Enhancing the Efficiency of Medium-Distance WPT Systems by Manipulating Coil Current Distribution Under Detuned Conditions

Abstract

As wireless power transfer (WPT) systems extend to medium distances, their efficiency declines significantly. This article proposes a novel method, distinct from traditional zero-phase angle (ZPA) operation, to enhance efficiency at medium distances by manipulating the current distribution between the primary and secondary coils under detuned conditions. Based on the series/series-parallel (S/SP) system, this study reveals that quasi-load-independent constant voltage (CV) output can be achieved under detuned conditions, while remaining unaffected by the secondary parallel component. This flexibility in detuning allows for adjusting coil current distribution without altering the system output. The system’s efficiency optimal mode (EOM) is further developed, demonstrating that when the coupling coefficient falls below a critical value, the EOM achieves significantly higher efficiency than the ZPA mode. The experimental results validate the proposed method. At a transmission distance-to-coil diameter ratio of 1 and an operating frequency of 86.6 kHz, the system achieved 87.1% efficiency and a 4-kW power output, representing a 12.8% improvement over ZPA conditions.