Abstract
To enable the geometrical freedom envisioned for wireless power transfer (WPT), fast dynamic adaptation to unpredictable changes in receiver position is needed. In this paper, we propose an adaptive impedance-searching system that achieves good impedance matching quickly. For fast and robust operation, the proposed method consists of three steps: system calibration, coarse search, and fine search. The proposed WPT system is characterized using distance variation and lateral and angular misalignment between coils. The measured results indicate that the proposed method significantly reduces searching time from a few minutes to approximately one second. Furthermore, the proposed system achieves impedance matching with good accuracy. The robust impedance-searching capability of the proposed system significantly improves power transfer efficiency. At 6.78 MHz, we achieve a maximum efficiency of 89.7% and a high efficiency of >80% up to a distance of 50 cm. When the center-to-center misalignment is 35 cm, the efficiency is improved from 48.4% to 74.1% with the proposed method. At a distance of 40 cm, the efficiency is higher than 74% for up to 60° of angular rotation. These results agree well with the simulated results obtained using a lumped-element circuit model.
Highlights
In recent years, the potential of power transmission through wireless means has attracted a great deal of research and commercial interest [1]
Inductive coupling has been used for wireless power transfer (WPT) in many commercial applications
At d = 15 cm and 40 cm, respectively. These results indicate that the proposed tunable matching network achieves good impedance matching
Summary
The potential of power transmission through wireless means has attracted a great deal of research and commercial interest [1]. This interest is closely related to the increasing number of mobile devices in our daily lives, which require frequent battery charging because of their high power consumption. Power Consortium (WPC) recently developed a new standard, Qi 1.1 [2] This standard development reflects the substantial interest in the wide range of wireless power charging applications. Inductive coupling has been used for wireless power transfer (WPT) in many commercial applications. The drawback of wireless power charging using inductive coupling is that the operation is limited to a very short range. To extend the power transfer to a more convenient midrange distance, WPT based on resonant coupling has recently been demonstrated experimentally [6,7,8,9,10]
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