Study On Magnetic Coupled Resonance Wireless Power Transfer With Multiple Coils

With the development of scientific technology,a variety of electronic device has been widely used in people’s life.Conduction of electrical power from the power supply to electrical equipment is mainly accomplished by the direct contact of metal wire.Such power line brings many problems.Wire friction,aging process and leakage will affect the lifetime and safety of the electrical equipment.Massive wires and sockets are annoying.Charging line of implanted medical device increases patients’ pain.In order to overcome these increasing safety,convenience and applicability problems of power line,researchers conduct in-depth works of magnetic resonance coupled wireless power transfer(MCR-WPT).This paper focuses on the transfer mechanism of MCR-WPT with multiple coils,parameter identification,frequency splitting,capacitance compensation and power allocation.The ideas and methods in this study provide theoretical and practical guidance for wireless charging of the mobile phone or electric vehicle.The main research contents and results are involved in the following.1)The equivalent circuit model of three-coil system is established.As the transmitting coil and the relay coil is fixed,parameter identification equations are derived under the condition of movable or fixed receiving coil.The effect of random error on identified parameters is discussed.For the movable receiving coil,vector network analyzer is employed to extract multi-frequency input impedance.The dual frequency method and Newton Raphson iterative algorithm are proposed to approximately calculate parameters.For the fixed the receiving coil,the combination of parameter identification module and transfer efficiency can realize the simultaneous recognition of the load resistance and transfer efficiency.2)Frequency characteristic of transfer efficiency is analyzed based on the circuit model of the three-coil system.Discussions of different influence factors on the frequency splitting are carried out.The theoretical and experimental results show that when the load resistance is smaller or the relay coil is closer to the receiving coil,the frequency splitting phenomenon is more serious.When the frequency splitting occurs,frequency adjustment technology can compensate the drop of efficiency.The small change rate of efficiency near critical coupling can effectively enhance the stability when the receiving coil is parallelly placed.3)Based on circuit model of three-coil structure,the mathematical expressions of optimal compensation capacitors are derived and the influence of the coil position,load resistance and working frequency on the optimal compensation reactance,transfer efficiency is,respectively,discussed.When the frequency splitting is more serious,the efficiency improvements is greater by using compensation capacitors.Compared with frequency adjustment technology,the compensation capacitors are better in response to frequency splitting.Experiments on real-time capacitor tuning are carried out and maximum transfer efficiency is achieved.4)Power allocation scheme of a multi-load WPT is proposed.For the double-receiver structure,we present three kinds of power allocation methods,which are load adjustment,double-power supply and time-sharing technology.The theoretical and experimental results show that using these three methods,double loads can receive arbitrary powers when two receiving coils are placed at different positions.The load adjustment technology is extended to the multi-load system.For the coaxial multi-receiver structure,the expressions of load resistances corresponding to the identical power are deduced and the position of the source coil is discussed.For the circular and branched distribution structures,particle swarm algorithm is presented to determine these load resistances.