Adaptive Impedance Matching for Efficient Wireless Power Transmission via a Perturbance and Observation Method

Impedance mismatching is a prevalent issue in wireless power transfer (WPT) systems across various power levels and operating frequencies. In scenarios where coils are closely coupled, the maximum power transfer does not occur at the natural resonant frequency of the coupled coils due to impedance mismatching between the internal impedance of the power source and the WPT system’s input impedance. This results in the frequency splitting phenomenon. This paper first examines the frequency splitting phenomenon using the maximum power transfer theorem. Subsequently, a Perturbation and Observation (P&O)-based method with a variable step size is proposed to enhance power transfer efficiency over a range of coil-to-coil distances. Unlike conventional, time-consuming search-and-find impedance matching (IM) methods, this approach achieves optimal IM network parameters in a single step. A scaled-down 20-watt prototype is fabricated to validate the effectiveness of the proposed method in terms of input current, active and reactive input powers, as well as power factor correction (PFC).