITEE.1600029