Simulation and Experimental Study of Oil Injection Cooling for PMSM With Hairpin Winding

Recently, the power density of permanent magnet synchronous motor (PMSM) with hairpin winding for electric vehicles was increasing. But the motor performance will be limited by the high temperature rise. As a result, oil cooling methods with higher cooling efficiency are widely used. In this article, an oil-injection-cooled hairpin winding PMSM with a rated power of 55kW is designed. The fluid field of the oil cooling structure under different oil injection hole diameters and arrangements is analyzed by the computational fluid dynamics (CFD) method. In addition, a resin housing with the cooling channel is built by 3-D printing methods, and the nozzle on the housing is replaceable. An experimental platform for measuring flow rate is also established, and the accuracy of the simulation analysis is verified by the experiment. Besides, unlike traditional equivalent methods, a winding model close to real situation is established, which can accurately reflect the flow state of cooling oil at the winding ends and greatly improve the accuracy of temperature field calculation. On this basis, the motor temperature distribution at different oil injection effects is analyzed and compared. Finally, the optimal injection hole diameter and the arrangement of cooling structure are determined, which significantly improve the cooling efficiency.