Study On Eddy Current Loss And Electromagnetic Force Of Cryogenic And High-speed Permanent Magnet Motor

Liquefied natural gas(LNG)has been widely used in various countries due to its clean and environmentally friendly properties,the imports of LNG in China have increased year by year.LNG pumps have been widely used in the process of transporting LNG.As one of the core power components of LNG pump,the motor applied for LNG pump works at high speed in cryogenic environment.Therefore,the research on the performance of cryogenic and high-speed permanent magnet motor applied for LNG pump has theoretical and practical significance.According to the requirements of cryogenic environment,the change characteristics of electromagnetic properties of stator winding and permanent magnet are discussed,and the transient electromagnetic field-circuit coupled finite element mathematical model of the motor is established.The differences between no-load air-gap flux density,flux density of permanent magnet surface,no-load back-EMF,and harmonic electromagnetic torque in cryogenic and room temperature environments are calculated and compared.The rationality of electromagnetic field performance proves the accuracy of electromagnetic design and model establishment of the motor.Aiming at the issues of high speed and high loss of cryogenic high-speed permanent magnet motor,the distribution characteristics and variation of three-dimensional electromagnetic field and eddy current loss of cryogenic high-speed permanent magnet motor are studied.Attenuation law of the end magnetic field of the cryogenic and high-speed permanent magnet motor is revealed,Three-dimensional finite element method is used to analyze the influence of sleeve properties on eddy current loss of rotor,the difference of eddy current loss ofpermanent magnet in cryogenic and normal temperature environment is explored,and the transient characteristics of eddy current density of permanent magnet and sleeve during the dynamic transition process of current commutation are studied.Furthermore,weakening effect of segmentation of the permanent magnet and the sleeve on the eddy current loss of rotor is analyzed and calculated.Aiming at the issues that the change of the material properties of the motor affects the electromagnetic force characteristics in cryogenic environment,the dynamic electromagnetic force distribution characteristics and variation rules before and after eccentric fault of the cryogenic and high-speed permanent magnet motor are studied.A dynamic electromagnetic force calculation model is established,which combines the eccentric fault finite element method with Maxwell tensor method.The dynamic electromagnetic force of sleeve surface position,stator tooth top and stator tooth wall are calculated,and the difference of the electromagnetic force distribution compared with that in room temperature environment is analyzed.The evolution law of electromagnetic force and the location of stress concentration after eccentric fault are quantitatively described.The accuracy of electromagnetic force calculation results is verified from the perspective of space-time characteristics of air gap electromagnetic force and electromagnetic torque.When considering the influence of eddy current reaction,the results of electromagnetic torque calculated by virtual displacement method and Maxwell tensor method are consistent,which proves that the results of electromagnetic force and eddy current loss are reasonable.The calculation method and research content involved in this thesis can provide reference for the design and operation performance analysis of similar motors.