A traditional magnetic resonant coupling wireless power transfer (MRC-WPT) system is highly sensitive to the distance between transmitting and receiving coils. The transfer performance deteriorates at short distance due to magnetic over-coupling and magnetic weak-coupling at long distance which also results in the decrease of power. In order to improve the power transfer ability, this paper presents an MRC-WPT system with a novel design of resonant loops. Unlike the conventional system in which the receiving coil is identical with the transmitting coil, the receiving coil in the proposed system is different from the transmitting coil in terms of distance between turns. Theoretical equivalent models are presented to investigate the impact of the mutual inductance on the transfer efficiency. Based on numerical simulation, it is found that relatively more uniform mutual inductance can be obtained with the proposed resonant loops. With the proposed MRC-WPT system, the results show that the power transfer ability at short and long distances is improved. The average transfer efficiency is enhanced about 10% compared with the conventional system. Furthermore, the sensitivity of the proposed MRC-WPT system to lateral and angular misalignments is studied and compared with the conventional system. An experimental prototype of the proposed MRC-WPT system is designed for validation. The results show that the performance of the proposed MRC-WPT system outperforms the conventional system without adding any complicated control circuits.
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