Inductive Power Transfer Based On Independent Inductive Energy Injection And Free Resonance Topology

As a new mode of electric power transmission,inductive power transfer(IPT)system has received great attentions and has been developed in recent years.IPT system based on electromagnetic coupling has been commercialized in low-power applications such as mobile phones and sweeping robots charging,but many difficulties still exit in high-power applications such as electric vehicle charging.In this paper,a topology of independent inductive energy injection and free resonance(IIEIFR)and its control strategy for IPT are proposed,which are expected to contribute to the IPT system in high-power applications.In order to solve the problems of high viscosity between the converter and the resonance network,high reactive power and difficult power control in traditional IPT system,the topology of IIEIFR is proposed.The topology is composed of three stages:independent inductive energy injection stage,adaptive free resonance stage and shutdown stage.The proposed topology can decouple the converter and resonance network and reduce the order of IPT system.It is expected to eliminate the reactive power and solve the difficulties of system detuning and power control.The main work of this paper is as follows:By connecting the transmitter to the converter and resonance network at different time stages,the topology of IIEIFR IPT system is designed.The model of the topology is established,and the operational principle and modal conversion law of the IPT system are analyzed in detail.The analytical solutions of current,voltage and power are derived.Soft switching conditions and control strategies are proposed.A prototype of IIEIFR topology is built verifying the rationality and feasibility of the proposed system.A kind of power control strategy based on the IIEIFR IPT system is proposed.By controlling the phase ratio the transfer power can be controlled.Because each stage of IIEIFR IPT is independent from each other,the converter and resonance network are completely decoupled.The difficulty of power control which is seriously related to the load and the coupling coefficient is reduced.The viscosity problem of power control associated with the system parameters in a traditional IPT system is solved.Four power control methods based on input voltage,injection time,number of free resonant periods,and turn-off time are studied.Through theoretical analysis,it is proved that these four methods can all control the power independently.The influence of load and coupling coefficient on power control is eliminated.The feasibility of the method and the correctness of the theoretical derivations are proved by experiments.The effect of frequency bifurcation on the dynamic behavior of the IPT system is studied.Combined with the characteristics of three stages:independent inductive energy injection,free resonance and shutdown stage,the adaptivity of the resonance frequency under different parameters is studied.It is proved theoretically that frequency bifurcation dose not exit in the proposed IIEIFR IPT system.The frequency tracking process in the IIEIFR IPT system is described,and the control strategy based on time margin is proposed.The control strategy can offer a large enough time period for the switching devices to accomplish the stage transition,greatly reducing the difficulty of stage transition and enabling soft switching of all switching devices.The IIEIFR IPT system are proved to work well under a large range of coupling coefficient k.Based on the relationship between primary impedance,secondary impedance and reflection impedance,the power transfer principles under the condition of over-coupling,under-coupling and critical-coupling are analyzed.By analyzing the influence of the coupling coefficient k on the system performance in the energy injection stage and free resonance stage,the adaptivity of IIEIFR IPT system operate under a large range of coupling coefficient k is proved.