Optimized Design Of Coil And Compensation Network For Wireless Charging

As an emerging power transmission method,wireless charging has the advantages of small floor area,safe and convenient,no mechanical wear,good corrosion and oxidation resistance,no spark and electric shock,flexible application,and strong environmental adaptability.It has become a research hotspot for domestic and overseas research institutions and major companies.This thesis conducted research on the wireless power transfer system based on magnetic induction coupling.With regard to coil design,the flat rectangular coil has the characteristics of saving cost,compact structure,high space utilization,simple control and strong anti-displacement capability.Therefore,this thesis investigates the loosely-coupled transformer with flat rectangular coil,and summarizes a new iterative design method for loosely-coupled transformer.In order to reduce the coupling coil size,the coil is wound as full as possible,and the relationship between turn spacing,coil outer diameter and turns number is obtained.The dimension is calculated according to the empirical formula,then the coil is drawn and simulated to obtain an estimated self-inductance.It is compared with the expected value,then the number of turns and dimensions are further adjusted accordingly to obtain the final coil parameters.The influence of turns,coil size,core area and distance on the self-inductance,mutual inductance and coupling coefficient of the core is analyzed by finite element simulation in Ansys Maxwell.With regard to design of the compensation network,the LCC-S topology has a small secondary-side volume and weight,which can realize constant current output of the primary side and the constant voltage output of the secondary side with good light-load performance.Moreover,the parameters of the compensation network are not affected by mutual inductance and load,and the system has high robustness.Therefore,this thesis studies the structure of LCC-S resonance compensation network,establishes the loss model of the system,obtains the efficiency formula,and then divides the efficiency optimization into two stages: parameter design stage and operation stage.In the parameter design stage,an optimization method for resonance parameters is designed by the efficiency formula.Compared with traditional parameter calculation schemes,the optimization method has lower loss,higher efficiency and less component stress.The optimization method takes the efficiency of the whole system into account,which makes it more convenient to calculate the resonance parameter values to realize the maximum efficiency operation of the system in the parameter design stage.For a system with resonance parameters,the effect of load impedance and coupling coefficient on efficiency is verified by simulation.The efficiency increases with the increase of load.When the maximum value is reached,the load efficiency will decrease when the load continues increasing.The efficiency increases with the increase of coupling coefficient and tends to a stable value.Therefore,in the operation stage,the efficiency optimization of the system can be realized by further adjusting the coupling coefficient to match different loads.In this thesis,the output performance of the system is simulated in Matlab.The output characteristics of the system are obtained,such as constant current of the primary side and constant voltage of the secondary side.The gain is not affected by the load,and the coupling coefficient is monotonously increasing.The output power decreases with the increase of the load,which is in line with the theoretical analysis.Finally,the 3kW static wireless power transfer experimental platform is built,which realizes the full wireless power transfer at 375 V input voltage,and verifies the influence of load,coil distance and coil position on the output of the system.