Modeling and analysis of phase-shift controlled LCL resonant converter in wireless charging systems

In this paper, a simplified low order linear model for LCL compensated WCS is presented using Extended Describing Function (EDF) technique. It turns out that the six-order LCL type WCS behaves as a second-order under-damped system within low frequency range. The simplified reduced order model provides intuitive understanding into both steady and dynamic performance of the converter and also facilitates controller design. The stability boundary and ripple suppression condition using PI controller is given. Considering the limitation of conventional PI controller, the improved PI combining notch filter is proposed to acquire minimal charging ripple and quick dynamic response simultaneously. Experimental results are presented to verify the accuracy and robustness of proposed model and control design.