Study On Thermal Characteristics Of High Torque Density Motor Under Limiting Operating Conditions

In recent years,the concept of green environmental protection has attracted much attention,and low-carbon energy-saving products have become a research hotspot.In the automotive industry,electric vehicles have become an inevitable trend due to the advantages of environmental protection and high efficiency.As the driving motor of electric vehicle,the motor studied in this paper needs to output large torque in short time at low speed and high power continuously at high speed besides rated torque.Compared with the rated condition,the copper loss of the motor increases greatly in the maximum torque condition,and the additional loss of winding and eddy current loss of permanent magnet increase greatly in the maximum speed condition,which puts forward higher requirements for the cooling and heat dissipation of the motor.It is necessary to study the heating and cooling of the motor in depth.In this paper,the thermal characteristics of motor under rated and limiting operating conditions are studied from the aspects of motor loss analysis,cooling system design and heat dissipation law:Firstly,the loss of high torque density motor is studied.From the angle of enhancing cooling effect of winding,flat copper wire is used in motor winding,and on this basis,the additional copper loss rule and restraining method of flat copper wire winding are analyzed.In order to improve the accuracy of temperature field calculation,the distribution of iron loss,the suppression method of eddy current loss of permanent magnet and the variation law of motor loss in frequency conversion power supply are studied.The additional copper loss law under rated and limiting operating conditions and the influence law of frequency conversion power supply on the loss are compared and analyzed.Thirdly,the stator thermal characteristics of high torque density motors under limiting operating conditions are studied.The model of water cooling and heat network for flat copper wire and circular wire motor housing is established.The heat dissipation law of winding is analyzed,and the heat dissipation law of rated and limiting operating conditions of winding is summarized.Based on the water cooling and heating network model of flat copper wire motor housing,the effects of loss loading mode,thermal conductivity of insulation in slot,conductor size and placement position on the heat dissipation of windings are studied,which provides guidance for the optimization of heat dissipation of windings.The heat network model of oil immersion cooling for flat copper wire motor stator is established,and the heat dissipation characteristics of stator under rated and limiting operating conditions are compared and analyzed.Finally,the thermal characteristics of the rotor under the highest speed condition of high torque density motor are studied.In order to improve the accuracy of rotor temperature calculation,the heat dissipation path of the rotor is analyzed.Based on the condition of maximum speed,the effects of surface roughness,slotting,physical properties of air gap,end air and shaft opening on rotor heat dissipation are analyzed.Based on the heat dissipation analysis of the rotor,the heat dissipation characteristics of the rotor under rated and limiting operating conditions are compared.