| In order to save energy and reduce environmental pollution,electric vehicles have been vigorously promoted all over the world.However,short driving range,long charging time,and battery temperature influence have become the main factors restricting the development of electric vehicles.Wireless Power Transfer(WPT)technology realizes the mobile charging of electric vehicles,which can completely get rid of the shackles of battery problems and has a good development prospects.However,the wireless charging of electric vehicles is a dynamic process.Factors such as transmission distance fluctuations,relative position deviation of transmission coils,and uneven magnetic field environment will change the charging parameters,causing the system to lose matching,resulting in low charging efficiency;transmission efficiency is an important indicator to measure the performance of the WPT system.WPT will achieve maximum efficiency transmission under specific impedance conditions.Therefore,configuring a suitable impedance matching network is an important method to improve the transmission efficiency of the WPT system.In this paper,aiming at the system mismatch problem in the dynamic wireless charging process of electric vehicles.Focus on the analysis of the reasons for the mismatch and the restore matching conditions,the impedance matching network having an adaptive adjustment capability was embedded secondary circuit,so that the electric vehicle can adaptively adjust the impedance matching according to the current working conditions,and stabilize the transmission efficiency under the conditions of changing operating conditions.The specific research work of this paper is as follows:(1)Four basic equivalent circuit models of SS,SP,PS,and PP are established using equivalent circuit theory.Calculate the loop impedance,power and efficiency of the model by Kirchhoff’s law.the SS model is selected as the research object of this article.Modeling and analyzing three types of impedance matching networks of L-type,Π-type and T-type,respectively calculating the matching parameters of the three models,and choosing the inverted L-type as the impedance matching network of this article;Calculating and analyzing six types of DC converters,and compare the relationship between the equivalent input resistance and load of each type of converter,and choose Buck-Boost circuit as the DC converter in this article,providing a theoretical basis for subsequent research.(2)In order to enable dynamic wireless power transfer(DWPT)of electric vehicles to perform adaptive impedance matching according to the current working conditions,the secondary side is embedded with an impedance matching network composed of a matrix capacitor + DC/DC in this paper,the matrix capacitor controls the series-parallel relationship of the capacitors in the array,realizing the improvement of adjustment accuracy and adjustment width when the number of capacitors is small;the maximum efficiency matching condition is derived by analyzing the power transfer relationship of the secondary equivalent circuit,and the maximum efficiency impedance matching parameter is derived according to the circuit resonance condition and impedance matching condition.According to the calculation result of the parameter equation,the series-parallel relationship of the capacitor array is switched to realize the dynamic impedance matching of the WPT system.(3)Dynamic wireless power transfer of electric vehicles system needs to accurately estimate the coupling coefficient before impedance matching.In response to this problem,this paper establishes a non-coaxial coil model,and the formula for calculating the mutual inductance of a plane spiral coil at any position is derived according to the Niemann theorem,and uses Maxwell electromagnetic simulation software to simulate and analyze the non-coaxial model,and the influence of key parameters on mutual inductance is summarized;then from the perspective of the actual working conditions of electric vehicle dynamic wireless power transmission,Kirchhoff’s law is used to derive the coupling coefficient estimation equation based on the secondary side parameters,so that the electric vehicle completes the coupling coefficient estimation in real time by detecting its own parameters,and provides a parameter basis for the adaptive impedance matching of the electric vehicle.(4)WPT experimental platform was composed of signal generator,power amplifier,transmission coil,capacitor matrix,rectifier bridge,DC/DC and load resistance was built.In the experiment,the coupling coefficient is estimated by detecting the current and voltage of the secondary side,and the secondary side impedance matching network is adjusted in real time according to the current coupling coefficient to realize the dynamic impedance matching of the WPT system and stabilize the transmission efficiency of the system.Both experiment and simulation results verify the effectiveness of the adaptive impedance matching method on the secondary side of this dynamic wireless power transmission system. |
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