Design The Coil Structures For WPT System Based On The Optimized Method Of Penalty Function

The technology of wireless power transmisson(WPT)has been widely applied to electric vehicles,mobile phones and other fields,which has greatly improved the quality of human life.The efficiency of wireless power transmission system is closely related to the mutual inductance between coupling coils.Based on the internal penalty function method,this paper analyses how to optimize the layout of cores in wireless power supply coils,especially focuses on the influence which cores with different quantity,length and location made on the mutual inductance of coils.First of all,this paper studies the principle and composition of WPT system,and then deduces the formula of power and efficiency of WPT system based on mutual inductance model.Next,based on equivalent magnetic circuit model,this paper puts forward that the mutual inductance between coupling coils can be improved by optimizing the length and location of cores.In addtion,according to the relationship among cores’ length,location and mutual inductance that Maxwell simulation data reflected,this paper sets up an objective function with Matlab.This function uses cores’ length and location as main variables,and meanwhile sets up some constraints.Furthermore,the augmented objective function is established by means of internal penalty function method,in order to obtain the optimal cores’ length and layout in a reasonable-power coils design.This method can obtain the optimal cores’ length and location under corresponding conditions whether the radius and number of cores are specific or not.This paper selects power coupling coils with radius of 100 mm and 150 mm,and five unequal-length but equal-width and equal-height ferrite cores with different quantities to do the experiment.The specification fo five cores are 40 mm * 15 mm * 5 mm,50 mm * 15 mm * 5 mm,60 mm * 15 mm * 5 mm,70 mm * 15 mm * 5 mm and 85 mm * 15 mm * 5 mm,and the quantities of cores are divided into eight,nine,and ten.After the experiment,this paper draws a conclusion that the optimal length of power coupling coils with the radius of 100 mm is 60 mm,and the optimal cores’ location is around-0.6 mm;the optimal length of power coupling coils with the radius of 150 mm is 85 mm,and the optimal location is around-1.5 mm,which is essentially consistent with the results of algorithm.All in all,the cores layout optimization proposed in this paper can effectively improve the mutual inductance between power coupling coils and the efficiency of wireless power transmission system.