Comprehensive investigation on misalignment tolerance of inductive power transfer systems

Inductive power transfer (IPT) technology is gaining popularity for wireless charging applications of future electric charging for its contactless power supply. The square and circular planar spiral coils are most widely used in wireless power charge due to its simple structure. This paper gives analyses of comparing these two geometry windings in detail. As for an inductive power transfer system, coupling structures, such as line spacing and magnetic core structure, are of paramount importance, because of their significant impact on power transfer efficiency and voltage stability. By analysing the characteristics of magnetic field distribution of the coupler, influences of coil shape, size, line spacing and core structures on coupling coefficient and coupling coefficient retaining ratio (CCRR) are firstly investigated. Misalignment tolerance under different coupler structures is then conducted, comprehensive optimization schemes of misalignment tolerance improvement are proposed. Results show that for the coupling coefficient and coupling coefficient retaining ratio, the optimal line spacing and core structures are highly dependent on the coil shape, size and air gap. A 3-kW IPT system was also built and experimental validations on original and optimized structures are performed. And the better misalignment tolerance was achieved with the optimal line spacing, transmitting coil and ferrite core structure.