Research On Wireless Power Transfer System Based On Coupled Nonlinear Resonators

Magnetically coupled resonant wireless power transfer(WPT)is to realize the effective transmission of energy with the magnetic inductive near field through transmitting and receiving coils at the same resonant frequency.Compared with the two transmission technologies based on electromagnetic induction and microwave radiation,the magnetically coupled resonant WPT technology can achieve a longer transmission distance,higher transmission efficiency,and small external radiation.Therefore,magnetically coupled resonant WPT is widely used in charging portable mobile devices,electric vehicles,smart homes,biomedical implantable devices,etc.It has become one of the hottest areas in current WPT research.Since many charged devices move in practical situations,they cause the relative positions between the transmit and receive coils to change.When such a change occurs,the power transmission performance will be affected adversely.This limits the broad application of the magnetically coupled resonant WPT technology.To address the issue,this thesis develops a position-insensitive WPT system based on the nonlinear Duffing resonant circuit;it can maintain a high output power transfer efficiency when the relative position between the transmit and receive changes.The more details are as follows:First,the power transfer mechanism and characteristics of the WPT system is analyzed with the near-field theory and coupled-mode theory.By considering the twocoil WPT system as a two-port network and applying the circuit theory,the effects of the four basic resonance-compensation circuit configurations are developed and analyzed.It is verified that the frequency-splitting phenomenon of the magnetically coupled resonant WPT system working in the over-coupling region will seriously degrade the power transmission performance.To tackle the issue,a nonlinear system,the Duffing system,is introduced and analyzed;it is introduced into the subsequent design of the nonlinear resonant WPT circuit with the use of a varactor.Then,built on the conventional magnetically coupled resonant WPT system and incorporating the nonlinear Duffing resonance model,a robust magnetically coupled resonant WPT system based on the nonlinear resonant circuit with a varactor is discussed.The operational principle of the varactor is analyzed,and the correspondence between the parameters of the Duffing equation model and those of the varactor element is presented,which facilitates the selection of the varactor diode.Finally,the model parameters are optimized through an optimization algorithm.The parameters of the varactor model are extracted.An accurate relationship between the capacitance of the reverse-series varactor and its bias is obtained through simulation.A WPT system with Duffing resonator is fully developed.The simulation and test results show that the proposed WPT system has an operating frequency of 2.2 MHz and can maintain a high level of load power stability in the over-coupling region.Its effective range of power transmission is from 44 mm to 200 mm.In comparison with that of the conventional WPT system,the effective range is increased by 2.12 times;the effective range of the WPT is significantly improved while good performances are maintained.