Research On Modeling And Optimization Of Wireless Charging Coils

Wireless Power Transmission（WPT）technology frees electronic devices from wires during the charging process.And planar coils are commonly used in the inductive WPT systems due to small size and low cost.In this paper,the lumped RLC parameters of planar coils are modelled theoretically for chip level（silicon-based）and board level（Printed Circuit Board,PCB）,and verified by simulations and experiments.Based on the modeling,we optimized PCB coils by varying the trace width and turn-to-turn spacing together to improve the power transfer efficiency.The first section of this paper makes a brief introduction about the WPT system.Secondly,the electrical characteristics model of the single-turn silicon-based integrated coil surrounded by a multi-layer dielectric is provided.In the modelling of the coil parasitic capacitance,multi-layer dielectrics around the coil was equivalented to a single-layer dielectric with an equivalent permittivity and verified by simulation.We also established an analytical RLC model for multi-turn PCB coil.For planar coils with variable trace width and spacing,the inductance formula is realized by decomposition and accumulation of coils turn by turn.And the substrate as well as connecting trace of coil is considered in the capacitance modelling to improve the accuracy.Afterward,combined with the existing models and curve fitting methods,a resistance formula is established.Finally,this paper proposed a new coil layout optimization method to improve the maximum available transmission efficiency.Specifically,we decreased the trace width of the coil proportionally from the outer turn to the inner turn and increase the spacing between traces at the same time.It has proved that the optimal scaling factorαof the trace width and the optimal frequency can be quickly estimated by using the accurate analytical model for the printed square coils.Results show that after optimization,the measuredη_max of the WPT system is increased by about 45%.