All-Detuned Three-Coil Configuration for Advantages in Inductive Power Transfer Systems

In inductive power transfer systems, some applications require working at higher power levels, transferring power with longer air gaps, and meeting geometric constraints. Many situations will decrease system coupling and affect performance. In this article, a three-coil configuration based on an all-detuned design is proposed to optimize the overall coupling and system efficiency. Primary and tertiary coils of the proposed topology are mounted on the same side. The three coil resonances in the proposed system, as extra degrees of freedom, do not match the switching frequency or each other. The key objectives of the proposed all-detuned design are to achieve a constant current output and unity power factor based on an equivalent two-coil circuit model; maximize the overall coupling coefficient to reduce the switching frequency or coil inductances by selecting a suitable tertiary resonant frequency; and optimize efficiency to be superior to those in a conventional two-coil system by minimizing coil currents. A 1-kW prototype has been prepared to verify the method. For example, when the main coupling coefficient is only 0.077, dc-dc efficiency of the proposed method ranges from 90.2% to 91.2% over a 2:1 load range, while that of the conventional two-coil system does not exceed 90%.