High-Performance Multi-Coil Inductive Power Transmission Links

Authors: Mehdi Kiani and Maysam Ghovanloo

Source: FERMAT, Volume 7, Article 3, Jan-Feb., 2015

Abstract: Inductive power transmission is widely used to energize implantable microelectronic devices (IMDs), and recharge batteries in mobile electronics and electric cars. Power transfer efficiency (PTE) and power delivered to the load (PDL) are two key parameters in wireless links. To improve the PTE, additional coils have been added to conventional 2-coil links to form 3- and 4-coil inductive links. Several analytical methods for estimating PTE of inductive links have been devised based on circuit and electromagnetic theories. Here, we have analyzed the PTE for multiple capacitively-loaded inductors based on both circuit and coupled-mode theories. We have proven that both methods basically result in the same set of equations in steady state and either method can be applied for short or mid-range coupling conditions. Through our comprehensive circuit analysis, we have also compared the PTE and PDL of 2-, 3-, and 4-coil links. Our analysis suggests that the 2-coil links are suitable when the coils are strongly coupled and a large PDL is needed. Three-coil links are the best when the coils are loosely coupled, the coupling distance varies considerably, and large PDL is necessary. Finally, 4-coil links are optimal when large PTE is key, the coils are loosely coupled, and their relative distance and alignment are stable.

Index Terms: Inductive Links, Wireless Power Transmission, Resonance Circuits, Power Transfer Efficiency, Near-Field, Coupled-Mode Theory

View PDF

High-Performance Multi-Coil Inductive Power Transmission Links