Discrete-Time Small-Signal Modeling of LLC Resonant Converter Considering the Nonlinearity of Voltage-Controlled Oscillator

The LLC resonant converter, featured with soft-switching capability, has been widely used in power conversions. For achieving the fast dynamic performance of the LLC resonant converter, it is required to increase the control bandwidth, and thus an accurate small-signal model is necessary. In this article, with the discrete-time modeling method, the small-signal model of the power stage of the LLC resonant converter in full load range is derived. Meanwhile, an accurate small-signal model for the voltage-controlled oscillator (VCO), which is usually adopted for frequency control for resonant converters, is deduced, and this model can reflect the nonlinearity of the VCO. Finally, the experimental results are provided to verify the validity of the proposed model.

I. Introduction

Due to the merits of soft-switching in full load range, the LLC resonant converter can achieve high efficiency and high power density, and has been widely used in diverse applications, such as aerospace, data center, electric vehicle, photovoltaic power system, and consumer electronics [1], [2], [3], [4], [5], [6]. With the rapid development of these fields, a fast dynamic response of the LLC resonant converter is required especially in data center [7], [8], [9]. So, the control bandwidth should be increased, and it is desirable to establish an accurate small-signal model of the LLC resonant converter.