Research On Rotor Loss And Heat Dissipation Of Ultra-high Speed Permanent Magnet Motor

Ultra-high speed permanent magnet synchronous motor is widely used in ultra-high speed air compressor,flywheel energy storage machine tool,CNC machine tool,high-speed motorized spindle and other fields because of its high speed and high power density.However,when the ultra-high speed permanent magnet motor operates at high frequency,the iron and copper losses in the stator and winding are large,and the air friction loss and eddy current loss on the rotor surface can not be ignored.In addition,due to the small heat dissipation area of the rotor,the heat dissipation problem of the rotor is more prominent.The rise of rotor temperature may overheat the permanent magnet,resulting in irreversible demagnetization,which will seriously affect the normal operation of the motor.Therefore,effectively reducing the rotor loss and reasonably designing the cooling system suitable for rotor heat dissipation are of great significance to suppress the temperature rise of permanent magnet and ensure the safe and stable operation of motor.Firstly,10 kW,100000r/min ultra-high speed permanent magnet motor is taken as an example,the rotor eddy current loss of ultra-high speed permanent magnet motor is calculated by 2D finite element method,and the factors affecting eddy current loss are analyzed,including slot opening width,air gap length,permanent magnet segmentation,inverter carrier ratio,sheath conductivity,sheath thickness and copper shielding layer.Secondly,the 3D fluid field method is used based on the finite volume method and the traditional analytical method,the influence of rotating speed on the air friction loss of the rotor is calculated,and the calculation formula of air friction loss is modified.Then the effects of axial air velocity,rotor surface roughness,air gap length and slot opening width on air friction loss are calculated by 3D fluid field method.Finally,aiming at the difficulty of heat dissipation of ultra-high speed permanent magnet motor rotor,an axial fan for motor self fan cooling is designed.The 10 kW,100000r/min ultra-high speed permanent magnet motor is taken as an example,the fan is designed by the isolated airfoil method.The optimal shape of the blade is obtained by comparing the fluid structure coupling method.The cooling effects of self fan cooling mode and forced air cooling mode,and whether axial ventilation duct is added between the motor stator and the casing are compared.The temperature rise of a 15 kW,15000r/min water-cooled high-speed permanent magnet motor is calculated by simulation method.The experimental values are compared with the calculation to prove the effectiveness of the fluid structure coupling simulation analysis results.The research content of this thesis provides a reference for the design of cooling system suitable for rotor heat dissipation of ultra-high speed permanent magnet motor with low power grade.