| Wireless power transfer(WPT)system is a power system that using electromagnetic induction of primary and secondary coils to transfer energy.Due to the loose coupling characteristics of primary coil and secondary coil,when the loop is in a resonant state,the partial pressure of the load is high,and the reactive power of the system is small.At this time,there is a large system output of active power and high energy transmission efficiency.,power supply capacity is small as well as the distance of power transmission can be greatly improved.Therefore,the WPT system resonant circuit is the main circuit of the common inductive power transmission system,and is beneficial to low energy consumption,high efficiency and green environmental protection.In the research of WPT system,we can find that there is resonant frequency drifting of the system due to the tolerance of the components.As a result,the system load voltage is reduced,and in order to keep the load voltage constant,it is necessary to provide a larger primary loop current,thereby increasing the loss of the primary loop and reducing the energy transmission efficiency of the system.Taking the WPT system based on series-series compensation as the research object,a measurement coil is parallel mounted with the transmitter coil to measure the phase of receiver current.Then,the phase differences of the transmitter and receiver currents is adopted as the feedback control parameters.Finally,the switching frequency of the inverter is regulated based on the resonant condition of receiver,so that not only the receiver operates under resonant condition but also the voltage gain,output power and the efficiency can be improved under all the circumstances.The control methods with and without the proposed strategy are employed to verified the performance,the maximum output power and system efficiency of proposed strategy are both increased when the receiver appears inductive and capacitive with tolerance.Furthermore,under normal circumstances,the impedance characteristics of the external performance of the WPT system secondary rectifier bridge are considered to be purely resistive.However,in the actual operating process,the impedance exhibited by the secondary rectifier bridge under different voltage and current conditions was found changed,and the resistance characteristic is shown.The secondary impedance changes due to changing operation conditions or other environmental factors,which also causes the change of equivalent impedance in the primary side.This leads to the deviation of resonance and softswitching condition and requires higher capacity of the power supplyin the primary side.To solve the problem,aminimum voltage tracking based receiver’s resonant frequency tracking technique is employed in the WPT system.This approach adopts real-time detection of the DC-DC output voltage and the operating frequency of the inverter to restore resonance of the primary circuit by constantly tracking the minimum DC-DC output voltage.The experimental result shows the validity of the proposed approach.It has been shown that the proposed approach lowers system capacity and helps to achieve soft-switching conditionin the primary side. |
