Thermal Calculation and Optimization Design of Mine Low Speed and Large Torque Permanent Magnet Direct Drive Motor

Introduction: This study aims to optimize the motor cooling system to enhance the heat dissipation efficiency of the rotor, reduce the risk of demagnetization of the permanent magnet rotor caused by high temperatures, and ensure the long-term stable operation of the motor. Methods: Based on the field synergy theory of computational fluid dynamics and convective heat transfer optimization, an 800 kW permanent magnet direct-drive motor was selected as the research object. Two rotor structural cooling schemes were designed according to the specific structural characteristics of the motor. A coupled analysis model of the permanent magnet direct-drive motor was established, and simulation analyses were conducted for both structures. The temperature distributions of the windings and permanent magnets under the two different rotor cooling structures were compared. Finally, the simulation results were validated through prototype testing. Results: Thermal calculations were performed for the two motor cooling structures to determine the thermal distribution patterns of key components, including the stator windings, permanent magnet stator core, and rotor core temperatures. Under the second rotor cooling structure, the rotor temperature was reduced by 15°C compared to the first structure. The motor temperature rise was calculated using the thermal resistance method, and the deviation from the simulated temperature rise was only 5.9%. Discussion: Improving the rotor ventilation structure contributes to an overall reduction in temperature and a more uniform temperature distribution, thereby maintaining the permanent magnet temperature within a safe operational range. Conclusion: The enhanced rotor-cooling structure demonstrates the superior heat-dissipation capability of the new design and can serve as a reference for the cooling system design of high-power permanent-magnet direct-drive motors. Furthermore, the technical route of “field synergy theory + fluid-thermal coupling simulation + prototype verification” proposed in this study can be transferred to the heat dissipation design of high-power permanent magnet motors in fields such as wind power and rail transit. This contributes to the application expansion of high-power permanent magnet motors under harsh operating conditions.