Analysis and Tracking of Optimal Load in Wireless Power Transfer Systems

• Published in: IEEE transactions on power electronics Vol. 30; no. 7; pp. 3952 - 3963
• Main Authors: Fu, Minfan, Yin, He, Zhu, Xinen, Ma, Chengbin
• Format: Journal Article
• Language: English
• Published: IEEE 01.07.2015
• Subjects: Coils; Couplings; DC-DC power converters; Impedance; Integrated circuit modeling; Resistance; Resonant frequency; tracking of optimum load resistance; wireless power transfer; inductive resonance coupling; Efficiency analysis
• ISSN: 0885-8993; 1941-0107
• DOI: 10.1109/TPEL.2014.2347071

All the wireless power transfer (WPT) systems share a similar configuration including a power source, a coupling system, a rectifying circuit, a power regulating, and charging management circuit and a load. For such a system, both a circuit- and a system-level analyses are important to derive requirements for a high overall system efficiency. Besides, unavoidable uncertainties in a real WPT system require a feedback mechanism to improve the robustness of the performance. Based on the above basic considerations, this paper first provides a detailed analysis on the efficiency of a WPT system at both circuit and system levels. Under a specific mutual inductance between the emitting and receiving coils, an optimal load resistance is shown to exist for a maximum overall system efficiency. Then, a perturbation-and-observation-based tracking system is developed through additional hardware such as a cascaded boost-buck dc-dc converter, an efficiency sensing system, and a controller. Finally, a 13.56-MHz WPT system is demonstrated experimentally to validate the efficiency analysis and the tracking of the optimal load resistances. At a power level of 40 W, the overall efficiency from the power source to the final load is maintained about 70% under various load resistances and relative positions of coils.