Design of a Compact Concentric Solenoidal Coupler for Resonant Inductive Wireless Power Transfer

This paper presents a design of an optimized high-frequency concentric coupler with a target input resistance for compact, light-weight stationary and rotary applications using wireless power transfer (WPT). The coupler features near-gap concentric solenoid coupling coils with series-series (S-S) compensation for improved transmission efficiency. This coupler design provides impedance matching without the use of a matching network, reducing the number of requisite components and eliminating their associated losses. With fixed parameters, the minimal number of turns per coil required to obtain the target input resistance is ascertained to design a coil of minimum size. The candidate designs were evaluated in a finite element simulator, and their theoretical input impedances were calculated using the resulting simulated Z-parameters. Using the process outlined in this paper, we designed and constructed two optimized couplers in hardware. At 13.56 MHz, the first concentric coupler presented an input resistance of 53.6 Ω while the second coupler presented an input resistance of 11.9 Ω. The concentric couplers were tested with inverters designed for 50 Ω and 10 Ω loads, which resulted in system efficiencies of 88.3% and 91.2% under ZVS conditions for the 50 Ω and 10 Ω input impedance couplers, respectively. The corresponding output powers were 31 W and 83 W, while the input voltage was set at 50 V for both designs.