Research On Impedance Matching Method Under The Optimal Efficiency Of Wireless Power Transfer Via Strongly Coupled Magnetic Resonances

Strongly coupled magnetic resonance wireless power transfer system using two identical self-resonant coils with the same resonant frequency and quality factor, in resonance condition they tend to exchange energy efficiently and strongly between each other, to achieve energy-efficient transfer. This technology has a long transmission distance, high transmission efficiency and power, no radiation, non-metal penetration, without direction and other advantages, so it has good prospects.Firstly by using coupled-mode theory and circuit theory to analyze magnetic coupled resonance wireless power transfer system, mathematically explain the "resonance" and "strong-coupling" concept. Based on the impedance characteristics of the system under optimal efficiency analysis, derived the optimal matching condition of load impedance.The traditional power transmission system efficiency reaches the maximum by the optimal matching condition of load impedance, however, the real load impedance is just not the best load impedance. In order to improve the efficiency of the entire power transmission system, a improved load impedance topology is proposed, after the secondary coil with additional a matching feeding coil, the load impedance matching condition to achieve the best. By matching feeding coil adjusting the inherent parameters to match the different load, so that the load to achieve optimum matching condition to maximize transmission efficiency.Strong magnetic coupling resonant wireless power transfer system on variable load condition, will cause severe impedance mismatch problem, which is the main cause of system inefficiency and instability frequency. Based on this, the PWM rectifier load impedance matching method is proposed in this paper. After the matching feeding coil with additional a PWM rectifier, the duty cycle of MOSFET was controlled by PWM rectifier from realizing the equivalent transformation to achieve the impedance matching, and deduced the related calculation formula.In this paper, to build a strong magnetic coupled resonance wireless power transmission experiment platform, verified the feasibility of matching feeding coil load impedance matching method and the PWM rectifier load impedance matching method, and quantitativeexperiment on the system. The experimental results show that, to match different load results by this method, can make the system efficiency is very close to the theoretical value, the measured data and the derived formula to calculate the theoretical values agrees well.