Design and analysis of water-cooled structure for outer-rotor low-speed permanent magnet motor

WANG Dexi; LI Wenkai; CHEN Gong

doi:10.7688/j.issn.1000-1646.2025.04.14

Abstract：[Objective]With the gradual improvement of requirements for motor energy efficiency grade,outer-rotor low-speed 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 industrial sector,the design of outer-rotor low-speed permanent magnet motors 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.[Methods]To address the problem of high temperature rise in outer-rotor low-speed permanent magnet motors under heavy-load operation conditions,this paper established the physical model of outer-rotor low-speed permanent magnet motors and calculated the distribution of motor losses.First,based on the basic theory of computational fluid dynamics,according to the heat source distribution and structural characteristics of outer-rotor low-speed permanent magnet motors,the study designed and installed axial and circumferential Z-shaped water-cooled structures in stator bracket near the inner surface of the stator core.The simulation model with water inlet and outlet at the motor bottom was also established.The flow field and temperature field of two water-cooled structures were simulated and analyzed using Fluent software.The circumferential Z-shape structure was determined as a more suitable water-cooled design structure.Second,by the calculation method coupling fluid flow and heat transfer,the temperature field of the motor equipped with a circumferential Z-shaped 9-channel water-cooled structure was analyzed using Fluent software.Whether the water-cooled structure meeting the heat dissipation requirements of the outer-rotor low-speed permanent magnet motors was verified with the maximum temperature of the permanent magnet and insulation.Finally,based on the theoretical analysis,this paper determined the factors influencing heat dissipation in water-cooled structures,including water channel number,cooling water flow rate,and radial width of water channel section.The influences of different factors on motor temperature rise were studied using Fluent software.[Results]The results indicate that the flow rate distribution of the circumferential Z-shaped water-cooled structure is more uniform with a smaller inlet and outlet pressure difference,which is more suitable for outer-rotor low-speed permanent magnet motors.As the number of water channels,cooling water flow rate,and radial width of water channel section increase,the heat dissipation is enhanced.However,after each factor reaches a certain value,the motor temperature tends to stabilize.According to the analysis results,the final design includes 7 water channels with a radial width of 17 mm and a cooling water flow rate of 0.5 m/s.[Conclusion]The research results can provide a theoretical basis for the application of water-cooled systems of outer-rotor low-speed permanent magnet motors in high-load working environments.