Abstract
Multi-coil WPT systems require mutual inductance information between coils to increase the power transmission efficiency. However, in the high frequency (HF) bands such as 6.78 MHz and 13.56 MHz, the presence of surrounding coils changes the value of the mutual inductance between the two coils due to the parasitic element effect of the coils. These parasitic effects make it harder to estimate the mutual inductance among three or more coils. In contrast to ideal mutual inductance, which has a constant value regardless of frequency and surrounding coils, we define the practical mutual inductance as the mutual inductance varied by parasitic elements. In this paper, a new method is presented to estimate the practical mutual inductance between multiple coils in the HF band. The proposed method simply configures the expression of practical mutual inductance formula because only one of two bilateral dependent voltage sources generated by mutual inductance is considered. For several coils placed along the same axis, the practical mutual inductances between coils were measured with respect to the distance between them to validate the proposed method. The practical mutual inductance obtained from the proposed method was consistent with the simulated and measured values in HF band.
Highlights
Multi-coil wireless power transfer (WPT) systems using three or more coils have been proposed to achieve a high power transfer efficiency (PTE) at greater distance than in the case of a conventional two-coil WPT system [1,2,3,4,5,6,7,8,9,10,11,12]
The practical mutual inductance among multiple coils was measured with respect to the distance using the four-port vector network analyzer (VNA), Agilent’s
The ideal mutual inductance does not depend on the frequency, but the practical mutual inductances are proportional to frequency
Summary
Multi-coil wireless power transfer (WPT) systems using three or more coils have been proposed to achieve a high power transfer efficiency (PTE) at greater distance than in the case of a conventional two-coil WPT system [1,2,3,4,5,6,7,8,9,10,11,12]. The multi-coil WPT systems are categorized into the domino structure and multiple transmitting (or receiving) coils structure. The domino structure means that one or more coils are placed between transmitting and receiving coils [1,2,3,4,5,6]. The WPT system with multiple transmitting coils usually maximizes the power in the receiving coil through entering power of different magnitude or phase into transmitting coils. Sometimes, this technique is called magnetic beamforming [7,8]
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