论文部分内容阅读
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.