Numerical Study On Cooling System Of A Permanent Magnet Motor

With the rapid development of high-speed railway technology and the emergence of highperformance permanent magnet materials,the research and application of permanent magnet motors in the field of rail transportation and high-speed EMUs are increasingly widespread.Permanent magnet motors have unparalleled advantages of traditional excitation motors such as small size,low noise,high efficiency,and obvious energy saving.It meets the national requirements for the development of railways in the direction of green and low carbon.It is the core component of the next generation train traction system-a permanent magnet traction system.However,due to the small size,high power density and fully enclosed structure of the permanent magnet motor for traction,the temperature rise of the motor is large,and the permanent magnet will be permanently demagnetized due to high temperature.Therefore,it is particularly important to design an efficient and reliable cooling system for permanent magnet motors.The paper takes a permanent magnet motor with a power of 35 kW as an example.Based on Maxwell’s electromagnetic field theory,using Maxwell to simulate it,obtains the copper loss,iron loss and mechanical loss.Based on fluid mechanics and heat transfer theory,the temperature field is simulated by Fluent and related conclusions are obtained.By comparing the common cooling schemes and structures,determine the cooling scheme with chassis.The thesis designs a set of efficient permanent magnet motor cooling system after analyzing the influence of factors such as the structure of the cooling chassis,the number of water channels,the flow rate of the water inlet,the thickness of the inner wall of the chassis and the chassis material.The following conclusions are obtained in this research:(1)The magnetic flux density distribution of the iron core has a periodic law,and several points can be selected to represent the overall situation.Increasing the division area of the representative points and processing the waveform to improve its sine degree can both improve the accuracy of iron loss calculation.(2)In the calculation of hysteresis loss and eddy current loss,the result of the FFT decomposition method> diameter and tangential decomposition method> the direct method of ignoring harmonics.Decomposing the magnetic flux density by the diameter and tangential decomposition method and FFT decomposition method can both improve the calculation accuracy of the core loss and the latter is better.Hysteresis loss accounts for more than eddy current loss in iron loss.(3)The copper loss occupies about 1/5 of the total loss,which is equivalent to the mechanical loss.The iron loss occupies more than half of the total loss,which is the main loss of the motor loss,a main reason causes temperature rise.The permanent magnet eddy current loss only accounts for 1/20 of the core eddy current loss.(4)The maximum temperature of the research object reaches 116.8 ℃ during the natural cooling in the environment with a temperature of 25 ℃,and the minimum temperature is 71.0 ℃.The high temperature area mainly concentrates in the stator core and the chassis.The permanent magnet temperature exceeds the demagnetization resistance temperature by 80 ℃.The temperature of the insulation layer exceeds the temperature specified by the insulation class A,close to the temperature of E,both of them need to be dissipated by the cooling system.(5)The paper designs a water-cooled structure,and the research results show that: The number of water channels increases,the flow rate increases,the motor temperature rise decreases,and the heat dissipation performance increases;The cooling water inlet flow increases,the flow rate increases,the motor temperature rise decreases,and when the flow rate is less than 10 L/min,the flow rate increases and the motor temperature drops faster,when the flow rate is greater than 10 L/min,the motor temperature decreases slowly,the optimal inlet flow rate is 10 L/min;The thickness of the inner wall of the chassis increases,the temperature rise of the motor increases,and the heat dissipation performance decreases,but it is not obvious;The greater the thermal conductivity of the material,the better the heat dissipation performance,but the cost of material should be considered.