Light-Load Efficiency-Optimized Variable Duty Cycle Control Strategy for SP-Compensated Wireless Power Transfer Systems

This paper presents an efficient control strategy for a wireless power transfer (WPT) system based on a series–parallel (SP) compensation topology, specifically optimized to enhance efficiency under a wide load range, including light-load conditions. The system employs a half-bridge inverter on the transmitter side and a semi-active rectifier (SAR) on the receiver side to achieve zero phase angle (ZPA) operation. Zero voltage switching (ZVS) is achieved by synchronizing and phase-adjusting the SAR switching signals with the rectified input voltage, thereby effectively reducing switching losses. Furthermore, a perturbation and observation (P&O)-based variable duty cycle (VDC) control is applied to the half-bridge inverter to dynamically optimize the light-load efficiency, thereby enhancing efficiency when conventional fixed duty methods underperform. The proposed control strategy is implemented using a TI TMS320F28335 digital signal processor. Experimental results demonstrate that the method significantly improves system efficiency at light loads while maintaining high performance at heavy loads, verifying its practical feasibility for diverse WPT applications.