Hybrid LLC and Full Bridge Paralleled Converter With Variable-Frequency Plus Phase-Shift Control for Wide Voltage Gain Range Application

LLC converters are attractive with their ability of enable to achieve soft switching, but there is a trade-off between voltage gain and efficiency in wide voltage regulation range applications. In this paper, a novel hybrid LLC and full-bridge (FB) converter is proposed for wide voltage gain applications. The converter consists of a half bridge (HB) LLC resonant converter and a switch-off current-clamp FB converter connected in parallel. The turn-off current of the LLC converter over the entire range is significantly reduced through the clamping operation of the FB converter. Consequently, all primary-side switches of LLC converter achieve zero-voltage switching-on (ZVS) and low-current switching-off (LCS), while secondary-side diodes achieve zero-current switching-off (ZCS), leading to a substantial reduction in switching losses. Furthermore, a smooth transition variable-frequency plus phase-shift control strategy is proposed to achieve wide-range of voltage regulation. The proposed control has three operation modes: variable-frequency with a shift angle <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\varphi $ </tex-math></inline-formula> is 0 mode, phase-shift mode, and variable-frequency with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\varphi $ </tex-math></inline-formula> of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pi $ </tex-math></inline-formula>. These modes cover the low, medium, and high voltage gain ranges, respectively. A 7.5 kW-rated experimental prototype is designed to convert a 400 V input to a 150-750 V wide output. The prototype demonstrates a peak efficiency of 98.04% and maintains an efficiency of over 93.8% from 30% load to full load across the 150-750 V output range.