Research on LLC Resonant Converter Based on Magnetorheological Fluid-Gap Variable Resonant Inductor for Wide Input Voltage Range

The variable inductor-controlled LLC resonant converter achieves output voltage stabilization by designing the resonant inductor as a variable inductor and changing its inductance to regulate the resonant frequency of the converter to achieve the impedance distribution of the resonant cavity, thereby changing the voltage gain. The converter operates in the fixed frequency mode, which solves the problem of the wide range of switching frequency variation of the traditional frequency control in wide range applications. Based on this, a new type of variable inductor is proposed in this paper, which uses magnetorheological fluid to replace the air gap in the conventional variable inductor, and is characterized by a greater variation of inductance with bias current under the same inductor structure. Therefore, compared with the conventional variable inductor with air gap, it can make the inductance variation range significantly larger, thus making the voltage regulation range wider. For comparison, the conventional variable inductor and the proposed variable inductor with magnetorheological fluid gap are fabricated in this paper using the same type of ferrite core with the same number of turns and gap length. An experimental prototype with 380V input and 12V/1150W output was built to verify the feasibility and practicality of the proposed inductor.