Research On Key Technologies Of High Speed Permanent Magnet Motor Rotor

High speed permanent magnet motor has become one of the research hotspots in the field of electrical machines because of its advantages of high power density,high efficiency and direct connection with load.High loss density and poor heat dissipation conditions of the High speed permanent magnet motor rotor can lead to excessive rotor temperature easily,which affects the performance of the motor.At the same time,the permanent magnet in the rotor of high speed permanent magnet motor has low tensile strength,and it is easy to be destroyed by huge centrifugal force at high speed.In addition,when the working speed of the rotor is close to its critical speed,the bending and resonance of the rotor will occur.In view of the above problems,this paper studies the rotor of high speed permanent motor from three aspects: rotor temperature rise,rotor stress and rotor dynamics.Firstly,according to the requirements of rotor thermal analysis,the eddy current loss of the rotor is calculated by finite element simulation,and the eddy current loss results of different sleeve rotors are compared.Then,based on the analytical formulas,the wind friction loss and convective heat transfer coefficient of the rotor surface at high rotating speed are calculated.According to these conditions,the rotor temperature is simulated by finite element method,and the temperature distribution of the rotor is obtained.On this basis,the distribution gradient of temperature along the radius and the variation of temperature along the axis at the center of the rotor are studied,and the influence of sleeve material on the temperature rise of the rotor is analyzed.Secondly,according to the structure characteristics and operation status of the rotor,considering the temperature gradient of the rotor,based on the thick-walled cylinder theory in elasticity,the stress analysis model of the motor rotor is derived.The correctness of the analytical model is verified by finite element method.The stress distributions in sleeve and permanent magnet are further analyzed.The stress changes in rotor sleeve and permanent magnet under different working conditions are compared.According to the analytical mode of rotor stress,the effects of static interference between sleeve and permanent magnet,sleeve thickness,sleeve material and inner diameter of permanent magnet on the stress of sleeve and permanent magnet are analyzed.Finally,considering the influence of turbine disk,the dynamic analysis of high speed permanent magnet motor rotor is carried out based on finite element method,and the modal parameters such as natural frequency and first-order critical speed of the rotor system and Campbell diagram are obtained.On this basis,the effects of the normal stiffness factor of the contact surfaces between the rotor components,the sleeve material and the inner diameter of the permanent magnet on the first-order critical speed of the rotor system are analyzed.