Influence of Asymmetric Coil Parameters on the Output Power Characteristics of Wireless Power Transfer Systems and Their Applications

Abstract

Nowadays, it is a trend to update electronic products by replacing the traditional wire charging with emerging wireless charging. However, other features of the products must generally be left unchanged, which limits the options in receiving coil design. As a result, asymmetric coil designs should be adopted in wireless charging systems. In this paper, a wireless power transfer system with asymmetric transmitting and receiving coils is modelled using circuit theory. The output power of the asymmetric system is analyzed, and the conditions of the maximum power splitting phenomenon are addressed in detail. Cases for different resonant frequency conditions are elaborated. The splitting frequencies and critical coupling coefficient are obtained, which are different and more complicated compared with the symmetric counterparts. Asymmetric coil designs can be adopted based on the proposed method, so that adequate and efficient output power transfer can be realized. Finally, the asymmetric coils design is utilized in an experimental prototype in order to contactlessly charge a portable power tool lithium-ion battery pack with 18 V DC and 56 W output through 220 V AC input, without altering its original configuration, and the correctness of proposed analysis can thus be verified.

Power Transfer Analysis of an Asymmetric Wireless Transmission System Using the Scattering Parameters

“…Much less research has been carried out on the asymmetric structure. The analysis resulting from symmetric cases cannot be used straightforwardly for the system with asymmetric structure as they will not be accurate enough [28]. Therefore, the calculation and selection of the asymmetric system's operating frequency depends on system parameters, which need to be optimized [29].…”

Experimental Results and Analysis of Midrange Underwater Asymmetric Wireless Power Transfer

“…WPT systems with asymmetric coils are analyzed in air in [21][22][23]. In [24], compared with traditional symmetric WPT systems, the coupling coefficient and load under asymmetric transmitting and receiving coils have different effects on the output power. There are fewer studies on asymmetric coil systems in seawater.…”

“…In [25], couplers with symmetric and asymmetric structures were designed and compared for underwater unmanned systems. The influence of the circuit parameters on the output performance was explored in [24,25]. However, these two papers did not mention how to improve the transfer efficiency.…”