Research On Rotary Loosely-coupled Transformer Based On The Analysis Of Magnetic Characteristics Of Core Material

In recent years,the wireless power transmission technology has been gradually applied to various rotary equipment such as supplying power to motor field windings.Since the rotating equipment cannot be powered by the direct contact of the cable,the slip ring mainly contacted by the brush is usually used to supply power.However,the sparks and wear debris caused by friction may cause the slip ring to short-circuit,overheat and even explode.The use of rotary loosely-coupled transformers to replace slip rings can solve these problems.Considering that the rotary loosely-coupled transformer works at high frequency,in order to improve its transmission performance and reduce its volume,this thesis proposed to replace the traditional soft ferrite block material with nanocrystalline strip as the core material of the rotary looselycoupled transformer according to the analysis of the magnetic properties of nanocrystalline and soft ferrite materials.The change of the core material will cause the structural change of the rotary loosely coupled transformer,and in this thesis,a new type of core structure of a rotary loosely-coupled transformer and two winding structure schemes were developed.The magnetic field distribution and transmission performance were simulated and calculated and the rationality of the proposed structure was analyzed.The main research contents are as follows:Firstly,on the basis of studying the structural characteristics and working principles of the rotary wireless power transmission system,the equivalent circuit model of the loosely-coupled transformer was given and the transmission characteristics of the rotary loosely-coupled transformer were deduced and analyzed.Secondly,based on the existing iron core high-frequency magnetic characteristic measurement system in the laboratory,the magnetic properties of nanocrystalline and soft ferrite under sine wave and square wave excitation were measured and analyzed.After comparative analysis compared with soft ferrite,the nanocrystals have more advantages in high-frequency magnetic properties.For this reason,it was proposed to use the nanocrystalline as the core material of the rotary loosely-coupled transformer.Thirdly,the structural design of the new rotary loosely-coupled transformer was carried out.Due to the change in the shape of the core material,the traditional pot core structure was no longer suitable for nanocrystalline ribbons.As a result,a new type of rotary loosely-coupled transformer core structure was proposed,two winding structure schemes were presented,and further the analysis and calculation on the material of the winding coil and the number of turns of the coil were determined.Finally,through the 2D and 3D magnetic field simulation calculation under square wave excitation of the new rotary loosely-coupled transformer,the feasibility of the new rotary loosely-coupled transformer structure was verified.Based on the magnetic field simulation results,the Steinmetz empirical formula was used to calculate core loss and the coupling performance and transmission performance were analyzed.It is verified that the new rotary loosely-coupled transformer has better transmission performance.