Wireless Power Transfer: Types of Reflected Impedances and Maximum Power Transfer Theorem

In this letter, different types of resonant reflected impedances (real, imaginary, and negative) and conditions for their existence are introduced using power flow paths. The condition necessary to achieve maxima of power delivery at a high (>0.5) system efficiency is derived while maintaining a power factor of 0.85 or above. A 4-coil wireless power transfer system operating at 4.7 MHz is implemented, to demonstrate that by controlling the different types of reflected impedances it is possible to overcome MPT induced constraints. The implemented example utilizes four nonoverlapping coils of 35 mm radius; a maxima in power delivery is experimentally obtained while maintaining the efficiency and power factor above 0.5 and 0.85, respectively.