Research Of Submerged Cryogenic Permanent Magnet Synchronous Motor

Submerged cryogenic motor mainly refers to the motor which is submerged and operating at-183° C(90K)Liquid Oxygen(LOX),-161° C(112K)Liquid Natural Gas(LNG)or-196° C(77K)Liquid nitrogen(LN2).Because the characteristics of the material and parameters of the motor under cryogenic temperature are significantly different from those at ordinary temperature,the operation conditions and performance of the motor are greatly different,which brings some special problems to the design and manufacture.At present,J.C.Carter of the United States,Cryostar of France,and Ebara,Nikkiso,Shinko of Japan,etc.have mastered key technologies such as material selection,electromagnetic-thermal coupling simulation models and operating characteristics of cryogenic induction motors,and are in a technological monopoly phenomenon.However,the efficiency and torque density of cryogenic induction motors have certain limitations,which is not conducive to the efficient and reliable operation of the cryogenic system,so as to seriously restrict the promotion of cryogenic motors.The key technology of submerged cryogenic motors in China is still in its infancy,and its design theory and efficiency improvement technologies are currently blank.Therefore,it is of great significance to study submerged cryogenic motors.This paper investigates the submerged cryogenic permanent magnet synchronous motor(PMSM)for LNG submersible pump as the research goal,and focuses on the in-depth research on the structural characteristics,mathematical model,magnetic field distribution and analysis methods,performance parameters of the PMSM at cryogenic temperature.The design method of PMSM at cryogenic temperature was established,and the theory and technical system of the design and analysis of cryogenic PMSM were established to lay the theoretical and technical foundation for the research and application of similar cryogenic motor.The main research works of the paper are as follows:1.Taking the "V" rotor magnet structure cryogenic PMSM as the research object,the structure and characteristics were analyzed,focusing on its mathematical model,and quantifying the variation law of permanent magnet(PM)remanence and stator winding resistivity in cryogenic environment.The expression and design flow of the cryogenic PMSM for the volume of the PM and the groove area of the stator were proposed,which can quickly determine the PM and stator slot size of PMSM in the cryogenic environment.2.The size and structure of the cryogenic PMSM was studied in depth,focusing on the analysis of its key parameters and the impact of the operation of the cryogenic environment on the electromagnetic performance of the motor.The law of motor dimensions changing with torque,speed and efficiency changes was obtained.The design and optimization of the torque characteristics for cryogenic PMSM were carried out from three main aspects: electromagnetic constraint,temperature rise constraint and mechanical constraint.3.Aiming at the basic theory of cryogenic PMSM design,the coupling principle of electric field,magnetic field,thermal field and mechanical stress field of cryogenic PMSM were analyzed.The electromagnetic field-temperature field-stress field multiphysics coupling model of the motor was established.The electromagnetic properties and mechanical properties of the stator core silicon steel sheet material under deep cooling temperature were studied.The electromagnetic properties and mechanical properties of PM materials at cryogenic temperatures are simulated.In addition,the phenomenon of locking,crack and gap were analyzed,for the case that the degree of shrinkage is different when the temperature difference between the rotor magnet groove and the PM is large.4.A prototype of cryogenic PMSM was developed,and a manufacturing process for cryogenic treatment of various metal materials and electromagnetic materials of the motor was proposed.For safety reasons,an overall test platform for submersible pump with-196℃ liquid nitrogen as cryogenic medium was built.Test methods and procedures were proposed to test the performance of key components of the cryogenic PMSM and the LNG submerged pump system.Finally,the power density test was carried out compared to a normal temperature PMSM with similar temperature rise.The experimental results verified the accuracy and feasibility of the prototype design analysis.