Research On Rotor Eddy Current Loss And Stress Of Cryogenic High-Speed Permanent Magnet Motor For Liquefied Natural Gas Pump

As the research hot spot of clean energy sources in our country and even the world at present,liquefied natural gas(LNG)has gradually attracted the attention of various countries in transportation,reception and utilization.In the transfer and transportation of liquefied natural gas,the wide application of LNG pumps provides a guarantee for the safety and reliability of the transportation process.As the core component of LNG pump,the research of cryogenic motor is of great significance and value,especially for the research of cryogenic and high-speed permanent magnet motor.High-speed permanent magnet motors have high working frequency and fast rotating speed,which makes their loss higher than that of ordinary motors.In addition,too much centrifugal force on the rotor may lead to loose permanent magnets and other dangers.Therefore,the analysis of rotor eddy current loss and mechanical strength cannot be ignored for high-speed permanent magnet motors.In this dissertation,a 40 kW,35000r/min LNG pump with low temperature highspeed permanent magnet synchronous motor was served as an example,according to the special requirements in low temperature environment of the stator winding,the rotor materials during the process of design and the special consideration,determine the basic performance indexes of low temperature motor,gave the design steps and design schemes of the motor,low temperature motor two-dimensional finite element model is constructed.Time-step finite element method was used to calculate the basic electromagnetic performance of the motor in low temperature environment,and the accuracy of electromagnetic design scheme was verified by analyzing the simulation results.Aiming at the issue of high loss of low temperature and high speed permanent magnet motor,the mechanism of rotor eddy current loss for cryogenic motor was analyzed,and the influence of electromagnetic characteristics for sleeve on the electromagnetic performance of the motor was studied.A composite sleeved rotor structure with coating on the outer surface of the rotor was proposed,and a physical model for solving the eddy current loss of a composite sleeved rotor was established by using the finite element method.By changing the material,relative position of the shielding layer and the sleeve,the distribution of rotor eddy current loss under the composite sleeve scheme with different thickness ratios was studied.According to the distribution of rotor eddy current loss under the sleeve scheme,the optimal composite sleeve scheme was obtained,and the scheme was analyzed and verified.Aiming at the mechanical strength issue which may be caused by the excessively high speed of low temperature high speed permanent magnet motor,the strength analysis of each part of rotors was carried out based on the theory of thick-walled cylinder.The stress distribution of each part of the rotor was studied under the three factors of interference amount,rotating speed and sleeve thickness at working temperature and low temperature.Based on the eddy current loss distribution of the composite sleeve structure in the previous part,the stress analysis of the composite sleeve scheme was carried out.The optimal design scheme of composite sleeve for low temperature environment considering eddy current loss and rotor strength was presented.