Active Impedance Matching Network Based Single-Stage Constant Power Wireless Charger With Reduced Battery Charging Time

Inductive power transfer (IPT) converters suffer efficiency degradation when operating away from the optimal load point during battery charging. This challenge is exacerbated in fast constant power (CP) charging, where higher power levels enable faster charging but often result in load resistances below the optimal value, making load matching more difficult. To address this, a novel load matching scheme is proposed, employing a half-wave rectifier to step up the load resistance effectively. Additionally, a switch-controlled inductor is integrated into a passive impedance matching network (PIMN), forming an active impedance matching network (AIMN) to achieve load matching and maintain a stable CP output. The scheme operates at a fixed frequency with secondary-side control, eliminating the need for wireless feedback communication. Compared to existing single-stage CP charging methods, the proposed single-stage charger design reduces the charging time by 50%, significantly improving user convenience. A 500 W hardware prototype is constructed to validate the performance of the proposed charger, achieving a maximum efficiency of 90.6%. The system's robustness under open-circuit load conditions is further demonstrated through experimental results.