The Research On Dynamic Tuning Method Of Frequency Tracking Based On The Minimum Current Ratio For Wireless Power Transfer System

In recent years,with the development of high frequency power electronics technology,the wireless power transfer technology has gradually become a hotspot in the field of electrical engineering.Wireless Power Transfer(WPT)technology transmits electrical energy from power supply to load in a contactless way with the principle of magnetic field,electric field and so on.WPT technology has removed those long-standing defects of traditional power transmission methods such as bare wires,electric spark and worn plugs and brings a number of advantages including electrical safety,reliability and flexibility.With further research and application of WPT technology,it has been widely used in medical equipment,lighting,electric vehicles,consumer electronics and other fields.In order to ensure a higher power capacity and higher efficiency,the static compensation capacitance is used in the WPT system to realize the resonance.However,in the practical operation of the WPT system,the air-gap between the primary coil and the secondary coil is variable.For example,the airgap will be changed due to a change of the load of the electric vehicle.Not only the mutual inductance but also the self-inductance will drift as the variation of the airgap of the electromagnetic coupling mechanism with the magnetic cores between the primary coil and the secondary coil.Then,the requir ed capacity of the source will increase,and the efficiency of the overall system will decrease because of the detuning of the WPT system.Therefore,it is necessary to work out a dynamic tuning method to restore the resonant state of the WPT system.Firstly,this paper studies the working principle of WPT system,analyzing four typical topologies in WPT system,and focuses on the transmission model and formula expression of SS(Series and Series)topology.Secondly,this paper explores the reason for the detuning of the WPT system by analyzing possible factors that lead the change of the mutual inductance and self-inductance of the primary coil and the secondary coil.In this process,two factors are highlighted: the variation of the air-gap and system frequency.Thirdly,a formula has been derived on the efficiency of the WPT system when the self-inductance of the primary coil and the secondary coil changes.Finally,a dynamic tuning method tracking the minimum current ratio of the primary coil and the DC source is proposed in this paper to tune the WPT system.By adjusting the frequency of WPT system dynamically,system performance can be improved accordingly.Multiple experiments are conducted against the different air-gap distance between the primary side and the secondary side by a prototype setup.The test results show that WPT system can be tuned back to resonance with various air-gap distance by adopting the proposed method so that the required capacity of the DC source is saved and the efficiency of the overall system is increased compared to that without control.In this way,the effectiveness and validity of the proposed dynamic tuning method are further verified.