Reseach On The Nonlinear Phenomena In Wireless Power Transfer

Magnetically Coupled Resonant Wireless Power Transfer(MCR-WPT) is a new method of energy transfer, which has become a hot topic in recent years for its advantages of long distance and hight power characteristics. WPT system consists of power signal generation module, power transmission and receiving module, rectifier load module, which contains a lot of nonlinear devices such as switching devices and magnetic devices. Hence, WPT system is a typical high-frequency high-order nonlinear system. This thesis commences the study focusing on the nonlinearities introduced to WPT system, and main points of this paper are as follows:1. In this thesis, magnetic material is applied to MCR-WPT system. Model of plannar coil with magnetic core is studied from the points of distribution of magnetic field, inductance of plannar coil, coupling coefficient between two coils, and influence of magnetic core on the performance of WPT system. Both theories and experiments are conducted to verifiy the efficiency improvement of WPT system in short distance.2. This thesis studies frequency splitting phenomenon in this system from the perspective of coupled circuit. By solving zero state response of lossless and lossy coupled circuits, this thesis studies relationship between resonant frequency of coupled circuit and separated LC circuit, which explains why frequency splitting phenomenon existing in WPT system. By comparing resonant frequency of coupled circuit and splitting phenomenon, conclusion that low resonant frequency is more stable is conducted. Besides, methods of control splitting phenomenon are given.3. Considering the nonlinear characteristics of magnetic material, this thesis obtains nonlinear mathematical model of planar core coil with the help of Maxwell. Then, nonlinear dynamical equation of WPT system is established. Numerical analysis results show that nonlinear dynamical behavior such as bifurcation will occure in this system. Conditions of bifurcation phenomenon occuring are presented. To verifiy the existence of bifurcation phenomenon, firstly, this thesis establishes SPICE model of nonlinear WPT system, secondly, experiment is conducted and succeeds in verifying bifurcation phenomenon. Effect of nonlinear phenomenon on efficiency of this system is also conducted in this experiment.4. Another nonlinearity module rectifier load is also studied in this thesis. Model of this system with switching devices is established with the method of piecewise linear approach. The phenomenon of quasi-periodic modulation is also studied with software simulation.