Coil design approach for indirect-fed resonant wireless power transfer system

A novel coil design approach for an indirect-fed resonant wireless power transfer (RWPT) system is proposed in this paper. The design goal is to find the minimum size of the coils for the RWPT to deliver a minimum desired power in all positions in a given distance range. Neumann formula is applied to the extensions of circuit models to obtain dimension-bound equations for output power. The design bottleneck is shown to be the power delivered at the farthest distance in the range dictating the size of the coils. It is also observed that designs with unequal coil sizes cannot provide an optimal power delivery. Using the flowchart introduced in this paper, the minimal size of coils which satisfies the minimum output power are determined. Moreover, effects of changing the optimal size on mutual inductance and knee point relocation are investigated. The simulations are given for a 15W load for a range of 40-80 cm.