Admittance Reconfiguration for Cascaded-System Stability Enhancement in Two-Stage Electrolytic-Capacitor-Less WPT System

Matrix converter (MC) and semi-active rectifier (SAR)-based two-stage wireless power transfer (WPT) systems can eliminate electrolytic capacitors while achieving wide-range power regulation and buck-boost capability. However, the cascaded current-source configuration introduces intrinsic system-level instability, which limits the practical feasibility of such capacitor-less architectures. In this paper, the stability characteristics of the cascaded system are systematically investigated using admittance-based modeling. The admittance interaction between the source and load subsystems is analyzed. It is revealed that overall stability cannot be guaranteed even when each subsystem is locally stable. To address this problem, an admittance reconfiguration strategy is proposed. The strategy reshapes the load-subsystem admittance through feedforward compensation. In this way, the closed-loop admittance approximates the open-loop characteristic that favors system-level stability. The experimental results verify that the proposed method effectively enhances the stability margin of the cascaded system while maintaining fast dynamic response.