Study On Loss And Heat Of Low-speed High-torque Permanent Magnet Synchronous Motor

Low-speed High-torque Permanent Magnet Synchronous Motor(LHPMSM)can directly drive the mechanical load without the variable speed gear,which improves the operating efficiency and reliability of the system.However,because the rotor of LHPMSM is directly connected to the large mechanical load,it is prone to cause bearing wear and eccentric failure of the rotor,which results in a series of problems such as the rises of loss,temperature,vibration,noise and so on.To study the influences of rotor static eccentricity on loss and heat of LHPMSM,in this thesis,the electromagnetic field and the temperature field of a 400 k W,20r/min built-in tangential LHPMSM is studied by finite element method.Firstly,a 2D nonlinear time-varying electromagnetic field model of LHPMSM and its calculation models of stator copper loss,iron loss and rotor eddy current loss are analyzed and established,in which the rotor eddy current loss is considered in detail.Secondly,a 3D anisotropic temperature field model of LHPMSM is analyzed and established.The calculation formulas of equivalent thermal conductivity and surface heat dissipation coefficient are determined reasonably.Thirdly,the influences of rotor static eccentricity on the air-gap magnetic field,electromagnetic performances,loss and temperature rise distribution of LHPMSM are studied by finite element analysis and calculation,and the temperature rises under natural air-cooling and forced air-cooling are compared and analyzed.Finally,to reduce the loss and heat of the prototype,the structure of the prototype is improved and the improved effect is verified by finite element analysis.The results show that,with the increase of rotor eccentricity,the back EMF and the stator core loss change quite little,but the harmonic distortion rate of air-gap flux density,armature current,electromagnetic torque,cogging torque,stator copper loss,rotor losses,as well as the motor heat increase obviously,and the temperature rise near the stator winding on the opposite side of the rotor eccentricity increases.After the natural air-cooling method is replaced by the forced air-cooling method,the maximal temperature can be reduced effectively and the temperature rise distribution is more uniform.By improving the guage of stator winding,the sizes of stator slot and magnetic insulated aluminum block,the loss and heat of the prototype can be effectively reduced.The research results of this thesis are valuable for the design optimization of LHPMSM.