Resonant Frequency Tracking Scheme for <i>LLC</i> Converter Based on Large and Small Signal Combined Model
Runhui He, Bo Xue, Mingde Zhou, Minfan Fu, Junrui Liang, Yu Liu, Haoyu Wang
Abstract
To achieve optimal system performance, it is recommended to operate an <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant converter at its resonant frequency. However, in mass production, the resonant parameters of different products can deviate significantly. This means that active tracking of the resonant frequency is necessary during practical usage. To address this issue, this manuscript presents a novel automatic control scheme for the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> converter that tracks the resonant frequency. The proposed control scheme is based on an accurate small-signal model and an extended state observer, which provides small-signal characteristics at the operating frequency. The controller examines the voltage gain of the converter and combines large-signal with small-signal models to effectively control the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> converter. Compared with conventional automatic resonant frequency tracking (ARFT) control schemes, the proposed control scheme is easier to implement and requires fewer sensors. Experimental results demonstrate its effectiveness in tracking the resonant frequency.