Research On The Design And Optimization Of Water-cooled Structure For Outer Rotor Low-speed High-torque Permanent Magnet Motor

In recent years,with the gradual improvement of motor energy efficiency grade requirements,outer rotor low-speed high-torque permanent magnet motors are widely used in the industrial field,due to their advantages of high torque density,high efficiency,and energy-saving.To meet the working conditions of heavy-load start-up and long-term low-speed heavy-load operation of large-scale transmission equipment,the design of outer rotor low-speed high-torque permanent magnet motor is developing in the direction of improving motor torque density.Accordingly,the issue of high heat generation caused by the high torque density of motors is becoming a focus of research.In view of the above problems,based on the basic theory of fluid mechanics,a water-cooled structure is designed to meet the heat dissipation requirements of outer rotor low-speed high-torque permanent magnet motor.Using the coupling method of fluid flow and heat transfer,the temperature field of motor under water cooling condition is analyzed using Fluent software.The purpose is to provide a theoretical basis for the application research of the water-cooled system of outer rotor low-speed high-torque permanent magnet motor in high load working environment.The main conclusions of this thesis include:(1)The physical model of outer rotor low-speed high-torque permanent magnet motor was established.According to the main loss of motor,the temperature field of outer rotor low-speed high-torque permanent magnet motor under natural cooling conditions was simulated using Fluent software.The results show that the temperature of the insulation and permanent magnet exceeds the allowable temperature of F-grade insulation(155 °C)and N48SH(150 °C),respectively,and efficient cooling structure design is required.(2)Based on the basic computational fluid dynamics theory,according to heat source distribution of outer rotor low-speed high-torque permanent magnet motor,axial and circumferential Z-shaped water-cooled structures installed in stator bracket near the inner surface of the stator core were designed.The flow field and temperature field of two water-cooled structures were simulated and analyzed using Fluent software.The results show that the cooling effect of both water-cooled structures is similar.However,circumferential Z-shaped flow velocity distribution is more uniform,and the pressure difference between the inlet and outlet is smaller,making it more suitable for the water-cooled structure of the outer rotor low-speed high-torque permanent magnet motor.(3)By the coupling calculation method for fluid flow and heat transfer,the temperature field of the motor equipped with a circumferential Z-9 channel water-cooled structure was analyzed using Fluent software.The results show that the maximum temperature of the permanent magnet is 89.14 °C,while insulation reaches a maximum temperature of 53.4 °C,meeting allowable temperature requirements for F-grade insulation and permanent magnet.(4)Based on the theoretical analysis,the factors affecting heat dissipation in water-cooled structures are determined,including water channel number,cooling water flow velocity,radial width of water channel section,cooling water initial temperature,and water-cooled structure material.The influences of different factors on motor temperature rise were studied using Fluent software.The results show that the motor temperature decreases with the increase of water channel number,radial width of water channel section and cooling water inlet flow velocity,but temperature tends to be stable after increasing to a certain value.The lower initial temperature of cooling water,the cooling effect is better.However,cooling water with lower temperature requires additional cooling device,which will increase the production cost.The higher thermal conductivity of water-cooled structural materials,the cooling effect is better.Based on the research results,a circumferential Z-shaped water-cooled structure design scheme with 7 channels and rectangular channel section of 17 mm × 32 mm is determined.