Abstract
Magnetically coupled resonant (MCR) wireless power transmission (WPT) has the advantages of high efficiency, large transmission power and so on. It is suitable for medium-distance power supply. However, the traditional MCR WPT system based on the single one-way spiral coil (SOSC) will suffer frequency splitting due to the over-coupling between the transmitting and receiving coils during short-distance transmission. After analyzing the effect of coupling coefficient on the transmission efficiency of such systems, this paper proposed a double two-way spiral coil (DTSC) design method. This method used the structural features of the designed spiral coil to counteract the increased coupling coefficient due to short-distance transmission, thereby weakening the over-coupling between the transmitting coil and the receiving coil, narrowing the over-coupling region of the system, and compensating the effect of frequency splitting on the transmission efficiency during short-distance WPT. This method narrowed the system’s frequency splitting region and improved the system’s short-distance transmission efficiency. This paper analyzed the effect of the inner and the outer radius, the number of turns, and the pitch of the DTSC on the efficiency of the WPT system. This study showed that compared with the WPT system based on the SOSC, the WPT system based on the DTSC could narrow the frequency splitting region and significantly improve the short-distance transmission efficiency of the system. The correctness of the theoretical analysis has been verified by simulations and experiments.
Highlights
More than a century ago, Tesla proposed the theory of wireless power transmission (WPT)
Simulation and experimental results showed that compared with the Magnetically coupled resonant (MCR) WPT system based on the single one-way spiral coil (SOSC), the WPT system based on the double two-way spiral coil (DTSC) could narrow the frequency splitting region and significantly improve the short-distance transmission efficiency of the system
At the same distance of 300 mm, the WPT system based on the SOSC has frequency splitting, while the WPT system based on the DTSC has no frequency splitting only because of the reduction of mutual coupling, which proved that the frequency splitting region can be reduced by reducing the coupling coefficient k23
Summary
More than a century ago, Tesla proposed the theory of WPT. Since scientists from all over the world have begun to study the technology, but have not achieved satisfactory results. A multi-layer printed spiral coil structure was proposed because of the great influence of the coil on the performance of the MCR WPT systems in Ref. 11, which realized the miniaturization of medical implantation coils with higher inductance and lower resonant frequency, but still cannot improved the frequency splitting in short-distance WPT. Ref. 15 proposed a 3D coil model, which reduced the sensitivity of the MCR WPT system to the offset between coils, but did not improve the frequency splitting phenomenon of the short-distance WPT. Based on previous disc resonators and anti-parallel rectangular coil circuit boards, and without changing the current operating frequency of the WPT system, this paper proposed a DTSC design method This method solved the problem that the transmission efficiency was reduced due to the frequency splitting in short-distance WPT. Simulation and experimental results showed that compared with the MCR WPT system based on the SOSC, the WPT system based on the DTSC could narrow the frequency splitting region and significantly improve the short-distance transmission efficiency of the system
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