Research On The Application Of Hollow Shaft Rotor In High Power High Speed Permanent Magnet Synchronous Motor

Due to the demand of military and civilian,high speed permanent magnet motor has been paid more and more attention because of its excellent performance since the end of last century.Compared with ordinary motor,high speed motor has many good points,like high speed,high power density,small volume,small inertia,high efficiency and so on.However,high speed,high power density and small size bring a large loss of unit volume,high temperature rise and cooling problems at the same time.Based on a 1.12 MW,18000rpm high speed permanent magnet motor,a hollow shaft rotor is put forward,which will bring great help on heat dissipation of rotor when the cooling medium is used in the hollow shaft.which will bring great help on heat dissipation of rotor.On this basis,this thesis mainly studies the following aspects:(1)The size of hollow shaft internal diameter not only affects the heat dissipation effect of the rotor,but also has a great influence on the shafting strength and modal of the motor.The heat dissipation is not obvious if the inner diameter is too small,but when it is too large,the shaft strength and modal of the motor may not meet the requirements.Based on the data of mechanical design manual,the appropriate hollow shaft internal diameter is calculated.(2)The temperature rise of the high speed motor mainly comes from the loss of all parts of the motor,the accurate calculation of the loss of the motor is the foundation and premise of the temperature field analysis.Due to the influence of high frequency,the influence of harmonic and rotating magnetization should be considered in the calculation of stator iron loss.The calculation of copper loss should consider the skin and proximity effect.The harmonic caused by the stator current and the stator slot opening are the main causes of the permanent magnetic eddy current losses,the finite element method is used to calculate the eddy current losses.Because the speed of the high speed permanent magnet motor can be up to 10000 rpm or more,the wind friction loss of rotor surface is big and not negligible,it is necessary to be analyzed and calculated.At the same time,the effects of different factors on the rotor wind friction are analyzed,like speed,inlet wind velocity and so on.(3)Based on the fluid motion theory,the cooling system of the motor is analyzed and designed.A reasonable simplified motor model is established and the corresponding boundary conditions are given.The equivalent heat dissipation coefficient of the water cooling casing and hollow hole through water is obtained by using MATLAB software and the temperature distribution before and after the hollow shaft rotor of the motor is obtained by using ANSYS software.The influence of different factors on the motor temperature is analyzed at the same time,like different inlet wind speed,different cooling medium and so on.(4)The permanent magnet of high speed permanent magnet motor cannot bear larger tensile stress.The huge centrifugal force caused by high rotational speed may damage the permanent magnet,a protection measure must be taken.In this paper,high strength carbon fiber material is used to protect permanent magnets.Based on the theoretical analysis of the rotor strength of the motor,the rotor strength of the motor is analyzed by finite element method.Then the effects of different temperature and rotational speed,different permanent magnet structure,different hollow shaft internal diameter on the rotor stress is analyzed.(5)The high speed permanent magnet motor is difficult to design as a rigid rotor,generally for the flexible rotor,the safe area between the first order critical speed and second order critical speed.Firstly,the correlation theory of rotor mode of high speed permanent magnet motor is studied,the rotor modal and critical speed of high-speed motor are calculated by finite element.Then the influence of different factors on the rotor mode and critical speed is analyzed,such as rotor bearing,rotor with impeller,different hollow shaft internal diameter and different rotor structure.