Hollow Shaft Liquid Cooling Method for Performance Improvement of Permanent Magnet Synchronous Motors Used in Electric Vehicles

Operating condition of rotor embedded magnet materials for permanent magnet synchronous motor (PMSM) critically affect electric vehicle (EV) range and dynamic characteristics. The rotor liquid cooling technique has a deep influence on PMSM performance improvement, and begin to be studied and applied increasingly in EV field. Here, the fluid, thermal, and electromagnetic characteristics of motor with and without hollow-shaft cooling are researched comprehensively based on 100 kW PMSM with housing water jacket (HWJ) and hollow-shaft rotor water jacket (SWJ). The solid models are constructed considering temperature-dependent power loss and anisotropic thermal conductivity. After the fluid models are set up by using Reynolds stress model (RSM), conjugate heat transfer is conducted through computational fluid dynamics (CFD) simulation, and is verified by real PMSM test bench experiments. The thermal-electromagnetic coupled analyses are carried out via finite element methods (FEM) taking into account the temperature-dependent magnet operating point. Compared to HWJ-alone cooling at the motor rated condition, the winding temperature with SWJ cooling has 20°C lowers, and 70°C lowers in magnet position, as well as the motor output power is improved by 3% to 4%. This cooling method will provide a great helpness on motor's power density, module lightweighting, and system economy.