High Speed And High Power Permanent Magnet Motor Rotor Structure Strength Analysis And Optimization

High-speed and high-power permanent magnet motors have many advantages,such as relatively simple structure,high efficiency,high operational reliability,and long constant power range.Compared to surface-mounted permanent magnet motors(SPMSM),the internal permanent magnet motor(IPMSM)has advantages of high torque density and a wide speed range,making it more widely used in driving motor applications.Due to the high rotational speed and large rotor mass,the stress on the rotor’s magnetic bridge is high for high-speed and high-power permanent magnet motors.Therefore,in motor design,special attention should be paid to the structural strength of the rotor,and the magnetic bridge structure used must meet the requirements of rotor strength while considering the significant effect of the thickness of the magnetic bridge on the motor’s electromagnetic performance.Therefore,this thesis focuses on researching the structural strength of the rotor while ensuring that the IPMSM meets the required electromagnetic performance.This article takes a high-speed and high-power permanent magnet motor with a rated power of 4.45 MW,a speed of 5000r/min and a protective sleeve tied to the rotor surface as the research object,studies the rotor topology,electromagnetic performance,structural strength,comprehensive performance optimization and other issues of the motor.Firstly,this thesis conducts a design study on the electromagnetic scheme of high-speed and high-power motors,including the selection of motor materials,pole slot fitting,winding form and main structural dimensions.The electromagnetic design scheme meets the technical requirements.Based on this,two different rotor topologies,namely internal V-type without protective sleeve and internal V-type with protective sleeve are studied.The size parameters of the two schemes are determined mainly based on the gap size of the permanent magnet synchronous motor,the thickness of the magnetic bridge,the thickness and material of the protective sleeve,and the size of the permanent magnet.The electromagnetic performance of the two schemes is comprehensively compared to determine the rotor structure of the high-speed and high-power permanent magnet motor.Secondly,the mechanical strength of rotors is studied using three-dimensional finite element method.The analytical formula of rotor strength is derived by the equivalent ring method and the spoke rotor model method,the three-dimensional simulation model of the rotor is established by the finite element method,and the accuracy of the analytical formula is verified through the finite element method.The impact of design parameters of high-power permanent magnet motors on the strength at various locations is revealed,and the optimal range of thickness of the protective sleeve and the two side magnetic bridges is obtained.Finally,based on the obtained optimized range of the sleeve and the thickness of the magnetically insulated bridges on both sides,a multi-objective optimization method using Kriging model is used to explore the optimal balance point between the mechanical strength and electromagnetic performance of the motor rotor.The NSGA-II algorithm is used for optimization to obtain the Pareto set with the optimal values,and the optimal combination is selected considering comprehensive factors while satisfying the requirements for rotor strength to optimize the electromagnetic performance of the motor.