Design And Implementation Of Wireless Power Transmission System Based On Magnetic Resonance Coupling

Wireless power transfer via coupled magnetic resonances is a mid-range wireless power transmission technology which emerges in the past ten years. The principle is using magnetic resonance of the coupled circuits to increase the power and distance of transmission. With the advantages of transmission distance, power, cost and flexibility, this technology has become a research hotspot in the field of wireless power transmission. Existing researches have shown that a frequency splitting phenomenon will occur when the magnetically coupled resonators are in over-coupled region, thus the frequency of exciting source becomes an important constraint factor of power increasing in the transmission. Moreover, because the distance between the transmitter and receiver has a random feature, it is difficult to ensure the coincidence of the received and rated power. This thesis will analyze the rules of frequency-splitting phenomenon and power attenuation theoretically, and propose adaptive strategies of frequency tracking and power controlling.As to frequency tracking, when it comes to the relationship between coupling coefficient and frequency, the theory of mutual inductance is a classical choise for modeling in the resonant circuit. It is indicated that the impedance of the circuit greatly changes when the system is in the state of over-coupled. As a result, the frequency of maximum power transfer moves away from the natural resonant point. However, the transmitting circuit remains resonant if the frequency of exciting source changes as well. Therefore, the transmission power can be improved by tracking the resonant frequency in the transmitting circuit. As a means of frequency tracking, a modified Royer oscillator is adopted with the function of resonant frequency tracking, voltage inverter and power amplification.As to power controlling, previous researches have shown that power decays rapidly with the increase of coils' distance. In order to keep the coincidence of received power and rated power, it is necessary to set up a communication link between the transmitter and receiver. By the real time monitoring and feedback regulation of received power, the power can be keep in stability and accuracy all the time. Since the proportional relationship between resonant voltage, changing rate of magnetic flux and induced voltage, this thesis proposes to use the boost converter to control the received power. According to the requirement of boost converter, the system uses a PID controller to adjust the input voltage of Royer oscillator, so as to achieve the purpose of power regulation.Based on the analysis of the circuit theory and simulation results, a complete system with hardware and software is designed for experimental measurement, in which resonant frequency, received power and efficiency is recorded in different conditions of load and distance. Eventually, it is shown that the system can realize a stable power transmission of 5 watts within the distance of 12 cm in the experiments.