Novel Half-Bridge LLC Resonant Converter With Variable Resonant Inductor

This article proposes a novel half-bridge LLC resonant converter featuring a variable resonant inductor. The resonant inductor in a traditional LLC resonant converter is divided into two inductors. One inductor is connected to an auxiliary circuit composed of a transformer with a full-bridge circuit. The variable inductance is achieved by regulating the duty cycle of the auxiliary switches to restrict the time and voltage across the inductor, allowing for participation in the resonance operation. This proposed architecture enables control of the equivalent inductances of the converter under various loads, resulting in improved overall conversion efficiency. Additionally, the proposed architecture can operate in boost or buck modes under abnormal input voltages by adjusting the duty ratios of the auxiliary switches to maintain the rated output voltage. A half-bridge LLC resonant converter is designed and implemented with an input voltage of 380 V, an output voltage of 12 V, and a rated output current of 50 A. Experimental results demonstrate that selecting suitable resonant inductances for the proposed converter yields a maximum conversion efficiency improvement of approximately 3% at light loads and higher almost whole-load conversion efficiency than a traditional LLC resonant converter. Furthermore, the proposed converter can maintain the rated output voltage for input voltages ranging from 200 V to 400 V, with a better hold-up time.