Mutual Inductance Modeling and Parameter Optimization of Wireless Power Transfer System with Combined Series-Wound Hexagonal Coils

The coupler is the core component realizing the efficient and reliable operation of the wireless power transfer (WPT) system, and its high anti-misalignment performance is a key issue to be solved urgently to promote the application and development of WPT technology. Due to the uncertainty of the position of the receiving coil, the misalignment problem will inevitably exist between the transmitter and the receiver in actual operation, causing the mutual inductance of the traditional coupler to decrease, resulting in a significant decrease in the transmission efficiency and power of the WPT system. The traditional coupler adopts a monotonic winding method to meet various application scenarios, and the analysis of coupling characteristics mainly relies on magnetic circuit models and finite element analysis methods, which are cumbersome, inefficient, and not universal. In order to improve the misalignment tolerance and robustness of WPT system, it is necessary to study the high anti-misalignment coupler, establish its mutual inductance model and multi-parameter optimization method. Firstly, taking hexagonal coil as an example, the spatial distribution of magnetic flux density of tightly wound, loosely wound and combined series wound coil is compared and analyzed. A design idea of a combined series wound hexagonal coil coupler is provided, which derive from the distribution characteristics of the magnetic flux density and their respective advantages of tightly wound coils and loosely wound coils. On this basis, the mutual inductance and self-inductance models of the proposed coupler are established using electromagnetic theory. The influence mechanism of transmission distance and lateral misalignment on the coupling coefficient are also analyzed, and the correctness of the models is verified by Maxwell software simulation. In order to further optimize the parameters of the coupler, the maximum coupling coefficient is taken as the optimization objective, and taking the coil self-inductance and the inner and outer diameter, the number of turns, and the turn spacing as the constraints. The genetic algorithm is used to realize the adaptive optimization of the multiple coil parameters. In addition, considering the cost and transmission efficiency, different core layout schemes are compared and analyzed. Finally, a 100 W experimental prototype is built using GaN power switch GS66508B to verify the effectiveness of the proposed coupling mechanism and its parameter optimization method. The results showed that the magnetic flux density of the combined series wound coupler is still dense on both sides, and can made up for the weak magnetic flux density in the central region. The spatial distribution is more uniform than tightly wound and loosely wound, which is beneficial to improve the coupling coefficient and anti-misalignment ability of the coupler. Genetic algorithm can realize the adaptive optimization of multiple parameters of coupler quickly and has strong universality. After optimization, the transmission efficiency of WPT system is increased by 4.2%. In addition, adding ferrite core can further improve the transmission efficiency of the combined series wound hexagonal coil WPT system. On the basis of the above research, the influence of magnetic core and shielding material on mutual inductance between coils can be comprehensively considered in the future, so as to further improve the structure and analysis model of the coupler. © 2023 Chinese Machine Press. All rights reserved.