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.
林辉品,靳晓光,解良,胡进,吕征宇. 一种新颖的用于宽输入电压范围的LLC谐振变换器的变模态控制策略[J]. Frontiers of Information Technology & Electronic Engineering, 2017, 18(3): 410-422.
Hui-pin LIN,Xiao-guang JIN,Liang XIE,Jin HU,Zheng-yu LU. A new variable-mode control strategy for LLC resonant converters operating in a wide input voltage range. Front. Inform. Technol. Electron. Eng, 2017, 18(3): 410-422.
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