High Efficiency Wireless Power Transmission Via Coupled Magnetic Resonances

Coupled magnetic resonance technology is an innovational method of wireless power transmission, which transfers power by magnetic coupling between resonant coils in non-radiative near field. Currently, studies on this technology are still in the initial stage. The energy transmission mechanism and the system design theory are not perfect, and many problems need to be solved.Fundamental researches and experiments are carried out in this thesis by following parts:First, system model was established and theoretical analysis was carried out. Coupled-mode theory was introduced and the defects when it applying to wireless power transfer system was discussed. Vibration theory was adopted to analyze the natural response and driven response of coupled resonators, and explain principles and conditions of long-distance power transmission. Based on equivalent double-loop model, mutual inductance coupling theory was adopted to analyze the power transfer features when system works at resonant frequency, and transducer power gain was obtained with vibration of coupling factor; the frequency splitting phenomenon was expounded from the view of maximum power transfer theory, splitting frequency and peak expression were founded; the impact of frequency offset on the system was studied; the concept of matching factor was proposed to analyze the matching characteristic of system.Second, electromagnetic simulation and analysis were carried out using finite element software HFSS. Resonant frequency and vibration modes of single helical coil and coupled helical coils were obtained utilizing eigenmode solver; scattering parameter of four-coil system and impacts of coil parameter on power transmission property were obtained utilizing driven mode solver. Simulation results are consistent with theory analysis.Third, system optimization by adding single repeating coil was studied. Effect of repeating coil was theoretically analyzed and compared with the original four-coil system; the influence of repeating coil placement was studied; finite element simulation of system with repeating coil was carried out.Finally, experiments were conducted to verify theory analysis. Helical coils using to transfer power were designed and tuned to same resonant frequency; distance property, frequency property and matching property were tested; power transfer properties of system with repeating coil were tested. A preliminary study of high power wireless power transfer was carried out.