Analysis Of Mechanical Strength And Rotor Modal Of High Speed Permanent Magnet Motor

The high-speed permanent magnet motor has a relatively high power density and a high rpm,which is of great significance for reducing the size and weight of the equipment.However,due to the poor tensile strength of the permanent magnet material in the motor,it is difficult to withstand the centrifugal force under high-speed rotation,and the rotor must pass through the first-order or multi-step critical speed during the start,run and stop.The strength analysis and dynamic characteristics analysis of the rotor become the key to the research of high-speed permanent magnet motor.This article has conducted in-depth research on these two aspects,the main content includes the following aspects:1)Structural design and strength analysis of high speed permanent magnet motor rotor system.Designed with motor parameters such as rated power 4KW and rated speed of 60000r/min,combined with theoretical formulas such as torsional stiffness and strength and Workbench simulation analysis method,the dimensions of assembly rotor(rotary shaft,sheath,permanent magnet)meeting the strength requirements are designed..The analysis of electromagnetic characteristics by Ansoft shows that the distribution of magnetic lines and magnetic flux density are reasonable,which proves that the designed motor rotor has good electromagnetic characteristics and can guarantee the operation of the motor under rated conditions.The workbench is used to analyze the stress distribution of the rotor of the motor under different temperature and speed.The causes are analyzed and the optimal design measures are proposed.2)Rotor system dynamics modeling and critical speed solution.It is divided into the calculation of the rotating shaft and the calculation of the assembly rotor.The first part is the calculation of the critical speed of the rotating shaft.The finite element method is used to divide the rotating shaft into a rotating shaft system which is connected by an elastic shaft segment and several mass points to establish the power of the rotating shaft.Learn the equation and calculate the critical speed of the shaft through Matlab.The second part is the calculation of the critical speed of the assembly rotor.Firstly,the permanent magnet and the sheath are simplified into mass points,and applied to the corresponding nodes of the dynamic model of the rotating shaft to establish the dynamic equation of the assembly rotor.Secondly,the assembly structure is considered.For the influence of the overall stiffness,the stiffness enhancement coefficient is calculated and substituted into the dynamic equation.Finally,the critical speed of the assembly rotor is obtained by Matlab.3)Modal analysis of the rotor system.Using the Workbench simulation software,the modal analysis is performed on the rotating shaft and the assembly rotor respectively.The modal analysis results are consistent with the finite element method.It should be noted that when using the Workbench for modal analysis of the assembly rotor,it is necessary to set the contact characteristics of the assembly structure and the rotating shaft(such as the interference fit amount and the normal stiffness)in order to obtain accurate results.Finally,the critical speed changes of the rotor of the motor under different supporting stiffness and speed are analyzed,and the rules are summarized.4)Modal experiment of the rotor system.The LMS hammering system is used to test the static natural frequency of the rotor system,and the experimental results are compared with the mathematical model calculation results and the Workbench simulation results.The results are all consistent,indicating that the contact characteristics of the assembly rotor are fully considered.More accurate modal analysis.